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Removal efficiency of Cu2+, Cd2+ and Pb2+ by waste brewery biomass : pH and cation association effects

Marques, Paula Alexandra; Pinheiro, Helena Maria; Teixeira, J. A.; Rosa, M. F.
Fonte: Elsevier Science B.V. Publicador: Elsevier Science B.V.
Tipo: Artigo de Revista Científica
Publicado em //1999 ENG
Relevância na Pesquisa
65.91%
In this work two distinct (flocculent and non-flocculent) yeast wastes from Portuguese breweries were used for the selective removal of Cu2+, Cd2+ and Pb2+ from aqueous solutions. One of the goals was to establish both the pH profiles for the removal of each metal ion (1.0 mM) and the effect on the biomass biosorption capacity of pH adjustment during the process. The effect of the presence of multiple metal ions, in the 0.1-1.0 mM range, on metal removal efficiency was also studied. The results showed that, in the absence of pH adjustment, the optimum initial pH for the removal of three cations was in the 4.5-5.5 range for both types of biomass. However, a gradual pH increase was observed during the removal process, up to a final equilibrium value of 7.0-8.0. Regarding the biomass efficiency for metal removal in multi-cation systems, it was verified that only Cu2+ was significantly affected by the presence of the other metals in solution and only when the non-flocculent yeast biomass was used as biosorbent. Cd2+ was only slightly affected by the presence of both Cu2+ and Pb2+, and Pb2+ removal was not affected by the presence of any or both of the interferent metals for the two biosorbents used in this work. The highest and lowest metal removal yields were obtained for Pb2+ and Cu2+...

Enterprise Resource Planning nas Instituições de Ensino não Superior : um estudo empírico

Loureiro, Joaquim Alexandre Borges Teófilo
Fonte: Universidade Católica Portuguesa Publicador: Universidade Católica Portuguesa
Tipo: Dissertação de Mestrado
Publicado em 25/11/2013 POR
Relevância na Pesquisa
25.73%
Os avanços das tecnologias e dos sistemas de informação promoveram novas formas de gestão, ao nível do planeamento, controlo e tomada de decisões, para as or-ganizações. Neste contexto, os sistemas ERP (Enterprise Resource Planning) surgem como uma oportunidade para os gestores conduzirem as suas organizações mais eficien-temente, uma vez que permitem interligar diferentes departamentos de forma mais eficaz, melhorar a informação que existe dentro das organizações e agilizar o processo de gestão. Estes sistemas são cada vez mais comuns nas organizações industriais e de serviços, e a sua aplicação nas instituições de ensino deve ser equacionada pela mais-valia que poderá oferecer-lhes. Esta investigação centra-se no estudo de caso de três instituições de ensino não superior que implementaram sistemas ERP, com o objetivo de analisar as motivações, os impactos, as dificuldades enfrentadas e os fatores críticos de sucesso no que diz res-peito à sua implementação. A metodologia utilizada foi a de estudos de casos múltiplos e baseou-se na recolha direta de dados através da observação, análise documental e rea-lização de entrevistas. O estudo permitiu constatar que as motivações que levam as instituições de en-sino a adoptar o sistema ERP são alcançadas com a sua implementação...

Renal transport of neutral amino acids. Demonstration of Na+-independent and Na+-dependent electrogenic uptake of L-proline, hydroxy-L-proline and 5-oxo-L-proline by luminal-membrane vesicles.

