An exemplar-based random walk model of speeded classification

The authors propose and test an exemplar-based random walk model for predicting response times in tasks of speeded, multidimensional perceptual classification. The model combines elements of R. M. Nosofsky's (1986) generalized context model of categorization and G. D. Logan's (1988) instance-based model of automaticity. In the model, exemplars race among one another to be retrieved from memory, with rates determined by their similarity to test items. The retrieved exemplars provide incremental information that enters into a random walk process for making classification decisions. The model predicts correctly effects of within- and between-categories similarity, individual-object familiarity, and extended practice on classification response times. It also builds bridges between the domains of categorization and automaticity.     

Spatial learning deficits in mice with a targeted glucocorticoid receptor gene disruption

Previous studies in rats using the Morris water maze suggested that the processing of spatial information is modulated by corticosteroid hormones through mineralocorticoid and glucocorticoid receptors in the hippocampus. Mineralocorticoid receptors appear to be involved in the modulation of explorative behaviour, while additional activation of glucocorticoid receptors facilitates the storage of information. In the present study we used the water maze task to examine spatial learning and memory in mice homozygous and heterozygous for a targeted disruption of the glucocorticoid receptor gene. Compared with wild-type controls, homozygous and heterozygous mice were impaired in the processing of spatial but not visual information. Homozygous mutants performed variably during training, without specific platform-directed search strategies. The spatial learning disability was partly compensated for by increased motor activity. The deficits were indicative of a dysfunction of glucocorticoid receptors as well as of mineralocorticoid receptors. Although the heterozygous mice performed similarly to wild-type mice with respect to latency to find the platform, their strategy was more similar to that of the homozygous mice. Glucocorticoid receptor-related long-term spatial memory was impaired. The increased behavioural reactivity of the heterozygous mice in the open field points to a more prominent mineralocorticoid receptor-mediated function. The findings indicate that (i) the glucocorticoid receptor is of critical importance for the control of spatial behavioural functions, and (ii) mineralocorticoid receptor-mediated effects on this behaviour require interaction with functional glucocorticoid receptors. Until the development of site-specific, inducible glucocorticoid receptor mutants, glucocorticoid receptor-knockout mice present the only animal model for the study of corticosteroid-mediated effects in the complete absence of a functional receptor.     

Induction of a Citrus gene highly homologous to plant and yeast thi genes involved in thiamine biosynthesis during natural and ethylene-induced fruit maturation

In response to a light pulse, hamsters normally generate phase advances that are positively correlated with the length of their circadian period (tau). To determine whether this is a general property of the phase-shifting oscillator, the present study looked for a correlation between tau and phase-advance size not only for photic but also for nonphotic shifts. Syrian hamsters, Mesocricetus auratus, were entrained to light-dark cycles with a periodicity of either 23.67 h (the short-T group) or 24.33 h (the long-T group); after release into constant darkness, the short-T and long-T groups exhibited short and long taus, respectively. These animals were then induced to run in a novel exercise wheel for 3 h, starting at circadian time (CT) 7, or were exposed to 20 min of light, starting at CT 19. The size of the ensuing phase advances did not differ between the short-T and long-T groups not only for the nonphotic stimulus but also for the photic one, an unexpected result for the photic stimulus. Within the short-T groups for photic and nonphotic stimuli, the shorter tau was, the larger the phase advances were, another unexpected relationship. Another experiment where phase delays were induced by light pulses at CT 15 also failed to yield significant differences between the short-T and long-T groups. Independently of their after-effects on tau, T cycles may influence the capacity of the pacemaker to phase shift in ways that are still unclear but at least similar for both photic and nonphotic shifts.     

Cavitation Damage of the single-crystal nickel-base superalloy SRR99 during creep at 850°C

Various heat treatments of the single-crystal nickel-base superalloy SRR99 have been carried out to produce a wide range of initial γ′ phase morphology. The cavitation damage has been studied after creep fracture at 850°C and stresses between 400MPa and 650 Mpa. The crep fracture surfaces and longitudinal sections of crept specimens have been examined by image analysing system in order to determine the size distribution and the area fraction of (001)-planes cracks on fracture surface characterise the creep crack damage level. The cracking morphology in fractured material as a function of stress and γ′-phase size has also been investigated. The results show, that crack propagation occurred anisotropically on (001) crystallographic planes perpendicular to the aplied stress along the γ/γ′ interfaces. It was found, that creep cracks dependent on the shape and size of γ′-phases developing at the temperature and stress level.     

