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61.
For satellite communications systems which use frequencies above 10 GHz, rain and clouds attenuate signals severely, leading to an increase in bit error rate (BER) in digital links. This may be coped with by using two or more receivers on the ground, spaced far enough apart to avoid simultaneous rain outages. In this paper, a BER-minimizing decision processor is derived for two receivers and QPSK modulation. In particular, it is applied to a linear attenuating transmission channel adding independent white Gaussian noise. It is found that gains of nearly 3 dB compared to a switched system are possible in down-link limited cases. 相似文献
62.
Haberl F. Ober M.H. Hofer M. Fermann M.E. Wintner E. Schmidt A.J. 《Photonics Technology Letters, IEEE》1991,3(12):1071-1073
Optimum low-noise operation modes of a passively mode-locked fiber laser are described and characterized. The laser produces 60 fs bandwidth limited pulses with root mean square amplitude fluctuations of 0.4% in a frequency-band from 30 Hz to 100 kHz. It is shown that low-noise operation up to 5 dB below the amplitude noise of the pump laser is possible with overall negative cavity group-velocity dispersion and a large difference between the intracavity loss under free-running and mode-locked laser operation. Additional frequency stabilization reduces the timing jitter to 4 fs in a frequency band from 1 kHz to 100 kHz and 110 fs in the 30 Hz to 100 kHz band 相似文献
63.
Enhancement of thermopower is achieved by doping the narrow‐band semiconductor Ag6.52Sb6.52Ge36.96Te50 (acronym TAGS‐85), one of the best p‐type thermoelectric materials, with 1 or 2% of the rare earth dysprosium (Dy). Evidence for the incorporation of Dy into the lattice is provided by X‐ray diffraction and increased orientation‐dependent local fields detected by 125Te NMR spectroscopy. Since Dy has a stable electronic configuration, the enhancement cannot be attributed to 4f‐electron states formed near the Fermi level. It is likely that the enhancement is due to a small reduction in the carrier concentration, detected by 125Te NMR spectroscopy, but mostly due to energy filtering of the carriers by potential barriers formed in the lattice by Dy, which has large both atomic size and localized magnetic moment. The interplay between the thermopower, the electrical resistivity, and the thermal conductivity of TAGS‐85 doped with Dy results in an enhancement of the power factor (PF) and the thermoelectric figure of merit (ZT) at 730 K, from PF = 28 μW cm?1 K?2 and ZT ≤ 1.3 in TAGS‐85 to PF = 35 μW cm?1 K?2 and ZT ≥ 1.5 in TAGS‐85 doped with 1 or 2% Dy for Ge. This makes TAGS‐85 doped with Dy a promising material for thermoelectric power generation. 相似文献
64.
Henrik Sjo¨land 《Analog Integrated Circuits and Signal Processing》1999,21(1):57-65
The power amplifier tends to be one of the most demanding parts to fully integrate when building an entire radio on a CMOS chip. In this paper the design of a fully integrated RF power amplifier without inductors is described. As inductors in CMOS technology are associated with various problems, it is interesting to examine what performance can be achieved without them. An amplifier with an operating band from 60 MHz to 300 MHz (–3 dB) is built in 0.8 m CMOS. A 3 V supply is used. The measured midband power gain is 30 dB with 50 resistive source and load impedance. As linearity is important for many modern modulation schemes, the amplifier is designed to be as linear as possible. The measured third order intercept point is 23 dBm and the 1 dB compression point is 10 dBm, both referred to the output. The output is single ended to avoid an off-chip differential to single ended transformer. 相似文献
65.
Hallstrom AP Stein PK Schneider R Hodges M Schmidt G Ulm K 《IEEE transactions on bio-medical engineering》2004,51(8):1414-1420
Decreased left ventricular ejection fraction is the most commonly used risk factor for identification of patients at high-risk for lethal ventricular arrhythmic events. Twenty-four-hour electrocardiographic (ECG) approaches to risk stratification include: counts of ventricular premature contractions (VPCs), measures of heart rate variability (HRV), and heart rate turbulence (HRT) which has two components, turbulence onset and turbulence slope (TS). Refinement of these ECG risk stratifiers could enhance their clinical utility. We explored the structural relationships between heart rate (HR) and HRV and HRT measures. Our goal was to separate out the component of these measures due to the underlying average heart rate (HR), thus potentially reducing the variability of the measures and increasing their power to stratify risk. We proposed re-scaling tachograms of heart-beat intervals so that the re-scaled tachogram has a HR of 75 (or equivalently an average interval of 800 ms) and calculating HRV and HRT from the rescaled time series. We also explored the relationship between the number of VPCs and HRT. We showed that TS is structurally related to the number of VPCs (and hence to the length of the ECG recording). We proposed an adjusted TS that is independent of the number of VPCs. We also addressed the ability of shorter ECG recording to estimate HRV and HRT measures. We evaluated standard and rescaled HRV and HRT measures using qualifying ambulatory ECG recordings from 744 patients in the Cardiac Arrhythmia Suppression Trial. We found that measures based on the rescaled tachogram had reduced variance (20% to 40%). Correlations between measures were also substantially reduced. We also found substantial circadian effects on some, but not all HRV indices, not explained by the circadian pattern in HR and possibly pointing to additional measures for risk prediction. In conclusion, we found that adjusting for HR and the number of VPCs in heart-beat related ambulatory ECG measures has the potential to significantly improve the power of these measures to risk stratify cardiac patients. 相似文献
66.
