Search

This article develops a multi-perspective view on motivations and methods for tobamovirus purification through the ages and presents a novel, efficient, easy-to-use approach that can be well-adapted to different species of native and functionalized virions. We survey the various driving forces prompting researchers to enrich tobamoviruses, from the search for the causative agents of mosaic diseases in plants to their increasing recognition as versatile nanocarriers in biomedical and engineering applications. The best practices and rarely applied options for the serial processing steps required for successful isolation of tobamoviruses are then reviewed. Adaptations for distinct particle species, pitfalls, and 'forgotten' or underrepresented technologies are considered as well. The article is topped off with our own development of a method for virion preparation, rooted in historical protocols. It combines selective re-solubilization of polyethylene glycol (PEG) virion raw precipitates with density step gradient centrifugation in biocompatible iodixanol formulations, yielding ready-to-use particle suspensions. This newly established protocol and some considerations for perhaps worthwhile further developments could serve as putative stepping stones towards preparation procedures appropriate for routine practical uses of these multivalent soft-matter nanorods. [ABSTRACT FROM AUTHOR]

LDPE (low-density polyethylene) foams were prepared using the improved compression moulding technique (ICM) with relative densities ranging from 0.3 to 0.7 and with different levels of chemical blowing agents (from 1% to 20%). The density gradients, cellular structure and thermal conductivity of the foams were characterized. The density and amount of CBA used were found to have a significant effect on the cellular structure both at the mesoscale (density gradients) and at the microscale (different cell sizes and cell densities). In addition, the thermal conductivity of the samples is very sensitive to the local structure where the heat flux is located. The technique used to measure this property, the Transient Plane Source method (TPS), makes it possible to detect the presence of density gradients. A simple method for determining these gradients based on thermal conductivity data was developed. [ABSTRACT FROM AUTHOR]

To presents a novel clinically oriented system to report stone attenuation on non-contrast computed tomography (NCCT) using colour-coded density-gradients stone mapping and its clinical applications. This study was performed on 50 patients with 63 stones. All patients had a recent history of failed shockwave lithotripsy (SWL) or failed dissolution therapy by alkalinisation of urine for radiolucent stones. A multi-detector NCCT examination of the abdomen and pelvis was performed in all patients. The stones were isolated and displayed in 'Volume Rendering Technique' using four-colour encoding. Eight patients with failed dissolution therapy for radiolucent stones showed an outer layer of >500 Hounsfield units (HU) or a heterogeneous composition. A total of 42 patients with failed SWL had mean attenuations of <1000 HU on NCCT. Subsequent colour-coded stone mapping showed a dense core in all stones (>1000 HU) that failed to be clearly demonstrated by the mean HU alone. The initial use of a colour-coded density-gradients stone mapping reporting system for stone density on NCCT is useful for explaining failure of SWL or failure of dissolution therapy for radiolucent stones in selected cases. Abbreviations: HU: Hounsfield units; MSD: mean stone density; NCCT: non-contrast computed tomography; PCNL: percutaneous nephrolithotomy; SWL: shockwave lithotripsy; VRT: Volume Rendering Technique [ABSTRACT FROM AUTHOR]

The high‐latitude ionosphere is highly dynamical with significant irregularities and density gradients. However, the spatial and temporal distributions of density gradients and irregularities are very different between the Arctic and Antarctic. In this report, we study the interhemispheric asymmetry of the large‐scale (100 km) density gradients in both polar caps. Our results show that density gradients in the Arctic are enhanced during local winter (December solstice) with a peak around 19 UT. The UT and spatial distributions in the Antarctic local winter (June solstice) are similar to the Arctic except that they are reversed by 12 hr, which indicates a mirror symmetry between hemispheres. The 12‐hr difference in the peak density gradients can be explained by the displacements between the geographic and geomagnetic poles. The only asymmetry (anomaly) is the persistence of strong density gradients in the southern polar cap during local summer (December solstice). Plain Language Summary: The high‐latitude ionosphere is highly variable with significant fluctuations in plasma density. So far, the long‐term studies have been conducted in the Arctic due to better ground‐based data coverage, while the knowledge of the Antarctic is limited. We take advantage of the Swarm mission to study the long‐term behaviors in both the Arctic and Antarctic. New statistics reveal phenomena that we understand and an "anomaly" that do not understand. The results during local winter (December in the Arctic and June in the Antarctic) are similar and can be explained by the previous knowledge. However, the anomaly is the persistence of strong density fluctuations in the Antarctic during local summer (December solstice). Key Points: Density gradients (100 km) in the Arctic are enhanced from autumn to spring equinoxes with a significant "hole" during 3–12 UT near December solsticeThe variations of density gradients are mirror symmetric for two hemispheres during local winterDensity gradients in the Antarctic are strong and persistent during local summer (December solstice) [ABSTRACT FROM AUTHOR]

