964 research outputs found
Physiological Reflux and Venous Diameter Change in the Proximal Lower Limb Veins During a Standardised Valsalva Manoeuvre
AbstractObjectives: the aim of this study was to provide normal values for venous diameter at rest, and venous diameter and physiologic venous reflux during a standardised Valsalva manoeuvre. The impact of the patient's sex, body mass index (BMI), and family history was investigated. Material and methods: eighty legs of 40 healthy volunteers were investigated in a supine position. The median age was 28 years (range 20–66 years). The common femoral vein (CFV), the proximal superficial femoral vein (SFV) and the proximal long saphenous vein (LSV) were investigated by duplex sonography. The following parameters were assessed: resting diameter (VDrest) and maximum diameter (VDmax) as well as reflux time (tr) during the Valsalva manoeuvre. The Valsalva manoeuvre was elicited by a forceful expiration into a tube system. The standard values used were a pressure of 30 mmHg, established within 0.5 seconds (s) and maintained over a time period of at least 3 s. Results: mean VDrestand VDmaxwere 8.3±2.2 and 11.1±2.8 mm in the CFV, 5.9±1.3 and 7.2±1.6 mm in the SFV and 3.5±0.9 and 4.3±1.4 mm in the LSV. Mean values for trwere 0.61±0.63 s in the CFV, 0.25±0.26 s in the SFV and 0.28±0.40 s in the LSV. A BMI >22.5 kg/m2was associated with statistically significant larger values for VDrestand tr. If adjusted for BMI, trin the SFV and the LSV did not differ by sex. For healthy subjects with first-degree relatives suffering from varicose veins (n=19), mean VDrestin the SFV as well as VD in the LSV was significantly larger (p=0.02, 0.05, respectively). Coefficients of variation for repeated measurements (VDrest, VDmax, tr) in the same segment varied between 3.3% and 16.4% for the three investigated sites.Conclusions: normal values for VDrestand VDmaxas well as reflux time during a standardised Valsalva manouevre were assessed in the proximal lower limb veins. The influences of BMI, sex and family history were investigated. The described standardised Valsalva manoeuvre led to highly reproducible results and can be recommended for further research projects or as a routine procedure for the assessment of venous reflux
An updated analysis of NN elastic scattering data to 1.6 GeV
An energy-dependent and set of single-energy partial-wave analyses of
elastic scattering data have been completed. The fit to 1.6~GeV has been
supplemented with a low-energy analysis to 400 MeV. Using the low-energy fit,
we study the sensitivity of our analysis to the choice of coupling
constant. We also comment on the possibility of fitting data alone. These
results are compared with those found in the recent Nijmegen analyses. (Figures
may be obtained from the authors upon request.)Comment: 17 pages of text, VPI-CAPS-7/
Transverse Phase Locking for Vortex Motion in Square and Triangular Pinning Arrays
We analyze transverse phase locking for vortex motion in a superconductor
with a longitudinal DC drive and a transverse AC drive. For both square and
triangular arrays we observe a variety of fractional phase locking steps in the
velocity versus DC drive which correspond to stable vortex orbits. The locking
steps are more pronounced for the triangular arrays which is due to the fact
that the vortex motion has a periodic transverse velocity component even for
zero transverse AC drive. All the steps increase monotonically in width with AC
amplitude. We confirm that the width of some fractional steps in the square
arrays scales as the square of the AC driving amplitude. In addition we
demonstrate scaling in the velocity versus applied DC driving curves at
depinning and on the main step, similar to that seen for phase locking in
charge-density wave systems. The phase locking steps are most prominent for
commensurate vortex fillings where the interstitial vortices form symmetrical
ground states. For increasing temperature, the fractional steps are washed out
very quickly, while the main step gains a linear component and disappears at
melting. For triangular pinning arrays we again observe transverse phase
locking, with the main and several of the fractional step widths scaling
linearly with AC amplitude.Comment: 10 pages, 14 postscript figure
The Slavic NBN founder mutation: a role for reproductive fitness?
