bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of the13C/12C ratio of soil‐plant individual sugars by gas chromatography/combustion/isotope‐ratio mass spectrometry of silylated derivatives
Authors: Derrien Delphine , Balesdent Jérôme , Marol Christine , Santaella Catherine
Published: December 2003

Carbohydrate is an important pool in the terrestrial carbon cycle. The potential offered by natural and artificial13C‐labelling techniques should therefore be applied to the investigation of the dynamics of individual sugars in soils. For this reason, we evaluated the method of13C sugar analysis by gas chromatography/combustion/isotope‐ratio mass spectrometry (GC/C/IRMS) after hydrolysis and direct trimethylsilylation. Trimethylsilylation involved the addition of several carbon atoms per sugar. These atoms have to be taken into account in the estimation of the carbon isotope ratio. The analysis of standard and natural pentoses and hexoses of known13C enrichments revealed that the number of analysed added carbon atoms was less than expected from stoichiometry. This was attributed to incomplete derivatization and/or incomplete oxidation of methylsilyl carbon before IRMS. Using a calibration of the number of analysed added carbon atoms, the isotope excess of enriched samples could be determined with a relative error close to 5%. Concerning the determination of natural abundances by GC/C/IRMS, we could measure the delta13C of standard C3‐ and C4‐derived sugars with an accuracy of ±1.5‰ using the previous calibration. We were able to apply this technique to plant‐soil systems labelled by pulse‐chase of13CO2, revealing the nature and dynamics of sugars in the plant rhizosphere. Copyright © 2003 John Wiley & Sons, Ltd.
Randomization helps to perform independent tasks reliably
Authors: Chlebus Bogdan S. , Kowalski Dariusz R.
Published: December 2003

This paper is about algorithms that schedule tasks to be performed in a distributed failure‐prone environment, when processors communicate by message‐passing, and when tasks are independent and of unit length. The processors work under synchrony and may fail by crashing. Failure patterns are imposed by adversaries. Linearly‐bounded adversaries may fail up to a constant fraction of the processors. Weakly‐adaptive adversaries have to select, prior to the start of an execution, a subset of processors to be failure‐prone, and then may fail only the selected processors, at arbitrary steps, in the course of the execution. Strongly adaptive adversaries have a total number of failures as the only restriction on failure patterns. The measures of complexity are work, measured as the available processor steps, and communication, measured as the number of point‐to‐point messages. A randomized algorithm is developed, that attains both 𝒪(nlog*n) expected work and 𝒪(nlog*n) expected communication, against weakly‐adaptive linearly‐bounded adversaries, in the case when the numbers of tasks and processors are both equal ton. This is in contrast with performance of algorithms against strongly‐adaptive linearly‐bounded adversaries, which has to be Ω(nlogn/log logn) in terms of work. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
Coloring uniform hypergraphs with few colors
Authors: Kostochka Alexandr
Published: December 2003

Let m(r, k) denote the minimum number of edges in an r‐uniform hypergraph that is not k‐colorable. We give a new lower bound on m(r, k) for fixed k and large r. Namely, we prove that if k ≥ 2n, then m(r, k) ≥ ϵ(k)kr(r/ln r)n/(n+1). © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
Impact of avoidance angle mitigation techniques on the interference produced by non‐GSO systems in a multiple non‐GSO interference environment
Authors: Fortes José Mauro P. , Sampaio‐Neto Raimundo
Published: December 2003

This paper adresses the impact of avoidance angle mitigation techniques on the interference produced by non‐GSO systems in a multiple non‐GSO interference environment. It considers a situation involving a victim LEO system and two other non‐GSO interfering systems (one MEO and another LEO) that mitigate around (and only around) the victim LEO system. Interference statistics are obtained using the so called Analytical Method for non‐GSO interference computations. The methodology described, including the interference model adopted, and the type of result obtained in Section 3, that shows the variation of the percentage of the total time allowance used by the interference as a function of the Earth station‐based and the satellite‐based avoidance angles, are very helpful in the process of selecting adequate values for these angles. The burden imposed on the mitigating systems by the use of avoidance angle strategies was evaluated through its impact on the coverage capability of the mitigating systems. Copyright © 2003 John Wiley & Sons, Ltd.
Median regression for longitudinal data
Authors: He Xuming , Fu Bo , Fung Wing K.
Published: December 2003

We review and compare three estimators of median regression in linear models with longitudinal data. The estimators are constructed based on well‐known ideas of weighting, decorrelating, and the working assumption of independence. Both asymptotic efficiency calculations and finite‐sample Monte Carlo studies are used to assess the performance of these estimators. We find that their relative performances depend on the nature of covariates. The estimator under the working assumption of independence is computationally simple and yet has good relative performance when the covariates are invariant over time or when the within‐subject correlations are small. Its relative performance in finite samples is also found to be more favourable than suggested by the asymptotic comparisons. Copyright © 2003 John Wiley & Sons, Ltd.
Comparing Cox and parametric models in clinical studies
Authors: Nardi Alessandra , Schemper Michael
Published: December 2003

Parametric models are only occasionally used in the analysis of clinical studies of survival although they may offer advantages over Cox's model. In this paper, we report experiences that we have made fitting parametric models to data sets from different clinical trials mainly performed at the Vienna University Medical School. We emphasize the role of residuals for discriminating among candidate models and judging their goodness of fit. The effect of misspecification of the baseline distribution on parameter estimates and testing has been explored. The results from parametric analyses have always been contrasted with those from Cox's model. Copyright © 2003 John Wiley & Sons, Ltd.
Simulating global software evolution processes by combining simple models: an initial study
Authors: Wernick Paul , Hall Tracy
Published: December 2003

