4,277 research outputs found
Emergence of the fuzzy horizon through gravitational collapse
For a large enough Schwarzschild black hole, the horizon is a region of space
where gravitational forces are weak; yet it is also a region leading to
numerous puzzles connected to stringy physics. In this work, we analyze the
process of gravitational collapse and black hole formation in the context of
light-cone M theory. We find that, as a shell of matter contracts and is about
to reveal a black hole horizon, it undergoes a thermodynamic phase transition.
This involves the binding of D0 branes into D2's, and the new phase leads to
large membranes of the size of the horizon. These in turn can sustain their
large size through back-reaction and the dielectric Myers effect - realizing
the fuzzball proposal of Mathur and the Matrix black hole of M(atrix) theory.
The physics responsible for this phenomenon lies in strongly coupled 2+1
dimensional non-commutative dynamics. The phenomenon has a universal character
and appears generic.Comment: 24 pages, 4 figures; v2: minor clarifications, citations adde
Estimating seasonal variations in cloud droplet number concentration over the boreal forest from satellite observations
Seasonal variations in cloud droplet number concentration (NCD) in low-level stratiform clouds over the boreal forest are estimated from MODIS observations of cloud optical and microphysical properties, using a sub-adiabatic cloud model to interpret vertical profiles of cloud properties. An uncertainty analysis of the cloud model is included to reveal the main sensitivities of the cloud model. We compared the seasonal cycle in NCD, obtained using 9 yr of satellite data, to surface concentrations of potential cloud activating aerosols, measured at the SMEAR II station at Hyytiälä in Finland. The results show that NCD and cloud condensation nuclei (CCN) concentrations have no clear correlation at seasonal time scale. The fraction of aerosols that actually activate as cloud droplet decreases sharply with increasing aerosol concentrations. Furthermore, information on the stability of the atmosphere shows that low NCD is linked to stable atmospheric conditions. Combining these findings leads to the conclusion that cloud droplet activation for the studied clouds over the boreal forest is limited by convection. Our results suggest that it is important to take the strength of convection into account when studying the influence of aerosols from the boreal forest on cloud formation, although they do not rule out the possibility that aerosols from the boreal forest affect other types of clouds with a closer coupling to the surfac
Dynamical Decompactification and Three Large Dimensions
We study string gas dynamics in the early universe and seek to realize the
Brandenberger - Vafa mechanism - a goal that has eluded earlier works - that
singles out three or fewer spatial dimensions as the number which grow large
cosmologically. Considering wound string interactions in an impact parameter
picture, we show that a strong exponential suppression in the interaction rates
for d > 3 spatial dimensions reflects the classical argument that string
worldsheets generically intersect in at most four spacetime dimensions. This
description is appropriate in the early universe if wound strings are heavy -
wrapping long cycles - and diluted. We consider the dynamics of a string gas
coupled to dilaton-gravity and find that a) for any number of dimensions the
universe generically stays trapped in the Hagedorn regime and b) if the
universe fluctuates to a radiation regime any residual winding modes are
diluted enough so that they freeze-out in d > 3 large dimensions while they
generically annihilate for d = 3. In this sense the Brandenberger-Vafa
mechanism is operative.Comment: 20 pages, 2 figures, minor changes, updated figures, as will appear
in Phys.Rev.
Thermal diffractive corrections to Casimir energies
We study the interplay of thermal and diffractive effects in Casimir
energies. We consider plates with edges, oriented either parallel or
perpendicular to each other, as well as a single plate with a slit. We compute
the Casimir energy at finite temperature using a formalism in which the
diffractive effects are encoded in a lower dimensional non-local field theory
that lives in the gap between the plates. The formalism allows for a clean
separation between direct or geometric effects and diffractive effects, and
makes an analytic derivation of the temperature dependence of the free energy
possible. At low temperatures, with Dirichlet boundary conditions on the
plates, we find that diffractive effects make a correction to the free energy
which scales as T^6 for perpendicular plates, as T^4 for slits, and as T^4 log
T for parallel plates.Comment: 31 pages, 7 figures, LaTeX. v2: minor typos fixed, version to appear
in PR
Climate research Netherlands : research highlights
In the Netherlands the temperature has risen, on average, by 1.6°C since 1900. Regional climate scenarios for the 21st century developed by the Dutch Royal Meteorological Institute [1] show that temperature in the Netherlands will continue to rise and mild winters and hot summers will become more common. On average winters will become wetter and extreme precipitation amounts will increase. The intensity of extreme rain showers in summer will increase and the sea level will continue to rise. Changing climate will affect all segments and sectors of the society and the economy of the Netherlands, but it also brings new opportunities for major innovation
Instantons, supersymmetric vacua, and emergent geometries
We study instanton solutions and superpotentials for the large number of
vacua of the plane-wave matrix model and a 2+1 dimensional Super Yang-Mills
theory on with sixteen supercharges. We get the superpotential in
the weak coupling limit from the gauge theory description. We study the gravity
description of these instantons. Perturbatively with respect to a background,
they are Euclidean branes wrapping cycles in the dual gravity background.
Moreover, the superpotential can be given by the energy of the electric charge
system characterizing each vacuum. These charges are interpreted as the
eigenvalues of matrices from a reduction for the 1/8 BPS sector of the gauge
theories. We also discuss qualitatively the emergence of the extra spatial
dimensions appeared on the gravity side.Comment: 29 pages, 3 figures, latex. v2: references added, comments added. v3:
accepted version in PR
Receipt of interpersonal citizenship: fostering agentic emotion, cognition, and action in organizations
With an eye to fostering an energized and empowered workforce, we explore the discrete emotion of selfâ assurance (characterized by boldness, pride, and audacity), investigating how receipt of interpersonal citizenship behavior (ICB) fuels this agentic emotion. ICB includes acts of everyday concern that may be of a personâ or taskâ focused nature. With two survey samples, we propose and test a model that situates selfâ assurance as a mechanism linking ICBâ receipt to employee thriving and empowerment. Additionally, we find links to citizenship enactment, as reported by coworkers. Notably, personâ focused ICBâ receipt may be just as beneficial to selfâ assurance as taskâ focused ICBâ receipt. These results hold equally for working women and men. Our multiâ study, multiâ source results underscore the role of agentic emotion in cultivating a proactive workforce.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136264/1/jasp12421_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136264/2/jasp12421.pd
Probing black holes in non-perturbative gauge theory
We use a 0-brane to probe a ten-dimensional near-extremal black hole with N
units of 0-brane charge. We work directly in the dual strongly-coupled quantum
mechanics, using mean-field methods to describe the black hole background
non-perturbatively. We obtain the distribution of W boson masses, and find a
clear separation between light and heavy degrees of freedom. To localize the
probe we introduce a resolving time and integrate out the heavy modes. After a
non-trivial change of coordinates, the effective potential for the probe agrees
with supergravity expectations. We compute the entropy of the probe, and find
that the stretched horizon of the black hole arises dynamically in the quantum
mechanics, as thermal restoration of unbroken U(N+1) gauge symmetry. Our
analysis of the quantum mechanics predicts a correct relation between the
horizon radius and entropy of a black hole.Comment: 30 pages, LaTeX, 8 eps figures. v2: references added. v3: more
reference
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