bluuebunny/crossref_metadata_2025 huggingface dataset:
Multivariate longitudinal models for complex change processes
Authors: Beckett L. A. , Tancredi D. J. , Wilson R. S.
Published: January 2004

Longitudinal studies offer us an opportunity to develop detailed descriptions of the process of growth and development or of the course of progression of chronic diseases. Most longitudinal analyses focus on characterizing change over time in a single outcome variable and identifying predictors of growth or decline. Both growth and degenerative diseases, however, are complex processes with multiple markers of change, so that it may be important to model more than one outcome measure and to understand their relationship over time. We consider random effects models for the association between the trajectories of two outcomes over time, and then compare their properties to approaches based on separate ordinary least‐squares estimates of change. We then illustrate with an example from the Religious Orders Study, a longitudinal cohort study of more than 900 members of Catholic religious orders who have had up to eight annual clinical examinations. Copyright © 2004 John Wiley & Sons, Ltd.
Test bias in a cognitive test: differential item functioning in the CASI
Authors: Crane Paul K. , Belle Gerald van , Larson Eric B.
Published: January 2004

Assessment of test bias is important to establish the construct validity of tests. Assessment of differential item functioning (DIF) is an important first step in this process. DIF is present when examinees from different groups have differing probabilities of success on an item, after controlling for overall ability level. Here, we present analysis of DIF in the Cognitive Assessment Screening Instrument (CASI) using data from a large cohort study of elderly adults. We developed an ordinal logistic regression modelling technique to assess test items for DIF. Estimates of cognitive ability were obtained in two ways based on responses to CASI items: using traditional CASI scoring according to the original test instructions as well as using item response theory (IRT) scoring. Several demographic characteristics were examined for potential DIF, including ethnicity and gender (entered into the model as dichotomous variables), and years of education and age (entered as continuous variables). We found that a disappointingly large number of items had DIF with respect to at least one of these demographic variables. More items were found to have DIF with traditional CASI scoring than with IRT scoring. This study demonstrates a powerful technique for the evaluation of DIF in psychometric tests. The finding that so many CASI items had DIF suggests that previous findings of differences between groups in cognitive functioning as measured by the CASI may be due to biased test items rather than true differences between groups. The finding that IRT scoring diminished the impact of DIF is discussed. Some preliminary suggestions for how to deal with items found to have DIF in cognitive tests are made. The advantages of the DIF detection techniques we developed are discussed in relation to other techniques for the evaluation of DIF. Copyright © 2004 John Wiley & Sons, Ltd.
Reconsidering the odds ratio as a measure of 2×2 association in a population
Authors: Kraemer Helena Chmura
Published: January 2004

The odds ratio (OR) is probably the most widely used measure of 2×2 association in epidemiology, but it often produces results that are puzzling or misleading. Receiver operating characteristic (ROC) methods are used to take a fresh look at the OR and show where and why such puzzling results arise. When researchers choose to report a summary measure of association, the OR is one of many measures of association that might be considered, not one that should be considered the ‘gold standard’ of 2×2 measures of association. In a randomized clinical trial with binary outcome for success, either the success or failure rates in treatment and control groups might be reported separately or the number needed to treat to achieve one extra success, to emphasize the cost of unnecessary treatment needed to achieve a success. In studies assessing reliability or heritability, we recommend the intraclass kappa. In studies in which one binary variable is assessed against a binary criterion, we recommend the weighted kappa. Copyright © 2004 John Wiley & Sons, Ltd.
Selecting pre‐screening items for early intervention trials of dementia—a case study
Authors: Li Lang , Huang Jeffrey , Sun Sharon , Shen Jianzhao , Unverzagt Frederick W. , Gao Sujuan , Hendrie Hugh H. , Hall Kathleen , Hui Siu L.
Published: January 2004

Our goal was to review and extend statistical methods for discriminating between normal subjects and those with dementia or cognitive impairment. We compared six different methods to one constructed by expert opinion, in their brevity and predictive power. The methods include logistic regression and neural networks, with standard and least absolute shrinkage and selection operator (LASSO) variable selection, as well as decision trees with and without boosting. These methods were applied to the baseline data of a subgroup of subjects in a dementia study, using their screening interview items to predict their clinical diagnosis of normal or non‐normal (cognitively impaired or demented). The derived models were then validated on a different subgroup of subjects in the same study who had the screening and clinical diagnosis two to five years later. Performance of different models was compared based on their sensitivity and specificity in the validation sample. Generally, the six statistical methods performed slightly to moderately better than the expert‐opinion model. Neural networks generally performed better than the logistic and decision tree models. LASSO improved the performance of logistic and neural network models, but it eliminated few input variables in the neural network. The single decision tree performed at least as well as the standard logistic model, and with fewer items, making it an attractive pre‐screening tool. Using the boosting option for decision trees did not substantially improve the performance. We recommend that for each situation, different methods of classification should be attempted to obtain optimal results for a given purpose. Copyright © 2004 John Wiley & Sons, Ltd.
Designing a large prevention trial: statistical issues
Authors: Kryscio Richard J. , Mendiondo Marta S. , Schmitt Frederick A. , Markesbery William R.
Published: January 2004

Recent research in Alzheimer's disease (AD) is centred about the early detection and prevention of this disease. Several recent moderate size clinical trials targeted at high risk cohorts have been designed along this theme. There have been few attempts to design a large trial to prevent this disease in elderly individuals at low risk for the disease. The purpose of this paper is to suggest a framework for designing a simple, large AD prevention trial. This framework uses a discrete time hazard model for decreasing the incidence of AD when participants are randomly assigned to one or more active prevention agents or placebo. This design allows for differential incidence among participants due to age, family history, genetic disposition, and ethnicity. It takes into account the length of the follow‐up period, participant mortality, drop‐outs, drop‐ins, and loss to follow‐up. This framework is illustrated by PREADVISE, a recently initiated large add‐on prevention trial investigating the use of anti‐oxidants for preventing AD among men enrolled in a even larger prostate cancer prevention study, SELECT. Copyright © 2004 John Wiley & Sons, Ltd.
Analytical, practical and regulatory issues in prevention studies
Authors: Ellenberg Susan S.
Published: January 2004

