bluuebunny/crossref_metadata_2025_split huggingface dataset:
BER performance of MQAM withL‐branch MRC diversity reception over correlated Nakagami‐mfading channels
Authors: Patterh Manjeet S. , Kamal T. S. , Sohi B. S. 
Published: May 2003

AbstractExact and closed form generalized expressions for bit error rate (BER) of M‐ary quadrature amplitude modulation (MQAM) withL‐branch maximal ratio combining (MRC) space diversity reception in fading channels are derived and analyzed. The fading channels are modeled as identical but correlated frequency‐nonselective slow Nakagami‐mfading channels corrupted by additive white Gaussian noise (AWGN). Analytical results obtained are in terms of few finite range integrals with an integrand composed of elementary functions. Because of their simple form, these analytical results readily allow numerical evaluation in cases of practical interest. The results are also general enough to include Nakagami‐mfading channels with and without correlation, no diversity system, Rayleigh fading channels with and without correlation, and AWGN as special cases. The numerical results for the case of 16QAM are shown graphically and also in tabular form in order to examine the effects of fading severity, order of diversity, and branch correlation on the BER performance. The two correlation models considered are constant correlation model and exponential correlation model. One may be interested to know how the BER of MQAM is related to symbol error rate (SER) of MQAM. Therefore, the BER results obtained in this paper are also compared with that obtained directly from the SER. It is expected that the analytical results presented in this paper will provide a convenient tool for design and analysis of a radio communication system with space diversity reception in uncorrelated and correlated fading environment. Copyright © 2002 John Wiley & Sons, Ltd.
A HiperLAN II frame processor implementation
Authors: Vasilakopoulou E. P. , Papadopoulos G. D. , Karastergios G. E. 
Published: May 2003

AbstractIn recent years, wireless access networks offer an alternative method for connecting subscribers to the global communication network. Several high‐speed Wireless LAN's (WLAN) standards have emerged and among them the ETSI BRAN HiperLAN II standard is distinguished for its performance and QoS support.This paper, starting with a short overview of HiperLAN II main features and Medium Access (MAC) protocol, presents the architecture of an implemented high‐speed Frame Processor that realizes the medium access control (MAC) protocol of the HiperLAN II standard. The main goal of the Frame Processor is the real‐time management of the air interface as well as to bridge the upper network layers with the wireless world, relieving the data link control (DLC) layer of time‐consuming tasks such as slot map allocation extraction, bit‐by‐bit processing of data units, framing and synchronization. Copyright © 2003 John Wiley & Sons, Ltd.
Radio resource management schemes for combined GSM/GPRS mobile systems
Authors: Konstantinopoulou C. N. , Koutsopoulos K. A. , Demestichas P. P. , Theologou M. E. , Lyberopoulos G. L. 
Published: May 2003

AbstractData services like Web browsing, e‐mail and file transfer are becoming more and more popular in cellular systems. In contemporary systems like Global System for Mobile communications (GSM), data transfer has been circuit‐switched, that is, physical resources are allocated to a user for the entire call/session duration. However, this is inefficient in case of bursty traffic, where bursts are separated by long intervals of inactivity. This has been the main reason for the introduction of General Packet Radio Service (GPRS), which on the one hand acts as a mobile access network to the Internet, while on the other hand it enables the operator to offer a wide variety of value‐added services [Wireless Access Protocol (WAP) over GPRS, e/m‐banking, e/m‐commerce, push services, etc.] efficiently.However, in contemporary commercial implementations of GPRS the radio resource allocation algorithm does not take into account the Quality of Service (QoS)‐related service characteristics—although such information is exchanged between the terminal and the network—and consequently all service requests are treated the same way (‘best effort’). In this paper, we propose and evaluate via a simulation platform various Radio Resource Management (RRM) schemes capable of differentiating the handling of ‘service requests’ (in uplink and downlink), taking into account the GPRS‐related QoS parameters (precedence, reliability, delay, mean and peak throughput). The evaluation is performed for a range of voice (circuit‐switched) traffic loads, number of Transmit Receive eXchange (TRXs), offered data (packet‐switched) services characteristics, number of dedicated Packet Data Channels (PDCHs), and so on, taking into account the respective QoS requirements for both service types (circuit‐ and packet‐switched). Copyright © 2003 John Wiley & Sons, Ltd.
LEO satellite communication networks—a routing approach
Authors: Makki S. A. M. , Pissinou Niki , Daroux Philippe 
Published: May 2003

