Critical behavior at the mott-anderson transition: a typical-medium theory perspective.

We present a detailed analysis of the critical behavior close to the Mott-Anderson transition. Our findings are based on a combination of numerical and analytical results obtained within the framework of typical-medium theory-the simplest extension of dynamical mean field theory capable of incorporating Anderson localization effects. By making use of previous scaling studies of Anderson impurity models close to the metal-insulator transition, we solve this problem analytically and reveal the dependence of the critical behavior on the particle-hole symmetry. Our main result is that, for sufficiently strong disorder, the Mott-Anderson transition is characterized by a precisely defined two-fluid behavior, in which only a fraction of the electrons undergo a "site selective" Mott localization; the rest become Anderson-localized quasiparticles.

Multiple energy scales at a quantum critical point.

We report thermodynamic measurements in a magnetic-field-driven quantum critical point of a heavy fermion metal, YbRh2Si2. The data provide evidence for an energy scale in the equilibrium excitation spectrum that is in addition to the one expected from the slow fluctuations of the order parameter. Both energy scales approach zero as the quantum critical point is reached, thereby providing evidence for a new class of quantum criticality.

Disorder screening in strongly correlated systems.

Electron-electron interactions generally reduce the low temperature resistivity due to the screening of the impurity potential by the electron gas. In the weak-coupling limit, the magnitude of this screening effect is determined by the thermodynamic compressibility which is proportional to the inverse screening length. We show that when strong correlations are present, although the compressibility is reduced, the screening effect is nevertheless strongly enhanced. This phenomenon is traced to the same nonperturbative Kondo-like processes that lead to strong mass enhancements, but which are absent in weak-coupling approaches. We predict metallicity to be strongly stabilized in an intermediate regime where the interactions and the disorder are of comparable magnitude.

Calculated phonon spectra of plutonium at high temperatures.

We constructed computer-based simulations of the lattice dynamical properties of plutonium using an electronic structure method, which incorporates correlation effects among the f-shell electrons and calculates phonon spectra at arbitrary wavelengths. Our predicted spectrum for the face-centered cubic delta phase agrees well with experiments in the elastic limit and explains unusually large shear anisotropy of this material. The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.

Effective Lorentz force due to small-sngle impurity scattering: magnetotransport in high- Tc superconductors.

We show that a scattering rate which varies with angle around the Fermi surface has the same effect as a periodic Lorentz force on magnetotransport coefficients. This effect, together with the marginal Fermi liquid inelastic scattering rate, gives a quantitative explanation of the temperature dependence and the magnitude of the observed Hall effect and magnetoresistance with just the measured zero-field resistivity as input.

Correlated electrons in delta-plutonium within a dynamical mean-field picture.

Given the practical importance of metallic plutonium, there is considerable interest in understanding its fundamental properties. Plutonium undergoes a 25 per cent increase in volume when transformed from its alpha-phase (which is stable below 400 K) to the delta-phase (stable at around 600 K), an effect that is crucial for issues of long-term storage and disposal. It has long been suspected that this unique property is a consequence of the special location of plutonium in the periodic table, on the border between the light and heavy actinides-here, electron wave-particle duality (or itinerant versus localized behaviour) is important. This situation has resisted previous theoretical treatment. Here we report an electronic structure method, based on dynamical mean-field theory, that enables interpolation between the band-like and atomic-like behaviour of the electron. Our approach enables us to study the phase diagram of plutonium, by providing access to the energetics and one-electron spectra of strongly correlated systems. We explain the origin of the volume expansion between the alpha- and delta-phases, predict the existence of a strong quasiparticle peak near the Fermi level and give a new viewpoint on the physics of plutonium, in which the alpha- and delta-phases are on opposite sides of the interaction-driven localization-delocalization transition.

What angle-resolved photoemission experiments tell about the microscopic theory for high-temperature superconductors.

Recent angular-resolved photoemission experiments on high-temperature superconductors are consistent with a phenomenological description of the normal state of these materials as marginal Fermi liquids. The experiments also provide constraints on microscopic theories.

Isolation of Angiostrongylus costaricensis first-stage larvae from rodent feces on a Percoll gradient.

Several density gradients were tested for the isolation of parasitic nematode, Angiostrongylus costaricensis, first-stage larvae from rodent feces. With a 45/72% Percoll gradient, 83-99% (89.56+/-6.57%) of the larvae were recovered in a clean preparation.

Insult after injury: pressure ulcers in trauma patients.

DESIGN: Nonexperimental-Descriptive. SAMPLE: The inclusion criteria were trauma patients, ages 15 and older, who were hospitalized for > 2 days, and who did not have preexisting skin breakdown. A total of 148 consecutive trauma patients admitted to the study institution meeting the inclusion criteria were prospectively enrolled. METHODS: Patients were assessed every 3 days for skin breakdown. Information on the patient's bed type, therapies, medical devices, and nutrition was collected. The Braden Scale for predicting pressure ulcer risk was completed at each assessment. FINDINGS: Of the 148 patients enrolled, 30 developed at least one area of skin breakdown for a prevalence of 20.3% in patients hospitalized more than 2 days. The most common cause of breakdown was positional pressure (47.4%). Cervical collars were the second leading cause at 23.7%, followed by tracheostomy/endotracheal tubes at 10.5%. The mobility subscale of the Braden Pressure Ulcer Risk Assessment tool was significantly predictive of skin breakdown (p < .001). IMPLICATIONS FOR NURSING RESEARCH: Skin breakdown is a significant problem in trauma patients who are hospitalized for more than 2 days. Aggressive protocols on positioning, cervical collar use, and airway adjuncts, as well as additional active nursing interventions for immobile patients, may be ways to decrease the skin breakdown prevalence in this population.

