bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluorescence lifetime imaging using a compact, low-cost, diode-based all-solid-state regenerative amplifier
Authors: Mendez E. , Elson D. S. , Koeberg M. , Dunsby C. , Bradley D. D. C. , French P. M. W.
Published: April 2004

A fluorescence lifetime imaging (FLIM) system is described that utilizes a new compact and low-cost ultrafast laser source based on a gain-switched laser diode-seeded all-solid-state Cr:LiSAF regenerative amplifier that has been designed for this application. The pulse parameters of this source (0.5 μJ, 827 nm, 100 ps, 5 kHz) are shown to be appropriate to time-domain FLIM using a gated optical intensifier and the application to functional imaging of biological tissue is demonstrated, as well as the first evaluation of organic light emitting diodes using FLIM.
Density measurements of heavy-ion-beam-induced stress waves in solid matter by a sensitive laser deflection technique
Authors: Constantin C. , Niemann C. , Dewald E. , Udrea S. , Jacoby J. , Varentsov D. , Schwab P. , Wieser J. , Hoffmann D. H. H.
Published: April 2004

We present a sensitive density diagnostic based on the deflection of a laser beam by refractive index gradients. The method is used to investigate stress waves in plexiglass, created by the irradiation of multilayered metal–plexiglass targets with intense relativistic heavy-ion beams. Measured laser deflection angles are of the order of 1 mrad, with a resolution of the apparatus of 50 μrad. Results are in excellent agreement with interferometric measurements. The deflection technique is superior to an imaging interferometer in terms of simplicity and sensitivity.
Energy analyzer for spin polarized Auger electron spectroscopy
Authors: Petrov V. N. , Kamochkin A. S.
Published: April 2004

A double-pass cylindrical mirror energy analyzer for spin polarized Auger electron spectroscopy (SPAES) has been constructed and tested. The analyzer has high transmission, small electron emission angle (for the collection of electrons into an additional Mott detector), and large focal distance. The combination of this energy analyzer with a compact classical Mott detector provides a SPAES spectrometer with very high efficiency.
Micro-electro-mechanical systems microtweezers for the manipulation of bacteria and small particles
Authors: Jericho S. K. , Jericho M. H. , Hubbard T. , Kujath M.
Published: April 2004

We describe the construction and characteristics of microtweezers. The tweezers consist of 2 μm thick polysilicon foils that are manufactured by standard micro-electro-mechanical systems fabrication methods. The tweezers’ foils when mounted on a piezoelectric strip actuator device can be used to manipulate micron size objects in air or in electrolytes. The tweezers’ performance is demonstrated with images showing the manipulation of micron size latex beads as well as bacteria.
Apparatus for investigating metalorganic chemical vapor deposition-grown semiconductors with ultrahigh-vacuum based techniques
Authors: Hannappel T. , Visbeck S. , Töben L. , Willig F.
Published: April 2004

An apparatus is described here in detail for the transfer of a sample from a metalorganic chemical vapor deposition (MOCVD) reactor to an ultrahigh-vacuum (UHV) chamber without introducing any contamination. The surface of the sample does not change during transfer as is borne out by the identical reflectance difference (RD) spectrum measured first in the MOCVD reactor, i.e., in situ, and afterwards again in the UHV chamber. Making use of the earlier apparatus a semiconductor can be grown in the MOCVD reactor and can afterwards be investigated with any desired tool of surface science, in particular also those that require UHV. All the data collected in UHV can be identified with the RD spectrum measured already in the MOCVD reactor. Several examples are presented here for data collection in UHV on III–V semiconductors grown in the MOCVD reactor. They illustrate the ease and reliability of the here described apparatus for contamination-free sample transfer. Signals are presented in particular for the genuine MOCVD-grown P-rich seemingly (2×1)/(2×2)InP(100) reconstructed surface that until now can only be investigated in UHV if one makes use of the sample transfer system described in this article.
Diode laser microwave induced plasma cavity ringdown spectrometer: Performance and perspective
Authors: Wang Chuji , Koirala Sudip P. , Scherrer Susan T. , Duan Yixiang , Winstead Christopher B.
Published: April 2004

