18 research outputs found
Synchronization, Diversity, and Topology of Networks of Integrate and Fire Oscillators
We study synchronization dynamics of a population of pulse-coupled
oscillators. In particular, we focus our attention in the interplay between
networks topological disorder and its synchronization features. Firstly, we
analyze synchronization time in random networks, and find a scaling law
which relates to networks connectivity. Then, we carry on comparing
synchronization time for several other topological configurations,
characterized by a different degree of randomness. The analysis shows that
regular lattices perform better than any other disordered network. The fact can
be understood by considering the variability in the number of links between two
adjacent neighbors. This phenomenon is equivalent to have a non-random topology
with a distribution of interactions and it can be removed by an adequate local
normalization of the couplings.Comment: 6 pages, 8 figures, LaTeX 209, uses RevTe
Multi-plateau magnetization curves of one-dimensional Heisenberg ferrimagnets
Ground-state magnetization curves of ferrimagnetic Heisenberg chains of
alternating spins and are numerically investigated. Calculating several
cases of , we conclude that the spin- chain generally exhibits
magnetization plateaux even at the most symmetric point. In the double- or
more-plateau structure, the initial plateau is generated on a classical basis,
whereas the higher ones are based on a quantum mechanism.Comment: 6 pages, 6 figures embedded, to appear in Phys. Rev. B 01 August 200
Bosonic representation of one-dimensional Heisenberg ferrimagnets
The energy structure and the thermodynamics of ferrimagnetic Heisenberg
chains of alternating spins S and s are described in terms of the Schwinger
bosons and modified spin waves. In the Schwinger representation, we average the
local constraints on the bosons and diagonalize the Hamiltonian at the
Hartree-Fock level. In the Holstein-Primakoff representation, we optimize the
free energy in two different ways introducing an additional constraint on the
staggered magnetization. A new modified spin-wave scheme, which employs a
Lagrange multiplier keeping the native energy structure free from temperature
and thus differs from the original Takahashi Scheme, is particularly stressed
as an excellent language to interpret one-dimensional quantum ferrimagnetism.
Other types of one-dimensional ferrimagnets and the antiferromagnetic limit S=s
are also mentioned.Comment: to be published in Phys. Rev. B 69, No. 6, 0644XX (2004
Theoretical study of lepton events in the atmospheric neutrino experiments at SuperK
Super-Kamiokande has reported the results for the lepton events in the
atmospheric neutrino experiment. These results have been presented for a 22.5kT
water fiducial mass on an exposure of 1489 days, and the events are divided
into sub-GeV, multi-GeV and PC events. We present a study of nuclear medium
effects in the sub-GeV energy region of atmospheric neutrino events for the
quasielastic scattering, incoherent and coherent pion production processes, as
they give the most dominant contribution to the lepton events in this energy
region. We have used the atmospheric neutrino flux given by Honda et al. These
calculations have been done in the local density approximation. We take into
account the effect of Pauli blocking, Fermi motion, Coulomb effect,
renormalization of weak transition strengths in the nuclear medium in the case
of the quasielastic reactions. The inelastic reactions leading to production of
leptons along with pions is calculated in a - dominance model by
taking into account the renormalization of properties in the nuclear
medium and the final state interaction effects of the outgoing pions with the
residual nucleus. We present the results for the lepton events obtained in our
model with and without nuclear medium effects, and compare them with the Monte
Carlo predictions used in the simulation and the experimentally observed events
reported by the Super-Kamiokande collaboration.Comment: 23 pages, 13 figure
High-resolution aerosol concentration data from the Greenland NorthGRIP and NEEM deep ice cores
Records of chemical impurities from ice cores enable us to reconstruct the past deposition of aerosols onto polar ice sheets and alpine glaciers. Through this they allow us to gain insight into changes of the source, transport and deposition processes that ultimately determine the deposition flux at the coring location. However, the low concentrations of the aerosol species in the ice and the resulting high risk of contamination pose a formidable analytical challenge, especially if long, continuous and highly resolved records are needed. Continuous flow analysis, CFA, the continuous melting, decontamination and analysis of ice-core samples has mostly overcome this issue and has quickly become the de facto standard to obtain high-resolution aerosol records from ice cores after its inception at the University of Bern in the mid-1990s.
Here, we present continuous records of calcium (Ca2+), sodium (Na+), ammonium (NH+4), nitrate (NO-3) and electrolytic conductivity at 1 mm depth resolution from the NGRIP (North Greenland Ice Core Project) and NEEM (North Greenland Eemian Ice Drilling) ice cores produced by the Bern Continuous Flow Analysis group in the years 2000 to 2011 (Erhardt et al., 2021). Both of the records were previously used in a number of studies but were never published in full 1 mm resolution. Alongside the 1 mm datasets we provide decadal averages, a detailed description of the methods, relevant references, an assessment of the quality of the data and its usable resolution. Along the way we will also give some historical context on the development of the Bern CFA system.
The data is available in full 1 mm and 10-year-averaged resolution on PANGAEA (https://doi.org/10.1594/PANGAEA.935838, Erhardt et al., 2021