363 research outputs found
Tunneling Density of States of the Interacting Two-Dimensional Electron Gas
We investigate the influence of electron--electron interactions on the
density of states of a ballistic two--dimensional electron gas. The density of
states is determined nonperturbatively by means of path integral techniques
allowing for reliable results near the Fermi surface, where perturbation theory
breaks down. We find that the density of states is suppressed at the Fermi
level to a finite value. This suppression factor grows with decreasing electron
density and is weakened by the presence of gates.Comment: 4 pages, 2 figures; slightly shortened version published in PR
Second Primary Neoplasms in Patients With Uveal Melanoma: A SEER Database Analysis
PURPOSE:
To determine the risk of second primary neoplasms (SPNs) in subjects previously diagnosed with uveal melanoma (UM), including an analysis on whether radiotherapy is a risk factor to develop these SPNs.
DESIGN:
Retrospective cohort study.
METHODS:
Using the Surveillance, Epidemiology, and End Results (SEER) 9 database, we identified patients diagnosed with UM as their first malignancy between 1973 and 2011 (n = 3976). We obtained standardized incidence ratios (SIR) and excess absolute risks of SPNs on patients with UM compared to a reference population. Multivariate Cox regression models were used to evaluate the effect of radiotherapy in SPN risk.
RESULTS:
Sixteen percent (n = 641) of the patients developed SPNs during a median follow-up of 83 months (range, 1-463 months). This represented an 11% excess risk compared to the reference population, mainly owing to a significantly increased risk of skin melanomas (SIR = 2.93, 95% CI: 2.23-3.78) and kidney tumors (SIR = 1.91, 95% CI: 1.27-2.76), primarily in those diagnosed between 30 and 59 years of age. The occurrence of second UM was also increased (SIR = 16.90, 95% CI: 9.00-28.90), which likely includes recurrences misclassified as a second cancer. Radiotherapy was performed in 39% (n = 1538) of the patients. Multivariate analysis revealed that this treatment was not an independent risk factor for SPNs (hazard ratio = 1.06, 95% CI: 0.88-1.26, P = .54).
CONCLUSIONS:
Patients with UM presented an 11% higher risk of SPNs compared to the reference population. Radiotherapy does not seem to be a risk factor. SPNs should be considered in the surveillance of UM.info:eu-repo/semantics/publishedVersio
The zero-dimensional O(N) vector model as a benchmark for perturbation theory, the large-N expansion and the functional renormalization group
We consider the zero-dimensional O(N) vector model as a simple example to
calculate n-point correlation functions using perturbation theory, the large-N
expansion, and the functional renormalization group (FRG). Comparing our
findings with exact results, we show that perturbation theory breaks down for
moderate interactions for all N, as one should expect. While the
interaction-induced shift of the free energy and the self-energy are well
described by the large-N expansion even for small N, this is not the case for
higher-order correlation functions. However, using the FRG in its one-particle
irreducible formalism, we see that very few running couplings suffice to get
accurate results for arbitrary N in the strong coupling regime, outperforming
the large-N expansion for small N. We further remark on how the derivative
expansion, a well-known approximation strategy for the FRG, reduces to an exact
method for the zero-dimensional O(N) vector model.Comment: 13 pages, 13 figure
CLASH-VLT: Environment-driven evolution of galaxies in the z=0.209 cluster Abell 209
The analysis of galaxy properties and the relations among them and the
environment, can be used to investigate the physical processes driving galaxy
evolution. We study the cluster A209 by using the CLASH-VLT spectroscopic data
combined with Subaru photometry, yielding to 1916 cluster members down to a
stellar mass of 10^{8.6} Msun. We determine: i) the stellar mass function of
star-forming and passive galaxies; ii) the intra-cluster light and its
properties; iii) the orbits of low- and high-mass passive galaxies; and iv) the
mass-size relation of ETGs. The stellar mass function of the star-forming
galaxies does not depend on the environment, while the slope found for passive
galaxies becomes flatter in the densest region. The color distribution of the
intra-cluster light is consistent with the color of passive members. The
analysis of the dynamical orbits shows that low-mass passive galaxies have
tangential orbits, avoiding small pericenters around the BCG. The mass-size
relation of low-mass passive ETGs is flatter than that of high mass galaxies,
and its slope is consistent with that of field star-forming galaxies. Low-mass
