bluuebunny/crossref_metadata_2025_split huggingface dataset:
Symmetry Breaking in the Transformation of Nanoporous Carbons Solids
Authors: Foley H. C. , Stevens Mark , Acharya Madhav , Kane Michael 
Published: April 2011

ABSTRACTNanoporous carbons (NPC) or carbogenic molecular sieves (CMS) are unique materials that are able to produce shape selectivity for very precise molecular separations, such as that of oxygen from nitrogen on the basis of size. Surprisingly, the structure of NPC is globally amorphous. This seems at first irreconcilable, since regular transport behavior is expected to arise from regular porous solids such as zeolites and other crystalline molecular sieves. With this problem in mind as motivation, in this paper we describe some of the more intriguing aspects of the nanopore formation process. It is argued that at the nanoscale the NPC are both regular and structurally self similar, consisting of curved aromatic nanodomains that arise from the broken symmetry of hexagonal arrays. The symmetry breaking process is a direct result of the dissipation that takes place during pyrolysis leading to small molecules and a defect-laden carbogenic solid. In this context, some preliminary results illustrating how these NPC structures can be used to stabilize cesium for base catalysis and to prepare supported molecular sieve membranes for small molecule separations.
Dynamic Heterogeneity by Higher Moments of a Relaxing Quantity
Authors: Richert R. 
Published: April 2011

ABSTRACTA relaxation experiment usually acquires a measure for the mean energetic distance of the system from the thermodynamic equilibrium and its temporal evolution. For sufficiently small perturbations necessary to assure linear responses such data is bound to remain undecisive as regards the spatial nature of the relaxation process, heterogeneous or homogeneous. The technique of solvation dynamics near the glass transition can probe the entire distribution of site specific energies and its approach towards equilibrium, so that apart from the mean solvation energy v(t) also higher moments in terms of the inhomogeneous optical linewidth σinh(t) become accessible. While v(t) maps the dielectric relaxation behaviour of the liquid, σinh(t) is found to be sensitive to the spatial nature of the underlying process. Contrasting experiment and simulation leads to the conclusion, that the relaxation time is a site specific quantity, i.e. the heterogeneous nature is found to dominate.
Cooperative Length Scale of Aroclor Near its Dynamic Glass Transition
Authors: Rizos A. K. , Ngai K. L. 
Published: April 2011

ABSTRACTPhoton correlation spectroscopy in the depolarized mode has been used to monitor the reorientational dynamics of Aroclor (A 1248) (polychlorinated biphenyls) that contain in solutions various amounts of low and high molecular weight (Mw) polymers. For the high Mw polymer/A1248 solutions we observe a very small dependence of the stretched exponential parameter β on temperature. In contrast, the low Mw polymer/A 1248 solutions display a pronounced temperature dependence of β. These preliminary experiments allow us to use the effect of modification of the solvent dynamics by added polymer to estimate the length scale of cooperative motion in glass forming systems from the size of the polymer chain.
Rotational Dynamics of a Molecular Probe in Tri-Cresyl Phosphate: From “Stick” to “Slip” Boundary Conditions
Authors: Bagliesi M. G. , Cianflone F. , Leporini D. 
Published: April 2011

ABSTRACTThe rotational dynamics of a molecular probe dissolved in the glass-former tri-cresyl phospate has been studied by linear and non-linear Electron Spin Resonance spectroscopy. At the highest temperatures the Debye-Stokes-Einstein (DSE) law with stick boundary conditions holds. On cooling, a transition region is crossed and then a new regime sets in which is accounted for by the DSE law provided that slip boundary conditions are assumed. At the lowest temperatures the rotational diffusion and the shear viscosity are decoupled. The onset of the decoupling takes place close to Tc, the critical temperature predicted by the Mode Coupling Theory.
From Spin Glasses to Glasses
Authors: Bouchaud J. P. , Mezard M. 
Published: April 2011

ABSTRACTWe discuss some aspects of the links between the behaviour and theory of spin glasses and that of structural glasses of the fragile type. We review the present status of the conjecture according to which a certain class of spin glass mean field theories (those with first order transitions) could provide a mean field theory for the glass transition. Recent developments pointing in that direction include the existence of spin glasses without disorder, and the general link between Mode-Coupling Theory (MCT) and the motion of a particle in a random potential. This link enables one to generalize the MCT equations for temperatures below the glass transition, and to describe aging effects. We compare these results with those obtained within more phonomonological ‘trap’ models.
Slow Dynamics in Supercooled Water
Authors: Sciortino Francesco , Tartaglia Piero , Gallo Paola , Chen Sow-Hsin 
Published: April 2011

