Biomedical subjects

R Côté

Publications and source records attributed to R Côté.

At least 19 recordsLinked to original sources

PubMed2006

Anisotropic states of two-dimensional electrons in high magnetic fields.

We study the collective states formed by two-dimensional electrons in Landau levels of index n > or = near half filling. By numerically solving the self-consistent Hartree-Fock (HF) equations for a set of oblique two-dimensional lattices, we find that the stripe state is an anisotropic Wigner crystal (AWC), and determine its precise structure for varying values of the filling factor. Calculating the elastic energy, we find that the shear modulus of the AWC is small but finite (nonzero) within the HF approximation. This implies, in particular, that the long-wavelength magnetophonon mode in the stripe state vanishes q(3/2) like as in an ordinary Wigner crystal, and not like q(5/2) as was found in previous studies where the energy of shear deformations was neglected.

Journal Article↗

PubMed2005

Spectroscopic determination of the s-wave scattering lengths of 86Sr and 88Sr.

We report the use of photoassociative spectroscopy to determine the ground-state s-wave scattering lengths for the main bosonic isotopes of strontium, 86Sr and 88Sr. Photoassociative transitions are driven with a laser red detuned by up to 1400 GHz from the 1S0-1P1 atomic resonance at 461 nm. A minimum in the transition amplitude for 86Sr at -494 +/- 5 GHz allows us to determine the scattering lengths 610a0 < a86 < 2300a0 for 86Sr and a much smaller value of -1a0 < a88 < 13a0 for 88Sr.

Journal Article↗

PubMed2005

Evanescent-wave mirror for ultracold diatomic polar molecules.

We describe the interaction of an ultracold diatomic polar molecule with an evanescent-wave mirror. Several features of this system are explored, such as the coupling between internal rovibrational states of the molecule and the laser field. Numerical simulations show quantum reflection and state selection under attainable physical conditions. Such molecular optics components will facilitate the manipulation and trapping of ultracold molecules, and might serve in future applications in several fields, e.g., as devices to filter and select a state for ultracold chemistry, to measure extremely low temperatures of molecules, or to manipulate states for quantum information processing.

Journal Article↗

PubMed2005

Photoassociative spectroscopy at long range in ultracold strontium.

We report photoassociative spectroscopy of 88Sr(2) in a magneto-optical trap operating on the 1S0-->3P1 intercombination line at 689 nm. Photoassociative transitions are driven with a laser red detuned by 600-2400 MHz from the 1S0-->1P1 atomic resonance at 461 nm. Photoassociation takes place at extremely large internuclear separation, and the photoassociative spectrum is strongly affected by relativistic retardation. A fit of the transition frequencies determines the 1P1 atomic lifetime (tau=5.22+/-0.03 ns) and resolves a discrepancy between experiment and recent theoretical calculations.

Journal Article↗

PubMed2004

Local blockade of Rydberg excitation in an ultracold gas.

In the laser excitation of ultracold atoms to Rydberg states, we observe a dramatic suppression caused by van der Waals interactions. This behavior is interpreted as a local excitation blockade: Rydberg atoms strongly inhibit excitation of their neighbors. We measure suppression, relative to isolated atom excitation, by up to a factor of 6.4. The dependences of this suppression on both laser irradiance and atomic density are in good agreement with a mean-field model. These results are an important step towards using ultracold Rydberg atoms in quantum information processing.

Journal Article↗

PubMed2004

Quantum depinning transition of quantum Hall stripes.

We examine the effect of disorder on the electromagnetic response of quantum Hall stripes using an effective elastic theory to describe their low-energy dynamics, and replicas and the Gaussian variational method to handle disorder effects. Within our model we demonstrate the existence of a depinning transition at a critical partial Landau level filling factor Deltanu(c). For Deltanu Deltanu(c). For Deltanu> or =Deltanu(c), we find a partial RSB solution in which there is free sliding only along the stripe direction. The transition is analogous to the Kosterlitz-Thouless phase transition.

Journal Article↗

PubMed2004

Phytoaccumulation of heavy metals by aquatic plants.

