2,916 research outputs found
A DSMC investigation of gas flows in micro-channels with bends
Pressure-driven, implicit boundary conditions are implemented in an open source direct simulation Monte Carlo (DSMC) solver, and benchmarked against simple micro-channel flow cases found in the literature. DSMC simulations are then carried out of gas flows for varying degrees of rarefaction along micro-channels with both one and two ninety-degree bends. The results are compared to those from the equivalent straight micro-channel geometry. Away from the immediate bend regions, the pressure and Mach number profiles do not differ greatly from those in straight channels, indicating that there are no significant losses introduced when a bend is added to a micro-channel geometry. It is found that the inclusion of a bend in a micro-channel can increase the amount of mass that a channel can carry, and that adding a second bend produces a greater mass flux enhancement. This increase happens within a small range of Knudsen number (0.02 Knin 0.08). Velocity slip and shear stress profiles at the channel walls are presented for the Knudsen showing the largest mass flux enhancement
The Stellar Populations of Low-redshift Clusters
We present some preliminary results from an on-going study of the evolution
of stellar populations in rich clusters of galaxies. This sample contains core
line-strength measurements from 183 galaxies with b_J <= 19.5 from four
clusters with ~0.04. Using predictions from stellar population models to
compare with our measured line strengths we can derive relative
luminosity-weighted mean ages and metallicities for the stellar populations in
each of our clusters. We also investigate the Mgb'-sigma and Hbeta_G'-sigma
scaling relations. We find that, consistent with previous results, Mgb' is
correlated with sigma, the likely explanation being that larger galaxies are
better at retaining their heavier elements due to their larger potentials.
Hbeta', on the other hand, we find to be anti-correlated with sigma. This
result implies that the stellar populations in larger galaxies are older than
in smaller galaxies.Comment: 3 pages, 2 figures, to appear in the Proceedings of IAU Colloquium
195: "Outskirts of Galaxy Clusters: intense life in the suburbs", Torino
Italy, March 12-16 200
LHC Charge Asymmetry as Constraint on Models for the Tevatron Top Anomaly
The forward-backward asymmetry in top quark production at
the Tevatron has been observed to be anomalously large by both CDF and D0. It
has been suggested that a model with a coupling to and might
explain this anomaly, and other anomalies in mesons. Single-top-quark
production in this model is large, and arguably in conflict with Tevatron
measurements. However the model might still be viable if is
somewhat smaller than its current measured central value. We show that even
with smaller couplings, the model can be discovered (or strongly excluded) at
the LHC using the 2010 data sets. We find that a suitable charge-asymmetry
measurement is a powerful tool that can be used to constrain this and other
sources of anomalous single-top production, and perhaps other new high-energy
charge-asymmetric processes.Comment: 25 pages, 4 figures, note adde
The 2018 Camp Fire: Meteorological analysis using in situ observations and numerical simulations
The November 2018 Camp Fire quickly became the deadliest and most destructive wildfire in California history. In this case study, we investigate the contribution of meteorological conditions and, in particular, a downslope windstorm that occurred during the 2018 Camp Fire. Dry seasonal conditions prior to ignition led to 100-h fuel moisture contents in the region to reach record low levels. Meteorological observations were primarily made from a number of remote automatic weather stations and a mobile scanning Doppler lidar deployed to the fire on 8 November 2018. Additionally, gridded operational forecast models and high-resolution meteorological simulations were synthesized in the analysis to provide context for the meteorological observations and structure of the downslope windstorm. Results show that this event was associated with mid-level anti-cyclonic Rossby wave breaking likely caused by cold air advection aloft. An inverted surface trough over central California created a pressure gradient which likely enhanced the downslope winds. Sustained surface winds between 3-6 m s1 were observed with gusts of over 25 m s-1 while winds above the surface were associated with an intermittent low-level jet. The meteorological conditions of the event were well forecasted, and the severity of the fire was not surprising given the fire danger potential for that day. However, use of surface networks alone do not provide adequate observations for understanding downslope windstorm events and their impact on fire spread. Fire management operations may benefit from the use of operational wind profilers to better understand the evolution of downslope windstorms and other fire weather phenomena that are poorly understood and observed
Competition of reactive signals and thiol modifications of proteins
It is clear that cells are constantly bombarded by multiple signals, often initiating similar, or even conflicting, responses. Important players in this suite of signals are the reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), the reactive nitrogen species (RNS), such as nitric oxide (NO) and sulfur-based molecules, such as hydrogen sulfide (H2S). These compounds are often involved in stress responses and dysfunction of these signaling systems is often involved in disease [1-3]. This commentary discusses the interactions of such signals, which was discussed in a previous paper [3]. It was argued that all these molecules are not acting in the same manner, and that H2S was acting in a role which moderated the effects of ROS and NO
Soil nitrogen affects phosphorus recycling: foliar resorption and plant–soil feedbacks in a northern hardwood forest
Previous studies have attempted to link foliar resorption of nitrogen and phosphorus to their respective availabilities in soil, with mixed results. Based on resource optimization theory, we hypothesized that the foliar resorption of one element could be driven by the availability of another element. We tested various measures of soil N and P as predictors of N and P resorption in six tree species in 18 plots across six stands at the Bartlett Experimental Forest, New Hampshire, USA. Phosphorus resorption efficiency (P , 0.01) and proficiency (P ¼ 0.01) increased with soil N content to 30 cm depth, suggesting that trees conserve P based on the availability of soil N. Phosphorus resorption also increased with soil P content, which is difficult to explain based on single-element limitation, but follows from the correlation between soil N and soil P. The expected single-element relationships were evident only in the O horizon: P resorption was high where resin-available P was low in the Oe (P , 0.01 for efficiency, P , 0.001 for proficiency) and N resorption was high where potential N mineralization in the Oa was low (P , 0.01 for efficiency and 0.11 for proficiency). Since leaf litter is a principal source of N and P to the O horizon, low nutrient availability there could be a result rather than a cause of high resorption. The striking effect of soil N content on foliar P resorption is the first evidence of multiple-element control on nutrient resorption to be reported from an unmanipulated ecosystem
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