Molecular dynamics simulations of liquid water using various long-range electrostatics techniques

Water is one of the most extensively studied molecules, owing to its crucial role in biological processes. The water molecule is both highly polar and highly polarizable. Properties of water computed from molecular simulations are therefore critically dependent on both the intermolecular potential and the method for computing long-range electrostatic corrections. In this paper, the effects of the potential and the long-range electrostatic corrections are quantified for liquid water from 260 to 400?K. Simulations were carried out for a system of 256 molecules in the NVT ensemble. Thermodynamic, structural, dynamical, hydrogen bonding and dielectric properties have been computed for the flexible SPC and rigid SPC, SPC/E, TIP4P, TIP4P-Ew and TIP4P-FQ potentials, using the Lekner, Ewald and reaction field techniques to handle long-range electrostatics. The Lekner method gave the best overall agreement with experimental data, while the reaction field approach produced poorer results. Some measurable differences were found between the Lekner and Ewald techniques. For dielectric properties, the performance of the TIP4P-FQ model was superior relative to other potentials. For 256 molecules, the computational speeds of the Ewald and reaction field methods were found to be 2.5 to 3 times and 3.5 to 5 times faster than the Lekner technique, respectively.     

Characterization and ethylene adsorption of natural and modified clinoptilolites

The ethylene adsorption of Turkey clinoptilolite-rich tuff from Gordes and Bigadic region of western of Anatolia and their exchanged forms (K⁺, Na⁺ and Ca²⁺) were investigated. The clinoptilolite samples were characterized using XRD, TG-DTA and nitrogen adsorption methods. Adsorption isotherms for ethylene on natural and modified forms of both adsorbents at 277 K and 293 K were obtained at pressures up to 38 kPa. Uptake of ethylene increased as Na-CLN < Ca-CLN < K-CLN < Natural CLN for Gordes zeolite at 277 K, 293 K and for Bigadic zeolite at 277 K. For Bigadic zeolites at 293 K, uptake of ethylene increased in the order Ca-CLN < Na-CLN < K-CLN < Natural CLN. It was found that ethylene adsorption capacity of Bigadic clinoptilolite samples was much greater than Gordes clinoptilolite samples except K⁺ modified forms at both temperatures. These results show that both natural clinoptilolites have a considerable potential for the removal of ethylene.     

Characterization of water exposed plasma sprayed oxide coating materials using XPS

The surface compositions and oxidation states of non-exposed and water exposed plasma sprayed oxide coatings were studied using X-ray photoelectron spectroscopy (XPS). Coating materials were TiO₂, Al₂O₃ and Cr₂O₃ and their mixtures. Water exposures were performed for free standing coating disks at mild electrolyte (1 mmol NaCl solution) at pH 4, 7 and 9. The exposure time was two weeks.It was observed that pure plasma sprayed TiO₂ material was chemically stable over whole experiment pH range and only slight surface hydroxylation was observed for this material.In case of plasma sprayed Al₂O₃ materials the surface O/Al ratio increased considerably during water exposure especially at exposure pH 7. This was probably result of surface conversion to hydrous form. No surface oxidation state changes were observed for this material.The non-exposed Cr₂O₃ materials contained both Cr(III) and Cr(VI) oxides. The water exposures increased the surface oxygen and Cr(VI) contents at the expense of Cr(III). The most probable reason for that was the dissolution of surface Cr(VI) oxide phase during water exposures and the (re)adsorption of dissolved Cr(VI) species back to the surface.     

Fibronectin adsorption studied using neutron reflectometry and complementary techniques

In implantology it is known that fibronectin affects cell-substrate adhesion, consequently, the structure and composition of the initially adsorbed fibronectin layer to a large extent determines the biological response to a biomaterial implanted into the body. In this study we have used neutron reflectometry and quartz-crystal microbalance with dissipation to investigate the amount of fibronectin adsorbed, the layer density, thickness and structure of films adsorbed to polished silicon oxide surfaces. We have cultured MG63 osteoblast-like cells on surfaces coated and uncoated with fibronectin and monitored the cellular response to these surfaces. The results show that at fibronectin concentrations in the range 0.01 to 0.1mg/ml a single highly hydrated layer of fibronectin approximately 40-50Å in thickness adsorbs to a polished silicon oxide surface and is likely to correspond to one diffuse monolayer of fibronectin arranged side-on. Cells cultured on this fibronectin layer have dramatically different morphology and growth to those grown on bare surfaces. Using a model silicon oxide surface has enabled us to study the substrate/protein interface, together with the impact of a fibronectin layer on the cellular response using consistent experimental conditions across a unique set of experimental techniques.     

