8,685 research outputs found

### Response of Photon Dosimeters and Survey Instruments to New Operational Quantities Proposed by ICRU RC26

Operational quantities in radiation protection are defined as conservative
estimates of the protection quantities, which are generally not accessible to
measurement. Radiation protection dosimeters and monitors are calibrated in the
operational quantities. An ICRU Report Committee works on a proposal to replace
the operational quantities for external radiation ambient dose equivalent and
personal dose equivalent by quantities which are defined in close relation to
the protection quantities. In this note, the response of dosimeters and survey
instruments for photon radiation to these new operational quantities is
evaluated.Comment: 14 page

### Whole genome sequencing and microsatellite analysis of the Plasmodium falciparum E5 NF54 strain show that the var, rifin and stevor gene families follow Mendelian inheritance

Background:
Plasmodium falciparum exhibits a high degree of inter-isolate genetic diversity in its variant surface antigen (VSA) families: P. falciparum erythrocyte membrane protein 1, repetitive interspersed family (RIFIN) and subtelomeric variable open reading frame (STEVOR). The role of recombination for the generation of this diversity is a subject of ongoing research. Here the genome of E5, a sibling of the 3D7 genome strain is presented. Short and long read whole genome sequencing (WGS) techniques (Ilumina, Pacific Bioscience) and a set of 84 microsatellites (MS) were employed to characterize the 3D7 and non-3D7 parts of the E5 genome. This is the first time that VSA genes in sibling parasites were analysed with long read sequencing technology.
Results:
Of the 5733 E5 genes only 278 genes, mostly var and rifin/stevor genes, had no orthologues in the 3D7 genome. WGS and MS analysis revealed that chromosomal crossovers occurred at a rate of 0â€“3 per chromosome. var, stevor and rifin genes were inherited within the respective non-3D7 or 3D7 chromosomal context. 54 of the 84 MS PCR fragments correctly identified the respective MS as 3D7- or non-3D7 and this correlated with var and rifin/stevor gene inheritance in the adjacent chromosomal regions. E5 had 61 var and 189 rifin/stevor genes. One large non-chromosomal recombination event resulted in a new var gene on chromosome 14. The remainder of the E5 3D7-type subtelomeric and central regions were identical to 3D7.
Conclusions:
The data show that the rifin/stevor and var gene families represent the most diverse compartments of the P. falciparum genome but that the majority of var genes are inherited without alterations within their respective parental chromosomal context. Furthermore, MS genotyping with 54 MS can successfully distinguish between two sibling progeny of a natural P. falciparum cross and thus can be used to investigate identity by descent in field isolates

### Producer income instability and farmers' risk response: The case of major Kenyan export crops

The instability of export earnings in LDCs and its presumably harmful economic effects have been broadly discussed in the economic literature and among policy makers in international meetings. In analyzing these effects, the destabilization of producer incomes and farmers' risk response play a prominent role. Producer incomes may be destabilized by either domestic factors on the supply side (yield instability due to weather, crop diseases, etc.), or by fluctuating producer prices reflecting the instability of international primary commodity markets. If unstable producer incomes induce risk aversion among farmers, the sectoral factor input will be reduced and will be suboptimal from a welfare point of view, thus possibly hampering economic growth. The purpose of this paper is to quantify the effects of producer income instability on farmers' planting and long-run supply decisions in the coffee, tea, and sisal production of the Kenyan large farm sector. Coffee, tea, and sisal are the leading Kenyan export crops, the domestic consumption of which is negligible. About half of the Kenyan coffee and tea, and all the sisal are grown in the large farm sector, and nearly always on plantations. Coffee, tea, and sisal are permanent crops the planting of which requires long-run decisions. It is the long-run we shall focus on in this paper; hence the influence of income instability on short-term production planning will be neglected. The analysis will be based on a time series approach covering the period 1951-1975. In the following section we shall develop the methodological framework of how to measure the risk response of farmers. Next the estimation equations will be specified, and the estimation techniques will be demonstrated. Subsequently, the regression results are presented and interpreted. Some tentative conclusions are drawn in the final section.

