1,203 research outputs found
A növénytermesztés szerkezetének optimalizálása a kockázatok figyelembevételével
Az utĂłbbi Ă©vekben egyre Ă©lesebben jelentkeznek a globális Ă©ghajlatváltozás hatásai, Ă©s emiatt – a vitathatatlan genetikai Ă©s technolĂłgiai el?rehaladás ellenĂ©re – megn?tt a termĂ©singadozás a növĂ©nytermesztĂ©sben. Ez az ágazat egyĂ©bkĂ©nt is a legkockázatosabb ágazatok közĂ© tartozik, ezĂ©rt már a tervkĂ©szĂtĂ©s szintjĂ©n, a döntĂ©s-el?kĂ©szĂtĂ©si szakaszban cĂ©lszer? figyelembe venni a kockázatot. A mez?gazdaságban leggyakrabban kockázatprogramozási modelleket alkalmaznak, melyek a döntĂ©shozĂł kockázathoz valĂł hozzáállását is figyelembe veszik, azaz hasznosságmaximalizálĂł modellek. A kockázatprogramozási modellek esetĂ©n el?ször azt kell eldöntenĂĽnk, hogy a kockázatot hogyan jellemezzĂĽk. A kockázat mĂ©rtĂ©kĂ©nek meghatározására – többek között – a szĂłrĂłdási mutatĂłk is alkalmasak. PĂ©nzĂĽgyi portfĂłliĂłk optimalizálásakor a portfĂłliĂł varianciájával adják meg leggyakrabban a kockázatot. A varianciát alkalmazzák a várhatĂł Ă©rtĂ©k – variancia (E-V) modellekben is. A variancia minimalizálásakor egy kvadratikus cĂ©lfĂĽggvĂ©ny? modellt kapunk. A variancia alternatĂvája lineáris programozási modellben az abszolĂşt átlageltĂ©rĂ©s alkalmazása. E cikk cĂ©lja a pĂ©nzĂĽgyi befektetĂ©si gyakorlatban általánosan használt portfoliĂł modell alkalmazási lehet?sĂ©gĂ©nek a bemutatása a növĂ©nytermesztĂ©si szerkezet optimalizálásban Ă©s a kockázat minimalizálásban.</jats:p
Neutron Multiplicity Counting with the Analysis of Continuous Detector Signals
Neutron multiplicity counting is a non-destructive assay method for determining the mass of fissile materials (primarily plutonium) using the measured values of the singles, doubles and triples detection rates. Traditionally, the detection rates are obtained from the counting statistics of neutron detectors. The main problem with this approach is that it is sensitive to the overlapping of pulses which, especially at high count rates, lead to dead time losses in the counting electronics. This feature limits the applicability of the method to the measurement of samples with low emission intensities. To overcome this constraint, an alternative version of neutron multiplicity counting has been developed. The new approach is based on the direct analysis of the continuous voltage signals of the detectors (primarily fission chambers). Since the procedure does not rely on counting individual pulses, it is inherently free from dead time losses caused by their overlapping. As a result, the proposed method provides an alternative to traditional multiplicity counting, especially when measuring high intensity samples, like spent nuclear fuel. The thesis presents the complete process of establishing the new version of multiplicity counting. Based on a stochastic model of continuous detector signals, expressions are derived for some of their one- two and three-point (in time) moments (including their mean, covariance function and bicovariance function) and it is shown that the singles, doubles and triples detection rates can be recovered from them. In a computational study, detector signals are simulated and analysed in order to investigate the effect of certain parameters (the measurement time, the detection efficiency, the amplitude of the electronic noise and the intensity of non-neutron pulses) on the estimated values of the detection rates. To demonstrate the practical use of the proposed method, measurements have been performed using a Cf-252 source and the detection rates recovered from the moments of the recorded signals were compared with reference values obtained with pulse counting
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