94 research outputs found
Instrument for measuring potentials on two dimensional electric field plots Patent
Instrument for measuring potentials on two dimensional electric field plo
Hall Effect in a Quasi-One-Dimensional System
We consider the Hall effect in a system of weakly coupled one-dimensional
chains with Luttinger interaction within each chain. We construct a
perturbation theory in the inter-chain hopping term and find that there is a
power law dependence of the Hall conductivity on the magnetic field with an
exponent depending on the interaction constant. We show that this perturbation
theory becomes valid if the magnetic field is sufficiently large.Comment: 20 page
Dimensional crossover and metal-insulator transition in quasi-two-dimensional disordered conductors
We study the metal-insulator transition (MIT) in weakly coupled disordered
planes on the basis of a Non-Linear Sigma Model (NLM). Using two
different methods, a renormalization group (RG) approach and an auxiliary field
method, we calculate the crossover length between a 2D regime at small length
scales and a 3D regime at larger length scales. The 3D regime is described by
an anisotropic 3D NLM with renormalized coupling constants. We obtain
the critical value of the single particle interplane hopping which separates
the metallic and insulating phases. We also show that a strong parallel
magnetic field favors the localized phase and derive the phase diagram.Comment: 16 pages (RevTex), 4 poscript figure
Spinons in a Crossed-Chains Model of a 2D Spin Liquid
Using Random Phase Approximation, we show that a crossed-chains model of a
spin-1/2 Heisenberg spins, with frustrated interchain couplings, has a
non-dimerized spin-liquid ground state in 2D, with deconfined spinons as the
elementary excitations. The results are confirmed by a bosonization study,
which shows that the system is an example of a `sliding Luttinger liquid'. In
an external field, the system develops an incommensurate field-induced long
range order with a finite transition temperature.Comment: 4 pages, 3 figures; added references; scaling analysis, preserving
spin rotational invariance, is extended to finite temperatur
Finite-temperature perturbation theory for quasi-one-dimensional spin-1/2 Heisenberg antiferromagnets
We develop a finite-temperature perturbation theory for quasi-one-dimensional
quantum spin systems, in the manner suggested by H.J. Schulz (1996) and use
this formalism to study their dynamical response. The corrections to the
random-phase approximation formula for the dynamical magnetic susceptibility
obtained with this method involve multi-point correlation functions of the
one-dimensional theory on which the random-phase approximation expansion is
built. This ``anisotropic'' perturbation theory takes the form of a systematic
high-temperature expansion. This formalism is first applied to the estimation
of the N\'eel temperature of S=1/2 cubic lattice Heisenberg antiferromagnets.
It is then applied to the compound CsCuCl, a frustrated S=1/2
antiferromagnet with a Dzyaloshinskii-Moriya anisotropy. Using the next leading
order to the random-phase approximation, we determine the improved values for
the critical temperature and incommensurability. Despite the non-universal
character of these quantities, the calculated values are different by less than
a few percent from the experimental values for both compounds.Comment: 11 pages, 6 figure
Strong-Coupling Expansion for the Hubbard Model
A strong-coupling expansion for models of correlated electrons in any
dimension is presented. The method is applied to the Hubbard model in
dimensions and compared with numerical results in . Third order expansion
of the Green function suffices to exhibit both the Mott metal-insulator
transition and a low-temperature regime where antiferromagnetic correlations
are strong. It is predicted that some of the weak photoemission signals
observed in one-dimensional systems such as should become stronger as
temperature increases away from the spin-charge separated state.Comment: 4 pages, RevTex, 3 epsf figures include
Universal scaling behavior of coupled chains of interacting fermions
The single-particle hopping between two chains is investigated by
exact-diagonalizations techniques supplemented by finite-size scaling analysis.
