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Tintype of Man with Derby Hat leaning against Chair [n.d.]

Fonte: Brock University Publicador: Brock University
Tipo: Artigo de Revista Científica
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An unidentified young Black gentleman poses beside a chair in this small tintype photograph. Both the name of the photographer and the date the photo was taken are unknown. The upper and lower left-hand corners have been cut and the tintype is slightly discolored and bent. This tintype was among the family memorabilia in the possession of Iris Sloman Bell, of St. Catharines, Ontario. The Bell - Sloman families are descended from former slaves from the United States."Tintypes were the invention of Prof. Hamilton Smith of Ohio. They begin as thin sheets of iron, covered with a layer of black paint. This serves as the base for the same iodized collodion coating and silver nitrate bath used in the ambrotype process. First made in 1856, millions were produced well into the twentieth century. When tintypes were finished in the same sorts of mats and cases used for ambrotypes, it can be almost impossible to distinguish which process was used without removing the image to examine the substrate." Source: American Museum of Photography http://www.photographymuseum.com/primer.html

A woman wearing a black mourning dress in Moore Town, Portland, Jamaica; The Bryant Slides Collection; The Bryant Slides Collection, Jamaica

Unknown ( Photographer )
Tipo: still image Formato: 35 mm
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The slides were taken on collecting trips sponsored by the William L. Bryant Foundation, where books, music and art indigenous to the regions were gathered. The are organized by geographical location.; In this picture, an older woman is wearing a black dress and hat as a sign of mourning. In the background is a wooden hut. Inhabitants of Moore Town, Portland, Jamaica are descendants of Maroons, escaped slaves who were able to maintain some aspects of their African cultures. Slide labeled Jam. Moore Town in mourning.

The Black Arts Movement and its Influence on Contemporary Visual Art, Music, and Literature

Labisch, Martin
Tipo: ResearchPaper
Português
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Erörterung der Einflüsse die das Black Arts Movement in den Bereichen Musik, Literatur und visueller Kunst hatte und immer noch hat.; Explanation of the influences the Black Arts Movement had and still has in the fields of music, literature, and visual art.

Hochauflösende Untersuchungen von Biomarkern an epikontinentalen Schwarzschiefern des Unteren Toarciums (Posidonienschiefer, Lias e) von SW-Deutschland; High-resolution biomarker investigations of Lower Toarcian epicontinental black shales (Posidonia Shale, SW-Germany)

Frimmel, Andreas
Tipo: Dissertação
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Die detaillierte Beprobung eines Komposit-Profils des Posidonienschiefers (Unteres Toarcium) aus dem Raum Dotternhausen (SW-Deutschland) hat einen hochauflösenden organisch-geochemischen Datensatz geliefert. Im Vordergrund der Untersuchungen stand die genaue Charakterisierung und Beschreibung der Zusammensetzung des organischen Materials anhand von Biomarkern und stabilen Isotopen. Ziel dieser Arbeit war es, die Kopplung klimatischer und ozeanographischer Faktoren mit der Sauerstoffverfügbarkeit und damit die Lebensbedingungen am Meeresboden und in der nahen Wassersäule der epikontinentalen Schwarzschiefer zu rekonstruieren. Die sequenzstratigraphische Entwicklung des Meeresspiegels im Posidonienschiefer von SW-Deutschland, die sich anhand des C27/C29-Steran-Verhältnisses sowie durch sedimentologische und palökologische Beobachtungen ableiten lässt, steht im engen Zusammenhang mit den Veränderungen der Sauerstoffverfügbarkeit im Posidonienschiefer-Meer. Verschiedene Redox- und Alkalinitätsparameter folgen dem Verlauf der Meeresspiegelkurve 3. Ordnung und lassen sich gut mit den untergeordneten Zyklen 4. Ordnung korrelieren. Erstmals konnten neben sulfatreduzierenden Bakterien durch langkettige Isoprenoide auch methanogene Archaebakterien im Posidonienschiefer von SW-Deutschland identifiziert werden. Das Zusammenwirken methanoxidierender und sulfatreduzierender Bakterien im Bereich der anaeroben Methanoxidations-Zone führte zu einer Zunahme der Alkalinität im Porenwasser...

