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91.
Marian Vîrgolici Corneliu Ponta Mihaela Manea Daniel Neguţ Mihalis Cutrubinis Ioan Moise Rareş Şuvăilă Eugen Teodor Costel Sârbu Andrei Medvedovici 《Journal of chromatography. A》2010,1217(12):1977-1987
Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution & Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis “like” macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers. 相似文献
92.
Recently, the steady sedimentation profile of a dilute suspension of chemically powered colloids was studied experimentally [J. Palacci et al., Phys. Rev. Lett. 105, 088304 (2010)]. It was found that the sedimentation length increases quadratically with the swimming speed of the active Brownian particles. Here we investigate theoretically the sedimentation of self-propelled particles undergoing translational and rotational diffusion. We find that the measured increase of the sedimentation length is coupled to a partial alignment of the suspension with the mean swimming direction oriented against the gravitational field. We suggest realistic parameter values to observe this polar order. Furthermore, we find that the dynamics of the active suspension can be derived from a generalized free energy functional. 相似文献
93.
N. V. Sopinskii V. S. Khomchenko O. S. Litvin A. K. Savin N. A. Semenenko A. A. Evtukh V. P. Sobolevskii G. P. Ol’khovik 《Technical Physics》2011,56(11):1665-1669
The properties of low-refractive-index carbon films obtained by close-spaced vapor transport at graphite sublimation are studied.
The optical properties of the films are investigated by monochromatic multiple-angle ellipsometry, and their morphology is
examined by AFM. It is found that the films have a columnar structure with a background surface roughness of about 1 nm. In
addition, the surface of the film contains islands up to 50 nm in height with a footprint of ≈200 nm. A low-refractive-index
carbon film deposited by close-spaced vapor transport on silicon tips is found to decrease the field emission threshold and
drastically raise the current. 相似文献
94.
Magdalena Ulmeanu Iuliana Iordache Mihaela Filipescu Valentin Craciun Simona Cinta Pinzaru Andreas Hörner 《Central European Journal of Physics》2011,9(5):1280-1287
Experimental studies on patterning hexagonal Ge nanostructures have been conducted on Si substrates through deposition of
Ge with colloidal particles as a mask. The deposited Ge thin film possesses, according to the X-ray diffraction measurements,
in plane texture, being epitaxial and aligned with the (111) Si substrate. The size distribution of the patterned Ge nanostructures
is narrow, as indicated by the atomic force microscopy and scanning electron microscopy measurements. We have obtained Ge
nanostructures with lateral dimension of 490 nm (height 12 nm), 200 nm (height 6 nm) and 82 nm (height 6 nm) by using different
sizes of polystyrene spheres. We have performed in depth studies of the Ge nanostructures’ behavior due to thermal and rapid
thermal post-annealing processes. FT micro-Raman spectroscopy shows that there is no Si intermixing during the annealing process.
In order to quantify the changes in the height and lateral dimension, we have performed atomic force microscopy and white
light interferometry analysis. The changes in shape and the decrease in the area of a cross-section of Ge nanostructure will
be discussed in respect to similar results shown in the literature for Ge thin films during the annealing process. 相似文献
95.
Roslinda Nazar Mihaela Jaradat Norihan M. Arifin Ioan Pop 《Central European Journal of Physics》2011,9(5):1195-1202
In this paper, the stagnation-point flow and heat transfer towards a shrinking sheet in a nanofluid is considered. The nonlinear
system of coupled partial differential equations was transformed and reduced to a nonlinear system of coupled ordinary differential
equations, which was solved numerically using the shooting method. Numerical results were obtained for the skin friction coefficient,
the local Nusselt number as well as the velocity and temperature profiles for some values of the governing parameters, namely
the nanoparticle volume fraction φ, the shrinking parameter λand the Prandtl number Pr. Three different types of nanoparticles are considered, namely Cu, Al2O3 and TiO2. It was found that nanoparticles of low thermal conductivity, TiO2, have better enhancement on heat transfer compared to nanoparticles Al2O3 and Cu. For a particular nanoparticle, increasing the volume fraction φ results in an increase of the skin friction coefficient and the heat transfer rate at the surface. It is also found that
solutions do not exist for larger shrinking rates and dual solutions exist when λ < −1.0. 相似文献
96.
V. E. Fortov A. P. Nefedov O. S. Vaulina A. M. Lipaev V. I. Molotkov A. A. Samaryan V. P. Nikitskii A. I. Ivanov S. F. Savin A. V. Kalmykov A. Ya. Solov’ev P. V. Vinogradov 《Journal of Experimental and Theoretical Physics》1998,87(6):1087-1097
The dynamics of the formation of ordered structures of macroparticles charged by photoemission under the action of solar radiation
under microgravitational conditions without the use of electrostatic traps to confine the particles is studied experimentally
and theoretically. The working conditions needed for the formation of structures of charged macroparticles are chosen as a
result of a numerical solution of the problem posed, the particle charges and the interparticle interaction parameter are
determined, and the characteristic times specifying the dynamics of the formation of an ordered system of macroparticles are
calculated. The behavior of an ensemble of macroparticles under the effect of solar radiation is observed experimentally on
board the Mir space station. An analysis and comparison of the results of the experimental and theoretical investigations
permit drawing a conclusion regarding the possibility of the existences of extended ordered formations of macroparticles charged
by photoemission under microgravitational conditions.
Zh. éksp. Teor. Fiz. 114, 2004–2021 (December 1998) 相似文献
97.
Russian Journal of Organic Chemistry - 相似文献
98.
We propose a novel approach to modeling advertising dynamics for a firm operating over a distributed market domain based on
controlled partial differential equations of the diffusion type. Using our model, we consider a general type of finite-horizon
profit maximization problem in a monopoly setting. By reformulating this profit maximization problem as an optimal control
problem in infinite dimensions, we derive sufficient conditions for the existence of its optimal solutions under general profit
functions, as well as state and control constraints, and provide a general characterization of the optimal solutions. Sharper,
feedback-form characterizations of the optimal solutions are obtained for two variants of the general problem.
The first author gratefully acknowledges financial support by the NSF, the DAAD, the SFB 611 (Bonn), and the Max-Planck-Institut
für Mathematik (Leipzig) through an IPDE fellowship. 相似文献
99.
V. G. Kiptilyi A. V. Livke V. I. Nagornyi Yu. Ya. Nefedov M. V. Savin V. I. Semenov V. A. Chirkin 《Technical Physics》1998,43(4):471-472
The quality of suppression of neutrons by lithium hydride 6LiH filters for narrow and wide beams from a neutron generator incorporating deuterium and tritium targets is investigated.
The experimental data can be used for the design of measurement apparatus operating in high neutron fields.
Zh. Tekh. Fiz. 68, 136–138 (April 1998) 相似文献
100.