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AJUR Volume 13 Issue 3 (August 2016)
Links to individual manuscripts, abstracts and keywords are provided in the section below:
Xavier Shiu & J. Conceicao
ABSTRACT The effects of electronegativity on the bonding between boron and second row elements are studied in this paper. Calculations using Density Functional Theory (DFT), Moller-Plesset Theory (MP2) and Natural Bonding Orbital (NBO) analysis were performed on BF3, B(OH)3 and B(NH2)3 and the localized bonding properties of these molecules were elucidated. All of these molecules showed the absence of pi-bonding and did not obey the octet rule. With decreasing electronegativity of the terminal atoms, F, O and N in BF3, B(OH)3, B(NH2)3 there is increasing the propensity of electron donation from these terminal atoms to the empty p-orbital of the central boron. Within the BH2−F, BH2−OH and BH2−NH2 series, the amino-borane showed the largest change in relative bond length and angle across this set. Furthermore, the borate anion, −O−B(OH) 2 was subjected to identical analysis and pi-bond formation was observed. Our results show that a good match orbital energies between the donor and acceptor orbitals are important for pi-bond formation.
KEYWORDS Electronegativity; Boron Trifluoride; Boric Acid; Triaminoborane; Borate Anion; Octet Rule; Density Functional Theory; Natural Bonding Orbital; Pi-Bond; Double Bond
ABSTRACT When people conceptualize abstract ideas, different perspectives can help them to make connections and develop their reasoning. In this study, three third grade students who engaged in a body-based angle task, using the Kinect for Windows, were analyzed. Descriptions of their interviews are presented, including a detailed analysis of their patterns of perspective-taking and factors that might have been conducive to their learning. It was observed that students typically adopted a body-based perspective before transitioning to other perspectives. Further, the design of the task and interviewer comments were important factors that prompted students to take different perspectives. The implications for perspectives and their impacts on learning are discussed.
KEYWORDS Embodied Cognition; Angles; Mathematics Education; Perspectives; Movement
Isaac Ahern & Sam Cook
ABSTRACT Killing vectors are generators of symmetries in a spacetime. This article defines certain generalizations of Killing vectors, called affine symmetry tensors, or simply affine tensors. While the affine vectors of the Minkowski spacetime are well known, and partial results for valence n = 2 have been discussed, affine tensors of valence n > 2 have never been exhibited. In this article, we discuss a computational algorithm to compute affine tensors in Minkowski spacetime, and discuss the results for affine tensors of valence 2 ≤ n ≤ 7. After comparison with analogous results concerning Killing tensors, we make several conjectures about the spaces of affine tensors in Minkowski spacetime.
KEYWORDS Affine Symmetry Tensors; Affine Vectors; Killing Tensors; Killing Vectors; Minkowski Spacetime; Dimension; Maple CAS; Lie Derivative; Generalized Killing Tensor
ABSTRACT Participants in this study were randomly assigned to one of three interval groups of either one, three, or five minutes. All participants were asked to estimate a group-assigned time interval and complete the state portion of the State Trait Anxiety Inventory (STAI). It was hypothesized that higher levels of state anxiety would cause participants to overestimate the passage of time. It was also hypothesized that shorter interval durations would be estimated more accurately than longer interval durations. Results of a t-test did not support the first hypothesis. Results of a linear trend analysis did support the second hypothesis (P < .05). These results indicate that state-anxiety does not cause the passage of time to be overestimated and that interval duration length affects how accurately time is estimated. Implications of this study are important to the understanding of human time-management ability and time estimation errors.
KEYWORDS Time estimation; Perception; State-anxiety; Attention; Working memory; Emotion
Shekh Mohammed Zahid & Prasanta Kumar Ray
ABSTRACT In the article ‘There are Truth and Beauty in Undergraduate Mathematics Research’, the author posted a problem regarding the closure properties of irrational and transcendental numbers under addition and multiplication. In this study, we investigate the problem using elementary mathematical methods and provide a new approach to the closure properties of irrational numbers. Further, we also study the closure properties of transcendental numbers.
KEYWORDS Irrational numbers; Transcendental numbers; Dedekind cuts; Algebraic numbers
Ryan D. Pappal, Ilse M. Espina & Zubaid Rafique
ABSTRACT While peaked T-waves have traditionally been associated with hyperkalemia cases, previous studies have called their reliability for hyperkalemia diagnosis into question. This study examined 89 ESRD patients totaling to 736 patient visits. Linear regressions and receiver operating characteristic (ROC) analyses were utilized to assess the reliability of peaked T-waves as a diagnostic criterion for hyperkalemia. Poor correlations between T/R ratio (leads V2-V4) and serum potassium were found, r = 0.23, 0.17, and 0.17, p < 0.001. R2 values ranged from 0.03 to 0.05. ROC analysis found poor sensitivity and specificity of T/R as a predictor of hyperkalemia (area under the curve: 0.61 – 0.66), and the T/R ≥ 0.75 threshold yielded a sensitivity of 0.83 with a specificity of 0.40 when predicting hyperkalemia (serum potassium > 5.5 mEq/L). We conclude that the peaked T-wave is a poor indicator for the early identification of hyperkalemia in ESRD patients presenting to the emergency department.
KEYWORDS Hyperkalemia; Electrocardiography; End-stage Renal Disease; Hemodialysis; Arrhythmias, Potassium; Sensitivity and Specificity; ROC Curve
Sara Stoudt, Pamela Badian-Pessot, Blanche Ngo Mahop, Erika Earley, Jordan Menter, Yadira Flores, Danielle Williams, Weijia Zhang, Liza Maharjan, Yixin Bao, Laura Rosenbauer, Van Nguyen, Veena Mendiratta & Nessy Tania
ABSTRACT A traffic generation model is a stochastic model of the data flow in a communication network. These models are useful during the development of telecommunication technologies and for analyzing the performance and capacity of various protocols,algorithms, and network topologies. We present here two modeling approaches for simulating internet traffic. In our models, we simulate the length and interarrival times of individual packets, the discrete unit of data transfer over the internet. Our first modeling approach is based on fitting data to known theoretical distributions. The second method utilizes empirical copulae and is completely data driven. Our models were based on internet traffic data generated by different individuals performing specific tasks (e.g., web browsing, video streaming, and online gaming). When combined, these models can be used to simulate internet traffic from multiple individuals performing typical tasks.
KEYWORDS Internet Traffic Simulation; Stochastic Models; Empirical Copula; Cumulative distribution function; Wireshark