The recent literature has shown that the risk of hypertension in the old strongly depends on their physical abilities. However, it is unknown whether general practitioners (GPs) adapt their treatment strategies to the patient’s independence. This study was conducted to investigate the treatment intentions of GPs for patients aged 80 and older with hypertension in relation to the patients’ level of dependency.n = 305) were invited, directly or indirectly, by email to fill out a questionnaire, consisting of nine cases (three themes). In each theme, the level of dependency gradually increased. Per case, a score depending on the GP’s treatment intention was calculated (range 0–3). The total score represented the ‘Intention to Treat Hypertension in Older Persons’ scale . The difference between the score for robust patients and strongly dependent patients was calculated (delta score).A vignette study in Belgium. Flemish GPs . The GP’s experience showed an inverse relationship to the total and the delta score.Large differences in treatment intentions for hypertension in the very old exist between GPs, but the patient’s level of dependency is not responsible for these differences.The online version of this article (doi:10.1186/s12875-016-0523-y) contains supplementary material, which is available to authorized users. The Western world is facing a grey epidemic. In 2011, the life expectancy in Belgium was 78 years for men and 83 years for women [Cardiovascular morbidity and mortality remain important problems in the oldest old . The manThe Hyvet study showed that antihypertensive treatment reduced stroke mortality as well as total mortality . HoweverThe heterogeneity of the oldest old most likely plays an important role in the explanation of the differences in the risk of hypertension for cardiovascular and total mortality. A recent publication found that the association between blood pressure and mortality depended on the physical abilities, in particular the walking speed, of the study subjects. In slower walking adults, no association between an elevated systolic or diastolic blood pressure and total mortality was found . To dateTherefore, this survey sought to explore the differences in the treatment intentions between GPs for hypertension in patients aged 80 and older and to investigate whether their treatment intentions depended on the patients’ level of dependency.In Belgium there is no general database of email addresses of GPs. Two strategies were used to invite GPs. First, email addresses of potential GPs were obtained from different GP societies and the National Order of Physicians. Second, when email addresses were protected for privacy reasons, the presidents of local GP associations were asked to forward our invitation to their members. In total a potential of some 5000 practicing Flemish (Flanders = northern Dutch-speaking part of Belgium) GPs or GPs in training (under the age of 70) were invited to participate in the survey. All contacts received the invitation twice by email.For each participating GP, the following data were recorded: age, gender, function , region , and years of practice (experience).Following standard procedures at the University of Leuven (Belgium) the ethical review board of the Medical Faculty of the University of Leuven approved the study. When entering the electronic survey, all participating GPs were asked to give informed consent.The electronic survey contained nine case vignettes. The case vignettes were split into three themes: the patient living at home without important comorbidity case 1, 2, 3), the cardiovascular patient  and the patient with cognitive decline . Each vignette described a patient of at least 80 years old, with or without a previous history of arterial hypertension. All cases presented with an average systolic blood pressure >170 mmHg. In the three consecutive cases of one theme, the level of dependency progressively increased (from robust to moderately and strongly dependent)  was based on the treatment intention of the respondent. The lower the score, the less the respondent had the intention to change the antihypertensive treatment. A score of 3 was given when the GP strove for a strict antihypertensive treatment, and the target systolic blood pressure was lower than 140 mmHg. If the respondent chose to start a new antihypertensive medication with a target systolic blood pressure ≥140 mmHg, he received a score of 2. If only the dose of the present medication was increased, the respondent received a score of 1. Finally, if the antihypertensive treatment was not changed, the respondent received a score of 0. The total score (range 0–27) was calculated per respondent and represented the ‘Intention to Treat Hypertension in Older Persons’ scale . Subscores were for the different clusters of cases with the same level of dependency , moderately dependent  and strongly dependent ).th October 2013 until 20th December 2013.First, the electronic survey was evaluated by 5 GPs in order to assess its face- and content validity. The definitive survey was performed from 15t test. For each respondent, the difference in the treatment intention according to the level of dependency was defined as the difference (delta score) between the subscore for the robust cases and the subscore for the strongly dependent cases. The internal consistency of the scale was assessed by means of Cronbach’s alpha coefficient.The mean scores and subscores and their 95 % confidence intervals (CIs) are presented with error bars. The differences between the subscores were investigated with the paired p = persons c = cases and d = level of dependency).A generalisability analysis was performed to analyse the contribution of the several potential sources of error in the measurements –15. GeneLinear regression analysis was performed with the total score as the dependent variable, and gender, function, region and experience (or age) as independent variables. Next, linear regression analysis with the delta score as the dependent variable and the total score, gender, function, region and experience (or age) as the independent variables.A random sample, adjusted for age and gender according to the general Flemish GP population was created and a sensitivity analysis was performed  and GENOVA software .n = 12), the missing scores were replaced by the respondent’s average score of the first two cases with the same level of dependency. The final analyses were performed for a total of 305 respondents. The background variables of the GP’s are reported in Table A total of 409 GPs opened the survey, of which 293 finished the survey completely. For those who finished at least six cases n = 2, the miP < 0.001). No difference was found between the subscores for moderately and strongly dependent cases (P = 0.98). The delta score ranged from −3 to 7 with a mean score of 1.7 ± 1.8.The scores on the ITHOP scale were normally distributed and ranged from 0 to 27 with a mean (± standard deviation (SD)) of 15.2 ± 6.0. Cronbach’s alpha of the scale was 0.83. Figure The generalisability analysis produced a reproducibility index of 0.82 for the total score (Table P = 0.010). The delta score also showed an inverse relationship to the experience or the age of the respondent , P = 0.034). No relationship was observed between the delta score and the total score , P = 0.72). There was no multivariate analysis performed for the delta score.The multivariate analysis Table  showed tn = 158) to perform a sensitivity analysis. The analyses on the subsample showed the same results compared to the analyses on the entire population  scale was shown to be reproducible with a G coefficient of 0.82. The variations in the treatment intentions were mainly attributed to the differences between the GPs and not to differences between the cases (themes) or to the differences in the level of dependency. An inverse relationship was found between the experience or age of the GP and the total score, but the delta score also showed an inverse relationship to the experience of the GP. Thus, the older the physician, the lower the overall treatment intention, and the smaller the difference between the treatment intentions for robust patients and strongly dependent patients.The current findings are consistent with what has been previously described regarding the assessment of medical competence as “case-specificity”, which means that scores on a particular case poorly predict scores on another case (or item) in a test. The intention to adapt a treatment or not appears to be highly context dependent . The meaDifferences in clinical experience between the GPs were observed as a possible explanation for the differences in treatment intentions. The current analyses showed that younger or less experienced physicians had an overall higher treatment intention than older or more experienced doctors. As physicians age, they seem to use less stringent treatment targets or become less aggressive in reaching the defined goals. Possibly, older doctors are more receptive to a negative perception of the ageing process. On the other hand, the treatment strategies of more experienced physicians seem to be less influenced by the level of dependency of their patients. Patients with a higher level of dependency were treated even more intensively by older GPs than by younger GPs. Possibly, younger GP’s are more familiar with concepts such as ‘patient-centered’ and ‘goal-oriented’ care, as a result of their more recent graduation . Older dThis study is the first survey that investigated the treatment intentions of GPs for patients aged 80 and over with hypertension. The ITHOP scale that was embedded in the survey appeared to have a high internal consistency and the G-analysis confirmed the reliability of the scores produced by the scale. The interindividual differences probably reflected the absence of guidelines on the treatment of hypertension in the oldest old and highlighted the importance of future research on these issues. Moreover, this study was the first to examine the impact of the level of the patient’s dependency on the GP’s treatment intention.The present study showed that differences in treatment intentions for hypertension in older patients are primarily associated with differences between GPs. However, to date, it is unclear whether these differences are related to a difference in knowledge or a difference in attitude. This indicates the need for additional qualitative research that may bring more clarity regarding these issues. Moreover, there are no guidelines for the management of hypertension in those aged 80 and over.A few limitations should be considered. First, participating GPs were more often female and younger than the average Flemish GP, making these results less representative for Flemish GPs . HoweverA significant difference in the treatment intention of GPs for people aged 80 and over with hypertension was found between robust patients and strongly dependent patients. The treatment intention was significantly higher in robust cases versus moderately or strongly dependent cases. On the other hand, large differences in overall treatment intentions were observed and could be mainly explained by differences between GPs and not by differences between cases or by differences in the patient’s level of dependency. This study underscores the need to develop adapted guidelines for the management of hypertension in the oldest old.


