5,520 research outputs found
Fast calculation of real fluid properties for steam turbine CFD analysis with the new IAPWS standard on the spline-based table look-Up method (SBTL)
Workshop byl částečně podpořen projektem CZ.1.07/2.3.00/20.0139. Tento projekt je spolufinancován
Evropským sociálním fondem a státním rozpočtem České republiky
Separated Oscillatory Fields for High-Precision Penning Trap Mass Spectrometry
Ramsey's method of separated oscillatory fields is applied to the excitation
of the cyclotron motion of short-lived ions in a Penning trap to improve the
precision of their measured mass. The theoretical description of the extracted
ion-cyclotron-resonance line shape is derived out and its correctness
demonstrated experimentally by measuring the mass of the short-lived Ca
nuclide with an uncertainty of using the ISOLTRAP Penning
trap mass spectrometer at CERN. The mass value of the superallowed beta-emitter
Ca is an important contribution for testing the conserved-vector-current
hypothesis of the electroweak interaction. It is shown that the Ramsey method
applied to mass measurements yields a statistical uncertainty similar to that
obtained by the conventional technique ten times faster.Comment: 5 pages, 4 figures, 0 table
Link and subgraph likelihoods in random undirected networks with fixed and partially fixed degree sequence
The simplest null models for networks, used to distinguish significant
features of a particular network from {\it a priori} expected features, are
random ensembles with the degree sequence fixed by the specific network of
interest. These "fixed degree sequence" (FDS) ensembles are, however, famously
resistant to analytic attack. In this paper we introduce ensembles with
partially-fixed degree sequences (PFDS) and compare analytic results obtained
for them with Monte Carlo results for the FDS ensemble. These results include
link likelihoods, subgraph likelihoods, and degree correlations. We find that
local structural features in the FDS ensemble can be reasonably well estimated
by simultaneously fixing only the degrees of few nodes, in addition to the
total number of nodes and links. As test cases we use a food web, two protein
interaction networks (\textit{E. coli, S. cerevisiae}), the internet on the
autonomous system (AS) level, and the World Wide Web. Fixing just the degrees
of two nodes gives the mean neighbor degree as a function of node degree,
, in agreement with results explicitly obtained from rewiring. For
power law degree distributions, we derive the disassortativity analytically. In
the PFDS ensemble the partition function can be expanded diagrammatically. We
obtain an explicit expression for the link likelihood to lowest order, which
reduces in the limit of large, sparse undirected networks with links and
with to the simple formula . In a
similar limit, the probability for three nodes to be linked into a triangle
reduces to the factorized expression .Comment: 17 pages, includes 11 figures; first revision: shortened to 14 pages
(7 figures), added discussion of subgraph counts, deleted discussion of
directed network
A balancing act: Evidence for a strong subdominant d-wave pairing channel in
We present an analysis of the Raman spectra of optimally doped based on LDA band structure calculations and the
subsequent estimation of effective Raman vertices. Experimentally a narrow,
emergent mode appears in the () Raman spectra only below
, well into the superconducting state and at an energy below twice the
energy gap on the electron Fermi surface sheets. The Raman spectra can be
reproduced quantitatively with estimates for the magnitude and momentum space
structure of the s pairing gap on different Fermi surface sheets, as
well as the identification of the emergent sharp feature as a
Bardasis-Schrieffer exciton, formed as a Cooper pair bound state in a
subdominant channel. The binding energy of the exciton relative
to the gap edge shows that the coupling strength in this subdominant
channel is as strong as 60% of that in the dominant
channel. This result suggests that may be the dominant pairing
symmetry in Fe-based sperconductors which lack central hole bands.Comment: 10 pages, 6 Figure
Thermodynamic properties of sea air
Very accurate thermodynamic potential functions are available for fluid water, ice, seawater and humid air covering wide ranges of temperature and pressure conditions. They permit the consistent computation of all equilibrium properties as, for example, required for coupled atmosphere-ocean models or the analysis of observational or experimental data. With the exception of humid air, these potential functions are already formulated as international standards released by the International Association for the Properties of Water and Steam (IAPWS), and have been adopted in 2009 for oceanography by IOC/UNESCO. <br><br> In this paper, we derive a collection of formulas for important quantities expressed in terms of the thermodynamic potentials, valid for typical phase transitions and composite systems of humid air and water/ice/seawater. Particular attention is given to equilibria between seawater and humid air, referred to as "sea air" here. In a related initiative, these formulas will soon be implemented in a source-code library for easy practical use. The library is primarily aimed at oceanographic applications but will be relevant to air-sea interaction and meteorology as well. <br><br> The formulas provided are valid for any consistent set of suitable thermodynamic potential functions. Here we adopt potential functions from previous publications in which they are constructed from theoretical laws and empirical data; they are briefly summarized in the appendix. The formulas make use of the full accuracy of these thermodynamic potentials, without additional approximations or empirical coefficients. They are expressed in the temperature scale ITS-90 and the 2008 Reference-Composition Salinity Scale
Soft X-ray coronal spectra at low activity levels observed by RESIK
The quiet-Sun X-ray emission is important for deducing coronal heating
mechanisms, but it has not been studied in detail since the Orbiting Solar
Observatory (OSO) spacecraft era. Bragg crystal spectrometer X-ray observations
have generally concentrated on flares and active regions. The high sensitivity
of the RESIK (REntgenovsky Spectrometer s Izognutymi Kristalami) instrument on
the CORONAS-F solar mission has enabled the X-ray emission from the quiet
corona to be studied in a systematic way for the first time. Our aim is to
deduce the physical conditions of the non-flaring corona from RESIK line
intensities in several spectral ranges using both isothermal and multithermal
assumptions. We selected and analyzed spectra in 312 quiet-Sun intervals in
January and February 2003, sorting them into 5 groups according to activity
level. For each group, the fluxes in selected spectral bands have been used to
calculate values parameters for the best-fit that lead to a intensities
characteristic of each group. We used both isothermal and multitemperature
assumptions, the latter described by differential emission measure (DEM)
distributions. RESIK spectra cover the wavelength range (3.3-6.1 A). This
includes emission lines of highly ionized Si, S, Cl, Ar, and K, which are
suitable for evaluating temperature and emission measure, were used. The RESIK
spectra during these intervals of very low solar activity for the first time
provide information on the temperature structure of the quiet corona. Although
most of the emission seems to arise from plasma with a temperature between 2MK
and 3MK, there is also evidence of a hotter plasma (T approx. 10MK) with an
emission measure 3 orders smaller than the cooler component. Neither coronal
nor photospheric element abundances appear to describe the observed spectra
satisfactorily.Comment: Submitting 1 Latex and 7 figure file
Penning trap and vacuum noise
A number of comments are provided on Rogers's model experiment to measure the
circular Unruh vacuum noise by means of a hyperbolic Penning trap inside a
microwave cavity. It is suggested that cylindrical Penning traps, being
geometrically simpler, and controlled almost at the same level of accuracy as
the hyperbolic trap, might be a better choice for such an experiment. Besides,
the microwave modes of the trap itself, of known analytical structure, can be
directly used in trying to obtain measurable results for such a tiny noise
effect.Comment: 7 LaTex pages, published text and references with title
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