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排序方式: 共有237条查询结果,搜索用时 15 毫秒
81.
We analyze the political economy of timber taxation in Ghana. Our results show that politicians maintain control over allocation of timber rights, that taxation constitutes an insignificant share of the value of the timber resource, and that the distribution of timber revenues hardly contributes towards the official forest policy justifications. Our analysis suggests that politicians wield control over rent-seeking opportunities that are exchanged for political support through patron–client networks. This speaks to a larger literature on why governments waste resources and constitutes an argument for increased attention to the political economy underlying natural resource policies. 相似文献
82.
Zijlstra C Lund I Justesen AF Nicolaisen M Jensen PK Bianciotto V Posta K Balestrini R Przetakiewicz A Czembor E van de Zande J 《Pest management science》2011,67(6):616-625
The possibility of combining novel monitoring techniques and precision spraying for crop protection in the future is discussed. A generic model for an innovative crop protection system has been used as a framework. This system will be able to monitor the entire cropping system and identify the presence of relevant pests, diseases and weeds online, and will be location specific. The system will offer prevention, monitoring, interpretation and action which will be performed in a continuous way. The monitoring is divided into several parts. Planting material, seeds and soil should be monitored for prevention purposes before the growing period to avoid, for example, the introduction of disease into the field and to ensure optimal growth conditions. Data from previous growing seasons, such as the location of weeds and previous diseases, should also be included. During the growing season, the crop will be monitored at a macroscale level until a location that needs special attention is identified. If relevant, this area will be monitored more intensively at a microscale level. A decision engine will analyse the data and offer advice on how to control the detected diseases, pests and weeds, using precision spray techniques or alternative measures. The goal is to provide tools that are able to produce high-quality products with the minimal use of conventional plant protection products. This review describes the technologies that can be used or that need further development in order to achieve this goal. 相似文献
83.
Mark D. C. Schmitt Dale J. Trippler John N. Wachtler Gail V. Lund 《Water, air, and soil pollution》1988,39(1-2):157-168
A total of 2454 samples were collected to evaluate the degree, extent, and distribution of Pb contaminated soil in Minnesota. Samples were collected primarily at locations where susceptible populations were concentrated. Soil Pb concentrations in chilldren's play areas, urban gardens, and at open sites were generally below 100 μg g ?1 when Pb painted structures were absent. Street side and yard soils typically had Pb concentrations between 10 to 300 μg g?1, with samples collected near major highways or Pb painted structures exhibiting greater values. The most severely contaminated soils were found in localized areas around the foundations of private residences, where concentrations up to 20 136 μg g?1 were detected. Exterior Pb based house paint is the major Pb source in these soils, and its presence greatly influences the distribution of contaminated soil in individual yards. Contamination attributable to autoemissions is less concentrated but more widespread than contamination from paint. A higher proportion of soils exceeding 1000 wg g?1 Pb was found in large cities than elsewhere. However, a sufficient number were detected in small cities and rural areas to confirm that high soil Pb levels are not exclusively an urban phenomenon. By examining the degree, extent, and distribution of Pb contaminated soils in Minnesota, this study provides information useful in guiding response actions to reduce children's exposure to Pb by this pathway. 相似文献
84.
The leachability of B and salts from two fly ash-amended soils was conducted in a column leaching experiment. Fly ash was applied to the surface 3 cm of a Baywood (acid) sand and an Arizo (calcareous) sandy, loam at 5% by weight; the columns were continously leached with Colorado River water at two different pH's. Boron from fly ash was solubilized more readily in the Baywood than in the Arizo soil. Addition of fly ash increased B levels in the leachates from 0.25 to 2.35 μg ml?1 (Baywood) and 0.93 μg ml?1 (Arizo). Acidified leaching water had no significant effect on B leaching patterns but resulted in leaching higher soluble salts. Approximately 348 and 161 cm of water for the Arizo and the Baywood soils respectively, would be required to reduce the B concentration below a critical limit for B sensitive crops. It is suggested that crops planted when fly ash is applied for disposal/recycling on land should be both salt and B tolerant. 相似文献
85.
Antioxidant properties of carnosine re-evaluated in a ferrylmyoglobin model system and in cooked pork patties 总被引:1,自引:0,他引:1
Carlsen CU Kröger-Ohlsen M Lund MN Lund-Nielsen T Rønn B Skibsted LH 《Journal of agricultural and food chemistry》2002,50(24):7164-7168
The antioxidative effect of purified carnosine (i.e., separated from the common contaminant hydrazine) has been evaluated in two systems: (i) Carnosine was found to possess poor reducing properties toward the prooxidant ferrylmyoglobin; at pH approximately 5 the presence of carnosine did not increase the rate of reduction of MbFe(IV)=O compared to autoreduction, whereas at pH 7.4 the rate constant for reduction by carnosine was 0.010 +/- 0.002 M(-1).s(-1) (I = 0.16; 25.0 degrees C). (ii) In cooked pork patties prepared from meat (longissimus dorsi and masseter) with purified or nonpurified carnosine added, the effect of purified carnosine was insignificant when compared to control patties, whereas patties with carnosine contaminated with hydrazine had a lower oxidation level than patties with purified carnosine. Carnosine is concluded not to deactivate the prooxidant ferrylmyoglobin and not to have any antioxidative effect in cooked pork. 相似文献
86.
