School connectedness as a protective factor against childhood exposure to violence and social deprivation: A longitudinal study of adaptive and maladaptive outcomes.

School connectedness, a construct indexing supportive school relationships, has been posited to promote resilience to environmental adversity. Consistent with prominent calls in the field, we examined the protective nature of school connectedness against two dimensions of early adversity that index multiple levels of environmental exposure (violence exposure, social deprivation) when predicting both positive and negative outcomes in longitudinal data from 3,246 youth in the Fragile Families and Child Wellbeing Study (48% female, 49% African American). Child and adolescent school connectedness were promotive, even when accounting for the detrimental effects of early adversity. Additionally, childhood school connectedness had a protective but reactive association with social deprivation, but not violence exposure, when predicting externalizing symptoms and positive function. Specifically, school connectedness was protective against the negative effects of social deprivation, but the effect diminished as social deprivation became more extreme. These results suggest that social relationships at school may compensate for low levels of social support in the home and neighborhood. Our results highlight the important role that the school environment can play for youth who have been exposed to adversity in other areas of their lives and suggest specific groups that may especially benefit from interventions that boost school connectedness.

Prospective longitudinal associations between harsh parenting and corticolimbic function during adolescence.

Childhood adversity is thought to undermine youth socioemotional development via altered neural function within regions that support emotion processing. These effects are hypothesized to be developmentally specific, with adversity in early childhood sculpting subcortical structures (e.g., amygdala) and adversity during adolescence impacting later-developing structures (e.g., prefrontal cortex; PFC). However, little work has tested these theories directly in humans. Using prospectively collected longitudinal data from the Fragile Families and Child Wellbeing Study (FFCWS) (N = 4,144) and neuroimaging data from a subsample of families recruited in adolescence (N = 162), the current study investigated the trajectory of harsh parenting across childhood (i.e., ages 3 to 9) and how initial levels versus changes in harsh parenting across childhood were associated with corticolimbic activation and connectivity during socioemotional processing. Harsh parenting in early childhood (indexed by the intercept term from a linear growth curve model) was associated with less amygdala, but not PFC, reactivity to angry facial expressions. In contrast, change in harsh parenting across childhood (indexed by the slope term) was associated with less PFC, but not amygdala, activation to angry faces. Increases in, but not initial levels of, harsh parenting were also associated with stronger positive amygdala-PFC connectivity during angry face processing.

Differential associations of parental harshness and parental disengagement with overall cortisol output at 15 years: Implications for adolescent mental health.

Psychosocial stress in childhood and adolescence is linked to stress system dysregulation, although few studies have examined the relative impacts of parental harshness and parental disengagement. This study prospectively tested whether parental harshness and disengagement show differential associations with overall cortisol output in adolescence. Associations between overall cortisol output and adolescent mental health problems were tested concurrently. Adolescents from the Fragile Families and Child Wellbeing Study (FFCWS) provided hair samples for cortisol assay at 15 years (N = 171). Caregivers reported on parental harshness and disengagement experiences at 1, 3, 5, 9, and 15 years, and adolescents reported at 15 years. Both parent and adolescent reported depressive and anxiety symptoms and antisocial behaviors at 15. Greater parental harshness from 1-15 years, and harshness reported at 15 years in particular, was associated with higher overall cortisol output at 15. Greater parental disengagement from 1-15 years, and disengagement at 1 year specifically, was associated with lower cortisol output. There were no significant associations between cortisol output and depressive symptoms, anxiety symptoms, or antisocial behaviors. These results suggest that the unique variances of parental harshness and disengagement may have opposing associations with cortisol output at 15 years, with unclear implications for adolescent mental health.

Amygdala-prefrontal cortex white matter tracts are widespread, variable and implicated in amygdala modulation in adolescents.

