Bragg diffraction from crystallized ion plasmas     

WM Itano  JJ Bollinger  JN Tan  B Jelenkovic  X Huang  DJ Wineland 《Science (New York, N.Y.)》1998,279(5351):686-689

Single crystals of a one-component plasma were observed by optical Bragg diffraction. The plasmas contained 10(5) to 10(6) single-positive beryllium-9 ions (9Be+) at particle densities of 10(8) to 10(9) per cubic centimeter. In approximately spherical plasmas, single body-centered cubic (bcc) crystals or, in some cases, two or more bcc crystals having fixed orientations with respect to each other were observed. In some oblate plasmas, a mixture of bcc and face-centered cubic ordering was seen. Knowledge of the properties of one-component plasma crystals is required for models of white dwarfs and neutron stars, which are believed to contain matter in that form.  相似文献   

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere     

PO Wennberg  TF Hanisco  L Jaegle  DJ Jacob  EJ Hintsa  EJ Lanzendorf  JG Anderson  R Gao  ER Keim  SG Donnelly  LAD Negro  DW Fahey  SA McKeen  RJ Salawitch  CR Webster  RD May  RL Herman  MH Proffitt  JJ Margitan  EL Atlas  SM Schauffler  F Flocke  CT McElroy  TP Bui 《Science (New York, N.Y.)》1998,279(5347):49-53

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.  相似文献   

Sensitivity of boreal forest carbon balance to soil thaw   总被引：6，自引：0，他引：6  

ML Goulden  SC Wofsy  JW Harden  SE Trumbore  PM Crill  ST Gower  T Fries  BC Daube  S Fan  DJ Sutton  A Bazzaz  JW Munger 《Science (New York, N.Y.)》1998,279(5348):214-217

We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 +/- 0.5 metric ton of carbon per hectare per year (ton C ha-1 year-1) from 1994 to 1997, with a gain of 0.6 +/- 0.2 ton C ha-1 year-1 in moss and wood offset by a loss of 0.8 +/- 0.5 ton C ha-1 year-1 from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool ( approximately 150 tons C ha-1) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.  相似文献   

Measuring the spin polarization of a metal with a superconducting point contact     

Soulen Jr RJ  JM Byers  MS Osofsky  B Nadgorny  T Ambrose  SF Cheng  Broussard C T Tanaka PR  J Nowak  JS Moodera  A Barry  JMD Coey 《Science (New York, N.Y.)》1998,282(5386):85-88

A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals. Because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermi surface, the differential conductance of the point contact can reveal the spin polarization of the metal. This technique has been applied to a variety of metals where the spin polarization ranges from 35 to 90 percent: Ni0.8Fe0.2, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2.  相似文献   

Benign masses in the pericardium of two dogs   总被引：1，自引：0，他引：1  

DJ SIMPSON  GB HUNT  DB CHURCH  JA BECK 《Australian veterinary journal》1999,77(4):225-229

Two miniature Schnauzer dogs were treated for pericardial masses. In one dog the mass consisted of necrotic fat that was attached to the apex of the pericardium by a pedicle. No obvious communication with the abdomen was present. The second dog had a peritoneopericardial hernia associated with a chronic cystic haematoma. In each case the mass was presumed to have arisen following congenital displacement of the omentum into the pericardium. The pericardial mass was removed and subtotal pericardectomy performed in both dogs. Recovery was complete in each case.  相似文献   

A survey for mycoplasmas in bulk-tank milk of dairy herds in Western Australia     

PD JELINEK  DJ DEVEREAUX  PAJ MARTIN  NB BULLER 《Australian veterinary journal》1993,70(1):30-30

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An estimate of specificity for a Johne's disease absorbed ELISA in northern Australian cattle     

DJ PITT  DS PINCH  A. JANMAAT  RJ CONDRON 《Australian veterinary journal》2002,80(1):57-60

