Theoretical study of the permeation of water through TiO2 nanotubes using molecular dynamics simulation

In this study, the theoretical structures of armchair (6, 6) and zigzag (12, 0) TiO₂ nanotubes (TiNTs) were constructed by rolling the (101) layer of an anatase TiO₂ crystal. The (101) layer was made using Materials Studio (MS) by cutting the cleave plane (101) of the anatase TiO₂ crystal. Based on these structures, the basic properties of TiO₂ nanotubes were investigated using MS. Molecular dynamics simulations were performed using the software NAMD to investigate the status and permeation of water through the TiO₂ nanotubes. Structure analysis shows that both the inner and outer walls of the structures were terminated with oxygen atoms. The thicknesses of single tube walls are smaller than that of a perfect triple layer (2.20?Å) in bulk anatase TiO₂. With regard to the bulk Ti–O bond length, the Ti–O bonds in the outer layer are elongated, and are shortened in the inner layer. Molecular dynamics simulation shows that the water molecules in the nanotubes move back and forth, as in one-dimensional Brownian motion. Moreover, the penetration properties of TiNTs are associated with their radii, with the TiNT with larger radii having better penetration properties. Thus, when used in drug delivery or filtration systems, armchair TiNT has a better effect than zigzag TiNT.     

CO2 laser cutting of slate

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate.Following the previous work focused on the drilling and cutting of slate tiles using a Nd : YAG laser, we present in this paper the results of the work carried out to explore the possibilities to cut slate plates by using a CO₂ laser. A 1.5 kW CO₂ laser was used to perform different experiments in which, the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO₂ laser is a feasible tool for a successful cutting of slate.     

Energy efficiency of drilling granite and travertine with a CO2 laser and 980 nm diode laser

Using lasers to drill hard rock presents potential advantages compared to conventional mechanical drilling, such as higher penetration rates and reduced vibration. Before realistic drilling tools can be proposed, the influence of important parameters and the mechanisms involved in drilling different rocks with different lasers must be understood. In this work, we investigate the efficiency of laser drilling of granite and travertine with a CO₂ laser and a 980 nm fiber coupled diode laser. At the drilling surface, the maximum CW power delivered by the CO₂ laser was 140 W, while the diode laser delivered up to 215 W. Even at these modest power levels, it was possible to drill holes with diameters of the order of 8 mm at efficiencies varying from 40 kJ/cm³ to 150 kJ/cm³. The optimum laser exposure period of time was also investigated. Finally, x-ray diffraction and fluorescence analysis, as well as Tg (Thermogravimetry) and DTA (Differential Thermal Analysis) measurements, were performed on the rocks samples used.     

Energy absorption and exposure build-up factors in hydroxyapatite

The effective atomic number (Z_eff) and electron density (N_el) of hydroxyapatite (HA) and cortical bone have been computed for total photon interaction in the wide energy range of 1 keV–100 GeV using WinXCom. The variations of effective atomic number and electron density with energy of HA are compared with that of cortical bone. GP. fitting method has been used to compute energy absorption and exposure build-up factor of HA for wide energy range (0.015 MeV–15 MeV) up to the penetration depth of 40mean free path. The computed absorption build-up factor is used to estimate specific absorbed fraction of energy (Ф) and relative dose of photon in HA. Build-up factor increases with increase of penetration depth. The results of the present paper will also help in estimating safe dose levels for radiotherapy patients and also will be useful in dosimetry and diagnostics.     

The microwave response of MgB2 /Al2O3 superconducting thin films

Microwave characteristics of MgB2/Al2O3 superconducting thin films were investigated by coplanar resonator technique. The thin films studied have different grain sizes resulting from different growth techniques. The experimental results can be described very well by a grain-size model which combines coplanar resonator theory and Josephson junction network model. It was found that the penetration depth and surface resistance of thin films with smaller grain sizes are larger than those of thin films with larger grain sizes.     

Accumulation and Release of Self-Field Generated Vortices in Percolative YBa2Cu3O7-δ-Films

Pulsed laser heating of current biased percolative YBa₂Cu₃O_7--films can be used to generate and release self-field induced vortices. A laser pulse yields a voltage signal due to penetration of bias current induced magnetic flux in absence of an external magnetic field. Upon retooling, strongly pinned vortices remain in the film. These remanent vortices have been detected after disconnecting the bias source in the currentless film. Applying a subsequent second laser pulse, again yields a signal voltage but of inverse sign due to magnetic flux redistribution.     

