| 1. |
- Stoll, O. M., et al.
(author)
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Hysteresis and fractional matching in thin Nb films with rectangular arrays of nanoscaled magnetic dots
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:10
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Journal article (peer-reviewed)abstract
- We have investigated the periodic pinning of magnetic flux quanta in thin Nb films with rectangular arrays of magnetic dots. In this type of pinning geometry, a change in the periodicity and shape of the minima in the magnetoresistance occurs for magnetic fields exceeding a certain threshold value. This was explained recently in terms of a reconfiguration transition of the vortex lattice due to an increasing vortex-vortex interaction with increasing magnetic field. In this picture the dominating elastic energy at high fields forces the vortex lattice to form a square symmetry, rather than being commensurate with the rectangular geometry of the pinning array. In this paper we present a comparative study of rectangular arrays with Ni dots, Co dots, and holes. In the magnetic dot arrays we found a strong fractional matching effect up to the second-order matching field. In contrast, no clear fractional matching is seen after the reconfiguration. Additionally, we discover the existence of hysteresis in the magnetoresistance in the crossover between the low- and high-field regimes. We find evidence that this effect is correlated with the reconfiguration phenomenon rather than to the magnetic state of the dots. The temperature and angular dependences of the effect are measured, and possible models are discussed to explain this behavior.
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| 2. |
- Bermin, Hans-Peter, et al.
(author)
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Local vega index and variance reduction methods
- 2003
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In: Mathematical Finance. - : Wiley. - 1467-9965 .- 0960-1627. ; 13:1, s. 85-97
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Journal article (peer-reviewed)abstract
- In this article we discuss a generalization of the Greek called vega which is used to study the stability of option prices and hedging portfolios with respect to the volatility in various models. We call this generalization the local vega index. We compute through Monte Carlo simulations this index in the cases of Asian options under the classical Black-Scholes setup. Simulation methods using Malliavin calculus and kernel density estimation are compared. Variance reduction methods are discussed.
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| 3. |
- Cisneros, David A., et al.
(author)
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Inversion of the allosteric response of Escherichia coli glucosamine-6-P deaminase to N-acetylglucosamine 6-P, by single amino acid replacements
- 2004
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In: Archives of Biochemistry and Biophysics. - : Elsevier BV. - 0003-9861 .- 1096-0384. ; 421:1, s. 77-84
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Journal article (peer-reviewed)abstract
- Amino acid replacements in the active site of glucosamine-6-P deaminase from Escherichia coli (GlcN6P deaminase, EC 3.5.99.6) involving the residues D141 and E148 produce atypical allosteric kinetics. These residues are located in the chain segment 139-156 which is part of the active site and which also forms several intersubunit contacts close to the allosteric site. In the D141N and E148Q mutant forms of this deaminase, there is an inversion of the effect of its physiological allosteric effector, N-acetylglucosamine 6-P, which becomes an inhibitor at substrate concentrations above a critical value. For both mutants, this particular point appears at low substrate concentration and the inhibition by the allosteric activator is the dominant effect in velocity versus substrate curves. These effects are analyzed as a particular case of the concerted allosteric model, assuming that the R state, the conformer displaying the higher affinity for the substrate, is the less catalytic state, thus producing an inverted allosteric response.
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| 4. |
- Montero, M. I., et al.
(author)
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Flux pinning by regular nanostructures in Nb thin films : Magnetic vs. structural effects
- 2003
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In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 63:1, s. 118-124
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Journal article (peer-reviewed)abstract
- Periodic pinning effects in indented Nb films and Nb films with rectangular arrays of submicrometric Ni dots were studied. The indented samples consisted of Nb film deposited on top of Si substrates patterned with rectangular arrays of nanoholes. Pinning effects can be observed in the evolution of resistivity and critical current with the applied magnetic field, showing the same qualitative behavior, for both types of samples. The main difference between them is that the matching effects are more pronounced in the samples with magnetic dots. The analysis and comparison of these results allows determining the pinning as due to superconductivity suppression around the nanostructures (indentations or dots) due to a thickness reduction. For the samples with magnetic dots, this suppression of superconductivity is reinforced by the magnetic proximity effect.
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