Electrical transport quantum effects in the In0.53Ga0.47As/In0.52Al0.48As heterostructure on silicon

Electrical transport in a modulation doped heterostructure of In0.53Ga0.47As/In0.52Al0.48As grown on Si by molecular beam epitaxy has been measured. Quantum Hall effect and Subnikov¿De Haas oscillations were observed indicating the two¿dimensional character of electron transport. A mobility of 20¿000 cm2/V¿s was measured at 6 K for an electron sheet concentration of 1.7×1012 cm¿2. Transmission electron microscopy observations indicated a significant surface roughness and high defect density of the InGaAs/InAlAs layers to be present due to the growth on silicon. In addition, fine¿scale composition modulation present in the In0.53Ga0.47As/In0.52Al0.48As may further limit transport properties.

On the nucleation of GaP/GaAs and the effect of buried stress fields

We have recently shown that spatial ordering for epitaxially grown InP dots can be obtained using the periodic stress field of compositional modulation on the InGaP buffer layer. The aim of this present work is to study the growth of films of GaP by Chemical Beam Epitaxy (CBE), with in-situ monitoring by Reflection High Energy Electron Diffraction (RHEED), on layers of unstressed and stressed GaAs. Complementary, we have studied the role of a buried InP dot array on GaP nucleation in order to obtain three-dimensional structures. In both cases, the topographical characteristics of the samples were investigated by Atomic Force Microscopy (AFM) in non-contact mode. Thus vertically-coupled quantum dots of different materials have been obtained keeping the in-place spatial ordering originated from the composition modulation. © 2006 Materials Research Society.

Impact of N on the atomic-scale Sb distribution in quaternary GaAsSbN-capped InAs quantum dots

The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure.

Lattice Engineering of III-Nitride Heterostructures and Their Applications

III-Nitride materials have recently become a promising candidate for superior applications over the current technologies. However, certain issues such as lack of native substrates, and high defect density have to be overcome for further development of III-Nitride technology. This work presents research on lattice engineering of III-Nitride materials, and the structural, optical, and electrical properties of its alloys, in order to approach the ideal material for various applications. We demonstrated the non-destructive and quantitative characterization of composition modulated nanostructure in InAlN thin films with X-ray diffraction. We found the development of the nanostructure depends on growth temperature, and the composition modulation has impacts on carrier recombination dynamics. We also showed that the controlled relaxation of a very thin AlN buffer (20 ~ 30 nm) or a graded composition InGaN buffer can significantly reduce the defect density of a subsequent epitaxial layer. Finally, we synthesized an InAlGaN thin films and a multi-quantum-well structure. Significant emission enhancement in the UVB range (280 – 320 nm) was observed compared to AlGaN thin films. The nature of the enhancement was investigated experimentally and numerically, suggesting carrier confinement in the In localization centers.

Autonomic modulation and its relation with body composition in swimmers

This study compared autonomic modulation in swimmers and non-athletes in relation to body composition. A total of 28 athletes with a mean age of 19.7 +/- 2.9 years were evaluated who had at least 2 years of swimming training, trained approximately 7,000 m per day, with a frequency of 5 days per week, and who competed at national level. The control group was made up of 21 volunteers (23.0 +/- 2.5 years), who did not practice regular physical activity (<2 hours per week). Body composition was estimated using dual-energy x-ray absorptiometry, and autonomic modulation was assessed by heart rate variability (HRV). The results show that there were significant differences in autonomic modulation and body composition between the groups, and that the athletes had a higher overall variability (standard deviation of all normal intervals between consecutive heart beats [SDNN]: 78.1 [72.5-93.5] x 61.1 [56.4-75.7], p = 0.022) and greater autonomic balance (LF/HF: 0.96 [0.88-1.35] x 0.71 [0.56-0.93], p = 0.023), compared with the non-athletes, respectively. In addition, a moderate and positive relation was obtained between fat-free mass and the square root of the squared differences between consecutive heartbeat intervals (RMSSD: r = 0.526, p = 0.004 x r = 0.456, p = 0.038), (SDNN: r = 0.617, p = 0.001 x r = 0.571, p = 0.007) and low frequency (LFms(2): r = 0.517, p = 0.005 3 r = 0.600, p = 0.004) in the athletes and non-athletes, respectively, without a correlation between fat mass (FM). The conclusion is that young highly trained swimmers had lower FM, increased fat-free mass, and better HRV than young adult non-athletes and suggests that a lower quantity of FM and, especially, a greater fat-free mass (FFM) are linked to better autonomic modulation. Thus, this study could contribute to coaches and trainers establishing greater performance by better autonomic modulation and greater quantity of FFM.

