bluuebunny/crossref_metadata_2025 huggingface dataset:
Immobilization of Zirconocene into Silica Prepared by Non‐Hydrolytic Sol‐Gel Method
Authors: Fisch Adriano , Petry Cristiane F. , Pozebon Dirce , Stedile Fernanda C. , Cardozo Nilo S. M. , Secchi Argimiro R. , dos Santos João H. Z.
Published: February 2007

Concomitant immobilization of zirconocene (Cp2ZrCl2) into a silica matrix was performed during the SiO2 synthesis through non‐hydrolytic sol‐gel method. Two different routes, varying the SiCl4:Si(OEt)4 ratio were evaluated in terms of zirconocene content and catalyst activity in ethylene polymerization, using methylaluminoxane (MAO) as cocatalyst. The catalysts were characterized by Rutherford backscattering spectrometry, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy and X‐ray dispersive spectroscopy. The zirconocene content laid between 0.60 and 1.02 wt.% Zr/SiO2, depending upon the components ratio employed in the sol‐gel synthesis. Catalyst grains presented of irregular shape (20–100 µm size) and zirconocene distribution was not uniform. Both routes led to supported catalysts active in ethylene polymerization. Catalyst activity was intermediate between that exhibited by the homogeneous and the grafted zirconocene on silica. Resulting polyethylenes presented narrow molecular weight distribution and molecular weight slightly higher than that observed in the case of polymer produced with the homogeneous system.
Modification of Model Ethylene‐Butene Copolymers Using Gamma Radiation and an Organic Peroxide
Authors: Andreucetti Noemí , Pérez Javier , Failla Marcelo , Vallés Enrique
Published: February 2007

Well‐characterized linear ethylene‐butene copolymers with polydispersities lower than 1.1 were modified using gamma radiation and an organic peroxide with the purpose of assessing the relative importance and form of evolution of the chain‐linking processes with these two methods. The copolymers used in this work were obtained by hydrogenation of polybutadienes, which were synthesized by anionic polymerization of butadiene. Part of these materials were irradiated by gamma rays in a 60Co radiation facility and the rest was modified with 2,5‐dimethyl‐2,5 di(terbutyl peroxy)‐hexane in the molten state. As expected, the critical radiation dose and the critical concentration of peroxide required for the onset of gelation decreases with average molecular weight of the original copolymer. Although, the chain‐linking reactions govern the modification process, there is a fraction of molecular chains that suffers scission. The measurable fraction of molecules having molecular weights lower than the original quasi‐monodisperse copolymers is, for both processes, about 5% of the total modified polymer. On the post‐gel region, the gel amount increases continuously with the radiation dose and the peroxide concentration added to the copolymers. For the radiation modified polymers, the calculation of the evolution of the molecular weights assuming ideal network forming conditions agreed very well with the experiments both, before and after the gel point. This is not accomplished when the modification process is done with the use of peroxides. Also, the results obtained from the peroxide modification processes at low relative concentrations with respect to the critical one for gelation show that the evolution of the structural modification evolves at a considerable lower rate than that observed in the radiation results.
Thermal Properties of Nanostructured Poly(acrylonitrile)–Silica Materials
Authors: Ruzimuradov Olim , Rajan Guru , Mark James
Published: February 2007

This report describes the thermal properties of nanostructured poly(acrylonitrile)–silica materials having potential as chromatography sorbents. Thermal analysis of nanostructured materials obtained by simultaneously polymerization of acrylonitrile and hydrolytical polycondensation of tetraethoxysilane are showed the presence of two exothermic peaks in the thermogramms of the poly(acrylonitrile)–silica materials.
Synthetic Paper from Plastic Waste: The Effect of CaCO3 on Physical, Surface Properties and Printability
Authors: Corrêa Ana Carolina , de Santi Cristiano Ribeiro , Manrich Sati
Published: February 2007

This article is a description of recent work in the development of composite sheet materials from blends of recycled high‐impact polystyrene (HIPS) and high‐density polyethylene (HDPE), with a view to using them as synthetic paper for the printing trade. Four monolayer films of differing composition were characterized in terms of their physical and surface properties. They were further evaluated compared with each other and with commercial synthetic and cellulose papers, to discover relationships between CaCO3 filler loadings, film structure and properties that could lead to improvements. In terms of their whiteness and water base inks printing properties, these sheets were generally inferior to the cellulose and synthetic papers. Notwithstanding this, in some tests they showed superior quality; thus, in offset printing, the high surface gloss, probably due to the HIPS content, made the colors brighter in some mono‐oriented film samples.
Crosslink Density of Peroxide Cured TPV
Authors: Vennemann Norbert , Bökamp Klaus , Bröker Dirk
Published: February 2007

