bluuebunny/crossref_metadata_2025 huggingface dataset:
Organometallic Molybdenum(V) Complexes with Primary Phosphine Ligands. Syntheses, Spectroscopic Properties and Molecular Structures of [Cp°MoCl4(PH2R)] (R = But, 1‐Ad, Cy, Ph, 2, 4, 6‐Me3C6H2, 2, 4, 6‐Pri3C6H2, Cp° = C5EtMe4)
Authors: Felsberg Reinhard , Blaurock Steffen , Junk Peter C. , Kirmse Reinhard , Voigt Andreas , Hey‐Hawkins Evamarie
Published: May 2004

[Cp°MoCl4] (Cp° = C5EtMe4) reacts with primary phosphines PH2R to give the paramagnetic phosphine complexes [Cp°MoCl4(PH2R)] [Cp° = C5EtMe4, R = But (1), 1‐Ad (1‐Ad = 1‐adamantyl; 2), Cy (3), Ph (4), Mes (Mes = 2, 4, 6‐Me3C6H2; 5), Tipp (Tipp = 2, 4, 6‐Pri3C6H2; 6)]. 1—6 were characterized spectroscopically (IR, MS), and X‐ray crystal structures were determined for 1—4 and 6. EPR investigations in liquid and frozen solution confirmed the presence of MoV species, and the data were used to analyze the spin‐density distribution in the first coordination sphere. Complexes 3 and 4 react with two equivalents of NEt3 with formation of [Cp°MoCl2(η3‐P4Cy4H)] (7) and [Cp°2Mo2(μ‐Cl)2(μ‐P4Ph4)] (8), respectively, in low yield. Complexes 7 and 8 were characterized by X‐ray crystallography.
Diimido‐, Imido(oxo)‐, Dioxo‐ und Imido(alkyliden)‐Halbsandwich‐Verbindungen über selektive Hydrolyse und α—H‐Abstraktion an Organylkomplexen des sechswertigen Molybdäns und Wolframs
Authors: Radius Udo , Wahl Günter , Sundermeyer Jörg
Published: May 2004

Organometall‐Imide [(η5‐C5R5)M(NR′)2Ph] (M = Mo, W, R = H, Me, R′ = Mes, tBu) 4 — 8 lassen sich durch Umsetzung der chlorfunktionellen Halbsandwich‐Verbindungen [(η5‐C5R5)M(NR′)2Cl] mit Phenyllithium in guten Ausbeuten darstellen. Ausgehend von den Phenylverbindungen 4—8 von sowie von bereits zuvor beschriebenen Methylverbindungen [(η5‐C5Me5)M(NtBu)2Me] (M = Mo, W) werden mit verdünnter Salzsäure die Imido(oxo)‐Methyl‐ bzw. Phenyl‐Komplexe [(η5‐C5Me5)M(NtBu)(O)(R)] M = Mo, R = Me (9), Ph (10); M = W, R = Ph (11) und die Dioxo‐Komplexe [(η5‐C5Me5)M(O)2(CH3)] M = Mo (12), M = W (13) gewonnen. Die Hydolyse von Organometall‐Imiden unter Erhalt von M‐C σ‐ und π‐Bindungen stellt somit eine interessante Alternative zur Gewinnung von Organometall‐Oxiden dar, verglichen mit bekannten Strategien, die sich der oxidativen Decarbonylierung niedervalenter Alkyl‐Carbonyl‐ und Alkyl‐Nitrosylkomplexe bedienen. Auch die Protolyse von [(η5‐C5H5)W(NtBu)2(CH3)] und [(η5‐C5Me5)Mo(NtBu)2(CH3)] mit HCl‐Gas führt unter Erhalt der M‐C‐Bindungen zu [(η5‐C5H5)W(NtBu)Cl2(CH3)] 14 und [(η5‐C5Me5)Mo(NtBu)Cl2(CH3)] 15. Die Inertheit der recht unpolaren M‐C‐σ‐Bindung gegenüber Protolyse bietet somit eine Strategie zur gezielten Synthese von Methylchloro‐Komplexen, die auf anderem Weg, etwa über die partielle Methylierung von [(η5‐C5R5)M(NR′)Cl3] mit MeLi nicht rein darstellbar sind. Als Reinstoffe lassen sich aus dieser Reaktion lediglich die Trimethylverbindungen [(η5‐C5R5)M(NtBu)(CH3)3] 16‐18, M = Mo, W, R = H, Me, gewinnen. Imido(benzyliden)‐Komplexe [(η5‐C5Me5)M(NtBu)(CHPh)(CH2Ph)] M = Mo (19), W (20) entstehen dagegen unter α‐H‐Abstraktion bei Alkylierung von [(η5‐C5Me5)M(NtBu)Cl3] mit PhCH2MgCl. Auf Basis von NMR‐Daten zeichnet sich ein Trend abnehmender Donorfähigkeit der Liganden [NtBu]2— > [O]2— > [CHR]2— ≫ 2 [CH3]— > 2 [Cl]— ab.
Das erste oxidische T5‐Supertetraeder: Na26Mn39O55
Authors: Möller Angela , Amann Peter , Kataev Vladislav , Schittner Norbert
Published: May 2004