• The influence of non-uniform airflow on optical deformation measurements were studied. • The relationships between deformation measurement error caused by non-uniform airflow and different flow regions, flight parameters such as Mach number and angle of attack are obtained. • The strain error varies linearly with the square of Mach number and the reciprocal of the cosine of the angle of attack. The beam propagation of the camera through the upstream region rather than the downstream region might cause the strain error to fall by approximately 50%. Non-uniform airflow over a wing causes distortion in real time optically recorded images, which can lead to the erroneous displacement or strain measurement. This situation is more severe when an aeronautical object is tested in high-speed airflow for wind-tunnel or in-flight deformation measurement. In this paper, the principle of the deformation measurement error caused by non-uniform airflow is presented firstly. Then, wind-tunnel experiments were conducted on a two-dimensional OA309 airfoil over the Mach number range from 0.3 to 0.7 and the angle of attack varied from -7.02° to 12.18°. After this, the effect of non-uniform airflow was validated using virtual displacement and strain obtained by image correlation technique. The results showed that the virtual strain varies linearly with the square of Mach number and reciprocal of the cosine of the angle of attack. The beam propagation of the camera through the upstream region rather than the downstream region behind the wing might cause the virtual strain to fall by approximately 50%. To mitigate the effects of non-uniform airflow on measurements, an optimization of the experimental setup is necessary to enable appropriate placement of the camera. [ABSTRACT FROM AUTHOR]

• Ocean temperature and salinity were obtained from sensors deployed on Weddell seals. • Erosion of the upper water column summer stratification is observed. • Surface heat content accumulated during summer is eroded by synoptic wind events. Temperature and salinity measurements obtained from sensors deployed on Weddell seals (Leptonychotes weddellii) between late austral summer and the following spring for 2010–2012 were used to describe the temporal and spatial variability of hydrographic conditions in the western Ross Sea, with particular emphasis on the inner-shelf region off Victoria Land and McMurdo Sound. Potential temperature-salinity diagrams constructed for regions where the seals remained for extended periods showed four water masses on the continental shelf: Modified Circumpolar Deep Water, Antarctic Surface Water, Shelf Water and Modified Shelf Water. Depth-time distributions of potential density and buoyancy frequency showed the erosion of the upper water column stratification associated with the transition from summer to fall/winter conditions. The within-year and interannual variability associated with this transition was related to wind speed. Changes in upper water column density were positively correlated with cross-shelf wind speeds >5.5 m s−1 with a 3–4 day lag. A range of wind speeds was required to erode the density structure because of different levels of stratification in each year. A comparison of wind mixing potential versus stratification (Wedderburn number) showed that synoptic scale wind events during 2012 with speeds of 5.5 and 6.5 m s−1 were needed to erode the summer stratification for Ross Island and Victoria Land regions, respectively. Stronger winds (>8.5 m s−1) were required during 2010 and 2011. The interannual variability in total heat content accumulated during summer (about 20%) was related to the duration of open water, with the largest heat content occurring in 2012, which was characterized by a summer sea ice minimum stronger than other years and relatively higher mCDW influence over the mid and outer-shelf regions. The heat content was lost after mid-April and reached a minimum in winter as a result of deep winter convection. The quantitative analysis of hydrographic variability of the inner-shelf region of the western Ross Sea obtained from the seal-derived measurements provides a baseline for assessing future changes. [ABSTRACT FROM AUTHOR]

Abstract: The use of a Sanderson prism for the visualization of density gradients in a compressible flow is shown to be an inexpensive and versatile substitute for Wollaston prisms in the application of shearing interferometry. Experimentation using the Sanderson prism in a schlieren optical setup was performed to examine the effectiveness of the prism's use for flow visualization. A range of polycarbonate prisms were tested for a range of prism heights and different physical deflections to produce a range of divergence angles. For each prism height and deflection, tests were done using a hair dryer, helium jet, a soldering iron and a moving shock wave interaction to generate flow density gradients. The light which passes through the prism was also focused at different distances to determine the effects that different fringe arrangements have on the visibility of the flow. Tests were also done comparing horizontal and vertical fringe arrangements. It was found that the colour of the infinite fringe selected had an influence on the results because the larger the difference in colour between that of the adjacent fringes, the better the contrast in the final result. It was also found that infinite fringe use showed better results due to flow features such as shocks and vortices being more easily identified against a uniform background. It is shown that the technique produces good visualization of the density gradients that form in the flow.Graphical abstract: [ABSTRACT FROM AUTHOR]

