bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal and electrical properties of nitrile‐containing polyimide/BaTiO3 composite films
Authors: Hamciuc Elena , Hamciuc Corneliu , Bacosca Irina , Cristea Mariana , Okrasa Lidia
Published: April 2011

Polyimide composite films were prepared by mixing the BaTiO3 particles into poly(amic acid) solution followed by film casting and thermal imidization under controlled temperature conditions. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(4‐aminophenoxy)benzonitrile, using N‐methyl‐2‐pyrrolidone as solvent. The surface of BaTiO3 particles was modified by treating with an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to characterize the structure and properties of the composites. The influence of BaTiO3 content on the composite film properties was evidenced. The films exhibited good thermal stability having the initial decomposition temperature above 520°C. They had stable dielectric properties over large intervals of temperature and frequency. The dielectric constant and the dielectric loss increased with the increase of BaTiO3 content. The dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions γ and β. At higher temperature an α‐relaxation that corresponds to the glass transition and a conductivity process were evidenced. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
Isolated prenatal choroid plexus cysts do not affect child development
Authors: DiPietro Janet A. , Cristofalo Elizabeth A. , Voegtline Kristin M. , Crino Jude
Published: April 2011

Objective

To examine the effect of isolated prenatal choroid plexus cysts (CPCs) on child cognitive, behavioral, motor, and autonomic development at 18 months of age.

Methods

A prospective design was implemented to identify CPC cases and controls in mid‐pregnancy. Cases (n = 25) and controls (n = 45) participated in a follow‐up visit when children were 18 months of age. Child mental and motor development was assessed using standard developmental assessments, socioemotional and behavioral functioning during testing was rated by examiners, and accelerometers provided measures of motor activity and energy expenditure. Cardiac patterns were collected using a three‐lead electrocardiogram (ECG) and quantified as indicators of autonomic control of the heart, including vagal tone.

Results

No significant differences were found in any outcome measure between children with prenatal CPC detection and those without.

Conclusion

Findings should provide reassurance to practitioners and parents that isolated CPCs in fetuses with normal karyotypes do not affect child development after birth. Copyright © 2011 John Wiley & Sons, Ltd.
Identification of response bias on apparent pregnancy outcome after second trimester ultrasound
Authors: Kozlowski Peter , Stressig Ruediger , Hammer Ruediger , Siegmann Hans Joerg , Froehlich Susanne , Verde Pablo Emilio , Knippel Alexander Johannes
Published: April 2011

Objectives

To investigate whether there is a response bias in outcome studies after prenatal ultrasound and to quantify this potential effect by information source.

Materials and methods

All normal ultrasound scans between week 17 and week 24 and 6 days performed in the years 2004 and 2005 were investigated. A multinomial logistic regression model was applied to investigate the association between responders' outcome (questionnaire, phone interview and inquiry to birth clinic) and the following explanatory variables: maternal age, smoking status, body mass index, congenital anomaly status, low birthweight and preterm deliveries.

Results

From the 12 439 women, 7747 (62.3%) sent back the questionnaire, 3032 (24.4%) were interviewed by telephone and in 1660 cases (13.3%) the outcome was obtained from the birth clinic. Maternal age > 34 years [odds ratio (OR) 0.72, confidence interval (CI) 0.61‐0.85/0.35, CI 0.29‐0.42, telephone/birth clinic] and minor anomalies (OR 0.52, CI 0.28‐0.98, birth clinic) were significantly underrepresented in nonresponders. Preterm delivery (OR 1.29, CI 1.11‐1.50/1.30, CI 1.08‐1.57), maternal smoking (OR 1.14, CI 1.07‐1.25/1.31, CI 1.22‐1.40) and stillbirths (OR 2.30, CI 1.09‐4.87, birth clinic) were significantly, major anomalies (OR 1.83, CI 0.94‐3.55/1.80, CI 0.79‐4.10) were considerably overrepresented in these groups.

Conclusion

Spontaneous responding to prenatal follow‐up questionnaires is significantly biased towards older and nonsmoking mothers with normal pregnancy outcome. Copyright © 2011 John Wiley & Sons, Ltd.
Improvement of melt spinning properties and conductivity of immiscible polypropylene/polystyrene blends containing carbon black by addition of styrene‐ethylene‐butene‐styrene block copolymer
Authors: Strååt Martin , Boldizar Antal , Rigdahl Mikael , Hagström Bengt
Published: April 2011

Conducting polymeric materials prepared from immiscible blends, such as polypropylene (PP)/polystyrene (PS), together with carbon black (CB), are known to have a relatively high electrical conductivity, because of a selective distribution of CB (double percolation). Melt spinning of immiscible blends containing CB has, however, not been extensively reported on previously. An immiscible 1:1 blend of PP and PS to which 4 wt% CB was added exhibited a very low melt draw‐down ratio at rupture compared wit PP with the same content of CB. By adding 5 wt% SEBS (styrene‐ethylene‐butene‐styrene block copolymer), the ultimate melt draw‐down ratio increased about 10 times, which made the material more suitable for melt spinning. As‐extruded samples of the immiscible blends (with CB) did not have higher electrical conductivities than PP/CB. A heat treatment increased the conductivity of immiscible PP/PS/CB composites, and longer treatment times and higher temperatures promoted the conductivity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Preparation of polystyrene particles with different morphologies
Authors: Chen Jiafu , Li Yan , Xue Fengfeng , Chen Zhimin , Xu Qun
Published: April 2011

