Low temperature limit of the vortex core radius and the kramer-pesch effect in NbSe2

Muon spin rotation ( &mgr;SR) has been used to measure the magnetic field distribution in the vortex state of the type-II superconductor NbSe2 ( T(c) = 7.0 K) below T = 2 K. The distribution is consistent with a highly ordered hexagonal vortex lattice with a well resolved high-field cutoff associated with the finite size of the vortex cores. The temperature dependence of the core radius is much weaker than the temperature dependence predicted from the Bogoliubov-de Gennes theory. Furthermore, the vortex radius measured by &mgr;SR near the low temperature quantum limit is about an order of magnitude larger than predicted.     

Chromatic thresholds in dense random graphs

The chromatic threshold of a graph H with respect to the random graph G (n, p ) is the infimum over d > 0 such that the following holds with high probability: the family of H‐free graphs with minimum degree has bounded chromatic number. The study of the parameter was initiated in 1973 by Erd?s and Simonovits, and was recently determined for all graphs H . In this paper we show that for all fixed , but that typically if . We also make significant progress towards determining for all graphs H in the range . In sparser random graphs the problem is somewhat more complicated, and is studied in a separate paper. © 2017 Wiley Periodicals, Inc. Random Struct. Alg., 51, 185–214, 2017     

Experimental investigation of a blunt trailing edge flow field with application to sound generation

The unsteady lift generated by turbulence at the trailing edge of an airfoil is a source of radiated sound. The objective of the present research was to measure the velocity field in the near wake region of an asymmetric beveled trailing edge in order to determine the flow mechanisms responsible for the generation of trailing edge noise. Two component velocity measurements were acquired using particle image velocimetry. The chord Reynolds number was 1.9 × 10⁶. The data show velocity field realizations that were typical of a wake flow containing an asymmetric periodic vortex shedding. A phase average decomposition of the velocity field with respect to this shedding process was utilized to separate the large scale turbulent motions that occurred at the vortex shedding frequency (i.e., those responsible for the production of tonal noise) from the smaller scale turbulent motions, which were interpreted to be responsible for the production of broadband sound. The small scale turbulence was found to be dependent on the phase of the vortex shedding process implying a dependence of the broadband sound generated by the trailing edge on the phase of the vortex shedding process.     

On sourcing and stocking policies in a two-echelon,multiple location,repairable parts supply chain

This research develops policies to minimize spare part purchases and repair costs for maintaining a fleet of mission-critical systems that operate from multiple forward (base) locations within a two-echelon repairable supply chain with a central depot. We take a tactical planning perspective to support periodic decisions for spare part purchases and repair sourcing, where the repair capabilities of the various locations are overlapping. We consider three policy classes: a central policy, where all repairs are sourced to a central depot; a local policy, whereby failures are repaired at forward locations; and a mixed policy, where a fraction of the parts is repaired at the bases and the remainder is repaired at the depot. Parts are classified based on their repair cost and lead time. For each part class, we suggest a solution that is based on threshold policies or on the use of a heuristic solution algorithm that extends the industry standard of marginal analysis to determine spare parts positioning by including repair fraction sourcing. A validation study shows that the suggested heuristic performs well compared to an exhaustive search (an average 0.2% difference in cost). An extensive numerical study demonstrates that the algorithm achieves costs which are lower by about 7–12% on average, compared to common, rule-based sourcing policies.     

Reduction of Ekman circulation within Taylor-Couette flow

We demonstrate experimentally that independently rotating intermediary end-rings between the cylinders of a Taylor–Couette apparatus can be utilized to reduce friction-driven secondary flow, i.e. Ekman circulation. This allows for velocity profiles in a device of small aspect ratio to be less constrained by ‘end effects’, so that the resulting wide-gap flows can be made to have a radial distribution of circumferential velocity that resembles a narrow-gap Couette solution.     

A sufficient condition for the subordination principle in ergodic optimization

Let T : X X be a continuous surjection of a topologicalspace, and let f : X be upper semi-continuous. Wewish to identify those T-invariant measures µ which maximize f dµ. We call such measures f-maximizing, and denotethe maximum by ß(f). The study of such measures andtheir properties has recently been dubbed ergodic optimization.A first step to understanding the structure of a function'smaximizing measures is to establish the following subordinationprinciple defined by T. Bousch: if µ and are T-invariantmeasures such that supp supp µ and µ is f-maximizing,then is also f-maximizing. Previous authors have approachedthis result by constructing a continuous function g : X such that f – ß(f) g T – g. We providea sufficient condition for the subordination principle whichhas advantages when the space X is noncompact.     

Three-dimensional fluid pressure mapping in porous media using magnetic resonance imaging with gas-filled liposomes

This paper presents and demonstrates a method for using magnetic resonance imaging to measure local pressure of a fluid saturating a porous medium. The method is tested both in a static system of packed silica gel and in saturated sintered glass cylinders experiencing fluid flow. The fluid used contains 3% gas in the form of 3-mum average diameter gas filled 1,2-distearoyl-sn-glycero-3-phosphocholine (C18:0, MW: 790.16) liposomes suspended in 5% glycerol and 0.5% Methyl cellulose with water. Preliminary studies at 2.35 T demonstrate relative magnetic resonance signal changes of 20% per bar in bulk fluid for an echo time T(E)=40 ms, and 6-10% in consolidated porous media for T(E)=10 ms, over the range 0.8-1.8 bar for a spatial resolution of 0.1 mm(3) and a temporal resolution of 30 s. The stability of this solution with relation to applied pressure and methods for improving sensitivity are discussed.     

Estimating attenuation of ultraviolet radiation in streams: field and laboratory methods

We adapted and tested a laboratory quantitative filter pad method and field-based microcosm method for estimating diffuse attenuation coefficients (K(d)) of ultraviolet radiation (UVR) for a wide range of stream optical environments (K(d320) = 3-44 m(-1)). Logistical difficulties of direct measurements of UVR attenuation have inhibited widespread monitoring of this important parameter in streams. Suspended sediment concentrations were manipulated in a microcosm, which was used to obtain direct measurements of diffuse attenuation. Dissolved and particulate absorption measurements of samples from the microcosm experiments were used to calibrate the laboratory method. Conditions sampled cover a range of suspended sediment (0-50 mg L(-1)) and dissolved organic carbon concentrations (1-4 mg L(-1)). We evaluated four models for precision and reproducibility in calculating particulate absorption and the optimal model was used in an empirical approach to estimate diffuse attenuation coefficients from total absorption coefficients. We field-tested the laboratory method by comparing laboratory-estimated and field-measured diffuse attenuation coefficients for seven sites on the main stem and 10 tributaries of the Lehigh River, eastern Pennsylvania, USA. The laboratory-based method described here affords widespread application, which will further our understanding of how stream optical environments vary spatially and temporally and consequently influence ecological processes in streams.