339 research outputs found
A first-principles study of oxygen vacancy pinning of domain walls in PbTiO3
We have investigated the interaction of oxygen vacancies and 180-degree
domain walls in tetragonal PbTiO3 using density-functional theory. Our
calculations indicate that the vacancies do have a lower formation energy in
the domain wall than in the bulk, thereby confirming the tendency of these
defects to migrate to, and pin, the domain walls. The pinning energies are
reported for each of the three possible orientations of the original Ti-O-Ti
bonds, and attempts to model the results with simple continuum models are
discussed.Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.htm
Localized Random Lasing Modes and a New Path for Observing Localization
We demonstrate that a knowledge of the density-of-states and the eigenstates
of a random system without gain, in conjunction with the frequency profile of
the gain, can accurately predict the mode that will lase first. Its critical
pumping rate can be also obtained. It is found that the shape of the
wavefunction of the random system remains unchanged as gain is introduced.
These results were obtained by the time-independent transfer matrix method and
finite-difference-time-domain (FDTD) methods. They can be also analytically
understood by generalizing the semi-classical Lamb theory of lasing in random
systems. These findings provide a new path for observing the localization of
light, such as looking for mobility edge and studying the localized states.
%inside the random systems..Comment: Sent to PRL. 3 figure
Penta-quark states with hidden charm and beauty
More and more hadron states are found to be difficult to be accommodated by
the quenched quark models which describe baryons as 3-quark states and mesons
as antiquark-quark states. Dragging out an antiquark-quark pair from the gluon
field in hadrons should be an important excitation mechanism for hadron
spectroscopy. Our recent progress on the penta-quark states with hidden charm
and beauty is reviewed.Comment: Plenary talk at the 5th Asia-Pacific Conference on Few-Body Problems
in Physics 2011 (APFB2011), 22-26 Aug., 2011, Seoul, Kore
Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis
In this paper, the scattering/transmission inside a step-modulated
subwavelength metal slit is investigated in detail. We firstly investigate the
scattering in a junction structure by two types of structural changes. The
variation of transmission and reflection coefficients depending on structural
parameters are analyzed. Then a multi-mode multi-reflection model based on ray
theory is proposed to illustrate the transmission in the step-modulated slit
explicitly. The key parts of this model are the multi-mode excitation and the
superposition procedure of the scatterings from all possible modes, which
represent the interference and energy transfer happened at interfaces. The
method we use is an improved modal expansion method (MEM), which is a more
practical and efficient version compared with the previous one [Opt. Express
19, 10073 (2011)]. In addition, some commonly used methods, FDTD, scattering
matrix method, and improved characteristic impedance method, are compared with
MEM to highlight the preciseness of these methods.Comment: 25 pages, 9 figure
The three-dimensional random field Ising magnet: interfaces, scaling, and the nature of states
The nature of the zero temperature ordering transition in the 3D Gaussian
random field Ising magnet is studied numerically, aided by scaling analyses. In
the ferromagnetic phase the scaling of the roughness of the domain walls,
, is consistent with the theoretical prediction .
As the randomness is increased through the transition, the probability
distribution of the interfacial tension of domain walls scales as for a single
second order transition. At the critical point, the fractal dimensions of
domain walls and the fractal dimension of the outer surface of spin clusters
are investigated: there are at least two distinct physically important fractal
dimensions. These dimensions are argued to be related to combinations of the
energy scaling exponent, , which determines the violation of
hyperscaling, the correlation length exponent , and the magnetization
exponent . The value is derived from the
magnetization: this estimate is supported by the study of the spin cluster size
distribution at criticality. The variation of configurations in the interior of
a sample with boundary conditions is consistent with the hypothesis that there
is a single transition separating the disordered phase with one ground state
from the ordered phase with two ground states. The array of results are shown
to be consistent with a scaling picture and a geometric description of the
influence of boundary conditions on the spins. The details of the algorithm
used and its implementation are also described.Comment: 32 pp., 2 columns, 32 figure
Asymptotic Expansions for Stationary Distributions of Perturbed Semi-Markov Processes
New algorithms for computing of asymptotic expansions for stationary
distributions of nonlinearly perturbed semi-Markov processes are presented. The
algorithms are based on special techniques of sequential phase space reduction,
which can be applied to processes with asymptotically coupled and uncoupled
finite phase spaces.Comment: 83 page
An Ionic Molecular Glass as Electron Injection Layer for Efficient Polymer Light-Emitting Diode
An ionic molecular glass based on a dendronized monoammonium salt has been facilely synthesized and utilized as an interfacial electron-injection layer in a light-emitting diode (LED). The characterization of a yellow-green LED that involves an Al cathode and a thin layer of the new compound spin cast from a methanol solution has shown device performances comparable to those obtained with a Ba/Al cathode. Photovoltaic measurements under white light irradiation reveal that a thin layer of the new compound can significantly increase the built-in potential and thus facilitate electron injection from an Al cathode. Furthermore, it is interesting to observe that the new ionic salt could undergo reorganization on the emissive conjugated polymer layer, which leads to the formation of nearly uniform nanoaggregates
Electroweak Radiative Corrections to Associated WH and ZH Production at Hadron Colliders
Higgs-boson production in association with W or Z bosons, p pbar -> WH/ZH +
X, is the most promising discovery channel for a light Standard Model Higgs
particle at the Fermilab Tevatron. We present the calculation of the
electroweak O(alpha) corrections to these processes. The corrections decrease
the theoretical prediction by up to 5-10%, depending in detail on the
Higgs-boson mass and the input-parameter scheme. We update the cross-section
prediction for associated WH and ZH production at the Tevatron and at the LHC,
including the next-to-leading order electroweak and QCD corrections, and study
the theoretical uncertainties induced by factorization and renormalization
scale dependences and by the parton distribution functions.Comment: 32 pages, LaTeX, 21 figures. Uses axodraw.sty and feynarts.sty. Added
reference
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Cancer immunoediting by the innate immune system in the absence of adaptive immunity
Cancer immunoediting is the process whereby immune cells protect against cancer formation by sculpting the immunogenicity of developing tumors. Although the full process depends on innate and adaptive immunity, it remains unclear whether innate immunity alone is capable of immunoediting. To determine whether the innate immune system can edit tumor cells in the absence of adaptive immunity, we compared the incidence and immunogenicity of 3'methylcholanthrene-induced sarcomas in syngeneic wild-type, RAG2, and RAG2x γc mice. We found that innate immune cells could manifest cancer immunoediting activity in the absence of adaptive immunity. This activity required natural killer (NK) cells and interferon γ (IFN-γ), which mediated the induction of M1 macrophages. M1 macrophages could be elicited by administration of CD40 agonists, thereby restoring editing activity in RAG2x γc mice. Our results suggest that in the absence of adaptive immunity, NK cell production of IFN-γ induces M1 macrophages, which act as important effectors during cancer immunoediting
- …