395 research outputs found
Diffraction effects in the Recoil-Frame Photoelectron Angular Distributions of Halomethanes
No full textCitation: Bomme, C., Anielski, D., Savelyev, E., Boll, R., Erk, B., Bari, S., . . . Rolles, D. (2015). Diffraction effects in the Recoil-Frame Photoelectron Angular Distributions of Halomethanes. 635(11). doi:10.1088/1742-6596/635/11/112020We have measured the Recoil Frame-Photoelectron Angular Distributions (RF-PADs) for inner-shell photoionization of CH3F, CH3I and CF3I halomethane molecules for photoelectron energies up to 300 eV detected within a 4? solid angle in the gas-phase. For high kinetic energies, the RF-PADs are dominated by diffraction effects that encode information on the molecular geometry. © Published under licence by IOP Publishing Ltd
UWB FMCW Radar for Concealed Weapon Detection: RF front-end development
No full textCurrent methods for concealed weapon detection are mainly used at stationary security check-points due to complexity and other serious limitations for real-time outdoor scenarios. A mobile imaging radar is considered as a proper solution for fast screening of people at mass events because of its ability to detect both metal and non-metal weapons through clothes. In this thesis, the design of an RF front-end for an UWB Microwave Imaging Radar based on MIMO 2-D array and multichannel FMCW electronics is presented. Requirements to the design were low power emissions and minimization of data acquisition time, cost and complexity. The UWB technology provides high resolution, while MIMO technique helps reducing the number of required antennas in the 2-D array, without a net degradation of performance. The final RF-scheme was selected based on the availability of commercial off-the-shelves RF-components. The performance of the designed RF front-end was evaluated both via theoretical analysis and simulations in a dedicated software Advanced Design System (ADS, by Agilent). The obtained results in terms of sensitivity, dynamic range, down-range resolution and measurement speed demonstrate that the proposed solution is feasible for through-dress detection of concealed weapons.Microwave Technology and Systems for RadarTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Probing the Gate-Voltage-Dependent Surface Potential of Individual InAs Nanowires Using Random Telegraph Signals RID C-6303-2008
No full textWe report a novel methocl for probing the gate-voltage dependence of the surface potential of individual semiconductor nanowires. The statistics of electronic occupation of a single defect on the surface of the nanowire, determined from a random telegraph signal, is used as a. measure for the local potential. The method, is demonstrated for the case of one or two switching defects in indium arsenide (InAs) nanowire field effect transistors at temperatures T = 25-77 K. Comparison with a self consistent model shows that surface potential variation is retarded In the conducting regime due to screening by surface states with density D(ss) approximate to 10(12) cm(-2) ev(-1). Temperature-dependent dynamics of, electron capture and emission producing the random telegraph signals are also analyzed, and multiphonon emission is identified as the process responsible for capture and emission of electrons from the surface traps. Two defects studied in detail had capture activation energies of E(B) approximate to 50 meV and E(B) approximate to 110 meV and cross sections of sigma(infinity) approximate to 3 x 10(-19) cm(2) and sigma(infinity) approximate to 2 x 10(-17) cm(2), respectively. A lattice relaxation energy of s (h) over bar omega = 187 +/- 15 meV was found for the first defect
Global Fukaya category I
No full textLet denote the Frechet Lie group of Hamiltonian
symplectomorphisms of a monotone symplectic manifold . Let be the -nerve of the Fukaya category , and let denote the component of the ``space of -categories'' .
