MAL’TSEV CONDITIONS, LACK OF ABSORPTION, AND SOLVABILITY

Abstract. We provide a new characterization of several Mal’tsev conditions for locally finite varieties using hereditary term properties. We show a particular example how lack of absorption causes collapse in the Mal’tsev hierarchy, and point out a connection between solvability and lack of absorption. As a consequence, we provide a new and conceptually simple proof of a result of Hobby and McKenzie, saying that locally finite varieties with a Taylor term possess a term which is Mal’tsev on blocks of every solvable congruence in every finite algebra in the variety. 1

Optimal Labelling Problems, their Relaxation and Equivalent Transformations

Рассмотрена оптимизационная задача разметок, которая есть обобщением известной задачи о совместимости ограничений, и ее размытая модификация. Описаны два подхода к поиску оптимальной размытой разметки, их достоинства и недостатки. Предложены направления дальнейших исследований.The optimal labeling problem is considered, which is a generalization of the known Constraint Satisfaction Problem, and its relaxed simplification. Two approaches for the relaxed labeling optimization are described as well as their advantages and shortcomings. A direction of future researches is suggested.Розглянуто оптимізаційну задачу розміток, що узагальнює відому задачу про сумісність обмежень, та її розмиту модифікацію. Описано два підходи до пошуку оптимальної розмитої розмітки, їх переваги і недоліки. Наведено напрями подальших досліджень

Electrical Characterization of Intrinsic and Induced Deep Level Defects in Hexagonal SiC

Deep level defects in hexagonal SiC were studied using digital deep level transient spectroscopy (DLTS) methods over the temperature range of 100 to 800 deg K. New centers were found in bulk and epitaxial 6H-SiC with ionization energies between 0.38 to 1.3 eV, and levels from 0.2 to 0.856 eV were identified in 4H-SiC epitaxy. Direct correlation between inequivalent lattice sites was identified for energetic pairs associated with both vanadium and ion implanted Mg impurities. Nonradioative carrier capture mechanisms were studied and deep level trapping was found to proceed via lattice relaxation multi-phonon emission, indicating efficient electronic lattice coupling in the wide bandgap material. Junction transport characteristics of 4H-SiC p+/n bipolar devices were observed to be dominated by deep level defects in the epitaxial layers. Significant tunneling conduction in both forward and reverse bias conditions was directly correlated to deep level centers in these devices

The Meta-Problem for Conservative Mal'tsev Constraints

International audienceIn the algebraic approach to CSP (Constraint Satisfaction Problem), the complexity of constraint languages is studied using closure operations called poly-morphisms. Many of these operations are known to induce tractability of any language they preserve. We focus on the meta-problem: given a language Γ, decide if Γ has a polymorphism with nice properties. We design an algorithm that decides in polynomial-time if a constraint language has a conservative Mal'tsev poly-morphism, and outputs one if one exists. As a corollary we obtain that the class of conservative Mal'tsev constraints is uniformly tractable, and we conjecture that this result remains true in the non-conservative case