Recent studies combining an atmospheric-pressure plasma source (inductively coupled plasma or microwave induced plasma) with cavity ringdown spectroscopy (plasma-CRDS) have indicated significant promise for ultra-sensitive elemental measurements. Initial plasma-CRDS efforts employed an inductively coupled plasma as the atomization source and a pulsed laser system as the light source. In an effort to improve the portability and reduce the cost of the system for application purposes, we have modified our approach to include a compact microwave induced plasma and a continuous wave diode laser. A technique for controlling the coupling of the continuous wave laser to the ringdown cavity has been implemented using a standard power combiner. No acouto-optic modulator or cavity modulation is required. To test the system performance, diluted standard solutions of strontium (Sr) were introduced into the plasma by an in-house fabricated sampling device combined with an ultrasonic nebulizer. SrOH radicals were generated in the plasma and detected using both a pulsed laser system and a diode laser via a narrow band transition near 680 nm. The experimental results obtained using both light sources are compared and used for system characterization. The ringdown baseline noise and the detection limit for Sr are determined for the current experimental configuration. The results indicate that a plasma-CRDS instrument constructed using diode lasers and a compact microwave induced plasma can serve as a small, portable, and sensitive analytical tool.
Highly miniaturized laser ablation time-of-flight mass spectrometer for a planetary rover
Authors: Rohner Urs , Whitby James A. , Wurz Peter , Barabash Stas
Published: April 2004

We report the development and testing of a highly miniaturized mass spectrometer and ion source intended to be deployed on an airless planetary surface to measure the elemental and isotopic composition of solids, e.g., rocks and soils. Our design concentrates at this stage on the proposed BepiColombo mission to the planet Mercury. The mass analyzer is a novel combination of an electrostatic analyzer and a reflectron time-of-flight design. The ion source utilizes a laser induced plasma, which is directly coupled into the mass analyzer. Laser ablation gives high spatial resolution and avoids the need for sample preparation. Our prototype instrument has a demonstrated mass resolution m/Δm full width at half maximum in excess of 180 and a predicted dynamic range of better than five orders of magnitude. We estimate that a flight instrument would have a mass of 280 g (including laser and all electronics), a volume of 84 cm3, and could operate on 3 W power.
Compact high-resolution ion Doppler spectrometer for quartz ultraviolet line emissions
Authors: Gu Peimin , Nagata Masayoshi , McCollam Karsten J. , Jarboe Thomas R. , Nelson Brian A. , Redd Aaron J.
Published: April 2004

A high-resolution quartz ultraviolet spectrometer based on a single compact 16-channel multianode photomultiplier tube (MAPMT) has been developed and tested on coaxial helicity injection and ohmic transformer current drive plasmas generated on the Helicity Injected Torus at the University of Washington. The use of the compact MAPMT allows a simple design with high light collection and high resolution for an ion Doppler shift diagnostic. The high quality and low cost of the design make it uniquely attractive for university scale plasma experiments. The Doppler shift of impurity ion emission lines from two chords of equal impact parameter but of opposite rotational sense is used to determine chord-averaged toroidal flow velocity. The width of the Doppler broadening is used to calculate the ion temperature. A detailed description of the ion Doppler spectrometer measurement system and some typical results are presented.
Adaptive dynamic focusing system for ultrasonic nondestructive testing of pipeline girth welds
Authors: Huang J. , Que P. W. , Jin J. H.
Published: April 2004

An adaptive dynamic focusing system used for the ultrasonic nondestructive testing of pipeline girth welds is developed. This system relies on ultrasonic linear phased array transducers connected to a multichannel acquisition system, which provides delay and amplitude laws, allowing one to control the ultrasonic beams dynamically. We introduce a testing method for welds and the system’s structure. Optimization of array transducers has also been pursued based on a mathematical model of the acoustic field for a linear phased array. The experimental results have proved that the phased array transducers system has the same capability to detect as a conventional ultrasonic transducers system, but the components of the system can be simplified greatly, and the testing flexibility and the testing speed can be improved greatly. It provides an excellent basis for further research and development of defect inspection of pipeline girth welds.
Magnetic field influence on laser-produced ion stream
Authors: Wołowski J. , Badziak J. , Ivanova-Stanik I. , Parys P. , Stȩpniewski W. , Woryna E.
Published: April 2004

Laser-produced plasma has been proposed to be an efficient source of ions which can be used for different applications (e.g., particle accelerators and ion implantation technology). In this article we present a study of the influence of an axial magnetic field on angular distributions of ions emitted from tungsten plasma produced using a 1 ns Nd:glass laser beam of energy 0.2–2 J at intensities of 1010–1011 W/cm2. Investigations were performed at magnetic field induction of 1.2 T. An electrostatic ion energy analyzer and a set of ion collectors located at different angles with respect to the target normal were applied for measurements of the ion stream characteristics. The results of measurements of angular distributions of ion emission show that the magnetic field causes a significant increase of a current density in ions close to the magnetic field axis (parallel to the target normal). The maximum current density of ions that expand in the magnetic field and considerably lower maximum current density of freely expanding ions increase fast with an increase of laser pulse energy. Simple Monte-Carlo simulations of laser-produced ions that expand freely and those expanding in the presence of an axial magnetic field are compared.
A macroscopic chemistry method for the direct simulation of gas flows
Authors: Lilley Charles R. , Macrossan Michael N.
Published: April 2004

