Acoustophoretic microfluidic devices are promising non-contact and high-throughput tools for particle manipulation. Although the effectiveness of this technique has been widely demonstrated for applications based on micrometer-sized particles, the manipulation and focusing of sub-micrometer ones is challenging due to the presence of acoustic streaming. In this article, our study has the aim to investigate and understand which geometrical parameters could be changed to limit the acoustic streaming effect. We numerically study the well-known rectangular cross section of a microfluidic channel and perform a parametric study of the aspect ratio for several particle sizes. The efficiency of the focusing, is explored for different sized particles in order to identify a trend for which the acoustic streaming does not drastically influence the focusing motion of the particles. The possibility to efficiently separate different solid components in liquid suspensions, i.e. the whole blood, is crucial for all applications that require a purified medium such as plasmapheresis or an increase of the concentration of specific subpopulation as the outcome, such as proteomics, cancer biomarker detections and extracellular vesicles separation. This technique is based on the excitation of a standing acoustic wave inside a fluid chamber2. If particles are suspended in a medium enclosed in a chamber and an acoustic field is applied, resulting in the formation of a standing acoustic wave, they will experience two effects. The former one is the acoustic radiation force which appears when there is a difference in density and compressibility between the particles and the medium, and the latter is the Stokes drag force, depending on the relative velocity of the particles respect to the acoustic streaming flow3. This latter phenomenon represents the main limiting factor of acoustophoretic application for sub-micrometer particles separation5. Commonly, the acoustic wave is generated by an actuated piezoelectric material which converts electrical voltage to mechanical displacement and strain6. Several experimental and theoretical studies are present in literature where a rectangular section with a half-wavelength resonance is considered13. With this assumption, the single node of the standing wave is in the center of the channel, while two anti-nodes are at the sides. This configuration is usually adopted when the aim of the device is to focus particles. When the particle radius is around 1 µm and they present a positive acoustic contrast factor3, the acoustic radiation force moves them in the node of the acoustic wave. For particles smaller, with size less than a certain critical radius, the focusing is prevented due to the acoustic streaming3. The first theoretical analysis of the boundary-driven acoustic streaming was done by Lord Rayleigh14 and then this theory was deepened and investigated by several studies18. In the recent years, different approaches were numerically explored to overcome the lower size limit19. In particular, two half-wavelength resonances excited in a channel with a squared section can generate, instead of the common acoustic streaming, a vortex in the center of the section19. Despite the disadvantage of obtaining two standing waves instead of one, with this different shape of the vortex, sub-micrometer particles, that feel both the contribution of the acoustic radiation force and the Stokes force, are dragged into a focal point in the center. Another numerical study demonstrates that the simultaneous excitation of two different modes can change the shape and the dimension of the acoustic streaming, effectively decreasing the lower size limit for which the acoustophoretic concentration occurs9. An experimental work performed by Hoyos and Castro demonstrates that a pulsed actuation, instead of a steady one, leads to a reduced value of the acoustic streaming, enabling a low, sub-micron particle focusing20. A more recent work claimed the possibility to considerably reduce the acoustic streaming by introducing an inhomogeneous fluid in the microfluidic channel21, however this approach leads to a more complex experimental setup. One of the latest studies about the suppression of the acoustic streaming is based on the investigation of shape-optimized section to achieve the lower acoustic streaming influence22. Another important result came from a variation of the aspect ratio (AR) of the channel section, as described by Muller et al.3. In this work they observed, from numerical results, that by increasing the height of the channel, acoustic streaming does not occur across the entire cross section of the channel. This result could be exploited in devices for applications designed to concentrate the highest number of particles independently of their sizes. Recently, different and pioneering ways to model the acoustophoretic devices were implemented, paving the way to a new 3D approach. Lei et al. applied the limiting velocity finite element method. This strategy allowed them to calculate the driving boundary condition without taking in account of the effects in the boundary layer on a 3D finite fluid volume23. A few years later, Bach et al. developed a theoretical description that permitted them to perform numerical simulations of acoustics in a liquid-filled chamber with an arbitrary shape and oscillating elastic solids24. In this paper, we chose to extend the model proposed by Muller et al.7 to numerically analyze different values of AR and its effect on the acoustic streaming over different particles sizes. Since there is a wide number of theoretical and experimental works using the rectangular section investigated by Bruus and coworker, it was adopted as reference system. On the best of our knowledge this is the first systematic study that investigated the effect of different aspect ratios on the focusing performance. Firstly, we changed the height of the channel, keeping constant both the displacement of the actuated walls and the actuating frequency, to obtain a variable acoustic energy density inside the chambers. As second step we investigated the case with acoustic energy density constant, sweeping the displacement of the walls and maintaining the frequency at resonance value of the reference system. This could be interpreted as a voltage sweep in an experimental setup. Then we kept constant the acoustic energy density, fixing the frequency at resonance values and tuning the displacements. Finally, the extension of the section of the channel was set constant for all the aspect ratios and the tests indicated above were repeated. Performing these parametric studies, the principal aim of the work is to improve particle focusing by confining the acoustic streaming far from the focusing region, without adopting an elaborate and complex strategy.In the field of focusing and separation of particles, the acoustophoretic approach has gained great interest25, the perturbation theory is used to derive first order and second-order acoustic fields in a compressible Newtonian liquid. Similarly, we considered only the fluidic domain, thus the high acoustic impedance solid material, typically glass-silicon, is considered as the ideal boundary for hard rigid walls. For estimating the quantitative difference in assuming an adiabatic system instead of considering all the thermoviscous effect, we performed tests with the model proposed more recently by Muller et al.26—the results are shown in Table T0, density ρ0, pressure p0 and quiescence, v0 = 0. If the entropy is conserved due to the adiabatic assumption, the thermodynamics of the system could be described by only the pressure p. The changes from the equilibrium in density dρ could be described as related to the change in pressure dp through the isentropic compressibility ks, as follows3:In this section, we present the governing equations used in the model. As described firstly by Muller et al.0, 1 and 2):Using the standard perturbation theory all the fields could be write as series of orders 0.5. From Eq. , the equations are implemented as PDE weak form, and the particle motion is computed using the built-in module of Particle Tracing for Fluid Flow. Since the right propagation of the bulk acoustic waves inside the fluid requires a device with high acoustic impedance material (i.e. silicon/glass device), it is reasonable to assume the top and the bottom walls as rigid, without any displacement. The actuation on the right and left walls is modeled adding a harmonically oscillating boundary condition of the first order velocity, while for the second order velocity field the zero-mass flux through these walls is set as boundary condition26, as expressed in Eqs. ,,3, thus  in Eqs. .10.1\docbd, set equal to The whole rectangular section of the channel was divided in four subdomains as shown in Fig. bd to W/2 − wbd, is discretized using a Free Quad mesh with a maximum element size w equal to wbd, while the boundary domain is divided, using a mapped mesh, in N elements. As shown in Fig. –3. It is estimated by considering a general solution for g and the reference solution gref, calculated using the finest mesh, as follows:The viscous boundary layer for a chamber filled with water is typical about 0.4 µm for a frequency of 2 MHz. The bulk domain, that goes from − W/2 + w3. We focused our attention to the domain that is defined between -W/4 and W/4, which hereinafter we refer to as “central domain”.The reference mesh is chosen to maintain an element size in the bulk that is equal to w and with N = 20, which corresponds with an element size inside the boundary bulk that is equal to 0.5 32. The balance between acoustic radiation force and drag force is strictly dependent on the particle size. In fact, the acoustic radiation force is function of the cubic of the radius .After the computation of the entire acoustic field, we can use the results to calculate all the forces experienced by the particles. In a finite domain, the streaming can be computed and the total force experienced by a particle suspended in a medium is the sum of the acoustic radiation force and the streaming-induced Stokes drag forcedius Eq.  and the dius Eq. . This med in Eq. , where aThe time-averaged Stokes drag force is defined through the difference between the time averaged acoustic streaming a equal to 250 nm, 500 nm, 750 nm, 1 µm and 2 µm respectively, were studied. We observed that the release grid spacing, thus the concentration of particles, influenced the results, especially for smaller particles. Therefore, we performed some tests for the most critical situation, i.e. AR of 0.42 and particles radius of 250 nm . A schematic summary of how the study was structured is reported in Table 0 to 0.1 nm and the width W of the channel at 380 µm. The adopted aspect ratios were 0.42, 1, 1.2, 1.5 and 2, respectively. As a first step, the frequency was kept constant at 1.9669 MHz, which corresponds to the resonance frequency of the reference system, and the corresponding acoustic energy densities, calculated with Eq. . Results obtained from the particle tracing are reported in Fig. After obtaining the results and keeping constant all the actuation parameters, we varied the displacement of the walls to maintain constant the acoustic energy density inside the chamber at the same frequency of 1.9669 MHz. A parametric sweep on the displacement lThe combination of resonance frequency and the voltage is important to ensure the optimal transmission of mechanical energy into the device. In order to understand if the condition of resonance could influence the results, we performed the same study as in the section above but set the frequency at resonance values optimized for each aspect ratios see Fig. b. There 2 corresponding to the reference channel 380 µm width and a 160 µm height), investigating the same values of AR. The width and height used for the following sections are reported in Tables If the height of the channel was varied for each aspect ratio, while the width was maintained constant, the area of the channel cross section changed. Obviously, this changes the resonance and the energy density harvested and transformed by the system. We analyzed the condition of constant area (by keeping fixed the cross section at the value of 60,800 µmEven in this case the excitation frequency was properly tuned to keep constant the acoustic energy density at around 106 Pa. Obviously, these values do not correspond to the resonance frequency, which leads to a tenfold increase in acoustic energy density. As in the previous section, we maintained 106 Pa to have a good comparison with the reference system and the frequencies used to remain at this value are reported in Table As done in the case with a constant width, we also investigated the case in which the resonance frequency is applied, meanwhile the acoustic energy density is maintained at 106 Pa. The values of frequency and wall displacement used in this section are listed in Table 8, but they are still referred a “common” rectangular section with aspect ratio lower than one. Instead of that our study aims to pave the way to the usage of different aspect ratios. We hope that this could trigger also other researcher to go further in this topic. Moreover, the experimental part of the work is certainly of interest to us, so it will be absolutely a topic for future works.We numerically solved the isothermal acoustic problem in a microfluidic channel for the first mode of resonance. Stokes drag force and acoustic radiation force were calculated from the obtained fields and used to perform the particle tracing. To the best of our knowledge, we present the first systematic parametric study to analyze the effect of the aspect ratio on the ability to focus particles with diameter from 500 nm up to 4 µm due to acoustic streaming. Two different approaches were simulated and analyzed. The former was a study of different operating conditions in which the width of the channel was kept constant. The second was the same study but considering a constant S for all the aspect ratios. We show that in both the conditions with a constant width and cross-sectional area, a higher aspect ratio increased capability to efficiently focus particles, even with particles of smaller radius. This is due to the formation of a central “free zone” where the acoustic streaming does not influence the flow of the fluid and the acoustic radiation force is dominant. We observed also that working with a constant S is more efficient in terms of percentages of particles collected in the center of the channel. Any experimental studies were present in literature which could fit for our purpose. Unfortunately, the only reasonable data to consider are exposed in the already cited papers of Muller et al.Supplementary Information.


