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Framework flexibility and rational design of new zeolites for catalysis
Asel Sartbaeva,Stephen A. Wells
Applied Petrochemical Research , 2012, DOI: 10.1007/s13203-012-0017-3
Abstract: Zeolite materials have proved very useful as chemical catalysts and the search for new zeolite structures with novel channel and pore shapes is ongoing. We discuss a geometric feature of zeolite frameworks, the flexibility window, which may provide a criterion to identify hypothetical structures which can be synthesised as zeolites. In recent research using data on zeolite frameworks under compression, we show strong links between this geometric feature and the physics of zeolite frameworks.
Flexibility: components, proprioceptive mechanisms and methods
Estélio H. M. Dantas, Prof., Rejane Daoud, Alexis Trott, Rudy J. Nodari, Jr., Mario C. S. C. Concei o
Biomedical Human Kinetics , 2011, DOI: 10.2478/v10101-011-0009-2
Abstract: A literature review on physical flexibility was presented and discussed. This included definitions and components that influence the performance of movements requiring large joint motion ranges and muscle elasticity. Flexibility was discussed with reference to specific age groups, e.g. children and the elderly. Proprioceptive mechanisms and components directly related to flexibility were overviewed, as well as suitable approaches towards flexibilisation, i.e. maintaining and/or enhancing flexibility.
Local Flexibility within an Accountability System  [cached]
Benjamin Scafidi,Catherine Freeman,Stan DeJarnett
Education Policy Analysis Archives , 2001,
Abstract: Over the past decade, several states have created comprehensive accountability systems designed to increase student learning in public schools. These accountability systems are based on "high-stakes" standardized testing of a state curriculum. Rewards and interventions for local educators are based largely upon students' performance on these tests. Using the recent accountability reforms in Georgia as a backdrop, this article considers the role of local flexibility within such an accountability system--flexibility over paperwork, resources, personnel, and curriculum for local educators. Increased flexibility for local educators is not merely an option in a world where local educators are subject to a comprehensive accountability system imposed by a state--it is a requirement for success. We make a case for providing local flexibility and provides a discussion regarding types of flexibility, vehicles for granting flexibility, and who should receive flexibility.
Flexibility within the Rotor and Stators of the Vacuolar H+-ATPase  [PDF]
Chun Feng Song, Kostas Papachristos, Shaun Rawson, Markus Huss, Helmut Wieczorek, Emanuele Paci, John Trinick, Michael A. Harrison, Stephen P. Muench
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0082207
Abstract: The V-ATPase is a membrane-bound protein complex which pumps protons across the membrane to generate a large proton motive force through the coupling of an ATP-driven 3-stroke rotary motor (V1) to a multistroke proton pump (Vo). This is done with near 100% efficiency, which is achieved in part by flexibility within the central rotor axle and stator connections, allowing the system to flex to minimise the free energy loss of conformational changes during catalysis. We have used electron microscopy to reveal distinctive bending along the V-ATPase complex, leading to angular displacement of the V1 domain relative to the Vo domain to a maximum of ~30°. This has been complemented by elastic network normal mode analysis that shows both flexing and twisting with the compliance being located in the rotor axle, stator filaments, or both. This study provides direct evidence of flexibility within the V-ATPase and by implication in related rotary ATPases, a feature predicted to be important for regulation and their high energetic efficiencies.
Inherent flexibility determines the transition mechanisms of the EF-hands of Calmodulin  [PDF]
Swarnendu Tripathi,John J. Portman
Quantitative Biology , 2008, DOI: 10.1073/pnas.0806872106
Abstract: We explore how inherent flexibility of a protein molecule influences the mechanism controlling the kinetics of allosteric transitions using a variational model inspired from work in protein folding. The striking differences in the predicted transition mechanism for the opening of the two domains of calmodulin (CaM) emphasizes that inherent flexibility is key to understanding the complex conformational changes that occur in proteins. In particular, the C-terminal domain of CaM (cCaM) which is inherently less flexible than its N-terminal domain (nCaM) reveals "cracking" or local partial unfolding during the open/closed transition. This result is in harmony with the picture that cracking relieves local stresses due to conformational deformations of a sufficiently rigid protein. We also compare the conformational transition in a recently studied "even-odd" paired fragment of CaM. Our results rationalize the different relative binding affinities of the EF-hands in the engineered fragment compared to the intact "odd-even" paired EF-hands (nCaM and cCaM) in terms of changes in flexibility along the transition route. Aside from elucidating general theoretical ideas about the cracking mechanism, these studies also emphasize how the remarkable intrinsic plasticity of CaM underlies conformational dynamics essential for its diverse functions.