Na26Mn39O55 wurde durch eine Redoxreaktion von metallischem Mangan mit CdO in Gegenwart von Na2O und Na2SO4 als Mineralisator in Form roter Einkristalle mit oktaedrischem Habitus erhalten. Die Kristallstruktur konnte anhand von Einkristalldaten bestimmt werden (Fd3¯m, Z = 8, a = 2377, 4(3) pm bei 293 K und a = 2372, 5(2) pm bei 130 K). Das seltene charakteristische Strukturelement eines T5‐Supertetraeders, [Mn35O56], zeichnet die Kristallstruktur des neuen gemischtvalenten Natrium‐Oxomanganats(II, III), Na26Mn39O55, aus. Über erste Untersuchungen des ungewöhnlichen magnetischen Verhaltens wird berichtet.
Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 60 [1] Strukturelle, einkristalloptische und magnetooptische Untersuchungen von Trialkylphosphat‐Addukten des Grundkörpers Tris(cyclopentadienyl)lanthanid(III) (Ln = La, Pr) sowie Ergebnisse vergleichender optischer Studien an [Pr(Ind)3(OP(OEt)3)] (Ind = Indenyl)
Authors: Apostolidis Christos , Morgenstern Alfred , Walter Olaf , Reddmann Hauke , Amberger Hanns‐Dieter
Published: May 2004

[Ln(Cp)3(OP(OR)3)] (Cp = η5‐Cyclopentadienyl; Ln = La, R = Et (1); Ln = Pr, R = Me (2); Ln = Pr, R = Et (3)) und [Pr(Ind)3(OP(OEt)3)] (4) wurden synthetisiert und spektroskopisch sowie teilweise strukturell (nur Verbindungen 1 und 2) charakterisiert. Auf der Grundlage der bei variablen Temperaturen aufgenommenen α‐Absorptionsspektren eines orientierten Einkristalls, der magnetischen Zirkulardichroismusspektren von gelöstem, und der Lumineszenzspektren von gepulvertem Material konnte ein fast vollständiges Kristallfeld(KF)‐Aufspaltungsmuster von 3 aufgestellt und durch Anpassung der freien Parameter eines phänomenologischen Hamilton‐Operators simuliert werden. Die hierbei verwendeten Parameter erlaubten die Berechnung der vom Pr3+‐Zentralion wahrgenommenen globalen KF‐Stärke, die Abschätzung der nephelauxetischen und relativistischen nephelauxetischen Parameter, sowie die Aufstellung der experimentorientierten nichtrelativistischen und relativistischen Molekülorbital‐Schemata im f‐Bereich. Die optischen Spektren von Verbindung 4 weisen auf die Existenz zweier unterschiedlicher Spezies bei tiefen Temperaturen hin, wodurch eine erfolgreiche KF‐Analyse der Spektren verhindert wird.
On the Reaction of [(CO)3Fe(μ‐Me2NCO)2Fe(CO)2(NHMe2)] with Chelating Ligands — X‐Ray Structures of New Binuclear μ‐Carbamoyl Complexes
Authors: Petz Wolfgang , Neumüller Bernhard , Pudewills Jens
Published: May 2004

Reaction of the binuclear μ‐carbamoyl complex [(CO)3Fe(μ‐Me2NCO)2Fe(CO)2(HNMe2)] (1) in toluene with the chelating ligands Ph2PCH2PPh2 (dppm) and Ph2PCH2CH2PPh2 (dppe) gives different results. With dppm only the complex [(CO)3Fe(μ‐Me2NCO)2Fe(CO)2(dppm)] (3) with a dangling ligand is obtained under replacement of amine, whereas with dppe depending on the reaction conditions up to three compounds are found. A 1 : 1 mixture of the educts generates the related complex [(CO)3Fe(μ‐Me2NCO)2Fe(CO)2(dppe)] (4) together with the tetranuclear complex [{(CO)3Fe(μ‐Me2NCO)2Fe(CO)2}2(dppe)] (5). 4 slowly converts into [(CO)3Fe(μ‐Me2NCO)2Fe(CO)(dppe)] (6) with dppe acting as a chelating ligand. 6 is the first compound in this series in which one of the five CO groups is replaced by another donor. A 2 : 1 molar ratio of 1 and dppe quantitatively produces 5. Addition of CO to a solution of 6 proceeds under slow reversible conversion of the complex into 4. The compounds were characterized by the usual spectroscopic methods; 3, 5 and 6 were also studied by X‐ray diffraction analyses.
A One‐dimensional Lead(II) Coordination Polymer with Bridging Saccharinate and 2‐Aminomethylpyridine Ligands: Synthesis, IR Spectra, and Crystal Structure of [Pb(ampy)(μ‐sac)2]n
Authors: Yilmaz Veysel T. , Caglar Sema , Harrison William T. A.
Published: May 2004

A complex with eight‐coordinate lead(II) atom and saccharinate (sac) and 2‐aminomethylpyridine ligands was characterized by IR, elemental analysis and X‐ray crystallography. The lead(II) complex crystallizes in the monoclinic crystal system with space group P21/c. The single crystal X‐ray analysis shows that the complex is a coordination polymer, [Pb(ampy)(μ‐sac)2]n, in which the lead(II) ions have a highly distorted bicapped trigonal antiprism coordination. Lead(II) ions are bridged by carboxyl groups of sac forming one‐dimensional linear chains, running parallel to the a axis. The intrachain Pb···Pb distances are 4.4490(3) and 4.4679(3)Å. The individual chains are connected by N—H···Osulfonyl and Campy—H···Osulfonyl type hydrogen bonds, resulting in a three‐dimensional network. The sac ligand acts as bidentate and bridging ligand, while ampy behaves as an N, N′ donor. The IR spectra of the lead(II) complex are discussed in detail.
Metallat‐Ionen [Al(OR)4]— als Chelatliganden für Übergangsmetall‐Kationen
Authors: Pauls Jochen , Iravani Effat , Köhl Peter , Neumüller Bernhard
Published: May 2004

