4,993 research outputs found
Nonlinear dielectric response at the excess wing of glass-forming liquids
We present nonlinear dielectric measurements of glass-forming glycerol and
propylene carbonate applying electrical fields up to 671 kV/cm. The
measurements extend to sufficiently high frequencies to allow for the
investigation of the nonlinear behavior in the regime of the so-far mysterious
excess wing, showing up in the loss spectra of many glass formers as a second
power law at high frequencies. Surprisingly, we find a complete lack of
nonlinear behavior in the excess wing, in marked contrast to the
alpha-relaxation where, in agreement with previous reports, a strong increase
of dielectric constant and loss is found.Comment: 8 pages (including 3 pages Supplementary Information), 4 + 1 figures.
Revised according to suggestions of referee
Negative curves on algebraic surfaces
We study curves of negative self-intersection on algebraic surfaces. We
obtain results for smooth complex projective surfaces X on the number of
reduced, irreducible curves C of negative self-intersection C^2. The only known
examples of surfaces for which C^2 is not bounded below are in positive
characteristic, and the general expectation is that no examples can arise over
the complex numbers. Indeed, we show that the idea underlying the examples in
positive characteristic cannot produce examples over the complex number field.
The previous version of this paper claimed to give a counterexample to the
Bounded Negativity Conjecture. The idea of the counterexample was to use Hecke
translates of a smooth Shimura curve in order to create an infinite sequence of
curves violating the Bounded Negativity Conjecture. To this end we applied
Hirzebruch Proportionality to all Hecke translates, simultaneously
desingularized by a version of Jaffee's Lemma which exists in the literature
but which turns out to be false. Indeed, in the new version of the paper, we
show that only finitely many Hecke translates of a special subvariety of a
Hilbert modular surface remain smooth. This new result is based on work done
jointly with Xavier Roulleau, who has been added as an author. The other
results in the original posting of this paper remain unchanged.Comment: 14 pages, X. Roulleau added as author, counterexample to Bounded
Negativity Conjecture withdrawn and replaced by a proof that there are only
finitely many smooth Shimura curves on a compact Hilbert modular surface; the
other results in the original posting of this paper remain unchange
Fifth-order susceptibility unveils growth of thermodynamic amorphous order in glass-formers
Glasses are ubiquitous in daily life and technology. However the microscopic
mechanisms generating this state of matter remain subject to debate: Glasses
are considered either as merely hyper-viscous liquids or as resulting from a
genuine thermodynamic phase transition towards a rigid state. We show that
third- and fifth-order susceptibilities provide a definite answer to this
longstanding controversy. Performing the corresponding high-precision nonlinear
dielectric experiments for supercooled glycerol and propylene carbonate, we
find strong support for theories based upon thermodynamic amorphous order.
Moreover, when lowering temperature, we find that the growing transient domains
are compact - that is their fractal dimension d_f = 3. The glass transition may
thus represent a class of critical phenomena different from canonical
second-order phase transitions for which d_f < 3.Comment: 9 pages, 3 figure
Construction and Test of MDT Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the AT-
LAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurized drift tubes on either side of a space frame carrying an optical
monitoring system to correct for deformations. The full-scale prototype of a
large MDT chamber has been constructed with methods suitable for large-scale
production. X-ray measurements at CERN showed a positioning accuracy of the
sense wires in the chamber of better than the required 20 ?microns (rms). The
performance of the chamber was studied in a muon beam at CERN. Chamber
production for ATLAS now has started
Construction and Test of the Precision Drift Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the
ATLAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurised drift tubes on either side of a space frame carrying an optical
deformation monitoring system. The chambers have to provide a track position
resolution of 40 microns with a single-tube resolution of at least 80 microns
and a sense wire positioning accu- racy of 20 ?microns (rms). The feasibility
was demonstrated with the full-scale prototype of one of the largest MDT
chambers with 432 drift tubes of 3.8 m length. For the ATLAS muon spectrometer,
88 chambers of this type have to be built. The first chamber has been completed
with a wire positioning accuracy of 14 microns (rms)
Non-factorizable Contributions to Decays
We investigate to what extent the experimental information on
branching fractions and CP asymmetries can be used to better understand the QCD
dynamics in these decays. For this purpose we decompose the independent isospin
amplitudes into factorizable and non-factorizable contributions. The former can
be estimated within the framework of QCD factorization for exclusive
decays. The latter vanish in the heavy-quark limit, , and are
treated as unknown hadronic parameters. We discuss at some length in which way
the non-factorizable contributions are treated in different theoretical and
phenomenological frameworks. We point out the potential differences between the
phenomenological treatment of power-corrections in the ``BBNS approach'', and
the appearance of power -suppressed operators in soft-collinear effective
theory (SCET). On that basis we define a handful of different (but generic)
scenarios where the non-factorizable part of isospin amplitudes is parametrized
in terms of three or four unknowns, which can be constrained by data. We also
give some short discussion on the implications of our analysis for decays. In particular, since non-factorizable QCD effects in
may be large, we cannot exclude sizeable non-factorizable effects, which
violate flavour symmetry, or even isospin symmetry (via long-distance
QED effects). This may help to explain certain puzzles in connection with
isospin-violating observables in decays.Comment: published version, minor correction
Photofission of heavy nuclei at energies up to 4 GeV
Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and
natPb have been measured simultaneously, using tagged photons in the energy
range Egamma=0.17-3.84 GeV. This was the first experiment performed using the
Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the
photofission cross section for 238U relative to that for 237Np is about 80%,
implying the presence of important processes that compete with fission. We also
observe that the relative photofission cross sections do not depend strongly on
the incident photon energy over this entire energy range. If we assume that for
237Np the photofission probability is equal to unity, we observe a significant
shadowing effect starting below 1.5 GeV.Comment: 4 pages of RevTex, 6 postscript figures, Submitted to Phys. Rev. Let
Fabrication and characterization of solution-processed methanofullerene-based organic field-effect transistors
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