University of Jyväskylä

About: University of Jyväskylä is a education organization based out in Jyvaskyla, Finland. It is known for research contribution in the topics: Population & Neutron. The organization has 8066 authors who have published 25168 publications receiving 725033 citations. The organization is also known as: Jyväskylän yliopisto & Kasvatusopillinen korkeakoulu.

Permeability and effective porosity of porous media

Abstract: The concept of permeability of porous media is discussed, and a modification of Kozeny's permeability equation to include the effect of effective porosity is introduced. An analytical expression for the specific surface area of a system constructed of randomly placed identical obstacles with unrestricted overlap is derived, and a lattice-gas cellular automaton method is then used to simulate the dependence on porosity of permeability, tortuosity, and effective porosity for a flow of Newtonian uncompressible fluid in this two-dimensional porous substance. The simulated permeabilities can well be explained by the concept of effective porosity, and the exact form of the specific surface area. The critical exponent of the permeability near the percolation threshold is also determined from the simulations.

Structural phase transitions on the nanoscale: The crucial pattern in the phase-change materials Ge 2 Sb 2 Te 5 and GeTe

Abstract: Phase-change materials are of immense importance for optical recording and computer memory, but the structure of the amorphous phases and the nature of the phase transition in the nanoscale bits pose continuing challenges. Massively parallel density functional simulations have been used to characterize the amorphous structure of the prototype materials ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ and GeTe. In both, there is long-ranged order among Te atoms and the crucial structural motif is a four-membered ring with alternating atoms of types $A$ (Ge and Sb) and $B$ (Te), an ``$ABAB$ square.'' The rapid amorphous-to-crystalline phase change is a reorientation of disordered $ABAB$ squares to form an ordered lattice. There are deviations from the ``$8\ensuremath{-}N$ rule'' for coordination numbers, with Te having near threefold coordination. Ge atoms are predominantly fourfold coordinated, but---contrary to recent speculation---tetrahedral coordination is found in only approximately one-third of the Ge atoms. The average coordination number of Sb atoms is 3.7, and the local environment of Ge and Sb is usually ``distorted octahedral'' with $AB$ separations from $3.2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ in the first coordination shell. The number of $A--A$ bonds is significantly greater in GeTe than in ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$. Vacancies (voids) in the disordered phases of these materials provide the necessary space for the phase transitions to take place. The vacancy concentration in ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ (11.8%) is greater than in GeTe (6.4%), which is consistent with the better phase-change performance of the former.

Knee and ankle joint stiffness in sprint running.

Abstract: KUITUNEN, S., P. V. KOMI, and H. KYROLAINEN. Knee and ankle joint stiffness in sprint running. Med. Sci. Sports Exerc., Vol. 34, No. 1, 2002, pp. 166–173.IntroductionStiffness has often been considered as a regulated property of the neuromuscular system. The purpose of this study was to examine the

Age of onset of drinking and the use of alcohol in adulthood: a follow‐up study from age 8–42 for females and males

Abstract: Aim To investigate longitudinally for both genders the relation between the age of onset of drinking and several indicators of alcohol use. Design and setting In the Finnish Jyvaskyla Longitudinal Study of Personality and Social Development, data have been collected by interviews, inventories, and questionnaires. Data on alcohol consumption was gathered at ages 14, 20, 27, 36 and 42 years; behavioural data at age 8. Participants A total of 155 women and 176 men; 90.4% of the original sample consisting of 12 complete school classes in 1968. Measurements The age of onset of drinking was determined based on participants’ responses that were closest to the actual age of onset of drinking. Four indicators of the adult use of alcohol were used: frequency of drinking, binge drinking, Cut-down, Annoyed, Guilt, Eye-opener (CAGE) and Malmo modified Michigan Alcoholism Screening Test (Mm-MAST). Socio-emotional behaviour at age 8 was assessed using teacher ratings and peer nominations. Findings Early onset of drinking was related to the four indicators of the use of alcohol in adulthood both in men and women. The level of adult alcohol use and alcohol problems was significantly higher in men. The risk for heavy drinking was highest in men and women if drinking was started at less than age 16 years. Socio-emotional behaviour and school success at age 8 did not predict the age of onset of drinking. Conclusions Delaying the initiation of drinking from early adolescence to late adolescence is an important goal for prevention efforts. No clear risk group for early initiators of drinking could be identified on the basis of preceding behaviour among 8-year-olds.