Development of flashlamp-pumped Q-switched Ho:Tm:Cr:YAG lasers for mid-infrared LIDAR application

A flashlamp-pumped 2.1 micron Ho:Tm:Cr:YAG laser was studied for both normal mode and Q-switched operations under a wide variety of experimental conditions in order to optimize performance. Laser output energy, slope efficiency, threshold and pulselength were determined as a function of operating temperature, output mirror reflectivity, input electrical energy and Q-switch opening time. The measured normal-mode laser thresholds of a Ho(3+) (0.45 atomic percent):Tm(3+) (2.5 atomic percent):Cr(3+) (0.8 atomic percent):YAG crystal ranged form 26 to 50 J between 120 and 200 K with slope efficiencies up to 0.36 percent with a 60 percent reflective output mirror. Under Q-switched operation the slope efficiency was 90 percent of the normal-mode result. Development of solid state lasers with Ho(3+), Tm(3+) and/or Er(3+) doped crystals has been pursued by NASA for eye-dafe mid-infrared LIDAR (light detection and ranging) application. As a part of the project, the authors have been working on evaluating Ho(3+):Tm(3+):Cr(3+):YAG crystals for normal-mode and Q-switched 2.1 micron laser operations in order to determine an optimum Tm(3+) concentration under flashlamp pumping conditions. Lasing properties of the Ho(3+) in the mid-infrared region have been studied by many research groups since the early 1960's. However, the technology of those lasers is still premature for lidar application. In order to overcome the inefficiency related to narrow absorption bands of the Ho(3+), Tm(3+) and Er(3+), the erbium has been replaced by chromium. The improvement in flashlamp-pumped Ho(3+) laser efficiency has been demonstrated recently by several research groups by utilizing the broad absorption spectrum of Cr(3+) which covers the flashlamp's emission spectrum. Efficient energy transfer to the Tm(3+) and then the Ho(3+) occurs subsequently. It is known that high Tm(3+) concentration and low Ho(3+) concentration are preferred to achieve a quantum efficiency approaching two and to avoid large reabsorption losses. However, determination of the optimum Tm(3+) concentration required to ensure efficient energy transfer from Cr(3+) to Tm(3+) and from Tm(3+) to Ho(3+) has not been made in the Ho:Tm:CR:YAG crystal. The results obtained so far are given

Neural Network Compression for Noisy Storage Devices

Compression and efficient storage of neural network (NN) parameters is critical for applications that run on resource-constrained devices. Although NN model compression has made significant progress, there has been considerably less investigation in the actual physical storage of NN parameters. Conventionally, model compression and physical storage are decoupled, as digital storage media with error correcting codes (ECCs) provide robust error-free storage. This decoupled approach is inefficient, as it forces the storage to treat each bit of the compressed model equally, and to dedicate the same amount of resources to each bit. We propose a radically different approach that: (i) employs analog memories to maximize the capacity of each memory cell, and (ii) jointly optimizes model compression and physical storage to maximize memory utility. We investigate the challenges of analog storage by studying model storage on phase change memory (PCM) arrays and develop a variety of robust coding strategies for NN model storage. We demonstrate the efficacy of our approach on MNIST, CIFAR-10 and ImageNet datasets for both existing and novel compression methods. Compared to conventional error-free digital storage, our method has the potential to reduce the memory size by one order of magnitude, without significantly compromising the stored model's accuracy.Comment: 19 pages, 9 figure

Molecular signatures of neurodegeneration in the cortex of PS1/PS2 double knockout mice