Wasserfreies CoCl2 kann mit [{Li(Diglyme)}{Al(OtBu)4}] in THF zum Komplex [Li(THF)4][{CoCl2}{Al(OtBu)4}] umgesetzt werden. Zusatz von Diglyme zu den Reaktionslösungen liefert die blaue Verbindung [Li(Diglyme)2][{CoCl2}{Al(OtBu)4}] (1). Nach der gleichen Vorgehensweise bildet sich mit FeCl2 der FeII‐Komplex [Li(Diglyme)2][{FeCl2}2{Al(OtBu)4}] (2). [{Li(Diglyme)}{Al(OtBu)4}] in THF/Diglyme dient als Alkoxid‐Übertragungsreagenz auf TiCl4 und führt zum Neutralkomplex [TiCl2(OtBu)2(Diglyme)] (3). Wird Li[Al(OCH2Ph)4] mit CoCl2 in THF zur Reaktion gebracht, bildet sich das himmelblaue Salz [Li(THF)4]2[{CoCl2}3{Al(OCH2Ph)4}2] (4). Nach Behandlung von 4 mit Diglyme findet teilweise Ligandenredistribution statt, was zum himmelblauen [Li(Diglyme)2]2[{CoCl2}3{Al(OCH2Ph)4}2] (5) und zum veilchenblauen [Li(Diglyme)2]2[Co2Cl5(OCH2Ph)] (6) führt. Ein entprechendes Salz kann auch direkt aus Li[Al(OtBu)4] und CoCl2 in Diglyme als [Li(Diglyme)2]2[Co2Cl5(OtBu)] (7) isoliert werden.

1 — 7 wurden mittels IR‐Spektroskopie, teilweise durch Massenspektrometrie und Röntgenstrukturanalysen charakterisiert. Von 1 und 5 wurden dazu UV‐VIS‐Spektren angefertigt. Nach den Röntgenstrukturanalysen sind sowohl die MII‐Ionen [MII = Fe2+, Co2+] als auch die AlIII‐Ionen in allen Fällen verzerrt tetraedrisch koordiniert. In 1, 2, 4 und 5 wirkt die Einheit [Al(OR)4]— auch wie erhofft als Chelatligand.
Commentary on women‐centered reproductive health services
Authors: Toro Olga Lucia
Published: May 2004

From women's perspectives, the primary principles of a reproductive health framework in the developing world are as follows:

Family planning is a basic human right to which all human beings are entitled. Provision of family planning services must be comprehensive, including safe and low cost methods, freedom of choice about both contraception and pregnancy termination, timely and honest information, privacy and confidentiality, individual needs assessment, and counseling of women, men or the couple. Wide contraceptive choice requires more research on methods that are less invasive of women's anatomy and physiology and more supportive of women's control of their own bodies. These parameters of quality care in family planning must be centered on women's needs, desires and expectations.

The concept of conscious contraception implies an attitude of conscious sexuality. When a woman accepts that sexual gratification independent of reproduction is a legitimate right, she is better prepared to engage in the pursuit of her own health and happiness. If family planning programs do not include sexuality as a key issue to discuss with clients, all long‐term strategies will fall short in modifying people's attitudes, especially women's reluctance to contracept.

Sexual and reproductive health includes emotional health. As Dr. Sai points out, the effects of underdevelopment and poverty strike women in dramatic ways, and quite often all the pressures to which they are exposed lead to precarious emotional health. They become victims of violence and repeat the cycle of violence with their children. We, as advocates of sexual and reproductive rights, must also consider the psychological and emotional implications of sexuality and reproduction, and learn to deal with them in our clinics and services.

We must discuss, understand and take firm positions regarding major ethical issues in sexual and reproductive health. These include regulation of drug marketing, of policies for research on human subjects, and of coercion of individuals or governments to accept contraception, or abortion, for whatever reasons.

Finally, we must understand that the pursuit of sexual and reproductive health requires the decriminalization of abortion. Legal restrictions on abortion are lethal means of violence against women. Silence on these restrictions masks an enormous amount of suffering among women in Third World countries.

I invite you to make a commitment to women's rights by exploring, with courage and dedication, creative and simple ways to provide comprehensive reproductive health services.
Range fragmentation in the spectacled bear Tremarctos ornatus in the northern Andes
Authors: Kattan Gustavo , Hernández Olga Lucía , Goldstein Isaac , Rojas Vladimir , Murillo Oscar , Gómez Carolina , Restrepo Héctor , Cuesta Francisco
Published: May 2004

This paper addresses the conservation status of the spectacled bear Tremarctos ornatus in the northern Andes (Venezuela, Colombia and Ecuador) by analysing the degree of range fragmentation and estimating habitat availability. From satellite images we constructed maps of remnant habitat blocks, consisting of Andean forest and páramo (high elevation shrublands and grassland) ecosystems. This information was overlain with a road map to determine potential isolation of populations, and a human accessibility model was used to estimate the core area of each block. This analysis revealed that the species' range is fragmented by landscape transformation and roads into 113 blocks >100 km2, representing 42% of the original extent of the bear's distribution. Forty percent of the blocks are <500 km2, and only nine are >5,000 km2. However, taking into account only core area, 56% of the blocks are <500 km2 and only six are >5,000 km2. In addition, many blocks have internal patches of colonization, further reducing habitat quality. This effect is more severe in smaller fragments, where internal disturbances constitute a high proportion of the block area. We used a high population density estimate of 0.25, a medium density of 0.11 and a low density of 0.04 bears per km2 to estimate population sizes. Twenty-nine populations are likely to have >500 individuals with the high estimate, but only nine with the medium and one with the low estimate (largest estimated population was 9,048 bears). These estimates are much lower if only the core area of blocks is used. Hunting has been identified as a major threat for many bear populations. Our analyses indicate that a regional conservation strategy for spectacled bear should focus on maintaining or increasing habitat availability in larger blocks, and reducing human-induced mortality across the region.
The availability of resting and pupping habitat for the Critically Endangered Mediterranean monk seal Monachus monachus in the archipelago of Madeira
Authors: Karamanlidis Alexandros A. , Pires Rosa , Silva Nadia Carina , Neves Henrique Costa
Published: May 2004

