Electronic and valleytronic properties of crystalline boron-arsenide tuned by strain and disorder.

Ab initio density functional theory (DFT) and DFT plus coherent potential approximation (DFT + CPA) are employed to reveal, respectively, the effect of in-plane strain and site-diagonal disorder on the electronic structure of cubic boron arsenide (BAs). It is demonstrated that tensile strain and static diagonal disorder both reduce the semiconducting one-particle band gap of BAs, and a V-shaped p-band electronic state emerges - enabling advanced valleytronics based on strained and disordered semiconducting bulk crystals. At biaxial tensile strains close to 15% the valence band lineshape relevant for optoelectronics is shown to coincide with one reported for GaAs at low energies. The role played by static disorder on the As sites is to promote p-type conductivity in the unstrained BAs bulk crystal, consistent with experimental observations. These findings illuminate the intricate and interdependent changes in crystal structure and lattice disorder on the electronic degrees of freedom of semiconductors and semimetals.

Giant optical nonlinearity interferences in quantum structures.

Second-order optical nonlinearities can be greatly enhanced by orders of magnitude in resonantly excited nanostructures. These resonant nonlinearities continually attract attention, particularly in newly discovered materials. However, they are frequently not as heightened as currently predicted, limiting their exploitation in nanostructured nonlinear optics. Here, we present a clear-cut theoretical and experimental demonstration that the second-order nonlinear susceptibility can vary by orders of magnitude as a result of giant destructive, as well as constructive, interference effects in complex systems. Using terahertz quantum cascade lasers as a model source to investigate interband and intersubband nonlinearities, we show that these giant interferences are a result of an unexpected interplay of the second-order nonlinear contributions of multiple light and heavy hole states. As well as of importance to understand and engineer the resonant optical properties of nanostructures, this advanced framework can be used as a novel, sensitive tool to elucidate the band structure properties of complex materials.

Expanding spatial domains and transient scaling regimes in populations with local cyclic competition.

We investigate a six-species class of May-Leonard models leading to the formation of two types of competing spatial domains, each one inhabited by three species with their own internal cyclic rock-paper-scissors dynamics. We study the resulting population dynamics using stochastic numerical simulations in two-dimensional space. We find that as three-species domains shrink, there is an increasing probability of extinction of two of the species inhabiting the domain, with the consequent creation of one-species domains. We determine the critical initial radius beyond which these one-species spatial domains are expected to expand. We further show that a transient scaling regime, with a slower average growth rate of the characteristic length scale L of the spatial domains with time t, takes place before the transition to a standard L∝t^{1/2} scaling law, resulting in an extended period of coexistence.

Caspase-2 promotes obesity, the metabolic syndrome and nonalcoholic fatty liver disease.

Obesity and its resulting metabolic disturbances are major health threats. In response to energy surplus, overtaxed adipocytes release fatty acids and pro-inflammatory factors into the circulation, promoting organ fat accumulation (including nonalcoholic fatty liver disease), insulin resistance and the metabolic syndrome. Recently, caspase-2 was linked to lipoapoptosis, so we hypothesized that caspase-2 might be a critical determinant of metabolic syndrome pathogenesis. Caspase-2-deficient and wild-type mice were fed a Western diet (high-fat diet, enriched with saturated fatty acids and 0.2% cholesterol, supplemented with fructose and glucose in the drinking water) for 16 weeks. Metabolic and hepatic outcomes were evaluated. In vitro studies assessed the role of caspase-2 in adipose tissue proliferative properties and susceptibility for lipoapoptosis. Caspase-2-deficient mice fed a Western diet were protected from abdominal fat deposition, diabetes mellitus, dyslipidemia and hepatic steatosis. Adipose tissue in caspase-2-deficient mice was more proliferative, upregulated mitochondrial uncoupling proteins consistent with browning, and was resistant to cell hypertrophy and cell death. The liver was protected from steatohepatitis through a decrease in circulating fatty acids and more efficient hepatic fat metabolism, and from fibrosis as a consequence of reduced fibrogenic stimuli from fewer lipotoxic hepatocytes. Caspase-2 deficiency protected mice from diet-induced obesity, metabolic syndrome and nonalcoholic fatty liver disease. Further studies are necessary to assess caspase-2 as a therapeutic target for those conditions.

Optical sideband generation up to room temperature with mid-infrared quantum cascade lasers.

Mid-infrared (MIR) sideband generation on a near infrared (NIR) optical carrier is demonstrated within a quantum cascade laser (QCL). By employing an externally injected NIR beam, E(NIR), that is resonant with the interband transitions of the quantum wells in the QCL, the nonlinear susceptibility is enhanced, leading to both frequency mixing and sideband generation. A GaAs-based MIR QCL (E(QCL) = 135 meV) with an aluminum-reinforced waveguide was utilized to overlap the NIR and MIR modes with the optical nonlinearity of the active region. The resulting difference sideband (E(NIR) - E(QCL)) shows a resonant behavior as a function of NIR pump wavelength and a maximum second order nonlinear susceptibility, χ((2)), of ~1 nm/V was obtained. Further, the sideband intensity showed little dependence with the operating temperature of the QCL, allowing sideband generation to be realized at room temperature.

[Individualized monitoring of the therapy with gentamycin using pharmacokinetic methods. Which method to choose?]. / Monitorização individualizada da terapêutica com gentamicina por métodos farmacocinéticos. Que Método escolher?

