The Variation of “Surface” Pressure in a Nanocrystal as a Function of Temperature

The Mie-Lennard-Jones potential of interatomic interaction is used to derive an expression for “surface” pressure in a nanocrystal with free surface. The nanocrystal has the form of a parallelepiped with a square base. The number of atoms N may vary from eight to ∞. It is found that a certain “inversion temperature” T _i exists for any substance, where the temperature dependences of surface pressure for different sizes of nanocrystal intersect. When the crystal disperses in the T < T _i region, the “surface” pressure increases, and in the T > T _i region decreases, with decreasing size of nanocrystal: P _sf(N) ～ N ^?1/3. The greater the deviation of the nanocrystal shape from cubic, the stronger the dependence P _sf(N). It is demonstrated that, at some temperatures (T < T ₀), the “surface” pressure compresses the nanocrystal, and at other temperatures-stretches this nanocrystal, as its size decreases. The more clearly the quantum effects are defined in the crystal, the lower the value of the “temperature of zero surface pressure” T ₀, which depends on the nanocrystal size and shape.     

Comparison of the cytotoxicity of molybdenum as powder and as alloying element in a niobium–molybdenum alloy

Commercially pure metal niobium (c.p. Nb) as well as niobium–molybdenum (Nb–Mo) alloys were produced following several powder metallurgical routes. In brief, niobium and molybdenum powders were blended and milled in order to form Nb–Mo alloys. The alloy powders and the c.p. Nb were then either pressed and sintered, or cold isostatically pressed followed by hot isostatically pressing. In order to assess the cytotoxicity of the c.p. Nb and c.p. Mo powders, a 72 h minimal essential medium-extraction test was performed according to ISO/EN 10993–5. The cytotoxicity of the c.p. Nb metal and the Nb–Mo alloys was tested in a 72 h direct contact test. Compared to a negative control (UHMWPE), c.p. Nb was non-toxic, but c.p. Mo was moderately toxic. None of the powder metallurgically produced materials were toxic. Neither differences in molybdenum concentration, nor in porosity of the samples, due to different production routes, had any influence on the toxicity of the materials. Rat bone marrow cultures showed that only on c.p. Nb was a mineralized extracellular matrix formed, while on the more porous Nb–Mo alloys, cell growth was observed, but no mineralization. In conclusion, c.p. Mo powder is moderately toxic, however, as an alloying element it is non-toxic. Material porosity seems to influence differentiation of bone tissue in vitro. © 1998 Kluwer Academic Publishers     

Temperature Characteristics of Platinum–Cobalt Resistance Thermometers Based on the ITS-90 Above 14 K

Three platinum–cobalt resistance thermometers (PtCoRTs), which are manufactured in a structure similar to a capsule-type standard platinum resistance thermometer (SPRT), were calibrated against the capsule-type SPRTs, which was calibrated based on the International Temperature Scale of 1990 (ITS-90) at NMIJ. The thermometers were calibrated in the temperature range from the triple point of equilibrium hydrogen to the triple point of water by using the dissemination system of the ITS-90 at NMIJ. In this study, the temperature dependence of the resistance ratio, \(W\) , which is the ratio of the resistance obtained at each temperature by the calibration to the resistance at the triple point of water, is obtained for each PtCoRT. In the temperature region below the triple point of Ne, the temperature dependence of \(W\) of each PtCoRT is fitted by a 4th-order polynomial. In the temperature region above the triple point of Ne, a 13th-order polynomial is fitted to the temperature dependence of \(W\) . It was found that residuals for the polynomial fits of each PtCoRT were less than 0.3 mK in both temperature regions.     

Low Temperature Epitaxial Growth of Semiconductors Using Synchrotron Radiation as a Light Source

Results of our recent experiments relating to the synchrotron radiation (SR) excited growth of Ⅱ-V compounds using metalorganic sources are described. We discuss mainly the growth characteristics of films in addition to the characterization of the deposited films. ZnTe epitaxial layer without carbon and oxygen contamination is attainable even at room temperature using SR as a light source. The quantum yield for forming ZnTe molecules was estimated to be higher than 3%. Through these experiments, we propose that the SR-excited growth is a powerful technique for a novel low temperature growth of compounds.     

Modeling and Investigation of Nonstationary Pressure and Temperature Fields in a Deformable Formation During the Filtration of a Gas–Condensate Mixture

Journal of Engineering Physics and Thermophysics - A procedure and an algorithm have been proposed that allow modeling the problem of identification of parameters of a deformable formation during...     

