Description of laser pulses using Fourier analysis

The output of lasers in various modes of operation is described in a unified way, using Fourier analysis. A novel model for treating an active Fabry-Perot cavity, including the case of high gain, is developed resulting in a more exact expression for the spectral width of the cavity modes. Simple mathematical tools are given to relate the observed pulse length with the average gain and with the initial population inversion in the laser medium. It is shown that lasers with homogeneously broadened spectral lines have cavity modes of equal width and that if the modes are locked together the resulting ultrashort pulses are of equal duration. For lasers with inhomogeneously broadened spectral lines the cavity modes vary in width along the gain curve and, when mode-locked, the ultrashort pulses increase monotonically in duration along the emitted pulse train.     

Low temperature preparation of polycrystalline lead-tin tellurides in a lead iodide flux

Lead-tin telluride was prepared as a polycrystalline powder by heating a mixture of the component elements in a lead iodide flux at about 650°C. The powder, as prepared, can be used as raw material for single crystal growth or epitaxial film preparation.     

Current-induced light modulation using quantum wells in the collector of heterojunction bipolar transistors

We incorporated InGaAs quantum wells within the collector of InP-based heterojunction bipolar transistors to form novel light-modulating devices. We studied the properties of these devices as light modulators by direct current injection. The devices were characterized using differential photocurrent and transmission spectroscopies. Our results demonstrate the feasibility of light modulation based on current rather than electric field modulation. Maximum modulation is achieved when the accumulated carriers quench the excitonic absorption resonance.     

On the solution of maximization problems of optimal design by geometric programming

Summary A geometric programming method, recently developed for the constrained maximization of posynomials, is presented and illustrated by an application to the optimal design of a torsion bar spring.Research supported by the National Science Foundation, Project GP 13546.     

Key Recovery Attacks on Iterated Even–Mansour Encryption Schemes

Iterated Even–Mansour (EM) encryption schemes (also named “key-alternating ciphers”) were extensively studied in recent years as an abstraction of commonly used block ciphers. A large amount of previous works on iterated EM concentrated on security in an information-theoretic model. A central question studied in these papers is: What is the minimal number of rounds for which the resulting cipher is indistinguishable from an ideal cipher? In this paper, we study a similar question in the computational model: What is the minimal number of rounds, assuring that no attack can recover the secret key faster than trivial attacks (such as exhaustive search)? We study this question for the two natural key scheduling variants that were considered in most previous papers: the identical subkeys variant and the independent subkeys variant. In the identical subkeys variant, we improve the best known attack by an additional round and show that \(r=3\) rounds are insufficient for assuring security, by devising a key recovery attack whose running time is about \(n/\log (n)\) times faster than exhaustive search for an \(n\)-bit key. In the independent subkeys variant, we also extend the known results by one round and show that for \(r=2\), there exists a key recovery attack whose running time is faster than the benchmark meet-in-the-middle attack. Despite their generic nature, we show that the attacks can be applied to improve the best known attacks on several concrete ciphers, including the full \({\hbox {AES}^{2}}\) (proposed at Eurocrypt 2012) and reduced-round LED-128 (proposed at CHES 2012).     

Palmitic Acid and Health: Introduction

Interest in the dietary role and metabolic effect of saturated fatty acids has been recently renewed on the basis of epidemiologic observations and economical approach to health and well-being. Saturated fats may favorably increase blood HDL-Cholesterol levels without significant changes of the total cholesterol/HDL-Cholesterol ratio. Also, the negative effect of saturated fat on cardiovascular diseases risk has recently been challenged. Palmitic acid, among all, may have special structural and functional roles in utero and in infancy, and indeed is it is being delivered in a unique form in human milk. Future research should include objective cost-benefit analyses when disentangling the role of saturated fats in dietary recommendations.     

Bounded Degree Interval Sandwich Problems

The problems of Interval Sandwich (IS) and Intervalizing Colored Graphs (ICG) have received a lot of attention recently, due to their applicability to DNA physical mapping problems with ambiguous data. Most of the results obtained so far on the problems were hardness results. Here we study the problems under assumptions of sparseness, which hold in the biological context. We prove that both problems are polynomial when either (1) the input graph degree and the solution graph clique size are bounded, or (2) the solution graph degree is bounded. In particular, this implies that ICG is polynomial on bounded degree graphs for every fixed number of colors, in contrast with the recent result of Bodlaender and de Fluiter. Received October 2, 1997; revised April 1, 1998.     

Medical image categorization and retrieval for PACS using the GMM-KL framework.

This paper presents an image representation and matching framework for image categorization in medical image archives. Categorization enables one to determine automatically, based on the image content, the examined body region and imaging modality. It is a basic step in content-based image retrieval (CBIR) systems, the goal of which is to augment text-based search with visual information analysis. CBIR systems are currently being integrated with picture archiving and communication systems for increasing the overall search capabilities and tools available to radiologists. The proposed methodology is comprised of a continuous and probabilistic image representation scheme using Gaussian mixture modeling (GMM) along with information-theoretic image matching via the Kullback-Leibler (KL) measure. The GMM-KL framework is used for matching and categorizing X-ray images by body regions. A multidimensional feature space is used to represent the image input, including intensity, texture, and spatial information. Unsupervised clustering via the GMM is used to extract coherent regions in feature space that are then used in the matching process. A dominant characteristic of the radiological images is their poor contrast and large intensity variations. This presents a challenge to matching among the images, and is handled via an illumination-invariant representation. The GMM-KL framework is evaluated for image categorization and image retrieval on a dataset of 1500 radiological images. A classification rate of 97.5% was achieved. The classification results compare favorably with reported global and local representation schemes. Precision versus recall curves indicate a strong retrieval result as compared with other state-of-the-art retrieval techniques. Finally, category models are learned and results are presented for comparing images to learned category models.     

Mechanical and optical properties of the chalcogenide glass system As2Se3-xTex

Chalcogenide glasses of As2Se3-xTex(0 leq x leq 3) were fabricated with special care to avoid traces of oxygen, using very pure raw materials. From part of these materials, special plates were made, and from the rest fibers were pulled. From transmittance measurements, the existence of absorption bands was shown, corresponding to the presence of small crystallites of As2O3. The attenuation in the infrared of these plates increased from 14 dB/m for As2Se3to 29 dB/m for As2Se0.5Te2.5. Conversely, a decrease of microhardness VHwas observed. The attenuation of CO2laser light (lambda = 10.6 mum) transmitted through the pulled fibers was measured as a function of the Te(x) content. and an increase of the attenuation was observed from 18.1 dB/m for As2Se3to 66.7 dB/m for As5Se1.5Te1.5. The surface of each fiber was examined in the scanning electron microscope and an increase of the defects (e.g., crystallites) when the Te content was increased, was observed. These defects (crystallites) are the main factors for finding an increase in the absorption in IR.