Dynamics of neural cryptography

Synchronization of neural networks has been used for novel public channel protocols in cryptography. In the case of tree parity machines the dynamics of both bidirectional synchronization and unidirectional learning is driven by attractive and repulsive stochastic forces. Thus it can be described well by a random walk model for the overlap between participating neural networks. For that purpose transition probabilities and scaling laws for the step sizes are derived analytically. Both these calculations as well as numerical simulations show that bidirectional interaction leads to full synchronization on average. In contrast, successful learning is only possible by means of fluctuations. Consequently, synchronization is much faster than learning, which is essential for the security of the neural key-exchange protocol. However, this qualitative difference between bidirectional and unidirectional interaction vanishes if tree parity machines with more than three hidden units are used, so that those neural networks are not suitable for neural cryptography. In addition, the effective number of keys which can be generated by the neural key-exchange protocol is calculated using the entropy of the weight distribution. As this quantity increases exponentially with the system size, brute-force attacks on neural cryptography can easily be made unfeasible.Comment: 9 pages, 15 figures; typos correcte

Genetic attack on neural cryptography

Different scaling properties for the complexity of bidirectional synchronization and unidirectional learning are essential for the security of neural cryptography. Incrementing the synaptic depth of the networks increases the synchronization time only polynomially, but the success of the geometric attack is reduced exponentially and it clearly fails in the limit of infinite synaptic depth. This method is improved by adding a genetic algorithm, which selects the fittest neural networks. The probability of a successful genetic attack is calculated for different model parameters using numerical simulations. The results show that scaling laws observed in the case of other attacks hold for the improved algorithm, too. The number of networks needed for an effective attack grows exponentially with increasing synaptic depth. In addition, finite-size effects caused by Hebbian and anti-Hebbian learning are analyzed. These learning rules converge to the random walk rule if the synaptic depth is small compared to the square root of the system size.Comment: 8 pages, 12 figures; section 5 amended, typos correcte

A Window Into Functional Communication: Leveraging Naturalistic Speech Samples in Primary Progressive Aphasia

Purpose: Naturalistic speech samples should be routinely collected in the assessment of individuals with communication difficulties. However, even when these samples are collected, they are often underutilized. We propose that the analysis of naturalistic speech samples can greatly enhance our understanding and evaluation of the functional impact of primary progressive aphasia (PPA) on communication. First, we review the current practices of evaluating PPA. Second, we provide a framework to optimize the collection, analysis, and interpretation of speech samples to accomplish this goal. In particular, we demonstrate how speech samples can be evaluated for measures of informativeness, the presence of atypical patterns of speech, articulatory rate, and pausing, all of which are helpful metrics in characterizing disordered speech. These factors can be leveraged to identify both the strengths and difficulties an individual may face in everyday communication. / Conclusion: The collection of naturalistic speech in both clinical and naturalistic settings with typical communication partners is highly recommended to best diagnose, monitor, and inform treatment plans for individuals with PPA

Convergence Radii for Eigenvalues of Tri--diagonal Matrices

Consider a family of infinite tri--diagonal matrices of the form $L+ zB,$ where the matrix $L$ is diagonal with entries $L_{kk}= k^2,$ and the matrix $B$ is off--diagonal, with nonzero entries $B_{k,{k+1}}=B_{{k+1},k}= k^\alpha, 0 \leq \alpha < 2.$ The spectrum of $L+ zB$ is discrete. For small $|z|$ the $n$-th eigenvalue $E_n (z), E_n (0) = n^2,$ is a well--defined analytic function. Let $R_n$ be the convergence radius of its Taylor's series about $z= 0.$ It is proved that $$ R_n \leq C(\alpha) n^{2-\alpha} \quad \text{if} 0 \leq \alpha <11/6.$

The space station assembly phase: Flight telerobotic servicer feasibility, volume 1

