652 research outputs found
The population of damselflies (Agriocnemis sp.) during growing phase of paddy at Kawasan Sawah Tengah Padang, Merlimau Melaka / Syaza Izzati Mat Sod
This study was aimed to study relationship between populations of Damselflies (Agriocnemis sp.) in growing phase of paddy by weekly and its relation with the diversity of alternate host plant in paddy farming surrounding area. This study was conducted in paddy field at Kawasan Sawah Tengah Padang, Merlimau, Melaka. The samplings visits were made starting from the 20th July until 11th September 2018 was covered 10 weeks of data collections periods. One sampling method is used which is yellow sticky trap and set up randomly in field. Only one species that was recorded which damselflies (Agriocnemis sp.) order of Odonata. A few of species host plant also recorded comprising Perennial Water Primrose (Ludwigia perennis L. Onagraceae), Jungle rice (Echinochloa colona), Fringe-rush (Fimbristylis dichotoma), Shrubby False Buttonweed (Spermacoce verticillata), Pill-Bearing Spurge (Euphorbia Hirta syn. E. pilulifera), Airport grass (Chloris barbata Sw), Rumput Minyak (Panicum milliforme) and Broadleaved Bristle Grass (Setarid palmifolia). Results indicated that the population of Damselflies (Agriocnemis sp.) by weekly during the growing phase of paddy has no significance since (p>0.05). Meanwhile, there is no significance relationship between the numbers of population damselflies with the diversity of host in paddy farming surrounding area. As a result, farmer should ensure a good balance between the populations of damselflies and insect pest also host plant as unwanted weed during the various phases of paddy development without any appreciable loss in yield. An effective way is crucial to conserve, use and enhance biodiversity for sustainable food security
A Density Independent Formulation of Smoothed Particle Hydrodynamics
The standard formulation of the smoothed particle hydrodynamics (SPH) assumes
that the local density distribution is differentiable. This assumption is used
to derive the spatial derivatives of other quantities. However, this assumption
breaks down at the contact discontinuity. At the contact discontinuity, the
density of the low-density side is overestimated while that of the high-density
side is underestimated. As a result, the pressure of the low (high) density
side is over (under) estimated. Thus, unphysical repulsive force appears at the
contact discontinuity, resulting in the effective surface tension. This tension
suppresses fluid instabilities. In this paper, we present a new formulation of
SPH, which does not require the differentiability of density. Instead of the
mass density, we adopt the internal energy density (pressure), and its
arbitrary function, which are smoothed quantities at the contact discontinuity,
as the volume element used for the kernel integration. We call this new
formulation density independent SPH (DISPH). It handles the contact
discontinuity without numerical problems. The results of standard tests such as
the shock tube, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, point like
explosion, and blob tests are all very favorable to DISPH. We conclude that
DISPH solved most of known difficulties of the standard SPH, without
introducing additional numerical diffusion or breaking the exact force symmetry
or energy conservation. Our new SPH includes the formulation proposed by
Ritchie & Thomas (2001) as a special case. Our formulation can be extended to
handle a non-ideal gas easily.Comment: 24 pages, 21 figures. Movies and high resolution figures are
available at http://v1.jmlab.jp/~saitoh/sph/index.htm
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Survey of numerical methods for compressible fluids
The finite difference methods of Godunov, Hyman, Lax-Wendroff (two-step), MacCormack, Rusanov, the upwind scheme, the hybrid scheme of Harten and Zwas, the antidiffusion method of Boris and Book, and the artificial compression method of Harten are compared with the random choice known as Glimm's method. The methods are used to integrate the one-dimensional equations of gas dynamics for an inviscid fluid. The results are compared and demonstrate that Glimm's method has several advantages. 16 figs., 4 tables
Dusty gas with SPH - II. Implicit timestepping and astrophysical drag regimes
In a companion paper (Laibe & Price 2011b), we have presented an algorithm
for simulating two-fluid gas and dust mixtures in Smoothed Particle
Hydrodynamics (SPH). In this paper, we develop an implicit timestepping method
that preserves the exact conservation of the both linear and angular momentum
in the underlying SPH algorithm, but unlike previous schemes, allows the
iterations to converge to arbitrary accuracy and is suited to the treatment of
non- linear drag regimes. The algorithm presented in Paper I is also extended
to deal with realistic astrophysical drag regimes, including both linear and
non-linear Epstein and Stokes drag. The scheme is benchmarked against the test
suite presented in Paper I, including i) the analytic solutions of the dustybox
problem and ii) solutions of the dustywave, dustyshock, dustysedov and
dustydisc obtained with explicit timestepping. We find that the implicit method
is 1- 10 times faster than the explicit temporal integration when the ratio r
between the the timestep and the drag stopping time is 1 < r < 1000.Comment: Accepted for publication in MNRA
An axis-free overset grid in spherical polar coordinates for simulating 3D self-gravitating flows