EPDM/PP model compounds were dynamically vulcanized by use of varying amounts of an organic peroxide and a trifunctional methacrylate to produce thermoplastic vulcanizates (TPV) materials with different properties. Tensile strength and ultimate elongation as well as compression set data of these materials are comparable to existing commercial TPV products. Although, crosslinking of the elastomer phase is the most important step during the production process, there is a lack of suitable test methods until now to determine the cross link density precisely. Therefore, a new test method, Temperature Scanning Stress Relaxation (TSSR) was examined to determine the crosslink density of the EPDM – phase. The results are in good agreement with results obtained from conventional swell measurements. The advantages of TSSR measurements over swell measurements are quite obvious. Whereas swelling measurements are very time consuming, TSSR tests are much easier and faster to perform. Additionally, information about the relaxation behavior and degradation of the PP ‐ phase was obtained from TSSR measurements.
Non‐heme iron through the three domains of life
Authors: Andreini Claudia , Banci Lucia , Bertini Ivano , Elmi Sara , Rosato Antonio
Published: February 2007

Metalloproteins are proteins capable of binding one or more metal ions, which are often required for their biological function or for regulation of their activities or for structural purposes. In high‐throughput genome‐level protein investigation efforts, such as Structural Genomics, the systematic experimental characterization of metal‐binding properties (i.e. the investigation of the metalloproteome) is not always pursued, and remains far from trivial. In the present work we have applied a bioinformatic approach to investigate the occurrence of (putative) non‐heme iron‐binding proteins in 57 different organisms spanning the entire tree of life. It is found that the non‐heme iron‐proteome constitutes between 1% and 10% of the entire proteome of an organism. However, the iron‐proteome constitutes a higher fraction of the proteome in archaea (on average 7.1% ± 2.1%) than in bacteria (3.9% ± 1.6%) and in eukaryota (1.1% ± 0.4%). The analysis of the function of each putative iron‐protein identified suggests that extant organisms have inherited the large majority of their iron‐proteome from the last common ancestor. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Influence of cation mismatch on electrical, magnetic and magnetoresistance properties of Pr0.67A0.33MnO3manganites
Authors: Venkataiah G. , Venugopal Reddy P.
Published: February 2007

With a view to investigate the influence of A‐site cation mismatch on electrical, magnetic and magnetoresistance properties of Pr0.67A0.33MnO3, (A = Ca, Sr, Pb and Ba) manganites, a systematic investigation has been undertaken by preparing the materials using citrate gel route. The samples were characterized by X‐ray diffraction (XRD) and scanning electron microscopy. The XRD data were analyzed by Rietveld refinement method, while the crystallite sizes were estimated using the peak broadening technique. The unusual behavior of large magnetoresistance at low temperatures and at high magnetic fields has also been investigated. Finally, the high temperature electrical resistivity data were analyzed using variable range hopping and small polaron conduction mechanisms. A systematic investigation of the influence of average ionic radius of the A‐site (〈rA〉) and cation mismatch (σ2) on electrical and magnetic properties, viz., transition temperatures, density of states at Fermi level, polaron activation energies etc., has been undertaken. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrically driven quantum dot single photon source
Authors: Lochmann A. , Stock E. , Schulz O. , Hopfer F. , Bimberg D. , Haisler V. A. , Toropov A. I. , Bakarov A. K. , Scholz M. , Büttner S. , Benson O.
Published: February 2007

We report on a miniature solid state emitter structure, which allows electrical pumping of only one single InAs quantum dot (QD) grown in the Stranski‐Krastanow mode. The emitter demonstrates a strongly monochromatic polarized emission of a single QD exciton. Correlation measurements of the emitted photons show a clear antibunching behavior. The structure is thus attractive for practical implementation as effective single photon source for quantum cryptography. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical Landau state mapping with in‐plane electric fields
Authors: Karmakar Biswajit , Schardt Michael , Malzer Stefan , Arora Brij. M. , Döhler Gottfried H.
Published: February 2007

We report on a theoretical and experimental investigation of magneto‐absorption in quantum wells (QWs) in the presence of a uniform in‐plane electric field. From a simple theoretical model a linear real‐space shift of the electron Landau level wave functions relative to the hole counterparts is expected under increasing in‐plane electric field. As a result, quadratic Stark shifts, fading of the zero‐field allowed transitions, and increasing oscillator strength for the originally forbidden transitions are predicted. These predictions are confirmed by experiments on GaAs/AlGaAs‐QWs and found to be in reasonably good agreement with simulations based on a simple model. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy gap and bond lengths of AlxGayIn1–x –yN, AlxGayIn1–x –yP and AlxGayIn1–x –yAs quaternary alloys
Authors: Marques M. , Teles L. K. , Ferreira L. G. , Scolfaro L. M. R. , Furthmüller J. , Bechstedt F.
Published: February 2007

We use the Generalized Quasi‐Chemical Approach (GQCA) combined with ab initio ultrasoft pseudopotential calculations within density functional theory in order to obtain the structural and electronic properties of Alx Gay In1–x –y X (X = As, P or N) quaternary alloys in the zincblende structure. Results for the bond lengths show that their variations with composition are approximately linear and that they do not deviate much from the values of the corresponding binary compounds. For the variation of the band gaps, we obtain a bowing parameter b = 0.26 eV for the (Ga0.47In0.53As)z (Al0.48In0.52As)1–z quaternary alloy lattice matched to InP, in very good agreement with experimental data. In the case of AlGaInN, a bowing parameter of 0.22 eV is obtained for zincblende AlGaInN lattice matched to GaN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Omni‐directional gap of 1‐D photonic crystals based on porous silicon with a Gaussian profile refractive index
Authors: Arriaga J.
Published: February 2007

