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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Clathrin assemblies in vitreous ice : A structural analysis by image reconstruction

Vigers, G. P. A. January 1986 (has links)
No description available.
2

The aerodynamic buffeting force between passing mine cages

Hurlin, R. S 12 February 2010 (has links)
Ph.D. thesis, Faculty of Engineering (Mechanical Engineering), University of the Witwatersrand, 1993 (2 v.)
3

Organic Imine Cages : Self-Sorting and Application

Acharyya, Koushik January 2015 (has links) (PDF)
Biological systems have the incredible ability to accomplish uncommon chemical transformations with supreme delicacy. Many of those chemical transformations take place within the pocket of enzymes, which provide unique micro environment. From the quest of better understanding and to mimic such complex biological systems chemists have developed their own prototypes having well-defined cavity. To this end, in last few years many aesthetically elegant 3D discrete architectures have been devised by employing noncovalent interactions especially metal-ligand co-ordination and hydrogen bonding. Conversely, architectures based on purely covalent interactions are relatively limited in number, owing to the laborious traditional covalent synthesis, which involves multi-step synthetic protocols and irreversible covalent bond formations. Nevertheless, in recent times by utilizing dynamic covalent chemistry (DCC) several such organic 3D discrete ensembles have been developed with ease and efficiency from simple and easily accessible building blocks. Interestingly in most of such cases imine condensation reaction has been utilized due to easy formation and cleavage of the imine bonds in an efficient and reversible manner. However, it is quite surprising that even though the dynamic nature of imine bonds has been well established; self-sorting/self-selection process has been overlooked in organic cage systems. Self-sorting in biological realm is a well-established synthetic protocol. DNA double helix formation via hydrogen bonding between the complimentary base pairs is probably the best known example of biological self-sorting. Self-sorting process has the ability to discriminate self from non-self to achieve highly ordered architectures from within a random reaction mixture. The credit of self-sorting/self-selection process goes to the hidden ‘molecular instructions’ encrypted within the complimentary building blocks. The foremost objective of the present thesis work is to implement the self-sorting/self-selection protocol in organic cage formation by harnessing the dynamic imine chemistry. During the course of the investigation it has been observed that non-covalent interaction especially hydrogen bonding could manipulate the outcome of such a process. Besides that, selective formation of a single isomer of an organic cage from a reaction mixture of an unsymmetrical aldehyde and a flexible amine has been successfully achieved by simply fine tuning the geometric features (shape and size) of the reacting aldehyde. Such three-dimensional cages are well appreciated by the scientific community owing to their potential applications in anion sensing, catalysis and gas storage/separation. However, they have not been explored as sensors for nitroaromatic explosives. Therefore, at this juncture several fluorescent organic cages have been synthesized and their potential application as chemosensor for the nitroaromatics has been tested. Moreover, a new synthetic protocol has been introduced for the post-synthetic modification of organic cages. Chapter 1 covers a brief introduction about dynamic covalent chemistry with main emphasis on dynamic imine chemistry and its use in covalent cage synthesis. Moreover, this chapter accounts the very recent applications of such cage compounds in various fields such as a pours material for gas storage/separation, a molecular host for the stabilization of reactive species and for the recognition of ions or molecules. Chapter 2 describes first time ever achieved self-sorting process in three-dimensional purely organic cages. First of all, four different [3+2] cages were synthesized by treating two different triamines with two different dialdehydes separately, by employing dynamic imine chemistry. The formation of desired cages was ascertained by various spectroscopic techniques. When a mixture of all the four components (two aldehydes and two amines) was subjected to reaction, only two cages were found to form (Scheme 1) out of several equally probable possibilities, which suggest a high-fidelity self-recognition. The issue of partner preferences was further verified by transforming a non-self-sorted cage into a self-sorted cage by treating the former with appropriate triamine or dialdehyde. For an in-depth understanding on this subject, theoretical calculations (gas phase DFT) were carried out, which suggested that observed self-sorting is a thermodynamically governed process. Scheme 1. Self-sorting in organic imine cages through partner preferences. Chapter 3 focuses that supramolecular interaction especially hydrogen-boding could be a possible way to direct a self-sorting process operating in imine based organic cage systems. It is a well-accepted fact that in most of the cases self-sorting process operates owing to the difference in geometric features (shape and size) of the competing building blocks. Thus increasing similarity in geometric features would create the situation more complex. It is anticipated that in such circumstances H-bonding could have a decisive role in partner selection. In order to investigate this, four different dialdehydes (A, B, C and D) having similar geometric background were synthesized. These aldehydes upon treatment with flexible amine X were found to form three nanosocpic [3+2] organic cages (aldehyde C gave insoluble uncharacterized material). When a one-pot reaction of triamine X with mixture of all the four aldehydes was carried out, selective formation of cage B3X2 was observed (Scheme 2). Conversely, the same reaction in absence of aldehyde B resulted in the formation of mixture of products. Theoretical and experimental studies fully support the fact that the presence of hydroxyl moiety adjacent to the formyl group in aldehyde B has the key role in selective formation of cage B3X2 from a complex reaction mixture, in which there are numerous equally probable possibilities. Such remarkable selection was further examined by converting a non-hydroxy (non-preferred) cage into hydroxy cage B3X2 (preferred) by treating the former with aldehyde B. The role of the H-bond in self-sorting process of two dialdehydes and two triamines has been established. Furthermore, the possibility of cage–to- cage transformation through imine bond metathesis has also been addressed. Scheme 2. H-bond directed 15-fold (2+3) incomplete self-sorting in organic imine cages. Chapter 4 presents the investigation on the formation of single isomeric species of a [3+2] oligoimine cage from a reaction mixture of an unsymmetrical dialdehyde and a flexible triamine. So far, most of the reported organic cages are derived by symmetric building units. Asymmetric building blocks for the construction of such organic architectures are not the desirable choices, as they could lead to form mixture of isomeric cages. However, the asymmetric building blocks might form selectively one isomer only under the thermodynamic bias, which prefers the formation of one isomer over the other (s). In order to understand the factors that can direct such a process, three asymmetric dialdehydes (A, B and C) were synthesized and their reaction with a flexible amine X was carried out. Experimental outcomes suggested a striking difference in the abilities of isomer selection between aldehydes A/B and C. In case of aldehyde A/B selective formation of one oligoimine cage was observed, whereas aldehyde C led to form two isomeric oligoimine cages (Scheme 3). Experimental and theoretical findings have pointed out that the geometric features (shape and size) of the aldehyde play a decisive role in such isomer selection process. Scheme 3. Shape and size directed self-selection in organic imine cages. Part A of Chapter 5 describes the synthesis and characterization of a fluorescent organic cage compound and its application as a sensor for the detection of explosive picric acid (PA). Picric acid is known to be as explosive as trinitrotoluene (TNT) and one of the principle constituents of many unexplored landmines. Though there are several fluorescent polymers, metal-organic frameworks and small molecule based sensors have been devised in last few years but very little attention has been given towards selective and sensitive detection of picric acid. In this context desired organic cage compound 4 was synthesized by employing imine condensation between 4,4-diformyltriphenylamine (1) with 1,3,5-tris(aminomethyl)-2,4,6-trimethylbenzene (2) followed by reduction of the imine bonds (Scheme 4). This fluorescent nature of the cage in both the solid and solution has been utilized for the detection of nitroaromatic compounds (NACs). Among the various NACs tested it has been found that PA induces highest quenching of the initial fluorescence intensity of the cage solution. Furthermore, this cage has the ability to discriminate PA from other nitrophenolic compounds, such as 2,4-dinitrophenol (DNP) and 4-nitrophenol. In addition to solution phase detection cage 4 has also been successfully utilized for the solid phase detection of PA. The experimental results demonstrates that high sensitivity of the cage towards PA is attributed to the stronger ground state complex formation between the cage and PA as well as excitation v energy transfer (EET) process from protonated cage to the picrate. This represents the first report of a cage compound as a sensor for nitroaromatic compounds. Scheme 4. Synthesis of a fluorescent organic cage for the selective detection of picric acid. Part B of Chapter 5 reports a new synthetic methodology to decorate covalent organic cages post-synthetically, based on one-pot copper(I) catalyzed A3 coupling. A3-coupling is a three-component reaction between formaldehyde, secondary amine and terminal alkyne. In the present study selected organic cage 4 is furnished with six secondary amine moieties and thus it was allowed to react with 6 equiv. of formaldehyde and 6 equiv. of terminal alkyne in presence of CuI as a catalyst (Scheme 5). By employing this synthetic strategy parent cage 4 has been modified to cages 5a-c with appendages phenyl-, xylyl- and napthyl-actylenes. The resulting decorated cages were characterized by multinuclear NMR (1H and 13C), MALDI-TOF and FTIR spectroscopy. All the post-synthetically decorated cages were found to be fluorescent in nature and thus in v order to explore their potential use as a chemosensor for nitroaromatic compounds, cage 5a was tested. Experimental findings have suggested high selectivity of the cage towards nitroaromatic compounds. Interestingly, among the various nitroaromatics tested it has been observed that the cage is more sensitivity towards nitrophenolic compounds, whereas among the various nitrophenols tested, picric acid induced highest quenching. Scheme 5. Post-synthetic modification of an organic cage via cu+ catalyzed A3 coupling.
4

