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Biomedical subjects

N G Parker

Publications and source records attributed to N G Parker.

7 recordsLinked to original sources
PubMed2005

Emergence and decay of turbulence in stirred atomic Bose-Einstein condensates.

We show that "weak" elliptical deformation of an atomic Bose-Einstein condensate rotating at close to the quadrupole instability frequency leads to turbulence with a Kolmogorov energy spectrum. The turbulent state is produced by energy transfer to condensate fragments that are ejected by the quadrupole instability. This energy transfer is driven by breaking the twofold rotational symmetry of the condensate. Subsequently, vortex-sound interactions damp the turbulent state leading to the crystallization of a vortex lattice.

Journal Article↗
PubMed2004

Parametric driving of dark solitons in atomic Bose-Einstein condensates.

A dark soliton oscillating in an elongated harmonically confined atomic Bose-Einstein condensate continuously exchanges energy with the sound field. Periodic optical paddles are employed to controllably enhance the sound density and transfer energy to the soliton, analogous to parametric driving. In the absence of damping, the amplitude of the soliton oscillations can be dramatically reduced, whereas with damping, a driven soliton equilibrates as a stable soliton with lower energy, thereby extending the soliton lifetime up to the lifetime of the condensate.

Journal Article↗
PubMed2004

Controlled vortex-sound interactions in atomic Bose-Einstein condensates.

The low temperature dynamics of a vortex in a trapped quasi-two-dimensional Bose-Einstein condensate are studied quantitatively. Precession of an off-centered vortex in a dimple trap, embedded in a weaker harmonic trap, leads to the emission of sound in a dipolar radiation pattern. Sound emission and reabsorption can be controlled by varying the depth of the dimple. In a shallow dimple, the power emitted is proportional to the vortex acceleration-squared over the precession frequency, whereas for a deep dimple, periodic sound reabsorption stabilizes the vortex against radiation-induced decay.

Journal Article↗
PubMed2003

Soliton-sound interactions in quasi-one-dimensional Bose-Einstein condensates.

Longitudinal confinement of dark solitons in quasi-one-dimensional Bose-Einstein condensates leads to sound emission and reabsorption. We perform quantitative studies of the dynamics of a soliton oscillating in a tight dimple trap, embedded in a weaker harmonic trap. The dimple depth provides a sensitive handle to control the soliton-sound interaction. In the limit of no reabsorption, the power radiated is found to be proportional to the soliton acceleration squared. An experiment is proposed to detect sound emission as a change in amplitude and frequency of soliton oscillations.

Journal Article↗
PubMed2000

Citalopram in the treatment of depression.

OBJECTIVE: To review the efficacy and safety of citalopram in the treatment of depression. DATA SOURCES: MEDLINE search (1966-April 2000), Current Contents search, additional references listed in articles, and unpublished data obtained from the manufacturer were used to identify data from scientific literature. Studies evaluating citalopram (i.e., abstracts, clinical trials, data on file with the manufacturer) were considered for inclusion. STUDY SELECTION: English-language literature was reviewed to evaluate the pharmacology, pharmacokinetics, therapeutic use, and adverse effects of citalopram. DATA EXTRACTION: Controlled animal and human clinical studies published in the English-language literature were reviewed and evaluated. Clinical trials selected for inclusion were limited to those in human subjects and included data from animals if human data were not available. DATA SYNTHESIS: Citalopram is an antidepressant belonging to the class of selective serotonin-reuptake inhibitors (SSRIs) available for the treatment of depression. Citalopram offers therapeutic efficacy similar to that of the other SSRIs and a more favorable adverse effect profile than that of the tricyclic antidepressants (TCAs). Citalopram does not cause anticholinergic or cardiovascular adverse effects associated with the TCAs. Citalopram is the most selective SSRI and, unlike other SSRIs, seems to be relatively free of interaction mediated by the cytochrome P450 system. Citalopram is also the least expensive antidepressant available to date. This review of citalopram includes data from clinical trials comparing safety, tolerability, efficacy, and pharmacoeconomics with TCAs and SSRIs. CONCLUSIONS: Clinical trials demonstrate that citalopram's therapeutic efficacy is significantly greater than that of placebo and is comparable with that of other antidepressants. Citalopram has a favorable adverse effect profile, and thus may be useful in treating depressed patients who cannot tolerate anticholinergic or cardiovascular adverse effects associated with TCAs. It may also be useful in patients with comorbid illnesses requiring concomitant medicines.

Antidepressive Agents, Tricyclic↗
PubMed1999

Atypical antipsychotics: Part II: Adverse effects, drug interactions, and costs.

OBJECTIVE: To compare the adverse effects, drug interactions, and costs of conventional and atypical agents, and to provide a summary of therapeutic guidelines. Part I compared the pharmacology, pharmacokinetics, and efficacy of atypical and conventional agents. DATA SOURCES: Information was retrieved from a MEDLINE English-language literature search from June 1986 to June 1998 and by review of references. Indexing terms included atypical antipsychotics, neuroleptics, clozapine, risperidone, olanzapine, sertindole, quetiapine, and ziprasidone. STUDY SELECTION: Comparative studies were selected when possible; placebo-controlled studies were included when data were limited on newer atypical antipsychotics. DATA EXTRACTION: Emphasis was placed on properly designed clinical trials that assessed dosage, expanded efficacy, enhanced adverse effect profile, and cost. DATA SYNTHESIS: Significant adverse effects are agranulocytosis with clozapine, dose-dependent extrapyramidal side effects (EPS) with risperidone, and neuroleptic malignant syndrome with clozapine and risperidone. Clinically relevant drug interactions may occur with clozapine-lorazepam, clozapine-fluvoxamine, and sertindole-quinidine. Newer atypical agents have high acquisition costs but may reduce noncompliance and rehospitalization rates. CONCLUSIONS: Risperidone or olanzapine are recommended as first-line agents for schizophrenia due to accumulating controlled trials and clinical experience. Quetiapine should be considered with partial response or if EPS develop, and clozapine is an option with treatment-refractory patients. Atypical agents may contribute to a better quality of life, but conventional neuroleptics are the first choice for strictly cost considerations.

Antipsychotic Agents↗