The optical and thermal properties of quantum cascade lasers

The optical and thermal properties of quantum cascade lasers (QCLs) are investigated through the development of comprehensive theoretical models. The optical properties of various multilayer quantum cascade laser waveguides are investigated by solving Maxwell’s equations using a transfer-matrix method. The complex material refractive indices are calculated using a Drude-Lorentz model which takes into account both phonon and plasma contributions to the material properties. A Caughey-Thomas-like mobility model is used to estimate the temperature dependence of the electron mobility which is found to have a significant effect on the optical waveguide properties. The incorporation of this effect leads to better agreement with experimentally measured threshold current densities. In order to investigate the thermal properties of QCLs, a multi-dimensional anisotropic heat diffusion model is developed which includes temperature-dependent material parameters. The model is developed using finite-difference methods in such a way that is can be solved in both the time-domain and in the steady-state. Various heat management techniques were compared in the time-domain in order to extract the heat dissipation time constants. In the steady-state, the model is used to extract the temperature dependence of the cross-plane thermal conductivity of a GaAs-based THz QCL and compare the thermal properties of THz and InP-based mid-infrared QCL optical waveguides. In addition, fully self-consistent scattering rate equation modelling of carrier transport in short-wavelength QCLs is carried out in order to understand the internal carrier dynamics. This knowledge is then used to optimise the device design and the model predicts significant improvements in the performance of the optimised device

Durability of Structural Lumber Products at High Temperatures. Part I. 66°C at 75%RH and 82°C at 30%RH

Background. The effect of temperature on properties can be separated into reversible and permanent effects. The National Design Specification (NDS) provides factors (Ct) for reducing properties for reversible effects but provides little guidance on permanent effects.Objectives. The primary objective of this paper is to evaluate the effect of prolonged heating (permanent effect) on the flexural properties of solid-sawn and composite lumber products exposed at 66°C and 75% relative humidity (RH) and at 82°C and 30% RH. A second objective is to determine how to estimate total effects.Procedures. Solid-sawn lumber, laminated veneer lumber (LVL), and laminated strand lumber (LSL) were heated continuously for up to 6 years. After each exposure period, the lumber was conditioned to room temperature at the specified RH and then tested on edge in third-point bending. Some lumber was also tested hot at 66°C after 48 h of exposure and after 3 years of exposure.Results. After 3 years of continuous exposure at 66°C and 75% RH, solid-sawn Spruce-Pine-Fir (SPF) and Douglas-fir retained about 72% of their original modulus of rupture (MOR) and southern pine about 47%. For the first 2 to 3 years of exposure, changes in MOR of LVL were similar to that of solid-sawn SPF and Douglas-fir. After almost 6 years of exposure, SPF retained about 67% MOR and LVL 26% to 49%. The MOR of LSL was more sensitive to duration of exposure than was the MOR of either solid-sawn lumber or LVL, with a residual MOR of 47% after 28 months. After 21 months at 82°C and 30% RH, solid-sawn lumber retained 50% to 55% MOR, LVL 41%, and LSL 45%. For all products, modulus of elasticity was less sensitive to thermal degradation than was MOR.Conclusions. The effect of temperature on MOR of solid-sawn lumber is independent of grade. Composite lumber is more sensitive than solid-sawn to change in strength due to thermal degradation. The difference in MOR between species and product types may be less at low humidity levels than at high. The total effect of temperature on MOR can be estimated by adding the reversible plus the permanent effects. Available literature suggests that the wood used in attics of residential construction is not likely to experience significant accumulation of exposure at temperatures ≥66°C over the life of the structure

The Implementation and Evaluation of the Emergency Response Dose Assessment System (ERDAS) at Cape Canaveral Air Station/Kennedy Space Center

The Emergency Response Dose Assessment System (ERDAS) is a system which combines the mesoscale meteorological prediction model RAMS with the diffusion models REEDM and HYPACT. Operators use a graphical user interface to run the models for emergency response and toxic hazard planning at CCAS/KCS. The Applied Meteorology Unit has been evaluating the ERDAS meteorological and diffusion models and obtained the following results: (1) RAMS adequately predicts the occurrence of the daily sea breeze during non-cloudy conditions for several cases. (2) RAMS shows a tendency to predict the sea breeze to occur slightly earlier and to move it further inland than observed. The sea breeze predictions could most likely be improved by better parameterizing the soil moisture and/or sea surface temperatures. (3) The HYPACT/REEDM/RAMS models accurately predict launch plume locations when RAMS winds are accurate and when the correct plume layer is modeled. (4) HYPACT does not adequately handle plume buoyancy for heated plumes since all plumes are presently treated as passive tracers. Enhancements should be incorporated into the ERDAS as it moves toward being a fully operational system and as computer workstations continue to increase in power and decrease in cost. These enhancements include the following: activate RAMS moisture physics; use finer RAMS grid resolution; add RAMS input parameters (e.g. soil moisture, radar, and/or satellite data); automate data quality control; implement four-dimensional data assimilation; modify HYPACT plume rise and deposition physics; and add cumulative dosage calculations in HYPACT

