278 research outputs found
Absence of skew scattering in two-dimensional systems: Testing the origins of the anomalous Hall effect
We study the anomalous Hall conductivity in spin-polarized, asymmetrically
confined two-dimensional electron and hole systems, focusing on skew-scattering
contributions to the transport. We find that the skew scattering, principally
responsible for the extrinsic contribution to the anomalous Hall effect,
vanishes for the two-dimensional electron system if both chiral Rashba subbands
are partially occupied, and vanishes always for the two-dimensional hole gas
studied here, regardless of the band filling. Our prediction can be tested with
the proposed coplanar two-dimensional electron/hole gas device and can be used
as a benchmark to understand the crossover from the intrisic to the extrinsic
anomalous Hall effect.Comment: 4 pages, 2 figures include
Tolerance without clonal expansion: Self-antigen-expressing B cells program self-reactive T cells for future deletion
B cells have been shown in various animal models to induce immunological tolerance leading to reduced immune responses and protection from autoimmunity. We show that interaction of B cells with naive T cells results in T cell triggering accompanied by the expression of negative costimulatory molecules such as PD-1, CTLA-4, B and T lymphocyte attenuator, and CD5. Following interaction with B cells, T cells were not induced to proliferate, in a process that was dependent on their expression of PD-1 and CTLA-4, but not CD5. In contrast, the T cells became sensitive to Ag-induced cell death. Our results demonstrate that B cells participate in the homeostasis of the immune system by ablation of conventional self-reactive T cells
Aeroelastic Design of the oLAF Reference Aircraft Configuration
One of the main aims of the EU Flightpath 2050 is to significantly reducet he fuel consumption of upcoming designs for transport aircraft. To achieve this challenging goal, new technologies have to be investigated. In this context, the development of the 'optimally load adaptive aircraft' (oLAF) for a conventional design is one of the main goals of the DLR project oLAF. Since the lift-to-drag ration, the structural mass and the thrust specific fuel consumption are the main drivers of the aircraft's fuel consumption, an improvement in all three topics seems to be a promising approach to fulfill the intended aims of the European Union. That's why the design of the new oLAF configuration is equipped with a next generation three shaft geared turbofan engine with an ultra-high bypass-ration and an optimized aerodynamic performance combined with aggressive loadalleviation (LA) techniques to lighten the load-carrying structure of the aircraft significantly compared to a conventional state-of-the-art aircraft. Multiple design cycles with different degree of fidelity and LA approaches are planned to be performed within oLAF. At the current state of the project, three different
designs are available. On the one hand, there is the more basic configuration of the overall aircraft design (OAD) further called 'oLAF_SLv1'. On the other hand, there are configurations with more mature
aerodynamic characteristics further called the oLAF_ASv0 configuration as start design for a multidisciplinary-design-optimization (MDO) process and the 'oLAF_ASv1' as the optimized result of the MDO. All configurations have been analyzed and evaluated using the aeroelastic structural design tool
cpacs-MONA. The optimized 'oLAF_ASv1' configuration has furthermore been checked on aeroelastic stability. Conclusively, the stiffness of the structural pylon model has been adapted to shift a hump-mode of the new generation engine to higher airspeeds, so that the instability occurs outside of the flight envelope
TurboSMARTS: Accurate microarchitecture simulation sampling in minutes
Recent research proposes accelerating processor microarchitecture simulation through statistical sampling. Prior simulation sampling approaches construct accurate model state for each measurement by continuously warming large microarchitectural structures (e.g., caches and the branch predictor) while emulating the billions of instructions between measurements. This approach, called functional warming, occupies hours of runtime while the detailed simulation that is measured requires mere minutes. To eliminate the functional warming bottleneck, we propose TurboSMARTS, a simulation framework that stores functionally-warmed state in a library of small, reusable checkpoints. TurboSMARTS enables the creation of the thousands of checkpoints necessary for accurate sampling by storing only the subset of warmed state accessed during simulation of each brief execution window. TurboSMARTS matches the accuracy of prior simulation sampling techniques (i.e., ±3% error with 99.7% confidence), while estimating the performance of an 8-way out-of-order superscalar processor running SPEC CPU2000 in 91 seconds per benchmark, on average, using a 12 GB checkpoint library
An Evaluation of Stratified Sampling of Microarchitecture Simulations
Recent research advocates applying sampling to accelerate microarchitecture simulation. Simple random sampling offers accurate performance estimates (with a high quantifiable confidence) by taking a large number (e.g., 10,000) of short performance measurements over the full length of a benchmark. Simple random sampling does not exploit the often repetitive behaviors of benchmarks, collecting many redundant measurements. By identifying repetitive behaviors, we can apply stratified random sampling to achieve the same confidence as simple random sampling with far fewer measurements. Our oracle limit study of optimal stratified sampling of SPEC2K benchmarks demonstrates an opportunity to reduce required measurement by 43x over simple random sampling. Using our oracle results as a basis for comparison, we evaluate two practical approaches for selecting strata, program phase detection and IPC profiling. Program phase detection is attractive because it is microarchitec- ture independent, while IPC profiling directly minimizes stratum variance, therefore minimizing sample size. Unfortunately, our results indicate that: (1) program phase stratification falls far short of optimal opportunity, (2) IPC profiling requires expensive microarchitecture- specific analysis, and (3) both methods require large sampling unit sizes to make strata selection feasible, offsetting reductions in sample size. We conclude that, without better stratification approaches, stratified sampling does not provide a clear advantage over simple random sampling
Prevalence, Enabling Factors, and Clinical Outcome
Background: Striatocapsular infarcts (SCIs) are defined as large subcortical
infarcts involving the territory of more than one lenticulostriate artery. SCI
without concomitant ischemia in the more distal middle cerebral artery (MCA)
territory [isolated SCI (iSCI)] has been described as a rare infarct pattern.
