News from Academy Bay

Recent appointments in Washington office. El Niño volume available. Ira Wiggins dies. Nominations to the Royal Society. Index to Noticias de Galápagos. Dictionaries wanted - used or new. International workshops focus on Galápagos.

Spectral density of first order Piecewise linear systems excited by white noise

The Fokker-Planck (FP) equation is used to develop a general method for finding the spectral density for a class of randomly excited first order systems. This class consists of systems satisfying stochastic differential equations of form ẋ + f(x) = m/Ʃ/j = 1 h_j(x)n_j(t) where f and the h_j are piecewise linear functions (not necessarily continuous), and the n_j are stationary Gaussian white noise. For such systems, it is shown how the Laplace-transformed FP equation can be solved for the transformed transition probability density. By manipulation of the FP equation and its adjoint, a formula is derived for the transformed autocorrelation function in terms of the transformed transition density. From this, the spectral density is readily obtained. The method generalizes that of Caughey and Dienes, J. Appl. Phys., 32.11.

This method is applied to 4 subclasses: (1) m = 1, h₁ = const. (forcing function excitation); (2) m = 1, h₁ = f (parametric excitation); (3) m = 2, h₁ = const., h₂ = f, n₁ and n₂ correlated; (4) the same, uncorrelated. Many special cases, especially in subclass (1), are worked through to obtain explicit formulas for the spectral density, most of which have not been obtained before. Some results are graphed.

Dealing with parametrically excited first order systems leads to two complications. There is some controversy concerning the form of the FP equation involved (see Gray and Caughey, J. Math. Phys., 44.3); and the conditions which apply at irregular points, where the second order coefficient of the FP equation vanishes, are not obvious but require use of the mathematical theory of diffusion processes developed by Feller and others. These points are discussed in the first chapter, relevant results from various sources being summarized and applied. Also discussed is the steady-state density (the limit of the transition density as t → ∞).

Bassenthwaite Lake: a general assessment of environmental and biological features and their susceptibility to change

Bassenthwaite (Lake) is one of the larger Cumbrian lakes, certainly one of the most distinctive, and of considerable conservation and amenity value. Although its shores lack sizeable settlements, its main inflow receives sewage effluent from a major tourist centre (Keswick) and is subject to episodic floods. These influences, the growing development of leisure activities at the lake (e.g. sailing, time-share units), and recent road-construction, have led to past appraisals of ecological impacts and lake management. The lake has not been the subject of intense and long-term ecological study, but much scattered information exists that is relevant to future management decisions. In the present Report, commissioned by North West Water, such information - published and unpublished - is surveyed. Especial attention is given to evidence bearing on susceptibility to change, affecting the lake environment and its biota or species of conservation interest. Extensive use has been made of the results of a recent (1986-7) seasonal survey by the FBA.

A general assessment of environmental and biological features of Windermere and their susceptibility to change

Bassenthwaite (Lake) is one of the larger Cumbrian lakes, certainly one of the most distinctive, and of considerable conservation and amenity value. Although its shores lack sizeable settlements, its main inflow receives sewage effluent from a major tourist centre (Keswick) and is subject to episodic floods. These influences, the growing development of leisure activities at the lake (e.g. sailing, time-share units), and recent road-construction, have led to past appraisals of ecological impacts and lake management. The lake has not been the subject of intense and long-term ecological study, but much scattered information exists that is relevant to future management decisions. In the present Report, commissioned by North West Water, such information - published and unpublished - is surveyed. Especial attention is given to evidence bearing on susceptibility to change, affecting the lake environment and its biota or species of conservation interest. Extensive use has been made of the results of a recent (1986-7) seasonal survey by the FBA.

Comparison of systems of biological indication approved during the course of the joint Anglo-Soviet investigations held under the auspices of the Institute of Hydrobiology of the Academy of Sciences of the Ukrainian SSR

In accordance with the plan for joint Anglo-Soviet scientific and technical collaboration on environmental problems, the comparative evaluation of systems of hydrobiological analysis of the surface water quality started in 1977 at the Regional Laboratory of the Severn-Trent Water Authority in Nottingham were continued in the spring of 1978. The investigations were carried out under the auspices of the Institute of Hydrobiology of the Academy of Sciences of the Ukrainian SSR. Hydrobiological and hydrochemical samples were collected by Soviet and British specialists from the Kiev reservoir and the rivers Dnieper, Sozh, Desna and Snov. The samples were processed on the expedition ships and in the Laboratory for the Hydrobiology of Small Water Bodies of the Institute of Hydrobiology of the Academy of Sciences of the Ukrainian SSR. The possible approved methods to be adopted were evaluated from the samples using the phytoperiphyton, phytoplankton, zooplankton and zoobenthos against a background of hydrochemical characteristics. The study concludes that weather conditions complicated the work on testing the systems of biological indication of water quality and made it inadvisable to use those methods of comparison which were used when similar work was carried out in Nottingham.