In the case of two coupled strongly-correlated chains of spinless fermions, the
Taylor expansion of the expectation value of the single-particle interchain
hopping operator of an electron at momentum k_F in powers of the interchain
hopping t_perp is shown to become unstable in the thermodynamic limit. In the
regime alpha<alpha_{tp} (alpha_{tp} simeq 0.41) where transverse two-particle
hopping is less relevant than single-particle hopping, the finite-size effects
can be described in terms of a universal scaling function. From this analysis
it is found that the single-particle transverse hopping behaves as
t_perp^{alpha/(1-alpha)} in agreement with a RPA-like treatment of the
interchain coupling. For alpha>alpha_{tp}, the scaling law is proven to change
its functional form, thus signaling, for the first time numerically, the onset
of coherent transverse two-particle hopping.Comment: 12 pages, Late
Dimensional Crossovers in the Doped Ladder System: Spin Gap, Superconductivity and Interladder Coherent Band Motion
Based on the perturbative renormalization group (PRG) approach, we have
studied dimensional crossovers in Hubbard ladders coupled via weak interladder
one-particle hopping, . We found that the one-particle crossover is
strongly suppressed through growth of the intraladder scattering processes
which lead the isolated Hubbard ladder system toward the spin gap metal (SGM)
phase. Consequently when sets in, there exists, for any finite
intraladder Hubbard repulsion, , the region where the two-particle
crossover dominates the one-particle crossover and consequently the d-wave
superconducting transition, which is regarded as a bipolaron condensation,
occurs. By solving the scaling equations for the interladder one-particle and
two-particle hopping amplitudes, we give phase diagrams of the system with
respect to , (initial value of ) and the
temperature, . We compared the above dimensional crossovers with those in a
weakly coupled chain system, clarifying the difference between them.Comment: 26 pages, 19 eps figures, to appear J. Phys. Soc. Jpn. Vol.67 No.
Particle emission characteristics of a gas turbine with a double annular combustor
The total climate, air quality and health impact of aircraft black carbon (BC) emissions depends on quantity (mass and number concentration), as well as morphology (fractal dimension and surface area) of emitted BC aggregates. This study examines multiple BC emission metrics from a gas turbine with a double annular combustor, CFM56-5B4-2P. As a part of the SAMPLE III.2 campaign, concurrent measurements of particle mobility, particle mass, particle number concentration and mass concentration, as well as collection of transmission electron microscopy (TEM) samples, allowed for characterization of the BC emissions. Mass- and number-based emission indices were strongly influenced by thrust setting during pilot combustion and ranged from <1 to 208 mg/kg-fuel and 3×1012 to 3×1016 particles/kg-fuel, respectively. Mobility measurements indicated that mean diameters ranged from 7-44 nm with a strong dependence on thrust during pilot-only combustion. Using aggregation and sintering theory with empirical effective density relationships, a power law relationship between primary particle diameter and mobility diameter is presented. Mean primary particle diameter ranged from 6-19 nm, however, laser induced incandescence (LII) and mass-mobility calculated primary particle diameters demonstrated opposite trends with thrust setting. Similarly, mass-mobility-calculated aggregate mass specific surface area and LII-measured surface area were not in agreement, indicating both methods need further development and validation before use as quantitative indicators of primary particle diameter and mass-specific surface area.The authors express their gratitude to a number of people and organizations in helping to plan, conduct, finance and provide instruments for this measurement campaign. The 537 European Aviation Safety Agency (EASA) funded the SAMPLE III SC02 campaign (EASA.2010.FC.10, Specific Contract No: SC02). The Federal Office of Civil Aviation, Switzerland (FOCA) was critical in for providing additional financial support and arranging facilities which made this study possible. We also thank the SR Technics test bed staff, including Frithjof Siegerist, for operating the engines and enabling access to the test facility. We thank AVL, Cambustion, Grimm & TSI supplying both instruments and expertise.This is the author accepted manuscript. The final version is available from Taylor & Francis via http://dx.doi.org/10.1080/02786826.2015.107845
Interactions and Disorder in Multi-Channel Quantum Wires
Recent experiments have revealed that the temperature dependence of the
conductance of quasi-ballistic quantum wires bears clear features of the
Luttinger-liquid state. In this paper, the conductance of an N-channel quantum
wire is calculated within the model of N coupled Luttinger liquids and under
the assumption of weak disorder. It is shown that as the number of channels
increases, a crossover from the Luttinger-liquid to the Fermi-liquid behavior
occurs. This crossover manifests itself in the 1/N decrease of the scaling
exponent of the temperature dependence. An exact expression for the scaling
exponent for the case of N coupled Luttinger chains is obtained, and the large
N limit is studied for the case of a quantum wire. The case of N=2 for
electrons with spin is analyzed in detail, and a qualitative agreement with the
experiment is achieved.Comment: 9 pages, REVTex with 1 Postscript figur
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