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Indirect Methods (indirect + methods)
Selected AbstractsOptimal Control of Rigid-Link Manipulators by Indirect MethodsGAMM - MITTEILUNGEN, Issue 1 2008Rainer Callies Abstract The present paper is a survey and research paper on the treatment of optimal control problems of rigid-link manipulators by indirect methods. Maximum Principle based approaches provide an excellent tool to calculate optimal reference trajectories for multi-link manipulators with high accuracy. Their major drawback was the need to explicitly formulate the complicated system of adjoint differential equations and to apply the full apparatus of optimal control theory. This is necessary in order to convert the optimal control problem into a piecewise defined, nonlinear multi-point boundary value problem. An accurate and efficient access to first- and higher-order derivatives is crucial. The approach described in this paper allows it to generate all the derivative information recursively and simultaneously with the recursive formulation of the equations of motion. Nonlinear state and control constraints are treated without any simplifications by transforming them into sequences of systems of linear equations. By these means, the modeling of the complete optimal control problem and the accompanying boundary value problem is automated to a great extent. The fast numerical solution is by the advanced multiple shooting method JANUS. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The application of distance distribution functions to structural analysis of core,shell particlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Oleksandr O. Mykhaylyk The structure of core,shell latex particles of polymethylmethacrylate (the core) and polyurethane (the shell) have been investigated by methods of small-angle X-ray scattering (SAXS) and atom-force microscopy. A set of SAXS patterns has been obtained using contrast variation method. Indirect methods have been used to follow the evolution of distance distribution functions from SAXS for lattices in various sucrose solutions over a range of solution density, yielding structural parameters of the particles such as core size, shell thickness and density of the polymers including density deviations within the particle's core and shell. A model for an ensemble of core,shell particles with a normal distribution of average electron density of both the core and the shell has been developed to fit the distance distribution functions using a random search algorithm. The effects of nanophase separation in the polyurethane is estimated using Monte Carlo simulations of the distance distribution functions where the phase-separated polyurethane is represented by spherical truncated cones in a shell simulating the location of hard and soft polyurethane blocks, respectively. [source] Quantitative MRI for the assessment of bone structure and function,NMR IN BIOMEDICINE, Issue 7 2006Felix W. Wehrli Abstract Osteoporosis is the most common degenerative disease in the elderly. It is characterized by low bone mass and structural deterioration of bone tissue, leading to morbidity and increased fracture risk in the hip, spine and wrist,all sites of predominantly trabecular bone. Bone densitometry, currently the standard methodology for diagnosis and treatment monitoring, has significant limitations in that it cannot provide information on the structural manifestations of the disease. Recent advances in imaging, in particular MRI, can now provide detailed insight into the architectural consequences of disease progression and regression in response to treatment. The focus of this review is on the emerging methodology of quantitative MRI for the assessment of structure and function of trabecular bone. During the past 10 years, various approaches have been explored for obtaining image-based quantitative information on trabecular architecture. Indirect methods that do not require resolution on the scale of individual trabeculae and therefore can be practiced at any skeletal location, make use of the induced magnetic fields in the intertrabecular space. These fields, which have their origin in the greater diamagnetism of bone relative to surrounding marrow, can be measured in various ways, most typically in the form of R2,, the recoverable component of the total transverse relaxation rate. Alternatively, the trabecular network can be quantified by high-resolution MRI (µ-MRI), which requires resolution adequate to at least partially resolve individual trabeculae. Micro-MRI-based structure analysis is therefore technically demanding in terms of image acquisition and algorithms needed to extract the structural information under conditions of limited signal-to-noise ratio and resolution. Other requirements that must be met include motion correction and image registration, both critical for achieving the reproducibility needed in repeat studies. Key clinical applications targeted involve fracture risk prediction and evaluation of the effect of therapeutic intervention. Copyright © 2006 John Wiley & Sons, Ltd. [source] General theory of domain decomposition: Indirect methodsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 3 2002Ismael Herrera Abstract According to a general theory of domain decomposition methods (DDM), recently proposed by Herrera, DDM may be classified into two broad categories: direct and indirect (or Trefftz-Herrera