1,204 research outputs found
Integrable models of galactic discs with double nuclei
We introduce a new class of 2-D mass models, whose potentials are of
St\"ackel form in elliptic coordinates. Our model galaxies have two separate
strong cusps that form double nuclei. The potential and surface density
distributions are locally axisymmetric near the nuclei and become {\it highly}
non-axisymmetric outside the nucleus. The surface density diverges toward the
cuspy nuclei with the law . Our model is sustained by
four general types of regular orbits: {\it butterfly}, {\it nucleuphilic
banana}, {\it horseshoe} and {\it aligned loop} orbits. Horseshoes and
nucleuphilic bananas support the existence of cuspy regions. Butterflies and
aligned loops control the non-axisymmetric shape of outer regions. Without any
need for central black holes, our distributed mass models resemble the nuclei
of M31 and NGC4486B. It is also shown that the self-gravity of the stellar disc
can prevent the double nucleus to collapse.Comment: 8 pages, accepted for publication in MNRA
Prevalence of asthma symptoms in Golestan schoolchildren aged 6–7 and 13–14 years in Northeast Iran
Asthma is the most common chronic disease among children, and its incidences are often imminent among elementary schoolchildren. This study aimed to examine the prevalence of asthma symptoms in Golestan schoolchildren aged 6–7 and 13–14 years in Northeast Iran. The prevalence rate was compared according to age group (aged 6–7 years vs. aged 13–14 years) and gender (male vs. female). In this cross-sectional study, 1706 Iranian schoolchildren aged 6–7 and 13–14 years in Golestan Province were enrolled. Participants completed questionnaires between February and July 2014. Asthma symptoms were assessed using the questionnaire of the International Study of Asthma and Allergies in Childhood protocol in Persian. The logistic regression model was used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of the asthma symptoms for each of the gender and age groups. The prevalence rates of “current asthma” symptoms and “asthma ever” in all the children were estimated as 9.5% and 7.5%, respectively. The prevalence of asthma (“asthma ever” and “wheezing in the past 12 months”) in junior high schoolchildren (aged 13–14 years) is higher than that in elementary schoolchildren (aged 6–7 years) (P < 0.05). The prevalence of the severity of wheezing in girls is lower than that in boys (OR = 1.7, 95%CI = 1.06–2.96, P = 0.02). Asthma is still a major public health problem. This study shows that the prevalence of the asthma symptoms in boys is lower than that in girls in both age groups, and the severity of asthma in girls is higher than that in boys aged 13–14 years. © 2016 Higher Education Press and Springer-Verlag Berlin Heidelber
Theory of Nucleosome Corkscrew Sliding in the Presence of Synthetic DNA Ligands
Histone octamers show a heat-induced mobility along DNA. Recent theoretical
studies have established two mechanisms that are qualitatively and
quantitatively compatible with in vitro experiments on nucleosome sliding:
Octamer repositiong through one-basepair twist defects and through ten-basepair
bulge defects. A recent experiment demonstrated that the repositioning is
strongly suppressed in the presence of minor-groove binding DNA ligands. In the
present study we give a quantitative theory for nucleosome repositioning in the
presence of such ligands. We show that the experimentally observed octamer
mobilities are consistent with the picture of bound ligands blocking the
passage of twist defects through the nucleosome. This strongly supports the
model of twist defects inducing a corkscrew motion of the nucleosome as the
underlying mechanism of nucleosome sliding. We provide a theoretical estimate
of the nucleosomal mobility without adjustable parameters, as a function of
ligand concentration, binding affinity, binding site orientiation, temperature
and DNA anisotropy. Having this mobility at hand we speculate about the
interaction between a nucleosome and a transcribing RNA polymerase and suggest
a novel mechanism that might account for polymerase induced nucleosome
repositioning.Comment: 23 pages, 4 figures, submitted to J. Mol. Bio
Lead contamination in fishes of the Kor River
Lead concentration in muscle, liver, kidney, brain and gonad tissues of two cyprinid fishes, Cyprinus carpio and Copoeta spp., from three sections of the upper, middle and lower parts of the Kor River was evaluated in 2006. Totally 225 specimens were caught for this purpose (75 specimens from each zone). Tissue samples were digested in acid and their lead concentrations were assayed by ICP method. Statistical analysis of data showed significantly (p0.05) were seen between sexes and species. The same pattern of contamination was also observed in water and sediment samples from three sampling zones. The maximum amount of lead measured in this study (1.85mg/kg), was, however, less than the maximum allowance in fish tissues by European Unions
Iodination of Alcohols over Keggin-type Heteropoly Compounds: A Simple, Selective and Expedient Method for the Synthesis of Alkyl Iodides
Different catalysts derived from Keggin-type heteropoly compounds were prepared and their catalytic activities have been compared in the iodination of benzyl alcohol with KI under mild reaction conditions. A high catalytic activity was found over tungstophosphoric acid supported on silica and titania. The effect of catalyst loading, iodine source and the nature of substituents on the aromatic ring of benzyl alcohol were investigated. Finally, several competitive reactions were studied between structurally diverse alcohols. This protocol provides a mild and expedient way for the conversion of various alcohols to their corresponding alkyl iodides with high selectivity.Keywords: Keggin-type Heteropoly Compounds, Supported Catalyst, Alcohols, Alkyl Iodides, Potassium Iodid
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