Micron‐sized, cross‐linked polystyrene (PS) particles with different morphologies were prepared by the developed dispersion polymerization. By scanning electron microscope (SEM) observation, it was found that these PS particles had interesting shapes such as deformed sphere, hollow hemisphere and spheroid‐like shape when initial monomer concentration, reaction time, and temperature and addition way of the reagent added in the third stage were different. The shape of the PS particles was changed from hollow hemisphere to spheroid‐like shape with prolongation of the reaction time. It was remarkable that the rough surface of hollow‐hemisphere‐like PS particles became smooth and the hollow structure of smooth‐hollow‐hemisphere‐like PS particles grew into solid structure at the same time. The formation mechanism behind these phenomena was discussed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Kinetic and structural studies of the polymerization of N,N′‐bismaleimide‐4,4′‐diphenylmethane with barbituric acid
Authors: Su Heng‐Lei , Hsu Jung‐Mu , Pan Jing‐Pin , Wang Tsung‐Hsiung , Yu Fu‐En , Chern Chorng‐Shyan
Published: April 2011

Both the isothermal and non‐isothermal polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) with barbituric acid (BTA) were investigated by the differential scanning calorimeter. The experimental results showed that the polymerizations of BMI with BTA were governed by the competitive Michael addition reaction and free radical polymerization mechanisms. Furthermore, the contribution of free radical polymerization becomes more important when the mole fraction of BTA decreases. 1H NMR and 13C NMR measurements further support the coexistence of the Michael addition reaction and free radical polymerization mechanisms. A preliminary kinetic model that took into account the competitive Michael addition reaction and free radical polymerization mechanisms was developed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Thermomechanical properties of arylamine‐based benzoxazine resins alloyed with epoxy resin
Authors: Rimdusit Sarawut , Kunopast Pathomkorn , Dueramae Isala
Published: April 2011

Effects of epoxy resin on various arylamine‐based benzoxazine resins, i.e., aniline (BA‐a), m‐toluidine (BA‐mt), and 3,5‐xylidine (BA‐35x), have been investigated. Processing windows of BA‐35x, BA‐mt, and BA‐a were found to be widened with the amount of the epoxy. Gel points of benzoxazine‐epoxy resin mixtures can be predicted by an Arrhenius equation, e.g., gel time of BA‐35x and epoxy mixture at 70:30 mass ratio can be estimated by tgel = 0.7012 × 10−7 exp (10.563/T). Glass transition temperature (Tg) of BA‐a and BA‐mt alloyed with epoxy exhibited a synergistic behavior with the maximum Tg value at the benzoxazine‐epoxy composition of 80:20 mass ratio. However, in the BA‐35x and epoxy mixture, the decreasing trend in Tg from 241°C to 223°C with an addition of epoxy was observed. Furthermore, flexural strength and strain‐at‐break of those alloys were found to increase with increasing amount of the epoxy while modulus increased with the polybenzoxazine mass fraction. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Method to characterization of the overmolded polymer penetration into the fabric
Authors: Martinez Arantza , Castany Javier , Serraller Francisco
Published: April 2011

A penetration into the fabric is a typical defect which appears when plastic is injected over textile and it is able to pass through the fabric to reach the aesthetic side of the part. Once that penetration takes place, the faulty piece is rejected and a possible solution to eliminate the defect is the trial and error process, changing successively the injection parameters, and therefore increasing the production costs. For that reason, it is very important to characterize these penetrations in order to anticipate the injection conditions that cause the defect and consequently, to optimize the overmolded injection process, reducing to the maximum the number of rejected pieces. In this article, the work consists of designing a methodology to combine injection parameters and fabric tension that causes the penetration that appears to characterize them. The combination of minimum tension, minimum injection temperature, and minimum injection pressure in the exact point in which defect appears will characterize the penetration. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Development of a multiple‐hole die for the production of single large blocks of low‐density polystyrene using carbon dioxide as a blowing agent
Authors: van Spronsen Jaap , van Luijtelaer Jeroen P.H. , Stoop Albert , Scheper J. Christian , de Vries Tjerk J. , Kroon Maaike C.
Published: April 2011

A multiple‐hole die for the production of single large blocks of polystyrene foam with carbon dioxide as blowing agent was developed. First, single‐hole die experiments were carried out with different hole sizes (2.0, 1.0, and 0.50 mm). Using these single‐hole dies dimensionally‐stable foam was produced with a density of 31 kg m−3 and an open cell structure. Next, the hole diameter and hole distances for a newly constructed multiple‐hole die were chosen on basis of the radial expansion in the single‐hole die experiments. Tests with the multiple‐hole die showed that the seven strings could melt together forming one large string with a diameter of about 20 mm and a density of 50 kg m−3. Therefore, the concept of using a multiple‐hole die for producing single large blocks of polystyrene was proven. However, larger block sizes were not possible because of the limited capabilities of the extruder. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Effects of thermo‐oxidative aging on chain mobility, phase composition, and mechanical behavior of high‐density polyethylene
Authors: Shi Xiaomei , Wang Jingdai , Stapf Siegfried , Mattea Carlos , Li Wei , Yang Yongrong
Published: April 2011

