393 research outputs found
Perturbations of higher-dimensional spacetimes
We discuss linearized gravitational perturbations of higher dimensional
spacetimes. For algebraically special spacetimes (e.g. Myers-Perry black
holes), we show that there exist local gauge invariant quantities linear in the
metric perturbation. These are the higher dimensional generalizations of the 4d
Newman-Penrose scalars that (in an algebraically special vacuum spacetime)
satisfy decoupled equations of motion. We show that decoupling occurs in more
than four dimensions if, and only if, the spacetime admits a null geodesic
congruence with vanishing expansion, rotation and shear. Decoupling of
electromagnetic perturbations occurs under the same conditions. Although these
conditions are not satisfied in black hole spacetimes, they are satisfied in
the near-horizon geometry of an extreme black hole.Comment: 21 pages (v2:Minor corrections, accepted by CQG.
Marine stratocumulus cloud characteristics from multichannel satellite measurements
Understanding the effects of aerosols on the microphysical characteristics of marine stratocumulus clouds, and the resulting influence on cloud radiative properties, is a primary goal of FIRE. The potential for observing variations of cloud characteristics that might be related to variations of available aerosols is studied. Some results from theoretical estimates of cloud reflectance are presented. Also presented are the results of comparisons between aircraft measured microphysical characteristics and satellite detected radiative properties of marine stratocumulus clouds. These results are extracted from Mineart where the analysis procedures and a full discussion of the observations are presented. Only a brief description of the procedures and the composite results are presented
Generalization of the Geroch-Held-Penrose formalism to higher dimensions
Geroch, Held and Penrose invented a formalism for studying spacetimes
admitting one or two preferred null directions. This approach is very useful
for studying algebraically special spacetimes and their perturbations. In the
present paper, the formalism is generalized to higher-dimensional spacetimes.
This new formalism leads to equations that are considerably simpler than those
of the higher-dimensional Newman-Penrose formalism employed previously. The
dynamics of p-form test fields is analyzed using the new formalism and some
results concerning algebraically special p-form fields are proved.Comment: 24 page
On the structure of the ergosurface of Pomeransky-Senkov black rings
We study the properties of the ergosurface of the Pomeransky-Senkov black
rings, and show that it splits into an "inner"' and an "outer" region. As for
the singular set, the topology of the "outer ergosurface" depends upon the
value of parameters.Comment: 14 pages, 1 figur
A new special class of Petrov type D vacuum space-times in dimension five
Using extensions of the Newman-Penrose and Geroch-Held-Penrose formalisms to
five dimensions, we invariantly classify all Petrov type vacuum solutions
for which the Riemann tensor is isotropic in a plane orthogonal to a pair of
Weyl alligned null directionsComment: 4 pages, 1 table, no figures. Contribution to the proceedings of the
Spanish Relativity Meeting 2010 held in Granada (Spain
The Q-test: Know Your Self-Monitoring Style in 6 Seconds
The current study compared the Q-test, a colloquial measure of self-monitoring, to the reliable and validated 18-item Self-Monitoring Scale-Revised (Gangestad & Snyder, 1985). Self-monitoring theory contends that individuals differ on how they regulate their self-presentation, and via self-observation individuals can adjust their behaviors to accommodate social situations (Snyder, 1987). Tracing the capital letter “Q” on the forehead can supposedly provide a rough measure of self-monitoring. The “Q” can be traced on the forehead in two different orientations. It can be traced such that its tail is placed in such a way that it is pointing towards the person’s left shoulder, making the capital “Q” readable to their audience. It can also be traced in such that its tail is placed in such a way that it is pointing towards the person’s right shoulder, making the capital “Q” readable to the person. In theory, a “Q” that is readable to others corresponds to high self-monitors and “Q” readable to the individual corresponds to low self-monitors. Results showed that the Q-test carries some merit; the correlation between the Q-test and Gangestad and Snyder’s (1985) 18-item Self-Monitoring Scale-Revised was statistically significant
Formal Reasoning Using an Iterative Approach with an Integrated Web IDE
This paper summarizes our experience in communicating the elements of
reasoning about correctness, and the central role of formal specifications in
reasoning about modular, component-based software using a language and an
integrated Web IDE designed for the purpose. Our experience in using such an
IDE, supported by a 'push-button' verifying compiler in a classroom setting,
reveals the highly iterative process learners use to arrive at suitably
specified, automatically provable code. We explain how the IDE facilitates
reasoning at each step of this process by providing human readable verification
conditions (VCs) and feedback from an integrated prover that clearly indicates
unprovable VCs to help identify obstacles to completing proofs. The paper
discusses the IDE's usage in verified software development using several
examples drawn from actual classroom lectures and student assignments to
illustrate principles of design-by-contract and the iterative process of
creating and subsequently refining assertions, such as loop invariants in
object-based code.Comment: In Proceedings F-IDE 2015, arXiv:1508.0338
Truth In Accounting: Dont Let It Die
Truth in Accounting, it seems to have a nice ring to it. Managed Earnings, this does not sound so good to us. This paper is about what is happening in the Accounting world and what needs to be done and by whom. This document highlights current and past events, such as Enron, Continental Vending and others, that have neglected to perpetuate truth in accounting
Type III and N Einstein spacetimes in higher dimensions: general properties
The Sachs equations governing the evolution of the optical matrix of geodetic
WANDs (Weyl aligned null directions) are explicitly solved in n-dimensions in
several cases which are of interest in potential applications. This is then
used to study Einstein spacetimes of type III and N in the higher dimensional
Newman-Penrose formalism, considering both Kundt and expanding (possibly
twisting) solutions. In particular, the general dependence of the metric and of
the Weyl tensor on an affine parameter r is obtained in a closed form. This
allows us to characterize the peeling behaviour of the Weyl "physical"
components for large values of r, and thus to discuss, e.g., how the presence
of twist affects polarization modes, and qualitative differences between four
and higher dimensions. Further, the r-dependence of certain non-zero scalar
curvature invariants of expanding spacetimes is used to demonstrate that
curvature singularities may generically be present. As an illustration, several
explicit type N/III spacetimes that solve Einstein's vacuum equations (with a
possible cosmological constant) in higher dimensions are finally presented.Comment: 19 page
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