The surface tension generated by the magnetic pressure, on the surface delimiting the brain region subject to relevant field and gradients, is found to range between 10–1 and 1 mN⋅m–1. These pressures seem to be strong enough to interfere with the elastic and electrostatic energies involved in the channel activation-inactivation-deactivation mechanisms of biological membranes. It has been described that small mechanical force can activate voltage gated potassium channels. Moreover, stretch-activated ion channels are widely described in different biological tissues. Virtually, all these channels can modify their activity if stressed by a sufficient pressure delivered for enough time. We propose mechanical stimulation – possibly not exclusively – as a candidate mechanism how static magnetic field can produce effects in biological systems. It must be emphasized, that such field gradients were not previously proposed as a possible source of neural activity modification.Static magnetic fields have been shown to induce effects on the human brain. Different experiments seem to support the idea that moderate static magnetic field can exert some influence on the gating processes of the membrane channels. In this article we visit the order of magnitude of the energy magnetic terms associated with moderate applied field (between 10 and 200 milliteslas). It is shown that gradients of the Zeeman energy associated with the inhomogeneous applied fields can induce pressures of the order of 10 Static magnetic fields have been shown to induce effects on the human brain , and theThe brain cells have electric properties, and the connections between brain cells are largely due to an electric coupling. The link between magnetic fields and electricity is well-known. Despite a number of reports about the possibility that static magnetic fields might interfere with the physiological brain functions, a mechanistic explanation of these effects is lacking. In this article, we show that static magnetic fields as those used in references  produce Up to now, two main streams of studies have been carried out on the possible disturbance of the microscopic biological systems induced by the action of externally applied static magnetic fields. (A) Action on paramagnetic or possible superparamagnetic or ferromagnetic molecules or aggregates  and (B) Static fields only can produce Lorentz force on the electric charges in motion and magnetic moments that form the matter. Therefore, the effect of fields on live matter can emerge from the Lorentz force exerted on different charges or moments and can be classified as follows:a)I that runs along a total length Δs, the magnetic field created by this current would be proportional to the product I⋅Δs, which for a neuron is about 10 fA⋅m (10–14 A⋅m), and inversely proportional to the square of the distance between the segment Δs and the point where the field is measured. Considering Δs to be 0.1 mm, and, that for a single neuron, the typical presynaptic current ranges between 102 and 104 fA; for instance. From these estimations, it turns out that the Lorentz force exerted by applied static fields weaker than 1 T on any single ionic current flowing during the neural activity is lower than 10–15 N . On the other hand, the electrostatic field acting along the direction perpendicular to the membrane is due to a gradient of 70 mV through 1 nm of membrane thickness. Therefore, this field is approximately of 107 V/m and exerts on the K+ ion an electric force of 10–11 N which is four orders of magnitude larger than the Lorentz force.Ionic currents, only present through the cell membranes. The magnetic field produced by these currents are used in magnetoencephalography observations. Considering a current of intensity b)–3 times that due to the electronic contribution.Permanent magnetic moments of atomic nuclei that in the case of hydrogen are used in nuclear magnetic resonance diagnosis. The contribution to the macroscopic magnetization of the atomic nuclei is expected to be 10c)Permanent magnetic moments of free radicals, produced during some biological chemical reactions, and molecules and macromolecules containing few paramagnetic atoms, as is the case of deoxyhemoglobine, or macromolecules for which the paramagnetic atoms constitute a large volume fraction and that eventually might behave as superparamagnetic nanoparticles, as is the case of ferritine. Effects on ferritine and Fe atoms contained in proteins have been shown by Meister to be energetically irrelevant as concerns disturbance of the normal biological activity . In factd)Diamagnetic anisotropy. Tissues, some of them formed by macromolecules showing high anisotropy as is the case of assemblies of parallel oriented uniaxial units, as lipid bi-layers and some proteins as microtubules. Helfrich calculated the elastic effect produced by a magnetic field of 1 T intensity on a single spherical cell , 1974. De)Artificially introduced magnetic nanoparticles that has been used for generating high magnetic field gradients and membrane stresses modulated by external applied fields . As MeisOnce the aforementioned effects have been initially disregarded as causes of the transcranial static magnetic stimulation, we focus on the macroscopic effect produced by an inhomogeneous magnetic field on a continuous medium with average diamagnetic susceptibility χ.It is well-known that inhomogeneous magnetic fields exert measurable forces on diamagnetic substances . Gouy meM. For linear magnetic materials, it stands that M = χH, where the proportionality factor χ is called susceptibility, a dimensionless constant, scalar or tensor that relates the magnetization developed by a substance under the effect of an applied magnetic field . Typical values of diamagnetic mass susceptibility (corresponding to a kilogram of the substance) are, in SI units, −0.91⋅10−8 for water, −2.5⋅10−8 for hydrogen and −1.71⋅10−8 for bismuth.When a large number of atoms and molecules are aggregated forming tissues or cell membranes, they can be treated in terms of a continuum medium and the magnetic moment of the electrons, atoms and molecules are depicted by means of the density of magnetic moment or magnetic moment per unit volume, mass or mole. This density is known as magnetization, ic field . Accordi–3. It is also usual to use the centimeter-gram-second system (CGS unit system), for which the mass susceptibility is expressed in grams and obtained by dividing the value in SI units by −4π⋅10−3.Another common way of depicting the diamagnetic properties of matter is through the molar susceptibility, that can be obtained by multiplying the mass susceptibility by the molecular weight and by 10Diamagnetism is the common magnetic behavior of the biological matter, since biological molecules lack permanent magnetic moment and form assemblies that macroscopically behave as diamagnetic media.mol = −5.36⋅10−6, in CGS units, is found for planar peptide groups with resonance between two valence bonds.In general, the molecular magnetic susceptibility of biological molecules as lipids and proteins is anisotropic. Various diamagnetic biological systems as retinal-rod outer segment , lipids mol < 0) has been studied by analyzing the enhancement of the perpendicular edges of the powder lineshapes in the resonance spectra . We show that gradients of the Zeeman energy associated with the inhomogeneous applied fields can induce pressures of the order of 10COMSOL Multiphysics has been used. This software employs a finite element method to calculate and provide the spatial distribution of the physical parameters of interest for a user-defined model. In this case, the studied system consists of a cylindrical  NdFeB permanent magnet, characterized by a remanent magnetization of Mr = 1018400A/m parallel to the long axis, and surrounded by vacuum. Further details of the model and the simulations will be given below.The goal of this article is to estimate the magnetic pressure exerted by a diamagnetic biological medium onto its surroundings when such medium is placed near a static magnetic field gradient. In order to obtain a detailed characterization of the magnetic field gradient generated by the considered static source, the software H. Since for these linear materials B≈μ0H), the Zeeman energy can be rewritten as:As it has been explained, diamagnetic materials only present a non-zero macroscopic magnetic moment in presence of an external applied magnetic field The Zeeman energy per unit volume can be expressed in terms of the magnetization:Hence, the force associated with the Zeeman energy per unit volume is given by:z = z2−z1 where the z component of the magnetic field varies linearly ΔHz = Hz2−Hz1 as shown in Let us consider the case of an isotropic linear diamagnetic material with homogeneous susceptibilityFirst of all, it is important to notice that for this case Equation (4) can be rewritten as:H. Note that this corresponds to the second term of Equation (1), which is the one dependant on the gradient of the magnetic field.Where If we consider that the only field gradient present in this region is along the z-axis direction and varies linearly, the pressure (magnetic force per unit area) exerted by this region over the rest of the material is given by:The detailed calculation which leads to Equation (6) can be found in the z = z2−z1, with a total variation Δχ = χ2−χ1 as shown in Now, if the case considered is that of a linear isotropic diamagnetic material with magnetic susceptibility that varies linearly in the range ΔH|2 both axially and radially.In order to estimate the volume which is affected by the magnetic field created by the cylindrical magnet, and thus the effective surface where the magnetic pressure is being exerted, it must be considered the distribution of |σ, using the Young-Laplace equation:Once the effective surface has been estimated, it is possible to obtain the surface tension, R is the radius of curvature of the surface and ΔP is the pressure acting on it. As explained below, we will assume for our estimations that ΔP = Pz, since the contribution from the vertical gradient of Where For this study, the model shown in COMSOL Multiphysics has been used, as mentioned earlier. The simulations were performed in a simple model consisting on a solid cylindrical magnet  with a remanence of Mr = 1018400A/m along the z-axis. This magnet is placed inside an air sphere with radius of 10 cm which is large enough to ensure that the magnetic field distribution near the magnet is not altered by the boundary conditions . A meshing with elements of 10–3–10–2 m was set for the