The ultimate tactics of self-referential systems

Mathematics is usually regarded as a kind of language. The essential behavior of physical phenomena can be expressed by mathematical laws, providing descriptions and predictions. In the present essay I argue that, although mathematics can be seen, in a first approach, as a language, it goes beyond this concept. I conjecture that mathematics presents two extreme features, denoted here by {\sl irreducibility} and {\sl insaturation}, representing delimiters for self-referentiality. These features are then related to physical laws by realizing that nature is a self-referential system obeying bounds similar to those respected by mathematics. Self-referential systems can only be autonomous entities by a kind of metabolism that provides and sustains such an autonomy. A rational mind, able of consciousness, is a manifestation of the self-referentiality of the Universe. Hence mathematics is here proposed to go beyond language by actually representing the most fundamental existence condition for self-referentiality. This idea is synthesized in the form of a principle, namely, that {\sl mathematics is the ultimate tactics of self-referential systems to mimic themselves}. That is, well beyond an effective language to express the physical world, mathematics uncovers a deep manifestation of the autonomous nature of the Universe, wherein the human brain is but an instance.Comment: 9 pages. This essay received the 4th. Prize in the 2015 FQXi essay contest: "Trick or Truth: the Mysterious Connection Between Physics and Mathematics

Design study for LANDSAT D attitude control system

A design and performance evaluation is presented for the LANDSAT D attitude control system (ACS). Control and configuration of the gimballed Ku-band antenna system for communication with the tracking and data relay satellite (TDRS). Control of the solar array drive considered part of the ACS is also addressed

Design study for LANDSAT-D attitude control system

The gimballed Ku-band antenna system for communication with TDRS was studied. By means of an error analysis it was demonstrated that the antenna cannot be open loop pointed to TDRS by an onboard programmer, but that an autotrack system was required. After some tradeoffs, a two-axis, azimuth-elevation type gimbal configuration was recommended for the antenna. It is shown that gimbal lock only occurs when LANDSAT-D is over water where a temporary loss of the communication link to TDRS is of no consequence. A preliminary gimbal control system design is also presented. A digital computer program was written that computes antenna gimbal angle profiles, assesses percent antenna beam interference with the solar array, and determines whether the spacecraft is over land or water, a lighted earth or a dark earth, and whether the spacecraft is in eclipse

Femto-Photography of Protons to Nuclei with Deeply Virtual Compton Scattering

Developments in deeply virtual Compton scattering allow the direct measurements of scattering amplitudes for exchange of a highly virtual photon with fine spatial resolution. Real-space images of the target can be obtained from this information. Spatial resolution is determined by the momentum transfer rather than the wavelength of the detected photon. Quantum photographs of the proton, nuclei, and other elementary particles with resolution on the scale of a fraction of a femtometer is feasible with existing experimental technology.Comment: To be published in Physical Review D. Replaces previous version with minor changes in presentatio

Probing nuclear skins and halos with elastic electron scattering

I investigate the elastic electron scattering off nuclei far from the stability line. The effects of the neutron and proton skins and halos on the differential cross sections are explored. Examples are given for the charge distribution in Sn isotopes and its relation to the neutron skin. The neutron halo in $^{11}$Li and the proton halo in $^{8}$B are also investigated. Particular interest is paid to the inverse scattering problem and its dependence on the experimental precision. These studies are of particular interest for the upcoming electron ion colliders at the GSI and RIKEN facilities.Comment: 27 pages, 9 figures, accepted for publication in J. Phys.

Long-term observations of Uranus and Neptune at 90 GHz with the IRAM 30m telescope - (1985 -- 2005)

The planets Uranus and Neptune with small apparent diameters are primary calibration standards. We investigate their variability at ~90 GHz using archived data taken at the IRAM 30m telescope during the 20 years period 1985 to 2005. We calibrate the planetary observations against non-variable secondary standards (NGC7027, NGC7538, W3OH, K3-50A) observed almost simultaneously. Between 1985 and 2005, the viewing angle of Uranus changed from south-pole to equatorial. We find that the disk brightness temperature declines by almost 10% (~2sigma) over this time span indicating that the south-pole region is significantly brighter than average. Our finding is consistent with recent long-term radio observations at 8.6 GHz by Klein & Hofstadter (2006). Both data sets do moreover show a rapid decrease of the Uranus brightness temperature during the year 1993, indicating a temporal, planetary scale change. We do not find indications for a variation of Neptune's brightness temperature at the 8% level. If Uranus is to be used as calibration source, and if accuracies better than 10% are required, the Uranus sub-earth point latitude needs to be taken into account.Comment: accepted for publication in A&