The vast majority of patients with Nijmegen Breakage Syndrome (NBS) are of Slavic origin and carry a deleterious deletion (c.657del5; rs587776650) in the NBN gene on chromosome 8q21. This mutation is essentially confined to Slavic populations and may thus be considered a Slavic founder mutation. Notably, not a single parenthood of a homozygous c.657del5 carrier has been reported to date, while heterozygous carriers do reproduce but have an increased cancer risk. These observations seem to conflict with the considerable carrier frequency of c.657del5 of 0.5% to 1% as observed in different Slavic populations because deleterious mutations would be eliminated quite rapidly by purifying selection. Therefore, we propose that heterozygous c.657del5 carriers have increased reproductive success, i.e., that the mutation confers heterozygote advantage. In fact, in our cohort study of the reproductive history of 24 NBS pedigrees from the Czech Republic, we observed that female carriers gave birth to more children on average than female non-carriers, while no such reproductive differences were observed for males. We also estimate that c.657del5 likely occurred less than 300 generations ago, thus supporting the view that the original mutation predated the historic split and subsequent spread of the 'Slavic people'. We surmise that the higher fertility of female c.657del5 carriers reflects a lower miscarriage rate in these women, thereby reflecting the role of the NBN gene product, nibrin, in the repair of DNA double strand breaks and their processing in immune gene rearrangements, telomere maintenance, and meiotic recombination, akin to the previously described role of the DNA repair genes BRCA1 and BRCA2
NMR and NQR Fluctuation Effects in Layered Superconductors
We study the effect of thermal fluctuations of the s-wave order parameter of
a quasi two dimensional superconductor on the nuclear spin relaxation rate near
the transition temperature Tc. We consider both the effects of the amplitude
fluctuations and the Berezinskii-Kosterlitz-Thouless (BKT) phase fluctuations
in weakly coupled layered superconductors. In the treatment of the amplitude
fluctuations we employ the Gaussian approximation and evaluate the longitudinal
relaxation rate 1/T1 for a clean s-wave superconductor, with and without pair
breaking effects, using the static pair fluctuation propagator D. The increase
in 1/T1 due to pair breaking in D is overcompensated by the decrease arising
from the single particle Green's functions. The result is a strong effect on
1/T1 for even a small amount of pair breaking. The phase fluctuations are
described in terms of dynamical BKT excitations in the form of pancake
vortex-antivortex (VA) pairs. We calculate the effect of the magnetic field
fluctuations caused by the translational motion of VA excitations on 1/T1 and
on the transverse relaxation rate 1/T2 on both sides of the BKT transitation
temperature T(BKT)<Tc. The results for the NQR relaxation rates depend strongly
on the diffusion constant that governs the motion of free and bound vortices as
well as the annihilation of VA pairs. We discuss the relaxation rates for real
multilayer systems where the diffusion constant can be small and thus increase
the lifetime of a VA pair, leading to an enhancement of the rates. We also
discuss in some detail the experimental feasibility of observing the effects of
amplitude fluctuations in layered s-wave superconductors such as the
dichalcogenides and the effects of phase fluctuations in s- or d-wave
superconductors such as the layered cuprates.Comment: 38 pages, 12 figure
Metastable States in Spin Glasses and Disordered Ferromagnets
We study analytically M-spin-flip stable states in disordered short-ranged
Ising models (spin glasses and ferromagnets) in all dimensions and for all M.
Our approach is primarily dynamical and is based on the convergence of a
zero-temperature dynamical process with flips of lattice animals up to size M
and starting from a deep quench, to a metastable limit. The results (rigorous
and nonrigorous, in infinite and finite volumes) concern many aspects of
metastable states: their numbers, basins of attraction, energy densities,
overlaps, remanent magnetizations and relations to thermodynamic states. For
example, we show that their overlap distribution is a delta-function at zero.
We also define a dynamics for M=infinity, which provides a potential tool for
investigating ground state structure.Comment: 34 pages (LaTeX); to appear in Physical Review
Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Deep-inelastic positron-proton interactions at low values of Bjorken-x down
to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons
are studied with the H1 experiment at HERA. The inclusive cross section for
pi^0 mesons produced at small angles with respect to the proton remnant (the
forward region) is presented as a function of the transverse momentum and
energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x.
Measurements are also presented of the transverse energy flow in events
containing a forward pi^0 meson. Hadronic final state calculations based on QCD
models implementing different parton evolution schemes are confronted with the
data.Comment: 27 pages, 8 figures and 3 table
Search for Doubly-Charged Higgs Boson Production at HERA
A search for the single production of doubly-charged Higgs bosons H^{\pm \pm}
in ep collisions is presented. The signal is searched for via the Higgs decays
into a high mass pair of same charge leptons, one of them being an electron.
The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment
at HERA. No evidence for doubly-charged Higgs production is observed and mass
dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs
boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only
decays into an electron and a muon via a coupling of electromagnetic strength
h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the
H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged
Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3,
masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl
Azimuthal anisotropy of K0s and Lambda prduction at mid-rapidity from Au+Au collisions at root s = 130 GeV
We report STAR results on the azimuthal anisotropy parameter v2 for strange
particles K0S, L and Lbar at midrapidity in Au+Au collisions at sNN = 130 GeV
at RHIC. The value of v2 as a function of transverse momentum of the produced
particles pt and collision centrality is presented for both particles up to pt
3.0 GeV/c. A strong pt dependence in v2 is observed up to 2.0 GeV/c. The v2
measurement is compared with hydrodynamic model calculations. The physics
implications of the pt integrated v2 magnitude as a function of particle mass
are also discussed.Comment: 6 pages, 4 figures, by the STAR collaboratio
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