788 research outputs found
Spacelike intersection curve of three spacelike hypersurfaces in
In this paper, we compute the Frenet vectors and the curvatures of the spacelike intersection curve of three spacelike hypersurfaces given by their parametric equations in four-dimensional Minkowski space
Pollen characteristics and in vitro pollen germination of Cedrus libani A. Rich.
This study aims to determine the germination characteristics, pollen tube developments, effects of germination media and temperature and incubation durations of the pollens obtained from the four clones (11342, 11344, 11345 and 11351) of Cedrus libani A. Rich. (Lebanon Cedrus) obtained from clonalseed orchard (with national registration no: Eskisehir 117) between 2004 and 2006 as well as of those taken from clone no: 11351 in 2004. They were stored at 3°C for 13 months till they were investigated experimentally. MS medium was preferred for pollen germination for its relative superiority. Three-day incubation period at 33°C temperature, in dark was applied along with the MS medium. The highest germination rate in MS medium was achieved in clone no.11342 with 84.77% among the pollen samplesof 2005. On the other hand the germination rate of the pollens taken from clone no: 11351 was determined as 49.95%
Chemical abundances of the metal-poor horizontal-branch stars CS 22186-005 and CS 30344-033
We report on a chemical-abundance analysis of two very metal-poor
horizontal-branch stars in the Milky Way halo: CS 22186-005 ([Fe/H]=-2.70) and
CS 30344-033 ([Fe/H]=-2.90). The analysis is based on high-resolution spectra
obtained at ESO, with the spectrographs HARPS at the 3.6 m telescope, and UVES
at the VLT. We adopted one-dimensional, plane-parallel model atmospheres
assuming local thermodynamic equilibrium. We derived elemental abundances for
13 elements for CS 22186-005 and 14 elements for CS 30344-033. This study is
the first abundance analysis of CS 30344-033. CS 22186-005 has been analyzed
previously, but we report here the first measurement of nickel (Ni; Z = 28) for
this star, based on twenty-two NiI lines ([Ni/Fe]=-0.210.02); the
measurement is significantly below the mean found for most metal-poor stars.
Differences of up to 0.5 dex in [Ni/Fe] ratios were determined by different
authors for the same type of stars in the literature, which means that it is
not yet possible to conclude that there is a real intrinsic scatter in the
[Ni/Fe] ratios. For the other elements for which we obtained estimates, the
abundance patterns in these two stars match the Galactic trends defined by
giant and turnoff stars well. This confirms the value of horizontal-branch
stars as tracers of the chemical properties of stellar populations in the
Galaxy. Our radial velocities measurements for CS 22186-005 differ from
previously published measurements by more than the expected statistical errors.
More measurements of the radial velocity of this star are encouraged to confirm
or refute its radial velocity variability
Metal–semiconductor–metal photodetector on as-deposited TiO2 thin films on sapphire substrate
Cataloged from PDF version of article.TiO2 thin films are prepared on c-plane sapphire substrates by the RF magnetron sputtering method. The performance of the Pt contact metal–semiconductor–metal (MSM) photodetector fabricated on as-deposited films is studied. The dark current density and the responsivity obtained were 1.57 × 10−9 A/cm2 at 5 V bias and 1.73 A/W at 50 V bias, respectively. Breakdown is not observed up to 50 V bias. Rise and fall times for the photocurrent were 7 and 3 s, respectively. Our results show that high quality MSM photodetectors can be fabricated without high temperature and complicated fabrication steps
Low dark current and high speed ZnO metal–semiconductor–metal photodetector on SiO2/Si substrate
Cataloged from PDF version of article.ZnO thin films are deposited by radio-frequency magnetron sputtering on thermally grown SiO2 on Si substrates. Pt/Au contacts are fabricated by standard photolithography and lift-off in order to form a metal-semiconductor-metal (MSM) photodetector. The dark current of the photodetector is measured as 1 pA at 100V bias, corresponding to 100 pA/cm(2) current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100V bias. The rise and fall times for the photocurrent are measured as 22 ps and 8 ns, respectively, which are the lowest values to date. Scanning electron microscope image shows high aspect ratio and dense grains indicating high surface area. Low dark current density and high speed response are attributed to high number of recombination centers due to film morphology, deducing from photoluminescence measurements. These results show that as deposited ZnO thin film MSM photodetectors can be used for the applications needed for low light level detection and fast operation. (C) 2014 AIP Publishing LLC
Metalorganic chemical vapor deposition growth and thermal stability of the AllNN/GaN high electron mobility transistor structure
Cataloged from PDF version of article.The AlxIn1-xN barrier high electron mobility transistor (HEMT) structure has been optimized with varied barrier composition and thickness grown by metalorganic chemical vapor deposition. After optimization, a transistor structure comprising a 7 nm thick nearly lattice-matched Al0.83In0.17 N barrier exhibits a sheet electron density of 2.0 x 10(13) cm(-2) with a high electron mobility of 1540 cm(2) V-1 s(-1). AnAl(0.83)In(0.17)N barrier HEMT device with 1 mu m gate length provides a current density of 1.0 A mm(-1) at V-GS = 0 V and an extrinsic transconductance of 242 mS mm(-1), which are remarkably improved compared to that of a conventional Al0.3Ga0.7N barrier HEMT. To investigate the thermal stability of the HEMT epi-structures, post-growth annealing experiments up to 800 degrees C have been applied to Al0.83In0.17N and Al0.3Ga0.7N barrier heterostructures. As expected, the electrical properties of an Al0.83In0.17N barrier HEMT structure showed less stability than that of an Al0.3Ga0.7N barrier HEMT to the thermal annealing. The structural properties of Al0.83In0.17N/GaN also showed more evidence for decomposition than that of the Al0.3Ga0.7N/GaN structure after 800 degrees C post-annealing
