22 research outputs found
Global geometry of two-dimensional charged black holes
The semiclassical geometry of charged black holes is studied in the context
of a two-dimensional dilaton gravity model where effects due to pair-creation
of charged particles can be included in a systematic way. The classical
mass-inflation instability of the Cauchy horizon is amplified and we find that
gravitational collapse of charged matter results in a spacelike singularity
that precludes any extension of the spacetime geometry. At the classical level,
a static solution describing an eternal black hole has timelike singularities
and multiple asymptotic regions. The corresponding semiclassical solution, on
the other hand, has a spacelike singularity and a Penrose diagram like that of
an electrically neutral black hole. Extremal black holes are destabilized by
pair-creation of charged particles. There is a maximally charged solution for a
given black hole mass but the corresponding geometry is not extremal. Our
numerical data exhibits critical behavior at the threshold for black hole
formation.Comment: REVTeX, 13 pages, 12 figures; Reference adde
Semi-classical geometry of charged black holes
At the classical level, two-dimensional dilaton gravity coupled to an abelian
gauge field has charged black hole solutions, which have much in common with
four-dimensional Reissner-Nordstrom black holes, including multiple asymptotic
regions, timelike curvature singularities, and Cauchy horizons. The black hole
spacetime is, however, significantly modified by quantum effects, which can be
systematically studied in this two-dimensional context. In particular, the
back-reaction on the geometry due to pair-creation of charged fermions
destabilizes the inner horizon and replaces it with a spacelike curvature
singularity. The semi-classical geometry has the same global topology as an
electrically neutral black hole.Comment: REVTeX, 4 pages, 2 figures; references adde
Ten myths about character, virtue and virtue education – plus three well-founded misgivings
Initiatives to cultivate character and virtue in moral education at school continue to provoke sceptical responses. Most of those echo familiar misgivings about the notions of character, virtue and education in virtue – as unclear, redundant, old-fashioned, religious, paternalistic, anti-democratic, conservative, individualistic, relative and situation dependent. I expose those misgivings as ‘myths’, while at the same time acknowledging three better-founded historical, methodological and practical concerns about the notions in question
c=1 Boundary Conformal Field Theory Revisited
Correlation functions of discrete primary fields in the c=1 boundary
conformal field theory of a scalar field in a critical periodic boundary
potential are computed using the underlying SU(2) symmetry of the model. Bulk
amplitudes are unambigously determined and we give a prescription for
amplitudes involving discrete boundary fields.Comment: LaTex, 8 pages, 1 figure, uses IOP style files. To appear in the
proceedings of the RTN workshop "The quantum structure of spacetime and the
geometric nature of fundamental interactions", Copenhagen, September 15-20,
200
Decoupling limits of N=4 super Yang-Mills on R x S^3
We find new decoupling limits of N=4 super Yang-Mills (SYM) on R x S^3 with
gauge group SU(N). These decoupling limits lead to decoupled theories that are
much simpler than the full N=4 SYM but still contain many of its interesting
features. The decoupling limits correspond to being in a near-critical region,
near a point with zero temperature and critical chemical potentials. The new
decoupling limits are found by generalizing the limits of hep-th/0605234 to
include not only the chemical potentials for the SU(4) R-symmetry of N=4 SYM
but also the chemical potentials corresponding to the SO(4) symmetry. In the
decoupled theories it is possible to take a strong coupling limit in a
controllable manner since the full effective Hamiltonian is known. For planar
N=4 SYM on R x S^3 all the decoupled theories correspond to fully integrable
spin chains. We study the thermodynamics of the decoupled theories and find the
Hagedorn temperature for small and large values of the effective coupling. We
find an alternative formulation of the decoupling limits in the microcanonical
ensemble. This leads to a characterization of certain regimes of weakly coupled
N=4 SYM in which there are string-like states. Finally, we find a similar
decoupling limit for pure Yang-Mills theory, which for the planar limit leads
to a fully integrable decoupled theory.Comment: 48 pages, 1 figure; added references, published versio
Cosmological Models and Renormalization Group Flow
We study cosmological solutions of Einstein gravity with a positive
cosmological constant in diverse dimensions. These include big-bang models that
re-collapse, big-bang models that approach de Sitter acceleration at late
times, and bounce models that are both past and future asymptotically de
Sitter. The re-collapsing and the bounce geometries are all tall in the sense
that entire spatial slices become visible to a comoving observer before the end
of conformal time, while the accelerating big-bang geometries can be either
short or tall. We consider the interpretation of these cosmological solutions
as renormalization group flows in a dual field theory and give a geometric
interpretation of the associated c-function as the area of the apparent
cosmological horizon in Planck units. The covariant entropy bound requires
quantum effects to modify the early causal structure of some of our big-bang
solutions.Comment: 26 pages, 11 figures, v2: improved discussion of entropy bounds,
references added, v3: minor changes, reference adde
Matching gauge theory and string theory in a decoupling limit of AdS/CFT
We identify a regime of the AdS/CFT correspondence in which we can
quantitatively match N=4 super Yang-Mills (SYM) for small 't Hooft coupling
with weakly coupled type IIB string theory on AdS_5 x S^5. We approach this
regime by taking the same decoupling limit on both sides of the correspondence.
