1,646 research outputs found
Giant pop-ins and amorphization in germanium during indentation
Sudden excursions of unusually large magnitude (>1 μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium(Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered
Accurate prediction of gene feedback circuit behavior from component properties
A basic assumption underlying synthetic biology is that analysis of genetic circuit elements, such as regulatory proteins and promoters, can be used to understand and predict the behavior of circuits containing those elements. To test this assumption, we used time‐lapse fluorescence microscopy to quantitatively analyze two autoregulatory negative feedback circuits. By measuring the gene regulation functions of the corresponding repressor–promoter interactions, we accurately predicted the expression level of the autoregulatory feedback loops, in molecular units. This demonstration that quantitative characterization of regulatory elements can predict the behavior of genetic circuits supports a fundamental requirement of synthetic biology
Post-hospital medical respite care and hospital readmission of homeless persons
Medical respite programs offer medical, nursing, and other care as well as accommodation for homeless persons discharged from acute hospital stays. They represent a community-based adaptation of urban health systems to the specific needs of homeless persons. This article examines whether post-hospital discharge to a homeless medical respite program was associated with a reduced chance of 90-day readmission compared to other disposition options. Adjusting for imbalances in patient characteristics using propensity scores, respite patients were the only group that was significantly less likely to be readmitted within 90 days compared to those released to Own Care. Respite programs merit attention as a potentially efficacious service for homeless persons leaving the hospital
Developing Freight Analysis Zones at a State Level: A Cluster Analysis Approach
The ability to forecast freight to support transportation infrastructure decisions is limited by data availability at a level of detail meaningful to the transportation planner. The Freight Analysis Framework Version 2 is a national, comprehensive public freight database. The difficulty that transportation planners encounter when using this data is due to extensive aggregation. In this paper, the authors develop a methodology for creating freight analysis zones (FAZs) at a sub-state level by partitioning a state into meaningful zones that support freight transportation planning and analysis. The authors conc
A Survey of Alkali Line Absorption in Exoplanetary Atmospheres
We obtained over 90 hours of spectroscopic observations of four exoplanetary
systems with the Hobby-Eberly Telescope (HET). Observations were taken in
transit and out of transit, and we analyzed the differenced spectra---i.e., the
transmission spectra---to inspect it for absorption at the wavelengths of the
neutral sodium (\ion{Na}{1}) doublet at and neutral
potassium (\ion{K}{1}) at . We used the transmission spectrum at
\ion{Ca}{1} ---which shows strong stellar absorption but is not an
alkali metal resonance line that we expect to show significant absorption in
these atmospheres---as a control line to examine our measurements for
systematic errors. We use an empirical Monte Carlo method to quantity these
systematic errors. In a reanalysis of the same dataset using a reduction and
analysis pipeline that was derived independently, we confirm the previously
seen \ion{Na}{1} absorption in HD 189733b at a level of
(the average value over a 12 \AA{} integration
band to be consistent with previous authors). Additionally, we tentatively
confirm the \ion{Na}{1} absorption seen in HD 209458b (independently by
multiple authors) at a level of , though the
interpretation is less clear. Furthermore, we find \ion{Na}{1} absorption of
at in HD 149026b; features apparent in
the transmission spectrum are consistent with real absorption and indicate this
may be a good target for future observations to confirm. No other results
(\ion{Na}{1} in HD 147506b and \ion{Ca}{1} and \ion{K}{1} in all four targets)
are significant to , although we observe some features that we
argue are primarily artifacts.Comment: 38 total pages (preprint format), 9 color figures, 4 tables, accepted
for publication in Ap
Measuring single-cell gene expression dynamics in bacteria using fluorescence time-lapse microscopy
Quantitative single-cell time-lapse microscopy is a powerful method for analyzing gene circuit dynamics and heterogeneous cell behavior. We describe the application of this method to imaging bacteria by using an automated microscopy system. This protocol has been used to analyze sporulation and competence differentiation in Bacillus subtilis, and to quantify gene regulation and its fluctuations in individual Escherichia coli cells. The protocol involves seeding and growing bacteria on small agarose pads and imaging the resulting microcolonies. Images are then reviewed and analyzed using our laboratory's custom MATLAB analysis code, which segments and tracks cells in a frame-to-frame method. This process yields quantitative expression data on cell lineages, which can illustrate dynamic expression profiles and facilitate mathematical models of gene circuits. With fast-growing bacteria, such as E. coli or B. subtilis, image acquisition can be completed in 1 d, with an additional 1–2 d for progressing through the analysis procedure
An agonistic anti-CD137 antibody disrupts lymphoid follicle structure and T-cell-dependent antibody responses
CD137 is a costimulatory receptor expressed on natural killer cells, T cells, and subsets of dendritic cells. An agonistic monoclonal antibody (mAb) against CD137 has been used to reduce tumor burden or reverse autoimmunity in animal models and clinical trials. Here, we show that mice treated with an agonistic anti-CD137 mAb have reduced numbers of germinal center (GC) B cells and follicular dendritic cells (FDCs) in lymphoid tissues, which impair antibody responses to multiple T-cell-dependent antigens, including infectious virus, viral proteins, and conjugated haptens. These effects are not due to enhanced apoptosis or impaired proliferation of B cells but instead correlate with changes in lymphoid follicle structure and GC B cell dispersal and are mediated by CD137 signaling in CD
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