Habituation of electrically induced readiness to gnaw     

Cain RE  Skriver CP  Carlson RH 《Science (New York, N.Y.)》1971,173(3993):262-264

Electrical stimulation of the hypothalamus in prairie dogs (Cynomys ludovicianus) produced a readiness to gnaw which decreased over time, exhibited spontaneous recovery, and could be dishabituated by foot shock. The response decrement was in part habituatory and could modify the interaction between a stimulation-induced readiness to gnaw and a physiologically induced hunger. Functional plasticity of stimulation-induced behavior might be accounted for, in part, by habituation.  相似文献   

Gastric cancer originating from bone marrow-derived cells     

Houghton J  Stoicov C  Nomura S  Rogers AB  Carlson J  Li H  Cai X  Fox JG  Goldenring JR  Wang TC 《Science (New York, N.Y.)》2004,306(5701):1568-1571

Epithelial cancers are believed to originate from transformation of tissue stem cells. However, bone marrow-derived cells (BMDCs), which are frequently recruited to sites of tissue injury and inflammation, might also represent a potential source of malignancy. We show that although acute injury, acute inflammation, or transient parietal cell loss within the stomach do not lead to BMDC recruitment, chronic infection of C57BL/6 mice with Helicobacter, a known carcinogen, induces repopulation of the stomach with BMDCs. Subsequently, these cells progress through metaplasia and dysplasia to intraepithelial cancer. These findings suggest that epithelial cancers can originate from marrow-derived sources and thus have broad implications for the multistep model of cancer progression.  相似文献   

Organic superconductors--new benchmarks     

Williams JM  Schultz AJ  Geiser U  Carlson KD  Kini AM  Wang HH  Kwok WK  Whangbo MH  Schirber JE 《Science (New York, N.Y.)》1991,252(5012):1501-1508

Recent advances in the design and synthesis of organic synthetic metals have yielded materials that have the highest superconducting transition temperatures (T(c) approximately 13 kelvin) reported for these systems. These materials have crystal structures consisting of alternating layers of organic donor molecules and inorganic anions. Organic superconductors have various electronic and magnetic properties and crystal structures that are similar to those of the inorganic copper oxide superconductors (which have high T(c) values); these similarities include highly anisotropic conductivities, critical fields, and short coherence lengths. The largest number of organic superconductors, including those with the highest T(c) values, are charge-transfer salts derived from the electron donor molecule BEDT-TTF or ET [bis(ethylenedithio)-tetrathiafulvalene]. The synthesis and crystal structures of these salts are discussed; their electrical, magnetic, and band electronic structure properties and their many similarities to the copper oxide superconductors are treated as well.  相似文献   

PAMELA measurements of cosmic-ray proton and helium spectra     

Adriani O  Barbarino GC  Bazilevskaya GA  Bellotti R  Boezio M  Bogomolov EA  Bonechi L  Bongi M  Bonvicini V  Borisov S  Bottai S  Bruno A  Cafagna F  Campana D  Carbone R  Carlson P  Casolino M  Castellini G  Consiglio L  De Pascale MP  De Santis C  De Simone N  Di Felice V  Galper AM  Gillard W  Grishantseva L  Jerse G  Karelin AV  Koldashov SV  Krutkov SY  Kvashnin AN  Leonov A  Malakhov V  Malvezzi V  Marcelli L  Mayorov AG  Menn W  Mikhailov VV  Mocchiutti E  Monaco A  Mori N  Nikonov N  Osteria G  Palma F  Papini P  Pearce M 《Science (New York, N.Y.)》2011,332(6025):69-72

Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in our Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 gigavolt to 1.2 teravolts performed by the satellite-borne experiment PAMELA (payload for antimatter matter exploration and light-nuclei astrophysics). We find that the spectral shapes of these two species are different and cannot be described well by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data.  相似文献   

The fate of Amazonian forest fragments: A 32-year investigation   总被引：2，自引：0，他引：2  

