6,283 research outputs found
Heat transfer in rotating serpentine passages with trips normal to the flow
Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction
An Enhanced Fractional Order Model of Ionic Polymer-Metal Composites Actuator
Ionic polymer-metal composites (IPMCs) are electroactive polymers which transform the mechanical forces into electric signals and vice versa. The paper proposes an enhanced fractional order transfer function (FOTF) model for IPMC membrane working as actuator. In particular the IPMC model has been characterized through experimentation, and a more detailed structure of its FOTF has been determined via optimization routines. The minimization error was attained comparing the simple genetic algorithms with the simplex method and considering the error between the experimental and model derived frequency responses as cost functions
STOCHASTIC DYNAMICS OF LARGE-SCALE INFLATION IN DE~SITTER SPACE
In this paper we derive exact quantum Langevin equations for stochastic
dynamics of large-scale inflation in de~Sitter space. These quantum Langevin
equations are the equivalent of the Wigner equation and are described by a
system of stochastic differential equations. We present a formula for the
calculation of the expectation value of a quantum operator whose Weyl symbol is
a function of the large-scale inflation scalar field and its time derivative.
The unique solution is obtained for the Cauchy problem for the Wigner equation
for large-scale inflation. The stationary solution for the Wigner equation is
found for an arbitrary potential. It is shown that the large-scale inflation
scalar field in de Sitter space behaves as a quantum one-dimensional
dissipative system, which supports the earlier results. But the analogy with a
one-dimensional model of the quantum linearly damped anharmonic oscillator is
not complete: the difference arises from the new time dependent commutation
relation for the large-scale field and its time derivative. It is found that,
for the large-scale inflation scalar field the large time asymptotics is equal
to the `classical limit'. For the large time limit the quantum Langevin
equations are just the classical stochastic Langevin equations (only the
stationary state is defined by the quantum field theory).Comment: 21 pages RevTex preprint styl
Stochastic Inflation:The Quantum Phase Space Approach
In this paper a quantum mechanical phase space picture is constructed for
coarse-grained free quantum fields in an inflationary Universe. The appropriate
stochastic quantum Liouville equation is derived. Explicit solutions for the
phase space quantum distribution function are found for the cases of power law
and exponential expansions. The expectation values of dynamical variables with
respect to these solutions are compared to the corresponding cutoff regularized
field theoretic results (we do not restrict ourselves only to \VEV{\F^2}).
Fair agreement is found provided the coarse-graining scale is kept within
certain limits. By focusing on the full phase space distribution function
rather than a reduced distribution it is shown that the thermodynamic
interpretation of the stochastic formalism faces several difficulties (e.g.,
there is no fluctuation-dissipation theorem). The coarse-graining does not
guarantee an automatic classical limit as quantum correlations turn out to be
crucial in order to get results consistent with standard quantum field theory.
Therefore, the method does {\em not} by itself constitute an explanation of the
quantum to classical transition in the early Universe. In particular, we argue
that the stochastic equations do not lead to decoherence.Comment: 43 page
Prospects for detecting the 21cm forest from the diffuse intergalactic medium with LOFAR
We discuss the feasibility of the detection of the 21cm forest in the diffuse
IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been
derived using simulations of reionization which include detailed radiative
transfer of ionizing photons. We find that the spectra from reionization models
with similar total comoving hydrogen ionizing emissivity but different
frequency distribution look remarkably similar. Thus, unless the reionization
histories are very different from each other (e.g. a predominance of UV vs.
