PubMed Health⌕ Search

Biomedical subjects

P Cloutier

Publications and source records attributed to P Cloutier.

At least 19 recordsLinked to original sources
PubMed2007

Electron photoemission from charged films: absolute cross section for trapping 0-5 eV electrons in condensed CO2.

The electron trapping or attachment cross section of carbon dioxide (CO2) condensed as thin films on a spacer of Ar is obtained using a simple model for electron trapping in a molecular film and then charge releasing from the same film by photon absorption. The measurements are presented for different electron exposures and impact energies, film thicknesses, and probing photon energies. The cross section for trapping an electron of incident energy between 0 and 5 eV reveals three different attachment processes characterized by a maximum at about 0.75 eV, a structured feature around 2.25 eV, and a shoulder around 3.75 eV. From the measurement of their dependence with the probing photon energy, the two lowest processes produce traps having a vertical electron binding energy of approximately 3.5 eV, whereas the highest one yields a slightly higher value of approximately 3.7 eV. The 0.75 eV maximum corresponds to the formation of vibrational Feshbach resonances in (CO2)n- anion clusters. The 2.25 eV feature is attributed to the formation of a vibrationally excited 2Piu anion in (CO2)n- clusters, followed by fast decay into its vibrational ground state without undergoing autodetachment. Finally, 3.75 eV shoulder is assigned to the well-known dissociative electron attachment process from 2Piu anion state producing the O- anion in the gas phase and the (CO2)nO- anions in clusters.

Carbon Dioxide↗
PubMed2006

Electron stimulated desorption of anionic fragments from films of pure and electron-irradiated thiophene.

The electron stimulated desorption (ESD) of anions is used to explore the effects of electron irradiation on a thiophene film and we report measurements for electron impact on multilayer thiophene condensed on a polycrystalline platinum substrate. Below 22 eV and at low electron dose, desorbed anions include H- (the dominant signal) as well as S-, CH2-, SH- and SCH2-. Yield functions show that anions are desorbed both by dissociative electron attachment (DEA) with resonances observed at 9.5, 11, and 16 eV, and for energies >13 eV, by dipolar dissociation (DD). An increase in the S- signal from electron irradiated (beam-damaged) thiophene films and the appearance of a new DEA resonance in the S- yield function at 6 eV are linked to rupture of the thiophene ring and the formation of sulfur-terminated products within the film. The threshold energy for ring rupture is 5 eV. The desorption of new anions such as C4H3S- (Thiophene-H)- is also observed from electron irradiated films and these likely arise from the decomposition of large radiation product molecules synthesized in the film. The yield functions of H-, S-, SH-, (Thiophene-H)-, and (Thiophene+H)- anions from irradiated thiophene films that have been annealed to 300 K, each exhibit a single resonant feature centered around 5.1 eV, suggesting that all signals derive from DEA to the same molecular radiation product. In contrast, only H- and S- are observed to desorb from films of 2-2-bithiophene and no resonance is seen below approximately 10 eV in the anion yield functions. These data suggest that electron irradiation causes formation of ring-opened oligomers, and that closed-ring or 'classical" oligomers, (similar to bithiophene) if formed, contribute little to the ESD of anions.

Journal Article↗
PubMed2006

Validity of foot-to-foot bioelectrical impedance analysis in overweight and obese children and parents.