The amygdala is critically involved in processing emotion. Through bidirectional connections, the prefrontal cortex (PFC) is hypothesized to influence amygdala reactivity. However, research that elucidates the nature of amygdala-PFC interactions - through mapping amygdala-prefrontal tracts, quantifying variability among tracts, and linking this variability to amygdala activation - is lacking. Using probabilistic tractography to map amygdala-prefrontal white matter connectivity in 142 adolescents, the present study found that white matter connectivity was greater between the amygdala and the subgenual cingulate, orbitofrontal (OFC), and dorsomedial (dmPFC) prefrontal regions than with the dorsal cingulate and dorsolateral regions. Then, using a machine-learning regression, we found that greater amygdala-PFC white matter connectivity was related to attenuated amygdala reactivity. This effect was driven by amygdala white matter connectivity with the dmPFC and OFC, supporting implicit emotion processing theories which highlight the critical role of these regions in amygdala regulation. This study is among the first to map and compare specific amygdala-prefrontal white matter tracts and to relate variability in connectivity to amygdala activation, particularly among a large sample of adolescents from a well-sampled study. By examining the association between specific amygdala-PFC tracts and amygdala activation, the present study provides novel insight into the nature of this emotion-based circuit.

Amygdala habituation and uncinate fasciculus connectivity in adolescence: A multi-modal approach.

Despite prior extensive investigations of the interactions between the amygdala and prefrontal cortex, few studies have simultaneously considered activation and structural connectivity in this circuit, particularly as it pertains to adolescent socioemotional development. The current multi-modal study delineated the correspondence between uncinate fasciculus (UF) connectivity and amygdala habituation in a large adolescent sample that was drawn from a population-based sample. We then examined the influence of demographic variables (age, gender, and pubertal status) on the relation between UF connectivity and amygdala habituation. 106 participants (15-17 years) completed DTI and an fMRI emotional face processing task. Left UF fractional anisotropy was associated with left amygdala habituation to fearful faces, suggesting that increased structural connectivity of the UF may facilitate amygdala regulation. Pubertal status moderated this structure-function relation, such that the association was stronger in those who were less mature. Therefore, UF connectivity may be particularly important for emotion regulation during early puberty. This study is the first to link structural and functional limbic circuitry in a large adolescent sample with substantial representation of ethnic minority participants, providing a more comprehensive understanding of socioemotional development in an understudied population.

Research Review: Neural response to threat in children, adolescents, and adults after child maltreatment - a quantitative meta-analysis.

BACKGROUND: Child maltreatment is common and has long-term consequences for affective function. Investigations of neural consequences of maltreatment have focused on the amygdala. However, developmental neuroscience indicates that other brain regions are also likely to be affected by child maltreatment, particularly in the social information processing network (SIPN). We conducted a quantitative meta-analysis to: confirm that maltreatment is related to greater bilateral amygdala activation in a large sample that was pooled across studies; investigate other SIPN structures that are likely candidates for altered function; and conduct a data-driven examination to identify additional regions that show altered activation in maltreated children, teens, and adults. METHODS: We conducted an activation likelihood estimation analysis with 1,733 participants across 20 studies of emotion processing in maltreated individuals. RESULTS: Maltreatment is associated with increased bilateral amygdala activation to emotional faces. One SIPN structure is altered: superior temporal gyrus, of the detection node, is hyperactive in maltreated individuals. The results of the whole-brain corrected analysis also show hyperactivation of the parahippocampal gyrus and insula in maltreated individuals. CONCLUSIONS: The meta-analysis confirms that maltreatment is related to increased bilateral amygdala reactivity and also shows that maltreatment affects multiple additional structures in the brain that have received little attention in the literature. Thus, although the majority of studies examining maltreatment and brain function have focused on the amygdala, these findings indicate that the neural consequences of child maltreatment involve a broader network of structures.

fNIRS evidence of prefrontal regulation of frustration in early childhood.

The experience of frustration is common in early childhood, yet some children seem to possess a lower tolerance for frustration than others. Characterizing the biological mechanisms underlying a wide range of frustration tolerance observed in early childhood may inform maladaptive behavior and psychopathology that is associated with this construct. The goal of this study was to measure prefrontal correlates of frustration in 3-5-year-old children, who are not readily adaptable for typical neuroimaging approaches, using functional near infrared spectroscopy (fNIRS). fNIRS of frontal regions were measured as frustration was induced in children through a computer game where a desired and expected prize was "stolen" by an animated dog. A fNIRS general linear model (GLM) was used to quantify the correlation of brain regions with the task and identify areas that were statistically different between the winning and frustrating test conditions. A second-level voxel-based ANOVA analysis was then used to correlate the amplitude of each individual's brain activation with measure of parent-reported frustration. Experimental results indicated increased activity in the middle prefrontal cortex during winning of a desired prize, while lateral prefrontal cortex activity increased during frustration. Further, activity increase in lateral prefrontal cortex during frustration correlated positively with parent-reported frustration tolerance. These findings point to the role of the lateral prefrontal cortex as a potential region supporting the regulation of emotion during frustration.

