Search

Methyl bromide (MeBr) is an important and effective soil fumigant commonly used to control weeds and soilborne pests. Because MeBr has been implicated as a contributor to the depletion of stratospheric ozone, it is scheduled for phaseout by 2005. This study examined nonchemical and chemical practices as alternatives to MeBr. Off-season flooding followed by a series of soil preplant chemical treatments [MeBr with 33% Pic; 1,3-D mixed with 17% (C-17) and 35% (C-35) Pic combined with Peb; and metam-Na combined with 1,3-D and Peb were evaluated on spring tomato (Lycopersicon esculentum Mill.) and eggplant (Solanum melongena) production in northern Florida. Pest control and tomato and eggplant yields were not significantly different between the flooded and non-flooded control plots. The most effective alternatives to MeBr were 1,3-D and Pic mixtures (C-17 and C-35) combined with Peb. Tomato and eggplant yields for these chemicals were statistically equivalent to that of MeBr. Tomato, but not eggplant, yield and nematode control were poor with metam-Na combined with 1,3-D and Peb in comparison to the other fumigant combinations. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitromethane [chloropicrin (Pic)]; S-propyl butyl(ethyl)thiocarbamate [pebulate (Peb)]; sodium N-methyldithiocarbamate (metam-sodium (metam-Na)].

One of the proposed alternative chemicals for methyl bromide is 1,3-D. The most common forms of 1,3-D products are cis- or trans-isomers of 1,3-D with the fungicidal agent, chloropicrin, containing such mixtures as 65% 1,3-D and 35% chloropicrin (C-35). Soil fumigants are commonly applied under a polyethylene film in Florida raised bed vegetable production. Much of the research regarding cropping system effects of alternative fumigants to methyl bromide has focused primarily on plant growth parameters, with little regard to the atmospheric fate of these chemicals. The objective of this research was to determine both the atmospheric emission of 1,3-D under different plastic film treatments and to evaluate effects of application rates of 1,3-D and C-35 on plant pests, growth, and yield of Sunex 9602 summer squash (Cucurbita pepo L.). Results showed that use of a high barrier polyethylene film (or virtually impermeable film - VIF) greatly reduced fumigant emission compared to ground cover with conventional polyethylene films or uncovered soil. Summer squash seedling survival was a severe problem in several of the 1,3-D alone treatments where no fungicidal agent was added, whereas C-35 resulted in excellent disease control at both full and one-half of the recommended application rates for this chemical. Both 1,3-D and C-35 provided good plant stands and higher yields when applied at their recommended application rates. However, all squash yields were lower than typical squash production levels due to late planting and early winter frost kill. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitropropene (chloropicrin).

Thin film composites of YBa 2 Cu 3 O 7 (YBCO) with gold were deposited by inverted cylindrical magnetron sputtering on SrTiO 3 (STO), MgO, and yttrium stabilized zirconium (YSZ) substrates using a bilayer deposition process. The material and electrical properties of crystal structure, surface morphology, resistivity, transition temperature ( T c ), resistance ratio, and critical current ( I c ) as a function of temperature and small magnetic fields were investigated. Films deposited on STO showed little degradation in superconducting properties up to 500 A of gold with 1 kA of YBCO; for YSZ and MgO, the films showed a rapid fall-off in T c with gold thickness. For YSZ, 3–10 A of gold caused the films to become insulating; however, for gold greater than 25 A, the films were superconducting but T c rapidly fell to zero by 500 A of gold. Composites on MgO showed the most rapid fall-off in T c going to zero by 200 A of gold. The temperature dependence of I c was predominately quadratic. However, some films showed a crossover between quadratic and linear temperature dependence in I c . The I c of all the composites showed a response to small magnetic fields with the films on STO being the least sensitive and those on MgO the most. There was a trade-off between T c and field response with the film having the greatest response having the lowest T c . These composite films show potential for vortex flow device development.