Røigaard-Petersen, H; Sheikh, M I
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/05/1984 EN
Relevância na Pesquisa
25.74%
Uptake of L-proline, hydroxy-L-proline and 5-oxo-L-proline by luminal-membrane vesicles isolated either from whole cortex or from pars convoluta or pars recta of proximal tubules was studied by a spectrophotometric method. Uptake of L-proline and hydroxy-L-proline by vesicles from whole cortex was mediated by both Na+-dependent and Na+-independent, but electrogenic, processes, whereas transport of 5-oxo-L-proline in these vesicles was strictly Na+-dependent. Eadie-Hofstee analysis of saturation-kinetic data suggested the presence of multiple transport systems in luminal-membrane vesicles from whole renal cortex for the uptake of all these amino acids. Tubular localization of the transport systems was studied by the use of vesicles derived from pars convoluta and from pars recta. In pars recta transport of all three amino acids was strictly dependent on Na+ and occurred via a high-affinity system (half-saturation: 0.1-0.3 mM). Cation-dependent but Na+-unspecific transport of low affinity for L-proline and hydroxy-L-proline was exclusively localized to the pars convoluta, which also contained a Na+-preferring system of intermediate affinity (half-saturation: L-proline, 0.75 mM; hydroxy-L-proline, 1.3 mM). 5-Oxo-L-proline was transported by low-affinity and Na+-dependent systems in both pars convoluta and pars recta. Competition experiments revealed that transport systems for L-proline and hydroxy-L-proline are common...

Newer systems for bacterial resistances to toxic heavy metals.

Silver, S; Ji, G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1994 EN
Relevância na Pesquisa
25.73%
Bacterial plasmids contain specific genes for resistances to toxic heavy metal ions including Ag+, AsO2-, AsO4(3-), Cd2+, Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, Sb3+, and Zn2+. Recent progress with plasmid copper-resistance systems in Escherichia coli and Pseudomonas syringae show a system of four gene products, an inner membrane protein (PcoD), an outer membrane protein (PcoB), and two periplasmic Cu(2+)-binding proteins (PcoA and PcoC). Synthesis of this system is governed by two regulatory proteins (the membrane sensor PcoS and the soluble responder PcoR, probably a DNA-binding protein), homologous to other bacterial two-component regulatory systems. Chromosomally encoded Cu2+ P-type ATPases have recently been recognized in Enterococcus hirae and these are closely homologous to the bacterial cadmium efflux ATPase and the human copper-deficiency disease Menkes gene product. The Cd(2+)-efflux ATPase of gram-positive bacteria is a large P-type ATPase, homologous to the muscle Ca2+ ATPase and the Na+/K+ ATPases of animals. The arsenic-resistance system of gram-negative bacteria functions as an oxyanion efflux ATPase for arsenite and presumably antimonite. However, the structure of the arsenic ATPase is fundamentally different from that of P-type ATPases. The absence of the arsA gene (for the ATPase subunit) in gram-positive bacteria raises questions of energy-coupling for arsenite efflux. The ArsC protein product of the arsenic-resistance operons of both gram-positive and gram-negative bacteria is an intracellular enzyme that reduces arsenate [As(V)] to arsenite [As(III)]...

Effects of extracellular ATP on ion transport systems and [Ca2+]i in rat parotid acinar cells. Comparison with the muscarinic agonist carbachol

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/02/1990 EN
Relevância na Pesquisa
25.73%
The effects of extracellular ATP on ion fluxes and the intracellular free Ca2+ concentration ([Ca2+]i) were examined using a suspension of rat parotid acinar cells and were contrasted with the effects of the muscarinic agonist carbachol. Although ATP and carbachol both rapidly increased [Ca2+]i about threefold above the resting level (200-250 nM), the effect of ATP was due primarily to an influx of Ca2+ across the plasma membrane, while the initial response to carbachol was due to a release of Ca2+ from intracellular stores. Within 10 s, ATP (1 mM) and carbachol (20 microM) reduced the cellular Cl- content by 39-50% and cell volume by 15-25%. Both stimuli reduced the cytosolic K+ content by 57-65%, but there were marked differences in the rate and pattern of net K+ movement as well as the effects of K+ channel inhibitors on the effluxes initiated by the two stimuli. The maximum rate of the ATP- stimulated K+ efflux (approximately 2,200 nmol K+/mg protein per min) was about two-thirds that of the carbachol-initiated efflux rate, and was reduced by approximately 30% (vs. 60% for the carbachol-stimulated K+ efflux) by TEA (tetraethylammonium), an inhibitor of the large conductance (BK) K+ channel. Charybdotoxin, another K+ channel blocker...