Using the transfer matrix method we calculate the omni‐directional band gap of a 1‐D photonic crystal consisting of alternating layers of two dielectric materials A and B with refractive index nA and nB, respectively. The refractive index of layer A is constant and the refractive index of layer B varies according to the envelope of a Gaussian function. We find that under certain circumstances it is possible to obtain 100% reflectivity for both polarizations and any value of the incident angle of the electromagnetic waves. Although the structure considered does not posses a higher omni‐directional band gap than the periodic sequence of low and high constant refractive indexes, it can be used to produce a new type of omni‐directional mirrors without abrupt interfaces. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetries and couplings in double quantum dot molecule
Authors: Bahamon D. A. , Camacho A.
Published: February 2007

Electronic transport through a quantum dot molecule attached to leads has been very successfully studied finding very interesting effects like Fano and Kondo. In particular, the symmetry in quantum dot molecules going from the parallel to series coupling seems to play a very interesting role showing very different density of states spectra, these results have been obtained by fixing the interdot coupling equal to the coupling to the leads. In this work we go a step further by changing the value of the interdot coupling and the addition of on‐site Coulomb interaction with the help of Slave Boson Mean Field theory (SBMFT), Keldysh non equilibrium Green function technique and the equation of motion approach the density of states and the conductance of this system are calculated and analyzed in the Kondo regime. We also studied the asymmetric molecule set up of dots of different size in order to analyze the density of states and the Fano interference in an anticrossing region. Comparison of the results taking into account the Coulomb interaction is presented, which gives rise to the appearance of the Kondo effect in these systems. We also studied the interplay between the Kondo and Fano effects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitonic effects in nonlinear optical rectification in small semi‐parabolic quantum dots
Authors: Baskoutas S. , Paspalakis E. , Terzis A. F.
Published: February 2007

We study the effects of excitons in nonlinear optical rectification in one‐dimensional semi‐parabolic quantum dots. We consider the case that the electron and the hole are confined in semi‐parabolic potential with the same oscillator frequency. We present approximate analytical results in the strong confinement regime and find a closed‐form relation between the nonlinear optical rectification coefficient of an exciton in the structure and the corresponding coefficient when only one electron exists in the structure. These results are also verified by numerical calculations performed with the potential morphing method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physical properties of quantum‐confined europium sulfide nanocrystals
Authors: Redígolo M. L. , Koktysh D. S. , Rosenthal S. J. , Dickerson J. H.
Published: February 2007

We report the synthesis and the characterization of quantum‐confined europium sulphide nanocrystals, which possess intriguing size‐dependent optical and magnetic properties. Transmission electron microscopy, X‐ray diffraction spectroscopy, and SQUID magnetization measurements provide evidence for the quantum‐confinement effects in this monochalcogenide nanomaterial. Photoluminescence measurements indicate a blue‐shifted spectrum for the nanocrystals compared with bulk europium sulphide. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ground state properties of zinc‐blende and wurtzite phases of MgS
Authors: Duman S. , Baǧcı S. , Tütüncü H. M. , Srivastava G. P.
Published: February 2007

We present an ab initio pseudopotential study, within the generalised gradient approximation, of the structural and electronic properties of zinc‐blende and wurtzite phases of MgS. The calculated structural parameters are in good agreement with previous experimental and theoretical results. Using the density‐functional perturbation theory, the phonon spectrum and density of states for the two phases have also been calculated. The calculated phonon modes for the zinc‐blende phase compare very well with a Raman scattering data at the zone‐centre. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ground state configurations of vertically coupled quantum rings
Authors: Castelano L. K. , Hai G.‐Q. , Partoens B. , Peeters F. M.
Published: February 2007

The ground states of two vertically coupled quantum rings are studied within the spin density functional theory for systems containing up to 13 electrons. Quantum tunneling effects on the electronic structure of the coupled rings are analyzed. New ground state configurations are found showing the formation of new diatomic artificial ring molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time‐resolved photoluminescence and steady‐state optical studies of GaInNAs and GaInAs single quantum wells
Authors: Sun Y. , Lombez L. , Braun P. F. , Ulug B. , Ulug A. , Yilmaz M. , Balkan N. , Marie X. , Carrere H. , Arnoult A.
Published: February 2007

Time‐resolved photoluminescence spectroscopy is used to investigate carrier dynamics of Ga1–xInxNyAs1–y (x ∼ 0.33, y ∼ 0.01) single quantum well (QW) structures. PL spectra measured as a function of temperature together with the PL decay times at wavelengths around and below the PL peak energy are used to determine de‐trapping activation energies and time constants. The results are interpreted in terms of simultaneous thermal excitation of deep localized excitons to shallow localized states. According to the model, with increasing temperatures, localized excitons gain enough thermal energy to populate the free exciton states in quantum well with shorter lifetimes due to coherent nature of free excitons. In addition, at temperatures around and above 80 K, more non‐radiative channels become available to compete with the radiative processes leading to shorter time constants. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin polarised properties of optically injected VCSELs
Authors: Homayounfar A. , Adams M. J.
Published: February 2007