A type of overlapping grid in spherical coordinates called the Yin-Yang grid
is successfully implemented into a 3D version of the explicit Eulerian
grid-based code PROMETHEUS including self-gravity. The modified code
successfully passed several standard hydrodynamic tests producing results which
are in very good agreement with analytic solutions. Moreover, the solutions
obtained with the Yin-Yang grid exhibit no peculiar behaviour at the boundary
between the two grid patches. The code has also been successfully used to model
astrophysically relevant situations, namely equilibrium polytropes, a
Taylor-Sedov explosion, and Rayleigh-Taylor instabilities. According to our
results, the usage of the Yin-Yang grid greatly enhances the suitability and
efficiency of 3D explicit Eulerian codes based on spherical polar coordinates
for astrophysical flows.Comment: 15 pages, 17 figures, 2 tables, accepted for publication in A&
Functional properties of roselle (Hibiscus sabdariffa L.) seed and its application as bakery product
Roselle (Hibiscus sabdariffa L.) seed is a valuable food resource as it has an excellent source of dietary fibre. Therefore, this study examined the functional properties of roselle seeds. Replacement of cookie flour with roselle seed powder at levels of 0–30 % was investigated for its effect on functional and nutritional properties of cookies. Among the four formulations cookies, the most preferred by panelists was 20 % roselle seed powder cookie (F3), followed by 10 % roselle seed powder cookie (F2) and 30 % roselle seed powder cookie (F4). The least preferred formulation among all was control cookie (F1). Cookie with 20 % roselle seed powder added showed higher content of total dietary fibre (5.6 g/100 g) as compared with control cookie (0.90 g/100 g). Besides that, cookies incorporated with roselle seed powder exhibited improved antioxidant properties. Thus, roselle seed powder can be used as a dietary fibre source and developed as a functional ingredient in food products
Pion Interferometry for a Granular Source of Quark-Gluon Plasma Droplets
We examine the two-pion interferometry for a granular source of quark-gluon
plasma droplets. The evolution of the droplets is described by relativistic
hydrodynamics with an equation of state suggested by lattice gauge results.
Pions are assumed to be emitted thermally from the droplets at the freeze-out
configuration characterized by a freeze-out temperature . We find that the
HBT radius decreases if the initial size of the droplets decreases.
On the other hand, depends on the droplet spatial distribution and
is relatively independent of the droplet size. It increases with an increase in
the width of the spatial distribution and the collective-expansion velocity of
the droplets. As a result, the value of can lie close to
for a granular quark-gluon plasma source. The granular model of the emitting
source may provide an explanation to the RHIC HBT puzzle and may lead to a new
insight into the dynamics of the quark-gluon plasma phase transition.Comment: 5 pages, 4 figure
Inviscid SPH
In smooth-particle hydrodynamics (SPH), artificial viscosity is necessary for
the correct treatment of shocks, but often generates unwanted dissipation away
from shocks. We present a novel method of controlling the amount of artificial
viscosity, which uses the total time derivative of the velocity divergence as
shock indicator and aims at completely eliminating viscosity away from shocks.
We subject the new scheme to numerous tests and find that the method works at
least as well as any previous technique in the strong-shock regime, but becomes
virtually inviscid away from shocks, while still maintaining particle order. In
particular sound waves or oscillations of gas spheres are hardly damped over
many periods.Comment: 14 pages (15 in arXiv), 15 figures, accepted for publication in MNRA
Kelvin-Helmholtz instabilities in Smoothed Particle Hydrodynamics
In this paper we investigate whether Smoothed Particle Hydrodynamics (SPH),
equipped with artificial conductivity, is able to capture the physics of
density/energy discontinuities in the case of the so-called shearing layers
test, a test for examining Kelvin-Helmholtz (KH) instabilities. We can trace
back each failure of SPH to show KH rolls to two causes: i) shock waves
travelling in the simulation box and ii) particle clumping, or more generally,
particle noise. The probable cause of shock waves is the Local Mixing
Instability (LMI), previously identified in the literature. Particle noise on
the other hand is a problem because it introduces a large error in the SPH
momentum equation.
We also investigate the role of artificial conductivity (AC). Including AC is
necessary for the long-term behavior of the simulation (e.g. to get
KH rolls). In sensitive hydrodynamical simulations great care
is however needed in selecting the AC signal velocity, with the default
formulation leading to too much energy diffusion. We present new signal
velocities that lead to less diffusion.
The effects of the shock waves and of particle disorder become less important
as the time-scale of the physical problem (for the shearing layers problem:
lower density contrast and higher Mach numbers) decreases. At the resolution of
current galaxy formation simulations mixing is probably not important. However,
mixing could become crucial for next-generation simulations.Comment: 16 pages, 23 figures, accepted for publication in MNRA
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