Net ecosystem exchange, evapotranspiration and canopy conductance in a riparian forest     

John Kochendorfer  Eugenia G. CastilloEdward Haas  Walter C. OechelKyaw Tha Paw U. 《Agricultural and Forest Meteorology》2011,151(5):544-553

The ecosystem fluxes of mass and energy were quantified for a riparian cottonwood (Populus fremontii S. Watson) stand, and the daily and seasonal courses of evapotranspiration, CO₂ flux, and canopy conductance were described, using eddy covariance. The ecosystem-level evapotranspiration results are consistent with those of other riparian studies; high vapor pressure deficit and increased groundwater depth resulted in reduced canopy conductance, and the annual cumulative evapotranspiration of 1095 mm was more than double the magnitude of precipitation. In addition, the cottonwood forest was a strong sink of CO₂, absorbing 310 g C m⁻² from the atmosphere in the first 365 days of the study. On weekly to annual time scales, hydrology was strongly linked with the net atmosphere-ecosystem exchange of CO₂, with ecosystem productivity greatest when groundwater depth was ∼2 m below the ground surface. Increases in groundwater depth beyond the depth of 2 m corresponded with decreased CO₂ uptake and evapotranspiration. Saturated soils caused by flooding and shallow groundwater depths also resulted in reduced ecosystem fluxes of CO₂ and water.  相似文献   

Survival of pathogens of Brussels sprouts (Brassica oleracea Gemmifera Group) in crop residues     

J. Köhl  M. Vlaswinkel  B. H. Groenenboom‐de Haas  P. Kastelein  R. A. van Hoof  J. M. van der Wolf  M. Krijger 《Plant pathology》2011,60(4):661-670

Mycosphaerella brassicicola (ringspot), Alternaria brassicicola and A. brassicae (dark leaf spot) and Xanthomonas campestris pv. campestris (black spot) can infect leaves of Brussels sprouts resulting in yield losses. Infections of outer leaves of sprouts cause severe losses in quality. Crop residues can be a major primary inoculum source of the pathogens. Their population dynamics were followed in residues of leaves and stalks of crops of Brussels sprouts during 24 months using real‐time PCR assays. Leaf residues on the soil surface or buried in soil decomposed within 4 months. However, residues of stalks were present in the field after 24 months. In such residues, M. brassicicola populations increased during the first 2 months, but decreased thereafter and the pathogen was found only occasionally in the second year. Alternaria brassicicola multiplied on stalks exposed on the surface of field soil and was present on such residues after 24 months. Survival was less on residues buried in soil. Alternaria brassicae population increased in stalks exposed on the soil surface during the first months but decreased thereafter under the detection limit. Xanthomonas campestris cv. campestris populations fluctuated in time but 1 × 10⁴ cells mg^?1 stalk residue were still found after 24 months. Additionally, the four pathogens were present in residues of 11 commercial rapeseed crops that were analysed. The observed variation in population sizes of the pathogens between individual pieces of crop residues indicates a stochastic spread of pathogens. Unravelling the underlying processes will support the development of novel methods for sustainable disease prevention.  相似文献   

OBJECTIVE AND HUMAN PHYSICS     

Haas A 《Science (New York, N.Y.)》1927,66(1716):463-469

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A RELATION BETWEEN THE AVERAGE MASS OF THE FIXED STARS AND THE COSMIC CONSTANTS     

Haas AE 《Science (New York, N.Y.)》1938,87(2252):195-196

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Dating Caral, a preceramic site in the Supe Valley on the central coast of Peru     

Solis RS  Haas J  Creamer W 《Science (New York, N.Y.)》2001,292(5517):723-726

Radiocarbon dates from the site of Caral in the Supe Valley of Peru indicate that monumental corporate architecture, urban settlement, and irrigation agriculture began in the Americas by 4090 years before the present (2627 calibrated years B.C.) to 3640 years before the present (1977 calibrated years B.C.). Caral is located 23 kilometers inland from the Pacific coast and contains a central zone of monumental, residential, and nonresidential architecture covering an area of 65 hectares. Caral is one of 18 large preceramic sites in the Supe Valley.  相似文献   

Harnessing nonlinearity: predicting chaotic systems and saving energy in wireless communication   总被引：2，自引：0，他引：2  

Jaeger H  Haas H 《Science (New York, N.Y.)》2004,304(5667):78-80

We present a method for learning nonlinear systems, echo state networks (ESNs). ESNs employ artificial recurrent neural networks in a way that has recently been proposed independently as a learning mechanism in biological brains. The learning method is computationally efficient and easy to use. On a benchmark task of predicting a chaotic time series, accuracy is improved by a factor of 2400 over previous techniques. The potential for engineering applications is illustrated by equalizing a communication channel, where the signal error rate is improved by two orders of magnitude.  相似文献   

CYTOCHROME B2     

Haas E  Horecker BL  Hogness TR 《Science (New York, N.Y.)》1942,95(2468):406-407

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A low threshold calcium spike mediates firing pattern alterations in pontine reticular neurons   总被引：4，自引：0，他引：4  

R W Greene  H L Haas  R W McCarley 《Science (New York, N.Y.)》1986,234(4777):738-740

Intracellular electrical recordings in an in vitro slice preparation of the brainstem medial pontine reticular formation, a region thought to be important in mediation of desynchronized sleep phenomena, demonstrate a population of neurons that have a calcium-dependent, low threshold spike. This low threshold spike was inactivated at relatively depolarized membrane potential levels and, when this spike was deinactivated, it induced a burst of action potentials. The membrane potential dependence of the spike may underlie changes in action potential firing patterns associated with behavioral state change because the baseline membrane potential in neurons of the medial pontine reticular population depolarizes during passage from waking and slow wave sleep to desynchronized sleep, which is characterized by the absence of burst firing.  相似文献   

A Simple Aid for the Cannulation of Small Blood Vessels     

Haas E  Goldblatt H 《Science (New York, N.Y.)》1948,108(2798):166

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A SIMPLE METHOD OF MEASURING PHOTOSYNTHESIS     

Osterhout WJ  Haas AR 《Science (New York, N.Y.)》1918,47(1217):420-422

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