1,297 research outputs found
Laser-induced microexplosion confined in a bulk of silica: formation of nanovoids
We report on the nanovoid formation inside synthetic silica, viosil, by single femtosecond pulses of 30–100nJ energy, 800nm wavelength, and 180fs duration. It is demonstrated that the void is formed as a result of shock and rarefaction waves at pulse power much lower than the threshold of self-focusing. The shock-compressed region around the nanovoid is demonstrated to have higher chemical reactivity. This was used to reveal the extent of the shock-compressed region by wet etching. Application potential of nanostructuring of dielectrics is discussed
Modification of refractive index by a single femtosecond pulse confined inside a bulk of a photorefractive crystal
We demonstrate that the interaction of intense femtosecond pulse with photorefractive crystal at conditions close to the optical-breakdown threshold differs drastically from that of long pulse and cw illumination. Our theoretical estimations show that the high number density of excited electrons modifies the dielectric function leading to the transient negative change in the refractive index, Δn/ n0 ∼- 10-2 that vanishes on nanosecond time scale. Moreover, the high-frequency laser field, two orders of magnitude larger than the field of spontaneous polarization, prevents the stationary charge distribution during the pulse. The diffusion and recombination of charge carriers continues over a nanosecond time scale, after the end of the pulse. The main driving force for the current after the pulse is the field of spontaneous polarization in the ferroelectric medium: the current terminates when the field of charge separation balances this field. We show here that the stationary modification of refractive index according to this model is then independent of the polarization of the pump light beam, in agreement with experiments, and saturates at Δn 10-3 in semiquantitative fit to the experimental data
The Wide-Angle Outflow of the Lensed z = 1.51 AGN HS 0810+2554
We present results from X-ray observations of the gravitationally lensed z =
1.51 AGN HS 0810+2554 performed with the Chandra X-ray Observatory and
XMM-Newton. Blueshifted absorption lines are detected in both observations at
rest-frame energies ranging between ~1-12 keV at > 99% confidence. The inferred
velocities of the outflowing components range between ~0.1c and ~0.4c. A strong
emission line at ~6.8 keV accompanied by a significant absorption line at ~7.8
keV is also detected in the Chandra observation. The presence of these lines is
a characteristic feature of a P-Cygni profile supporting the presence of an
expanding outflowing highly ionized iron absorber in this quasar. Modeling of
the P-Cygni profile constrains the covering factor of the wind to be > 0.6,
assuming disk shielding. A disk-reflection component is detected in the
XMM-Newton observation accompanied by blueshifted absorption lines. The
XMM-Newton observation constrains the inclination angle to be < 45 degrees at
90% confidence, assuming the hard excess is due to blurred reflection from the
accretion disk. The detection of an ultrafast and wide-angle wind in an AGN
with intrinsic narrow absorption lines (NALs) would suggest that quasar winds
may couple efficiently with the intergalactic medium and provide significant
feedback if ubiquitous in all NAL and BAL quasars. We estimate the mass-outflow
rate of the absorbers to lie in the range of 1.5 and 3.4 Msolar/yr for the two
observations. We find the fraction of kinetic to electromagnetic luminosity
released by HS 0810+2554 is large (epsilon = 9 (-6,+8)) suggesting that
magnetic driving is likely a significant contributor to the acceleration of
this outflow.Comment: 27 pages, 13 figures, Accepted for publication in Ap
Leading Temperature Corrections to Fermi Liquid Theory in Two Dimensions
We calculate the basic parameters of the Fermi Liquid: the scattering vertex,
the Landau interaction function, the effective mass, and physical
susceptibilities for a model of two-dimensional (2D) fermions with a short
ranged interaction at non-zero temperature. The leading temperature dependences
of the spin components of the scattering vertex, the Landau function, and the
spin susceptibility are found to be linear. T-linear terms in the effective
mass and in the ``charge-sector''- quantities are found to cancel to second
order in the interaction, but the cancellation is argued not to be generic. The
connection with previous studies of the 2D Fermi-Liquid parameters is
discussed.Comment: 4 pages, 1 figur
Laser matter interaction in the bulk of transparent dielectrics: Confined micro-explosion
We present here the experimental and theoretical studies of drastic transformations induced by a single powerful femtosecond laser pulse tightly focused inside a transparent dielectric, that lead to void formation in the bulk. We show that the laser pulse energy absorbed within a volume of less than 1μm3 creates the conditions with pressure and temperature range comparable to that formed by an exploding nuclear bomb. At the laser intensity above 6 × 1012 W/cm2 the material within this volume is rapidly atomized, ionized, and converted into a tiny super-hot cloud of expanding plasma. The expanding plasma generates strong shock and rarefaction waves which result in the formation of a void. Our modelling indicates that unique states of matter can be created using a standard table-top laser in well-controlled laboratory conditions. This state of matter has temperatures 105 K, heating rate up to the 1018 K/s, and pressure more than 100 times the strength of any solid. The laser-affected sites in the bulk were detected ("read") by generation of white continuum using probe femtosecond pulses at much lower laser intensity of 1010 W/cm 2 - 1011 W/cm2. Post-examination of voids with an electron microscope revealed a typical size of the void ranges from 200 to 500 nm. These studies will find application for the design of 3D optical memory devices and for formation of photonic band-gap crystals
Driven transverse shear waves in a strongly coupled dusty plasma
The linear dispersion properties of transverse shear waves in a strongly
coupled dusty plasma are experimentally studied by exciting them in a
controlled manner with a variable frequency external source. The dusty plasma
is maintained in the strongly coupled fluid regime with (1 < Gamma << Gamma_c)
where Gamma is the Coulomb coupling parameter and Gamma_c is the
crystallization limit. A dispersion relation for the transverse waves is
experimentally obtained over a frequency range of 0.1 Hz to 2 Hz and found to
show good agreement with viscoelastic theoretical results.Comment: The manuscripts contains five pages and 6 figure
Quantum criticality around metal-insulator transitions of strongly correlated electrons
Quantum criticality of metal-insulator transitions in correlated electron
systems is shownto belong to an unconventional universality class with
violation of Ginzburg-Landau-Wilson(GLW) scheme formulated for symmetry
breaking transitions. This unconventionality arises from an emergent character
of the quantum critical point, which appears at the marginal point between the
Ising-type symmetry breaking at nonzero temperatures and the topological
transition of the Fermi surface at zero temperature. We show that Hartree-Fock
approximations of an extended Hubbard model on square latticesare capable of
such metal-insulator transitions with unusual criticality under a preexisting
symmetry breaking. The obtained universality is consistent with the scaling
theory formulated for Mott transition and with a number of numerical results
beyond the mean-field level, implying that the preexisting symmetry breaking is
not necessarily required for the emergence of this unconventional universality.
