Improved Temperature Characteristics Research Articles

Substituting Both the N-Terminal and "Cord" Regions of a Xylanase from Aspergillus oryzae to Improve Its Temperature Characteristics.

To improve the temperature characteristics of AoXyn11A, a mesophilic glycoside hydrolase family (GHF) 11 xylanase from Aspergillus oryzae CICC40186, its N-terminal and "cord" regions were selected to be substituted by means of the computer-aided analysis and calculation. In brief, one mutant, named ATX11A41, possessing the lowest root-mean-square deviation (RMSD) value was designed based on the molecular dynamics (MD) simulation by substituting the N-terminal 41 amino acids of AoXyn11A with the corresponding 42 ones of pXYL11, a thermophilic GHF11 xylanase from Thermobifida fusca. On the basis of the primary structure alignment of pXYL11 with ATX11A41 (or AoXyn11A), another mutant, named ATX11A41/cord, was designed by substituting the cord region (93GTYNPGSGG101) of ATX11A41 with the corresponding one (93GTYRPTG99) of pXYL11. Both mutant-encoding genes, ATx11A41 and ATx11A41/cord, were constructed as designed theoretically by a megaprimer PCR technique and were expressed in Pichia pastoris GS115. The specific activities of recombinant (re) AoXyn11A, ATX11A41, and ATX11A41/cord were 2916.7, 2667.6, and 2457.0U/mg, respectively. The analysis of temperature characteristics displayed that the temperature optimum (Topt) of reATX11A41 or reATX11A41/cord was 65°C, which was 15°C higher than that of reAoXyn11A. The thermal inactivation half-life (t1/2) values of reATX11A41 and reATX11A41/cord at 60°C were 55 and 83min, respectively, whereas that of reAoXyn11A was only 18min at 50°C. The melting temperature (Tm) values of reAoXyn11A, reATX11A41, and reATX11A41/cord were 54.2, 66.7, and 71.9°C, respectively. In conclusion, the above findings indicated that the substitution of both the N-terminal and cord regions of a mesophilic AoXyn11A greatly contributed to its improved temperature characteristics.

Improved temperature characteristics of an Aspergillus oryzae GHF11 xylanase, by in silico design and site-directed mutagenesis

To improve the temperature characteristics of a mesophilic glycoside hydrolase family (GHF) 11 xylanase AoXyn11A from Aspergillus oryzae, both introduction of a disulfide bridge and the substitution of a specific amino acid were carried out by in silico design and site-directed mutagenesis. Based on the analysis of a known crystal structure of thermophilic xylanase TlXynA from Thermomyces lanuginosus, and the alignment of primary structures between AoXyn11A and TlXynA, one mutant AoXyn11AM with a disulfide bridge (Cys108–Cys152) was designed by replacing the Ser108 and Asn152 of AoXyn11A with Cys residues, respectively. Additionally, based on the analysis of amino acid B-factor values, another mutant AoXyn11AM-G22A was predicted by substituting Gly22 of AoXyn11AM (having the maximum B-factor value of 69.25 A, with the corresponding Ala23 of TlXynA. Thereafter, two mutant xylanase-encoding genes, Aoxyn11AM and Aoxyn11AM-G22A, were constructed by site-directed mutagenesis. Aoxyn11A and two mutant genes were expressed in E. coli BL21(DE3) respectively, and three expressed recombinant xylanases, reAoXyn11A, reAoXyn11AM and reAoXyn11AM-G22A, were purified to homogeneity. The temperature optima of reAoXyn11AM and reAoXyn11AM-G22A were 60 and 65°C, respectively, being 5 and 10°C higher than that of reAoXyn11A. Their thermal inactivation half-lives at 50°C were 1.8- and 8.4-folds longer than that of reAoXyn11A. There were no obvious alterations after mutations in specific activity and enzymatic properties, except for the temperature characteristics.

Improved temperature characteristics of highly stacked InGaAs/GaAs quantum dot lasers

AbstractUp to 24‐stacked‐layer In0.4Ga0.6As/GaAs quantum dot laser diodes were fabricated using ultrahigh‐rate molecular beam epitaxy. The operation of these devices was investigated between 298 and 353 K. The characteristic temperatures for the threshold currents improved from 72 K to 80 K with an increase in the stacking number from 12 to 19. The gain curves were also evaluated at 298 K for laser diodes with various cavity lengths. The obtained saturated modal gain increased with increasing stacking number. The laser diode with a stacking number of 24 exhibited the highest saturated modal gain at 155 cm‐1. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

