22,724 research outputs found
Paradoxes related to the rate of transmission of information
This paper discusses paradoxes related to the possibility of infinite information capacity of certain types of channels. First, a paradox of this type is derived which shows that such paradoxes are not necessarily dependent on the assumption of Gaussian statistics.Next, in the case where signal and noise are assumed to be Gaussian, a different example of this type of paradox is derived; also, a necessary and sufficient condition for the avoidance of this form of the paradox is derived. This condition is shown to be satisfied in a class of plausible physical situations
Random Access Game in Fading Channels with Capture: Equilibria and Braess-like Paradoxes
The Nash equilibrium point of the transmission probabilities in a slotted
ALOHA system with selfish nodes is analyzed. The system consists of a finite
number of heterogeneous nodes, each trying to minimize its average transmission
probability (or power investment) selfishly while meeting its average
throughput demand over the shared wireless channel to a common base station
(BS). We use a game-theoretic approach to analyze the network under two
reception models: one is called power capture, the other is called signal to
interference plus noise ratio (SINR) capture. It is shown that, in some
situations, Braess-like paradoxes may occur. That is, the performance of the
system may become worse instead of better when channel state information (CSI)
is available at the selfish nodes. In particular, for homogeneous nodes, we
analytically present that Braess-like paradoxes occur in the power capture
model, and in the SINR capture model with the capture ratio larger than one and
the noise to signal ratio sufficiently small.Comment: 30 pages, 5 figure
Virtual Gravity and the Duality of Reality
It is shown that a hypothesis about gravity having a virtual cause implies there are two primary reference frames, a reality and a functional virtual reality and an equivalence principle relating the two is postulated. A mathematical expression relating the primary reference frames to the state of reality provides an explanation of particle-wave duality and resolves the controversy about the speed of gravity. A model for motion, time and particle formation is briefly discussed, in which the hypothesis about the virtual cause of gravity and supporting postulates are valid. It is further shown that such model provides solutions to unsolved paradoxes and a unification of consistent but contradictory ancient theories of matter and motion. Finally, a reference is made about the basis for devising experiments and testing the predictions of the model
Sending Signals to Space-Like Separated Regions
Two recent works suggest a possibility of sending signals to a space-like
separated region, contrary to the spirit of special relativity. In the first
work [J. Grunhaus, S. Popescu, and D. Rohrlich, Phys. Rev. A 53, 3781 (1996)]
it has been shown that sending signals to particular union of space-like
separated region cannot cause causality paradoxes. Another work [Y. Aharonov
and L. Vaidman, Phys. Rev. A 61, 052108 (2000)] showed that the relative phase
of quantum superposition of a particle in two separate locations can be
measured locally. Together with the possibility of changing the relative phase
in a nonlocal way using potential effect we, apparently, have a method of
sending signals to space-like separated regions. These arguments are critically
analyzed in this paper.Comment: 6 pages. Contribution to the "Mysteries and Paradoxes in Quantum
Mechanics", Garda Lake 200
On the propagation speed of evanescent modes
The group-velocity of evanescent waves (in undersized waveguides, for
instance) was theoretically predicted, and has been experimentally verified, to
be Superluminal (v_g > c). By contrast, it is known that the precursor speed in
vacuum cannot be larger than c. In this paper, by computer simulations based on
Maxwell equations only, we show the existence of both phenomena. In other
words, we verify the actual possibility of Superluminal group velocities,
without violating the so-called (naive) Einstein causality. (Subject classes:
General physics, Classical physics, Optics, Special Relativity; PACS nos.:
73.40Gk, 03.80+z, 03.65Bz; Keywords: evanescent waves; tunnelling photons;
Hartman effect; group velocity; Superluminal waves; precursors; transient
waves; front velocity; Maxwell equations; electromagnetic waves; computer
simulations; Special Relativity; Extended Relativity).Comment: plain LaTeX file (14 pages), plus 15 figures in .jp
Optimal Eavesdropping in Quantum Cryptography. II. Quantum Circuit
It is shown that the optimum strategy of the eavesdropper, as described in
the preceding paper, can be expressed in terms of a quantum circuit in a way
which makes it obvious why certain parameters take on particular values, and
why obtaining information in one basis gives rise to noise in the conjugate
basis.Comment: 7 pages, 1 figure, Latex, the second part of quant-ph/970103
Decoherence - Fluctuation Relation and Measurement Noise
We discuss fluctuations in the measurement process and how these fluctuations
are related to the dissipational parameter characterising quantum damping or
decoherence. On the example of the measuring current of the variable-barrier or
QPC problem we show there is an extra noise or fluctuation connected with the
possible different outcomes of a measurement. This noise has an enhanced short
time component which could be interpreted as due to ``telegraph noise'' or
``wavefunction collapses''. Furthermore the parameter giving the the strength
of this noise is related to the parameter giving the rate of damping or
decoherence.Comment: 6 pages, no figures, for Okun Festschrift, Physics Report
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