William F. Laurance  José L.C. Camargo  Regina C.C. Luizão  Susan G. Laurance  Stuart L. Pimm  Emilio M. Bruna  Philip C. Stouffer  G. Bruce Williamson  Julieta Benítez-Malvido  Heraldo L. Vasconcelos  Kyle S. Van Houtan  Charles E. Zartman  Sarah A. Boyle  Raphael K. Didham  Ana Andrade  Thomas E. Lovejoy 《Biological conservation》2011,(1):56-67

We synthesize findings to date from the world’s largest and longest-running experimental study of habitat fragmentation, located in central Amazonia. Over the past 32 years, Amazonian forest fragments ranging from 1 to 100 ha have experienced a wide array of ecological changes. Edge effects have been a dominant driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage, fauna, and other aspects of fragment ecology. However, edge-effect intensity varies markedly in space and time, and is influenced by factors such as edge age, the number of nearby edges, and the adjoining matrix of modified vegetation surrounding fragments. In our study area, the matrix has changed markedly over the course of the study (evolving from large cattle pastures to mosaics of abandoned pasture and regrowth forest) and this in turn has strongly influenced fragment dynamics and faunal persistence. Rare weather events, especially windstorms and droughts, have further altered fragment ecology. In general, populations and communities of species in fragments are hyperdynamic relative to nearby intact forest. Some edge and fragment-isolation effects have declined with a partial recovery of secondary forests around fragments, but other changes, such as altered patterns of tree recruitment, are ongoing. Fragments are highly sensitive to external vicissitudes, and even small changes in local land-management practices may drive fragmented ecosystems in markedly different directions. The effects of fragmentation are likely to interact synergistically with other anthropogenic threats such as logging, hunting, and especially fire, creating an even greater peril for the Amazonian biota.  相似文献   

Biomass allocation and foliage heteroblasty in hard pine species respond differentially to reduction in rooting volume     

José Climent  Maria Regina Chambel  Marta Pardos  Francisco Lario  Pedro Villar-Salvador 《European Journal of Forest Research》2011,130(5):841-850

Rooting space is considered as a resource in plants, but comparative studies on the biomass allocation plasticity in response to rooting volume (RV) are rare. We compared responses in growth, biomass allocation and ontogenetic heteroblasty in nine hard pine species of contrasted ecology. Seedlings were cultivated in containers of 0.2, 0.5, 1.0, 2.8 and 7 L for two growing seasons (425 days). Reduction in RV caused a reduction in plant absolute and relative growth rate and biomass allocated to stems but it increased biomass allocated to roots. RV affected to a lesser extent and in a less consistent direction allocation to leaves. Species that grew faster (higher relative growth rate) had a steeper decrease in growth with the reduction in RV. Ontogenetic heteroblasty, evaluated as the proportion of secondary needles in the needle biomass, showed highly different plasticity patterns in response to RV. Decrease in RV caused negligible or no change either in the most ontogenetically delayed Mediterranean pines or in the most ontogenetically advanced pines, the mesic Pinus sylvestris and P. uncinata. By contrast, ontogenetically intermediate species showed steep reaction norms in response to reduction in RV. While P. pinaster and P. brutia showed marked rejuvenation, P. nigra accelerated the development of adult foliage.  相似文献   

Effects of selected trace metals on germinating seeds of six plant species     

Claire L. Carlson  Domy C. Adriano  Kenneth S. Sajwan  Steven L. Abels  David P. Thoma  Joseph T. Driver 《Water, air, and soil pollution》1991,59(3-4):231-240

Seeds of cabbage, lettuce, millet, radish, turnip, and wheat were treated with solutions containing Be, Ni, Tl, or V, and subsequent effects on seed germination and radicle elongation were measured after three days. Treatment with low concentrations of Be, Ni, or V stimulated root elongation in most species. Higher concentrations of these elements and all treatment with Tl caused reductions in root elongation. In general, turnip and lettuce were the most sensitive of the plants studied to the metals tested, while wheat and millet were the least sensitive.  相似文献   

