8,175 research outputs found
Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy
The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced
Painlev\'{e} analysis of the coupled nonlinear Schr\"{o}dinger equation for polarized optical waves in an isotropic medium
Using the Painlev\'{e} analysis, we investigate the integrability properties
of a system of two coupled nonlinear Schr\"{o}dinger equations that describe
the propagation of orthogonally polarized optical waves in an isotropic medium.
Besides the well-known integrable vector nonlinear Schr\"{o}dinger equation, we
show that there exist a new set of equations passing the Painlev\'{e} test
where the self and cross phase modulational terms are of different magnitude.
We introduce the Hirota bilinearization and the B\"{a}cklund transformation to
obtain soliton solutions and prove integrability by making a change of
variables. The conditions on the third-order susceptibility tensor imposed by these new integrable equations are explained
Back reaction, covariant anomaly and effective action
In the presence of back reaction, we first produce the one-loop corrections
for the event horizon and Hawking temperature of the Reissner-Nordstr\"om black
hole. Then, based on the covariant anomaly cancelation method and the effective
action technique, the modified expressions for the fluxes of gauge current and
energy momentum tensor, due to the effect of back reaction, are obtained. The
results are consistent with the Hawking fluxes of a (1+1)-dimensional blackbody
at the temperature with quantum corrections, thus confirming the robustness of
the covariant anomaly cancelation method and the effective action technique for
black holes with back reaction.Comment: 17 page
Protective Effect of (-)-Epigallocatechin Gallate against Photo-Damage Induced by Ultraviolet A in Human Skin Fibroblasts
Purpose: To investigate the photoprotective effect of (-)-epigallocatechin gallate (EGCG), one of tea catechins, on human skin fibroblast (HSF) irradiated by ultraviolet A.Methods: HSF cells were incubated in serum-free Dulbecco's Modified Eagle's Medium (DMEM) with or without EGCG for 2 h, and then irradiated by UV A. Blank (control) was incubated in DMEM without EGCG and UV A-irradiation. Cell viability was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyltetrazolium bromide (MTT) method. Protein concentration of the samples was determined using a PA102 Bradford protein assay kit. Malondialdehyde (MDA), glutathione peroxidase (GSH-Px) and superoxide anion radicals were determined using MDA assay kit, GSH-Px assay kit and superoxide anion radical assay kit, respectively.Results: HSF viability decreased with dosage of UV A irradiation with 50 % lethal dose (LD50)of 9 J/cm2. Pre-incubation of HSF in 10 μg/mL EGCG aqueous solution for 2 h before exposure to UV A alleviated the suppressive effect of UV A on HSF. Compared to UVA irradiation alone, HSF viability and GSH-Px activity in the EGCG pretreatment increased by 18.3 and 103.4 %, accompanying decrease in level of superoxide anion radicals and MDA by 44.6 and 16.6 %, respectively.Conclusion: EGCG alleviates UV A-induced HSF photo-damage through relieving oxidative stress by increasing activity of GSH-Px and scavenging capacity of superoxide anion radical.Keywords: Irradiation, Catechins, Photoaging, Photoprotection, Malondialdehyde, Glutathione peroxidase, Superoxide anion radica
Anomalies and Hawking radiation from the Reissner-Nordstr\"om black hole with a global monopole
We extend the work by S. Iso, H. Umetsu and F. Wilczek [Phys. Rev. Lett. 96
(2006) 151302] to derive the Hawking flux via gauge and gravitational anomalies
of a most general two-dimensional non-extremal black hole space-time with the
determinant of its diagonal metric differing from the unity () and use it to investigate Hawking radiation from the Reissner-Nordstrom
black hole with a global monopole by requiring the cancellation of anomalies at
the horizon. It is shown that the compensating energy momentum and gauge fluxes
required to cancel gravitational and gauge anomalies at the horizon are
precisely equivalent to the -dimensional thermal fluxes associated with
Hawking radiation emanating from the horizon at the Hawking temperature. These
fluxes are universally determined by the value of anomalies at the horizon.Comment: 18 pages, 0 figure. 1 footnote and 4 new reference adde
Fermions tunnelling from the charged dilatonic black holes
Kerner and Mann's recent work shows that, for an uncharged and non-rotating
black hole, its Hawking temperature can be exactly derived by fermions
tunnelling from its horizons. In this paper, our main work is to improve the
analysis to deal with charged fermion tunnelling from the general dilatonic
black holes, specifically including the charged, spherically symmetric