Using Floer-Fukaya theory for a monotone we construct a natural
up to homotopy classifying map \begin{equation*}
BHam (M, \omega) \to (|\mathbb{S}|, NFuk (M, \omega)). \end{equation*} This
verifies one sense of a conjecture of Teleman on existence of action of on the Fukaya category of . This construction is very
closely related to the theory of the Seidel homomorphism and the quantum
characteristic classes of the author, and this map is intended to be the
deepest expression of their underlying geometric theory. In part II the above
map is shown to be nontrivial by an explicit calculation. In particular, we
arrive at a new non-trivial ``quantum'' invariant of any smooth manifold, which
motives the statement of a kind of ``quantum'' Novikov conjecture.Comment: To appear in IMRN, 61 page
Electronic properties of quantum dot systems realized in semiconductor nanowires
No full textCatalyst-assisted growth of semiconductor nanowires has opened up several new and exciting possibilities for low-dimensional semiconductor structures. The authors review progress on the realization of quantum dots in semiconductor nanowires, and their characterization by transport spectroscopy. Emphasis is placed on the wide range electronic properties exhibited due to flexibility of the growth process in terms of nanostructure composition and size. Particular attention is placed on studies of spin in few-electron quantum dots
Calculations of the binding-energy differences for highly-charged Ho and Dy ions
No full textThe binding-energy differences for and
ions with ionization degrees , , and
are calculated. The calculations are performed using the large-scale
relativistic configuration-interaction and relativistic coupled-clusters
methods. The contributions from quantum-electrodynamics, nuclear-recoil, and
frequency-dependent Breit-interaction effects are taken into account. The final
uncertainty does not exceed eV. Combining the obtained results with the
binding-energy difference for neutral atoms calculated in [Savelyev et al.,
Phys. Rev. A 105, 012806 (2022)], we get the secondary differences of the
ion-atom binding energies. These values can be used to evaluate the amount of
energy released in the electron capture process in atom
(the value), provided mass differences of highly charged ions
and is known from experiment.
The value is required by experiments on the determination of the absolute
scale of the electron neutrino mass by studying the beta-decay process.Comment: 4 pages, Jetp Lett. (2023
Hamiltonian elements in algebraic K-theory
No full textRecall that topological complex -theory associates to an isomorphism class
of a complex vector bundle over a space an element of the complex
-theory group of . Or from algebraic -theory perspective, one assigns
a homotopy class , where is the ring of
compact operators on the Hilbert space. We show that there is an analogous
story for algebraic -theory of a general commutative ring , replacing
complex vector bundles by certain Hamiltonian fiber bundles. The construction
actually first assigns elements in a certain categorified algebraic -theory,
analogous to To\"en's secondary -theory of . And there is a natural map
from this categorified algebraic -theory to the classical variant.Comment: 11 pages. Comments welcom
3D imaging by fast deconvolution algorithm in short-range UWB radar for concealed weapon detection
No full textA fast imaging algorithm for real-time use in short-range (ultra-wideband) radar with synthetic or real-array aperture is proposed. The reflected field is presented here as a convolution of the target reflectivity and point spread function (PSF) of the imaging system. To obtain a focused 3D image, the proposed algorithm deconvolves the PSF out from the acquired data volume with high speed due to fast Fourier transform and implementation in frequency-wavenumber domain. Then the result is tested against two numerical criteria for efficiency, namely error and instability, whose optimal values can be obtained iteratively. Since the PSF differs with distance, the algorithm suits mainly applications with relatively small objects such as concealed weapon detection. Using several PSFs allows us to image a certain range of interest by their successive deconvolution from the same data. Performance of the algorithm has been evaluated experimentally and compared with that of Kirchhoff migration. Measurements were carried out by a 5–25 GHz synthetic aperture radar in the lab, and scenarios included a gun and a ceramic knife in free space, on a large metal plate, and a gun concealed on a dummy under a thick raincoat. The results demonstrate sufficient image quality obtained in a fraction of time.Electrical Engineering, Mathematics and Computer Scienc
Romp: The Method of Choice for Precise Macromolecular Engineering and Synthesis of Smart Materials
No full textWeighted near-field focusing in an array-based GPR
No full textThis paper presents a 3-D imaging technique for an ultra-wideband (UWB) ground penetrating radar (GPR) with a single transmit antenna and a linear receive array. The video impulse GPR working in the frequency band of 0.3–3 GHz has been designed in IRCTR for landmine detection, i.e., for a near-field application. Installed on a vehicle it can image in one mechanical scan a strip of 84 cm width due to the length of array aperture. The imaging is done by software means only. The developed imaging technique combines a real aperture focusing in the array plane with a synthetic aperture focusing in the mechanical scan direction. To compensate for parasitic time delays in the array channels, a calibration procedure is also described. Owing to directional properties of transmit antenna, the distribution of signal strength over the array is nonuniform that requires an amplitude correction when focusing the real aperture. The authors analyzed how this affects the footprint of the focused array, its cross-range resolution capability and the image quality of antipersonnel plastic landmines which were buried under different array channels. The analysis bases on experimental data sets acquired in the facilities of IRCTR and TNO-DSS. As a result, the authors propose a weighted array focusing that improves the cross-range resolution and provides proper imaging of typical buried landmines.International Research Centre for Telecommunication and RadarElectrical Engineering, Mathematics and Computer Scienc
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