simulations, allowing a 0.05 scaling when necessary for narrow regions.In order to obtain a detailed characterization of the magnetic field generated by the considered static source, the software As expected, the results of the simulation that can be seen in x,y = 0), since this is the area for which the magnetic field is the strongest. The values for the horizontal (Bx) and vertical (Bz) components of the magnetic field vector, as well as the first derivative As they are required to calculate the induced local forces, the magnetic field components and its spatial derivatives have been evaluated. The region chosen for the study is a vertical line which crosses the center of the magnet  and two organic molecules with χ = −1.13⋅10−6(S.I) (lecithin) and χ = −10.4⋅10−6(S.I) (tyrosine). When considering the full thickness (2 mm)o f the medium, the total magnetic pressure Pzχ exerted on the cortex model is obtained. The same calculation has been performed for several diamagnetic media, each one composed by a uniform distribution of a single molecule. Note that for the real scenario, a uniform average susceptibility composed from those of these different components should be used. The results obtained are summarized in The force per unit volume suffered by an isotropic diamagnetic medium placed at 2 cm over the magnet was calculated using the magnetic field gradient obtained from the simulation. As previously mentioned, the thickness of this medium is 2 mm which approximately accounts for the average thickness of the human cerebral cortex. The magnetic pressure resulting from this force acting on the diamagnetic medium depends on the thickness considered as it is derived from Equation (6). This is shown in PzH have been calculated and summarized also in z = 2cm and considering that the medium of interest (χ2) is an organic material surrounded by extracellular or intracellular liquid whose susceptibility (χ1 has been assumed to be approximately that of water [χ = −9.1⋅10−6(S.I)].Regarding the second scenario considered, which is an interface with a linear variation of susceptibility Δχ but under constant magnetic field, the values of B2 obtained from the simulations, as shown in Finally, the effective surface has also been estimated using the value of z = 3 cm, since B2 has fallen to ∼6% and the gradient of B2 to ∼10% of its respective maximum values. With an analogous reasoning, the axial limit of the affected volume can be set from r = 3 cm (note that r can be either the x or y Cartesian coordinate due to the symmetry of the system). Following these estimations, we can consider that the surface affected by the magnetic pressure has a radius of curvature of ∼3 cm.From Introducing in Equation (8) the estimated radius as well as the values of the pressure presented in It is well-established that through the influence of the surface tension on the structure of the channel proteins, the membrane deformations and modification of its surface tension affect the kinetics of voltage channel gating mechanism. The influence of pressure on the elastic energy of any membrane has been described and thoroughly analyzed in an extensive literature . Please + and K+ voltage channels are mechanosensitive even though they are not mechanosensors . For instance, the threshold pressure for inner hair cells of ear sensitivity is 10–5 Pa  the pressure induced by the static magnetic field will interfere with the pressure of the moving structure. The resulting features from the interplay between both processes acting simultaneously have yet to be explored.We propose that a mechanical mechanism may contribute to the long-lasting effects of the tSMS over the cortex. Hitherto, this is not necessary the unique mechanism that can determine the neurophyological effects. During tSMS, the brain and arteries  are moving within a magnetic field, so electrical currents are generated. This means that a repetitive electrical stimulation is interfering with the neural cell functions. Moreover, we cannot exclude other mechanisms causing the tSMS effects on cortical excitability by acting directly or indirectly on the nervous system. Future studies on isolated preparation  or on single neurons  may clarify the real importance of each of these mechanisms.In summary, it has been shown that the magnetic field gradient created by a permanent magnet is able to exert pressures on different homogeneous biological media which induce surface tensions whose strength can alter substantially the gating probability of mechanosensitive channels.The mechanisms how static magnetic fields modulate cortical activity are largely unknown. We suggest that mechanical stimulation – may be not exclusively – is a possible mechanism how static magnetic field can produce effects in biological systems. These effects are possibly due to the modification of channel (and receptor) characteristics caused by the persistent pressure produced by the static magnetic field.The datasets generated for this study are available on request to the corresponding author.All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.AO and JA were cofounders of the company Neurek SL, which is a spinoff of the Foundation of the Hospital Nacional de Parapléjicos. AO and JA were inventors listed on the following patents: P201030610 and PCT/ES2011/070290 (patent abandoned). The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


In their study, the authors performed an experiment where poppy seeds were applied to the surface of bread roll dough, and the dough was baked at 190°C for 25 min. Table 8 in their manuscript does generally show higher mean values for opium alkaloids in unprocessed seeds compared to those either subjected to dry heat or applied to the surface of bread dough and exposed to the baking treatment. Yet, as noted by the authors, there was a large range in the levels of opium alkaloids in the unprocessed poppy seeds . The high variability in opium alkaloid concentrations makes it difficult to ascertain how the thermal processing affected levels of these compounds. High natural variation of opium alkaloid concentrations in poppy seeds has been previously reported, which has led some authors to suggest using a relatively large sample size for analysis—such as 10 g poppy seeds or greater—to reduce analyte variance . As CarlIn addition to the high sample variability in opium alkaloid levels in poppy seeds used in the study, there are several other important aspects of the experimental design that we believe make it difficult to draw definitive conclusions from the thermal processing experiments. Because Carlin et al. analyzed seeds scraped from the top of the finished baked product, it is plausible that the reported loss of alkaloids might be due to transfer of alkaloids from the surface of the seeds to the batter. Opium alkaloids in poppy seeds can be significantly reduced by washing the surface of the seeds, but lack of reported recovery experiments by the authors leave unanswered whether losses are “true losses” due to degradation of the alkaloid compounds, or are an artifact of the compounds simply transferring to the batter . We hypoEa) values and half-lives of the major opium alkaloids in poppy seeds, which showed relatively low thermal sensitivity of morphine and codeine. Indeed, our experiments indicated that the half-lives of these alkaloids at 200°C ranged from 32 to 39 min.Moreover, although the baking experiments exposed the poppy seed-coated bread dough in an oven set at 190°C, Carlin et al. did not monitor the actual temperature of the surface of the baking dough. Due to moisture retained in dough throughout the baking process, it is important to monitor the temperature of the baked product, as there can be large differences between the set oven temperature and the surface/interior of the baked product. In contrast to the conclusions made by Carlin et al., our group’s research has found that baking poppy seeds either incorporated in a baked product (a muffin) or applied to the product’s surface resulted in no significant effect on opium alkaloid levels See  Shetge . The resWe posit that the lack of a change in opium alkaloid levels in our experiments during baking in a 200°C oven may be because the interior of the muffin did not exceed 100°C under these conditions, and the surface of the muffin reached only ∼136°C at the end of the 16 min baking time period. At these temperatures, the thermal degradation data from our experiments predict that this baking time would not be of sufficient length to result in even a 50% reduction of morphine and codeine.Although Carlin et al. cites previous work that suggested baking conditions may significantly reduce levels of opium alkaloids in poppy seeds , we haveWe believe that it is important to continue to pursue research on the topic of alkaloid degradation on or in poppy seeds. As such, we acknowledge that Carlin et al. has added interesting and insightful contributions through their present work. Still, as researchers we believe that it is critical to note where the data do not support conclusions made by Carlin et al. in order to help drive this field forward. Further, as published data on reduction of opium alkaloids in poppy seeds has been used by governmental bodies to provide safety and processing recommendations in this area , it is iThe idea for the manuscript was conceptualized by BR, and all authors contributed to the writing and review of the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Longitudinal inhomogeneity of tracks inscribed in a YAG crystal and the statistics of nonlinear transmittance of the writing beam is studied under conditions of direct femtosecond laser writing in non-thermal mode. Nonlinear transmittance fluctuations inherent in the laser writing were discovered, and their correlation with track inhomogeneity is established. A model of femtosecond laser writing in crystals is built that includes three modes of plastic deformation in the laser impact zone. The modification threshold of the femtosecond direct laser writing is identified with reaching yield stress. The method allows one to form spatial distribution of refractive index with a micron resolution by means of a simple coded movement of a tightly focused femtosecond laser beam without any additional technological stages, as opposed to electronic lithography. DWL in crystals is a particularly intriguing technology, because it opens far-reaching perspectives for waveguide formation in any crystals4. Being a laser medium, the crystal waveguides often have advantages in comparison with optical fibers because they can incorporate large