The question is addressed which was raised by the Critical Evaluation Task Force (CETF) analysis of the space station: if a Flight Telerobotic Servicer (FTS) of a given technical risk could be built for use during space station assembly, could it save significant extravehicular (EVA) resources. Key issues and trade-offs associated with using an FTS to aid in space station assembly phase tasks such as construction and servicing are identified. A methodology is presented that incorporates assessment of candidate assembly phase tasks, telerobotics performance capabilities, development costs, operational constraints (STS and proximity operations), maintenance, attached payloads, and polar platforms. A discussion of the issues is presented with focus on potential FTS roles: (1) as a research-oriented test bed to learn more about space usage of telerobotics; (2) as a research-based test bed with an experimental demonstration orientation and limited assembly and servicing applications; or (3) as an operational system to augment EVA, to aid the construction of the space station, and to reduce the programmatic (schedule) risk by increasing the flexibility of mission operations. During the course of the study, the baseline configuration was modified into Phase 1 (a station assembled in 12 flights), and Phase 2 (a station assembled over a 30 flight period) configuration

Stand-alone flat-plate photovoltaic power systems: System sizing and life-cycle costing methodology for Federal agencies

A simple methodology to estimate photovoltaic system size and life-cycle costs in stand-alone applications is presented. It is designed to assist engineers at Government agencies in determining the feasibility of using small stand-alone photovoltaic systems to supply ac or dc power to the load. Photovoltaic system design considerations are presented as well as the equations for sizing the flat-plate array and the battery storage to meet the required load. Cost effectiveness of a candidate photovoltaic system is based on comparison with the life-cycle cost of alternative systems. Examples of alternative systems addressed are batteries, diesel generators, the utility grid, and other renewable energy systems

Glycerol confined in zeolitic imidazolate frameworks: The temperature-dependent cooperativity length scale of glassy freezing

In the present work, we employ broadband dielectric spectroscopy to study the molecular dynamics of the prototypical glass former glycerol confined in two microporous zeolitic imidazolate frameworks (ZIF-8 and ZIF-11) with well-defined pore diameters of 1.16 and 1.46 nm, respectively. The spectra reveal information on the modified alpha relaxation of the confined supercooled liquid, whose temperature dependence exhibits clear deviations from the typical super-Arrhenius temperature dependence of the bulk material, depending on temperature and pore size. This allows assigning well-defined cooperativity length scales of molecular motion to certain temperatures above the glass transition. We relate these and previous results on glycerol confined in other host systems to the temperature-dependent length scale deduced from nonlinear dielectric measurements. The combined experimental data can be consistently described by a critical divergence of this correlation length as expected within theoretical approaches assuming that the glass transition is due to an underlying phase transition.Comment: 14 pages, 5 figures + Supplemental Material (4 pages, 6 figures). Final version as accepted for publicatio

TeleCPT: Delivery of a Better Conversations Approach to Communication Partner Training During a Global Pandemic and Beyond

Purpose: This case report provides an overview of telehealth delivery of our Better Conversations approach to communication partner training (CPT) for people with primary progressive aphasia (PPA) and their communication partner (CP). The purpose is to advance the knowledge of speech and language therapists/pathologists (SLTs) on this type of CPT and empower them to deliver teleCPT as part of their clinical practice. // Method: We provide a case report describing therapy delivery, outcomes, and self-reflections from our clinical practice, which represents a collaboration between a UK National Health Service CPT clinic and the Better Conversations Research Lab at University College London, UK. A man with PPA and his CP (a dyad) video-recorded everyday conversations at home using a video conferencing platform. These formed the basis of an evaluation of conversation barriers and facilitators, which led to four weekly 1-hr therapy sessions covering the mechanics of conversation, identification of barriers and facilitators, goal setting, and practice of positive conversation strategies. // Results: Dyad self-rating of goal attainment revealed that three of four conversation strategies were achieved much more than expected, a positive outcome given the progressive nature of F.F.'s condition. SLT access to the dyad at home via teleCPT facilitated the carryover of strategies from the session to everyday conversations in the home environment. TeleCPT was acceptable to this couple during a global pandemic, with benefits including no travel, ease of therapy scheduling around the CP's work and family commitments, and access to a specialist CPT clinic outside their geographical area. // Conclusions: TeleCPT is feasible and acceptable to clients, improving access to therapy in a way that should not just be the preserve of service delivery during a global pandemic. SLTs can enable clients and their families to have better conversations despite communication difficulties by offering teleCPT. We have shared practical suggestions for delivering teleCPT