Search

Jain SV, Simakajornboon S, Shapiro SM, Morton LD, Leszczyszyn DJ, Simakajornboon N. Obstructive sleep apnea in children with epilepsy: prospective pilot trial. Acta Neurol Scand: 2012: 125: e3–e6. © 2011 John Wiley & Sons A/S. Background – Obstructive sleep apnea (OSA) is prevalent in adults with epilepsy, especially refractory, but limited data exist in children with epilepsy. Aims– We conducted a prospective pilot study in children with epilepsy to identify the prevalence of OSA and its relationship to the use of antiepileptic drugs (AEDs) and epilepsy types. Methods – We used Michigan Pediatric Sleep Questionnaire (PSQ) in children with epilepsy. Patients were classified by seizures frequency as mild (0–1 seizure/month) or severe, refractory epilepsy (>1 seizures/month). We used PSQ ≥ 0.33 as a cutoff point to assess the risk of OSA. Results – Of 84 children, 52 were classified as mild and 32 as severe. Prevalence of OSA was significantly higher in the severe (43.8%) vs the mild group (30.7%, P 1 AED had significantly higher prevalence of OSA (45.8%) than children on ≤1 AED (30.6%, P

To identify antecedent clinical and health services events in infants (/=35 weeks gestational age (GA)) who were discharged as healthy from their place of birth and subsequently sustained kernicterus. We conducted a root-cause analysis of a convenience sample of 125 infants/=35 weeks GA cared for in US healthcare facilities (including off-shore US military bases). These cases were voluntarily reported to the Pilot USA Kernicterus Registry (1992 to 2004) and met the eligibility criteria of acute bilirubin encephalopathy (ABE) and/or post-icteric sequelae. Multiple providers at multiple sites managed this cohort of infants for their newborn jaundice and progressive hyperbilirubinemia. Clinical signs of ABE, verbalized by parents, were often inadequately elicited or recorded and often not recognized as an emergency. Clinical signs of ABE were reported in 7 of 125 infants with a subsequent diagnosis of kernicterus who were not re-evaluated or treated for hyperbilirubinemia, although jaundice was noted at outpatient visits. The remaining infants (n=118) had total serum bilirubin (TSB) levels20 mg per 100 ml (342 micromol l(-1); range: 20.7 to 59.9 mg per 100 ml). No specific TSB threshold coincided with onset of ABE. Of infants37 weeks GA with kernicterus, 34.9% were LGA (large for gestational age) as compared with 24.7% of term infants (37 weeks GA). Although90% mothers initiated breast-feeding, assessment of milk transfer and lactation support was suboptimal in most. Mortality was 4% (5 of 125) in infants readmitted at age/=1 week. Along with a rapid rise of TSB (0.2 mg per 100 ml per hour), contributing factors, alone or in combination, included undiagnosed hemolytic disease, excessive bilirubin production related to extra-vascular hemolysis and delayed bilirubin elimination (including increased enterohepatic circulation, diagnosed and undiagnosed genetic disorders) in the context of known late prematurity (37 weeks), glucose 6-phosphate-dehydrogenase deficiency, infection and dehydration. Readmission was at age/=5 days in 81 of 118 (69%) infants and10 days in 101 of 118 (86%) infants. TSB levels were/=35 mg per 100 ml (598 micromol l(-1)) in 46 (39%) infants, of whom one died before exchange transfusion, one was untreated and one was lost to follow-up. Timely and efficacious bilirubin reduction interventions defined by 'crash-cart' initiation of immediate intensive phototherapy and urgent exchange transfusion were accomplished in 11 of 43 infants, which were compared with 12 of 43 infants in whom a timely exchange sometimes could not be accomplished. No overt sequelae were found in 8 of 11 infants (73%) treated with a 'crash-cart' approach compared with none without sequelae when exchange was delayed by pre-admission delays, technical factors or need to transfer to a tertiary facility. None of the remaining 20 of 43 infants treated only with phototherapy escaped sequelae. Regardless of age at readmission and intervention, infants with peak measured TSB35 mg per 100 ml had post-icteric sequelae (n=73). There was a narrow margin of safety between birthing hospital discharge or home birth and readmission to a tertiary neonatal/pediatric facility. Progression of hyperbilirubinemia to hazardous levels and onset of neurological signs were often not identified as infant's care and medical supervision transitioned during the first week after birth. The major underlying root cause for kernicterus was systems failure of services by multiple providers at multiple sites and inability to identify the at-risk infant and manage severe hyperbilirubinemia in a timely manner.