In most chemistry methods developed for the direct simulation Monte Carlo (DSMC) technique, chemical reactions are computed as an integral part of the collision simulation routine. In the macroscopic chemistry method developed here, the simulation of collisions and reactions are decoupled in that reactions are computed independently, after the collision routine. The number of reaction events to perform in each cell is calculated using the macroscopic reaction rates k± and equilibrium constant K*, with local macroscopic flow conditions. The macroscopic method is developed for the symmetrical diatomic dissociating gas. For each dissociation event, a single diatomic simulator particle is selected with a probability based on its internal energy, and is replaced by two atomic particles. For each recombination event, two atomic particles are selected at random, and are replaced by a single diatomic particle. The dissociation energy is accounted for by adjusting the translational thermal energies of all particles in the cell. The macroscopic method gives density profiles in agreement with experimental data for the chemical relaxation region downstream of a strong shock in nitrogen. In the nonequilibrium region within the shock, and along the stagnation streamline of a blunt cylinder in rarefied flow, the macroscopic method gives results in excellent agreement with those obtained using the most common conventional DSMC chemistry method in which reactions are calculated during the collision routine. The number of particles per computational cell has a minimal effect on the results provided by the macroscopic method. Unlike most DSMC chemistry methods, the macroscopic method is not limited to simple forms of k± and K*. Any forms may be used, and these may be any function of the macroscopic conditions. This is demonstrated by using a two-temperature rate model, and a form of K* with a number density dependence. With the two-temperature model, the macroscopic method gives densities in the post-shock chemical relaxation region that also agree with the experimental data. For a form of K* with a number density dependence, the macroscopic method can accurately reproduce chemical recombination behavior. In a primarily dissociative flow, the number density dependence of K* has very little effect on the flow. The macroscopic method requires slightly less computing time than the most common DSMC chemistry method.
Inferred pressure gradient and fluid flow in a condensing sessile droplet based on the measured thickness profile
Authors: Gokhale Shripad J. , Plawsky Joel L. , Wayner Peter C. , DasGupta Sunando
Published: April 2004

The thickness and curvature profiles of partially wetting condensing drops of 2-propanol on a quartz surface were measured using image analyzing interferometry and a new data analysis procedure. The profiles give fundamental insight into the phenomena of phase change, pressure gradient, fluid flow and spreading in a condensing drop, and the physics of interfacial phenomena in the contact line region of a polar fluid. The precursor adsorbed film and interfacial slope (a measure of the contact angle) and curvature profiles are consistent with previous concepts based on interfacial models. The curvature profiles, which were obtained using a new data reduction procedure, clearly demonstrate the convex nature of the drop near the thicker part (negative value of curvature), whereas, in the thinner region, the drop is concave (positive curvature) where the partially wetting liquid merges with a flat adsorbed film. The pressure profiles inside the drop are calculated from the augmented Young–Laplace equation showing that the pressure gradient increases with an increase in the spreading velocity (rates of condensation) to support the higher liquid flow rates associated with the growth of the drop. Internal flow is towards the point of maximum positive curvature from both the thin film and convex regions. Apolar and polar components of the spreading coefficient help describe the interfacial phenomena occurring. The experimental techniques are relatively simple but very revealing.
Effects of nonperfect thermal sources in turbulent thermal convection
Authors: Verzicco R.
Published: April 2004

The effects of the plates thermal properties on the heat transfer in turbulent thermal convection are investigated by direct numerical simulations of the Navier–Stokes equations with the Boussinesq approximation. It has been found that the governing parameter is the ratio of the thermal resistances of the fluid layer Rf and the plates Rp; when this ratio is smaller than a threshold value (Rf/Rp≈300 arbitrarily defined by requiring that the actual heat transfer differs by less than 2% from its ideal value), the finite conductivity of the plates limits the heat transfer in the cell. In addition, since Rf decreases for increasing Rayleigh numbers, any experimental apparatus is characterized by a threshold Rayleigh number that cannot be exceeded if the heat transfer in the cell has not to be influenced by the thermal properties of the plates. It has been also shown that the plate effects cannot be totally corrected by subtracting the temperature drop occurring within the plates from the measured total temperature difference. This is due to the changes produced in the thermal plume dynamics by the reduced local heat flux at the plate/fluid interface. A model with a correction factor has been derived to account for the plates effects and it gave the appropriate correction for a recent experiment in which the heat transfer measurements were systematically smaller than a theoretical prediction. In view of the present correction the discrepancy between theory and experiments addressed by Nikolaenko and Ahlers [Phys. Rev. Lett. 91, 084501 (2003)] can be therefore resolved. The application of the proposed correction to the results in the literature can also reconcile the heat transfer measurements for water and mercury that appear systematically smaller than in other fluids.
Magnetic Reynolds number effects in compressible magnetohydrodynamic turbulence
Authors: Ladeinde F. , Gaitonde D. V.
Published: April 2004

