816 research outputs found
Robotic Partial Nephrectomy for a Peripheral Renal Tumor
Partial nephrectomy (PN) is the preferred surgical treatment for T1 renal tumors whenever technically feasible. When properly performed, it allows preservation of nephron mass without compromising oncologic outcomes. This reduces the postoperative risk of renal insufficiency, which translates into better overall survival for the patients. PN can be technically challenging, because it requires the surgeon to complete the tasks of tumor excision, hemostasis and renorrhaphy, all within an ischemic time of preferably below 30 minutes. The surgeon needs to avoid violating the tumor margins while leaving behind the maximal parenchymal volume at the same time. Variations such as zero ischemia, early unclamping, and selective clamping have been developed in an attempt to reduce the negative impact of renal ischemia, but inevitably add to the steep learning curves for any surgeon. Being able to appreciate the fine details of each surgical step in PN is the fundamental basis to the success of this surgery. The use of the robotic assistance allows a good combination of the minimally invasive nature of laparoscopic surgery and the surgical exposure and dexterity of open surgery. It also allows the use of adjuncts such as concurrent ultrasound assessment of the renal mass and intraoperative fluorescence to aid the identification of tumor margins, all with a simple hand switch at the console. Robot-assisted laparoscopic PN is now the most commonly performed type of PN in the United States and is gaining acceptance on the global scale. In this video, we illustrate the steps of robot-assisted laparoscopic PN and highlight the technical key points for success
Meson-Meson Scattering in Relativistic Constraint Dynamics
Dirac's relativistic constraint dynamics have been successfully applied to
obtain a covariant nonperturbative description of QED and QCD bound states. We
use this formalism to describe a microscopic theory of meson-meson scattering
as a relativistic generalization of the nonrelativistic quark-interchange model
developed by Barnes and Swanson.Comment: 5 pages, 1 figure in LaTex, talk present at the First Meeting of the
APS Topical Group on Hadronic Physics (Fermilab, October 24-26, 2004
Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas
The coupling of the spin of electrons to their motional state lies at the
heart of recently discovered topological phases of matter. Here we create and
detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form
of quantum degenerate matter. We reveal the spin-orbit gap via spin-injection
spectroscopy, which characterizes the energy-momentum dispersion and spin
composition of the quantum states. For energies within the spin-orbit gap, the
system acts as a spin diode. To fully inhibit transport, we open an additional
spin gap, thereby creating a spin-orbit coupled lattice whose spinful band
structure we probe. In the presence of s-wave interactions, such systems should
display induced p-wave pairing, topological superfluidity, and Majorana edge
states
Impact of positive surgical margins on overall survival after partial nephrectomy—A matched comparison based on the National Cancer Database
Introduction
The impact of positive surgical margins (PSM) in partial nephrectomy (PN) has been a controversy. Previous studies on the relationship between PSM and overall survival (OS) were either underpowered or had highly dissimilar groups. We used the National Cancer Database with propensity score matching to determine the association between PSM and OS after PN.
Materials and methods
We identified patients with T1/T2 N0M0 renal cancer treated with PN between 2004 and 2009, and divided them into 2 groups based on their margin status. We used propensity score matching to ensure similarities in age, comorbidity score (CCI), tumor size, histology, and grade between groups. Covariates were compared by χ2 test. Cox multiple regression was used to estimate the hazard ratios (HR) for all-cause mortality. OS between matched groups were compared by log-rank, Breslow and Tarone-Ware tests.
Results
After excluding those with missing data on margin or survival status, 20,762 patients were eligible for matching. Each matched group had 1,265 patients, similar in age, sex, race, CCI, tumor size, histology, and grade. There were 386 recorded all-cause mortalities over a median follow-up duration of 72.6 months. Cox multiple regression showed a higher risk of all-cause mortality among cases with PSM (HR: 1.393, P = 0.001). Old age, high CCI, and large tumors had higher risks, while papillary and chromophore histologic subtypes had lower risks. PSM was associated with significantly worse OS by log-rank, Breslow, and Tarone-Ware tests.
