Methods for solving a semi-differential vibration equation

Fractional-order (or, shortly, fractional) derivatives are used in viscoelasticity since the late 1980´s, and they grow more and more popular nowadays. However, their efficient numerical calculation is nontrivial, because, unlike integer-order derivatives, they require evaluation of history integrals in every time step. Several authors tried to overcome this difficulty. In the followings, some of the proposed methods will be examined for a derivative of order 1/2 (that is sometimes called a semi-derivative)

NON-LINEAR FINITE ELEMENT ANALYSIS OF A POLYMER-MADE MACHINE PART

Polymers are more and more popular as structural materials nowadays. However, their material behaviour is much more complicated than that of metals. In the present paper, a polypropylene-made automobile part is studied. The point of interest is its response to periodic excitations. Both geometric and material nonlinearities are present in the problem. To solve it, a finite element model, composed of thick shell elements is prepared and presented. It uses a three-parameter Maxwell material model that is built by the authors based on measurement data from the literature. To verify the finite element results, measurements are also done and evaluated. Eigenfrequencies (of the nonlinear system) are quite well approximated. However, as shown, other effects such as modal dissipation depending on frequency can not be modeled with this material law

Palaeoenvironments on a Middle Eocene carbonate ramp in the Vértes Mountains, Hungary

Eocene sediments of the Hungarian Paleogene Basin – located on the Northern margin of the Tethys – unconformably overlie Mesozoic rocks, which were uplifted during Late Cretaceous to Early Eocene time. In the Vértes Mountains, there was a Bartonian, narrow, low-angle subtropical carbonate ramp with 40-50 m thick limestone (Szőc Limestone Formation) directly covering the karstic surface of Triassic limestone and dolomite. Ramp sediments were overlain basinward by Upper Lutetian - Bartonian brackish and normal marine deposits. Seven facies were distinguished by semi-quantitative microfacies analysis of Szőc Limestone. The inner ramp is represented by four facies: (1) extraclast rudstone to extraclast-bioclast floatstone (basal beds of Szőc Limestone), (2) bioturbated foraminifer-mollusc-echinoderm packstone/grainstone (interpreted as sea-grass meadow), (3) skeletal grainstone (bioclastic sand shoals), and (4) Nummulites perforatus rudstone/packstone (Nummulites banks). On the mid-ramp, larger foraminiferal floatstone and red algal facies with 3 subfacies – coral-algal boundstone (small patch reefs), larger foraminiferal-red algal and larger foraminiferal-rhodolith floatstones – were recognized. The lower mid-ramp to upper outer ramp is characterized by glauconitic larger foraminiferal grainstone (bioclastic sand deposition effected by currents). All facies record normal marine conditions. Main palaeoecological parameters influencing palaeoenvironments were hydrodynamic energy, depth, light conditions, substrate and nutrient availability

Absorption-reduced waveguide structure for efficient terahertz generation

An absorption-reduced planar waveguide structure is proposed for increasing the efficiency of terahertz (THz) pulse generation by optical rectification of femtosecond laser pulses with tiltedpulse- front in highly nonlinear materials with large absorption coefficient. The structure functions as waveguide both for the optical pump and the generated THz radiation. Most of the THz power propagates inside the cladding with low THz absorption, thereby reducing losses and leading to the enhancement of the THz generation efficiency by up to more than one order of magnitude, as compared with a bulk medium. Such a source can be suitable for highly efficient THz pulse generation pumped by low-energy (nJ-lJ) pulses at high (MHz) repetition rates delivered by compact fiber lasers

Ultrarövid infravörös és távoli infravörös (THz-es) fényimpulzusok előállítása és alkalmazása = Generation and application of ultrashort infrared and far-infrared (THz pulses) light pulses

A projekt célja olyan eszközök kutatása és fejlesztése volt, amelyek ultrarövid impulzusokat állítanak elő a közeli és a távoli infravörös spektrumtartományon. A közeli infravörös (1-1,5 mikrométer) impulzusokat az ultragyors kommunikációs eszközök, és az ezekben alkalmazott anyagok kutatásában és fejlesztésében lehet alkalmazni. A távoli infravörös (THz-es) impulzusok lehetővé teszik a kisenergiájú gerjesztések nagy időfelbontású dinamikájának vizsgálatát a szilárdtest fizika, a kémia és a biológia területén. Mindkét tartomány esetén, a széles körben elterjedt Ti:zafír lézerek fényimpulzusainak nemlineáris optikai frekvenciakonverziójával (OPO, illetve optikai egyenirányítás segítségével) állítottuk elő az impulzusokat. Legfontosabb eredményeink: - Minden eddiginél rövidebb (12 fs időtartamú) impulzusokat előállító OPO-t terveztünk. - Új elven, az ultrarövid pumpáló impulzusok intenzitásfrontjának dőlésén alapuló, optikai egyenirányítást felhasználó, néhány THz frekvenciájú impulzusokat előállító elrendezést terveztünk. Nemlineáris kristályként litium-niobátot alkalmazva, 0,5 mJ pumpáló energia esetén 260 nJ energiájú THz-es impulzusokat állítottunk elő, és 10 % kvantumhatásfokot értünk el. Ezek az értékek ezerszer (!) nagyobbak, mint amit valaha is elértek. - Részletesen megvizsgáltuk a litium-niobát fotorefrakciójának, valamint THz-es törésmutatójának és abszorpciójának a függését a Li/Nb aránytól és a (fotorefrakció csökkentésére használt) Mg tartalomtól. | The aim of the project was to research and develop devices producing ultrashort pulses on the near-infrared and far-infrared spectral region. The near-IR (1-1.5 micrometer) pulses can be used in the research and development of ultrafast communication devices and the materials used in them. The far-IR (or THz) pulses make it possible to investigate the dynamics of low energy excitations with high temporal resolution in the field of solid state physics, chemist and biology. For both region nonlinear frequency conversion (using optical parametric oscillator (OPO) and optical rectification, respectively) was used to produce the pulses. Our main results are: - Designing an OPO producing the shortest (12 fs) pulses. - Designing of a set-up producing THz pulses by accomplishing the optical rectification and a new idea, the tilting of the intensity front of the pump pulses. Using lithium-niobate as the nonlinear crystal THz pulses having 260 nJ energy were produced by pump pulses having 0.5 mJ energy. The quantum efficiency reached 10 %. These values are one thousand times (!) larger than what have been ever reached earlier. - We have investigated thoroughly the dependence of the photorefraction of lithium-niobate and its index of refraction and absorption on the Li/Nb ratio and the content of Mg (which is used to decrease the photorefraction)