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Results recently reported on the effect of thermochemical treatments on the (He-Cd) laser-excited emission spectra of strontium titanate (STO) are re-analyzed here and compared with results obtained under ion-beam irradiation. Contributing bands centered at 2.4 eV and 2.8 eV, which appear under laser excitation, present intensities dependent upon previous thermal treatments in oxidizing (O2) or reducing atmosphere (H2). As a key result, the emission band centered at 2.8 eV is clearly enhanced in samples exposed to a reducing atmosphere. From a comparison with the ionoluminescence data, it is concluded that the laser-excited experiments can be rationalized within a framework developed from ion-beam excitation studies. In particular, the band at 2.8 eV, sometimes attributed to oxygen vacancies, behaves as expected for optical transitions from conduction-band (CB) states to the ground state level of the self-trapped exciton center. The band at 2.0 eV reported in ion-beam irradiated STO, and attributed to oxygen vacancies, is not observed in laser-excited crystals. As a consequence of our analysis, a consistent scheme of electronic energy levels and optical transitions can now be reliably offered for strontium titanate. Graphical abstract

Pyruvate kinase (PK) is a highly regulated enzyme that catalyzes the final step of glycolysis. PK from the hyperthermophilic archaeon Pyrobaculum aerophilum (PaPK) is distinguished from most PK enzymes of eukarya and bacteria by not responding to any known allosteric effectors and apparently exhibiting only cooperative regulation. We determined the crystal structure of PaPK to 2.2 Å resolution and, in a manner consistent with the lack of a response to conventional effectors, observed that the canonical allosteric site is occluded by a tyrosine. Unexpectedly, though, a bound sulfate was observed at a position equivalent to the 6'-phosphate of sugar effectors, suggesting an allosteric site, but for an unknown effector and sharing only the phosphate position. A search of three-carbon intermediates of glycolysis revealed 3-phosphoglycerate (3PG) as a potent allosteric activator of PaPK. The response was abolished by mutation of residues that contact the sulfate and of an arginine proposed to interact with the 3PG carboxylate group. Regulation of PK by 3PG is consistent with the ancestral glycolysis of hyperthermophilic archaea in which this intermediate is produced by an irreversible enzyme, glyceraldehyde 3-phosphate ferredoxin oxidoreductase. Coordinated regulation within the lower half of glycolysis contrasts sharply with conventional glycolysis in which 3PG is produced reversibly and PK is regulated by fructose 1,6-bisphosphate, the product of phosphofructokinase, an irreversible enzyme in the upper half of the pathway. Regulation of PaPK by a carboxylate molecule rather than a sugar phosphate may reflect a step in the evolution of glycolysis that predates the dominance of sugars in metabolism.

The pathogenic fungus Cryptococcus neoformans must overcome multiple stressors to cause disease in its human host. In this study, we report that C. neoformans rapidly and transiently repressed ribosomal protein (RP) transcripts during a transition from 30°C to host-temperature. This repression was accompanied by accelerated mRNA degradation mediated by the major deadenylase, Ccr4, and influenced by the dissociable RNA polymerase II subunit, Rpb4. Destabilization and deadenylation of RP transcripts were impaired in an rpb4Δ mutant, suggesting that Rpb4 may be involved in host-temperature induced Ccr4-mediated decay. Accelerated decay of ER Stress transcripts one hour following a shift to host-temperature was also impaired in the rpb4Δ mutant. In response to host-temperature, Rpb4 moved from the nucleus to the cytoplasm, supporting a role for Rpb4 in coupling transcription and degradation. The PKH signaling pathway was implicated as a regulator of accelerated degradation of the RP transcripts, but not of the ER stress transcripts, revealing a further level of specificity. When transcription and degradation were uncoupled by deletion of Rpb4, growth at host-temperature was impaired and virulence was attenuated. These data suggest that mRNA synthesis and decay are coupled in C. neoformans via Rpb4, and this tight coordination promotes host-temperature adaptation and pathogenicity.

