RESUMEN

The local effect of an interstitial hydrogenlike particle on localized f electrons was studied in PrPb3 by means of micro+ spin rotation and relaxation. Spontaneous micro+ spin precession with harmonic frequencies was observed for the first time in f electron compounds. We demonstrate that the signal is derived from a coupling between the micro+ spin and the hyperfine-enhanced nuclear spin of nearest neighbor (NN) 141Pr with Ising-like anisotropy. The signal also suggests a marked suppression of spin dynamics of the NN 141Pr in comparison with that of the bulk 141Pr. These facts strongly indicate modification of the f electronic state due to the interstitial charged particle.

RESUMEN

The high-field superconducting state in CeCoIn(5) has been studied by transverse field muon spin rotation measurements with an applied field parallel to the crystallographic c axis close to the upper critical field mu(0)H(c2) = 4.97 T. At magnetic fields mu(0)H > or = 4.8 T the muon Knight shift is enhanced and the superconducting transition changes from second order towards first order as predicted for Pauli-limited superconductors. The field and temperature dependence of the transverse muon spin relaxation rate sigma reveal paramagnetic spin fluctuations in the field regime from 2 T < or = mu(0)H < 4.8 T. In the normal state close to H(c2) correlated spin fluctuations as described by the self-consistent renormalization theory are observed. The results support the formation of a mode-coupled superconducting and antiferromagnetically ordered phase in CeCoIn(5) for H directed parallel to the c axis.

RESUMEN

Passive sound-localization acuity for 100-msec noise bursts was determined behaviorally for two species of non-echolocating bats: the Straw-colored fruit bat, Eidolon helvum, a large frugivore, and the Dog-faced fruit bat, Cynopterus brachyotis, a small frugivore. The mean minimum audible angle for two E. helvum was 11.7 degrees, and for two C. brachyotis was 10.5 degrees. This places their passive sound-localization acuity near the middle of the range for echolocating bats as well as the middle of the range for other mammals. Sound-localization acuity varies widely among mammals, and the best predictor of this auditory function remains the width of the field of best vision (r=.89, p<.0001). Among echolocating and non-echolocating bats, as well as among other mammals, the use of hearing to direct the eyes to the source of a sound still appears to serve as an important selective factor for sound localization. Absolute visual acuity and the magnitude of the binaural locus cues available to a species remain unreliable predictors of sound-localization acuity.

Asunto(s)

RESUMEN

PURPOSE: Currently, only a small fraction of patients are able to receive reperfusion therapy for myocardial infarctions. We hypothesize that myometrial cell patch transplantation could be an alternative approach for the treatment of myocardial infarction. DESIGN: We performed a preliminary study to determine the feasibility of this novel therapeutic approach in a rabbit model. PROCEDURES: Six adult female New Zealand rabbits were used. Myocardial infarction was induced by left anterior descending artery ligation. A segment of uterus was removed via a laparotomy incision, and this uterine segment was transplanted as an autologous graft over the infarcted myocardium, which was then reinforced by greater omentum. Statistical methods and outcome measures: Hemodynamic measurements and histological studies. MAIN FINDINGS: All uterine myometrial patches survived in the test animals. Fluoroscopic hemodynamic measurements were made for ejection fractions at 8 weeks after the application of the uterine patch. Histological study demonstrated well-healed myometrial-myocardium junctions with minimum scar tissue. Angiogenesis occurred in the transplanted myometrium. Connexin 43 expression was demonstrated in the transplanted patches. CONCLUSION: Our noncontrolled preliminary rabbit experiments indicate that patches of uterine myometrium reinforced by greater omentum can be used as autologous transplant therapy for infracted myocardium. This is an innovative technique that could lead to future treatment for individuals who may suffer from an infarcted myocardium and may not be eligible for traditional reperfusion therapy.

