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The optimal design of asymmetric quantum well structures for generation of entangled photons in the mid-infrared range by spontaneous parametric downconversion is considered, and the efficiency of this process is estimated. Calculations show that a reasonably good degree of entanglement can be obtained, and that the optical interaction length required for optimal conversion is very short, in the few μm range.

Capacitance probes are a fast, safe and relatively inexpensive means of measuring the relative permittivity of soils, which can then be used to estimate soil water content. Initial experiments with capacitance probes used empirical calibrations between the frequency response of the instrument and soil water content. This has the disadvantage that the calibrations are instrument-dependent. A twofold calibration strategy is described in this paper; the instrument frequency is turned into relative permittivity (dielectric constant) which can then be calibrated against soil water content. This approach offers the advantages of making the second calibration, from soil permittivity to soil water content. instrument-independent and allows comparison with other dielectric methods, such as time domain reflectometry. A physically based model, used to calibrate capacitance probes in terms of relative permittivity (εr) is presented. The model, which was developed from circuit analysis, predicts, successfully, the frequency response of the instrument in liquids with different relative permittivities, using only measurements in air and water. lt was used successfully to calibrate 10 prototype surface capacitance insertion probes (SCIPS) and a depth capacitance probe. The findings demonstrate that the geometric properties of the instrument electrodes were an important parameter in the model, the value of which could be fixed through measurement. The relationship between apparent soil permittivity and volumetric water content has been the subject of much research in the last 30 years. Two lines of investigation have developed, time domain reflectometry (TDR) and capacitance. Both methods claim to measure relative permittivity and should therefore be comparable. This paper demonstrates that the IH capacitance probe overestimates relative permittivity as the ionic conductivity of the medium increases. Electrically conducting ionic solutions were used to test the magnitude of this effect on the determination of relative permittivity. The response was modelled so that the relative permittivity, independent of ionic conductivity, could be determined in solutions with an electrical conductivity of up to 0.25 S m-1. It was found that a solution EC of less than 0.05 S m-1 had little impact on the permittivity measurement.

Perfectly-matched-layer (PML) boundary conditions are derived for finite-difference time-domain analysis of acoustic waves within piezoelectric crystals. The robustness and effectiveness of the derived boundary conditions are demonstrated by simulating acoustic wave propagation in the bismuth germanate material system-a system in which simple absorbing boundary conditions cause instabilities. An investigation into the stability and effectiveness of the PML is then presented in terms of the PML thickness and absorption profile. A range of optimised absorption profiles were determined by finding the maximum permissible absorption within the stability limit of the system. In the optimised case, the form of the absorption profile had little influence on the effectiveness of the PML. However, in the unoptimised case the linearly increasing absorption profile was found to be the most effective.

We report the time-domain analysis of fast pulses emitted by a quantum cascade laser (QCL) operating at ~3.1 THz using superconducting THz detectors made from either NbN or YBa2Cu3O7- (YBCO) thin films. The ultra-fast response from these detectors allows resolution of emission features occurring on a nanosecond time-scale, which is not possible with commercially available Ge or InSb bolometers owing to their much larger time constants. We demonstrate that the time-dependent emission can be strongly affected by relatively small variations in the driving pulse. The QCL output power–current relationship was determined, based on correlation of the time-dependent emission of radiation with current flow in the QCL, under different QCL bias conditions. We show that this relationship differs from that obtained using bolometric detectors that respond only to the integrated pulse energy. The linearity of the detectors, and their agreement with measurements using a Ge bolometer, was also established by studying the QCL emission as a function of bias voltage and excitation pulse length. This measurement scheme could be readily applied to the study of ultra-fast modulation and mode-locking of THz-QCLs.

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

We describe the theoretical and experimental studies of GaN/AlGaN based resonant tunnelling diodes, and in particular analyse the effects and typical values of interface roughness, and then discuss the implications of these, realistic material quality parameters on performance of unipolar optoelectronic devices.

Considerable interest exists for sensing and imaging technologies in the terahertz (THz) spectral range, in particular for the interrogation of materials of an organic or biological nature. Development in THz quantum cascade lasers is seeing higher operating temperatures and peak output powers in pulsed mode, accentuating their place as the preferred source of coherent THz frequency radiation. Technological development of interferometric sensing schemes continues to take advantage of practical improvements in THz quantum cascade lasers. In this Summary, we give a brief overview of some recent developments in this regard.

