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Research on the discharge of synthetic microfibres to aquatic environments has typically focused on laundering, where fibres can be discharged via wastewater effluent. However emerging research suggests that microfibres generated during the wear of textiles in normal use could present a major, additional, pathway for microfibre pollution to the environment. This study aimed to quantify and compare the quantities of microfibre entering the marine environment via both these pathways; wastewater discharge and atmospheric deposition. Areas of high and low population density were also evaluated. Samples were collected in and around two British cities (Bristol and Plymouth) both of which are located on tidal waters. Fibres originating from the atmosphere were deposited at an average rate of 81.6 fibres m

Across three experiments, we examined the cuing properties of metric (distance and direction) and nonmetric (lighting) cues in different tasks. In Experiment 1, rats were trained on a response problem in a T-maze, followed by four reversals. Rats that experienced a change in maze orientation (Direction group) or a change in the length of the start arm (Distance group) across reversals showed facilitation of reversal learning relative to a group that experienced changes in room lighting across reversals. In Experiment 2, rats learned a discrimination task more readily when distance or direction cues were used than when light cues were used as the discriminative stimuli. In Experiment 3, performance on a go/no-go task was equivalent using both direction and lighting cues. The successful use of both metric and nonmetric cues in the go/no-go task indicates that rats are sensitive to both types of cues and that the usefulness of different cues is dependent on the nature of the task.

Resonant ultrasound spectroscopy (RUS) was used to analyze the elastic and anelastic behavior associated with canted antiferromagnetic ordering at 36 K in the radical, $\ensuremath{\beta}$-$p$-NCC${}_{6}$F${}_{4}$CNSSN, 1. On cooling through the magnetic ordering transition there is anomalous elastic behavior away from the expected uniform stiffening with decreasing temperature, consistent with magnetoelastic coupling. The excess in the elastic stiffness follows the magnetic order parameter linearly below the magnetic ordering temperature. A much larger change in elastic properties is associated with short-range ordering between ${T}_{\mathrm{c}}$ and 150 K which appears to correlate with an excess heat capacity (and entropy). Thus it appears that the onset of long-range order to this spin canted system might only be a partial contribution to the whole phase transition.

Spatial imaging of thin-layer chromatography plates using laser-induced fluorescence and surface-enhanced Raman scattering has been accomplished with a stationary two-dimensional Hadamard encoding mask. Detection of three nanograms of pararosaniline hydrochloride on a thin-layer chromatography plate was made possible by means of the surface-enhanced Raman phenomenon. The imaging capabilities of the stationary two-dimensional Hadamard encoding mask coupled with the depth profiling ability of photoacoustic detection allows for the three-dimensional photoacoustic imaging of a multiple analyte sample.

The Hadamard transform technique has been extended to include photoacoustic detection. The feasibility of Hadamard transform photoacoustic spectrometry in the visible spectral region has been demonstrated. Depth profiling has been illustrated in a layered sample consisting of a thin (20 μm) surface layer of neodymium oxide dispersed in a polystyrene matrix on a thick (2.5 mm) interior layer of holmium oxide dispersed in a polystyrene matrix. Depth profiling may be accomplished by varying the modulation frequency or by phase-sensitive detection at the appropriate modulation frequency.

Because anticoagulant and GP IIb/IIIa inhibitors reduce mortality, myocardial ischemia, AMI, and reintervention, these agents are now becoming the standard of care for patients with USA and NQWMI. Unanswered questions remain about the best treatment regimen, appropriate dosing, long-term benefit, and cost-effectiveness of these agents, however, and many additional trials are ongoing or planned. As nurses administer these drugs, assess the patients' responses to therapy, and educate patients and families about these agents, they contribute to recent advances in preventing ischemic heart disease.

The electron mobility in p‐type GaAs, μpe, has been determined as a function of temperature by measuring the common‐emitter cutoff frequency, fT, of an AlGaAs/GaAs n‐p‐n heterojunction bipolar transistor. The base was 0.6 μm thick and it was doped with 4×1018 cm−3 Be. The 300 K value of 1055 cm2/V s and 79 K value of 5000 cm2/V s for μpe are comparable to the previously measured values. The discrepancy with the calculated values is pointed out. The recombination lifetime is also measured as a function of temperature for minority carriers. The results agree reasonably well with the calculated radiative recominbation time.

Oscillatory current‐voltage characteristics of n+‐GaAs/semi‐insulating Al0.8Ga0.2As/nGaAs heterojunction barriers (400 A thick) grown by molecular beam epitaxy on n+‐GaAs (100) substrates are observed at 4 K when the heterostructures are placed under the transverse uniaxial stress along 〈011〉 direction (perpendicular to current direction) above 4 kbar. We attribute these oscillations to the resonant indirect Fowler–Nordheim tunneling via 〈011〉 oriented transverse X valleys, where the change of wave vector is required for tunneling.

