Collimation of a spherical collisionless particles stream in Kerr space-time

We examine the propagation of collisionless particles emitted from a spherical shell to infinity. The number distribution at infinity, calculated as a function of the polar angle, exhibits a small deviation from uniformity. The number of particles moving from the polar region toward the equatorial plane is slightly larger than that of particles in the opposite direction, for an emission radius $> 4.5M$ in extreme Kerr space-time. This means that the black hole spin exerts an anti-collimation effect on the particles stream propagating along the rotation axis. We also confirm this property in the weak field limit. The quadrupole moment of the central object produces a force toward the equatorial plane. For a smaller emission radius $r<4.5M$, the absorption of particles into the black hole, the non-uniformity and/or the anisotropy of the emission distribution become much more important.Comment: 11 pages, 8 figures; accepted for publication in CQ

Fusing data mining, machine learning and traditional statistics to detect biomarkers associated with depression

BACKGROUND: Atheoretical large-scale data mining techniques using machine learning algorithms have promise in the analysis of large epidemiological datasets. This study illustrates the use of a hybrid methodology for variable selection that took account of missing data and complex survey design to identify key biomarkers associated with depression from a large epidemiological study. METHODS: The study used a three-step methodology amalgamating multiple imputation, a machine learning boosted regression algorithm and logistic regression, to identify key biomarkers associated with depression in the National Health and Nutrition Examination Study (2009-2010). Depression was measured using the Patient Health Questionnaire-9 and 67 biomarkers were analysed. Covariates in this study included gender, age, race, smoking, food security, Poverty Income Ratio, Body Mass Index, physical activity, alcohol use, medical conditions and medications. The final imputed weighted multiple logistic regression model included possible confounders and moderators. RESULTS: After the creation of 20 imputation data sets from multiple chained regression sequences, machine learning boosted regression initially identified 21 biomarkers associated with depression. Using traditional logistic regression methods, including controlling for possible confounders and moderators, a final set of three biomarkers were selected. The final three biomarkers from the novel hybrid variable selection methodology were red cell distribution width (OR 1.15; 95% CI 1.01, 1.30), serum glucose (OR 1.01; 95% CI 1.00, 1.01) and total bilirubin (OR 0.12; 95% CI 0.05, 0.28). Significant interactions were found between total bilirubin with Mexican American/Hispanic group (p = 0.016), and current smokers (p&lt;0.001). CONCLUSION: The systematic use of a hybrid methodology for variable selection, fusing data mining techniques using a machine learning algorithm with traditional statistical modelling, accounted for missing data and complex survey sampling methodology and was demonstrated to be a useful tool for detecting three biomarkers associated with depression for future hypothesis generation: red cell distribution width, serum glucose and total bilirubin

Dietary intake of fish and PUFA, and clinical depressive and anxiety disorders in women

Fish and PUFA consumption are thought to play a role in mental health; however, many studies do not take into account multiple sources of PUFA. The present study analysed data from a sample of 935 randomly selected, population-based women aged 20&ndash;93 years. A validated and comprehensive dietary questionnaire ascertained the consumption of n-3 and n-6 PUFA. Another assessed fish and energy intake and provided data for a dietary quality score. The General Health Questionnaire-12 (GHQ-12) measured psychological symptoms and a clinical interview (Structured Clinical Interview for DSM-IV-TR Research Version, Non-patient edition) assessed depressive and anxiety disorders. Median dietary intakes of long-chain n-3 fatty acids (310 mg/d) were below suggested dietary target levels. The only PUFA related to categorical depressive and anxiety disorders was DHA. There was a non-linear relationship between DHA intake and depression; those in the second tertile of DHA intake were nearly 70 % less likely to report a current depressive disorder compared to those in the first tertile. The relationship of DHA to anxiety disorders was linear; for those in the highest tertile of DHA intake, the odds for anxiety disorders were reduced by nearly 50 % after adjustments, including adjustment for diet quality scores, compared to the lowest tertile. Those who ate fish less than once per week had higher GHQ-12 scores, and this relationship was particularly obvious in smokers. These are the first observational data to indicate a role for DHA in anxiety disorders, but suggest that the relationship between DHA and depressive disorders may be non-linear

Tobacco smoking as a risk factor for major depressive disorder : a population-based study

