Suffolk University

About: Suffolk University is a education organization based out in Boston, Massachusetts, United States. It is known for research contribution in the topics: Population & Sugar beet. The organization has 6462 authors who have published 9321 publications receiving 235328 citations.

Nanoelectromechanics of piezoresponse force microscopy

Abstract: To achieve quantitative interpretation of piezoresponse force microscopy (PFM), including resolution limits, tip bias- and strain-induced phenomena and spectroscopy, analytical representations for tip-induced electroelastic fields inside the material are derived for the cases of weak and strong indentation. In the weak indentation case, electrostatic field distribution is calculated using an image charge model. In the strong indentation case, the solution of the coupled electroelastic problem for piezoelectric indentation is used to obtain the electric field and strain distribution in the ferroelectric material. This establishes a complete continuum mechanics description of the PFM contact mechanics and imaging mechanism. The electroelastic field distribution allows signal generation volume in PFM to be determined. These rigorous solutions are compared with the electrostatic point-charge and sphere-plane models, and the applicability limits for asymptotic point-charge and point-force models are established. The implications of these results for ferroelectric polarization switching processes are analyzed.

British Association of Dermatologists' guidelines for the management of cutaneous warts 2014

Abstract: British Association of Dermatologists’ guidelines for the management of cutaneous warts 2014 J.C. Sterling, S. Gibbs, S.S. Haque Hussain, M.F. Mohd Mustapa and S.E. Handfield-Jones Addenbrooke’s Hospital, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge CB2 OQQ, U.K. Great Western Hospital, Marlborough Road, Swindon SN3 6BB, U.K. British Association of Dermatologists, Willan House, 4 Fitzroy Square, London W1T 5HQ, U.K. West Suffolk Hospital, Hardwick Lane, Bury St Edmunds, Suffolk IP33 2QZ, U.K.

Rheotropism in fishes

Abstract: Summary (1) The fluid properties of air and water enable animals to orientate to flow and this behaviour in water is termed rheotaxis. Fish, however, have a wide range of responses to currents, extending beyond simple orientation, and the term rheotropism is therefore used as a ‘portmanteau’ word to describe all such reactions. (2) Fish detect currents directly by flow over the body surface or indirectly by other stimuli. Indirect responses are more common and occur in response to visual, tactile and inertial stimuli resulting from displacement of the fish by the current. Reactions to displacement of visual images are called optomotor reactions. The lateral line is not involved except in the detection of small localized jets of water. It has not been demonstrated that any fish can detect the current by electrical stimuli, although it is theoretically possible for some to do so. (3) In the basic form of rhotaxis the fish heads upstream and maintains station by stemming the current. Current detection thresholds fall within the range 0.4 to 10 cm/s for tactile stimuli but may be as low as 0.03 cm/s for visual stimuli. (4) Visual responses have been studied by simulating displacement by the current in optomotor apparatus. Fish respond to a rotating black-and-white-striped background by compensatory movements of the head and eyes - optokinetic nystagmus - or by the optomotor reaction, in which the fish swims with the background. (5) Fish show an orthokinesis in optomotor apparatus, their mean swimming speed increasing with the speed of rotation of the background. The precise form of the relationship varies between species and there is also considerable individual variation in performance. Fish accelerate and decelerate relative to the background, fixating on a particular stripe for short periods. (6) Factors limiting the appearance of the optomotor response are contrast, illuminance, acuity, critical flicker fusion frequency and spectral sensitivity. (7) Fish tolerate retinal image movements equivalent to those received when they are carried forwards by the current but not to those received when they are carried backwards. There are ganglion cells in the optic tectum which are sensitive to the direction of movement of targets across the visual field. In the goldfish there are significantly more units sensitive to movements in the temporo-nasal than in the opposite direction. (8) There are close parallels between the behaviour of fish in schools and in an optomotor apparatus. The optomotor response is apparently innate, occurring in newly hatched fry. (9) Physical and chemical factors can modify rheotaxis. Temperature and olfactory stimuli affect both the sign of the taxis and the kinetic component of the behaviour. (10) Thyroid hormones which are involved in the control of migration have been shown to affect the kinetic component of rheotaxis. (11) Fish show a number of hydrodynamic adaptations to life in currents. Morphological modifications are greatest in fish from torrential streams, which show extreme dorsoventral flattening and have specialized adhesive organs. Other fish select areas of low velocity or decrease their buoyancy with increasing current speed. (12) Rheotropic behaviour plays an important role in the distribution of fish within stream systems, in the maintenance of territory and station and in feeding behaviour. Territory, station and spawning sites in salmonids are all selected in relation to water velocity. (13) Water currents are thought to provide either a transport system or directional clues for fish on migration. The fish either does not respond to the current and is carried passively downstream, or it makes an orientated movement, swimming up- or downstream. (14) Eggs and larvae are known to drift passively downstream from their spawning grounds and some adult fish may also drift passively. In the sea both adult and juvenile fish use a form of modulated drift associated with vertical migration. Fish move up into midwater either by direct tidal selection or in relation to the diel cycle of illuminance. In fresh water the downstream migrations of salmonid fry, and smolts under some conditions, occur by modulated drift. (15) There is no evidence that fish migrating in the sea orientate to the current, but in fresh water the upstream migrations of diadromous fish are clearly orientated movements. (16) Water velocity is a major factor for salmonids migrating upstream. For fry it limits the occurrence of upstream migrations and for adults it can also prevent upstream movement. But migrations are often initiated by freshets, and changing water velocity is thought to be the most important factor associated with a freshet. (17) Both environmental and genetic factors affect the direction of migration in relation to the current. In some sockeye salmon fry direction is determined by temperature, but in others the overall direction of movement is genetically determined and environmental factors only modify the behaviour. (18) Rheotropic behaviour has a number of important practical applications in the capture of fish and in guiding them past dams and power stations. (19) The optomotor response plays a basic role in the capture of roundfish by trawls under conditions when the fish can see the gear. Many fish are caught because they become fatigued after a prolonged period of swimming at the same speed as the trawl. (20) Most success in guiding fish away from hazardous areas and bypassing them round dams has been achieved with mechanical barriers which depend on rheotropic reactions of the fish. (21) Louvre screens are very successful in deflecting juvenile salmonids migrating downstream past small dams but are impracticable at large dams. Instead, the turbine intakes are commonly sited at a considerable depth and fish are bypassed by mechanical screens either at the surface of the forebay or into the gatewells immediately upstream of the turbine intakes. (22) With upstream migrants the basic problem is to attract fish to the lower end of the fishways. An adequate ‘attraction velocity’ is an important feature of fishways, which must be sited so that the fish avoid the high velocity discharges from spillways and turbines.

