Metallic, magnetic and molecular nanocontacts

Scanning tunnelling microscopy and break-junction experiments realize metallic and molecular nanocontacts that act as ideal one-dimensional channels between macroscopic electrodes. Emergent nanoscale phenomena typical of these systems encompass structural, mechanical, electronic, transport, and magnetic properties. This Review focuses on the theoretical explanation of some of these properties obtained with the help of first-principles methods. By tracing parallel theoretical and experimental developments from the discovery of nanowire formation and conductance quantization in gold nanowires to recent observations of emergent magnetism and Kondo correlations, we exemplify the main concepts and ingredients needed to bring together ab initio calculations and physical observations. It can be anticipated that diode, sensor, spin-valve and spin-filter functionalities relevant for spintronics and molecular electronics applications will benefit from the physical understanding thus obtained

Plasma anti-müllerian hormone allows reproductive selection of donors with greater potential of embryo production

Reproductive technologies, such as ovum-pick-up (OPU) and in vitro embryo production (IVEP) are important tools to accelerate genetic gain associated with reproductive efficiency. The antral follicular population (AFP) can directly affect the success of OPU and may be used as a characteristic to select the oocyte donor cows with greater reproductive potential that will be used in OPUIVEP programs. Although highly repeatable within animal, the AFP appears to be extremely variable across individuals. Thus, the investigation of consistent endocrine markers that can trustable predict AFP in cattle has been targeted in several recent studies. In this context, the plasmatic levels of anti-Müllerian hormone (AMH) have been reported to be correlated with the size of AFP and it has the potential of being an endocrine marker to help the identification of donor cows with greater number of follicles available for OPU, greater superovulation response and, consequently, increased in vivo and in vitro embryo production in cattle. This review summarizes recent information regarding AFP and its relationship with AMH, and the possibility of using AMH as a marker for the selection of donor cows that will start reproductive programs to disseminate genetics and eventually to enhance fertility in cattle

Estrategies to improve fertility in cattle: artificial insemination following estrus versus timed artificial insemination

Artificial insemination (AI) is currently the major biotechnique used worldwide to disseminate superior genetics and to improve reproductive efficiency in bovine herds. Conversely, reports from different parts of the world indicate low pregnancy rates in cattle submitted to AI, due to both mistakes in heat detection or a high incidence of anestrous. In dairy cattle, the use of AI following visual detection of estrus is relatively easier to be used because their routine of management is intense (milking two to three times a day), allowing a frequent contact with cows for estrus observation. However, for beef cattle, the implementation of AI programs based on estrus detection is harder to be used because of several management conditions. Beef cows are frequently raised extensively, with great walking distances between their pasture to the corral where the AI is performed, the number of employers designated for cattle management is reduced and they have several activities besides reproduction. Because of the necessity of at least two periods of estrus observation per day and the conduction of cattle to the corral around 12 h following estrus detection to be inseminated, the AI is somehow unfeasible in beef farms. The development of timed AI (TAI) enabled insemination of cows in commercial scale, because it allows the programmed AI of large number of cows in the same day without the need for estrus detection. Besides, the use of TAI in early postpartum dairy and beef females reduces the interval partum-conception and, consequently the interval between parturitions, which has a dramatic effect on farm economic return. For beef cattle, TAI also brings the advantages of concentrating around half of the conceptions at the first days of the breeding season and stimulating cyclicity and a synchronous estrus return in cows that did not become pregnant at TAI. Thus, the calving season is also concentrate in the best periods of the year to generate offspring with greater weight and potential of development. TAI programs are currently important tools of reproductive management to improve reproductive performance of cattle. The adequate incorporation of these programs has the potential to enhance reproductive efficiency of livestock and consequently increase overall productivity of the farm

Control of ovulation with a GnRH agonist after superstimulation of follicular growth in buffalo: fertilization and embryo recovery

The potential to use a GnRH agonist bioimplant and injection of exogenous LH to control the time of ovulation in a multiple ovulation and embryo transfer (MOET) protocol was examined in buffalo. Mixed-parity buffalo (Bubalus bubalis; 4-15-year-old; 529 13 kg LW) were randomly assigned to one of five groups (n = 6): Group 1, conventional MOET protocol; Group 2, conventional MOET with 12 It delay in injection of PGF(2alpha); Group 3, implanted with GnRH agonist to block the pre-ovulatory surge release of LH; Group 4, implanted with GnRH agonist and injected with exogenous LH (Lutropin(R), 25 mg) 24 h after 4 days of superstimulation with FSH; Group 5, implanted with GnRH agonist and injected with LH 36 h after superstimulation with FSH. Ovarian follicular growth in all buffaloes was stimulated by treatment with FSH (Folltropin-V(R), 200 mg) administered over 4 days, and was monitored by ovarian ultrasonography. At the time of estrus, the number of follicles greater than or equal to8 mm. was greater (P < 0.05) for buffaloes in Group 2 (12.8) than for buffaloes in Groups 1 (8.5), 3 (7.3), 4 (6.1) and 5 (6.8), which did not differ. All buffaloes were mated by AI after spontaneous (Groups 1-3) or induced (Groups 4 and 5) ovulation. The respective number of buffalo that ovulated, number of corpora lutea, ovulation rate (%), and embryos + oocytes recovered were: Group 1 (2, 1.8 +/- 1.6, 18.0 +/- 13.6, 0.2 +/- 0.2); Group 2 (4, 6.1 +/- 2.9, 40.5 +/- 17.5, 3.7 +/- 2.1); Group 3 (0, 0, 0, 0); Group 4 (6, 4.3 +/- 1.2, 69.3 +/- 14.2, 2.0 +/- 0.9); and Group 5 (1, 2.5 +/- 2.5, 15.5 +/- 15.5, 2.1 +/- 2.1). All buffaloes in Group 4 ovulated after injection of LH and had a relatively high ovulation rate (69%) and embryo recovery (46%). It has been shown that the GnRH agonist-LH protocol can be used to improve the efficiency of MOET in buffalo. (C) 2002 Elsevier Science Inc. All rights reserved