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Short strong hydrogen bonds: can they explain enzymic catalysis?

It has been proposed that some remarkable enzymic catalytic effects can be explained by the existence of unusually strong hydrogen bonds within the enzyme's active site. Although such hydrogen bonds may be short, and may have unusual properties, there is no evidence that unusually strong hydrogen bonds exist in solution or in enzyme active sites. Thus there is no basis for invoking strong hydrogen bonds to explain enzymic rate enhancements.

Catalysis↗

Does low birth weight help to explain the increased prevalence of asthma among African-Americans?

BACKGROUND: Racial disparities in asthma prevalence are not fully explained. Previous studies have reported an association between low birth weight (LBW) and asthma. African-Americans are at a heightened risk for both conditions. OBJECTIVE: The objective of this analysis was to study a sample of suburban schoolchildren to determine if increased asthma prevalence in African-Americans could be explained by report of LBW. METHODS: Logistic regression was used to analyze telephone survey and clinical data for a sample of 126 children, aged 6 to 8 years. RESULTS: African-Americans reported asthma (12.5% vs 5.3%) and LBW (16.6% vs 3.9%) more frequently than non-African-Americans. After adjusting for LBW, the odds ratio for the association of African-American race to asthma was reduced from 2.6 to 1.8, whereas LBW remained independently associated with asthma, adjusted odds ratio = 5.1 (95% CI:1.4 to 18.9). The adjusted population risk for asthma due to LBW was 0.31. CONCLUSIONS: High rates of LBW for African-Americans may contribute to racial disparities in asthma prevalence.

Asthma↗

When pain is not fully explained by organic lesion: a psychiatric perspective on chronic pain patients.

Recent literature demonstrates the relationship between psychopathology and medically unexplained pain, even if the results of several studies show a high degree of variability. The present study was planned with the aim of analysing both the possible relationship between the level (low/high) of organicity and the presence of psychopathology, and the degree to which these differences are related to methodological problems. Between 1998 and 2000, four hundred and thirty six consecutive patients seen at the Pisa Pain Therapy and Palliative Care Unit were requested to fill in a questionnaire, the GHQ-12, to screen the subjects probably with (GHQ-12>3) or without (GHQ-12</=3) psychopathology. All the patients scoring above the GHQ-12 threshold (score of 3), and a randomised sample of those scoring below the GHQ-12 threshold, were included in the study. These patients were then interviewed using three different instruments: the Mini International Neuropsychiatric Interview (MINI) for a standardised psychiatric diagnosis, the Semistructured Interview for Depression (SID) for the characterisation of temperament, and the Italian Pain Questionnaire (IPQ) for the evaluation of pain. Our results suggest that Somatisation Disorders are more frequent in the medically unexplained pain group than in the medically explained pain group, whereas the other psychiatric disorders have a similar prevalence in the two pain groups. Mood and anxiety disorders are correlated with high scores on GHQ-12 and medically explained pain has a higher prevalence of GHQ-12>3 than the medically unexplained pain group. These results confirm that methodology is an important factor that could modify results in psychiatric research. Both medically unexplained pain and the presence of psychopathology are significantly correlated with sex, and age: females and young patients have a higher prevalence of psychopathology and of medically unexplained pain. Our results suggest that in the correlation between the low organicity of pain and psychopathology, the age and sex play a relevant role.

Age Factors↗

Untreated growth hormone deficiency explains premature mortality in patients with hypopituitarism.

Untreated growth hormone deficiency (GHD) might explain the increased mortality reported in patients with hypopituitarism. These statistics appear to be largely attributable to cardiovascular disease. Differences in fibrinolytic activity regulators, together with dyslipidaemias, abdominal obesity and raised blood pressure in hypopituitarism might explain this increased risk. There is growing evidence that treatment with growth hormone (GH) can rectify most of the cardiovascular abnormalities associated with GHD. The reported improved psychosocial well-being in response to GH treatment may also be important in lowering risk in this group of patients.

Cardiovascular Diseases↗

Do the abilities of children with cerebral palsy explain their activities and participation?

