A-site size effect in a family of unfilled ferroelectric tetragonal tungsten bronzes : Ba4R0.67Nb10O30 (R = La, Nd, Sm, Gd, Dy and Y)

JG acknowledges the EPSRC and EaStCHEM for provision of a studentship via the doctoral training grant.The effect of A-cation size on the structural and electrical properties in a family of ferroelectric tetragonal tungsten bronzes (TTBs) Ba4R0.67□1.33Nb10O30 (R = La, Nd, Sm, Gd, Dy and Y; □ = vacancy) was investigated. In each case, the crystal structure, as determined from lab-based ambient powder X-ray diffraction (PXRD), is metrically tetragonal and can be refined in the P4bm space group. XRD data show an increased splitting of hk0 00l reflections with decreasing R cation size indicating an increasing tetragonal distortion (measured by tetragonality c/a). Dielectric data and ferroelectric measurements indicate that the ferroelectric Curie temperature, TC, increases with decreasing R size and so a direct correlation between TC and tetragonality/ionic radius of R is demonstrated. Rietveld refinements show that the large A2-site is fully occupied by Ba2+ and, in addition to the R cation size, the presence of vacancies at the A1-site (perovskite-like site) is also shown to strongly affect the stability of ferroelectricity in this structure type.Peer reviewe

Behaviour of concrete filled stainless steel elliptical hollow sections

This paper presents the behaviour and design of axially loaded concrete filled stainless steel elliptical hollow sections. The experimental investigation was conducted using normal and high strength concrete of 30 and 100 MPa. The current study is based on stub column tests and is therefore limited to cross-section capacity. Based on the existing design guidance in Eurocode 4 for composite columns, the proposed design equations use the continuous strength method to determine the strength of the stainless steel material. It is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel elliptical hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance

Wire grid forming apparatus Patent

Apparatus for forming wire grids for electric strain gage

Forming blocks speed production of strain gage grids

A tool is designed which facilitates the forming of wire grids used in manufacturing strain gage grids. Flattening the grid wire by a cold working process produces a stabilized grid which can be readily handled for storage or shipment

Timing performance of phased-locked loops in optical pulse position modulation communication systems

An optical digital communication system requires that an accurate clock signal be available at the receiver for proper synchronization with the transmitted signal. Phase synchronization is especially critical in M-ary pulse position modulation (PPM) systems where the optimum decision scheme is an energy detector which compares the energy in each of M time slots to decide which of M possible words was sent. Timing errors cause energy spillover into adjacent time slots (a form of intersymbol interference) so that only a portion of the signal energy may be attributed to the correct time slot. This effect decreases the effective signal, increases the effective noise, and increases the probability of error. A timing subsystem for a satellite-to-satellite optical PPM communication link is simulated. The receiver employs direct photodetection, preprocessing of the detected signal, and a phase-locked loop for timing synchronization. The variance of the relative phase error is examined under varying signal strength conditions as an indication of loop performance, and simulation results are compared to theoretical calculations

Mathematical model predictions and optimization study of the gamma ray atmospheric density sensor

Mathematical model predictions and optimization study of gamma ray atmospheric density senso

Service quality measurements for IPv6 inter-networks

Measurement-based performance evaluation of network traffic is becoming very important, especially for networks trying to provide differentiated levels of service quality to the different application flows. The non-identical response of flows to the different types of network-imposed performance degradation raises the need for ubiquitous measurement mechanisms, able to measure numerous performance properties, and being equally applicable to different applications and transports. This paper presents a new measurement mechanism, facilitated by the steady introduction of IPv6 in network nodes and hosts, which exploits native features of the protocol to provide support for performance measurements at the network (IP) layer. IPv6 Extension Headers have been used to carry the triggers involving the measurement activity and the measurement data in-line with the payload data itself, providing a high level of probability that the behaviour of the real user traffic flows is observed. End-to-end one-way delay, jitter, loss, and throughput have been measured for applications operating on top of both reliable and unreliable transports, over different-capacity IPv6 network configurations. We conclude that this technique could form the basis for future Internet measurements that can be dynamically deployed where and when required in a multi-service IP environment

