Size Effect of Insulating Nano-Inclusions in Y�CBa�CCu�CO Bulk Superconductors Fabricated by Seeded Infiltration Growth

We have conducted an experimental study on the effect of the pinning centers size on the superconducting properties in textured YBCO samples. In this work, we investigated the effectiveness of the addition of an insulating inclusion on the superconducting and magnetic properties of textured YBCO bulk materials. The purpose of this study was to ascertain whether the size of artificial pinning centers is able to affect the superconducting properties of our samples. To this effect insulating nano-pinning centers with two different particle size distributions of about 20 nm and 130 nm have been successfully incorporated within YBCO matrix by slight doping with nano-particle alumina dispersions. The microstructure and superconducting properties were investigated by scanning electron microscopy (SEM) and SQUID. The results indicate that slight inclusions of nano-alumina can enhance the flux-pinning capability of samples. This study underlines the dependence of the pinning force on the size of the pinning centers.     

The Magnetic Behavior and Physical Characterization of?Cu�CMn�CAl Ferromagnetic Shape Memory Alloy

In this study, Cu?CAl?CMn alloys with different weight percentages were fabricated by melting metal powders in an induction furnace under argon atmosphere and then by applying rapid solidification. Due to the changes of the alloy percentages after the casting processes, alloy rates were determined by using energy-dispersive X-ray spectroscopy results received from least three different zones. For five different samples, the alloy percentages were found as Cu?C11.96%Al?C3.21%Mn, Cu?C14.09%Al?C10.78%Mn, Cu?C13.73%Al?C13.12%Mn, Cu?C13.44%Al?C12.68%Mn and Cu?C12.14%Al?C15.67%Mn, respectively. The magnetic properties of CuAlMn alloys were investigated as a function of Mn concentration. From the measurements, two important properties were observed. One of them is the temperature-dependent behavior, which indicates that the Curie temperatures of the samples are high (they are in the range of 304?C344?°C). The other property is the saturation magnetization, which is highly dependent on the Mn concentration. Although the Mn atoms want to cluster and interact antiferromagnetically, it is observed that the saturation magnetization is increased with increasing Mn concentration in these alloys. From these observations, it is suggested that the magnetic interactions in our samples are mostly due to the Mn and Al centers.     

The acceleration potential in fluid�Cbody interaction problems

The velocity potential ${\phi}$ is commonly used when solving fluid?Cbody interaction problems. The acceleration potential ${\frac{\partial \phi}{\partial t}}$ is a supplementary concept that offers several advantages. It increases temporal accuracy when solving large-amplitude motions numerically. It also results in better time-stepping stability when solving body equations of motion in the time-domain. The acceleration-potential formulation requires solving the velocity-potential problem first, and in many interesting cases increases accuracy and stability while improving overall computational efficiency. This paper reviews various formulations of the acceleration potential found in potential-flow hydrodynamics. For brevity, only the radiation-problem is considered where waves are due to the motion of the body. First, the velocity-potential problem is stated, including conventions and coordinate systems. The form of the rigid-body equations of motions is briefly discussed, as well as the coupling to the hydrodynamic problem. The various acceleration-potential formulations are reviewed and compared mathematically. Analytic and numerical solutions are also evaluated and analyzed. The computer simulations include convergence studies and large-amplitude motions. Finally, conclusions are presented discussing the applicability and advantages of the methods described, as well as the general use of the acceleration potential.     

Cobalt�CCarbon Eutectic Fixed Point for Contact Thermometry

Two Co?CC eutectic fixed points were constructed for thermocouple calibration. The eutectic fixed points were measured with a Pt/Pd thermocouple calibrated at the freezing temperatures of Sn, Zn, Al, Ag, and Au. A temperature of (1323.99 ± 0.52) °C (k = 2) was determined via this method. The cell design allowed filling to be accomplished in a single step. Each cell was held above 1300 °C for at least 42 h and was subjected to at least 20 melt/freeze cycles with no mechanical failure occurring.     