High Fidelity Kinetic Self-Sorting in Multi-Component Systems Based on Guests with Multiple Binding Epitopes

Mukhopadhyay, Pritam; Zavalij, Peter Y.; Isaacs, Lyle
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/11/2006 EN
Relevância na Pesquisa
25.9%
The molecular recognition platforms of Natural systems often possess multiple binding epitopes each of which has programmed functional consequences. We report the dynamic behavior of a system comprising CB[6], CB[7], and guests cyclohexanediammonium (1) and adamantanealkylammonium (2) which we refer to as a two faced guest because it contains two distinct binding epitopes. We find that the presence of the two-faced guest – just as is observed for protein targeting in vivo – dictates the kinetic pathway that the system follows toward equilibrium. The influence of two-faced guest structure, cation concentration, cation identity, and individual rate and equilibrium constants on the behavior of the system was explored by a combination of experiment and simulation. Deconstruction of this system led to the discovery of an anomalous host-guest complex (CB[6] ·1) whose dissociation rate constant (kout= 8.5 × 10−10 s−1) is ≈ 100-fold slower than the widely used avidin·biotin affinity pair. This result, in combination with the analysis of previous systems which uncovered extraordinarily tight binding events (Ka ≥ 1012 M−1), highlights the inherent potential of pursuing a systems approach toward supramolecular chemistry.

Multiple Ion Binding Equilibria, Reaction Kinetics, and Thermodynamics in Dynamic Models of Biochemical Pathways

Vinnakota, Kalyan C.; Wu, Fan; Kushmerick, Martin J.; Beard, Daniel A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
25.79%
The operation of biochemical systems in vivo and in vitro is strongly influenced by complex interactions between biochemical reactants and ions such as H+, Mg2+, K+, and Ca2+. These are important second messengers in metabolic and signaling pathways that directly influence the kinetics and thermodynamics of biochemical systems. Herein we describe the biophysical theory and computational methods to account for multiple ion binding to biochemical reactants and demonstrate the crucial effects of ion binding on biochemical reaction kinetics and thermodynamics. In simulations of realistic systems, the concentrations of these ions change with time due to dynamic buffering and competitive binding. In turn, the effective thermodynamic properties vary as functions of cation concentrations and important environmental variables such as temperature and overall ionic strength. Physically realistic simulations of biochemical systems require incorporating all of these phenomena into a coherent mathematical description. Several applications to physiological systems are demonstrated based on this coherent simulation framework.

Raphé neurons stimulate respiratory circuit activity by multiple mechanisms via endogenously released serotonin and substance P

Ptak, Krzysztof; Yamanishi, Tadashi; Aungst, Jason; Milescu, Lorin S.; Zhang, Ruli; Richerson, George B.; Smith, Jeffrey C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/03/2009 EN
Relevância na Pesquisa
25.73%
Brainstem serotonin (5-HT) neurons modulate activity of many neural circuits in the mammalian brain, but in many cases endogenous mechanisms have not been resolved. Here, we analyzed actions of raphé 5-HT neurons on respiratory network activity including at the level of the pre–Bötzinger complex (pre-BötC) in neonatal rat medullary slices in vitro, and in the more intact nervous system of juvenile rats in arterially perfused brainstem-spinal cord preparations in situ. At basal levels of activity, excitation of the respiratory network via simultaneous release of 5-HT and substance P (SP), acting at 5-HT2A/2C, 5-HT4 and/or neurokinin-1 receptors, was required to maintain inspiratory motor output in both the neonatal and juvenile systems. The midline raphé obscurus contained spontaneously active 5-HT neurons, some of which projected to the pre-BötC and hypoglossal motoneurons, co-localized 5-HT and SP, and received reciprocal excitatory connections from the pre-BötC. Experimentally augmenting raphé obscurus activity increased motor output by simultaneously exciting pre-BötC and motor neurons. Biophysical analyses in vitro demonstrated that 5-HT and SP modulated background cation conductances in pre-BötC and motor neurons, including a non–selective cation leak current that contributed to the resting potential...

