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Biomedical subjects

J Levesque

Publications and source records attributed to J Levesque.

11 recordsLinked to original sources

Controlling high harmonic generation with molecular wave packets.

We show that, by controlling the alignment of molecules, we can influence the high harmonic generation process. We observed strong intensity modulation and spectral shaping of high harmonics produced with a rotational wave packet in a low-density gas of N2 or O2. In N2, where the highest occupied molecular orbital (HOMO) has sigma(g) symmetry, the maximum signal occurs when the molecules are aligned along the laser polarization while the minimum occurs when it is perpendicular. In O2, where the HOMO has pi(g) symmetry, the harmonics are enhanced when the molecules are aligned around 45 degrees to the laser polarization. The symmetry of the molecular orbital can be read by harmonics. Molecular wave packets offer a means of shaping attosecond pulses.

Journal Article↗

Tomographic imaging of molecular orbitals.

Single-electron wavefunctions, or orbitals, are the mathematical constructs used to describe the multi-electron wavefunction of molecules. Because the highest-lying orbitals are responsible for chemical properties, they are of particular interest. To observe these orbitals change as bonds are formed and broken is to observe the essence of chemistry. Yet single orbitals are difficult to observe experimentally, and until now, this has been impossible on the timescale of chemical reactions. Here we demonstrate that the full three-dimensional structure of a single orbital can be imaged by a seemingly unlikely technique, using high harmonics generated from intense femtosecond laser pulses focused on aligned molecules. Applying this approach to a series of molecular alignments, we accomplish a tomographic reconstruction of the highest occupied molecular orbital of N2. The method also allows us to follow the attosecond dynamics of an electron wave packet.

Journal Article↗

Changing rates of cancer. The hazards of using a single definition.

Changing cancer rates, abstracted from tumor registries, are used to make inferences about the effect of carcinogens and cancer treatments on a population-wide basis. We compared the annual age-standardized incidence rates of extremity soft tissue sarcomas from two large tumor registries using different case definitions. We identified all limb soft tissue sarcoma cases diagnosed 1973-1993 in the Ontario Cancer Registry (OCR) and the Surveillance, Epidemiology, and End Results (SEER) databases. Two case definitions for limb soft tissue sarcoma were used based on missing data, incomplete diagnostic methods and ICD-9 codes; an upper limit estimate of the rates which included all possible cases of limb soft tissue sarcoma and a lower limit estimate of the rates which included all definite cases of limb soft tissue sarcoma (with the true rates lying in between). The upper limit OCR rates showed a statistically significant decreasing linear trend (slope = -0.021, P < 0.01). Whereas the slope of the OCR lower limit regression line showed a statistically significant increase in rates (slope = 0.01, P = 0.04). Neither the upper or lower limit SEER rates had a statistically significant linear trend (slope = 0.002, P = 0.60 and slope = 0.001, P = 0.18, respectively). Case definition affects incidence rates and changing rates of cancer. Thus the use of a single case definition along with changing coding practices may alone explain changing cancer rates.

Age Factors↗

Determinants and outcomes of inpatient versus home based rehabilitation following elective hip and knee replacement.

OBJECTIVE: There are large variations in practice patterns and costs of rehabilitation following total joint replacement (TJR). We evaluated the determinants of rehabilitation setting (home based vs inpatient) after TJR, and its influence on early functional outcomes. METHODS: We studied a retrospective cohort of 146 primary total hip and knee replacements. Ninety-six patients completed a mailed survey consisting of the Western Ontario and McMaster University Osteoarthritis Index (WOMAC), the Medical Outcomes Survey Short Form-36 (SF-36), and a satisfaction questionnaire. RESULTS: The mean age of the cohort was 66 years, 70% were women, and osteoarthritis was the primary diagnosis in 79%. Thirty-nine percent received home based rehabilitation. Determinants of home based rehabilitation included preference for home based rehabilitation, male sex, and knowledge regarding TJR. At a mean followup of 8 months post TJR, there were no significant differences between the inpatient and home based rehabilitation groups with respect to the WOMAC, SF-36, and satisfaction scores. CONCLUSION. These results support continued use of home based rehabilitation.

Aged↗

Improving patient satisfaction with time spent in an orthopedic outpatient clinic.

OBJECTIVE: To determine if patient satisfaction can be improved by changing patients' expectations of the clinic visit and by decreasing the total time spent in the clinic. DESIGN: A prospective comparative analysis carried out in 4 phases. SETTING: An university-affiliated orthopedic outpatient clinic. PATIENTS: All patients seen in the orthopedic outpatient clinic were eligible. Phase 1 determined the total clinic time required by patient type; phase 2 assessed baseline satisfaction; phase 3 altered patients' expectations; and phase 4 altered patients' expectations and scheduled visits by patient type. INTERVENTION: Patient questionnaires. MAIN OUTCOME MEASURE: Patient satisfaction with time spent in the clinic. RESULTS: Of 708 distributed questionnaires, 622 (88%) were completed (547 totally complete, 75 partially complete). Total time spent in the clinic decreased across phases 2, 3 and 4 (mean 99.2, 94.7 and 85.2 minutes, respectively, but was significantly different only between phases 3 and 4; p = 0.05, Duncan's multiple range test). The percentage of patients who rated their waiting time as "excellent" increased across phases 2, 3 and 4 (14.6%, 18.8% and 31.1%, respectively; p = 0.0004, chi 2 test). CONCLUSION: Patient satisfaction can be improved by altering patient expectations and by decreasing the total time spent in clinic.