Predictors of non-fatal suicide attempts among Veterans Health Administration (VHA) patients who experienced military sexual trauma.

OBJECTIVE: Military sexual trauma (MST) has been identified as a risk factor for suicidal behavior. To inform suicide prevention efforts within the Veterans Health Administration (VHA), this study evaluates predictors of non-fatal suicide attempts (NFSAs) among VHA patients who experienced MST. METHODS: For VHA patients in fiscal year (FY) 2019 who previously screened positive for a history of MST, documented NFSAs were assessed. Using multivariable logistic regression, demographic, clinical, and VHA care utilization predictors of NFSAs were assessed. RESULTS: Of the 212,215 VHA patients who screened positive for MST prior to FY 2019 and for whom complete race, service connection, and rurality information was available, 1742 (0.8%) had a documented NFSA in FY 2019. In multivariable logistic regression analyses, total physical and mental health morbidities were not associated with NFSA risk. Predictors of a documented NFSA included specific mental health diagnoses [adjusted odds ratio (aOR) range: 1.28-1.94], receipt of psychotropic medication prescriptions (aOR range: 1.23-2.69) and having a prior year emergency department visit (aOR = 1.32) or inpatient psychiatric admission (aOR = 2.15). CONCLUSIONS: Among VHA patients who experienced MST, specific mental health conditions may increase risk of NFSAs, even after adjustment for overall mental health morbidity. Additionally, indicators of severity of mental health difficulties such as receipt of psychotropic medication prescriptions and inpatient psychiatric admissions are also associated with increased risk above and beyond risk associated with diagnoses. Findings highlight targets for suicide prevention initiatives among this vulnerable group within VHA and may help identify patients who would benefit from additional support.

Comprehensive Caregiver Supports and Ascertainment and Treatment of Veteran Pain.

Disabled Veterans commonly experience pain. The Program of Comprehensive Assistance for Family Caregivers (PCAFC) provides training, a stipend, and services to family caregivers of eligible Veterans to support their caregiving role. We compared ascertainment of veteran pain and pain treatment through health care encounters and medications (pain indicators) of participants (treated group) and non-participants (comparison group) using inverse probability treatment weights. Modeled results show that the proportion of Veterans with a pain indicator in the first year post-application was higher than that pre-application for both groups. However, the proportion of Veterans with a pain indicator was substantially higher in the treatment group: 76.1% versus 63.9% in the comparison group (p < .001). Over time, the proportion of Veterans with any pain indicator fell and group differences lessened. However, differences persisted through 8 years post-application (p < .001). PCAFC caregivers appear to help Veterans engage in pain treatment at higher rates than caregivers not in PCAFC.

Mortality following non-fatal suicide attempts by Veterans in Veterans Health Administration care.

INTRODUCTION: Little is known regarding long-term mortality outcomes after non-fatal suicide attempts among Veterans Health Administration (VHA) patients, which may inform services delivery and program evaluation. METHODS: For 4,601,081 Veterans with 2005 VHA encounters, we assessed unadjusted and age-adjusted all-cause and cause-specific mortality through 2017, overall and for Veterans with (N = 8243) versus without (N = 4,592,838) 2005 VHA suicide attempt documentation. Standardized mortality ratios compared mortality rates by suicide attempt status. Multivariable proportional hazards regression models assessed age- and gender-adjusted mortality risk. RESULTS: Among Veteran VHA users with non-fatal suicide attempt diagnoses, 1.6% died of suicide, 4.6% of non-suicide external causes, and 30.7% of any cause. In age- and gender-adjusted analyses, Veterans who attempted suicide had increased suicide (hazard ratio [HR] = 4.52, 95% confidence interval [CI] = 3.82-5.36), non-suicide external cause (HR = 3.75, 95% CI = 3.38-4.17), and all-cause (separate due to non-proportional hazards: 2006, HR = 2.05, 95% CI = 1.81-2.31; 2007-2017, HR = 1.72, 95% CI = 1.65-1.80) mortality through 2017. CONCLUSION: Over 12 years, Veteran VHA patients with non-fatal suicide attempt diagnoses had increased risk of suicide, non-suicide external cause, and all-cause mortality. Over 98% of Veteran VHA users who had a diagnosed non-fatal attempt did not die by suicide, highlighting additional program evaluation outcomes and opportunities to support physical and mental health.