Three aquatic plants were examined for their ability to remove heavy metals from contaminated water: parrot feather (Myriophylhum aquaticum), creeping primrose (Ludwigina palustris), and water mint (Mentha aquatic). The plants were obtained from a Solar Aquatic System treating municipal wastewater. All the three plants were able to remove Fe, Zn, Cu, and Hg from the contaminated water. The average removal efficiency for the three plant species was 99.8%, 76.7%, 41.62%, and 33.9% of Hg, Fe, Cu, and Zn, respectively. The removal rates of zinc and copper were constant (0.48 mg/l/day for Zn and 0.11 mg/l/day for Cu), whereas those of iron and mercury were dependent on the concentration of these elements in the contaminated water and ranged from 7.00 to 0.41 mg/l/day for Fe and 0.0787 to 0.0002 mg/l/day for Hg. Parrot feather showed greater tolerance to toxicity followed by water mint and creeping primrose. The growth of creeping primrose was significantly affected by heavy metal toxicity. The selectivity of heavy metals for the three plant species was the same (Hg>Fe>Cu>Zn). The mass balance preformed on the system showed that about 60.45-82.61% of the zinc and 38.96-60.75% of the copper were removed by precipitation as zinc phosphate and copper phosphate, respectively.

Chemical Precipitation↗

PubMed2004

A task-orientated intervention enhances walking distance and speed in the first year post stroke: a randomized controlled trial.

OBJECTIVE: To evaluate the efficacy of a task-orientated intervention in enhancing competence in walking in people with stroke. DESIGN: Two-centre observer-blinded stratified block-randomized controlled trial. SETTING: General community. SUBJECTS: Between May 2000 and February 2003, 91 individuals with a residual walking deficit within one year of a first or recurrent stroke consented to participate. INTERVENTIONS: The experimental intervention comprised 10 functional tasks designed to strengthen the lower extremities and enhance walking balance, speed and distance. The control intervention involved the practice of upper extremity activities. Subjects in both groups attended sessions three times a week for six weeks. MAIN MEASURES: Six-minute walk test (SMWT), 5-m walk (comfortable and maximum pace), Berg Balance Scale, timed 'up and go'. RESULTS: At baseline, subjects in the experimental (n = 44) and control (n = 47) groups walked an average distance of 209 m (SD = 126) and 204 m (SD =131), respectively, on the SMWT. Mean improvements of 40 m (SD =72), and 5 m (SD =66) were observed following the experimental and control interventions, respectively. The between-group difference was 35 m (95% confidence interval (CI) 7, 64). Significant between-group effects of 0.21 m/s (95% CI 0.12, 0.30) and of 0.11 m/s (95% CI 0.03, 0.19) in maximum and comfortable walking speed, respectively, were observed. People with a mild, moderate or severe walking deficit at baseline improved an average of 36 (SD =96), 55 (SD = 56) and 18 m (SD = 23), respectively, in SMWT performance following the experimental intervention. CONCLUSIONS: Study findings support the efficacy of a task-orientated intervention in enhancing walking distance and speed in the first year post stroke, particularly in people with moderate walking deficits.

Adult↗

PubMed2003

Long-range molecular resonances in a cold Rydberg gas.

We present evidence for molecular resonances in a cold dense gas of rubidium Rydberg atoms. Single UV photon excitation from the 5s ground state to np Rydberg states (n=50-90) reveals resonances at energies corresponding to excited atom pairs (n-1)d+ns. We attribute these normally forbidden transitions to avoided crossings between the long-range molecular potentials of two Rydberg atoms. These strong van der Waals interactions result in avoided crossings at extremely long range, e.g., approximately 58 000 times the Bohr radius (a(0)) for n=70.

Journal Article↗

PubMed2002

Mesoscopic molecular ions in Bose-Einstein condensates.

We study the possible formation of large (mesoscopic) molecular ions in an ultracold degenerate bosonic gas doped with charged particles (ions). We show that the polarization potentials produced by the ionic impurities are capable of capturing hundreds of atoms into loosely bound states. We describe the spontaneous formation of these hollow molecular ions via phonon emission and suggest an optical technique for coherent stimulated transitions of condensate atoms into a specific bound state. These results open up new possibilities for manipulating tightly confined ensembles.

Journal Article↗

PubMed2000

From classical mobility to hopping conductivity: charge hopping in an ultracold gas.

Studies of charge mobilities in an ultracold gas are reported. Calculations for the Na + Na+ system have been carried out as a function of temperature T and densities, and the conductivity of the ultracold charged gas is obtained. The total charge mobility exhibits a sharp increase as T is lowered, indicating a transition from an almost insulating to a conducting system at few microK. It is shown that the nature of the charge mobility changes with temperature: at high T, the charges are transported by massive centers (i.e., the ions), and at low T, by electrons jumping from neighboring atoms onto the positive ions (the positive holes exhibit hopping conductivity). An experiment is proposed to detect this effect.

Journal Article↗

PubMed2000

Stability of the smectic quantum hall state: a quantitative study.

