Standard and Non-Standard Solar Models

We summarize the physical input and assumptions commonly adopted in modern standard solar models that also produce good agreement with solar oscillation frequencies. We discuss two motivations for considering non-standard models: the solar neutrino problem and surface lithium abundance problem. We begin to explore the potential for mixed core models to solve the neutrino problem, and compare the structure, neutrino flux, and oscillation frequency predictions for several models in which the inner 25% of the radius is homogenized, taking into account the effects of non-local equilibrium abundances of ³He. The results for the neutrino flux and helioseismic predictions are far from satisfactory, but such models have the potential to reduce the predicted ⁷Be/⁸B neutrino flux ratio, and further studies are warranted. Finally, we discuss how much the neutrino problem can be alleviated in the framework of the standard solar model by using reaction rates, abundances and neutrino capture cross-sections at the limits of their uncertainties, while still satisfying the constraints of helioseismology.     

Ultraviolet irradiation of naphthalene in H2O ice: Implications for meteorites and biogenesis

Abstract— The polycyclic aromatic hydrocarbon (PAH) naphthalene was exposed to ultraviolet radiation in H₂O ice under astrophysical conditions, and the products were analyzed using infrared spectroscopy and high‐performance liquid chromatography. As we found in our earlier studies on the photoprocessing of coronene in H₂O ice, aromatic alcohols and ketones (quinones) were formed. The regiochemistry of the reactions is described and leads to specific predictions of the relative abundances of various oxidized naphthalenes that should exist in meteorites if interstellar ice photochemistry influenced their aromatic inventory. Since oxidized PAHs are present in carbon‐rich meteorites and interplanetary dust particles (IDPs), and ubiquitous in and fundamental to biochemistry, the delivery of such extraterrestrial molecules to the early Earth may have played a role in the origin and evolution of life.     

A Simplified Kinetic Element Formulation for the Rotation of a Perturbed Mass-Asymmetric Rigid Body

Euler's equations, describing the rotation of an arbitrarily torqued mass asymmetric rigid body, are scaled using linear transformations that lead to a simplified set of first order ordinary differential equations without the explicit appearance of the principal moments of inertia. These scaled differential equations provide trivial access to an analytical solution and two constants of integration for the case of torque-free motion. Two additional representations for the third constant of integration are chosen to complete two new kinetic element sets that describe an osculating solution using the variation of parameters. The elements' physical representations are amplitudes and either angular displacement or initial time constant in the torque-free solution. These new kinetic elements lead to a considerably simplified variation of parameters solution to Euler's equations. The resulting variational equations are quite compact. To investigate error propagation behaviour of these new variational formulations in computer simulations, they are compared to the unmodified equations without kinematic coupling but under the influence of simulated gravity-gradient torques.     

Protostellar evolution during time-dependent anisotropic collapse

The formation and collapse of a protostar involves the simultaneous infall and outflow of material in the presence of magnetic fields, self-gravity and rotation. We use self-similar techniques to self-consistently model the anisotropic collapse and outflow by using a set of angle-separated self-similar equations. The outflow is quite strong in our model, with the velocity increasing in proportion to radius, and material formally escaping to infinity in the finite time is required for the central singularity to develop.
Analytically tractable collapse models have been limited mainly to spherically symmetric collapse, with neither magnetic field nor rotation. Other analyses usually employ extensive numerical simulations, or either perturbative or quasistatic techniques. Our model is unique as an exact solution to the non-stationary equations of self-gravitating magnetohydrodynamics (MHD), which features co-existing regions of infall and outflow.
The velocity and magnetic topology of our model is quadrupolar, although dipolar solutions may also exist. We provide a qualitative model for the origin and subsequent evolution of such a state. However, a central singularity forms at late times, and we expect the late-time behaviour to be dominated by the singularity, rather than depend on the details of its initial state. Our solution may, therefore, have the character of an attractor among a much more general class of self-similarity.     

The porosity and permeability of chondritic meteorites and interplanetary dust particles

Abstract— We have investigated the porosity of a large number of chondritic interplanetary dust particles (IDPs) and meteorites by three techniques: standard liquid/gas flow techniques, a new, noninvasive ultrasonic technique, and image processing of backscattered images. The latter technique is obviously best-suited to sub-kilogram sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, nondestructive pressure release technique. We find that chondritic IDPs have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. Type 1–3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1–3 chondrites have the same approximate range as exhibited by the matrix, which indicates that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as the matrix. These results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar, which implies that similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, chondrite type or porosity.     

The influence of seismotectonics on precursory changes in groundwater composition for the 1995 Kobe earthquake, Japan

It is shown that temporal variation in hydrochemistry may be attributed, in part, to continuous seismotectonic activity occurring before the onset of the 1995 “Kobe” earthquake, Japan, challenging the “one earthquake–one signal” hypothesis with respect to potential precursory signals to this devastating event. A possible continuous seismotectonic influence on chloride and sulphate ion-concentration is evaluated with aggregate earthquake-information by transforming a multivariate earthquake time series (including coordinates and magnitude) into a one-dimensional time series (considering geometric relationships between earthquakes and the well-site). A piecewise analysis of ion-concentration and seismotectonic-activity time series compares trends and change points between the two time series: a positive correlation (before the proposed onset of the preparation stage) is followed by a negative correlation (during the proposed preparation stage) which, in turn, is succeeded by a positive correlation (after the heaviest aftershock sequences). This suggests that seismotectonic processes occurring before the Kobe earthquake dynamically influenced aquifer characteristics, leading to temporal variations in the hydrochemical time series. Accordingly, a dynamic change in the mixing ratios of waters with different hydrochemical characteristics is proposed as a mechanism for explaining observed variation. The research can be extended by considering vectors in the stress field that lead to changes in the aquifer-well system.The influence of seismotectonics on precursory changes in groundwater composition for the 1995 Kobe earthquake, Japan.     

