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111.
Casey PG Butler D Gardiner GE Tangney M Simpson P Lawlor PG Stanton C Ross RP Hill C Fitzgerald GF 《Journal of food protection》2004,67(12):2797-2800
Salmonella carriage in pigs represents a serious health problem that undoubtedly contributes to the spread of human disease. Thus, the efficient and reliable testing of farm animals for bacteria such as Salmonella is an important aspect of any efficient control strategy. Serological analysis of 15 meat juice samples detected antibodies against Salmonella in some. but not all, of the animals identified bacteriologically as harboring the pathogen, indicating a lack of correlation between the bacteriological and serological methods used for Salmonella detection. The results suggest that testing by enzyme-linked immunosorbent assay is appropriate at the herd level, with culture methods preferable for individual animal analysis. A novel culture protocol detected Salmonella in the cecal contents of 15 pigs, whereas a method based on the European Standard identified only 9 pigs as being Salmonella-positive. During the study, an unusual finding was the relatively high incidence of Salmonella London carriage in the pigs tested. 相似文献
112.
A new algorithm for ranking the input features and obtaining the best feature subset is developed and illustrated in this paper. The asymptotic formula for mutual information and the expectation maximisation (EM) algorithm are used to developing the feature selection algorithm in this paper. We not only consider the dependence between the features and the class, but also measure the dependence among the features. Even for noisy data, this algorithm still works well. An empirical study is carried out in order to compare the proposed algorithm with the current existing algorithms. The proposed algorithm is illustrated by application to a variety of problems. 相似文献
113.
Hexachlorocyclohexanes in the North American atmosphere 总被引:2,自引:0,他引:2
Shen L Wania F Lei YD Teixeira C Muir DC Bidleman TF 《Environmental science & technology》2004,38(4):965-975
Annually integrated air concentrations of alpha- and gamma-hexachlorocyclohexane (HCH) were determined in 2000/2001 at 40 stations across North America using XAD-based passive air samplers to understand atmospheric distribution processes on a continental scale. Elevated levels of gamma-HCH in the atmosphere of the Canadian Prairies are consistent with the ongoing use of lindane as a seed treatment on canola and confirm the feasibility of detecting the agricultural use of a pesticide using long-term integrated passive air sampling. In contrast to gamma-HCH, the atmospheric concentrations of alpha-HCH show a rather uniform distribution across Canada and the United States, which is expected for a chemical with no current use on the continent. Higher levels in the atmosphere over Atlantic Canada can be explained by alpha-HCH evaporating from the waters of the Labrador Current, which is supported bythe chiral composition of alpha-HCH and the temperature dependence of its atmospheric concentrations along the east coast of Canada. Similarly, alpha-HCH is volatilizing from Lake Superior. Atmospheric HCH levels increase with elevation in the Canadian Rocky Mountains. The results suggest that evaporation, in particular from cold water bodies, is an important source of alpha-HCH to the North American atmosphere. Low levels of HCHs in Central America hint at efficient degradation under tropical conditions. Chiral analysis shows that (+)-alpha-HCH is often enriched in air over continental areas and at the Pacific Coast, which is opposite to the enantiomeric enrichment in the proximity to the Great Lakes and the Atlantic Ocean. Passive air sampling is a powerful tool to discern the large-scale variability of semivolatile and persistent organic chemicals in the atmosphere. 相似文献
114.
Mass spectrometry (MS)-based techniques have enormous potential for kinetic studies on enzyme-catalyzed processes. In particular, the use of electrospray ionization (ESI) MS for steady-state measurements is well established. However, there are very few reports of MS-based studies in the pre-steady-state regime, because it is difficult to achieve the time resolution required for this type of experiment. We have recently developed a capillary mixer with adjustable reaction chamber volume for kinetic studies by ESI-MS with millisecond time resolution (Wilson, D. J.; Konermann, L. Anal. Chem. 2003, 75, 6408-6414). Data can be acquired in kinetic mode, where the concentrations of selected reactive species are monitored as a function of time, or in spectral mode, where entire mass spectra are obtained for selected reaction times. Here, we describe the application of this technique to study the kinetics of enzyme reactions. The hydrolysis of p-nitrophenyl acetate by chymotrypsin was chosen as a simple chromophoric model system. On-line addition of a "makeup solvent" immediately prior to ionization allowed the pre-steady-state accumulation of acetylated chymotrypsin to be monitored. The rate constant for acetylation, as well as the dissociation constant of the enzyme-substrate complex obtained from these data, is in excellent agreement with results obtained by conventional stopped-flow methods. Bradykinin was chosen to illustrate the performance of the ESI-MS-based method with a nonchromophoric substrate. In this case, the unfavorable rate constant ratio for acylation and deacylation of the enzyme precluded measurements in the pre-steady-state regime. Steady-state experiments were carried out to determine the turnover number and the Michaelis constant for bradykinin. The methodologies used in this work open a wide range of possibilities for future ESI-MS-based kinetic assays in enzymology. 相似文献
115.
