Controlled Temperature Gradient Research Articles

QUALITY CHARACTERISTICS OF BREAD WHEAT GROWN UNDER ELEVATED CO2 AND TEMPERATURE

Elevated CO_2 concentrations and temperatures under global climate change scenarios projected for coming decades could impact bread wheat (Triticum aestivum) quality. Hence, there is a need to understand the effects of these environmental factors on crop quality. The objective of this study was to experimentally test the effects of elevated CO_2, temperature, and their interactions on wheat grain quality characteristics relevant to its processing, including grain protein content, wet gluten content, sedimentation value, and falling number (alpha-amylase activity). Bread wheat (`Liaochun 10') was field grown in CO_2 and temperature gradient chamber (CTGC) and ambient controlled temperature gradient chamber (TGC). The results indicated that elevated CO_2 concentrations (433.3 to 610.2 μmol·mol -1) had negative effects on grain protein content, wet gluten content and sedimentation value of bread wheat, but gradual temperature increases (2 ℃ range) had positive effects on these three main quality characteristics. The interaction between gradual increases in CO_2 levels from 433.3 to 551.5 μmol·mol -1 and temperature increases (+2 ℃ range) showed a similar benefit on grain protein content, wet gluten content and sedimentation value of bread wheat, but when CO_2 concentrations approached 610.2 μmol·mol -1 and mean daytime temperature increased more than 2 ℃, the interaction of CO_2 and temperature had a negative effect on the three bread wheat quality characteristics. In addition, under CO_2 concentrations of 433.3-610.2 μmol·mol -1 and gradually increasing temperatures, CO_2 enrichment reduced alpha-amylase activity of bread wheat whereas elevated temperatures and the interaction of elevated CO_2 and temperature enhanced alpha-amylase activity of bread wheat.

DNA hybridization assays using temperature gradient focusing and peptide nucleic acids.

Two types of DNA hybridization assays are demonstrated with temperature gradient focusing (TGF) and peptide nucleic acids (PNAs). In TGF, the application of a controlled temperature gradient along the length of a microchannel filled with an appropriate temperature-dependent buffer results in the formation of a gradient in both the electric field and electrophoretic velocity. Ionic species move in this gradient and concentrate at a unique point where the total velocity sums to zero. The first assay is a mixing assay in which PNA is allowed to flow through spatially focused DNA targets within a capillary. The second assay detects single base pair mutations (SBPM) by monitoring the fluorescence intensity of PNA/DNA duplexes as a function of temperature within the capillary. The SBPM analysis can be performed in less than 5 min with 100-fold more dilute analyte compared to conventional UV melting measurements.

A novel tunable dispersion slope compensator based on nonlinearly thermally chirped fiber Bragg grating

We propose a novel method for introducing a chirp on a fiber Bragg grating. Applying a controllable nonlinear temperature gradient across a uniformly written Bragg grating chirps it nonlinearly to realize a tunable dispersion slope compensator for waveform distortion compensation. This scheme allows an adjustable, repeatable, stable, and precise nonlinear chirp onto the grating. The dispersion slope of the device was tuned from −37.06 to −199.45 ps/nm 2, with observed GDR as low as ±5 ps.

Inexpensive set-up for determination of decomposition temperature for volatile compounds

The utility of precursors for atomic layer chemical vapour deposition (ALCVD) growth is limited by the sublimation and decomposition temperatures. Sublimation temperatures are conveniently obtained by thermogravimetry (TG) under vacuum. We present here a relatively inexpensive method to obtain information about the decomposition temperature for a precursor candidate for ALCVD. This approach requires an oven with a controlled temperature gradient and a long ampoule for each precursor. The precursors tested in this work comprise the thd complexes (Hthd=2,2,6,6-tetramethylheptane-3,5-dione) of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, La, and Ca.

