Ultrasound imaging is affected by coherent noise or speckle, which reduces contrast and overall image quality and degrades the diagnostic precision of the collected images. Elevational angular compounding (EAC) is an attractive means of addressing this limitation, since it reduces speckle noise while operating in real-time. However, current EAC implementations rely on mechanically rotating a one-dimensional (1D) transducer array or electronically beam steering of two-dimensional (2D) arrays to provide different elevational imaging angles, which increases the size and cost of the systems. Here we present a novel EAC implementation based on a 1D array, which does not necessitate mechanically rotating the transducer. The proposed refraction-based elevational angular compounding technique (REACT) instead utilizes a translating cylindrical acoustic lens that steers the ultrasound beam along the elevational direction. Applying REACT to investigate phantoms and excised tissue samples demonstrated superior suppression of ultrasound speckle noise compared to previous EAC methods, with up to a two-fold improvement in signal- and contrast-to-noise ratios. The effects of elevational angular width on speckle reduction was further investigated to determine the appropriate conditions for applying EAC. This study introduces acoustic refractive elements as potential low cost solutions to noise reduction, which could be integrated into current medical ultrasound devices. While speckle can be exploited to obtain dynamic information (e.g. on blood flow)5, it can also degrade both the resolution and contrast of static structures and blur the boundaries of layered tissues, which can hinder the interpretation of tissue morphology and fine structure and adversely affect diagnostic procedures10. Image post-processing or compounding methods are commonly used to reduce speckle in US imaging20. Post-processing is based on image filter algorithms that use information extracted from the images13, which limits realistic enhancement of structures obscured by speckle noise. Compounding methods average sequential images from the same field of view (FOV) with varied spatial or frequency content10, enhancing correlated features while removing uncorrelated speckle noise, which can reveal structures obscured by speckle in individual images. Frequency compounding methods either vary the emitted frequency or decompose the spectrum of the echo signal to obtain images with uncorrelated speckle patterns, while spatial compounding methods acquire images at different US beam orientations20. However, both compounding methods typically result in a loss of spatial or temporal resolution, as capturing multiple images reduces acquisition speeds and collecting signals from adjacent fields of view reduces the lateral resolution18.Speckle noise is an inherent property of ultrasound (US) imaging that results from constructive and destructive interference of backscattered acoustic waves caused by heterogeneities in tissue19. EAC obtains partially correlated images by steering the elevational imaging plane with small angular steps20. EAC methods typically employ either one-dimensional (1D) arrays that can only control the US beam in the azimuthal direction  or two-dimensional (2D) arrays that can control the US beam in both the azimuthal and elevational directions (the latter being perpendicular to the imaging plane)23. US systems with 1D arrays are simple and inexpensive. However, implementing EAC in such systems necessitates bulky mechanical stages to physically move or rotate the 1D array in order to steer the beam in the elevational direction19, which is impractical in clinical applications. In contrast, US systems integrating 2D arrays can electronically steer the beam along the elevational direction without changing the detector’s position23.However, EAC has only been preliminarily validated in systems integrating 2D detector arrays on simulated data and, although this implementation was reported in patents25, it has not thus far been experimentally validated. Furthermore, the use of 2D array detectors increases the size and cost of the US system. Thus, there is a need for a means of incorporating EAC into US systems that are both economical and have a small form factor.Elevational angular compounding (EAC) is a type of spatial compounding that can simultaneously offer high speckle noise reduction and good temporal resolution, making it desirable for medical applicationsIn this work, we aimed to develop a method of implementing EAC, which could be integrated into simple and low cost US system without sacrificing the image enhancement capabilities. We hypothesized that an acoustic refractive lens could steer a US beam from a 1D transducer array, imparting it with the elevational steering ability of a stationary 2D array while retaining the advantages in size, cost, and simplicity of a 1D array. Furthermore, linear micro-translation of a refractive element should impart precision control of elevational angular steering in a 1D transducer array while minimizing motion artefacts compared to rotating the entire transducer. We describe herein this refraction-based EAC technique (REACT) and assess its qualitative and quantitative enhancements of US images in experiments on phantoms and tissues ex vivo. Moreover, we examine the effect of experimental parameters that can cause image deformation due to compounding different elevational angular views.The implementation scheme of REACT using an acoustic refractive element is shown in Fig. 27. The lenses were fabricated from 2.5 mm ± 4 µm thick PMMA blocks. Figure 6 kg/m2s) and water 27. The distance between the transducer and ACL was held to < 1 mm (while avoiding contact) to minimize the effect of multiple reflection artefacts on the image due to the impedance mismatch between the PMMA and water. Each ACL can produce a characteristic maximum elevational angular deflection, which is 0° for ACL1, 2.5° for ACL2, and 5° for ACL3. Given the radius of curvature, the usable scanning length (w) is geometrically constrained and the translation step is defined to acquire a fixed number of images (N = 100). ACL1 and ACL2 were scanned with steps of δ1 = δ2 = 150 µm, whereas ACL3 was scanned in steps of δ3 = 100 µm. The total deflection angle was theoretically calculated using Snell’s law as c1sinθ2 = c2sinθ1 29 and confirmed experimentally as follows.Customized ACLs designed to cover the full sensor area were manufactured from Polymethyl methacrylate (PMMA), which has a sound speed of 2750 m/s and low acoustic attenuation of 1.4 dB/cm/MHzi), without ACLs, was first determined by measuring the distance between two opposing needle tips, which were inserted into opposite sides of an agar phantom until they just appeared on each side of the image. By recording their imaging depth, an inherent elevation angular FOV of 29.5° was calculated for the employed linear transducer. Similarly, the extended elevational angular FOVs (θE) when employing ACL2 and ACL3 were calculated as 32° and 34.5°, respectively. The effective compounding angles of 0° , 2.5° (ACL2), and 5° (ACL3) were computed by subtracting the inherent transducer angular elevation FOV from the extended ones obtained for each ACL.The transducer’s inherent elevational angular FOV , frustum (intermediate diameter gradient), and cone (high diameter gradient) and was used to explore the effect of elevational angular width and the target’s cross-sectional variation on EAC image fidelity. An excised chicken heart and swine kidney were utilized as biological phantoms to further explore the importance of the cross-sectional appearance of the sample on image fidelity for a given elevational angular width using REACT. The chicken heart was chosen due to its conical shape to represent a sample with high cross-sectional variation. The swine kidney, which is larger than a chicken heart, was selected because of its low cross-sectional variation. For comparability, US images of the biological phantoms were captured and despeckled under the same imaging condition utilizing ACL3. The phantoms were stabilized during imaging by pinning them to polystyrene foam. No live specimens were used in the experiments.Custom acoustic phantoms (50 mm × 20 mm × 15 mm) comprising 2% agar and 4% TiO30 , i.e. two effective Δ values. A single image and two compounded images using 5° elevational angular deflection are shown in Fig. 1, smaller Δ). The cone with an intermediate diameter gradient  shows image fidelity for both Δ cases, without blurry edges. The impacts of these findings were further explored using a biological phantom of an excised chicken heart , which efficiently de-speckles US images using an acoustic refractive element. This method enables EAC in a US system comprising a low-cost 1D detector array without moving or tilting the entire transducer head, eliminating the need for bulky mechanical stages or costly 2D arrays and easing implementation in current US imaging systems equipped with 1D arrays.14. While the widest angle employed in our study was 5°, the selection of the optimal compounding angle should take into account the trade-off between speckle reduction efficiency and image distortion (discussed below). Our results in Table 14. This superior enhancement could be attributed to a reduction in motion artefacts because of the fixed transducer. Note that imaging through the PMMA refractive lenses caused a 7.5% signal loss due to acoustic attenuation and reflection  and utilizing diffraction lenses with lower effective thicknesses31.In contrast to previous EAC implementations, REACT uses a fixed 1D transducer array with a translating acoustic cylindrical lens. Visual and quantitative inspection of US images depicted in Fig. 14. Our results demonstrate that image deformation can also occur in EAC with narrow elevational angles, particularly from deeper imaging positions, due to the associated increase in elevational angular width (Δ). Image fidelity in EAC, or in other words, accurate representation of structural features from the despeckled plane, is affected by interference from structures in adjacent elevational planes. We explored the trade-off between imaging depth and elevational angular width when employing EAC methods on targets with shapes that have no (cylinder), low (frustum), and high (cone) diameter gradient along the elevational direction (Fig. ex vivo chicken heart and swine kidney with REACT, which demonstrated the importance of accounting for the morphology of the sample for a given elevational angular width in EAC. The spatial resolution along elevational direction is the main limiting factor in all EAC implementation and depends on the total elevational beam width. Hence, out of plane signals can degrade compounding quality, particularly when imaging small organs. This was confirmed in our experiments, where the high variation of the cross-sectional appearance of the chicken heart resulted in distortions in the compounded image (Fig. Although EAC is recognized as an efficient way to suppress speckle noise in US images, it suffers from anatomic structure deformation and edge blurriness in compounded images captured within wide elevational angular viewsion Fig. . We founage Fig. f,g, wherIn summary, we utilized acoustic refraction to introduce elevational angular steering into existing 1D transducer arrays and demonstrated its application in a novel implementation of EAC called REACT. Such a low-cost and simple compounding de-speckling method can be of great benefit in clinics to improve current US visualization and interpretation during disease diagnosis. Further work aims at miniaturising ACL embodiments and allowing real-time despeckling by automating the position of the lens and synchronizing frames to evaluate REACT in a clinical context.


