559 research outputs found
Combining particle acceleration and coronal heating via data-constrained calculations of nanoflares in coronal loops
We model nanoflare heating of extrapolated active-region coronal loops via
the acceleration of electrons and protons in Harris-type current sheets. The
kinetic energy of the accelerated particles is estimated using semi-analytical
and test-particle-tracing approaches. Vector magnetograms and photospheric
Doppler velocity maps of NOAA active region 09114, recorded by the Imaging
Vector Magnetograph (IVM), were used for this analysis. A current-free field
extrapolation of the active-region corona was first constructed. The
corresponding Poynting fluxes at the footpoints of 5000 extrapolated coronal
loops were then calculated. Assuming that reconnecting current sheets develop
along these loops, we utilized previous results to estimate the kinetic-energy
gain of the accelerated particles and we related this energy to nanoflare
heating and macroscopic loop characteristics. Kinetic energies of 0.1 to 8 keV
(for electrons) and 0.3 to 470 keV (for protons) were found to cause heating
rates ranging from to 1 . Hydrodynamic
simulations show that such heating rates can sustain plasma in coronal
conditions inside the loops and generate plasma thermal distributions which are
consistent with active region observations. We concluded the analysis by
computing the form of X-ray spectra generated by the accelerated electrons
using the thick target approach that were found to be in agreement with
observed X-ray spectra, thus supporting the plausibility of our
nanoflare-heating scenario.Comment: 11 figure
CLIPS enhanced with objects, backward chaining and explanation facilities
In this project we extend C Language Production System (CLIPS), an existing Expert System shell, by creating three new options. Specifically, first we create a compatible with CLIPS environment that allows for defining objects and object hierarchies, second we provide means to implement backward chaining in a pure forward chaining environment, and finally we give some simple explanation facilities for the derivations the system has made. Objects and object hierarchies are extended so that facts can be automatically inferred, and placed in the fact base. Backward chaining is implemented by creating run time data structures which hold the derivation process allowing for a depth first search. The backward chaining mechanism works not only with ground facts, but also creates bindings for every query that involves variables, and returns the truth value of such a query as well as the relevant variable bindings. Finally, the WHY and HOW explanation facilities allow for a complete examination of the derivation process, the rules triggered, and the bindings created. The entire system is integrated with the original CLIPS code, and all of its routines can be invoked as CLIPS commands
Interdiffusion in dilute polymer mixtures. A subtle concentration effect
Dynamic light scattering has been used to investigate the diffusional dynamics in very dilute polystyrene/poly(propylene oxide), PS/PPO, polymer blends. Compared to previous investigations in the field, this system is more suitable for this type of investigation due to the significant refractive index difference between the two components and the fact that the matrix (PPO) dynamics do not interfere with the measurements. The tracer diffusion coefficient of PS thus obtained in the limit of infinite dilution scales as Nâ0.8±0.04PS with the PS degree of polymerization, i.e., behavior intermediate between the limits of nondraining Zimm and freeâdraining Rouse behavior. The effect of the addition of a third component even at tracer concentrations on the diffusion dynamics was investigated both experimentally and theoretically in the framework of the dynamic random phase approximation. Similarities and differences between theory and experiment were found that are rather due to a modification of hydrodynamic interactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70731/2/JCPSA6-101-4-3222-1.pd
THESSALONIKI SEISMIC HAZARD ASSESSMENT: PROBABILISTIC AND DETERMINISTIC APPROACH FOR ROCK SITE CONDITIONS
Within the framework of four research projects (RISK-EU, EUROSEISRISK, SRM_LIFE and
LESSLOSS) extensive calculations were carried out assessing the seismic hazard in the Thessaloniki
and surrounding area. The main results were derived from probabilistic and deterministic approaches
taking into account rock site conditions for each examined site in the Metropolitan area of
Thessaloniki. The expected strong-ground motions were calculated applying different methodologies.
Two different groups worked for the assessment of the seismic hazard, the first one constituted of the
INGV (Istituto Nazionale di Geofisica e Vulcanologia, Italy) and LSMF (Laboratory of Soil
Mechanics and Foundation Engineering, Thessaloniki, Greece) and the second one of LSMF and
ITSAK (Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki,
Greece)
Kinetic description of particle interaction with a gravitational wave
The interaction of charged particles, moving in a uniform magnetic field,
with a plane-polarized gravitational wave is considered using the
Fokker-Planck- Kolmogorov (FPK) approach. By using a stochasticity criterion,
we determine the exact locations in phase space, where resonance overlapping
occurs. We investigate the diffusion of orbits around each primary resonance of
order (m) by deriving general analytical expressions for an effective diffusion
coeficient. A solution to the corresponding diffusion equation (Fokker-Planck
equation) for the static case is found. Numerical integration of the full
equations of motion and subsequent calculation of the diffusion coefficient
verifies the analytical results.Comment: LaTeX file, 15 page
New Method for Phase transitions in diblock copolymers: The Lamellar case
A new mean-field type theory is proposed to study order-disorder transitions
(ODT) in block copolymers. The theory applies to both the weak segregation (WS)
and the strong segregation (SS) regimes. A new energy functional is proposed
without appealing to the random phase approximation (RPA). We find new terms
unaccounted for within RPA. We work out in detail transitions to the lamellar
state and compare the method to other existing theories of ODT and numerical
simulations. We find good agreements with recent experimental results and
predict that the intermediate segregation regime may have more than one scaling
behavior.Comment: 23 pages, 8 figure
Modelling the spectral evolution of classical double radio sources
The spectral evolution of powerful double radio galaxies (FR II's) is thought
to be determined by the acceleration of electrons at the termination shock of
the jet, their transport through the bright head region into the lobes and the
production of the radio emission by synchrotron radiation in the lobes. Models
presented to date incorporate some of these processes in prescribing the
electron distribution which enters the lobes. We have extended these models to
include a description of electron acceleration at the relativistic termination
shock and a selection of transport models for the head region. These are
coupled to the evolution of the electron spectrum in the lobes under the
influence of losses due to adiabatic expansion, by inverse Compton scattering
on the cosmic background radiation and by synchrotron radiation. The
evolutionary tracks predicted by this model are compared to observation using
the power/source-size (P-D) diagram. We find that the simplest scenario, in
which accelerated particles suffer adiabatic losses in the head region which
become more severe as the source expands produces P-D-tracks which conflict
with observation, because the power is predicted to decline too steeply with
increasing size. Agreement with observation can be found by assuming that
adiabatic losses are compensated during transport between the termination shock
and the lobe by a re-acceleration process distributed throughout the head
region.Comment: 14 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Diblock copolymers at a homopolymer-homopolymer-interface: a Monte Carlo simulation
The properties of diluted symmetric A-B diblock copolymers at the interface
between A and B homopolymer phases are studied by means of Monte Carlo (MC)
simulations of the bond fluctuation model. We calculate segment density
profiles as well as orientational properties of segments, of A and B blocks,
and of the whole chain. Our data support the picture of oriented ``dumbbells'',
which consist of mildly perturbed A and B Gaussian coils. The results are
compared to a self consistent field theory (SCFT) for single copolymer chains
at a homopolymer interface. We also discuss the number of interaction contacts
between monomers, which provide a measure for the ``active surface'' of
copolymers or homopolymers close to the interface
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