AbstractIn the modern world of telecommunications, the concept of wireless global coverage is of the utmost importance. However, real global coverage can only be achieved by satellite systems. Until recently, the satellites were in geostationary orbit and their high altitude could not allow real‐time communication such as cellular networks. The development of LEO satellite networks seems to overcome this limit. However, LEO satellite systems have specific characteristics that need to be taken into account. In the same manner, the TCP/IP standard was developed for terrestrial network. The need is then to come up with a solution that would permit the use of TCP/IP on LEO satellite networks without losing too many packets.The idea is to develop a routing algorithm that maximizes the RTT delays compared to the TCP timer granularity. For that matter, we use an FSA‐based link assignment that simulates the satellite constellation as a fixed network for a predetermined time interval. In this configuration, the problem becomes a static routing problem where an algorithm can find the best solution. Copyright © 2003 John Wiley & Sons, Ltd.
One‐dimensional Cadmium(II) Coordination Polymers: Syntheses and Crystal Structures of [Cd(H2O)3(C5H6O4)]·2H2O, Cd(H2O)2(C6H8O4), and Cd(H2O)2(C8H12O4)
Authors: Sun Jie , Zheng Yue‐Qing 
Published: May 2003

Abstract[Cd(H2O)3(C5H6O4)]·2H2O (1) and Cd(H2O)2(C6H8O4) (2) were prepared from reactions of fresh CdCO3 precipitate with aqueous solutions of glutaric acid and adipic acid, respectively, while Cd(H2O)2(C8H12O4) (3) crystallized in a filtrate obtained from the hydrothermal reaction of CdCl2·2.5H2O, suberic acid and H2O. Compound 1 consists of hydrogen bonded water molecules and linear {[Cd(H2O)3](C5H6O4)2/2} chains, which result from the pentagonal bipyramidally coordinated Cd atoms bridged by bis‐chelating glutarato ligands. In 2 and 3, the six‐coordinate Cd atoms are bridged by bis‐chelating adipato and suberato ligands into zigzag chains according to {[Cd(H2O)3](C5H6O4)2/2} and {[Cd(H2O)2](C8H12O4)2/2}, respectively. The hydrogen bonds between water and the carboxylate oxygen atoms are responsible for the supramolecular assemblies of the zigzag chains into 3D networks. Crystallographic data: (1) P1¯ (no. 2), a = 8.012(1), b = 8.160(1), c = 8.939(1) Å, α = 82.29(1)°, β = 76.69(1)°, γ = 81.68(1)°, U = 559.6(1) Å3, Z = 2; (2) C2/c (no. 15), a = 16.495(1), b = 5.578(1), c = 11.073(1) Å, β = 95.48(1)°, U = 1014.2(1) Å3, Z = 4; (3) P2/c (no. 13), a = 9.407(2), b = 5.491(1), c = 11.317(2) Å, β = 95.93(3)°, U = 581.4(2) Å3, Z = 2.
Synthesis, Crystal Structure, and Spectral Properties of a Cobalt(II) Complex with N‐Salicylidene‐p‐Toluidine
Authors: Cseh Liliana , Csunderlik Carol , Pantenburg Ingo , Meyer Gerd , Costisor Otilia 
Published: May 2003

AbstractThe complex Co(C14H13NO)2Cl2 with the protonated N‐salicylidene‐p‐toluidine ligand was synthesized from an ethanolic solution of CoCl2·6H2O and N‐salicylidene‐p‐toluidine. The crystal structure was determined from X‐ray single crystal data (monoclinic, space group Cc, a = 1496.2(3) pm, b = 1257.4(4) pm, c = 1544.6(3) pm, β = 115.01(1)°, Z = 4). Co2+ adopts a distorted tetrahedral geometry. The UV‐Vis and IR spectra of the complex are discussed.
ACu9X4 ‐ Neue Verbindungen mit der CeNi8, 5Si4, 5‐Struktur (A: Sr, Ba; X: Si, Ge)
Authors: Kranenberg C. , Mewis A. 
Published: May 2003

