A simple local expression for the prefactor in transition state theory.

We present a simple and accurate computational technique to determine the frequency prefactor in harmonic transition state theory without necessitating full phonon density of states (DOS) calculations. The atoms in the system are partitioned into an "active region," where the kinetic process takes place, and an "environment" surrounding the active region. It is shown that the prefactor can be obtained by a partial phonon DOS calculation of the active region with a simple correction term accounting for the environment, under reasonable assumptions regarding atomic interactions. Convergence with respect to the size of the active region is investigated for different systems, as well as the reduction in computational costs when compared to full phonon DOS calculation. Additionally, we provide an open source implementation of the algorithm that can be added as an extension to Large-scale Atomic/Molecular Massively Parallel Simulator software.

Electronic Origins of Anomalous Twin Boundary Energies in Hexagonal Close Packed Transition Metals.

Density-functional-theory calculations of twin-boundary energies in hexagonal close packed metals reveal anomalously low values for elemental Tc and Re, which can be lowered further by alloying with solutes that reduce the electron per atom ratio. The anomalous behavior is linked to atomic geometries in the interface similar to those observed in bulk tetrahedrally close packed phases. The results establish a link between twin-boundary energetics and the theory of bulk structural stability in transition metals that may prove useful in controlling mechanical behavior in alloy design.

Ab initio calculations of the melting temperatures of refractory bcc metals.

We present ab initio calculations of the melting temperatures for bcc metals Nb, Ta and W. The calculations combine phase coexistence molecular dynamics (MD) simulations using classical embedded-atom method potentials and ab initio density functional theory free energy corrections. The calculated melting temperatures for Nb, Ta and W are, respectively, within 3%, 4%, and 7% of the experimental values. We compare the melting temperatures to those obtained from direct ab initio molecular dynamics simulations and see if they are in excellent agreement with each other. The small remaining discrepancies with experiment are thus likely due to inherent limitations associated with exchange-correlation energy approximations within density-functional theory.

A complete representation of structure-property relationships in crystals.

Whereas structure-property relationships have long guided the discovery and optimization of novel materials, formal quantitative methods to identify such relationships in crystalline systems are beginning to emerge. Among them is cluster expansion, which has been successfully used to parametrize the configurational dependence of important scalar physical properties such as bandgaps, Curie temperatures, equation-of-state parameters and densities of states. However, cluster expansion is currently unable to handle anisotropic properties, a key distinguishing feature of crystalline systems central to the design of modern epitaxial structures and devices. Here, I introduce a tensorial cluster expansion enabling the prediction of fundamental tensor-valued material properties such as elasticity, piezoelectricity, dielectric constants, optoelectric coupling, anisotropic diffusion coefficients, surface energy and stress. As an application, I develop predictive ab initio models of anisotropic properties relevant to the design and optimization of III-V semiconductor epitaxial optoelectronic devices.

The free energy of mechanically unstable phases.

Phase diagrams provide 'roadmaps' to the possible states of matter. Their determination traditionally rests on the assumption that all phases, even unstable ones, have well-defined free energies under all conditions. However, this assumption is commonly violated in condensed phases due to mechanical instabilities. This long-standing problem impedes thermodynamic database development, as pragmatic attempts at solving this problem involve delicate extrapolations that are highly nonunique and that lack an underlying theoretical justification. Here we propose an efficient computational solution to this problem that has a simple interpretation, both as a topological partitioning of atomic configuration space and as a minimally constrained physical system. Our natural scheme smoothly extends the free energy of stable phases, without relying on extrapolation, thus enabling a formal assessment of widely used extrapolation schemes.

Effect of prolonged infusion of ritodrine on uteroplacental blood flow and cardiac output distribution in unanesthetized pregnant guinea pigs.

The effects of ritodrine, 15 micrograms X min-1 X kg-1 administered intravenously, on the maternal circulation and uteroplacental blood flow were investigated in eight chronically catheterized pregnant guinea pigs near term. Cardiac output and its distribution were measured by means of the radionuclide-labelled microsphere technique before, and after 2 and 6 h of infusion of ritodrine. Ritodrine produced a sustained elevation of cardiac output to 135 and 137% of the control value after 2 and 6 h, respectively. The carcass and gastrointestinal tract together accounted for the greatest portion of the extra blood flow, 77 and 84% at the times of the two flow measurements during treatment. After 2 h of ritodrine, mean placental blood flow was reduced to 85% of the control level (n.s.), uteroplacental vascular resistance was 127% of its initial value (n.s.), and the placental fraction of cardiac output had decreased from 18 to 12% (P less than 0.02). Continuation of the infusion to 6 h resulted in an increase in mean placental blood flow to 107% of the control value and return of uteroplacental vascular resistance to its initial level. The placental fraction of cardiac output increased to 14%, significantly (P less than 0.05) different from both the initial and the 2-h values. Blood flow to the skin, lungs, spleen and mammary glands decreased between the 2- and 6-h flow measurements. These observations are compatible with the hypothesis that the changes in uteroplacental blood flow during administration of ritodrine are passive, resulting from the balance between the increase in cardiac output and vasodilatation in extrauterine vascular beds.