Serotonergic modulation of muscle acetylcholine receptors of different subunit composition.

Modulation of muscle acetylcholine (AcCho) receptors (AcChoRs) by serotonin [5-hydroxytryptamine (5HT)] and other serotonergic compounds was studied in Xenopus laevis oocytes. Various combinations of alpha, beta, gamma, and delta subunit RNAs were injected into oocytes, and membrane currents elicited by AcCho were recorded under voltage clamp. Judging by the amplitudes of AcCho currents generated, the levels of functional receptor expression were: alpha beta gamma delta > alpha beta delta > alpha beta gamma > alpha gamma delta. The alpha beta gamma delta and alpha beta delta AcChoR Subtypes were strongly blocked by 5HT, whereas the alpha beta gamma receptor was blocked only slightly. The order of blocking potency of AcChoRs by 5HT was: alpha beta delta > alpha beta gamma delta > alpha beta gamma. 5HT receptor antagonists, such as methysergide and spiperone, were even more potent blockers of AcChoRs than 5HT but did not show much subunit selectivity. Blockage of alpha beta gamma delta and alpha beta delta receptors by 5HT was voltage-dependent, and the voltage dependence was abolished when the delta subunit was omitted. These findings may need to be taken into consideration when trying to elucidate the mode of action of many clinically important serotonergic compounds.

Modulation of the Silica Sol–Gel Composition for the Promotion of Direct Electron Transfer to Encapsulated Cytochrome c

The direct electron transfer between indium–tin oxide electrodes (ITO) and cytochrome c encapsulated in different sol–gel silica networks was studied. Cyt c@silica modified electrodes were synthesized by a two-step encapsulation method mixing a phosphate buffer solution with dissolved cytochrome c and a silica sol prepared by the alcohol-free sol–gel route. These modified electrodes were characterized by cyclic voltammetry, UV–vis spectroscopy, and in situ UV–vis spectroelectrochemistry. The electrochemical response of encapsulated protein is influenced by the terminal groups of the silica pores. Cyt c does not present electrochemical response in conventional silica (hydroxyl terminated) or phenyl terminated silica. Direct electron transfer to encapsulated cytochrome c and ITO electrodes only takes place when the protein is encapsulated in methyl modified silica networks.

Suppression of nuclear factor-κB activity in macrophages by chylomicron remnants: modulation by the fatty acid composition of the particles

Current evidence indicates that chylomicron remnants (CMR) induce macrophage foam cell formation, an early event in atherosclerosis. Inflammation also plays a part in atherogenesis and the transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated. In this study, the influence of CMR on the activity of NF-kappaB in macrophages and its modulation by the fatty acid composition of the particles were investigated using macrophages derived from the human monocyte cell line THP-1 and CMR-like particles (CRLPs). Incubation of THP-1 macrophages with CRLPs caused decreased NF-kappaB activation and downregulated the expression of phospho-p65-NF-kappaB and phospho-IkappaBalpha (pIkappaBalpha). Secretion of the inflammatory cytokines tumour necrosis factor alpha, interleukin-6 and monocyte chemoattractant protein-1, which are under NF-kappaB transcriptional control, was inhibited and mRNA expression for cyclooxygenase-2, an NF-kappaB target gene, was reduced. CRLPs enriched in polyunsaturated fatty acids compared with saturated or monounsaturated fatty acids had a markedly greater inhibitory effect on NF-kappaB binding to DNA and the expression of phospho-p65-NF-kappaB and pIkappaB. Lipid loading of macrophages with CRLPs enriched in polyunsaturated fatty acids compared with monounsaturated fatty acids or saturated fatty acids also increased the subsequent rate of cholesterol efflux, an effect which may be linked to the inhibition of NF-kappaB activity. These findings demonstrate that CMR suppress NF-kappaB activity in macrophages, and that this effect is modulated by their fatty acid composition. This downregulation of inflammatory processes in macrophages may represent a protective effect of CMR which is enhanced by dietary polyunsaturated fatty acids.