### Spatio-Temporal Stability Analysis in Two-Phase Mixing Layers: Effect of a Velocity Deficit near the Interface

Die vorliegende Arbeit befasst sich mit dem Wachstum wellenfĂ¶rmiger
StĂ¶rungen an der Fluidgrenze in Zwei-Phasen-Mischungsschichten. Dieses
PhĂ¤nomen tritt z.B. beim primĂ¤ren ZerstĂ¤ubungsprozess von FlĂĽssigkeiten
durch ein angrenzendes oder die FlĂĽssigkeit umschlieĂźendes Gas auf. Im
Rahmen der linearen StabilitĂ¤tstheorie wird sowohl der Einfluss der
verschiedenen StoffgrĂ¶Ăźen als auch jener der Beschaffenheit der
GrundstrĂ¶mung betrachtet. Die gegebene GrundstrĂ¶mung, auf der sich die
StĂ¶rungen ausbreiten, ist dabei durch ein ebenes Geschwindigkeitsfeld mit
parallelen Stromlinien gegeben. Ferner wird die charakteristische Struktur
des Geschwindigkeitsfeldes am DĂĽsenausgang berĂĽcksichtigt: ZunĂ¤chst werden
im Inneren der DĂĽse FlĂĽssigkeit und Gas getrennt voneinander auf
unterschiedliche Geschwindigkeiten beschleunigt. Infolge der trennenden
Wand im Inneren der DĂĽse kommt es zur Bildung von
Geschwindigkeitsgrenzschichten in beiden Medien an der festen Wand. Nach
anschlieĂźendem Kontakt beider StrĂ¶me bildet sich somit ein
Geschwindigkeitsfeld mit NachlaufstrĂ¶mung in der Umgebung der GrenzflĂ¤che
heraus. FĂĽr anwachsende wellenfĂ¶rmige StĂ¶rungen in unmittelbarer NĂ¤he der
GrenzflĂ¤che zwischen beiden Fluiden werden die WellenlĂ¤ngen und
Wachstumsraten untersucht, wobei sowohl die zeitliche als auch die
rĂ¤umliche Ausbreitung der StĂ¶rungen von Interesse ist. Die AbhĂ¤ngigkeit der
GrĂ¶Ăźen von den Stoffparametern, Fluidgeschwindigkeiten, sowie dem
Geschwindigkeitsdefekt relativ zu den mittleren Geschwindigkeiten der
flĂĽssigen und gasfĂ¶rmigen Phase werden dokumentiert. Dabei wird die
OberflĂ¤chenspannung berĂĽcksichtigt, jedoch EinflĂĽsse des Schwerefeldes
vernachlĂ¤ssigt.Motivated by the atomization of liquids by fast gas streams, the present
work is focussed on the growth of wavy perturbations on the liquid-gas
interface in two-phase mixing layers. In the framework of linear stability
theory it is analyzed how the parallel basic flow is affected by various
fluid properties, flow parameters, and also the velocity field itself. The
planar basic velocity distribution is modeled by taking into account the
particular flow structure near the tip of the splitter plate: separated
streams form boundary layers on the splitter plate, where the liquid and
gas have zero velocity, causing a wake-like distribution once the streams
come into contact. In terms of both temporal and spatial modes the main
interest is in the wavelengths and growth rates of the growing interfacial
waves that appear near the nozzle or splitter plate. Surface tension is
taken into account, but gravity effects are neglected

