17 research outputs found
On the Degree of Crystallinity in Natural Rubber. I. An Improved Method to Determine the Degree of Crystallization in Rubber
No full textAbstract
There are indications that the degree of crystallization in high polymeric substances is of importance in studying mechanical properties. With regard to the crystallization of rubber, few measurements have been made, mainly by Field. The results, however, are in contradiction to estimates of an earlier date, and therefore the necessity was felt to have them checked. An x-ray method, in some respecta differing from that of Field, was developed, the results of which diverged considerably from the figures reported by Field. The present article deals with a description of the method.</jats:p
On the Degree of Crystallinity in Natural Rubber. II. The Orientation of Rubber Crystallites in Stretched Samples
No full textAbstract
In the foregoing article a method for determining the proportion of crystalline rubber in stretched samples has been described. A complication due to varying crystallite orientation in different samples appeared to interfere with the application. A simple relation is given between the degree of orientation and an empirical constant which makes possible a rapid determination of the degree of crystallization, regardless of the orientation in the sample under investigation.</jats:p
The Degree of Crystallinity in Natural Rubber. V. A Discussion of the X-Ray Results on Natural Rubber in Connection with the Work of Flory, Gee and Wildschut
No full textAbstract
A recent theory, developed by Flory, makes it possible to calculate the degree of crystallization from thermodynamical measurements if certain parameters are properly evaluated. Such evaluation is possible by combining Wildschut's thermodynamical measurements with the x-ray results presented in previous papers. Thus the average length of molecule chains between cross-linkages can be derived; it closely corresponds to the results of swelling measurements carried out by Gee. Other parameters are also evaluated in agreement with their physical meaning.</jats:p
The Degree of Crystallinity in Natural Rubber. IV. The Degree of Crystallization in Frozen Raw Rubber and Stretched Vulcanized Rubber
No full textAbstract
An improved x-ray technique has been worked out to determine the degree of crystallinity in natural rubber. Inaccuracies which sometimes occur in quantitative x-ray measurements were eliminated, and it has been shown that the amount of crystalline rubber, both in frozen samples of raw rubber and in stretched vulcanized rubber, could be determined fairly accurately. More experiments were carried out and the results are described. These results, which confirm the current views on the problem of crystallization, point to relatively low degress of crystallization, even in highly stretched rubber, and they agree with some other experimental evidence and with a recent theoretical investigation.</jats:p
X-Ray Investigation of the Calender Effect in Rubber Sheets
No full textAbstract
Rubber sheets were calendered with a slight and with a strong calender effect. The x-ray diagrams did not show any crystalline structure 2 days after calendering. Gradually x-ray reflections developed, the sheet with calender effect showing the reflections much quicker and stronger than the one with a slight calender effect.</jats:p
Crystallization of trans 1, 4 polyisoprene morphology and kinetics.
No full textPhDA detailed electron microscopic study of the morphology and
kinetics of crystallization of trans-1,4-polyisoprene with cis
isoprene units varying from Of to 19.8 has been carried out.
Two crystal structures of trans3., 4-polyisoprene (LIS and in p)
were generally observed.
In an unstrained film, lamellar single crystals which developed
into hedrites, sheaves and spherulites of both crystal modifications
were observed. The morphology attained was determined by the
growth rate and the nucleation density of the crystals. Electron
diffraction study suggests that the lamellar crystals have a
chain-folded configuration. In a strained film, a row nucleation
morphology was observed LIT and FIMP lamellar crystals were observed
to nucleate from the same central 'backbones'. The row nucleation
density of the lamellar crystals increases with strain. The growth
habits of the lamellar crystals in, both strained and unstrained
films were dependent on the film thinness, and on the proximity
and the orientation of the neighbouring crystals. Models for
the observed growth habits were discussed.
The lamellar thickness data agrees with the kinetic theory of
chain folding. The lamellar thickness of both crystal structures
increases with decreasing degree of supercooling. The fold surface
free energies estimated were 45.1 x 10-3 J/n2 and 60.1 x 10-3 J/m2
for the LIT and F ULF crystals of gotta percha respectively.
The growth kinetics data of the lamellar crystals determined
agrees with the existing theories of crystal growth. At the range
of temperature from 400 to 560, the HMF crystal has a faster growth
rate than the LMF crystallized at the same temperature. At the
same degree of supercooling, the LMF crystal has a faster
growth rate. The growth rates of both the LMF and HMF crystals
decrease as the cis content on a trans polymer chain increases.
