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931.
Several new compounds based on the ionic ferromagnet Rb2CrCl4 but with Br or I substituting for Cl have been prepared in powder and single crystal form. The compounds have been characterised by chemical and X-ray analysis. The ordering of the anions within the K2NiF4 type structure is discussed. 相似文献
932.
Walker Watson F. Tseng Fung-I Sarkar Tapan K. Cross John 《Geoscience and Remote Sensing, IEEE Transactions on》1983,(4):446-454
The energy spectrum [X2(f)] of a ?windowed sample? of an unmodulated RF carrier will generally exhibit a peak value at or near the carrier frequency. The location of this peak is frequently used in signal analysis as an estimate of the true carrier frequency. This paper investigates the error in such estimates in cases where the signal arrives in the presence of ?broad-band? additive noise and shows that the error is due to both the added noise and spectral ?leakage? effects. Both these error mechanisms are affected by window duration and window shape. This paper proceeds further to pose two optimization criteria for the selection of a ?best window? shape for the minimization of estimation error. The two criteria are related to two differing views of prior un-certainty about the actual carrier frequency. These criteria accordingly provide different, but similar forms for the optimum window. Moreover, in worsening signal-to-noise conditions, both forms of optimum window tend to a rectangular shape. 相似文献
933.
934.
Love P.E.D. Edwards D.J. Irani Z. Walker D.H.T. 《Engineering Management, IEEE Transactions on》2009,56(3):425-435
Construction and engineering projects are typically complex in nature and are prone to cost and schedule overruns. A significant factor that often contributes to these overruns is rework. Omissions errors, in particular, have been found to account for as much as 38% of the total rework costs experienced. To date, there has been limited research that has sought to determine the underlying factors that contribute to omission errors in construction and engineering projects. Using data derived from 59 in-depth interviews undertaken with various project participants, a generic systemic causal model of the key factors that contributed to omission errors is presented. The developed causal model can improve understanding of the archetypal nature and underlying dynamics of omission errors. Error management strategies that can be considered for implementation in projects are also discussed. 相似文献
935.
Ciara N. Murphy Susan P. Walker Teresa M. MacDonald Emerson Keenan Natalie J. Hannan Mary E. Wlodek Jenny Myers Jessica F. Briffa Tania Romano Alexandra Roddy Mitchell Carole-Anne Whigham Ping Cannon Tuong-Vi Nguyen Manju Kandel Natasha Pritchard Stephen Tong Tuuhevaha J. Kaituu-Lino 《International journal of molecular sciences》2021,22(14)
Biomarkers for placental dysfunction are currently lacking. We recently identified SPINT1 as a novel biomarker; SPINT2 is a functionally related placental protease inhibitor. This study aimed to characterise SPINT2 expression in placental insufficiency. Circulating SPINT2 was assessed in three prospective cohorts, collected at the following: (1) term delivery (n = 227), (2) 36 weeks (n = 364), and (3) 24–34 weeks’ (n = 294) gestation. SPINT2 was also measured in the plasma and placentas of women with established placental disease at preterm (<34 weeks) delivery. Using first-trimester human trophoblast stem cells, SPINT2 expression was assessed in hypoxia/normoxia (1% vs. 8% O2), and following inflammatory cytokine treatment (TNFα, IL-6). Placental SPINT2 mRNA was measured in a rat model of late-gestational foetal growth restriction. At 36 weeks, circulating SPINT2 was elevated in patients who later developed preeclampsia (p = 0.028; median = 2233 pg/mL vs. controls, median = 1644 pg/mL), or delivered a small-for-gestational-age infant (p = 0.002; median = 2109 pg/mL vs. controls, median = 1614 pg/mL). SPINT2 was elevated in the placentas of patients who required delivery for preterm preeclampsia (p = 0.025). Though inflammatory cytokines had no effect, hypoxia increased SPINT2 in cytotrophoblast stem cells, and its expression was elevated in the placental labyrinth of growth-restricted rats. These findings suggest elevated SPINT2 is associated with placental insufficiency. 相似文献
936.
For nearly four decades, adaptive beamforming (ABF) algorithms have been applied in RADAR and SONAR signal processing. These algorithms reduce the contribution of undesired off-axis signals while maintaining a desired response along a specific look direction. Typically, higher resolution and contrast is attainable using adaptive beamforming at the price of an increased computational load. In this paper, we describe a novel ABF designed for medical ultrasound, named the Time-domain Optimized Near-field Estimator (TONE). We performed a series of simulations using synthetic ultrasound data to test the performance of this algorithm and compared it to conventional, data independent, delay and sum beamforming (CBF) method. We also performed experiments using a Philips SONOS 5500 phased array imaging system. CBF was applied using the default parameters of the Philips scanner, whereas TONE was applied on per channel, unfocused data using an unfocused transmit beam. TONE images were reconstructed at a sampling of 67 microm laterally and 19 microm axially. The results obtained for a series of five 20-microm wires in a water tank show a significant improvement in spatial resolution when compared to CBF. We also analyzed the performance of TONE as a function of speed of sound errors and array sparsity, finding it robust to both. 相似文献
937.
Frederic Buck Irina Kistner Christoph Rösler Andreas Schulz Matthias Walker Günter E. M. Tovar Thomas Schiestel 《化学,工程师,技术》2019,91(8):1117-1122
For the first time the combination of a separation process with a plasma process was successfully tested. In this case, a mixed‐conducting perovskite membrane separates the oxygen. At 1 kW a permeation of 2.24 mL min?1cm?2 could be achieved. Corresponding perovskite membranes have been manufactured as hollow fibers with a very good CO2 stability. The hollow fibers showed a constant permeation over more than 200 h. Furthermore, a spinning process with a sulphur‐free polymer binder has been established. 相似文献
938.
939.
Jeffrey F. Wheeldon Christopher E. Valdivia Alexandre W. Walker Gitanjali Kolhatkar Abdelatif Jaouad Artur Turala Bruno Riel Denis Masson Norbert Puetz Simon Fafard Richard Ars Vincent Aimez Trevor J. Hall Karin Hinzer 《Progress in Photovoltaics: Research and Applications》2011,19(4):442-452
Four tunnel junction (TJ) designs for multijunction (MJ) solar cells under high concentration are studied to determine the peak tunnelling current and resistance change as a function of the doping concentration. These four TJ designs are: AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs. Time‐dependent and time‐average methods are used to experimentally characterize the entire current–voltage profile of TJ mesa structures. Experimentally calibrated numerical models are used to determine the minimum doping concentration required for each TJ design to operate within a MJ solar cell up to 2000‐suns concentration. The AlGaAs/GaAs TJ design is found to require the least doping concentration to reach a resistance of <10−4 Ω cm2 followed by the GaAs/GaAs TJ and finally the AlGaAs/AlGaAs TJ. The AlGaAs/InGaP TJ is only able to obtain resistances of ≥5 × 10−4 Ω cm2 within the range of doping concentrations studied. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
940.