The purpose of this study was to assess the prevalence of iSCI in patients
treated with endovascular thrombectomy (ET), to evaluate baseline and
procedural parameters associated with this condition, and to describe the
clinical course of iSCI patients. Methods: A retrospective analysis of 206
consecutive patients with an isolated MCA occlusion involving the
lenticulostriate arteries and treated with ET was performed. Baseline patient
and procedural characteristics and ischemic involvement of the striatocapsular
and distal MCA territory [iSCI, as opposed to non-isolated SCI (niSCI)] were
analyzed using multivariate logistic regression models. Prevalence of iSCI was
assessed, and clinical course was determined with the rates of substantial
neurological improvement and good functional short- and mid-term outcome
(discharge/day 90 Modified Rankin Scale ≤2). Results: iSCI was detected in 53
patients (25.7%), and niSCI was detected in 153 patients (74.3%). Successful
reperfusion [thrombolysis in cerebral infarction (TICI) 2b/3] [adjusted odds
ration (aOR) 8.730, 95% confidence interval (95% CI) 1.069–71.308] and good
collaterals (aOR 2.100, 95% CI 1.119–3.944) were associated with iSCI. In
successfully reperfused patients, TICI 3 was found to be an additional factor
associated with iSCI (aOR 5.282, 1.759–15.859). Patients with iSCI had higher
rates of substantial neurological improvement (71.7 vs. 37.9%, p < 0.001) and
higher rates of good functional short- and mid-term outcome (58.3 vs. 23.7%, p
< 0.001 and 71.4 vs. 41.7%, p < 0.001). However, while iSCI patients, in
general, had a more favorable outcome, considerable heterogeneity in outcome
was observed. Conclusion: High rates of successful reperfusion (TICI 2b/3) and
in particular, complete reperfusion (TICI 3) are associated with iSCIs. The
high prevalence of iSCI in successfully reperfused patients with good
collaterals corroborates previous concepts of iSCI pathogenesis. iSCI, once
considered a rare pattern of cerebral ischemia, is likely to become more
prevalent with increases in endovascular stroke therapy. This may have
implications for patient rehabilitation and pathophysiological analyses of
ischemic damage confined to subcortical regions of the MCA territory
Simulation sampling with live-points
Current simulation-sampling techniques construct accurate model state for each measurement by continuously warming large microarchitectural structures (e.g., caches and the branch predictor) while functionally simulating the billions of instructions between measurements. This approach, called functional warming, is the main performance bottleneck of simulation sampling and requires hours of runtime while the detailed simulation of the sample requires only minutes. Existing simulators can avoid functional simulation by jumping directly to particular instruction stream locations with architectural state checkpoints. To replace functional warming, these checkpoints must additionally provide microarchitectural model state that is accurate and reusable across experiments while meeting tight storage constraints. In this paper, we present a simulation-sampling framework that replaces functional warming with live-points without sacrificing accuracy. A live-point stores the bare minimum of functionally-warmed state for accurate simulation of a limited execution window while placing minimal restrictions on microarchitectural configuration. Live-points can be processed in random rather than program order, allowing simulation results and their statistical confidence to be reported while simulations are in progress. Our framework matches the accuracy of prior simulation-sampling techniques (i.e., ±3% error with 99.7% confidence), while estimating the performance of an 8-way out-of-order superscalar processor running SPEC CPU2000 in 91 seconds per benchmark, on average, using a 12 GB live-point librar
HI in four star-forming low-luminosity E/S0 and S0 galaxies
We present HI data cubes of four low-luminosity early-type galaxies which are
currently forming stars. These galaxies have absolute magnitudes in the range
M_B=-17.9 to -19.9 (H_o=50 km/s/Mpc). Their HI masses range between a few times
10^8 and a few times 10^9 M_sun and the corresponding values for M_HI/L_B are
between 0.07 and 0.42, so these systems are HI rich for their morphological
type. In all four galaxies, the HI is strongly centrally concentrated with high
central HI surface densities, in contrast to what is typically observed in more
luminous early-type galaxies. In two galaxies (NGC 802 and ESO 118-G34), the
kinematics of the HI suggests that the gas is in a strongly warped disk, which
we take as evidence for recent accretion of HI. In the other two galaxies (NGC
2328 and ESO 027-G21) the HI must have been part of the systems for a
considerable time. The HI properties of low-luminosity early-type galaxies
appear to be systematically different from those of many more luminous
early-type galaxies, and we suggest that these differences are due to a
different evolution of the two classes. The star formation history of these
galaxies remains unclear. Their UBV colours and Halpha emission-line strengths
are consistent with having formed stars at a slowly-declining rate for most of
the past 10^10 years. However, the current data do not rule out a small burst
of recent star formation overlaid on an older stellar population.Comment: To appear in AJ, LateX, figures in gif format, paper also available
at http://www.nfra.nl/~morganti/LowLu
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