Wideband wattmeter for instant measurement of real power

Portable, solid state wattmeter with wideband (dc to 1 MHz) linear multiplier which provides true four quadrant operation permitting instantaneous indication of real power as oscilloscope display is described

Classical Model for Broadband Squeezed Vacuum Driving Two-Photon Absorption or Sum Frequency Generation

We address theoretically the question of classical stochastic fields mimicking quantum states of light in the context of nonlinear spectroscopy and nonlinear optics, in particular two-photon absorption (TPA) and sum-frequency generation (SFG) driven by weak or bright broadband squeezed vacuum with time-frequency entanglement between photons. Upon using a well-defined but ad hoc subtraction of vacuum-energy terms (renormalization), we find that the classical stochastic model yields exactly the same predictions as the full quantum-field theory for all of the phenomena considered here, in both the low-gain and high-gain regimes of squeezed vacuum. Such predictions include the linear-flux scaling of TPA and SFG rates at low incident photon flux, as well as the dependence of TPA and SHG rates on the relative linewidths of the squeezed light and the ground-to-final-state transition in the material system, and the spectrum of SFG generated by bright squeezed vacuum

The influence of the brittle-ductile transition zone on aftershock and foreshock occurrence

Aftershock occurrence is characterized by scaling behaviors with quite universal exponents. At the same time, deviations from universality have been proposed as a tool to discriminate aftershocks from foreshocks. Here we show that the change in rheological behavior of the crust, from velocity weakening to velocity strengthening, represents a viable mechanism to explain statistical features of both aftershocks and foreshocks. More precisely, we present a model of the seismic fault described as a velocity weakening elastic layer coupled to a velocity strengthening visco-elastic layer. We show that the statistical properties of aftershocks in instrumental catalogs are recovered at a quantitative level, quite independently of the value of model parameters. We also find that large earthquakes are often anticipated by a preparatory phase characterized by the occurrence of foreshocks. Their magnitude distribution is significantly flatter than the aftershock one, in agreement with recent results for forecasting tools based on foreshocks

Fluorescence-detected Fourier transform electronic spectroscopy by phase-tagged photon counting

Fluorescence-detected Fourier transform (FT) spectroscopy is a technique in which the relative paths of an optical interferometer are controlled to excite a material sample, and the ensuing fluorescence is detected as a function of the interferometer path delay and relative phase. A common approach to enhance the signal-to-noise ratio in these experiments is to apply a continuous phase sweep to the relative optical path, and to detect the resulting modulated fluorescence using a phase-sensitive lock-in amplifier. In many important situations, the fluorescence signal is too weak to be measured using a lock-in amplifier, so that photon counting techniques are preferred. Here we introduce an approach to low-signal fluorescence-detected FT spectroscopy, in which individual photon counts are assigned to a modulated interferometer phase ('phase-tagged photon counting,' or PTPC), and the resulting data are processed to construct optical spectra. We studied the fluorescence signals of a molecular sample excited resonantly by a pulsed coherent laser over a range of photon flux and visibility levels. We compare the performance of PTPC to standard lock-in detection methods and establish the range of signal parameters over which meaningful measurements can be carried out. We find that PTPC generally outperforms the lock-in detection method, with the dominant source of measurement uncertainty being associated with the statistics of the finite number of samples of the photon detection rate.Comment: 32 pages, 8 figure

Indications for phosphorus fertilizer-derived uranium mobilization from arable soils to groundwater

Uranium (U) and many trace elements are enriched in phosphorus fertilizers. Concentrations up to 260 mg/kg P2O5 indicate the potential of U contamination of the environment. Two fertilized long-time soil monitoring fields (BDF) in Lower Saxony have higher top soil concentration than comparable unfertilized top soils sampled at the Green-Belt in the vicinity of the BDFs. Extraction experiments could show that fertilizer-derived U is easier mobilized and hence might be leached faster to the groundwater than the geogenic U in soils. Groundwater analyses in an area of intense agricultural production show U in correlation with nitrate, indicating an impact of anthropogenic fertilization on the U concentration in shallow groundwater. The results of soil, soil extract and groundwater analyses are giving indications for fertilizer-derived U leaching to groundwater aquifers and hence show the potential hazard for our drinking water resources

The Counterpart Principle of Analogical Support by Structural Similarity

We propose and investigate an Analogy Principle in the context of Unary Inductive Logic based on a notion of support by structural similarity which is often employed to motivate scientific conjectures