1,730 research outputs found
Modeling the deformation textures and microstructural evolutions of a FeâMnâC TWIP steel during tensile and shear testing
The high manganese austenitic steels with low stacking fault energy (SFE) present outstanding mechanical properties due to the occurrence of two strain mechanisms: dislocation glide and twinning. Both mechanisms are anisotropic. In this paper, we analyzed the effect of monotonous loading path on the texture, the deformation twinning and the stressâstrain response of polycrystalline high Mn TWIP steel. Experimental data were compared to predicted results obtained by two polycrystalline models. These two models are based on the same single crystal constitutive equations but differ from the homogenization scheme. The good agreement between experiments and calculations suggest that the texture plays a key role in twinning activity and kinetics with regard to the intergranular stress heterogeneities. Rolling direction simple shear induces single twinning while rolling and transverse direction uniaxial tensions induce multi-twinning leading to lower twin volume fractions due to twinâtwin interactions
Modeling the deformation textures and microstructural evolutions of a FeâMnâC TWIP steel during tensile and shear testing
The high manganese austenitic steels with low stacking fault energy (SFE) present outstanding mechanical properties due to the occurrence of two strain mechanisms: dislocation glide and twinning. Both mechanisms are anisotropic. In this paper, we analyzed the effect of monotonous loading path on the texture, the deformation twinning and the stressâstrain response of polycrystalline high Mn TWIP steel. Experimental data were compared to predicted results obtained by two polycrystalline models. These two models are based on the same single crystal constitutive equations but differ from the homogenization scheme. The good agreement between experiments and calculations suggest that the texture plays a key role in twinning activity and kinetics with regard to the intergranular stress heterogeneities. Rolling direction simple shear induces single twinning while rolling and transverse direction uniaxial tensions induce multi-twinning leading to lower twin volume fractions due to twinâtwin interactions
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High-resolution mapping of fluoroquinolones in TB rabbit lesions reveals specific distribution in immune cell types.
Understanding the distribution patterns of antibiotics at the site of infection is paramount to selecting adequate drug regimens and developing new antibiotics. Tuberculosis (TB) lung lesions are made of various immune cell types, some of which harbor persistent forms of the pathogen, Mycobacterium tuberculosis. By combining high resolution MALDI MSI with histology staining and quantitative image analysis in rabbits with active TB, we have mapped the distribution of a fluoroquinolone at high resolution, and identified the immune-pathological factors driving its heterogeneous penetration within TB lesions, in relation to where bacteria reside. We find that macrophage content, distance from lesion border and extent of necrosis drive the uneven fluoroquinolone penetration. Preferential uptake in macrophages and foamy macrophages, where persistent bacilli reside, compared to other immune cells present in TB granulomas, was recapitulated in vitro using primary human cells. A nonlinear modeling approach was developed to help predict the observed drug behavior in TB lesions. This work constitutes a methodological advance for the co-localization of drugs and infectious agents at high spatial resolution in diseased tissues, which can be applied to other diseases with complex immunopathology
Course-based Science Research Promotes Learning in Diverse Students at Diverse Institutions
Course-based research experiences (CREs) are powerful strategies for spreading learning and improving persistence for all students, both science majors and nonscience majors. Here we address the crucial components of CREs (context, discovery, ownership, iteration, communication, presentation) found across a broad range of such courses at a variety of academic institutions. We also address how the design of a CRE should vary according to the background of student participants; no single CRE format is perfect. We provide a framework for implementing CREs across multiple institutional types and several disciplines throughout the typical four years of undergraduate work, designed to a variety of student backgrounds. Our experiences implementing CREs also provide guidance on overcoming barriers to their implementation
Continuous-wave Doppler-cooling of hydrogen atoms with two-photon transitions
We propose and analyze the possibility of performing two-photon
continuous-wave Doppler-cooling of hydrogen atoms using the 1S-2S transition.
"Quenching" of the 2S level (by coupling with the 2P state) is used to increase
the cycling frequency, and to control the equilibrium temperature. Theoretical
and numerical studies of the heating effect due to Doppler-free two-photon
transitions evidence an increase of the temperature by a factor of two. The
equilibrium temperature decreases with the effective (quenching dependent)
width of the excited state and can thus be adjusted up to values close to the
recoil temperature.Comment: 11 pages, 4 figures in eps forma
Tau energy losses at ultra-high energy: continuous versus stochastic treatment
We study the energy losses of the tau lepton in matter through
electromagnetic processes at ultra-high energy (UHE). We use both a stochastic
and a continuous framework to treat these interactions and compare the flux of
tau leptons propagated after some amount of matter. We discuss the accuracy of
the approximation of continuous energy losses by studying the propagation in
standard rock of taus with both mono-energetic and power law injection spectra.Comment: 7 pages, 8 figure
Time Resolved Correlation measurements of temporally heterogeneous dynamics
Time Resolved Correlation (TRC) is a recently introduced light scattering
technique that allows to detect and quantify dynamic heterogeneities. The
technique is based on the analysis of the temporal evolution of the speckle
pattern generated by the light scattered by a sample, which is quantified by
, the degree of correlation between speckle images recorded at
time and . Heterogeneous dynamics results in significant
fluctuations of with time . We describe how to optimize TRC
measurements and how to detect and avoid possible artifacts. The statistical
properties of the fluctuations of are analyzed by studying their
variance, probability distribution function, and time autocorrelation function.
We show that these quantities are affected by a noise contribution due to the
finite number of detected speckles. We propose and demonstrate a method to
correct for the noise contribution, based on a extrapolation
scheme. Examples from both homogeneous and heterogeneous dynamics are provided.
Connections with recent numerical and analytical works on heterogeneous glassy
dynamics are briefly discussed.Comment: 19 pages, 15 figures. Submitted to PR
A convenient criterion under which Z_2-graded operators are Hamiltonian
We formulate a simple and convenient criterion under which skew-adjoint
Z_2-graded total differential operators are Hamiltonian, provided that their
images are closed under commutation in the Lie algebras of evolutionary vector
fields on the infinite jet spaces for vector bundles over smooth manifolds.Comment: J.Phys.Conf.Ser.: Mathematical and Physical Aspects of Symmetry.
Proc. 28th Int. colloq. on group-theoretical methods in Physics (July 26-30,
2010; Newcastle-upon-Tyne, UK), 6 pages (in press
Aging in the random energy model
In this letter we announce rigorous results on the phenomenon of aging in the
Glauber dynamics of the random energy model and their relation to Bouchaud's
'REM-like' trap model. We show that, below the critical temperature, if we
consider a time-scale that diverges with the system size in such a way that
equilibrium is almost, but not quite reached on that scale, a suitably defined
autocorrelation function has the same asymptotic behaviour than its analog in
the trap model.Comment: 4pp, P
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