3,115 research outputs found

    Linear statistical models

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    The metron model: Towards a uniļ¬ed deterministic theory of ļ¬elds and particles

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    A summary is given of the principal concepts of a uniļ¬ed deterministic theory of ļ¬elds and particles that have been developed in more detail in a pre- vious comprehensive four-part paper (Hasselmann, 1996a,b, 1997a,b). The model is based on the Einstein vacuum equations, Ricci tensor RLM = 0, in a higher-dimensional space. A space of at least eight dimensions is re- quired to incorporate all other forces as well as gravity in Einsteinā€™s gen- eral relativistic formalism. It is hypothesized that the equations support soliton-type solutions (ā€metronsā€) that are localized in physical space and are periodic in extra (ā€harmonicā€) space and time. The solitons represent waves propagating in harmonic space that are locally trapped in physical space within a wave guide produced by a distortion of the background met- ric. The metric distortion, in turn, is generated by nonlinear interactions (radiation stresses) of the wave ļ¬eld. (The mutual interaction mechanism has been demonstrated for a simpliļ¬ed Lagrangian in Part 1 of the previous paper). In addition to electromagnetic and gravitational ļ¬elds, the metron solutions carry periodic far ļ¬elds that satisfy de Broglieā€™s dispersion relation. These give rise to wave-like interference phenomena when particles interact with other matter, thereby resolving the wave-particle duality paradox. The metron solutions and all particle interactions on the microphysical scale (with the exception of the kaon system) satisfy strict time-reversal symmetry, an arrow of time arising only at the macrophysical level through the introduc- tion of time-asymmetrical statistical assumptions. Thus Bellā€™s theorem on the non-existence of deterministic (hidden variable) theories, which depends crucially on an arrow-of-time, is not applicable. Similarly, the periodic de Broglie far ļ¬elds of the particles do not lead to unstable radiative damping, the time-asymmetrical outgoing radiation condition being replaced by the time-symmetrical condition of zero net radiation. Assuming suitable polarization properties of the metron solutions, it can be shown that the coupled ļ¬eld equations of the Maxwell-Dirac-Einstein sys- tem as well as the Lagrangian of the Standard Model can be derived to low- est interaction order from the Einstein vacuum equations. Moreover, since Einsteinā€™s vacuum equations contain no physical constants (apart from the introduction of units, namely the velocity of light and a similar scale for the harmonic dimensions, in the deļ¬nition of the ļ¬‚at background metric), all physical properties of the elementary particles (mass, charge, spin) and all universal physical constants (Planckā€™s constant, the gravitational constant, and the coupling constants of the electroweak and strong forces) must fol- low from the properties of the metron solutions. A preliminary inspection of the structure of the solutions suggests that the extremely small ratio of gravitational to electromagnetic forces can be explained as a higher-order nonlinearity of the gravitational forces within the interior metron core. The gauge symmetries of the Standard Model follow from geometrical symme- tries of the metron solutions. Similarly, the parity violation of the weak interactions is attributed to a reļ¬‚exion asymmetry of the metron solutions (in analogy to molecules with left- and right-rotational symmetry), rather than to a property of the basic Lagrangian. The metron model also yields further interaction ļ¬elds not contained in the Standard Model, suggesting that the Standard Model represents only a ļ¬rst-order description of elemen- tary particle interactions. While the Einstein vacuum equations reproduce the basic structure of the ļ¬elds and lowest-order interactions of quantum ļ¬eld theory, the particle content of the metron model has no correspondence in quantum ļ¬eld theory. This leads to an interesting interpretation of atomic spectra in the metron model. The basic atomic eigenmodes of quantum electrodynamics appear in the metron model as the scattered ļ¬elds generated by the interaction of the orbiting electron with the atomic nucleus. For certain orbits, the eigenmodes are in resonance with the orbiting electron. In this case, the eigenmode and orbiting electron represent a stable self-supporting conļ¬guration. For circular orbits, the resonance condition is identical to the integer-action condition of the Bohr orbital model. Thus the metron interpretation of atomic spectra yields an interesting amalgam of quantum electrodynamics and the original Bohr model. However, it remains to be investigated whether higher-order computations of the metron model are able to reproduce atomic spectra to the same high degree of agreement with experiment as QED. On a more fundamental level, the basic questions of the existence, structure, stability and discreteness of the postulated metron solutions still need to be addressed. However, it is encouraging that, already on the present exploratory level, the basic properties of elementary particles and ļ¬elds, including the origins of particle properties and the physical constants, can be explained within a uniļ¬ed classical picture based on a straightforward Kaluza-Klein extension to a higher dimensional space of the simplest vacuum form of Einsteinā€™s gravitational equations