methods). This article is devoted to formulate systematically indirect methods and apply them to differential equations in several dimensions. They have interest since they subsume some of the best-known formulations of domain decomposition methods, such as those based on the application of Steklov-Poincaré operators. Trefftz-Herrera approach is based on a special kind of Green's formulas applicable to discontinuous functions, and one of their essential features is the use of weighting functions which yield information, about the sought solution, at the internal boundary of the domain decomposition exclusively. A special class of Sobolev spaces is introduced in which boundary value problems with prescribed jumps at the internal boundary are formulated. Green's formulas applicable in such Sobolev spaces, which contain discontinuous functions, are established and from them the general framework for indirect methods is derived. Guidelines for the construction of the special kind of test functions are then supplied and, as an illustration, the method is applied to elliptic problems in several dimensions. A nonstandard method of collocation is derived in this manner, which possesses significant advantages over more standard procedures. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 296,322, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/num.10008 [source] Electrochemical Nitric Oxide Sensors for Biological Samples , Principle, Selected Examples and ApplicationsELECTROANALYSIS, Issue 1 2003Fethi Bedioui Abstract The discoveries made in the 1980s that NO could be synthesized by mammalian cells and could act as physiological messenger and cytotoxic agent had elevated the importance of its detection. The numerous properties of NO, that enable it to carry out its diverse functions, also present considerable problems when attempting its detection and quantification in biological systems. Indeed, its total free concentration in physiological conditions has been established to be in nanomolar range. Thus, detection of nitric oxide remains a challenge, pointing out the difficult dual requirements for specificity and sensitivity. Exception made for the electrochemical techniques, most of the approaches (namely UV-visible spectroscopy, fluorescence, electron paramagnetic resonance spectroscopy) use indirect methods for estimating endogenous NO, relying on measurements of secondary species such as nitrite and nitrate or NO-adducts. They also suffer from allowing only ex situ measurements. So, the only strategies that allow a direct and in vivo detection of NO are those based on the use of ultramicroelectrodes. The reality is that surface electrode modification is needed to make the ultramicroelectrode material selective for NO. Therefore, the design of modified electrode surfaces using organized layers is very attractive and provides the ideal strategy. This review addresses a global description of the various approaches that have involved chemically modified microelectrodes specially designed for the electrochemical detection of NO in biological media. Selected significant examples of applications in biological tissues are also reported in order to highlight the importance of this approach in having new insights into the modulatory role of NO in physiology and pathophysiology. [source] Concept Acquisition within the Context of an AS Media Studies CourseENGLISH IN EDUCATION, Issue 2 2003Vivien Whelpton Abstract This article explores the means by which students' concept formation can be promoted and outlines findings from an action research project undertaken with a class of 17-year-old AS Media Studies students as a submission for the British Film Institute's MA Certificate in Media Education in 2001. It argues that academic concepts can neither be allowed to develop spontaneously nor be directly taught, but that indirect methods of teacher intervention can be found. It also examines the relationship between thought and language and argues that, while contact with academic discourse can be alienating, its features include a fluency which the handling of complex and abstract ideas requires, particularly in the written mode. The writer suggests that, while this discourse cannot be explicitly taught or learned, modelling techniques may offer a useful approach. [source] Optimal Control of Rigid-Link Manipulators by Indirect MethodsGAMM - MITTEILUNGEN, Issue 1 2008Rainer Callies Abstract The present paper is a survey and research paper on the treatment of optimal control problems of rigid-link manipulators by indirect methods. Maximum Principle based approaches provide an excellent tool to calculate optimal reference trajectories for multi-link manipulators with high accuracy. Their major drawback was the need to explicitly formulate the complicated system of adjoint differential equations and to apply the full apparatus of optimal control theory. This is necessary in order to convert the optimal control problem into a piecewise defined, nonlinear multi-point boundary value problem. An accurate and efficient access to first- and higher-order derivatives is crucial. The approach described in this paper allows it to generate all the derivative information recursively and simultaneously with the recursive formulation of the equations of motion. Nonlinear state and control constraints are treated without any simplifications by transforming them into sequences of systems of linear equations. By these means, the modeling of the complete optimal control problem and the accompanying boundary value problem is automated to a great extent. The fast numerical solution is by the advanced multiple shooting method JANUS. