1,807 research outputs found
Can Electric Field Induced Energy Gaps In Metallic Carbon Nanotubes?
The low-energy electronic structure of metallic single-walled carbon nanotube
(SWNT) in an external electric field perpendicular to the tube axis is
investigated. Based on tight-binding approximation, a field-induced energy gap
is found in all (n, n) SWNTs, and the gap shows strong dependence on the
electric field and the size of the tubes. We numerically find a universal
scaling that the gap is a function of the electric field and the radius of
SWNTs, and the results are testified by the second-order perturbation theory in
weak field limit. Our calculation shows the field required to induce a 0.1
gap in metallic SWNTs can be easily reached under the current
experimental conditions. It indicates a kind of possibility to apply nanotubes
to electric signal-controlled nanoscale switching devices
Area-Constrained Planar Elastica
We determine the equilibria of a rigid loop in the plane, subject to the
constraints of fixed length and fixed enclosed area. Rigidity is characterized
by an energy functional quadratic in the curvature of the loop. We find that
the area constraint gives rise to equilibria with remarkable geometrical
properties: not only can the Euler-Lagrange equation be integrated to provide a
quadrature for the curvature but, in addition, the embedding itself can be
expressed as a local function of the curvature. The configuration space is
shown to be essentially one-dimensional, with surprisingly rich structure.
Distinct branches of integer-indexed equilibria exhibit self-intersections and
bifurcations -- a gallery of plots is provided to highlight these findings.
Perturbations connecting equilibria are shown to satisfy a first order ODE
which is readily solved. We also obtain analytical expressions for the energy
as a function of the area in some limiting regimes.Comment: 23 pages, several figures. Version 2: New title. Changes in the
introduction, addition of a new section with conclusions. Figure 14 corrected
and one reference added. Version to appear in PR
A generalized integral fluctuation theorem for general jump processes
Using the Feynman-Kac and Cameron-Martin-Girsanov formulas, we obtain a
generalized integral fluctuation theorem (GIFT) for discrete jump processes by
constructing a time-invariable inner product. The existing discrete IFTs can be
derived as its specific cases. A connection between our approach and the
conventional time-reversal method is also established. Different from the
latter approach that was extensively employed in existing literature, our
approach can naturally bring out the definition of a time-reversal of a
Markovian stochastic system. Additionally, we find the robust GIFT usually does
not result into a detailed fluctuation theorem
Molecular Motor of Double-Walled Carbon Nanotube Driven by Temperature Variation
An elegant formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and a new molecular motor of
double-walled carbon nanotube whose inner tube is a long (8,4) SWNT and outer
tube a short (14,8) SWNT is constructed. The interaction between inner an outer
tubes is analytically derived by summing the Lennard-Jones potentials between
atoms in inner and outer tubes. It is proved that the molecular motor in a
thermal bath exhibits a directional motion with the temperature variation of
the bath.Comment: 9 pages, 4 figures, revtex
Electronic phase diagram of LixCoO2 revisited with potentiostatically de-intercalated single crystals
Electronic phase diagram of LixCoO2 has been re-examined using
potentiostatically de-intercalated single crystal samples. Stable phases of x ~
0.87, 0.72, 0.53, 0.50, 0.43, and 0.33 were found and isolated for physical
property studies. A-type and chain-type antiferromagnetic orderings have been
suggested from magnetic susceptibility measurement results in x ~ 0.87 and 0.50
below ~ 10 K and 200 K, respectively, similar to those found in NaxCoO2 system.
There is no Li vacancy superlattice ordering observed at room temperature for
the electronically stable phase Li0.72CoO2 as revealed by synchrotron X-ray
Laue diffraction. The peculiar magnetic anomaly near ~ 175 K as often found in
powder samples of x ~ 0.46-0.78 cannot be isolated through this single crystal
potentiostatic method, which supports the previously proposed explanation to be
surface stabilized phase of significant thermal hysteresis and aging character.Comment: 9 pages, 9 figures, 1 tabl
Theory on quench-induced pattern formation: Application to the isotropic to smectic-A phase transitions
During catastrophic processes of environmental variations of a thermodynamic
system, such as rapid temperature decreasing, many novel and complex patterns
often form.
To understand such phenomena, a general mechanism is proposed based on the
competition between heat transfer and conversion of heat to other energy forms.
We apply it to the smectic-A filament growth process during quench-induced
isotropic to smectic-A phase transition. Analytical forms for the buckling
patterns are derived and we find good agreement with experimental observation
[Phys. Rev. {\bf E55} (1997) 1655]. The present work strongly indicates that
rapid cooling will lead to structural transitions in the smectic-A filament at
the molecular level to optimize heat conversion. The force associated with this
pattern formation process is estimated to be in the order of
piconewton.Comment: 9 pages in RevTex form, with 3 postscript figures. Accepted by PR
Bending and Base-Stacking Interactions in Double-Stranded Semiflexible Polymer
Simple expressions for the bending and the base-stacking energy of
double-stranded semiflexible biopolymers (such as DNA and actin) are derived.
The distribution of the folding angle between the two strands is obtained by
solving a Schr\"{o}dinger equation variationally. Theoretical results based on
this model on the extension versus force and extension versus degree of
supercoiling relations of DNA chain are in good agreement with the experimental
observations of Cluzel {\it et al.} [Science {\bf 271}, 792 (1996)], Smith {\it
et al.} [{\it ibid.} {\bf 271}, 795 (1996)], and Strick {\it et al.} [{\it
ibid.} {\bf 271}, 1835 (1996)].Comment: 8 pages in Revtex format, with 4 EPS figure
Primary role of the barely occupied states in the charge density wave formation of NbSe2
NbSe2 is a prototypical charge-density-wave (CDW) material, whose mechanism
remains mysterious so far. With angle resolved photoemission spectroscopy, we
mapped out the CDW gap and recovered the long-lost nesting condition over a
large broken-honeycomb region in the Brillouin zone, which consists of six
saddle band point regions with high density of states (DOS), and large regions
away from Fermi surface with negligible DOS at the Fermi energy. We show that
the major contributions to the CDW come from these barely occupied states
rather than the saddle band points. Our findings not only resolve a long
standing puzzle, but also overthrow the conventional wisdom that CDW is
dominated by regions with high DOS.Comment: 5 pages, 4 figure
Remote generation of entanglement for individual atoms via optical fibers
The generation of atomic entanglement is discussed in a system that atoms are
trapped in separate cavities which are connected via optical fibers. Two
distant atoms can be projected to Bell-state by synchronized turning off the
local laser fields and then performing a single quantum measurement by a
distant controller. The distinct advantage of this scheme is that it works in a
regime that , which makes the scheme insensitive to
cavity strong leakage. Moreover, the fidelity is not affected by atomic
spontaneous emission.Comment: 4 pages, 3 figure
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