Animal Models for Limbal Stem Cell Deficiency: A Critical Narrative Literature Review
\ua9 2024, The Author(s). This literature review will provide a critical narrative overview of the highlights and potential pitfalls of the reported animal models for limbal stem cell deficiency (LSCD) and will identify the neglected aspects of this research area. There exists significant heterogeneity in the literature regarding the methodology used to create the model and the predefined duration after the insult when the model is supposedly fully fit for evaluations and/or for testing various therapeutic interventions. The literature is also replete with examples wherein the implementation of a specific model varies significantly across different studies. For example, the concentration of the chemical, as well as its duration and technique of exposure in a chemically induced LSCD model, has a great impact not only on the validity of the model but also on the severity of the complications. Furthermore, while some models induce a full-blown clinical picture of total LSCD, some are hindered by their ability to yield only partial LSCD. Another aspect to consider is the nature of the damage induced by a specific method. As thermal methods cause more stromal scarring, they may be better suited for assessing the anti-fibrotic properties of a particular treatment. On the other hand, since chemical burns cause more neovascularisation, they provide the opportunity to tap into the potential treatments for anti-neovascularisation. The animal species (i.e., rats, mice, rabbits, etc.) is also a crucial factor in the validity of the model and its potential for clinical translation, with each animal having its unique set of advantages and disadvantages. This review will also elaborate on other overlooked aspects, such as the anaesthetic(s) used during experiments, the gender of the animals, care after LSCD induction, and model validation. The review will conclude by providing future perspectives and suggestions for further developments in this rather important area of research
Dynamical transition, hydrophobic interface, and the temperature dependence of electrostatic fluctuations in proteins
Molecular dynamics simulations have revealed a dramatic increase, with
increasing temperature, of the amplitude of electrostatic fluctuations caused
by water at the active site of metalloprotein plastocyanin. The increased
breadth of electrostatic fluctuations, expressed in terms of the reorganization
energy of changing the redox state of the protein, is related to the formation
of the hydrophobic protein/water interface allowing large-amplitude collective
fluctuations of the water density in the protein's first solvation shell. On
the top of the monotonic increase of the reorganization energy with increasing
temperature, we have observed a spike at 220 K also accompanied by a
significant slowing of the exponential collective Stokes shift dynamics. In
contrast to the local density fluctuations of the hydration-shell waters, these
spikes might be related to the global property of the water solvent crossing
the Widom line.Comment: 9 pages, 8 figure
Screening of medicinal plant extracts as novel DNA gyrase inhibitors
Bioactivities of a number of medicinal plants; Alkanna tinctoria (L.) Tausch, Alnus glutinosa (L.) Gaertn., Calamintha nepeta Willk. and C. nepeta, Centaurea iberica Trevir. ex Spreng., Citrus paradisi Macfad., C. paradisi, Citrus sinensis (L.) Osbeck, Colutea cilicica Boiss. & Balansa, Cotinus coggygria Scop., Cuscuta arvensis Beyr. ex Engelm., Equisetum palustre L., Lapsana communis L., Laurus nobilis L., Olea europea L., Plantago major L., Rhus coriaria L, Salvia verticillata L., Sambucus ebulus L., Sedum acre L, Thymus capitatus (L.) Hoffmanns. & Link, T. capitatus, Thymbra spicata L., T. spicata (n: 20), which are used for the prevention and treatment of diverse diseases, were investigated. The antimicrobial activities of extracts were evaluated using broth microdilution assay. The cytotoxicities of extracts were investigated on HeLa cell line by MTT assay. Statistical analysis was performed using GraphPad Prism (5.0). The effects of the extracts, which have the highest antimicrobial activity, on the Escherichia coli and Staphylococcus aureus DNA gyrase gene expression were determined by using quantitative reverse transcription polymerase chain reaction (qRT-PCR). The MICs (µg/ml) of extracts were determined as 32-64, 2-128, 8-128,1-128, 4-128 against Gram-positive, Gram-negative bacteria, yeasts, dermatophytes, and Mycobacterium spp., respectively. No cytotoxicity has been observed in plant extracts tested. DNA gyrase activity was determined for T. capitatus-SFE (128 µg/mL) and L. nobilis-Hx (128 µg/mL) extracts according to the inhibition of DNA gyrase gene expression. Overall, T. capitatus-SFE and L. nobilis-Hx are good candidates for further antimicrobial studies.
Theory of biopolymer stretching at high forces
We provide a unified theory for the high force elasticity of biopolymers
solely in terms of the persistence length, , and the monomer spacing,
. When the force f>\fh \sim k_BT\xi_p/a^2 the biopolymers behave as Freely
Jointed Chains (FJCs) while in the range \fl \sim k_BT/\xi_p < f < \fh the
Worm-like Chain (WLC) is a better model. We show that can be estimated
from the force extension curve (FEC) at the extension
(normalized by the contour length of the biopolymer). After validating the
theory using simulations, we provide a quantitative analysis of the FECs for a
diverse set of biopolymers (dsDNA, ssRNA, ssDNA, polysaccharides, and
unstructured PEVK domain of titin) for . The success of a specific
polymer model (FJC or WLC) to describe the FEC of a given biopolymer is
naturally explained by the theory. Only by probing the response of biopolymers
over a wide range of forces can the -dependent elasticity be fully
described.Comment: 20 pages, 4 figure
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