On the gauge theory side only the states in the SU(2) sector survive, and in
the planar limit the Hamiltonian is given by the XXX_{1/2} Heisenberg spin
chain. On the string theory side we show that the decoupling limit corresponds
to a non-relativistic limit. In this limit some of the bosonic modes and all of
the fermionic modes of the string become infinitely heavy and decouple. We
first take the decoupling limit of the string sigma-model classically. This
enables us to identify a semi-classical regime with semi-classical string
states even though we are in a regime corresponding to small 't Hooft coupling.
We furthermore analyze the quantum corrections that enter in taking the limit.
From this we infer that gauge theory and string theory match, both in terms
of the action and the spectrum, for the leading part and the first correction
away from the semi-classical regime. Finally we consider the implications for
the hitherto unexplained matching of the one-loop contribution to the energy of
certain gauge theory and string theory states, and we explain how our results
give a firm basis for the matching of the Hagedorn temperature in
hep-th/0608115.Comment: 29 pages, 1 figure. v2: Version published in JHEP, section 4 improve
A homozygous loss-of-function mutation leading to CYBC1 deficiency causes chronic granulomatous disease
Publisher's version (útgefin grein)
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.Mutations in genes encoding subunits of the phagocyte NADPH oxidase complex are
recognized to cause chronic granulomatous disease (CGD), a severe primary immunodeficiency. Here we describe how deficiency of CYBC1, a previously uncharacterized protein in
humans (C17orf62), leads to reduced expression of NADPH oxidase’s main subunit (gp91phox)
and results in CGD. Analyzing two brothers diagnosed with CGD we identify a homozygous
loss-of-function mutation, p.Tyr2Ter, in CYBC1. Imputation of p.Tyr2Ter into 155K chipgenotyped Icelanders reveals six additional homozygotes, all with signs of CGD, manifesting
as colitis, rare infections, or a severely impaired PMA-induced neutrophil oxidative burst.
Homozygosity for p.Tyr2Ter consequently associates with inflammatory bowel disease (IBD)
in Iceland (P = 8.3 × 10−8; OR = 67.6), as well as reduced height (P = 3.3 × 10−4; −8.5 cm).
Overall, we find that CYBC1 deficiency results in CGD characterized by colitis and a distinct
profile of infections indicative of macrophage dysfunction.We wish to thank the family of the two probands, as well as all the other individuals who
participated in the study and whose contribution made this work possible.Peer Reviewe
Íslenskt sjávarfang : greining á stöðu og valkostir
Þessi ritgerð fjallar um ytra umhverfi og innra starf fiskvinnslufyrirtækisins Íslenskt Sjávarfang í Hrísey. Ritgerðin er byggð upp eftir ákveðinni aðferðafræði sem kennd er við hefðbundna stefnumótun.
Ytri greining leiddi í ljós ýmsar ógnanir. Þær helstu eru; minnkandi fiskneysla, lágt verð á staðkvæmdarvörum, minna framboð fisks á fiskmörkuðum og vaxandi samningsstyrkur stærstu kaupenda. Ýmis tækifæri eru fyrir hendi innan atvinnugreinarinar og má þar helst nefna aukna neyslu á forelduðum mat, vinnslu tengdri fiskeldi og sókn á nýja markaðshluta.
Íslenskt sjávarfang er að mörgu leyti illa statt fyrirtæki, t.a.m. er fjárhagsstaðan slæm og mikið hefur skort á skipulag í rekstri félagsins. Helstu styrkleikar ÍS liggja í mannauð og framleiðslutækjum. Aukið samstarf við Samherja á eflaust eftir að styrkja félagið til framtíðar.
Almennt séð þarf félagið að bæta skipulag og áætlanagerð, en auk þess þarf að standa betur að hráefnisinnkaupum og einfalda vinnsluna. Ýmsir valkostir eru í stöðunni fyrir Íslenskt sjávarfang, en ljóst er að fyrirtækið hefur enga burði til að standa í tilraunastarfsemi.
Útbúið var rekstrarlíkan sem byggir að mestu á rauntölum úr rekstri Íslensks sjávarfangs. Að því gefnu að forsendur líkansins séu réttar, ætti fyrirtækið að geta skilað jákvæðri rekstrarniðurstöðu.
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