15,764 research outputs found
Some symmetry classifications of hyperbolic vector evolution equations
Motivated by recent work on integrable flows of curves and 1+1 dimensional
sigma models, several O(N)-invariant classes of hyperbolic equations for an -component vector are considered. In each
class we find all scaling-homogeneous equations admitting a higher symmetry of
least possible scaling weight. Sigma model interpretations of these equations
are presented.Comment: Revision of published version, incorporating errata on geometric
aspects of the sigma model interpretations in the case of homogeneous space
Three-dimensional Binary Superlattices of Oppositely-charged Colloids
We report the equilibrium self-assembly of binary crystals of
oppositely-charged colloidal microspheres at high density. By varying the
magnitude of the charge on near equal-sized spheres we show that the structure
of the binary crystal may be switched between face-centered cubic, cesium
chloride and sodium chloride. We interpret these transformations in terms of a
competition between entropic and Coulombic forces
Interferometric CO observations of the ultraluminous IRAS galaxies ARP 220, IC 694/NGC 3690, NGC 6420 and NGC 7469
High resolution CO observations of the IRAS galaxies Arp 220, IC 694/NGC 3690, NGC 6240 and NGC 7469 were made with the Millimeter Wave Interferometer of the Owen Valley Radio Observatory. These yield spatial information on scales of 1 to 5 kpc and allow the separation of compact condensations from the more extended emission in the galaxies. In the case of the obviously interacting system IC 694/NGC 3690 the contributions of each component can be discerned. For that galaxy, and also for Arp 220, the unusually high lumonisities may be produced by nonthermal processes rather than by intense bursts of star formation
Classical and quantum fingerprinting with shared randomness and one-sided error
Within the simultaneous message passing model of communication complexity,
under a public-coin assumption, we derive the minimum achievable worst-case
error probability of a classical fingerprinting protocol with one-sided error.
We then present entanglement-assisted quantum fingerprinting protocols
attaining worst-case error probabilities that breach this bound.Comment: 10 pages, 1 figur
Quantum process tomography with coherent states
We develop an enhanced technique for characterizing quantum optical processes
based on probing unknown quantum processes only with coherent states. Our
method substantially improves the original proposal [M. Lobino et al., Science
322, 563 (2008)], which uses a filtered Glauber-Sudarshan decomposition to
determine the effect of the process on an arbitrary state. We introduce a new
relation between the action of a general quantum process on coherent state
inputs and its action on an arbitrary quantum state. This relation eliminates
the need to invoke the Glauber-Sudarshan representation for states; hence it
dramatically simplifies the task of process identification and removes a
potential source of error. The new relation also enables straightforward
extensions of the method to multi-mode and non-trace-preserving processes. We
illustrate our formalism with several examples, in which we derive analytic
representations of several fundamental quantum optical processes in the Fock
basis. In particular, we introduce photon-number cutoff as a reasonable
physical resource limitation and address resource vs accuracy trade-off in
practical applications. We show that the accuracy of process estimation scales
inversely with the square root of photon-number cutoff.Comment: 18 pages, 2 figure
Forming Galaxies with MOND
Beginning with a simple model for the growth of structure, I consider the
dissipationless evolution of a MOND-dominated region in an expanding Universe
by means of a spherically symmetric N-body code. I demonstrate that the final
virialized objects resemble elliptical galaxies with well-defined relationships
between the mass, radius, and velocity dispersion. These calculations suggest
that, in the context of MOND, massive elliptical galaxies may be formed early
(z > 10) as a result of monolithic dissipationless collapse. Then I reconsider
the classic argument that a galaxy of stars results from cooling and
fragmentation of a gas cloud on a time scale shorter than that of dynamical
collapse. Qualitatively, the results are similar to that of the traditional
picture; moreover, the existence, in MOND, of a density-temperature relation
for virialized, near isothermal objects as well as a mass-temperature relation
implies that there is a definite limit to the mass of a gas cloud where this
condition can be met-- an upper limit corresponding to that of presently
observed massive galaxies.Comment: 9 pages, 9 figures, revised in response to comments of referee. Table
added, extended discussion, accepted MNRA
Single-qubit optical quantum fingerprinting
We analyze and demonstrate the feasibility and superiority of linear optical
single-qubit fingerprinting over its classical counterpart. For one-qubit
fingerprinting of two-bit messages, we prepare `tetrahedral' qubit states
experimentally and show that they meet the requirements for quantum
fingerprinting to exceed the classical capability. We prove that shared
entanglement permits 100% reliable quantum fingerprinting, which will
outperform classical fingerprinting even with arbitrary amounts of shared
randomness.Comment: 4 pages, one figur
Probing for evolutionary links between local ULIRGs and QSOs from NIR spectroscopy
We present a study of the dynamical evolution of Ultraluminous Infrared
Galaxies (ULIRGs), merging galaxies of infrared luminosity >10^12 L_sun. During
our Very Large Telescope large program, we have obtained ISAAC near-infrared,
high-resolution spectra of 54 ULIRGs (at several merger phases) and 12 local
Palomar-Green QSOs to investigate whether ULIRGs go through a QSO phase during
their evolution. One possible evolutionary scenario is that after nuclear
coalescence, the black hole radiates close to Eddington to produce QSO
luminosities. The mean stellar velocity dispersion that we measure from our
spectra is similar (~160 km/s) for 30 post-coalescence ULIRGs and 7 IR-bright
QSOs. The black holes in both populations have masses of order 10^7-10^8 M_sun
(calculated from the relation to the host dispersion) and accrete at rates >0.5
Eddington. Placing ULIRGs and IR-bright QSOs on the fundamental plane of
early-type galaxies shows that they are located on a similar region (that of
moderate-mass ellipticals), in contrast to giant ellipticals and radio-loud
QSOs. While this preliminary comparison of the ULIRG and QSO host kinematical
properties indicates that (some) ULIRGs may undergo a QSO phase in their
evolutionary history before they settle down as ellipticals, further data on
non-IR excess QSOs are necessary to test this scenario.Comment: To appear in the "QSO Host Galaxies: Evolution and Environment"
conference proceedings; meeting held in Leiden, August 200
Reductions of integrable equations on A.III-type symmetric spaces
We study a class of integrable non-linear differential equations related to
the A.III-type symmetric spaces. These spaces are realized as factor groups of
the form SU(N)/S(U(N-k) x U(k)). We use the Cartan involution corresponding to
this symmetric space as an element of the reduction group and restrict generic
Lax operators to this symmetric space. The symmetries of the Lax operator are
inherited by the fundamental analytic solutions and give a characterization of
the corresponding Riemann-Hilbert data.Comment: 14 pages, 1 figure, LaTeX iopart styl
Small doubling in groups
Let A be a subset of a group G = (G,.). We will survey the theory of sets A
with the property that |A.A| <= K|A|, where A.A = {a_1 a_2 : a_1, a_2 in A}.
The case G = (Z,+) is the famous Freiman--Ruzsa theorem.Comment: 23 pages, survey article submitted to Proceedings of the Erdos
Centenary conferenc
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