AIM: The aim of this study was to evaluate the validity of foot-to-foot bioelectrical impedance analysis (FF-BIA) in the measurement of body composition in overweight and obese children and their parents by comparison to dual-energy X-ray absorptiometry (DXA). METHODS: Seventeen, 7-12 year old overweight and obese children (6 boys, 11 girls) and 17 parents (5 fathers, 12 mothers) were evaluated for body composition with FF-BIA and DXA. Measures of percent body fat (PBF), fat mass (FM) and fat free mass (FFM) derived from FF-BIA and DXA were compared. Measures of validity were determined by Pearson correlations between FF-BIA and DXA, paired t-tests to assess mean differences, as well as biases and limits of agreement using the Bland Altman tests. RESULTS: FF-BIA produced estimates of body composition that were highly correlated with DXA in overweight and obese children and parents. For children, the correlations for PBF, FM, and FFM were 0.85, 0.97, and 0.94, respectively. For parents, the correlations for PBF, FM, and FFM were 0.92, 0.97, and 0.91, respectively. However, mean differences between FF-BIA and DXA were significant in children but not in parents. Bland-Altman tests of agreement showed moderate to large within-subject differences in body composition variables between FF-BIA and DXA. CONCLUSIONS: FF-BIA is strongly related to DXA in the measurement of body composition in both overweight and obese preadolescent children and parents, but the two measures may not be used interchangeably. Although FF-BIA may lack the precision to assess small changes in body composition in overweight and obese individuals, it is appropriate for epidemiological use.

Absorptiometry, Photon↗
PubMed2004

Script generation following frontal and parietal lesions.

The purpose of this investigation was to distinguish putative effects of parietal lobe lesions on script generation, in distinction from the better known and established effects of frontal lobe lesions. Nine patients, most with excised parietal lesions, were compared to nine age, gender and education matched normal participants. Eleven patients with excised tumors of the frontal lobe were compared to twelve age, gender and education matched normal subjects. Participants were requested to generate, out loud, scripts corresponding to everyday activities. Half the scripts were relatively more demanding with respect to temporal representation (understanding the time line of events) and the other half with respect to spatial representation (understanding the layout of the actions in space). These two conditions were further broken down into conditions of high and low demands on working memory (reciting the scripts backwards versus forward). The frontal lobe patients enunciated significantly fewer actions overall. They were also significantly more impaired than the normal participants on all tasks with high demands on working memory, and more often, high temporal demands (sequencing and perseverative errors). The parietal lobe patients had significant difficulty in sequencing in all conditions, and manifested no perseveration. Though script generation tasks have been primarily associated with frontal lobe function until now, consideration should be given to the type of activity being scripted as a function of relative demands on spatial or temporal representation, as well as working memory, and the contributions of other lobes ought to be taken into consideration.

Adolescent↗
PubMed2003

Dissociative electron attachment to DNA.

Electron-stimulated desorption of anions from thin films of linear and supercoiled DNA is investigated in the range 3-20 eV. Resonant structures are observed with maxima at 9.4+/-0.3, 9.2+/-0.3, and 9.2+/-0.3 eV, respectively, in the yield dependence of H-, O-, and OH- on the incident electron energy. Their formation is attributed to dissociative electron attachment.

Anions↗
PubMed2002

Cross sections for low-energy (10-50 eV) electron damage to DNA.

We report direct measurements of the formation of single-, double- and multiple strand breaks in pure plasmid DNA as a function of exposure to 10-50 eV electrons. The effective cross sections to produce these different types of DNA strand breaks were determined and were found to range from approximately 10(-17) to 3 x 10(-15) cm(2). The total effective cross section and the effective range for destruction of supercoiled DNA extend from 3.4 to 4.4 x 10(-15) cm(2) and 12 to 14 nm, respectively, over the range 10-50 eV. The variation of the effective cross sections with electron energy is discussed in terms of the electron's inelastic mean free path, penetration depth, and dissociation mechanisms, including resonant electron capture; the latter is found to dominate the effective cross sections for single- and double-strand breaks at 10 eV. The most striking observations are that (1) supercoiled DNA is approximately one order of magnitude more sensitive to the formation of double-strand breaks by low-energy electrons than is relaxed circular DNA, and (2) the dependence of the effective cross sections on the incident electron energy is unrelated to the corresponding ionization cross sections. This finding suggests that the traditional notion that radiobiological damage is related to the number of ionization events would not apply at very low energies.

DNA↗
PubMed2001

Sertraline effects in adolescent major depression and dysthymia: a six-month open trial.

