Monte Carlo calculations of the dose distribution in teeth due to internal exposure from 90Sr: application to EPR tooth dosimetry

This paper addresses issues in the application of the electron paramagnetic resonance (EPR) retrospective dosimetry with dental tissues exposed by radionuclides accumulated in the dentin. A simple dosimetric model of a tooth incorporating 90Sr is presented. The tooth is modelled as two concentric cylinders: the inner cylinder composed of dentin, and the outer cylindrical shell of enamel. Extensive Monte Carlo calculations were done to obtain the distributions of absorbed dose in dentin and enamel for teeth of different sizes. The results were used to calculate the mean absorbed doses in enamel that are directly measurable by EPR. A relationship between such measured doses and the specific activity of 90Sr in dentin was derived based on a simple model of 90Sr accumulation. The roles of different tooth tissues as dose detectors are analysed, and the importance of dentin as a dosimetric material for internal exposure is pointed out.     

Creep of CoO single crystals

Cobalt monoxide single crystals having a [100] orientation were creep tested in compression over ranges of temperature, stress and oxygen pressure. The creep curves were S-shaped and only the inflection creep rate, ₂, was analysed. In the range of 1000 to 1200° C, 850 to 1700 psi and 10^–3 to 1 atm oxygen, ₂ was given by ₂=A po ₂ ^{0.45 7.1}exp(– Q _c /RT) where Q _c =87±6 kcal/mol at 0.01 atm O ₂ and 100±16 kcal/mol at 1 atm O ₂. Slip occurred on two orthogonal {011} 0¯11 slip systems. The presence of subboundaries was observed by optical and transmission electron microscopy. It is suggested that the creep rate is controlled by oxygen diffusion.     

The oxidation behavior of Ni-Cr-Al-2ThO2 alloys at 1093° and 1204°C

A pack diffusion process has been developed which permits the introduction of nearly 6 wt pct Al into solid solution in the near surface region of TDNiCr (Ni-20 wt pct Cr-2 vol pct ThO₂) and Ni-20Cr. Alumina scales, adherent under cyclic heating and cooling conditions, were produced on TDNiCr-5.86A1 upon exposure to an environment of 1.33 × 10³N/m² (10 torr) or 1.01 × 10⁵N/m² (760 torr) air at temperatures of 1093° and 1204°C. While the same oxidation kinetics were observed in isothermal tests for Ni-14.6Cr-5.86Al as were obtained for the TDNiCr-5.86A1, the dispersion strengthened alloy exhibited superior oxide scale adhesion during cyclic testing. At 1204°C continuous weight gains were observed under all test conditions for TDNiCr-5.86A1, in contrast to the weight loss with time which occurred several hours after exposure of TDNiCr to an oxidizing environment. TDNiCr with an initial aluminum surface concentration of 4.95 wt pct has nearly comparable oxidation resistance to the TDNiCr-5.86Al alloy. Specimens with 4.3 wt pct Al at the surface have inadequate aluminum to form Al₂O₃ scales, and weight losses are observed after 40 h upon exposure of these specimens to 1.01 × 10⁵N/m² (760 torr) air at 1204°C.     

Density effect for the ionization loss of charged particles in various substances

The density-effect correction δ(β) for the ionization energy loss of charged particles has been evaluated as a function of the particle velocity for a total of 278 substances, including 98 cases of elements of the periodic table (12 gases and 86 condensed materials, including liquid hydrogen and graphite of three different densities) and 180 chemical compounds and substances of biological interest (13 gases and 167 liquid or solid substances). In the calculations, up-to-date values of the mean excitation potential I and of the atomic absorption edges hv_i were employed as input data for the general equations for δ(β) previously derived by Sternheimer.     

