SET based experiments for HTSC materials: II

The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. In this note we further discuss our original suggestion of using Single Electron Tunneling Transistor [SET] based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classed in a general sense as mesoscopic and nano characterization of cuprates and related materials. In principle such experiments can show if electron is fractionalized in cuprates as indicated by ARPES data. In contrast to flux trapping experiments SET based experiments are more direct in providing evidence about spin-charge separation. In addition a detailed picture of nano charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P: P10-0

Long Run Properties of Technical Efficiency in the U.S. Airline Industry

This paper takes an innovative approach to test the relationship between technical efficiency and the market structure hypothesis which states that competitive pressure enhances relative efficiency. DEA and FDH time series of technical efficiency scores, for a panel of 11 US airlines observed quarterly during 1970-1990, are examined for cointegration and convergence. For almost all firm pairs (>90% for both efficiency measures), the null hypothesis of cointegration cannot be rejected; meanwhile, the null of no cointegration is rejected for approximately one-third of the firm pairs. Furthermore, convergence tests document less dispersion in firm performance over time. These results indicate that the scores move together and, in fact, the firms are becoming more alike one another in terms of efficiency. ZUSAMMENFASSUNG - (Langfristige Eigenschaften der technischen Effizienz in der US-Luftfahrtindustrie) In diesem Beitrag wird ein innovativer Ansatz entwickelt, um die Beziehung zwischen technischer Effizienz und der Marktstrukturhypothese zu überprüfen, die besagt, daß Wettbewerbsdruck die relative Effizienz erhöht. Die DEA- und FDH-Zeitreihen der technischen Effizienz für ein Panel-Datensatz von 11 US-Fluggesellschaften, die während der Periode 1970 bis 1990 beobachtet wurden, werden im Hinblick auf Kointegration und Konvergenz analysiert. Für nahezu alle Unternehmenspaare (mehr als 90% bei beiden Effizienzmaßen) kann die Nullhypothese der Kointegration nicht zurückgewiesen werden, wo hingegen die Nullhypothese, daß keine Kointegration vorliegt, für etwa ein Drittel der Unternehmenspaare zurückgewiesen wird. Außerdem zeigt der Konvergenztest, daß die Streuung des Unternehmenserfolgs im Zeitablauf abnimmt. Die Ergebnisse deuten darauf hin, daß die Effizienzwerte sich auf einander zu bewegen und daß in der Tat, die Unternehmen im Hinblick auf Effizienz sich immer ähnlicher werden.

Isostaticity of Constraints in Jammed Systems of Soft Frictionless Platonic Solids

The average number of constraints per particle $$ in mechanically stable systems of Platonic solids (except cubes) approaches the isostatic limit at the jamming point ($\rightarrow 12$), though average number of contacts are hypostatic. By introducing angular alignment metrics to classify the degree of constraint imposed by each contact, constraints are shown to arise as a direct result of local orientational order reflected in edge-face and face-face alignment angle distributions. With approximately one face-face contact per particle at jamming chain-like face-face clusters with finite extent form in these systems.Comment: 4 pages, 3 figures, 4 tabl

Variable-cell method for stress-controlled jamming of athermal, frictionless grains

A new method is introduced to simulate jamming of polyhedral grains under controlled stress that incorporates global degrees of freedom through the metric tensor of a periodic cell containing grains. Jamming under hydrostatic/isotropic stress and athermal conditions leads to a precise definition of the ideal jamming point at zero shear stress. The structures of tetrahedra jammed hydrostatically exhibit less translational order and lower jamming-point density than previously described `maximally random jammed' hard tetrahedra. Under the same conditions, cubes jam with negligible nematic order. Grains with octahedral symmetry jam in the large-system limit with an abundance of face-face contacts in the absence of nematic order. For sufficiently large face-face contact number, percolating clusters form that span the entire simulation box. The response of hydrostatically jammed tetrahedra and cubes to shear-stress perturbation is also demonstrated with the variable-cell method.Comment: 10 pages, 8 figure

Revealing the nature of antiferro-quadrupolar ordering in Cerium Hexaboride: CeB6_6

Cerium-hexaboride (CeB$_6$) f-electron compound displays a rich array of low-temperature magnetic phenomena, including `magnetically hidden' order, identified as multipolar in origin via advanced x-ray scattering. From first-principles electronic-structure results, we find that the \emph{antiferro-quadrupolar} (AFQ) ordering in CeB$_{6}$ arises from crystal-field splitting and yields band structure in agreement with experiments. With interactions of $p$-electrons between Ce and B$_{6}$ being small, the electronic state of CeB$_{6}$ is suitably described as Ce(4$f^{1}$)$^{3+}$(e$^{-}$)(B$_{6}$)$^{2-}$. The AFQ state of orbital spins is caused by an exchange interaction induced through spin-orbit interaction, which also splits J=5/2 state into $\Gamma_{8}$ ground state and $\Gamma_{7}$ excited state. Within the smallest antiferromagnetic (111) configuration, an orbital-ordered AFQ state appears during charge self-consistency, and supports the appearance of `hidden' order. Hydrostatic pressure (either applied or chemically induced) stabilizes the AFM (AFQ) states over a ferromagnetic one, as observed at low temperatures.Comment: 6 pages, 4 figure