Quantitative control and detection of heterovalent impurities in ZnO thin films grown by pulsed laser deposition

Impurities in ZnO specimens, including targets for pulsed laser deposition and thin films resulting from their use, were analyzed by secondary ion mass spectroscopy (SIMS). Negatively charged complex ions bound with oxygen (71Ga16O− and N14O-16) were found to be the most reliable species with which to evaluate the Ga and N content of ZnO films by clarifying possible mass interference effects in SIMS analysis. Calibrations were carried out to determine the Ga concentration (CGa) and the nitrogen concentration (CN) by normalizing the signal intensities for G71O-16 and N14O-16, respectively, to that for Z70O-16. Alternative ablation of pure single crystal and Ga-doped ceramic ZnO targets was found to be effective not only for achieving systematic control of the Ga concentration in ZnO:(Ga,N) films, but also for minimizing the contamination of undesired impurities from the sintered targets. The substrate temperature plays a decisive role in control of CN due to a thermally activated desorption process of N-related species during deposition. Systematic control of the CN/CGa ratio in a ZnO:(Ga,N) film was carried out on a ScAlMgO4 substrate by introducing a controlled temperature gradient on the substrate during deposition. A region with the correct concentration ratio of CN/CGa=2, where p-type conduction of the ZnO film was theoretically predicted, was included in the composition spread sample in which the CN/CGa ratio was continuously varied over a wide range.

Base growth temperatures, germination rates and growth response of contemporary spring wheat ( Triticum aestivum L .) cultivars from the US Pacific Northwest

In eastern Washington, spring wheat cultivars that germinate and grow fast at low temperatures will provide the crop with a competitive advantage over spring emerging weeds in commercial production fields compared to cultivars that germinate and grow more slowly. The objective of this research was to develop a protocol to identify spring wheat cultivars that would germinate and grow more quickly at low temperatures. A novel data analysis method was used to separate the germination process into three components: (1) base temperature, (2) time to initiation of germination, and (3) germination rate. Spring wheat cultivars Edwall, Vanna, Wawawai, Wampum, Express, and Spillman were assessed through a series of controlled temperature gradient plate experiments. Base temperatures were not different ( P=0.1) across cultivars, and once germination was initiated, germination rates among varieties were uniform ( P=0.5). However, significant ( P<0.001) differences were detected among varieties for time to germination. A subsequent growth chamber experiment confirmed differences in emergence and growth rate among spring wheat cultivars.

Tunable chirped fiber Bragg gratings by a distributed heater

We propose a new design for introducing a tun- able chirp on a uniform fiber Bragg grating by a controllable temperature gradient. The device consists of an unchirped Bragg grating in a bare fiber that is mounted in a plastic sleeve whose surface is coiled with a length of wire heater. The desired temperature distribution produces a chirp on the grating and at a rate that can be adjusted by varying the current. We demonstrate an electrically tunable chirped fiber Bragg grating that enables a tuning range of an average chirp rate up to 0.93 nm/cm with an electrical power of 3.3 W. We also demonstrate a tunable chirped fiber Bragg grat- ing in which dispersion is adjustable from 21632 to 2667 ps/nm with an electrical power of less than 0.5 W. © 2001

Co-doping Approach for β-type ZnO with Combinatorial Laser MBE Method

AbstractWe show here three different ways of combinatorial experiments for achieving precise control of dopant concentration in ZnO thin films. Alternating ablation of highly pure single crystal target and ceramics target doped with concentrated Ga dopant yielded in a systematic control of Ga concentration with keeping minimal contamination of undesired impurity. Secondary ion mass spectroscopy for a stack of several ZnO films grown at different temperatures under a constant exposure of N radical gave us a systematic calibration curve for the N concentration. With using a special heating method to give a controlled temperature gradient on a substrate, we demonstrate that continuous spread of N concentration can be built in a film on a substrate with keeping constant Ga concentration. Such systematic experiments taking into account the “combinatorial” concept enable us to make ZnO films with controlled dopant concentrations.

Contactless heating of moving wires

A novel method is described for uniform radio frequency (RF) heating of static or moving wires at atmospheric pressure, over long lengths, without the use of contacts or brushes. Conventional induction heating of wires is not possible because of the large annular coil gap and the RF skin effect if the wire diameter is comparable to the skin thickness. The method described involves placing a rod, of length equal to the heated zone required, parallel to the wire to be heated and about 2 cm from it, which allows the wire to be enclosed in a glass tube containing a protective atmosphere if required. The rod is connected to a 13.56 MHz RF power source. Heated wire lengths tested ranged from 1 mm to 70 cm, and no indication was found of an upper limit of heated length. No special tuned length of wire is required and there is no upper limit to the temperature obtainable. The temperature along the wire can be either uniform or a temperature gradient can be set up by bending the RF rod closer to or further from the wire in a local region. A simple RF safety screen of 2 cm wire mesh size was found to prevent RF emission to the operator and environment. The method is of interest in wire processing and in chemical vapour deposition of coatings on wires, including insulating coatings, etc. The alternative method of resistive heating with physical contacts may cause surface damage and sparking and does not allow optional controlled temperature gradients along the wire, nor heating at all if there is an insulating coating.

