Operational slope-limiting circuit

Circuit limits slope of arbitrary waveform to avoid exceeding rate limit of subsequent amplifier, or to form trapezoidal wave with adjustable rise and fall rates from square wave of arbitrary frequency. Integrator provides delay needed to develop output waveform. DC coupling is used to preserve original dc offset

Jarzynski equation for a simple quantum system: Comparing two definitions of work

The validity of the Jarzynski equation for a very simple, exactly solvable quantum system is analyzed. The implications of two different definitions of work proposed in the literature are investigated. The first one derives from measurements of the system energy at the beginning and at the end of the process under consideration making the work a classical stochastic variable with transition probabilities derived from quantum mechanics. In the second definition an operator of work is introduced and the average in the Jarzynski equation is a quantum expectation value. For the first definition a general quantum mechanical version of the Jarzynski equation is known to hold. For the second one the Jarzynski equation fails to yield the free energy difference at low temperature.Comment: 5 papes, 1 figure largly rewritten and slightly enlarged versio

First atmospheric observations of three chlorofluorocarbons

We report the first atmospheric observations of the Chlorofluorocarbons (CFCs) trifluorochloroethene, 3-chloropentafluoropropene and 4,4-dichlorohexafluoro-1-butene by means of Gas Chromatography with Electron Capture and Mass Spectrometric detection (GC-ECD-MS) in air samples taken at the Taunus Observatory operated by the University of Frankfurt (Main) and the Jungfraujoch High Altitude Research Station in Switzerland. These substances belong to a class of CFCs containing a double bond and are suspected to originate from the production and thermal degradation of widely used fluoropolymers like polychlorotrifluoroethene (PCTFE). Their atmospheric lifetimes are expected to be rather short. A quantitative calibration could only be derived for trifluorochloroethene but not for the other species by now. Thus, we use a relative sensitivity method to get a first indication of the observed atmospheric abundances. Identification was possible because of an air plume containing high concentrations of these substances. We suggest that the abundances found on this occasion originated from a local source. However, we have also observed the novel CFCs in air masses representative of background conditions, though with much lower concentrations. These species and some of their degradation products are toxic and could also be relevant for stratospheric and tropospheric ozone depletion

On the electromagnetic force on a polarizable body

The force on a macroscopic polarizable body in an inhomogenous electromagnetic field is calculated for three simple exactly solvable situations. Comparing different approaches we pinpoint possible pitfalls and resolve recent confusion about the force density in ferrofluids.Comment: 8 pages, 3 figures, submitted to Am. J. Phy

Asymptotics of work distributions: The pre-exponential factor

We determine the complete asymptotic behaviour of the work distribution in driven stochastic systems described by Langevin equations. Special emphasis is put on the calculation of the pre-exponential factor which makes the result free of adjustable parameters. The method is applied to various examples and excellent agreement with numerical simulations is demonstrated. For the special case of parabolic potentials with time-dependent frequencies, we derive a universal functional form for the asymptotic work distribution.Comment: 12 pages, 12 figure

Water quality modeling using geographic information system (GIS) data

Protection of the environment and natural resources at the Kennedy Space Center (KSC) is of great concern. The potential for surface and ground water quality problems resulting from non-point sources of pollution was examined using models. Since spatial variation of parameters required was important, geographic information systems (GIS) and their data were used. The potential for groundwater contamination was examined using the SEEPAGE (System for Early Evaluation of the Pollution Potential of Agricultural Groundwater Environments) model. A watershed near the VAB was selected to examine potential for surface water pollution and erosion using the AGNPS (Agricultural Non-Point Source Pollution) model