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Biomedical subjects

A Bellavance

Publications and source records attributed to A Bellavance.

54 records · Page 3Linked to original sources
PubMed2001

Branching ratio measurement of the decay K(L) --> e(+)e(-)mu(+)mu(-).

We have collected a 43 event sample of the decay K(L)-->e(+)e(-)mu(+)mu(-) with negligible backgrounds and measured its branching ratio to be (2.62+/-0.40+/-0.17)x10(-9). We see no evidence for CP violation in this decay. In addition, we set the 90% confidence upper limit on the combined branching ratios for the lepton flavor violating decays K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+) at B(K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+))< or =1.23x10(-10), assuming a uniform phase space distribution.

Journal Article↗
PubMed2001

Measurement of the branching ratio and form factor of K(L)-->mu(+)mu(-)gamma.

We report on the analysis of the rare decay K(L)-->mu(+)mu(-)gamma the 1997 data from the KTeV experiment at Fermilab. A total of 9327 candidate events are observed with 2.4% background, representing a factor of 40 increase in statistics over the current world sample. We find that B(K(L)-->mu(+)mu(-)gamma) = (3.62 +/- 0.04(stat) +/- 0.08(syst)) x 10(-7). The form factor parameter alpha(K*) is measured to be alpha(K*) = -0.160(+0.026)(-0.028). In addition, we make the first measurement of the parameter alpha from the D'Ambrosio-Isidori-Portolés form factor, finding alpha = -1.54 +/- 0.10. In that model, this alpha measurement limits the Cabibbo-Kobayashi-Maskawa parameter rho>-0.2.

Journal Article↗
PubMed2001

Measurements of the rare decay K(L) --> e(+)e(-)e(+)e(-).

We observe 441 K(L)-->e(+)e(-)e(+)e(-) candidate events with a background of 4.2 events and measure B(K(L)-->e(+)e(-)e(+)e(-)) = [3.72+/-0.18(stat)+/-0.23(syst)]x10(-8) in the KTeV/E799II experiment at Fermilab. Using the distribution of the angle between the planes of the e(+)e(-) pairs, we measure the CP parameters beta(CP) = -0.23+/-0.09(stat)+/-0.02(syst) and gamma(CP) = -0.09+/-0.09(stat)+/-0.02(syst). We also present the first detailed study of the e(+)e(-) invariant mass spectrum in this decay mode.

Journal Article↗
PubMed2001

Measurement of the branching ratio and asymmetry of the decay Xi degrees -->Sigma degrees gamma.

We have studied the rare weak radiative hyperon decay Xi degrees -->Sigma degrees gamma in the KTeV experiment at Fermilab. We have identified 4045 signal events over a background of 804 events. The dominant Xi degrees -->Lambdapi degrees decay, which was used for normalization, is the only important background source. An analysis of the acceptance of both modes yields a branching ratio of B(Xi degrees -->Sigma degrees gamma)/B(Xi degrees -->Lambdapi degrees ) = (3.34+/-0.05+/-0.09)x10(-3). By analyzing the final state decay distributions, we have also determined that the Sigma degrees emission asymmetry parameter for this decay is alpha(XiSigma) = -0.63+/-0.09.

Journal Article↗
PubMed2001

Study of the K(0)(L) --> pi(+)pi(-)gamma Direct Emission Vertex.

We have performed studies of the K(0)(L)-->pi(+)pi(-)gamma direct emission ( DE) and inner Bremsstrahlung ( IB) vertices, based on data collected by KTeV during the 1996 Fermilab fixed target run. We find a(1)/a(2) = -0.737+/-0.034 GeV2 for the DE form-factor parameter in the rho-propagator parametrization, and report on fits of the form factor to linear and quadratic functions as well. We concurrently measure gamma(K(0)(L)-->pi(+)pi(-)gamma,E(*)(gamma)>20 MeV)/gamma(K(0)(L)-->pi(+)pi(-)) = (20.8+/-0.3)x10(-3), and a K(0)(L)-->pi(+)pi(-)gamma DE/(DE+IB) branching ratio of 0.683+/-0.011.

Journal Article↗
PubMed2001

Search for the decay KL --> pi(0)e+e-.

We report on a search for the decay KL-->pi(0)e+e- carried out by the KTeV/E799 experiment at Fermilab. This decay is expected to have a significant CP violating contribution and the measurement of its branching ratio could support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or could point to new physics. Two events were observed in the 1997 data with an expected background of 1.06+/-0.41 events, and we set an upper limit B(KL-->pi(0)e+e-)<5.1 x 10(-10) at the 90% confidence level.

Journal Article↗
PubMed2001

Physical impairments in cervicogenic headache: traumatic vs. nontraumatic onset.