AbstractDurch Erhitzen entsprechender Elementgemenge auf 1000° ‐ 1100 °C entstehen SrCu9Si4 (a = 8, 146(1), c = 11, 629(2)Å), BaCu9Si4 (a = 8, 198(2), c = 11, 735(2)Å), SrCu9Ge4 (a = 8, 273(2), c = 11, 909(5)Å) sowie BaCu9Ge4 (a = 8, 338(4), c = 12, 011(7)Å) in Form dunkelgrauer Pulver. Die Verbindungen sind isotyp (I4/mcm, Z = 4) und kristallisieren in einer geordneten Besetzungsvariante des kubischen NaZn13‐Typs, der auch von der binären Phase BaCu13 gebildet wird. Deren Cu2‐Positionen werden bei den ternären Verbindungen geordnet von Kupfer und Silicium bzw. Germanium besetzt. Dies führt zu einer Erniedrigung der Symmetrie und einer Verzerrung der Koordinationspolyeder. Messungen des elektrischen Widerstands an BaCu9Si4 weisen die Verbindungen als metallische Leiter aus.
[Mn4Br(CH=CMe2)3(μ3‐NPEt3)4] — ein 2‐Methyl‐prop‐1‐enyl‐Phosphaniminato‐Komplex von Mangan(II) mit Heterokubanstruktur
Authors: Rölle Ulrike , Harms Klaus , Dehnicke Kurt 
Published: May 2003

Abstract[Mn4Br(CH=CMe2)3(μ3‐NPEt3)4] — a 2‐Methyl‐prop‐1‐enyl‐Phosphoraneiminato Complex of Manganese(II) with Heterocubane Structure[Mn4Br(CH=CMe2)3(μ3‐NPEt3)4] (1) has been prepared from [MnBr(μ3‐NPEt3)]4 and BrMg(CH=CMe2) in thf solution and subsequent extraction of the solvent‐free residue with n‐hexane. 1 forms red single crystals from diethylether solution, which are characterized by a crystal structure determination. Space group P1¯, Z = 2, lattice dimensions at —80 °C: a = 1144.7(1), b = 1411.3(2), c = 1521.8(2) pm, α = 91.581(14), β = 90.163(14), γ = 91.947(14)°, R1 = 0.0448. 1 exhibits a Mn4N4 heterocubane core, a terminally coordinated bromine ligand and three Mn—CH=CMe2 groups with M—C bond lengths of 213.8 pm on average.
Synthese und Kristallstruktur von Te3O3(PO4)2, einer Verbindung mit fünffach koordiniertem Tellur(IV)
Authors: Mayer Helmut , Weil Matthias 
Published: May 2003

AbstractPolykristallines Te3O3(PO4)2 bildet sich bei der Entwässerung von (Te2O3)(HPO4) über die Zwischenstufe (Te8O10)(PO4)4. Farblose Einkristalle der Titelverbindung können gezielt durch Tempern stöchiometrischer Mengen der binären Oxide P2O5 und TeO2 im geschlossenen Kieselglasrohr bei 590 °C für 8 Stunden erhalten werden. Die Kristallstruktur (P21/c, Z = 4, a = 12.375(2), b = 7.317(1), c = 9.834(1)Å, β = 98.04(1)°, 1939 Strukturfaktoren, 146 Parameter, R[F2 > 2σ(F2)] = 0.0187, wR2(F2 alle) = 0.0367) wurde aus Vierkreisdiffraktometerdaten bestimmt und besteht aus [TeO5]‐Polyedern und PO4‐Tetraedern als einfachste Baueinheiten. In der Netzwerkstruktur sind zwei Telluratome über sehr kurze Bindungen zu Oxidsauerstoffen zu [Te2O3]2+‐Zickzackketten verbunden, die sich entlang [001] erstrecken. Das dritte Te‐Atom ist mit einer kurzen Te‐O‐Bindung seitlich an dieser Kette verankert und mit den Ecken von PO4‐Tetraedern zu den anionischen [Te(PO4)2]2—‐Einheiten verknüpft. Dadurch bilden sich Schichten der Zusammensetzung [Te2O3][Te(PO4)2] parallel zur bc‐Ebene aus, die über schwache Te‐O‐Bindungen dreidimensional verknüpft werden.
MNE Nitrido Bridges with Transition Metal Nitrogen Multiple Bonds and E = Phosphorus, Sulfur, and Chlorine
Authors: Dehnicke Kurt 
Published: May 2003

