8 research outputs found
Dynamics of a ferromagnetic domain wall: avalanches, depinning transition and the Barkhausen effect
We study the dynamics of a ferromagnetic domain wall driven by an external
magnetic field through a disordered medium. The avalanche-like motion of the
domain walls between pinned configurations produces a noise known as the
Barkhausen effect. We discuss experimental results on soft ferromagnetic
materials, with reference to the domain structure and the sample geometry, and
report Barkhausen noise measurements on FeCoB amorphous
alloy. We construct an equation of motion for a flexible domain wall, which
displays a depinning transition as the field is increased. The long-range
dipolar interactions are shown to set the upper critical dimension to ,
which implies that mean-field exponents (with possible logarithmic correction)
are expected to describe the Barkhausen effect. We introduce a mean-field
infinite-range model and show that it is equivalent to a previously introduced
single-degree-of-freedom model, known to reproduce several experimental
results. We numerically simulate the equation in , confirming the
theoretical predictions. We compute the avalanche distributions as a function
of the field driving rate and the intensity of the demagnetizing field. The
scaling exponents change linearly with the driving rate, while the cutoff of
the distribution is determined by the demagnetizing field, in remarkable
agreement with experiments.Comment: 17 RevTeX pages, 19 embedded ps figures + 1 extra figure, submitted
to Phys. Rev.
Drug Insight: clinical use of agonists and antagonists of luteinizing-hormone-releasing hormone
This article reviews the clinical uses of agonists and antagonists of luteinizing-hormone-releasing hormone (LHRH), also known as gonadotropin-releasing hormone. In particular, the state of the art treatment of breast, ovarian and prostate cancer, reproductive disorders, uterine leiomyoma, endometriosis and benign prostatic hypertrophy is reported. Clinical applications of LHRH agonists are based on gradual downregulation of pituitary receptors for LHRH, which leads to inhibition of the secretion of gonadotropins and sex steroids. LHRH antagonists immediately block pituitary LHRH receptors and, therefore, achieve rapid therapeutic effects. LHRH agonists and antagonists can be used to treat uterine leiomyoma and endometriosis; furthermore, both types of LHRH analogs are used to block the secretion of endogenous gonadotropins in ovarian-stimulation programs for assisted reproduction. The preferred primary treatment of patients with advanced, androgen-dependent prostate cancer is based on the periodic administration of depot preparations of LHRH agonists; these agonists can be likewise used to treat estrogen-sensitive breast cancer in premenopausal women. LHRH antagonists have been successfully used to treat prostate cancer and benign prostatic hypertrophy. Since receptors for LHRH are present on a variety of human tumors, (notably breast, prostate, ovarian, endometrial and renal cancers), cytotoxic therapy that targets these tumors with hybrid molecules of LHRH might be possible in the near future. Analogs of LHRH are now a well-established means of treating sex-steroid-dependent, benign and malignant disorders