Evidence of sub-MeV EMIC-driven electron precipitation

Electromagnetic ion cyclotron (EMIC) waves are potentially important drivers of the loss of energetic electrons from the radiation belts. Numerous theoretical calculations exist with conflicting predictions of one of the key parameters: the minimum resonance energy of electrons precipitated into the atmosphere by EMIC waves. In this study we initially analyze an EMIC electron precipitation event using data from two different spacecraft instruments to investigate the energies involved. Combining observations from these satellites, we find that the electron precipitation has a peak flux at ∼250 keV. Extending the analysis technique to a previously published database of similar scattering events, we find that the peak electron precipitation flux occurs predominantly around 300 keV, with only ∼11% of events peaking in the 1–4 MeV range. Such a significant population of low-energy EMIC-driven electron precipitation events highlights the possibility for EMIC waves to be significant drivers of radiation belt electron losses

Theology, News and Notes - Vol. 46, No. 02

Theology News & Notes was a theological journal published by Fuller Theological Seminary from 1954 through 2014.https://digitalcommons.fuller.edu/tnn/1136/thumbnail.jp

Amorphous Systems in Athermal, Quasistatic Shear

We present results on a series of 2D atomistic computer simulations of amorphous systems subjected to simple shear in the athermal, quasistatic limit. The athermal quasistatic trajectories are shown to separate into smooth, reversible elastic branches which are intermittently broken by discrete catastrophic plastic events. The onset of a typical plastic event is studied with precision, and it is shown that the mode of the system which is responsible for the loss of stability has structure in real space which is consistent with a quadrupolar source acting on an elastic matrix. The plastic events themselves are shown to be composed of localized shear transformations which organize into lines of slip which span the length of the simulation cell, and a mechanism for the organization is discussed. Although within a single event there are strong spatial correlations in the deformation, we find little correlation from one event to the next, and these transient lines of slip are not to be confounded with the persistent regions of localized shear -- so-called "shear bands" -- found in related studies. The slip lines gives rise to particular scalings with system length of various measures of event size. Strikingly, data obtained using three differing interaction potentials can be brought into quantitative agreement after a simple rescaling, emphasizing the insensitivity of the emergent plastic behavior in these disordered systems to the precise details of the underlying interactions. The results should be relevant to understanding plastic deformation in systems such as metallic glasses well below their glass temperature, soft glassy systems (such as dense emulsions), or compressed granular materials.Comment: 21 pages, 18 figure

Classical XY model with conserved angular momentum is an archetypal non-Newtonian fluid

We find that the classical one-dimensional (1D) XY model, with angular-momentum-conserving Langevin dynamics, mimics the non-Newtonian flow regimes characteristic of soft matter when subjected to counter-rotating boundaries. An elaborate steady-state phase diagram has continuous and first-order transitions between states of uniform flow, shear-banding, solid-fluid coexistence and slip-planes. Results of numerically studies and a concise mean-field constitutive relation, offer a paradigm for diverse non-equilibrium complex fluids

Peptidoglycan recognition in Drosophila is mediated by LysMD3/4

Microbial recognition is a key step in regulating the immune signaling pathways of multicellular organisms. Peptidoglycan, a component of the bacterial cell wall, exhibits immune stimulating activity in both plants and animals. Lysin motif domain (LysMD) family proteins are ancient peptidoglycan receptors that function in bacteriophage and plants. This report focuses on defining the role of LysMD-containing proteins in animals. Here, we characterize a novel transmembrane LysMD family protein. Loss-of-function mutations at the lysMD3/4 locus in Drosophila are associated with systemic innate immune activation following challenge, so we refer to this gene as immune active (ima). We show that Ima selectively binds peptidoglycan, is enriched in cell membranes, and is necessary to regulate terminal innate immune effectors through an NF-kB-dependent pathway. Hence, Ima fulfills the key criteria of a peptidoglycan pattern recognition receptor. The human Ima ortholog, hLysMD3, exhibits similar biochemical properties. Together, these findings establish LysMD3/4 as the founding member of a novel family of animal peptidoglycan recognition proteins

Characterization of a large sex determination region in Salix purpurea L. (Salicaceae).

Dioecy has evolved numerous times in plants, but heteromorphic sex chromosomes are apparently rare. Sex determination has been studied in multiple Salix and Populus (Salicaceae) species, and P. trichocarpa has an XY sex determination system on chromosome 19, while S. suchowensis and S. viminalis have a ZW system on chromosome 15. Here we use whole genome sequencing coupled with quantitative trait locus mapping and a genome-wide association study to characterize the genomic composition of the non-recombining portion of the sex determination region. We demonstrate that Salix purpurea also has a ZW system on chromosome 15. The sex determination region has reduced recombination, high structural polymorphism, an abundance of transposable elements, and contains genes that are involved in sex expression in other plants. We also show that chromosome 19 contains sex-associated markers in this S. purpurea assembly, along with other autosomes. This raises the intriguing possibility of a translocation of the sex determination region within the Salicaceae lineage, suggesting a common evolutionary origin of the Populus and Salix sex determination loci