328 research outputs found
A new interpretation of dielectric data in molecular glass formers
Literature dielectric data of glycerol, propylene carbonate and
ortho-terphenyl (OTP) show that the measured dielectric relaxation is a decade
faster than the Debye expectation, but still a decade slower than the breakdown
of the shear modulus. From a comparison of time scales, the dielectric
relaxation seems to be due to a process which relaxes not only the molecular
orientation, but the entropy, the short-range order and the density as well. On
the basis of this finding, we propose an alternative to the
Gemant-DiMarzio-Bishop extension of the Debye picture.Comment: 7 pages, 4 figures, 68 references; 3. version extended following
referee advic
Stretching Folding Instability and Nanoemulsions
Here we show a folding-stretching instability in a microfluidic flow focusing
device using silicon oil (100cSt) and water. The fluid dynamics video
demonstrates an oscillating thread of oil focused by two co-flowing streams of
water. We show several high-speed sequences of these oscillations with 30,000
frames/s. Once the thread is decelerated in a slower moving pool downstream an
instability sets in and water-in-oil droplets are formed. We reveal the details
of the pinch-off with 500,000 frames/s. The pinch-off is so repeatable that
complex droplet patterns emerge. Some of droplets are below the resolution
limit, thus smaller than 1 micrometer in diameter
Two Photon Radiation in W and Z Boson Production at the Tevatron Collider
We present a calculation of two photon radiation in W and Z boson production
in hadronic collisions, based on the complete matrix elements for the processes
q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma,
including finite charged lepton masses. In order to achieve stable numerical
results over the full phase space, multiconfiguration Monte Carlo techniques
are used to map the peaks in the differential cross section. Numerical results
are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure
Photospheric Abundances of the Hot Stars in NGC1399 and Limits on the Fornax Cluster Cooling Flow
We present far-UV spectroscopy of the giant elliptical galaxy NGC 1399,
obtained with the Far Ultraviolet Spectroscopic Explorer. Of all quiescent
ellipticals, NGC 1399 has the strongest known ``UV upturn'' -- a sharp spectral
rise shortward of 2500 A. It is now well-established that this emission comes
from hot horizontal branch (HB) stars and their progeny; however, the chemical
composition of these stars has been the subject of a long-standing debate. For
the first time in observations of any elliptical galaxy, our spectra clearly
show photospheric metallic absorption lines within the UV upturn. The abundance
of N is at 45% solar, Si is at 13% solar, and C is at 2% solar. Such abundance
anomalies are a natural consequence of gravitational diffusion. These
photospheric abundances fall in the range observed for subdwarf B stars of the
Galactic field.
Although NGC1399 is at the center of the Fornax cluster, we find no evidence
for O VI cooling flow emission. The upper limit to 1032,1038 emission is
3.9E-15 erg/s/cm2, equivalent to 0.14 M_sun/yr, and less than that predicted by
simple cooling flow models of the NGC 1399 X-ray luminosity.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in ApJ Letters. Revised
figure placemen
Dielectric and thermal relaxation in the energy landscape
We derive an energy landscape interpretation of dielectric relaxation times
in undercooled liquids, comparing it to the traditional Debye and
Gemant-DiMarzio-Bishop pictures. The interaction between different local
structural rearrangements in the energy landscape explains qualitatively the
recently observed splitting of the flow process into an initial and a final
stage. The initial mechanical relaxation stage is attributed to hopping
processes, the final thermal or structural relaxation stage to the decay of the
local double-well potentials. The energy landscape concept provides an
explanation for the equality of thermal and dielectric relaxation times. The
equality itself is once more demonstrated on the basis of literature data for
salol.Comment: 7 pages, 3 figures, 41 references, Workshop Disordered Systems,
Molveno 2006, submitted to Philosophical Magazin
Measurements of Lifetimes and a Limit on the Lifetime Difference in the Neutral D-Meson System
Using the large hadroproduced charm sample collected in experiment E791 at
Fermilab, we report the first directly measured constraint on the decay-width
difference Delta Gamma for the mass eigenstates of the D0-D0bar system. We
obtain our result from lifetime measurements of the decays D0 --> K-pi+ and D0
--> K-K+, under the assumption of CP invariance, which implies that the CP
eigenstates and the mass eigenstates are the same. The lifetime of D0 --> K-K+
(the CP-even final state is \tau_KK = 0.410 +/- 0.011 +/- 0.006 ps, and the
lifetime of D0 --> K-pi+ (an equal mixture of CP-odd and CP-even final states
is tau_Kpi = 0.413 +/- 0.003 +/- 0.004 ps. The decay-width difference is Delta
Gamma = 2(Gamma_KK - Gamma_Kpi) = 0.04 +/- 0.14 +/- 0.05 ps^-1. We relate these
measurements to measurements of mixing in the neutral D-meson system.Comment: 8 pages + 3 figures + 2 table
UV continuum emission and diagnostics of hydrogen-containing non-equilibrium plasmas
For the first time the emission of the radiative dissociation continuum of
the hydrogen molecule ( electronic
transition) is proposed to be used as a source of information for the
spectroscopic diagnostics of non-equilibrium plasmas. The detailed analysis of
excitation-deactivation kinetics, rate constants of various collisional and
radiative transitions and fitting procedures made it possible to develop two
new methods of diagnostics of: (1) the ground state
vibrational temperature from the relative intensity
distribution, and (2) the rate of electron impact dissociation
(d[\mbox{H_{2}}]/dt)_{\text{diss}} from the absolute intensity of the
continuum. A known method of determination of from relative
intensities of Fulcher- bands was seriously corrected and simplified
due to the revision of transition probabilities and cross sections of
electron impact excitation. General considerations are illustrated
with examples of experiments in pure hydrogen capillary-arc and H+Ar
microwave discharges.Comment: REVTeX, 25 pages + 12 figures + 9 tables. Phys. Rev. E, eprint
replaced because of resubmission to journal after referee's 2nd repor
Propylene Carbonate Reexamined: Mode-Coupling Scaling without Factorisation ?
The dynamic susceptibility of propylene carbonate in the moderately viscous
regime above is reinvestigated by incoherent neutron and
depolarised light scattering, and compared to dielectric loss and solvation
response. Depending on the strength of relaxation, a more or less
extended scaling regime is found. Mode-coupling fits yield consistently
and K, although different positions of the
susceptibility minimum indicate that not all observables have reached the
universal asymptotics
Top Pair Production Beyond Double-Pole Approximation: pp, pp~ --> 6 Fermions and 0, 1 or 2 Additional Partons
Hadron collider cross sections for tt~ production and di-lepton,
single-lepton and all-jet decays with up to 2 additional jets are calculated
using complete LO matrix elements with 6-, 7- and 8-particle final states. The
fixed-width, complex-mass and overall-factor schemes (FWS, CMS & OFS) are
employed and the quality of narrow-width and double-pole approximations (NWA &
DPA) is investigated for inclusive production and suppressed backgrounds to new
particle searches. NWA and DPA cross sections differ by 1% or less. The
inclusion of sub- and non-resonant amplitudes effects a cross section increase
of 5-8% at pp supercolliders, but only minor changes at the Tevatron. On-shell
tt~/Wtb backgrounds for the H --> WW decay in weak boson fusion, the hadronic
\tau decay of a heavy H^\pm and the \phi --> hh --> \tau\tau bb~ radion decay
at the LHC are updated, with corrections ranging from 3% to 30%. FWS and CMS
cross sections are uniformly consistent, but OFS cross sections are up to 6%
smaller for some backgrounds.Comment: 20 pages, 6 tables, 1 figur
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