The aim of this study was to use family-assessed instruments and details of children's impairments to explore factors affecting the activities and participation of children with cerebral palsy (CP). A postal survey was conducted with families of a geographically defined population of children with CP aged 6 to 12 years. Family-assessed indices of children's activities and participation were the Activities Scale for Kids (ASK) and Lifestyle Assessment Questionnaire (LAQ-CP). Families also assessed children's abilities using the Gross Motor Function and Manual Ability Classification Systems (GMFCS; MACS). Details of children's impairments were available from the 4Child epidemiological database and used with the GMFCS and MACS as explanatory variables in multiple regression analyses to identify their effect on children's activities and participation. Families of 175/314 (56%) children returned an assessment using the GMFCS and 129 (41%) children participated fully by returning all the questionnaires. Full participants (72 males, 57 females) did not differ from those who did not take part by their age, sex, CP characteristics, or associated impairments: GMFCS Level I-25, Level II-43, Level III-15, Level IV-14, Level V-23; MACS Level I-14, Level II-30, Level III-18, Level IV-13, Level V-13. Scores for the ASK and LAQ-CP Physical Independence and Mobility domains were predicted well by children's movement, manual, and intellectual disability, and also, to some extent, by the presence of seizures or speech problems. LAQ-CP domains for Economic and Clinical Burden and Social Integration were not well explained by children's abilities and impairments. Family assessment, therefore, offers a useful method for measuring children's activities and participation; however, currently available instruments do not fully represent all the domains in the International Classification of Functioning, Disability and Health. Children's abilities only partially explain their activities and participation.

Aptitude↗

Can biased symptom perception explain false-alarm choking sensations?

BACKGROUND: Breathlessness in asthma often cannot be explained with objective variables indicating airways obstruction. The hypothesis that unrealistic breathlessness results from false interpretation of sensations was tested. METHODS: Sixty-four children and adolescents with asthma, aged 9-18 years, were randomly assigned to; (1) standardized physical exercise for induction of general symptoms; (2) equipment causing itching through skin irritation; or (3) physical exercise combined with equipment causing itching through skin irritation. Pre-test and post-test measures were: lung function; breathlessness; general symptoms; itching; state anxiety; and worry. RESULTS: Lung function decreased within normal parameters (3.8%, 1.1%, 2.6%, respectively) and did not differ significantly between conditions. Breathlessness increased significantly after exercise, particularly in condition 3. Breathlessness correlated with general symptoms and worrying, but not with changes in lung function, age, or asthma severity. CONCLUSION: Biased symptom perception can explain unrealistic breathlessness. Prerequisites are situational cues triggering selective perception and ambiguous sensations associated with the anticipated (feared) physical state. Excessive breathlessness may often warrant objective confirmation by means of lung-function testing.

Adolescent↗

Schizophrenia among Surinamese in the Netherlands: high admission rates not explained by high emigration rates.

BACKGROUND: A high risk of schizophrenia has been found among Caribbean immigrants in the Netherlands and Great Britain. One hypothesis to explain these findings is that patients with a diagnosis of schizophrenia or patients with symptoms of psychosis not specifically diagnosed, emigrate more than the general population. Such selection might account for high rates of Surinamese patients with a diagnosis of schizophrenia in Netherlands psychiatric hospitals. We examined this hypothesis. METHODS: The files of patients with schizophrenia or patients suffering from unspecified psychosis were selected from the archives of the National Psychiatric Hospital in Surinam. These patients were traced to investigate patterns of emigration. Data from the Central Bureau for Statistics in the Netherlands and from the Central Population Bureau in Surinam provided the percentage of the general Surinamese population that emigrated to the Netherlands. The difference between the two percentages was evaluated using the chi-squared test. Using the same method the percentage of remigration from the Netherlands among Surinamese patients was compared with the percentage of remigration among the general Surinamese population. RESULTS: Surinamese patients with schizophrenia or unspecified psychosis did not emigrate more frequently to the Netherlands compared with the general Surinamese population. They did remigrate significantly more frequently. CONCLUSION: High migration rates do not explain the high hospital admission rates for schizophrenia among Surinamese in the Netherlands.

Adolescent↗

Color constancy in natural scenes explained by global image statistics.

To what extent do observers' judgments of surface color with natural scenes depend on global image statistics? To address this question, a psychophysical experiment was performed in which images of natural scenes under two successive daylights were presented on a computer-controlled high-resolution color monitor. Observers reported whether there was a change in reflectance of a test surface in the scene. The scenes were obtained with a hyperspectral imaging system and included variously trees, shrubs, grasses, ferns, flowers, rocks, and buildings. Discrimination performance, quantified on a scale of 0 to 1 with a color-constancy index, varied from 0.69 to 0.97 over 21 scenes and two illuminant changes, from a correlated color temperature of 25,000 K to 6700 K and from 4000 K to 6700 K. The best account of these effects was provided by receptor-based rather than colorimetric properties of the images. Thus, in a linear regression, 43% of the variance in constancy index was explained by the log of the mean relative deviation in spatial cone-excitation ratios evaluated globally across the two images of a scene. A further 20% was explained by including the mean chroma of the first image and its difference from that of the second image and a further 7% by the mean difference in hue. Together, all four global color properties accounted for 70% of the variance and provided a good fit to the effects of scene and of illuminant change on color constancy, and, additionally, of changing test-surface position. By contrast, a spatial-frequency analysis of the images showed that the gradient of the luminance amplitude spectrum accounted for only 5% of the variance.

Color↗

Exposure-pathway models explain causality in whole sediment toxicity tests.

