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Biomedical subjects

J McKeever

Publications and source records attributed to J McKeever.

12 recordsLinked to original sources
PubMed2003

Experimental realization of a one-atom laser in the regime of strong coupling.

Conventional lasers (from table-top systems to microscopic devices) typically operate in the so-called weak-coupling regime, involving large numbers of atoms and photons; individual quanta have a negligible impact on the system dynamics. However, this is no longer the case when the system approaches the regime of strong coupling for which the number of atoms and photons can become quite small. Indeed, the lasing properties of a single atom in a resonant cavity have been extensively investigated theoretically. Here we report the experimental realization of a one-atom laser operated in the regime of strong coupling. We exploit recent advances in cavity quantum electrodynamics that allow one atom to be isolated in an optical cavity in a regime for which one photon is sufficient to saturate the atomic transition. The observed characteristics of the atom-cavity system are qualitatively different from those of the familiar many-atom case. Specifically, our measurements of the intracavity photon number versus pump intensity indicate that there is no threshold for lasing, and we infer that the output flux from the cavity mode exceeds that from atomic fluorescence by more than tenfold. Observations of the second-order intensity correlation function demonstrate that our one-atom laser generates manifestly quantum (nonclassical) light, typified by photon anti-bunching and sub-poissonian photon statistics.

Journal Article↗
PubMed2003

State-insensitive cooling and trapping of single atoms in an optical cavity.

Single cesium atoms are cooled and trapped inside a small optical cavity by way of a novel far-off-resonance dipole-force trap, with observed lifetimes of 2-3 s. Trapped atoms are observed continuously via transmission of a strongly coupled probe beam, with individual events lasting approximately 1 s. The loss of successive atoms from the trap N>/=3-->2-->1-->0 is thereby monitored in real time. Trapping, cooling, and interactions with strong coupling are enabled by the trap potential, for which the center-of-mass motion is only weakly dependent on the atom's internal state.

Journal Article↗
PubMed2000

Anesthetic and analgesic practices in Avicenna's Canon of Medicine.

Anesthetic and analgesic practices during the Middle Ages and the Renaissance are presented from a translation of the relevant sections of the Canon of Medicine by Avicenna (980-1037) one of the most widely read and authoritative textbooks of the period. Avicenna described tracheotomy, oropharyngeal intubation and a method for clearing upper airway secretions for the treatment of stridor and respiratory distress. He also identified certain plants with pharmacological action such as mandragora or nightshade, opium and henbane and gives various recipes for inducing both anesthesia and analgesia before surgery.

Analgesics↗
PubMed1994

Oxygen free radical activity in experimental colonic carcinoma.

Oxygen free radical activity has been implicated in carcinogenesis through DNA lysis. This study measured chemiluminescence and superoxide dismutase (SOD) inhibition as an index of oxygen free radical activity in azoxymethane-induced colonic carcinoma. After 3 weeks of acclimatization, ten Fisher 344 rats were injected with azoxymethane (7 mg kg-1 week-1) over 10 weeks. All animals were killed at 37 weeks and colonic mucosa (5-25 mg wet weight) was sampled from sites of histologically confirmed gross tumour and sites 3-5 cm distant from tumour as well as from ten paired normal controls. The samples were processed in buffered luminol and chemiluminescence was measured in a luminometer. Each sample was then placed in a solution of SOD for 3 min before a second chemiluminescence estimation. Mean(s.e.m.) chemiluminescence from control mucosal samples decreased from 8.1(1.0) to 3.9(1.1) mV per 100 mg tissue (P < 0.05) after incubation in SOD, suggesting that oxygen free radical activity was being measured. There was an increase to 20.2(0.9) mV per 100 mg in azoxymethane-treated colon remote from tumour and to 53.9(2.1) mV per 100 mg at tumour sites; both were reduced significantly after incubation with SOD to 6.7(0.7) and 11.0(0.8) mV per 100 mg respectively (P < 0.001). Chemiluminescence was significantly increased in azoxymethane-induced colonic carcinoma, both remote from and maximally at the tumour site, suggesting a field change in carcinogenesis associated with oxygen free radical activity.

Animals↗
PubMed1983

Multiple theoretical approaches to supervision: choices in family therapy training.

The supervision techniques used in structural, strategic, family-of-origin, and experiential family therapy training are discussed and compared, with emphasis on the isomorphism between supervision and therapy in each school. The usefulness of each supervisory model is related to supervisees' needs at different levels of training. Recommendations are made about the sequence of family therapy training, including the utility of eclectic versus purist family therapy training programs for trainees at different levels of experience.

Family↗
PubMed1979

Assessment of the association between habitual salt intake and high blood pressure: methodological problems.

Despite the finding in cross-cultural comparisons that habitual sodium intake correlates with levels of blood pressure, similar studies from within population groups have yielded inconsistent results. The data presented in this report indicate that in industrialized societies the high degree of intra-individual variability of sodium intake, compared to much smaller inter-individual differences, may obscure potential biological correlations. A quantitative statistical method is presented to assess and minimize the effect of the large intra-individual variation in daily urinary sodium excretion.

Adult↗