2,154 research outputs found
A method for constructing directional surface wave spectra from ICESat-2 altimetry
Sea ice is important for Earth's energy budget as it influences surface albedo and air–sea fluxes in polar regions. On its margins, waves heavily impact sea ice. Routine and repeat observations of waves in sea ice are currently lacking, and therefore a comprehensive understanding of how waves interact with sea ice and are attenuated by it is elusive.
In this paper, we develop methods to separate the two-dimensional (2D) surface wave spectra from sea-ice height observations made by the ICESat-2 (IS2) laser altimeter, a polar-orbiting satellite. A combination of a linear inverse method, called generalized Fourier transform (GFT), to estimate the wave spectra along each beam and a Metropolis–Hastings (MH) algorithm to estimate the dominant wave's incident angle was developed. It allows us to estimate the 2D wave signal and its uncertainty from the high-density, unstructured ATL03 ICESat-2 photon retrievals. The GFT is applied to re-binned photon retrievals on 25 km segments for all six beams and outperforms a discrete Fourier transform (DFT) in accuracy while having fewer constraints on the data structure.
The MH algorithm infers wave direction from beam pairs every 25 km using coherent crests of the most energetic waves. Assuming a dominant incident angle, both methods together allow a decomposition into 2D surface wave spectra with the advantage that the residual surface heights can potentially be attributed to other sea-ice properties. The combined GFT–MH method shows promise in routinely isolating waves propagating through sea ice in ICESat-2 data. We demonstrate its ability on a set of example ICESat-2 tracks, suggesting a detailed comparison against in situ data is necessary to understand the quality of retrieved spectra.</p
Holography and Variable Cosmological Constant
An effective local quantum field theory with UV and IR cutoffs correlated in
accordance with holographic entropy bounds is capable of rendering the
cosmological constant (CC) stable against quantum corrections. By setting an IR
cutoff to length scales relevant to cosmology, one easily obtains the currently
observed rho_Lambda ~ 10^{-47} GeV^4, thus alleviating the CC problem. It is
argued that scaling behavior of the CC in these scenarios implies an
interaction of the CC with matter sector or a time-dependent gravitational
constant, to accommodate the observational data.Comment: 7 pages, final version accepted by PR
Dark Energy and Neutrino Mass Limits from Baryogenesis
In this brief report we consider couplings of the dark energy scalar, such as
Quintessence to the neutrinos and discuss its implications in studies on the
neutrino mass limits from Baryogenesis. During the evolution of the dark energy
scalar, the neutrino masses vary, consequently the bounds on the neutrino
masses we have here differ from those obtained before.Comment: 5 pages,3 figures. Version accepted for publication in Phys. Rev.
How the Charge Can Affect the Formation of Gravastars
In recent work we physically interpreted a special gravastar solution
characterized by a zero Schwarzschild mass. In fact, in that case, none
gravastar was formed and the shell expanded, leaving behind a de Sitter or a
Minkowski spacetime, or collapsed without forming an event horizon, originating
what we called a massive non-gravitational object. This object has two
components of non zero mass but the exterior spacetime is Minkowski or de
Sitter. One of the component is a massive thin shell and the other one is de
Sitter spacetime inside. The total mass of this object is zero Schwarzschild
mass, which characterizes an exterior vacuum spacetime. Here, we extend this
study to the case where we have a charged shell. Now, the exterior is a
Reissner-Nordstr\"om spacetime and, depending on the parameter
of the equation of state of the shell, and the charge, a
gravastar structure can be formed. We have found that the presence of the
charge contributes to the stability of the gravastar, if the charge is greater
than a critical value. Otherwise, a massive non-gravitational object is formed
for small charges.Comment: 17 pages and 7 figures, several typos corrected, accepted for
publication in JCA
Radial stability analysis of the continuous pressure gravastar
Radial stability of the continuous pressure gravastar is studied using the
conventional Chandrasekhar method. The equation of state for the static
gravastar solutions is derived and Einstein equations for small perturbations
around the equilibrium are solved as an eigenvalue problem for radial
pulsations. Within the model there exist a set of parameters leading to a
stable fundamental mode, thus proving radial stability of the continuous
pressure gravastar. It is also shown that the central energy density possesses
an extremum in rho_c(R) curve which represents a splitting point between stable
and unstable gravastar configurations. As such the rho_c(R) curve for the
gravastar mimics the famous M(R) curve for a polytrope. Together with the
former axial stability calculations this work completes the stability problem
of the continuous pressure gravastar.Comment: 17 pages, 5 figures, References corrected, minor changes wrt v1,
matches published versio
Mass-Varying Neutrinos from a Variable Cosmological Constant
We consider, in a completely model-independent way, the transfer of energy
between the components of the dark energy sector consisting of the cosmological
constant (CC) and that of relic neutrinos. We show that such a cosmological
setup may promote neutrinos to mass-varying particles, thus resembling a
recently proposed scenario of Fardon, Nelson, and Weiner (FNW), but now without
introducing any acceleronlike scalar fields. Although a formal similarity of
the FNW scenario with the variable CC one can be easily established, one
nevertheless finds different laws for neutrino mass variation in each scenario.