The effects of external optical injection taking account of polarisation and electron spin dynamics in vertical‐cavity surface‐emitting lasers at values of pumping close to threshold are discussed. The stability map inside and outside the locking bandwidth is given in terms of elliptical and linear polarised phenomena. Finally quasi‐periodicity in terms of two carrier densities and polarised fields is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of pH on the formation of host‐guest type material: zinc‐aluminium‐layered double hydroxide‐4‐chlorophenoxy acetate nanocomposite
Authors: Zobir Hussein Mohd , Halimah Sarijo Siti , Hj Yahaya Asmah , Zainal Zulkarnain
Published: February 2007

Layered organic‐inorganic hybrid nanocomposite material containing 4‐chlorophenoxy acetate (4‐CPA) in an inorganic interlayer was prepared using 4‐CPA as guest anion in Zn‐Al layered double hydroxide inorganic host by direct precipitation method at various pHs. A well‐ordered nanolayered organic‐inorganic hybrid nanocomposite, with the expansion of the basal spacing from 8.9 Å in the layered double hydroxide to 19.5‐20.1 Å were obtained. The nanocomposites show that they are of mesoporous‐type with the percentage of 4‐CPA intercalated of around 35–39% (w/w) and the Zn to Al molar ratio of 3.5‐4.0. Generally, as the pH of the mother liquor increased, the Zn to Al molar ratio in the resulting nanocomposites is also increased, but the percentage of 4‐CPA intercalated and the BET surface area, decreased. This shows that the pH of the mother liquor plays an important role in determining the resulting physicochemical properties of the synthesized materials. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interplay of acoustic phonons and Overhauser interaction in spin blockade removal in double quantum dots
Authors: Iñarrea Jesús , Platero Gloria , MacDonald Allan H.
Published: February 2007

The electronandnuclei spindynamics andtheir interplaydue tothe Hyperfine interactionare self‐consistently analyzed within the framework of the density matrix formalism. Our results indicate that the current leakage experimentally observed in the spin‐blockade region of the current‐voltage curve, occurs due to spin‐flip processes induced by hyperfine interaction. A microscopical model for this interaction is presented. Our model includes a self‐consistent description of inelastic transitions where the energy is exchanged through interactions with acoustic phonons in the environment. We show as well how a magnetic field applied parallel to the current allows excited states to participate in the electronic current and removes spin blockade. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic structures of finite double‐walled carbon nanotubes
Authors: Lee C. H. , Ho Y. H. , Chen R. B. , Li T. S. , Lin M. F.
Published: February 2007

Electronic properties of finite double‐walled carbon nanotubes are calculated in the tight‐binding model. Energy levels, energy gap, and the density of states strongly depend on the symmetry configurations, the nanotube length, and the transverse electric field. The intertube interactions change the level spacing, modify the energy gap, and destroy state symmetry about the Fermi level. The transverse electric field induces state crossing, destruction of state degeneracy, increase of low‐energy states, and strong modulation of energy gap. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Golden rules for coherent transport relaxation rates in semiconductor superlattices in the field‐induced localization regime
Authors: Minot Christophe
Published: February 2007

Coherence decay rates are derived from first principles in electronic systems the quantum states of which are localized by an electric field. The decay rates are written down as golden rules in which the transition matrix elements and the energy conservation relations involve different quantum states. A numerical evaluation is carried out in GaAs/Al0.3Ga0.7As superlattices for the electron‐LO phonon interaction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical and dielectric studies on nanoparticles and atomically‐engineered surfaces of superparaelectric SrTiO3
Authors: Mochizuki Shosuke , Fujishiro Fumito
Published: February 2007

In order to find useful surface properties of SrTiO3 (STO) crystal, the photoluminescence and dielectric properties of STO nanoparticles and STO bulk single crystal with nanometer steps have been measured at different temperatures. The obtained results are compared with those obtained for STO bulk single crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoreflectance and contactless electroreflectance of an InAs quantum dash laser structure
Authors: Motyka M. , Rudno‐Rudziński W. , Sęk G. , Kudrawiec R. , Misiewicz J. , Somers A. , Schwertberger R. , Reithmaier J. P. , Forchel A.
Published: February 2007

Photoreflectance (PR) and contactless electroreflectance (CER) spectroscopies have been used to study optical transitions in an InP‐based laser structure emitted at 1.55 μm with the active region including InAs quantum dashes (QDashes). Optical transitions related to all relevant parts of the structure, i.e. In0.53Ga0.05Al0.42As n‐ and p‐type cladding layers, quaternary In0.53Ga0.23Al0.24As QDash barrier layers, InGaAlAs‐GRINSCH region, and InAs QDashes have been clearly observed at room temperature. Moreover, it has been found that some of the transitions are not observable in CER spectra whereas they are very strong in PR spectra. This phenomenon is associated with different modulation mechanisms in the two electromodulation techniques. It means that the combination of PR and CER techniques with traditional photoluminescence measurements allows much better characterization of the electronic structure for semiconductor devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MBE growth of vertically ordered Ge quantum dots on Si
Authors: Nikiforov A. I. , Ulyanov V. V. , Teys S. A. , Gutakovsky A. K. , Pchelyakov O. P. , Yakimov A. I. , Fonseca A. , Leitão J. P. , Sobolev N. A.
Published: February 2007

