bluuebunny/crossref_metadata_2025 huggingface dataset:
Epoxy resin/exfoliated clay hybrid materials with high thermal properties
Authors: Fu Tiezhu , Yu Lianxiang , Wang Zhe , Yu Wenzhi , Zhao Chengji , Zhong Shuangling , Cui Jiwen , Shao Ke , Na Hui
Published: June 2008

A new type of organophilic clay grafted with the protonated 4, 4′‐methylenediamine was prepared. The epoxy was modified using the organophilic clay and was prepared by “acetone‐clay slurry” method. The morphology of the clay platelets into epoxy matrix were characterized by wide angle X‐ray diffraction and transmission electron microscopy. The results indicated that the epoxy resin/exfoliated clay hybrid materials were successfully prepared and the exfoliation of clay into epoxy matrix occurred in the curing process. The excellent thermal mechanical properties of the hybrid materials with the values of the storage modulus and glass transition temperature (Tg) of the hybrid materials were studied by dynamic mechanical analysis. When 7 wt% of modified clay was added into epoxy, the storage modulus of hybrid materials increased to 1131 MPa at 110°C, and 51 MPa at 220°C in comparison to the pristine cured epoxy (661 MPa at 110°C and 6 MPa at 220°C). The high thermal stabilities of the hybrid materials especially in high temperature were also been researched by thermogravimetric analysis. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Modelling the nonlinear shear stress–strain behavior of a carbon fabric reinforced polyphenylene sulphide from rail shear and [(45°,−45°)]4s tensile test
Authors: De Baere Ives , Van Paepegem Wim , Degrieck Joris
Published: June 2008

In this article, the nonlinear shear stress–strain relationship of a carbon fabric‐reinforced polyphenylene sulphide is investigated by performing and comparing both the [+45°/−45°]ns tensile test and the three‐rail shear test. First, quasi‐static and hysteresis tests are performed to obtain the data necessary for the material model. Then, the material constants are optimized by comparing finite element simulations with the data derived from the experiments. The conducted experiments are simulated and the results are compared with the experiments, with excellent correspondence. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Formation of Boron‐doped region using spin‐on dopant: investigation on the impact of metallic impurities
Authors: Jourdan J. , Veschetti Y. , Dubois S. , Desrues T. , Monna R.
Published: June 2008

Investigation on the electrical properties ofp+‐dopedregions formed by spin‐on‐dopant (SOD) technique was achieved. Using this technique, boron‐diffused regions were formed on bothp‐typeandn‐typefloat zone wafers. Homogeneous sheet resistances were obtained for both types of wafers. Bulk properties were investigated by measuring effective carrier lifetime. An iron contamination was observed after the boron diffusion step and interstitial iron concentrations were deduced from lifetime measurements. More investigations proved that the iron was initially present within the SOD film. A phosphorus diffusion allows to remove this bulk contamination, leading to an improvement of effective lifetime values. Nevertheless, the corresponding emitter saturation current density was estimated onn‐typewafers and presented a high value. It is likely that this poor electrical quality is the consequence of a high iron concentration which remains in the diffused region. Some possibilities are suggested to avoid or to limit this contamination. Copyright © 2008 John Wiley & Sons, Ltd.
Modification of gamma‐radiation response in mice by green tea polyphenols
Authors: Lee Hae June , Kim Joong Sun , Moon Changjong , Kim Jong Choon , Lee Yun Sil , Jang Jong Sik , Jo Sung Kee , Kim Sung Ho
Published: June 2008

In this study we evaluated the effect of water extracts of green tea (GT) and mixtures of green tea polyphenols (GTPs), epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC) and epicatechin (EC) on jejunal crypt survival, endogenous spleen colony formation, and apoptosis in jejunal crypt cells of mice irradiated with gamma‐ray. The radioprotective effect of green tea was compared with the effect of diethyldithiocarbamate (DDC). Jejunal crypts were protected by pretreatment of GT and ECG. Administration of GT, GTPs and EC prior to irradiation resulted in an increase in the formation of endogenous spleen colonies. The frequency of apoptosis in crypt cells was also reduced by pretreatment of GT, GTPs, EGCG, ECG and EGC. In the experiment on the effect of catechins, the effects were partly contradicted in irradiated mice. The rank order of activity was ECG > EGC > EGCG > EC on intestinal crypt survival assay, EC > EGC > ECG > EGCG on the spleen colony formation assay, EGCG > EGC > EC > ECG on inhibiting the death of cells caused by apoptosis. The results indicate that GT and GTPs may have a major radioprotective effect. Each one of the catechins was a much less effective radioprotector, suggesting that total extract or a mixture of GTPs may be more effective than individual catechins. Copyright © 2008 John Wiley & Sons, Ltd.
Dynamics of photoexcitations with interchain coupling in conjugated polymers
Authors: de Oliveira Neto Pedro Henrique , da Cunha Wiliam Ferreira , Gargano Ricardo , e Silva Geraldo Magela
Published: June 2008

In this article, we study the photoexcitation dynamics of two coupled trans‐polyacetylene chains. The approach used was an extended version of the Su, Scherieffer, and Heeger model for a pair of interacting chains and impurity. An electron excitation from one fully dimerized chain to another was simulated. The chain length influence were analyzed and shown to be of importance when the spectrum is concerned. It was also observed that the electron excitation generates a pair of neutral solitons on the second chain. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Conformations and charge distributions of diazocyclopropanes
Authors: Borges Itamar
Published: June 2008