Abstract: Electron density gradients in the polar F region ionosphere are essential for the structuring processes through the gradient‐drift instability (GDI). The information about the typical strength of gradients is important for the theoretical studies and modeling of the GDI waves, but rarely available because of significant experimental challenges in evaluation of the gradients, particularly at small scales and in 3‐D. In this study, multipoint density measurements of the Resolute Bay Incoherent Scatter Radar North working in a special high‐spatial‐resolution mode are employed to address the above question in a systematical manner. The 3‐D gradient vectors as well as their horizontal and vertical components are estimated for the first time and analyzed statistically utilizing a large Resolute Bay Incoherent Scatter Radar North data set. Statistical analysis of the gradient strength shows that the vertical components of the gradient strength vectors are larger than their horizontal counterparts, especially in the lower portion of the F region (below 220 km). The sharpness of the density gradients reveals a significant increase around magnetic midnight due to a decreased effect of the solar smoothing. Further, sharp density gradients occur during magnetically quiet times, possibly because of the presence of the polar holes and reduced plasma precipitation. The peak of occurrence for the horizontal components of the gradient strength vectors occurs at 0.5 × 10−6 m−1, whereas 15.5% of horizontal gradients exceeds 10−5 m−1. These gradients are strong enough for a direct generation of GDI waves at decameter scale (i.e. in linear regime), which implies that nonlinear turbulent cascade is not necessarily required for at least some GDI waves. [ABSTRACT FROM AUTHOR]

Attempts to scientifically capture and quantify glass homogeneity have been based on optical methods, namely, on those based on the work of Christiansen, Raman, and Shelyubskii. In industrial practice, a number of further methods are in use. In this study, glass homogeneity is determined by the measurement of density fluctuation. The method of 'density titration' proposed in earlier literature is used in an essentially improved procedure. In this method, the density distribution is determined for a representative ensemble of glass particles prepared from a bulk glass sample. The particles float on a heavy liquid which is diluted, step by step, by a miscible liquid of lower density. The particle fraction with density exceeding the density of the mixture sinks. When the method is performed on quenched or hyperquenched glass, then two types of inhomogeneities contribute to the overall homogeneity, i.e., thermal and chemical contributions. By two consecutive measurements, one performed on a sample of quenched glass, one on the same sample relaxed at [ABSTRACT FROM AUTHOR]

Hydrodynamic conditions in Loch Linnhe, a dynamifcally wide estuary on the west coast of Scotland, are primarily influenced by wind forcing, freshwater input, and tides. Winds in the region are orographically steered along the axis of the estuary due to surrounding mountains. A large rainfall catchment area results in a large freshwater inflow into Loch Linnhe which in turn produces low salinity waters at the head of the estuary. This, combined with a connection to the open sea with coastal salinities, leads to salinity gradients in the horizontal and vertical. Even though a range of observational programmes have focussed on Loch Linnhe, the literature still lacks an evaluation of its physical dynamics. Here we present a first description of the hydrodynamics in Loch Linnhe based on observations. Wind stress predominantly influences the surface layer, especially at low frequencies and with a stronger influence than tides during neap tides. The buoyancy-driven flow due to the large river runoff influences the circulation independent of wind stress. Seasonal (spring, autumn) and interannual (2011, 2012) variability of water masses occur especially in the surface layer. Tides are dominated by the semi-diurnal constituent M 2 with tidal ellipses aligned in the along-estuary direction and a stronger influence during spring tides compared to wind. An evaluation of dimensionless numbers reveal laterally and vertically sheared exchange flows. Compared to other Scottish estuaries Loch Linnhe is wide enough to be influenced by the Earth's rotation and demonstrates an enhanced freshwater outflow along its north-western coast as the freshwater is diverted to the right in the direction of the flow. These observed patterns are important for the sustainable environmental management of this socio-economically valuable region, e.g. through their relevance to aquaculture pathogen transmission patterns. A thorough understanding of the dynamics of the system is essential for a successful evidence-based marine planning framework. [ABSTRACT FROM AUTHOR]

Within the oil sands industry, tailings ponds are used as a means of retaining tailings until a reclamation technology such as end pit lakes (EPLs) can be developed and optimized to remediate such tailings with a water cap (although dry-land strategies for tailing reclamation are also being developed). EPLs have proven successful for other mining ventures (e.g. metal rock mines) in eventually mitigating contaminant loads to receiving waters once biochemical remediation has taken place (although the duration for this to occur may be decades). While the biological interactions at the sediment water interface of tailings ponds or EPLs have been shown to control biogeochemical processes (i.e. chemical fluxes and redox profiles), these have often been limited to static microcosm conditions. Results from such experiments may not tell the whole story given that the sediment water interface often represents a dynamic environment where erosion and deposition may be occurring in association with microbial growth and decay. Mobilization of sediments and associated contaminants may therefore have a profound effect on remediation rates and, as such, may decrease the effectiveness of EPLs as viable reclamation strategies for mining industries. Using a novel core erosion system (U-GEMS), this paper examines how the microbial community can influence sediment water interface stability and how the biofilm community may change with tailings age and after disturbance (biofilm reestablishment). Shear strength, eroded mass measurements, density gradients, high-resolution microscopy, and microbial community analyses were made on 2 different aged tailings (fresh and ∼38 years) under biotic and abiotic conditions. The same experiments were repeated as duplicates with both sets of experiments having consolidation/biostabilization periods of 21 days. Results suggest that the stability of the tailings varies between types and conditions with the fresh biotic tailings experiencing up to 75% more biostabilization than the same abiotic tailings. Further, greater microbial diversity in the aged pond could be a contributing factor to the overall increase in stability of this material over the fresh tailings source. [ABSTRACT FROM AUTHOR]

