Networks of Recurrent Events, a Theory of Records, and an Application to Finding Causal Signatures in Seismicity

We propose a method to search for signs of causal structure in spatiotemporal data making minimal a priori assumptions about the underlying dynamics. To this end, we generalize the elementary concept of recurrence for a point process in time to recurrent events in space and time. An event is defined to be a recurrence of any previous event if it is closer to it in space than all the intervening events. As such, each sequence of recurrences for a given event is a record breaking process. This definition provides a strictly data driven technique to search for structure. Defining events to be nodes, and linking each event to its recurrences, generates a network of recurrent events. Significant deviations in properties of that network compared to networks arising from random processes allows one to infer attributes of the causal dynamics that generate observable correlations in the patterns. We derive analytically a number of properties for the network of recurrent events composed by a random process. We extend the theory of records to treat not only the variable where records happen, but also time as continuous. In this way, we construct a fully symmetric theory of records leading to a number of new results. Those analytic results are compared to the properties of a network synthesized from earthquakes in Southern California. Significant disparities from the ensemble of acausal networks that can be plausibly attributed to the causal structure of seismicity are: (1) Invariance of network statistics with the time span of the events considered, (2) Appearance of a fundamental length scale for recurrences, independent of the time span of the catalog, which is consistent with observations of the ``rupture length'', (3) Hierarchy in the distances and times of subsequent recurrences.Comment: 19 pages, 13 figure

A multi-satellite climatology of clouds, radiation and precipitation in southern West Africa and comparison to climate models

Southern West Africa (SWA) has a large population that relies on highly variable monsoon rainfall, yet climate models show little consensus over projected precipitation in this region. Understanding of the current and future climate of SWA is further complicated by rapidly increasing anthropogenic emissions and a lack of surface observations. Using multiple satellite observations, the ERA-Interim reanalysis, and four climate models, we document the climatology of cloud, precipitation and radiation over SWA in June-July, highlight discrepancies among satellite products, and identify shortcomings in climate models and ERA-Interim. Large differences exist between monthly mean cloud cover estimates from satellites, which range from 68 to 94 %. In contrast, differences among satellite observations in top of atmosphere outgoing radiation and surface precipitation are smaller, with monthly means of about 230 W m–2 of longwave radiation, 145 W m–2 of shortwave radiation and 5.87 mm day–1 of precipitation. Both ERA-Interim and the climate models show less total cloud cover than observations, mainly due to underestimating low cloud cover. Errors in cloud cover, along with uncertainty in surface albedo, lead to a large spread of outgoing shortwave radiation. Both ERA-Interim and the climate models also show signs of convection developing too early in the diurnal cycle, with associated errors in the diurnal cycles of precipitation and outgoing longwave radiation. Clouds, radiation and precipitation are linked in an analysis of the regional energy budget, which shows that inter-annual variability of precipitation and dry static energy divergence are strongly linked

Misreporting in a randomized clinical trial for smoking cessation in adolescents

Introduction: Misreporting smoking behavior is common among younger smokers participating in clinical trials for smoking cessation. This study focused on the prevalence of and factors associated with adolescent misreporting of smoking behaviors within the context of a randomized clinical trial for smoking cessation. Methods: Adolescent smokers (N = 129) participated in a randomized clinical trial that compared two brief interventions for smoking cessation. Following the final (6-month) follow-up, a confidential, self-administered exit questionnaire examined the extent to which participants admitted to having misreported smoking quantity, frequency and/or consequences during the study. Factors associated with under- and over-reporting were compared to accurate-reporting. Results: One in 4 adolescent smokers (25.6%) admitted to under-reporting during the study and 14.7% admitted to over-reporting; 10.9% of the adolescents admitted to both under- and over-reporting. Rates of admitted misreporting did not differ between treatment conditions or recruitment site. Compared to accurate-reporting, under- and over-reporting were significantly associated with home smoking environment and the belief among adolescents that the baseline interviewer wanted them to report smoking more or less than they actually smoked. Compared to accurate reporters, over-reporters were more likely to be non-White and to report being concerned with the confidentiality of their responses. Conclusions: A post-study confidential debriefing questionnaire can be a useful tool for estimating rates of misreporting and examining whether potential differences in misreporting might bias the interpretation of treatment effects. Future studies are needed to thoroughly examine potentially addressable reasons that adolescents misreport their smoking behavior and to develop methods for reducing misreporting

Motivational interviewing to reduce substance-related consequences: Effects for incarcerated adolescents with depressed mood

Background: The impact of depressed mood on Motivational Interviewing (MI) to reduce risky behaviors and consequences in incarcerated adolescents was examined in this brief report. Methods: Adolescents (N = 189) were randomly assigned to receive MI or Relaxation Training (RT). Results: At 3-month follow-up assessment, MI significantly reduced risks associated with marijuana use, with a trend towards reducing risks associated with alcohol use. There was also a trend for depressive symptoms to be associated with reduced risks after release. Interaction effects were non-significant, indicating no moderating effects for depressed mood on treatment outcome. Conclusions: MI may be a useful treatment for incarcerated adolescents in order to reduce risks and consequences associated with substance use after release

Randomized Clinical Trial of Motivational Enhancement of Substance Use Treatment Among Incarcerated Adolescents: Post-Release Condom Non-Use

