Zero energy bound states in tunneling conductance spectra at the interface of an s-wave superconductor and a topological insulator in NbN-Bi2Se3Bi_2Se_3-Au thin film junctions

Measurements of conductance spectra in a superconductor - topological insulator - normal metal thin film junctions of NbN-$\rm Bi_2Se_3$-Au are reported. Junctions with ex-situ and in-situ prepared $\rm NbN-Bi_2Se_3$ interfaces were studied. At low temperatures, all the ex-situ junctions showed coherence peaks in their conductance spectra, but imbedded robust zero bias conductance peaks were observed only in junctions with a metallic or a metal to insulator transition below $\rm T_c$ of the NbN electrode. The in-situ junctions which had about two orders of magnitude lower resistance at low temperatures, generally showed flat conductance spectra at low bias, with no coherence or broad Andreev peaks, since the critical current of the NbN electrode was reached first, at voltage bias below the energy gap of the superconductor. A weak zero bias conductance peak however, was observed in one of these junctions. We conclude that significant tunneling barriers, as in the ex-situ prepared junctions, are essential for the observation of coherence peaks and the zero energy bound states. The later seem to originate in the $\rm Bi_2Se_3$-NbN interface, as they are absent in reference Au-NbN junctions without the topological layer sandwiched in between.Comment: Published versio

Investigating Bimodal Clustering in Human Mobility

We apply a simple clustering algorithm to a large dataset of cellular telecommunication records, reducing the complexity of mobile phone users' full trajectories and allowing for simple statistics to characterize their properties. For the case of two clusters, we quantify how clustered human mobility is, how much of a user's spatial dispersion is due to motion between clusters, and how spatially and temporally separated clusters are from one another.Comment: 4 pages, 2 figure

Critical current measurements in superconductor - ferromagnet - superconductor junctions of YBa2Cu3OyYBa_2Cu_3O_y-SrRuO3SrRuO_3-YBa2Cu3OyYBa_2Cu_3O_y: No evidence for a dominant proximity induced triplet superconductivity in the ferromagnetic barrier

Transport measurements in ramp-type junctions of $YBa_2Cu_3O_y-SrRuO_3-YBa_2Cu_3O_y$ with $T_c$ values of either 80-90 K or 60-70 K are reported. In both type of junctions but without a barrier ("shorts"), the supercurrent densities at 4.2 K reached 7.5 and 3.5 MA/cm$^2$, respectively, indicating the high quality of the fabrication process. Plots of the critical current versus thickness of the ferromagnetic barrier at 4.2 K show exponential decays with decay lengths of 1.1 nm for the 90 K phase and 1.4 nm for the 60 K phase, which are much shorter than the relevant coherence lengths $\xi_F\sim 5-6$ nm or $\xi_N\sim$16 nm of $SrRuO_3$. We thus conclude that there is no dominant proximity induced triplet superconductivity in the ferromagnet in our junctions.Comment: 5 figure

Oracle-Based Robust Optimization via Online Learning

Robust optimization is a common framework in optimization under uncertainty when the problem parameters are not known, but it is rather known that the parameters belong to some given uncertainty set. In the robust optimization framework the problem solved is a min-max problem where a solution is judged according to its performance on the worst possible realization of the parameters. In many cases, a straightforward solution of the robust optimization problem of a certain type requires solving an optimization problem of a more complicated type, and in some cases even NP-hard. For example, solving a robust conic quadratic program, such as those arising in robust SVM, ellipsoidal uncertainty leads in general to a semidefinite program. In this paper we develop a method for approximately solving a robust optimization problem using tools from online convex optimization, where in every stage a standard (non-robust) optimization program is solved. Our algorithms find an approximate robust solution using a number of calls to an oracle that solves the original (non-robust) problem that is inversely proportional to the square of the target accuracy

Leapover lengths and first passage time statistics for L\'evy flights

Exact results for the first passage time and leapover statistics of symmetric and one-sided Levy flights (LFs) are derived. LFs with stable index alpha are shown to have leapover lengths, that are asymptotically power-law distributed with index alpha for one-sided LFs and, surprisingly, with index alpha/2 for symmetric LFs. The first passage time distribution scales like a power-law with index 1/2 as required by the Sparre Andersen theorem for symmetric LFs, whereas one-sided LFs have a narrow distribution of first passage times. The exact analytic results are confirmed by extensive simulations.Comment: 4 pages, 5 figures, REVTe

