22,192 research outputs found
On Non-Commutative Integrable Burgers Equations
We construct the recursion operators for the non-commutative Burgers
equations using their Lax operators. We investigate the existence of any
integrable mixed version of left- and right-handed Burgers equations on higher
symmetry grounds.Comment: 8 page
The Bright Side of Dark Matter
We show that it is not possible in the absence of dark matter to construct a
four-dimensional metric that explains galactic observations. In particular, by
working with an effective potential it is shown that a metric which is
constructed to fit flat rotation curves in spiral galaxies leads to the wrong
sign for the bending of light i.e. repulsion instead of attraction. Hence,
without dark matter the motion of particles on galactic scales cannot be
explained in terms of geodesic motion on a four- dimensional metric. This
reveals a new bright side to dark matter: it is indispensable if we wish to
retain the cherished equivalence principle.Comment: 7 pages, latex, no figures. Received an honorable mention in the 1999
Gravity research Foundation Essay Competition. Submitted to Phys. Rev. Let
Continuous-variable quantum teleportation of entanglement
Entangled coherent states can be used to determine the entanglement fidelity
for a device that is designed to teleport coherent states. This entanglement
fidelity is universal, in that the calculation is independent of the use of
entangled coherent states and applies generally to the teleportation of
entanglement using coherent states. The average fidelity is shown to be a poor
indicator of the capability of teleporting entanglement; i.e., very high
average fidelity for the quantum teleportation apparatus can still result in
low entanglement fidelity for one mode of the two-mode entangled coherent
state.Comment: 5 pages, 1 figure, published versio
Two-Dimensional Molecular Patterning by Surface-Enhanced Zn-Porphyrin Coordination
In this contribution, we show how zinc-5,10,15,20-meso-tetradodecylporphyrins (Zn-TDPs) self-assemble into stable organized arrays on the surface of graphite, thus positioning their metal center at regular distances from each other, creating a molecular pattern, while retaining the possibility to coordinate additional ligands. We also demonstrate that Zn-TDPs coordinated to 3-nitropyridine display a higher tendency to be adsorbed at the surface of highly oriented pyrolytic graphite (HOPG) than noncoordinated ones. In order to investigate the two-dimensional (2D) self-assembly of coordinated Zn-TDPs, solutions with different relative concentrations of 3-nitropyridine and Zn-TDP were prepared and deposited on the surface of HOPG. STM measurements at the liquid-solid interface reveal that the ratio of coordinated Zn-TDPs over noncoordinated Zn-TDPs is higher at the n-tetradecane/HOPG interface than in n-tetradecane solution. This enhanced binding of the axial ligand at the liquid/solid interface is likely related to the fact that physisorbed Zn-TDPs are better binding sites for nitropyridines.
Nonclassical Fields and the Nonlinear Interferometer
We demonstrate several new results for the nonlinear interferometer, which
emerge from a formalism which describes in an elegant way the output field of
the nonlinear interferometer as two-mode entangled coherent states. We clarify
the relationship between squeezing and entangled coherent states, since a weak
nonlinear evolution produces a squeezed output, while a strong nonlinear
evolution produces a two-mode, two-state entangled coherent state. In between
these two extremes exist superpositions of two-mode coherent states manifesting
varying degrees of entanglement for arbitrary values of the nonlinearity. The
cardinality of the basis set of the entangled coherent states is finite when
the ratio is rational, where is the nonlinear strength. We
also show that entangled coherent states can be produced from product coherent
states via a nonlinear medium without the need for the interferometric
configuration. This provides an important experimental simplification in the
process of creating entangled coherent states.Comment: 21 pages, 2 figure
Mid-infrared and optical spectroscopy of ultraluminous infrared galaxies: A comparison
New tools from Infrared Space Observatory (ISO) mid-infrared spectroscopy
have recently become available to determine the power sources of dust-obscured
ultraluminous infrared galaxies (ULIRGs). We compare ISO classifications -
starburst or active galactic nucleus (AGN) - with classifications from optical
spectroscopy, and with optical/near-infrared searches for hidden broad-line
regions. The agreement between mid-infrared and optical classification is
excellent if optical LINER spectra are assigned to the starburst group. The
starburst nature of ULIRG LINERs strongly supports the suggestion that LINER
spectra in infrared-selected galaxies, rather than being an expression of the
AGN phenomenon, are due to shocks that are probably related to galactic
superwinds. Differences between ISO and optical classification provide clues on
the evolution of ULIRGs and on the configuration of obscuring dust. We find few
ISO AGN with optical HII or LINER identification, suggesting that highly
obscured AGN exist but are not typical for the ULIRG phenomenon in general.
