Subnanometer-Diameter Wires Isolated in a Polymer Matrix by Fast Polymerization

The preparation and analysis of inorganic-organic polymer nanocomposites consisting of inorganic nanowires and multiwire "cables" in a random-coil organic polymer host is reported. Dissolution of inorganic (LiMo3Se3)n wires in a strongly coordinating monomer, vinylene carbonate, and the use of a rapid polymerization in the presence of a cross-linking agent produce nanocomposites without phase separation. Polymerization of dilute solutions yields a material containing mostly (Mo3Se3(-))n mono- and biwires, 6 to 20 angstroms in diameter and 50 to 100 nanometers long. Polymerization of more concentrated liquid crystalline solutions yields a nanocomposite containing oriented multiwire cables, 20 to 40 angstroms in diameter and up to 1500 nanometers long, that display optical anisotropy and electrical conductivity.     

Ovarian Follicular Dynamics. A review with Emphasis on the Bovine Species. Part II: Antral Development,Exogenous Influence and Future Prospects

During an oestrous cycle, a cohort of antral follicles develops into – depending on the species – one or more ovulatory follicles. The bovine oestrous cycle is characterized by two to three such cohorts or growth waves, only the last of which will result in an ovulation. In every growth wave, several antral follicles are recruited for development. Recruited follicles are subjected to a selection process, whereby ever decreasing levels of follicle stimulating hormone (FSH) are available to the FSH dependent follicles. In the cow, a single follicle from the cohort will acquire dominance. The ability of the dominant follicle to prosper under basic FSH levels is ascribed to a transition in hormone dependency from FSH to luteinizing hormone. The exact follicle selection mechanism remains, however, to be elucidated. The beginning of this article focuses on the recruitment, selection and dominance phases in antral follicle development. Subsequently, the conditions leading to successful maturation and ovulation are discussed. The next section expounds upon the mechanisms for exogenous modulation of follicular dynamics with the aim of superovulation/superstimulation, and finally prospective future research directions are sketched.     

Polyolefin spheres from metallocenes supported on noninteracting polystyrene

To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of alpha-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 degreesC affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.     

Quantification and Viability Assessment of Isolated Bovine Primordial and Primary Ovarian Follicles Retrieved Through a Standardized Biopsy Pick-Up Procedure

The feasibility of repeated collection and enzymatic isolation of large numbers of viable primordial and primary follicles from living donor cows were tested. Ovarian cortical biopsies were collected transvaginally by the Biopsy Pick-Up (BPU) device, a modification of an Ovum Pick-Up instrument. Follicles were enzymatically isolated from the retrieved cortical tissue samples, and follicle viability was determined by a live/dead fluorescent assay. Six cows were subjected to BPU once per week during 4 consecutive weeks, and in each BPU session 4 cortical tissue samples were collected per ovary. Over the 4-week trial period, a total of 1443 primordial and primary follicles were collected, 1358 (94%) of which were primordial and 85 (6%) were primary follicles. In each BPU session, an average 60.1 ± 10.7 (mean ± SEM) primordial and primary follicles were isolated per cow. The number of follicles varied considerably throughout the trial period and between cows. Statistical analysis of the data, however, did not support the presence of any distinct trends in the follicle yields over time or between cows. A total of 111 enzymatically isolated follicles were analyzed for viability with fluorescent probes. The vast majority of isolated follicles (92.8%) were totally viable. We conclude that the standardized BPU procedure generates sufficiently large numbers of vital primordial and primary follicles, thus validating BPU as a new tool for research into early bovine follicular development.