Longitudinal optic phonon-plasmon coupling in delta-doped metamorphic InAlAs/InGaAs high-electron-mobility transistor structures on GaAs substrates

InAlAs/InGaAs metamorphic high-electron-mobility transistor structures with different spacer layers on GaAs substrates are characterized by Raman measurements. The influence of In0.52Al0.48As spacer thickness on longitudinal optic phonon-plasmon coupling is investigated. It is found that the intensity of GaAs-like longitudinal optic phonon, which couples with collective intersubband transitions of two-dimensional electron gas, is strongly affected by the different subband energy spacings, subband electron concentrations, and wave function distributions, which are determined by different spacer thicknesses. (C) 2001 American Institute of Physics.

New modulation structures observed in Bi2.13Sr1.87CuO6+delta superconductors

A new two-dimensional structure modulation along c- and b-axes has been discovered in superconducting single crystals of Bi2.13Sr1.87CuO6+delta (Bi2201) by x-ray scattering. Such modulation structure does not exist in non-superconducting Bi2201 single crystals, but instead lattice distortions are observed in the a-b-plane. This phenomenon may indicate that both strain relaxation and charge modulation in the a-b-plane are important to the occurrence of superconductivity in the copper oxides.

Delta-resonance effective mass in medium

Based on the relativistic chiral effective field theory, we study the effective mass of the Delta-resonance in medium by investigating the self-energy of the Delta-resonance related to the pi N decay channel in symmetric nuclear matter. We find that the effective mass of Delta-resonance decreases evidently with increasing nuclear density rho. In our calculation, we also consider the influence of the shifts of the nucleon mass, pion mass and its decay constant due to the restoration of chiral symmetry in medium. The results are roughly consistent with the data given by Lawrence Berkeley National Laboratory.

Effects of Pairing Correlations on Formation of Proton Halo in C-9

Properties for the ground state of C-9 are studied in the relativistic continuum Hartree-Bogoliubov theory with the NLSH, NLLN and TM2 effective interactions. Pairing correlations are taken into account by a density-dependent delta-force with the pairing strength for protons determined by fitting either to the experimental binding energy or to the odd-even mass difference from the five-point formula. The effects of pairing correlations on the formation of proton halo in the ground state of C-9 are examined. The halo structure is shown to be formed by the partially occupied valence proton levels p(3/2) and p(1/2).

Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C14H12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C14H12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T = 78 K and T = 390 K. The solid-liquid phase transition of the compound has been observed to be T-fus = (376.567 +/- 0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Delta(fus)H(m) = (26.273 +/- 0.013) kJ (.) mol(-1) and Delta(fus)S(m) = (69.770 +/- 0.035) J (.) K-1 (.) mol(-1). The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Delta(c)U(C14H12O, s) = -(7125.56 +/- 4.62) kJ (.) mol(-1) and Delta(c)H(m)degrees(C14H12O, s) = -(7131.76 +/- 4.62) kJ (.) mol(-1), by means of a homemade precision oxygen-bomb combustion calorimeter at T = (298.15 +/- 0.001) K. The standard molar enthalpy of formation of the compound has been derived, Delta(f)H(m)degrees (C14H12O, s) = -(92.36 +/- 0.97) kJ (.) mol(-1), from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle. (C) 2004 Elsevier Ltd. All rights reserved.

Preparation and electrical properties of new oxide ion conductors Ce6-xDyxMoO15-delta (0.0 <= x <= 1.8)

Ce6-xDyxMoO15-delta (0.0 <= x <= 1.8) were synthesized by modified sol-gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 degrees C and 800 degrees C indicated a sharp increase in conductivity for the system containing small amount of Dy2O3. The Ce5.6Dy0.4MoO15-delta detected to be the best conducting phase with the highest conductivity (sigma(t) = 8.93 x 10(-3) S cm(-1)) is higher than that of Ce5.6Sm0.4MoO15-delta (sigma(t) = 2.93 x 10(-3) S cm(-1)) at 800 degrees C, and the corresponding activation energy of Ce5.6Dy0.4MoO15-delta (0.994 eV) is lower than that of Ce5.6Sm0.4MoO15-delta (1.002 eV).