We present an effective elastic theory which quantitatively describes the stripe phase of the two-dimensional electron gas in high Landau levels ( N>/=2). The dynamical matrix is obtained with remarkably high precision using the time-dependent Hartree-Fock approximation. A renormalization group analysis shows that at T = 0, as the partial filling factor Deltanu identical withnu- left floornu right floor moves away from 1/2, the anisotropic conducting state may undergo quantum phase transitions: stripes may get pinned along their conducting direction by disorder, or may lock into one another to form a crystal. The transitions should be reflected in the temperature dependence of the dissipative conductivity.

Journal Article↗

PubMed2000

Prolongation of brainstem auditory-evoked responses in autistic probands and their unaffected relatives.

BACKGROUND: Brain function, as indexed by brain electrical activity, is heritable in humans, and it may be impaired in autism. Autism also has strong genetic determinants, and like all major psychiatric disorders, its complex clinical phenotype renders genetic studies difficult. Innovative strategies focused on alternative biological phenotypes are needed. METHODS: The early brain auditory-evoked response was assessed in 73 autistic probands and 251 relatives who were compared with 521 normal controls. RESULTS: We first confirmed in the autistic probands the presence of a slowing in nerve conduction in the auditory system as expressed by the prolongation of early brain auditory-evoked response under the form of I-III interpeak latencies (IPLs). Furthermore, we observed the same I-III IPL prolongation in the unaffected first degree relatives of the autistic probands compared with controls. Despite clear evidence of a coaggregation of autism and I-III IPL prolongation in families, the IPLs did not seem to be the sole liability factor for autism as suggested by the observation of 52% of families in which the autistic proband and relatives showed normal IPLs. CONCLUSION: A prolongation of the early brain auditory-evoked response IPLs may be a marker for one of several deficits underlying autism and deserves further analysis as a potential alternative phenotype for the disorder.

Adult↗

PubMed2000

There's no place like home : an evaluation of early supported discharge for stroke.

BACKGROUND AND PURPOSE: Because stroke management is aimed at facilitating community reintegration, it would be logical that the sooner the patient can be discharged home, the sooner reintegration can commence. The purpose of this study was to determine the effectiveness of prompt discharge combined with home rehabilitation on function, community reintegration, and health-related quality of life during the first 3 months after stroke. METHODS: A randomized trial was carried out involving patients who required rehabilitation services and who had a caregiver at home. When medically ready for discharge, persons with stroke were randomized to either the home intervention group (n=58) or the usual care group (n=56). The home group received a 4-week, tailor-made home program of rehabilitation and nursing services; persons randomized to the usual care group received services provided through a variety of mechanisms, depending on institutional, care provider, and personal preference. The main outcome measure was the Physical Health component of the Measuring Outcomes Study Short-Form-36 (SF-36). Associated outcomes measures included the Timed Up & Go (TUG), Barthel Index (BI), the Older Americans Resource Scale for instrumental activities of daily living (OARS-IADL), Reintegration to Normal Living (RNL), and the SF-36 Mental Health component. RESULTS: The total length of stay for the home group was, on average, 10 days, 6 days shorter than that for the usual care group. There were no differences between the 2 groups on the BI or on the TUG at either 1 or 3 months after stroke; however, there was a significantly beneficial impact of the home intervention on IADL and reintegration (RNL). By 3 months after stroke, the home intervention group showed a significantly higher score on the SF-36 Physical Health component than the usual care group. The total number of services received by the home group was actually lower than that received by the usual care group. CONCLUSIONS: Prompt discharge combined with home rehabilitation appeared to translate motor and functional gains that occur through natural recovery and rehabilitation into a greater degree of higher-level function and satisfaction with community reintegration, and these in turn were translated into a better physical health.

Aged↗

PubMed2000

Hemostatic markers in patients at risk of cerebral ischemia.

BACKGROUND: Increased levels of markers of hemostasis may assist in the determination of the extent of carotid occlusive disease and the identification of neurologically intact individuals at increased risk of ischemic events. METHODS: We conducted a prospective study of 304 subjects, including 82 with a recent (< or =7 days) transient ischemic attack (TIA), 157 asymptomatic individuals with a cervical bruit, and 65 control subjects. Baseline evaluation included a neurological assessment, ECG, cervical ultrasonography, and cerebral CT and/or MRI. Levels of markers of coagulation and fibrinolytic activity were also determined. Results were analyzed in relation to the degree of carotid disease and the subsequent occurrence of cerebral and cardiac ischemic events. RESULTS: Over a mean follow-up period of 2.8 years (SD, 1.3 years), 114 ischemic events occurred. Survival analyses showed that prothrombin fragment 1.2 (F(1.2)) was a predictor of time to cerebral and cardiac ischemic events in the combined TIA and asymptomatic bruit group (relative risk [RR], 1.46; 95% CI, 1.18 to 1.81) as well as in the asymptomatic bruit group separately (RR, 1.70; 95% CI, 1.14 to 2.53). In the TIA group, both F(1.2) (RR, 2.36; 95% CI, 1.19 to 4.68) and severe (> or =80%) carotid stenosis (RR, 3.53; 95% CI, 1.19 to 10.51) were predictive of time to ischemic stroke, myocardial infarction, or vascular death. CONCLUSIONS: In patients with TIAs and in asymptomatic individuals with cervical bruits, F(1.2) levels were found to be independent predictors of subsequent cerebral and cardiac ischemic events. Our results are consistent with an active role of the coagulation system through upregulation of thrombin in carotid disease progression and in the pathogenesis of ischemic events in patients at risk.

