458 research outputs found
Note: a dual temperature closed loop batch reactor for determining the partitioning of trace gases within CO2-water systems
An experimental approach is presented which can be used to determine partitioning of trace gases within CO2-water systems. The key advantages of this system are (1) The system can be isolated with no external exchange, making it ideal for experiments with conservative tracers. (2) Both phases can be sampled concurrently to give an accurate composition at each phase at any given time. (3) Use of a lower temperature flow loop outside of the reactor removes contamination and facilitates sampling. (4) Rapid equilibration at given pressure/temperature conditions is significantly aided by stirring and circulating the water phase using a magnetic stirrer and high-pressureliquid chromatography pump, respectively
Quantum-Classical Dynamics of Wave Fields
An approach to the quantum-classical mechanics of phase space dependent
operators, which has been proposed recently, is remodeled as a formalism for
wave fields. Such wave fields obey a system of coupled non-linear equations
that can be written by means of a suitable non-Hamiltonian bracket. As an
example, the theory is applied to the relaxation dynamics of the spin-boson
model. In the adiabatic limit, a good agreement with calculations performed by
the operator approach is obtained. Moreover, the theory proposed in this paper
can take nonadiabatic effects into account without resorting to surface-hopping
approximations. Hence, the results obtained follow qualitatively those of
previous surface-hopping calculations and increase by a factor of (at least)
two the time length over which nonadiabatic dynamics can be propagated with
small statistical errors. Moreover, it is worth to note that the dynamics of
quantum-classical wave fields here proposed is a straightforward
non-Hamiltonian generalization of the formalism for non-linear quantum
mechanics that Weinberg introduced recently.Comment: Manuscript accepted by The Journal of Chemical Physic
Entanglement for all quantum states
It is shown that a state that is factorizable in the Hilbert space
corresponding to some choice of degrees of freedom, becomes entangled for a
different choice of degrees of freedom. Therefore, entanglement is not a
special case but is ubiquitous in quantum systems. Simple examples are
calculated and a general proof is provided. The physical relevance of the
change of tensor product structure is mentioned.Comment: 9 page
PT Symmetry as a Generalization of Hermiticity
The Hilbert space in PT-symmetric quantum mechanics is formulated as a linear
vector space with a dynamic inner product. The most general PT-symmetric matrix
Hamiltonians are constructed for 2*2 and 3*3 cases. In the former case, the
PT-symmetric Hamiltonian represents the most general matrix Hamiltonian with a
real spectrum. In both cases, Hermitian matrices are shown to be special cases
of PT-symmetric matrices. This finding confirms and strengthens the early
belief that the PT-symmetric quantum mechanics is a generalization of the
conventional Hermitian quantum mechanics.Comment: 13 page
Optimal Monitoring of Position in Nonlinear Quantum Systems
We discuss a model of repeated measurements of position in a quantum system
which is monitored for a finite amount of time with a finite instrumental
error. In this framework we recover the optimum monitoring of a harmonic
oscillator proposed in the case of an instantaneous collapse of the
wavefunction into an infinite-accuracy measurement result. We also establish
numerically the existence of an optimal measurement strategy in the case of a
nonlinear system. This optimal strategy is completely defined by the spectral
properties of the nonlinear system.Comment: 4 pages, REVTeX 3.0, 4 PostScript figure
Spin-dependent electron-impurity scattering in two-dimensional electron systems
We present a theoretical study of elastic spin-dependent electron scattering
caused by a charged impurity in the vicinity of a two-dimensional electron gas.
We find that the symmetry properties of the spin-dependent differential
scattering cross section are different for an impurity located in the plane of
the electron gas and for one at a finite distance from the plane. We show that
in the latter case asymmetric (`skew') scattering can arise if the polarization
of the incident electron has a finite projection on the plane spanned by the
normal vector of the two-dimensional electron gas and the initial propagation
direction. In specially preparated samples this scattering mechanism may give
rise to a Hall-like effect in the presence of an in-plane magnetic field.Comment: 4.1 pages, 2 figure
Multi-order interference is generally nonzero
It is demonstrated that the third-order interference, as obtained from
explicit solutions of Maxwell's equations for realistic models of three-slit
devices, including an idealized version of the three-slit device used in a
recent three-slit experiment with light (U. Sinha et al., Science 329, 418
(2010)), is generally nonzero. The hypothesis that the third-order interference
should be zero is shown to be fatally flawed because it requires dropping the
one-to-one correspondence between the symbols in the mathematical theory and
the different experimental configurations.Comment: Replaced Figs. 4,5 and caption of Fig.
EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited
In 1930 Einstein argued against consistency of the time-energy uncertainty
relation by discussing a thought experiment involving a measurement of mass of
the box which emitted a photon. Bohr seemingly triumphed over Einstein by
arguing that the Einstein's own general theory of relativity saves the
consistency of quantum mechanics. We revisit this thought experiment from a
modern point of view at a level suitable for undergraduate readership and find
that neither Einstein nor Bohr was right. Instead, this thought experiment
should be thought of as an early example of a system demonstrating nonlocal
"EPR" quantum correlations, five years before the famous
Einstein-Podolsky-Rosen paper.Comment: 11 pages, revised, accepted for publication in Eur. J. Phy
Archaeological Geophysical Prospection in Peatland Environments: case studies and suggestions for future practice
Peatland environments, in contrast to ‘dry-land’ sites, preserve organic material, including anthropogenic objects, because they are anaerobic, and are therefore of great importance to archaeology. Peat also preserves macro- and micro- paleoenvironmental evidence and is the primary resource for understanding past climates and ecology. Archaeological sites often lie within or at the base of wet, deep, homogenous peat rendering them invisible to surface observers. As a result, they most often c..
Molecular, 13C, and 14C evidence for the allochthonous and ancient origin of C16-C18 n-alkanes in modern soils
International audienceThe heterogeneous isotopic composition of C3 and C4 plants can be used to to follow the fate of plant carbon into soil organic molecules. Thus, after 23 years of cropping of maize (C4) on a soil which was previously under C3 vegetation, C25 C33 soil n-alkanes are 13C-enriched up to 9‰ relatively to the initial C3 soil, reflecting the input of 13C-enriched n-alkanes from maize waxes. In sharp contrast, C16-C18 soil n alkanes do not show any significant 13C/12C variation over the same time interval. This absence of isotopic variation, along with consideration of their relative concentration, absolute concentration and biodegradability, demonstrate that these substances must represent a regular input from an external source. Evidence of a large contribution of an ancient source, amounting to more than 65% of the alkane fraction, is given by a 14C-age of 8510 yrs BP. Moreover, short-chain n-alkanes from soils, diesel fuel, diesel automobile exhaust and petroleum products exhibit similar distributions and δ13C values. These findings suggests that C16-C18 soil n alkanes represent a non-point source pollution of ancient hydrocarbons either carried by aerosols or entering the soil via continuous hydrocarbon seepage from the deep sedimentary rocks of the Paris basin
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