Characterization of magnetic materials by low-field microwave absorption techniques

A low-field non-resonant microwave absorption has recently been observed in a variety of magnetically ordered materials at low DC fields (−1000 Oe H_DC+1000 Oe), which is known as low-field microwave absorption (LFA). It has been shown that LFA is essentially similar to giant magnetoimpedance (GMI), and clearly different from ferromagnetic resonance (FMR). LFA strongly depends on the anisotropy field of the sample. In contrast with FMR (which can be described as the homogeneous precession of spins in the saturated state), LFA can be thought as a spin rotation process occurring during the magnetic saturation. In this work, we present a detailed study of the basic features of LFA in several types of materials: ferrites and amorphous microwires and ribbons; in particular the effects sample shape, temperature up to the Curie transition, the influence of easy axis and the effects of annealings. These examples show that once LFA is fully understood, it can become a powerful characterization tool.     

Volumetric spectral analysis of materials using terahertz-tomography techniques

We present for the first time a system and new algorithms for spectral THz-tomography. The electric field of single cycle ultra short THz-pulses can be measured time resolved in amplitude and phase. By focusing ultra short THz-pulses to a sample and analyzing the transmitted or reflected beams the inner structure of the sample can be investigated with a resolution up to 0.4 mm by evaluating the time resolved data. Thus a spectrum of every scanned THz-pulse can be calculated with the usage of the fast Fourier transform. In contrast to classical computed tomography (CT) with X-rays a higher amount of information can be obtained. Based on the characteristic absorption spectra of varying materials it is now possible to identify different substances inside a sample by terahertz-tomography with probabilities that are higher than 80%.     

Characterization of oxide thin films using optical techniques

Thin films of oxide materials are playing a growing role as critical elements in optoelectronic devices and nanoscale devices. In this work, thin films of some typical oxides such as WO₃, Ga₂O₃ and SrTiO₃ were investigated. We present measurements of those films, using various optical techniques like photoconductivity transients over a wide time range and photo-Hall measurements. Analysis of the photo-Hall and photoconductivity data permits the determination of the contribution to the photoconductivity made by the carrier mobility and concentration. A model for dispersive carrier transport was proposed to explain the relaxation of the photoconductivity in oxide thin films. In addition, photoluminescence characterization was used to study microstructures and energy band in oxide thin films. The broad emission from oxide host, consisting of several band peaks, was likely due to a recombination process with several possible paths. The dependence of the luminescent intensity on the annealing atmosphere was associated with the presence of oxygen vacancies. It is suggested that our optical analysis efforts have improved the understanding of oxide thin films, and this should lead to the necessary advancements in a variety of devices.     

Remote cure monitoring of epoxy materials using optical techniques

A remote all-optical technique for the generation and detection of ultrasonics in materials is described. This technique uses a robust wideband optical fiber interferometer for detection. Using this interferometer, non-contact measurements of ultrasonic propagation times in epoxy materials are reported throughout the complete cure cycle.     

Characterization of fractured permeable porous media using relaxation-weighted imaging techniques

The inversion time (TI) weighted inversion-recovery spin-echo (IRSE) imaging technique was used for laboratory characterization of fractures and porous matrix in permeable media. The method is based on the fact that relaxation rates in fractures and those in surrounding porous matrix are substantially different. Thus, by selectively suppressing imaging signals from either fractures or porous matrix, one can highlight fluid distributions in either of these regions so that fractures can be unambiguously identified and surrounding porous structures can be characterized. The advantages over conventional NMR spin-echo imaging are demonstrated with various fractured porous rock types. A technique to speed acquisitions of images of fluid distributions in porous matrix is also demonstrated.     