On the mechanism of the interaction between oxygen and close-packed single-crystal aluminum surfaces

Using periodic first principles simulations we investigate the interaction of oxygen molecules with both regular Al(111) and Al(001) surfaces as well as a stepped Al(111) substrate. The limitation of this approach is the use of thin metallic slabs with a limited range for their coverage by adsorbed oxygen. The advantage is the detailed modeling that is possible at an atomic level. On the regular Al(111) surface, we have been able to follow the oxidation process from the approach of O₂ molecules to the surface, through the chemisorption and absorption of O atoms, up to the formation of first Al₂O₃ formula units. An energetically feasible mechanism for the formation of these Al₂O₃ ‘molecules’ is proposed but their aggregation to Al₂O₃ growth nuclei can only be surmised. On the Al(001) surface, absorption of oxygen atoms occurs more readily without any restrictions on the density of their surface overlayer, in agreement with the failure to observe a distinct chemisorption stage for O on Al(001) experimentally. The stepped Al(111) surface contains both {111} and {001} microfacets: the latter are obviously preferred for penetration of the oxygen adatoms into the subsurface space of the substrate. Before considering the O/Al interfaces the computational method is tested thoroughly by simulations on bulk Al and close-packed aluminum surfaces.     

An investigation into melt flow dynamics during repetitive pulsed laser drilling of transparent media

This paper presents an investigation into the dynamics of repetitive pulsed laser drilling of a visually transparent media using a CO₂ laser source. This enabled the use of a high-speed imaging system for observing, in real time, the behaviour of the drilling process in the laser drilled cavity of 1.5 mm diameter holes of up to 18.5 mm in depth. The work revealed that the instantaneous drilling velocity within each laser pulse can vary considerably from the average drilling velocity as a result of the non-uniform temporal pulse shape and the oscillation of the melt ejection rate. During beam breakthrough, both upward and downward melt ejections were observed to occur inside the drilled hole for a short period of time, after which the material was ejected through the exit end of the holes. It has been shown in this work that the downward melt flow velocity increases with hole depth for a positively tapered hole (from 0.09 to 1.43 m/s) and decreases with hole depth for a negatively tapered hole geometry (from 0.4 to 0.1 m/s), as a result of the change in the assist gas velocity inside the drilled hole with respect to the hole taper geometry. The mechanisms of forming the positively and negatively tapered holes in the transparent media have been correlated with the hole geometry and melt flow velocity. The work has demonstrated a new method of studying the melt dynamics in laser drilling.     

Driving mechanism of keyhole evolution during multi-pulse drilling with a millisecond laser

To better understand the physical processes of multi-pulse laser drilling, this study investigates the keyhole evolution and its driving mechanism in a time-resolved observation system. The evolution characteristics suggested a two-phase process of rapid penetration followed by moderate penetration. As revealed in the ejection and vaporization behavior, the keyhole evolution was dominated by ejection and vaporization during the rapid and moderate penetration stages, respectively. In a single laser-pulsed drilling experiment, the driving mechanism itself was found to be affected by the dimensionless laser power density. The effect of dimensionless laser power density on depth increment was then discussed by comparing the experimental observations with numerical simulation results. The results further confirmed the driving mechanism of the keyhole evolution. The results in this paper are useful for understanding the driving mechanism of the keyhole evolution during multi-pulse laser drilling.     

The density functional calculations on the structural and electronic properties of the endohedral fullerene dimer (N2@C60)2

The generalised gradient approximation based on density functional theory is used to study the structural and electronic properties of the endohedral fullerene dimer (N 2 @C 60) 2.Four N atoms sit at the cage centres in the form of two N 2 molecules.The density of states and Mulliken charge analysis explore that the energy levels from-6 to-10 eV are mainly influenced by the N 2 molecules.     