A number of studies of the long‐term evolution of commercial software products over many releases have established a consistent pattern for growth in the size of the systems examined. This shows a trend towards a progressive slowdown in growth over time. The work described here forms the first step in developing a simulation of the combined effects of the causes of this trend. A number of simple system dynamics simulations, each capturing the causal structure and behaviour of one of a number of causes believed to contribute to the observed behaviour, and its calibration to follow the observed trend, is presented. These models are then combined into a single simulation model reflecting the effect in combination of these causes. Possible causes considered here are: the reduction over time in both the conceptual space which can be searched for new uses of a system and the design spaces constraining developers' ability to modify their systems, the effects of the degradation of the structure of a software system as is it is evolved in unanticipated directions, and the reducing coverage of developers' knowledge of the structure of the system. The combined model incorporates all of these causal mechanisms and introduces a relative weighting for each. The long‐term aim of this work is to produce a simulation embodying those possible causes which are found to be supported by actual evidence. Calibration of this model to reflect the relative importance of each cause in a real‐world situation should then enable it to reproduce the actual software system size trend, so assisting in identifying those causes which affect most significantly the growth trend of that system. Copyright © 2003 John Wiley & Sons, Ltd.
Improved verification of linear‐time properties within fairness: weakly continuation‐closed behaviour abstractions computed from trace reductions
Authors: Ultes‐Nitsche Ulrich , St James Simon
Published: December 2003

The satisfaction of linear‐time temporal properties within fairness introduces an implicit fairness constraint to the verification process. To be applied to practical verification tasks, weakly continuation‐closed abstractions preserve properties satisfied within fairness. Being defined on the complete behaviour of a distributed system, weakly continuation‐closed abstractions require, in principle, an exhaustive state space construction prior to abstraction. Constructing the state space of a practically relevant specification exhaustively, however, is usually not feasible.

Based on the notion of traces, i.e. certain equivalence classes of behaviours, trace reductions are defined in this paper. Trace reduction is a particular partial‐order reduction based on the persistent‐set selective search technique. It is shown that a trace reduction can be used on behalf of the complete behaviour of a distributed system in order to compute abstractions as well as to check whether the abstractions are weakly continuation closed. Thus, trace reductions allow one, in the discussed context, to overcome the requirement of an exhaustive state‐space construction prior to abstraction. Copyright © 2003 John Wiley & Sons, Ltd.
Pushing to the edge: Rutgers astrophysics institute motivates talented high school students
Authors: Etkina Eugenia , Matilsky Terry , Lawrence Michael
Published: December 2003

The Rutgers Astrophysics Institute is a program in which gifted high school students learn about contemporary science and its methods, and conduct independent authentic research using real‐time data. The students use the processes of science to acquire knowledge, and serve as cognitive apprentices to an expert astrophysicist. A variety of naturalistic and statistical methods were employed to gather data concerning various changes in the students as a result of their participation in the institute. Specifically, we concluded that students were able to (a) distinguish between observational data and models, devise testing experiments, and reflect on the analysis and the interpretation of X‐ray data; (b) achieve results comparable to those of regular Advanced Placement (AP) students on individual AP exam problems (the students had not taken AP Physics), (c) engage in elements of meaningful authentic research, and (d) change their approaches toward learning science. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 958–985, 2003
Teaching elements of nature of science: A yearlong case study of a fourth‐grade teacher
Authors: Akerson Valarie L. , Abd‐El‐Khalick Fouad
Published: December 2003

This study examined and supported the efforts of Tina, an experienced elementary teacher, in helping her fourth graders internalize informed views of the inferential, tentative, and creative nature of science (NOS). Tina held informed views of, and was motivated to teach about, NOS. The study aimed to answer the following question: What specific supports were needed to enable Tina to make the target NOS elements explicit in her teaching? The lead researcher visited Tina's classroom every week and interacted with her on a continuous basis. Data sources included classroom observations and videotapes, teacher NOS questionnaires and associated interviews, teacher–researcher communications, and teacher and researcher logs. Although Tina's understandings and intentions were necessary to enable her to teach about NOS, they were not sufficient. Tina needed support to translate her NOS views and intentions into pedagogically appropriate instructional activities that would make the target NOS aspects accessible to her students. Socially mediated support was needed at the personal level in terms of helping Tina activate her tacit NOS understandings, and at the professional level in terms of modeling explicit NOS instruction in Tina's own classroom by the lead researcher. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1025–1049, 2003
Progressive inquiry in a computer‐supported biology class
Authors: Hakkarainen Kai
Published: December 2003

The problem addressed in the study was whether 10‐ and 11‐year‐old children, collaborating within a computer‐supported classroom, could engage in progressive inquiry that exhibits an essential principal feature of mature scientific inquiry: namely, engagement in increasingly deep levels of explanation. Technical infrastructure for the study was provided by the Computer‐Supported Intentional Learning Environment (CSILE). The study was carried out by qualitatively analyzing written notes logged by 28 Grade 5/6 students to CSILE's database. Results of the study indicated that with teacher guidance, students were able to produce meaningful intuitive explanations about biological phenomena, guide this process by pursuing their own research questions, and engage in constructive peer interaction that helped them go beyond their intuitive explanations and toward theoretical scientific explanations. Expert evaluations by three widely recognized philosophers of science confirmed the progressive nature of students' inquiry. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1072–1088, 2003
Prevalence, function, and structure of photographs in high school biology textbooks
Authors: Leivas Pozzer Lilian , Roth Wolff‐Michael
Published: December 2003

Photographs are a major aspect of high school science textbooks, which dominate classroom approaches to teaching and learning. It is thus surprising that the function of photographs and their relation to captions and texts have not been the topic of analysis. The purpose of this study was to investigate the prevalence, function, and structure of photographs in high school science. Our motivating research question was, “What can students learn from textbooks when they study photographs?” To answer this and several subordinate questions, we selected and analyzed four Brazilian biology textbooks. We focus on the use of photographs and the relation among them, various types of texts, and the subject matter presented. Our analysis reveals that the structural elements of text, caption, and photographs and the relations among them differ across the textbooks and at times even within the same book. This, of course, will influence readers' interpretations of the photographs changing their role in the text. The results of our study have implications for textbook authors and textbook readers. We suggest that future studies may focus on students' and teachers' interpretation of photographs in real time. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1089–1114, 2003
Adapting an immersive virtual reality system for rehabilitation
Authors: Kizony Rachel , Katz Noomi , (Tamar) Weiss Patrice L.
Published: December 2003

