19,863 research outputs found
Elevated temperature strain gages
One of the goals of the HOST Program is the development of electrical resistance strain gages for static strain measurements at temperatures equal to or greater than 1273 K. Strain gage materials must have a reproducible or predictable response to temperature, time and strain. It is the objective of this research to investigate criteria for the selection of materials for such applications through electrical properties studies. The results of the investigation of two groups of materials, refractory compounds and binary alloy solid solutions are presented
The LHC di-photon Higgs signal predicted by little Higgs models
Little Higgs theory naturally predicts a light Higgs boson whose most
important discovery channel at the LHC is the di-photon signal . In this work we perform a comparative study for this signal in
some typical little Higgs models, namely the littlest Higgs model (LH), two
littlest Higgs models with T-parity (named LHT-I and LHT-II) and the simplest
little Higgs modes (SLH). We find that compared with the Standard Model
prediction, the di-photon signal rate is always suppressed and the suppression
extent can be quite different for different models. The suppression is mild
(\lsim 10%) in the LH model but can be quite severe () in other
three models. This means that discovering the light Higgs boson predicted by
the little Higgs theory through the di-photon channel at the LHC will be more
difficult than discovering the SM Higgs boson.Comment: 17 pages, 4 figures, 1 tabl
A new approach to upscaling fracture network models while preserving geostatistical and geomechanical characteristics
A new approach to upscaling two-dimensional fracture network models is proposed for preserving geostatistical and geomechanical characteristics of a smaller-scale “source” fracture pattern. First, the scaling properties of an outcrop system are examined in terms of spatial organization, lengths, connectivity, and normal/shear displacements using fractal geometry and power law relations. The fracture pattern is observed to be nonfractal with the fractal dimension D ≈ 2, while its length distribution tends to follow a power law with the exponent 2 < a < 3. To introduce a realistic distribution of fracture aperture and shear displacement, a geomechanical model using the combined finite-discrete element method captures the response of a fractured rock sample with a domain size L = 2 m under in situ stresses. Next, a novel scheme accommodating discrete-time random walks in recursive self-referencing lattices is developed to nucleate and propagate fractures together with their stress- and scale-dependent attributes into larger domains of up to 54 m × 54 m. The advantages of this approach include preserving the nonplanarity of natural cracks, capturing the existence of long fractures, retaining the realism of variable apertures, and respecting the stress dependency of displacement-length correlations. Hydraulic behavior of multiscale growth realizations is modeled by single-phase flow simulation, where distinct permeability scaling trends are observed for different geomechanical scenarios. A transition zone is identified where flow structure shifts from extremely channeled to distributed as the network scale increases. The results of this paper have implications for upscaling network characteristics for reservoir simulation
Spin-one ferromagnets with single-ion anisotropy in a perpendicular external field
In this paper, the conventional Holstein-Primakoff method is generalized with
the help of the characteristic angle transformation [Lei Zhou and Ruibao Tao,
J. Phys. A {\bf 27} 5599 (1994)] for the spin-one magnetic systems with
single-ion anisotropies. We find that the weakness of the conventional method
for such systems can be overcome by the new approach. Two models will be
discussed to illuminate the main idea, which are the ``easy-plane" and the
``easy-axis" spin-one ferromagnet, respectively. Comparisons show that the
current approach can give reasonable ground state properties for the magnetic
system with ``easy-plane" anisotropy though the conventional method never can,
and can give a better representation than the conventional one for the magnetic
system with ``easy-axis" anisotropy though the latter is usually believed to be
a good approximation in such case. Study of the easy-plane model shows that
there is a phase transition induced by the external field, and the
low-temperature specific heat may have a peak as the field reaches the critical
value.Comment: Using LaTex. To be published in the September 1 issue of Physical
Review B (1996). Email address: [email protected]
Towards Intelligent Databases
This article is a presentation of the objectives and techniques
of deductive databases. The deductive approach to databases aims at extending
with intensional definitions other database paradigms that describe
applications extensionaUy. We first show how constructive specifications can
be expressed with deduction rules, and how normative conditions can be defined
using integrity constraints. We outline the principles of bottom-up and
top-down query answering procedures and present the techniques used for
integrity checking. We then argue that it is often desirable to manage with
a database system not only database applications, but also specifications of
system components. We present such meta-level specifications and discuss
their advantages over conventional approaches
LDA+Gutzwiller Method for Correlated Electron Systems: Formalism and Its Applications
We introduce in detail our newly developed \textit{ab initio} LDA+Gutzwiller
method, in which the Gutzwiller variational approach is naturally incorporated
with the density functional theory (DFT) through the "Gutzwiller density
functional theory (GDFT)" (which is a generalization of original Kohn-Sham
formalism). This method can be used for ground state determination of electron
systems ranging from weakly correlated metal to strongly correlated insulators
with long-range ordering. We will show that its quality for ground state is as
high as that by dynamic mean field theory (DMFT), and yet it is computationally
much cheaper. In additions, the method is fully variational, the charge-density
self-consistency can be naturally achieved, and the quantities, such as total
energy, linear response, can be accurately obtained similar to LDA-type
calculations. Applications on several typical systems are presented, and the
characteristic aspects of this new method are clarified. The obtained results
using LDA+Gutzwiller are in better agreement with existing experiments,
suggesting significant improvements over LDA or LDA+U.Comment: 20 pages, 11 figure
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