The Dynamics of Periodically Forced Systems

The classical and quantum dynamics of a one-dimensional atomic system perturbed by a periodic electric field of frequency, Ω, in the regimes of high and low field frequency is studied. At high frequencies various ionisation mechanisms are considered in both dynamics. We show that for systems having analytic potentials, and for sufficiently high frequencies, the classical system can ionize through regular orbits, in contradistinction to the driven Coulomb system. An area-preserving map is constructed which approximates the classical motion well at high frequencies; explicit quantization of this map, in terms of the Fourier components of the classical motion, provides a very efficient means of obtaining approximate solutions to the one-dimensional, time-dependent Schrödinger equation. The Morse oscillator is considered in detail: the classical map is found to agree well with the numerical solution of Hamilton’s equations. Classical and quantal ionization probabilities are compared and circumstances delineated where they agree. Comparisons of various theoretical models with experimental data for the ionization of excited hydrogen atoms in low frequency microwave fields arc used to distinguish between tunnelling through and classical escape over the slowly oscillating barrier and between one- and many-state dynamical processes. Formulae used to interpret low frequency laser multi-photon ionization data are found not to describe the experimental data which are best reproduced by the new semiclassical model presented here. Ranges of validity of other models are delineated. A new analytic approximation for the solutions of the two-state equations of motion is obtained and used to predict the positions and widths of each member of the infinite set of resonances between any finite value of Ω and 0. This analysis shows why recent experiments on the microwave ionization of hydrogen atoms by low frequency fields failed to observe any resonances

The impact of mining polymetallic nodules on deep-seabed communities

Polymetallic nodules were first discovered during the 1872-1876 expedition of HMS Challenger expedition at depths of 3800 to 5700 m. The International Seabed Authority has issued exploration licences for the potential extraction of these nodules. There are concerns that long-term environmental damage, including species extinctions, irreversible habitat damage, and unknown consequences for the carbon flux to the deep-sea floor may result from nodule mining. Over 500 deep-sea scientists have signed a statement that transition to the exploitation of mineral resources be paused, until sufficient and robust scientific information has been obtained to make informed decisions as to whether deep-sea mining can be authorized without significant damage to the marine environment and, if so, under what condition

A new nascent spreading centre at the Wagner Basin in the northern Gulf of California: a possible geothermal resource?

The probable geothermal reserves of Mexico sum up to only 1400 MW; however, they have been estimated on the basis of the high temperature systems and do not include the unconventional geothermal sources. Submarine hydrothermal systems may become in the near future a feasible energy source, especially those that occur at shallow depths. Recently discovered hydrothermal activity in the Wagner Basin may be harnessed to produce electricity using an environmentally friendly system

The history of the Journal of the Marine Biological Association of the United Kingdom and the influence of the publication on marine research

The origin and development of the Journal of the Marine Biological Association of the United Kingdom is described on the occasion of the publication of the 100th volume. Papers in the Journal demonstrate how the techniques and approaches to the study of the marine environment have evolved over the 120 years of publication. The early papers provided a baseline description of the marine environment and of marine communities that allowed the effects of later perturbations of the environment to be determined. Both the early papers and the long time series of records have proved to be particularly relevant as marine scientists try to predict the long-term results of climatic and anthropogenic effects on the marine ecosystem. The Journal has now become increasingly international, with most papers coming from outside Europe

Management and Conservation of Hydrothermal Vent Ecosystems Report from the InterRidge Workshop: Management and Conservation of Hydrothermal Vent Ecosystems

This report presents the first formal consideration by the international scientific community of the threat to the isolated hydrothermal vent "oasis" ecosystems from human activities. The aim of the report is to increase awareness among all potential users about the importance, fragility and potential value to society, through sustainable exploitation, of hydrothermal vent ecosystems. It is recognised that human impact on these ecosystems will only increase in the future and that gaining knowledge about them is crucial to sensible management or conservation policies. Because of the current poor understanding of these unique ecosystems, a conservative and precautionary approach is suggested to proposals for future use. The major findings of the report [with page numbers] are listed below. A section proposing measures for conservation and sustainable use begins near the end of the report on page 25

Microarray profiling emphasizes transcriptomic differences between hippocampal in vivo tissue and in vitro cultures" for publication in Brain Communications.

