Avoided valence transition in a plutonium superconductor.

The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5--the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)--and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability--therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5.

A multi-component Fermi surface in the vortex state of an underdoped high-Tc superconductor.

To understand the origin of superconductivity, it is crucial to ascertain the nature and origin of the primary carriers available to participate in pairing. Recent quantum oscillation experiments on high-transition-temperature (high-T(c)) copper oxide superconductors have revealed the existence of a Fermi surface akin to that in normal metals, comprising fermionic carriers that undergo orbital quantization. The unexpectedly small size of the observed carrier pocket, however, leaves open a variety of possibilities for the existence or form of any underlying magnetic order, and its relation to d-wave superconductivity. Here we report experiments on quantum oscillations in the magnetization (the de Haas-van Alphen effect) in superconducting YBa(2)Cu(3)O(6.51) that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole-doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible density-wave model with spiral or related modulated magnetic order, consistent with experimental observations.

Metal-insulator quantum critical point beneath the high Tc superconducting dome.

An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high T(c) cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa(2)Cu(3)O(6+x), revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in T(c) in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability.

Quantum oscillations from nodal bilayer magnetic breakdown in the underdoped high temperature superconductor YBa2Cu3O(6+x).

We report quantum oscillations in underdoped YBa2Cu3O6.56 over a significantly large range in magnetic field extending from ≈24 to 101 T, enabling three well-spaced low frequencies at ≈440±10, 532±2, and 620±10 T to be clearly resolved. We show that a small nodal bilayer coupling that splits a nodal pocket into bonding and antibonding orbits yields a sequence of frequencies, F0-ΔF, F0, and F0+ΔF and accompanying beat pattern similar to that observed experimentally, on invoking magnetic breakdown tunneling at the nodes. The relative amplitudes of the multiple frequencies observed experimentally in quantum oscillation measurements are shown to be reproduced using a value of nodal bilayer gap quantitatively consistent with that measured in photoemission experiments in the underdoped regime.

Cascade of magnetic field induced spin transitions in LaCoO3.

We present magnetization and magnetostriction studies of LaCoO3 in magnetic fields approaching 100 T. In contrast with expectations from single-ion models, the data reveal two distinct first-order transitions and well-defined magnetization plateaus. The magnetization at the higher plateau is only about half the saturation value expected for spin-1 Co3+ ions. These findings strongly suggest collective behavior induced by interactions between different electronic configurations of Co3+ ions. We propose a model that predicts crystalline spin textures and a cascade of four magnetic phase transitions at high fields, of which the first two account for the experimental data.

Magnetic quantum oscillations in YBa2Cu3O6.61 and YBa2Cu3O6.69 in fields of up to 85 T: patching the hole in the roof of the superconducting dome.

We measure magnetic quantum oscillations in the underdoped cuprates YBa2Cu3O6+x with x=0.61, 0.69, using fields of up to 85 T. The quantum-oscillation frequencies and effective masses obtained suggest that the Fermi energy in the cuprates has a maximum at hole doping p approximately 0.11-0.12. On either side, the effective mass may diverge, possibly due to phase transitions associated with the T=0 limit of the metal-insulator crossover (low-p side), and the postulated topological transition from small to large Fermi surface close to optimal doping (high p side).

Polycrystalline gamma-plutonium's elastic moduli versus temperature.

Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline (239)Pu in the gamma-phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease in all elastic moduli with increasing temperature was observed. The Poisson ratio was calculated and an increase from 0.242 at 519 K to 0.252 at 571 K was found. These measurements on extremely well-characterized pure Pu are in agreement with other reported results where overlap occurs. We calculated an approximate Debye temperature Theta(D)=144 K. Determined from the temperature variation in the bulk modulus, gamma-Pu shows the same Gruneisen parameter as copper.

Spin-order driven Fermi surface reconstruction revealed by quantum oscillations in an underdoped high Tc superconductor.

We use quantum oscillation measurements to distinguish between spin and orbital components of the lowest energy quasiparticle excitations in YBa(2)Cu(3)O(6.54), each of which couple differently to a magnetic field. Our measurements reveal the phase of the observed quantum oscillations to remain uninverted over a wide angular range, indicating that the twofold spin degeneracy of the Landau levels is virtually unaltered by the magnetic field. The inferred suppression of the spin degrees of freedom indicates a spin-density wave is responsible for creation of the small Fermi surface pockets in underdoped YBa(2)Cu(3)O(6+x)--further suggesting that excitations of this phase are important contributors to the unconventional superconducting pairing mechanism.

Fermi surface of CeIn3 above the Néel critical field.

