Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions

We calculate quantum transport for metal-graphene nanoribbon heterojunctions within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is paid on both the chemical aspects of the interface bonding as well the one-dimensional electrostatics along the ribbon length. Band-bending and doping effects strongly influence the transport properties, giving rise to conductance asymmetries and a selective suppression of the subband formation. Junction electrostatics and p-type characteristics drive the conduction mechanism in the case of high work function Au, Pd and Pt electrodes, while contact resistance becomes dominant in the case of Al.Comment: 4 pages, 5 figure

Phenomenological study of the atypical heavy flavor production observed at the Fermilab Tevatron

We address known discrepancies between the heavy flavor properties of jets produced at the Tevatron collider and the prediction of conventional-QCD simulations. In this study, we entertain the possibility that these effects are real and due to new physics. We show that all anomalies can be simultaneously fitted by postulating the additional pair production of light bottom squarks with a 100% semileptonic branching fraction.Comment: 30 pages, 13 figures, 3 tables. Submitted to Phys. Rev.

Study of sequential semileptonic decays of b hadrons produced at the Tevatron

We present a study of rates and kinematical properties of lepton pairs contained in central jets with transverse energy E_T > 15 GeV that are produced at the Fermilab Tevatron collider. We compare the data to a QCD prediction based on the HERWIG and QQ Monte Carlo generator programs.We find that the data are poorly described by the simulation, in which sequential semileptonic decays of single b quarks (b --> l c X with c --> l s X) are the major source of such lepton pairs.Comment: 25 pages, 8 figures. Some typos were fixed in the text and bibliography. Submitted to Phys. Rev.

Machine learning for gravitational-wave detection: surrogate Wiener filtering for the prediction and optimized cancellation of Newtonian noise at Virgo

The cancellation of noise from terrestrial gravity fluctuations, also known as Newtonian noise (NN), in gravitational-wave detectors is a formidable challenge. Gravity fluctuations result from density perturbations associated with environmental fields, e.g., seismic and acoustic fields, which are characterized by complex spatial correlations. Measurements of these fields necessarily provide incomplete information, and the question is how to make optimal use of available information for the design of a noise-cancellation system. In this paper, we present a machine-learning approach to calculate a surrogate model of a Wiener filter. The model is used to calculate optimal configurations of seismometer arrays for a varying number of sensors, which is the missing keystone for the design of NN cancellation systems. The optimization results indicate that efficient noise cancellation can be achieved even for complex seismic fields with relatively few seismometers provided that they are deployed in optimal configurations. In the form presented here, the optimization method can be applied to all current and future gravitational-wave detectors located at the surface and with minor modifications also to future underground detectors

Displacement power spectrum measurement of a macroscopic optomechanical system at thermal equilibrium

The mirror relative motion of a suspended Fabry-Perot cavity is studied in the frequency range 3-10 Hz. The experimental measurements presented in this paper, have been performed at the Low Frequency Facility, a high finesse optical cavity 1 cm long suspended to a mechanical seismic isolation system identical to that one used in the VIRGO experiment. The measured relative displacement power spectrum is compatible with a system at thermal equilibrium within its environmental. In the frequency region above 3 Hz, where seismic noise contamination is negligible, the measurement distribution is stationary and Gaussian, as expected for a system at thermal equilibrium. Through a simple mechanical model it is shown that: applying the fluctuation dissipation theorem the measured power spectrum is reproduced below 90 Hz and noise induced by external sources are below the measurement.Comment: 11 pages, 9 figures, 2 tables, to be submitte

Pharmacokinetics of orally administered tetrahydrobiopterin in patients with phenylalanine hydroxylase deficiency

Summary: The oral loading test with tetrahydrobiopterin (BH4) is used to discriminate between variants of hyperphenylalaninaemia and to detect BH4-responsive patients. The outcome of the loading test depends on the genotype, dosage of BH4, and BH4 pharmacokinetics. A total of 71 patients with hyperphenylalaninaemia (mild to classic) were challenged with BH4 (20 mg/kg) according to different protocols (1 × 20 mg or 2 × 20 mg) and blood BH4 concentrations were measured in dried blood spots at different time points (T0, T2, T4, T8, T12, T24, T32 and T48 h). Maximal BH4 concentrations (median 22.69 nmol/g Hb) were measured 4 h after BH4 administration in 63 out of 71 patients. Eight patients presented with maximal BH4 concentrations ∼44% higher at 8 h than at 4 h. After 24 h, BH4 blood concentrations dropped to 11% of maximal values. This profile was similar using different protocols. The following pharmacokinetic parameters were calculated for BH4 in blood: t max = 4 h, AUC (T0−32) = 370 nmol × h/g Hb, and t 1/2 for absorption (1.1 h), distribution (2.5 h), and elimination (46.0 h) phases. Maximal BH4 blood concentrations were not significantly lower in non-responders and there was no correlation between blood concentrations and responsiveness. Of mild PKU patients, 97% responded to BH4 administration, while one was found to be a non-responder. Only 10/19 patients (53%) with Phe concentrations of 600-1200 μmol/L responded to BH4 administration, and of the patients with the severe classical phenotype (blood Phe > 1200 μmol/L) only 4 out of 17 patient responded. An additional 36 patients with mild hyperphenylalaninaemia (HPA) who underwent the combined loading test with Phe+BH4 were all responders. Slow responders and non-responders were found in all groups of HP