Prevention studies, as distinguished from studies investigating treatments for established disease, present some distinct challenges. Perhaps the most extensive experience with preventive agents is in the area of infectious diseases; vaccines have been extremely effective in preventing many such diseases. Vaccines have been, and continue to be, studied in other disease areas such as certain cancers, but as yet have not achieved success outside of infectious disease prevention. One obvious and important feature of prevention studies is that they enrol healthy individuals; thus such studies require particularly high standards for the safety of those enrolled (and those who might ultimately receive the product being tested). Prevention studies often need to be quite large, as the types of diseases most important to prevent tend to be uncommon. Large studies usually require simplified approaches; to ensure high quality of data on the key variables it may be necessary to compromise on the amount of data collected, frequency of data collection, and other aspects of trial design. The reliability of randomization and blinding may be especially important in these large studies, as bias could easily overwhelm the small effects that are usually sought. Often, biomarkers thought to indicate developing but as yet subclinical disease, will be important to evaluate; whether such markers can serve as primary endpoints in prevention studies has been a contentious issue in many contexts. Studies in older populations, such as those at risk for Alzheimer's Disease, raise challenges such as accounting for competing risks, and considering potential interactions of preventive agents with multiple medications often used by the elderly. Published in 2004 by John Wiley & Sons, Ltd.
The evaluation of disease modifying therapies in Alzheimer's disease: a regulatory viewpoint
Authors: Mani Ranjit B.
Published: January 2004

Several drugs have received marketing approval in this country for the treatment of dementia of the Alzheimer's type. Their approval has been based on clinical trial designs that do not permit a distinction to be made between an effect of the drug on the symptoms of that disease, and an effect on the pathophysiological mechanisms that underlie that disorder. The latter effect has been referred to as ‘disease‐modifying.’

In recent years there has been considerable interest in developing disease‐modifying treatments for Alzheimer's disease (AD), using either specific clinical designs, or surrogate markers, such as brain imaging modalities. This paper outlines the regulatory framework governing how the Food and Drug Administration addresses new drug claims, the current basis for approving drugs for the treatment of AD, clinical trial designs that have been proposed as a means of demonstrating disease‐modifying effects, a general and regulatory background to the use of surrogate markers in drug development, and, finally, views about the possible role of surrogate markers, especially brain imaging, as outcome measures in clinical trials intended to produce disease‐modifying effects in Alzheimer's Disease. Copyright © 2004 John Wiley & Sons, Ltd.
A comparison of classification methods for differentiating fronto‐temporal dementia from Alzheimer's disease using FDG‐PET imaging
Authors: Higdon Roger , Foster Norman L. , Koeppe Robert A. , DeCarli Charles S. , Jagust William J. , Clark Christopher M. , Barbas Nancy R. , Arnold Steven E. , Turner R. Scott , Heidebrink Judith L. , Minoshima Satoshi
Published: January 2004

Flurodeoxyglucose positron emission tomography (FDG‐PET) is being explored to determine its ability to differentiate between a diagnosis of Alzheimer's disease (AD) and fronto‐temporal dementia (FTD). We have examined statistical discrimination procedures to help achieve this purpose and compared the results to visual ratings of FDG‐PET images. The methods are applied to a data set of 48 subjects with autopsy confirmed diagnoses of AD or FTD (these subjects come from a multi‐centre collaborative study funded by the National Alzheimer's Coordinating Center). FDG‐PET images are composed of thousands of voxels (volume elements) so one is left with a situation where there are vastly more variables than subjects. Therefore, it is necessary to perform a data reduction before a statistical procedure can be applied. Approaches using both the entire image and summary statistics calculated on a number of volumes of interest (VOI) are examined. We performed the data reduction techniques of principal components analysis (PCA) and partial least‐squares (PLS) on the entire image and then used linear discriminant analysis (LDA), quadratic (QDA) or logistic regression (LR) to classify subjects as having AD or FTD. Some of these methods achieve diagnostic accuracy (as assessed by leave‐one‐out cross‐validation) that is similar to visual ratings by expert raters. Methods using PLS appear to be more successful. Averaging or using VOI data may also be helpful. Copyright © 2004 John Wiley & Sons, Ltd.
Two macroscopic and microscopic brain imaging studies of human hippocampus in early Alzheimer's disease and schizophrenia research
Authors: Lange Nicholas , Lake Stephen , Sperling Reisa , Brown John , Routledge Carol , Albert Marilyn , Heckers Stephan
Published: January 2004

Among the many diseases that affect the hippocampus, a small yet highly important brain region responsible for memory and identity, Alzheimer's disease and schizophrenia are among the most devastating. We describe a two‐stage, region‐of‐interest based linear mixed model approach to the analysis of a longitudinal functional magnetic resonance (FMRI) study of human memory function under several drug challenges. We then describe a Monte Carlo approach to testing members of nested hierarchies of linear models in a stereological study of different types and locations of human hippocampal neurons. Last, we attempt to draw the attention of the biostatistical community interested in imaging neuroscience to the intriguing complexities of human hippocampal research in early Alzheimer's disease, schizophrenia and other brain diseases via brain imaging methods. Copyright © 2004 John Wiley & Sons, Ltd.
Managing and analysing data from a large‐scale study on Framingham Offspring relating brain structure to cognitive function
Authors: Massaro Joseph M. , Srem Ralph B. D'Agostino , Sullivan Lisa M. , Beiser Alexa , DeCarli Charles , Au Rhoda , Elias Merrill F. , Wolf Philip A
Published: January 2004

