63,752 research outputs found
Inclusive angular distribution of alpha and Li fragments produced in the Fe-C and Fe-Pb collisions at 1.88 GeV/u
The LS (laboratory system) emission angles theta for 2188 and 298 Li fragments, produced inclusively in relativistic Fe-C and Fe-Pb collisions, have been measured in reference to incident Fe-ion beam tracks nearby in nuclear emulsion. An empirical differential frequency formula, dN(cot theta) = exp (a + b cot theta)d(cot theta) is obtained with the constant b approx. = -0.026 at 1.88 GeV/u, which seems to be independent on the kinds of target nucleus as well as on the kinds of projectile fragments
Fast Fight Detection
Action recognition has become a hot topic within computer vision. However, the action recognition community has focused mainly on relatively simple actions like clapping, walking, jogging, etc. The detection of specific events with direct practical use such as fights or in general aggressive behavior has been comparatively less studied. Such capability may be extremely useful in some video surveillance scenarios like prisons, psychiatric centers or even embedded in camera phones. As a consequence, there is growing interest in developing violence detection algorithms. Recent work considered the well-known Bag-of-Words framework for the specific problem of fight detection. Under this framework, spatio-temporal features are extracted from the video sequences and used for classification. Despite encouraging results in which high accuracy rates were achieved, the computational cost of extracting such features is prohibitive for practical applications. This work proposes a novel method to detect violence sequences. Features extracted from motion blobs are used to discriminate fight and non-fight sequences. Although the method is outperformed in accuracy by state of the art, it has a significantly faster computation time thus making it amenable for real-time applications
Canonical Quantization of the Self-Dual Model coupled to Fermions
This paper is dedicated to formulate the interaction picture dynamics of the
self-dual field minimally coupled to fermions. To make this possible, we start
by quantizing the free self-dual model by means of the Dirac bracket
quantization procedure. We obtain, as result, that the free self-dual model is
a relativistically invariant quantum field theory whose excitations are
identical to the physical (gauge invariant) excitations of the free
Maxwell-Chern-Simons theory. The model describing the interaction of the
self-dual field minimally coupled to fermions is also quantized through the
Dirac bracket quantization procedure. One of the self-dual field components is
found not to commute, at equal times, with the fermionic fields. Hence, the
formulation of the interaction picture dynamics is only possible after the
elimination of the just mentioned component. This procedure brings, in turns,
two new interaction terms, which are local in space and time while
non-renormalizable by power counting. Relativistic invariance is tested in
connection with the elastic fermion-fermion scattering amplitude. We prove that
all the non-covariant pieces in the interaction Hamiltonian are equivalent to
the covariant minimal interaction of the self-dual field with the fermions. The
high energy behavior of the self-dual field propagator corroborates that the
coupled theory is non-renormalizable. Certainly, the self-dual field minimally
coupled to fermions bears no resemblance with the renormalizable model defined
by the Maxwell-Chern-Simons field minimally coupled to fermions.Comment: 16 pages, no special macros, no corrections in the pape
Constraining the QCD phase diagram by tricritical lines at imaginary chemical potential
We present unambiguous evidence from lattice simulations of QCD with three
degenerate quark species for two tricritical points in the (T,m) phase diagram
at fixed imaginary \mu/T=i\pi/3 mod 2\pi/3, one in the light and one in the
heavy mass regime. These represent the boundaries of the chiral and
deconfinement critical lines continued to imaginary chemical potential,
respectively. It is demonstrated that the shape of the deconfinement critical
line for real chemical potentials is dictated by tricritical scaling and
implies the weakening of the deconfinement transition with real chemical
potential. The generalization to non-degenerate and light quark masses is
discussed.Comment: 4 pages, 5 figure
Spin relaxation of two-dimensional holes in strained asymmetric SiGe quantum wells
We analyze spin splitting of the two-dimensional hole spectrum in strained
asymmetric SiGe quantum wells (QWs). Based on the Luttinger Hamiltonian, we
obtain expressions for the spin-splitting parameters up to the third order in
the in-plane hole wavevector. The biaxial strain of SiGe QWs is found to be a
key parameter that controls spin splitting. Application to SiGe field-effect
transistor structures indicates that typical spin splitting at room temperature
varies from a few tenth of meV in the case of Si QW channels to several meV for
the Ge counterparts, and can be modified efficiently by gate-controlled
variation of the perpendicular confining electric field. The analysis also
shows that for sufficiently asymmetric QWs, spin relaxation is due mainly to
the spin-splitting related D'yakonov-Perel' mechanism. In strained Si QWs, our
estimation shows that the hole spin relaxation time can be on the order of a
hundred picoseconds at room temperature, suggesting that such structures are
suitable for p-type spin transistor applications as well
Voltage dependent conductance and shot noise in quantum microconstriction with single defects
The influence of the interference of electron waves, which are scattered by
single impurities and by a barrier on nonlinear conductance and shot noise of
metallic microconstriction is studied theoretically. It is shown that the these
characteristics are nonmonotonic functions on the applied bias.Comment: 18 pages,5 figure
The Revival of the Unified Dark Energy-Dark Matter Model ?
We consider the generalized Chaplygin gas (GCG) proposal for unification of
dark energy and dark matter and show that it admits an unique decomposition
into dark energy and dark matter components once phantom-like dark energy is
excluded. Within this framework, we study structure formation and show that
difficulties associated to unphysical oscillations or blow-up in the matter
power spectrum can be circumvented. Furthermore, we show that the dominance of
dark energy is related to the time when energy density fluctuations start
deviating from the linear behaviour.Comment: 6 pages, 4 eps figures, Revtex4 style. New References are added. Some
typos are corrected. Conclusions remain the sam
Photonic Crystal Cavities and Waveguides
Recently, it has also become possible to microfabricate high reflectivity mirrors by creating two- and three-dimensional periodic structures. These periodic "photonic crystals" can be designed to open up frequency bands within which the propagation of electromagnetic waves is forbidden irrespective of the propagation direction in space and define photonic bandgaps. When combined with high index contrast slabs in which light can be efficiently guided, microfabricated two-dimensional photonic bandgap mirrors provide us with the geometries needed to confine and concentrate light into extremely small volumes and to obtain very high field intensities. Here we show the use of these "artificially" microfabricated crystals in functional nonlinear optical devices, such as lasers, modulators, and waveguides
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