In the Euryarchaeota species Pyrococcus furiosus and Thermococcus litoralis, phosphoglucose isomerase (PGI) activity is catalyzed by an enzyme unrelated to the well known family of PGI enzymes found in prokaryotes, eukaryotes, and some archaea. We have determined the crystal structure of PGI from Pyrococcus furiosus in native form and in complex with two active site ligands, 5-phosphoarabinonate and gluconate 6-phosphate. In these structures, the metal ion, which in vivo is presumed to be Fe2+, is located in the core of the cupin fold and is immediately adjacent to the C1-C2 region of the ligands, suggesting that Fe2+ is involved in catalysis rather than serving a structural role. The active site contains a glutamate residue that contacts the substrate, but, because it is also coordinated to the metal ion, it is highly unlikely to mediate proton transfer in a cis-enediol mechanism. Consequently, we propose a hydride shift mechanism of catalysis. In this mechanism, Fe2+ is responsible for proton transfer between O1 and O2, and the hydride shift between C1 and C2 is favored by a markedly hydrophobic environment in the active site. The absence of any obvious enzymatic machinery for catalyzing ring opening of the sugar substrates suggests that pyrococcal PGI has a preference for straight chain substrates and that metabolism in extreme thermophiles may use sugars in both ring and straight chain forms.

This report presents a continuation of studies from these laboratories that have been concerned with the crystallization behavior of ethylene copolymers. More specifically a comparison is made between the thermodynamic properties of ethylene–norbornene copolymers with those of the 1-alkene copolymers. In addition a detailed comparison is made of the thermodynamic, tensile, morphological and structural properties and the overall crystallization kinetics between the ethylene–1-alkene copolymers that do or do not contain small concentrations of long-chain branches. Except for the crystallization kinetics, the crystallization properties have been found to be essentially the same for both types of copolymers. A correlation has also been developed between the lamellar and supermolecular structures, the chemical nature of the comonomer and its concentration. Supermolecular structures range from spherulitic to micellar, depending on both comonomer type and concentration. Analysis of the overall crystallization kinetics demonstrates that the interfacial free energies that govern nucleation are independent of the lamellar and superstructures that evolve.

Objective: To review the clinical findings in the first 1000 veterans seen in the Ministry of Defence9s Gulf war medical assessment programme to examine whether there was a particular illness related to service in the Gulf. Design: Case series of 1000 veterans who presented to the programme between 11 October 1993 and 24 February 1997. Subjects: Gulf war veterans. Main outcome measures: Diagnosis of veterans9 conditions according to ICD-10 (international classification of diseases, 10th revision). Cases referred for psychiatric assessment were reviewed for available diagnostic information from consultant psychiatrists. Results: 588 (59%) veterans had more than one diagnosed condition, 387 (39%) had at least one condition for which no firm somatic or psychological diagnosis could be given, and in 90 (9%) veterans no other main diagnosis was made. Conditions characterised by fatigue were found in 239 (24%) of patients. At least 190 (19%) patients had a psychiatric condition, which in over half was due to post-traumatic stress disorder. Musculoskeletal disorders and respiratory conditions were also found to be relatively common (in 182 (18%) and 155 (16%) patients respectively). Conclusion: Many Gulf war veterans had a wide variety of symptoms. This initial review shows no evidence of a single illness, psychological or physical, to explain the pattern of symptoms seen in veterans in the assessment programme. As the veterans assessed by the programme were all self selected, the prevalence of illness in Gulf war veterans cannot be determined from this study. Furthermore, it is not known whether the veterans in this study were representative of sick veterans as a group.

Nominal stress-strain curves of a series of random ethylene-hexene copolymers having narrow composition and most probable molecular weight distributions were investigated. A series of such molecular weight copolymers with a constant concentration of branches were crystallized under a variety of conditions. In each molecular weight series the level of crystallinity was approximately constant. Particular attention was focused on the yield region and the nature of the yielding process. It was found, quite surprisingly, that the yield stress was not solely dependent on the crystallinity level. Moreover, the shape of the force-elongation curve in the yield region was very dependent on the molecular weight and the crystallization mode. These changes in yielding correlated quite well with the overall crystallite structure that was characterized by thin section transmission electron microscopy. The orthorhombic unit cell of polyethylene was maintained in all the samples despite the changes that occurred in the overall crystallite structure. © 1997 John Wiley & Sons, Inc.