830-nm AlGaAs-InGaAs Graded Index Double Barrier Separate Confinement Heterostructures Laser Diodes With Improved Temperature and Divergence Characteristics

The 830-nm AlGaAs/InGaAs laser diodes (LDs) adopting multistep-graded index double-barrier separate confinement heterostructures (GRIN-DBSCHs) with small divergence beams and improved temperature characteristics under a high-output-power operation are reported. The double-barrier separate confinement heterostructure (DBSCH) design provides good carrier confinement and prevents current leakage by adding a multistep grading layer between cladding and waveguide layers. Simultaneously, the DBSCH design can facilitate reducing the divergence angle at high-power operation and widening the transverse mode distribution to decrease the power density around emission facets. In addition, the p-side doping depth is optimized to effectively raise the barrier height for reducing the electron overflow. Gaussian-like narrow far-field patterns are measured with the full-width at half-maximum vertical divergence angle to be between 11° and 13°. A threshold current of 16.5 mA and a slop efficiency of 0.98 W/A are obtained in the continuous-wave operation condition at room temperature. The maxima optical power densities of 21.5 MW/cm2 per laser facet and good characteristic temperature values of threshold current (T0) and slope efficiency (T1) are achieved.

Improved temperature characteristics of single-wall carbon nanotube single electron transistors using carboxymethylcellulose dispersant

Single-wall carbon nanotube (SWNT) based single electron transistors were fabricated by the dispersion method using carboxymethylcellulose (CMC) as a dispersant to make SWNT suspension. The temperature characteristics were improved compared to the one fabricated with a Triton X-100/water SWNT suspension, so that the regular Coulomb oscillations were observed up to 80K. This could be due to the increased barrier height, which may be originated from extra dipoles induced by the adsorbed CMC molecules at the SWNT/metal interface.

Piezoelectric vibrator ladder-type filter using piezoeletric vibrator and double-mode piezolectric filter

A piezoelectric vibrator which uses lithium tantalate as a piezoelectric material and of which main vibration is thickness shear vibration. The thickness direction of the vibrator forms angle of 0°±5° to the X-axis of a single crystal. The longitudinal direction of vibrator lies, with the X-axis used as a rotation axis, in direction n +57°±2° clockwise from the Y-axis of the single crystal. A ratio L/H of the length L of the vibrator to the thickness H is not less than 15. A ratio Le/H of the length Le of the exciting electrode to the thickness H of the vibrator element portion is 3–6. Accordingly, a vibrator having improved temperature characteristics and a large Q is realized.

Improved performance of 1.3 µm InGaAsP–InP lasers with an AlInAs electron stopper layer

We have fabricated 1.3 µm InGaAsP–InP strained-layer multi-quantum-well (MQW) lasers with an AlInAs electron stopper layer (ESL). The ESL was inserted between the MQW active layer and the p-side separate confinement heterostructure (SCH) layer to suppress electron leakage in the conduction band from the active region to the p-cladding layer. Lasers with an ESL exhibited much improved temperature characteristics of threshold current and external slope efficiency. As a result, a lower power penalty of 2.2 dB from 25 °C to 85 °C was achieved at an injected current of 60 mA. The insertion of an AlInAs ESL into the SCH layer is a successful way to realize the uncooled operation of 1.3 µm InGaAsP–InP lasers at high temperatures.

Improved temperature characteristics of laser diodes with nonidentical multiple quantum wells due to temperature-induced carrier redistribution

Laser diodes with nonidentical multiple quantum wells could have the lasing wavelength very insensitive to temperature variation. For temperature varying from 33 to 260 K, the lasing energy changes less than 5 meV, while the band gap energy changes more than 50 meV. The origin is due to the strongly temperature-dependent Fermi–Dirac distribution, which favors carriers in high-energy states at large temperature. The temperature-induced carrier redistribution could even cause negative characteristic temperature for a certain temperature range because the low-energy quantum wells behave like reservoirs to overcome the detrimental influence of temperature.

GaInNAs microspheres for wavelength division multiplexing

The GaInNAs range of compounds is suitable for optoelectronic device applications in 1.3 and 1.55 µm lasers, because of the large conduction band discontinuity resulting in good electron confinement and improved temperature characteristics. GaInNAs is suited to wavelength division multiplexing (WDM) applications in high-speed optical communication networks. Since WDM techniques are available for steady-state traffic, there is a need for an all-optical packet-switching layer at the end of the optical to electronic conversion domain, which consists of all-optical gates, such as semiconductor optical amplifiers, channel dropping filters, interferometers, resonant cavity enhanced photodetectors, and optical random access memory elements. In these planar lightwave circuits, GaInNAs microspheres with their morphology-dependent resonances, can be used as compact optical filtering elements. The spectral filtering characteristics of GaInNAs microspheres are analysed by calculating the elastic scattering spectra optimised for both transverse electric and transverse magnetic resonance modes at the optical communication wavelengths of 1.3 and 1.55 µm.

