14,729 research outputs found
Polarization dependence of the third-harmonic generation in multiband superconductors
In a superconductor the third-harmonic generation (THG) of a strong THz pulse
is enhanced below Tc by the resonant excitation of lattice-modulated charge
fluctuations (LCF), which modulate the response according to the polarization
of the field. Here we compute the THG within a multiband model for the
prototype NbN superconductor. We show that the non-resonant contribution coming
from the instantaneous electronic response and the finite width of the pulse
significantly suppress the polarization dependence of the signal, challenging
its observation in real systems.Comment: Final version, as publishe
KRAS early testing. Consensus initiative and cost-effectiveness evaluation for metastatic colorectal patients in an italian setting
KRAS testing is relevant for the choice of the most appropriate first-line therapy of metastatic colorectal cancer (CRC). Strategies for preventing unequal access to the test should be implemented, but their relevance in the practice is related to economic sustainability. The study adopted the Delphi technique to reach a consensus on several topics. Issues related to execution of KRAS testing were identified by an expert's board and proposed to 108 Italian oncologists and pathologists through two subsequent questionnaires. The emerging proposal was evaluated by decision analyses models employed by technology assessment agencies in order to assess cost-effectiveness. Alternative therapeutic strategies included most commonly used chemotherapy regimens alone or in combination with cetuximab or bevacizumab. The survey indicated that time interval for obtaining KRAS test should not exceed 15 days, 10 days being an optimal interval. To assure the access to proper treatment, a useful strategy should be to anticipate the test after radical resection in patients at high risk of relapse. Early KRAS testing in high risk CRC patients generates incremental cost-effectiveness ratios between 6,000 and 13,000 Euro per quality adjusted life year (QALY) gained. In extensive sensitivity analyses ICER's were always below 15,000 Euro per QALY gained, far within the threshold of 60,000 Euro/QALY gained accepted by regulatory institutions in Italy. In metastatic CRC a time interval higher than 15 days for result of KRAS testing limits access to therapeutic choices. Anticipating KRAS testing before the onset of metastatic disease in patients at high risk does not affect the sustainability and cost-effectiveness profile of cetuximab in first-line mCRC. Early KRAS testing may prevent this inequality in high-risk patients, whether they develop metastases, and is a cost-effective strategy. Based on these results, present joined recommendations of Italian societies of Oncology and Pathology should be updated including early KRAS testing
Field sources in a Lorentz symmetry breaking scenario with a single background vector
This paper is devoted to investigating the interactions between stationary
sources of the electromagnetic field, in a model which exhibits explicit
Lorentz-symmetry breaking due to the presence of a single background vector. We
focus on physical phenomena that emerge from this kind of breaking and which
have no counterpart in Maxwell Electrodynamics
Double-Spin Transverse Asymmetries in Drell-Yan Processes
We calculate the double-spin transverse asymmetries for the Drell-Yan lepton
pair production in p-p and p-anti p collisions. We assume the transverse and
the longitudinal polarization densities to be equal at a very small scale, as
it is suggested by confinement model results. Using a global fit for the
longitudinal distributions, we find transverse asymmetries of order of 10^-2 at
most, in the accessible kinematic regions.Comment: 8 pages, REVTeX, 6 figures included as file figures.tar.g
New point-like sources and a conducting surface in Maxwell-Chern-Simons electrodynamics
We investigate some aspects of the Maxwell-Chern-Simons electrodynamics
focusing on physical effects produced by the presence of stationary sources and
a perfectly conducting plate (mirror). Specifically, in addition to point
charges, we propose two new types of point-like sources called topological
source and Dirac point, and we also consider physical effects in various
configurations that involve them. We show that the Dirac point is the source of
the vortex field configurations. The propagator of the gauge field due to the
presence of a conducting plate and the interaction forces between the plate and
point-like sources are computed. It is shown that the image method is valid for
the point-like charges as well as for Dirac points. For the topological source
we show that the image method is not valid and the symmetry of spatial
refection on the mirror is broken. In all setups considered, it is shown that
the topological source leads to the emergence of torques.Comment: 17 Latex pages, 7 figure
Measurement of the current-phase relation of superconducting atomic contacts
We have probed the current-phase relation of an atomic contact placed with a
tunnel junction in a small superconducting loop. The measurements are in
quantitative agreement with the predictions of a resistively shunted SQUID
model in which the Josephson coupling of the contact is calculated using the
independently determined transmissions of its conduction channels.Comment: to be published in Physical Review Letter
Bistability in superconducting rings containing an inhomogeneous Josephson junction
We investigate the magnetic response of a superconducting Nb ring containing
a ferromagnetic PdNi Josephson junction and a tunnel junction in parallel. A
doubling of the switching frequency is observed within certain intervals of the
external magnetic field. Assuming sinusoidal current-phase relations of both
junctions our model of a dc-SQUID embedded within a superconducting ring
explains this feature by a sequence of current reversals in the ferromagnetic
section of the junction in these field intervals. The switching anomalies are
induced by the coupling between the magnetic fluxes in the two superconducting
loops.Comment: 5 pages, 4 figure
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