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351.
The powered resonance tube (PRT) actuator and its variants are new developments in active flow control (AFC) technology. The
PRT is attractive because it has no moving parts and can produce acoustic tones that have amplitudes greater than 150 dB over
a large frequency bandwidth. The first part of this paper deals with the resonance characteristics of the PRT as a function
of the operating parameters such as jet-to-tube spacing (Sp), tube depth (d), and nozzle pressure ratio (NPR). It was found that: (1) at low NPR (3.33), the PRT resonates at discrete combinations of
spacing and depth. (2) Using theoretical estimates for predicting shock cell lengths, one could observe a correlation between
the theoretical prediction for shock cell length and the spacing at which the PRT resonates. (3) At high NPR (4.29), for a
fixed depth, the PRT resonates at virtually all spacings. (4) The frequency at which the PRT resonates remains approximately
constant, regardless of spacing. The second part of the study focused on examining the directivity of the acoustic radiation
from the PRT—significant for developing orientation strategies of the PRT with respect to the target flow in the end application.
The directivity of the fundamental PRT tone and that of its harmonics were studied for a variety of resonance frequencies,
both separately as well as cumulatively. It was found that the fundamental part of the actuation signal radiated predominantly
in the downstream direction of the jet for low resonance frequencies. As the resonance frequency was increased from 3 to 12 kHz,
the directivity changed from downstream of the jet to vertically upward, and finally upstream of the jet at the higher frequencies.
相似文献
Shekhar SarpotdarEmail: |
352.
Registration of real-time 3-D ultrasound images of the heart for novel 3-D stress echocardiography 总被引:2,自引:0,他引:2
Shekhar R Zagrodsky V Garcia MJ Thomas JD 《IEEE transactions on medical imaging》2004,23(9):1141-1149
Stress echocardiography is a routinely used clinical procedure to diagnose cardiac dysfunction by comparing wall motion information in prestress and poststress ultrasound images. Incomplete data, complicated imaging protocols and misaligned prestress and poststress views, however, are known limitations of conventional stress echocardiography. We discuss how the first two limitations are overcome via the use of real-time three-dimensional (3-D) ultrasound imaging, an emerging modality, and have called the new procedure "3-D stress echocardiography." We also show that the problem of misaligned views can be solved by registration of prestress and poststress 3-D image sequences. Such images are misaligned because of variations in placing the ultrasound transducer and stress-induced anatomical changes. We have developed a technique to temporally align 3-D images of the two sequences first and then to spatially register them to rectify probe placement error while preserving the stress-induced changes. The 3-D spatial registration is mutual information-based. Image registration used in conjunction with 3-D stress echocardiography can potentially improve the diagnostic accuracy of stress testing. 相似文献
353.
Vivekanand Jha Shekhar Verma Nupur Prakash Garima Gupta 《Wireless Personal Communications》2018,101(1):325-337
This paper shows the trade off between different modulation techniques such as multi level quadrature amplitude modulation, multi level phase shift keying, and multi level differential phase shift keying for upgrading direct detection optical orthogonal frequency division multiplexing systems with possible transmission distance up to 15,000 km and total bit rate of 2.56 Tb/s. The 2.56 Tb/s signal is generated by multiplexing 64 OFDM signals with 40 Gb/s for each OFDM. Variations of optical signal to noise ratio (OSNR), signal to noise ratio (SNR), and bit error rate (BER) are studied with the variations of transmission distance. Maximum radio frequency power spectrum, and output electrical power after decoder are measured for different multi level modulation techniques with carrier frequency. It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems. Maximum output power after decoder is enhanced with both 32-PSK, and 64-QAM. Quadrature signal amplitude level at encoder is upgraded with 64-QAM. It is noticed that OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK. 相似文献
354.
Shekhar KC Roshan K. Dhungana Namrata Khanal Prof. Ramesh Giri 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8124-8128
We report a Ni-catalyzed regioselective α-carbonylalkylarylation of vinylarenes with α-halocarbonyl compounds and arylzinc reagents. The reaction works with primary, secondary, and tertiary α-halocarbonyl molecules, and electronically varied arylzinc reagents. The reaction generates γ,γ-diarylcarbonyl derivatives with α-secondary, tertiary, and quaternary carbon centers. The products can be readily converted to aryltetralones, including a precursor to Zoloft, an antidepressant drug. 相似文献
355.
Metal 2-ethylhexanoates and related compounds as useful precursors in materials science 总被引:1,自引:0,他引:1
This critical review deals with the chemistry and applications of metal alkanoates with medium size (C5 to C12) carbon chain length. A particular emphasis is given to metal 2-ethylhexanoates, which find wide applications as metal-organic precursors in materials science, as catalysts for ring opening polymerizations and also in painting industries for their properties as driers. After a brief introduction and an overview of synthesis, structural and physico-chemical properties, this article discuses extensively the applications of these compounds in materials science. Finally, it identifies and signifies the areas for future research in the looking ahead section. The aim of this review is to bridge the areas of precursor's chemistry and materials science by providing a reference text for researchers working either in or at the interface of these two areas (125 references). 相似文献
356.
Chee Kyun Ng Nor Kamariah Noordin Borhanuddin Mohd Ali Sudhanshu Shekhar Jamuar 《Wireless Personal Communications》2011,58(2):315-335
In code division multiple access (CDMA), two or more chips are grouped together to form symbols and each symbol is transmitted
during the symbol period. The phase shift keying (PSK) modulation techniques map the digital baseband data into two or more
possible signals by varying the phase of a radio frequency (RF) carrier. The recently proposed PSK scheme called ternary PSK
(TPSK) scheme can convey three possible symbols. In this paper, a novel ternary based CDMA sequence so-called large area synchronous
even ternary (LAS-ET) sequence is introduced to increase spectrum efficiency in TPSK scheme. Its sequence duty ratio and cross-correlation
are analyzed. The performance analysis of this sequence is compared with the large area synchronous (LAS) sequence in term
of symbol error rate and chip error rate (CER) over various channel models. It is shown that TPSK scheme in LAS-ET sequence
outperforms LAS sequence in terms of CER evaluation. At the same time, the spectrum efficiency is doubled when a pair of chips
in LAS-ET sequence is mapped into one symbol. 相似文献
357.
Shekhar C 《Chemistry & biology》2011,18(10):1199-1200
358.
359.
Pranay Kumar Sinha Shekhar Kumar U. Kamachi Mudali R. Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(3):667-674
Reversed TALSPEAK (RT) Solvent [0.3 M di-(2-ethyl hexyl) phosphoric acid or D2EPHA in 0.2 M TBP in normal paraffinic diluent]
is used as extractant in partitioning of lanthanides and actinides in post-UREX process flow sheets. There is no experimental
data available in literature describing pressurization either due to the thermal decomposition or the reaction of RT solvent
with nitric acid at elevated temperatures. Experiments were conducted for heating of RT solvent and acid equilibrated RT solvent
under closed-vent adiabatic conditions. During these experiments, considerable pressurization was observed. In this paper,
results of these experiments are discussed in detail. 相似文献
360.
Biplab Das Shekhar Kumar P. Mondal 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(2):503-505
Flash point of a chemical characterizes its operating safety envelope. Tri-isoamyl phosphate (TiAP) is being proposed as an
alternate to conventional nuclear solvent tri-n-butyl phosphate but flash point of TiAP containing organic solutions are not available in literature. Flash points of C8–C16
n-alkanes and 36% TiAP/C8–C16
n-alkane solutions were experimentally measured and correlated by means of empirical correlations. This paper is probably the
first reported work in the literature on flash points of TiAP containing solutions. 相似文献