We propose a method of pinning and propagating domain walls in artificial multiferroic nanowires using electrically induced surface acoustic waves. Using finite-element micromagnetic simulations and 1D semi-analytical modelling, we demonstrate how a pair of interdigitated acoustic transducers can remotely induce an array of attractive domain wall pinning sites by forming a standing stress/strain wave along a nanowire's length. Shifts in the frequencies of the surface acoustic waves allow multiple domain walls to be synchronously transported at speeds up to 50 ms−1. Our study lays the foundation for energy-efficient domain wall devices that exploit the low propagation losses of surface acoustic waves to precisely manipulate large numbers of data bits.

Recent research shows that terahertz quantum cascade lasers are well-suited to high speed free space communication. The results of both theoretical and laboratory work indicate the devices are able to deliver bandwidths in the gigahertz to tens of gigahertz range without the burden of relaxation oscillations found in diode lasers. Using a novel rate equation model we explore the frequency response characteristics of a real device and report on the finding of a strongly peaked bias current-dependent response.

Summary Background Airway bypass is a bronchoscopic lung-volume reduction procedure for emphysema whereby transbronchial passages into the lung are created to release trapped air, supported with paclitaxel-coated stents to ease the mechanics of breathing. The aim of the EASE (Exhale airway stents for emphysema) trial was to evaluate safety and efficacy of airway bypass in people with severe homogeneous emphysema. Methods We undertook a randomised, double-blind, sham-controlled study in 38 specialist respiratory centres worldwide. We recruited 315 patients who had severe hyperinflation (ratio of residual volume [RV] to total lung capacity of ≥0·65). By computer using a random number generator, we randomly allocated participants (in a 2:1 ratio) to either airway bypass (n=208) or sham control (107). We divided investigators into team A (masked), who completed pre-procedure and post-procedure assessments, and team B (unmasked), who only did bronchoscopies without further interaction with patients. Participants were followed up for 12 months. The 6-month co-primary efficacy endpoint required 12% or greater improvement in forced vital capacity (FVC) and 1 point or greater decrease in the modified Medical Research Council dyspnoea score from baseline. The composite primary safety endpoint incorporated five severe adverse events. We did Bayesian analysis to show the posterior probability that airway bypass was superior to sham control (success threshold, 0·965). Analysis was by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00391612. Findings All recruited patients were included in the analysis. At 6 months, no difference between treatment arms was noted with respect to the co-primary efficacy endpoint (30 of 208 for airway bypass vs 12 of 107 for sham control; posterior probability 0·749, below the Bayesian success threshold of 0·965). The 6-month composite primary safety endpoint was 14·4% (30 of 208) for airway bypass versus 11·2% (12 of 107) for sham control (judged non-inferior, with a posterior probability of 1·00 [Bayesian success threshold >0·95]). Interpretation Although our findings showed safety and transient improvements, no sustainable benefit was recorded with airway bypass in patients with severe homogeneous emphysema. Funding Broncus Technologies.

The collared peccary (Pecari tajacu) is a social species that recently has expanded its historical range, yet little is known of its dispersal behavior at the population or biogeographic level. We used autosomal and cytoplasmic markers to assess whether the genetic variation among 4 populations in Texas retains a signal of historically recent founding events. Genetic differentiation based on mitochondrial DNA (mtDNA) haplotype frequencies (FST) among these 4 populations was substantial. The mtDNA haplotype mismatch distributions indicate that P. tajacu recently has expanded its range across Texas; however, microsatellite-based standard analyses of molecular variance (AMOVAs) and pairwise FST estimates indicated little variation among populations, suggesting that dispersal is accomplished primarily by males. We also tested the alternative power of mtDNA haplotype or microsatellite genotype distribution patterns to detect a sex bias in instantaneous short-distance dispersal. Sex-specific hierarchic...

Terahertz-frequency quantum cascade lasers (THz QCLs) based on bound-to-continuum active regions are difficult to model owing to their large number of quantum states. We present a computationally efficient reduced rate equation (RE) model that reproduces the experimentally observed variation of THz power with respect to drive current and heat-sink temperature. We also present dynamic (time-domain) simulations under a range of drive currents and predict an increase in modulation bandwidth as the current approaches the peak of the light-current curve, as observed experimentally in mid-infrared QCLs. We account for temperature and bias dependence of the carrier lifetimes, gain, and injection efficiency, calculated from a full rate equation model. The temperature dependence of the simulated threshold current, emitted power, and cut-off current are thus all reproduced accurately with only one fitting parameter, the interface roughness, in the full REs. We propose that the model could therefore be used for rapid dynamical simulation of QCL designs. (C) 2015 AIP Publishing LLC

