Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

Effect of harmonic confinement on correlation studies of a spin-polarized s-wave superconductor

We study different correlation functions for a spin imbalanced and harmonically trapped Fermi gas in two dimensions described by an attractive Hubbard model. Eigensolutions obtained via numerically solving Bogoliubov de Gennes equations are used to compute the local pairing amplitudes which show significantly different behaviour for the trapped case where the profile is radially modulated in contrast with a spatial modulation extending throughout the lattice geometry when trap effects are switched off. Further, different experimentally accessible quantities, such as pair–pair, density–density correlations and local density fluctuations show characteristic fluctuations for the spin polarized phase, which however wash away as the trapping effects are turned on. A contrasting scenario is presented corresponding to the case when the spin polarization effects are turned off.     

Neon ion irradiation studies on MgB2 superconductor

160 MeV of neon ion irradiation has been carried out on MgB₂ polycrystalline pellets at various doses. There has not been any significant change in T_c except at the highest dose of 1×10¹⁵ ions/cm². Increase in resistivity has been noticed. Resistivity data have been fitted with Bloch-Grüneisen function to extract the values of Debye temperature, residual resistivity and temperature coefficient of resistivity for irradiated as well as unirradiated samples. There has not been any significant effect on electron-phonon coupling due to irradiation as evident from Debye temperature and the electron-phonon coupling constant.     

Thin films of YBaCuO high-temperature superconductor grown in a simplified magnetron sputterer and their microwave application

The physicochemical properties of YBa₂Cu₃O_7?δ high-temperature superconductor exclude designing standard magnetron sputterers and adopting standard film growth conditions that would ensure good and highly reproducible results. A simple and flexible magnetron sputterer making it possible to grow high-quality films (with a critical temperature of 90 K, a critical current density of 4 MA/cm², and a surface resistance of ≤0.5 mΘ at a frequency of 10 GHz and 77 K) is described. The high quality of the films is proved by successfully applying them in a microwave circuit demonstrating an intrinsic Q factor of 58 000 at a frequency of 70 MHz and 77 K, which is higher than the results obtained by other teams of researchers.     

Relaxation of ferromagnetic nanoparticles in macrophages: In vitro and in vivo studies

The relaxation characteristics of magnetic nanoparticles (CoFe₂O₄) were investigated in J774A.1 macrophages and after voluntary inhalation. In dry form 25% of the particles showed Néel relaxation. Relaxation in macrophages occurred within minutes and could be inhibited by fixation, showing Brownian relaxation and intracellular transport processes. Relaxation in the lung happened similarly, but was dependent on the time after deposition. The particles were cleared from the lung within 2 weeks.     

Photoemission studies of the high TC superconductor,YBa2Cu3O7

Considerable changes are observed in the spectra of the valence band and O(ls) regions in YBa₂Cu₃O₇, when the temperature is lowered from 300K to 80K. The results are interpreted in terms of a progressive formation of O^2- ₂-like species with decreasing temperature. This is accompanied by the transformation of Cu to Cu. It is suggested that the holes generated at the top of the valence band forming the O^2- ₂-like species may play a crucial role in the superconductivity of the oxide.     

In vitro studies of PEG thin films with different molecular weights deposited by MAPLE

In this work, polyethylene glycol (PEG) films were produced by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The possibility to tailor the properties of the films by means of polymer molecular weight was explored. The films of PEG of average molecular weights 400 Da, 1450 Da, and 10000 Da (PEG₄₀₀, PEG₁₄₅₀, and PEG₁₀₀₀₀) were investigated in vitro, in media similar with those inside the body (phosphate buffer saline PBS with pH 7.4 and blood). The mass of the polymer did not change during this treatment, but the polymer molecular weight was found to strongly influence the films properties and their behavior in vitro. Thus, immersion in PBS induced swelling of the PEG films, which was more pronounced for PEG polymers of higher molecular weight. Prior to immersion in PBS, the PEG films of higher molecular weight were more hydrophilic, the water contact angles decreasing from ～66 grd for PEG₄₀₀ to ～41 grd for PEG₁₄₅₀ and to ～15 grd for PEG₁₀₀₀₀. The same trend was observed during immersion of the PEG films in PBS. Before immersion in PBS, the refractive index of the films increased from ～1.43 for PEG₄₀₀ to ～1.48 for PEG₁₄₅₀ and to ～1.68 for PEG₁₀₀₀₀. During immersion in PBS the refractive index decreased gradually, but remained higher for the PEG molecules of higher mass. Finally, blood compatibility tests showed that the PEG films of higher molecular weight were most compatible with blood.     