The purpose of this paper is to present an overview of the adaptations that have been done to VividGroup's Gesture Xtreme projected VR scenarios in order to facilitate their use in neurological rehabilitation. First, the scenarios and the adaptation (control of the type, speed, location and direction of all stimuli) are briefly described. The advantages and limitations of the adapted VR system as a rehabilitation tool are presented. Next, initial results and two examples of case studies, one a patient following stroke and one who requires balance training as a result of complete spinal cord injury, are used to illustrate applications of this VR system to rehabilitation. Copyright © 2003 John Wiley & Sons, Ltd.
Medium access control protocols for wireless mobile ad hoc networks: issues and approaches
Authors: Issariyakul Teerawat , Hossain Ekram , In Kim Dong
Published: December 2003

In this article, a comprehensive survey of the medium access control (MAC) approaches for wireless mobile ad hoc networks is presented. The complexity in MAC design for wireless ad hoc networks arises due to node mobility, radio link vulnerability and the lack of central coordination. A series of studies on MAC design has been conducted in the literature to improve medium access performance in different aspects as identified by the different performance metrics. Tradeoffs among the different performance metrics (such as between throughput and fairness) dictate the design of a suitable MAC protocol. We compare the different proposed MAC approaches, identify their problems and discuss the possible remedies. The interactions among the MAC and the higher layer protocols such as routing and transport layer protocols are discussed and some interesting research issues are also identified. Copyright © 2003 John Wiley & Sons, Ltd.
Ultra‐wideband wireless communications
Authors: Zhuang Weihua , Shen Xuemin (Sherman) , Bi Qi
Published: December 2003

Ultra‐wideband (UWB) communication techniques have attracted a great interest in both academia and industry in the past few years for applications in short‐range wireless mobile systems. This is due to the potential advantages of UWB transmissions such as low power, high rate, immunity to multipath propagation, less complex transceiver hardware, and low interference. However, tremendous R&D efforts are required to face various technical challenges in developing UWB wireless systems, including UWB channel characterization, transceiver design, coexistence and interworking with other narrowband wireless systems, design of the link and network layers to benefit from UWB transmission characteristics. This paper is to provide an overview of UWB communications, summarize the previous research results, and identify further research issues that need to be tackled. The emphasis is placed on the commercial wireless communications. Copyright © 2003 John Wiley & Sons, Ltd.
Isotropic air‐interface technologies for fourth generation wireless communications
Authors: Chen Hsiao‐Hwa , Lin Jin‐Xiao , Chu Shin‐Wei , Wu Chi‐Feng , Chen Guo‐Sheng
Published: December 2003

To implement 4G wireless that should deliver a much higher data‐rate than that possible in the current 3G systems, development of innovative air‐link technologies is the key. This article reviews our on‐going research activities in the design of ‘isotropic air‐interface technologies’ capable of substantially improving air‐link performance of a CDMA wireless system. To enable bidirectional high‐speed data transmission in the future 4G systems, the problem associated with incompatible up‐ and down‐link performance in 2–3G systems has to be addressed. The importance of the issue becomes even more evident due to the fact that the future wireless needs to support ‘mobile server’ applications, where a mobile terminal may act as a data source such that up‐link traffic can possibly exceed that in down‐link. In this article, two alternative methods enabling isotropic air‐interface will be discussed, either using ‘isotropic spreading techniques’ that ensure a homogeneous link‐performance regardless of its operation mode (synchronous or asynchronous), or relying on a precision up‐link synchronization control techniques to pave a way for successful application of orthogonal codes in up‐link channels, which otherwise are asynchronous and destroy the ‘orthogonality’ amongst the codes. The isotropic spreading techniques can minimize multiple access interference (MAI) and multipath‐interference (MI), the prevalent impairing effects in the current 2–3G systems. This article will introduce a promising complete complementary CC/DS‐CDMA scheme based on isotropic spreading techniques, which carries several extremely attractive properties such as MAI‐free, MI‐free, near–far effect resistance and low hardware complexity. The performance of the proposed CC/DS‐CDMA scheme is limited only by noise. To implement up‐link synchronization control, smart antenna and GPS‐based techniques play an important role and a working example based on TD‐SCDMA standard will be illustrated. Finally, we will also discuss the TDD techniques and its significance to implement isotropic air‐interface technologies for the future 4G systems. Copyright © 2003 John Wiley & Sons, Ltd.
The future evolution of wireless mobile communications
Authors: Bi Qi , Seymour James
Published: December 2003

At the start of the 21st century, wireless mobile communications has witnessed an unprecedented growth fueled by information explosion and technology revolution. After much fierce technology competitions and uncertainties, two third‐generation (3G) wideband standards have emerged to dominate the wireless mobile communications for years to come. They are the CDMA2000 [1] and the universal mobile terrestrial system (UMTS) [2] standards, both of which are based on code‐division multiple‐access (CDMA) technology. In this paper, we shall indicate how current 2G digital wireless systems might evolve into these 3G systems. We shall examine the likely innovative techniques to be adopted for further evolution of the two systems and the possible capacity gains obtainable by utilizing these techniques. Copyright © 2003 John Wiley & Sons, Ltd.
Downlink radio resource optimization in wide‐band CDMA systems
Authors: Chen Yue , Cuthbert Laurie
Published: December 2003