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A New Method for Estimating Race/Ethnicity and Associated Disparities Where Administrative Records Lack Self-Reported Race/EthnicityHEALTH SERVICES RESEARCH, Issue 5p1 2008Marc N. Elliott Objective. To efficiently estimate race/ethnicity using administrative records to facilitate health care organizations' efforts to address disparities when self-reported race/ethnicity data are unavailable. Data Source. Surname, geocoded residential address, and self-reported race/ethnicity from 1,973,362 enrollees of a national health plan. Study Design. We compare the accuracy of a Bayesian approach to combining surname and geocoded information to estimate race/ethnicity to two other indirect methods: a non-Bayesian method that combines surname and geocoded information and geocoded information alone. We assess accuracy with respect to estimating (1) individual race/ethnicity and (2) overall racial/ethnic prevalence in a population. Principal Findings. The Bayesian approach was 74 percent more efficient than geocoding alone in estimating individual race/ethnicity and 56 percent more efficient in estimating the prevalence of racial/ethnic groups, outperforming the non-Bayesian hybrid on both measures. The non-Bayesian hybrid was more efficient than geocoding alone in estimating individual race/ethnicity but less efficient with respect to prevalence (p<.05 for all differences). Conclusions. The Bayesian Surname and Geocoding (BSG) method presented here efficiently integrates administrative data, substantially improving upon what is possible with a single source or from other hybrid methods; it offers a powerful tool that can help health care organizations address disparities until self-reported race/ethnicity data are available. [source] Direct and indirect methods to simulate the actual evapotranspiration of an irrigated overhead table grape vineyard under Mediterranean conditionsHYDROLOGICAL PROCESSES, Issue 2 2008Gianfranco Rana Abstract Two methods, indirect and direct, for simulating the actual evapotranspiration (E) were applied to an irrigated overhead table grape vineyard during summer, situated in the Mediterranean region (south Italy), over two successive years. The first method, indirect but more practical, uses the crop coefficient (Kc) approach and requires determination of the reference evapotranspiration E0 (FAO (Food and Agriculture Organization) method). This method underestimated on average by 17% the daily values of the actual evapotranspiration E. The analysis in this paper shows that the values of Kc for the table grapes determined by the FAO method seem to not be valid in our experimental conditions. Similar conclusions can be found in the literature for the table grape cultivated under different experimental conditions and using different training systems. The second method, is a direct method for estimating the evapotranspiration. It requires development of a model for the overhead table grape vineyard E, following the Penman,Monteith one-step approach, and using standard meteorological variables as inputs for the determination of the canopy resistance. This method, which needs a particularly simple calibration, provided a better simulation of the hourly and daily evapotranspiration than the indirect method. In additon, the standard error of the daily values for the direct method ( ± 0 · 41 mm) was about 50% lower than that obtained for the indirect method, also when the indirect method used a locally calibrated coefficient Kc instead of a generic Kc. Both, for practical application and theoretical issues, the advantages and disadvantages linked to the use of each tested method are discussed in detail. Copyright © 2007 John Wiley & Sons, Ltd. [source] Direct detection of the protein quaternary structure and denatured entity by small-angle scattering: guanidine hydrochloride denaturation of chaperonin protein GroELJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2002Yasutaka Seki A change in the higher-order structure of an oligomeric protein is directly detectable by small-angle scattering. A small-angle X-ray scattering (SAXS) study of the denaturation process of the chaperonin protein GroEL by guanidine hydrochloride (GdnHCl) showed that the disappearance of the quaternary structure can be monitored by using a Kratky plot of the scattered intensities, demonstrating the advantage of the SAXS method over other indirect methods, such as light scattering, circular dichroism (CD), fluorescence and sedimentation. The collapse of the quaternary structure was detected at a GdnHCl concentration of 0.8,M for a solution containing ADP (adenosine diphosphate)/Mg2+(2,mM)/K+. From pairwise plots of the change in forward scattering intensity J(0)/C (weight-average molecular weight) and the z -average (root mean square) radius of gyration against the GdnHCl concentration, the stability and nature of the denatured protein can be determined. The SAXS results suggest that the GroEL tetradecamer directly dissociates to the unfolded coil without going through a globular monomer state. The denatured ensemble is not a single unfolded monomer coil particle, but some mixture of entangled aggregates and a monomer