We have measured the current-voltage (I-V) characteristics of thin film composites made from YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) and Ag. When deposited upon a substrate, this material appears to form arrays of superconducting-normal-superconducting (SNS) junctions. To make these measurements, the films were patterned into microbridges and immersed directly into the cryogen to provide a constant temperature environment and to avoid problems of local heating. The data were fitted by several phenomenological models in an effort to understand the dissipation mechanism appropriate to these materials.

We have investigated thin film composites of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) with Ag for fluxonic device applications. YBCO/Ag composite films are produced by first depositing a layer of Ag onto a substrate and then heating the film to the YBCO deposition temperature of 680/spl deg/C or higher. YBCO is deposited by off-axis sputtering onto the Ag-coated substrate. The resulting YBCO/Ag film is a composite of YBCO with well-defined Ag regions several microns in size. Scanning electron micrograph images of the films' surfaces show a background of smooth YBCO grains dotted with Ag clusters. For a wide range of increasing Ag composition, the transition temperatures of the composite films on SrTiO/sub 3/ remain high, while the critical current densities have been reduced as much as 65 times. On MgO substrates, critical current density has been reduced by more than four orders of magnitude. Also on MgO, significant voltage response is seen in external magnetic fields of less than 1 mT. These measurements suggest that the films may be arrays of superconductor-normal-superconductor (SNS) junctions formed by weakly coupled YBCO grains with Ag in the grain boundaries. The field responsivity and low critical current densities of these composites make them potentially useful for fabrication of fluxonic devices.

Food that we are culturally habituated to consume is usually thought to be safe. However, some foods are naturally contaminated with substances, the effects of which are unknown. Crops are sprayed with pesticides while they are being cultivated; some animals are injected with hormones while being raised. Meanwhile, other foods are mechanically processed in ways that could risk contamination. This article discusses food contamination with heavy metals, the heavy metals involved, their toxicities, and their sources in the environment. A brief consideration of medical management is also included. Five metals are considered in this category: lead, mercury, cadmium, nickel, and bismuth.

The maternal requirement for most nutrients during lactation is higher than during pregnancy because of the need to replace the substantial amounts secreted in breast milk. This chapter first describes the overall approaches used by Food and Agriculture Organization/World Heath Organization, and the Institute of Medicine, to establish dietary requirements for nutrients in lactating women. It then provides more details of the requirements for macronutrients, and some minerals (calcium and zinc) and vitamins (vitamin A, folate, and other vitamins B).

Over the past 40 years there have been dramatic changes in the recommendations for optimal maternal weight gain during pregnancy. Current recommendations in the United States are based on weight changes in pregnancy that have been taken from records and are known to be compatible with a healthy pregnancy outcome, i.e., low risk of cesarian or preterm delivery, low or high birth weight, excessive postpartum weight retention, and subsequent childhood obesity. The US recommendations have been widely accepted by many other Western countries. Because several maternal factors influence the amount of weight gained in pregnancy, especially maternal body mass index (fatness) at conception, which is inversely related to weight gain, these have been taken into consideration in the current recommendations, which are based on actual weight gain in healthy pregnancies. Maternal energy intake is likely a relatively small contributor to variability in weight gain among women.

Total dietary fiber is the sum of dietary fiber and functional fiber. Dietary fiber consists of nondigestible carbohydrates and lignins from plants. Functional fiber, which may either occur naturally in food or be produced during food processing, consists of nondigestible carbohydrates that by definition have a beneficial effect on human health. The clearest beneficial effect of fiber is that it lowers total and low-density lipoprotein cholesterol; soluble and functional fibers are most effective in this regard. Fiber also reduces the glycemic index of a diet and may help to prevent hyperglycemia in people with diabetes. It is also important for preventing constipation, and diverticular disease may be less common in people following a higher fiber diet. The evidence for high fiber diets preventing any form of cancer is still controversial.

