4,084 research outputs found
Hydrodynamics: Fluctuating Initial Conditions and Two-particle Correlations
Event-by-event hydrodynamics (or hydrodynamics with fluctuating initial
conditions) has been developed in the past few years. Here we discuss how it
may help to understand the various structures observed in two-particle
correlations.Comment: 7 pages, 9 figures, presented at the Workshop on Saturation, the
Color Glass Condensate and Glasma: What Have we Learned from RHIC
Dynamic noise, chaos and parameter estimation in population biology
We revisit the parameter estimation framework for population biological dynamical systems, and apply it to calibrate various models in epidemiology with empirical time series, namely influenza and dengue fever. When it comes to more complex models such as multi-strain dynamics to describe the virus–host interaction in dengue fever, even the most recently developed parameter estimation techniques, such as maximum likelihood iterated filtering, reach their computational limits. However, the first results of parameter estimation with data on dengue fever from Thailand indicate a subtle interplay between stochasticity and the deterministic skeleton. The deterministic system on its own already displays complex dynamics up to deterministic chaos and coexistence of multiple attractors
Sensitivity curves for spaceborne gravitational wave interferometers
To determine whether particular sources of gravitational radiation will be
detectable by a specific gravitational wave detector, it is necessary to know
the sensitivity limits of the instrument. These instrumental sensitivities are
often depicted (after averaging over source position and polarization) by
graphing the minimal values of the gravitational wave amplitude detectable by
the instrument versus the frequency of the gravitational wave. This paper
describes in detail how to compute such a sensitivity curve given a set of
specifications for a spaceborne laser interferometer gravitational wave
observatory. Minor errors in the prior literature are corrected, and the first
(mostly) analytic calculation of the gravitational wave transfer function is
presented. Example sensitivity curve calculations are presented for the
proposed LISA interferometer. We find that previous treatments of LISA have
underestimated its sensitivity by a factor of .Comment: 27 pages + 5 figures, REVTeX, accepted for publication in Phys Rev D;
Update reflects referees comments, figure 3 clarified, figure 5 corrected for
LISA baselin
Imaginary Phases in Two-Level Model with Spontaneous Decay
We study a two-level model coupled to the electromagnetic vacuum and to an
external classic electric field with fixed frequency. The amplitude of the
external electric field is supposed to vary very slow in time. Garrison and
Wright [{\it Phys. Lett.} {\bf A128} (1988) 177] used the non-hermitian
Hamiltonian approach to study the adiabatic limit of this model and obtained
that the probability of this two-level system to be in its upper level has an
imaginary geometric phase. Using the master equation for describing the time
evolution of the two-level system we obtain that the imaginary phase due to
dissipative effects is time dependent, in opposition to Garrison and Wright
result. The present results show that the non-hermitian hamiltonian method
should not be used to discuss the nature of the imaginary phases in open
systems.Comment: 11 pages, new version, to appear in J. Phys.
Mix design, properties and cost analysis of fly ash-based geopolymer foam
This study has investigated the joint effect of several mix parameters on the properties of foam geopolymers.
The mix parameters analysed through a laboratory experiment of 54 different mortar mixes were,
sodium silicate/sodium hydroxide mass ratio (2.5, 3.5, 4.5), activator/binder mass ratio (0.6, 0.8, 1.0),
chemical foaming agent type (hydrogen peroxide (H2O2) and sodium perborate (NaBO3)) and foaming
agent mass ratio content (1%, 2%, 3%). Properties, SEM and FTIR analysis and cost analysis are included.
The results show that the sodium perborate over performs hydrogen peroxide leading to a lower overall
thermal conductibility of foam geopolymers. Mixtures with a low thermal conductivity of around 0.1 W/
(m K) and a compressive strength of around 6 MPa were achieved. The cost analysis show that the foaming
agents are responsible for a small percentage of foam geopolymers total cost being that the alkaline
activators are responsible for more than 80%
Importance of Granular Structure in the Initial Conditions for the Elliptic Flow
We show effects of granular structure of the initial conditions (IC) of
hydrodynamic description of high-energy nucleus-nucleus collisions on some
observables, especially on the elliptic-flow parameter v2. Such a structure
enhances production of isotropically distributed high-pT particles, making v2
smaller there. Also, it reduces v2 in the forward and backward regions where
the global matter density is smaller, so where such effects become more
efficacious.Comment: 4 pages, 5 figure
Smoothed Particle Hydrodynamics for Relativistic Heavy Ion Collisions
The method of smoothed particle hydrodynamics (SPH) is developped
appropriately for the study of relativistic heavy ion collision processes. In
order to describe the flow of a high energy but low baryon number density
fluid, the entropy is taken as the SPH base. We formulate the method in terms
of the variational principle. Several examples show that the method is very
promising for the study of hadronic flow in RHIC physics.Comment: 14 pages, 8figure
New order parameters in the Potts model on a Cayley tree
For the state Potts model new order parameters projecting on a group of
spins instead of a single spin are introduced. On a Cayley tree this allows the
physical interpretation of the Potts model at noninteger values q of the number
of states. The model can be solved recursively. This recursion exhibits chaotic
behaviour changing qualitatively at critical values of . Using an
additional order parameter belonging to a group of zero extrapolated size the
additional ordering is related to a percolation problem. This percolation
distinguishes different phases and explains the critical indices of percolation
class occuring at the Peierls temperature.Comment: 16 pages TeX, 5 figures PostScrip
Performance of a fly ash geopolymeric mortar for coating of ordinary portland cement concrete exposed to harsh chemical environments
Premature degradation of ordinary Portland cement (OPC) concrete infrastructures is a
current and serious problem with overwhelming costs amounting to several trillion dollars. The use
of concrete surface treatments with waterproofing materials to prevent the access of aggressive
substances is an important way of enhancing concrete durability. The most common surface
treatments use polymeric resins based on epoxy, silicone (siloxane), acrylics, polyurethanes or
polymethacrylate. However, epoxy resins have low resistance to ultraviolet radiation while
polyurethanes are sensitive to high alkalinity environments. Geopolymers constitute a group of
materials with high resistance to chemical attack that could also be used for coating of concrete
infrastructures exposed to harsh chemical environments.
This article presents results of an experimental investigation on the resistance to chemical attack (by
sulfuric and nitric acid) of several materials: OPC concrete, high performance concrete (HPC),
epoxy resin, acrylic painting and a fly ash based geopolymeric mortar. Three types of acids, each
with high concentrations of 10%, 20% and 30%, were used to simulate long term degradation by
chemical attack. The results show that the epoxy resin had the best resistance to chemical attack,
irrespective of the acid type and acid concentration
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