We address these issues in this reply.In a comment on our Article “Sublethal Dosage of Imidacloprid Reduces the Microglomerular Density of Honey Bee Mushroom Bodies”, Rössler  We noticed that 4 selected areas within the so-called dense region of Fig. 1B clearly have more dense labelling when compared to the unselected central area1. This effect is also apparent in Fig. 1B in the Rössler et al. paper. Thus it seems clear that just by choosing a particular region of interest  would cause bias. It was for this very reason therefore, that the entirety of the calyces was counted in our study. It is thus reasonable that our results showed that the densities are overall lower compared with previous reports due to the particular regions selected and methods used in those studies. In summary, earlier methods that assumed uniform density are difficult to compare with our method that comprehensively measured all regions, and thereby quantified the regional differences for the first time.The earlier study reported by Groh 2. The image was three-dimensional and was thus difficult to present how the MGs were distributed. Therefore, we chose as an example only one layer of the captured image to indicate the phenomenon. This one layer does not represent the whole picture of the distribution of microglomeruli in the calyces. The Fig. 1 in Rössler et al.’s paper used our example figure and put a yellow box on it intending to show the density of microglumerli in a volume of 10 μm × 10 μm × 10 μm. We do not think this is a proper method for comparison given that much less than the whole data set is used, the authors, again, ignore the uneven distribution of the microglomeruli in the calyces.In our study, each calyce underwent a thorough scanning of the entire structure, and were later processed by software to count MGset al.1. The purpose of our study was to compare the MG number and density before and after the imidacloprid treatment during the larval stage. Therefore, we must build new baselines for every region of the calyx so that we could compare before and after applying the same method and analyze the data statistically. The honey bees fed with sublethal dosages certainly show lower density of microglomeruli in the calyces than normal ones. The results showed a profound impact on their nervous system.We were aware that the densities reported in our study are lower than previous research. But this contrast may be caused by the different counting methods, sampling methods and different populations etc. The foragers in our study were the ones carrying pollen on their corbiculate legs we collected outside the hive. Those foragers are elder than 20 days but younger than 30. It is possible that the young forgers of our study had a lower number of microglomeruli when compared with 35-day-old foragers in Groh


Numerous treatments of the diffuse reflecting properties of scattering media have been described. Many theories give an adequate account of the reflectance for a specific set of conditions for which the model was constructed and the solution tested experimentally. Only those models which are considered to be fairly general are considered here.It is convenient to divide the theories into those based upon continuum models and those based upon statistical models. The continuum models typically describe the scattering and absorbing properties of a given medium in terms of two phenomenological constants. These models may all be regarded as varying levels of approximate solution to the general equation of radiative transfer. This provides a convenient basis for comparison of the various theories.The statistical models are based upon a summation of transmittances and reflectances from individual layers or particles. Thus, some assumptions must be made about the nature of the fundamental units, and the validity of the ultimate result will depend upon how closely these assumptions correspond with reality. Only the statistical models lead to expressions from which absolute absorptivities and scattering coefficients can be calculated and related to the actual particle characteristics.The relationship between the various models will be discussed and the features which typify the absorptivity and scattering coefficient according to each will be compared and related to the available experimental data. This leads to a consideration of the characteristics of appropriate model systems and standards. It is now recognized that diffuse reflectance spectroscopy is a very useful companion technique to transmission spectroscopy. Not only can it provide absorption data in some cases where transmission measurements fail, but for many industrial and research applications, it may in fact be the preferred technique.Our discussion will be concerned with the behavior of radiation within a scattering medium. For simplicity we assume the scattering centers, which may also absorb radiation, are imbedded in a medium which neither scatters nor absorbs. The medium may usually be taken as air, although there are many other cases of interest in which the refractive index of the medium is much greater than unity. We will not deal specifically with these cases in the present review, nor with those processes which alter the frequency of the radiation, such as luminescence and fluorescence.Scattering takes place under a wide variety of conditions. One may be concerned with the glowing photosphere of the sun, which is surrounded by a cloud of electrons that reradiate the direct sunlight incident on them. Sunlight is also reradiated by cosmic dust, which accounts for the outer part of the corona.In a more down-to-earth situation one may be dealing in the laboratory with the spectroscopy of a powder, paper, opal glass, photographic emulsion, etc. As so often happens, concepts developed in one area of science are slow to find their way into another. We will attempt to show that there is a close relationship between the astrophysical solutions, which are based largely on radiative transfer theory, and the various models which are more familiar to the spectroscopist.Since we will not be following a historical development, it may be useful to point out some relationships between the early studies. The first attempt to account for transmission and reflection of a layered material was carried out by Stokes in about 1860  and Mie The radiative transfer theory and various models stemming from it are referred to as Continuum Models. They have in common the characterization of the scattering and absorbing properties of the medium through phenomenological constants, usually two in number. These theories will be considered in section II. A completely satisfactory theory must of course relate the measurable quantities to fundamental properties of the scattering material, such as particle size, refractive index, and absorptivity. This is the goal of the statistical theories. Many have been proposed; those which show the most promise are discussed in section III. In section IV we discuss some of the strengths and weaknesses of the various models and some relationships between them. Section V considers the meaning of the absorption and scattering coefficients often used to interpret reflectance data, as well as the characteristics required of appropriate model systems.We will limit our discussion to ideal, homogeneous dispersions. There have been interesting developments in the theory of nonhomogeneous media, mixtures, luminescing materials, diffusing media in which photochemical reactions are taking place, and reflectance for materials dispersed in a highly refracting matrix, but these topics are considered to be outside the scope of the present review. Many of these topics are covered in the books which have been written on the subject ,8,9. FurThe present paper may be regarded as an update to a former review of the subject by the author . Most ofAs is often the case with applications of physical theory, the real media with which diffuse reflectance spectroscopy is concerned are intermediate between two extreme cases, each of which is well understood. The one limiting case involves the propagation of radiation through quasi-homogeneous matter, where the radiation field is characterized by smoothly and slowly varying functions of the coordinates. The other extreme involves the emission, absorption, and scattering of radiation by single particles in a homogeneous medium. The local transformation of the radiation field at the boundaries of quasihomogeneous media is a special case which has likewise been characterized for a long time, and leads to such well-known phenomena as reflection, refraction, etc.In dense scattering media, it is important to consider the manner in which the radiation fields from the various scattering centers interact with one another. Rozenberg , 14, 15 dI, is equal to the radiation which is lost through absorption and scattering –κρIdx plus that which is scattered in this direction from all other directions, jρdx:ρ is the density, κ is the attenuation coefficient, j is the scattering function, and dx is the element of path length. The scattering function can be written asσ is the scattering coefficient and p is the phase function which defines the probability that radiation which travels initially in the direction  is scattered into the direction . θ as the angle with respect to the inward surface normal givesµ = cos θ and J=j/σ is the source function.The concept that each volume element is irradiated by scattering from every other volume element of the medium (The Principle of Self-Illumination), is a basic concept of radiative transfer theory which clearly pervades the writings of such early workers as Schuster , 17, KinThe equation of radiative transfer can be generalized to include dispersion effects as well as scattering , 15. In The term iR, jR and iT, jT as the reflectances and transmittances for radiation incident in one direction, and I, RJR and IT, jT as the reflectances and transmittances for radiation incident in the other direction.A model in which the scattering medium is approximated by plane-parallel layers has been used by numerous workers as a basis for reflectance theory , 8. We ciR is reflected and the portion iT transmitted by the first layer. At the second layer the portion