Suicide Mortality Among Veterans Health Administration Care Recipients With Suicide Risk Record Flags.

OBJECTIVE: In 2008, the Veterans Health Administration (VHA) established a suicide high-risk flag (HRF) for patient records. To inform ongoing suicide prevention activities as part of operations and quality improvement work in the U.S. Department of Veterans Affairs, the authors evaluated suicide risk following HRF activations and inactivations. METHODS: For annual cohorts of VHA users, HRF receipt and demographic and clinical care contexts in the 30 days before HRF activations were examined for 2014-2016 (N=7,450,831). Veterans were included if they had VHA inpatient or outpatient encounters during the index or previous year. Suicide rates in the 12 months after HRF activations and inactivations were assessed. Using multivariable Cox proportional hazards regression, the authors compared suicide risk following HRF activation and inactivation with veterans without HRFs, adjusted for age, gender, and race-ethnicity. RESULTS: HRF activation (N=47,015) was commonly preceded within 30 days by a documented suicide attempt (39.5%) or inpatient mental health admission (40.1%). Suicide risk was elevated in the 12 months after flag activation (crude suicide rate=682 per 100,000 person-years, adjusted hazard ratio [HR]=21.00, 95% confidence interval [CI]=18.55-23.72) compared with risk among VHA users without HRF activity. Risk after HRF inactivation (N=41,251) was also elevated (crude suicide rate=408 per 100,000 person-years, adjusted HR=12.43, 95% CI=10.57-14.63) compared with risk among VHA users without HRF activity. CONCLUSIONS: Suicide risk after HRF activation was substantially elevated and also high after HRF inactivation. Findings suggest the importance of comprehensive suicide risk mitigation and support recent VHA process enhancements to formalize inactivation criteria and support veterans after HRF inactivation.

Personality disorder and suicide risk among patients in the veterans affairs health system.

Among veterans in Veterans Health Administration (VHA) care, patients with mental health and substance use conditions experience elevated suicide rates. However, despite previously demonstrated high rates of suicidal behavior, little is known regarding suicide rates among veteran VHA users with personality disorders (PDs) as a whole, or by PD clusters (A: Eccentric; B: Dramatic; C: Fearful; and PD-not otherwise specified). PD prevalence and suicide rates were assessed through 2017; overall and by clusters for 5,517,024 veterans alive as of 12/31/2013 and with more than 2 VHA encounters in 2012-2013. In all, 46,050 (.83%) had a PD diagnosis in 2012-2013. Suicide risk was examined using proportional hazards regressions adjusted for age, sex, veteran status, clustering within a geographic region, and other mental health diagnoses. Patients with PDs had greater suicide risk than those without (156.5 vs. 46.7 per 100,000 person-years). Individuals in Cluster B, which includes borderline and antisocial PDs, were at the highest risk (178.5 per 100,000 person-years), followed by PD-not otherwise specified and Cluster C (152.6 and 121.4 per 100,000 person-years, respectively). Rates of PDs in the VHA system were lower than those usually found in community samples. Veterans with a PD diagnosis had an increased risk of suicide, which was especially elevated for those with Cluster B diagnoses. Study findings document the importance of enhancing diagnosis and treatment for veterans with PDs and targeted suicide prevention services. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Comparative risks of all-cause mortality for Veterans with schizophrenia with ongoing receipt of clozapine and other antipsychotic medications.

To guide care for patients with schizophrenia, the Veterans Health Administration (VHA) evaluated the associations between current or recent use of clozapine and all-cause mortality and explored associations for other antipsychotic medications. Using a case-control design, patients with schizophrenia who died in fiscal years 2014-2018 were matched on age, sex, race, and VHA facility to up to 10 controls who were alive on the case's date of death (index date). Medication coverage during the 91 days before the index date was classified as none, partial (1-44 days), and consistent (45-91 days). Medication coverage patterns during the index period were compared to coverage patterns during the period of 92-182 days prior to index date with each medication coverage classified as no change, no coverage, increased, or decreased. Conditional logistic regression analyses controlling for patient characteristics identified no associations of consistent or increasing clozapine coverage with mortality; partial and decreasing coverage were associated with greater mortality and these effects did not differ from those of other the medications considered. Exploratory analyses considering non-clozapine antipsychotic agents suggest that consistent coverage by olanzapine may be associated with increased mortality, that mortality associated with olanzapine may be greater than aripiprazole, and that this effect can be attributed primarily to patients with diabetes. Further study of this topic is needed.

