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Biomedical subjects

J S Gardner

Publications and source records attributed to J S Gardner.

At least 19 recordsLinked to original sources

Field-induced order and spin waves in the pyrochlore antiferromagnet Tb2Ti207.

High resolution time-of-flight neutron scattering measurements on Tb(2)Ti(2)0(7) reveal a rich low temperature phase diagram in the presence of a magnetic field applied along [110]. In zero field at T = 0.4 K, Tb(2)Ti(2)0(7) is a highly correlated cooperative paramagnet with disordered spins residing on a pyrochlore lattice of corner-sharing tetrahedra. Application of a small field condenses much of the magnetic diffuse scattering, characteristic of the disordered spins, into a new Bragg peak characteristic of a polarized paramagnet. At higher fields, a magnetically ordered phase is induced, which supports spin wave excitations indicative of continuous, rather than Ising-like, spin degrees of freedom.

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Novel coexistence of superconductivity with two distinct magnetic orders.

The heavy fermion system exhibits properties that range from an incommensurate antiferromagnet for small to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of and a new, commensurate antiferromagnetism that orders separately. The coexistence of -electron superconductivity with two distinct -electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.

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Magnetic ordering in the spin-ice candidate Ho2Ru2O7.

Neutron scattering measurements on the spin-ice candidate material Ho2Ru2O7 have revealed two magnetic transitions at T approximately 95 and approximately 1.4 K to long-range ordered states involving the Ru and Ho sublattices, respectively. Between these transitions, the Ho3+ moments form short-ranged ordered spin clusters. The internal field provided by the ordered S=1 Ru4+ moments disrupts the fragile spin-ice state and drives the Ho3+ moments to order. We have directly measured a slight shift in the Ho3+ crystal field levels at 95 K from the Ru ordering.

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Dynamic properties of a diluted pyrochlore cooperative paramagnet (Tb(p)Y(1-p))2Ti2O7.

Investigations of the spin dynamics of the geometrically frustrated pyrochlore (Tb(p)Y(1-p))2Ti2O7, using muon spin relaxation and neutron spin echo, as a function of magnetic coverage p, have been carried out. Our major finding is that paramagnetic fluctuations prevail as T-->0 for all values of p, and that they are sensitive to dilution, indicating a cooperative spin motion. However, the percolation threshold pc is not a critical point for the fluctuations. We also find that the low temperature spectral density has a 1/f behavior, and that dilution slows down the spin fluctuations.

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Pressure-induced crystallization of a spin liquid.

Liquids are expected to crystallize at low temperature. The only exception is helium, which can remain liquid at 0 K, owing to quantum fluctuations. Similarly, the atomic magnetic moments (spins) in a magnet are expected to order at a temperature scale set by the Curie-Weiss temperature theta(CW) (ref. 3). Geometrically frustrated magnets represent an exception. In these systems, the pairwise spin interactions cannot be simultaneously minimized because of the lattice symmetry. This can stabilize a liquid-like state of short-range-ordered fluctuating moments well below theta(CW) (refs 5-7). Here we use neutron scattering to observe the spin liquid state in a geometrically frustrated system, Tb(2)Ti(2)O(7), under conditions of high pressure (approximately 9 GPa) and low temperature (approximately 1 K). This compound is a three-dimensional magnet with theta(CW) = -19 K, where the negative value indicates antiferromagnetic interactions. At ambient pressure Tb(2)Ti(2)O(7) remains in a spin liquid state down to at least 70 mK (ref. 8). But we find that, under high pressure, the spins start to order or 'crystallize' below 2.1 K, with antiferromagnetic order coexisting with liquid-like fluctuations. These results indicate that a spin liquid/solid mixture can be induced by pressure in geometrically frustrated systems.

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Temperature dependence of the magnetic penetration depth in the vortex state of the pyrochlore superconductor, Cd2Re2O7.

We report transverse-field and zero-field muon spin rotation and relaxation studies of the superconducting rhenium oxide pyrochlore, Cd2Re2O7. Transverse-field measurements (H=0.007 T) show line broadening below T(c), which is characteristic of a vortex state, demonstrating conclusively the type-II nature of this superconductor. The penetration depth is seen to level off below about 400 mK (T/T(c) approximately 0.4), with a rather large value of lambda(T=0) approximately 7500 A. The temperature independent behavior below approximately 400 mK is consistent with a nodeless superconducting energy gap. Zero-field measurements indicate no static magnetic fields developing below the transition temperature.

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Frustration driven lattice distortion: an NMR investigation of Y(2)Mo(2)O(7).

We have investigated the (89)Y NMR spectrum and spin lattice relaxation, T(1), in the magnetically frustrated pyrochlore Y(2)Mo(2)O(7). We find that upon cooling the spectrum shifts, and broadens asymmetrically. A detailed examination of the low T spectrum reveals that it is constructed from multiple peaks, each shifted by a different amount. We argue that this spectrum is due to discrete lattice distortions and speculate that these distortions relieve the frustration and reduce the system's energy.

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Spin correlations in Ho2Ti2O7: a dipolar spin ice system.