Multiple Factors Influence Calcium Synchronization in Arterial Vasomotion

Kapela, Adam; Parikh, Jaimit; Tsoukias, Nikolaos M.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 18/01/2012 EN
Relevância na Pesquisa
35.68%
The intercellular synchronization of spontaneous calcium (Ca2+) oscillations in individual smooth muscle cells is a prerequisite for vasomotion. A detailed mathematical model of Ca2+ dynamics in rat mesenteric arteries shows that a number of synchronizing and desynchronizing pathways may be involved. In particular, Ca2+-dependent phospholipase C, the intercellular diffusion of inositol trisphosphate (IP3, and to a lesser extent Ca2+), IP3 receptors, diacylglycerol-activated nonselective cation channels, and Ca2+-activated chloride channels can contribute to synchronization, whereas large-conductance Ca2+-activated potassium channels have a desynchronizing effect. Depending on the contractile state and agonist concentrations, different pathways become predominant, and can be revealed by carefully inhibiting the oscillatory component of their total activity. The phase shift between the Ca2+ and membrane potential oscillations can change, and thus electrical coupling through gap junctions can mediate either synchronization or desynchronization. The effect of the endothelium is highly variable because it can simultaneously enhance the intercellular coupling and affect multiple smooth muscle cell components. Here, we outline a system of increased complexity and propose potential synchronization mechanisms that need to be experimentally tested.

Regulation of Actin by Ion-Linked Equilibria

Kang, Hyeran; Bradley, Michael J.; Elam, W. Austin; De La Cruz, Enrique M.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 17/12/2013 EN
Relevância na Pesquisa
25.85%
Actin assembly, filament mechanical properties, and interactions with regulatory proteins depend on the types and concentrations of salts in solution. Salts modulate actin through both nonspecific electrostatic effects and specific binding to discrete sites. Multiple cation-binding site classes spanning a broad range of affinities (nanomolar to millimolar) have been identified on actin monomers and filaments. This review focuses on discrete, low-affinity cation-binding interactions that drive polymerization, regulate filament-bending mechanics, and modulate interactions with regulatory proteins. Cation binding may be perturbed by actin post-translational modifications and linked equilibria. Partial cation occupancy under physiological and commonly used in vitro solution conditions likely contribute to filament mechanical heterogeneity and structural polymorphism. Site-specific cation-binding residues are conserved in Arp2 and Arp3, and may play a role in Arp2/3 complex activation and actin-filament branching activity. Actin-salt interactions demonstrate the relevance of ion-linked equilibria in the operation and regulation of complex biological systems.

Effect of cations on structural stability of salt-affected soils.

Marchuk, Alla
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2013
Relevância na Pesquisa
25.92%
About 35% of the total land area in Australia is affected by different categories of salt-affected soils. Apart from natural salinity, a significant proportion of the cultivated land has become saline due to irrigation, particularly where groundwater or recycled waters were used. Sodium salts tend to dominate salt affected soils and groundwater in Australia, therefore sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) are currently used to assess the effects of sodium on soil structure. However, the literature review has identified that the solutions of salt–affected and fresh water or wastewater irrigated soils may contain elevated concentrations of potassium and/or magnesium, which may affect the levels of soluble and exchangeable cations, and lead to soil structural deterioration due to clay dispersion and swelling. Traditional indices SAR and ESP, used for assessing soil structure, do not take into account the effects of K on soil clay dispersion and swelling. Furthermore, although exchangeable Mg has not been included within the common definition of sodicity, there has been disagreement concerning its influence on the behaviour of sodic soils. In addition, in the SAR model Ca²⁺ is equated to Mg²⁺ in flocculating power. Consequently the use of SAR and ESP...

