Structural changes from polyimide films to graphite: Part IV. Novax and PPT

1995 ◽  
Vol 10 (4) ◽  
pp. 1024-1027 ◽  
Author(s):  
C. Bourgerette ◽  
A. Oberlin ◽  
M. Inagaki
Keyword(s):  
Long Range ◽  
Structural Changes ◽  
Film Plane ◽  
High Rank ◽  
Polyimide Films ◽  
Electron Microscopies ◽  
Higher Temperature ◽  
Cross Linker ◽  
Graphite Part

Various polyimide films (Kapton, Upilex, Novax, and PPT) were carbonized and graphitized up to 3000 °C. They were studied by optical and electron microscopies. All films retaining oxygen as a cross linker over 1000 °C, i.e., Kapton, Upilex, and Novax, graphitize as anthracites (high rank coals) do. They get a long range statistical orientation parallel to the film plane with a nanotexture of flattened pores. Graphitization is both sudden and perfect above 2100 °C when the pore walls break. Since oxygen is released at 1000 °C, the film PPT behaves as a compact nonporous graphitizing carbon (orientation parallel to the film plane). Thermal graphitization is progressive and begins at a higher temperature.

scholarly journals Structural Changes in the Acceptor Site of Photosystem II upon Ca2+/Sr2+ Exchange in the Mn4CaO5 Cluster Site and the Possible Long-Range Interactions

Biomolecules ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 371
Author(s):  
Koua
Keyword(s):  
Crystal Structure ◽  
Photosystem Ii ◽  
Long Range ◽  
Electron Acceptor ◽  
Structural Changes ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Long Range Interactions ◽  
Structural Perturbations ◽  
Oxygen Evolving

The Mn4CaO5 cluster site in the oxygen-evolving complex (OEC) of photosystem II (PSII) undergoes structural perturbations, such as those induced by Ca2+/Sr2+ exchanges or Ca/Mn removal. These changes have been known to induce long-range positive shifts (between +30 and +150 mV) in the redox potential of the primary quinone electron acceptor plastoquinone A (QA), which is located 40 Å from the OEC. To further investigate these effects, we reanalyzed the crystal structure of Sr-PSII resolved at 2.1 Å and compared it with the native Ca-PSII resolved at 1.9 Å. Here, we focus on the acceptor site and report the possible long-range interactions between the donor, Mn4Ca(Sr)O5 cluster, and acceptor sites.

scholarly journals Correlation between long range and local structural changes in Ni-rich layered materials during charge and discharge process

2019 ◽  
Vol 412 ◽  
pp. 336-343 ◽  
Author(s):  
Shiyao Zheng ◽  
Chaoyu Hong ◽  
Xiaoyun Guan ◽  
Yuxuan Xiang ◽  
Xiangsi Liu ◽  
...  
Keyword(s):  
Long Range ◽  
Structural Changes ◽  
Layered Materials ◽  
Discharge Process

scholarly journals Long-Range Structural Changes in the Meiotic Nucleus Revealed by Changes in Stress Communication Along the Chromosome

2018 ◽  
Vol 114 (3) ◽  
pp. 30a
Author(s):  
Trent Newman ◽  
Bruno G. Beltran ◽  
James McGehee ◽  
Cori Cahoon ◽  
Daniel Elnatan ◽  
...  
Keyword(s):  
Long Range ◽  
Structural Changes

scholarly journals Phosphorylated cellulose nanofibers exhibit exceptional capacity for uranium capture

Cellulose ◽  
2020 ◽  
Vol 27 (18) ◽  
pp. 10719-10732
Author(s):  
Janika Lehtonen ◽  
Jukka Hassinen ◽  
Avula Anil Kumar ◽  
Leena-Sisko Johansson ◽  
Roni Mäenpää ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Structural Changes ◽  
Cellulose Nanofibers ◽  
Aqueous Media ◽  
Isotherm Models ◽  
Batch Adsorption ◽  
Maximum Adsorption Capacity ◽  
Electron Microscopies ◽  
Network Scanning ◽  
Aqueous Matrices

AbstractWe investigate the adsorption of hexavalent uranium, U(VI), on phosphorylated cellulose nanofibers (PHO-CNF) and compare the results with those for native and TEMPO-oxidized nanocelluloses. Batch adsorption experiments in aqueous media show that PHO-CNF is highly efficient in removing U(VI) in the pH range between 3 and 6. Gelling of nanofiber hydrogels is observed at U(VI) concentration of 500 mg/L. Structural changes in the nanofiber network (scanning and transmission electron microscopies) and the surface chemical composition (X-ray photoelectron spectroscopy) gave insights on the mechanism of adsorption. The results from batch adsorption experiments are fitted to Langmuir, Freundlich, and Sips isotherm models, which indicate a maximum adsorption capacity of 1550 mg/g, the highest value reported so far for any bioadsorbent. Compared to other metals (Zn, Mn, and Cu) and typical ions present in natural aqueous matrices the phosphorylated nanofibers are shown to be remarkably selective to U(VI). The results suggest a solution for the capture of uranium, which is of interest given its health and toxic impacts when present in aqueous matrices.

