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排序方式: 共有322条查询结果,搜索用时 31 毫秒
71.
Daniel J. ODonnell Stan O. Sigle K.Darrell Berlin Gene P. Sturm James W. Vogh 《Fuel》1980,59(3):166-174
High-boiling (535–675 °C) distillate fractions of Wilmington (Calif. USA) and Gach Saran (Iran) crude oils were separated into saturate, monoaromatic, diaromatic and polyaromatic-polar fractions by passage through a silica-gel—alumina dual packed chromatography column. These fractions were further separated on the basis of molecular volume by gel-permeation chromatography (g.p.c.). Select g.p.c. fractions were then analyzed by 1H and 13C n.m.r. spectroscopy. The fraction of aromatic carbons (Ar-C) of the total carbon content of a given series of g.p.c. fractions, obtained directly from the 13C n.m.r. spectra, showed a significant range of values (e.g. 13.2% to 29.2%) within each series. Furthermore, the values of %Ar-C within a series of g.p.c. fractions showed a maximum in each case. No such maximum was observed in the 1H n.m.r. spectra for the fraction of aromatic proton (%Ar-H) content compared to the total proton content of any of the g.p.c. fraction series. Signals observed in the 13C n.m.r. spectra confirmed the presence of aliphatic chains attached to aromatic structures in the monoaromatic, diaromatic and polyaromatic-polar g.p.c. series of each distillate fraction. Well-defined signals, not attributable to straight-chain aliphatic material, were also observed in the 13C n.m.r. spectra. Comparison of the chemical shifts of these 13C n.m.r. signals with those spectra of model compounds obtained experimentally, and with appropriate systems in the literature, strongly suggested the presence of saturated terpenoid-like structures as well as the presence of methyl groups in sterically hindered positions on an aromatic ring system. Gated decoupling techniques and the use of a relaxation agent were used to overcome the deleterious effects of slow relaxation times and Nuclear Overhauser Enhancement (NOE) on the analytical quality of the 13C n.m.r. spectra. 相似文献
72.
Ajinkya Kale Johannes Sturm Vijaya Sankara Rao Pasupureddi 《International Journal of Circuit Theory and Applications》2019,47(4):549-560
In this work, a reconfigurable multistandard subsampling receiver with dynamic carrier frequency detection and system-level EVM optimizations is proposed. Ideal software defined radio (SDR) receivers promise complete flexibility at the expense of high-performance analog-to-digital converters (ADCs) that are challenging to implement in current technologies for low-power applications. This scenario leads to the research of digital intensive sampling receivers with discrete-time signal processing (DTSP) implemented in analog domain. This approach makes it feasible to move channel selection filtering and dynamic gain adaptability from analog to digital domain. The proposed receiver employs subsampling down-conversion along with subband filters to dynamically detect the carrier frequency of the incoming signal, estimate its bandwidth, and identify if the signal is present in one of the target standard bands. This carrier detection provides a unique capability to reconfigure the receiver dynamically. Additionally, in this work, system-level EVM optimization is proposed considering frequency synthesizer phase noise, IQ mismatch, sampling frequency selection and block-level gain, noise, and nonlinearity. The RF front end of the proposed receiver is modeled in Verilog-AMS whereas the digital signal processing is implemented in Simulink-Matlab. The complete receiver has been verified to detect and process three different bands belonging to three different standards (GSM, UMTS, and WLAN) with the carrier frequency ranging from 0.9 to 2.5 GHz. Test signals with 4-QAM modulation, maximum bandwidth of 20 MHz, and input-dynamic range from –109 to –20 dBm is utilized to demonstrate the receiver performance including an EVM of –40 dB. 相似文献
73.
N. Hoepffner B. Sturm Z. Finenko D. Larkin 《International journal of remote sensing》2013,34(7):1435-1456
Existing satellite numerical models and data interpolation methods were used to evaluate the scales of variation in the vertical distribution of the phytoplankton biomass and the daily rate of primary production within the subtropical and tropical NE Atlantic Ocean (5-40 N; 6-30 W). The choice of this area was dictated principally by its economical importance, as it represents a large fishing ground due to upwelling activities along the coast of Morocco and Mauritania. After geographical partition of the area of study into 'bio-geochemical provinces' based on bathymetry and surface circulation, up to 300 satellite scenes obtained from the defunct Coastal Zone Color Scanner (CZCS) and covering the full year 1983 were processed into maps of surface chlorophyll and were further analysed into integrated primary production. Analyses of satellite data included a specific method to account for the sensitivity loss of the sensor during the studied period. The results of the productivity model are presented in terms of seasonal variations in the daily and annual photosynthetic carbon production in the various provinces and their contribution to the productivity of the overall study area. A total of 0.82 GtC y-1 was computed for the subtropical and tropical NE Atlantic. One third of this is produced within the coastal zone although it accounts for only 14% of the total area. 相似文献
74.
Georg Sturm Harald Weigand Clemens Marb Wilfried Weiß Bernd Huwe 《Journal of Applied Electrochemistry》2010,40(6):1069-1078
The static lifetime of primary phosphate stocks is estimated as one century. Thus, the exploitation of secondary phosphorus
sources becomes increasingly important. This study focussed on the feasibility of an electrokinetic phosphorus recovery from
sewage sludge ash (P-content ~5 wt%). Packed bed experiments were conducted under varied electric conditions with and without
acid pre-treatment and employing porous and ion exchange materials as electrode wells. Maximum values of phosphate concentration
obtained in all experiments were around 2.5 g L−1. Galvanostatic conditions were superior to potentiostatic conditions and acid pre-treatment is preferable over packed bed
saturation with water. Ion-exchange membranes improved the product quality but increased the energy demand. Phosphorus recovery
below 1% of the initial contents shows that the recovery setup must be improved in view of a marketable application. 相似文献
75.