of the coil molecules. Small-angle scattering is a powerful method for the detection and study of changes in quaternary and higher-order structures of oligomeric proteins. [source] Quarterly real GDP estimates for China and ASEAN4 with a forecast evaluationJOURNAL OF FORECASTING, Issue 6 2004Tilak Abeysinghe Abstract The growing affluence of the East and Southeast Asian economies has come about through a substantial increase in their economic links with the rest of the world, the OECD economies in particular. Econometric studies that try to quantify these links face a severe shortage of high-frequency time series data for China and the group of ASEAN4 (Indonesia, Malaysia, Philippines and Thailand). In this paper we provide quarterly real GDP estimates for these countries derived by applying the Chow,Lin related series technique to annual real GDP series. The quality of the disaggregated series is evaluated through a number of indirect methods. Some potential problems of using readily available univariate disaggregation techniques are also highlighted. Copyright © 2004 John Wiley & Sons, Ltd. [source] 146 Methodological Problems of Marine Macroalgae Age EstimationJOURNAL OF PHYCOLOGY, Issue 2003O. N. Selivanova To know the birthdate of any organism is the best way to estimate its age. Unfortunately direct chronometric method, being the most reliable, can't be generally applied. In these cases indirect methods are used. One of them , morphobiometric , is used to estimate age of trees by the number of year rings in the stem or fucoid algae by the number of dichotomic branching. Both methods are widely used however the data obtained may deviate considerably from the true age of the plants. In this study I compared chronometric data on algal age to those obtained by calculation of the number of dichotomic branching in Fucus evenescens growing in Kamchatka, Russia. Field experiments were carried out from 1999 to 2002. No marked with plastic lables plants survived for 3 years. The comparison showed that morphobiometric data exceeded true age of algae at least in 2,3, sometimes even in 5 times. The first year plants can produce up to 5 dichotomous branching per season and can become fertile in the first months of their life. There is information in Russian literature that Kamchatka's F. evenescens age can reach 12,15 years. I consider these data erroneous and suppose underestimation of the number of branches in the early stages of Fucus development to be the cause of overestimation of its true age. In my opinion it is not more than 4,5 years. Application of morphobiometric method is more problematic in case of polytomy. Besides that this method usually causes damage or death of the plant. So I consider that only chronometric method can give the researcher exact information on the age of macroalgae. [source] General theory of domain decomposition: Indirect methodsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 3 2002Ismael Herrera Abstract According to a general theory of domain decomposition methods (DDM), recently proposed by Herrera, DDM may be classified into two broad categories: direct and indirect (or Trefftz-Herrera methods). This article is devoted to formulate systematically indirect methods and apply them to differential equations in several dimensions. They have interest since they subsume some of the best-known formulations of domain decomposition methods, such as those based on the application of Steklov-Poincaré operators. Trefftz-Herrera approach is based on a special kind of Green's formulas applicable to discontinuous functions, and one of their essential features is the use of weighting functions which yield information, about the sought solution, at the internal boundary of the domain decomposition exclusively. A special class of Sobolev spaces is introduced in which boundary value problems with prescribed jumps at the internal boundary are formulated. Green's formulas applicable in such Sobolev spaces, which contain discontinuous functions, are established and from them the general framework for indirect methods is derived. Guidelines for the construction of the special kind of test functions are then supplied and, as an illustration, the method is applied to elliptic problems in several dimensions. A nonstandard method of collocation is derived in this manner, which possesses significant advantages over more standard procedures. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 296,322, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/num.10008 [source] Comparing indirect methods of digit ratio (2D:4D) measurementAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2009Christoph J. Kemper The ratio of the lengths of the second and fourth finger (2D:4D) has been proposed to index prenatal exposure to androgens. Different methods have been utilized to measure digit ratio, however, their measurement precision and economy have not been systematically compared yet. Using different indirect methods (plastic ruler, caliper, computer software), three independent raters measured finger lengths of 60 participants. Generally, measurement precision (intraclass correlation coefficient, technical error of measurement, and relative technical error of measurement) was acceptable for each method. However, precision estimates were highest for the computer software, indicating excellent measurement precision. Estimates for the caliper method were somewhat lower