Microwave-assisted rapid discharge sintering of a bioactive glass�Cceramic

Bioactive glass-ceramics have been developed as successful bone graft materials. Although conventional sintering in an electrically-heated furnace is most commonly used, an alternative microwave plasma batch processing technique, known as rapid discharge sintering (RDS), is examined to crystallise the metastable base glass to form one or more ceramic phases. Apatite-mullite glass-ceramics (AMGC) were examined to elucidate the effects of RDS on the crystallization of a bioactive glass-ceramic. By increasing the fluorine content of the glass, the fluorapatite (FAp) and mullite crystallization onset temperatures can be reduced. Samples were sintered in a hydrogen and hydrogen/nitrogen discharge at temperatures of ≈800 and 1000 °C respectively with the higher sintering temperature required to form mullite. Results show that the material can be densified and crystallised using RDS in a considerably shorter time than conventional sintering due to heating and cooling rates of ≈400 °C/min.     

Mapping of Indian computer science research output, 1999�C2008

The research output of India in computer science during 1999?C2008 is analyzed in this paper on several parameters including total research output, its growth, rank and global publication share, citation impact, share of international collaborative papers and major collaborative partner countries and patterns of research communication in most productive journals. It also analyses the characteristics of most productive institutions, authors and high-cited papers. The publications output and impact of India is also compared with China, South Korea, Taiwan and Brazil.     

Influence of calcinated and non calcinated nanobioglass particles on hardness and bioactivity of sol�Cgel-derived TiO2�CSiO2 nano composite coatings on stainless steel substrates

Thick films of calcinated and non calcinated nanobioglass (NBG)-titania composite coatings were prepared on stainless steel substrates by alkoxide sol-gel process. Dip-coating method was used for the films preparation. The morphology, structure and composition of the nano composite films were evaluated using environmental scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscope. The SEM investigation results showed that prepared thick NBG-titania films are smooth and free of macrocracking, fracture or flaking. The grain size of these films was uniform and nano scale (50-60 nm) which confirmed with TEM. Also FTIR confirmed the presence of Si-O-Si bands on the calcinated NBG-titania films. The hardness of the prepared films (TiO(2)-calcinated NBG and TiO(2)-Non calcinated NBG) was compared by using micro hardness test method. The results verified that the presence of calcinated NBG particles in NBG-titania composite enhanced gradually the mechanical data of the prepared films. The in vitro bioactivity of these films was discussed based on the analysis of the variations of Ca and P concentrations in the simulated body fluid (SBF) and their surface morphologies against immersion time. Surface morphology and Si-O-Si bands were found to be of great importance with respect to the bioactivity of the studied films. The results showed that calcinated NBG-titania films have better bioactivity than non calcinated NBG-titania films.     

Design, Construction, and Evaluation of Ni�CC Eutectic Fixed Points

In this article the design, construction, and evaluation of eutectic fixed points for contact and non-contact measurements that have been recently developed at MIRS/UL/FE-LMK are presented. The design of the cells is made in such way that it can be used for only thermocouple calibration in vertical or horizontal furnaces, for calibration of pyrometers in a horizontal furnace, and for simultaneous calibration of contact and non-contact thermometers in a horizontal furnace. Special care has been taken to achieve repeatability and reproducibility of the transition temperatures and mechanical robustness of the cell. This includes also usage of a carbon sleeve in combination with carbon sheets, in a so-called hybrid design of the eutectic cell. With such a design, significant improvement in mechanical robustness of the cell and temperature stability of the cell has been achieved. All the measurements are performed within specially designed seven-zone furnaces within which different gradients, and different heating and cooling rates can be realized. The melting temperature of Ni?CC ((1328.44 ± 0.70) °C) measured with a thermocouple type R, calibrated at the zinc, aluminum, silver, copper, and palladium fixed points, and a non-contact thermometer, calibrated by comparison against different blackbodies, agree within their expanded uncertainties of 0.7 °C and 1.5 °C, respectively.     

