Change of surface critical current in the surface superconductivity and mixed states of superconducting Niobium

A systematic study of irreversible magnetization was performed in bulk Niobium after different surface treatments. Starting with smooth surfaces and abrading them, a strong increase of the critical current is observed up an apparent limiting value. An impressive change of the critical current is also observed in the surface superconductivity (SSC) state, reaching values of the same order of magnitude as in the mixed state. We explain also the observation of strong SSC for magnetic field perpendicular to larges facets in terms of nucleation of SC along bumps of a corrugated surface.Comment: Accepted for publication in Superconducing Science and Technolog

Suggestion systems: a usability-based evaluation model

Usability has been used to design and assess products and websites. This paper takes the concept of usability one step further and proposes a framework to assess suggestion systems. Thus taking the concept of usability one step further and applying it in the area of ideas management through suggestion system. The fundamental premise of the article is that a suggestion system designed, with usability in mind, will improve innovation among employees, and hence increase participation. This framework was then used to assess four suggestion systems in an oil and gas company in the middle-east. These systems were further assessed for employee perception of their usability and participation. After collecting data on these three different aspects conclusions are drawn. Out of the four systems analyzed, the most usable suggestion system had the highest participation rate and the least usable system attracted the fewest suggestions

Data comparison schemes for Pattern Recognition in Digital Images using Fractals

Pattern recognition in digital images is a common problem with application in remote sensing, electron microscopy, medical imaging, seismic imaging and astrophysics for example. Although this subject has been researched for over twenty years there is still no general solution which can be compared with the human cognitive system in which a pattern can be recognised subject to arbitrary orientation and scale. The application of Artificial Neural Networks can in principle provide a very general solution providing suitable training schemes are implemented. However, this approach raises some major issues in practice. First, the CPU time required to train an ANN for a grey level or colour image can be very large especially if the object has a complex structure with no clear geometrical features such as those that arise in remote sensing applications. Secondly, both the core and file space memory required to represent large images and their associated data tasks leads to a number of problems in which the use of virtual memory is paramount. The primary goal of this research has been to assess methods of image data compression for pattern recognition using a range of different compression methods. In particular, this research has resulted in the design and implementation of a new algorithm for general pattern recognition based on the use of fractal image compression. This approach has for the first time allowed the pattern recognition problem to be solved in a way that is invariant of rotation and scale. It allows both ANNs and correlation to be used subject to appropriate pre-and post-processing techniques for digital image processing on aspect for which a dedicated programmer's work bench has been developed using X-Designer

PDA mobile learning using indoor intelligent wireless whiteboard

The information and the educational technologies has rapidly changed in recent years. The application of information technology typically Mobile has become as new technology that can enhance the quality of learning. More class time and assignments in introduction to information technology should be dedicated. This paper reports on the designing the interface of a mobile learning PDA based on wireless whiteboard classroom architecture. Developing an adaptive and context aware mobile learning system is presented. Therein, the proposed technique would definitely enhance the lecturer's hand written notes to integrate PDAs in classroom. Future development approaches for systems supporting learning environments is considered

Investigation of aldehyde oxidase and xanthine oxidoreductase in rainbow trout (Oncorhynchus mykiss)

Molybdo-flavoenzymes (MFEs), aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR) are involved in the oxidation of N-heterocyclic compounds and aldehydes, many of which are environmental pollutants, drugs and vitamins. This biotransformation generally generates more polar compounds that are more easily excreted, thus MFEs have been classed as detoxication enzymes. To date there has been scant study of the properties, substrate and inhibitor specificities of MFEs in non-mammalian vertebrate organisms. This investigation focuses on MFEs in rainbow trout (Oncorhynchus mykiss) as it belongs to a class of fish that host a single AOX (AOXβ) and one XOR. In this study the substrate specificity of rainbow trout liver AOX and XOR was investigated using HPLC and spectrophotometric assays. AOX in hepatic cytosol was found to be able to catalyse the oxidation of azanaphthalenes belonging to a group of compounds that are environmental pollutants such as phenanthridine, phthalazine and cinchonine. In addition, xenobiotic aromatic aldehydes (vanillin and dimethylaminocinnamaldehyde) and drugs such as allopurinol and pyrazinamide were substrates. Several endogenous vitamins including pyridoxal (vitamin B6), all-trans retinal (vitamin A) and N1-methylnicotinamide were also biotransformed by the rainbow trout AOX. In contrast to liver no AOX activity was detectable in kidney and gill tissue. XOR activity in rainbow trout liver was measurable with the endogenous purine xanthine, purine drug metabolites (1-methylxanthine and 6-thioxanthine) and N-heterocyclic drugs (allopurinol and pyrazinamide). Unlike mammalian XOR that can utilise both NAD+ and O2 as electron acceptors, trout XOR was exclusively NAD+-dependent with no activity being detected with O2. Eadie-Hofstee plots were using to determine the Km and Vmax of rainbow trout AOX and XOR with different substrates and it was found the Vmax of the rainbow trout enzymes were generally lower and Km generally higher than mammalian AOX and XOR. Inhibitors of mammalian AOX were tested to determine if they could interact with the piscine AOX. Environmental pollutants (17α-ethinyl estradiol and phenanthridine), an endogenous steroid (estradiol) and drugs (chlorpromazine and menadione) were found to be effective inhibitors and were classed as competitive, non-competitive and uncompetitive respectively using Lineweaver-Burk plots. The drug metabolite, oxipurinol, was a non-competitive inhibitor of rainbow trout XOR. In order to further characterise trout AOX protein purification was carried out. In contrast to mammalian AOX, the piscine enzyme was not thermotolerant at 55°C nor was it inhibited by benzamidine, thus heat treatment and affinity chromatography could not be used as a purification steps. Trout AOX was purified 210-fold using ammonium sulphate fractionation, together with ion exchange and gel filtration chromatography. The native molecular mass of the piscine AOX was 295 kDa, which is similar to mammalian AOXs. In conclusion this study yields new insight into groups of anthropogenic environmental pollutants, drugs and vitamins that are substrates and inhibitors of an ancestral vertebrate AOX. The toxicological relevance of these findings is discussed

