5,145 research outputs found
Superfluid-insulator transition of the Josephson junction array model with commensurate frustration
We have studied the rationally frustrated Josephson-junction array model in
the square lattice through Monte Carlo simulations of D XY-model. For
frustration , the model at zero temperature shows a continuous
superfluid-insulator transition. From the measurement of the correlation
function and the superfluid stiffness, we obtain the dynamical critical
exponent and the correlation length critical exponent . While the dynamical critical exponent is the same as that for cases
, 1/2, and 1/3, the correlation length critical exponent is surprisingly
quite different. When , we have the nature of a first-order transition.Comment: RevTex 4, to appear in PR
Salt stress induced ion accumulation, ion homeostasis, membrane injury and sugar contents in salt-sensitive rice (Oryza sativa L. spp. indica) roots under isoosmotic conditions
Excess salt induced ionic and osmotic stresses that disturbed metabolism and led to reduction of plant development. Previous studies reported that sugars in stressed plants were involved in stress tolerance. However, the role of sugars in salt-stressed plants against only ionic effects is still unclear. The objective of this research was to investigate accumulation and homeostasis of ions, membrane injury, water content, growth characters and sugar contents in roots, in-response to salt stress under iso-osmotic conditions. Salt-sensitive rice, Pathumthani1 (PT1) was grown on MS culture medium for 7 days and was adjusted to salt stress under iso-osmotic conditions (-1.75 ± 0.20 MPa) by mannitol for 4 days. An increase in NaCl increased Na+ and Na+:K+ in PT1 roots leading to increased membrane injury, while the water content was decreased. Additionally, growth characters, including number, length, fresh weight and dry weight of roots, were inhibited. Sugar accumulations in PT1 roots were enhanced by increases in NaCl. The increase in Na+ was positively related to total soluble sugars, resulting in an osmotic adjustment of the membrane that maintained water availability. The accumulation of sugars in PT1 roots may be a primary salt-defense mechanism and may function as an osmotic control.Key words: Mannitol, membrane injury, oligosaccharides, sodium ion, potassium ion, sodium chloride
Phase diagram of a Disordered Boson Hubbard Model in Two Dimensions
We study the zero-temperature phase transition of a two-dimensional
disordered boson Hubbard model. The phase diagram of this model is constructed
in terms of the disorder strength and the chemical potential. Via quantum Monte
Carlo simulations, we find a multicritical line separating the weak-disorder
regime, where a random potential is irrelevant, from the strong-disorder
regime. In the weak-disorder regime, the Mott-insulator-to-superfluid
transition occurs, while, in the strong-disorder regime, the
Bose-glass-to-superfluid transition occurs. On the multicritical line, the
insulator-to-superfluid transition has the dynamical critical exponent and the correlation length critical exponent ,
that are different from the values for the transitions off the line. We suggest
that the proliferation of the particle-hole pairs screens out the weak disorder
effects.Comment: 4 pages, 4 figures, to be published in PR
Nova-Like Cataclysmic Variable TT Ari: QPO Behaviour Coming Back From Positive Superhumps
We study the variability of the nova-like cataclysmic variable TT Ari, on
time-scales of between minutes and months. The observations in the filter R
were obtained at the 40-cm telescope of the Chungbuk National University
(Korea). TT Ari was in the "negative superhump" state after its return from the
"positive superhump" state, which lasted 8 years. The ephemeris for 12 best
pronounced minima is where
numbers in digits are errors in units of the last digit. The phases of minima
may reach 0.2, indicating non-eclipse nature of these minima. The
quasi-periodic oscillations (QPO) are present with a mean "period" of 21.6 min
and mean semi-amplitude of 36 mmag. This value is consistent with the range
15-25 minutes reported for previous "negative superhump" states and does not
support the hypothesis of secular decrease of the QPO period.
Either the period, or the semi-amplitude show significant night-to-night
variations. According to the position at the two-parameter diagrams, the
interval of observations was splitted into 5 parts, showing different
characteristics which are discussed in this paper. The system is an excellent
laboratory to study processes resulting in variations at time-scales from
seconds to decades and needs further monitoring at various states of activity.Comment: 14pages,10figures, accepted in Astronomy and Astrophysic
Phase Transitions in the Two-Dimensional XY Model with Random Phases: a Monte Carlo Study
We study the two-dimensional XY model with quenched random phases by Monte
Carlo simulation and finite-size scaling analysis. We determine the phase
diagram of the model and study its critical behavior as a function of disorder
and temperature. If the strength of the randomness is less than a critical
value, , the system has a Kosterlitz-Thouless (KT) phase transition
from the paramagnetic phase to a state with quasi-long-range order. Our data
suggest that the latter exists down to T=0 in contradiction with theories that
predict the appearance of a low-temperature reentrant phase. At the critical
disorder and for there is no
quasi-ordered phase. At zero temperature there is a phase transition between
two different glassy states at . The functional dependence of the
correlation length on suggests that this transition corresponds to the
disorder-driven unbinding of vortex pairs.Comment: LaTex file and 18 figure
Fabrication of Robust Thermal Transition Modules and First Cryogenic Experiment with the Refurbished COLDDIAG
Two sets of thermal transition modules as a key component for the COLDDIAG (cold vacuum chamber for beam heat load diagnostics) refurbishment were manufactured, based on the previous design study. The modules are installed in the existing COLDDIAG cryostat and tested with an operating temperature of approximately 50 K at both a cold bore and a thermal shield. This cool-down experiment is a preliminary investigation aiming at beam heat-load studies at the FCC-hh where the beam screens will be operated at almost the same temperature. In this contribution, we report the fabrication processes of the mechanically robust transition modules and the first thermal measurement results with the refurbished COLDDIAG in a cryogenic environment. The static heat load in the refurbished cryostat remains unchanged, compared to that in the former one (4-K cold bore and 50-K shield with thin transitions), despite the increase in the transition thickness. It originates from the identical temperature at the cold bore and the shield, which can theoretically allow the heat intakes by thermal conduction and radiation between them to vanish
Dissociation of ssDNA - Single-Walled Carbon Nanotube Hybrids by Watson-Crick Base Pairing
The unwrapping event of ssDNA from the SWNT during the Watson-Crick base
paring is investigated through electrical and optical methods, and binding
energy calculations. While the ssDNA-metallic SWNT hybrid shows the p-type
semiconducting property, the hybridization product recovered metallic
properties. The gel electrophoresis directly verifies the result of wrapping
and unwrapping events which was also reflected to the Raman shifts. Our
molecular dynamics simulations and binding energy calculations provide
atomistic description for the pathway to this phenomenon. This nano-physical
phenomenon will open up a new approach for nano-bio sensing of specific
sequences with the advantages of efficient particle-based recognition, no
labeling, and direct electrical detection which can be easily realized into a
microfluidic chip format.Comment: 4 pages, 4 figure
The Field-Tuned Superconductor-Insulator Transition with and without Current Bias
The magnetic-field-tuned superconductor-insulator transition has been studied
in ultrathin Beryllium films quench-condensed near 20 K. In the zero-current
limit, a finite-size scaling analysis yields the scaling exponent product vz =
1.35 +/- 0.10 and a critical sheet resistance R_{c} of about 1.2R_{Q}, with
R_{Q} = h/4e^{2}. However, in the presence of dc bias currents that are smaller
than the zero-field critical currents, vz becomes 0.75 +/- 0.10. This new set
of exponents suggests that the field-tuned transitions with and without dc bias
currents belong to different universality classes.Comment: RevTex 4 pages, 4 figures, and 1 table minor change
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