The Heat of Fusion of Ice

Students have learned that when heat energy is added to any substance the temperature of this substance increases and, conversely, when heat energy escapes from the substance the temperature decreases. Based upon this concept, the idea of the heat of fusion of ice does not make sense. The idea that each gram of ice a 0° C can absorb 80 calories of heat energy and become a gram of water with the temperature still 0°C does not seem logical. The student may accept the “if you say so approach, but some meaningful laboratory data will be more convincing. The usual laboratory procedure for measuring the heat of fusion involves starting with a measured quantity of water in a double walled calorimeter. Pieces of ice are dried with a paper towel and, hopefully before more of the ice can melt, are added to the water in the calorimeter. These pieces of ice are all owed to melt in the calorimeter. I have found that with this procedure the students become lost in the maze of measurements and calculations. When the investigation has been completed, they are not sure what they have discovered. Also, the results are usually so poor that the experiment becomes a discouraging experience. My physics students have obtained surprisingly good results with the ice calorimeter procedure for measuring the heat of fusion of ice. The results are usually within one or two calories per gram when compared with the accepted value. Also, the simplicity of the measurements and calculations make it possible for the students to understand what they are doing. The results are meaningful to the students

Developing Physics Concepts Through the Process of Variation

The present trend in the design of physics courses is to place emphasis on understanding rather than the rote memory of ideas and processes. The development of systematic approaches to direct thought patterns decreases the memory burden. The process of variation provides a universal thought pattern that can be applied in almost all phases of physics. This paper provides a brief description of some selected sample applications. It is hoped that these will illustrate the scope and the merit of this approach

A Noteworthy Physics Program: Is Individualization the Answer?

My career as a physics teacher began in 1938. This was the year that I was assigned to teach my first physics class. My undergraduate field was biology. I needed something to compensate for my very inadequate background in physics

Theoretical Intensity-Dependent Response of Nonlinear Periodic Structures

We have modeled the response of a nonlinear periodic structure by means of the Abelés 2×2 matrix method. Our structure differs from the usual rejection‐band filter designs, in that we have chosen the filter elements to be index matched in the absence of radiation, providing a rejection band that both grows and shifts as a function of incident intensity. The intensity output function of the model not only directly demonstrates optical bistability, but also limiting, switching, self‐pulsing, and chaos

Theoretical Intensity-Dependent Response of Nonlinear Periodic Structures

We have modeled the response of a nonlinear periodic structure by means of the Abelés 2×2 matrix method. Our structure differs from the usual rejection‐band filter designs, in that we have chosen the filter elements to be index matched in the absence of radiation, providing a rejection band that both grows and shifts as a function of incident intensity. The intensity output function of the model not only directly demonstrates optical bistability, but also limiting, switching, self‐pulsing, and chaos

Clinical profile of stroke in 900 patients with hypertrophic cardiomyopathy

AbstractObjectivesWe sought to assess the occurrence and clinical significance of stroke and peripheral arterial embolizations at non-central nervous system sites in a large, community-based cohort with hypertrophic cardiomyopathy (HCM).BackgroundSuch vascular events are insufficiently appreciated complications of HCM for which there is limited information on occurrence, clinical profile and determinants.MethodsWe assessed the clinical features of patients with stroke and other peripheral vascular events in a consecutive group of patients with HCM from four regional cohorts not subject to significant tertiary referral bias.ResultsOf the 900 patients, 51 (6%) patients experienced stroke or other vascular events over 7 ± 7 years, including 44 patients with stroke; 21 (41%) of these 51 patients died or were permanently disabled. The overall incidence was 0.8%/year and 1.9% for patients >60 years old. Age at first event ranged from 29 to 86 years (mean 61 ± 14 years). Most (n = 37; 72%) events occurred in those >50 years, although 14 (28%) younger patients (≤50 years) also had events. Multivariate analysis showed stroke and other peripheral vascular events to be independently associated with congestive symptoms and advanced age, as well as with atrial fibrillation (in 45 [88%] of 51 patients), at the initial evaluation. The cumulative incidence of these events among patients with atrial fibrillation was significantly higher in non-anticoagulated patients as compared with patients receiving warfarin (31% vs. 18%; p < 0.05).ConclusionsStroke and peripheral embolizations showed a 6% prevalence rate and an incidence of 0.8%/year in a large, unselected HCM group. These profound complications of HCM, which may lead to disability and death, were substantially more common in the elderly, occurred almost exclusively in patients with paroxysmal or chronic atrial fibrillation and appeared to be reduced in frequency by anticoagulation