An elastic and inelastic X-ray scattering investigation of the anomalous lattice properties of the heavy fermion compound CeRu2Si2 is reported. Thermal expansion, thermal diffuse scattering and phonon spectra were measured between 300 and 10 K. The static properties reflect the Kondo regime while no anomaly is found in the phonon dynamics. The present experiment also demonstrates the possibility of performing inelastic X-ray scattering in strongly absorbing compounds.

We describe a material, cubic CaCu 3 Ti 4 O 12 , which exhibits a large dielectric response, the temperature-dependence of which has not been seen, to our knowledge, in any existing material. This compound possesses a low-frequency dielectric constant, e ∼10 4 [1] , which is only weakly varying in the temperature range 100–400 K. Below T∼100 K , however, there is an abrupt 100-fold reduction in the value of e . X-ray diffraction and thermodynamic data argue against an explanation in terms of ferroelectricity, i.e. the collective ordering of local dipole moments. Both the low-frequency dielectric response as well as Raman scattering data suggest the existence of highly polarizable relaxational modes with a characteristic gap energy of 28 meV.

Short-range order effects in amorphous polycondensates, including the technologically important bisphenol-A-polycarbonate, have been investigated by elastic diffuse neutron scattering with spin polarization analysis. Selectively deuterated samples of each polycondensate have been used in order to vary the scattering contrast and thereby emphasize different pair correlations. The technique of spin polarization analysis allowed a reliable separation of the coherent scattering and an intensity calibration on the basis of the incoherent scattering as an internal standard. Thus, (dσ/dΩ)coh has been measured directly by this method. The experimental results are compared to calculated cross-sections from computer-generated structures. Simulations have been performed with the “amorphous cell” method which models the static structure of the amorphous polymer in full chemical detail on the basis of a “random coil” conformation. The results of the simulations yield a fertily ground for the discussion of the measured cross-sections, though a direct comparison with the experiment is not always satisfactory. The observed discrepancies indicate a still insufficient structural relaxation of the simulated structures.

Obstructive sleep apnea (OSA) is prevalent in adults with epilepsy, especially refractory, but limited data exist in children with epilepsy.We conducted a prospective pilot study in children with epilepsy to identify the prevalence of OSA and its relationship to the use of antiepileptic drugs (AEDs) and epilepsy types.We used Michigan Pediatric Sleep Questionnaire (PSQ) in children with epilepsy. Patients were classified by seizures frequency as mild (0-1 seizure/month) or severe, refractory epilepsy (1 seizures/month). We used PSQ ≥ 0.33 as a cutoff point to assess the risk of OSA.Of 84 children, 52 were classified as mild and 32 as severe. Prevalence of OSA was significantly higher in the severe (43.8%) vs the mild group (30.7%, P0.05). Children on1 AED had significantly higher prevalence of OSA (45.8%) than children on ≤1 AED (30.6%, P0.05). There was no significant correlation between the prevalence of OSA and seizure types. OSA is more prevalent in refractory epilepsy and in children who are on multiple AEDs. While further studies are needed to confirm these findings and to assess the consequences of OSA, we believe it is important to screen the children with epilepsy for OSA.

It is shown that an adaptive transient phase can be formed along the martensitic transformation path to overcome thermodynamic and nucleation barriers caused by the transformation strain. A possible role of the adaptive phase in the thermal nucleation of the martensite is discussed. The structure of the adaptive phase is predicted from the strain accommodation condition. An example of the cubic→tetragonal transformation is considered. The crystal lattice parameters of the adaptive phase are expressed through those of the parent cubic phase and tetragonal normal martensite

Brookhaven National Laboratory's High Flux Beam Reactor (HFBR) was built because the scientist always wants ‘more.’ In the mid-50's the Brookhaven Graphite reactor was churning away, producing anumber of new results, when the current generation of scientists, led by Donald Hughes, realized the need for a high flux reactor and started down the political, scientific and engineering path that led to the HFBR. The effort was joined by a number of engineers and scientists such as Chemick, Hastings, Kouts, and Hendrie that came up with the novel design of the HFBR. The two innovative features that have been incorporated in nearly all other research reactors built since are: (i) an undermoderated core arrangement which enables the thermal flux to peak outside the core region where beam tubes can be placed, and (ii) beam tubes that are tangential to the core which decrease the fast neutron background without affecting the thermal beam intensity. Construction began in the fall of 1961 and four years later...