Actuation of DNA cages and their potential biological applications

Entwistle, Ngai Mun Aiman January 2015 (has links)
DNA cages are polyhedra self-assembled from synthetic oligonucleotides in a one-pot process. The main system described in this thesis is a reconfigurable, wire-framed DNA tetrahedron in nanometre-scale. On one of its vertices this tetrahedron has an overhang that can hybridise with a specific sequence of nucleic acids and open the cage. We describe the design of a reconfigurable cage that remained closed under physiological conditions and only opened in the presence of an appropriate signal in solution. Fluorescence techniques were employed to distinguish the open and closed states of the cage. We used flow cytometry and confocal microscopy to successfully established the open and closed states of the cage inside live cultured mammalian cells. Further experiments revealed that the DNA cage could be opened by a separately transfected signalling strand. Hybridisation between two separately transfected systems was possible. The DNA cage was then simplified to a DNA duplex so that the intracellular interactions between the two nucleic acids systems could be studied more efficiently. Microscopy images showed that the interaction occurred in membrane-bound compartments. We describe an investigation into the use of various cellular RNAs, including full-length mRNA and tRNA-RNA fusion, to actuate the DNA cages. Choosing an appropriate cellular opening signal remains a challenge. Analysis showed that bulky cellular RNA experienced steric hindrance with the rigid DNA cage. Finally, other potential biological applications of DNA cages, such as using DNA nanostructures as the carriers for genetic therapeutic agents, were also presented.
5

f-Block and d,f-block phosphonate cages : synthesis, structure and magnetic properties

Zangana, Karzan January 2015 (has links)
Research into molecular magnetism has undergone a revival over the past two decades following the discovery of Single Molecule Magnetism (SMM). Compounds which show this property have the potential to increase the storage capacity of magnetic media by many orders of magnitude compared to current generation devices. Developments in the field have come from synthesis involving mainly simple bridging ligands such as carboxylates, alkoxides, pyridonates and heterocyclic ligands. The use of phosphonic acid ligands in the synthesis of 4f-phosphonate or 3d-4f phosphonate clusters has recently begun to be explored, primarily for interest into their magnetic properties. The present work builds on studies which show that the reaction of oxo-centred metal triangles with phosphonate ligands can generate larger clusters retaining some motifs of the starting material. There are only few examples on the use of lanthanide carboxylates, such as [Ln2(O2CtBu)6(HO2CtBu)6] (Ln = Dy, Gd, Tb, Ho or Er) and/or a preformed cluster [Cr(III)3(µ3-O)(O2CtBu)6(H2O)3][O2CtBu] in combination with phosphonate ligands. This work investigates the use of bi-metallic lanthanide and tri-metallic transition metal starting materials in conjunction with the flexible tertiary-butylphosphonic acid ligand, to yield novel 4f-phosphonate and 3d-4f cages. Several Cr-4f phosphonate cages have been obtained, where each structure contains two oxo-centred {Cr3} triangles, bridged by phosphonates and lanthanides. Additionally, new 4f-phosphonate clusters have been synthesised by treating tertiary-butylphosphonic acid ligand with lanthanide nitrate salts or preformed lanthanide dimers. A number of 4f-phosphonate cages reported in the thesis show interesting structural or magnetic properties, for example, {Ln10P6} is the largest 4f-phosphonate odd number metal ring centred by a tenth metal site, the {Gd8P6} cluster demonstrates interesting MCE properties, and the {Dy4P2} complex is shown to be an SMM.
6

