bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toward a physical understanding of electron‐sharing two‐center bonds. I. General aspects
Authors: Bitter T. , Ruedenberg K. , Schwarz W. H. E. 
Published: December 2006

AbstractIn 1916, Lewis and Kossel laid the empirical ground for the electronic theory of valence, whose quantum theoretical foundation was uncovered only slowly. We can now base the classification of the various traditionalchemicalbond types in a threefold manner on the one‐ and two‐electron terms of the quantum‐physicalHamiltonian (kinetic, atomic core attraction, electron repulsion). Bond formation is explained by splitting up the real process into two physical steps: (i) interaction of undeformed atoms and (ii) relaxation of this nonstationary system. We aim at a flexible bond energy partitioning scheme that can avoid cancellation of large terms of opposite sign. The driving force of covalent bonding is a lowering of the quantum kinetic energy density by sharing. The driving force of heteropolar bonding is a lowering of potential energy density by charge rearrangement in the valence shell. Although both mechanisms are quantum mechanical in nature, we can easily visualize them, since they are of one‐electron type. They are however tempered by two‐electron correlations. The richness of chemistry, owing to the diversity of atomic cores and valence shells, becomes intuitively understandable with the help of effective core pseudopotentials for the valence shells. Common conceptual difficulties in understanding chemical bonds arise from quantum kinematic aspects as well as from paradoxical though classical relaxation phenomena. On this conceptual basis, a dozen different bond types in diatomic molecules will be analyzed in the following article. We can therefore examine common features as well as specific differences of various bonding mechanisms. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 411–422, 2007
Electronic reorganization: Origin of sigma trans promotion effect
Authors: Khoroshun Dmitry V. , Musaev Djamaladdin G. , Morokuma Keiji 
Published: December 2006

AbstractBinding of two ligands trans to each other by some transition metal complexes may be cooperative [Khoroshun et al., Mol Phys 2002, 100, 523]. Several interesting consequent effects include (i) inverse relationship between bond strength and binding affinity; (ii) smaller coordination barriers to formation of weaker bonds; (iii) enhancement of Lewis acidity with increased number of ligands. We describe a simple model, σ trans promotion effect (TPE), which considers electronic reorganization between two Lewis structures, and predicts the above‐mentioned effects. The applied result of present study is the unified perspective on several facts of heme chemistry. Particularly, we reiterate an important but often overlooked notion, developed previously within the spin pairing model [Drago and Corden, Acc Chem Res 1980, 13, 353], that, in hemoproteins, the proximal histidine and the distal ligand such as O2 or CO cooperate in promoting electronic reorganization. As a result, depopulation of d orbital upon ligand binding contributes to the phenomenon of hemoglobin cooperativity. The presented density functional (B3LYP) calculations on realistic models, the processes of carbon monoxide binding by Fe(II) porphyrins and dinitrogen binding by triamido/triamidoamine Mo(III) complexes, particularly the evaluation of the coordination barriers due to spin‐state change by location of the minima on seams of crossing, support the TPE model predictions. From a broader theoretical perspective, the present study would hopefully stimulate the development of much needed frameworks and tools for facile comparisons of wave functions and their properties between different geometries, species, and electronic states. Advancement of practical wave function comparisons may yield fresh qualitative perspectives on chemical reactivity, and promote better understanding of related concepts such as electronic reorganization. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 423–441, 2007
Why does electron sharing lead to covalent bonding? A variational analysis
Authors: Ruedenberg Klaus , Schmidt Michael W. 
Published: December 2006

AbstractGround state energy differences between related systems can be elucidated by a comparative variational analysis of the energy functional, in which the concepts of variational kinetic pressure and variational electrostatic potential pull are found useful. This approach is applied to the formation of the bond in the hydrogen molecule ion. A highly accurate wavefunction is shown to be the superposition of two quasiatomic orbitals, each of which consists to 94% of the respective atomic 1s orbital, the remaining 6% deformation being 73% spherical and 27% nonspherical in character. The spherical deformation can be recovered to 99.9% by scaling the 1s orbital. These results quantify the conceptual metamorphosis of the free‐atom wavefunction into the molecular wavefunction by orbital sharing, orbital contraction, and orbital polarization. Starting with the 1s orbital on one atom as the initial trial function, the value of the energy functional of the molecule at the equilibrium distance is stepwise lowered along several sequences of wavefunction modifications, whose energies monotonically decrease to the ground state energy of H. The contributions of sharing, contraction and polarization to the overall lowering of the energy functional and their kinetic and potential components exhibit a consistent pattern that can be related to the wavefunction changes on the basis of physical reasoning, including the virial theorem. It is found that orbital sharing lowers the variational kinetic energy pressure and that this is the essential cause of covalent bonding in this molecule. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 391‐410, 2007
Globalisation and poverty: impacts on households of employment and restructuring in the textiles industry of South Africa
Authors: Bezuidenhout Andries , Khunou Grace , Mosoetsa Sarah , Sutherland Kirsten , Thoburn John 
Published: December 2006

