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| 2. |
- Boström, Mathias, et al.
(författare)
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Specific ion effects : The role of co-ions in biology
- 2003
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 63:4, s. 610-615
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Tidskriftsartikel (refereegranskat)abstract
- Co-ions are as essential in biological systems as they are ignored. The purpose of this letter is to demonstrate the importance of including ionic dispersion potentials acting between ions and interfaces in any realistic theoretical modeling of biological systems. We demonstrate through a well-known biological example that co-ion effects can be understood once these previously ignored forces are included. Experiments have in the past revealed that addition of salt solutions with different co-ions give fundamentally different results for the formation of meta 2 rhodopsin (which is involved in dim light vision). For systems with low salt concentrations, addition of salt favors the formation of meta 1 rhodopsin. Exactly the opposite is observed in high-concentration salt solutions. This is true even after surface pH. effects have been screened out with the addition of 0.5 M sodium acetate buffer. A theoretical explanation for the role of co-ions behind this effect is here given in terms of ionic dispersion potentials and ion specific surface pH.
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| 3. |
- Bulgakov, E.N., et al.
(författare)
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Rectangular microwave resonators with magnetic anisotropy. Mapping onto pseudointegrable rhombus
- 2002
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 57:2, s. 198-204
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Tidskriftsartikel (refereegranskat)abstract
- A rectangular microwave resonator filled with ferrite with uniaxial magnetic anisotropy is considered. It is shown that this task can be reduced to an empty rhombus resonator with the vertex angle defined by an external magnetic field, provided that the magnetic anisotropy of the ferrite is strong. Therefore, the statistics of eigenfrequencies for TM modes is described by the Brody or semi-Poisson distribution with some exceptional cases.
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| 4. |
- Carbone, V, et al.
(författare)
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To what extent can dynamical models describe statistical features of turbulent flows?
- 2002
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 58:3, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- Statistical features of "bursty" behaviour in charged and neutral fluid turbulence are compared to statistics of intermittent events in a GOY shell model, and avalanches in different models of Self-Organized Criticality (SOC). It is found that inter-burst times show a power law distribution for turbulent samples and for the shell model, a property which is shared only in a particular case of the running sandpile model. The breakdown of self-similarity generated by isolated events observed in the turbulent samples is well reproduced by the shell model, while it is absent in all SOC models considered. On this base, we conclude that SOC models are not adequate to mimic fluid turbulence, while the GOY shell model constitutes a better candidate to describe the gross features of turbulence.
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| 5. |
- Dugne, Jean-Jacques, et al.
(författare)
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Preon trinity : a schematic model of leptons, quarks and heavy vector bosons
- 2002
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 60:2, s. 188-194
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Tidskriftsartikel (refereegranskat)abstract
- Quarks, leptons and heavy vector bosons are suggested to be composed of stable spin- (1/2) preons, existing in three flavours, combined according to simple rules. Straightforward consequences of an SU(3) preon-flavour symmetry are the conservation of three lepton numbers, oscillations and decays between some neutrinos, and the mixing of the d and s quarks, as well as of the vector fields W0 and B0. We find a relation between the Cabibbo and Weinberg mixing angles, and predict new (heavy) leptons, quarks and vector bosons, some of which might be observable at the Fermilab Tevatron and the future CERN LHC. A heavy neutrino might even be visible in existing data from the CERN LEP facility.
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| 6. |
- Evaldsson, Martin, et al.
(författare)
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Spin splitting in open quantum dots
- 2004
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 68:2, s. 261-267
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the magnetoconductance of small lateral quantum dots in the strongly coupled regime (i.e. when the leads can support one or more propagating modes) shows a pronounced splitting of the conductance peaks and dips which persists over a wide range of magnetic fields (from zero field to the edge-state regime) and is virtually independent of the magnetic field strength. Our numerical analysis of the conductance based on the Hubbard Hamiltonian demonstrates that this is essentially a many-body/spin effect that can be traced to a splitting of degenerate levels in the corresponding closed dot. The above effect in open dots can be regarded as a counterpart of the Coulomb-blockade effect in weakly coupled dots, with the difference, however, that the splitting of the peaks originates from interactions between electrons of opposite spin.
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| 7. |
- Hayashi, Yoshikatsu
(författare)
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All-or-none (or something in between) transition of DNA
- 2004
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 68:4, s. 536-542
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Tidskriftsartikel (refereegranskat)abstract
- DNA compaction can be caused by multivalent ions as condensing agents. Both discontinuous (all-or-none) and continuous (pearl-necklace structure) transitions have been observed in experiments as the concentration of the condensing agent was increased. We have investigated the DNA transition by analytical calculations in the infinite-chain limit. A mechanism for pearl-necklace structures could be a combinatorial entropy term, which favours a mixture of globules and coils in a single chain. However, when a surface term is taken into account, it gives rise to a discontinuous transition. We also consider the role of surface charges on the globule.
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| 8. |
- Holme, Petter, et al.
(författare)
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A zero-temperature study of vortex mobility in two-dimensional vortex glass models
- 2002
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 60:3, s. 439-445
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Tidskriftsartikel (refereegranskat)abstract
- Three different vortex glass models are studied by examining the energy barrier against vortex motion cross the system. In the two-dimensional gauge glass this energy barrier is found to increase logarithmically with system size which opens up for the existence of low-temperature phase with zero resistivity. Associated with the large-energy barriers is breaking of ergodicity which explains why the well-established results from equilibrium studies could fail. The behavior of the more realistic random pinning model is however different with decreasing energy barriers and no finite critical temperature.
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| 9. |
- Holme, Petter
(författare)
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Efficient local strategies for vaccination and network attack
- 2004
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 68:6, s. 908-914
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Tidskriftsartikel (refereegranskat)abstract
- We study how a fraction of a population should be vaccinated to most efficiently stop epidemics. Our starting point is that only local information-about the neighborhood of specific vertices-is usable in practice. For this reason we consider only local vaccination strategies. The efficiency of the vaccination strategies is investigated with both static and dynamic measures. We test the strategies on real-world networks and model networks with real-world characteristics. Among other things, we find that the most efficient strategy for many real-world situations is to iteratively vaccinate the neighbor of the previous vaccinee that has the most links out of the neighborhood.
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| 10. |
- Holme, Petter
(författare)
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Network dynamics of ongoing social relationships
- 2003
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 64:3, s. 427-433
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Tidskriftsartikel (refereegranskat)abstract
- Many recent large-scale studies of interaction networks have focused on networks of accumulated contacts. In this letter we explore social networks of ongoing relationships with an emphasis on dynamical aspects. We find a distribution of response times (times between consecutive contacts of different direction between two actors) that has a power law shape over a large range. We also argue that the distribution of relationship duration (the time between the first and last contacts between actors) is exponentially decaying. Methods to reanalyze the data to compensate for the finite sampling time are proposed. We find that the degree distribution for networks of ongoing contacts fits better to a power law than the degree distribution of the network of accumulated contacts do. We see that the clustering and assortative mixing coefficients are of the same order for networks of ongoing and accumulated contacts, and that the structural fluctuations of the former are rather large.
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