Free-carrier screening of polarization fields in wurtzite GaN/InGaN laser structures

The free-carrier screening of macroscopic polarization fields in wurtzite GaN/InGaN quantum wells lasers is investigated via a self-consistent tight-binding approach. We show that the high carrier concentrations found experimentally in nitride laser structures effectively screen the built-in spontaneous and piezoelectric polarization fields, thus inducing a ``field-free'' band profile. Our results explain some heretofore puzzling experimental data on nitride lasers, such as the unusually high lasing excitation thresholds and emission blue-shifts for increasing excitation levels.Comment: RevTeX 4 pages, 4 figure

RNA-binding activity of the rat calmodulin-binding PEP-19 protein and of the long PEP-19 isoform

Synthesis of H1\u2da histone protein, in the developing rat brain, seems to be regulated mainly at the post-transcriptional level. Since regulation of RNA metabolism depends on a series of RNA-binding proteins, we have been searching for RNA-binding proteins involved in the post-transcriptional regulation of the H1\u2da gene. We recently reported isolation, from a cDNA expression library, of an insert encoding a novel protein, the C-terminal half of which is identical to that of PEP-19, a brain-specific protein involved in calcium metabolism. The novel protein was called long PEP-19 isoform (LPI). Herein we show that LPI, as well as PEP-19, can bind H1\u2da RNA. Moreover, in order to improve production of functional LPI/PEP-19, we modified the protocol normally adopted for preparing histidine tagged-proteins from bacteria, by adding an additional purification step. We also found that both LPI and PEP can compete for H1\u2da RNA binding with PIPPin (CSD-C2), another RNA-binding protein previously discovered in our laboratory. Since PEP19/LPI contain a calmodulin binding domain, we finally investigated whether their ability to bind RNA is affected by calmodulin. Our results show that calmodulin interferes with binding of H1\u2da RNA to both PEP-19 and LPI, while it is not able to bind RNA on its own. This finding suggests that calcium/calmodulin may have a role in controlling H1\u2da mRNA metabolism in the developing brain

Characterization of the interface between composites and embedded Fiber Optic sensors or NiTiNOL wires

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Doping screening of polarization fields in nitride heterostructures

Using self-consistent tight-binding calculations, we show that modulation doping can be used to screen macroscopic polarization fields in nitride quantum wells. The blue-shift of photoluminescence peak as well as the reduction of radiative recombination lifetime at increasing doping density is explained and correlated to polarization-field screening. The field-induced ionization of the dopants and its relation with alloy composition in the heterostructure barriers is also analyzed. (C) 2000 American Institute of Physics. [S0003-6951(00)05026-9]

Evaluation of pre-processing on the meta-analysis of DNA methylation data from the Illumina HumanMethylation450 BeadChip platform

Introduction Meta-analysis is a powerful means for leveraging the hundreds of experiments being run worldwide into more statistically powerful analyses. This is also true for the analysis of omic data, including genome-wide DNA methylation. In particular, thousands of DNA methylation profiles generated using the Illumina 450k are stored in the publicly accessible Gene Expression Omnibus (GEO) repository. Often, however, the intensity values produced by the BeadChip (raw data) are not deposited, therefore only pre-processed values -obtained after computational manipulation- are available. Pre-processing is possibly different among studies and may then affect meta-analysis by introducing non-biological sources of variability. Material and methods To systematically investigate the effect of pre-processing on meta-analysis, we analysed four different collections of DNA methylation samples (datasets), each composed of two subsets, for which raw data from controls (i.e. healthy subjects) and cases (i.e. patients) are available. We pre-processed the data from each dataset with nine among the most common pipelines found in literature. Moreover, we evaluated the performance of regRCPqn, a modification of the RCP algorithm that aims to improve data consistency. For each combination of pre-processing (9 7 9), we first evaluated the between-sample variability among control subjects and, then, we identified genomic positions that are differentially methylated between cases and controls (differential analysis). Results and conclusion The pre-processing of DNA methylation data affects both the between-sample variability and the loci identified as differentially methylated, and the effects of pre-processing are strongly dataset-dependent. By contrast, application of our renormalization algorithm regRCPqn: (i) reduces variability and (ii) increases agreement between meta-analysed datasets, both critical components of data harmonization