ABSTRACTWe review some recent results on the self-dynamics in deep supercooled (simulated) water, obtained by analyzing very long Molecular Dynamics simulations. We discuss the possibility of interpreting the observed slowing down of the dynamics in terms of Mode Coupling Theory for supercooled liquids and, at the same time, of associating the experimentally observed anomalies of the transport coefficients in water on lowering the temperature to the formation of long living cages. The so-called critical Angeli temperature TA in supercooled water could be interpreted as kinetic glass transition temperature, relaxing the need of a thermodynamic singularity for the explanation of the dynamic anomalies of liquid water. In the end we discuss the possibility that TA acts as cross-over temperature from fragile to strong liquid behavior.
Dynamics at the Glass Transition in Polymers: Results from Neutron Spectroscopy
Authors: Richter D. , Arbe A. , Colmenero J. 
Published: April 2011

ABSTRACTThis short review presents quasielastic neutron scattering and dielectric experiments on the α and βslow relaxation in polybutadiene and polyvinylchloride. Exploiting the momentum transfer dependent dynamic structure factor, spatial information about the underlying molecular motions is obtained. While the βSlow process reveals itself as a local jump with average jump distances of about 1.5 Å, the a relaxation is diffusive and occurs statistically independently from the βslow process. With this result a consistent interpretation of dielectric spectra on the same polymer is achieved. Finally some new results on the a process in PVC are presented.
Metastability and Properties of Metallic Bulk Glass Forming Alloys
Authors: Fecht H.-J. 
Published: April 2011

ABSTRACTGlasses are generally produced from the highly undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of potent heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of bulk metallic glass with a complex multicomponent chemistry and advanced engineering properties. With these alloys crystallization can be avoided over a broad temperature / time window. As such, the relevant thermodynamic properties of the metastable glassy and undercooled liquid states can be directly measured below and above the glass transition temperature, respectively. The obtained data give new insight into the nature of the glass transition suggesting that it is not a phase transition in the classical sense but kinetic freezing triggered by an underlying entropie instability to avoid crystallization. Further measurements of the mechanical and wear properties point to the unique engineering properties of these highly disordered materials for technological applications.
Crystalline, Glassy and Molten Electrolytes: Conductivity Spectra and Model Consdderations
Authors: Funke K. 
Published: April 2011

ABSTRACTConductivity spectra of crystalline, glassy and molten electrolytes are presented and discussed. The spectra cover fourteen decades on the frequency scale as well as wide temperature ranges. In some crystalline ion conductors, the translational and vibrational contributions to the conductivity are well separated on the frequency scale. This is not observed in glasses and melts. In these cases, the vibrational components can, however, often be removed from the total spectra, yielding the translational component. We find that in crystalline, glassy, and molten electrolytes the conductivity caused by translational motion of the ions exhibits plateaux at both low and high frequencies, with a dispersive regime in between. The dispersive sections of the conductivity isotherms always cover a triangular area in a log-log plot of conductivity times temperature versus frequency. For an interpretation, the jump relaxation model turns out to be appropriate for crystalline electrolytes. The existence of different kinds of site is typical of glasses. For fragile molten electrolytes, a simple semimicroscopic model is presented which explains the experimental findings including the Vogel-Fulcher-Tammann temperature dependence of the dc conductivity.
Proteins and Glasses
Authors: Frauenfelder Hans 
Published: April 2011

ABSTRACTThe structure, the energy landscape, and the dynamics of proteins and glasses are similar. Both types of systems display characteristic nonexponential time dependencies of relaxation phenomena. Experiments suggest that both, proteins and glasses, are heterogeneous and that this fact causes the observed time dependence. This result is discussed in terms of the rough energy landscape characteristic of complex systems.
Liquid and Glassy State Polyamorphism in the System Y2O3-Al2O3
Authors: McMillan Paul F. , Ho Chung , Aasland Siv , Yeganeh-Haeri Amir , Weber Richard 
Published: April 2011