Perceptions of SME Growth Constraints in Nigeria

Abstract: This study investigates the factors that influence the growth, performance, and development of small and medium-sized enterprises (SMEs) in Nigeria and what implications these factors have for policy. The study is justified for a number of reasons. Most importantly, since its independence, the Nigerian government has been spending an immense amount of money obtained from external funding institutions for entrepreneurial and small business development programs, which have generally yielded poor results (Mainbula 1997). Given the large domestic market and plethora of raw materials in Nigeria, there is little progress in terms of manufacturing value-added products, either for import substitution, exports, or employment creation. It therefore becomes pertinent to identify the factors that impede small business development in Nigeria. For this study, 32 small business entrepreneurs were interviewed across the country. In addition, other sources were interviewed to check and confirm the validity of the entrepreneu rs' responses. Research Methodology A mixed-method strategy is one in which more than one method of approach is used in data collection and analysis while conducting research (Romano 1989). This approach is similar to what Mikkelsen (1995) and Denzin (1978) described as triangulation. The multiple-method strategy was adopted for this study to reduce the possibility of personal bias by not depending on only one method of approach or response coming from only one firm or sector. Adopting this method of approach supports the authenticity of the study. Both qualitative and quantitative data were used in a variety of ways, including a detailed overview of survey results in terms of a general profile and a model of Nigerian small firms. Semi-structured interviews based on open-ended, flexible questionnaires and some structured interviews were conducted with several groups of people interested or involved with the small business sector in Nigeria. The idea behind this was to obtain cross-referencing data and some independent confirmation of data, as well as a range of opinions. Input from the following groups were solicited: (1) government officials who formulate and implement policies on SME promotion and industrial development in Nigeria; (2) officials responsible for raw material supply to small companies; (3) managers of other large scale businesses operating in the same sector and economy as the SMEs; (4) representatives of development banks who may be requested to give loans to small-scale businesses; (5) industrial experts and consultants who conduct research and are well-informed about the present state of the industrial sector in Nigeria; and (6) selected customers who buy and distribute products as retailers to the public or to other small businesses or larger firms. The Perceptions of Constraints on Small Business in Nigeria What the 32 small firms studied in Nigeria considered to be the main constraints on their firms' growth and overall performance are presented in Table 1. In addition, some entrepreneurs indicated that government policies and attitudes of public officials adversely affect their businesses, especially the harsh economic policy of the structural adjustment programme (SAP) implemented by the government in 1986. The policy caused the value of the national currency to decline. Most small businesses could not afford to train their workers, and manufacturers found it difficult to obtain foreign exchange to order or purchase machinery and spare parts. There is also the problem of frequent harassment by government officials who extort money from the businesses. Poor infrastructure, including bad roads, inadequate water shortage, erratic electric supply and a poor telecommunications system are additional obstacles. Lack of these facilities cost most firms higher overheads because they have to be responsible for obtaini ng such facilities at their own expense. …