Kevin P. Musselman Andrew Marin Andreas Wisnet Christina Scheu Judith L. MacManus‐Driscoll Lukas Schmidt‐Mende 《Advanced functional materials》2011,21(3):573-582
A novel buffering method is presented to improve the stability of zinc oxide processed in aqueous solutions. By buffering the aqueous solution with a suitable quantity of sacrificial zinc species, the dissolution of functional zinc oxide structures and the formation of unwanted impurities can be prevented. The method is demonstrated for ZnO films and nanowires processed in aqueous solutions used for the selective etching of mesoporous anodic alumina templates and the electrochemical deposition of Cu2O. In both cases, improved ZnO stability is observed with the buffering method. ZnO‐Cu2O heterojunction solar cells (bilayer and nanowire cells) synthesized using both traditional and buffered deposition methods are characterized by impedance spectroscopy and solar simulation measurements. Buffering the Cu2O deposition solution is found to reduce unwanted recombination at the heterojunction and improve the photovoltaic performance. 相似文献
67.
Peng Gao Isil Berkun Robert D. Schmidt Matthew F. Luzenski Xu Lu Patricia Bordon Sarac Eldon D. Case Timothy P. Hogan 《Journal of Electronic Materials》2014,43(6):1790-1803
Mg2(Si,Sn) compounds are promising candidate low-cost, lightweight, nontoxic thermoelectric materials made from abundant elements and are suited for power generation applications in the intermediate temperature range of 600 K to 800 K. Knowledge on the transport and mechanical properties of Mg2(Si,Sn) compounds is essential to the design of Mg2(Si,Sn)-based thermoelectric devices. In this work, such materials were synthesized using the molten-salt sealing method and were powder processed, followed by pulsed electric sintering densification. A set of Mg2.08Si0.4?x Sn0.6Sb x (0 ≤ x ≤ 0.072) compounds were investigated, and a peak ZT of 1.50 was obtained at 716 K in Mg2.08Si0.364Sn0.6Sb0.036. The high ZT is attributed to a high electrical conductivity in these samples, possibly caused by a magnesium deficiency in the final product. The mechanical response of the material to stresses is a function of the elastic moduli. The temperature-dependent Young’s modulus, shear modulus, bulk modulus, Poisson’s ratio, acoustic wave speeds, and acoustic Debye temperature of the undoped Mg2(Si,Sn) compounds were measured using resonant ultrasound spectroscopy from 295 K to 603 K. In addition, the hardness and fracture toughness were measured at room temperature. 相似文献
68.
Source wavelength modulation by feedback of the interference signal of an unbalanced fiber-optic Michelson interferometer to the driver of the semiconductor laser source gives rise to sawtooth shaped fringes under fiber strain. The dependence of the theoretically predicted fringe asymmetry on feedback gain is verified experimentally. Elimination of the fringe counting directional ambiguity via differentiation of the asymmetric closed loop interference signal is demonstrated for the first time 相似文献
69.
S. Strehle H. Schumacher D. Schmidt M. Knaut M. Albert J.W. Bartha 《Microelectronic Engineering》2008,85(10):2064-2067
The deposition of ultra thin Ta(N) films by ALD is a possibility to achieve conformal film thickness and suitable step coverage for microelectronic applications. Due to the sorption of a precursor molecule to the substrate surface, the chemical interface conditions are important. In the present study selected substrate pretreatments were investigated by in situ XPS and spectroscopic ellipsometry in reference to the amount of carbon containing contamination and oxygen and in reference to the ALD growth rate of Ta(N) films. Furthermore, surface roughness was measured by AFM and will be discussed in dependence on the individual pretreatment and the ALD Ta(N) cycle number. 相似文献
70.
Xin Jin Jun Li Schmidt C.C. Schmit T.J. Jinlong Li 《Geoscience and Remote Sensing, IEEE Transactions on》2008,46(2):479-488
Geostationary imagers such as the Advanced Baseline Imager (ABI) proposed for the next generation of Geostationary Operational Environmental Satellites (GOESs), i.e., GOES Series R and beyond, and the spinning enhanced visible and InfraRed Imager (SEVIRI) onboard METEOSAT 8 provide atmospheric total column ozone (TCO) with high temporal (better than 15 min) and spatial (better than 5 km) resolutions. The purpose of this paper is to present a method that evolved from the current GOES sounder TCO retrieval that can be applied to ABI, with SEVIRI serving as a proxy for ABI. Although ABI and SEVIRI have fewer infrared spectral bands than the current series of GOES (-8 to -P) sounders, ABI and SEVIRI can provide TCO with an accuracy that is comparable to the current GOES sounder by using forecast temperature profiles as additional a priori information. Despite the need for additional data, the greatest advantage of ABI and SEVIRI is their fast 15-min coverage of the full disk. The SEVIRI TCO demonstrates how well geostationary imagers can capture ozone transport and change at high temporal and spatial resolutions. The estimated TCO has very good agreement (R = 0.92 and root-mean-square error = 3.7%) with the total ozone measurements from the Ozone Monitoring Instrument (OMI) onboard the Earth Observing System aura platform. 相似文献