This research involves the study of thin films for use in three-terminal, non-linear two-terminal, and photodetector superconducting devices. The morphological and electrical properties of composite films fabricated from YBCO and noble metals have been investigated for use in these devices. Films of Ag and Au, when heated to YBCO deposition temperatures, coalesce into small, approximately micron-sized islands. We take advantage of this property to form a composite film with distinct YBCO and noble metal regions by depositing a layer of YBCO on the array of noble metal islands. With certain compositions the films exhibit reduction of critical current density by a factor of 65 over YBCO and show no significant degradation of critical temperature. Also, the current-voltage characteristics of the composites are sensitive to small, applied magnetic fields. These properties make the YBCO/noble metal composites potentially well suited for the fabrication of devices whose transport is dependent upon vortex motion. Photoresponse measurements taken on a 1 mm × 1 mm YBCO/Au bridge irradiated by red laser light showed a possible non-bolometric response below the composite superconducting transition temperature.

The occurrence of a transverse voltage peak has been observed in YBCO thin films. This phenomenon occurs under conditions of temperature and current in the earth's magnetic field such that the films are in the mixed state. The magnitude of the peak was found to scale with both temperature and current, and exhibited a Sin(/spl theta/) orientational dependence measured between the film-substrate and the position of the measurement electrodes on the film surface. These observations are similar to observations made in conventional superconducting thin films such as Nb, NbN, NbCN, and PbBi. >

We are using a novel bilayer deposition process to grow composite films of Au with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. The composites have well-separated regions of Au and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//, and we see no evidence for structural or chemical degradation of the grains and grain boundaries. For composite films on MgO substrates, the transport properties indicate the presence of weakened superconductivity in the films. Composites on SrTiO/sub 3/ and LaAlO/sub 3/ do not show this as strongly. The MgO composites behave like arrays of Josephson junctions and show promise as materials for flux flow devices. >

Midday reductions of stomatal conductance and carbon dioxide assimilation rates (Aco2) in Citrus are typically attributed to large leaf-to-air vapor-pressure differences or high atmospheric vapor-pressure deficits (VPD). This study investigated air temperature (Ta) and available soil water (ASW) level as corollary factors of atmospheric VPD that influence midday reduction of net gas exchange in citrus leaves. The influence of elevated atmospheric CO2 under conditions that inhibit net canopy Aco2 was also investigated. Net canopy Aco2 and evapotranspiration rates of Carrizo citrange [Poncirus trifoliata Raf × Citrus sinensis (L.) Osbeck] and Swingle citrumelo (P. trifoliata Raf × C. paradisii Macf.) seedlings grown in outdoor controlled-environment growth chambers were measured under two levels of Ta with concomitant changes in VPD and two levels of atmospheric CO2 concentration, which were changed in steps over time. Cyclical depletion of ASW was allowed to occur at each set of Ta/VPD and CO2 combinations. Highest net canopy Ace, rates at ambient CO2 concentration (330 μmol·mol-1) were obtained at the low Ta/VPD level (29C/2.4 kPa) and ASW >50%. Diurnal canopy CO2 uptake rates decreased at the high Ta/VPD level (37C/3.6 kPa), and midday depression of canopy Aco2 was observed at ASW levels co2 decreased at higher levels of ASW under the high Ta/VPD treatment than at the low Ta/VPD treatment. At the elevated CO2 concentration (840 μmol·mol-1) net canopy CO2 uptake rates were double those that occurred at ambient CO2 levels and they did not exhibit midday reduction. Our data indicate that, when soil water is not readily available, citrus seedlings are more sensitive to high levels of Ta and VPD which results in reduction of CO2 uptake. The inhibitory effects of elevated VPD and reduced ASW on citrus net Aco2 were lessened at the elevated atmospheric CO2 level.

