The effect of moist layer location on the stability of trapped gravity waves in an almost saturated atmosphere

The stability characteristics of trapped gravity waves, generated by an isothermal bounded tanh (z) velocity profile in the presence of a saturated finite layer, are studied. The saturated layer is introduced at different levels above the inlection point and the variations of moisture content, layer thickness and distance from the origin are examined. The growthyrates and phase speeds of the unstable modes are obtained by solving numerically the equations of motion in the linear, inviscid, Boussinesq limit, via the technique of Lalas and Einaudi (1976). It is shown that the presence of the saturated layer can significantly affect the stability characteristics of the waves. inereases in moisture, layer thickness and distance of the layer from the inflection point are found to amplify the wave response because the saturated layer behaves as a top boundtry to the shear flow. The presence of such effective boundaries is found to stabilize short wavelengths and destabilize longer wavelengths. Finally, an application of the results to a rainband case produces values of the wave parameters in good agreement with the observed ones. © 1991 Springer-Verlag

The distribution of global and net radiation over Greece

In the present study an attempt is made to establish the distribution of global and net radiation over Greece, with the help of meteorological data. An empirical formula based on that proposed by Budyko[1] is derived which reproduces satisfactorily the available actual measurements at the National Observatory of Athens. Parameters utilized in the equations were: elevation, absolute humidity, cloud cover, air temperature at the screen height, surface albedo. The results indicate that the main factors which contribute to the distribution of global radiation over Greece are elevation and cloudiness. The extreme values are 4.2 Kly/month over Macedonia during the winter and 18.0 Kly/month over the mountainous regions of Crete during the summer. On the other hand the main factors which contribute to the distribution of net radiation over Greece are the absolute humidity and the air temperature. The extreme values are -0.35 Kly/month over eastern Macedonia during the winter and 7.8 Kly/month over Crete and the western Peloponnesos during the summer. © 1979

The effect of moist layer location on the stability of trapped gravity waves in an almost saturated atmosphere

The stability characteristics of trapped gravity waves, generated by an isothermal bounded tanh (z) velocity profile in the presence of a saturated finite layer, are studied. The saturated layer is introduced at different levels above the inlection point and the variations of moisture content, layer thickness and distance from the origin are examined. The growthyrates and phase speeds of the unstable modes are obtained by solving numerically the equations of motion in the linear, inviscid, Boussinesq limit, via the technique of Lalas and Einaudi (1976). It is shown that the presence of the saturated layer can significantly affect the stability characteristics of the waves. inereases in moisture, layer thickness and distance of the layer from the inflection point are found to amplify the wave response because the saturated layer behaves as a top boundtry to the shear flow. The presence of such effective boundaries is found to stabilize short wavelengths and destabilize longer wavelengths. Finally, an application of the results to a rainband case produces values of the wave parameters in good agreement with the observed ones. © 1991 Springer-Verlag

Glycerol and glycerol-based deep eutectic mixtures as emerging green solvents for polyphenol extraction: The evidence so far

The acknowledgement that uncontrolled and excessive use of fossil resources has become a prime concern with regard to environmental deterioration, has shifted the orientation of economies towards the implementation of sustainable routes of production, through the valorization of biomass. Green chemistry plays a key role in this regard, defining the framework of processes that encompass eco-friendly methodologies, which aim at the development of highly efficient production of numerous bioderived chemicals, with minimum environmental aggravation. One of the major concerns of the chemical industry in establishing sustainable routes of production, is the replacement of fossil-derived, volatile solvents, with bio-based benign ones, with low vapor pressure, recyclability, low or no toxicity, availability and low cost. Glycerol is a natural substance, inexpensive and non-toxic, and it is a principal by-product of biodiesel industry resulting from the transesterification process. The ever-growing market of biodiesel has created a significant surplus of glycerol production, resulting in a concomitant drop of its price. Thus, glycerol has become a highly available, low-cost liquid, and over the past decade its use as an alternative solvent has been gaining unprecedented attention. This review summarizes the utilization of glycerol and glycerol-based deep eutectic mixtures as emerging solvents with outstanding prospect in bioactive polyphenol extraction. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Tropospheric gravity waves: Their detection by and influence on rawinsonde balloon data