iRjT is reflected and iTjT is transmitted. The beam iRjT strikes the underside of layer i where iRjTIT is transmitted, while iRjRIT is reflected. Continuing this process indefinitely  and T(x) for iR and iT in R(dx) and T(dx) from jR and j.T Writing i+jR and i+jT as R(x + dx) and T(x+dx) allows We now make the assumption that the layers are homogeneous and thick compared with individual particle dimensions so that no intrinsic inhomogeneities are evident. We can then write that the reflectance of a given layer is proportional to its thickness ,R(dx)=KR(0)=0, T(0) =1 givesR∞ is the reflectance of an infinitely thick layer, and it is related to K1 and K2 throughL is given byIntegrating this set of coupled differential equations subject to the boundary conditions I+, traveling from the illuminated sample surface, and the other, I− traveling toward the illuminated surface (see S) and absorption (K) within the medium. If we make the following definition,−/I+.R = Ix of the scattering medium to obtain [gR is the reflectance of the background x→∞[The Kubelka-Munk theory  is basedface see . As radio obtain R= are coefficients which depend only on the angles of incidence  and observation , and on the form of the scattering indicatrix.For a homogeneous semi-infinite medium, a good approximate treatment of the reflectance for strong absorbers has been given by Rozenberg –15. The ield see . The aiti=IiC/I1 is the polarization of the reflected radiation. It will be observed that as β increases, scattering of higher multiplicities becomes less important. Ambartsumian [β ≥ 1/3, a fairly accurate solution is obtained by inclusion of terms up to second or third degree. It is further assumed that the scatter is independent of β, which should be a good approximation for mixtures of polydispersive media with different α and σ; i.e., as with the addition of dye to a suspension. The resulting equation isR0 is the reflectance of the medium itself (when β=β0), andQ is a quantity which defines the relative contribution of higher multiplicities of scattering when β=β0. Both it and R0 are constants which are independent of the nature and concentration of the colorant.The reflectance of the medium is given byait(1+β)twhere Ci=r), forward scatter (t), and absorption (a) constants of a single scattering layer(a+r +t=1) used by Chekalinskaia, the Rozenberg constants can be writtenβ ≫ 1, ozenberg  have demβ ≪ 1, Rozenberg [h, S, and q are quantities which depend on the form of the scattering indicatrix. Romanova [In the other limit; i.e., where ozenberg , 27 has Romanova  has deteIn problems of spectroscopy we often assume isotropic scatter. We know that in no case is single scatter actually isotropic , althougω0 is known as the albedo of single scatter. It represents the fraction of the radiation lost by scattering in a medium where both absorption (α) and scattering (σ) take place. With this assumption, the equation of radiative transfer for a plane-parallel semi-infinite medium becomes independent of the azimuthal angle ϕ and we haveFor the simple case of isotropic scatter, the phase function see  can be wja are Gaussian weighting functions given byjµ is one of the zeros of the Legendre polynomial, nP(µ).The integral occurring in n→∞ gives an exact solution which Chandrasekhar [rI(µ) is the reflected intensity in the direction µ from a collimated incident beam in the direction µ0, whose flux per unit area normal to the beam is πΦe(µ0). The H–integrals are defined byPassing to the limit rasekhar  has show′)μ+μ′dμ′and tableμ0 isH – integral, which occurs in Giovanelli  has giveExact solutions to the equation of radiative transfer can be derived for other phase functions as well. In general, the phase function may be expanded as a series of Legendre polynomialsy little , 37, andion also .P1(μ), 1 + P2(μ), and 1 + P3(μ). This suggests that the reflectance is not a sensitive function of the scattering indicatrix, and the isotropic solutions are in fact a good approximation for real scattering media.olutions  may be uf=(1−μ¯)σwhereμ¯=Continuum models, as we have seen, are somewhat limited. They involve the use of phenomenological constants with no obvious relationship in general to the fundamental constants with which we are familiar . Statistical theories, on the other hand, involve the construction of an appropriate model and the success of the theory depends on just how closely the model approximates real sample conditions.It appears certain that one of the most severe limitations of continuum models is the assumption that they remain valid even when infinitesimal thicknesses are considered. This is in fact contrary to the assumption of homogeneous layers previously invoked (see section II–A), and it is this contradiction which is largely responsible for limiting the range of applicability of continuum models, as our subsequent discussion will show.i to be the first layer and layer j to be the combination of all the other layers of an n-layer sample, we haven→∞, we writer and t can be dropped. R∞ to give an expression for the reflectance of an infinitely thick sample in terms of the reflectance and transmittance of a single layer. The result isr and t.Let us return to ∞R we getWe have seen that the Kubelka-Munk theory leads to a solution of the form,l, where l may be interpreted as the mean particle diameter of the sample. Then the fundamental differential equations of the Kubelka-Munk theory (i and (i+1) refer to the ith. and (i+1)st sample layers, respectively. Now for an infinitely thick sample,a is the fraction of the incident radiation which is absorbed by the layer.We assume with Simmons  that thek theory  are replF(R∞) versus K deviates from linearity for high values of K [K are probably a result of anomalous dispersion effects also, but The difference between the traditional and modified Kubelka-Munk solutions may be seen by writing ues of K –9, and ir and t. We will denote the simple reflectance of the layer surface by r0, the absorptivity (defined through I=I0 exp (−kx)) by k, and the layer thickness  by l Then according to Bodó  used a pr0=0.10. Karvaly [R∞ is a very sensitive function of r0. Karvaly  has showBauer  showed tp layers and that the mean number of attenuating reflections which the rays undergo in the 2p traversals is yp, so that the reflectance is given byy can be regarded as an adjustable parameter which gives a semi-empirical account of multiple reflections as well as scattering losses. The sum for an infinite number of layers isJohnson  has carry should be set equal to 4 for the case of no multiple reflections. In such a case only one half of the incident light is reflected, however. Johnson has suggested that y can be estimated from ∞R = 1 for k=0. This givesy=2 is seen to be a satisfactory approximation for refractive indices smaller than 1.5. A smaller value of y is required for larger refractive indices. Companion and Winslow [It will be observed from  Winslow  have user0 be equated to 1.5 times the normal Fresnel reflectance. This is meant to account for the random distribution of particle surfaces and corresponds with an average incidence angle of approximately 30°. It was shown [Johnson  also sugas shown  that eq Antonov-Romanovsky  has devel, actually being somewhat smaller.For spherical particles the radiation impinges on the surface from within at the same angle that it entered the particle, since the angles which the cord of a circle makes with respect to the surface normal must be the same. Therefore, total internal reflection is impossible, and l but somewhat larger.In the case of the parallelepiped, some total internal reflection is possible, but most radiation probably exits through an opposite face without further reflection. In this case also it is obvious that r02≪1.Thus for regularly shaped particles it is assumed that fl is defined as the “free” path length. The effective path length is thenFor irregularly shaped particles it is assumed that the emerging radiation meets the surface of the particle with an equal probability for all angles. This will be the case if the mean number of reflections in the layer l the mean particle diameter. We writeThe assumption that the emerging radiation is independent of angle allows us to divide it equally between the two sides of the layer whose thickness is In contrast with the statistical theories previously discussed, Melamed carried out a summation over the reflectance and transmittance of individual particles rather than layers . Some fee is used to indicate reflection of externally incident radiation. Here u is defined as the radiation emerging per unit solid angle from a particle. 4πu is the solid angle which would be observed from the second layer if a particle were removed  and inside  the sample:Proceeding in this manner we can write the following expressions for the reflectance and transmittance of a layer for radiation from outside (into cf. R∞=r1+t1kl≤1) and that the radiation leaves the sphere isotropically,u0 for close-packed spherical particles is 0.284. The transmittance of a single spherical particle including multiple internal reflections is written in terms of the internal reflectivity r(θ),cθ is the critical angle.The application of gle pass . The measine law . Here θcFassler and Stodolski –52 have a to represent the part which is absorbed in the layer, including the effect of multiple reflections, then the part (1−a) rf and tf to represent the fractions of the radiation directed upward and downward, whererf=tf, corresponding with the Antonov-Romanovsky treatment of irregular particles. In the general case, r<ft.fr=ftf=½ can be put into F(R)∞ is once again the Kubelka-Munk function. Solving a givesA model which preserves some of the features of the Melamed theory, but which removes the inconsistency, has been constructed by Fassler and Stodolski as follows: we assume radiation to be externally incident on a particle layer. The part t) as the fraction absorbed, where t represents the transmittance of a given particle taking multiple reflections into account. Letting su represent the fraction of the radiation from a given particle which remains within the layer, we have stu as the part which enters a neighboring particle where (1−t)stu is absorbed. Continuing in this way we once