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Several Proposals (several + proposal)
Selected AbstractsThe innervation of FGF-induced additional limbs in the chick embryoJOURNAL OF ANATOMY, Issue 1 2003B. W. Turney Abstract Motoneurones that supply the vertebrate limb innervate their muscle targets in a highly reproducible manner. As development proceeds, these limb-specific motoneurones send out axons, which grow towards the developing limb and then congregate at its base to form the plexus. In the plexus, in response to unknown positional cues, these axons rearrange, often changing their original spatial relationships, before sorting out to emerge in the defined nerve trunks that innervate the limb. Several proposals have been put forward to explain how this reproducible innervation pattern is achieved. These include (1) that early differences in the motoneurone identity dictate their future axonal trajectories, (2) that axons actively respond to attractive or repulsive positional cues provided by the limb bud itself, or (3) that motor axons are passively deployed, following pathways of least mechanical resistance. We have addressed the question of the relative roles of motoneurone identity and the signals that the axons encounter on their journey towards the limb bud. Using the developing chick embryo as our experimental model we tested the effect of providing an additional limb target for motor axons leaving the flank level of the spinal cord. To do this we placed FGF-soaked beads in the presumptive flank of 2-day-old chick embryos. This treatment induces an additional limb containing muscles. We investigated whether such additional limbs are innervated and by which neurones. We show that rather than the additional limbs being solely supplied by axons diverted from the two existing limb plexuses, motoneurones that normally supply the flank alter their trajectories to enter the induced limb. Once in the limb, axons respond to positional cues within the bud to generate the stereotypical innervation pattern. Our results show that the tendency of ,flank' motoneurones to innervate flank can be overcome by the presence of an additional limb. [source] An analysis of all the relevant facts and arguments indicates that enzyme catalysis does not involve large contributions from nuclear tunnelingJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2010Shina C. L. Kamerlin Abstract Enzymatic reactions are crucial toward controlling and performing most life processes, and, as such, understanding how they really work has both fundamental and practical importance. Thus, one of the major current challenges of biophysics involves understanding the origin of the enormous catalytic power of enzymes, an issue that is still not widely understood and remains controversial within the scientific community. Several proposals have been put forth to try to explain the origin of enzyme catalysis, one of which is the idea that enzyme catalysis involves special factors such as nuclear quantum mechanical (NQM) effects, and, in particular, nuclear tunneling. Here, we will discuss both the factors for and against this proposition, and demonstrate that an analysis of all the relevant facts and arguments seems to establish that enzyme catalysis does not involve large contributions from nuclear tunneling. Copyright © 2010 John Wiley & Sons, Ltd. [source] Refuting patients' obligations to clinical training: a critical analysis of the arguments for an obligation of patients to participate in the clinical education of medical studentsMEDICAL EDUCATION, Issue 3 2001Jude T Waterbury Context The clinical teaching of medical students is essential to the continuation of medicine, but it has a major impact on the patient's health care and autonomy. Some people believe that there is a moral obligation for patients to participate in this training. Such an obligation, real or perceived, may endanger patients' autonomy. Objectives The author makes a critical analysis of the main arguments he encounters supporting such an obligation. These arguments are: (1) the furthering of medical education; (2) compensation when uninsured or unable to pay; (3) an equitable return for the care received in a teaching hospital, and (4) fulfilment of a student's need for (and some say right to) clinical training. Methods Related literature is reviewed in search of evidence and/or support for such arguments. Conclusions The review reveals that these arguments either cannot be verified or do not necessarily place any obligations on the patient. It is argued that, while a medical student may have a right to clinical education, the obligation to fulfil this right rests with the medical university and not on the patients of its teaching hospitals. Solutions Several proposals are made about how to satisfy this need without infringing on the patient's right to refuse participation, explaining the patient's rights and role in clinical teaching, and the use of standardized patients where necessary. [source] Distributional Implications of Tax Relief on Voluntary Private Pensions in Spain,FISCAL STUDIES, Issue 2 2007José-Ignacio Antón Using taxation statistics, this paper explores the distributional implications of tax relief on private