2,223 research outputs found
-AlN-Mg(OH) vdW Bilayer Heterostructure: Tuning the excitonic characteristics
Motivated by recent studies that reported the successful synthesis of
monolayer Mg(OH) [Suslu \textit{et al.}, Sci. Rep. \textbf{6}, 20525
(2016)] and hexagonal (\textit{h}-)AlN [Tsipas \textit{et al}., Appl. Phys.
Lett. \textbf{103}, 251605 (2013)], we investigate structural, electronic, and
optical properties of vertically stacked -AlN and Mg(OH), through
\textit{ab initio} density-functional theory (DFT), many-body quasi-particle
calculations within the GW approximation, and the Bethe-Salpeter equation
(BSE). It is obtained that the bilayer heterostructure prefers the
stacking having direct band gap at the with Type-II band
alignment in which the valance band maximum and conduction band minimum
originate from different layer. Regarding the optical properties, the imaginary
part of the dielectric function of the individual layers and hetero-bilayer are
investigated. The hetero-bilayer possesses excitonic peaks which appear only
after the construction of the hetero-bilayer. The lowest three exciton peaks
are detailedly analyzed by means of band decomposed charge density and the
oscillator strength. Furthermore, the wave function calculation shows that the
first peak of the hetero-bilayer originates from spatially indirect exciton
where the electron and hole localized at -AlN and Mg(OH),
respectively, which is important for the light harvesting applications.Comment: Accepted by Physical Review
Half-metallic properties of atomic chains of carbon-transition metal compounds
We found that magnetic ground state of one-dimensional atomic chains of
carbon-transition metal compounds exhibit half-metallic properties. They are
semiconductors for one spin-direction, but show metallic properties for the
opposite direction. The spins are fully polarized at the Fermi level and net
magnetic moment per unit cell is an integer multiple of Bohr magneton. The
spin-dependent electronic structure can be engineered by changing the number of
carbon and type of transition metal atoms. These chains, which are stable even
at high temperature and some of which keep their spin-dependent electronic
properties even under moderate axial strain, hold the promise of potential
applications in nanospintronics.Comment: 11 pages, 3 figures, 1 table
Strange Particles in Dense Matter and Kaon Condensates
We discuss the role of strangeness in dense matter and especially in neutron
stars. The early (in density) introduction of hyperons found in many
calculations is probably delayed by the decrease in vector mean field acting on
the neutron. The decrease results from both conventional many-body rescattering
effects and from the movement towards asymptotic freedom at high densities.
Subthreshold -meson production by the KaoS collaboration at GSI shows that
the -mass must be substantially lowered, by 200 MeV at . It is shown that explicit chiral symmetry breaking through the kaon
mass may be responsible for -nucleon and -nucleon scalar
attraction being weaker than obtained by simple quark scaling. The normal mode
of the strangeness minus, charge , excitation is constructed as a linear
combination of -meson and , neutron-hole state. Except for zero
momentum, where the terms are unmixed the "kaesobar" is a linear combination of
these two components.Comment: 10 pages, 8 postscript figures, Talk given at the International
Conference on Hypernuclear and Strange Particle Physics (HYP97), Brookhaven
Nat'l Lab., USA, October 13-18, 1997, to be published in Nucl. Phys.
AlN-based piezoelectric micropower generator for low ambient vibration energy harvesting
AbstractIn this paper a resonant micropower generator based on the transverse piezoelectric effect is presented. The generator consists of a large silicon mass attached to an polysilicon cantilever covered with an AlN thinfilm as piezoelectric material. To maximize the power density of the generator, a parametric study by means of analytical modeling and FEM simulation has been performed. Different optimized generators with resonance frequencies in the range from 100Hz up to 1kHz have been designed and fabricated, using dedicated MEMS technology processes. First unpackaged prototypes showed a quality factor of about 500 under atmospheric pressure and were able to generate an electrical output power of up to 1.9μW at an external acceleration of 1.6 m/s2
Aminolevulinic Acid mediated Photodynamic Therapy of Human Meningioma: an in vitro Study on Primary Cell Lines
Objective: Five-aminolevulinic acid (5-ALA)-induced porphyrins in malignant gliomas are potent photosensitizers. Promising results of ALA-PDT (photodynamic therapy) in recurrent glioblastomas have been published. Recently, 5-ALA-induced fluorescence was studied in meningioma surgery. Here, we present an experimental study of ALA-PDT in an in vitro model of primary meningioma cell lines. Methods: We processed native tumor material obtained intra-operatively within 24 h for cell culture. Epithelial membrane antigen (EMA) immunohistochemistry was performed after the first passage to confirm that cells were meningioma cells. For 5-ALA-PDT treatment, about 5000 cells per well were seeded in 20 wells of a blank 96-well plate. Each block of 4 wells was inoculated with 150 µL of 0, 25, 50 and 100 µg/mL 5-ALA solutions; one block was used as negative control without 5-ALA and without PDT. Following incubation for 3 h PDT was performed using a laser (635 nm, 18.75 J/cm2). The therapeutic response was analyzed by the water soluble tetrazolium salt (WST-1) cell viability assay 90 min after PDT. Results: 5-ALA-PDT was performed