Quantized Orbits and Resonant Transport

A tight binding representation of the kicked Harper model is used to obtain an integrable semiclassical Hamiltonian consisting of degenerate "quantized" orbits. New orbits appear when renormalized Harper parameters cross integer multiples of $\pi/2$. Commensurability relations between the orbit frequencies are shown to correlate with the emergence of accelerator modes in the classical phase space of the original kicked problem. The signature of this resonant transport is seen in both classical and quantum behavior. An important feature of our analysis is the emergence of a natural scaling relating classical and quantum couplings which is necessary for establishing correspondence.Comment: REVTEX document - 8 pages + 3 postscript figures. Submitted to Phys.Rev.Let

Ensayo de vida de lámparas halógenas de bajo voltaje con reflector dicroico

El uso masivo que se ha producido en el Uruguay de la lámpara halógena de bajo voltaje con reflector dicroico (generalmente llamada lámpara dicroica) ha despertado el especial interés de proyectistas y técnicos en iluminación respecto a las características particulares de estas lámparas, en especial, en lo que se refiere a su vida media. Se ha observado que en muchas instalaciones donde se han utilizado estas lámparas la frecuencia de falla ha sido muy superior a la esperada. Por otra parte, se ha observado una gran dispersión de estos valores dependiendo del fabricante, aún en los casos en que la vida media nominal especificada por todos ellos era la misma. El Grupo LUXROU, integrado por profesionales que trabajan en iluminación y por docentes del Grupo de Fotometría e Iluminación de la Facultad de Ingeniería, se propuso realizar un ensayo de vida a tensión nominal controlada, tomando una muestra de lámparas de todos los fabricantes disponibles en el Uruguay, resultando en un total de 60 lámparas ensayadas. Luego de aproximadamente dos años de ensayos se presentan en este trabajo los resultados del mismo. Se realiza un especial análisis de la evolución del flujo de las lámparas, realizando una comparación con la evolución esperada, utilizando los datos disponibles del fabricante. Asimismo se muestran los momentos de muerte de las lámparas y la evolución de las características del reflector dicroico. Por otra parte, y como consecuencia de la experiencia obtenida, se analizan cuáles deben ser las mejores condiciones de instalación para estas lámparas de forma de asegurar un desempeño adecuado de las mismas

Model Independent Form Factors for Spin Independent Neutralino-Nucleon Scattering from Elastic Electron Scattering Data

Theoretical calculations of neutralino-nucleon interaction rates with various nuclei are of great interest to direct dark matter searches such as CDMS, EDELWEISS, ZEPLIN, and other experiments since they are used to establish upper bounds on the WIMP-proton cross section. These interaction rates and cross sections are generally computed with standard, one or two parameter model-dependent nuclear form factors, which may not exactly mirror the actual form factor for the particular nucleus in question. As is well known, elastic electron scattering can allow for very precise determinations of nuclear form factors and hence nuclear charge densities for spherical or near-spherical nuclei. We use charge densities derived from elastic electron scattering data to calculate model independent, analytic form factors for various target nuclei important in dark matter searches, such as Si, Ge, S, Ca and others. We have found that for nuclear recoils in the range of 1-100 keV significant differences in cross sections and rates exist when the model independent form factors are used: at 30 keV nuclear recoil the form factors squared differ by a factor of 1.06 for $^{28}$Si, 1.11 for $^{40}$Ca, 1.27 for $^{70}$Ge, and 1.92 for $^{129}$Xe. We show the effect of different form factors on the upper limit on the WIMP-proton cross section obtained with a hypothetical $^{70}$Ge detector during a 100 kg-day effective exposure. Helm form factors with various parameter choices differ at most by 10--20% from the best (Fourier Bessel) form factor, and can approach it to better than 1% if the parameters are chosen to mimic the actual nuclear density.Comment: 20 pages, 8 figure