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1.
The encapsulation of graphite-type carbon wires in the regular, 3-nanometer-wide hexagonal channels of the mesoporous host MCM-41 is reported. Acrylonitrile monomers are introduced through vapor or solution transfer and polymerized in the channels with external radical initiators. Pyrolysis of the intrachannel polyacrylonitrile results in filaments whose microwave conductivity is about 10 times that of bulk carbonized polyacrylonitrile. The MCM host plays a key role in ordering the carbon structure, most likely through the parallel alignment of the precursor polymer chains in the channels. The fabrication of stable carbon filaments in ordered, nanometer-sized channels represents an important step toward the development of nanometer electronics. 相似文献
2.
Yonas Yohannes Olga Shibistova Asferachew AbateMasresha Fetene Georg Guggenberger 《Forest Ecology and Management》2011,261(6):1090-1098
Variability of soil CO2 efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO2 efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO2 flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO2 efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO2 efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration. 相似文献
3.
RP Andres T Bein M Dorogi S Feng JI Henderson CP Kubiak W Mahoney RG Osifchin R Reifenberger 《Science (New York, N.Y.)》1996,272(5266):1323-1325
Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms). 相似文献
4.
Small differences between the lattice energies of different zeolites suggest that kinetic factors are of major importance in controlling zeolite nucleation. Thus, it is critical to control the nucleation kinetics in order to obtain a desired microporous material. Here, we demonstrate how careful investigation of the very early stages of zeolite crystallization in colloidal systems can provide access to important nanoscale zeolite phases while avoiding the use of expensive organic templates. We report the effective synthesis of ultrasmall (6- to 15-nanometer) crystals of the large-pore zeolite EMT from template-free colloidal precursors at low temperature (30°C) and very high yield. 相似文献
5.
Yohannes Misskire Tekalign Mamo Abi M. Taddesse Uri Yermiyahu 《Journal of plant nutrition》2019,42(4):307-322
Vertisols are characterized by deficiency of nutrients and recently, potassium (K), a major plant nutrient in crops, is gaining attention because of crop removal, fixation by clay minerals and leaching. A field experiment was conducted during the 2015 and 2016 main cropping seasons to test the effect of potash fertilizer on Vertisols of East Gojjam at Gudalima and Dejen/Tik sites using teff crop. The K rates (applied as muriate of potash) were 0, 50,100, and 150?kg ha?1. The experiment was laid out in a randomized complete block design in three replications. The results indicated that the plant height, panicle length, number of effective tillers, dry matter and grain yield of teff increased significantly (P?<?0.05) with applied K. The highest dry matter and grain yield (6966.4 and 2418.2 kg ha?1, respectively) were obtained from the application of 100 kg ha?1 KCl. Total uptake of N, P, and K were enhanced significantly with K treated plots than those without and K efficiency was improved due to the rate of K. The present study demonstrated the importance of K application to supplement NPS for optimum dry matter and grain yield of teff on Vertisols of the study sites. 相似文献
6.
Two experiments were conducted simultaneously to evaluate the effects of different concentrates to roughage ratios on growth
performance and attainment of puberty in Friesian–Boran crossbred heifers. Weaned 50% Friesian–Boran crossbred female calves
were used in both experiments with 25 and 20 calves in experiments I and II, respectively. In experiment I, the calves were
offered diets with concentrate to roughage ratios of 50:50 (treatment 1) or 30:70 (treatment 2). In experiment II, the calves
grazed for 8 h a day and supplemented with 2 kg hay and 1 kg concentrate per head per day (treatment 1) or only 2 kg hay per
head per day (treatment 2). The concentrate mixture was composed of 34% wheat bran, 31% wheat middling, 31% noug cake, 3%
limestone, and 1% salt. In experiment I, heifers fed a ration with 50% concentrate and 50% roughage had higher (P < 0.05) daily body weight gain (0.532 kg) and attained puberty at 221 kg (65% of the mature body weight) in 15 months, while
heifers fed a diet with 30% concentrate and 70% roughage gained 0.434 kg/day and reached puberty at 247 kg (70% of the mature
body weight), about 3 months later. Heifers in treatments 1 and 2 of experiment II reached puberty 5 and 12 months later,
respectively, than those in experiment I. In experiment II, heifers given 1 kg of concentrate supplement had higher (P < 0.05) daily body weight gain (0.346 kg) than those given only 2 kg hay in addition to grazing (0.278 kg). Growth rate of
crossbred heifers was enhanced and age at puberty was reduced by changing the rearing management from outdoor to indoor and
with increasing level of concentrate in the ration. This helps to bring the dairy heifer into production earlier and enhance
to the overall productivity of the dairy industry. 相似文献
7.