Clonidine therapy for comorbid attention deficit hyperactivity disorder and conduct disorder: preliminary findings in a children's inpatient unit

This retrospective study examined the clinical course of 18 prepubertal boys (aged 6 to 12) who had dual diagnoses of attention deficit hyperactivity disorder and conduct disorder and who received clonidine on an inpatient basis after failed trials of conventional drug therapy, consisting predominantly of psychostimulants. The effects of clonidine were assessed during inpatient treatment and after discharge at intervals of 1 to 2 months. Eleven (61%) of the children had marked improvement as measured by clinical impression. Transient sedation lasting 2 to 3 days occurred after initial administration or dosage increase; otherwise, clonidine was well tolerated. Our findings suggest that clonidine may prove to be an alternative treatment of comorbid attention deficit hyperactivity disorder and conduct disorder.     

Plasma Asp13-Ki-ras oncoprotein expression in vinyl chloride monomer workers in Taiwan

Vinyl chloride (VC) workers are known to be at risk for development of liver angiosarcoma, a rare tumor. Previously, more than 80% of VC workers with liver angiosarcoma have been found to have an Asp-13 c-Ki-ras oncogene mutation, and more than 50% of VC-exposed workers without liver tumors were found to have Asp13-Ki-ras oncoprotein in their plasma. Some workers in Taiwan had also been exposed to VC, and some have contracted liver tumors. In this study, we used enhanced chemiluminescence Western blotting to detect Asp13-p21-Ki-ras in the sera of VC-exposed workers in Taiwan. There were 14 of 113 (12.4%) VC workers positive for the Asp13-Ki-ras oncoprotein in plasma, but 0 of 18 controls were positive. There were 10 of 69 (14.5%) plasma-positives among the more highly exposed (> 1000 ppm-months) workers and 4 of 48 (9.1%) plasma-positives among the lesser exposed (< or = 1000 ppm-months). Compared with the unexposed controls, the odds ratios (and 95% confidence intervals [CI]) for plasma-positivity were 4.11 (95% CI = 0.21, 80.4) in the lower-exposed workers and 6.53 (95% CI = 0.37, 116.9) in the higher-exposed workers, and there was a linear trend between exposure and plasma-positivity (P = 0.073). After adjusting for age and drinking status, the odds ratios (and 95% CIs) were 1.64 (95% CI = 0.17, 15.8), and 2.65 (95% CI = 0.42, 16.8), respectively, and there was a significant linear trend between exposure and plasma-positivity (P = 0.048). In summary, Asp13-Ki-ras oncoprotein can be found in the plasma of VC workers in Taiwan, and a significant dose-response relationship exists between plasma oncoprotein expression and VC exposure.     

Genetic evidence for the role of isocytochrome c2 in photosynthetic growth of Rhodobacter sphaeroides Spd mutants

In Rhodobacter sphaeroides, cytochrome c2 (cyt c2)-deficient mutants are photosynthetically incompetent (PS-). However, mutations which suppress the photosynthetic deficiency (spd mutations) of cyt c2 mutants increase the levels of a cyt c2 isoform, isocyt c2. To determine whether isocyt c2 was required for photosynthetic growth of Spd mutants, we used Tn5 mutagenesis to generate a PS- mutant (TP39) that lacks both cyt c2 and isocyt c2. DNA sequence analysis of wild-type DNA that restores isocyt c2 production and photosynthetic growth to TP39 indicates that it encodes the isocyt c2 structural gene, cycI. The Tn5 insertion in TP39 is approximately 1.5 kb upstream of cycI, and our results show that it is polar onto cycI. The cycI gene has been physically mapped to a region of chromosome I that is approximately 700 kb from the R. sphaeroides photosynthetic gene cluster. Construction of a defined cycI null mutant and complementation of several mutants with the cycI gene under the control of the cyt c2 promoter region indicate that an increase in the levels of isocyt c2 alone is necessary and sufficient for photosynthetic growth in the absence of cyt c2. The data are discussed in terms of the obligate role of isocyt c2 in cyt c2-independent photosynthesis of R. sphaeroides.