Soils ranging in texture from sand to clay were used to compare permittivity measurements made using a Surface Capacitance Insertion Probe (SCIP) and time domain reflectometer (TDR). Measurements were made using the same electrodes embedded in each soil, making the measurements directly comparable. The objective of the work was to test a model describing the frequency response of the SCIP to both permittivity and electrode conductance, and to compare results with TDR and network analyzer measurements. The model was tested using liquids of known permittivity and in saline, dielectric solutions. Surface Capacitance Insertion Probe and TDR determined permittivity values are similar for sandy soils but diverge for loam and clay soils. Using Topp's values as a reference, the SCIP-determined permittivities for loams and clays lay close to the curve at water contents

This paper summarizes the results of a comparative study on seismic design of highway bridges jointly undertaken by the U.S. Federal Highway Administration and Japan's Public Works Research Institute. The seismic design specifications for highway bridges of the two countries are reviewed and compared with respect to their design philosophies and procedures. Some major design parameters including design seismic forces, response modification factors and minimum support lengths are addressed in detail. The differences between the two specifications are illustrated via a design example of a reinforced concrete column for simple, two-span bridges common in both countries. Three different scale models of the column are designed in accordance with the seismic design specifications of the United States and Japan, and tested on a shake table for their comparative seismic performance. The results of the shake table tests are discussed separately in a companion paper.

An experimental study of water fluxes from roofs in a residential area has quantified water fluxes from different types of roof and identified the major controls on the process. Roofs with pitches of 0°, 22° and 50° and orientations of 15° (from true north) (NNE) and 103° (ESE) were selected. A novel automatic system for monitoring has been developed. Noticeable differences in rainfall, runoff and evaporation were found for different roof slopes, aspects and heights. Depending on height, flat roofs collected 90 to 99% of rainfall recorded at ground level. Roofs with a 22° slope; facing south-south-west (i.e. facing the prevailing wind) captured most rain, whereas east-south-east facing roofs with slopes of 50° received the least. Depending on the roof slope, the average rainfall captured ranged from 62 to 93% of that at ground level. For the same slope, the results indicated that from roofs orientated normal to the prevailing wind; (i) captured rainfall was higher, (ii) evaporation was higher and (iii) runoff was less than that from roofs having other aspects. Monthly variations in the runoff–rainfall ratio followed the rainfall distribution, being lowest in summer and highest in winter. The highest mean ratio (0·91) was associated with the steeper roof slope; the lowest ratio (0·61) was for roofs facing the prevailing wind direction. For the same amount of rainfall, the runoff generated from a steeper roof was significantly higher than that generated by a moderate roof slope, but the lowest runoff was from roofs facing the prevailing wind. The results have also shown that the amount of runoff collected (under UK climatic condition) was sufficient to supply an average household in the studied area with the major part of its annual water requirements. The use of this water not only represents a financial gain for house owners but also will help protect the environment by reducing demand on water resources through the reduction of groundwater abstraction, construction of new reservoirs, and a reduction of the flood risk as its in situ use is considered a preventive measure known as a source control. Copyright © 2003 John Wiley & Sons, Ltd.

Lack of accurate data has led some hydrologists and city planners to assume that urban infiltration is zero and runoff is 100% of the rainfall. These assumptions lead to an over estimation of road runoff volume and an underestimation of direct recharge to groundwater, which is already rising under some UK cities. This study investigates infiltration and runoff processes and quantifies the percentage of rainfall that contributes to storm drainage, and that which infiltrates through different types of road surface. Access tubes were installed for measuring soil water content using a neutron probe in three car parks, a road and a grass site at the Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford. Storm drainage was recorded at the exit of the Thamesmead Estate in Crowmarsh Gifford, just before the drain joins the River Thames at Wallingford. Rainfall and water table depth were also recorded. Weekly measurements of soil moisture content indicated that the top 40 cm layer is not influenced by water-table fluctuations and, therefore, positive changes in soil moisture could be attributed to infiltration of rainfall through the surface. Depending on the nature of the surface, subsurface layers, level of traffic, etc., between 6 and 9% of rainfall was found to infiltrate through the road surfaces studied. The storm drainage generated by road runoff revealed a flow pattern similar to that of the receiving watercourse (River Thames) and increased with the increase of infiltration and soil water content below the road surface. The ratio of runoff to rainfall was 0·7, 0·9 and 0·5 for annual, winter (October–March) and summer (April–September) respectively. As the results of the infiltration indicated that 6 to 9% of annual rainfall infiltrates through the road surface, this means that evaporation represents, 21–24% of annual rainfall, with more evaporation taking place during summer than winter. Copyright © 2003 John Wiley & Sons, Ltd.

