109 research outputs found
Security consideration for virtualization
Virtualization is not a new technology, but has recently experienced a resurgence
of interest among industry and research. New products and technologies are emerging
quickly, and are being deployed with little considerations to security concerns.
It is vital to understand that virtualization does not improve security by default.
Hence, any aspect of virtualization needs to undergo constant security analysis
and audit. Virtualization is a changeable and very dynamic field with an uncertain
outcome. In this paper we outline the security model of hypervisors and illustrate
the significance of ongoing security analysis by describing different state of the
art threat models. Finally, we provide recommendations and design considerations
for a more secure virtual infrastructure
Spinoza i platonizm. Cz. II
The first Polish translation of a classic work on the relation of Spinoza and Platonism (part II)Jolanta Żelazna (tłumaczka, Uniwersytet Mikołaja Kopernika w Toruniu
Spinoza i platonizm. Cz. I
The first Polish translation of a classic work on the relation of Spinoza and Platonism (part I)Przekład i opracowanie Jolanta Żelazn
The Centers of Early-Type Galaxies with HST III: Non-Parametric Recovery of Stellar Luminosity Distributions
We have non-parametrically determined the luminosity density profiles and
their logarithmic slopes for 42 early-type galaxies observed with HST. Assuming
that the isodensity contours are spheroidal, then the luminosity density is
uniquely determined from the surface brightness data through the Abel equation.
For nearly all the galaxies in our sample, the logarithmic slope of the
luminosity density measured at 0.1" (the innermost reliable measurement with
the uncorrected HST) is significantly different from zero; i.e. most elliptical
galaxies have cusps. There are only two galaxies for which an analytic core
cannot be excluded. The distribution of logarithmic slopes at 0.1" appears to
be bimodal, confirming the conclusion of Lauer et al. (1995) that early-type
galaxies can be divided into two types based on their surface-brightness
profiles; i.e., those with cuspy cores and those whose steep power-law profiles
continue essentially unchanged in to the resolution limit. The peaks in the
slope distribution occur at -0.8 and -1.9. More than half of the galaxies have
slopes steeper than -1.0. Taken together with the recent theoretical work of
Merritt & Fridman, these results suggest that many (and maybe most) elliptical
galaxies are either nearly axisymmetric or spherical near the center, or slowly
evolve due to the influence of stochastic orbits.Comment: uuencoded compressed tarfile 21 pages with 6 fig, 1 tabl
KI-Methoden beim Entwurf komplexer Gebäude
Anhand von Ergebnissen aus dem FABEL-Projekt wird gezeigt, welche Beiträge Methoden der Künstlichen Intelligenz, insbesondere der Wissensverarbeitung beim Entwurf komplexer Gebäude leisten können. Exemplarisch werden spezialisierte wissensintensive Methoden, und allgemeine fallbasierte Methoden zum Retrieval und zur Wiederverwendung früherer Entwürfe vorgestellt. Es werden Fragen der Integration von Wissen, Fällen und Daten diskutiert. Der Prototyp des FABEL-Projekts verwendet die Metapher der virtuellen Baustelle, um die verschiedenen Methoden als Planungswerkzeuge in einem CAD-System integriert anzubieten. Ein Planungsmodell dient der zusätzlichen Orientierung des Planers. Die Ergebnisse sind interessant für den Entwurf komplexer Unikate, dürften aber auch als Zusatz zu elektronisch angebotenen Katalogen relevant sein
Spectroscopic Evidence for a Supermassive Black Hole in NGC 4486B
The stellar kinematics of the dwarf elliptical galaxy NGC 4486B have been
measured in seeing sigma_* = .22 arcsec with the Canada-France-Hawaii
Telescope. Lauer et al. 1996, ApJ, 471, L79 have shown that NGC 4486B is
similar to M31 in having a double nucleus. We show that it also resembles M31
in its kinematics. The velocity dispersion gradient is very steep: sigma
increases from 116 +- 6 km/s at r = 2" - 6" to 281 +- 11 km/s at the center.
