Weight, height, skinfold thicknesses, circumference measurements, and 72-hour food records were collected from pregnant women (N=51) at four-week intervals between the 12th and 40th weeks of gestation. Subjects were divided Into two groups according to percent standard prepregnant weight for height: overweight > 110% (N=17) and normal weight < 110% (N=28). Changes In weight, skinfold thicknesses and circumference measurements were similar between the two groups during the third trimester (weeks 28 to 40 of gestation). Significant increases in weight (1.58 kg per four weeks) and waist circumference and significant decreases in calf and abdominal skinfold thicknesses are reported. When the second and third trimesters (weeks 12 to 40 of gestation) were considered mean weight gain was 1 .87 kg per four-week interval. Overweight gravidas demonstrated a significantly greater decrease in abdominal skinfold thickness than normal-weight gravidas. The patterns of change over the second and third trimesters were different between the two groups for abdominal, knee, and calf skinfold thickness, hips and thigh circumference, body fat, and percent body fat. Caloric and macronutrient consumption was similar between groups and did not change throughout the second the two and third trimesters. Maternal weight gain was significantly associated with infant birth weight in both groups. / M.S.

Massive nylon lends itself to many applications because of its outstanding toughness, abrasion-resistance, and chemical resistance. These properties make it a satisfactory bearing material, and in some applications it is superior to metallic bearings. However, the disadvantages of low melting point and low thermal conductivity prevent nylon from being used more extensively. A previous investigation of the effect on thermal conductivity of change in crystallinity brough about by rolling and annealing nylon 66 indicated that it exhibits anisotropy of conductivity and that its thermal conductivity depends on primary physical factors related to its molecular structure. The purpose of this investigation was to determine the relationships of anisotropy of thermal conductivity, bond strength, degree of crystallinity, molecular orientation, and the changes resulting from the rolling-annealing treatment of nylon 66. A survey was made of the literature on the thermal conductivity of nylon in particular and non-metallic solids in general, of anisotropy of thermal conductivity, of the internal structure of nylon, of the effect of physical treatment on the internal structure and physical properties of nylon, and on test methods. The experimental part of the work consisted of measuring the thermal conductivity of nylon along three directions of heat flux, and the changes in internal structure and thermal conductivity in the three directions of heat flux resulting from rolling and annealing treatment. The thermal conductivity of six samples of nylon 66 was determined. The first three samples were cut from a slab of cast nylon ¼ inch thick. The conductivity was measured in a direction perpendicular to the plane of the sample and to the greatest length of the slab, in the plane of the sample, but perpendicular to the greatest length of the slab, and in the plane and in the direction of the greatest length of the slab. The other three samples were prepared from a ¼-inch thick cast slab which had been cold-rolled to half the original thickness and then annealed for two hours at 240 °C. To determine the effect of physical treatment on the internal structure and thermal conductivity, the density and degree of crystallinity were determined and x-ray diffraction patterns of the samples were made. Standard laboratory procedures were used in all of the tests. The thermal conductivity was measured using the ASTM method Cl77-45, the guarded hot plate method. In this method two sheets of nylon five inches square were sandwiched between an electrical heater and two brass cooling blocks. The quantity of heat which flowed through the samples was measured by measuring the electric power input to the heater. The temperature drop across the samples was measured by means of thermocouples. The sample thickness and area were measured, and from these quantities the thermal conductivity was calculated. The density was determined by weighing one to six-gram samples in air and in water, according to the standard method. The degree of crystallinity was calculated from the density of dried samples by assuming a linear relationship between density and degree of crystallinity. This method of calculation was worked out by Hermans for cellulose and used by Snow for nylon. The results of this investigation showed that when nylon slabs were rolled and annealed, the degree of crystallinity was increased, confirming the conclusions of previous investigators. The thermal conductivity was affected mainly by an orientation of the molecule produced by rolling rather than by the change in degree of crystallinity. Because of a preferential orientation of the molecules in the direction of rolling, the nylon thermal conductivity became anisotropic. These results support Rehner’s hypothesis that the thermal conductivity of polymers is mainly dependent on the strength of the bonds in the molecular chain, and that thermal conduction in polymers is mainly molecular conduction, not lattice conduction. The following conclusions were reached from tests made on the nylon slabs. / Master of Science