The thermo‐oxidative degradation behavior of high‐density polyethylene (HDPE) was investigated during oven aging at 100°C. 1H low‐field solid‐state nuclear magnetic resonance (NMR) was used to characterize the behaviors of molecular chains and the changes in phase content of HDPE during aging. NMR free induction decays (FIDs) were fitted by three components corresponding to the crystalline phase, interphase, and amorphous phase, respectively. The prolongation of aging led to a progressive increase in the crystalline phase at the expense of the other two phases. A slight decrease in chain mobility of the crystalline phase and interphase was observed simultaneously. The results obtained from other traditional technical approaches are also discussed in the context of the molecular dynamics properties revealed by NMR. The reduction in molecular weight, in chain mobility and the increase in crystallinity during thermo‐oxidation were the main factors, which caused the loss of mechanical performance of HDPE. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Novel hyperbranched polyphenylsilsesquioxane‐modified cyanate ester resins with improved toughness and stiffness
Authors: Zhuo Dongxian , Gu Aijuan , Liang Guozheng , Hu Jiang‐tao , Yuan Li , Ji Lifu
Published: April 2011

High‐performance thermosetting resins should have good toughness and stiffness, so simultaneously toughening and stiffening is the main target in developing high‐performance resins. A novel modified cyanate ester resin with improved toughness and stiffness was developed by copolymerizing 2,2′‐bis(4‐cyanatophenyl)isopropylidene (CE) with hyperbranched polyphenylsilsesquioxane (HBPPSi). The mechanical properties and their nature were systematically investigated from the viewpoint of structure‐property relations using positron annihilation lifetime spectroscopy and spectral analyses. It is found that a suitable content of HBPPSi in CE resin can effectively improve toughness and stiffness. In the case of the CE resin modified with 10 wt% HBPPSi, its impact and flexural strengths are 21 kJ m−2 and 148 MPa, respectively, about 2.6 and 1.4 times of those of neat CE resin. The flexural modulus increases from 3.0 (for neat CE resin) to 3.4 GPa. The results of dynamic mechanical analyses also corroborate the static mechanical properties. The improved toughness and stiffness of CE resin can be attributed to the synergistic effect resulting from changes of both polymer chain structure and aggregation state structure. These attractive features of HBPPSi/CE resins suggest that the method proposed herein may be a new approach for the development of high‐performance resins for cutting‐edge industries. Copyright © 2011 Society of Chemical Industry
Supramolecular fuzzy recognition leads to effective differentiation of similar molecules
Authors: Wan Decheng , Pu Hongting , Jin Ming , Wang Guowei , Huang Junlian
Published: April 2011

The separation of structurally similar molecules remains a general challenge; here, we report that a roughly defined macromolecular nanocapsule can efficiently separate a variety of structurally similar mixtures. The nanocapsule is a core−shell amphiphilic macromolecule (CAM) hydrophobically derived from hyperbranched polyethylenimine with 2‐hexadecyloxymethyloxirane. It is found that with further chemical core engineering of the CAM, its guest selectivity can be radically enhanced, although specific host−guest interaction is absent or ignorable in the system. As a result, two groups of structurally similar guests such as fluorescein/tetrachlorofluorescein, and rose bengal/erythrosine B/eosin Y, can be well recognized by the CAMs. It is known that a complex (fuzzy) system is generally characterized by complexity and nonlinearity; thus core engineering of a CAM is possible to amplify the difference of the competitive guests and lead to effective guest differentiation, such a mechanism is called supramolecular fuzzy recognition (SFR). Our results demonstrate that with appropriate combination of various elementary interaction styles, SFR can lead to effective recognition of a wide spectrum of mixtures. Moreover, a SFR host can be roughly defined in structure and thus readily available. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Rendering polyureas melt processible
Authors: Kang Jungmee , Erdodi Gabor , Kennedy Joseph P.
Published: April 2011

Because of the presence of extensive H‐bonding in the hard segments, polyureas are processed by solution techniques (e.g., dry spinning) by the use of relatively costly and environmentally unfriendly solvents. Thus, the objective of this research was to render polyureas melt processible, (i.e., to reduce their flow temperature, Tflow) without compromising their excellent mechanical properties. We hypothesized and herein demonstrate that by using conventional chain extenders (CEs) in combination with small amounts of H‐bond acceptor chain extenders (HACEs), the Tflow of polyureas can be significantly reduced from ∼230 to ∼180 °C, and thus melt processible products with excellent mechanical properties can be obtained. We document the synthesis of conventional polytetramethylene oxide‐based and novel polyisobutylene (PIB)‐based polyureas with Tflows ∼ 180 °C and excellent mechanicals by the addition of few percents of commercially available HACEs. Products were characterized by various techniques, including Instron (tensile strengths, elongations), durometer (Shore A Hardness), dynamic mechanical thermal analysis (Tflow), and thermal gravimetric analysis (TGA) (thermal weight loss). According to TGA, a polyurea with Tflow of ∼180 °C did not degrade up to ∼234 °C in air. A micromorphology for melt processible polyureas is proposed that emphasizes flexibilized hard segments in the presence of HACEs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Comparative study on polyimides from isomeric 3,3′‐, 3,4′‐, and 4,4′‐linked bis(thioether anhydride)s
Authors: Wei Haibing , Pei Xueliang , Fang Xingzhong
Published: April 2011