Synthesis and Electrical Properties of New Solid State Electrolyte Materials Ce6-xHoxMoO15-delta(0.0 <= x <= 1.2)

Ce6-xHoxMoO15-delta(0.0 <= x <= 1.2) was synthesized by modified sol-gel method and characterized by differential X-ray diffraction(XRD), Raman, and X-ray photoelectron spectroscopy(XPS) methods. The oxide ionic conductivity of the samples was investigated by AC impedance spectroscopy. It shows that all the samples are single phase with a cubic fluorite structure. The solid solution Ce6-xHoxMoO15-delta(x=0.6) was detected to be the best conducting phase with the highest conductivity(sigma(t)=1.05x10(-2) S/cm) at 800 degrees C and the lowest activation energy(E-a=1.09 eV). These properties suggest that this kind of material has a potential application in intermediate-low temperature solid oxide fuel cells.

Synthesis, characterization and electrical properties of solid state electrolyte materials La2-xCaxMo1.7W0.3O9-delta (0 <= x <= 0.2)

The new compounds La2-xCaxMo1.7W0.3O9-delta (0 <= x <= 0.2) in which La3+ substituted with Ca2+ were synthesized by dry-chemistry techniques based on the oxygen Ionic conductor La2Mo1.7W0.3O9. The new series were characterized by X-ray Diffraction (XRD), Raman and X-ray Photoelectron Spectroscopy (XPS) and the electrical conductivity of samples were investigated by AC impedance spectroscopy. The lattice parameters were reduced due to the smaller atomic radius of the Ca2+ compared with that of the La3+. Furthermore, Additional oxygen vacancies were introduced into La2Mo1.7W0.3O9 lattice by substitution, and then the oxygen ionic conductivity was increased. At 550 degrees C, the conductivity increased 89.9%, that is, from 0.79 x 10(-4) S center dot cm(-1) (x=0) to 1.5 X 10(-4)S center dot cm(-1) (x=0.16, 0.2).

Preparation, structure and oxide ion conductivity in Ce6-xYxMoO15-delta (x=0.1-1.4) solid solutions

The Ce6-xYxMoO15-delta solid solution with fluorite-related structure have been characterized by differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), IR, Raman, scanning electric microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The electric conductivity of samples is investigated by Ac impedance spectroscopy. An essentially pure oxide-ion conductivity of the oxygen-deficiency was observed in pure argon, oxygen and air. The highest oxygen-ion conductivity was found in Ce5.5Y0.5MoO15-delta ranging from 5.9 X 10(-5)(S cm(-1)) at 300 degrees C to 1.3 X 10(-2)(S cm(-1)) at 650 degrees C, respectively. The oxide-ion conductivities remained stable over 80 h-long test at 800 degrees C. These properties suggested that significant oxide-ionic conductivity exists in these materials at moderately elevated temperatures.

Synthesis, characterization and electrical properties of the new solid electrolyte materials Ce6-xErxMoO15-delta (0.0 < x < 1.5)

A new series of oxides, Ce6-xErxMoO15-delta (0.0 less than or equal to x less than or equal to 1.5), was synthesized using wet-chemistry techniques. The precursors and resultant oxide powders were characterized by differential thermal analysis/thermogravimetry, x-ray diffraction, and IR, Raman and x-ray photoelectron spectroscopy. The formation temperature of the powders was found to be as low as 350degreesC. Ce6-xErxMoO15-delta crystallized to a fluorite-related cubic structure. The electrical conductivity of the samples was investigated by using ac impedance spectroscopy. This showed that the presence of Er was related to the oxygen-ion conductivity, and that the highest oxygen-ion conductivity was found in Ce6-xErxMoO15-delta (x = 0.4), ranging from 5.9 x 10(-5) S cm(-1) at 300degreesC to 1.26 x 10(-2) S cm(-1) at 700degreesC, respectively. This kind of material shows a potential application in intermediate-temperature solid oxide fuel cells.

Synthesis, structure and properties of alpha-Keggin-type of K6H3[ZnW11O40Al]center dot 9.5H(2)O

A new heteropolycomplex, K6H3[ZnW11O40Al] . 9.5H(2)O was prepared and characterized by means of elemental analysis, IR, UV spectroscopy, Al-27 NMR, electrochemistry and X-ray crystallography. The crystal of K6H3[ZnW11O40Al] . 9.5H(2)O is cubic, space group Fm-3m, with lattice constants a=b=c=2. 144 8(2) nm, V = 9.866(2) nm(3), Mo radiation, R = 0.057 8 for 497 independent data with [I>2 delta(I)]. The anion is of alpha-type Keggin structure with C-s symmetry.