In order to quantify the physical impairments associated with different types of headache, 77 subjects belonging to four different groups (postmotor vehicle accident cervicogenic headache subjects, cervicogenic headache subjects nontraumatic, migraine patients and control subjects) were evaluated using the following variables: posture, cervical range of motion, strength of the neck flexors and extensors, endurance of the short neck flexors, manual segmental mobility, proprioception of the neck, and pain (McGill Pain Questionnaire and the skin roll test). The results of this study showed that postmotor vehicle accident cervicogenic patients have significantly limited active cervical range of motion (in flexion/extension and rotations), present decreased strength and endurance of neck flexors and decreased strength of the extensor muscles. Our results suggest that there are enough differences between the postmotor vehicle accident and nontraumatic cervicogenic headache subjects to warrant caution when analysing the data of these two subgroups together, as several studies have done in the past. The onset of headache is therefore an important variable that should be controlled for when attempting to characterize the physical impairments associated with cervicogenic headache.

Accidents, Traffic↗
PubMed2000

Search for the decay K(L) --> pi(0)&mgr;(+)&mgr;(-)

We report on a search for the decay K(L)-->pi(0)&mgr;(+)&mgr;(-) carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CP violating contribution and a direct measurement will either support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87+/-0.15 events, and we set an upper limit B(K(L)-->pi(0)&mgr;(+)&mgr;(-))<3. 8x10(-10) at the 90% confidence level.

Journal Article↗
PubMed2000

Search for the weak decay of a lightly bound H0 dibaryon

We present results of a search for a new form of hadronic matter, a six-quark, dibaryon state called the H0, a state predicted to exist in several theoretical models. Analyzing data collected by experiment E799-II at Fermilab, we searched for the decay H0-->Lambdappi(-) and found no candidate events. We place an upper limit on [B(H0-->Lambdappi(-))dsigma(H)/dOmega]/(dsigma(Xi)/dOmega) and, in the context of published models, exclude the region of lightly bound mass states just below the LambdaLambda mass threshold, 2.194<M(H)<2.231 GeV/c(2), with lifetimes from approximately 5x10(-10) sec to approximately 1x10(-3) sec.

Journal Article↗
PubMed2000

Observation of CP violation in K(L)-->pi(+)pi(-)e(+)e(-) decays

We report the first observation of a manifestly CP violating effect in the K(L)-->pi(+)pi(-)e(+)e(-) decay mode. A large asymmetry was observed in the distribution of these decays in the CP-odd and T-odd angle straight phi between the decay planes of the e(+)e(-) and pi(+)pi(-) pairs in the K(L) center of mass system. After acceptance corrections, the overall asymmetry is found to be [13.6+/-2. 5(stat)+/-1.2(syst)]%. This is the largest CP-violating effect yet observed when integrating over the entire phase space of a mode and the first such effect observed in an angular variable.

Journal Article↗
PubMed2000

Seizures after stroke: a prospective multicenter study.

BACKGROUND: Studies of seizures after stroke have largely been retrospective, with small patient numbers and limited statistical analysis. Much of the doctrine about seizures after stroke is not evidenced based. OBJECTIVE: To determine the incidence, outcome, and risk factors for seizures after stroke. DESIGN: International, multicenter, prospective, analytic inception cohort study conducted for 34 months. PATIENTS AND SETTING: There were 2021 consecutive patients with acute stroke admitted to university teaching hospitals with established stroke units. After exclusion of 124 patients with previous epilepsy or without computed tomographic diagnosis, 1897 were available for analysis. Mean follow-up was 9 months. MAIN OUTCOME MEASURES: Occurrence of 1 or more seizures after stroke, stroke disability, and death after stroke. RESULTS: Seizures occurred in 168 (8.9%) of 1897 patients with stroke (28 [10.6%] of 265 with hemorrhagic and 140 [8.6%] of 1632 with ischemic stroke). On Kaplan-Meier survival analysis, patients with hemorrhagic stroke were at significantly greater risk of seizures (P =.002), with an almost 2-fold increase in risk of seizure after stroke (hazard ratio [HR], 1.85; 95% confidence interval [CI], 1.26-2.73; P =.002). On multivariate analysis, risk factors for seizures after ischemic stroke were cortical location of infarction (HR, 2.09; 95% CI, 1. 19-3.68; P<.01) and stroke disability (HR, 2.10; 95% CI, 1.16-3.82; P<.02). The only risk factor for seizures after hemorrhagic stroke was cortical location (HR, 3.16; 95% CI, 1.35-7.40; P<.008). Recurrent seizures (epilepsy) occurred in 47 (2.5%) of 1897 patients. Late onset of the first seizure was an independent risk factor for epilepsy after ischemic stroke (HR, 12.37; 95% CI, 4.74-32.32; P<. 001) but not after hemorrhagic stroke. CONCLUSIONS: Seizures occur more commonly with hemorrhagic stroke than with ischemic stroke. Only a small minority later develop epilepsy. Patients with a disabling cortical infarct or a cortical hemorrhage are more likely to have seizures after stroke; those with late-onset seizures are at greater risk of epilepsy.

Aged↗
PubMed1997

Educational level and neuropsychological heterogeneity in dementia of the Alzheimer type.