ABSTRACTDuring a recent study of supercooled liquids in the system Y2O3-Al2O3, a first-order phase transition between two liquid phases with the same composition, but different structure and density, was observed to occur. The transition occurred close to the glass transformation of the two liquids, so that both phases were quenched to metastably coexisting glasses. We report further studies on the liquids and glasses in this system, prepared by rapid (roller) quenching and by containerless levitation techniques.
2D Lattices on Substrates with Randomly Distributed Pinning Centers: A Possible Scaling Law for Domain Sizes
Authors: Sen Surajit , Cai Zhi-Xiong , Schummer J. 
Published: April 2011

ABSTRACTWe consider 2D lattices which are disordered by an external field, in this case by a dense, random distribution of attractive pinning centers of an underlying substrate. The preferred configuration of the 2D system with screened-Coulomb two-body interactions and a fixed number of particles is a triangular lattice configuration. The pinning centers strongly affect the triangular lattice configuration. By keeping the location and the density of the pinning centers fixed, we study the effects of pinning strength on the structural properties of the lattice. We find that the strongly disordered lattice prefers to form irregular domains of size s which are composed entirely of topological defects. The distribution of sizes of these domains, D(s) suggest that s−τ for sufficiently large s. Our results are consistent with τ ≥ 2 in the solid phase and τ < 2 in the liquid phase. We present a general argument in support of our findings and suggest that the physics which dictates the structure of 2D lattices on substrates with randomly distributed pinning centers is the same as that for a broad range of problems in which an external field strongly influences the behavior of an interacting physical system.
Dielectric Spectroscopy at High Frequencies on Glass Forming Liquids
Authors: Lunkenhemer P. , Pimenov A. , Dressel M. , Gorshunov B. , Schneider U. , Schiener B. , Böhmer R. , Loedl A. 
Published: April 2011

ABSTRACTDielectric spectroscopy up to 950 GHz has been performed on various glass formers as glycerol, propylene-carbonate, and Salol. Special attention is given to the dielectric loss, ε″, in the crossover regime from the a-relaxation to the far-infrared (FIR) response where it can be directly compared to the dynamic susceptibilities obtained by neutron and light scattering techniques. We observe a minimum in ε″(ν) at high frequencies which cannot be explained by a simple transition from a-relaxation peak to the FIR bands but has to be attributed to additional fast processes. In all materials investigated, ε″(ν) increases significantly sublinear above the minimum. The ratio of the intensity of the α-process and the fast process as determined from our dielectric experiments is significantly higher compared to the results from the scattering experiments.
Spectral Characterization and Excited-State Interactions Between Rare Earth Ions Doped in Borosilicate and Sol-Gel Glasses: Energy Transfer Up-Conversion in the Pr-Sm System
Authors: Assefa Z. , Haire R. G. , Stump N. A. 
Published: April 2011

ABSTRACTSpectroscopie properties of selected 4f-elements in a sol-gel and two high temperature silicate based glasses are reported. In particular, the spectral properties of the Eu3+ ion have been used to probe the local coordination environment of the f-elements in these glass matrices. Luminescence studies of the high temperature glasses indicated that the electric dipole allowed f-f transitions dominate the spectra which suggests that the local symmetry around the 4f-ions is low. Temperature-dependent spectroscopie studies of the sol-gel glasses indicated that the f-elements retain a “solution-like” environment prior to thermal processing. After heat treatment, an increase in the emission intensities of the electric-dipole transitions is accompanied by a concomitant decrease in the magnetic-dipole allowed transitions. Moreover, excited state interactions has also been observed in the high temperature glasses that contain certain multiple f-elements. In Pr-Sm systems, exclusive excitation of the Sm3+ ion with a 514 nm argon ion laser line provides a higher-energy emission band (ca. 490 nm) from the Pr3+ ion (3P0 → 3H4) transition. This energy up-conversion is attributed to energy transfer from the 6H13/2 level of the Sm3+ ion to the 3Hg6 state of the Pr3+ ion. Following a second photon absorption, the Pr3+ ion is excited to the emitting 3P0level.
Relaxation Processes and the Mixed Alkali Effect in Alkali Metasilicate Glasses
Authors: Habasaki J. , Okada I. , Hiwatari Y. 
Published: April 2011