Electrochemical behavior and antioxidant activity of tetradentate Schiff bases and their copper (II) complexes

U doktorskoj disertaciji je ispitano elektrohemijsko ponašanje tetradentatnih Šifovih baza i njihovih bakar(II) kompleksa primenom ciklične voltametrije. Izvršena je optimizacija uslova pri kojima je urañeno ispitivanje. Ispitan je uticaj strukture i uticaj supstuenata na elektrohemijsko ponašanje. Utvrñeno je da supstituenti imaju merljiv efekat na elektrohemijsko ponašanje Šifovih baza i njihovih bakar (II) kompleksa. Induktivni i sterni efekti, različitih supstituenata, utiču na promenu elektronske gustine jona metala, kao i na baznost atoma azota, koji je prisutan u diaminskom mostu. Utvrñena je razlika i pravilnost u elektrohemijskom ponašanju posmatranog seta jedinjenja, što se detektuje pomeranjem anodnih i katodnih potencijala zbog prirode Šifovih baza, kada su slobodni (kao ligandi) ili koordinativno vezani u kompleksima bakra(II). Pored toga odreñena je antioksidativna aktivnosti navedenih jedinjenja primenom TLCDPPH eseja. Primenom ove metode omogućen je kontakt, a samim tim i reakcija izmeñu jedinjenja i slobodnih radikala nezavisno od primenjenog rastvarača što je prednost u poreñenju sa spektrofotometrijskom metodom. Ispitana je veza izmeñu strukture (definisane molekulskim deskriptorima) i antioksidativne aktivnosti, elektrohemijskog ponašanja i antioksidativne aktivnosti i pretpostavljen je mehanizam ispoljavanja antioksidativne aktivnosti posmatrane serije jedinjenja. Uspostavljene su korelacije izmeñu redoks potencijala i antioksidativne aktivnosti. Jedinjenja sa jakim antioksidativnim aktivnostima pokazuju sposobnost oksidacije na niskim potencijalima, što omogućava da se oksidacioni potencijal primeni kao pokazatelj sposobnosti eliminacije slobodnih radikala. U cilju boljeg razumevanja reakcionog puta i mehanizma ispoljavanja antioksidativne aktivnosti urañena su DFT izračunavanja kvantno-hemijskih deskriptora. Dipolni moment, energija disocijacije veze, naelektrisanje na atomima kiseonika i azota (N7 i N10) pokazuju jako visoku korelaciju sa eksperimentalno odreñenom antioksidativnom aktivnošću. Antioksidativna aktivnost bakar (II) kompleksa je u direktnoj zavisnosti od dela strukture koju definiše helatni ugao ravni i ukupna spinska gustina. Na osnovu odabranih deskriptora, koji pokazuju visoku korelaciju sa antioksidativnom aktivnošću, pretpostavljen je mehanizam reakcije ispoljavanja ove aktivnosti. Slobodni radikal (DPPH) može da bude neutralisan ili direktnom redukcijom putem premeštanja elektrona (kompleksi Šifovih baza) ili proton (Šifove baze)...In this doctoral dissertation was examined the electrochemical behavior tetradentatnih Schiff bases and their copper (II) complexes using cyclic voltammetry. The optimization of conditions and investigation of effects of the structure and impact of substituents the electrochemical behavior was done. It has be found that the substituents have a detectable effect on the electrochemical behavior of the Schiff bases and their copper(II) complexes. Their inductive and steric effects influence the change in electron density on metal ion and basicity of nitrogen. Therefore, there is the difference in electrochemical behavior, which is detected by shifting of anodic and cathodic potentials values strongly influenced by the nature of the Schiff base when they free or bound as ligands in the complex compounds. In addition it was determined the antioxidant activity of investigated compounds with TLC-DPPH assay. This method provides an opportunity to contact and reaction of the compounds and free radicals independent of the solvent used to prepare the solution, which is an advantage compared to the spectrophotometric method. Based on results was investigated the relationship between structure (defined molecular descriptors) and antioxidant activity, electrochemical behavior and antioxidant activity and assumes a mechanism to manifest antioxidant activity observed series of compounds. The correlation between the redox potential and antioxidant activity was established. Compounds with a strong antioxidative activities show the ability of the low oxidation potential, which allows the oxidation potential to be applied as indication of the ability of eliminating of free radicals. For better understanding the reactivity patterns and mechanisms of activity of antioxidants, the DFT-based quantum-chemical descriptors were calculated. Quantum-chemical descriptors are the numerical representation of the molecular structures. Dipole moment, bond dissociation energy, charge on oxygen atoms and charge on hydrogen atoms on N7 and N10 show high correlation with antioxidant activity of the investigated Schiff bases. Antioxidant activity of copper(II) complexes is highly correlated with chelate plane angle and sum spin density descriptors. Selected descriptors, which have the best correlation with antioxidant activity, shed light on the reaction mechanism of scavenging/antioxidant activity of the studied compounds..