1,871 research outputs found
Spectra of Maser Radiation from a Turbulent, Circumnuclear Accretion Disk. III. Circular polarization
Calculations are performed for the circular polarization of maser radiation
from a turbulent, Keplerian disk that is intended to represent the sub-parsec
disk at the nucleus of the galaxy NGC4258. The polarization in the calculations
is a result of the Zeeman effect in the regime in which the Zeeman splitting is
much less than the spectral linebreadth. Plausible configurations for turbulent
magnetic and velocity fields in the disk are created by statistical methods.
This turbulence, along with the Keplerian velocity gradients and the blending
of the three hyperfine components to form the masing
transition of water, are key ingredients in determining the appearance of the
polarized spectra that are calculated. These spectra are quite different from
the polarized spectra that would be expected for a two-level transition where
there is no hyperfine structure. The effect of the hyperfine structure on the
polarization is most striking in the calculations for the maser emission that
represents the central (or systemic) features of NGC4258. Information about
magnetic fields is inferred from observations for polarized maser radiation and
bears on the structure of accretion disks.Comment: Latex, uses aastex, eucal, to be published in the Astrophysical
Journa
Extraction and measurement of adenosine triphosphate from marine sediment, The
Includes bibliographical references (pages 479-480).A technique has been developed, using boiling sodium bicarbonate buffer, to extract adenosine triphosphate (ATP) from marine sediments and has been tested on a variety of sediments, including those with high organic content, clay, and carbonate. Recovery of ATP, as measured by the addition of bacteria of known ATP content to sediment, varied from 64-100%. The technique also was as effective as the conventional Tris buffer for extraction of ATP from both pure cultures of bacteria grown in broth and natural seawater samples.Publisher version: http://www.jstor.org/stable/2835285
The Quantum Mechanics of Hyperion
This paper is motivated by the suggestion [W. Zurek, Physica Scripta, T76,
186 (1998)] that the chaotic tumbling of the satellite Hyperion would become
non-classical within 20 years, but for the effects of environmental
decoherence. The dynamics of quantum and classical probability distributions
are compared for a satellite rotating perpendicular to its orbital plane,
driven by the gravitational gradient. The model is studied with and without
environmental decoherence. Without decoherence, the maximum quantum-classical
(QC) differences in its average angular momentum scale as hbar^{2/3} for
chaotic states, and as hbar^2 for non-chaotic states, leading to negligible QC
differences for a macroscopic object like Hyperion. The quantum probability
distributions do not approach their classical limit smoothly, having an
extremely fine oscillatory structure superimposed on the smooth classical
background. For a macroscopic object, this oscillatory structure is too fine to
be resolved by any realistic measurement. Either a small amount of smoothing
(due to the finite resolution of the apparatus) or a very small amount of
environmental decoherence is sufficient ensure the classical limit. Under
decoherence, the QC differences in the probability distributions scale as
(hbar^2/D)^{1/6}, where D is the momentum diffusion parameter. We conclude that
decoherence is not essential to explain the classical behavior of macroscopic
bodies.Comment: 17 pages, 24 figure
Information-theoretic equilibration: the appearance of irreversibility under complex quantum dynamics
The question of how irreversibility can emerge as a generic phenomena when
the underlying mechanical theory is reversible has been a long-standing
fundamental problem for both classical and quantum mechanics. We describe a
mechanism for the appearance of irreversibility that applies to coherent,
isolated systems in a pure quantum state. This equilibration mechanism requires
only an assumption of sufficiently complex internal dynamics and natural
information-theoretic constraints arising from the infeasibility of collecting
an astronomical amount of measurement data. Remarkably, we are able to prove
that irreversibility can be understood as typical without assuming decoherence
or restricting to coarse-grained observables, and hence occurs under distinct
conditions and time-scales than those implied by the usual decoherence point of
view. We illustrate the effect numerically in several model systems and prove
that the effect is typical under the standard random-matrix conjecture for
