Lake Tahoe bottom characteristics extracted from SHOALS lidar waveform data and compared to backscatter data from a Multibeam echo sounder

The waveforms recorded by airborne lidar bathymetry (ALB) systems are currently processed only for depth information. In addition to bathymetry, multibeam echo sounder (MBES) systems provide backscatter data in which regions of different acoustic properties are distinguishable. These regions can often be correlated to different bottom types. Initial attempts to extract equivalent data from the ALB waveforms have confirmed the expectation that such information is encoded in those waveforms. Water clarity, bathymetry, and bottom type control the detailed shapes of ALB waveforms in different ways. Specific features of a bottom-reflected signal can be identified, for example its rise-time and amplitude, and used for clustering and classifying the individual data points. Two data sets from Lake Tahoe are available for comparison: ALB data from the SHOALS (scanning hydrographic operational airborne lidar survey) system of the US Army Corps of Engineers, and Simrad EM1000 MBES data from the USGS. Feature extraction, clustering, and classification of the SHOALS data reveals changes in the optical bottom reflectance characteristics that are echoed in the acoustic bottom backscatter properties

Structural dynamics division research and technology accomplishments for FY 1989 and plans for FY 1990

The purpose is to present the Structural Dynamics Division's research accomplishments for FY 1989 and research plans for FY 1990. The work under each Branch (technical area) is described in terms of highlights of accomplishments during the past year and highlights of plans for the current year as they relate to five year plans for each technical area. This information will be useful in program coordination with other government organizations and industry in areas of mutual interest

Population stability: regulating size in the presence of an adversary

We introduce a new coordination problem in distributed computing that we call the population stability problem. A system of agents each with limited memory and communication, as well as the ability to replicate and self-destruct, is subjected to attacks by a worst-case adversary that can at a bounded rate (1) delete agents chosen arbitrarily and (2) insert additional agents with arbitrary initial state into the system. The goal is perpetually to maintain a population whose size is within a constant factor of the target size $N$. The problem is inspired by the ability of complex biological systems composed of a multitude of memory-limited individual cells to maintain a stable population size in an adverse environment. Such biological mechanisms allow organisms to heal after trauma or to recover from excessive cell proliferation caused by inflammation, disease, or normal development. We present a population stability protocol in a communication model that is a synchronous variant of the population model of Angluin et al. In each round, pairs of agents selected at random meet and exchange messages, where at least a constant fraction of agents is matched in each round. Our protocol uses three-bit messages and $\omega(\log^2 N)$ states per agent. We emphasize that our protocol can handle an adversary that can both insert and delete agents, a setting in which existing approximate counting techniques do not seem to apply. The protocol relies on a novel coloring strategy in which the population size is encoded in the variance of the distribution of colors. Individual agents can locally obtain a weak estimate of the population size by sampling from the distribution, and make individual decisions that robustly maintain a stable global population size

Unstable Layers in the Mesopause Region Observed with Na Lidar During the Turbulent Oxygen Mixing Experiment (TOMEX) Campaign

The Na wind/temperature lidar located at Starfire Optical Range near Albuquerque, New Mexico, provided real time measurements of wind, temperature, and Na density in the mesopause region during the TOMEX rocket campaign in October 2000. The state of the atmosphere in which the rocket was launched into was examined using the lidar measurements. Both convectively and dynamically unstable layers were observed at various times and altitudes during the night. The low convective stability region below 90 km was found to be associated with the diurnal tide. The unstable layers are the combined results of wave and tidal perturbations. Comparison with the thermosphere/ionosphere/mesopshere/electrodynamics general circulation model (TIMEGCM) simulation showed that the model can produce the general feature of the observed atmospheric structure (but with a much smaller diurnal amplitude in temperature), which likely leads to underestimate of instability and gravity wave effects

Unstable Layers in the Mesopause Region Observed with Na Lidar During the Turbulent Oxygen Mixing Experiment (TOMEX) Campaign