Texture generation by postdeposition annealing in a temperature gradient

A simple process for improving texture and electrical mobility of polycrystalline films is described. The technique involves annealing the film in a controlled temperature gradient and produces chainlike structures of impurity-free grains; dopants and other defects are confined to grain boundaries. The diffusion of impurities, as well as self-diffusion of the host lattice, produces a combing effect and causes grain reorientation in the annealed films. The electrical sheet conductance increases with increasing temperature gradient but attains an optimum value, above which the conductance falls due to microcracking of the film.

Preparation of thick films of (Pb,Cd)Sr2(Y,Ca)Cu2O7 using a mist pyrolysis technique

Mist pyrolysis is a relatively new innovation in the technology of ceramic processing, but the use of related spray processes is well established [1]. The mist pyrolysis technique relies on the ultrasonic atomization of a feed solution to form solute droplets of uniformly small size, usually , 1 im, which are reacted in situ to form a fully-reacted ultra-®ne powder with a narrow size distribution. The formation of a fully-reacted product at the end of a single process is the major advantage of mist pyrolysis over other spray based techniques, and was ®rst developed for the preparation of thin ®lms of metallic compounds [2]. Since its invention, the technique has been widely researched in the ®eld of electro-ceramics for both the production of powders and the deposition of ®lms [3±6]. Mist pyrolysis has been applied to the fabrication of high Tc superconductors. Single step preparation of YBa2Cu3O7-a (YBCO) and (Bi2yxPbx)Sr2Ca2Cu3O10 a (BSCCO) has been reported by either using direct mist spraying onto a hot substrate or by particulate deposition [7±14]. Direct mist spraying involves the deposition of a mist onto a heated substrate maintained at relatively low temperatures (typically 673 K). The low temperature of the substrate invariably leads to the formation of amorphous or poorly crystallized ®lms but, when annealed, fully superconducting coatings are obtained. The fabrication of ®lms by particulate deposition involves the deposition of fully-reacted sub-micrometer-sized particulates onto a substrate which, after annealing, consolidates to form a thick ®lm coating. We have designed and built a mist pyrolysis system to fabricate thick ®lms of a new high temperature superconducting material (Pb1y yCd y)Sr2(Y1yxCax)Cu2O7 a ((Pb,Cd)-1212) by both direct mist spraying and particulate deposition. The system con®gurations used to achieve ®lm deposition by both these mechanisms are shown in Fig. 1. A three zone furnace was used, allowing a controlled temperature gradient to be set up in a 500 mm hot zone. A high volume nebuliser generated mist at a controlled rate which was fed into a 50 mm SiO2 reactor tube. The design of the nebuliser allowed a known volume of reactant solution to be placed in a plastic diaphragm which was immersed in a water bath, thus preventing any solution coming into contact with the ultrasonic transducer. The sample holder was constructed from Al2O3 and was positioned in the centre of the furnace hot zone for direct mist spraying and at the far end of the furnace for particulate deposition. A powder extraction=exhaust gas ®ltering system, consisting of a ®lter, dessicant jar, ow meter and diaphragm pump, was attached to the end of the reactor tube. The ®lter arrangement consisted of a disposable glass ®bre ®lter with nominal pore size 1 im held in position on a large pore sized sintered glass ®lter by the suction of the diaphragm pump. Direct powder synthesis was accomplished by passing 0.1 M nitrate or EDTA solution directly down the furnace and trapping the reacted particles in the ®lter at the collection end. We were able to retain 99.98% of < 0:3 im-sized particles under the optimized operating conditions of T ˆ 823 K and

Large-scale DNA typing for human platelet alloantigens by PCR-PHFA (preferential homoduplex formation assay).

