Lloyd V. Berkner (1905-1967)

Lloyd V. Berkner, a Fellow of the Arctic Institute and one of the outstanding American scientists of modern time, suffered a fatal heart attack in Washington on 4 June 1967 while attending a meeting of the National Academy of Sciences. On 7 June he was buried in Arlington National Cemetery. Dr. Berkner was known widely as the "Father of the International Geophysical Year" and more than anyone else in North America developed the idea and gave early impetus to that worldwide effort that did much to promote and improve scientific co-operation throughout the world. He was born in 1905 in Milwaukee, Wisconsin. At the time of his death his legal residence was in Florida. After graduating in 1927 with a B.S. degree in Electrical Engineering, he really had three careers: one as a research scientist, one as a research administrator, and one as a naval officer. He excelled in all three. Early in his career he supervised the installation of the first radio range system. A little later he became a member of the first Byrd Antarctic Expedition and played an important part in designing and installing the communications system for that expedition. Part of that time he spent in New Zealand and established the relay system for antarctic communications. He made constructive studies of long-range radio propagation, and also designed and constructed the first sweep frequency ionospheric sounder. Berkner was appointed the first Executive Secretary of the Research and Development Board of the newly created Department of Defence, and strongly influenced the coordination of the research and development programs of the three armed services. In 1950, at the request of the Secretary of State, he carried out a study of the relationships of science and foreign policy. In his report, Berkner recommended the establishment of the post of Science Adviser to the Secretary of State, as well as the appointment of science attaches in the principal embassies of the United States. These recommendations now have been put into effect. In 1951 he became head of Associated Universities, Inc., and in that capacity for ten years supervised the operation of the Brookhaven National Observatory for the Atomic Energy Commission. Next he accepted the invitation of a group of southwestern businessmen to organize the Graduate Research Centre of the Southwest, with headquarters in Texas. The purpose was to stimulate graduate education and advanced training in that region. In 1927 Berkner was commissioned an Ensign in the U.S. Naval Reserve and designated a Naval Aviator. From 1941 to February 1946 he served in the active naval service. He worked in electronics in the Bureau of Aeronautics and rose to the rank of Captain in 1945. Early that year he was assigned to the Pacific Fleet and served aboard the U.S.S. Enterprise in the Okinawa campaign. Although he was returned to inactive duty in February 1946, he kept up his Naval Reserve status and in 1955 was promoted to Rear Admiral. Doctor Berkner was awarded many honours during his active and productive career. He held at least eight honorary degrees from universities in the United States and from the universities of Calcutta, Uppsala, and Edinburgh. Among his military and civilian awards were: Commendation Ribbon of the Secretary of the Navy; Legion of Merit; Honorary Officer, Order of the British Empire; Special Congressional Gold Medal; Gold Medal of the City of New York; and Silver Medal of the Aeronautical Institute

Sources of individual variation in plasma testosterone levels

The steroid hormone testosterone (T) plays a central role in the regulation of breeding in males, because many physiological, morphological and behavioural traits related to reproduction are T dependent. Moreover, in many seasonally breeding vertebrates, male plasma T levels typically show a pronounced peak during the breeding season. While such population-level patterns are fairly well worked out, the sources and the implications of the large variability in individual T levels within the seasonal cycle remain surprisingly little understood. Understanding the potential sources of individual variation in T levels is important for behavioural and evolutionary ecologists, for at least two reasons. First, in ‘honest signalling’ theory, T is hypothesized to play a critical role as the assumed factor that enforces honesty of the expression of sexually selected quality indicators. Second, T is often considered a key mediator of central life-history trade-offs, such as investment in survival versus reproduction or in mating versus parental care. Here, we discuss the patterns of within- and between-individual variation in male plasma T levels in free-living populations of birds. We argue that it is unclear whether this variability mainly reflects differences in underlying individual quality (intrinsic factors such as genetic or maternal effects) or in the environment (extrinsic factors including time of day, individual territorial status and past experience). Research in avian behavioural endocrinology has mainly focused on the effects of extrinsic factors, while other sources of variance are often ignored. We suggest that studies that use an integrative approach and investigate the relative importance of all potential sources of variation are essential for the interpretation of data on individual plasma T levels

Many-Electron Systems with Constrained Current

A formulation for transport in an inhomogeneous, interacting electron gas is described. Electronic current is induced by a constraint condition imposed as a vector Lagrange multiplier. Constrained minimization of the total energy functional on the manifold of an arbitrary constant current leads to a many-electron Schroedinger equation with a complex, momentum-dependent potential. Constant current Hartree-Fock and Kohn-Sham approximations are formulated within the method and application to transport for quantum wires is developed. No appeal is made to near equilibrium conditions or other approximations allowing development of a general ab initio electronic transport formulation

A hybrid ARIMA and artificial neural networks model to forecast particulate matter in urban areas: The case of Temuco, Chile

