400 research outputs found
On the Low-Frequency Current and Temperature Fluctuations Along the Shelf Break in the South Atlantic Bight
Current and temperature data collected along the shelf edge in the South Atlantic Bight were analyzed using a spectral analysis technique. The power spectra of both alongshore currents and temperatures (upon removal of seasonal trends) in the mid- to lower water column suggest a significant energy peak at 28 days. The spatial characteristics of the fluctuations around this period band were determined using the frequency domain empirical orthogonal function (EOF) analysis applied to the concurrent current and temperature records. Consistent results were obtained from the upstream side of the Charleston Bump. Around the 28-day period, temperature seems to have little correlation with currents, suggesting distinct controlling mechanisms over the two variables. Temperature fluctuations in the mid- to lower water column appear to be advected downstream by the mean current. The first and second current EOF modes each represent a southward propagating signal with a wavelength ca. 5000 km and a northward propagating signal with a wavelength ca. 360 km. This modes account for 64.5% and 18.2% of the total normalized variance, respectively. The first mode is probably related to the interaction between topographically induced wave signals and the Gulf Stream current. The wave characteristics of the second mode fit the dispersion relationship sought by Brooks (1978) for similar bottom topographic profile and mean flow conditions. The nature of the second alongshore current mode is therefore likely to be a barotropic shelf wave.
Although the limitation of the current data in the cross-shore direction prohibited calculating the cross-shore shear of the mean flow, the signs of the transfer of energy between the fluctuations and the mean flow were determined. The results were consistent with earlier findings (e.g., Schmitz and Niiler, 1969; Csanady, 1989; Lee, Yoder and Atkinson, 1991) in that the transfer is a two-way process: the fluctuations draw energy from the mean flow and at times also feed back to the mean flow. It seems, though, there are preferable areas where the transfer is a predominantly one-way process
Gravitational Fluctuations as an Alternative to Inflation II. CMB Angular Power Spectrum
Power spectra always play an important role in the theory of inflation. In
particular, the ability to reproduce the galaxy matter power spectrum and the
CMB temperature angular power spectrum coefficients to high accuracy is often
considered a triumph of inflation. In our previous work, we presented an
alternative explanation for the matter power spectrum based on nonperturbative
quantum field-theoretical methods applied to Einstein's gravity, instead of
inflation models based on scalar fields. In this work, we review the basic
concepts and provide further in-depth investigations. We first update the
analysis with more recent data sets and error analysis, and then extend our
predictions to the CMB angular spectrum coefficients, which we did not consider
previously. Then we investigate further the potential freedoms and
uncertainties associated with the fundamental parameters that are part of this
picture, and show how recent cosmological data provides significant constraints
on these quantities. Overall, we find good general consistency between theory
and data, even potentially favoring the gravitationally-motivated picture at
the largest scales. We summarize our results by outlining how this picture can
be tested in the near future with increasingly accurate astrophysical
measurements.Comment: 43 pages, 8 figures (typos fixed, references added
Gravitational Fluctuations as an Alternative to Inflation
The ability to reproduce the observed matter power spectrum to high
accuracy is often considered as a triumph of inflation. In this work, we
explore an alternative explanation for the power spectrum based on
nonperturbative quantum field-theoretical methods applied to Einstein's
gravity, instead of ones based on inflation models. In particular the power
spectral index, which governs the slope on the graph, can be related to
critical scaling exponents derived from the Wilson renormalization group
analysis. We find that the derived value fits favorably with the Sloan Digital
Sky Survey telescope data. We then make use of the transfer functions, based
only on the Boltzmann equations which describe states out of equilibrium, and
Einstein's General Relativity, to extrapolate the power spectrum to the Cosmic
Microwave Background (CMB) regime. We observe that the results fit rather well
with current data. Our approach contrasts with the conventional explanation
which uses inflation to generate the scale invariant Harrison-Zel'dovich
spectrum on CMB scales, and uses the transfer function to extrapolate it to
galaxy regime. The results we present here only assume quantum field theory and
Einstein's Gravity, and hence provide a competing explanation of the power
spectrum, without relying on the assumptions usually associated with
inflationary models. At the end, we also outline several testable predictions
in this picture that deviate from the conventional picture of inflation, and
which hopefully will become verifiable in the near future with increasingly
accurate measurements.Comment: 33 pages, 6 figures. One figure added following the July 2018 release
of new Planck data. Typos fixed, more references added. Paper now conforms to
the published versio
Dyson's Equations for Quantum Gravity in the Hartree-Fock Approximation
Unlike scalar and gauge field theories in four dimensions, gravity is not
perturbatively renormalizable and as a result perturbation theory is badly
divergent. Often the method of choice for investigating nonperturbative effects
has been the lattice formulation, and in the case of gravity the Regge-Wheeler
lattice path integral lends itself well for that purpose. Nevertheless, lattice
methods ultimately rely on extensive numerical calculations, leaving a desire
for alternate calculations that can be done analytically. In this work we
outline the Hartree-Fock approximation to quantum gravity, along lines which
are analogous to what is done for scalar fields and gauge theories. The
starting point is Dyson's equations, a closed set of integral equations which
relate various physical amplitudes involving graviton propagators, vertex
functions and proper self-energies. Such equations are in general difficult to
solve, and as a result not very useful in practice, but nevertheless provide a
basis for subsequent approximations. This is where the Hartree-Fock
approximation comes in, whereby lowest order diagrams get partially dressed by
the use of fully interacting Green's function and self-energies, which then
lead to a set of self-consistent integral equations. Specifically, for quantum
gravity one finds a nontrivial ultraviolet fixed point in Newton's constant G
for spacetime dimensions greater than two, and nontrivial scaling dimensions
between d=2 and d=4, above which one obtains Gaussian exponents. In addition,
the Hartree-Fock approximation gives an explicit analytic expression for the
renormalization group running of Newton's constant, suggesting gravitational
antiscreening with Newton's G slowly increasing on cosmological scales.Comment: 71 pages, 21 figures. More typos fixed, references adde
Asteroid g-2 experiments: new fifth force and ultralight dark sector tests
We study for the first time the possibility of probing long-range fifth
forces utilizing asteroid astrometric data, via the fifth force-induced orbital
precession. We examine nine Near-Earth Object (NEO) asteroids whose orbital
trajectories are accurately determined via optical and radar astrometry.