Asunto(s)

RESUMEN

Passive sound-localization acuity for 100-ms noise bursts was determined behaviorally for two species of bats: Phyllostomus hastatus, a large bat that eats fruit and vertebrates, and Carollia perspicillata, a small species that eats fruit and nectar. The mean minimum audible angle for two P. hastatus was 9 degrees , and that for two C. perspicillata was 14.8 degrees . This places their passive sound-localization acuity near the middle of the range for mammals. Sound localization varies widely among mammals and the best predictor of a species' acuity remains the width of the field of best vision (r=.89, p<.0001). The five echolocating bats that have been tested do not deviate from this relationship suggesting that despite their specialization for echolocation, the use of hearing to direct the eyes to the source of a sound still serves as an important selective factor for sound localization.

Asunto(s)

RESUMEN

Comparing the hearing abilities of echolocating and non-echolocating bats can provide insight into the effect of echolocation on more basic hearing abilities. Toward this end, we determined the audiograms of two species of non-echolocating bats, the straw-colored fruit bat (Eidolon helvum), a large (230-350 g) African fruit bat, and the dog-faced fruit bat (Cynopterus brachyotis), a small (30-45 g) bat native to India and Southeast Asia. A conditioned suppression/avoidance procedure with a fruit juice reward was used for testing. At 60 dB SPL, the hearing range of E. helvum extends from 1.38 to 41 kHz with best sensitivity at 8k Hz; the hearing range of C. brachyotis extends from 2.63 to 70 kHz with best sensitivity at 10 kHz. As with all other bats tested so far, neither species was able to hear below 500 Hz, suggesting that they may not use a time code for perceiving pitch. Comparison of the high-frequency hearing abilities of echolocating and non-echolocating bats suggests that the use of laryngeal echolocation has resulted in additional selective pressure to hear high frequencies. However, the typical high-frequency sensitivity of small non-echolocating mammals would have been sufficient to support initial echolocation in the early evolution of bats, a finding that supports the possibility of multiple origins of echolocation.

Asunto(s)

RESUMEN

Central core disease (CCD) is mainly a disease of infancy and childhood and represents a member of a group of muscular disorders known as "congenital, benign (non-progressive) myopathies". It is an uncommon disease of infancy and early childhood, and presentation is rare in adulthood. The disease is mainly familial with an autosomal-dominant pattern of inheritance, yet sporadic cases can occur. The diagnosis is based on a muscle biopsy, which documents unique morphological abnormalities of focal loss of oxidative enzyme in type I muscular fibers. The basis for this loss of such activities is represented by a near-total absence of mitochondria and sarcoplasmic reticulum in the cores. We describe a 58-year-old man diagnosed with CCD, who is one of the oldest individuals reported with CCD diagnosed by a muscle biopsy. The clinical, pathological and genetic features of this rare entity are discussed herein.

Asunto(s)

RESUMEN

Using neutron pair distribution function analysis over the temperature range from 1000 to 15 K, we demonstrate the existence of local polarization and the formation of medium-range, polar nanoregions (PNRs) with local rhombohedral order in a prototypical relaxor ferroelectric Pb(Mg(1/3)Nb(2/3))O3. We estimate the volume fraction of the PNRs as a function of temperature and show that this fraction steadily increases from 0% to a maximum of approximately 30% as the temperature decreases from 650 to 15 K. Below T approximately 200 K the volume fraction of the PNRs becomes significant, and PNRs freeze into the spin-glass-like state.

RESUMEN

Extended x-ray absorption fine structure (EXAFS) experiments have been carried out on PrRu(4)P(12) and PrOs(4)P(12) to study the metal-to-insulator (MI) phase transition in PrRu(4)P(12). No Pr displacement was observed across the MI transition temperature from the EXAFS data. Instead, our EXAFS data clearly show that a Ru displacement is associated with this MI transition. The very high Debye temperature for the Ru-P bond (Theta(D) = 690 K) suggests that a slight rotation/displacement of relatively rigid RuP(6) octahedra leads to this small Ru displacement, which accompanies the MI transition at 62 K in PrRu(4)P(12).

RESUMEN

Depth-controlled beta-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam of highly spin-polarized 8Li+ ions was slowed down and implanted into a 50 nm film of Ag deposited on a SrTiO3 substrate. A novel high field beta-NMR spectrometer was used to observe two well resolved resonances which are attributed to Li occupying substitutional and octahedral interstitial sites in the Ag lattice. The temperature dependence of the Knight shifts and spin relaxation rates are consistent with the Korringa law for a simple metal, implying that the NMR of implanted 8Li reflects the spin suspectibility of bulk metallic silver.