Pharmacokinetic Disposition and Clinical Outcomes in Infants and Children Receiving Intravenous Busulfan for Allogeneic Hematopoietic Stem Cell Transplantation

AbstractWe conducted a retrospective pharmacokinetic analysis of i.v. busulfan in children undergoing hematopoietic stem cell transplantation (HSCT) and describe its relation to transplantation outcomes. Forty-five children (median age, 3 yr) underwent HSCT at The Hospital for Sick Children from April 2003 through January 2006 and received i.v. busulfan every 6 h as part of their conditioning regimen. Initial busulfan doses were based on actual patient weight: <9 kg, 0.95 mg/kg per dose; 9-16 kg, 1.2 mg/kg per dose; 16-23 kg, 1.1 mg/kg per dose; 24-34 kg, 0.95 mg/kg per dose; >34 kg, 0.8 mg/kg per dose. Plasma busulfan concentrations were obtained after the first dose. The fourth and subsequent busulfan doses were adjusted to achieve an area under the concentration versus time curve (AUC) of 900-1500 μM·min. Development of hepatic venous occlusive disease (HVOD; modified Baltimore criteria) and engraftment (absolute neutrophil count ≥0.5 × 109/L) were evaluated. Busulfan pharmacokinetic parameters were calculated using 1-compartment methods. Mean busulfan pharmacokinetic parameters were maximum concentration (Cmax; 4.7 ± 0.75 μM), volume of distribution at steady state (0.68 ± 0.17 L/kg), elimination rate constant (0.0051 ± 0.0010 min−1), total body clearance (3.5 ± 1.23 mL/[min·kg]), and AUC (1271 ± 280 μM·min). Mean volume of distribution at steady state was larger in children <1 yr of age (0.77 ± 0.24 vs 0.64 ± 0.11 L/kg; P = .040) and children <4 yr of age (0.73 ± 0.18 vs 0.60 ± 0.11 L/kg; P = .001) than in older children. Compared with older children, mean weight-adjusted total body clearance was higher in children <4 yr of age (3.8 ± 1.40 versus 3.0 ± 0.76 mL/[min·kg]). HVOD was diagnosed in 8 children (18%), including 4 children <1 yr of age. Children who developed HVOD achieved a lower Cmax than did those without HVOD (4.2 ± 0.68 versus 4.8 ± 0.73 μM; P = .035). Other than Cmax, no association was observed between busulfan disposition and development of HVOD in children for whom i.v. busulfan doses were adjusted to achieve a target AUC. The influence of factors other than busulfan disposition on transplantation outcomes, such as genetic polymorphisms, should be evaluated

Back to the "Gold Standard": How Precise is Hematocrit Detection Today?

Introduction: The commonly used method for hematocrit detection, by visual examination of microcapillary tube, known as "micro-HCT", is subjective but remains one of the key sources for fast hematocrit evaluation. Analytical automation techniques have increased the standardization of RBC index detection; however, indirect hematocrit measurements by blood analyzer, the automated HCT, do not correlate well with "micro-HCT" results in patients with hematological pathologies. We aimed to overcome those disadvantages in "micro-HCT" analysis using "ImageJ" processing software. Methods: 223 blood samples from the "general population" and 19 from sickle cell disease patients were examined in parallel for hematocrit values using the automated HCT, standard "micro-HCT," and "ImageJ" micro-HCT methods. Results: For the "general population" samples, the "ImageJ" values were significantly higher than the corresponding values evaluated by standard "micro-HCT" and automated HCT, except for the 0 to 2 month old newborns, in which the automated HCT results were similar to the "ImageJ" evaluated HCT. Similar to the "general population" cohort, we found significantly higher values measured by "ImageJ" compared to either "micro-HCT" or the automated HCT in SCD patients. Correspondent differences for the MCV and MCHC were also found. Discussion: This study introduces the "micro-HCT" assessment technique using the image-analysis module of "ImageJ" software. This procedure allows overcoming most of the data errors associated with the standard "micro-HCT" evaluation and can replace the use of complicated and expensive automated equipment. The presented results may also be used to develop new standards for calculating hematocrit and associated parameters for routine clinical practice. Keywords: Image analysis; Microcapillary hematocrit; RBC indices