Anomalous diffusion evidenced by particle tracking at high frame rates.

Diffusion is a common phenomenon in nature and generally is associated with a system trying to reach a local or a global equilibrium state, as a result of highly irregular individual particle motion. Therefore it is of fundamental importance in physics, chemistry and biology. Particle tracking in complex fluids can reveal important characteristics of its properties. In living cells, we coat the microbead with a peptide (RGD) that binds to integrin receptors at the plasma membrane, which connects to the CSK. This procedure is based on the hypothesis that the microsphere can move only if the structure where it is attached move as well. Then, the observed trajectory of microbeads is a probe of the cytoskeleton (CSK), which is governed by several factors, including thermal diffusion, pressure gradients, and molecular motors. The possibility of separating the trajectories into passive and active diffusion may give information about the viscoelasticity of the cell structure and molecular motors activity. And also we could analyze the motion via generalized Stokes-Einstein relation, avoiding the use of any active techniques. Usually a 12 to 16 Frames Per Second (FPS) system is used to track the microbeads in cell for about 5 minutes. Several factors make this FPS limitation: camera computer communication, light, computer speed for online analysis among others. Here we used a high quality camera and our own software, developed in C++ and Linux, to reach high FPS. Measurements were conducted with samples for 10£ and 20£ objectives. We performed sequentially images with different intervals, all with 2 ¹s exposure. The sequences of intervals are in milliseconds: 4 5 ms (maximum speed) 14, 25, 50 and 100 FPS. Our preliminary results highlight the difference between passive and active diffusion, since the passive diffusion is represented by a Gaussian in the distribution of displacements of the center of mass of individual beads between consecutive frames. However, the active process, or anomalous diffusion, shows as long tails in the distribution of displacements.

High mobility rates during the period of the "Celtic migrations"? - 87 Sr, 86 Sr and delta 18 O evidence from Early La Tène Europe

Although the period of the historic “Celtic migrations” is archaeologically extensively studied, the long-lasting question whether mass migration or increased individual mobility caused the expansion of the La Tène culture throughout continental Europe persist. Strontium (Sr) and in part oxygen (O) isotope analysis of human remains from the early La Tène cemeteries of Nebringen (Germany), Münsingen-Rain (Switzerland), Monte Bibele (Italy) and the Czech cemeteries of Radovesice I, Radovesice II and Kutná Hora was, therefore, carried out to investigate the importance of residential changes during this time period. These isotope analyses showed that most analysed individuals either came from the area they were buried in or from the surrounding area of the cemetery. An exception was formed by the Czech cemeteries, where almost a quarter of the studied individuals appeared non-local. Together with Nebringen, these cemeteries also had the most varied Sr isotope ratios, which suggest highly mobile communities in which individuals regularly changed their residency. The isotopic ratios of the cemeteries of Münsingen-Rain and Monte Bibele appeared far less varied. In part, these differences might be explained by the community structures of these cemeteries. Morphological kinship analysis in Münsingen-Rain demonstrated biological relatedness among most of the analysed individuals. These related individuals also shared similar isotope signatures, which suggest an origin from the surrounding Aar Valley. In the vicinity of the cemetery of Monte Bibele, an associated settlement site was discovered. The deceased presumably not only shared this settlement, but also cultivated the same land plots. Dispersed settlement structures were suggested for Nebringen, Radovesice and Kutná Hora, as these agriculturally favourable landscapes were densely populated during prehistoric times. Connected to these community structures are the prevailing geological conditions in these areas. Both Münsingen-Rain and Monte Bibele are located in a region where homogeneous geological conditions prevail, whereas the landscapes of Nebringen, Radovesice and Kutná Hora are characterised by complex heterogeneous geological conditions. As the majority of individuals in Nebringen and the Czech cemeteries correspond to the expected isotope values for the studied areas, regularly changing land plots might have contributed to the observed variation. Although mass migration as depicted by the historical sources was not observed individual mobility of a small part of these studied communities certainly played a role. Males appeared, thereby, to have slightly more often a non-local birthplace or moved during childhood. Male mobility was, however, not always associated with burial as a warrior. Females, on the other hand, originated more often from the region. Patrilocal residential patterns, with the exception of the Czech cemeteries, were nevertheless not observed. Objects and ideas also seem to have been exchanged freely, as there are no indications that individuals with particular grave goods came from specific areas. It rather appears that the individuals buried with them were either local or had different places of origin. This can be explained by the fact that the exact origin of grave goods is difficult to establish and the occurrence of similar 87Sr/86Sr values in different areas. This study provided important new insights on the period of the “Celtic migrations” and the way of life of these prehistoric people.