Three diazo‐substituted cyclopropane compounds, which have been suggested as new potential high energy compounds, were studied employing the B3LYP‐DFT/6‐31G(d,p) method. Geometries were optimized. Distributed multipole analysis, computed from the B3LYP‐DFT/6‐31G(d,p) density matrix, was used to describe the details of the molecular charge distribution of the three molecules. It was verified that electron withdrawing from the C ring atoms and charge build‐up on the N atoms bonded to the ring increased with the number of diazo groups. These effects were related to increased sensitivity to impact and easiness of CN bond breaking in the three compounds. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Empirical analysis of the Lieb–Oxford bound in ions and molecules
Authors: Odashima Mariana M. , Capelle K.
Published: June 2008

Universal properties of the Coulomb interaction energy apply to all many‐electron systems. Bounds on the exchange‐correlation energy, in particular, are important for the construction of improved density functionals. Here we investigate one such universal property—the Lieb‐Oxford lower bound—for ionic and molecular systems. In recent work [J Chem Phys 127, 054106 (2007)], we observed that for atoms and electron liquids this bound may be substantially tightened. Calculations for a few ions and molecules suggested the same tendency, but were not conclusive due to the small number of systems considered. Here we extend that analysis to many different families of ions and molecules, and find that for these, too, the bound can be empirically tightened by a similar margin as for atoms and electron liquids. Tightening the Lieb‐Oxford bound will have consequences for the performance of various approximate exchange‐correlation functionals. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Computational study of the solvation of protoporphyrin IX and its Fe2+ complex
Authors: Guizado Teobaldo Cuya , da Rocha Pita Samuel , Wanderley Louro Sonia R. , Geraldo Pascutti Pedro
Published: June 2008

Molecular dynamics (MD) simulations of a well known hydrophobic structure, the heme (ferroprotoporphyrin IX) and its precursor in the heme synthesis, protoporphyrin IX (PPIX) are presented. The objective of the present study is to determine the stability of both structures in an aqueous medium, as well as the structure‐solvent relation, hydration shells, and discuss their implications for biological processes. The density functional theory (DFT) is used for the electronic and structural characterization of both PPIX and its Fe2+ complex. A classical approach based on the Gromacs package is used for the MD. The radial distribution function g(r) is used to examine the allocation of water molecules around different regions of the porphyrins. The calculations demonstrate the heterogeneous character of the porphyrins with respect to the affinity with water molecules, the general hydrophobic character of the porphyrin ring bonded or not to the ion Fe, the hydrophilic character of the carboxylic oxygen that is unchanged upon iron binding, and the low hydrophilicity of Fe2+ in the heme. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
DFT/PCM investigation of the Mn(II) chemical speciation in aqueous solution
Authors: de Abreu Heitor Avelino , Guimarães Luciana , Duarte Hélio Anderson
Published: June 2008

Chemical speciation of Mn(II) in aqueous solution has been investigated by means of density functional methods. Different geometries and electronic states of all species arising from the Mn(II) hydrolysis have been calculated. The Gibbs free energy of the hydrolysis reaction and the respective equilibrium constants have been estimated and compared with the available experimental data. Polarizable continuum model (PCM‐UAHF/6‐31+G(d)) was used to estimate the solvation energy. The ionization potential of the predominant species are linearly dependent on the number of hydroxyls in their structure. The Mn(II)/Mn(III) oxidation potential estimate is in good agreement with the experimental value, about 0.2 V smaller. The estimated hydrolysis reaction energies are in good agreement with the experimental values with an error of about 3 kcal mol−1 (PBE/TZVP). The unique exception is the [Mn(OH)3]− hydrolysis constant which is not in good agreement with the experimental value. This is attributed to inaccuracy of the presently available experimental value and the PCM solvation free energy estimate. The results shown in this work reinforce the importance of the chemical speciation in order to understand at a molecular level the mechanism of processes involving transition metal ions. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Relativistic corrections to the partial wave expansion of two‐electron atoms
Authors: Kutzelnigg Werner
Published: June 2008

The asymptotic behavior of the partial wave expansion (or the CI expansion in terms of AOs with angular quantum number l) of the leading relativistic correction for two‐electron atomic ions in a 1S state is studied analytically. In agreement with earlier numerical findings, the partial wave increments of the leading relativistic correction go as (l + 1/2)−2, whereas the nonrelativistic increments go as (l + 1/2)−4. The coefficient of the leading term is 2 α2 π2 ∫ | ψ(r,r,0)|2r3dr for the Dirac Coulomb operator, and surprisingly also the full Dirac‐Breit operator, while the Gaunt term gives a contribution of −4α2π2∫|ψ(r,r,0)|2r3dr. The results obtained here rely entirely on the nonrelativistic correlation cusp, and do not require assumptions on a no‐pair projection or a short‐range regularization of the electron interaction. They do not give any information on what happens beyond the leading order of relativistic corrections. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Lead in soil by field‐portable x‐ray fluorescence spectrometry—an examination of paired In Situ and laboratory ICP‐AES results
Authors: Binstock David A. , Gutknecht William F. , McWilliams Andrea C.
Published: June 2008