High-resolution X-ray scattering experiments have been performed on single crystals of the incommensurate system Rb2ZnCl4 with emphasis on the kinetics of the lock-in phase transition. The nearly perfect single crystal (mosaic spread approximately=0.6 min) displayed a large hysteresis of 20 K. As the sample was cooled quickly from the paraelectric phase into the commensurate phase, via the incommensurate phase, the time evolution of the disappearance of the incommensurate peak intensity was monitored. The time becomes longer when the sample is quenched to lower than the lock-in temperature, which is contrary to the expected kinetic behaviour of nucleation and growth. The characteristic time of decay exhibits an Arrhenius-like behaviour with an energetic barrier Eb to overcome of the order of 0.37 eV. The origin of the energetic barrier is interpreted in terms of an order-disorder process of the ZnCl4 tetrahedra network.

The momentum and temperature dependence of the lifetimes of acoustic phonons in the elemental superconductors lead and niobium were determined by resonant spin-echo spectroscopy with neutrons. In both elements, the superconducting energy gap extracted from these measurements was found to converge with sharp anomalies originating from Fermi-surface nesting (Kohn anomalies) at low temperatures. The results indicate electron many-body correlations beyond the standard theoretical framework for conventional superconductivity. A possible mechanism is the interplay between superconductivity and spin- or charge-density-wave fluctuations, which may induce dynamical nesting of the Fermi surface.

High-resolution x-ray and neutron-scattering experiments have been performed on the same sample of KMnF{sub 3} in order to compare the temperature behavior of the neutron central peak'' and of the x-ray quasi-Bragg'' peak. It is found that the peak intensity of both the central and quasi-Bragg peaks evolves similarly as ({ital T}{minus}{Tc}){sup {minus}{gamma}} with {gamma}{sub CP}=1.34{plus minus}0.08 and {gamma}{sub QBP}=1.26{plus minus}0.04. This result, together with considerations about experimental conditions, strongly suggests that the central peak and the quasi-Bragg peak are the same feature even if they are not observed in the same range of temperature.

Nb-Ru is a high-temperature shape-memory alloy that undergoes a martensitic transformation from a parent cubic {beta}-phase into a tetragonal {beta}{sup '} phase at T{sub M}{approx}900 deg. C. Measurements of the phonon dispersion curves on a single crystal show that the [110]-TA{sub 2} phonon branch, corresponding in the q=0 limit to the elastic constant C{sup '}=1/2(C{sub 11}-C{sub 12}) has an anomalous temperature dependence. Nearly the entire branch softens with decreasing temperature as T{sub M} is approached. The temperature dependence of the low-q phonon energies suggests that the elastic constants would approach 0 as T approaches T{sub M}, indicating a second-order transition. No additional lattice modulation is observed in the cubic phase.

Revised concepts of bilirubin encephalopathy have been revealed by studies of bilirubin toxicity in cultured CNS cells and in congenitally jaundiced Gunn rats. Bilirubin neurotoxicity is related to the unbound (free) fraction of unconjugated bilirubin (Bf), of which the dominant species at physiological pH is the protonated diacid, which can passively diffuse across cell membranes. As the binding affinity of plasma albumin for bilirubin decreases strikingly as albumin concentration increases, previously reported Bf values were underestimated. Newer diagnostic tests can detect reversible neurotoxicity before permanent damage occurs from precipitation of bilirubin (kernicterus). Early toxicity can occur at Bf only modestly above aqueous saturation and affects astrocytes and neurons, causing mitochondrial damage, resulting in impaired energy metabolism and apoptosis, plus cell-membrane perturbation, which causes enzyme leakage and hampers transport of neurotransmitters. The concentrations of unbound bilirubin in the cerebro-spinal fluid and CNS cells are probably limited mainly by active export of bilirubin back into plasma, mediated by ABC transporters present in the brain capillary endothelium and choroid plexus epithelium. Intracellular bilirubin levels may be diminished also by oxidation, conjugation and binding to cytosolic proteins. These new concepts may explain the varied susceptibility of neonates to develop encephalopathy at any given plasma bilirubin level and the selective distribution of CNS lesions in bilirubin encephalopathy. They also can suggest better strategies for predicting, preventing and treating this syndrome.