Thermal characterization of a liquid resin for 3D printing using photothermal techniques

Thermal properties of a liquid resin were studied by thermal lens spectrometry (TLS) and open photoacoustic cell (OPC), respectively. In the case of the TLS technique, the two mismatched mode experimental configuration was used with a He–Ne laser, as a probe beam and an Argon laser was used as the excitation source. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression to the experimental data in order to obtain the thermal diffusivity (α) of the resin. On the other hand, the sample thermal effusivity (e) was obtained by using the OPC technique. In this technique, an Argon laser was used as the excitation source and was operated at 514 nm with an output power of 30 mW. From the obtained thermal diffusivity (α) and thermal effusivity (e) values, the thermal conductivity (k) and specific heat capacity per unit volume (ρc) of resin were calculated through the relationships k = e(α)^1/2 and ρc = e/(α)^1/2. The obtained thermal parameters were compared with the thermal parameters of the literature. To our knowledge, the thermal characterization of resin has not been reported until now. The present study has applications in laser stereo-lithography to manufacture 3D printing pieces.     

Theory of coupling of electronic systems: Experimental structures using advanced lithographic techniques

This paper focuses on the physics of disorder-induced localization and the important role of advanced material microfabrication technology for realizing novel microstructures as physical models. Present and future microfabrication capabilities for tailoring materials in the submicron and ultrasubmicron range offer the opportunity to fabricate controllable physical models, approaching atomic scale, for the fundamental study of coupling of electronic systems and the effect of dimensionality on transport properties. These physical models will require the ingenious exploitation of advanced lithographic/patterning techniques for controlling lateral dimensions, particularly if this is combined with advanced vapor or molecular beam deposition technique for controlling vertical dimensions. The type of studies discussed here have great significance in understanding and designing highly-dense very large-scale/ultra large-scale integrated (VLSI/ULSI) circuits and interconnecting-lines-dominated neural network IC systems, as well as in the studies of the scaling theories of localization. It is expected that these studies will lead to the design of novel device concepts.     

Comparison of various dispersion compensation techniques at high bit rates using CSRZ format

In this paper, the dispersion compensation techniques are compared on the basis of eye opening, eye closure, bit error rate and Q-factor. These techniques are applied to CSRZ system, which operates at bit rates of 2.5, 5, 10, 15 and 20 Gbps bit rates. The technique using fiber Bragg grating (FBG) for dispersion compensation is the best technique as this technique gives larger values of eye opening at 10 and 20 Gbps bit rate, smaller values of eye closure at 10 and 20 Gbps, minimum value of BER at 15 Gbps and maximum value of Q-factor at 15 Gbps when compared with other techniques. The RDF technique is the next best technique since this technique gives maximum value of eye opening when other techniques give almost similar values of eye opening at 15 Gbps, minimum value of eye closure at 15 Gbps, minimum value of BER at 15 Gbps and maximum value of Q-factor at 15 Gbps when compared with other techniques. The DCF is the next best technique as this technique gives maximum and minimum values of eye opening and eye closure at 20 Gbps (next best to FBG at 20 Gbps).     

High-speed residue-free transfer of two-dimensional materials using PDMS stamp and water infiltration

A high-speed residue-free transfer method using PDMS (polydimethylsiloxane) stamp and water infiltration between graphene and a hydrophilic surface is reported. Monolayer graphene was transferred from an enhanced fluorinated Al₂O₃ surface using PDMS. Water infiltration dramatically reduced the time required to separate the graphene from the Al₂O₃ substrate to a few minutes. The graphene was then successfully transferred to a target substrate (SiO₂) using the PDMS stamp. Atomic force microscopy and lateral force microscopy was used to confirm the absence of residue on the transferred graphene surface.     

Characterization of planar photonic crystals using surface coupling techniques at large wavelengths

We report a non-destructive characterization of planar two-dimensional (2D) photonic crystals (PhCs) made in silicon on insulator (SOI) wafers using ellipsometric or Fourier transformed infrared (FTIR) spectroscope. At large wavelengths, devices behave as homogeneous isotropic materials defined by an effective filling factor. The experimental results related to the PhC limited dimensions confirm this characterization.     

Design and development of second-generation titanium oxide photocatalyst materials operating under visible light irradiation by applying advanced ion-engineering techniques

Advanced ion-beam techniques such as metal ion-implantation, ionized cluster beam (ICB) deposition and RF-magnetron sputtering (RF-MS) deposition were found to enable the development of unique titanium oxide photocatalyst materials which are able to absorb and work not only under UV but also visible or solar light irradiation. Thus prepared visible light-responsive TiO₂ act as efficient photocatalysts for the NO decomposition reaction into N₂ and O₂ as well as the H₂ and O₂ evolution reaction from water.