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Practical Difficulties (practical + difficulty)
Selected AbstractsEnhancement of ultrafiltration using gas sparging: a comparison of different membrane modules,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2-3 2003Zhanfeng Cui Abstract Ultrafiltration is widely used in the chemical, pharmaceutical, food and water industries. Practical difficulties arise in designing and operating the process due to concentration polarisation and membrane fouling. Enhancement of ultrafiltration is highly desirable to achieve a higher permeate flux at a fixed energy input, or a reduced energy input whilst maintaining the level of permeate flux, or an improved selectivity of the membrane. One effective, simple, and economic technique used to enhance ultrafiltration is the use of gas bubbles, ie injecting gas into the feed stream to create a gas,liquid two-phase cross-flow operation. In this paper, an attempt is made to compare the effect of ,bubbling' on the ultrafiltration performance, using different membrane modules (in particular, tubular and hollow fibre membrane modules). The difference in performance can be related to the feature of two-phase flow hydrodynamics and its respective effect on mass transfer. The advantages and drawbacks of using this technique to enhance ultrafiltration are discussed. © 2003 Society of Chemical Industry [source] Environmental power analysis , a new perspectiveENVIRONMETRICS, Issue 5 2001David R. Fox Abstract Power analysis and sample-size determination are related tools that have recently gained popularity in the environmental sciences. Their indiscriminate application, however, can lead to wildly misleading results. This is particularly true in environmental monitoring and assessment, where the quality and nature of data is such that the implicit assumptions underpinning power and sample-size calculations are difficult to justify. When the assumptions are reasonably met these statistical techniques provide researchers with an important capability for the allocation of scarce and expensive resources to detect putative impact or change. Conventional analyses are predicated on a general linear model and normal distribution theory with statistical tests of environmental impact couched in terms of changes in a population mean. While these are ,optimal' statistical tests (uniformly most powerful), they nevertheless pose considerable practical difficulties for the researcher. Compounding this difficulty is the subsequent analysis of the data and the impost of a decision framework that commences with an assumption of ,no effect'. This assumption is only discarded when the sample data indicate demonstrable evidence to the contrary. The alternative (,green') view is that any anthropogenic activity has an impact on the environment and therefore a more realistic initial position is to assume that the environment is already impacted. In this article we examine these issues and provide a re-formulation of conventional mean-based hypotheses in terms of population percentiles. Prior information or belief concerning the probability of exceeding a criterion is incorporated into the power analysis using a Bayesian approach. Finally, a new statistic is introduced which attempts to balance the overall power regardless of the decision framework adopted. Copyright © 2001 John Wiley & Sons, Ltd. [source] A new role for MSY in single-species and ecosystem approaches to fisheries stock assessment and managementFISH AND FISHERIES, Issue 1 2001In 1977, Peter Larkin published his now-famous paper, ,An epitaph for the concept of maximum sustained yield'. Larkin criticized the concept of single-species maximum sustained yield (MSY) for many reasons, including the possibility that it may not guard against recruitment failure, and the impossibility of maximising sustainable yields for all species simultaneously. However, in recent years, there has been a fundamental change in the perception of the fishing mortality associated with MSY (FMSY) as a limit to be avoided rather than a target that can routinely be exceeded. The concept of FMSY as a limit is embodied in several United Nations Food and Agriculture Organization (FAO) agreements and guidelines, and has now been incorporated into the US Magnuson,Stevens Fishery Conservation and Management Act. As a result, the United States now requires the development of overfishing definitions based on biological reference points that treat the FMSY as a limit reference point and must also define a lower limit on biomass below which rebuilding plans with strict time horizons must be developed. This represents a major paradigm shift from the previously mandated (but often unachieved) objective to simply maintain fishing mortalities at levels below those associated with recruitment overfishing. In many cases, it requires substantial reductions in current fishing mortality levels. Therefore, the necessity of the new paradigm is continually questioned. This paper draws on examples from several