A compact planar antenna sources with on-chip fabrication and high directivity in order to achieve large depth-of-field for better image resolution is the prospective demand for THz imaging application. Therefore, the small-gap photoconductive dipole antennas have been explored to fulfil such applications demand. However, there are certain modalities for improving the photoconductive dipole antenna performance which need to identify to accomplish high THz average radiated power and improved total efficiency. The unit-cell small-gap photoconductive dipole antenna radiation power enhancement methods need to optimize the design parameters with photoconductive material selection from theoretical simulation. Further, the potential improvement of coupling efficiency of THz wave with air as well as femto-second laser incident efficiency is also important parameters to enhance the radiation power of small-gap photoconductive dipole antenna. In this paper, we have presented an analytical procedure employing explicit mathematical expression leading to the physical behaviour of small-gap photoconductive dipole antenna. The effects of biased lines on the antenna performance parameters are discussed with the help of proposed equivalent circuit model. We have explored the effect of gap-size on the THz radiated power and on total radiation efficiency from the proposed photoconductive dipole antennas. 相似文献
This paper reports the effect of proton irradiation on the electrical properties of a-As2S3 in the temperature range of 323–418 K and frequency range 0.1–100 kHz. The variation of transport property is studied with proton irradiation dose (1 × 1013 ions/cm2 and 1 × 1015 ions/cm2). It has been observed that proton irradiation changes the dc conductivity (σdc), dc activation energy (ΔEdc) and ac conductivity (σac(ω)). The σdc and σac(ω) increases with dose of proton irradiation. The value of frequency exponent (s) decreases with the temperature and irradiation dose. These results are explained in terms of change in density of defect states in these glasses. 相似文献
Wide‐bandgap semiconductor nanowires with surface defect emission centers have the potential to be used as sensitive thermometers and optical probes. Here, we show that the green luminescence of multiferroic BiFeO3 (BFO) nanowires shows an anomalous negative thermal quenching (NTQ) with increasing temperatures. The release of trapped carriers from localized surface defect states is suggested as the possible mechanism for the increased green luminescence which was experimentally observed at elevated temperatures. A reasonable interpretation of the photoluminescence (PL) processes in BFO nanowires is achieved, and the activation energies of the PL quenching and thermal hopping are deduced. Negative thermal quenching of BFO nanowires provides a new strategy for optical thermometry at higher temperatures. 相似文献
Polymer nanocomposite has been proven to improve the property of polymer salt complex. Organo-modified clay and inorganic oxides are the most commonly used filler for polymer nanocomposite (PNC). However, single wall carbon nanotube (SWCNT)/multiwall carbon nanotube (MWCNT) are becoming popular filler for PNC for their high surface area and high mechanical stability. In this work, a series of PNC sample has been prepared by using polyethylene oxide (PEO)-polydimethylsiloxane (PDMS) blend as polymer matrix, an optimized salt stoichiometry of Ö/Li ~15, and surface-modified MWCNT as filler. The effect of ion-polymer and ion-MWCNT interaction in the polymer nanocomposite has been investigated by using XRD, SEM, FTIR, and electrical study. X-ray diffraction pattern confirms the dispersion of MWCNT inside the polymer chain and modifies the structural parameter of the polymer matrix. FTIR spectra indicate inclusion of MWCNT inside the polymer salt complex which changes the ion dissociation/association in the polymer host matrix. Further, the changes in structural, thermal, and electrical property of the polymer salt complex system have been studied by using SEM, DSC, and impedance analysis. Dc conductivity study shows that optimized PNC sample has conductivity of 8.04 × 10−5 S cm−1. This is almost two order enhancement from pure polymer salt system (10−6 S cm−1).
