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PubMed2004

[Should sex specific differences in venous diseases be explained by pregnancies and hormone intake?].

AIM OF THE STUDY: Diseases of the venous system are among the most frequently occurring diseases in the German population. However, the last comprehensive population-based German data were obtained in 1979. Since then, diagnostic methods have improved substantially. Here, we examine the prevalence of venous diseases in women and their association with pregnancies and intake of hormones. METHODS: We conducted a population-based cross-sectional study in Bonn and rural environments (Recruitment period: 11/2000 - 11/2001; response: 59 %; 3072 study participants (1350 men, 1722 women), 18 to 79 years of age; investigation: standardised medical history, physical examination, duplex sonography, photography and CEAP-classification of veins of the legs). The following definitions were used: 1) Varicosis: clinical classification C2-C6 (primary varicosis only, excluding those showing spider-bursts exclusively); 2) Chronic venous insufficiency (CVI): C3-C6. For women, the risk factors examined were the number of pregnancies (P) and intake of hormones. Odds ratios (OR) and 95 % confidence intervals (95 %-CI) were calculated by multiple logistic regression (adjusted for age, region of residence and socioeconomic status). In addition, never pregnant women and men were compared regarding the two outcome variables. RESULTS: 713 participants (23 %) had varicosis and 522 (17 %) CVI. The OR for women (reference group: men) was OR = 1.4, 95 %-CI: 1.25 - 1.79 (varicosis) and OR = 1.2, 95 %-CI: 0.93 - 1.42 (CVI). There was a positive dose-response relationship between the number of pregnancies and varicosis: 1 P: OR = 1.3 (95 %-CI: 0.89 - 1.96), 2 P: OR = 1.4 (95 %-CI: 1.00 - 2.07), 3 P: OR = 1.6 (95 %-CI: 1.05 - 2.41), 4 P: OR = 1.9 (95 %-CI: 1.18 - 3.20), > or = 5 P: OR = 2.2 (95 %-CI: 1.28 - 3.74) and this trend was similar for CVI. Never-pregnant women (n = 518) and men had a similar prevalence. We did not see a consistent effect of intake of hormones in varicosis (OR = 0.9 [95 %-CI: 0.68 - 1.22]), but a negative association with CVI (OR = 0.6 [95 %-CI: 0.47 - 0.89]). CONCLUSIONS: Our results confirm the known association between diseases of the venous system and pregnancies, which seem to explain a big share of the sex-specific differences in the prevalence of these diseases.

Adolescent↗

PubMed2004

[Does co-operation research provide approaches to explain the changes in the German hospital market?].

UNLABELLED: The German hospital market faces an extensive process of consolidation. In this change hospitals consider cooperation as one possibility to improve competitiveness. AIM: To investigate explanations of changes in the German hospital market by theoretical approaches of cooperation research. METHOD: The aims and mechanism of the theories, their relevance in terms of contents and their potential for empirical tests were used as criteria to assess the approaches, with current and future trends in the German hospital market providing the framework. Based on literature review, six theoretical approaches were investigated: industrial organization, transaction cost theory, game theory, resource dependency, institutional theory, and co-operative investment and finance theory. In addition, the data needed to empirically test the theories were specified. RESULTS: As a general problem, some of the theoretical approaches set a perfect market as a precondition. This precondition is not met by the heavily regulated German hospital market. Given the current regulations and the assessment criteria, industrial organization as well as resource-dependency and institutional theory approaches showed the highest potential to explain various aspects of the changes in the hospital market. CONCLUSION: So far, none of the approaches investigated provides a comprehensive and empirically tested explanation of the changes in the German hospital market. However, some of the approaches provide a theoretical background for part of the changes. As this dynamic market is economically of high significance, there is a need for further development and empirical testing of relevant theoretical approaches.

Cooperative Behavior↗

PubMed2006

An alternate hypothesis to explain the high frequency of "revertants" in hothead mutants in Arabidopsis.

Lolle et al. reported a high frequency of genomic changes in ARABIDOPSIS plants carrying the hothead mutation and proposed that the changes observed were the result of a gene correction system mediated by a hypothetical RNA cache. Here, we propose a very different hypothesis to explain the data reported by Lolle et al. Our hypothesis is based on a relatively straightforward developmental aberration in which maternal cells ("Legacy cells") fuse with the developing embryo, resulting in a chimera, which could then give rise to the aberrant genetic segregations reported by Lolle et al.

Arabidopsis↗

PubMed2005

Multivariate statistics of the pyrolysis products of high molecular components in pulping wastewaters to explain their toxicity.

