bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low Frequency Dynamics of Confined Proteins
Authors: Korb Jean-Pierre , Bryant Robert G. 
Published: April 2011

ABSTRACTWe present the frequency dependence of the proton spin-lattice relaxation rate 1/T1 in variously hydrated proteins. We present also the case of proteins confined in heavily hydrated gels where the rotation has been immobilized. The relaxation efficiency increases according to a power law at low frequencies. The temperature dependence of the protein protons T1 demonstrates that relaxation results from a direct spin-phonon process instead of a Raman process at temperatures above 273K. We propose a theory that accounts for experiments and depends on the dynamical distribution of states, the localization of the disturbances along and transverse to the peptide chains, and the spatial distribution of hydrogen in the structure. In hydrated and confined proteins, the motions of the backbone that dominate the relaxation process are transverse rather than along the peptide chain. We show that the protein structure adjusts to hydration from the lyophilized state to the fully hydrated state in small increment steps.
Interplay between slow interfacial water diffusion and colloid dynamics: A way to probe colloidal transitions.
Authors: Levitz P.E. 
Published: April 2011

ABSTRACTParticle fluctuations in colloidal suspensions are generally considered to be much slower than the embedded fluid dynamics. It was recently proposed that the fluid self-diffusion nearby an interface follows Lévy statistics, extending the time domain of the fluid dynamics towards the low frequency range. It is then possible to probe colloidal particle motion and especially its evolution during a phase transition looking at the slow dynamics of the fluid molecule close to an particle surface. Using field cycling NMR relaxometry, we show how the slow and confined water dynamics at proximity of a colloidal surface provide an original way to follow the glass transition of a colloidal system made of plate-like Laponite particles, a synthetic clay. The interplay between fluid Levy dynamics and particle jamming is discussed. An analytical model involving correlated elementary water time steps on the colloidal interface is proposed and critically compared to our experimental data. The method permits probing of colloidal motions and especially their evolution during a phase transition in a new way. This method can be extended to other systems including mineral lyotropic liquid crystals and biological molecular structures.
Slow Dynamics and the Glass Transition in Confining Systems
Authors: Wang Li-Min , He Fang , Richert Ranko 
Published: April 2011

ABSTRACTThe slow dynamics associated with the structural relaxation of glass forming materials near the glass transition is very sensitive to the effects of small confining geometries. Based upon the experimental results of triplet state solvation dynamics, we explore the extent to which confinement effects can be rationalized solely in terms of interfacial dynamics which are modified relative to the bulk situation. The importance of the interfacial conditions is emphasized by observing the changes due to the surface chemistry, by comparing relaxation times at and further away from the surface, and by studying the effects of ‘soft’ versus ‘hard’ confining materials. While ‘hard’ confinement by porous solids is observed to result in slower dynamics and an increased glass transition temperature Tg for propylene glycol, our 4.6 nm nanodroplets suspended in a more fluid environment display faster structural relaxation, equivalent to a reduction of Tg as observed in free standing polymer films.
Metal – polymer interfaces and their effect on the glass transition of thin polystyrene films
Authors: Sharp J.S. , Forrest J.A. 
Published: April 2011

ABSTRACTWe present a study of polystyrene-metal interfaces and discuss the relationship between the interfacial structure and anomalies in the measured glass transition temperature (Tg) of thin metal capped polystyrene (PS) films. The PS films used in these studies were coated with an evaporated metal layer of either Aluminum (Al) or gold (Au) and the Tg values were measured with ellipsometry. Uncoated PS films were also measured and these samples showed Tg values that were reduced relative to the bulk value for film thicknesses (h) less than 40 nm. Films coated with Au were shown to have measured Tg values that were the same as the bulk value (Tgbulk=370 K) for all the film thicknesses studied (h ≥ 8nm). The Al coated PS films had measured Tg values that were the same as the uncoated PS films. The observed differences are discussed in terms of the differences in the structure of the metal-polymer interfaces produced during thermal evaporation of the metal layers. A novel sample preparation procedure was developed to enable us to use Atomic Force Microscopy (AFM) to directly measure the structure of the buried polymer-metal interfaces. The measurements performed on these systems support the suggestion that the interfacial structure is different for the two metal-polymer interfaces studied and that these differences may be the cause of the anomalies in the measured Tgs of these samples.
Fatigue Crack Growth and Fracture Toughness in Bimodal Al 5083
Authors: Pao P. S. , Jones H. N. , Feng C. R. 
Published: April 2011

