24 research outputs found
Universally Composable Authentication and Key-exchange with Global PKI
Message authentication and key exchange are two of the most basic tasks of
cryptography. Solutions based on public-key infrastructure (PKI) are
prevalent. Still, the state of the art in composable security analysis of
PKI-based authentication and key exchange is somewhat unsatisfactory.
Specifically, existing treatments either (a)~make the unrealistic assumption
that the PKI is accessible only within the confines of the protocol itself,
thus failing to capture real-world PKI-based authentication, or (b)~impose
often-unnecessary requirements---such as strong on-line
non-transferability---on candidate protocols, thus ruling out natural
candidates.
We give a modular and universally composable analytical framework for PKI-based
message authentication and key exchange protocols. This framework guarantees
security even when the PKI is pre-existing and globally available, without
being unnecessarily restrictive. Specifically, we model PKI as a global set-up
functionality within the \emph{Global~UC} security model [Canetti \etal, TCC
2007] and relax the ideal authentication and key exchange functionalities
accordingly. We then demonstrate the security of basic signature-based
authentication and key exchange protocols. Our modeling makes minimal security
assumptions on the PKI in use; in particular, ``knowledge of the secret key\u27\u27
is not needed
Searching for plasticity in dissociated cortical cultures on multi-electrode arrays
We attempted to induce functional plasticity in dense cultures of cortical cells using stimulation through extracellular electrodes embedded in the culture dish substrate (multi-electrode arrays, or MEAs). We looked for plasticity expressed in changes in spontaneous burst patterns, and in array-wide response patterns to electrical stimuli, following several induction protocols related to those used in the literature, as well as some novel ones. Experiments were performed with spontaneous culture-wide bursting suppressed by either distributed electrical stimulation or by elevated extracellular magnesium concentrations as well as with spontaneous bursting untreated. Changes concomitant with induction were no larger in magnitude than changes that occurred spontaneously, except in one novel protocol in which spontaneous bursts were quieted using distributed electrical stimulation
Human NK Cells Differ More in Their KIR2DL1-Dependent Thresholds for HLA-Cw6-Mediated Inhibition than in Their Maximal Killing Capacity
In this study we have addressed the question of how activation and inhibition of human NK cells is regulated by the expression level of MHC class I protein on target cells. Using target cell transfectants sorted to stably express different levels of the MHC class I protein HLA-Cw6, we show that induction of degranulation and that of IFN-γ secretion are not correlated. In contrast, the inhibition of these two processes by MHC class-I occurs at the same level of class I MHC protein. Primary human NK cell clones were found to differ in the amount of target MHC class I protein required for their inhibition, rather than in their maximum killing capacity. Importantly, we show that KIR2DL1 expression determines the thresholds (in terms of MHC I protein levels) required for NK cell inhibition, while the expression of other receptors such as LIR1 is less important. Furthermore, using mathematical models to explore the dynamics of target cell killing, we found that the observed delay in target cell killing is exhibited by a model in which NK cells require some activation or priming, such that each cell can lyse a target cell only after being activated by a first encounter with the same or a different target cell, but not by models which lack this feature
The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf
We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)—a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R ⊕ to 1.6 R ⊕. All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system
TOI-677 b: A Warm Jupiter (P=11.2d) on an eccentric orbit transiting a late F-type star
We report the discovery of TOI-677 b, first identified as a candidate in
light curves obtained within Sectors 9 and 10 of the Transiting Exoplanet
Survey Satellite (TESS) mission and confirmed with radial velocities. TOI-677 b
has a mass of M_p = 1.236 M_J, a radius of R_p = 1.170 +-
0.03 R_J,and orbits its bright host star (V=9.8 mag) with an orbital period of
11.23660 +- 0.00011 d, on an eccentric orbit with e = 0.435 +- 0.024. The host
star has a mass of M_* = 1.181 +- 0.058 M_sun, a radius of R_* = 1.28 +- 0.03
R_sun, an age of 2.92 Gyr and solar metallicity, properties
consistent with a main sequence late F star with T_eff = 6295 +- 77 K. We find
evidence in the radial velocity measurements of a secondary long term signal
which could be due to an outer companion. The TOI-677 b system is a well suited
target for Rossiter-Mclaughlin observations that can constrain migration
mechanisms of close-in giant planets.Comment: Submitted to AAS journals, 15 pages, 8 figure
Mechanical Stress Induces Remodeling of Vascular Networks in Growing Leaves
International audienceDifferentiation into well-defined patterns and tissue growth are recognized as key processes in organismal development. However, it is unclear whether patterns are passively, homogeneously dilated by growth or whether they remodel during tissue expansion. Leaf vascu-lar networks are well-fitted to investigate this issue, since leaves are approximately two-dimensional and grow manyfold in size. Here we study experimentally and computationally how vein patterns affect growth. We first model the growing vasculature as a network of viscoelastic rods and consider its response to external mechanical stress. We use the so-called texture tensor to quantify the local network geometry and reveal that growth is heterogeneous , resembling non-affine deformations in composite materials. We then apply mechanical forces to growing leaves after veins have differentiated, which respond by anisotropic growth and reorientation of the network in the direction of external stress. External mechanical stress appears to make growth more homogeneous, in contrast with the model with viscoelastic rods. However, we reconcile the model with experimental data by incorporating randomness in rod thickness and a threshold in the rod growth law, making the rods viscoelastoplastic. Altogether, we show that the higher stiffness of veins leads to their reorientation along external forces, along with a reduction in growth heterogeneity. This process may lead to the reinforcement of leaves against mechanical stress. More generally , our work contributes to a framework whereby growth and patterns are coordinated through the differences in mechanical properties between cell types
Sensing ultrashort electronic coherent beating at conical intersections by single-electron pulses
SignificanceIn a theoretical study, we present an ultrafast technique for probing time-dependent molecular charge densities. An ultrafast optical pump first brings the molecule into an electronic nonstationary state. This is followed by coherent inelastic scattering of a broadband single-electron probe pulse with a variable delay T, which is detected spectrally. The technique is applied to reveal phase-sensitive background-free coherent electron beating in the conical intersection passage in uracil and reveals the otherwise elusive coherent beating of strongly coupled electrons and nuclei
From Users to (Sense)Makers: On the Pivotal Role of Stigmergic Social Annotation in the Quest for Collective Sensemaking
The web has become a dominant epistemic environment, influencing people's
beliefs at a global scale. However, online epistemic environments are
increasingly polluted, impairing societies' ability to coordinate effectively
in the face of global crises. We argue that centralized platforms are a main
source of epistemic pollution, and that healthier environments require
redesigning how we collectively govern attention. Inspired by decentralization
and open source software movements, we propose Open Source Attention, a
socio-technical framework for "freeing" human attention from control by
platforms, through a decentralized eco-system for creating, storing and
querying stigmergic markers; the digital traces of human attention.Comment: Blue-sky ideas track of the 33rd ACM Conference on Hypertext and
Social Media, Barcelona, 202