Three isomeric bis(thioether anhydride) monomers, 4,4′‐bis(2,3‐dicarboxyphenylthio) diphenyl ketone dianhydride (3,3′‐PTPKDA), 4,4′‐bis(3,4‐dicarboxyphenylthio) diphenyl ketone dianhydride (4,4′‐PTPKDA), and 4‐(2,3‐dicarboxyphenylthio)‐4′‐(3,4‐dicarboxyphenylthio) diphenyl ketone dianhydride (3,4′‐PTPKDA), were prepared through multistep reactions. Their structures were determined via Fourier transform infrared, NMR, and elemental analysis. Three series of polyimides (PIs) were prepared from the obtained isomeric dianhydrides and aromatic diamines in N‐methyl‐2‐pyrrolidone (NMP) via the conventional two‐step method. The PIs showed excellent solubility in common organic solvents such as chloroform, N,N‐dimethylacetamide, and NMP. Their glass‐transition temperatures decreased according to the order of PIs on the basis of 3,3′‐PTPKDA, 3,4′‐PTPKDA, and 4,4′‐PTPKDA. The 5% weight loss temperatures (T5%) of all PIs in nitrogen were observed at 504–519 °C. The rheological properties of isomeric PI resins based on 3,3′‐PTPKDA/4,4′‐oxydianiline/phthalic anhydride showed lower complex viscosity and better melt stability compared with the corresponding isomers from 4,4′‐ and 3,4′‐PTPKDA. In addition, the PI films based on three isomeric dianhydrides and 2,2′‐bis(trifluoromethyl)benzidine had a low moisture absorption of 0.27–0.35%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Chemical modification of chain end in nylon 4 and improvement of its thermal stability
Authors: Tachibana Koichiro , Hashimoto Kazuhiko , Tansho Noriyuki , Okawa Haruki
Published: April 2011

Two kinds of nylon 4 having an acyllactam group at one or both chain ends were synthesized by the anionic ring‐opening polymerization of 2‐pyrrolidone using N‐benzoyl‐2‐pyrrolidone (BP) or N,N′‐isophthaloylbis‐2‐pyrrolidone (IPP) and potassium tert‐butoxide as an initiator and a catalyst, respectively, and carefully isolated with the suppression of moisture adsorption. The acyllactam at one chain end in the low molecular weight of nylon 4 was quantitatively converted to other functional groups such as carboxy, amine and so on, which were confirmed by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI TOF) mass spectroscopy. Terminal acyllactam groups telechelating in the nylon 4 at both chain ends were also modified to carboxy and amino groups. From the thermogravimetric analysis (TGA), thermal decomposition point of the modified nylon 4 was increased in comparison with that of the original acyllactam‐type nylon 4, although the acyllactam chain end caused the backbiting depolymerization accompanied with the generation of 2‐pyrrolidone monomer. The direct heating of the acyllactam‐telechelic low molecular weight of nylon 4 mixed with the diamine in bulk also led to improve its thermal stability significantly by the chain extension through the polyaddition reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Polymerization mechanism of trimethylene carbonate carried out with zinc(II) acetylacetonate monohydrate
Authors: Pastusiak Malgorzata , Dobrzynski Piotr , Kaczmarczyk Bozena , Kasperczyk Janusz
Published: April 2011

The proposed mechanism of initiation and course of ring‐opening polymerization of cyclic trimethylene carbonate (TMC) involving zinc(II) acetylacetonate is in accordance with the mechanism of monomer activation. At the first stage of the process, coordination of carbonate to Zn(Acac)2·H2O complex occurs with the release of weakly coordinated water molecules. This free water molecule reacts with active TMC–Zn(Acac)2 complex. The reaction results in the formation of propanediol and CO2 emission. During further stages of the investigated process, the formed propanediols, or later the oligomeric diols produced with polymerization, are cocatalysts of the chain propagation reaction. The chain propagation occurs because of repeating activation of the TMC monomer through the creation of an active structure resulting in the exchange/transfer reaction between the zinc complex and the monomer, with its following attachment to the hydroxyl groups, carbonate ring opening, and formation of the carbonic unit of polymer chain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Challenges due to aging plants
Authors: Ramírez Pedro A. Pérez , Utne Ingrid Bouwer
Published: April 2011

The management of aging of plants has become an important issue for oil and gas (O&G) companies that intend to extend the lifetime of their facilities. Important requirements are that the installations must be safe and economical to remain in operation. This can be achieved by implementing aging plant management programs to control and mitigate the degradation of the facilities. Aging plants have been a crucial topic for several years within the nuclear power industry, but it is a relatively novel area for the offshore O&G industry. To develop a successful aging plant management program for an existing offshore O&G installation, it is necessary not only to learn from the experience of other industries but also to understand and address the specific challenges for managing the aging of these facilities. The objective of this article is to outline these issues and to highlight future challenges. © 2011 American Institute of Chemical Engineers Process Saf Prog 2011
Time‐resolved ultrafast carrier dynamics in CdTe quantum dots under high pressure
Authors: Liu Bingguo , He Chunyuan , Jin Mingxing , Ding Dajun , Gao Chunxiao
Published: April 2011

