Estimating stomatal diffusion resistance for Douglas-fir,lodgepole pine and white oak under light saturated conditions     

James R Simpson  Leo J Fritschen  Richard B Walker 《Agricultural and Forest Meteorology》1985,33(4):299-313

Stomatal diffusion (leaf) resistance (r_s) of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), lodgepole pine (Pinus contorta Dougl. ex Loud.) and white oak (Quercus alba L.) in a variety of natural environments is described during conditions of light saturation as a function of the product of the predawn (base) xylem pressure potential of twigs (ψ_xb) or the soil water potential (ψ_s), and the saturation deficit of the atmosphere (δ_e). This general functional form was derived from an analysis based on an Ohm's law analog for water flow in the soil—plant—atmosphere system. The specific form used in each case was determined using regression analysis, where dependent variables considered were xylem pressure potential of the twigs or leaves (ψ_x) and air temperature (T) as well as δe and ψ_xb (or ψ_s). For three independent sets of Douglas-fir data, it is shown qualitatively that a single function describes the combined data as well as the functions derived for each of three data sets individually. The results imply that it may be possible to describe stomatal response of Douglas-fir, and perhaps other species, over a range of environmental conditions using the same model.  相似文献   

Tracks of cosmic rays in plastics     

Fleischer RL  Price PB  Walker RM  Filz RC  Fukui K  Friedlander MW  Holeman E  Rajan RS  Tamhane AS 《Science (New York, N.Y.)》1967,155(3759):187-189

Cosmic ray nuclei have been observed with the use of plastic trackdetecting solids in satellites and high-altitude balloon flights. Nuclear emulsions in the stacks of plastic sheets allowed the positive identification of cosmic raynuclei as light as nitrogen. The most striking new information was the failure to observe relativistic iron nuclei, a result which has led to an advance in the understanding of track registration criteria.  相似文献   

Phonotaxis of crickets in flight: attraction of male and female crickets to male calling songs     

Ulagaraj SM  Walker TJ 《Science (New York, N.Y.)》1973,182(4118):1278-1279

Large numbers of two species of mole crickets flew to loudspeakers playing the appropriate calling song outdoors. Mated females were more frequently captured than unmated ones, and males were 12 percent of the catch. Crickets of three other subfamilies were trapped as they flew to mole cricket songs resembling their own.  相似文献   

Fossil alpha-particle recoil tracks: a new method of age determination     

Huang WH  Walker RM 《Science (New York, N.Y.)》1967,155(3766):1103-1106

The discovery of a new type of fossil nuclear track in mica is reported. This track is produced by the recoil nucleus accompanying the alpha-particle decay of uranium and thorium impurities. The tracks are very short and can be seen with phase contrast microscopy. Measurement of fossil alpha-recoil track densities, coupled with determinations of the thorium and uranium contents, provides a new dating technique analogous to the previously discovered "fission-track method." The primary advantage of the alpha-recoil method is a several-thousand-fold increase in sensitivity over the fission-track technique. The alpha-recoil method should also prove useful in studying the problem of extinct isotopes in meteorites.  相似文献   

A METHOD OF NUMBERING LABORATORY RATS     

Walker G 《Science (New York, N.Y.)》1935,82(2130):397-398

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Sulfur mustard: reaction with L-cells treated with 5-fluorodeoxyuridine     

I G Walker 《Science (New York, N.Y.)》1966,151(706):99-101

After exposure to 5-fluorodeoxyuridine, L-cells are considerably more sensitive to the lethal effect of sulfur mustard than after they have been released from this block by addition of thymidine and allowed to proceed into the G2 phase of the division cycle. Nevertheless, for both populations, the amounts of mustard bound per cell and per nucleus (expressed as the amount of mustard per unit of protein) were the same. Likewise, the amounts of mustard bound per unit of DNA were the same for both populations.  相似文献   

INEXPENSIVE AERATED AQUARIA     

Walker JH 《Science (New York, N.Y.)》1931,73(1904):709-710

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A Drosophila mechanosensory transduction channel     

Walker RG  Willingham AT  Zuker CS 《Science (New York, N.Y.)》2000,287(5461):2229-2234

Mechanosensory transduction underlies a wide range of senses, including proprioception, touch, balance, and hearing. The pivotal element of these senses is a mechanically gated ion channel that transduces sound, pressure, or movement into changes in excitability of specialized sensory cells. Despite the prevalence of mechanosensory systems, little is known about the molecular nature of the transduction channels. To identify such a channel, we analyzed Drosophila melanogaster mechanoreceptive mutants for defects in mechanosensory physiology. Loss-of-function mutations in the no mechanoreceptor potential C (nompC) gene virtually abolished mechanosensory signaling. nompC encodes a new ion channel that is essential for mechanosensory transduction. As expected for a transduction channel, D. melanogaster NOMPC and a Caenorhabditis elegans homolog were selectively expressed in mechanosensory organs.  相似文献   

Radiohalos in coalified wood: new evidence relating to the time of uranium introduction and coalification     

Gentry RV  Christie WH  Smith DH  Emery JF  Reynolds SA  Walker R  Cristy SS  Gentry PA 《Science (New York, N.Y.)》1976,194(4262):315-318

The discovery of embryonic halos around uranium-rich sites that exhibit very high (238)U/(206)Pb ratios suggests that uranium introduction may have occurred far more recently than previously supposed. The discovery of (210)Po halos derived from uranium daughters, some elliptical in shape, further suggests that uranium-daughter infiltration occurred prior to coalification when the radionuclide transport rate was relatively high and the matrix still plastically deformable.  相似文献   

Evidence for homologous actions of pro-opiocortin products   总被引：2，自引：0，他引：2  

J M Walker  H Akil  S J Watson 《Science (New York, N.Y.)》1980,210(4475):1247-1249

alpha-Melanocyte-stimulating hormone (alpha-MSH), a modified fragment of adrenocorticotropic hormone, derives from the same biosynthetic route as beta-endorphin and is stored by the same arcuate neurons. Microinjection of alpha-melanocyte-stimulating hormone and several related peptides into the periaqueductal gray matter significantly reduced responsiveness to pain and had a behavioral profile similar to that produced by beta-endorphin.  相似文献