6,001 research outputs found
Surface Acoustic Wave Electromagnetic Transducer Modeling and Design for NDE Applications
I\u27ll be talking mainly about surface acoustic wave electromagnetic transducers, EMT\u27s. These are useful for examining near surface flaws, defects or stress gradients, and they are also very useful for examining rough or painted, or dirty, or hot, or curved surfaces, not necessarily in that order. Recently, this technology has developed to the point where it\u27s possible to fabricate identical transducers. What I\u27d like to show this morning is that it\u27s also very straightforward to design them. There is quite a large flexibility in the design of these transducers, and they give very clean, reproducible and predictable characteristics, which are, of course, what you need for reproducible quantitative NDE measurements. I\u27ll be describing the work we did last year, the development of a model for these transducers. This work was done by myself, Harold Frost, and Jim Sethares
Graphs without proper subgraphs of minimum degree 3 and short cycles
We study graphs on n vertices which have 2n−2 edges and no proper induced subgraphs of minimum degree 3. Erdős, Faudree, Gyárfás, and Schelp conjectured that such graphs always have cycles of lengths 3,4,5,...,C(n) for some function C(n) tending to in finity. We disprove this conjecture, resolve a related problem about leaf-to-leaf path lengths in trees, and characterize graphs with n vertices and 2n−2 edges, containing no proper subgraph of minimum degree 3
Proof of Kolmogorovian Censorship
Many argued (Accardi and Fedullo, Pitowsky) that Kolmogorov's axioms of
classical probability theory are incompatible with quantum probabilities, and
this is the reason for the violation of Bell's inequalities. Szab\'o showed
that, in fact, these inequalities are not violated by the experimentally
observed frequencies if we consider the real, ``effective'' frequencies. We
prove in this work a theorem which generalizes this result: ``effective''
frequencies associated to quantum events always admit a Kolmogorovian
representation, when these events are collected through different experimental
set ups, the choice of which obeys a classical distribution.Comment: 19 pages, LaTe
The ratio FK/Fpi in QCD
We determine the ratio FK/Fpi in QCD with Nf=2+1 flavors of sea quarks, based
on a series of lattice calculations with three different lattice spacings,
large volumes and a simulated pion mass reaching down to about 190 MeV. We
obtain FK/Fpi=1.192 +/- 0.007(stat) +/- 0.006(syst). This result is then used
to give an updated value of the CKM matrix element |Vus|. The unitarity
relation for the first row of this matrix is found to be well observed.Comment: 15 pages, 4 figures, 2 table
Medical Diagnostic Ultrasound
As early as 250 BCE, captains of ancient Greek ships would drop lead weights overboard to provide an estimate of water depth. They would count until those “sounders” produced an audible thud and in that way measure the propagation time of the falling weight. Even though the practice has given way to other technologies for sounding, one still hears the phrase “to sound something out.” In the 17th century, Isaac Newton became fascinated with sound propagation and was one of the first to describe relationships between the speed of sound and measurable properties of the propagation medium, such as density and pressure. Section 8 of Book 2 of the Principia, for example, is devoted to “the motion propagated through fluids” and includes the proposition that the sound speed is given by the square root of the ratio of the “elastic force” to the density of the medium
Exchange effects on electron scattering through a quantum dot embedded in a two-dimensional semiconductor structure
We have developed a theoretical method to study scattering processes of an
incident electron through an N-electron quantum dot (QD) embedded in a
two-dimensional (2D) semiconductor. The generalized Lippmann-Schwinger
equations including the electron-electron exchange interaction in this system
are solved for the continuum electron by using the method of continued
fractions (MCF) combined with 2D partial-wave expansion technique. The method
is applied to a one-electron QD case. Cross-sections are obtained for both the
singlet and triplet couplings between the incident electron and the QD electron
during the scattering. The total elastic cross-sections as well as the
spin-flip scattering cross-sections resulting from the exchange potential are
presented. Furthermore, inelastic scattering processes are also studied using a
multichannel formalism of the MCF.Comment: 11 pages, 4 figure
Precision computation of the kaon bag parameter
Indirect CP violation in K \rightarrow {\pi}{\pi} decays plays a central role
in constraining the flavor structure of the Standard Model (SM) and in the
search for new physics. For many years the leading uncertainty in the SM
prediction of this phenomenon was the one associated with the nonperturbative
strong interaction dynamics in this process. Here we present a fully controlled
lattice QCD calculation of these effects, which are described by the neutral
kaon mixing parameter B_K . We use a two step HEX smeared clover-improved
Wilson action, with four lattice spacings from a\approx0.054 fm to
a\approx0.093 fm and pion masses at and even below the physical value.
Nonperturbative renormalization is performed in the RI-MOM scheme, where we
find that operator mixing induced by chiral symmetry breaking is very small.
Using fully nonperturbative continuum running, we obtain our main result
B_K^{RI}(3.5GeV)=0.531(6)_{stat}(2)_{sys}. A perturbative 2-loop conversion
yields B_K^{MSbar-NDR}(2GeV)=0.564(6)_{stat}(3)_{sys}(6)_{PT}, which is in good
agreement with current results from fits to experimental data.Comment: 10 pages, 7 figures. v2: Added one reference and one figure, replaced
2 figures for better readability and updated ensembles, conclusions
unchanged. Final, published versio
A new sdO+dM binary with extreme eclipses and reflection effect
We report the discovery of a new totally-eclipsing binary (RA=06:40:29.11;
Dec=+38:56:52.2; J=2000.0; Rmax=17.2 mag) with an sdO primary and a strongly
irradiated red dwarf companion. It has an orbital period of
Porb=0.187284394(11) d and an optical eclipse depth in excess of 5 magnitudes.
We obtained two low-resolution classification spectra with GTC/OSIRIS and ten
medium-resolution spectra with WHT/ISIS to constrain the properties of the
binary members. The spectra are dominated by H Balmer and He II absorption
lines from the sdO star, and phase-dependent emission lines from the irradiated
companion. A combined spectroscopic and light curve analysis implies a hot
subdwarf temperature of Teff(spec) = 55 000 +/- 3000K, surface gravity of log
g(phot) = 6.2 +/- 0.04 (cgs) and a He abundance of log(nHe/nH) = -2.24 +/-
0.40. The hot sdO star irradiates the red-dwarf companion, heating its
substellar point to about 22 500K. Surface parameters for the companion are
difficult to constrain from the currently available data: the most remarkable
features are the strong H Balmer and C II-III lines in emission. Radial
velocity estimates are consistent with the sdO+dM classification. The
photometric data do not show any indication of sdO pulsations with amplitudes
greater than 7mmag, and Halpha-filter images do not provide evidence of the
presence of a planetary nebula associated with the sdO star.Comment: 13 pages, 5 figures; accepted for publication in Ap
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