bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melt transesterification and characterization of segmented block copolyesters containing 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol
Authors: Zhang Musan , Moore Robert B. , Long Timothy E. 
Published: June 2012

AbstractConventional melt transesterification successfully produced high‐molecular‐weight segmented copolyesters. A rigid, high‐Tg polyester precursor containing the cycloaliphatic monomers, 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol, and dimethyl‐1,4‐cyclohexane dicarboxylate allowed molecular weight control and hydroxyl difunctionality through monomer stoichiometric imbalance in the presence of a tin catalyst. Subsequent polymerization of a 4000 g/mol polyol with monomers comprising the low‐Tg block yielded high‐molecular‐weight polymers that exhibited enhanced mechanical properties compared to a nonsegmented copolyester controls and soft segment homopolymers. Reaction between the polyester polyol precursor and a primary or secondary alcohol at melt polymerization temperatures revealed reduced transesterification of the polyester hard segment because of enhanced steric hindrance adjacent to the ester linkages. Differential scanning calorimetry, dynamic mechanical analysis, and tensile testing of the copolyesters supported the formation of a segmented multiblock architecture. Further investigations with atomic force microscopy uncovered unique needle‐like, interconnected, microphase separated surface morphologies. Small‐angle X‐ray scattering confirmed the presence of microphase separation in the segmented copolyesters bulk morphology. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Facile synthesis of nanoparticles via assembly of photopolymerized and self‐crosslinked random copolymers in selective organic media
Authors: Honglawan Apiradee , Xu Lebo , Yang Shu 
Published: June 2012

AbstractWe report the facile synthesis of vesicular nanoparticles via self‐assembly of random copolymers in selective organic solvents. The polymers were synthesized via photopolymerization in bulk from acryloyl chloride (AC) containing a small amount of hydrolyzed acrylic acid (AA) at ambient condition. Fourier transform infrared spectroscopy of the photopolymerized product revealed two main chemical components: poly(acryloyl chloride) (PAC) and acid anhydride. The later peak intensified when increasing the initial AA composition in the monomer solution, suggesting that the hydrolyzed AC contributed to the formation of crosslinked anhydride, leading to amphiphilicity of the polymer with solvophobic anhydride and solvophilic PAC chains. At an optimal UV dosage (2000 mJ cm−2), vesicular nanoparticles (∼90 nm in diameter) were obtained from polymers assembled in acetone. The particle size and morphology were confirmed by scanning electron microscopy, transmission electron microscopy, and dynamic and static light‐scattering measurements. Further, we found that the random copolymers self‐organized into vesicles in merely good solvents of PAC chains, including acetonitrile, tetrahydrofuran, and 1,4‐dioxane, but became aggregated and precipitated out in poor solvents of PAC, such as isopropanol, ethanol, toluene, xylene, and hexane. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Preparation and Properties of an AP/RDX/SiO2 Nanocomposite Energetic Material by the Sol‐Gel Method
Authors: Chen Renjie , Luo Yunjun , Sun Jie , Li Guoping 
Published: June 2012

AbstractA nanocomposite energetic material was prepared using sol‐gel processing. It was incorporated into the nano or submicrometer‐sized pores of the gel skeleton with a content up to 95 %. AP, RDX, and silica were chosen as the energetic crystal and gel skeleton, respectively. The structure and its properties were characterized by SEM, BET methods, XRD, TG/DSC, and impact sensitivity measurements. The structure of the AP/RDX/SiO2 cryogel is of micrometer scale powder with numerous pores of nanometer scale and the mean crystal size of AP and RDX is approx. 200 nm. The specific surface area of the AP/RDX/SiO2 cryogel is 36.6 m2 g−1. TG/DSC analyses indicate that SiO2 cryogel can boost the decomposition of AP and enhance the interaction between AP and RDX. By comparison of the decomposition heats of AP/RDX/SiO2 at different mass ratios, the optimal mass ratio was estimated to be 6.5/10/1 with a maximum decomposition heat of 2160.8 J g−1. According to impact sensitivity tests, the sensitivity of the AP/RDX/SiO2 cryogel is lower than that of the pure energetic ingredients and their mixture.
Benchtop Energetics: Hyperthermal Species Detection
Authors: Fossum Emily C. , Molek Christopher D. , Lewis William K. , Fajardo Mario E. 
Published: June 2012