Gentamicin has an excellent cost/efficacy ratio for gram negative infections treatment. Its use is often limited in clinical practice by its narrow safety margins and a high incidence of toxicity. Gentamicin related nephrotoxicity is a major adverse effect, mostly in patients with other concomitant potential risk factors. As many other Authors we have found in our Internal Medicine Service during 1992 a gentamicin related nephrotoxicity incidence of 22.5%. Various empiric methods and nomograms have shown a significant incidence of error in predicting individualized gentamicin dosage regimens. Pharmacokinetics methods have demonstrated much better results regarding efficacy and toxicity. The aim of this prospective study carried out during 1993-1994 was to individualize by pharmacokinetics methods dosage regimens of gentamicin in patients with one or more concomitant risk factors of nephrotoxicity. The purpose of pharmacokinetics dosage regimens has been to achieve trough serum concentrations of gentamicin in therapeutics range-0.5 to 2 micrograms/ml-on the first 24 to 48 hours of treatment, and the maintenance in this range during all the treatment, avoiding both toxic and under therapeutic levels. The incidence of gentamicin related nephrotoxicity has been evaluated in this population. Twenty patients were studied: 18 males and 2 females aged 59.6 years (19 to 85). All had one or more potential risk factors for nephrotoxicity-65 years or more: 13, previous renal failure: 6, other nephrotoxic drugs: 10, diuretics: 4, dehydration: 5, congestive heart failure: 5, diabetes: 3, hypertension: 3. For the first 10 patients gentamicin dosage regimens have been determined by Sawchuk-Zaske pharmacokinetics method and for the subsequent 10 patients by Bayesian method. The two subpopulations had no significant differences regarding mean age, sex and potential risk factors for nephrotoxicity. Results of Sawchuk-Zaske method: 53 trough gentamicin serum concentration were obtained; 86.8% were within the therapeutic range, 7.5% were toxic and 5.7% were under therapeutic. Results of Bayesian method: 44 determinations of gentamicin through concentrations were obtained; 86.3% within therapeutic range, 2.4% were toxic and 11.3% were under therapeutic. A great variability in pharmacokinetic patient's profile has been found and explains the great variability of individualized dosage regimens of gentamicin (30 to 320 mg/day). No patients had gentamicin related nephrotoxicity. Both pharmacokinetics methods lead to a efficient and save employment of gentamicin in patients with previous renal failure and other potential risk factors for nephrotoxicity.

Assay of liver cytosol lipoxygenase by differential pulse polarography.

Lipoxygenase activity assayed by differential pulse polarography was found to be more sensitive than that determined by the increase in absorption at 234 nm. The lipoxygenase activity level in the liver cytosol of rats fed oxidized palm oil was significantly higher than that of the control animals fed either saline or fresh palm oil. The effects of flavonoids on the inhibition of lipoxygenase activity level in liver cytosol of rats were in the decreasing order quercetin greater than myricetin greater than morin greater than phloretin. The observed free malonaldehyde (MDA) in liver cytosol of rats determined by high-performance liquid chromatography using malonaldehyde-dinitro-phenylhydrazine complex was 23, 25, and 51.2% for rats fed saline, fresh palm oil, and oxidized palm oil, respectively. A linear relationship between the lipoxygenase activity and the free liver cytosol MDA was shown. The assay of lipoxygenase by differential pulse polarography provides a simple, sensitive, and quantitative method for the study of liver lipid peroxidation.

Effects of dietary palm oil on serum lipid peroxidation, antithrombin III, plasma cyclic AMP, and platelet aggregation.

Intravascular thrombus formation in association with lipid depositions in the arterial wall is thought to be involved in the process of atheroma formation. We have previously shown the beneficial effect of palm oil on the serum lipid profile resulting in a lowering of serum triacylglycerol and an elevation of the HDL/LDL ratio. The present study investigates the effect of dietary palm oil on the biochemical parameters associated with clotting and platelet aggregation in young rats (70 g body wt) fed a palm oil diet over a period of 10 weeks. Palm oil-fed rats showed significantly lower levels of fibrinogen and serum lipid peroxide and elevated AtIII levels resulting in a prolongation of clotting time. Reduced platelet aggregation and ATP release associated with a prolongation of bleeding time were also found. These findings, together with our earlier findings on the effect of palm oil on the serum lipid profile, suggest that dietary palm oil may be antithrombotic as well as beneficial in preventing the deposition of lipids on the vessel wall and may, therefore, be protective against the development of atherosclerosis.

Effect of dietary palm oil on lipoprotein lipases: lipoprotein levels and tissue lipids in rat.

The aims of our study were to investigate the effect of dietary palm oil on the levels of lipoprotein lipase, hepatic lipase, fat distribution (in the aorta and liver), and total cholesterol, HDL, LDL, and triacylglycerol levels in young rats (70 g body wt) over a period of 10 weeks. Palm oil-fed rats showed higher growth rate and lower triacylglycerol levels than the control group. Hepatic lipase activity was correlated to the liver fat distribution (correlation coefficient, r = +0.682) as seen by histopathological sections and was similar for both the palm oil and the control diets. Palm oil-fed rats exhibited a significantly higher HDL cholesterol to total plasma cholesterol ratio when compared to animals fed the control diet. The triacylglycerol levels correlated inversely to the HDL cholesterol levels (r = -0.536) while the lipoprotein lipase (LPL) activity correlated directly to the LDL level (r = +0.617) for both groups of animals. The fatty acid profiles of adipose and liver tissues and plasma revealed that saturated fatty acids--palmitic and stearic--were preferentially incorporated in liver and adipose tissues and less in the plasma. This accounts for lack of deposition in the arterial wall and for the antithrombotic tendency of palm oil. Thus, our present findings suggest that dietary palm oil may not contribute to the risk for coronary heart disease.