The binary network flow problem is logspace complete for P

AbstractIt is shown that the problem of whether the maximum flow in a given network exceeds a given natural number is logspace many-one complete for P if the edge capacities are presented in binary (even if the problem is restricted to acyclic graphs). This improves a result by Goldschlager et al. (1982) that this problem is logspace Turing complete for P

The Complexity of Computing the Size of an Interval

Given a p-order A over a universe of strings (i.e., a transitive, reflexive, antisymmetric relation such that if (x, y) is an element of A then |x| is polynomially bounded by |y|), an interval size function of A returns, for each string x in the universe, the number of strings in the interval between strings b(x) and t(x) (with respect to A), where b(x) and t(x) are functions that are polynomial-time computable in the length of x. By choosing sets of interval size functions based on feasibility requirements for their underlying p-orders, we obtain new characterizations of complexity classes. We prove that the set of all interval size functions whose underlying p-orders are polynomial-time decidable is exactly #P. We show that the interval size functions for orders with polynomial-time adjacency checks are closely related to the class FPSPACE(poly). Indeed, FPSPACE(poly) is exactly the class of all nonnegative functions that are an interval size function minus a polynomial-time computable function. We study two important functions in relation to interval size functions. The function #DIV maps each natural number n to the number of nontrivial divisors of n. We show that #DIV is an interval size function of a polynomial-time decidable partial p-order with polynomial-time adjacency checks. The function #MONSAT maps each monotone boolean formula F to the number of satisfying assignments of F. We show that #MONSAT is an interval size function of a polynomial-time decidable total p-order with polynomial-time adjacency checks. Finally, we explore the related notion of cluster computation.Comment: This revision fixes a problem in the proof of Theorem 9.

Dialectical Topoi

a) Topics and Objectives: Dialectical topoi constitute an essential component of Aristotelian logic and theory of argumentation (dialectics). These can be characterized as essential patterns of argumentation which allow us to found premises which are suited to the establishment of specific theses. Our research group concentrates on two themes: the first working focus consists of a precise investigation of the topos-based dialectical logic found in Aristotle. We are concerned in particular with the dialectical texts contained in the Organon (Topics, Rhetoric, Sophistical Refutations), and we are considering their relationship to the formal logic developed in the Prior Analytics. The second focus of our work is an investigation of the reception of Aristotelian dialectics in the Renaissance. Occurring in the 16th century was in intensive reception of the Aristotelian Topics, as suggested by numerous new translations and commentaries. We are concentrating on the relationship between veritas/scientia and opinio/probabilitas in the epistemology of the Renaissance. In particular, we are interested in the question of how the dialectics and rhetoric of the Renaissance were influenced by the form and genre of the dialogue, and in the role played in the Renaissance by the spatial dimension, which is contained both in Aristotle’s definition of the topos as the »place from which the attack comes«, as well as in Cicero’s definition of the locus as the »seat of the argument« (sedes argumentorum). b) Methods: Relevant passages from the texts of the Aristotelian Organon are analyzed and set into relationship with one another. Consulted in particular in interpreting these texts is the inventory of 20th century theories dealing with logic and argumentation; modern mereological and topological systems, for example, are used in reconstructing Aristotelian logic, albeit without overlooking the historical specificity of the problems that are bound up with these antique texts. c) State of the Discussion: The group has concluded that Aristotelian formal logic is dependent upon and was shaped in various ways by topos-based dialectical logic. Aristotelian predication theory, for example, plays a decisive role for various aspects of the Aristotelian syllogistic which is contained in the Prior Analytics. Beyond this, the group has demonstrated that interpretations of the Aristotelian Topics made an essential contribution to the emergence of a relativistic epistemology in the Renaissance. The status of opinio/probabilitas in the Renaissance, for example, was influenced by interpretations of the Aristotelian concept of endoxon

08271 Abstracts Collection -- Topological and Game-Theoretic Aspects of Infinite Computations

From June 29, 2008, to July 4, 2008, the Dagstuhl Seminar 08271 ``Topological and Game-Theoretic Aspects of Infinite Computations\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, many participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Characterizing small depth and small space classes by operators of higher types

Motivated by the question of how to define an analog of interactive proofs in the setting of logarithmic time- and space-bounded computation, we study complexity classes defined in terms of operators quantifying over oracles. We obtain new characterizations of NC1, L, NL, NP, and NSC (the nondeterministic version of SC). In some cases, we prove that our simulations are optimal (for instance, in bounding the number of queries to the oracle)

Sulfate-Reducing Microorganisms in Wetlands – Fameless Actors in Carbon Cycling and Climate Change

