Practical Experience with 'Electronic Nose' Systems for Monitoring the Quality of Dairy Products

The present paper reports some practical experience acquired by testing five sensor technologies and four instruments over approximately one year with Swiss Emmental cheese samples of different stage of ripening. Up to now, the metal-oxide semiconductor (MOS) technology has given the best discrimination between the measured samples. However, sensors of this type seem to be damaged by short-chain fatty acids released from Swiss Emmental cheese. Organic conducting polymer sensors showed a poor sensitivity to volatile components of cheese, the main problem being a rapid drift of the sensors. The response of quartz microbalance sensors was too weak to detect differences between cheese samples. Discrimination using a newly designed mass-spectrometry system was difficult due to the low sensitivity of this instrument for the volatile compounds of cheese. Metal-oxide semiconductor field effect transistor sensors did not give good discrimination between the samples. However, their combination with MOS sensors seems to produce a favourable system for application in cheese evaluation. Further studies with other types of cheese and other dairy products are still necessary to define reliable and practical applications of this analytical tool in the dairy industry

Preservation of Positivity by Dynamical Coarse-Graining

We compare different quantum Master equations for the time evolution of the reduced density matrix. The widely applied secular approximation (rotating wave approximation) applied in combination with the Born-Markov approximation generates a Lindblad type master equation ensuring for completely positive and stable evolution and is typically well applicable for optical baths. For phonon baths however, the secular approximation is expected to be invalid. The usual Markovian master equation does not generally preserve positivity of the density matrix. As a solution we propose a coarse-graining approach with a dynamically adapted coarse graining time scale. For some simple examples we demonstrate that this preserves the accuracy of the integro-differential Born equation. For large times we analytically show that the secular approximation master equation is recovered. The method can in principle be extended to systems with a dynamically changing system Hamiltonian, which is of special interest for adiabatic quantum computation. We give some numerical examples for the spin-boson model of cases where a spin system thermalizes rapidly, and other examples where thermalization is not reached.Comment: 18 pages, 7 figures, reviewers suggestions included and tightened presentation; accepted for publication in PR

Signatures of the Unruh effect from electrons accelerated by ultra-strong laser fields

We calculate the radiation resulting from the Unruh effect for strongly accelerated electrons and show that the photons are created in pairs whose polarizations are maximally entangled. Apart from the photon statistics, this quantum radiation can further be discriminated from the classical (Larmor) radiation via the different spectral and angular distributions. The signatures of the Unruh effect become significant if the external electromagnetic field accelerating the electrons is not too far below the Schwinger limit and might be observable with future facilities. Finally, the corrections due to the birefringent nature of the QED vacuum at such ultra-high fields are discussed. PACS: 04.62.+v, 12.20.Fv, 41.60.-m, 42.25.Lc.Comment: 4 pages, 1 figur

On the Canonical Reduction of Spherically Symmetric Gravity

In a thorough paper Kuchar has examined the canonical reduction of the most general action functional describing the geometrodynamics of the maximally extended Schwarzschild geometry. This reduction yields the true degrees of freedom for (vacuum) spherically symmetric general relativity. The essential technical ingredient in Kuchar's analysis is a canonical transformation to a certain chart on the gravitational phase space which features the Schwarzschild mass parameter $M_{S}$, expressed in terms of what are essentially Arnowitt-Deser-Misner variables, as a canonical coordinate. In this paper we discuss the geometric interpretation of Kuchar's canonical transformation in terms of the theory of quasilocal energy-momentum in general relativity given by Brown and York. We find Kuchar's transformation to be a ``sphere-dependent boost to the rest frame," where the ``rest frame'' is defined by vanishing quasilocal momentum. Furthermore, our formalism is general enough to cover the case of (vacuum) two-dimensional dilaton gravity. Therefore, besides reviewing Kucha\v{r}'s original work for Schwarzschild black holes from the framework of hyperbolic geometry, we present new results concerning the canonical reduction of Witten-black-hole geometrodynamics.Comment: Revtex, 35 pages, no figure

SDSS Observations of Kuiper Belt Objects: Colors and Variability

Colors of Trans Neptunian Objects (TNOs) are used to study the evolutionary processes of bodies in the outskirts of the Solar System, and to test theories regarding their origin. Here I describe a search for serendipitous Sloan Digital Sky Survey (SDSS) observations of known TNOs and Centaurs. I present a catalog of SDSS photometry, colors and astrometry of 388 measurements of 42 outer Solar-System objects. I find a weak evidence, at the ~2-sigma level (per trial), for a correlation between the g-r color and inclination of scattered disk objects and hot classical KBOs. I find a correlation between the g-r color and the angular momentum in the z direction of all the objects in this sample. Light curves as a function of phase angle are constructed for 13 objects. The steepness of the slopes of these light curves suggests that the coherent backscatter mechanism plays a major role in the reflectivity of outer Solar-System small objects at small phase angles. I find a weak evidence for an anti-correlation, significant at the 2-sigma confidence level (per trial), between the g-band phase angle slope parameter and the semi-major axis, as well as the aphelion distance, of these objects. I discuss the origin of this possible correlation and argue that if this correlation is real it probably indicates that "Sedna"-like objects have a different origin than other classes of TNOs. Finally, I identify several objects with large variability amplitudes (abridged).Comment: 8 pages, ApJ in pres