Soft handover is analysed and optimized in the downlink direction of a WCDMA system in this paper. Downlink is chosen because the asymmetric nature of most new services supported by the next generation of mobile networks requires more capacity in that direction, and so this is likely to be the limiting factor. The study also sets out to resolve the often controversial opinions about the system level performance with soft handover in the downlink direction. Here, the performance of soft handover is investigated on the link level and on the system level separately. Apart from power control, the cell‐selection scheme and power limits (which are ignored by most of the previous work in the literature) are also included. Results show that from the point of view of link quality, soft handover can prevent the downlink traffic channel power going beyond the power limit. From the system level point of view, the downlink capacity can be increased by choosing a proper soft handover overhead. The optimum value of the overhead depends closely on the cell‐selection threshold and the radio environment. The paper proves that soft handover is an effective way for interference‐reduction and radio resource optimization in the downlink direction for WCDMA systems. Copyright © 2003 John Wiley & Sons, Ltd.
Reverse link capacity of SIR‐based power‐controlled CDMA systems with antenna arrays
Authors: Yu Jin , Yao Yu‐Dong
Published: December 2003

In this paper, reverse link capacity, in terms of user capacity, of a code‐division multiple access (CDMA) system with both beamforming and antenna diversity under a multipath environment is analyzed and compared. Signal‐to‐interference ratio (SIR) based power control is assumed in the system. Antenna elements are divided into several groups to achieve antenna diversity gain. Antenna elements in a group are closely spaced to perform beamforming in order to suppress the own‐cell and other‐cell interference, while those groups are widely spaced to achieve the diversity gain. Based on the comparison, a most efficient use of the antenna array according to the distribution of antenna elements among the groups is obtained. Instead of using tedious iterative methods to evaluate user capacity, a simple closed‐form capacity expression with respect to antenna diversity and beamforming gains, a target SIR and the CDMA processing gain is derived. Numerical results indicate significant capacity improvement with the antenna array. Copyright © 2003 John Wiley & Sons, Ltd.
Spectrum demand for systems beyond IMT‐2000 based on data rate estimates
Authors: Mohr Werner
Published: December 2003

In different regions, research activities on systems beyond third generation mobile communication started already around 1999. The major drivers for these systems are the increasing demand for personal mobile communications with respect to performance, applications, traffic demand and easy to use including communications involving machines. From the user perspective, increasing personal mobility enforces mobile communications in business and the private sector. ITU‐R WP8F, ITU‐T SSG and bodies like WWRF are currently working on the vision of systems beyond IMT‐2000 on global basis in cooperation with the research activities and are defining the basic requirements. New elements of these systems for the mobile access (up to 100 Mbps peak cell capacity) and the nomadic/wireless local area access (up to 1 Gbps peak cell capacity) are being discussed. These requirements result in a huge amount of needed spectrum. In this paper, the impact on spectrum demand for a new mobile broadband access element is investigated with respect to estimated data rate requirements from the user perspective. For that purpose, the radio interface is described in generic form based on a modified Shannon channel capacity formula to obtain generalized results independent of a particular radio interface concept. With the relation between cluster size, carrier/interference‐ratio and coverage requirements the spectrum demand and system throughput is calculated in closed form for the case of a radio interface with fixed and adaptive modulation and coding. The nomadic/wireless local area access according to ITU‐R is not considered here. These investigations are based on simplified system concepts without considering advanced antenna, scheduling and network deployment concepts. Copyright © 2003 John Wiley & Sons, Ltd.
Future mobile broadband wireless networks: a radio resource management perspective
Authors: Periyalwar Shalini , Hashem Bassam , Senarath Gamini , Au Kelvin , Matyas Robert
Published: December 2003

Future wireless evolution envisages high rates, low hierarchy in the network architecture, antenna array processing, multiple access modes and multihop operation as part of the system concept. To exploit the increased capabilities of the systems in conception, efficient resource management strategies need to be developed. The goal of this paper is to examine the key aspects of the evolution which impact radio resource management for the mobile broadband wireless network, and to emphasize the areas that need to be addressed for servicing mobile users with varying quality of service requirements. Copyright © 2003 John Wiley & Sons, Ltd.
Benefits of the control‐hold mode for the support of the forward packet data channel in IS‐2000
Authors: Gholmieh Ralph , Khaleghi Farideh
Published: December 2003

The most recent revisions of the IS‐2000 standards are being designed with the view of maximizing the achievable throughput while maintaining an acceptable Quality‐of‐Service (QoS) for the supported voice and data sessions. Revision C of the IS‐2000 standard is specifically geared towards maximizing the throughput on the forward link. However, this increase in forward link capacity requires adding new reverse link overhead channels thereby decreasing reverse link capacity. This paper describes the Control‐Hold mode designed to reduce the resource usage of reverse link overhead channels. In particular, the focus is on the DV‐control‐hold (DVCH) mode jointly proposed by Ericsson and Nortel for the 1xEVDV standard and adopted as an optional feature in the IS‐2000 standard as part of its Revision C 5. The DV‐control‐hold mode is an intermediary state between the active and dormant modes of a mobile. In this state, a mobile station uses less resources than when active and can also be quickly reactivated (typically in 20 ms). The QoS achieved for mobile stations (MSs) that use the Active‐DVCH‐Dormant state machine is compared to the performance of MSs with regular Active‐Dormant state machines. Simulation results show that the introduction of the DVCH mode increases both, the achievable forward link throughput and the number of admissible mobiles per sector. When the DVCH mode is introduced and for the typical ‘Active‐to‐Dormant’ timer values of 3 and 6 s, the number of admissible sessions per sector increases by 35% and 66% respectively, while the corresponding throughput increases by 14% and 50%. Copyright © 2003 John Wiley & Sons, Ltd.
Linear successive interference cancellation in DS‐CDMA systems
Authors: Berggren Fredrik , Slimane S. Ben
Published: December 2003