Genome-wide investigation reveals high evolutionary rates in annual model plants

Background: ;Rates of molecular evolution vary widely among species. While significant deviations from molecular clock have been found in many taxa, effects of life histories on molecular evolution are not fully understood. In plants, annual/perennial life history traits have long been suspected to influence the evolutionary rates at the molecular level. To date, however, the number of genes investigated on this subject is limited and the conclusions are mixed. To evaluate the possible heterogeneity in evolutionary rates between annual and perennial plants at the genomic level, we investigated 85 nuclear housekeeping genes, 10 non-housekeeping families, and 34 chloroplast;genes using the genomic data from model plants including Arabidopsis thaliana and Medicago truncatula for annuals and grape (Vitis vinifera) and popular (Populus trichocarpa) for perennials.;Results: ;According to the cross-comparisons among the four species, 74-82% of the nuclear genes and 71-97% of the chloroplast genes suggested higher rates of molecular evolution in the two annuals than those in the two perennials. The significant heterogeneity in evolutionary rate between annuals and perennials was consistently found both in nonsynonymous sites and synonymous sites. While a linear correlation of evolutionary rates in orthologous genes between species was observed in nonsynonymous sites, the correlation was weak or invisible in synonymous sites. This tendency was clearer in nuclear genes than in chloroplast genes, in which the overall;evolutionary rate was small. The slope of the regression line was consistently lower than unity, further confirming the higher evolutionary rate in annuals at the genomic level.;Conclusions: ;The higher evolutionary rate in annuals than in perennials appears to be a universal phenomenon both in nuclear and chloroplast genomes in the four dicot model plants we investigated. Therefore, such heterogeneity in evolutionary rate should result from factors that have genome-wide influence, most likely those associated with annual/perennial life history. Although we acknowledge current limitations of this kind of study, mainly due to a small sample size available and a distant taxonomic relationship of the model organisms, our results indicate that the genome-wide survey is a promising approach toward further understanding of the;mechanism determining the molecular evolutionary rate at the genomic level.

Derived Bedrock Elevations, Strain Rates and Stresses from Measured Surface Elevations and Velocities - Jakobshavns-Isbrae, Greenland

Jakobshavns Isbrae (69 degrees 10'N, 49 degrees 5'W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbrae basin of about 10 000 km(2) was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block-aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid paints 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates, X, Y pointing eastward and northward. and curvilinear coordinates, L, T pointing longitudinally and transversely to the changing ice-flow direction. Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10-15 km before Jakobshavns Isbrae becomes afloat in Jakobshavns IsfJord.

High colonization rates of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in Swiss Travellers to South Asia- a prospective observational multicentre cohort study looking at epidemiology, microbiology and risk factors.

BACKGROUND International travel contributes to the worldwide spread of multidrug resistant Gram-negative bacteria. Rates of travel-related faecal colonization with extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae vary for different destinations. Especially travellers returning from the Indian subcontinent show high colonization rates. So far, nothing is known about region-specific risk factors for becoming colonized. METHODS An observational prospective multicentre cohort study investigated travellers to South Asia. Before and after travelling, rectal swabs were screened for third-generation cephalosporin- and carbapenem-resistant Enterobacteriaceae. Participants completed questionnaires to identify risk factors for becoming colonized. Covariates were assessed univariately, followed by a multivariate regression. RESULTS Hundred and seventy persons were enrolled, the largest data set on travellers to the Indian subcontinent so far. The acquired colonization rate with ESBL-producing Escherichia coli overall was 69.4% (95% CI 62.1-75.9%), being highest in travellers returning from India (86.8%; 95% CI 78.5-95.0%) and lowest in travellers returning from Sri Lanka (34.7%; 95% CI 22.9-48.7%). Associated risk factors were travel destination, length of stay, visiting friends and relatives, and eating ice cream and pastry. CONCLUSIONS High colonization rates with ESBL-producing Enterobacteriaceae were found in travellers returning from South Asia. Though risk factors were identified, a more common source, i.e. environmental, appears to better explain the high colonization rates.

