30,145 research outputs found
Non-relativistic classical mechanics for spinning particles
We study the classical dynamics of non-relativistic particles endowed with
spin. Non-vanishing Zitterbewegung terms appear in the equation of motion also
in the small momentum limit. We derive a generalized work-energy theorem which
suggests classical interpretations for tunnel effect and quantum potential
Bs Mixing, DeltaGamma_s and CP Violation
We discuss the results from the Tevatron experiments on mixing and {\sf CP}
violation in the system, with particular emphasis to the
first measurements of the decay width-difference and the {\sf
CP} violating phase using flavor tagging information. We also briefly
review the charge asymmetry measurements in semileptonic decays and in
decays.Comment: 6 pages, 4 figures, Pub. Proceedings of the XLIIIrd Rencontres de
Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy,
March 1-8, 200
Balloon-borne three-meter telescope for far-infrared and submillimeter astronomy
The study and revision of the gimbal design of the Three-Meter Balloon Borne Telescope (TMBBT) is discussed. Efforts were made to eliminate the alignment and limited rotation problems inherent in the flex-pivot design. A new design using ball bearings to replace the flex-pivots was designed and its performance analyzed. An error analysis for the entire gondola pointing system was also prepared
A Formal Sociologic Study of Free Will
We make a formal sociologic study of the concept of free will. By using the
language of mathematics and logic, we define what we call everlasting
societies. Everlasting societies never age: persons never age, and the goods of
the society are indestructible. The infinite history of an everlasting society
unfolds by following deterministic and probabilistic laws that do their best to
satisfy the free will of all the persons of the society.
We define three possible kinds of histories for everlasting societies:
primitive histories, good histories, and golden histories. In primitive
histories, persons are inherently selfish, and they use their free will to
obtain the personal ownerships of all the goods of the society. In good
histories, persons are inherently good, and they use their free will to
distribute the goods of the society. In good histories, a person is not only
able to desire the personal ownership of goods, but is also able to desire that
a good be owned by another person. In golden histories, free will is bound by
the ethic of reciprocity, which states that "you should wish upon others as you
would like others to wish upon yourself". In golden societies, the ethic of
reciprocity becomes a law that partially binds free will, and that must be
abided at all times. In other words, the verb "should" becomes the verb "must"
Binarity as the solution to the stellar evolution enigma posed by NGC 6791
Binary evolution is investigated as the source for the extreme horizontal
branch (EHB) stars in the old and metal rich open cluster NGC~6791. Employing
an updated version of our binary stellar evolution code we demonstrate that EHB
stars naturally emerge from the common envelope phase. In sum, the binary model
reproduces the observed (, ) and temporal properties of
the EHB over-density tied to NGC 6971, without needing an ad-hoc and anomalous
mass-loss prescription.Comment: 9 pages, 5 eps figures, accepted for publication in the Astrophysical
Journal Letter
Time Evolution and the Nature of the Near-Infrared Jets in GRS1915+105
We observed the galactic microquasar GRS1915+105 in the K (m) band
on October 16 and 17, 1995 UTC using the COB infrared (IR) imager on the Kitt
Peak National Observatory 2.1-m telescope with a 0.2-arcsec/pixel plate scale
and under good (-arcsec) seeing conditions. Using a neighboring star
in the image frames to determine the point spread function (PSF), we
PSF-subtract the images of GRS1915+105. We find no evidence of extended
emission such as the apparent near-IR jets seen by Sams et al. (1996) in July,
1995. Simple modelling of the star + jet structure allows us to place an upper
limit on any similar emission at that position of at the 95%
confidence level, as compared to as seen by Sams et al. (1996). This
lack of extended IR flux during continued hard X-ray flaring activity confirms
the hypothesis that the extended IR emission arises from the superluminal
radio-emitting jets rather than reprocessing of the X-ray emission on other
structures around the compact central object. Given the large apparent velocity
of the radio-emitting jets, by the time of our observations the Sams et al.
feature would have moved arcsec from GRS1915+105, and we can place a limit
of (95% confidence level) on any infrared emission in this region. We
can thus place an upper limit on the radiative timescale of the feature of
days, which is consistent with synchrotron jet emission.Comment: 10 pages, 3 figures; submitted to ApJ Letter
Covariant Formulation of the Invariant Measure for the Mixmaster Dynamics
We provide a Hamiltonian analysis of the Mixmaster Universe dynamics showing
the covariant nature of its chaotic behavior with respect to any choice of time
variable. We construct the appropriate invariant measure for the system (which
relies on the existence of an ``energy-like'' constant of motion) without
fixing the time gauge, i.e. the corresponding lapse function. The key point in
our analysis consists of introducing generic Misner-Chitr\'e-like variables
containing an arbitrary function, whose specification allows one to set up the
same dynamical scheme in any time gauge.Comment: 11 pages, 1 figur
The determination of velocity fluctuations in shear flows by means of PTV
The present study considers the effects of some parameters in image acquisition and analysis procedures in connection with the use of the Particle Tracking Velocimetry (PTV) technique. The interest is focused towards flow fields with large velocity gradients as shear flows; in the paper, velocity measurements by PTV are performed in a turbulent channel flow upstream and downstream of a backward facing step at low Reynolds numbers. This is a flow field largely investigated in the past with available numerical and experimental to make comparison with. Among the possible parameters to be chosen in particle image acquisition and analysis, the following are considered
- the concentration of seeding particles in the imaged region;
- the spatial resolution of the image acquisition system;
- the parameters used in the image analysis algorithm
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