Successive interference cancellation techniques have the potential to reduce the interference and therefore increase the capacity of cellular radio systems. In this work, we analyze a linear DS‐CDMA receiver utilizing soft feedback interference cancellation. To be able to meet diverse QoS requirements, we introduce a power control scheme that takes into account heterogeneous service levels as well as the impact of imperfect interference cancellation. We address the capacity resulting from this receiver and give its user capacity region on closed‐form. We show that our results are general and provide a framework for capacity comparison for many proposed linear successive cancellation receiver models. Several receiver modifications are included, partial interference cancellation; when only part of the signal is canceled, and limited cancellation; when not every signal is canceled. We derive the minimum power solution of a single‐cell, from which convergent multicellular distributed power control algorithms that iteratively update the powers are suggested. The numerical results show that there are large gains in user capacity from interference cancellation when theEb/I0requirements are high. However, regardless of the required targets the maximum capacity is always achieved through partial successive interference cancellation. It is also found that the power levels are sensitive to the cancellation efficiency and worse performance than single‐user detection can occur. Copyright © 2003 John Wiley & Sons, Ltd.
Identifying the Effect of Tidal Height on Offshore Wind Speed Profiles
Authors: Khan Demian , Watson Simon J. , Infield David G.
Published: December 2003

The rise and fall of the sea surface due to the tide effectively moves an offshore wind turbine hub through the wind shear profile. Offshore wind farms are being built around the coasts of Europe, including in the Baltic and the North Sea. Tidal ranges in the North Sea are greater than those in the Baltic, and the potential effect on the wind shear profile of the change in sea surface height is likely to be more significant. This article seeks to identify the effect of tidal height on the shear profile at a mast off the east coast of the UK where the maximum tidal range is 7 m. Definite evidence for the effect of tidal height on wind shear is presented, though the effect is small and there is considerable scatter in the data. Copyright © 2003 John Wiley & Sons, Ltd.
Synthese und Kristallstruktur von bis‐1, 3‐Dimethoxyethan‐trichloro‐samarium(III) und tris‐N, N‐Diisopropylcarbamato‐samarium(III)
Authors: Baisch Ulrich , Schnick Wolfgang
Published: December 2003

Das Diisopropylcarbamat von Samarium konnte durch Umsetzung von SmCl3(DME)2 (DME = 1, 2‐Dimethoxyethan) mit Diisopropylamin und gasförmigem CO2 in Toluol in Form hellgelber Einkristalle erhalten werden, die mittels Einkristall‐Röntgenstrukturanalyse untersucht wurden (Sm4(O2CNiPr2)12, C2/c, Z = 4, a = 2914, 2(2); b = 1974, 2(1), c = 2328, 7(2) pm, T = 200 K, R1 = 0, 0345, 15050 unabhängige Reflexe, 590 verfeinerte Parameter). Sm4(O2CNiPr2)12 ist im Festkörper tetramer, dabei ist Samarium auf drei verschiedene Arten von Carbamat‐Liganden koordiniert bzw. von diesen verbrückt. SmCl3(DME)2 wurde aus Sm2O3 und SOCl2 in überschüssigem DME erhalten und kristallisiert in Form farbloser Kristalle (SmCl3(DME)2, P21/c, Z = 4, a = 1160, 8(2); b = 898, 9(2), c = 1572, 9(2) pm, R1 = 0, 0349, 4639 unabhängige Reflexe, 146 verfeinerte Parameter). SmCl3(DME)2 liegt monomer vor, dabei ist Samarium verzerrt pentagonal‐pyramidal von drei Cl sowie zwei DME umgeben.
Mononucleare Oxalamidinkomplexe von Kupfer(I), Palladium(II) und Ruthenium(II) durch gekoppelte Kation‐/Anionkoordination
Authors: Böttcher Lars , Scholz Alexander , Walther Dirk , Weisbach Nancy , Görls Helmar
Published: December 2003

Oxalamidine R1N=C(NHR2)‐C(=NHR2)=NR1 (H2A: R1 = R2 = p‐tolyl; H2B: R1 = R2 = mesityl) reagieren mit [Cu(CH3CN)4] (BF4)/PPh3 unter Bildung der Einkernkomplexe {[(Ph3P)2Cu]AH2(F4B)} (1) und {[(Ph3P)Cu]BH2(F4B)} (2). Die Kristallstrukturanalysen von Einkristallen zeigen, dass CuI an die 1, 4‐Diazadieneinheit koordiniert ist, während Tetrafluoroborat über Wasserstoffbrücken an die 1, 2‐Diamineinheit gebunden ist („gekoppelte Kation‐/Anionkoordination”︁). [(allyl)PdCl]2 reagiert mit H2A zum Allylkomplex [(allyl)PdAH2···Cl2(allyl)Pd] (3). Mit H2B wird die analoge Verbindung 4 gebildet. In diesen Komplexen ist das (allyl)Pd+‐Fragment an den 1, 4‐Diazadienteil des neutralen Oxalamidinliganden koordiniert und das Anion [allylPdCl2]‐ über Wasserstoffbrücken an der gegenüberliegenden 1, 2‐Diaminseite gebunden. Durch analoge gekoppelte Kation‐/Anionkoordination lassen sich auch RuII‐Komplexe, z. B.[(p‐Cymo l)Ru(Cl)CH2···Cl] (6) und [(4, 4′, 4″‐tri‐t‐butyl‐terpyridin)(Cl)RuAH2···Cl] (9) herstellen.
Cyclopentadienyl Complexes of Samarium with Bis(phosphanyl)amides
Authors: Gamer Michael T. , Canseco‐Melchor Graciela , Roesky Peter W.
Published: December 2003