followed by ruler which had the lowest precision. On the contrary, the software-based measurements took somewhat longer to complete than the other methods. Nonetheless, we would favor the use of these tools in digit ratio research because of their relative superior reliability which could be crucial when associations with other variables are expected to be low to moderate or sample size is limited. Software offers several promising opportunities that may contribute to an accurate identification of the proximal finger crease (e.g., zooming, adjusting contrast, etc.). Am. J. Hum. Biol., 2009. © 2008 Wiley-Liss, Inc. [source] Runner balancing by a direct genetic optimization of shrinkagePOLYMER ENGINEERING & SCIENCE, Issue 10 2004Kevin Alam The proposed approach to the runner-balancing problem evaluates differences in shrinkage among the cavities and uses this direct measure of product quality to balance runner systems instead of the indirect methods traditionally used. The runner-balancing problem was characterized by multiple objectives, which consider both cost and product quality. The resulting multi-objective optimization problem was solved with a multi-objective genetic algorithm. Runner-balancing optimizations varied the diameters and lengths of the runners and the processing conditions. The results suggest that balanced runner systems, which exhibit large differences in cavity pressure profiles, can have lower product costs than systems characterized by similar fill times and cavity pressure profiles. The optimization of the secondary runner lengths and processing conditions also reduced costs significantly. Polym. Eng. Sci. 44:1949,1959, 2004. © 2004 Society of Plastics Engineers. [source] Dimensions and dynamics of irregular migrationPOPULATION, SPACE AND PLACE (PREVIOUSLY:-INT JOURNAL OF POPULATION GEOGRAPHY), Issue 3 2010Khalid Koser Abstract This contribution critically reviews existing data and other recent sources to provide an overview of the dimensions and dynamics of contemporary irregular migration. First it considers the utility and uses of irregular migrant statistics, considering their inherent inaccuracy, their inability to distinguish different types of irregular migrant, the way that data is collected, and the purposes to which it is put. The second section reviews the conceptual and practical challenges associated with counting irregular migrants. Conceptual challenges include: differentiating stocks from flows, addressing the variety of routes into irregularity, distinguishing migrant smuggling from human trafficking, separating asylum from aggregate statistics, and acknowledging that migrants' legal status can change quickly. Practical challenges associated with a series of direct and indirect methods for collecting statistics (including national censuses) are reviewed, and the difficulty for researchers to access official statistics highlighted. The third section presents estimates of the scale and scope of irregular migration, and data from regularisation programmes in various high-income countries. The fourth section reviews explanations for irregular migration, distinguishing macro-level explanations that focus on structural causes from meso-level explanations concerned with the role of policies and intermediaries, and also notes the shortage of micro-level explanations concerned with individual and family decision-making. The final section considers the consequences of irregular migration, with a particular focus on security. The review suggests that while irregular migration can undermine state sovereignty, the implications of irregular migration for the ,human security' of those involved should not be underestimated. The conclusion considers some implications for future research. Copyright © 2009 John Wiley & Sons, Ltd. [source] Biodistribution of the RD114/mammalian type D retrovirus receptor, RDRTHE JOURNAL OF GENE MEDICINE, Issue 3 2004Bronwyn J. Green Abstract Background The limited expression of viral receptors on target cells is a recognized barrier to therapeutic gene transfer. Previous analysis of receptor expression has been performed using indirect methods due to a lack of receptor-specific antibodies. Methods In this report we have used anti-RDR antiserum to provide direct histochemical and flow cytometric analysis of the expression of RDR, which is the cognate receptor for RD114-pseudotyped vectors as well as being a neutral amino acid transporter. Results RDR was present on a range of normal tissues with relevance to gene therapy including: colon, testis, ovary, bone marrow and skeletal muscle. It was also highly expressed on immature cells present in the squamous epithelia of skin, cervix, nasal mucosa, bronchus and tonsil. Of relevance to possible germline gene transfer, we demonstrated a lack of RDR expression on male or female germ cells. RDR expression on mature hemopoietic cell subsets showed up to 5-fold variability between individuals within each lineage,with some individuals expressing low levels of RDR across all blood lineages. Both myeloid and monocytic lineages contained the highest fraction of cells expressing RDR, whereas lymphoid lineages showed the lowest. Coexpression of CD34 and RDR ranged from 2.04 to 0.44% in G-CSF-mobilized peripheral blood samples. Conclusions As a means to optimize gene transfer protocols, biodistribution studies such as these are fundamental to enable targeting of the virus receptor most