Optical conductivity measurements on the perovskite-related oxide CaCu 3 Ti 4 O 12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is ∼80 at room temperature, which is far smaller than the value of ∼10 5 obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (≲500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.

Results of neutron diffraction measurements on TbNiSn in magnetic fields up to 6T are reported. This material shows successive phase transitions at T1 = 7.6 K, T2 = 6.0 K, T3 = 2.0 K and TN = 18.5 K in zero field, and a giant magnetoresistance effect (GMR) near four successive metamagnetic transitions at low temperatures. Propagation vectors and main signatures of the magnetic phases appearing at elevated fields applied along the b axis at low temperatures are determined. We find large hysteresis at several phase boundaries. In some cases a co-existence of magnetic structures is detected.

It is shown that an appearance of an intermediate martensite phase called adaptive martensite may be expected if the surface energy of a boundary between two orientational variants of the normal martensite phase is very low and the typical lattice-mismatch-related elastic energy is high. The adaptive martensite is formed as an elastically constrained phase when the scale of structure heterogeneities induced by the crystal-strain accommodation is reduced to the microscopic scale commensurate with the twin-plane interplanar distance. An example of the cubic\ensuremath{\rightarrow}tetragonal transformation is considered where the adaptive phase has a pseudo-orthorhombic lattice. The crystal-lattice parameters of the adaptive phase are expressed through those of the parent cubic phase and tetragonal normal martensite. It is shown that the (5,2\ifmmode\bar\else\textasciimacron\fi{})7R martensite in \ensuremath{\beta}'NiAl alloys and the intermediate phase recently found just above the temperature of the fcc\ensuremath{\rightarrow}fct martensitic transformation in Fe-Pd are examples of the adaptive martensite. A possible role of the adaptive phase in the thermal nucleation of the martensite is discussed. The nucleation of the normal martensite may be bypassed by nucleation of the adaptive phase, which transforms to the normal martensite during the growth.

Gen Shirane recently celebrated his 40th anniversary at Brookhaven National Laboratory by giving a special Physics Department Colloquium on March 5, 2002. He gave an informative talk, laced with typical “Gen humor” entitled, “Piezoelectricity, Waterfalls, and Neutrons,” where he described his latest work on understanding the phase diagrams of mixed crystal ferroelectrics and why only certain compositions have very high piezoelectric properties—an important discovery that alluded scientists for over fifty years.

Laboratory after nearly 30 years of neutron scattering research. Brookhaven organized a symposium to honor John for his significant contributions t o condensed matter science, the neutron scattering community, Brook-haven and the Department of Energy.

Phonon softening was observed in the parent phase of a AuCd alloy which transforms from the β2(B2) parent to ζ2 ′(trigonal) martensite at M s=304 K. Since Cd strongly absorbs neutrons, the isotope 114Cd was used in preparing the single crystal for the measurements. The [ζζ0]TA2( u//[1\bar0]) phonon branch was measured and found to be anomalously low. A minimum is present at ζ=0.35 which softens as M s approaches from above. The results are consistent with the model proposed by Ohba et al. [Materials Trans. JIM 33 (1992) 29] based upon a crystallographic study of the ζ2 ′ phase.

The local hydrogen vibrations are measured by inelastic neutron scattering techniques in the FeTiHx system for x=0.06 ( alpha phase), 0.94 ( beta 1 phase), 1.4 ( beta 2 phase) and 1.86 ( gamma phase) as well as a function of temperature in the gamma phase. The spectra exhibit both sharp and broad peaks in the energy range of 60-110 meV and are strongly dependent upon H concentration and temperature.

