The causal meaning of Fisher's average effect

In order to formulate the Fundamental Theorem of Natural Selection, Fisher defined the average excess and average effect of a gene substitution. Finding these notions to be somewhat opaque, some authors have recommended reformulating Fisher's ideas in terms of covariance and regression, which are classical concepts of statistics. We argue that Fisher intended his two averages to express a distinction between correlation and causation. On this view the average effect is a specific weighted average of the actual phenotypic changes that result from physically changing the allelic states of homologous genes. We show that the statistical and causal conceptions of the average effect, perceived as inconsistent by Falconer, can be reconciled if certain relationships between the genotype frequencies and non-additive residuals are conserved. There are certain theory-internal considerations favoring Fisher's original formulation in terms of causality; for example, the frequency-weighted mean of the average effects equaling zero at each locus becomes a derivable consequence rather than an arbitrary constraint. More broadly, Fisher's distinction between correlation and causation is of critical importance to gene-trait mapping studies and the foundations of evolutionary biology

Performance of a building integrated collector for solar heating and radiant cooling

Due to their limited temperature range, unglazed solar collectors have long been relegated to providing low cost heating in applications such as swimming pool heating systems. This limited temperature range is due to heat loss: firstly by convection to the surrounding air and secondly by radiant heat transfer to the cold sky. During the day an unglazed collector can be operated as a standard solar absorber to heat water in a storage tank. However, it is possible to take advantage of radiant cooling of unglazed solar collectors by operating them at night. Under night conditions when there is no solar radiation and the sky temperature is low, the collector can radiate heat to the sky and cool a cold storage tank to provide cooling in the building the following day. This study theoretically and experimentally examines the performance of a building integrated collector for heating and cooling and explores the contribution it can make to heating and cooling loads in typical New Zealand and Australian buildings

Experimental performance of water cooled building integrated photovoltaic/thermal solar collectors

The idea of integrating water cooled photovoltaic/thermal collectors into building structures (BIPVT collectors) to provide electrical and heat energy is an area that has received only limited attention. BIPVT collectors are particularly attractive, as the integration of a single photovoltaic and thermal collector into the long-run roofing structure of a building could provide greater opportunity for the use of renewable solar energy technologies. In this study, the thermal efficiency of a novel low cost water cooled building integrated photovoltaic/thermal (BIPVT) solar collector was experimentally measured. The results show that despite being made of a typical roofing material, the thermal efficiency is not unreasonably affected. Furthermore, it is shown that the measured efficiency is similar to that predicted by the Hottel-Whillier equations

Performance of a building integrated solar combisystem

Solar combisystems providing both water and space heating to buildings are becoming commonplace in European and North American locations. However, the use of these systems in Australia and New Zealand is still in its infancy. While significant work has been undertaken to characterise the performance of these systems in northern hemisphere locations, this does not necessarily reflect their performance in Australia or New Zealand. This work examines the performance of solar combisystems utilising TRNSYS and F-chart simulations of an integrated solar thermal combisystem installed in a single storey detached dwelling under typical Australian and New Zealand climatic conditions. In doing this, it shows that there is significant scope for increased use of solar combisystems in the cooler climate regions of Australia and New Zealand

An assessment of base load concentrating solar thermal power generation for New Zealand

With increasing pressure being placed on traditional energy sources, both in terms of supply and also regulatory, there is an increasing need to explore alternative generation technologies. In global terms, solar energy has the potential to make a significant contribution to worldwide energy demands in the future. This study examines recent developments in the emerging field of concentrating solar thermal power generation and explores the potential for base load electricity generation using this technology in New Zealand

The development of a novel large area building integrated solar collector for pool heating

Unglazed solar collectors have often been used a means of providing low cost heating to swimming pools. However, these systems are typically polymer style “mats” that are laid on top of a roof, often leading to poor aesthetics due to their lack of integration with the building itself. This study charts the development of a novel large area unglazed building integrated solar pool heating system (BIT), based on long run sheet metal roofing, from its initial conceptualisation through to its implementation. It discusses the design of the building integrated solar collector modules, the assessment of their performance through theoretical modelling and experimental validation. Subsequently, it shows the scaling of laboratory scale testing to a large area array through modelling and discusses the performance of the system in the “as-built” configuration. In doing this, it provides a succinct illustration of the design process for the development of the University of Waikato’s building integrated pool heating system

External inverse-Compton emission from blazar jets

According to leptonic models for the high-energy emission from blazars, relativistic electrons in the inner jets inverse-Compton scatter photons from a variety of sources. Seed photons are certainly introduced via the synchrotron process from the electrons themselves, but external sources of seed photons may also be present. In this paper, we present detailed derivations of the equations describing external inverse-Compton scattering from two sources of seed photons: direct emission from the accretion disk, and accretion disk photons that have scattered off the broad line region. For each source, we derive the seed photon spectrum incident on the jet, the single electron energy loss rate, and the emitted photon spectrum. Subject headings: BL Lacertae Objects: general — galaxies: jets — radiation mechanisms: non-thermal–3– 1

Performance of coloured solar collectors

The use of solar collectors with coloured absorbers for water heating is an area of particular interest when considering their integration with buildings. By matching the absorber colour with that of the roof or façade of the building, it is possible to achieve an architecturally and visually pleasing result. Despite the potential for the use of coloured absorbers very little work has been undertaken in the field. In this study, the thermal performance of a series of coloured, ranging from white to black, water heating solar collectors is examined. Subsequently, the annual solar fraction for typical water heating systems with coloured absorbers is calculated. The results show that coloured solar collector absorbers can make noticeable contributions to heating loads. Furthermore, although their thermal efficiency is lower than highly developed selective coating absorbers, they offer the advantage of sensitive integration with buildings

A combined optical, thermal and electrical performance model of a Building Integrated Photovoltaic/Thermal Concentrator (BIPVTC)

The electrical output of concentrating photovoltaic devices is significantly affected by the temperature of the photovoltaic cells. The ability to actively cool photovoltaic cells under concentrated radiation allows their electrical efficiency to be maintained particularly during periods of high solar radiation when concentration offers the maximum benefit. In this study, the design of a novel photovoltaic/thermal solar concentrator for building integration (BIPVTC) is discussed. The optical, thermal and electrical performance of the collector was theoretically modelled and validated with experimental data. The results show that BIPVTC offers improved electrical yields from both concentrating radiation onto the photovoltaic cells and also by actively cooling them