<p>Abstract</p> <p>Background</p> <p>Familial Alzheimer's disease-linked variants of presenilin (PSEN1 and PSEN2) contribute to the pathophysiology of disease by both gain-of-function and loss-of-function mechanisms. Deletions of <it>PSEN1 </it>and <it>PSEN2 </it>in the mouse forebrain result in a strong and progressive neurodegenerative phenotype which is characterized by both anatomical and behavioral changes.</p> <p>Results</p> <p>To better understand the molecular changes associated with these morphological and behavioral phenotypes, we performed a DNA microarray transcriptome profiling of the hippocampus and the frontal cortex of the <it>PSEN1/PSEN2 </it>double knock-out mice and littermate controls at five different ages ranging from 2–8 months. Our data suggest that combined deficiencies of <it>PSEN1 </it>and <it>PSEN2 </it>results in a progressive, age-dependent transcriptome signature related to neurodegeneration and neuroinflammation. While these events may progress differently in the hippocampus and frontal cortex, the most critical expression signatures are common across the two brain regions, and involve a strong upregulation of <it>cathepsin </it>and <it>complement </it>system transcripts.</p> <p>Conclusion</p> <p>The observed neuroinflammatory expression changes are likely to be causally linked to the neurodegenerative phenotype observed in mice with compound deletions of <it>PSEN1 </it>and <it>PSEN2</it>. Furthermore, our results suggest that the evaluation of inhibitors of PS/γ-secretase activity for treatment of Alzheimer's Disease must include close monitoring for signs of calpain-cathepsin system activation.</p

Interpreting the Morphology of Diffuse Light Around Satellite Galaxies

Recent observations of surface brightness distributions of both Milky Way and M31 satellite galaxies have revealed many instances of sudden changes or breaks in the slope of the surface brightness profiles (at some break radius, r_break). These breaks are often accompanied by increasingly elliptical isophotes and sometimes by isophote twisting. We investigate the hypothesis of a tidal origin for these features by applying the same ellipse fitting techniques that are used on observed galaxies to numerical simulations of the destruction of satellites, represented by spherical, single-component systems. We examine how observed quantities such as r_break, ellipticity and position angle of the fitted ellipses and amplitude of extra-break population vary with the satellite's orbital eccentricity and phase, and our viewpoint relative to the orbit. We also look at orbit and viewpoint dependence of the rate of change of the latter three quantities with radius. We find that there are trends with orbital phase and eccentricity in all observed quantities, many of which are preserved through a wide variety of viewing angles. In particular, a generic feature of all simulations is a depletion zone just interior to an excess zone, regions in which the surface brightness is lower and higher, respectively, than the initial profile. A clear interpretation of any individual image, however, is likely to be hampered by the dependence of the observable features on these multiple parameters. For example, breaks can be excited by several physical processes and can occur well within the bound satellite population. Nevertheless, we do find we can place loose constraints on the tidal radius, mass loss rate, orbital type and phase of the satellite, and nature of breaks using photometric data alone.Comment: 41 pages, including 17 figures; accepted for publication in AJ; minor changes made to the text, Figure 1 adde

A Corticothalamic Circuit Trades off Speed for Safety during Decision-Making under Motivational Conflict

Decisions to act while pursuing goals in the presence of danger must be made quickly but safely. Premature decisions risk injury or death, whereas postponing decisions risk goal loss. Here we show how mice resolve these competing demands. Using microstructural behavioral analyses, we identified the spatiotemporal dynamics of approach–avoidance decisions under motivational conflict in male mice. Then we used cognitive modeling to show that these dynamics reflect the speeded decision-making mechanisms used by humans and nonhuman primates, with mice trading off decision speed for safety of choice when danger loomed. Using calcium imaging in paraventricular thalamus and optogenetic inhibition of the prelimbic cortex to paraventricular thalamus pathway, we show that this speed-safety trade off occurs because increases in paraventricular thalamus activity increase decision caution, thereby increasing approach–avoid decision times in the presence of danger. Our findings demonstrate that a discrete brain circuit involving the paraventricular thalamus and its prefrontal input adjusts decision caution during motivational conflict, trading off decision speed for decision safety when danger is close. We identify the corticothalamic pathway as central to cognitive control during decision-making under conflict

