8,757 research outputs found
On the nature of continuous physical quantities in classical and quantum mechanics
Within the traditional Hilbert space formalism of quantum mechanics, it is
not possible to describe a particle as possessing, simultaneously, a sharp
position value and a sharp momentum value. Is it possible, though, to describe
a particle as possessing just a sharp position value (or just a sharp momentum
value)? Some, such as Teller (Journal of Philosophy, 1979), have thought that
the answer to this question is No -- that the status of individual continuous
quantities is very different in quantum mechanics than in classical mechanics.
On the contrary, I shall show that the same subtle issues arise with respect to
continuous quantities in classical and quantum mechanics; and that it is, after
all, possible to describe a particle as possessing a sharp position value
without altering the standard formalism of quantum mechanics.Comment: 26 pages, LaTe
The Geometry of PSR B0031-07
PSR B0031-07 is well known to exhibit three different modes of drifting
sub-pulses (mode A, B and C). It has recently been shown that in a
multifrequency observation, consisting of 2700 pulses, all driftmodes were
visible at low frequencies, while at 4.85 GHz only mode-A drift or non-drifting
emission was detected. This suggests that modes A and B are emitted in
sub-beams, rotating at a fixed distance from the magnetic axis, with the mode-B
sub-beams being closer to the magnetic axis than the mode-A sub-beams. Diffuse
emission between the sub-beams can account for the non-drifting emission. Using
the results of an analysis of simultaneous multifrequency observations of PSR
B0031-07, we set out to construct a geometrical model that includes emission
from both sub-beams and diffuse emission and describes the regions of the radio
emission of PSR B0031-07 at each emission frequency for driftmodes A and B.
Based on the vertical spacing between driftbands, we have determined the
driftmode of each sequence of drift. To restrict the model, we calculated
average polarisation and intensity characteristics for each driftmode and at
each frequency. The model reproduces the observed polarisation and intensity
characteristics, suggesting that diffuse emission plays an important role in
the emission properties of PSR B0031-07. The model further suggests that the
emission heights of this pulsar range from a few kilometers to a little over 10
kilometers above the pulsar surface. We also find that the relationships
between height and frequency of emission that follow from curvature radiation
and from plasma-frequency emission could not be used to reproduce the observed
frequency dependence of the width of the average intensity profiles.Comment: 15 pages, 9 figures, 8 tables, accepted for publication in A&
A Decidable Multi-agent Logic for Reasoning About Actions, Instruments, and Norms
We formally introduce a novel, yet ubiquitous, category of norms: norms of instrumentality. Norms of this category describe which actions are obligatory, or prohibited, as instruments for certain purposes. We propose the Logic of Agency and Norms (LAN) that enables reasoning about actions, instrumentality, and normative principles in a multi-agent setting. Leveraging LAN , we formalize norms of instrumentality and compare them to two prevalent norm categories: norms to be and norms to do. Last, we pose principles relating the three categories and evaluate their validity vis-à-vis notions of deliberative acting. On a technical note, the logic will be shown decidable via the finite model property
Constraint rule-based programming of norms for electronic institutions
Peer reviewedPostprin
Quantum Cryptography
Quantum cryptography is a new method for secret communications offering the
ultimate security assurance of the inviolability of a Law of Nature. In this
paper we shall describe the theory of quantum cryptography, its potential
relevance and the development of a prototype system at Los Alamos, which
utilises the phenomenon of single-photon interference to perform quantum
cryptography over an optical fiber communications link.Comment: 36 pages in compressed PostScript format, 10 PostScript figures
compressed tar fil
The open future, bivalence and assertion
It is highly intuitive that the future is open and the past is closed—whereas it is unsettled whether there will be a fourth world war, it is settled that there was a first. Recently, it has become increasingly popular to claim that the intuitive openness of the future implies that contingent statements about the future, such as ‘there will be a sea battle tomorrow,’ are non-bivalent (neither true nor false). In this paper, we argue that the non-bivalence of future contingents is at odds with our pre-theoretic intuitions about the openness of the future. These are revealed by our pragmatic judgments concerning the correctness and incorrectness of assertions of future contingents. We argue that the pragmatic data together with a plausible account of assertion shows that in many cases we take future contingents to be true (or to be false), though we take the future to be open in relevant respects. It follows that appeals to intuition to support the non-bivalence of future contingents is untenable. Intuition favours bivalence
ACME Stellar Spectra. I. Absolutely Calibrated, Mostly Empirical Flux Densities of 55 Cancri and its Transiting Planet 55 Cancri e
The ACME Spectra project provides absolutely calibrated, mostly empirical
spectra of exoplanet host stars for use in analysis of the stars and their
planets. Spectra are obtained from ground-based telescopes and are tied
directly to calibrated ground- and space-based photometry. The spectra remain
only "mostly" empirical because of telluric absorption, but interpolation of
stellar models over the gaps in wavelength coverage provides continuous stellar
spectra. Among other uses, the spectra are suitable for precisely converting
observed secondary eclipses (occultations) into absolute flux units with
minimal recourse to models. In this letter I introduce ACME's methods and
present a calibrated spectrum of the nearby, super-Earth hosting star 55 Cancri
that spans the range from 0.81-5.05 micron. This spectrum is well-suited for
interpreting near- and thermal-infrared eclipse observations. With this
spectrum I show that the brightness temperature of the small, low-mass
transiting planet 55 Cnc e is 1950 +260/-190 K at 4.5 micron (cooler than
previously reported), which corresponds to a planetary flux of 0.44 +0.12/-0.08
mJy. This result suggests the planet has some combination of a nonzero albedo,
a moderately efficient redistribution of absorbed stellar irradiation, and/or
an optically thick atmosphere, but more precise eclipse measurements are
required to distinguish between these scenarii.Comment: Accepted to A&A. 6 pages, 1 figure, 1 electronic table. See
http://irtfweb.ifa.hawaii.edu/~spex/IRTF_Spectral_Library/ for an alternative
spectru
Delegation of Obligations and Responsibility
Part 6: Policy Compliance and ObligationsInternational audienceIn this paper, we discuss the issue of responsibilities related to the fulfillment and the violation of obligations. We propose to formally define the different aspects of responsibility, namely causal responsibility, functional responsibility, liability as well as sanctions, and to examine how delegation influences these concepts. Our main aim is to identify the responsibility of each agent that is involved in the delegation of obligations. More precisely, we try to answer to the following questions: who is responsible for the obligation fulfillment? When a violation occurs, which agents are causally responsible for this violation? Who is liable for this violation and to whom? And finally, who must be sanctioned
Constraining Antimatter Domains in the Early Universe with Big Bang Nucleosynthesis
We consider the effect of a small-scale matter-antimatter domain structure on
big bang nucleosynthesis and place upper limits on the amount of antimatter in
the early universe. For small domains, which annihilate before nucleosynthesis,
this limit comes from underproduction of He-4. For larger domains, the limit
comes from He-3 overproduction. Most of the He-3 from antiproton-helium
annihilation is annihilated also. The main source of He-3 is
photodisintegration of He-4 by the electromagnetic cascades initiated by the
annihilation.Comment: 4 pages, 2 figures, revtex, (slightly shortened
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