again generate a geometric series which can be summed to give the absorbance of the layer:If we assume the radiation within the powder layer to be isotropic, we can write (1−uu), going down (du), and going sideways (su):d=uu=uu0, and sou0=0.284 for spherical particles. Using this in M F(∞R)≪1 and δF(∞R)≪1, and Following Melamed  the radion for M  leads toSimmons  has usede) must equal that returning from it (Φe′) except for the part which is absorbed:e=πl2eM where eM is the radiant flux density, andThe law of conservation of energy requires that the total radiant flux impinging on a particle  is transmitted, and of this, the fraction Since the reflectance of an infinitely thick sample is independent of depth, we can write the two alternative expressions for the reflectance,ximation   by Karvaly and Pinter [Karvaly  has showd Pinter  have shoR→0 as n→1, as must be the case since there are then no scattering centers in the medium [l≫λ. This allows scattering to be neglected in the Johnson and Bodó models. The dependence of R on n in the Melamed theory is apparently due to the scattering of radiation internally incident on the particle surface which is taken to be independent of n. It is interesting to note that the three theories give about the same reflectance for refractive indices 1.7<n<2.0.As mentioned above, the Melamed theory fails to predict that e medium . In the It is of course not necessary to assume that the particles are rough-surfaced, i.e., that they scatter according to the Lambert cosine law. In the other limit they may be approximated as smooth-surfaced spheres whose reflection and refraction is governed by Fresnel’s laws. This case has been treated by Simmons  and reprThe recently published modified particle model theory of Simmons  Equatio removes The Fassler and Stodolski theory also shows considerable promise, but has not yet been thoroughly tested. It does lend itself to the investigation of important effects such as the influence of particle size distribution on reflectance properties , 65, andOne of the difficulties with weighing the relative merits of the various reflectance theories is the necessity of comparing them over a wide range of experimental conditions. In general, the data are rather incomplete and we must content ourselves with pointing out the physical significance of the parameters used. We will do this in the present section, together with making some remarks concerning the characteristics of appropriate model systems.a and b are previously defined  defines the anisotropy of radiation in the particle layer. ξ is the effective cross section for holes in the particle layer, By taking the particle size distribution into account, Fassler and Stodolski  were abltodolski  emphasizThe effect of particle shape is also important. It appears at the present time that there is no better way to test the various reflectance theories than to make transmission and reflectance measurements on a given glass sample before and after grinding, respectively. The characteristics of glass samples subjected to various grinding conditions have been studied by Karvaly and Pintér . These f


Moreover, in these specimens, the MN was significantly thinner (p = 0.003). The ulnar head was present in 43 limbs (86%). The MN passed between the heads of the PT muscle (74%) or under the muscle (26%). In the majority of cases, it provided two motor branches (66%). There is an association between the morphologic variation of the PT muscle heads and the course and branching pattern of the MN. Both are related to differences in forearm length. This may have an impact on the risk of PT syndrome and the performance of MN electrostimulation.The pronator teres (PT) muscle is a forearm flexor with radial and ulnar heads. It is innervated by the median nerve (MN), which passes between these heads. Nerve entrapment, known as “PT syndrome”, may occur in this passage. Anatomical variations in this region may be potential risk factors of this pathology. Therefore, the aim of the study was to determine the relationship between morphologic variations of the PT and the MN. In 50 isolated, formalin-fixed upper limbs, the cubital region and the forearm were dissected. The following measurements were taken: origin of the PT muscle heads, the length of these heads, the length of the forearm, diameter of the MN and the number of its muscular branches to the pronator teres muscle. The forearms with the humeral head originating from the medial humeral epicondyle and medial intermuscular septum (72%) were significantly shorter ( The pronator teres (PT) is a fusiform muscle located mostly laterally in a superficial layer of the anterior forearm muscles  that passes between the heads of the PT and then travels inferior to the flexor digitorum superficialis  were obtained from adult cadavers. Permission for the study was given by the Local Bioethics Commission (agreement no. RNN/44/16/KE). A dissection of the cubital region and the proximal part of the forearm was performed by using traditional techniques  were compared based on contingency tables and the Chi2 test, with appropriate corrections. The distribution of continuous data was evaluated with the Shapiro–Wilk test; non-parametric tests were then applied to evaluate non-normal data. The Mann–Whitney test was used to compare measurements regarding the number of PT heads or their origin between two groups. The Kruskal–Willis ANOVA with dedicated post hoc test was used to compare muscle/forearm dimensions according to the number of MN muscular branches. Correlations were assessed with the Spearman’s rank correlation coefficient.Statistical analysis was performed with Statistica software. A The results section is divided into two parts. The first part concerns the morphology of the PT and its association with the course of the MN, while the second describes variations in the number of muscular branches supplying the PT. In all cases, the radial artery ran in front of the PT tendon.p = 0.0088). Furthermore, in the former group, the MN was significantly thinner (5.6 ± 0.6 mm) than in specimens with the PT origin located only on the medial humeral epicondyle (6.3 ± 0.7 mm) (p = 0.003). The ulnar head of the PT was present in 43 limbs (86%), and in all cases it originated from the coronoid process of the ulna. Forearms where the ulnar head was absent were significantly longer  and had significantly wider nerves (6.2 ± 0.2 mm vs. 5.9 ± 0.7) than those where it was present.Two types of PT origin were observed. In 36 cases 72%), the humeral head of the PT originated from the medial humeral epicondyle and medial intermuscular septum   Fig. b.The PT possessed only a humeral head, and the MN passed deep to it: seven cases (14%) Fig. c.The median nerve was observed to follow three course variants in relation to the PT:R2 = 0.60, p = 0.0001) and the radial head of the PT muscle , but not with the length of the ulnar head . On the other hand, a significant negative correlation was found only between the distance from the intercondylar line to the passage of the MN and the length of the ulnar head .There was no significant difference in any of the analyzed measurements according to the type of MN course Table . HoweverA few variants were found in the number of muscular branches to the PT arising from the MN. If both heads of the PT were present, there were three types of PT innervation pattern: type I—with one muscular branch arising from the main trunk of the MN, this type occurred in seven cases 14%)—, two muscular branches arising from the main trunk of the MN were observed. Selected parameters were correlated with the number of muscular branches of the MN (Table 4%, two mThe present study describes the morphologic variations of the origins of the PT and their association with the course and branching pattern of the MN. Entrapment syndromes of the MN are still an important clinical problem. Thus, our research provides a valuable data and knowledge concerning morphologic variations as a potential risk factor of MN entrapment neuropathy.Entrapment neuropathies within the upper limb can be diagnosed with both ultrasound and magnetic resonance imaging. However, due to the lower cost and dynamic character of the examination, ultrasound seems to present important advantages (Chen et al. Concerning the ethology, compression of the MN in the region of the elbow joint has been associated with the morphology of the PT or with the presence of Struther’s ligament or a supracondylar process of the humerus bone (Bilecenoglu et al. In our study, the distribution of the origin types of the PT humeral head was found to be comparable to those identified in former studies. A previous study by Vymazalová et al.  found thIn the present study, the ulnar head of the PT always originated from the coronoid process of the ulna, although a previous study found it to attach to the trochlea of the humerus in 3.1% of examined cases (Vymazalová et al. The course of the MN in relation to the PT is clinically important because of the difficulty in diagnosing PT syndrome. Although neuropathy of the median nerve can vary significantly depending on the compression site, it also can be very similar and unambiguous (Lee et al. The course of the MN in relation to PT depends on the morphology of the muscle and its adjacent anatomical structures Table  Jamieso. SimilarKnowledge of the number of nerve branches is not only of value for the anatomist, physiotherapist and physiologist, but also for the clinician by allowing the appropriate type of electrostimulation (Safwat and Abdel-Meguid Chantelot et al.  differenAn understanding of the different MN course types and variation in the insertions of the PT heads is essential in diagnosing patients with MN neuropathies. In the majority of cases, the median nerve passes between both heads of the pronator teres muscle. The knowledge that the cubital region is a potential site of proximal MN entrapment should be taken into account to better differentiate PT syndrome from carpal tunnel syndrome. Most often, the main trunk of the MN gave off two muscular branches to the PT. The knowledge of the number and location of muscular branches of the nerve may also be essential for the proper commencement of the electrostimulation process.