RESUMEN

The temperature and pressure dependence of the thermal displacements and lattice parameters were obtained across the gamma-->alpha phase transition of Ce using high-pressure, high-resolution neutron and synchrotron x-ray powder diffraction. The estimated vibrational entropy change per atom in the gamma-->alpha phase transition, DeltaS(gamma-alpha)(vib) approximately (0.75+/-0.15)k(B), is about half of the total entropy change. The bulk modulus follows a power-law pressure dependence that is well described using the framework of electron-phonon coupling. These results clearly demonstrate the importance of lattice vibrations, in addition to the spin and charge degrees of freedom, for a complete description of the gamma-->alpha phase transition in elemental Ce.

RESUMEN

Muon spin rotation/relaxation measurements have been performed in the itinerant helical magnet MnSi at ambient pressure and at 8.3 kbar. We have found the following: (a) the spin-lattice relaxation rate 1/T(1) shows divergence as T1T proportional, variant (T-T(c))(beta) with the power beta larger than 1 near T(c); (b) 1/T(1) is strongly reduced in an applied external field B(L) and the divergent behavior near T(c) is completely suppressed at B(L)> or =4000 G. We discuss that (a) is consistent with the self-consistent renormalization theory and reflects a departure from "mean-field" behavior, while (b) indicates selective suppression of spin fluctuations of the q=0 component by B(L).

RESUMEN

Transverse-field muon-spin rotation measurements in the vortex-lattice of the heavy-fermion (HF) superconductor PrOs4Sb12 yield a temperature dependence of the magnetic penetration depth lambda indicative of an isotropic or nearly isotropic energy gap. This is not seen to date in any other HF superconductor and is a signature of isotropic pairing symmetry, possibly related to a novel nonmagnetic "quadrupolar Kondo" HF mechanism in PrOs4Sb12. The T=0 relaxation rate sigma(s)(0)=0.91(1) micros(-1) yields an estimated magnetic penetration depth lambda(0)=3440(20) A, which is considerably shorter than in other HF superconductors.

RESUMEN

Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCu5-xPdx, x = 1.0 and 1.5, have been studied using muon spin-lattice relaxation. The sample-averaged asymmetry function G(t) indicates strongly inhomogeneous spin fluctuations and exhibits the scaling G(t,H) = G(t/H(gamma)) expected from glassy dynamics. At 0.05 K gamma(x = 1.0) = 0.35+/-0.1, but gamma(x = 1.5) = 0.7+/-0.1. This is in contrast to inelastic neutron scattering results, which yield gamma = 0.33 for both concentrations. There is no sign of static magnetism approximately greater than 10(-3)(B)/U ion in either material above 0.05 K. Our results strongly suggest that both alloys are quantum spin glasses.

RESUMEN

Behavioral audiograms were determined for five species of rodents: groundhog (Marmota monax), chipmunk (Tamias striatus), Darwin's leaf-eared mouse (Phyllotis darwinii), golden hamster (Mesocricetus auratus), and Egyptian spiny mouse (Acomys cahirinus). The high-frequency hearing of these animals was found to vary inversely with interaural distance, a typical mammalian pattern. With regard to low-frequency hearing, the animals fell into two groups: those with extended low-frequency hearing (chipmunks, groundhogs, and hamsters hear below 100 Hz) and those with restricted low-frequency hearing (spiny and leaf-eared mice do not hear appreciably below 1 kHz). An analysis of mammalian hearing reveals that the distribution of low-frequency hearing limits is bimodal with the two distributions separated by a gap from 125 to 500 Hz. The correspondence of this dichotomy with studies of temporal coding raises the possibility that mammals that do not hear below 500 Hz do not use temporal encoding for the perception of pitch.

Asunto(s)

RESUMEN

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.