Molecular cloning, characterization and evolutionary analysis of phytoene desaturase (PDS) gene from Haematococcus pluvialis

Phytoene desaturase is one of the most important enzymes necessary for the biosynthesis of carotenoids in some cyanobacteria, green algae and plants. In this study, genomic DNA and cDNA of pds were cloned from unicellular green alga Haematococcus pluvialis strain323 using PCR and RT-PCR methods. The cDNA was cloned into plasmid pET-28a and efficiently expressed in Escherichia coli BL21. The complete genomic PDS gene of H. pluvialis, 3.3 kb in size, included eight exons and seven introns. To locate transcriptional regulation elements, an approximate 1 kb of 5'-flanking region was isolated by genome-walking method. Results of bioinformatic analysis showed several putative cis-elements e.g. the ABRE motif (abscisic acid responsive element), the C-repeat/DRE (dehydration responsive element) motif and the GCN4 motif were located in 5'-flanking region of pds. Results of phylogenetic analyses reveal that different sources of PDS genes form a separate clade, respectively, with 100% bootstrap support. Moreover, a maximum likelihood approach was employed to detect evidence of positive selection in the evolution of PDS genes. Results of branch-site model analysis suggest that 7.9% of sites along the green algal branch are under positive selection, and the PDS gene in green algae exhibits a different evolutionary pattern from its counterparts in cyanobacteria and plants.

delta C-13 and delta N-15 reveal significant differences in the coastal foodwebs of the seas surrounding Trinidad and Tobago

This study assessed nearshore, marine ecosystem function around Trinidad and Tobago (TT). The coastline of TT is highly complex, bordered by the Atlantic Ocean, the Caribbean Sea, the Gulf of Paria and the Columbus Channel, and subject to local terrestrial runoff and regional riverine inputs (e.g. the Orinoco and Amazon rivers). Coastal organisms can assimilate energy from allochthonous and autochthonous Sources, We assessed whether stable isotopes delta C-13 and delta N-15 Could be used to provide a rapid assessment of trophic interactions in primary consumers around the islands. Filter-feeding (bivalves and barnacles) and grazing organisms (gastropods and chitons) were collected from 40 marine sites during the wet season. The flesh of organisms was analysed for delta C-13 and delta N-15. Results indicate significant variation in primary consumers (by feeding guild and sampling zone). This variation was linked to different energy Sources being assimilated by consumers. Results suggest that offshore production is fuelling intertidal foodwebs; for example, a depleted delta C-13 signature in grazers from the Gulf of Paria, Columbus Channel and the Caribbean and Atlantic coastline of 9 Tobago indicates that carbon with an offshore origin (e.g. phytoplankton and dissolved organic matter) is more important than benthic or littoral algae (luring the wet season. Results also confirm findings from other studies indicating that much of the coastline is subject to Cultural eutrophication. This Study revealed that ecosystem function is spatially variable around the coastline of TT, This has clear implications for marine resource management, as a single management approach is unlikely to be successful at a national level.

Methods for the transfer function design of multiple narrow-band bandpass sigma-delta modulators

This paper presents the design analysis of novel tunable narrow-band bandpass sigma-delta modulators, which can achieve concurrent multiple noise-shaping for multi-tone input signals. Four different design methodologies based on the noise transfer functions of comb filters, slink filters, multi-notch filters and fractional delay comb filters are applied for the design of these multiple-band sigma-delta modulators. The latter approach utilises conventional comb filters in conjunction with FIR, or allpass IIR fractional delay filters, to deliver the desired nulls for the quantisation noise transfer function. Detailed simulation results show that FIR fractional delay comb filter-based sigma-delta modulators tune accurately to most centre frequencies, but suffer from degraded resolution at frequencies close to Nyquist. However, superior accuracies are obtained from their allpass IIR fractional delay counterpart at the expense of a slight shift in noise-shaping bands at very high frequencies. The merits and drawbacks of each technique for the various sigma-delta topologies are assessed in terms of in-band signal-to-noise ratios, accuracy of tunability and coefficient complexity for ease of implementation.