Theoretical model for the images formed by a spherical particle in a coherent imaging system: comparison

A simple theoretical model is presented that allows calculation of the image produced by a spherical absorbing particle illuminated by monochromatic, coherent laser light. Results presented in this paper are restricted to a singe-lens imaging system, although generalization to more complex imaging system configurations would be straightfoward. The method uses classic Lorenz-Mie scattering theory to obtain the electromagnetic field external to an absorbing spherical particle and a Fourier optics approach to calculate the intensities in the image plane. Experimental results evaluating focus characteristics are examined for 50 um diameter water droplets using an N2 laser imaging system in conjunction with a digital image processor, and the experimental images are compared with a digital image processor, and the experimental images are compared to the results of the theoretical model. Comparative focus criteria results are particularly useful in aerosol science research involving dynamic particle size measuremetns in which criteria for focus and depth of field must be established

Electromagnetic wave propagation in rain and polarization effects

This paper summarizes our study on microwave and millimeter-wave propagation in rain with special emphasis on the effects of polarization. Starting from a recount of our past findings, we will discuss developments with these and how they are connected with subsequent research

PyMieDAP: a Python--Fortran tool to compute fluxes and polarization signals of (exo)planets

PyMieDAP (the Python Mie Doubling-Adding Programme) is a Python--based tool for computing the total, linearly, and circularly polarized fluxes of incident unpolarized sun- or starlight that is reflected by, respectively, Solar System planets or moons, or exoplanets at a range of wavelengths. The radiative transfer computations are based on an adding--doubling Fortran algorithm and fully include polarization for all orders of scattering. The model (exo)planets are described by a model atmosphere composed of a stack of homogeneous layers containing gas and/or aerosol and/or cloud particles bounded below by an isotropically, depolarizing surface (that is optionally black). The reflected light can be computed spatially--resolved and/or disk--integrated. Spatially--resolved signals are mostly representative for observations of Solar System planets (or moons), while disk--integrated signals are mostly representative for exoplanet observations. PyMieDAP is modular and flexible, and allows users to adapt and optimize the code according to their needs. PyMieDAP keeps options open for connections with external programs and for future additions and extensions. In this paper, we describe the radiative transfer algorithm that PyMieDAP is based on and the code's principal functionalities. And we provide benchmark results of PyMieDAP that can be used for testing its installation and for comparison with other codes. PyMieDAP is available online under the GNU GPL license at http://gitlab.com/loic.cg.rossi/pymiedapComment: 15 pages, 7 figures, 4 tables. Accepted for publication in Astronomy and Astrophysic

Spartan Daily, September 10, 2008

Volume 131, Issue 7https://scholarworks.sjsu.edu/spartandaily/10491/thumbnail.jp

Turbulence induced cloud voids: Observation and interpretation

The phenomenon of cloud voids, i.e., elongated volumes inside a cloud that are devoid of droplets, was observed with laser sheet photography in clouds at a mountain-top station. Two experimental cases, similar in turbulence conditions yet with diverse droplet size distributions and cloud void prevalence, are reported. A theoretical explanation is proposed based on the study of heavy inertial sedimenting particles inside a Burgers vortex. A general conclusion regarding void appearance is drawn from theoretical analysis. Numerical simulations of polydisperse droplet motion with realistic vortex parameters and Mie scattering visual effects accounted for can explain the presence of voids with sizes similar to that of the observed ones. Preferential concentration and sorting effects in a vortex tube are discussed for reasonable cloud conditions