A stationary 2-D Hadamard encoding mask has been incorporated into a Hadamard transform photoacoustic spectrometer to combine imaging and spectral separation in a form of 3-D spectrometry with two-spatial dimensions and one spectral dimension.

The Hadamard transform technique has been extended to include imaging with a two- dimensional stationary Hadamard encoding mask. Images have been obtained by measuring laser induced fluorescence, Raman scattering, and surface enhanced Raman scattering. Spots on thin-layer chromatography plates have been imaged using laser induced fluorescence and surface enhanced Raman scattering.

Hadamard transform spectrometry (HTS) has been of interest to our research group for over a decade1,2 HTS is a unique combination of dispersive and multiplexing spectrometries.3 The main focus of our efforts has been the application of Hadamard transform techniques to visible4-7 and near-infrared8-17 Raman spectrometry. This chapter will discuss the application of the Hadamard transform techniques to photoacoustic spectrometry (PAS) and depth profiling.

The SSE Data Storage System is a very flexible system for data storage designed to support the needs of scientists in data collection, reduction and analysis. This paper describes the DSS and how it can be viewed as a simple Persistent Object Store. Some suggestions for extensions to make it a true POS are presented together with some ideas for the design of a high-level language that integrates with the DSS to give a Persistent Programming Environment (PPE).

We have studied the properties of metal–oxide–semiconductor structures fabricated by plasma enhanced chemical vapor deposition of SiO2 upon GaAs substrates. We have characterized the dependence of these properties upon the presence of a silicon interlayer, the type and the degree of misorientation of the substrate, and the type of plasma enhancement. We conclude that the presence of a silicon interlayer is beneficial for n‐type GaAs if the oxide is deposited by a remote plasma technique. For such oxides on n‐type GaAs coated with silicon, integration of the quasi‐static capacitance curve suggests a band‐bending range of 0.6–0.9 V. Also for these samples, we observe a hysteresis of order 0.6 V, and shifts of only 0.2 V in the midpoint of the rise from minimum to maximum capacitance upon changing frequency from 10 to 200 kHz. The benefits of using a silicon interlayer with a direct plasma deposited SiO2 film are less evident. It is assumed that much of the improvement of these results arises not from a larg...

By processing pixel data, a low-cost halftone method is proposed to improve viewing-angle characteristics of TN-mode TFTLCDs. The algorithm reduces the occurence of pixels in natural images with mid-tone graylevels, preserving the local luminance. The improvement in viewing-angle characteristics occurs with some loss of image detail. As the pixel density is increased, the halftone pattern becomes less noticeable.

The IBM T220/T221 monitor has 9.2 million pixels with a density of 204 pixels per inch. This is the highest information content display ever produced, and received by SID 2001 Display of the Year Silver Award. This talk describes the key LCD technologies enabling the production of this display.

Using a narrow‐bandwidth, short‐wavelength (0.94 μm) pyrometer, we have observed apparent temperature oscillations during molecular‐beam epitaxy (MBE) growth of III–V heterostructures, due to optical interference between different heterostructure layers. These observations confirm the results of SpringThorpe (Refs. 1 and 2) for GaAs and AlAs growth, which indicate that simple interferometric techniques can be used as an alternative to reflection electron diffraction (RED) oscillation techniques for accurate, in situ measurements of growth rate. We have also measured temperature changes in the growth of lattice‐mismatched (In,Ga)As and InAs, for which RED oscillation techniques are more difficult. For In0.2Ga0.8As growth on GaAs at 500 °C, we observe strong oscillations, with a gradual increase in the average temperature. For InAs growth on GaAs, the indicated temperature rises approximately 60 °C during the first 1000 A of growth and shows only small, strongly‐damped temperature oscillations. Using the In...

The band alignment in GaAs:(Al,Ga)As heterostructures has been investigated over the full range of alloy composition. The valence‐band discontinuity ΔEv is determined by measuring the activation energy for thermionic emission of holes from p‐GaAs over an undoped, square (Al,Ga)As barrier. The use of p‐type structures to measure ΔEv circumvents a number of complications involved in the measurement of ΔEc. The parameters required for analysis are determined by different measurements on the same structures and the analysis is performed so that the activation energy, extrapolated to zero bias, yields ΔEv directly. It is found that ΔEv is a linear function of the aluminum mole fraction xAl: ΔEv ≂0.55xAl (eV) (0≤xAl≤1). The validity of these data is supported by measurements of ΔEc in the direct band‐gap regime, where complementary values of ΔEv and ΔEc add up to the expected band‐gap difference. This relationship provides a simple description of the full band alignment in this heterosystem and should prove val...