    Intertemporal accounting of climate change - Harmonizing economic efficiency and climate stewardship

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    Continuing a discussion on the intertemporal accounting of climate-change damages initiated by Nordhaus, Heal and Brown in response to the recent demonstration of Hasselmann et al. that standard exponential discounting applied uniformly to all goods and services invariably leads to a `climate catastrophe' in cost-benefit analyses, it is argued that (1) there exists no economically satisfactory alternative to cost-benefit analysis for the determination of optimal climate protection strategies, and (2) it is essential to allow for the different long-term evolution of climate damage costs relative to mitigation costs in determining the optimal cost-benefit solution. A climate catastrophe can be avoided only if it is assumed that climate damage costs increase significantly in the long term relative to mitigation costs. Cost-benefit analysis is regarded here in the generalized sense of optimizing a social welfare function that incorporates all relevant `quality-of-life' factors, including not only consumption and the value of the environment, but also the ethical values of equitable intertemporal and intrasocietal distribution. Thus, economic efficiency and climate stewardship are not regarded as conflicting goals, but as synonyms for a single encompassing economic optimization exercise. The same reasoning applies generally to the problem of sustainable development. To quantify the concept of sustainable development in cost-benefit analyses, the projected time evolution of the future values of natural resources and the environment (judged by the present generation, acting as representative agents of future generations) must be related to the time-evolution of all other relevant quality-of-life factors. Different ethical interpretations of the concept of sustainable development can be readily operationalized by incorporation in a generalized cost-benefit analysis in which the evolution paths of all relevant material and ethical values are explicitly specified

    A similarity relation for the non-linear energy-transfer in a finite-depth gravity-wave spectrum

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    The energy transfer in a finite-depth gravity-wave spectrum is investigated in the approximation of a narrow spectrum. It is shown that for ocean depths larger than approximately one tenth of the wavelength (kh [ges ] 0Ā·7) the finite-depth case can be reduced to Longuet-Higginsā€™ (1976) result for an infinitely deep ocean by a similarity transformation involving changes in scale of the angular spreading function and the transfer rate. For shallower water (kh < 0Ā·7) Longuet-Higginsā€™ expansion technique is no longer applicable without modification, as the nonlinear coupling coefficient develops a discontinuity at the origin of the expansion. In the range kh [ges ] 0Ā·7 both the magnitude and the two-dimensional frequency-directional distribution of the energy transfer are found not to differ significantly (to within variations by a factor of 2) from the case of an infinitely deep ocean. The transformation rules relating the infinite-depth and finite-depth cases may provide a useful guide for constructing parametrizations of the nonlinear transfer for finite-depth wave prediction models

    Effective average action based approach to correlation functions at finite momenta

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    We present a truncation scheme of the effective average action approach of the nonperturbative renormalization group which allows for an accurate description of the critical regime as well as of correlation functions at finite momenta. The truncation is a natural modification of the standard derivative expansion which includes both all local correlations and two-point and four-point irreducible correlations to all orders in the derivatives. We discuss schemes for both the symmetric and the symmetry broken phase of the O(N) model and present results for D=3. All approximations are done directly in the effective average action rather than in the flow equations of irreducible vertices. The approach is numerically relatively easy to implement and yields good results for all N both for the critical exponents as well as for the momentum dependence of the two-point function.Comment: 6 pages, 1 figure, 3 table

    Interplay of topology and geometry in frustrated 2d Heisenberg magnets

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    We investigate two-dimensional frustrated Heisenberg magnets using non-perturbative renormalization group techniques. These magnets allow for point-like topological defects which are believed to unbind and drive either a crossover or a phase transition which separates a low temperature, spin-wave dominated regime from a high temperature regime where defects are abundant. Our approach can account for the crossover qualitatively and both the temperature dependence of the correlation length as well as a broad but well defined peak in the specific heat are reproduced. We find no signatures of a finite temperature transition and an accompanying diverging length scale. Our analysis is consistent with a rapid crossover driven by topological defects.Comment: 12 pages, 8 figures, final version to appear in Physical Review

    Techniques of linear prediction, with application to oceanic and atmospheric fields in the tropical Pacific

