Control of very-long-wavelength infrared HgCdTe detector-cutoff wavelength

Hg_1-xCd_xTe is an important material for infrared (IR) detection applications where the bandgap of the alloy varies from semimetal to 1.4 eV. The large variation in bandgap energy with HgCdTe composition causes difficulty in controlling detector-cutoff wavelength, particularly for the long-wavelength IR and very-long-wavelength infrared (VLWIR, greater than 12 μm) spectral bands. Our ability to control the HgCdTe composition and compositional profile during growth by molecular beam epitaxy (MBE) is improved significantly by using automated feedback control from spectroscopic ellipsometry (SE) measurements, where the standard deviation in the error in composition has improved by a factor of 5, from σ=0.0081 to σ=0.0016. To improve our ability to predict cutoff wavelength from IR transmission measurements, we have used a model of the absorption in HgCdTe to revise our past empirical cutoff relationship to include the effect of compositional grading. We have achieved a mean detector-cutoff wavelength of 14.1 μm and standard deviation of σ=0.25 μm for a series of 19 processed layers with a target cutoff of 14 μm. The excellent control in VLWIR detector cutoff we have observed is attributed to automated compositional control and an improved cutoff-prediction model.     

Managing dynamic automated communities with MPLS-based VPNs

This paper describes a novel architecture for supporting orchestrated distributed computing and other forms of dynamic communities that can benefit from on-demand access to processing and communications resources. This effectively provides a mechanism that allows network operators to sell communication and resource management services rather than ‘connections’. It offers a cost-effective solution, for example, for SMEs or other end users, who can delegate some backoffice processing to the operator. We show that this system is achievable by extending 21CN functionalities. The operator is no longer seen as simply providing infrastructure, but also generic services upon that infrastructure. A key feature of the approach is to capitalise on MPLS technology, enabling specific quality of service requirements to be accommodated. This communications infrastructure is used to support on-demand operations, coupling end users with resources owned by the network operator or third party providers. Furthermore, given the importance of security, the paper considers VPN-specific security issues.     

Free carrier absorption and lattice vibrational modes in bulk ZnO

The electronic properties of semiconductors are highly dependent on carrier scattering mechanisms determined by crystalline structure, band structure, and defects in the material. Experimental characteristics of lattice vibrational modes and free carrier absorption in single-crystal ZnO samples obtained from different sources are presented in this work to provide a further understanding of carrier scattering processes pertaining to electronic properties. Infrared absorption measurements indicate strong absorption peaks due to a combination of optical and nonpolar phonon modes in the 9–13 μm spectral region. The Raman spectra obtained for these samples similarly reveal the presence of these phonon modes. Infrared absorption measurements also demonstrate free carrier absorption in the 3–9 μm spectral region for higher conductivity samples, where a λ^m dependence is observed with m=2.7–3, indicating both longitudinal optical phonon scattering and ionized impurity scattering. From these results, we show that infrared absorption can be used as a routine nondestructive technique to determine the material characteristics and quality of bulk ZnO.     

Accurate analytical method for the extraction of solar cell model parameters

Analytical expressions are derived for the rapid extraction of solar cell single diode model parameters from experimental data. The resulting parameter values are shown to have less than 5% error for most solar cells     

Effect of long term ingestion of gum arabic on the adipose tissues of female mice

Abdominal obesity is the most prevalent manifestation of metabolic syndrome. The anti-obese effects of dietary fiber is generally accepted, but specifically the anti-obese properties of the dietary fiber, gum arabic (GA) has not been well studied. In this investigation, we offered GA to the female 90 days old mice in the form of drink (1% w/v) for 180 days. Such GA in drinking water reduced age-dependent fat deposition in the visceral adipose tissue and improved the gastrocnemius muscle reduction. This inhibition of fat deposition effect is due to the β3-adrenergic stimulation of adipocytes in which TNFα down-regulation is probably involved. Modification of large intestinal microflora, as evidenced by a modification of cecal short-chain fatty acid profile and of 16S rDNA profile, may contribute to such reduction in TNFα expression in the adipose tissues.     

