8,973 research outputs found
Quantifying Shannon's Work Function for Cryptanalytic Attacks
Attacks on cryptographic systems are limited by the available computational
resources. A theoretical understanding of these resource limitations is needed
to evaluate the security of cryptographic primitives and procedures. This study
uses an Attacker versus Environment game formalism based on computability logic
to quantify Shannon's work function and evaluate resource use in cryptanalysis.
A simple cost function is defined which allows to quantify a wide range of
theoretical and real computational resources. With this approach the use of
custom hardware, e.g., FPGA boards, in cryptanalysis can be analyzed. Applied
to real cryptanalytic problems, it raises, for instance, the expectation that
the computer time needed to break some simple 90 bit strong cryptographic
primitives might theoretically be less than two years.Comment: 19 page
Quantifying Resource Use in Computations
It is currently not possible to quantify the resources needed to perform a
computation. As a consequence, it is not possible to reliably evaluate the
hardware resources needed for the application of algorithms or the running of
programs. This is apparent in both computer science, for instance, in
cryptanalysis, and in neuroscience, for instance, comparative neuro-anatomy. A
System versus Environment game formalism is proposed based on Computability
Logic that allows to define a computational work function that describes the
theoretical and physical resources needed to perform any purely algorithmic
computation. Within this formalism, the cost of a computation is defined as the
sum of information storage over the steps of the computation. The size of the
computational device, eg, the action table of a Universal Turing Machine, the
number of transistors in silicon, or the number and complexity of synapses in a
neural net, is explicitly included in the computational cost. The proposed cost
function leads in a natural way to known computational trade-offs and can be
used to estimate the computational capacity of real silicon hardware and neural
nets. The theory is applied to a historical case of 56 bit DES key recovery, as
an example of application to cryptanalysis. Furthermore, the relative
computational capacities of human brain neurons and the C. elegans nervous
system are estimated as an example of application to neural nets.Comment: 26 pages, no figure
Spin injection across magnetic/non-magnetic interfaces with finite magnetic layers
We have reconsidered the problem of spin injection across
ferromagnet/non-magnetic-semiconductor (FM/NMS) and
dilute-magnetic-semiconductor/non-magnetic-semiconductor interfaces, for
structures with \textit{finite} magnetic layers (FM or DMS). By using
appropriate physical boundary conditions, we find expressions for the
resistances of these structures which are in general different from previous
results in the literature. When the magnetoresistance of the contacts is
negligible, we find that the spin-accumulation effect alone cannot account for
the dependence observed in recent magnetoresistance data. In a limited
parameter range, our formulas predict a strong dependence arising from the
magnetic contacts in systems where their magnetoresistances are sizable.Comment: 6 pages, 3 eps figs. (extended version- new title + two new figures
added
Formal modelling of L1 and L2 perceptual learning: Computational linguistics versus machine learning
Hall viscosity from gauge/gravity duality
In (2+1)-dimensional systems with broken parity, there exists yet another
transport coefficient, appearing at the same order as the shear viscosity in
the hydrodynamic derivative expansion. In condensed matter physics, it is
referred to as "Hall viscosity". We consider a simple holographic realization
of a (2+1)-dimensional isotropic fluid with broken spatial parity. Using
techniques of fluid/gravity correspondence, we uncover that the holographic
fluid possesses a nonzero Hall viscosity, whose value only depends on the
near-horizon region of the background. We also write down a Kubo's formula for
the Hall viscosity. We confirm our results by directly computing the Hall
viscosity using the formula.Comment: 12 page
Generating topological order from a 2D cluster state using a duality mapping
In this paper we prove, extend and review possible mappings between the
two-dimensional Cluster state, Wen's model, the two-dimensional Ising chain and
Kitaev's toric code model. We introduce a two-dimensional duality
transformation to map the two-dimensional lattice cluster state into the
topologically-ordered Wen model. Then, we subsequently investigates how this
mapping could be achieved physically, which allows us to discuss the rate at
which a topologically ordered system can be achieved. Next, using a lattice
fermionization method, Wen's model is mapped into a series of one-dimensional
Ising interactions. Considering the boundary terms with this mapping then
reveals how the Ising chains interact with one another. The relationships
discussed in this paper allow us to consider these models from two different
perspectives: From the perspective of condensed matter physics these mappings
allow us to learn more about the relation between the ground state properties
of the four different models, such as their entanglement or topological
structure. On the other hand, we take the duality of these models as a starting
point to address questions related to the universality of their ground states
for quantum computation.Comment: 5 Figure
Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO/SrTiO Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission
LaNiO (LNO) is an intriguing member of the rare-earth nickelates in
exhibiting a metal-insulator transition for a critical film thickness of about
4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such
thin films also show a transition to a metallic state in superlattices with
SrTiO (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to
better understand this transition, we have studied a strained LNO/STO
superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an
(LaAlO)(SrAlTaO) substrate using soft x-ray
standing-wave-excited angle-resolved photoemission (SWARPES), together with
soft- and hard- x-ray photoemission measurements of core levels and
densities-of-states valence spectra. The experimental results are compared with
state-of-the-art density functional theory (DFT) calculations of band
structures and densities of states. Using core-level rocking curves and x-ray
optical modeling to assess the position of the standing wave, SWARPES
measurements are carried out for various incidence angles and used to determine
interface-specific changes in momentum-resolved electronic structure. We
further show that the momentum-resolved behavior of the Ni 3d eg and t2g states
near the Fermi level, as well as those at the bottom of the valence bands, is
very similar to recently published SWARPES results for a related
LaSrMnO/SrTiO superlattice that was studied using the
same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which
further validates this experimental approach and our conclusions. Our
conclusions are also supported in several ways by comparison to DFT
calculations for the parent materials and the superlattice, including
layer-resolved density-of-states results
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