Chris Eagle: Ripples in the Gene Pool - Creating Genetic: Mutations to Survive the Vulnerability Window [video]

Eagle, Chris
Tipo: Vídeo
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Reverse engineers often like to argue that a prime motivator for their activities is the desire to discover and patch vulnerabilities in closed-source binary software. Given the veritable plethora.. nay, Katrina-like flood of vulnerabilities being discovered on a near daily basis, one has to wonder where all these binary patches are hiding. Clearly this argument is a sham to make reverse engineers feel better about their DMCA violating activities. Now, just to be clear, there have been one or two third party binary patches released in the past year, but why haven't there been more? Is it truly a difficult task to develop such a patch or are our sights simply set too high? Is a true fix to the problem a requirement or is it sufficient to modify the vulnerable program just enough to make it immune to scripted attacks, the goal being to provide sufficient protection to survive until a vendor supplied patch can truly fix the problem. Dan Geer argued that a software monoculture is a dangerous thing leading to the rapid spread of malicious code in the event of a public vulnerability disclosure. The goal of this talk is to discuss simple yet effective measures to introduce sufficient genetic diversity into an inbred piece of software to allow it to survive in the wild until a vendor supplied update becomes available. Bio: Chris Eagle is a Defcon Black Badge holder...

A woman wearing black in Moore Town, Portland, Jamaica; The Bryant Slides Collection; The Bryant Slides Collection, Jamaica

Unknown ( Photographer )
Tipo: still image Formato: 35 mm
Português
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37.10106%
The slides were taken on collecting trips sponsored by the William L. Bryant Foundation, where books, music and art indigenous to the regions were gathered. The are organized by geographical location.; This older woman, pictured, is wearing a black dress and hat. In the background is a wooden house with a zinc roof. On the house's verandah are tables and chairs with pots and a cup. Inhabitants of Moore Town, Portland, Jamaica are descendants of Maroons, escaped slaves who were able to maintain some aspects of their African cultures. Slide labeled Jam. Moore Town.

Black Hole in Thermal Equilibrium with a Spin-2 Quantum Field

Hochberg, David; Sushkov, Sergey V.
Tipo: Artigo de Revista Científica
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An approximate form for the vacuum averaged stress-energy tensor of a conformal spin-2 quantum field on a black hole background is employed as a source term in the semiclassical Einstein equations. Analytic corrections to the Schwarzschild metric are obtained to first order in $\epsilon = {\hbar}/M^2$, where $M$ denotes the mass of the black hole. The approximate tensor possesses the exact trace anomaly and the proper asymptotic behavior at spatial infinity, is conserved with respect to the background metric and is uniquely defined up to a free parameter $\hat c_2$, which relates to the average quantum fluctuation of the field at the horizon. We are able to determine and calculate an explicit upper bound on $\hat c_2$ by requiring that the entropy due to the back-reaction be a positive increasing function in $r$. A lower bound for $\hat c_2$ can be established by requiring that the metric perturbations be uniformly small throughout the region $2M \leq r < r_o$, where $r_o$ is the radius of perturbative validity of the modified metric. Additional insight into the nature of the perturbed spacetime outside the black hole is provided by studying the effective potential for test particles in the vicinity of the horizon.; Comment: 21 pages in plain LaTex. Three figures available upon request from the first author

The Dirac Equation in Kerr-Newman-AdS Black Hole Background

Belgiorno, Francesco; Cacciatori, Sergio L.
Tipo: Artigo de Revista Científica
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We consider the Dirac equation on the Kerr-Newman-AdS black hole background. We first perform the variable separation for the Dirac equation and define the Hamiltonian operator $\hat H$. Then we show that for a massive Dirac field with mass $\mu\geq \frac{1}{2l}$ essential selfadjointness of $\hat H$ on $C_0^{\infty} ((r_+,\infty) \times S^2)^4$ is obtained even in presence of the boundary-like behavior of infinity in an asymptotically AdS black hole background. Furthermore qualitative spectral properties of the Hamiltonian are taken into account and in agreement with the existing results concerning the case of stationary axi-symmetric asymptotically flat black holes we infer the absence of time-periodic and normalizable solutions of the Dirac equation around the black hole in the non-extremal case.; Comment: 27 pages, AMS style. Some misprints corrected. Improvements in sections 1,5 and 6 and in Appendix A (improved discussion of the Dirac quantization condition). References added