ABSTRACTThe fatigue crack growth rates and fracture toughness of bulk nanocrystalline Al 5083 having a bimodal grain size distribution were investigated. The nanocrystalline powders were prepared by mechanically ball milling spray atomized Al 5083 powders in liquid nitrogen. This nanocrystalline powder was blended with 50 wt% spray atomized large grained Al 5083 powders. The blended powder was then cold pressed, degassed, and extruded into rods. The bimodal Al 5083 thus produced consists of nanocrystalline grain bands and coarse grain bands. While the yield strength of the bimodal Al 5083 is about 25% lower than that of the all nanocrystalline Al 5083, its tensile ductility is almost 50% greater. In addition, the fracture toughness of the bimodal material is about 85% higher than that of the all nanocrystalline counterpart. Fatigue crack growth rates of bimodal Al 5083 are about 30% lower than those of all nanocrystalline Al 5083. The lower fatigue crack growth rates are accompanied by more tortuous crack paths when the crack propagated through the coarse grain regions in the bimodal Al 5083.
Dislocation Confinement and Ultimate Strength in Nanoscale Polycrystals
Authors: Li Qizhen , Anderson Peter M. , Mills Michael , Hazzledine Peter 
Published: April 2011

ABSTRACTNanoscale polycrystalline metals typically exhibit increasing hardness with decreasing grain size down to a critical value on the order of 5 to 30 nm. Below this, a plateau or decrease is often observed. Similar observations are made for nanoscale multilayer thin films. There, TEM observations and modeling suggest that the hardness peak may be associated with the inability of interfaces to contain dislocations within individual nanoscale layers. This manuscript pursues the same concept for nanoscale polycrystalline metals via an analytic study of dislocation nucleation and motion within a regular 2D hexagonal array of grains. The model predicts a hardness peak and loss of dislocation confinement in the 5 to 30 nm grain size regime, but only if the nature of dislocation interaction with grain boundaries changes in the nanoscale regime.
Numerical Derivative Analysis of Load-Displacement Curves in Depth-Sensing Indentation
Authors: Juliano Tom , Domnich Vladislav , Buchheit Tom , Gogotsi Yury 
Published: April 2011

ABSTRACTThe use of load-displacement derivative behavior and power-law curve fitting is applied to find the location of events for a number of different materials during depth-sensing indentation. Load-displacement curves for Berkovich indentations on fused silica, fullerene thin film on sapphire, CdTe thin film on silicon, single crystal silicon, carbide derived carbon, and a polymethylmethacrylate/hydroxyapatite (PMMA/HA) particle composite are examined. The analysis is applied to quantify the location of different events that occur during material loading and unloading.
Vibrational Frequency of MgO Nanoparticles in a polymer matrix
Authors: Jha Prafulla K. , Talati Mina 
Published: April 2011

ABSTRACTBy using elastic continuum model for a spherical body along with the appropriate boundary conditions at the surface of the body, vibrational frequencies of MgO nanoparticles are calculated in the present paper. It is found that the vibrational frequencies corresponding to these eigen values depend strongly on the size of the nano particles and the peaks in the Raman spectra shift to the higher frequencies side as size of the nano particles decreases. We have also investigated the effect of a polymer matrix on the frequencies and Raman shift of MgO nanoparticles. The damping constant is found to vary linearly with the size of nano particles which shows that the mechanical damping is the prominent mechanism in the damping of the acoustic phonon modes.
Mechanical Properties of Chemically Functionalized Clay Vinyl Ester Nanocomposites
Authors: Balakrishnan S. , Raghavan D. 
Published: April 2011

ABSTRACTThis study focuses on the role of chemistry of onium salt(s) used in functionalizing clay and the processing conditions in achieving exfoliated clay vinyl ester nanocomposites. Two different clay treatments were added to vinyl ester resin and three different processing conditions were examined in the formulation of nanocomposite. Through this study, we demonstrate that the degree of exfoliation and dispersion of layered silicate nanocomposite is affected by both processing and the clay chemical treatment. At an organoclay loading of only 3.5wt%, the modulus improved by 20% in partially reactive organoclay system, while the modulus improved by 10% in nonreactive organoclay system compared to that of pristine vinyl ester resin.
Structural and Mechanical Properties of Boron Nanotubes
Authors: Evans Matthew H. , Joannopoulos John D. , Pantelides Sokrates T. 
Published: April 2011