In order to describe the resting and pupping habitat of the Critically Endangered Mediterranean monk seal Monachus monachus and facilitate the identification of preferences by the species for suitable habitat for resting and pupping, 94 sea caves in the archipelago of Madeira were located, charted, and categorized using six characteristics. A cluster analysis indicated that there are eight different types of cave, in three groups. Observations of cave usage indicate that monk seals in the archipelago do not appear to exhibit a preference for certain cave types for resting. When taking care of young, however, the species appears to prefer sea caves that have beaches above sea level during high tide and long entrance corridors. Based on these preferences we believe that although there is a large number of caves in the area that are suitable for resting, only 16 (17%) of the caves are suitable for pupping. The survival of the Critically Endangered Mediterranean monk seal will depend on the allocation of sufficient suitable habitat for reproduction.
The decline of the Chinese giant salamander Andrias davidianus and implications for its conservation
Authors: Wang Xiao-ming , Zhang Ke-jia , Wang Zheng-huan , Ding You-zhong , Wu Wei , Huang Song
Published: May 2004

The Chinese giant salamander Andrias davidianus is the largest living amphibian. Most wild populations are threatened and some are already extinct. The Chinese government has declared the species a Class II Protected Species, and it is listed as Critically Endangered in the Chinese Red Book of Amphibians and Reptiles and as Data Deficient on the IUCN Red List. Populations of the species have declined sharply in both range and number since the 1950s because of habitat loss and fragmentation, and hunting for the commercial luxury food trade. Remaining populations appear to be distributed in 12 areas across 17 provinces in the mountainous areas of the middle Yangtze, Yellow and Pearl Rivers. Since the 1980s, 14 nature reserves, with a total area of more than 355,000 ha, have been established for the conservation of the Chinese giant salamander. We carried out habitat and questionnaire surveys for the species in 13 locations, and based on the results and on the little amount of published information, most of it in Chinese, we assess the current status of the species and make recommendations for its conservation management. Conservation of the Chinese giant salamander should be given a high priority and considered an important part of wetland management.
Data‐model comparison search analysis of coincident PBO Balmer α, EURD Lyman β geocoronal measurements from March 2000
Authors: Bishop J. , Mierkiewicz E. J. , Roesler F. L. , Gómez J. F. , Morales C.
Published: May 2004

Recent Lyman series and Balmer series airglow measurements provide a fresh opportunity to investigate the density distribution and variability of atomic hydrogen in the upper atmosphere. Dedicated nightside Balmer α Fabry‐Perot spectrometer measurements at the Pine Bluff Observatory (PBO), University of Wisconsin‐Madison, have been acquired since late 1999 taking advantage of several technological advances. Extreme ultraviolet spectral radiance measurements by the Espectrógrafo Ultravioleta extremo para la Radiación Difusa (EURD) instrument on the Spanish MINISAT‐1 satellite from October 1997 to December 2001 provide extensive sets of geocoronal Lyman β, Lyman γ and He 584 Å emission intensities. In this paper, coincident EURD Lyman β and PBO Balmer α radiance measurements from the early March 2000 new moon period are presented. In addition to serving as examples of the data sets now available, the data volume poses an analysis challenge not faced in prior geocoronal studies. A data‐model comparison search procedure employing resonance radiation transport results for extensive sets of parametric density distribution models is being developed for use in analyses of multiple large data sets; this is described, and example results for the PBO and EURD March 2000 data sets are presented. The tightness of the constraints obtained for the solar line‐center Lyman β irradiance and the atomic hydrogen column abundance is somewhat surprising, given the crudeness of the parameter binning in the search procedure and the fact that a small number of recognized corrections remain to be made to each data set.
The radial gradient of relativistic electrons at geosynchronous orbit
Authors: Onsager T. G. , Chan A. A. , Fei Y. , Elkington S. R. , Green J. C. , Singer H. J.
Published: May 2004

Earth's outer electron radiation belt is a highly dynamic region, driven externally by the solar wind and controlled within the magnetosphere by numerous source and loss processes. Critical to assessing the importance of the different source and loss processes and to developing accurate physics‐based models of the radiation belts is knowing phase space density and its radial gradient in terms of adiabatic invariants. In this paper, we demonstrate a new technique for determining the radial gradient of relativistic electron phase space density at geosynchronous orbit. This technique utilizes the fact that the GOES geosynchronous satellites are located at different geomagnetic latitudes because of their separation in longitude, even though both are located on the geographic equator. From simultaneous measurements at different geomagnetic latitudes, and therefore in different L shells, we are able to obtain the local radial gradient of phase space density. We have restricted these initial calculations to a single value of magnetic moment (M = 6000 MeV/G) and to equatorially mirroring particles. In order to minimize the sensitivity of our results to the magnetic field model used, we have analyzed data from a time period with quiet geomagnetic conditions, when the relativistic electron flux was elevated and steady. We find that during this time period the radial gradient of phase space density was positive. This indicates that the direction of radial diffusion was inward, transporting electrons from outside to within geosynchronous orbit.
Streamflow increase due to rupturing of hydrothermal reservoirs: Evidence from the 2003 San Simeon, California, Earthquake
Authors: Wang Chi‐Yuen , Manga Michael , Dreger Douglas , Wong Alexander
Published: May 2004