concentrations of rare-earth ions, have better thermal conductivity, larger damage threshold, and have lower impurities causing losses in mid-IR5. Waveguides in non-center-symmetric crystals are used in Pockels cells with low control voltage, and as an efficient frequency convertor of low intensity light8. Recently demonstrated combination DWL and etching open the door to manufacturing of photonic crystal waveguides9.Direct femtosecond laser writing (DWL) in the bulk of transparent glasses and crystals is a quick and flexible method of forming waveguides and waveguide circuits in a 3D format11, or the nanogratings formation12, whereas in thermal mode there is an additional aspect to that mechanism—diffusion of ions of which the glass consists14. Diffusion normally increases the contrast of the refractive index in comparison with a non-thermal mode.Admittedly, the mechanism and nature of refractive index change in glasses is basically clear. It is connected with the structural rearrangement of the glass grid in a non-thermal modification mode, hence a change in polarization and density3. The only example of the well-understood nature of refractive index change in crystals is amorphization in quartz17 and sapphire18. Unfortunately, waveguides inscribed in quartz and sapphire under the amorphization mode possess high propagation loss due to crack formation inevitably accompanying the laser writing19.As opposed to glass the mechanism of the refractive index change in crystals suitable for low loss waveguide writing is still not understood, although a broad range of modification regimes was reported for waveguide writing in crystals20. However, micro-Raman spectra, shown in this paper, allows us to state that the crystal phase is well preserved in the damage area, because Raman linewidths for the damaged crystal region are identical to corresponding linewidths for the pristine crystal. Moreover, the mid-IR reflectance spectra obtained from the modified area in YAG also showed that a crystal lattice survived after modification as opposed to Ródenas’s conclusions21. Thus, there is no agreement in the scientific community about the nature of DWL in YAG. Forming of voids and phase transformation in sapphire is an example of extreme impact of ultrashort laser pulses on a single crystal, and such mode obviously is not suitable for writing of low loss waveguides23. Earlier we reported on phase transformation in single crystal YAG, where we wrote tracks in extreme thermal mode, however we haven’t been able to obtain any waveguides in this mode so far24.Ródenas claimed that the cause of the refractive index decrease in ceramic YAG is amorphization too35. Meanwhile, knowledge of the state of the matter obtained in the result of moderate modification in crystals in a non-thermal mode is important for discovering ways to improve the uniformity of the modification tracks composing waveguides, as this knowledge opens the way to reduction of scattering loss, which is usually a dominant part in total propagation loss in the depressed cladding waveguides29.In cases of low loss waveguides inscribed in crystals, the nature of the refractive index change in the exposed region has not been discoveredHere we focused on the study of longitudinal nonuniformity of tracks and the statistics of transmitted pulse energy in the course of track writing in YAG:Nd single crystal and silica glass, and these findings allowed us to draw a conclusion about the nature of modifications in broad ranges of sample translation speeds and laser pulse energies, starting from the modification threshold, which is for the energy range where most smooth tracks are formed suitable for the writing of waveguides with low propagation loss.Ein were obtained under the condition where each laser pulse was focused to a new, unmodified place in the plate in order to avoid the memory effect36  10 × 5 × 3 mm plate, which was parallel to the crystallographic plane (211), and the translation direction of the plate was along the [111] crystallographic axis and perpendicular to the [110] crystallographic axis. Dependences of nonlinear transmittances of the YAG:Nd plate and the fused silica plate on the laser pulse energy 3:D is the diameter of the laser beam waist, frep is the laser pulse repetition rate. Below we will call this parameter as the overlap P.To analyse the statistics of the nonlinear transmittance, it appeared to be more convenient to present the experimental dependences on the number of laser pulses that overlap with each other in the modification region than on the translation speed20. The transverse size of the track along the beam will be referred to as the track height h. Figure h in the YAG:Nd crystal against the overlap P for different laser pulse energies Ein.The inscribed tracks of reduced refractive index in YAG:Nd crystal had a traditional cross section shape, strongly elongated along the beamFigure  formula  . Howeve formula a. Theref formula c.R against the overlap P are shown in Fig. Longitudinal inhomogeneity of the tracks in YAG:Nd was investigated with Fourier analysis of their phase images (Method). The plots of the track longitudinal inhomogeneity P = 2.7–11 do not differ in amplitude and characteristic spatial frequencies from those in unirradiated crystal regions. The increased phase fluctuations along the track with P = 2 are obviously caused by a purely geometric factor due to a very small overlap, which is not relevant to our study. In tracks inscribed with overlaps P > 12 both the amplitude and the frequencies of random phase oscillations are significantly increased compared to pristine crystal regions.In order to understand the dynamics of writing we have investigated the ending of a mm-long track written in YAG:Nd under the condition where the laser was switched on while the beam waist was scanning inside the crystal at constant speed. The optical phase profiles along the central lines of tracks under view along the direction of the laser beam are shown in Fig. P = 3–7, the phase incursion is smooth and uniform along the track, and hardly visible on the background of random phase fluctuations of apparatus and pristine crystal. A regular phase modulation in the form of oblique stripes is observed along the tracks with overlaps P = 9–13, while the direction of the stripes coincides with the direction of the crystallographic axis [100]. The period of the regular modulation lies in the range of 1.19 – 1.27 μm. Chaos is observed in the phase images of the tracks with a large overlap of 17 or greater.Figure While writing tracks, we recorded videos under top view in the direction of the laser beam. Two representative videos of the writing under small and large overlaps (P = 3.3 and 23) are in the Supplementary Videos38. Next, the conversion of the electron plasma energy into the energy of the crystal lattice occurs, with a small fraction of the energy being emitted by the plasma. We believe that the modification of the YAG:Nd crystal under the impact of femtosecond pulses, i.e., constant changes in the crystal lattice, is plastic deformation accompanied by a generation of vacancies, their fusion into vacancy disks, and the subsequent generation of dislocations on them. Generation of slip dislocations is a necessary condition for plastic deformation40. A decrease in the refractive index in the modification region is the result of the crystal density decrease during the plastic tension under the impact of internal pressure arising in the region of the electron plasma, and under conditions of comprehensive compression from the side of the surrounding unirradiated crystal lattice. While writing a track, the plasma region moves throughout the crystal from pulse-to-pulse. The crystal was subjected to the highest tension at the plasma region, and the tension partially relaxed in the track outside the plasma region. Thus, the end of a track, where the last laser pulses impacted, is subjected to highest tension. This is reflected in the phase profile along the track. The dip at the end of writing corresponds to the region with the highest tension, and the dip amplitude increases with the overlap P  exceeds 1 μs even for the smallest ds ≈ 6 μm. Immediately after the pulse passage (t≈0.5 ps) the crystal lattice has not heated up from the absorbed energy yet, and the Gibbs free energy Φ of the electron plasma region has increased by the absorbed pulse energy 45. On the other hand, in accordance with the basic thermodynamic relation V0 is the volume occupied by the electron plasma, p0 is the excessive pressure in the electron plasma region. Thus, we obtain the formula for pressure:Next, we show that at the modification threshold the generated pressure fairly matches YAG yield stress. The events associated with the deformation of the crystal in the region of modification finish on the time interval of 10 ns3. In accordance with formula . According to Fig. entclass1pt{minima47, and the deformation of nanoceramics48, it was found that a pressure of 4 GP is required to activate plastic deformation of YAG microcrystals at a temperature less than 400 °C (yield stress). The activation pressure decreases to 2 GPa with the temperature increasing up to 1500 °C. Based on the arguments of the previous section, we believe that such pressure locally arises within the plasma zone, and it initiates plastic deformation of the crystal.When studying the synthesis of YAG nanoceramicsP due to the small changes in the linear and nonlinear refractive indexes and multiphoton absorption coefficient. However, the modification region size h depends on overlap P  observed in YAG50, nor with volume nano-gratings observed in fused silica12. These statements are supported by experimental facts: (1) orientation of the stripes follows crystallographic axes and is not related to polarization; (2) the structure is not formed under high overlap of laser pulses. We believe that we are dealing with self-organization deformation processes that are intrinsic to crystals, and the laser beam plays the role of an initiator only. When the dislocation density reaches some critical value, a track with homogeneous dislocation distribution becomes an unstable dissipative system51. Periodical agglomeration of dislocation reduces system energy and makes it stable53. A sharp spontaneous transition from the chaotic agglomeration of dislocation to the regular structure happens with some delay after the beginning of track inscription, and it can be considered as a bifurcation point51. The amplitude of delay is obviously connected with dislocation mobility, which is reduced with the overlap.The