Phase separation and microwave response of epitaxial and polycrystalline manganite films

The resistance, magnetoresistance, and resistance response under microwave irradiation (f=10 and 35GHz) were measured for epitaxial and polycrystalline La 0.67 Ca 0.33 MnO 3 and La 0.67 Sr 0.33 MnO 3 thin films in the temperature range 78÷300K. The microwave induced resistance increase observed for the epitaxial films in a narrow temperature range below the ferromagnetic to paramagnetic transition temperature T c certifies coexistence of low resistance (ferromagnetic) and high resistance (paramagnetic) regions in the manganites. Resistance of polycrystalline films decreased under microwave irradiation in a wide temperature range below T c . The effect was explained in terms of microwave assisted hopping of carriers in high resistance regions formed at grain boundaries of the polycrystalline films

Reflecting and Polarizing Properties of Conductive Fabrics in Ultra-High Frequency Range

The system based on ultra-wide band (UWB) signals was employed for qualitative estimation of attenuating, reflecting and polarizing properties of conductive fabrics, capable to prevent local static charge accumulation. Pulsed excitation of triangle monopole antenna of 6.5 cm height by rectangular electric pulses induced radiation of UWB signals with spectral density of power having maximum in ultra-high frequency (UHF) range. The same antenna was used for the radiated signal receiving. Filters and amplifiers of different passband were employed to divide UHF range into subranges of 0.3-0.55 GHz, 0.55-1 GHz, 1-2 GHz and 2-4 GHz bands. The free space method, when conductive fabric samples of 50x50 cm2 were placed between transmitting and receiving antennas, was used to imitate a practical application. Received wideband signals corresponding to the defined range were detected by unbiased detectors. The fabrics made of two types of warps, containing different threads with conductive yarns, were investigated. It was estimated attenuation and reflective properties of the fabrics when electric field is collinear or perpendicular to thread direction. In the UHF range it was revealed good reflecting properties of the fabrics containing metallic component in the threads. The system has advantages but not without a certain shortcoming. Adapting it for specific tasks should lead to more effective usage, including yet unused properties of the UWB signals.</p

Estimation of Electrical Properties of Hidden Objects Using Microwave Signals

Pulsed excitation of a horn antenna for generating large B wideband electromagnetic pulses was used. The antenna was excited by electrical pulses with rise time of 200 ps and pulse voltage of 15 V. The spectral properties of the electromagnetic pulses were investigated using different wide band antennas and (0 – 18) GHz passband sampling oscilloscope. It was found that the signal spectra is wide and ranges from 0.3 GHz to higher than 12 GHz. Hollow cylinders made from opaque for visible light materials were used to hide other cylinders with certain electrical properties. To reveal their presence we employ the electromagnetic pulses. Transmitted through and reflected from investigated objects pulses were received by several antennas having different frequency ranges and detected to obtain needed information. The experiments show that analyzing this information leads to conclusions about the presence of the object and its electrical properties. This methodic supposedly can be employed to disclose electrical properties of objects having complex electrical properties if broadband amplifiers and digital oscilloscopes are used. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6331</p

Numerical simulation of a research vessel's aftpart hull form

This paper presents results of numerical simulation of the aftpart hull form of a research vessel. The wake rolls onto the transom platform, therefore creating additional resistance to the movement of the vessel. To solve the problem and to propose the optimal transom form, the study was carried out using the method of successive approximations and computational fluid dynamics (CFD) algorithms. The flow lines around the hull of the vessel and the wave pattern behind the hull were analysed, and the optimal transom form was chosen. Water resistance analysis was carried out to prove the efficiency of the chosen solution

Mediators influence in conflict decision: case of Nagorno-Karabakh

Armenian and Azerbaijan conflict for Nagorno-Karabakh territory lasts for more than two decades. Because of this confrontation both countries loses significant funds, persistent armed conflicts kill civilian victims, educational and political systems suffer, refugees can not return to the homelands. For all the endless problems and unresolved international community, represented by the mediators, named "Minsk" group, is often accused. That is why the evaluation of the mediators’ influence in the today's conflict phase is so important

Gyrotropic waveguides analysis

An algorithm and program in MATLAB® for the dispersions characteristics calculation in wide frequency range 15–100 GHz was created. We calculated and analyzed in ferrite and semiconductor waveguides, then they are longitudinally magnetized, also we analyzed main mode HE11 and higher modes EH11 and HE12 dispersion characteristics. We analyzed semiconductor p-Ge, p-GaAs waveguides and compared gyromagnetic and gyroelectric waveguides bandwidth with dielectrical layer. We decided that outer dielectrical layer changed waveguide working frequency range. We draw conclusion that it can be used for made microwave devices for example phase shifters or other devices. Article in Lithuanian Girotropinių bangolaidžių tyrimas Santrauka Pristatomi bendrieji elektrodinaminis ir matematinis girotropinių bangolaidžių modeliai. Sukuriamas bendrasis algoritmas ir programa MATLAB® terpėje atvirųjų cilindrinių apskritojo skerspjūvio girotropinių bangolaidžių tyrimui. Apskaičiuojamos ir tiriamos giromagnetiniuose feritiniuose bei giroelektriniuose puslaidininkiniuose bangolaidžiuose, kuriuos išilgai veikia pastovusis magnetinis laukas, sklindančių pagrindinio HE11 ir aukštesniųjų tipų EH11 bei HE12 bangų dispersinės charakteristikos. Lyginamas bangolaidžių iš YIG G-113 markės ferito ir n-InAs puslaidininkio be išorinio dielektriko sluoksnio ir su juo plačiajuostiškumas. Tiriami puslaidininkiniai p-Ge, p-GaAs bangolaidžiai 15–100 GHz dažnių ruože. Nustatoma jų darbo dažnių juosta, jos centrinis dažnis ir bangolaidžių plačiajuostiškumas. Reikšminiai žodžiai: MATLAB® , girotropiniai, giromagnetiniai, giroelektriniai bangolaidžiai, Maksvelo lygtys, dispersinės charakteristikos

Skeg optimization analysis of KU scientific research vessel

Purpose of this thesis is to analyze and optimize stern of KU scientific research vessel. Introduced main information and theory about ship hydrodynamics, resistance, stern construction, Computational Fluid Dynamics. Also presented information and recommendations for making proper stern shape and CFD analysis. CFD simulation was created with FLOW-3D solver to determine MINTIS vessel‘s hydrodynamic characteristics and flow around a hull. Main object of interest was hydrodynamical phenomena in stern and skeg area. Depending on simulation data and results, few alternative hull forms has been created and investigated with CFD solver. Conclusions about resistance of those hull shapes was introduced