dilatonic black hole, the rotating Einstein-Maxwell-Dilaton-Axion (EMDA) black
hole and the rotating Kaluza-Klein (KK) black hole. As a result, the correct
Hawking temperatures are well recovered by charged fermions tunnelling from
these black holes.Comment: 16 pages, revised version to appear in Class. Quant. Gra
Exploring the Thermodynamics of a Universal Fermi Gas
From sand piles to electrons in metals, one of the greatest challenges in
modern physics is to understand the behavior of an ensemble of strongly
interacting particles. A class of quantum many-body systems such as neutron
matter and cold Fermi gases share the same universal thermodynamic properties
when interactions reach the maximum effective value allowed by quantum
mechanics, the so-called unitary limit [1,2]. It is then possible to simulate
some astrophysical phenomena inside the highly controlled environment of an
atomic physics laboratory. Previous work on the thermodynamics of a
two-component Fermi gas led to thermodynamic quantities averaged over the trap
[3-5], making it difficult to compare with many-body theories developed for
uniform gases. Here we develop a general method that provides for the first
time the equation of state of a uniform gas, as well as a detailed comparison
with existing theories [6,14]. The precision of our equation of state leads to
new physical insights on the unitary gas. For the unpolarized gas, we prove
that the low-temperature thermodynamics of the strongly interacting normal
phase is well described by Fermi liquid theory and we localize the superfluid
transition. For a spin-polarized system, our equation of state at zero
temperature has a 2% accuracy and it extends the work of [15] on the phase
diagram to a new regime of precision. We show in particular that, despite
strong correlations, the normal phase behaves as a mixture of two ideal gases:
a Fermi gas of bare majority atoms and a non-interacting gas of dressed
quasi-particles, the fermionic polarons [10,16-18].Comment: 8 pages, 5 figure
Matched Pulse Propagation in a Three-Level System
The B\"{a}cklund transformation for the three-level Maxwell-Bloch equation is
presented in the matrix potential formalism. By applying the B\"{a}cklund
transformation to a constant electric field background, we obtain a general
solution for matched pulses (a pair of solitary waves) which can emit or absorb
a light velocity solitary pulse but otherwise propagate with their shapes
invariant. In the special case, this solution describes a steady state pulse
without emission or absorption, and becomes the matched pulse solution recently
obtained by Hioe and Grobe. A nonlinear superposition rule is derived from the
B\"{a}cklund transformation and used for the explicit construction of two
solitons as well as nonabelian breathers. Various new features of these
solutions are addressed. In particular, we analyze in detail the scattering of
"invertons", a specific pair of different wavelength solitons one of which
moving with the velocity of light. Unlike the usual case of soliton scattering,
the broader inverton changes its sign through the scattering. Surprisingly, the
light velocity inverton receives time advance through the scattering thereby
moving faster than light, which however does not violate causality.Comment: 20 pages, Latex, 12 eps figure files some comments and references are
added. postscript file with 12 figures can be obtained at
http://photon.kyunghee.ac.kr/~qhpark
REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture
Reflective electro-absorption modulation-intensity modulators (REAM-IMs) are utilized, for the first time, to experimentally demonstrate colorless ONUs in single-fiber-based, bidirectional, intensity-modulation and direct-detection (IMDD), optical OFDM PONs (OOFDM-PONs) incorporating 25km SSMFs and OLT-side-seeded CW optical signals. The colorlessness of the REAM-IMs is characterized, based on which optimum REAM-IM operating conditions are identified. In the aforementioned PON architecture, 10Gb/s colorless upstream transmissions of end-to-end realtime OOFDM signals are successfully achieved for various wavelengths within the entire C-band. Over such a wavelength window, corresponding minimum received optical powers at the FEC limit vary in a range as small as <0.5dB. In addition, experimental measurements also indicate that Rayleigh backscattering imposes a 2.8dB optical power penalty on the 10Gb/s over 25km upstream OOFDM signal transmission. Furthermore, making use of on-line adaptive bit and power loading, a linear trade-off between aggregated signal line rate and optical power budget is observed, which shows that, for the present PON system, a 10% reduction in signal line rate can improve the optical power budget by 2.6dB. © 2012 Optical Society of America
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