Correlations between ground and excited state spectra of a quantum Dot

The ground and excited state spectra of a semiconductor quantum dot with successive electron occupancy were studied with linear and nonlinear magnetoconductance measurements. A direct correlation was observed between the mth excited state of the N-electron system and the ground state of the (N + m)-electron system for m up to 4. The results are consistent with a single-particle picture in which a fixed spectrum of energy levels is successively filled, except for a notable absence of spin degeneracy. Further departures from the single-particle picture due to electron-electron interaction were also observed. Magnetoconductance fluctuations of ground states show anticrossings where wave function characteristics are exchanged between adjacent levels.     

Slow fertilization of stickleback eggs: the result of sexual conflict?

Background  

The fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm. The time delay between sequential ejaculations may further influence the outcome of sperm competition. Such a time interval can load the raffle over fertilization if fertilization takes place very fast. Short fertilization times are generally assumed for externally fertilizing fish such as the three-spined stickleback (Gasterosteus aculeatus). In this pair-spawning fish, territorial males often try to steal fertilizations in nests of neighbouring males. This sneaking behaviour causes sperm competition. Sneakers will only get a share of paternity when eggs are not fertilized immediately after sperm release. Contrary to males, females may be interested in multiple paternity of their clutch of eggs. There thus may be a sexual conflict over the speed of fertilization.     

Influence of Superovulatory Protocols on In Vitro Production of Nellore (Bos indicus) Embryos

There are indications in the literature that delaying the period between ovarian superestimulation and ovum pick up (OPU) would induce follicles to a condition of initial atresia, which could be beneficial to oocyte development. In this work, we compared three protocols for OPU and in vitro production (IVP) of embryos, in Nellore cattle. Nellore cows (n = 18) were randomly allocated in three groups: Group 1 (OPU), Group 2 [Follicle stimulating hormone (FSH) and OPU] and Group 3 (FSH deprivation and OPU). Three OPUs were performed, and the animals were switched to a different group each time (crossover), in such a way that at the end of the experiment all cows received the 3 protocols. At random stage of the oestrous cycle (D‐2), all follicles ≥ 6 mm were aspirated to induce a new follicular wave 2 days afterwards (D0). In Group 1, OPU was performed on D2 and oocytes were processed to IVP. In Group 2, starting on D0, cows were superstimulated (FSH, Folltropin^®, 30 mg administered daily, i.m., during three consecutive days, total dose = 180 mg), and 6 h after the last FSH dose, they received exogenous luteinizing hormone (LH) (12.5 mg, i.m., Lutropin^®, D3). The OPU was performed 6 h after LH administration, i.e. 12 h after the last dose of FSH. Animals in Group 3 received the same treatment as those in Group 2, except that LH was administered 42 h after the last dose of FSH, and OPU occurred 6 h later. Therefore, in this group, follicles were deprived of FSH at 48 h. Both cleavage and blastocyst rates were similar (p > 0.05, anova ) among oocytes from Groups 1, 2 and 3, respectively: 77.4% (144/185) and 42.70% (79/185); 75.54% (105/139) and 31.65% (44/139); 63.52% (101/159) and 33.33% (53/159). However, hatched blastocyst rate was higher (p < 0.01) in Group 1 (30.27%, 56/185) when compared with Group 2 (11.51%, 16/139) or 3 (15.72%, 25/159). It is concluded that, contrary to previous work on European breeds (Bos taurus), ovarian superstimulation associated with deprivation of FSH and OPU (Group 3) did not increase IVP of Nellore embryos (Bos indicus). On the contrary, the highest hatched blastocyst rates were observed in oocytes from non‐superstimulated cows.     

A real-time polymerase chain reaction assay for the detection of Mycoplasma agalactiae

AIM: To develop a real-time PCR for the detection of Mycoplasma agalactiae, using PCR primers targeting the ma-mp81 gene.

METHODS: A group of 15 M. agalactiae isolates, 21 other Mycoplasma spp. isolates and 21 other bacterial isolates was used in evaluation of the assay.

RESULTS: All M. agalactiae isolates were detected by the assay and none of the non-target isolates was amplified. The analytical detection limit of the assay was 10 fg of purified genomic DNA and 10⁴ cfu/ml milk inoculated with M. agalactiae. When applied to goat-milk samples collected from three herds free of M. agalactiae infection, the assay had a specificity of 100%.

CONCLUSIONS: The assay would be useful in a diagnostic laboratory, providing specific, sensitive and rapid detection of M. agalactiae.     

Development and spatial distribution of the free-living stages of Teladorsagia circumcincta and Trichostrongylus colubriformis on pasture: A pilot study

Abstract

AIMS: To measure the development of Teladorsagia (=Ostertagia) circumcincta and Trichostrongylus colubriformis eggs to third-stage infective larvae (L3) at different times of the year. Also, to measure the spatial distribution of L3 across herbage, soil and faeces, in order to assess whether spatial issues could be important in larval dynamics on pasture.

METHODS: Field plots were contaminated with sheep faeces containing approximately 20,000 eggs of each of T. circumcincta and T. colubriformis on five separate occasions, viz 01 December 1996 (summer), 18 March 1998 (autumn), 17 June 1998 (winter), 15 October 1998 (spring), and 23 July 1999 (winter). Replicate plots (n=10) were harvested at intervals for up to 12 months after deposition of faeces, and the number and distribution of L3 were measured. Larvae were sampled from faeces (where these remained), herbage, and three soil zones to a depth of 145 mm.

RESULTS: There were large differences between contamination dates in the percentage of eggs that developed to L3. For both species the highest percentage development was for eggs deposited in December (7.8% and 25.9% for T. circumcincta and T. colubriformis, respectively) and the lowest for June (0.4% and 0.03% T. circumcincta and T. colubriformis, respectively). Development in winter was often delayed, and this was always associated with a low yield of larvae, probably due to compounding mortalities associated with long periods of exposure to low temperatures.

The relative distribution of L3 present on herbage, in faeces or in the soil varied between sampling times. However, overall the most L3 were recovered from soil (74% and 66% for T.circumcincta and T. colubriformis, respectively, averaged over all samples), and the lowest recoveries were from the herbage.

CONCLUSIONS: Although the data are limited, the results indicated that the highest percentage of eggs developed to infective larvae in summer and only minimal development occurred in winter. The data do not support the view that substantial contamination of pastures with sheep parasites occurs over winter. Large numbers of larvae were recovered from soil, which indicates that, assuming they can subsequently migrate onto herbage, soil is a potentially important reservoir ofinfective larvae in New Zealand. Therefore, the spatial distribution of L3 on pasture may affect both the dynamics and transmission of parasite populations. Further work on both these issues is warranted.