The bearable lightness of being

How are philosophical questions about what kinds of things there are to be understood and how are they to be answered? This paper defends broadly Fregean answers to these questions. Ontological categories-such as object, property, and relation-are explained in terms of a prior logical categorization of expressions, as singular terms, predicates of varying degree and level, etc. Questions about what kinds of object, property, etc., there are are, on this approach, reduce to questions about truth and logical form: for example, the question whether there are numbers is the question whether there are true atomic statements in which expressions function as singular terms which, if they have reference at all, stand for numbers, and the question whether there are properties of a given type is a question about whether there are meaningful predicates of an appropriate degree and level. This approach is defended against the objection that it must be wrong because makes what there depend on us or our language. Some problems confronting the Fregean approach-including Frege's notorious paradox of the concept horse-are addressed. It is argued that the approach results in a modest and sober deflationary understanding of ontological commitments

Complete chaotic synchronization in mutually coupled time-delay systems

Complete chaotic synchronization of end lasers has been observed in a line of mutually coupled, time-delayed system of three lasers, with no direct communication between the end lasers. The present paper uses ideas from generalized synchronization to explain the complete synchronization in the presence of long coupling delays, applied to a model of mutually coupled semiconductor lasers in a line. These ideas significantly simplify the analysis by casting the stability in terms of the local dynamics of each laser. The variational equations near the synchronization manifold are analyzed, and used to derive the synchronization condition that is a function of the parameters. The results explain and predict the dependence of synchronization on various parameters, such as time-delays, strength of coupling and dissipation. The ideas can be applied to understand complete synchronization in other chaotic systems with coupling delays and no direct communication between synchronized sub-systems.Comment: 22 pages, 6 figure

Evolution of the Pairwise Peculiar Velocity Distribution Function in Lagrangian Perturbation Theory

The statistical distribution of the radial pairwise peculiar velocity of galaxies is known to have an exponential form as implied by observations and explicitly shown in N-body simulations. Here we calculate its statistical distribution function using the Zel'dovich approximation assuming that the primordial density fluctuations are Gaussian distributed. We show that the exponential distribution is realized as a transient phenomena on megaparsec scales in the standard cold-dark-matter model.Comment: 19 pages, 8 Postscript figures, AAS LaTe

Room to Glo: A systematic comparison of semantic change detection approaches with word embeddings

Word embeddings are increasingly used for the automatic detection of semantic change; yet, a robust evaluation and systematic comparison of the choices involved has been lacking. We propose a new evaluation framework for semantic change detection and find that (i) using the whole time series is preferable over only comparing between the first and last time points; (ii) independently trained and aligned embeddings perform better than continuously trained embeddings for long time periods; and (iii) that the reference point for comparison matters. We also present an analysis of the changes detected on a large Twitter dataset spanning 5.5 years.This work was supported by The Alan Turing Institute under the EPSRC grant EP/N510129/1

Conduction-Electron Screening in the Bulk and at Low-Index Surfaces of Ta Metal

High-resolution core-level photoemission spectra from Ta(100) have been measured. The well-resolved peak from the first atomic layer allows a separate assessment of bulk and surface-layer screening responses: singularity indices αB=0.10±0.01 and α100=0.205±0.025, respectively, are obtained. The measured surface-atom lifetime broadening of 70±20 meV (compared to 37±5 meV in the bulk) is consistent with published Auger–photoemission coincidence measurements. The result for the bulk singularity index has been applied in the analysis of previous data in order to extract the screening response in the first atomic layer of Ta(111) (α111=0.16±0.01) and Ta(110) (α110=0.150±0.015). The trend in surface α’s implies an increasingly atomic character for the surface-layer atoms as one proceeds from Ta(110) to Ta(111) to Ta(100)

Thermally Induced Core-Electron Binding-Energy Shifts in Transition Metals: An ExperimentalInvestigation of Ta(100)

High-resolution photoemission spectra from the 4f7/2 levels of Ta(100) have been obtained between 77 K and room temperature. The data show an increase in both the surface and bulk core-level binding energies (BE’s) as the temperature is raised: between 77 and 293 K the bulk and surface BE’s increase by 31±3 and 13±2 meV, respectively. A model calculation of the bulk binding-energy increase, which is based upon the lattice expansion of the solid, is in good agreement with the experimental results and indicates that the shifts arise from both initial- and final-state effects that are of comparable magnitude. The model is further used to estimate thermally induced shifts for the whole 5d transition-metal series. © 1996 The American Physical Society

Performance of distributed mechanisms for flow admission in wireless adhoc networks

Given a wireless network where some pairs of communication links interfere with each other, we study sufficient conditions for determining whether a given set of minimum bandwidth quality-of-service (QoS) requirements can be satisfied. We are especially interested in algorithms which have low communication overhead and low processing complexity. The interference in the network is modeled using a conflict graph whose vertices correspond to the communication links in the network. Two links are adjacent in this graph if and only if they interfere with each other due to being in the same vicinity and hence cannot be simultaneously active. The problem of scheduling the transmission of the various links is then essentially a fractional, weighted vertex coloring problem, for which upper bounds on the fractional chromatic number are sought using only localized information. We recall some distributed algorithms for this problem, and then assess their worst-case performance. Our results on this fundamental problem imply that for some well known classes of networks and interference models, the performance of these distributed algorithms is within a bounded factor away from that of an optimal, centralized algorithm. The performance bounds are simple expressions in terms of graph invariants. It is seen that the induced star number of a network plays an important role in the design and performance of such networks.Comment: 21 pages, submitted. Journal version of arXiv:0906.378

Snake-Oil Security Claims the Systematic Misrepresentation of Product Security in the E-Commerce Arena

The modern commercial systems and software industry in the United States have grown up in a snake-oil salesman\u27s paradise. The largest sector of this industry by far is composed of standard commercial systems that are marketed to provide specified functionality (e.g. Internet web server, firewall, router, etc.) Such products are generally provided with a blanket disclaimer stating that the purchaser must evaluate the suitability of the product for use, and that the user assumes all liability for product behavior. In general, users cannot evaluate and cannot be expected to evaluate the security claims of a product. The ability to analyze security claims is important because a consumer may place unwarranted trust in the security abilities of a web server (or other computer device) to perform its stated purpose, thereby putting his own organization at risk, as well as third parties (consumers, business partners, etc.) All but the largest and most capable organizations lack the resources or expertise to evaluate the security claims of a product. More importantly, no reasonable and knowledgeable person would expect them to be able to do so. The normal legal presumptions of approximate equality of bargaining power and comparable sophistication in evaluating benefits and risks are grievously unjust in the context of software security. In these transactions, it is far wiser to view the general purchaser, even if that purchaser is a sizable corporation, as an ignorant consumer. Hence, often purchasers accept what appear to be either implied merchantability claims of the vendor or claims of salespersons\u27 made outside of the context of a written document. These claims frequently have little, if any, basis in fact. These standard commercial systems form the bulk of the critical infrastructure of existing Internet functionality and e-commerce systems. Often, these systems are not trustworthy, yet the use of these systems by misinformed purchasers created massive vulnerability for both purchasers and third parties (including a substantial fraction of both U.S. and international citizens). The frequent disclosure of individual credit card information from supposedly secure commercial systems illustrates an aspect of this vulnerability and raises serious questions concerning the merchantability of these systems. While it is impossible to avoid all risks, they can be reduced to a very small fraction of their current level. Vendors have willfully taken approaches and used processes that do not allow assurance of appropriate security properties, while simultaneously and recklessly misrepresenting the security properties of their products to their customers