The incommensurate phase of RbD3(SeO3)2 has been re-examined by high resolution neutron diffraction techniques. The positions and widths of the superlattice peaks have been determined with high precision. In comparison with the earlier measurements the transition temperatures in the present sample are 7°K higher and the maximum incommensurability is a factor of 2 lower. These differences suggest that defects play an important role in the incommensurate phase.

Preliminary results of neutron scattering and dielectric measurements on NaNO2 are reported. The dielectric data reveal that the width TN - TC of the incommensurate phase decreases with increasing hydrostatic pressure up to 1000 psi and then increases. TN - TC and the amplitude of the incommensurate modulation both decrease with increasing electric field Eb while the modulation wavevector is insensitive to Eb.

Phonon dispersion curves for the [110] 〈1\ifmmode\bar\else\textasciimacron\fi{}10〉 ${\mathrm{TA}}_{2}$ branch in ${\mathrm{Ni}}_{\mathrm{x}}$${\mathrm{Al}}_{100\mathrm{\ensuremath{-}}\mathrm{x}}$ (50lxl65) reveal a pronounced minimum whose position in q space is composition dependent but whose frequency does not change appreciably with temperature. In the same q range, substantial elastic scattering also appears which is associated with localized embryos of a low-temperature phase. The diffuse scattering from the elastic displacement field about these embryos is highly anisotropic, giving rise to the striated strain contrast (tweed) in the electron microscope image. A common electronic origin of these effects is proposed.

The elastic constants (in units of 1011 dyn cm-2) of Na beta -alumina as measured by inelastic neutron scattering are c11=33.8, c33=24.5, c44=5.0 and c12=14.3, c44 varies with the substitution of other ions for Na, with c44=5.6, 6.2 and 7.3 for Ag, K and Rb respectively. A dispersionless phonon mode observed at 5-6 meV for q>0.2 rlu is attributed to the Na motion, but its energy is not in agreement with Raman and far-infrared measurements.

The authors report neutron scattering and magnetic susceptibility results for CeAl. The material orders antiferromagnetically at TN=10.2K, with the ordered moment 1.73+or-0.1 mu B in a structure that can be described as a layered nearly uniaxial metamagnet, with a small canting of the spins away from the b direction. Strong ferromagnetic and antiferromagnetic fluctuations are observed above TN; the critical exponent is beta =0.37+or-0.04. Inelastic scattering exhibits a magnon line in the ordered state at 3 meV, whose width is less than 1 meV, and a crystal field at 10.5 meV. These features can be understood as manifestations of metamagnetic behaviour in a system of conventional localised spins. Valence fluctuation effects are absent.

In the shape-memory alloy, NiTi:Fe, the martensitic transformation is well separated from the premartensitic (PM) phase and the latter can be studied in detail. X-ray diffraction studies in the PM phase reveal satellites near ${\stackrel{\ensuremath{\rightarrow}}{q}}_{I}=\frac{1}{3}(0,\overline{1},1)$ and ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}}_{\mathrm{II}}=\frac{1}{3}(1,1,1)$. For both $q$ values, the satellites are incommensurate and the surprising feature observed is that the incommensurate wave vector $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\delta}}$ and the width of the satellites depend upon the Brillouin zone studied. This contradicts a simple condensed charge-density and/or lattice-wave description of the PM phase. If the shift is neglected, the structure in the PM phase can be explained by a condensation of three [$\ensuremath{\zeta}\overline{\ensuremath{\zeta}}0$]${\mathrm{TA}}_{2}$ modes with $\ensuremath{\zeta}=\frac{1}{3}$. In addition we propose a relationship between the well-known $\ensuremath{\omega}$ phase and the PM phase observed in this experiment and for other alloys.

The low-temperature phase of the dilute Ising antiferromagnet ${\mathrm{Fe}}_{0.55}$${\mathrm{Mg}}_{0.45}$${\mathrm{Cl}}_{2}$ in zero field is studied by specific-heat, ac-susceptibility, and neutron-scattering experiments. We find that in this phase, spin-glass behavior and antiferromagnetic long-range order coexist. Such a mixed-order phase is predicted by the mean-field theory of reentrant spin-glasses, but has never been observed before.

