2,883 research outputs found
One-Loop QCD Spin Chain and its Spectrum
We study the renormalization of gauge invariant operators in large Nc QCD. We
compute the complete matrix of anomalous dimensions to leading order in the 't
Hooft coupling and study its eigenvalues. Thinking of the mixing matrix as the
Hamiltonian of a generalized spin chain we find a large integrable sector
consisting of purely gluonic operators constructed with self-dual field
strengths and an arbitrary number of derivatives. This sector contains the true
ground state of the spin chain and all the gapless excitations above it. The
ground state is essentially the anti-ferromagnetic ground state of a XXX1 spin
chain and the excitations carry either a chiral spin quantum number with
relativistic dispersion relation or an anti-chiral one with non-relativistic
dispersion relation.Comment: 54 pages, v2: minor changes, references adde
DYNAMIC STABILIZATION IN COLLEGIATE FEMALE VOLLEYBALL PLAYERS: EFFECTS OF LEG DOMINANCE AND OFF-SEASON
Adequate dynamic stabilization can be a key factor in preventing non-contact lower extremity injuries, especially in sports which require agile movements, such as volleyball. Individuals with functional ankle instability (FAI) took longer to stabilize in static and dynamic tasks when examining anterior/posterior (AP) and medial/lateral (ML) responses (Ross & Guskiewicz, 2004). In an effort to detect FAI in athletes, differences in time to stabilization (TTS) between post- and pre-seasons and between dominant and non-dominant legs should be identified. The purpose of the study was to identify those differences (post- vs. pre-season; leg dominance) across various hopping directions. It was hypothesized that the pre-season test and dominant leg conditions exhibit greater stability (i.e., shorter TTS) in all hopping directions
Carbon Flashes in the Heavy Element Ocean on Accreting Neutron Stars
We show that burning of a small mass fraction of carbon in a neutron star
ocean is thermally unstable at low accumulated masses when the ocean contains
heavy ashes from the hydrogen burning rapid proton (rp) process. The key to
early unstable ignition is the low thermal conductivity of a heavy element
ocean. The instability requires accretion rates in excess of one-tenth the
Eddington limit when the carbon mass fraction is 0.1 or less. The unstable
flashes release 10^{42} to 10^{43} ergs over hours to days, and are likely the
cause of the recently discovered large Type I X-ray bursts (so-called
``superbursts'') from six Galactic low mass X-ray binaries. In addition to
explaining the energetics, recurrence times, and durations of the superbursts,
these mixed carbon/heavy element flashes have an accretion rate dependence of
unstable burning similar to that observed. Though the instability is present at
accretion rates near Eddington, there is less contrast with the accretion
luminosity there, explaining why most detections are made at accretion rates
between 0.1 and 0.3 Eddington. Future comparisons of time dependent
calculations with observations will provide new insights into the rp process.Comment: Submitted to Astrophysical Journal Letters (6 pages, 3 figures
The Accretion Flows and Evolution of Magnetic Cataclysmic Variables
We have used a model of magnetic accretion to investigate the accretion flows
of magnetic cataclysmic variables. Numerical simulations demonstrate that four
types of flow are possible: discs, streams, rings and propellers. The
fundamental observable determining the accretion flow, for a given mass ratio,
is the spin-to-orbital period ratio of the system. If IPs are accreting at
their equilibrium spin rates, then for a mass ratio of 0.5, those with
Pspin/Porb < 0.1 will be disc-like, those with 0.1 < Pspin/Porb < 0.6 will be
stream-like, and those with Pspin/Porb ~ 0.6 will be ring-like. The spin to
orbital period ratio at which the systems transition between these flow types
increases as the mass ratio of the stellar components decreases.