Thin‐film, composite mixtures of YBa2Cu3O7−δ (YBCO) and Y2O3 (yttria) have been grown by off‐axis sputtering onto (100) SrTiO3 and (100) and (110) MgO. X‐ray‐diffraction measurements for films grown on (100) substrates show the presence of c‐axis‐oriented YBCO and (h00)‐ordered yttria. The composites deposited on (110) MgO are insulating, and x‐ray analysis shows the presence of Y2Ba1Cu1O5 along with c‐axis YBCO. Scanning electron microscopy analysis shows the films to be very granular. The superconducting transition temperature and resistivity ratios between 300 and 100 K of the composites grown on the (100) substrates have been measured. A dramatic change is seen in these transport properties around 70% (volume) of YBa2Cu3O7−δ, which may be explained by the phase diagram for Y‐Ba‐Cu‐O.

YBa2Cu3O7−x films have been deposited on MgO by reactive, off‐axis magnetron sputtering in an argon, oxygen, and hydrogen gas mixture. The material and electrical properties of the films were studied for deposition temperatures from 600 to 760 °C. The films, all approximately 300 nm thick, were predominantly a‐axis oriented when deposited at or below 620 °C but were c‐axis oriented when deposited at temperatures above 640 °C. The surfaces of films deposited between 640 and 710 °C were partially covered with a‐axis grains. Surface roughness measurements indicated the smoothest films occurred for deposition temperatures below 680 °C. Resistance ratios as great as 3.1 were observed for some films. Transition temperatures exceeded 89 K and resistivities at 100 K were less than 150 μΩ cm for the best films. Low‐temperature critical current densities exceeded 107 A/cm2 for films deposited from 640 to 720 °C. The temperature dependence of the critical current density near the transition temperature had a power l...

Single-crystalline cubic SiC Layers have been grown on Si(111) substrates by molecular beam epitaxy (MBE) using graphite and silicon solid sources at relatively low substrate temperatures (800°C). The growth process employs initial carbonization of the (111) Si surface followed by direct deposition of both Si and C. Reflection high energy electron diffraction (RHEED), X-ray diffraction, cross-sectional and plan-view transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and optical Nomarski microscopy were used to characterize the films. Atomic ratio of Si to C during the growth was found to be critical in terms of the crystalline quality as well as surface morphology of the films. To the extent of the instrumental accuracy, AES shows the SiC films to be stoichiometric. X-ray diffraction and TEM measurements confirm the crystalline nature of the SiC films.

We have prepared thin film composites of Y1Ba2Cu3O7−y (‘‘123’’) and Y2Ba1Cu1O5 (‘‘211’’) by off‐axis sputtering from separate targets of the 123 and 211 material. X‐ray diffraction on the films shows the presence of c‐axis oriented 123, and (00L) ordered Y2O3, but no indication of 211 lines. The c‐axis lattice constant does not show any change compared to our pure 123 films. As the volume percentage of 211 material increases, we see a reduction in Tc and Jc, and an increase in the resistivity. The temperature and field dependence of the critical current are different for our composites compared to our pure 123 films.

Multilayer films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ with composites of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ and LaAlO/sub 3/ have been grown on

YBa/sub 2/Cu/sub 3/O/sub 7/ thin films have been deposited on MgO substrates by off-axis magnetron sputtering in argon, oxygen, and an additional gas. Additions of nitrogen, hydrogen, methane, air, and water vapor in amounts of up to 25% were used in this investigation. Each gas stabilized the target voltage and growth rate for the duration of the deposition. Growth rates improved by over 50% with as little as 3% hydrogen. When used with a target which had degraded after more than 150 h of use, the added gas improved T/sub c/ and J/sub c/ beyond levels attained from the new target. T/sub c/ increased from 82 K without hydrogen to 89 K with hydrogen and J/sub c/ (12 K) from 3*10/sup 4/ to >7*10/sup 6/ A/cm/sup 2/. Nitrogen yielded less dramatic effects. These improvements are attributed to the catalytic effect of these gases in maintaining elevated levels of atomic oxygen during film growth. >