Ultrafast carrier relaxation in CdTe quantum dots (QDs) was studied under high pressure by using femtosecond transient absorption spectroscopy. The pressure effects on the carrier relaxation time are obtained for surface trapped electron‐hole recombination and electronic Auger recombination processes. The decrease of the transient absorption signals and the change of sample colour with pressure are assigned to the shift of the energy levels. This shift of the energy levels can lead to an electron transition for materials. And the abrupt changes of the relaxation time at 0.5 and 1.5 GPa are attributed to the electron transition in CdTe QDs under high pressure. Therefore, the high‐pressure ultrafast carrier dynamics research provides a new approach for studying the electron transition in condensed matter.
Study on phase transition of SrTiO3 by in situ impedance measurement under high pressure
Authors: Wang Qinglin , Yang Jie , Liu Bao , Liu Cailong , Hu Tingjing , Li Yan , Su Ningning , Sang Dandan , Han Yonghao , Gao Chunxiao
Published: April 2011

The pressure dependence of electrical resistance of perovskite SrTiO3 has been studied by in situ impedance measurement in diamond anvil cell up to 31 GPa at room temperature. Two discontinuous changes in resistance were observed at about 9.8 and 21 GPa, which are coincident with the pressure‐induced phase transitions from cubic phase to tetragonal phase and then to orthorhombic phase, respectively. High‐pressure angle dispersive X‐ray diffraction experiments on SrTiO3 powders have also been performed up to 35 GPa. It was found that a structure phase transition from cubic to tetragonal phase begins to take place at about 6.49 GPa but clear indication for a further transition to an orthorhombic phase at higher pressure up to 35 GPa is hardly seen in our X‐ray diffraction data.
The phase transition of Zn0.854Cu0.146O under high pressure
Authors: Jin Yunxia , Zhang Jian , Zhu Pinwen , Gao Wei , Cui Qiliang
Published: April 2011

Pressure induced phase transition of hexagonal Zn0.854Cu0.146O is studied by using synchrotron angle dispersive X‐ray diffraction (ADXRD) up to 43.1 GPa at room temperature. A structural transformation from a hexagonal phase to a cubic phase is observed, which starts at 10.2 GPa and finishes at about 16.5 GPa. The phase transition leads to a volume collapse of 17% at 10.2 GPa. The cubic phase of Zn0.854Cu0.146O remains stable up to the highest experiment pressure. The pressure–volume data are fitted with the Birch–Murnaghan equation of state. The bulk modulus obtained upon compression from the fitting are 175(2) and 259(6) GPa for the hexagonal and cubic phases, respectively.
Influence of high electron concentration on band gap and effective electron mass of InN
Authors: Donmez O. , Yilmaz M. , Erol A. , Ulug B. , Arikan M. C. , Ulug A. , Ajagunna A. O. , Iliopoulos E. , Georgakilas A.
Published: April 2011

Effects of high electron concentration on the band gap energy of InN films having different layer thicknesses as 600 and 800 nm are investigated experimentally and theoretically. Electron concentrations of the samples are obtained through the Hall measurements accomplished between 77 K and room temperature. Optical characterization of the samples is carried out using the photoluminescence (PL) measurements and the observed PL spectra are explained considering the high electron concentration related effects, i.e. Burstein–Moss shift, band renormalization and band tailing in non‐parabolic k · p model. Extracted PL results indicate that the samples have approximately 0.685 eV band gap energy at 77 K. Effective mass of the carriers, which is calculated as 0.097 m0 for electron concentration of ∼1019 cm−3, are also observed to be influenced by the high carrier concentration.
Wavelength selective switching in dilute nitrides multi quantum well photonic band gap waveguides
Authors: Calò Giovanna , Alexandropoulos Dimitris , D'Orazio Antonella , Petruzzelli Vincenzo
Published: April 2011

The analysis of the gain behaviour in active GaInNAs–GaInAs Photonic Band Gap (PBG) ridge waveguides is reported. The analysis is performed using proprietary codes, based on the Bidirectional Beam Propagation Method with the Method of Lines, introducing the rate equations. The bandstructure of the active material is modelled using the k · p theory for the valence band mixing effects and the band anticrossing model for the conduction band. A wavelength selective switch configuration is proposed exploiting a periodic grating patterned on a ridge waveguide in which an active defect is inserted. The presence of the active defect allows the localization of states and the transmission of the optical signal within the PBG. The wavelength selective switching mechanism stems from the possibility of shifting the wavelength of the localized state by properly choosing the defect length and the injected current density. From the numerical analysis, the proposed device exhibits, at the switching wavelength λB = 1.289 µm, good values of the crosstalk CT = −11.55 dB, the contrast ratio CR = 14.29 dB, the modulation depth MD = 0.93, and the bandwidth Δλ = 0.8 nm.
Investigation of the In composition in InGaN/GaN quantum wells deposited by MOVPE and/or MBE with emission from violet to green
Authors: Mutta G. R. , Ruterana P. , Doualan J. L. , Chauvat M. P. , Ivaldi F. , Kret S. , Kaufmann N. A. K. , Dussaigne A. , Martin D. , Grandjean N.
Published: April 2011

Transmission electron microscopy and photoluminescence investigations have been carried out on a series of quantum wells grown by molecular beam epitaxy and metal organic vapour phase epitaxy. In both cases, the emission wavelength and the peak width agree with the indium local composition as extracted from strain measurements and with the well width. As could be expected, the data is at small variance with the nominal values as set during growth, but the general trends are similar.
High pressure Raman study of LiBC
Authors: Zhu Pinwen , Han Dandan , Tang Ruilian , Li Nana , Gao Wei , Wang Xin
Published: April 2011