Measurements of lethal effect concentrations (LC50) and bioaccumulation following water-only and whole-sediment exposures of the amphipod, Melita plumulosa, and the bivalve, Tellina deltoidalis, to copper, were combined with bioenergetic-based kinetic models of exposure pathways to explain causality in whole-sediment toxicity tests. For both organisms, lethal body concentrations (LBCs) were greater for water-only exposures than for sediment exposures and indicated that the rate of copper accumulation and/or the mode of toxicity of copper assimilated were different for dissolved and particulate phases. The net assimilation of copper, expressed as a lethal exposure concentration (LEC) that was independent of the postexposure copper efflux, was shown to better explain the observed toxicity. The LEC of copper was the same for both water-only and whole-sediment toxicity tests. It is predicted that, for each species, a large range of effect concentrations may be measured for sediments having the same total copper concentration. These are conditional effect concentrations, as their value will be determined by total copper concentrations, partitioning (Kd) relationships (sediment properties), organism physiology (uptake rates from waters, assimilation efficiencies from solids), and organism feeding behavior (feeding selectivity). The importance of these factors to the development of sediment quality guidelines for metals based on species sensitivity distributions is discussed.

Amphipoda↗

Ambident reactivity of the thiocyanate anion revisited: can the product ratio be explained by the hard soft acid base principle?

Laser flash photolysis and stopped-flow methods have been employed to determine the kinetics of the reactions of benzhydrylium ions with both termini of the thiocyanate ion. In contrast to previous investigations which reported sulfur/nitrogen ratios of k(S)/k(N) = 2-10 for the reactions of carbocations with SCN(-), values of k(S)/k(N) = 10(3)-10(4) are now derived from absolute rate constants. This discrepancy is explained by the fact that the data determined in this investigation are the first which refer to activation-controlled attack of carbocations at both termini of the thiocyanate ion, while previous reactivity ratios included diffusion-controlled reactions. It is concluded that the selectivities of the reactions of carbocations with the thiocyanate ion cannot be explained by the hard soft acid base principle.

Journal Article↗

Intensity and persistence profiles of flavor compounds in synthetic solutions. Simple model for explaining the intensity and persistence of their aftersmell.

Hydroalcoholic solutions containing a single aroma-active compound were evaluated by a sensory panel to determine the difference between ortho and retronasal odor intensities (DeltaI(ro)), buccal savoring, and aftersmell duration. Eight compounds were used. Buccal perception seems to be just a physiologically restricted form of retronasal perception. DeltaI(ro) values were dependent on the panel, although results from the two panels were significantly correlated. Such differences and the aftersmell persistence were also significantly correlated with different physicochemical parameters related to volatility. A simple model to explain such dependence is proposed. The model considers the mouth-throat system as a perfect mixing tank with a finite amount of odorants being progressively diluted by swallowing and purging (both taken as continuous processes). Retronasal intensity is modeled from the odor properties of the liquid in such a tank calculated from orthonasal odor intensity versus concentration (I/log C) curves. The model explains successfully experimental results and has also been successfully applied to instrumental data from other authors.

Alcohols↗

Impact ionization can explain carrier multiplication in PbSe quantum dots.

The efficiency of conventional solar cells is limited because the excess energy of absorbed photons converts to heat instead of producing electron-hole pairs. Recently, efficient carrier multiplication has been observed in semiconductor quantum dots. In this process, a single, high-energy photon generates multiple electron-hole pairs. Rather exotic mechanisms have been proposed to explain the efficiency of carrier multiplication in PbSe quantum dots. Using atomistic pseudopotential calculations, we show here that the more conventional impact ionization mechanism, whereby a photogenerated electron-hole pair decays into a biexciton in a process driven by Coulomb interactions between the carriers, can explain both the rate (<<1 ps) and the energy threshold ( approximately 2.2 times the band gap) of carrier multiplication, without the need to invoke alternative mechanisms.

Computer Simulation↗

A homeostatic model of oxidative damage explains paradoxes observed in earlier aging experiments: a fusion and extension of older theories of aging.

The Rate of Living and the Threshold Theories of Aging are two contradicting approaches used to explain experimental facts about aging in fruit flies. In this paper we suggest an approach that unifies these theories and removes the contradiction. The approach involves quantitative description of the oxidative stress theory of aging, which is presented in the form of a mathematical homeostatic model. The crucial variable in the model is called 'homeostatic capacity', which is analogous to the classical notion of vitality. We model the process of aging as the age-related accumulation of damage produced by oxidative stress, which reduces the homeostatic capacity of the organism. The model is tested with the experimental data obtained in the classical experiments by Maynard Smith in 1958-1963. Our homeostatic model explains the well-known results of these experiments more accurate than any one of the early theories of aging. We form an hypothesis about the mechanisms underlying the results observed in the experiments and analyze a possible interplay of these mechanisms. Our virtual replication of Maynard Smith's classical experiments demonstrates that mathematical modeling can be a powerful tool to reveal and investigate the inherent genetic and physiological processes underlying the data observed in complicated insect experiments.

