Esters of hydroxystearic acids as primary low-temperature plasticizers for a vinyl chloride—Vinyl acetate copolymer

Summary Thirty-one acyloxy or aryloxy esters prepared from hydroxystearic acids have been evaluated as plasticizers for a vinyl chloride-vinyl acetate copolymer (95∶5). Many of them were found to be primary plasticizers, having outstanding low-temperature performance when employed at the 35% level. Formulations with these compounds compared quite favorably in tensile properties with those containing the di-2-ethylhexyl esters of phthalic, sebacic, azelaic, and adipic acids. Volatility losses were similar to those of the four di-2-ethylhexyl esters. The loss of plasticizer through migration was equal to or less than that from compositions containing the esters of sebacic, azelaic, and adipic acids but was greater than that of the phthalate ester. A mechanistic scheme of plasticizer-polymer interaction has been presented, proposing that the rate of diffusion of plasticizer through the polymer mass is a controlling factor in both good low-temperature performance and the resulting high migration losses. Methyl esters, some aromatic esters, and esters containing three or more polar centers have improved permanence but show a more rapid change in torsional modulus as the temperature is lowered during the determination of the Clash-Berg stiffening temperature. Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Viscosity index. I. Evaluation of selected copolymers incorporating n-octadecyl acrylate as viscosity index improvers

Compositionally and structurally varied copolymers all containing n-octadecyl acrylate were prepared and evaluated as viscosity index improvers in a common base oil under conditions of low shear. Systems evaluated over a range of copolymer and blend composition were: copolymers of n-octadecyl acrylate with, respectively, methyl methacrylate, 2-ethylhexyl acrylate, and n-dodecyl acrylate; and homopolymers of poly(n-octadecyl acrylate), prepared with a wide range of molecular weights. Properties were compared with those of blends of commercial methacrylate copolymers (acryloids) which had been freed of their entraining liquid. Mixtures of base oil with copolymers of n-octadecyl acrylate and methyl methacrylate, compared at fixed SAE viscosities, were the most efficient of all blends studied. They had the smallest rate of change of viscosity with temperature (as measured by their ASTM slopes), particularly in the composition region of incipient polymer precipitation at room temperature. Efficiency of certain of these composition was somewhat greater than that of the acryloids. A parameter that related concentration and weight-average molecular weight was used to correlate all of the data for ASTM slope and viscosity. Empirical relations developed by using this parameter enabled rheological data to be estimated that agree within 6% of experimental values for the case of thermodynamically good base oil solvents. These data demonstrated the relatively small contributions of copolymer structure to viscosity index improvement.     

Development of a Dew-Point Generator for Gases Other than Air and Nitrogen and Pressures up to 6?MPa

A new primary humidity standard is currently being developed at VSL that, in addition to ordinary operation with air and nitrogen at atmospheric pressure, can be operated also with special carrier gases such as natural gas and SF₆ and at pressures up to 6?MPa. In this paper, the design and construction of this new primary dew-point generator and the preliminary tests performed on the generator are reported. The results of the first efficiency tests, performed for the dew-point temperature range from ?50?°C to 20°C, for pressures up to 0.7MPa and for carrier gas flow rates up to 4L·?min^?1, showed satisfactory generator performance when used in the single-pass mode, i.e., with no recirculation of the carrier gas.     

Investigation of the Equivalence of National Dew-Point Temperature Realizations in the ?50?°C to +?20?°C Range

In the field of humidity quantities, the first CIPM key comparison, CCT-K6 is at its end. The corresponding European regional key comparison, EUROMET.T-K6, was completed in early 2008, about 4?years after the starting initial measurements in the project. In total, 24 NMIs from different countries took part in the comparison. This number includes 22 EURAMET countries, and Russia and South Africa. The comparison covered the dew-point temperature range from ?50?°C to +20?°C. It was carried out in three parallel loops, each with two chilled mirror hygrometers as transfer standards in each loop. The comparison scheme was designed to ensure high quality results with evenly spread workload for the participants. It is shown that the standard uncertainty due to the long-term instability was smaller than 0.008?°C in all loops. The standard uncertainties due to links between the loops were found to be smaller than 0.025?°C at ?50?°C and 0.010?°C elsewhere. Conclusions on the equivalence of the dew-point temperature standards are drawn on the basis of calculated bilateral degrees of equivalence and deviations from the EURAMET comparison reference values (ERV). Taking into account 16 different primary dew-point realizations and 8 secondary realizations, the results demonstrate the equivalence of a large number of laboratories at an uncertainty level that is better than achieved in other multilateral comparisons so far in the humidity field.     