The crucial assumption made in the retrieval of radio-occultated atmospheric parameters is the spherical symmetry of the atmospheric refractive index, which implies that no horizontal gradient of the refractive index exists along the spherical shell. Nevertheless, the presence of density irregularities will lead to scintillation and multipath effects that often create highly fluctuating and random electron density profiles. In this study, it is proposed a reliable data quality control (QC) approach to remove questionable electron density profiles (due to the presence of ionospheric irregularities) retrieved using the COSMIC radio occultation (RO) technique based on two parameters, namely, the gradient and fluctuation of the topside density profile. Statistics of seven years density profiles (July 2006–May 2013) are presented by determining the aforementioned parameters for every density profile. The main advantage of this data QC is that it uses COSMIC RO electron density profiles retrieved from the slant total electron content (TEC) that is estimated from the excess phases of the GPS L1 and L2 frequencies only to delete the questionable profiles, instead of relying on any model and other observations. A systematic criterion has been developed based on the statistics to relinquish the so-called questionable density profiles. The computed gradients and fluctuations of the topside ionosphere electron density profiles have shown a few important features including, solar activity dependency and pronounced variations in between around +40° and −40° latitudes. After the removal of questionable profiles, both peak densities and heights of the ionosphere F layer are presented globally in different seasons of years during 2007 and 2012 that revealed several important features. [ABSTRACT FROM AUTHOR]

Understanding estuarine sediment dynamics and particularly turbidity maximum dynamics is crucial for the management of these coastal systems. Various processes impact the formation, movement and structure of the turbidity maximum. Several studies have shown that tidal asymmetry and density gradients are responsible for the presence of this suspended sedimentary mass. The Charente estuary is a highly turbid system (with suspended sediment concentrations often in excess of 5 g/L) that remains poorly understood despite its strong impact on local activities. In this study, a three-dimensional hydrosedimentary model is developed to represent the sediment dynamics of this estuary. Model validation demonstrates good accuracy, especially on reproducing semi-diurnal and spring-neap variability. Several simulations are performed to evaluate the influence of tides and river discharge on the turbidity maximum. Mean and maximum suspended sediment concentrations ( SSC ) and sediment stratification are calculated. SSC transects are also used to visualize the suspended sediment distribution along the estuary. The turbidity maximum generally oscillates between the river mouth and the Rochefort area (20–30 km upstream). The model shows strong variations at different time scales, and demonstrates that SSC is mainly driven by deposition/resuspension processes. Spring-neap comparisons show that the turbidity maximum is not well-defined during neap tides for low and mean runoff conditions. Simulations of spring tides and/or high runoff conditions all result in a compact suspended sedimentary mass. Performing simulations without taking density gradients into account demonstrates that tidal asymmetry is the main mechanism leading to the formation of the turbidity maximum. However, density gradients contribute to maintaining the stability of the turbidity maximum. Vertical stratification traps sediments at the bottom. Longitudinal stratification ensures a sharper edge at the downstream limit of the suspended sedimentary mass, preventing a massive export of sediments. [ABSTRACT FROM AUTHOR]

Bacterial colonization of medical devices causes infections and is a significant problem in healthcare. The use of antibacterial coatings is considered as a potential solution to this problem and has attracted a great deal of attention. Using concentration density gradients of immobilized quaternary ammonium compounds it was demonstrated that a specific threshold of surface concentration is required to induce significant bacterial death. It was determined that this threshold was 4.18% NR4+bonded nitrogen with a surface potential of + 120.4 mV. Furthermore, it is shown for the first time that adhesion of constituents of the culture medium to the quaternary ammonium modified surface eliminated any cytotoxicity towards eukaryotic cells such as primary human fibroblasts. The implications of this type of surface fouling on the antimicrobial efficacy of surface coatings are also discussed. [ABSTRACT FROM AUTHOR]

Marine snow aggregates are often a dominant component of carbon flux and are sites of high bacterial activity; thus, small-scale changes in the settling behavior of marine snow can affect the vertical locations of carbon export and remineralization in the surface ocean. In this study, we experimentally investigated the sinking velocities of marine snow aggregates formed in roller tanks as they settled through sharp density gradients. We observed between 8 and 10 aggregates in 3 different experiments, each of which displayed delayed settling behavior — that is, a settling velocity minimum — as they crossed the density transitions. Characteristics of delayed settling behavior were also compared to density stratification and aggregate density and size; aggregate settling velocity decreased more, and for longer periods of time, when density gradients were sharper and when aggregates were less dense. The observed relationships between non-dimensional parameters and aggregate settling allow for direct application of our results to the field, providing insight into the conditions under which strong delayed settling behavior is likely to occur. Activities of extracellular enzymes (the initial step in microbial remineralization of organic matter) were more than an order of magnitude higher in the aggregates compared to the surrounding water from which the aggregates were derived. Coupling measured enzyme activities with observations of delayed settling behavior demonstrates that the extent as well as the vertical location of enzyme activity is strongly affected by aggregate settling behavior: total enzyme activity within the region of the density transition increased by a factor of 18 with increasing stratification. This study, which combines direct measurements of small-scale aggregate settling and microbial enzyme activity, offers an opportunity to determine the potential implications of delayed settling behavior for local and larger-scale carbon cycling in the ocean. [ABSTRACT FROM AUTHOR]

