1,388 research outputs found
A simple expression for the ADM mass
We show by an almost elementary calculation that the ADM mass of an
asymptotically flat space can be computed as a limit involving a rate of change
of area of a closed 2-surface. The result is essentially the same as that given
by Brown and York. We will prove this result in two ways, first by direct
calculation from the original formula as given by Arnowitt, Deser and Misner
and second as a corollary of an earlier result by Brewin for the case of
simplicial spaces.Comment: 9 pages, 1 figur
1,2,6-thiadiazinones as novel narrow spectrum calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) inhibitors
We demonstrate for the first time that 4H-1,2,6-thiadiazin-4-one (TDZ) can function as a chemotype for the design of ATP-competitive kinase inhibitors. Using insights from a co-crystal structure of a 3,5-bis(arylamino)-4H-1,2,6-thiadiazin-4-one bound to calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2), several analogues were identified with micromolar activity through targeted displacement of bound water molecules in the active site. Since the TDZ analogues showed reduced promiscuity compared to their 2,4-dianilinopyrimidine counter parts, they represent starting points for development of highly selective kinase inhibitors
Elastic deformation of a fluid membrane upon colloid binding
When a colloidal particle adheres to a fluid membrane, it induces elastic
deformations in the membrane which oppose its own binding. The structural and
energetic aspects of this balance are theoretically studied within the
framework of a Helfrich Hamiltonian. Based on the full nonlinear shape
equations for the membrane profile, a line of continuous binding transitions
and a second line of discontinuous envelopment transitions are found, which
meet at an unusual triple point. The regime of low tension is studied
analytically using a small gradient expansion, while in the limit of large
tension scaling arguments are derived which quantify the asymptotic behavior of
phase boundary, degree of wrapping, and energy barrier. The maturation of
animal viruses by budding is discussed as a biological example of such
colloid-membrane interaction events.Comment: 14 pages, 9 figures, REVTeX style, follow-up on cond-mat/021242
Vibrational Study of 13C-enriched C60 Crystals
The infrared (IR) spectrum of solid C60 exhibits many weak vibrational modes.
Symmetry breaking due to 13C isotopes provides a possible route for optically
activating IR-silent vibrational modes. Experimental spectra and a
semi-empirical theory on natural abundance and 13C-enriched single crystals of
C60 are presented. By comparing the experimental results with the theoretical
results, we exclude this isotopic activation mechanism from the explanation for
weakly active fundamentals in the spectra.Comment: Accepted for Phys. Rev. B, typeset in REVTEX v3.0 in LaTeX.
Postscript file including figures is available at
http://insti.physics.sunysb.edu/~mmartin/papers/c13twocol2.ps File with
figures will be e-mailed by reques
Brane cosmological perturbations
We address the question of cosmological perturbations in the context of brane
cosmology, where our Universe is a three-brane where matter is confined,
whereas gravity lives in a higher dimensional spacetime. The equations
governing the bulk perturbations are computed in the case of a general warped
universe. The results are then specialized to the case of a five-dimensional
spacetime, scenario which has recently attracted a lot of attention. In this
context, we decompose the perturbations into `scalar', `vector' and `tensor'
modes, which are familiar in the standard theory of cosmological perturbations.
The junction conditions, which relate the metric perturbations to the matter
perturbations in the brane, are then computed.Comment: 14 pages, Latex; no figur
Generalized Quantum Theory of Recollapsing Homogeneous Cosmologies
A sum-over-histories generalized quantum theory is developed for homogeneous
minisuperspace type A Bianchi cosmological models, focussing on the particular
example of the classically recollapsing Bianchi IX universe. The decoherence
functional for such universes is exhibited. We show how the probabilities of
decoherent sets of alternative, coarse-grained histories of these model
universes can be calculated. We consider in particular the probabilities for
classical evolution defined by a suitable coarse-graining. For a restricted
class of initial conditions and coarse grainings we exhibit the approximate
decoherence of alternative histories in which the universe behaves classically
and those in which it does not. For these situations we show that the
probability is near unity for the universe to recontract classically if it
expands classically. We also determine the relative probabilities of
quasi-classical trajectories for initial states of WKB form, recovering for
such states a precise form of the familiar heuristic "J d\Sigma" rule of
quantum cosmology, as well as a generalization of this rule to generic initial
states.Comment: 41 pages, 4 eps figures, revtex 4. Modest revisions throughout.