Mineral fibres and asbestos bodies in human lung tissue: A case study

One of the open questions regarding the asbestos problem is the fate of the mineral fibres in the body once inhaled and deposited in the deep respiratory system. In this context, the present paper reports the results of an electron microscopy study of both mineral fibres and asbestos bodies found in the lung tissue of a patient who died of malignant mesothelioma due to past occupational exposure. In concert with previous in vivo animal studies, our data provide evidence that amphibole asbestos fibres are durable in the lungs, whereas chrysotile fibres are transformed into a silica-rich product, which can be easily cleared. Amphibole fibres recovered from samples of tissue of the deceased display a high degree of crystallinity but also show a very thin amorphous layer on their surface; 31% of the fibres are coated with asbestos bodies consisting of a mixture of ferroproteins (mainly ferritin). Here, we propose an improved model for the coating process. Formation of a coating on the fibres is a defence mechanism against fibres that are longer than 10 µm and thinner than 0.5 µm, which macrophages cannot engulf. The mature asbestos bodies show signs of degradation, and the iron stored in ferritin may be released and potentially increase oxidative stress in the lung tissue

Quasiparticle energies for large molecules: a tight-binding GW approach

We present a tight-binding based GW approach for the calculation of quasiparticle energy levels in confined systems such as molecules. Key quantities in the GW formalism like the microscopic dielectric function or the screened Coulomb interaction are expressed in a minimal basis of spherically averaged atomic orbitals. All necessary integrals are either precalculated or approximated without resorting to empirical data. The method is validated against first principles results for benzene and anthracene, where good agreement is found for levels close to the frontier orbitals. Further, the size dependence of the quasiparticle gap is studied for conformers of the polyacenes ($C_{4n+2}H_{2n+4}$) up to n = 30.Comment: 10 pages, 5 eps figures submitted to Phys. Rev.

Esophagogastric dissociation versus fundoplication: Which is best for severely neurologically impaired children?

Purpose: Neurologically impaired children (NIC) often have swallowing difficulties, severe gastroesophageal reflux, recurrent respiratory infections, and malnutrition. Bianchi pro posed esophagogastric dissociation (EGD) as an alternative to fundoplication and gastrostomy. The authors compared these 2 approaches.Methods: Twenty-nine consecutive symptomatic NIC refractory to medical therapy were enrolled in a prospective study and divided into 2 groups: A (n = 12), NIC who underwent fundoplication and gastrostomy; B (n = 14), NIC who underwent EGD. Three were excluded because of previous fundoplication, Anthropometric (percentage of the 50th percentile/ age of healthy children) and biochemical parameters, respiratory infections per year, hospitalization (days per year), feeding time (minutes), and "quality of life" (parental psychological questionnaire, range 0 to 60), were analyzed (t test and Mann-Whitney test) preoperatively and 1 year postoperatively. Complications were recorded.Results: Compared with group A, group B presented a statistically significant increase of all anthropometric and nearly all biochemical parameters with a statistical difference in terms of respiratory infections, hospital stay, feeding time, and psychological questionnaire. In group A, 2 bowel obstructions, 1 tight fundoplication, 1 dumping syndrome, and 3 failures of fundoplication occurred. Group B presented 1 anastomotic stricture, 1 paraesophageal hernia, and 1 bowel obstruction.Conclusions: Compared with fundoplication and gastrostomy, EGD offered better nutritional rehabilitation, reduction in respiratory infections, and improved quality of life. EGD can be rightfully chosen as a primary procedure. J Pediatr Surg 36:677-680. Copyright (C) 2001 by W.B. Saunders Company

Photoluminescence efficiency of Substituted Quaterthiophene Crystals

none8The photoluminescence (PL) efficiency of substituted α-conjugated quaterthiophene crystals shows marked differences depending on crystal packing and molecular geometry. This effect is studied by evaluating the role of the intermolecular interactions and the effects of the single molecule conformation on the intersystem crossing (ISC) rate. The comparison of these calculations with absolute quantum efficiency measurements and with the experimental temperature dependence of the PL decay time, indicates that the differences in PL efficiency are not inherent to crystal packing effects but they are determined by the ISC rate.G.GIGLI; F.DELLA SALA; M.LOMASCOLO; M.ANNI; G.BARBARELLA; A.DI CARLO; P.LUGLI; R. CINGOLANIGigli, Giuseppe; F., DELLA SALA; M., Lomascolo; Anni, Marco; G., Barbarella; A., DI CARLO; P., Lugli; Cingolani, Robert

Cosmic-ray interactions with the Sun

The solar disk is a bright gamma-ray source in the sky. The interactions of cosmic rays with the solar atmosphere produce secondary particles which can reach the Earth. In this work we present a comprehensive calculation of the yields of secondary particles such as gamma-rays, electrons, positrons, neutrons and neutrinos, performed with the FLUKA code. We also estimate the intensity at the Sun and the fluxes at the Earth of these secondary particles by folding their yields with the intensities of cosmic rays impinging on the solar surface. The results are sensitive to the assumptions on the magnetic field near the Sun and to the cosmic-ray transport in the magnetic field in the inner solar system