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91.
What are the best quantitative methods for studying cognitive decline? This question was investigated in a sample of 638 individuals aged 50 years and older from the Swedish Adoption/Twin Study of Aging. A battery of cognitive tests tapping multiple domains was administered to each individual from 2 to 7 times over a span of 10 years. Four methods of operationalizing cognitive decline were compared: change scores, a criterion-based method, least squares, and random effects regression (RER). The RER results were most consistent with a significant decline across measures and differences between demented and nondemented individuals. Predicted slopes from the RER model also showed the strongest interrelationships within and across cognitive domains as indicated by factor analysis results and stronger associations with demographic, health, and psychosocial predictors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
Quality VoIP — An Engineering Challenge   总被引:1,自引:0,他引:1  
Initial impressions of VoIP quality have not always been favourable. This paper discusses the issues behind delivering an 'appropriate' quality of service, specifically voice quality, by showing how design choices ultimately affect, and potentially limit, a customer's perception of VoIP quality.The paper continues by introducing new signal processing techniques that are helping to measure and optimise the performance of VoIP solutions.  相似文献   
93.
94.
This study investigated the effects of urban concrete materials, of different particle sizes, immersed in water through a laboratory-based experiment. Water was sourced from a high conservation-value wetland (Blue Mountains upland swamp). Prior to the experiment, wetland water was dilute (32.5 μS/cm), acidic (pH 5.3) and had detectable major ion concentrations of only sodium and chloride. Water was exposed to three treatments of different concrete fragment sizes (whole, crushed and fine). All treatments increased conductivity and pH and also resulted in modified ionic composition where calcium, potassium, hydroxide, carbonate and sulphate were recorded at much high levels. The extent and speed of water chemistry changes was linked to the particle size of the concrete. The results of this study support the hypothesis that concrete can be an environmentally hazardous material influencing water quality in urban catchments.  相似文献   
95.
Ammonium nitrate (AN), gunpowder (GP), and an ammonium nitrate gunpowder mixture (AN/GP) were studied for impact sensitivity by four laboratories using the drop hammer apparatus. Bruceton and Neyer methods were used as experimental protocols and for data reduction. The results are presented as 50 % probability of reaction (DH50). For AN, the DH50 values are widely varied among the participants, from sensitive to completely insensitive (limit of the equipment), with no real correlation among results. GP and the AN/GP mixture exhibited much more sensitivity overall and were in some cases within statistical values extrapolated from previous studies of RDX. The variability in results for the AN data is attributed to the difficulty in determining a positive reaction event for AN, as detailed by Neyer experiments and photography during positive reactions. Variability in results for the GP and AN/GP mixtures is attributed to equipment environment and detection criteria. This work was performed by the Integrated Data Collection Analysis (IDCA) program, a multi‐laboratory effort to standardize safety testing of improvised or homemade explosives funded by the Department of Homeland Security.  相似文献   
96.
Small and very small meat-processing facilities in the United States are in need of a pathogen reduction technology that would be both effective and economical. In the present study, the effectiveness of a commercial household steam cleaner for reducing naturally occurring bacterial populations on freshly slaughtered beef and hog carcasses was evaluated in four small or very small meat-processing plants. Three anatomical sites on the right half of each carcass were exposed to a 60-s steam treatment, and the corresponding left half of the carcass remained untreated. Samples were collected from 72 beef and 72 hog carcasses before, immediately after, and 24 h after the steam treatment. The mean populations of total aerobes, coliforms, and Enterobacteriaceae recovered from three anatomical sites on the beef carcasses were 1.88, 1.89, and 1.36 log CFU/cm2, respectively, before the steam treatment, 1.00, 0.71, and 0.52 log CFU/cm2, respectively, immediately after the steam treatment, and 1.10, 0.95, and 0.50 log CFU/cm2, respectively, 24 h after the steam treatment. On hog carcasses, the mean populations of total aerobes, coliforms, and Enterobacteriaceae recovered from the three anatomical sites were 2.50, 2.41, and 1.88 log CFU/cm2, respectively, before the steam treatment, 0.50, 0.94, and 0.21 log CFU/cm2, respectively, immediately after the steam treatment, and 0.91, 1.56, and 0.44 log CFU/cm2, respectively, 24 h after the steam treatment. The steam treatment significantly reduced the total aerobes, coliforms, and Enterobacteriaceae at all three anatomical locations on both types of carcasses (P < 0.05). The order of mean bacterial populations recovered before steam treatment was midline > neck > rump for beef carcasses and belly > jowl > ham for hog carcasses except for the total coliform counts at the midline and neck areas on the beef carcasses. Of the 144 carcasses evaluated, 5 (3.47%) were positive for Salmonella before steam treatment, but all carcasses tested negative for Salmonella after the treatment. Results indicate that the household steam cleaner can effectively reduce overall bacterial populations on freshly slaughtered beef and hog carcasses in small and very small meat-processing facilities.  相似文献   
97.