We report measurements of the de Haas-van Alphen effect in CeIn(3) in magnetic fields extending to approximately 90 T, well above the Néel critical field of mu(0)H(c) approximately 61 T. The unreconstructed Fermi surface a sheet is observed in the high magnetic field polarized paramagnetic limit, but with its effective mass and Fermi surface volume strongly reduced in size compared to that observed in the low magnetic field paramagnetic regime under pressure. The spheroidal topology of this sheet provides an ideal realization of the transformation from a "large Fermi surface" accommodating f electrons to a "small Fermi surface" when the f-electron moments become polarized.

Alpha-plutonium's polycrystalline elastic moduli over its full temperature range.

alpha-plutonium's volume-corrected polycrystal elastic moduli were measured between 18 K and the upper limit of its occurrence, near 400 K. The two independent moduli for a polycrystal-bulk and shear-behave smoothly, indicating no phase transition. Both moduli show the same 50% increase on cooling, an order of magnitude larger than in other metals. The Debye temperature obtained from low-temperature elastic moduli, 207 K, significantly exceeds most previous estimates. The Gruneisen parameter gamma=5.3, obtained from the temperature dependence of the bulk modulus, is intermediate among previous estimates using other approaches, alpha-plutonium's Poisson ratio nu is low: 0.18, nearly temperature independent, and its small decrease on warming opposes usual behavior. The high gamma, large but equal bulk modulus and shear modulus fractional stiffening on cooling, and near-temperature-invariant nu are attributed to a single mechanism: 5-f electron localization-delocalization.

Comparative effects of aspirin and acetaminophen on hemostasis.

The influences of aspirin and of acetaminophen on hemostasis were studied in normal healthy volunteers and in patients with either severe hemophilia A or hemophilia B. Acetaminophen did not alter the template bleeding time or the results of tests of platelet function in either group. Aspirin did prolong the template bleeding time and impaired platelet aggregation; these changes were most pronounced in patients with either form of hemophilia, and some (7/19) required plasma component therapy. Neither drug influenced the coagulation proteins or the fibrinolytic mechanism, as measured. The influences of a single dose (ranging from 975 to 1,950 mg) of acetaminophen and of a single dose (ranging from 325 to 2,925 mg) of aspirin were similar to those observed in persons receiving multiple doses. Acetaminophen is preferred in patients in whom a hemostatic influence is undesirable. However, either aspirin or acetaminophen can be used in normal healthy subjects.

Colchicine toxicity: a multisystem disease.

A 23-year-old black man survived a life-threatening multisystem disturbance resulting from a large single dose of colchicine administered intraurethrally for condyloma acuminata. Gastroenteritis and probable pancreatitis rapidly evolved into severe respiratory failure, marked neuromuscular problems, alopecia, and complete bone marrow aplasia. Within two months he had completely recovered. This patient demonstrates that colchicine should be used with extreme caution, if at all, for the therapy of condyloma acuminata.

Therapeutic leukapheresis in hairy cell leukemia.

Therapeutic leukapheresis was performed on three patients, and plasmapheresis on two patients with far-advanced hairy cell leukemia. Two of the three patients who were treated with leukapheresis had many hairy cells in their peripheral blood, while the other had relatively few. In each patient, dramatic clinical and hematologic improvements were observed that have sustained for more than 23, 10, and 26 months, respectively. Plasmapheresis of similar intensity failed to show any appreciable therapeutic effects on two other patients with similar clinical and hematologic findings. We believe that the favorable therapeutic effects of leukapheresis are due to the removal of factors capable of inhibiting normal hematopoiesis. This factor(s) is present in the cells that were removed by leukapheresis. The exact nature of this factor(s) or the cells that produce this factor(s) remains to be identified.

Influence of aspirin on platelets and the bleeding time.

Aspirin influences the bleeding time, presumably through the inhibition of prostaglandin biosynthesis and the resultant platelet secretion reaction. This can be measured by prolongation of the bleeding time and changes in platelet function results. Despite these changes, bleeding is rarely a problem in patients who have normal hemostatic mechanisms. To investigate this, we have studied the technical variables associated with the determination of the bleeding time. Both venostasis and direction of the incision play a major role in the bleeding time prolongation induced by aspirin. When a bleeding time determination is performed with vertical incision without venostasis, there is almost no detectable prolongation of the bleeding time. These studies support our previous observations that aspirin has a mild influence on primary hemostasis.

Altered factor VIII complexes in patients with acute respiratory insufficiency.

Acute respiratory failure is an often-fatal syndrome of multiple etiologies in which altered factor VIII may be a marker of endothelial disease. 12 women with overwhelming viral pneumonia were studied with serial factor VIII antigen, procoagulant activity, and von Willebrand's factor assays. Antigen levels were elevated (range: 86--1644%) out of proportion to procoagulant activity (range: 35--521% by a one-stage assay), and factor VIII antigen to activity ratios were as high as 16:1. Von Willebrand's factor was normal but correlated best with procoagulant activity. All patients had abnormal antigen patterns on crossed immunoelectrophoresis, with increases in protein of both fast and slow mobility. These changes in factor VIII correlated with the patient's clinical courses.