The pyrochlore material Ho2Ti2O7 has been suggested to show "spin ice" behavior. We present neutron scattering and specific heat results that establish unambiguously that Ho2Ti2O7 exhibits spin ice correlations at low temperature. Diffuse magnetic neutron scattering is quite well described by a nearest neighbor spin ice model and very accurately described by a dipolar spin ice model. The heat capacity is well accounted for by the sum of a dipolar spin ice contribution and an expected nuclear spin contribution, known to exist in other Ho3+ salts. These results settle the question of the nature of the low temperature spin correlations in Ho2Ti2O7 for which contradictory claims have been made.

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Multiparticle states in the S = 1 chain system CsNiCl3.

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound CsNiCl3 in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point Qc = pi, the continuum lies higher in energy than the Haldane gapped excitations. At 6 K the integrated intensity of the continuum is about 12(2)% of the total spectral weight. This result is considerably larger than the 1%-3% weight predicted by the nonlinear sigma model for the three-particle continuum.

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Anomalous weak magnetism in superconducting YBa2Cu3O6+x.

For some time now, there has been considerable experimental and theoretical effort to understand the role of the normal-state "pseudogap" phase in underdoped high-temperature cuprate superconductors. Recent debate has centered on the question of whether the pseudogap is independent of superconductivity. We provide evidence from zero-field muon spin relaxation measurements in YBa2Cu3O6+x for the presence of small spontaneous static magnetic fields of electronic origin intimately related to the pseudogap transition. Our most significant finding is that, for optimal doping, these weak static magnetic fields appear well below the superconducting transition temperature. The two compositions measured suggest the existence of a quantum critical point somewhat above optimal doping.

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Adolescents' use of emergency contraception provided by Washington State pharmacists.

STUDY OBJECTIVE: To increase knowledge about adolescents who obtained emergency contraceptive pills (ECP) directly from a pharmacist without first contacting a physician. DESIGN: Cross-sectional self-administered survey. SETTING: Fifteen randomly selected pharmacies providing ECP in western Washington State. PARTICIPANTS: Adolescents 15-21 years old (n = 126) who obtained ECP directly from a pharmacist. OUTCOME MEASURES: Responses to a 20-item questionnaire examining adolescents' reasons for seeking care from a pharmacist, need for additional medical evaluation, risk for not receiving additional medical care, and satisfaction with care provided by the pharmacist. RESULTS: The most common reasons for using the pharmacy were convenience (44%), lack of knowledge about alternatives (38%), and privacy (31%). If the pharmacy service were not available, 58% said they would see a doctor, 22% said they would wait to see if they got pregnant, and 20% did not know. Based on self-report, 81% of adolescents needed a new method of ongoing contraception, an evaluation for sexually transmitted disease, or both. Among these adolescents, 36% had risk factors for not receiving this care. Adolescents were satisfied with the pharmacy service; 94% said they would recommend the service to a friend. CONCLUSIONS: ECP provision by pharmacists is a useful way to increase access to emergency contraception. However, many adolescents using ECP need additional medical care. Programs designed to increase ECP access should use these opportunities to link adolescents with more comprehensive reproductive health care services.

Adolescent↗

Modeling the cost and outcomes of pharmacist-prescribed emergency contraception.

OBJECTIVES: This study investigated the effect on the risk and cost of unintended pregnancies of emergency contraceptive pills obtained directly from a pharmacist. METHODS: We used a decision model to compare outcomes for private and public payers following unprotected intercourse from. RESULTS: Obtaining emergency contraceptive pills from a pharmacy, compared with obtaining them from a physician or clinic, resulted in a $158 (95% confidence interval (CI) =$76, $269) reduction in costs for private payers and a $48 (95% CI = $16, $93) reduction for public payers. CONCLUSIONS: Our findings suggest that under varied assumptions, obtaining emergency contraceptive pills directly from a pharmacist reduces the number of unintended pregnancies and is cost saving.

Ambulatory Care Facilities↗

Observation of two time scales in the ferromagnetic manganite La1-xCaxMnO3, x approximately 0.3.

We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which suggest at least two spatially separated regions possessing very different Mn-ion spin dynamics. One region displays diffusive relaxation, "critical slowing down" near T(C) and an increasing volume fraction below T(C), suggesting overdamped FM spin waves below T(C). The second region possesses more slowly fluctuating spins, a linewidth independent of q, and a decreasing volume fraction below T(C). The estimated length scale for the inhomogeneity is <or=30 A.

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Tramadol and seizures: a surveillance study in a managed care population.