Quantization of Field Theories Generalizing Gravity-Yang-Mills Systems on the Cylinder

Pure gravity and gauge theories in two dimensions are shown to be special cases of a much more general class of field theories each of which is characterized by a Poisson structure on a finite dimensional target space. A general scheme for the quantization of these theories is formulated. Explicit examples are studied in some detail. In particular gravity and gauge theories with equivalent actions are compared. Big gauge transformations as well as the condition of metric nondegeneracy in gravity turn out to cause significant differences in the structure of the corresponding reduced phase spaces and the quantum spectra of Dirac observables. For $R^2$ gravity coupled to SU(2) Yang Mills the question of quantum dynamics (`problem of time') is addressed. [This article is a contribution to the proceedings (to appear in LNP) of the 3rd Baltic RIM Student Seminar (1993). Importance is attached to concrete examples. A more abstract presentation of the ideas underlying this article (including new developments) is found in hep-th/9405110.]Comment: 26, pages, TUW-94-

The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit

We use the results of a new, multi-epoch, multi-wavelength, near-infrared census of the Trapezium Cluster in Orion to construct and to analyze the structure of its infrared (K band) luminosity function. Specifically, we employ an improved set of model luminosity functions to derive this cluster's underlying Initial Mass Function (IMF) across the entire range of mass from OB stars to sub-stellar objects down to near the deuterium burning limit. We derive an IMF for the Trapezium Cluster that rises with decreasing mass, having a Salpeter-like IMF slope until near ~0.6 M_sun where the IMF flattens and forms a broad peak extending to the hydrogen burning limit, below which the IMF declines into the sub-stellar regime. Independent of the details, we find that sub-stellar objects account for no more than ~22% of the total number of likely cluster members. Further, the sub-stellar Trapezium IMF breaks from a steady power-law decline and forms a significant secondary peak at the lowest masses (10-20 times the mass of Jupiter). This secondary peak may contain as many as \~30% of the sub-stellar objects in the cluster. Below this sub-stellar IMF peak, our KLF modeling requires a subsequent sharp decline toward the planetary mass regime. Lastly, we investigate the robustness of pre-main sequence luminosity evolution as predicted by current evolutionary models, and we discuss possible origins for the IMF of brown dwarfs.Comment: 74 pages, 30 figures, AASTeX5.0. To be published in the 01 July 2002 ApJ. For color version of figure 1 and online data table see http://www.astro.ufl.edu/~muench/PUB/publications.htm

The importance of calcium and amorphous silica for arctic soil CO₂ production

Future warming of the Arctic not only threatens to destabilize the enormous pool of organic carbon accumulated in permafrost soils but may also mobilize elements such as calcium (Ca) or silicon (Si). While for Greenlandic soils, it was recently shown that both elements may have a strong effect on carbon dioxide (CO2) production with Ca strongly decreasing and Si increasing CO2 production, little is known about the effects of Si and Ca on carbon cycle processes in soils from Siberia, the Canadian Shield, or Alaska. In this study, we incubated five different soils (rich organic soil from the Canadian Shield and from Siberia (one from the top and one from the deeper soil layer) and one acidic and one non-acidic soil from Alaska) for 6 months under both drained and waterlogged conditions and at different Ca and amorphous Si (ASi) concentrations. Our results show a strong decrease in soil CO2 production for all soils under both drained and waterlogged conditions with increasing Ca concentrations. The ASi effect was not clear across the different soils used, with soil CO2 production increasing, decreasing, or not being significantly affected depending on the soil type and if the soils were initially drained or waterlogged. We found no methane production in any of the soils regardless of treatment. Taking into account the predicted change in Si and Ca availability under a future warmer Arctic climate, the associated fertilization effects would imply potentially lower greenhouse gas production from Siberia and slightly increased greenhouse gas emissions from the Canadian Shield. Including Ca as a controlling factor for Arctic soil CO2 production rates may, therefore, reduces uncertainties in modeling future scenarios on how Arctic regions may respond to climate change

Classical and Quantum Gravity in 1+1 Dimensions, Part I: A Unifying Approach

We provide a concise approach to generalized dilaton theories with and without torsion and coupling to Yang-Mills fields. Transformations on the space of fields are used to trivialize the field equations locally. In this way their solution becomes accessible within a few lines of calculation only. In this first of a series of papers we set the stage for a thorough global investigation of classical and quantum aspects of more or less all available 2D gravity-Yang-Mills models.Comment: 24 pages, no figures, some sign errors in Eqs. 52--59 have been corrected (according to the Erratum