regular structure that looks like stripes nearly parallel to the [100] crystallographic axis at overlaps ing Fig. . EarlierR and RSDT on the overlap at the same range overlaps of 11–15  upon overlap P  unlike the common view on direct laser writing in crystals which implies that the smooth and homogeneous optical properties along the waveguide can be obtained under a large overlap.Humankind has been taking advantage of plastic deformation since the dawn of time, for example in metal shaping. However, in our research we are possibly the first to describe plastic deformation initiated not on the surface of a crystal, which usually happens when a sample is exposed to mechanical pressure, but inside it.54.We expect that the proposed model of laser writing can be expanded on other crystals and will create a new approach in the study of direct femtosecond laser writing in crystals. We believe that plastic deformation is the basic phenomenon underlying the dramatically increased etching rate of YAG crystal exposed by ultrashort pulses, and could play a key role in the development of nanolithography for crystals1. The femtosecond laser beam at a wavelength of 1030 nm was focused by a 0.65 numerical aperture objective lens under a polished surface of a 3 mm thick plate at a depth of 50 μm. The plate was mounted on a precision 3D translation stage (Aerotech) and translated parallel to the polished surface at a constant speed Vsc in the direction perpendicular to the beam. The plane of the laser beam polarization was perpendicular to the translation. The calculated beam waist diameter D was 1.0 μm. The pulse duration was 180 fs, and the repetition rate did not exceed 2.5 kHz, and was equal to 1 kHz in most of the experiments. Such low repetition rate allowed for avoiding effects with heat accumulation from pulse to pulse. The energy of the laser pulse incident on the sample Ein was controlled using a polarization attenuator, while 30% of the beam power was diverted by the beam splitter to the energy meter head . In addition to the standard direct laser writing setup, the beam that passed through the sample was collected on a second energy meter head with an objective lens having a numerical aperture of 0.75. Thus, the energies of each pulse incident on the sample and transmitted through it were simultaneously measured, and subsequently the statistics of the non-linear transmittance were analysed.The statistics of nonlinear transmittance of femtosecond laser pulses of YAG:Nd (0.3 at%) and silica glass plates in the course of writing tracks of a modified refractive index in them was studied using a commonly used transverse scheme for direct laser writing of waveguidesFluctuations in the non-linear transmittance have three contributions of different natures. Aside from the stochastic part of absorption/reflection of the electron plasma, the noises of the laser itself and the pulse energy detector contribute to these fluctuations. In Appendix 57. Image capture was done on optical microscope Olympus BX-61 equipped with camera Retiga 3000 and an objective lens Olympus UPlanFLN-40x (NA = 0.75). The sample was back illuminated by green light from a halogen lamp passing through an interference filter centred at 503 nm with bandwidth of 10 nm. An image focused on a track and two images defocused by ± 1 μm were captured using computer-controlled z-stage with a piezo actuator. The two-dimensional phase incursion distribution was computed from above three images with QPm software (Iatia Ltd.) and was obtained for each pair of the laser pulse energy Ein and the overlap P P = 17 and Ein = 80 nJ, and its Fourier transformation is shown in Fig. ωy > ω1 and ωy < ω1 , where ω1 is some cut-off frequency. Therefore, the formula expressing the root-mean square phase inhomogeneity across the track reads:N and M is the number of pixels in this image by abscissa (across a track) and ordinate  correspondingly, A phase image underwent a two-dimensional discrete Fourier transform (DFT) with the Hamming weight function. For example, a section of the track inscribed with entclass1pt{minimaSupplementary Video Legends.Supplementary Appendixes.Supplementary Video 1.Supplementary Video 2.


Digital fingerprints are being used more and more to secure applications for logical and physical access control. In order to guarantee security and privacy trends, a biometric system is often implemented on a secure element to store the biometric reference template and for the matching with a probe template (on-card-comparison). In order to assess the performance and robustness against attacks of these systems, it is necessary to better understand which information could help an attacker successfully impersonate a legitimate user. The first part of the paper details a new attack based on the use of a priori information  that could be exploited by an attacker. In the second part, a new countermeasure against brute force and zero effort attacks based on fingerprint classification given a minutiae template is proposed. These two contributions show how fingerprint classification could have an impact for attacks and countermeasures in embedded biometric systems. Experiments show interesting results on significant fingerprint datasets. Biometrics is a commonly used technology for unlocking smartphones, secure border controls or physical access to buildings. Yet, biometrics data are sensitive, since it is not possible in general to revoke them in case of an attack. Thus, these data have to be protected as well as possible. In the case of digital fingerprints, the reference template (a set of minutiae) is usually stored in a secure element (SE) (such as e-passports). Due to the limitation of memory size and computational capabilities, the reference template is stored following the ISO Compact Card II standard . This reRegarding security, biometric systems have many vulnerabilities. As presented by Ratha et al.  and moreIn general, the attacker has to generate a biometric template to carry out an attack. Considering embedded biometric comparison algorithms on a SE, the attacker sends random probes in an attempt to pretend to be the legitimate user until success. Since theoretically and in the worst case, the attacker generates all possible combinations of template, this attack is called brute force. Different studies have been investigated to prevent this type of attack ,5. AnothIn this work, we consider the vulnerability on point 4  the type of sensor, (2) the fingerprint image resolution, (3) the minutiae number and (4) the fingerprint type. This methodology is new and could be used for any other a priori information. The second contribution is the design of a fingerprint classification method only considering information contained in a minutiae template . Once again, very few works have concerned this topic in the literature. This method could be useful to detect brute force and zero effort attacks by checking the fingerprint type of probes. The common point of these two contributions concerns the fingerprint classification that could be useful both for attackers and defenders of biometric systems.The paper is organized as follows. The fingerprint class, according to the Henry’s classification  for whicSensor type used during the enrollment ;Image resolution;Number of extracted minutiae in the reference template.Our hypothesis is that an attacker has a logical access to the system and has the possibility to send fake biometric templates to the OCC by exploiting some a priori information. The available knowledge on any biometric sensor is categorized as:In this section, we propose to investigate their impact on the success of attacks. We assume that an attacker can only send digital templates or images to the OCC, thus implementing the vulnerabilities 2 and 4 defined in the Ratha model by (1) modifying the resolution of the image supplied at the sensor output thereby influencing the minutiae extraction, (2) setting the fingerprint class, (3) providing information on the type of sensor used during the enrollment process and (4) when the attack is performed right after the minutiae extraction process, the attacker can know the number of minutiae extracted saved in the reference template in the SE. All extracted minutiae are stored in a template following the ISO Compact Card II format.z and D a comparison algorithm based on a distance between a reference and a biometric probe. The success of an attack by an impostor is given by:z or the biometric system. Our goal is to estimate the advantage for an attacker to build z. In the next section, we design the experimental protocol in order to estimate the advantage an impostor has knowing some or all information.We want to quantify the contribution of the attacker’s knowledge of the parameters used by the sensor to increase the efficiency of an attack. This probability is based on the False Acceptance Rate (FAR) which can be considered as the probability of a successful attack. We define We have to define many aspects of the experimental protocol such as the biometric datasets, the matching algorithms, the testing scenarios and the software platform for running experiments.We used the SFinge software  to generReference database: this database contains the reference templates of all users. We randomly generated one sample per user for 500 individuals (given a random and distinct seed for each user). This database contains 500 fingerprints;Attack database: we generated a database with 1000 different fingerprint samples (one sample per user). This database has been randomly generated (by using different seeds than the reference database) and is used for attacks.For each of the four a priori information, two types of databases are designed:When using SFinge, we can choose the type of sensor among capacitive and optical. This leads to the construction of four databases (a reference database and an attack one by sensor type). Considering the resolution level of the fingerprint image, we have three possible values  inducing six databases. For the number of minutiae, we have created two categories (number of minutiae <38 or >38) inducing four databases. Finally, when considering the fingerprint class , 10 databases are generated (two per class).DB_SFinge. The only parameters we have set are the number of users (100) and the number of templates per user (8). Finally, we get a total of 800 fingerprints.In order to set the decision threshold Equation , we propDB_SFinge database. The value obtained was equal to 1.03% with a decision threshold value Bozorth3 algorithm : The EERDB_SFinge database. The value obtained