2,753 research outputs found
Multi-Mode Wireless Videophony
No full textA comparative study of arbitrarily programmable, but fixed-rate videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s is offered. These codecs were designed to allow direct replacement of mobile radio voice codecs in second generation wireless systems, such as the Pan-European GSM, the American IS-54 and IS-95 as well as the Japanese systems, operating at 13, 8, 9.6 and 6.7 kbps, respectively, although better video quality is maintained over higher-rate, 32kbps cordless systems, such as the Japanese PHS and the European DECT and CT2 systems. Best overall performance was achieved by our vector-quantised codecs, followed by the discrete cosine transformed and the quadtree-based schemes, which were characterised by the bit allocation schemes of Table 1. The associated video Peak Signal-to-Noise Ratio (PSNR) was around 30 dB, while the subjective quality can be viewed under http://www-mobile.ecs.soton.ac.uk. A range of multimode wireless transceivers were also proposed, which are characterised by Table 2
Dual-Mode Vector-Quantised Low-Rate Cordless Videophone Systems for Indoors and Outdoors Applications
No full textDual-mode reconfigurable wireless videophone transceivers are proposed for noise-, rather than interference-limited indoors and outdoors applications and their video quality, bit rate, robustness, and complexity issues are analyzed. A suite of fixed, but arbitrarily programmable low-rate, perceptually weighted vector quantized (VQ) codecs with and without run-length compression (RLC) are contrived for quarter common intermediate format (QCIF) videophone sequences. The 11.36-kb/s Codec 1 is Bose–Chaudhuri–Hochquenghem (BCH) (127,71,9) coded to a rate of 20.32 kb/s and this arrangement is comparatively studied along with the 8-kb/s Codec 2 and BCH(127,50,13) scheme, which has the same 20.32-kb/s overall rate. The source-sensitivity matched Systems 1–6 characterized in Table IV were contrived to comparatively study the range of system design options. For example, using Codec 1 in System 1 and coherent pilot symbol assisted 16-level quadrature amplitude modulation (16-PSAQAM), an overall signaling rate of 9 kBd was yielded, if the noise-limited channel had a signal-to-noise ratio (SNR) in excess of about 22 dB in the vicinity of the basestation or in indoors scenarios. In contrast, over lower quality outdoors channels near the fringes of the cell, the more robust 4-QAM mode of operation had to be invoked, which required twice as many time slots to accommodate the resulting 18-kBd stream and hence, reduced the total number of users supported. The robustness of Systems 2–4, and 6 was increased using automatic repeat requests (ARQ), again, inevitably reducing the number of users supported, which was between 6 and 16. In a bandwidth of 200 kHz, similarly to the Pan-European GSM mobile radio system’s speech channel, using systems 1, 3, 4, or 5, for example, 16 and eight videophone users can be supported in the 16- and 4-QAM modes, respectively, while in dual-mode cells the number of users is between eight and 16. The basic system characteristics are highlighted in Table IV. Index Terms—Fixed-rate video coding, QAM video communications, vector-quantized video coding, wireless video telephony
Biotin in microbes, the genes involved in its biosynthesis, its biochemical role and perspectives for biotechnological production
No full textBiotin (vitamin H) is one of the most fascinating cofactors involved in central pathways in pro- and eukaryotic cell metabolism. Since its original discovery in 1901, research has led to the discovery of the complete biotin biosynthesis pathways in many different microbes and much work has been done on the highly intriguing and complex biochemistry of biotin biosynthesis. While humans and animals require several hundred micrograms of biotin per day, most microbes, plants and fungi appear to be able to synthesize the cofactor themselves. Biotin is added to many food, feed and cosmetic products, creating a world market of 10-30 t/year. However, the majority of the biotin sold is synthesized in a chemical process. Since the chemical synthesis is linked with a high environmental burden, much effort has been put into the development of biotin-overproducing microbes. A summary of biotin biosynthesis and its biological role is presented; and current strategies for the improvement of microbial biotin production using modem biotechnological techniques are discussed
SIMPLE COULOMB CORRECTION FOR PHASE-SHIFTS AND APPLICATION TO THE P-P SYSTEM
No full textFROHLICH J, Streit L, ZANKEL H, ZINGL H. SIMPLE COULOMB CORRECTION FOR PHASE-SHIFTS AND APPLICATION TO THE P-P SYSTEM. JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS. 1980;6(7):841-852
Distribution of GABA-like immunoreactivity in the pigeon brain.
