297 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
Detectability of dirty dust grains in brown dwarf atmospheres
Dust clouds influence the atmospheric structure of brown dwarfs, and they
affect the heat transfer and change the gas-phase chemistry. However, the
physics of their formation and evolution is not well understood. In this
letter, we predict dust signatures and propose a potential observational test
of the physics of dust formation in brown dwarf atmosphere based on the
spectral features of the different solid components predicted by dust formation
theory. A momentum method for the formation of dirty dust grains (nucleation,
growth, evaporation, drift) is used in application to a static brown dwarf
atmosphere structure to compute the dust grain properties, in particular the
heterogeneous grain composition and the grain size. Effective medium and Mie
theory are used to compute the extinction of these spherical grains. Dust
formation results in grains whose composition differs from that of grains
formed at equilibrium. Our kinetic model predicts that solid amorphous SiO2[s]
(silica) is one of the most abundant solid component followed by amorphous
MgSiO4[s] and MgSiO3[s], while SiO2[s] is absent in equilibrium models
because it is a metastable solid. Solid amorphous SiO2[s] possesses a strong
broad absorption feature centered at 8.7mum, while amorphous
Mg2SiO4[s]/MgSiO3[s] absorb at 9.7mum beside other absorption features at
longer wavelength. Those features at lambda < 15mum are detectable in
absorption if grains are small (radius < 0.2mum) in the upper atmosphere as
suggested by our model. We suggest that the detection of a feature at 8.7mum in
deep infrared spectra could provide evidence for non-equilibrium dust formation
that yields grains composed of metastable solids in brown dwarf atmospheres.
This feature will shift towards 10mum and broaden if silicates (e.g. fosterite)
are much more abundant.Comment: A&A Letter, accepte
Infrared singularities in one-loop amplitudes
In this talk we discuss a purely numerical approach to next-to-leading order
calculations in QCD. We present a simple formula, which provides a local
infrared subtraction term for the integrand of a one-loop amplitude. In
addition we briefly comment on local ultraviolet subtraction terms and on the
required deformation of the contour of integration.Comment: 6 pages, talk given at the conference "Loops and Legs", Woerlitz,
201
Spatially resolved mid-infrared observations of the triple system T Tauri
To enhance our knowledge of the characteristics and distribution of the
circumstellar dust associated with the individual components of the young
hierarchical triple system T Tau, observations in the N-band with MIDI at the
VLTI were performed. Our study is based on both the interferometric and the
spectrophotometric measurements and is supplemented by new visual and infrared
photometry. Also, the phases were investigated to determine the dominating
mid-infrared source in the close southern binary. The data were fit with the
help of a sophisticated physical disc model. This model utilises the radiative
transfer code MC3D that is based on the Monte-Carlo method. Extended
mid-infrared emission is found around all three components of the system.
Simultaneous fits to the photometric and interferometric data confirm the
picture of an almost face-on circumstellar disc around T Tau N. Towards this
star, the silicate band is seen in emission. This emission feature is used to
model the dust content of the circumstellar disc. Clear signs of dust
processing are found. Towards T Tau S, the silicate band is seen in absorption.