Female↗

31P NMR first spectral moment study of the partial magnetic orientation of phospholipid membranes.

Structural data can be obtained on proteins inserted in magnetically oriented phospholipid membranes such as bicelles, which are most often made of a mixture of long and short chain phosphatidylcholine. Possible shapes for these magnetically oriented membranes have been postulated in the literature, such as discoidal structures with a thickness of one bilayer and with the short acyl chain phosphatidylcholine on the edges. In the present paper, a geometrical study of these oriented structures is done to determine the validity of this model. The method used is based on the determination of the first spectral moment of solid-state (31)P nuclear magnetic resonance spectra. From this first moment, an order parameter is defined that allows a quantitative analysis of partially oriented spectra. The validity of this method is demonstrated in the present study for oriented samples made of DMPC, DMPC:DHPC, DMPC:DHPC:gramicidin A and adriamycin:cardiolipin.

Biophysical Phenomena↗

Residual disease following unplanned excision of soft-tissue sarcoma of an extremity.

Sixty-five patients who had been referred to our unit for additional management after an unplanned excision of a soft-tissue sarcoma of an extremity at another institution were studied retrospectively to determine the prevalence of residual tumor and to identify factors that predict which patients will have a tumor following such an excision. Unplanned excision was defined as excisional biopsy or unplanned resection of the lesion without benefit of preoperative imaging and without regard for the necessity to resect the lesion with a margin of normal tissue. In each patient, histological evaluation of the specimen removed at the unplanned excision had demonstrated positive resection margins, but postoperative physical examination on our unit revealed no gross evidence of residual tumor and no tumor was identified on cross-sectional imaging of the local site. Patients who had evidence of residual disease on physical examination or on imaging were thought to have definite evidence of sarcoma at the site of the operative wound and were therefore excluded from the study. After multidisciplinary consultation, all patients had a repeat resection at our cancer center. Extensive pathological sampling of the specimen from this second procedure was carried out, with sections obtained at mean intervals of 1.2 +/- 0.7 centimeters. Nodules initially thought to indicate disease were identified grossly in twenty-seven (42 percent) of the sixty-five patients, but histological evaluation confirmed the presence of tumor in only sixteen (59 percent). Histological evidence of sarcoma was identified in seven additional patients in whom gross nodules were not apparent in the specimen. Thus, sarcoma was identified in a total of twenty-three (35 percent) of the sixty-five patients. The mean duration of follow-up was forty-six months (range, twenty-four to eighty months; median, thirty-nine months). The margins of the second resection were positive in nine (39 percent) of the twenty-three patients who had residual sarcoma. Five (22 percent) of the twenty-three had a local recurrence. Four of the five patients who had a local recurrence had positive margins on repeat resection. This rate of local recurrence (five of twenty-three patients) was significantly higher than that in the remainder of our patients who had a soft-tissue sarcoma of an extremity (sixteen [7 percent] of 227) (p = 0.03). There was no association between the detection of sarcoma at the second procedure and the initial size or grade of the tumor, the use of irradiation preoperatively, or the interval between the initial, unplanned excision and referral to our cancer center. These data indicate that it is not possible to predict which patients will have residual tumor at the site of the operative wound. Therefore, it is prudent to advise repeat excision for all patients who have had an unplanned excision of a soft-tissue sarcoma of an extremity. Unplanned excision complicates decision-making in the treatment of this disease and should be avoided.

Biopsy↗

Cognitive effects of psychostimulant medication in hyperactive children.

Hyperactive and normal children were given a test of selective attention (Stroop test) and a neurocognitive test sensitive to a functional deficit of prefrontal cortex (Wisconsin Card Sorting Test). Hyperactive children showed significant deficits on both measures. After a year of psychostimulant medication, the hyperactive children all showed clinical and neurocognitive improvement, but continued to show a selective attention deficit compared with normal children. The results indicate a dissociation between the cognitive processes measured by the Wisconsin test and selective attention as measured by the Stroop, and that the selective attention deficit is more resistant to psychostimulant intervention.

Attention↗

Helping the patient cope with the sequelae of trauma through the self-help group approach.

Trauma Recovery is a developing organization which focuses on the psychosocial concerns of those recovering from multiple trauma. Utilizing the self-help group concept, recovering trauma patients participate in a program which enables of their injuries. Components of the program include group counseling, education, socialization, and outreach to others in similar circumstances.

Adult↗