Hysteretic properties of a two dimensional array of small magnetic particles: a test-bed for the Preisach model

The magnetization process of a regular two-dimensional array of small, strongly uniaxial single domain magnetic garnet particles, groups of particles, and major loop properties of a "macroscopic" sample, has been investigated experimentally and simulated numerically. These particles correspond to the assumptions of a simple Preisach model. The switching mode is by rotation. Each particle has a square hysteresis loop, with no reversible or apparent reversible component. Requirements of wiping-out and congruency properties are satisfied. From measurements of the up- and down switching fields on individual particles, the major loop can be reconstructed, and it is shown to be in in excellent agreement with the measured one. The transition from individual to collective behavior is smooth and the properties of a system, consisting of 100 particles, correspond to the major loop behavior. The numerically simulated major hysteresis loops agree very well with the measured loops, the switching sequence and the magnetization curve for particle assembly was derived from the calculated interaction fields and found to be in a very good agreement with the measured values, demonstrating the reliability of numerical modeling. A new property, not included into the existing models, is the magnetization dependence of the standard deviation of the interaction field

A fast EM algorithm for fitting marked Markovian arrival processes with a new special structure

This paper presents an EM algorithm for fitting traces with Markovian arrival processes (MAPs). The proposed algorithm operates on a special subclass of MAPs. This special structure enables the efficient implementation of the EM algorithm; it is more orders of magnitudes faster than methods operating on the general MAP class while providing similar or better likelihood values. An other important feature of the algorithm is that it is able to fit multi-class traces with marked Markovian arrival processes as well. Several numerical examples demonstrate the efficiency of the procedure

Klímaváltozás és egy hitelintézet = Climate Change and a Credit Institution

A globális éghajlatváltozás korunk mindannyiunkat egyformán negatívan érintő jelensége. Az Európai Újjáépítési és Fejlesztési Bank fenntartható fejlődés mandátuma révén sokat tehet a működési területén lévő országok környezeti felzárkóztatásában. Ebbéli tevékenységét azonban sok bírálat éri, teljesítménye nem egyértelmű. A tanulmányban az intézmény – elsősorban energetikai, közlekedési, önkormányzati-infrastruktúra, ill. klímaügyi – beszámolóit és projektadatait tekintem át, majd ütköztetem az EBRD legtapasztaltabb felügyelője, a CEE Bankwatch Network kritikáival. Az elemzésből kiderül, hogy bár a Bank valóban számos, a fenntartható fejlődést támogató projektet finanszíroz, az összkép e téren ambivalens. A szervezet ugyanis még mindig szerepet vállal környezetromboló projektekben, a megújuló energia fogalmát túl tágan értelmezi, és klímacéljai sem egyértelműek. E kritikákat nem mellőzve, lehetséges magyarázatként a megörökölt energiapiaci körülmények, az energiabiztonság kérdése, a Bank arculatához kötődő óriásprojektek jellege, valamint a társadalom lassú alkalmazkodóképessége merülhet fel. A tanulmány az első magyarul megjelent írás, amely a Bank ez irányú tevékenységét összefoglalóan értékeli

The complexity of the equivalence and equation solvability problems over meta-Abelian groups

We provide polynomial time algorithms for deciding equation solvability and identity checking over groups that are semidirect products of two finite Abelian groups. Our main method is to reduce these problems to the sigma equation solvability and sigma equivalence problems over modules for commutative unital rings

Review of subsurface flow treatment wetland feasibility in Finland

Constructed wetlands are engineered systems for treating wastewater. They have normally been used only as secondary treatment systems. However, over the last five decades, they have started to be utilized more extensively, as problems with operation and maintenance are gradually being solved. In Finland, treatment wetland is still ignored as a way to replace expensive chemicals for wastewater treatment purposes. The wetland system is rejected partly because the biological and chemical processes are temperature dependent, and secondly, there are concerns about ice formation and its effect on hydraulic flow, hydrology and hydraulics. Thermal consequences for biologically or microbiologically mediated treatment processes are the main constraints. Constructed wetland systems in Finland have commonly failed because the temperature coefficient has not been designed carefully, and clogging by organic matter has occurred in the inlet of the pool. Therefore, energy and water balance calculations as well as thermal modeling are useful tools to prevent design, operation and maintenance failure. Studies of constructed wetlands have shown less sensitivity to temperature swings in full-scale experiments than laboratory-scale ones. The lab-scale results should not prevent a full-scale trial because biological living beings in the nature interact with and affect the environment in ways which cannot be predicted in laboratory-scale testing. The wetland treatment method relies on anaerobic and partly aerobic conditions, which are essential for the transformation of nutrients and organic pollution to take place. A common problem with treating wastewater with an SSF wetland system is clogging failure. Also, oxygen transfer is reduced significantly by the need to use an insulating mulch layer, compared with situations where a mulch layer is unnecessary. Nitrogen removal is low due to the lack of oxygen availability, but this can be increased by artificial aeration