A major aspect of lead hazard control is the evaluation of soil lead hazards around housing coated with lead‐based paint. The use of field‐portable X‐ray fluorescence (FPXRF) to do detailed surveying, with limited laboratory confirmation, can provide lead measurements in soil (especially for planning abatement activities) in a far more cost‐efficient and timely manner than laboratory analysis. To date, one obstacle to the acceptance of FPXRF as an approved method of measuring lead in soil has been a lack of correspondence between field and laboratory results. In order to minimize the differences between field and laboratory results, RTI International (RTI) has developed a new protocol for field drying and sieving soil samples for field measurement by FPXRF. To evaluate this new protocol, composite samples were collected in the field following both U.S. Department of Housing and Urban Development (HUD) guidelines and ASTM International (ASTM) protocols, measured after drying by FPXRF, and returned to the laboratory for confirmatory inductively coupled plasma atomic emission spectroscopy (ICP‐AES) analysis. Evaluation of study data from several diverse sites revealed no statistical difference between paired FPXRF and ICP‐AES measurements using the new method. © 2008 Wiley Periodicals, Inc.
Transition covering tests for systems with queues
Authors: Huo Jiale , Petrenko Alexandre
Published: June 2008

This paper introduces a method to cover transitions of a concurrent system under test through a context consisting of infinite‐capacity queues. Concurrent systems have many important applications, but they are very difficult and expensive to test. One of the difficulties in testing concurrent systems is caused by the fact that queues in the test context can distort the behaviour of a concurrent system under test and can cause state explosion in test derivation. The proposed method derives transition covering tests directly from the specification of a concurrent system, not its composition with queues. As transition coverage is an important industrial metric of test quality, the results of the paper have practical applications. A case study is presented to illustrate one of the applications. Copyright © 2008 John Wiley & Sons, Ltd.
Changes in signaling pathways of cell proliferation and apoptosis during NK/Ly lymphoma aging
Authors: Panchuk R.R. , Boiko N.M. , Lootsik M.D. , Stoika R.S.
Published: June 2008

Expression of specific proteins involved in regulation of cell proliferation and apoptosis was studied at the initial (7–8 days after tumor inoculation), median (13–14 days), and terminal (20–21 days) stages of murine NK/Ly lymphoma development. Western‐blot analysis using antibodies to MEK—ERK signaling pathway, E2F‐1/2 and c‐Myc, pSTAT1, pSTAT3, pSTAT5, anti‐apoptotic Bcl‐XL and pro‐apoptotic p53 and Rb proteins, as well as active cleaved forms of caspases‐3, −6, −7, was carried out to investigate the growth and survival status of NK/Ly cells. There was a marked increase in the expression of E2F‐1/2 transcription factors, MAPK signaling cascade and c‐Myc, which suggests intensive proliferation of lymphoma cells at terminal stage of tumor development. However, cytomorphological investigation and electrophoretic study of DNA fragmentation have shown degeneration of NK/Ly lymphoma cells and increase in their death. No expression of p53 protein or cleaved forms of caspases‐3, −6, −7 was found, which suggests a caspase‐independent type of apoptosis in these cells. Ascitic fluid collected at a terminal stage of NK/Ly lymphoma development was significantly weaker in supporting tumor cell growth than ascitic fluid collected at the initial stage of tumor development. It is suggested that uncontrolled cell proliferation at terminal stage of the NK/Ly lymphoma development causes nutrient deprivation and deficiency of specific growth factors in the ascitic fluid, due to overexpression of MEK—ERK, E2F and c‐Myc, thereby leading to the induction of apoptosis.
The effects of prenatal stress on expression of p38 MAPK in offspring hippocampus
Authors: Cai Qing , Huang Shuyun , Zhu Zhongliang , Li Hui , Li Qinghong , Jia Ning , Liu Jankang
Published: June 2008

The hippocampus, which has the highest density of GC receptors in the brain, is involved in the regulation of the HPA and the behavioral responses to stress. Overexposure to corticosteroid hormones is harmful to hippocampal neuron integrity. Our purpose is to investigate the effects of prenatal stress (PNS) on expression of p38 mitogen‐activated protein kinase (p38 MAPK) in offspring hippocampal neurons using Western blotting and Immunohistochemistry. The prenatal restraint stress induces significant increase in the expression of p‐p38 MAPK and total p38 MAPK in female offspring hippocampus. The level of p‐p38 MAPK in PNS female offspring rats was significantly increased (126.41 ± 3.937, n = 6) compared with that in the control female offspring rats (101.35 ± 3.468, n = 6, P < 0.01). Immunoblot analysis revealed there was significant difference in the level of total p38 MAPK between the female control and prenatal restraint stress offspring rats (101.70 ± 3.162 vs. 128.111 ± 2.724, respectively, P < 0.01). Immunodensity of p38 MAPK was significantly increased above female control in PNS female offspring hippocampal CA3 and CA4 fields (P < 0.001 vs. control group, CON). The data suggest that exposure of animals to a period of stressful experience during a critical phase could impose lasting effects on the offspring hippocampal neurons cellular signalling of offspring hippocampus.
Ultrasonographic assessment of the feline mammary gland
Authors: Payan-Carreira Rita , Martins-Bessa Ana C.
Published: June 2008