Lattice Mismatched LPE Growth of InGaP on Patterned InP Substrate

The performance enhancement of the semiconductor laser for 1.3μm optical communications has been required. But lasing characteristics in the high-temperature operation are poor for the present InGaAsP/InP double-heterostructure (DH) lasers. As a means for solving it, 1.3μm-wavelength InGaAs/InGaP DH lasers with improved temperature characteristics which reduced the leakage current by greatly taking the bandgap difference of cladding layer and active layer is presented. The epitaxial lateral overgrowth (ELO) technique in which growth of the crystal with the large lattice constant difference is possible is very attractive. As a first step of realizing 1.3μm InGaAs/InGaP DH lasers, liquid phase epitaxial growth of the In0.8Ga0.2P (λ=820nm) cladding layer (1.4% lattice mismatched to the InP(100) substrate) was carried out by using the ELO technique.

Lattice Mismatched LPE Growth of InGaP on Patterned InP Substrate

The performance enhancement of the semiconductor laser for 1.3μm optical communications has been required. But lasing characteristics in the high-temperature operation are poor for the present InGaAsP/InP double-heterostructure (DH) lasers. As a means for solving it, 1.3μm-wavelength InGaAs/InGaP DH lasers with improved temperature characteristics which reduced the leakage current by greatly taking the bandgap difference of cladding layer and active layer is presented. The epitaxial lateral overgrowth (ELO) technique in which growth of the crystal with the large lattice constant difference is possible is very attractive. As a first step of realizing 1.3μm InGaAs/InGaP DH lasers, liquid phase epitaxial growth of the In 0.8 Ga 0.2 P (λ=820nm) cladding layer (1.4% lattice mismatched to the InP(100) substrate) was carried out by using the ELO technique.

Improved temperature characteristics of 1.55 [micro sign]m InAlGaAs quantum well lasers with multiquantum barrier at p-cladding layer

A multiquantum barrier and graded-index separate confinement heterostructure are employed in a 1.55 µm InAlGaAs multiquantum well laser to reduce the threshold current and temperature sensitivity. A characteristic temperature as high as 77 K is measured between 25 and 75°C for as-cleaved 1000 µm-long uncoated devices. The degradation of slope efficiency in the same temperature range is less than 30%.

1.5 [micro sign]m InGaAlAs-strained MQW ridge-waveguide laser diodes with hot-carrier injection suppression structure

The authors have developed a ridge-waveguide laser diode (LD) with a layer structure which suppresses hot-carrier injection into separate confinement heterostructure layers as well as effectively confining carriers in the multiquantum well layers. Fabricated LDs show low threshold currents and improved temperature characteristics due to a decrease in the leakage current outside the ridge-waveguide caused by reduced carrier diffusion length.

High-power near-resonant 1.55 μm emitting InGaAsP/InP antiguided diode laser arrays

We present high peak-pulsed coherent power results from large-aperture, 1.55 μm antiguided laser arrays. The InP-based devices have a compressively strained InGaAsP double-quantum-well active region and are fabricated by two-step self-aligned metalorganic chemical vapor deposition. We have obtained 2.5 W front-facet peak power in a 2.6° wide beam [6×diffraction limit (D.L.)], with 1.2 W in the central lobe, from 40-element, 250 μm aperture devices. The width of the central lobe remains constant from 4 to 15×threshold. Devices with improved temperature characteristics and of geometry closer to the resonance condition provide 1 W peak power in a beam 1.2° wide (2.7×D.L.), with 61% of the energy in the central lobe; and 1.75 W peak power in a 1.5° wide beam (3.5×D.L.) at heatsink temperatures between 15 and 45 °C.

Piezoelectric enzyme sensor with improved temperature characteristics for determining urea in urine

Based on the conductivity change produced by the urea/urease reaction, a piezoelectric enzyme sensor is applied to the detection of urea in urine. The influence of the variation in solution temperature on frequency measurement is greatly reduced by using a buffer giving solution conditions with a near-zero frequency temperature coefficient for the sensor. The sum of the frequency shifts over the reaction time was used to increase the sensitivity of the determination. The linear range of the method is 1–30 μg/ml for urea, with RSDs of 1–2.6%. The detection limit is 0.01 μg/ml.