fisheries, but specifically focuses on the recent US experience illustrating the practical difficulties of reducing fishing mortality to levels below those corresponding to MSY. However, several studies suggest that even more substantial reductions in fishing mortality may be necessary if ecosystem considerations, such as multispecies interactions, maintenance of biodiversity and genetic diversity, and reduction of bycatch and waste, are taken into account. The pros and cons of moving beyond single-species assessment and management are discussed. A US plan for improving stock assessments indicates that even a ,basic' objective such as ,adequate baseline monitoring of all managed species' may be extremely costly. Thus, the suggestion of Larkin (1983, 1997) that the costs of research and management should not exceed 10,20% of the landed value of the catch may preclude comprehensive ecosystem management. More importantly, neither single-species nor ecosystem-based fisheries management is likely to improve appreciably unless levels of fishing capacity are aligned with resource productivity, as is currently being promoted by FAO and several individual nations. [source] Simulation of an integrated PCM,wallboard systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2003J.-S. Kim Abstract Heat transfer barriers and other practical difficulties do currently hamper the development and application of (phase change materials) PCM,wallboard systems. In this study thermal performance of randomly mixed PCM and laminated PCM,wallboard systems have been numerically evaluated and results compared. The laminated system displayed up to 50% increment in heat flux enhancement and about 18% increase in heat transfer rates. Consequently, the laminated PCM,wallboard system has greater potential for heating and cooling application in buildings than the randomly mixed system. Experimental validation and investigation into manufacturing techniques are however needed to establish the commercial viability. Copyright © 2002 John Wiley & Sons, Ltd. [source] Hemoprotein time-resolved X-ray crystallographyIUBMB LIFE, Issue 3 2008Mario Milani Abstract In the last decade the role of structural dynamics in controlling protein function was actively investigated using new and advanced experimental approaches. In particular, time resolved crystallography, despite some practical difficulties, is being used extensively to complement the study of protein structure-function relationships with information on the dynamics, based on experimental evidence. Here we present a short overview of the results obtained on dynamical properties of myoglobin and homologous hemoproteins, where the photosensitive heme-Fe,ligand bond has allowed transient intermediates to be studied by different flash photolysis methods coupled to Laue X-ray diffraction, thus highlighting some of the dynamical events that characterize diffusion of a diatomic ligand to/from the heme in model hemoproteins. © 2008 IUBMB IUBMB Life, 60(3): 154,158, 2008 [source] Pain: a review of three commonly used pain rating scalesJOURNAL OF CLINICAL NURSING, Issue 7 2005Amelia Williamson MSc Aims and objectives., This review aims to explore the research available relating to three commonly used pain rating scales, the Visual Analogue Scale, the Verbal Rating Scale and the Numerical Rating Scale. The review provides information needed to understand the main properties of the scales. Background., Data generated from pain-rating scales can be easily misunderstood. This review can help clinicians to understand the main features of these tools and thus use them effectively. Method., A MedLine review via PubMed was carried out with no restriction of age of papers retrieved. Papers were examined for methodological soundness before being included. The search terms initially included pain rating scales, pain measurement, Visual Analogue Scale, VAS, Verbal Rating Scale, VRS, Numerical/numeric Rating Scale, NRS. The reference lists of retrieved articles were used to generate more papers and search terms. Only English Language papers were examined. Conclusions., All three pain-rating scales are valid, reliable and appropriate for use in clinical practice, although the Visual Analogue Scale has more practical difficulties than the Verbal Rating Scale or the Numerical Rating Scale. For general purposes the Numerical Rating Scale has good sensitivity and generates data that can be statistically analysed for audit purposes. Patients who seek a sensitive pain-rating scale would probably choose this one. For simplicity patients prefer the Verbal Rating Scale, but it lacks sensitivity and the data it produces can be misunderstood. Relevance to clinical practice., In order to use pain-rating scales well clinicians need to appreciate the potential for error within the tools, and the potential they have to provide the required information. Interpretation of the data from a pain-rating scale is not as straightforward as it might first appear. [source] Policing a complex community; political