The first heteroleptic bisphosphanylamide complex of the lanthanides, [(η5‐C5Me5)2Sm{η2‐N(PPh2)2}] is reported. [(η5‐C5Me5)2Sm{η2‐N(PPh2)2}] can be obtained by the reaction of the potassium bisphosphanylamide complex, [K(THF)n][N(PPh2)2] (n = 1.25 ‐ 1.5) with [(η5‐C5Me5)2Sm(μ‐Cl)2K(THF)]∞ or in a one‐pot reaction starting from SmCl3 and [K(THF)n][N(PPh2)2] followed by an addition of KC5Me5. Both, [(η5‐C5Me5)2Sm{η2‐N(PPh2)2}] and [(η5‐C5Me5)2Sm(μ‐Cl)2K(THF)]∞ have been characterized by standard analytical/spectroscopic techniques, and their solid‐state structures were established by single crystal X‐ray diffraction.
Erste Dipyridylamide der Selten‐Erd‐Elemente: Neuartige Selten‐Erd‐Stickstoff‐Koordinationen in [Ln(N(C5H4N)2)3]2, Ln = La, Gd, Yb
Authors: Müller‐Buschbaum Klaus
Published: December 2003

Die solvensfreien Reaktionen der Selten‐Erd‐Elemente Lanthan, Gadolinium und Ytterbium mit einer Schmelze von 2‐2′‐Dipyridylamin ergaben farblose bis gelbe, transparente Kristalle der Verbindungen [Ln(N(C5H4N)2)3]2, Ln = La, Gd, Yb. Es handelt sich um die ersten Dipyridylamide der Selten‐Erd‐Elemente. Alle drei Verbindungen sind homoleptisch und zeigen ausschließlich N‐Atome als Koordinationspartner der Selten‐Erd‐Elemente. Neben endständigen, einfach chelatisierenden Dipyridylamid‐Gruppen, verbrücken weitere Amid‐Liganden unter Heranziehen aller drei N‐Atome doppelt chelatisierend. Es bilden sich Dimere ohne Metall‐Metall‐Bindungen. Die stark unterschiedlichen Ionenradien von LaIII, GdIII und YbIII bewirken deutlich unterschiedliche Umgebungen der Selten‐Erd‐Atome, obwohl Bindungstypen und Stöchiometrie gleich sind. Yb und Gd zeigen eine C.N. von acht, La hingegen von zehn N‐Atomen. Deutlich unterschiedliche Kristallstrukturen und IR‐Spektren sind die Folge.
Synthesen und Kristallstrukturen der homöotypen Selenitbromide Bi8(SeO3)9Br6 und CsSm21(SeO3)24Br16
Authors: Ruck Michael , Schmidt Peer
Published: December 2003

Bi8(SeO3)9Br6 wurde auf der Basis thermodynamischer Berechnungen aus BiOBr und SeO2 über eine Autotransportreaktion im Temperaturgradienten von 670 nach 660 K synthetisiert. Kristalle von CsSm21(SeO3)24Br16 entstanden aus der Umsetzung äquimolarer Gemenge von SmOBr und SeO2 im CsBr‐Flux bei 1070 K. Beide Selenitbromide kristallisieren in der orthorhombischen Raumgruppe B2/b 2/a 2/b(Nr. 68) mit pseudo‐tetragonaler Gittermetrik (Bi8(SeO3)9Br6: a = b = 1588, 4(5), c = 1830, 5(5) pm, Z = 533, 3; CsSm21(SeO3)24Br16: a = b = 1579, 7(2), c = 1796, 3(2) pm, Z = 2). In den Kristallstrukturen sind die Schweratome in quadratischen Netzen organisiert. Die O‐Atome der pyramidalen Selenit‐Gruppen verknüpfen sie zu Schichtpaketen [BiIII21, 33(SeIVO3)24Br16] bzw. [CsSmIII21(SeIVO3)24Br16], die nach [001] gestapelt sind. In CsSm21(SeO3)24Br16 gewährleistet der Ersatz eines SmIII‐Kations pro Formeleinheit durch ein CsIKation die Elektroneutralität; im Fall von Bi8(SeO3)9Br6 = BiIII21, 33(SeIVO3)24Br16 wird die Ladungsbilanz durch Unterbesetzung von Bi‐Atomlagen ausgeglichen. Die Eigensymmetrie der konstituierenden Schichtpakete, welche der quadratischen Schichtgruppe P (4/n) 2/b 2/m entspricht, führt zur Ausbildung pseudo‐meroedrischer Zwillinge nach [110].
The Electronic Structure of Tantalum Oxynitride and the Falsification of α‐TaON
Authors: Lumey Marck‐Willem , Dronskowski Richard
Published: December 2003

We have performed electronic structure calculations from first principles (LDA & GGA, plane waves & muffin‐tin orbitals, pseudopotentials & all‐electron techniques) on the two reported polymorphs of TaON. For the experimentally well‐characterized β‐TaON adopting the baddeleyite structure type, there is excellent agreement between all accessible observables despite the supposedly correlated character of an oxynitride phase. Concerning hexagonal α‐TaON proposed first in 1966, one finds tremendous contradictions between theory and experimentally reported data (molar volume, total energy differences, electronic transport etc.) In combination with the communicated X‐ray diffraction diagram, α‐TaON is considered an erroneous entry in the solid‐state chemical literature that needs to be removed from the crystallographic databases.
GaP5 und InP5: Ungewöhnliche Moleküle eröffnen neue Wege zur Reindarstellung von III/V‐Halbleitermaterialien
Authors: Köppe R. , Steiner J. , Schnöckel H.
Published: December 2003

In Analogie zu η5‐gebundenem Ga(CH)5 werden für isolobale GaP5‐ und InP5‐ Moleküle quantenchemische Rechnungen zur thermodynamischen Stabilität durchgeführt. Auf dieser Basis lassen sich die Zersetzungsgleichgewichte (z. B. GaP5 (g) = GaP(f) + P4 (g)) berechnen. Durch Transportversuche bei hohen Phosphordrücken können diese theoretischen Ergebnisse bestätigt werden, d. h. GaP3 und GaP5 bzw. InP3 und InP5 sind die für GaP und InP transportrelevanten Gasphasenspezies. Diese Ergebnisse aus der Grundlagenforschung ermöglichen es erstmals, die zahlreichen in jüngster Zeit erschienenen Arbeiten über nanoskalige GaP/InP‐Systeme zu verstehen und weitere Anwendungen im Bereich der Abscheidung von reinsten III/V‐Halbleitern zu erschließen.
[{(C2H5)2NH2}2In2Ge2S8] · [(C2H5)2NH]0.25: A Three‐Dimensional Thiogermanate‐Indate Framework Based on the Interconnection of [In2Ge2S6S4/2]2‐ Adamantane‐Like Building Units
Authors: Pitzschke Dragan , Bensch Wolfgang
Published: December 2003