The effects of pressure on the zone‐center optical phonon modes of LiBC, which is structurally and electronically similar to the superconductor MgB2, have been investigated by Raman spectroscopy. At ambient pressure, four main lattice modes have been revealed with frequencies at 1173, 831, 552, and 174 cm−1, respectively, while only lines at 1173 and 174 cm−1 correspond to the expected Raman active E2g modes. The longitudinal‐optical phonon modes involving the Li sheets which can provide a coupling between neighboring B–C planes are expected to couple with the plasmon mode and are suggested to be related with the appearance of the forbidden lines. With increasing pressures, it is found that LiBC remains stable up to 15.5 GPa. All the observed modes harden and exhibit broadening effects under high pressure, especially for the B–C bond stretching mode (at 1173 cm−1) which shows a nonlinear pressure dependence. It indicates that the broadening may be caused by complex coupling interactions, and the pressure‐enhanced coupling should give rise to a strongly anharmonic behavior of these modes.
Phase transition of ZnxMn1‐xS dilute magnetic semiconductor nanoparticles under ultra‐high pressure
Authors: Zong Zhaocun , Ma Yanmei , Hu Tingting , Cui Qiliang , Zhang Mingzhe , Zou Guangtian
Published: April 2011

The high‐pressure behavior of different doping content of ZnS nanocrystals has been investigated using angle‐dispersive synchrotron X‐ray powder diffraction up to 45.1 GPa. A phase transformation from the zinc‐blende(ZB) to the rock‐salt (RS) structure is observed at pressures of about 17.7 and 18.3 GPa at room temperature, corresponding to the Mn2+ ion mole percent content solutions 0.85% and 1.26%, respectively. The obtained results indicate that the Mn2+ doping could obviously enhance the phase transition pressure of ZnS nanocrystal. The elevation of phase transition pressure could origin from the higher surface energy induced by ion doping (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of slow light in the coupled resonator optical waveguides using the local Fourier modal method
Authors: Park Junghyun , Kim Hwi , Lee Byoungho
Published: April 2011

We present the Bloch modal analysis of photonic crystal coupled resonator optical waveguide (CROW) based on the local Fourier modal method (LFMM). The objective of this analysis is to extract the dispersion relation and analyze optical Bloch eigenmodes of the structure. The evolution of each Bloch eigenmode with varying frequency can be visualized with the proposed LFMM. The recently proposed CROW structure of NTT Basic Research Laboratory group with missing center holes and perturbed lateral shift of holes near the center is taken as the exemplary CROW structure (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evidence of anti free volume creation during deformation induced nanocrystallization of Nd–Fe–B metallic glass
Authors: Shukla Shashwat , Banas Agnieszka , Ramanujan Raju
Published: April 2011

The Extended X‐ray Absorption Fine‐Structure (EXAFS) technique was used to study the time evolution of the structure of Nd–Fe–B metallic glass undergoing nanocrystallization during mechanical milling. Negative as well as positive fluctuations in atomic density were observed, providing direct evidence of the creation of deformation‐induced pairs of free volume and anti‐free volume defects. These defects migrated during milling, leading to the atomic redistribution and precipitation of nanocrystals. Our results demonstrate that atomic defects caused by deformation of metallic glasses involve more extensive athermal changes in short‐range order than nearest neighbour bond breaking as suggested by the free volume model. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron smearing in DFT calculations: A case study of doxorubicin interaction with single‐walled carbon nanotubes
Authors: Basiuk Vladimir A.
Published: April 2011

To address the choice of an appropriate value of electron smearing to facilitate self‐consistent field (SCF) convergence, we studied the interaction of doxorubicin with short armchair and zigzag single‐walled carbon nanotube models with closed caps, at the PWC/DNP level of density functional theory. By gradually reducing the electron smearing value from a large and most commonly used one of 0.005 Ha to zero (Fermi occupation), we monitored the changes in close contacts between the interacting species, total energy of the molecular system, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy and isosurfaces, HOMO‐LUMO gap energy, and plots of electrostatic potential. It became evident that the commonly used smearing values of ≥0.001 Ha can alter the results significantly (for example, by one order of magnitude for HOMO–LUMO gap energy). We suggest the setting of electron smearing value at 0.0001 Ha, which does not imply too high computation cost and can guarantee the results close to the ones obtained with Fermi occupation. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
Computational study of the catalytic synthesis of 5‐nitro‐1,2,4‐triazol‐3‐one
Authors: Cheng Ken‐Fa , Liu Min‐Hsien , Yang Ping‐Hua
Published: April 2011

In this study, 5‐nitro‐1,2,4‐triazol‐3‐one (NTO) was theoretically synthesized from urea via chlorination followed by amination, formylation, and nitration under aqueous and gaseous environments based on experience of experimental methods, and metal chlorides and metal oxides were used as catalysts to promote reaction. Reaction routes closely related to experimental processes were successfully constructed, and the corresponding energy barriers were estimated for each elementary reaction. Reaction conditions distinct from those reported in the literature (including the adoption of aluminum chloride, ferric chloride, aluminum oxide, ferrous oxide, and chromium oxide catalysts, the use of nitric acid and dinitrogen pentoxide as nitration agents, and adjustment of the reaction temperature) were used in corresponding reaction systems, and the modeling results suggested that ferric chloride is a good catalyst for the chlorination reaction, ferrous oxide is suitable for catalyzing amination, formylation, and nitration, and nitric acid is the better agent for nitration. Estimates of the comparable energy barriers for each reaction stage were considered to imply more feasible pathways for NTO synthesis. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
CCSD(T)‐F12 investigations on HBNH and its isotopologues
Authors: Brites Vincent , Léonard Céline
Published: April 2011