Geodetske mobilne mjerne metode za praćenje erozije obala rijeka

Rivers are relief features susceptible to change over time more than any other. Dynamic and intensity of those changes depend on a series of factors that have been a research topic for decades, all with the goal of predicting and/or preventing changes that have a negative effect on ecological and administrative systems alike. This is especially evident on big river systems. The topic of water course related erosion, being a phenomenon that changes the shape, position and flow of a water course, has not, to this day, been exhausted, primarily due to a myriad of factors directly and indirectly influencing the process. At the same time, determining the influence of each of those individual factors is not possible without the use of adequate measurement methods that allow fast acquisition of relevant data, based on witch correct conclusions can be made about individual processes. Emphasis on fast acquisition must be made here because rivers are dynamic bodies and the changes they cause are also relatively fast. Geodesy, including measuring techniques and methods that it uses, has experienced major development in the past decades. This has opened new possibilities for addressing those previously mentioned needs of river systems erosional processes and their research. Considering all of the above and supplementing with a fact that Danube is the largest and strongest river flowing through Croatia, it can be concluded that Danube is the one most interesting from the aspect of determining erosion phenomena frequency/intensity in Croatia. For acquiring relevant data in a relatively short time adequate survey methods need to be applied. Hence, Danube and its particularly interesting segments were selected for determining applicability of contactless mobile measurement solutions with the purpose of assessing those systems in determining and predicting erosional risks and cumulative rates.Rijeke su reljefni oblici koji su podložniji promjenama tokom vremena od bilo kojih drugih. Dinamika i intenzitet tih promjena ovisi o nizu faktora koji su desetljećima tema istraživanja sa ciljem predviđanja i/ili prevencije promjena koje imaju negativan utjecaj na kako ekološke tako i administrativne sustave. To je posebno izraženo na velikim riječnim sustavima. Tema erozije pod utjecajem tekućih voda, kao fenomena koji mijenja oblik, položaj i tok rijeka, nije, do današnjeg dana, u potpunosti iscrpljena primarno zbog nebrojenih faktora koji direktno ili indirektno utječu na taj proces. Istovremeno, utvrđivanje utjecaja pojedinog faktora nije moguće bez upotrebe adekvatnih mjernih metoda, koje omogućavaju brzo prikupljanje relevantnih podataka na osnovu kojih je moguće donijeti ispravne zaključke o pojedinim procesima. Naglasak se stavlja na brzinu prikupljanja s obzirom da su rijeke dinamična tijela, što znači da su i promijene, koje one posljedično uzrokuju, također, relativno brze. Geodezija, primarno mjerna tehnologija i metodologija koja se koristi, je u proteklim desetljećima doživjela značajan razvoj. Time su se otvorile nove mogućnosti za zadovoljavanje navedenih potreba pri istraživanju erozivnih procesa riječnih sustava. Uzevši u obzir sve navedeno te dodajući podatak da je Dunav najveća i najsnažnija rijeka koja teče kroz Hrvatsku, moguće je zaključiti da je upravo ta rijeka najzanimljivija po pitanju utvrđivanja učestalosti/intenziteta erozivnog fenomena u Hrvatskoj. Za prikupljanje relevantnih podataka, u relativno kratkom vremenu, nužno je primijeniti adekvatne metode. Stoga je Dunav, odnosno njegovi najzanimljiviji dijelovi, odabran za utvrđivanje primjenjivosti bezkontaktnih mobilnih mjernih rješenja sa svrhom ocjene takvih sustava za određivanje i predviđanje rizika od erozije te njenog iznosa

Geodetske mobilne mjerne metode za praćenje erozije obala rijeka

Rivers are relief features susceptible to change over time more than any other. Dynamic and intensity of those changes depend on a series of factors that have been a research topic for decades, all with the goal of predicting and/or preventing changes that have a negative effect on ecological and administrative systems alike. This is especially evident on big river systems. The topic of water course related erosion, being a phenomenon that changes the shape, position and flow of a water course, has not, to this day, been exhausted, primarily due to a myriad of factors directly and indirectly influencing the process. At the same time, determining the influence of each of those individual factors is not possible without the use of adequate measurement methods that allow fast acquisition of relevant data, based on witch correct conclusions can be made about individual processes. Emphasis on fast acquisition must be made here because rivers are dynamic bodies and the changes they cause are also relatively fast. Geodesy, including measuring techniques and methods that it uses, has experienced major development in the past decades. This has opened new possibilities for addressing those previously mentioned needs of river systems erosional processes and their research. Considering all of the above and supplementing with a fact that Danube is the largest and strongest river flowing through Croatia, it can be concluded that Danube is the one most interesting from the aspect of determining erosion phenomena frequency/intensity in Croatia. For acquiring relevant data in a relatively short time adequate survey methods need to be applied. Hence, Danube and its particularly interesting segments were selected for determining applicability of contactless mobile measurement solutions with the purpose of assessing those systems in determining and predicting erosional risks and cumulative rates.Rijeke su reljefni oblici koji su podložniji promjenama tokom vremena od bilo kojih drugih. Dinamika i intenzitet tih promjena ovisi o nizu faktora koji su desetljećima tema istraživanja sa ciljem predviđanja i/ili prevencije promjena koje imaju negativan utjecaj na kako ekološke tako i administrativne sustave. To je posebno izraženo na velikim riječnim sustavima. Tema erozije pod utjecajem tekućih voda, kao fenomena koji mijenja oblik, položaj i tok rijeka, nije, do današnjeg dana, u potpunosti iscrpljena primarno zbog nebrojenih faktora koji direktno ili indirektno utječu na taj proces. Istovremeno, utvrđivanje utjecaja pojedinog faktora nije moguće bez upotrebe adekvatnih mjernih metoda, koje omogućavaju brzo prikupljanje relevantnih podataka na osnovu kojih je moguće donijeti ispravne zaključke o pojedinim procesima. Naglasak se stavlja na brzinu prikupljanja s obzirom da su rijeke dinamična tijela, što znači da su i promijene, koje one posljedično uzrokuju, također, relativno brze. Geodezija, primarno mjerna tehnologija i metodologija koja se koristi, je u proteklim desetljećima doživjela značajan razvoj. Time su se otvorile nove mogućnosti za zadovoljavanje navedenih potreba pri istraživanju erozivnih procesa riječnih sustava. Uzevši u obzir sve navedeno te dodajući podatak da je Dunav najveća i najsnažnija rijeka koja teče kroz Hrvatsku, moguće je zaključiti da je upravo ta rijeka najzanimljivija po pitanju utvrđivanja učestalosti/intenziteta erozivnog fenomena u Hrvatskoj. Za prikupljanje relevantnih podataka, u relativno kratkom vremenu, nužno je primijeniti adekvatne metode. Stoga je Dunav, odnosno njegovi najzanimljiviji dijelovi, odabran za utvrđivanje primjenjivosti bezkontaktnih mobilnih mjernih rješenja sa svrhom ocjene takvih sustava za određivanje i predviđanje rizika od erozije te njenog iznosa