BACKGROUND, AIM AND SCOPE: At present, large-scale paper manufacture involves delignification and bleaching by elemental chlorine free (ECF), or totally chlorine free (TCF) processes. The wastewater is purified by secondary treatment (mechanical, chemical and biological) which removes most of the toxic substances from the discharge. However, we found residual toxicity in the high molecular (> 1000 D) matter (HMWM) of the discharge by test of the RET (reverse electronic transfer) inhibition. This fraction consists mainly of polydispersed lignin (LIG) and carbohydrate (CH) macromolecules. Structural units in these molecules are studied by pyrolysis gas chromatography/mass spectrometry (Pyr-GC/MS). In the present work, our aim was to find out those structural units which could explain the RET toxicity of LIG or CH molecules. We compared statistically RET toxicity values of the HMWM samples from treated wastewaters of pilot pulping experiments and intensity variation of the pyrolysis product gas chromatograms of these samples. This application is a novel study procedure. METHODS: Pyrolysis products (Py-GC/MS results) and inhibition of RET (reverse electronic transport toxicity) as TU50 and TU20 of HMWM (High Molecular Weight Material; Mw > 1000 D) were compared by multivariate statistics. The samples were from laboratory pilot stages of TCF (Totally Chlorine Free) and ECF (Elemental Chlorine Free) manufacture of softwood pulp. Py-GC/MS was done without and with the addition of TMAH (Tetra Methyl Ammonium Hydroxide). The name and structure of each abundant fragment compound was identified from its retention time and mass spectrum compared to authentic reference compounds or literature. Four sets of Toxicity Units (TUs) and GC peak areas of the pyrolysis fragments were obtained. The data were normalized by division with LIG (lignin content of each sample). TU values were dependent and the fragment values independent (explanatory) variables in statistical treatments by SPSS system. Separate analyses of correlations, principal components (PCA) and stepwise multiple linear regression (SMLR) were performed from the four sample sets TCF and ECF with and without TMAH. RESULTS AND DISCUSSION: From the CH fragments, 2-furfural in TCF, and from the LIG fragments, styrene in ECF showed the highest probabilities of originating from source structures of toxicity. Other possible compounds in concern were indicated to be CH fragment 2-methyl-2-cyclopenten-1-one in ECF and LIG fragments 2-methoxy-4-methylphenol, 4,5-dimethoxy-2-methylphenol and 2-methylphenol in TCF.

Alkylating Agents↗

PubMed2000

Electrocardiographic presentation of blacks with first myocardial infarction does not explain race differences in thrombolysis administration.

BACKGROUND: Previous studies have suggested that thrombolysis is used less often in blacks than in whites. However, whether the greater prevalence of contraindications or less specific electrocardiographic manifestations of myocardial infarction (MI) account for this difference is unclear. METHODS AND RESULTS: We studied 498 consecutive patients (32% blacks) with first MI. Initial electrocardiograms were analyzed, blinded to race and outcome, for ST-segment deviation and bundle branch block to determine eligibility for thrombolysis. The relation of electrocardiographic eligibility for thrombolysis and actual use of thrombolysis in both races was explored. Among blacks, 45% received thrombolysis compared with 66% of whites (P <.001). A similar proportion of blacks and whites were eligible for thrombolysis (59% and 66% respectively, P =. 116), but 62% of electrocardiography-eligible blacks were treated with thrombolysis compared with 75% of whites (P =.016). After accounting for eligibility for electrocardiography and other clinical variables likely to affect the decision to administer thrombolysis by means of conditional logistic regression, blacks were still less likely to receive thrombolysis (relative risk 0.73; 95% confidence interval 0.55 to 0.97). CONCLUSIONS: We conclude that the differences in thrombolysis administration to blacks and whites are not accounted for by differences in electrocardiographic presentation or other measured variables. Unmeasured differences in clinical presentation of MI may explain racial differences in thrombolysis and merits further study.

Adult↗

PubMed1978

Explaining imaginal inference by operations in a propositional format.

Solving problems by imaginal inference often seems inefficient for an organism that is manipulating propositions. One explanation for the apparent inefficiency is that the problems are being solved not in propositional format by operations in an analogue format. Imaginal inference might then be the most efficient method compatible with the limitations inherent in the analogue format. In the present paper an alternative rationale is given for the use of imaginal inference by explaining how the processes involved in mental problem solving are related to those in perception: it is suggested that the mechanisms used in problem solving have evolved from a perceptual system in which hypotheses about events in the sensory field are generated from an internal representation of the world. This thesis denies that perception is passive and suggests that originally for perception. Acceptance of the thesis implies that the capabilities of a propositional format in problem solving would be limited. This limitation could account for the apparently inefficient use of that format in imaginal inference.