At the Framingham Heart Study under separate research grant funding from the National Institute of Aging, NIH, we are gathering brain structure and cognitive information on the Framingham Offspring, creating one of the largest known data sets to assess changes in brain structure associated with normative ageing and cognitive decline. Subject recruitment, data collection, data management and statistical analysis require a collaborative integrated effort on the part of the Framingham project team. Here we describe this effort, as well as the various brain structure and cognitive function parameters we are now collecting. We are currently performing analyses of data collected through 2002, and we discuss the statistical issues arising relating brain structure parameters to cognitive function. Copyright © 2004 John Wiley & Sons, Ltd.
Global and political strategies in deregulated industries: the asymmetric behaviors of former monopolies
Authors: Bonardi Jean‐Philippe
Published: January 2004

In deregulated industries former monopolies often adopt asymmetric behaviors: these firms impede the entry of foreign competitors in their home market, especially using defensive political strategies, and, at the same time, aggressively develop international strategies in foreign markets. To account for this behavior, I develop a game theoretic model involving three players: the former monopoly, its home government, and the host government of the country into which the firm wants to enter. I show first that there are in fact different asymmetric strategies that former monopolies can use in such a setting, and that a global strategy cannot always be implemented by those firms because of cooperation issues between the two governments. I also study the conditions under which these issues can be solved and show that this can happen only when the firm develops a political strategy that integrates both defensive and offensive activities. Overall, this paper therefore argues that asymmetric strategies are not always adopted to maintain monopoly rents but are also dictated by the nature of the international relationships between the governments involved. Copyright © 2003 John Wiley & Sons, Ltd.
Entry in the presence of dueling options
Authors: Folta Timothy B. , O'Brien Jonathan P.
Published: January 2004

This paper investigates the influence of industry uncertainty on the decision by established firms to enter a new industry. Specifically, we examine the tension between the option to defer, which discourages entry in the presence of uncertainty, and the option to grow, which may encourage entry in the presence of uncertainty when there are early mover advantages. Empirical analysis on data from a broad array of industries revealed that the effect of uncertainty on entry is not monotonic. Our findings are the first to find support for the nonmonotonic effect of uncertainty that has only recently emerged in theoretical treatments of real options theory, and amplify the importance of considering both the option to defer and the option to grow when contemplating entry. Furthermore, we found evidence that the relationship between uncertainty and entry is moderated by: (a) irreversibility, which influences the value of the option to defer; (b) the total value of growth opportunities; and (c) early mover advantages, which magnify the value of growth options. Copyright © 2003 John Wiley & Sons, Ltd.
Strategy and industry effects on profitability: evidence from Greece
Authors: Spanos Yiannis E. , Zaralis George , Lioukas Spyros
Published: January 2004

The present study examines the impact of firm and industry‐specific factors on profitability, using census data on Greek manufacturing. At the firm level, particular attention is given to strategy effects. Based on a modification of Porter's typology, these effects are captured through different forms of both ‘pure’ and ‘hybrid’ strategies. Industry effects are represented using industry concentration, entry barriers, and growth. Hypotheses are developed taking into account both previous research and the particular idiosyncrasies of the national context. The results obtained provide important insights on specific determinants of firm profitability. With respect to strategy, results confirm the hypothesis that hybrid strategies are clearly preferable compared to pure ones. In addition, it was found that the more generic strategy dimensions are included in the strategy mix, the more profitable the strategy is, provided that one of the key ingredients is low cost. Industry‐level effects, although weaker, show strong impact of industry entry barriers. Moreover, the findings suggest that while both sets of factors significantly contribute to firm profitability, firm‐specific factors explain more than twice as much profit variability as industry factors. Copyright © 2003 John Wiley & Sons, Ltd.
Sorting things out: valuation of new firms in uncertain markets
Authors: Sanders Wm. Gerard , Boivie Steven
Published: January 2004

New business models combined with a lack of objective operating data result in significant information asymmetry and uncertainty in the valuation of new firms in emerging markets. Information asymmetry increases the risks of both adverse selection and moral hazard. When traditional differentiators of firm quality are lacking, such as in emerging economic sectors, markets may turn to secondary information sources to filter and sort firms. We investigate the roles played by observable corporate governance characteristics as indirect indicators of new firms' potential qualitative differences. Markets may sort firms based on such characteristics because they are perceived to be correlated with desired but unobservable characteristics and actions and they lower the risks of both adverse selection and moral hazard. Our study of publicly traded U.S. Internet firms found that firm market valuation was strongly associated with corporate governance characteristics (e.g., executive and director stock‐based incentives, institutional and blockholder stock ownership, board structure, and venture capital participation). In addition, firm age moderated how markets used some quality proxies to determine firm valuation during the post‐IPO period. Copyright © 2003 John Wiley & Sons, Ltd.
Meta‐analyses of post‐acquisition performance: indications of unidentified moderators
Authors: King David R. , Dalton Dan R. , Daily Catherine M. , Covin Jeffrey G.
Published: January 2004

Empirical research has not consistently identified antecedents for predicting post‐acquisition performance. We employ meta‐analytic techniques to empirically assess the impact of the most commonly researched antecedent variables on post‐acquisition performance. We find robust results indicating that, on average and across the most commonly studied variables, acquiring firms' performance does not positively change as a function of their acquisition activity, and is negatively affected to a modest extent. More importantly, our results indicate that unidentified variables may explain significant variance in post‐acquisition performance, suggesting the need for additional theory development and changes to M&A research methods. Copyright © 2003 John Wiley & Sons, Ltd.
Synthesis, Crystal Structure and Properties of Rubidium Dihydrogentricyanomelaminate Semihydrate Rb[H2C6N9] · 1/2 H2O
Authors: Jürgens Barbara , Höppe Henning A. , Schnick Wolfgang
Published: January 2004