The structural form and elemental distribution of material originating from different Fukushima Daiichi Nuclear Power Plant reactors (Units 1 and 3) is hereby examined to elucidate their contrasting release dynamics and the current in-reactor conditions to influence future decommissioning challenges. Complimentary computed X-ray absorption tomography and X-ray fluorescence data show that the two suites of Si-based material sourced from the different reactor Units have contrasting internal structure and compositional distribution. The known event and condition chronology correlate with the observed internal and external structures of the particulates examined, which suggest that Unit 1 ejecta material sustained a greater degree of melting than that likely derived from reactor Unit 3. In particular, we attribute the near-spherical shape of Unit 1 ejecta and their internal voids to there being sufficient time for surface tension to round these objects before the hot (and so relatively low viscosity) silicate melt cooled to form glass. In contrast, a more complex internal form associated with the sub-mm particulates invoked to originate from Unit 3 suggest a lower peak temperature, over a longer duration. Using volcanic analogues, we consider the structural form of this material and how it relates to its environmental particulate stability and the bulk removal of residual materials from the damaged reactors. We conclude that the brittle and angular Unit 3 particulate are more susceptible to further fragmentation and particulate generation hazard than the round, higher-strength, more homogenous Unit 1 material. W 9.0 earthquake that occurred off the countries eastern coast1. In the days that followed, a vast amount of radioactive material, in varying forms  was emitted into the environment—both locally as well as globally. The total summed source-term inventory of the individual radionuclides (excluding volatile noble gases) released from the FDNPP is approximated to 520 PBq  or 10% of the total inventory emitted in 1986 following the accident from the Chernobyl Nuclear Power Plant (ChNPP)3. Although less radiation was released, the accident at the FDNPP was similarly rated at Level 7 (the most severe) on the International Atomic Energy Agency (IAEA) International Nuclear Event Scale (INES)—a measure of the global ramifications of the world’s second worst ever nuclear accident4. In contrast to the single reactor associated with the incident at the ChNPP, this high event severity at the FDNPP is a direct consequence of the multiple reactor Units involved—with contamination releases arising from three of the six boiling water reactor (BWR) Units5.In March 2011, the Fukushima Daiichi Nuclear Power Plant (FNDPP) was inundated with a 15 m high tsunami following the M6. Attached to Unit 3, via shared pipework and ducting, the neighboring reactor Unit 4  was undergoing planned maintenance on 11th March 20117; with the inventory of 1331 fuel elements having been moved to its own dedicated spent fuel storage pond (FSP—a deep water-filled recirculated cooling facility) located above the reactors primary containment vessel (PCV), which itself houses the main reactor pressure vessel (RPV) where the fuel is located during operation8. As a consequence of the recent transfer of still ‘thermally hot’ (as well as highly radioactive) fuel into the reactor Unit 4 FSP, a notable cooling requirement still existed on the material within the ponds9. In contrast, the sites remaining two (and most recently constructed) reactors, Units 5 and 6 , were in a period of extended ‘cold’ shutdown for planned maintenance at the time of the earthquake and tsunami; with the fuel assemblies still inside each of the RPVs , in addition to a greater number stored in each of the above-reactor FSP facilities . Owing to the time that reactors 5 and 6 had been placed in shut-down, the thermal output from these partially used (or ‘burnt’) fuel assemblies was greatly diminished, such that a significant cooling provision to the FSP was no longer required3. Stemming from the time difference in the construction of each of the BWR reactor Units, alongside increasing electrical output, a number of design and system variations are evident between Unit 1 and Unit 6. The most noticeable of which is the transition from Mark-I to Mark-II designs of the PCV3—from the classic ‘inverted lightbulb’ (torus) shape to the more structurally robust and resilient design with greater suppression pool/chamber capacity.At the time of the accident, reactor Units 1, 2 and 3  were in power generation mode. However, following the detection of the first seismic activity, each of these reactors successfully entered an emergency shutdown (or ‘SCRAM’) through the as-standard insertion of neutron-absorbing and fission inhibiting control rods2 in Units 1 and 2; UO2 and a U/Pu mixed oxide (MOX) in Unit 3) and other reactor components5. This resulted in the structural failure, and ‘slumping’, of the reactor fuel assemblies in each of the three reactors 12. So extensive and at such high temperatures was this molten core composition  ‘Corium’ mass, that following its melting through of the stainless-steel RPV, the flowing mass continued downwards onto the underlying concrete pedestal installed within the PCV—resulting in highly complex molten core-concrete interactions (MCCI)13.While each of the operational Units  successfully ceased further reactivity (through a cessation of neutron generation) and power production, there still remained a significant amount of residual heat within each RPV that required removal in order to protect the integrity of the reactor and the fuel within. Following the detection of seismic activity and reactor shut-down, core cooling was sufficiently facilitated by the suite of in-built safety features; including the reactor core isolation cooling (RCIC) and a number of emergency core-cooling systems (ECCS). However, after the destruction of the power supplies that facilitated this heat removal  by the ensuing 15 m high tsunami (that arrived 30 min after the earthquake), it became impossible to suppress the rapidly rising temperatures of each core and cool the highly radioactive reactor fuel assemblies. Consequently, there resulted a series of loss of coolant incidents (LOCI) as the temperature within each RPV exceeded the melting point of the fuel  were highly visual and/or detectable. The releases from reactor Units 1 and 3 were associated with large hydrogen explosions; both of which destroyed the reactor building superstructures. However, the most widespread and largest inventory activity release resulted from the non-explosive discharge from reactor Unit 2—invoked to have resulted from a breach in the structural integrity of the PCV 15. Alongside subtle differences in the low levels of enrichment of the UO2 fuel  and the incorporation of a partial core MOX loading (within reactor Unit 3)7, the primary characteristic for fingerprinting each of the reactors is the 134Cs/137Cs (radiocaesium) activity ratio (amongst other activity and isotope ratios). A summary of this Cs activity variation is illustrated in Figure 134Cs/137Cs activity ratio are observed down the vertical length of a used fuel element (greatest towards the base owing to the increased neutron fluxes) and also its position in the reactor core itself 16, a widely accepted single representative value for each reactor Unit/FSP has been calculated15. It is such values of < 1.0 (Unit 1), circa. 1.08 (Unit 2) and circa. 1.04 (Unit 3) that have resulted in the primary 35 km north-west trending contamination plume being attributed to reactor Unit 2—with plumes of smaller spatial extent that surround the plant ascribed to the releases of reactor Units 1 and 319.The ability to provenance each of the discrete radioactive release events and associated particulate material derived from each reactor Unit is a consequence of the differing operational histories, fuel characteristics and burn-ups of the fuel contained within each of the sites boiling water reactors5.As well as the indicative bulk radiocaesium (activity) ratios for each of reactor Unit (and FSP), all of the FDNPP reactors are further characterized by a unique cooling chronology over the duration of the accident; a schematic of which is shown in Fig. 22, this work examines and compares the larger diameter (> 100 µm) radioactive particulates emitted from reactor Unit 1 to those invoked to derive from reactor Unit 3. While both releases were the result of violent hydrogen gas accumulation explosions3; as is shown in Fig. 5. However, despite the periodic venting of the reactors , the pressure build-up within Unit 3 was for a greater duration than for Unit 1—with core melting  at a reduced rate and to a lesser extent23.In contrast to earlier works that studied the fine-scale and highly spherical (~ 2 µm diameter) release material from reactor Unit 2ameter > 00 µm rad134Cs/137Cs activity ratio, 135Cs/137Cs atomic (isotopic) ratio, radiocaesium concentration and geographical sampling location) was first proposed by Satou et al.25 and has since been widely adopted following the extensive analysis of such FDNPP-derived material. Like the radioactive particulates released into the environment from the 1986 Chernobyl accident26, this work defined two distinct groupings of material; ‘Type A’ and ‘Type B’—a review of which is provided Igarashi et al.22. Such ‘Type A’ particulates are highly spherical, and resulting from their 134Cs/137Cs activity signature being analogous to the modelled core inventory15, are attributed to have been derived reactor Unit 2. Due to their small diameter and readily transported nature; entrained within buoyant atmospheric air masses, they have been isolated using high-volume aerosol samplers at locations over 170 km from the FDNPP site27, with a subset of these “Cs-balls” identified as containing reactor core composition U within their cores21. With the internal Cs component distributed in some instances homogeneously21 and others heterogeneously (concentrated within the particulates outermost ‘rind’)28, the specific activity (activity per unit volume) of this micron-scale ‘Type A’ material is significantly greater than that of the larger ‘Type B’ particulates25. Such ‘Type B’ material  has conversely been ascribed to reactor Unit 1; exhibiting a highly irregular surface form, 70–400 µm largest dimension and strongly near-plant occurrence.A reactor Unit origin nomenclature of FDNPP release particulates  had been undocumented ahead of the studies of both Zhang et al.29 and Igarashi et al.23. Alongside their complimentary Sr and Pu signatures analysis, respectively, the studies examined ‘dust particles’ (DP)—provenanced to Unit 1, in addition to a new form of isolated ‘soil particle’ (SP). Resulting from their dissimilar form, compositional and isotopic signatures (including a comparison to 137Cs/90Sr activity ratios of particulates with known reactor origin), these studies both invoked such (‘SP’) material to have resulted from a new emission source—reactor Unit 3, and a ‘Type C’ particulate material.The absence of a radioactive release particulate attributable to Unit 3  FDNPP-sourced particulate. Alongside elucidating the current in-reactor conditions, we consider the likely environmental implications of this new form of ejecta particulate by evaluating its likelihood to breakdown, mobilize and introduce subsequent contamination hazards within the dynamic Fukushima environment close to the plant. In this work, laboratory X-ray tomography (XRT) combined with synchrotron radiation (SR) XRT and X-ray fluorescence (XRF) analysis is applied to a suite of Unit 3 derived particulates—the results of which are compared to formerly examined Unit 1 material31, applying analogues associated with volcanic ejecta (pyroclasts).This work follows earlier studies on Unit 1 derived materials134Cs/137Cs activity ratios and consequently to confirm the FDNPP reactor responsible for its release, are shown in Table 134Cs/137Cs activity ratio of < 1  determined for the CF-xx particulates—obtained from a region to the north-west of the plant through which low-altitude aerial mapping had formerly attributed a similar (Unit 1) provenance to the contamination19. This CF-xx particulates 134Cs/137Cs activity ratio is in direct contrast to that of the OH-xx inventory of material, all of which possess a 134Cs/137Cs activity ratio of > 1  particle EDS, with the results of this analysis on two representative Unit 1 (CF-01-T18 and CF-01-R024) and two representative Unit 3 (OH-06-10 and OH-06-07) particulates presented in Fig. 27, however, a fundamental difference between such significantly larger (Unit 1 and Unit 3) particulates and the micron-scale (Unit 2) ‘Cs-balls’ is the detectable occurrence of Cs via EDS analysis (where limits of detection are ~ 0.1 wt%). As determined during earlier studies that examined the Cs abundance within reactor Unit 1 particulate31, the ‘per particle’ activity, and therefore the concentration of radiocaesium within such Units 1 and 3 particles is more than 4 orders of magnitude less per unit volume than the smaller Unit 2 material25, and is highly concentrated within the material—rather than being associated with the material’s spherical outer surface. Such a low abundance, combined with the concentrated nature within the similar Unit 1 material, therefore elucidates as to the inability to detect Cs within such Unit 3 material via EDS.This compositional similarity between Unit 1 and Unit 3 particulate is also shared with the smaller, and highly spherical, material derived from reactor Unit 231 that examined Unit 1 material, and as shown in Fig. Absorption contrast XRT sections obtained at perpendicular orientations through the central axes of representative Unit 1 and Unit 3 particulates are shown in Fig. The internal forms of the Unit 3 ejecta material, revealed by the orthogonal XRT sections of the two representative particles shown in Fig. Furthermore, the location and distribution of  voids within the Unit 3 sourced particulates , the tomographic sections of which are shown in Fig. The forms (shape) of voids in representative suites of Unit 1 and Unit 3 particulates were quantified with the aspect ratio (i.e. the length of longest axis divided by the dimension measured perpendicular to the long axis) measured on image slices from laboratory XRT analysis Fig. . From FiComplementary to the surface EDS analysis results presented in Fig. 33.Such a superior detection limit of SR-µ-XRF, combined with entire volumetric analysis (opposed to purely surface quantification afforded by EDS) additionally details the occurrence of Ba, Zr and trace quantities of Cs within the Unit 1 sample Fig. a, with t2 gas events at the two FDNPP reactors.Alongside the occurrence of V, Se, Br and Y as constituents of the Unit 3 material, in contrast to the Unit 1 particulate, from the two SR-µ-XRF spectra presented in Fig. 2 correlation) exists for the vast majority of elements, we observe significant (> 0.3) species correlation for a number of elemental pairings; Mn–Fe, Pb–Fe, Pb–Cu and Zn–Pb, with greatest correlation (> 0.6) between Zn–Cu and Ti–V. Albeit with a degree of variability, we determine these species pairings as representative for the Unit 3 material examined.Applying discretization to the 3D SR-µ-XRF results of the Unit 3 particulate typical of the reactor-derived inventory of material, yields the elemental correlation analysis displayed in Fig. 2 value of 0.32 between Mn and Ti, and values of 0.12–0.21 for Zr associated pairings. As formerly identified in earlier works studying Unit 1 particulates31, both Cs and Sr are similarly observed in the representative Unit 3 material to occur at enriched near bubbles.Such a high degree of species co-incidence between a number of elements is in contrast to the inter-elemental distribution we observe for Unit 1 particulate the results from a subset of the largest comparison are presented in Fig. 32, it is widely accepted that glass fibre insulation material is the source of the bulk Si that is the primary constituent of the particulates released following the explosive H2 gas explosion at reactor Unit 1. This insulation, which was used extensively around the reactor Unit, especially around the PCV, was formed through a two-step melting and extrusion process of a silicate rock precursor that produced fibers of 4–5 µm mean diameter. We invoke a similar provenance to the bulk material constituting the invoked Unit 3 particulates because their compositions are similar to those from Unit 1; with equivalent insulation used within Unit 3 (surrounding the PCV34) and the explosive release mechanisms also being identical.With prior electron microscope analysis having identified its fibrous nature 31, concluding that their intricate internal structure is the consequence of the complex high-temperature and high-pressure in-reactor environment. This material was emitted during the first of the release events on the 12th March 2011, while the reactor existed at the greatest temperatures following the complete loss of core cooling provision  to volatile (137Cs) species, reactor Unit 1 reached the greater temperatures at the time of radioactive particulate formation than either of Unit 2 or 3. Satou34 also concluded that the temperature within Unit 1 was the greatest of the three FDNPP reactor Units from the application of empirically derived volatility differences in Ag (110mAg) and Cs (137Cs)35. Such reasoning aligns with the known event history presented in Fig. Through an assessment of the elemental and isotopic constituents and ratios, Igarashi et al.volatile 37Cs spec134+137Cs), the SR-µ-XRF analysis of the OH-xx suite of particulates does not identify the occurrence of Cs within any such sample, therefore suggesting that the concentration is very low—likely distributed throughout the entire particulate volume rather than a discrete, high-concentration, occurrence.While the composition of the material examined in this study, that we invoke to have been derived from Unit 3, is largely analogous to that derived from reactor Unit 1, a number of minor compositional differences are observed. Despite its radioactivity being a result of radiocaesium (89Y (stable); 81Br (stable); alongside various Se; 77Se (stable), 78Se (stable), 79Se (t1/2 = 105 years), 80Se (stable), 82Se (t1/2 = 1020 years).This first measured occurrence of Se, Br and Y (using SR-µ-XRF) within Fukushima-derived (and Unit 3) particulates is a consequence of the inclusion, into the bulk silicate precursor material, of such volatilized  or molten (Y) fission product species over the duration at which the PCV existed at elevated temperatures and pressures—allowing their diffusion and amalgamation. The combination of the non-detection of such species via EDS—requiring SR analysis to identify their existence, signifies the low abundance of such fission product elements within the bulk particulates. A radiogenically stable or long-lived nature of the Y, Br and Se accounts for their absence when such particulate was subjected to gamma-ray spectroscopy analysis despite the significant counting times. Therefore, these elements are most likely the isotopes of The compositional coincidences recorded within the Unit 3 particulate likely result from the elemental associations of the precursor contributing materials—remaining associated with one another during the subsequent melt process. Regions of Ti–V and Fe–Mn arise from alloying additions within steels; whereas the Cu–Zn pairing having been input into the particulates from electrical components, wiring, or the possible existence of brass components. The high degree of correlation between the number of Pb-based elemental pairings  could represent the combination of the once extensive volume of Pb shielding with the constituents of the RPV/PCV stainless steel superstructure . The occurrence of Pb-Cu coincidence is similarly the result of Pb sourced from the shielding materials—combined with Cu derived from electronics, wiring, or potentially, brass components.35, Igarashi et al.23 determined that particulates derived from reactor Unit 1, formed under the highest temperature atmosphere—contained the greatest actinide abundances. This is a consequence of non-volatile radionuclides, such as U, Np and Pu, being more volatile at extreme fuel temperatures (~ 2200 °C)36; with the underpinning experimental studies of Pontillon et al.37 deriving release fractions of 