The effects of the magnetic Reynolds number, Reσ, on decaying two-dimensional compressible magnetohydrodynamic (MHD) turbulence are investigated through direct numerical simulations. The initial relative intensities of, and the correlation between, the fluctuating velocity (u) and magnetic induction (b) fields are also varied, as measured with the respective parameters f and angle θ. The investigations cover the parameter ranges 1⩽Reσ⩽250, 0°⩽θ⩽90°, and 1⩽f⩽3. The results suggest that, at the lowest Reσ investigated, the magnetic field has a negligible impact on the evolution of the turbulence kinetic energy Ek. At higher Reσ values, when magnetic effects are important, the magnetic field tends to accelerate the decay of the turbulence energy relative to non-MHD flows. On the other hand, the magnetic energy Eb shows the opposite trend, being rapidly driven from its initial values to essentially zero very early in the transient at lower Reσ values, while higher Reσ values significantly retard this decay. An enhancement of density fluctuations is noted in the intermediate Reσ range. An interesting observation pertaining to the normalized cross helicity is the fast decay to zero of this quantity when Reσ=1, independent of the values of θ and f. That is, the fluctuating u and b fields tend to be uncorrelated when the magnetic Reynolds number is low. In this case, the role of the magnetic field is passive, and it is merely convected by the velocity field. The conditions required to maintain a high correlation during the evolution are discussed. We have also seen that the Eb decay mode is less sensitive to the value of θ than that of Ek. The relative contribution of Ek, Eb, and the internal energy Ei to the total energy Et is discussed in relation to the values of f, θ, and Reσ.
Sustaining crop production in saline groundwater areas: A case study from Pakistani Punjab
Authors: Qureshi Asad S. , Asghar M. N. , Ahmad S. , Masih I.
Published: April 2004

In the Indus Basin of Pakistan, multi-strainer shallow tubewells often called 'skimming wells' are used to extract groundwater from thin fresh lenses underlain by saline groundwater. Most of these wells face problems such as deteriorating water quality and reduction in discharge due to inadequate design and poor operational and management strategies. This paper evaluates the current practices of farmers in the Chaj doab area of Pakistani Punjab and suggests improvements in design and operation of skimming wells to ensure long-term sustainability of irrigated agriculture in the area. The effect of existing design and operation of skimming wells on pumped groundwater quality was evaluated using MODFLOW. To study the long-term effects of skimmed groundwater use on crop production and soil salinity development, the soil water flow and solute transport model SWAP was applied. The results revealed that farmers could reduce the number of strainers from 16 to 6 without reducing the anticipated discharges. For the conditions considered, the maximum discharge of skimming wells should be 4–8 L/s and they should not be operated for more than 2–4 h per day. Increasing discharge rate or daily operational hours can disturb the interface between fresh and saline groundwater resulting in reduced quality pumped groundwater. Weekly operational schedules together with recommended discharge rate and operational hours will be the best strategy to use skimmed groundwater for achieving optimal crop yields while maintaining root-zone salinity within acceptable limits. To avoid aquifer degradation, skimming wells should be used for supplemental irrigation rather than full irrigation of crops. Due to low discharge rates, skimming wells cannot be used to irrigate crops through surface irrigation methods. Therefore, pressurised irrigation methods should be used. The results also suggest that continuation of present irrigation practices could lead to serious problems of land and aquifer degradation. Therefore, farmers need to adjust their irrigation and leaching requirements annually considering crop evapotranspiration, precipitation, and salinity status of soils.
Yield increase and higher flesh firmness of 'Arctic Snow' nectarines both at harvest in Australia and after export to Taiwan following pre-harvest application of ReTain Plant Growth Regulator (aminoethoxyvinylglycine, AVG)
Authors: Rath A. C. , Prentice A. J.
Published: April 2004