Self-assembly of gold nanoparticles into one-dimensional (1D) nanostructures with finite primary units was achieved by introducing a thin salt (NaCl) solution layer into density gradient before centrifugation. The electrostatic interactions between Au nanoparticles would be affected and cause 1D assembly upon passing through the salt layer. A negatively charged polymer such as poly(acrylic acid) was used as an encapsulation/stabilization layer to help the formation of 1D Au assemblies, which were subsequently sorted according to unit numbers at succeeding separation zones. A centrifugal field was introduced as the external field to overcome the random Brownian motion of NPs and benefit the assembly effect. Such a facile 'one-tube synthesis' approach couples assembly and separation in one centrifuge tube by centrifuging once. The method can be tuned by changing the concentration of interference salt layer, encapsulation layer, and centrifugation rate. Furthermore, positively charged fluorescent polymers such as perylenediimide-poly(N,N-diethylaminoethyl methacrylate) could encapsulate the assemblies to give tunable fluorescence properties. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EV) are small (100-1000 nm) particles that cells release into the extracellular space that have become increasingly famous for their potential in regenerative medicine and for their alterations in diseases such as cancer to promote disease progression, in particular for their potential for intercellular communication. However, studying EV can be challenging due to the broad diversity of both the EV themselves as well as the methods used to study them. This chapter aims to help investigators new to the EV field by describing challenges with studying EV, methods for enriching EV, and a simple EV enrichment protocol using differential ultracentrifugation., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Distance sampling is extensively used for estimating animal density or abundance. Conventional methods assume that location of line or point transects is random with respect to the animal population, yet transects are often placed along linear features such as roads, rivers or shorelines that do not randomly sample the study region, resulting in biased estimates of abundance. If it is possible to collect additional data that allow an animal density gradient with respect to the transects to be modelled, we show how to extend the conventional distance sampling likelihood to give asymptotically unbiased estimates of density for the covered area. We illustrate the proposed methods using data for a kangaroo population surveyed by line transects laid along tracks, for which the true density is known from an independent source, and the density gradient with respect to the tracks is estimated from a sample of GPS collared animals. For this example, density of animals increases with distance from the tracks, so that detection probability is overestimated and density underestimated if the non-random location of transects is ignored. When we account for the density gradient, there is no evidence of bias in the abundance estimate. We end with a list of practical recommendations to investigators conducting distance sampling surveys where density gradients could be an issue. [ABSTRACT FROM AUTHOR]

Formation of density gradients in green bodies during powder compaction and the resulting sintering distortion still poses a problem in the powder metal industry. Consequently, the design and optimization of powder metallurgical production processes is of paramount relevance to avoid these part defects in the green bodies. However, this technology is currently based to a large extent on expert knowledge. The numerical simulation based on the Finite Element Method (FEM), represents a cost and time-saving alternative in comparison to the 'trial and error' method. With the help of FE calculations, powder compaction processes can be optimized in terms of reducing the density gradients and the resulting sintering distortion already in their development and design phase. [ABSTRACT FROM AUTHOR]

This study investigates the balance between forces of standardization and differentation in the evolution of residential density in Canada's four largest metropolitan regions between 1971 and 2006. The leading factors of standardized development are the continentwide postwar adaptation of urban form to the automobile and growing housing space consumption. The influence of these factors is manifested in increasing convergence in the density levels of the four metropolitan regions as one moves from older to newer zones. Nonetheless, inherited urban forms, topography, economic and demographic performance, and land-use and transportation policies all have the potential to shape distinct density patterns. Each metropolitan region presents a specific density trajectory: Toronto registers a pattern that can be qualified as stable and recentralized; Montreal emerges as a decentralizing metropolitan region; Vancouver shows clear signs of intensification; and in Ottawa-Hull the trajectory combines decentralization and stability. These different metropolitan trajectories offer lessons for intensification strategies. Findings suggest that continentwide tendencies are shaped by features specific to each metropolitan region, and that successful intensification policies must build on those features. [ABSTRACT FROM AUTHOR]

The Ayers expectation value of size consistent operator averages is analyzed, leading to a general description of Fukui functions in terms of a possibly multidimensional gradient. The expectation value involves the density of an arbitrary collective of chosen ions or excited states. Molecular Orbital (MO) densities and Fukui functions are proved to be connected through the gradient of the first order state density functions with respect to the MO occupation numbers. The mathematical development taken as a whole opens the way to a general framework, where Fukui functions arise as a general theoretical tool to study molecular reactivity. Finally, shape functions appear as a plausible link between Ayers framework and the general ideas presented in this study. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