### Empirical Business Valuation and Asset Pricing: An Analysis from an Economic Perspective

Common basis of all empirical accounting-based asset pricing models is their attempt to explain todayâ€™s asset prices or returns with accounting characteristics that are observable today. Technically, empirical accounting-based asset pricing is implemented in the literature with a wide variety of statistical methods: regression approaches, method of multiples, and error measures, a fact that results in several problems.
First problem
Given that regression approaches, method of multiples, and error measures deal with empirical asset pricing, the multitude of conceptually different and non-connected approaches is puzzling and gives rise to two questions:
(i) If regression approaches, method of multiples, and error measures are applied empirically, they might lead to vastly different valuation results. Therefore, wouldnâ€™t it be useful to elaborate conceptual similarities and differences between these statistical methods and even find a superordinate category?
(ii) With respect to regression approaches, the existing literature uses just a small subset of possible statistical methods for empirical asset pricing, i.e., ordinary least squares, weighted least squares, or quantile regressions. Wouldnâ€™t it be rational to enlarge this subset of regression approaches by using other functions of the residuals, e.g., higher (and not first or second) order of absolute values of residuals or the maximum error?
With respect to the method of multiples, wouldnâ€™t it be useful to possess a pricing formula that can integrate different methods of computing means as well as using several accounting figures?
With respect to error measures, wouldnâ€™t it be reasonable to have a pricing framework (= objective function) that is consistent with the error measure (= quality assessment).
Given these questions, the first objective of this thesis in Chapter II is to analyze which of the existing empirical asset pricing approaches are conceptually similar, i.e., can be summarized to a superordinate category and present statistical methods that can be considered as quasi-natural extensions to existing empirical asset pricing models.
Second problem
Based on this overview over empirical asset pricing models and the literature, it can be strongly assumed that the chosen factors (numbers and specific selection of explanatory variables) as well as the specific statistical method used (e.g., ordinary least squares regression, quantile regression) have an important influence on the explanatory power of an empirical analysis. Since the only concern of the majority of existing papers is the previously mentioned explanatory power, they can be regarded as dealing with statistical significance of factors/specific statistical methods, whereas the economic relevance is far less analyzed.
Since price differences are the decisive aspect of valuation models in practice and not statistical significance, analyzing their economic significance is essential and inevitable. Nobody will pay a higher price for a company just because a specific valuation method produces a high out-of-sample RÂ˛. Moreover, business decisions should not be based only on whether a p-value passes a specific threshold because statistical significance (p-value) cannot measure the size of an effect or the importance of a result.
Therefore, it is the second objective of this thesis in Chapter III to analyze the economic significance of different factors/specific statistical methods.
Third problem
If, however, different factors/specific statistical methods lead to economically significant differences in value, a model-selection criterion is needed that is based on economic instead of statistical criteria. While arbitrage theory provides a general guideline for economic model evaluation for theoretical asset pricing models (i.e., prices must be a linear function of their future cash flows), empirical asset pricing models do not rely on present values of cash flows, but on assumed relations between accounting characteristics/factor returns and company prices/returns. For that reason, no theoretical guidelines regarding the components of the model exist. In particular, there are neither hints regarding the number and type of explanatory variables nor the specific statistical approach.
Given this high need for an economic model evaluation criterion, the third objective of this thesis in Chapter IV is to develop an economic model evaluation criterion and come up with an economic ranking of different empirical models.
Fourth problem
From the perspective of asset pricing theory such a model evaluation criterion is superfluous because the correct business valuation model is clear: the present value of future cash flows. Practically, forecasts of the future are difficult and, in particular, the determination of discount factors proves problematic. Therefore, it might be better to use a theoretically less convincing but easier applicable modelâ€”e.g., use of accounting characteristicsâ€”instead of a theoretically superior but inadequately implementable modelâ€”present value. However, the superior practicability of existing accounting-based valuations comes at a high cost: a relatively weak foundation in asset pricing theory:
(i) Multiples
Multiples essentially argue that similar accounting characteristics should result in similar prices.
Problems from the perspective of asset pricing theory: While such a valuation statement is intuitive, it is not backed up by asset pricing/arbitrage theory that states: Identical cash flow streams must possess identical prices. In other words, there are three differences between multiples and arbitrage theory. First, accounting characteristics are considered instead of cash flow streams. Second, similar instead of identical positions are examined. Third, one accounting characteristic is regarded as enough to characterize a company completely.
(ii) Implementing discounted cash flow models with the help of accounting characteristics
In literature, there are discounted cash flow models that use (functions of) accounting figures in order to express cash flows, the horizon value and/or the discount rate.
Problems from the perspective of asset pricing theory: Irrespective of the specific inclusion of the accounting characteristics in the discounted cash flow models, they can only serve as an approximation, i.e., the models contain assumptions that do not generally hold in reality.
(iii) Empirical accounting-based approaches
Empirical accounting-based approaches explain stock prices with the help of accounting characteristics.
Problems from the perspective of asset pricing theory: These empirical accounting-based approaches belong to the field of value relevance studies and, thus, are only interested in statistical significance of accounting characteristics, but not economic significance, i.e., they do not derive pricing statements. In principle, the regression coefficients of value relevance studies can also be used to obtain business values. However, valuation differences between different regression approaches are huge and these models have a weak economic backing when contrasted with the economic principle.
All these problems underline the trade-off between asset pricing rigor and practicability of models: Present value models are theoretically superior, but their practical implementation in form of constant discount rates and horizon models is far from economically convincing. Accounting-based models are characterized by less asset pricing theory rigor, however, can be implemented without sacrificing much of their theoretical basis. Obtaining better asset pricing models, hence, means either improve the implementation of present value models or the theoretical foundations of accounting-based models. Two reasons favor the improvement of the asset pricing foundation of empirical accounting-based models. On the one hand, the accounting literature so far has not fully exploited the asset pricing potential of accounting-based valuation models: It can be increased visibly without sacrificing practicability. On the other hand, purely empirical models always create a justification problem: Who would pay a higher price for a company because sales multiples result in higher prices than earnings multiples? Who would pay a higher price for a company because a lower discount rate for earnings is used? Who would pay a higher price for a company because an empirical estimation procedure, which possesses a higher RÂ˛, recommends a higher price than other empirical estimation procedures?
Therefore, it is the fourth objective of this thesis in Chapter V to connect the practicability of accounting-based valuation models with the theoretical rigor of asset pricing theory