CCSD(T)‐F12 ab initio computations are performed to investigate the isomerization path between HBNH and BNH2, and the six‐dimensional potential energy surface of the electronic ground state X̃1Σ+ of the linear isomer. The equilibrium geometries and harmonic wavenumbers obtained at the CCSD(T)‐F12a/aug‐cc‐pVTZ level of theory are nearly those computed with the CCSD(T)/aug‐cc‐pV5Z level, but with a smaller amount of CPU time for the evaluation of the total energy. The analytical representation of the potential energy surface is used in variational calculations of the rovibrational energy levels of H11BNH and isotopologues. The computed rovibrational energy levels are compared with the available experimental data, and a good agreement is generally noticed. We also propose an assignment of the rovibrational energy levels of H11BNH up to 3000 cm−1 above the zero point energy. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
Theoretical study of static (Hyper)polarizabilities of twisted intramolecular charge transfer chromophores
Authors: Liu Liuxia , Xue Ying , Wang Xin , Chu Xiang , Yang Mingli
Published: April 2011

Density functional theory calculations are performed to study the (hyper)polarizabilities of a series of planar and twisted intramolecular charge transfer molecules (tictoids) with different electron‐donating and electron‐withdrawing groups. Both similarity and difference between the planar and twisted molecules are noted in their (hyper)polarizability variation with respect to substituent and solvent dielectric constant. When compared with dramatic enhancements resulting from geometry twist and solvent effect, substitution to D/A pairs leads to relatively moderate variation in (hyper) polarizability. In addition, tictoids with different substituents may exhibit different solvent effects in their hyperpolarizability magnitudes. Our calculations suggest that the nonlinear optical response of the tictoids could be tuned by appropriately selecting the donor/acceptor pairs and solvents. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
Approximate Hamilton decompositions of random graphs
Authors: Knox Fiachra , Kühn Daniela , Osthus Deryk
Published: April 2011

We show that if pn ≫ log n the binomial random graph Gn,p has an approximate Hamilton decomposition. More precisely, we show that in this range Gn,p contains a set of edge‐disjoint Hamilton cycles covering almost all of its edges. This is best possible in the sense that the condition that pn ≫ log n is necessary. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2012
Assessing the sensitivity of [11C]p943, a novel 5‐HTIB radioligand, to endogenous serotonin release
Authors: Cosgrove Kelly P. , Kloczynski Tracy , Nabulsi Nabeel , Weinzimmer David , Lin Shu‐Fei , Staley Julie K. , Bhagwagar Zubin , Carson Richard E.
Published: April 2011

The main objective of the current study was to determine the sensitivity of the positron emission tomography (PET) radioligand [11C]P943 to fenfluramine‐induced changes in endogenous 5‐HT in nonhuman primate brain. Fenfluramine‐induced changes in 5‐HT1B occupancy were compared to those obtained by self‐block with unlabeled P943. Two baboons and 1 rhesus monkey were given preblocking or displacing doses of fenfluramine (1–5 mg/kg) or preblocking doses of unlabeled P943 (0.2 mg/kg) and imaged with [11C]P943 PET. Receptor occupancy by the low dose of fenfluramine (1 mg/kg) in the baboons was 25 and 29% and by the high dose of fenfluramine (5 mg/kg) in the rhesus macaque was 42%. Receptor occupancy by P943 (0.2 mg/kg) was 68 and 86% in the baboons. PET imaging of 5‐HT1B receptors with [11C]P943 may be a useful approach for measuring changes in endogenous 5‐HT in the living human brain. Synapse, 2011. © 2011 Wiley‐Liss, Inc.
Selection of STOP‐free sequences from random mutagenesis for ‘loss of interaction’ two‐hybrid studies
Authors: Lickfeld Manuela , Schmitz Hans‐Peter
Published: April 2011

The investigation of protein–protein interactions is an essential part of biological research. To obtain a deeper insight into regulatory protein networks, the identification of the components, domains and especially single residues that are involved in these interactions is helpful. A widespread and attractive genetic tool for investigation of protein–protein interactions is the yeast two‐hybrid system. This method enables large‐scale screens and its application is cheap and relatively simple. For identification of the amino acids in a protein sequence that are essential for interaction with a specific partner, yeast two‐hybrid assays can be combined with random mutagenesis of the sequence of interest. A common problem with such an experiment is the generation of stop codons within the mutagenized fragments, leading to the isolation of many false positives when screening for loss of interaction using the two‐hybrid method. To overcome this problem, we modified the yeast two‐hybrid system to allow selection for sequences without stop codons. To achieve this, we fused the ScURA3 marker‐gene in frame to the mutagenized fragments. We show here that this marker is fully functional when fused to a two‐hybrid construct with a nuclear localization signal, such as a Gal4 activation domain and a prey protein, thus allowing selection of stop‐free sequences on media without uracil. Using the Rho‐binding domain from a Bni1‐like formin and different Rho‐type GTPases from Ashbya gossypii as examples, we further show that our system can be used to screen large numbers of transformants for loss of protein–protein interactions in combination with random mutagenesis. Copyright © 2011 John Wiley & Sons, Ltd.
Hydrophilic Interaction Liquid Chromatography: ESI–MS/MS of Plasmalogen Phospholipids from Pectinatus Bacterium
Authors: Řezanka Tomáš , Siristova Lucie , Matoulková Dagmar , Sigler Karel
Published: April 2011

