Proximity of the superconducting dome and the quantum critical point in the two-dimensional Hubbard model.

We use the dynamical cluster approximation to understand the proximity of the superconducting dome to the quantum critical point in the two-dimensional Hubbard model. In a BCS formalism, T(c) may be enhanced through an increase in the d-wave pairing interaction (V(d)) or the bare pairing susceptibility (χ(0d)). At optimal doping, where V(d) is revealed to be featureless, we find a power-law behavior of χ(0d)(ω=0), replacing the BCS log, and strongly enhanced T(c). We suggest experiments to verify our predictions.

Pure Mott phases in confined ultracold atomic systems.

We propose a novel scheme for confining atoms to optical lattices by engineering a spatially inhomogeneous hopping matrix element in the Hubbard-model (HM) description, a situation we term off-diagonal confinement (ODC). We show, via an exact numerical solution of the boson HM with ODC, that this scheme possesses distinct advantages over the conventional method of confining atoms using an additional trapping potential, including incompressible Mott phases at commensurate filling and a phase diagram that is similar to the uniform HM. The experimental implementation of ODC will thus allow a more faithful realization of correlated phases in cold-atom experiments.

Relationship between Hirsch-Fye and weak-coupling diagrammatic quantum Monte Carlo methods.

Two weak-coupling continuous time quantum Monte Carlo (CTQMC) methods are shown to be equivalent for Hubbard-type interactions. A relation between these CTQMC methods and the Hirsch-Fye quantum Monte Carlo (HFQMC) method is established, identifying the latter as an approximation within CTQMC and providing a diagrammatic interpretation. Both HFQMC and CTQMC are shown to be equivalent when the number of time slices in HFQMC becomes infinite, implying the same degree of fermion sign problem in this limit.

Psychiatric comorbidity in patients with generalized anxiety disorder.

OBJECTIVE: The goal of this study was to test the validity of generalized anxiety disorder as an independent diagnostic entity and to evaluate the prevalence and type of other psychiatric disorders coexisting with generalized anxiety disorder. Although a few published studies have addressed the subject, this study presents data from a larger group of subjects and excludes concurrent major depression as a potential confound. METHOD: The authors studied patients with a primary diagnosis of generalized anxiety disorder assigned after evaluation with the Structured Clinical Interview for DSM-III-R. Patients with a concurrent major depressive episode were excluded. All diagnoses for which the patient met criteria were determined, including lifetime occurrence of major depressive episode and substance use. RESULTS: One hundred nine patients with generalized anxiety disorder were included in the analysis. Twenty-eight (26%) of these patients were not given any other lifetime psychiatric diagnosis. The most prevalent comorbid diagnoses were social phobia (25 [23%] of the patients) and simple phobia (23 [21%] of the patients). Forty-six (42%) of the patients with generalized anxiety disorder had experienced at least one major depressive episode during their lifetime. CONCLUSIONS: These results support previous findings of high rates of psychiatric comorbidity in generalized anxiety disorder and validate the usefulness of generalized anxiety disorder as a separate diagnostic entity.

Psychological aspects of obesity and very-low-calorie diets.

This paper selectively reviews available evidence concerning psychological characteristics associated with obesity, psychological changes accompanying very-low-calorie diets (VLCDs), and the influence of certain psychological factors on response to VLCD treatment. The obese population as a whole does not show an elevated incidence of psychopathology. Treatment-seeking obese do show more psychiatric disturbance, at a level comparable to other medical/surgical patients. There appear to be no global personality traits or profiles that are associated with obesity. However, obese people differ from non-obese groups on psychological and behavioral variables related to weight and eating and more frequently display perceptual and emotional body image anomalies. Binge eating appears rather common among obese groups. VLCDs have generally neutral to positive effects on hunger, depression, and anxiety. New data on body image suggest that VLCDs are associated with post-treatment underestimation of body size. Finally, recent data on possible psychological and behavioral correlates of VLCDs outcome are presented.

Hyperkalemic periodic paralysis. Effects of potassium, exercise, glucose, and acetazolamide on blood chemistry.