AbstractThis paper addresses an important but often neglected theme in debates on globalisation—the consequences for workers of engagement in global markets, particularly for those workers who are retrenched in the process. Using the South African textiles industry as a case study, the paper investigates the impact on workers' household livelihoods of industrial restructuring following trade liberalisation in the 1990s. Interviews with textile workers and retrenched textile workers were conducted in five locations in three provinces—the Western Cape, the Eastern Cape and KwaZulu‐Natal—in order to capture different local dynamics. Workers employed in textiles generally enjoy a relatively stable formal sector wage, which, though less than the manufacturing average, is well above the national poverty line. However, the benefits were not evenly spread between the regions and job insecurity has been increasing. Workers retrenched from textile employment have faced extreme difficulties in a country with exceptionally high levels of open unemployment, and many families have fallen into deep poverty, which may now be transmitted intergenerationally. Copyright © 2006 John Wiley & Sons, Ltd.
Travel and communication and international differences in GDP per capita
Authors: Anderson Edward 
Published: December 2006

AbstractEconomic theory predicts that wage and income levels will be higher in those developing countries to which business travel and telecommunication from developed countries is cheaper and easier. Cross‐country regression analysis, using data from the World Tourism Organisation and the method of two‐stage least squares, supports this prediction. Levels of per capita GDP are higher in those developing countries which receive higher inflows of business travel from other countries, even when controlling for other influences on per capita GDP with which those inflows are correlated. There is also evidence that governments in developing countries can attract higher inflows of business travel from developed countries by investing in travel and communications infrastructure. Copyright © 2006 John Wiley & Sons, Ltd.
Antimicrobial susceptibility of coagulase‐negative staphylococci on tissue allografts and isolates from orthopedic patients
Authors: Saegeman Veroniek , Lismont Daniel , Verduyckt Bert , Ectors Nadine , Stuyck Jos , Verhaegen Jan 
Published: December 2006

AbstractAllograft infection occurs at a rate not different from that of similar procedures with large allografts or sterilized prosthetic devices and is usually caused by coagulase‐negative staphylococci (CNS). CNS are feared for their limited antimicrobial susceptibility. We aimed at investigating this risk. CNS were isolated from 260 of 1461 allograft tissue grafts and compared with 384 consecutive clinical isolates from a general orthopedic population (258 patients). The CNS were identified and examined for their susceptibility to nine antibiotics used in routine practice. Staphylococcus epidermidis was the most commonly identified (35%) and the most resistant species of the allograft isolates. Comparing the overall antibiotic susceptibility patterns, clinical pathogens were significantly more resistant to six of the nine antibiotics (p < 0.01), namely penicillin, oxacillin, erythromycin, clindamycin, ofloxacin, and gentamicin. In conclusion, massive allograft infection is a well‐known life‐threatening surgical risk. However, we did demonstrate that allograft‐related in contrast to orthopedic clinics‐related CNS, are susceptible to commonly used first and second line antibiotics. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:501–507, 2007
Retraining cervical joint position sense: The effect of two exercise regimes
Authors: Jull Gwendolen , Falla Deborah , Treleaven Julia , Hodges Paul , Vicenzino Bill 
Published: December 2006