Liquid chromatography–electrospray tandem mass spectrometry (LC/ESI–MS/MS) was used to analyze phospholipids from three species of the anaerobic beer‐spoilage bacterial genus Pectinatus. Analysis of total lipids by HILIC (Hydrophilic Interaction Liquid Chromatography) column succeeded in separating diacyl‐ and plasmalogen phospholipids. Plasmalogens were then analyzed by means of the ESI–MS/MS and more than 220 molecular species of four classes of plasmalogens (PlsCho (choline plasmalogen), PlsEtn (ethanolamine plasmalogen), PlsGro (glycerol plasmalogen), and PlsSer (serine plasmalogen)) were identified. Major molecular species were c‐p19:0/15:0 PlsEtn and PlsSer, which accounted for more than 4% of the total lipids.
Globalizing Responsibility for Climate Change
Authors: Vanderheiden Steve
Published: April 2011

Who should pay the costs associated with anthropogenic climate change, how much should they pay, and why? This burden-distribution problem has become the central question of climate justice among scholars and activists, and it remains the primary obstacle to the development of an effective climate regime. The costs are expected to be significant and varied, but can generally be categorized in terms ofmitigation—that is, those costs associated with reducing further human contributions toward the increasing atmospheric concentrations of heat-trapping greenhouse gases (GHGs) that cause climate change; andadaptation—that is, those costs that result from attempting to insulate humans from the harms associated with the anthropogenic environmental damage of climate change. Since mitigation actions undertaken by developed countries under the auspices of the Kyoto Protocol are self-financed and mitigation targets accepted by developing countries are widely viewed as contingent upon financing from developed countries, imperatives to reduce GHGs are fundamentally matters of allocating mitigation costs. Adaptation intervenes in the causal chain between climate change and human harm, allowing the former but preventing the latter, but when this is not possible, a third category ofcompensationcosts must be assigned in order to remedy failed mitigation and adaptation efforts. Because the formulas for assessing liability for adaptation and for compensation are identical, and since climate justice requires adaptation efforts that render compensation unnecessary, for the purposes of this essay the category of adaptation shall be understood to include prevention of harm as well asex postcompensation for it. As expected, the “Copenhagen Accord” that emerged from the Fifteenth session of the Conference of the Parties (COP15) to the 1992 UN Framework Convention on Climate Change (UNFCCC) in December 2009 failed to satisfactorily address this core burden-allocation issue, making its resolution the primary problem to be addressed at the COP16 in Cancún, Mexico, at the end of 2010.
Clean Trade in Natural Resources
Authors: Wenar Leif
Published: April 2011

The “resource curse” can strike countries that derive a large portion of their national income from exporting high-value natural resources, such as oil, gas, metals, and gems. Resource-exporting countries are subject to four overlapping curses: they are more prone to authoritarianism, they tend to suffer more corruption, they are at a higher risk for civil wars, and they exhibit greater economic instability.
Heroism: A Conceptual Analysis and Differentiation between Heroic Action and Altruism
Authors: Franco Zeno E. , Blau Kathy , Zimbardo Philip G.
Published: April 2011

Heroism represents the ideal of citizens transforming civic virtue into the highest form of civic action, accepting either physical peril or social sacrifice. While implicit theories of heroism abound, surprisingly little theoretical or empirical work has been done to better understand the phenomenon. Toward this goal, we summarize our efforts to systematically develop a taxonomy of heroic subtypes as a starting point for theory building. Next we explore three apparent paradoxes that surround heroism—the dueling impulses to elevate and negate heroic actors; the contrast between the public ascription of heroic status versus the interior decision to act heroically; and apparent similarities between altruism, bystander intervention and heroism that mask important differences between these phenomena. We assert that these seeming contradictions point to an unrecognized relationship between insufficient justification and the ascription of heroic status, providing more explanatory power than risk-type alone. The results of an empirical study are briefly presented to provide preliminary support to these arguments. Finally, several areas for future research and theoretical activity are briefly considered. These include the possibility that extension neglect may play a central role in public's view of nonprototypical heroes; a critique of the positive psychology view that heroism is always a virtuous, prosocial activity; problems associated with retrospective study of heroes; the suggestion that injury or death (particularly in social sacrifice heroes) serves to resolve dissonance in favor of the heroic actor; and a consideration of how to foster heroic imagination.
Power laws, memory capacity, and self-tuned critical branching in an LIF model with binary synapses
Authors: Kello Christopher , Kerster Bryan
Published: April 2011

Both fluctuations and distributions of spontaneous neural spiking activity have been observed to closely follow a variety of power laws. Multiple explanations have been offered for each observation, but few lead to mechanisms that encompass their widespread occurrence. A canonical, leaky integrate-and-fire model is presented in which synapses are updated based on the timing of pre- and post-synaptic spikes in order to maintain a state of critical branching. Results showed that 1) the self-tuning algorithm maintained critical branching under a range of parameters; 2) power laws were obtained in spiking activity fluctuations (1/f scaling), size distributions of network bursts (neural avalanches), and temporal correlations in interspike intervals (Allan factor); 3) power laws disappeared once the self-tuning algorithm was disabled; and 4) critical branching was adaptive in that it maximized the network’s memory capacity when assessed as a liquid state machine.