Nonlinear $\hat{W}_{\infty}$ Current Algebra in the SL(2,R)/U(1) Coset Model

Yu, Feng; Wu, Yong-Shi
Tipo: Artigo de Revista Científica
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Previously we have established that the second Hamiltonian structure of the KP hierarchy is a nonlinear deformation, called $\hat{W}_{\infty}$, of the linear, centerless $W_{\infty}$ algebra. In this letter we present a free-field realization for all generators of $\hat{W}_{\infty}$ in terms of two scalars as well as an elegant generating function for the $\hat{W}_{\infty}$ currents in the classical conformal $SL(2,R)/U(1)$ coset model. After quantization, a quantum deformation of $\hat{W}_{\infty}$ appears as the hidden current algebra in this model. The $\hat{W}_{\infty}$ current algebra results in an infinite set of commuting conserved charges, which might give rise to $W$-hair for the 2d black hole arising in the corresponding string theory at level $k=9/4$.; Comment: 11p

Where angular momentum goes in a precessing black hole binary

Lousto, Carlos O.; Zlochower, Yosef
Tipo: Artigo de Revista Científica
Português
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We evolve a set of 32 equal-mass black-hole binaries with collinear spins (with intrinsic spin magnitudes $|\vec{S}_{1,2}/m^2_{1,2}|=0.8$) to study the effects of precession in the highly nonlinear plunge and merger regimes. We compare the direction of the instantaneous radiated angular momentum, $\hat{\delta J}_{\rm rad}(t)$, to the directions of the total angular momentum, $\hat{J}(t)$, and the orbital angular momentum, $\hat{L}(t)$. We find that $\hat{\delta J}_{\rm rad}(t)$ approximately follows $\hat{L}$ throughout the evolution. During the orbital evolution and merger, we observe that the angle between $\vec{L}$ and total spin $\vec{S}$ is approximately conserved to within $1^\circ$, which allows us to propose and test models for the merger remnant's mass and spin. For instance, we verify that the \hangup effect is the dominant effect and largely explains the observed total energy and angular momentum radiated by these precessing systems. We also verify that the total angular momentum, which significantly decreases in magnitude during the inspiral, varies in direction by less than $\sim 5^\circ$. The maximum variation in the direction of $\vec J$ occurs when the spins are nearly antialigned with the orbital angular momentum. Based on our results...

Holographic phase transitions from higgsed, non abelian charged black holes

Giordano, Gaston L.; Lugo, Adrian R.
Tipo: Artigo de Revista Científica
Português
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We find solutions of a gravity-Yang-Mills-Higgs theory in four dimensions that represent asymptotic anti-de Sitter charged black holes with partial/full gauge symmetry breaking. We then apply the AdS/CFT correspondence to study the strong coupling regime of a $2+1$ quantum field theory at temperature $T$ and finite chemical potential, which undergoes transitions to phases exhibiting the condensation of a composite charged vector operator below a critical temperature $T_c$, presumably describing $p+ip/p$-wave superconductors. In the case of $p+ip$-wave superconductors the transitions are always of second order. But for $p$-wave superconductors we determine the existence of a critical value $\alpha_c$ of the gravitational coupling (for fixed Higgs v.e.v. parameter $\hat m_W$) beyond which the transitions become of first order. As a by-product, we show that the $p$-wave phase is energetically favored over the $p+ip$ one, for any values of the parameters. We also find the ground state solutions corresponding to zero temperature. Such states are described by domain wall geometries that interpolate between $AdS_4$ spaces with different light velocities, and for a given $\hat m_{W}$, they exist below a critical value of the coupling. The behavior of the order parameter as function of the gravitational coupling near the critical coupling suggests the presence of second order quantum phase transitions. We finally study the dependence of the solution on the Higgs coupling...

Characterizing Seller-Driven Black-Hat Marketplaces

Farooqi, Shehroze; Ikram, Muhammad; Irfan, Gohar; De Cristofaro, Emiliano; Friedman, Arik; Jourjon, Guillaume; Kaafar, Mohamed Ali; Shafiq, M. Zubair; Zaffar, Fareed
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.350527%
This paper investigates two seller-driven black-hat online marketplaces, SEOClerks and MyCheapJobs, aiming to shed light on the services they offer as well as sellers and customers they attract. We perform a measurement-based analysis based on complete crawls of their websites and find that the vast majority of services target popular social media and e-commerce websites, such as website backlinks, Instagram followers, or Twitter retweets, and estimate revenues to be at least $1.3M for SEOClerks and$116K for MyCheapJobs. Our analysis uncovers the characteristics of these two non-underground seller-driven marketplaces and shows that many top sellers belong to an "insider ring", where accounts created close to the marketplaces' launch account for the majority of the sales. We provide first-of-its-kind evidence that marketplace operators may be involved in perpetuating fraudulent activities and hope to facilitate deployment of technical, legal, and economic countermeasures.