pensions in Spain in 2002. For this purpose, the author suggests a decomposition of the Kakwani index and its generalisations that allows us to distinguish between the regressivity caused by targeting and that due to benefits allocation among recipients. This paper finds that these tax incentives are regressive - mainly for the latter reason - and have negative although small distributional effects. Finally, this work presents several proposals for reform of the current system and simulates their implications for equity. [source] Why do we need children's participation?JOURNAL OF COMMUNITY & APPLIED SOCIAL PSYCHOLOGY, Issue 6 2001The importance of children's participation in changing the city Abstract After examining the characteristics of the degradation of the urban environment and the costs that this entails for the child's development, in particular as far as play experience and autonomous mobility are concerned, the article goes on to discuss the role of the children's contribution to the promotion of real and consistent change in the city. The reasons underlying the recent increase in the number of experiments of children's participation are examined together with the main characteristics of this strategy as a privileged access to knowledge concerning the needs of our younger citizens and as an innovative resource in solving the city's problems. It is shown how children's participation experiences can lead to the acquisition of a fresh sensitivity and competence by city administrators and technicians. An analysis is made of several proposals made by children in the course of participation experiments followed by the authors in cities in Italy and abroad during 10 year's of activities in the ,The Children's City' project. These proposals confirm the children's capacity to identify the city's problems as they emerge and to propose solutions that are often innovative or useful for all members of the population. Copyright © 2001 John Wiley & Sons, Ltd. [source] Theoretical study of ribonucleotide reductase mechanism-based inhibition by 2,-azido-2,-deoxyribonucleoside 5,-diphosphatesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2004Susana Pereira Abstract 2,-Azido-2,-deoxyribonucleoside 5,-diphosphates are mechanism-based inhibitors of Ribonucleotide Reductase. Considerable effort has been made to elucidate their mechanism of inhibition, which is still controversial and not fully understood. Previous studies have detected the formation of a radical intermediate when the inhibitors interact with the enzyme, and several authors have proposed possible structures for this radical. We have conducted a theoretical study of the possible reactions involved, which allowed us to identify the structure of the new radical among the several proposals. A new reactional path is also proposed that is the most kinetically favored to yield this radical and ultimately inactivate the enzyme. The energetic involved in this mechanism, both for radical formation and radical decay, as well as the calculated Hyperfine Coupling Constants for the radical intermediate, are in agreement with the correspondent experimental values. This mechanistic alternative is fully coherent with remaining experimental data. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 227,237, 2004 [source] In vivo horizontal forces on implants depending on the type of occlusionJOURNAL OF ORAL REHABILITATION, Issue 9 2002T. MORNEBURG Minimizing horizontal forces on implants is one of the important aims of an occlusal design. Therefore, several proposals have been made in literature, e.g. flat cuspal slopes or narrow occlusal surfaces. Our aim was to test how these occlusal designs would influence horizontal forces. Ten healthy subjects with unilateral partially edentulous arches were provided with fixed partial dentures (FPD) on two ITI-implants. The opposing jaw was fully dentate. After an adaptation of 6 month measurement setups with a measuring FPD were put into the mouth. The sensoring device, which consisted of two abutments equipped with strain gauges, evaluated the forces in three dimensions. For each person three FPDs were made with a different design of the occlusal surface. The first FPD exhibited cusps with steep slopes (S), the second showed flat cusps (F) and the third had a narrow occlusal surface (N). The peak forces of the chewing cycles of each patient were evaluated. While chewing wine gum the average values of the vertical forces of the three different FPDs showed no significant differences and amounted to between 253·8 N (s.d. 85·7 N) and 273·9 N (s.d. 63·7 N). With the first FPD (S) mean horizontal forces of 47·9 N (s.d. 34·8 N) were found whereas with the flat surface an average force of 47·4 N (s.d. 37·1 N) was measured. The narrow occlusal surface was associated with an average reduction of the horizontal forces of about 50·9% to a mean value of 24·4 N (s.d. 10·6 N) (P < 0·005). The inclination of occlusal slopes did neither affect vertical nor horizontal forces significantly. However, narrowing of the occlusal surface in the oro-vestibular direction by 30% showed a significant reduction of the lateral forces exerted on the implants by more than 50%. A reduced oro-vestibular width of the