Effect of Trypanosoma lewisi (Kinetoplastida: Trypanosomatidae) on the infection of white rats with Toxoplasma gondii (Eucoccidia: Sarcocystidae) oocysts.

White rats were inoculated with 10(6) trypomastigotes of Trypanosoma lewisi, simultaneously or two days before and after inoculation with 10(5) oocysts of T. gondii. A greater number of cysts was found in the brain of the animals having concomitant inoculations, as compared with rats inoculated with either one of the two parasites. An apparent immunosuppressive effect is likely. Since both organisms can be found in rats, it is possible that infections with T. lewisi, could make this rodent another intermediate host for Toxoplasma infections.

Increasing of Toxoplasma gondii (Coccidia, Sarcocystidae) infections by Trypanosoma lewisi (Kinetoplastida, Trypanosomatidae) in white rats.

To demonstrate that T. lewisi infection increases T. gondii multiplication in white rats, groups of five Wistar or Sprague Dawley rats were inoculated with 10(6) T. lewisi trypomastigotes and four or seven days later infected with Toxoplasma tachyzoites. Host survival time was monitored, and the presence of T. gondii was confirmed in all dead rats by studying peritoneal exudate smears and lung tissue sections stained with haematoxylin-eosin. The presence of Toxoplasma cysts or antibodies was checked in the brain of surviving rats. The increase is observed four days after trypanosome inoculation and is dependent on rat strain, but not on inoculum size or rat age. Humoral and cellular factors may have a role in the increase as has been reported for other experimental infections with African trypanosomes and T. cruzi.

Increasing of Toxoplasma gondii (Coccidia, Sarcocystidae) infections by Trypanosoma lewisi (Kinetoplastida, Trypanosomatidae) in white rats

To demonstrate that T. lewisi infection increases T. gondii multiplication in white rats, groups of five Wistar or Sprague Dawley rats were inoculated with 10(6) T. lewisi trypomastigotes and four or seven days later infected with Toxoplasma tachyzoites. Host survival time was monitored, and the presence of T. gondii was confirmed in all dead rats by studying peritoneal exudate smears and lung tissue sections stained with haematoxylin-eosin. The presence of Toxoplasma cysts or antibodies was checked in the brain of surviving rats. The increase is observed four days after trypanosome inoculation and is dependent on rat strain, but not on inoculum size or rat age. Humoral and cellular factors may have a role in the increase as has been reported for other experimental infections with African trypanosomes and T. cruzi

[A simple method for determining the presence of Toxoplasma gondii (Eucoccidia: Sarcocystidae) in meat]. / Método sencillo para determinar la presencia de Toxoplasma gondii (Eucoccidia: Sarcocystidae) en carne.

Presence of T. gondii in meat from several sources was determined by traditional methods and by a new simplified method in which animals are fed meat directly without any previous treatment with artificial gastric fluid. Tissues are ground and the animals ingest them naturally. Determination of Toxoplasma in lungs or brain (as well as by specific antibody test), showed no statistically significant differences between both methods.

[Susceptibility of Sigmodon hispidus (Rodentia: Cricetidae) to Toxoplasma gondii (Eucoccidia: Sarcocystidae)]. / Susceptibilidad de la rata Sigmodon hispidus (Rodentia: Cricetidae) al Toxoplasma gondii (Eucoccidia: Sarcocystidae).

Sigmodon hispidus, a cotton rat, was inoculated with tachyzoites or oocysts of Costa Rican strains of Toxoplasma gondii to demonstrate the resistance to this parasite, as compared with mice, hamster and white rat infection. Susceptibility to tachyzoite inoculation was higher in this animal than in white rats but lower than in the other animals. Independent to the Toxoplasma strain studied, oocyst infection was less lethal for S. hispidus when compared with mice and hamsters; the results were similar to those observed for white rats. There is a probable participation of this wild animal in the natural Toxoplasma life cycle.

Age influence in the natural resistance of white rat and mice to the protozoan Toxoplasma gondii.

Groups of 1, 5, 10, 15 and 30 day old rats (Sprague Dawley) and Wistar mice were infected per os with different inocula of Toxoplasma gondii oocysts from an avirulent strain. Infection pattern was followed by determination of survival time, tissue lesions, parasite presence and serology. Although all the animals survived the total experimental period (30 day), there were important differences between both rodents regarding to Toxoplasma natural resistance. Brain cysts, as well as tachyzoites in other organs were regularly present in mice but not in rats. On the other hand, most of the organs from mice presented characteristic T. gondii lesions, while in rats a normal tissues were observed, with the exception of an acute reaction found in the brain of a 15d old animal.