2,396,255 research outputs found
Multichannel spectroscopy guide
System makes use of diverging duct walls for conducting the light from entrance slips to the conductors by means of multiple reflectors. This system simultaneously records, photoelectrically, the intensities of several closely spaceed narrow wavelengths in the ultraviolet and infrared areas of the spectrum
Strangeness Balance in HADES Experiments and the Xi- Enhancement
HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are
analyzed within a minimal statistical model. The total negative strangeness
content is fixed by the observed K^+ multiplicities on event-by-event basis.
Particles with negative strangeness are assumed to remain in chemical
equilibrium with themselves and in thermal equilibrium with the environment
until a common freeze-out. Exact strangeness conservation in each collision
event is explicitly preserved. This implies that Xi baryons can be released
only in events where two or more kaons are produced. An increase of the
fireball volume due to application of a centrality trigger in HADES experiments
is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and
Sigma/K+ can be satisfactorily described provided in-medium potentials are
taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be
significantly smaller compared to the measured value (8 times lower than the
experimental median value and 3 times lower than the lower error bar). Various
scenarios to explain observed Xi enhancement are discussed. Arguments are given
in favor of the Xi production in direct reactions. The rates of the possible
production processes are estimated and compared.Comment: 13 pages, 3 figure
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Numerical treatment of seismic accelerograms and of inelastic seismic structural responses using harmonic wavelets
The harmonic wavelet transform is employed to analyze various kinds of nonstationary signals common in aseismic design. The effectiveness of the harmonic wavelets for capturing the temporal evolution of the frequency content of strong ground motions is demonstrated. In this regard, a detailed study of important earthquake accelerograms is undertaken and smooth joint time-frequency spectra are provided for two near-field and two far-field records; inherent in this analysis is the concept of the mean instantaneous frequency. Furthermore, as a paradigm of usefulness for aseismic structural purposes, a similar analysis is conducted for the response of a 20-story steel frame benchmark building considering one of the four accelerograms scaled by appropriate factors as the excitation to simulate undamaged and severely damaged conditions for the structure. The resulting joint time-frequency representation of the response time histories captures the influence of nonlinearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event. In this context, the potential of the harmonic wavelet transform as a detection tool for global structural damage is explored in conjunction with the concept of monitoring the mean instantaneous frequency of records of critical structural responses
D-instantons and multiparticle production in N=4 SYM
N=4 Super-symmetric Yang-Mills theory (N=4 SYM) in the strong coupling regime
has been successfully applied (through the AdS/CFT correspondence) to the
description of strongly coupled plasma which is a multiparticle state. Yet, the
high-energy scattering in the strong coupling limit of N=4 SYM is purely
elastic, so this multiparticle final state can never be produced: this is
because in this limit the theory is dual to weak supergravity, and the dominant
interaction is the elastic graviton exchange. Here we propose a resolution of
this dilemma by considering the contribution of D-instantons in bulk
space to the scattering amplitude. We argue that D-instantons coupled to
dilatons and axions are responsible for multiparticle production in strongly
coupled N=4 SYM, and the corresponding cross section increases with energy. We
evaluate the intercept and the slope of the corresponding Pomeron trajectory in
terms of the typical size of the D-instanton, and argue that the resulting
physical picture may resemble the real world.Comment: 22 pp and 11 figures in the eps forma
A cryocooler for applications requiring low magnetic and mechanical interference
A very low-power, low-interference Stirling cryocooler is being developed based on principles and techniques described in several previous publications over the last four years. It differs in several important details from those built previously. It uses a tapered displacer based upon an analytical optimization procedure. The displacer is driven by an auxiliary piston and cylinder (rather than by mechanical linkage) using some of the working fluid itself to provide the driving force. This provides smooth, vibration-free motion, and, more importantly, allows complete mechanical and spatial separation of the cryostat from the pressure-wave generator. Either of two different pressure-wave generators can be used. One is a non-contaminating, unlubricated ceramic piston and cylinder. The other is a compressed-air-operated rubber diaphragm with motor-driven valves to cycle the pressure between appropriate limits
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