60,365 research outputs found
Impact for Agents
Impact for agents. Most of the agent research community has been predicting greater impact for years and many of us have been working to help the process along. Yet the tremendous growth on the research front has not been met with
Abdominopelvic SplenosisâAn Unusual Cause of Tenesmus
Splenosis is a rare condition defined as seeding and autotransplantation of splenic tissue, typically after blunt
abdominal trauma (e.g. from road traffic collision). Sites of splenosis ranging from intrathoracic to intrapelvic have
been reported, and symptoms vary greatly depending on the site and size of lesions. We present the use of Tc-99m
sulphur colloid SPECT/CT in diagnosing a case of multiple abdominopelvic splenosis as the cause of new-onset
tenesmus and constipation, which was initially thought to be due to colorectal malignancy, 47 years following the
initial abdominal trauma
The drive system of the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope
The MAGIC telescope is an imaging atmospheric Cherenkov telescope, designed
to observe very high energy gamma-rays while achieving a low energy threshold.
One of the key science goals is fast follow-up of the enigmatic and short lived
gamma-ray bursts. The drive system for the telescope has to meet two basic
demands: (1) During normal observations, the 72-ton telescope has to be
positioned accurately, and has to track a given sky position with high
precision at a typical rotational speed in the order of one revolution per day.
(2) For successfully observing GRB prompt emission and afterglows, it has to be
powerful enough to position to an arbitrary point on the sky within a few ten
seconds and commence normal tracking immediately thereafter. To meet these
requirements, the implementation and realization of the drive system relies
strongly on standard industry components to ensure robustness and reliability.
In this paper, we describe the mechanical setup, the drive control and the
calibration of the pointing, as well as present measurements of the accuracy of
the system. We show that the drive system is mechanically able to operate the
motors with an accuracy even better than the feedback values from the axes. In
the context of future projects, envisaging telescope arrays comprising about
100 individual instruments, the robustness and scalability of the concept is
emphasized.Comment: 15 pages, 12 (10) figures, submitted to Astroparticle Physics, a high
resolution version of the paper (particularly fig. 1) is available at
http://publications.mppmu.mpg.de/2008/MPP-2008-101/FullText.pd
Minimal Flavor Violation and the Scale of Supersymmetry Breaking
In this paper we explore the constraints from B-physics observables in SUSY
models of Minimal Flavor Violation, in the large tan beta regime, for both low
and high scale supersymmetry breaking scenarios. We find that the rare B-decays
b -> s gamma and B_s -> mu+ mu- can be quite sensitive to the scale M at which
supersymmetry breaking is communicated to the visible sector. In the case of
high scale supersymmetry breaking, we show that the additional gluino
contribution to the b -> s gamma and B_s -> mu+ mu- rare decay rates can be
significant for large tan beta, mu and M_3. The constraints on B_u -> tau nu
are relatively insensitive to the precise scale of M. We also consider the
additional constraints from the present direct Higgs searches at the Tevatron
in the inclusive H/A -> tau tau channel, and the latest CDMS direct dark matter
detection experiments. We find that altogether the constraints from B-physics,
Higgs physics and direct dark matter searches can be extremely powerful in
probing regions of SUSY parameter space for low M_A and large tan beta, leading
to a preference for models with a lightest CP-even Higgs mass close to the
current experimental limit. We find interesting regions of parameter space that
satisfy all constraints and can be probed by Higgs searches at the Tevatron and
the LHC and by direct dark matter searches in the near future.Comment: 24 pages, 6 figures. Added citations. Published in PR
Information on the structure of the a1 from tau decay
The decay is analysed using different methods to
account for the resonance structure, which is usually ascribed to the a1. One
scenario is based on the recently developed techniques to generate axial-vector
resonances dynamically, whereas in a second calculation the a1 is introduced as
an explicit resonance. We investigate the influence of different assumptions on
the result. In the molecule scenario the spectral function is described
surprisingly well by adjusting only one free parameter. This result can be
systematically improved by adding higher order corrections to the iterated