AbstractThis study compared the effects of conventional proprioceptive training and craniocervical flexion (C‐CF) training on cervical joint position error (JPE) in people with persistent neck pain. The aim was to evaluate whether proprioceptive training was superior in improving proprioceptive acuity compared to another form of exercise, which has been shown to be effective in reducing neck pain. This may help to differentiate the mechanisms of effect of such interventions. Sixty‐four female subjects with persistent neck pain and deficits in JPE were randomized into two exercise groups: proprioceptive training or C‐CF training. Exercise regimes were conducted over a 6‐week period, and all patients received personal instruction by an experienced physiotherapist once per week. A significant pre‐ to postintervention decrease in JPE, neck pain intensity, and perceived disability was identified for both the proprioceptive training group (p < 0.001) and the C‐CF training group (p < 0.05). Patients who participated in the proprioceptive training demonstrated a greater reduction in JPE from right rotation compared to the C‐CF training group (p < 0.05). No other significant differences were observed between the two groups. The results demonstrated that both proprioceptive training and C‐CF training have a demonstrable benefit on impaired cervical JPE in people with neck pain, with marginally more benefit gained from proprioceptive training. The results suggest that improved proprioceptive acuity following intervention with either exercise protocol may occur through an improved quality of cervical afferent input or by addressing input through direct training of relocation sense. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007
Kinematic changes of the foot and ankle in patients with systemic rheumatoid arthritis and forefoot deformity
Authors: Khazzam Michael , Long Jason T. , Marks Richard M. , Harris Gerald F. 
Published: December 2006

AbstractMinimal published data exist characterizing the effect of rheumatoid arthritis of the forefoot (RA) on multi‐segmental gait kinematics. The purpose of this study was to examine specific changes in segmental foot motion in patients with RA as compared to persons without foot/ankle pathology. This was a cross‐sectional, descriptive study consisting of 22 preoperative adult patients (29 feet) diagnosed with RA and 25 adult patients with no known foot pathology (Control). All RA patients were evaluated by the same orthopaedic surgeon. This group consisted of 20 women and 2 men with a mean age of 54 years (range, 17–76 years). The Control cohort consisted of 13 men and 12 women with a mean age of 41 years (range, 27–73 years). Foot and ankle motion data for the RA population were obtained using a 15‐camera Vicon Motion Analysis System (Vicon Motion Systems, Inc., Lake Forest, CA). Anterior–posterior, lateral, and modified coronal radiographic views were obtained to relate marker position to underlying bony anatomy. Temporal and three‐dimensional kinematic parameters were obtained via the 4‐segment Milwaukee Foot Model. Quantitative comparisons of range of motion values during the seven phases of gait were made between RA and Control ankles using unpaired nonparametric methods. The RA group showed significant differences (p < 0.001) as compared to Controls with prolonged stance time, shortened stride length, increased cadence, and a walking speed that was 80% of Control. Overall, kinematic data in the RA cohort showed significant differences (p < 0.001) in motion for tibial, hindfoot, and forefoot motion as compared to Controls. The effect of RA on segmental foot motion is poorly understood. This study characterized the effect that RA has on motion about the foot and ankle during gait, providing insight into this pathology to improve quantitative assessment, treatment planning, and rehabilitative care. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007
Symposium on the musculoskeletal aspects of marfan syndrome: Meeting report and state of the science
Authors: Jones Kevin B. , Sponseller Paul D. , Erkula Gurkan , Sakai Lynn , Ramirez Francesco , Dietz Harry C. , Kost‐Byerly Sabine , Bridwell Keith H. , Sandell Linda 
Published: December 2006

AbstractThe National Marfan Foundation sponsored a symposium in August 2005 to review recent progress in the area of Marfan‐related musculoskeletal research. Orthopaedic surgeons, molecular geneticists, medical geneticists, and pain specialists met to review a variety of topics. This report reviews and summarizes the proceedings of the symposium, with emphasis on future directions for study that were identified in the course of the meeting. Areas covered include clinical detection, diagnosis, growth, spine deformity, molecular mechanisms, dural ectasia, protrusio acetabuli, and pain in Marfan syndrome. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007
Increased accumulation of superficial zone protein (SZP) in articular cartilage in response to bone morphogenetic protein‐7 and growth factors
Authors: Khalafi Afshin , Schmid Thomas M. , Neu Corey , Reddi A. Hari 
Published: December 2006