Infrared laser (λ=3.2 μm) based on broken-gap type II heterojunctions with improved temperature characteristics

Laser structures based on broken-gap type II p-GaInAsSb/n-InGaAsSb heterojunctions in the active region are proposed and studied. Lasing at 3.2–3.4 μm has been obtained in the temperature range 77–195 K with a threshold current density of 400 A/cm2 at 77 K and a characteristic temperature T0=47 K.

Optical current transducer with bulk type Bi12SiO20 faraday sensor for power systems

Two types of optical current transducers (OCTs) have a bulk Faraday sensor inserted into the gap of an iron core and a porcelain insulator with optical fiber. The sensor consists of Bi12SiO20 (BSO) single crystal, a polarizer, and an analyzer. The OCTs satisfied the target performance requirement for fault location and metering and demonstrated maintained performance at some power utilities in Japan and the US. We have developed a fault location system that immediately detects the fault current with the OCTs, there by locating the fault section. The OCT can easily replace the existing support insulators for the disconnecting switch without any modifications to structure height or bus-bar. For metering requiring 0.3% class accuracy, use of a BSO with right optical rotatory power combined with BSO with left optical rotatory power results in a Faraday sensor with improved temperature characteristics. The OCT demonstrated 0.3% class accuracy for metering described in the current transformer Specifications of IEEE C57–13, 1993.

Two-step annealed polycrystalline silicon thin-film transistors

The performance of polysilicon thin-film transistors fabricated by two-step annealing, which consists of furnace annealing and the subsequent excimer laser annealing, is described. It was found that the average grain size of low-temperature furnace-annealed polysilicon films was several times larger than that of excimer-laser-annealed polysilicon films while the density of in-grain defect of low-temperature furnace-annealed films was much higher than that of excimer-laser-annealed film. However, the device characteristics of the low-temperature furnace-annealed polysilicon thin-film transistors were improved significantly by postannealing, such as high-temperature furnace annealing and excimer laser annealing, due to the effective elimination of in-grain defects. We found that the significantly improved temperature characteristics of drain current and hydrogen passivation rate of two-step annealed polysilicon thin-film transistors were also caused by the significantly reduced in-grain defects by postannealing. The density of trap states, which was extracted from the transfer curves of polysilicon thin-film transistors, was used to demonstrate the effects of modifying the deep and tail trap levels by two-step annealing.

Glass pH electrodes with improved temperature characteristics. Part 2. Systems with conventional inner reference electrodes

Glass electrodes with internal filling solutions containing zwitterionic buffers are shown to have standard potentials that vary linearly with temperature over a wide range (at least 5–50 °C). This reduces the errors of temperature compensation compared with the proprietary electrodes currently available. A judicious choice of buffer and inner reference element yields an electrode with almost the ideal characteristics of isopotential pH (=7) and zero-point pH (=7), which enable it to be used with all pH meters. Other electrodes could readily be used with modern microprocessor-based meters. In other aspects of their performance (slope factor, hysteresis, response time) the new electrodes are at least as good as commercial sensors.

Glass pH electrodes with improved temperature characteristics: use of a low-impedance pH sensor as the inner reference electrode

Glass electrodes are generally preferred to the various types of low-impedance pH electrodes, despite their greater susceptibility to electrical noise and need for a better grade of electronics. This preference arises from the reversibility of the glass electrode and its freedom from interference by redox and complexing agents, with the result that it has an ideal (Nernstian) response over a wide pH range. pH meters apply a linear correction for changes in temperature, but for most electrodes this is a good approximation only over a range of ±10 °C, because of the properties of the solution inside the glass electrode. By use of a low-impedance pH electrode in controlled (interference-free) conditions inside the glass electrode, it was hoped to eliminate the variation of the internal pH as a factor in temperature compensation. A preliminary assessment of various candidate electrodes indicated that the mercury-mercury(II) oxide electrode was the best choice. Glass electrodes with Hg-HgO inner electrodes had good general characteristics, i.e., their slope factors and standard potentials agreed with theory, and their temperature characteristics were better than those of some commercial pH electrodes, being linear from 10 to 50 °C. Deviation from linearity was, however, observed at lower temperatures. Because of the limitations of many pH meters, it is desirable that electrodes have the characteristic that both the isopotential pH (pHiso) and the pH at which the e.m.f. of the cell is zero (pH°)= 7, i.e., the e.m.f. at pH 7 is 0 mV at all temperatures. With the Hg-HgO inner electrode, however, pHiso= 3.8 and pH°= 11.3.