Hardware design of cryptographic algorithms for low-cost RFID tags

Martín González, Honorio
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
25.73%
Radio Frequency Identification (RFID) is a wireless technology for automatic identification that has experienced a notable growth in the last years. RFID is an important part of the new trend named Internet of Things (IoT), which describes a near future where all the objects are connected to the Internet and can interact between them. The massive deployment of RFID technology depends on device costs and dependability. In order to make these systems dependable, security needs to be added to RFID implementations, as RF communications can be accessed by an attacker who could extract or manipulate private information from the objects. On the other hand, reduced costs usually imply resource-constrained environments. Due to these resource limitations necessary to low-cost implementations, typical cryptographic primitives cannot be used to secure low-cost RFID systems. A new concept emerged due to this necessity, Lightweight Cryptography. This term was used for the first time in 2003 by Vajda et al. and research on this topic has been done widely in the last decade. Several proposals oriented to low-cost RFID systems have been reported in the literature. Many of these proposals do not tackle in a realistic way the multiple restrictions required by the technology or the specifications imposed by the different standards that have arose for these technologies. The objective of this thesis is to contribute in the field of lightweight cryptography oriented to low-cost RFID tags from the microelectronics point of view. First...

Sistema visual para Ground Truth de sistemas autónomos

Nunes, Nuno Filipe Borges Teixeira
Fonte: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto Publicador: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto
Tipo: Dissertação de Mestrado
Publicado em //2012 POR
Relevância na Pesquisa
25.8%
Este trabalho visa contribuir para o desenvolvimento de um sistema de visão multi-câmara para determinação da localização, atitude e seguimento de múltiplos objectos, para ser utilizado na unidade de robótica do INESCTEC, e resulta da necessidade de ter informação externa exacta que sirva de referência no estudo, caracterização e desenvolvimento de algoritmos de localização, navegação e controlo de vários sistemas autónomos. Com base na caracterização dos veículos autónomos existentes na unidade de robótica do INESCTEC e na análise dos seus cenários de operação, foi efectuado o levantamento de requisitos para o sistema a desenvolver. Foram estudados os fundamentos teóricos, necessários ao desenvolvimento do sistema, em temas relacionados com visão computacional, métodos de estimação e associação de dados para problemas de seguimento de múltiplos objectos . Foi proposta uma arquitectura para o sistema global que endereça os vários requisitos identi cados, permitindo a utilização de múltiplas câmaras e suportando o seguimento de múltiplos objectos, com ou sem marcadores. Foram implementados e validados componentes da arquitectura proposta e integrados num sistema para validação...

Plant-Specific Cation/H+ Exchanger 17 and Its Homologs Are Endomembrane K+ Transporters with Roles in Protein Sorting*

Chanroj, Salil; Lu(路, Yongxian, 永憲); Padmanaban, Senthilkumar; Nanatani(七, Kei, 谷圭); Uozumi(魚, Nobuyuki, 住信之); Rao, Rajini; Sze(斯, Heven, 海文)
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.85%
The complexity of intracellular compartments in eukaryotic cells evolved to provide distinct environments to regulate processes necessary for cell proliferation and survival. A large family of predicted cation/proton exchangers (CHX), represented by 28 genes in Arabidopsis thaliana, are associated with diverse endomembrane compartments and tissues in plants, although their roles are poorly understood. We expressed a phylogenetically related cluster of CHX genes, encoded by CHX15–CHX20, in yeast and bacterial cells engineered to lack multiple cation-handling mechanisms. Of these, CHX16–CHX20 were implicated in pH homeostasis because their expression rescued the alkaline pH-sensitive growth phenotype of the host yeast strain. A smaller subset, CHX17–CHX19, also conferred tolerance to hygromycin B. Further differences were observed in K+- and low pH-dependent growth phenotypes. Although CHX17 did not alter cytoplasmic or vacuolar pH in yeast, CHX20 elicited acidification and alkalization of the cytosol and vacuole, respectively. Using heterologous expression in Escherichia coli strains lacking K+ uptake systems, we provide evidence for K+ (86Rb) transport mediated by CHX17 and CHX20. Finally, we show that CHX17 and CHX20 affected protein sorting as measured by carboxypeptidase Y secretion in yeast mutants grown at alkaline pH. In plant cells...

