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1.
This article describes a method for the determination of gasoline range, diesel range, and mineral oil range organics in soils and water. It represents the culmination of a series of efforts to go beyond typical GRO and DRO methodology currently available in the literature to include a quantitative determination of mineral oil organics having a boiling range up to C44. It also is the result of an attempt to develop a cost‐effective method that enables the analyst to quantify three different types of hydrocarbon components in one GC run under conditions without a concentration step. Method performance is comparable to that of current protocols for GRO and DRO determinations and validated further by comparisons to certified standards and in‐house standards. Accuracy as percentage recovery for GRO in water is 82 to 84 and 91 to 92% for soils. Accuracy as percentage recovery for MRO in water is 84 to 102 and 75 to 80% for soils. Accuracy as percentage recovery for DRO in water is 78 to 100 and 71 to 90% for soils. Results from the analysis of in‐house standards and certified standards for DRO and MRO gave higher recoveries than was demonstrated in the MDL studies. The MDL for DRO in water is 31 mg/l and 14 mg/kg for soils. The MDL for GRO in water is 8 mg/l and 4 mg/kg for soils. For MRO in water, the MDL is 7 mg/l and for soils 10 mg/kg. Future proposed improvements to this method will involve updated software that will allow automatic blank subtraction, automatic calculation of surrogate recoveries and the automatic incorporation of dry weight factors in the final calculations for soils. In addition, a GRO method with a run time of only 24 min will be used routinely when only GRO analyses have to be performed.  相似文献   

2.
Causation and Disease: The Henle-Koch Postulates Revisited   总被引:23,自引:0,他引:23       下载免费PDF全文
The Henle-Koch postulates are reviewed in terms of their full validity in Koch's day and in light of subsequent developments. The changing guidelines developed for viral diseases, for viruses in relation to cancer and to chronic central nervous system infection, and for causative agents in chronic diseases are discussed chronologically. A set of guidelines for both acute infectious and chronic diseases is presented. The need for recognizing the role of the host and the spectrum of host responses, for sound biologic sense in evaluating causal roles of agents in disease, and for flexibility in adapting our guidelines to new knowledge are emphasized.  相似文献   

3.
Alginate–carbon beads were prepared in order to develop a biocompatible matrix for laccase and glucose oxidase immobilization for application in biofuel cell technology. The enzyme loading capacity was high (91%) in pure alginate beads for glucose oxidase. For laccase, the loading capacity was enhanced from 75% to 83% by introducing carbon. Desorption out of the matrix was controlled by the enzymes’ diffusion and reached a plateau after 40 h for laccase and 70 h for glucose oxidase. Two-thirds of both enzymes was irreversibly retained inside the alginate beads. This proportion increased to 80% for laccase in combined alginate/carbon beads. Half-life of the adsorbed enzyme was enhanced to 74 days for laccase in carbon/alginate beads and 45 days for glucose oxidase in pure alginate as compared to 38 days and 23 days for free enzymes, respectively.  相似文献   

4.
The apparent Michaelis constant, Km, for transport of a number of neutral amino acids has been compared between intestine, heart, brain and erythrocytes among a variety of animals using values available in the literature. Neutral amino acids with side chains containing 3, 4, 7 and 9 carbon atoms had approximately equal mean Km values when tested for intestinal transport among a variety of species; alanine appeared to have a mean Km value that was larger than those found for the first group, and glycine had a significantly greater mean Km than all of the other compounds tested. Km values for phenylalanine and tryptophan measured in rat heart were found to be close to the means measured for these substrates in intestine. The mean Km values measured in mammalian brain for each of the neutral amino acid substrates were found not be significantly different from each other. When the means of Km values for the neutral amino acids tested were compared between intestine and brain, only the glycine means were shown to differ significantly between the organs. Based on data for several mammalian species, brain appears to have a greater average apparent affinity for glycine than does intestine. In the human erythrocytes and in a few other mammalian species, Km values for all neutral amino acids tested with exception of glycine were found to be similar in magnitude to each other and to the Km averages of neutral amino acids found in intestine for the series containing 3-9 carbon atoms. The Km value for glycine in the human erythrocyte was noted to be substantially lower in value than the averages for glycine in brain or intestine. Avian red blood cells appear to have high apparent affinity for neutral amino acid transport when compared with red cells of several mammalian species.  相似文献   