The new compound [{(C2H5)2NH2}2In2Ge2S8] · [(C2H5)2NH]0.25 was synthesized under solvothermal conditions using elemental In, Ge, and S in diethylamine. The title compound crystallizes in the orthorhombic space group Pna21 with a = 12.804(3)Å , b = 17.615(4)Å, c = 13.067(3)Å, V = 2947.2Å3, and Z = 4. The structure consists of (In/Ge)S4 tetrahedra as primary building units and four such tetrahadra are joined via common corners to form [In2Ge2S6S4/2]2‐ adamantane‐like building units. These building units are interconnected yielding a three‐dimensional anionic tetrahedral framework resembling that of cristobalite if the adamantane‐like cages are seen as supertetrahedra. Three types of channels with diameters ranging from 8.2 · 10.3Å to 8.5 · 13.1Å intersect the structure. Charge compensation is achieved by [(C2H5)2NH2]+ cations which are located within the voids of the anionic network. The compound decomposes in two steps yielding In2S3 and Ge as solid residue.
Synthesis and Characterization of the First (1, 2‐Benzenedithiolato)iron(III) Complexes with Tripodal Ligands
Authors: Merkel Michael , Pascaly Matthias , Wieting Michael , Duda Mark , Rompel Annette
Published: December 2003

The reaction of iron(III) perchlorate nonahydrate with the tripodal tetradentate ligand tris[(2‐pyridyl)methyl]amine (tpa) or bis[(2‐pyridyl)methyl][(1‐methylimidazol‐2‐yl)methyl]amine (bpia) and 1, 2‐benzenedithiolate (dtc) yields the iron(III) coordination compounds [Fe(tpa)(dtc)]ClO4·0.25 MeOH (1) and [Fe(bpia)(dtc)]ClO4 (2), respectively. These are the first iron(III) complexes with tripodal ligands and dtc, resulting in a N4S2 coordination environment. The new compounds were isolated and characterized by single crystal X‐ray crystallography as well as spectroscopic methods. Compound 1 crystallizes in the monoclinic space group P21/c (No. 14) with a = 29.636(6), b = 12.502(3), c = 14.390(3)Å, β = 102.19(3)°, V = 5211(2)Å3, Z = 8. Compound 2 crystallizes in the orthorhombic space group P212121 (No. 19) with a = 8.881(2), b = 16.155(3), c = 17.895(4)Å, V = 2567.4(9)Å3, Z = 4. Furthermore the new compound [Fe(tpa)(tcc)](ClO4)·0.25 H2O (3) (where tcc = tetrachlorocatecholate dianion) is presented and compared to the dithiolato complexes. 3 crystallizes in the monoclinic space group P21/c (No. 14) with a = 8.982(1)Å, b = 34.329(6)Å, c = 8.648(1)Å, β = 94.22(1)°, V = 2659.3(6)Å3, Z = 4.
Nicht länger im Dunkeln: Die Kristallstruktur von AuPS4
Authors: Jörgens Stefan , Johrendt Dirk , Mewis Albrecht
Published: December 2003

AuPS4 wurde durch Erhitzen der Elemente auf 600 °C (24h) und anschließendes langsames Abkühlen (10°/h) in Form dunkelrot durchscheinender Kristallnadeln erhalten. Die röntgenographische Untersuchung eines Einkristalls ergab trikline Symmetrie (P1¯; Z = 2) mit a = 5, 891(1), b = 6, 961(1), c = 8, 063(2)Å, α = 78, 18(3)°, β = 87, 59(3)°, γ = 79, 29(3)<°. Die Verbindung besteht aus [AuS4/2PS4/2]‐Ketten, in denen sich nahezu quadratisch planare AuS4‐Einheiten mit PS4‐Tetraedern abwechseln und über gemeinsame Kanten miteinander verknüpft sind. Zwischen den Ketten, die längs [111] verlaufen, sind nur van der Waals Kräfte wirksam, was einen enorm faserigen Kristallhabitus verursacht. Die Bindungsverhältnisse werden mit selbstkonsistenten DFT‐Bandstrukturrechnungen diskutiert.
Catecholate Adducts of Binuclear Copper Complexes Modelling the Type 3 Copper Active Site — Spectroscopic Characterization and Relevance to the Tyrosinase Reaction
Authors: Plenge Tanja , Dillinger Renée , Santagostini Laura , Casella Luigi , Tuczek Felix
Published: December 2003

The p‐nitrochatecholate (NCat) adducts 2 and 4 of the two copper(II) complexes [Cu2(L66)](ClO4)4 (1; L66 = α, α′‐bis{bis[2‐(1′‐methyl‐2′‐benzimidazolyl)ethyl]amino}‐m‐xylene) and [Cu(L6)](ClO4)2 (3; L6 = N, N‐bis[2‐(1′‐methyl‐2′‐benzimidazolyl)ethyl]amine), respectively, have been prepared and investigated by infrared, Raman and electronic absorption spectroscopies. The combined spectroscopic information suggests that the binding mode of p‐nitrocatecholate in 2 and 4 is similar for both adducts although for catecholate complexes of mononuclear Cu complexes like 4 an η2 coordination applies and for binuclear copper sites like 2 an η1:η1 bridging modes has been postulated. In addition a double catecholate adduct of 1, [Cu2(L66)(NCat)2] (5), has been prepared which again shows spectral features similar to 1 and 3. Based on these results it is suggested in all cases catecholate is binding in an η2 mode to one copper atom, eventually exhibiting an additional η1 bridging coordination to a second copper atom. This arrangement also plays an important role in inhibitor complexes of type 3 copper proteins like tyrosinase and catechol oxidase. The relevance of the η1:η2 binding mode of catecholate to the mechanism of the tyrosinase reaction is discussed.
Low Dimensional Arrangements of the Zintl Ion [Ge9‐Ge9]6— and Chemical Bonding in [Ge6]2—, [Ge9‐Ge9]6—, and {[Ge9]}2—
Authors: Hauptmann Ralf , Fässler Thomas F.
Published: December 2003