ABSTRACTWe report the results of first-principles calculations showing that boron can form a wide variety of metastable planar and tubular forms with unusual electronic and mechanical properties. The preferred planar structure is a buckled triangular lattice that breaks the threefold ground state degeneracy of the flat triangular plane. When the plane is rolled into a tube, the ground state degeneracy leads to a strong chirality dependence of the binding energy and elastic response, an unusual property that is not found in carbon nanotubes. The achiral (n, 0) tubes derive their structure from the flat triangular plane. The achiral (n,n) boron nanotubes arise from the buckled plane, and have large cohesive energies and novel structures as a result.
In situ TEM study of irradiation-induced transformation in TiNi shape memory alloys
Authors: Zu X. T. , Wan F.R. , Zhu S. , Wang L. M. 
Published: April 2011

ABSTRACTTiNi shape memory alloy (SMA) has potential applications for nuclear reactors and its phase stability under irradiation is becoming an important topic. Some irradiation-induced diffusion-dependent phase transformations, such as amorphization, have been reported before. In the present work, the behavior of diffusion-independent phase transformation in TiNi SMA was studied by electron irradiation at room temperature. The effect of irradiation on the martensitic transformation of TiNi shape memory alloys was studied by Transmission Electron Microscopy (TEM) with in-situ observation and differential scanning calorimeter (DSC). The results of TEM and DSC measurements show that the microstructure of samples is R phase at room temperature. Electron irradiations were carried out using several different TEM with accelerating voltage of 200 kV, 300 kV, 400 kV and 1000 kV. Also the accelerating voltage in the same TEM was changed to investigate the critical voltage for the effect of irradiation on phase transformation. It was found that a phase transformation occurred under electron irradiation above 320 kV, but never appeared at 300 kV or lower accelerating voltage. Such phase transformation took place in a few seconds of irradiation and was independent of atom diffusion. The mechanism of Electron-irradiation-induced the martensitic transformation due to displacements of atoms from their lattice sites produced by the accelerated electrons.
Can we trust TEM images of silicate glasses?
Authors: Jiang Nan 
Published: April 2011

ABSTRACTElectron irradiation-induced modifications in two glasses, K2O – SiO2 and Au doped Na2O – B2O3 – SiO2, were observed in electron microscope. The products of modifications were “nano-particle” like contrasts in transmission electron microscopy (TEM) images, which can be easily confused with real nano-particles and phase separation. The driving force for the modifications in the glasses is the tendency of elimination of non-bridging oxygen (NBO) through the removal of cations. The phase separation into cation rich and poor region is their nature under electron irradiation. Therefore, it is absolutely essential to record in situ frames when the TEM images are used to provide microstructure information of glasses. Additionally, charging effects in glasses have also been discussed.
Damage Evolution and Annealing of Au-Irradiated Samarium Titanate Pyrochlore
Authors: Zhang Y. , Shutthanandan V. , Thevuthasan S. , McCready D. E. , Young J. , Devanathan R. , Andreasen J. , Balakrishnan G. , Paul D. M. , Weber W. J. 
Published: April 2011

ABSTRACTDamage evolution and thermal recovery of 1 MeV Au2+ irradiated samarium titanate pyrochlore (Sm2Ti2O7) single crystals were studied by Rutherford backscattering spectroscopy and nuclear reaction analysis. The damage accumulation follows a nonlinear dependence on dose that is well described by a disorder accumulation model, which indicates a predominant role of defect-stimulated amorphization processes. The critical dose for amorphization at 170 and 300 K is ∼0.14 dpa, and a higher dose of ∼ 0.22 dpa is observed for irradiation at 700 K, which agrees with previous in-situ transmission electron microscopy (TEM) data for polycrystalline Sm2Ti2O7. Annealing in an 18O environment reveals a damage recovery stage at ∼ 850 K that coincides with a significant increase in 18O exchange due to oxygen vacancy mobility. This thermal recovery stage is also consistent with the critical temperature for amorphization measured by in-situ TEM in polycrystalline samples.
Mössbauer study of 50MeV Li3+ion irradiated Mg0.9Mn0.1InxFe2-xO4ferrite
Authors: Singh M. , Dogra Anjana , Kumar Ravi 
Published: April 2011