scholarly journals Mediator facilitates transcriptional activation and dynamic long-range contacts at the IgH locus during class switch recombination

2016 ◽  
Vol 213 (3) ◽  
pp. 303-312 ◽  
Author(s):  
Anne-Sophie Thomas-Claudepierre ◽  
Isabelle Robert ◽  
Pedro P. Rocha ◽  
Ramya Raviram ◽  
Ebe Schiavo ◽  
...  
Keyword(s):  
B Cells ◽  
Long Range ◽  
Transcriptional Activation ◽  
Transcription Initiation ◽  
Structural Changes ◽  
Class Switch Recombination ◽  
Mediator Complex ◽  
Loop Formation ◽  
Class Switch ◽  
Igh Locus

Immunoglobulin (Ig) class switch recombination (CSR) is initiated by the transcription-coupled recruitment of activation-induced cytidine deaminase (AID) to Ig switch regions (S regions). During CSR, the IgH locus undergoes dynamic three-dimensional structural changes in which promoters, enhancers, and S regions are brought to close proximity. Nevertheless, little is known about the underlying mechanisms. In this study, we show that Med1 and Med12, two subunits of the mediator complex implicated in transcription initiation and long-range enhancer/promoter loop formation, are dynamically recruited to the IgH locus enhancers and the acceptor regions during CSR and that their knockdown in CH12 cells results in impaired CSR. Furthermore, we show that conditional inactivation of Med1 in B cells results in defective CSR and reduced acceptor S region transcription. Finally, we show that in B cells undergoing CSR, the dynamic long-range contacts between the IgH enhancers and the acceptor regions correlate with Med1 and Med12 binding and that they happen at a reduced frequency in Med1-deficient B cells. Our results implicate the mediator complex in the mechanism of CSR and are consistent with a model in which mediator facilitates the long-range contacts between S regions and the IgH locus enhancers during CSR and their transcriptional activation.

Role of LHCII-containing macrodomains in the structure, function and dynamics of grana

2000 ◽  
Vol 27 (3) ◽  
pp. 279 ◽  
Author(s):  
G. Garab ◽  
L. Mustárdy
Keyword(s):  
Excitation Energy ◽  
Long Range ◽  
Structural Changes ◽  
Higher Plants ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Lateral Heterogeneity ◽  
Long Distance ◽  
3D Network

In higher plants and green algae two types of thylakoids are distinguished, granum (stacked) and stroma (unstacked) thylakoids. They form a three-dimensional (3D) network with large lateral heterogeneity: photosystem II (PSII) and the associated main chlorophyll a/b light-harvesting complex (LHCII) are found predominantly in the stacked region, while PSI and LHCI are located mainly in the unstacked region of the membrane. This picture emerged from the discovery of the physical separation of the two photosystems (Boardman and Anderson 1964). Granal chloroplasts possess significant flexibility, which is essential for optimizing the photosynthetic machinery under various environmental conditions. However, our understanding concerning the assembly, structural dynamics and regulatory functions of grana is far from being complete. In this paper we overview the significance of the three-dimensional structure of grana in the absorption properties, ionic equilibrations, and in the diffusion of membrane components between the stacked and unstacked regions. Further, we discuss the role of chiral macrodomains in the grana. Lateral heterogeneity of thylakoid membranes is proposed to be a consequence of the formation of macrodomains constituted of LHCII and PSII; their long range order permits long distance migration of excitation energy, which explains the energetic connectivity of PSII particles. The ability of macrodomains to undergo light-induced reversible structural changes lends structural flexibility to the granum. In purified LHCII, which has also been shown to form stacked lamellar aggregates with long range chiral order, excitation energy migrates for large distances; these macroaggregates are also capable of undergoing light-induced reversible structural changes and fluorescence quenching. Hence, some basic properties of grana appear to originate from its main constituent, the LHCII.

scholarly journals Influence of Erbium Doping on Dielectric Properties of Zinc Borotellurite Glass System

2016 ◽  
Vol 846 ◽  
pp. 161-171 ◽  
Author(s):  
Siti Shafinas Zulkefly ◽  
Halimah Mohamed Kamari ◽  
Muhammad Nor Azlan Abdul Azis ◽  
Wan Mohd Daud Wan Yusoff
Keyword(s):  
Dielectric Properties ◽  
Molar Volume ◽  
Structural Changes ◽  
Low Frequency ◽  
Interfacial Polarization ◽  
Xrd Analysis ◽  
Glass System ◽  
Response Measurement ◽  
Xrd Pattern ◽  
Higher Temperature

