Relationship of social and economic factors to mental disorders among population-based samples of Jamaicans and Guyanese

BACKGROUND: There have been growing concerns about increasing mental health problems in the Caribbean region. This study explores rates and factors associated with selected mental health disorders within 2 Caribbean countries: Jamaica and Guyana. METHODS: Probability samples of 1218 Jamaicans and 2068 Guyanese participants were used. A modified version of the WHO Composite International Diagnostic Interview (WHO CIDI) defined by the Diagnostic Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) was administered in order to assess lifetime mental disorders. Descriptive statistics, χ(2) and hierarchical regression analytic procedures were used to examine rates and factors associated with mental disorders. RESULTS: Rates of mental health conditions were different across contexts and were generally higher for Guyanese compared with Jamaicans for alcohol abuse (3.6% vs 2.2%), drug abuse (1.4% vs 1.3%), substance abuse (4.7% vs 2.7%) and mania (0.4% vs 0.1%). The rate of depression, however, was higher among Jamaicans than Guyanese (7.4% vs 4.1%). There were also noticeable differences in rates in both countries, due to social and economic factors, with social factors playing a larger contributory role in the mental health status of individuals across countries. CONCLUSIONS: The results of this study suggest the need for more indepth analyses of factors contributing to mental health conditions of peoples within the Caribbean region, including the influence of additional sources of stress, quality of care and help-seeking behaviours of individuals

Breakdown of a conservation law in incommensurate systems

We show that invariance properties of the Lagrangian of an incommensurate system, as described by the Frenkel Kontorova model, imply the existence of a generalized angular momentum which is an integral of motion if the system remains floating. The behavior of this quantity can therefore monitor the character of the system as floating (when it is conserved) or locked (when it is not). We find that, during the dynamics, the non-linear couplings of our model cause parametric phonon excitations which lead to the appearance of Umklapp terms and to a sudden deviation of the generalized momentum from a constant value, signalling a dynamical transition from a floating to a pinned state. We point out that this transition is related but does not coincide with the onset of sliding friction which can take place when the system is still floating.Comment: 7 pages, 6 figures, typed with RevTex, submitted to Phys. Rev. E Replaced 27-03-2001: changes to text, minor revision of figure

Strongly Temperature Dependent Sliding Friction for a Superconducting Interface

A sudden drop in mechanical friction, between an adsorbed nitrogen monolayer and a lead substrate, occurs when the lead passes through the superconducting transition temperature. We attribute this effect to a sudden drop at the superconducting transition temperature of the substrate Ohmic heating. The Ohmic heating is due to the electronic screening current that results from the sliding adsorbed film.Comment: Revte

Substance Use, Mental Disorders and Physical Health of Caribbeans at-Home Compared to Those Residing in the United States

This study compares the health conditions of domestic Caribbeans with those living in the United States to explore how national context and migration experiences might influence substance use (i.e., alcohol or drug) and other mental and physical health conditions. The study is based upon probability samples of non-institutionalized Caribbeans living in the United States (1621), Jamaica (1216) and Guyana (2068) 18 years of age and over. Employing descriptive statistics and multivariate analytic procedures, the results revealed that substance use and other physical health conditions and major depressive disorder and mania vary by national context, with higher rates among Caribbeans living in the United States. Context and generation status influenced health outcomes. Among first generation black Caribbeans, residing in the United States for a longer length of time is linked to poorer health outcomes. There were different socio-demographic correlates of health among at-home and abroad Caribbeans. The results of this study support the need for additional research to explain how national context, migratory experiences and generation status contribute to understanding substance use and mental disorders and physical health outcomes among Caribbean first generation and descendants within the United States, compared to those remaining in the Caribbean region

Effects of Defects on Friction for a Xe Film Sliding on Ag(111)

The effects of a step defect and a random array of point defects (such as vacancies or substitutional impurities) on the force of friction acting on a xenon monolayer film as it slides on a silver (111) substrate are studied by molecular dynamic simulations and compared with the results of lowest order perturbation theory in the substrate corrugation potential. For the case of a step, the magnitude and velocity dependence of the friction force are strongly dependent on the direction of sliding respect to the step and the corrugation strength. When the applied force F is perpendicular to the step, the film is pinned forF less than a critical force Fc. Motion of the film along the step, however, is not pinned. Fluctuations in the sliding velocity in time provide evidence of both stick-slip motion and thermally activated creep. Simulations done with a substrate containing a 5 percent concentration of random point defects for various directions of the applied force show that the film is pinned for the force below a critical value. The critical force, however, is still much lower than the effective inertial force exerted on the film by the oscillations of the substrate in experiments done with a quartz crystal microbalance (QCM). Lowest order perturbation theory in the substrate potential is shown to give results consistent with the simulations, and it is used to give a physical picture of what could be expected for real surfaces which contain many defects.Comment: 13 pages, 17 figures, latex plus postscript files for figure

Theory of friction: contribution from fluctuating electromagnetic field

We calculate the friction force between two semi-infinite solids in relative parallel motion (velocity $V$), and separated by a vacuum gap of width $d$. The friction force result from coupling via a fluctuating electromagnetic field, and can be considered as the dissipative part of the van der Waals interaction. We consider the dependence of the friction force on the temperature $T$, and present a detailed discussion of the limiting cases of small and large $V$ and $d$.Comment: 15 pages, No figure