Platelets, hemostasis, and thromboembolism during treatment of acute respiratory insufficiency with extracorporeal membrane oxygenation.

Twenty-eight patients were supported with long-term extracorporeal membrane oxygenation as a treatment for acute respiratory insufficiency. Clinical, laboratory, and autopsy data concerning platelets, hemostasis, and thromboembolic disease are presented for the periods during and after bypass. During bypass, a "foreign-surface coagulopathy" was encountered which consisted of abnormal bleeding plus frequent, generalized, small and large vessel thromboembolic events. The abnormal bleeding is attributed to heparin, thrombocytopenia, and a qualitative platelet defect. Possible causes of the thromboembolic events including disseminated intravascular coagulation are also discussed, and speculations are offered concerning clinical management and directions for future investigation.

Blood platelets and extracorporeal circulation; kinetic studies on dogs on cardiopulmonary bypass.

Platelet kinetics and functions were studied in dogs during extracorporeal circulation. A transient platelet sequestration in the liver occurs during the bypass. This reversible disappearance is accompanied by a loss of the ability of platelets to adhere or aggregate. The platelets which return to the circulation have normal functions and a normal life span. The irreversible damage is mainly due to the direct blood-gas interface. Impairment of lung function by platelet aggregates is discussed and the importance of an in vivo model to study the factors which affect the platelets, such as antiaggregating agents, is pointed out.

The use of time step simulations and difference equations (TSSADEQ) in modeling heparin pharmacokinetics.

A model in which the clearance of heparin requires the binding of heparin to a finite and regenerated pool of binding was constructed using time step simulations and difference equations (TSSADEQ). A simulation of a heparin i.v. bolus demonstrated a dose-dependent, triphasic pharmacokinetic curve with (1) an initial log-linear phase representing first-order association of heparin with binding sites, (2) an intermediate plateau phase representing constant regeneration of heparin binding sites, and (3) a terminal log-linear phase occurring when the quantity of regenerated sites exceeded the remaining heparin. Sensitivity analysis based on the literature produced estimates of the k at 1.39 to 2.77 h-1, the pool of binding sites of 50 units/kg, and the regeneration rate of 15 to 20 unit/kg/h--virtually identical to the empirically derived guidelines for the bolus size and infusion rate for unfractionated heparin. A pilot study of bolus dosing of unfractionated heparin in normal volunteers confirmed the model.

Effects of zomepirac on hemostasis in healthy adults and on platelet function in vitro.

Zomepirac, a new nonnarcotic analgesic, was studied in 25 healthy adults for possible effects on hemostasis. Given in a single 200-mg dose or for 15 days at 300 mg/day, zomepirac prolonged template bleeding time and caused transient decreases in platelet adhesiveness, in stimulated platelet aggregation, and in the release of platelet serotonin. The short duration of these effects contrasts with the known week-long duration of the effects of aspirin. Data from in vitro platelet function studies, correlated with plasma level determinations, indicate that these effects on platelet function in man are probably dependent only on the presence of intact zomepirac and not on any metabolites. The qualitative effects of zomepirac on platelets are assumed to be the consequence of reversible inhibition of prostaglandin synthetase in these cells. Platelet concentration and the humoral clotting mechanism were not affected by zomepirac. Although no unusual bleeding has been noted in patients given zomepirc postoperatively, it should be used with the same caution as aspirin in patients with known defects in platelet function or coagulation.

Coronary artery calcium, coronary artery disease, and diabetes.

Diabetes is a known risk factor for cardiovascular disease, which is the leading cause of death in the US. Most sufferers are unaware that they have coronary artery disease, and death is often quite sudden. Electron beam computed tomography (EBCT) is a non-invasive procedure that detects coronary artery disease (CAD) by measuring the amount of coronary artery calcium (CAC). We employ this procedure to study the effect of diabetes on CAC. EBCT was employed to measure the amount of coronary artery calcium in a population of 3389 patients referred to the Spokane Coronary Artery Center. This was a cross-sectional study. The average and median CAC values were computed for two groups of patients, namely those with diabetes and those without. Patients were also divided by gender and five age groups (0-39, 40-49, 50-59, 60-69, and >69 years). The mean and median CAC values were much larger for those with diabetes compared to those without for all age groups and in both sexes. Both men and women with diabetes have a greater plaque burden, when compared to a population with coronary artery disease with no history of diabetes. This plaque burden is greater in males than in females. CAC may play a useful role in following the progression of CAD in patients with diabetes, as well as evaluating the influence of risk factor intervention and diabetic control.