7,090 research outputs found
Nonadiabatic generation of coherent phonons
The time-dependent density functional theory (TDDFT) is the leading
computationally feasible theory to treat excitations by strong electromagnetic
fields. Here the theory is applied to coherent optical phonon generation
produced by intense laser pulses. We examine the process in the crystalline
semimetal antimony (Sb), where nonadiabatic coupling is very important. This
material is of particular interest because it exhibits strong phonon coupling
and optical phonons of different symmetries can be observed. The TDDFT is able
to account for a number of qualitative features of the observed coherent
phonons, despite its unsatisfactory performance on reproducing the observed
dielectric functions of Sb. A simple dielectric model for nonadiabatic coherent
phonon generation is also examined and compared with the TDDFT calculations.Comment: 19 pages, 11 figures. This is prepared for a special issue of Journal
of Chemical Physics on the topic of nonadiabatic processe
Influence of aluminum oxide film on thermocompression bonding of gold wire to evaporated aluminum film
The influence of Al surface condition on the thermocompression bonding of Au wires to Al electrodes for integrated electric circuits was studied. Au wires were connected to Al electrodes by nail-head bonding after various Al surface treatments. Bonding was evaluated by measuring the wire pull strength and fraction of the number of failures at Au-Al bonds to the total number of failures. Dependence of the fraction on applied load was derived theoretically with a parameter named critical load to take into consideration the differences in Al surface condition. The relation also held explicately for various surface treatments. Characterization of the Al surface was carried out by electron microscopy for chemical analysis
Cohomogeneity one manifolds and selfmaps of nontrivial degree
We construct natural selfmaps of compact cohomgeneity one manifolds with
finite Weyl group and compute their degrees and Lefschetz numbers. On manifolds
with simple cohomology rings this yields in certain cases relations between the
order of the Weyl group and the Euler characteristic of a principal orbit. We
apply our construction to the compact Lie group SU(3) where we extend identity
and transposition to an infinite family of selfmaps of every odd degree. The
compositions of these selfmaps with the power maps realize all possible degrees
of selfmaps of SU(3).Comment: v2, v3: minor improvement
A New Measurement of the Stellar Mass Density at z~5: Implications for the Sources of Cosmic Reionization
We present a new measurement of the integrated stellar mass per comoving
volume at redshift 5 determined via spectral energy fitting drawn from a sample
of 214 photometrically-selected galaxies with z'<26.5 in the southern GOODS
field. Following procedures introduced by Eyles et al. (2005), we estimate
stellar masses for various sub-samples for which reliable and unconfused
Spitzer IRAC detections are available. A spectroscopic sample of 14 of the most
luminous sources with =4.92 provides a firm lower limit to the stellar mass
density of 1e6 Msun/Mpc^3. Several galaxies in this sub-sample have masses of
order 10^11 Msun implying significant earlier activity occurred in massive
systems. We then consider a larger sample whose photometric redshifts in the
publicly-available GOODS-MUSIC catalog lie in the range 4.4 <z 5.6. Before
adopting the GOODS-MUSIC photometric redshifts, we check the accuracy of their
photometry and explore the possibility of contamination by low-z galaxies and
low-mass stars. After excising probable stellar contaminants and using the z'-J
color to exclude any remaining foreground red galaxies, we conclude that 196
sources are likely to be at z~5. The implied mass density from the unconfused
IRAC fraction of this sample, scaled to the total available, is 6e6 Msun/Mpc^3.
We discuss the uncertainties as well as the likelihood that we have
underestimated the true mass density. Including fainter and quiescent sources
the total integrated density could be as high as 1e7 Msun/Mpc^3. Using the
currently available (but highly uncertain) rate of decline in the star
formationhistory over 5 <z< 10, a better fit is obtained for the assembled mass
at z~5 if we admit significant dust extinction at early times or extend the
luminosity function to very faint limits. [abridged]Comment: Accepted for Publication in ApJ, 39 page
Pickoff and spin-conversion quenchings of ortho-positronium in oxygen
The quenching processes of the thermalized ortho-positronium(o-Ps) on an
oxygen molecule have been studied by the positron annihilation age-momentum
correlation techinique(AMOC). The Doppler broadening spectrum of the 511 keV
gamma-rays from the 2gamma annihilation of o-Ps in O_2 has been measured as a
function of the o-Ps age. The rate of the quenching, consisting of the pickoff
and the spin-conversion, is estimated from the positron lifetime spectrum. The
ratio of the pickoff quenching rate to the spin-conversion rate is deduced from
the Doppler broadening of the 511 keV gamma-rays from the annihilation of the
o-Ps. The pickoff parameter ^1Z_eff, the effective number of the electrons per
molecule which contribute to the pickoff quenching, for O_2 is determined to be