No full textThe distribution of GABA-like immunoreactivity in glutaraldehyde-fixed pigeon brains was studied by means of a monoclonal antibody. GABA-like immunoreactivity was observed in neuronal perikarya of different sizes as well as in neuropil and in certain fiber tracts. Certain staining patterns indicated the existence of several GABAergic projection systems in the pigeon brain. Indeed, a high density of immunostained perikarya and a low density of labeled terminal-like elements was the prominent pattern in the nuclei subpretectalis and posteroventralis, while an absence of perikaryal GABA-like immunoreactivity and accumulations of immunoreactive dots were observed in the isthmo-optic nucleus, amongst others. In the optic tectum, stained cell bodies with radially oriented processes in layer IIi (10) and with horizontally oriented processes in layer IId (5) were seen and were reminiscent of autoradiographic labeling patterns obtained previously following tectal injection of tritiated GABA. In the cerebellum, GABA-like immunoreactivity involved all types of neurons with the exception of granule cells. Purkinje cells showed regionally different intensities of immunostaining. In addition, in folium X no stained basket-like elements were observed. Although there is no evidence as yet about the function of GABA in most of the structures, the present results indicate an important role for this neurotransmitter in the pigeon brain
Wilson's map operations on regulat dessins and cyclotomic fields of definition
No full textDessins d’enfants can be seen as bipartite graphs embedded in compact orientable surfaces. According to Grothendieck and others, a dessin uniquely determines a complex structure on the surface, even an algebraic structure as a projective algebraic curve defined over a number field. Combinatorial properties of the dessin should therefore determine the equations and also structural properties of the curve, such as the field of moduli or the field of definition. However, apart from a few series of examples, very few general results concerning such correspondences are known. As a step in this direction, we present a graph theoretic characterisation of certain quasiplatonic curves defined over cyclotomic fields, based on Wilson's operations on maps: these leave invariant the graph but change the cyclic ordering of edges around the vertices, therefore they change the embeddings, and hence the dessins, and hence the conformal and algebraic structure of the underlying curves. Under suitable assumptions, satisfied by many series of regular dessins, these changes coincide with the effect of Galois conjugation. This coincidence allows one to draw conclusions about Galois orbits and fields of definition of dessins. The possibilities afforded by these techniques, and their limitations, are illustrated by a new look at some known examples and a study of dessins based on the regular embeddings of complete graphs. <br/
Streit (Georges). L'affaire Zappa, conflit gréco-roumain.
No full textStreit (Georges). L'affaire Zappa, conflit gréco-roumain.. In: Revue des Études Grecques, tome 7, fascicule 26,1894. p. 256
Streit (Georges). L'affaire Zappa, conflit gréco-roumain.
No full textStreit (Georges). L'affaire Zappa, conflit gréco-roumain.. In: Revue des Études Grecques, tome 7, fascicule 26,1894. p. 256
Ist der Sprachenstreit ein Streit um die Sprache?
No full textWeingart P. Ist der Sprachenstreit ein Streit um die Sprache? Psychologische Rundschau. 1989;40(2):96-98
PREDICTION OF N-HE-4 PHASE-SHIFTS FROM P-HE-4 DATA BETWEEN 20 AND 55 MEV
No full textFROHLICH J, KRIESCHE H, Streit L, ZANKEL H. PREDICTION OF N-HE-4 PHASE-SHIFTS FROM P-HE-4 DATA BETWEEN 20 AND 55 MEV. NUCLEAR PHYSICS A. 1982;384(1-2):97-111
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