Single-Electron Transport in Ropes of Carbon Nanotubes

The electrical properties of individual bundles, or "ropes," of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.     

Effet de la densité et de la proportion des plantes lors de renvahissement de la luzerne par Taraxacum officinale Weber

Des expériences ont été conduites en salle climatisée pour mesurer l'influence de la densité et de la proportion des plantes sur l'envahisse-ment de la luzerne (Medicago sativa L.) établie par le pissenlit (Taraxacum officinale Weber). La durée de l'interférence et la densité de la luzerne ont permis d'expliquer la variation de la biomasse aérienne chez la luzerne cultivée en mélange avec le pissenlit. La densité du pissenlit a été toutefois un facteur important permettant d'expliquer la variation de la biomasse racinaire de la luzerne. La biomasse aérienne et racinaire du pissenlit a varié en fonction de la durée de la compétition, de la densité du pissenlit, de la densité de la luzerne et de la photopériode. Les équations de surface de réponse et hyper-boliques Iinéarisées ont permis de déterminer que la compétition dépendait de la densité plutôt que des proportions de chaque espèce dans le mélange. Effect of plant density and proportion on invasion of lucerne by Taraxacum officinale Weber Experiments were conducted in a growth chamber to establish the effect of plant density and proportion on invasion by dandelion (Taraxacum officinale Weber) of established lucerne (Medicago sativa). Duration of competition and lucerne density accounted for the variation in shoot biomass of lucerne growth in mixture with dandelion. The dandelion density explained a large proportion of the variation in lucerne root biomass. Dandelion root and shoot biomass varied according to duration of competition, dandelion density, lucerne density and photoperiod. Response surface and linearized hyperbolic equations suggested that competition was related more to density than to the proportion of each species in the mixture. Einfluβ der Pflanzendichte und-verteilung auf die Verunkrautung von Lucerne durch Taraxacum officinale Weber In Klimakammerversuchen zum Einfluß der Pflanzendichte und-verteilung auf die Verunkrautung von Luzerne (Medicago sativa L.) durch Löwenzahn (Taraxacum officinale Weber) erwiesen sich die Konkurrenzdauer und die Luzernendichte als wichtige Faktoren für die Bildung der Sproßbiomasse der Luzerne in Mischbeständen mit Löwenzahn, dessen Dichte für die Wurzelbiomasse der Luzerne ausschlaggebend war. Sproß- und Wurzelbiomasse der Löwenzahns variierten mit der Konkurrenzdauer, der Unkraut- sowie der Luzernendichte und der Photoperiode. Die Pflanzendichte erwies sich für die Konkurrenz wichtiger als das Mischungsverhältnis der Arten.     

关于啄木鸟控制光肩星天牛的初步探讨研究

文章介绍了内蒙古自治区巴盟乌拉特前旗利用啄木鸟防治光肩星天牛的措施和效果 ,具普遍意义和可行性。     

论沙化土地的治理

乌拉特前旗属干旱、半干旱地区,地貌类型复杂多样,造林立地条件较差。恶劣的自然条件,使大量土地日趋沙化,直接影响着这些地区的造林成活率和保存率的提高。文章对当前制约造林的沙化土地因素进行调查分析,提出治理的具体措施,可为同类地区提供造林技术参考。     

提高造林“两率”问题的探讨

内蒙古乌拉特前旗属干旱、半干旱地区,地形、地貌复杂,土壤类型多样,造林立地条件较差。恶劣的自然条件,严重制约着造林成活率和保存率的提高。文章对当前制约该区造林成活率、保存率的因素进行调查分析,提出提高"两率"的具体措施,可为同类地区提供造林技术参考。     

Structural requirements of Angiotensin I-converting enzyme inhibitory peptides: quantitative structure-activity relationship study of di- and tripeptides

A database consisting of 168 dipeptides and 140 tripeptides was constructed from published literature to study the quantitative structure--activity relationships of angiotensin I-converting enzyme (ACE) inhibitory peptides. Two models were computed using partial least squares regression based on the three z-scores of 20 coded amino acids and further validated by cross-validation and permutation tests. The two-component model could explain 73.2% of the Y-variance (inhibitor concentration that reduced enzyme activity by 50%, IC50) with the predictive ability of 71.1% for dipeptides, while the single-component model could explain 47.1% of the Y-variance with the predictive ability of 43.3% for tripeptides. Amino acid residues with bulky side chains as well as hydrophobic side chains were preferred for dipeptides. For tripeptides, the most favorable residues for the carboxyl terminus were aromatic amino acids, while positively charged amino acids were preferred for the middle position, and hydrophobic amino acids were preferred for the amino terminus. According to the models, the IC50 values of seven new peptides with matchable primary sequences within pea protein, bovine milk protein, and soybean were predicted. The predicted peptides were synthesized, and their IC50 values were validated through laboratory determination of inhibition of ACE activity.     

Angiotensin I converting enzyme-inhibitory peptides from commercial wet- and dry-milled corn germ

Bioprocesses were developed to enhance the value of proteins from deoiled corn germ. Proteins were hydrolyzed with trypsin, thermolysin, GC 106, or Flavourzyme to generate the bioactive peptide sequences. At an enzyme to substrate ratio of 1:100, protein hydrolysis of wet-milled germ was greatest using thermolysin followed by trypsin, GC 106, and Flavourzyme. For the dry-milled corn germ, protein hydrolysis was greatest for GC 106 and least for Flavourzyme. Electrophoretic patterns indicated that the hydrolysis conditions used were adequate for generating low molecular weight peptides for both germs. Unhydrolyzed dry- and wet-milled corn germ did not appear to contain angiotensin I converting enzyme (ACE)-inhibitory peptides. After hydrolysis with trypsin, thermolysin, and GC 106 but not Flavourzyme, ACE inhibition was observed. ACE inhibition was greatest for the GC 106 hydrolysate for both wet- and dry-milled corn germ. Denaturing the protein with urea before hydrolysis, in general, increased the amount of ACE-inhibitory peptides found in the hydrolysate. Membrane fractionations of both the wet- and dry-milled hydrolysates indicated that most of the ACE-inhibitory peptides were in the <1 kDa fraction. Examination of the control total protein extracts (before treatment with proteases) from wet- and dry-milled germ revealed that neither had ACE-inhibitory properties. However, when both total corn germ control protein extracts were fractionated, the <1 kDa fraction of wet-milled corn germ proteins exhibited ACE inhibition, whereas the comparable low molecular weight fraction from dry-milled corn germ did not.