We show that as long as the neutrino number density dilutes canonically, only a
very slow variation of the neutrino mass is possible. For neutrino masses to
vary significantly (as in the FNW scenario), a considerable deviation from the
canonical dilution of the neutrino number density is also needed. We note that
the present `coincidence' between the dark energy density and the neutrino
energy density can be obtained in our scenario even for static neutrino masses.Comment: 8 pages, minor corrections, two references added, to apear in JCA
How does particulate organic matter (POM) swelling affect soil -water interactions and soil structural stability on different scales?
Particulate organic matter (POM), root mucilage and synthetic polymers are swellable polymeric substances (“hydrogels”) which form a three-dimensional polymer network between soil particles. On the one hand, hydrogels can alter soil hydrological properties via their strong influence on water holding capacity and soil wettability. On the other hand, it has been recently shown that the presence of swollen hydrogel structures between soil particles can significantly contribute to soil structural stability. However, until now, only model polymer hydrogels have been used, and the findings still need to be transferred to soils which contain natural swellable organic substances. In this study, we investigated how the swelling of different POM fractions in soil contributes to soil-water-hydrogel interactions and to soil structural stability on different scales. We assumed that the swelling of easily available inter-aggregate POM (frPOM) and occluded intra-aggregate POM (iPOM) differ in their contribution to soil structural stability. For this purpose, we investigated the structural stability and soil-water interactions of a silty sand soil in a 2x2 nested design comprising tilled and non-tilled as well as compost-fertilized and non-fertilized sub-treatments. POM fractions were isolated by soil density fractionation and subsequently characterized for their swelling and water binding properties. Soil-water interactions in terms of water distribution and water mobility were assessed by one- and two-dimensional 1H-NMR relaxometry and pulsed-field-gradient (PFG) NMR. Results from 1H‑NMR measurements were linked with soil structural stability measurements conducted on the micro- and macroscale using soil rheology, wet sieving and crushing tests. On the micro- and macroscale, soil structural stability was higher for compost-fertilized samples than for non-fertilized with different effects of tillage. This was especially related to the presence of frPOM- and iPOM-associated water which revealed a significantly higher viscosity than mineral pore water. On the microscale, frPOM showed the highest contribution to soil structural stability, whereas iPOM predominantly stabilized the soil structure on the macroscale. The relationships suggest that the spatial location and hence the swellability of organic structures in soil could explain the nature of hydrogel-induced soil structural stability
Dynamical approach to chains of scatterers
Linear chains of quantum scatterers are studied in the process of
lengthening, which is treated and analysed as a discrete dynamical system
defined over the manifold of scattering matrices. Elementary properties of such
dynamics relate the transport through the chain to the spectral properties of
individual scatterers. For a single-scattering channel case some new light is
shed on known transport properties of disordered and noisy chains, whereas
translationally invariant case can be studied analytically in terms of a simple
deterministic dynamical map. The many-channel case was studied numerically by
examining the statistical properties of scatterers that correspond to a certain
type of transport of the chain i.e. ballistic or (partially) localised.Comment: 16 pages, 7 figure
Quantum-classical correspondence on compact phase space
We propose to study the -norm distance between classical and quantum
phase space distributions, where for the latter we choose the Wigner function,
as a global phase space indicator of quantum-classical correspondence. For
example, this quantity should provide a key to understand the correspondence
between quantum and classical Loschmidt echoes. We concentrate on fully chaotic
systems with compact (finite) classical phase space. By means of numerical
simulations and heuristic arguments we find that the quantum-classical fidelity
stays at one up to Ehrenfest-type time scale, which is proportional to the
logarithm of effective Planck constant, and decays exponentially with a maximal
classical Lyapunov exponent, after that time.Comment: 26 pages. 9 figures (31 .epz files), submitted to Nonlinearit
diagnostics on the nature of dark energy
The two dominant components of the cosmic budget today, pressureles matter
and dark energy, may or may not be interacting with each other. Currently, both
possibilities appear compatible with observational data. We propose several
criteria based on the history of the Hubble factor that can help discern
whether they are interacting and whether dark energy is phantom or quintessence
in nature.Comment: 22 pages, 7 figures. Accepted for publication in IJMP
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