Defects in semiconductors: some fatal, some vital

REVIEW The role of defects as essential entities in semiconductor materials is reviewed. Early experiments with semiconductors were hampered by the extreme sensitivity of the electronic properties to minute concentrations of impurities. Semiconductors were viewed as a family of solids with irreproducible properties. Scientific efforts overcame this idiosyncrasy and turned the art of impurity doping into today's exceedingly useful and reproducible technology that is used to control precisely electrical conductivity, composition, and minority-carrier lifetimes over wide ranges. Native defects such as vacancies and self-interstitials control basic processes, foremost self- and dopant diffusion. The structural properties of dislocations and higher dimensional defects have been studied with atomic resolution, but a thorough theoretical understanding of their electronic properties is incomplete. Reactions between defects within the host lattices are increasingly better understood and are used for gettering and electrical passivation of unwanted impurities. Metastable defects such as DX centers and the EL2-related arsenic antisite are briefly discussed. The recent development of isotopically controlled semiconductors has created new research opportunities in this field.     

对推行兽药GMP工作的思考

对推行实施兽药GMP工作中存在的问题进行了分析,提出了建议和对策,并指出兽药行业的规范化管理,除了要推行实施兽药GMP外,还应加快对兽药的经营、使用、研发、临床试验等各环节的立法,建立健全机构,加强队伍建设,特别是要尽快推行兽药经营质量管理规范(GSP),否则兽药GMP将很难长期坚持下去.     

First report and histological features of Chlamydia pecorum encephalitis in calves in New Zealand

CASE HISTORY: Between September and October 2013, 40 of 150 crossbred Friesian dairy calves on a farm in the Manawatu region of New Zealand developed neurological signs when between 1 and 3 months of age. Calves were grazed in multiple mobs and calves from each mob were affected. A variable response was observed to initial treatment with thiamine, fluoroquinolone antibiotics and non-steroidal anti-inflammatory drugs.

CLINICAL AND PATHOLOGICAL FINDINGS: Affected calves exhibited a range of neurological signs that included generalised depression, hind limb ataxia with a stiff gait, and knuckling of the fetlocks. In advanced cases, calves became recumbent with opisthotonous. Over a 4-week period, 13 calves died or were subject to euthanasia and a thorough necropsy was performed on three of these calves. Necropsy findings included fibrinous peritonitis, pleuritis and pericarditis, with no gross abnormalities visible in the brain or joints. Histology of the brain was possible in seven of the affected calves, with lesions ranging from lymphocytic and histiocytic vasculitis and meningoencephalitis, to extensive thrombosis and neutrophilic inflammation. Immunohistochemistry using an anti-chlamydial lipopolysaccharide antibody revealed positive immuno-staining in all seven cases, with no brain samples exhibiting immunostaining for Histophilus somni. DNA was extracted from a sample of fresh brain from one case and chlamydial DNA sequences were amplified by PCR and found to be identical to Chlamydia pecorum. PCR was also performed on formalin-fixed brain tissue from three of the other cases, but no chlamydial DNA was amplified.

DIAGNOSIS: Chlamydia pecorum meningoencephalomyelitis (sporadic bovine encephalomyelitis).

CLINICAL RELEVANCE: This is the first time that C. pecorum has been confirmed as a cause of clinical disease in New Zealand. Practitioners should be aware of this disease as a differential in calves with neurological signs, and submit samples of formalin-fixed brain as well as fresh brain to enable confirmation of suspected cases using PCR analysis. Furthermore, these cases illustrate that the histological lesions in the brains of calves with C. pecorum are more variable than previously reported, and pathologists should be aware that histological features may overlap with those traditionally ascribed to other organisms, such as H. somni.     

Captive Breeding of Cheetahs in South Africa – 30 Years of Data from the de Wildt Cheetah and Wildlife Centre

The de Wildt Cheetah and Wildlife Centre was established in 1971 and the first cheetah cubs were born in 1975. During the period 1975–2005, 242 litters were born with a total of 785 cubs. Mean cub survival from 1 to 12 months and greater than 12 months of age was 71.3 and 66.2%, respectively. The majority of losses (84.9%) occurred during the first month postpartum whereas only 15.1% deaths took place between 1 and 12 months of age. Females were first bred at an age of approximately 3 years, reached maximum reproductive age at 6–8 years, where after fertility declined. Males reached peak reproduction at 6 and maintained this for up to 12 years of age. Male fertility was best correlated with sperm morphology. During recent years, for practical purposes, males were allocated to 'good' (≥70% normal), 'fair' (40–70% normal) and 'poor' (<40% normal) categories according to sperm morphology count. The breeding males were selected from the good (preferably) and fair categories but poor category males were also used at times. Average litter sizes for 'good', 'fair' and 'poor' males were 3.44 (n = 21), 3.14 (n = 18) and 2.28 (n = 18), respectively. In females the heritability for litter size was high at 0.5848 (532 progeny, 1975–2007) and the maternal heritability for cub mortality was estimated to be 0.596. The data from the de Wildt Cheetah and Wildlife Centre and two other centres in the world (Kapama and Wassenaar) demonstrate that cheetah can be bred successfully in captivity.     

