Does the local structure play a role in high temperature superconductivity?

Many highT_csystems exhibit structural distortions or anomalies, some of which correlate withT_c. We present our results for three such systems and discuss them in the context of providing any evidence for coupling of the lattice to the superconducting pairs. We then propose a modulation type of experiment that should provide unambiguous results if a significant lattice-pair coupling does exist.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Wavelength-Resolved 3-Dimensional Fluorescence Lifetime Imaging

We have developed a compact system for wide-field fluorescence imaging, resolved in three spatial dimensions, lifetime and wavelength, that is based on a gated optical intensifier and an all-solid-state diode pumped Cr:LiSAF oscillator-amplifier system. Exploiting spectral separation, the system has been applied to human teeth, obtaining good lifetime contrast between enamel, dentin and caries. Exploiting spectral separation combined with depth resolution, the study of fluorescent microspheres led to an enhancement in both lifetime contrast and lateral resolution.     

A study of the 138Ba(d,p)139Ba reaction at 19 MeV

The ¹³⁸Ba(d,p) reaction has been studied at an incident deuteron energy of 19 MeV, using the injector-tandem accelerator and the multichannel magnetic spectrograph of the University of Oxford. Deuteron and proton optical model parameters have been obtained from the analysis of elastic scattering experiments on a ¹³⁸Ba target. The parameters have been used to calculate theoretical (d, p) angular distributions on the basis of the DWBA. From the comparison of experimental and theoretical distributions, orbital angular momentum transfers have been deduced and spectroscopic factors determined for all the levels observed up to an excitation energy of 2.5 MeV in ¹³⁹Ba. The spectroscopic information thus obtained is more complete than that from previous studies, and is in satisfactory agreement with expected sum rule limits. A notable item of new information is the assignment of an l_n = 6 transition to the level at 1.54 MeV in ¹³⁹Ba.     

A study of the 144Sm(d,p) reaction at 19 MeV

The ¹⁴⁴Sm(d, p) reaction has been studied at an incident deuteron energy of 19 MeV using the injector-tandem accelerator and the multichannel magnetic speetrograph of the University of Oxford. Angular distributions have been measured for transitions to levels of ¹⁴⁵Sm up to an excitation energy of 3.2 MeV. Theoretical (d, p) distributions have been calculated using the program DWUCK. and orbital angular momentum transfers and spectroscopic factors have been deduced by comparing these calculations with the experimental data. The spectroscopic information derived from this study is more complete than that previously reported and many new assignments have been made. The level scheme of ¹⁴⁵Sm has been found to resemble closely the level schemes of the other N = 83 nuclei.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Multiple melting transitions in fractions of partially isotactic poly(propylene oxide)

Three transitions are detected dilatometrically when partially isotactic poly(propylene oxide) melts. One transition, the temperature of which is independent of the crystallization temperature over a wide range below 60°C, is ascribed to the melting of lamellar crystallites which are limited in thickness by the average isotactic sequence length alone. The other two transitions, the temperatures of which vary with the crystallization temperature, are ascribed to the melting of lamellar crystallites with thickness determined predominantly by three- and two-dimensional primary nucleation acts. The theory of Flory is adapted and applied quantitatively to the melting points of three crystalline fractions of poly(propylene oxide), obtained from a polymer produced via the zinc diethyl and water catalyst system. This method leads to a thermodynamic melting point of isotactic poly(propylene oxide) near 82°C.     

Electroproduction of π0 mesons in the resonance region at q2=1.0 (GeV/c)2

Data are presented for the reaction ep → epπ⁰ at a nominal momentum transfer squared of 1.0 (GeV/c)². The data were obtained using an extracted electron beam from NINA and two magnetic spectrometers for coincidence detection of the electron and proton. Differential cross sections have been measured for isobar masses in the range 1.19–1.73 GeV/c².     

Lattice disorder and size-induced kondo behavior in CeAl2 and CePt(2+x)

When the size of CeAl2 and CePt(2+x) particles is reduced to the nanometer scale, antiferromagnetism is suppressed and Kondo behavior predominates, with the Kondo temperature T(K) either decreasing (CeAl2) or increasing (CePt(2+x)) relative to the bulk. Local structure measurements show that these nanoparticles are significantly distorted. While such distortions should strongly affect magnetic and electronic properties, we find they cannot explain the observed changes in T(K). Other size-induced changes to the electronic structure must, therefore, play a significant role.