Thermodynamic properties of two gaseous halogenated ethers from speed-of-sound measurements: Difluoromethoxy-difluoromethane and 2-difluoromethoxy-1,1,1-trifluoroethane

We present measurements of the speed of sound in gaseous difluoromethoxy-difluoromethane (CHF₂-O-CHF₂) and 2-difluoromethoxy-1,1,1-trifluoroethane (CF₃-CH₂-O-CHF₂). These measurements were performed in an all-metal apparatus between 255 and 384 K. We have obtained ideal-gas heat capacities and second acoustic virial coefficients from analysis of these measurements. Two methods of correlating the second acoustic virial coefficients, a square well model of the intermolecular interaction and a function due to Pitzer and Curl, are presented.     

Stress relaxation of an AISI 1080 steel

Stress relaxation is a simple test which offers means for evaluating the deformation dynamics of materials. The principal advantage of this method is that it scans a broad range of strain rates while straining the specimen by only a small amount. Therefore, it is possible to assume that the substructure of the material remains approximately constant during the test in order to obtain the stress as a function of the strain rate during this particular strain condition. The principal inconvenience of this test is the requirement of a highly stable testing machine—especially at very slow strain rates. In the present investigation, stress relaxation tests have been done at room temperature on an AISI 1080 steel fabricated by Companhia Belgo-Mineira and used for prestressed concrete. The tests were done using a servohydraulic machine in the strain control mode. The results indicate the existence of a mechanical equation of state.     

Coronary occlusion site as a determinant of the cardiac rhythm effects of atropine and vagotomy

We have previously demonstrated that atropine pretreatment increases the incidence of fatal ventricular arrhythmias induced by left anterior descending coronary artery (LAD) occlusion. The purpose of the present study was to determine whether the deleterious effect of atropine also applies to arrhythmias induced by right coronary artery (RCA) occlsusion. Occlusion of the RCA resulted in ventricular arrhythmias in all 20 animals studied, followed by ventricular fibrillation in three animals (15 per cent). Right coronary occlusion also resulted in bradycardia (-30.3 +/- 5.1 beats per minute) and hypotension (-23.1 +/- 4.9 mm. Hg). Pretreatment of 15 animals with atropine caused no significant increase in the incidence of ventricular fibrillation (i.e., 20 per cent). In addition, atropine pretreatment had no effect on the fall in heart rate and hypotension associated with RCA ligation. Sectioning the vagus nerves produced results similar to atropine pretreatment with the exception that a significant portion of the bradycardia was prevented. These results indicate that the increase in deaths after atropine observed in animals undergoing experimental LAD occlusion in not demonstrated with RCA occlusion. The results also indicate that the potential for deleterious effects of atropine in acute infarction might depend on the anatomic location of the involved myocardium.     

Experimental and numerical investigation of shock response in 3.5 and 2.5 in. form factor hard disk drives

The shock performance of the head/disk interface (HDI) of 3.5 and 2.5 in. hard disk drives (HDDs) is investigated. The displacement of the actuator arm, the suspension, and the disk due to linear shock loads is studied experimentally for both non-operating and operating states of the disk drive. A finite element model of the disk drive was developed to simulate the shock response. Numerical simulation results and experimental results are compared and presented.     

Nanoscale imaging of Bacillus thuringiensis flagella using atomic force microscopy

Because bacterial flagella play essential roles in various processes (motility, adhesion, host interactions, secretion), studying their expression in relation to function is an important challenge. Here, we use atomic force microscopy (AFM) to gain insight into the nanoscale surface properties of two wild-type and four mutant strains of Bacillus thuringiensis exhibiting various levels of flagellation. We show that, unlike AFM in liquid, AFM in air is a simple and reliable approach to observe the morphological details of the bacteria, and to quantify the density and dimensions of their flagella. We found that the amount of flagella expressed by the six strains, as observed at the nanoscale, correlates with their microscopic swarming motility. These observations provide novel information on flagella expression in gram-positive bacteria and demonstrate the power of AFM in genetic studies for the fast assessment of the phenotypic characteristics of bacterial strains altered in cell surface appendages.     

Effect of coronary angioplasty on precordial QT dispersion

Dispersion of the QT interval is a measure of inhomogeneity of ventricular repolarization. Because ischemia is associated with regional abnormalities of conduction and repolarization, we hypothesized that the surface electrocardiographic interval dispersion would increase in patients with symptomatic coronary artery disease in the absence of myocardial infarction and that successful revascularization would reduce QT interval dispersion. Thirty-seven consecutive patients with ischemia due to 1-vessel coronary artery disease without prior myocardial infarction who underwent percutaneous transluminal coronary angioplasty (PTCA) were evaluated. Standard 12-lead electrocardiograms were performed 24 hours before, 24 hours after, and late (>2 months) after PTCA. Precordial QT interval dispersions were determined from differences in the maximum and minimum corrected QT intervals. Mean QT interval dispersion before PTCA was 60 +/- 9 ms, immediately after PTCA 23 +/- 14 ms (p <0.001), and late after PTCA 29 +/- 18 ms (p <0.001 vs before PTCA). The shortest precordial QT interval increased immediately after PTCA (367 +/- 40 vs 391 +/- 39 ms; p <0.02) and then remained stable late after PTCA (376 +/- 36 ms, p = NS vs immediately after PTCA). Symptomatic recurrent ischemia in 8 patients with documented restenosis increased QT interval dispersion (56 +/- 15 ms [p <0.01] vs 25 +/- 14 ms immediately after PTCA), which decreased again after successful repeat PTCA (22 +/- 13 ms [p <0.01] vs before the second PTCA). QT interval dispersion decreases after successful coronary artery revascularization and increases with restenosis. Therefore, QT interval dispersion may be a marker of recurrent ischemia due to restenosis after PTCA.     

Progress Toward Redetermining the Boltzmann Constant with a Fixed-Path-Length Cylindrical Resonator

A single, fixed-path-length cylindrical-cavity resonator was used to measure c ₀ = (307.825 2 ± 0.001 2) m · s^?1, the zero-density limit of the speed of sound in pure argon at the temperature of the triple point of water. Three even and three odd longitudinal modes were used in this measurement. Based on the ratio M/?? ₀ = (23.968 644 ± 0.000 033) g · mol^?1, determined from an impurity and isotopic analysis of the argon used in this measurement and the measured c ₀, the value k _B = 1.380 650 6 × 10^?23J · K^?1 was obtained for the Boltzmann constant. This value of k _B has a relative uncertainty u _r(k _B) = 7.9 × 10^?6 and is fractionally, (0.12 ± 8.1) × 10^?6 larger than the value recommended by CODATA in 2006. (The uncertainty is one standard uncertainty.) Several, comparatively large imperfections of our prototype cavity affect the even longitudinal modes more than the odd modes. The models for these imperfections are approximate, but they suggest that an improved cavity will significantly reduce the uncertainty of c ₀.