5.
OBJECTIVE--To assess effects of price, income, and health publicity on cigarette smoking by age, sex, and socioeconomic group. DESIGN--Econometric multiple regression analysis of data on cigarette smoking from the British general household survey. SUBJECTS--Random sample of adult population in Britain interviewed for biennial general household surveys 1972-90. MAIN OUTCOME MEASURES--Changes in cigarette consumption and prevalence of smoking. RESULTS--Price elasticities of demand for cigarettes (percentage change in cigarette consumption for a 1% change in price) were significant at -0.5 (95% confidence interval -0.8 to -0.1) for men and -0.6 (-0.9 to -0.3) for women, were highest in socioeconomic group V (-1.0 for men and -0.9 for women), and lowest (not significantly different from zero) in socioeconomic groups I and II. The gradient in price elasticities by socioeconomic group was significant for men (F = 5.6, P = 0.02) and for women (F = 6.1, P = 0.02). Price was a significant factor in cigarette consumption by age for women in every age group and for men aged 25-34. Cigarette consumption by young men aged 16-34 increased with income. There was a significant decrease in smoking over time by women in socioeconomic groups I and II and by men in all age and social groups except socioeconomic group V attributable to health publicity. Price significantly affected smoking prevalence in socioeconomic group V (-0.6 for men and -0.5 for women) and for all women (-0.2). CONCLUSIONS--Men and women in lower socioeconomic groups are more responsive than are those in higher socioeconomic groups to changes in the price of cigarettes and less to health publicity. Women of all ages, including teenagers, appear to have been less responsive to health publicity than have men but more responsive to price. Response to health publicity decreased linearly with age. Real price increases in cigarettes could narrow differences between socioeconomic groups in smoking and the related inequalities in health, but specific measures would be necessary to ameliorate effects on the most deprived families that may include members who continue to smoke. The use of a policy to steadily increase cigarette tax is likely to help achieve the government''s targets for smoking and smoking related diseases.  相似文献   

6.
Boron, which is ubiquitous in the environment, causes developmental and reproductive effects in experimental animals. This observation has led to efforts to establish a Tolerable Intake value for boron. Although risk assessors agree on the use of fetal weight decreases observed in rats as an appropriate critical effect, consensus on the adequacy of toxicokinetic data as a basis for replacement of default uncertainty factors remains to be reached. A critical analysis of the existing data on boron toxicokinetics was conducted to clarify the appropriateness of replacing default uncertainty factors (10-fold for interspecies differences and 10-fold for intraspecies differences) with data-derived values. The default uncertainty factor for variability in response from animals to humans of 10-fold (default values of 4-fold for kinetics and 2.5-fold for dynamics) was recommended, since clearance of boron is 3-to 4-fold higher in rats than in humans and data on dynamic differences—in order to modify the default value—are unavailable. A data-derived adjustment of 6-fold (1.8 for kinetics and 3.1 for dynamics) rather than the default uncertainty factor of 10-fold was considered appropriate for intrahuman variability, based on variability in glomerular filtration rate during pregnancy in humans and the lack of available data on dynamic differences. Additional studies to investigate the toxicokinetics of boron in rats would be useful to provide a stronger basis for replacement of default uncertainty factors for interspecies variation.  相似文献   

7.
The response of stomata to changes in humidity for a single surface of an amphistomatous leaf was investigated in Xanthium strumarium and Vicia faba using gas exchange and direct observation of stomatal apertures. The stomatal response to humidity for a given surface was found to be the same whether or not the humidity for the opposite surface was changed concurrently. Stomata on the surface for which humidity was constant showed no response to changes in humidity for the opposite surface. Despite large changes in epidermal turgor on the surface for which humidity was changed, there was no change in epidermal turgor for the surface with constant humidity. Measurements of transpiration and epidermal turgor as functions of the mole fraction gradient of water between leaf and air were used to calculate a value for leaf hydraulic resistance. The results suggest that in these species, the mechanism for the stomatal response to humidity resides in the epidermis or the mesophyll very close to the epidermis, and that most of the hydraulic resistance of the leaf occurs between the xylem and the evaporating sites.  相似文献   