Following the Mw = 6.5 San Simeon, California, earthquake on December 22, 2003, USGS stream gauges documented two consecutive increases in streamflow in the Salinas River and Lopez Creek in the central Coast Ranges. The first increase occurred within 15 minutes after the earthquake and lasted about an hour; the second one occurred a few hours later and lasted much longer. Evidence and simulation suggest that these increases were caused by earthquake‐induced rupturing of pressurized hydrothermal reservoirs.
Improving trapping success for rare species by targeting habitat types using remotely sensed data: a case study of the heath mouse (Pseudomys shortridgei) in Western Australia
Authors: Quinlan Kirsty , Moro Dorian , Lund Mark
Published: May 2004

The rare heath mouse (Pseudomys shortridgei) is the only rodent lacking a conservation program in Western Australia. Little is known about the habitat requirements of P. shortridgei in Western Australia, and there is a lack of trapping focus that could target specific habitat components that this species may use. The purpose of this study was to (1) relate the occurrence of this species to measurable components of its habitat; (2) incorporate habitat information into a GIS modelling system to identify other areas of potentially suitable habitat; and (3) test for the presence of P. shortridgei in predicted areas. In Lake Magenta Nature Reserve, 93% of P. shortridgei captures (14�of 15 mice) were associated with characteristics of a mixed laterite heath community representing 57 plant species and a dense structural layer up to 1.2 m. Aerial photography and satellite imagery were used to identify the occurrence of mixed laterite heath elsewhere within the reserve. Ground-truthing using pre-defined habitat criteria found that the best predictive model to define habitat was aerial photography. Trapping was undertaken in two areas of the reserve predicted by the modelling and resulted in the successful capture of the target species. This study demonstrates that aerial photography maps can provide a basis for focusing future trapping effort within reserves where P. shortrigei is likely to occur. The use of this GIS method provides a low-cost and simple method for improving the chances of locating additional populations of P. shortridgei in other nature reserves.
Humanized anti-CD25 (daclizumab) inhibits disease activity in multiple sclerosis patients failing to respond to interferon β
Authors: Bielekova Bibiana , Richert Nancy , Howard Thomas , Blevins Gregg , Markovic-Plese Silva , McCartin Jennifer , Würfel Jens , Ohayon Joan , Waldmann Thomas A. , McFarland Henry F. , Martin Roland
Published: May 2004

Identifying effective treatment combinations for MS patients failing standard therapy is an important goal. We report the results of a phase II open label baseline-to-treatment trial of a humanized monoclonal antibody against CD25 (daclizumab) in 10 multiple sclerosis patients with incomplete response to IFN-β therapy and high brain inflammatory and clinical disease activity. Daclizumab was very well tolerated and led to a 78% reduction in new contrast-enhancing lesions and to a significant improvement in several clinical outcome measures.
Neurotrophins regulate Schwann cell migration by activating divergent signaling pathways dependent on Rho GTPases
Authors: Yamauchi Junji , Chan Jonah R. , Shooter Eric M.
Published: May 2004

Neurotrophins are recognized widely as essential factors in the developing nervous system. Previously, we demonstrated that neurotrophin 3 activation of TrkC inhibits Schwann cell myelination and enhances the migration of primary Schwann cells through the signaling pathway regulated by the Rho GTPases Rac1 and Cdc42. Here, we show that neurotrophins activate divergent signaling pathways to promote or inhibit Schwann cell migration. Endogenous brain-derived neurotrophic factor acting through p75
NTR
inhibits Schwann cell migration dramatically by Src kinase-dependent activation of the guanine-nucleotide exchange factor Vav2 and RhoA. Together, these results suggest that neurotrophins and their receptors differentially regulate Schwann cell migration through the signaling pathways that depend on Rho GTPases.
What is the future for undergraduate dissertations?
Authors: Rowley Jennifer , Slack Frances
Published: May 2004

This article argues that the changing nature of the dissertation experience, and its associated supervision, calls for more detailed attention to the development of dissertation supervisors. Dissertations have always played a major role in student learning. The following themes constitute the kernel of the article: the role of the dissertation in the student's learning experience, managing the link between theory and practice, digitization of information resources, research methodologies and design, and finally, the implications for the role of the supervisor. It is suggested that without an awareness of the changing nature of the dissertation experience, and a more proactive approach to supervisor development, there may be serious degradation of the dissertation experience and outcomes.
Shape selection menu for grand scale discontinua systems
Authors: Rougier E. , Munjiza A. , Latham J.P.
Published: May 2004

It is now widely recognised that particle shape plays an important role in the behaviour of grand scale discontinua systems and may be partially responsible for some of the unexplained phenomena of particulate physics. It is therefore very important that a virtual discontinua modelling workbench includes a library comprising a large spectrum of shapes including real‐shaped particles of interest to scientists and engineers. In this context a question of selecting a particle from such a library arises. In this paper, a particular selection procedure based on shape selection chart is proposed.
Discrete element modeling with dilated particles
Authors: Hopkins Mark A.
Published: May 2004

