arXiv subjects

Kasper Astrup Eriksen

Publications and source records attributed to Kasper Astrup Eriksen.

7 recordsLinked to original sources

arXiv2003

Diffusion on Complex Networks : A way to probe their large scale topological structures

A diffusion process on complex networks is introduced in order to uncover their large scale topological structures. This is achieved by focusing on the slowest decaying diffusive modes of the network. The proposed procedure is applied to real-world networks like a friendship network of known modular structure, and an Internet routing network. For the friendship network, its known structure is well reproduced. In case of the Internet, where the structure is far less well-known, one indeed finds a modular structure, and modules can roughly be associated with individual countries. Quantitatively the modular structure of the Internet manifests itself in an approximately 10 times larger participation ratio of its slowest decaying modes as compared to the null model -- a random scale-free network. The extreme edges of the Internet are found to correspond to Russian and US military sites.

cond-mat.stat-mech↗

arXiv2003

Localization of DNA damage by current exchanging repair enzymes: effects of cooperativity on detection time

How DNA repair enzymes find the relatively rare sites of damage is not known in great detail. Recent experiments and molecular data suggest that the individual repair enzymes do not work independently of each other, but rather interact with each other through currents exchanged along DNA. A damaged site in DNA hinders this exchange and this makes it possible to quickly free up resources from error free stretches of DNA. Here the size of the speedup gained from this current exchange mechanism is calculated and the characteristic length and time scales are identified. In particular for Escherichia coli we estimate the speedup to be 50000/N, where N is the number of repair enzymes participating in the current exchange mechanism. Even though N is not exactly known a speedup of order 10 is not entirely unreasonable. Furthermore upon over expression of repair enzymes the detection time only varies as one over the squareroot of N and not as 1/N. This behavior is of interest in assessing the impact of stress full and radioactive environments on individual cell mutation rates.

q-bio.BM↗

arXiv2003

Upstream Plasticity and Downstream Robustness in Evolution of Molecular Networks

Evolving biomolecular networks have to combine the stability against perturbations with flexibility allowing their constituents to assume new roles in the cell. Gene duplication followed by functional divergence of associated proteins is a major force shaping molecular networks in living organisms. Recent availability of system-wide data for yeast S. Cerevisiae allow us to access the effects of gene duplication on robustness and plasticity of molecular networks. We demonstrate that the upstream transcriptional regulation of duplicated genes diverges fast, losing on average 4% of their common transcription factors for every 1% divergence of their amino acid sequences. In contrast, the set of physical interaction partners of their protein products changes much slower. The relative stability of downstream functions of duplicated genes, is further corroborated by their ability to substitute for each other in gene knockout experiments. We believe that the combination of the upstream plasticity and the downstream robustness is a general feature determining the evolvability of molecular networks.

q-bio.MN↗

arXiv2002

Modularity and Extreme Edges of the Internet

We study the spectral properties of a diffusion process taking place on the Internet network focusing on the slowest decaying modes. These modes allow us to identify an underlying modular structure of the Internet roughly corresponding to individual countries. For instance in the slowest decaying mode the diffusion current flows from Russia towards US military sites. These two regions thus constitute the extreme edges of the Internet. Quantitatively the modular structure of the Internet manifests itself in approximately 10 times larger participation ratio of its slow decaying modes compared to the null model - a random scale-free network. We propose to use the fraction of nodes participating in slow decaying modes as a general measure of the modularity of a network. For the 100 slowest decaying modes of the Internet we measured this fraction to be around 30%. Finally we suggest, that the degree of isolation of an individual module can be assessed by comparing its participation in different diffusion modes. Using the proportionality of response as a criterion we find that the independent module approximation works well for the Internet.

cond-mat.stat-mech↗

arXiv2001

A single-particle path integral for composite fermions and the renormalization of the effective mass

To study composite fermions around an even denominator fraction, we adapt the phase space single-particle path integral technique for interacting electrons in zero magnetic field developed recently by D.S. Golubev and A.D. Zaikin, Phys. Rev. B {\bf 59}, 9195 (1999). This path integral description gives an intuitive picture of composite fermion propagation very similar to the Caldeira-Leggett treatment of a particle interacting with an external environment. We use the new description to explain the origin of the famous cancellation between the self-energy and the vertex corrections in semi-classical transport measurements. The effective range of the cancellation is given by the size of the propagating particle, which for the Coulomb interaction scales with the temperature T as T^{-1/4} |log T|^{-1} in the semi-classical limit. Using this scheme we find that the effective mass in the semi-classical limit for composite fermions in GaAs is approximately 6 times the bare mass.

cond-mat.mes-hall↗

arXiv1998

On loss of quantum coherence in an interacting Fermi gas

We clarify the path integral calculation, recently suggested by Golubev and Zaikin, and show, contrary to their claim, that quasiparticles become fully coherent quantum particles in the $T \to 0$ limit. The important physical point is the inclusion of the recoil of the quasiparticle when interacting with fluctuations in the rest of the Fermi gas.

cond-mat.mes-hall↗

arXiv1998

Excitations in antiferromagnetic cores of superconducting vortices

We study excitations of the predicted antiferromagnetically ordered vortex cores in the superconducting phase of the newly proposed SO(5) model of strongly correlated electrons. Using experimental data from the literature we show that the susceptibilities in the spin sector and the charge sector are nearly equal, and likewise for the stiffnesses. In the case of strict equality SO(5) symmetry is possible, and we find that if present the vortices give rise to an enhanced neutron scattering cross section near the so called pi resonance at 41 meV. In the case of broken SO(5) symmetry two effects are predicted. Bound excitations can exist in the vortex cores with ``high'' excitation energies slightly below 41 meV, and the massless Goldstone modes corresponding to the antiferromagnetic ordering of the core can acquire a mass and show up as core excitation with ``low'' excitation energies around 2 meV.

cond-mat.str-el↗