F Lobago M Bekana H Gustafsson JF Beckers G Yohannes Y Aster H Kindahl 《Reproduction in domestic animals》2009,44(4):685-692
This study presents serum concentrations of pregnancy‐associated glycoprotein (PAG), oestrone sulphate (E1‐S) and progesterone (P4), and the effects of some dam and foetus‐related factors on these profiles during gestation in Borana and crossbred cattle. The PAG concentrations at 4th week post‐conception ranged from 1.5–5.5 and 2.1–4.7 ng/ml in Borana (n = 6) and crossbred (n = 8) cattle, respectively. The mean PAG concentrations increased progressively from 4th to 33rd week of gestation (from 3.3–173 ng/ml for Borana and 4.2–240 ng/ml for crossbred cattle) and reached peak around calving. Breed, parity status, dam body weight, foetal sex and foetal birth weight significantly influenced the PAG concentrations. After delivery, the PAG concentrations declined steadily to 5.7 ng/ml in Borana (n = 7) and 3.9 ng/ml in crossbred (n = 6) cattle 10 weeks post‐partum. The serum E1‐S concentrations at 17th week of pregnancy ranged from 0.3–2.6 and 0.9–5.7 ng/ml in Borana (n = 8) and crossbred (n = 9) cattle, respectively. The mean E1‐S concentrations increased progressively from 17th to 33rd week of gestation (from 1.1–4.6 ng/ml for Borana and 2.7–10.8 ng/ml for crossbred). Breed, parity status, dam body weight and foetal sex significantly influenced E1‐S concentrations. The P4 concentrations at 4th week of pregnancy ranged from 3.2–5.1 and 1.7–8.9 ng/ml in Borana (n = 6) and crossbred (n = 8) cattle, respectively. The P4 level remained elevated throughout pregnancy. This study indicated that the serum PAG and P4 concentrations at 4th and E1‐S approximately 17th week of pregnancy were above the cut‐off value for pregnancy test and the hormonal profiles observed were comparable to the previous reports. Furthermore, the PAG and E1‐S profiles were considerably influenced by factors such as breed, weight and parity status of the dam, and foetal sex and foetal birth weight (only PAG). 相似文献
8.
Stone bunding ( kab ) is an age‐old local conservation practice at Mesobit‐Gedeba. This study was conducted to assess the effect of this indigenous practice on crop yield. We compared original ground slope, terrace width, and slope position of the terraced area. The effect of slope width and slope position were found significant (p < 0·05) for both grain and biomass yields of the terraced sites. The mean grain and biomass yields decreased as the original ground slope of the terraced site increased. Both grain and biomass yields decreased with the width of the inter‐terrace area. Significant differences (p < 0·05) in mean grain and biomass yields were observed between the three slope positions. They decreased as one moved up the slope within the inter‐terrace area. In general, the study indicated that indigenous stone bunding has a positive effect on sorghum yield. Future studies should address different locations and crops and ways of integrating indigenous stone bunding with the current conservation programmes of the region. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
9.
Oladele Ogunremi John Pasick Yohannes Berhane 《Canadian journal of veterinary research》2013,77(4):309-313
A needle-free delivery system was assessed as a route for providing quick, safe, and effective vaccination against avian influenza (AI). Two groups of chickens were vaccinated with a commercially available inactivated H5N3 virus vaccine delivered either with a needle-free device or with the conventional syringe-and-needle method recommended by the vaccine manufacturer. The kinetic aspects of seroconversion, peak antibody levels, and antibody titers were measured by a combination of an indirect enzyme-linked immunosorbent assay and the hemagglutination-inhibition test and were all found to be similar in the 2 groups of chickens. We conclude that the needle-free delivery system could result in effective immunization against H5N1 AI epidemics and pandemics in chickens. 相似文献
10.