We present experimental results demonstrating that fractal conductance fluctuations are remarkably robust to deviations from the semiclassical conduction regime. We find that the fractal dimension depends solely on an empirical parameter that quantifies the resolution of the billiard's discrete energy level spectrum. Non-fractal fluctuations are obtained only in the extreme classical and quantum-mechanical conduction regimes.

We present a comprehensive study of the dependence of fractal conductance fluctuations (FCF) on semiconductor billiard parameters. We find that the fractal dimension depends solely on an empirical parameter that quantifies the resolution of the discrete energy level spectrum of the billiard. We have also investigated the effect of profile softness using billiards formed in a double two-dimensional electron gas heterostructure and find that FCF are robust to the changes in profile softness achieved.

Isoflavone reductase (IFR) from alfalfa catalyzes the NADPH-dependent reduction of 2′-hydroxy isoflavones to 2′-hydroxyisoflavanones such as vestitone, thereby performing a key step in isoflavonoid phytoalexin biosynthesis. Tobacco (Nicotiana tabacum L. cv. Xanthi) was transformed with an alfalfa cDNA encoding IFR regulated by an enhanced cauliflower mosaic virus 35S promoter and used to generate cell suspension cultures. Transformed cells expressed high levels of IFR activity and could take up 2′-hydroxyformononetin (2′OHF; IFR substrate) and convert it to vestitone. Both 2′OHF and vestitone were each converted to two sugar conjugates. The structure of the most abundant vestitone conjugate was determined using NMR spectroscopic analysis to be a novel vestitone 2′-O-glucoside. Liquid chromatography-mass spectroscopy (LC-MS) indicated that the molecular weights of the three less abundant conjugates were consistent with hexose conjugates of vestitone and 2′OHF. The IFR reduction and conjugation reactions were complete within 4 h, with the net percentage conversion of 2′OHF to vestitone ranging as high as 60%.

A model describing the increase in the relative permittivity of water with distance from the soil mineral surface is presented. The model assumes an exponential increase in the value of permittivity with increasing distance from the mineral surface; arguments are presented supporting this approach. The volume of bound water (within the bandwidth of time domain reflectometry, (TDR) 0.01–1 GHz) is considered to be equivalent to the soil hygroscopic water content. The refractive index mixing equation is used as a geometric base into which the model is incorporated. The new equation is tested using measurements of permittivity collected from two drying undisturbed soil cores that contained ∼10% hygroscopic water. The RMSE of predicted permittivity as a function of water content was found to decrease from ∼3.5 to less than 1. The model was further tested on data previously presented in the literature and found to correspond reasonably well.

This research investigated seismic performance of a reinforced concrete bridge column under repeated earthquake ground motions by shake-table experimentation on a scale model. The specimen was subjected to a series of simulated ground motions at different levels of shaking intensity. The deformation and damage evolution of the test column was addressed in terms of selected mechanical quantities including the effective stiffness, hysteretic energy dissipation, residual displacement, and dominant vibration frequency. The test column, designed according to the AASHTO seismic design specifications, survived successive ground motions by virtue of its outstanding energy-absorption and ductility capacity. Analysis of the experimental data indicates that structural degradation of the column closely correlates with its decreasing effective stiffness and increasing hysteretic energy dissipation. The residual displacement measured at the column top after each shaking event increases with the growth of damage in the column. A frequency-domain analysis of the vibration response of the column during successive ground motions indicates that increase in the structural degradation of the column results in a decrease in the dominant vibration frequency of the column.

SUMMARY The bovine spongiform encephalopathy (BSE) maternal cohort study provided robust evidence of an enhanced risk of developing BSE for offspring of BSE-affected dams. We present for the first time, but in retrospect, an interim analysis of the BSE maternal cohort study and set it in historical context, some of which has only been revealed through the BSE inquiry. We also consider the implications for design of extending the BSE maternal cohort study once an enhanced risk to exposed calves had been established, to assess the risk to calves born further from the clinical onset of BSE in the dam than those in the original study. We demonstrate that, if a data monitoring committee had been established, conclusions similar to those based on the final results could have been drawn several years before the completion of the BSE maternal cohort study. Further, we conclude that an extension of the cohort study is unlikely to have been commissioned because of the substantial financial investment required, yet low power, and practical difficulties associated with implementation of any worthwhile extension.