0.6 +- 0.4. The cross-section for the elastic spin-conversion quenching is
determined to be (1.16 +- 0.01) * 10^{-19} cm^2.Comment: 4 pages with 5 eps figures, LaTeX2e(revtex4
Mitochondrial proteomics: analysis of a whole mitochondrial extract with two-dimensional electrophoresis
Mitochondria are complex organelles, and their proteomics analysis requires a
combination of techniques. The emphasis in this chapter is made first on
mitochondria preparation from cultured mammalian cells, then on the separation
of the mitochondrial proteins with two-dimensional electrophoresis (2DE),
showing some adjustment over the classical techniques to improve resolution of
the mitochondrial proteins. This covers both the protein solubilization, the
electrophoretic part per se, and the protein detection on the gels, which makes
the interface with the protein identification part relying on mass
spectrometry
Nonbipartite Dulmage-Mendelsohn Decomposition for Berge Duality
The Dulmage-Mendelsohn decomposition is a classical canonical decomposition
in matching theory applicable for bipartite graphs, and is famous not only for
its application in the field of matrix computation, but also for providing a
prototypal structure in matroidal optimization theory. The Dulmage-Mendelsohn
decomposition is stated and proved using the two color classes, and therefore
generalizing this decomposition for nonbipartite graphs has been a difficult
task. In this paper, we obtain a new canonical decomposition that is a
generalization of the Dulmage-Mendelsohn decomposition for arbitrary graphs,
using a recently introduced tool in matching theory, the basilica
decomposition. Our result enables us to understand all known canonical
decompositions in a unified way. Furthermore, we apply our result to derive a
new theorem regarding barriers. The duality theorem for the maximum matching
problem is the celebrated Berge formula, in which dual optimizers are known as
barriers. Several results regarding maximal barriers have been derived by known
canonical decompositions, however no characterization has been known for
general graphs. In this paper, we provide a characterization of the family of
maximal barriers in general graphs, in which the known results are developed
and unified
The Rest-Frame UV Luminosity Density of Star-Forming Galaxies at Redshifts z>3.5
We have measured the rest--frame lambda~1500 Ang comoving specific luminosity
density of star--forming galaxies at redshift 3.5<z<6.5 from deep images taken
with the Hubble Space Telescope (HST)and the Advanced Camera for Surveys (ACS),
obtained as part of the Great Observatories Origins Deep Survey (GOODS). We
used color selection criteria to construct samples of star--forming galaxies at
redshifts z~4, 5 and 6, identified by the signature of the 912 Ang Lyman
continuum discontinuity and Lyman-alpha forest blanketing in their rest--frame
UV colors (Lyman--break galaxies). The ACS samples cover ~0.09 square degree,
and are also relatively deep, reaching between 0.2 and 0.5 L_3^*, depending on
the redshift, where is the characteristic UV luminosity of Lyman--break
galaxies at z~3. The specific luminosity density of Lyman--break galaxies
appears to be nearly constant with redshift from z~3 to z~6, although the
measure at z~6 remains relatively uncertain, because it depends on the accurate
estimate of the faint counts of the z~6 sample. If Lyman--break galaxies are
fair tracers of the cosmic star formation activity, our results suggest that at
z~6 the universe was already producing stars as vigorously as it did near its
maximum several Gyr later, at 1<~z<~3. Thus, the onset of large--scale star
formation in the universe is to be sought at around z~6 or higher, namely at
less than ~7% of the current cosmic age.Comment: AAS LaTeX macros 4.0, 11 pages, 1 postscript figure. Accepted for
publication in The Astrophysical Journal, Letter. Minor changes to the figure
caption. The data and the GOODS-group papers can be found at
http://www.stsci.edu/science/goods
Molecular hydrogen, deuterium and metal abundances in the damped Ly-alpha system at z = 3.025 toward QSO 0347-3819
We have detected in high resolution spectra of the quasar Q0347--3819
obtained with the UVES spectrograph at the VLT/Kueyen telescope over 80
absorption features in the Lyman and Werner H2 bands at the redshift of a
damped Ly-alpha system at z = 3.025. The z = 3.025 system spans over 80 km/s
and exhibits a multicomponent velocity structure in the metal lines. The main
component at z = 3.024855 shows a total H2 column density N(H2) =
(4.10\pm0.21)*10^{14} cm^{-2} and a fractional molecular abundance f(H2) =
(1.94\pm0.10)*10^{-6} derived from the H2 lines arising from J=0 to 5
rotational levels of the ground electronic-vibrational state. For the first
time we unambiguously reveal a pronounced [alpha-element/iron-peak] enhancement
of [O,Si/Zn] = 0.6\pm0.1 (6 sigma c.l.) at high redshift. The simultaneous
analysis of metal and hydrogen lines leads to D/H = (3.75\pm0.25)*10^{-5}. This
value is consistent with standard big bang nucleosynthesis if the
baryon-to-photon ratio, eta, lies within the range 4.37*10^{-10} <= eta <=
5.32*10^{-10}, implying 0.016 <= Omega_b h^2_100 <= 0.020.Comment: 32 pages, 16 ps figures, accepted to Ap
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