Copernican Crystallography

Redundancies are pointed out in the widely used extension of the crystallographic concept of Bravais class to quasiperiodic materials. Such pitfalls can be avoided by abandoning the obsolete paradigm that bases ordinary crystallography on microscopic periodicity. The broadening of crystallography to include quasiperiodic materials is accomplished by defining the point group in terms of indistinguishable (as opposed to identical) densities.Comment: 12 pages [The author apologizes for intruding on this archive, but suspects that this way of relaxing the definition of a group of transformations may be familiar to some of you in other contexts. He would welcome comments.

In the wake of the erbium-doped fiber amplifier - functional fibers and their impact

There have been a number of laser developments in recent years that are quite staggering in their simplicity, that are so powerful in their operation that engineers and scientist have to rethink the laser future. One such is the high power fibre laser, born out of the optical telecoms revolution. It challenges currently held views on how to make things, how to repair things, and how to destroy things. With small size, maintenance-free operation, high thermal and electrical efficiency and outstanding beam quality, it has the potential to change every industry and discipline it encounters

Model-Independent Analytic Nonlinear Blind Source Separation

Consider a time series of measurements of the state of an evolving system, x(t), where x has two or more components. This paper shows how to perform nonlinear blind source separation; i.e., how to determine if these signals are equal to linear or nonlinear mixtures of the state variables of two or more statistically independent subsystems. First, the local distributions of measurement velocities are processed in order to derive vectors at each point in x-space. If the data are separable, each of these vectors must be directed along a subspace of x-space that is traversed by varying the state variable of one subsystem, while all other subsystems are kept constant. Because of this property, these vectors can be used to construct a small set of mappings, which must contain the unmixing function, if it exists. Therefore, nonlinear blind source separation can be performed by examining the separability of the data after it has been transformed by each of these mappings. The method is analytic, constructive, and model-independent. It is illustrated by blindly recovering the separate utterances of two speakers from nonlinear combinations of their audio waveforms.Comment: 21 pages, 4 figures. This paper contains a more complete and didactic explanation of the ideas introduced in http://arxiv.org/abs/1601.0341

What is quantum mechanics trying to tell us?

I explore whether it is possible to make sense of the quantum mechanical description of physical reality by taking the proper subject of physics to be correlation and only correlation, and by separating the problem of understanding the nature of quantum mechanics from the hard problem of understanding the nature of objective probability in individual systems, and the even harder problem of understanding the nature of conscious awareness. The resulting perspective on quantum mechanics is supported by some elementary but insufficiently emphasized theorems. Whether or not it is adequate as a new Weltanschauung, this point of view toward quantum mechanics provides a different perspective from which to teach the subject or explain its peculiar character to people in other fields.Comment: 37 pages, no figures. This is the published version of the lecture notes that expand on my earlier ``Ithaca interpretation of quantum mechanics'', quant-ph/9609013. ``Wootters' theorem'' has become the SSC theorem, an earlier citation has been added, and a joke about Talmudic scholarship has been dropped at the request of a refere

Nuclear physics and cosmology

Nuclear physics has provided one of two critical observational tests of all Big Bang cosmology, namely Big Bang Nucleosynthesis. Furthermore, this same nuclear physics input enables a prediction to be made about one of the most fundamental physics questions of all, the number of elementary particle families. The standard Big Bang Nucleosynthesis arguments are reviewed. The primordial He abundance is inferred from He-C and He-N and He-O correlations. The strengthened Li constraint as well as D-2 plus He-3 are used to limit the baryon density. This limit is the key argument behind the need for non-baryonic dark matter. The allowed number of neutrino families, N(nu), is delineated using the new neutron lifetime value of tau(n) = 890 + or - 4s (tau(1/2) = 10.3 min). The formal statistical result is N(nu) = 2.6 + or - 0.3 (1 sigma), providing a reasonable fit (1.3 sigma) to three families but making a fourth light (m(nu) less than or equal to 10 MeV) neutrino family exceedly unlikely (approx. greater than 4.7 sigma). It is also shown that uncertainties induced by postulating a first-order quark-baryon phase transition do not seriously affect the conclusions