Characterization of electrodeposited Bi2S3 thin films by holographic interferometry

Optical non destructive evaluation methods, using lasers as the object illumination source, include holographic interferometry. It is widely used to measure stress, strain, and vibration in engineering structures. Double exposure holographic interferometry (DEHI) technique is used to determine thickness and stress of electrodeposited bismuth trisulphide (Bi₂S₃) thin films for various deposition times. The same is tested for other concentration of the precursors. It is observed that, increase in deposition time, increases thickness of thin film but decreases stress to the substrate. The structural, optical and surface wettability properties of the as deposited films have been studied using X-ray diffraction (XRD), optical absorption and contact angle measurement, respectively. The X-ray diffraction study reveals that the films are polycrystalline with orthorhombic crystal structure. Optical absorption study shows the presence of direct transition with band bap 1.78 eV. The water contact angle measurement shows hydrophobic nature of Bi₂S₃ thin film surface.     

Simultaneous measurement of thermal and dielectric properties in a conduction calorimeter: Application to the lock-in transition in Rb2ZnCl4 single crystal

A device for simultaneous measurement of thermal properties (specific heat, latent heat and related properties) and electric properties (such as permittivity, dielectric spectroscopy) based on conduction calorimetry is explained. The device is used to study the commensurate-incommensurate (lock-in) phase transition in Rb₂ZnCl₄ single crystal. This transition is found to be first-order. Thermal and dielectric anomalies are discussed.     

Excellent stability of plasma-sprayed bioactive Ca3ZrSi2O9 ceramic coating on Ti-6Al-4V

In this work, novel zirconium incorporated Ca-Si based ceramic powder Ca₃ZrSi₂O₉ was synthesized. The aim of this study was to fabricate Ca₃ZrSi₂O₉ coating onto Ti-6Al-4V substrate using atmospheric plasma-spraying technology and to evaluate its potential applications in the fields of orthopedics and dentistry. The phase composition, surface morphologies of the coating were examined by XRD and SEM, which revealed that the Ca₃ZrSi₂O₉ coating was composed of grains around 100 nm and amorphous phases. The bonding strength between the coating and the substrate was 28 ± 4 MPa, which is higher than that of traditional HA coating. The dissolution rate of the coating was assessed by monitoring the ions release and mass loss after immersion in the Tris-HCl buffer solution. The in vitro bioactivity of the coating was determined by observing the formation of apatite on its surface in simulated body fluids. It was found that the Ca₃ZrSi₂O₉ coating possessed both excellent chemical stability and good apatite-formation ability, suggesting its potential use as bone implants.     

Creating a collimated ultrasound beam in highly attenuating fluids

We have devised a method, based on a parametric array concept, to create a low-frequency (300-500 kHz) collimated ultrasound beam in fluids highly attenuating to sound. This collimated beam serves as the basis for designing an ultrasound visualization system that can be used in the oil exploration industry for down-hole imaging in drilling fluids. We present the results of two different approaches to generating a collimated beam in three types of highly attenuating drilling mud. In the first approach, the drilling mud itself was used as a nonlinear mixing medium to create a parametric array. However, the short absorption length in mud limits the mixing length and, consequently, the resulting beam is weak and broad. In the second improved approach, the beam generation process was confined to a separate “frequency mixing tube” that contained an acoustically non-linear, low attenuation medium (e.g., water) that allowed establishing a usable parametric array in the mixing tube. A low-frequency collimated beam was thus created prior to its propagation into the drilling fluid. Using the latter technique, the penetration depth of the low frequency ultrasound beam in the drilling fluid was significantly extended. We also present measurements of acoustic nonlinearity in various types of drilling mud.     

Mechanical properties and electronic structure of TiC,Ti0.75W0.25C,Ti0.75W0.25C0.75N0.25, TiC0.75N0.25 and TiN

The first-principles calculations are performed to investigate the mechanical properties and electronic structure of TiC, Ti_0.75W_0.25C, Ti_0.75W_0.25C_0.75N_0.25, TiC_0.75N_0.25 and TiN. Density functional theory and ultrasoft pseudopotentials are used in this study. From the formation energy, it is found that nitrogen can increase the stability of TiC. The calculated elastic constants and elastic moduli of TiC compare favorably with other theoretical and experimental values. Tungsten and nitrogen are observed to significantly increase the bulk, shear and Young's modulus of TiC. Through the analysis of B/G and Cauchy pressure, tungsten can significantly improve the ductility of TiC. The electronic structure of TiC, TiN, Ti_0.75W_0.25C, Ti_0.75W_0.25C_0.75N_0.25, and TiC_0.75N_0.25 are used to describe nonmetal–metal and metal–metal bonds. Based on the Mulliken overlap population analysis, the hardness values of TiC, Ti_0.75W_0.25C, Ti_0.75W_0.25C_0.75N_0.25, TiC_0.75N_0.25 and TiN are estimated.     

