Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.     

Controlling factors for the brittle-to-ductile transition in tungsten single crystals

Materials performance in structural applications is often restricted by a transition from ductile response to brittle fracture with decreasing temperature. This transition is currently viewed as being controlled either by dislocation mobility or by the nucleation of dislocations. Fracture experiments on tungsten single crystals reported here provide evidence for the importance of dislocation nucleation for the fracture toughness in the semibrittle regime. However, it is shown that the transition itself, in general, is controlled by dislocation mobility rather than by nucleation.     

Effects of Dietary Supplementation of β‐hydroxy‐β‐methylbutyrate on Sow Performance and mRNA Expression of Myogenic Markers in Skeletal Muscle of Neonatal Piglets

The effects of dietary β‐hydroxy‐β‐methylbutyrate (HMB) supplementation during gestation on reproductive performance of sows and the mRNA expression of myogenic markers in skeletal muscle of neonatal pigs were determined. At day 35 of gestation, a total of 20 sows (Landrace × Yorkshire, at third parity) were randomly assigned to two groups, with each group receiving either a basal diet or the same diet supplemented with 4 g/day β‐hydroxy‐β‐methylbutyrate calcium (HMB‐Ca) until parturition. At parturition, the total and live litter size were not markedly different between treatments, however, the sows fed HMB diet had a decreased rate of stillborn piglets compared with the sows fed the control (CON) diets (p < 0.05). In addition, piglets from the sows fed HMB diet tended to have an increased birth weight (p = 0.08), and a reduced rate of low birth weight piglets (p = 0.05) compared with piglets from the CON sows. Nevertheless, lower feed intake during lactation was observed in the sows fed the HMB diet compared with those on the CON diet (p < 0.01). The relative weights of the longissimus dorsi (LD) and semitendinosus (ST) muscle were higher (p < 0.05) in neonatal pigs from the HMB than the CON sows. Furthermore, maternal HMB treatment increased the mRNA levels of the myogenic genes, including muscle regulatory factor‐4 (MRF4, p < 0.05), myogenic differentiation factor (MyoD) and insulin‐like growth factor‐1 (IGF‐1, p < 0.01). In conclusion, dietary HMB supplementation to sows at 4 g/day from day 35 of gestation to term significantly improves pregnancy outcomes and increases the expression of myogenic genes in skeletal muscle of neonatal piglets, but reduces feed intake of sows during lactation.     

Interferometric observations of an artificial satellite

Very-long-baseline interferometric observations of radio signals from the TACSAT synchronous satellite, even though extending over only 7 hours, have enabled an excellent orbit to be deduced. Precision in differenced delay and delay-rate measurements reached 0.15 nanosecond ( approximately 5 centimeters in equivalent differenced distance) and 0.05 picosecond per second ( approximately 0.002 centimeter per second in equivalent differenced velocity), respectively. The results from this initial three-station experiment demonstrate the feasibility of using the method for accurate satellite tracking and for geodesy. Comparisons are made with other techniques.     

Pathological and Bacteriological Studies of Hydrosalpinx in Buffaloes

The objectives of the present study were to investigate the bacteria accompanying hydrosalpinx of the buffalo cow and investigate the correlation between bacterial infection of the uterus and hydrosalpinx. Buffalo cows’ reproductive tracts were collected from Mosul abattoir. A total 385 uterine samples were examined of which 25 were having hydrosalpinx. Swabs for bacteriology, fluid for cytology and biopsies for histopathology were collected from the hydrosalpinx and the uterus from each samples included in this study. Results of this study indicated high prevalence of hydrosalpinx (6.5%) including unilateral (n = 19; 76%) and bilateral (n = 6; 24%) hydrosalpinx. Although 16 samples (64%) of the hydrosalpinx samples had no bacterial growth, the most prevalent bacteria recovered from hydrosalpinx were Corynebacterium hemolyticum and Actinomyces bovis, 42.8% and 28.6%, respectively. The most prevalent bacteria in the uterus were Archanobacterium pyogenes (18.5%), Staphylococcus aureus (14.8%), and Listeria monocytogenes (11.0%). Higher rates of leukocytes infiltration (p < 0.01) were observed in the uterine discharge than hydrosalpinx. A significant (p < 0.01) increase in lymphocytes was found in uterine discharge. Microscopic examination of the hydrosalpinx showed mucosal atrophy and dilatation of oviductal lumen without any signs of inflammation. It could be concluded that there is no correlation between bacteria isolated from uterus and hydrosalpinx. No association was found between bacteriological cultures and hydrosalpinx. Inflammation of the uterine tissue could be extended to utero‐tubal junction producing local inflammation resulting in fibrosis and tubal obstruction. The obstruction in the lumen of the oviducts resulted in accumulation of fluid.     

Precision Geodesy via Radio Interferometry

Very-long-baseline interferometry experiments, involving observations of extragalactic radio sources, were performed in 1969 to determine the vector separations between antenna sites in Massachusetts and West Virginia. The 845.130-kilometer baseline was estimated from two separate experiments. The results agreed with each other to within 2 meters in all three components and with a special geodetic survey to within 2 meters in length; the differences in baseline direction as determined by the survey and by interferometry corresponded to discrepancies of about 5 meters. The experiments also yielded positions for nine extragalactic radio sources, most to within 1 arc second, and allowed the hydrogen maser clocks at the two sites to be synchronized a posteriori with an uncertainty of only a few nanoseconds.     

Astronomical applications of differential interferometry

Intercomparison of radio signals received simultaneously at several sites from several sources with small mutual angular separation provides a powerful astrometric tool. Applications include tracking the Lunar Rover relative to the Lunar Module, determining the moon's libration, measuring winds in Venus's lower atmosphere, mapping Mars radiometrically, and locating the planetary system in an inertial frame.     

鸭瘟活疫苗生产工艺改进试验

利用尿囊腔接种法替代绒毛尿囊膜接种法生产鸭瘟活疫苗,收获的胚液和绒毛尿囊膜及胎儿的病毒含量(ELD50)均高于<中华人民共和国兽用生物制品规程>2000年版中的病毒含量标准,而且降低了早死率,提高了鸡胚利用率.