Optical Diode Effect at Spin-Wave Excitations of the Room-Temperature Multiferroic BiFeO_{3}.

Multiferroics permit the magnetic control of the electric polarization and the electric control of the magnetization. These static magnetoelectric (ME) effects are of enormous interest: The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. This phenomenon, if realized at room temperature, would allow the development of optical diodes which transmit unpolarized light in one, but not in the opposite, direction. Here, we report strong unidirectional transmission in the room-temperature multiferroic BiFeO_{3} over the gigahertz-terahertz frequency range. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. These findings are an important step toward the realization of optical diodes, supplemented by the ability to switch the transmission direction with a magnetic or electric field.

magnetic dispersion and anisotropy in multiferroic BiFeO3.

We have determined the full magnetic dispersion relations of multiferroic BiFeO3. In particular, two excitation gaps originating from magnetic anisotropies have been clearly observed. The direct observation of the gaps enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction and the single ion anisotropy. The DM interaction supports a sizable magnetoelectric coupling in this compound.

Spin rotation technique for non-collinear magnetic systems: application to the generalized Villain model.

This work develops a generalized technique for determining the static and dynamic properties of any non-collinear magnetic system. By rotating the spin operators into the local spin reference frame, we evaluate the zeroth, first, and second order terms in a Holstein-Primakoff expansion, and through a Green's functions approach, we determine the structure factor intensities for the spin-wave frequencies. To demonstrate this technique, we examine the spin-wave dynamics of the generalized Villain model with a varying interchain interaction. The new interchain coupling expands the overall phase diagram with the realization of two non-equivalent canted spin configurations. The rotational Holstein-Primakoff expansion provides both analytical and numerical results for the spin dynamics and intensities of these phases.

Comprehensive inelastic neutron scattering study of the multiferroic M n 1 - x C o x W O 4 .

Using high-resolution inelastic neutron scattering, we examine the spin dynamics of M n 1 - x C o x W O 4 in the collinear AF1, the a c - b spiral AF2, and the a c cycloidal AF5 phases. The spin wave excitations are well described by a Heisenberg model with competing long-range exchange interactions ( J i up to 12th nearest neighbors) and the single-ion anisotropy K induced by the spin-orbit interaction. While the exchange constants are relatively unchanged, the dominant effect of doping is to change the single-ion anisotropy from easy axis ( K > 0 ) in the collinear AF1 phase to easy plane ( K < 0 ) in the two multiferroic phases.

Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4.

Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV2O4, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration.

Ferrier's mistake revisited, or when it comes to the brain, nothing is simple.

OBJECTIVE: To review the work of David Ferrier (1843-1928), the British pioneer in the localization of function in the cerebral cortex. In his experiments on monkeys, Ferrier mistakenly located the center for vision in the angular gyrus of the parietal lobe. What led him to this error? DATA SOURCES: Ferrier included details of his technique and many of his original laboratory observations in his published papers and books; these published works have allowed a reconstruction of his thought processes as he struggled to assess vision in untrained animals. CONCLUSIONS: The occipital lobe lesions produced by Ferrier did not yield vision defects that were gross enough to be detected by observing a monkey's random behavior. On the other hand, the posterior parietal lesions produced by Ferrier did change a monkey's behavior in ways in which Ferrier misinterpreted as being due to induced blindness. Ferrier had probably induced visual neglect and a disinclination in the monkey to move its body, as well as actual vision disturbances in guiding voluntary limb movements.

Severe pancreatic involvement in three generations in von Hippel-Lindau disease.

Von Hippel-Lindau disease is a hereditary neoplastic disorder that is most commonly manifested as vascular tumors of the retina and cerebellum. Although visceral involvement is uncommon and is almost always clinically silent, we have encountered three closely related patients with extensive symptomatic pancreatic involvement. One patient had pronounced exocrine pancreatic insufficiency.

Roentgenographic simulation of colonic cancer by benign masses in Crohn's colitis.