10% for U and Np, while a very low value (< 1%) was measured for Pu. In this study on Unit 3 derived material, no actinide species were observed within any of the particulates (in contract those formerly examined from Unit 130). The absence of such non-volatile radionuclides aligns with the conclusions of Igarashi et al.23 and the known in-reactor temperature conditions of Unit 3 (and Unit 2) at the time of release—with the temperature suppressed to limit the release fraction.Through their assessment of the reactor core temperatures (at the time of the radionuclide releases), Pu isotope mass spectrometry analysis and the known temperature-dependent species  release behavior under accident conditions5—composed of fission products, noble gases, and hydrogen38.The suites of highly porous glassy airfall material from both reactor Units have similarities with primary volcanic particles and there may be analogous processes and dynamics involved in their evolution. In particular, as a fragment of molten material is ejected, it will rapidly decompress and cool—with this decompression resulting in expansion of any pre-existing bubbles contained within the melt while simultaneously driving the exsolution of other volatile elements. This coupled process together results in the nucleation and growth of bubbles—with additional contributions arising from the extensive gaseous volume within the physical environment surrounding the reactor39). The EDS-derived SiO2 wt% content of all particulates examined in this study is between 64 and 69% (average: 66%), comparable to a typical dacite magmatic melt, wherein applying the formulation of Giordano et al.40 yields a viscosity of 6 Pa s at 1800 °C, 9 × 103 Pa s at 1200 °C, and a corresponding glass transition temperature (i.e. a viscosity of 1012 Pa s) at approximately 700 °C. While these values represent an appropriate estimate for the bulk silicate material of homogenous composition, as identified formerly31, the minor variations in the X-ray attenuation , observed in Fig. 41. As Cs and Sr are enriched near bubbles, we suggest that these haloes reflect late-stage volatile resorption as the molten particle cooled, before the volatiles were quenched in the glass. The halo may, therefore, appear bright because of the high atomic number of Cs and Sr, relative to Si.The overriding factor on the form and internal void morphology within different volcanically or FDNPP emission particulates is the viscosity, or resistance to deformation. Typical of many fluid scenarios, as the melt cools it becomes increasingly viscous, with ductile deformation ceasing as it crosses the glass transition  diffusion of volatiles out of the particle inhibiting bubble growth in the margin28. For the cooling rate mechanism, the interior must remain at elevated temperatures for longer than the margin—with the bubbles having greater time to expand  in the interior. The outer surface of these particles is smooth and not fractured  in the Unit 1 particulates have an overall bi-modal size distribution, but as shown in Fig. 31. The particulates would have rapidly thermally equilibrated with the surrounding environment due to their small size (each with maximum dimensions of < 500 µm). This is evidenced through the timescale for cooling (τcool) by conduction43:cool = 0.01 s for D = 10–6 m2/s and a typical particle size with L = 100 mm. Consequently, temperature gradients within the (formerly molten) particulates at the time of release would have been short-lived. The rate at which the molten particle cools (e.g. time to reach the glass transition temperature at which it becomes solid) will therefore depend strongly on the particles trajectory and the temperature of the environment into which it is ejected.A more detailed study of the distribution of species with different diffusivities in conjunction with physical modeling would be needed to be definitive on the mechanism for generating the bubble texture pattern. However, due to the lack of evidence of volatile depletion in the marginal glass, we tentatively propose that the larger bubbles in the interior are dominantly due to a greater time for expanse as the interior cooled slightly slower than the margin44. This rounding is resisted by the viscosity of the melt, with the characteristic timescale for rounding (τround) given by45:–1 N/m), η is the melt viscosity, and r is the radius of curvature of the interface (i.e. the radius of the particle or bubble). From this equation, the rounding of particles and internal bubbles can be seen as occurring faster if they are (i) smaller, and (ii) if the melt is less viscous. The sensitivity of the melt viscosity to temperature therefore means that the temperature of the ejected melt fragment could have the dominant control on how much rounding occurs before it is quenched, passing through the glass transition, forming a solid. Furthering the complimentary geological example of a dacite, discussed above, with r = 100 μm and Γ = 0.1 N/m; a τround of 0.006 s is observed at 1800 °C (η = 6 Pa s), in contrast to a τround of 9 s at 1200 °C (η = 9 × 103 Pa s).We invoke the most likely explanation for the rounder shapes of Unit 1 particulates, as well as the more spherical bubbles within them, in comparison to Unit 3 particles, is that the molten precursor fragments that formed Unit 1 silicate particles were hotter and therefore the melt was considerably less viscous—supported by the known cooling chronologies of both reactors  while still hot.The sharp, angular margins of this homogeneous outer glassy region indicate brittle fracture. We suggest that this fracturing results from thermal stresses in the glass when these  Unit 3 particles cooled, and that it corresponds to a secondary fragmentation stage after the primary  event that generated the particle material—a subsequent episode not associated with the Unit 1 particulates. We do not have data to precisely constrain whether the primary fragmentation was brittle or fluidal  for any of the particles. Lower viscosities (higher-temperatures) are conducive to fluidal breakup, but even the hot melt of Unit 1 could fragment in a brittle manner if the strain rates were large enoughWithin this work, we investigated the composition and, for the first time, the structure of a suite of particulates invoked to have been derived from the FDNPP reactor Unit 3—contrasting their form and composition to those released from reactor Unit 1, as illustrated in Fig. 47, we deduce that as the associated drag forces , particle free-fall  and the resultant distribution are dominated by the particle size—with secondary, and less substantial factors, being both the density (influenced by bubble content) and shape of the particulates, that both suites of material are to be observed at similar radial distances away from the FDNPP. As there likely occurs a location dependent particle size gradation with increased radial distance from the FDNPP, there would exist a finning of the particle (grain) size  until further size reductions of the material are no longer observed. Such a lower-bound in particle size is attributed to the terminal velocity of the particles being less than the entraining flows turbulence velocity. Therefore, such fragmental particulate would not be encountered beyond a specific, and as yet undetermined, distance from the release center—a function of the transporting plume velocity.Of the two particulate types, we invoke the angular shape of the Unit 3 particles would be more susceptible to mechanical abrasion and attritional erosion of its sharp apices—resulting in its fragmentation and dispersion as finer-grained radioactive sub-particulates. However, the highly round and smoothed Unit 1 particles would be increasingly resistant to such mechanical breakdown. With respect to the environmental dispersion and transport of particulates, again drawing analogues to geological scenarios48, the radioactive dust production will be minimal, with material removal occurring via ‘as-cut’ volumes. In contrast, the inherent brittleness and associated high particulate generation potential of the angular material from reactor Unit 3 will likely result in the need for an alternate removal strategy be identified to mitigate against the significant aerosol generation hazard. However, although an issue for particulate formation, unlike the mechanically resilient fuel debris of reactor Unit 1, the reactor Unit 3 material is likely to be much more easily removed from within the confines of the PCV.As a result of these structural characteristics, we invoke that while the particulate derived from reactor Unit 1 would be largely stable and of low susceptibility to mechanical breakdown under surface environmental conditions (supported by their well-rounded form); contrasting behavior is to be associated with material from reactor Unit 3. Demonstrated by the fractured exterior surfaces, the non-spherical (and strength affording) bubbles and significant internal stresses, we identify such particulate as being highly likely to further fragment into smaller sub-particulates—with implications for subsequent radiological contamination migration. Such disparities in material brittleness and mechanical strength are additional considerations that should be evaluated when debris retrieval and reactor decommissioning operations are conducted at either reactor, where both particulates and residues of the precursor material are to be encountered. In the Fukushima case, it is hereby invoked that the angular silicate material from reactor Unit 3 represents a greater particulate generation hazard than the rounder and smoother, and so more mechanically resilient Unit 1 particles, which we attribute to the higher temperature of Unit 1 material when released, which allowed it to round before quenching to glass. During soon-to-commence decommissioning and dismantling operations within the damaged PCV structures of both reactors Unit 1 and 3 (as well as Unit 2) to remove the ‘slumped’ Corium and MCCI materials, by translating properties from the aforementioned magmatic system, we foresee that while the debris of Unit 1 will be significantly more challenging to remove via the proposed mechanical milling and scouring methods33, Satou et al.25 and Martin