RESUMEN

Bilateral auditory cortex lesions in Japanese macaques result in an aphasia-like deficit in which the animals are unable to discriminate two forms of their coo vocalizations. To determine whether this deficit is sensory in nature, two monkeys with bilateral lesions were tested for their ability to discriminate frequency and frequency change. The results indicated that although the animals were able to discriminate between sounds of different frequencies, they were unable to determine whether a sound was changing in frequency. Because the animals' coo vocalizations differ primarily in the predominant direction of their frequency change and not in their absolute frequency content, the aphasia-like deficit of animals with bilateral auditory cortex lesions appears to be a sensory disorder.

Asunto(s)

RESUMEN

Passive sound-localization acuity and its relationship to vision were determined for the echolocating Jamaican fruit bat (Artibeus jamaicensis). A conditioned avoidance procedure was used in which the animals drank fruit juice from a spout in the presence of sounds from their right, but suppressed their behavior, breaking contact with the spout, whenever a sound came from their left, thereby avoiding a mild shock. The mean minimum audible angle for three bats for a 100-ms noise burst was 10 degrees-marginally superior to the 11.6 degrees threshold for Egyptian fruit bats and the 14 degrees threshold for big brown bats. Jamaican fruit bats were also able to localize both low- and high-frequency pure tones, indicating that they can use both binaural phase- and intensity-difference cues to locus. Indeed, their ability to use the binaural phase cue extends up to 6.3 kHz, the highest frequency so far for a mammal. The width of their field of best vision, defined anatomically as the width of the retinal area containing ganglion-cell densities at least 75% of maximum, is 34 degrees. This value is consistent with the previously established relationship between vision and hearing indicating that, even in echolocating bats, the primary function of passive sound localization is to direct the eyes to sound sources.

Asunto(s)

RESUMEN

BACKGROUND: Partial succinate dehydrogenase deficiency (15% to 50% of normal reference enzyme activity) in skeletal muscle causes mitochondrial myopathy with various symptoms, for example, brain involvement, cardiomyopathy, and/or exercise intolerance. The deficiency may be isolated or may coexist with other respiratory-chain enzyme defects. The histopathologic assessment of succinate dehydrogenase activity in muscle biopsies of patients with suspected mitochondrial myopathies has focused on the finding of increased staining, usually in ragged-red fibers, rather than on reduced staining. OBJECTIVES: To determine the prevalence of muscle succinate dehydrogenase deficiency among patients with respiratory-chain defects and to determine whether the reduced activity is present histochemically and is comparable to the quantitative reduction found in muscle homogenates. PATIENTS AND METHODS: One hundred eight muscle biopsies were evaluated from patients with suspected mitochondrial myopathies by qualitative histochemical analysis and quantitative biochemical analyses of respiratory-chain enzymes using standard methodologies. RESULTS: Fifty-two patients had defects in respiratory-chain complexes; of these patients, 12 (23%) had partial deficiencies in succinate dehydrogenase activity either alone or together with reductions in other enzymes. The reduced activity was detectable histochemically in muscle biopsies with residual enzyme activity of up to 34% of the normal reference activity, while 2 biopsies with higher residual activity (49% and 68% of normal) could not be distinguished from normal biopsies. CONCLUSIONS: Of the patients with respiratory-chain enzyme defects, 23% had partial deficiencies of succinate dehydrogenase activity in muscle biopsies. This reduction could be detected histochemically in biopsies in most cases. The marked prevalence of succinate dehydrogenase deficiency among patients with respiratory-chain defects and its detection initially by histochemical analysis are important findings.

Asunto(s)

RESUMEN

When sufficient numbers of holes are introduced into the two-dimensional CuO2 square lattice, dynamic magnetic correlations become incommensurate with underlying lattice in all previously investigated La(2-x)A(x)Cu(1-z)B(z)O(4+y) ( A = Sr or Nd, B = Zn) including high T(c) superconductors and insulators, and in bilayered superconducting YBa2Cu3O6.6 and Bi2Sr2CaCu2O8. Magnetic correlations also become incommensurate in structurally related La2NiO4 when doped with Sr or O. We report an exception to this so-far well-established experimental "rule" in La(2)Cu(1-z)Li(z)O4 in which magnetic correlations remain commensurate.