The thermodynamic properties of alkaline earth ruthenate ARuO3 (A?=?Ca, Sr, and Ba) perovskites have been investigated for the first time by means of a modified rigid ion model at temperature 1 K?≤?T?≤?300 K. As strong electron–phonon interactions are present in these compounds, the lattice contribution to the specific heat deserves proper attention. The values of specific heat calculated by us have shown remarkably good agreement with corresponding experimental data. We have found that in ARuO3 (A?=?Ca, Sr, and Ba) ruthenate family, Debye temperature increases inversely with the ionic radius of the alkaline earth A cations. In addition, the results on the temperature dependence of thermal expansion coefficient (α), cohesive energy (?), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θD), and Grüneisen parameter (γ) are also reported. 相似文献
The crystal polymorphism of the anthelmintic drug, triclabendazole ( TCB ), is described. Two anhydrates (Forms I and II), three solvates, and an amorphous form have been previously mentioned. This study reports the crystal structures of Forms I ( 1 ) and II ( 2 ). These structures illustrate the uncommon phenomenon of tautomeric polymorphism. TCB exists as two tautomers A and B. Form I (Z′=2) is composed of two molecules of tautomer A while Form II (Z′=1) contains a 1:1 mixture of A and B. The polymorphs are also characterized by using other solid‐state techniques (differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), PXRD, FT‐IR, and NMR spectroscopy). Form I is the higher melting form (m.p.: 177 °C, ΔHf=≈105±4 J g?1) and is the more stable form at room temperature. Form II is the lower melting polymorph (m.p.: 166 °C, ΔHf=≈86±3 J g?1) and shows high kinetic stability on storage in comparison to the amorphous form but it transforms readily into Form I in a solution‐mediated process. Crystal structure analysis of co‐crystals 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 further confirms the existence of tautomeric polymorphism in TCB . In 3 and 11 , tautomer A is present whereas in 4 , 5 , 6 , 7 , 8 , 9 , 10 the TCB molecule exists wholly as tautomer B. The DFT calculations suggest that the optimized tautomers A and B have nearly the same energies. Single point energy calculations reveal that tautomer A (in Form I) exists in two low‐energy conformations, whereas in Form II both tautomers A and B exist in an unfavorable high‐energy conformation, stabilized by a five‐point dimer synthon. The structural and thermodynamic features of 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 are discussed in detail. Triclabendazole is an intriguing case in which tautomeric and conformational variations co‐exist in the polymorphs. 相似文献
A standard protocol was developed to determine the water content by thermal analysis of milk of magnesia (MoM). Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used in a novel manner for examining the physical characteristics of the commercial pharmaceutical suspensions. Moisture analyzer and oven-dry methods validate the proposed protocol. MoM consists primarily of water and magnesium hydroxide [Mg(OH)2]. Experimental design of the thermal analysis parameters were considered including sample size, flowing atmosphere, sample pan, and heating rate for both DSC and TG. The results established the optimum conditions for minimizing heat and mass transfer effect. Sample sizes used were: (5?C15?mg) for DSC and (30?C50?mg) for TG. DSC analysis used crimped crucibles with a pinhole, which allowed maximum resolution and gave well-defined mass (water) loss. TG analysis used a heating rate of 10?°C/min?1 in an atmosphere of nitrogen. The heat of crystallization, heat of fusion, and heat of vaporization of unbound water are 334, 334, and 2,257?Jg?1, respectively (Mitra et al. Proc NATAS Annu Conf Therm Anal Appl 30:203?C208, 2002). The DSC average water content of (MoM) was 80?wt% for name brand and 89.5?wt% for generic brand, based on the relative crystallization, melting and vaporization heats/Jg?1 of distilled water in the recently purchased (2011) MoM samples. The TG showed a two-step process, losing water at 80?C135?°C for unbound water and bound water (MgO·H2O) at 376?C404?°C, yielding a total average water loss of 91.9?% for name brand and 90.7?% for generic brand by mass. The difference between the high-temperature TG and the lower-temperature DSC can be attributed for the decomposition of magnesium hydroxide or MgO·H2O. Therefore in performing this new approach to water analysis by heating to a high temperature decomposed the magnesium hydroxide residue. It was determined that the TG method was the most accurate for determining bound and unbound water. 相似文献
Photophysical properties of two widely used antibiotic fluoroquinolone drugs, namely Norfloxacin (NOR) and Ofloxacin (OFL) have been investigated in biomimicking environments formed by bile salts. Experimental results demonstrate that photophysical enhancement and fall of a particular prototropic species are sensitive to the excitation wavelength in bile salt aggregates. Excitation at shorter wavelengths reveals quenching of fluorescence of these fluoroquinolone with addition of sodium deoxycholate (NaDC), sodium taurocholate (NaTC) and sodium glycodeoxycholate (NaGDC). On the contrary, we observe a steady increase in the fluorescence intensity with a continuous redshift upon excitation at longer wavelength. The experimental results were rationalized in terms of the fact that, neutral and zwitterionic species of fluoroquinolone molecules in bile salt aggregates are selectively excited at shorter wavelength while the cationic form of fluoroquinolone molecules are excited at longer wavelength. The excess hydronium ions in the hydrophilic surface of bile salt aggregates convert the neutral species of NOR and OFL into cationic species causing an enhancement in the emission intensity. We found that NaGDC and NaTC because of the conjugate head group are more effective in converting the neutral species of fluoroquinolones into a cationic species than NaDC. The quenching order is in accordance with hydrophobicity indices of bile salt. 相似文献