12,410 research outputs found
Miniaturisasi Antena Mikrostrip dengan Desain Fraktal untuk Aplikasi Global Positioning System
Paper ini membahas mengenai desain dengan bentuk Fraktal antena mikrostip dengan tujuan untuk mendapatkan ukuran antena yang lebih kecil untuk aplikasi Global Positioning System pada frekuensi 1575 MHz. Pada hasil percobaan didapatkan frekuensi kerja GPS pada 1575 MHz, return loss sebesar -18,56 dB dengan VSWR 1,27
Accelerating Universe as Window for Extra Dimensions
Homogeneous cosmological solutions are obtained in five dimensional space
time assuming equations of state and where p
is the isotropic 3 - pressure and , that for the fifth dimension. Using
different values for the constants k and many known solutions are
rediscovered. Further the current acceleration of the universe has led us to
investigate higher dimensional gravity theory, which is able to explain
acceleration from a theoretical view point without the need of introducing dark
energy by hand. We argue that the terms containing higher dimensional metric
coefficients produce an extra negative pressure that apparently drives an
acceleration of the 3D space, tempting us to suggest that the accelerating
universe seems to act as a window to the existence of extra spatial dimensions.
Interestingly the 5D matter field remains regular while the \emph{effective}
negative pressure is responsible for the inflation. Relaxing the assumptions of
two equations of state we also present a class of solutions which provide early
deceleration followed by a late acceleration in a unified manner. Interesting
to point out that in this case our cosmology apparently mimics the well known
quintessence scenario fuelled by a generalised Chaplygin-type of fluid where a
smooth transition from a dust dominated model to a de Sitter like one takes
place.Comment: 20 pages,3 figure
Thermal Radiation from Nucleons and Mesons
Thermal photon emission rates due to meson-nucleon interactions have been
evaluated. An exhaustive set of reactions involving p(\bar p), n(\bar n), rho,
omega, a_1, pi and eta is seen to provide a sizeable contribution to the
emission rate from hot hadronic matter. Contributions from baryonic resonances
are found to be negligibly small
Excitation of the Earth's Chandler wobble by a turbulent oceanic double-gyre
We develop a layer-averaged, multiple-scale spectral ocean model and show how an oceanic double-gyre can communicate with the Earth's Chandler wobble. The overall transfers of energy and angular momentum from the double-gyre to the Chandler wobble are used to calibrate the turbulence parameters of the layer-averaged model. Our model is tested against a multilayer quasi-geostrophic ocean model in turbulent regime, and base states used in parameter identification are obtained from mesoscale eddy resolving numerical simulations. The Chandler wobble excitation function obtained from the model predicts a small role of North Atlantic ocean region on the wobble dynamics as compared to all oceans, in agreement with the existing observations
A two measure model of dark energy and dark matter
In this work we construct a unified model of dark energy and dark matter.
This is done with the following three elements: a gravitating scalar field, phi
with a non-conventional kinetic term, as in the string theory tachyon; an
arbitrary potential, V(phi); two measures -- a metric measure (sqrt{-g}) and a
non-metric measure (Phi). The model has two interesting features: (i) For
potentials which are unstable and would give rise to tachyonic scalar field,
this model can stabilize the scalar field. (ii) The form of the dark energy and
dark matter that results from this model is fairly insensitive to the exact
form of the scalar field potential.Comment: 8 pages,no figures, revtex, typos corrected to match published
versio
Proposal of a topological M(atrix) theory
Keeping in mind the several models of M(atrix) theory we attempt to
understand the possible structure of the topological M(atrix) theory
``underlying'' these approaches. In particular we are motivated by the issue
about the nature of the structure of the vacuum of the topological M(atrix)
theory and how this could be related to the vacuum of the electroweak theory.
In doing so we are led to a simple topological matrix model. Moreover it is
intuitively expected from the current understanding that the noncommutative
nature of ``spacetime'' and background independence should lead to a
topological Model. The main purpose of this note is to propose a simple
topological Matrix Model which bears relation to F and M theories. Suggestions
on the origin of the chemical potential term appearing in the matrix models are
given.Comment: 14 pages revte
Nonparametric Dark Energy Reconstruction from Supernova Data
Understanding the origin of the accelerated expansion of the Universe poses
one of the greatest challenges in physics today. Lacking a compelling
fundamental theory to test, observational efforts are targeted at a better
characterization of the underlying cause. If a new form of mass-energy, dark
energy, is driving the acceleration, the redshift evolution of the equation of
state parameter w(z) will hold essential clues as to its origin. To best
exploit data from observations it is necessary to develop a robust and accurate
reconstruction approach, with controlled errors, for w(z). We introduce a new,
nonparametric method for solving the associated statistical inverse problem
based on Gaussian Process modeling and Markov chain Monte Carlo sampling.
Applying this method to recent supernova measurements, we reconstruct the
continuous history of w out to redshift z=1.5.Comment: 4 pages, 2 figures, accepted for publication in Physical Review
Letter
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