The in plane lattice constant of the silicon film on germanium is shown to alter as the film grows; the changes reflect the process of strains relaxation of that result from the misfit of the Ge and Si lattice constants. The thickness allowing detection of changes in the in plane lattice constant of the Si film during the growth on the Ge surface depends on the germanium layer thickness. The thickness of the silicon film where elastic relaxation is determined as dependent on the germanium layer thickness. TEM studies indicate the vertical ordering of the germanium island layers when the thickness of the Si layer in between Ge layers is not sufficient to provide the full strain relaxation. The vertical ordering of Ge islands in the multilayer structure results in a decrease in the island density at reduced dispersion of their shape and size. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin polarized and degenerate tunneling spectra in intrinsic Josephson junctions of Bi2212
Authors: Ozdemir M. , Ozyuzer L. , Kurter C.
Published: February 2007

Tunneling characteristics of HgBr2 intercalated superconducting Bi2212 single crystals have been obtained by using 10 x 10 mm2 intrinsic Josephson junction stacks, so called mesa structures. The spin degenerate current is driven along the c‐axis with Au layer using point contact tunneling assembly at 4.2 K. The spin polarized current is also driven along the c‐axis of crystals with Au/Co/Au multilayer. In order to understand the role of ferromagnetic layer (Co), quasiparticle branches are examined with and without magnetic field. The magnetic field evolution of switching currents are obtained for gaining further insight about the spin injection through the stack. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of carbon produced by methane pulsed discharge
Authors: Musa Geavit , Ekem Naci , Akan Tamer , Pat Suat , Zafer Balbag M. , Ilker Cenik M. , Vladoiu Rodica , Tanisli Murat , Ozen Ozlem
Published: February 2007

Pulsed discharges of methane gas at atmospheric pressure were generated using high voltage power supply (20 kV–25 kHz) to produce the carbon. The pulsed discharge of methane gas was generated between two sharp wolfram electrodes. It brings out carbon and acetylene and other hydrocarbons at the same time. In this study, carbon samples are produced and some of the physical properties of them were analyzed. The production rate of carbon was also determined. Carbon samples were investigated by Scanning Electron Microscopy, Energy Dispersive X‐ray spectroscopy and X‐ray diffraction. The produced carbon samples have amorphous structure according to XRD results and include no contamination according to EDX results. The samples have the strongest peak at 26.516° at XRD spectra. Production rate is 0.52 mg/min at d (discharge space) being 8 mm and (flux of the methane gas) ϕ is 0.3 l/min. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling effects on electron‐phonon scattering in double quantum dots
Authors: Ramirez H. Y. , Camacho A. S. , Lew Yan Voon L. C.
Published: February 2007

In this work we study the electron‐phonon interaction in GaAs/AlGaAs double‐dot systems for cylindrical and spherical geometries with finite confinement, coupled by a tunnelling barrier and an external dc electric field. The eigenenenergies and envelope wave functions are numerically obtained for different values of the external bias. We study the effects of field and the dots‐shape on the relaxation rates of electronic transitions between double‐dot states by electron‐acoustic phonon and electron‐optical phonon interaction. We found the piezoelectric interaction to be small compared with the deformation potential one, and the spherical more convenient than the cylindrical geometry to reduce the electron‐phonon decay rates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interference effects on Andreev reflection through double quantum dots
Authors: Tanaka Yoichi , Kawakami Norio
Published: February 2007

We study transport through double quantum dots (DQD) coupled to normal and superconducting leads. Especially, we focus on the interplay between the Andreev reflection and the interference effect, which occurs in a parallel DQD but not in a serial DQD system. In the parallel DQD system, it is elucidated that the differential conductance has Fano‐type dip structures in addition to four peaks, which are caused by the interference between the distinct transport channels via Andreev bound states. We further discuss a T‐shaped DQD system, which is another typical system sensitive to the interference effect. In this system, we find that the shift of the dot energy‐level gives rise to intriguing properties in the conductance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Localization of electrons in type‐II Ge/Si quantum dots stacked in a multilayer structure
Authors: Yakimov A. I. , Nikiforov A. I. , Dvurechenskii A. V. , Bloshkin A. A.
Published: February 2007

Space‐charge spectroscopy was employed to study electronic structure of a single layer of Ge quantum dots and of a stack of four layers of Ge islands embedded in an n ‐type Si(001) matrix. For a multilayer sample, the evidence for an electron localization in strained Si in the vicinity of Ge dots was found. From the temperature‐ and frequency‐dependent measurements the electron binding energy was determined to be 40–70 meV for different quantum states. The electron accumulation was not observed in a sample with a single layer of Ge dots. Existence of localized electronic states is explained by a modification of the conduction band alignment induced by inhomogeneous tensile strain in Si around the buried Ge dots. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Light scattering in an electron‐hole double quantum well in the presence of spin‐orbit interaction
Authors: Yang C. H. , Zhang C. , Xu Wen , Zeng Z.
Published: February 2007