Objective To estimate the specificity of an absorbed enzyme-linked immuno-sorbent assay kit^d for Johne's disease (JD) when used in mature cattle populations resident in northern Australia.
Design Blood samples were collected from beef cattle in northern Queensland, the Northern Territory and northern Western Australia, and from dairy cattle in northern Queensland. The specificity of a serological test for JD was estimated by testing the blood samples with an absorbed ELISA kit. Further samples were collected from cattle with positive ELISA results to determine the presence or absence of infection with Mycobacterium avium subsp paratuberculosis .
Procedure During 1995 and 1996, blood, tissue and gut contents were collected from beef cattle at abattoirs in Queensland and the Northern Territory; and blood and faecal samples were collected from dairy cattle in herds assessed to be most at risk for JD in northern Queensland. The blood samples were tested using an absorbed ELISA kit. Tissues and gut contents from beef cattle that had positive ELISA results were cultured for M avium subsp paratuberculosis , and tissues were examined histo-logically. Faecal samples from dairy cattle with positive ELISA results were cultured for M avium subsp paratuberculosis .
Results Estimates of specificity for this absorbed ELISA in mature northern Australian cattle were 98.0% (97.0 to 98.8%, 95% CI) in beef cattle, and 98.3% (96.7 to 99.3%, 95% CI) in dairy cattle.
Conclusion Estimates of specificity in this study were lower for beef cattle from the Northern Territory and northern Western Australia and for dairy cattle from northern Queensland than those quoted from studies on cattle in southern Western Australia. This should be considered when serological testing using the JD ELISA is carried out on northern Australian cattle.  相似文献   

Clinical and research applications of real-time ultrasonography in bovine reproduction: a review.          下载免费PDF全文

R Rajamahendran  D J Ambrose    B Burton 《The Canadian veterinary journal. La revue veterinaire canadienne》1994,35(9):563-572

Transrectal real-time ultrasonography has proved to be a rapid and reliable technique for studying reproductive functions in cattle. Through ultrasonography it is now established that follicular growth occurs in wave-like patterns during each estrous cycle. It has been shown that follicular growth and regression continue during early pregnancy, as well as in the postpartum anestrous period. Ultrasound has also helped us to understand the influence of dominant follicles on medium and small follicles. Among the numerous demonstrated applications of ultrasonography, early pregnancy diagnosis, fetal sexing, and postpartum reproductive management appear to be promising areas for immediate application. The new information that has been generated through ultrasound has thrown light on hitherto poorly understood areas of ovarian follicular dynamics, corpus luteum function, pregnancy establishment, and embryonic development in cattle, thereby opening newer areas for research. Still there is great potential for the continued application of this technology to further our understanding of the reproductive processes and to maximize reproductive efficiency of the bovine species. The significant contributions of real-time ultrasonography to the study of bovine reproduction in general and its practical applications in particular are discussed in this paper. The need for taking up technology assessment studies and for the introduction of low-cost portable equipment are stressed. Literature search for this review was done by scanning Current Contents Series 1991-92, AGRICOLA 1980-92, and MEDLINE 1990-92.  相似文献   

Isolation of Treponema hyodysenteriae from a wild rat living on a piggery     

DJ HAMPSON  BG COMBS  SJ HARDERS  ID CONNAUGHTON  VA FAHY 《Australian veterinary journal》1991,68(9):308-308

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Influence of head posture on the respiratory tract of healthy horses     

DJ RACKLYEFT  DN LOVE 《Australian veterinary journal》1990,67(11):402-405

Twenty four normal, confined mares were unable to lower their heads for 24 or 48 h. In 21 mares this resulted in increases in the proportion of neutrophils and/or numbers of bacteria in transtracheal aspirates. In eight mares the changes in tracheal washes were accompanied by clinical evidence of mild respiratory disease. In three additional cases respiratory signs were accompanied by systemic illness. These changes reversed once the mares were able to lower their heads. Haematological changes (absolute neutrophilia and/or hyperfibrinogenamia) were mild and occurred more commonly in horses restrained for 48 h. The results suggest that keeping the heads of healthy horses raised leads to an increased bacterial burden in their tracheobronchial secretions. These changes appeared to be related to head posture effects and not simply confinement in stocks. These findings give further weight to the theory that postural drainage may facilitate clearance of bacteria from the tracheobronchial tree. The possible relevance of such findings to post-transportation pneumonia in horses is discussed.  相似文献