Following the suggestion that therapeutic change is accelerated in time-limited psychotherapy, this study investigated the across-session patterns of session impact in the treatments of 117 depressed clients who were randomly allocated to 8 or 16 sessions of cognitive-behavioral (CB) or psychodynamic-interpersonal (PI) therapy. After each session, all clients completed the Session Evaluation Questionnaire and 75 of the clients completed the Session Impacts Scale. Session ratings indicated that sessions were perceived increasingly positively on most impact dimensions (e.g., session depth and smoothness, relationship with the therapist, feelings of understanding and problem solving, postsession positive mood) as treatment progressed. Early in treatment, PI therapy sessions were less smooth (i.e., more tense and uncomfortable) and less focused on problem solving, but PI sessions changed more rapidly than CB sessions on these dimensions, so that later in treatment, sessions of both treatments were equivalently positive. In both treatments, the trend toward more positive sessions was more rapid (i.e., the across-session slope was steeper) in 8-session treatments than in 16 session treatments. Such accelerated changes in session impact may reflect the suggested acceleration … (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
98.
The creep of uranium dioxide has been investigated as a function of grain size. At high stresses, when creep is controlled by dislocation movement, grain boundaries exert a strengthening effect and this strengthening is correlated with the Hall-Petch equation. The degree of strengthening diminishes with increases in temperature. At lower stresses, when creep is controlled by mass transport, grain boundaries exert a weakening effect owing to the reduction in diffusion path length as grain size is reduced. In this range behaviour is correlated with the Nabarro-Herring equation with stress replaced by an effective stress E=–0 where 0 is a threshold stress for diffusional creep associated with the limitation of the ability of boundaries to emit and absorb vacancies. 0 appears to decrease as grain size is increased.  相似文献   
99.
Hondo 850 °F residuum was separated into saturate, aromatic, resin, and asphaltene fractions by a modified D 2007 and asphaltene separation. Two different asphaltene precipitation solvents were used — isooctane and heptane — and differences in selected physical and chemical properties of the derived fractions were compared.

The principal difference in the use of the two solvents was weight recovery after the separation. Isooctane yielded good recovery, while heptane exhibited poor recovery. Isooctane precipitated substantially more asphaltenes, as predicted from the solubility parameters of the two solvents.

The metals concentrations in the fractions were comparable for each solvent — no metals in the saturate and aromatic fractions, approximately 300 and 1500 ppm Ni + V in the resin and asphaltene fractions respectively. The relative distribution was also similar for both solvents, with the highest percentage coming from the asphaltenes.  相似文献   
100.
The selection of an optimal checkpointing strategy has most often been considered in the transaction processing environment where systems are allowed unlimited repairs. In this environment an optimal strategy maximizes the time spent in the normal operating state and consequently the rate of transaction processing. This paper seeks a checkpoint strategy which maximizes the probability of critical-task completion on a system with limited repairs. These systems can undergo failure and repair only until a repair time exceeds a specified threshold, at which time the system is deemed to have failed completely. For such systems, a model is derived which yields the probability of completing the critical task when each checkpoint operation has fixed cost. The optimal number of checkpoints can increase as system reliability improves. The model is extended to include a constraint which enforces timely completion of the critical task  相似文献   
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