galaxies are also more compact within the scale radius of 0.65 Mpc. The ratio
between stellar and number density profiles shows a mass segregation in the
center. The comparative analysis of the stellar and total density profiles
indicates that this effect is due to dynamical friction. Our results are
consistent with a scenario in which the "environmental quenching" of low-mass
galaxies is due to mechanisms such as harassment out to R200, starvation and
ram-pressure stripping at smaller radii, as supported by the analysis of the
mass function, of the dynamical orbits and of the mass-size relation of passive
early-types in different regions. Our analyses support the idea that the
intra-cluster light is formed through the tidal disruption of subgiant
galaxies.Comment: 17 pages, 20 figures, A&A in pres
Reproducibility of lymphovascular space invasion (LVSI) assessment in endometrial cancer
Aims Lymphovascular space invasion (LVSI) in endometrial cancer (EC) is an important prognostic variable impacting on a patient's individual recurrence risk and adjuvant treatment recommendations. Recent work has shown that grading the extent of LVSI further improves its prognostic strength in patients with stage I endometrioid EC. Despite this, there is little information on the reproducibility of LVSI assessment in EC. Therefore, we designed a study to evaluate interobserver agreement in discriminating true LVSI from LVSI mimics (Phase I) and reproducibility of grading extent of LVSI (Phase II). Methods and results Scanned haematoxylin and eosin (H&E) slides of endometrioid EC (EEC) with a predefined possible LVSI focus were hosted on a website and assessed by a panel of six European gynaecological pathologists. In Phase I, 48 H&E slides were included for LVSI assessment and in Phase II, 42 H&E slides for LVSI grading. Each observer was instructed to apply the criteria for LVSI used in daily practice. The degree of agreement was measured using the two-way absolute agreement average-measures intraclass correlation coefficient (ICC). Reproducibility of LVSI assessment (ICC = 0.64, P < 0.001) and LVSI grading (ICC = 0.62, P < 0.001) in EEC was substantial among the observers. Conclusions Given the good reproducibility of LVSI, this study further supports the important role of LVSI in decision algorithms for adjuvant treatment
Collective fields in the functional renormalization group for fermions, Ward identities, and the exact solution of the Tomonaga-Luttinger model
We develop a new formulation of the functional renormalization group (RG) for
interacting fermions. Our approach unifies the purely fermionic formulation
based on the Grassmannian functional integral, which has been used in recent
years by many authors, with the traditional Wilsonian RG approach to quantum
systems pioneered by Hertz [Phys. Rev. B 14, 1165 (1976)], which attempts to
describe the infrared behavior of the system in terms of an effective bosonic
theory associated with the soft modes of the underlying fermionic problem. In
our approach, we decouple the interaction by means of a suitable
Hubbard-Stratonovich transformation (following the Hertz-approach), but do not
eliminate the fermions; instead, we derive an exact hierarchy of RG flow
equations for the irreducible vertices of the resulting coupled field theory
involving both fermionic and bosonic fields. The freedom of choosing a momentum
transfer cutoff for the bosonic soft modes in addition to the usual band cutoff
for the fermions opens the possibility of new RG schemes. In particular, we
show how the exact solution of the Tomonaga-Luttinger model emerges from the
functional RG if one works with a momentum transfer cutoff. Then the Ward
identities associated with the local particle conservation at each Fermi point
are valid at every stage of the RG flow and provide a solution of an infinite
hierarchy of flow equations for the irreducible vertices. The RG flow equation
for the irreducible single-particle self-energy can then be closed and can be
reduced to a linear integro-differential equation, the solution of which yields
the result familiar from bosonization. We suggest new truncation schemes of the
exact hierarchy of flow equations, which might be useful even outside the weak
coupling regime.Comment: 27 pages, 15 figures; published version, some typos correcte
Subgap tunneling through channels of polarons and bipolarons in chain conductors
We suggest a theory of internal coherent tunneling in the pseudogap region
where the applied voltage is below the free electron gap. We consider quasi 1D
systems where the gap is originated by a lattice dimerization like in
polyacethylene, as well as low symmetry 1D semiconductors. Results may be
applied to several types of conjugated polymers, to semiconducting nanotubes