et al.30. An established imaging plate (IP) methodology was used to isolate the radioactive particles from an enclosing matrix49, using a BAS-SR 2025 (FUJIFILM Corporation) digital radiography scanner, with the material containing the microparticles having been prior screened using a wet separation method, based upon their differential density50. Through the multi-stage process comprising repeated autoradiography  and sample division steps, the sub-mm particles that induced a localized blackening of the IP film were identified and removed using a manual micro-manipulation setup . Post-removal, the particulate was placed onto a small piece of adhesive carbon tape for subsequent initial scanning electron microscope (SEM)/energy dispersive spectroscopy (EDS) analysis and gamma-ray spectroscopy measurements. Following this surface characterisation, the radioactive particulate was then removed from the tape and fully enclosed within a double layer of adhesive Kapton film (DuPont Ltd.).Bulk sediment, road debris and dust, as well as fabric/cloth samples determined in the field (using handheld a radiation detector) to exhibit elevated levels of radioactivity were collected from sampling sites at 37.4379° N, 141.0222° E (CF designation), 37.4075° N, 141.0272° E (OH-02 designation) and 37.40° N, 141.02° E (OH-06 designation), both within 5 km of the site and to the north-west and south-west of the FDNPP, respectively. The material collected in each instance comprised between 10 and 150 g of sample and was selected due to its undisturbed nature and isolated position, where the potential for resuspension and re-contamination from other sources  was determined to be minimal. Similar source material was formerly studied in the works of Ono et al.Surface examination and compositional quantification of each particulate sample was performed using a Zeiss SIGMA Variable Pressure (VP) Scanning Electron Microscope (SEM) with complementary Octane Plus Si-drift characteristic Energy Dispersive Spectroscopy (EDS) X-ray detector from EDAX (AMETEK Ltd.). Each sample, attached to the adhesive carbon tape, was mounted onto a standard SEM pin-stub for analysis. During both imaging and EDS elemental analysis, a consistent 25 kV accelerating voltage, 120 µm aperture and 9 mm working distance were employed—all in the machines ‘High Current’ mode to enhance the on-sample current. The negate against the detrimental influence of sample charging resulting from the non-conductive nature of the material examined, the VP function of the instrument was used—maintaining a constant flow of nitrogen gas over the particle to rapidly remove electron-induced charge build-up. All bulk EDS spectrum were obtained over a user-defined region comprising no less than 85% of the particles surface, with an acquisition period of no less than 200 s (true detector live time) to derive sufficient peak intensity appropriate for deriving quantifiable results. Both control of the detector and the subsequent processing of results were performed using the instruments EDAX TEAM software.134Cs (net count) was recorded.For attribution of each of the particulates to their reactor Unit source, quantitative gamma-ray spectroscopy results were derived by placing each sub-mm sample (enclosed inside Kapton film) within a cryogenically cooled High Purity Germanium (HPGe) detector; GEM40-76,  with associated multi-channel analyzer (MCA). Prior to each measurement, a calibration of the detectors efficiency and emission peak energy position was undertaken using a ‘multi-source’ reference standard from the Japan Radioisotope Association (JRA). In order to ensure appropriate signal-to-noise in each spectrum, the counting time for each sample was varied such that a total of 10,000 counts of Prior to the limited synchrotron radiation (SR) beamtime analysis, pre-screening of all Kapton enclosed particulates was performed using complementary laboratory X-ray tomography (XRT) to identify regions appropriate for subsequent (synchrotron radiation) analysis. Whereas the synchrotron is capable of delivering significantly more X-ray photons onto the sample, the laboratory XRT is able to obtain finer absorption contrast pixel (voxel) spatial resolutions—on the order of 50 nm, opposed to the micron-scale pixels attainable at the synchrotron, albeit at significantly slower acquisition rates. While the laboratory XRT provides superior tomographic spatial resolutions, unlike SR however, it is not possible to obtain spatially derived compositional information (via X-ray fluorescence) using the laboratory setup—with such information obtainable only using synchrotron radiation.For the X-ray analysis, each Kapton enclosed particle was mounted onto the tip of a stainless-steel support pin attached to a magnetic base, which was then installed within the instruments multi-axis (+ rotation) stage. A Zeiss Xradia 520 Versa μXRT was used to obtain 3D tomographic data of the samples, which operated at 80 kV with no additional filtering. Collection was obtained using either the 20 × or 40 × optical magnification, depending on the sample size, with the generated image collected on an ANDOR low-light camera.51 were used to determine; (i) the proportion of each slice that was composed of (black) space and therefore a void, alongside (ii) the aspect ratio of each such void—defined as the ratio of the longest to the shortest axis52, shown schematically in Figure Statistical analysis and quantification of the internal void diameters and associated aspect ratio within the particles was performed on the TIFF slices generated from each of the tomographic reconstructions. The opensource ImageJ software suite and image processing plug-insThe SR analysis was undertaken on a subset of particulates identified as possessing representative features , elemental composition and isotopic activities from both groups (CF-xx and OH-xx), at the Diamond Light Source synchrotron . In all instances, the analysis utilized the same Kapton sample enclosures as used for laboratory X-ray studies to contain the sub-mm particulates. Two of Diamond’s beamlines were used in this study; I13-1 (coherence imaging) and I18 (micro-focus spectroscopy)—with reactor Unit 1 materials examined on I13-1, and reactor Unit 3 samples analysed using the I18 beamline.53—with the beamline capable of exploiting X-rays with energies of 4–23 keV  with an on-sample flux of 109 photons/s.As the longest beamline at the facility, in order to maintain special coherence through the vertically aligned experimental optics, a distance of 250 m exists between the insertion device (canted undulator) and the sample54, with an iterative algorithm simultaneously used to correct for the degree of sample self-absorption that occurred (employing prior synchrotron tomography results). The reconstructed images were produced using ImageJ and Python software platforms.To derive the 3D volumetric XRF compositional analysis of the particle, following standard beamline focusing optics, the broad X-ray beam was subsequently focused through a 5 μm pinhole to produce a corresponding diameter on-sample beam spot. At each 4.5° rotational angle of the 3D XRF scan (over 180°), the sample was translated with respect to the centered beam in a raster grid of 40 × 20 steps—with each step of 2.5 μm, therefore yielding a field of view/scan volume of 100 μm × 50 μm comprising 32,000 spectrum containing measurement points. A corresponding pixel size of approximately 2.5 µm was hence produced. At each scan position, the XRF spectrum was acquired using a Vortex single channel silicon drift X-ray detector placed level with the height of the sample, normal to the beam path. From the computed stacks of fluorescence projections, the three-dimensional volume for each element was reconstructed using the ordered-subset penalized maximum likelihood algorithm, with weighted linear and quadratic penalty algorithms in the TomoPy framework55. Resulting from the beamlines closer position to the insertion device and the absence of necessity to maintain special coherence of the beam, a greater on-sample photon flux is achieved, with a full beam size flux at 10 keV of 1012 photons/s—focused to a 2 µm × 2 µm incident beam. To fully utilise this more highly focused beam, the Kapton™ encapsulated particle sample was also rastered in 2 µm translational steps, therefore, resulting in a 2 µm × 2 µm spatial (pixel) resolution.A comparable optical setup was also used on the I18 beamline, with the beamline attaining a comparable incident X-ray energy range of 3–22 keV , using a cryogenically cooled Si-111 monochromator for beam energy selection56 and ‘Dawn’ processing suite57. Derivation of the entire particle (bulk) XRF spectrum was obtained through summing the fluorescence signals associated with each tomographic slice; processed and peak fitted using the Python Multichannel Analyzer (PyMCA) software suite.In a methodology contrasting with that of I13-1, to derive the 3D XRF reconstructions of the particle on the I18 beamline, a series of XRF tomographic ‘slices’ (each 2 µm in thickness) of the particulate were obtained by translating/rastering the sample through the beam path—yielding a 2 µm × 2 µm 2D scan, with signal generated from the entire sectional volume. The sample was then rotated by 0.5° and a subsequent 2D raster scan of the sample obtained. This was repeated through 0°–180° of sample rotation before the sample height was changed and the 2D rastering and rotation sequence repeated to yield a total of nine sections each separated by 23 µm. Computation of these 2D sections into 3D volumetric data for analysis and visualisation was performed using the Diamond Light Sources tomographic reconstruction software ‘Savu’2) correlation using the SR-µ-XRF results. From the cross-sectional slices derived for each element (using element-specific energy windows within the XRF spectra) a pixel-by-pixel comparison of the volumetrically normalised signal intensities was performed—with the results combined to yield an inter-element coincidence value.Determination of the qualitative degree of elemental spatial correlation within particulate samples was derived using a custom Python analysis script to yield values of the R-Squared (RSupplementary Figures.


