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Biomedical subjects

P Corkum

Publications and source records attributed to P Corkum.

7 recordsLinked to original sources
PubMed2001

Attosecond metrology.

The generation of ultrashort pulses is a key to exploring the dynamic behaviour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic processes occurring on an attosecond (1 as = 10-18 s) timescale. Here we trace electronic dynamics with a time resolution of </= 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible light pulse. Our measurement indicates an attosecond response of the atomic system, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchronism of the soft-X-ray pulse with the light field. The demonstrated experimental tools and techniques open the door to attosecond spectroscopy of bound electrons.

Journal Article↗
PubMed2001

Actigraphy and parental ratings of sleep in children with attention-deficit/hyperactivity disorder (ADHD).

STUDY OBJECTIVES: To assess various sleep parameters in latency-aged children with ADHD and their normally developing peers through the use of multiple sleep measures. DESIGN: Six sleep parameters were evaluated for two groups of children, ADHD and normal comparison. Each group consisted of 25 children (20 males, 5 females) who ranged in age from 7 to 11 years. All children underwent rigorous diagnostic procedures and the ADHD subjects were selected only if they displayed pervasiveness in their symptomatology and were medication naive. Parents completed a retrospective questionnaire which evaluated sleep problems over the past six months. Additionally, each child wore an actigraph for seven consecutive nights, and the child's parents completed a sleep diary during this time period. SETTING: N/A. PATIENTS OR PARTICIPANTS: N/A. INTERVENTIONS: N/A. RESULTS: Based on the findings from the questionnaire, parents of children with ADHD reported significantly more sleep problems than parents of normally developing children. However, the majority of these sleep differences were not verified through actigraphy or sleep diary data, with the exception of longer sleep duration for children with ADHD and parent reports that describe increased bedtime resistence. It was also found that child-parent interactions during bedtime routines were more challenging in the ADHD group. CONCLUSIONS: Despite the possibility of intrinsic sleep problems such as longer sleep duration, results indicate that many of the sleep problems of children with ADHD may be due to challenging behaviours during bedtime routines. The reason for discrepancies among sleep studies employing objective measures as well as between retrospective and prospective measures are discussed.

Attention Deficit Disorder with Hyperactivity↗
PubMed1999

Sleep problems in children with attention-deficit/hyperactivity disorder: impact of subtype, comorbidity, and stimulant medication.

OBJECTIVE: To determine the relationship of sleep problems to attention-deficit/hyperactivity disorder (ADHD), diagnostic subtype, comorbid disorders, and the effects of stimulant treatment. METHOD: On the basis of clinical diagnostic interviews, children aged 6 to 12 years were assigned to 4 groups: unmedicated ADHD (n = 79), medicated ADHD (n = 22), clinical comparison (n = 35), and healthy nonclinical comparison (n = 36). These groups were compared on 2 sleep questionnaires completed by the parents that assessed current sleep problems and factors associated with sleep difficulties (i.e., sleep routines, sleep practices, child and family sleep history). RESULTS: Factor analysis revealed 3 sleep problem categories: dyssomnias, parasomnias, and sleep-related involuntary movements. Linear regression analyses showed that (1) dyssomnias were related to confounding factors (i.e., comorbid oppositional defiant disorder and stimulant medication) rather than ADHD; (2) parasomnias were similar in clinical and nonclinical children; and (3) the DSM-IV combined subtype of ADHD was associated with sleep-related involuntary movements. However, sleep-related involuntary movements were more highly associated with separation anxiety. CONCLUSIONS: The results suggest that the relationship between sleep problems and ADHD is complex and depends on the type of sleep problem assessed as well as confounding factors such as comorbid clinical disorders and treatment with stimulant medication.

Attention Deficit Disorder with Hyperactivity↗
PubMed1999

Parental knowledge of attention-deficit hyperactivity disorder and opinions of treatment options: impact on enrollment and adherence to a 12-month treatment trial.

OBJECTIVE: This study examines the relationship between parents' knowledge of attention-deficit hyperactivity disorder (ADHD) and opinions of treatment and their impact on enrolment in and adherence to both pharmacological and nonpharmacological interventions for children with ADHD. METHOD: Participants in the study were the parents of 81 children who reached diagnostic criteria for ADHD and who were referred to a treatment study of ADHD involving stimulant medication and parent groups. The mothers completed a modified version of the ADHD Knowledge and Opinion Scale (AKOS) prior to receiving diagnostic feedback and prior to the families' decisions to participate in a 12-month randomized trial (medication [methylphenidate or placebo] and parent groups [training or support]). Treatment enrolment and adherence were monitored over the 12-month trial, and families who remained in the study at 12 months completed another modified AKOS. RESULTS: A higher level of knowledge of ADHD was found to be related to more favourable opinions of parent groups but not of medication. Moreover, parents who were more knowledgeable about ADHD were more likely to enroll in both pharmacological and nonpharmacological treatments. Adherence to pharmacological and nonpharmacological treatments was not predicted by parental knowledge of ADHD or opinions of the treatment. CONCLUSION: Parents' knowledge of ADHD and opinions of treatments play a significant role in enrollment in treatments for their children with ADHD. Providing information to parents regarding ADHD prior to offering treatment modalities could have a favourable impact on treatment enrollment and hence treatment adherence.

Adult↗
PubMed1998

Sleep disturbances in children with attention-deficit/hyperactivity disorder.

OBJECTIVE: To evaluate the relationship between sleep disturbances and attention-deficit/hyperactivity disorder (ADHD). METHOD: Empirical research published since 1970 on sleep disturbances in children with ADHD was systematically reviewed. A "box-score" approach was used to examine consistency of findings across the studies, which used different outcome measures. RESULTS: Although subjective accounts of sleep disturbances in ADHD were prevalent, objective verification of these disturbances was less robust. The only consistent objective findings were that children with ADHD displayed more movements during sleep but did not differ from normal controls in total sleep time. An additional finding was that stimulant medication led to changes in the children's sleep (e.g., prolonged sleep latency, increased length of onset to first rapid eye movement cycle), but these changes were believed to be nonpathological. CONCLUSIONS: The exact nature of the sleep problems in children with ADHD remains to be determined. Many of the relevant issues have not been adequately addressed. Factors such as poorly defined diagnostic groups, small sample sizes, few studies, and methodological and procedural limitations make it difficult to determine the relationship between ADHD and sleep problems.

Attention Deficit Disorder with Hyperactivity↗