and to quantum wires of semiconductors. The approach may be generalized to
tunneling in strongly correlated systems showing the pseudogap effect, like the
family of High Tc materials in the undoped limit. We demonstrate the evolution
of tunneling current-voltage characteristics from smearing the free electron
gap down to threshold for tunneling of polarons and further down to the region
of bi-electronic tunneling via bipolarons or kink pairs.Comment: 14 pages, 8 postscript figure
Inhibition of HCV 3a genotype entry through Host CD81 and HCV E2 antibodies
<p>Abstract</p> <p>Background</p> <p>HCV causes acute and chronic hepatitis which can eventually lead to permanent liver damage hepatocellular carcinoma and death. HCV glycoproteins play an important role in HCV entry by binding with CD81 receptors. Hence inhibition of virus at entry step is an important target to identify antiviral drugs against HCV.</p> <p>Methods and result</p> <p>The present study elaborated the role of CD81 and HCV glycoprotein E2 in HCV entry using retroviral pseudo-particles of 3a local genotype. Our results demonstrated that HCV specific antibody E2 and host antibody CD81 showed dose- dependent inhibition of HCV entry. HCV E2 antibody showed 50% reduction at a concentration of 1.5 ± 1 μg while CD81 exhibited 50% reduction at a concentration of 0.8 ± 1 μg. In addition, data obtained with HCVpp were also confirmed with the infection of whole virus of HCV genotype 3a in liver cells.</p> <p>Conclusion</p> <p>Our data suggest that HCV specific E2 and host CD81 antibodies reduce HCVpp entry and full length viral particle and combination of host and HCV specific antibodies showed synergistic effect in reducing the viral titer.</p
Correlation functions of higher-dimensional Luttinger liquids
Using higher-dimensional bosonization, we study correlation functions of
fermions with singular forward scattering. Following Bares and Wen [Phys. Rev.
B 48, 8636 (1993)], we consider density-density interactions in d dimensions
that diverge for small momentum transfers as q^{- eta} with eta = 2 (d-1). In
this case the single-particle Green's function shows Luttinger liquid behavior.
We discuss the momentum distribution and the density of states and show that,
in contrast to d=1, in higher dimensions the scaling behavior cannot be
characterized by a single anomalous exponent. We also calculate the irreducible
polarization for q close to 2 k_F and show that the leading singularities
cancel. We discuss consequences for the effect of disorder on
higher-dimensional Luttinger liquids.Comment: 7 RevTex pages, 2 figures, minor modifications, to appear in Phys.
Rev. B (Feb. 1999
CLASH-VLT: Substructure in the galaxy cluster MACS J1206.2-0847 from kinematics of galaxy populations
In the effort to understand the link between the structure of galaxy clusters
and their galaxy populations, we focus on MACSJ1206.2-0847 at z~0.44 and probe
its substructure in the projected phase space through the spectrophotometric
properties of a large number of galaxies from the CLASH-VLT survey. Our
analysis is mainly based on an extensive spectroscopic dataset of 445 member
galaxies, mostly acquired with VIMOS@VLT as part of our ESO Large Programme,
sampling the cluster out to a radius ~2R200 (4 Mpc). We classify 412 galaxies
as passive, with strong Hdelta absorption (red and blue galaxies, and with
emission lines from weak to very strong. A number of tests for substructure
detection are applied to analyze the galaxy distribution in the velocity space,
in 2D space, and in 3D projected phase-space. Studied in its entirety, the
cluster appears as a large-scale relaxed system with a few secondary, minor
overdensities in 2D distribution. We detect no velocity gradients or evidence
of deviations in local mean velocities. The main feature is the WNW-ESE
elongation. The analysis of galaxy populations per spectral class highlights a
more complex scenario. The passive galaxies and red strong Hdelta galaxies
trace the cluster center and the WNW-ESE elongated structure. The red strong
Hdelta galaxies also mark a secondary, dense peak ~2 Mpc at ESE. The emission
line galaxies cluster in several loose structures, mostly outside R200. The
observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the
direction of the main cluster accretion, traced by passive galaxies and red
strong Hdelta galaxies. The red strong Hdelta galaxies, interpreted as
poststarburst galaxies, date a likely important event 1-2 Gyr before the epoch
of observation. The emission line galaxies trace a secondary, ongoing infall
where groups are accreted along several directions.Comment: A&A accepted, 19 pages, 30 figures, minor language change
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