16 research outputs found
Thermodynamics of Large AdS Black Holes
We consider leading order quantum corrections to the geometry of large AdS
black holes in a spherical reduction of four-dimensional Einstein gravity with
negative cosmological constant. The Hawking temperature grows without bound
with increasing black hole mass, yet the semiclassical back-reaction on the
geometry is relatively mild, indicating that observers in free fall outside a
large AdS black hole never see thermal radiation at the Hawking temperature.
The positive specific heat of large AdS black holes is a statement about the
dual gauge theory rather than an observable property on the gravity side.
Implications for string thermodynamics with an AdS infrared regulator are
briefly discussed.Comment: 17 pages, 1 figure, v2. added reference
Hawking Radiation from AdS Black Holes
We investigate Hawking radiation from black holes in (d+1)-dimensional
anti-de Sitter space. We focus on s-waves, make use of the geometrical optics
approximation, and follow three approaches to analyze the radiation. First, we
compute a Bogoliubov transformation between Kruskal and asymptotic coordinates
and compare the different vacua. Second, following a method due to Kraus,
Parikh, and Wilczek, we view Hawking radiation as a tunneling process across
the horizon and compute the tunneling probablility. This approach uses an
anti-de Sitter version of a metric originally introduced by Painleve for
Schwarzschild black holes. From the tunneling probability one also finds a
leading correction to the semi-classical emission rate arising from the
backreaction to the background geometry. Finally, we consider a spherically
symmetric collapse geometry and the Bogoliubov transformation between the
initial vacuum state and the vacuum of an asymptotic observer.Comment: 13 pages, latex2e, v2: some clarifications and references adde
Coulomb-gas formulation of SU(2) branes and chiral blocks
We construct boundary states in WZNW models using the bosonized
Wakimoto free-field representation and study their properties. We introduce a
Fock space representation of Ishibashi states which are coherent states of
bosons with zero-mode momenta (boundary Coulomb-gas charges) summed over
certain lattices according to Fock space resolution of . The Virasoro
invariance of the coherent states leads to families of boundary states
including the B-type D-branes found by Maldacena, Moore and Seiberg, as well as
the A-type corresponding to trivial current gluing conditions. We then use the
Coulomb-gas technique to compute exact correlation functions of WZNW primary
fields on the disk topology with A- and B-type Cardy states on the boundary. We
check that the obtained chiral blocks for A-branes are solutions of the
Knizhnik-Zamolodchikov equations.Comment: 14 pages, 3 figures, revtex4. Essentially the published versio
Strings in the Extended BTZ Spacetime
We study string theory on the extended spacetime of the BTZ black hole, as
described by an orbifold of the SL(2,R) WZW model. The full spacetime has an
infinite number of disconnected boundary components, each corresponding to a
dual CFT. We discuss the computation of bulk and boundary correlation functions
for operators inserted on different components. String theory correlation
functions are obtained by analytic continuation from an orbifold of the
SL(2,C)/SU(2) coset model. This yields two-point functions for general
operators, including those describing strings that wind around the horizon of
the black hole.Comment: 35 pages, harvmac, 5 eps figures, uses epsf.tex. (v2): Extended
discussion in section 3.1, typo corrections, references adde
Nanomateriaalit osana yhteiskuntaa : Kohti turvallista nanoteknologian tulevaisuutta
Katsaus sisältää tietoa nanomateriaalien käytöstä, turvallisuuteen liittyvistä kysymyksistä, sääntelystä, sekä tutkimuksesta Suomessa. Nanomateriaaleissa vähintään yksi niiden ulottuvuus on välillä 1–100 nanometriä. Aineella voi nanokoossa olla kemiallisia, fysikaalisia, sähköisiä ja mekaanisia erityisominaisuuksia. Nanoteknologiaa käytetään tuotteiden ominaisuuksien parantamiseen. Teollisesti tuotettuja nanomateriaaleja käytetään lähes kaikilla teollisuuden aloilla. Ihmistoiminnan seurauksena syntyy myös tahattomasti poltto- ja prosessiperäisiä nanohiukkasia. Nanomateriaalien terveydelle tai ympäristölle aiheuttamia vaikutuksia ei vielä täysin tunneta. Terveys- ja ympäristöriskien arviointi perustuu tietoihin nanomateriaalien vaaraominaisuuksista ja altistumistasoista. Teollisesti tuotetuille nanomateriaaleille on mahdollista altistua valmistuksessa ja käytössä. Altistuminen kuluttajatuotteista on pääsääntöisesti vähäistä. Nanomateriaalien sääntelyssä sovelletaan EU- ja kansallisia säädöksiä, jotka koskevat kemikaaleja, elintarvikkeita tai lääkkeitä. Lisäksi EU:ssa on sektorikohtaisia säädöksiä nanomateriaalien turvalliselle käytölle. Euroopan komissio rahoittaa yhä enemmän nanomateriaalien turvallisuuteen liittyvää tutkimista. Suomen yliopistoissa ja valtion tutkimuslaitoksissa tehdään ansiokasta nanomateriaaleja koskevaa materiaali- ja turvallisuustutkimusta
Nanomaterials as part of society : Towards a safe future of nanotechnology
Nanomaterials as part of society : Towards a safe future of nanotechnologyThe review contains information on the use of nanomaterials and safety issues, regulation and research related to nanomaterials in Finland. Nanomaterials have at least one dimension between 1–100 nanometers. At the nanoscale, materials can exhibit unique chemical, physical, electronic and mechanical properties. Nanotechnology is used to improve the properties of materials. Manufactured nanomaterials are used in nearly all industrial sectors. As a result of human activity, nanoparticles are also generated unintentionally through various processes and combustion. The impact that nanomaterials have on health or the environment is not yet fully understood. The assessment of health and environmental risks is based on information on the hazardous properties and exposure levels of nanomaterials. Exposure to manufactured nanomaterials may occur during the production process or the use of these products. However, as a rule, the risk of exposure to manufactured nanomaterials in consumer products is minimal. The regulation of nanomaterials builds on EU and national legislation concerning chemicals, food and medicines. The EU also has sector-specific legislation on the safe use of nanomaterials. The European Commission is directing more and more funding to the research on the safety of nanomaterials. In Finland, universities and government research institutes conduct valuable safety and material-related research on nanomaterials