Examinations of fluctuation effects indicate that the obtained critical
exponents remain essentially exact beyond the mean-field level. Detailed
analyses on the criticality, containing diverging carrier density fluctuations
around the marginal quantum critical point, are presented from microscopic
calculations and reveal the nature as quantum critical "opalescence". Analyses
on crossovers between GLW type at nonzero temperature and topological type at
zero temperature show that the critical exponents observed in (V,Cr)2O3 and
kappa-ET-type organic conductor provide us with evidences for the existence of
the present marginal quantum criticality.Comment: 24 pages, 19 figure
HS 1700+6416: the first high redshift non lensed NAL-QSO showing variable high velocity outflows
We present a detailed analysis of the X-ray emission of HS 1700+6416, a high
redshift (z=2.7348), luminous quasar, classified as a Narrow Absorption Line
(NAL) quasar on the basis of its SDSS spectrum. The source has been observed 9
times by Chandra and once by XMM from 2000 to 2007. Long term variability is
clearly detected, between the observations, in the 2-10 keV flux varying by a
factor of three (~3-9x10^-14 erg s^-1 cm^-2) and in the amount of neutral
absorption (Nh < 10^22 cm^-2 in 2000 and 2002 and Nh=4.4+-1.2x10^22 cm^-2 in
2007). Most interestingly, one broad absorption feature is clearly detected at
10.3+-0.7 keV (rest frame) in the 2000 Chandra observation, while two similar
features, at 8.9+-0.4 and at 12.5+-0.7 keV, are visible when the 8 contiguous
Chandra observations of 2007 are stacked together. In the XMM observation of
2002, strongly affected by background flares, there is a hint for a similar
feature at 8.0+-0.3 keV. We interpreted these features as absorption lines from
a high velocity, highly ionized (i.e. Fe XXV, FeXXVI) outflowing gas. In this
scenario, the outflow velocities inferred are in the range v=0.12-0.59c. To
reproduce the observed features, the gas must have high column density
(Nh>3x10^23 cm^-2), high ionization parameter (log(xi)>3.3 erg cm s^-1) and a
large range of velocities (Delta V~10^4 km s^-1). This Absorption Line QSO is
the fourth high-z quasar displaying X-ray signatures of variable, high velocity
outflows, and among these, is the only one non-lensed. A rough estimate of the
minimum kinetic energy carried by the wind of up to 18% L(bol), based on a
biconical geometry of the wind, implies that the amount of energy injected in
the outflow environment is large enough to produce effective mechanical
feedback.Comment: 10 pages, 6 figures. Accepted for publication in Astronomy and
Astrophysic
ParaHaplo 2.0: a program package for haplotype-estimation and haplotype-based whole-genome association study using parallel computing
<p>Abstract</p> <p>Background</p> <p>The use of haplotype-based association tests can improve the power of genome-wide association studies. Since the observed genotypes are unordered pairs of alleles, haplotype phase must be inferred. However, estimating haplotype phase is time consuming. When millions of single-nucleotide polymorphisms (SNPs) are analyzed in genome-wide association study, faster methods for haplotype estimation are required.</p> <p>Methods</p> <p>We developed a program package for parallel computation of haplotype estimation. Our program package, ParaHaplo 2.0, is intended for use in workstation clusters using the Intel Message Passing Interface (MPI). We compared the performance of our algorithm to that of the regular permutation test on both Japanese in Tokyo, Japan and Han Chinese in Beijing, China of the HapMap dataset.</p> <p>Results</p> <p>Parallel version of ParaHaplo 2.0 can estimate haplotypes 100 times faster than a non-parallel version of the ParaHaplo.</p> <p>Conclusion</p> <p>ParaHaplo 2.0 is an invaluable tool for conducting haplotype-based genome-wide association studies (GWAS). The need for fast haplotype estimation using parallel computing will become increasingly important as the data sizes of such projects continue to increase. The executable binaries and program sources of ParaHaplo are available at the following address: <url>http://en.sourceforge.jp/projects/parallelgwas/releases/</url></p
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