Home About us Contact
|
Home About us Contact | ||
|
|
||
Iterative Cycles (iterative + cycle)
Selected AbstractsA framework for teaching scientific inquiry in upper secondary school chemistryJOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 7 2010Lisette van Rens Abstract A framework for teaching scientific inquiry in upper secondary chemistry education was constructed in a design research consisting of two research cycles. First, in a pilot study a hypothetical framework was enriched in collaboration with five chemistry teachers. Second, a main study in this community of teachers and researchers was conducted on the process of designing teaching scientific inquiry based on the enriched framework. Also, the enactment by five teachers and 80 students (age 17) of a designed inquiry module on "Diffusion: moving particles" was studied. This resulted in a theoretically and practically founded framework for teaching scientific inquiry, in which an iterative cycle of inquiry for students and a student inquiry community are essential. © 2009 Wiley Periodicals, Inc. J Res Sci Teach 47:788,806, 2010 [source] Electrochemically Induced Modulation of the Catalytic Activity of a Reversible Redoxsensitive RiboswitchELECTROANALYSIS, Issue 9 2008Denise Strohbach Abstract Over the past decade, RNA conformation has been shown to respond to external stimuli. Thus, dependent on the presence of a high affinity ligand, specifically designed ribozymes can be regulated in a classical allosteric way. In this scenario, a binding event in one part of the RNA structure induces conformational changes in a separated part, which constitutes the catalytic centre. As a result activity is switched on (positive regulation) or off (negative regulation). We have developed a hairpin aptazyme responding to flavine mononucleotide (FMN). Ribozyme activity is dependent on binding of FMN and thus is switched on in the presence of FMN in its oxidized form. Under reducing conditions, however, FMN changes its molecular geometry, which is associated with loss of binding and consequently down-regulation of ribozyme activity. While in previous experiments sodium dithionite was used for reduction of FMN, we now present an assay for electrochemically induced activity switching. We have developed an electrochemical microcell that allows for iterative cycles of reduction/oxidation of FMN in an oxygen free atmosphere and thus for reversible switching of ribozyme activity. The reaction proceeds in droplets of 3 to 10,,L at micro- to nanomolar concentrations of the reaction components. [source] Determining elastic constants of transversely isotropic rocks using Brazilian test and iterative procedureINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2008Yen-Chin Chou Abstract The elastic constants of rocks are the basic parameters for rock mechanics, and play a very important role in engineering design. There are many laboratory methods to determine the elastic constants of transversely isotropic rocks, and the Brazilian test is a popular method. This paper presented a method combination of the Brazilian test, back calculation, and iterative procedure to evaluate the five independent elastic constants of transversely isotropic rocks in laboratory. The strain data at the centre of discs were obtained using Brazilian test. The stresses at the centre of discs were computed using numerical programs. By using back calculation, the temporary elastic constants were computed after the stresses and stains were substituted into elastic mechanics equations. After iterative procedure, the convergent values of the elastic constants can be obtained. One numerical example and three experimental cases were proposed to show the applicability of this method. The convergent values of the five independent elastic constants can be obtained in no more than 10 iterative cycles. The results coming from numerical analysis method exhibited satisfactory outcome in accordance with those of generalized reduced gradient method. The merits of this method include convenient specimen preparation of the Brazilian test, simple iterative procedure, and readily available commercially numerical programs, so that this method can be easily popularized in research and engineering analysis. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dynamic Newton,gradient-direction-type algorithm for multilayer structure determination using grazing X-ray specular scattering: numerical simulation and analysisACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009F. N. Chukhovskii A new dynamic iterative algorithm code for retrieving macroscopic multilayer structure parameters (the layer thickness and complex refraction index for each layer, the surface roughness and the interface roughness between the layers) from specular scattering angular scan data is proposed. The use of conventional direct methods, particularly the well known Newton algorithm and gradient-direction-type algorithm operating dynamically to minimize the error functional in a least-squares fashion, is explored. Such an approach works well and seems to be effective in solving the inverse problem in the high-resolution X-ray reflectometry (HRXR) method. In order to demonstrate some features of the proposed iterative algorithm, numerical calculations for retrieving three-layer structure parameters are carried out using simulated HRXR angular scan data. The calculations indicate clearly that the dynamic iterative algorithm is convergent and capable of yielding the true solution. It is important that the performance coefficient for successful iterative cycles for the absolute minimization of the HRXR error functional is quite high even if the initial values of the search parameters are chosen rather far from the true values. It is particularly noteworthy that the relative number of successful iterative cycles is of the order of 90,40% when only moderately accurate initial parameter values, varying by ±10,40% from the true values, are presumed. [source] Self-interaction chromatography as a tool for optimizing conditions for membrane protein crystallizationACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Mads Gabrielsen The second virial coefficient, or B value, is a measurement of how well a protein interacts with itself in solution. These interactions can lead to protein crystallization or precipitation, depending on their strength, with a narrow range of B values (the `crystallization slot') being known to promote crystallization. A convenient method of determining the B value is by self-interaction chromatography. This paper describes how the light-harvesting complex 1,reaction centre core complex from Allochromatium vinosum yielded single straight-edged crystals after iterative cycles of self-interaction chromatography and crystallization. This process allowed the rapid screening of small molecules and detergents as crystallization additives. Here, a description is given of how self-interaction chromatography has been utilized to improve the crystallization conditions of a membrane protein. [source] | ||||||||||