Female mammals in good condition can maximize their inclusive fitness by investing more in male offspring than in female offspring during periods of poor environmental quality. To test this hypothesis, we measured the effects of undernutrition and crowding before and during gestation on the sex ratio and weight of offspring at parturition and at weaning in Mus domesticus. Sex ratio was not significantly affected by density. Dams altered the sex ratio of their offspring in response to food availability, but only if variance in competitive success within the experimental subpopulation was evident. Thus ad lib fed females produced litters with an unbiased sex ratio, competitively successful females under moderate food availability produced a male-biased sex ratio, and severely food deprived females produced litters with a female-biased sex ratio. In groups that experienced competition for food, successful dams favoured male offspring during lactation. These results are consistent with the predictions of Trivers and Willard (1973). Analysis of within-cell variance and covariance suggests that the interaction of social structure and food availability provides specific cues for the dams' tactical reproductive choices.

We report our operational experiences with a gallium phosphide source of P2 vapor in the MBE growth of GaP. The use of a P2 source results in much more favorable vacuum characteristics than the use of P4, as generated by an elemental phosphorus source, introducing no complications compared to the growth of arsenides. The phosphorus background pressure during growth is actually lower than the background pressure present during GaAs growth using an elemental arsenic As4 source, for comparable flux rates. The few P4 molecules that do form by association of P2 condense as white phosphorus on the cryobaffles and re‐evaporate upon warmup. However, the pressure peaks at a value no higher than the background pressure during growth. Furthermore, the bakeout pressures are not significantly higher than those obtained using arsenic only. The P2 beam generated by the GaP source contains less Ga than one might expect from equilibrium vapor pressure considerations, thus greatly facilitating the independent control of Ga...

We report measurements of the capture barrier for the DX center in Si‐doped AlxGa1−xAs as a function of the alloy composition. A model of the capture process which requires a distribution of capture barrier heights has been fit to the data for samples with x=0.35. A simple technique is used to extract the average capture barrier height from data for samples with AlAs mole fraction ranging from x=0.27 to x=0.55. The barrier height varies strongly with the composition and has a minimum at x=0.35. The implications of these results are discussed.

We have measured the electron velocity in low-doped GaAs and in AlGaAs/GaAs modulation-doped heterostructures at electric fields up to 8000 V/cm at both 300 and 77 K. In order to avoid the charge domain formation which occurs in DC measurements at these fields, this measurement uses 35 GHz radiation to supply the electric field. These measurements indicate that the peak velocity for electrons in the heterostructures is lower than for electrons in bulk low-doped GaAs. This result is explained in terms of modified intervalley transfer, real space transfer, and an enhanced scattering with polar optical phonons.

The measurement of the energy band discontinuities in GaAs:(Al,Ga)As heterostructures is described. These values are deduced from the activation energy governing current transport in the direction perpendicular to the heterojunction interface. Using complementary structures (fabricated with an Al mole fraction of ≂0.38), we study both electron and hole transport to independently measure the conduction and valence‐band discontinuities respectively. The results obtained are self‐consistent and indicate that the total band‐gap difference distributes approximately in the ratio 60:40 between the conduction band and valence band. Measurement of the conduction‐band discontinuity for an Al mole fraction of ≂0.24 yields a similar ratio. Preliminary measurements of the valence‐band discontinuity in structures fabricated using (Al,Ga)As with an indirect band gap (Al mole fraction of ≂0.60) are also described.

We have measured the electron velocity in low‐doped GaAs and in AlGaAs/GaAs modulation‐doped heterostructures at electric fields up to 8000 V/cm at both 300 and 77 K. In order to avoid the charge domain formation which occurs in dc measurements at these fields, this measurement uses 35 GHz radiation to supply the electric field. These measurements indicate that the peak velocity for electrons in the heterostructures is lower than for electrons in bulk low‐doped GaAs. This result is explained in terms of modified intervalley transfer, real space transfer, and an enhanced scattering with polar optical phonons.

Cyclotron resonance of a two‐dimensional electron gas at a GaAs/GaAlAs interface is measured in the far infrared at intensities of up to 10 kW/cm2. Both the cyclotron mass and the carrier density are independent of intensity but the relaxation time changes with a dependence which is similar to that observed earlier in high dc field mobility studies.

