Process development of two high strength tantalum base alloys (ASTAR-1211C and ASTAR-1511C)

Two tantalum base alloys, Ta-12W-1.0Re-0.7Hf-0.025C(ASTAR-1211C) and Ta-15W-1.0Re-0.7Hf-0.025C(ASTAR-1511C), were cast as 12.5 cm (5 inch) diameter ingots and processed to swaged rod, sheet, forged plate, and tubing. Swaged rod was evaluated with respect to low temperature ductility, elevated temperature tensile properties, and elevated temperature creep behavior. A standard swaging process and final annealing schedule were determined. Elevated temperature tensile properties, low temperature impact properties, low temperature DBTT behavior, and extended elevated temperature creep properties were determined. A process for producing ASTAR-1211C and ASTAR-1511C sheet were developed. The DBTT properties of GTA and EB weld sheet given post-weld anneal and thermal aging treatments were determined using bend and tensile specimens. High and low temperature mechanical properties of forging ASTAR-1211C and ASTAR-1511C plate were determined as well as elevated temperature creep properties. Attempts to produce ASTAR-1211C tubing were partially successful while attempts to make ASTAR-1511C tubing were completely unsuccessful

Development of advanced high strength tantalum base alloys. Part 2: Scale-up investigation

Three experimental tantalum alloy compositions containing 14-16% W, 1% Re, 0.7% Hf, 0.025% C or 0.015% C and 0.015% N were prepared as two inch diameter ingots by consumable electrode vacuum arc melting. The as-cast ingots were processed by extrusion and swaging to one inch and 0.4 inch diameter rod and evaluated. Excellent high temperature forging behavior was exhibited by all three compositions. Creep strength at 2000 F to 2400 F was enhanced by higher tungsten additions as well as substitution of nitrogen for carbon. Weldability of all three compositions was determined to be adequate. Room temperature ductility was retained in the advanced tantalum alloy compositions as well as a notched/unnotched strength ratio of 1.4 for a notched bar having a K sub t = 2.9

Application of the density matrix renormalization group method to finite temperatures and two-dimensional systems

The density matrix renormalization group (DMRG) method and its applications to finite temperatures and two-dimensional systems are reviewed. The basic idea of the original DMRG method, which allows precise study of the ground state properties and low-energy excitations, is presented for models which include long-range interactions. The DMRG scheme is then applied to the diagonalization of the quantum transfer matrix for one-dimensional systems, and a reliable algorithm at finite temperatures is formulated. Dynamic correlation functions at finite temperatures are calculated from the eigenvectors of the quantum transfer matrix with analytical continuation to the real frequency axis. An application of the DMRG method to two-dimensional quantum systems in a magnetic field is demonstrated and reliable results for quantum Hall systems are presented.Comment: 33 pages, 18 figures; corrected Eq.(117

Zero-variance principle for Monte Carlo algorithms

We present a general approach to greatly increase at little cost the efficiency of Monte Carlo algorithms. To each observable to be computed we associate a renormalized observable (improved estimator) having the same average but a different variance. By writing down the zero-variance condition a fundamental equation determining the optimal choice for the renormalized observable is derived (zero-variance principle for each observable separately). We show, with several examples including classical and quantum Monte Carlo calculations, that the method can be very powerful.Comment: 9 pages, Latex, to appear in Phys. Rev. Let

Control of Superconducting Correlations in High-Tc Cuprates

A strategy to enhance d-wave superconducting correlations is proposed based on our numerical study for correlated electron models for high-Tc cuprates. We observe that the pairing is enhanced when the single-electron level around (pi,0) is close to the Fermi level E_F, while the d-wave pairing interaction itself contains elements to disfavor the pairing due to shift of the (pi,0)-level. Angle-resolved photoemission results in the cuprates are consistently explained in the presence of the d-wave pairing interaction. Our proposal is the tuning of the (pi,0)-level under the many-body effects to E_F by optimal design of band structure.Comment: 4 pages, 6 eps figure

Consistent reduction of charged D3-D7 systems

We provide a consistent reduction to five dimensions of the system of D3-branes at Calabi-Yau singularities coupled to D7-branes with world-volume gauge flux. The D3-branes source the dual to would-be conformal quiver theories. The D7-branes, which are homogeneously distributed in their transverse directions, are dual to massless matter in the fundamental representation at finite (baryon) density. We provide the five-dimensional action and equations of motion, and discuss a few sub-truncations. The reduction can be used in the study of transport properties and stability of D3-D7 charged systems.Comment: 23 pages. v2: references added and minor change

Towards the biocontrol of bindweeds with a mycoherbicide

Within the framework of the European COST Action 816, afive-year collaboration between scientists from five Europeancountries has made an important contribution to biologicalcontrol of field and hedge bindweeds (Convolvulus arvensis andCalystegia sepium, respectively). A fungus Stagonosporaconvolvuli strain LA39, able to infect both field and hedgebindweed, was found in the UK and its biocontrol efficacyimproved by optimising mass production, formulation and storagetechniques. This fungus controlled bindweeds in both a cemeteryand in maize crops. Its use fits best in an integrated pestmanagement system where a green cover controls most of the weedsexcept the bindweeds. DNA marker analyses indicate that thefungus reproduces sexually, which could be used to furtherimprove this mycoherbicide. In addition, the insect Melanagromyzaalbocilia, which itself exhibits biocontrol potential againstbindweeds, may be used in combination with LA39 to improve theability of the fungus to penetrate the stem of bindweeds.Overall, the results suggest that S. convolvuli LA39 haspromising potential as a bioherbicide for control of field andhedge bindwee

Quantification of volumetric morphometry and optical property in the cortex of human cerebellum at micrometer resolution

The surface of the human cerebellar cortex is much more tightly folded than the cerebral cortex. Volumetric analysis of cerebellar morphometry in magnetic resonance imaging studies suffers from insufficient resolution, and therefore has had limited impact on disease assessment. Automatic serial polarization-sensitive optical coherence tomography (as-PSOCT) is an emerging technique that offers the advantages of microscopic resolution and volumetric reconstruction of large-scale samples. In this study, we reconstructed multiple cubic centimeters of ex vivo human cerebellum tissue using as-PSOCT. The morphometric and optical properties of the cerebellar cortex across five subjects were quantified. While the molecular and granular layers exhibited similar mean thickness in the five subjects, the thickness varied greatly in the granular layer within subjects. Layer-specific optical property remained homogenous within individual subjects but showed higher cross-subject variability than layer thickness. High-resolution volumetric morphometry and optical property maps of human cerebellar cortex revealed by as-PSOCT have great potential to advance our understanding of cerebellar function and diseases

Black holes in three dimensional higher spin gravity: A review

We review recent progress in the construction of black holes in three dimensional higher spin gravity theories. Starting from spin-3 gravity and working our way toward the theory of an infinite tower of higher spins coupled to matter, we show how to harness higher spin gauge invariance to consistently generalize familiar notions of black holes. We review the construction of black holes with conserved higher spin charges and the computation of their partition functions to leading asymptotic order. In view of the AdS/CFT correspondence as applied to certain vector-like conformal field theories with extended conformal symmetry, we successfully compare to CFT calculations in a generalized Cardy regime. A brief recollection of pertinent aspects of ordinary gravity is also given.Comment: 49 pages, harvmac, invited contribution to J. Phys. A special volume on "Higher Spin Theories and AdS/CFT" edited by M. R. Gaberdiel and M. Vasilie