We report on generation of pulsed broadband terahertz radiation utilizing the inverse spin hall effect in Fe/Pt bilayers on MgO and sapphire substrates. The emitter was optimized with respect to layer thickness, growth parameters, substrates and geometrical arrangement. The experimentally determined optimum layer thicknesses were in qualitative agreement with simulations of the spin current induced in the ferromagnetic layer. Our model takes into account generation of spin polarization, spin diffusion and accumulation in Fe and Pt and electrical as well as optical properties of the bilayer samples. Using the device in a counterintuitive orientation a Si lens was attached to increase the collection efficiency of the emitter. The optimized emitter provided a bandwidth of up to 8 THz which was mainly limited by the low-temperature-grown GaAs (LT-GaAS) photoconductive antenna used as detector and the pulse length of the pump laser. The THz pulse length was as short as 220 fs for a sub 100 fs pulse length of the 800 nm pump laser. Average pump powers as low as 25 mW (at a repetition rate of 75 MHz) have been used for terahertz generation. This and the general performance make the spintronic terahertz emitter compatible with established emitters based on optical rectification in nonlinear crystals. In particular, the ISHE transforms a pure spin current into a transverse charge current due to spin-orbit coupling. Extensive studies based on the ISHE have been performed since ISHE was first experimentally demonstrated by using non local detection techniques3 and by detecting electrically pure spin currents generated in spin pumping experiments4. Spin pumping effect refers to the generation of a spin current from a precessing magnetization in a magnetic layer (FM). The spin current appears at the interface of the magnetic layer with a non magnetic metallic layer (NM) and it propagates in the NM layer which has to exhibit a large spin-orbit coupling like for example Pt. The ISHE in a non magnetic layer then acts as an electrical detector of the spin currents. The utilisation of ISHE in sensing spin currents has been also applied in measuring spin caloritronic effects6.The use of spin Hall effects to generate and manipulate spin currents has provided a large thrust in the research field of spintronics the last decade. Spin Hall effect and its reciprocal, the inverse spin Hall effect (ISHE), provide the means for conversion between spin and charge currents8. THz spintronics has the potential of application in ultra-fast current and computer technologies9. In the particular case of THz emission induced by the ISHE in FM/NM layers, a femtosecond laser pulse pumps a FM/NM heterostructure and generates non equilibrium spin polarized electrons in the FM layer. Subsequently, these electrons are diffused in the non-magnetic layer through a super diffusive process11. The spin current is then converted into a transient transverse charge current due to the ISHE in the NM layer. This transient current generates a short terahertz pulse that propagates perpendicular to the electrical current. The experimental demonstration of THz emission from FM/NM heterostructures due to ISHE has been beautifully shown recently13. However, the thickness dependence of the efficiency of the spintronic emitters, in particular for very small layer thicknesses has not been well understood. Seifert et al.7, have shown that the THz signal exhibits a maximum for a specific total thickness of the metallic bilayer, although, according to their equation of the terahertz field amplitude7, the signal should scale with the metal thickness. They have attributed this behavior to a resonant enhancement in a kind of a Fabry-Pérot cavity formed by the bilayer. In contrast, Yang et al.13, have found no maximum in the signal by varying the Pt thickness in Fe (1.4 nm)/Pt (0–5 nm) bilayers. Instead, the signal was saturated above 3 nm Pt, possibly due to the spin diffusion length in Pt13. Furthermore, no pronounced maximum was observed in the Fe-thickness dependence curve for the Fe (0–5 nm)/Pt (3 nm) bilayer. Likewise, Wu et al.12, reported an increase and a saturation of the peak amplitude of THz signals for a NM/Co (4 nm)/SiO2 system as the thickness of the nonmagnetic layer (Pt or W) increased. By varying the thickness of the Co layer (0–10 nm) the THz peak reached a maximum value and then a gradual decrease. In this work, we present the effect of THz radiation from fully epitaxial Fe/Pt systems. We show the influence of the thickness of the individual layers on the THz emission amplitude and we discuss the role of the substrate. We demonstrate that for both Fe- and Pt-thickness dependencies the THz signal exhibits a maximum and a fast decrease after that. We quantify this behavior by using a model that takes into account generation of spin polarization starting at a minimum layer thickness of the magnetic material, spin diffusion, spin accumulation, and the electrical as well as optical properties of the bilayer samples.Recently, the decisive role of the ISHE effect on extending the field of spintronics into the terahertz (THz) regime was revealed2O3 substrates with Pt as the outer layer. In principle, the layer structures can be pumped from both sides, the substrate side or the side with the Pt layer. In our experiments, the layer structures were pumped from the metal side and THz emission was detected from the substrate surface. As the Pt layer thickness is in the order of 3 nm for optimized emitters most of incident pump radiation is transmitted into the magnetic layer. For experiments with thicker Pt layers the additional absorption and reflection losses have to be taken into account when comparing the experimental results with simulations. We have therefore measured directly the total absorbed pump power for the metal layer structure. Only a certain fraction of this absorbed power will be converted into spin polarized electrons in a small layer close to the Fe/Pt boundary. This has to be taken into account in our model presented below. The counterintuitive geometry has the following advantages: In order to collimate the strongly divergent THz beam a hyperhemispherical silicon lens was attached directly to the substrate with the Fe/Pt plane in the focal point of the lens without damaging the delicate Pt surface. A schematic of the structures is shown in Fig. The Fe/Pt layer structures were epitaxially grown on 0.5 mm thick MgO or Al14 suppressing any reflections from the substrate surface. This is illustrated in Fig. Pumping the structure from the substrate side will always cause additional reflections from the substrate-air interface which in turn lead to strong oscillations in the corresponding THz spectra. In our geometry, the metal surface acts as an anti-reflection coating for the THz beam15 resulting in a relaxation time in the order of 5 fs in Pt16. Such a relaxation time supports bandwidths up to several tens of THz and does not limit the bandwidth we have observed in our experiments.The pulse length and bandwidth of the THz pulse strongly depend on the rise and fall time of the transient electrical current in the nonmagnetic layer induced via the ISHE. Whereas the rise time is mainly determined by the pump pulse length and the diffusion properties of the spin current, the fall time is limited by the relaxation time of the electrons in the conducting material. For the relaxation time we have considered a superdiffusive transport process according to studies by M. Battiato2O3, respectively. The minimum pulse width was measured to be below 250 fs for both substrates with a tendency to shorter pulses for the Al2O3 substrate  and even shorter pump pulses a much broader bandwidth can be obtained. This has been shown recently by Kampfrath et al.7.In addition, absorption in the layer structures and the substrate influence both pulse length and bandwidth. A typical pulse and the corresponding spectra are shown in Fig. see Fig. . Spectrasee Fig.  extendinIn order to optimize our THz emitter we have performed a systematic study of the dependence of the THz amplitude on the thickness of the Pt and Fe layers for samples epitaxially grown on 0.5 mm thick MgO substrates. In a first set of experiments the Fe layer thickness was kept constant to 12 nm whereas the Pt layer thickness was varied from 0.25 nm to 12 nm. In the second set the Pt layer thickness was fixed at 3 nm while the Fe layer thickness was changed from 1 nm to 12 nm. The results are shown in Fig. air, nMgO and Z0 are the index of refraction of air, the index of refraction of MgO at THz frequencies and the impedance of vacuum, respectively.The variation in pump beam absorption through Pt layers with changing thicknesses has been taken into account for the comparison. The theoretical fitting curve in Fig. Fe + dPt). The second term describes generation and diffusion of the generated spin current flowing in Fe towards the interface with Pt; to elaborate the possibility that extra thin Fe layers can loose their ferromagnetic properties below a certain thickness we introduce the term d0 in equation λpol. Magneto-optical Kerr effect measurements confirm this assumption (see Methods section).Equation λPt of the spin current in Pt. The symbols σFe and σPt are the electrical conductivities of the two materials, respectively. This part of the equation is according to the theory of spin pumping effect18 and includes the shunting effect of the parallel connection of the resistances of the individual Fe and Pt layers. Although the electrical conductivity depends on layer thickness for very thin layers we have used a constant value for the layer thicknesses. This value is considerably smaller than the bulk value as in the thickness ranges in our experiments the bulk value has not been reached19.The third and forth term, the tangent hyberbolic function divided by the total impedance, refers to the spin accumulation in Pt which is responsible for the strength of the THz radiation and it depends on the finite diffusion length THz as an effective inverse attenuation coefficient of THz radiation in the two metal layers). In the case of small losses the attenuation can be taken into account by this single exponential factor and the third factor which accounts for the multiple reflections of the THz pulse at the metal/dielectric interfaces (see Methods section). All terms together describe the layer