Influence of Ovulation Status,Seasonality and Embryo Transfer Method on Development of Cloned Porcine Embryos

To improve pig cloning efficiency, the present study evaluated the effect of ovulation status, seasonality and embryo transfer (ET) method on in vivo development of cloned porcine embryos. Cloned embryos were transferred to surrogate mothers on the same day of somatic cell nuclear transfer. In pre‐ovulation stage (PO), pregnancy rate (PR) and delivery rate (DR) were 36.3% and 9.4%, respectively. In post‐ovulation stage, 22.7% PR and 2.1% DR were recorded (both PR and DR are significantly higher in PO). When ET was performed during winter (December–February), spring (March–May), summer (June–August) and autumn (September–November), the PRs were 13.4%, 37.3%, 24.6% and 51.0%, while DRs were 0%, 12.7%, 4.3% and 7.8%, respectively. The highest PRs were recorded in autumn groups. However, DRs were significantly lower in autumn (7.8%) group compared with spring (12.7%) group. The PR was the lowest and no piglets were born in winter group, which might be because of the effect of low temperature during ET. To overcome the low PR in winter group, 0.25 ml straws were used for ET to minimize exposure time of embryos to ambient temperature. The straw ET group showed significantly higher PR in the winter group (23. 9%) compared with the conventional catheter‐loading group (7.7%). We suggest that using PO recipient and ET in spring is the best condition for pig cloning. In addition, alternative method to reduce cold shock during ET in winter is necessary.     

Clinical presentation and disease prevalence of captive central bearded dragons (Pogona vitticeps) at veterinary clinics in Australia

Central bearded dragons (Pogona vitticeps) are one of the most popular reptile pets in Australia and around the world. Diseases, including metabolic bone disease, periodontal disease, and gastrointestinal endoparasites commonly affect captive animals. To determine the common reasons these lizards were presented to the veterinarian and to establish the prevalence of disease seen in captive P. vitticeps in Australia, this retrospective study evaluated the clinical records of three exotic pet veterinary hospitals. Records from 724 P. vitticeps were analysed, with 70 reasons for presentation and 88 diseases identified across 1000 visits to the veterinarian. Lethargy was the most reported reason for presentation (n = 181). The gastrointestinal tract (18.25%) and skin (18.25%) were the equally most commonly affected organ systems, followed by the musculoskeletal system (15.17%). Endoparasites were the most common single disease process (n = 103), followed by metabolic bone disease (n = 65), skin wounds (n = 59) and periodontal disease (n = 48). Of the patients that presented for routine preventive health examinations (n = 159), 45.30% received some form of intervention to treat or prevent disease. Many of the conditions that were identified by the veterinarians in this study are traditionally correlated with suboptimal husbandry and may be easily prevented. This study identified the common reasons for presentation to the veterinarian and the prevalence of disease in captive P. vitticeps in Australia, providing the first extensive retrospective analysis of objective reference literature for central bearded dragon owners and aspiring reptile veterinarians.     

Re-examination of the metabolizable energy contents of various rations containing different types and levels of bacterially fermentable substrates in digestibility experiments with growing pigs

Introduction   Feedstuffs with elevated contents of bacterially fermentable substrates (BFS: GFE 1987) offered to pigs have intermediate metabolizable energy (ME) contents compared with feedstuffs mainly composed of starch or hardly fermentable fibre (H adorn et al. 1996a,b). Consequently, BFS-elevated feeds could be used as major components enabling pig fattening rations to obtain the ME values required for feed calculation from tabulated values (DLG 1991) or equations based on nutrient composition (GFE 1996). The main field of application for BFS-elevated feeds is, however, still the feeding of adult, non-lactating sows, with the majority of investigations on fermentation characteristics also being conducted with sows. In fattening pigs a higher accuracy of estimated ME contents is required than in non-lactating sows. Furthermore, the ME values of feeds with elevated BFS contents might be systematically different in sows and fattening pigs because a still incomplete evolution of the fermentative capacity of the hindgut of growing pigs cannot be totally excluded (J entsch et al. 1990). The efficiency of hindgut bacterial protein synthesis might also be different from that being assumed from sow data (e.g. K irchgessner et al. 1989, 1994).
The objective of the present study was to determine the actual ME and BFS contents of rations varying widely in type and level of BFS in three experiments with growing pigs. By comparing these values with those calculated from equations or from tabulated values a re-examination of the currently applied feed evaluation system should be carried out. Furthermore, interactions of BFS with dietary protein reduction were investigated, since in low-protein rations fermentation efficiency might be limited by a lack of nitrogen in the hindgut (M osenthin 1987).     

VASA (DDX4) is a Putative Marker for Spermatogonia,Spermatocytes and Round Spermatids in Stallions

Expression of the protein DDX4/MVH, or VASA, has been reported in germ cells of several species. The main objectives of this study were to (i) investigate VASA expression patterns in testicular cells of stallions at two different reproductive stages (pre‐pubertal and post‐pubertal) and (ii) evaluate the use of VASA antibody as a molecular marker for single germ cells from stallions. Testicular tissues were obtained from stallions and categorized as pre‐pubertal and post‐pubertal based on the formation of lumen and status of spermatogenesis on the cross section of seminiferous tubules. The results of Western blot showed a VASA protein band located at 76 kDa, indicating that the rabbit antibody has a cross‐reactivity with horse testicular tissues. The result of immunolabelling showed that VASA was expressed in the cytoplasm of spermatogonia at both reproductive stages and in spermatocytes and round spermatids at the post‐pubertal stage. GATA4‐positive Sertoli cells and Leydig cells located in the interstitial space were not immunolabelled with VASA. These results suggest that VASA can be utilized as a molecular marker for germ cells of stallions at pre‐pubertal and post‐pubertal stages. Interestingly, immunolabelling intensity was significantly higher in pachytene spermatocytes compared to spermatogonia and round spermatid. VASA antibody was also effective for staining of single germ cell preparations. In conclusion, VASA protein expression can be used as a marker for identification of spermatogonia, spermatocytes and round spermatids in testicular tissues of stallions.