Rubidium dihydrogentricyanomelaminate semihydrate Rb[H2C6N9] · 1/2 H2O was obtained as colorless rod‐like single crystals from a solution of Rb3[C6N9] · H2O and 0.1 M HCl after water evaporation at room temperature. According to the X‐ray single‐crystal structure determination (Rb[H2C6N9] · 1/2 H2O: C2/c (no. 15), a = 2007.4(3) pm, b = 512.2(1) pm, c = 2168.0(4) pm, β = 111.66(2)°, Z = 8, R1 = 0.059, 2391 independent reflections, 159 parameters) Rb+ and cyclic planar [H2C6N9]— ions as well as hydrate water molecules occur in the crystal. Rb[H2C6N9] · 1/2 H2O was investigated by FTIR and Raman spectroscopy, TG measurements and temperature‐dependent X‐ray powder diffraction. According to the thermoanalytic investigations, dehydration of Rb[H2C6N9] · 1/2 H2O starts above 60 °C and is finished below 250 °C.
Ab Initio High Pressure Investigations of InI
Authors: Becker Daniel , Beck Horst P.
Published: January 2004

The high pressure behaviour of InI is studied by DFT‐calculations and compared with experimental data. The existence of a 5s2 electron pair in In+ represents an unfavourable bonding situation for high symmetry structures because of effective closed shell repulsion. Since cations with a ns2 electron pair are highly polarizable and the electronic situation is more favourable in the low symmetry structure InI prefers a TlI‐type structure at ambient pressure. A pressure induced transition to the more densely packed high symmetry CsCl‐type structure takes place at about 19 GPa according to our calculations.

At ambient pressure the interactions are predominantly ionic. However with increasing pressure the distances between In+ cations in the TlI‐type structure diminish drastically, mainly due to the changing space requirement of the lone electron pair. Apart from ionic interactions further bonding interactions between the In+ cations occur. At elevated pressure the electron localization function (ELF) as well as the band structure diagrams suggest metallic bonding between the In+ within the zigzag chain, i. e. increasing bonding interactions between the In+ cations due to the electron pair and its s‐p‐mixing. At ambient pressure In‐In interactions are rather weak and the space requirement of the lone electron pair mainly determines the characteristic arrangement of the ions. At elevated pressure the In‐In interactions become stronger and stabilise themselves additionally the specific structural arrangement.
Synthese und Kristallstrukturen neuer komplexer Chloride der Lanthanide mit 3, 5‐Dimethylpyridiniumkationen: (3, 5‐Dimethylpyridinium)2[LnCl4(H2O)2]Cl (Ln = La, Pr) und (3, 5‐Dimethylpyridinium)3[TbCl6]
Authors: Hallfeldt Jens , Urland Werner
Published: January 2004

Kristalle der komplexen Chloride (3, 5‐Dimethylpyridinium)2[LaCl4(H2O)2]Cl (1), (3, 5‐Dimethylpyridinium)2[PrCl4(H2O)2]Cl (2) und (3, 5‐Dimethylpyridinium)3[TbCl6] (3) konnten durch Reaktion von LnCl3 · x H2O (Ln = La, Pr, Tb; x = 6‐7) mit 3, 5‐Dimethylpyridiniumchlorid in ethanolisch/butanolischer Lösung dargestellt und die Kristallstrukturen anhand von röntgenographischen Einkristalldaten ermittelt werden.

Die Verbindungen 1 und 2 sind miteinander isotyp und kristallisieren triklin in der Raumgruppe P1¯ (Z = 2). Die 3, 5‐Dimethylpyridiniumionen werden über Wasserstoffbrückenbindungen mit der anionische Teilstruktur bestehend aus Strängen kantenverknüpfter Trigondodekaeder [LnCl4/2Cl2(H2O)2]— und isolierten Chloridionen verknüpft. Die organischen Einheiten sind nach Art eines “π‐stackings” angeordnet.

3 kristallisiert monoklin in der Raumgruppe P21/c (Z = 4). In der Kristallstruktur liegen oktaedrische Koordinationspolyeder der Zusammensetzung [TbCl6]3— vor. Die Oktaeder sind über Wasserstoffbrückenbindungen mit den organischen Kationen zu Strängen parallel [0 0 1] verknüpft.
Bariumstannat‐Pulver durch hydrothermale Synthese und durch Thermolyse von Bariumzinn(IV)‐glykolaten. Synthese und Struktur von [Ba(C2H6O2)4][Sn(C2H4O2)3] und [Ba(C2H6O2)2][Sn(C2H4O2)3]·CH3OH
Authors: Jäger Lothar , Lorenz Volker , Müller Thomas , Abicht Hans‐Peter , Rössel Michael , Görls Helmar
Published: January 2004

Durch hydrothermale sowie mikrowellenassistierte hydrothermale Reaktion von SnO2·aq mit Bariumhydroxid entsteht Ba[Sn(OH)6] (1) in Form stäbchenförmiger Partikel. Verbindung 1 gleicher Morphologie kann auch durch hydrothermale Umsetzung von [Ba(C2H6O2)4][Sn(C2H4O2)3] (3) gewonnen werden. Durch Umsetzung von SnO2·aq mit Ba(OH)2·8H2O in Ethylenglykol erhält man das Glykolat [Ba(C2H6O2)4][Sn(C2H4O2)3] (3), das durch Rekristallisation aus Methanol [Ba(C2H6O2)2][Sn(C2H4O2)3]· CH3OH (4) bildet.