In situ dilatometry experiments using high energy synchrotron X-ray diffraction in transmission mode were carried out at the high energy material science beamline P07@PETRAIII at DESY (Deutsches Elektronen Synchrotron) for the tempering steel AISI 4140 at defined mechanical loading. The focus of this study was on the initial tempering state ( T are given or a so called temperature factor T [Manufacturing of technical components is always accompanied by the generation of characteristic residual stress distributions. Oftentimes compressive residual stresses, particularly in the near surface regions, are desired, since in most applications the integrity of the parts can be effectively enhanced as, for example, fatigue strength and wear resistance ,2. Theses (DECs)  can be cer model ,6, descrer model . For indncy on T . Apart fncy on T ,9. Theseardening ,11 thereM1426-14  in whichψ-method  is carriardening ,11. In tThe investigated material is the common tempering steel AISI 4140 in a quenched and tempered state. Cylindrical samples (full cylinders) with the dimension ® windows that allow the primary X-ray beam to enter and the diffracted beam to exit the dilatometer chamber was used. A scheme of the experimental setup is given in At the high energy material science beamline P07@PETRA III at DESY (Deutsches Elektronen Synchrotron) in Hamburg, Germany, operated by the Helmholtz-Zentzrum Geesthacht (HZG), multiple in situ X-ray load dilatometry experiments were performed. A double crystal monochromator (DCM) equipped with two SiThe performed experiments are divided by phase into The samples were heated up with a heating rate of Furthermore, the datasets obtained for the different lattice planes were used to average values to also provide values for the macroscopic temperature-dependent elastic constants TM. For the determination of peak positions the different diffraction lines were fitted using a Pseudo-Voigt function. At the investigated temperatures the plane specific lattice spacings x. Subsequently, we assume the macroscopic stress x direction are axisymmetric. Hence, the principle strain directions x, y and z can be substituted in agreement with The Debye Scherrer rings that were recorded time resolved were evaluated according to Reference  in the tThis leads to a simple expression for the lattice plane-specific axial strain (Equation ):(4)ε0∘hEquation )(5)ε90∘Here quations  and 5)  νhkl is  Daymond  presenteEquation 6)ε¯x=∑re index  which waε¯x=∑re iEquation .(7)ε¯y,The results of Equations  and 7)  7) are uEquation .(8)ε¯y,The relationships between eference , in EquaErrorbars for The different experiments were numbered from no. 1 to 7 according to the applied temperatures between 0 ∘C see . In Figux and y is given in x the peak shows a clear shift to higher y the less pronounced opposite is observed ε¯hkFurthermore in Equation  the slopIn For the determination of the lattice plane specific In The corresponding plot for the In both figures the results are plotted alongside data based on single crystal elastic constants from References ,7 for α- (≈0.2%)  and ther′smoduli . It can eference  up to a n et al.  describen et al.  observedThe results from averaging the lattice plane specific data according to Daymond  is givenAdditionally, the temperature course of pic data  determinquations  and 7)..E¯ and νIn situ X-ray diffraction load dilatometry experiments provide a suitable tool to determine lattice plane specific elastic constants and hence The experiments are much faster in comparison to conventional laboratory X-ray diffraction experiments for determination of Macroscopic Only for high-indexed planes with For lower indexed planes In summary, for temperatures higher than Multiple in situ X-ray diffraction dilatometric load experiments were performed for different temperatures and the lattice plane specific temperature-dependent elastic constants for four different  Daymond  from theThe shown results are useful in two regards. First, high temperature X-ray diffraction stress analysis of AISI 4140 becomes more reliable using the determined temperature-dependent


Using molecular dynamics simulations with Gibbs free energy calculations, we reveal that water dissolving in [emim][Tf2N] is energetically favorable, but it takes significant energy for [emim][Tf2N] ions to dissolve in water. Our findings may significantly advance the DSE technology as a solution to the challenges in the global water-energy nexus.Seawater desalination plays a critical role in addressing the global water shortage challenge. Directional Solvent Extraction (DSE) is an emerging non-membrane desalination technology that features the ability to utilize very low temperature waste heat (as low as 40 °C). This is enabled by the subtly balanced solubility properties of directional solvents, which do not dissolve in water but can dissolve water and reject salt ions. However, the low water yield of the state-of-the-art directional solvent (decanoic acid) significantly limits its throughput and energy efficiency. In this paper, we demonstrate that by using ionic liquid as a new directional solvent, saline water can be desalinated with much higher production rate and thus significantly lower the energy and exergy consumptions. The ionic liquid identified suitable for DSE is [emim][Tf Directional Solvent Extraction is an emerging non-membrane desalination technology for sea water desalination but is limited by throughput and energy efficiency. Here, the authors demonstrate that the production rate and energy efficiency can be increased by using ionic liquids as directional solvent. Given that ocean and subterranean saline aquifers contain 97.5% of the global water, desalination is a promising means for meeting fresh water demand. While membrane-based desalination processes like reverse osmosis (RO) have drawn considerable attention, the need for high grid electricity renders their application in low-resource settings challenging2. RO can be energy-efficient (as low as 2 kWh/m3) in centralized plants largely due to the implementation of mechanical energy recovery systems3, but at smaller scales the energy cost can be much higher (up to 17 kWh/m3)4. In contrast, directional solvent extraction (DSE), named one of the top ten world-changing ideas by Scientific American in 20125, is an attractive alternative as it requires comparatively low operation temperatures relying almost exclusively on the consumption of waste heat or unconcentrated solar energy7. The conceptual basis behind DSE centers on the use of a task-specific directional solvent (DS) that can solvate water in high yield, defined as the water solubility change per degree of temperature change (%/°C), is insoluble in water, and will not solvate salt ions8. It has been proposed that these directional solubilities are a result of the subtle balance between the hydrophilic and hydrophobic features of the solvent and the resulting intermolecular interactions with the solute7. Not surprisingly, a major impediment to the implementation of DSE processes is the identification of an optimal DS. Currently, decanoic acid, with a water yield of 0.027%/°C, represents the best performing DS to date9. This exceptionally low yield results in a low water production rate and relatively high energy consumption6. In contrast to aliphatic acids, we speculated that a readily functionalized heteroaromatic core would enable the desirable balance of hydrophobic and hydrophilic properties amenable to optimal DS performance. While tuning hydrophilicity of solids has been investigated that can contribute to thermal desalination12, studies of liquid phase hydrophilicity for similar purposes have not been seen. Herein, we report the identification of an N-heterocyclic task-specific ionic liquid (TSIL) for DSE, discovered through the combined use of experiments and molecular dynamics (MD) simulations, that exhibits a ten-fold improvement in fresh water yield over decanoic acid.The shortage of viable water resources is rapidly reaching critical status on a global scale. While extended droughts in many areas is a contributing factor17. The structural versatility and variability of many ILs enable extraordinary freedom in solvent design, as the cation and anion components can be individually engineered to achieve the desired directional solubilities. As illustrated in Fig. a), which then upon heating, draws only water into the IL while leaving the salts in the water phase yielding a high salinity brine (MX) (b). Removal of the MX byproduct (c) followed by a reduction in temperature leads to decreased solubility of water in the IL (d) that could then be readily separated to provide the desired fresh water. Upon separation, the recovered IL is recycled for subsequent process turnover of the DSE cycle (e). Given the variable water and salt solubility of many ILs, we were faced with the challenge of identifying a working fluid that would accommodate each phase of this DSE cycle.Ionic liquids (ILs) have demonstrated an exceptional promise as a molecular framework for the development of task-specific fluids due to their design flexibility and inherently low volatility. ILs comprised of organic ions residing in a liquid state between room temperature and 100 °C have shown promise as working fluids across a variety of applications, including the separation of organic compounds, sequestration of transition metals, capturing carbon dioxide, and desalinating aqueous media18 that demonstrated the feasibility of phosphonium sulfonate ILs as draw solutions for low temperature forward osmosis (FO), we began our study by examining a series of sulfonate anion-based TSILs as DSs for DSE desalination. We initially targeted the p-toluene sulfonate anion salts of tetrabutylphosphonium IL [P4444][TsO], and the corresponding 1-ethyl-3-methylimidazolium-based IL [emim][TsO] was also synthesized due to the well−established physical attributes of the imidazolium ILs  followed by thorough mixing at elevated temperatures of 45, 60, or 75 °C (see “Methods” section). The mixture was held for ~10 min at each stage to allow for complete phase separation. We note that for the most promising IL ([emim][Tf2N]) identified, a settling time as low as 2-min was found sufficient. The water-enriched IL phase was then removed and allowed to cool to room temperature, which resulted in a second separation of the IL and desalinated water. The amount of residual NaCl and IL in the recovered aqueous phase was then measured using atomic emission spectroscopy and liquid chromatography-mass spectrometry . While the imidazolium IL [emim][TsO] also induced a salt metathesis reaction, the bistriflimide [emim][Tf2N] exhibited