was equal to 0% for a decision threshold Minutia Cylinder-Code (MCC) algorithm : The EERIn this study, we used two matching algorithms from the research community in biometrics:Scenario 1: we simulated a brute force attack. We randomly selected 500 min templates, following a uniform distribution, in the database generated using SFinge, which constitutes the reference database. The attack database was generated by building 1000 biometric templates randomly but respecting the ISO format, itself coming from SFinge.Scenario 2: For each of the given a priori information, a reference database was generated with the SFinge software containing 500 min templates. In addition, for each of the a priori information, an attack database containing 1000 biometric probe templates is generated and is compared with the reference database. For example, considering the sensor type, we obtain four comparisons as shown in For any attack, an impostor provides a biometric probe to be authenticated as a legitimate user. Two scenarios are used to simulate an attack:In order to evaluate the impact of an a priori information on the efficiency of an attack, we use the EVABIO platform  to charaAttacks module was updated because it contains methods for testing the useful knowledge for an attacker such as the sensor type, the image resolution captured by the sensor, the fingerprint class or the number of minutiae extracted from the image. Given each information, we determined whether this type of knowledge is important for an attacker to succeed in impersonating individuals. This module also contains a method for generating an ISO compliant biometric template using SFinge. It is possible to generate random fingerprint templates to attack the matching algorithms. The Evaluation module generates performance metrics such as We have developed a new attack module to carry out this study in order to test different attack methods when evaluating an OCC fingerprint system. In this study, the In this section, we present the results of this experimental study for each separately considered a priori information.Regarding the knowledge of the sensor type used to generate the biometric reference of the individual, we compute the value With the knowledge of this a priori information, , we compute the brute force attack and The obtained results show that for Bozorth3, the probability value of a successful attack is equal to 0.0141% with the brute force attack and 0.0162% when we know the number of minutiae in the biometric reference. For the MCC algorithm, the probability value of a successful attack is equal to In order to analyze whether the knowledge of the number of minutiae of the biometric reference has an impact on the effectiveness of this attack, we apply the following scenario: we only consider the scores between the reference template and the tests having the same number of minutiae. In this case, we have two sets of brute force attack and In terms of knowledge of the image resolution, we calculate the We can see, in both cases, the small advantage for an attacker to know the resolution of the original image extracted by the sensor. In order to analyze whether the resolution of the original image has an impact on the efficiency of this attack, we apply the following protocol: we only consider the scores between the reference and attack models with the same resolution images. In this case, we have three sets of For the Bozorth3 matching algorithm, we can see that it is quite impossible to have a successful attack with a high resolution image (1000 dpi), as opposed to a low resolution image (250 dpi). The same remark can be formulated for the MCC algorithm. We also compute the value In order to analyze its impact, we apply the following methodology: we only consider the scores between the reference template and attack probes having the same fingerprint class to calculate the In this study, we wanted to know which a priori information could be important for an attacker in order to impersonate an individual enrolled on an embedded biometric system. We have shown that the knowledge that helps an attacker the most is the fingerprint class. Indeed, our experiments show that knowing the fingerprint class generally increases the probability of usurping a legitimate user. On the contrary, the knowledge of the number of minutiae, the sensor type or the image resolution are less informative. The algorithm on which we obtain the best rate of identity theft is Bozorth3 with Arch-type fingerprints. We hypothesize that this algorithm is less efficient and not optimized for Arch-type fingerprints. If we look at the other types of fingerprints for the two matching algorithms, we notice that the usurpation rate is quite low which is quite logical and coherent. Moreover, for both algorithms, the highest acceptance rate is on Whorl, which are the most common fingerprint type . In geneIn the next section, we propose a second contribution on fingerprint classification. This could be useful in detecting brute force and zero effort attacks, i.e., detecting attempts with different fingerprint classes.In the previous section, we identified many attacks consisting it sending a fake probe to the biometric system. The brute force attack is realized by sending random templates and the Zero effort by one some real samples captured directly from the impostor. Both attacks could be easily detected if the fingerprint class of the probe does not correspond to the legitimate one. Consequently, it is necessary to recognize the fingerprint class from an ISO fingerprint template . BecauseIn 1996, Karu and Jain defined the first method for fingerprint classification based on singular points in fingerprint images . They obAll these methods provide very good results but require having the fingerprint image as input. This induces a lot of computational resources as well as time. This is not possible in embedded biometric systems. Indeed, it is not possible to store the fingerprint image in such devices, only the minutiae template is available mainly due to memory limitation. Our objective is to propose a fingerprint classification method with only the minutiae template as input, i.e., without any access to the fingerprint image. However, very few works have considered this problem. To the best of our knowledge, the paper by Ross et al.  is the oj of the user k.In this study, we only process ISO Compact Card II minutiae templates. This format consists of four features The proposed method consists in defining new features from the minutiae template.From the minutiae template, we design a first statistical features vector called IsoStructIn order to take into account the spatial distribution of minutiae, we propose to use the Delaunay triangulation as translation and rotation invariant representation ,28. Delaj of an individual k can be represented by a feature vector j for user k. j of user k. From these two feature vectors Thus, each template In order to define a model for each of the five classes of fingerprints, we use a statistical learning technique. From all the existing classification schemes, we have chosen the technique based on Support Vector Machine (SVM) because of its high classification rate obtained in many works ,37,38, aSince SVMs are binary classifiers, several binary SVM classifiers are required for a multi-class classification problem when using a SVM classification technique. A final decision is then taken from all the outputs of the  binary SWe enumerate here all the elements necessary for our experiments.SFinge databases: The FVC databases usually used in fingerprint works do not provide any information about the fingerprint class. We have therefore generated five databases with the SFinge software , one forIn order to recognize the fingerprint class associated with a template, it is necessary to train the SVM on a learning dataset. A test dataset is required to measure the effectiveness of the generated classifier. To do this, several test-learning sequences have been executed. In each sequence, the fingerprint database was subdivided into separate sets for learning and tests. In each test, 80% of the database was selected for learning and 20% for testing for each of the 5 databases. More specifically, each training set contains 640 fingerprints, while the test set contains the remaining 260 fingerprints. We performed 1000 random draws have and the recognition rate is averaged. We used the libsvm library  from NISWe analyze the efficiency of the two proposed features vectors (IsoStruct and TemplateStruct) in the two next sections.One of the first elements we need to test is the number of quantization levels in the normalized histograms. We tested different quantization levels  on the structure of the characteristics. The results are presented in Since the minutiae template contains only four pieces of information, we want to know which ones are important for the fingerprint classification. We can conclude that the characteristic We used the same protocol as defined in the When performing the same procedure as before, we obtain the correct classification rates presented in The addressed problem in this paper is to determine the fingerprint class given the minutiae template. We proposed two methods mainly based on the proposal of features vectors. The first one concatenates histograms of each information in the minutiae template. With this approach , we get 80.37% as the recognition rate. We observed that the orientation of minutiae was the most discriminating parameter allowing to achieve a good recognition rate of 80.23%. This is why the second feature vector is based on a geometric approach based on the Delaunay triangulation, allowing us to obtain more parameters while keeping the ISO_Angle parameter. With this method, we increase the recognition rate by 9% and we get 89% of accuracy for fingerprint classification.We have demonstrated that only two a priori information help acceptance by the system, the image resolution and, most significantly, the fingerprint type. Perspectives of this work concern the study of other a priori information that could be interesting for an attacker. We could think of the knowledge of the used sensor  for the enrollment or gender as for example. A combination of studied a priori information could be investigated to confirm these results.We proposed in this study some new features allowing us to reach an accuracy of 89% for fingerprint classification, given a minutiae template as input. In order to improve the fingerprint classification, we could think of using deep learning approaches to increase the accuracy.


