630 research outputs found
Internal structure and origin of the double reefs of North Bohol and the Olango reef flat (Philippines)
Nine holes were drilled with a submersible hydraulic drill into the slopes and reef flats of the Caubyna and Calituban reefs as well as of Olango Flat. The maximum depth of core penetration was 11 m. 14C ages showed that the Caubyan and Caltituban reefs were formed within the last 6,000 years. Corals settled on a pre-existing relief prallel to the island of Bohol, building a framework for other carbonate-producing organisms. The reef flat south of Olango has a different structure. Formation took place during a Pleistocene high sea level, e.g. 125,000 years ago
Electron-spin dynamics induced by photon spins
Strong rotating magnetic fields may cause a precession of the electron's spin
around the rotation axis of the magnetic field. The superposition of two
counterpropagating laser beams with circular polarization and opposite helicity
features such a rotating magnetic field component but also carries spin. The
laser's spin density, that can be expressed in terms of the lase's
electromagnetic fields and potentials, couples to the electron's spin via a
relativistic correction to the Pauli equation. We show that the quantum
mechanical interaction of the electron's spin with the laser's rotating
magnetic field and with the laser's spin density counteract each other in such
a way that a net spin rotation remains with a precession frequency that is much
smaller than the frequency one would expect from the rotating magnetic field
alone. In particular, the frequency scales differently with the laser's
electric field strength depending on if relativistic corrections are taken into
account or not. Thus, the relativistic coupling of the electron's spin to the
laser's spin density changes the dynamics not only quantitatively but also
qualitatively as compared to the nonrelativistic theory. The electron's spin
dynamics is a genuine quantum mechanical relativistic effect
Spin dynamics in relativistic light-matter interaction
Various spin effects are expected to become observable in light-matter
interaction at relativistic intensities. Relativistic quantum mechanics
equipped with a suitable relativistic spin operator forms the theoretical
foundation for describing these effects. Various proposals for relativistic
spin operators have been offered by different authors, which are presented in a
unified way. As a result of the operators' mathematical properties only the
Foldy-Wouthuysen operator and the Pryce operator qualify as possible proper
relativistic spin operators. The ground states of highly charged hydrogen-like
ions can be utilized to identify a legitimate relativistic spin operator
experimentally. Subsequently, the Foldy-Wothuysen spin operator is employed to
study electron-spin precession in high-intensity standing light waves with
elliptical polarization. For a correct theoretical description of the predicted
electron-spin precession relativistic effects due to the spin angular momentum
of the electromagnetic wave has to be taken into account even in the limit of
low intensities
Relativistic spin operators in various electromagnetic environments
Different operators have been suggested in the literature to describe the
electron's spin degree of freedom within the relativistic Dirac theory. We
compare concrete predictions of the various proposed relativistic spin
operators in different physical situations. In particular, we investigate the
so-called Pauli, Foldy-Wouthuysen, Czachor, Frenkel, Chakrabarti, Pryce, and
Fradkin-Good spin operators. We demonstrate that when a quantum system
interacts with electromagnetic potentials the various spin operators predict
different expectation values. This is explicitly illustrated for the scattering
dynamics at a potential step and in a standing laser field and also for energy
eigenstates of hydrogenic ions. Therefore, one may distinguish between the
proposed relativistic spin operators experimentally
A Network of Text, Data and People for the Earth System Sciences
Earth System Science is an outstanding example of a field of research which yields important results especially when conducted in multidisciplinary and global cooperation. The International Polar Year and its expected legacy are used as an example to illustrate this assertion and the financial and intellectual expense invested. It follows that any effort to make more out of the globally distributed – if not fragmented – results and to network the knowledge gained would be valuable indeed. An experimental implementation of such a system, connecting journal articles to datasets, expeditions and researchers involved, is introduced. Some developments necessary to implement comparable and more powerful systems on a global scale are discussed
Schmidt Analysis of Pure-State Entanglement
We examine the application of Schmidt-mode analysis to pure state
entanglement. Several examples permitting exact analytic calculation of Schmidt
eigenvalues and eigenfunctions are included, as well as evaluation of the
associated degree of entanglement.Comment: 5 pages, 3 figures, for C.M. Bowden memoria
Quantum chaos and QCD at finite chemical potential
We investigate the distribution of the spacings of adjacent eigenvalues of
the lattice Dirac operator. At zero chemical potential , the
nearest-neighbor spacing distribution follows the Wigner surmise of
random matrix theory both in the confinement and in the deconfinement phase.
This is indicative of quantum chaos. At nonzero chemical potential, the
eigenvalues of the Dirac operator become complex. We discuss how can be
defined in the complex plane. Numerical results from an SU(3) simulation with
staggered fermions are compared with predictions from non-hermitian random
matrix theory, and agreement with the Ginibre ensemble is found for .Comment: LATTICE98(hightemp), 3 pages, 10 figure
Entanglement and interference between different degrees of freedom of photons states
In this paper, photonic entanglement and interference are described and
analyzed with the language of quantum information process. Correspondingly, a
photon state involving several degrees of freedom is represented in a new
expression based on the permutation symmetry of bosons. In this expression,
each degree of freedom of a single photon is regarded as a qubit and operations
on photons as qubit gates. The two-photon Hong-Ou-Mandel interference is well
interpreted with it. Moreover, the analysis reveals the entanglement between
different degrees of freedom in a four-photon state from parametric down
conversion, even if there is no entanglement between them in the two-photon
state. The entanglement will decrease the state purity and photon interference
visibility in the experiments on a four-photon polarization state.Comment: 11 pages and 2 figure
What is the relativistic spin operator?
Although the spin is regarded as a fundamental property of the electron,
there is no universally accepted spin operator within the framework of
relativistic quantum mechanics. We investigate the properties of different
proposals for a relativistic spin perator. It is shown that most candidates are
lacking essential features of proper angular momentum operators, leading to
spurious Zitterbewegung (quivering motion) or violating the angular momentum
algebra. Only the Foldy-Wouthuysen operator and the Pryce operator qualify as
proper relativistic spin operators. We demonstrate that ground states of highly
charged hydrogen-like ions can be utilized to identify a legitimate
relativistic spin operator experimentally
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