Evaluation of the radiographic threshold detection level of subsurface crack-like defects in aluminum welds

Radiographic techniques determining aluminum weld surface and subsurface cracks using aluminum penetrameter

Stochastic models for atomic clocks

For the atomic clocks used in the National Bureau of Standards Time Scales, an adequate model is the superposition of white FM, random walk FM, and linear frequency drift for times longer than about one minute. The model was tested on several clocks using maximum likelihood techniques for parameter estimation and the residuals were acceptably random. Conventional diagnostics indicate that additional model elements contribute no significant improvement to the model even at the expense of the added model complexity

Structural equation modeling of food craving across the menstrual cycle T using behavioral, neuroendocrine, and metabolic factors

Objective: To identify associations between circulating endocannabinoids and craving during the luteal phase of the menstrual cycle. This report is a secondary analysis of a trial registered in clinicaltrials.gov as NCT01407692. Methods: Seventeen premenopausal women were studied during the follicular and luteal phases of their menstrual cycle. Previously we had reported fasting plasma estradiol, progesterone, leptin associations with luteal phase cravings for carbohydrate, fat, sweet-rich foods, and eating behavior. Here, we measured fasting plasma endocannabinoids (ECs) endocannabinoid-like substances (ECLs), and postprandial metabolic responses to a mixed meal challenge. Structural equation modeling was used to evaluate relationships between measured variables and cravings. Results: Oleoylethanolamide (OEA) and postprandial lipids were inversely associated with craving sweet-rich foods, while progesterone was positively associated (RMSEA = 0.041, χ2 p: 0.416 i.e. hypothetical and physiological models not different). OEA, progesterone and disinhibition were positively associated with craving carbohydrates (RMSEA: \u3c 0.001, χ2 p: 0.919). ECs and ECLs combined were stronger predictors of craving than clinical metabolic parameters, ECs only, satiety hormones or gonadocorticoids. Conclusions: Our theoretical model suggests that ECs and ECLs influence craving. Since these metabolites can be modulated via dietary fat intake, they could be potential targets to alter menstrual cycle cravings

Quantum Tunneling Effect in Oscillating Friedmann Cosmology

It is shown that the tunneling effect in quantum cosmology is possible not only at the very beginning or the very end of the evolution, but also at the moment of maximum expansion of the universe. A positive curvature expanding Friedmann universe changes its state of evolution spontaneously and completely, {\it without} any changes in the matter content, avoiding recollapse, and falling into oscillations between the nonzero values of the scale factor. On the other hand, an oscillating nonsingular universe can tunnel spontaneously to a recollapsing regime. The probability of such kind of tunneling is given explicitly. It is inversely related to the amount of nonrelativistic matter (dust), and grows from a certain fixed value to unity if the negative cosmological constant approaches zero.Comment: 18 pages Latex + 2 figures available by fax upon reques

Prediction of Evapotranspiration in a Mediterranean Region Using Basic Meteorological Variables

A critical need for farmers, particularly those in arid and semiarid areas is to have a reliable, accurate and reasonably accessible means of estimating the evapotranspiration rates of their crops to optimize their irrigation requirements. Evapotranspiration is a crucial process because of its influence on the precipitation that is returned to the atmosphere. The calculation of this variable often starts from the estimation of reference evapotranspiration, for which a variety of methods have been developed. However, these methods are very complex either theoretically and/or because of the large amount of parameters on which they are based, which makes the development of a simple and reliable methodology for the prediction of this variable important. This research combined three concepts such as cluster analysis, multiple linear regression (MLR), and Voronoi diagrams to achieve that end. Cluster analysis divided the study area into groups based on its weather characteristics, whose locations were then delimited by drawing the Voronoi regions associated with them. Regression equations were built to predict daily reference evapotranspiration in each cluster using basic climate variables produced in forecasts made by meteorological agencies. Finally, the Voronoi diagrams were used again to regionalize the crop coefficients and calculate evapotranspiration from the values of reference evapotranspiration derived from the regression models. These operations were applied to the Valencian region (Spain), a Mediterranean area which is partly semiarid and for which evapotranspiration is a critical issue. The results demonstrated the usefulness and accuracy of the methodology to predict the water demands of crops and hence enable farmers to plan their irrigation needs.This paper was possible thanks to the research project RHIVU (Ref. BIA2012-32463), financed by the Spanish Ministry of Economy and Competitiveness with funds from the State General Budget (PGE) and the European Regional Development Fund (ERDF). The authors also wish to express their gratitude to the Spanish Ministry of Agriculture, Food and Environment (MAGRAMA) for providing the data necessary to develop this study

Can the Universe Create Itself?

The question of first-cause has troubled philosophers and cosmologists alike. Now that it is apparent that our universe began in a Big Bang explosion, the question of what happened before the Big Bang arises. Inflation seems like a very promising answer, but as Borde and Vilenkin have shown, the inflationary state preceding the Big Bang must have had a beginning also. Ultimately, the difficult question seems to be how to make something out of nothing. This paper explores the idea that this is the wrong question --- that that is not how the Universe got here. Instead, we explore the idea of whether there is anything in the laws of physics that would prevent the Universe from creating itself. Because spacetimes can be curved and multiply connected, general relativity allows for the possibility of closed timelike curves (CTCs). Thus, tracing backwards in time through the original inflationary state we may eventually encounter a region of CTCs giving no first-cause. This region of CTCs, may well be over by now (being bounded toward the future by a Cauchy horizon). We illustrate that such models --- with CTCs --- are not necessarily inconsistent by demonstrating self-consistent vacuums for Misner space and a multiply connected de Sitter space in which the renormalized energy-momentum tensor does not diverge as one approaches the Cauchy horizon and solves Einstein's equations. We show such a Universe can be classically stable and self-consistent if and only if the potentials are retarded, giving a natural explanation of the arrow of time. Some specific scenarios (out of many possible ones) for this type of model are described. For example: an inflationary universe gives rise to baby universes, one of which turns out to be itself. Interestingly, the laws of physics may allow the Universe to be its own mother.Comment: 48 pages, 8 figure

Fomin's conception of quantum cosmogenesis

The main aim of this paper is to extend the early approach to quantum cosmogenesis provided by Fomin. His approach was developed independently to the well-known Tryon description of the creation of the closed universe as a process of quantum fluctuation of vacuum. We apply the Fomin concept to derive the cosmological observables. We argue that Fomin's idea from his 1973 work, in contrast to Tryon's one has impact on the current Universe models and the proposed extension of his theory now can be tested by distant supernovae SNIa. Fomin's idea of the creation of the Universe is based on the intersection of two fundamental theories: general relativity and quantum field theory with the contemporary cosmological models with dark energy. As a result of comparison with contemporary approaches concerning dark energy, we found out that Fomin's idea appears in the context of the present acceleration of the Universe explanation: cosmological models with decaying vacuum. Contemporary it appears in the form of Ricci scalar dark energy connected with the holographic principle. We show also that the Fomin model admits the bounce instead of the initial singularity. We demonstrate that the Fomin model of cosmogenesis can be falsified and using SNIa data the values of model parameters is in agreement with observations.Comment: 12 pages, 4 figures; (v2) 22 pages, references added, figures improved; (v3) rewritten using revtex4; (v4) minor changes; (v5) improved formulas and extended statistical analysi