AbstractA compilation is given on new syntheses, properties, and structures of complexes with M≡N—E ↔ M=N=E nitrido bridges with transition metal nitrogen multiple bonds and participation of the main group elements E of phosporus, sulfur, and chlorine.1. MNP: This atomic sequence is realized in phosphoraneiminato complexes with transition metals in high oxidation states and termal bond of the (NPR3—) ligand. A series of new complexes of this type is reported with M = zirconium, hafnium, molybdenum, tungsten, and rhenium, among these the homoleptic species [Hf(NPPh3)4] and [M(NPPh3)4]2+ with M = Mo and W. Therefrom the isolobal complexes [:N≡Mo(NPPh3)3], [:O≡W(NPPh3)3]+, [(O)2Mo(NPPh3)2], and [(O)3Re(NPPh3)] are derived.2. MNS: Adding to compounds with this atomic sequence, new complexes were developed on the basis of the functional ligand groups thionitrosyl (a), dinitridosulphate(II) (b), dinitridosulphate(IV) (c), and cyclothiazeno (d) (cyclo‐3, 5‐dithia‐2, 4, 6‐triazino):magnified image3. MNCl: Novel N‐chloroimido complexes of tungsten are described. [F4W≡N—Cl]4, which is tetrameric according to the IR spectrum, was obtained by direct fluorination from [Cl4W≡N—Cl]2 or, surprisingly, from W(N)Cl3. With acetonitrile the monomeric molecular complex [CH3CN→WF4(≡N—Cl)] is formed. In an unexpected pathway K[F5W≡N—Cl] was obtained from a redox reaction of W(N)Cl3 with trimethylstannyl fluoride in the presence of potassium fluoride. The ionic compound forms double layers with short Cl···F contacts.
Recent Advances in the Synthesis of N‐Heteroatom Substituted Imido Complexes Containing a Nitrido Bridge [M=N—E] (M = Group 4, 5 and 6 Metal, E = B, Si, Ge, P, S)
Authors: Weber Klaus , Korn Klaus , Schorm Andrea , Kipke Jennifer , Lemke Martin , Khvorost Alexander , Harms Klaus , Sundermeyer Jörg 
Published: May 2003

AbstractThe focus of the current report lies on recent developments of synthetic methods applied to the synthesis of some high‐valent complexes containing the nitrido functionality [N]3— as a link between a group 4, 5 or 6 transition metal and a main group element E (E = B, Si, Ge, P, S). Emphasis is put on results, that have been obtained within the “Schwerpunktprogramm “Nitridobrücken” funded by the Deutsche Forschungsgemeinschaft. The synthetic methods include condensation reactions of reactive chloro and oxo complexes (M = V, Nb, Ta, Cr, Mo, W) with silylamines, sulfonylamides, with N‐silyl and N‐lithio iminophosphoranes, furthermore methatesis reactions of oxo complexes with N‐sulfonyl sulfinyl amides (M = V, Cr, Mo, W), the oxidative addition of element azides to d2 metal centers (M = V, W), and finally transamination reactions of N‐H iminophosphoranes with amido complexes (M = Ti, Sm).
Reactions of the Complexes ReNCl2(PMe2Ph)3, [ReNCl4]—, [OsO3N]—, and Cl3VNCl with Metal Halides
Authors: Strähle Joachim 
Published: May 2003