Cation-π Interactions: Computational Analyses of the Aromatic Box Motif and the Fluorination Strategy for Experimental Evaluation

Davis, Matthew R.; Dougherty, Dennis A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 28/10/2015 EN
Relevância na Pesquisa
25.88%
Cation-π interactions are common in biological systems, and many structural studies have revealed the aromatic box as a common motif. With the aim of understanding the nature of the aromatic box, several computational methods were evaluated for their ability to reproduce experimental cation-π binding energies. We find the DFT method M06 with the 6-31G(d,p) basis set performs best of several methods tested. The binding of benzene to a number of different cations (sodium, potassium, ammonium, tetramethylammonium, and guanidinium) was studied. In addition, the binding of the organic cations NH4+ and NMe4+ to ab initio generated aromatic boxes as well as examples of aromatic boxes from protein crystal structures were investigated. These data, along with a study of the distance dependence of the cation-π interaction, indicate that multiple aromatic residues can meaningfully contribute to cation binding, even with displacements of more than an angstrom from the optimal cation-π interaction. Progressive fluorination of benzene and indole was studied as well, and binding energies obtained were used to reaffirm the validity of the “fluorination strategy” to study cation-π interactions in vivo.

Solvation of the Morpholinium Cation in Acetonitrile. Effect of an Anion

Chaban, Vitaly V.; Andreeva, Nadezhda A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/11/2015
Relevância na Pesquisa
25.82%
Ionic liquids constitute a fast growing class of compounds finding multiple applications in science and technology. Morpholinium-based ionic liquids (MBILs) and their mixtures with polar molecular co-solvents are interesting as sustainable electrolyte systems for electrochemistry. We investigate local structures of protic and propton-free morpholinium cations in acetonitrile (ACN) using semi-empirical molecular dynamics (MD) simulations. An impact of an anion (acetate) on the cation solvation regularities is discussed. Unlike oxygen, nitrogen of the morpholine ring is a strong electrophilic binding center. This site is responsible for the interactions of the cation with the solvent and with the anion. In protic MBILs, the role of nitrogen is delegated to the proton, which is linked to nitrogen. The acetate anion weakens solvation of the cation due to occupation of space near nitrogen or proton. The analysis reveals a favorable solvation of MBILs in ACN, which is a prerequisite for a new high-performance electrolyte system. The reported structural data are validated through a point-to-point comparison with the MP2 post-Hartree-Fock theory.

Structural properties and cation ordering in layered hexagonal CaxCoO2

Yang, H. X.; Shi, Y. G.; Liu, X.; Xiao, R. J.; Tian, H. F.; Li, J. Q.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/08/2005
Relevância na Pesquisa
25.79%
A series of CaxCoO2 (0.15 <= x <= 0.40) materials have been prepared by means of ion exchange reaction from NaxCoO2. Transmission electron microscopy (TEM) measurements revealed a rich variety of structural phenomena resulting from cation ordering, structural distortion and twinning. Systematical structural analysis, in combination with the experimental data of NaxCoO2 (0.15 <= x <= 0.8) and SrxCoO2 (1.5 <= x <= 0.4) systems, suggests that there are two common well-defined cation ordered states corresponding respectively to the orthorhombic superstructure at around x = 1/2 and the 31/2a31/2a superstructure at around x = 1/3 in this kind of system. Multiple ordered states, phase separation, and incommensurate structural modulations commonly appear in the materials with 0.33 < x < 0.5. The TEM observations also reveals an additional periodic structural distortion with q2 = a* / 2 in materials for x <= 0.35. This structural modulation also appears in the remarkable superconducting phase Na0.33CoO2 1.3H2O.; Comment: 22 pages, 6 figures