The purpose of this investigation was to compare the frequencies of normal and abnormal findings from exercise electrocardiography (ECG) and post-exercise echocardiography (ECHO) studies in a series of hypertensive and normotensive individuals who underwent diagnostic testing. Data for the ECG and ECHO variables were obtained simultaneously in association with treadmill exercise studies. Eighty consecutive cases were included in this retrospective study. Records were excluded if patients had: history of myocardial infarction; valvular heart disease; ECG evidence of abnormal Q waves, left ventricular hypertrophy (LVH) with abnormal ST/T wave pattern, or left bundle branch block (LBBB); medications that would alter blood pressure responses or ECG interpretation; technically uninterpretable records; or failure to attain 85% of age-adjusted maximal heart rates in the exercise tests. Subjects were defined as hypertensive (HYP) if any one of the following criteria were met: 1) SBP ≥ 140 mmHg or DBP ≥ 90 mmHg; 2) current use of antihypertensive medications; or 3) history of hypertension. Normotensive subjects (NORM) were defined as absence of the above criteria. In each test, ECG data were taken at peak exercise, and ECHO data were taken immediately post-exercise (~ 45 sec). The ECG response was considered abnormal if the ST shifted ≥ 0.1 mV from baseline at J₆₀ while the ECHO response was considered abnormal when new or worsening of pre-existing wall motion abnormalities was observed. Chi square analysis demonstrated that high blood pressure status Significantly increased the frequency of clinically abnormal findings with ECHO (X²=9.15; p ≤ 0.01). This was not the case for exercise ECG (X²=2.12; p > 0.05). However, there waS no Significant difference in the frequency of normal findings when comparing the two testing methods for both subject groups. These results indicate that resting blood pressure status may influence the rate of occurrence of abnormal vs normal ECG and ECHO findings; these data warrant further evaluation studies with invasive criterion measures of CAD status. / Master of Science

Recently it has been concluded that the SiO₄ silicate tetrahedra in crystals behave as rigid bodies. This conclusion is based on analyses of the atomic displacement factors of Si and O atoms obtained from single crystal diffraction experiments wherein the amplitudes of atomic vibrations are ascribed to translational, librational and screw-correlated modes of motion for the entire SiO₄ group. If the displacement ellipsoids are considered to represent time averaged quadratic surfaces of equal configurational potential energy about the mean position of an atom, then an analysis of the these displacements should provide detailed information about the SiO₄ group and the crystal. The apparent SiO bond lengths recorded for silicates over a range of temperatures are typically either invariant or exhibit a contraction with increasing temperature. A rigid-body thermal analysis was completed for the tetrahedra in nine silicates whose structures have been determined over a range of temperatures from 15 K to 1250 K and whose tetrahedra seem to behave as rigid units. The coordinates provided by the analysis yield bond lengths and polyhedral volumes corrected for the librational motion of each silicate tetrahedron. The bond lengths and volumes estimated for tetrahedra with four bridging oxygens seem to increase with temperature at a faster rate than those with four nonbridging oxygen atoms. Those for tetrahedra with two or three nonbridging oxygen atoms tend to increase at an intermediate rate. An analysis of the rigid-body motion of coordinated polyhedra yields a simple but accurate expression for correcting bond lengths for thermal vibrations. Observed anisotropic displacement parameters for Si and O atoms indicate that the SiO₄ tetrahedra in quartz behave as rigid bodies. A configurational potential energy curve, constructed from the librational components of the rigid body motion of the tetrahedra, shows a double well for α quartz and a single well for β quartz when plotted as a function of the displacement of the O atom with temperature. The configurational energetics of α and β quartz are examined with a theoretical potential energy function based on parameters obtained from molecular orbital calculations. The calculations indicate that the temperature behavior of a quartz is governed by the energetics of the SiOSi angle, in contrast to β quartz which is governed by the energetics of the SiO bond. The mechanism of the α ⇌ β transition is examined in terms of the experimental and modeled configurational potential energy curves. Evidence for the proposal that π bonding is the driving mechanism for the transition is lacking. Structural and volume compressibility data for α-cristobalite were determined by single crystal X-ray diffraction methods for pressures up to ~1.6 GPa, where cristobalite undergoes a reversible phase transition. The bulk modulus was determined to be 11.5(7) GPa with a pressure derivative of 9(2). The SiOSi angle shows a greater decrease than observed for quartz and coesite while the SiO bond lengths and the OSiO angles remain essentially unchanged. The responses of V/V₀ and SiOSi angle to pressure for the silica polymorphs are compared and it is found that the percentage decrease in the volume is linearly correlated with the percentage decrease in the SiOSi angle, regardless of the framework structure type. A mathematical modeling of the energies of the structural changes that are induced by pressure suggests that the contribution to the total energy ascribed to Si0Si angle bending terms is the same in quartz and cristobalite. / Ph. D.

M.S.

M.S.