435 research outputs found
Correlation of mechanical factors and gallbladder pain
Acalculous biliary pain occurs in patients with no gallstones, but is similar to that experienced by patients with gallstones. Surgical removal of the gallbladder (GB) in these patients is only successful in providing relief of symptoms to about half of those operated on, so a reliable pain-prediction model is needed. In this paper, a mechanical model is developed for the human biliary system during the emptying phase, based on a clinical test in which GB volume changes are measured in response to a standard stimulus and a recorded pain profile. The model can describe the bile emptying behaviour, the flow resistance in the biliary ducts, the peak total stress, including the passive and active stresses experienced by the GB during emptying. This model is used to explore the potential link between GB pain and mechanical factors. It is found that the peak total normal stress may be used as an effective pain indicator for GB pain. When this model is applied to clinical data of volume changes due to Cholecystokinin stimulation and pain from 37 patients, it shows a promising success rate of 88.2% in positive pain prediction
MANAGEMENT OF SOLITARY THYROID NODULES IN RURAL AFRICA
Objectives: To review a simple protocol for the management of solitary thyroid nodulesand to document the spectrum of pathological diagnoses associated with this condition.Design: A retrospective review of all solitary solid thyroid nodules excised over a threeyearperiod from 1st January 1999 to 31st December 2001.Setting: A rural church-based hospital in Kenya.Subjects: All patients undergoing thyroidectomy for solitary solid thyroid nodule overa three-year period at Kijabe Hospital.Interventions: A simple protocol was used to manage this condition involving history,clinical examination, needle aspiration of the lesion, and excision when clinicallyindicated.Main Outcome Measures: Clinical diagnosis, tribe, operation performed, pathology, andcomplications of surgery.Results: Eighty-one operations were performed for a solitary thyroid nodule. The mostcommon operations were lobectomy and isthmusectomy. There were two complicationsaneck haematoma that required surgery and one recurrent laryngeal nerve injury. Thecommonest pathological diagnosis was multinodular goitre (42%). There was a 16%malignancy rate with eight papillary carcinomas, five follicular carcinomas, and onehurthle cell carcinoma.Conclusions: The simple protocol described gives good results in a rural African hospital.Solitary solid thyroid nodules should be routinely excised due to the 16% malignancyrate in this condition. There is a possibility that there is a shift in the ratio of papillaryto follicular carcinomas compared to older African studies and this would be aninteresting area for further study
Quantum Chaos in Open versus Closed Quantum Dots: Signatures of Interacting Particles
This paper reviews recent studies of mesoscopic fluctuations in transport
through ballistic quantum dots, emphasizing differences between conduction
through open dots and tunneling through nearly isolated dots. Both the open
dots and the tunnel-contacted dots show random, repeatable conductance
fluctuations with universal statistical proper-ties that are accurately
characterized by a variety of theoretical models including random matrix
theory, semiclassical methods and nonlinear sigma model calculations. We apply
these results in open dots to extract the dephasing rate of electrons within
the dot. In the tunneling regime, electron interaction dominates transport
since the tunneling of a single electron onto a small dot may be sufficiently
energetically costly (due to the small capacitance) that conduction is
suppressed altogether. How interactions combine with quantum interference are
best seen in this regime.Comment: 15 pages, 11 figures, PDF 2.1 format, to appear in "Chaos, Solitons &
Fractals
Ultra-high energy cosmic ray investigations by means of EAS muon density measurements
A new approach to investigations of ultra-high energy cosmic rays based on
the ground-level measurements of the spectra of local density of EAS muons at
various zenith angles is considered. Basic features of the local muon density
phenomenology are illustrated using a simple semi-analytical model. It is shown
that muon density spectra are sensitive to the spectrum slope, primary
composition, and to the features of hadronic interaction. New experimental data
on muon bundles at zenith angles from 30 degrees to horizon obtained with the
coordinate detector DECOR are compared with CORSIKA-based simulations. It is
found that measurements of muon density spectra in inclined EAS give
possibility to study characteristics of primary cosmic ray flux in a very wide
energy range from 10^15 to 10^19 eV.Comment: 7 pages, 7 figures. Presented at CRIS-2006, Catania, Italy, May 29 -
June 2, 2006. Accepted for publication in Nucl. Phys. B (Proc. Suppl.
Probe-configuration dependent dephasing in a mesoscopic interferometer
Dephasing in a ballistic four-terminal Aharonov-Bohm geometry due to charge
and voltage fluctuations is investigated. Treating two terminals as voltage
probes, we find a strong dependence of the dephasing rate on the probe
configuration in agreement with a recent experiment by Kobayashi et al. (J.