Evaluated impact of motivational enhancement (ME) of substance abuse treatment compared to relaxation training (RT) on sex without condoms (overall and involving substance use) 3 months following release among incarcerated adolescents. This randomized clinical trial involved 114 incarcerated adolescents from the Northeast. Regression analyses determined if treatment condition, baseline levels of depressive symptoms, and their interaction predicted condom non-use 3 months post-release, controlling for baseline condom non-use. Among those who reported fewer baseline depressive symptoms, those in ME condition reported significantly less condom non-use, in general and involving marijuana use compared with those in RT condition. Periods of incarceration represent opportunities to help juvenile detainees reduce behaviors that impact their health and the health of those with whom they interact in the community

Motivation to change alcohol use and treatment engagement in incarcerated youth

Adolescents have been reported to be less motivated to engage and remain in substance abuse treatment than adults. When they appear motivated, it is often due to external motivators such as family pressure or court mandated treatment. The purpose of this study was to determine if adolescents\u27 motivation to change alcohol use was related to treatment engagement while incarcerated and alcohol use after release. Participants (N = 114) were youth in a state correctional facility in the Northeast and included adolescents who engaged in at least monthly drinking. Motivation to change alcohol use was measured by the Alcohol Ladder (AL), and treatment engagement was measured by the Treatment Participation Questionnaire (comprised of positive and negative treatment engagement). Measures were administered at baseline, 2 months in facility follow up, and 3 months post release follow up. Analysis indicated acceptable test-retest stability (r = .388, p ≤ .001). The AL at 3 months post release significantly predicted quantity and frequency of alcohol use after release. The AL at baseline also significantly predicted positive and negative treatment engagement at 2 months into incarceration (i.e., 2 months in facility follow up) indicating predictive validity. These results suggest that the AL is a reliable, valid, and useful instrument for incarcerated youth

Globalisation, adjustment and the structural transformation of African economies?: the role of international financial institutions

Under the auspices of the World Bank and IMF, for almost two decades, sub-Saharan African countries have implemented structural adjustment, an orthodox package of economic reform measures. During this period there has been an unprecedented proliferation of technology investment and trade in the world economy. However sub-Saharan Africa has performed poorly under adjustment and has been largely marginalized from the international economy. The paper investigates the problems with the theoretical model underlying structural adjustment policies to explain why the model is not conducive to either African development or Africa’s increasing participation in the global economy. An example is used to illustrate the existence of an alternative set of policies that may be better suited for Africa

Increased Ventricular Premature Contraction Frequency During REM Sleep in Patients with Coronary Artery Disease and Obstructive Sleep Apnea

Background Patients with obstructive sleep apnea are reported to have a peak of sudden cardiac death at night, in contrast to patients without apnea whose peak is in the morning. We hypothesized that ventricular premature contraction (VPC) frequency would correlate with measures of apnea and sympathetic activity.Methods Electrocardiograms from a sleep study of 125 patients with coronary artery disease were evaluated. Patients were categorized by apnea-hypopnea index (AHI) into Moderate (AHI <15) or Severe (AHI>15) apnea groups. Sleep stages studied were Wake, S1, S2, S34, and rapid eye movement (REM). Parameters of a potent autonomically-based risk predictor for sudden cardiac death called heart rate turbulence were calculated.Results There were 74 Moderate and 51 Severe obstructive sleep apnea patients. VPC frequency was affected significantly by sleep stage (Wake, S2 and REM, F=5.8, p<.005) and by AHI (F=8.7, p<.005). In Severe apnea patients, VPC frequency was higher in REM than in Wake (p=.011). In contrast, patients with Moderate apnea had fewer VPCs and exhibited no sleep stage dependence (p=.19). Oxygen desaturation duration per apnea episode correlated positively with AHI (r2=.71, p<.0001), and was longer in REM than in non-REM (p<.0001). The heart rate turbulence parameter TS correlated negatively with oxygen desaturation duration in REM (r2=.06, p=.014).Conclusions Higher VPC frequency coupled with higher sympathetic activity caused by longer apnea episodes in REM sleep may be one reason for increased nocturnal death in apneic patients

Regulatory T Cells and IL-10 Independently Counterregulate Cytotoxic T Lymphocyte Responses Induced by Transcutaneous Immunization

The imidazoquinoline derivate imiquimod induces inflammatory responses and protection against transplanted tumors when applied to the skin in combination with a cognate peptide epitope (transcutaneous immunization, TCI). Here we investigated the role of regulatory T cells (T(reg)) and the suppressive cytokine IL-10 in restricting TCI-induced cytotoxic T lymphocyte (CTL) responses.TCI was performed with an ointment containing the TLR7 agonist imiquimod and a CTL epitope was applied to the depilated back skin of C57BL/6 mice. Using specific antibodies and FoxP3-diphteria toxin receptor transgenic (DEREG) mice, we interrogated inhibiting factors after TCI: by depleting FoxP3(+) regulatory T cells we found that specific CTL-responses were greatly enhanced. Beyond this, in IL-10 deficient (IL-10(-/-)) mice or after blocking of IL-10 signalling with an IL-10 receptor specific antibody, the TCI induced CTL response is greatly enhanced indicating an important role for this cytokine in TCI. However, by transfer of T(reg) in IL-10(-/-) mice and the use of B cell deficient JHT(-/-) mice, we can exclude T(reg) and B cells as source of IL-10 in the setting of TCI.We identify T(reg) and IL-10 as two important and independently acting suppressors of CTL-responses induced by transcutaneous immunization. Advanced vaccination strategies inhibiting T(reg) function and IL-10 release may lead the development of effective vaccination protocols aiming at the induction of T cell responses suitable for the prophylaxis or treatment of persistent infections or tumors