Die Verbindungen 1, 3 und 4 liefern bei unterschiedlichen Temperaturen BaSnO3‐Pulver (2) unterschiedlicher Morphologie; aufgrund der Korngröße der resultierenden Pulver sind die Verbindungen 3 und 4 als Precursor für die Herstellung von Keramiken geeignet.
The Solid Solution MgxIn3—xIr — Formation of the FeGa3 Type up to x = 0.73 and the Cementite Structure with x = 0.92
Authors: Hlukhyy Viktor , Hoffmann Rolf‐Dieter , Pöttgen Rainer
Published: January 2004

Various compounds within the solid solution MgxIn3—xIr (x = 0—0.92) have been prepared from the elements by melting in glassy carbon crucibles in a water‐cooled sample chamber in a high‐frequency furnace. The structures of six single crystals with x = 0.25, 0.58, 0.62, 0.64, 0.71, and 0.73 have been refined from X‐ray diffractometer data. These intermetallics crystallize with the tetragonal FeGa3 structure, space group P42/mnm: a = 700.6(1), c = 709.1(1) pm, wR2 = 0.0397, 296 F2 values, 18 parameters for Mg0.73In2.27Ir. This structure is an intergrowth of AlB2 and >W related slabs. The 4c and 8j indium sites show mixed occupancy with magnesium. For all crystals the 4c site within the cubes has a higher magnesium population. With increasing magnesium content, a switch in the structure type is observed. Mg0.92In2.08Ir adopts the Fe3C structure, space group Pnma: a = 745.5(3), b = 837.7(3), c = 514.2(2) pm, wR2 = 0.0724, 738 F2 values, 25 parameters. The iridium atoms are coordinated by eight (FeGa3 type) and nine (Fe3C type) indium/magnesium atoms in both structure types. The FeGa3 and the Fe3C type both derive from the aristotype U3Si2 as presented by a group‐subgroup scheme.
Die Kristallstrukturen von Hexachalcogeno‐Hypodiphosphaten des Magnesiums und Zinks
Authors: Jörgens Stefan , Mewis Albrecht
Published: January 2004

Es wurden fünf Chalcogeno‐Hypodiphosphate dargestellt und röntgenographisch mit Einkristallmethoden charakterisiert. Mg2P2S6 (C2/m; a = 6, 085(1), b = 10, 560(2), c = 6, 835(1)Å, β = 106, 97(3)°; Z = 2) kristallisiert im Fe2P2S6‐Typ, während Mg2P2Se6 (a = 6, 404(1), c = 20, 194(4)Å) und Zn2P2Se6 (a = 6, 290(3), c = 19, 93(2)Å) den Fe2P2Se6‐Typ (R3; Z = 3) bilden. Ihr Aufbau wird von einer CdCl2‐ bzw. CdI2‐analogen S‐bzw. Se‐Anordnung geprägt, deren Oktaederlücken geordnet zur Hälfte von Mg2+‐ bzw. Zn2+‐Ionen und P2‐Hanteln eingenommen werden. Wird in Mg2P2S6 die Hälfte der Mg2+‐ durch Ag+‐Ionen ersetzt, entsteht mit Ag2MgP2S6 (C2/n; a = 6, 364(1), b = 10, 975(2), c = 13, 999(3)Å, β = 108, 29(3)°; Z = 4) eine Verbindung, bei der die frei gewordenen Oktaeder von Ag+‐Ionen besetzt werden. Diese sind fehlgeordnet, sie befinden sich in zwei Dreieckslücken des Oktaeders bzw. sind etwas aus dieser Position in Richtung der van der Waals Lücken ausgelenkt. Eine analoge Substitution bei Mg2P2Se6 durch K+‐Ionen führt zu K2MgP2Se6 (P21/n; a = 6, 546(1), b = 12, 724(3), c = 7, 599(2)Å, β = 103, 02(3)°; Z = 2) mit einer zu K2FeP2S6 analogen Struktur. Charakteristisches Merkmal sind Ketten von alternierend flächenverknüpften Se‐Oktaedern (Mg‐zentriert) und trigonalen Se‐Antiprismen (P2‐zentriert), die entlang [100] verlaufen und durch K+‐Ionen miteinander verknüpft sind.
Synthese, Kristallstruktur und elektronische Bandstruktur der isotypen Sulfidchloride CuBiSCl2 und AgBiSCl2
Authors: Ruck Michael , Poudeu Poudeu Pierre Ferdinand , Söhnel Tilo
Published: January 2004

Schwarze, plättchenförmige Kristalle von MBiSCl2 (M = Cu, Ag)werden durch thermische Umsetzung äquimolarer Gemenge von MCl und BiSCl erhalten. Aus Röntgenbeugungsuntersuchungen an Pulvern und Einkristallen geht hervor, dass die Verbindungen isotyp im Raumgruppentyp Cmcm kristallisieren (M = Cu/Ag: a = 396, 9(1)/397, 1(1); b = 1278, 6(3)/1371, 2(3); c = 859, 7(2)/882, 4(2) pm). In den Kristallstrukturen sind die BiIII‐Kationen in Form zweifach überdachter trigonaler Prismen durch zwei Sulfid‐ und sechs Chlorid‐Ionen koordiniert. Die Polyeder sind über gemeinsame Flächen und Kanten zu [BiS2/2Cl6/3—]‐Schichten verknüpft. Dazwischen finden sich MI‐Kationen, deren verzerrt oktaedrische Koordination sich in zwei kurze, trans‐ständige M—S Bindungen und vier rund 50 pm längere M—Cl Bindungen gliedert. Nach relativistischen Bandstrukturrechnungen (DFT) ist AgBiSCl2 ein indirekter Halbleiter mit einer Bandlücke von etwa 1, 0 eV.
Präparation, Kristallstruktur, Schwingungsspektren und thermische Analyse von Kupfer‐tetrahydrogen‐decaoxo‐diperiodat‐hexahydrat CuH4I2O10·6H2O
Authors: Botova M. , Nagel R. , Haeuseler H.
Published: January 2004

Kupfer‐tetrahydrogendecaoxodiperiodat‐hexahydrat CuH4I2O10·6H2O wurde durch Kristallisation aus stark saurem Milieu erhalten. In der Struktur der Verbindung ((S.G. P 21/c, Nr.14), Z = 2, a = 1060, 2(2) pm, b = 551, 1(1) pm, c = 1164, 7(2) pm, β = 111, 49(3)°) liegen centrosymmetrische [H4I2O10]2— Anionen in Form kantenverknüpfter Oktaeder vor, die über Wasserstoffbrückenbindungen zwischen den sauren, trans‐ständigen OH‐Gruppen der Anionen zu Schichten verknüpft sind. Die Ramanspektren der Verbindung werden im Bereich der inneren Schwingungen des Periodat‐Anions analysiert. Die Entwässerung von CuH4I2O10·6H2O erfolgt über CuH4I2O10·3H2O zu Cu(H2IO5)2, das sich bei 170 °C zu Cu(IO3)2 zersetzt.
Novel Copper(I)‐Thioantimonates(III): Solvothermal Synthesis, Crystal Structures, Thermal Stability and Magnetic Properties of (C2N2H10)0.5Cu2SbS3, (C3N2H12)0.5Cu2SbS3, and (C4N2H14)0.5Cu2SbS3
Authors: Spetzler Volker , Rijnberk Herme , Näther Christian , Bensch Wolfgang
Published: January 2004