News from Academy Bay

Oil Spill in Galápagos. Derrame de Combustible en las Aguas de Galápagos. Beagle V: The Station's New Vessel. Children Conservationists. Niños Conservacionistas. Fruto del Empeño: Nuevo Edificio en San Cristóbal. New Building in Isla San Cristóbal. CDRS Director in Argentina. Van Straelen Gift. Change in Directorship at the CDRS. Cambio del Director en la Estación Científica. International Symposium/Workshop on the Herpetology of the Galápagos Islands: Research & Conservation.

News from Academy Bay

Proclamation of a Great Galapagos Marine Reserve. Recovery of the Marine Iguana Population After the El Niño Catastrophe. The Española Tortoises - a Very Special Case. A Botanical Workshop at the Darwin Station. The Campaign to Save the Hawaiian Petrel. Visitors to the Galapagos National Park. Re-opening of the Cristobal Bonifaz Building. Joint Operational Planning. Meeting of the Permanent Commission for the South Pacific. Galapagos Conservationists Receive WWF Award.

News from Academy Bay

Donacion Japonesa. Japanese Donation. Nuevo Gerente en la ECCD. New Manager for the CDRS. Un "Rose-breasted Grosbeak" en Galapagos. A Rose-breasted Grosbeak in Galapagos.

News from Academy Bay

Donation Made in Memory of Last Grandchild of Ecuador's First President. Deaths of CDF Board Members. Major Gift by Mrs. Louise Van Straelen-Poirier. Itasca to Galápagos. Station Research Vessel.

News from Academy Bay

Change in Directorship at the Charles Darwin Research Station. H.R.H. Prince Henri of Luxembourg Visits Galápagos. 25 More Years : Agreement Renewed Between the Ecuadorian Government and the Charles Darwin Foundation to Operate the Charles Darwin Research Station. A Dawn of Despair : Journey to Alcedo.

News from Academy Bay

Ecología de los Chivos Ferales (Capra hircus) en el Volcán Alcedo. Ecology of Feral Goats (Capra hircus) on Alcedo Volcano. Pepino War, 1992.

On the Dynamics of the Adenylate Energy System: Homeorhesis vs Homeostasis

Biochemical energy is the fundamental element that maintains both the adequate turnover of the biomolecular structures and the functional metabolic viability of unicellular organisms. The levels of ATP, ADP and AMP reflect roughly the energetic status of the cell, and a precise ratio relating them was proposed by Atkinson as the adenylate energy charge (AEC). Under growth-phase conditions, cells maintain the AEC within narrow physiological values, despite extremely large fluctuations in the adenine nucleotides concentration. Intensive experimental studies have shown that these AEC values are preserved in a wide variety of organisms, both eukaryotes and prokaryotes. Here, to understand some of the functional elements involved in the cellular energy status, we present a computational model conformed by some key essential parts of the adenylate energy system. Specifically, we have considered (I) the main synthesis process of ATP from ADP, (II) the main catalyzed phosphotransfer reaction for interconversion of ATP, ADP and AMP, (III) the enzymatic hydrolysis of ATP yielding ADP, and (IV) the enzymatic hydrolysis of ATP providing AMP. This leads to a dynamic metabolic model (with the form of a delayed differential system) in which the enzymatic rate equations and all the physiological kinetic parameters have been explicitly considered and experimentally tested in vitro. Our central hypothesis is that cells are characterized by changing energy dynamics (homeorhesis). The results show that the AEC presents stable transitions between steady states and periodic oscillations and, in agreement with experimental data these oscillations range within the narrow AEC window. Furthermore, the model shows sustained oscillations in the Gibbs free energy and in the total nucleotide pool. The present study provides a step forward towards the understanding of the fundamental principles and quantitative laws governing the adenylate energy system, which is a fundamental element for unveiling the dynamics of cellular life.

News from Academy Bay

One Hundred and Fifty Years Ago. The Great Fire on Isabela. Campaign for a CDF Endowment Fund. The Extraordinary Consequences of the Extraordinary El Niño. Eternal Vigilance.

News from Academy Bay

President Febres Cordero visits the Galapagos. Ordeal by fire and water. Unusual reports on the Galapagos albatross. Protecting the Hawaiian Petrel. Sealion gives birth to twins. CDF officers decorated by the Government of Ecuador. Staff changes. The question of re-introducing Galapagos hawks to certain islands - a clarification. Visits and events at the Charles Darwin Research Station.

News from Academy Bay

The 25th anniversary of the Galapagos National Park. Fire at the Darwin Research Station. The control of introduced mammals. Good news about the Hood tortoises. The endangered land iguanas. Penguins, cormorants and flamingos in 1984. A workshop on national parks. International conservation award to Secretary Ripley. Visits and events at the Charles Darwin Research Station.