The Mean Variance Mixing GARCH (1,1) model

Here we present a general framework for a GARCH (1,1) type of process with innovations with a probability law of the mean- variance mixing type, therefore we call the process in question the mean variance mixing GARCH \ (1,1) or MVM GARCH\(1,1). One implication is a GARCH\ model with skewed innovations and constant mean dynamics. This is achieved without using a location parameter to compensate for time dependence that affects the mean dynamics. From a probabilistic viewpoint the idea is straightforward. We just construct our stochastic process from the desired behavior of the cumulants. Further we provide explicit expressions for the unconditional second to fourth cumulants for the process in question. In the paper we present a specification of the MVM-GARCH process where the mixing variable is of the inverse Gaussian type. On the basis on this assumption we can formulate a maximum likelihood based approach for estimating the process closely related to the approach used to estimate an ordinary GARCH (1,1). Under the distributional assumption that the mixing random process is an inverse Gaussian i.i.d process the MVM-GARCH process is then estimated on log return data from the Standard and Poor 500 index. An analysis for the conditional skewness and kurtosis implied by the process is also presented in the paperGARCH Skewness Conditional Skewness

Approximating the probability distribution of functions of random variables: A new approach

We introduce a new approximation method for the distribution of functions of random variables that are real-valued. The approximation involves moment matching and exploits properties of the class of normal inverse Gaussian distributions. In the paper we we examine the how well the different approximation methods can capture the tail behavior of a function of random variables relative each other. This is obtain done by simulate a number functions of random variables and then investigate the tail behavior for each method. Further we also focus on the regions of unimodality and positive definiteness of the different approximation methods. We show that the new method provides equal or better approximations than Gram-Charlier and Edgeworth expansioApproximation of random variables

Approximating the Probability Distribution of Functions of Random Variables: A New Approach

We introduce a new approximation method for the distribution of functions of random variables that are real-valued. The approximation involves moment matching and exploits properties of the class of normal inverse Gaussian distributions. In the paper we examine the how well the different approximation methods can capture the tail behavior of a function of random variables relative each other. This is done by simulate a number functions of random variables and then investigate the tail behavior for each method. Further we also focus on the regions of unimodality and positive definiteness of the different approximation methods. We show that the new method provides equal or better approximations than Gram-Charlier and Edgeworth expansions. Nous introduisons une nouvelle méthode pour approximer la distribution de variables aléatoires. L'approximation est basée sur la classe de distribution normale inverse gaussienne. On démontre que la nouvelle approximation est meilleure que les expansions Gram-Charlier et Edgeworth.normal inverse Gaussian, Edgeworth expansions, Gram-Charlier, distribution normale inverse gaussienne, expansions d'Edgeworth, Gram-Charlier

Gamma Rays from Heavy Neutralino Dark Matter

We consider the gamma-ray spectrum from neutralino dark matter annihilations and show that internal bremsstrahlung of W pair final states gives a previously neglected source of photons at energies near the mass of the neutralino. For masses larger than about 1 TeV, and for present day detector resolutions, this results in a characteristic signal that may dominate not only over the continuous spectrum from W fragmentation, but also over the \gamma-\gamma and \gamma-Z line signals which are known to give large rates for heavy neutralinos. Observational prospects thus seem promising.Comment: 4 pages, 4 figures; revised to match published versio

System analysis of a diesel engine with VGT and EGR

A system analysis of a diesel engine with VGT and EGR is performed in order to obtain insight into a VGT and EGR control problem where the goal is to control the performance variables oxygen fuel ratio λO and EGR-fraction xegr using the VGT actuator uvgt and the EGR actuator uegr. Step responses over the entire operating region show that the channels uvgt → λO, uegr → λO, and uvgt → xegr have non-minimum phase behaviors and sign reversals. The fundamental physical explanation of these system properties is that the system consists of two dynamic effects that interact: a fast pressure dynamics in the manifolds and a slow turbocharger dynamics. It is shown that the engine frequently operates in operating points where the non-minimum phase behaviors and sign reversals occur for the channels uvgt → λO and uvgt → xegr, and consequently, it is important to consider these properties in a control design. Further, an analysis of zeros for linearized multiple input multiple output models of the engine shows that they are non-minimum phase over the complete operating region. A mapping of the performance variables λO and xegr and the relative gain array show that the system from uegr and uvgt to λO and xegr is strongly coupled in a large operating region. It is also illustrated that the pumping losses pem −pim decrease with increasing EGR-valve and VGT opening for almost the complete operating region. Content

Fundamentals of organic agriculture

Organic agriculture can be traced back to the early 20th century, initiated by the Austrian spiritual philosopher Rudolf Steiner. It was later diversified by a number of key people, and more recent versions are guided by principles issued by the International Federation of Organic Agricultural Movements (IFOAM), founded in 1972. Organic practices were built upon the life philosophies and convictions of the founders regarding how to perceive nature. Today, those original views and ideas are considered as history. However, to understand the principles and opinions of modern organic agriculture, such as the exclusion of water-soluble inorganic fertilisers, we analysed the original ideas and arguments of the founders, who shared the common principle of relying on natural processes and methods, seen as a prerequisite for human health. For example, the British agriculturalist Sir Albert Howard, who together with Lady Eve Balfour founded the British Soil Association, claimed that healthy soils are the basis for human health on earth. In their view, healthy soils could only be obtained if the organic matter content was increased or at least maintained. Later, the German physician and microbiologist Hans-Peter Rusch together with the Swiss biologists Hans and Maria Müller, focused on applying natural principles in agriculture, driven by the conviction that nature is our master and always superior. Even though these early ideas have been abandoned or modified in modern organic agriculture, the principle of the founders regarding exclusion of synthetic compounds (fertilisers and pesticides) is still the main driver for choosing crops and pest control methods

The reliability of a 10-test package for patients with prolonged back and neck pain: could an examiner without formal medical education be used without loss of quality? A methodological study

BACKGROUND: In the rehabilitation of patients with prolonged back and neck pain, the physical impairment should be assessed. Previous research has exclusively engaged medically educated examiners, mostly physiotherapists. However, less biased evaluations of efforts at rehabilitation might be achieved by personnel standing outside the treatment work itself. Therefore, if medically untrained examiners could be used without cost to the quality, this might produce a better evaluation at defensible cost and could also be useful in a research context. The aim of this study was to answer the question: given a 10-test package for patients with prolonged back and neck pain, could an examiner without formal medical education be used without loss of quality? Five of the ten tests required the examiner to keep a firm hold against the foundation of those parts of the participant's body that were not supposed to move during the test. METHODS: Examination by an experienced physiotherapist (A) in performing the package was compared with that by a research assistant (B) without formal medical education. The reliability, including inter- and intra-rater reliability, was assessed. In the inter-rater reliability study, 50 participants (30 patients + 20 healthy subjects) were tested once each by A and B. In the intra-rater reliability study, the 20 healthy subjects were tested twice by A or B. One-way ANOVA intra-class-correlation coefficient (ICC) was calculated and its possible systematic error was determined using a t-test. RESULTS: All five tests that required no manual fixation had acceptable reliability (ICC > .60 and no indication of systematic error). Only one of the five tests that required fixation had acceptable reliability. The difference (five vs. one) was significant (p = .01). CONCLUSION: In a 10-test package for patients with prolonged back and neck pain, an examiner without formal medical education could be used without loss of quality, at least for the five tests requiring no manual fixation. To make our results more generalizable and their implications more searching, a similar study should be conducted with two or more examiners with and without formal medical education, and the intra-rater reliability study should also include patients and involve more participants