Los Alamos National Laboratory

About: Los Alamos National Laboratory is a facility organization based out in Los Alamos, New Mexico, United States. It is known for research contribution in the topics: Neutron & Laser. The organization has 31079 authors who have published 74688 publications receiving 2999590 citations. The organization is also known as: LANL & Project Y.

Vegetation demographics in Earth System Models: A review of progress and priorities.

Abstract: Numerous current efforts seek to improve the representation of ecosystem ecology and vegetation demographic processes within Earth System Models (ESMs). These developments are widely viewed as an important step in developing greater realism in predictions of future ecosystem states and fluxes. Increased realism, however, leads to increased model complexity, with new features raising a suite of ecological questions that require empirical constraints. Here, we review the developments that permit the representation of plant demographics in ESMs, and identify issues raised by these developments that highlight important gaps in ecological understanding. These issues inevitably translate into uncertainty in model projections but also allow models to be applied to new processes and questions concerning the dynamics of real-world ecosystems. We argue that stronger and more innovative connections to data, across the range of scales considered, are required to address these gaps in understanding. The development of first-generation land surface models as a unifying framework for ecophysiological understanding stimulated much research into plant physiological traits and gas exchange. Constraining predictions at ecologically relevant spatial and temporal scales will require a similar investment of effort and intensified inter-disciplinary communication.

A Power-Aware Run-Time System for High-Performance Computing

Abstract: For decades, the high-performance computing (HPC) community has focused on performance, where performance is defined as speed. To achieve better performance per compute node, microprocessor vendors have not only doubled the number of transistors (and speed) every 18-24 months, but they have also doubled the power densities. Consequently, keeping a large-scale HPC system functioning properly requires continual cooling in a largemachine room, thus resulting in substantial operational costs. Furthermore, the increase in power densities has led (in part) to a decrease in system reliability, thus leading to lost productivity. To address these problems, we propose a power-aware algorithm that automatically and transparently adapts its voltage and frequency settings to achieve significant power reduction and energy savings with minimal impact on performance. Specifically, we leverage a commodity technology called "dynamic voltage and frequency scaling" to implement our power-aware algorithm in the run-time system of commodity HPC systems.

High-efficiency carrier multiplication through direct photogeneration of multi-excitons via virtual single-exciton states

Abstract: We have previously demonstrated that absorption of a single photon by a nanocrystal quantum dot can generate multiple excitons with an efficiency of up to 100%. This effect, known as carrier multiplication, should lead to substantial improvements in the performance of a variety of optoelectronic and photocatalytic devices, including solar cells, low-threshold lasers and entangled photon sources. Here we present detailed analysis of the dynamics that govern the ultrafast growth of multi-exciton populations in CdSe and PbSe nanocrystals and propose a model of how such populations arise. Our analysis indicates that the generation of multi-excitons in these systems takes less than 200 fs, which suggests that it is an instantaneous event. We explain this in terms of their direct photogeneration via multiple virtual single-exciton states. This process relies on both the confinement-enhanced Coulomb coupling between single excitons and multi-excitons and the large spectral density of high-energy single- and multi-exciton resonances that occur in semiconductor nanocrystals.

Mathematical analysis of delay differential equation models of HIV-1 infection

Abstract: Models of HIV-1 infection that include intracellular delays are more accurate representations of the biology and change the estimated values of kinetic parameters when compared to models without delays. We develop and analyze a set of models that include intracellular delays, combination antiretroviral therapy, and the dynamics of both infected and uninfected T cells. We show that when the drug efficacy is less than perfect the estimated value of the loss rate of productively infected T cells, δ, is increased when data is fit with delay models compared to the values estimated with a non-delay model. We provide a mathematical justification for this increased value of δ. We also provide some general results on the stability of non-linear delay differential equation infection models.

Statistical analyses of deformation twinning in magnesium

Abstract: To extract quantitative and meaningful relationships between material microstructure and deformation twinning in magnesium, we conduct a statistical analysis on large data sets generated by electron backscattering diffraction (EBSD). The analyses show that not all grains of similar orientation and grain size form twins, and twinning does not occur exclusively in grains with high twin Schmid factors or in the relatively large grains of the sample. The number of twins per twinned grain increases with grain area, but twin thickness and the fraction of grains with at least one visible twin are independent of grain area. On the other hand, an analysis of twin pairs joined at a boundary indicates that grain boundary misorientation angle strongly influences twin nucleation and growth. These results question the use of deterministic rules for twin nucleation and Hall–Petch laws for size effects on twinning. Instead, they encourage an examination of the defect structures of grain boundaries and their role in twin ...