The novel copper(I)‐thioantimonates(III) (enH22+)0.5Cu2SbS3 (I) (en = ethylendiamine), (1, 3‐DAPH22+)0.5Cu2SbS3 (II) (1, 3‐DAP = 1, 3 diaminopropane) and (1, 4‐DABH22+)0.5Cu2SbS3 (III) (1, 4‐DAB = 1, 4‐diaminobutane) were synthesized under solvothermal conditions reacting Sb2S3, CuCl2·2H2O, S with the amines. The compounds crystallize in the monoclinic space group P21/n. The primary building units are a SbS3 trigonal pyramid and two distorted CuS3 units. In the structures the SbS3 pyramid is connected to six CuS3 moieties and every S atom has bonds to one Sb atom and to two Cu atoms. Further interconnection leads to the formation of ten‐membered (10 MR) Cu3Sb2S5 and six‐membered (6 MR) Cu2SbS3 rings. Every 10 MR is condensed to four 10 MR and four 6 MR to form a single layer within the (010) plane. Two such single layers are connected to a double layer thus forming the final [Cu2SbS3]— layered anion. The [CuSbS3]— protonated amines are located between the layers and the interlayer spacing depends on the size and orientation of these amines. Between the Sb atom and one Cu atom a remarkable short distance of about 2.7Å is observed. At elevated temperatures the compounds decompose into CuSbS2 and Cu3SbS4 suggesting a complex redox reaction. Diamagnetic susceptibilities indicate the copper(I) in the metal sulfide frameworks. All three compounds are semiconductors with intermediate band gaps of about 2 eV.
Über Sesquiselenide der Lanthanoide: Einkristalle von Ce2Se3 im C‐, Gd2Se3 im U‐ und Lu2Se3 im Z‐Typ
Authors: Folchnandt Matthias , Schneck Christof , Schleid Thomas
Published: January 2004

Einkristalle von Lanthanoid‐Sesquiseleniden (M2Se3; hier: M = Ce, Gd, Lu) gewinnt man bei der Umsetzung der Elemente (Lanthanoid und Selen) im molaren Verhältnis von 2:3 innerhalb von sieben Tagen bei 850 °C in evakuierten Quarzglasampullen, wenn äquimolare Mengen an NaCl als Flußmittel zugegen sind. Im Falle von Ce2Se3 (a = 897, 74(6) pm) und Gd2Se3 (a = 872, 56(5) pm) entsteht der kubische C‐Typ (I4¯3d, Z = 5, 333) in Form von dunkelroten Perlen, für Lu2Se3 (a = 1125, 1(1); b = 798, 06(8); c = 2387, 7(2) pm) der orthorhombische Z‐Typ (Fddd, Z = 16) als orangegelbe Quader. Bei der Oxidation von Monochlorid‐Hydriden (MClHx bzw. AyMClHx; M = Ce, Gd, Lu; x = 1; A = Li, Na; y = 0, 5) mit Selen werden aus verschweißten Tantal‐Ampullen mit C‐Ce2Se3 und Z‐Lu2Se3 die gleichen Hauptprodukte erhalten, selbst wenn Überschüsse an NaCl bzw. LiCl als Flußmittel zum Einsatz kommen. Im Falle von Gd2Se3 bilden sich dagegen schwarzrote Nadeln vom orthorhombischen U‐Typ (Pnma, Z = 4; a = 1118, 2(1); b = 403, 48(4); c = 1097, 1(1) pm) an Stelle von C‐Gd2Se3. C‐Ce2Se3 kristallisiert gemäß Ce2, 667□0, 333Se4 mit Z = 4 in einer kationendefekten Th3P4‐Struktur (Ce2S3‐Typ) mit Z = 5, 333 für die Formel Ce2Se3. Ce3+ ist hier von acht Se2—‐Anionen trigondodekaedrisch koordiniert. In U‐Gd2Se3 (U2S3‐Typ) liegen zwei kristallographisch unterschiedliche Gd3+‐Kationen mit Koordinationszahlen von 7 (Gd1) bzw. 7+1 (Gd2) und ein‐ bzw. zweifach überkappten trigonalen Prismen als Koordinationspolyedern vor. Auch Z‐Lu2Se3 (Sc2S3‐Typ) weist zwei verschiedene Lu3+‐Kationen auf, die sich jedoch beide in oktaedrischer Sechser‐Koordination der Se2—‐Anionen befinden.
Chemical Bonding and Pressure‐Induced Change of the Electron Configuration of Ytterbium in β‐YbAgGa2
Authors: Schwarz Ulrich , Schmidt Marcus , Gumeniuk Roman , Schnelle Walter , Hanfland Michael , Klementiev Konstantin , Grin Yuri
Published: January 2004

