5,820 research outputs found
Research on a special scarifier mechanism with finite element analysis method
Abstract—A scarifier mechanism with rotary tillage and antirotary grubbing is proposed for inducing the power of tillage in hardens soil. MAT147 material modal is amended by experimental method and soil high-speed cutting finite element modal is build through SPH method, further, the tools parameter of proposed mechanism and soil cutting speed are studied by FEA numerical simulation through orthogonal experiments method. Finally, the result shows that the proposed mechanism with proper structural parameters and work speeds can reduce the requirement of power of tillage and increase the working efficiency of small agricultural machinery
First normal stress difference and crystallization in a dense sheared granular fluid
The first normal stress difference () and the microstructure
in a dense sheared granular fluid of smooth inelastic hard-disks are probed
using event-driven simulations. While the anisotropy in the second moment of
fluctuation velocity, which is a Burnett-order effect, is known to be the
progenitor of normal stress differences in {\it dilute} granular fluids, we
show here that the collisional anisotropies are responsible for the normal
stress behaviour in the {\it dense} limit. As in the elastic hard-sphere
fluids, remains {\it positive} (if the stress is defined in
the {\it compressive} sense) for dilute and moderately dense flows, but becomes
{\it negative} above a critical density, depending on the restitution
coefficient. This sign-reversal of occurs due to the {\it
microstructural} reorganization of the particles, which can be correlated with
a preferred value of the {\it average} collision angle in the direction opposing the shear. We also report on the shear-induced
{\it crystal}-formation, signalling the onset of fluid-solid coexistence in
dense granular fluids. Different approaches to take into account the normal
stress differences are discussed in the framework of the relaxation-type
rheological models.Comment: 21 pages, 13 figure
Note on the energy-momentum tensor for general mixed tensor-spinor fields
This note provides an explicit proof of the equivalence of the Belinfante's
energy-momentum tensor and the metric energy-momentum tensor for general mixed
tensor-spinor fields.Comment: 7 pages, title changed, typos corrected, accepted for publication in
Communications in Theoretical Physic
A quasilocal calculation of tidal heating
We present a method for computing the flux of energy through a closed surface
containing a gravitating system. This method, which is based on the quasilocal
formalism of Brown and York, is illustrated by two applications: a calculation
of (i) the energy flux, via gravitational waves, through a surface near
infinity and (ii) the tidal heating in the local asymptotic frame of a body
interacting with an external tidal field. The second application represents the
first use of the quasilocal formalism to study a non-stationary spacetime and
shows how such methods can be used to study tidal effects in isolated
gravitating systems.Comment: REVTex, 4 pages, 1 typo fixed, standard sign convention adopted for
the Newtonian potential, a couple of lines added to the discussion of gauge
dependent term
Scaling of mean first-passage time as efficiency measure of nodes sending information on scale-free Koch networks
A lot of previous work showed that the sectional mean first-passage time
(SMFPT), i.e., the average of mean first-passage time (MFPT) for random walks
to a given hub node (node with maximum degree) averaged over all starting
points in scale-free small-world networks exhibits a sublinear or linear
dependence on network order (number of nodes), which indicates that hub
nodes are very efficient in receiving information if one looks upon the random
walker as an information messenger. Thus far, the efficiency of a hub node
sending information on scale-free small-world networks has not been addressed
yet. In this paper, we study random walks on the class of Koch networks with
scale-free behavior and small-world effect. We derive some basic properties for
random walks on the Koch network family, based on which we calculate
analytically the partial mean first-passage time (PMFPT) defined as the average
of MFPTs from a hub node to all other nodes, excluding the hub itself. The
obtained closed-form expression displays that in large networks the PMFPT grows
with network order as , which is larger than the linear scaling of
SMFPT to the hub from other nodes. On the other hand, we also address the case
with the information sender distributed uniformly among the Koch networks, and
derive analytically the entire mean first-passage time (EMFPT), namely, the
average of MFPTs between all couples of nodes, the leading scaling of which is
identical to that of PMFPT. From the obtained results, we present that although
hub nodes are more efficient for receiving information than other nodes, they
display a qualitatively similar speed for sending information as non-hub nodes.
Moreover, we show that the location of information sender has little effect on
the transmission efficiency. The present findings are helpful for better
understanding random walks performed on scale-free small-world networks.Comment: Definitive version published in European Physical Journal
Global parameter test ideals
This paper shows the existence of ideals whose localizations and completions at prime ideals are parameter test ideals of the localized and completed rings. We do this for Cohen-Macaulay localizations (resp., completions) of non-local rings, for generalized Cohen-Macaulay rings, and for non-local rings with isolated non Cohen-Macaulay points, each being an isolated non -rational point. The tools used to prove this results are constructive in nature and as a consequence our results yield algorithms for the computation of these global parameter test ideals. Finally, we illustrate the power of our methods by analyzing the HSL numbers of local cohomology modules with support at any prime ideal
Spin diffusion at finite electric and magnetic fields
Spin transport properties at finite electric and magnetic fields are studied
by using the generalized semiclassical Boltzmann equation. It is found that the
spin diffusion equation for non-equilibrium spin density and spin currents
involves a number of length scales that explicitly depend on the electric and
magnetic fields. The set of macroscopic equations can be used to address a
broad range of the spin transport problems in magnetic multilayers as well as
in semiconductor heterostructure. A specific example of spin injection into
semiconductors at arbitrary electric and magnetic fields is illustrated
Integrating Al with NiO nano honeycomb to realize an energetic material on silicon substrate
Nano energetic materials offer improved performance in energy release, ignition, and mechanical properties compared to their bulk or micro counterparts. In this study, the authors propose an approach to synthesize an Al/NiO based nano energetic material which is fully compatible with a microsystem. A two-dimensional NiO nano honeycomb is first realized by thermal oxidation of a Ni thin film deposited onto a silicon substrate by thermal evaporation. Then the NiO nano honeycomb is integrated with an Al that is deposited by thermal evaporation to realize an Al/NiO based nano energetic material. This approach has several advantages over previous investigations, such as lower ignition temperature, enhanced interfacial contact area, reduced impurities and Al oxidation, tailored dimensions, and easier integration into a microsystem to realize functional devices. The synthesized Al/NiO based nano energetic material is characterized by scanning electron microscopy, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry
Knuth-Bendix algorithm and the conjugacy problems in monoids
We present an algorithmic approach to the conjugacy problems in monoids,
using rewriting systems. We extend the classical theory of rewriting developed
by Knuth and Bendix to a rewriting that takes into account the cyclic
conjugates.Comment: This is a new version of the paper 'The conjugacy problems in monoids
and semigroups'. This version will appear in the journal 'Semigroup forum
Active-matrix GaN micro light-emitting diode display with unprecedented brightness
Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 10⁶ cd/m²
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