Biological Evolution↗

PubMed2002

Latency correction explains the classical geometrical illusions.

There is a significant delay between the time when light hits the retina and the time of the consequent percept. It has been hypothesized that the visual system attempts to correct for this latency by generating a percept representative of the way the world probably is at the time the percept is elicited, rather than a percept of the recent past. Here we show that such a 'perceiving the present' hypothesis explains a number of classical geometrical illusions: the Hering, Orbison, Müller-Lyer, Double Judd, Poggendorff, Corner, and Upside-down-T illusions. Each stimulus is perceived as it would project in the next moment were the observer moving through the scene the stimulus probably represents. We also examine one general class of predictions made by the hypothesis, and report psychophysical experiments confirming the predictions.

Humans↗

PubMed2004

Perceived contrast explains asymmetries in visual-search tasks with shaded stimuli.

Shaded stimuli have traditionally been used in the context of three-dimensional (3-D) shape perception. Many studies have shown a persistent asymmetry in that a circle filled with a shaded gradient that is dark at the top and bright at the bottom (top-dark circle) is much easier to locate among top-bright circles than in the opposite arrangement (a top-bright circle among top-dark circles). The immediate 3-D interpretation of top-dark and top-bright circles as hollows and protuberances, respectively, and the asymmetry just described have been explained in terms of 3-D percepts. The work described here challenges this view: the results of the first experiment show that top-dark circles are perceived as having 10% higher contrast than top-bright circles of the same physical contrast. Experiment 2 replicates classical visual-search experiments but adding a new condition where target and distractors were subjectively equated in contrast. For five of six subjects, the ubiquitous asymmetry disappears in this condition.

Adult↗

PubMed2004

Sexual selection explains Rensch's rule of size dimorphism in shorebirds.

Sexual size dimorphism shows a remarkably widespread relationship to body size in the animal kingdom: within lineages, it decreases with size when females are the larger sex, but it increases with size when males are the larger sex. Here we demonstrate that this pattern, termed Rensch's rule, exists in shorebirds and allies (Charadriides), and it is determined by two components of sexual selection: the intensity of sexual selection acting on males and the agility of the males' display. These effects are interactive so that the effect of sexual selection on size dimorphism depends on male agility. As a control, we also examine dimorphism in bill length, which is a functionally selected trait. As such, dimorphism in bill length neither exhibits Rensch's rule nor is associated with sexual selection and display. Our results show that variation among taxa in the direction and magnitude of sexual size dimorphism, as manifested as Rensch's rule, can be explained by the interaction between the form and strength of sexual selection acting on each sex in relation to body size.

Animals↗

PubMed2004

A biochemical oscillator explains several aspects of Myxococcus xanthus behavior during development.

During development, Myxococcus xanthus cells produce a series of spatial patterns by coordinating their motion through a contact-dependent signal, the C-signal. C-signaling modulates the frequency at which cells reverse their gliding direction. It does this by interacting with the Frz system (a homolog of the Escherichia coli chemosensory system) via a cascade of covalent modifications. Here we show that introducing a negative feedback into this cascade results in oscillatory behavior of the signaling circuit. The model explains several aspects of M. xanthus behavior during development, including the nonrandom distribution of reversal times, and the differences in response of the reversal frequency to both moderate and high levels of C-signaling at different developmental stages. We also propose experiments to test the model.

Bacterial Proteins↗

PubMed2004

Heterogeneity explains features of "anomalous" thermodynamics and statistics.

Phenomena characterized by power-law probability distributions abound in nature and the applied sciences. We show that many of these power laws are well described by the Student, or t, distribution, and we discuss the origin of this universality based on three examples (Brownian motion, Knudsen diffusion in rough pores, and bubbly multiphase flow). These case studies are representative for a large class of systems with heterogeneous features, examples of which can be found from Earth sciences to astrophysics, and even in the social sciences. We show that common forms of polydispersity, such as polydispersity arising naturally as a result of aggregation-fragmentation phenomena, typically lie at the basis of the observed scaling. We conclude that complicated arguments based on long-range correlations or nonergodicity are often incorrect or misleading in explaining many naturally observed power laws and, in particular, those described by the Student distribution.