We report a systematic and quantitative study of near-infrared intersubband absorption in strained AlGaN/GaN and lattice-matched AlInN/GaN superlattices grown by plasma-assisted molecular-beam epitaxy as a function of Si-doping profile with and without \ensuremath{\delta} doping. For AlGaN/GaN, we obtained good theoretical agreement with experimental measurements of transition energy, integrated absorbance and linewidth by considering many-body effects, interface roughness, and calculations of the transition lifetime that include dephasing. For the AlInN/GaN system, experimental measurements of the integrated absorbance due to the superlattice transitions produced values more than one order of magnitude lower than AlGaN/GaN heterostructures at similar doping levels. Furthermore, observed transition energies were roughly 150 meV higher than expected. The weak absorption and high transition energies measured in these structures is attributed to columnar alloy inhomogeneity in the AlInN barriers observed in high-angle annular dark-field scanning transmission electron microscopy. We simulated the effect of these inhomogeneities using three-dimensional band-structure calculations. The inhomogeneities were modeled as AlInN nanorods with radially varying In composition embedded in the barrier material of the superlattice. We show that inclusion of the nanorods leads to the depletion of the quantum wells (QWs) due to localization of charge carriers in high-In-containing regions. The higher energy of the intersubband transitions was attributed to the relatively uniform regions of the QWs surrounded by high Al (95$%$) composition barriers. The calculated transition energy assuming Al${}_{0.95}$In${}_{0.05}$N barriers was in good agreement with experimental results.

Measurement of the apparent dielectric permittivity of soils (dielectric constant) is becoming a popular way of estimating soil volumetric water content. This paper focuses on the measurement of apparent permittivity in four sandy soils using; time domain reflectometry (TDR), a surface capacitance insertion probe (SCIP) and a Theta probe. Measurement of the apparent permittivity using the SCIP and Theta probe are compared with the apparent permittivity measured using the TDR. Calibration of such instrumentation has remained relatively empirical following the engineering approximation presented by Topp et al. (Topp, G.C., Davies, J.L., Anan, A.P., 1980. Electromagnetic determination of soil water content: measurements in coaxial transmission lines. Water Res. Research 16, 574–582.). The refractive index model proposed by Whalley (Whalley, W.R., 1993. Considerations on the use of time domain reflectometry (TDR) for measuring soil water content. J. Soil Sci. 44(1), 1–9.) based on that of Birchak et al. (Birchak, J.R., Gardner, C.Z.G., Hipp, J.E., Victor, J.M., 1974. High dielectric constant microwave probes for sensing soil moisture. Proc. IEEE 62(1), 93–98.) is investigated as a means of gaining some physical understanding of the relative contributions of the different dielectric components in soils. Predictions made by the model are tested against results using multiple linear regression. The predictions agree well with the observed measurements. Inter-electrode conductivity is found to contribute significantly to the apparent permittivity measured using the SCIP and to a lesser extent the TDR but not the Theta probe. Inclusion of inter-electrode conductivity in regression analysis improved results. The Theta probe was found to overestimate the apparent permittivity of the soil by ∼1.5 when compared with TDR results. It is suggested that this may be the result of compaction of the soil close to the electrodes, coupled with a strong bias in the sensitivity of the probe to the region very close to the central electrode.

In this work, a description is given of a simulation technique employed to model the interaction between surface acoustic waves and ridge-waveguide quantum cascade lasers (QCLs). Firstly, a finite-difference time-domain (FDTD) scheme for modelling acoustic wave propagation in arbitrary semiconductor structures is outlined, and verified by comparison with experimental measurements of the frequency response of surface acoustic wave transmission between interdigitated transmitters and receivers on a bulk crystal. The model is developed further to represent the ridge-waveguide as a prominence above the surface and the active region of the laser is accounted for by a free-charge region buried within the structure. The modulation of this free charge, or carrier concentration by the propagating surface acoustic wave, is then used as an input to a rate equation model of a QCL to show how the gain will be affected. It is this control of the gain through the amplitude of the surface acoustic wave which will allow for modulation of the mid-infrared or terahertz output of the laser and hence its incorporation in many new applications.

A need exists to improve the effectiveness of the network of communities, organizations, and agencies that are concerned with reducing the negative impact of natural hazards in the USA. The issue is to find ways to integrate community need assessment, research and development, education and training, policy formulation, implementation, and evaluation to improve practices that reduce vulnerability at the community, regional, and national levels. To this end, we propose to create a disaster reduction network that supports a cycle of development and application activities relating to natural hazards mitigation standards, diffusion of loss reduction practice, and consensus building in communities and in technical and professional associations. The expected benefit is a more efficient use of resources and a sustained and effective national infrastructure.

