Manipulating Chlorine Atom Bonding on the Si(100)-(2 x 1) Surface with the STM

Chlorine atoms strongly chemisorbed at dangling bond sites on the Si(100)-(2 x 1) surface are observed by scanning tunneling microscopy (STM) to hop between adjacent sites. The origin of this behavior is suggested to be an interaction between the field of the probe tip and the dipole moment of the silicon-chlorine bond. Chlorine atom migration is shown to be facilitated by the presence of a metastable chlorine bridge-bonded minimum. The STM probe was used to excite single chlorine atoms into this bridging configuration, resulting in a local population inversion. Selective application of voltage pulses between the probe tip and the surface rearranged the local bonding and induced transformations between different types of chlorine sites. In this manner, adsorbed species can be dissected and their composition and structure directly probed.     

Response of Thawed Epidi dymal Red Deer Spermatozoa to Increasing Concentrations of Hydrogen Peroxide,and Importance of Individual Male Variability

Oxidative stress represents a challenge during sperm manipulation. We have tested the effect of increasing hydrogen peroxide (H₂O₂) levels on red deer spermatozoa after cryopreservation, and the role of male‐to‐male variation in that response. In a first experiment, eight thawed samples were submitted to 0, 25, 50, 100 and 200 μm H₂O₂ for 2 h at 37°C. Intracellular reactive oxygen species (H₂DCFDA‐CM) increased with H₂O₂ concentration, but we only detected a decrease in sperm function (motility by CASA and chromatin damage by sperm chromatin structure assay) with 200 μm . Lipoperoxidation assessed by the thiobarbituric acid reactive substance (TBARS) method increased slightly with 50 μm H₂O₂ and above. In a second experiment, samples from seven males were submitted to 0 and 200 μm H₂O₂ for 2 h, triplicating the experiment within each male. Males differed at thawing and regarding their response to incubation and H₂O₂ presence. We found that the kinematic parameters reflected male‐to‐male variability, whereas the response of the different males was similar for lipid peroxidation and viability. A multiparametric analysis showed that males grouped differently if samples were assessed after thawing, after incubation without H₂O₂ or after incubation with H₂O₂. Red deer spermatozoa are relatively resilient to H₂O₂ after thawing, but it seems to be a great male‐to‐male variability regarding the response to oxidative stress. The acknowledgement of this individual variability might improve the development of optimized sperm work protocols.     

Is the Production of Embryos in Small‐Scale Farming an Economically Feasible Enterprise?

The present assay attempts to evaluate the feasibility of using embryo transfer in small community farmers by in vivo study and by modelling the results obtained. From the total of 59 donor cows, 62.7% responded to treatment, with a significant difference (p = 0.002) in the percentage of the response between breeds, being 90.5% (19/21) in Holstein and 47.4% (18/38) in Brahman. A total of 283 embryos were graded as transferable, while 141 as non‐transferable, without difference in the percentage of transferable embryo by breed (p = 0.18). The mean of transferable embryos graded as class I and II was not different between Holstein and Brahman (p = 0.96 and p = 0.92, respectively); besides, no differences were observed in the other grades (non‐transferable). The highest difference in costs, regardless of its quality by breed, was seen in the lower levels of probable fertility of the embryo transferred, even reaching several hundred dollars. When modelling the expected costs for embryo produced and transferred, values can reach nearly $2000.00 when the probable fertility is only 10%. However, when the probable fertility was 60%, embryo cost was close to $300.00. This technology seems to be viable on average or high‐scale systems, having a superovulatory response between 60 and 80% with 4–6 transferrable embryos. Yet, in small‐scale farming, due to the reduced number of donors and/or recipients, the costs surpass the economical feasibility of the technique.     

Dangling bond dynamics on the silicon (100)-2x1 surface: dissociation, diffusion, and recombination

The dynamics of dangling bond (DB) diffusion was studied after deuterium desorption from the silicon (100)-2x1 surface. At elevated temperatures, paired DB sites produced after desorption unpaired as deuterium atoms hopped from adjacent dimers. Below 620 kelvin, the unpaired configuration most commonly observed corresponded to two DBs on adjacent silicon dimers. At higher temperatures, unpaired DBs executed one-dimensional walks along the dimer rows, and recombination was observed with the same partner after walks lasting many minutes. The frequency and extent of these excursions increased with temperature. Above 660 kelvin, complete dissociation was observed and was sometimes followed by recombination by means of partner exchange. The implications for low-temperature materials growth are discussed.     