influence on policing and its impact on local and central accountabilityJOURNAL OF COMMUNITY & APPLIED SOCIAL PSYCHOLOGY, Issue 3 2005Robin Fletcher Abstract During the 1970s a series of events irrevocably changed the way in which policing was carried out in England and Wales. This paper describes how the police became politicized as it enforced government policies that resulted in violent police/public confrontation. It then explores how the Metropolitan Police Service began a process of re-engagement with the highly complex society of London, by community-focused policing models. The theoretical and practical difficulties of community policing are discussed in relation to legislation that required greater community involvement in policing. A theme of accountability is generated throughout the paper showing how political extremism challenged a bi-partite system of police governance, unique to the Metropolitan Police in the context of the UK, by demanding local accountability. This resulted in conflicting legislation that promotes both localized and centralized forms of accountability. The paper concludes with a speculative theory of how policing may develop in London as a department of a local government. Copyright © 2005 John Wiley & Sons, Ltd. [source] A MULTINOMIAL APPROXIMATION FOR AMERICAN OPTION PRICES IN LÉVY PROCESS MODELSMATHEMATICAL FINANCE, Issue 4 2006Ross A. Maller This paper gives a tree-based method for pricing American options in models where the stock price follows a general exponential Lévy process. A multinomial model for approximating the stock price process, which can be viewed as generalizing the binomial model of Cox, Ross, and Rubinstein (1979) for geometric Brownian motion, is developed. Under mild conditions, it is proved that the stock price process and the prices of American-type options on the stock, calculated from the multinomial model, converge to the corresponding prices under the continuous time Lévy process model. Explicit illustrations are given for the variance gamma model and the normal inverse Gaussian process when the option is an American put, but the procedure is applicable to a much wider class of derivatives including some path-dependent options. Our approach overcomes some practical difficulties that have previously been encountered when the Lévy process has infinite activity. [source] The ,ghosts' that pester studies on learning in mosquitoes: guidelines to chase them offMEDICAL AND VETERINARY ENTOMOLOGY, Issue 2 2006W. J. ALONSO Abstract The identification of memory and learning in medically important mosquito species has been of epidemiological interest mainly because of the implications of learning on the pattern of contact between vectors and hosts. Empirical results either showing or suggesting the existence of cognitive abilities in mosquitoes have been reported in a number of experimental studies, mainly based on the observation of individual fidelity towards subsets of specific resources, such as hosts, resting sites or breeding sites. A closer inspection of the design of these experiments shows that, with the exception of recent studies providing stronger evidence of learning in the genus Culex (Diptera: Culicidae), methodological shortcomings still hinder the possibility of eliminating alternative interpretations for these findings, in some cases because the experiments were not specifically designed to identify the phenomenon, but mostly because of a lack of appropriate controls or replication. By highlighting these limitations, while acknowledging the practical difficulties that are inherent to the field, we aim to help expel from future research the ,ghosts' that still preclude the achievement of more definite conclusions about the prevalence of memory and learning in this group of insects. [source] Intraperitoneal Insemination in Mammals: A ReviewREPRODUCTION IN DOMESTIC ANIMALS, Issue 2 2002JL Yaniz Contents This review focuses on factors associated with the development of intraperitoneal insemination in mammals. Findings to date indicate that fertility improves as the sperm cell concentration rises, but that the optimal sperm number differs in each species. Sperm washing before intraperitoneal insemination favours fertility. Peritoneal fluid shows a variable effect on spermatozoa, depending on the hormonal status of the female. The optimal time for insemination appears to be just prior to ovulation. The technique may be performed either through the abdominal or the vaginal wall. Verification of sperm deposition in the proximity of the ovaries improves fertility rates. Although associated with some risk of infection and an immune reaction against spermatozoa, the intraperitoneal technique rarely gives rise to severe anaphylactic shock, peritonitis, adhesion formation and the production of anti-sperm antibodies and these complications may be prevented by adequate sperm pretreatment and antibiotic therapy. The success of intraperitoneal insemination in humans, with results comparable with those of intrauterine