We have prepared thin film samples composed of Y 1 Ba 2 Cu 3 O 7−y («123») and Y 2 Ba 1 Cu 1 O 5 («211») by off-axis sputtering from separate targets of the « 123» and «211» material. X-ray diffraction on the films shows the presence of c-axis oriented «123», but no indication of ordered «211» lines. The c-axis lattice constant does not show any change compared to our pure «123» films. As the volume percentage of «211» material increases, we see a reduction in T c and J c , and an increase in the resistivity. The temperature and field dependence of the critical current are different for our composites compared to our pure «123» films

The photoresponse of Y1Ba2Cu3O7−x step, weak‐link devices on MgO substrates has been measured using a He‐Ne laser light source. The temperature and magnetic‐field dependencies of the device critical current density were investigated. Single‐step and multistep devices were fabricated and found to have a bolometric response in the resistive region and weak‐link, video‐detection response in the superconducting region. These devices are suitable for operation over a wide range of temperatures from 4 to 90 K. Responsivities greater than 1000 V/W were measured at low temperature for some devices.

Three variations of sputtering for growing thin films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ are examined: a three-metal cosputtering technique requiring a postanneal at high temperatures, an in situ process using a inverted cylindrical magnetron sputter gun, and another in situ process using an planar target in an off-axis geometry. The films are grown primarily on a magnesium oxide substrate because it is readily available, inexpensive, and its low dielectric constant permits convenient microwave circuit design. It is found that the cosputter process with postanneal produces films with depressed T/sub c/'s and J/sub c/'s. The inverted cylindrical magnetron sputtering has yielded the best films, showing complete transitions as high as 87 K and J/sub c/=4*10/sup 6/ A/cm/sup 2/ at 4 K. The off-axis results are not quite as good, with 79 K complete transitions. By lowering the substrates further out of the plasma in the off-axis system, films can be improved by avoiding damage from negative ions.

Superconducting, silver‐doped films of Y1Ba2Cu3O7−δ have been deposited by spray pyrolysis of aqueous nitrate solutions onto MgO substrates. The superconducting transport properties, microstructure, and microwave losses have been characterized for various amounts of AgNO3 added to the spraying solution. These films had resistive transition temperatures between 79 and 85 K with widths from 3 to 7 K. The room‐temperature resistivity was a strong function of the silver doping, dropping by a factor of 50 for the heavily doped films. Critical current densities at 4 K were typically several 103 A/cm2 with little correlation to the silver doping. Lattice constants also were not significantly affected by the silver doping level, however, lightly doped films were denser, had the strongest c axis preferred orientation, and a smoother surface. Rf surface resistance was measured at 18 GHz, and for the best films dropped a factor of 10 below copper by 40 K. The London penetration depth was estimated to be approximatel...

High dielectric ceramic thin films incorporated into microelectronic packaging will extend both the performance and functions of advanced microelectronic packaging. The low processing temperatures, excellent composition control and low capital manufacturing costs may make the sol-gel film preparation route a prime manufacturing method. For this technique to be a useful alternative to competing vacuum deposition methods, the interactions between the commonly employed packaging materials set and the Sol gel derived films must be understood. To integrate these films into applications the development of thin film stresses and resulting defects must be understood. In this study, we are examining the processing of sol-gel derived barium titanate thin films for use as integrated decoupling capacitors as our model system. Stress measurements are made by measuring curvature of thin film coated wafers as a function of temperature and time. The films exhibit both plastic and elastic behavior at different processing stages. These films are microscopically examined to observe the formation of microstructure including cracking and pinholes. By tailoring the thermal process to the viscoelastic film behavior high quality films may be produced.

