Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime

Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10-100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH^*, PAH^+* and PAH^2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH²⁺ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.

Tricyclic drugs for depression in children and adolescents

BACKGROUND

There is a need to identify effective and safe treatments for depression in children and adolescents. While tricyclic drugs are effective in treating depression in adults, individual studies involving children and adolescents have been equivocal.

OBJECTIVES

To assess the effects of oral tricyclic antidepressants compared to placebo in the treatment of child and adolescent depression.

SEARCH STRATEGY

We searched MEDLINE (1966-1997), EMBASE, Excerpta Medica (June 1974-1997), the Cochrane Collaboration Depression, Anxiety and Neurosis Group trials register (most recent search 25/1/2000) and bibliographies of previously published reviews and papers describing original research were cross-checked. Current Contents was screened for recent publications. We contacted authors of relevant abstracts in conference proceedings of the American Academy of Child and Adolescent Psychiatry, and we hand searched the Journal of the American Academy of Child and Adolescent Psychiatry (1978-1999).

SELECTION CRITERIA

Randomised controlled trials comparing the efficacy of orally administered tricyclic medication with placebo in depressed people aged 6-18 years.

DATA COLLECTION AND ANALYSIS

Most studies reported multiple outcome measures including depression scales and clinical global impression scales. For each study the best available depression measure was taken as the index measure of depression outcome. Predetermined criteria were established to assist in the ranking of measures. Where authors reported categorical outcomes we calculated individual and pooled odds ratios for the odds of improvement in treated compared with control subjects. For continuous outcomes pooled effect sizes were calculated as the number of standard deviations by which the change in depression scores for the treatment group exceeded those for the control groups.

MAIN RESULTS

Thirteen trials (involving 506 participants) were included. No overall improvement with treatment compared to placebo was seen for children or adolescents (odds ratio = 0.84, 95% confidence interval 0.56 to 1.25). A statistically significant but small benefit of treatment over placebo was seen in reducing symptoms (effect size (standardised mean difference) = -0.31, 95% confidence interval -0.62 to -0.01). Subgroup analyses suggest a larger benefit among adolescents (effect size = -0.47, 95% confidence interval -0.92 to -0.02), and no benefit among children (effect size = 0.15, 95% confidence interval -0.34 to 0.64). Treatment with a tricyclic antidepressant caused more vertigo (odds ratio = 4.38, 95% confidence interval 2.33 to 8.25), orthostatic hypotension (odds ratio = 6.78, 95% confidence interval 2.06 to 22.26), tremor (odds ratio 6.29, 95% confidence interval 1.78 to 22.17) and dry mouth (odds ratio = 5.17, 95% confidence interval 2.68 to 29.99) than did placebo, but no statistically significant difference was found for other possible adverse effects.

REVIEWER'S CONCLUSIONS

Data suggest tricyclic antidepressants are not useful in treating depression in pre pubertal children. There is marginal evidence to support the use of tricyclic antidepressants in the treatment of depression in adolescents, although the magnitude of effect is likely to be moderate at best.

The lack of standardization of cardiac troponin I assay systems

The lack of standardization of cardiac troponin I (cTnI) assay systems has meant an inability to compare absolute values between methods, and non-traceability of cTnI measurement in clinical laboratories. The present study tested whether a common calibrator for cTnI would harmonize values between different methods. Twenty fresh-frozen plasma samples and a common calibrator were analyzed in duplicate using the Dade Behring Stratus II, Chiron ACS:180, Abbott AxSYM, and Beckman Coulter Access immunoassay systems. Uncorrected cTnI values varied up to 60-fold between systems, and when correlated to the Stratus, linear regression slopes were 0.97 (ACS:180), 4.86 (AxSYM), and 0.03 (Access), verifying the differences in calibration. After correction for calibration differences by reference to the common calibrator, among-assay CV ranged from 2.7% to 55%, and was >25% for eight samples. However, the exclusion of Access results reduced the CV to 32% with only four outliers. The results show that comparable cTnI values between methods are possible by the use of a common calibrator. The lack of method harmonization for some samples may be due to non-equal antibody immunoreactivity of different plasma cTnI forms. The complete standardization of cTnI measurement requires both a secondary reference material and standardization of manufacturers' cTnI antibodies.

Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time. Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g-stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided. Plants at two stages of coleoptile development were tested. Plant responses were obtained using time-lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0 g and from 2 to 130 min, respectively. For threshold g-doses the reciprocity rule was obeyed. The threshold dose was of the order of 55 g s and 120 g s, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g-doses, chiefly because the data were more variable. It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm x t) with m-values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well-defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the data was large.

Efficacy of tricyclic drugs in treating child and adolescent depression: a meta-analysis

OBJECTIVE

To examine whether tricyclic antidepressants are superior to placebo in the treatment of child and adolescent depression.

DESIGN

Meta-analysis of 12 randomised controlled trials comparing the efficacy of tricyclic antidepressants with placebo in depressed subjects aged 6-18 years.

MAIN OUTCOME MEASURES

Most studies employed several depression rating scales. For each study the "best available" measure was chosen by using objective criteria, and individual and pooled effect sizes were calculated as the number of standard deviations by which the change scores for the treatment groups exceeded those for the control groups. Where authors had reported numbers "responding" to treatment we calculated individual and pooled ratios for the odds of improvement in treated compared with control subjects.

RESULTS

From the six studies presenting data which enabled an estimation of effect size the pooled effect size was 0.35 standard deviations (95% confidence interval of -0.16 to 0.86) indicating no significant benefit of treatment. From the five studies presenting data on the number of "responders" in each group, the ratio of the odds of a response in the treated compared with the control subjects was calculated and the pooled odds ratio was 1.08 (95% confidence interval of 0.53 to 2.17); again indicating no significant benefit of treatment. The pooled sample had more than an 80% chance of detecting a treatment effect of 0.5 standard deviations or greater. There was an inverse relation between study quality and estimated treatment effect.

CONCLUSIONS

Tricyclic antidepressants appear to be no more effective than placebo in the treatment of depression in children and adolescents.