Vortex�CAntivortex Dynamics in a Mesoscopic Superconducting Prism with a Centered Antidot

In this work, we investigated theoretically the dynamics of the annihilation of a vortex?Cantivortex pair in a superconducting mesoscopic prism of square transversal section with a square antidot inserted at its center. The sample is immersed in a magnetic field applied perpendicular to the sample plane. It is assumed that the inner hole is made of a material whose properties are accounted on de Gennes boundary conditions via de Gennes extrapolation length (b parameter). We analyze the nucleation of vortices and antivortices by increasing the magnetic field from zero until the first vortex is created and then reversing the polarity of the applied magnetic field until an antivortex is also created. Depending on the b parameter, the vortex?Cantivortex encounter can take place at the hole or at the superconducting region around it. In the framework of the time dependent Ginzburg?CLandau theory, we calculate the magnetization, order parameter topology, the position and the velocity of the vortex and antivortex singularities as a function of time.     

Capacitance�Cvoltage characteristics of Pt/Bi2VO5.5/p-Si structures

Ferroelectric Bi₂VO_5.5 thin films were fabricated on p-type (100) Si substrates by sol?Cgel method and then annealed at different temperatures. The microstructures and surface morphologies of the Bi₂VO_5.5 thin films were examined by X-ray diffraction and atomic force microscope, respectively. The results indicate that the Bi₂VO_5.5 thin films show high c-axis preferred orientation and are compatible well with p-type Si substrates. The capacitance?Cvoltage characteristics of Pt/Bi₂VO_5.5/Si capacitors measured at 1 MHz shows a clockwise hysteresis loop. The memory window of the hysteresis loop is 0.42 V with the gate voltage from ?4 to 4 V. It is found that the memory window may be determined by the competition between ferroelectric polarization and charge injection.     

Structural, Optical and Magnetic Properties of Ce�CGaN Based Diluted Magnetic Semiconductor

First ever Ce based GaN diluted magnetic semiconductor is reported. MOCVD grown GaN thin films were implanted with 3×10¹⁴ cm^?2 dose of cerium ions. Photoluminescence (PL), optical transmission, Raman, high-resolution X-ray diffraction (HRXRD) measurements were performed on samples to study the optical and structural properties of the materials. Band gap narrowing is observed in optical transmission measurements, which points to incorporation of cerium ions into GaN host lattice. Superconducting Quantum Interference device (SQUID) was used in order to investigate the magnetic properties of implanted samples as a function of temperature and applied field. Hysteresis loops were recorded at 100 K and 300 K for implanted and as-grown samples. Hysteresis behavior and temperature-dependent magnetization measurements revealed the presence of ferromagnetic ordering in Ce implanted GaN samples, which points to the realization of Ce:GaN diluted magnetic semiconductor.     

Atomic Hydrogen in Thick H2 Films at Temperatures 0.05�C2?K

We describe experiments on hydrogen atoms stabilized in a 100 ??m thick H₂ film at temperatures between 0.05 and 2 K. The molecular hydrogen matrix was condensed directly from natural hydrogen gas. The H atoms are produced with a plasma discharge at temperatures below 1 K and studied with electron spin resonance. H densities of 2×10¹⁹ cm^?3 in solid H₂ were reached. As observed earlier in thin H₂ films, we found a high stability of atomic populations and strong deviation from Boltzmann statistics of lowest two hyperfine states at the lowest temperatures. In thick films we found that the ESR resonance lines consisted of two closely spaced components with different widths indicating separate regions of high and low concentrations of H atoms in the H₂ matrix. Upon warming, the two components show very different rates of recombination with the higher density component having a faster recombination rate at T>1 K. We discuss the atomic interactions and mobility, and also the structure of the samples of H atoms in the H₂ matrix.     

Identifying the Pairing Mechanism in Fe�CAs Based Superconductors: Gaps and Isotope Effects

The temperature dependencies of the coupled superconducting gaps, observed in Fe?CAs based superconducting compounds is calculated and a universal temperature scaling observed which is only present if the coupled order parameters both have s-wave symmetry. Predictions for possible isotope effects on the superconducting transition temperature T _c are made if phonons are involved in the pairing or polaronic effects are of importance. Comparison to experimental data is given where these are available.     