Modulation of cutaneous inflammation induced by ticks in contrasting phenotypes of infestation in bovines

Tick saliva contains molecules that are inoculated at the site of attachment on their hosts in order to modulate local immune responses and facilitate a successful blood meal. Bovines express heritable, contrasting phenotypes of infestations with the cattle tick, Rhipicephalus (Boophilus) microplus: breeds of Bos taurus indicus are significantly note resistant than those of Bos taurus taurus. Tick saliva may contain molecules that interfere with adhesion of leukocytes to endothelium and resistant hosts may mount an inflammatory profile that is more efficient to hamper the tick`s blood meal. We show in vitro that adhesion of peripheral blood mononuclear cells to monolayers of cytokine-activated bovine umbilical endothelial cells was significantly inhibited by tick saliva. The inflammatory response to bites of adults of R. microplus mounted by genetically resistant and susceptible bovine hosts managed in the same pasture was investigated in vivo. The inflammatory infiltrates and levels of message coding for adhesion molecules were measured in biopsies of tick-bitten and control skin taken when animals of both breeds were exposed to low and high tick infestations. Histological studies reveal that cutaneous reactions of resistant hosts to bites of adult ticks contained significantly more basophils and eosinophils compared with reactions of the susceptible breed. Expression of the adhesion molecules - intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P-selectin - was higher in adult-infested skin of susceptible hosts undergoing low infestations compared to resistant hosts; when host was exposed to high infestations expression of these adhesion molecules was down-regulated in both phenotypes of infestations. Expression of leukocyte adhesion glycoprotein-1 (LFA-1) was higher in skin from susceptible hosts undergoing low or high infestations compared to resistant hosts. Conversely, higher levels of E-selectin, which promotes adhesion of memory T cells, were expressed in skin of resistant animals. This finding may explain the resistant host`s ability to mount more rapid and efficient secondary responses that limit hematophagy and infestations. The expression profiles observed for adhesion molecules indicate that there are differences in the kinetics of the inflammatory reactions mounted by resistant and susceptible hosts and the balance between tick and host is affected by the number of tick bites a host receives. We show that the contrasting phenotypes of infestations seen in bovines infested with R. microplus are correlated with differences in the cellular and molecular composition of inflammatory infiltrates elicited by bites with adult ticks. (C) 2009 Published by Elsevier B.V.

Spermine modulation of the glutamate(NMDA) receptor is differentially responsive to conantokins in normal and Alzheimer's disease human cerebral cortex

The pharmacology of the N -methyl-d-aspartate (NMDA) receptor site was examined in pathologically affected and relatively spared regions of cerebral cortex tissue obtained at autopsy from Alzheimer's disease cases and matched controls. The affinity and density of the [H-3]MK-801 binding site were delineated along with the enhancement of [H-3]MK-801 binding by glutamate and spermine. Maximal enhancement induced by either ligand was regionally variable; glutamate-mediated maximal enhancement was higher in controls than in Alzheimer's cases in pathologically spared regions, whereas spermine-mediated maximal enhancement was higher in controls in areas susceptible to pathological damage. These and other data suggest that the subunit composition of NMDA receptors may be locally variable. Studies with modified conantokin-G (con-G) peptides showed that Ala(7)-con-G had higher affinity than Lys(7)-con-G, and also defined two distinct binding sites in controls. Nevertheless, the affinity for Lys(7)-con-G was higher overall in Alzheimer's brain than in control brain, whereas the reverse was true for Ala(7)-con-G. Over-excitation mediated by specific NMDA receptors might contribute to localized brain damage in Alzheimer's disease. Modified conantokins are useful for identifying the NMDA receptors involved, and may have potential as protective agents.