in 14 primary meningioma cell lines. EMA expression was verified in 10 primary cell cultures. The remaining 4 were EMA negative and PDT was without any effect in these cultures. All 10 EMA-positive cell lines showed a significant and dose-dependent decrease in viability rate (p < 0.001). Cell survival at 5-ALA concentrations of 12.5, 25, 50 and 100 μg/mL was 96.5% ± 7.6%, 67.9% ± 29.9%, 24.0% ± 16.7% and 13.8% ± 7.5%, respectively. For the negative controls (no 5-ALA/PDT and ALA/no PDT), the viability rates were 101.72% ± 3.5% and 100.17% ± 3.6%, respectively. The LD50 for 5-ALA was estimated between 25 and 50 µg/mL. Conclusion: This study reveals dose-dependent cytotoxic effects of 5-ALA-PDT on primary cell lines of meningiomas. Either 5-ALA or PDT alone did not affect cell survival. Further efforts are necessary to study the potential therapeutic effects of 5-ALA-PDT in vivo
Determination of structural parameters characterizing thin films by optical methods: A comparison between scanning angle reflectometry and optical waveguide lightmode spectroscopy
International audienceWe present a comparative study of the structural parameters characterizing thin macromolecular adsorbed films that are obtained from two optical techniques: optical waveguide lightmode spectroscopy ͑OWLS͒ and scanning angle reflectometry ͑SAR͒. We use polyelectrolyte multilayers and polyelectrolyte multilayers/protein films to perform this study. The comparison between the information obtained with the two methods is possible because the buildup of the polyelectrolyte multilayers is known to become substrate independent after the deposition of the first few polyelectrolyte layers. The analysis of the optical data requires usually to postulate a refractive index profile for the interface. Two profiles have been used: the homogeneous and isotropic monolayer and the bilayer profiles. When the refractive index profile of an adsorbed film is well approximated by a homogeneous and isotropic monolayer, as shown by using an analysis of the deposited films in terms of optical invariants, the two optical techniques lead to similar values for the film thickness and the optical mass. The situation is more complex in the case of the multilayers/protein films for which the calculated parameters can strongly depend upon the refractive index profile that is postulated to analyze the optical data. Whereas the optical mass and, to a lesser extent, the thickness seem fairly model independent for OWLS, they appear to be extremely sensitive to the model for SAR. For proteins deposited on top of the polyelectrolyte film, optical mass and protein thickness were found to be comparable when determined by OWLS and by SAR using the bilayer model. The data analysis of the SAR curves with the monolayer model leads to much larger and even physically unreasonable film thicknesses and optical masses. This was particularly noticeable for proteins having a large size ͑human serum albumin and fibrinogen͒, whereas both models lead to similar results for small sized proteins. By means of the different refractive index profiles, we show that great care must be taken in the physicochemical interpretation of the structural parameters determined by these optical techniques
Nonextensive statistical effects in the hadron to quark-gluon phase transition
We investigate the relativistic equation of state of hadronic matter and
quark-gluon plasma at finite temperature and baryon density in the framework of
the nonextensive statistical mechanics, characterized by power-law quantum
distributions. We study the phase transition from hadronic matter to
quark-gluon plasma by requiring the Gibbs conditions on the global conservation
of baryon number and electric charge fraction. We show that nonextensive
statistical effects play a crucial role in the equation of state and in the
formation of mixed phase also for small deviations from the standard
Boltzmann-Gibbs statistics.Comment: 13 pages, 10 figure
Is a soft nuclear equation of state extracted from heavy-ion data incompatible with pulsar data?
We discuss the recent constraints on the nuclear equation of state from
pulsar mass measurements and from subthreshold production of kaons in heavy-ion
collisions. While recent pulsar data points towards a hard equation of state,
the analysis of the heavy-ion data allows only for soft equations of state. We
resolve the apparent contradiction by considering the different density regimes
probed. We argue that future measurements of global properties of low-mass
pulsars can serve as an excellent cross-check to heavy-ion data.Comment: 8 pages, 1 figure, contribution to the proceedings of the
international conference on 'Nuclear Physics in Astrophysics III', Dresden,
Germany, March 26-31, 2007, minor corrections to match published version, JPG
in pres
Theoretical and numerical studies of chemisorption on a line with precursor layer diffusion
We consider a model for random deposition of monomers on a line with
extrinsic precursor states. As the adsorbate coverage increases, the system
develops non-trivial correlations due to the diffusion mediated deposition
mechanism. In a numeric simulation, we study various quantities describing the
evolution of the island structure. We propose a simple, self-consistent theory
which incorporates pair correlations. The results for the correlations, island
density number, average island size and probabilities of island nucleation,
growth and coagulation show good agreement with the simulation data.Comment: 17 pages(LaTeX), 11 figures(1 PS file, uuencoded), submmited to Phys.
Rev.
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