Box-Jenkins Time Series (ARIMA) and the multivariate linear models (MLM) have been important and popular linear tools in air quality forecasting during the past decade for urban areas. On the other hand, artificial neural networks (ANN) recently have been used successfully as a nonlinear tool in several research studies of pollution forecasting. A hybrid model that combines both ARIMA and ANN tools was proposed to improve the unique capabilities of ARIMA and ANN tools in linear and non linear modeling on particulate matter forecasting. To examine the effectiveness of the proposed hybrid model over real particulate matter data, the time series of PM10 and meteorological data observed in ambient air during 2000-2006 at a site in Temuco, Chile, was used In 2005, this city was declared a non-attainment area for PM10, whose pollution is the result of a great economic growth, a fast urban expansion, woodstoves, industrial sources, and a strong diesel vehicles growth. Experimental results with meteorological and PM10 data sets indicated that the hybrid model can be an effective tool to improve the forecasting accuracy obtained by either of the models used separately, and compared with a statistical multivariate linear regression. This is an abstract of a paper presented at the 100th Annual Conference and Exhibition of the Air and Waste Management Association 2007 (Pittsburgh, PA, 6/26-29/2007)

Localization and Causality for a free particle

Theorems (most notably by Hegerfeldt) prove that an initially localized particle whose time evolution is determined by a positive Hamiltonian will violate causality. We argue that this apparent paradox is resolved for a free particle described by either the Dirac equation or the Klein-Gordon equation because such a particle cannot be localized in the sense required by the theorems.Comment: 9 pages,no figures,new section adde

Justification of the coupled-mode approximation for a nonlinear elliptic problem with a periodic potential

Coupled-mode systems are used in physical literature to simplify the nonlinear Maxwell and Gross-Pitaevskii equations with a small periodic potential and to approximate localized solutions called gap solitons by analytical expressions involving hyperbolic functions. We justify the use of the one-dimensional stationary coupled-mode system for a relevant elliptic problem by employing the method of Lyapunov--Schmidt reductions in Fourier space. In particular, existence of periodic/anti-periodic and decaying solutions is proved and the error terms are controlled in suitable norms. The use of multi-dimensional stationary coupled-mode systems is justified for analysis of bifurcations of periodic/anti-periodic solutions in a small multi-dimensional periodic potential.Comment: 18 pages, no figure

A hybrid ARIMA and artificial neural networks model to forecast particulate matter in urban areas: The case of Temuco, Chile

Air quality time series consists of complex linear and non-linear patterns and are difficult to forecast. Box-Jenkins Time Series (ARIMA) and multilinear regression (MLR) models have been applied to air quality forecasting in urban areas, but they have limited accuracy owing to their inability to predict extreme events. Artificial neural networks (ANN) can recognize non-linear patterns that include extremes. A novel hybrid model combining ARIMA and ANN to improve forecast accuracy for an area with limited air quality and meteorological data was applied to Temuco, Chile, where residential wood burning is a major pollution source during cold winters, using surface meteorological and PM10 measurements. Experimental results indicated that the hybrid model can be an effective tool to improve the PM10 forecasting accuracy obtained by either of the models used separately, and compared with a deterministic MLR. The hybrid model was able to capture 100% and 80% of alert and pre-emergency episodes, respectively. This approach demonstrates the potential to be applied to air quality forecasting in other cities and countries

Uniqueness of diffeomorphism invariant states on holonomy-flux algebras

Loop quantum gravity is an approach to quantum gravity that starts from the Hamiltonian formulation in terms of a connection and its canonical conjugate. Quantization proceeds in the spirit of Dirac: First one defines an algebra of basic kinematical observables and represents it through operators on a suitable Hilbert space. In a second step, one implements the constraints. The main result of the paper concerns the representation theory of the kinematical algebra: We show that there is only one cyclic representation invariant under spatial diffeomorphisms. While this result is particularly important for loop quantum gravity, we are rather general: The precise definition of the abstract *-algebra of the basic kinematical observables we give could be used for any theory in which the configuration variable is a connection with a compact structure group. The variables are constructed from the holonomy map and from the fluxes of the momentum conjugate to the connection. The uniqueness result is relevant for any such theory invariant under spatial diffeomorphisms or being a part of a diffeomorphism invariant theory.Comment: 38 pages, one figure. v2: Minor changes, final version, as published in CM

Dynamical aspects of mean field plane rotators and the Kuramoto model

The Kuramoto model has been introduced in order to describe synchronization phenomena observed in groups of cells, individuals, circuits, etc... We look at the Kuramoto model with white noise forces: in mathematical terms it is a set of N oscillators, each driven by an independent Brownian motion with a constant drift, that is each oscillator has its own frequency, which, in general, changes from one oscillator to another (these frequencies are usually taken to be random and they may be viewed as a quenched disorder). The interactions between oscillators are of long range type (mean field). We review some results on the Kuramoto model from a statistical mechanics standpoint: we give in particular necessary and sufficient conditions for reversibility and we point out a formal analogy, in the N to infinity limit, with local mean field models with conservative dynamics (an analogy that is exploited to identify in particular a Lyapunov functional in the reversible set-up). We then focus on the reversible Kuramoto model with sinusoidal interactions in the N to infinity limit and analyze the stability of the non-trivial stationary profiles arising when the interaction parameter K is larger than its critical value K_c. We provide an analysis of the linear operator describing the time evolution in a neighborhood of the synchronized profile: we exhibit a Hilbert space in which this operator has a self-adjoint extension and we establish, as our main result, a spectral gap inequality for every K>K_c.Comment: 18 pages, 1 figur