14,948 research outputs found
Concurrent Magnetic and Metal-Insulator Transitions in (Eu,Sm)B_6 Single Crystals
The effects of magnetic doping on a EuB_6 single crystal were investigated
based on magnetic and transport measurements. A modest 5% Sm substitution for
Eu changes the magnetic and transport properties dramatically and gives rise to
concurrent antiferromagnetic and metal-insulator transitions (MIT) from
ferromagnetic MIT for EuB6. Magnetic doping simultaneously changes the
itinerant carrier density and the magnetic interactions. We discuss the origin
of the concurrent magnetic MIT in (Eu,Sm)B_6.Comment: 13 pages, 3 figures, final version to appear in Appl. Phys. Lett
Lanczos exact diagonalization study of field-induced phase transition for Ising and Heisenberg antiferromagnets
Using an exact diagonalization treatment of Ising and Heisenberg model
Hamiltonians, we study field-induced phase transition for two-dimensional
antiferromagnets. For the system of Ising antiferromagnet the predicted
field-induced phase transition is of first order, while for the system of
Heisenberg antiferromagnet it is the second-order transition. We find from the
exact diagonalization calculations that the second-order phase transition
(metamagnetism) occurs through a spin-flop process as an intermediate step.Comment: 4 pages, 4 figure
Johnson-Kendall-Roberts theory applied to living cells
Johnson-Kendall-Roberts (JKR) theory is an accurate model for strong adhesion
energies of soft slightly deformable material. Little is known about the
validity of this theory on complex systems such as living cells. We have
addressed this problem using a depletion controlled cell adhesion and measured
the force necessary to separate the cells with a micropipette technique. We
show that the cytoskeleton can provide the cells with a 3D structure that is
sufficiently elastic and has a sufficiently low deformability for JKR theory to
be valid. When the cytoskeleton is disrupted, JKR theory is no longer
applicable
Kink-induced transport and segregation in oscillated granular layers
We use experiments and molecular dynamics simulations of vertically
oscillated granular layers to study horizontal particle segregation induced by
a kink (a boundary between domains oscillating out of phase). Counter-rotating
convection rolls carry the larger particles in a bidisperse layer along the
granular surface to a kink, where they become trapped. The convection
originates from avalanches that occur inside the layer, along the interface
between solidified and fluidized grains. The position of a kink can be
controlled by modulation of the container frequency, making possible systematic
harvesting of the larger particles.Comment: 4 pages, 5 figures. to appear in Phys. Rev. Let
Study of Prenucleation Ion Clusters: Correlation between Ion Mobility Spectra and Size Distributions
Additional studies regarding our earlier electrothermodynamic theory are presented. Comparisons to recent expansion cloud chamber ion mobility measurements are made, indicating general agreement with observations. This theory predicts more stable and ordered structure for prenucleation ion-water cluster systems than accounted for by the classical Thomson\u27s theory. In the limiting case of the dielectric constant ε = 1, our monopole electrostatic energy term contributed by the foreign ion center precisely converges to that of Thomson. Predicted ion cluster size distributions are found to correlate well with ion cluster size spectra obtained from the ion mobility measurements of hydrated ion clusters and Champman-Enskog theory. In view of good correlation between the theory and observation, we believe that ion mobility study at sufficiently low electric field is a powerful tool for studying prenucleation dynamics
U(1)' solution to the mu-problem and the proton decay problem in supersymmetry without R-parity
The Minimal Supersymmetric Standard Model (MSSM) is plagued by two major
fine-tuning problems: the mu-problem and the proton decay problem. We present a
simultaneous solution to both problems within the framework of a U(1)'-extended
MSSM (UMSSM), without requiring R-parity conservation. We identify several
classes of phenomenologically viable models and provide specific examples of
U(1)' charge assignments. Our models generically contain either lepton number
violating or baryon number violating renormalizable interactions, whose
coexistence is nevertheless automatically forbidden by the new U(1)' gauge
symmetry. The U(1)' symmetry also prohibits the potentially dangerous and often
ignored higher-dimensional proton decay operators such as QQQL and UUDE which
are still allowed by R-parity. Thus, under minimal assumptions, we show that
once the mu-problem is solved, the proton is sufficiently stable, even in the
presence of a minimum set of exotics fields, as required for anomaly
cancellation. Our models provide impetus for pursuing the collider
phenomenology of R-parity violation within the UMSSM framework.Comment: Version published in Phys. Rev.
A Spectral Line Survey from 138.3 to 150.7 GHZ toward Orion-KL
We present the results of a spectral line survey from 138.3 to 150.7 GHz
toward Orion-KL. The observations were made using the 14 m radio telescope of
Taeduk Radio Astronomy Observatory. Typical system temperatures were between
500 and 700 K, with the sensitivity between K in units of .
A total of 149 line spectra are detected in this survey. Fifty lines have
been previously reported, however we find 99 new detections. Among these new
lines, 32 are `unidentified', while 67 are from molecular transitions with
known identifications. There is no detection of H or He recombination lines.
The identified spectra are from a total of 16 molecular species and their
isotopic variants. In the range from 138.3 to 150.7 GHz, the strongest spectral
line is the J=3-2 transition of CS molecule, followed by transitions of the
, , , and . Spectral lines from
the large organic molecules such as , , , and are prominent; with 80 % of the
identified lines arising from transitions of these molecules. The rotational
temperatures and column densities are derived using the standard rotation
diagram analysis for (), , and with and . These estimates are fairly comparable to the values for the
same molecule in other frequency regions by other studies.Comment: 10 figures, 2 tex files for a manuscript and tables, accepted to Ap
Dynamic behaviors in directed networks
Motivated by the abundance of directed synaptic couplings in a real
biological neuronal network, we investigate the synchronization behavior of the
Hodgkin-Huxley model in a directed network. We start from the standard model of
the Watts-Strogatz undirected network and then change undirected edges to
directed arcs with a given probability, still preserving the connectivity of
the network. A generalized clustering coefficient for directed networks is
defined and used to investigate the interplay between the synchronization
behavior and underlying structural properties of directed networks. We observe
that the directedness of complex networks plays an important role in emerging
dynamical behaviors, which is also confirmed by a numerical study of the
sociological game theoretic voter model on directed networks
Cotunneling Transport and Quantum Phase Transitions in Coupled Josephson-Junction Chains with Charge Frustration
We investigate the quantum phase transitions in two capacitively coupled
chains of ultra-small Josephson-junctions, with emphasis on the external charge
effects. The particle-hole symmetry of the system is broken by the gate voltage
applied to each superconducting island, and the resulting induced charge
introduces frustration to the system. Near the maximal-frustration line, where
the system is transformed into a spin-1/2 Heisenberg antiferromagnetic chain,
cotunneling of the particles along the two chains is shown to play a major role
in the transport and to drive a quantum phase transition out of the
charge-density wave insulator, as the Josephson-coupling energy is increased.
We also argue briefly that slightly off the symmetry line, the universality
class of the transition remains the same as that right on the line, still being
driven by the particle-hole pairs.Comment: Final version accepted to Phys. Rev. Lett. (Longer version is
available from http://ctp.snu.ac.kr/~choims/
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