thickness dependence of the measured THz amplitudes. The influence of the silicon lens on the thickness dependence of the generation process can be neglected as the distance between lens and metallic layers is five orders of magnitude larger than the layer thicknesses itself. Experiments with and without silicon lens resulted in the same thickness dependence.The last term describes the attenuation of the THz radiation during propagation through the metal layers . There are no electrical connections required for the operation of the emitter. The polarization of the generated THz radiation can easily be changed by changing the weak magnetic field perpendicular to the direction of the pump beam. The average pump power levels required to generate useful THz signals is comparable to power levels used in optical rectification methods in nonlinear crystals. As the excitation of electrons in the Fe layer is independent of wavelength other pulsed laser sources can be used which are easier to operate like e.g. fs fiber lasers at 1.5 μm. The THz pulse length and bandwidth is, in principle, only limited by the relaxation time of hot electrons in the Pt material. The best configuration of the THz emitter was revealed by varying Fe and Pt layer thicknesses. Samples with 2 nm Fe and 3 nm Pt gave the maximum THz amplitude. To quantify the thickness dependence of the THz amplitude we have successfully developed a model that takes into account the optical absorption in the metal layers, the generation and diffusion of hot carries in Fe, the shunting effect, spin accumulation in Pt and the THz absorption in Fe. The optimization and the modeling of the radiation with the materials properties is necessary for future applications of the effect.We have shown that Fe/Pt epitaxial bilayer systems can be considered as a competitive THz radiation source of spintronic nature. The spintronic THz emitter based on the ISHE presented here has a number of advantages compared to other optical and electro-optical THz emitters: The alignment of the emitter with respect to the pump beam is simplified as one has a free choice choosing the focusing spot within the sample surface. A collimating Si lens can be attached directly to the substrate of the bilayer sample collecting most of the strongly divergent THz beam. Thus, changing the NM/FM bilayer samples becomes possible without loss of alignment of the total THz system. Up to pump fluences of 5 mJ/cm21, has been used for generation and measurements of THz waveforms from different spintronic emitters  THz-setup both the emitter and the detector operate with photoconductive antennas (PCA) whereas in the present work the PCA emitter is substituted by a spintronic (ST) Fe/Pt bilayer sample which is placed in a weak magnetic (20 mT) field perpendicular to the direction of the pump beam and in the direction of the easy axis of Fe. The direction of the magnetic field determines the polarization of the THz field which is perpendicular to the direction of the magnetic field. Changing the direction of magnetic field into the opposite direction changes the phase of the detected THz waveforms by 180°  system, described in detail elsewheresee Fig. . The sys80° Fig. . In thisμm dipole length limits the observable bandwidth. With this dipole length a maximum in the detector response around 1 THz can be expected with a reduction to 50% at 330 GHz and 2 THz. The 10% values are at 100 GHz and 3 THz. This estimation is based on calculations by Jepsen et al.22. Above 3 THz the frequency response of the detector is very flat and at 8 THz a strong phonon resonance in GaAs which is used as substrate material for the photoconductive antenna causes strong absorption of the THz radiation. Above 8 THz no THz radiation was detected.The optical pump beam that is sharply focused onto the sample at normal incidence by an aspherical short-focus lens, excites spin polarized electrons in the magnetic layer (Fe) which give rise to a spin-current, which in turn excites a transverse transient electric current in the Pt layer. The latter results in THz pulse generation of sub-picosecond duration being emitted forward and backward into free space in the form of a strongly divergent beam. The central wavelength within the beam is about 200 µm and is much longer than the diameter of its source which is smaller than 10 µm. That is why the emitted THz field would fill the half-space behind the sample. A hyperhemispherical Si-lens being attached to the back side of the sample collects it into a divergent beam in the form of a cone and directs it further. With the lens attached an enhancement factor of up to 30 in electric field amplitude has been observed. After the lens the beam is collimated with an off-axis parabolic mirror and sent to an identical parabolic mirror in the reversed configuration. The latter focuses the beam to the second Si-lens which finally focuses the beam through the GaAs substrate of the detector PCA onto the dipole gap for detection. In this way the THz optical system consisting of the two Si-lenses and the two parabolic mirrors images the point source of THz wave on the emitter surface onto the gap of the detector PCA and ensures an efficient transfer of the emitted THz emission from its source to the detector. In the present paper a 4-mirror THz-optics is used making it possible -besides two collimated beam paths- also to have an intermediate focus of the THz beam aimed at imaging applications Fig. ). In ourThe delay line provides for the synchronous arrival of the weaker part of the optical pulse and that of the THz pulse at the detector antenna gap from either side, as well as for scanning in time the “open” state of the gap along the THz pulse duration. In each position of the delay line the transient current induced in the detector by the electric field of the THz sub-picosecond pulse is proportional to its instantaneous electrical field value. It is summed up from many laser pulses which reach the detector during the single step of the delay line and integrated within the “open” state time window. It is measured as one single point of the THz wave-form and is in the order of several nano amperes at the maximum of the THz pulse. Hence, for its measurement lock-in technique has to be used. For that purpose the pump beam is mechanically chopped at 1.35 kHz frequency. By scanning the “open” state of the detector in time the THz pulse shape can be sampled. Utilizing the magnetic field dependence of the THz polarization the THz beam can, in principle, be chopped electrically by means of an alternating magnetic field around the emitter.μm of our delay line, a scan speed of 30 μm/s and an integration time of 100 ms.In order to compare our results with results from other THz emitters we have characterized the generated THz radiation using the maximum dynamic range which is the maximum spectral amplitude above noise level and the maximum frequency above noise level. The last quantity, of course, grows with measurement time up to a maximum measurement time limited by the stability of the whole system. For our measurements we have used a scan range of 33 ps with a step width of 0.4 μm radius, a repetition rate of 75 MHz of our pump laser and a maximum average output power of 350 mW we changed the pump fluence on the sample from 0.5 mJ/cm2 to approximately 5 mJ/cm2 without any damage of the sample. The slight onset of saturation of the THz signal may be caused by a temperature increase of the sample  substrates by molecular beam epitaxy (MBE) technique in an ultrahigh vacuum (UHV) chamber with a base pressure of 3 × 10−10 mbar. The growth rate was R = 0.05 Å/s controlled by a quartz crystal during the deposition procedure. The incident Fe beam was perpendicular to the substrates. The cleaning protocol of the MgO (001) 1 × 1 cm2 substrates involved heating at 600 °C for 1 hour. The deposition of Fe was performed at 300 °C temperature. At a next growth stage, on top of the Fe layer, a Pt layer was deposited at the same temperature. The thickness of the individual layers has been varied for Fe (1–12 nm) and for Pt (1–18 nm) as it was monitored in-situ by a calibrated quartz crystal oscillator and confirmed ex-situ by X-ray reflectivity (XRR) measurements. X-rays diffraction (XRD) measurements have shown for the thicker samples (Fe and Pt thicknesses greater than 2 nm) the presence of Fe (002) peaks revealing the epitaxy of Fe layer on the MgO substrate, with Fe(001)//MgO (011) for all samples. Diffraction peaks of Pt (200) and Pt (400) arising from the Pt top layer parallel to the Fe (200) planes were observed revealing the epitaxial relation of Pt on Fe. The growth of the fcc Pt layer on bcc Fe along the [100] plane direction is correlated to the Bain epitaxial orientation24 when the Pt cell is 45 degrees rotated with respect to the Fe lattice. The structural quality of the Fe/Pt bilayers was further investigated by measuring in-plane XRD polar plots and selectively transmission electron microscopy (TEM). Both methods confirmed the epitaxial quality of the bilayers. The growth of Fe on sapphire (0001) is not perfect epitaxial because of a larger mismatch in lattice constants. This may also influence the THz generation. In our experiments we have observed a weaker spectral amplitude at the maximum frequency whereas there is no obvious absorption at higher frequencies.Fe thin films were grown epitaxially on the 0.5 mm-thick MgO (100) and Alc in Pt responsible for THz generation depends on the generated spin polarization in Fe, the diffusion of spin polarized electrons in Fe and the diffusion of spin polarized electrons in Pt which are converted into a charge current via the inverse spin Hall effect.The charge current jFe + dPt) assuming a constant diameter of the pump beam and an almost linear dependence of the absorbed power on layer thickness.The first term in equation in is the incoming laser power focused on to the emitter, Ptrans is the laser power transmitted by the emitter and Pabs the laser power absorbed by the emitter. To determine the absorptance A we have measured R and T and use Both assumptions are valid in our case for layer thicknesses investigated in our experiments. Typical absorption measurements are shown in Fig. 0 and increases with a certain constant λpol which is characteristic for the saturation of spin polarization with layer thickness 25.The very steep onset of THz