This 6-month open-label study evaluated the efficacy, tolerability, and safety of sertraline in 21 adolescent psychiatric outpatients, ages 12 to 18 years, diagnosed with major depressive disorder (MDD, n = 13) or dysthymic disorder (DD, n = 8). Both groups showed clinically significant improvements on the Hamilton Depression Scale (HAM-D), Hamilton Anxiety Scale, and the Clinical Global Impression Scale-Severity (CGI-S). The MDD group showed maximal clinical response (based on the method of last observation carried forward) on the HAM-D and CGI at weeks 12 (76.9%) and 20 (76.9%), respectively. Response rates were maintained at week 24 with all six MDD study completers (100%) responding to treatment. The DD group achieved maximal response on the HAM-D (100%) and the CGI (75%) at week 6. Response rates in this group did not remain as elevated over time with two out of three (66.7%) DD study completers responding to treatment at week 24. Generally, sertraline was safe and well tolerated. Most adverse events were mild to moderate in severity and resolved with no action taken. Results suggest that sertraline may be efficacious in acute and continuation treatment of MDD in adolescents. DD patients showed evidence of clinical response and improvement, particularly in the acute treatment phase. Incorporating a longer evaluation period in the study of antidepressant therapy for adolescents with MDD and/or DD is emphasized.

Adolescent↗
PubMed2001

Suicidal children and adolescents with first emergency room presentations: predictors of six-month outcome.

OBJECTIVE: To examine risk of future documented suicide attempts and emergency room (ER) returns among children and adolescents with first suicidal ER presentations. METHOD: A total of 548 consecutive ER presentations of suicidal 5- to 19-year-olds to a Canadian center over a 1-year period (1997-1998) were reviewed. Relative risk analyses were performed on 224 first-time patients (mean age 14.6+/-2.1) to determine the strength of associations between predictors and outcomes (ER return and suicide attempts). RESULTS: At 6-month follow-up, 32.6% (n = 73) had returned to the ER, 24.1% (n = 54) had a documented suicide attempt, and 14.3% (n = 32) required psychiatric hospitalization. Predictors for both ER return and future documented suicide attempts included 15- to 19-year age range, past foster/group home placement, past mental health care, a suicide plan, reported mood symptoms, sobriety at ER visit, and general substance use. Child welfare guardianship and abuse history were also predictors of ER returns. CONCLUSIONS: Clinicians should be aware of these risk factors when assessing and managing suicidal youths with first ER presentations.

Adolescent↗
PubMed2001

Low-energy (5-40 eV) electron-stimulated desorption of anions from physisorbed DNA bases.

We present the results of experiments on anion desorption from the physisorbed DNA bases adenine, thymine, guanine and cytosine induced by the impact of low-energy (5-40 eV) electrons. Electron bombardment of DNA base films induces ring fragmentation and desorption of H(-), O(-), OH(-), CN(-), OCN(- ) and CH(2)(-) anions through either single or complex multibond dissociation. We designate the variation of the yield of an anion with electron energy as the yield function. Below 15 eV incident electron energy, bond cleavage is controlled mainly by dissociative electron attachment. Above 15 eV, the portion of a yield function that increases linearly is attributed to nonresonant processes, such as dipolar dissociation. A resonant structure is superimposed on this signal around 20 eV in the anion yield functions. This structure implicates dissociative electron attachment and/or resonant decay of the transient anion into the dipolar dissociation channel, with a minimal contribution from multiple inelastic electron scattering. The yields of all desorbing anions clearly show that electron resonances contribute to the damage of all DNA bases bombarded with 5-40 eV electrons. Comparison of the ion yields indicates that adenine is the least sensitive base to slow electron attack. Electron-irradiated guanine films exhibit the largest yields of desorbed anions.

Adenine↗
PubMed2000

Resonant formation of DNA strand breaks by low-energy (3 to 20 eV) electrons.

Most of the energy deposited in cells by ionizing radiation is channeled into the production of abundant free secondary electrons with ballistic energies between 1 and 20 electron volts. Here it is shown that reactions of such electrons, even at energies well below ionization thresholds, induce substantial yields of single- and double-strand breaks in DNA, which are caused by rapid decays of transient molecular resonances localized on the DNA's basic components. This finding presents a fundamental challenge to the traditional notion that genotoxic damage by secondary electrons can only occur at energies above the onset of ionization, or upon solvation when they become a slowly reacting chemical species.

