89 research outputs found
New method for the quantum ground states in one dimension
A simple, general and practically exact method is developed to calculate the
ground states of 1D macroscopic quantum systems with translational symmetry.
Applied to the Hubbard model, a modest calculation reproduces the Bethe Ansatz
results
Entanglement perturbation theory for the quantum ground states in two dimensions
A simple, general and practically exact method, Entanglement Perturbation
Theory (EPT), is formulated to calculate the ground states of 2D macroscopic
quantum systems with translational symmetry. An emphasis will be placed on the
applicability of EPT to fermions. We will discuss some preliminary evidences
which indicate a potential of EPT
Photonic realization of the relativistic Kronig-Penney model and relativistic Tamm surface states
Photonic analogues of the relativistic Kronig-Penney model and of
relativistic surface Tamm states are proposed for light propagation in fibre
Bragg gratings (FBGs) with phase defects. A periodic sequence of phase slips in
the FBG realizes the relativistic Kronig-Penney model, the band structure of
which being mapped into the spectral response of the FBG. For the semi-infinite
FBG Tamm surface states can appear and can be visualized as narrow resonance
peaks in the transmission spectrum of the grating
Euler-Calogero-Moser system from SU(2) Yang-Mills theory
The relation between SU(2) Yang-Mills mechanics, originated from the
4-dimensional SU(2) Yang-Mills theory under the supposition of spatial
homogeneity of the gauge fields, and the Euler-Calogero-Moser model is
discussed in the framework of Hamiltonian reduction. Two kinds of reductions of
the degrees of freedom are considered: due to the gauge invariance and due to
the discrete symmetry. In the former case, it is shown that after elimination
of the gauge degrees of freedom from the SU(2) Yang-Mills mechanics the
resulting unconstrained system represents the ID_3 Euler-Calogero-Moser model
with an external fourth-order potential. Whereas in the latter, the IA_6
Euler-Calogero-Moser model embedded in an external potential is derived whose
projection onto the invariant submanifold through the discrete symmetry
coincides again with the SU(2) Yang-Mills mechanics. Based on this connection,
the equations of motion of the SU(2) Yang-Mills mechanics in the limit of the
zero coupling constant are presented in the Lax form.Comment: Revtex, 14 pages, no figures. Abstract changed, strata analysis have
been included, typos corrected, references adde
Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
We report a first measurement for ultra-high energy cosmic rays of the
correlation between the depth of shower maximum and the signal in the water
Cherenkov stations of air-showers registered simultaneously by the fluorescence
and the surface detectors of the Pierre Auger Observatory. Such a correlation
measurement is a unique feature of a hybrid air-shower observatory with
sensitivity to both the electromagnetic and muonic components. It allows an
accurate determination of the spread of primary masses in the cosmic-ray flux.
Up till now, constraints on the spread of primary masses have been dominated by
systematic uncertainties. The present correlation measurement is not affected
by systematics in the measurement of the depth of shower maximum or the signal
in the water Cherenkov stations. The analysis relies on general characteristics
of air showers and is thus robust also with respect to uncertainties in
hadronic event generators. The observed correlation in the energy range around
the `ankle' at differs significantly from
expectations for pure primary cosmic-ray compositions. A light composition made
up of proton and helium only is equally inconsistent with observations. The
data are explained well by a mixed composition including nuclei with mass . Scenarios such as the proton dip model, with almost pure compositions, are
thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray
flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Air-exposure behavior: a restricted or a common conduct among intertidal hermit crabs?
A new behavior related to shell care was recently reported for the intertidal hermit crab Clibanarius erythropus (Latreille, 1818) in the Gulf of Cádiz (southwestern Europe). It also has been observed in other species of the diogenid genera Clibanarius Dana, 1952, and Calcinus Dana, 1951, however, it has not been described as an active behavior. In the present study, intertidal hermit crabs from different species and localities were sampled to assess if air-exposure is a shell cleaning behavior restricted to some species of intertidal hermit crabs or if it is a more generalized behavior among species inhabiting intertidal habitats. The results revealed that air-exposure is an active behavior in species of Clibanarius and Calcinus, since we observed it also in Clibanarius albidigitus Nobili, 1901, and Calcinus obscurus Stimpson, 1859, from the Pacific coast of Costa Rica, although not in other intertidal species studied by us. We found interspecific differences in tolerance to physical stress of emerged hermit crabs. This air-exposure tolerance can be interpreted as a physiological adaptation to desiccation stress and is also related to the shell type they inhabit. Also, we provide additional features and details of the air-exposure behavior, combining observations of the first description in 2015 with our new field observations.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí
Astrophysical Interpretation Of Pierre Auger Observatory Measurements Of The Uhecr Energy Spectrum And Mass Composition
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