complex quantum systems.Comment: 15 pages, 7 figures. Discussion has been clarified and additional
numerical evidence for information theoretic equilibration is provided for a
variant of the Heisenberg model as well as one and two-dimensional random
local Hamiltonian
Circular Polarization of Circumstellar Water Masers around S Per
We present the first circular polarization measurements of circumstellar H2O
masers. Previously the magnetic field in circumstellar envelopes has been
estimated using polarization observations of SiO and OH masers. SiO masers are
probes of the high temperature and density regime close to the central star. OH
masers are found at much lower densities and temperatures, generally much
further out in the circumstellar envelope. The detection of the circular
polarization of the (6_16 - 5_23) rotational transition of the H2O maser could
be attributed to Zeeman splitting due to the magnetic field in the intermediate
temperature and density regime. The fields inferred here agree well with
predicted values for a combination of the r^{-2} dependence of a solar-type
magnetic field, and the coupling of the field to the high density masing
regions. We also discuss the unexpected narrowing of the circular polarization
spectrum.Comment: 4 pages, 4 figures; accepted for publication in Astronomy and
Astrophysics Letter
Witnessing eigenstates for quantum simulation of Hamiltonian spectra
The efficient calculation of Hamiltonian spectra, a problem often intractable
on classical machines, can find application in many fields, from physics to
chemistry. Here, we introduce the concept of an "eigenstate witness" and
through it provide a new quantum approach which combines variational methods
and phase estimation to approximate eigenvalues for both ground and excited
states. This protocol is experimentally verified on a programmable silicon
quantum photonic chip, a mass-manufacturable platform, which embeds entangled
state generation, arbitrary controlled-unitary operations, and projective
measurements. Both ground and excited states are experimentally found with
fidelities >99%, and their eigenvalues are estimated with 32-bits of precision.
We also investigate and discuss the scalability of the approach and study its
performance through numerical simulations of more complex Hamiltonians. This
result shows promising progress towards quantum chemistry on quantum computers.Comment: 9 pages, 4 figures, plus Supplementary Material [New version with
minor typos corrected.
Improved Error-Scaling for Adiabatic Quantum State Transfer
We present a technique that dramatically improves the accuracy of adiabatic
state transfer for a broad class of realistic Hamiltonians. For some systems,
the total error scaling can be quadratically reduced at a fixed maximum
transfer rate. These improvements rely only on the judicious choice of the
total evolution time. Our technique is error-robust, and hence applicable to
existing experiments utilizing adiabatic passage. We give two examples as
proofs-of-principle, showing quadratic error reductions for an adiabatic search
algorithm and a tunable two-qubit quantum logic gate.Comment: 10 Pages, 4 figures. Comments are welcome. Version substantially
revised to generalize results to cases where several derivatives of the
Hamiltonian are zero on the boundar
Stoichiometry of C, N, P, and Si fluxes in a temperate-climate embayment
Dissolved C, N, P, and Si budgets for Tomales Bay, California, have been used to solve simultaneous stoichiometric equations which describe a plausible material balance for net organic matter reactions in the bay. Dissolved Si and P were both exported hydrographically. Dissolved C and fixed N were imported hydrographically. If we assume that C, N, P, and Si were supplied to the bay as organic detritus and remineralized at a rate required to balance dissolved Si and P exports, we can calculate reasonable rates of denitrification and CO2 gas evasion across the air-water interface. The system is thus interpreted to have been net heterotrophic at the time of our investigation.Fluxes attributed to individual components in the system (benthic respiration, water-column material turnover, biochemical transformations between fixed and gaseous N) were of sufficient magnitude to account for the system-wide net fluxes, although too noisy to allow piecewise derivation of net system fluxes. Denitrification and limitation of primary production by dissolved fixed N in aquatic ecosystems may be symptoms of other system-scale constraints on net C metabolism, rather than themselves being system-level controls of net C metabolism
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