AbstractWe propose a novel scheme for monitoring the transition between deflagration and “detonation‐like” behavior of small‐scale explosive samples‐in‐vacuum subjected to short duration shock stimuli. Our approach relies on measuring the chemical identities and velocity distributions of the gaseous species produced by such samples; e.g. the relatively low velocity expansion‐quenched reaction intermediates produced by deflagration versus the hyperthermal thermodynamically stable molecules generated by the termination of a detonation wave at an explosive‐vacuum interface. We demonstrate our ability to detect such species by time‐of‐flight mass spectrometry (TOFMS) using fast Al atoms produced by laser ablation of aluminum metal. Extensive SIMION simulations of ion trajectories in our mass spectrometer lead to a semi‐quantitative model connecting the system operating parameters and the velocity‐dependent neutral species detection efficiency. We present a method for correcting our data for these detection biases, and for transforming them into neutral species velocity and kinetic energy distributions. We also present preliminary TOFMS data of hyperthermal organic molecular species produced by direct laser ablation/ignition of thin‐film nitrocellulose samples.
On the Relationship between Shock and Thermal Initiating Conditions for Various Reactive Powder Mixtures
Authors: Jetté François‐Xavier , Goroshin Samuel , Frost David L. , Higgins Andrew J. , Lee Julian J. 
Published: June 2012

AbstractThe critical conditions for initiation of reaction by shock loading in various compositions that produce little or no gas upon reaction were investigated. Shock recovery experiments using Mn+S were first carried out in two different apparatus geometries and for two different initial sample densities. In one geometry, the sample was subjected to a planar shock followed by interactions with the confining walls. In the other geometry, a curved shock free of wall interactions was delivered to the sample. The low‐density (55 % TMD) Mn+S was found to be significantly more sensitive to the curved shock than to the planar shock with wall interactions. For high‐density (90 % TMD) Mn+S samples however, shock sensitivity was the same in both apparatuses. Next, the reaction onset temperature and the critical initiating shock pressure were determined for a number of powder mixtures using DTA and shock recovery (in the geometry producing planar shocks with interactions with the confinement walls), respectively. For the majority of the mixtures tested, the minimum shock energy required to cause the entire sample mixture to react was found to be much less than the enthalpy of the sample at its reaction onset temperature, with no significant correlation between these two parameters. The process of arrested ball‐milling, which results in a reduction of the reaction onset temperature of a mixture, may lead to an increase in shock sensitivity. Additionally, thermal sensitivity in the particular mixtures considered was not increased when they were first shock‐compacted by sub‐critical shocks.
Oxidation of CdTe thin film in air coated with and without a CdCl2 layer
Authors: Bai Zhizhong , Wang Deliang 
Published: June 2012

AbstractDuring the fabrication process of a CdS/CdTe solar cell, oxygen is often present or intentionally introduced in the CdTe growth and annealing atmospheres. In this study a comparative study was carried out on the oxidation of thin CdTe films during the annealing process in air when coated with and without a CdCl2 layer, respectively. It was found that the presence of a thin CdCl2 coating layer on the CdTe film surface enhanced the oxidation of the CdTe surface. Near the film surface, the film was composed of a low‐melting eutectic mixture of CdTe and oxides of CdTe and Te. The formation of the low‐melting mixture was assisted by the much lowered melting point of CdCl2, the presence of oxides, and the CdTe compound. This low‐melting layer enhanced the oxygen reaction with the CdTe film. The dominant oxide was CdTeO3. A CdTe solar cell with an efficiency of 9.9% was fabricated with a CdTe film subjected to an annealing in air at 400 °C with the presence of a CdCl2 coating layer.
Magnetic properties of Mg‐doped AlN zigzag nanowires
Authors: Hui Yeung Yu , Ye Jing , Lortz Rolf , Teng Kar Seng , Lau Shu Ping 
Published: June 2012