Canonical bases for cyclotomic fields

It is shown how the use of a certain integral basis for cyclotomic fields enables one to perform the basic operations in their ring of integers efficiently. In particular, from the representation with respect to this basis, one obtains immediately the smallest possible cyclotomic field in which a given sum of roots of unity lies. This is of particular interest when computing with the ordinary representations of a finite group.1980 Mathematics subject classification (1985): 11R, 11Y     

Contribution of job control and other risk factors to social variations in coronary heart disease incidence

BACKGROUND: The first Whitehall Study showed an inverse social gradient in mortality from coronary heart disease (CHD) among British civil servants--namely, that there were higher rates in men of lower employment grade. About a quarter of this gradient could be attributed to coronary risk factors. We analysed 5-year CHD incidence rates from the Whitehall II study to assess the contribution to the social gradient of psychosocial work environment, social support, coronary risk factors, and physical height. METHODS: Data were collected in the first three phases of examination of men and women in the Whitehall II study. 7372 people were contacted on all three occasions. Mean length of follow-up was 5.3 years. Characteristics from the baseline, phase 1, questionnaire, and examination were related to newly reported CHD in people without CHD at baseline. Three self-reported CHD outcomes were examined: angina and chest pain from the Rose questionnaire, and doctor-diagnosed ischaemia. The contribution of different factors to the socioeconomic differences in incident CHD was assessed by adjustment of odds ratios. FINDINGS: Compared with men in the highest grade (administrators), men in the lowest grade (clerical and office-support staff) had an age-adjusted odds ratio of developing any new CHD of 1.50. The largest difference was for doctor-diagnosed ischaemia (odds ratio for the lowest compared with the highest grade 2.27). For women, the odds ratio in the lowest grade was 1.47 for any CHD. Of factors examined, the largest contribution to the socioeconomic gradient in CHD frequency was from low control at work. Height and standard coronary risk factors made smaller contributions. Adjustment for all these factors reduced the odds ratios for newly reported CHD in the lowest grade from 1.5 to 0.95 in men, and from 1.47 to 1.07 in women. INTERPRETATION: Much of the inverse social gradient in CHD incidence can be attributed to differences in psychosocial work environment. Additional contributions were made by coronary risk factors--mainly smoking--and from factors that act early in life, as represented by physical height.     

Frameless stereotactic lesion contour-guided surgery using a computer-navigated microscope

BACKGROUND: The Zeiss MKM System is a recently developed computerized operating microscope for image-guided neurosurgery. The clinical advantages, reliability, accuracy, and limitations of this technique were investigated. METHODS: Since February 1995, 78 consecutive frameless stereotactic image-guided procedures were performed in 73 patients (30 males, 43 females; mean age, 46.9 years; range, 16-77 years) for tumor surgery (50/64.1%), cavernoma removal (16/20.5%), and functional procedures (12/15.4%). Skin markers (74 cases) or bone markers (4 cases) and a standard imaging protocol (2-mm cranial computed tomography (CCT) in 59 cases/1.5-mm magnetic resonance imaging (MRI) in 19 cases) were used. RESULTS: The main advantages were pre-operative skin incision, craniotomy and corticotomy planning, and determination of lesion boundaries. Useful registration and system reliability were noted in 97% (76/78) of the procedures. A significant improvement in registration accuracy was observed over the test period from a mean of 4.8 mm (SD = 3.36; Cases 1-25) to a mean of 2.2 mm (SD = 0.86; Cases 26-78). This resulted in an improvement in application accuracy from <5 mm in 71% (Cases 1-25) to <2 mm in 95% (Cases 26-78) of cases, and the accuracy led to successful localization of the lesion in every case. Accuracy was reliable at the beginning of every procedure, but degraded to values >5 mm by the end of the procedure in 29% (22/78) of cases. MRI cases achieved higher application accuracy values (2.1 mm mean) than CT cases (3.7 mm mean). CONCLUSIONS: The system offers a reliable alternative to frame-assisted stereotactic craniotomies in lesion targeting, but would need an intraoperative image update for resection guidance.     

Predictive value of HemoCue capillary whole blood glucose measurements in pregnancy

OBJECTIVE: We determined the ability of capillary whole blood glucose concentrations to predict venous plasma and whole blood glucose levels. METHODS: During a standard oral glucose tolerance test in 29 pregnant women, paired capillary and venous blood samples were collected for analysis of glucose concentrations by the HemoCue photometer and by central laboratory methods. RESULTS: Glucose concentrations determined serially in a single blood sample by the HemoCue method were highly reproducible, with a coefficient of variation of 2.3%. However, glucose levels in blood from two different fingersticks from the same patient varied on average by 3 mg/dL, with a maximum difference of 14 mg/dL. Although capillary whole blood glucose results obtained by the HemoCue method correlated well with venous plasma or whole blood glucose measurements (r = 0.98 and r = 0.97, respectively) over the range investigated (60-250 mg/dL), individual capillary whole blood glucose measurements were only a fair predictor of venous values, with 95% of measured venous levels within +/- 26 mg/dL and +/- 20 mg/dL for concentrations predicted for plasma and whole blood, respectively. CONCLUSION: Sampling factors rather than measurement accuracy limit the ability of capillary whole blood glucose measurements to predict venous concentrations.