Weinberg-Tomozawa interaction. Treating the a1 as an explicit resonance on the
other hand leads to peculiar properties
Energy based method for numerical fatigue analysis of multidirectional carbon fibre reinforced plastics
This paper describes experiments on multiaxial fibre reinforced plastic laminates, which were performed to obtain calibration data for numerical fatigue analyses. For this purpose, fatigue tests of laminates with multidirectional layers subjected to constant amplitude and block loading (0 <= R<1 or R<1) were analysed. The presented simulation results display the fatigue behaviour of carbon fibre reinforced plastics for unidirectional loading conditions and a selected laminate
Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
The main background above 3\,MeV for in-beam nuclear astrophysics studies
with -ray detectors is caused by cosmic-ray induced secondaries. The
two commonly used suppression methods, active and passive shielding, against
this kind of background were formerly considered only as alternatives in
nuclear astrophysics experiments. In this work the study of the effects of
active shielding against cosmic-ray induced events at a medium deep location is
performed. Background spectra were recorded with two actively shielded HPGe
detectors. The experiment was located at 148\,m below the surface of the Earth
in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data
with the same detectors at the Earth's surface, and at depths of 45\,m and
1400\,m, respectively.Comment: Minor errors corrected; final versio
Higgs-Stoponium Mixing Near the Stop-Antistop Threshold
Supersymmetric extensions of the standard model contain additional heavy
neutral Higgs bosons that are coupled to heavy scalar top quarks (stops). This
system exhibits interesting field theoretic phenomena when the Higgs mass is
close to the stop-antistop production threshold. Existing work in the
literature has examined the digluon-to-diphoton cross section near threshold
and has focused on enhancements in the cross section that might arise either
from the perturbative contributions to the Higgs-to-digluon and
Higgs-to-diphoton form factors or from mixing of the Higgs boson with stoponium
states. Near threshold, enhancements in the relevant amplitudes that go as
inverse powers of the stop-antistop relative velocity require resummations of
perturbation theory and/or nonperturbative treatments. We present a complete
formulation of threshold effects at leading order in the stop-antistop relative
velocity in terms of nonrelativistic effective field theory. We give detailed
numerical calculations for the case in which the stop-antistop Green's function
is modeled with a Coulomb-Schr\"odinger Green's function. We find several
general effects that do not appear in a purely perturbative treatment.
Higgs-stop-antistop mixing effects displace physical masses from the threshold
region, thereby rendering the perturbative threshold enhancements inoperative.
In the case of large Higgs-stop-antistop couplings, the displacement of a
physical state above threshold substantially increases its width, owing to its
decay width to a stop-antistop pair, and greatly reduces its contribution to
the cross section.Comment: 45 pages, 13 figures, minor corrections, references added, figures
2--5 updated, version published in Phys. Rev.
Large System Analysis of Linear Precoding in Correlated MISO Broadcast Channels under Limited Feedback
In this paper, we study the sum rate performance of zero-forcing (ZF) and
regularized ZF (RZF) precoding in large MISO broadcast systems under the
assumptions of imperfect channel state information at the transmitter and
per-user channel transmit correlation. Our analysis assumes that the number of
transmit antennas and the number of single-antenna users are large
while their ratio remains bounded. We derive deterministic approximations of
the empirical signal-to-interference plus noise ratio (SINR) at the receivers,
which are tight as . In the course of this derivation, the
per-user channel correlation model requires the development of a novel
deterministic equivalent of the empirical Stieltjes transform of large
dimensional random matrices with generalized variance profile. The
deterministic SINR approximations enable us to solve various practical
optimization problems. Under sum rate maximization, we derive (i) for RZF the
optimal regularization parameter, (ii) for ZF the optimal number of users,
(iii) for ZF and RZF the optimal power allocation scheme and (iv) the optimal
amount of feedback in large FDD/TDD multi-user systems. Numerical simulations
suggest that the deterministic approximations are accurate even for small
.Comment: submitted to IEEE Transactions on Information Theor
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