Crohn's colitis has recently been shown to predispose the patient to cancer of the colon. Unfortunately, many of the manifestations of colonic malignancy, such as polypoid intraluminal masses and strictures, can be simulated roentgenographically by Crohn's colitis. We present five patients in whom this diagnostic difficulty arose. As established by total or subtotal colectomy, none proved to have malignancy; instead, pronounced transmural inflammation and, in two cases, multiple large pseudopolyps were found to account for the roentgenographically indeterminate lesions. These findings exemplify the difficulty in roentgenographic diagnosis of colonic mass lesions in patients with Chrohn's colitis.

Systemic mastocytosis with review of gastrointestinal manifestations.

A 63-year-old man presented with fever, splenomegaly, steatorrhea, diarrhea, and weight loss. A tissue diagnosis of systemic mastocytosis was made. This case is unusual in that diarrhea and steatorrhea were present in the absence of skin lesions and because fever was a prominent symptom. Thus, systemic mastocytosis should be included in the differential diagnosis of intestinal malabsorption even when the skin shows no abnormalities. The gastrointestinal manifestations of systemic mastocytosis are reviewed.

Metabolic myopathy as a cause of the exercise limitation in lung transplant recipients.

BACKGROUND: Cardiopulmonary exercise (CPEx) studies of lung transplant (LTx) recipients have found low maximum oxygen consumptions because of an as yet unexplained mechanism. Although it is likely that a significant problem resides within the mitochondria, this study determines whether a defect in oxygen uptake or utilization is present. METHODS: Six LTx recipients and six age- and sex-matched, healthy control subjects were studied to assess the possibility of a mitochondrial myopathy in LTx recipients. We used standard CPEx testing in conjunction with near-infrared spectroscopy (NIRS), a noninvasive optical technique to assess peripheral oxygen uptake in exercising muscle. NIRS analyzes the absorption spectra of hemoglobin and myoglobin at 760 and 850 nm to determine the relative oxygen saturation of these compounds during exercise with respect to baseline values. Relative changes in oxygen saturation are determined from the application of Beers law to changes in absorbance to compute changes in optical density (deltaOD). The LTx recipients and control subjects performed maximal noninvasive CPEx studies with NIRS analysis of the vastus lateralis muscle. RESULTS: All subjects had a circulatory limitation to exercise. The LTx group had a significantly lower percent predicted maximum oxygen consumption than the control group (45.3%+/-14% vs 100.8%+/-15.6%, [mean +/- SD] P < .001) and earlier onset of the anaerobic threshold (30.3%+/-7.6% vs 60.3%+/-8.0% of predicted VO2max, P < .0001) The LTx recipients demonstrated a significantly smaller deltaOD at maximum exercise as determined by NIRS analysis (0.024+/-0.005 deltaOD vs 0.054+/-0.03 deltaOD, P < .05). CONCLUSIONS: LTx recipients have an impaired maximal exercise capacity because of a disorder of peripheral oxygen utilization. This may be caused by a cyclosporine-induced mitochondrial myopathy.

Determinants of abnormal maximum oxygen uptake after lung transplantation for chronic obstructive pulmonary disease.

BACKGROUND: Single lung transplantation for chronic obstructive pulmonary disease relieves a ventilatory limit to incremental exercise, but maximum oxygen uptake remains abnormal. The purpose of this study was to define the relative contributions of Fick principle variables to abnormal aerobic capacity after lung transplantation. METHODS: Twelve paired incremental cardiopulmonary exercise test results obtained before and 3 to 6 months after single lung transplantation for chronic obstructive pulmonary disease were compared. RESULTS: Maximum workload nearly doubled after operation (42.5+/-4.2 vs 25.5+/-4.7 watts, P < .05). Peak exercise minute ventilation increased (32.8+/-3.3 vs 21+/-2.4 L/min, n = 11, P < .05), but maximum oxygen uptake remained markedly abnormal after transplantation (46.6%+/-4.4% vs 32.1%+/-2.9% predicted, P < .05, n = 8). Peak exercise cardiac output was normal (11.0+/-1.4 L/min, 89% predicted), but arterial-mixed venous oxygen content difference at peak exercise was only half of normal (7.2+/-0.61 mL/dL), as a result in part of the failure of mixed venous oxygen saturation to fall normally (peak exercise SvO2 = 49.8%+/-2.8%). CONCLUSIONS: Lung transplantation for chronic obstructive pulmonary disease relieves a ventilatory limit to exercise, but maximum aerobic capacity remains abnormal, in part because of abnormal systemic O2 extraction.