Tidal Interaction between a Fluid Star and a Kerr Black Hole in Circular Orbit

Wiggins, Paul; Lai, Dong
Tipo: Artigo de Revista Científica
Português
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We present a semi-analytic study of the equilibrium models of close binary systems containing a fluid star (mass $m$ and radius $R_0$) and a Kerr black hole (mass $M$) in circular orbit. We consider the limit $M\gg m$ where spacetime is described by the Kerr metric. The tidally deformed star is approximated by an ellipsoid, and satisfies the polytropic equation of state. The models also include fluid motion in the stellar interior, allowing binary models with nonsynchronized stellar spin (as expected for coalescing neutron star-black hole binaries) to be constructed. Tidal disruption occurs at orbital radius $r_{\rm tide}\sim R_0(M/m)^{1/3}$, but the dimensionless ratio $\hat r_{\rm tide}=r_{\rm tide}/[R_0(M/m)^{1/3}]$ depends on the spin parameter of the black hole as well as on the equation of state and the internal rotation of the star. We find that the general relativistic tidal field disrupts the star at a larger $\hat r_{\rm tide}$ than the Newtonian tide; the difference is particularly prominent if the disruption occurs in the vicinity of the black hole's horizon. In general, $\hat r_{\rm tide}$ is smaller for a (prograde rotating) Kerr black hole than for a Schwarzschild black hole. We apply our results to coalescing black hole-neutron star and black hole-white dwarf binaries. The tidal disruption limit is important for characterizing the expected gravitational wave signals and is relevant for determining the energetics of gamma ray bursts which may result from such disruption.; Comment: 29 pages including 8 figures. Minor changes and update. To appear in ApJ...

Black Hole Entropy

Frolov, Valeri
Tipo: Artigo de Revista Científica
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In the talk different definitions of the black hole entropy are discussed and compared. It is shown that the Bekenstein-Hawking entropy $S^{BH}$ (defined by the response of the free energy of a system containing a black hole on the change of the temperature) differs from the statistical- mechanical entropy $S^{SM}=-\mbox{Tr}(\hat{\rho}\ln \hat{\rho})$ (defined by counting internal degrees of freedom of a black hole). A simple explanation of the universality of the Bekenstein-Hawking entropy (i.e. its independence of the number and properties of the fields which might contribute to $S^{SM}$) is given.; Comment: 16 pages, LaTeX; Talk at the Winnipeg Heat Kernel Conference (Aug,94)

Exact and asymptotic black branes with spherical compactification

Chopovsky, Alexey; Eingorn, Maxim; Zhuk, Alexander
Tipo: Artigo de Revista Científica
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In the six-dimensional Kaluza-Klein model with the multidimensional cosmological constant $\Lambda_6$, we obtain the black brane with spherical compactification of the internal space. The matter source for this exact solution consists of two parts. First, it is a fine-tuned homogeneous perfect fluid which provides spherical compactification of the internal space. Second, it is a gravitating massive body with the dustlike equation of state in the external space and tension $\hat p_1=-(1/2)\hat\varepsilon$ in the internal space. This solution exists both in the presence and absence of $\Lambda_6$. In the weak-field approximation, we also get solutions of the linearized Einstein equations for the model with spherical compactification. Here, the gravitating matter source has the dustlike equation of state in the external space and an arbitrary equation of state $\hat p_1=\Omega \hat\varepsilon$ in the internal space. In the case $\Lambda_6>0$ and $\Omega\neq -1/2$, these approximate solutions tend asymptotically to the weak-field limit of the exact black brane solution. Both the exact and asymptotic black branes satisfy the gravitational experiments at the same level of accuracy as general relativity.; Comment: 6 pages, no figures

Thermodynamics of Third Order Lovelock-Born-Infeld Black Holes

Li, Peng; Yue, Rui-Hong; Zou, De-Cheng
Tipo: Artigo de Revista Científica
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We here explore black holes in the third order Lovelock gravity coupling with nonlinear Born-Infeld electromagnetic field. Considering special second and third order coefficients ($\hat{\alpha}_2^2=3\hat{\alpha}_3=\alpha^2$), we analyze the thermodynamics of third order Lovelock-Born-Infeld black holes and, in 7-dimensional AdS space-time, discuss the stability of black holes in different event horizon structures. We find that the cosmological constant $\Lambda$ plays an important role in the distribution of stable regions of black holes.; Comment: 11 pages, 21 figures