The effects ReTain Plant Growth Regulator (830 g in 1000 L water/ha) applied to a commercial block of 'Arctic Snow' nectarines 7 days before the first harvest was assessed in relation to harvest delay, fruit size, fruit quality (flesh firmness and brix), as well as the quality of the fruit following export to Taiwan. The untreated block (0.87 ha) and the ReTain-treated block (1.0 ha) were harvested according to the orchard's standard maturation criteria of background colour, size and percent blush colour. Based on picking schedules, the maturation of the ReTain block was delayed by 2.75 days (P<0.05). The fruit continued to grow during this delay and resulted in a 12.3% increase in yield and an increase of 393 packed cartons/ha. There were more (P<0.001) cartons of ReTain-treated fruit packed in grade sizes 69–78 mm diameter and less of smaller size classes (51–66 mm) compared with untreated fruit. The increase in both the number of cartons of class 1 fruit and fruit size on the ReTain block resulted in a Return on Investment (ROI) of 14.7 : 1 with an additional net return of AU$17 655/ha over the untreated block. There was a correlation between fruit size and flesh firmness with larger fruit being firmer than smaller fruit (P<0.001), however, packed ReTain-treated fruit was 3.2 N firmer on average (P<0.001) than packed untreated fruit for all size grades and from all harvests and packs. Brix levels increased (P<0.001) with fruit size but there was no difference (P = 0.568) between ReTain-treated fruit and untreated fruit. Two containers of fruit (early and late picks) were exported to Taiwan. The containers held a temperature of 0.5–2.0°C for the 14–15 day transit time from Australia to Taiwan. ReTain-treated fruit in both containers was 1.7 N firmer (P = 0.022) than untreated fruit upon arrival in Taiwan. After ambient storage (23°C) of fruit from container 1 for 45 h, fruit firmness declined (P<0.001) from an average of 65.7 to 43.2 N and there was no difference (P = 0.826) between treated or untreated fruit. It is concluded that ReTain application to 'Arctic Snow' nectarines can increase financial returns to growers through increased fruit size and quality benefits as well as maintain a higher flesh firmness following export.
Hydration and mobility of HO-(aq)
Authors: Asthagiri D. , Pratt Lawrence R. , Kress J. D. , Gomez Maria A.
Published: April 2004

The hydroxide anion plays an essential role in many chemical and biochemical reactions. But a molecular-scale description of its hydration state, and hence also its transport, in water is currently controversial. The statistical mechanical quasichemical theory of solutions suggests that\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HO}}{\cdot}[{\mathrm{H}}_{2}{\mathrm{O}}]_{3}^{-}\end{equation*}\end{document}is the predominant species in the aqueous phase under standard conditions. This result agrees with recent spectroscopic studies on hydroxide water clusters and with the available thermodynamic hydration free energies. In contrast, a recentab initiomolecular dynamics simulation has suggested that\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HO}}{\cdot}[{\mathrm{H}}_{2}{\mathrm{O}}]_{4}^{-}\end{equation*}\end{document}is the only dominant aqueous solution species. We apply adiabaticab initiomolecular dynamics simulations and find good agreement with both the quasichemical theoretical predictions and experimental results. The present results suggest a picture that is simpler, more traditional, but with additional subtlety. These coordination structures are labile but the tricoordinate species is the prominent case. This conclusion is unaltered with changes in the electronic density functional. No evidence is found for rate-determining activated interconversion of a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HO}}{\cdot}[{\mathrm{H}}_{2}{\mathrm{O}}]_{4}^{-}\end{equation*}\end{document}trap structure to\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{HO}}{\cdot}[{\mathrm{H}}_{2}{\mathrm{O}}]_{3}^{-}\end{equation*}\end{document}mediating hydroxide transport. The view of HO-diffusion as the hopping of a proton hole has substantial validity, the rate depending largely on the dynamic disorder of the water hydrogen-bond network.
Response experiments for nonlinear systems with application to reaction kinetics and genetics
Authors: Vlad Marcel O. , Arkin Adam , Ross John
Published: April 2004

A unified type of response experiment is suggested for complex systems made up of individual species (atoms, molecules, quasi-particles, biological organisms, etc.). We make the following assumptions: (
i
) some of the species may exist in two forms, labeled and unlabeled, respectively; (
ii
) the kinetic and transport properties of the labeled and unlabeled species are the same, respectively (neutrality assumption); (
iii
) the experiment preserves the total input and output fluxes; only the fractions of the labeled compounds in the input and output fluxes are varied. Under these circumstances a linear integral superposition law connects the fractions of labeled species in the input and output fluxes. This linear superposition law is valid for homogeneous and inhomogeneous systems and for systems with intrinsic (hidden) state variables; it arises from the neutrality condition and holds even though the underlying dynamics of the process may be highly nonlinear. Because this response law does not involve the linearization of the evolution equations it has great potential for the analysis of complex physical, chemical, and biological systems. We compare our approach with the linearization techniques used in biochemistry and genetics. We consider a simple reaction network involving replication, transformation, and disappearance steps and study the influence of experimental (measurement) and linearization errors on the evaluated values of rate coefficients. We show that the method involving the linearization of the kinetic equations leads to unpredictable results; because of the interference between measurement and linearization errors, either error compensation or error amplification occurs. Although our approach does not eliminate the effects of measurement errors, it leads to more consistent results. For a broad range of input fractions no error amplification or compensation occurs, and the error range for the rate coefficients is about the same as the error range of the measurements.
Recruitment of a cytoplasmic response regulator to the cell pole is linked to its cell cycle-regulated proteolysis
Authors: Ryan Kathleen R. , Huntwork Sarah , Shapiro Lucy
Published: April 2004