We present experimental results which clearly separate the various physical mechanisms which cause persistent photoconductivity in GaAs/AlxGa1−xAs heterojunctions. For high Al mole fraction the major contribution is from the donor‐related DX center. This contribution is eliminated by reducing the Al mole fraction x, but we observe a ‘‘residual’’ effect for x≲0.2. We show that this is due to the persistent photovoltage developed between channel and semi‐insulating substrate. Charge trapping in the epitaxial GaAs buffer layer contributes negligibly, contrary to the assumptions of other workers. This is demonstrated by fabricating modulation‐doped field‐effect transistors of low Al mole fraction on conductive substrates. In these devices persistent photoconductivity is eliminated as long as the substrate (back gate) potential is fixed with respect to the channel.

The recombination (electron capture) kinetics of the ionized DX center in AlxGa1−xAs have been measured as a function of temperature and silicon doping concentration. It is shown that for x≂0.35, the silicon concentration dependence of the recombination kinetics is dominated by effects of the electron distribution in the conduction band, and is insensitive to changes in the trap characteristics. In a model kinetic calculation consistent with the data the trap is found to capture through a level 0.202 eV from the bottom of the conduction band with a width of 0.045 eV, independent of DX center concentration.

The mobility of electrons in p‐type GaAs, μPn has been determined by measuring the common emitter cutoff frequency fT of heterojunction bipolar transistors with a wide, uniformly doped base. At 295 K, μPn =1150 cm2/(V s) is found for a hole concentration of 3.6×1018 cm−3. At 77 K, μPn =6000 cm2/(V s). The room‐temperature value is considerably smaller and the 77 K value considerably larger than the electron mobility in comparably doped n‐type material.

Transient measurements of drain current are made as the gate voltage is pulsed in Al0.35Ga0.65As/GaAs depletion mode modulation‐doped field‐effect transistors. Large nonexponential decays are observed in the switching characteristics. Evidence is given which shows that these transients are caused by the emptying and filling of deep donors in the Al0.35Ga0.65As.

The kinetics of charge capture by deep donors in AlxGa1-xAs have been measured. The time dependence indicates that a single energy cannot be used to describe the trap. A model assuming thermally activated capture into a resonance in the conduction band with a range of energies gives excellent fits to the data and provides a measure of the energy range for the trap. This model is consistent with the large lattice relaxation model for DX centers. The increase of the activation energy for capture as the Al mole fraction is decreased contradicts the model which attributes the decay of the persistent photoconductivity to tunneling through the heterojunction barrier in modulationdoped structures.

Recent studies of plasma‐enhanced chemical vapor deposition of SiO2 upon Si epitaxial layers grown in situ upon epitaxial GaAs layers, with the deposited interfacial Si of order 10 A, strongly suggest that greatly reduced state densities at SiO2/GaAs interfaces have been attained with this approach. We report spectroscopic ellipsometry results for molecular‐beam epitaxy (MBE) Si/GaAs samples both before and after SiO2 deposition, as well as before and after annealing. The ellipsometric results indicate that the SiO2/GaAs interface is

The high‐energy Auger spectra were measured for a large number of molecular‐beam epitaxial (Al, Ga)As layers, and analyzed for Al composition using electron microprobe and reflection electron diffraction oscillations for calibration. A simple analysis employs this calibration and avoids assumptions of column III/V stoichiometry. Thus the bulk composition can be established to within a few percent from the Auger peak heights, in spite of a large variation in the As surface coverage. An effort is made to account for differences between Auger sensitivity factors determined for as‐grown surfaces (this study) and those obtained from measurements performed during Ar+ ion sputtering. Our measurements support recent measurements of the band gap of AlxGa1−xAs which place the direct/indirect crossover composition between x=0.37 and 0.39.

Soft x‐ray photoemission spectroscopy (SXPS) measurements of metals on clean, ordered InxGa1−xAs(100) surfaces reveal that Fermi level stabilization energies depend strongly on the particular metal, i.e., the Fermi level is not pinned. For InxGa1−xAs, x>0, the range of Fermi level movement is comparable to or greater than the semiconductor band gap. For the same metal on different alloys, we observe regular trends in stabilization energies. The trend for Au is strikingly different from previous, air‐exposed values. Our results challenge Schottky barrier models based on simple native defects, metal‐induced gap states, or the ‘‘common‐anion’’ rule. Observed variations in semiconductor outdiffusion provide a chemically‐modified interface work function model which accounts for the data across the alloy series.

We describe an improvement in optical pyrometry of GaAs substrates, by restricting the pyrometer wavelength to a band of 0.91 to 0.97 μm. This allows temperature measurement of nonbonded GaAs wafers during molecular‐beam epitaxial growth, without interference from the radiation emitted by the substrate heater. Error‐free readings have been obtained for substrate temperatures as low as 440 °C, which is particularly important for the automated growth of alloys such as (In,Ga)As. By detecting a larger substrate surface area and using a calibration curve, the useful measurement range can be extended even lower.