Journal Article↗

PubMed2003

Single-locus heterotic effects and dominance by dominance interactions can adequately explain the genetic basis of heterosis in an elite rice hybrid.

The genetic basis of heterosis of an elite rice hybrid was investigated by using an "immortalized F(2)" population produced by randomly permutated intermating of 240 recombinant inbred lines from a cross between the parents of Shanyou 63, the most widely cultivated hybrid in China. Measurements of heterosis for crosses in the immortalized F(2) population were obtained from replicated field trials over 2 years by inter-planting the hybrids with the parental recombinant inbred lines. The analyses were conducted making use of a linkage map comprising 231 segregating molecular marker loci covering the entire rice genome. Heterotic effects were detected at 33 loci for the four traits with modified composite interval mapping. The heterotic loci showed little overlap with quantitative trait loci for trait performance, suggesting that heterosis and trait performance may be conditioned by different sets of loci. Large numbers of digenic interactions were resolved by using two-way ANOVA and confirmed by randomization tests. All kinds of genetic effects, including partial-, full-, and overdominance at single-locus level and all three forms of digenic interactions (additive by additive, additive by dominance, and dominance by dominance), contributed to heterosis in the immortalized F(2) population, indicating that these genetic components were not mutually exclusive in the genetic basis of heterosis. Heterotic effects at the single-locus level, in combination with the marginal advantages of double heterozygotes caused by dominance by dominance interaction at the two-locus level could adequately explain the genetic basis of heterosis in Shanyou 63. These results may help reconcile the century-long debate concerning the genetic basis of heterosis.

Analysis of Variance↗

PubMed2005

Destabilization of apoprotein is insufficient to explain Cu,Zn-superoxide dismutase-linked ALS pathogenesis.

The relative stabilities and structural properties of a representative set of 20 ALS-mutant Cu,Zn-superoxide dismutase apoproteins were examined by using differential scanning calorimetry and hydrogen-deuterium (H/D) exchange followed by MS. Contrary to recent reports from other laboratories, we found that ALS-mutant apoproteins are not universally destabilized by the disease-causing mutations. For example, several of the apoproteins with substitutions at or near the metal binding region (MBR) (MBR mutants) exhibited melting temperatures (Tm) in the range 51.6 degrees C to 56.2 degrees C, i.e., similar to or higher than that of the WT apoprotein (Tm = 52.5 degrees C). The apoproteins with substitutions remote from the MBR (WT-like mutants) showed a wide range of Tms, 40.0 degrees C to 52.4 degrees C. The H/D exchange properties of the mutants were also wide-ranging: the MBR mutant apoproteins exhibited H/D exchange kinetics similar to the WT apoprotein, as did some of the more stable WT-like mutant apoproteins, whereas the less stable apoproteins exhibited significantly less protection from H/D exchange than the WT apoprotein. Most striking were the three mutant apoproteins, D101N, E100K, and N139K, which have apparently normal metallation properties, and differ little from the WT apoprotein in either thermal stability or H/D exchange kinetics. Thus, the ALS mutant Cu,Zn-superoxide dismutase apoproteins do not all share reduced global stability, and additional properties must be identified and understood to explain the toxicity of all of the mutant proteins.

Amino Acid Substitution↗

PubMed2005

The Poggendorff illusion explained by natural scene geometry.

One of the most intriguing of the many discrepancies between perceived spatial relationships and the physical structure of visual stimuli is the Poggendorff illusion, when an obliquely oriented line that is interrupted no longer appears collinear. Although many different theories have been proposed to explain this effect, there has been no consensus about its cause. Here, we use a database of range images (i.e., images that include the distance from the image plane of every pixel in the scene) to show that the probability distribution of the possible locations of line segments across an interval in natural environments can fully account for all of the behavior of this otherwise puzzling phenomenon.

Databases, Factual↗

PubMed2005

Changes in hydrogen-bond strengths explain reduction potentials in 10 rubredoxin variants.

The rubredoxin from Clostridium pasteurianum (CpRd) provides an excellent system for investigating how the protein sequence modulates the reduction potential of the active site in an iron-sulfur protein. (15)N NMR spectroscopy has allowed us to determine with unprecedented accuracy the strengths of all six key hydrogen bonds between protein backbone amides and the sulfur atoms of the four cysteine residues that ligate the iron in the oxidized (Fe(III)) and reduced (Fe(II)) forms of wild-type CpRd and nine mutants (V44G, V44A, V44I, V44L, V8G, V8A, V8I, V8L, and V8G/V44G). The length (or strength) of each hydrogen bond was inferred from the magnitude of electron spin delocalized across the hydrogen bond from the iron atom onto the nitrogen. The aggregate lengths of these six hydrogen bonds are shorter in both oxidation states in variants with higher reduction potential than in those with lower reduction potential. Differences in aggregate hydrogen bonding upon reduction correlate linearly with the published reduction potentials for the 10 CpRd variants, which span 126 mV. Sequence effects on the reduction potential can be explained fully by their influence on hydrogen-bond strengths.

