Polarisation Observables in Antiproton Proton to Lepton Antilepton Reactions

The electromagnetic form factors of hadrons as measured both in the space like and time like domains provide fundamental information on the nucleon structure and internal dynamics. General expressions, including the lepton mass, for the spin averaged differential cross section for the annihilation reaction lepton antilepton to proton antiproton are given, as well as general formulae for the single and double spin asymmetries. The time reversed reaction would involve a kinematic factor. We also present general expressions for the helicity amplitudes for this reaction.Comment: 4 pages, to be published in the Proceedings of the 17th International Spin Physics Symposium (SPIN 2006), Kyoto, Japan; October 2-7, 200

High resolution infrared spectroscopy of planetary molecules using diode lasers and Fourier transform spectrometers

Modern observations of infrared molecular lines in planets are performed at spectral resolutions which are as high as those available in the laboratory. Analysis of such data requires laboratory measurements at the highest possible resolution, which also yield accurate line positions and intensities. For planetary purposes the spectrometer must be coupled to sample cells which can be reduced in temperature and varied in pressure. An approach which produces the full range of required molecular line parameters uses a combination of tunable diode lasers and Fourier transform spectrometers (FTS). The FTS provides board spectral coverage and good calibration accuracy, while the diode laser can be used to study those regions which are not resolved by the FTS

Shock isolator for operating a diode laser on a closed-cycle refrigerator

A diode laser mounted within a helium refrigerator is mounted using a braided copper ground strap which provides good impact shock isolation from the refrigerator cold-tip while also providing a good thermal link to the cold-tip. The diode mount also contains a rigid stand-off assembly consisting of alternate sections of nylon and copper which serve as cold stations to improve thermal isolation from the vaccum housing mounting structure. Included in the mount is a Pb-In alloy wafer inserted between the cold-tip and the diode to damp temperature fluctuations occurring at the cold-tip

Diode laser spectra of CCl2F2 near 10.8 muon M: Air-broadening effects

Laboratory spectra of CCL2F2 in the 10.8 micron region was recorded, using a tuneable diode laser spectrometer. Effects of air-broadening at pressures up to 48 Torr show that spectral structure should be exhibited under high resolution at altitudes as low as 19 Km. The single line, pressure-broadening coefficient for CCL2F2 was estimated to be 8 MHz/Torr FWHM

Astronomical observations with the University College London balloon borne telescope

The characteristics of a telescope system which was developed for high altitude balloon astronomy are discussed. A drawing of the optical system of the telescope is provided. A sample of the signals recorded during one of the flights is included. The correlation between the infrared flux and the radio continuum flux is analyzed. A far infrared map of the radio and infrared peaks of selected stars is developed. The spectrum of the planet Saturn is plotted to show intensity as compared with wavenumber

Ground based infrared astronomy

Infrared spectroscopic instrumentation has been developed for ground-based measurements of astrophysical objects in the intermediate infrared. A conventional Michelson interferometer is limited for astronomical applications in the intermediate infrared by quantum noise fluctuations in the radiation form the source and/or background incident on the detector, and the multiplex advantage is no longer available. One feasible approach to recovering the multiplex advantage is post-dispersion. The infrared signal after passing through telescope and interferometer, is dispersed by a low resolution grating spectrometer onto an array of detectors. The feasibility of the post-dispersion system has been demonstrated with observations of astrophysical objects in the 5 and 10 micrometer atmospheric windows from ground-based telescopes. During FY87/88 the post-disperser was used at the Kitt Peak 4-meter telescope and McMath telescope with facility Fourier transform spectrometers. Jupiter, Saturn, Mars, and Venus were observed. On Jupiter, the resolution at 12 micrometer was 0.01/cm, considerably higher than had been acheived previously. The spectrum contains Jovian ethane and acetylene emission. Construction was begun on the large cryogenic grating spectrometer

The nu sub 2 band CHD3; ground state parameters for CHD3 from combination differences

The nu sub 2 fundamental band of CHD3, centered near 2143/cm, was recorded at a resolution of 0.015-0.25/cm. Analysis of ground state combination differences yielded well-determined values for the ground state molecular parameters for CHD3. These parameters were used in the determination of the alpha and beta molecular parameters for nu sub 2

Thermal compensator for closed-cycle helium refrigerator

The wave length of an infrared, semiconductor laser diode having an output frequency that is dependent on the diode temperature is maintained substantially constant by maintaining the diode temperature constant. The diode is carried by a cold tip of a closed cycle helium refrigerator. The refrigerator has a tendency to cause the temperature of the cold tip to oscillate. A heater diode and a sensor diode are placed on a thermal heat sink that is the only highly conductive thermal path between the laser diode and the cold tip. The heat sink has a small volume and low thermal capacitance so that the sensing diode is at substantially the same temperature as the heater diode and substantially no thermal lag exists between them. The sensor diode is connected in a negative feedback circuit with the heater diode so that the tendency of the laser diode to thermally oscillate is virtually eliminated

Forming efficient agent groups for completing complex tasks

In this paper we produce complexity and impossibility results and develop algorithms for a task allocation problem that needs to be solved by a group of autonomous agents working together. In particular, each task is assumed to be composed of several subtasks and involves an associated predetermined and known overall payment (set by the task’s owner) for its completion. However, the division of this payment among the corresponding contributors is not predefined. Now to accomplish a particular task, all its subtasks need to be allocated to agents with the necessary capabilities and the agents’ corresponding costs need to fall within the preset overall task payment. For this scenario, we first provide a cooperative agent system designer with a practical solution that achieves an efficient allocation. However, this solution is not applicable for non-cooperative settings. Consequently, we go on to provide a detailed analysis where we prove that certain design goals cannot be achieved if the agents are self interested. Specifically, we prove that for the general case, no protocol achieving the efficient solution can exist that is individually rational and budget balanced. We show that although efficient protocols may exist in some settings, these will inevitably be setting-specific

How BAO measurements can fail to detect quintessence

We model the nonlinear growth of cosmic structure in different dark energy models, using large volume N-body simulations. We consider a range of quintessence models which feature both rapidly and slowly varying dark energy equations of state, and compare the growth of structure to that in a universe with a cosmological constant. The adoption of a quintessence model changes the expansion history of the universe, the form of the linear theory power spectrum and can alter key observables, such as the horizon scale and the distance to last scattering. The difference in structure formation can be explained to first order by the difference in growth factor at a given epoch; this scaling also accounts for the nonlinear growth at the 15% level. We find that quintessence models which feature late $(z<2)$, rapid transitions towards $w=-1$ in the equation of state, can have identical baryonic acoustic oscillation (BAO) peak positions to those in $\Lambda$CDM, despite being very different from $\Lambda$CDM both today and at high redshifts $(z \sim 1000)$. We find that a second class of models which feature non-negligible amounts of dark energy at early times cannot be distinguished from $\Lambda$CDM using measurements of the mass function or the BAO. These results highlight the need to accurately model quintessence dark energy in N-body simulations when testing cosmological probes of dynamical dark energy.Comment: 10 pages, 7 figures, to appear in the Invisible Univers International Conference AIP proceedings serie