ABSTRACTA molecular dynamics simulation (MD) of lithium metasilicate (Li2SiO3) and related mixed alkali system (LiKSiO3) has been performed. Changes in the mean squared displacement and the corresponding clear two-step (β and α1) relaxations in a density correlation function have been observed at 700 K (self-part) for each ion in Li2SiO3 following an exponential decay by vibrational motion in a simulation up to 300 ps (run I). The mean squared displacement of the atoms shows the change in the slope at ca. 300 ps when the simulation is extended up to 1 ns (run II). Here we call the slowest relaxation (ca. 300 ps∼) the α2 region.Oscillation, which is clearer for O and Si than for Li, is found in the second (β-relaxation) region of the function, which is attributed to the so called “boson peak”. Both the β-relaxation and the boson peak are found to be due to the correlated motion.The slower relaxation (α1-relaxation) can be fitted to a stretched exponential form and the origin of this type of decay is confirmed to be waiting time distribution of jump motions. The back-correlated jumps also decrease the decay rate.Components A and B in α1 and α2 regions for Li ion are analyzed, where the Li ion of component A is located within the first neighboring sites and that of component B moves longer than the nearest neighbor distances by cooperative jump motion. The component B shows accelerated dynamics larger than t-linear ones (∼ t1.77) in the region 50–300 ps, and the dynamics can be characterized as Lévy flight.We have found that the contribution of the cooperative jumps decreases in the mixed alkali glass. This explains the maximum of the Haven ratio accompanied with the mixed alkali effect.
Quantitative Analysis of Segregation to Grain Boundaries in Steels
Authors: Garratt-Reed A. J. , Cliff G. , Lorimer G. W. , Pilkington R. 
Published: April 2011

ABSTRACTGrain boundary segregation of phosphorous in model reactor steels has been measured using EDX Spectroscopy in the FEG-STEM. The results have been compared with Auger spectroscopy measurements made on similar materials. The results were in excellent agreement.
Transmission Electron Microscopy (TEM) Studies of Interfaces in TiB2-ZrO2 Composites
Authors: Stemmer S. , Vleugels J. , Van Der Biest O. 
Published: April 2011

ABSTRACTTEM studies of the microstructure and of chemical reactions at interfaces in TiB2-ZrO2 composites are presented. Samples with 70 vol% of Y2O3-stabilized ZrO sintered at 1700 °C showed reaction zones around the TiB2 grains, that consisted of a solid-solution of TiO2 and ZrO2(Y2O3). In addition, nontransformable, tetragonal t'-ZrO2 was observed in these samples. In contrast, the interphase boundaries in composites sintered at 1450 °C contained no reaction products, and the ZrO2 matrix consisted of small, transformable tetragonal grains, as required for transformation toughening of the composites.
Modification of Fracture Energy of Niobium/sapphire Interface By Impurity Doping
Authors: Ji Hong , Was Gary S. , Wayne Jones J. , Moody Neville R. 
Published: April 2011

ABSTRACTThe effect of interface composition on the fracture energy and fracture toughness of the niobium/sapphire system was studied. Niobium films with thickness of 100 nm were deposited on (0001) sapphire substrates by physical vapor deposition (PVD). The interface was doped with silver to reduce the interfacial cohesion. The amount of silver ranged from less than 2.1 monolayers to 6.4 monolayers as measured by Rutherford backscattering spectrometer (RBS). The microscratch test was used in determining the interfacial fracture energy and the interfacial fracture toughness. Both interfacial fracture energy Gc and fracture toughness Kc decrease non-linearly with the amount of silver, and level off for samples with larger silver thickness ( > 4.2 monolayers). The values of interfacial fracture energy range from 3.43 J/m2 - 9.20 J/m2 for the sample doped with 2.1 monolayer silver (sample B) to 0.05 J/m2 - 0.5 J/m2 for samples with silver levels above 4.2 monolayers (samples D and E). The corresponding fracture toughnesses are 0.80 MPa-m½ - 1.29 MPa-m½ for sample B and 0.09 MPa-m½ - 0.30 MPa-m½ for samples D and E.
The Influence of Film-Substrate and Internal Interfaces on the Strength and Ductility of <001> Oriented B2 NiAl-Based Alloys
Authors: Misra A. , Kim J. T. , Gibala R. 
Published: April 2011