In previous reports, the isolation of embryonic stem cell (ESC)-derived germ cells utilized fluorescent protein knock-in cell lines that could be sorted by flow cytometry. The present study aimed to isolate putative germ stem cells from embryoid bodies (EB) using Percoll and Nycodenz density gradients. The optimal ESC concentration to establish EB was identified as 15,000 cells per 30 µl drop and the optimal culture lime to obtain the highest number of germ cells within EB was identified as 120 h, with over 25% of cells confirmed as germ cells for the specific cell line used. Germ cells were isolated from 120-hour-old EB by Percoll and Nycodenz density gradients, while isolation of primordial germ cells from genital ridges of embryonic day 12.5 fetuses was used as a control. Putative germ cells were isolated from EB at proportions of 80.3 ± 3.0% (SEM) and 75.8 ± 0.9% for Percoll and Nycodenz respectively. Primordial germ cells were isolated from genital ridges at rates of 89.7 ± 2.7% and 89.5 ± 0.9% respectively. Although the purity of the isolated germ cells was similar between the two gradients, more germ cells with higher viability were obtained with the Percoll gradient. [ABSTRACT FROM AUTHOR]

Abstract: In order to close the global overturning circulation the buoyancy loss to the atmosphere associated with the formation of deep and bottom water at high latitudes must be balanced by buoyancy gain elsewhere. In case of water that is not in contact with the atmosphere except in its formation region the required buoyancy gain is accomplished primarily by diapycnal mixing. Recent observations suggest that a significant portion of the diapycnal buoyancy fluxes in the abyss is associated with overflows in submarine valleys or canyons, especially on the flanks of slow-spreading mid-ocean ridges. In the present study, hydrographic and velocity data from an overflow across a sill rising 1000m above the floor of the rift valley of the Mid-Atlantic Ridge near 36°N were used to infer the associated diapycnal mixing. The cross-sill density gradients are characterized by a vertical dipole, with an upper layer of streamwise density increase overlying a lower layer where the density decreases along the flow. This is qualitatively consistent with the effects of diapycnal mixing transferring buoyancy from the upper into the lower layer. Hydrographic and velocity profiles provide evidence for strong mixing associated with the overflow across the sill: in addition to thick layers that are susceptible to shear instability, there are numerous density overturns indicating a spatially averaged diffusivity of order . Inversions of the density equation reveal that the cross-sill gradients can be accounted for either by adiabatic vertical advection or by vertical eddy diffusion, although the adiabatic solutions are considered energetically implausible because they require upwelling in the layer of cross-sill density increase. Eddy-diffusive solutions, both with and without adiabatic downwelling, are characterized by diffusivity profiles attaining local maxima of order above the sill depth. The vertical structure of the inversion-derived diffusivities is consistent with the Thorpe-scale based estimates and with observations from overflows in major ocean passages, which also are often characterized by local diffusivity maxima of order a few 100m above sill depth. Combining the diffusivity profiles near the sill with budget-derived bulk estimates for 150km of rift valley implies that of the mixing in the rift valley is associated with overflows, while the remainder is caused by other processes, including the breaking of tidally forced internal waves. [Copyright &y& Elsevier]

Abstract: Phil and I started our careers on somewhat similar scientific paths. I had an undergraduate degree in physics from Swarthmore College and a Ph.D. degree in physics from Yale for research in the field for ultraviolet spectroscopy. Phil received an undergraduate degree in Physics from Oberlin College, joined the Yale Physics Department in 1954, and transferred to the new Biophysics Department in 1955. We began our interactions then by virtue of the fact that Phil had to take a Laboratory Course in Experimental Physics, one part of which was spectroscopy in which I was the instructor. One of my principal interests was in the effects of different wavelengths of ultraviolet (UV) radiation on proteins, viruses and bacterial cells. So what was more natural than for Phil to dream up a Ph.D. research project to investigate the effects of different wavelengths of UV on macromolecular synthesis in Escherichia coli. I became his mentor with expertise in UV, whereas he did most of the microbiological/biochemical work. Thus began a collaboration and a communicating friendship, the latter going on for 50 years. That communication was essential in elucidating some of the important steps in nucleotide excision repair—a field in which Phil is a pre-eminent scholar and investigator. [Copyright &y& Elsevier]

Abstract: Green machining of powder metallurgy (P/M) components appears as an interesting procedure to solve the eternal problems associated with the poor machining behaviour of porous metallic samples. With the increasing usage of sinter-hardenable powders for high performance applications, green machining is an attractive method to lower production costs and compete against other shaping processes. Green machining is not a straightforward procedure. There is quite more to control in green machining than the cutting parameters. Several variables must be optimized to obtain adequate results in terms of surface finish, geometrical conformance and productivity. Other considerations such as density gradients in green compacts also influence the final outcome of this process. This study presents a new technique, based on cutting force measurements during green turning, to quickly and precisely characterize density gradients in powder metallurgy components. This new technique also allows the characterization of green machinability. Moreover, this study shows that timing sprockets can be produced by green machining of gear blanks. Timing sprockets produced by this process show a surface finish comparable to that of powder metallurgy components machined after sintering. [Copyright &y& Elsevier]