AbstractThe nitrido complexes ReNCl2(PMe2Ph)3 and [OsO3N]— have strong basic terminal nitrido ligands which can react with Lewis acidic metal halides to form nitrido bridges. The synthesis and structure of complexes with ReNCl2(PMe2Ph)3 and nitrido bridges Re≡N‐M (M = B, Ga, Sn, Ti, Zr, V, Nb, Ta, Mo, Re, Pd, Au, and Zn) as well as of complexes with [OsO3N]— and nitrido bridges Os≡N‐M (M = Pd and Pt) are reported. Strong Lewis acids can also remove phosphine or chloro ligands from ReNCl2(PMe2Ph)3. The resulting complex fragments subsequently combine to yield oligomeric complexes with nitrido bridges Re≡N‐Re. If the reaction with strong Lewis acids is carried out in a chlorinated solvent the solvent can be decomposed to form HCl which then protonates the nitrido ligand affording an imido complex. [ReNCl4]— is able to form nitrido bridges to electrophilic halides if a donor ligand is coordinated in trans position to the nitrido ligand to enhance its basicity sufficiently. The synthesis and structure of examples with nitrido bridges Re≡N‐M (M = Pd, Pt, Ta) are reported.The chloro imido complex Cl3V≡N‐Cl can act as a nitride ion transfer reagent. Its reaction with MoCl5 yields Mo2NCl8 whereas with MoCl3 the nitride chlorides Mo3N2Cl11 and MoNCl3 are obtained. Cl3VNCl can also act as an reactive intermediate by the reaction of VN with a halide as was shown by the reaction of MoCl5 with VN yielding Mo2NCl7. The structures of these molybdenum nitride chlorides are discussed.
Reactions of Rhenium and Technetium Nitrido Complexes with ER3 Fragments (E = B, Ga, Al, C, P; R = H, Alkyl, Aryl)
Authors: Abram Ulrich , Schmidt‐Brücken Burkhard , Hagenbach Adelheid , Hecht Maren , Kirmse Reinhard , Voigt Andreas 
Published: May 2003

AbstractTerminal ‘N3—’ ligands in rhenium and technetium nitrido complexes are sufficiently nucleophilic to react with Lewis acids under formation of nitrido‐bridged compounds. The reactivity of the nucleophilic centre and the nature of the formed compounds are strongly dependent on the Lewis acid and the composition of the metal complex used.Air‐stable compounds with Re≡N‐ER3 bridges are formed when ER3 is BR3 (R = H, Cl, Br, Ethyl, Phenyl, C6F5), BCl2Ph, GaCl3, CPh3+, or PPh3. The six‐co‐ordinate rhenium(V) complexes [ReNX2(PMe2Ph)3] (X = Cl, Br), [ReN(X)(Et2dtc)(PMe2Ph)2] (Et2dtc— = diethyldithiocarbamate) and [ReN(Et2dtc)2(PMe2Ph)] have been proved to be excellent starting materials for this type of reactions, whereas the five‐co‐ordinate precursors [ReNCl2(PPh3)2], [ReN(Et2dtc)2], [ReN{Ph2P(S)NP(S)Ph2}2] or [ReNCl4]— only react with the most reactive Lewis bases of the examples mentioned above such as BCl2Ph or B(C6F5)3. The rhenium‐nitrido bond lengths remain almost unchanged by the adduct formation, whereas a significant decrease of the trans‐influence of the nitrido complexes has been observed as can be seen by a shortening of the corresponding bond lengths or dimerization of five‐co‐ordinate precursors.Electrophilic attack of the Lewis acid to a donor atom of the equatorial co‐ordination sphere of the rhenium complex results in the formation of ‘underco‐ordinate’ metal centres which resemble to di‐, tri or tetrameric units with asymmetric nitrido bridges between each two rhenium atoms.EPR spectroscopy is an excellent tool to reflect the formation of nitrido bridges at the paramagnetic (d1) [ReNX4]— core (X = F, Cl, Br, NCS). The spectral parameters derived for the products of reactions of [ReNCl4]— with various boron compounds indicate an increase of the covalency of the equatorial Re‐L bonds as a consequence of the formation of a nitrido bridge.The tendency for the formation of nitrido bridges with Lewis acids is significantly lower for technetium compounds compared to their rhenium analogues. Only a few examples with BH3 and BPhCl2 have been established.
N‐Silylaminotitanium Chlorides — Synthesis, Structures, Multinuclear Magnetic Resonance, and some Applications
Authors: Wrackmeyer Bernd , Weidinger Jürgen , Pedall Andreas , Milius Wolfgang 
Published: May 2003