Background : Smoking is disproportionately prevalent among people with psychiatric illness. Aims : To investigate smoking as a risk factor for major depressive disorder. Method : A population-based sample of women was studied using case&ndash;control and retrospective cohort study designs. Exposure to smoking was self-reported, and major depressive disorder diagnosed using the Structured Clinical Interview for DSM&ndash;IV&ndash;TR (SCID&ndash;I/NP). Results : Among 165 people with major depressive disorder and 806 controls, smoking was associated with increased odds for major depressive disorder (age-adjusted odds ratio (OR)=1.46, 95% CI 1.03&ndash;2.07). Compared with non-smokers, odds for major depressive disorder more than doubled for heavy smokers (&gt;20 cigarettes/day). Among 671 women with no history of major depressive disorder at baseline, 13 of 87 smokers and 38 of 584 non-smokers developed de novo major depressive disorder during a decade of follow-up. Smoking increased major depressive disorder risk by 93% (hazard ratio (HR)=1.93, 95% CI 1.02&ndash;3.69); this was not explained by physical activity or alcohol consumption. Conclusions : Evidence from cross-sectional and longitudinal data suggests that smoking increases the risk of major depressive disorder in women

Habitual physical activity and the risk for depressive and anxiety disorders among older men and women

Background: Regular physical activity is generally associated with psychological well-being, although there are relatively few prospective studies in older adults. We investigated habitual physical activity as a risk factor for de novo depressive and anxiety disorders in older men and women from the general population.Methods: In this nested case-control study, subjects aged 60 years or more were identified from randomly selected cohorts being followed prospectively in the Geelong Osteoporosis Study. Cases were individuals with incident depressive or anxiety disorders, diagnosed using the Structured Clinical Interview for DSM-IV-TR (SCID-I/NP); controls had no history of these disorders.Habitual physical activity,measured using a validated questionnaire, and other exposures were documented at baseline, approximately four years prior to psychiatric interviews. Those with depressive or anxiety disorders that pre-dated baseline were excluded.Results: Of 547 eligible subjects, 14 developed de novo depressive or anxiety disorders and were classified as cases; 533 controls remained free of disease. Physical activity was protective against the likelihood of depressive and anxiety disorders; OR = 0.55 (95% CI 0.32&ndash;0.94), p = 0.03; each standard deviation increase in the transformed physical activity score was associated with an approximate halving in the likelihood of developing depressive or anxiety disorders. Leisure-time physical activity contributed substantially to the overall physical activity score. Age, gender, smoking, alcohol consumption, weight and socioeconomic status did not substantially confound the association.Conclusion: This study provides evidence consistent with the notion that higher levels of habitual physical activity are protective against the subsequent risk of development of de novo depressive and anxiety disorders.<br /

Psychiatric disorders, psychotropic medication use and falls among women: an observational study

BACKGROUND: Psychotropic agents known to cause sedation are associated with an increased risk of falls, but the role of psychiatric illness as an independent risk factor for falls is not clear. Thus, this study aimed to investigate the association between psychiatric disorders, psychotropic medication use and falls risk. METHODS: This study examined data collected from 1062 women aged 20-93 yr (median 50 yr) participating in the Geelong Osteoporosis Study, a large, ongoing, population-based study. Depressive and anxiety disorders for the preceding 12-month period were ascertained by clinical interview. Current medication use and falls history were self-reported. Participants were classified as fallers if they had fallen to the ground at least twice during the same 12-month period. Anthropometry, demographic, medical and lifestyle factors were determined. Logistic regression was used to test the associations, after adjusting for potential confounders. RESULTS: Fifty-six women (5.3%) were classified as fallers. Those meeting criteria for depression within the past 12 months had a 2.4-fold increased odds of falling (unadjusted OR&thinsp;=&thinsp;2.4, 95% CI 1.2-4.5). Adjustment for age and mobility strengthened the relationship (adjusted OR&thinsp;=&thinsp;2.7, 95% CI 1.4-5.2) between depression and falling, with results remaining unchanged following further adjustment for psychotropic medication use (adjusted OR&thinsp;=&thinsp;2.7, 95% CI 1.3-5.6). In contrast, past (prior to 12-month) depression were not associated with falls. No association was observed between anxiety and falls risk. Falling was associated with psychotropic medication use (unadjusted OR&thinsp;=&thinsp;2.8, 95% CI 1.5-5.2), as well as antidepressant (unadjusted OR&thinsp;=&thinsp;2.4, 95% CI 1.2-4.8) and benzodiazepine use (unadjusted OR&thinsp;=&thinsp;3.4, 95% CI 1.6-7.3); associations remained unchanged following adjustment for potential confounders. CONCLUSION: The likelihood of falls was increased among those with depression within the past 12 months, independent of psychotropic medication use and other recognised confounders, suggesting an independent effect of depression on falls risk. Psychotropic drug use was also confirmed as an independent risk factor for falls, but anxiety disorders were not. Further research into the underlying mechanisms is warranted

So depression is an inflammatory disease, but where does the inflammation come from?