Study of the Performance of Natural Fiber Reinforced Composites for Wind Turbine Blade Applications

Availability of some form of energy is essential for human survival and social development. However, the way energy has been generated within the last century has brought forward the quest for generation of energy without polluting the environment, which is nowadays considered to be the biggest global challenge. The materials used for wind turbine blades can be classified under this challenge of polluting the environment. One of the materials expected to reduce this problem is natural fiber reinforced composite (FRC). Thus, the focus of this paper is to evaluate the potential of different natural FRC materials for small wind turbine blade application. Eleven different natural fibers reinforced composite in epoxy resin are studied. The modified Halphin-Tsai semi-empirical model has been used to compute the physical properties of the composites, since it has a good agreement with experimental results. Stress, deformation, and weight of wind turbine blade under different loadings are analyzed aimed to search for a fiber type that may extend the life span of the blade. Finally, flap wise, edge wise, longitudinal and torsional natural frequencies are computed numerically by using finite element method in Qblade software (QFEM) under different mode types and the effects are analysed. Upon comparing the results with a common composite material for wind turbine blade (E-glass/epoxy), it has been observed that the selected natural fiber composites have equivalent and better mechanical performance. The environmental friendliness of natural fibers, i.e. biodegradability, comes as a plus to their advantage as materials of wind turbine blades.publishedVersio

New spectral functions of the near-ground albedo derived from aircraft diffraction spectrometer observations

The airborne spectral observations of the upward and downward irradiances are revisited to investigate the dependence of the near-ground albedo as a function of wavelength in the entire solar spectrum for different surfaces (sand, water, snow) and under different conditions (clear or cloudy sky). The radiative upward and downward fluxes were determined by a diffraction spectrometer flown on a research aircraft that was performing multiple flight paths near the ground. The results obtained show that the near-ground albedo does not generally increase with increasing wavelengths for all kinds of surfaces as is widely believed today. Particularly, in the case of water surfaces it was found that the albedo in the ultraviolet region is more or less independent of the wavelength on a long-term basis. Interestingly, in the visible and near-infrared spectra the water albedo obeys an almost constant power-law relationship with wavelength. In the case of sand surfaces it was found that the sand albedo is a quadratic function of wavelength, which becomes more accurate if the ultraviolet wavelengths are neglected. Finally, it was found that the spectral dependence of snow albedo behaves similarly to that of water, i.e. both decrease from the ultraviolet to the near-infrared wavelengths by 20–50%, despite the fact that their values differ by one order of magnitude (water albedo being lower). In addition, the snow albedo vs. ultraviolet wavelength is almost constant, while in the visible near-infrared spectrum the best simulation is achieved by a second-order polynomial, as in the case of sand, but with opposite slopes