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    Wyświetlanie 1-13 z 13
    Tytuł:
    Differential Reflection Spectroscopy: A Novel Method for Explosive Detection
    Autorzy:
    Yuksel, S.
    Dubroca, T.
    Hummel, R.
    Gader, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399730.pdf
    Data publikacji:
    2013-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.25.Gz
    78.90.+t
    Opis:
    In the aftermath of the recent terrorist attacks, there has been an increasing need for automated, high-speed detection technologies that can detect trace amounts of explosives without human intervention. Our group at the University of Florida has developed differential reflection spectroscopy which can detect explosive residue on surfaces such as parcel, cargo and luggage. In this differential reflection device, explosives show spectral finger-prints at specific wavelengths, for example, the spectrum of 2,4,6, trinitrotoluene shows an absorption edge at 420 nm. Additionally, we have developed a support vector machine based computer software to classify the explosives and non-explosive materials. In this study we will (i) describe this system and give an insight into the operation of our prototype, (ii) demonstrate our software for the detection of the spectral finger-prints, and (iii) discuss the normalization of the data which significantly increases classification rates and decreases the number of parameters.
    Źródło:
    Acta Physica Polonica A; 2013, 123, 2; 263-264
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    New High Performance Scintillators Based on Re-Activated Insulator Materials
    Autorzy:
    Wojtowicz, A. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1945553.pdf
    Data publikacji:
    1996-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.90.+t
    78.55.-m
    61.80.Ed
    29.40.-n
    Opis:
    In this paper we address the problem of the host-to-ion energy transfer in some RE-activated wide band gap materials excited by ionizing radiation. We argue that, despite the expected self-localization of holes, the dominant mechanism in efficient materials involves sequential trapping of both charge carriers (holes and electrons) by an activating RE-ion followed by a radiative recombination via the ion producing scintillation light. Selected experimental results are presented to illustrate how various energy transfer processes manifest themselves in the spectroscopy of scintillator materials. Experimental results combined with simple considerations are used to identify these RE-ions which are likely to act as hole or electron traps in tri- and difluorides, thus initiating the recombination sequence leading to efficient scintillation.
    Źródło:
    Acta Physica Polonica A; 1996, 90, 1; 215-222
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Luminescence and Scintillation Properties of Ce$\text{}_{x}$La$\text{}_{1-x}$F$\text{}_{3}$ Monocrystals
    Autorzy:
    Wojtowicz, A.
    Balcerzyk, M.
    Lempicki, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1929799.pdf
    Data publikacji:
    1993-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.90.+t
    78.55.-m
    61.80.Ed
    29.40.-n
    Opis:
    In this communication we present our results concerning luminescence and scintillation properties of mixed cerium-lanthanum trifluoride monocrystals, Ce$\text{}_{x}$La$\text{}_{1-x}$F$\text{}_{3}$. The luminescence, luminescence excitation spectra and decays are complex, indicating the presence of Ce$\text{}^{3+}$ ions in regular and parasitic "perturbed" sites. The efficient energy transfer from regular Ce$\text{}^{3+}$ ions (emitting at 286 and 303 nm) to "perturbed" Ce$\text{}^{3+}$ ions (emitting at 340 nm) and the lack of the fast energy migration between Ce$\text{}^{3+}$ ions are responsible for non-exponential decays of the short-wavelength emission and a relatively long rise-time of the long-wavelength emission. The short-wavelength emission decays are described by the Inokuti-Hirayama model of statistically distributed donors and acceptors. Our estimates of oscillator strengths, at 13.1 × 10$\text{}^{-3}$ for Ce$\text{}^{3+}$, and 13.5 × 10$\text{}^{-3}$ for Ce$\text{}^{3+}$$\text{}_{per}$, confirm that the d-f transition on the Ce$\text{}^{3+}$ ion in a different site must be responsible for the long-wavelength emission. Calculations of the Ce-Ce and Ce-Ce$\text{}_{per}$ energy transfer rates give 7.7 × 10$\text{}^{5}$ s$\text{}^{-1}$ and 1.56 × 10$\text{}^{9}$ s$\text{}^{-1}$. The concentration of "perturbers" in good CeF$\text{}_{3}$ samples has been reduced down to about 0.11%. It is likely that the constant and significant progress made by crystal growers (Optovac Inc.) may eventually produce a superior material for applications in high energy and nuclear physics.
    Źródło:
    Acta Physica Polonica A; 1993, 84, 5; 963-968
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spectroscopy and Thermoluminescence of LuAlO$\text{}_{3}$:Ce
    Autorzy:
    Wiśniewski, D.
    Drozdowski, W.
    Wojtowicz, A.
    Lempicki, A.
    Dorenbos, P.
    de Haas, J. T. M.
    van Eijk, C. W. E.
