Search results for "Structural change"
showing 10 items of 44 documents
X-ray powder diffraction and LIESST-effect of the spin transition material [Fe(bpp)2](NCS)2·2H2O
2006
Abstract We have studied the X-ray powder diffraction of the spin transition material [Fe(bpp)2](NCS)2 · 2H2O (bpp: 2,6-bis(pyrazol-3-yl)pyridine) at room temperature. Two crystallographic phases have been observed depending on the sample history of this material. The results obtained corroborate the earlier observations from magnetic and calorimetric studies. Relatively prolonged exposure of the sample to X-rays caused a structural change. LIESST and Reverse-LIESST effects, characterised by 57Fe Mossbauer spectroscopy, have been observed in this material.
Structural photoactivation of a full-length bacterial phytochrome
2016
Time-resolved x-ray solution scattering reveals the conformational signaling mechanism of a bacterial phytochrome.
Structural Changes in Nanoporous MFI Zeolites Induced by Tetrachloroethene Adsorption: A Joint Experimental and Simulation Study
2011
A joint experimental and molecular simulation study was performed to investigate the adsorption of tetrachloroethene on two MFI zeolites, ZSM-5 with a Si/Al ratio of 26.5, and silicalite-1, which is the pure silica form of ZSM-5. Adsorption isotherms and isosteric heats of adsorption of tetrachloroethene were measured and compared to molecular simulation results. Experimental curves for both MFI zeolites show a step at loading of 4 molecules·uc−1 that was interpreted in terms of a structural change of the host framework. A thermodynamic analysis based on the osmotic ensemble scheme allowed attributing this step to a symmetry change from ORTHO (orthorhombic form with Pnma symmetry) to PARA (…
The Effect of Bias Field on Dielectric Response in Lead Ferrotantalate Ceramics
2011
Studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics at low- and infra-low-frequencies under bias field over a wide range of temperatures are reported. Applied bias field is found to broaden the ϵ′(Т) maxima shifting positions Тm of the maximums to higher temperatures. Additional anomalies in the dielectric response are revealed at T<Тm. The anomalies in the vicinity of Тm are related to structural change at phase transition, while those observed at TТm – to magneto-electric interactions in PbFe1/2Ta1/2O3.
Unveiling the timescale of the R-T transition in human hemoglobin.
2010
Time-resolved wide-angle X-ray scattering, a recently developed technique allowing to probe global structural changes of proteins in solution, was used to investigate the kinetics of R-T quaternary transition in human hemoglobin and to systematically compare it to that obtained with time-resolved optical spectroscopy under nearly identical experimental conditions. Our data reveal that the main structural rearrangement associated with the R-T transition takes place approximately 2 mus after the photolysis of hemoglobin at room temperature and neutral pH. This finding suggests that the 20-mus step observed with time-resolved optical spectroscopy corresponds to a small and localized structural…
Aroma behaviour during steam cooking within a potato starch-based model matrix.
2012
To help understand the organoleptic qualities of steam cooked foods, the kinetics of aroma release during cooking in a potato starch based model matrix was studied. Behaviour of components having a major impact in potato flavour were studied using solid phase micro extraction-gas chromatography (SPME-GC). Evolution of microstructure of potato starch model-matrix during steam cooking process was analyzed using environmental scanning electron microscopy (ESEM). Both aroma compounds that are naturally present in starch matrix and those that were added were analyzed. Both the aroma compounds naturally presented and those added had different behaviour depending on their physico-chemical properti…
Synchrotron powder-diffraction study of the spin transition compound [Fe(bpp)2](NCS)2·2H2O and soft X-ray-induced structural phase conversion
2008
Abstract We have studied the high spin and low spin structural phases of the two-step spin transition compound [Fe(bpp) 2 ](NCS) 2 ·2H 2 O (bpp: 2,6-bis(pyrazol-3-yl)pyridine) of different sample history with X-ray synchrotron ( λ ∼ 0.32 A) powder diffraction at different temperatures as well as with usual X-ray ( λ ∼ 1.54 A) powder diffraction at room temperature by performing rapid repeated scans at regular intervals of time. A structural phase transition occurs only during the first step of the spin transition. Time dependent interconversions of the two crystallographic phases have been observed at room temperature for this material. The results indicate that a soft X-ray (Cu-K α )-ind…
Counterfactual Distribution Dynamics across European Regions
2009
This paper proposes a methodology which combines elements of parametric regression analysis with the nonparametric distribution dynamics approach in order to analyse the role of some variables in the convergence of productivity across European regions over the period 1980-2002. We find that the initial productivity crucially accounts in the convergence process across European regions. Differently, employment growth seems not to play a role, while the Structural and Cohesion Funds seem to play a positive role, even though such effect seems to be very low and statistically significant only at the low bound of the range of initial productivity. The structural change of regional economies plays a p…
Productivity Dynamics across European Regions: the Impact of Structural and Cohesion Funds
2009
This paper analyzes the impact of the European Union regional policy of the three programming periods 1975-1988, 1989-1993 and 1994-1999 on the dynamics of productivity of European regions. On average, funding had a positive, but concave, effect on productivity growth. In particular, a share of funds on GVA of 10% GVA is estimated to raise the regional growth rate of about 0.9% per year. However, by separately considering the three programming periods and the composition of the funds according to the objectives defined by the EU, we find that: i) only the funds allocated in the second and third programming periods, when they remarkably increased, had a significant impact; and ii) only Objective…
Improvement of the photo-stability of polystyrene-block-polybutadiene-block-polystyrene through carbon nanotubes
2015
Abstract The photo-stability of Polystyrene-Polybutadiene-Polystyrene (SBS) based nanocomposites containing bare multi-walled carbon nanotubes (CNTs) and carbon nanotubes bearing carboxylic functional groups (CNTs-COOH) in comparison to that of pristine SBS has been studied. The photo-oxidation of pristine SBS occurs through crosslinking reactions and oxidized species formation and both these processes begin at early stage of exposure. The formation of crosslinking, formerly in polybutadiene phase, assessed by spectroscopical (FTIR), mechanical, dynamic mechanical and rheological analysis, leads to occurrence of internal mechanical stresses in the solid state and the SBS samples become prem…