The Voice Capacity of WiFi for Best Effort and Prioritized Traffic

Crucial to supporting voice over 802.11b is the knowledge of voice capacity (Nc) of a single Access Point. This paper provides an analytical formulation of Nc in the case where all traffic in the network is voice. Our formulation, which can apply to a range of voice codec specifications, are verified by detailed simulations. We also investigate how to deliver, within the 802.11b standard, priority service to voice in the presence of best effort background traffic. It is known that the voice capacity degrades very quickly in the presence of other traffic sources if all packets are treated as best effort. Using an experimental deployment in which all voice packets are prioritized by having their channel back-off times set to zero, we determine the rate of the best effort background traffic below which our analytical formulation of voice-only capacity remains useful

Stellar evolution and nucleosynthesis of Post-AGB Stars

I discuss recent new models of post-Asymptotic Giant Branch stellar evolution. These models aim to clarify the evolutionary origin and status of a variety of hydrogen-deficient post-AGB stars such as central stars of planetary nebulae of Wolf-Rayet spectral type, PG1159 stars or Sakurai's object. Starting with AGB models with overshoot such stars can evolve through one of four distinct channels. Each of these channels has typical abundance patterns depending on the relative timing of the departure from the AGB and the occurrence of the last thermal pulse. I discuss the responsible mechanisms and observational counterparts.Comment: 9 pages, 1 figure, conference paper, workshop "Post-AGB objects (proto-planetary nebulae) as a phase of stellar evolution", Jul 5-7, 2000, Torun, Poland, to appear in Ap&S

The Confrontation between General Relativity and Experiment

The status of experimental tests of general relativity and of theoretical frameworks for analysing them is reviewed. Einstein's equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of special relativity, and the gravitational redshift experiment. Future tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational-wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and other binary pulsar systems have yielded other tests, especially of strong-field effects. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible.Comment: 89 pages, 8 figures; an update of the Living Review article originally published in 2001; final published version incorporating referees' suggestion

A primordial 4He constraint on Dirac neutrino masses

The implications of the Z0-width experiment for the number of neutrino flavors taken together with the 4He constraint on the energy density at the nucleosynthesis epoch, can give a limit on the extent to which a right-handed neutrino sea could contribute to the expansion rate of the universe during Big Bang nucleosynthesis. Since the population of the right-handed neutrino sea depends on the neutrino mass we can extract a Dirac neutrino mass limit of mv ≪ 150 keV. This limit could apply to νμ or ντ if they have purely Dirac masses. © 1991

New cosmological limit on neutrino mass.

We show that considerations of the equilibration of right- and left-handed neutrino seas in the early Universe and the well-known He4 constraint on the number of relativistic degrees of freedom extant at the nucleosynthesis epoch lead to a new limit on the Dirac neutrino mass of 300keV. This constraint would apply to any neutrino so long as it had a purely Dirac mass and a lifetime exceeding the nucleosynthesis time scale. © 1991 The American Physical Society

A primordial 4He constraint on Dirac neutrino masses

The implications of the Z0-width experiment for the number of neutrino flavors taken together with the 4He constraint on the energy density at the nucleosynthesis epoch, can give a limit on the extent to which a right-handed neutrino sea could contribute to the expansion rate of the universe during Big Bang nucleosynthesis. Since the population of the right-handed neutrino sea depends on the neutrino mass we can extract a Dirac neutrino mass limit of mv ≪ 150 keV. This limit could apply to νμ or ντ if they have purely Dirac masses. © 1991

New cosmological limit on neutrino mass.

We show that considerations of the equilibration of right- and left-handed neutrino seas in the early Universe and the well-known He4 constraint on the number of relativistic degrees of freedom extant at the nucleosynthesis epoch lead to a new limit on the Dirac neutrino mass of 300keV. This constraint would apply to any neutrino so long as it had a purely Dirac mass and a lifetime exceeding the nucleosynthesis time scale. © 1991 The American Physical Society

Neutrino oscillations and the leptonic charge of the universe

The most stringent bounds on the individual lepton numbers of the universe arise from considerations of primordial nucleosynthesis. We consider the effect of resonant neutrino flavor oscillations on these limits. In particular, we include the contributions from neutrino-neutrino forward scattering to the effective mass of each neutrino flavor. We find that there can be significant modifications to the neutrino number densities and energy distributions for each flavor over a large range of neutrino vacuum masses and mixing angles. Modifi-cations to the neutrino distributions occurring prior to the nucleosynthesis epoch can substantially alter the previously derived limits on the lepton number for each flavor and its associated degeneracy parameter

Neutrino oscillations and the leptonic charge of the universe

The most stringent bounds on the individual lepton numbers of the universe arise from considerations of primordial nucleosynthesis. We consider the effect of resonant neutrino flavor oscillations on these limits. In particular, we include the contributions from neutrino-neutrino forward scattering to the effective mass of each neutrino flavor. We find that there can be significant modifications to the neutrino number densities and energy distributions for each flavor over a large range of neutrino vacuum masses and mixing angles. Modifi-cations to the neutrino distributions occurring prior to the nucleosynthesis epoch can substantially alter the previously derived limits on the lepton number for each flavor and its associated degeneracy parameter