A new contact detection technique for discrete element modeling is described. This technique is suitable for a large family of particle shapes that are based on the dilation process from mathematical morphology. In the dilation process an arbitrary shape is dilated by placing the center of a sphere of fixed diameter at every point in the basic shape. Defining a contact between two objects in this class is equivalent to determining which spheres amongst the infinite number that compose each object is in contact. The algorithm is derived for general ellipsoidal particles and demonstrated with a series of biaxial deformation simulations using a range of ellipsoidal particle shapes.
Engineering identities
Authors: Brown Alan
Published: May 2004

Employers attempt to shape employees' work identities through the organisation of work. However, they are partly constrained by employee expectations related to education and training, the occupational structure and the labour market. Employees, individually and collectively, also attempt to influence how their work is performed and play an active role in shaping their own work identities. Work identities are therefore influenced both by structural factors and the agency of employers and employees. This article concentrates upon how individuals working in engineering seek to shape their own work identities. An overview of the broad structural context of working in engineering and metal working in France, Germany, Spain and the UK is given, followed by an outline of how employers sought to shape work identities.
Work identities of nurses
Authors: Kirpal Simone
Published: May 2004

This paper reports on a comparative qualitative study across four European countries which explored the formation of work identity amongst nurses and other professionals in the field of health care. Within this sector, it identifies trends towards a more flexible, more highly skilled and more mobile workforce. Conversely, however, it is becoming difficult to recruit and retain staff due to increasing workload, decreasing job satisfaction and comparatively low pay. Occupational identity is theorised as a multi‐dimensional phenomenon, with structural, social and individual‐psychological components. A number of emerging common themes across the three dimensions and across the four national settings include structural conflicts between cost efficiency and quality of care, and individual conflicts between the core activity of caring for patients and the increasing demands of administration and other peripheral work. The study identifies a number of strategies used by nurses to balance these conflicting demands. Overall, the professional identity of nurses remains strong, but it is important for policy makers to be aware of the potential negative effects, in terms of staff turnover, mobility and job (dis)satisfaction, of the current state of the health care sector.
Identification‐flexibility dilemma of IT specialists
Authors: Loogma Krista , Ümarik Meril , Vilu Raivo
Published: May 2004

Information technology (IT) is a new service sector characterised by an intensive dynamic that puts high demands of learning, flexibility and mobility on IT specialists. This article identifies two features that are decisive for the formation of work identities of employees working in the sector: first, an “entrepreneurial” employment model that transfers responsibilities for skills acquisition, professional development and risk management to the individual; and second, a conflict between a strong identification with IT‐related technology and flexibility requirements. The article analyses the implications these features have in terms of the role of initial and continuing vocational training, skills demands and the professional development of employees working in the sector. It also discusses how boundaryless career paths, characterised by ambiguity and uncertainty, influence work‐related identities of IT specialists.
Corporate governance and the role of non‐executive directors in large UK companies: an empirical study
Authors: Pass Christopher
Published: May 2004

In the 1990s various committees (Cadbury, Greenbury, Hempel) reported on governance issues, including the role played by non‐executive directors in promoting “best practice”. Following public concern at cases of “excessive” pay awards to executive directors and financial irregularities the government has recently appointed the Higgs Committee to review again the contribution of non‐executive directors. This paper presents an empirical study of the involvement of non‐executives in large UK companies, assesses the extent to which these companies now “conform” to the recommendations of “best practice” proposed by the earlier committees and looks at the general and specific controversies surrounding the employment of non‐executives as part of companies corporate governance structures.
The ethical dilemma of merging the roles of CEO and chairman of the board
Authors: Sora Sebastian A. , Natale Samuel M.
Published: May 2004

The intent of this article is to explore the resultant conundrum that arises when the role of the chief executive officer (CEO) and the role of the chairman of the corporate board are merged into one person. There is a resultant loss in checks and balances and this can result in a decrease in vigilance in the operation of the corporation. Given this loss of vigilance power begins to center in one leader, the CEO/chairman, that can be used for personal gain at the expense of the other stakeholders of the corporation. This creates an environment of greed and corruption that eventually creates mistrust in the viability of the stock of the corporation as well as loss of personnel that can right the course. The article raises the concern and sees an answer for such issues in government regulation as it relates to the corporate structure.
Fundamentals of Survival Data
Authors: Hougaard Philip
Published: May 2004

Summary.Survival data stand out as a special statistical field. This paper tries to describe what survival data is and what makes it so special. Survival data concern times to some events. A key point is the successive observation of time, which on the one hand leads to some times not being observed so that all that is known is that they exceed some given times (censoring), and on the other hand implies that predictions regarding the future course should be conditional on the present status (truncation). In the simplest case, this condition is that the individual is alive. The successive conditioning makes the hazard function, which describes the probability of an event happening during a short interval given that the individual is alive today (or more generally able to experience the event), the most relevant concept. Standard distributions available (normal, log‐normal, gamma, inverse Gaussian, and so forth) can account for censoring and truncation, but this is cumbersome. Besides, they fit badly because they are either symmetric or right skewed, but survival time distributions can easily be left‐skewed positive variables. A few distributions satisfying these requirements are available, but often nonparametric methods are preferable as they account better conceptually for truncation and censoring and give a better fit. Finally, we compare the proportional hazards regression models with accelerated failure time models.
A Model for Thermograms
Authors: Robin Stéphane
Published: May 2004

