Discipline, Task and Reader Characteristics of Introductory Physics Students’ Graph Comprehension in Mathematics and Kinematics

Students’ comprehension of graphs may be affected by the characteristics of the discipline in which the graph is used, the type of the task, as well as the background of the students who are the readers or interpreters of the graph. This research study investigated these aspects of the graph comprehension from 152 first year undergraduate physics students by comparing their responses to the corresponding tasks in the mathematics and physics disciplines. The discipline characteristics were analysed for four task-related constructs, namely coordinates, representations, area and slope. Students’ responses to corresponding visual decoding and judgement tasks set in mathematics and kinematics contexts were statistically compared. The effects of the participants’ gender, year of school completion and study course were determined as reader characteristics. The results of the empirical study indicated that participants generally transferred their mathematics knowledge on coordinates and representation of straight-line graphs to the physics contexts, but not in the cases of parabolic and hyperbolic functions or area under graphs. Insufficient understanding of the slope concept contributed to weak performances on this construct in both mathematics and physics contexts. Discipline characteristics seem to play a vital role in students’ understanding, whilst reader characteristics had insignificant to medium effects on their responses

Investigating First Year University Physics Students’ Ability to Integrate Algebraic and Kinematics Graphs

Published ArticleAn important tool in the teaching and learning or study of physics is regarded as Mathematics, i.e., it will not be easy to study Physics without the basic knowledge and skills in Mathematics. Mathematics as a “language of science”, and is an expected requirement for students to study physics (Redish, 2005). He furthers argues that physicists blend conceptual physics with mathematical skills and use them to solve and interpret equations and graphs. For instance, in kinematics, different aspects from mathematics such as knowledge of functions and the solving of equations are combined with physics concepts. Many introductory physics students perform poorly on the use of mathematical skills and interpretations of graphs in physics. Two possible reasons may be as follows: i. Students lack the necessary mathematical skills needed to solve the physics problems. ii. Students do not know how to apply and relate their mathematical skills in the context of physics. These two possible reasons were investigated in a Masters Research project which probed first year university students’ interpretations of graphs in kinematics and in mathematics. This paper used the idea of Beichner’s standardized questionnaire on kinematic graphs. From this questionnaire, an equivalent questionnaire was devised in the context of Mathematical equations and graphs. The results of the investigation tend to indicate the deficiencies in the students’ mathematical conceptual knowledge as well as in the transfer of mathematical skills that they possess to solve kinematic equations and graphs. New teaching approaches in the introductory physics, a pre-requite for all STEM studies were thus recommended to enhance student performance in this subject

Mutual exclusion between related phages

The discovery of the breakdown of superinfecting phage needs to be supplemented by genetic tests to find out whether the phage whose nucleic acid is broken down is, indeed, unable to contribute genetic markers to the progeny. The present paper presents experiments of this kind, whose results leave no doubt that the breakdown of superinfecting phage is strictly paralleled by exclusion from the progeny of the genetic markers it contains. We are presenting also some experiments in which the stimulating phage alone or both the stimulating and the superinfecting phage have been inactivated by irradiation with ultraviolet light. These experiments serve to characterize functions which have remained unimpaired in ultraviolet treated phage and their relation to multiplicity reactivation of ultraviolet treated phage

Bacteriophage-mediated competition in Bordetella bacteria

Apparent competition between species is believed to be one of the principle driving forces that structure ecological communities, although the precise mecha nisms have yet to be characterized. Here we develop a model system that isolates phage-mediated interactions by neutralizing resource competition using two genetically identical Bordetella bronchiseptica strains that differ only in that one is the carrier of a phage and the other is susceptible to the phage. We observe and quantify the competitive advantage of the bacterial strain bearing the prophage in both invading and in resisting invasion by bacteria susceptible to the phage, and use our measurements to develop a mathematical model of phage-mediated competition. The model predicts, and experimental evidence confirms, that the competitive advantage conferred by the phage depends only on the relative phage pathology and is independent of other phage and host parameters. This work combines experimental and mathematical approaches to the study of phage-driven competition, and provides an experimentally tested framework for evaluation of the effects of pathogens/parasites on interspecific competition.Comment: 10pages, 8 figure

Chromosomal DNA deletion confers phage resistance to Pseudomonas aeruginosa.

Bacteria develop a broad range of phage resistance mechanisms, such as prevention of phage adsorption and CRISPR/Cas system, to survive phage predation. In this study, Pseudomonas aeruginosa PA1 strain was infected with lytic phage PaP1, and phage-resistant mutants were selected. A high percentage (~30%) of these mutants displayed red pigmentation phenotype (Red mutant). Through comparative genomic analysis, one Red mutant PA1r was found to have a 219.6 kb genomic fragment deletion, which contains two key genes hmgA and galU related to the observed phenotypes. Deletion of hmgA resulted in the accumulation of a red compound homogentisic acid; while A galU mutant is devoid of O-antigen, which is required for phage adsorption. Intriguingly, while the loss of galU conferred phage resistance, it significantly attenuated PA1r in a mouse infection experiment. Our study revealed a novel phage resistance mechanism via chromosomal DNA deletion in P. aeruginosa

Alternative mechanism for bacteriophage adsorption to the motile bacterium Caulobacter crescentus