Perish, then publish: Thomas Harriot and the sine law of refraction.

A talented young scientist, Thomas Harriot, wrote the first English account of the New World, "A Briefe and True Report of the New Found Land of Virginia," distinguished by its serious effort to describe and understand the American Indian. Harriot went on to make innovations in mathematics and was one of the first astronomers to use the telescope. His largely unappreciated contribution to the history of ophthalmology was the first formulation of the sine law of refraction of light, found in his unpublished papers long after his death in 1621. Willebrord Snell discovered the sine law in Holland in 1621 but also died without formally publishing it. Rene Descartes first published the sine law in 1637. The sine law of refraction became not only the prime law of all lens systems but ushered in a new world of physical laws.

Dietary effects on exercising muscle metabolism and performance by 31P-MRS.

To determine how diet modulates short-term exercise capacity, skeletal muscle pH and bioenergetic state were examined by 31P-magnetic resonance spectroscopy in nine healthy volunteers. Subjects performed incremental quadriceps exercise to exhaustion after 5 days of high-carbohydrate (HCHO) or high-fat (HFAT) diet randomly assigned in crossover fashion and separated by a 2.5-day period of ad libitum mixed diet. Simultaneous measurements were made of pulmonary gas exchange, minute ventilation, and quadriceps muscle pH and phosphorylation potential. At rest and peak exercise, respiratory exchange ratio and minute ventilation were higher after HCHO than after HFAT (P < 0.05), reflecting greater CHO utilization. Peak O2 consumption (VO2) was not increased after HCHO (P > 0.05), but exercise duration was (339 +/- 34 s for HCHO vs. 308 +/- 25 s for HFAT; P < 0.05). HCHO was associated with a blunted early fall of phosphocreatine (PCr)/Pi vs. VO2 (-4.1 +/- 0.7 x 10(-2) min/ml for HCHO vs. -5.6 +/- 1.2 x 10(-2) min/ml for HFAT; P < 0.05). On both study days, the slope of PCr/Pi vs. VO2, before and after the PCr threshold, was correlated with exercise time. The results suggest that a diet rich in CHO improves exercise efficiency through beneficial effects on intracellular phosphorylation potential.

Delayed diagnosis of pituitary tumors.

Of 38 patients with presumed or proven pituitary adenomas, 24 first presented with ocular complaints. Of these, ten patients had a physician-caused delay in the formulation of the correct diagnosis. Reasons for the physician-caused delay in diagnosis include inadequate history evaluation, failure to perform adequate testing, provide follow-up examination, and recognize typical signs of pituitary adenomas.

Spin-wave dynamics of magnetic heterostructures: application to Dy/Y multilayers.

We examine the spin-wave (SW) dynamics of Dy/Y multilayers in order to separate the contribution of the Dy-Y interface from that of bulk Dy. The SW frequencies and intensities of bulk Dy are determined analytically. When the Dy layers in a multilayer geometry are decoupled, the SW dispersion relations are discontinuous with discrete excitations. With a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction coupling through the Y spacer, the discrete excitations become dispersive and the main SW branches split due to the multilayer geometry. Regardless of the strength of the intermediate RKKY interaction, the dispersion signature of the bulk remains.