Dry matter partitions and specific leaf weight of soybean change with tree competition in an intercropping system

In 2004 and 2005, the yield, leaf area, dry weight and dry weight partitions of soybeans were determined at the Agroforestry Research Site (ARS) (est. 1987, Ontario, Canada). Soybean was intercropped with poplar (Populus deltoides x nigra DN-177 L., 556 m³crown tree⁻¹), silver maple (Acer saccharinum L., 308 m³), black walnut (Juglans nigra L., 148 m³) and pecan (Carya illinoensis Wangenh., 114 m³), or grown alone (monoculture). Yield of soybean was not different in either year between the monoculture and the black walnut or pecan intercrops. In the poplar and silver maple treatments, yield was 66 and 85% (2004 and 2005) lower than in the monoculture. Despite the fact that different tree species were used, there was a significant negative linear regression between yield and tree crown volume (R ² = 0.76, P = 0.0049 and R ² = 0.93, P < 0.0001 in 2004 and 2005, respectively). With increasing tree crown volume, soybean tended to partition more dry matter to the photosynthetic and reproductive parts and less to structural tissue and petiole. This demonstrates the phenotypic flexibility of the crop component in agroforestry systems. Contrary to theoretical predictions, soybean leaves were thicker as shade increased (increase by 6.2 × 10⁻⁴–1.2 × 10⁻³ mg cm⁻², per unit of crown volume), pointing to competitive interactions specific to tree-based intercrops.     

The intensity of resistance by mature Merino ewes against Haemonchus contortus and Tichostrongylus colubriformis in single-species and combined-species infection

Three-year-old, non-lactating and non-pregnant Merino ewes, raised on pasture under a program of strategic treatment with anthelmintic and found to be extremely resistant to "trickle" infection with Haemonchus contortus, were given single-dose infections with either H. contortus or Trichostrongylus colubriformis or both species together. The purpose was to ascertain the intensity of protective immunity against the 2 parasites in sheep with immunity acquired from a presumably slight exposure to infection. To provide a criterion, some infected ewes were immunosuppressed with corticosteroid, dexamethasone. Untreated ewes were extremely resistant to challenge infection with either 15,000 or 150,000 H. contortus or 15,000 T. colubriformis. Surprisingly, when mixed infection was given, egg counts for H. contortus were significantly elevated compared with infection by that species alone. Antibody to antigens from infective larval and adult H. contortus was measured in serum by enzyme-linked-immunosorbent assay (ELISA) during the course of infection. Serum titres against larval antigens were significantly depressed when infections with either H. contortus or T. colubriformis were permitted by immunosuppression with dexamethasone, whereas those against adult antigen were depressed when infection with T. colubriformis was permitted.     

疑似碘酊致牛死亡一例

笔者在临床上曾遇到一疑似“碘酊”致牛死亡的病例,由于未曾见过碘酊致牛死亡的报道,查阅资料也终未得到答案.笔者将其整理如下,供同行探讨。     

POSSIBLE PATHWAYS OF CONTAMINATION OF MEAT AND BONE MEAL WITH SALMONELLA

Samples taken at various points along the processing line in 2 rendering plants showed that post-processing contamination occurs almost immediately after termination of the heat process in the percolator and surge bin. Further contamination occurs at each processing stage. In plant A 12.5% of the samples collected from material leaving the surge bin, 36% of the samples of product after it has passed the milling stage and 61% of samples collected from the stored product were found to be contaminated with salmonellas. In plant B the results were 15%, 40% and 69% respectively. Heavy contamination of product left overnight in percolators and surge bins, which are not cleaned routinely, was considered an important source of early post-processing contamination. The ecology was found to be similar at both plants despite the fact that in one plant the uncooked and cooked areas were separated completely, whilst this was not the case in the other plant. None of the air samples collected yielded salmonellas, while nearly all the insect samples collected in the rendering plants yielded salmonellas.