			Home About us Contact

Positional Parameters (positional + parameter)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Quality counts: new parameters in blood cell counting

INTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY, Issue 3 2009
C. BRIGGS
Summary Recently several parameters have been introduced to the complete blood count such as nucleated red blood cells, immature granulocytes; immature reticulocyte fraction, immature platelet fraction and red cell fragments as well as new parameters for detection of functional iron deficiency. Leucocyte positional parameters, which may diagnose specific diseases (e.g. differentiate between abnormal lymphocytes in leukaemia and viral conditions and may also detect malarial infection) are now available. At this time they are only used for research; however, generally such parameters later become reportable. One manufacturer's routine analyser allows measurement of cells by flow cytometry using monoclonal antibodies. Currently, there are no accredited external quality assessment schemes (EQAS) for these parameters. For a number of parameters, on some instruments, there is no internal quality control, which brings into question whether these parameters should be used for clinical decision making. Other more established parameters, such as mean platelet volume, red cell distribution width and the erythrocyte sedimentation rate do not have EQAS available. The UK National EQAS for General Haematology held a workshop earlier this year in 2008 to discuss these parameters. Participants were asked to provide a consensus opinion on which parameters are the most important for inclusion in future haematology EQAS. [source]

Automated detection of malaria by means of the haematology analyser Coulter® GEN.STM

INTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY, Issue 6 2004
C. FOURCADE
Summary The haematology analysers Coulter® GEN.STM and LHTM give a set of data ,,positional parameters', which define each WBC population by mean of index values, the mean and the standard deviation (SD) of volume, conductivity and scatter, used to identify the WBC populations. These parameters were analysed in patients investigated for suspicion of malaria, in order to show a difference between malaria negative and malaria positive patients and to use it for malaria detection. The six parameters exhibiting a significant difference between the two groups were submitted to a ROC analysis, which showed both sensitivity >90% and specificity >60% for two parameters, lymphocyte and monocyte SDs of volumes. A discriminator combining the two parameters showed a sensitivity of 96.9% and a specificity of 82.5%. The cut off of the discriminative value was calculated. Because of the good stability and reproducibility of the parameters selected, the test can be used in order to detect patients having a high probability to be malaria positive and to pay particular attention to these blood smears. For more extensive diagnostic use, a standard control procedure of the positional parameters should be introduced. [source]

Mode crystallography of distorted structures

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010
J. M. Perez-Mato
The description of displacive distorted structures in terms of symmetry-adapted modes is reviewed. A specific parameterization of the symmetry-mode decomposition of these pseudosymmetric structures defined on the setting of the experimental space group is proposed. This approach closely follows crystallographic conventions and permits a straightforward transformation between symmetry-mode and conventional descriptions of the structures. Multiple examples are presented showing the insight provided by the symmetry-mode approach. The methodology is shown at work, illustrating its various possibilities for improving the characterization of distorted structures, for example: detection of hidden structural correlations, identification of fundamental and marginal degrees of freedom, reduction of the effective number of atomic positional parameters, quantitative comparison of structures with the same or different space group, detection of false refinement minima, systematic characterization of thermal behavior, rationalization of phase diagrams and various symmetries in families of compounds etc. The close relation of the symmetry-mode description with the superspace formalism applied to commensurate superstructures is also discussed. Finally, the application of this methodology in the field of ab initio or first-principles calculations is outlined. At present, there are several freely available user-friendly computer tools for performing automatic symmetry-mode analyses. The use of these programs does not require a deep knowledge of group theory and can be applied either a posteriori to analyze a given distorted structure or a priori to parameterize the structure to be determined. It is hoped that this article will encourage the use of these tools. All the examples presented here have been worked out using the program AMPLIMODES [Orobengoa et al. (2009). J. Appl. Cryst.42, 820,833]. [source]

How to easily replace the independent atom model , the example of bergenin, a potential anti-HIV agent of traditional Asian medicine