Freshwater wetlands are a major source of the greenhouse gas methane but at the same time can function as carbon sink. Their response to global warming and environmental pollution is one of the largest unknowns in the upcoming decades to centuries. In this review, we highlight the role of sulfate-reducing microorganisms (SRM) in the intertwined element cycles of wetlands. Although regarded primarily as methanogenic environments, biogeochemical studies have revealed a previously hidden sulfur cycle in wetlands that can sustain rapid renewal of the small standing pools of sulfate. Thus, dissimilatory sulfate reduction, which frequently occurs at rates comparable to marine surface sediments, can contribute up to 36–50% to anaerobic carbon mineralization in these ecosystems. Since sulfate reduction is thermodynamically favored relative to fermentative processes and methanogenesis, it effectively decreases gross methane production thereby mitigating the flux of methane to the atmosphere. However, very little is known about wetland SRM. Molecular analyses using dsrAB [encoding subunit A and B of the dissimilatory (bi)sulfite reductase] as marker genes demonstrated that members of novel phylogenetic lineages, which are unrelated to recognized SRM, dominate dsrAB richness and, if tested, are also abundant among the dsrAB-containing wetland microbiota. These discoveries point toward the existence of so far unknown SRM that are an important part of the autochthonous wetland microbiota. In addition to these numerically dominant microorganisms, a recent stable isotope probing study of SRM in a German peatland indicated that rare biosphere members might be highly active in situ and have a considerable stake in wetland sulfate reduction. The hidden sulfur cycle in wetlands and the fact that wetland SRM are not well represented by described SRM species explains their so far neglected role as important actors in carbon cycling and climate change

Electronic and Thermoelectric Properties of RuIn_{3-x}A_{x} (A = Sn, Zn)

Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)] transport measurements on the semiconducting intermetallic system RuIn3 and its substitution derivatives RuIn_{3-x}A_{x} (A = Sn, Zn). Higher values of the thermoelectric figure of merit (zT = 0.45) compared to the parent compound were achieved by chemical substitution. Here, using density functional theory based calculations, we report on the microscopic picture behind the measured phenomenon. We show in detail that the electronic structure of the substitution variants of the intermetallic system RuIn_{3-x}A_{x} (A = Sn, Zn) changes in a rigid-band like fashion. This behavior makes possible the fine tuning of the substitution concentration to take advantage of the sharp peak-like features in the density of states of the semiconducting parent compound. Trends in the transport properties calculated using the semi-classical Boltzmann transport equations within the constant scattering time approximation are in good agreement with the former experimental results for RuIn_{3-x}Sn_{x}. Based on the calculated thermopower for the p-doped systems, we reinvestigated the Zn-substituted derivative and obtained ZnO-free RuIn_{3-x}Zn_{x}. The new experimental results are consistent with the calculated trend in thermopower and yield large zT value of 0.8.Comment: PRB Accepted, 11 pages, 10 figure

Development and Characterization of Nonpeptidic Small Molecule Inhibitors of the XIAP/Caspase-3 Interaction

AbstractElevated expression of inhibitor of apoptosis protein (IAP) family members in various types of cancers is thought to provide a survival advantage to these cells. Thus, antiapoptotic functions of IAPs, and their potential as novel anticancer targets have attracted considerable interest. Among the IAPs, the X chromosome-linked inhibitor of apoptosis protein (XIAP) is regarded as the most potent suppressor of mammalian apoptosis through direct binding and inhibition of caspases. A high-throughput biochemical screen of a combinatorial chemical library led to the discovery of a novel nonpeptidic small molecule that has the ability to disrupt the XIAP/caspase-3 interaction. The activity of this nonpeptidic small molecule inhibitor of the XIAP/caspase-3 interaction has been characterized both in vitro and in cells. Molecules of this type can be used to conditionally inhibit the cellular function of XIAP and may provide insights into the development of therapeutic agents that act by modulating apoptotic pathways

EXOPEPTIDASE CATALYZED SITE-SPECIFIC BONDING OF SUPPORTS, LABELS AND BIOACTIVE AGENTS TO PROTEINS

An auxiliary substance such as a label, support, or bioactive agent is attached to a protein at a site that is remote from the active site of the protein by the use of exopeptidase and a nucleophile which is an amino acid, amino acid derivative, amine or alcohol. In one embodiment, the nucleophile is attached to the carboxy terminus of a protein by catalysis with exopeptidase to form an adduct and then the adduct or its combination with a linker arm is bound to the auxiliary substance. In another embodiment, the auxiliary substance or its combination with a linker arm is bound to the nucleophile to form an intermediate substance which is then coupled by catalysis with exopeptidase to the carboxy terminus of a protein