Latest Developments of HgCdTe e-APDs at CEA LETI-Minatec

In this communication, we report on the electro-optical characterization of planar back-side-illuminated HgCdTe electron initiated avalanche photodiode (e-APD) test arrays with cut-off wavelengths λ _c = 2.4 μm, λ _c = 4.8 μm, and λ _c = 9.2 μm. The e-APDs were manufactured at LETI using absorption layers grown by molecular beam epitaxy (MBE). We present measurements of the distributions in gain, noise, and equivalent input dark current. The mid-wave (MW) diodes yielded a very low dispersion (2%) and high operability (98%) for gains up to M = 200. The excess noise factor and equivalent input current (I _{eq_in}) operability were slightly lower, due to defects in the depletion region. The lowest measured value of I _{eq_in} = 1 fA corresponds to the lowest level measured so far in HgCdTe e-APDs and opens the way to new applications. The gain in the long-wave (LW) diodes was limited by tunnelling currents to a value of M = 2.4, associated with an average noise factor F = 1.2. A gain of M = 20 at a bias of −22.5 V was demonstrated in the short-wave (SW) e-APDs.     

Novel Hoogsteen-like bases for configurational recognition of the T-A base pair by DNA triplex formation

Effective sequence-specific recognition of duplex DNA is possible by triplex formation with natural oligonucleotides via Hoogsteen H-bonding. However, triplex formation is in practice limited to pyrimidine oligonucleotides binding duplex A-T or G-C base-pair DNA sequences specifically at homopurine sites in the major groove as T-A-T and C+.G-C triplets. Here we report the successful modeling of novel unnatural nucleosides that recognize the T-A DNA base pair by Hoogsteen interaction. Since the DNA triplex can be considered to assume an A-type or B-type conformation, these novel Hoogsteen nucleotides are tested within model A-type and B-type conformation triplex structures. A triplet consisting of the T-A base pair and one of the novel Hoogsteen nucleotides replaces the central T.A-T triplet in the triplex using the same deoxyribose-phosphodiester and base-deoxyribose dihedral angle configuration. The entire triplex is energy minimized and the presence of any structural or energetic perturbations due to the central triplet is assessed with respect to the unmodified energy-minimized (T.A-T)11 proposed starting structures. Incorporation of these novel triplets into both A-type and B-type natural tiplex structures provokes minimal change in the configuration of the central and adjacent triplets. The plan is to produce a series of Hoogsteen-like bases that preferentially bind the T-A major groove in either an A-type or B-type conformation. Selective recognition of the T-A major groove with respect to the G-C major groove, which presents similar keto and amine placement, is also assessed with configurational preference. Evaluation of the triplex solution structure by using these unnatural bases as binding conformational probes is a prerequisite to the further design of triplet forming bases.     

Enol esters. VII. Isolation and rearrangement of terminal fatty oxirane esters

Isopropenyl esters of mono- and dibasic fatty acids were epoxidized with m-chloroperbenzoic acid in carbon tetrachloride. The isolation of the resulting oxirane ester was difficult because of the spontaneous rearrangement to a hydroxyacetone ester. Rapid gel filtration was the only method that consistently afforded good yields of the oxiranes. The infrared spectra of these oxirane esters had many strong, sharp bands which were completely lacking in the rearranged product. The isomerization, carried out in several ways, could easily be followed spectrally and a qualitative estimate of purity made. Previous paper in series: E. S. Rothman, J. Org. Chem.32, 1683–1684 (1967). E. Utilz. Res. Dev. Div., ARS, USDA.     

Evidence that cholesteryl ester hydrolase and triglyceride lipase are different enzymes in rat liver

Studies on intracellular cholesteryl ester hydrolase (CEH) and triglyceride lipase (TGL) from rat adipose tissue and adrenal cortex have suggested that a single protein is responsible for both activities. To determine whether one hepatic protein catalyzes both reactions, we studied several properties of CEH and TGL in rat liver. During liver perfusion with heparin, perfusate peaks of TGL and CEH did not consistently coincide, and TGL activity was considerably higher and less heat-stable than that of CEH. Significant TGL, but not CEH, activity was released during incubation of isolated hepatocytes. Although microsomes isolated from hepatocytes contained both activities, the specific activities of CEH and TGL in cytosol from hepatocytes were 95% and 3%, respectively, of those found in cytosol from whole liver. Preincubation of liver cytosol with 5 mM Mg²⁺ decreased CEH, but not TGL, activity. Intracellular CEH and TGL activities were completely separated by prep-disc gel electrophoresis. Finally, both cytosolic and microsomal TGL, but not CEH, activities were inhibited by antiserum against rat hepatic TGL. We conclude that extracellular TGL does not have CEH activity and intracellular CEH differs from TGL.     