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    The problem of constructing optimal linear prediction models by multivariance regression methods is reviewed. It is well known that as the number of predictors in a model is increased, the skill of the prediction grows, but the statistical significance generally decreases. For predictions using a large number of candidate predictors, strategies are therefore needed to determine optimal prediction models which properly balance the competing requirements of skill and significance. The popular methods of coefficient screening or stepwise regression represent a posteriori predictor selection methods and therefore cannot be used to recover statistically significant models by truncation if the complete model, including all predictors, is statistically insignificant. Higher significance can be achieved only by a priori reduction of the predictor set. To determine the maximum number of predictors which may be meaningfully incorporated in a model, a model hierarchy can be used in which a series of best fit prediction models is constructed for a (prior defined) nested sequence of predictor sets, the sequence being terminated when the significance level either falls below a prescribed limit or reaches a maximum value. The method requires a reliable assessment of model significance. This is characterized by a quadratic statistic which is defined independently of the model skill or artificial skill. As an example, the method is applied to the prediction of sea surface temperature anomalies at Christmas Island (representative of sea surface temperatures in the central equatorial Pacific) and variations of the central and east Pacific Hadley circulation (characterized by the second empirical orthogonal function (EOF) of the meridional component of the trade wind anomaly field) using a general multipleā€timeā€lag prediction matrix. The ordering of the predictors is based on an EOF sequence, defined formally as orthogonal variables in the composite space of all (normalized) predictors, irrespective of their different physical dimensions, time lag, and geographic position. The choice of a large set of 20 predictors at 12 time lags yields significant predictability only for forecast periods of 3 to 5 months. However, a prior reduction of the predictor set to 4 predictors at 10 time lags leads to 95% significant predictions with skill values of the order of 0.4 to 0.7 up to 6 or 8 months. For infinitely long time series the construction of optimal prediction models reduces essentially to the problem of linear system identification. However, the model hierarchies normally considered for the simulation of general linear systems differ in structure from the model hierarchies which appear to be most suitable for constructing pure prediction models. Thus the truncation imposed by statistical significance requirements can result in rather different models for the two cases. The relation between optimal prediction models and linear dynamical models is illustrated by the prediction of eastā€west sea level changes in the equatorial Pacific from wind field anomalies. It is shown that the optimal empirical prediction is statistically consistent in this case with both the firstā€order relaxation and damped oscillator models recently proposed by McWilliams and Gent (but with somewhat different model parameters than suggested by the authors). Thus the data do not allow a distinction between the two physical models; the simplest acceptable model is the firstā€order damped response. Finally, the problem of estimating forecast skill is discussed. It is usually stated that the forecast skill is smaller than the true skill, which in turn is smaller than the hindcast skill, by an amount which in both cases is approximately equal to the artificial skill. However, this result applies to the mean skills averaged over the ensemble of all possible hindcast data sets, given the true model. Under the more appropriate side condition of a given hindcast data set and an unknown true model, the estimation of the forecast skill represents a problem of statistical inference and is dependent on the assumed prior probability distribution of true models. The Bayesian hypothesis of a uniform prior distribution yields an average forecast skill equal to the hindcast skill, but other (equally acceptable) assumptions yield lower forecast skills more compatible with the usual hindcastā€averaged expressio

    Development of a satellite SAR image spectra and altimeter wave height data assimilation system for ERS-1

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    The applicability of ERS-1 wind and wave data for wave models was studied using the WAM third generation wave model and SEASAT altimeter, scatterometer and SAR data. A series of global wave hindcasts is made for the surface stress and surface wind fields by assimilation of scatterometer data for the full 96-day SEASAT and also for two wind field analyses for shorter periods by assimilation with the higher resolution ECMWF T63 model and by subjective analysis methods. It is found that wave models respond very sensitively to inconsistencies in wind field analyses and therefore provide a valuable data validation tool. Comparisons between SEASAT SAR image spectra and theoretical SAR spectra derived from the hindcast wave spectra by Monte Carlo simulations yield good overall agreement for 32 cases representing a wide variety of wave conditions. It is concluded that SAR wave imaging is sufficiently well understood to apply SAR image spectra with confidence for wave studies if supported by realistic wave models and theoretical computations of the strongly nonlinear mapping of the wave spectrum into the SAR image spectrum. A closed nonlinear integral expression for this spectral mapping relation is derived which avoids the inherent statistical errors of Monte Carlo computations and may prove to be more efficient numerically
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