8.
Recent studies with Nile tilapia have shown divergent results regarding the possibility of selecting on morphometric measurements to promote indirect genetic gains in fillet yield (FY). The use of indirect selection for fillet traits is important as these traits are only measurable after harvesting. Random regression models are a powerful tool in association studies to identify the best time point to measure and select animals. Random regression models can also be applied in a multiple trait approach to analyze indirect response to selection, which would avoid the need to sacrifice candidate fish. Therefore, the aim of this study was to investigate the genetic relationships between several body measurements, weight and fillet traits throughout the growth period and to evaluate the possibility of indirect selection for fillet traits in Nile tilapia. Data were collected from 2042 fish and was divided into two subsets. The first subset was used to estimate genetic parameters, including the permanent environmental effect for BW and body measurements (8758 records for each body measurement, as each fish was individually weighed and measured a maximum of six times). The second subset (2042 records for each trait) was used to estimate genetic correlations and heritabilities, which enabled the calculation of correlated response efficiencies between body measurements and the fillet traits. Heritability estimates across ages ranged from 0.05 to 0.5 for height, 0.02 to 0.48 for corrected length (CL), 0.05 to 0.68 for width, 0.08 to 0.57 for fillet weight (FW) and 0.12 to 0.42 for FY. All genetic correlation estimates between body measurements and FW were positive and strong (0.64 to 0.98). The estimates of genetic correlation between body measurements and FY were positive (except for CL at some ages), but weak to moderate (−0.08 to 0.68). These estimates resulted in strong and favorable correlated response efficiencies for FW and positive, but moderate for FY. These results indicate the possibility of achieving indirect genetic gains for FW and by selecting for morphometric traits, but low efficiency for FY when compared with direct selection.  相似文献   

9.
After a single exposure to doses ranging from 0.05 to 0.50 Gy, the SOD activities in immune organs of the irradiated rats, at 4 h after whole-body X irradiation, showed significant increases by 50 to 90% (hereinafter p less than 0.05) in comparison with the control groups. The dose in the brain and liver showed tendencies to increase by 30 to 50% for doses ranging from 0.50 to 2.50 Gy. The levels of TBARS (lipid peroxides) in immune organs decreased significantly by 20 to 50% in contrast with the control groups for doses ranging from 0.10 to 1.00 Gy. Decreases by 20 to 30% were observed in brains and livers for doses near 0.50 Gy. When the dose was 0.25 Gy, the SOD activities in the spleen showed a persistent radiation-induced increase for at least 12 weeks, livers for 8 weeks, brains and thymuses for 4 weeks, and bone marrows for about 1 week. The TBARS levels in the brain and thymus showed persistent decreases due to irradiation for at least 12 weeks, and those in bone marrows for 8 h.  相似文献   

10.
Calls for evaluating general principles in landscape genetics reflect a broader recognition that multispecies inference is a promising strategy for supporting conservation actions across wide-ranging taxonomies and geographies. Formal evaluation of frameworks for multispecies inference is critical to identify opportunities for generalization and to avoid misguided extrapolation that results in ineffective conservation and management efforts. Traits-based approaches are now widely recognized as useful in addressing knowledge gaps where species-specific data may not be available or feasible to obtain. Here we present a case for the application of traits-based approaches in landscape genetics to improve conservation application. We discuss the fundamental theoretical framework and growing empirical evidence supporting the utility of traits-based approaches in landscape genetics, and we highlight an example of the implementation of traits to predict landscape genetic relationships for a range of aquatic taxa native to the southwestern United States. Finally, we discuss opportunities, challenges, and future directions of using traits to characterize landscape genetic relationships. Ultimately, traits-based approaches can help address growing calls for the development and testing of general principles in landscape genetics in order to improve application to conservation challenges.  相似文献   