The pathogenic fungus Cryptococcus neoformans must overcome multiple stressors to cause disease in its human host. In this study, we report that C. neoformans rapidly and transiently repressed ribosomal protein (RP) transcripts during a transition from 30°C to host-temperature. This repression was accompanied by accelerated mRNA degradation mediated by the major deadenylase, Ccr4, and influenced by the dissociable RNA polymerase II subunit, Rpb4. Destabilization and deadenylation of RP transcripts were impaired in an rpb4Δ mutant, suggesting that Rpb4 may be involved in host-temperature induced Ccr4-mediated decay. Accelerated decay of ER Stress transcripts one hour following a shift to host-temperature was also impaired in the rpb4Δ mutant. In response to host-temperature, Rpb4 moved from the nucleus to the cytoplasm, supporting a role for Rpb4 in coupling transcription and degradation. The PKH signaling pathway was implicated as a regulator of accelerated degradation of the RP transcripts, but not of the ER stress transcripts, revealing a further level of specificity. When transcription and degradation were uncoupled by deletion of Rpb4, growth at host-temperature was impaired and virulence was attenuated. These data suggest that mRNA synthesis and decay are coupled in C. neoformans via Rpb4, and this tight coordination promotes host-temperature adaptation and pathogenicity.

In order to answer the questions arising from the health concerns of Gulf veterans, the Defence Medical Services have collated relevant health data so that they may be systematically analysed. However, data coverage is limited and there are concerns about its quality. Intramural studies alone will not be robust enough to determine if veterans are experiencing an excess of ill-health so a programme of epidemiological studies will be commissioned in collaboration with the Medical Research Council.

Discrete dislocation dynamics simulations have been generally limited to modeling systems described by isotropic elasticity. Effects of anisotropy on dislocation interactions, which can be quite large, have generally been ignored because of the computational expense involved when including anisotropic elasticity. We present a different formalism of dislocation dynamics in which the dislocations are represented by the deformation tensor, which is a direct measure of the slip in the lattice caused by the dislocations and can be considered as an eigenstrain. The stresses arising from the dislocations are calculated with a fast Fourier transform (FFT) method, from which the forces are determined and the equations of motion are solved. Use of the FFTs means that the stress field is only available at the grid points, which requires some adjustments/regularizations to be made to the representation of the dislocations and the calculation of the force on individual segments, as is discussed hereinafter. A notable advantage of this approach is that there is no computational penalty for including anisotropic elasticity. We review the method and apply it in a simple dislocation dynamics calculation.

We present results of the growth of InAsxP1−x/InP strained heterostructures by low pressure metalorganic vapor phase epitaxy. A large incorporation of arsenic into the InAsP ternary was observed using tertiarylbutylarsine as precursor. High resolution x-ray diffraction, photoluminescence, and optical absorption measurements for InAsP/InP strained multiple quantum wells reveal that the InAsP/InP interface is very sensitive to growth interruption. A systematic study of a growth in terruption sequence designed to improve the InAs/InP interface was carried out. For nonoptimal growth interruption procedures a large density of interface states is created, probably as a consequence of compositional modifications within the interface region. We find that the absorption spectrum may reveal a significant density of interface states. Thus, photoluminescence on its own is insufficient to characterize the interface roughness even for structures showing narrow low-temperature photoluminescence peaks. We also observe an enhancement of the As content for structures grown on InP (001) relative to those simultaneously grown on InP(001) two degrees off toward [100], which suggests that the composition of As in the ternary is limited by its surface diffusion.

