18,037 research outputs found
Investigation of a universal behavior between N\'eel temperature and staggered magnetization density for a three-dimensional quantum antiferromagnet
We simulate the three-dimensional quantum Heisenberg model with a spatially
anisotropic ladder pattern using the first principles Monte Carlo method. Our
motivation is to investigate quantitatively the newly established universal
relation near the quantum critical
point (QCP) associated with dimerization. Here , , and are
the N\'eel temperature, the spinwave velocity, and the staggered magnetization
density, respectively. For all the physical quantities considered here, such as
and , our Monte Carlo results agree nicely with the
corresponding results determined by the series expansion method. In addition,
we find it is likely that the effect of a logarithmic correction, which should
be present in (3+1)-dimensions, to the relation
near the investigated QCP only sets in significantly in the region
with strong spatial anisotropy.Comment: 5 pages, 7 figures, 2 table
A novel delta current method for transport stoichiometry estimation.
BackgroundThe ion transport stoichiometry (q) of electrogenic transporters is an important determinant of their function. q can be determined by the reversal potential (Erev) if the transporter under study is the only electrogenic transport mechanism or a specific inhibitor is available. An alternative approach is to calculate delta reversal potential (ΔErev) by altering the concentrations of the transported substrates. This approach is based on the hypothesis that the contributions of other channels and transporters on the membrane to Erev are additive. However, Erev is a complicated function of the sum of different conductances rather than being additive.ResultsWe propose a new delta current (ΔI) method based on a simplified model for electrogenic secondary active transport by Heinz (Electrical Potentials in Biological Membrane Transport, 1981). ΔI is the difference between two currents obtained from altering the external concentration of a transported substrate thereby eliminating other currents without the need for a specific inhibitor. q is determined by the ratio of ΔI at two different membrane voltages (V1 and V2) where q = 2RT/(F(V2 -V1))ln(ΔI2/ΔI1) + 1. We tested this ΔI methodology in HEK-293 cells expressing the elctrogenic SLC4 sodium bicarbonate cotransporters NBCe2-C and NBCe1-A, the results were consistent with those obtained with the Erev inhibitor method. Furthermore, using computational simulations, we compared the estimates of q with the ΔErev and ΔI methods. The results showed that the ΔErev method introduces significant error when other channels or electrogenic transporters are present on the membrane and that the ΔI equation accurately calculates the stoichiometric ratio.ConclusionsWe developed a ΔI method for estimating transport stoichiometry of electrogenic transporters based on the Heinz model. This model reduces to the conventional reversal potential method when the transporter under study is the only electrogenic transport process in the membrane. When there are other electrogenic transport pathways, ΔI method eliminates their contribution in estimating q. Computational simulations demonstrated that the ΔErev method introduces significant error when other channels or electrogenic transporters are present and that the ΔI equation accurately calculates the stoichiometric ratio. This new ΔI method can be readily extended to the analysis of other electrogenic transporters in other tissues
A Panchromatic View of Brown Dwarf Aurorae
Stellar coronal activity has been shown to persist into the low-mass star
regime, down to late M-dwarf spectral types. However, there is now an
accumulation of evidence suggesting that at the end of the main sequence there
is a transition in the nature of the magnetic activity from chromospheric and
coronal to planet-like and auroral, from local impulsive heating via flares and
MHD wave dissipation to energy dissipation from strong large-scale
magnetospheric current systems. We examine this transition and the prevalence
of auroral activity in brown dwarfs through a compilation of multi-wavelength
surveys of magnetic activity, including radio, X-ray, and optical. We compile
the results of those surveys and place their conclusions in the context of
auroral emission as the consequence of large-scale magnetospheric current
systems that accelerate energetic electron beams and drive the particles to
impact the cool atmospheric gas. We explore the different manifestation of
auroral phenomena in brown dwarf atmospheres, like H, and define their
distinguishing characteristics. We conclude that large amplitude photometric
variability in the near infrared is most likely a consequence of clouds in
brown dwarf atmospheres, but that auroral activity may be responsible for
long-lived stable surface features. We report a connection between auroral
H emission and quiescent radio emission in ECMI pulsing brown dwarfs,
suggesting a potential underlying physical connection between the quiescent and
auroral emissions. We also discuss the electrodynamic engines powering brown
dwarf aurorae and the possible role of satellites around these systems to both
power the aurorae and seed the magnetosphere with plasma.Comment: 26 pages, 17 figures, and 2 tables; accepted to Ap
Fragmentation and quark distribution functions for the pion and kaon with explicit flavor-SU(3)-symmetry breaking
We investigate the unpolarized pion and kaon fragmentation functions,
employing the nonlocal chiral-quark model, which manifests the nonlocal
interactions between the quarks and pseudoscalar mesons, considering the
explicit flavor-SU(3)-symmetry breaking in terms of the current-quark masses.
Moreover, we study the quark-distribution functions, derived from the
fragmentation ones with the Drell-Yan-Levi relation. Numerical results are
evaluated to higher Q^2 by the DGLAP evolution and compared with the empirical
data. The ratios between the relevant valance quark-distribution functions are
also discussed. It turns out that the present results are in relatively good
agreement with available data and other theoretical estimations.Comment: 13 pages, 16 figure
Architecture and data processing alternatives for the tse computer. Volume 4: Image rotation using tse operations
The tse computer's capability of achieving image congruence between temporal and multiple images with misregistration due to rotational differences is reported. The coordinate transformations are obtained and a general algorithms is devised to perform image rotation using tse operations very efficiently. The details of this algorithm as well as its theoretical implications are presented. Step by step procedures of image registration are described in detail. Numerous examples are also employed to demonstrate the correctness and the effectiveness of the algorithms and conclusions and recommendations are made
An optimum settling problem for time lag systems
Lagrange multiplier in Banach space for settling optimal control in time lag syste
A new approach to active vibration isolation for microgravity space experiments
A new method was developed to design an active vibration isolation system for microgravity space experiments. This method yields the required controller transfer functions for a specified transmissibility ratio. Hence, it is a straightforward task to guarantee that the desired vibration isolation performance is achieved at each frequency. The theory for such a controller design was presented by considering a single degree of freedom system. In addition, the magnitude of the input required by the new method has been found to be less than that used by a standard phase lead/lag compensator
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