AbstractQuasi‐aligned hexagonal Mg‐doped aluminum nitride zigzag nanowires (AlN:Mg ZNWs) were fabricated on sapphire substrates using chemical vapor deposition method. A saturated magnetic moment of ∼1 emu/cm3 was found in the AlN:Mg ZNWs when a magnetic field was applied parallel to the sample. The AlN:Mg ZNWs exhibited magnetic anisotropy. The magnetic moment was about 50% larger and the coercivity was about 20% smaller when the field was applied parallel to the sample as compared to the applied field perpendicular to the sample. The Curie temperature of the AlN:Mg ZNWs was above 400 K. The origin of the ferromagnetism in the AlN:Mg ZNWs could be attributed to the formation of Mg–N complex which leads to magnetic coupling as revealed by X‐ray photoelectron spectroscopy.
Electronic and magnetic properties of NiMn1−xHoxSb compounds
Authors: Grasin Robert , Rusu Calin , Laslo Ancuta , Dudric Roxana , Mican Sever , Neumann Manfred , Tetean Romulus 
Published: June 2012

AbstractWe study the effects of holmium doping in the half‐Heusler compound NiMnSb. Band structure calculations show that the half‐metallic properties are completely conserved if holmium atoms substitute the manganese ones. The antiparallel coupling of Ho and transition metal magnetic moments was found to be more favorable. The magnetization measurements are in agreement with the results of the structural and XPS analysis and confirm that the holmium atoms occupy lattice sites. There is a very good agreement between the experimental magnetic moments determined at 4.2 K and the calculated ones in the case of antiferromagnetic coupling between the Ho and transition metal magnetic moments.
Effect of strain on the excitonic polarization in graphene ribbons
Authors: Peng Feng , Wang Yatao 
Published: June 2012

AbstractWe study the coherent polarization of excitons in strained graphene ribbons using a bosonization scheme. Within linear elastic theory and a tight‐binding approach, we observe that strain can generate a marked influence on the coherent polarization of excitons and even effectively enhance polarization of excitons on certain conditions. We find that the polarization direction of the positive‐wavevector excitons is opposite to that of the negative‐wavevector excitons under high strain. We explain the micromechanism of generating these phenomena.
Preface: Phys. Status Solidi C 6/2012
Authors: Dappe Yannick , Jelínek Pavel , Cháb Vladimír 
Published: June 2012

AbstractThis issue of physica status solidi collects the Proceedings of the 13th International Conference on the Formation of Semiconductor Interfaces (ICFSI‐13) held in Prague between July 3 and 8, 2011. This series of conferences was organized by the Institute of Physics of the Academy of Sciences of the Czech Republic in cooperation with a group of scientists who started the organization of these meetings in Marseille (France) in 1985. The conferences bring together members of semiconductor physics communities to present and discuss advances of frontier trends in the broad area of semiconductor surface and interface formation. Generally, the scope of the series is concentrated on structure, electronic states, chemistry and dynamical phenomena and their role for future electronics. The meeting addressed the topics of application of theoretical approaches and simulations of interfaces and nanostructures.Proof of the vitality of the conference series was given by the participation of scientists from 29 countries, where 4 out of them came from America, 6 from Asia and 2 from Africa. As much as 230 participants attended the event, and more than a hundred out of them were Ph.D. students or young scientists.The participants have presented 35 invited talks, 76 oral contributions and more than 190 posters. Invited talks highlighted basic research in physics and chemistry at interfaces, mostly between semiconductors and organic molecules. The quality and diversity of the remainder of contributions, both oral and posters, opened up the conference as a steering pell‐mell for future electronics developments. The conference included also one workshop aimed at illustrating the fast developing area of single molecule application for molecular electronics.We thank the International Steering and Program Committees for their wise suggestions on speakers and topics. We also warmly thank the local committee that had helped us tremendously. Finally, we would like to thank all sponsors of the ICFSI‐13 conference.The next conference of this series will be held in Korea, 2013, chaired by of Prof. Han Woong Yeom.
Absorption and emission properties of various substituted cinnamic acids and cinnamates, based on TDDFT investigation
Authors: Promkatkaew Malinee , Suramitr Songwut , Karpkird Thitinun , Ehara Masahiro , Hannongbua Supa 
Published: June 2012