radiation at very thin Fe layer thicknesses above a certain minimum Fe thickness is described by the second term in equation 26. In such case the “dead” magnetic layer can be estimated to be below 0.8 nm. This is also in agreement with results obtained by Allensbach et al.25 where for thicknesses up to 2 ML of Fe on Cu (001) no spin polarization was detected. For the case of a few ML of Fe there is also the possibility that the spin polarization has a perpendicular component26. Unfortunately, we have no experimental access to measure the out-of-plane component of the magnetization. However, the presence or non-presence of perpendicular magnetization is not going to change our results since our THz signal is sensitive to the in-plane component of the magnetization.In order to support this assumption we have studied the magnetic properties of our sample series with the help of longitudinal magneto-optic magnetometry. The results are illustrated in Fig. c or no in-plane component due to the perpendicular orientation of the magnetization) the MOKE data justify our assumption of a “dead” magnetic layer for the THz emission below 0.8 nm of Fe.Regardless of the reason (either close to TλPt) of the spin current in Pt. This part of the equation is according to the theory of generation of THz radiation from a current source based on the inverse spin Hall effect18.The third and forth term, the tangent hyberbolic function divided by the total impedance, refers to the spin accumulation in Pt which is responsible for the strength of the THz radiation and it depends on the finite diffusion length 8. Taking into account small losses for the generated THz radiation and replacing the real wave vector κ the imaginary part of the index of refraction, ω the angular frequency, and c the vacuum speed of light, respectively. Assuming only small losses the attenuation factor is independent from z and the E field is constant across the metal layer if the thickness is small compared to typical attenuation lengths. Following the derivation of Seifert et al8. this factor becomes a constant factor which is independent from other parameters and only depends on the total thickness of the metal layers. The smaller the layer thicknesses the better is this approximation. Due to multiple reflections in the metal . To get the real attenuation length our fitted effective inverse absorption constant has to be multiplied by the finesse.The last term accounts for losses in the metal layers. It can be described by a single exponential attenuation factor under the following assumptions: Deriving the generated THz signal via the ISHE using Green’s function only negligible losses were assumed and a real wave vector k was used for the THz propagation in the metal layers (see e. g. Seifert mentclass2pt{minimThe influence of the substrate is neglected in our model as the attenuation of the THz radiation in the substrate is constant for different layer thicknesses and we are discussing only the dependence on Fe/Pt layer thicknesses. The influence of the substrate can be seen in the spectral amplitude. Above 3 THz there is a strong THz absorption which reduces the THz bandwidth. There is of course a different THz absorption in different substrates which has to be taken into account when comparing different substrates.


Dormancy is a bet‐hedging strategy that allows organisms to persist through conditions that are suboptimal for growth and reproduction by entering a reversible state of reduced metabolic activity. Dormancy allows a population to maintain a reservoir of genetic and phenotypic diversity  that can contribute to the long‐term survival of a population. This strategy can be potentially adaptive and has long been of interest to ecologists and evolutionary biologists. However, comparatively little is known about how dormancy influences the fundamental evolutionary forces of genetic drift, mutation, selection, recombination, and gene flow. Here, we investigate how seed banks affect the processes underpinning evolution by reviewing existing theory, implementing novel simulations, and determining how and when dormancy can influence evolution as a population genetic process. We extend our analysis to examine how seed banks can alter macroevolutionary processes, including rates of speciation and extinction. Through the lens of population genetic theory, we can understand the extent that seed banks influence the evolutionary dynamics of microorganisms as well as other taxa. Resource availability, disease pressure, and temperature are just a few of the abiotic and biotic factors that fluctuate over space and time. Variation in these and other factors have important consequences for the growth, survival, and reproduction of individuals. Many taxa respond to variable environmental conditions by entering a reversible state of reduced metabolic activity, a phenomenon known as dormancy  cells in the oceans live underneath continents and on the sediment floor in a subsurface habitat known as the “deep biosphere”  and the per‐generation mutation rate (μ). When the rate that genetic diversity acquired by mutation is equal to the rate that it is lost by drift , our expectation for the maximum amount of genetic diversity that can be maintained in an ideal population of haploid individuals is θ = 2Nμ. This equation can conveniently be interpreted as the ratio of the rate that genetic diversity is acquired by mutation (2μ) and lost by drift (1/N) each generation  that can be maintained in an ideal population of finite size is determined by the number of individuals in the population  in a population with M dormant individuals is E[π]=θ+θMN. This equation can be interpreted as the amount of genetic diversity expected in an ideal population with N actively reproducing individuals (θ = 2Nμ) plus the seed bank's contribution toward reducing the rate of genetic drift scaled by the relative excess of dormant individuals (MN). However, it is important to point out that the strong seed‐bank effect can require an extremely long period of time to take effect in large populations. For example, assuming a population of Escherichia coli of size 109 that is only 10% active , a strong seed bank can only occur if on average dormant individuals spend approximately 109 generations in a dormant state. Assuming an average growth rate of ~6.67 generations per day for active individuals  individuals, the majority of newly acquired genetic variation is due to genome replication errors acquired during cell division Kunkel, . Given tBacillus by the extremely low water content in the endospore coat and small, acid‐soluble proteins that bind to the DNA   IV under times of stress, a highly mutagenic polymerase that is capable of synthesizing DNA across lesions in the genome that would stop alternative polymerases  accelerates quadratically with the average number of generations that an individual spends in a dormant state . As expected, we found that the average amount of time required for a beneficial allele to reach fixation increases with the average number of generations that an individual spends in the seed bank , where it then fluctuated below a frequency of one as individuals continued to exit and enter the seed bank, in a fashion analogous to back‐mutation in a single‐locus model. By examining the active portion of a population with a seed bank in a simulation of selection on a single locus, we found that the average number of generations required for a beneficial allele to reach quasi‐fixation is similar to that for the dormant portion up until the average time in the seed‐bank approaches the number of active individuals in the population , the threshold between weak and strong seed‐bank effects Figure b. SurpriTfix for the active portion of a population subject to the strong seed‐bank effect has important implications for the long‐term evolutionary dynamics of microbial populations. Because the majority of a given bacterial genome is likely clonal, the rate of evolution in a population undergoing adaptive evolution can be sufficiently described by the beneficial mutation rate (U) and the strength of selection (S) operating on a population of constant effective size (N)  is much greater than Tfix, the population will evolve at a rate (v), which is proportional to the rate that beneficial mutations of small effect arise and fix within a population    is a major evolutionary feature that can promote the spread of beneficial genes within a population  . The ability to enter a dormant state can increase the chance that any two individuals share a common ancestor within a population  and reduce the amount of estimated differentiation among populations . However, if seed banks buffer the aggregated effects of multiple evolutionary forces over long periods of time, then dormancy may have important implications for macroevolutionary phenomena. In the following section, we examine how dormancy influences macroevolutionary processes and patterns including the rate of molecular evolution, shared ancestry among lineages, speciation, and extinction.3.1Firmicutes possess the ability to form endospores, which are thought to be one of the most metabolically inert forms of life on the planet  can dormancy push microbial populations into the multiple mutation regimes, (ii) how does dormancy as an environmentally dependent adaptive trait alter evolutionary dynamics and the process of adaptation, and (iii) how has dormancy altered the rate of molecular evolution across the microbial tree of life? By considering the short‐term population genetic and long‐term macroevolutionary implications of dormancy as an adaptive trait, we can understand the extent that dormancy has impacted the evolutionary dynamics of the most abundant and metabolically diverse group of organisms on the planet. Determining the extent that dormancy influences microbial evolution will require empirical research on whether dormant microorganisms in the environment are engaging in a life‐history strategy as well as continued development of the population genetic theory that accounts for the evolutionary effects of dormancy.https://github.com/LennonLab/EvoDorm).The data and code for the simulations used in this study can be found in a public GitHub repository (WRS and JTL conceived of the ideas for the article; WRS created and executed the simulations; WRS and JTL wrote the article. Click here for additional data file.