Rigid polyurethane foams are used as thermal or vibration insulators and energy absorption material, and are often molded directly in place, where a smooth, thin skin forms between the mold and the cellular structure. Density gradients and the presence of a skin are known to affect the mechanical properties of the foam. We investigate the effect of processing temperature (25, 40, 65, and 85° C) and mold size (aluminum cylinders with diameters of 29, 41, and 51 mm) on the average density and density gradients (radial and vertical) of a free-rise, water blown, rigid polyurethane foam system, and measure the effects on compressive modulus of elasticity and collapse stress. In general, both average density and radial density gradients decrease with increasing processing temperature and larger mold sizes. A reduction in average foam density corresponds with decreases in the elastic modulus and compressive strength. These mechanical properties are compared to reference samples extracted from very large batches of foam with a uniform density of 0.10 g/cc, where normalization of the compressive data shows the elastic modulus to exhibit the strongest dependence on processing temperature and mold size. [ABSTRACT FROM AUTHOR]

Although much attention has recently been directed to analytical ultracentrifugation (AUC), the revival of interest has hardly addressed the applications of this technology in genome analysis, and the extent to which AUC studies can quickly and effectively complement modern sequence-based analyses of genomes, e.g. by anticipating, extending or checking results that can be obtained by cloning and sequencing. In particular, AUC yields a quick overview of the base compositional structure of a species' genome even if no DNA sequences are available and the species is unlikely to be sequenced in the near future. The link between AUC and DNA sequences dates back to 1959, when a precise linear relation was discovered between the GC (guanine+cytosine) level of DNA fragments and their buoyant density in CsCl as measured at sedimentation equilibrium. A 24-hour AUC run of a high molecular weight sample of a species' total DNA already yields the GC distribution of its genome. AUC methods based on this principle remain sensitive tools in the age of genomics, and can now be fine-tuned by comparing CsCl absorbance profiles with the corresponding sequence histograms. The CsCl profiles of vertebrates allow insight into structural and functional properties that correlate with base composition, and their changes during vertebrate evolution can be monitored by comparing CsCl profiles of different taxa. Such comparisons also allow consistency checks of phylogenetic hypotheses at different taxonomic levels. We here discuss some of the information that can be deduced from CsCl profiles, with emphasis on mammalian DNAs. [ABSTRACT FROM AUTHOR]

This paper examines the changing urban form of the Halifax-Dartmouth region between 1970 and 1996 many empirical studies employ the negative exponential density function to study such change, this paper studies urban form by examining the spatial pattern of development. Using disaggregate parcel level data, we compute kernel estimates to investigate the decentralization and deconcentration of residential and commercial land parcels, and to examine the segregation of land uses. The results of the kernel estimates suggest that changes in the urban form of Halifax-Dartmouth were a combined result of infill, contiguous, and leapfrog development. However, it is apparent that residential and commercial land parcels exhibit different spatial patterns of development [ABSTRACT FROM AUTHOR]

High-aspect ratio beams of alumina were slip cast at 30–50 vol.% solids with a level of poly(acrylic) acid corresponding to the minimum in viscosity. The beams, which were sintered in an unconstrained manner, deform into the shape of an arc at elevated temperature. The curvature of the beams was seen to increase with increasing solids loading and to depend on measures related to the particle velocity during casting. When an acrylic binder was added to the slurry, the degree of curvature was seen to increase as compared to when no binder was present. The composition of the plaster molds was seen to have a negligible effect on the magnitude of the bending. A model based upon strain mismatch indicates that a 3% variation in the green density within the beams would account for the observed amount of curvature. [Copyright &y& Elsevier]

We present a method for the selective, physical separation of active and non-active bacterial cells from natural communities. The method exploits the reduction of tetrazolium salts to form insoluble formazan crystals intracellularly in response to the addition of different oxidisable substrates. The intracellular deposition of formazan alters the bouyant density of active cells enabling them to be separated by density gradient centrifugation. The method has been successfully applied to the fractionation and collection of large whole cell sub-populations of active and non-active cells from sea-water samples. Removal of the bands from the density gradient, followed by PCR amplification and DGGE analyses showed distinct differences in the PCR amplicon diversity associated with the active and non-active cell fractions; an indication of changes in bacterial community structure in response to the addition of oxidisable substrate. Thus, based on their in situ respiration potential, the approach enables the cytochemical enrichment and molecular characterisation of mixed bacterial populations in natural environments. [ABSTRACT FROM AUTHOR]