The aim of this study is to characterise the feline mammary echotexture using B-mode ultrasonography, which is not routinely used to examine the feline mammary gland. Using a 5–9 MHz linear transducer the ultrasonographic appearance of non-stimulated and stimulated mammary glands was determined in 35 mature intact non-pregnant, pregnant and lactating queens aged from 16 months to 8 years. In intact non-pregnant queens, mammary glands are fairly underdeveloped and on the ultrasonograms they appear with a regular hypoechoic texture and generally show a thickness of less than 2.0 mm. The stimulated mammary tissue typically presents a more hyperechoic appearance compared to the non-stimulated gland and a fine granular echotexture. Maximum echogenicity of the mammary gland is reached during lactation. In late pregnancy, the mammary glands reach 6–9 mm in thickness. During lactation, the size of the glands depends on the existence of a suckling stimulus, with the suckled glands reaching about 11 mm in thickness. Ductal structures can only be imaged during late pregnancy and lactation. Ultrasonographic evaluation of the feline mammary gland can become a valuable diagnostic tool to characterise physiological changes and may further contribute to a better characterisation of diseased mammary tissue.
Idiopathic polyradiculoneuropathy in a Bengal cat: electrophysiological findings and 1 year follow-up
Authors: Granger Nicolas , Stalin Catherine E. , Brown Thomas B. Harcourt , Jeffery Nick D.
Published: June 2008

This report describes a rapidly progressive loss of motor function in a 16-month-old male neutered Bengal cat, beginning in the pelvic limbs and progressing to involve all limbs and rendering the cat non-ambulatory. The neurological examination revealed flaccid tetraparesis with decreased spinal reflexes but preserved conscious proprioception and skin sensation. Extensive electrophysiological tests were conducted including electromyography, motor and sensory peripheral nerves potential recordings and ‘late’ potentials, defining the electrodiagnostic characteristics of this disease. Based on the electrophysiological findings, a generalised proximal and predominantly axonal neuropathy affecting the ventral (motor) nerve roots was suspected. As no aetiology was identified, this disease was classified as idiopathic polyradiculoneuropathy. Over a year, the cat presented three separate episodes of tetraparesis, each with a spontaneous complete recovery, consistent with the reportedly good prognosis for this disease.
Arbeitsaufwand, Anspruchsniveau und Steuerehrlichkeit
Authors: Muehlbacher Stephan , Kirchler Erich
Published: June 2008

Untersucht wird, ob der Arbeitsaufwand, mit dem steuerpflichtiges Einkommen erzielt wurde, und das daraus resultierende Anspruchsniveau Entscheidungen zur Steuerehrlichkeit beeinflussen. Aus der Literatur lassen sich zwei konkurrierende Hypothesen ableiten. Einerseits könnten mit hohem Aufwand der subjektive Wert des Einkommens steigen und Steuern somit besonders belastend erlebt werden. Andererseits ist anzunehmen, dass gerade bei hohem Arbeitsaufwand nicht riskiert wird, für unvollständige Deklaration Strafe zu zahlen und letztlich weniger für die erbrachte Leistung zu erhalten als bei ordnungsgemäßer Deklaration. In der ersten Studie trafen 113 Teilnehmer eine Hinterziehungsentscheidung, nachdem ihnen das zu versteuernde Nettoeinkommen als leicht bzw. hart verdient beschrieben wurde. In der zweiten Studie trafen 155 Teilnehmer dieselbe Entscheidung. Dabei wurde neben dem Arbeitsaufwand auch das Anspruchsniveau manipuliert, definiert als Erwartung eines Einkommens in spezifischer Höhe. In beiden Studien wurde häufiger hinterzogen, wenn das Einkommen leicht verdient war. Entgegen der Erwartung führte aber ein höheres Anspruchsniveau zu ehrlicherer Deklaration.
An “in situ” calibration correction procedure (KCICLO) based on AOD diurnal cycle: Application to AERONET–El Arenosillo (Spain) AOD data series
Authors: Cachorro V. E. , Toledano C. , Berjón A. , de Frutos A. M. , Torres B. , Sorribas M. , Laulainen N. S.
Published: June 2008

Aerosol optical depth (AOD) very often shows a distinct diurnal cycle pattern, which seems to be an artifact resulting from an incorrect calibration (or an equivalent effect, such as filter degradation). The shape of this fictitious AOD diurnal cycle varies as the inverse of the solar air mass (m) and the magnitude of the effect is greatest at midday. The observation of this effect is not easy at many field stations, and only those stations with good weather conditions permit an easier detection and the possibility of its correction. By taking advantage of this dependence on the air mass, we propose an improved “in situ” correction‐calibration procedure to AOD measured data series. The method is named KCICLO because the determination of a constant K and the behavior of AOD as a cycle (ciclo, in Spanish). We estimate it has an accuracy of 0.2–0.5% for the calibration ratio constant K, or 0.002–0.005 in AOD at field stations. Although the KCICLO is an “in situ” calibration method, we recommend it to be used as an AOD correction method for field stations. At high‐altitude sites, it may be used independently of the classical Langley method (CLM). However, we also recommend it to be used as a complement to CLM, improving it considerably. The application of this calibration correction method to the nearly 5 year AOD data series at El Arenosillo (Huelva, southwestern Spain) station belonging to Aerosol Robotic Network (AERONET)‐PHOTONS shows that 8 (50%) of 16 filters of the four analyzed Sun photometers were outside of the 0.02 uncertainty of AERONET specification. The largest departures reached values of 0.06. The results show the efficiency of the method and a significant improvement over other “in situ” methods, with no other information required beyond the same AOD data.
Seismic reflections reveal a massive melt layer feeding Campi Flegrei caldera
Authors: Zollo Aldo , Maercklin Nils , Vassallo Maurizio , Dello Iacono Dario , Virieux Jean , Gasparini Paolo
Published: June 2008