From Crossref journal articles via Jisc Publications RouterHistory: epub 2021-07-07, issued 2021-07-07Article version: AMPublication status: PublishedAbstract Primary hippocampal cell cultures are routinely used as an experimentally accessible model platform for the hippocampus and brain tissue in general. Containing multiple cell types including neurons, astrocytes and microglia in a state that can be readily analysed optically, biochemically and electrophysiologically, such cultures have been used in many in vitro studies. To what extent the in vivo environment is recapitulated in primary cultures in an on-going question. Here we compare the transcriptomic profiles of primary hippocampal cell cultures and intact hippocampal tissue. In addition, by comparing profiles from wild type and the PrP 101LL transgenic model of prion disease, we also demonstrate that gene conservation is predominantly conserved across genetically altered lines

Seeps and vents of the Bering Sea

This special issue focuses on hydrothermal vent and methane seep fauna and communities in the Bering Sea. Although fragmentary information has been previously published on the hydrothermal vents, data on methane seep communities from the Bering Sea are presented here for the first time. Hydrocarbon seeps and hydrothermal vents provide specific habitats that are influenced by seabed emissions of fluids rich in reduced compounds. Communities inhabiting hydrothermal vents and seeps below the photic zone, mostly depend on autochthonous primary organic matter synthesized by symbiotic and free-living microbes through chemoautolithotrophy or methanotrophy. Chemosynthetic communities are highly productive, compared to the surrounding benthic areas. Discovered nearly 40 years ago (Corliss et al., 1979; Paull et al., 1984), and intensively studied since then (Van Dover, 2000; German et al., 2011; Levin et al., 2016 and others), vent and seep communities are still of great research interest. This includes: faunistic and ecological distinctiveness of chemosynthetic communities, adaptations to extreme conditions and understanding the evolution of marine ecosystems. Recent proposals for seabed mineral exploitation also require knowledge on chemosynthetic ecosystems for rational management decisions (Jones et al., 2020; Van Dover et al., 2018)

Superiority of semiclassical over quantum mechanical calculations for a three-dimensional system

In systems with few degrees of freedom modern quantum calculations are, in general, numerically more efficient than semiclassical methods. However, this situation can be reversed with increasing dimension of the problem. For a three-dimensional system, viz. the hyperbolic four-sphere scattering system, we demonstrate the superiority of semiclassical versus quantum calculations. Semiclassical resonances can easily be obtained even in energy regions which are unattainable with the currently available quantum techniques.Comment: 10 pages, 1 figure, submitted to Phys. Lett.

Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)

Submarine groundwater discharge (SGD) from subseafloor aquifers, through muddy sediments, was studied in Eckernförde Bay (western Baltic Sea). The fluid discharge was clearly traced by 222Rn enrichment in the water column and by the chloride profiles in pore water. At several sites, a considerable decrease in chloride, to levels less than 10% of bottom-water concentrations, was observed within the upper few centimeters of sediment. Studies at 196 sites revealed that >22% of the seafloor of the bay area was affected by freshwater admixture and active fluid venting. A maximal discharge rate of .9 L m−2 d−1 was computed by modeling pore water profiles. Based on pore water data, the freshwater flow from subseafloor aquifers to Eckernförde Bay was estimated to range from 4 x 106 to 57 × 106 m3 yr−1. Therefore, 0.3–4.1% of the water volume of the bay is replaced each year. Owing to negligible surface runoff by rivers, SGD is a significant pathway within the hydrological cycle of this coastal zone. High-resolution bathymetric data and side-scan sonar surveys of pockmarks, depressions up to 300 m long, were obtained by using an autonomous underwater vehicle. Steep edges, with depths increasing by more than 2 m within 8–10 m in lateral directions, equivalent to slopes with an angle of as much as 11°, were observed. The formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents. Fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread, but easily overlooked, pathway affecting the cycle of methane and dissolved constituents to coastal waters of the Baltic Sea