Alloimmunization against human platelet alloantigens (HPA) is known to be involved in disorders such as neonatal alloimmune thrombocytopenic purpura, posttransfusion purpura, and refractoriness to platelet transfusion therapy. HPA typing is essential in diagnosis and management of patients. Therefore a reliable and speedy method is necessary for HPA typing. We have successfully applied a new DNA typing method, PCR-preferential homoduplex formation assay (PHFA) method, to typing for the HPA-1, -2, -3, -4, -5 and -6 systems. This method is based on DNA strand competition during hybridization under a precisely controlled temperature gradient between a double-labelled amplicon (standard DNA), prepared from biotin- and DNP-labelled primers, and an unlabelled amplicon (sample DNA). The results obtained by PCR-PHFA typing were in good agreement with the allotypes determined by serological typing and by other DNA typing methods. The PCR-PHFA method can be easily automated, is suitable for typing both small and large numbers of samples, and thus is applicable to routine HPA typing.

Engineering Desired Grain Orientation and Boundaries Separating Adjacent Grains in Polycrystalline Thin Films

AbstractA simple process, involving a controlled temperature gradient on the surface of the substrate during the deposition of a thin film is described. This technique is similar to zone-refining but produces chains of impurity free grains. Simultaneously, dopants and other defects are confined to the grain boundaries separating two such chains. For a small temperature gradient only preferred orientation is obtained within a chain. For medium values of temperature gradient the grain boundaries within a chain are engineered to be either on a low energy coincidence site lattice (CSL) or a twin depending on the magnitude of gradient. For high magnitudes of temperature gradient, the chain is predicted to be a single crystal strip.

A controllable temperature gradient furnace for the fabrication of large grain YBCO ceramics

Large grain high temperature superconducting (HTS) materials have the potential to trap relatively large magnetic fields at liquid nitrogen temperatures (77 K), which makes them particularly attractive for a number of permanent magnet type engineering applications [1, 2]. As a result, a variety of melt processing techniques have been developed in recent years to fabricate large grain YBa2Cu307_ ~, (YBCO) ceramic which superconducts at 92 K. In general, melt processing techniques are based on the principles of semi-solid growth (solidification of a material consisting of liquid and solid [3, 4] and directional solidification (propagation of a macroscopic solidification front along specific directions [5]). The advantages of using semi-solid processes in the fabrication of electronic ceramics include the potential to (i) implement net shape processing, (ii) control the growth pattern and crystallographic orientation of individual grains, (iii) fabricate new kinds of composites and (iv) engineer the properties of the as-grown materials. YBCO is particularly well suited to growth by a melt process since it undergoes a peritectic transition at 1015°C (i.e. the solid decomposes to form a second solid phase and a liquid) [1]. Melt processedYBCO samples containing grains up to several centimetres in diameter have trapped fields in excess of 2 T at 77 K [6], which underlines the potential of this technique for the fabrication of practical HTS materials. The solidification rate in melt growth processes can be influenced significantly by the presence of a temperature gradient, which may be adjusted to facilitate heterogeneous grain nucleation along the direction of the thermal gradient. A variety of specialist techniques may be employed to generate the required gradient, including zone heating [3], infrared heating [7] and laser heating [3]. The controllability of the growth morphology of the specimen may be enhanced further by the use of either a "cold finger" or a seed crystal technique to generate a single heterogeneous nucleation site in a partially molten ceramic. This is common practice in the growth of single crystals by the Czochralski method, in particular [8]. It is important that temperature gradients used in the solidification process are both large and available over a wide temperature range if a single furnace is

Implementation and characterization of fiber Bragg gratings linearly chirped by a temperature gradient

We propose a new method for introducing a chirp on a fiber Bragg grating. Uniformly written fiber Bragg gratings are linearly chirped through the use of a controllable temperature gradient device. This device allows the linear chirp conditions to be totally adjustable in a nondestructive repeatable manner. These conditions can be selected with great precision and are very stable, once defined. To characterize the resulting chirped gratings, we have measured their dispersion. Dispersion of the order of 200 ps/nm have been obtained for 1-cm-long fiber Bragg gratings with temperature gradients near 20 degrees C.

A simple method for detecting single base substitutions and its application to HLA-DPB1 typing.