Derek C. Oppen 《Theoretical computer science》1980,12(3):291-302
We restrict our attention to decidable quantifier-free theories, such as the quantifier-free theory of integers under addition, the quantifier-free theory of arrays under storing and selecting, or the quantifier-free theory of list structure under cons, car and cdr. We consider combinations of such theories: theories whose sets of symbols are the union of the sets of the symbols of the individual theories and whose set of axioms is the union of the sets of axioms of the individual theories. We give a general technique for determining the complexity of decidable combinations of theories, and show, for example, that the satisfiability problem for the quantifier-free theory of integers, arrays, list structure and uninterpreted function symbols under +, ≤, store, select, cons, car and cdr is NP-complete. We next consider the complexity of the satisfiability problem for formulas already in disjunctive normal form: why some combinations of theories admit deterministic polynomial time decision procedures while for others the problem is NP-hard. Our analysis hinges on the question of whether the theories being combined are convex; that is, whether any conjunction of literals in the theory can entail a proper disjunction of equalities between variables. This leads to a discussion of the role that case analysis plays in deciding combinations of theories. 相似文献
116.
Discusses the theory that asserts that the residual reading abilities seen in deep dyslexia entirely reflect the operation of an intact right hemisphere reading system rather than a partially disabled left hemisphere reading system. Evidence from an experiment with normal Ss in a report by the present author and colleagues (1983) is presented, which suggests that the right hemisphere contains no lexical entries for abbreviations that can be accessed by visual presentation. Data are presented from studies by K. E. Patterson (1980; see also PA, Vols 63:12203 and 64:10691) on 2 male deep dyslexic's understanding of printed abbreviations, along with observations of a young female deep dyslexic who was tested on understanding of abbreviations and on letter-naming abilities. Considerable sparing of the ability to obtain semantic information from printed abbreviations was evidenced in all 3 Ss. This contrast suggests that the current right hemisphere account of the residual reading abilities seen in deep dyslexia is not a sufficient one and should be modified. (French abstract) (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
117.
The Likens-Nickerson concurrent steam distillation-solvent extraction apparatus was used to obtain an essence from malt extract. The essence was submitted to combined gas chromatography-mass spectrometry (g.c.-m.s.), to examination by sulphurspecific and nitrogen-specific detectors, and to sensory evaluation of the components eluted from gas chromatographic capillary columns. Some 33 compounds were identified by direct examination by g.c.-m.s., another 14 by trapping and re-injection, which provides an efficient method of concentration, and a further six, which had not been previously identified due to interference from the solvent peak, by the use of charcoal adsorption traps. Results indicate that several compounds need to be combined to simulate malt flavour. The odour contributions of several components are discussed. 相似文献
118.
Coherent anti-Stokes Raman spectroscopy (CARS) is a nonlinear optical wave mixing process that is used in gas-phase systems to determine the energy distribution of the probed species (usually N2) and, through a fitting procedure, the temperature giving rise to it. CARS signal strengths are maximized when the phase matching condition is met. Because gases are generally non-dispersive, this phase matching condition can be found geometrically as a function of the crossing angles between the CARS beams and their wavelengths. In addition, perfect phase matching in non-dispersive media occurs automatically for collinear beams. To improve spatial resolution, however, intersecting the laser beams is desirable. Being a third-order process, phase matching for CARS in gases typically requires three input laser beams. This paper discusses and demonstrates the issues of phase matching for CARS when the medium is dispersive, and the ability for CARS phase matching to occur with only two crossed laser beams (one pump and one probe). This two-beam X-CARS in dispersive media can be used as an alignment tool for gas-phase CARS and may be relevant as a simpler diagnostic in high-pressure environments. The paper also discusses the effects of non-ideal phase matching in dispersive and non-dispersive media. 相似文献
119.
A nanometre-scale pore in a solid-state membrane provides a new way of electronically probing the structure of single linear polymers, including those of biological interest in their native environments. Previous work with biological protein pores wide enough to let through and sense single-stranded DNA molecules demonstrates the power of using nanopores, but many future tasks and applications call for a robust solid-state pore whose nanometre-scale dimensions and properties may be selected, as one selects the lenses of a microscope. Here we demonstrate a solid-state nanopore microscope capable of observing individual molecules of double-stranded DNA and their folding behaviour. We discuss extensions of the nanopore microscope concept to alternative probing mechanisms and applications, including the study of molecular structure and sequencing. 相似文献
120.
In this paper, the design and development of a physical and virtual environment to support assembly of micron sized devices
is discussed. Micro assembly involves handling and assembling of micron sized parts (10−6 m). As manual assembly of micron-sized parts is difficult and tedious, the design of computer assisted micro-assembly techniques
becomes crucial. An Integrated Physical and Virtual Reality (VR) environment has been created to aid in the assembly of such
micro devices, which supports the establishment of an interface between a virtual and physical micro assembly work cell. The
overall architecture and the various modules implemented in this environment are outlined in this paper. 相似文献