Campi Flegrei is an active, resurgent caldera that is located a few kilometres west of the city of Naples, a densely populated urban settlement in southern Italy. Identifying, locating at depth and better defining the geometry of the magma feeding system of the caldera is highly relevant for assessing and monitoring its volcanic hazard. Based on a high resolution seismic reflection data set, we investigated the deep structure of the volcano. Here we show that seismic wave amplitude variations with distance from the radiating source provide clear evidence for large amplitude seismic reflections from the top of an extended supercritical fluid‐bearing rock formation at about 3,000 m and of an about 7,500 m deep, 1,000 m thick, low velocity layer, which is associated with a mid‐crust, partial melting zone beneath the caldera. The modeling of magma properties based on measured seismic velocities indicates a relatively high melt percentage (in the range 80–90%). These new data suggest that a large magmatic sill is present well within the basement formations, which is possibly linked to the surface through a system of deep fractures bordering the caldera. The lateral extension and similar depth of the melt zone observed beneath the nearby Mt.Vesuvius support the hypothesis of a single continuous magma reservoir feeding both of these volcanoes.
Atomic scale characterization of buried InxGa1−xAs quantum dots using pulsed laser atom probe tomography
Authors: Müller M. , Cerezo A. , Smith G. D. W. , Chang L. , Gerstl S. S. A.
Published: June 2008

Atom probe tomography (APT) has been used to study InxGa1−xAs quantum dots buried in GaAs. The dots have an average base width of 16.1±1.1nm and height of 3.5±0.3nm, but a wide range of sizes. APT composition profiles across the dots are similar to a previous study by cross-sectional scanning transmission electron microscopy, but show significant gallium incorporation (average x=0.22±0.01). The direct three-dimensional nature of the APT data also reveals the complex spatial distribution of indium within the dots. Data such as these are vital for optimizing the performance of quantum dot materials and devices.
Hyperthermal Ar atom scattering from a C(0001) surface
Authors: Gibson K. D. , Sibener S. J. , Upadhyaya Hari P. , Brunsvold Amy L. , Zhang Jianming , Minton Timothy K. , Troya Diego
Published: June 2008

Experiments and simulations on the scattering of hyperthermal Ar from a C(0001) surface have been conducted. Measurements of the energy and angular distributions of the scattered Ar flux were made over a range of incident angles, incident energies (2.8–14.1eV), and surface temperatures (150–700K). In all cases, the scattering is concentrated in a narrow superspecular peak, with significant energy exchange with the surface. The simulations closely reproduce the experimental observations. Unlike recent experiments on hyperthermal Xe scattering from graphite [Watanabe et al., Eur. Phys. J. D 38, 103 (2006)], the angular dependence of the energy loss is not approximated by the hard cubes model. The simulations are used to investigate why parallel momentum conservation describes Xe scattering, but not Ar scattering, from the surface of graphite. These studies extend our knowledge of gas-surface collisional energy transfer in the hyperthermal regime, and also demonstrate the importance of performing realistic numerical simulations for modeling such encounters.
Numerical simulation of phase separation of immiscible polymer blends on a heterogeneously functionalized substrate
Authors: Shang Yingrui , Kazmer David , Wei Ming , Mead Joey , Barry Carol
Published: June 2008

The spinodal phase decomposition of an immiscible binary polymer blend system is investigated with numerical models in two-dimensional and three-dimensional (3D). The effect of the elastic energy is included. The mechanism of the evolution of the phase separation is studied and the characteristic length R(t) is shown to be proportional to t1∕3. In the case when the phase separation is directed by a heterogeneously functionalized substrate, the increase in the characteristic length is divided into two stages by a critical time. The R(t)∼t1∕3 diagram can be fitted with a straight line in both the first and second stages. The slope of the fitting line significantly decreases after the critical time. The compatibility of the resulting pattern to the substrate pattern is also measured by a factor CS. It is observed that there is also a critical time in the evolution of the compatibility for the cases with and without elastic energy. The critical time of CS is identical with the respective critical time of R(t). The lateral and vertical composition profiles functionalized substrate is observed with the 3D model. The difference mechanism of the cases with and without elastic energy is discussed.
DNA adsorption at functionalized Si/buffer interfaces studied by x-ray reflectivity
Authors: Douarche C. , Cortès R. , Henry de Villeneuve C. , Roser S. J. , Braslau A.
Published: June 2008

The adsorption of DNA on chemically homogeneous, functionalized, oxide-free single-crystal silicon surfaces is studied by x-ray reflectivity. The adsorption of monodisperse, 294 base-pair double-stranded DNA on a positively charged surface is detected through the deformation of the molecular monolayer of aminated alkyl-chain molecules covalently bonded to the surface. The adsorption of single-stranded DNA does not lead to the same deformation. A detailed quantitative characterization of the density profiles yield surface densities of the covalently grafted, molecular monolayers that are in excellent agreement with infrared spectroscopic measurements. The additional mass density that is measured following the adsorption of DNA corresponds either to the partial embedding of a densely-packed adsorbed layer or to a deeper penetration into the soft surface layer at a lower surface density of the adsorbed double-stranded DNA molecules. The adsorption is found to be irreversible under high added salt concentrations, suggesting a partial dehydration of the double-stranded DNA.
Multiphoton absorption induced amplified spontaneous emission from biocatalyst-synthesized ZnO nanorods
Authors: Zhang Chunfeng , Zhang Fan , Qian Shixiong , Kumar Nitin , Hahm Jong-in , Xu Jian
Published: June 2008