This is much higher than expected for an elliptical galaxy of absolute
magnitude M_B = -16.8: NGC 4486B is far above the scatter in the Faber-Jackson
correlation between sigma and bulge luminosity. Therefore the King core
mass-to-light ratio, M/L_V = 20, is unusually high compared with normal values
for old stellar populations. We construct dynamical models with isotropic
velocity dispersions and show that they reproduce black hole (BH) masses
derived by more detailed methods. We also fit axisymmetric, three-integral
models. Isotropic models imply that NGC 4486B contains a central dark object,
probably a BH, of mass M_BH = 6^{+3}_{-2} x 10^8 M_sun. However, anisotropic
models fit the data without a BH if the ratio of radial to azimuthal
dispersions is ~ 2 at 1". Therefore this is a less strong BH detection than the
ones in M31, M32, and NGC 3115. A 6 x 10^8 M_sun BH is 9 % of the mass M_bulge
in stars; even if M_BH is smaller than the isotropic value, M_BH/M_bulge is
likely to be unusually large. Double nuclei are a puzzle because the dynamical
friction timescales for self-gravitating star clusters in orbit around each
other are short. Since both M31 and NGC 4486B contain central dark objects, our
results support models in which the survival of double nuclei is connected with
the presence of a BH (e. g., Tremaine 1995, AJ, 110, 628).Comment: 5 pages, 5 figs, TeX, ApJL in pres
The Centers of Early-Type Galaxies with HST. IV. Central Parameter Relations
We analyze Hubble Space Telescope surface-brightness profiles of 61
elliptical galaxies and spiral bulges (hot galaxies). Luminous hot galaxies
have cuspy cores with steep outer power-law profiles that break at r ~ r_b to
shallow inner profiles with logslope less than 0.3. Faint hot galaxies show
steep, largely featureless power-law profiles at all radii and lack cores. The
centers of power-law galaxies are up to 1000 times denser in mass and
luminosity than the cores of large galaxies at a limiting radius of 10 pc. At
intermediate magnitudes (-22.0 < M_V < -20.5), core and power-law galaxies
coexist, and there is a range in r_b at a given luminosity of at least two
orders of magnitude. Central properties correlate with global rotation and
shape: core galaxies tend to be boxy and slowly rotating, whereas power-law
galaxies tend to be disky and rapidly rotating. The dense power-law centers of
disky, rotating galaxies are consistent with their formation in gas-rich
mergers. The parallel proposition that cores are simply the by-products of
gas-free stellar mergers is less compelling. For example, core galaxies accrete
small, dense, gas-free galaxies at a rate sufficient to fill in low-density
cores if the satellites survived and sank to the center. An alternative model
for core formation involves the orbital decay of massive black holes (BHs): the
BH may heat and eject stars from the center, eroding a power law if any exists
and scouring out a core. An average BH mass per spheroid of 0.002 times the
stellar mass yields reasonably good agreement with the masses and radii of
observed cores and in addition is consistent with the energetics of AGNs and
kinematic detections of BHs in nearby galaxies.Comment: 40 pages (Tex) with 10 figures and 4 tables (Postscript). To appear
in the November 1997 Astronomical Journal. The discussion section is
significantly revised from the original submission to Astro-ph, dated October
1996. One figure is slightly altered, and the data tables are the sam
The slope of the black-hole mass versus velocity dispersion correlation
Observations of nearby galaxies reveal a strong correlation between the mass
of the central dark object M and the velocity dispersion sigma of the host
galaxy, of the form log(M/M_sun) = a + b*log(sigma/sigma_0); however, published
estimates of the slope b span a wide range (3.75 to 5.3). Merritt & Ferrarese
have argued that low slopes (<4) arise because of neglect of random measurement
errors in the dispersions and an incorrect choice for the dispersion of the
Milky Way Galaxy. We show that these explanations account for at most a small
part of the slope range. Instead, the range of slopes arises mostly because of
systematic differences in the velocity dispersions used by different groups for
the same galaxies. The origin of these differences remains unclear, but we
suggest that one significant component of the difference results from Ferrarese
& Merritt's extrapolation of central velocity dispersions to r_e/8 (r_e is the
effective radius) using an empirical formula. Another component may arise from
dispersion-dependent systematic errors in the measurements. A new determination
of the slope using 31 galaxies yields b=4.02 +/- 0.32, a=8.13 +/- 0.06, for
sigma_0=200 km/s. The M-sigma relation has an intrinsic dispersion in log M
that is no larger than 0.3 dex. In an Appendix, we present a simple model for
the velocity-dispersion profile of the Galactic bulge.Comment: 37 pages, 9 figure
- …