Seroprevalence of brucellosis and its associated risk factors in cattle from smallholder dairy farms in Zimbabwe 总被引:2,自引:2,他引:0
Matope G Bhebhe E Muma JB Oloya J Madekurozwa RL Lund A Skjerve E 《Tropical animal health and production》2011,43(5):975-982
A cross-sectional study was conducted to investigate seroprevalence of brucellosis and the associated risk factors in cattle
from smallholder dairy farms in Gokwe, Marirangwe, Mushagashe, Nharira, Rusitu and Wedza areas of Zimbabwe. A total of 1,440
cattle from 203 herds were tested serially for Brucella antibodies using Rose Bengal test and the competitive ELISA. Weighted seroprevalence estimates were calculated and risk factors
in individual cattle investigated using logistic regression analysis. The overall individual animal brucellosis seroprevalence
was low, with mean of 5.6% (95% confidence interval (CI), 4.4%, 6.8%). Gokwe had the highest individual (12.6%; 95% CI, 3.9%,
21.4%) and herd-level (40.0%; 95% CI, 22.1%, 58.0%), while Wedza had the lowest individual (2.3%; 95% CI, 0%, 5.3%) and herd-level
(8.0%; 95% CI, 0.0%, 18.9%) brucellosis seroprevalence, respectively. In individual cattle, the area of origin, age and history
of abortion were independently associated with brucellosis seroprevalence. While the seroprevalence was independent of sex,
it decreased with increasing age. Cattle 2–4 years old had higher odds (odds ratio (OR) = 3.2; 95% CI, 1.1%, 9.1%) of being
seropositive compared to those >7 years. Cows with a history of abortion were more likely to be seropositive (OR = 7.9; 95%
CI, 3.1, 20.1) than controls. In conclusion, the area-to-area variation of brucellosis may be linked to ecological factors
and differences in management practices. The implementation of stamping out policy, bleeding and testing animals before movement
and promoting the use self-contained units are likely to significantly reduce the public health risks associated with Brucella infections in cattle. 相似文献
87.
Connelley T Storset AK Pemberton A Machugh N Brown J Lund H Morrison IW 《Veterinary research》2011,42(1):37
ABSTRACT: Natural killer (NK) cells are well recognized as playing a key role in innate immune defence through cytokine production and cytotoxic activity; additionally recent studies have identified several novel NK cell functions. The ability to study NK cells in the sheep has been restricted due to a lack of specific reagents. We report the generation of a monoclonal antibody specific for ovine NKp46, a receptor which in a number of mammals is expressed exclusively in NK cells. Ovine NKp46+ cells represent a population that is distinct from CD4+ and γδ+ T-cells, B-cells and cells of the monocytic lineage. The NKp46+ cells are heterogenous with respect to expression of CD2 and CD8 and most, but not all, express CD16 - characteristics consistent with NK cell populations in other species. We demonstrate that in addition to populations in peripheral blood and secondary lymphoid organs, ovine NKp46+ populations are also situated at the mucosal surfaces of the lung, gastro-intestinal tract and non-gravid uterus. Furthermore, we show that purified ovine NKp46+ populations cultured in IL-2 and IL-15 have cytotoxic activity that could be enhanced by ligation of NKp46 in re-directed lysis assays. Therefore we conclude that ovine NKp46+ cells represent a population that by phenotype, tissue distribution and function correspond to NK cells and that NKp46 is an activating receptor in sheep as in other species. 相似文献
88.
Canine juvenile‐onset generalized demodicosis (JOGD) is a common skin disorder suspected to be associated with multiple risk factors, including breed predispositions. These risk factors have not been well documented in a large population. A retrospective case–control study was conducted by searching the electronic medical records of 1 189 906 dogs examined at 600 hospitals during 2006 in order to assess the risk factors associated with JOGD in the USA. Multivariate analyses were conducted using logistic regression to estimate the relative risk with the odds ratio for variables hypothesized to influence the risk for canine demodicosis. Breeds (odds ratio) found to have the greatest association with a diagnosis of JOGD were American Staffordshire terrier (35.6), Staffordshire bull terrier (17.1) and Chinese shar‐pei (7.2). Nonbreed risk factors (odds ratio) significantly associated with a diagnosis of JOGD were the diagnosis of pyoderma (5.5), coccidiosis (2.7) or hookworms (1.5), short coat (1.9) and nonenrolment in a preventative care wellness plan (1.5). Documenting these risk factors may help veterinarians to prioritize differential diagnoses and will aid in the design of prospective studies to elucidate the pathogenesis of demodicosis in dogs. 相似文献
89.
90.
Clinical Trial Design: Veterinary Perspectives 总被引:2,自引:1,他引:1
Elizabeth M. Lund DVM MPH Katherine M. James James D. Neaton 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(5):317-322
Tremendous potential exists for the use of the randomized clinical trial (RCT) in veterinary clinical research. Understanding the fundamentals of RCT design not only benefits clinical researchers, but it can enhance the ability of practitioners to interpret published RCT reports. In this article, the essential components of RCT design and implementation are described using examples from clinical veterinary medicine. 相似文献