Chemical Phenomena↗
PubMed2000

Induction of single- and double-strand breaks in plasmid DNA by 100-1500 eV electrons.

PURPOSE: To investigate the induction of DNA strand breaks by electrons with energies ranging from 0.1 to 1.5 keV. MATERIALS AND METHODS: Dry supercoiled plasmid DNA was irradiated with electrons of energies ranging from 0.1 to 1.5 keV and the results were compared with those obtained by gamma-irradiation of the same plasmid in solution. For electron irradiation, the plasmid was deposited on a gold substrate under a controlled atmosphere to minimize contamination of the DNA film. Electron bombardments were performed under ultra-high vacuum conditions (UHV 10(-9) torr). DNA damage was detected by gel electrophoresis followed by quantitation of the DNA bands by fluorescence or by hybridization with a radioactive probe. RESULTS: Electrons with energies from 0.1 to 1.5 keV induced single, double and multiple double-strand breaks in supercoiled plasmid DNA. For equal doses, we observed a marked increase in the efficiency of induction of double- and multiple-strand breaks in supercoiled DNA as a function of electron energy. In contrast to gamma-irradiation, the formation of small DNA fragments by electrons did not seem to be related to the production of the linear form of the plasmid. CONCLUSIONS: Electrons within the energy; range of the secondary electrons generated by high-energy ionizing radiation induce single, double and multiple double-strand breaks in DNA. Problems associated with low-energy electron irradiation experiments and dose calculations in thin films are also discussed.

DNA↗
PubMed1999

Global distribution of crustal magnetization discovered by the mars global surveyor MAG/ER experiment

Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between approximately 100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian highlands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch ( approximately 4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 x 10(17) ampere-meter2 in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.

Journal Article↗
PubMed1998

Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of approximately 100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 x 10(21) Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.

Journal Article↗
PubMed1998

Child extrafamilial sexual abuse: predicting parent and child functioning.

OBJECTIVE: This study evaluated the emotional and behavioral adjustment of parents and children within 3 months and 1 year after the discovery of child extrafamilial sexual abuse. METHOD: Ninety-two case parents (63 mothers, 29 fathers) and 56 children were compared to a nonclinical comparison group of 136 parents (74 mothers, 62 fathers) and 75 children. Parent adjustment was assessed using self-report measures while child functioning was assessed using a combination of child-, parent- and teacher-report measures. RESULTS: Mothers, fathers and sexually abused children experienced clinically significant effects both initially and at 12 months post-disclosure. Children's perceptions of self-blame and guilt for the abuse and the extent of traumatization predicted their self-reported symtomatology at 3 months and 1 year post-disclosure. Child age and gender also significantly contributed to the prediction of many of the child outcome measures. No abuse-related variable was related to any child self-report measure. Mothers' satisfaction in the parenting role, perceived support and intrusive symptoms predicted their initial emotional functioning. Avoidant symptoms, child's internalizing behavior and mothers' initial emotional functioning were significant predictors of longer-term emotional functioning. CONCLUSIONS: Results emphasize the need to address children's abuse-related attributions and underscore the need to expand our focus beyond the child victims to the traumatized families.

Adolescent↗
PubMed1996

Emotionally focused marital intervention for couples with chronically ill children.

Couples with chronically ill children are at risk for experiencing marital stress. The present study was a randomized control trial that assessed the efficacy of emotionally focused therapy (EFT) in decreasing marital distress in this population of couples. Thirty-two couples with chronically ill children seen at a tertiary care pediatric hospital were randomly assigned to EFT or to a waitlist control group. EFT couples demonstrated significant decreases in marital distress at posttreatment and at a 5-month follow-up in comparison to controls. Clinical improvements in marital functioning following EFT were also demonstrated.

Adaptation, Psychological↗