997 research outputs found
Acoustic Integrity Codes: Secure Device Pairing Using Short-Range Acoustic Communication
Secure Device Pairing (SDP) relies on an out-of-band channel to authenticate
devices. This requires a common hardware interface, which limits the use of
existing SDP systems. We propose to use short-range acoustic communication for
the initial pairing. Audio hardware is commonly available on existing
off-the-shelf devices and can be accessed from user space without requiring
firmware or hardware modifications. We improve upon previous approaches by
designing Acoustic Integrity Codes (AICs): a modulation scheme that provides
message authentication on the acoustic physical layer. We analyze their
security and demonstrate that we can defend against signal cancellation attacks
by designing signals with low autocorrelation. Our system can detect
overshadowing attacks using a ternary decision function with a threshold. In
our evaluation of this SDP scheme's security and robustness, we achieve a bit
error ratio below 0.1% for a net bit rate of 100 bps with a signal-to-noise
ratio (SNR) of 14 dB. Using our open-source proof-of-concept implementation on
Android smartphones, we demonstrate pairing between different smartphone
models.Comment: 11 pages, 11 figures. Published at ACM WiSec 2020 (13th ACM
Conference on Security and Privacy in Wireless and Mobile Networks). Updated
reference
Mordell-Weil Torsion and the Global Structure of Gauge Groups in F-theory
We study the global structure of the gauge group of F-theory compactified
on an elliptic fibration . The global properties of are encoded in the
torsion subgroup of the Mordell-Weil group of rational sections of .
Generalising the Shioda map to torsional sections we construct a specific
integer divisor class on as a fractional linear combination of the
resolution divisors associated with the Cartan subalgebra of . This divisor
class can be interpreted as an element of the refined coweight lattice of the
gauge group. As a result, the spectrum of admissible matter representations is
strongly constrained and the gauge group is non-simply connected. We exemplify
our results by a detailed analysis of the general elliptic fibration with
Mordell-Weil group and as well as a further
specialization to . Our analysis exploits the
representation of these fibrations as hypersurfaces in toric geometry.Comment: 42 pages, 10 figures; v2: references adde
Early Life Relict Feature in Peptide Mass Distribution
Molecular mass of a biomolecule is characterized in mass spectroscopy by the monoisitopic mass M~mono~ and the average isotopic mass M~av~. We found that peptide masses mapped on a plane made by two parameters derived from M~mono~ and M~av~ form a peculiar global feature in form of a band-gap 5-7 ppm wide stretching across the whole peptide galaxy, with a narrow (FWHM 0.2 ppm) line in the centre. The a priori probability of such a feature to emerge by chance is less than 1:100. Peptides contributing to the central line have elemental compositions following the rules S=0; Z = (2C - N - H)/2 =0, which nine out of 20 amino acid residues satisfy. The relative abundances of amino acids in the peptides contributing to the central line correlate with the consensus order of emergence of these amino acids, with ancient amino acids being overrepresented in on-line peptides. Thus the central line is a relic of ancient life, and likely a signature of its emergence in abiotic synthesis. The linear correlation between M~av~ and M~mono~ reduces the complexity of polypeptide molecules, which may have increased the rate of their abiotic production. This, in turn may have influenced the selection of these amino acid residues for terrestrial life. Assuming the line feature is not spurious, life has emerged from elements with isotopic abundances very close to terrestrial levels, which rules out most of the Galaxy
Nonanalytic Corrections to the Landau Diamagnetic Susceptibility
We analyze potential non-analytic terms in the Landau diamagnetic
susceptibility, , at a finite temperature and/or finite
magnetic field . To do this, we express the diamagnetic susceptibility as
, where
is the transverse component of the static current-current
correlator, and evaluate for a system of fermions with
Hubbard interaction to second order in Hubbard by combining self energy,
Maki-Thompson, and Aslamazov-Larkin diagrams. We find that at , the
expansion of in is regular, but at a finite
and/or , it contains and/or terms. Similar terms have been
previously found for the paramagnetic Pauli susceptibility. We obtain the full
expression for the non-analytic when both and
are finite, and show that the dependence is similar to that for the Pauli
susceptibility.Comment: 21 pages, 5 figure
Influence of tailored MLI for complex surface geometries on heat transfer
Complex, non-developable surfaces require a tailored multi-layer insulation (MLI) for lowest heat load. The most experiments showing the heat transfer through MLI are performed under quasi-ideal conditions determining the principle insulation quality. But the surface to be insulated in real cryostats implies feed-throughs and other non-developable surface parts. The thermal performance of MLI is degraded significantly at cutting points. To investigate this degrading effect a LN-filled cylinder with a diameter of 219 mm and a length of 1820 mm was insulated with MLI and the heat load was measured by means of calorimetry. In addition the heat load to an insulated cylinder with eighteen branches was measured. Both cylinders have the same surface of 1.37 m for a comparison of the results. This article describes the experiments with different ways of tailoring the MLI for the cylinder with branches and discusses their results. It was shown that the cutting points at the branches have a significant degrading influence on the thermal performance of MLI
Evolutionary Trends in the Physciaceae
The current delimitation of the family Physciaceae has been generally accepted since detailed descriptions of ascus characters allowed for a more natural circumscription of lichenized ascomycetes. The generic relations within the family are, however, still controversial and depend on the importance different authors attribute to specific morphological or chemical characteristics. The aim of this paper is to describe ascospore ontogeny and to test the present taxonomic structure of the family against a parsimony-based cladistic analysis, which includes three different scenarios of a priori character weighting. A study of ascospore ontogeny revealed two distinct developmental lines. One line revealed a delayed septum formation, which clearly showed transitions from spores with apical and median thickenings to spores without apical, but still well developed median thickenings, and to spores without any thickenings. In the second developmental line with an early septum formation again taxa with no thickenings, median thickenings, and both median and apical thickenings were found. Although these characters were constant at a species level, median wall thickenings especially varied among otherwise closely related taxa. In the cladistic analyses the current taxonomic structure of the Physciaceae was only obtained after the five character groups, namely morphology and anatomy of the vegetative thallus, conidiomata and conidia, morphology and anatomy of the apothecia, ontogeny of the ascospores, and secondary metabolites of the thallus, were given equal importance, and after a subjective a priori weighting further increased the weight of the three characters ‘conidial shape', ‘presence of apical thickenings', and ‘spore septation delayed'. This structure was not supported by a cladistic analysis with equally weighted characters but reflected the biased character weighting of the present day Physdaceae taxonomy. The taxonomic importance of conidial characters and of anatomical and ontogenetical spore characteristics need, therefore, a careful reconsideration in futur
World caf\ue9 method to engage smart energy-district project partners in assessing urban co-benefits
Urban energy-district projects introduce outstanding technological innovation in buildings and energy systems increasing sustainability in city neighborhoods. Such projects generate additional co-benefits for the city beyond changes in physical elements and development of social and institutional relationships (e.g. local employment, environmental quality, public health, property values, innovation attitude, etc.). Since exceeding main declared goals or not always clearly foreseen in the early project phase, these co-benefits are often not properly understood and considered. However, only their explicit recognition will make possible their inclusion in the assessment of the whole project\u2019s performance. From these considerations, this study faces the issue of engaging project partners in assessing co-benefits in order to consider a broad spectrum of relevant, positive effects in the evaluation process. Group knowledge and group thinking of this complex topic are investigated through the world caf\ue9 method, providing an atmosphere of trust and open discussions among participants. This empirical work lays the foundations to go beyond the mere economic measure as the sole criterion for assessing project effects, also including changes in end-user behavior and intangible asset
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