We retrospectively assessed the data from 24 patients with dementia of the Alzheimer type (DAT) who underwent comprehensive neuropsychological evaluations in order to determine whether there is a relationship between neuropsychological heterogeneity and educational level. Postmortem neuropathological examination results were made available for seven cases, confirming the diagnosis of DAT. Thirteen patients had < or = 8 years of schooling (less educated subgroup), and the other 11 had > or = 8 years (higher educated subgroup). There were no significant differences between the two subgroups regarding age and duration of symptoms. Performance within each subgroup was compared with that of a specific set of education-matched elderly controls. In the less educated subgroup, 10 patients evidenced a homogeneous pattern of cognitive impairment, with all cognitive areas being similarly affected. Conversely, 10 higher educated patients had at least one cognitive area relatively preserved in comparison with the others, characterizing a heterogeneous pattern of impairment. These data suggest that a high level of education may lead to a greater capacity to compensate for neuronal damage and determines specific patterns of cognitive impairment in DAT.

Aged↗
PubMed1993

Painful intervertebral dysfunction: Robert Maigne's original contribution to headache of cervical origin. The Quebec Headache Study Group.

Professor Robert Maigne, a French Orthopedic Medicine and Functional Rehabilitation specialist, has put forward new concepts leading to a better understanding of common pain of spinal origin. Maigne explains that pain in the spine is due to an intervertebral dysfunction of the mobile segment which consists of the intervertebral disc, ligaments and the facet joints. Any benign mechanical dysfunction of the mobile segment can induce a pain radiating in the dermatome at the same level as the vertebral problem. Maigne also described signs found in the skin (cellulalgia), in the muscles (myalgic bands) and in the bony insertions of tendons (tenalgia). These signs are to be found in the same dermatome, myotome and sclerotome as the spinal dysfunction. For headache of cervical origin due to painful intervertebral dysfunction, the most frequent dysfunctional mobile segment is located at the C2-C3 level. This induces pain mostly in the posterior parts of the head and cellulalgia in the C2 and C3 dermatomes. Painful tumefaction is also found over the posterior aspects of the facet joints on palpation at this level. These findings are key elements for the diagnosis of painful intervertebral dysfunction. The recognition of these signs is changing our understanding of the role of the cervical spine in headaches. Painful intervertebral dysfunction is very frequently found in chronic daily headaches.

Headache↗
PubMed1993

Efficacy of ticlopidine and aspirin for prevention of reversible cerebrovascular ischemic events. The Ticlopidine Aspirin Stroke Study.

BACKGROUND AND PURPOSE: This subgroup analysis from the Ticlopidine Aspirin Stroke Study (TASS) compared ticlopidine, a new antiplatelet agent, with aspirin for the prevention of recurrent transient ischemic attacks in patients who had a recent reversible cerebrovascular event. METHODS: This was a multicenter, double-blind, randomized trial in patients with a recent cerebral ischemic history. Patients with a reversible cerebral ischemic event within 3 months of enrollment were eligible for the study. All patients received either aspirin 650 mg twice daily or ticlopidine 250 mg twice daily for up to 5.8 years. The primary end point in this analysis was the first occurrence of a reversible ischemic event either alone or combined with nonfatal stroke or death and fatal or nonfatal stroke. RESULTS: Overall, ticlopidine was better than aspirin for reducing the risk of reversible ischemic events either alone or as a composite with death and/or stroke or with fetal and/or nonfatal stroke (P = .007 to P < .001). The risk reductions with ticlopidine were maintained for the duration of the 5-year follow-up. The most frequent or clinically important adverse effects associated with ticlopidine were diarrhea, rash, and neutropenia. Neutropenia was severe in 13 patients but resolved promptly with discontinuation of therapy. CONCLUSIONS: The results in this subgroup of patients with reversible ischemic disease, as well as the overall analysis of TASS, suggest that ticlopidine is a more effective agent than aspirin for the prevention of recurrent transient ischemic attacks.

Adult↗
PubMed1980

Neuropathy and mitochondrial myopathy.

It has been stated that peripheral neuropathy can be a feature of so-called ophthalmoplegia-plus syndrome, but to date only one case of hypertrophic neuropathy has been reported. This study is concerned with the clinical, electrophysiological, and pathological observations in a 37-year-old man with progressive external ophthalmoplegia and a ragged-red fiber myopathy associated with severe sensorimotor neuropathy. Histological and morphometric studies of the sural nerve revealed a marked loss of large myelinated fibers and an occasional degenerating axon. Residual fibers had disproportionately thin myelin sheaths in relation to axon calibers. In contrast to the muscle biopsy findings, no mitochondrial paracrystalline inclusions were observed in the nerve. However, the number of mitochondria per square micron of Schwann cell cytoplasm was elevated when compared with values obtained from normal subjects and a patient with a chronic neuropathy. These findings may indicate an alteration of mitochondrial function common to muscle fibers and Schwann cells which, in nerves, could lead to axon loss and abnormality of myelination.

Humans↗