47 research outputs found
Defects and glassy dynamics in solid He-4: Perspectives and current status
We review the anomalous behavior of solid He-4 at low temperatures with
particular attention to the role of structural defects present in solid. The
discussion centers around the possible role of two level systems and structural
glassy components for inducing the observed anomalies. We propose that the
origin of glassy behavior is due to the dynamics of defects like dislocations
formed in He-4. Within the developed framework of glassy components in a solid,
we give a summary of the results and predictions for the effects that cover the
mechanical, thermodynamic, viscoelastic, and electro-elastic contributions of
the glassy response of solid He-4. Our proposed glass model for solid He-4 has
several implications: (1) The anomalous properties of He-4 can be accounted for
by allowing defects to freeze out at lowest temperatures. The dynamics of solid
He-4 is governed by glasslike (glassy) relaxation processes and the
distribution of relaxation times varies significantly between different
torsional oscillator, shear modulus, and dielectric function experiments. (2)
Any defect freeze-out will be accompanied by thermodynamic signatures
consistent with entropy contributions from defects. It follows that such
entropy contribution is much smaller than the required superfluid fraction, yet
it is sufficient to account for excess entropy at lowest temperatures. (3) We
predict a Cole-Cole type relation between the real and imaginary part of the
response functions for rotational and planar shear that is occurring due to the
dynamics of defects. Similar results apply for other response functions. (4)
Using the framework of glassy dynamics, we predict low-frequency yet to be
measured electro-elastic features in defect rich He-4 crystals. These
predictions allow one to directly test the ideas and very presence of glassy
contributions in He-4.Comment: 33 pages, 13 figure
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Energetic particle influence on the Earth's atmosphere
This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally
galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere
are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere
Statistical strategies for avoiding false discoveries in metabolomics and related experiments
Modeling, Design, and Testing of a Microchannel Split-System Air Conditioner
A steady-state microchannel split-system simulation model has been developed based on
previous research at the ACRC. This model was utilized as a design tool to optimize a
microchannel split system with the goal of minimizing TEWI, or total equivalent warming
impact. The system components were then selected and the optimized microchannel heat
exchangers were fabricated. Next, the entire system was assembled and extensive tests were run
at steady state conditions over a wide range of outdoor ambient conditions in a calorimeter test
facility. The experimental results have been compared to the simulations for the purpose of
model refinement and its eventual validation. The full system model overpredicts the total
capacity of the system with a minimum error of 0.2%, a mean error of 5%, and a maximum error
of 11 %. The evaporator submodel overpredicts the total capacity as well, with a minimum error
of 0.7%, a mean error of 7%, and a maximum error of 11%. The condenser submodel also
overpredicts with a minimum error of 0.5%, a mean error of 2%, and a maximum error of 6%. A
major reason for the lower accuracy with the evaporator is because of the refrigerant
maldisribution observed in the experiments. The model assumes perfect distribution, hence one
reason for the overprediction of the system's capacity.Air Conditioning and Refrigeration Project 6