AbstractThe purpose of this study was to investigate the role of bone morphogenetic proteins (BMPs), such as BMP‐7, growth factors, and cytokines, in the accumulation of superficial zone protein (SZP) in bovine articular cartilage. Calf superficial articular cartilage discs and chondrocytes were obtained for explant and monolayer culture systems, respectively. Dose‐ and time‐dependent actions of BMP‐7 on SZP accumulation were investigated in both explant and monolayer culture systems. In addition, actions of various morphogens and growth factors [BMP‐2, BMP‐4, fibroblast growth factor 2 (FGF‐2), insulin‐like growth factor 1 (IGF‐1), platelet‐derived growth factor (PDGF), and transforming growth factor β (TGF‐β1)], and cytokines [interleukin (IL)‐1α, IL‐1β, and tumor necrosis factor (TNF‐α)] alone, and in combination with BMP‐7, on SZP accumulation were investigated in monolayer culture systems. SZP accumulation was quantified in both the cartilage and the medium using SDS‐PAGE and subsequent immunoblotting. In both explant and monolayer cultures, BMP‐7 increased SZP accumulation in a dose‐ and time‐dependent fashion (p < 0.05). Furthermore, SZP accumulation was significantly increased in monolayer cultures by FGF‐2, IGF‐1, PDGF, and TGF‐β1 (p < 0.05). Both IL‐1α and TNF‐α significantly reduced SZP accumulation (p < 0.05). The inhibition of SZP accumulation by TNF‐α was partially alleviated by concurrent treatment with BMP‐7. The results of this investigation provide novel insights into the role of morphogens, especially BMP‐7, growth factors, and cytokines in the accumulation of SZP in articular cartilage. This information has clinical implications because stimulation of SZP may ameliorate the pathology of joint function in arthritis. Furthermore, tissue engineering approaches to articular cartilage may depend on the optimal synthesis and assembly of SZP in the superficial zone to ensure functional tissue architecture. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007
Single Polyelectrolyte Microcapsules Fabricated By Glutaraldehyde‐Mediated Covalent Layer‐By‐Layer Assembly
Authors: Tong Weijun , Gao Changyou , Möhwald Helmuth 
Published: December 2006

AbstractSummary: Single polyelectrolyte component microcapsules and multilayers, exemplified by poly(allylamine hydrochloride) (PAH), have been prepared using a method of glutaraldehyde (GA)‐mediated covalent layer‐by‐layer (LbL) assembly. The GA cross‐linking of the adsorbed PAH results in surfaces covered by reactive aldehyde groups, which can then react with PAH to result in another layer of covalently linked PAH. The repeated assembly of single polyelectrolyte in an LbL manner can be thus achieved. The PAH multilayers can grow linearly along with the layer number, and their thickness can be controlled at the nanometer scale, as verified by UV‐vis absorption spectrometry and ellipsometry. Single polyelectrolyte microcapsules are obtained after removal of the template cores at low pH. The morphology and integrity are confirmed by scanning force microscopy and confocal laser scanning microscopy.Schematic illustration of the preparation of a single polyelectrolyte component microcapsule by GA‐mediated covalent LbL assembly.magnified imageSchematic illustration of the preparation of a single polyelectrolyte component microcapsule by GA‐mediated covalent LbL assembly.
Creep Behavior of Polystyrene/Fluorohectorite Micro‐ and Nanocomposites
Authors: Siengchin Suchart , Karger‐Kocsis József 
Published: December 2006

AbstractSummary: Pristine FH is incorporated into a PS matrix by melt blending with and without latex precompounding of PS and FH. Direct melt blending results in microcomposites, whereas the latex‐mediated (masterbatch) technique results in PS/FH nanocomposites. The tensile creep response of the micro‐ and nanocomposites are determined in short‐term creep tests. The resistance to creep is improved with increasing dispersion of FH in the PS matrix. Master curves (creep compliance vs. time), constructed based on isothermal creep tests performed in the temperature range between 5 and 45 °C, show that the FH reinforcement affects mostly the initial creep compliance (interphase effect). On the other hand, the stable creep is matrix (bulk) dominated. It is established that the Williams‐Landel‐Ferry equation is fairly applicable to the creep results.Scheme of the change of creep compliance as a function of time for micro‐ and nanocomposites with an amorphous matrix.magnified imageScheme of the change of creep compliance as a function of time for micro‐ and nanocomposites with an amorphous matrix.
Particle Size Effects in TEMPO‐Mediated Radical Polymerization of Styrene in Aqueous Miniemulsion
Authors: Nakamura Tadashi , Zetterlund Per B. , Okubo Masayoshi 
Published: December 2006

