1,755 research outputs found
Geometrical Phase Transition on WO Surface
A topographical study on an ensemble of height profiles obtained from atomic
force microscopy techniques on various independently grown samples of tungsten
oxide WO is presented by using ideas from percolation theory. We find that
a continuous 'geometrical' phase transition occurs at a certain critical
level-height below which an infinite island appears. By using the
finite-size scaling analysis of three independent percolation observables i.e.,
percolation probability, percolation strength and the mean island-size, we
compute some critical exponents which characterize the transition. Our results
are compatible with those of long-range correlated percolation. This method can
be generalized to a topographical classification of rough surface models.Comment: 3 pages, 4 figures, to appear in Applied Physics Letters (2010
Anisotropic hybrid excitation modes in monolayer and double-layer phosphorene on polar substrates
We investigate the anisotropic hybrid plasmon-SO phonon dispersion relations
in monolayer and double-layer phosphorene systems located on the polar
substrates, such as SiO2, h-BN and Al2O3. We calculate these hybrid modes with
using the dynamical dielectric function in the RPA by considering the
electron-electron interaction and long-range electric field generated by the
substrate SO phonons via Frohlich interaction. In the long-wavelength limit, we
obtain some analytical expressions for the hybrid plasmon-SO phonon dispersion
relations which represent the behavior of these modes akin to the modes
obtaining from the loss function. Our results indicate a strong anisotropy in
plasmon-SO phonon modes, whereas they are stronger along the light-mass
direction in our heterostructures. Furthermore, we find that the type of
substrate has a significant effect on the dispersion relations of the coupled
modes. Also, by tuning the misalignment and separation between layers in
double-layer phosphorene on polar substrates, we can engineer the hybrid modes.Comment: 10 pages, 7 figure
A new formalism for the estimation of the CP-violation parameters
In this paper, we use the time super-operator formalism in the 2-level
Friedrichs model \cite{fried} to obtain a phenomenological model of mesons
decay. Our approach provides a fairly good estimation of the CP symmetry
violation parameter in the case of K, B and D mesons. We also propose a crucial
test aimed at discriminating between the standard approach and the time
super-operator approach developed throughout the paper
Gold nanoparticle and mean inactivation dose of human intestinal colon cancer HT-29 cells
Background: Mean inactivation dose is a useful radiobiological parameter for the comparison of human cell survival curves. Objectives: Given the importance and accuracy of these parameters, in the present study, the radio sensitivity enhancement of colon cancer (HT-29) cells in the presence of gold nanoparticles (GNPs) were studied using the mean inactivation dose (MID). Materials and Methods: Naked-GNPs with 50 nm diameters were incubated with HT-29 cells. The cytotoxicity and uptake of these particles on HT-29 cells were assessed. After determining the optimum GNPs concentration, the cells were incubated with gold nanoparticle for 24 hours. The change in the MID value as well as the radio sensitization enhancement under irradiation with 9 MV X-ray beams in the presence of GNPs were evaluated by multiple (3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium)MTS assay. Results: Cell survival in the presence of GNPs was more than 90% and the maximum uptake of GNPs was observed at 60 μM of gold nanoparticles. In contrast, in the presence of GNPs combined with radiation, cell survival and MID value significantly decreased, so that the radio sensitization enhancement was 1.4. Conclusions: Due to the significant reduction in the mean inactivation dose of colon cancer cells in the presence of gold nanoparticles, it seems that GNPs are suitable options to achieve a new approach in order to improve radiotherapy efficiency without increasing the prescribed radiation dose
Matrix product state comparison of the numerical renormalization group and the variational formulation of the density matrix renormalization group
Wilson's numerical renormalization group (NRG) method for solving quantum
impurity models yields a set of energy eigenstates that have the form of matrix
product states (MPS). White's density matrix renormalization group (DMRG) for
treating quantum lattice problems can likewise be reformulated in terms of MPS.
Thus, the latter constitute a common algebraic structure for both approaches.
We exploit this fact to compare the NRG approach for the single-impurity
Anderson model to a variational matrix product state approach (VMPS),
equivalent to single-site DMRG. For the latter, we use an ``unfolded'' Wilson
chain, which brings about a significant reduction in numerical costs compared
to those of NRG. We show that all NRG eigenstates (kept and discarded) can be
reproduced using VMPS, and compare the difference in truncation criteria, sharp
vs. smooth in energy space, of the two approaches. Finally, we demonstrate that
NRG results can be improved upon systematically by performing a variational
optimization in the space of variational matrix product states, using the
states produced by NRG as input.Comment: 19 pages, 14 figure
Prevention of Acoustic Trauma-Induced Hearing Loss by N-acetylcysteine Administration in Rabbits
Background: Acoustic trauma is an injury to the hearing mechanisms in the inner ear due to excessive noise. This injury is the most prevalent cause of sensorineural hearing loss in humans, especially from occupational exposure. Previous studies have shown the essential role of free radical formation in the inner ear hearing loss caused by acoustic trauma.
Objectives: This study was performed to determine the effect of N-acetylcysteine (NAC) administration for reducing acute acoustic trauma in rabbits.
Materials and Methods: Twenty four rabbits were assigned to four groups including: control, noise plus saline, noise plus NAC administration (325 mg/kg body weight by intraperitoneal injection (IP), three days before exposure to noise and three days after noise exposure), and NAC alone. Auditory brain stem response (ABR) threshold was measured before exposure and one hour and 14 days after exposure.
Results: The saline plus noise group had on average a 49 decibel (dB) temporary threshold shift (TTS) and 23.9 dB permanent threshold shift (PTS) at the studied frequencies, while rabbits in the NAC administration plus noise group had a 31.5 dB TTS and 10.7 dB PTS averaged across the frequencies.
Conclusions: Administration of NAC can provide appropriate protection against acoustic trauma-induced hearing loss in rabbits at all studied frequencies
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