Wigner equation of motion for time-dependent potentials

The equation of motion is obtained for the Wigner distribution for time-dependent potentials. It is shown that one cannot obtain an equation of motion for the standard Wigner distribution but one can do so for the fourdimensional distribution of the variables position, momentum, time, and frequency. Three forms are given and it is shown that for time-independent potentials the new form reduces to the equations originally obtained by Wigner and Moyal.     

PRELIMINARY EVALUATION OF THE APPLICATION OF THE FTIR SPECTROSCOPY TO CONTROL THE GEOGRAPHIC ORIGIN AND QUALITY OF VIRGIN OLIVE OILS

ABSTRACT

A rapid Fourier transform infrared (FTIR) attenuated total reflectance spectroscopic method was applied to determine qualitative parameters such as free fatty acid (FFA) content and the peroxide value (POV) in virgin olive oils. Calibration models were constructed using partial least squares regression on a large number of virgin olive oil samples. The best results (R² = 0.955, root mean square error in cross validation [RMSECV] = 0.15) to evaluate FFA content expressed in oleic acid % (w/w) were obtained considering a calibration range from 0.2 to 9.2% of FFA relative to 190 samples. For POV determination, the result obtained, built on 80 olive oil samples with a calibration range from 11.1 to 49.7 meq O₂/kg of oil, was not satisfactory (R² = 0.855, RMSECV = 3.96). We also investigated the capability of FTIR spectroscopy, in combination with multivariate analysis, to distinguish virgin olive oils based on geographic origin. The spectra of 84 monovarietal virgin olive oil samples from eight Italian regions were collected and elaborated by principal component analysis (PCA), considering the fingerprint region. The results were satisfactory and could successfully discriminate the majority of samples coming from the Emilia Romagna, Sardinian and Sicilian regions. Moreover, the explained variance from this PCA was higher than 96%.

PRACTICAL APPLICATIONS

The verification of the declared origin or the determination of the origin of an unidentified virgin olive oil is a challenging problem. In this work, we have studied the applicability of Fourier transform infrared coupled with multivariate statistical analysis to discriminate the geographic origin of virgin olive oil samples from different Italian regions.

     

Chlorophyll Stability During Continuous Aseptic Processing and Storage

Spinach puree was aseptically processed and packaged at four time-temperature treatments (19.2 and 5.3 sec @ 142°C; 19.2 and 12.2 sec @ 137°C). Samples processed at 142°C for 5.3 sec retained 68% of total chlorophyll compared to blanched samples while all chlorophylls were degraded in retorted product. The rate of chlorophyll b degradation and pheophytin b formation during storage in flexible containers at 4, 25, and 40°C fit a first order kinetic model. Apparent activation energies during storage for each time-temperature treatment ranged between 11.1 and 14.3 kcal/mol. Analyses of degradation products indicated oxidation during storage was not a dominant factor in chlorophyll conversion and color loss.     

Application of the Wigner distribution to nonlinear systems

A new way to study nonlinear oscillations is presented, based on Time—Frequency Analysis, a technique that allows the representation and study of the instantaneous spectral content of a signal. The investigation of nonlinear oscillations is an interesting subject in many areas of physics and engineering, especially in nonlinear optics where this phenomenon arises directly from the interaction of electromagnetic waves and matter. Here it is shown how Time—Frequency Analysis can clarify the nature of a free nonlinear oscillation, which is proven to have a peculiar yet physically reasonable instantaneous spectrum.     

IMPERFECT SQUEEZING FLOW VISCOSIMETRY OF SELECTED TOMATO PRODUCTS1

The rheological properties of different brands of commercial tomato paste, sauce, puree and ketchup were estimated by imperfect squeezing flow viscosimetry using a wide plate and a shallow container. The tests were performed with polished and grooved surfaces. In both, slip was prominent to such an extent that the equations for lubricated squeezing flow had to be used for the calculation of rheological parameters. Despite its crudeness, the procedure was sensitive enough to consistently monitor rheological differences between commercial products of different brands in terms of the apparent stress at a given specimen height, the consistency, K , and flow index, n, of the pseudoplastic liquid constitutive equation, and the apparent biaxial elongational viscosity, μ_b and its strain rate dependency. In tomato paste, the flow behavior index was approximately the same in all the brands (n ～ 0.5), and the values of K and μ_b had a linear relationship. Residual forces after relaxation provided an additional textural measure related to the yield stress. Differences between products of different brands could be consistently monitored regardless of whether the test was performed at a fixed specimen height or a preset initial force.     

