595 research outputs found
Vulnerabilities and cyberspace: a new kind of crisis
While cyberspace has become central to all vital processes in our global economy and our social lives it also carries a wide variety of risks. Framing these risks is no easy feat: some lead to harm in cyberspace itself, while others lead to harm in the offline world as well. Moreover, sometimes harm is brought about intentionally, while at other times it may be the result of accidents. The âcyber harm modelâ brings these challenges together, and provides us with an opportunity to get a comprehensive overview of the different types of incidents related to cyberspace. It also reveals where the biggest challenges for cyber crisis management lie and it provides us with a typology of different types of cyber crises that may arise. Cyber-induced crises have characteristics that make them hard to grapple with, for instance the fact that they can be induced remotely and instantaneously at multiple locations. Moreover, cyber crises are not always easily traceable, and sometimes it is difficult to see that the cause of a particular crisis in the offline world is an act in cyberspace. Finally, the borderless nature of cyberspace leads to potential large-scale geographical spread for cyber crises. Â Cyber crises also lead to a number of specific challenges for leadership, especially with respect to sense-making, meaning-making, decision-making, termination and learning.Cybersecurity en cybergovernanceSecurity and Global Affair
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Systematics of String Loop Corrections in Type IIB Calabi-Yau Flux Compactifications
We study the behaviour of the string loop corrections to the N=1 4D
supergravity Kaehler potential that occur in flux compactifications of IIB
string theory on general Calabi-Yau three-folds. We give a low energy
interpretation for the conjecture of Berg, Haack and Pajer for the form of the
loop corrections to the Kaehler potential. We check the consistency of this
interpretation in several examples. We show that for arbitrary Calabi-Yaus, the
leading contribution of these corrections to the scalar potential is always
vanishing, giving an "extended no-scale structure". This result holds as long
as the corrections are homogeneous functions of degree -2 in the 2-cycle
volumes. We use the Coleman-Weinberg potential to motivate this cancellation
from the viewpoint of low-energy field theory. Finally we give a simple formula
for the 1-loop correction to the scalar potential in terms of the tree-level
Kaehler metric and the correction to the Kaehler potential. We illustrate our
ideas with several examples. A companion paper will use these results in the
study of Kaehler moduli stabilisation.Comment: 34 pages and 3 figures; typos corrected and references adde
Lifetime of Stringy de Sitter Vacua
In this note we perform a synopsis of the life-times from vacuum decay of
several de Sitter vacuum constructions in string/M-theory which have a single
dS minimum arising from lifting a pre-existing AdS extremum and no other local
minima existent after lifting. For these vacua the decay proceeds via a
Coleman--De Luccia instanton towards the universal Minkowski minimum at
infinite volume. This can be calculated using the thin--wall approximation,
provided the cosmological constant of the local dS minimum is tuned
sufficiently small. We compare the estimates for the different model classes
and find them all stable in the sense of exponentially long life times as long
as they have a very small cosmological constant and a scale of supersymmetry
breaking > TeV.Comment: 1+16 pages, 2 figures, LaTeX, uses JHEP3 class, v2: references added,
inclusion of an additional subclass of de Sitter vacu
An evolutionary computation approach for optimizing connectivity in disaster response scenarios
Stability of Attractive Bose-Einstein Condensates in a Periodic Potential
Using a standing light wave trap, a stable quasi-one-dimensional attractive
dilute-gas Bose-Einstein condensate can be realized. In a mean-field
approximation, this phenomenon is modeled by the cubic nonlinear Schr\"odinger
equation with attractive nonlinearity and an elliptic function potential of
which a standing light wave is a special case. New families of stationary
solutions are presented. Some of these solutions have neither an analog in the
linear Schr\"odinger equation nor in the integrable nonlinear Schr\"odinger
equation. Their stability is examined using analytic and numerical methods.
Trivial-phase solutions are experimentally stable provided they have nodes and
their density is localized in the troughs of the potential. Stable
time-periodic solutions are also examined.Comment: 12 pages, 18 figure
de Sitter String Vacua from Kahler Uplifting
We present a new way to construct de Sitter vacua in type IIB flux
compactifications, in which the interplay of the leading perturbative and
non-perturbative effects stabilize all moduli in dS vacua at parametrically
large volume. Here, the closed string fluxes fix the dilaton and the complex
structure moduli while the universal leading perturbative quantum correction to
the Kahler potential together with non-perturbative effects stabilize the
volume Kahler modulus in a dS_4-vacuum. Since the quantum correction is known
exactly and can be kept parametrically small, this construction leads to
calculable and explicitly realized de Sitter vacua of string theory with
spontaneously broken supersymmetry.Comment: 1+21 pages, 5 figures, LaTeX, uses JHEP3 class, v3: conforms with
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