In our studies of the behavior of materials forming thin film composites with Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), we have characterized thin film composite mixtures of YBCO and Y/sub 2/O/sub 3/ (yttria) grown onto (100) MgO and (100) SrTiO/sub 3/ substrates by off-axis sputtering. We have examined the transport properties of the films, in particular the critical current density, J/sub c/. The temperature dependence of J/sub c/ for composites on SrTiO/sub 3/ is identical to that of our pure YBCO films, while for composites on MgO the J/sub c/ is similar to measurements on our earlier composites of YBCO and Y/sub 2/Ba/sub 1/Cu/sub 1/O/sub 5/ ("211"). The field dependence of J/sub c/ for the YBCO/yttria composites is different from our pure YBCO films, and from our earlier composites, but the magnitude of the flux pinning is similar. >

Using a novel bilayer deposition process, we have grown composite films of Au with YBa2Cu3O7−δ on various substrates. Our composites have well‐segregated regions of Au and YBa2Cu3O7−δ, and we have not observed structural degradation of the grains or grain boundaries in the films. Transition temperatures and critical current density measurements have behaviors consistent with regions of weakened grain boundary coupling in the films. Photoresponse measurements are also reported. We believe that Au is diffusing into the grain boundaries and weakening the coupling between YBa2Cu3O7−δ grains. By varying the amount of Au in the films, the coupling can be adjusted. These Au/YBa2Cu3O7−δ composite films are promising materials for device applications relying on vortex motion.

Summary form only given. The trend in microelectronic technology is toward nanometer size scales. Thermodynamic properties of material having small nanometer dimensions can be considerably different as compared to material in bulk form (e.g., the reduction of melting point). This occurs because of the tremendous influence of the surface energy. Calorimetry is the standard experimental technique used to measure thermodynamics properties such as the melting point and the heat of fusion. However, conventional differential scanning calorimetry (DSC) techniques are extremely difficult to apply to the study of small structures because the total amount of heat generated during the transformation is too small as compared with the background beat capacity of the calorimeter. In this talk I=9211 discuss a new nanocalorimetry technique which we have developed for the measurement of nanoscale systems. This nanocalorimeter is fabricated using standard MEMS thin film techniques and it has the capability of measuring the dynamics of the energy exchange at the level of 0.2 nanojoule. This technique is so sensitive that it can easily measure the melting process of 1 Angstrom of Sn which has been deposited on a Si-N surface. Results of specific materials studies will be discussed including the size-dependent melting point depression of small particles of Sn and Al and preliminary work on the coalescence of small clusters.

Evolution of the Ti/a-Ge/Si trilayer reactions has been investigated using transmission electron microscopy and four-point sheet resistance measurement. Instead of amorphous phase formation, as usually observed in the Ti/Si bilayer reaction, a crystalline Ti/sub 6/Ge/sub 5/ is the first phase observed during the reaction preceding the equilibrium C54-Ti(Si,Ge)/sub 2/, a substitutional solid solution type C49-Ti(Si,Ge)/sub 2/ forms upon annealing at 550/spl sim/600/spl deg/C, regardless of the replacement of amorphous phase by the crystalline phase. The C49-to-C54 polymorphic transformation occurs at /spl sim/650/spl deg/C. The reaction path is also correlated with the change in film resistance obtained from a-four-point sheet resistance measurement.

Y1Ba2Cu3O7 thin films have been grown on MgO by off‐axis magnetron sputtering using mixtures of argon, oxygen, and hydrogen. Reduction in film transition temperature resulting from cumulative target sputtering time (target degradation) is minimized by adding hydrogen to the sputtering gas. Without hydrogen, new targets which had produced films with 87.5 K transition temperatures degraded with deposition time and produced films with transition temperatures of only 82 K. After addition of hydrogen, these targets produced films with transition temperatures of nearly 89 K. Critical‐current densities for the films made at optimum hydrogen flow were greater than 3×106 A/cm2 at 4 K. With the addition of hydrogen, we observed a significant increase in the sputtergun cathode voltage and a dramatic increase in the deposition rate. The films were predominantly c‐axis oriented, and we observed a minimum c‐axis lattice parameter for optimum hydrogen flow. We attribute these improvements in material properties to the c...

