20,680 research outputs found
A glance beyond the quantum model
One of the most important problems in Physics is how to reconcile Quantum
Mechanics with General Relativity. Some authors have suggested that this may be
realized at the expense of having to drop the quantum formalism in favor of a
more general theory. However, as the experiments we can perform nowadays are
far away from the range of energies where we may expect to observe non-quantum
effects, it is difficult to theorize at this respect. Here we propose a
fundamental axiom that we believe any reasonable post-quantum theory should
satisfy, namely, that such a theory should recover classical physics in the
macroscopic limit. We use this principle, together with the impossibility of
instantaneous communication, to characterize the set of correlations that can
arise between two distant observers. Although several quantum limits are
recovered, our results suggest that quantum mechanics could be falsified by a
Bell-type experiment if both observers have a sufficient number of detectors
Evaluation of management measures of software development. Volume 1: Analysis summary
The conceptual model, the data classification scheme, and the analytic procedures are explained. The analytic results are summarized and specific software measures for collection and monitoring are recommended
Proof of the Generalized Second Law for Quasistationary Semiclassical Black Holes
A simple direct explicit proof of the generalized second law of black hole
thermodynamics is given for a quasistationary semiclassical black hole.Comment: 12 pages, LaTeX, report Alberta-Thy-10-93 (revision of paper in
response to Phys. Rev. Lett. referees' comments, which suffered a series of
long delays
Transient Observers and Variable Constants, or Repelling the Invasion of the Boltzmann's Brains
If the universe expands exponentially without end, ``ordinary observers''
like ourselves may be vastly outnumbered by ``Boltzmann's brains,'' transient
observers who briefly flicker into existence as a result of quantum or thermal
fluctuations. One might then wonder why we are so atypical. I show that tiny
changes in physics--for instance, extremely slow variations of fundamental
constants--can drastically change this result, and argue that one should be
wary of conclusions that rely on exact knowledge of the laws of physics in the
very distant future.Comment: 4 pages, LaTeX; v2: added references; v3: more discussion of setting,
alternative approaches, now 5 pages; v4: added discussion of the effect of
quantum fluctuations on varying constants, appendix added, now 7 pages; v5:
new reference, minor correctio
Towards operational measures of computer security
Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of ‘the ability of the system to resist attack’. That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit ‘more secure behaviour’ in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behaviour will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working towards measures of ‘operational security’ similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches (cf rate of occurrence of failures in reliability), or the probability that a specified ‘mission’ can be accomplished without a security breach (cf reliability function). This new approach is based on the analogy between system failure and security breach. A number of other analogies to support this view are introduced. We examine this duality critically, and have identified a number of important open questions that need to be answered before this quantitative approach can be taken further. The work described here is therefore somewhat tentative, and one of our major intentions is to invite discussion about the plausibility and feasibility of this new approach
Software Engineering Laboratory (SEL). Data base organization and user's guide, revision 1
The structure of the Software Engineering Laboratory (SEL) data base is described. It defines each data base file in detail and provides information about how to access and use the data for programmers and other users. Several data base reporting programs are described also
How Fast Does Information Leak out from a Black Hole?
Hawking's radiance, even as computed without account of backreaction, departs
from blackbody form due to the mode dependence of the barrier penetration
factor. Thus the radiation is not the maximal entropy radiation for given
energy. By comparing estimates of the actual entropy emission rate with the
maximal entropy rate for the given power, and using standard ideas from
communication theory, we set an upper bound on the permitted information
outflow rate. This is several times the rates of black hole entropy decrease or
radiation entropy production. Thus, if subtle quantum effects not heretofore
accounted for code information in the radiance, the information that was
thought to be irreparably lost down the black hole may gradually leak back out
from the black hole environs over the full duration of the hole's evaporation.Comment: 8 pages, plain TeX, UCSBTH-93-0
An approach to software cost estimation
A general procedure for software cost estimation in any environment is outlined. The basic concepts of work and effort estimation are explained, some popular resource estimation models are reviewed, and the accuracy of source estimates is discussed. A software cost prediction procedure based on the experiences of the Software Engineering Laboratory in the flight dynamics area and incorporating management expertise, cost models, and historical data is described. The sources of information and relevant parameters available during each phase of the software life cycle are identified. The methodology suggested incorporates these elements into a customized management tool for software cost prediction. Detailed guidelines for estimation in the flight dynamics environment developed using this methodology are presented
Entropy bounds for charged and rotating systems
It was shown in a previous work that, for systems in which the entropy is an
extensive function of the energy and volume, the Bekenstein and the holographic
entropy bounds predict new results. In this paper, we go further and derive
improved upper bounds to the entropy of {\it extensive} charged and rotating
systems. Furthermore, it is shown that for charged and rotating systems
(including non-extensive ones), the total energy that appear in both the
Bekenstein entropy bound (BEB) and the causal entropy bound (CEB) can be
replaced by the {\it internal} energy of the system. In addition, we propose
possible corrections to the BEB and the CEB.Comment: 12 pages, revte
- …