The response regulator CtrA, which silences the
Caulobacter
origin of replication and controls multiple cell cycle events, is specifically proteolyzed in cells preparing to initiate DNA replication. At the swarmer-to-stalked cell transition and in the stalked compartment of the predivisional cell, CtrA is localized to the cell pole just before its degradation. Analysis of the requirements for CtrA polar localization and CtrA proteolysis revealed that both processes require a motif within amino acids 1-56 of the CtrA receiver domain, and neither process requires CtrA phosphorylation. These results strongly suggest that CtrA polar localization is coupled to its cell cycle-regulated proteolysis. The polarly localized DivK response regulator promotes CtrA localization and proteolysis, but it does not directly recruit CtrA to the cell pole. Mutations in the
divJ
and
pleC
histidine kinases perturb the characteristic asymmetry of CtrA localization and proteolysis in the predivisional cell. We propose that polar recruitment of CtrA evolved to ensure that CtrA is degraded only in the stalked half of the predivisional cell, perhaps by localizing a proteolytic adaptor protein to the stalked pole. This is an example of controlled proteolysis of a cytoplasmic protein that is associated with its active recruitment to a specific subcellular address.
Low Pay and Income in Urban and Rural Areas: Evidence from the British Household Panel Survey
Authors: Gilbert Alana , Phimister Euan , Theodossiou Ioannis
Published: April 2004

This paper examines the extent of urban-rural differences in low pay and the link between low pay and low incomes using data on urban and rural residents from the British Household Panel Survey for 1991-98. The results suggest that, overall, urban wages were significantly less than accessible rural but significantly more than remote rural wages even after adjustments were made for differences in observed characteristics. A lower percentage of urban workers who experienced low pay were also resident in low-income households. Lower urban in-employment and in-self-employment poverty were found relative to poor remote rural households even after differences in the characteristics across the different samples were controlled for.
Induced Demand: A Microscopic Perspective
Authors: Parthasarathi Pavithra , Levinson David M. , Karamalaputi Ramachandra
Published: April 2004

This paper analyses the induced demand hypothesis using a disaggregate approach at the link level. A panel data-set of Minneapolis-Saint Paul highway network for the years 1980-98 is constructed. A model that predicts the traffic flow on the link in terms of vehicle kilometres travelled (VKT) based on the flow and capacity conditions existing on the link in the previous years is specified and estimated. The flow and capacity conditions existing on the identified neighbouring parallel links are also taken into account. Socio-demographic characteristics like population of the Minor Civil Division (MCD) to which the link belongs and the surrounding MCDs are also considered. The results indicate that capacity enhancements in the previous years, given by lane additions, have a positive and significant effect on the VKT of the link, confirming the induced demand hypothesis. The elasticities are lower than reported in previous research, indicating the importance of separating new construction from the expansion of existing links.
Government Policies and Household Mobility Behaviour in Singapore
Authors: Neo Poh Har , Lee Nai Jia , Ong Seow Eng
Published: April 2004

This paper provides a rigorous study on the change in Central Provident Fund (CPF) policy in Singapore on 1 September 2002, on household mobility in general and on the affordability and accessibility of potential home-buyers in particular. The change brought about increased accessibility but reduced affordability for home-buyers. The latter has an impact on the shortfall months which are positively related to changes in mortgage rate, mortgage term and property price and negatively related to the amount of CPF available for home purchases. Further, the low critical price that households can afford without experiencing any shortfall implies that the majority of public and private home-buyers will be affected by the policy change. Consequently, the improvement in accessibility by allowing the use of CPF for downpayment may stimulate demand at the cost of higher financial risk to home-buyers and mortgage lenders.
Determinants of Call Centre Location: Some Evidence for UK Urban Areas
Authors: Bishop Paul , Gripaios Peter , Bristow Gillian
Published: April 2004

This paper presents new evidence concerning the spatial distribution of UK call centre activity and analyses the determinants of this distribution. The study adopts a restructuring perspective, viewing call centre growth as a strategic response by companies seeking to develop competitive advantage and a process that is changing the spatial division of labour. The data indicate that there is an uneven spatial distribution of call centre activity in the UK. The results of econometric models, utilising Tobit and negative binomial regression techniques, suggest that regional aid, population density, the existing spatial division of labour and a large local labour force have a positive influence on call centre activity. Surprisingly, there is no evidence that labour costs influence call centre location.
Socioeconomic Factors and Suicide Rates at Large-unit Aggregate Levels: A Comment
Authors: Neumayer Eric
Published: April 2004

Can socioeconomic factors seemingly explain variation in suicide rates at large-unit aggregate levels only due to an ecological fallacy? This is what Kunce and Anderson (2002) suggest based on fixed-effects estimation of US state suicide rates, in which they find little evidence that socioeconomic factors matter. This paper demonstrates that this result does not hold true for other large-unit aggregate levels in an analysis of suicide at the cross-national level. It is found that many socioeconomic factors have a statistically significant impact. It is concluded that sociological and economic theories explaining variation in suicide rates at the large-unit aggregate level with the help of aggregate socioeconomic factors cannot simply be dismissed because of an alleged ecological fallacy.
The key role of educational research in the development and evaluation of the national numeracy strategy
Authors: Brown Margaret , Askew Mike , Millett Alison , Rhodes Valerie
Published: April 2004