Summary.Thermograms are curves resulting from thermal analysis and are of great interest in the study of various food and biological products physical properties. A method to separate underlying peaks is proposed, and statistical properties of estimates for some characteristic parameters are derived. The total number of peaks can be estimated with a sequential analysis of the residual plots. For each new peak, a statistical criterion is proposed to check whether it is significantly different from the noise of the recording. As an example, the method is applied to a summer milk fat fusion thermogram.
Mixed Effects Models with Bivariate and Univariate Association Parameters for Longitudinal Bivariate Binary Response Data
Authors: Ten Have Thomas R. , Morabia Alfredo
Published: May 2004

Summary.When two binary responses are measured for each study subject across time, it may be of interest to model how the bivariate associations and marginal univariate risks involving the two responses change across time. To achieve such a goal, marginal models with bivariate log odds ratio and univariate logit components are extended to include random effects for all components. Specifically, separate normal random effects are specified on the log odds ratio scale for bivariate responses and on the logit scale for univariate responses. Assuming conditional independence given the random effects facilitates the modeling of bivariate associations across time with missing at random incomplete data. We fit the model to a dataset for which such structures are feasible: a longitudinal randomized trial of a cardiovascular educational program where the responses of interest are change in hypertension and hypercholestemia status. The proposed model is compared to a naive bivariate model that assumes independence between time points and univariate mixed effects logit models.
Unconditional Versions of Several Tests Commonly Used in the Analysis of Contingency Tables
Authors: Freidlin Boris , Gastwirth Joseph L.
Published: May 2004

Summary. By focusing on a confidence interval for a nuisance parameter, Berger and Boos (1994, Journal of the American Statistical Association89, 1012–1016) proposed new unconditional tests. In particular, they showed that, for a 2 × 2 table, this procedure generally was more powerful than Fisher's exact test. This paper utilizes and extends their approach to obtain unconditional tests for combining several 2×2 tables and testing for trend and homogeneity in a 2 ×K table. The unconditional procedures are compared to the conditional ones by reanalyzing some published biomedical data.
A Goodness‐of‐fit Test for Capture‐Recapture Model Mt Under Closure
Authors: Stanley Thomas R. , Burnham Kenneth P.
Published: May 2004

Summary. A new, fully efficient goodness‐of‐fit test for the time‐specific closed‐population capture‐recapture model Mt is presented. This test is based on the residual distribution of the capture history data given the maximum likelihood parameter estimates under model Mt, is partitioned into informative components, and is based on chi‐square statistics. Comparison of this test with Leslie's test (Leslie, 1958, Journal of Animal Ecology, 27, 84–86) for model Mt, using Monte Carlo simulations, shows the new test generally outperforms Leslie's test. The new test is frequently computable when Leslie's test is not, has Type I error rates that are closer to nominal error rates than Leslie's test, and is sensitive to behavioral variation and heterogeneity in capture Probabilities. Leslie's test is not sensitive to behavioral variation in capture probabilities but, when computable, has greater power to detect heterogeneity than the new test.
Applying the Cox Proportional Hazards Model When the Change Time of a Binary Time‐Varying Covariate Is Interval Censored
Authors: Goggins William B. , Finkelstein Dianne M. , Zaslavsky Alan M.
Published: May 2004

Summary.This paper develops methodology for estimation of the effect of a binary time‐varying covariate on failure times when the change time of the covariate is interval censored. The motivating example is a study of cytomegalovirus (CMV) disease in patients with human immunodeficiency virus (HIV) disease. We are interested in determining whether CMV shedding predicts an increased hazard for developing active CMV disease. Since a clinical screening test is needed to detect CMV shedding, the time that shedding begins is only known to lie in an interval bounded by the patient's last negative and first positive tests. In a Cox proportional hazards model with a time‐varying covariate for CMV shedding, the partial likelihood depends on the covariate status of every individual in the risk set at each failure time. Due to interval censoring, this is not always known. To solve this problem, we use a Monte Carlo EM algorithm with a Gibbs sampler embedded in the E‐step. We generate multiple completed data sets by drawing imputed exact shedding times based on the joint likelihood of the shedding times and event times under the Cox model. The method is evaluated using a simulation study and is applied to the data set described above.
An Empirical Comparison of Several Clustered Data Approaches Under Confounding Due to Cluster Effects in the Analysis of Complications of Coronary Angioplasty
Authors: Berlin Jesse A. , Kimmel Stephen E. , Have Thomas R. Ten , Sammel Mary D.
Published: May 2004

Summary. In the analysis of binary response data from many types of large studies, the data are likely to have arisen from multiple centers, resulting in a within‐center correlation for the response. Such correlation, or clustering, occurs when outcomes within centers tend to be more similar to each other than to outcomes in other centers. In studies where there is also variability among centers with respect to the exposure of interest, analysis of the exposure–outcome association may be confounded, even after accounting for within‐center correlations. We apply several analytic methods to compare the risk of major complications associated with two strategies, staged and combined procedures, for performing percutaneous transluminal coronary angioplasty (PTCA), a mechanical means of relieving blockage of blood vessels due to atherosclerosis. Combined procedures are used in some centers as a cost‐cutting strategy. We performed a number of population‐averaged and cluster‐specific (conditional) analyses, which (a) make no adjustments for center effects of any kind; (b) make adjustments for the effect of center on only the response; or (c) make adjustments for both the effect of center on the response and the relationship between center and exposure. The method used for this third approach decomposes the procedure type variable into within‐center and among‐center components, resulting in two odds ratio estimates. The naive analysis, ignoring clusters, gave a highly significant effect of procedure type (OR = 1.6). Population average models gave marginally to very non significant estimates of the OR for treatment type ranging from 1.6 to 1.2 with adjustment only for the effect of centers on response. These results depended on the assumed correlation structure. Conditional (cluster‐specific) models and other methods that decomposed the treatment type variable into among‐ and within‐center components all found no within‐center effect of procedure type (OR = 1.02, consistently) and a considerable among‐center effect. This among‐center variability in outcomes was related to the proportion of patients who receive combined procedures and was found even when conditioned on procedure type (within‐center) and other patient‐ and center‐level covariates. This example illustrates the importance of addressing the potential for center effects to confound an outcome‐exposure association when average exposure varies across clusters. While conditional approaches provide estimates of the within‐cluster effect, they do not provide information about among‐center effects. We recommend using the decomposition approach, as it provides both types of estimates.
A Bayesian Semiparametric Accelerated Failure Time Model
Authors: Walker Stephen , Mallick Bani K.
Published: May 2004

