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T Caldwell

Publications and source records attributed to T Caldwell.

12 recordsLinked to original sources
PubMed2005

Unconventional superconductivity in PuCoGa5.

In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form (Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials--the copper oxides and a set of Ce- and U-based compounds. But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa5 has a transition temperature intermediate between those classes and therefore may bridge these extremes. Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa5, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials (a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered.

Journal Article↗
PubMed2001

Structural characterization of MAO and related aluminum complexes. 1. Solid-state (27)Al NMR with comparison to EFG tensors from ab initio molecular orbital calculations.

Experimental and ab initio molecular orbital techniques are developed for study of aluminum species with large quadrupole coupling constants to test structural models for methylaluminoxanes (MAO). The techniques are applied to nitrogen- and oxygen-containing complexes of aluminum and to solid MAO isolated from active commercial MAO preparations. (Aminato)- and (propanolato)aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three (27)Al NMR techniques optimized for large (27)Al quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. Four-membered (aminato)aluminum complexes with AlN(4) coordination yield slightly smaller C(q) values than similar AlN(2)C(2) sites: 12.2 vs 15.8 MHz. Planar 3-coordinate AlN(2)C sites have the largest C(q) values, 37 MHz. In all cases, molecular orbital calculations of the electric field gradient tensors yields C(q) and eta values that match with experiment, even for a large hexameric (aminato)aluminum cage. A D(3d) symmetry hexaaluminum oxane cluster, postulated as a model for MAO, yields a calculated C(q) of -23.7 MHz, eta = 0.7474, and predicts a spectrum that is too broad to match the field-swept NMR of methylaluminoxane, which shows at least three sites, all with C(q) values greater than 15 MHz but less than 21 MHz. Thus, the proposed hexaaluminum cluster, with its strained four-membered rings, is not a major component of MAO. However, calculations for dimers of the cage complex, either edge-bridged or face-bridged, show a much closer match to experiment. Also, MAO preparations differ, with a gel form of MAO having significantly larger (27)Al C(q) values than a nongel form, a conclusion reached on the basis of (27)Al NMR line widths in field-swept NMR spectra acquired from 13 to 24 T.

Journal Article↗
PubMed1984

Effect of nursing-staff support groups on the quality of newborn intensive care.

ICU support groups are widely recommended to mitigate the effects of stress on staff performance, thereby improving patient care. The usefulness of a nursing-staff support group was assessed in the neonatal ICUs of both a city/county hospital (10,000 births/yr) and a private hospital (3200 births/yr). Support-group meetings focused on communication and patient care and were conducted every 1 to 2 wk by psychiatrists experienced in intensive care support groups. Nevertheless, attendance diminished and the groups lasted only 6 to 7 months. Moreover, the quality of routine, emergency, and overall care did not differ significantly during intervention vs. control months. Our findings suggest that sources of ICU stress may be best addressed by methods other than nursing-staff support groups. Under the conditions of the study, we found little evidence to justify the expense and effort required to conduct ICU support groups.

Crisis Intervention↗
PubMed1984

Secondary agoraphobia: two case reports.

Two patients with agoraphobic symptoms and major depressive disorder exhibited dexamethasone nonsuppression. Antidepressant pharmacotherapy was associated with remission of depressive symptoms and DST normalization. This improvement predated remission of agoraphobic symptoms by 1-2 months. It is suggested that agoraphobia was secondary to the depression in both cases.

Aged↗
PubMed1983

Stresses and coping in ICU nursing: why support groups fail.

A successful nurse support group was contrasted with two unsuccessful support groups. The authors concluded that support groups work best if they are initiated in response to a felt need by the nurses, if the nurses have experienced the group leader as helpful in the past, if the group is highly structured and does not allow early discharge of intense negative feelings, and if the group's problems are primarily interpersonal and can be dealt with in the group and not primarily environmental or administrative problems such as noise, overcrowding, or understaffing.

Adaptation, Psychological↗
PubMed1981

Stresses and coping in ICU nursing. I. A review.

The literature on stresses in ICU nursing is reviewed to help the liaison psychiatrist facilitate nurses' coping with the considerable stresses in their work environment. Excessive workloads and understaffing have been found to be the most intense stresses. Also important are intrapsychic and interpersonal issues such as emotional reaction to loss, conflicts between ICU personnel, and insecurity stimulated by great responsibility in patient care. The studies reviewed suggest that nurses cope with these stresses by talking things out, by active mastery of complex technical procedures, and by drawing on mutually shared past experiences. Based on the above findings, the authors suggest means to reduce stress and enhance ICU nurses' coping.

Adaptation, Psychological↗
PubMed1981

Stresses and coping in ICU nursing. II. Nurse support groups on intensive care units.

Intensive care units (ICU) of hospitals are characteristically stressssful environments with high turnover of personnel. Support groups to help nurses deal with the stresses of the ICU environment have been widely recommended as a means to raise morale and increase communication, but are infrequently reported. Data on these groups are fragmentary. A review of the literature and correspondence with the authors of published papers demonstrated that most nurse support groups are open-ended groups with open membership, usually meeting for an hour a week, occasionally attended by nursing supervisors and unit physicians, and usually conducted by a liaison psychiatrist or a psychiatric consultant. Such groups are reported as positive experiences by nurses and group leaders. The small amounts of available objective evidence of the impact of support groups is positive; further research is required to arrive at a more definitive evaluation.

Adaptation, Psychological↗
PubMedDate not supplied

The process and impact of an ICU nurse support group.

This questionnaire study of a nurse support group on a pediatric intensive care unit confirms previous subjective reports of increased morale and better communication. The authors were also able to demonstrate reduced turnover rate of ICU nurses at the same that the turnover rate for the rest of the hospital increased, and found that the group had a positive influence on nurses' lives away from the hospital.

Critical Care↗