exceptional ion rejection at >96% with low solubility in water in the range of 130–150 ppm and a surprisingly high-water yield of 0.3%/°C (Table 2N] provided a significantly lower water yield of <0.082%/°C despite a reasonable ion rejection rate of ~70% and favorable solubility in water (<90 ppm).Of the characterized ILs, two were identified as potentially viable frameworks for DSE, and their DSE-relevant solubilities are shown in Table 2N], we next examined the fresh water recovery of this IL at elevated temperatures. Exposure of [emim][Tf2N] to a 3.7 wt% NaCl saline feed at 45, 60, and 75 °C revealed an average water yield of 0.3 ± 0.023%/°C , [emim][Tf2N] exhibited outstanding ion rejection rates of 97.0–98.3%  as the feed saline. Gratifyingly, we observed an ion rejection rate of 96.0–96.8% even when [emim][Tf2N] was exposed to high concentrations of aqueous NaCl. These results would indicate that [emim][Tf2N] exhibits promising physical attributes to conduct desalination of water at both moderate and high salinity. Experiments with saturated NaCl used as feed saline is also performed, and the result indicates that we can still effectively perform desalination using DSE with [emim][Tf2N]. The ion rejection rate of the DSE cycle can still reach 96.5% in this case. In the meantime, the fresh water yield indeed drops to 0.157%/°C. The reduction can be understood as that water in higher salinity saline is more thermodynamically stable due to the ion-water electrostatic interaction and more difficult to extract, which was previously examined and also observed for decanoic acid6. However, the water yield of IL for saturated saline is still 5.8 times that of decanoic acid treating 3.8% NaCl feed water (0.027%/°C). Additionally, the water yield of [emim][Tf2N] is consistent over a temperature range of 45–75 °C, which suggests that low quality waste heat may be suitable to power this desalination process. All these DSE experiments have been repeated for several cycles by reusing the [emim][Tf2N], and no performance degradation in ion-rejection or water yield is observed. This confirms that ion removal using [emim][Tf2N] in DSE is not due to the IL absorbing NaCl ions from saline water, but caused by IL rejecting these ions. We have performed additional experiments to measure IL concentration in the brine with different salinities. In our experiment, the brine  is simulated to “gradually appear” into the solution, and free energy needed for this process is calculated as the solvation free energy20. The values from our calculation are for solvation from a vacuum state to the solution state, where the vacuum state serves as the common reference for comparing the thermodynamic stability of the solute molecule in different solvents. All calculations are performed at 350 K. Details of the simulations can be found in the “Methods” section. By comparing the solvation free energies, we were able to determine thermodynamic stability in the respective environments for each solute molecule, which ultimately aided our understanding of the variable solvation tendencies. The calculated solvation free energy of NaCl in [emim][Tf2N] is −677.7 kJ/mol, which is in contrast to −699.5 kJ/mol found for NaCl in water. This indicates that the NaCl salt favors solvation in the aqueous media over the corresponding IL phase, and rationalizes the observed ion rejection capability of [emim][Tf2N] in the DSE process. Similarly, the solvation free energy of water in [emim][Tf2N] of −26.5 kJ/mol is lower than that of water in water (−22.9 kJ/mol), which is consistent with the observed propensity for water to dissolve into the IL. Additionally, the calculated solvation free energy of −38.6 kJ/mol for [emim][Tf2N] in itself is significantly less than that of [emim][Tf2N] in water (−23.3 kJ/mol), which suggests that it is thermodynamically unfavorable for the IL to dissolve in water. We note that the above two cases related to [emim][Tf2N] solvation used the state of a [emim][Tf2N] ionic pair in vacuum as the reference level. Overall, these calculations are consistent with our experimental observations, revealing that [emim][Tf2N] displays favorable DS thermodynamic properties of water insolubility while concurrently capable of solvating water molecules and rejecting salt ions. The above simulations used the TIP4P as the water model. We have also used the TIP3P water model and found the same solvation tendencies (see Employing molecular dynamics (MD) simulations in combination with thermodynamic integration to calculate the solvation free energies at room temperature for NaCl, water, and [emim][Tfcies see .2N] at 350 K for a duration of 30 ns  constitutes a significant advantage wherein waste heat is a viable source of operating power. Exergy is the maximum amount of extractable work from a heat source with Carnot efficiency, and is a useful measure of the overall system efficiency when comparing different desalination technologies21. As shown in Fig. 2N] and decanoic acid both increase with increasing heat source temperature. A DSE process operated with [emim][Tf2N] has an exergy cost of 2.4 kWh/m3 at 45 °C and 5.9 kWh/m3 at 75 °C. The pumping power requirement is 0.31 kWh/m3 at 45 °C, and this value will be smaller at higher temperature, according to another study22 27 is also provided for comparison. Besides the advantage of utilizing lower temperature (45–75 °C) heat sources compared to MSF (>85 °C), the exergy consumption of DSE using [emim][Tf2N] is significantly lower than that of the MSF. While decanoic acid exhibits comparable performance advantages over MSF, these are only realized at operating temperatures below ~55 °C 4, largely due to the lack of centralized infrastructures for mechanical energy recovery.The ability to operate a DSE process at the relatively mild temperatures shown with [emim][Tf] e.g., 4 °C const] e.g., 4 °C const2N] in the recovered water should be low (130–150 ppm), there is no established toxicity standard for this IL in drinking water. To completely remove and recover all IL from the produced water, we can use nanofiltration (NF) as implemented by Cai et al.18 and Elimelech et al.3 for their IL-FO desalination for similar residue removal purposes. It will also eliminate the loss of IL during operation. The exergy cost for the NF process is a mere 0.011 KWh/m3 given the low osmotic pressure associated with a minimal concentration of residual IL, thereby avoiding a significant energy penalty  as efficiently as [emim][Tf2N] or decanoic acid and has lower solubility in water (<90 ppm) as well as water yield (0.082 %/°C), which we attest to the lengthened aliphatic chain. The [bmim]+ cation has an increased hydrophobicity due to increased chain length as well as a weaker cation–anion interaction as longer aliphatic chain lengths present larger steric interaction with the [Tf2N]− anion. Therefore, a stronger interaction may be achieved between [bmim][Cl] and [Na][Tf2N] due to the relative size differences yielding more intimate ion pairs sequestering more NaCl. As a result, the salt rejection rate is only around 70% according to our tests. It, however, might be used for treating low salinity water (<1600 ppm), where the 70% ion rejection rate can bring the salinity down to meet the drinking water standard of 500 ppm. The increased hydrophobicity of the [bmim]+ cation compared to the [emim]+ cation can also explain its comparatively lower water yield. We have performed MD simulations to calculate the free energy of water in [bmim][Tf2N], and the result (−24.3 kJ/mol) is indeed higher than that of water in [emim][Tf2N] (−26.5 kJ/mol).The efficacy of IL-based DSs appear to be modulated dramatically by structural perturbations of the IL. The optimal IL discovered being [emim][Tf4448][Tf2N], (The concentration of recovered water is even higher than the feed water.) whose viscosity is 0.433 Pa s, which is very high (See Section 4 in In comparison to the imidazolium-based cations whose positive charge is resonated into the aromatic system, the tetraalkyl phosphonium cations have a point charge dispersed over a smaller area (See Section 1 in 2N]. The DSE technique, which can utilize the low temperature heat, can potentially result in low resource setting applications. By analyzing the results of several tested ILs and their DSE behavior, we have also rationalized the chemistry–property relation, which might be helpful for further identification of task specific DS ILs. The work is also expected to further stimulate research around the DSE technology, especially the exploration of even higher-performance DSs. To move DSE closer to practical deployment, mass production of the identified ILs, process optimization, thermal system design with the potential integration of waste heat or renewable energy are topics worth additional research or engineering.In summary, we have demonstrated that DSE can effectively extract fresh water from saline sources, even saturated saline water, by using [emim][TfSynthesis and characterization details of the ILs are included in Section 1 in the Detailed procedure and experimental parameters of the DSE process to screen candidate ILs are included in Section 2 in the Details of MD simulations and free energy calculation using thermodynamic integration are discussed in Sections 5 and 6 in Details of energy and exergy calculations are included in Section 7 of the Supplementary InformationPeer Review File


