6,453 research outputs found
Twist-2 Generalized TMDs and the Spin/Orbital Structure of the Nucleon
Generalized transverse-momentum dependent parton distributions (GTMDs) encode
the most general parton structure of hadrons. Here we focus on two twist-2
GTMDs which are denoted by and in parts of the literature.
As already shown previously, both GTMDs have a close relation to orbital
angular momentum of partons inside a hadron. However, recently even the mere
existence of and has been doubted. We explain why this
claim does not hold. We support our model-independent considerations by
calculating the two GTMDs in the scalar diquark model and in the quark-target
model, where we also explicitly check the relation to orbital angular momentum.
In addition, we compute and at large transverse momentum in
perturbative Quantum Chromodynamics and show that they are nonzero.Comment: 29 pages, 6 figures; two clarifications and a reference added;
version to appear in Phys. Rev.
Determination of the lowest energy structure of Ag from first-principles calculations
The ground-state electronic and structural properties, and the electronic
excitations of the lowest energy isomers of the Ag cluster are calculated
using density functional theory (DFT) and time-dependent DFT (TDDFT) in real
time and real space scheme, respectively. The optical spectra provided by TDDFT
predict that the D dodecahedron isomer is the structural minimum of
Ag cluster. Indeed, it is borne out by the experimental findings.Comment: 4 pages, 2 figures. Accepted in Physical Review A as a brief repor
Device and Method for Digital-To-Analog Transformations and Reconstructions of Multi-Channel Electrocardiograms
The present invention includes a method and apparatus for digital to analog conversion and reconstruction of multichannel electrocardiograms. The method may include receiving digital information representative of a plurality of independent signals, producing a plurality of analog outputs from said digital information wherein a first analog output is designated as a common reference, and imposing a predetermined voltage on a second analog output with respect to said common reference, which provides for a substantial recreation of the original independent signals. The apparatus may comprise a processor operable for receiving digital information representative of independent lead signals from a first ECG machine and digital to analog circuitry for substantially reproducing the original lead signals for analysis on a second ECG machine for convenient and efficient second opinions of cardiac data
Detection of an optical filament in the Monogem Ring
The Monogem Ring is a huge bright soft X-ray enhancement with a diameter of ~
25\degr. This 0.3 kpc distant structure is a peculiar Galactic supernova
remnant in that it is obviously visible only in X-rays, due to its expansion
into a region of extremely low ambient density: hence, practically no optical
emission or a neutral HI shell was expected to be detectable. - Here we report
on the discovery of a very faint arc-like nebula on a POSS II R film copy, at
the south-eastern borders of the MR. Spectroscopy revealed this filament to
have a very large [SII] 6716+6731/Halpha ratio of up to ~ 1.8,
indicating shock excitation, and a low density of N_e <100 cm^{-3}. There is no
hint of [OIII] emission in the spectra. On deep wide-field direct images in
Halpha and in [SII] the nebula appears as a ~ 20 arcmin long, thin (~ 1
arcmin), structured filament, stretching N-S. We believe that this filament
belongs to the MR and became visible due to the interaction of the expanding
remnant with a mild density increase in the interstellar medium. Only one other
possible optical filament of the MR has been reported in the literature, but no
spectrum was provided.Comment: 6 pages, 4 figures, of which 2 in jpeg format and degraded because of
size constraints. Accepted for publication in A&
A simple method for isolation of PCR fragments from silver-stained polyacrylamide gels by scratching with a fine needle
This project investigated how NoSQL databases can be used together with a logical layer, instead of a relational database with separated backend logic, to search for products with customer specific constraints in an e-commerce scenario. The motivation behind moving from a relational database was the scalability issues and increased read latencies experienced as the data increased. The work resulted in a framework called Cauldron that uses pipelines a sequence of execution steps to expose its data stored in an in-memory key-value store and a document database. Cauldron uses write replication between distributed instances to increase read throughput at the cost of write latency. A product database with customer specific constraints was implemented using Cauldron to compare it against an existing solution based on a relational database. The new product database can serve search queries 10 times faster in the general case and up to 25 times faster in extreme cases compared to the existing solution.Projektet undersökte hur NoSQL databaser tillsammans med ett logiskt lager, istället för en relationsdatabas med separat backend logik, kan användas för att söka på produkter med kundunika restriktioner. Motivationen till att byta ut relationsdatabasen berodde på skalbarhetsproblem och långsammare svarstider när datamängden ökade. Arbetet resulterade i ett ramverk vid namn Cauldron som använder pipelines sammankopplade logiska steg för att exponera sin data från en minnesbunden nyckel-värde-databas och en dokumentdatabas. Cauldron använder replikering mellan distribuerade instanser för att öka läsgenomstömmningen på bekostnad av högre skrivlatenser. En produktdatabas med kundunika restriktioner implementerades med hjälp av Cauldron för att jämföra den mot en befintlig lösning baserad på en relationsdatabas. Den nya databasen kan besvara sökförfrågningar 10 gånger snabbare i normalfallen och upp till 25 gånger snabbare i extremfallen jämfört med den befintliga lösningen
Extreme UV QSOs
We present a sample of spectroscopically confirmed QSOs with FUV-NUV color
(as measured by GALEX photometry) bluer than canonical QSO templates and than
the majority of known QSOs. We analyze their FUV to NIR colors, luminosities
and optical spectra. The sample includes a group of 150 objects at low redshift
(z 0.5), and a group of 21 objects with redshift 1.7z2.6. For the low
redshift objects, the "blue" FUV-NUV color may be caused by enhanced Ly
emission, since Ly transits the GALEX FUV band from z=0.1 to z=0.47.
Synthetic QSO templates constructed with Ly up to 3 times stronger than
in standard templates match the observed UV colors of our low redshift sample.
The H emission increases, and the optical spectra become bluer, with
increasing absolute UV luminosity. The UV-blue QSOs at redshift about 2, where
the GALEX bands sample restframe about 450-590A (FUV) and about 590-940A(NUV),
are fainter than the average of UV-normal QSOs at similar redshift in NUV,
while they have comparable luminosities in other bands. Therefore we speculate
that their observed FUV-NUV color may be explained by a combination of steep
flux rise towards short wavelengths and dust absorption below the Lyman limit,
such as from small grains or crystalline carbon. The ratio of Ly to CIV
could be measured in 10 objects; it is higher (30% on average) than for
UV-normal QSOs, and close to the value expected for shock or collisional
ionization. FULL VERSION AVAILABLE FROM AUTHOR'S WEB SITE:
http://dolomiti.pha.jhu.edu/papers/2009_AJ_Extreme_UV_QSOs.pdfComment: Astronomical Journal, in pres
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