In this work, we study theoretically the lineshape and intensity of light scattering in an electron‐hole double quantum well structure in the presence of spin‐orbit interaction (SOI). Using the random phase approximation and Green function approach, the dispersion and the excitation spectra in this structure have been calculated. It is shown that scattering intensity can be tuned by the spin‐orbit (SO) couple via the applied electrical field. The peaks shift as the polarization of electron or hole increases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiar band gap structure of graphene nanoribbons
Authors: Ezawa Motohiko
Published: February 2007

The cover picture of this issue of physica status solidi (c) has been taken from the article [1]. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evaluation of a biodegradable foam for protective packaging applications
Authors: Arif Samina , Burgess Gary , Narayan Ramani , Harte Bruce
Published: February 2007

Green Cell® foam (GCF) is a biodegradable foam packaging material produced from a proprietary cornstarch blend. It is commercially available in a variety of laminations and constructions. Cushioning ability and thermal resistance (R‐value) are the fundamental properties needed to compete against synthetic foams. Since GCF is starch based and biodegradable, a concern was that moisture would likely affect its physical properties. Cushioning characteristics and insulation R‐values of 1 and 2 inch foams were determined as a function of temperature and moisture content. The ASTM method D1596 was used to determine the cushioning properties and an ice melt test was used to determine the thermal resistance. Moisture sorption isotherms were developed at three temperatures (20, 25 and 30°C) to determine its moisture sensitivity. The 1‐inch‐thick foam had lower G values at lower static stresses than synthetic foams, but had higher G values at higher static stresses. The 2‐inch‐foam had G values similar to that of synthetic foam materials. Dimensional changes were observed at higher relative humidity (RH) conditions, especially at 30°C. The R‐values at higher humidities were also less than that of synthetic materials. Copyright © 2007 John Wiley & Sons, Ltd.
Zur Problematik der Zwischenbewitterung von Epoxidharz‐Teil beschichtungen an Brückenbauwerken
Authors: Gelhaar Andreas , Schneider Andreas
Published: February 2007

Für den Korrosionsschutz von Brückenbauwerken kommen aufgrund der geforderten langen Schutzdauer überwiegend zweikomponentige Beschichtungssysteme auf Basis von Epoxidharz/Polyurethan nach Blatt 87 der TL/TP‐KOR‐Stahlbauten zum Einsatz. Bei der meistens praktizierten Aufteilung des Gesamtsystems in Werkstatt‐ und Baustellenbeschichtung kann es durch Zwischenbewitterung der Epoxidharz‐Teil beschichtung zu Verbundproblemen kommen, was bereits zu Schadensfällen geführt hat. Der Beitrag beinhaltet Untersuchungsergebnisse zu dieser Problematik an in Nutzung befindlichen Bauwerken und berichtet über Erkenntnisse, die beim Brückenneubau bei dem Anlegen von Probebeschichtungen auf unterschiedlich vorbereiteten Oberflächen gewonnen wurden. Aus den Ergebnissen werden Schlußfolgerungen und Empfehlungen zur weiteren Verfahrensweise abgeleitet.
Information on the composition of fats from their high‐resolution13C nuclear magnetic resonance spectra
Authors: Gunstone F. D.
Published: February 2007

Based on the interpretation of the high‐resolution13C nuclear magnetic resonance spectra of 15 spreading fats, baking fats, vegetable creams and an infant formula, it is possible to decide whether the sample contains butterfat, lauric oils, partially hydrogenated fat, linoleic acid or linolenic acid. The data have been interpreted in a semiquantitative manner, and this provides an insight into the nature of the material present in each sample.
Characterization of the volatile decomposition products of oxidized methyl arachidonate
Authors: Artz W. E. , Perkins E. G. , Salvador‐Henson L.
Published: February 2007

The volatile thermal and oxidative decomposition products of methyl arachidonate were separated by capillary gas chromatography and identified by mass spectrometry. Various aldehydes, ketones, aldehyde esters, hydrocarbons and alcohols were identified. The major products included hexanal, methyl 5‐oxopentanoate, pentane, methyl butanoate and 2,4‐decadienal, which could be important to off‐odor development in oxidized food systems containing arachidonate.
Antioxidative properties of methanolic extracts from peanut hulls
Authors: Yen Gow‐Chin , Duh Pin‐Der
Published: February 2007

Antioxidative properties of methanolic extracts from peanut hulls (MEPH) have been investigated. MEPH had good thermal stability and showed an 85.2% inhibition of peroxidation of linoleic acid when heated at 185°C for 2 h. Only a slight decrease in antioxidative activity of MEPH occurred when the extract was stored at different temperatures (∓20, 5 and 30°C) under air or nitrogen (30°C) for 70 d. Antioxidative activity of MEPH decreased with an increase of pH from 3 to 9. No synergistic effect of ascorbic acid, citric acid, cysteine or α‐tocopherol was observed on the inhibitory effect of MEPH. The reducing power of MEPH increased with an increase in concentration and was significantly correlated (r=0.9793,P<0.05) to the extent of antioxidative activity. MEPH also showed good inhibitory activity in lard oxidation when compared with butylated hydroxyanisole.
Substrate preferences for lipase‐mediated acyl‐exchange reactions with butteroil are concentration‐dependent
Authors: Kuo Shu‐Jung , Parkin Kirk L.
Published: February 2007

