50,712 research outputs found
Conformal or Walking? Monte Carlo renormalization group studies of SU(3) gauge models with fundamental fermions
Strongly coupled gauge systems with many fermions are important in many
phenomenological models. I use the 2-lattice matching Monte Carlo
renormalization group method to study the fixed point structure and critical
indexes of SU(3) gauge models with 8 and 12 flavors of fundamental fermions.
With an improved renormalization group block transformation I am able to
connect the perturbative and confining regimes of the N_f=8 flavor system, thus
verifying its QCD-like nature. With N_f=12 flavors the data favor the existence
of an infrared fixed point and conformal phase, though the results are also
consistent with very slow walking. I measure the anomalous mass dimension in
both systems at several gauge couplings and find that they are barely different
from the free field value.Comment: 26 pages, 11 figure
First-principles calculations of a high-pressure synthesized compound PtC
First-principles density-functional method is used to study the recently
high-pressure synthesized compound PtC. It is confirmed by our calculations
that the platinum carbide has a zinc-blende ground-state phase at zero pressure
and the rock-salt structure is a high-pressure phase. The theoretical
transition pressure from zinc-blende to rock-salt is determined to be 52GPa.
Furthermore, our calculation shows the possibility that the experimentally
synthesized PtC by Ono et al. under high pressure condition might undergo a
transition from rock-salt structure to zinc-blende after the pressure quench to
ambient condition.Comment: A revised versio
A New Model for Evaluating the Future Options of Integrating Ground Source Heat Pumps in Building Construction
Decision-making for effective infrastructure integration is challenging because the performances of long-lasting objects
often depends on conditions which are either outside the control of the designer or difficult to foresee at the design
stage. In this paper we examine a new approach to estimating the range of cost-effective solutions for integrating
the construction/retrofit of two or more different types of infrastructure. Infrastructure integration has many perceived
benefits, but also faces serious new challenges and doubts from practitioners, particularly in sectors with complex
construction process, long asset lives, uncertain cost parameters, and slow and unwieldy decision-making, such as
is common with civil engineering works. We test all main options in integrating a ground source heat pump (GSHP)
system with the construction and retrofit of an archetypal, office building. A new simulation model is developed and
parameterized using actual data in the UK. We incorporate unavoidable uncertainties and randomness in how the
decisions are triggered, and test the effectiveness of proactive measures to embed future options. The model highlights
how sensitive the range of cost-effective solutions is to the setting of renewable energy incentives, discount rates,
technical performance and life-cycle asset management of interdependent infrastructure. This points to a clear need for
establishing appropriate regulatory standards. We expect this model to find increasing applications in the planning and
designing of integrated complexes of buildings, transport facilities, renewable energy supply, water supply and waste
management in dense urban areas, which are an increasingly key part of sustainable urban development
The Abel-Zeilberger Algorithm
We use both Abel's lemma on summation by parts and Zeilberger's algorithm to
find recurrence relations for definite summations. The role of Abel's lemma can
be extended to the case of linear difference operators with polynomial
coefficients. This approach can be used to verify and discover identities
involving harmonic numbers and derangement numbers. As examples, we use the
Abel-Zeilberger algorithm to prove the Paule-Schneider identities, the
Apery-Schmidt-Strehl identity, Calkin's identity and some identities involving
Fibonacci numbers.Comment: 18 page
Global Models of Planet Formation and Evolution
Despite the increase in observational data on exoplanets, the processes that
lead to the formation of planets are still not well understood. But thanks to
the high number of known exoplanets, it is now possible to look at them as a
population that puts statistical constraints on theoretical models. A method
that uses these constraints is planetary population synthesis. Its key element
is a global model of planet formation and evolution that directly predicts
observable planetary properties based on properties of the natal protoplanetary
disk. To do so, global models build on many specialized models that address one
specific physical process. We thoroughly review the physics of the sub-models
included in global formation models. The sub-models can be classified as models
describing the protoplanetary disk (gas and solids), the (proto)planet (solid
core, gaseous envelope, and atmosphere), and finally the interactions
(migration and N-body interaction). We compare the approaches in different
global models and identify physical processes that require improved
descriptions in future. We then address important results of population
synthesis like the planetary mass function or the mass-radius relation. In
these results, the global effects of physical mechanisms occurring during
planet formation and evolution become apparent, and specialized models
describing them can be put to the observational test. Due to their nature as
meta models, global models depend on the development of the field of planet
formation theory as a whole. Because there are important uncertainties in this
theory, it is likely that global models will in future undergo significant
modifications. Despite this, they can already now yield many testable
predictions. With future global models addressing the geophysical
characteristics, it should eventually become possible to make predictions about
the habitability of planets.Comment: 30 pages, 16 figures. Accepted for publication in the International
Journal of Astrobiology (Cambridge University Press
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