The photoluminescence spectra of InAsP/InP strained multiple quantum wells have been experimentally determined in the temperature range 7–300 K. In order to understand the temperature behavior of the photoluminescence, a theoretical calculation is presented that takes into account the temperature‐induced variations in band gap, carrier effective mass, biaxial strain, and exciton binding energy. The results show that the energy of the transition E1H between the n=1 electron subband and the n=1 heavy‐hole subband changes as a function of temperature, and depends mainly on the evolution of the strained band gap of the InAsP layers. This is because in the temperature range 7–300 K the variations of the electron subband energy and the exciton binding energy are much less than those of the strained band gap, while the variation of the heavy‐hole subband energy can be neglected. These results also explain why, for a lattice‐matched quantum well, the variation of exciton peak energies with temperature follows tha...

A detailed investigation of the structural and optoelectronic properties of thick GaInP epilayers on sulfur‐doped InP substrates is reported. Significant variations of the optical absorption and photoluminescence transition energies from light‐ and heavy‐hole states are observed as a function of the epilayer composition as well as of the degree of relaxation of the misfit strain. High‐resolution x‐ray measurements were used to determine the Ga concentrations and the strains and indicate significant anisotropic relaxation in several films. Even small relaxations result in a significant increase in the optical linewidths and a rapid drop in the transition intensities. A model with no free parameters based on the strain Hamiltonian of Pikus and Bir provides excellent agreement with the transition energies and serves to identify unambiguously the transitions observed in the optical spectra. Within this model, isotropic in‐plane relaxation produces a shift of both light‐ and heavy‐hole energies whereas anisotr...

We present a photoluminescence study of the free-exciton singlet and triplet ground states in GaTe as a function of temperature from 5 to 40 K. Over the range 5-25 K, the temperature variation of excitonic-emission linewidth and peak energy comes mainly from exciton-acoustic-phonon interactions via the deformation potential. The contribution from exciton scattering by optical phonons of energy 14 meV begins at temperatures above ∼25 K. The exciton-optical-phonon interaction is the dominant scattering process above 30 K and effectively dissociates excitons since the energy of the optical phonon mode is close to the exciton binding energy. The luminescence thus decreases rapidly above 30 K and disappears at about 40 K

InAs microclusters embedded in an InP matrix and InAs x P 1– x /InP (0.1 ≤ x ≤0.3) strained multiple quantum wells (SMQW) have been prepared by LP-MOCVD using tertiarybutylarsine (TBAs) as a substitute for AsH 3 . The relatively large cracking efficiency of TBAs resulted in low As/In ratios (from 4.3 to 8.8) for InAs/InP structures and low As/P ratios (from 1×10 -3 to 3.5×10 -3 for InAs x P 1– x /InP (0.1 ≤ x ≤0.3). High-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) show that the TBAs-grown material is of high quality. The HRXRD patterns of InAs microclusters embedded in the InP matrix demonstrate that the InAs unit cell is tetragonally distorted in accordance with the elasticity theory. For InAs microclusters embedded in the InP matrix, the 7 K emission PL peak shifts from 1.35 to 1.39 eV when the InAs coverage is reduced from 0.8 to 0.2 monolayers, a clear indication of a lateral size effect. Picosecond time resolved PL shows a weak coupling of excitons confined by these InAs microclusters. We report also the results of a study of the interface roughness of InAs x P 1– x /InP heterostructures. HRXRD, PL, absorption and photoconductivity (PC) measurements for InAsP/InP SMQW reveal that the InAsP/InP interface is very sensitive to growth procedure. For nonoptimal growth procedures a large density of interface states is created, probably as a consequence of compositional modifications within the interface region. The optical measurements clearly resolve the fundamental intersubband transitions in the InAsP/InP SMQW, including heavy hole-light splittings, even at room temperature.

In a survey of the smoking habits of over 6,000 young soldiers, it was found that the prevalence of regular smoking was 45%. Though the prevalence of regular smoking in young soldiers is higher than the general prevalence rate for smoking in 16 to 19-year olds in the civilian population, the excess is considered to be a reflection of the social and geographical background of Army recruits. The survey found that young soldiers who smoke, smoke heavily. Eighty two percent smoked more than 20 cigarettes per week, 58% more than 40 cigarettes per week. This is higher than has been recorded by any previous survey of young soldiers. The proportion of young soldiers who have never smoked has risen markedly over the years. This survey found that 34% had never smoked.

