Laser-induced ferroelectric structural order in an organic charge-transfer crystal     

Collet E  Lemée-Cailleau MH  Buron-Le Cointe M  Cailleau H  Wulff M  Luty T  Koshihara SY  Meyer M  Toupet L  Rabiller P  Techert S 《Science (New York, N.Y.)》2003,300(5619):612-615

We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene-p-chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order. The x-ray data indicate a macroscopic ferroelectric reorganization after the laser irradiation. Refinement of the structures before and after laser irradiation indicates structural changes at the molecular level.  相似文献   

Plant species identification using Elliptic Fourier leaf shape analysis   总被引：6，自引：0，他引：6  

Joo Camargo Neto  George E. Meyer  David D. Jones  Ashok K. Samal 《Computers and Electronics in Agriculture》2006,50(2):121-134

Elliptic Fourier (EF) and discriminant analyses were used to identify young soybean (Glycine max (L.) merrill), sunflower (Helianthus pumilus), redroot pigweed (Amaranthus retroflexus) and velvetleaf (Abutilon theophrasti Medicus) plants, based on leaf shape. Chain encoded, Elliptic Fourier harmonic functions were generated based on leaf boundary. A complexity index of the leaf shape was computed using the variation between consecutive EF functions. Principle component analysis was used to select the Fourier coefficients with the best discriminatory power. Canonical discriminant analysis was used to develop species identification models based on leaf shapes extracted from plant color images during the second and third weeks after germination. The classification results showed that plant species during the third week were successfully identified with an average of correct classification rate of 89.4%. The discriminant model correctly classified on average: 77.9% of redroot pigweed, 93.8% of sunflower, 89.4% of velvetleaf and 96.5% of soybean. Using all of the leaves extracted from the second and the third weeks, the overall classification accuracy was 89.2%. The discriminant model correctly classified 76.4% of redroot pigweed, 93.6% of sunflower, 81.6% of velvetleaf, 91.5% of soybean leaf extracted from trifoliolate and 90.9% of soybean unifoliolate leaves. The Elliptic Fourier shape feature analysis could be an important and accurate tool for weed species identification and mapping.  相似文献   

Transmembrane segments of syntaxin line the fusion pore of Ca2+-triggered exocytosis     

Han X  Wang CT  Bai J  Chapman ER  Jackson MB 《Science (New York, N.Y.)》2004,304(5668):289-292

The fusion pore of regulated exocytosis is a channel that connects and spans the vesicle and plasma membranes. The molecular composition of this important intermediate structure of exocytosis is unknown. Here, we found that mutations of some residues within the transmembrane segment of syntaxin (Syx), a plasma membrane protein essential for exocytosis, altered neurotransmitter flux through fusion pores and altered pore conductance. The residues that influenced fusion-pore flux lay along one face of an alpha-helical model. Thus, the fusion pore is formed at least in part by a circular arrangement of 5 to 8 Syx transmembrane segments in the plasma membrane.  相似文献   

Cyclic AMP-responsive DNA-binding protein: structure based on a cloned placental cDNA   总被引：117，自引：0，他引：117  

J P Hoeffler  T E Meyer  Y Yun  J L Jameson  J F Habener 《Science (New York, N.Y.)》1988,242(4884):1430-1433

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Eine elektromechanische Wiegevorrichtung für Lysimeter     

B. Homeyer  K. O. Labenski  B. Meyer 《植物养料与土壤学杂志》1973,136(3):240-242

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Eine Infiltrationsmethode zur Messung der hydraulischen Leitfähigkeit im Felde     

St. Gth  H.-G. Frede  B. Meyer 《植物养料与土壤学杂志》1990,153(1):1-4

An infiltration method for measuring the saturated hydraulic conductivity under field conditions A new field method to measure the hydraulic conductivity under field conditions, developed by Reynolds and Elrick (1985), is presented and compared with a laboratory method using 100 cm³ cylinder cores.  相似文献   

Atmosphärische Deposition von Bioelementen in Agrarökosysteme 1. Mitteilung: Deposition von Bioelementen mit dem Niederschlag     

J. Bttcher  H.-G. Frede  B. Meyer 《植物养料与土壤学杂志》1984,147(6):753-759

Atmospheric deposition of bioelements in agrar-ecosystems 1. Report: Deposition of bioelements by precipitation The bioelement deposition by precipitation was measured in 1977–1981 in Göttingen (Niedersachsen). The bioelement concentrations and the deposited quantities are in good agreement with the results of other authors. The mean pH-values of the collected precipitation water in 1980 and '81 in Göttingen was 4,60. The difference to the pH-values measured by Ulrich et al. (1979) in the Solling is explained by the different geographical locations of the ecosystems in connection with the transport of dust and variations in the composition of the soils of the areas. From the view of plant nutrition and soil acidification the contribution of the deposition by precipitation is insignificant for agriculture. Only about 6% of the typical annual Ca-leaching from loamy soils are caused by the H⁺ input by precipitation. The rest is caused by other influences, especially the soil respiration.  相似文献   

Strauch,D., W. Baader und C. Tietjen (Hrsgb.): Abfälle aus der Tierhaltung. Verl. Ulmer,Stuttgart, 1977, 391 S., 165 Abb., 97 Tab., 78,-DM     

B. Meyer  P. Hugenroth 《植物养料与土壤学杂志》1978,141(2):254-255

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Different sources of heavy metals and their long-term effects on soil microbial properties   总被引：9，自引：3，他引：9  

Krishan Chander  Jens Dyckmans  Rainer Joergensen  Brunk Meyer  Markus Raubuch 《Biology and Fertility of Soils》2001,34(4):241-247

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Veränderung des Scher- und Kompressionsverhaltens von Ap-Horizont-Material aus Löß-Parabraunerden durch Kalkung     

F. Beese  B. Meyer  J. Pollehn 《植物养料与土壤学杂志》1979,142(2):245-257

Change of shear resistance and compressibility of Ap-horizon material from loess-derived Parabraunerde Standardized artificial bodies prepared from soil material of a loessderived parabraunerde-Ap-horizon were tested with respect to their shear resistance and compressibility. The noncalcareous material was enriched with lime (2 stepts), soil humidity changed (3 steps) and the normal pressure increased (4 steps). Liming generally caused an increased initial shear resistance and led to a lowering of compressibility. The effect of lime is interpreted as an result of flocculation of the clay particles at the points of contact between silt grains in the soil matrix. The problems of transferring those results to the field are discussed.  相似文献