With 66 cis units, the growth rate of the isomerized specimen
decreased to a value of 1/6 to 1/8 of that for gutta percha (0f
cis), whereas in cis-polyisoprene, the growth rate is retarded
by 100 times with the inclusion of trans isoprene unit.
This, difference in behaviour is discussed in terms of the possibility
of including non-crystallizable units in the crystal lattice.
The growth rate analysis showed the importance of determining
the equilibrium melting temperature and glass transition
temperature for each isomerized specimen to obtain meaningful
estimates o
'Medicamenteuze interventies bij drugverslaving'; een advies van de Gezondheidsraad
No full textAddiction is a relapsing brain disease with a tendency towards chronicity. Biological, psychological and socio-cultural factors play a role in the onset and course of this disease. The Health Council of the Netherlands has issued a report on pharmacotherapeutic interventions. The treatment of addiction should be regarded as a medical intervention. A growing number of effective pharmacotherapies are becoming available for the treatment of heroin addiction, although not all of those are available in the Netherlands. Currently, no effective pharmacotherapies are available for the treatment of cocaine addiction. In polydrug addicts, pharmacotherapeutic interventions should be directed at the various separate addictions. In the majority of cases pharmacotherapy is part of an integrated treatment approach in which supportive psychosocial interventions are also important. The long-term continuation of treatment is usually indicated. The Health Council recommends that addiction physicians be put in charge of the multidisciplinary treatment. Medical schools should pay attention to the practical aspects of the treatment and management of addicts. The organisation and workforce of addiction treatment services should comply with the demands that are placed upon healthcare services. Public information campaigns about addiction and the treatment options for addicts can contribute to the destigmatisation of this patient categor
Efficacy and safety of tenecteplase in combination with enoxaparin, abciximab, or unfractionated heparin: The ASSENT-3 randomised trial in acute myocardial infarction
No full textBackground: Current fibrinolytic therapies fail to achieve optimum reperfusion in many patients. Low-molecular-weight heparins and platelet glycoprotein IIb/IIIa inhibitors have shown the potential to improve pharmacological reperfusion therapy. We did a randomised, open-label trial to compare the efficacy and safety of tenecteplase plus enoxaparin or abciximab, with that of tenecteplase plus weight-adjusted unfractionated heparin in patients with acute myocardial infarction. Methods: 6095 patients with acute myocardial infarction of less than 6 h were randomly assigned one of three regimens: full-dose tenecteplase and enoxaparin for a maximum of 7 days (enoxaparin group; n=2040), half-dose tenecteplase with weight-adjusted low-dose unfractionated heparin and a 12-h infusion of abciximab (abciximab group; n=2017), or full-dose tenecteplase with weight-adjusted unfractionated heparin for 48 h (unfractionated heparin group; n=2038). The primary endpoints were the composites of 30-day mortality, in-hospital reinfarction, or in-hospital refractory ischaemia (efficacy endpoint), and the above endpoint plus in-hospital intracranial haemorrhage or in-hospital major bleeding complications (efficacy plus safety endpoint). Analysis was by intention to treat. Findings: There were significantly fewer efficacy endpoints in the enoxaparin and abciximab groups than in the unfractionated heparin group: 233/2037 (11.4%) versus 315/2038 (15.4%; relative risk 0.74 [95% CI 0.63-0.87], p=0.0002) for enoxaparin, and 223/2017 (11.1%) versus 315/2038 (15.4%; 0.72 [0.61-0.84], p<0.0001) for abciximab. The same was true for the efficacy plus safety endpoint: 280/2037 (13.7%) versus 347/2036 (17.0%; 0.81 [0.70-0.93], p=0.0037) for enoxaparin, and 287/2016 (14.2%) versus 347/2036 (17.0%; 0.84 [0.72-0.96], p=0.01416) for abciximab. Interpretation: The tenecteplase plus enoxaparin or abciximab regimens studied here reduce the frequency of ischaemic complications of an acute myocardial infarction. In light of its ease of administration, tenecteplase plus enoxaparin seems to be an attractive alternative reperfusion regimen that warrants further study
Dexmedetomidine versus propofol/opioid for sedation in TAVI: a propensity matched analysis of effects on perioperative gas exchange and haemodynamic support
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