Multiphoton absorption-induced photoluminescence and amplified spontaneous emission (ASE) have been observed from ZnO nanorod arrays upon near-infrared excitation (λexc∼800nm). A low threshold of ∼12mJ∕cm2 was demonstrated for the ASE process. The ultraviolet emission can be attributed to the recombination of carriers coexcited by the processes of three-photon and off-resonant two-photon absorption, which was confirmed by the excitation wavelength-dependent experiments. Additionally, it has been observed that the processes of ASE and second harmonic generation in ZnO nanorods appear to enhance each other when the excitation wavelength approaches the resonant wavelength for two-photon absorption.
Unified formalism for nonautonomous mechanical systems
Authors: Barbero-Liñán María , Echeverría-Enríquez Arturo , Diego David Martín de , Muñoz-Lecanda Miguel C. , Román-Roy Narciso
Published: June 2008

We present a unified geometric framework for describing both the Lagrangian and Hamiltonian formalisms of regular and nonregular time-dependent mechanical systems, which is based on the approach of Skinner and Rusk [“Generalized Hamiltonian dynamics I. Formulation on T*Q⊗TQ,” J. Math. Phys. 24, 2589 (1983)]. The dynamical equations of motion and their compatibility and consistency are carefully studied, making clear that all the characteristics of the Lagrangian and the Hamiltonian formalisms are recovered in this formulation. As an example, a semidiscretization of the nonlinear wave equation is studied, proving the applicability of the proposed formalism.
Comment on “Two-dimensional potential theory for translating and rotating solids” [Phys. Fluids 15, 3576 (2003)]
Authors: Reisin Hernán D.
Published: June 2008

The two-dimensional potential theory for translating and rotating solids developed in Minotti [Phys. Fluids 15, 3576 (2003)] is briefly revised and formulas of the force and moment of the force are given in their correct form.
Nonlinear free surface flows past a semi-infinite flat plate in water of finite depth
Authors: Maleewong M. , Grimshaw R. H. J.
Published: June 2008

We consider the steady free surface two-dimensional flow past a semi-infinite flat plate in water of a constant finite depth. The fluid is assumed to be inviscid, incompressible and the flow is irrotational; surface tension at the free surface is neglected. Our concern is with the periodic waves generated downstream of the plate edge. These can be characterized by a depth-based Froude number F and the depth d (draft) of the depressed plate. Previous analytical studies have been restricted to small values of d and subcritical flows F<1, when linearized theory can be used. Here, our main concern here is with the critical regime, F≈1, where we use a weakly nonlinear long-wave analysis, For finite values of d, we solve the fully nonlinear problem numerically using a boundary integral equation method. Our results confirm previous studies and extend these to the critical regime. As d increases, our numerical results demonstrate that the downstream waves approach the highest possible wave. We also find some wave-free solutions, which when compared to the weakly nonlinear results are essentially just one-half of a solitary wave.
Ferroelectric solid solutions with morphotropic boundaries: Vanishing polarization anisotropy, adaptive, polar glass, and two-phase states
Authors: Rossetti G. A. , Khachaturyan A. G. , Akcay G. , Ni Y.
Published: June 2008

The generic case of a ferroelectric solid solution is considered wherein different symmetry phases located at opposing ends of the diffusionless phase diagram are separated by a morphotropic boundary (MB). It is shown that the Landau theory of weak first-order phase transformations automatically predicts vanishing of the anisotropy of polarization, continuity of thermodynamic properties, and a drastic decrease in domain wall energy near the MB line that results in the formation of adaptive ferroelectric nanodomain states. Low-resolution diffraction from these adaptive states acquired at the coherence lengths of elastic x-ray or neutron scattering probes will produce the same diffraction pattern as attributed to monoclinic (MA,MB,MC) phases. It is further shown that the electric- or stress-field-induced reconfiguration of these adaptive nanodomain states results in a softening of the piezoelectric, elastic, and dielectric properties near the MB line. In addition, the spherical degeneration of the polarization direction, reflecting the decoupling of the polarization from the crystal lattice at the MB, also predicts the formation of a polar glass state whose properties should be similar to the special properties of amorphous ferromagnets. In particular, the vanishing of the polarization anisotropy at the MB should result in ferroelectric domains with irregular shapes exhibiting high configurational sensitivity to external forces. The theory further predicts that two tricritical points will occur on the line of paraelectric→ferroelectric transitions and it is shown that all two-phase equilibrium lines of the diffusionless phase diagram—including the MB line—must be replaced by two-phase fields. Within these two-phase fields, the adjacent ferroelectric-ferroelectric and paraelectric-ferroelectric phases coexist. Possible topologies of the equilibrium MB phase diagram illustrating these two-phase equilibrium fields are computed and discussed.
Comment on “Free energy simulations of single and double ion occupancy in gramicidin A” [J. Chem. Phys. 126, 105103 (2007)]
Authors: Roux Benoît , Andersen Olaf S. , Allen Toby W.
Published: June 2008