• Shock-waves and index gradients distort quantitative holographic measurements. • RIPPH is a practical numerical technique for phase distortion cancellation. • Simulations and experiments demonstrate successful distortion cancellation. • RIPPH cancel distortions in supersonic and explosive shock-wave environments. • RIPPH shows benefits over DIH, PCDIH, electric field, and iterative phase methods. Digital holography is a three-dimensional (3D) measurement technique that can be used to quantitatively determine the size and 3D location of the objects inside a field-of-view. However, in systems where refractive index gradients are present, variations in optical phase due to high-speed shock-waves or low-speed thermal gradients can cause distortions that obscure objects. While techniques like phase-conjugate digital in-line holography and iterative phase measurement techniques have been developed in the past for phase removal or phase measurement, they require either nonlinear four-wave-mixing or iterative algorithms to operate. In this paper, we demonstrate a novel recalculated intensity propagation phase holography (RIPPH) method that captures distorted holograms using low-power continuous lasers, refocuses the hologram to the plane of the distortion, and cancels the phase distortion numerically in a single post-processing step. The resulting hologram can be numerically refocused to provide distortion-free 3D information describing objects that absorb or scatter light. In RIPPH, only the approximate z -locations of the phase distortions are needed, making this method significantly faster to compute than phase retrieval methods. Theoretical simulations are first used to describe and assess the distortion removal process. Experiments are then conducted to demonstrate at least 3 × lower edge distortion for RIPPH compared to traditional digital in-line holography. We demonstrate, for the first time, how phase distortions from supersonic air jets, particle-laden spherically expanding shock-waves, and convectively-driven thermal gradients are numerically cancelled and show how objects of interest are accurately recovered. [ABSTRACT FROM AUTHOR]

Copyright of Andrologie (11662654) is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The buoyant densities of subtilisin Carlsberg in dissolved and crystalline states, including glutaraldehyde crosslinked crystals, have been determined by equilibrium centrifugation at neutral pH in the analytical ultracentrifuge in concentrated solutions of CsCl. Due to the negligible diffusion of suspended crystals they form a sharp band at the position in the gradient corresponding to their density. Different crystal preparations may be separated in a single gradient when their densities differ by more than 0.005 g·ml and the results are reproducible to±0.001 g·ml-. Glutaraldehyde stabilized crystals were found to have higher buoyant densities than crystals of unmodified subtilisin. The increase in density due to the glutaraldehyde cross-linking can be explained if a polymer composed of approximately 5 glutaraldehyde residues is bound per pair of blocked lysine residues. Unmodified subtilisin Carlsberg shows identical densities in the crystalline and soluble states in CsCl solutions. The observation is consistent with identical molar volumes of subtilisin Carlsberg in solution and crystals and no charged groups being involved in intermolecular binding in the crystals. [ABSTRACT FROM AUTHOR]

Some standardized experimental procedures for the characterization of most common homogeneous insulating materials, in particular, low-density high- thickness mineral wool products, are based on some analytical models (two-flux model) which take into account combined heat transfer by conduction and radiation in homogeneous media. Interlaboratory comparisons and experimental validation of the models during some years has now covered most commercial products and proved that agreement is far better than testing accuracy. However, the above proce dures can no longer be applied when a density gradient occurs along the thickness of the specimen and hence a gradient of the radiative extinction coefficients is orig inated. The gradient occurs due to the weight of the upper layers of the product on the lower layers during binder polymerization. The system of differential equations which described the above models was therefore improved to take this effect into ac count.The solution was only possible by splitting the insulation into three layers, two facing the bounding surfaces of the product and a third forming a core. The solution is then used as the interpolating function of measured data in a procedure to characterize mineral wool products with density gradients, exceeding the maximum specimen thickness for the apparatus to be used, and such that the homogeneity assumption of standard models does not supply acceptable accuracy levels. [ABSTRACT FROM PUBLISHER]

Many sponges produce and store secondary metabolites with interesting pharmacological bioactivities. Identification of the cell type(s) responsible for the production and/or storage of these compounds may be a crucial step for the future culture and production of these substances if the biosynthesis is not envisageable and the producer organism is rare or too slow-growing for feasible exploitation. Localisation of these cells within the sponge may also contribute to ascertaining the ecological role of these compounds. The cell type containing the main bioactive metabolite (avarol) and its derivative avarone in the sponge Dysidea avara has been identified by cell isolation in a density gradient and by chromatographic techniques. Preliminary cytological characterisation of the cell types in each particular sponge species under study is required, otherwise the identification of the cells in suspensions is inaccurate. In contrast with the findings reported for other sponge species, the active metabolites of D. avara are not contained within spherulous cells but within choanocytes that line the chambers of the aquiferous system. The possible ecological role of avarol is discussed in the light of its internal position and the biological functions of the cells storing the bioactive compounds. [ABSTRACT FROM AUTHOR]

The study of plant mitochondria often requires isolation of mitochondria from plant tissues in intact and functional form. Here, we describe an effective procedure of mitochondrial isolation from leaf tissues and whole seedlings of the model dicot species Arabidopsis thaliana by using differential centrifugation and continuous Percoll density gradients., (© 2022. Springer Science+Business Media, LLC, part of Springer Nature.)