Our results demonstrate as much as a 30% dose decrease and 2 cm penumbral increase when this is done compared to field shaping at the insert level. The magnitude of this dosimetric error qualifies as a therapeutic misadministration in many states depending on how many treatments are delivered in this manner. Based on this finding, we recommend that routine use of lead strip blocking be discouraged in favor of custom inserts due to the potential for inappropriate placement on some linear accelerators.Lead or cerrobend blocking strips are used to shape electron treatment fields when an appropriate custom insert is not available. For the Varian 2100C accelerator, the structural supports of the electron applicators impede the free placement of these field‐shaping strips on the open custom insert frame while placement at the top of the applicator is unimpeded. We have investigated the dosimetric ramifications of placing field shaping strips at the top level of the PACS number(s): 87.53.–j, 87.52.–g Electron beam field shaping is typically accomplished by one of two methods. In the first method, an appropriate thickness of lead can be placed on the patient's skin to define the area to be irradiated. In the second more frequently used method, the linear accelerator has an electron applicator that has at its exit a place for a custom‐made cerrobend insert that then defines the field shape. Either of these field‐shaping methods can produce the desired field shape and intensity. When a custom cerrobend insert is not available and the patient's treatment field is planned on the treatment couch immediately followed by treatment, there is the need to create the field shape from available cerrobend or lead strips. However, for some accelerators, i.e., Varian 1800, Clinac 20, 2500, 2100C, 2300C, and the new EX series high energy machines , the applicator structure can impede the correct placement of these blocking strips at the location of the insert, but provides an open surface at the top of the applicator upon which blocking strips may be placed. Although placing the strips at the top of the applicator may be faster and more convenient than at the insert level, dose delivery errors may result. This procedure has been reported to us as having been performed at multiple radiation therapy facilities in the United States. In this study, we quantify the potential dosimetric errors created by using the top of a Varian 2100C electron applicator as a shelf to place cerrobend strips for field shaping.15 cm×15 cm electron applicator. Measurements of beam profiles were made with Kodak XV‐2 film  and of dmax dose with a PTW 30001 0.6–cc farmer‐type ionization chamber  and Keithley 35040 electrometer . The effects of applying field shaping cerrobend slabs at the top of the applicator (top‐level) [Fig. All measurements were performed on a Varian 2100C linear accelerator using the el) Fig.  vs applyel) Fig.  were meaIn each case, a 5‐cm‐wide, 15‐cm‐long light field was obtained at the isocenter. Since the top‐level of the electron applicator is 40 cm from the isocenter, the actual width of the opening produced by the two cerrobend slabs was 3 cm, while at the insert level, which is 5 cm from the isocenter, the width was 4.8 cm.dmax. At least three measurements were taken for each combination of energy and shaping method and were then averaged.Relative dose was determined for each field shaping method by using the ionization chamber inserted in a polystyrene phantom. An appropriate buildup thickness of polystyrene was placed on top of the phantom depending on the electron energy under investigation. The top of the phantom was always set to the isocenter and the beam was directed downward on it in the vertical plane. For each energy, measurements were also made for the open field at dmax depth for each electron energy on top of the film. The slabs were placed on the treatment couch, centered under the beam, so that the surface of the top slab was at the isocenter. In all cases, the gantry was set so that the beam was directed downward in the vertical plane. 40 MU were delivered for each energy for the insert‐level shaping while 57, 49, and 44 MU were delivered for 6‐, 9‐, and 16‐MeV electrons, respectively, for the top‐level shaping in order to produce approximately the same optical density on each film. These monitor units were determined from the relative dose measurements found when using the ionization chamber. A Multidata film scanner  scanned each film through central axis across the 5‐cm dimension and each resulting profile was corrected by using the appropriate optical density to dose conversion function.Dose uniformity was tested for the two field shaping configurations by placing a sheet of film on a polystyrene backscattering slab and then placing a polystyrene slab of thickness equal to the 15 cm×5 cm fields produced doses within 2% of the expected doses relative to the open 15 cm×15 cm fields. This finding confirms that the method used to create the fields at the insert‐level was equivalent to having used a custom insert. Table For each energy, the insert‐level shaped In Figs. In a busy department where electron beam treatments are frequently planned in the treatment room and then immediately delivered, custom made shaping for the first one or more treatments is often not practical. If a previously made insert is not suitable, lead strips are often used to define the field shape by placing them in the electron applicator so that they produce a light field shadow which matches the lines drawn on the patient by the radiation oncologist. However, due to the construction of the applicator, it may be difficult to place these lead strips on the area surrounding the cerrobend insert Fig. . For the––15×15 standard insert) travels about 40 cm to isocenter vs 5 cm for insert‐level shaping. In addition, when field shaping is done at the top level, the aperture for electrons to pass through is only 3‐cm wide in order to produce the 5‐cm light field width at the isocenter. Also, consider scattered electrons that are outside the divergent rays connecting the edges of the 3‐cm‐wide aperture at the top level and the 5‐cm‐wide aperture at the insert level. Some of these would have scattered into the field by the time they reached the insert level but are instead stopped in the top‐level shaping material and fail to contribute to the dose at central axis. Thus the 3‐cm‐wide top‐level opening is at the same time stopping some scattered electrons from reaching the isocenter as well as permitting electrons, otherwise blocked by the insert‐level cerrobend, from reaching several centimeters lateral to the intended field border. These effects are largest for the smallest electron energy. In addition, inspection of Fig. It is well known that the distance from the electron beam‐shaping device to the patient surface is a critical parameter in the determination of both the absolute dose as well as the shape of the beam.The findings of this study demonstrate that shaping electron fields by applying lead blocking material at a position closer to the source of radiation decreases the delivered dose by up to 30% for low energies as well as broadens the beam to extend well past the light field border. These dosimetry errors could significantly contribute to lack of tumor control as well as cause radiation toxicity to sensitive normal structures thought to be outside the radiation field.It is our suggestion, based on these findings, that routinely shaping electron beams with lead strips should generally be avoided. Although properly placing these strips on the insert level of the electron applicator produces beam characteristics consistent with those produced when using a custom insert, the temptation to place the lead strips in inappropriate but more convenient places in the applicator risks misadministration of the treatment. If field‐shaping strips are to be used for emergency treatments, the staff should be trained to ensure that the strips are properly placed at the insert level.