8,208 research outputs found
Non-equilibrium dynamics in an interacting nanoparticle system
Non-equilibrium dynamics in an interacting Fe-C nanoparticle sample,
exhibiting a low temperature spin glass like phase, has been studied by low
frequency ac-susceptibility and magnetic relaxation experiments. The
non-equilibrium behavior shows characteristic spin glass features, but some
qualitative differences exist. The nature of these differences is discussed.Comment: 7 pages, 11 figure
Memory and superposition in a spin glass
Non-equilibrium dynamics in a Ag(Mn) spin glass are investigated by
measurements of the temperature dependence of the remanent magnetisation. Using
specific cooling protocols before recording the thermo- or isothermal remanent
magnetisations on re-heating, it is found that the measured curves effectively
disclose non-equilibrium spin glass characteristics such as ageing and memory
phenomena as well as an extended validity of the superposition principle for
the relaxation. The usefulness of this "simple" dc-method is discussed, as well
as its applicability to other disordered magnetic systems.Comment: REVTeX style; 8 pages, 4 figure
Memory and chaos in an Ising spin glass
The non-equilibrium dynamics of the model 3d-Ising spin glass
- FeMnTiO - has been investigated from the temperature
and time dependence of the zero field cooled magnetization recorded under
certain thermal protocols. The results manifest chaos, rejuvenation and memory
features of the equilibrating spin configuration that are very similar to those
observed in corresponding studies of the archetypal RKKY spin glass Ag(Mn). The
sample is rapidly cooled in zero magnetic field, and the magnetization recorded
on re-heating. When a stop at constant temperature is made during the
cooling, the system evolves toward its equilibrium state at this temperature.
The equilibrated state established during the stop becomes frozen in on further
cooling and is retrieved on re-heating. The memory of the aging at is not
affected by a second stop at a lower temperature
. Reciprocally, the first equilibration at has no influence on
the relaxation at , as expected within the droplet model for domain
growth in a chaotic landscape.Comment: REVTeX style; 4 pages, 4 figure
Comprehensive airborne characterization of aerosol from a major bovine source
We report an extensive airborne characterization of aerosol downwind of a massive bovine source in the San Joaquin Valley (California) on two flights during July 2007. The Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter probed chemical composition, particle size distribution, mixing state, sub- and supersaturated water uptake behavior, light scattering properties, and the interrelationship between these parameters and meteorology. Total PM_(1.0) levels and concentrations of organics. nitrate. and ammonium were enhanced in the plume from the source as compared to the background aerosol. Organics dominated the plume aerosol mass (~56-64%), followed either by sulfate or nitrate. and then ammonium. Particulate amines were detected in the plume aerosol by a particle-into-liquid sampler (PILS) and via mass spectral inarkers in the Aerodvne C-ToF-AMS. Amines were found to be a significant atmospheric base even in the presence of arnmonia; particulate amine concentrations are estimated as at least 14-23% of that of ammonium in the plume. Enhanced sub- and supersaturated water uptake and reduced refractive indices were coincident with lower organic mass fractions, higher nitrate mass fractions, and the detection of amines. The likelihood of suppressed droplet growth owing to kinetic limitations from hydrophobic organic material is explored. After removing effects associated with size distribution and mixing state, the normalized activated fraction of cloud condensation nuclei (CCN) increased as a function of the subsaturated hygroscopic growth factor, with the highest activated fractions being consistent with relatively lower organic mass fractions and higher nitrate mass fractions. Subsaturated hygroscopic growth factors for the organic fraction of the aerosol are estimated based on employing the Zdanovskii-Stokes Robinson (ZSR) mixing rule. Representative values for a parameterization treating particle water uptake in both the sub- and supersaturated regimes are reported for incorporation into atmospheric models
Characterisation and airborne deployment of a new counterflow virtual impactor inlet
A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterisation tests and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (∼15 l min^(−1)) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterised the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7–13.1 μm. The mean percentage error between cut size measurements and predictions from aerodynamic drag theory is 1.7%. The CVI was deployed on the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California in July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream of the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter
Long-Time Dynamics of Variable Coefficient mKdV Solitary Waves
We study the Korteweg-de Vries-type equation dt u=-dx(dx^2 u+f(u)-B(t,x)u),
where B is a small and bounded, slowly varying function and f is a
nonlinearity. Many variable coefficient KdV-type equations can be rescaled into
this equation. We study the long time behaviour of solutions with initial
conditions close to a stable, B=0 solitary wave. We prove that for long time
intervals, such solutions have the form of the solitary wave, whose centre and
scale evolve according to a certain dynamical law involving the function
B(t,x), plus an H^1-small fluctuation.Comment: 19 page
Searches for Physics Beyond the Standard Model at Colliders
All experimental measurements of particle physics today are beautifully
described by the Standard Model. However, there are good reasons to believe
that new physics may be just around the corner at the TeV energy scale. This
energy range is currently probed by the Tevatron and HERA accelerators and
selected results of searches for physics beyond the Standard Model are
presented here. No signals for new physics have been found and limits are
placed on the allowed parameter space for a variety of different particles.Comment: Proceedings for 2007 Europhysics Conference on High Energy Physics,
Manchester, July 200
Finite-Size and surface effects in maghemite nanoparticles: Monte Carlo simulations
Finite-size and surface effects in fine particle systems are investigated by
Monte Carlo simulation of a model of a -FeO (maghemite) single
particle. Periodic boundary conditions have been used to simulate the bulk
properties and the results compared with those for a spherical shaped particle
with free boundaries to evidence the role played by the surface on the
anomalous magnetic properties displayed by these systems at low temperatures.
Several outcomes of the model are in qualitative agreement with the
experimental findings. A reduction of the magnetic ordering temperature,
spontaneous magnetization, and coercive field is observed as the particle size
is decreased. Moreover, the hysteresis loops become elongated with high values
of the differential susceptibility, resembling those from frustrated or
disordered systems. These facts are consequence of the formation of a surface
layer with higher degree of magnetic disorder than the core, which, for small
sizes, dominates the magnetization processes of the particle. However, in
contradiction with the assumptions of some authors, our model does not predict
the freezing of the surface layer into a spin-glass-like state. The results
indicate that magnetic disorder at the surface simply facilitates the thermal
demagnetization of the particle at zero field, while the magnetization is
increased at moderate fields, since surface disorder diminishes ferrimagnetic
correlations within the particle. The change in shape of the hysteresis loops
with the particle size demonstrates that the reversal mode is strongly
influenced by the reduced atomic coordination and disorder at the surface.Comment: Twocolumn RevTex format. 19 pages, 15 Figures included. Submitted to
Phys. Rev.
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