A refined classification of single amplifier filters

It is shown that Single Amplifier Biquads (SAB's) may be grouped into two major categories, the Enhanced Negative Feedback (ENF) and the Enhanced Positive Feedback (EPF). These two major classes of circuit are related by the complementary transformation and hence exhibit identical sensitivity performance. In the extreme, the ENF class degenerates to the familiar Negative Feedback (NF) class while the EPF class reduces to the Positive Feedback (PF) case where the op amp is connected in a unity-gain configuration. Depending on the order of the RC feedback network, each class includes two subclasses with different sensitivity performance. The paper examines in detail the ‘enhanced feedback’ mechanism, and investigates the optimum design of the Deliyannis—Friend circuit and its complement the Sallen and Key positive feedback configuration.     

The use of touch in psychotherapy: Theoretical and ethical considerations.

Discusses the importance of touch in human communication, reviews the development of a taboo against touching among early psychoanalytic writers, and considers more recent arguments that counter this strict taboo against touching psychotherapy patients. Suggestions are outlined for appropriate uses of touch in psychotherapy, and the ethics of touch are discussed in the context of theoretical issues and ethical principles. The authors believe a rigid, rule-bound approach regarding touch in therapy is precluded by the complexities of this issue and by insufficient attention having been paid to linking theoretical arguments to ethical considerations. A 3-level approach of ethical, therapeutic, and decision-making guidelines in considering the use of touch is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do teacher standards for assigning grades affect student evaluations of instruction?

Conducted 2 experiments to determine the effects of teacher standards for assigning grades on student ratings of teachers and student achievement. 143 undergraduates participated in Exp 1, in which instructor expressiveness (high, low), lecture content (high, low), and grading standards (B, C+, C) were factorially manipulated. In Exp II with 278 undergraduates, student incentive (high, low), instructor expressiveness (high, low), and grading standards (B+, B, C+, C) were factorially manipulated. Standards failed to affect student achievement in either experiment. Significant effects of standards on ratings were found, but not consistently for all types of ratings, instructors, or differences in standards. The size of the differences are considered to be relatively unimportant when ratings are used to make gross distinctions between teachers. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Global information technology and global citizenship education

The Council for Education in World Citizenship has been working with Kingston University and the UK National Commission for UNESCO, taking advantage of global information technology developments in order to build new programmes for global citizenship education. The paper reports on practical experience, inviting new network partners. The IST-Africa 2007 conference provided an opportunity to build on these foundations, with initiatives in primary, secondary, further, adult and higher education, and continuing professional development for teachers.     

Improving Generalization with Active Learning

Active learning differs from learning from examples in that the learning algorithm assumes at least some control over what part of the input domain it receives information about. In some situations, active learning is provably more powerful than learning from examples alone, giving better generalization for a fixed number of training examples.In this article, we consider the problem of learning a binary concept in the absence of noise. We describe a formalism for active concept learning calledselective sampling and show how it may be approximately implemented by a neural network. In selective sampling, a learner receives distribution information from the environment and queries an oracle on parts of the domain it considers useful. We test our implementation, called anSG-network, on three domains and observe significant improvement in generalization.A preliminary version of this article appears as Cohn et al. (1990).     

Queen Sex Pheromone of the Slave-making Ant, Polyergus breviceps

Workers of the slave-making ant, Polyergus breviceps, raid nests of Formica ants and return with Formica pupae that mature into worker ants in the slave-makers’ colony. These Formica workers then tend the Polyergus brood, workers, and reproductives. During raids in the mating season, winged virgin Polyergus queens accompany the workers in the raiding columns. During the raid, the virgin queens release a pheromone that attracts males that quickly mate with the queens. We report the identification, synthesis, and bioassay of the sex attractant pheromone of the queens as an approximately 1:6 ratio of (R)-3-ethyl-4-methylpentan-1-ol and methyl 6-methylsalicylate. The ants produce exclusively the (R)-enantiomer of the alcohol, and the (S)-enantiomer has no biological activity, neither inhibiting nor increasing attraction to blends of methyl 6-methylsalicylate with the (R)-enantiomer.     

Concerted diurnal patterns in riverine nutrient concentrations and physical conditions

Several long-term sets of hourly nitrate concentration data were obtained through deployment of a nitrate sensor in an upper reach of the River Taw, a small moorland-fed river in the South West of the UK. Examination of the data obtained during periods of low flow and the absence of rainfall in the catchment revealed the presence of marked diurnal cycles, which were in concert and negatively correlated with diurnal cycles in water temperature. After verifying that these cycles were natural, an intensive 90-h field monitoring campaign was conducted, in which river water was sampled hourly and immediately analysed in the laboratory for molybdate-reactive phosphorus (P), nitrate, nitrite, ammonium, and pH. Coincident measurements of water temperature, river discharge and solar energy were also taken at, or close to, the site. All measurements revealed diurnal patterns and all patterns were concerted. The cycles of P, nitrate, nitrite, and discharge had two maxima and minima per 24 h, while the cycle of water temperature had one, with a maximum at 20.00 and a minimum at 08.00. The amplitudes of the cycles of P and nitrate were each about 30% of the mean values, while the amplitude of the nitrite cycle was as great as 80% of the mean value on occasions. Both biological and physical mechanisms for the cycling could operate through water temperature and/or incident radiation to account for the observed phenomenon, but there remains uncertainty of which is the more important. The observations have important implications for both the accuracy of pollution assessment in rivers and the physiological rhythms of riverine organisms.     

Impact of Nonuniform Fouling on Operating Temperatures in Heat Exchanger Networks

ABSTRACT

Investigations of fouling in heat exchangers are mainly focused on two factors: commercial impact due to energy losses, and environmental impact manifested through higher CO₂ emissions. The purpose of this paper is to introduce a third factor relating to safety in operations. This paper presents two case studies, one for a hydroprocessing unit with feed/effluent heat exchangers and another for preheat train exchangers installed upstream of the atmospheric furnace in a refinery crude unit. Due to a wide range of process temperatures examined in both case studies, the heat exchangers in the network are subject to various fouling mechanisms. As illustrated in the pictures of actual tube bundles, some of the exchangers within the network are heavily fouled, while the other exchangers operate in nearly clean conditions. Detailed simulations indicate that nonuniform fouling results in heat exchanger operating temperatures that are significantly higher than those predicted by conventional analyses using uniform fouling. Higher than anticipated process fluid temperatures may result in exceeding the threshold limits for certain corrosion mechanisms and/or significantly higher than expected rates of corrosion.