insemination in the treatment of infertility, suggest the potential use of this technique in domestic mammals, especially in those in which intrauterine insemination poses practical difficulties. Some of the methods applied in human intraperitoneal insemination, such as confirming the position of the needle in the peritoneal cavity, and sperm pre-treatments might also improve results in domestic species. Conversely, the use of the animal model should help to develop some aspects of this technique in humans. [source] Measuring the Impact of Crime Reduction Interventions Involving Sports Activities for Young PeopleTHE HOWARD JOURNAL OF CRIMINAL JUSTICE, Issue 3 2004Geoff Nichols It draws on the authors' experience of sports-related programmes. Interventions are categorised using a combination of Brantingham and Faust's (1976) categorisation of programmes as primary, secondary, or tertiary prevention and the mechanism by which the intervention is likely to work (Pawson and Tilley 1997). This shows that the impact of some types of intervention is not only inherently more difficult to measure, but also demands far more resources to do so. This applies particularly to interventions such as the Youth Justice Board supported summer Splash programmes, which involve casual participation, and target geographical areas rather than individuals. The relationship of the categorisation to the technical and practical difficulties of measuring impact shows that the ideal of evidence-led policy is not easy to achieve, however, using this categorisation, the article makes some suggestions for evaluation methods, based on experience. The article also shows that in some cases the resources required to produce the evidence exceeds those available to many programmes. The implications of this are considered. [source] An analysis of the skin care patient mix attending a primary care-based nurse-led NHS Walk-in CentreBRITISH JOURNAL OF DERMATOLOGY, Issue 5 2005S.J. Ersser Summary Background, NHS Walk-in Centres (WiCs) are a new and expanding point of nurse-led primary care access for patients requiring skin care. Little is known about the dermatology case profile of such patients. Objectives, To investigate the skin care patient mix attending a WiC and the feasibility and usefulness of retrieving data from the NHS Clinical Assessment System (CAS), as used by NHS Direct. Methods, Patients over 2 years of age presenting to a WiC in southern England with a nurse-assessed skin condition were recruited over a 12-week period (n = 233). A data set was extracted from CAS and analysed using Excel. Results, Of the total 31 591 patients attending the WiC in the first 2 years, 21% had a skin-related problem. During the 12-week study period, 88 of 233 eligible patients (38%) consented to participate. The typical patient profile was of female patients, 17,35 years (27%) attending during the week before 9 a.m. (35%) or after 5 p.m. (27%) from the locality (72%). CAS employs generic algorithms to specify clinical problems (e.g. rash) rather than medical diagnoses. Most patients presented with a rash (89%). No physical treatment was required in 77% of patients, although this was advised for 46%; 49% were advised to seek help but not return to the WiC; 16% were recommended to contact their general practitioner. There were practical difficulties accessing data from CAS software for research due to research governance requirements. Conclusions, A significant number of patients with dermatological conditions could be seeking primary care through new NHS WiCs. Detailed dermatological appraisal of the patient mix is difficult due to the system of clinical categorization. There is scope to investigate further the nature of dermatological need and the patient education given. CAS is a cumbersome data extraction tool for research. [source] ALTERNATIVE CURRICULUM: The integration of an alternative curriculum: Skill ForceBRITISH JOURNAL OF SPECIAL EDUCATION, Issue 3 2009Lynne Rogers The introduction of alternative curricula in the UK for students in the secondary phase is one of a number of strategies designed to improve attendance at school, reduce exclusion and improve attainment. Skill Force is a charitable youth initiative that offers 14- to 16-year-old students a key skills based vocational alternative to the traditional curriculum. In this article, Lynne Rogers, Susan Hallam and Jacquelene Shaw of the Institute of Education, University of London, and Jasmine Rhamie of the University of Southampton set out to explore the views of Skill Force instructors and team leaders, school staff and Skill Force Regional Directors. These participants perceived the critical factors in the successful integration of Skill Force to be: effective introduction of the programme to pupils and parents; careful selection of students; clear introduction of the programme to staff; integrated discipline policies; strong support from senior management; good communication; and a willingness to resolve practical difficulties. [source] | |||||||||||||