In this paper we discuss the interaction of a tropospheric gravity wave, detected by a radar and a microbarograph array, with a normal rawinsonde balloon. By calculating the wave properties and comparing them to balloon data, we show that such data can provide information about tropospheric gravity waves. We also draw attention to the consequences of the wave‐induced differences between the measured and the actual background state of the atmosphere. The differences may be critical, for example, in predicting clear air turbulence and in evaluating remote sensing instrumentation. Copyright © 1980 Royal Meteorological Societ

Development of a low-temperature and high-performance green extraction process for the recovery of polyphenolic phytochemicals fromwaste potato peels using hydroxypropyl β-cyclodextrin

Potato peels (PP) are a major agri-food side-stream originating from potato processing, but to date, their green valorization as a bioresource of antioxidant polyphenols is limited to extraction processes involving mainly water/ethanol-based solvents, whereas other eco-friendly methodologies are scarce. This study aimed at developing a simple, straight-forward and green extraction methodology to effectively recover PP polyphenols, using hydroxypropyl β-cyclodextrin (HP-β-CD). After an initial assay to identify the optimal HP-β-CD concentration that would provide increased extraction yield, optimization based on response surface methodology enabled maximization of the extraction performance, providing a total polyphenol yield of 17.27 0.93 mg chlorogenic acid equivalent g-1 dry mass, at 30 °C. Testing of temperatures higher than 30 °C and up to 80 °C did not favor higher yields. The extracts obtained with HP-β-CD were slightly richer in polyphenols than extracts prepared with conventional solvents, such as aqueous ethanol and methanol, displaying similar antioxidant characteristics. The major polyphenols that could be identified in the extracts were neochlorogenic, chlorogenic, caffeic and ferulic acids. The outcome of this study demonstrated that HP-β-CD may be used as a highly effective green means of recovering PP polyphenols, at near-ambient temperature. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

An analysis of wind power potential in Greece

In this paper an analysis of the available wind data for the Aegean Sea region of Greece is carried out to ascertain its potential for wind energy development. The effect of the limited number of daily observations available on the accuracy of the mean wind speed and annual wind energy estimates is ascertained. The applicability of the Weibull distribution is then examined and plots of the Weibull parameters are given. The annual average wind energy flux is calculated and found to be quite high (in excess of 600 W/m2 per yr at 10 m) which makes the Aegean Islands likely candidates for wind power utilization. © 1983

The role of gravity waves in tropospheric processes

The nature and the role of gravity waves in the troposphere is briefly discussed and reviewed. After describing some basic properties of gravity waves and their generation mechanisms, we analyze their ability to influence phase changes, trigger and organize convective cells, to produce and interact with turbulence, and to affect diffusive processes in the atmosphere. Throughout, the emphasis is placed on the physical processes involved in the interaction of gravity waves with mesoscale and planetary boundary layer phenomena. Also discussed and reviewed are those remote sensing devices which are particularly useful in revealing and measuring such waves. Finally, an attempt is made to outline possible lines of future work for the purpose of fully understanding the role of gravity waves in mesoscale and microscale dynamics. © 1978 Birkhäuser Verlag

Hydroxypropyl-β-cyclodextrin as a green co-solvent in the aqueous extraction of polyphenols from waste orange peels

There is, to-date, an expanding interest concerning the use of cyclodextrins as green food-grade co-solvents in the aqueous extraction of polyphenols, however, data regarding polyphenol extraction from waste orange peels (WOP) are lacking. On this ground, hydroxypropyl β-cyclodextrin (HP-β-CD), a highly water-soluble cyclodextrin, was used to develop a simple and straightforward methodology for the effective recovery of WOP polyphenols. Process optimization by response surface showed that maximum total polyphenol recovery (26.30 ± 1.49 mg gallic acid equivalents g−1 dry mass) could be accomplished with 15 mM HP-β-CD at 40◦C. On the other hand, integration of ultrasonication pretreatment was found unsuitable, as it resulted in reduced polyphenol yield. Examination of solvent acidity indicated that polyphenol extraction may be enhanced at pH 4, but the difference was non-significant (p > 0.05) compared to yields attained at pH 2, 3, and 5. Extraction of WOP polyphenols with HP-β-CD was shown to provide significantly higher hesperidin yield compared to 60% (v/v) aqueous ethanol, which suggested selectivity of HP-β-CD toward this polyphenolic metabolite. © 2020 by the authors. Licensee MDPI, Basel, Switzerland