abundantly expressed on relevant populations. The inter-individual variation of receptor expression seen here also raises the possible requirement for tailor-made gene therapy protocols. Copyright © 2004 John Wiley & Sons, Ltd. [source] Recruiting older adults to health research studies: A systematic reviewAUSTRALASIAN JOURNAL ON AGEING, Issue 3 2009Josephine Auster Aim:, To provide a systematic review of papers comparing the effectiveness of different strategies to recruit older adults (aged 50 years and over) to participate in health research studies, to guide successful recruitment in future research. Methods:, Four major databases were searched for papers published between 1995 and 2008 with: target group aged 50 years or over; participants allocated to receive one of two or more recruitment strategies; and an outcome measure of response rate or enrolment in study. Results:, Twelve papers were included in the review. Conclusion:, For postal questionnaires, recruitment strategies used with older adults had comparable outcomes to those used to recruit from the general population. For other types of studies, strategies involving face-to-face contact may be more effective than indirect methods, but this needs to be balanced against feasibility. Overall, little evidence on the topic exists and more rigorous investigation is necessary. [source] EPISTEMOLOGICAL CONSIDERATIONS ON NEUROIMAGING , A CRUCIAL PREREQUISITE FOR NEUROETHICSBIOETHICS, Issue 6 2009CHRISTIAN G. HUBER ABSTRACT Purpose: Whereas ethical considerations on imaging techniques and interpretations of neuroimaging results flourish, there is not much work on their preconditions. In this paper, therefore, we discuss epistemological considerations on neuroimaging and their implications for neuroethics. Results: Neuroimaging uses indirect methods to generate data about surrogate parameters for mental processes, and there are many determinants influencing the results, including current hypotheses and the state of knowledge. This leads to an interdependence between hypotheses and data. Additionally, different levels of description are involved, especially when experiments are designed to answer questions pertaining to broad concepts like the self, empathy or moral intentions. Interdisciplinary theoretical frameworks are needed to integrate findings from the life sciences and the humanities and to translate between them. While these epistemological issues are not specific for neuroimaging, there are some reasons why they are of special importance in this context: Due to their inferential proximity, ,neuro-images' seem to be self-evident, suggesting directness of observation and objectivity. This has to be critically discussed to prevent overinterpretation. Additionally, there is a high level of attention to neuroimaging, leading to a high frequency of presentation of neuroimaging data and making the critical examination of their epistemological properties even more pressing. Conclusions: Epistemological considerations are an important prerequisite for neuroethics. The presentation and communication of the results of neuroimaging studies, the potential generation of new phenomena and new ,dysfunctions' through neuroimaging, and the influence on central concepts at the foundations of ethics will be important future topics for this discipline. [source] Enantioresolution of dl -penicillamineBIOMEDICAL CHROMATOGRAPHY, Issue 1 2010Ravi Bhushan Abstract Penicillamine (PenA) is a nonproteinogenic amino acid containing a thiol group. The three functional groups in penicillamine undergo characteristic chemical reactions and differ in their ability to participate in various chemical and biochemical reactions. d -penicillamine is more active pharmacologically, while the l -isomer occurs ,naturally'. This review deals with the enantioresolution of PenA both by direct and indirect methods using liquid chromatography. HPLC separation of its diastereomers prepared with different chiral derivatizing reagents (on reversed-phase columns) and separation of the derivatives prepared with achiral reagents (on chiral columns or via ligand exchange mode) has been discussed. Separation of enantiomers tagged with achiral reagent (to add a chromophore for ehanced detection) when there is no diastereomer formation has been considered separately. In addition, application of PenA and its derivatives as chiral selector for enentioresolution of certain other compounds has also been discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Determination of absolute configuration,An overview related to this Special IssueCHIRALITY, Issue 5 2008Stig Allenmark Abstract Rapid progress in asymmetric synthesis stimulated a further development of methods and techniques for the determination of absolute configuration of chiral molecules. In recent years the direct methods, i.e. X-ray diffraction analysis, circular dichroism (vibrational and electronic), Raman optical activity, optical rotation measurements, as well as indirect methods for relative configuration assignment with the use of NMR spectroscopy or enzymatic transformations, are receiving increasing attention not only by specialists in the field but also by synthetic and structural chemists alike. This paper provides a short overview of the methods currently used, as well as references to contributions collected in this Thematic Issue of Chirality. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||