Current Issue : October - December Volume : 2016 Issue Number : 4 Articles : 6 Articles
Background: The need for practical and adaptable terahertz sources is apparent in the areas of application such as early cancer\ndiagnostics, nondestructive inspection of pharmaceutical tablets, visualization of concealed objects. We outline the operation principle\nand suggest the design of a simple appliance for generating terahertz radiation by a system of nanoobjects ââ?¬â?? gold nanobars\n(GNBs) or nanorings (GNRs) ââ?¬â?? irradiated by microwaves.\nResults: Our estimations confirm a feasibility of the idea that GNBs and GNRs irradiated by microwaves could become terahertz\nemitters with photon energies within the full width at half maximum of the longitudinal acoustic phononic DOS of gold\n(ca. 16ââ?¬â??19 meV, i.e., 3.9ââ?¬â??4.6 THz). A scheme of the terahertz radiation source is suggested based on the domestic microwave oven\nirradiating a substrate with multiple deposited GNBs or GNRs.\nConclusion: The size of a nanoobject for optimal conversion is estimated to be approx. 3 nm (thickness) by approx. 100 nm (length\nof GNB, or along the GNR). This detailed prediction is open to experimental verification. An impact is expected onto further\nstudies of interplay between atomic vibrations and electromagnetic waves in nanoobjects....
Photoacoustic spectroscopy was used to test the photoacoustic properties of sulfur hexafluoride,\nan optically thick and potent greenhouse gas. While exploring the photoacoustic effect of sulfur\nhexafluoride, the effects of the position of the microphone within a gas cell were determined. Using\na 35 cm gas cell, microphones were positioned at 17.5 cm, the middle of the gas cell, 12.5 cm,\n7.5 cm, and 2.5 cm from the window of the cell. From the photoacoustic signal produced for each\nresonance frequency at each microphone position, the effects of acoustic pressure produced at\neach position on the signal recorded were observed. This is the first study done by experimentation\nwith the photoacoustic effect to show that standing waves have different amplitudes at different\nmicrophone positions....
This work aims to improve the PEA calibration technique through defining a well-conditioned transfer matrix. To this end, a\nnumerical electroacoustic model that allows determining the output voltage of the piezoelectric sensor and the acoustic pressure is\ndeveloped with the software COMSOL�®.Theproposed method recovers the charge distribution within the sample using an iterative\ndeconvolutionmethod that uses the transfermatrix obtained with the newcalibration technique.The obtained results on theoretical\nand experimental signals show an improvement in the spatial resolution compared with the standard method usually used....
There is a new method of calculating the trajectory of sound waves (rays) in layered stratified\nspeed of sound in ocean without dispersion. A sound wave in the fluid is considered as a vector.\nThe amplitudes occurring at the boundary layers of the reflected and refracted waves are calculated\naccording to the law of addition of vectors and using the law of conservation of energy, as\nwell as the laws that determine the angles of reflection and refraction. It is shown that in calculating\nthe trajectories, the reflected wave must be taken into account. The reflecting wave�s value\nmay be about 1 at certain angles of the initial wave output from the sours. Reflecting wave forms\nthe so-called water rays, which do not touch the bottom and the surface of the ocean. The conditions\nof occurrence of the water rays are following. The sum of the angles of the incident and refracted\nwaves (rays) should be a right angle, and the tangent of the angle of inclination of the incident\nwave is equal to the refractive index. Under these conditions, the refracted wave amplitude\nvanishes. All sound energy is converted into the reflected beam, and total internal reflection occurs.\nIn this paper, the calculation of the amplitudes and beam trajectories is conducted for the\ncanonical type of waveguide, in which the speed of sound is asymmetric parabola. The sound\nsource is placed at the depth of the center of the parabola. Total internal reflection occurs in a\nnarrow range of angles of exit beams from the source 43 - 45. Within this range of angles, the\nwater rays form and not touch the bottom and surface of ocean. Outside this range, the bulk of the\nbeam spreads, touching the bottom and the surface of the ocean. When exit corners, equal and\ngreater than 77, at some distance the beam becomes horizontal and extends along the layer,\nwithout leaving it. Calculation of the wave amplitudes excludes absorption factor. Note that the\nformula for amplitudes of the sound waves applies to light waves....
Small amplitude vibrations of a structure completely filled with a fluid are considered.\nDescribing the structure by displacements and the fluid by its pressure field, the free vibrations\nare governed by a non-self-adjoint eigenvalue problem. This survey reports on a framework for\ntaking advantage of the structure of the non-symmetric eigenvalue problem allowing for a variational\ncharacterization of its eigenvalues. Structure-preserving iterative projection methods of the the\nArnoldi and of the Jacobiââ?¬â??Davidson type and an automated multi-level sub-structuring method are\nreviewed. The reliability and efficiency of the methods are demonstrated by a numerical example...
Exciton-polariton systems can sustain macroscopic quantum states (MQSs) under a periodic potential\nmodulation. In this paper, we investigate the structure of these states in acoustic square lattices by\nprobing their wave functions in real and momentum spaces using spectral tomography.Weshow that\nthe polariton MQSs, when excited by a Gaussian laser beam, self-organize in a concentric structure,\nconsisting of a single, two-dimensional gap-soliton (GS) state surrounded by one dimensional (1D)\nMQSs with lower energy. The latter form at hyperbolical points of the modulated polariton dispersion.\nWhile the size of the GS tends to saturate with increasing particle density, the emission region of the\nsurrounding 1D states increases. The existence of these MQSs in acoustic lattices is quantitatively\nsupported by a theoretical model based on the variational solution of the Grossââ?¬â??Pitaevskii equation.\nThe formation of the 1D states in a ring around the central GS is attributed to the energy gradient in\nthis region, which reduces the overall symmetry of the lattice. The results broaden the experimental\nunderstanding of self-localized polariton states, which may prove relevant for functionalities\nexploiting solitonic objects....
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