CHARACTERIZATION OF THE COUNT RATE PERFORMANCE AND EVALUATION OF THE EFFECTS OF HIGH COUNT RATES ON MODERN GAMMA CAMERAS

CHARACTERIZATION OF THE COUNT RATE PERFORMANCE AND EVALUATION OF THE EFFECTS OF HIGH COUNT RATES ON MODERN GAMMA CAMERAS Michael Stephen Silosky, B.S. Supervisory Professor: S. Cheenu Kappadath, Ph.D. Evaluation of count rate performance (CRP) is an integral component of gamma camera quality assurance and measurement of system dead time (τ) is important for quantitative SPECT. The CRP of three modern gamma cameras was characterized using established methods (Decay and Dual Source) under a variety of experimental conditions. For the Decay method, input count rate was plotted against observed count rate and fit to the paralyzable detector model (PDM) to estimate τ (Rates method). A novel expression for observed counts as a function of measurement time interval was derived and the observed counts were fit to this expression to estimate τ (Counts method). Correlation and Bland-Altman analysis were performed to assess agreement in estimates of τ between methods. The dependencies of τ on energy window definition and incident energy spectrum were characterized. The Dual Source method was also used to estimate τ and its agreement with the Decay method under identical conditions and the effects of total activity and the ratio of source activities were investigated. Additionally, the effects of count rate on several performance metrics were evaluated. The CRP curves for each system agreed with the PDM at low count rates but deviated substantially at high count rates. Estimates of τ for the paralyzable portion of the CRP curves using the Rates and Counts methods were highly correlated (r=0.999) but with a small (~6%) difference. No significant difference was observed between the highly correlated estimates of τ using the Decay or Dual Source methods under identical experimental conditions (r=0.996). Estimates of τ increased as a power-law function with decreasing ratio of counts in the photopeak to the total counts and linearly with decreasing spectral effective energy. Dual Source method estimates of τ varied as a quadratic with the ratio of the single source to combined source activities and linearly with total activity used across a large range. Image uniformity, spatial resolution, and energy resolution degraded linearly with count rate and image distorting effects were observed. Guidelines for CRP testing and a possible method for the correction of count rate losses for clinical images have been proposed.

Is Group Lending A Good Enforcement Scheme for Achieving High Repayment Rates?: Evidence from Field Experiments in Vietnam

Microfinance institutions employ various kinds of incentive schemes but estimating the effect of each scheme is not easy due to endogeneity bias. We conducted field experiments in Vietnam to capture the role of joint liability, monitoring, cross-reporting, social sanctions, communication and group formation in borrowers’ repayment behavior. We find that joint liability contracts cause serious free-riding problems, inducing strategic default and lowering repayment rates. When group members observe each others’ investment returns, participants are more likely to choose strategic default. Even after introducing a cross-reporting system and/or penalties among borrowers, the default rates and the ratios of participants who chose strategic default under joint liability are still higher than those under individual lending. We also find that joint liability lending often failed to induce mutual insurance among borrowers. Those who had been helped or who had repaid a little in the previous round were more likely to default strategically and repay a little again in the current round and those who paid large amounts were always the same individuals.

Influence of texture on the recrystallization mechanisms in an AZ31 Mg sheet alloy at dynamic rates

An AZ31 rolled sheet alloy has been tested at dynamic strain rates View the MathML source at 250 °C up to various intermediate strains before failure in order to investigate the predominant deformation and restoration mechanisms. In particular, tests have been carried out in compression along the rolling direction (RD), in tension along the RD and in compression along the normal direction (ND). It has been found that dynamic recrystallization (DRX) takes place despite the limited diffusion taking place under the high strain rates investigated. The DRX mechanisms and kinetics depend on the operative deformation mechanisms and thus vary for different loading modes (tension, compression) as well as for different relative orientations between the loading axis and the c-axes of the grains. In particular, DRX is enhanced by the operation of 〈c + a〉 slip, since cross-slip and climb take place more readily than for other slip systems, and thus the formation of high angle boundaries is easier. DRX is also clearly promoted by twinning.