Aged↗

PubMed1999

The prognosis of amaurosis fugax and hemispheric transient ischemic attacks.

BACKGROUND: The natural history of amaurosis fugax and of hemispheric transient ischemic attacks (TIAs) may be different. We analysed the ischemic risk factors, carotid status and prognosis with respect to future ischemic events in a cohort of patients who presented with either of these transient ischemic episodes. METHODS: The charts of patients who presented to our institution between February 1983 and April 1995 with amaurosis fugax or hemispheric TIAs were reviewed. Patients under the age of 45 years with a history of migraine or previous carotid surgery were excluded. Follow-up by a clinical visit or telephone interview was performed. Information was obtained regarding demographic features, presenting symptoms, ischemic risk factors, carotid status (as measured by duplex ultrasonography), type of medical treatment prescribed and occurrence of subsequent ischemic events. Outcome ischemic events were graded as major (myocardial infarction, cerebrovascular accident or death due to either of these) or minor (recurrent amaurosis fugax or hemispheric TIA). RESULTS: A total of 141 patients were followed for a mean of 47 months. Risk factors were more prevalent in patients with hemispheric TIAs than in those with amaurosis fugax. Most patients had a low degree of carotid stenosis. There was no statistically significant difference in the occurrence of major outcome events between the two groups. Kaplan-Meier survival curves were similar for the two groups. INTERPRETATION: Amaurosis fugax and hemispheric TIA both carry a risk for future ischemic events. However, we did not find a statistically significant difference in prognosis between the two groups.

Aged↗

PubMed1998

The evaluation and hazard classification of toxicological information for Workplace Hazardous Materials Information System material safety data sheets.

Hazardous materials used occupationally in Canada are subject to the legislated requirements of the Workplace Hazardous Materials Information System (WHMIS). This paper describes the administrative framework of WHMIS and how toxicological data are evaluated to determine if a substance triggers WHMIS classification for the toxicological endpoints of acute toxicity, skin irritation, eye irritation, corrosion, dermal sensitization, respiratory sensitization, chronic toxicity, mutagenicity, teratogenicity/embryotoxicity, and carcinogenicity. Problems encountered with the information on material safety data sheets are also discussed for each of the toxicological endpoints.

Carcinogenicity Tests↗

PubMed1997

Predictive power of duplex ultrasonography in asymptomatic carotid disease.

BACKGROUND: Duplex ultrasonography is considered a valid measure of stenosis of the carotid arteries, but the prognostic value of repeated ultrasonographic examinations is unknown. OBJECTIVE: To determine the ability of serial ultrasonographic measurements to predict cerebrovascular events in patients with asymptomatic carotid disease. DESIGN: Secondary analysis of data from a natural history study of asymptomatic carotid disease. PATIENTS: Asymptomatic patients with cervical bruits. MEASUREMENTS: Duplex ultrasonography of the carotid arteries was done at study enrollment and biannually thereafter. Multivariable Cox proportional hazards models with fixed and time-dependent covariates were used for analysis. RESULTS: 61 transient ischemic attacks (TIAs) and 38 strokes occurred in 715 participants over a mean follow-up period of 3.2 years; 4 strokes were disabling, and no deaths from stroke occurred. Sixty percent of strokes occurred in persons who did not have severe stenosis. One fifth of participants had stenosis progression. Baseline carotid stenosis was a significant predictor of the outcome "TIA or stroke" (relative risk, 1.5 [95% CI, 1.2 to 1.7]) and retained its predictive ability for more than 3 years. Progression of stenosis to 80% or more significantly increased the risk for cerebrovascular events and death. The sensitivity and positive predictive value of progression as an independent predictor of TIA or stroke were low. CONCLUSION: Severe carotid stenosis is associated with a higher risk for cerebrovascular events, but the power of repeated ultrasonography to predict ischemic events is limited by low incidence rates and low rates of progression. The evidence does not support the routine use of serial ultrasonography to determine the risk for stroke in unselected patients with asymptomatic carotid disease.

Adult↗