We have developed a simple and reliable method, PCR-PHFA (polymerase chain reaction dependent preferential homoduplex formation assay), for detection of single base substitutions within PCR amplicons. This technique is based upon strand competition during hybridization between a double labeled amplicon, prepared from biotin and DNP labeled primers, and an unlabeled amplicon. Under the precisely controlled temperature gradient, the preferential formation of a homoduplex over a heteroduplex occurs. After annealing, the identical sequence of the double labeled and unlabeled amplicon resulted in a low population of regenerated double labeled dsDNA due to strand exchange between them. Even when the two differed by only a single base substitution, double labeled molecule was regenerated efficiently because of preferential homoduplex formation. The regenerated double labeled molecule was captured onto a streptavidin coated microtiter plate and quantified enzymatically with a chromogenic substrate. The technique has been successfully applied in HLA-DPB1 typing. Furthermore, we detected a mutated gene even in the presence of a large excess of the corresponding normal gene.

The assessment of populations of soil-inhabiting invertebrates

Soil-inhabiting invertebrates are extremely diverse in form, differ greatly in size and numbers, and are often aggregated in horizontal and vertical distribution. Methods available for assessing populations are all based on representative samples. They include field counting, use of attractant traps or pitfall traps, and assessing numbers of invertebrates in soil samples. Invertebrates can be separated from soil either by wet or dry methods based on physical principles, or by dynamic methods which use stimuli to make them leave the samples. Physical methods of separation include hand sorting of soil, soil washing and flotation, elutriation in an upward flow of water, use of a technique which involves passing soil over plates covered with a grease film in which the invertebrates become embedded, and centrifuging soil samples in water or dense solutions so that invertebrates come to the surface. Dynamic methods suitable for most arthropods include the use of dry funnels with, high controlled temperature and moisture gradients, and wet-funnel methods which are used mainly for nematodes and echytraeid worms. Dry funnels which are easy to use are the most popular technique, but have the drawback that they do not extract eggs or resting stages. Wet funnels, which are more laborious, recover these stages, but also dead individuals. Flotation methods are best for sandy soils, whereas dry funnels are more efficient for peat or clay soils. For most soils, dry funnels are most efficient for the extraction of micro- and mesoarthropods, but flotation is usually preferable for macroarthropods.

Determination of nickel accumulation in single biological cells using porphyrinic microsensors

Carbon fiber ultramicroelectrodes modified with a conductive polymeric film of tetrakis(3-methoxy-4-hydroxyphenyl)nickel porphyrin (< 1–3 μm diameter) were used for monitoring the concentration of unbound nickel in individual BC3H-1 myocytes and H4-11-C3 rat hepatoma cells. Detection limits of 8×10 −6 M and 1×10 −6 M, respectively, were obtained. A method is described for fabricating sensors with the length and area of the electroactive surface appropriate for the dimensions of the cells under investigation. The method consists in carefully burning a fiber coated with wax in a controlled temperature gradient obtained with a microburner to sharpen the tip. The length and shape of the electroactive area obtained are controlled by the thickness of the wax coating, which is determined by the temperature of the melted wax. The sharpened tip of the 0.5–1-μm fiber was covered electrochemically with 10–90 monolayers of polymeric porphyrin, demetalated, implanted and used for nickel(II) accumulations and current determinations.

Growth of polycrystalline silicon sheet by Hoxan cast ribbon process

Polycrystalline silicon sheet for low-cost solar cells has been obtained by the Hoxan cast ribbon process which has a high growth rate. This process involves a new ribbon growth technique. The silicon sheet is formed in a mold, rather than using the capillary action of silicon in a die, by controlling temperature gradients along all three mold axes. The silicon sheet obtained had a thickness of 0.3 mm and widths of 25 mm or 100 mm. The growth rate was 200–400 mm/min; the average grain size was 2–3 mm and it had a columnar structure. Using these sheets, solar cells with efficiencies as high as 10.9% (2.5 cm×2.5 cm, AM1.5, 100 mW/cm 2) were obtained.

Dielectrophoretic transients effects on liquid stability

Effects of dielectrophoretic transients on stability ofn-pentane and methyl methacrylate have been experimentally studied. Dielectrophoretic transients have been found to demonstrate anomalous effects in methyl methacrylate. The effects are observed both on the application of electric field and its subsequent turning off to zero and are equal in magnitude and direction during both the operations. Results have been explained on the basis of the body forces acting on the dielectric in presence of a non-uniform electric field and a temperature gradient. Heater surface thermodynamics has been studied under controlled temperature and electric field gradients. A striking feature of the experiment is the application of a high voltage directly on the heater surface making the body force calculations more realistic.