Molecular beam epitaxy growth of HgCdTe on Ge for third-generation infrared detectors

The Leti-Lir has studied II–VI compounds for infrared (IR) detection for more than 20 years. The need to reduce the production cost of IR focal plane arrays (FPAs) sparked the development of heteroepitaxy on large-area substrates. Germanium has been chosen as the heterosubstrate for the third generation of IR detectors. First, we report on the progress achieved in HgCdTe growth on 3-in. and 4-in. (211)B CdTe/Ge. Then, we discuss the choice of a new machine for larger size and better homogeneity. Finally, we present the latest results on third-generation IR multicolor and megapixel devices. First-time results regarding a middle wavelength infrared (MWIR) dual-band FPA, with a reduced pitch of 25 μm, and a MWIR 1,280×1,024 FPA will be shown. Both detectors are based on molecular beam epitaxy (MBE)-grown HgCdTe on Ge. The results shown validate the choice of Ge as the substrate for third-generation detectors.     

High temperature corrosion of superalloys in an environment containing both oxygen and chlorine

The corrosion behavior of a series of commercial superalloys in flowing argon-20 pct oxygen-2 pct chlorine at 900 °C has been investigated using thermogravimetric analysis and examination of the condensed corrosion products using X-ray diffraction analysis and optical and scanning electron microscopy. Most of the alloys exhibited decreases in mass due to formation of volatile chloride or oxychloride corrosion products. An exception is the alloy 214 which showed little change in mass due to the formation of a protective alumina scale. Alloys which are high in refractory metals, notably alloys S and C-276, snowed the highest rates of attack. In addition to the metal wastage, several of the alloys were subject to internal attack in the region near the corroded surface. Formerly Graduate Student, Department of Civil Engineering, Mechanics, and Metallurgy, University of Illinois at Chicago     

Specifying the determinants of the initiation and maintenance of behavior change: An examination of self-efficacy, satisfaction, and smoking cessation.

Using data from smokers (N = 591) who enrolled in an 8-week smoking cessation program and were then followed for 15 months, the authors tested the thesis that self-efficacy guides the decision to initiate smoking cessation but that satisfaction with the outcomes afforded by quitting guides the decision to maintain cessation. Measures of self-efficacy and satisfaction assessed at the end of the program, 2 months, and 9 months were used to predict quit status at 2, 9, and 15 months, respectively. At each point, participants were categorized as either initiators or maintainers on the basis of their pattern of cessation behavior. Across time, self-efficacy predicted future quit status for initiators, whereas satisfaction generally predicted future quit status for maintainers. Implications for models of behavior change and behavioral interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic droplet vaporization threshold: effects of pulse duration and contrast agent

The use of superheated liquid perfluorocarbon droplets encased in albumin shells has been proposed as a minimally invasive alternative to current treatment of cancer by means of occlusion therapy. In response to an applied acoustic field, these droplets, which are small enough to pass through capillaries, vaporize into large gas bubbles that subsequently lodge in the vasculature. This technique, known as acoustic droplet vaporization (ADV) has been shown to successfully reduce blood flow in vivo, but for in situ conditions where attenuation is present, lower acoustic frequency and ADV threshold may be desirable. Thus, two methods to lower the ADV threshold at a lower 1.44 MHz were explored. The first part of this study investigated the role of pulse duration on ADV. The second part investigated the role of inertial cavitation (IC) external to a droplet by lowering the IC threshold in the host liquid with the presence of Definity contrast agent (CA). The threshold was found to be 5.5-5.9 MPa for short microsecond pulses and decreased for millisecond pulses (3.8-4.6 MPa). When CAs were present and long millisecond pulses were used, the ADV threshold decreased to values as low as 0.41 MPa.