Black Hole Entropy: Off-Shell vs On-Shell

Frolov, V. P.; Fursaev, D. V.; Zelnikov, A. I.
Tipo: Artigo de Revista Científica
Português
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Different methods of calculation of quantum corrections to the thermodynamical characteristics of a black hole are discussed and compared. The relation between on-shell and off-shell approaches is established. The off-shell methods are used to explicitly demonstrate that the thermodynamical entropy $S^{TD}$ of a black hole, defined by the first thermodynamical law, differs from the statistical-mechanical entropy $S^{SM}$, determined as $S^{SM}=-\mbox{Tr}(\hat{\rho}^H\ln\hat{\rho}^H)$ for the density matrix $\hat{\rho}^H$ of a black hole. It is shown that the observable thermodynamical black hole entropy can be presented in the form $S^{TD}=\pi {\bar r}_+^2+S^{SM}-S^{SM}_{Rindler}$. Here ${\bar r}_+$ is the radius of the horizon shifted because of the quantum backreaction effect, and $S^{SM}_{Rindler}$ is the statistical-mechanical entropy calculated in the Rindler space.; Comment: 47 pages, latex, 7 postscript figures have been included since the first submission of the article

Dyonic Non-Abelian Black Holes

Brihaye, Y.; Hartmann, B.; Kunz, J.; Tell, N.
Tipo: Artigo de Revista Científica
Português
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We study static spherically symmetric dyonic black holes in Einstein-Yang-Mills-Higgs theory. As for the magnetic non-abelian black holes, the domain of existence of the dyonic non-abelian black holes is limited with respect to the horizon radius and the dimensionless coupling constant $\alpha$, which is proportional to the ratio of vector meson mass and Planck mass. At a certain critical value of this coupling constant, $\hat \alpha$, the maximal horizon radius is attained. We derive analytically a relation between $\hat \alpha$ and the charge of the black hole solutions and confirm this relation numerically. Besides the fundamental dyonic non-abelian black holes, we study radially excited dyonic non-abelian black holes and globally regular gravitating dyons.; Comment: LaTeX, 22 pages, 16 figures, three figures added, file manipulation error in previous replace

Black Hole Entropy: Thermodynamics, Statistical-Mechanics and Subtraction Procedure

Frolov, V. P.; Fursaev, D. V.; Zelnikov, A. I.
Tipo: Artigo de Revista Científica
The thermodynamical one-loop entropy $S^{TD}$ of a two-dimensional black hole in thermal equilibrium with the massless quantum gas is calculated. It is shown that $S^{TD}$ includes the Bekenstein-Hawking entropy, evaluated for the quantum corrected geometry, and the finite difference of statistical mechanical entropies $-Tr\hat{\rho}\ln\hat{\rho}$ for the gas on the black hole and Rindler spaces. This result demonstrates in an explicit form that the relation between thermodynamical and statistical-mechanical entropies of a black hole is non-trivial and requires special subtraction procedure.; Comment: 11 pages, latex file
We present results on the mass and spin of the final black hole from mergers of equal mass, spinning black holes. The study extends over a broad range of initial orbital configurations, from direct plunges to quasi-circular inspirals to more energetic orbits (generalizations of Newtonian elliptical orbits). It provides a comprehensive search of those configurations that maximize the final spin of the remnant black hole. We estimate that the final spin can reach a maximum spin $a/M_h \approx 0.99\pm 0.01$ for extremal black hole mergers. In addition, we find that, as one increases the orbital angular momentum from small values, the mergers produce black holes with mass and spin parameters $\lbrace M_h/M, a/M_h \rbrace$ ~spiraling around the values $\lbrace \hat M_h/M, \hat a/M_h \rbrace$ of a {\it golden} black hole. Specifically, $(M_h-\hat M_h)/M \propto e^{\pm B\,\phi}\cos{\phi}$ and $(a-\hat a)/M_h \propto e^{\pm C\,\phi}\sin{\phi}$, with $\phi$ a monotonically growing function of the initial orbital angular momentum. We find that the values of the parameters for the \emph{golden} black hole are those of the final black hole obtained from the merger of a binary with the corresponding spinning black holes in a quasi-circular inspiral.; Comment: Version accepted for publication in Phys. Rev. D Rapid Comm.