Conception de capsules organiques par auto-organisation d’hétérocycles fonctionnalisés / Conception of organic capsules by self-organization of functionalized heterocycles

Krykun, Serhii 15 May 2019 (has links)
Ce travail traite de la synthèse et de la caractérisation de nouvelles cages moléculaires discrètes riches en électrons préparées via la méthodologie d'auto-assemblage dirigée par les métaux, ainsi que de leurs propriétés redox et d’encapsulation. Les concepts généraux guidant la méthodologie d’auto-assemblage pilotée par les métaux sont présentés. Trois types de ligands tétratopiques rédox-actifs (L) constitués de tétrathiafulvalène (TTF), de dithiol-fluorène (DTF) ou de tétrathiafulvalène π étendu (exTTF) ont été conçus. Leur capacité à générer des cages auto-assemblées avec divers complexes (M) a été étudiée. Dans le premier cas, des métallacages M8L2 dont la géométrie offre une opportunité unique de favoriser des interactions inter-TTF étroites au cours du processus d’oxydation ont été décrites. Ces interactions ont été confirmées par des études électrochimiques ainsi que par DRX à partir d’un sel oxydé électrocristallisé. Dans le second cas, plusieurs auto-assemblages discrets MxLy (cages, clips) ont été obtenus à partir de nouveaux ligands électroactifs basés sur l'unité 9- (1,3-dithiol-2-ylidène) fluorène (DTF). Leurs propriétés rédox ainsi que leur capacité à complexer des unités électro-déficientes sont fortement dépendantes de la géométrie de l’auto-assemblage. Concernant le ligand exTTF, de grandes métallacages électroactives M12L6 (environ 4 000 Å3) ont été obtenus par combinaison avec des complexes trans de palladium ou d'argent. Ces dernières se désassemblent lors de l'oxydation, donnant lieu à une transformation sans précédent d'une cage métallique discrète en un polymère de coordination. Enfin, un nouveau squelette aromatique benzo[1,2-b:4,5-b'] dithiophène est décrit en tant qu’alternative aux dérivés riches en électrons π étendus. Le rôle critique des interactions non-covalentes 1,5 S ···S est démontré par une approche combinée expérimentale et théorique. / This work deals with the synthesis and characterization of new electron-rich discrete molecular cages, prepared via the coordination-driven self-assembly methodology, as well as on evaluating their redox and host-guest properties. The general concepts guiding the metal-driven self-assembly methodology are presented. Three types of redox-active tetratopic ligands (L) featuring either a tetrathiafulvalene (TTF), a dithiol-fluorene (DTF) or a π-extended tetrathiafulvalene (exTTF) have been designed. Their ability to generate self-assembled cages upon combination with various metal complexes (M) has been studied. In the first case, M8L2 metallacages were obtained, whose geometry offers a unique opportunity to promote close inter-TTF interactions upon oxidation, as confirmed through electrochemical studies as well as from single-crystal DRX from an electrocrystallized oxidized salt. In the second case, several discrete self-assemblies MxLy (cages, clips) were obtained and characterized from new electro-active ligands based on the 9-(1,3-dithiol-2-ylidene)fluorene (DTF) unit. Their redox properties as well as their binding ability towards electro-deficient planar species show a strong dependence to the self-assembly geometry. Considering the exTTF ligand, large (ca. 4000 Å3) electroactive M12L6 metallacages were obtained from combining with trans palladium or silver complexes. Le latter exhibits a disassembling process upon oxidation, giving rise to an unprecedented redox-triggered transformation of discrete metalla-cage into a coordination polymer. Finally, a new benzo[1,2-b:4,5-b'] dithiophene aromatic scaffold is investigated as an alternative π-extended electron-rich derivative. The critical role of non-covalent 1,5 S···S interactions is demonstrated by a combined experimental and theoretical approach.
7