Summary.A Bayesian semiparametric approach is described for an accelerated failure time model. The error distribution is assigned a Polya tree prior and the regression parameters a noninformative hierarchical prior. Two cases are considered: the first assumes error terms are exchangeable; the second assumes that error terms are partially exchangeable. A Markov chain Monte Carlo algorithm is described to obtain a predictive distribution for a future observation given both uncensored and censored data.
Stochastic Algorithms for Markov Models Estimation with Intermittent Missing Data
Authors: Deltour Isabelle , Richardson Sylvia , Hesran Jean‐Yves Le
Published: May 2004

Summary.Multistate Markov models are frequently used to characterize disease processes, but their estimation from longitudinal data is often hampered by complex patterns of incompleteness. Two algorithms for estimating Markov chain models in the case of intermittent missing data in longitudinal studies, a stochastic EM algorithm and the Gibbs sampler, are described. The first can be viewed as a random perturbation of the EM algorithm and is appropriate when the M step is straightforward but the E step is computationally burdensome. It leads to a good approximation of the maximum likelihood estimates. The Gibbs sampler is used for a full Bayesian inference. The performances of the two algorithms are illustrated on two simulated data sets. A motivating example concerned with the modelling of the evolution of parasitemia byPlasmodium falciparum(malaria) in a cohort of 105 young children in Cameroon is described and briefly analyzed.
Bayesian Analysis and Model Selection for Interval‐Censored Survival Data
Authors: Sinha Debajyoti , Chen Ming‐Hui , Ghosh Sujit K.
Published: May 2004

Summary.Interval‐censored data occur in survival analysis when the survival time of each patient is only known to be within an interval and these censoring intervals differ from patient to patient. For such data, we present some Bayesian discretized semiparametric models, incorporating proportional and nonproportional hazards structures, along with associated statistical analyses and tools for model selection using sampling‐based methods. The scope of these methodologies is illustrated through a reanalysis of a breast cancer data set (Finkelstein, 1986,Biometrics42, 845–854) to test whether the effect of covariate on survival changes over time.
Monte Carlo EM for Missing Covariates in Parametric Regression Models
Authors: Ibrahim Joseph G. , Chen Ming‐Hui , Lipsitz Stuart R.
Published: May 2004

Summary. We propose a method for estimating parameters for general parametric regression models with an arbitrary number of missing covariates. We allow any pattern of missing data and assume that the missing data mechanism is ignorable throughout. When the missing covariates are categorical, a useful technique for obtaining parameter estimates is the EM algorithm by the method of weights proposed in Ibrahim (1990, Journal of the American Statistical Association85, 765–769). We extend this method t o continuous or mixed categorical and continuous covariates, and for arbitrary parametric regression models, by adapting a Monte Carlo version of the EM algorithm as discussed by Wei and Tanner (1990, Journal of the American Statistical Association85, 699–704). In addition, we discuss the Gibbs sampler for sampling from the conditional distribution of the missing covariates given the observed data and show that the appropriate complete conditionals are log‐concave. The log‐concavity property of the conditional distributions will facilitate a straightforward implementation of the Gibbs sampler via the adaptive rejection algorithm of Gilks and Wild (1992, Applied Statistics41, 337–348). We assume the model for the response given the covariates is an arbitrary parametric regression model, such as a generalized linear model, a parametric survival model, or a nonlinear model. We model the marginal distribution of the covariates as a product of one‐dimensional conditional distributions. This allows us a great deal of flexibility in modeling the distribution of the covariates and reduces the number of nuisance parameters that are introduced in the E‐step. We present examples involving both simulated and real data.
SIMEX Variance Component Tests in Generalized Linear Mixed Measurement Error Models
Authors: Lin Xihong , Carroll Raymond J.
Published: May 2004

Summary. In the analysis of clustered data with covariates measured with error, a problem of common interest is to test for correlation within clusters and heterogeneity across clusters. We examined this problem in the framework of generalized linear mixed measurement error models. We propose using the simulation extrapolation (SIMEX) method to construct a score test for the null hypothesis that all variance components are zero. A key feature of this SIMEX score test is that no assumptions need to be made regarding the distributions of the random effects and the unobserved covariates. We illustrate this test by analyzing Framingham heart disease data and evaluate its performance by simulation. We also propose individual SIMEX score tests for testing the variance components separately. Both tests can be easily implemented using existing statistical software.
Memory in Coal Tits: An Alternative Model
Authors: Ridout Martin S.
Published: May 2004

Summary. Jolliffe and Jolliffe (1997, Biometrics53, 1136–1142) proposed various models for data from an experiment on memory in coal tits. This article describes an alternative model, which fits equally well and which may be simpler to interpret.