A fast and easy method for water transfer of iron oxide nanoparticle based on the hydrophobic interaction of oleic acid coated nanoparticles with the amphiphilic PAMAM-C12 dendrimer is described. The process may be conveniently performed in water and yields nanoparticles with good size distribution, diameter modulation and high crystallinity. The nanoparticles have been functionalized with gadolinium ions to obtain T1/T2 dual mode contrast agents. Furthermore, the possibility to deliver and release lipophilic drugs was investigated.
Wandering of a laser beam in the atmosphere is due to fluctuations of the refractive index of the atmosphere and, having
a strong dependence on the path length, is very useful to investigate random or continuous changes of the refractive
index during time. First, we describe methods we developed and applied to locally investigate the parameters of
turbulence (inner scale, outer scale and structure constant) based on our previous theory of propagation of "thin" beams.
Then we describe use of thin beams to investigate the evolution of the refractive index gradient and show experimental
results including non stationary and non isotropic conditions.
The refractive index gradient, averaged over short horizontal paths, in the atmosphere was experimentally investigated by using a method we developed, based on the use of thin parallel laser beams. Horizontal and vertical components of the gradient were shown to be directly related to the corresponding lateral displacements of the beams at the end of the path. The method is here described and results of measurements made in different locations and conditions are presented. Some cases of strong anisotropy were also found, which can be related to the local air convective movements from the ground.
We recently developed a method1 to measure the gradient of the refractive index of the atmosphere, by using the lateral fluctuations of thin laser beams along a given path. We showed that the horizontal and vertical instantaneous fluctuations of a ray on a screen, at the end of a path of length L, are related to the horizontal and vertical components, averaged along the path, of the refractive index gradient, respectively.
Our method, which is based on the geometrical optics approximation, requires that the beams are "thin", that is that their transverse dimension be not larger than the dimensions of the smallest inhomogeneities of the atmosphere (inner scale of turbulence). In practice, it allows "local" measurements, that is measurements over short horizontal paths, even few meters' paths. Experiments were made in the open air.
Here we describe the method and present results of measurements made in different locations and conditions, at near ground levels. Temperature and transverse wind velocity were also measured and some correlation of these quantities to the refractive index gradient will be presented. Some cases of strong vertical anisotropy are also shown, which can be related to the local air convective movements from the ground.
We recently developed method for estimating the outer scale of tmospheric turbulence based on the correlation functions of lateral displ cements of thin beams propagating horizont lly over short paths.Here,the method is briefly summerized and comparison between the results of the method obtained by using the von Karman and
Hill-Andrews models of turbulence is presented.
Use of fractional moments of low order, recently proposed by Consortini and Rigal for investigating probability density functions (PDF's) in laser scintillation statistics through atmospheric turbulence, is here proposed for overcoming the saturation effects of the electronics due to low dynamics acquisition systems.
Use of fractional moments of low order is here proposed for processing data of intensity fluctuations from optical atmospheric propagation measurements. In this paper we check the accuracy of low order moment estimation and their ability to discriminate which one, among a number of candidate theoretical distributions, better represents the experimental histograms of intensity. The comparison method is tested by sampling sets of data from three popular distributions, that is Ln, LnME and K distribution. Applications to experimental sets of data are also presented.
Non-stationarity of atmospheric turbulence gives rise to some practical problems when one wants to determine the probability density function (PDF) of intensity fluctuations from laser atmospheric propagation experimental data. For strong fluctuations, the number of uncorrelated data that can be collected in stationary conditions is generally not enough to correctly evaluate intensity moments of order greater than two 1} . In the case of very strong fluctuations even the second order moment (and also variance) can not be estimated with accuracy [2] This is due to the fact that the stronger the fluctuations the longer is the tail of the distribution, which represents the main contribution in high order moment evaluation. If only integer moments are considered, information about intensity PDF that can be extracted from its moments is thus very poor because only a few of them are correctly estimated
The distributions of intensity fluctuations generally found in atmospheric optical scintillation measurements are characterized by a large range of intensity values, I, whose probability level, even if low, is not negligible. The range of I-values with a significant probability depends on the experimental conditions and can go from zero to several hundred times the mean value, < I <, of the distribution in the case of strong scintillation. In principle, an acquisition system should have dynamics able to cover the whole significant range of measured intensities. Of course, this requirement is not limited to scintillation measurements and the application of low order fractional moments we present here can be employed every time we face a measured quantity with a "long tail" distribution.
In atmospheric and astronomical optics, as well as in applications involving optical propagation through the atmosphere, atmospheric turbulence plays an important role in deterioration of information. Recently, adaptive systems allow correction of aberrations produced by turbulence. In all cases knowledge is necessary of atmospheric turbulence and its characteristic parameters, i.e. inner scale, outer scale and the so called structure constant.
Intensity moments of any order are proposed and moments of low order (less than 2) are shown to be suitable for overcoming the problem of lack of data, due to turbulence non-stationarity, for correctly measuring higher order integer moments in atmospheric optical scintillation.
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