Resonance frequency, damping, and differential gain in 1.5 μmmultiple quantum-well lasers

A systematic investigation is presented into the intrinsic frequency response of quantum-well lasers, using parasitic-free relative intensity noise (RIN) measurements. There is shown to be a strong dependence of the resonance frequency on the number of quantum wells in the active region, originating from variations both in internal losses and in differential gain. The differential gain is found to have values higher than in corresponding bulk lasers, but only in devices with a large number of wells. The damping is also found to vary in a manner consonant with the changes in differential gain; however, comparison with bulk lasers indicates substantially stronger gain suppression in the quantum-well lasers studied     

Overlapping and nonoverlapping cortical projections to cortex of the superior temporal sulcus in the rhesus monkey: double anterograde tracer studies

To examine how fibers from functionally distinct cortical zones interrelate within their target areas of the superior temporal sulcus (STS) in the rhesus monkey, separate anterograde tracers were injected in two different regions of the same hemisphere known to project to the STS. Paired injections were placed in dorsal prearcuate cortex and the caudal inferior parietal lobule (IPL), interconnected regions that are part of a hypothesized distributed network concerned with visuospatial analysis or directed attention; in a presumed auditory region of the superior temporal gyrus (STG) and in extrastriate visual cortex, the caudal IPL and lower rim of the intraparietal sulcus; and in dorsal prearcuate cortex and the STG. Overlapping and nonoverlapping projections were then examined in STS visual and polysensory areas. Prefrontal and parietal fibers directly overlapped extensively in area MST and all subdivisions of presumed polysensory cortex (areas TPOc, TPOi, and TPOr), although nonoverlapping connections were also found. Although STG and IPL fibers targeted all TPO subdivisions, connections were to nonoverlapping, but often adjacent, columns. Paired prefrontal and STG injections revealed largely nonoverlapping vertical columns of connections but substantial overlap within layers VI and I or areas TPOc and TPOi. The findings suggest that area TPO contains differently connected modules that may maintain at least initial segregation of visual versus auditory inputs. Other modules within area TPO receive directly converging input from the posterior parietal and the prefrontal cortices and may participate in a distributed cortical network concerned with visuospatial functions.     

Web-based digital radiology teaching file: facilitating case input at time of interpretation

OBJECTIVE: Our goal was to develop a software system that allows easy and rapid input of digital radiology images and text reports, at the time of interpretation, into an easily searchable electronic teaching file database using the Internet and the World-Wide Web protocols, servers, and browsers. CONCLUSION: Using the Internet, the World-Wide Web, and our software system, we can rapidly input digital radiology images and associated text reports into an easily searchable database accessed by privileged users. This inexpensive and simple method for building a digital teaching file database allows cross-platform access for users who have a Web browser.     

Changes in the U.S. Primary Standards for the Air Kerma From Gamma-Ray Beams

Monte Carlo photon-electron transport calculations have been done to derive new wall corrections for the six NBS-NIST standard graphite-wall, air-ionization cavity chambers that serve as the U.S. national primary standard for air kerma (and exposure) for gamma rays from ⁶⁰Co, ¹³⁷Cs, and ¹⁹²Ir sources. The data developed for and from these calculations have also been used to refine a number of other factors affecting the standards. The largest changes are due to the new wall corrections, and the total changes are +0.87 % to +1.11 % (depending on the chamber) for ⁶⁰Co beams, +0.64 % to +1.07 % (depending on the chamber) for ¹³⁷Cs beams, and −0.06 % for the single chamber used in the measurement of the standardized ¹⁹²Ir source. The primary standards for air kerma will be adjusted in the near future to reflect the changes in factors described in this work.     

A review of neuropsychological differences between paranoid and nonparanoid schizophrenia patients

This review examines the literature on neuropsychological differences between paranoid and nonparanoid schizophrenia subjects. Thirty-two studies related to intellectual functioning, attention, memory, language, visual-spatial, and motor functions are discussed. Subjects with paranoid schizophrenia did not demonstrate higher intellectual functioning than those with nonparanoid schizophrenia, and both groups performed similarly on tests of verbal ability and visual-spatial functions. Several studies suggest that the paranoid subtype is associated with higher performance on tests of executive functions, attention, memory, and motor skills. However, the findings are inconsistent. Methodological issues in the literature are examined, including varying degrees of participants' chronicity and severity of illness among studies, criteria for diagnostic group membership, medication effects, reliability and validity of the neuropsychological measures, and statistical power.