Size Dependence of Structural Metastability in Semiconductor Nanocrystals     

CC Chen  AB Herhold  CS Johnson  AP Alivisatos 《Science (New York, N.Y.)》1997,276(5311):398-401

The kinetics of a first-order, solid-solid phase transition were investigated in the prototypical nanocrystal system CdSe as a function of crystallite size. In contrast to extended solids, nanocrystals convert from one structure to another by single nucleation events, and the transformations obey simple unimolecular kinetics. Barrier heights were observed to increase with increasing nanocrystal size, although they also depend on the nature of the nanocrystal surface. These results are analogous to magnetic phase transitions in nanocrystals and suggest general rules that may be of use in the discovery of new metastable phases.  相似文献   

EFFECTS OF PERENNIAL PEANUT AND COMMON BERMUDAGRASS ON NITROGEN AND WATER UPTAKE OF YOUNG CITRUS TREES     

J. Linares  J. Scholberg  D. Graetz  K. Boote  R. McSorley  C. Chase 《Journal of plant nutrition》2013,36(2):200-218

A greenhouse experiment was conducted using a Soil-N Uptake Monitoring (SUM) system to determine nitrogen (N) and water uptake dynamics of citrus (CIT), perennial peanut (PP) (Arachis glabrata Benth), and common bermudagrass (BG) (Cynodon dactylon L.) over time. We also assessed the competition for water and N uptake between citrus and groundcover species and compared citrus N uptake measured using the SUM system with the ¹⁵N method. Nitrogen uptake followed cyclic patterns and was greatest for bermudagrass-based systems, while values were similar for PP and citrus systems. Competition for N uptake did occur during the summer months between citrus and BG, while no obvious competition for N uptake occurred between citrus and PP. Water uptake was greatest for the mixed systems and BG monoculture. Citrus, PP, and BG competed for water during the spring and summer seasons. None of the groundcovers significantly affected overall citrus tree growth. Nitrogen use efficiency was greatest for mixed systems and bermudagrass.  相似文献   

The relationship between flesh quality and numbers of Kudoa thyrsites plasmodia and spores in farmed Atlantic salmon, Salmo salar L     

Dawson-Coates JA  Chase JC  Funk V  Booy MH  Haines LR  Falkenberg CL  Whitaker DJ  Olafson RW  Pearson TW 《Journal of fish diseases》2003,26(8):451-459

Atlantic salmon, Salmo salar L., were exposed to Kudoa thyrsites (Myxozoa, Myxosporea)-containing sea water for 15 months, and then harvested and assessed for parasite burden and fillet quality. At harvest, parasites were enumerated in muscle samples from a variety of somatic and opercular sites, and mean counts were determined for each fish. After 6 days storage at 4 degrees C, fillet quality was determined by visual assessment and by analysis of muscle firmness using a texture analyzer. Fillet quality could best be predicted by determining mean parasite numbers and spore counts in all eight tissue samples (somatic and opercular) or in four fillet samples, as the counts from opercular samples alone showed greater variability and thus decreased reliability. The variability in both plasmodia and spore numbers between tissue samples taken from an individual fish indicated that the parasites were not uniformly distributed in the somatic musculature. Therefore, to best predict the probable level of fillet degradation caused by K. thyrsites infections, multiple samples must be taken from each fish. If this is performed, a mean plasmodia count of 0.3 mm(-2) or a mean spore count of 4.0 x 10(5) g(-1) of tissue are the levels where the probability of severe myoliquefaction becomes a significant risk.  相似文献   

Disentangling the drivers of β diversity along latitudinal and elevational gradients     

Kraft NJ  Comita LS  Chase JM  Sanders NJ  Swenson NG  Crist TO  Stegen JC  Vellend M  Boyle B  Anderson MJ  Cornell HV  Davies KF  Freestone AL  Inouye BD  Harrison SP  Myers JA 《Science (New York, N.Y.)》2011,333(6050):1755-1758

Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (β diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in β diversity caused simply by changes in the sizes of species pools. For example, forest inventories sampled along latitudinal and elevational gradients show the well-documented pattern that β diversity is higher in the tropics and at low elevations. However, after correcting for variation in pooled species richness (γ diversity), these differences in β diversity disappear. Therefore, there is no need to invoke differences in the mechanisms of community assembly in temperate versus tropical systems to explain these global-scale patterns of β diversity.  相似文献   

Infrared thermal mapping of the martian surface and atmosphere: first results     

Kieffer HH  Chase SC  Miner ED  Palluconi FD  Münch G  Neugebauer G  Martin TZ 《Science (New York, N.Y.)》1976,193(4255):780-786

The Viking infrared thermal mapper measures the thermal emission of the martian surface and atmosphere and the total reflected sunlight. With the high resolution and dense coverage being achieved, planetwide thermal structure is apparent at large and small scales. The thermal behavior of the best-observed areas, the landing sites, cannot be explained by simple homogeneous models. The data contain clear indications for the relevance of additional factors such as detailed surface texture and the occurrence of clouds. Areas in the polar night have temperatures distinctly lower than the CO(2) condensation point at the surface pressure. This observation implies that the annual atmospheric condensation is less than previously assumed and that either thick CO(2) clouds exist at the 20-kilometer level or that the polar atmosphere is locally enriched by noncondensable gases.  相似文献   