Effects of soil properties and humidity regimes on semi-natural meadow productivity     

Regina Skuodiene  Kazimieras Katutis  Rita Nekrosiene  Regina Repsiene  Danute Karcauskiene 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2016,66(8):653-663

ABSTRACT

The research has been conducted for four years in five phytocenoses affected by the processes of naturalization. Two of them are located in non-flooded, relatively abandoned meadows and the remaining - flooded meadows in different parts of the Nemunas delta (Western Lithuania). The aim of the research was to estimate the influence of ecological conditions (humidity regimes, soil agrochemical parameters) on semi-natural meadow productivity. Humidity regimes and nitrogen amount in the soil influenced dry matter (DM) yield of meadow phytocesosis. The biggest DM yield (8.64 ± 0.77 t ha^-1) was found in flooded meadow in the central part of the Nemunas delta in Terric Histosol (HSs) soil, which had moderate acidity and was rich in nitrogen. The economic value depended on the prevailing plant species and was the highest in non-flooded meadows. Botanical composition and plant species number depended on agrochemical characteristics of the soil and management activities: the greatest plant species diversity and the best plant population stability were established in flooded meadow in the riverside part of the Nemunas delta behind a levee in soil rich in phosphorus and potassium and low acidity. A similar number of plant species and similar ecological stability parameters were found in non-flooded meadow, whose soil was low in nutrients, but there was intensified farming.  相似文献   

Redistribution of 10B Absorbed by Leaves and Roots of Cashew Seedlings     

Regina Célia Faria Simão Canesin  Salatiér Buzetti  Juliana Aparecida de Souza 《Journal of plant nutrition》2015,38(4):639-646

Boron (B) is transported mainly in the xylem, but by using isotopic tracers it was possible to verify that B has significant mobility in the phloem of polyols-producing species. Thus, the objective of this study was to evaluate the mobility of ¹⁰B applied to cashew plants. The experiment was conducted from 05/10 to 07/10/2010 in a greenhouse of University of São Paulo State-UNESP, Ilha Solteira Campus, State of São Paulo, Brazil. 0.5 mg of B L^?1 of soil was used in the substrate. A solution of 255 mg of B L^?1 was used in recently mature and fully developed leaves. The total content of B and and percentage of boron in the plant derived from fertilizer (Bppf%) were evaluated in the old and new leaves stemming at 30 and 60 days after the application of ¹⁰B. As evidenced, B applied to leaves had restricted mobility in cashew tree. However, B applied in the substrate was absorbed and translocated to young leaves.  相似文献   

Resolution of a Left Ureteral Stone Using Electrohydraulic Lithotripsy in a Thoroughbred Colt   总被引：1，自引：0，他引：1  

Lynn D. Rodger  Gary P. Carlson  Michael E. Moran  Tom B. Yarbrough  John R. Pascoe  Jay A. Reynolds 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1995,9(4):280-282

A 3-year-old Thoroughbred colt was presented for evaluation of azotemia and anorexia. Physical examination revealed a ureterolith in the left ureter, approximately 10 cm from the bladder, which was thought to obstruct urine flow by approximately 90% when viewed cystoscopically. Ultrasonographic examination of both kidneys revealed indistinct corticomedullary junctions, and the right kidney was more hyperechoic. A percutaneous biopsy of the right kidney revealed chronic interstitial nephritis with marked interstitial medullary fibrosis. Medical therapy consisting of IV fluids, sodium chloride PO, and ammonium chloride PO was initiated. Ureteroscopic electrohydraulic lithotripsy via a perineal urethrostomy was used to successfully remove the stone. Klebsiella oxytoca , which responded to oral enrofloxacin therapy, was cultured from the urine after surgery. Azotemia resolved and the horse resumed training.  相似文献