For the first time we present evolutionary tracks of mCVs which allow
investigation of how their accretion flow changes with time. As systems evolve
to shorter orbital periods and smaller mass ratios, in order to maintain spin
equilibrium, their spin-to-orbital period ratio will generally increase. As a
result, the relative occurrence of ring-like flows will increase, and the
occurrence of disc-like flows will decrease, at short orbital periods. The
growing number of systems observed at high spin-to-orbital period ratios with
orbital periods below 2h, and the observational evidence for ring-like
accretion in EX Hya, are fully consistent with this picture.Comment: Accepted for publication in ApJ. 6 figures - included here at low
resolutio
The N=8 Supergravity Hamiltonian as a Quadratic Form
We conjecture that the light-cone Hamiltonian of N=8 Supergravity can be
expressed as a quadratic form. We explain why this rewriting is unique to
maximally supersymmetric theories. The N=8 quartic interaction vertex is
constructed and used to verify that this conjecture holds to second order in
the coupling constant.Comment: 23 pages, minor corrections in appendix
THE EFFECT OF COMPRESSION TIGHTS AND DURATION OF TESTING ON CONTINUOUS JUMPING MECHANICAL POWER
INTRODUCTION: In order to improve their performance, athletes seek advancements in technology, such as clothing. Manufacturers of compression tights, advertise that their product adds support to lower extremity musculature, thus may slow the onset of fatigue. Few scientific studies, however, have been conducted to identify how advancements in apparel influence an athlete’s performance (Kraemer et al., 1996). The purpose of the present study was to identify the effects of compression tights on mechanical power for continuous jumping. Secondly, the effect of duration on the mechanical power output by using Bosco’s method (1983) over 15, 30, 45, and 60 sec time-frames, as well as the interaction between apparel and duration
SYNTHESIS OF STAR POLY(4-VINYLPYRIDINE) ARCHITECTURE BY NITROXIDE MEDIATED POLYMERISATION
This study proposed multifunctional alkoxyamine 2-({tert-butyl [[1-
(diethoxyphosphoryl)-2,2-dimethylpropyl]amino}oxy)-2-methylpropanoic acid
(MAMA-SG1) initiators for the ‘grafting-from’ method to obtain star architecture of
poly 4-vinylpyridine (P4VP) from JEFFAMINE®. The structure of macroinitiator
was confirmed by amide bond present in NMR and FTIR spectroscopy.
Furthermore, the macroinitiator was used to polymerise 4VP. P4VP from
JEFFAMINE-SG1 shows a monomodal peak in the SEC chromatogram, indicating
more control polymerisation process
GPS radio occultation with CHAMP and SAC-C: global monitoring of thermal tropopause parameters
In this study the global lapse-rate tropopause (LRT) pressure, temperature, potential temperature, and sharpness are discussed based on Global Positioning System (GPS) radio occultations (RO) from the German CHAMP (CHAllenging Minisatellite Payload) and the U.S.-Argentinian SAC-C (Satelite de Aplicaciones Cientificas-C) satellite missions. Results with respect to seasonal variations are compared with operational radiosonde data and ECMWF (European Centre for Medium-Range Weather Forecast) operational analyses. Results on the tropical quasi-biennial oscillation (QBO) are updated from an earlier study. CHAMP RO data are available continuously since May 2001 with on average 150 high resolution temperature profiles per day. SAC-C data are available for several periods in 2001 and 2002. In this study temperature data from CHAMP for the period May 2001-December 2004 and SAC-C data from August 2001-October 2001 and March 2002-November 2002 were used, respectively. The bias between GPS RO temperature profiles and radiosonde data was found to be less than 1.5K between 300 and 10hPa with a standard deviation of 2-3K. Between 200-20hPa the bias is even less than 0.5K (2K standard deviation). The mean deviations based on 167699 comparisons between CHAMP/SAC-C and ECMWF LRT parameters are (-2.1±37.1)hPa for pressure and (0.1±4.2)K for temperature. Comparisons of LRT pressure and temperature between CHAMP and nearby radiosondes (13230) resulted in (5.8±19.8)hPa and (-0.1±3.3)K, respectively. The comparisons between CHAMP/SAC-C and ECMWF show on average the largest differences in the vicinity of the jet streams with up to 700m in LRT altitude and 3K in LRT temperature, respectively. The CHAMP mission generates the first long-term RO data set. Other satellite missions will follow (GRACE, COSMIC, MetOp, TerraSAR-X, EQUARS) generating together some thousand temperature profiles daily
- …