Wake‐up circuits in smart microsystems make huge contributions to energy conservation of electronic networks in unmanned areas, which still require higher pressure‐triggering sensitivity and lower power consumption. In this work, a bionic triboelectric nanogenerator (bTENG) is developed to serve as a self‐powered motion sensor in the wake‐up circuit, which captures slight mechanical disturbances and overcomes the drawback of conventional self‐powered motion sensors in the wake‐up circuit that the circuit can only be triggered when a considerable pressure is applied on the sensor. The bTENG mimics the structure of plants and the addition of the leaf‐shaped tentacle structures can increase the electrical outputs by four times, which largely extends the detection range of the wake‐up circuit. The bTENG can detect both noncontact and contact mechanical disturbances; and voltages generated from both situations can trigger the wake‐up system. Moreover, the specially designed circuit that is compatible with the bTENG can help more accurately control the wake‐up system and prolong the battery life of the electronic networks to 12.4 times. An intrusion detection system is established in the wake‐up circuit to distinguish human motion and judge the scene. This work opens new horizons for wake‐up technologies, and provides new routes for persistent sensing. A wake‐up system with low quiescent power consumption, large wake‐up range, and ability to distinguish false trigger is developed based on a plant‐shaped bionic triboelectric nanogenerator, which can be awakened by contact and noncontact mechanical disturbances. This work provides new routes for persistent sensing and may have broad applications in areas such as environmental monitoring, threat detection, perimeter monitoring, and critical infrastructure protection. First of all, since most of the common sensors require power supplies, it is a great challenge to reduce quiescent power consumption. Second, the current motion sensors of wake‐up circuits generally require large amplitude vibrations in order to generate large enough voltages to wake up the circuit. Third, the fabrication processes of the existing sensors used in wake‐up systems are generally complex and expensive. To further reduce the quiescent power consumption, one possible solution is to replace the power‐consuming sensors with self‐powered sensors that can work without system power supply; and to increase the wake‐up system's wake‐up range and sensitivity towards slight mechanical action, new sensors that are capable of generating large enough voltages to trigger the wake‐up circuit under slight touch or even no direct touch need to be developed. In addition, sensors with simple and scalable fabrication processes are desirable, from the perspectives of economy and large‐scale production.With the advent of the information age, the smart microsystem, which is a combination of micro‐electro‐mechanical system and microelectronics technology, has become a global research hotspot. It integrates sensors, actuators, signal collectors, data processors, and control circuits for applications in unattended security, infrastructure monitoring, and the Internet of things. To enhance the service life of the sensor network in the area where the battery cannot be replaced, the defense advanced research projects agency proposed the concept of “Near Zero Power RF and Sensor Operations (N‐ZERO)” that is, wake‐up systems sense the environment 100% of the time with ultralow quiescent power consumption and use the energy in signals to activate an internal signal processing circuit.1, 2 However, the PENGs, which work based on the piezoelectric effect, have low output power density and strict applied conditions. The PENGs can only generate electrical outputs when an applied pressure induces strain inside the piezoelectric material, and the small voltage generated by a slight touch cannot easily overcome the high switching threshold in the wake‐up circuit. These characteristics impose limits on the sensing ability of slight touch and wake‐up range of the wake‐up system. Therefore, low power‐consumption wake‐up systems with self‐powered motion sensors that can sense weak mechanical disturbances and have long sensing distances are in urgent demand. The triboelectric nanogenerator (TENG), which is based on the conjunction of contact electrification and electrostatic induction, has attracted intense attention since its invention. Since the TENG has the property of zero power consumption and can output high voltages even when triggered by noncontact mechanical movements, the TENG is a possible solution to meet the demands of self‐powered sensors for wake‐up systems that may enable the system to wake up under slight touch and enlarge the wake‐up range. In addition, the TENG has the advantages including low cost, lightweight property and simple fabrication.At present, there are self‐powered sensors that have been used in the wake‐up circuit for detection of mechanical disturbance, which are mostly piezoelectric nanogenerators (PENGs).4, 5In this work, a plant‐shaped bionic TENG with no power consumption is developed in the wake‐up system, which can trigger the wake‐up system under slight touch or even no touch and largely extends the battery life of the system. Compared with the PENGs that are commonly used in the wake‐up circuits, the bTENG is superior for slight touch sensing. Moreover, the addition of leaf‐shaped tentacles and nanostructures in the bTENG increases the output voltage by four times when sensing slight touch, which improves the detection range of the wake‐up system in the process of environmental monitoring. Also, a wake‐up circuit is specially designed to be compatible with the bTENG and achieve ultralow quiescent power consumption. The wake‐up system with the bTENG can extend the battery life of the electronic network to 12.4 times. To highlight the characteristics of intelligence in our system, a computer program is elaborated to distinguish human motion and judge the wake‐up scene according to the audio signal recorded by the microcontroller after awaking. This work endows the TENG with a new role as a self‐powered sensor for slight touch in the wake‐up circuit and opens up new ideas for the design of wake‐up systems with ultralow quiescent power consumption.22.1Figure The typical structure of the bTENG is illustrated in The micro/nanostructures imitating the nanostructures of lotic leaves Figure  are crea The periodical contact and separation between the single‐electrode‐mode bTENG and the approaching object  can causes electrical potential variation between the copper electrode and the ground in the open‐circuit condition . The TENG produces continuous pulse voltage signals of 23 V when exerted by a pressure of 95 Pa. Moreover, it is found that when objects made of different materials exert pressure on the TENG, the maximum output voltages are all more than 6 V when the pressure is less than 700 Pa . These two experiments demonstrate TENG's superiority as a self‐powered sensor for detecting noncontact and slight touch disturbances.In the experiment of contact motion that exerts pressure during contact, we used a gauge to control the force applied on the sensors’ surface Figure . The app It is found that the electrical output of the TENG is 20 times higher than that of the PENG in the slight‐touch experiment; and the PENG generates no electrical outputs in the noncontact experiment . Note that the detailed theoretical explanation for the TENG's superior performance to the PENG's in slight‐touch sensing can be found in Note S1, Figures S4c and S5, Supporting Information. A feather‐touch experiment is also conducted to demonstrate the TENG's advantage in detecting slight touch. When a feather wavered to the bTENG, the bTENG generates a voltage of 1.2 V  are connected to the bTENG, respectively. It is found that when the open‐circuit voltages of the bTENG are the same, the smaller the MOSFET's parasitic capacitance, the larger the actual output voltage of the bTENG . Therefore, for practical applications, the bTENG based wake‐up system can be more precisely controlled by adding a MOSFET with a certain threshold voltage and a certain parasitic capacitance according to practical requirements. In addition, when choosing a MOSFET for the wake‐up system, it should be kept in mind that the MOSFET needs to have the characteristic of low drain leakage current in order to reduce the power consumption of the system and high breakdown voltage in order to ensure the safety of the circuit.In this article, when the voltage signal generated by bTENG turns on the MOSFET, the MOSFET will send a pulse signal to the connected dormant microcontroller and wake up the CPU with short delay (<10 µs) to start the subsequent work. The output signal of the MOSFET with a low threshold voltage (0.45 V) when triggered by the bTENG is illustrated in Figure  The detailed explanation of the basic description of MSP430 can be found in Note S3, Supporting Information. Using MATLAB software, we write a program extracting the mel‐frequency cepstrum coefficient (MFCC) of the recorded signal to facilitate the subsequent comparative analysis which greatly reduce data quantity by 2%. Methods of extracting the MFCC and the key code can be found in Note S4, Supporting Information. After learning 50 groups of characteristic parameters of environmental noise and ambient sounds (human footsteps) by support vector machine learning method, which can be changed according to the factual requests, the program can compare the received recording with the previous learning result and judge the wake‐up scene . Note that the specific processes of judging scene based on the analysis of the audio signal are introduced in Figure S10, Supporting Information.To distinguish human motion and rule out false triggers, an intrusion detection system is also developed for the scenario that an alarm alert is released only when human intrusion happens. The intrusion detection system is established by analyzing the sound recorded by the peripheral recording device of the microcontroller when unexpected event happens. The specific implementation method is as follows. The triggering signal wakes up the microcontroller, and the microcontroller turns on the recorder to record the audio signal of the wake‐up scene. Then the sound signal is sent to the remote computer through peripheral Bluetooth.34 TheWhen an intrusion occurs, the intrusion detection system will judge the scene: if the intrusion is not initiated by a person, the computer will display “SAFETY;” and if the intrusion is initiated by a person, the wake‐up system will be triggered and the computer will display an “ALARM” alert.2.4 Compared with the nondormant system with the bTENG, the wake‐up system with the bTENG that is set to be woke up every 10 min consumes only one‐seventh of the voltage supply, after the same operation time of 140 min. When the wake‐up time interval is set to be 10 min, the voltage supply consumed by the wake‐up system with the bTENG is only half of that consumed by the wake‐up system with a commercial motion/vibration sensor, after the same operation time of 140 min. The wake‐up system with the bTENG has a battery life that is two times longer than the wake‐up system with a commercial motion/vibration sensor; and the battery life of the wake‐up system with the bTENG is 12.4 times longer than that of the nondormant system with a commercial motion/vibration sensor .40 Comr Figure . These e2.5To demonstrate the practicability of the bTENG‐based wake‐up system, two types of bTENGs are fabricated to meet the requirements of different wake‐up scenarios: bTENGs shaped like shepherd's purse in the noncontact wake‐up mode and bTENGs shaped like philodendron in the contact wake‐up mode.Figure Voc of ≈4.8 V when triggered by noncontact approaching/departing motion, which is 2.4 times higher than the Voc of the bTENG with only the base structure , large wake‐up range that can be awakened by human striding over or slight touch, low cost, and environmental concealment. This work overcomes a bottleneck problem of the power limitations of persistent sensing and provides a new wake‐up method with low quiescent power consumption, which can be widely applied in the areas such as Internet of things and remote environmental monitoring.4Polydimethylsiloxane (PDMS) mixed in a ratio of 1:5 (DC184) was poured onto the positive surface of the dried lotus leaf cut in a leaf shape. The solution stood for half an hour to expel bubbles, and then was heated for full solidification . After the solidification of PDMS, the dried lotus leaves were removed from the surface of the PDMS. Copper wire wound in vein shape and silicone rubber (Ecoflex 00‐30) mixed in 1:1 ratio was put into PDMS mold. The wire at the tail of the tentacle was exposed and connected with a metal plate. The metal plate connected with the blade‐shaped component was placed on a Petri dish that had solidified a layer of silicone rubber beforehand, and then the silicone rubber was poured into the Petri dish for solidification. After curing, the silicone rubber and PDMS could be separated. The device could be folded in half to break the PDMS without damaging the silicone rubber, so as to separate the silicone rubber and the PDMS.VOC, ISC, and QSC of the TENG were measured by a voltage preamplifier (Keithley 6514). One terminal of the instrument was connected with the output of the TENG, and the other terminal was connected to the ground. The software platform was constructed based on LabVIEW, which was capable of realizing real‐time data acquisition control and analysis. A field emission scanning electron microscope  was used to characterize the surface morphologies of the etched film.The output The authors declare no conflict of interest.Supporting InformationClick here for additional data file.Supplemental Movie 1Click here for additional data file.Supplemental Movie 2Click here for additional data file.Supplemental Movie 3Click here for additional data file.Supplemental Movie 4Click here for additional data file.Supplemental Movie 5Click here for additional data file.Supplemental Movie 5Click here for additional data file.