Taillandier AS Domine F Simpson WR Sturm M Douglas TA Severin K 《Environmental science & technology》2006,40(24):7521-7527
The detailed physical characteristics of the subarctic snowpack must be known to quantify the exchange of adsorbed pollutants between the atmosphere and the snow cover. For the first time, the combined evolutions of specific surface area (SSA), snow stratigraphy, temperature, and density were monitored throughout winter in central Alaska. We define the snow area index (SAI) as the vertically integrated surface area of snow crystals, and this variable is used to quantify pollutants' adsorption. Intense metamorphism generated by strong temperature gradients formed a thick depth hoar layer with low SSA (90 cm(2) g-1) and density (200 kg m(-3)), resulting in a low SAI. After snowpack buildup in autumn, the winter SAI remained around 1000 m(2)/m(2) of ground, much lower than the SAI of the Arctic snowpack, 2500 m(2) m-(2). With the example of PCBs 28 and 180, we calculate that the subarctic snowpack is a smaller reservoir of adsorbed pollutants than the Arctic snowpack and less efficiently transfers adsorbed pollutants from the atmosphere to ecosystems. The difference is greater for the more volatile PCB 28. With climate change, snowpack structure will be modified, and the snowpack's ability to transfer adsorbed pollutants from the atmosphere to ecosystems may be reduced, especially for the more volatile pollutants. 相似文献
76.
Helena Gleskova I-Chun Cheng Sigurd Wagner James C. Sturm Zhigang Suo 《Solar Energy》2006,80(6):687-693
When devices are fabricated on thin foil substrates, any mismatch strain in the device structure makes the work piece curve. Any change of the radius of curvature produces a change in the size of the work piece, and thereby misalignment between individual device layers. To achieve tight tolerances, changes of curvature must be minimized throughout the fabrication process.Amorphous silicon thin-film transistors and solar cells respond differently to externally applied tensile strain. The elastic deformation of the transistor is correlated with small increase in the electron mobility. When the tensile strain reaches 0.34%, crack formation starts and causes an abrupt change in the transistor performance. The performance of solar cells, on the other hand, does not change for tensile strain up to 0.7%. At larger strain the short-circuit current, open-circuit voltage, fill factor, and the efficiency gradually decrease. 相似文献
77.
Sturm J. Leifhelm M. Schatzmayr H. Groiss S. Zimmermann H. 《Solid-State Circuits, IEEE Journal of》2005,40(7):1406-1413
In this paper, an optoelectronic receiver IC for CD, DVD, and Blue-Laser optical data storage applications is presented. The IC was developed in a 0.5-/spl mu/m BiCMOS technology with integrated PIN photodiodes. It includes a new architecture of high-speed and low-noise variable gain transimpedance amplifiers witch current preamplifier input. The amplifier transimpedance gain is programmable over a gain range of 130 /spl Omega/ to 270 k/spl Omega/ by a serial interface. The amplifier small-signal bandwidth is 260 MHz for the highest gain, which gives a gain-bandwidth product of 70 THz/spl Omega/ and a sensitivity improvement by a factor of 2 compared to published OEICs. The amplifiers support a special write/clip mode which realizes a nonlinear gain reduction for high input signals. The output voltage buffers are 130-/spl Omega/ impedance matched for optimized data transmission over a flex cable. The impedance is generated by active-impedance synthesis to increase the output dynamic range. 相似文献
78.
79.
Srikumar Ramalingam Suresh K. Lodha Peter Sturm 《Computer Vision and Image Understanding》2006,103(3):218
We introduce a generic structure-from-motion approach based on a previously introduced, highly general imaging model, where cameras are modeled as possibly unconstrained sets of projection rays. This allows to describe most existing camera types including pinhole cameras, sensors with radial or more general distortions, catadioptric cameras (central or non-central), etc. We introduce a structure-from-motion approach for this general imaging model, that allows to reconstruct scenes from calibrated images, possibly taken by cameras of different types (cross-camera scenarios). Structure-from-motion is naturally handled via camera independent ray intersection problems, solved via linear or simple polynomial equations. We also propose two approaches for obtaining optimal solutions using bundle adjustment, where camera motion, calibration and 3D point coordinates are refined simultaneously. The proposed methods are evaluated via experiments on two cross-camera scenarios—a pinhole used together with an omni-directional camera and a stereo system used with an omni-directional camera. 相似文献
80.
Balásházy I Farkas A Szöke I Hofmann W Sturm R 《Radiation protection dosimetry》2003,105(1-4):129-132
In this study local distributions of deposited inhaled particles such as radon progenies in realistic human airway bifurcation models of bronchial generations one to six are computed for different geometries, inlet flow profiles, flow rates and particle sizes with computational fluid particle dynamics methods. The movement of the mucus layer in the large central human airways is also simulated by computational fluid dynamic techniques. There is experimental evidence that bronchogenic carcinomas mainly originate at the central zone of the large airway bifurcations, where primary hot-spots of deposition have been found. However, current lung deposition models do not take into consideration the inhomogeneity of deposition within the airways. The inhomogeneous movement of the mucus layer may strongly influence the effect of primary deposition. On the basis of our results, both the deposition and the clearance patterns are highly non-uniform, especially in the vicinity of the carinal ridge of the bifurcations. 相似文献