Phys. Soc. Jpn. 71, 2094 (2002)). Voltage fluctuations in the measurement
circuit are shown to be the source of the configuration dependence.Comment: 4 pages, 3 figure
Dephasing in Open Quantum Dots
Shape-averaged magnetoconductance (weak localization) is used for the first
time to obtain the electron phase coherence time in open
ballistic GaAs quantum dots. Values for in the range of
temperature T from 0.335 to 4 K are found to be independent of dot area, and
are not consistent with the behavior expected for
isolated dots. Surprisingly, agrees quantitatively with the
predicted dephasing time for disordered two-dimensional electron systems.Comment: 9 pages, 4 figure
Ultra Long Period Cepheids: a primary standard candle out to the Hubble flow
The cosmological distance ladder crucially depends on classical Cepheids
(with P=3-80 days), which are primary distance indicators up to 33 Mpc. Within
this volume, very few SNe Ia have been calibrated through classical Cepheids,
with uncertainty related to the non-linearity and the metallicity dependence of
their period-luminosity (PL) relation. Although a general consensus on these
effects is still not achieved, classical Cepheids remain the most used primary
distance indicators. A possible extension of these standard candles to further
distances would be important. In this context, a very promising new tool is
represented by the ultra-long period (ULP) Cepheids (P \geq 80 days), recently
identified in star-forming galaxies. Only a small number of ULP Cepheids have
been discovered so far. Here we present and analyse the properties of an
updated sample of 37 ULP Cepheids observed in galaxies within a very large
metallicity range of 12+log(O/H) from ~7.2 to 9.2 dex. We find that their
location in the colour(V-I)-magnitude diagram as well as their Wesenheit (V-I)
index-period (WP) relation suggests that they are the counterparts at high
luminosity of the shorter-period (P \leq 80 days) classical Cepheids. However,
a complete pulsation and evolutionary theoretical scenario is needed to
properly interpret the true nature of these objects. We do not confirm the
flattening in the studied WP relation suggested by Bird et al. (2009). Using
the whole sample, we find that ULP Cepheids lie around a relation similar to
that of the LMC, although with a large spread (~0.4 mag).Comment: 8 pages, 4 figures, accepted for publication in Astrophysics & Space
Scienc
New constraints on the mass composition of cosmic rays above 10^17 eV from Volcano Ranch measurements
Linsley used the Volcano Ranch array to collect data on the lateral
distribution of showers produced by cosmic rays at energies above 10^17 eV.
Very precise measurements of the steepness of the lateral distribution function
were made on 366 events. The current availability of sophisticated hadronic
interaction models has prompted an interpretation of the measurements. In this
analysis we use the AIRES Monte Carlo code to generate showers, together with
GEANT4 to simulate the detector response to ground particles. The results show
that, with the assumption of a bi-modal proton and iron mix, iron is the
dominant component of cosmic rays between 5x10^17 and 10^19 eV, assuming that
hadronic interactions are well-described by QGSJET at this energy range.Comment: Submitted to Astropart. Phy
Long Lived Superheavy Dark Matter with Discrete Gauge Symmetries
The recently observed ultra-high energy (UHE) cosmic rays beyond the
Greisen-Zatsepin-Kuzmin bound can be explained by the decays of some superheavy
particles forming a part of dark matter in our universe. We consider
various discrete gauge symmetries to ensure the required long
lifetime () of the particle to explain
the UHE cosmic rays in the minimal supersymmetric standard model (MSSM) with
massive Majorana neutrinos. We show that there is no anomaly-free discrete
gauge symmetry to make the lifetime of the particle sufficiently long in
the MSSM with the particle. We find, however, possible solutions to this
problem especially by enlarging the particle contents in the MSSM. We show a
number of solutions introducing an extra pair of singlets and
which have fractional (N=2,3) charges. The present experimental
constraints on the particle are briefly discussed.Comment: 27 pages, Late
Light cone QCD sum rules study of the semileptonic heavy and transitions to and baryons
The semileptonic decays of heavy spin--1/2, and
baryons to the light spin-- 1/2, and baryons are investigated
in the framework of the light cone QCD sum rules. In particular, using the most
general form of the interpolating currents for the heavy baryons as well as the
distribution amplitudes of the and baryons, we calculate all
form factors entering the matrix elements of the corresponding effective
Hamiltonians in full QCD. Having calculated the responsible form factors, we
evaluate the decay rates and branching fractions of the related transitions.Comment: 30 Pages, 5 Figures and 18 Table
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