Van Enk and Ten Cate have provided an interesting perspective concerning entrustment . EntrustIn 2005, Olle ten Cate first proposed the concept of entrustment of professional activities in reaction to the granularity of competency frameworks and the divergence between educational theory and clinical practice . This arMy colleagues and I are investigating the contextual translation of the EPA concept in the Netherlands and work is under review at this journal. The use of EPAs is mandatory in the Netherlands, and each specialism has a national curriculum which must describe which EPAs are selected and how EPAs must be used for teaching. Different specialisms give a different meaning to EPAs in their curricula, e.g. some focus only on a selection of critical clinical activities suitable for the core of a training program, while other focus more on an EPA’s suitability for entrustment. Curriculum designers pick from the EPA concept what suits them and what is valuable for medical education in their situation. This is recognized at the level of specialisms and curriculum design, but it is also recognized in the way program directors and residents use the EPA concept within their local context and personal value systems. An example of such a value system is that for the sake of patient safety, some program directors require far more extensive proof of competence before they entrust a trainee to do risky treatments than other program directors do. Is one focus and attributed meaning better than another one? I believe that the perfection of the EPA concept will prove a quest for a universal truth rather than a man-made, subjective truth based on local context. The universal truth fits in a positivist paradigm, whereas the social constructivist’s paradigm would expect the truth to be dependent on stakeholders and context. The original manuscripts were written at a strategic level. In my opinion local versions of EPA implementation will differ. The truth is in the eye of the beholder.The entrustment concept is important and appealing. Investigations and discussions about the use of EPAs, such as the article by Van Enk and Ten Cate, are helpful to increase the knowledge of how the strategic concept may be effective in various ways in the reality of medical education. In our Dutch context, there have been various implementations of the original concept in medical education. It is important that we study the EPA implementations in different contexts so that we develop a better understanding of the relationship between the context in which the EPA is applied, the mechanisms by which EPA work and the outcomes the EPA implementation produces. When used without flexibility, the EPA concept has no magical power to solve issues of teaching, assessment and accountability. The magic is in how curriculum designers, clinical teachers and residents make optimal use of the EPA concept in their specific situation.


Riparian environments are highly dynamic ecosystems that support biodiversity and numerous services and that are conditioned by anthropogenic activities and climate change. In this work, we propose an integrated methodology that combines different research approaches—field studies and numerical and analytical modeling—in order to calibrate an ecohydrological stochastic model for riparian vegetation. The model yields vegetation biomass statistics and requires hydrological, topographical, and biological data as input. The biological parameters, namely, the carrying capacity and the flood‐related decay rate, are the target of the calibration as they are related to intrinsic features of vegetation and site‐specific environmental conditions. The calibration is here performed for two bars located within the riparian zone of the Cinca River (Spain). According to our results, the flood‐related decay rate has a spatial dependence that reflects the zonation of different plant species over the study site. The carrying capacity depends on the depth of the phreatic surface, and it is adequately described by a right‐skewed curve. The calibrated model well reproduces the actual biogeography of the Cinca riparian zone. The overall percentage absolute difference between the real and the computed biomass amounts to 9.3% and 3.3% for the two bars. The model is further used to predict the future evolution of riparian vegetation in a climate‐change scenario. The results show that the change of hydrological regime forecast by future climate projections may induce dramatic reduction of vegetation biomass and strongly modify the Cinca riparian biogeography. We combined remote sensing, field data, and numerical and stochastic modeling to study a riparian areaTopography and water level fluctuations condition the long‐term distribution of riparian vegetationSpatial clusters based on the probability of inundation detect areas of homogeneous vegetation It is one of the most diverse, complex, and active transitional habitats on Earth, supporting very high biodiversity  the hydrological fluctuations of the river flow, (ii) sediment transport dynamics, and (iii) the vegetation dynamics , the vegetation dynamics is crucially affected by the random fluctuations (noise) of water levels induced by stochastic rainfalls  the interspecies interactions due to synergy or competition are overlooked, although the features of the various species are taken in account to set the vegetation‐related parameters; (ii) a steady river morphology is considered, neglecting sedimentation, erosion, and feedback between topography and vegetation; and (iii) the time delay between the vertical oscillations of river water stage and the related change in the groundwater level in the adjacent unconfined aquifer is negligible, if compared to the timescale of interactions between vegetation and groundwater.h¯∗ and the transect width w¯∗ are adopted to scale the main variables According to CR06, the stochastic dynamics of vegetation are mainly affected by the topography and the temporal randomness of the flow. Geometrically speaking, the fluvial reach is identified as a generic riparian transect with the origin of the vertical axis coincident with the minimum value of water surface Figure . This coVegetation features are summarized by the dimensionless local carrying capacity t = m, n, and p are numeric constants depending on the features of the vegetation. The decay factor k is a decay coefficient related to the features of the vegetation and N is a normalization constant. Equation Supported by numerical simulations, CR06 showed that, if time is rescaled with the growth rate (process dνdt=−ανnel (p(ν)p(ν)=Nανβined as α(k)=kPI∫Equation PI<β/ and hydrological data over a long period. In addition, the degree of anthropogenic pressure is moderate, mainly due to the presence of a road connecting the two small towns of Ballobar and Zaidín and some field crops.In the considered reach, the river is wandering with moderately vegetated bars and islands. The braiding index related to the active channel  is lower than 1.5 , poplars , and some mastics (Pistacia lentiscus). Grass‐like plants, such as common reeds  and bulrush  was obtained by processing a free LiDAR data set provided by the Spanish National Center of Geographic Information IGN, . The stuThe LiDAR data set was processed through the software FUSION/LDV in order to have a DTM of the site and the statistics about vegetation height and cover . These statistics allowed for the biomass estimation, as explained in section  5.3The bed of the Cinca River is composed by coarse sediments (conglomerates and gravel) and a fine fraction of clay . As a result, the 2D flow field and the water levels over the study domain were obtained for each flow rate, allowing the rating curve (Q‐h relationships) to be defined for each computational cell. In addition, from the discharge time series  the elevation and (ii) the inundation probability. The first classification  is again superior than a). The former is in fact able to catch a positive correlation between the inundation rate and biomass, likely related to species zonation (see later). In the The first moment of the pdfs  is reported in Figure k—for k has arbitrarily been set as a constant value, ranging from 2.5 to 10 , which supports strategies for climate adaptation and mitigation by accounting for the effects of climate change at the global scale  of 15% (Alfieri et al., k and We replicated the hydrodynamic modeling section  in orderThe above projection shows that the extension of the highly vegetated areas decrease in response to the expected change in the hydrological forcing. This implies an overall reduction of the habitats and a loss in biodiversity. However, this simulation overlooks a crucial feature of natural systems, namely, adaptability. The gradual nature of the hydrological change may allow the riparian vegetation to adopt different adaption strategies. This might occur through morphological adaptation (Kozlowski, In light of the above remarks, we modified the biological parameters in order to mimic plant adaptation in the present modeling framework. To this aim, we arbitrarily increased the calibrated carrying capacity values reported in Figure % Figure . In a nu8Riparian environments are extremely biodiverse and delicate ecosystems, which are undergoing an intense human‐ and climate‐induced pressure. The need for conservation and restoration plans is becoming compelling and theoretical and quantitative ecomorphodynamic models could provide a useful support.In this paper, we have proposed an integrated methodology to calibrate a minimalist stochastic model for riparian vegetation dynamics onto real data. A major advantage of the model is that only few biological parameters need to be set for the intrinsic features of vegetation dynamics. Particularly, when the model is applied to investigate the steady‐state solutions of the biomass distribution, the required biological parameters reduce to two, namely, the local carrying capacity Regarding the biological parameters Figure , the fieThe calibrated model is then shown to well reproduce the actual biogeography of the Cinca riparian zone. The overall percentage absolute difference between the real and the computed biomass amounts to 9.3% and 3.3% for two different vegetated bars. We have also illustrated a possible application of the calibrated model as a LIM. To this aim, we evaluated the effects that a climate‐change scenario can induce on the riparian environment of the Cinca River, where a reduction of the mean water flow is expected (Alfieri et al., modus‐operandi can be adopted at every step of the procedure. For example, we calibrated and used the stochastic model by Camporeale and Ridolfi (The methodology and the calibration procedures here presented rely on a novel integration of different tools of river science, ranging from theoretical and numerical modeling, to stochastic processes, geomatics, and field activities. The conceptual scheme is summarized in Figure  Ridolfi , but the Ridolfi .We decided to adopt the Camporeale and Ridolfi  model siWe finally remark that, in our framework, the river morphology is considered as static. The riverbed of the Cinca River has been undergoing degradation since 1969, when the El Grado Reservoir was built. Indeed, a quick view to the timelapse on free database of Google Earth Engine imaging shows that the two bars focus of the analysis have not moved for the last 30 years Figure . Riverbe