AbstractSummary: 2,2,6,6‐Tetramethylpiperidinyl‐1‐oxy (TEMPO)‐mediated radical polymerization of styrene in aqueous miniemulsion at 125 °C using sodium dodecylbenzenesulfonate and poly(vinyl alcohol), respectively, as colloidal stabilizers has been investigated. The particle size had a dramatic effect on the polymerization process. Decreasing particle size led to a markedly higher polymerization rate, but less control and a lower degree of livingness. For particles with diameters greater than approximately 170 nm, the polymerization behavior was essentially the same as in the corresponding bulk system. By varying the particle size within an appropriate range, it is possible to tune the polymerization such that the polymerization rate is increased while still maintaining reasonable control and livingness.magnified image
Synthesis and Alignment of Iron Oxide Nanoparticles in a Regenerated Cellulose Film
Authors: Liu Shilin , Zhou Jinping , Zhang Lina , Guan Jianguo , Wang Jianbo 
Published: December 2006

AbstractSummary: A polymer‐iron oxide nanocomposite film has been successfully synthesized by using a microporous regenerated cellulose film as template and aqueous ferrous chloride as precursor. The nanocomposite film was investigated with XRD, XPS, SEM, TEM, and VSM. The nanoparticles synthesized in situ were disk‐shaped with a mean diameter of ≈24 and thicknesses of 2.5–3.5 nm. For the first time, the nanodisks were well aligned in the cellulose matrix to form an ordered multibilayer structure by the shrinkage of the hybrid film while drying. The nanocomposite film displayed anisotropic magnetic properties as a result of the alignment of magnetic nanodisks. This work provides a novel and facile method for template synthesis of nanoparticles and aligned nanocomposites.TEM image of the air‐dried nanocomposite film; slice perpendicular to the film plane.magnified imageTEM image of the air‐dried nanocomposite film; slice perpendicular to the film plane.
Microwave‐Assisted Ring‐Opening Polymerization of ε‐Caprolactone in the Presence of Ionic Liquid
Authors: Liao Liqiong , Liu Lijian , Zhang Chao , Gong Shaoqin (Sarah) 
Published: December 2006

AbstractSummary: Microwave‐assisted ring‐opening polymerization of ε‐caprolactone in the presence of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ionic liquid using zinc oxide as a catalyst is investigated. By adding 30 wt.‐% ionic liquid, poly(ε‐caprolactone) with a weight‐average molar mass of 28 500 g · mol−1 is obtained at 85 W for 30 min. The results indicate that the polymerization could be efficiently enhanced in the presence of ionic liquids under microwave irradiation because ionic liquids can effectively absorb microwave energy.
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Halogen‐Free Polyarylphosphonates and Polyelectrolyte Membranes for PEMFC by Nickel‐Catalyzed Phosphonylation with Silylated Phosphates
Authors: Bock Thorsten , Mülhaupt Rolf , Möhwald Helmut 
Published: December 2006

AbstractSummary: The nickel‐catalyzed arylphosphonylation with tris(trimethylsilyl) phosphite (TMSP) is applied to brominated high‐performance (HP) polymers in weakly coordinating high temperature solvents. At elevated temperatures, this affords halogen‐free, soluble, phosphonic acid‐functionalized polyelectrolytes and an unprecedented control of the degree of phosphonylation (dsP). Brominated polysulfone (PSU) of various degrees of bromination (dsBr) has been phosphonylated with TMSP in diphenyl ether at 200 °C in the presence of 1–10 mol‐% NiCl2. Upon methanolysis, arylphosphonic PSU with dsP up to 223 mol‐% is obtained in near quantitative bromine conversion. Catalyst residues are readily removed during methanolysis. This very versatile two‐step process affords soluble arylphosphonic polymers for casting tough membrane films. In contrast to sulfonated PSU, the arylphosphonic PSU membranes exhibit improved thermal and chemical stabilities, combined with far lower water swelling in accordance with the demands of polyelectrolyte membrane fuel cell (PEMFC) applications.Mass swelling (swM) in water of sulfonated (A–C) and phosphonylated PSU (D).magnified imageMass swelling (swM) in water of sulfonated (A–C) and phosphonylated PSU (D).