Spectroscopic comparison of aluminium welding plasmas produced by high power CO and CO2 lasers

Welding tests on the aluminium alloy AlMgSi1 (6082) by the use of a high power CO laser with good beam quality show higher penetration depths and better weld seam quality compared with the results obtained with a commercial industrial CO₂ laser. Spectroscopy of the laser-induced welding plasma shows a strong decrease of the intensities of Al(II) lines and no appearance of Al(III) lines in CO laser aluminium welding compared with CO₂ laser welding at the same process parameters. This is a consequence of the shorter 5 to 5.6 μm wavelength of the CO laser leading to reduced beam-plasma interaction.     

Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

Seeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C₃F₇CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF₆ environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C₂F₅CN, CF₃CN, COF₂ and CF₄ with the aluminium widely used in electrical equipment. It was found that the interaction between C₂F₅CN, CF₃CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF₂, CF₄ and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C₃F₇CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C₃F₇CN decomposition products and aluminium.     

In-plane magnetic penetration depth in FeSe1-xSx (x = 0, 0.04, 0.09) and FeTe1-xSex (x = 0.40) single crystals

The magnetization anomaly of FeSe_1–xS_x(x?=?0, 0.04, 0.09) and FeTe_1–xSe_x(x?=?0.40) single crystals are examined through our Modified Phenomenological Ginzburg–Landau (MPGL) theory applicable to two-band superconducting systems. The theory in the London limit calculates the values of λ_ab(0) as 445.695, 372.058 and 432.957?nm of FeSe_1–xS_x for x?=?0, 0.04, 0.09 which are very close to the experimental values reported by Hafiez et al. [Superconducting properties of sulfur-doped iron selenide. Phys Rev B. 2015;91(16):165109–165120] and as 534?nm for FeTe_1–xSe_x(x?=?0.40) single crystal, which is close to the experimental value reported by Yadav and Paulose [Upper critical field, lower critical field and critical current density of FeTe_0.60Se_0.40 single crystals. New J Phys 2009;11:103046]. In addition, the variation of temperature-dependent in-plane magnetic penetration depth λ_ab(T) with the temperature (T) has been presented, which agrees well as reported by Hafiez et al. [Superconducting properties of sulfur-doped iron selenide. Phys Rev B. 2015;91(16):165109–165120] and Yadav and Paulose [Upper critical field, lower critical field and critical current density of FeTe_0.60Se_0.40 single crystals. New J Phys. 2009;11:103046].     

Vitamin D and bone: — How does vitamin D regulate bone formation and resorption? —

Vitamin D was discovered as an anti-rachitic agent, but even at present, there is no direct evidence to support the concept that vitamin D directly stimulates osteoblastic bone formation and mineralization. It appears to be paradoxical, but vitamin D functions in the process of osteoclastic bone resorption. Osteoclasts, the only cells responsible for bone resorption, develop from hematopoietic cells of the monocyte-macrophage lineage. In 1992, we hypothesized that a membrane-bound factor, designated as “osteoclast differentiation factor (ODF)”, is expressed on the plasma membrane of osteoblasts/stromal cells in response to osteotropic factors including the active form of vitamin D₃, 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃]. Recently, four research groups including ours independently identified three key molecules (RANKL, RANK, and OPG) responsible for osteoclastogenesis. A long-sought-after ligand, ODF, was identical to RANKL. RANKL was a member of the membrane-associated TNF ligand family, which induced differentiation of spleen cells (osteoclast progenitors) into osteoclasts in the presence of M-CSF. RANK, a member of the TNF receptor family, was a signaling receptor essential for the RANKL-mediated osteoclastogenesis. OPG, a secreted member of the TNF receptor family, was a decoy receptor for RANKL. The discovery of RANKL, RANK and OPG opens a new era in the study of bone biology and the therapy of several metabolic bone diseases such as osteoporosis, rheumatoid arthritis, and periodontal diseases.