4,116 research outputs found
Bond angle distribution in amorphous germania and silica
The distribution of Ge-O-Ge and Si-O-Si bond angles alpha in amorphous
germania and silica is re-determined on the basis of diffraction experiments.
The bond angle alpha joining adjacent tetrahedra is the central parameter of
any continuous random network description (CRN) of these glasses. New high
energy photon diffraction experiments on amorphous germania (at photon energies
of 97 and 149 keV) are presented, covering the momentum transfer 0.6-33.5
AA^{-1}. In photon diffraction experiments on GeO2 the contribution of the OO
pairs is very small. To obtain a similar information for amorphous SiO2, high
energy photon diffraction experiments have been combined with neutron
diffraction data on amorphous silica in order to eliminate the OO- partial
structure factor. With this technique it is shown that the Si-O-Si angle
distribution is fairly narrow (sigma=7.5 degree) and in fact comparable in
width to the Ge-O-Ge angle distribution (sigma=8.3 degree), a result which
differs from current opinion. The narrower distribution found in this study are
in much better agreement to the determinations based on 29Si-MAS-NMR. Among the
various models relating the chemical shift to the bond angle, best agreement is
found with those models based on the secant model. Sharp components in the bond
angle distribution can be excluded within the reached real space resolution of
0.09 AA.Comment: 12 pages LATEX, 13 Postscript figures, experimental data includes as
LATEX comment
Quantum computers can search rapidly by using almost any transformation
A quantum computer has a clear advantage over a classical computer for
exhaustive search. The quantum mechanical algorithm for exhaustive search was
originally derived by using subtle properties of a particular quantum
mechanical operation called the Walsh-Hadamard (W-H) transform. This paper
shows that this algorithm can be implemented by replacing the W-H transform by
almost any quantum mechanical operation. This leads to several new applications
where it improves the number of steps by a square-root. It also broadens the
scope for implementation since it demonstrates quantum mechanical algorithms
that can readily adapt to available technology.Comment: This paper is an adapted version of quant-ph/9711043. It has been
modified to make it more readable for physicists. 9 pages, postscrip
A Widespread, Clumpy Starburst in the Isolated Ongoing Dwarf Galaxy Merger dm1647+21
Interactions between pairs of isolated dwarf galaxies provide a critical
window into low-mass hierarchical, gas-dominated galaxy assembly and the
buildup of stellar mass in low-metallicity systems. We present the first
VLT/MUSE optical IFU observations of the interacting dwarf pair dm1647+21,
selected from the TiNy Titans survey. The H emission is widespread and
corresponds to a total unobscured star formation rate (SFR) of 0.44 M
yr, 2.7 times higher than the SFR inferred from SDSS data. The implied
specific SFR (sSFR) for the system is elevated by more than an order of
magnitude above non-interacting dwarfs in the same mass range. This increase is
dominated by the lower-mass galaxy, which has a sSFR enhancement of 50.
Examining the spatially-resolved maps of classic optical line diagnostics, we
find the ISM excitation can be fully explained by star formation. The velocity
field of the ionized gas is not consistent with simple rotation. Dynamical
simulations indicate that the irregular velocity field and the stellar
structure is consistent with the identification of this system as an ongoing
interaction between two dwarf galaxies. The widespread, clumpy enhancements in
star formation in this system point to important differences in the effect of
mergers on dwarf galaxies, compared to massive galaxies: rather than the
funneling of gas to the nucleus and giving rise to a nuclear starburst,
starbursts in low-mass galaxy mergers may be triggered by large-scale ISM
compression, and thus be more distributed.Comment: Accepted for publication in ApJ. 11 pages, 5 figures, 1 table.