ISSUES IN REFORMING TARIFF-RATE IMPORT QUOTAS IN THE AGREEMENT ON AGRICULTURE IN THE WTO

Contents: The Economics of Tariff Rate Quotas and the Effects of Trade Liberalization; TRQs and GATT Rules; An Overview of Tariffs, Quotas and Imports Worldwide; TRQs in the European Union; U.S. TRQs for Sugar, Tobacco and Peanuts; Dairy TRQs in the United States; Tariff Rate Quota Implementation and Administration by Developing Countries; Management of Tariff Rate Quotas in Korea and Japan; Tariff Rate Quota Administration in Canadian Agriculture; The Case of Australia and New Zealand Facing TRQs; The 1999 WTO Panel Report on the EU's Common Market Organization for Bananas; AssessmentInternational Relations/Trade,

Slowing light with Fabry-Perot resonator arrays

We analyze the transmission of light through coupled-resonator optical waveguides in the form of evanescently coupled Fabry-Perot resonator arrays. We develop a transfer matrix method to calculate the amplitude and phase responses of the arrays. We also discuss the inclusion of optical gain in the system to compensate for losses in these structures. Owing to the compact length along the propagation direction in evanescently coupled arrays, large slowing factors of the order of 10^2-10^3 can be achieved even with a weak index contrast of ∼0.1%. The large slowing factor, coupled with weak index contrast, makes this structure a promising candidate for artificial slow light system

And then there were four: a study of UK market concentration - causes, consequences and the scope for market adjustment

While concentration measures are a good indicator of market structure, the link with competitiveness is more complex than often assumed. In particular, the modern theory of industrial organisation makes no clear statement regarding the impact of concentration on competition - the focus of this paper is concentration and no inferences are made about competitive aspects of the market. The extent and nature of concentration within the UK listed company audit market as at April, 2002 and, pro forma, after the collapse of Andersen is documented and analysed in detail (by firm, market segment and industry sector). The largest four firms held 90 per cent of the market (based on audit fees) in 2002, rising to 96 per cent with the demise of Andersen. A single firm, Pricewaterhouse-Coopers, held 70 per cent or more of the share of six out of 38 industry sectors, with a share of 50 per cent up to 70 per cent in a further seven sectors. The provision of non-audit services (NAS) by incumbent auditors is also considered. As at April 2002, the average ratio of non-audit fees (paid to auditor) to audit fees was 208 per cent, and exceeded 300 per cent in seven sectors. It is likely, however, that disposals by firms of their management consultancy and outsource firms, combined with the impact of the Smith Report on audit committees will serve to reduce these ratios. Another finding is that audit firms with expertise in a particular sector appeared to earn significantly higher nonaudit fees from their audit clients in that sector. The paper thus provides a solid empirical basis for debate. The subsequent discussion considers the implications for companies and audit firms of the high level of concentration in the current regulatory climate, where no direct regulatory intervention is planned

Three-dimensional imaging of cell and extracellular matrix elasticity using quantitative micro-elastography

Funding: Australian Research Council; Cancer Council Western Australia; Industrial Transformation Training Centre; The William and Marlene Schrader Trust of the University of Western Australia.Recent studies in mechanobiology have revealed the importance of cellular and extracellular mechanical properties in regulating cellular function in normal and disease states. Although it is established that cells should be investigated in a three-dimensional (3-D) environment, most techniques available to study mechanical properties on the microscopic scale are unable to do so. In this study, for the first time, we present volumetric images of cellular and extracellular elasticity in 3-D biomaterials using quantitative micro-elastography (QME). We achieve this by developing a novel strain estimation algorithm based on 3-D linear regression to improve QME system resolution. We show that QME can reveal elevated elasticity surrounding human adipose-derived stem cells (ASCs) embedded in soft hydrogels. We observe, for the first time in 3-D, further elevation of extracellular elasticity around ASCs with overexpressed TAZ; a mechanosensitive transcription factor which regulates cell volume. Our results demonstrate that QME has the potential to study the effects of extracellular mechanical properties on cellular functions in a 3-D micro-environment.Publisher PDFPeer reviewe