Modulation of inflammatory mediators by Opuntia ficus-indica and Prunus avium bioproducts using an in vitro cell-based model of intestinal inflammation

Dissertation to obtain a Master Degree in Biotechnology

Significance of schistosomal granuloma modulation

Hepatic Schistosoma mansoni periovular granulomas undergo changes in size, cellular composition and appearance with time. This phenomenom, known as "immunological modulation", has been thought to reflect host immunological status. However, as modulation has not been observed outside the liver, participation of local factors, hitherto little considered, seems crucial. Components of the extracellular matrix of periovular granulomas of the mouse were particularly studied in three different organs (liver, lung and intestine) and during three periods of infection time (acute, intermediate and chronic) by means of histological, biochemical and imunofluorescence techniques, while quantitative data were evaluated by computerized morphometry, in order to investigate participation of local factors in granuloma modulation. Results confirmed modulation as a exclusively hepatic phenomenom, since pulmonary and intestinal granulomas, formed around mature eggs, did not change size and appearance with time. The matricial components which were investigated (Type I, III and IV collagens, fibronectin, laminin, proteoglycans and elastin) were found in all granulomas and in all organs examined. However, their presence was much more prominent in the liver. Elastin was only found in hepatic granulomas of chronic infection. The large amount of extracellular matrix components found in hepatic granulomas was the main change responsible for the morphological aspects of modulation. Therefore, the peculiar environment of the liver ultimately determines the changes identified in schistosomal granuloma as "modulation".

Lead acetate toxicity in vitro: Dependence on the cell composition of the cultures.

It is well known that exposure to low doses of lead causes long-lasting neurobehavioural deficits, but the cellular changes underlying these behavioural changes remain to be elucidated. A protective role of glial cells on neurons through lead sequestration by astrocytes has been proposed. The possible modulation of lead neurotoxicity by neuron-glia interactions was examined in three-dimensional cultures of foetal rat telencephalon. Mixed-brain cell cultures or cultures enriched in either neurons or glial cells were treated for 10 days with lead acetate (10(-6) m), a concentration below the limit of cytotoxicity. Intracellular lead content and cell type-specific enzyme activities were determined. It was found that in enriched cultures neurons stored more lead than glial cells, and each cell type alone stored more lead than in co-culture. Moreover, glial cells but not neurons were more affected by lead in enriched culture than in co-culture. These results show that neuron-glia interactions attenuate the cellular lead uptake and the glial susceptibility to lead, but they do not support the idea of a protective role of astrocytes.

Lead acetate toxicity in vitro: Dependence on the cell composition of the cultures.

It is well known that exposure to low doses of lead causes long-lasting neurobehavioural deficits, but the cellular changes underlying these behavioural changes remain to be elucidated. A protective role of glial cells on neurons through lead sequestration by astrocytes has been proposed. The possible modulation of lead neurotoxicity by neuron-glia interactions was examined in three-dimensional cultures of foetal rat telencephalon. Mixed-brain cell cultures or cultures enriched in either neurons or glial cells were treated for 10 days with lead acetate (10(-6) m), a concentration below the limit of cytotoxicity. Intracellular lead content and cell type-specific enzyme activities were determined. It was found that in enriched cultures neurons stored more lead than glial cells, and each cell type alone stored more lead than in co-culture. Moreover, glial cells but not neurons were more affected by lead in enriched culture than in co-culture. These results show that neuron-glia interactions attenuate the cellular lead uptake and the glial susceptibility to lead, but they do not support the idea of a protective role of astrocytes.