Experimental verification of gamma ray atmospheric density sensor mathematical model predictions

Experimental verification of mathematical model performance predictions for gamma ray atmospheric density sensor

Comparative review of the effects of organic farming on biodiversity (OF0149)

This is the final report of Defra project OF0149 1. The report reviews the impact of different farming regimes and makes a comparative study of their influence on the biodiversity of arable farmland. 2. Within this review, the evaluation of impacts on biodiversity focuses on species and habitats, and includes both the number, abundance and activity of species (section 1.3). 3. Five farming regimes are defined and discussed, namely Conventional Arable, Conventional Mixed Lowland, Organic and two integrated production regimes - LEAF (Linking Environment and Farming) and IFS-Experimental regimes The main differences between the regimes in relation to the use of external inputs and other agricultural practices are discussed. The review draws on both UK and European information (section 1.4). 4. The effect of each farming regime on biodiversity is assessed according to the agricultural practices adopted and to the occurrence and management of uncropped land present. Agricultural practices are reviewed within the following categories: cultivation, crop production, crop protection and post-cropping practice (section 2.1). 5. Among the agricultural practices examined, those associated with crop protection and the artificial inputs associated with crop production were seen as the most adverse for biodiversity. Several practices were seen to benefit the biodiversity of arable land. These included set-aside, crop rotations with grass leys, spring sowing, permanent pasture, green manuring and intercropping (section 2.7). 6. Uncropped areas, such as sown grass strips (beetle banks), grass margins and conservation headlands, were seen as critical for the maintenance of biodiversity on arable farmland. Changes in the balance of cropped to uncropped land within some farming regimes, linked to increase in field size, have had a major impact on the diversity of flora and fauna associated with those regimes (section 3.4). 7. Based on the evaluation of agricultural practices used, the occurrence of uncropped land and the extent of the farming regime within England and Wales, it was concluded that Conventional Arable regimes act effectively to maintain the impoverished status of biodiversity on arable land. Extreme examples can be found of intensively managed farms that further deplete biodiversity and sympathetically managed farms that try to enhance it. Increased adoption of agricultural practices such as direct drilling, use of farmyard manure, set-aside, use of crop rotations with leys, or an increase in the incidence and sympathetic management of uncropped areas may well assist biodiversity on farms within this regime (sections 4.3 & 4.4) 8. Organic regimes were shown to have an overall benefit for biodiversity at the farm level, both in terms of the agricultural practices adopted and in the occurrence and management of uncropped areas (sections 4.3 & 4.4). 9. Conventional Mixed Lowland and LEAF regimes were both seen to have the potential for enhancing biodiversity on arable land. Here, adverse impacts associated with crop protection and crop production may be mitigated by beneficial effects associated with post-cropping practices, the occurrence of permanent pasture and uncropped land. At present, the extent to which enhancement may be achieved, may well depend on the extent, condition and management of uncropped land present within these regimes (sections 4.3 & 4.4). 10. IFS-experimental regimes were seen to have a beneficial effect on biodiversity, due to the stringent procedures used for targeting herbicides and pesticides and for establishing and managing uncropped areas. At present these regimes occupy a tiny area of the national resource of arable land and thus their impact on national biodiversity is likely to be insignificant at the present time (sections 4.3 & 4.4). 11. A number of areas are highlighted for further consideration. These include: • monitoring of biodiversity on farms pre- and post- conversion to organic farming, • comparative studies that focus on the effectiveness of different regimes or agricultural practices in enhancing biodiversity on species-impoverished intensively managed arable land, • manipulative experiments to determine the optimal balance of cropped to uncropped areas for enhancing biodiversity, • manipulative experiments to examine the separate impacts of rotational regimes and agricultural inputs on biodiversity, • an economic assessment of the costs and benefits in both production and biodiversity terms, of conversion to organic, integrated production or uptake of available agri-environment schemes