40,833 research outputs found
A biomimetic nanofluidic diode based on surface-modified polymeric carbon nitride nanotubes
A controllable ion transport including ion selectivity and ion rectification across nanochannels or porous membranes is of great importance because of potential applications ranging from biosensing to energy conversion. Here, a nanofluidic ion diode was realized by modifying carbon nitride nanotubes with different molecules yielding an asymmetric surface charge that allows for ion rectification. With the advantages of low-cost, thermal and mechanical robustness, and simple fabrication process, carbon nitride nanotubes with ion rectification have the potential to be used in salinity-gradient energy conversion and ion sensor systems
Ferromagnetism of Weakly-Interacting Electrons in Disordered Systems
It was realized two decades ago that the two-dimensional diffusive Fermi
liquid phase is unstable against arbitrarily weak electron-electron
interactions. Recently, using the nonlinear sigma model developed by
Finkelstein, several authors have shown that the instability leads to a
ferromagnetic state. In this paper, we consider diffusing electrons interacting
through a ferromagnetic exchange interaction. Using the Hartree-Fock
approximation to directly calculate the electron self energy, we find that the
total energy is minimized by a finite ferromagnetic moment for arbitrarily weak
interactions in two dimensions and for interaction strengths exceeding a
critical proportional to the conductivity in three dimensions. We discuss the
relation between our results and previous ones
B\"{a}cklund transformations for the constrained dispersionless hierarchies and dispersionless hierarchies with self-consistent sources
The B\"{a}cklund transformations between the constrained dispersionless KP
hierarchy (cdKPH) and the constrained dispersionless mKP hieararchy (cdmKPH)
and between the dispersionless KP hieararchy with self-consistent sources
(dKPHSCS) and the dispersionless mKP hieararchy with self-consistent sources
(dmKPHSCS) are constructed. The auto-B\"{a}cklund transformations for the
cdmKPH and for the dmKPHSCS are also formulated.Comment: 11 page
Integrable dispersionless KdV hierarchy with sources
An integrable dispersionless KdV hierarchy with sources (dKdVHWS) is derived.
Lax pair equations and bi-Hamiltonian formulation for dKdVHWS are formulated.
Hodograph solution for the dispersionless KdV equation with sources (dKdVWS) is
obtained via hodograph transformation. Furthermore, the dispersionless
Gelfand-Dickey hierarchy with sources (dGDHWS) is presented.Comment: 15 pages, to be published in J. Phys. A: Math. Ge
Recent Developments In Computational Fracture Mechanics At Cardiff
The following most recent developments in computational fracture mechanics at Cardiff University are reviewed: hybrid crack element (HCE) which can give directly the stress intensity factor (SIF) as well as the coefficients of higher order terms in the plane linear elastic crack tip asymptotic field; extended finite element method (XFEM) which avoids using a mesh conforming with the crack as is the case with the traditional FEM and gives highly accurate crack tip fields; penalty function technique for handling point loads; and compressed sparse row (CSR) storage scheme for efficient implementation of the above techniques. Possible future improvements are also discussed
Riemannian Geometry of Noncommutative Surfaces
A Riemannian geometry of noncommutative n-dimensional surfaces is developed
as a first step towards the construction of a consistent noncommutative
gravitational theory. Historically, as well, Riemannian geometry was recognized
to be the underlying structure of Einstein's theory of general relativity and
led to further developments of the latter. The notions of metric and
connections on such noncommutative surfaces are introduced and it is shown that
the connections are metric-compatible, giving rise to the corresponding Riemann
curvature. The latter also satisfies the noncommutative analogue of the first
and second Bianchi identities. As examples, noncommutative analogues of the
sphere, torus and hyperboloid are studied in detail. The problem of covariance
under appropriately defined general coordinate transformations is also
discussed and commented on as compared with other treatments.Comment: 28 pages, some clarifications, examples and references added, version
to appear in J. Math. Phy
The sino-german 6cm polarization survey of the galactic plane: A summary
We have finished the 6cm polarization survey of the Galactic plane using the
Urumqi 25m radio telescope. It covers 10deg<l<230deg in Galactic longitude and
|b| <5deg in Galactic latitude. The new polarization maps not only reveal new
properties of the diffuse magnetized interstellar medium, but also are very
useful for studying individual objects such as Hii regions, which may act as
Faraday screens with strong regular magnetic fields inside, and supernova
remnants for their polarization properties and spectra. The high sensitivity of
the survey enables us to discover two new SNRs G178.2-4.2 and G25.3-2.1 and a
number of Hii regions.Comment: 10 pages, 1 figure. International Journal of Modern Physics:
Conference Series (IJMPCS) for Proceedings of 3rd Galileo-Xu Guangqi meetin
Determination of Wave Function Functionals: The Constrained-Search--Variational Method
In a recent paper [Phys. Rev. Lett. \textbf{93}, 130401 (2004)], we proposed
the idea of expanding the space of variations in variational calculations of
the energy by considering the approximate wave function to be a
functional of functions rather than a function. The
space of variations is expanded because a search over the functions can
in principle lead to the true wave function. As the space of such variations is
large, we proposed the constrained-search-- variational method whereby a
constrained search is first performed over all functions such that the
wave function functional satisfies a physical constraint such as
normalization or the Fermi-Coulomb hole sum rule, or leads to the known value
of an observable such as the diamagnetic susceptibility, nuclear magnetic
constant or Fermi contact term. A rigorous upper bound to the energy is then
obtained by application of the variational principle. A key attribute of the
method is that the wave function functional is accurate throughout space, in
contrast to the standard variational method for which the wave function is
accurate only in those regions of space contributing principally to the energy.
In this paper we generalize the equations of the method to the determination of
arbitrary Hermitian single-particle operators as applied to two-electron atomic
and ionic systems. The description is general and applicable to both ground and
excited states. A discussion on excited states in conjunction with the theorem
of Theophilou is provided.Comment: 26 pages, 4 figures, 5 table
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