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During elementary physics courses, many examples in mechanics are studied without considering air resistance effects. We can mention, for example, projectile motion and free fall, among many others. Only brief studies of such systems in classical mechanics courses consider linear air resistance (F[subscript drag] [is proportional to] v), which is the simplest model to account for the drag effect by modeling objects moving in viscous media with small velocities (more precisely, small Reynolds number). Quadratic air resistance (F[subscript drag] [is proportional to] v[superscript 2]), which applies for objects moving in resistive media with high velocities (high Reynolds number), is hardly mentioned, but it can be found in many papers. However, in nature air resistance plays a big role in the motion of bodies and so it must be included when studying any kind of phenomena related to mechanics.

In Nigeria, 151,700 children die every year from diarrhoea disease. The use of a valid and reliable tool for eliciting information on what mothers do at home to manage diarrhoea is critical for healthcare providers and researchers. The study aimed to develop and validate the Home Management of Diarrhoea Assessment Scale (HMDAS) using Rasch Analysis among mothers of underfives in Nigeria. The cross-sectional survey design was employed among 376 mothers in one selected local government area in each of the 6 geopolitical zones of Nigeria recruited using multi-stage sampling technique. Data were collected for 6 months and were subjected to descriptive statistics and Rasch analysis. The HMDAS was developed after in-depth literature review and 3 rounds of input from 5 expert reviewers. fit analysis revealed that 12 items were misfits and were expunged from the tool. The HMDAS was found to be unidimensional with Eigen value of less than 1. Item and person separation index of the HMDAS were 11.1917 and 2.0123 respectively. Item and the person reliability index of the HMDAS were 0.9121 and 0.0820. The HMDAS was concluded to be a reliable and valid tool for data collection. It was recommended that the HMDAS should be utilized in generating data that can be used for designing interventions aimed at stemming the tide of diarrhoea in Nigeria. [ABSTRACT FROM AUTHOR]

Discusses multimedia authoring software that uses hypertext and reviews the ways in which use of this technology may support improvements in assessment. Describes research with sixth graders in England that investigated how pupil-produced multimedia documents can reveal aspects of performance that traditional tests may not recognize. (Author/LRW)

A method for traceability to SI for ac voltage and current based on high performance digitizers is presented. In contrast to the existing thermal-based methods, the proposed method utilizes direct traceability to quantum-based waveforms via the use of Josephson voltage systems. This allows not only a simplification of the traceability chain and reduced measurement times but also offers the potential for analysis of the ac voltage and current waveform spectral content, a feature which is not possible using thermal methods. Scaling of current and voltage is achieved by the use of current shunts and resistive voltage dividers respectively. Target operating ranges are up to 1 A and 100 V with a frequency range up to 1 kHz for both. The corresponding target uncertainty for this traceability route is 1 ÎĽV Vâˆ'1 and 2 ÎĽA Aâˆ'1 up to frequencies of 1 kHz. The traceability chain is described and various components are characterized to validate their suitability for this task. It is demonstrated that these uncertainty targets can be met under certain conditions. The use of multi-tone calibration waveforms is investigated to further reduce measurement time. An uncertainty analysis method based on simulation using real component performance data is demonstrated. [ABSTRACT FROM AUTHOR]

Valid samples are essential to the proper description of reservoir fluids; if the samples are not representative, all measurements on them will be invalid. This paper discusses the principal challenges facing fluid sampling including gas condensate reservoirs, compositional gradients, water content of hydrocarbon fluids, asphaltene deposition, wax formation, oil base mud contamination, and reactive components. It also reports the major technological advances recently made in this field. It reviews developments in sampling techniques such as MDT-type tools, new DST sampling tools, coiled tubing sampling, and isokinetic techniques, and it highlights common limitations. The value of making proper use of existing technology is emphasized, both with traditional techniques and new developments, with reference to correct well conditioning, interpretation of field data, and especially to optimum handling of samples. The paper emphasizes the need for better exchange of sampling knowledge between organizations, and highlights the lack of up-to-date industry standards with respect to fluid sampling. A solution is proposed in the form of a joint industry project to identify and document best practices. Des échantillons valables sont essentiels pour bien caractériser les fluides de gisements. Si les échantillons ne sont pas représentatifs, toutes les mesures ultérieures seront entachées d'erreurs. Cet article discute les principaux défis en matière d'échantillonnage, en particulier les réservoirs de gaz à condensats, les gradients compositionnels, la teneur en eau des fluides hydrocarbonés, les dépôts d'asphaltènes, les dépôts de paraffines, la contamination par les boues à base d'huile, et les constituants réactifs. Il relate également les principaux progrès technologiques récemment réalisés dans ce domaine et passe en revue les développements des techniques d'échantillonnage telles que les outils de type MDT, les nouveaux outils d'échantillonnage DST, l'échantillonnage par coiled tubing, et les méthodes isocinétiques. Il met également l'accent sur leurs limites. On insiste sur l'importance d'un usage optimal de la technologie existante, par combinaison des techniques traditionnelles et des développements nouveaux, qu'il s'agisse du conditionnement correct du puits, de l'interprétation des données du champ, ou surtout d'une manipulation adéquate des échantillons. Cet article insiste aussi sur le besoin d'un meilleur échange d'informations sur l'échantillonnage entre organisations, et rappelle le manque de normes industrielles à jour en matière d'échantillonnage des fluides. Il est proposé de constituer un projet industriel pour identifier et documenter les procédures adéquates.

Summary: Background: Headcollars (halters, US) are one of the most commonly used pieces of equestrian 'tack'. Despite this, there appears to be minimal information on their use, or more importantly, risk factors for injury of horses/handlers. Objective: To explore headcollar use and safety in equestrians. Study design: Quantitative cross‐sectional survey. Methods: An online survey (19 questions) exploring headcollar use and safety was disseminated through equestrian social media. Frequency analysis and multivariable modelling identified how headcollar type was linked to use and injury risk. Results: Most respondents (88%; n = 4786) used headcollars multiple times daily but for short time periods (66%, n = 3388, <30 min). A horse being injured as a result of wearing a headcollar was reported by 1615 (31%) respondents with 15% of incidents also injuring a person. Fractures (horses) occurred in 134 incidents, and 167 equine fatalities were reported. Across all headcollar types, the odds of injury risk increased by 1.7 times (confidence intervals (CI): 1.07–2.41, P<0.02) using a headcollar when mucking out. During travelling, headcollar use reduced the odds of risk of injury by 0.7 times (CI: 0.43–0.98, P<0.04). The odds of injury risk reduced when using leather (Odds ratio (OR): 0.8, CI: 0.66–0.96, P<0.01) or synthetic (OR: 0.8, CI: 0.58–0.85, P<0.0001) safety headcollars compared with standard headcollars of the same material. Thematic analysis identified three key themes: (1) need for increased education: fit, safety features and basic horse handling, (2) 'safer' leather headcollars, and (3) increased safety focus required. Main limitations: Data were self‐reported and may be subject to memory recall errors; online surveys are subject to self‐selection bias. Conclusions: Increased user knowledge of risk factors for headcollar injury, combined with standardised guidance on how to correctly fit and use headcollars, would be beneficial to reduce injury risk. [ABSTRACT FROM AUTHOR]

The role of ethanol O-d in nullifying the deuterolysis may be demonstrated by determining that transesterification of methyl acetoacetate of the ethyl ester occurs as well as deuterium exchange of the five acetoacetate hydrogens. The significant acidity of the methylene protons in the acetoacetate group, the efficacy of base catalysis, the role of elevated temperature in increasing the reaction rate, and the nullification of the effect of interfering side reactions are illustrated.