Glasses of the system {[ (TeO2)70 (B2O3)30]70 (ZnO)30}100-y (Er2O3)y containing different concentration of Er2O3 (ranging from 0 to 5 mol %) was prepared from melt-quenching technique. The structural changes were studied by XRD analysis and FTIR analysis. The XRD pattern shows the glasses are amorphous. The higher concentration of Er2O3, the more unit of TeO3 would transform to TeO4 and formation of B-O vibrational groups. The density and molar volume was obtained attribute to non-bridging oxygen (NBO) and are found the density and molar volume of the glass system are increasing. The densities range from 3630 kg/m3 to 3960 kg/m3. The dielectric constant ε’ and dielectric loss factor ε’’ which were characterized in the frequency range 10-2 – 106 Hz over temperature range 50°C – 200 °C, show a larger value at lower frequency and higher temperature (above 110°C ). The results of dielectric response measurement show that interfacial polarization at low frequency, and orientation polarization at intermediate and high frequency.Keywords: Dielectric properties; Activation Energy; Rare Earth; Polarization; Non-Bridging Oxygen;

Search for Explaining the Staebler-Wronski Effect

1997 ◽  
Vol 467 ◽  
Author(s):  
H. Fritzsche ◽  
Tucson Az
Keyword(s):  
Spatial Correlation ◽  
Long Range ◽  
Photon Energy ◽  
Structural Changes ◽  
Hydrogen Diffusion ◽  
Critical Value ◽  
Bond Breaking ◽  
Dangling Bond ◽  
High Fields ◽  
Staebler Wronski Effect

ABSTRACTFor twenty years we searched to understand the Staebler-Wronski effect (SWE). New results continue to emerge which invalidate prior interpretations. Recent evidence shows that the SWE is not associated with impurities. Long-range hydrogen diffusion is ruled out because the SWE occurs with comparable efficiency between 400K and the lowest temperatures. Nonradiative geminate recombinations might be important since high fields reduce the SWE significantly. It disappears when the bandgap or the photon energy falls below a critical value. The creation of a metastable density of dangling bond defects has been considered to be its sole manifestation. However, there is mounting evidence for light-induced structural changes which extend throughout the material. The weak bond breaking model emerges as the only viable explanation of the SWE if the expected spatial correlation between defects and hydrogen is destroyed by subsequent recombination events. The SWE is reduced by a favorable microstructure and low hydrogen content. It is suggested that defect pairs have larger recombination coefficients than isolated defects.

Multiple dielectric anomalies in xBiLaO3–(1 − x)PbTiO3 piezoelectrics

2008 ◽  
Vol 23 (2) ◽  
pp. 565-569 ◽  
Author(s):  
Runrun Duan ◽  
Michael S. Haluska ◽  
Robert F. Speyer
Keyword(s):  
Differential Scanning Calorimetry ◽  
Dielectric Constant ◽  
Excellent Agreement ◽  
Structural Changes ◽  
Dielectric Anomaly ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Thermally Induced ◽  
X Ray ◽  
Higher Temperature

Compositions of xBiLaO3–(1 − x) PbTiO3 over the range 0 ≤ x ≤ 0.225 were calcined and sintered. The dielectric constant with temperature and differential scanning calorimetry measurements were in excellent agreement with respect to Curie-like tetragonal to cubic transformations starting at 495 °C for pure PbTiO3, shifting to lower temperatures with increasing x. For compositions of x ≥ 0.05, a second higher-temperature (∼600 °C) endotherm, and matching dielectric anomaly, were consistently observed, for which there were no structural changes indicated by hot-stage x-ray diffraction. This transformation was speculated to be based on a thermally induced desegregation of B-site cations.

TRANSITION FROM SHORT-RANGE TO LONG-RANGE ORDER IN LEAD-BISMUTHATE OXIDE GLASS MATRICES

2000 ◽  
Vol 14 (29) ◽  
pp. 1025-1031 ◽  
Author(s):  
V. SIMON ◽  
R. POP ◽  
S. SIMON
Keyword(s):  
Glass Transition ◽  
Molar Volume ◽  
Long Range ◽  
Short Range ◽  
Structural Changes ◽  
Range Order ◽  
Oxide Glass ◽  
Compositional Variation ◽  
Long Range Order ◽  
Glass Matrices

Glass transition and nucleation temperatures as well as densities and molar volumes of x Bi 2 O 3·y PbO (0.5≤x/y≤4) are reported. The glass transition temperature and molar volume are further analysed in terms of structural data. The obtained results indicate the occurrence of structural changes from short range to long range order induced by the heat treatment applied at 550°C, as per DTA results. These changes depend on the x/y ratio between Bi 2 O 3 and PbO content. The compositional variation of the molar volume of untreated and heat-treated samples are evidences that both Bi 2 O 3 and PbO play the role of network formers.

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