2,705 research outputs found
Nonlinear waves in solids with slow dynamics: an internal-variable model
In heterogeneous solids such as rocks and concrete, the speed of sound
diminishes with the strain amplitude of a dynamic loading (softening). This
decrease known as "slow dynamics" occurs at time scales larger than the period
of the forcing. Also, hysteresis is observed in the steady-state response. The
phenomenological model by Vakhnenko et al. is based on a variable that
describes the softening of the material [Phys. Rev. E 70-1, 2004]. However,
this model is 1D and it is not thermodynamically admissible. In the present
article, a 3D model is derived in the framework of the finite strain theory. An
internal variable that describes the softening of the material is introduced,
as well as an expression of the specific internal energy. A mechanical
constitu-tive law is deduced from the Clausius-Duhem inequality. Moreover, a
family of evolution equations for the internal variable is proposed. Here, an
evolution equation with one relaxation time is chosen. By construction, this
new model of continuum is thermodynamically admissible and dissipative
(inelas-tic). In the case of small uniaxial deformations, it is shown
analytically that the model reproduces qualitatively the main features of real
experiments
The development of an advanced system to cool a man in a pressure suit
Conductive cooling system for cooling man in pressurized space sui
Місце та роль технопарку у регіональній інноваційній системі
Розглянуто сутність та складові регіональної інноваційної системи, проблеми формування РІС в регіонах України, роль технопарку в якості головного елементу РІС. Проаналізовано функції технопарку як головного елементу регіональної інноваційної системи та завдання, які вони повинні вирішувати.Determine the essence and components of the regional innovation system, the problem of RIS in the regions of Ukraine, the role of the Technoparks as the principal element of RIS. Analysis functions of park as a key element of regional innovation systems and the tasks that they need to be addressed
Mitochondrial Sirtuins and Their Relationships with Metabolic Disease and Cancer
Significance: Maintenance of metabolic homeostasis is critical for cellular and organismal health. Proper regulation of mitochondrial functions represents a crucial element of overall metabolic homeostasis. Mitochondrial sirtuins (SIRT3, SIRT4, and SIRT5) play pivotal roles in promoting this homeostasis by regulating numerous aspects of mitochondrial metabolism in response to environmental stressors. Recent Advances: New work has illuminated multiple links between mitochondrial sirtuins and cancer. SIRT5 has been shown to regulate the recently described post-translational modifications succinyl-lysine, malonyl-lysine, and glutaryl-lysine. An understanding of these modifications is still in its infancy. Enumeration of SIRT3 and SIRT5 targets via advanced proteomic techniques promises to dramatically enhance insight into functions of these proteins. Critical Issues: In this review, we highlight the roles of mitochondrial sirtuins and their targets in cellular and organismal metabolic homeostasis. Furthermore, we discuss emerging roles for mitochondrial sirtuins in suppressing and/or promoting tumorigenesis, depending on the cellular and molecular context. Future Directions: Currently, hundreds of potential SIRT3 and SIRT5 molecular targets have been identified in proteomic experiments. Future studies will need to validate the major targets of these enzymes, and elucidate how acetylation and/or acylation modulate their functionality. A great deal of interest exists in targeting sirtuins pharmacologically; this endeavor will require development of sirtuin-specific modulators (activators and inhibitors) as potential treatments for cancer and metabolic disease. Antioxid. Redox Signal. 22, 1060?1077.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140306/1/ars.2014.6213.pd
Events, processes, and the time of a killing
The paper proposes a novel solution to the problem of the time of a killing (ToK), which persistently besets theories of act-individuation. The solution proposed claims to expose a crucial wrong-headed assumption in the debate, according to which ToK is essentially a problem of locating some event that corresponds to the killing. The alternative proposal put forward here turns on recognizing a separate category of dynamic occurents, viz. processes. The paper does not aim to mount a comprehensive defense of process ontology, relying instead on extant defenses. The primary aim is rather to put process ontology to work in diagnosing the current state of play over ToK, and indeed in solving it
Homogenization of sound hard metamaterials in the time domain
International audienceWe present a homogenization method based on a matched asymptotic expansion technique for sound hard materials structured at subwavelength scale. Considering the wave equation in the time domain, jump conditions are derived for the acoustic pressure and the normal velocity across an equivalent interface with non zero thickness. These jump conditions are implemented in a numerical scheme and compared to the results of the direct problem
Conserving pattern and process in the Southern Ocean: designing a Marine Protected Area for the Prince Edward Islands
South Africa is currently proclaiming a Marine Protected Area (MPA) in the Exclusive Economic Zone (EEZ) of its sub-Antarctic Prince Edward Islands. The objectives of the MPA are to: 1) contribute to a national and global representative system of MPAs, 2) serve as a scientific reference point to inform future management, 3) contribute to the recovery of the Patagonian toothfish (Dissostichus eleginoides), and 4) reduce the bird bycatch of the toothfish fishery, particularly of albatrosses and petrels. This study employs systematic conservation planning methods to delineate a MPA within the EEZ that will conserve biodiversity patterns and processes within sensible management boundaries, while minimizing conflict with the legal toothfish fishery. After collating all available distributional data on species, benthic habitats and ecosystem processes, we used C-Plan software to delineate a MPA with three management zones: four IUCN Category Ia reserves (13% of EEZ); two Conservation Zones (21% of EEZ); and three Category IV reserves (remainder of EEZ). Compromises between conservation target achievement and the area required by the MPA are apparent in the final reserve design. The proposed MPA boundaries are expected to change over time as new data become available and as impacts of climate change become more evident
Free and smooth boundaries in 2-D finite-difference schemes for transient elastic waves
A method is proposed for accurately describing arbitrary-shaped free
boundaries in single-grid finite-difference schemes for elastodynamics, in a
time-domain velocity-stress framework. The basic idea is as follows: fictitious
values of the solution are built in vacuum, and injected into the numerical
integration scheme near boundaries. The most original feature of this method is
the way in which these fictitious values are calculated. They are based on
boundary conditions and compatibility conditions satisfied by the successive
spatial derivatives of the solution, up to a given order that depends on the
spatial accuracy of the integration scheme adopted. Since the work is mostly
done during the preprocessing step, the extra computational cost is negligible.
Stress-free conditions can be designed at any arbitrary order without any
numerical instability, as numerically checked. Using 10 grid nodes per minimal
S-wavelength with a propagation distance of 50 wavelengths yields highly
accurate results. With 5 grid nodes per minimal S-wavelength, the solution is
less accurate but still acceptable. A subcell resolution of the boundary inside
the Cartesian meshing is obtained, and the spurious diffractions induced by
staircase descriptions of boundaries are avoided. Contrary to what occurs with
the vacuum method, the quality of the numerical solution obtained with this
method is almost independent of the angle between the free boundary and the
Cartesian meshing.Comment: accepted and to be published in Geophys. J. In
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