ABSTRACTA series of samples of Mg0.9Mn0.1InxFe2-xO4for x=0, 0.3, 0.5 were prepared by conventional solid-state technique. The spinel structure of this ferrite was confirmed by X-ray diffraction technique. The samples were irradiated with 50 MeV Li3+ions with fluence 5×1013ions/cm2. The Mössbauer studies were performed on unirradiated as well as on irradiated samples. Mössbauer study for unirradiated samples show insignificant variation of isomer shifts at both the tetrahedral and octahedral sites. On irradiation isomer shift changes from negative to positive values. This anomalous character of isomer shift after irradiation is due to a change in the electronic configuration of Fe3+ions. The quadrupole splitting of unirradiated samples are negligibly small, indicates the presence of cubic symmetry at both the sites. On irradiation appreciable changes are observed in quadrupole splitting due to the presence of lattice strain. On irradiation super-exchange interaction energy is weakened which decrease the hyperfine field. PACS: 61.80, 76.80, 61.72
γ-Ray Irradiation Practical Conditions for Low Molecular Weight Chitosan Material Production
Authors: Yoksan Rangrong , Akashi Mitsuru , Miyata Mikiji , Biramontri Siriratana , Chirachanchai Suwabun 
Published: April 2011

ABSTRACTThe present work focuses on the γ-ray irradiation doses and conditions (dry solid state, solid state dispersing in 0.5–2 % aqueous H2O2 solution, solid state dispersing in 1% aqueous acetic acid, and 2% aqueous K2S2O8) to determine the level that the molecular weight of chitosan is lowered significantly without changing its primary structure. Molecular weight of chitosan (105-106 Dalton) is reduced approximately 50% under the γ-ray dose of 20 kGy in the dry solid state. The decrease in molecular weight is enhanced up to 80% when chitosan is suspended in 0.5–2 % aqueous H2O2 solution during γ-ray irradiation. In either condition, the backbone structure of the irradiated product is maintained with little change in the terminal chain. In the cases of (i) chitosan suspended in 2% aqueous K2S2O8 and (ii) chitosan in 1% aqueous acetic acid, chitosans lose their primary structures and physical properties.
Comparative Study of Defect Properties in GaN: Ab Initio and Empirical Potential Calculations
Authors: Gao Fei , Bylaska Eric J. , El-Azab Anter , Weber William J. 
Published: April 2011

ABSTRACTDensity functional theory (DFT) is used to study the formation, properties and atomic configurations of monovacancies, antisite defects and possible interstitials in GaN. The relaxation around a vacancy is generally small, but the relaxation around antisite defects is large, particularly for a Ga antisite defect, which is not stable and converts to an N-N<0001> split interstitial. All N interstitials, starting from any possible site, eventually transfer into the N-N split interstitials, forming N2 molecules with one N-N bond, but also some covalent bonds to the surrounding atoms. In the case of Ga interstitials, the most favorable configuration is the Ga octahedral interstitial. However, it is found that the Ga-Ga<1120> split interstitial can bridge the gap between non-bonded Ga atoms along the <1120> direction, which leads to the formation of Ga atomic wires in GaN, with bond distance (2.3Å) close to those noted in bulk Ga. In addition, two representative potentials, namely Stillinger-Weber and Tersoff-Brenner potentials, have been employed to determine the formation of defects using molecular dynamics (MD) method in GaN. The MD results are discussed and compared to DFT calculations. The present DFT and MD results provide guidelines for evaluating the quality and fit of empirical potentials for large-scale simulations of ion-solid interaction and thermal annealing of defects in GaN.
Microstructure and He Bubble Effects on Al-Cu Thin Films
Authors: Camacho C.S. , Fichtner P.F.P. , Zawislak F.C. , Feldmann G. 
Published: April 2011