The Na wind/temperature lidar located at Starfire Optical Range near Albuquerque, New Mexico, provided real time measurements of wind, temperature, and Na density in the mesopause region during the TOMEX rocket campaign in October 2000. The state of the atmosphere in which the rocket was launched into was examined using the lidar measurements. Both convectively and dynamically unstable layers were observed at various times and altitudes during the night. The low convective stability region below 90 km was found to be associated with the diurnal tide. The unstable layers are the combined results of wave and tidal perturbations. Comparison with the thermosphere/ionosphere/mesopshere/electrodynamics general circulation model (TIMEGCM) simulation showed that the model can produce the general feature of the observed atmospheric structure (but with a much smaller diurnal amplitude in temperature), which likely leads to underestimate of instability and gravity wave effects

Importance of equivariant features in machine-learning interatomic potentials for reactive chemistry at metal surfaces

Reactive chemistry of molecular hydrogen at surfaces, notably dissociative sticking and hydrogen evolution, play a crucial role in energy storage, fuel cells, and chemical synthesis. Copper is a particularly interesting metal for studying these processes due to its widespread use as both a catalyst in industry and a model catalyst in fundamental research. Theoretical studies can help to decipher underlying mechanisms and reaction design, but studying these systems computationally is challenging due to the complex electronic structure of metal surfaces and the high sensitivity towards reaction barriers. In addition, ab initio molecular dynamics, based on density functional theory, is too computationally demanding to explicitly simulate reactive sticking or desorption probabilities. A promising solution to such problems can be provided through high-dimensional machine learning-based interatomic potentials (MLIPs). Despite the remarkable accuracy and fidelity of MLIPs, particularly in molecular and bulk inorganic materials simulations, their application to different facets of hybrid systems and the selection of appropriate representations remain largely unexplored. This paper addresses these issues and investigates how feature equivariance in MLIPs impacts adaptive sampling workflows and data efficiency. Specifically, we develop high-dimensional MLIPs to investigate reactive hydrogen scattering on copper surfaces and compare the performance of various MLIPs that use equivariant features for atomic representation (PaiNN) with those that use invariant representations (SchNet). Our findings demonstrate that using equivariant features can greatly enhance the accuracy and reliability of MLIPs for gas surface dynamics and that this approach should become the standard in this field

Influence of uncertainty in dielectric properties on the design performance of a tunable composite right/left handed leaky wave antenna

Uncertainties of the order of 8 % in the accuracy of lithography used to define co-planar waveguides on ferroelectric thin films lead to a similar uncertainty in the value of relative permittivity of the film extracted from measurements. When such films are used as the tunable elements in a tunable composite right/left handed leaky wave antenna, such variations of the capacitance of the varactors can lead to a reduction in radiation and total efficiency around of the order of 1 dB in 5 dB due to the appearance of a bandgap in the frequency response

Ariel - Volume 10 Number 3

Executive Editors Madalyn Schaefgen David Reich Business Manager David Reich News Editors Medical College Edward Zurad CAHS John Guardiani World Mark Zwanger Features Editors Meg Trexler Jim O\u27Brien Editorials Editor Jeffrey Banyas Photography and Sports Editor Stuart Singer Commons Editor Brenda Peterso

Genome-Wide Gene Expression in relation to Age in Large Laboratory Cohorts of \u3ci\u3eDrosophila melanogaster\u3c/i\u3e

Aging is a complex process characterized by a steady decline in an organism’s ability to perform life-sustaining tasks. In the present study, two cages of approximately 12,000 mated Drosophila melanogaster females were used as a source of RNA from individuals sampled frequently as a function of age. A linear model for micro array data method was used for the micro array analysis to adjust for the box effect; it identified 1,581 candidate aging genes.Cluster analyses using a self-organizing map algorithm on the 1,581 significant genes identified gene expression patterns across different ages. Genes involved in immune system function and regulation, chorion assembly and function, and metabolism were all significantly differentially expressed as a function of age. The temporal pattern of data indicated that gene expression related to aging is affected relatively early in life span. In addition, the temporal variance in gene expression in immune function genes was compared to a random set of genes. There was an increase in the variance of gene expression within each cohort, which was not observed in the set of random genes.This observation is compatible with the hypothesis that D. melanogaster immune function genes lose control of gene expression as flies age