occlusal surface is recommended especially for diameter-reduced implants, in case of an unfavourable relationship between implant and crown length or for implants that are strongly inclined to the occlusal plane. [source] A multifaceted sensitivity analysis of the Slovenian public opinion survey dataJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 2 2009Caroline Beunckens Summary., Many models to analyse incomplete data have been developed that allow the missing data to be missing not at random. Awareness has grown that such models are based on unverifiable assumptions, in the sense that they rest on the (incomplete) data only in part, but that inferences nevertheless depend on what the model predicts about the unobserved data, given the observed data. This explains why, nowadays, considerable work is being devoted to assess how sensitive models for incomplete data are to the particular model chosen, a family of models chosen and the effect of (a group of) influential subjects. For each of these categories, several proposals have been formulated, studied theoretically and/or by simulations, and applied to sets of data. It is, however, uncommon to explore various sensitivity analysis avenues simultaneously. We apply a collection of such tools, some after extension, to incomplete counts arising from cross-classified binary data from the so-called Slovenian public opinion survey. Thus for the first time bringing together a variety of sensitivity analysis tools on the same set of data, we can sketch a comprehensive sensitivity analysis picture. We show that missingness at random estimates of the proportion voting in favour of independence are insensitive to the precise choice of missingness at random model and close to the actual plebiscite results, whereas the missingness not at random models that are furthest from the plebiscite results are vulnerable to the influence of outlying cases. Our approach helps to illustrate the value of comprehensive sensitivity analysis. Ideas are formulated on the methodology's use beyond the data analysis that we consider. [source] Flagellar oscillation: a commentary on proposed mechanismsBIOLOGICAL REVIEWS, Issue 3 2010David M. Woolley Eukaryotic flagella and cilia have a remarkably uniform internal ,engine' known as the ,9+2' axoneme. With few exceptions, the function of cilia and flagella is to beat rhythmically and set up relative motion between themselves and the liquid that surrounds them. The molecular basis of axonemal movement is understood in considerable detail, with the exception of the mechanism that provides its rhythmical or oscillatory quality. Some kind of repetitive ,switching' event is assumed to occur; there are several proposals regarding the nature of the ,switch' and how it might operate. Herein I first summarise all the factors known to influence the rate of the oscillation (the beating frequency). Many of these factors exert their effect through modulating the mean sliding velocity between the nine doublet microtubules of the axoneme, this velocity being the determinant of bend growth rate and bend propagation rate. Then I explain six proposed mechanisms for flagellar oscillation and review the evidence on which they are based. Finally, I attempt to derive an economical synthesis, drawing for preference on experimental research that has been minimally disruptive of the intricate structure of the axoneme. The ,provisional synthesis' is that flagellar oscillation emerges from an effect of passive sliding direction on the dynein arms. Sliding in one direction facilitates force-generating cycles and dynein-to-dynein synchronisation along a doublet; sliding in the other direction is inhibitory. The direction of the initial passive sliding normally oscillates because it is controlled hydrodynamically through the alternating direction of the propulsive thrust. However, in the absence of such regulation, there can be a perpetual, mechanical self-triggering through a reversal of sliding direction due to the recoil of elastic structures that deform as a response to the prior active sliding. This provisional synthesis may be a useful basis for further examination of the problem. [source] Exploring the Structural Complexities of Metal,Metalloid Nanoparticles: The Case of Ni,B as CatalystCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2009Junfeng Geng Dr. Abstract Understanding of the structural complexities of metal,metalloid nanoparticles is at the heart of several proposals for investigating the physical properties and practical applications of these bi-elemental nanomaterials. To date, the most widely studied metal,metalloid is the nickel,boron (Ni,B) system; however, the exact nature of the structure of the material itself has remained unclear. Herein we show our systematic investigations of the material in an attempt to reveal its fascinating nanostructure. The relation between its high catalytic activity and the ultrafine structure is explored, and the work has been further extended to the formation of colloidal Ni,B nanoparticles. The results presented in this work may represent a substantial progress toward a full understanding of the nickel,boron chemistry. 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