ABSTRACTThe effects of film morphology (mosaic- or bamboo-like grain structures) and of He bubbles on the redistribution of Cu, as well as on the formation of Al-Cu precipitates in 200 nm thick Al/SiO2 films similar to microelectronic device interconnects, are investigated using Rutherford backscattering spectrometry, elastic recoil detection analysis and transmission electron microscopy. As-deposited and pre-annealed Al films were implanted with Cu and/or He ions forming concentration profiles located 100 nm below the surface and with peak concentrations of about 3 at.%. It is shown that grain boundaries and/or He bubbles can affect the vacancy fluxes inside the grains and reduce or even inhibit the Cu redistribution as well as the nucleation and growth of θ and θ′ Al-Cu precipitates during post-implantation annealings at temperatures from 473 to 553 K. It is also shown that mosaic-like grain structures allow the control of grain size distribution within the 25 to 1500 nm size range, thus providing an additional microstructure engineering tool to improve device reliability against electromigration failures.
Ion Beam Manipulation to Fabricate Ordered Layered Structures and Amorphous Alloys in Some highly Immiscible Binary Metal Systems
Authors: Li X. Y. , Zhang R. F. , Liu B. X. 
Published: April 2011

ABSTRACTWe developed a new scheme, namely ion beam manipulation, i.e. interface-assisted ion beam mixing, for fabricating amorphous alloys and artificial solid-state microstructures in metal-metal multilayers, in which the individual layer thickness is down to about 2 nm, differing significantly from the typical thickness of 5–8 nm in conventional ion beam mixing. Employing the scheme, some interesting results were obtained in three highly immiscible systems. In the Ag-W system, which has the largest positive heat of formation among the transition metal alloys, amorphous alloys were obtained, for the first time, through a two-step structural transition, i.e. the initial polycrystalline Ag and W transformed into an intermediate bcc phase, which later transformed into an amorphous state. In the Ru-Pd system, the initial polycrystalline Pd and Ru first transformed into a single crystalline FCC phase, and then turned into a well-ordered structure, which showed an apparent tendency to transform back to the FCC phase upon over-irradiation. In the Ag-Co system, an ordered layered structure was observed and identified to consist of two overlapped FCC lattices, corresponding to a new magnetic state of Co atom with an average magnetic moment measured to be 2.84 μB, which was about twice the equilibrium datum and was the largest value ever observed. We present, in this paper, a brief review concerning the scheme of ion beam manipulation in fabricating the metastable alloys, the structural evolution upon ion irradiation and the associated magnetic properties of some ordered structures obtained by the scheme.
Trapping of argon in ion beam deposited thin films of CNx Hy
Authors: Kayani Asghar N. , Ingram David C. 
Published: April 2011

ABSTRACTUnbalanced magnetron sputtering deposition of CNx Hy films has been performed with various levels of negative substrate bias and with different flow rates of nitrogen and hydrogen. Argon was used as a sputtering gas and formed the majority of the gas in the plasma. The elemental concentrations of the films were measured in samples deposited on glassy carbon with a 2.2 MeV of He beam used to perform simultaneous RBS and ERS. Argon was found to be trapped in the non-hydrogenated films to a level of up to ∼ 4.6 %. The concentration of argon increased for the films deposited under higher negative bias. With the introduction of hydrogen, argon trapping was first minimized and later completely eliminated, even at higher bias conditions, suggesting that the softness of the films brought on by hydrogenation also caused the films to be unable to trap argon during growth and thus showing that argon stability is dependent on burial below a surface of particular structural properties.
High rate etching of GaAs and GaP by gas cluster ion beams
Authors: Nagano Masahiro , Houzumi Shingo , Toyoda Noriaki , Yamada Susumu , Akita Shirabe , Yamada Isao 
Published: April 2011

ABSTRACTGas cluster ion beam (GCIB) techniques have recently been proposed as new processing methods. We have been investigating the characteristics of GCIB techniques through sputtering GaAs and GaP by Ar gas cluster ion beams as a function of cluster size and acceleration energy. The Ar cluster size was selected by a magnetic spectrometer, and was obtained from the mass spectra measured by a time of flight mass spectrometer. The average sputtering yields of GaAs and GaP were 0–47 and 0–66 atoms/ion for 5–30 k V, respectively. The sputtering yields of GaAs and GaP were higher than those of an Ar monomer ion.