Rather, our results indicate that strong AGN activity, once triggered, quickly
breaks the obscuring screen at least in certain directions, thus becoming
detectable over a wide wavelength range.Comment: aastex, 1 eps figure. Accepted by ApJ (Letters
A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies
We present the first results of an ALMA survey of the lower fine structure
line of atomic carbon [C I](^3P_1\,-\,^{3}P_0) in far infrared-selected
galaxies on the main sequence at in the COSMOS field. We compare our
sample with a comprehensive compilation of data available in the literature for
local and high-redshift starbursting systems and quasars. We show that the [C
I]() luminosity correlates on global scales with the
infrared luminosity similarly to low- CO transitions. We report
a systematic variation of L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/ as a
function of the galaxy type, with the ratio being larger for main-sequence
galaxies than for starbursts and sub-millimeter galaxies at fixed .
The L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/ and / mass ratios are similar for main-sequence galaxies and for
local and high-redshift starbursts within a 0.2 dex intrinsic scatter,
suggesting that [C I] is a good tracer of molecular gas mass as CO and dust. We
derive a fraction of %
of the total carbon mass in the atomic neutral phase. Moreover, we estimate the
neutral atomic carbon abundance, the fundamental ingredient to calibrate [C I]
as a gas tracer, by comparing L'_{\rm [C\,I]^3P_1\,-\, ^3P_0} and available
gas masses from CO lines and dust emission. We find lower [C I] abundances in
main-sequence galaxies than in starbursting systems and sub-millimeter
galaxies, as a consequence of the canonical and gas-to-dust
conversion factors. This argues against the application to different galaxy
populations of a universal standard [C I] abundance derived from highly biased
samples.Comment: 14 pages + Appendix. Accepted for publication in ApJ. All the data
tables in Appendix will be also released in electronic forma
Modified gravity without dark matter
On an empirical level, the most successful alternative to dark matter in
bound gravitational systems is the modified Newtonian dynamics, or MOND,
proposed by Milgrom. Here I discuss the attempts to formulate MOND as a
modification of General Relativity. I begin with a summary of the
phenomenological successes of MOND and then discuss the various covariant
theories that have been proposed as a basis for the idea. I show why these
proposals have led inevitably to a multi-field theory. I describe in some
detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and
discuss its successes and shortcomings. This lecture is primarily pedagogical
and directed to those with some, but not a deep, background in General
RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School,
The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected,
references update
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Energy use for urban water management by utilities and Households in Los Angeles
Reducing energy consumption for urban water management may yield economic and environmental benefits. Few studies provide comprehensive assessments of energy needs for urban water sectors that include both utility operations and household use. Here, we evaluate the energy needs for urban water management in metropolitan Los Angeles (LA) County. Using planning scenarios that include both water conservation and alternative supply options, we estimate energy requirements of water imports, groundwater pumping, distribution in pipes, water and wastewater treatment, and residential water heating across more than one hundred regional water agencies covering over 9 million people. Results show that combining water conservation with alternative local supplies such as stormwater capture and water reuse (nonpotable or indirect potable) can reduce the energy consumption and intensity of water management in LA. Further advanced water treatment for direct potable reuse could increase energy needs. In aggregate, water heating represents a major source of regional energy consumption. The heating factor associated with grid-supplied electricity drives the relative contribution of energy-for-water by utilities and households. For most scenarios of grid operations, energy for household water heating significantly outweighs utility energy consumption. The study demonstrates how publicly available and detailed data for energy and water use supports sustainability planning. The method is applicable to cities everywhere
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