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Extensive horizontal gene transfer in cheese-associated bacteria.
Acquisition of genes through horizontal gene transfer (HGT) allows microbes to rapidly gain new capabilities and adapt to new or changing environments. Identifying widespread HGT regions within multispecies microbiomes can pinpoint the molecular mechanisms that play key roles in microbiome assembly. We sought to identify horizontally transferred genes within a model microbiome, the cheese rind. Comparing 31 newly sequenced and 134 previously sequenced bacterial isolates from cheese rinds, we identified over 200 putative horizontally transferred genomic regions containing 4733 protein coding genes. The largest of these regions are enriched for genes involved in siderophore acquisition, and are widely distributed in cheese rinds in both Europe and the US. These results suggest that HGT is prevalent in cheese rind microbiomes, and that identification of genes that are frequently transferred in a particular environment may provide insight into the selective forces shaping microbial communities
A multi-mode model of a non-classical atom laser produced by outcoupling from a Bose-Einstein condensate with squeezed light
We examine the properties of an atom laser produced by outcoupling from a
Bose-Einstein condensate with squeezed light. We introduce a method which
allows us to model the full multimode dynamics of the squeezed optical field
and the outcoupled atoms. We show that for experimentally reasonable parameters
that the quantum statistics of the optical field are almost completely
transferred to the outcoupled atoms, and investigate the robustness to the
coupling strength and the two-photon detuning.Comment: 6 pages, 4 figures. Accepted to Laser physics letter
Validating performance of automotive materials at high strain rate for improved crash design
This paper investigates sources of performance variability in high velocity testing of automotive crash structures. Sources of variability, or so called noise factors, present in a testing environment, arise from uncertainty in structural properties, joints, boundary conditions and measurement system. A box structure, which is representative of a crash component, is designed and fabricated from a high strength Dual Phase sheet steel. Crush tests are conducted at low and high speed. Such tests intend to validate a component model and material strain rate sensitivity data determined from high speed tensile testing. To support experimental investigations, stochastic modeling is used to investigate the effect of noise factors on crash structure performance variability, and to identify suitable performance measures to validate a component model and material strain rate sensitivity data. The results of the project will enable the measurement of more reliable strain rate sensitivity data for improved crashworthiness predictions of automotive structures
Interaction of laser generated ultrasonic waves with wedge-shaped samples
Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics
Analysis of existing mathematics textbooks for use in secondary schools.
Thesis (Ed.M.)--Boston University
Thesis (M.A.)--Boston Universit
Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2
The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a
superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent
compound, TiSe2, which shows a charge density wave transition and no
superconductivity. The crystal structure, characterized by high resolution
electron microscopy and powder x-ray diffraction, consists of two layers of
1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements
suggest that the superconductivity is induced by charge transfer from the PbSe
layers to the TiSe2 layers.Comment: 17 pages, 4 figures. To be published in Physical Review
Improving measurements of SF6 for the study of atmospheric transport and emissions
Sulfur hexafluoride (SF6) is a potent greenhouse gas and useful atmospheric tracer. Measurements of SF6 on global and regional scales are necessary to estimate emissions and to verify or examine the performance of atmospheric transport models. Typical precision for common gas chromatographic methods with electron capture detection (GC-ECD) is 1–2%. We have modified a common GC-ECD method to achieve measurement precision of 0.5% or better. Global mean SF6 measurements were used to examine changes in the growth rate of SF6 and corresponding SF6 emissions. Global emissions and mixing ratios from 2000–2008 are consistent with recently published work. More recent observations show a 10% decline in SF6 emissions in 2008–2009, which seems to coincide with a decrease in world economic output. This decline was short-lived, as the global SF6 growth rate has recently increased to near its 2007–2008 maximum value of 0.30±0.03 pmol mol−1 (ppt) yr−1 (95% C.L.)
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