Updating Properties of Nonlinear Dynamical Systems with Uncertain Input

Yuen, Ka-Veng; Beck, James L.
Fonte: American Society of Civil Engineers Publicador: American Society of Civil Engineers
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //2003
Relevância na Pesquisa
25.74%
A spectral density approach for the identification of linear systems is extended to nonlinear dynamical systems using only incomplete noisy response measurements. A stochastic model is used for the uncertain input and a Bayesian probabilistic approach is used to quantify the uncertainties in the model parameters. The proposed spectral-based approach utilizes important statistical properties of the Fast Fourier Transform and their robustness with respect to the probability distribution of the response signal in order to calculate the updated probability density function for the parameters of a nonlinear model conditional on the measured response. This probabilistic approach is well suited for the identification of nonlinear systems and does not require huge amounts of dynamic data. The formulation is first presented for single-degree-of-freedom systems and then for multiple-degree-of freedom systems. Examples using simulated data for a Duffing oscillator, an elastoplastic system and a four-story inelastic structure are presented to illustrate the proposed approach.

Cation–π interactions: computational analyses of the aromatic box motif and the fluorination strategy for experimental evaluation

Davis, Matthew R.; Dougherty, Dennis A.
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 21/11/2015
Relevância na Pesquisa
25.88%
Cation–π interactions are common in biological systems, and many structural studies have revealed the aromatic box as a common motif. With the aim of understanding the nature of the aromatic box, several computational methods were evaluated for their ability to reproduce experimental cation–π binding energies. We find the DFT method M06 with the 6-31G(d,p) basis set performs best of several methods tested. The binding of benzene to a number of different cations (sodium, potassium, ammonium, tetramethylammonium, and guanidinium) was studied. In addition, the binding of the organic cations NH_4+ and NMe_4+ to ab initio generated aromatic boxes as well as examples of aromatic boxes from protein crystal structures were investigated. These data, along with a study of the distance dependence of the cation–π interaction, indicate that multiple aromatic residues can meaningfully contribute to cation binding, even with displacements of more than an angstrom from the optimal cation–π interaction. Progressive fluorination of benzene and indole was studied as well, and binding energies obtained were used to reaffirm the validity of the “fluorination strategy” to study cation–π interactions in vivo.

Radium Isotope Geochemistry in Groundwater Systems: The Role of Environmental Factors

Vinson, David Stewart
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2011
Relevância na Pesquisa
25.91%

Prior studies of groundwater systems have associated increasing salinity and anoxic conditions with increasing radium (Ra) activities in water due to the decreasing effectiveness of Ra removal processes. However, the components of salinity (e.g. Ca vs. Na and SO42- vs. Cl--dominated waters), and the relative importance of salinity-sensitive vs. redox-sensitive processes for Ra mobilization, are less well understood. In this research, the response of Ra to hydrochemical change was examined using a multiple tracer approach to obtain detailed information on divalent cation and Ra mobility. A range of salinity and redox conditions was examined in five field-based studies in the United States and Morocco: (1) fresh waters in fractured crystalline rocks in the Piedmont region of North Carolina; (2) the Willcox Basin, an oxic alluvial basin-fill aquifer in southeastern Arizona; (3) the Jordan sandstone aquifer, a carbonate-cemented quartz sandstone in southeastern Minnesota; (4) an unconfined coastal aquifer undergoing salinization in the city of Agadir, Morocco; and (5) the confined, fresh to saline Cretaceous and Pliocene aquifers of the Atlantic Coastal Plain in North Carolina.

In addition to analysis of major element concentrations...