### Refractive X-ray beam shaping

This work introduces new refractive illumination optics in the hard X-ray region and describes a method for overcoming fabrication limitations of X-ray depth lithography. In particular, the problem of high aspect ratio in X-ray prism lenses was addressed. The refractive X-ray optics are developed for the photon energy range 8-100 keV. In the following, we report the development of a principal new focusing optics with large aperture, an illumination condenser for full-field X-ray microscopy and a so-called beam shaping optics to overcome the limitation of the field of view at 3rd and 4th generation synchrotron sources.
To reduce the absorption of X-rays in the material of the optical systems, the approach of X-ray prism lenses was pursued. Here, the optics consist of rows of micro prisms with an edge length of about 20 Âµm, which deflect the incident rays. This improves the ratio of the refractive power of the optics to the volume of the absorbing lens material. The mechanical stability of the fragile, very tall micro prisms is achieved by exposing thin, stabilizing support planes.
In order to achieve focal sizes smaller than the prism edge lengths, double parabolic biconcave micro-lenses were added to the prism rows. A similar arrangement with biconvex micro-lenses was used to achieve beam expansion while simultaneously homogenizing the illumination of the image field of a full-field X-ray microscope. Beam shaping optics consisting of kinoform Fresnel lens elements were developed for vertical beam expansion at high brilliance synchrotron sources.
In all cases, the theory is based on geometrical optics and ray tracing simulations. The optics were produced via deep X-ray lithography using the synchrotron radiation source at KIT at the LIGA I and II beamlines. The lens material is the negative resist mr-X, an epoxy resin-based polymer of type SU-8. The lenses were characterized at PETRA III, DESY in Hamburg and at ESRF in Grenoble

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