STUDY OBJECTIVE: To investigate the occurrence of tramadol-associated seizures. DESIGN: Retrospective cohort and case-control studies. SETTING: UnitedHealth Group-affiliated independent practice model health plans, from different regions of the United States, contracting with large networks of physicians. INTERVENTION: Analysis of administrative data from a large U.S. managed care population. PATIENTS: A cohort of 9218 adult tramadol users and 37,232 concurrent nonusers. MEASUREMENTS AND MAIN RESULTS: Fewer than 1% of users (80) had a presumed incident seizure claim after the first tramadol prescription. Risk of seizure claim was increased 2- to 6-fold among users adjusted for selected comorbidities and concomitant drugs. Risk was highest among those aged 25-54 years, those with more than four tramadol prescriptions, and those with history of alcohol abuse, stroke, or head injury. A case-control study among users was conducted to validate incident seizure outcomes from medical records. Only eight cases were confirmed, and all had cofactors associated with increased seizure risk. CONCLUSION: In a general population, risk of seizure may be associated with long-term therapy with tramadol or the presence of cofactors, or confined to a small sensitive population subset.

Adolescent↗

Therapeutic interchange of conjugated and esterified estrogens in a managed care organization.

A program designed to curb increases in drug costs in an HMO by substituting esterified for conjugated estrogens was developed and studied. Patients were voluntarily switched from conjugated to esterified estrogens at an HMO in Washington State. Women were informed about the conversion through newsletters and during clinic and pharmacy visits and received physician and pharmacist counseling. Cost savings were estimated, and patient acceptance was evaluated by interviewing women in four groups, including women who were switched from conjugated to esterified estrogens and then switched back (C-E-C group), women who were not switched (C-C group), and women who were switched to esterified estrogens and not switched back (C-E group). During the first six months, 14,601 (89.2%) of 16,364 women taking conjugated estrogens were switched to esterified estrogens; of these, 13,654 (93.5%) continued taking esterified estrogens for at least six months. The HMO avoided $653,119 of an expected $750,000 cost increase for oral estrogen therapy during the first year of the program. A total of 754 women were interviewed; 65.8% in the C-E-C group and 78.4% in the C-E group reported being satisfied with the information they received. The conversion experience was rated as positive by 28.3% of women in the C-E-C group and 41.5% of women in the C-E group, negative by 25.1%, and 8.9%, and neutral by 46.6% and 49.6%. An HMO avoided a large increase in drug costs by substituting esterified for conjugated estrogens; only 6.5% of patients were switched back to conjugated estrogens at their physicians' or their own request; most patients thought the conversion was a neutral or positive experience.

Adult↗

Medical records and privacy: empirical effects of legislation.

OBJECTIVE: To determine the effects of state legislation requiring patient informed consent prior to medical record abstraction by external researchers for a specific study. DATA SOURCES/STUDY SETTING: Informed consent responses obtained from November 1997 through April 1998 from members of a Minnesota-based IPA model health plan. STUDY DESIGN: Descriptive case study of consent to gain access to medical records for a pharmaco-epidemiologic study of seizures associated with use of a pain medication that was conducted as part of the FDA's post-marketing safety surveillance program to evaluate adverse events associated with approved drugs. DATA COLLECTION: The informed consent process approved by an institutional review board consisted of three phases: (1) a letter from the health plan's medical director requesting participation, (2) a second mailing to nonrespondents, and (3) a follow-up telephone call to nonrespondents. PRINCIPAL FINDINGS: Of 140 Minnesota health plan members asked to participate in the medical records study, 52 percent (73) responded and 19 percent (26) returned a signed consent form authorizing access to their records for the study. For 132 study subjects enrolled in five other health plans in states where study-specific consent was not required, health care providers granted access to patient medical records for 93 percent (123) of the members. CONCLUSION: Legislation requiring patient informed consent to gain access to medical records for a specific research study was associated with low participation and increased time to complete that observational study. Efforts to protect patient privacy may come into conflict with the ability to produce timely and valid research to safeguard and improve public health.

Cohort Studies↗

Identifying inflorescence phytoliths from selected species of wheat (Triticum monococcum, T. dicoccon, T. dicoccoides, and T. aestivum) and barley (Hordeum vulgare and H. spontaneum) (Gramineae).

Analysis of microfossil silica phytoliths is becoming an increasingly important research tool for taxonomists, archaeobotanists, and paleoecologists. Expanded use of phytolith analysis by researchers is dependent upon development of phytolith systematics. In this study phytoliths produced by the inflorescence bracts from four species of wheat, Triticum monoccocum, T. dicoccon, T. dicoccoides, and T. aestivum, and two species of barley, Hordeum vulgare, and H. spontaneum, were analyzed using computer-assisted image and statistical analysis with the intent to develop taxonomic tools to distinguish among the taxa. A classification key based on significant differences among the mean morphometries of the inflorescence phytoliths produced by each species was created and tested. Discriminant analysis of the morphometries of several morphotypes of phytoliths was also conducted to determine whether this computer-assisted statistical procedure could be used as another method to classify the taxa and to determine which morphotypes have measurements that can best be used in discriminant functions. Test results indicated that, at the genus level, both the classification key and discriminant analysis of certain morphotypes of phytoliths were relatively reliable tools for distinguishing among phytoliths produced in the inflorescence bracts of the taxa considered. For distinguishing among the taxa at the species level, the classification key was most reliable. Of the discriminant analyses tested, that based on all the phytolith morphotypes combined was more reliable than those based on only one morphotype.

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