Southern Ocean iron enrichment experiment: carbon cycling in high- and low-Si waters     

Coale KH  Johnson KS  Chavez FP  Buesseler KO  Barber RT  Brzezinski MA  Cochlan WP  Millero FJ  Falkowski PG  Bauer JE  Wanninkhof RH  Kudela RM  Altabet MA  Hales BE  Takahashi T  Landry MR  Bidigare RR  Wang X  Chase Z  Strutton PG  Friederich GE  Gorbunov MY  Lance VP  Hilting AK  Hiscock MR  Demarest M  Hiscock WT  Sullivan KF  Tanner SJ  Gordon RM  Hunter CN  Elrod VA  Fitzwater SE  Jones JL  Tozzi S  Koblizek M  Roberts AE  Herndon J  Brewster J  Ladizinsky N  Smith G  Cooper D  Timothy D  Brown SL  Selph KE  Sheridan CC  Twining BS 《Science (New York, N.Y.)》2004,304(5669):408-414

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.  相似文献   

Tuber yield, storability, and quality of Michigan cultivars in response to nitrogen management and seedpiece spacing   总被引：1，自引：0，他引：1  

Chris M. Long  Sieg S. Snapp  Dave S. Douches  Richard W. Chase 《American Journal of Potato Research》2004,81(5):347-357

Information is required on nitrogen (N) fertility and seedpiece management for new cultivars and advanced breeding lines. Interactions amongst N fertilizer rate, genotype, and seedpiece spacing are complex, and can affect tuber yield, quality, and storability as well as N fertilizer efficiency. A field study was carried out in 2001 and 2002 at MSU Montcalm Research Farm in central Michigan. Tuber yields and post-harvest quality characteristics were evaluated for five potato genotypes (MSG227-2, MSE192-8Rus, Jacqueline Lee, Liberator, and Snowden) in response to a factorial combination of three N levels (200 kg N ha^-1, 300 kg N ha^-1-, and 400 kg N ha^-1) and two seedpiece spacings, narrow (0.20 m or 0.25 m) and wide (0.33 m or 0.38 m). Narrow seedpiece spacing consistently produced the highest U.S. No. 1 yields in all genotypes tested (37 and 34 t ha^-1, narrow vs wide spacing, respectively). There was a tradeoff between seedpiece spacing and N level in 2001 as tuber yields were enhanced by higher N levels at wide seedpiece spacing, but not at narrow spacing. In 2002, tuber yield was not enhanced, but petiole nitrate-N and tuber-N increased as N fertilization increased. Genotype was the major factor that influenced tuber quality characteristics at harvest and for stored tubers (e.g., specific gravity, internal defects, bruising, chip color rating, sucrose, and glucose). Spacing had minimal effects, whereas higher levels of N slightly reduced specific gravity both years, reduced internal defects in 2001 and enhanced sucrose at harvest in 2002. The cultivars tested demonstrated excellent storage characteristics for different N fertility levels and seedpiece spacing combinations. Overall, the recommended N fertilizer level for moderately long-duration potato cultivars in Michigan (200 kg N ha^-1) and a narrow seedpiece spacing optimized yield and tuber quality performance while conserving N fertilizer.  相似文献   

Boulder: A round white multipurpose potato variety     

D. S. Douches  J. Coombs  K. Jastrzebski  R. Hammerschmidt  W. W. Kirk  C. Long  R. W. Chase  S. Snapp 《American Journal of Potato Research》2003,80(6):345-352

Boulder is a round white selection with medium specific gravity that can be used in both the tablestock and chip-processing markets. The tubers will chip process out-of-the-field and from 10 C storage. The tubers of Boulder are large in size with a low incidence of internal defects. Boulder was tested in Michigan State University trials, the North Central Regional trials, on-farm trials in Michigan and other out-of-state replicated agronomic trials. Under irrigated conditions in Michigan, the yield is similar to or better than Atlantic, but specific gravity is less. Boulder has a full-season vine maturity that is similar to Snowden, but the tubers size early. Based upon our trials, an in-row spacing of less than 25.4 cm to reduce the percentage of oversize tubers is recommended. In simulated bruise tests, Boulder had less blackspot bruising than Atlantic, but was more blackspot susceptible than Onaway. Based upon five years of trials, Boulder has resistance to scab that is greater than Atlantic, but less than Onaway.  相似文献   

Liberator: A round white chip- processing variety with resistance to scab     

D. S. Douches  K. Jastrzebski  J. Coombs  R. W. Chase  R. Hammerschmidt  W. W. Kirk 《American Journal of Potato Research》2001,78(6):425-431

Liberator is a round white chip-processing selection with medium-high specific gravity and resistance to scab (Streptomyces scabies Thaxter). The tubers will chip process out of the field and from 10 C storage. The tuber appearance is similar to Norchip. Post-harvest tuber tests indicate a tolerance to fusarium dry rot. Liberator was tested in the North Central Regional Trials and the National Snack Food Association Trials. Under irrigated conditions the yield and specific gravity are similar to Snowden and Atlantic. Liberator has a full-season vine maturity that is similar to Snowden and tuber dormancy equal to Atlantic.  相似文献   

Pre-storage washing of potatoes     

Gary T. Grigg  Richard W. Chase 《American Journal of Potato Research》1967,44(7):232-235

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