This update has described how Gulf health research has developed over the past two years. In January 1996, MoD asked the MRC for their assistance in commissioning a programme of research to investigate Gulf veterans' health concerns. The MRC issued a 'Call for Proposals' in May 1996. All proposals were peer-reviewed and detailed applications were invited from a short-list of nine. In October 1996 the MRC recommended to MoD that two epidemiological studies should be funded; one to be carried out by Professor Cherry from Manchester University and the other by Dr Doyle of the London School of Hygiene and Tropical Medicine. The MRC also recommended that these researchers should collaborate with Professor Wessely of King's College, London who had already been funded by the Americans to conduct an epidemiological study on British Gulf veterans. In making their recommendations, the MRC advised that the researchers should assess the feasibility of tracing ex-service personnel and the availability of exposure data. Both these areas are giving cause for concern. The researchers are working with MoD staff to improve the quality of available address data. The main challenge facing MoD now is to ensure that the input data provided to researchers is of a high enough standard to enable them to achieve acceptable response rates. Since commissioning the epidemiological studies, there have been two further initiatives. In May 1997, the Government announced that MoD would commission research to investigate potential adverse effects to the combination of medical counter-measures administered to British personnel during Operation GRANBY. Preliminary work on this programme has started. In March 1998, the Government announced that Professor Wessely's team would be funded to carry out a thorough neurophysiological assessment of unwell veterans and controls identified during his epidemiological study.

Phosphoglucose isomerase (PGI) is an enzyme of glycolysis that interconverts glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P) but, outside the cell, is a multifunctional cytokine. High-resolution crystal structures of the enzyme from mouse have been determined in native form and in complex with the inhibitor erythrose 4-phosphate, and with the substrate glucose 6-phosphate. In the substrate-bound structure, the glucose sugar is observed in both straight-chain and ring forms. This structure supports a specific role for Lys518 in enzyme-catalyzed ring opening and we present a "push-pull" mechanism in which His388 breaks the O5-C1 bond by donating a proton to the ring oxygen atom and, simultaneously, Lys518 abstracts a proton from the C1 hydroxyl group. The reverse occurs in ring closure. The transition from ring form to straight-chain substrate is achieved through rotation of the C3-C4 bond, which brings the C1-C2 region into close proximity to Glu357, the base catalyst for the isomerization step. The structure with G6P also explains the specificity of PGI for glucose 6-phosphate over mannose 6-isomerase (M6P). To isomerize M6P to F6P requires a rotation of its C2-C3 bond but in PGI this is sterically blocked by Gln511.

We report low temperature optical absorption measurements on GaxIn1−xP/InP (x

This update has described how Gulf health research has developed over the past two years. In January 1996, MoD asked the MRC for their assistance in commissioning a programme of research to investigate Gulf veterans' health concerns. The MRC issued a 'Call for Proposals' in May 1996. All proposals were peer-reviewed and detailed applications were invited from a short-list of nine. In October 1996 the MRC recommended to MoD that two epidemiological studies should be funded; one to be carried out by Professor Cherry from Manchester University and the other by Dr Doyle of the London School of Hygiene and Tropical Medicine. The MRC also recommended that these researchers should collaborate with Professor Wessely of King's College, London who had already been funded by the Americans to conduct an epidemiological study on British Gulf veterans. In making their recommendations, the MRC advised that the researchers should assess the feasibility of tracing ex-service personnel and the availability of exposure data. Both these areas are giving cause for concern. The researchers are working with MoD staff to improve the quality of available address data. The main challenge facing MoD now is to ensure that the input data provided to researchers is of a high enough standard to enable them to achieve acceptable response rates. Since commissioning the epidemiological studies, there have been two further initiatives. In May 1997, the Government announced that MoD would commission research to investigate potential adverse effects to the combination of medical counter-measures administered to British personnel during Operation GRANBY. Preliminary work on this programme has started. In March 1998, the Government announced that Professor Wessely's team would be funded to carry out a thorough neurophysiological assessment of unwell veterans and controls identified during his epidemiological study.