AbstractN‐Silylaminotitanium trichlorides, Me3S(R)N‐TiCl3 (18) [R = tBu (a), SiMe3 (b), 9‐borabicyclo[3.3.1]nonyl (9‐BBN)(c)], and (CH2SiMe2)2N‐TiCl3 (18d) were obtained in high yield and high purity from the reaction of the respective bis(silylamino)plumbylene with an excess of titanium tetrachloride. The crystal structure of 18a was determined by X‐ray analysis. The reactions of the analogous stannylenes with an excess of TiCl4 did not lead to 18. N‐Lithio‐trimethylsilyl[9‐(9‐borabicyclo[3.3.1]nonyl)]amine (8) was prepared, structurally characterized and used for the synthesis of a new bis(amino)stannylene 10 and a plumbylene 11. The compounds 18a—d served as ideal starting materials for the synthesis of bis(silylamino)titanium dichlorides, where the silylamino groups can be identical (19) or different (20). This was achieved either by the reaction of 18 again with bis(amino)plumbylenes or with lithium N‐silylamides. In contrast to the direct synthesis starting from titanium tetrachloride and two equivalents of the respective lithium amide, which in general affords 19 with identical amino groups only in low yield, the procedure starting from 18 is much more versatile and gave the pure compounds 19 or 20 in almost quantitative yield. Further treatment of the dichlorides 19 or 20 with lithium amides led to tris(amino)titanium chlorides 21. The dichlorides 19 or 20 reacted with two equivalents of alkynyllithium reagents to give the first well characterized examples of di(alkyn‐1‐yl)bis(N‐silylamino)titanium compounds 22—27. These compounds reacted with trialkylboranes (triethyl or tripropylborane) by 1, 1‐organoboration. In some cases, the extremely reactive reaction products could be identified as novel 1, 1‐bis(silylamino)titana‐2, 4‐cyclopentadienes 28—31 bearing a dialkylboryl group in 3‐position. In solution, the proposed structures of all products were deduced from a consistent set of data derived from multinuclear magnetic resonance spectroscopy (1H, 11B, 13C, 14N, 15N, 29Si, 35Cl NMR).
From [M≡N] and [M—N—E] Complexes to Models for Metal Oxidoreductases
Authors: Sellmann Dieter , Sutter Jörg 
Published: May 2003

AbstractThe article reviews results of research that was initially aiming at complexes containing new and unusual [M—N—E] element combinations (M = transition metal, E = main group element), but soon turned into studies on model complexes for metal enzymes such as nitrogenases, hydrogenases or CO dehydrogenases, because several of the resulting [M—N—E] complexes exhibited reactions relevant to these enzymes. It could be shown that alkylation of transition metal thiolate nitride complexes gives alkylimido complexes when bulky and mild alkylation reagents, e.g. Ph3C+, are used. Hydride addition to [Ru(NO)(pybuS4)]+ yielded [Ru(HNO)(pybuS4)], which contains a bifurcated [M—N(X, Y)] bridge. The diazene complex [μ‐N2H2{Ru(PCy3)(S4)}2] undergoes H+/D+ and H+/D2 exchange reactions that enabled to rationalize the until then inexplicable ‘N2 dependent HD formation’ catalyzed by nitrogenases. Out of a larger number of [Ni(NE)(S3)] complexes, the compound [Ni(NHPPr3)(S3)] proved capable to model structure and reactivity features of [NiFe] hydrogenases. The [Ni(L)(S3)] complexes with L = N3— and N(SiMe3)2— exhibit extremely high reactivity towards CO, CO2 and SO2. The reactions lead to NCO—, CN— and NSO— complexes and bear potential relevance for carbon monoxide dehydrogenase reactions.
Control of Oxidation States of Transition Elements (Cr, Mn) in Nitridometalates and the Solid Solution Series Li6(Ca1‐xSrx)2[Mn2N6]
Authors: Hochrein Oliver , Höhn Peter , Kniep Rüdiger 
Published: May 2003

AbstractThe formation of ternary nitridometalates from the elements in the case of the systems Li—Cr, V, Mn—N leads to compounds which contain the transition metals in the highest (VV, CrVI) or a comparably high (MnV) oxidation state. In the corresponding calcium and strontium systems, the transition metals show a lower oxidation state (VIII, CrIII, MnIII). Transition metals with intermediate oxidation states (CrV, MnIV) are present in the quaternary (mixed cation) compounds Li4Sr2[CrN6], Li6Ca2[MnN6], and Li6Sr2[MnN6] (R3¯(#148), a = 585.9(3) pm, c = 1908.6(4) pm, Z = 3), as well as in the solid solution series Li6(Ca1—xSrx)2[MnN6].