Cross spectra between pressure and temperature in a constant-area duct downstream of a hydrogen-fueled combustor

Pressure temperature cross spectra are necessary in predicting noise propagation in regions of velocity gradients downstream of combustors if the effect of convective entropy disturbances is included. Pressure temperature cross spectra and coherences were measured at spatially separated points in a combustion rig fueled with hydrogen. Temperature-temperature and pressure-pressure cross spectra and coherences between the spatially separated points as well as temperature and pressure autospectra were measured. These test results were compared with previous results obtained in the same combustion rig using Jet A fuel in order to investigate their dependence on the type of combustion process. The phase relationships are not consistent with a simple source model that assumes that pressure and temperature are in phase at a point in the combustor and at all other points downstream are related to one another by only a time delay due to convection of temperature disturbances. Thus these test results indicate that a more complex model of the source is required

Cross spectra between temperature and pressure in a constant area duct downstream of a combustor

The feasibility of measuring pressure temperature cross spectra and coherence and temperature-temperature cross spectra and coherence at spatially separated points along with pressure and temperature auto-spectra in a combustion rig was investigated. The measurements were made near the inlet and exit of a 6.44 m long duct attached to a J-47 combustor. The fuel used was Jet A. The cross spectra and coherence measurements show the pressure and temperature fluctuations correlate best at low frequencies. At the inlet the phenomena controlling the phase relationship between pressure and temperature could not be identified. However, at the duct exit the phase angle of the pressure is related to the phase angle of the temperature by the convected flow time delay

Studies on Host Responses to Aphanomyces invadans

Aphanomyces invadans is the pathogen that causes epizootic ulcerative syndrome (EUS), an economically devastating fish disease in southern Asia. The present thesis considered possible improvements to current methods of monitoring EUS, and examined the mechanisms of the host immune response to A. invadans in order to establish whether they could be enhanced to reduce the impact of EUS on aquaculture. Monoclonal antibody (MAb) technology was considered as a possible improvement to the histopathological methods currently used in diagnosis of EUS. Five MAbs were raised to day-old A. invadans germlings. Four gave weak reactions to A. invadans and cross-reacted with other Aphanomyces spp, though they may be useful for future studies on A. invadans. The other, designated MAb 3gJC9, only cross-reacted with the crayfish plague pathogen, A. astaci, and was used for the development of an immunohistochemistry protocol that may be of use in diagnosis. Immunohistochemistry with MAb 3gJC9, which recognised an extracellular product (ECP) of A. invadans, was specific to A. invadans in fish tissue, although it also recognised A. astaci in plague-infected crayfish. It also recognised the mycelium in fish infected with ulcerative mycosis, indicating that ulcerative mycosis is synonymous with EUS. Preliminary observations indicated that both ECPs and what appeared to be a hitherto unreported early stage of the mycelium are important in the pathology of EUS. Studies in vitro on the macrophages of EUS-susceptible giant gourami Osphronemus gouramy and silver barb Barbodes gonionotus, and EUS-resistant Nile tilapia Oreochromis niloticus, found that their macrophages were able to inhibit the growth of A. invadans. The macrophages of striped snakehead Channa striata did not inhibit A. invadans, which may account for their high EUS-susceptibility, especially as A. invadans strongly inhibited the respiratory burst of snakehead macrophages. Studies on humoral immune responses revealed that complement inhibited A. invadans in the case of snakeheads, gourami and barbs but not tilapia or swamp eels Monopterus albus. The humoral responses of the latter were very different to the four other species, and not elucidated. Low levels of anti A. invadans antibodies were found in tilapia and gourami from an EUS-endemic region, and high levels in snakehead. Snakehead antibodies appeared to be able to inhibit A. invadans even when complement was removed, but lower levels were produced at the low temperatures typically associated with EUS. A range of potential immunostimulants were screened for the ability to enhance resistance to EUS. The two successful products were administered as feed supplements to snakeheads and barbs that were subsequently injected intramuscularly with A. invadans. One, the algal extract Ergosan, showed some beneficial effects on snakeheads although the challenge was inconclusive. The other, the vitamin supplement Salar-bec, accelerated the cellular immune response and reduced mortality in snakeheads and barbs, and enhanced antibody production in snakeheads. The antibody response of snakeheads was further studied by comparing the anti- A. invadans antibody level, inhibitory activity of sera in vitro and protective capacity of sera from EUS-naïve snakeheads to that of snakeheads recently exposed to EUS and those subject to long term EUS-exposure. Sera of populations recently exposed to EUS showed an increased level of antibodies, but little improvement in inhibitory or protective activity. Sera from snakeheads that had endured long term exposure showed a wide range of antibody levels, but marked increases in inhibitory and protective activity. Antibodies cross-reacted with non-pathogenic Aphanomyces spp. in all cases

Measuring orbital angular momentum superpositions of light by mode transformation

We recently reported on a method for measuring orbital angular momentum (OAM) states of light based on the transformation of helically phased beams to tilted plane waves [Phys. Rev. Lett.105, 153601 (2010)]. Here we consider the performance of such a system for superpositions of OAM states by measuring the modal content of noninteger OAM states and beams produced by a Heaviside phase plate