Abstract The authors contest a politician's claim that the National Numeracy Strategy (NNS) in English primary schools has been an undisputed success with no contribution from educational researchers. First, the key role of researchers and research in the development of the NNS is outlined. Then there is a description of the Leverhulme Numeracy Research Programme, a linked set of research studies combining a large‐scale longitudinal survey and qualitative case studies. Results suggest that the NNS had a positive but small effect on numeracy standards, but that there are many schools, children and areas of mathematics for whom the effect has been negligible or negative. The discussion of reasons for this relates to evidence from the Leverhulme Programme and elsewhere about the effects of different factors on attainment. Finally, there is some question of whether government and government agencies are being completely open about the evidence of effectiveness of the NNS.
On the feasibility of conducting randomised trials in education: case study of a sex education intervention
Authors: Moore Laurence , Graham Anna , Diamond Ian
Published: April 2004

Abstract This article reports on the conduct and results of a randomised controlled trial to test the effectiveness of a teacher‐led intervention to improve teenagers' knowledge of emergency contraception. The trial was successfully conducted in 24 mixed‐sex state secondary schools in Avon, South‐west England. The intervention was popular with both teachers and pupils, and significantly improved pupils' knowledge of emergency contraception. The article uses the emergency contraception trial to demonstrate the feasibility of conducting large‐scale randomised trials in schools. The article focuses particularly on study design, specification of research question, recruitment of schools and method of randomisation to highlight methodological choices that can maximise the feasibility and value of such trials to answer questions regarding the effectiveness of complex educational interventions. The article also highlights the importance of using theory and mixed research methods both to thoroughly develop an intervention before it is tested in a trial, and also to evaluate factors affecting its success within a trial.
‘In praise of educational research’: formative assessment
Authors: Black Paul , Wiliam Dylan
Published: April 2004

Abstract The authors trace the development of the King's Formative Assessment Programme from its origins in diagnostic testing in the 1970s, through the graded assessment movement in the 1980s, to the present day. In doing so, they discuss the practical issues involved in reviewing research and outline the strategies that were used to try to communicate the findings to as wide an audience as possible (including policy‐makers and practitioners as well as academics). They describe how they worked with teachers to develop formative practice in classrooms, and discuss the impact that this work has had on practice and policy. Finally, they speculate about some of the reasons for this impact, and make suggestions for how the impact of educational research on policy and practice might be improved.
Becoming a manual occupation? The construction of a therapy manual for use with language impaired children in mainstream primary schools
Authors: McCartney Elspeth , Boyle James , Bannatyne Susan , Jessiman Emma , Campbell Cathy , Kelsey Cherry , Smith Jennifer , O'Hare Anne
Published: April 2004

Background: The construction of therapy protocols for a large‐scale randomized controlled trial comparing speech and language therapists and assistants, and group and individual therapy approaches for children aged 6–11 in mainstream schools is outlined.

Aims: The aim was to outline the decision‐making processes that led to the construction of the research therapy manual, and to give a preliminary report on compliance with the manual.

Methods & Procedures: A search of the research and professional literature and of published therapy materials was conducted to locate usable examples of effective language therapy for primary school children. Results were collated into a manual of therapy principles and activities to structure research intervention. The use of the manual with children (n=30) receiving individual or group direct therapy from a speech and language therapist in the first phase of intervention was audited.

Outcomes & Results: Very few high‐level research studies were found, but the professional literature gave added information. Therapies for comprehension monitoring, vocabulary development, later grammar and narrative were adapted for the research intervention, and procedures compiled into a manual to guide research speech and language therapists and assistants. The audit of direct therapy suggested that the manual was useable, providing a suitable range of activities and materials for therapy intervention. Its use helped to record the therapy offered to research children, and formed a sound basis for discussion amongst speech and language therapists and between speech and language therapist/assistant pairs.