Effects of strenous exercise, followed by rest, and of potassium administration on blood chemistry values were studied in two patients with hyperkalemic periodic paralysis and in normal volunteers. These procedures produced attacks of flaccid paralysis that occurred concomitantly with rapid rises in serum potassium concentrations and decreases in blood glucose and inorganic phosphate levels. With the exception of the serum potassium level which rose following exercise and potassium administration, there were no changes in the blood chemistry values of the normal volunteers. During the induced attacks of paralysis, the expired breath of the patients had a very strong odor of ketosis. Results of subsequent glucose tolerance tests were abnormal. Following 24 hour administration of acetazolamide, the studies were repeated. The drug appeared to cause lesser effects of stimuli on serum potassium levels and a stabilizing effect on blood glucose levels.

The effect of acidosis in hypokalemic periodic paralysis.

Metabolic acidosis was produced in two patients with hypokalemic periodic paralysis by the administration of ammonium chloride over a period of three days. The challenging test of glucose and insulin produced a substantially smaller reduction of both serum potassium concentration and muscle strength than when the patients were tested in normal acid-base balance. The findings agree with earlier work on acetazolamide, suggesting that metabolic acidosis provides protection against episodes of muscle weakness in periodic paralysis.

Acetazolamide treatment of hypokalemic periodic paralysis. Probable mechanism of action.

Following administration of glucose and insulin to three patients with hypokalemic periodic paralysis, serum K+ fell 1.9 mM. After administration of acetazolamide, 250 mg four times daily, serum K+ fell 0.9 mM, a substantial difference. In normal persons glucose and insulin lowered serum K+ 0.5 mM, and this was not changed substantially by acetazolamide. The metabolic acidosis induced by the drug appears to be responsible for the change in decrement of serum K+ and for the amelioration of symptoms in the patients. The findings agree with earlier reports that metabolic acidosis lowers the rate of entry of K+ into muscle, thus opposing the heightened or pathological entry of K+ into muscle cells during attacks of the disease.

d-wave superconductivity in the hubbard model

The superconducting instabilities of the doped repulsive 2D Hubbard model are studied in the intermediate to strong coupling regime with the help of the dynamical cluster approximation. To solve the effective cluster problem we employ an extended noncrossing approximation, which allows for a transition to the broken symmetry state. At sufficiently low temperatures we find stable d-wave solutions with off-diagonal long-range order. The maximal T(c) approximately 150 K occurs for a doping delta approximately 20% and the doping dependence of the transition temperatures agrees well with the generic high- T(c) phase diagram.

Pseudogaps in the 2D Hubbard Model.

We study the pseudogaps in the spectra of the 2D Hubbard model using both finite-size and dynamical cluster approximation (DCA) quantum Monte Carlo calculations. At half-filling, a charge pseudogap, accompanied by non-Fermi-liquid behavior in the self-energy, is shown to persist in the thermodynamic limit. The DCA (finite-size) method systematically underestimates (overestimates) the width of the pseudogap. A spin pseudogap is not seen at half-filling. At finite doping, a divergent d-wave pair susceptibility is observed.

Successful treatment of a persistent cyst, developing after ovarian transposition, with leuprolide acetate.

Persistent ovarian cysts are considered to be the most troublesome complication of ovarian transposition. Transabdominal drainage or surgical removal is often required. This paper reports the successful use of leuprolide acetate, a GnRH agonist, in the treatment of a symptomatic and persistent ovarian cyst which developed after ovarian transposition. The benefits of this therapy over others are discussed.

Fetal heart rate tracing during sickle cell crisis: a cause for transient late decelerations.

A case of maternal sickle cell anemia crisis is presented. A continuous fetal heart rate (FHR) tracing demonstrates late decelerations that reversed when the mother's condition improved. The importance of recognizing this reversible late deceleration problem is discussed in terms of increasing fetal maturity.

Vaginal delivery after cesarean section: a five-year study.

All pregnancies that were complicated by a previous cesarean section were reviewed for a five-year period from 1978 to 1982. Of 799 such pregnancies, 216 underwent a trial of labor, and 66% experienced successful vaginal delivery. When the primary cesarean section was for cephalopelvic disproportion, 54% delivered vaginally, 75% breech, and 70% for fetal distress or other nonrepeating indications. There was no evidence of uterine scar disruption in the vaginally delivered group. Vaginal delivery after previous cesarean section can be a safe alternative for carefully selected patients cared for in the proper environment.