Vortex Core Contribution to Textural Energy in 3He�CB Below 0.4T c

Vortex lines affect the spatial order-parameter distribution in superfluid ³He?CB owing to superflow circulating around vortex cores and due to the interaction of the order parameter in the core and in the bulk as a result of superfluid coherence over the whole volume. The step-like change of the latter contribution at 0.6T _c (at a pressure of 29 bar) signifies the transition from axisymmetric cores at higher temperatures to broken-symmetry cores at lower temperatures. We extended earlier measurements of the core contribution to temperatures below 0.2T _c, in particular searching for a possible new core transition to lower symmetries. As a measuring tool we track the energy levels of magnon condensate states in a trap formed by the order-parameter texture.     

Stability of Tungsten�CRhenium Thermocouples in the Range from 0?��C to 1500?��C

The effect of exposure up to 1500 °C on emf values of type C (95 % tungsten 5 % rhenium vs. 74 % tungsten 26 % rhenium) thermocouples were evaluated. Three thermocouples consisting of thermocouple wires of 0.5 mm diameter, twin-bore beryllia tubes, and tantalum sheaths were prepared. After three type C thermocouples were calibrated in the range from 0 °C to 1550 °C, which confirmed insignificant difference among them, the drifts of two among them were measured at the palladium?Ccarbon (Pd?CC) eutectic point (1492 °C). They indicated a similar tendency, where the emf of thermocouples increased rapidly within the first 30 h, and after that, decreased gradually. To investigate the mechanism of the drift, the inhomogeneities of thermocouples were examined at 160 °C using a water heat-pipe furnace during the drift measurements at the Pd?CC eutectic point. It was found that the increase of emf within the first 30 h exposure at around 1500 °C was caused by the emf change due to inhomogeneity above 700 °C, and after that, the decrease of emf was caused by that around 1400 °C.     

Homogenization of a reaction�Cdiffusion system modeling sulfate corrosion of concrete in locally periodic perforated domains

A reaction?Cdiffusion system modeling concrete corrosion in sewer pipes is discussed. The system is coupled, semi-linear, and partially dissipative. It is defined on a locally periodic perforated domain with nonlinear Robin-type boundary conditions at water?Cair and solid?Cwater interfaces. Asymptotic homogenization techniques are applied to obtain upscaled reaction?Cdiffusion models together with explicit formulae for the effective transport and reaction coefficients. It is shown that the averaged system contains additional terms appearing due to the deviation of the assumed geometry from a purely periodic distribution of perforations for two relevant parameter regimes: (a) all diffusion coefficients are of order of ${\mathcal{O}(1)}$ and (b) all diffusion coefficients are of order of ${\mathcal{O}(\varepsilon^2)}$ except the one for H₂S(g) which is of order of ${\mathcal{O}(1)}$ . In case (a) a set of macroscopic equations is obtained, while in case (b) a two-scale reaction?Cdiffusion system is derived that captures the interplay between microstructural reaction effects and the macroscopic transport.     

Effects of rare earth element Nd on the solderability and microstructure of Sn�CZn lead-free solder

Effects of trace amount addition of rare earth Nd on the properties of eutectic Sn?CZn solder were studied in this paper. Results indicate that adding trace rare earth element Nd could remarkably improve the solderability and mechanical properties of Sn?C9Zn solder joints. Especially when the content of Nd was 0.06 wt%, the wettability of the solder was improved significantly, and the shear force of Sn?C9Zn?C0.06Nd solder joint was enhanced by 19.6% as well as pull force increased by 26.6% compared to that of Sn?C9Zn solder joint,respectively. It is also found that addition of rare earth Nd could refine the microstructure of the solder and some NdSn₃ phase appeared in the solder matrix. Moreover, the IMCs thickness at the solder/Cu interface was reduced. NdSn₃ phase appeared at the interface with excessive addition of Nd, which is the key reason that deteriorates the mechanical properties of soldered joint.