Calcium silicate hydrate (C-S-H) gel is the cohesive phase in cement paste and critically controls the cement hydration. Atomistic models can reproduce reasonable structural and mechanical properties of C-S-H gel at the nano scale. However, the length and time scale of such all-atom modeling technique are restrained by limited computing power. Under this context, coarse-grained modeling technique emerges as a useful alternative for investigating cement paste at extended length and time scale. Here, we regard the building block of cement as ellipsoid and develop a coarse-grained model of cement matrix based on the Gay-Berne (GB) potential. Emphasis of the present paper is on the parameterization and interpretation of the GB potential formula.

The mechanism for the precipitation of multilayer graphene was investigated with respect to the use of an Al2O3 barrier layer and Au capping layer. The Al2O3 barrier layer suppresses the dissolution of carbon into the catalyst, especially at low temperature, and assists a decrease in the density of graphene nuclei. On the other hand, the Au capping layer is beneficial to weaken the strong binding between the catalyst and the graphene carbon atoms, and enhances the surface migration of precipitated carbon adatoms. A combination of the Al2O3 barrier layer and Au capping layer is useful for the synthesis of high-quality graphene with large grains. On a sample with both layers annealed for 60 min, the area of 5-layer graphene islands is as large as 10 μm, and covers 60% of the entire surface. The Raman D/G band intensity ratio of 0.024 indicates the precipitated graphene is high quality.

In this paper we present fast response processes in dye doped liquid crystal cell with ZnSe layers on electrodes. Two-wave mixing and grating monitoring experiments were performed to characterize this liquid crystal system. With the help of photoconductive layers, the response time was reduced to a few milliseconds, which improved further the response rate in liquid crystal photorefractive system. A peak in response time versus applied voltage and unexpected oscillations in diffraction efficiency dynamics were observed, which implies unconventionally complex charge dynamics associated with SPPs excited at one of the photoconductive layer/liquid crystal interfaces.

Yield shear stress dependence on dislocation density and crystal orientation was studied in bulk GaN crystals by nanoindentation examination. The yield shear stress decreased with increasing dislocation density which is estimated by dark spot density in cathodoluminescence, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane (0001) and m-plane (10-10) GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane (-1012) slip line right after plastic deformation, so called pop-in event. The agreement of the experimentally obtained atomic shuffle energy with the calculated twin boundary energy suggested that the nucleation of the local metastable twin boundary along the r-plane concentrated the indentation stress, leading to an r-plane slip. This nanoindentation examination is useful for the characterization of crystalline quality because the wafer mapping of the yield shear stress coincided the photoluminescence mapping which shows increase of emission efficiency due to reduction of non-radiative recombination process by dislocation.

An experimental study oriented to gather kinetic modelling data in the ethylene polymerization via metallocenes is reported. Also is illustrated the employment of two methods for determination of kinetic behavior and the instantaneous activity of Ziegler-Natta catalysts in the slurry polymerization of ethylene. The theoretical basis for both methods is described as well as the required instrumentation for its implantation at a laboratory level. An experimental program of polymerization with two different metallocenic systems was executed, showing that the direct (measurement of ethylene flow) as well as the calorimetric method (based on energy balances) give equivalent high quality information on the kinetic performance of the catalyst.

The use of detonation nanodiamond (DND) for drug delivery and cell-imaging is grounded on its chemical functionalization, and the key task to be addressed is the capability to simplify the process steps, to reduce the process times and to maximize the drug/ligand uptake. The idea underlying the present research is to modulate the loading capability of DND by controlled modification of the surface organic groups. To this aim the DND samples are treated either by wet chemistry, using medium-strong reducing agents, or by tunable H-plasmas produced in a custom-designed MW-RF reactor. The affinity of the treated DND surfaces for drugs has been probed by conjugating the ciproten (5,7- dimethoxycoumarin), a natural antioxidant molecule, and by testing in vitro the feasibility to use coumarin vehicled by nanodiamond (C@DND) as chemioterapeutic drug. The methodologies developed to modify the DND surfaces are offering practical solutions to the still open problems related to DND-based systems for drug delivery applications.

In this work, we studied the dissolution of three different refractory compositions belonging to the ternary system SiO2-CaO-MgO into two Simulated Lung Fluids (SLF). The initial powder mixtures were uniaxially pressed and then sintered at 1300-1400 °C. The sintered samples were immersed for times from 1 to 21 days into a given SLF at 37 °C. The samples were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The dissolution of Ca2+, Mg2+ and Si4+ into the SLF was quantified by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The in vitro studies suggested that all the considered materials had a potential to show a diminished biopersistence in vivo, due to reasons that depended on their chemical and phase composition.

The brain, a mixture of neural and glia cells, vasculature, and cerebrospinal fluid (CSF), is one of the most complex organs in the human body. To understand brain responses to traumatic injuries and diseases of the central nervous system it is necessary to develop accurate mathematical models and corresponding computer simulations which can predict brain biomechanics and help design better diagnostic and therapeutic protocols. So far brain tissue has been modeled as either a poroelastic mixture saturated by CSF or as a (visco)-elastic solid. However, it is not obvious which model is more appropriate when investigating brain mechanics under certain physiological and pathological conditions. In this paper we study brain’s mechanics by using a Kelvin-Voight (KV) model for a one-phase viscoelastic solid and a Kelvin-Voight-Maxwell-Biot (KVMB) model for a two-phase (solid and fluid) mixture, and explore the limit between these two models. To account for brain’s evolving microstructure, we replace in the equations of motion the classic integer order time derivatives by Caputo fractional order derivatives and thus introduce corresponding fractional KV and KVMB models. As in soil mechanics we use the displacements of the solid phase in the classic (fractional) KVMB model and respectively of the classic (fractional) KV model to define a poroelastic-viscoelastic limit. Our results show that when the CSF and brain tissue in the classic (fractional) KVMB model have similar speeds, then the model is indistinguishable from its equivalent classic (fractional) KV model.

