Dynamic anisotropy and heterogeneity of polystyrene thin films as studied by inelastic neutron scattering.

We studied the dynamic anisotropy and heterogeniety of polystyrene thin films in glassy state with inelastic neutorn scattering. Adjusting the scattering vector to the directions parallel and perpendicular to the film surface, we observed the elastic scattering intensities as a function of temperature. It was found for the 200 A film that the elastic intesity decreased with increasing temperature more rapidly in the perpendicular direction than in the pararell direction, showing the higher mobility in the perpendicular direction. However, such dynamical anisotropy was not observed in the 1000 A film. The decrease in the mobility was observed with the film thickness in both the directions. These results were explained in terms of an interface hard layer. We also evelauated the dynamical heterogeniety from the non-Gaussian parameter A0, which increased with decreasing the film thickness, showing the increase in the dynamical heterogeneity. Assuming a simple bi-layer model consisting of the interface hard layer and the bulk-like layer, we analyzed the thickness dependence of the non-Gaussian parameter A0 and the mean square displacement (u2) to find that the hard layer has a thickness of approximately 130 A and a mean square displacement of approximately 0.018 A2 at 230 K.

Magnetic form factor of alpha-Ce: towards understanding the magnetism of cerium.

A favored interpretation of the gamma <--> alpha phase transition in cerium postulates the transformation of the localized 4f state in gamma-Ce to a weakly correlated itinerant 4f band in alpha-Ce. However, results of high-energy neutron inelastic scattering measurements, presented here, show clearly that the magnetic susceptibility response from alpha-Ce follows the Ce3+ form factor despite the large, 30-fold, increase in its spectral width relative to that in gamma-Ce. This observation provides, for the first time, indisputable evidence for the localized character of the 4f state in the alpha phase. The present findings appear consistent with recent calculations combining dynamical mean-field theory with the local density approximation that indicate a strongly correlated 4f state in alpha-Ce. The localized 4f state is also fundamental to the Kondo volume collapse theories for the gamma <--> alpha phase transition in cerium.

Experimental evidence for anisotropic double-gap behavior in MgB2.

The behavior of a type II superconductor in the presence of a magnetic field is governed by two characteristic length scales, the London penetration depth and the coherence length. We present magnetization measurements on MgB2 powder showing an anisotropy in the upper critical field and hence the coherence length of 6. Using the technique of small angle neutron scattering we show that this anisotropy is not mirrored in the London penetration depth, which is almost isotropic. This result can be explained by the superconductivity residing in two distinct electronic bands of the material, only one of which is highly anisotropic.

Intrinsic behavior of flux lines in pure niobium near the upper critical field.

We report small-angle neutron-scattering (SANS) measurements of flux line properties near H(c2) in an ultrapure sample of niobium with weak pinning of flux in the bulk. These confirm in detail the Abrikosov picture of the flux line lattice to within 20 mK of the upper critical field line. However, it has recently been claimed [X. S. Ling et al., Phys. Rev. Lett. 86, 712 (2001)], on the basis of SANS observations of a disordering of flux lines in niobium, that the flux lattice melts at temperatures clearly separated from the upper critical field line. This discrepancy may possibly arise from differences in sample purity and pinning.

The influence of supernumerary embryos on the clinical outcome of IVF cycles.

PURPOSE: To assess the influence of the presence of quality supernumerary embryos on the clinical outcome and risk of multiple conception in patients having their first in vitro fertilization (IVF) cycle. METHODS: Retrospective cohort study of 1448 women having their first IVF treatment cycle who received 4004 embryos where at least six embryos were available for transfer treated in an Assisted Conception Unit based in a large teaching hospital. RESULTS: The replacement of three rather than two embryos to women under 35 years who had good-quality supernumerary embryos resulted in a higher twin (12.5 vs. 11.9%) and triplet birth rates (2.1 vs. 0%), without significantly improving the clinical pregnancy (50.5 vs. 45.2%) or total live birth rates (38.9 vs. 35.7%). In the absence of quality spare embryos, these women who had three rather than two embryos replaced had a significantly higher clinical pregnancy rate (39.3 vs. 28.8%; P = 0.04), total live birth (32.7 vs. 19.4%; P = 0.02) and singleton birth rate per cycle (20.8 vs. 14.4%; P = 0.04), without significantly influencing the multiple birth rate. In women over 35 years, the replacement of three instead of two embryos in the presence or absence of quality supernumerary embryos led to a significant improvement in clinical outcome, without being associated with a concurrent increase in the multiple birth rate. Women in both age groups who had either two or three embryos replaced in the presence of quality supernumerary embryos had a notably better clinical outcome compared with their counterparts who had the same number of embryos replaced, but with no quality embryos to spare. CONCLUSIONS: The presence of good-quality supernumerary embryos can be used as a reference to determine the optimal number of embryos to transfer and as an indicator of the probability of success of an individual couple in a given cycle. Optimal pregnancy rates and simultaneous reduction of multiple gestation can be achieved with a flexible embryo replacement policy that is based on embryo quality, maternal age, and the presence or absence of surplus quality embryos.

The relationship between follicular fluid aspirate volume and oocyte maturity in in-vitro fertilization cycles.

As a consequence of multiple follicular growth during ovarian stimulation for in-vitro fertilization (IVF), follicles of varying sizes often yield oocytes that vary in maturity and morphology of the oocyte-cumulus-corona complex. The objective of this prospective study was to explore the relationship between follicular fluid aspirate volume and the oocyte's developmental potential in an IVF treatment cycle. In total 9933 follicles were studied from 400 patients who underwent 535 consecutive IVF treatment cycles at St James's University Hospital, Leeds, UK, between February 1995 and February 1996. The volume of each individual follicle aspirated was recorded and related to the probability of obtaining an oocyte, its fertilizing capacity, the cleavage rate and the quality of embryos derived. We found no statistically significant difference in oocyte recovery rates between follicles with an aspirate volume < or = 1 ml and follicles with a volume > 1 ml. Although oocytes obtained from follicles with an aspirate volume > or = 1 ml showed a significantly lower fertilization rate, they went on to cleave at the same rate as oocytes obtained from larger follicles and resulted in embryos of comparable quality. Furthermore, there was no statistically significant difference in the implantation, clinical pregnancy or live birth rates per cycle between embryos derived from follicles with an aspirate volume < or = 1 ml and those derived from follicles with an aspirate volume > 1 ml. We conclude that follicular size and the oocyte's developmental potential in the stimulated ovary are not closely related and can be independent. This is in contrast to the Graafian follicle and the pre-ovulatory oocyte in the natural cycle.

DNA binding and helicase domains of the Escherichia coli recombination protein RecG.

The Escherichia coli RecG protein is a unique junction-specific helicase involved in DNA repair and recombination. The C-terminus of RecG contains motifs conserved throughout a wide range of DNA and RNA helicases and it is thought that this C-terminal half of RecG contains the helicase active site. However, the regions of RecG which confer junction DNA specificity are unknown. To begin to assign structure-function relationships within RecG, a series of N- and C-terminal deletions have been engineered into the protein, together with an N-terminal histidine tag fusion peptide for purification purposes. Junction DNA binding, unwinding and ATP hydrolysis were disrupted by mutagenesis of the N-terminus. In contrast, C-terminal deletions moderately reduced junction DNA binding but almost abolished unwinding. These data suggest that the C-terminus does contain the helicase active site whereas the N-terminus confers junction DNA specificity.