1,235 research outputs found
Direct numerical simulation of homogeneous nucleation and growth in a phase-field model using cell dynamics method
Homogeneous nucleation and growth in a simplest two-dimensional phase field
model is numerically studied using the cell dynamics method. Whole process from
nucleation to growth is simulated and is shown to follow closely the
Kolmogorov-Johnson-Mehl-Avrami (KJMA) scenario of phase transformation.
Specifically the time evolution of the volume fraction of new stable phase is
found to follow closely the KJMA formula. By fitting the KJMA formula directly
to the simulation data, not only the Avrami exponent but the magnitude of
nucleation rate and, in particular, of incubation time are quantitatively
studied. The modified Avrami plot is also used to verify the derived KJMA
parameters. It is found that the Avrami exponent is close to the ideal
theoretical value m=3. The temperature dependence of nucleation rate follows
the activation-type behavior expected from the classical nucleation theory. On
the other hand, the temperature dependence of incubation time does not follow
the exponential activation-type behavior. Rather the incubation time is
inversely proportional to the temperature predicted from the theory of
Shneidman and Weinberg [J. Non-Cryst. Solids {\bf 160}, 89 (1993)]. A need to
restrict thermal noise in simulation to deduce correct Avrami exponent is also
discussed.Comment: 9 pages, 8 figures, Journal of Chemical Physics to be publishe
One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin environment
Single electron spins coupled to multiple nuclear spins provide promising
multi-qubit registers for quantum sensing and quantum networks. The obtainable
level of control is determined by how well the electron spin can be selectively
coupled to, and decoupled from, the surrounding nuclear spins. Here we realize
a coherence time exceeding a second for a single electron spin through
decoupling sequences tailored to its microscopic nuclear-spin environment. We
first use the electron spin to probe the environment, which is accurately
described by seven individual and six pairs of coupled carbon-13 spins. We
develop initialization, control and readout of the carbon-13 pairs in order to
directly reveal their atomic structure. We then exploit this knowledge to store
quantum states for over a second by carefully avoiding unwanted interactions.
These results provide a proof-of-principle for quantum sensing of complex
multi-spin systems and an opportunity for multi-qubit quantum registers with
long coherence times
String Fields and the Standard Model
The Cremmer-Scherk mechanism is generalised in a non-Abelian context. In the
presence of the Higgs scalars of the standard model it is argued that fields
arising from the low energy effective string action may contribute to the mass
generation of the observed vector bosons that mediate the electroweak
interactions and that future analyses of experimental data should consider the
possibility of string induced radiative corrections to the Weinberg angle
coming from physics beyond the standard model.Comment: 4 pages, LATEX, no figure
Mass generation for non-Abelian antisymmetric tensor fields in a three-dimensional space-time
Starting from a recently proposed Abelian topological model in (2+1)
dimensions, which involve the Kalb-Ramond two form field, we study a
non-Abelian generalization of the model. An obstruction for generalization is
detected. However we show that the goal is achieved if we introduce a vectorial
auxiliary field. Consequently, a model is proposed, exhibiting a non-Abelian
topological mass generation mechanism in D=3, that provides mass for the
Kalb-Ramond field. The covariant quantization of this model requires ghosts for
ghosts. Therefore in order to quantize the theory we construct a complete set
of BRST and anti-BRST equations using the horizontality condition.Comment: 8 pages. To appear in Physical Review
The Abelian Topological Mass Mechanism From Dimensional Reduction
We show that the abelian topological mass mechanism in four dimensions,
described by the Cremmer-Sherk action, can be obtained from dimensional
reduction in five dimensions. Starting from a gauge invariant action in five
dimensions, where the dual equivalence between a massless vector field and a
massless second-rank antisymmetric field in five dimensions is established, the
dimensional reduction is performed keeping only one massive mode. Furthermore,
the Kalb-Ramond action and the Stuckelberger formulation for massive spin-1 are
recovered.Comment: Three references added, 6 pages, late
Extraction of BoNT/A, /B, /E, and /F with a Single, High Affinity Monoclonal Antibody for Detection of Botulinum Neurotoxin by Endopep-MS
Botulinum neurotoxins (BoNTs) are extremely potent toxins that are capable of causing respiratory failure leading to long-term intensive care or death. The best treatment for botulism includes serotype-specific antitoxins, which are most effective when administered early in the course of the intoxication. Early confirmation of human exposure to any serotype of BoNT is an important public health goal. In previous work, we focused on developing Endopep-MS, a mass spectrometry-based endopeptidase method for detecting and differentiating the seven serotypes (BoNT/A-G) in buffer and BoNT/A, /B, /E, and /F (the four serotypes that commonly affect humans) in clinical samples. We have previously reported the success of antibody-capture to purify and concentrate BoNTs from complex matrices, such as clinical samples. However, to check for any one of the four serotypes of BoNT/A, /B, /E, or /F, each sample is split into 4 aliquots, and tested for the specific serotypes separately. The discovery of a unique monoclonal antibody that recognizes all four serotypes of BoNT/A, /B, /E and /F allows us to perform simultaneous detection of all of them. When applied in conjunction with the Endopep-MS assay, the detection limit for each serotype of BoNT with this multi-specific monoclonal antibody is similar to that obtained when using other serotype-specific antibodies
Strings in gravity with torsion
A theory of gravitation in 4D is presented with strings used in the material
action in spacetime. It is shown that the string naturally gives rise to
torsion. It is also shown that the equation of motion a string follows from the
Bianchi identity, gives the identical result as the Noether conservation laws,
and follows a geodesic only in the lowest order approximation. In addition, the
conservation laws show that strings naturally have spin, which arises not from
their motion but from their one dimensional structure.Comment: 16 page
Fractional Statistics in Three Dimensions: Compact Maxwell-Higgs System
We show that a (3+1)-dimensional system composed of an open magnetic vortex
and an electrical point charge exhibits the phenomenon of Fermi-Bose
transmutation. In order to provide the physical realization of this system we
focus on the lattice compact scalar electrodynamics whose topological
excitations are open Nielsen-Olesen strings with magnetic monopoles attached at
their ends.Comment: 8 page
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