Access to timely mental health care treatment initiation among Veterans Health Administration patients with and without serious mental illness.

Timely care initiation is a priority within the Veterans Health Administration (VHA). Patients with serious mental illnesses (SMI) are a group that benefits from timely care initiation due to elevated risks of negative outcomes with delayed care. However, no evaluation has assessed whether VHA SMI patients disproportionately experience delays in mental health care initiation. VHA administrative care data were used to compare delays in mental health care initiation for VHA patients with and without SMI who had newly identified mental health needs. Analyses assessed rates of delayed initial mental health appointments within five settings (General Mental Health [GMH], Primary Care Mental Health Integration [PC-MHI], Post-Traumatic Stress Disorder [PTSD], Substance Use Disorder [SUD], and Psychosocial Rehabilitation clinics [PSR]). SMI patients were more likely to receive delayed initial appointments in three of five clinical settings (PTSD, SUD, PSR) and had significantly longer average wait times for an initial appointment when referred to the PTSD clinic for an initial appointment. Overall, SMI patients were equally as likely to receive delayed initial appointments. While VHA SMI patients were not more likely to experience delayed mental health care initiation overall, they were more likely to experience delays within three of the five treatment settings. Findings suggest that the majority of VHA SMI patients experience equivalent timeliness, though those with more complex needs, and particularly those with trauma-related care needs, may be more likely to experience treatment initiation delays. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Amygdala reactivity during socioemotional processing and cortisol reactivity to a psychosocial stressor.

Threat-related amygdala reactivity and the activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis have been linked to negative psychiatric outcomes. The amygdala and HPA axis have bidirectional connections, suggesting that functional variation in one system may influence the other. However, research on the functional associations between these systems has demonstrated mixed findings, potentially due to small sample sizes and cortisol sampling and data analytic procedures that investigate only pre-post differences in cortisol rather than the specific phases of the cortisol stress response. Further, previous research has primarily utilized samples of adults of mostly European descent, limiting generalizability to those of other ethnoracial identities and ages. Therefore, studies addressing these limitations are needed in order to investigate the functional relations between amygdala reactivity to threat and HPA axis stress responsivity. Using a sample of 159 adolescents from a diverse cohort (75% African American, ages 15-17 years), the present study evaluated associations between amygdala reactivity during socioemotional processing using fMRI and HPA axis reactivity to a socially-evaluative cold pressor task. Greater amygdala activation to fearful and neutral faces was associated with greater cortisol peak values and steeper activation slope. As cortisol peak values and cortisol activation slope capture the intensity of the cortisol stress response, these data suggest that greater activation of the amygdala in response to social distress and ambiguity among adolescents may be related to hyper-reactivity of the HPA axis.

Facility-Level Excess Mortality of VHA Patients With Mental Health or Substance Use Disorder Diagnoses.

OBJECTIVE: Individuals with mental or substance use disorders have higher mortality rates than people in the general population. How excess mortality varies across health care facilities is unknown. The authors sought to investigate facility-level mortality rates among Veterans Health Administration (VHA) patients who had received diagnoses of mental or substance use disorders. METHODS: An electronic medical records-based retrospective cohort study was conducted, encompassing 8,812,373 unique users of 139 VHA facilities from 2011 to 2016. Covariates included age, sex, and past-year diagnoses of serious mental illness, posttraumatic stress disorder, major depressive disorder, other mental health conditions, or substance use disorders. The outcome was all-cause mortality per comprehensive Veterans Affairs/Department of Defense searches of the National Death Index. Proportional hazards regression was used to calculate overall and facility-specific hazard ratios (HRs) for each diagnosis group, adjusted for age, sex, and comorbid medical conditions. RESULTS: Overall, all-cause mortality was statistically significantly elevated among VHA users with mental health diagnoses (HR=1.21, 95% confidence interval=1.20-1.22). HRs varied across facilities consistently over time. At the VHA facility level, diagnostic groups were significantly correlated with the degree of excess mortality. Results were similar in sensitivity analyses that excluded deaths from suicide or drug or alcohol overdose. CONCLUSIONS: VHA users with mental or substance use disorder diagnoses had elevated mortality rates. Correlation in excess mortality across two periods indicated that facility differences in excess mortality were persistent and therefore potentially associated with facility- and community-level factors, which may help inform quality improvement efforts to reduce mortality rates.

