Effect of Ga doping on magneto-transport properties in colossal magnetoresistive La0.7Ca0.3Mn1−xGaxO3 (0<x<0.1)

Samples of La_0.7Ca_0.3Mn_1−xGa_xO₃ with x=0, 0.025, 0.05 and 0.10 were prepared by standard solid-state reaction. They were first characterized chemically, including the microstructure. The magnetic properties and various transport properties, i.e. the electrical resistivity, magnetoresistivity (for a field below 8 T), thermoelectric power and thermal conductivity measured each time on the same sample, are reported. The markedly different behaviour of the x=0.1 sample from those with a smaller Ga content, is discussed. The dilution of the Mn³⁺/Mn⁴⁺ interactions with Ga doping considerably reduces the ferromagnetic double exchange interaction within the manganese lattice leading to a decrease of the Curie temperature. The polaron binding energy varies from 224 to 243 meV with increased Ga doping.     

Current and shot noise in two capacitively coupled single electron transistors with an atomic sized spacer

The currents and their fluctuations in two capacitively coupled single electron transistors are determined in the limit of sequential tunnelling. Our considerations are restricted to the case when the islands (dots) of the transistors are atomic-sized, which means each of them has only one single electronic level available for the tunnelling processes. The Coulomb interactions of accumulated charges on the both single electron transistors lead to the effect of the negative differential resistance. An enhancement of the current shot-noise was also found. Spectral decomposition analysis indicated the two main contributions to the shot-noise: low- and high-frequency fluctuations. It was found that the low frequency fluctuations (polarization noise) are responsible for a strong enhancement of the current noise. Received 9 October 2001 / Received in final form 8 March 2002 Published online 9 July 2002     

Phase behavior of four homologous compounds of 4-n-alkyl-4′-isothiocyanatobiphenyl (nBT) under pressure

The phase behavior of four homologous compounds of 4-n-nonyl-, 4-n-decyl-, 4-n-undecyl-, and 4-n-dodecyl-4′-isothiocyanatobiphenyl (9BT, 10BT, 11BT, and 12BT) was re-investigated to characterize their high-pressure mesophases under pressures up to 150 MPa using a polarizing optical microscope equipped with a high-pressure optical cell and a wide-angle X-ray diffractometer equipped with a high-pressure sample vessel. The pressure-induced mesophases of 9BT and 10BT appearing under pressures above about 60 and 100 MPa, respectively, were identified as nematic (N) and SmA phases, which indicate the reversible Cr–CrE–N–I and Cr–CrE–SmA–I phase transitions under elevated pressure. 11BT and 12BT exhibited the reversible transition of Cr–CrE–SmA–I in the low-pressure regions below about 5 and 23 MPa, respectively. Both the stable CrE phases changed into the monotropic (and metastable) one under higher pressures, in which the Cr–SmA–I and I–SmA–CrE–Cr phase transitions on heating and cooling processes, respectively, were recognized.     

Resolving the discrepancy of 135 MeV pd elastic scattering cross sections and relativistic effects

Three precise measurements for elastic pd scattering at 135 MeV/A have been performed with the three different experimental setups. The cross sections are described well by the theoretical predictions based on modern nucleon-nucleon forces combined with three-nucleon forces. Relativistic Faddeev calculations show that relativistic effects are restricted to backward angles. This result supports the two measurements recently reported by RIKEN and contradicts the KVI data.     

Equilibrated thermodesorption studies of adsorption of n-hexane and n-heptane on zeolites Y, ZSM-5 and ZSM-11

Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur.     

Exotic smoothness,noncommutative geometry,and particle physics

We investigate how exotic differential structures may reveal themselves in particle physics. The analysis is based on A. Connes' construction of the standard model. It is shown that, if one of the copies of the spacetime manifold is equipped with an exotic differential structure, a compact object of geometric origin may exist even if the spacetime is topologically trivial. Possible implications are discussed. AnSU(3) ⊗SU(2) ⊗U(1) gauge model is constructed. This model may not be realistic, but it shows what kind of physical phenomena might be expected due to the existence of exotic differential structures on the spacetime manifold.     

Structural and magnetic studies on RPtIn deuterides (R=Tb,Er, Tm)

In this communication, structural and magnetic properties of RPtInD_1.3 (R=Tb, Er, Tm) deuterides are reported. For the first time deuterium-rich compounds were synthesized for the RPtIn family. The investigated deuterides crystallize with the hexagonal ZrNiAl-type crystal structure, with slightly different lattice constants with respect to the basic compounds. In general, the a-lattice constant exhibit contraction, while the c-lattice constant tends to increase upon introducing deuterium. The compounds with Tb and Er shows magnetic ordering at 95 K and 15.5 K, respectively. On the other hand, for Tm based sample no magnetic ordering was evidenced down to 2 K.