Binding Sites↗

PubMed2006

Peptide motifs of the single dominantly expressed class I molecule explain the striking MHC-determined response to Rous sarcoma virus in chickens.

Compared with the MHC of typical mammals, the chicken MHC is smaller and simpler, with only two class I genes found in the B12 haplotype. We make five points to show that there is a single-dominantly expressed class I molecule that can have a strong effect on MHC function. First, we find only one cDNA for two MHC haplotypes (B14 and B15) and cDNAs corresponding to two genes for the other six (B2, B4, B6, B12, B19, and B21). Second, we find, for the B4, B12, and B15 haplotypes, that one cDNA is at least 10-fold more abundant than the other. Third, we use 2D gel electrophoresis of class I molecules from pulse-labeled cells to show that there is only one heavy chain spot for the B4 and B15 haplotypes, and one major spot for the B12 haplotype. Fourth, we determine the peptide motifs for B4, B12, and B15 cells in detail, including pool sequences and individual peptides, and show that the motifs are consistent with the peptides binding to models of the class I molecule encoded by the abundant cDNA. Finally, having shown for three haplotypes that there is a single dominantly expressed class I molecule at the level of RNA, protein, and antigenic peptide, we show that the motifs can explain the striking MHC-determined resistance and susceptibility to Rous sarcoma virus. These results are consistent with the concept of a "minimal essential MHC" for chickens, in strong contrast to typical mammals.

Amino Acid Motifs↗

PubMed2006

Nature designs tough collagen: explaining the nanostructure of collagen fibrils.

Collagen is a protein material with superior mechanical properties. It consists of collagen fibrils composed of a staggered array of ultra-long tropocollagen (TC) molecules. Theoretical and molecular modeling suggests that this natural design of collagen fibrils maximizes the strength and provides large energy dissipation during deformation, thus creating a tough and robust material. We find that the mechanics of collagen fibrils can be understood quantitatively in terms of two critical molecular length scales chi(S) and chi(R) that characterize when (i) deformation changes from homogeneous intermolecular shear to propagation of slip pulses and when (ii) covalent bonds within TC molecules begin to fracture, leading to brittle-like failure. The ratio chi(S)/chi(R) indicates which mechanism dominates deformation. Our modeling rigorously links the chemical properties of individual TC molecules to the macroscopic mechanical response of fibrils. The results help to explain why collagen fibers found in nature consist of TC molecules with lengths in the proximity of 300 nm and advance the understanding how collagen diseases that change intermolecular adhesion properties influence mechanical properties.

Biomechanical Phenomena↗

PubMed2006

Early-phase transmission of Yersinia pestis by unblocked fleas as a mechanism explaining rapidly spreading plague epizootics.

Plague is a highly virulent disease believed to have killed millions during three historic human pandemics. Worldwide, it remains a threat to humans and is a potential agent of bioterrorism. Dissemination of Yersinia pestis, the etiological agent of plague, by blocked fleas has been the accepted paradigm for flea-borne transmission. However, this mechanism, which requires a lengthy extrinsic incubation period before a short infectious window often followed by death of the flea, cannot sufficiently explain the rapid rate of spread that typifies plague epidemics and epizootics. Inconsistencies between the expected rate of spread by blocked rat fleas and that observed during the Black Death has even caused speculation that plague was not the cause of this medieval pandemic. We used the primary vector to humans in North America, Oropsylla montana, which rarely becomes blocked, as a model for studying alternative flea-borne transmission mechanisms. Our data revealed that, in contrast to the classical blocked flea model, O. montana is immediately infectious, transmits efficiently for at least 4 d postinfection (early phase) and may remain infectious for a long time because the fleas do not suffer block-induced mortality. These factors match the criteria required to drive plague epizootics as defined by recently published mathematical models. The scenario of efficient early-phase transmission by unblocked fleas described in our study calls for a paradigm shift in concepts of how Y. pestis is transmitted during rapidly spreading epizootics and epidemics, including, perhaps, the Black Death.

Animals↗