Structure of CdTe/ZnTe superlattices

The structure of CdTe/ZnTe superlattices has been analyzed through θ/2θ x‐ray diffraction, photoluminescence, and in situ reflection high‐energy electron diffraction (RHEED) measurements. Samples are found to break away from Cd_(x)Zn_(1−x)Te buffer layers as a consequence of the 6% lattice mismatch in this system. However, defect densities in these superlattices are seen to drop dramatically away from the buffer layer interface, accounting for the intense photoluminescence and high‐average strain fields seen in each of our samples. Observed variations in residual strains suggest that growth conditions play a role in forming misfit defects. This could explain discrepancies with calculated values of critical thickness based on models which neglect growth conditions. Photoluminescence spectra reveal that layer‐to‐layer growth proceeded with single monolayer uniformity, suggesting highly reproducible growth. Our results give hope for relatively defect‐free Cd_(x)Zn_(1−x)Te/Cd_(y)Zn_(1−y)Te superlattices with the potential for applications to optoelectronics offered by intense visible light emitters

Experimental high-dimensional two-photon entanglement and violations of generalised Bell inequalities

Quantum entanglement plays a vital role in many quantum information and communication tasks. Entangled states of higher dimensional systems are of great interest due to the extended possibilities they provide. For example, they allow the realisation of new types of quantum information schemes that can offer higher information-density coding and greater resilience to errors than can be achieved with entangled two-dimensional systems. Closing the detection loophole in Bell test experiments is also more experimentally feasible when higher dimensional entangled systems are used. We have measured previously untested correlations between two photons to experimentally demonstrate high-dimensional entangled states. We obtain violations of Bell-type inequalities generalised to d-dimensional systems with up to d = 12. Furthermore, the violations are strong enough to indicate genuine 11-dimensional entanglement. Our experiments use photons entangled in orbital angular momentum (OAM), generated through spontaneous parametric down-conversion (SPDC), and manipulated using computer controlled holograms

Tactile order memory: evidence for sequence learning phenomena found with other stimulus types

We examine serial order memory for sequences of tactile stimuli and investigate whether established characteristics of order memory, namely serial position effects, error distributions, and Hebb repetition learning, are observed with tactile memory. Visually obscured participants received six tactile stimulations: one to each of six fingers. At test, participants lifted the six fingers in the order of stimulation. For every third trial participants received the same order of stimulation (i.e. the Hebb sequence). Serial recall accuracy produced the canonical bowed serial position function found for immediate serial recall. In addition, recall for the Hebb sequence improved relative to the filler sequences, providing the first demonstration of the Hebb repetition effect with tactile stimuli. Analysis of errors revealed close similarities to that reported with verbal and visual stimuli. This experiment further generalises established features of order memory to tactile memory, supporting the utilisation of an analogous order memory mechanism across stimuli

Chewing gum modifies state-anxiety and alertness under conditions of social stress

Objectives: The finding that chewing gum can moderate state-anxiety under conditions of acute stress¹ has proved difficult to replicate.2,4 The present study examines the extent to which chewing gum can moderate state-anxiety under conditions of acute social stress. Method: In a between-participants design, 36 participants completed a task comprising a mock job interview (a variation on the Trier Social Stress Task3, which included a mental arithmetic component) whilst either chewing gum or without gum. Self-rated measures of mood and anxiety were taken at baseline, after a 10-minute presentation preparation stage, after the 10-minute presentation, and following a 5-minute recovery stage. Results: Post-presentation measures reflected increased state-anxiety and decrease self-rated calmness and contentedness. Chewing gum attenuated the rise in state-anxiety whilst increasing self-rated alertness. Chewing gum did not affect contentedness or calmness. Conclusions: The findings indicate that chewing gum can act to reduce anxiety under conditions of acute social stress: a finding consistent with Scholey et al.1 Furthermore, the data add to the growing body of literature demonstrating that chewing gum can increase alertness.1,2,4,

Accommodation of lattice mismatch in Ge_(x)Si_(1−x)/Si superlattices

We present evidence that the critical thickness for the appearance of misfit defects in a given material and heteroepitaxial structure is not simply a function of lattice mismatch. We report substantial differences in the relaxation of mismatch stress in Ge_(0.5)Si_(0.5)/Si superlattices grown at different temperatures on (100) Si substrates. Samples have been analyzed by x‐ray diffraction, channeled Rutherford backscattering, and transmission electron microscopy. While a superlattice grown at 365 °C demonstrates a high degree of elastic strain, with a dislocation density <10^5 cm^(−2) , structures grown at higher temperatures show increasing numbers of structural defects, with densities reaching 2×10^(10) cm^(−2) at a growth temperature of 530 °C. Our results suggest that it is possible to freeze a lattice‐mismatched structure in a highly strained metastable state. Thus it is not surprising that experimentally observed critical thicknesses are rarely in agreement with those predicted by equilibrium theories