This absorption is strongly pronounced towards the infrared companion T Tau Sa
as can be seen from the first individual N-band spectra for the two southern
components. Our fits support the previous suggestion that an almost edge-on
disc is present around T Tau Sa. This disc is thus misaligned with respect to
the circumstellar disc around T Tau N. The interferometric data indicate that
the disc around T Tau Sa is oriented in the north-south direction, which
favours this source as launching site for the east-western jet. We further
determine from the interferometric data the relative positions of the
components of the southern binary.Comment: 24 pages, 19 figures, accepted for publication in A&
The T Tauri star RY Tau as a case study of the inner regions of circumstellar dust disks
We study the inner region of the circumstellar disk around the TTauri star RY
Tau. Our aim is to find a physical description satisfying the available
interferometric data, obtained with the mid-infrared interferometric instrument
at the Very Large Telescope Interferometer, as well as the spectral energy
distribution. We also compare the findings with the results of similar studies,
including those of intermediate-mass stars. Our analysis is done within the
framework of a passive circumstellar disk, which is optionally supplemented by
the effects of accretion and an added envelope. To achieve a more consistent
and realistic model, we used our continuum transfer code MC3D. In addition, we
studied the shape of the 10um silicate emission feature in terms of the
underlying dust population, both for single-dish and for interferometric
measurements. We show that a modestly flaring disk model with accretion can
explain both the observed spectral energy distribution and the mid-infrared
visibilities obtained with the mid-infrared infrared instrument. We found an
interesting ambiguity: a circumstellar active disk model with an added
envelope, and a lower accretion rate than in the active disk model without
envelope, could represent the observations equally as well. This type of model
with the envelope should be considered a viable alternative in future models of
other TTauri stars. The approach of a disk with a puffed-up inner rim wall and
the influence of a stellar companion is also discussed. From the study of the
silicate emission feature we see evidence for dust evolution in a TTauri star,
with a decreasing fraction of small amorphous and an increasing fraction of
crystalline particles closer to the star.Comment: 19 pages, 23 figures; accepted by Astronomy & Astrophysic
Systematic study of the pp -> pp omega reaction
A systematic study of the production of omega-mesons in
proton-proton-collisions was carried out in a kinematically complete experiment
at three excess energies(epsilon= 92, 128, 173MeV). Both protons were detected
using the large-acceptance COSY-TOF spectrometer at an external beam line at
the Cooler Synchrotron COSY at Forschungszentrum J\"ulich. The total cross
section, angular distributions of both omega-mesons and protons were measured
and presented in various reference frames such as the overall CMS, helicity and
Jackson frame. In addition, the orientation of the omega-spin and invariant
mass spectra were determined. We observe omega-production to take place
dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and,
additionally, in Sd at epsilon= 173 MeV. No obvious indication of resonant
omega-production via N^*-resonances was found, as proton angular distributions
are almost isotropic and invariant mass spectra are compatible with phase space
distributions. A dominant role of ^3P_1 and ^1S_0 initial partial waves for
omega-production was concluded from the orientation of the decay plane of the
omega-meson. Although the Jackson angle distributions in the omega-p-Jackson
frame are anisotropic we argue that this is not an indication of a resonance
but rather a kinematical effect reflecting the anisotropy of the omega angular
distribution. The helicity angle distribution in the omega-p-helicity frame
shows an anisotropy which probably reflects effects of the omega angular
momenta in the final state; this observable may be, in addition to the
orientation of the omega decay plane, the most sensitive one to judge the
validity of theoretical descriptions of the production process.Comment: 17 pages, 16 figures, accepted for publication in EPJ
Production of Lambda and Sigma^0 hyperons in proton-proton collisions
This paper reports results on simultaneous measurements of the reaction
channels pp -> pK+\Lambda and pp -> pK+\Sigma^0 at excess energies of 204, 239,
and 284 MeV (\Lambda) and 127, 162, and 207 MeV (\Sigma^0). Total and
differential cross sections are given for both reactions. It is concluded from
the measured total cross sections that the high energy limit of the cross
section ratio is almost reached at an excess energy of only about 200 MeV. From
the differential distributions observed in the overall CMS as well as in the
Jackson and helicity frames, a significant contribution of interfering nucleon
resonances to the \Lambda production mechanism is concluded while resonant
\Sigma^0-production seems to be of lesser importance and takes place only
through specific partial waves of the entrance channel. The data also indicate
that kaon exchange plays a minor role in the case of \Lambda- but an important
role for \Sigma^0-production. Thus the peculiar energy dependence of the
\Lambda-to-\Sigma^0 cross section ratio appears in a new light as its
explanation requires more than mere differences between the p\Lambda and the
p\Sigma^0 final state interaction. The data provide a benchmark for theoretical
models already available or yet to come.Comment: 18 pages, 10 figures; accepted by The European Physical Journal A
(EPJ A
A randomized phase II trial of 5-fluorouracil, with or without human interferon-β, for advanced colorectal cancer
First Experiment at TASCA Towards X-Ray Fingerprinting of Element 115 Decay Chains
To identify the atomic number of superheavy nuclei produced in Ca-48-induced fusion-evaporation reactions, an experiment aiming at measuring characteristic X-rays is being prepared at GSI, Darmstadt, Germany. The gas-filled separator TASCA will be employed, sending the residues towards the multi-coincidence detector setup TASISpec. Two ion-optical modes relying on differing magnetic polarities of the quadrupole magnets can be used at TASCA. New simulations and experimental tests of transmission and background suppression for these two focusing modes into TASISpec are presented
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