Transmission electron microscopy (TEM) is a valuable methodology for investigating radiation-induced microstructural changes and elucidating the underlying mechanisms involved in the aging and degradation of nuclear reactor materials. However, the use of electrons for imaging may result in several inadvertent effects that can potentially change the microstructure and mechanisms active in the material being investigated. In this study, in situ TEM characterization is performed on nanocrystalline nickel samples under self-ion irradiation and post irradiation annealing. During annealing, voids are formed around 200 °C only in the area illuminated by the electron beam. Based on diffraction patterns analyses, it is hypothesized that the electron beam enhanced the growth of a NiO layer resulting in a decrease of vacancy mobility during annealing. The electron beam used to investigate self-ion irradiation ultimately significantly affected the type of defects formed and the final defect microstructure.

Metal organic chemical vapor deposition, as well as material and basic device properties of nitride-based high electron mobility transistor structures on (111) silicon substrates varying in diameter from 4 to 8 inch were studied using in-situ and ex-situ characterization techniques. All substrates used for the growth of the nitride structures in this study were of SEMI standard thicknesses. The total thickness of the nitride structures was in the range of 1.5 – 5 µm. It is reported that nitride structures can be grown on 4, 6 and 8 inch diameter substrates with very similar post-growth wafer shape, material and device characteristics. It is also shown that their crystal quality, 2DEG transport properties and isolation blocking voltages can be improved by increasing nitride structure thickness while maintaining post-growth wafer bow and warp less than 50 µm. The maximum thickness of nitride structures that can be successfully grown on 8 inch diameter SEMI standard substrates seems to be limited to about 4.5 µm due to plastic deformation of Si. Blocking voltages of more than 700 V were achieved using 4.5 µm thick nitride-based high electron mobility transistor structures grown on 8 inch Si substrate.

We present a simultaneous photoemission spectroscopic, low-energy electron diffraction and low-energy electron microscopic study of the metal-insulator transition of strained VO2. The fraction of rutile structure is extracted from the microscopic measurements throughout the transition, and compared with the fraction of the metallic electrons from photoemission data. We find that at intermediate temperatures, while the system is predominantly monoclinic-like in structure, the electronic component of the transition is much further advanced. Our results provide direct evidence for a monoclinic-like metallic phase of VO2 that is easily accessible at ambient temperatures and pressures.

The carbon nanotube community swims in the sea of superlatives. Researchers expect mechanical performance to achieve two extremes, an ultrastrong fibre taking us into space, and a superlubricant saving energy otherwise lost as heat. We examine CNT fibres in the light of traditional yarn science and present an interpretation of properties which combines aspects of these two extremes of performance.

We present a study of photoinduced charge carrier dynamics in single crystals and polycrystalline thin films of a functionalized fluorinated anthradithiophene (ADT) derivative, ADT-TES-F, combining measurements of time-resolved photocurrent with computational modeling. Simulations revealed two competing charge generation pathways: ultrafast charge separation and nanosecond (ns) time-scale exciton dissociation. Single crystals exhibited significantly enhanced fast charge photogeneration and charge carrier mobilities, as well as lower charge trap densities and free hole-trapped electron recombination, as compared to thin films. At sub-ns time scales after photoexcitation, the light intensity dependence of the photocurrents obtained in single crystals was determined by the carrier density-dependent recombination. At longer time scales, and at lower intensities, taking into account carrier concentration-dependent mobility improved agreement between numerically simulated and experimentally measured photocurrent data.

CZT is a semiconductor material that promises to be a good candidate for uncooled gamma radiation detectors. However, to date, technological difficulties in production of large size defect-free CZT crystals are yet to be overcome. The most common problem is accumulation of tellurium precipitates as microscopic inclusions. These inclusions influence the charge collection through charge trapping and electric field distortion. The common work-around solutions are to fabricate pixelated detectors by either grouping together many small volume CZT crystals to act as individual detectors, or to deposit a pixelated grid of electrical contacts on a larger, but defective, crystal, and selectively collect charge. These solutions are satisfactory in an R&D environment, but are unsuitable for mass production and commercial development. Our modeling effort is aimed at quantifying the various contributions of tellurium inclusions in CZT crystals to the charge generation, transport, and collection, as a function of inclusions size, position, and concentration. We model the energy deposition of gamma photons in the sensitive volume of the detector using LANL’s MCNP code. The electron-hole pairs produced at the energy deposition sites are then transported through the defective crystal and collected as integral charge at the electrical contact sites using CERN’s Garfield software package. The size and position distribution of tellurium inclusions is modeled by sampling experimentally measured distributions of such inclusions on a variety of commercially-grown CZT crystals using IR microscopy and image processing software packages.