Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5

We describe our theoretical formalism and computational scheme for making ab-initio calculations of the dynamic paramagnetic spin susceptibilities of metals and alloys at finite temperatures. Its basis is Time-Dependent Density Functional Theory within an electronic multiple scattering, imaginary time Green function formalism. Results receive a natural interpretation in terms of overdamped oscillator systems making them suitable for incorporation into spin fluctuation theories. For illustration we apply our method to the nearly ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5. We compare and contrast the spin dynamics of these two metals and in each case identify those fluctuations with relaxation times much longer than typical electronic `hopping times'Comment: 21 pages, 9 figures. To appear in Physical Review B (July 2000

Spatial distribution of γ-ray bursts observed by BATSE

THE nature of the sources of cosmic γ-ray bursts is a long-standing problem in astrophysics. Lack of knowledge of their true spatial distribution and of their intrinsic brightness has hampered theoretical understanding of these enigmatic events. The Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory has been detecting bursts at the rate of about one a day, and we report here an analysis of 153 events. The number versus intensity distribution does not follow the -3/2 power law expected for a spatially extended homogeneous distribution of sources, but at the same time the angular distribution is isotropic within statistical limits. Taken together, these results are inconsistent with the spatial distribution of any known population of galactic objects, but may be consistent with the bursts being at cosmological distances. © 1992 Nature Publishing Group

Imaging in cervical cancer.

Item does not contain fulltextCervical cancer traditionally has been staged clinically. Advances in imaging could improve the staging of cervical cancer by facilitating the detection of lymph node metastases and micrometastases in distant organs. Such progress could lead to improvements in treatment selection and therefore increase overall survival rates. At the Second International Conference on Clinical Cancer (Houston, TX, April 11-14, 2002), a panel composed of gynecologic oncologists, radiation oncologists, and diagnostic radiologists reviewed relevant technologies. Advances in lymphangiography, ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and lymphatic mapping were reviewed, along with the impact of these advances on the diagnosis, treatment, and survival of patients with cervical cancer. Few cancer centers still use lymphangiography, but the sensitivity of this method ranges from 28% to 83%, with specificity ranging from 47% to 100%. The roles of transabdominal and transvaginal ultrasonography in evaluating cervical cancer are expected to expand when new contrast agents increase the sensitivity of these techniques to parametrial invasion and lymph node metastases; meanwhile, ultrasonography's most significant contributions may involve the identification of uterine and cervical leiomyomas and the evaluation of urinary tract obstruction. Advances in CT have made it a rival technique to MRI, but limitations prevent CT from providing definitive information on certain parameters. MRI, which is valuable because of its superior soft tissue contrast resolution, multiplanar capabilities, and cost-effectiveness, is used to determine the size of the cervix and to detect certain types of invasion, characteristics of lymph nodes, and the presence of disease in the ureter, lung, and liver. PET with 2-[fluorine-18]fluoro-2-deoxy-D-glucose has been found to detect abnormal lymph node regions better than CT does but PET can also be used in conjunction with CT to measure tumor dimensions. PET also has become a method for identifying tumors that are unresponsive to chemoradiation. When used together with immunohistochemical and molecular techniques as well as conventional stains, sentinel lymph node mapping, an important development in the surgical management of solid tumors, is expected to improve gynecologic cancer management. Advances in imaging methods and in contrast agents, along with advances in the combined use of the two, are expected to make imaging technologies more valuable in cervical cancer assessment

Recurrent burst activity from the soft γ-ray repeater SGR 1900+14

Of the one thousand or so detected sources of cosmic γ-ray bursts (GRBs), only three are known to have exhibited recurrent activity1-4. These events differ from the majority of GRBs in that they are of much shorter duration and have relatively soft spectra5. The recurrent sources can thus be considered as a distinct class of objects - the soft gamma repeaters (SGRs). The embryonic distribution of the SGRs suggests that they are of galactic origin4, whereas the distribution6 of GRBs seems to be inconsistent with any known galactic source population. Here we report the detection by the Burst and Transient Source Experiment (BATSE) 7 of three short, very soft transient events from a location consistent with that of the 'old' repeater SGR 1900 + 14 (ref. 8). Our results suggest that the SGR active phase lasts at least 13 years, which, in conjunction with the arguments for a galactic origin, lends support to suggestions4,5 that SGRs are neutron stars. © 1993 Nature Publishing Group

Photographic, magnetic, and interferometric measurements of current sheet canting in a pulsed electromagnetic accelerator

The propagation speed and canting angle of current sheets in a pulsed electromagnetic accelerator were measured using three different techniques: high-speed photography, magnetic field probes, and laser interferometry. Current sheet canting may have ad-verse effects on accelerator performance. The goal of the present work is to provide a database of cant-ing angles under a variety of experimental condi-tions. Eight different propellants (hydrogen, deu-terium, helium, neon, argon, krypton, xenon, and methane) were tested in a rectangular-geometry ac-celerator, at pressures ranging from 50-400 mTorr. The photographic, magnetic, and interferometric di-agnostics were used to infer the spatial configura-tion of the current sheet by measuring the its opti-cal emission, current density, and electron density, respectively. The three techniques gave qualitative agreement; the magnetic and interferometric mea-surements gave general quantitative agreement as well. The canting angle was found to depend o