AbstractAbsorption and emission properties of the hydroxy‐, nitro‐, and fluoro‐group substituted at the ortho‐, meta‐, and para‐positions of cinnamic acids (1A–9A) and cinnamates (1E–9E) were investigated using the density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations. The ground (S0)‐ and excited (S1)‐state geometries were obtained at the B3LYP/6‐31G(d) and TD‐B3LYP/6‐31G(d) methods, respectively. On the basis of the optimized structures of the S0‐ and S1‐states, the TDDFT calculations with B3LYP and CAM‐B3LYP functionals were performed to compute the absorption and emission energies of the various substituted cinnamic acids and cinnamates. The solvent effect was examined by the polarizable continuum model in methanol solution. As result, all compounds had the local minimum at the planar structure conformation due to π‐conjugation. The characteristics of the absorption spectra for cinnamic acid and cinnamate derivatives were satisfactorily reproduced by TDDFT method in gas phase and in methanol solution in both peak position and intensity. The emission from the local minimum in the planar structure was calculated for various substituted cinnamic acids and cinnamates. The results obtained by TDDFT investigation provide a useful insight into the detailed information on the optical and electronic properties of these compounds and a useful tool for designing and developing the superior UV absorber compounds. © 2012 Wiley Periodicals, Inc.
Electronic structure of a beryllium half‐sandwich complex, Be(η5‐C5H5)
Authors: Dolgounitcheva Olga , Zakrzewski V. G. , Ortiz J. V. 
Published: June 2012

AbstractAb initio electron propagator calculations on the electron affinities of the
$ {\rm Be(\eta ^5-C_5H_5)}^{+} $
complex cation and electron detachment energies of the corresponding anion have been performed at the optimized geometry of the ground state of the neutral species. These results, obtained with a basis set that includes many diffuse and polarization functions, provide the relative energies of doublet states of
$ {\rm Be(\eta ^5-C_5H_5)} $. In the former set of calculations, energy differences between the 2A1 ground‐state and various excited doublet states are associated with promotion of an unpaired electron from the 6a1 molecular orbital that consists chiefly of s functions on the Be nucleus to higher Be‐centered molecular orbitals that exhibit various patterns of interference between s, p, and d functions. Differences between electron detachment energies of the anion provide the energy separation between the radical's ground state and an excited state in which an electron is promoted from ligand‐centered π orbitals to 6a1. Dyson orbitals and pole strengths corresponding to correlated electron binding energies calculated with various diagonal self‐energy approximations confirm these qualitative pictures of the electronic structure of the lowest states of
$ {\rm Be(\eta ^5-C_5H_5)} $. © 2012 Wiley Periodicals, Inc.
A generalized sector‐bound approach to feedback stabilization of nonlinear control systems
Authors: Alvergue Luis , Gu Guoxiang , Acharya Sumanta 
Published: June 2012

SUMMARYThis paper proposes and develops a generalized sector‐bound approach to feedback stabilization of nonlinear control systems described by state–space models. This approach is inherited from the methodology of the sector‐bounded or passive nonlinearities and influenced by the concept of absolute and quadratic stability. It aims not only to regionally stabilize the nonlinear dynamics asymptotically but also to maximize the estimated region of quadratic attraction and to ensure nominal performance at each equilibrium. More importantly, it has a close connection to gain scheduling and switching control. A path of equilibria is programmed on the basis of the assumption of centered‐ ε‐cover, which leads to a sequence of linear controllers that regionally stabilize the desired equilibrium asymptotically. Simulation results are worked out to illustrate our proposed design method. Copyright © 2012 John Wiley & Sons, Ltd.
Remarks on the relationship between stability and internal stability of nonlinear systems
Authors: Wang Xu , Grip Håvard Fjær , Saberi Ali , Stoorvogel Anton A. , Saberi Ingmar 
Published: June 2012

SUMMARYIn this paper, we investigate the relationship between stability and internal stability of nonlinear systems. It is shown that under certain conditions, stability implies attractivity of the equilibrium and that local stability with finite gain implies local asymptotic stability of the origin. Copyright © 2012 John Wiley & Sons, Ltd.
Discrete‐time robust H∞control of a class of nonlinear uncertain systems
Authors: Shaiju A.J. , Petersen Ian R. 
Published: June 2012