Aging↗

Explained and unexplained medical symptoms in generalized anxiety and panic disorder: relationship to the somatoform disorders.

We have examined the numbers and types of symptoms in a sample of 90 patients with generalized anxiety disorder (GAD) and 77 patients with panic disorder (PD) collected from six different sites during the conduct of a multicenter clinical trial. This information was obtained utilizing the Health Questionnaire, a 47-item self-report list of medical symptoms, patterned after the Somatization Disorder section of the Diagnostic Interview Schedule. Although the patients in this sample had a wide variety of medically explained and unexplained physical symptoms, none of them qualified for a diagnosis of somatization disorder by DSM-III-R criteria. GAD and PD patients reported remarkably similar numbers of explained and unexplained medical symptoms. The panoply of somatic symptoms presented by these patients presents a formidable diagnostic challenge for clinicians. These findings suggest that the pattern of overutilization of medical services that is well documented for PD patients may also be found for GAD patients.

Adult↗

Explaining sexual harassment judgments: looking beyond gender of the rater.

In two decades of research on sexual harassment, one finding that appears repeatedly is that gender of the rater influences judgments about sexual harassment such that women are more likely than men to label behavior as sexual harassment. Yet, sexual harassment judgments are complex, particularly in situations that culminate in legal proceedings. And, this one variable, gender, may have been overemphasized to the exclusion of other situational and rater characteristic variables. Moreover, why do gender differences appear? As work by Wiener and his colleagues have done (R. L. Wiener et al., 2002; R. L. Wiener & L. Hurt, 2000; R. L. Wiener, L. Hurt, B. Russell, K. Mannen, & C. Gasper, 1997), this study attempts to look beyond gender to answer this question. In the studies reported here, raters (undergraduates and community adults), either read a written scenario or viewed a videotaped reenactment of a sexual harassment trial. The nature of the work environment was manipulated to see what, if any, effect the context would have on gender effects. Additionally, a number of rater characteristics beyond gender were measured, including ambivalent sexism attitudes of the raters, their judgments of complainant credibility, and self-referencing that might help explain rater judgments. Respondent gender, work environment, and community vs. student sample differences produced reliable differences in sexual harassment ratings in both the written and video trial versions of the study. The gender and sample differences in the sexual harassment ratings, however, are explained by a model which incorporates hostile sexism, perceptions of the complainants credibility, and raters' own ability to put themselves in the complainant's position (self-referencing).

Adult↗

General slowing alone cannot explain age-related search effects: reply to Cerella (1991)

Cerella (1991) has argued that the performance of older adults in the Fisk and Rogers (1991) study is a linear function of the performance of younger adults that is independent of task-specific cognitive requirements. We demonstrate that this is not the case. First, we show that the scatter plot analyses used by Cerella can hide the very task-specific age-related slowing they were designed to reveal. Second, we demonstrate that the percentage of variance explained by such analyses can be misleading. Third, we show that there are reliable differences across tasks in the parameters relating younger and older adults' performance. Finally, we argue that the general, task-independent proportionate slowing that Cerella suggested explains so much of the variance in age-related performance is actually an average slowing that is a function of a relatively small task-independent and a relatively large task-dependent factor.

Adult↗

Usefulness of the protection motivation theory in explaining hearing protection device use among male industrial workers.

The present study examined the usefulness of personal variables: noise annoyance, and components of the protection motivation theory (R. W. Rogers, 1983) along with social-organizational factors in explaining hearing protection device (HPD) use among Israeli manufacturing workers. Participants were 281 men exposed to harmful noise levels for which routine HPD use is required by regulation. In practice, 3 HPD user groups were identified: nonusers (n = 38), occasional users (n = 125), and regular users (n = 118). HPD use was objectively verified. HPD use was primarily related to the personal variables but not to management pressure, coworker pressure, or family support. The most powerful predictors of HPD use were perceived self-efficacy (for long-term HPD use), perceived susceptibility (to hearing loss), and noise annoyance, together explaining 48% of the outcome variance. These findings have implications for interventions aimed at motivating workers to use HPDs regularly.

Adolescent↗

On measures of explained variance in nonrecursive structural equation models.

Whereas measures of explained variance in a regression and an equation of a recursive structural equation model can be simply summarized by a standard R2 measure, this is not possible in nonrecursive models in which there are reciprocal interdependencies among variables. This article provides a general approach to defining variance explained in latent dependent variables of nonrecursive linear structural equation models. A new method of its estimation, easily implemented in EQS or LISREL and available in EQS 6, is described and illustrated.

Analysis of Variance↗