Sequential pyrolysis of willow SRC at low and high heating rates:implications for selective pyrolysis

The main aim of the work is to investigate sequential pyrolysis of willow SRC using two different heating rates (25 and 1500 °C/min) between 320 and 520 °C. Thermogravimetric analysis (TGA) and pyrolysis - gas chromatography - mass spectroscopy (Py-GC-MS) have been used for this analysis. In addition, laboratory scale processing has been undertaken to compare product distribution from fast and slow pyrolysis at 500 °C. Fast pyrolysis was carried out using a 1 kg/h continuous bubbling fluidized bed reactor, and slow pyrolysis using a 100 g batch reactor. Findings from this study show that heating rate and pyrolysis temperatures have a significant influence on the chemical content of decomposition products. From the analytical sequential pyrolysis, an inverse relationship was seen between the total yield of furfural (at high heating rates) and 2-furanmethanol (at low heating rates). The total yield of 1,2-dihydroxybenzene (catechol) was found to be significant higher at low heating rates. The intermediates of catechol, 2-methoxy-4-(2-propenyl)phenol (eugenol); 2-methoxyphenol (guaiacol); 4-Hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde) and 4-hydroxy-3-methoxybenzaldehyde (vanillin), were found to be highest at high heating rates. It was also found that laboratory scale processing alters the pyrolysis bio-oil chemical composition, and the proportions of pyrolysis product yields. The GC-MS/FID analysis of fast and slow pyrolysis bio-oils reveals significant differences. © 2011 Elsevier Ltd. All rights reserved.

Synergy between Piezo1 and Piezo2 channels confers high-strain mechanosensitivity to articular cartilage.

Diarthrodial joints are essential for load bearing and locomotion. Physiologically, articular cartilage sustains millions of cycles of mechanical loading. Chondrocytes, the cells in cartilage, regulate their metabolic activities in response to mechanical loading. Pathological mechanical stress can lead to maladaptive cellular responses and subsequent cartilage degeneration. We sought to deconstruct chondrocyte mechanotransduction by identifying mechanosensitive ion channels functioning at injurious levels of strain. We detected robust expression of the recently identified mechanosensitive channels, PIEZO1 and PIEZO2. Combined directed expression of Piezo1 and -2 sustained potentiated mechanically induced Ca(2+) signals and electrical currents compared with single-Piezo expression. In primary articular chondrocytes, mechanically evoked Ca(2+) transients produced by atomic force microscopy were inhibited by GsMTx4, a PIEZO-blocking peptide, and by Piezo1- or Piezo2-specific siRNA. We complemented the cellular approach with an explant-cartilage injury model. GsMTx4 reduced chondrocyte death after mechanical injury, suggesting a possible therapy for reducing cartilage injury and posttraumatic osteoarthritis by attenuating Piezo-mediated cartilage mechanotransduction of injurious strains.

In-vehicle extremity injuries from improvised explosive devices : current and future foci

The conflicts in Iraq and Afghanistan have been epitomized by the insurgents’ use of the improvised explosive device against vehicle-borne security forces. These weapons, capable of causing multiple severely injured casualties in a single incident, pose the most prevalent single threat to Coalition troops operating in the region. Improvements in personal protection and medical care have resulted in increasing numbers of casualties surviving with complex lower limb injuries, often leading to long-term disability. Thus, there exists an urgent requirement to investigate and mitigate against the mechanism of extremity injury caused by these devices. This will necessitate an ontological approach, linking molecular, cellular and tissue interaction to physiological dysfunction. This can only be achieved via a collaborative approach between clinicians, natural scientists and engineers, combining physical and numerical modelling tools with clinical data from the battlefield. In this article, we compile existing knowledge on the effects of explosions on skeletal injury, review and critique relevant experimental and computational research related to lower limb injury and damage and propose research foci required to drive the development of future mitigation technologies.