Focusing on a Yukawa-type potential mediated by a new gauge field (dark photon)
or a baryon-coupled scalar, we estimate the sensitivity reach for the
fifth-force coupling strength and mediator mass in the mass range . Our estimated sensitivity is comparable to
leading limits from torsion balance experiments, potentially exceeding these in
a specific mass range. The fifth forced-induced precession increases with the
orbital semi-major axis in the small limit, motivating the study of objects
further away from the Sun. We discuss future exciting prospects for extending
our study to more than a million asteroids (including NEOs, main-belt
asteroids, Hildas, and Jupiter Trojans), as well as trans-Neptunian objects and
exoplanets.Comment: 2 figures, 1 table, 5 pages + reference
Two-photon absorption inside β-BBO crystal during UV nonlinear optical conversion
We measured the two-photon absorption (TPA) cross sections inside (beta) -BBO crystal during UV harmonic generation. We found that the 2-photon absorption is dominating the absorption effect inside the BBO crystal during UV harmonic generation. Both 2 UV photons and 1 UV photon + 1 fundamental photon absorption cross sections are significant. Possible explanations are presented, and compared with other nonlinear otpical crystals. Thermal profiles inside the crystal as a result of the strong absorption processes are discussed through a computer program that simulates the heat dissipation process. We conclude that TPA is the significant factor in high power scaling of UV harmonic generation inside nonlinear optical crystals
DNA Methylation Heterogeneity Patterns in Breast Cancer Cell Lines
Heterogeneous DNA methylation patterns are linked to tumor growth. In order to study DNA methylation heterogeneity patterns for breast cancer cell lines, we comparatively study four metrics: variance, I² statistic, entropy, and methylation state. Using the categorical metric methylation state, we select the two most heterogeneous states to identify genes that directly affect tumor suppressor genes and high- or moderate-risk breast cancer genes. Utilizing the Gene Set Enrichment Analysis software and the ConsensusPath Database visualization tool, we generate integrated gene networks to study biological relations of heterogeneous genes. This analysis has allowed us to contribute 19 potential breast cancer biomarker genes to cancer databases by locating “hub genes” – heterogeneous genes of significant biological interactions, selected from numerous cancer modules. We have discovered a considerable relationship between these hub genes and heterogeneously methylated oncogenes. Our results have many implications for further heterogeneity analyses of methylation patterns and early detection of breast cancer susceptibility
Multicrystal harmonic generator compensates for thermally induced phase mismatch
We use computer simulation to illustrate how thermally induced phase mismatch affect deep UV harmonic generation. A multicrystal harmonic generator that compensates for thermally include phase mismatch is then presented. We have tested this multicrystal design with a Nd:YAG lasers 4th harmonic generator based on two pieces of β-BaB_2O_4 crystals, and our results demonstrate that it compensates for the thermally include phase mismatch, effectively increasing the interaction length of nonlinear optical crystals during harmonic generation under high loading
Gravitational Fluctuations as an Alternative to Inflation III. Numerical Results
Power spectra play an important role in the theory of inflation, and their
ability to reproduce current observational data to high accuracy is often
considered a triumph of inflation, largely because of a lack of credible
alternatives. In previous work we introduced an alternative picture for the
cosmological power spectra based on the nonperturbative features of the quantum
version of Einstein's gravity, instead of currently popular inflation models
based on scalar fields. The key ingredients in this new picture are the
appearance of a nontrivial gravitational vacuum condensate (directly related to
the observed cosmological constant), and a calculable renormalization group
running of Newton's G on cosmological scales. Results obtained previously were
largely based on a semi-analytical treatment, and often suffered from the
limitations of various approximations and simplifying assumptions. In this
work, we extend and refine our previous calculations by laying out an updated
and extended analysis, which now utilizes a set of suitably modified
state-of-the-art numerical programs (ISiTGR, MGCAMB and MGCLASS) developed for
observational cosmology. As a result, we are able to remove some of the
approximations employed in our previous studies, leading to a number of novel
and detailed physical predictions. These should help in potentially distinguish
the vacuum condensate picture of quantum gravity from that of other models such
as scalar field inflation. Here, besides the matter power spectrum P(k), we
work out in detail predictions for what are referred to as the TT, TE, EE, BB
angular spectra, as well as their closely related lensing spectra. However, the
current limited precision of observational data today (especially on large
angular scales) does not allow us yet to clearly prove or disprove either set
of ideas.Comment: 44 pages, 10 figure
- …