The compounds [Rb(Benzo‐18‐crown‐6]2Rb4[Ge9‐Ge9](en)6 (1), [Rb(Benzo‐18‐crown‐6]2Rb4[Ge9‐Ge9](en)4 (2), [K(18‐crown‐6)]2K4[Ge9‐Ge9](en)2 (3), and [K(18‐crown‐6)]3Cs3[Ge9‐Ge9](en)2 (4) have been synthesized by dissolving the phases of the formal composition LiRb3Ge9, NaRb3Ge9, K4Ge9, and K2Cs2Ge9, respectively, in ethylenediamine followed by the addition of the crown ethers under consideration. All four compounds contain a dimeric [Ge9‐Ge9]6— unit. Whereas the [Ge9‐Ge9]6— units in 1, 2 and 3 are connected via the alkali metal atoms to infinite chains of the composition {A6[Ge9‐Ge9]} (A = K or Rb) the connection via the Cs atoms in 4 leads to layers of the composition {K2Cs3[Ge9‐Ge9]}1—. The increased number of dimers, which is now available, establishes the distortion of the clusters: The [Ge9] clusters have the shape of a monocapped quadratic anti prism, which is compressed along one of the diagonal of the open rectangle. In each compound two idealized C2v symmetric [Ge9] clusters are connected via an exo‐bond between two Ge atoms of the open rectangle to form a dimeric [Ge9‐Ge9]6— anion. In all cases the exo‐bond is oriented collinear to the shorter diagonal. Thus the square of the open rectangle of the cluster is compressed along the exo bond. The exo‐bond lenghts are in the range of 2.471Å and 2.521Å.

The analysis of the results of an Extended Hückel calculation using the electron localization function (ELF) reveals that a localized two‐centre‐two‐electron bond connects the clusters of the dimeric unit. The results are compared to the ELF of an octahedral [Ge6]2— cluster and of the polymer {[Ge9]}2—.
In‐vitro Crystallization of Calcium Carbonate in the Presence of Biological Additives — Comparison of the Ammonium Carbonate Method with Double‐Diffusion Techniques
Authors: Becker Alexander , Becker Wilhelm , Marxen Julia C. , Epple Matthias
Published: December 2003

The biomineralization process was simulated in vitro by the precipitation of calcium carbonate in the presence of two biological additives: bovine serum albumin (BSA) and soluble matrix from the shell of the freshwater snail Biomphalaria glabrata. The crystallization was carried out with the classical ammonium carbonate diffusion method and with a double diffusion setup under pH‐controlled conditions. The inhibiting effects of BSA and soluble shell matrix could only be observed in the double diffusion setup, but not with the ammonium carbonate method.
Synthesen und Kristallstrukturen neuer heterobimetallischer Niob‐Kupfer‐Chalkogen‐Cluster
Authors: Feuerhake Robert , Fenske Dieter
Published: December 2003

Die Reaktion des Thioniobates (NEt4)4[Nb6S17]·3MeCN mit Kupfersalzen CuX (X = Cl, OAc) führt in Anwesenheit tertiärer Alkylphosphane zu Niob‐Kupfer‐Sulfido‐ oder Niob‐Kupfer‐Selenido‐ Clustern 1—3, deren Strukturmotive schon aus derKoordinationschemie der Thiometallate elektronenarmer Übergangsmetalle bekannt sind.

Bei der direkten Umsetzung von NbCl5 und CuCl mit Se(R)SiMe3 (R = Ph, SiMe3) in Anwesenheit von Phosphanen entstehen dagegen Koordinationsverbindungen des Tetraselenoniobat‐Anions 4—7.

Mit Hilfe der Einkristall‐Strukturanalyse konnten die Strukturen folgender Verbindungen aufgeklärt werden: [NbCu3S4(PEt3)3] (1), [Nb3Cu9Cl4OS9(PEt3)9] (2), (NEt4)[Nb2Cu6Cl5S6(PPh3)6] (3), [NbCu3Se4(PEt3)4] (4), [NbCu5Cl2Se4(PEt3)5] (5), [NbCu6Cl3Se4(PiPr3)6] (6) und [NbCu2(SePh)6(PEt3)2] (7).
Über Münzmetall‐Quecksilber‐Chalkogenidhalogenide. III Zur Kristallstruktur von Ag2HgSI2
Authors: Keller Hans‐Lothar , Wimbert Lars
Published: December 2003

Ag2HgSI2 wird aus AgI und α‐HgS durch Umsetzung bei 120 °C in mikrokristalliner Form als gelbes Pulver erhalten. Die Substanz kristallisiert im Raumgruppentyp Cmc21 mit a = 1384, 35(6) pm, b = 746, 97(3) pm, c = 710, 29(3) pm und Z = 4. Die Struktur besteht aus einer verzerrt hexagonal dichtesten Packung von Schwefel‐ und Iodatomen, in der Quecksilber ein Drittel der Oktaederlücken und Silber ein Drittel der Tetraederlücken besetzt. Die Verzerrung der hexagonalen Struktur wird durch den Platzbedarf der freien Elektronenpaare am Schwefel und Iod hervorgerufen, was durch die Berechnung der Elektronenlokalisierungsfunktion (ELF) gezeigt werden konnte.