6,451 research outputs found
Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance
It is proposed that the presence of a tilted and anisotropic Dirac cone can
be verified using the interlayer magnetoresistance in the layered Dirac fermion
system, which is realized in quasi-two-dimensional organic compound
\alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic
Landau level wave functions and assuming local tunneling of electrons. It is
shown that the resistivity takes the maximum in the direction of the tilt if
anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is
described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.
Cache replacement for transcoding proxy caching
© 2005 IEEE.In this paper, we address the problem of cache replacement for transcoding proxy caching. First, an efficient cache replacement algorithm is proposed. Our algorithm considers both the aggregate effect of caching multiple versions of the same multimedia object and cache consistency. Second, a complexity analysis is presented to show the efficiency of our algorithm. Finally, some preliminary simulation experiments are conducted to compare the performance of our algorithm with some existing algorithms. The results show that our algorithm outperforms others in terms of the various performance metrics.Keqiu Li, Keishi Tajima, Hong She
Calibration System with Cryogenically-Cooled Loads for CMB Polarization Detectors
We present a novel system to calibrate millimeter-wave polarimeters for CMB
polarization measurements. This technique is an extension of the conventional
metal mirror rotation approach, however it employs cryogenically-cooled
blackbody absorbers. The primary advantage of this system is that it can
generate a slightly polarized signal ( mK) in the laboratory; this is
at a similar level to that measured by ground-based CMB polarization
experiments observing a 10 K sky. It is important to reproduce the
observing condition in the laboratry for reliable characterization of
polarimeters before deployment. In this paper, we present the design and
principle of the system, and demonstrate its use with a coherent-type
polarimeter used for an actual CMB polarization experiment. This technique can
also be applied to incoherent-type polarimeters and it is very promising for
the next-generation CMB polarization experiments.Comment: 7 pages, 9 figures Submitted to RS
Innovative Demodulation Scheme for Coherent Detectors in CMB Experiments
We propose an innovative demodulation scheme for coherent detectors used in
cosmic microwave background polarization experiments. Removal of non-white
noise, e.g., narrow-band noise, in detectors is one of the key requirements for
the experiments. A combination of modulation and demodulation is used to
extract polarization signals as well as to suppress such noise. Traditional
demodulation, which is based on the two- point numerical differentiation, works
as a first-order high pass filter for the noise. The proposed demodulation is
based on the three-point numerical differentiation. It works as a second-order
high pass filter. By using a real detector, we confirmed significant
improvements of suppression power for the narrow-band noise. We also found
improvement of the noise floor.Comment: 3 pages, 4 figure
Numerical study of the current sheet and PSBL in a magnetotail model
The current sheet and plasma sheet boundary layer (PSBL) in a magnetotail model are discussed. A test particle code is used to study the response of ensembles of particles to a two-dimensional, time-dependent model of the geomagnetic tail, and test the proposition (Coroniti, 1985a, b; Buchner and Zelenyi, 1986; Chen and Palmadesso, 1986; Martin, 1986) that the stochasticity of the particle orbits in these fields is an important part of the physical mechanism for magnetospheric substorms. The realistic results obtained for the fluid moments of the particle distribution with this simple model, and their insensitivity to initial conditions, is consistent with this hypothesis
Robustly Unstable Eigenmodes of the Magnetoshearing Instability in Accretion Disk
The stability of nonaxisymmetric perturbations in differentially rotating
astrophysical accretion disks is analyzed by fully incorporating the properties
of shear flows. We verify the presence of discrete unstable eigenmodes with
complex and pure imaginary eigenvalues, without any artificial disk edge
boundaries, unlike Ogilvie & Pringle(1996)'s claim. By developing the
mathematical theory of a non-self-adjoint system, we investigate the nonlocal
behavior of eigenmodes in the vicinity of Alfven singularities at
omega_D=omega_A, where omega_D is the Doppler-shifted wave frequency and
omega_A=k_// v_A is the Alfven frequency. The structure of the spectrum of
discrete eigenmodes is discussed and the magnetic field and wavenumber
dependence of the growth rate are obtained. Exponentially growing modes are
present even in a region where the local dispersion relation theory claims to
have stable eigenvalues. The velocity field created by an eigenmode is
obtained, which explains the anomalous angular momentum transport in the
nonlinear stage of this stability.Comment: 11pages, 11figures, to be published in ApJ. For associated eps files,
see http://dino.ph.utexas.edu/~knoguchi
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