The influence of network density and material critical thickness on the ultimate toughness of polymers

The deformation and toughness of amorphous polymers is discussed in terms of their mol. network structure and morphol. Both neat and (nonadhering) core-shell-rubber modified thermoplastics and thermosets are analyzed. The thermoplastic model system consists of miscible blends of polystyrene (I) and poly(2,6-dimethyl-1,4-phenylene ether) in different vol. ratios (consequently with different entanglement densities). The thermosetting system is based on epoxides with various degrees of crosslink d. Toughness is mainly detd. by the max. macroscopic strain at break since the yield stress of all polymers is approx. const. (50-80 MPa). The theor. max. draw ratio can be derived from the max. (entanglement or crosslink) network deformation. Brittle polymers, like I, suffer from catastrophic localization of strain and macroscopically show a strain to break far below this theor. max. However, below a certain dimension of the microstructure, expressed by the crit. matrix ligament thickness between added nonadhering core-shell rubbery particles (holes), the max. network extension can be reached on a macroscopic level. The crit. thickness depends on the mol. structure: with increasing network d. the value of the crit. ligament thickness increases from 0.05 mm for I (high mol. wt. between entanglements: Me = 19.1 kg mole-1) via 0.18 mm for the I blends contg. 40 wt. I (Me = 6.7 kg mole-1) to 0.3 mm for an epoxide having a mol. wt. between crosslinks, Mc, of approx. 4.4 kg mole-

The influence of network density and material critical thickness on the ultimate toughness of polymers

The deformation and toughness of amorphous polymers is discussed in terms of their mol. network structure and morphol. Both neat and (nonadhering) core-shell-rubber modified thermoplastics and thermosets are analyzed. The thermoplastic model system consists of miscible blends of polystyrene (I) and poly(2,6-dimethyl-1,4-phenylene ether) in different vol. ratios (consequently with different entanglement densities). The thermosetting system is based on epoxides with various degrees of crosslink d. Toughness is mainly detd. by the max. macroscopic strain at break since the yield stress of all polymers is approx. const. (50-80 MPa). The theor. max. draw ratio can be derived from the max. (entanglement or crosslink) network deformation. Brittle polymers, like I, suffer from catastrophic localization of strain and macroscopically show a strain to break far below this theor. max. However, below a certain dimension of the microstructure, expressed by the crit. matrix ligament thickness between added nonadhering core-shell rubbery particles (holes), the max. network extension can be reached on a macroscopic level. The crit. thickness depends on the mol. structure: with increasing network d. the value of the crit. ligament thickness increases from 0.05 mm for I (high mol. wt. between entanglements: Me = 19.1 kg mole-1) via 0.18 mm for the I blends contg. 40 wt. I (Me = 6.7 kg mole-1) to 0.3 mm for an epoxide having a mol. wt. between crosslinks, Mc, of approx. 4.4 kg mole-

Intellectual and motor development of young adults with congenital hypothyroidism diagnosed by neonatal screening

Contains fulltext : 35756.pdf (publisher's version ) (Open Access)CONTEXT: Long-term follow-up data on cognitive and motor functioning in adult patients with congenital hypothyroidism, diagnosed by neonatal screening, are scarce. Hence, it is still unclear whether the frequently reported cognitive and motor deficits observed during childhood persist in adulthood. OBJECTIVE: The objective of this study was to examine cognitive and motor functioning in young adults with congenital hypothyroidism, born in the first 2 yr after the introduction of the Dutch neonatal screening program. DESIGN/SETTING/PATIENTS: Seventy patients were tested (mean age, 21.5 yr); 49 of them were previously tested at 9.5 yr. The median age at the start of treatment was 28 d (range, 4-293 d). Congenital hypothyroidism was classified as severe, moderate, or mild, according to pretreatment T(4) concentrations. MAIN OUTCOME MEASUREMENT: The main outcome measurement was the influence of the severity of congenital hypothyroidism and age at which T(4) supplementation was started on cognitive and motor outcome. RESULTS: Patients, particularly those with severe congenital hypothyroidism, had significantly higher (i.e. worse) motor scores (total score, 7.8; ball skills, 2.0; balance, 4.1) compared with controls (total score, 3.2; ball skills, 0.7; balance, 1.1), and lower full-scale (95.8), verbal (96.4), and performance (95.6) intelligence quotient (IQ) scores than the normal population. No significant change in IQ from childhood to adulthood was found, and for the majority of patients, motor score classification remained the same. The severity of congenital hypothyroidism, but not the starting day of treatment, was correlated with IQ and motor scores. CONCLUSIONS: It is concluded that the severity of congenital hypothyroidism, but not the timing of treatment initiation, is an important factor determining long-term cognitive and motor outcome. Clearly, detrimental effects on developmental outcome in patients with congenital hypothyroidism persist over time

Soft Tuesday

soft aPancake Day. In English Hr. West and Ramea, Pancake Day is called Soft Tuesday. Soft Tuesday is the day before Ash Wednesday. . . .DNE-cit JH APR 1971Used I and SupUsed I and SupUsed Isoft cure; soft-bread; soft tack; soft tuesday [see 'Pancake Day', etc.

Radar remote sensing to support tropical forest management

This text describes an investigation into the potential of radar remote sensing for application to tropical forest management. The information content of various radar images is compared and assessed with regard to the information requirements of parties involved in tropical forest management at the global, national and local spatial levels. The study distinguishes between the use of radar remote sensing for application to forest resource assessment and forest resource monitoring. Both assessment and monitoring are essential components of procedures for sustainable forest management. The radar data studied are of tropical forest areas near the township of Mabura Hill in Guyana and the city of San José del Guaviare in Colombia. Mabura Hill is comprised of differing intact, primary forest types and forests that have been subjected to industrial selective logging. San José del Guaviare, on the other hand, is characterised by the presence of secondary forests and a variety of non-forest cover types. The available radar data set includes high resolution airborne radar images with differing wavelengths (i.e. X-, C-, L- and P-band) and polarizations, time-series images acquired by the first European remote sensing satellite ERS-1 and a collection of low altitude, nadir-looking, X-band scatterometer measurements.The study makes use of three fundamentally different information sources from the radar return signal: its strength or backscatter, polarization and phase, and spatial variability or texture. Results show that backscatter values computed from L- and P-band radar data and textural attributes computed from high resolution X- and C-band radar data make modest to good and complementary bases for region-based classification of tropical land cover at the level of primary forest types. Textural attributes and backscatter values computed per region from mono-temporal ERS-1 images make modest bases for classifying at the levels of primary forest, logged-over forest, secondary forest and non- forest and poor bases for classifying at the level of primary forest types. Roads are usually the most easily observable indicators of foregoing and/or forthcoming (selective) logging and other human activities in ERS-1 images. Detection of change in road networks by means of ERS-1 images would make a good first step in forest resource monitoring at the national spatial level, in particular. Textural attributes enable the ranking of forest types according to the degree of canopy roughness. Specific textural attributes also allow for quantification of canopy architectural properties. Despite differences in measurement scale, the canopy roughness of the land cover types studied was found to appear similarly in the texture of the available spaceborne and short wavelength airborne radar images