ABSTRACTThe effects of surface films and second phase interfaces on the room temperature ductility of <001> oriented β (B2) NiAl-based alloys were investigated. Significant reduction in flow stress and enhancement in plasticity, as compared to the monolithic β phase, were seen in both film-coated and ductile γ (fcc)/γ' (Ll2) second-phase-containing alloys. The constrained deformation at the film/substrate and interphase interfaces was effective in nucleating mobile a<100> dislocations in the β phase even though the loading axis was approximately parallel to <001>. For the case of film-coated NiAl single crystals deformed in compression, a micro-kinking model is proposed to explain the propagation of a<001> dislocations generated at the film/substrate interface. For multiphase β/γ+γ' alloys where 10–12% tensile ductility was observed, the role of crystallographic orientation relationships in promoting slip transfer is highlighted. In these multiphase alloys, the intrinsic tensile ductility of β phase by {011}<100> slip when deformed approximately along the <001>β orientation is explained using lattice rotation concepts.
Improvement of Abrasive Wear Resistance by Whisker Reinforcement in Alumina Ceramics
Authors: Iwasa Mikio 
Published: April 2011

ABSTRACTAlumina based composite ceramics with silicon carbide whisker were fabricated by hot-press sintering. Their abrasive or erosive wear properties were measured by abrasive waterjet method and micro-sandblast method, and the results were compared with those of normally sintered engineering ceramics. In the case of normal impact of abrasive waterjet, where micro-fracture may be the mam wear mechanism, the whisker composite showed considerable improvement of wear properties because of its higher toughness. In the case of low angle impact, where cutting is the mam wear mechanism, only a small improvement were observed by a small addition of whisker (5wt%SiC), but larger addition (30wt%SiC) resulted in higher wear. No effect of whisker was observed with the micro-sandblast method, perhaps because of its rather mild abrasive conditions.
Static Simulation of the Effect of Alkalline Metal Impurities on the Bonding of Al Atoms at the Grain Boundaries of Aluminum
Authors: Tu Geng , Itoh Akira , Kyuno Kentaro , Yamamoto Ryoichi 
Published: April 2011

ABSTRACTUnlike the iron based alloys, the embrittlement behavior of aluminum based alloys due to impuri ty segregation at the grain boundaries have not previously studied. Recently, experiments were performed on the Al-Mg alloys and it was found that more than 0.6ppm Na impurity atoms will cause embrittlement of these alloys. In the present study, we have created aluminum clusters containing about 20 atoms based on the structure of tilt grain boundries and then performed the first-principle calculations on these clusters with or without alkalline metal impurity atom(Li, Na, K,). The overlap populations between aluminum atoms were calculated so as to find the effect of impurity atoms on the bonding between aluminum atoms. Na impurity atom was found to weaken the bonding between the aluminum atoms around it.
Effect of α/β Interfaces on Creep Behavior of Single Colony Titanium Alloys at Room Temperature
Authors: Suri S. , Hou Vincent D. -H. , Neeraj T. , Scott J. M. , Mills M. J. 
Published: April 2011

ABSTRACTCreep occurs in two phase α/β Ti alloys at room temperature and at stresses below the yield strength. Creep strains in the Widmanstatten structure are affected by colony size and by sliding at the α/β interfaces. This paper reports the results of an investigation on single colony crystals of a near a Ti alloy to understand the dependence of creep on the orientation of the α/β interface and the operative slip system. Associated mechanisms of slip transfer across the α/β interface and possible interface sliding are investigated and the results obtained are presented.
Study of Dynamic Embrittlement in Alloy Bicrystals
Authors: Muthiah R. G. , Pfaendtner J. A. , McMahon C. J. , Lejcek P. , Paidar V. 
Published: April 2011

ABSTRACTIn a kinetic model [1] for the phenomenon of dynamic embrittlement, the cracking rate is predicted to be proportional to the diffusivity of the embrittling species along the grain boundary. To test this model, bicrystals of Cu-Sn and Fe-Si with Σ5 symmetrical tilt boundaries are used in which tin and sulfur, respectively, are the embrittling elements. The diffusivities parallel and perpendicular to the tilt axis are expected to be different, therefore the crack growth rates in these two directions should vary in the same ratio as the diffusivities.Preliminary measurements of crack growth rate along the [100] direction in the Cu-Sn alloy bicrystal are presented. The cracking occurred by decohesion along the grain boundary with almost no observable plasticity. The steady state crack growth was found to be approximately 10∼6 m/sec.