Porcine oxymyoglobin and lipid oxidation in vitro

The present study was carried out to investigate the effect of dietary α-tocopherol supplementation on porcine oxymyoglobin (OxyMb) and lipid oxidation (TBARS) in model lipid systems, and to determine the influence of 4-hydroxynonenal (4-HNE), a secondary product of lipid oxidation, on porcine OxyMb stability. Porcine metmyoglobin (MetMb) formation was greater in the presence of 4-HNE than the control (P<0.05). Western blot analyses confirmed the covalent modification of myoglobin (Mb) histidine residues by 4-HNE. When combined with microsomes, both equine and porcine OxyMb oxidation increased with time of incubation, and was greater at 37 than at 25?°C (P<0.05). Lower TBARS values were observed in microsomes prepared from vitamin E-supplemented than control pork livers (P<0.05). α-Tocopherol concentration did not affect OxyMb oxidation in microsomes at 25 or 37?°C (P>0.05). These results differ from those observed with beef muscle microsomes where both OxyMb and lipid oxidation were delayed with elevated α-tocopherol levels. These results suggest that the factors affecting Mb and lipid oxidation interactions may be species-dependent.     

Review: Modified Atmosphere Packaging and its effects on the microbiological quality and safety of produce

Modified Atmosphere Packaging and related technologies are increasingly used to extend shelf-life of fresh produce. This paper reviews the effect of such technology on the spoilage microbiological flora and food-borne pathogens which may be present in produce and also on the organoleptic properties of the product.     

Interaction of short chain and long chain fatty acid phosphoglycerides and bile salts with prothrombin

An equimolar mixture of phosphatidylserine and (dioleoyl) phosphatidyl-ethanolamine could substitute for brain cephalin preparations in the single stage prothrombin assay. However, no clot promoting activity was observed on the addition of any of the individual long chain fatty acid-containing phospholipids. Short chain fatty acid-containing phospholipids, such as diheptanoylphosphatidylcholine, diheptanoylphosphatidylethanolamine, diheptanoylphosphatidic acid, and dihexanoylphosphatidylcholine, or dihexanoylphosphatidylethanolamine were inhibitory under all conditions studied. Similar effects of these two general classes of phospholipids were observed in a two-stage thrombin generation system, in which a mixture of bovine Factor Xa, Factor Va, and Ca2+ were interacted with prothrombin. In the presence of 25 mM Ca2+, dioleoylphosphatidic acid or brain phosphatidylserine alone, and with other long chain phospholipids, formed complexes with bovine plasma prothrombin. On the other hand, dioleoyl-, diheptanoyl- or dihexanoylphosphatidylcholine under comparable conditions showed no binding to prothrombin. There appeared to be a small degree of binding of diheptanoylphosphatidic acid to prothrombin, but it was insufficient to cause any significant change in apparent molecular weight of prothrombin. A mixture of prothrombin, Factor V, diheptanoylphosphatidic acid/diheptanoylphosphatidylcholine and Ca2+ eluted in the void volume of Sephadex G-200, but showed a much reduced coagulant activity. Though a net negative charge on the phospholipid surface is required for phospholipid-protein interactions, this does not necessarily promote coagulant activity. Bile acids and bile salts, such as cholic acid, deoxycholic acid, taurocholic acid, glycocholic acid, lithocholic acid and dehydrocholic acid, exerted varying levels of stimulation on the prothrombin assay and thrombin generation system, but were not as effective as the phospholipids. Interestingly, no interaction of these bile acids or salts with prothrombin was noted in the presence of Ca2+. The results of these experiments suggest that negatively charged micelles per se are not sufficient for binding alone and that other chemical and physical characteristics of phospholipids are of prime importance.     

Inhibition of insulin degradation by nonsuppressible insulin-like activity

Nonsuppressible insulin-like activity, provided by three sources, was evaluated for its effect on the proteolytic degradation of insulin utilizing insulin protease obtained from rat liver homogenate as well as liver cell membranes. All three preparations of nonsuppressible insulin-like activity were found to be competitive inhibitors of insulin degradation. In addition human plasma was fractionated yielding an acetone precipitate which was found to have nonsuppressible insulin-like activity and to be a competitive inhibitor of insulin protease.     

Diagnosis of gonorrhoea in women

250 consecutive female contacts of men with gonorrhoea were examined in Lydia Department of Genito-urinary Medicine, St Thomas' Hospital, London, and 165 (66 per cent.) were found to be positive for gonorrhoea. Over 99 per cent. of the positive results were found by the first two sets of genital investigations. These results are compared with earlier and more recent results from our own and other centres and it is postulated that the higher early diagnosis rate is due to the introduction of a highly selective but non-inhibitory culture medium (VCNT), combined with a new incubator which accurately regulates temperature, humidity, and CO2 content. Reasons for the negative findings in 35 per cent. of the female gonorrhoea contacts are discussed.