复合式实验动物屏障系统一款集动物饲养、实验一体化的屏障设备的设计

目的依据节能、安全、高效、实用的原则,设计一款集饲养与实验一体化的屏障设施。方法在该屏障系统中主要设计了可以组合的传入单元、生活单元、过渡单元和实验单元。在动物和物品的传递流程中,加入了自动灭菌的控制。结果本设计能够提高工作效率,有效保障实验动物的清洁度。结论本系统可以满足清洁级和SPF级的中、小规模实验动物生产及实验需要。     

The Apachean Transition from the Subarctic to the Southwest

Abstract

A comparison of evidence from linguistics, archaeology, ethnography and history suggests that the separation of Northern and Southern Athabascans in the first millennium A.D. may have been provoked by warming conditions and resultant shifts in the distribution of major game species. The “mixed bag” subsistence pattern of most Athabascan groups, as well as their association with mountainous areas which provide access to a variety of ecological zones, lends weight to the hypothesis that mountain ranges were the medium for Apachean migration into the Southwest. A hypothetical reconstruction of this transition from the Subarctic to the Southwest is presented and discussed.     

Plant Hunting Expeditions of David Fairchild to The Bahamas

The plant hunting expeditions made by David Fairchild on board the research boat Utowana represented some of the most important contributions in the history of plant exploration. These expeditions targeted all the continents except Australia and Antarctica and provided germplasm for the United States Department of Agriculture. As part of our current research to document the details and outputs of David Fairchild’s plant hunting expeditions, in this paper we present an account pertinent to the three trips that he made to The Bahamas. Two of these trips were on board the Utowana and were part of larger expeditions that David Fairchild undertook to the West Indies, Central America and the Guianas between December 1931 and April 1933. No plant material was collected on the third trip when David Fairchild and his wife flew to Nassau in April 1939. We believe that the main focus of this last trip was to meet with Anne Archbold to make arrangements for the Chêng Ho expedition to the East Indies. This Asian endeavor was the only major expedition undertaken by David Fairchild to collect plant material for Fairchild Tropical Botanic Garden (FTBG). During the Bahamian expedition eleven islands/cays were visited, 94 germplasm accessions (73 species) were collected, and 132 photographs were taken. Our research has been largely based on documents and photographs that belonged to David Fairchild and that are deposited at the Library and Archives of FTBG. “The more than ten years that I spent in the office that Fairchild founded for our Department of Agriculture made me a great admirer of Dr. Fairchild and to appreciate even more the work that he, Wilson Popenoe, and others in the Division had done for our country. Among their accomplishments was the encouragement or establishment as a crop or industry the date, fig, avocado, mango, pistachio, and other lesser known crops. These explorers were also concerned with introducing germ plasm, or breeding stock, for the improvement of traditional field crops, vegetables, and fruit plants, as well as the introduction and establishment of ornamental and other economic plants such as bamboos and Meyer’s Zoysia grass.” [Donovan Correll, from his unpublished autobiography “Notes from a Singing Plant Explorer," January 1983 (Korber et al., 2013)].     

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer??s and Parkinson??s disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.     

Transition from academia to industry: a personal account

A career in industry has become a widely accepted alternative for those of us trained in medicine and/or science who have traditionally focused on careers in academia. Like any career decision, consideration of a position in industry should include asking yourself a series of fundamental questions. A few of the key questions should include: 1) What kind of work environment do you find most enjoyable? (e.g., patient care setting, basic research lab, team-oriented setting); 2) What are you focused on accomplishing in your career? (basic research discoveries, contributions to clinical medicine, compensation); 3) Are you team oriented in your interactions or are you more of an individual contributor? A successful career in any endeavor, including industry, starts with a careful and honest examination of what you are best suited for and inspired to do.     

Hunting the Wren: Transformation of Bird to Symbol

Hunting tfie Wren: Transformation of Bird to Symbol. Elizabeth Atwood Lawrence. Knoxville: University of Tennessee Press, 1997. 234 pp.     