Substrate preferences for pancreatic lipase‐mediated acyl‐exchange reactions with butteroil were concentration‐dependent for the series of acyl donors and alcohol acceptors evaluated. For acidolysis reactions, the initial reaction rates and percent reaction yields after 18 h at 50 µmol acyl donor per gram substrate mixture were similar forn‐fatty acids and their methyl and glycerol esters. At 400–500 µmol g−1 (and greater), order of initial reaction rates and percent reaction yield was fatty acid glycerol esters > fatty acid methyl esters > fatty acids. At concentrations above 300–500 µmol g−1, reaction inhibition was observed for fatty acid substrates, and inhibition took place at lower concentrations for the shorter‐chainlength fatty acids of those evaluated (5–17 carbons). Inhibition was primarily attributed to acidification of the microaqueous environment of the lipase. Desorption of water by the fatty acid substrate may be a secondary mode of inhibition. The concentration dependence of initial reaction rates and percent reaction yield was similar for then‐alcohol substrates evaluated (2–15 carbons) for alcoholysis reactions with butteroil. Optimum alcohol concentration was 375–500 µmol g−1 (except for butanol, which was 1 mmol g−1, above which reaction inhibition was observed. Inhibition was attributed to desorption of water from the enzyme by the alcohol substrate. Relative reactivity of classes of alcohols for this reaction system was primary alcohols > secondary alcohols > tertiary alcohols. Generally, alcoholysis reactions were faster than acidolysis reactions, and triacylglycerols were the best substrates for acidolysis reactions with butteroil at high levels (up to 2 mmol g−1) of acyl donor substrate.
Chemical interesterification with regioselectivity for edible oils
Authors: Konishi Hiroaki , Neff William E. , Mounts Timothy L.
Published: February 2007

Chemical interesterification reaction conditions that provide regioselectivity regarding fatty acid positions in triacylglycerol have been investigated. Sodium methoxide‐catalyzed ester interchange between soybean oil and methyl stearate was performed in hexane at low reaction temperature,i.e., 30 to 60°C. The results showed regioselectivity was obtained at 30°C. The ester interchange at 1,3‐carbons progressed 1.7 times faster than at 2‐carbon of the glycerol moiety of triacylglycerol at 24 h. Preheating of the mixture of reactant and catalyst at 60°C for 15 min promoted catalyst activation to accelerate the interesterification while maintaining regioselectivity. This method is believed to be feasible for modification of edible fats and oils.
Discernment of relative retention values of triglyceride α,β isomers on reverse phase high performance liquid chromatography
Authors: Kinoshita Kuninori , Kimura Minoru , Takahashi Koretaro , Zama Koichi
Published: February 2007

Discernment of α,β isomers of triglyceride on reverse phase high performance liquid chromatography (HPLC) was investigated by the use of a multiple regression analysis. The retention effect of triglyceride molecular species was considered to be dependent principally on the addition theorem of chemical potential of both position α and position β (acyl carbon numbers and numbers of double bonds in the acyl group), though it was observed that the retention effect of position α is somewhat larger than that of position β on HPLC when it has the same acyl group combination.
Conductometric investigations on lanthanum soap solutions
Authors: Mehrotra K. N. , Gahlaut A. S. , Sharma Meera
Published: February 2007

The critical micelle concentration (CMC), degree of dissociation and dissociation constant of lanthanum caprate in benzene‐methanol mixtures of varying composition were determined using conductometric measurements. The results show that the soap behaves as a weak electrolyte in these solutions below the CMC. The value of the CMC (0.0027 M) was found to be independent of the solvent composition but increases with the addition of dye.
Phase investigations of fats. II. Systems containing oleic and stearic acids and an organic solvent
Authors: Singleton W. S.
Published: February 2007

The ternary systems oleic acid‐stearic acid‐commercial hexane and oleic acid‐stearic acid‐acetone containing varying amounts of the three components have been equilibrated at 0°C., −10°C., −20°C., −30°C., and −40°C.

From compositional data of the liquid and solid phases in equilibrium at each isotherm, ternary phase diagrams have been constructed. From these diagrams it is possible to predict the degree of separation which can be obtained with any given mixture of oleic and stearic acids, using either acetone or commercial hexane as solvent.

With practical solvent ratios the phase diagrams at −20°C., −30°C., and −40°C., exhibit closed areas representing liquid phase composition. The liquid phase boundaries have been established for each isotherm investigated.

The intersolubilizing effect of oleic acid on stearic acid, greater in commercial hexane than in acetone, and the possible formation of mixed crystals of oleic and stearic acid have been noted.

Oleic acid of high purity can be obtained as one of the practical applications of these data.
Note on the hygroscopic equilibrium of cottonseed and cottonseed products
Authors: Karon M. L. , Adams Mabelle E.
Published: February 2007

Summary and Conclusions

The hygroscopic equilibrium of a sample of the Stoneville 2B variety of cottonseed and its derived products has been determined over the relative humidity range of 11 to 93%. In a previous publication (1) the hygroscopic equilibrium of a sample of the D and PL variety of cottonseed was determined over the range of 31 to 93% relative humidity: Comparison of the previous and present results show that the whole seed and kernels of both varieties exhibit the same hygroscopic equilibrium behavior. A comparison of the aforementioned results with those reported by Simpson (3) on Stoneville 2B variety, and by Franco (4) on the 1A 7387 variety grown in São Paulo, Brazil, show that for intact cottonseed the hygroscopic equilibrium behavior is the same.