Figures slightly degraded to meet arXiv size restrictions. For more
information about TiNy Titans see https://lavinia.as.arizona.edu/~tinytitans
Monocyte chemotactic protein-1 (MCP-1) as a predictor of prolonged urinary incontinence after radical prostatectomy
Objectives: To investigate monocyte chemotactic protein-1 (MCP-1) as a novel urinary biomarker to predict prolonged post prostatectomy incontinence. Methods: Men submitted urine samples prior to robotic radical prostatectomy. MCP-1 values were derived using an ELISA test. Pad usage at 7, 30, and 60 days were documented by patient post cards mailed when zero pads was reached. The primary outcome was defined as no incontinence pad usage at 30 days at prostatectomy. Results: After exclusions, 76 patients were included in analyses. Continence was reached by 29% (22/76), 56% (42/76), and (75/76) 98% at 7, 30, and 60 days, respectively. The average MCP-1 (p=0.258) was not different between the continent and incontinent groups. Highest quartile of MCP-1 (MCP > 166 pg/mL) and normalized MCP-1 (MCP-1/TV >0.53) noted a significant delay in continence at 30 days (p=0.050 and p=0.003). Only 26% (5/19) in the highest MCP1/TV quartile were continent, whereas 65% (37/57) of men in the 3 lower quartiles reached zero pad continence (p=0.003). In a logistic regression model the highest quartile of MCP1/TV had a significant chance of being incontinent at 30 days (OR 0.22; 95% CI 0.058-0.80; p=0.022). Conclusion: MCP-1/TV is a urinary biomarker that may predict prolonged urinary incontinence after radical prostatectomy
Probing impulsive strain propagation with x-ray pulses
Pump-probe time-resolved x-ray diffraction of allowed and nearly forbidden
reflections in InSb is used to follow the propagation of a coherent acoustic
pulse generated by ultrafast laser-excitation. The surface and bulk components
of the strain could be simultaneously measured due to the large x-ray
penetration depth. Comparison of the experimental data with dynamical
diffraction simulations suggests that the conventional model for impulsively
generated strain underestimates the partitioning of energy into coherent modes.Comment: 4 pages, 2 figures, LaTeX, eps. Accepted for publication in Phys.
Rev. Lett. http://prl.aps.or
Measurement of the Lifetime Difference Between B_s Mass Eigenstates
We present measurements of the lifetimes and polarization amplitudes for B_s
--> J/psi phi and B_d --> J/psi K*0 decays. Lifetimes of the heavy (H) and
light (L) mass eigenstates in the B_s system are separately measured for the
first time by determining the relative contributions of amplitudes with
definite CP as a function of the decay time. Using 203 +/- 15 B_s decays, we
obtain tau_L = (1.05 +{0.16}/-{0.13} +/- 0.02) ps and tau_H = (2.07
+{0.58}/-{0.46} +/- 0.03) ps. Expressed in terms of the difference DeltaGamma_s
and average Gamma_s, of the decay rates of the two eigenstates, the results are
DeltaGamma_s/Gamma_s = (65 +{25}/-{33} +/- 1)%, and DeltaGamma_s = (0.47
+{0.19}/-{0.24} +/- 0.01) inverse ps.Comment: 8 pages, 3 figures, 2 tables; as published in Physical Review Letters
on 16 March 2005; revisions are for length and typesetting only, no changes
in results or conclusion
Inclusive Search for Anomalous Production of High-pT Like-Sign Lepton Pairs in Proton-Antiproton Collisions at sqrt{s}=1.8 TeV
We report on a search for anomalous production of events with at least two
charged, isolated, like-sign leptons with pT > 11 GeV/c using a 107 pb^-1
sample of 1.8 TeV ppbar collisions collected by the CDF detector. We define a
signal region containing low background from Standard Model processes. To avoid
bias, we fix the final cuts before examining the event yield in the signal
region using control regions to test the Monte Carlo predictions. We observe no
events in the signal region, consistent with an expectation of
0.63^(+0.84)_(-0.07) events. We present 95% confidence level limits on new
physics processes in both a signature-based context as well as within a
representative minimal supergravity (tanbeta = 3) model.Comment: 15 pages, 4 figures. Minor textual changes, cosmetic improvements to
figures and updated and expanded reference
Measurement of the Strong Coupling Constant from Inclusive Jet Production at the Tevatron Collider
We report a measurement of the strong coupling constant, ,
extracted from inclusive jet production in collisions at
1800 GeV. The QCD prediction for the evolution of with
jet transverse energy is tested over the range 40<<450 GeV using
for the renormalization scale. The data show good agreement with QCD in
the region below 250 GeV. In the text we discuss the data-theory comparison in
the region from 250 to 450 GeV. The value of at the mass of the
boson averaged over the range 40<<250 GeV is found to be
. The associated theoretical uncertainties are mainly due to the choice
of renormalization scale (^{+6%}_{-4%}) and input parton distribution
functions (5%).Comment: 7 pages, 3 figures, using RevTeX. Submitted to Physical Review
Letter
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
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