In vivo non-invasive studies on the human lens.

Progress in biophysical technology now permits us to monitor aging and precataractous changes in the human ocular lens in vivo as well as in vitro. We are employing two noninvasive techniques to measure changes in lens fluorescence and in one lens water compartment (T2) utilizing Scheimpflug lens fluorescence densitography and magnetic resonance imaging. These studies demonstrate age-related changes in the normal lens as reflected by enhanced fluorescence and longer T2 values. Precataractous changes can also be detected with this approach.     

白宝石衬底上生长的MgxZn1-xO晶体薄膜的结构和光学性能

在白宝石 (sapphire)衬底上低温外延生长出了MgxZn1 -xO晶体薄膜 .x射线衍射 (XRD)及能量色散x射线 (EDX)分析表明 ,MgxZn1 -xO薄膜的晶体结构依赖于薄膜中Mg的组分x,随着Mg组分的增大 ,MgxZn1 -xO薄膜的结构从与ZnO晶体一致的六方结构转变为与MgO晶体一致的立方结构 .对MgxZn1 -xO薄膜的紫外透射光谱及紫外光致荧光谱 (UVPL)的分析表明 ,随着Mg组分的增大 ,光学吸收边产生明显的蓝移 ,表明MgxZn1 -xO晶体薄膜的带隙增大 ,且带隙连续可调 .吸收光谱和XRD测量显示 ,带隙高达 5 6 5eV的MgxZn1 -xO晶体薄膜与MgO之间的晶格失配仅为0 16 % .     

超导体/正常金属/半导体/正常金属/超导体结的研究

在约瑟夫逊效应的理论研究中,大体上有微观和宏观两种方法。采用的是宏观的方法。利用推广的Ja-cobson方法,讨论了超导体/正常金属/半导体/正常金属/超导体结的约瑟夫逊效应,并在小电流假设下,推导出了该结的电流密度与位相之间的关系。     

In vitro studies of PBT Nonwoven Fabrics adsorbent for the removal of low density lipoprotein from hyperlipemia plasma

Polyanion ligands such as acrylic acid (AA) and heparin were grafted on PBT Nonwoven Fabrics (PBTNF) to study their effect on the adsorption of low density lipoprotein (LDL). These modified PBTNFs were characterized by Horizontal Attenuated Total Reflectance Fourier Transform Infrared spectroscopy and X-ray Photoelectron spectroscopy. The blood compatibilities of the modified PBTNFs were examined using in vitro hemolysis rate (HR), platelet adhesion, total protein (TP) and activated partial thromboplastin time. The results showed that direct immobilized heparin could improve PBTNF-PAA's blood compatibility and decrease the adsorption capability of useful high density lipoprotein, but would possess so low bioactivity that could not further improve the absorption of LDL and TC. Since the PBTNF-PAA55-Heparin adsorbent had quite good adsorption selectivity for these proteins, it can be an excellent candidate for depletion of LDL with good blood compatibility.     

In situ synchrotron diffraction studies on the formation kinetics of jarosites

This paper reports the results of time‐resolved synchrotron powder diffraction experiments where jarosites with different K/H₃O, K/Na and Na/H₃O ratios were synthesized in situ at temperatures of 353, 368 and 393 K in order to observe the effect on kinetics and species produced. The Na/H₃O sample formed monoclinic jarosite at all three temperatures, whereas the K/H₃O and K/Na samples formed as rhombohedral jarosites at 353 K, and as mixtures of rhombohedral and monoclinic jarosites at the higher temperatures. The relative amount of the monoclinic phase increased with increase in temperature. Unit‐cell parameter changes with reaction time could be explained by changes in iron stoichiometry (samples become more stoichiometric with time) together with changes in K/H₃O and Na/H₃O ratios. The reaction kinetics have been fitted using a two‐stage Avrami model, with two different Avrami exponents corresponding to initial two‐dimensional growth followed by one‐dimensional diffusion‐controlled growth. Activation energies for the initial growth stage were calculated to be in the range 90–126 kJ mol^?1.