Conclusion
PSM is associated with significantly worse OS after PN
Potential Models and Lattice Gauge Current-Current Correlators
We compare current-current correlators in lattice gauge calculations with
correlators in different potential models, for a pseudoscalar charmonium in the
quark-gluon plasma. An important ingredient in the evaluation of the
current-current correlator in the potential model is the basic principle that
out of the set of continuum states, only resonance states and Gamow states with
lifetimes of sufficient magnitudes can propagate as composite objects and can
contribute to the current-current correlator. When the contributions from the
bound states and continuum states are properly treated, the potential model
current-current correlators obtained with the potential proposed in Ref. [11]
are consistent with the lattice gauge correlators. The proposed potential model
thus gains support to be a useful tool to complement lattice gauge calculations
for the study of states at high temperatures.Comment: 18 pages, 4 figures, to be published in Physcial Review
Quarkonia and Quark Drip Lines in Quark-Gluon Plasma
We extract the - potential by using the thermodynamic quantities
obtained in lattice gauge calculations. The potential is tested and found to
give dissociation temperatures that agree well with those from lattice gauge
spectral function analysis. Using such a - potential, we examine the
quarkonium states in a quark-gluon plasma and determine the `quark drip lines'
which separate the region of bound color-singlet states from the
unbound region. The characteristics of the quark drip lines severely limit the
region of possible bound states with light quarks to temperatures
close to the phase transition temperature. Bound quarkonia with light quarks
may exist very near the phase transition temperature if their effective quark
mass is of the order of 300-400 MeV and higher.Comment: 24 pages, 13 figures, in LaTe
Singularity Structures in Coulomb-Type Potentials in Two Body Dirac Equations of Constraint Dynamics
Two Body Dirac Equations (TBDE) of Dirac's relativistic constraint dynamics
have been successfully applied to obtain a covariant nonperturbative
description of QED and QCD bound states. Coulomb-type potentials in these
applications lead naively in other approaches to singular relativistic
corrections at short distances that require the introduction of either
perturbative treatments or smoothing parameters. We examine the corresponding
singular structures in the effective potentials of the relativistic
Schroedinger equation obtained from the Pauli reduction of the TBDE. We find
that the relativistic Schroedinger equation lead in fact to well-behaved wave
function solutions when the full potential and couplings of the system are
taken into account. The most unusual case is the coupled triplet system with
S=1 and L={(J-1),(J+1)}. Without the inclusion of the tensor coupling, the
effective S-state potential would become attractively singular. We show how
including the tensor coupling is essential in order that the wave functions be
well-behaved at short distances. For example, the S-state wave function becomes
simply proportional to the D-state wave function and dips sharply to zero at
the origin, unlike the usual S-state wave functions. Furthermore, this behavior
is similar in both QED and QCD, independent of the asymptotic freedom behavior
of the assumed QCD vector potential. Light- and heavy-quark meson states can be
described well by using a simplified linear-plus-Coulomb-type QCD potential
apportioned appropriately between world scalar and vector potentials. We use
this potential to exhibit explicitly the origin of the large pi-rho splitting
and effective chiral symmetry breaking. The TBDE formalism developed here may
be used to study quarkonia in quark-gluon plasma environments.Comment: 23 pages, 4 figure
Explicit Solution of the Time Evolution of the Wigner Function
Previously, an explicit solution for the time evolution of the Wigner
function was presented in terms of auxiliary phase space coordinates which obey
simple equations that are analogous with, but not identical to, the classical
equations of motion. They can be solved easily and their solutions can be
utilized to construct the time evolution of the Wigner function. In this paper,
the usefulness of this explicit solution is demonstrated by solving a numerical
example in which the Wigner function has strong spatial and temporal variations
as well as regions with negative values. It is found that the explicit solution
gives a correct description of the time evolution of the Wigner function. We
examine next the pseudoparticle approximation which uses classical trajectories
to evolve the Wigner function. We find that the pseudoparticle approximation
reproduces the general features of the time evolution, but there are
deviations. We show how these deviations can be systematically reduced by
including higher-order correction terms in powers of .Comment: 16 pages, in LaTex, invited talk presented at the Wigner Centennial
Conference, Pecs, Hungary, July 8-12, 2002, to be published in the Journal of
Optics B: Quantum and Classical Optics, June 200
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