The authors have measured the localised vibrational modes of hydrogen in a Nd0.93V0.07 alloy. As one cools the sample for the first time to 10K one observes that hydrogen is trapped at octahedral sites associated with two substitutional vanadium atoms. The trap energy is small (10-20 meV) and less than the precipitation enthalpy. The phenomenon exhibits an interesting hysteresis. On repeated cooling cycles the hydrogen atoms tend to precipitate rather than stay in the trap sites. This is due to the formation of additional nucleation sites on the first cooling cycle.

Previous ultrasonic measurements have shown a softening of one of the acoustic‐phonon branches in thallium phosphorus selenide (Tl3PSe4) when subject to hydrostatic pressure. These measurements also show a 60% softening between room temperature and 90 K. In order to further characterize this material and to investigate the possibility of a phase transition at temperatures less than 90 K, we have used inelastic neutron scattering to measure the phonon dispersion along symmetry directions. The measurements agree well with the ultrasonic measurements previously reported for all branches except the soft ab shear described by the strain component e6. The ab shear is found to be 60% stiffer than the ultrasonic value with very little temperature dependence.

Materials exhibiting structural phase transformations are well known to possess pretransitional phenomena. Below the transition temperature, Tc, an order parameter appears and the pretransitional effects are associated with the fluctuations of the order parameter. Neutron scattering techniques have proved invaluable in studying the temporal and spatial dependence of these fluctuations. SrTiO3 is the prototypical example of a structural phase transformation exhibiting features observable in other transformations such as martensitic and order-disorder. The experimental evolution of the understanding of the phase transformation in SrTiO3 will be reviewed and the features observed will be shown to typify other systems.

The field dependence of the magnetic excitations in the re-entrant spin glass (RSG) Fe28Cr72 is investigated over a wide range of temperatures. The zero-field spin dynamics are anomalous not only in the spin-glass phase but also in the paramagnetic phase. In an applied field (H=8.8 kOe) spin waves are induced at low temperatures with an energy gap g mu BH approximately=0.1 meV. This observation is in marked contrast with results from Fe1-xAlx, where no gap is induced. The results suggest that the ground state of RSG is not unique.

In order to investigate the phase transition in terms of lattice dynamics, the symmetry modes of the para- and ferroelectric phases of the semiconductor SbSI are analysed by means of group theory. Starting from the simplified C22h space group with two formula units per unit cell, the symmetry modes in the different phases are deduced and their correlation from one phase to another is also established. Raman scattering measurements of the crystal in the two phases and in the phase transition region were obtained. These results are compared with available IR and Raman data. On the basis of the proposed model which takes into account the accidental degeneracies of the modes, the main features of the observed IR and Raman spectra are satisfactorily explained; the assignment of observed frequencies to determined symmetry coordinates is performed. An effort is also made to identify the temperature dependence of the mode frequencies in the vicinity of the ferroelectric transition temperature. An optical band whose frequency is strongly temperature dependent is observed in the Raman investigation and is in agreement with earlier works. Fur die Untersuchung des Phasenubergangs mit der Gitterdynamik werden die Symmetriemoden der para- und ferroelektrischen Phase des Halbleiters SbSJ mittels Gruppentheorie analysiert. Ausgehend von der vereinfachten Raumgruppe C22h mit zwei Formeleinheiten pro Einheitszelle werden die Symmetriemoden in den verschiedenen Phasen hergeleitet und ihre Korrelation von einer Phase zur anderen aufgestellt. Messungen der Ramanstreuung des Kristalls in beiden Phasen und im Phasenubergangsbereich werden durchgefuhrt. Diese Ergebnisse werden mit verfugbaren IR- und Ramanwerten verglichen. Auf der Grundlage des vorgeschlagenen Modells, das zufallige Entartung der Moden berucksichtigt, werden die Hauptcharakteristiken der beobachteten IR- und Ramanspektren befriedigend erklart; eine Zuordnung der beobachteten Frequenzen zu den bestimmten Symmetriekoordinaten wird durchgefuhrt. Es wird auch der Versuch gemacht, die Temperaturabhangigkeit der Modenfrequenzen in der Nahe der Temperatur des ferroelektrischen ubergangs zu ermitteln. Eine optische Bande, deren Frequenz stark temperaturabhangig ist, wird bei den Ramanuntersuchungen beobachtet und befindet sich mit fruheren Arbeiten in ubereinstimmung.

