Correct determination of Staudinger's index (intrinsic viscosity) and of Huggins' constant

1965 ◽  
Vol 3 (2) ◽  
pp. 469-478 ◽  
Author(s):  
Fadel W. Ibrahim
1968 ◽  
Vol 12 (4) ◽  
pp. 971-972 ◽  
Author(s):  
O. F. Solomon ◽  
B. S. Gottesman

1958 ◽  
Vol 31 (4) ◽  
pp. 699-711
Author(s):  
I. Ya Poddubnyĭ ◽  
E. G. Ehrenburg

Abstract Branching in macromolecules of synthetic rubbers is one of their most important structural properties, exerting a pronounced influence on the physical behavior of these materials. The degree of branching evidently depends on the chemical nature of the free radicals or organometallic catalyst initiating the polymerization reaction. It also depends on the conditions of the reactions, particularly on the polymerization temperature, as the latter determines the relative rates of the propagation and branching reactions. The problem of developing a general quantitative method for the determination of branching in the molecules of high polymeric substances cannot yet be considered as solved. This problem appears to be very complicated and only a few experimental data are available. Therefore the development and application of methods with a sound physical background for the qualitative evaluation of branching have not lost their value. Most methods used for the determination of branching are based on the relations existing between the dimensions of molecular coils in solution and the degree of branching. Certain limitations of the methods commonly used for the determination of branching by values of Huggins' constant K′, the thermodynamic parameter μ, or the second virial coefficient arise from the fact that by such methods the above relation cannot be precisely accounted for. Therefore, in the present investigation, the degree of branching has been studied by viscosity measurements and also by determining the dynamo-optical properties of a polymer-fraction solution. The parameters found by this method, namely the dynamo-optical constant [Δn], obtained from the magnitude of the flow birefringence, the rotational friction coefficient, W, calculated from the orientation angles, as well as the intrinsic viscosity [η], all are determined by the dimensions of the molecular coils. By these methods, the investigation of the influence of the polymerization temperature on the branching for a number of synthetic rubbers obtained in the presence of different catalysts was carried out. Moreover, the intrinsic viscosity determinations made it possible, by the use of modern theories of polymer solutions, to estimate quantitatively branching in molecules of some synthetic rubbers.


Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2412
Author(s):  
Inés Ferrer ◽  
Ariadna Manresa ◽  
José Alberto Méndez ◽  
Marc Delgado-Aguilar ◽  
Maria Luisa Garcia-Romeu

Ultrasonic molding (USM) is a good candidate for studying the plasticization of polymer mixtures or other composite materials due to either the little amount of material needed for processing, low waste or the needed low pressure and residence time of the mold. Thus, the novelty of this research is the capability of USM technology to process PLA/PCL blends and their corresponding neat materials, encompassing all the production stages, from raw material to the final specimen. The major findings of the work revealed that the thermal properties of the blends were not affected by the USM process, although the crystallinity degree experienced variations, decreasing for PLA and increasing for PCL, which was attributed to the crystallization rate of each polymer, the high process speed, the short cooling time and the small particle size. The employed ultrasonic energy increased the molecular weight with low variations through the specimen. However, the degradation results aligned with the expected trend of these material blends. Moreover, this study also showed the effect pellet shape and dimensions have over the process parameters, as well as the effect of the blend composition. It can be concluded that USM is a technology suitable to successfully process PLA/PCL blends with the correct determination of process parameter windows.


Author(s):  
Robert Skov ◽  
David R Lonsway ◽  
Jesper Larsen ◽  
Anders Rhod Larsen ◽  
Jurgita Samulioniené ◽  
...  

Abstract Objectives Correct determination of penicillin susceptibility is pivotal for using penicillin in the treatment of Staphylococcus aureus infections. This study examines the performance of MIC determination, disc diffusion and a range of confirmatory tests for detection of penicillin susceptibility in S. aureus. Methods A total of 286 consecutive penicillin-susceptible S. aureus blood culture isolates as well as a challenge set of 62 MSSA isolates were investigated for the presence of the blaZ gene by PCR and subjected to penicillin-susceptibility testing using broth microdilution MIC determination, disc diffusion including reading of the zone edge, two nitrocefin tests and the cloverleaf test. Results Using PCR-based detection of blaZ as the gold standard, both broth microdilution MIC testing and disc diffusion testing resulted in a relatively low accuracy (82%–93%) with a sensitivity ranging from 49%–93%. Among the confirmatory tests, the cloverleaf test performed with 100% accuracy, while zone edge interpretation and nitrocefin-based tests increased the sensitivity of β-lactamase detection to 96%–98% and 82%–96% when using MIC determination or disc diffusion as primary test, respectively. Conclusions This investigation showed that reliable and accurate detection of β-lactamase production in S. aureus can be obtained by MIC determination or penicillin disc diffusion followed by interpretation of the zone edge as a confirmatory test for apparently penicillin-susceptible isolates. The more cumbersome cloverleaf test can also be used. Nitrocefin-based tests should not be used as the only test for confirmation of a presumptive β-lactamase-negative isolate.


