Magnetic field dependence of the thermopower of dilute aluminum alloys

Measurements are presented of the thermopowerS of pure Al and dilute Al alloys from 2 to 6 K in magnetic fields up to 20 kG. For all samples the data are consistent with the equationS(H)=A(H)T+B(H)T ³ , allowing a separation of the electron diffusion thermopower componentS _e (H)=A(H)T from the phonon-drag componentS _g (H)=B(H)T ³ . Zero-field characteristic values ofS _e were obtained for the impurities Cu, Cd, Tl, and Sn:S _e (Cu) =–0.6T×10^–8 V/K;S _e (Cd)=–4T×10^–8 V/K;S _e (Tl)=–3T×10^–8 V/K;S _e (Sn) =–2T×10^–8 V/K. The phonon-drag coefficientB was found to vary from impurity to impurity, a variation attributed to anisotropic electron-impurity scattering. Upon application of a transverse magnetic field,A(H) was found first to become more positive, and then to saturate in value at high fields. The quantity A=A(H)–A(H=0) was found to be very nearly the same for all impurities, varying in value only from 2.1–2.6×10^–8 V/K. Both the general behavior ofA(H) and this magnitude for A are shown to be determined primarily by the form of the Fermi surface of pure Al.B(H) was also observed to vary with magnetic field. This variation is tentatively attributed to a combination of a changing importance with magnetic field of electrons in the second and third Brillouin zones of Al and anisotropic electron-impurity scattering, but no detailed explanation is yet available. Finally, the Wiedemann-Franz ratio of an impure Al-Cu sample is found to have the value 2.43 ⁵ ±0.02×10^–8 W·/K ² at 4.5 K, independent ofH up to 20 kG, the highest field used. This value is in good agreement with the expected value :L ₀ =2.45×10^–8 W·/K ² .This work was supported in part by the U.S. Atomic Energy Commission under Contract No. AT(11-1)-1247 and in part by the N.S.F. under Grant No. GH-34124. Based primarily upon a thesis submitted by one of us (R.S.A.) in partial fulfillment of the requirements for the Ph.D. degree at Michigan State University.     

Progress on adaptive hp-finite element methods for the incompressible Navier-Stokes equations

This paper outlines recent results obtained in the development and application of hp-adaptive finite element methods to three-dimensional problems in incompressible viscous flow simulation.     

Radiotherapy, toxicity and dosimetry of copper-64-TETA-octreotide in tumor-bearing rats

The efficacy of 64Cu [T1/2 = 12.7 hr; beta+ (0.655 MeV; 19%); beta- (0.573 MeV; 40%)] as a radioisotope for radiotherapy has been recently established. Here we demonstrate that 64Cu-1,4,8,11 -tetraazacyclotetradecane-N,N',N",N'-tetraacetic acid (TETA)-octreotide, a somatostatin receptor ligand, inhibits the growth of CA20948 rat pancreatic tumors in Lewis rats at doses that cause minimal toxicity. METHODS: Tumor-bearing rats were administered a single 15 mCi (555 MBq) dose, a fractionated dose of 15 mCi given in 2-3 doses over 2-8 days, or control agents of buffer, unlabeled octreotide or 64Cu-labeled TETA. In certain experiments, blood was removed at times from 4-23 days post-treatment, and a complete blood count along with blood chemistry analyses were obtained. RESULTS: Tumor-growth inhibition was significantly greater in rats injected with a single 15 mCi dose than in rats injected with control agents (p < 0.05). Dose fractionation in two doses, either 1 or 2 days apart, induced significantly increased tumor-growth inhibition compared with rats given a single dose (p < 0.05). The only toxicity observed in treated rats was a decrease in the white blood cell count. This drop was more pronounced in rats treated with a single dose compared with those treated with a fractionated dose. Human absorbed doses of 64Cu-TETA-octreotide to normal organs were estimated from biodistribution data in Lewis rats, and these data indicate that radiotherapy with 64Cu-TETA-octreotide in humans would be feasible. CONCLUSION: Copper-64-TETA-octreotide is a promising radiopharmaceutical for targeted radiotherapy of somatostatin receptor-positive tumors.     

Quantum annealing for combinatorial clustering

Clustering is a powerful machine learning technique that groups “similar” data points based on their characteristics. Many clustering algorithms work by approximating the minimization of an objective function, namely the sum of within-the-cluster distances between points. The straightforward approach involves examining all the possible assignments of points to each of the clusters. This approach guarantees the solution will be a global minimum; however, the number of possible assignments scales quickly with the number of data points and becomes computationally intractable even for very small datasets. In order to circumvent this issue, cost function minima are found using popular local search-based heuristic approaches such as k-means and hierarchical clustering. Due to their greedy nature, such techniques do not guarantee that a global minimum will be found and can lead to sub-optimal clustering assignments. Other classes of global search-based techniques, such as simulated annealing, tabu search, and genetic algorithms, may offer better quality results but can be too time-consuming to implement. In this work, we describe how quantum annealing can be used to carry out clustering. We map the clustering objective to a quadratic binary optimization problem and discuss two clustering algorithms which are then implemented on commercially available quantum annealing hardware, as well as on a purely classical solver “qbsolv.” The first algorithm assigns N data points to K clusters, and the second one can be used to perform binary clustering in a hierarchical manner. We present our results in the form of benchmarks against well-known k-means clustering and discuss the advantages and disadvantages of the proposed techniques.     

General analysis of slab lasers using geometrical optics

A thorough and general geometrical optics analysis of a slab-shaped laser gain medium is presented. The length and thickness ratio is critical if one is to achieve the maximum utilization of absorbed pump power by the laser light in such a medium; e.g., the fill factor inside the slab is to be maximized. We point out that the conditions for a fill factor equal to 1, laser light entering and exiting parallel to the length of the slab, and Brewster angle incidence on the entrance and exit faces cannot all be satisfied at the same time. Deformed slabs are also studied. Deformation along the width direction of the largest surfaces is shown to significantly reduce the fill factor that is possible.     

Cyclin E2, a novel G1 cyclin that binds Cdk2 and is aberrantly expressed in human cancers

A novel cyclin gene was discovered by searching an expressed sequence tag database with a cyclin box profile. The human cyclin E2 gene encodes a 404-amino-acid protein that is most closely related to cyclin E. Cyclin E2 associates with Cdk2 in a functional kinase complex that is inhibited by both p27(Kip1) and p21(Cip1). The catalytic activity associated with cyclin E2 complexes is cell cycle regulated and peaks at the G1/S transition. Overexpression of cyclin E2 in mammalian cells accelerates G1, demonstrating that cyclin E2 may be rate limiting for G1 progression. Unlike cyclin E1, which is expressed in most proliferating normal and tumor cells, cyclin E2 levels were low to undetectable in nontransformed cells and increased significantly in tumor-derived cells. The discovery of a novel second cyclin E family member suggests that multiple unique cyclin E-CDK complexes regulate cell cycle progression.     

Fracture assessment of shallow-flaw cruciform beams tested under uniaxial and biaxial loading conditions

A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow, surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure–temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies, namely, the J–Q formulation, the Dodds–Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate with the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states.