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009
Birger Dittrich
Bergenin, which has been isolated from a variety of tropical plants, has several pharmacological applications in traditional Asian medicine. Its electron-density distribution was obtained from a room-temperature low-resolution X-ray data set measured with point detection making use of multipole populations from the invariom library. Two refinement models were considered. In a first step, positional parameters and ADPs were refined with fixed library multipoles (model E1). This model was suitable to be input into a second refinement of multipoles (model E2), which converged smoothly although based on Cu,K, room-temperature data. Quantitative results of a topological analysis of the electron density from both models were compared with Hartree,Fock and density-functional calculations. With respect to the independent atom model (IAM) more information can be extracted from invariom modelling, including the electrostatic potential and hydrogen-bond energies, which are highly useful, especially for biologically active compounds. The reliability of the applied invariom formalism was assessed by a comparison of bond-topological properties of sucrose, for which high-resolution multipole and invariom densities were available. Since a conventional X-ray diffraction experiment using basic equipment was combined with the easy-to-use invariom formalism, the procedure described here for bergenin illustrates how it can be routinely applied in pharmacological research. [source]

The influence of positional errors on the Debye effects

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2004
P. H. Zwart
The relation between a Gaussian perturbation of the atomic positional parameters and the average squared structure-factor amplitude is presented. Using an error-dependent radial distance distribution of an atomic protein model, it can be shown that the Debye effects diminish exponentially as a function of increasing positional errors. These relations can be used to estimate the quality of an atomic model and the corresponding phases. The limiting case of equal atoms with an infinitely large coordinate error results in the classical Wilson model. [source]

Atomic resolution crystal structure of squid ganglion DFPase

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 10-1 2002
Juergen Koepke
Diisopropylfluorophosphatases (DFP-ases) are capable of detoxifying chemical warfare agents like diisopropylfluorophosphate (DFP) by hydrolysis. The protein reported here was recombinantely expressed in E. coli. The X-ray cystal structure of this enzyme has been refined to a resolution of 0.85 Å and a crystallographic R value of 9.4%. Reversible flash-cooling improved both, mosaicity and resolution of the crystals considerably. The overall structure of this protein represents a six-bladed ,-propeller with two calcium ions bound in a central water filled tunnel. 496 water, 2 glycerol, 2 MES-buffer molecules, and 18 PEG fragments of different lengths could be refined in the solvent region. The 208 most reliable residues, without disorder or reduced occupancy in their side-chains, were finally refined without restraints. A subsequent full-matrix refinement cycle for the positional parameters yielded estimated standard deviations (esds) by matrix inversion. The herewith calculated bond lenghts and bond-esds were used to obtain averaged bond lengths, which have been compared to the restraints used in preceding refinement cycles. [source]

Lymphocyte volume and conductivity indices of the haematology analyser Coulter® GEN.STM in lymphoproliferative disorders and viral diseases

INTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY, Issue 1 2006
M. SILVA
Summary The haematology analyser Coulter® GEN.STM gives a set of data ,,positional parameters', defining white blood cell (WBC) populations by mean of index values (mean and standard deviation of volume, conductivity and scatter, used to identify the WBC populations). The volume and conductivity parameters related to the lymphocytes were analysed at diagnosis in patients suffering from chronic B-lymphocytic leukaemia (B-CLL), other non-CLL lymphoproliferative disorders (OLPD) and viral diseases. The standard deviation of volume index (SDVI) is significantly higher in the three groups, whereas the mean volume index (MVI) is significantly lower in B-CLL, and increased in OLPD and viral diseases. These two groups could be distinguished by their mean conductivity index (MCI), which is significantly lower in viral disease group. Cut-offs were calculated for each parameter by the mean of Receiver Operating Characteristic (ROC) analysis. The study of the detection performances showed that the combination of lymphocyte count with SDVI, MVI and MCI could be used with a good sensitivity and specificity to discriminate between the most frequent lymphocyte pathologies, even in patients with normal lymphocyte count. [source]