Computational work and efficient computation on general purpose machines

Computational work and efficient computation on general purpose machine

The complexity of deterministic source encoding with a fidelity criterion

Block encoding of discrete, memoryless sources with equiprobable outputs subject to a fidelity criterion is discussed. The encoder is assumed to be deterministic and a lower bound is derived on the amount of computational work required to encode such sources as a function of the code rate and fidelity of the encoding. An example is given to show that the bound cannot be substantially improved. These bounds apply primarily to sources and distortion measures which are such that the minimum distortion given by the rate-distortion bound is not achievable with a finite block length, deterministic encoder

A model of a pumped continuous atom laser

We present a model of a cw atom laser based on a system of coupled GP equations. The model incorporates continuous Raman outcoupling, pumping and three-body recombination. The outcoupled field has minimal atomic density fluctuations and is locally monochromatic.Comment: 10 pages, 8 eps figures, typos fixe

Stochastic assembly of sublithographic nanoscale interfaces

We describe a technique for addressing individual nanoscale wires with microscale control wires without using lithographic-scale processing to define nanoscale dimensions. Such a scheme is necessary to exploit sublithographic nanoscale storage and computational devices. Our technique uses modulation doping to address individual nanowires and self-assembly to organize them into nanoscale-pitch decoder arrays. We show that if coded nanowires are chosen at random from a sufficiently large population, we can ensure that a large fraction of the selected nanowires have unique addresses. For example, we show that N lines can be uniquely addressed over 99% of the time using no more than /spl lceil/2.2log/sub 2/(N)/spl rceil/+11 address wires. We further show a hybrid decoder scheme that only needs to address N=O(W/sub litho-pitch//W/sub nano-pitch/) wires at a time through this stochastic scheme; as a result, the number of unique codes required for the nanowires does not grow with decoder size. We give an O(N/sup 2/) procedure to discover the addresses which are present. We also demonstrate schemes that tolerate the misalignment of nanowires which can occur during the self-assembly process

First-principles quantum simulations of dissociation of molecular condensates: Atom correlations in momentum space

We investigate the quantum many-body dynamics of dissociation of a Bose-Einstein condensate of molecular dimers into pairs of constituent bosonic atoms and analyze the resulting atom-atom correlations. The quantum fields of both the molecules and atoms are simulated from first principles in three dimensions using the positive-P representation method. This allows us to provide an exact treatment of the molecular field depletion and s-wave scattering interactions between the particles, as well as to extend the analysis to nonuniform systems. In the simplest uniform case, we find that the major source of atom-atom decorrelation is atom-atom recombination which produces molecules outside the initially occupied condensate mode. The unwanted molecules are formed from dissociated atom pairs with non-opposite momenta. The net effect of this process -- which becomes increasingly significant for dissociation durations corresponding to more than about 40% conversion -- is to reduce the atom-atom correlations. In addition, for nonuniform systems we find that mode-mixing due to inhomogeneity can result in further degradation of the correlation signal. We characterize the correlation strength via the degree of squeezing of particle number-difference fluctuations in a certain momentum-space volume and show that the correlation strength can be increased if the signals are binned into larger counting volumes.Comment: Final published version, with updated references and minor modification

To germinate or not to germinate : a question of dormancy relief not germination stimulation

A common understanding of the control of germination through dormancy is essential for effective communication between seed scientists whether they are ecologists, physiologists or molecular biologists. Vleeshouwers et al. (1995) realized that barriers between disciplines limited progress and through insightful conclusions in their paper ‘Redefining seed dormancy: an attempt to integrate physiology and ecology’, they did much to overcome these barriers at that time. However, times move on, understanding develops, and now there is a case for ‘Redefining seed dormancy as an integration of physiology, ecology and molecular biology’. Finch-Savage and Leubner-Metzger (2006) had this in mind when they extended and re-interpreted the definition of dormancy proposed by Vleeshouwers et al. (1995), by considering dormancy as a having a number of layers that must be removed, with the final layer of dormancy being synonymous with the stimulation/induction of germination

Marine-Nonmarine Relationships in the Cenozoic Section of California

Highly fossiliferous marine sediments of Cenozoic age are widely distributed in the coastal parts of central and southern California, as well as in the Sacramento-San Joaquin Valley region farther inland. Even more widespread are nonmarine, chiefly terrestrial, sequences of Cenozoic strata, many of which contain vertebrate faunas characterized by a dominance of mammalian forms. These strata are most abundant in the Mojave Desert region and in the interior parts of areas that lie nearer the coast. Marine and nonmarine strata are in juxtaposition or interfinger with one another at many places, especially in the southern Coast Ranges and the San Joaquin basin to the east, in the Transverse Ranges and adjacent basins, and in several parts of the Peninsular Range region and the Coachella-Imperial Valley to the east. These occurrences of closely related marine and nonmarine deposits permit critical comparisons between the Pacific Coast mammalian (terrestrial) and invertebrate (marine) chronologies, and it is with these comparisons-examined in the light of known stratigraphic relations-that this paper is primarily concerned. The writers have drawn freely upon the published record for geologic and paleontologic data. In addition, Durham has reviewed many of the invertebrate faunas and has checked the field relations of marine strata in parts of the Ventura and Soledad basins, the Tejon Hills, and the Cammatta Ranch; Jahns has studied new vertebrate material from the Soledad basin and has mapped this area and critical areas in the vicinity of San Diego, in the Ventura basin, and in the Caliente Range; and Savage has made a detailed appraisal of the vertebrate assemblages, and has mapped critical areas in the Tejon Hills. The areas and localities that have been most carefully scrutinized are shown in figure 1. The manuscript was reviewed in detail by G. Edward Lewis of the U. S. Geological Survey, who made numerous comments and suggestions that resulted in considerable improvement. It should be noted that his views are not wholly compatible with some of those expressed in this paper, and that his critical appraisal thus was particularly helpful

Heavy Quark Fragmentation to Baryons Containing Two Heavy Quarks

We discuss the fragmentation of a heavy quark to a baryon containing two heavy quarks of mass $m_Q\gg\Lambda_{\rm QCD}$. In this limit the heavy quarks first combine perturbatively into a compact diquark with a radius small compared to $1/\Lambda_{\rm QCD}$, which interacts with the light hadronic degrees of freedom exactly as does a heavy antiquark. The subsequent evolution of this $QQ$ diquark to a $QQq$ baryon is identical to the fragmentation of a heavy antiquark to a meson. We apply this analysis to the production of baryons of the form $ccq$, $bbq$, and $bcq$.Comment: 9 pages, 1 figure included, uses harvmac.tex and epsf.tex, UCSD/PTH 93-11, CALT-68-1868, SLAC-PUB-622