3,577 research outputs found
Multi-step Fermi normal coordinates
We generalize the concept of Fermi normal coordinates adapted to a geodesic
to the case where the tangent space to the manifold at the base point is
decomposed into a direct product of an arbitrary number of subspaces, so that
we follow several geodesics in turn to find the point with given coordinates.
We compute the connection and the metric as integrals of the Riemann tensor. In
the case of one subspace (Riemann normal coordinates) or two subspaces, we
recover some results previously found by Nesterov, using somewhat different
techniques.Comment: 9 pages, 4 figure
Direct observation of non-classical photon statistics in parametric downconversion
We employ a high quantum efficiency photon number counter to determine the
photon number distribution of the output field from a parametric downconverter.
The raw photocount data directly demonstrates that the source is nonclassical
by forty standard deviations, and correcting for the quantum efficiency yields
a direct observation of oscillations in the photon number distribution
Improved Dynamic Predictions from Joint Models of Longitudinal and Survival Data with Time-Varying Effects using P-splines
In the field of cardio-thoracic surgery, valve function is monitored over
time after surgery. The motivation for our research comes from a study which
includes patients who received a human tissue valve in the aortic position.
These patients are followed prospectively over time by standardized
echocardiographic assessment of valve function. Loss of follow-up could be
caused by valve intervention or the death of the patient. One of the main
characteristics of the human valve is that its durability is limited.
Therefore, it is of interest to obtain a prognostic model in order for the
physicians to scan trends in valve function over time and plan their next
intervention, accounting for the characteristics of the data.
Several authors have focused on deriving predictions under the standard joint
modeling of longitudinal and survival data framework that assumes a constant
effect for the coefficient that links the longitudinal and survival outcomes.
However, in our case this may be a restrictive assumption. Since the valve
degenerates, the association between the biomarker with survival may change
over time.
To improve dynamic predictions we propose a Bayesian joint model that allows
a time-varying coefficient to link the longitudinal and the survival processes,
using P-splines. We evaluate the performance of the model in terms of
discrimination and calibration, while accounting for censoring
Highly nonclassical photon statistics in parametric down conversion
We use photon counters to obtain the joint photon counting statistics from
twin-beam non-degenerate parametric down conversion, and we demonstrate
directly, and with no auxiliary assumptions, that these twin beams are
nonclassical
Production and mechanical characterization of graphene micro-ribbons
Patterning of graphene into micro- and nano-ribbons allows for the tunability
in emerging fields such as flexible electronic and optoelectronic devices, and
is gaining interest for the production of more efficient reinforcement for
composite materials. In this work we fabricate micro-ribbons from CVD graphene
by combining UV photolithography and dry etching oxygen plasma treatments.
Raman spectral imaging confirms the effectiveness of the patterning procedure,
which is suitable for large-area patterning of graphene on wafer-scale, and
confirms that the quality of graphene remains unaltered. The produced
micro-ribbons were finally transferred and embedded into a polymeric matrix and
the mechanical response was investigated by in-situ mechanical investigation
combining Raman spectroscopy and tensile/compressive tests
Peripheral Mononuclear Cell Resistin mRNA Expression Is Increased in Type 2 Diabetic Women
Resistin has been shown to cause insulin resistance and to impair glucose tolerance in rodents, but in humans its physiological role still remains elusive. The aim of this study was to examine whether resistin mRNA expression in human peripheral mononuclear cells (PBMCs) and its corresponding plasma levels are altered in type 2 diabetes. Resistin mRNA levels were easily detectable in human PBMC, and found to be higher in DM2 compared to healthy women (P = .05). Similarly, mononuclear mRNA levels of the proinflammatory cytokines IL-1β, TNF-α, and IL-6 were all significantly higher in DM2 compared to control women (P < .001). The corresponding plasma resistin levels were slightly, but not significantly, increased in DM2 women (P = .051), and overall, they correlated significantly with BMI (r = 0.406, P = .010) and waist circumference (r = 0.516, P = .003), but not with fasting insulin levels or HOMA-IR. Resistin mRNA expression is increased in PBMC from DM2 women, together with increased expression of the inflammatory cytokines IL-1β, TNF-α, and IL-6, independent of obesity. These results suggest that resistin and cytokines might contribute to the low-grade inflammation and the increased atherogenic risk observed in these patients
Analysis of Imperfections in Practical Continuous-Variable Quantum Key Distribution
As quantum key distribution becomes a mature technology, it appears clearly
that some assumptions made in the security proofs cannot be justified in
practical implementations. This might open the door to possible side-channel
attacks. We examine several discrepancies between theoretical models and
experimental setups in the case of continuous-variable quantum key
distribution. We study in particular the impact of an imperfect modulation on
the security of Gaussian protocols and show that approximating the theoretical
Gaussian modulation with a discrete one is sufficient in practice. We also
address the issue of properly calibrating the detection setup, and in
particular the value of the shot noise. Finally, we consider the influence of
phase noise in the preparation stage of the protocol and argue that taking this
noise into account can improve the secret key rate because this source of noise
is not controlled by the eavesdropper.Comment: 4 figure
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