Physics unchanged. To appear in Phys. Rev.
Geology of the Nevado Coropuna volcanic complex
The Nevado Coropuna volcanic complex (NCVC), located in the northernmost CAVZ (15°3’ S, 72º39’ W), includes several edifices, aligned WNW-ESE above Neogene ignimbrites. Adjacent composite volcanoes include the Late Pliocene, eroded Sunjillpa to the WNW and the glacially eroded, 0.6-0.25 Ma-old Cunciacha to the ESE. Located on the west flank of the Western Cordillera, the asymmetric volcanic complex shows stubby lava flows overlying the NE, 4500 m-high plateau, contrasting with long, inverted lava flows and debris-avalanche deposits filling deep valleys draining the steep SW flanks. The central, highest NCVC is a cluster of five, aligned lava domes reaching 6160 and 6330 masl. The dome cluster and its voluminous lava flows overlie an old stratovolcano with inverted lava flows dated at 1.02 Ma. The 0.4 Ma-old base of dome cluster is overlain by lower lava flows c. 270 - 254 ka, middle lava flows c. 118 - 108 ka, and the uppermost lava domes 70 – 60 ka. A high-spatial resolution DEM shows six vents on the domes and one collapse scar open to the south. NCVC has grown atop a caldera as shown by AMS data collected on Early Quaternary ignimbrites dipping away west, south and east of NCVC, and by abnormal contacts with both adjacent volcanoes to the WNW and the ESE. All lavas show two major compositional fields of high-K andesites and dacites (SiO2 57-67%wt). Harker diagrams and trace elements suggest AFC magmatic processes. Although CNVC tephra and PDC deposits represent a small volume, we observed Late Glacial Plinian fallout are scattered and Holocene ashfall layers are associated with three lava flows, the youngest being 1700 to 2400 yr old. The Nevado Coropuna ice cap c. 44.1 km2 is arguably the largest in the world tropical belt
Sub-microsecond correlations in photoluminescence from InAs quantum dots
Photon correlation measurements reveal memory effects in the optical emission
of single InAs quantum dots with timescales from 10 to 800 ns. With above-band
optical excitation, a long-timescale negative correlation (antibunching) is
observed, while with quasi-resonant excitation, a positive correlation
(blinking) is observed. A simple model based on long-lived charged states is
presented that approximately explains the observed behavior, providing insight
into the excitation process. Such memory effects can limit the internal
efficiency of light emitters based on single quantum dots, and could also be
problematic for proposed quantum-computation schemes.Comment: 8 pages, 8 figure
The Centurion 18 telescope of the Wise Observatory
We describe the second telescope of the Wise Observatory, a 0.46-m Centurion
18 (C18) installed in 2005, which enhances significantly the observing
possibilities. The telescope operates from a small dome and is equipped with a
large-format CCD camera. In the last two years this telescope was intensively
used in a variety of monitoring projects.
The operation of the C18 is now automatic, requiring only start-up at the
beginning of a night and close-down at dawn. The observations are mostly
performed remotely from the Tel Aviv campus or even from the observer's home.
The entire facility was erected for a component cost of about 70k$ and a labor
investment of a total of one man-year.
We describe three types of projects undertaken with this new facility: the
measurement of asteroid light variability with the purpose of determining
physical parameters and binarity, the following-up of transiting extrasolar
planets, and the study of AGN variability. The successful implementation of the
C18 demonstrates the viability of small telescopes in an age of huge
light-collectors, provided the operation of such facilities is very efficient.Comment: 16 pages, 13 figures, some figures quality was degraded, accepted for
publication in Astrophysics and Space Scienc
Limiting Carleman weights and anisotropic inverse problems
In this article we consider the anisotropic Calderon problem and related
inverse problems. The approach is based on limiting Carleman weights,
introduced in Kenig-Sjoestrand-Uhlmann (Ann. of Math. 2007) in the Euclidean
case. We characterize those Riemannian manifolds which admit limiting Carleman
weights, and give a complex geometrical optics construction for a class of such
manifolds. This is used to prove uniqueness results for anisotropic inverse
problems, via the attenuated geodesic X-ray transform. Earlier results in
dimension were restricted to real-analytic metrics.Comment: 58 page
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