An Explicit Function Expression for dc Bias and Temperature Dependence of Magnetoresistances in Magnetic Tunnel Junctions

An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters.Two of these intrinsic parameters are the Curie temperature Tc and the density of state(DOS) for itinerant majority and minority electronsξ(ρM/ρm),which are the eigen parameters of ferromagnetic electrodes.Others are the spin-dependent matrix-element ratio(i.e.,|T^d)^2/{T^j}^2 )and the anisotropic-wavelength-cutoff energy Ec^γ of spin-wave spectrum in magnetic tunnel junction(MTj),which are the structure parameters of an MTj.These intrinsic parameters can be predetermined using the experimental measurement or,in principle,using the first-principle calculation method for an MTj with the three key layers of FM/1/FM.Furthermore,a series of experimental data for an MTj,for example,a spin-valve-type MTj of Ta(5nm)/Ni79Fe21(25nm)/Ir22Mn78(12nm)/Co75Fe25(4nm)/Al(0.8nm)-oxide/Co75Fe25(4nm)/Ni79Fe21(20nm)/Ta(5nm)in this work,can be self-consistently evaluated and explained using such explicit function formulations.     

Pulsed laser deposition film of a donor–acceptor–donor polymer as possible active layer in devices

A molecule having a ketone group between two thiophene groups was synthesized. Presence of alternating electron donating and accepting moieties gives this material a donor–acceptor–donor (DAD) architecture. PolyDAD was synthesized from DAD monomer by oxidative polymerization. Device quality films of polyDAD were fabricated using pulsed laser deposition technique. X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectra (FTIR) data of both as synthesized and film indicate the material does not degrade during ablation. Optical band gap was determined to be about 1.45 eV. Four orders of magnitude increase in conductivity was observed from as synthesized to pulsed laser deposition (PLD) fabricated film of polyDAD. Annealing of polyDAD films increase conductivity, indicating better ordering of the molecules upon heating. Rectifying devices were fabricated from polyDAD, and preliminary results are discussed.     

Preparation and evaluation of a timolol maleate drug–resin ophthalmic suspension as a sustained-release formulation in vitro and in vivo

Abstract

The aim of this work was to assess the performance of resin as an ocular delivery system. Timolol maleate (TM) was chosen as the model drug and an ion exchange resin (IER) as the carrier. The drug–resin complex was prepared using an oscillation method and then characterized regarding particle size, zeta potential, morphology, and drug content. After in vitro drug release study and corneal permeation study were performed, in vivo studies were performed in New Zealand albino rabbits using a suspension with particles sized 4.8?±?1.2?μm and drug loading at 43.00?±?0.09 %. The results indicate that drug released from the drug–resin ophthalmic suspension permeated the cornea and displayed a sustained-release behavior. Drug levels in the ocular tissues after administration of the drug–resin ophthalmic suspension were significantly higher than after treatment with an eye drop formulation but were lower in body tissues and in the plasma. In conclusion, resins have great potential as effective ocular drug delivery carriers to increase ocular bioavailability of timolol while simultaneously reducing systemic drug absorption.     

Temperature Effects on the Self-trapping Energy of a Polaron in a GaAs Parabolic Quantum Dot

The temperature and the size dependences of the self-trapping energy of a polaron in a GaAs parabolic quantum dot are investigated by the second order Rayleigh-Schrodinger perturbation method using the framework of the effective mass approximation. The numerical results show that the self-trapping energies of polaron in GaAs parabolic quantum dots shrink with the enhancement of temperature and the size of the quantum dot. The results also indicate that the temperature effect becomes obvious in small quantum dots     

The presence of fivefold germanium as a possible transitional phase in the iron–lead–germanate glass system

Glasses in the system xFe₂O₃·(100 − x)[7GeO₂·3PbO] with 0 ≤ x ≤ 60 mol% have been prepared from melt quenching method. In this article, we investigated changes in germanium coordination number in iron–lead–germanate glasses through molar volume analysis, measurements of densities, investigations of FTIR, and UV–VIS spectroscopy. The observations present in these mechanisms show that the lead ions have an affinity pronounced toward [GeO₅] and [FeO₄] structural units with non-bridging oxygens. The excess of oxygen can be supported into the glass network by the formation of [FeO₆] structural units and the apparition of the germanate anomaly. At higher content of iron (III) oxide, the anomaly behavior of the germanium is due to the formations of [FeO₆] structural units. Our results show that the presence of fivefold germanium as a possible transitional phase from four to sixfold germanium it is necessary for the formation of the [FeO₆] structural units and the apparition of the Fe₂O₃ crystalline phase. Pb⁺² ions with 6s² configuration show strong absorption in the ultraviolet due to parity allowed s²-sp transition.     