Light regulation of benthic sulfate reduction rates mediated by seagrass (Thalassia testudinum) metabolism

The effects of light reduction on community metabolism and sediment sulfate reduction rates (SRR) were assessed experimentally in a shallow (<2.0 m) seagrass (Thalassia testudinum) meadow along Florida's north-central Gulf coast. Nine experimental plots (1.5 m×1.5 m) were shaded differentially to achieve a 0–90% gradient in light reduction within the seagrass meadow. Gross primary production and net community production (NCP), estimated with in situ benthic chamber incubations, decreased with increasing light reduction. The compensation irradiance for community metabolism, i.e., the shading level at which NCP shifted from net autotrophic to net heterotrophic, was determined to be 52.5% of the incoming irradiance at canopy height in the seagrass bed (308.7 μE m⁻² s⁻¹ PAR at noon). Sediment SRR, determined with the use of a³⁵S−SO₄ ²⁻ radiotracer technique, increased quickly (within 5 d) and markedly with increased shade, i.e., simulated light reduction. SRR increased 50-fold when shading exceeded the light compensation point for the seagrass community, rendering the community net heterotrophic. Five days after restoring ambient light conditions, SRR had decreased sharply for all shading treatments. The observed decrease in NCP, coincident with the increase in the SRR with light reduction, suggests that light reduction has an indirect influence on sediment SRR mediated through its effect on seagrass metabolism.     

Inadvertent alkalization of a Florida lake caused by increased ionic and nutrient loading to its watershed

We evaluate the effects of land-use change since c.1890 on Little Lake Jackson in south-central Florida, USA. The lake currently is alkaline despite the prevalence of acidic lakes in the region. Watershed soils are acidic and poorly drained, but are underlain by limestone bedrock. Limnetic pH inferences, based on weighted-averaging tolerance regression of sedimented diatoms, indicate that Little Lake Jackson became significantly alkalized during the 1900s. Two driving forces that appear to be responsible for water-quality change are increased ionic loading and increased nutrient loading. Golf courses and residential lawns in the watershed receive substantial applications of lime, fertilizer, and irrigation with alkaline waters from deep wells, some of which reaches the lake in channelized runoff. Stormwater runoff and septic leachate also contribute to nutrient and solute loading. Sedimentary total P accumulation increased 5-fold and total N accumulation increased 3-fold since c. 1890. δ¹⁵N values suggest agricultural and septic sources for N loading. Sedimented pigments, inferred limnetic chlorophyll a values, and δ¹³C values of organic matter indicate that increased primary productivity occurred. Surface and subsurface inflow is nutrient-rich but low in hardness. Increased cation deposition in sediments indicates that ionic input might have reduced the lake’s natural resistance to alkalization. Lake waters remain low in ionic content, which suggests that the addition of base from carbonate sources is not responsible for all of the observed alkalization. Acid neutralization might have been facilitated by phosphate loading that led to increased base generation through greater nitrate assimilation. Inadvertent alkalization might occur commonly in regions where poorly buffered lakes are subject to significant ionic and nutrient loading from agriculture, turfgrass, and septic sources in their watersheds.     

The rise of forced plumes in a stably stratified crossflow

Solutions are found describing the rise of turbulent buoyant plumes in a neutral or stably stratified crossflow from a source having finite fluxes of buoyancy, momentum and volume. Plumes from such sources are known as forced plumes. The solutions arise from a unified theory having one disposable parameter, the entrainment constant, and they describe a wide range of behaviour of plumes and jets in a crossflow. Solutions for buoyant plumes indicate that, for any given source, heights of rise are reduced with increased crossflow velocity and increased stratification while for constant environmental parameters, heights of rise are increased with increased fluxes of source buoyancy and momentum and are decreased with source radius. Maximum dilutions occur in plumes from small sources with relatively large buoyancy fluxes in light crossflows with small stratification.     

The anomalous tides near Broad Sound

Observations of tidal current and height, in conjunction with theoretical mathematical models are used to investigate the propagation of the tide near Broad Sound, a narrowing estuary situated on a wide section of continental shelf toward the southern end of the Great Barrier Reef. The observations indicate that the dense offshore reefs severely inhibit tidal flow, with the result that tides flood toward Broad Sound from the north and from the south, along the main lagoon. There is a local magnification of the semi-diurnal tides within Broad Sound itself.Models of flow across reefs confirm the effectiveness of dense, shallow, and broad reefs in acting as a barrier to the tide. The diffraction of tides through large gaps in the reef is modelled using conformal mapping techniques and with the inclusion of energy leakage, the diffraction model predicts magnification of the semi-diurnal tidal heights by a factor of about 4 and a phase lag of 3 h on the shelf near Broad Sound, these values being consistent with observation. The observed convergence of the tide close to, and within Broad Sound itself is consistent with the proximity of the semi-diurnal tidal period to the natural period for flow in Broad Sound, considered as a narrowing estuary. This results in further amplification, by an additional factor of about 1.5, so that the tides in Broad Sound are increased by a factor of between 5 and 6, altogether, compared with those elsewhere on the east Australian coast.