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71.
Wen J Chowdhury P Fulton DB Datta A Das K Andreotti AH Petrich JW 《Photochemistry and photobiology》2003,77(1):5-9
Nuclear magnetic resonance measurements indicate that hypericin exists in the same "normal" tautomeric form irrespective of whether the solvent is dimethyl sulfoxide or tetrahydrofuran. This result is discussed in the context of previous experimental and theoretical work. It is concluded that solvent perturbations cannot induce tautomerization in hypericin. 相似文献
72.
We derive a relationship between the bandwidth and active length and a figure of merit for velocity- and near-velocity-matched lithium niobate traveling-wave electro-optic modulators. The figure of merit is given by the bandwidth per unit drive voltage squared and is independent of the length of the device. Alternatively, this figure of merit can be described by its inverse, which is proportional to the device's switching energy. 相似文献
73.
A novel design method for high Q piezoelectric resonators was presented and proposed using the 3-D equations of linear piezoelectricity with quasi-electrostatic
approximation which include losses attributed to mechanical damping in solid and resistance in current conduction. There is
currently no finite element sofware for estimating the Q of a resonator without apriori assumptions of the resonator impedance or damping. There is a necessity for better and more
realistic modeling of resonators and filters due to miniaturization and the rapid advances in frequency ranges in telecommunication.
We presented new three-dimensional finite element models of quartz and barium titanate resonators with mechanical damping
and resistance in current conduction. Lee, Liu and Ballato’s 3-D equations of linear piezoelectricity with quasi-electrostatic
approximation which include losses attributed to mechanical damping in solid and resistance in current conduction were formulated
in a weak form and implemented in COMSOL. The resulting finite element model could predict the Q and other electrical parameters for any piezoelectric resonator without apriori assumptions of damping or resistance. Forced
and free vibration analyses were performed and the results for the Q and other electrical parameters were obtained. Comparisons of the Q and other electrical parameters obtained from the free vibration analysis with their corresponding values from the forced
vibration analysis were found to be in excellent agreement. Hence, the frequency spectra obtained from the free vibration
analysis could be used for designing high Q resonators. Results for quartz thickness shear AT-cut and SC-cut resonators and thickness stretch poled barium titanate resonators
were presented. An unexpected benefit of the model was the prediction of resonator Q with energy losses via the mounting supports. 相似文献
74.
We present the calculation of envelope of boson and of both low-and high-mass fermion production at the end of inflation when
the coherently oscillating inflatons decay into bosons and fermions. We consider three different models of inflation and use
CWKB technique to calculate the envelope to understand the structure of resonance band formation. We observe that though low-mass
fermion production is not effective in preheating because of Pauli blocking, it is quite probable for high-mass fermion to
take part in pre-heating.
相似文献
75.
76.
Residual stress can adversely affect the mechanical, electronic, optical and magnetic properties of thin films. This work describes a simple stress measurement instrument based on the bending beam method together with a sensitive non-contact fibre optical displacement sensor. The fibre optical displacement sensor is interfaced to a computer and a Labview programme enables film stress to be determined from changes in the radius of curvature of the film-substrate system. The stress measurement instrument was tested for two different kinds of thin film, hard amorphous carbon nitride (CN) and soft copper (Cu) films on silicon substrates deposited by RF magnetron sputtering. Residual stress developed in 500 nm thick CN thin films deposited at substrate temperatures in the range 50-550 °C was examined and it was found that stress in CN films decreased from 0.83 to 0.44 GPa compressive with increase of substrate temperature. Residual stress was found to be tensile (121 MPa) for Cu films of thickness 1500 nm deposited at room temperature. 相似文献
77.
Paramita Saha Chowdhury 《Journal of luminescence》2007,124(2):327-332
Here, we have examined the role of capping agent on the optical properties of CdS nanoparticles by steady-state and time-resolved photoluminescence (PL) spectroscopy. The estimated particles sizes are 3.45, 2.5 and 2.39 nm for uncapped, capped with silica (SiO2) and thiosalicylic acid (TSA), respectively. The absorption and emission spectra show a clear blue shift to shorter wavelengths in presence of TSA- and SiO2-capped nanoparticles. It is found that the average decay time 〈τ〉 are 6.24, 4.54 and 2.84 ns for uncapped, capped with SiO2 and TSA nanoparticles, respectively. Our analysis suggests that the hole or the electron is trapped on thiol molecule of TSA or hydroxyl group of SiO2, then radiative recombination of the electron and hole is delayed, resulting in strong quenching of PL efficiency. 相似文献
78.
Teruyuki Hakoda Muhammed Alamgir Zaman Chowdhury Akihiko Shimada Koichi Hirota 《Plasma Chemistry and Plasma Processing》2009,29(6):549-557
The decomposition of dimethyl sulfide (DMS) at initial concentrations of 4.5–18.0 ppmv in air was studied under electron-beam
(EB) irradiation. Doses to decompose 90% of input DMS were 2.5 kGy for 4.5 ppmv, 3.4 kGy for 10.6 ppmv, and 3.9 kGy for 18.0 ppmv.
HCOOH, (CH3)2SO, and trace CH3OH and (CH3)2SO2 were produced as irradiation products in addition to CO2 and CO. Application of an O3 decomposition catalyst to an irradiated sample gas led to an enhancement in the oxidation of DMS and its products into CO2 and the decomposition of O3. For 10.6 ppmv DMS/air, the mineralization ratio increased from 41% via only EB irradiation to 100% via the combination treatment
at 6.3 kGy. The yield of CO2 to COx increased from 5.3 to 87.6% by combination with catalytic oxidation. This combination treatment enables the irradiation energy
used to deodorize gas streams containing DMS to be reduced. 相似文献
79.
Mihir B. Banerjee R. G. Shandil S. S. Chauhan & Daleep Sharma 《Studies in Applied Mathematics》2000,105(1):31-34
Results of the previous paper with this title ( M. B. Banerjee et al., Stud. Appl. Math. 103:43–50) are extended to the case of neutrally stable perturbations. 相似文献
80.
B. Chowdhury 《Journal of Thermal Analysis and Calorimetry》2001,64(2):433-441
Pyrolysis of normally insulating aromatic polyimide is known to impart electrical conductivity to the polymer due to the formation
of carbonized regions in an insulating matrix with a concomitant change in the polymer’s structural arrangement. The wholly
pyrolyzed polyimide is potentially useful for specific applications in certain types of semiconductor devices because of the
polyimide’s insulator/conductor transition which creates a barrier type conduction. Pyrolysis, however, degrades the required
mechanical integrity of the polyimide for construction of such devices. In order to evaluate the fundamental aspects of barrier
conduction by high voltage electron transfer from metal contact that can still produce measurable current in thermally treated
non-pyrolyzed polyimide, the nature of depolarization in Kapton was assessed by the thermally stimulated depolarization current
(TSDC) technique. The results show that thermal treatment of polyimide without pyrolysis and therefore without loss of mechanical
integrity offers a viable means of steady electron conduction for semiconductor operation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献