11.
All the deaths attributed to coronary artery disease and occurring in Belfast during one year were studied.The frequency distributions of the cases by interval of time between onset of the last attack and death are given for those not admitted to hospital, for those admitted to hospital, and for those already in hospital for some other cause of illness.Sixty per cent. of all the deaths occurred outside hospital. This indicates that the problem of cardiac resuscitation in coronary artery disease is to a considerable extent an extra-hospital one.Twenty-seven per cent. of the men and 22% of the women died within 15 minutes, but the median period of survival was 3 hours 30 minutes for men and 6 hours 18 minutes for women.The median time interval from the onset of the attack to sending for medical aid was 1 hour 17 minutes for men and 1 hour 6 minutes for women, and from summoning medical aid to sending for the ambulance 59 minutes for men and 1 hour 26 minutes for women. Ninety-six per cent. of the ambulance journeys to the patient were accomplished in less than 20 minutes.It was found among men, but not among women, that the duration of survival tended to be longer in older patients and in second or subsequent attacks.Of the 596 who did not gain admission to hospital 229 (23% of all the 998 patients) were known to have survived for more than half an hour after the onset of the fatal attack; 182 (18%) survived for more than one hour; and 143 (14%) survived for more than two hours. It is among these that there would appear to be special scope for the cardiac ambulance, providing that medical aid is sought and the ambulance is summoned without delay.  相似文献   

12.
The purpose of this study was to determine taste difference thresholds for monosodium glutamate (MSG) and sodium chloride (NaCl) in pigtail macaques (Macaca nemestrina) and spider monkeys (Ateles geoffroyi). Using a two-bottle preference test of brief duration, three animals of each species were presented with four different reference concentrations of 50, 100, 200, and 400 mM of a tastant and tested for their ability to discriminate these from lower concentrations of the same tastant. The just noticeable differences (JNDs), expressed as Weber ratios (DeltaI/I), were found to range from 0.1 to 0.5 for MSG and 0.2 to 0.45 for NaCl in the pigtail macaques, with a significant tendency for higher Weber ratios with higher reference concentrations. In the spider monkeys, JNDs ranged from 0.15 to 0.4 for MSG and 0.1 to 0.25 for NaCl, with Weber ratios staying fairly constant across the reference concentrations tested. Thus, the JNDs were found to be generally similar in both species and to be at least as low as those found in humans for MSG and NaCl, as well as those found in spider monkeys for sucrose. The results support the assumption that both pigtail macaques and spider monkeys may use differences in perceived intensity of MSG and NaCl as a criterion for food selection.  相似文献   

13.
14.
In this study, ageotropum pea mutant was used to determine the threshold time for perception of an osmotic stimulation in the root cap and the time requirement for transduction and transmission of the hydrotropic signal from the root cap to the elongation region. The threshold time for the perception of an osmotic stimulation was compared to current estimates of threshold times for graviperception in roots. The time required for transduction and transmission in the hydrotropic response of ageotropum was compared to the time requirement in the gravity response of Alaska pea roots. We determined that threshold time for perception of an osmotic stimulation in the root cap is very rapid, occurring in less than 2 min following the application of sorbitol to the root cap. Furthermore, a single 5 min exposure of sorbitol to the root cap fully induced a hydrotropic response. We also found that transduction and transmission of an osmotic stimulus requires 90-120 min for movement from the root cap to more basal tissues involved in differential growth leading to root curvature. The very rapid threshold time for perception of root hydrotropism is similar to those times reported for root gravitropism. However, the time required for the transduction and transmission of an osmotic stimulation from the root cap is significantly longer than the time required in gravitropism. These results suggest that there must exist some differences between root hydrotropism and gravitropism in either the rate or mechanisms of transduction and transmission of the tropistic signal from the root cap.  相似文献   

15.
Mouse lymphocytes were exposed in vitro for 2 h or in vivo for 24 h to benzidine and related aromatic amines to test for chromosome aberrations (CA) and mitotic indices. Uninduced mouse S9 was used to activate the amines for the in vitro tests to be consistent with the in vivo tests. Contrary to a previous report, no difference could be established in the genotoxicity of benzidine following activation with uninduced S9 compared to induced S9. There were concentration related increases in CA for benzidine and all the amines in vitro except for 4,4′-diaminostilbene which exhibited the greatest cellular toxicity towards cultured lymphocytes. Benzidine and its derivatives showed significant increases in CA in vivo compared to its negative control. The CA values for 4-aminostilbene were significantly higher than the other amines in both in vivo and in vitro studies. These genotoxicity results for 4-aminostilbene are consistent with our previous report of the pronounced CA effects in murine bone-marrow cells but would not be predicted from Salmonella mutagenicity tests.  相似文献   