2D and 3D cryo-electron microscopy, together with adsorption kinetics assays of ϕCb13 and ϕCbK phage-infected Caulobacter crescentus, provides insight into the mechanisms of infection. ϕCb13 and ϕCbK actively interact with the flagellum and subsequently attach to receptors on the cell pole. We present evidence that the first interaction of the phage with the bacterial flagellum takes place through a filament on the phage head. This contact with the flagellum facilitates concentration of phage particles around the receptor (i.e., the pilus portals) on the bacterial cell surface, thereby increasing the likelihood of infection. Phage head filaments have not been well characterized and their function is described here. Phage head filaments may systematically underlie the initial interactions of phages with their hosts in other systems and possibly represent a widespread mechanism of efficient phage propagation

The growth of bacteriophage and lysis of the host

1. A new strain of B. coli and of phage active against it is described, and the relation between phage growth and lysis has been studied. It has been found that the phage can lyse these bacteria in two distinct ways, which have been designated lysis from within and lysis from without. 2. Lysis from within is caused by infection of a bacterium by a single phage particle and multiplication of this particle up to a threshold value. The cell contents are then liberated into solution without deformation of the cell wall. 3. Lysis from without is caused by adsorption of phage above a threshold value. The cell contents are liberated by a distension and destruction of the cell wall. The adsorbed phage is not retrieved upon lysis. No new phage is formed. 4. The maximum yield of phage in a lysis from within is equal to the adsorption capacity. 5. Liberation of phage from a culture in which the bacteria have been singly infected proceeds at a constant rate, after the lapse of a minimum latent period, until all the infected bacteria are lysed. 6. If the bacteria are originally not highly in excess, this liberation is soon counterbalanced by multiple adsorption of the liberated phage to bacteria that are already infected. This leads to a reduction of the final yield

The growth of bacteriophage

1. An anti-Escherichia coli phage has been isolated and its behavior studied. 2. A plaque counting method for this phage is described, and shown to give a number of plaques which is proportional to the phage concentration. The number of plaques is shown to be independent of agar concentration, temperature of plate incubation, and concentration of the suspension of plating bacteria. 3. The efficiency of plating, i.e. the probability of plaque formation by a phage particle, depends somewhat on the culture of bacteria used for plating, and averages around 0.4. 4. Methods are described to avoid the inactivation of phage by substances in the fresh lysates. 5. The growth of phage can be divided into three periods: adsorption of the phage on the bacterium, growth upon or within the bacterium (latent period), and the release of the phage (burst). 6. The rate of adsorption of phage was found to be proportional to the concentration of phage and to the concentration of bacteria. The rate constant ka is 1.2 x 10–9 cm.8/min. at 15°C. and 1.9 x 10–9 cm.8/min. at 25°. 7. The average latent period varies with the temperature in the same way as the division period of the bacteria. 8. The latent period before a burst of individual infected bacteria varies under constant conditions between a minimal value and about twice this value. 9. The average latent period and the average burst size are neither increased nor decreased by a fourfold infection of the bacteria with phage. 10. The average burst size is independent of the temperature, and is about 60 phage particles per bacterium. 11. The individual bursts vary in size from a few particles to about 200. The same variability is found when the early bursts are measured separately, and when all the bursts are measured at a late time

Phage therapy: An alternative to antibiotics in the age of multi-drug resistance.

The practice of phage therapy, which uses bacterial viruses (phages) to treat bacterial infections, has been around for almost a century. The universal decline in the effectiveness of antibiotics has generated renewed interest in revisiting this practice. Conventionally, phage therapy relies on the use of naturally-occurring phages to infect and lyse bacteria at the site of infection. Biotechnological advances have further expanded the repertoire of potential phage therapeutics to include novel strategies using bioengineered phages and purified phage lytic proteins. Current research on the use of phages and their lytic proteins, specifically against multidrug-resistant bacterial infections, suggests phage therapy has the potential to be used as either an alternative or a supplement to antibiotic treatments. Antibacterial therapies, whether phage- or antibiotic-based, each have relative advantages and disadvantages; accordingly, many considerations must be taken into account when designing novel therapeutic approaches for preventing and treating bacterial infections. Although much is still unknown about the interactions between phage, bacteria, and human host, the time to take phage therapy seriously seems to be rapidly approaching

Molecular Characterisation of Bacteriophage K Towards Applications for the Biocontrol of Pathogenic Staphylococci

End of project reportThe aim of this work was to characterise staphylococcal bacteriophage (a bacterial virus) and to assess their potential as therapeutic agents against pathogenic strains of Staphylococcus aureus, particularly mastitis-causing strains. The project included the use of two newly isolated phage CS1 and DW2, and an existing polyvalent phage. The new phage were isolated from the farmyard and characterised by electron microscopy and restriction analysis. Both phage were shown to belong to the Siphoviridae family and were lytic for representatives of all three clonal groups of Irish mastitis-associated staphylococci. A cocktail of three phage (CS1, DW2 and K) at 108 (plaque forming units) PFU/ml was infused into cows teats in animal trials. The lack of an increase in somatic cell counts in milks indicated strongly that the phage did not irritate the animal. In addition, the most potent phage used in this study, phage K, was further studied by genome sequencing, which revealed a linear DNA genome of 127,395 base pairs, which encodes 118 putative ORFs (open reading frames)