Thin‐film composites of co‐sputtered Y1Ba2Cu3O7−x and LaAlO3 have been deposited by off‐axis magnetron sputtering. Scanning electron microscopy (SEM) and x‐ray diffraction studies suggest that LaAlO3 precipitates along the grain boundaries of the Y1Ba2Cu3O7−x grains. The normal state conductivity, transition temperature, and critical current density systematically decreased with increasing LaAlO3 composition, consistent with a decrease in the coupling between Y1Ba2Cu3O7−x grains. Inductive transition widths were only a few degrees wide for all LaAlO3 compositions, indicating homogeneous materials. Initial photoresponse measurements show bolometric behavior near Tc and increased response for greater LaAlO3 compositions.

Tunneling studies have been made using sputtered Cu/sub 2/O as an insulating barrier between an EBCO thin film and a normal metallic layer. Cu/sub 2/O was selected for its low potential for chemical reaction with the superconducting layer and for its photoconductive properties. Having a band gap in the visible (2 eV), Cu/sub 2/O is a suitable candidate for photosensitive tunneling experiments. EBCO thin films were deposited in situ onto MgO substrates using an off-axis sputtering technique. T/sub c/'s of as-deposited films were between 80 and 85 K. Inductively measured J/sub c/'s ranged between 10/sup 6/ and 10/sup 7/ A/cm/sup 2/ at 4 K. A 5-20-nm layer of Cu/sub 2/O was sputtered directly on top of the superconducting film. Room-temperature resistivities of the Cu/sub 2/O layer were typically greater than 10/sup 6/ Omega -cm. A normal metal layer (typically gold) was then deposited onto the Cu/sub 2/O layer. Transport properties of the structure were measured at temperatures ranging above and below the T/sub c/ of the superconducting layer. Measurements of structures fabricated to date showed no tunneling effects. Measurements of the I-V characteristic of a Cu/EBCO bilayer exhibited nonohmic behavior at 85 K and 4 K, indicating the existence of an extraneous interfacial layer. Preliminary results on one such structure indicate possible tunneling effects.

We have investigated the properties of off-axis co-sputtered films of YBCO and CeO/sub 2/ having CeO/sub 2/ concentrations up to 43%. Morphology investigations suggest that films with more than 29% CeO/sub 2/ may consist of a new material phase, T/sub c/ and resistance ratio decreased with increasing CeO/sub 2/ concentration. Degradation of T/sub c/, after photoresist processing the films was observed and reversed by a 20 minute oxygen plasma etch. The temperature dependence of the critical current near T/sub c/ showed two power law dependence regions with a crossover near 0.99 T/sub c/ for films having low concentrations of CeO/sub 2/. I/sub C/ 's were decreased by small applied magnetic fields, and for some samples the response was observed to increase at lower temperature. For a sample having 26% CeO/sub 2/, a 40% reduction in critical current was observed for a 2 Gauss applied field. This response indicates that this may be a candidate material for the development of Josephson vortex flow devices.

We have grown a series of composite films of Au with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// on various substrates using a bilayer deposition technique to study their suitability for flux flow applications. The T/sub c/'s and J/sub c/'s were measured, and results compared with plain YBCO films for the different substrates. The patterning process resulted in some damage to the composites, but an oxygen plasma treatment was effective in restoring T/sub c/'s and resistance ratios, J/sub c/ measurements suggest that Au/YBCO composites behave like SNS-coupled arrays of superconducting grains. Their increased response to small magnetic fields is consistent with Josephson vortices dominating the transport. These findings indicate that Au/YBCO composites are a promising material for flux flow applications.

A technique is described which enables contactless measurements at microwave frequencies of the superconducting transition. The approach employs an electrically small microwave loop antenna to sense the change in the reflected microwave signal as flux is expelled, due to the Meissner effect, from the superconductor. Advantages of this technique include the ability to measure small areas of a superconducting thin film after photolithographic patterning into a device geometry. This approach is very sensitive in the frequency range from 0.05 GHz to 5 GHz and for some YBCO films a dependence of the transition temperature width on frequency has been observed. Such frequency-dependent signatures may provide valuable information regarding improvements in film deposition and device processing.