BACKGROUND: We now know that depression is associated with a chronic, low-grade inflammatory response and activation of cell-mediated immunity, as well as activation of the compensatory anti-inflammatory reflex system. It is similarly accompanied by increased oxidative and nitrosative stress (O&NS), which contribute to neuroprogression in the disorder. The obvious question this poses is 'what is the source of this chronic low-grade inflammation?' DISCUSSION: This review explores the role of inflammation and oxidative and nitrosative stress as possible mediators of known environmental risk factors in depression, and discusses potential implications of these findings. A range of factors appear to increase the risk for the development of depression, and seem to be associated with systemic inflammation; these include psychosocial stressors, poor diet, physical inactivity, obesity, smoking, altered gut permeability, atopy, dental cares, sleep and vitamin D deficiency. SUMMARY: The identification of known sources of inflammation provides support for inflammation as a mediating pathway to both risk and neuroprogression in depression. Critically, most of these factors are plastic, and potentially amenable to therapeutic and preventative interventions. Most, but not all, of the above mentioned sources of inflammation may play a role in other psychiatric disorders, such as bipolar disorder, schizophrenia, autism and post-traumatic stress disorder

Electronic properties of guanine-based nanowires

We present a first-principle study of the electronic and conduction properties of a few classes of nanowires constituted of guanine (G) molecules, self-assembled in different geometries. We first analyze the effect of the vertical $\pi$-$\pi$ interaction in model G-stack columns. Then, we exploit the results obtained from those models to interpret the features of realistic stacked and hydrogen-bonded structures, namely the guanine quadruple helices and the planar ribbons. With respect to natural DNA, the different structures as well as the inclusion of metal cations, drastically affect the bonding pattern among the bases, introducing novel features in the electronic properties of the systems. These supramolecular G-aggregates, alternative to DNA, are expected to show intersting properties for molecular elec tronics applications.Comment: 30 pages (preprint format), 8 figures. To appear in Solid State Communications - Special Issue on "New advances on collective phenomena in one-dimensional systems

Crossing the Phantom Divide: Theoretical Implications and Observational Status

If the dark energy equation of state parameter w(z) crosses the phantom divide line w=-1 (or equivalently if the expression d(H^2(z))/dz - 3\Omega_m H_0^2 (1+z)^2 changes sign) at recent redshifts, then there are two possible cosmological implications: Either the dark energy consists of multiple components with at least one non-canonical phantom component or general relativity needs to be extended to a more general theory on cosmological scales. The former possibility requires the existence of a phantom component which has been shown to suffer from serious theoretical problems and instabilities. Therefore, the later possibility is the simplest realistic theoretical framework in which such a crossing can be realized. After providing a pedagogical description of various dark energy observational probes, we use a set of such probes (including the Gold SnIa sample, the first year SNLS dataset, the 3-year WMAP CMB shift parameter, the SDSS baryon acoustic oscillations peak (BAO), the X-ray gas mass fraction in clusters and the linear growth rate of perturbations at z=0.15 as obtained from the 2dF galaxy redshift survey) to investigate the priors required for cosmological observations to favor crossing of the phantom divide. We find that a low \Omega_m prior (0.2<\Omega_m <0.25) leads, for most observational probes (except of the SNLS data), to an increased probability (mild trend) for phantom divide crossing. An interesting degeneracy of the ISW effect in the CMB perturbation spectrum is also pointed out.Comment: Accepted in JCAP (to appear). Comments added, typos corrected. 19 pages (revtex), 8 figures. The numerical analysis files (Mathematica + Fortran) with instructions are available at http://leandros.physics.uoi.gr/pdl-cross/pdl-cross.htm . The ppt file of a relevant talk may be downloaded from http://leandros.physics.uoi.gr/pdl-cross/pdl2006.pp