We explain the origin of voltage variations due to self-mixing in a terahertz (THz) frequency quantum cascade laser (QCL) using an extended density matrix (DM) approach. Our DM model allows calculation of both the current–voltage (I–V) and optical power characteristics of the QCL under optical feedback by changing the cavity loss, to which the gain of the active region is clamped. The variation of intra-cavity field strength necessary to achieve gain clamping, and the corresponding change in bias required to maintain a constant current density through the heterostructure is then calculated. Strong enhancement of the self-mixing voltage signal due to non-linearity of the (I–V) characteristics is predicted and confirmed experimentally in an exemplar 2.6 THz bound-to-continuum QCL.

We investigate electron transport in epitaxially-grown nitride-based resonant tunneling diodes (RTDs) and superlattice sequential tunneling devices. A density-matrix model is developed, and shown to reproduce the experimentally measured features of the current–voltage curves, with its dephasing terms calculated from semi-classical scattering rates. Lifetime broadening effects are shown to have a significant influence in the experimental data. Additionally, it is shown that the interface roughness geometry has a large effect on current magnitude, peak-to-valley ratios and misalignment features; in some cases eliminating negative differential resistance entirely in RTDs. Sequential tunneling device characteristics are dominated by a parasitic current that is most likely to be caused by dislocations, however excellent agreement between the simulated and experimentally measured tunneling current magnitude and alignment bias is demonstrated. This analysis of the effects of scattering lifetimes, contact doping and growth quality on electron transport highlights critical\ud optimization parameters for the development of III-nitride unipolar electronic and optoelectronic devices.

CLN8 deficiency underlies one of a group of devastating childhood neurodegenerative disorders, the neuronal ceroid lipofuscinoses. The function of the CLN8 protein is currently unknown, but a role in lipid metabolism has been proposed. In human CLN8 diseased brains, alterations in lipid composition have been detected. To further investigate the connection of CLN8 to lipid metabolism, we characterized the lipid composition of early symptomatic Cln8-deficient mouse (Cln8(mnd)) brains.For lipid profiling, Cln8(mnd) cerebral cortical tissue was analysed by liquid chromatography/mass spectrometry. Galactolipid synthesis was measured through enzyme activity and real-time mRNA expression analyses. Based on the findings, myelination and white matter integrity were studied by immunohistochemistry, stereological methods, electron microscopy and magnetic resonance imaging. The development of myelin-forming oligodendrocytes was also studied in vitro.Sphingolipid profiling showed a selective reduction in myelin-enriched galactolipids. The mRNA expression and activity of UDP-galactose:ceramide galactosyltransferase (CGT), the key enzyme in the galactolipid synthesis, was reduced in the Cln8(mnd) brain. Expression of oligodendrocyte markers suggests a maturation defect. The amount of myelin was reduced in 1-month-old Cln8(mnd) mice, but reached normal levels by 5 months of age. The level of Cln8 gene expression followed the developmental pattern of myelin formation and was high in primary oligodendrocytes.Taken together, these observations suggest that galactolipid deficiency and delayed myelin maturation characterize the early CLN8 disease pathogenesis through a maturation defect of oligodendrocytes.

We describe a combined 6 × 6 k · p and one-band effective mass modelling tool to calculate absorption spectra in Ge-SiGe multiple quantum well (MQW) heterostructures. We find good agreement with experimentally measured absorption spectra of Ge-SiGe MQW structures described previously in the literature, proving its predictive capability, and the simulation tool is used for the analysis and design of electroabsorption modulators. We employ strain-engineering in Ge-SiGe MQW systems to design structures for modulation at 1310 nm and 1550 nm.