    Bos, A. J. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1945649.pdf
    Data publikacji:
    1996-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.90.+t
    78.55.-m
    61.80.Ed
    29.40.-n
    Opis:
    The present status of the LuAlO$\text{}_{3}$:Ce scintillator is reviewed. Scintillation mechanism of this material is based on capture by Ce$\text{}^{3+}$ of holes and then electrons from their respective bands. Results of spectroscopic and thermoluminescence experiments are presented to support this model.
    Źródło:
    Acta Physica Polonica A; 1996, 90, 2; 377-384
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Inelastic Mean Free Paths of Low-Energy Electrons in Solids
    Autorzy:
    Tanuma, S.
    Powell, C. J.
    Penn, D. R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1892433.pdf
    Data publikacji:
    1992-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    82.80.Pv
    79.20.Fv
    79.60.-i
    78.90.+t
    Opis:
    We present a summary of recent calculations of the electron inelastic mean free paths (IMFPs) of 50-2000 eV electrons in 27 elements and 15 inorganic compounds. These calculations are based in part on experimental optical data to represent the dependence of the inelastic scattering probability on energy loss and the theoretical Lindhard dielectric function to represent the dependence of the scattering probability on momentum transfer. The calculated IMFPs for the elements were fitted to a modified form of the Bethe equation for inelastic electron scattering in matter and the four parameters in this equation were empirically related to other material parameters. The resulting formula, designated TPP-2, provides a convenient means for predicting IMFPs in other materials. We have used two powerful integral equations or sum rules to evaluate the optical data on which our IMFP calculations are based. While the optical data for the elements satisfied these sum rules to an acceptable degree, there were significant deviations in the data for the compounds. In addition, differences in IMFPs calculated from the optical data for the compounds and the values predicted by TPP-2 correlated with the average errors of the optical data as determined by the sum rules. IMFPs calculated from TPP-2 for these compounds are therefore believed to be more reliable than IMFPs obtained from the imperfect optical data.
    Źródło:
    Acta Physica Polonica A; 1992, 81, 2; 169-186
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Weak Localization of Short Pulses in Disordered Waveguides
    Autorzy:
    Skipetrov, S. E.
    van Tiggelen, B. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2044615.pdf
    Data publikacji:
    2006-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    42.25.Dd
    78.90.+t
    Opis:
    We consider the phenomenon of weak localization of a short wave pulse in a quasi-1D disordered waveguide. We show that the long-time decay of the average transmission coefficient is not purely exponential, in contradiction with predictions of the diffusion theory. The diffusion theory breaks down completely for times exceeding the Heisenberg time. We also study the survival probability of a quantum particle in a disordered waveguide and compare our results with previous calculations using the super-symmetric nonlinear sigma model.
    Źródło:
    Acta Physica Polonica A; 2006, 109, 1; 101-108
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electrooptical Properties of Cylindrical Quantum Dots
    Autorzy:
    Schillak, P.
    Czajkowski, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1791330.pdf
    Data publikacji:
    2009-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.21.La
    78.30.Fs
    78.67.Hc
    78.67.-n
    78.90.+t
    Opis:
    We show how to compute the optical functions (the complex electrosusceptibility tensor, dielectric tensor, electroreflection spectra) for semiconductor quantum dots exposed to a uniform static electric field in the growth direction, including the excitonic effects. The method uses the microscopic calculation of the quantum dot excitonic wave functions and energy levels, and the macroscopic real density matrix approach to compute the electromagnetic fields and susceptibilities. The electron-hole screened Coulomb potential is adapted and the valence band structure is taken into account in the cylindrical approximation, thus separating light- and heavy-hole motions. In the microscopic calculations, using the effective-mass approximation, we solve the 6-dimensional two-particle Schrödinger equation by transforming it into an infinite set of coupled second order 2-dimensional differential equations with the appropriate boundary conditions. These differential equations are solved numerically giving the eigenfunctions and the energy eigenvalues. Having them, we can compute the quantum dot electrooptical functions. Numerical calculations have been performed for an InGaAs quantum dot with a constant electric field applied in the growth direction. A good agreement with experiment is obtained.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 5; 871-873
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Quantum and Spontaneous Breakage of Translational Symmetry due to Light Excitation in Photo-Induced Structural Phase Transitions
    Autorzy:
    Nasu, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1489998.pdf
    Data publikacji:
    2012-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.90.+t
    Opis:
    Real time quantum dynamics of the spontaneous translational symmetry breakage due to light excitation in the early stage of photo-induced structural phase transitions is reviewed under the guide of the Toyozawa theory, which is in exact compliance with the conservation law of the total momentum. At the Franck-Condon state, an electronic excitation just created by a visible photon is in a plane wave state, extended all over the crystal. While, after the lattice relaxation having been completed, it is localized as a new excitation. So, is there the shrinkage of the excitation wave function? No! The wave function never shrinks, but only the spatial (or inter lattice-site) quantum coherence (interference) of the excitation disappears, as the lattice relaxation proceeds. This is the breakage of translational symmetry.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 2; 347-349
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    X-Ray Optics for Synchrotron Radiation
    Autorzy:
    Malgrange, C.