Human dura mater allografts in repair of pelvic floor and abdominal wall defects.

Freeze-dried human dura mater has been used as an allograft for reconstructive gynecologic surgery since 1980. So far, 33 grafts have been placed. This versatile and immunologically inert material has been used to reconstruct the pelvic floor after exenterative procedures, replace rectus fascia in the repair of wound dehiscence and ventral or parastomal hernias, and cover the femoral vessels after nodal dissection. In seven patients, dura mater was grafted into infected sites without subsequent rejection. Biopsy of an allograft one year after implantation confirmed the natural tendency of the body to convert the dura mater to a viable and neovascularized tissue. This reconstructive material is a safe and versatile allograft for gynecologic oncologists.

The Kids' Eating Disorders Survey (KEDS): a study of middle school students.

OBJECTIVE: Anorexia nervosa and bulimia nervosa are known to occur in children although prevalence studies are lacking. METHOD: Using a newly developed self-report instrument, the Kids' Eating Disorders Survey (KEDS), 3,175 students (1,610 females, 1,565 males) enrolled in grades 5 to 8 were surveyed. RESULTS: More than 40% of respondents reported feeling fat and/or the wish to lose weight. These frequencies of weight control behaviors were reported, many of which were significantly greater in girls than boys (*p < 0.05, chi-square): dieting (31.4%*), fasting (8.7%*), diet pill use (2.4%*), vomiting (4.8%), diuretic use (1.5%). The effects of age, grade, weight, and race on responses are reviewed. CONCLUSIONS: Findings demonstrate that development of prevention programs aimed at recognizing problem eating behavior in children is indicated.

Reconstructive techniques in gynecologic oncology: the use of human dura mater allografts.

Human dura mater has been utilized in various reconstructive procedures following radical pelvic surgery at the Division of Gynecologic Oncology, University of Miami School of Medicine. Our preliminary results indicate that this allograft is strong, durable, and acts as a good biological barrier. However, it does not seem to prevent the development of enteropelvic fistulae in patients who undergo total pelvic exenteration following radiotherapy. Dura mater has also been employed in abdominal hernia repairs, repair of wound dehiscenses, and in the coverage of the femoral vessels after groin dissection. Provisional results with these reconstructive techniques appear promising. These results are discussed, and suggestions regarding the use of this allograft are delineated.

An in vitro investigation of the apical seal produced by a new thermoplasticized gutta-percha obturation technique.

This investigation quantitatively analyzed apical leakage in teeth in which one of two new thermoplasticized gutta-percha obturating techniques were used. Apical leakage observed after use of the thermoplasticized techniques was compared to leakage found in teeth that had been obturated with conventional lateral condensation. Statistically significant differences (P less than 0.05) were found among the three groups. The lateral condensation group exhibited the least leakage, followed by the thermoplasticized group, and the thermoplasticized twist-off group exhibited the most apical leakage.

Mean-field embedding of the dual-fermion approach for correlated electron systems.

To reduce the rapidly growing computational cost of the dual-fermion lattice calculation with increasing system size, we introduce two embedding schemes. One is the real fermion embedding, and the other is the dual-fermion embedding. Our numerical tests show that the real fermion and dual-fermion embedding approaches converge to essentially the same result. The application on the Anderson disorder and Hubbard models shows that these embedding algorithms converge more quickly with system size as compared to the conventional dual-fermion method, for the calculation of both single- and two-particle quantities.

Solving the parquet equations for the Hubbard model beyond weak coupling.

We find that imposing crossing symmetry in the iteration process considerably extends the range of convergence for solutions of the parquet equations for the Hubbard model. When crossing symmetry is not imposed, the convergence of both simple iteration and more complicated continuous loading (homotopy) methods is limited to high temperatures and weak interactions. We modify the algorithm to impose the crossing symmetry without increasing the computational complexity. We also imposed time reversal and a subset of the point group symmetries, but they did not further improve the convergence. We elaborate the details of the latency hiding scheme which can significantly improve the performance in the computational implementation. With these modifications, stable solutions for the parquet equations can be obtained by iteration more quickly even for values of the interaction that are a significant fraction of the bandwidth and for temperatures that are much smaller than the bandwidth. This may represent a crucial step towards the solution of two-particle field theories for correlated electron models.