Collision cascades in pure δ -plutonium

Molecular dynamics simulations of the formation and annealing of large collision cascades in delta-phase plutonium are presented. The defect evolution is followed with time up to 2 ns. Simulations are performed with the MEAM potential at three different temperatures; at 600 K where the pure delta phase is thermodynamically stable; at 300 K where the delta phase can only be maintained in a metastable state with minor additions of gallium or aluminum; and at 180 K where plutonium should transform to the alpha phase. It is found in all three cases that the atomic structure within the cascade evolves through a glass-like state. At 600 K, this structure recovers very slowly; at 300 K it persist up to 2 ns with no discernable trend to recover eventually; and at 180 K the amorphous structure initiated by the collision cascade spreads through the entire crystal and converts it to a glass-like structure.     

Platelet-activating factor stimulates expression of IL-1 beta mRNA in THP-1 cells

A human monocytic cell line (THP-1) was used to study the effects of PAF (platelet-activating factor) on the expression of IL-1 beta mRNA. THP-1 cells were incubated with 10 pM PAF in the presence or absence of 0.1 μg/mL endotoxin for 4 hr, after which cytoplasmic RNA was extracted and subjected to Northern hybridizations. PAF, alone and in combination with endotoxin, caused an increase in mRNA levels for IL-1 beta. The magnitude of the effects of PAF on IL-1 beta mRNA levels matched closely the effects seen at the level of protein synthesis, suggesting that the effects of PAF on IL-1 beta release may result largely from its effects on IL-1 beta mRNA levels.     

Doxorubicin in pregnancy: possible transplacental passage

Two pregnant women with lymphoproliferative disorders were treated with doxorubicin-containing regimens. Both patients delivered shortly after a dose of doxorubicin. One child was healthy and the other was stillborn. Measurements of anthracycline levels in placental, cord, and fetal tissues by high-performance liquid chromatography suggest that doxorubicin may be transported across the placenta.     

Use of 2-D-adaptive mesh in simulation of combustion front phenomena

Solutions to models with different length scales may contain regions such as shocks, steep fronts and other near discontinuities. Adaptive meshing strategies, in which a spatial mesh network is adjusted dynamically so as to capture the local behavior accurately, will be described. The algorithm will be tested on an example of solid-solid combustion.     

Cascade-driven mixing at metal oxide interfaces

Advanced nuclear fuel concepts sometimes involve metal oxide interfaces between fissile and nonfissile phases. During operation, cascade damage as secondary events from a fission track will occur throughout the material. Some of that damage will take place at the interface between phases. Here we simulate representative secondary events of this nature. As a model system, ongoing experiments consider a composite in which the nonfissile material is magnesia and the fissile phase is modeled via hafnia as a surrogate. In correspondence the experiments, the atomistic simulation cells are composed of hafnia in the fluorite structure and magnesia in the rocksalt structure. Molecular dynamics simulations of cascade damage across interfaces of these materials shows Hf cations becoming kinetically trapped in the magnesia phase. The Hf cations remained trapped for the duration of the 20-ps simulations. When the primary-knock-on atom energy is above a few hundred eV in the direction of the interface and is within five lattice spacings, the propensity for trapping is very high. Under these same conditions, an Mg cation will occasionally become trapped in the hafnia. Complementary electronic structure calculations indicate that Hf cations are thermodynamically unstable in magnesia. Furthermore, these calculations indicate that the charge on the Hf ions reduces by one electron if no compensating defect is present, but reverts to the charge in HfO₂ bulk in the presence of a defect such as an oxygen interstitial. Extensions of these observations to the behavior of urania and ceria are mentioned.     

Cognitive deficits and psychiatric rehabilitation outcomes in schizophrenia

Many patients with schizophrenia are characterized by cognitive deficits that limit their ability to benefit from psychiatric rehabilitation interventions. While this suggests that cognitive rehabilitation is important, more needs to be known about which cognitive deficits interfere with which aspects of outcome and functioning before effective interventions are developed. We report data on cognitive predictors of three types of outcome: acquisition and performance of skills in a skills training group; aspects of daily ward functioning; and ability to be discharged from a state hospital. Our data indicate that poorer outcomes in each of these areas are associated with different, but somewhat overlapping, profiles of cognitive deficits. These data are relevant for designing both ward-based and individualized interventions. Integrating traditional psychiatric rehabilitation approaches with targeted cognitive interventions is necessary to maximize the impact of psychiatric rehabilitation services on individuals with chronic schizophrenia.     

Time-Dependent Solution to the Tai-Chou Chemical Vapor Infiltration Model

A recently proposed steady-state isothermal model for chemical vapor infiltration in parallel cylindrical pores has been extended to include transient behavior. Availability of a time-dependent solution should prove useful in comparison with experimental data and validation of the assumed boundary conditions. Attention is also drawn to analogous problems in the heat transfer literature which may prove useful in development of enhanced vapor infiltration models of this class.     

Phase I trial of a 5-day infusion of L-leucovorin plus daily bolus 5-fluorouracil in patients with advanced gastrointestinal malignancies

Increased Na+/H+ exchanger activity is associated with cellular hyperplasia. Cellular hyperplasia is an adaptive response to small-intestinal resection. Therefore, we hypothesized that the small-intestinal Na+/H+ exchanger activity increases in response to small-intestinal resection. Twenty-one-d-old, male Sprague-Dawley rats were randomly divided to receive either a 70% small intestinal resection (n = 59), or a mid-small intestinal transection (n = 49). Seven d postoperatively, the animals were killed and the Na+/H+ exchanger activity of the intestinal remnants was studied by a well validated brush border membrane vesicle technique. The initial rate of Na+ uptake in the presence of an outwardly directed pH gradient and the Vmax of the amiloride-sensitive Na+ uptake were significantly increased (p < 0.01 and p < 0.001, respectively) in the resection as compared with the transection remnants and to a greater magnitude in the distal as compared with the proximal remnants. Km values were not significantly different. The amiloride-sensitive Na+ uptake in the setting of various intravesicular pH was significantly greater (p < 0.001) in the distal resection as compared with the distal transection remnants, with points of enhanced Na+/H+ exchanger activity of intravesicular pH 6.62 and 6.87, respectively. The presence and activation of the Na+/H+ exchanger's internal modifier site was confirmed by demonstrating the effect of intravesicular pH on Na+ efflux. The present study demonstrates an up-regulation of intestinal Na+/H+ exchange activity in a small-bowel resection model in the weanling rat.(ABSTRACT TRUNCATED AT 250 WORDS)     

Using the modified embedded-atom method to calculate the properties of Pu-Ga alloys

In this article, the semi-empirical modified embedded atom method is used to develop a model of Pu-Ga alloys. Employing classical calculations, the model is used to predict thermodynamic properties of these alloys as well as the complex Pu-Ga phase diagram. For more information contact M.I. Baskes, Los Alamos National Laboratory, P.O. Box 1663, MS-G755, Los Alamos, NM 87545, USA; (505) 667-1238; fax (505) 667-8021; baskes@lanl.gov.