Laying hens in furnished cages : use of facilities, exterior egg quality and bird health /

Wall, Helena. January 2003 (has links) (PDF)
Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003.
8

Taxas e intervalos de alimentação na produção de Tilápia em tanque-rede com dispensador automático de ração

Oliveira, Fernando Alcântara de [UNESP] 19 November 2007 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:27:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-11-19Bitstream added on 2014-06-13T18:56:22Z : No. of bitstreams: 1 oliveira_fa_me_botfmvz.pdf: 215221 bytes, checksum: c1d44302a65a88de54ca1d389cda16ab (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / Nas diversas atividades agropecuárias o objetivo principal é alcançar o melhor desempenho, com baixo custo e menor tempo de produção. Com o avanço tecnológico na alimentação de peixes, novos equipamentos estão sendo desenvolvidos para acelerar a produção. O objetivo deste trabalho foi avaliar o manejo alimentar, utilizando dispensadores automáticos de ração, com diferentes taxas e intervalos de alimentação em alta freqüência para tilápias na fase de engorda. Foram instalados dezoito tanques-rede (TR) de 1,0 m³, num viveiro de 2000 m² de espelho d’água. Sobre os TR foram colocados suportes metálicos para sustentar os dispensadores de ração. Foram utilizadas 93 tilápias, com peso médio de 186,57± 9,08 gramas, por TR. As taxas alimentares propostas foram de 4,0%, 3,0% e 2,0% do peso vivo em freqüência alimentar de 48 vezes, em intervalos de 30 ou 22 minutos entre cada refeição, durante o período experimental de 120 dias. Os valores médios do oxigênio dissolvido, pH e temperatura foram 3,20 mg/l; 8,03 e 25,43 ºC, respectivamente. O melhor desempenho foi alcançado por peixes alimentados com 4,0% do peso vivo, com intervalo de 22 minutos, interrompendo a alimentação por um período de seis horas durante a madrugada. / In the diverse farming activities, the main objective is to reach optimum performance, with low cost and decreasing productive time. With technological advances in the feeding of fish, new equipment have being developed to improve production. Therefore, the objective of this work was to optimize feeding strategies, using automatic feeders, to determine optimum ration level, interval and schedule of feeding of tilapias in finishing phase. It was allocated eighteen 1m³ net-cages (NC) 1 m³, into a pond of 2000m² of water mirror. On the NCs, a metallic support was placed to support the automatic feeders. Above 93 Nile tilapia with 186,57± 9,08 g, average weight were stocked into each NC. Feeding levels were 4%, 3% and 2% of the alive weight and feeding frequency were 48 times, in intervals of 22 and 30 min, during 120 days. The average values of the dissolved oxygen, pH and temperature were 3,20 mg/l, 8,03 and 25,43ºC, respectively. The level of 4% and period of 24 hours resulted in better growth performance reaching the 683,73 g of final weight.
9

Diferentes densidades de gaiola e suas implicações no comportamento de galinhas poedeiras e na qualidade dos ovos produzidos / Different cage densities and their implications on the behavior of laying hens and the quality of eggs

