6,347 research outputs found
Recent advances in minimally invasive colorectal cancer surgery
Laparoscopy has improved surgical treatment of various diseases due to its limited surgical trauma and has developed as an interesting therapeutic alternative for the resection of colorectal cancer. Despite numerous clinical advantages (faster recovery, less pain, fewer wound and systemic complications, faster return to work) the laparoscopic approach to colorectal cancer therapy has also resulted in unusual complications, i.e. ureteral and bladder injury which are rarely observed with open laparotomy. Moreover, pneumothorax, cardiac arrhythmia, impaired venous return, venous thrombosis as well as peripheral nerve injury have been associated with the increased intraabdominal pressure as well as patient's positioning during surgery. Furthermore, undetected small bowel injury caused by the grasping or cauterizing instruments may occur with laparoscopic surgery. In contrast to procedures performed for nonmalignant conditions, the benefits of laparoscopic resection of colorectal cancer must be weighed against the potential for poorer long-term outcomes of cancer patients that still has not been completely ruled out. In laparoscopic colorectal cancer surgery, several important cancer control issues still are being evaluated, i.e. the extent of lymph node dissection, tumor implantation at port sites, adequacy of intraperitoneal staging as well as the distance between tumor site and resection margins. For the time being it can be assumed that there is no significant difference in lymph node harvest between laparoscopic and open colorectal cancer surgery if oncological principles of resection are followed. As far as the issue of port site recurrence is concerned, it appears to be less prevalent than first thought (range 0-2.5%), and the incidence apparently corresponds with wound recurrence rates observed after open procedures. Short-term (3-5 years) survival rates have been published by a number of investigators, and survival rates after laparoscopic surgery appears to compare well with data collected after conventional surgery for colorectal cancer. However, long-term results of prospective randomized trials are not available. The data published so far indicate that the oncological results of laparoscopic surgery compare well with the results of the conventional open approach. Nonetheless, the limited information available from prospective studies leads us to propose that minimally invasive surgery for colorectal cancer surgery should only be performed within prospective trials
Analytical formula for the Uehling potential
The closed analytical expression for the Uehling potential is derived. The
Uehling potential describes the lowest-order correction on vacuum polarisation
in atomic and muon-atomic systems. We also derive the analytical formula for
the interaction potential between two electrically charged point particles
which includes correction to the vacuum polarisation, but has correct
asymptotic behaviour at larger . Our three-term analytical formula for the
Uehling potential opens a new avenue in the study of the vacuum polarisation in
light atomic systems.Comment: arXiv admin note: substantial text overlap with arXiv:1103.204
A Case Study of Low-Mass Star Formation
This article synthesizes observational data from an extensive program aimed
toward a comprehensive understanding of star formation in a low-mass
star-forming molecular cloud. New observations and published data spanning from
the centimeter wave band to the near infrared reveal the high and low density
molecular gas, dust, and pre-main sequence stars in L1551.Comment: 24 pages, 21 figures, ApJS accepte
New triple systems in the RasTyc sample of stellar X-ray sources
During the study of a large set of late-type stellar X-ray sources, we
discovered a large fraction of multiple systems. In this paper we investigate
the orbital elements and kinematic properties of three new spectroscopic triple
systems as well as spectral types and astrophysical parameters (T_eff, log g,
vsin i, log N(Li)) of their components. We conducted follow-up optical
observations, both photometric and spectroscopic at high resolution, of these
systems. We used a synthetic approach and the cross-correlation method to
derive most of the stellar parameters. We estimated reliable radial velocities
and deduced the orbital elements of the inner binaries. The comparison of the
observed spectra with synthetic composite ones, obtained as the weighted sum of
three spectra of non-active reference stars, allowed us to determine the
stellar parameters for each component of these systems. We found all are only
composed of main sequence stars. These three systems are certainly stable
hierarchical triples composed of short-period inner binaries plus a tertiary
component in a long-period orbit. From their kinematics and/or Lithium content,
these systems result to be fairly young.Comment: Accepted for publication in A&A (on July 22, 2008
The Chromo-Dielectric Soliton Model: Quark Self Energy and Hadron Bags
The chromo-dielectric soliton model (CDM) is Lorentz- and chirally-invariant.
It has been demonstrated to exhibit dynamical chiral symmetry breaking and
spatial confinement in the locally uniform approximation. We here study the
full nonlocal quark self energy in a color-dielectric medium modeled by a two
parameter Fermi function. Here color confinement is manifest. The self energy
thus obtained is used to calculate quark wave functions in the medium which, in
turn, are used to calculate the nucleon and pion masses in the one gluon
exchange approximation. The nucleon mass is fixed to its empirical value using
scaling arguments; the pion mass (for massless current quarks) turns out to be
small but non-zero, depending on the model parameters.Comment: 24 pages, figures available from the author
On the interaction of a single-photon wave packet with an excited atom
The interaction of a single-photon wave packet with an initially excited
two-level atom in free space is studied in semiclassical and quantum
approaches. It is shown that the final state of the field does not contain
doubly occupied modes. The process of the atom's transition to the ground state
may be accelerated, decelerated or even reversed by the incoming photon,
depending on parameters. The spectrum of emitted radiation is close to the sum
of the spectrum of the incoming single-photon wave packet and the natural line
shape, with small and complicated deviations.Comment: 17 pages, 5 figure
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