Conclusions: The construction and use of a therapy manual allowed the provision of replicable therapy within the research project whilst maintaining flexibility.
Movement Trajectories in the Presence of a Distracting Stimulus: Evidence for a Response Activation Model of Selective Reaching
Authors: Welsh Timothy N. , Elliott Digby
Published: April 2004

Consistent with action–based theories of attention, the presence of a nontarget stimulus in the environment has been shown to alter the characteristics of goal–directed movements. Specifically, it has been reported that movement trajectories veer away from (Howard & Tipper, 1997) or towards (Welsh, Elliott, & Weeks, 1999) the location of a nontarget stimulus. The purpose of the experiments reported in this paper was to test a response activation model of selective reaching conceived to account for these variable results. In agreement with the model, the trajectory changes in the movements appear to be determined by the activation levels of each competing response at the moment of response initiation. The results of the present work, as well as those of previous studies, are discussed within the framework of the model of response activation.
Nonword Repetition in Lexical Decision: Support for two Opposing Processes
Authors: Wagenmakers Eric-Jan M. , Zeelenberg René , Steyvers Mark , Shiffrin Richard , Raaijmakers Jeroen G. W.
Published: April 2004

We tested and confirmed the hypothesis that the prior presentation of nonwords in lexical decision is the net result of two opposing processes: (1) a relatively fast inhibitory process based on global familiarity; and (2) a relatively slow facilitatory process based on the retrieval of specific episodic information. In three studies, we manipulated speed-stress to influence the balance between the two processes. Experiment 1 showed item-specific improvement for repeated nonwords in a standard “respond-when-ready” lexical decision task. Experiment 2 used a 400-ms deadline procedure and showed performance for nonwords to be unaffected by up to four prior presentations. In Experiment 3 we used a signal-to-respond procedure with variable time intervals and found negative repetition priming for repeated nonwords. These results can be accounted for by dual-process models of lexical decision (e.g., Balota & Chumbley, 1984; Balota & Spieler, 1999).
Abstractionist versus Exemplar-Based Theories of Visual Word Priming: A Subsystems Resolution
Authors: Marsolek Chad J.
Published: April 2004

Three experiments addressed abstractionist versus exemplar-based theories of the visual representations underlying word priming. Participants first read centrally presented whole words (each displayed in all lowercase or in all uppercase letters), and then they completed laterally presented word stems (each displayed in all lowercase or in all uppercase letters). Word stem completion priming was letter-case specific (greater for same-case primed items than for different-case primed items) when stems were presented directly to the right cerebral hemisphere but not when stems were presented directly to the left cerebral hemisphere. This interaction was not influenced by the typicality of the test stems, but it was observed only for stems composed of letters with visually dissimilar lowercase and uppercase structures (e.g., bea/BEA) and not for stems composed of letters with visually similar lowercase and uppercase structures (e.g., sco/SCO). In contrast, cued recall was letter-case specific when similar-case or dissimilar-case stems were presented directly to the right hemisphere. Results do not support strongly abstractionist or exemplar-based theories. Instead, they suggest a resolution to these differing perspectives: Relatively independent neural subsystems operate in parallel to underlie abstract-category and specific-exemplar priming of word forms.
Object-based processes in the planning of goal-directed hand movements
Authors: Bekkering Harold , Pratt Jay
Published: April 2004

Theories in motor control suggest that the parameters specified during the planning of goal-directed hand movements to a visual target are defined in spatial parameters like direction and amplitude. Recent findings in the visual attention literature, however, argue widely for early object-based selection processes. The present experiments were designed to examine the contributions of object-based and space-based selection processes to the preparation time of goal-directed pointing movements. Therefore, a cue was presented at a specific location. The question addressed was whether the initiation of responses to uncued target stimuli could benefit from being either within the same object (object based) or presented at the same direction (space based). Experiment 1 replicated earlier findings of object-based benefits for non-goal-directed responses. Experiment 2 confirmed earlier findings of space-based benefits for goal-directed hand pointing movements. In Experiments 3 and 4, space-based and object-based manipulations were combined while requiring goal-directed hand pointing movements. The results clearly favour the notion that the selection processes for goal-directed pointing movements are primarily object based. Implications for theories on selective attention and action planning are discussed.
How long do the advantages of learning to read a transparent orthography last? An investigation of the reading skills and reading impairment of Welsh children at 10 years of age
Authors: Hanley Richard , Masterson Jackie , Spencer Llinos , Evans Dylan
Published: April 2004

Spencer and Hanley (2003) showed that Welsh-speaking children aged between 5 and 7 years who were learning to read Welsh (a transparent orthography) performed significantly better at reading both real words and nonwords than did English-speaking children living in Wales who were learning to read English (a deep orthography). In this study, the reading skills of these children were reexamined three years later, during their sixth year of formal reading instruction. The children learning to read English continued to perform poorly at reading low- and medium-frequency irregular words but no differences were observed in reading regular words or nonwords. These findings emphasize how long it takes to acquire a large sight vocabulary in English, but indicated that the reading skills of the majority of the English-speaking children had caught up with those of their Welsh-speaking counterparts. However, the poorest 25% of the English readers continued to perform much worse than the lowest performing 25% of Welsh readers on both words and nonwords. An underachieving tail of this kind was not observed in the reading performance of the Welsh-speaking group. Overall, these findings suggest that in the long term the detrimental effects of an opaque orthography are most damaging to the poorest readers.