Retail price levels and concentration of wholesalers, retailers, and hypermarkets

This paper examines retail grocery price levels with a very large (unbalanced) panel of stores that operate in well-defined local markets. We explain price variation across grocery retailers by the concentration of wholesalers and retailers, and the market share of hypermarkets (and control for a number of store and region specific factors). Our most important result is that concentration at the wholesale level is an important determinant of retail prices. The price effect of retail concentration and hypermarket market share are statistically significant but small in economic terms.Firm concentration; market structure; price competition; grocery retail; grocery wholesale

Adaptive methods for score function modeling in blind source separation

In signal processing and related fields, multichannel measurements are often encountered. Depending on the application, for instance, multiple antennas, multiple microphones or multiple biomedical sensors are used for the data acquisition. Such systems can be described using Multiple-Input Multiple-Output (MIMO) system models. In many cases, several source signals are present at the same time and there is only limited knowledge of their properties and how they contribute to each sensor output. If the source signals and the physical system are unknown and only the sensor outputs are observed, the processing methods developed for recovering the original signals are called blind. In Blind Source Separation (BSS) the goal is to recover the source signals from the observed mixed signals (mixtures). Blindness means that neither the sources nor the mixing system is known. Separation can be based on the theoretically limiting but practically feasible assumption that the sources are statistically independent. This assumption connects BSS and Independent Component Analysis (ICA). The usage of mutual information as a measure of independence leads to iterative estimation of the score functions of the mixtures. The purpose of this thesis is to develop BSS methods that can adapt to different source distributions. Adaptation makes it possible to separate sources without knowing the source distributions or even the characteristics of source distributions. Special attention is paid to methods that allow also asymmetric source distributions. Asymmetric distributions occur in important applications such as communications and biomedical signal processing. Adaptive techniques are proposed for the modeling of score functions or estimating functions. Three approaches based on the Pearson system, the Extended Generalized Lambda Distribution (EGLD) and adaptively combined fixed estimating functions are proposed. The Pearson system and the EGLD are parametric families of distributions and they are used to model the distributions of the mixtures. The strength of these parametric families is that they contain a wide class of distributions, including asymmetric distributions with positive and negative kurtosis, while the estimation of the parameters is still a relatively simple procedure. The methods may be implemented using existing ICA algorithms. The reliable performance of the proposed methods is demonstrated in extensive simulations. In addition to symmetric source distributions, asymmetric distributions, such as Rayleigh and lognormal distribution, are utilized in simulations. The score adaptive methods outperform commonly used methods due to their ability to adapt to asymmetric distributions.reviewe

Neural oscillations underlying behavior: adjustments after commission errors and temporal judgements

The current thesis aimed to: 1) explore whether alpha peak frequency (APF) as measured with electroencephalography (EEG) might be indicative of an internal clock. No systematic relationship between APF and temporal decision making was found, which suggests that a straightforward interpretation of APF reflecting the brain’s internal clock is too simplistic. 2) examine the role of oscillatory power on performance monitoring and temporal decision making. We found no evidence that medial frontal cortex used oscillatory power to influence subsequent processing in down-stream regions after an error was committed. Instead, we found phase-based connectivity after an error although the implications on behavioral adjustments remain unexplored. In the temporal decision making experiments we found increased theta power in correct compared to incorrect judgements after the short time interval had elapsed, which might suggest that theta power reflects evidence accumulation of temporal information. 3) examine the role of climbing neural activity in temporal decision making as reflected by slow evoked potentials (SEPs) in the EEG. No consistent evidence across the different experiments was observed, which suggests that SEPs do not reflect temporal evidence accumulation in the current time estimation task and differences are instead reflected in theta power differences

Aerospace Medicine and Biology - A continuing bibliography, with indexes, June 1967

Continuing bibliography on aerospace medicine and biolog

Development of a fluidic sensor for the detection of herbicides using thylakoid preparations immobilised on magnetic beads to aid regenerability

Following the industrial revolution and advances in chemical science, the pollution of the environment with trace organic pollutants has been steadily increasing, which is of concern, due to their effect on the environmental and human health. Tighter legislation that has been introduced in order to minimise the release of harmful pollutants has led to the initiation of monitoring programmes. For example, drinking water suppliers are obliged to systematically monitor drinking water supplied for human consumption for a large range of pollutants. The same applies for waste water treatment facilities. The well-established standard methods of environmental waters analysis require sampling and transportation of samples to the laboratory for detailed measurements. Therefore, the timescale from sampling to reporting is not ideal, as a considerable lag occurs. There is therefore the potential for the use of in situ methods that overcome this issue. As these do not currently exist, a need to address this is identified. Biosensors are sensing devices that rely on a biologically-derived component as an integral part of their detection mechanism. Biosensors that respond to pollutants could be used for rapid, low cost, field-based pre-screening of water samples. Herbicides are considered to be the most important class of pesticides used in the E.U. Herbicides can be highly toxic for human and animal health, and increase in the application of herbicides in agriculture during recent decades has resulted in immense pollution of both soil and water. About half of the herbicides used at present in agriculture inhibit the light reactions in photosynthesis, mostly by targeting the Photosystem II (PSII) complex. A method of detecting certain classes of herbicides is therefore proposed; the photosynthesis-inhibiting herbicides act by binding to PS II, a chlorophyll– protein complex which plays a vital role in photosynthesis, located in the thylakoid membrane of algae, cyanobacteria and higher plants. The inhibition of PS II causes a reduced photoinduced production of hydrogen peroxide, which can be measured by the HRP-mediated luminol chemiluminescence reaction. The design and development of a fluidic sensor unit for the detection of such herbicides, based upon their inhibition of the hydrogen peroxide production, will employ the use of superparamagnetic beads in order to address issues of reuse and regenerability. The illumination-dependent production of hydrogen peroxide by isolated thylakoids, and its inhibition by herbicides in a concentration-dependent manner, were achieved and measured with the HRP-mediated chemiluminescence reaction with luminol in a cuvette, batch format, allowing for the detection of herbicides down to 6.0 x 10-09.The integration of the above reactions has been achieved by designing and constructing a fluidic unit that combines the herbicide-dependent production and the detection of hydrogen peroxide in a single fluidic assay by combining all the individual steps in a compact, portable format, with both HRP and thylakoids covalently coupled on superparamagnetic beads. This addresses issues of regenerability, as the beads are introduced, used and discarded following a measurement, controlled only by magnetic and flow forces. Herbicide detection was achieved to a lower LOD of 5.5 x 10-10 M. The concept development, design and construction of the fluidic unit, as well as results of the detection of herbicides with the batch assay method has been published, in a paper by the author (Talanta, 2008, vol. 77, no. 1, pp. 42-47), Considerable progress has therefore been made towards developing a system that would be suitable for automated, field deployment applications for the detection of the most frequently used classes of herbicides; the lower LOD however is not within the stringent legislated maximum permissible limits set for herbicides measured in water, in European waters. An immediate step forward would be to achieve the required lower LOD, with the unit's development into a prototype instrument that can be field deployed being the further goal.EThOS - Electronic Theses Online ServiceGBUnited Kingdo