Manifestation of Landau level effects in optically-pumped NMR of semi-insulating GaAs.

Oscillations in the magnitude of optically generated nuclear spin polarization as a function of photon energy have been observed in bulk semiconductors using optically-pumped NMR (OPNMR). We compare experimental measurements of (69)Ga OPNMR with experimental measurements of magneto-absorption in bulk GaAs at low temperatures (6 K) and multiple magnetic fields. These data show that the photon energy dependence of both the OPNMR signal intensities and the magneto-absorption coefficients are well correlated over the studied energy regime approximately 1.515-1.568 eV, i.e., at and above the bandgap energy. Using the magneto-absorption coefficients as an input to a previously reported model of OPNMR, we are able to capture many of the oscillatory features in the (69)Ga signal, demonstrating that the origin of these oscillations are magnetic in nature, namely the formation of Landau levels. The nuclear spins as probed by OPNMR provide a measure of the circularly-polarized optical interband transitions between Landau levels. This correlation shows the importance of magneto-absorption measurements for understanding the complex photon energy dependence profile of OPNMR.

Optically pumped nuclear magnetic resonance of semiconductors.

Optically pumped NMR (OPNMR) of direct gap and indirect gap semiconductors has been an area of active research interest, motivated by both basic science and technological perspectives. Proposals to enhance and to spatially localize nuclear polarization have stimulated interest in this area. Recent progress in OPNMR has focused on exploring the experimental parameter space in order to elucidate details of the underlying photophysics of optical pumping phenomena. The focus of this review is on recent studies of bulk samples of GaAs and InP, namely, the photon energy dependence, the magnetic field dependence, and the phase dependence of OPNMR resonances. Models for the development of nuclear polarization are discussed.

Physical insights from a penetration depth model of optically pumped NMR.

A model of optically pumped NMR (OPNMR) behavior in GaAs that connects the photon energy dependence of the OPNMR signal intensity for (69)Ga with different polarizations of light has been developed. Inputs to this model include experimental conditions--external magnetic field (B(0)), temperature (T), and optical pumping parameters (tau(L), laser helicity)--as well as parameters that arise from sample-specific characteristics--electron spin lifetime (T(1e)), electron lifetime (tau(e)), electron-nuclear correlation time (tau(c)), and sample thickness (z). These various inputs affect the profile of the OPNMR signal intensity as a function of photon energy (E) in a predictable manner. Therefore, the profile can serve as a composite fingerprint by which individual parameters can be inferred when not known. Characteristics of the profile include the photon energy for maximum OPNMR signal intensity and the intensity ratio between sigma(+) and sigma(-) light.

Determination of 77Se-77Se and 77Se-13C J-coupling parameters for the clusters [Re5OsSe8(CN)6]3- and [Re4Os2Se8(CN)6]2-.

We have investigated rarely observed 77Se J-couplings (spin-spin couplings) in the mixed-metal face-capped octahedral clusters [Re5OsSe8(CN)6]3- and [Re4Os2Se8(CN)6]2- at natural abundance. To the best of our knowledge, these are the first observations of Se-Se spin-spin interactions between mu3-Se sites, important for stereochemical assignments in hexarhenium analogues, Chevrel phase materials, and similar cluster materials. NMR techniques such as COSY, INADEQUATE, and 2D J-resolved spectroscopy have been used in conjunction to study these interactions. The two isomers (cis and trans) of [Re4Os2Se8(CN)6]2- were distinguishable, and selective isotopic labeling of [Re5OsSe8(CN)6]3- with 13CN ligands enabled resonances to be assigned by observing the 2J (Se-M-C) couplings. For [Re5OsSe8(CN)6]3-, two different 2J (Se-M-Se) couplings were measurable on a single cluster, and these are related to one another through spin-spin interactions across a face diagonal or along an edge of the cube of inner selenium ligands. A rigorous analysis based on combinatorial math has been invoked to assign the couplings on the basis of the probability of multiple-spin interactions. The face diagonal association is found to result in a J-coupling interaction larger in magnitude than that from coupling along an edge of the cube-information critical for making stereochemical assignments of selenium sites.

Glycogen storage disease: report of 17 cases from southern India.

BACKGROUND: There are only four reports of glycogen storage disease (GSD), totalling six cases, from India. OBJECTIVE: To determine the clinical phenotypes of children diagnosed with GSD in southern India. METHODS: Liver biopsy reports from 1994 to 2005 were reviewed and GSD was confirmed in 17 patients. All 17 patients were tested for the three commonest GSD 1a mutations by restriction fragment length polymorphism: R83C, Q347X and G727T. RESULTS: They presented at mean age of 15 months (range, birth to 46 months) with hypoglycemia, hepatomegaly and delayed milestones. None of the patients showed R83C, Q347X or G727T mutation. CONCLUSION: Glycogen storage disease may not be rare in India. The commonest 1a mutations are probably rare here.

Esophageal Crohn disease in children: a clinical spectrum.

BACKGROUND: The incidence of esophageal Crohn disease (ECD) in adults ranges from 0.2% to 11.2% and in children is up to 43%. The aim of the study was to determine the clinical and endoscopic spectrum of ECD and its prevalence in our patient population. METHODS: Chart review of children with Crohn disease (CD). Esophageal Crohn disease was defined by accepted endoscopic and/or histologic findings. RESULTS: 210 children with CD were identified; 27 of those children had ECD. Nine children presented with specific upper GI symptoms; dysphagia, heartburn, nausea, vomiting, and odynophagia. Esophagoscopy in children with upper gastrointestinal symptoms revealed deep ulcers (n = 2), aphthous ulcers (n = l), erosions (n = l), edematous nodules, (n = l) and normal mucosa (n = 4). In asymptomatic children aphthous ulcers (n = 5), erosions (n = 3), deep ulcers (n = 3), and normal looking mucosa (n = 7) were seen. Twenty children also had gastric lesions, 3 children had duodenal lesions, and 3 children had both duodenal and gastric involvement. All 27 children had evidence of ileo-colonic or colonic disease. Acid suppressive medications were given only to children with upper GI symptoms and endoscopic esophageal lesions. The mean duration of follow-up from diagnosis of CD was 3.02 years (range 2 months-11.7 years). At last follow-up review, 7 children were receiving acid suppression and no children were receiving steroids. There were no complications related to ECD. CONCLUSION: The prevalence of endoscopic ECD is 7.6% but as many as 17.6% of our patient population had histologic evidence of ECD. The clinical and endoscopic spectrum of ECD are highly variable and poorly correlate with each other.