Transition from polar to duplicate patterns

The existence of symmetric nonuniform solutions in nonlinear reaction-diffusion systems is examined. In the first part of the paper, we establish systematically the bifurcation diagram of small amplitude solutions in the vicinity of the two first bifurcation points. It is shown that:

1. The system can adopt a stable symmetric solution (basic wave number 2) if the value of the bifurcation parameter is changed or if the initial polar structure (basic wave number 1) is sufficiently perturbed.
2. This behavior is independent of the particular reaction-diffusion model proposed and of the number of intermediate components (?2) involved.

In the second part of the paper, analogies are established between the possibilities offered by the bifurcation diagrams, involving only the two first primary branches, and the observation that in the early development of different organisms, appropriate experimental manipulations may switch the normal (polar) developmental pattern to a duplicate structure.     

Structural Transition from Helices to Hemihelices

Helices are amongst the most common structures in nature and in some cases, such as tethered plant tendrils, a more complex but related shape, the hemihelix forms. In its simplest form it consists of two helices of opposite chirality joined by a perversion. A recent, simple experiment using elastomer strips reveals that hemihelices with multiple reversals of chirality can also occur, a richness not anticipated by existing analyses. Here, we show through analysis and experiments that the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip''s cross-section. Our findings provides the basis for the deterministic manufacture of a variety of complex three-dimensional shapes from flat strips.     

Photoautotrophic potato cells: Transition from heterotrophic to autotrophic growth

Cells of potato (Solanum tuberosum L.) were obtained which were capable of photoautotrophic growth in liquid suspension culture under a photon flux density of 90–110 μmol m^?2 s^?1 PAR and in an atmosphere enriched with 2% CO₂. These photoautotrophic cells contained between 100 to 200 μg Chl (g fresh weight)^?1 and fixed CO₂ at a maximum rate of 16 μmol CO₂ (g fresh weight)^?1h^?1. In order to obtain cells capable of photoautotrophic growth it was necessary to adapt highly chlorophyllous heterotrophic cells (>50 μg Chl (g fresh weight)^?1) for growth in medium with 2.5 g sucrose 1^?1 (photomixotrophic cells). The photomixotropic cells had a Chl content of ca 100 μg Chl (g fresh weight)^?1 and were capable of photosynthetic activity which allowed them to survive after sugars had been depleted from the medium. It was from the photomixotrophic cells that cells capable of photoautotrophic growth were obtained. Heterotrophic cells initially established in liquid medium with 25 g sucrose I^?1 from chlorophyllous callus contained about 50 to 150 μg Chl (g fresh weight)^?1. However, after 5 to 10 passages the Chl content decreased to a maximum of 15 μg Chl (g fresh weight)^?1. These cells could not be adapted to photomixotrophic or photoautotrophic growth. These cells also were not able to regain Chl or initiate high rates of CO₂ fixation during the stationary phase of growth as did photomixotrophic cells or chlorophyllous heterotrophic cells. The loss of Chl exhibited by the cells during adaption to heterotrophic growth could be attributed at least in part to unbalanced growth (when cell division and growth exceeds Chl accumulation). Sucrose appeared to have an inhibitory effect directly on photosynthesis independent of Chl accumulation.     

Grassland Butterfly Fauna under Traditional Animal Husbandry: Contrasts in Diversity in Mown Meadows and Grazed Pastures

Semi-natural grasslands resulting from traditional land use practices (mowing and grazing) are severely endangered throughout Europe due to the intensification of agriculture. The ecological impact of mowing and grazing on grassland butterflies was studied in eight mown meadows and eight grazed pastures under traditional animal husbandry in NW Russia and adjacent Finland. Transect count data over 3 years (1997–1999) covered a total of 48 species and 5742 individuals. The butterfly fauna was rather similar under both management forms; species richness, diversity and total abundance did not differ significantly between meadows and pastures, yet meadows were preferred by more species. In both groups, the most abundant species were Aphantopus hyperantus, Pieris napi and Thymelicus lineola. Of 37 species observed as a minimum of five individuals, Polyommatus amandus, Ochlodes sylvanus and A. hyperantus showed a significant preference for mowing management. According to the ordination, butterfly communities were affected more by the origin and age of the grassland than the present management method. Landscape factors (meadow or pasture surrounded by forests or open environments), the abundance of nectar plants and the intensity of tilling were the most important factors differentiating older grasslands from the younger ones evolved from old Finnish hay fields cultivated prior to the 1940s.