The effect of a low-dose infusion of ritodrine on cardiac output distribution and uteroplacental blood flow in unanaesthetized pregnant guinea pigs.

Cardiac output and its distribution were measured using the microsphere technique before and at 2 and 6 h during the infusion of ritodrine, 1.5 microgram X min-1 X kg-1 i.v., into near-term pregnant guinea pigs. Average cardiac output increased 16 and 25%, and total peripheral resistance decreased 16 and 19% after 2 and 6 h of ritodrine infusion. The carcass and gastrointestinal tract together received two-thirds of the extra cardiac output. Uteroplacental blood flow and uteroplacental vascular resistance were not significantly different from the preinfusion values after 2 h of ritodrine treatment, but were increased 35% and decreased 31%, respectively (p less than 0.05 and less than 0.01), after 6 h of infusion. The increase in uteroplacental blood flow between the 2- and 6-h measurements was positively, and the decrease in uteroplacental vascular resistance negatively correlated with the increase in cardiac output during the same period.

[An rare cause of vaginal discharge: sarcoma botryoides]. / Een zeldzame oorzaak van fluor vaginalis: sarcoma botryoides.

A general practitioner was consulted by a 15-year-old girl, virgo, suffering from foetid vaginal discharge. The girl was seen by a gynaecologist after antimicrobial treatment had failed. Further investigations revealed that a embryonal rhabdomyosarcoma was present, a sarcoma botryoides. The tumour originating from the cervix uteri was resected completely after which chemotherapy was started. One year later there were no sequelae or indications of metastases. Sarcoma botryoides has a better prognosis than other types of rhabdomyosarcoma. The prognosis is also influenced by the site of origin, which is favourable for the cervix.

First-principles thermodynamics of coherent interfaces in samarium-doped ceria nanoscale superlattices.

Nanoscale superlattices of samarium-doped ceria layers with varying doping levels have been recently proposed as a novel fuel cell electrolyte. We calculate the equilibrium composition profile across the coherent {100} interfaces present in this system using lattice-gas Monte Carlo simulations with long-range interactions determined from electrostatics and short-range interactions obtained from ab initio calculations. These simulations reveal the formation of a diffuse, nonmonotonic, and surprisingly wide (11 nm at 400 K) interface composition profile, despite the absence of space charge regions.

Effect of isoproterenol on uterine blood flow and cardiac output distribution in pregnant guinea pigs.

The effects of isoproterenol, 0.05 micrograms X min-1 X kg-1 infused intravenously for 2 hours, on cardiac output distribution and uteroplacental blood flow were studied in six chronically catheterized guinea pigs between 60 and 68 days of pregnancy. Isoproterenol caused marked cardiac stimulation: Cardiac output was increased by 41%, of which 70% was distributed to the carcass and gastrointestinal tract. Absolute placental blood flow remained essentially unchanged, but the placental fraction of cardiac output decreased from 16% to 11%. Myometrial blood flow increased by 72%. Uteroplacental vascular resistance did not change significantly. In the guinea pig in late pregnancy beta-adrenergic receptors are present in the myoendometrial vessels but could not be demonstrated in the maternal vessels supplying the placenta.

Effect of ritodrine on uteroplacental blood flow and cardiac output distribution in unanesthetized pregnant guinea pigs.

The effects of ritodrine, 15 micrograms X min-1 X kg-1 infused intravenously for 2 hours, on cardiac output distribution and uteroplacental blood flow were investigated in 10 chronically catheterized guinea pigs between 57 and 63 days of pregnancy. Ritodrine produced an average 29% increase in cardiac output, three quarters of which was distributed to the carcass and myocardium. Absolute placental blood flow decreased by 10%, and the placental fraction of cardiac output decreased by one third. Uteroplacental vascular resistance increased by 41% during ritodrine infusion. The proportional changes in placental blood flow were positively correlated and those in placental vascular resistance negatively correlated with the change in cardiac output.

Relation between the iodine azide test and the TTCA test for exposure to carbon disulphide.

Exposure to carbon disulphide (CS2) in a viscose plant was measured by personal monitoring and by application of the iodine azide test and quantification of 2-thio-thiazolidine-4-carboxylic-acid (TTCA) in urine samples. A relation was found between the rise in urinary TTCA concentration during the workshift and the exposure index E1. The correlation (r) between the exposure index and the atmospheric concentrations of CS2 in workroom air below 100 mg CS2/m3 was 0.59 (n = 9). The correlation between the increase in TTCA concentrations during the workshift and the atmospheric CS2 concentrations was found to be higher when urine samples at the end of the workshift with creatinine concentrations below 1 mg/ml and above 3 mg/ml were disregarded (from r = 0.61; n = 20 to r = 0.84; n = 14). A high correlation was found (r = 0.86; n = 13) when the end of workshift urine samples were analysed, provided that their creatinine concentrations are not beyond the limits given above.