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Biomedical subjects

J Toner

Publications and source records attributed to J Toner.

At least 19 recordsLinked to original sources
PubMed2001

Universality and scaling in the disordering of a smectic liquid crystal.

We present experimental and theoretical studies of the effects of quenched disorder on one-dimensional crystal ordering in three dimensions. This fragile smectic liquid crystal layering, the material with the simplest positional order, is also the most easily deformed periodic structure and is, therefore, profoundly affected by disorder, introduced here by confinement in silica aerogel. Theory and experiment combine to characterize this system to an extraordinary degree, their close accord producing a coherent picture: crystal ordering is lost, giving way to extended short-range correlations that exhibit universal structure and scaling, anomalous layer elasticity, and glassy dynamics.

Journal Article↗
PubMed2000

A discotic disguised as a smectic: A hybrid columnar bragg glass

We show that discotics, lying deep in the columnar phase, can exhibit an x-ray scattering pattern which mimics that of a somewhat unusual smectic liquid crystal. This exotic, new glassy phase of columnar liquid crystals, which we call a "hybrid columnar Bragg glass," can be achieved by confining a columnar liquid crystal in an anisotropic random environment of, e.g., strained aerogel. Long-ranged orientational order in this phase makes single-domain x-ray scattering possible, from which a wealth of information could be extracted. We give detailed quantitative predictions for the scattering pattern in addition to exponents characterizing anomalous elasticity of the system.

Journal Article↗
PubMed2000

Nonequilibrium fluctuations, traveling waves, and instabilities in active membranes.

The stability of a flexible fluid membrane containing a distribution of mobile, active proteins (e.g., proton pumps) is shown to depend on the structure and functional asymmetry of the proteins. A stable active membrane is in a nonequilibrium steady state with height fluctuations whose statistical properties are governed by the protein activity. Disturbances are predicted to travel as waves at sufficiently long wavelength, with speed set by the normal velocity of the pumps. The unstable case involves a spontaneous, pump-driven undulation of the membrane, with clumping of the proteins in regions of high activity.

Kinetics↗
PubMed1999

Pregnancy following transfer of ooplasm from cryopreserved-thawed donor oocytes into recipient oocytes.

OBJECTIVE: To determine if frozen-thawed donor oocytes could be used to provide cytoplasm for transfer into patients' oocytes to improve subsequent embryonic development. DESIGN: Prospective evaluation of the procedure in consenting IVF patients. SETTING: Assisted reproductive technology program. PATIENT(S): The study was open to consenting IVF patients (of any age) with a history of poor embryo quality or those couples in which the wife's age was > or = 40 years. INTERVENTION(S): Transfer of donor egg cytoplasm from frozen-thawed oocytes into the oocytes of infertile recipients. MAIN OUTCOME MEASURE(S): Donor oocyte survival following cryopreservation, fertilization following cytoplasmic transfer into recipient oocytes, embryo quality, and pregnancy outcome. RESULT(S): Oocytes collected from four donors were cryopreserved and 61% (28/46) survived the thaw procedure. Cytoplasmic transfer was performed on the eggs of four patients, with fertilization occurring in 70.3% (26/37). Twin pregnancy was established in one patient (35 years of age) with a history of poor embryo quality. CONCLUSION(S): Cryopreserved donor oocytes may provide a source of cytoplasm for transfer into recipient oocytes, eliminating the need for cycle synchronization between donor and infertile patient.

Adult↗
PubMed1998

Semen quality: is there a paternal effect on pregnancy outcome in in-vitro fertilization/intracytoplasmic sperm injection?

The objective of this study was to investigate the role of the spermatozoon (paternal effects) on implantation and pregnancy outcome in in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI). Male individuals of three types were analysed: infertile men with oligoasthenoteratozoospermia (OAT), infertile men with normozoospermia and fertile men (donors). Female counterparts were judged to have comparable egg quality within two groups studied, i.e. infertile women with pure mechanical (tubal) infertility and recipients of donor eggs. There were significantly higher differences in implantation and pregnancy rates in groups using donor spermatozoa and donor egg recipients. Analyses of key set groups revealed a trend toward a poorer implantation and pregnancy outcome when comparing OAT versus normozoospermic patients within IVF, but not within ICSI treatments, in couples with tubal infertility. In couples who were recipients of donor eggs, no differences were observed between OAT patients treated by ICSI and normozoospermic patients treated with IVF. No significant differences were observed in miscarriage rates within any groups studied. In conclusion, the poorer results observed in OAT patients undergoing IVF may be secondary to spermatozoal effects due to a high insemination concentration. Overall, there does not seem to be a significant effect of severe male infertility (OAT) on implantation and pregnancy outcome. However, this does not preclude that specific sperm aberrations may exert a negative effect on embryogenesis and therefore on implantation potential following assisted or in-vivo reproduction.

Adult↗
PubMed1995

High doses of gonadotropins have no detrimental effect on in vitro fertilization outcome in normal responders.

OBJECTIVE: To examine the effect of high doses of gonadotropins on IVF outcome in normal (intermediate) responders. DESIGN: Retrospective analysis of patients undergoing IVF therapy from 1990 to 1994 at our institution. SETTING: Academic tertiary center. PATIENTS: A homogeneous group of women that consisted of intermediate responders examined in their initial attempt and who received differing amounts of gonadotropins were examined. INTERVENTIONS: All patients were stimulated using a combination of a GnRH-agonist and FSH and hMG and were allocated into two groups, based on the amount of gonadotropin administered initially (four or six ampules). MAIN OUTCOME MEASURES: Implantation and pregnancy (clinical and ongoing) rates were compared. RESULTS: There were no significant differences between patients receiving high doses versus those patients receiving lower doses of gonadotropins with regard to implantation and pregnancy rates. CONCLUSIONS: We conclude that high doses of gonadotropins have no detrimental effect on IVF outcome in normal (intermediate) responders.

Adult↗
PubMed1995

Intracytoplasmic sperm injection: achievement of high pregnancy rates in couples with severe male factor infertility is dependent primarily upon female and not male factors.

OBJECTIVE: To determine the efficacy and factors affecting outcome of intracytoplasmic sperm injection (ICSI) in patients with severe male factor infertility. DESIGN: Prospectively designed clinical trial of patients selected to participate in the study based upon the following inclusion criteria: previous total failed fertilization or unsuitable sperm parameters for conventional IVF. SETTING: Tertiary care academic center. PATIENTS: Ninety-two consecutive couples undergoing IVF therapy augmented with ICSI during April through December 1994 were studied. MAIN OUTCOME MEASURES: Fertilization and ongoing implantation and pregnancy rates (PRs). RESULTS: A total of 1,163 preovulatory oocytes were manipulated, yielding a diploid fertilization rate of 60.9%; the oocyte damage rate was 13.2%. The transfer rate was 95% with 43.1% of cycles having excess embryos that were cryopreserved. Overall, the clinical and ongoing PRs per transfer were 31.9% and 26.8%, respectively. None of the sperm parameters of the original semen analysis correlated with ICSI outcome. Female age did not affect fertilization results but had a significant impact on PR (< 34 years: 48.9%; 35 to 39 years: 22.9%; > or = 40 years: 5.9% clinical PR per transfer). CONCLUSIONS: Intracytoplasmic sperm injection offers a new and powerful therapeutic option to treat couples with severe male factor infertility associated with a variety of sperm abnormalities. An adequate female age is a pivotal factor determining a successful outcome.

Adult↗