International audience; Recent advances in the statistical analysis of microsatellite data permit calculation of sex-specific dispersal rates through sex- and age-specific comparisons of genetic variation. This approach, developed for the analysis of data derived from co-dominant autosomal markers, should be applicable to a sex-specific marker such as mitochondrial DNA. To test this premise, we amplified a 449 bp control region DNA sequence from the mitochondrial genome of the collared peccary (Pecari tajacu), and estimated intra-class correlations among herds sampled from three Texas populations. Analyses on data partitioned by breeding group showed a clear signal of male-biased dispersal; sex-specific fixation indices associated with genetic variation among social groups within populations yielded values for females (F(GP)=0.91), which were significantly larger than values for males (F(GP)=0.24; P=0.0015). The same general pattern emerged when the analyses were conducted on age classes (albeit nonsignificantly), as well as categories of individuals that were predicted a posteriori to be dispersers (adult males) and philopatric (adult females and all immatures). By extending a previously published methodology based on biparentally inherited markers to matrilineally inherited haploid data, we calculated sex-specific rates of contemporary dispersal among social groups within populations (m(male symbol)=0.37). These results support the idea that mitochondrial DNA haplotype frequency data can be used to estimate sex-specific instantaneous dispersal rates in a social species.

SUMMARY Case studies are presented of the use of soil water measurements to determine the pathways, timing and quantities of natural recharge to groundwater at sites on the Chalk and Triassic Sandstone aquifers in England. Water content and potential have been monitored for several years at seven sites and unsaturated hydraulic conductivity measured in situ at three of the chalk sites. Recharge was estimated using a combination of the zero flux plane (ZFP) method and a simple water balance. Examples of the water balance are presented for three sites. It is shown that a shallow (∼1 m) depth of permeable drift and soil increased the annual drainage from the soil to the underlying formation by about 34% at a pair of sites on the Chalk aquifer. Effects upon drainage timing are equally dramatic. On thin soil directly on chalk, drainage responds quickly to rainfall and, once evaporation starts to exceed rainfall, declines rapidly. On drift-covered sites, the drainage continues for a much longer period, as it does from the loamy soil overlying the sandstone site.

The St Louis International Lung Transplant Registry was begun inn 1988 and contains information from 1983 when the first successful single lung transplantation was performed for a patient vith pulmonary fibrosis. As a voluntary registry it helps to document the indications, complications, and results of lung transplantation. Since that first transplant in 1983, transplantation has become a viable alternative for patients suffering with end-stage lung disease. The following information is based on data reported to the Registry from 121 centers, as of 1 January 1995.

We report measurements of single-electron polarization in a coupled double-quantum-dot device isolated from current probes and demonstrate that the energetics observed for this process differs from that observed in double dots coupled to reservoirs. The movement of the electrons is detected by a quantum point contact. By analyzing the energy broadening corresponding to the tunneling of a single electron from one dot to the other we estimate a minimum for the intradot scattering time to be 0.2 ns. This energy broadening follows the predicted shot-noise variation in the detector with gate voltage, but is three orders-of-magnitude higher. We speculate that two-level systems could account for the discrepancy.

We present evidence for quantum dot cellular automata action in a cell consisting of four dots defined by submicron metal gates on the top surface of a molecular-beam-epitaxy-grown GaAs/AlGaAs heterostructure in which a two-dimensional electron gas layer was formed approximately 70 nm below the surface. The four-dot cell is separated by a strong barrier in two double-dot sets. We show that by polarizing one of the double-dot sets we can polarize the other set in the cell. The polarization is detected using noninvasive voltage probe without drawing electric currents from the cell.

Background The most likely human exposure to bovine spongiform encephalopathy (BSE) is dietary, through beef mechanically recovered meat (MRM) and head meat used in burgers, sausages and other meat products. The majority, reportedly 90% of beef MRM and 80% of head meat, was used in burgers. To enable quantification of UK dietary exposure to BSE, we quantified bovine carcass meat consumed as burgers, sausages and other meat products by birth cohort, gender and calendar period (1980-1989, 1990-1996). Methods Synthesis of dietary data (cross-sectional National Dietary and Nutrition Surveys, and serial National Food Surveys and Realeat Surveys) to simulate weekly consumption by one-thousandth of the UK population in each year from 1980 to 1996. Findings In 1980-1989, the highest number of consumers (per 7 days) of all three food groups was in the 1940-1969 birth cohort - averaging 3.7 million male consumers of burgers, 2.6 million of sausages and 8.5 million of other meat products. The post-1969 birth cohort had the next highest number of consumers of burgers (1.8 million males). In 1990-1996, consumer numbers declined for the two older cohorts, most strikingly for burgers (down to 2.5 million males in the 1940-1969 cohort). The 1940-1969 cohort retained the highest number of consumers of sausages and other meat products, and second place for burgers. Male consumption was higher, even in the pre-1940 birth cohort where, for demographic reasons, female consumers outnumbered males. In the post-1969 birth cohort, female consumption of bovine carcass meat weight as burgers increased from 68 tonnes in 1980-1989 to 81 tonnes in 1990-1996, and male consumption increased more markedly (by 41%) from 84 tonnes to 119 tonnes; and similarly for other meat products. Interpretation Properly marshalled age-group and gender-specific consumption data contribute to a clearer understanding of the demography of those who were at risk of dietary exposure to BSE and of when their exposure intensity was greatest. Other countries may need to consider using dietary data to model their human BSE exposure from UK and other BSE-affected regions.