    Powiązania:
    https://bibliotekanauki.pl/articles/1920813.pdf
    Data publikacji:
    1992-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.10.Dp
    78.90.+t
    Opis:
    This paper presents the main optical devices used to prepare a beam from X-ray synchrotron source: monochromators, flat or curved in order to intercept a larger angular divergence at the sample, mirrors and, finally, optics for polarized X-ray experiments. Since X-ray optics is based either on total reflection or on diffraction by perfect crystals, the basic fundamental results of X-ray dynamical theory, which are necessary to understand the reasons why one device should be chosen rather than the other, are also presented.
    Źródło:
    Acta Physica Polonica A; 1992, 82, 1; 13-32
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Excitation of Electron Wave Packets in Low-Dimensional Semiconductor Structures by Inhomogeneous Light Pulses
    Autorzy:
    Král, P.
    Mašek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1921602.pdf
    Data publikacji:
    1992-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    72.90.+y
    78.90.+t
    Opis:
    Generation of electron wave packets by space inhomogeneous light pulses is studied in low-dimensional semiconductor systems. Examination of their free propagation for ultrashort times as well as in the stationary excitation regime is performed. Non-classical effects related to the inhomogeneity of the source are predicted.
    Źródło:
    Acta Physica Polonica A; 1992, 82, 4; 697-701
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spin Density in Real and Momentum Space in Multi-Atom Alloys by KKR-CPA Method
    Autorzy:
    Kaprzyk, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1953167.pdf
    Data publikacji:
    1997-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.18.+y
    71.15.Cr
    78.90.+t
    Opis:
    The application of the spin-polarized version of multiple scattering theory for obtaining electron charge and spin densities in both real and momentum spaces of concentrated, multi-atom disordered alloys is presented. This method is based on the Korringa-Kohn-Rostoker (KKR) band structure approach and coherent potential approximation (CPA) method. The effective one-electron potential is constructed within local spin density approximation. The magnetic neutron form factors are in real space of our main interest. With the recent developments of new synchrotron photon sources, the Compton profile becomes the most interesting target in momentum space. In the most of examples, spin momentum density and its specific structure due to Fermi surface will be shown. To get accurate enough description in momentum space and quantity like Compton profile, the determination of the Fermi surface must be done with high precision. In this context we show how to apply generalized Lloyd formula for accurate determination of the Fermi level. Also we show how to use efficiently complex energy integration method for the computation of matrix elements, G(r,r) or G(p,p), of the KKR-CPA Green function. Results for the iron-silicon ferromagnetic binary alloys and half-metallic ferromagnetic Heusler alloys are presented.
    Źródło:
    Acta Physica Polonica A; 1997, 91, 1; 135-150
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Optics of Zero Dimensional Semiconductor Systems
    Autorzy:
    Ekimov, A. I.
    Efros, Al. L.
    Powiązania:
    https://bibliotekanauki.pl/articles/1877306.pdf
    Data publikacji:
    1991-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.90.+t
    Opis:
    The optical spectra of semiconductor microcrystals grown in transparent matrix of oxide glass are investigated. The size of microcrystals was varied in a controlled manner from a few tens to a few hundreds of angstroms. The microcrystal embedded in wide gap matrix represents three-dimensional potential well for electrons, holes and excitons. The optical properties of such zero-dimensional semiconductor structures are shown to be governed by the structure of energy spectra of confined electron-hole pairs. The phenomenon of the microcrystals ionization at interband optical excitation is observed. The Auger process in microcrystals containing two nonequilibrium electron-hole pairs is proposed to be responsible for this effect. The experimental dependencies of the ionization rate as a function of excitation intensity and the microcrystal size are in a good agreement with the theoretical predictions of the Auger recombiantion model.
    Źródło:
    Acta Physica Polonica A; 1991, 79, 1; 5-14
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Far-Infrared Narrow-Band Photodetector Based on Magnetically Tunable Cyclotron Resonance-Assisted Transitions in Pure n-Type InSb
    Autorzy:
    Dmowski, L. H.
    Cheremisin, M.
    Skierbiszewski, C.
    Knap, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1968062.pdf
    Data publikacji:
    1997-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.20.Ls
    72.40.+w
    78.90.+t
    Opis:
    We present the possibility of using magnetic field to enhance responsivity and to tune spectral range of far-infrared InSb detector (based on photoconductivity effect) beyond its standard range limited to about 30 cm$\text{}^{-1}$. We show that due to cyclotron resonance assisted transitions we can use it as a tunable detector working up to energies about 180 cm$\text{}^{-1}$ (22 meV). We have used such a detector as a spectrometer for measurements of the Landau emission from GaAs emitter.
    Źródło:
    Acta Physica Polonica A; 1997, 92, 4; 733-736
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-13 z 13

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