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1.
The coarse acquisition performance of a direct sequence spread-spectrum receiver is analyzed when a linear prediction filter is used for narrowband interference suppression. We show that once an appropriate matching strategy is identified, the linear prediction filter can provide favorable performance when narrowband interference is present over a considerable range of both interference power and bandwidth. In addition, the presence of the filter dramatically improves the performance over the case where there is no filter, except when the interference bandwidth and the power are both small (i.e., when the processing gain provides sufficient interference immunity without the filter). If long spreading sequences are used with moderately sized observation windows, the acquisition performance can be severely degraded when a parallel acquisition scheme is used due to the linear predication filter. We show, however, that a slower serial receiver will provide reliable performance.This work was supported in part by the Office of Naval Research under contract ONR N00014-91-J-1234, the Army Research Office under contract ARO DAAL03-91-0071, and the NSF Center for Ultra-High Speed Circuits and Systems (ICAS). 相似文献
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High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn4 to Mn9. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems. 相似文献
4.
R. L. Laurence J. C. Slattery 《Journal of polymer science. Part A, Polymer chemistry》1967,5(6):1327-1340
A study of sorption in a copolymer of ethylene and propylene is presented. Long-time sorption and desorption measurements provided the actual diffusion coefficient in the limit of zero concentration gradient. An analysis of the diffusion–sorption data reinforced the Frisch hypothesis about diffusion in a polymer matrix. The better solvent deforms the microstructure, allowing a more marked dependence of the diffusivity upon concentration. 相似文献
5.
To investigate by NMR the effects of adenine methylation, a set of oligodeoxynucleotides has been synthesized by phosphotriester or phosphoramidite procedures on silica-gel support. The preparation of fully protected 2′-deoxy-N6-methyladenosine 3′-phosphate 4 and (2′-deoxy-N6-methyladenosin-3′-O-yl)(methoxy)morpholinophosphine 5 is described. The large-scale chemical synthesis, purification by HPLC, and characterization by MS of these molecules containing N6-methyladenine is reported. 相似文献
6.
D. C. Dejongh R. Y. Van Fossen Laurence R. Dusold M. P. Cava 《Journal of mass spectrometry : JMS》1970,3(1):31-43
The mass spectra of eleven diazoketones have been obtained. High resolution mass measurements of selected ions have shown initial loss of nitrogen followed by loss of carbon monoxide. In many of the spectra, flat-topped metastables were observed. 相似文献
7.
The state-of-the-art of analysis for acrylamide in food is reviewed. The majority of analytical methods adopts a similar approach: addition of internal standard to the specimen, extraction with water, purification of extract using a solid-phase extraction cartridge, and then determination using either gas chromatography coupled to mass spectroscopy (GC/MS) after bromination, or direct measurement with liquid chromatography coupled to mass spectroscopy (LC/MS). The available methods generally show good agreement and are likely to be accurate. However, improvements in precision (within-laboratory) and repeatability (between-laboratory) are needed by particular data users. 相似文献
8.
Bastien Cochereau Laurence Meslet-Cladire Yves Franois Pouchus Olivier Grovel Catherine Roullier 《Molecules (Basel, Switzerland)》2022,27(10)
In nature, living organisms produce a wide variety of specialized metabolites to perform many biological functions. Among these specialized metabolites, some carry halogen atoms on their structure, which can modify their chemical characteristics. Research into this type of molecule has focused on how organisms incorporate these atoms into specialized metabolites. Several families of enzymes have been described gathering metalloenzymes, flavoproteins, or S-adenosyl-L-methionine (SAM) enzymes that can incorporate these atoms into different types of chemical structures. However, even though the first halogenation enzyme was discovered in a fungus, this clade is still lagging behind other clades such as bacteria, where many enzymes have been discovered. This review will therefore focus on all halogenation enzymes that have been described in fungi and their associated metabolites by searching for proteins available in databases, but also by using all the available fungal genomes. In the second part of the review, the chemical diversity of halogenated molecules found in fungi will be discussed. This will allow the highlighting of halogenation mechanisms that are still unknown today, therefore, highlighting potentially new unknown halogenation enzymes. 相似文献
9.
Paul Kirren Lucile Barka Saher Rahmani Nicolas Bondon Nicolas Donzel Philippe Trens Aurlie Bessire Laurence Raehm Clarence Charnay Jean-Olivier Durand 《Molecules (Basel, Switzerland)》2022,27(13)
(1) Background: Due to human activities, greenhouse gas (GHG) concentrations in the atmosphere are constantly rising, causing the greenhouse effect. Among GHGs, carbon dioxide (CO2) is responsible for about two-thirds of the total energy imbalance which is the origin of the increase in the Earth’s temperature. (2) Methods: In this field, we describe the development of periodic mesoporous organosilica nanoparticles (PMO NPs) used to capture and store CO2 present in the atmosphere. Several types of PMO NP (bis(triethoxysilyl)ethane (BTEE) as matrix, co-condensed with trialkoxysilylated aminopyridine (py) and trialkoxysilylated bipyridine (Etbipy and iPrbipy)) were synthesized by means of the sol-gel procedure, then characterized with different techniques (DLS, TEM, FTIR, BET). A systematic evaluation of CO2 adsorption was carried out at 298 K and 273 K, at low pressure. (3) Results: The best values of CO2 adsorption were obtained with 6% bipyridine: 1.045 mmol·g−1 at 298 K and 2.26 mmol·g−1 at 273 K. (4) Conclusions: The synthetized BTEE/aminopyridine or bipyridine PMO NPs showed significant results and could be promising for carbon capture and storage (CCS) application. 相似文献
10.
Abdelhouad Oukhrib Laurence Bonnafoux Armen Panossian Sandrine Waifang Duc Hanh Nguyen Martine Urrutigoity Françoise Colobert Maryse Gouygou Frédéric R. Leroux 《Tetrahedron》2014
A new family of non-symmetrical disubstituted dibenzophospholes possessing different steric and electronic effects have been synthesized and characterized. Their preliminary evaluation in rhodium-catalyzed hydroformylation reactions is presented. 相似文献