16.
17.
In a recent review article by Mani published in 1990, it was shown that the changes in the frequency of the morph carbonaria can be explained through a migration-selection model and the model is capable of reproducing the decrease in the carbonaria frequency since the enactment of Clean Air Acts. In this paper new data both for carbonaria and for insularia up to 1990 for West Kirby in NW England and for Cambridge are presented. In the earlier review, the data for West Kirby extended to 1987 and for Cambridge to 1985. Data not previously published for the carbonaria and the insularia frequencies at sites in Northwood in Middlesex, Egham in Surrey and Ringwood in Hampshire are also presented. A migration-selection model was used to predict the change in the frequencies of the melanic morphs up to the year 2010. All the data are compared with the predictions of the model. It is encouraging that the data follow the theoretical predictions.  相似文献   

18.
Lineage effects and the index of dispersion of molecular evolution   总被引:9,自引:4,他引:5  
Recent efforts to estimate the index of dispersion [R(t)] of molecular evolution-i.e., the ratio of the variance in the number of substitutions on a lineage to the mean number-have suffered from an inability to adjust the data for lineage effects. These effects may include the generation-time dependency of the rate of evolution or improper assumptions about the branching pattern of a phylogenetic tree. In the present paper a method for correcting for lineage effects in the estimation of R(t) is presented for trees made up of three species. The recent data published by Li et al. for 20 loci in three orders of mammals is examined, and the average R(t), corrected for lineage effects, is shown to be 7.75 for replacement substitutions and 3.3 for silent substitutions. Thus the high values reported earlier may not be dismissed as due to generation-time effects or improper assumptions about phylogenies. Computer simulations are presented to give confidence in the estimate for replacement substitutions but also to demonstrate that the estimate for silent substitutions is sensitive to corrections for multiple substitutions and is not as reliable. This work's implications for our understanding of the mechanism of molecular evolution are discussed, and the arguments in favor of the hypothesis that replacement substitutions are mostly selected while silent substitutions are mostly neutral is presented.  相似文献   

19.
A procedure is described for sectioning the stems of woody herbarium specimens by the paraffin method. The specimens are cut into convenient sizes; boiled for one-half to one hour in order to exclude air and soak up the cell walls and membranes; cooled and placed in 5% NaOH for 24 hours in order to expand the collapsed cells and remove excessive coloring matter; washed in running water for a few hours; placed in hydrofluoric acid until sufficiently softened to cut easily with a razor blade; washed in running water for 24 hours to remove the acid; dehydrated and embedded in paraffin of high melting point (56-58°C.) according to the n-butyl alcohol method; sectioned with the rotary microtome and completed by the ordinary method. Soaking the paraffin blocks in water for a period of several hours to a day or more before sectioning greatly improves the cutting and reduces electrification of the paraffin ribbon. The method proves satisfactory not only for herbarium material but for seeds and specimens of old bark and wood varying in hardness from balsa to ebony. For seeds or specimens containing only xylem, the NaOH treatment should be omitted.  相似文献   

20.
Pollen identification and classification are important not only for palynologists, but also for systematists and ecologists. Because palynological methods for the identification of pollen in surface soil until now could resolve at best to the generic level, we have developed a molecular approach to species-level identification of Chenopodiaceae pollen in surface soils. Surface soil samples were collected in the central area of Junggar Desert Basin, Xinjiang, China. Fresh leaves of 19 Chenopodiaceae species were sampled for DNA sequencing, establishing a database of internal transcribed spacer (ITS) regions of nuclear ribosomal DNA for Chenopodiaceae. Individual chenopod pollen grains in a soil sample were separated from the soil and the ITS1 region of each pollen grain was amplified using nested PCR and sequenced. By comparing the amplified ITS1 sequences to those in the Chenopodiaceous database, we identified the pollen in the soil samples to the level of species. The new method provides a technical reference for species identification of soil surface pollen for other families. This work is necessary for further efforts to interpret the relationship of surface soil pollen to vegetation characteristics. It also has significant potential for enhancing the ability to identify pollen in clinical airborne allergen or criminological studies.  相似文献   

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