Associations among ACEs, Health Behavior, and Veteran Health by Service Era.

Objectives: Despite substantial research linking adverse childhood experiences (ACEs) and health, it is unclear how associations differ by veteran status and military service era (draft, volunteer era). The current study evaluated differences in ACEs and health by veteran status and era, increasing understanding important for service provision as the volunteer era veteran population increases. Methods: Behavioral Risk Factor Surveillance System 2012 data were used in univariate and weighted multivariable logistic regression models to assess associations among veteran status, service era, ACEs, and health. Results: Volunteer era veterans experienced the most ACEs (M = 2.42); draft era veterans experienced the fewest (M = 1.04). Individuals reporting 3 or more ACEs were 3.67 times (95% CI = 3.22-4.19) more likely to endorse depression, 1.32 times (95% CI = 1.17-1.48) more likely to report poorer general health, and 1.77 times (95% CI = 1.58-1.97) more likely to endorse poorer physical health, compared to those reporting none. Volunteer era veterans were 2.43 times more likely to report poorer physical health (95% CI = 1.49-3.97) than draft era veterans, adjusting for ACEs. Conclusions: ACEs were associated with poorer health independent of veteran status and service era. Volunteer era veterans experienced more ACEs; need for trauma-informed services supporting whole health may increase.

Clarifying the Link Between Amygdala Functioning During Emotion Processing and Antisocial Behaviors Versus Callous-Unemotional Traits Within a Population-Based Community Sample.

Prominent theories suggest that disruptions in amygdala reactivity and connectivity when processing emotional cues are key to the etiology of youth antisocial behavior (AB) and that these associations may be dependent on co-occurring levels of callous-unemotional (CU) traits. We examined the associations among AB, CU traits, and amygdala reactivity and functional connectivity while viewing emotional faces (fearful, angry, sad, happy) in 165 adolescents (46% male; 73.3% African American) from a representative, predominantly low-income community sample. AB was associated with increased amygdala activation in response to all emotions and was associated with greater amygdala reactivity to emotion only at low levels of CU traits. AB and CU traits were also associated with distinct patterns of amygdala connectivity. These findings demonstrate that AB-related deficits in amygdala functioning may extend across all emotions and highlight the need for further research on amygdala connectivity during emotion processing in relation to AB and CU traits within community populations.

Can "deaths of despair" serve as a focus for planning and evaluating clinical and preventive services for Veterans?

Deaths of despair, a composite outcome including suicide and drug- and alcohol-related deaths, have been increasing, especially in subpopulations and geographic areas sensitive to economic and social hardships. The Veterans Health Administration (VHA) has begun evaluating the utility of this concept to guide planning and evaluations of clinical and preventive services for Veterans. In this study, mortality rates for middle-aged American men for 2013 to 2017 were from CDC WONDER, and rates for all Veterans, those using VHA healthcare services (VHA-utilizers), and other (non-VHA) Veterans were derived from National Death Index data. Findings demonstrated that rates for the composite were higher in VHA-utilizers and lower in non-VHA Veterans than middle-aged American men, consistent with use of VHA services by Veterans with the greatest needs. State rates in Veteran men were significantly and positively correlated with state rates for American men, and both were correlated with other characteristics of the social environment. The lack of correlation between rates for suicide and drug-related deaths indicates that deaths of despair cannot be modeled by assuming parallel paths from reactions to community-based stressors to the component outcomes; models should allow for an impact of community characteristics on partitioning between outcomes.

WITHDRAWN:Childhood violence exposure and social deprivation predict adolescent amygdala-orbitofrontal cortex white matter connectivity.

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. This error bears no reflection on the article or its authors. The publisher apologizes to the authors and the readers for this unfortunate error.