tLivin Displays Flexibility by Promoting Alternative Cell Death Mechanisms  [PDF]
Tamar Shiloach, Christian Berens, Christina Danke, Ortal Waiskopf, Riki Perlman, Dina Ben-Yehuda
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0101075
Abstract: Livin is a member of the Inhibitor of Apoptosis (IAP) protein family that inhibits apoptosis triggered by a variety of stimuli. We previously demonstrated that while Livin inhibits caspase activity, caspases can cleave Livin to produce a truncated protein, tLivin and that this newly formed tLivin paradoxically induces cell death. However to date, the mechanism of tLivin-induced cell death is not fully understood. In this study, we set out to characterize the form of cell death mediated by tLivin. Here we demonstrate that, unlike most death-promoting proteins, tLivin is a flexible inducer of cell death capable of promoting necrosis or apoptosis in different cell lines. The unusual flexibility of tLivin is displayed by its ability to activate an alternative form of cell death when apoptosis is inhibited. Thus, tLivin can promote more than one form of cell death in the same cell type. Interestingly, in cells where tLivin induces necrosis, deletion of the caspase binding BIR domain results in tLivin-induced apoptosis, suggesting the BIR domain can potentially hamper the ability of tLivin to induce apoptosis. We further elucidate that tLivin activates the JNK pathway and both tLivin-induced apoptosis and necrosis are partially mediated by JNK activity. Acquired resistance to apoptosis, common in many tumors, impinges on the efficiency of conventional anti-cancer agents that function primarily by inducing apoptosis. The ability of tLivin to induce death of apoptosis-compromised cells makes it an attractive candidate for targeted cancer therapy.
Effective Stress-Porosity Relationship above and Within the Oil Window in the North Sea Basin
Kenneth S. Okiongbo
Research Journal of Applied Sciences, Engineering and Technology , 2011,
Abstract: This study investigates the effective stress - porosity relationship above and within the oil window in the Kimmeridge Clay Formation (KCF) in the North Sea Basin (UK) using effective stress and porosity determined from wireline logs and pore pressure data. Porosity was determined from an empirical porosity - sonic transit - time transform, calibrated using shale and mudstone core porosity measurements from Jurassic shales in the North Sea. Effective stress was determined from the total overburden stress and pore pressure. The total overburden stress was calculated by integration of the density log. The results show that porosity range between ~11-20% in the pre-generation zone but decreased to <5% within the oil window. Compaction coefficient ($) values above the oil window vary from ~0.08-0.09 M/Pa, but vary from ~0.05-0.06 M/Pa within the oil window implying that deeper burial and a high degree of chemical precipitation and cementation has created a stiff matrix giving rise to low $ values. The effective stress-porosity relationship above and within the oil window reflects a possible decrease in effective stress occasioned by increase in porosity in the pregeneration zone.
Zeolites and Usage Areas  [cached]
Jale Gülen,Fatih Zorbay,Sabri Arslan
Karaelmas Science and Engineering Journal , 2012, DOI: http://dx.doi.org/10.7212%2fzkufbd.v2i1.80
Abstract: Zeolites are formed via several reactions from the minerals that consist of aluminium and silica. Zeolites, which have a growing significance in recent days are one of important industrial raw materials. As well as being used as a catalyst, theirability to do ion exchange and adsorption make them even more valuable. Zeolites are used in several industries such as energy, agriculture and animal husbandry, mining and metallurgy, construction, detergent, paper, etc. In this study, the definiton, formation and usage areas of zeolites are explained.
Eulalia Sosa Acevedo
Revista de Lingüística y Lenguas Aplicadas , 2012, DOI: 10.4995/rlyla.2012.1139
Abstract: This paper seeks to introduce an alternative perspective on the treatment of derivation within a functional framework like Role and Reference Grammar (RRG). By taking a functional perspective, we assume that word formation is a two-dimensional phenomenon involving both onomasiological and grammatical components. Furthermore, grammatical processes are considered to be semantically motivated. In order to properly account for the internal mechanisms involved in word formation, we formulate affixal lexical representations by using Lexical Templates as devised within the LCM (see Mairal Usón & Faber 2007; Mairal Usón & Ruíz de Mendoza 2008a,b; Ruiz de Mendoza & Mairal Usón 2008; Butler 2009; Cortés Rodríguez 2009, among others).
The hierarchical and functional connectivity of higher-order cognitive mechanisms: neurorobotic model to investigate the stability and flexibility of working memory  [PDF]
Fady Alnajjar,Yuichi Yamashita,Jun Tani
Frontiers in Neurorobotics , 2013, DOI: 10.3389/fnbot.2013.00002
Abstract: Higher-order cognitive mechanisms (HOCM), such as planning, cognitive branching, switching, etc., are known to be the outcomes of a unique neural organizations and dynamics between various regions of the frontal lobe. Although some recent anatomical and neuroimaging studies have shed light on the architecture underlying the formation of such mechanisms, the neural dynamics and the pathways in and between the frontal lobe to form and/or to tune the stability level of its working memory remain controversial. A model to clarify this aspect is therefore required. In this study, we propose a simple neurocomputational model that suggests the basic concept of how HOCM, including the cognitive branching and switching in particular, may mechanistically emerge from time-based neural interactions. The proposed model is constructed such that its functional and structural hierarchy mimics, to a certain degree, the biological hierarchy that is believed to exist between local regions in the frontal lobe. Thus, the hierarchy is attained not only by the force of the layout architecture of the neural connections but also through distinct types of neurons, each with different time properties. To validate the model, cognitive branching and switching tasks were simulated in a physical humanoid robot driven by the model. Results reveal that separation between the lower and the higher-level neurons in such a model is an essential factor to form an appropriate working memory to handle cognitive branching and switching. The analyses of the obtained result also illustrates that the breadth of this separation is important to determine the characteristics of the resulting memory, either static memory or dynamic memory. This work can be considered as a joint research between synthetic and empirical studies, which can open an alternative research area for better understanding of brain mechanisms.
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