Maria Amelia Flandres Cabrelon 26 January 2016 (has links)
Objetivou-se com esta pesquisa avaliar o efeito de diferentes densidades de galinhas poedeiras alojadas em gaiolas convencionais (50x45x40 cm) nos índices produtivos, na viabilidade, qualidade dos ovos e comportamento das aves. A pesquisa foi realizada na cidade de Bastos (SP) com duração de 18 semanas. Foram utilizadas 500 aves, da linhagem ISA Brown, distribuídas em 5 tratamentos com 25 repetições cada. Os tratamentos foram: tratamento 1: 6 aves/ gaiola (375,0 cm²), tratamento 2: 5 aves/gaiola (450,0 cm²); tratamento 3: 4 aves/gaiola (562,5 cm²); tratamento 4: 3 aves/ gaiola (750,0 cm²) e tratamento 5: 2 aves/gaiola (1.125,0 cm²). Adotou-se o delineamento inteiramente aleatorizado, este contendo cinco tratamentos e 25 repetições. De acordo com os resultados, verificou-se que o tratamento 1 apresentou as menores médias percentuais de produção quando relacionado aos demais tratamentos, diferindo-se estatisticamente. A viabilidade e qualidade dos ovos, não apresentaram diferença estatística entre os tratamentos. Já com relação ao comportamento das aves foi possível observar que o tratamento 5 (menor densidade) foi o que expressou diferentes comportamentos e diferiu-se estatisticamente dos demais. Observou-se também que, quanto à atividade, o tratamento 5 passou menor parte do tempo \"parado\". De acordo com esses resultados, conclui-se que com o aumento da densidade, ocorreu uma significativa redução na produção e na viabilidade, porém, quanto a qualidade dos ovos, não sofreu influência significativa, em relação aos comportamentos das aves, observouse que os animais expressaram melhor o seu comportamento natural quando estavam em menor densidade, ou seja, maior espaço. / The objective of this research was to evaluate the effect of different densities of laying hens housed in conventional cages (50x45x40 cm) in production rates, viability, quality of eggs and bird behavior. The survey was conducted in the city of Bastos (SP) lasting 18 weeks. They were used 500 birds, ISA Brown hens, distributed in 5 treatments with 25 repetitions each. The treatments were: Treatment 1: 6 / Bird Cage (375.0 cm²), treatment 2: 5 birds / cage (450.0 cm²); treatment 3: 4 birds / cage (562.5 cm²); Treatment 4: 3 birds / cage (750.0 cm²) and treatment 5: 2 / Bird Cage (1125.0 cm²). Adopted a completely randomized design, this containing five treatments and 25 repetitions. According to the results, it was found that the treatment 1 had the lowest average percentage of production when related to other treatments, differing statistically. The viability and quality of eggs, there was no statistical difference between treatments. In relation to the behavior of birds was observed that the treatment 5 (lower density) was expressed that the different behaviors and differed statistically from the others. It was also observed that, as the activity, treatment 5 spent less of their time \"stopped\". According to these results, we conclude that with the consolidation of the cages, it was noticeable that the production and mortality has a significant worsening, as the quality of eggs, there was no influence of the different densities of the conduct of the birds, it is observed that the animals best express their natural behavior when they are in lower density, or larger space.
10

Reversible directed phase transfer of M4IIL4 and M4IIL6 cages

Georges, Maureen Claire Alma January 2017 (has links)
A major function assessed by Nature is the transport of a cargo between two different media, such as anions through cell membranes. Mimicking this function using complex systems is one of the biggest challenge of supramolecular chemistry. Metallo-organic cages are an important breakthrough in the encapsulation and transport of small molecules, providing a crucial platform for the development of systems chemistry. Binding a network member within a tetrahedral cage allows it to be hidden and then revealed upon receipt of a release signal, or transported as a cargo between spatially distant parts of a network. Larger capsules may also isolate subsystems from each other in the manner of vesicles. These dynamic architectures are synthesised by self-assembly, which involves the simultaneous formation of multiple coordinative and dynamic covalent linkages during the same overall synthetic process. Their shape and binding properties can be tuned by changing the subcomponents such as metals or ligands. Great progress has been reported in recent years in the development of three-dimensional cages that can interact with specific guest species, but there are limitations associated with the transport of these systems. Recent work by Nitschke et al. have successfully addressed practical separations problems by transporting a tetrahedral cage and its cargo from water into an ionic liquid layer. However, this system is not ideal as the process is triggered by an anion exchange not by a direct stimulus. This thesis reports the synthesis of an ionic liquid inspired tetrahedral system achieving reversible transport between water and an immiscible organic solvent driven by a change in temperature. Once the switchable capsules were obtained and characterised, their ability to move between different solvent phases upon heating was investigated. A capsule-mediated transport system as developed that is both directional and reversible. The flow of the capsule and its encapsulated cargo is directed using stimuli such as temperature modification. Ultimately an apparatus that allows the switchable capsules to move along a channel has been developed.

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