Single‐phase polycrystalline samples of the intermetallic compound β‐YbAgGa2 were synthesized by inductive heating and subsequent annealing for eight weeks at 670 K. Magnetic properties were characterized by susceptibility measurements and indicated intermediate valence of ytterbium at ambient pressure. Angle‐dispersive X‐ray powder diffraction data of orthorhombic β‐YbAgGa2 indicate stability of the phase in the investigated pressure range from 0.1 MPa (ambient pressure) to 19 GPa. The pressure‐induced volume decrease is accompanied by an increase of the effective valence from 2.17 at ambient conditions to 2.71 at 16 GPa as evaluated by X‐ray absorption spectroscopy at the Yb LIII threshold. Analysis of the chemical bonding in β‐YbAgGa2 by integrating the electron density of the polyanion in basins as defined by the electron localization function results in an electron count Yb2.7+[(Ag0.2—)(Ga1(3b)1.0—)(Ga2(4b)1.5—)]. This finding is close to the expected values calculated by means of the Zintl rules and fits well the results of magnetic susceptibility measurements and XAS investigations.
NaCu5(C2)3: The First Alkali Metal Transition Metal Acetylide with a Three‐dimensional Framework Structure
Authors: Cremer Ulrich , Ruschewitz Uwe
Published: January 2004

By heating the red residue of the reaction of NaC2H and CuI in liquid ammonia at 463 K for 30 min in a dynamic vacuum orange polycrystalline NaCu5(C2)3 is obtained. The crystal structure was solved and refined from X‐ray powder diffraction data (orthorhombic, Pnma, a = 732.80(2) pm, b = 1099.63(4) pm, c = 726.15(2) pm, Z = 4, RB = 0.030). It consists of a three‐dimensional framework of CuI and C22— ions with small channels running parallel to [100] and [001]. The sodium ions reside at the intersections of these channels. The vibrational spectra of NaCu5(C2)3 show some similarities with the spectra of phenylethynylcopper(I), but they are different to those of Cu2C2. Therefore NaCu5(C2)3 does probably not represent a crystalline model compound for the unknown structure of amorphous Cu2C2.
Untersuchungen im System LaI2/H2: Phasenverhältnisse und Fehlordnung
Authors: Ryazanov Mikhail , Simon Arndt , Mattausch Hansjürgen
Published: January 2004

Erhitzen von LaI2 unter 1 bar Wasserstoff auf 650 °C führt zu hellgrauem LaI2H0.95(3), gleichzeitig ändert sich die Symmetrie von tetragonal nach hexagonal. Indizierung der scharfen Reflexe des Röntgenpulverdiagramms in P63/mmc ergibt a = 4.2158(7)Å und c = 15.508(3)Å. Diffus verbreiterte Linien weisen auf eine Stapelfehlordnung in der Struktur hin, die einer polytypen Verwachsung von MoS2‐ und NbS2‐Varianten entspricht. Erhöhung der Reaktionstemperatur auf 730 °C führt zu einem schärferen Pulverdiagramm, das im wesentlichen als 2H‐NbS2‐Typ beschreibbar ist.

Röntgenographische Untersuchungen von Proben LaI2Hn belegen die Mischungslücke zwischen LaI2 und LaI2Hn (0 ≤ n ≤ 0.5) in guter Übereinstimmung mit den früher ermittelten Werten. Mit sinkendem H‐Gehalt ändern sich die Gitterkonstanten im Homogenitätsgebiet gegenläufig und betragen für die untere Phasengrenze a = 4.236(1)Å, c = 15.39(2)Å.
Enantioselektive Katalysen. 155 [1] (Cymol)Ruthenium‐Halbsandwich‐Komplexe mit Pyrroloxazolin‐Liganden — Synthese, Stereochemie, Katalyse
Authors: Brunner Henri , Henning Frauke , Zabel Manfred
Published: January 2004

Die (Cymol)Ruthenium‐Halbsandwich‐Komplexe K1 und K2 mit chiralen Pyrroloxazolin‐Liganden wurden synthetisiert und charakterisiert. Die Komplexe bilden Diastereomere, die sich nur in der Metallkonfiguration unterscheiden. Der Komplex K1 kristallisiert in Form des reinen Diastereomers SRu, SC4, RC5. In Lösung erfolgt Epimerisierung SRu, SC4, RC5 ⇌ RRu, SC4, RC5 durch Konfigurationsänderung am Rutheniumatom. Die Halbwertszeit für diese Reaktion erster Ordnung bei 0.4 °C in CD2Cl2 beträgt 50.6 min. Damit stehen die beiden Diastereomeren bei Raumtemperatur miteinander im Gleichgewicht. Die Gleichgewichtsgemische von K1 und K2 wurden als Katalysatoren für die Transferhydrierung von Acetophenon und für die Diels‐Alder‐Reaktion von Cyclopentadien mit Methacrolein eingesetzt. Dabei wurden Enantiomerenüberschüsse bis 60 % ee erreicht.
Zur Synthese und Struktur von K3N
Authors: Fischer D. , Cancarevic Z. , Schön J. C. , Jansen M.
Published: January 2004

Durch simultane Bedampfung eines Saphirsubstrates mit Kalium und Stickstoff bei 77 K und anschließendem Aufwärmen wurden zwei Kaliumnitrid‐Phasen erhalten. Das Diffraktogramm der einen Phase läßt sich befriedigend unter der Annahme der Zusammensetzung K3N und Isotypie zu Cs3O (anti‐TiI3 Typ) interpretieren (hexagonal, P63/mcm, a = 779.8(2), c = 759.2(9) pm, Z = 2). Ein Vergleich mit Strukturmodellen, die mit theoretischen Methoden generiert und anschließend auf Hartree‐Fock‐ und DFT Niveau verfeinert wurden, zeigt, dass die hier für K3N beobachtete Modifikation nicht die thermodynamisch stabilste (vermutlich Li3P‐Typ) sondern eine der am wenigsten dichten Formen ist. Insofern sind die Verhältnisse analog zu denen bei Na3N. Das thermische Verhalten der Proben wurde untersucht. Danach wandelt sich hexagonales K3N bei 233 K in eine zweite K/N‐Phase um, deren Pulverdiffraktogramm sich orthorhombisch mit a = 1163, b = 596, c = 718 pm indizieren läßt. Bei 263 K findet Zersetzung unter Bildung von Kalium statt.
(LiI)2Li3SbS3: A mixed Alkali Metal Halide Thioantimonate with a novel Tetrahedron Network
Authors: Pfitzner Arno , Preitschaft Christian , Rau Franz
Published: January 2004