Reliable prediction of the preoperative risk is of crucial importance for patients undergoing aortic repair. In this retrospective cohort study, we evaluated the metabolic equivalent of task (MET) in the preoperative risk assessment with clinical outcome in a cohort of consecutive patients.Retrospective analysis of prospectively collected data in a single center unit of 296 patients undergoing open or endovascular aortic repair from 2009 to 2016. The patients were divided into four anatomic main groups , juxta- and para-renal (open n = 84), thoraco-abdominal (open n = 13) and thoracic . Out of these, 276 patients had a preoperative statement of their functional capacity in metabolic units and were evaluated concerning their postoperative outcome including survival, in-hospital mortality, postoperative complications, myocardial infarction and stroke, and the need of later cardiovascular interventions.The median follow-up of the cohort was 10.8 months. Patients with < 4MET had a higher incidence of diabetes mellitus (p = 0.0002), peripheral arterial disease (p < 0.0001), history of smoking (p = 0.003), obesity (p = 0.03) and chronic obstructive pulmonary disease (p = 0.05). Overall in-hospital mortality was 4.4% (13 patients). There was no significant difference in the survival between patients with a functional capacity of more than 4 MET  and patients with less than 4 MET  (p = 0.64). The mean survival of the infrarenal cohort (n = 169) was 74.3 months with no significant differences between both MET groups . The subgroup after open surgical technique with less than 4 MET had the lowest mean survival of 38.8 months. In 46 patients with > 4MET (20.9%) perioperative complications occurred compared to the group with < 4MET with 18 patients (32.1%) (p = 0.075). There were no significant differences in both groups in the late cardiovascular interventions (p = 0.91) and major events including stroke and myocardial infarction (p = 0.4) monitored during the follow up period. The risk to miss a potential need for cardiac optimization in patients > 4MET was 7%.Trial registration clinicaltrials.gov, registration number NCT03617601 (retrospectively registered).The functional preoperative evaluation by MET in patients undergoing aortic surgery is a useful surrogate marker of perioperative performance but cannot be seen as a substitute for preoperative cardiopulmonary testing in selected individuals.  For several reasons a reliable preoperative risk evaluation is of particular importance in vascular patients. Foremost the majority of indications is made for patients in sixth to eighth decade of their lives and a large portion of it remains of preventive intention such as elective aneurysm repair or carotid surgery for asymptomatic occlusive disease. Furthermore the presence of atherosclerotic disease is supposed to bear an own increased perioperative risk , 2. AlmoA prophylactic coronary revascularization in patients with stable coronary artery disease by percutaneous coronary intervention (PCI) or bypass operation did not show any benefit concerning the reduction of mortality or occurrence of perioperative myocardial infarction when compared to medical treatment , 6.2/kg/min i.e. 1.2 kcal/min for a 70 kg person) [The preoperative assessment of the metabolic equivalent of task (MET) is an easy clinical evaluation of functional capacity or exercise tolerance of an individual. A MET is defined as the resting metabolic rate, that is the amount of the consumed oxygen at rest (approximately 3.5 ml = 0The current guidelines of the European Society of Cardiology and European Society of Angiology (ESC/ESA) restrain from preoperative cardiac testing in non-cardiac surgery as it has failed to improve perioperative outcome . Alike, In this retrospective cohort study we investigated the MET concept in the preoperative risk assessment with clinical outcome parameters in a cohort of consecutive patients who received open or endovascular abdominal, thoraco-abdominal or thoracic aortic repair. We hypothesize that patients with a preoperative status of 4 MET and more had less perioperative complications, suffered less from postoperative myocardial infarction and stroke and had a lower in-hospital mortality compared to patients with a status under 4 MET. This might support the recommendation of non-indicated cardiac testing in patients who are fit for surgery.All relevant patients’ data were retrospectively extracted from the Swiss Vasc Registry, a prospective, mandatory nationwide computer-based vascular registry in Switzerland. After the extraction of the center-associated clinical data all files were completed with the current patients’ follow-up and rechecked for obvious entry mistakes in the hospital software Medfolio. From May 2009 till March 2016, 296 patients underwent open or endovascular aortic repair and were divided into four main groups depending on infrarenal, juxta- and para-renal, thoraco-abdominal and thoracic pathology  of the chosen endoprosthesis. Endovascular repair of aortic pathologies in landing zone < 3 according to Mitchell and Ishimaru were operated in functional cardiac arrest with rapid pacing . If treaAll patients with open infrarenal aortic repair had a duplex scan from the referring angiologist 3 months postoperative and clinical evaluation by the operating surgeon in order to evaluate clinical status and rule out incisional hernia. From then on, ultrasound and a physical examination was done every year. Patients with thoraco-abdominal open repair received an Angio-CT scan 3 months after surgery and then were followed with ultrasound. All endovascular repairs underwent postoperative CT scan after 3 months and one year. If sac diameter was in regression and endoleaks were absent it was switched to an ultrasound or contrast enhanced duplex scan.Descriptive statistics were generated by counting and calculation of percentages of the nominal and ordinal variables. Numeric variables were described with mean and standard deviation. Survival analysis was done according to the method described by Kaplan and Meier. For the analysis of differences between the groups the log rank test was used. Twenty patients out of 296 were emergencies without any information about preoperative MET status. These patients were excluded from the comparison between patients with > 4MET and < 4MET according demographic data, survival and follow up. Perioperative complications, postoperative cardiac interventions and postoperative severe events  were calculated separately for the emergency group without MET status. In-hospital mortality was calculated for all patient regardless of their MET status focusing on the localization of the procedure . Statsdirect software  was used for all statistical analyses.Based on additional cardiac assessment we were able to calculate the sensitivity and specifity of the diagnostic validity of MET. Sensitivity being the proportion of patients with a pathologic result of the assessment among patients with < 4MET, specificity the proportion with a normal result among patients with > 4MET.Based on results of the study—power of the results of the retrospective risk analysis—we performed a sample size calculation. This gives us an indication of the number of patients needed to detect a statistically significant difference, assuming that our hypothesis is true. Power: 100%—probability of not detecting the “true” difference. For this calculation we set the—error at 20%, power therefore being 80%..Patients with < 4MET had a significant higher incidence of diabetes mellitus p = 0.0002), peripheral artery occlusive disease (p < 0.0001), history of smoking (p = 0.003), adipositas (p = 0.03) and chronic obstructive pulmonary disease (p = 0.05). Furthermore, this group had a tendency to more previous cardiovascular interventions, otherwise the two cohorts were comparable  was 74 months. There was no significant difference between patients with a functional capacity of more than 4 MET  and patients with less than 4 MET  (p = 0.64)  perioperative complications occurred compared to the group with < 4METS with 18 patients (32.1%). There was no significant difference between both groups (p = 0.075), but a slight tendency for more complications in patients with < 4METS (32.1% vs 20.9%).Fifty-seven complications occurred in the 46 patients with > 4MET. Of these 57 complications, 21 36.8%) led to major reoperations and 11 (19.3%) to minor reoperations. Compared to the complications in the patient group with < 4MET, there was no significant difference regarding the number of major and minor reoperations   with > 4MET; 9 patients (16.1%) with < 4MET) without significant difference among the groups (p = 0.91).In the group of patients with > 4MET (220 patients), 3.6% (8 patients) developed a myocardial infarction (MI) after hospitalization and 1.8% (4 patients) had a stroke, which results in a cumulative rate of 5.5% (12 patients) with major events after hospitalization. Compared to the group with < 4MET (56 patients), 8.9% (5 patients) suffered a myocardial infarction and no stroke. Although, there was no significant difference among the groups (p = 0.40), there might be a slight tendency to more myocardial infarction in the group with < 4MET.Thirteen patients out of the whole cohort (n = 296) died, which results in an in-hospital mortality of 4.4% for all procedures and approaches (7 patients with > 4MET (3.2%), 2 patients with < 4MET (3.6%), 4 patients with unknown MET after emergency operation (20%). In the infrarenal group of 182 patients the in-hospital mortality was 3.8%. Seven patients died, two from cardiovascular events, five from other events. Six of these seven patients were operated conventionally by laparotomy, one received an endovascular prosthesis. In-hospital mortality after juxtarenal approach (n = 84) was 4.8% . During follow up, there were 8 deaths in the infrarenal (3 cardiovascular and 5 other) and 2 deaths (both cardiovascular) in the juxtarenal group.In the thoraco-abdominal (n = 13) and thoracic approach group (n = 17) respectively, one patient died from cardiovascular cause, which results in an in-hospital mortality of 7.7% and 5.9%. During follow up, there were no further deaths in both groups.In the subgroup analysis of infrarenal patients there were no significant differences concerning in-hospital mortality with regard to preoperative MET status (p = 0.99).One hundred patients with > 4MET received concomitant cardiac assessment before the operation. In two of these patients the result of the assessment was unknown, while 81 showed normal results and 17 had pathological findings (= 98 patients with > 4MET and cardiac assessment). In the group with < 4MET, 48 patients underwent preoperative cardiac work-up. Out of these 36 had normal results, whereas 12 showed pathological results in stress echocardiography or coronary angiography. Thus, sensitivity of functional capacity assessment with MET was 41% with a low positive predictive value of 25%. In the group of > 4MET with preoperative cardiac work-up (n = 98), 17 patients showed pathological results. In 7 (7%) out of these this had therapeutic consequences. In the group of < 4MET (n = 48), 4 (8.3%) out of 12 patients received preoperative interventions as a result of abnormal findings. Thus, the risk to miss a potential need for cardiac optimization in patients > 4MET was 7%  and the extent of preoperative cardiac testing. However, since there is so far no prospective study evaluating the predictive quality of MET status in aortic surgery, the limited results could encourage the implementation of the MET status in further prospective trials or large registries.The concept of MET analysis as a surrogate marker of patients’ performance in the preoperative assessment of patients undergoing aortic surgery does not substitute cardiopulmonary testing in indicated cases as it failed to indicate a clear threshold for extensive preoperative cardiac assessment in those patients.