In a recent article published by Bastug and Kuyucak [J. Chem. Phys.126, 105103 (2007)] investigated the microscopic factors affecting double ion occupancy in the gramicidin channel. The analysis relied largely on the one-dimensional potential of mean force of ions along the axis of the channel (the so-called free energy profile of the ion along the channel axis), as well as on the calculation of the equilibrium association constant of the ions in the channel binding sites. It is the purpose of this communication to clarify this issue.
Response to “Comment on ‘Free energy simulations of single and double ion occupancy in gramicidin A’ ” [J. Chem. Phys. 128, 227101 (2008)]
Authors: Baştuğ Turgut , Kuyucak Serdar
Published: June 2008

We respond to the criticism that one-dimensional (1D) construction of the potential of mean force (PMF) of ions in channels is flowed. Comparison of the 1D PMF results in the gramicidin A channel with independent free energy difference calculations obtained by using the free energy perturbation and thermodynamic integration methods shows complete agreement, thus providing a justifications for the 1D PMF approximation.
Energy stability analysis for impulsively decelerating swirl flows
Authors: Kim Min Chan , Song Kwang Ho , Choi Chang Kyun
Published: June 2008

The onset of Taylor–Görtler vortices in impulsively decelerating swirl flows is analyzed by using the recently developed, relative stability model. This model takes the growth rate of the kinetic energy of the base state and also that of disturbances into consideration. In the present system the primary transient swirl flow is laminar but for the Reynolds number Re>Rec secondary motion sets in at a certain time. The present model yields the critical Reynolds number of Rec=153. This value is larger than that from the strong stability model, but smaller than that from the propagation theory. For Re>Rec the dimensionless critical time to mark the onset of vortex instabilities, τc, is presented as a function of Re. It is found that the predicted τc value is much smaller than experimental detection time of first observable secondary motion. Therefore, it seems evident that small disturbances initiated at τc require some growth period until they are detected experimentally. Since the present system is a rather simple one, the present results will be helpful in comparing available stability models.
Dielectric fluctuations in force microscopy: Noncontact friction and frequency jitter
Authors: Yazdanian Showkat M. , Marohn John A. , Loring Roger F.
Published: June 2008

Electric force microscopy, in which a charged probe oscillates tens to hundreds of nanometers above a sample surface, provides direct mechanical detection of relaxation in molecular materials. Noncontact friction, the damping of the probe’s motions, reflects the dielectric function at the resonant frequency of the probe, while fluctuations in the probe frequency are induced by slower molecular motions. We present a unified theoretical picture of both measurements, which relates the noncontact friction and the power spectrum of the frequency jitter to dielectric properties of the sample and to experimental geometry. Each observable is related to an equilibrium correlation function associated with electric field fluctuations, which is determined by two alternative, complementary strategies for a dielectric continuum model of the sample. The first method is based on the calculation of a response function associated with the polarization of the dielectric by a time-varying external charge distribution. The second approach employs a stochastic form of Maxwell’s equations, which incorporate a fluctuating electric polarization, to compute directly the equilibrium correlation function in the absence of an external charge distribution. This approach includes effects associated with the propagation of radiation. In the experimentally relevant limit that the tip-sample distance is small compared to pertinent wavelengths of radiation, the two methods yield identical results. Measurements of the power spectrum of frequency fluctuations of an ultrasensitive cantilever together with measurements of the noncontact friction over a poly(methylmethacrylate) film are used to estimate the minimum experimentally detectable frequency jitter. The predicted jitter for this polymer is shown to exceed this threshold, demonstrating the feasibility of the measurement.
Complex coacervation: A field theoretic simulation study of polyelectrolyte complexation
Authors: Lee Jonghoon , Popov Yuri O. , Fredrickson Glenn H.
Published: June 2008

Using the complex Langevin sampling strategy, field theoretic simulations are performed to study the equilibrium phase behavior and structure of symmetric polycation-polyanion mixtures without salt in good solvents. Static structure factors for the segment density and charge density are calculated and used to study the role of fluctuations in the electrostatic and chemical potential fields beyond the random phase approximation. We specifically focus on the role of charge density and molecular weight on the structure and complexation behavior of polycation-polyanion solutions. A demixing phase transition to form a “complex coacervate” is observed in strongly charged systems, and the corresponding spinodal and binodal boundaries of the phase diagram are investigated.
Dynamical mode transitions of simply supported double-walled carbon nanotubes based on an elastic shell model
Authors: Yan Y. , Zhang L. X. , Wang W. Q.
Published: June 2008

The nonlinear vibration behaviors of double-walled carbon nanotubes (DWCNTs) are investigated based on Donnell’s cylindrical shell model with van der Waals (vdW) forces between the inner and outer tubes. The harmonic balance method is used to analyze the relationship between the amplitudes and the frequencies of natural vibrations of the tubes. Numerical analyses are carried out to understand the effects of vdW forces and nonlinearity on the carbon nanotubes (CNTs). The results show that the radial vibrational modes of the inner and outer tubes of simply supported DWCNTs have twice dynamical mode transitions as the frequency increases. The transitions correspond to twice the noncoaxial vibrations, which play a critical role in the electronic and transport properties of CNTs.
Analysis of the recombination velocity and of the electron beam induced current contrast at the interface between a metallic precipitate and a semiconductor matrix
Authors: Debez M. , Tarento R.-J. , Mekki D. E.
Published: June 2008