(LiI)2Li3SbS3 was prepared by solid‐state reaction of stoichiometric amounts of LiI, Li, Sb, and S in the ratio 2 : 3 : 1 : 3. The product is air and moisture sensitive. The crystal structure was determined from single crystals at room temperature. Colourless to pale yellow (LiI)2Li3SbS3 crystallizes in the orthorhombic system, space group Pnnm (no. 58) with a = 10.436(1)Å, b = 13.509(1)Å, c = 7.530(1)Å, V = 1061.6(1)Å3, and Z = 4 (data at 20 °C). The crystal structure of (LiI)2Li3SbS3 is closely related to that of (CuI)2Cu3SbS3 and (AgI)2Ag3SbS3, at least for the positions of I, Sb, and S. Thus, iodine forms an eutactic arrangement which resembles the structure of hexagonal diamond. [SbS3]3— units are embedded in this framework in a way that the sulphur atoms of two adjacent trigonal pyramids form distorted octahedral voids. The lithium ions are tetrahedrally coordinated and fully ordered within the anionic framework. The three‐dimensional connectivities in (LiI)2Li3SbS3 are significantly different from the homologous copper and silver compound due to the bonding necessities of Li and slightly different radii of the monovalent cations. Thus, a novel three‐dimensional network of edge sharing tetrahedra is observed in (LiI)2Li3SbS3. It exhibits strands of eight‐membered rings of edge sharing tetrahedra which are linked by common vertices and cross linked by double tetrahedra.
Volume Chemistry of Nitrogen in Binary Metal Nitrides and Subnitrides
Authors: Bronger Welf , Kniep Rüdiger , Kohout Miroslav
Published: January 2004

A comparison of the concept of volume increments created by W. Biltz with that based on quantum mechanical calculations by R.F.W. Bader was performed for crystal structures of binary metal nitrides and ‐subnitrides. The mutual comparison of both concepts permits insights into the bonding relationships of these compounds and reveals the considerable range of volume demand of a strongly polarisable bonding partner, such as the nitride ion. Finally it becomes clear that the Biltz volume increments show a quantum‐chemical relevance in the chemistry of solids.
Representativeness uncertainty in chemical data assimilation highlight mixing barriers
Authors: Lary David John
Published: January 2004

When performing chemical data assimilation the observational, representativeness, and theoretical uncertainties have very different characteristics. In this study, we have accurately characterized the representativeness uncertainty by studying the probability distribution function (PDF) of the observations. The average deviation has been used as a measure of the width of the PDF and of the variability (representativeness uncertainty) for the grid cell. It turns out that for long‐lived tracers such as N2O and CH4 the representativeness uncertainty is markedly different from the observational uncertainty and clearly delineates mixing barriers such as the polar vortex edge, the tropical pipe and the tropopause. Published by Elsevier Ltd on behalf of Royal Meteorological Society.
Effects of the menstrual cycle on mood, neurocognitive and neuroendocrine function in healthy premenopausal women
Authors: SYMONDS C. S. , GALLAGHER P. , THOMPSON J. M. , YOUNG A. H.
Published: January 2004

Background. Neurocognitive functioning may be impaired in the luteal phase of the menstrual cycle due to associated changes in hypothalamic–pituitary–adrenal (HPA) axis function. This study examines the relationship between changes in neurocognition and HPA axis function in different phases of the menstrual cycle.

Method. Fifteen female volunteers, free from psychiatric history and hormonal medication were tested twice, during mid-follicular and late-luteal phases in a randomized, crossover design. Mood, neurocognitive function, and basal cortisol and dehydroepiandrosterone (DHEA) were profiled.

Results. Relative to the follicular phase, verbal fluency was impaired in the luteal phase and reaction times speeded on a continuous performance task, without affecting overall accuracy. ‘Hedonic’ scores on the UWIST-MACL scale were decreased in the luteal phase. There was also evidence of changes in the function of the HPA axis, with 24 h urinary cortisol concentrations and salivary DHEA levels being significantly lower during the luteal phase.

Conclusions. These data suggest that luteal phase HPA axis function is lower than in the follicular phase in premenopausal healthy women. This putative biological difference may be important for our understanding of the aetiopathogenesis of menstrually related mood change and neurocognitive disturbance.
Treatment response in late-onset depression: relationship to neuropsychological, neuroradiological and vascular risk factors
Authors: BALDWIN R. , JEFFRIES S. , JACKSON A. , SUTCLIFFE C. , THACKER N. , SCOTT M. , BURNS A.
Published: January 2004

Background. Late-onset depressive disorder is associated with white matter lesions and neuropsychological deficits that in some studies are linked to a poorer outcome for depression. Some white matter lesions may be vascular in origin. This study investigated the relationship between response or non-response to antidepressant monotherapy and neuropsychological function, structural brain measures and vascular factors.

Method. This was a case–control study. Fifty patients with late-onset major depressive disorder (29 who were responders to antidepressant monotherapy and 21 who were not) were compared with 35 non-depressed control subjects. Measures included assessment of vascular risk factors, neuropsychological testing and a magnetic resonance imaging (MRI) scan.

Results. After adjustment for depressed mood and medication at evaluation, both patient groups had significantly more impairment compared to control subjects on verbal learning tasks involving immediate or delayed recall. Patients who did not respond to antidepressant monotherapy had significantly poorer performance than controls on tests involving visuospatial ability, language, word recognition and tests of executive function, whereas there were no differences between control subjects and responders. On two tests of executive function (verbal fluency and the Stroop test) non-responders scored significantly worse than responders. There were no significant group differences on MRI measures of atrophy or of white matter lesions apart from a higher periventricular hyperintensity score in non-responders compared to controls. There were no group differences on measures of vascular disease.

Conclusion. The results lend support to the emerging evidence that resistance to treatment in late-onset depression may be associated with impaired executive function. Subtle cerebrovascular mechanisms may be involved.