23,372 research outputs found
Azimuthal distinguishability of entangled photons generated in spontaneous parametric down-conversion
We experimentally demonstrate that paired photons generated in different
sections of a down-conversion cone, when some of the interacting waves show
Poynting vector walk-off, carry different spatial correlations, and therefore a
different degree of spatial entanglement. This is shown to be in agreement with
theoretical results. We also discuss how this azimuthal distinguishing
information of the down-conversion cone is relevant for the implementation of
quantum sources aimed at the generation of entanglement in other degrees of
freedom, such as polarization.Comment: 7 pages, 5 figures, submitted to Opt. Expres
Optical surface modes in the presence of nonlinearity and disorder
We investigate numerically the effect of the competition of disorder,
nonlinearity, and boundaries on the Anderson localization of light waves in
finite-size, one-dimensional waveguide arrays. Using the discrete Anderson -
nonlinear Schr\"odinger equation, the propagation of the mode amplitudes up to
some finite distance is monitored. The analysis is based on the calculated
localization length and the participation number, two standard measures for the
statistical description of Anderson localization. For relatively weak disorder
and nonlinearity, a higher disorder strength is required to achieve the same
degree of localization at the edge than in the interior of the array, in
agreement with recent experimental observations in the linear regime. However,
for relatively strong disorder and/or nonlinearity, this behavior is reversed
and it is now easier to localize an excitation at the edge than in the
interior.Comment: 5 double-column pages, 7 figures, submitted for publicatio
Alternative antibody for the detection of CA125 antigen: a European multicenter study for the evaluation of the analytical and clinical performance of the Access (R) OV Monitor assay on the UniCel (R) Dxl 800 Immunoassay System
Background: Cancer antigen CA125 is known as a valuable marker for the management of ovarian cancer. Methods: The analytical and clinical performance of the Access OV Monitor Immunoassay System (Beckman Coulter) was evaluated at five different European sites and compared with a reference system, defined as CA125 on the Elecsys System (Roche Diagnostics). Results: Total imprecision (%CV) of the OV Monitor ranged between 3.1% and 8.8%, and inter-laboratory reproducibility between 4.7% and 5.0%. Linearity upon dilution showed a mean recovery of 100% (SD+8.1%). Endogenous interferents had no influence on OV Monitor levels (mean recoveries: hemoglobin 107%, bilirubin 103%, triglycericles 103%). There was no high-dose hook effect up to 27,193 kU/L. Clinical performance investigated in sera from 1811 individuals showed a good correlation between the Access OV Monitor and Elecsys CA125 (R = 0.982, slope = 0.921, intercept = + 1.951). OV Monitor serum levels were low in healthy individuals (n = 267, median = 9.7 kU/L, 95th percentile = 30.8 kU/L), higher in individuals with various benign diseases (n = 549, medians = 10.9-16.4 kU/L, 95th percentiles = 44.2-355 kU/L) and even higher in individuals suffering from various cancers (n = 995, medians= 12.4-445 kU/L; 95th percentiles = 53.4-4664 kU/L). Optimal diagnostic accuracy for cancer detection against the relevant benign control group by the OV Monitor was found for ovarian cancer {[}area under the curve (AUC) 0.898]. Results for the reference CA125 assay were comparable (AUC 0.899). Conclusions: The Access OV Monitor provides very good methodological characteristics and demonstrates an excellent analytical and clinical correlation with Elecsys CA125. The best diagnostic accuracy for the OV Monitor was found in ovarian cancer. Our results also suggest a clinical value of the OV Monitor in other cancers
Length-dependent oscillations of the conductance through atomic chains: The importance of electronic correlations
We calculate the conductance of atomic chains as a function of their length.
Using the Density Matrix Renormalization Group algorithm for a many-body model
which takes into account electron-electron interactions and the shape of the
contacts between the chain and the leads, we show that length-dependent
oscillations of the conductance whose period depends on the electron density in
the chain can result from electron-electron scattering alone. The amplitude of
these oscillations can increase with the length of the chain, in contrast to
the result from approaches which neglect the interactions.Comment: 7 pages, 4 figure
Frequency and damping evolution during experimental seismic response of civil engineering structures
The results of the seismic tests on several reinforced-concrete shear walls and a four-storey frame are analysed in this paper. Each specimen was submitted to the action of a horizontal accelerogram, with successive growing amplitudes, using the pseudodynamic method. An analysis of the results allows knowing the evolution of the eigen frequency and damping ratio during the earthquakes thanks to an identification method working in the time domain. The method is formulated as a spatial model in which the stiffness and damping matrices are directly identified from the experimental displacements, velocities and restoring forces. The obtained matrices are then combined with the theoretical mass in order to obtain the eigen frequencies, damping ratios and modes. Those parameters have a great relevance for the design of this type of structures
Inhomogeneous soliton ratchets under two ac forces
We extend our previous work on soliton ratchet devices [L. Morales-Molina et
al., Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac
forces including non-harmonic drivings, as proposed for particle ratchets by
Savele'v et al. [Europhys. Lett. 67}, 179 (2004); Phys. Rev. E {\bf 70} 066109
(2004)]. Current reversals due to the interplay between the phases, frequencies
and amplitudes of the harmonics are obtained. An analysis of the effect of the
damping coefficient on the dynamics is presented. We show that solitons give
rise to non-trivial differences in the phenomenology reported for particle
systems that arise from their extended character. A comparison with soliton
ratchets in homogeneous systems with biharmonic forces is also presented. This
ratchet device may be an ideal candidate for Josephson junction ratchets with
intrinsic large damping
Ratchet behavior in nonlinear Klein-Gordon systems with point-like inhomogeneities
We investigate the ratchet dynamics of nonlinear Klein-Gordon kinks in a
periodic, asymmetric lattice of point-like inhomogeneities. We explain the
underlying rectification mechanism within a collective coordinate framework,
which shows that such system behaves as a rocking ratchet for point particles.
Careful attention is given to the kink width dynamics and its role in the
transport. We also analyze the robustness of our kink rocking ratchet in the
presence of noise. We show that the noise activates unidirectional motion in a
parameter range where such motion is not observed in the noiseless case. This
is subsequently corroborated by the collective variable theory. An explanation
for this new phenomenom is given
The Elder Economic Security Standard(TM) Index for California, 2007: County Amounts, Comparisons and Components
Provides county-by-county data on how much income retirees need to make ends meet, how it compares with the Federal Poverty Line, and by how much the maximum Supplemental Security Income payment and average Social Security payment each fall short
Multistability and localization in coupled nonlinear split-ring resonators
We study the dynamics of a pair of nonlinear split-ring resonators (a
`metadimer') excited by an alternating magnetic field and coupled magnetically.
Linear metadimers of this kind have been recently used as the elementary
components for three-dimensional metamaterials or 'stereometamaterials' [N. Liu
{\em et al}, Nature Photon. {\bf 3}, 157 (2009)]. We demonstrate that
nonlinearity offers more possibilities with respect to real-time tunability and
a multiplicity of states which can be reached by varying the external field.
Moreover, we demonstrate almost total localization of the energy in one of the
resonators in a broad range of parameters.Comment: 3 pages, 5 figure
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