The authors of this article contend that the transcervical approach for thymectomy allows the safe and complete removal of the thymus and [table: see text] provides equivalent benefit to the patients with regard to opportunity for clinical remission or freedom from progression of the symptoms of MG. The low morbidity and short hospitalization after transcervical thymectomy represent minimal barriers and allow increased willingness of the neurologist to refer a patient for surgical therapy and increased acceptance of the patient towards the recommendations. The authors believe that an early, safe, and complete thymectomy offers all the benefits of surgical removal of the thymus to a patient with MG with minimal risk for morbidity and postoperative pain.

We investigate how fractals evolve into nonfractal behavior as the generation process is gradually suppressed. Fractals observed in the conductance of semiconductor billiards are of particular interest because the generation process is semiclassical and can be suppressed by transitions towards either fully classical or fully quantum-mechanical conduction. Investigating a range of billiards, we identify a ``universal'' behavior in the changeover from fractal to nonfractal conductance, which is described by a smooth evolution rather than deterioration in the fractal scaling properties.

Immunosuppressive therapy has limited activity against the mesenchymal cell proliferation of obliterative bronchiolitis. Clotrimazole (CLT) has been shown to inhibit proliferation in normal and cancer cell lines. Here we investigate whether CLT inhibits the proliferation of lung mesenchymal cells.Proliferation of human lung fibroblasts (MRC-5) in the presence of CLT was determined by [3H]thymidine incorporation. Messenger ribonucleic acid (mRNA) expression of platelet-derived growth factor (PDGF)-B and transforming growth factor (TGF)-beta after treatment with CLT was measured by reverse transcriptase-polymerase chain reaction.Treatment of MRC-5 cells with CLT resulted in a significant reduction in proliferation as assessed by DNA incorporation and cell counts compared with dimethylsulfoxide alone. There was no cytotoxic effect associated with CLT treatment. Reverse transcriptase-polymerase chain reaction demonstrated a marked decrease in PDGF-B and TGF-beta mRNA levels in cells treated with CLT compared with those treated with dimethylsulfoxide.CLT inhibits proliferation of human lung fibroblasts. This inhibitory effect is associated with decreased levels of PDGF-B and TGF-beta mRNA expression and may have value in the prevention and treatment of obliterative bronchiolitis.

Both small and large variant Creutzfeldt Jakob disease (vCJD) epidemics are consistent with the current observed incidence. Uncertainty in vCJD projections could potentially be reduced by incorporating information on the prevalence of the infectious agent in persons incubating vCJD. The prospect of vCJD prevalence studies has been raised by detection of abnormal prion protein, thought to be the infectious agent, in appendices and tonsils removed from vCJD patients. Although unlinked anonymous testing of stored operative tissues for abnormal prion protein is very appealing, the design and interpretation of such prevalence studies is complicated by the lack of information on how early in the incubation period of vCJD the abnormal prion protein becomes detectable.We simulate a range of vCJD epidemics, consistent with the limited available information on the incidence of vCJD, to illustrate some of the potential problems encountered when interpreting the results from prevalence studies of detectable abnormal prion protein. We assume plausible incubation period distributions and dietary exposure patterns.We demonstrate, in the context of our simulated epidemics, that prevalence studies of detectable abnormal prion protein would require the testing of tens of thousands of operative specimens and, even then, that unlinked anonymous testing positives would be unexpected.

Hyperpolarized (3)He gas MRI was used to form maps of the effective diffusivity of gas in human lungs. Images of diffusion as well as spin density are presented from a study of 11 healthy volunteers and 5 patients with severe emphysema. The effective rate of diffusion, D(e), of the gas is reduced by the alveolar walls; tissue destruction in emphysema is hypothesized to result in larger D(e). Indeed, the mean value of D(e) in the emphysematous lungs is found here to be about 2.5 times that of healthy lungs, although still smaller than the unrestricted diffusivity of (3)He in free air. Histograms of D(e) values across coronal slices are presented. The results are discussed in terms of spatial variations, variations among individuals, healthy and diseased, and variations due to changes in lung volume. Magn Reson Med 44:174-179, 2000.