A self-consistent calculation of the barrier height and of the effective recombination velocity at the interface between a metallic precipitate and a semiconductor matrix has been performed within the Read–Hall–Shockley framework. The procedure has taken account of the bending of the minority carrier quasi-Fermi level across the precipitate space-charge region and in the quasineutral region assuming the rigid displacement of the bands. The interface energy states are considered to have a monoenergetic distribution in two limiting cases including the half-filled-level model. The recombination has been investigated versus the semiconductor parameters (doping concentration, defect concentration.) and the temperature. The precipitate size has a dramatic effect on recombination. This is due to the enhancement of the surface charge density on the metallic precipitate which increases as σch(R)=σ∞ch+A/Rα when the size decreases. However, the surface charge density reaches at small size a limiting value controlled by the defect concentration. The enhancement of the surface charge density tends to reach significant barrier height up to precipitate sizes of 150 Å. The continuity equation around the precipitate has been solved in the case of a low-level electron beam injection in order to determine the electron beam induced current contrast at the interface. The contrast has been investigated versus the size for different defect concentrations, incident beam energies, and for the two kinds of defect distribution.
Anharmonic infrared and Raman spectra in Car–Parrinello molecular dynamics simulations
Authors: Pagliai Marco , Cavazzoni Carlo , Cardini Gianni , Erbacci Giovanni , Parrinello Michele , Schettino Vincenzo
Published: June 2008

The infrared and Raman spectra of naphthalene crystal with inclusion of anharmonic effects have been calculated by adopting the generalized variational density functional perturbation theory in the framework of Car–Parrinello molecular dynamics simulations. The computational approach has been generalized for cells of arbitrary shape. The intermolecular interactions have been analyzed with and without the van der Waals corrections, showing the importance of such interactions in the naphthalene crystal to reproduce the structural, dynamical, and spectroscopic properties.
On the need for a tunneling pre-factor in Fowler–Nordheim tunneling theory
Authors: Forbes Richard G.
Published: June 2008

This paper argues that a tunneling prefactor should appear in expressions for the tunneling probability D relevant to cold field electron emission (CFE) and in Fowler–Nordheim (FN) type equations. Except in the case of the “ideally smooth” parabolic barrier, a prefactor is always present for barriers where D can be found by exact solution of the Schrödinger equation. A review of the Jeffreys–Wentzel–Kramers–Brillouin (JWKB) approach to solving the Schrödinger equation shows that tunneling barriers should be classified according to whether they are weak or strong and ideally smooth or not: there are four different JWKB-type formulas, depending on the nature of the barrier. CFE tunneling barriers are not ideally smooth but since the 1950s have usually been analyzed using the JWKB formulas for ideally smooth barriers. These analyses, and the standard Murphy–Good FN-type equation, seem mathematically and physically incomplete. The FN-type equations currently used to describe CFE should be revised to explicitly include a tunneling prefactor. Some implications are explored.
Polarization in optical near and far fields and its relation to shape and layout of nanostructures
Authors: Naruse M. , Yatsui T. , Hori H. , Yasui M. , Ohtsu M.
Published: June 2008

We discuss the polarization control in optical near fields and far fields by engineering nanostructures, focusing on the individual shapes of elemental structures and their arrangement, called elemental-shape and layout factors, respectively. These factors are physically related to electrical currents induced within elemental shapes and optical near fields between elemental shapes, respectively, which are then associated with polarization properties in a unified manner by using the concept of flow vectors. The proposed scheme explains polarizations in optical near and far fields in an intuitive manner, such as in analyzing layout dependence or symmetry of shapes. Together with the hierarchical properties of optical near fields, it also aids in the design of complex structures, such as three-dimensional multilayer nanostructures for polarization control devices.
Dependence of resistivity on surface profile in nanoscale metal films and wires
Authors: Feldman Baruch , Deng Rui , Dunham Scott T.
Published: June 2008

We extend quantum models of nanowire surface scattering to incorporate bulk resistivity and extract an expression for the increased resistivity due to surface roughness. To learn how to improve conductivity, we calculate conductivity degradation from individual wavelengths of surface roughness, and show how these can be convolved to give resistivity for arbitrary surfaces. We review measurements from Cu films and conclude that roughness at short wavelengths (less than 100 nm) dominates scattering, and that primarily specular scattering should be achievable for root-mean-square roughness below about 0.7 nm.
Gate-first inversion-type InP metal-oxide-semiconductor field-effect transistors with atomic-layer-deposited Al2O3 gate dielectric
Authors: Zhao Han , Shahrjerdi Davood , Zhu Feng , Zhang Manhong , Kim Hyoung-Sub , OK Injo , Yum Jung Hwan , Park Sung Il , Banerjee Sanjay K. , Lee Jack C.
Published: June 2008

We present n-channel enhancement-mode inversion-type indium phosphide (InP) metal-oxide-semiconductor field-effect transistors with atomic-layer-deposited Al2O3 gate dielectric. It has been found that applying sulfur passivation and postdeposition annealing in the process improves the drive current and subthreshold swing. Transistors on semi-insulating InP substrates show much higher drive current than the ones on p-type InP due to the asymmetric distribution of interface state along the bandgap between InP and Al2O3. The effects of transient and slow traps on the transistor performance have also been investigated using constant electrical stress measurements and pulse measurements.