Author(s):  
Darya Sergeevna Kareva ◽  
◽  
Sevinj Mahmud kyzy Ismailova ◽  
Elena Evgenievna Dozhdva ◽  
◽  
...  

The article substantiates the need to reform cameral tax control in Russia based on the experience of the United States. The necessity of introducing into the procedure of cameral control the mechanism of requesting all documents confirming the correct determination of tax obligations is determined. The aim of improving the process of desk audits of control is that the new procedure for conducting audits will reduce the likelihood of tax violations.


2018 ◽  
Vol 62 (2) ◽  
pp. 257-263
Author(s):  
Dariusz Teper ◽  
Piotr Semkiw ◽  
Piotr Skubida ◽  
Mikołaj Borański

Abstract The pollen analysis is currently the only reliable test to determine honey variety, but the results are sometimes burdened with error. The main reason for this is additional pollen that got into honey in a way other than with nectar collected by bees but through the centrifugation of combs containing bee bread cells. Studies were conducted in 2012 - 2013 on how different numbers of bee bread cells placed in the honey super influence lime honey pollen analysis. Bee bread pollen getting into honey during extraction in centrifugal-force honey extractors was proven to significantly influence the results of pollen analysis. In some extreme cases, it might skew the results so much that correct determination of honey variety by pollen analysis is no longer possible.


2010 ◽  
Vol 3 (1) ◽  
pp. 637-674
Author(s):  
A. Massling ◽  
N. Niedermaier ◽  
T. Hennig ◽  
E. Fors ◽  
E. Swietlicki ◽  
...  

Abstract. The performance of six custom-built Hygrocopicity-Tandem Differential Mobility Analyzers (H-TDMA) systems was investigated in the frame of an international calibration and intercomparison workshop held in Leipzig, February 2006. The goal of the workshop was to harmonize H-TDMA measurements and develop recommendations for atmospheric measurements and their data evaluation. The H-TDMA systems were compared in terms of the sizing of dry particles, relative humidity (RH) uncertainty and consistency in determination of number fractions of different hygroscopic particle groups. The experiments were performed in an air-conditioned laboratory using ammonium sulfate particles or an external mixture of ammonium sulfate and soot particles. The sizing of dry particles of the six H-TDMA systems was within 0.2 to 4.2% of the selected particle diameter depending on investigated size and individual system. With regard to RH uncertainties, the H-TDMA systems showed deviations up to 4.5% RH from the set point at RH=90% investigating the hygroscopic growth of ammonium sulfate particles and comparing the results with theory. The evaluation of number fractions investigating an externally mixed aerosol delivered differences up to +/−8% in calculated number fraction for one and the same aerosol type. We analysed the datasets of the different H-TDMAs with one fitting routine to investigate differences caused by the different data evaluation procedures. The results showed that the differences were reduced from +12/−13% to +8/−6%. We can conclude here that a common data evaluation procedure to determine the number fraction of externally mixed aerosols will improve the comparability of H-TDMA measurements. We finally recommend, to ensure a good calibration of all flow, temperature and RH sensors in the systems. It is most important to thermally insulate the RH control unit and the second DMA and to monitor those temperatures as accurately as 0.2 °C. For a correct determination of external mixtures, it is necessary to take into account size-dependent losses due to the diffusion in the pluming between the DMAs and in the aerosol humidification unit.


2009 ◽  
Vol 9 (3) ◽  
pp. 13569-13592 ◽  
Author(s):  
M. Penning de Vries ◽  
S. Beirle ◽  
T. Wagner

Abstract. The Absorbing Aerosol Index (AAI) is a useful tool for detecting aerosols that absorb UV radiation – especially in cases where other aerosol retrievals fail, such as over bright surfaces (e.g. desert) and in the presence of clouds. The AAI does not, however, consider contributions from "scattering" (hardly absorbing) aerosols and clouds: they cause negative AAI values and are usually discarded. In this paper, we demonstrate the use of the AAI's negative counterpart, the SCattering Index (SCI) to detect "scattering" aerosols. Maps of seasonally averaged SCI show significantly enhanced values in summer in Southeast USA and Southeast Asia, pointing to high production of "scattering" aerosols (presumably mainly sulphate aerosols and organic aerosols) in this season. The application of a cloud filter makes the presence of "scattering" aerosols even more clear. In a comparison of AOT from AERONET and our Aerosol Indices from SCIAMACHY, good agreement was found for two AERONET stations in Southeast USA, and two stations in Africa. This fact confirms the suitability of SCI as a tool to detect "scattering" aerosols. The combination of the UV Aerosol Indices AAI and SCI provides the unique possibility to characterise absorbing properties of aerosols from space. Accurate knowledge about aerosol absorption is crucial for the correct determination of the contribution of aerosols to the radiative budget.


1963 ◽  
Vol 7 (4) ◽  
pp. S30-S31 ◽  
Author(s):  
R. Z. Naar ◽  
H. H. Zabusky ◽  
R. F. Heitmiller

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