On the basis of the curves given in Figure 1 and on the assumption that the cottonseed used was representative of cottonseed in general, it is possible to calculate the equilibrium moisture content of the whole cottonseed or any component thereof. For example, cottonseed consisting of 12.1% linters, 87.9% delintered seed, 56.0% kernels, and 31.9% lint‐free hulls, and containing 12% moisture on a whole seed basis, will yield linters, delintered seed, kernels, and lint‐free hulls having 9.4, 12.7, 10.8, and 15.4% moisture, respectively.
Lipids and fatty acids of important finfish: New data for nutrient tables
Authors: Exler J. , Kinsella J. E. , Watt B. K.
Published: February 2007

There is an urgent need for thorough and reliable information on the lipid content and fatty acid composition of food. Data on fish lipids (1960 to the present) have been collected and evaluated for the preparation of nutrient and food composition tables for this important commodity. Some factors affecting these data include the lack of standardization in fish nomenclature, cut of fish, season and location of catch, and variability of methods of analysis. The derivation and use of conversion factors relating wt percent methyl ester data in the literature to g fatty acid/100 g fish are described. Tabulated data are presented for total lipid and 14 fatty acids in 11 important finfish.
Use of dimethylsilyl ether derivatives in gas chromatography
Authors: Supina Walter R. , Kruppa Richard F. , Henly Robert S.
Published: February 2007

The results show the use of dimethylsilyl (DMS) derivatives to be valuable for: 1) decreasing retention times of samples being analyzed by gas chromatography; 2) conducting analyses at lower temperatures; 3) analyses of mixtures which cannot be separated as trimethylsilyl (TMS) derivatives; and 4) analyses of mixtures of isomers on one column as both DMS and TMS derivatives rather than using two columns with one derivative. The work reported here is only of a preliminary nature and does not include a study of the kinetics of the reaction. It is hoped that this paper will stimulate more work in this area.
Microcolumn liquid analysis of lipids with flame ionization detection
Authors: Stouffer John E. , Oakes Phillip L.
Published: February 2007

A system for the rapid analysis of compounds which may be either too large or too sensitive to be subjected intact to gas chromatographic or other methods is described. Capillary columns of 0.5 mm and 1 mm I.D. and various lengths are packed with very fine particle size, specially prepared, silica gel and other media. A simple pumping arrangement is employed for either single solvent or gradient elution, and the solute in the effluent is detected by means of a highly sensitive flame ionization detector. The application of this system is illustrated by the separation of microgram and submicrogram amounts of triglycerides, steroids, and other neutral lipids, as well as some phospholipids.
The correlation of washability with the rate of surfactant adsorption
Authors: Vandegrift A. E. , Rutkowski Reverly J.
Published: February 2007

A relation between the rate of adsorption of surfactant molecules at a gas‐liquid interface and the soil removal ability of the surfactant solution is presented. The relation is of the form SR=A+Bk+Ck2 where SR is the percentage soil removed, A, B, and C are constants, and k is the first order rate constant for the adsorption process. The relation is empirical and as yet has not been coupled with a fundamental explanation of the detergency process on a molecular scale.

The maximum soil removal does not always occur at the highest rate constant but may reach a maximum at an intermediate value. The soil removal process seems to be different above the CMC than below it. For the different surfactants studied, the soil removal is higher for the surfactant with larger rate constants.

The rate of surfactant adsorption was obtained from dynamic surface tension measurements made with the oscillating jet technique. Soil removal information was obtained from laboratory tests using a Terg‐O‐Tometer and reflectance measurements on standard cloth swatches. Cationic, nonionic, and anionic surfactants were studied. Specifically, the surfactants were Triton X‐100 (an octyl phenol with 8 or 9 ethylene oxide units), NaDBS (sodium dodecylbenzene sulfonate), and CTAB (cetyl trimethylammonium bromide). The surface tension time range of 5 to 60 milliseconds and soil removal ability of these surfactants was investigated over the temperature range of 20 to 60C, and the concentration range of 0.0003 to 0.009 M.
Chemical reactions involved in the deep fat frying of foods. III. Identification of nonacidic volatile decomposition products of corn oil
Authors: Krishnamurthy R. G. , Chang Stephen S.
Published: February 2007

A total of 45 compounds were identified and an additional 20 compounds were tentatively identified in the nonacidic volatile decomposition products produced by corn oil under conditions simulating commercial deep fat frying. The 65 compounds consisted of 11 hydrocarbons, 7 alcohols, 2 esters, 6 lactones, 21 aldehydes, 9 ketones, and 9 aromatic compounds. Including the 30 acidic compounds reported in a previous paper, a total of 95 compounds have been identified as volatile decomposition products of corn oil.

The chemical structure of the identified compounds and the postulated mechanisms of their formation revealed some of the chemical reactions involved in the deep fat frying of foods. Many of the identified compounds had interesting odor characteristics. It is concluded that their effect on human health when inhaled or ingested should be investigated.