InAs single strained quantum wells and nanoclusters have been synthesized by low-pressure metalorganic-vapor-phase epitaxy. The samples were obtained by depositing InAs layers on InP with coverages ranging from several monolayers to a fraction of a monolayer and subsequently overgrowing with InP. These heterostructures were characterized by high-resolution x-ray diffractometry, steady-state and time-resolved photoluminescence, and photoluminescence excitation spectroscopy. In the case of the InAs quantum wells, the experimental x-ray diffraction patterns are in agreement with patterns simulated within the framework of dynamical diffraction theory, assuming that the InAs/InP interfaces are sharp and that the InAs unit cell is tetragonally distorted. The photoluminescence of the quantum wells reveals a series of discrete peaks whose energy positions can be well reproduced by a finite square-well model with a valence-band offset \ensuremath{\Delta}${\mathit{E}}_{\mathrm{hh}}$ of 240 meV. The excitation spectrum of a one-monolayer-thick quantum well exhibits two resonances which are attributed to heavy- and light-hole excitonic transitions. The fractional InAs monolayers were deposited on terraced InP surfaces. Their x-ray diffraction spectra indicate that the InAs nucleates into nanoclusters. A shift toward higher energies of their optical emission is observed and is attributed to a quantum effect caused by lateral confinement of the excitonic wave function. Time-resolved photoluminescence and photoluminescence excitation spectra show that there is enough overlap of the excitonic wave function between adjacent nanoclusters to result in the formation of delocalized excitonic states. The InAs nanoclusters thus form a quantum dot superlattice.

A systematic study of the effect of growth interruption on the interface roughness of InAsxPi1−x/InP heterostructures has been carried out. High resolution X-ray diffraction, photoluminescence and optical absorption measurements for InAsP/InP strained multiple quantum wells reveal that the InAsP/InP interface is very sensitive to growth interruption. For nonoptimal growth interruption procedures a large density of interface states is created, probably as a consequence of compositional modifications within the interface region. We find that photoluminescence on its own is insufficient to characterize the interface roughness in our samples, since even for narrow low-temperature peak emissions corresponding to the multiple quantum wells, the absorption spectrum may reveal a significant density of interface states.

The orthorhombic phase in the mixed Jahn-Teller Ising system Dy (AsxV1-x) O4 has been studied by neutron scattering. For x < 0.99 a metastable domain state is observed, with Bragg peaks broadened by random strain fields. At 4.2 K the x = 0.95 sample had domain sizes ≈ 105, 230, and 170 A before, during, and after application of an ordering field.

Ultrasonic measurements of the soft-mode elastic constant 1/2 (C11 - C12) have been performed to investigate the pseudospin susceptibility of the random-field system Dy (AsxV1-x) O4. The susceptibility critical exponent γ = 1.73 ± 0.07 for x = 0.17 is much larger than for the pure compound (x = 0), in reasonable agreement with predictions of the random-field Ising model.

The anomalous enhancement of the Schottky specific heat peak [1] and the temperature dependence of the electric susceptibility [2], [3] in cerium ethyl sulphate (CeES) have been interpreted using a model [4] in which the separation between the two lowest Ce3+ Kramers doublets varies with temperature due to the coupling between these electronic states and the lattice phonons. Since the effect occurs in the absence of a phase transition, these experiments indicate that CeES is an unusual example of a cooperative Jahn-Teller system in which the dominant coupling is to the uniform Alg strain modes, ezz and/or 1/2(exx+eyy) which do not lower the crystal symmtry, but change tAse c/a ratio of the hexagonal unit cell. To investigate this effect, we have measured the temperature dependence of the velocity of longitudinal ultrasonic waves propagating along the c axis, and find that the corresponding elastic constant C33 softens at low temperatures (Fig. 1), providing direct evidence of Jann-Teller coupling to this Alg lattice mode in CeES.