The projected doubling of current levels of atmospheric carbon dioxide concentration ([CO(2)]) during the next century along with increases in other radiatively active gases have led to predictions of increases in global air temperature and shifts in precipitation patterns. Additionally, stratospheric ozone depletion may result in increased ultraviolet-B (UV-B) radiation incident at the Earth's surface in some areas. Since these changes in the Earth's atmosphere may have profound effects on vegetation, the objectives of this paper are to summarize some of the recent research on plant responses to [CO(2)], temperature and UV-B radiation. Elevated [CO(2)] increases photosynthesis and usually results in increased biomass, and seed yield. The magnitude of these increases and the specific photosynthetic response depends on the plant species, and are strongly influenced by other environmental factors including temperature, light level, and the availability of water and nutrients. While elevated [CO(2)] reduces transpiration and increases photosynthetic water-use efficiency, increasing air temperature can result in greater water use, accelerated plant developmental rate, and shortened growth duration. Experiments on UV-B radiation exposure have demonstrated a wide range of photobiological responses among plants with decreases in photosynthesis and plant growth among more sensitive species. Although a few studies have addressed the interactive effects of [CO(2)] and temperature on plants, information on the effects of UV-B radiation at elevated [CO(2)] is scarce. Since [CO(2)], temperature and UV-B radiation may increase concurrently, more research is needed to determine plant responses to the interactive effects of these environmental variables.

Films of Y1Ba2Cu3O7-y have been grown by off-axis DC sputtering onto substrates of (100) SrTiO3. LaAlO, LaGaO3, Yttria-stabilized Zirconia, and MgO. Our best films, grown on SrTiO3 substrates at a temperature of 650°C and a sputtering pressure of 100 mTorr (consisting of 80 mTorr Ar and 20 mTorr O2) have room temperature resistivities of 280 μΩ-cm, an inductive Tcof 88 K and an inductive Jc 'Sof∼ 2.6 × 106 A/cm2 at 77 K and 3.9 × 107 A/cm2at 4.2 K. Films grown on YSZ tend to have higher resistivities (∼ 600 μΩ-cm) but still have Tc's of 86 K and Jc's of - 106 A/cm2 at 77 K. Films down to 550 Å still have Tc's of 86 K and Jc's at 77 K > 106 A/cm2. Films grown at lower temperatures (600°C) on S1TiO3 begin to show a-axis growth, but the superconducting properties deteriorate.

We have grown thin film composites of and YBa2Cu3O7−x and LaAlO3 by co-sputtering. A film with composition of 10% LaAIO3 by volume had a transition temperature of 58K and critical current density of 1.2 × 106 A/cm2 at 4K. We measured the temperature dependence of the critical current and obtained a good fit with Ginzburg-Landau theory for thin films. A perpendicular magnetic field was applied, and the critical current and pinning force measured. At 70 kOe, the critical current was suppressed only a factor of 4 from its zero-field value. The measured pinning force was 2 × 109 dyn/cm3 at 70 kOe and is comparable to that of YBa2Cu3O7−x films.

The analog control circuitry typically found in commercial electrophoresis power supplies was replaced by a digital microcomputer. Analog to digital converters were used to monitor the voltage applied to and current passed through an electrophoresis cell. Microcomputer programming was employed to compare converter input values with preselected operating parameters and then calculate a required output voltage. Timing sequences were generated through programming utilizing clocks located on the interface boards. A digital to analog converter was employed to apply a control voltage to a constant voltage power supply. This process was completed at least 20 times each second. BASIC programming subroutines were written to maintain constant voltage, current, power (wattage), and temperature. To these operating procedures, other techniques such as automated endpoint detection of isoelectric focusing and pulsed waveform outputs were easily added. This power supply containing a microcomputer system as the feedback element was shown to have a greater stability and versatility than conventional supplies.