SUMMARYThis paper presents an approach to discrete‐time robust H∞ control for a class of nonlinear uncertain systems on the basis of the use of Sum Quadratic Constraints. The approach involves controllers, which include copies of the system nonlinearities in the controller. The nonlinearities being considered are those that satisfy a certain global Lipschitz condition. The linear part of the controller is synthesized using linear robust H∞ control theory, and this leads to a nonlinear controller, which gives an upper bound on the attainable disturbance attenuation level. Copyright © 2012 John Wiley & Sons, Ltd.
Control over erasure channels: stochastic stability and performance of packetized unconstrained model predictive control
Authors: Reble Marcus , Quevedo Daniel E. , Allgöwer Frank 
Published: June 2012

SUMMARYIn this work, we consider the control of discrete‐time constrained nonlinear systems over unreliable packet‐based communication networks. The random packet dropouts are modeled by a two‐state Markov chain, and no acknowledgments of receipt are assumed. To weaken the impact of the packet dropouts, the controller transmits packets containing more than one future control input, and a suitable buffering is applied at the plant actuator side. Because the Markov chain model adopted does not ensure the number of consecutive packet dropouts to be bounded, deterministic stability cannot be guaranteed. Hence, we are interested in stochastic stability of the closed loop instead. We propose an unconstrained model predictive control scheme without additional terminal weighting term for the calculation of the control inputs. Two major advantages of this unconstrained model predictive control scheme can be emphasized. First, to guarantee stochastic stability, we do not require the knowledge of a global control Lyapunov function as terminal cost term but instead only a less restrictive controllability assumption. Second, guaranteed performance bounds on the expected infinite horizon cost of the closed loop can be obtained. Copyright © 2012 John Wiley & Sons, Ltd.
On decentralized group key management mechanism for vehicular ad hoc networks
Authors: Guo Ming‐Huang , Liaw Horng‐Twu , Chiu Meng‐Yu , Deng Der‐Jiunn 
Published: June 2012

AbstractIn a vehicular ad hoc network (VANET) environment, it is not easy to keep data secure and private. If the private data are stolen, the hacker might have the user identity and do some bad things. To provide secure transmitting, some data encryption mechanisms are necessary. In this paper, we proposed a group key management mechanism for data communication in VANETs. It is exploited on the basis of a decentralized architecture with the hierarchical key tree and cluster heads. The proposed mechanism not only provides a rekeying method in reducing the communication cost but also furnishes the forward security and backward security. Copyright © 2012 John Wiley & Sons, Ltd.
A survey on security issues in smart grids
Authors: Jokar Paria , Arianpoo Nasim , Leung Victor C. M. 
Published: June 2012

AbstractA key feature of the smart grid is the introduction of two‐way data communications into the power grid. This brings many security challenges, because of the large‐scale, difficult‐to‐secure environment, complexity of smart grid systems, and resource limitations of the smart grid deployments. In this paper, we focus on security and privacy concerns in the context of the smart grid. Existing security mechanisms developed for traditional information technology systems can be used as a basis for designing security measures for the smart grid. However, new methods that meet the special requirements and characteristics of the smart grid are also required. In spite of the obstacles against developing detailed security solutions for the future smart grid, such as uncertainty of the architecture and lack of practical experiences with security attacks, some research has been performed in this area over the last few years. We survey the existing literature on different security aspects of the smart grid and provide directions for further research. Copyright © 2012 John Wiley & Sons, Ltd.
Are Clergy Serving Yoked Congregations More Vulnerable to Burnout? A Study among Clergy Serving in the Presbyterian Church (USA)
Authors: Francis Leslie J. , Robbins Mandy , Wulff Keith 
Published: June 2012

AbstractPressures generated by increasing secularization and decreasing vocations to ordained ministry are resulting across denominations in a growing number of clergy serving more than one congregation. This study assesses the hypothesis that clergy serving more than one congregation are more susceptible to burnout. Data were provided by a sample of 735 clergy serving in The Presbyterian Church (USA) who completed the Francis Burnout Inventory together with the abbreviated Eysenck Personality Questionnaire Revised. Among these clergy, 82% served one congregation, 13% served two congregations, and 5% served three or more congregations. After controlling for individual differences in age and personality, the data demonstrated that clergy serving yoked congregations experienced no statistically significant differences in susceptibility to burnout, either in terms of levels of emotional exhaustion or in terms of levels of satisfaction in ministry, compared with colleagues serving just one congregation. Copyright © 2012 John Wiley & Sons, Ltd.