x-ray heating) we do not expect to distinguish them by means of observations of
the 21cm forest. Because the presence of a strong x-ray background would make
the detection of 21cm line absorption impossible, the lack of absorption could
be used as a probe of the presence/intensity of the x-ray background and the
thermal history of the universe. Along a random line of sight LOFAR could
detect a global suppression of the spectrum from z>12, when the IGM is still
mostly neutral and cold, in contrast with the more well-defined, albeit broad,
absorption features visible at lower redshift. Sharp, strong absorption
features associated with rare, high density pockets of gas could be detected
also at z~7 along preferential lines of sight.Comment: 12 pages, 13 figures. MNRAS, in pres
Quantum Computing for Fusion Energy Science Applications
This is a review of recent research exploring and extending present-day
quantum computing capabilities for fusion energy science applications. We begin
with a brief tutorial on both ideal and open quantum dynamics, universal
quantum computation, and quantum algorithms. Then, we explore the topic of
using quantum computers to simulate both linear and nonlinear dynamics in
greater detail. Because quantum computers can only efficiently perform linear
operations on the quantum state, it is challenging to perform nonlinear
operations that are generically required to describe the nonlinear differential
equations of interest. In this work, we extend previous results on embedding
nonlinear systems within linear systems by explicitly deriving the connection
between the Koopman evolution operator, the Perron-Frobenius evolution
operator, and the Koopman-von Neumann evolution (KvN) operator. We also
explicitly derive the connection between the Koopman and Carleman approaches to
embedding. Extension of the KvN framework to the complex-analytic setting
relevant to Carleman embedding, and the proof that different choices of complex
analytic reproducing kernel Hilbert spaces depend on the choice of Hilbert
space metric are covered in the appendices. Finally, we conclude with a review
of recent quantum hardware implementations of algorithms on present-day quantum
hardware platforms that may one day be accelerated through Hamiltonian
simulation. We discuss the simulation of toy models of wave-particle
interactions through the simulation of quantum maps and of wave-wave
interactions important in nonlinear plasma dynamics.Comment: 42 pages; 12 figures; invited paper at the 2021-2022 International
Sherwood Fusion Theory Conferenc
Effectiveness of diagnosis and early treatment of ocular motility alterations in premature infants
Objective: Prematurity often results in important developmental sequelae of brain structures, particularly those involved in processing visual information, such as the optic nerve, primary visual cortex and visuomotor integration areas. The aim of this study is to analyse the functionality of the sensory and motor pathways of the visual system by means of an orthoptic-ophthalmological assessment. Materials and methods: In this retrospective study, 151 records were examined, covering a period from 2000 to 2020, of preterm patients with gestational age < 32 weeks and birth weight †1,500 g up to an average age of about 8 years, referred to the Centre for Paediatric Ophthalmology and Strabology of the Ophthalmology Clinic of the Policlinico Umberto I, La Sapienza University of Rome, who underwent a complete ophthalmological and orthoptic assessment including the following tests measurement of ocular deviations according to the Hirschberg method, Lang I-II test, Titmus Stereotest, objective convergence assessment and ocular motility examination. Results: From the charts reviewed, 24.5% (37/151) of patients had Retinopathy of the Premature (ROP); while 38% of the whole sample (57/151) had strabismic amblyopia, of the latter only 31.5% (18/57) had ROP. In 8% of patients (12/151) the stereoscopic sense was absent, in 45% (8/151) stereopsis was gross (> 60 seconds of arc). In addition, 20.52 % (31/151) had a manifest eye deviation. 7.28% (11/151) had hypermetropia in the right eye (RE); 7.95% (12/151) hypermetropia in the left eye (OS); 3.31% of the patients (5/151) had myopia in the RE; 2% (3/151), myopia in the left eye (LE). In addition, the study of ocular motility revealed varying degrees of alteration poorly correlated with prematurity status. Conclusion: It was found that amblyopia, stereopsis and objective convergence are more affected by ROP than strabismus, refractive defects and ocular motility, indicating that premature children are particularly susceptible to ophthalmological and orthoptical alterations
CPO and quantitative textural analyses within sheath folds
Acknowledgments This has been a multi-national collaboration from authors based in Europe, North America, Australia and India. Erasmus funding to GIA in 2018 enabled a visit to Catania leading to discussion and initiation of this project. The authors are grateful to Amarnath Dandapat for preparation of superpolished rock thin sections at the Department of Geology and Geophysics (IIT Kharagpur, India). Niloy Bhowmik is thanked for assistance with SEM-EBSD data generation in the Central Research Facility (IIT Kharagpur, India). E.F. thanks Sibio Carmelo for thin sections preparation at the University of Turin (Italy). Authors are grateful to ANSTO laboratory personnel for the preparation of specimens (funded proposals: P9835 with the title âSheath fold texture characterisationâ, principal scientist: E.F.; co-proposers: G.I.A. and V.L.; DB6749 with the title âTexture analysis of rocksâ, principal scientist: V.L.; co-proposer: E.F.; DB9606 with the title âA pilot experiment for texture characterisation in a sheath foldâ, principal scientist: E.F..; co-proposers: G.I.A. and V.L.). L.N. and R.G. report that this publication has been assigned the NRCan contribution number 20230109. Many thanks to Richard D. Law and an anonymous reviewer for their careful revision that substantially improved the original version of the manuscript. We also thanks Dr. T.K. Cawood from the Geological Survey of Canada for her useful comments on the drafted manuscript. The editorial handling by Fabrizio Agosta is greatly appreciated.Peer reviewedPublisher PD
Supernovae - Optical Precursors of Short Gamma-Ray Bursts
The probability of observing "supernova - gamma-ray burst" (GRB) pair events
and recurrent GRBs from one galaxy in a time interval of several years has been
estimated. Supernova explosions in binary systems accompanied by the formation
of a short-lived pair of compact objects can be the sources of such events. If
a short GRB is generated during the collision of a pair, then approximately
each of ~300 short GRBs with redshift z must have an optical precursor - a
supernova in the observer's time interval <2(1+z)yr. If the supernova explosion
has the pattern of a hypernova, then a successive observation of long and short
GRBs is possible. The scenario for the generation of multiple GRBs in
collapsing galactic nuclei is also discussed.Comment: 12 pages, 1 figure; this paper has the e-precursor arXiv:1101.3298
[astro-ph.HE
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