Neutron scattering experiments have been performed on a spin‐glass CuMn (5 at. %, Tg =27.6 K). Polarized neutron measurements with coarse energy resolution show no change of instantaneous spatial spin correlation below T=60 K. Unpolarized neutron studies with fine energy resolution (ΔE=260 μeV) demonstrate that the slowing down of Mn spin fluctuations occur in the same way for all the wave vectors between 0.2 and 4.0 A−1. These results indicate that the spatial and dynamic spin correlations are completely decoupled in the spin freezing process. We also study the short‐range spatial correlation of the ‘‘frozen’’ spins at T=5 K using a simple model, and demonstrate the importance of the ferromagnetic coupling between the third nearest‐neighbor Mn moments.

A neutron-scattering study of the structural phase transition in hydrogen-reduced crystal of SrTiO/sub 3/ shows a systematic enhancement of the central-peak intensity with increasing defect concentration. T/sub c/ is found to decrease linearly with increasing carrier concentration. The results provide direct experimental evidence for the involvement of a defect mechanism in central-peak formation.

Elastic and inelastic neutron scattering studies were performed on the amorphous alloy (Fe7 7Cr2 3)7 5P1 6B6Al3. These measurements were conducted over a temperature range from 1.8 K to room temperature. The elastic scattering results obtained at Q=0.025 A− 1 indicated a Curie temperature ∼184 K in addition to a ferromagnetic‐spin glass transition below 15 K. These values are consistent with the phase diagram construction resulting from the magnetization and ac susceptibilitymeasurements of Yeshurun e t a l. Inelastic neutron scatteringmeasurements resulted in well‐defined spin waves being observed in the ferromagnetic phase. For the small Q range studied (0.05–0.1 A− 1), the spin wave energies followed a quadratic dispersion. As the temperature was lowered towards the spin glass regime, the spin wave energies decreased indicating a softening of the magnetic stiffness constant. Below 10 K, no well‐defined spin wave excitations were present; however, a quasielastic peak, which increased slightly as the temperature was lowered, was observed.

Inelastic neutron scattering studies have been performed on single crystals of TmSe. An excitation at h..omega..approx.10 meV is observed whose momentum, temperature, and sample dependences provide evidence that this spectral feature is due to an excitation across a hybridization gap in TmSe.

The spin dynamics of a number of mixed valent materials have now been extensively studied using varied experimental probes including EPR, Raman scattering, infrared spectroscopy and inelastic neutron scattering. In this paper we review briefly photon and neutron spectroscopic studies of the 7F0–7F1 excitation dynamics in semiconducting SmS, SmSe and SmTe. New results for the phonon dispersion relations in SmS are presented. We also discuss recent neutron scattering experiments by Axe, Lawrence, Parks and ourselves on the γ-α transition in Ce.74Th.26. It is found that the spin fluctuation energy evolves from ~20 to >70 meV in going from the γ to the α phase.

Competing interactions play an essential role in all types of phase transitions. In the much studied spin glasses it is well known that the competing ferro- and antiferromagnetic interactions lead to a spin’s frustration resulting in the frozen spin glass state at low temperatures /1/. In ferroelectrics, the competition is between short-range interatomic forces and longer range electric dipolar forces which leads to the structural instability associated with ferroelectric ordering /2/. In metals, where martensitic phase transitions occur, the competing forces are not as well defined, but are likely due to the interatomic forces and the longer range electronic interactions. Depending upon the electronic band structure and the phonon dispersion curves of the solid, a variety of structures and microstructures can appear over a wide range of temperatures and compositions.

The Auob River is one of two major rivers traversing the Kalahari Gemsbok National Park (Figure 1). The river is a relict of wetter epochs and flows approximately once every ten years. The Auob is in a region of low rainfall (200 mm) which is variable in amount and spatial distribution. The rain which does fall consequently has a dominating influence on the flora and fauna of the ecosystem.

Neutron scattering is now a well-established technique for probing atomic positions and motions in a solid or liquid.1 To a first approximation the neutron impinging on a sample is scattered by the nuclei and the energy and momentum of the scattered neutron is determined by the collective nature of the sample’s nuclei (coherent scattering process) or by the individual atom’s motion (incoherent scattering process).