Application of graphene–pyrenebutyric acid nanocomposite as probe oligonucleotide immobilization platform in a DNA biosensor

A stable and uniform organic–inorganic nanocomposite that consists of graphene (GR) and pyrenebutyric acid (PBA) was obtained by ultrasonication, which was characterized by scanning electron microscopy (SEM) and UV–vis absorption spectra. The dispersion was dropped onto a gold electrode surface to obtain GR–PBA modified electrode (GR–PBA/Au). Electrochemical behaviors of the modified electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy using [Fe(CN)₆]^3 ?/4 ? as the electroactive probe. A novel DNA biosensor was constructed based on the covalent coupling of amino modified oligonucleotides with the carboxylic group on PBA. By using methylene blue (MB) as a redox-active hybridization indicator, the biosensor was applied to electrochemically detect the complementary sequence, and the results suggested that the peak currents of MB showed a good linear relationship with the logarithm values of target DNA concentrations in the range from 1.0 × 10^? 15 to 5.0 × 10^? 12 M with a detection limit of 3.8 × 10^? 16 M. The selectivity experiment also showed that the biosensor can well distinguish the target DNA from the non-complementary sequences.     

Emittance Properties of Siliconized Silicon Carbide in the Temperature Range of 1400–2200 K

High Temperature - The results of an experimental study of the total hemispherical and spectral normal emittances powers of siliconized silicon carbide in the temperature range of 1400–2200 K...     

Numerical Simulation of Temperature Distribution and ThermalStress Field in a Turbine Blade with Multilayer-Structure TBCs by a Fluid–Solid Coupling Method

To study the temperature distribution and thermal-stress?eld in different service stages,a twodimensional model of a turbine blade with thermal barrier coatings is developed,in which the conjugate heat transfer analysis and the decoupled thermal-stress calculation method are adopted.Based on the simulation results,it is found that a non-uniform distribution of temperature appears in different positions of the blade surface,which has directly impacted on stress?eld.The maximum temperature with a value of 1030°C occurs at the leading edge.During the steady stage,the maximum stress of thermally grown oxide(TGO)appears in the middle of the suction side,reaching 3.75 GPa.At the end stage of cooling,the maximum compressive stress of TGO with a value of -3.5 GPa occurs at the leading edge.Thus,it can be predicted that during the steady stage the dangerous regions may locate at the suction side,while the leading edge may be more prone to failure on cooling.     

Characteristics of TiC dendrites in as solidified Ti–Al–C alloys

Abstract

Results are reported on the dendrite secondary arm spacing of a series of as cast Ti–C and Ti–Al–C alloys in the composition range up to 10 at.-%C and 15 at.-%Al. The presence of Al leads to a significant decrease in the dendrite spacing, an effect of potential interest for improving mechanical properties. The structural refinement is attributed mainly to the slower diffusion of Al as compared with carbon, in the solute partitioning required for coarsening of dendrite arms.     

Molecular Resolution Nanostructure and Dynamics of the Deep Eutectic Solvent—Graphite Interface as a Function of Potential

Interest in deep eutectic solvents (DESs), particularly for electrochemical applications, has boomed in the past decade because they are more versatile than conventional electrolyte solutions and are low cost, renewable, and non-toxic. The molecular scale lateral nanostructures as a function of potential at the solid–liquid interface—critical design parameters for the use of DESs as electrochemical solvents—are yet to be revealed. In this work, in situ amplitude modulated atomic force microscopy complemented by molecular dynamics simulations is used to probe the Stern and near-surface layers of the archetypal and by far most studied DES, 1:2 choline chloride:urea (reline), at the highly orientated pyrolytic graphite surface as a function of potential, to reveal highly ordered lateral nanostructures with unprecedented molecular resolution. This detail allows identification of choline, chloride, and urea in the Stern layer on graphite, and in some cases their orientations. Images obtained after the potential is switched from negative to positive show the dynamics of the Stern layer response, revealing that several minutes are required to reach equilibrium. These results provide valuable insight into the nanostructure and dynamics of DESs at the solid–liquid interface, with implications for the rational design of DESs for interfacial applications.