Bifacial Photovoltaic Panels with Sun Tracking

This paper analyzes the energy collected by bifacial photovoltaic panels that track the sun. A theoretical model is described that calculates the collection of light by both sides of a bifacial panel installed on a one- or two-axis tracker and placed against a variety of surroundings. The model has been verified experimentally, and then used to predict the annual energy collected at Madrid for a number of cases of practical interest. The results for two-axis tracked bifacial panels show that annual back energies of the order of 25% of the front energies can be obtained. This implies that the total (front plus back) annual energy collected by such panels can be 80% greater than that collected by a stationary monofacial panel, or some 30% greater than that collected by a stationary bifacial one.     

DIFFERENTIAL SCANNING CALORIMETRY DETECTION OF HIGH OLEIC SUNFLOWER OIL AS AN ADULTERANT IN EXTRA-VIRGIN OLIVE OIL

Differential scanning calorimetry (DSC) was employed to detect high oleic sunflower oil (HOSo) as an adulterant in extra-virgin olive oil (EVOo) by means of cooling and heating thermograms. Addition of HOSo did not significantly alter cooling profiles of EVOo except for onset temperature of crystallization, which was significantly shifted toward lower temperature at 40% of adulterant addition. At the same percentage of adulteration, the heating profile of EVOo was significantly changed as the major endotherm broadened and the minor event became smaller and less evident. Cooling thermograms of pure oils and their admixtures were deconvoluted into three constituent exothermic peaks in an attempt to detect addition of HOSo at levels lower than 40%. Thermal properties of the two lower-temperature exotherms (area percentage, offset temperature and range of transition) were significantly changed at ≥ 20% of HOSo substitution, suggesting that DSC can be employed to detect this oil as an EVOo adulterant.

PRACTICAL APPLICATIONS

Adulteration of extra-virgin olive oil (EVOo) with cheaper oils from other vegetable sources or seeds, as well as with lower quality olive oils, is a serious concern for oil suppliers and consumers and requires the use of new analytical techniques for their detection. Differential scanning calorimetry (DSC) exhibits some advantages over the classical analytical methods as it does not require sample preparation and use of solvents, thus resulting in a reduced environmental impact. Results suggested that its application to the detection of EVOo adulteration with high oleic sunflower oil, a vegetable oil largely employed for this type of fraud, is promising with the support of the deconvolution analysis of cooling thermograms.     

Isolation and Partial Characterization of a Natural Antioxidant from Shrimp (Pandalus jordani)

The nature of a natural antioxidant present in shrimp was investigated. From several solvents used in the extraction process, ethanol proved most effective. A diethyl ether extract exhibited no antioxidant activity. The compound responsible for the antioxidant effect was present in very low concentrations in its natural source. The chemical characteristics and chromatographic properties suggested that it was a polyhydroxylated derivative of an aromatic amino acid.     

DIRECT ABSORPTANCE MEASUREMENT OF FLUORESCENT AND TURBID SAMPLES IN A 4 π GEOMETRY

The determination of optical absorption in turbid media requires optical integrators to collect all the light scattered by the sample. If under these measurement conditions the sample fluoresces, its emission is collected as scattered light by the integrator and produces a signal of the opposite sign to that of an absorption. The magnitude of this effect is a function of the luminescent quantum efficiency of the sample and the spectral response of the detector. The implications of the effects of fluorescence on the absorption measurements of turbid media are discussed, along with a method for direct measurement of absorptance in a 4 π geometry. In the presence of turbidity, the measurement of regular transmittance is not valid if obtained with very small angles of detection. It is perfectly valid, however, if a detection acceptance angle of 4 π steradians is used.