Long-range interactions in Sznajd consensus model

The traditional Sznajd model, as well as its Ochrombel simplification, for opinion spreading are modified to have a convincing strength proportional to a negative power of the spatial distance. We find the usual phase transition in the full Sznajd model, but not in the Ochrombel simplification. We also mix the two rules, which favours a phase transition.Comment: Not ye4t submittted, waiting for your comments; 6 page

Temperaturabhängige optische, elektrooptische und piezoelektrische Untersuchungen ausgewählter azentrischer Kristalle

Die Kenntnis der Temperaturabhängigkeit von Brechwerten in nichtlinearen optischen Kristallen spielt eine Schlüsselrolle für ihre Klassifizierung als NLO-Material. So kann beispielsweise bereits eine kleine Temperaturänderung deutliche Auswirkungen auf Richtungen verursachen, in denen phasenangepaßte nichtlineare optische Prozesse realisierbar sind. In dieser Arbeit sind zwei Meßmethoden, basierend auf einer Anordnung des Jamin-Interferometers und des rotierenden Analysators zur Bestimmung der temperaturabhängigen Brechwertänderung vorgestellt. Es sind die temperaturabhängigen Brechwerte der folgenden azentrischen Borate: Zn4[O(BO2)6] (PSG: 43m), Li2B4O7 (PSG: 4mm), beta-BaB2O4 (PSG: 3m), PbB4O7 (PSG: mm2), BiB3O6 (PSG: 2), Bi2ZnB2O7 (PSG: mm2), die z.T. wichtige NLO-Materialien darstellen, vermessen, vorgestellt und diskutiert. Im Gegensatz zu den anderen untersuchten Boraten kann bei Bismuttriborat, BiB3O6 bereits eine kleine Temperaturänderung, die Richtungen, in denen Phasenanpassung möglich ist, beeinflussen. Weiterhin wurde am Beispiel des Zink-Guanidiniumsulfat, einer in der PSG 42m kristallisierenden Substanz, welche bei Tc=180(2) K eine strukturelle Phasenumwandlung erfährt, die temperaturabhängige Brechwertänderung, der temperaturabhängige piezoelektrische und elektrooptische Effekt untersucht und daraus Schlüsse auf die Symmetrie der Tieftemperaturphase gewonnen. In einem weiteren Schritt dieser Arbeit sind die Raumtemperaturwerte der piezoelektrischen Konstanten der Natriumlithiumsulfat-Hexahydrat-Gruppe Na3Li(XO4)2 6H2O mit X=(Mo, Cr, S, Se) (PSG: 3m), des Lithiumsulfat-Monohydrat und der dazu isotypen Selenatverbindung Li2XO4 H2O mit X=(S, Se) (PSG: 2), des Bismuttriborates BiB3O6 sowie des Sarcosiniumtatrates C3H8NO2+C4H5O6- (PSG: 1) bestimmt und diskutiert worden. Zu diesem Zweck wurde eine weiterentwickelte dynamische Druckzelle aufgebaut. Wegen der beachtlichen Größe der piezoelektrischen und der SHG-Koeffizienten wurde der Frage nach der Größe der elektrooptischen Konstanten in BiB3O6 nachgegangen und eine Untersuchung mittels Kompensator-Methode in Kombination mit einer Faraday-Zelle vorgenommen. Somit sind bei BiB3O6 die experimentellen Daten bzgl. des piezoelektrischen und elektrooptischen Effektes bis auf die elastooptischen Konstanten bekannt, um einen direkten Vergleich mit den vorhandenen Modellen bzw. Theorien des elektrooptischen Effektes vorzunehmen

Untersuchungen zu Mechanismen der Stressantwort und des Kaliumtransportes in Corynebacterium glutamicum

Die Stressantwort von Corynebacterium glutamicum auf verschiedene abiotische Faktoren wurde physiologisch und biochemisch untersucht. Bei tiefen externen pH-Werten und unter hyperosmotischen Bedingungen ist Kalium für das optimale Wachstum von C. glutamicum essentiell. Bei niedrigen pH-Werten kommt es durch die endogene Produktion von H2O2 zu oxidativem Stress, und die Limitation der Aktivität der Cystathionin-β-Lyase führt zu einer Störung der Thiolhomöostase, was das Wachstum der Zellen einschränkt. Kalium ist unter sauren Bedingungen für die Stimulation der Atmungskettenaktivität essentiell. Unter hyperosmotischen Bedingungen wird Kalium in großen Mengen intern akkumuliert, wo es essentiell zum Pool der Osmolyte beiträgt. Kalium ist dabei für die induzierte osmoregulierte Expression der Gene betP und proP notwendig. Der kaliumspezifische Kanal CglK fungiert in C. glutamicum sowohl bei niedrigen pH-Werten, als auch bei Osmostress als Hauptaufnahmesystem für Kalium, während der putative sekundär aktive Kup-Transporter keine Funktion hat. Die mRNA von cglK wird in ein membranintegriertes CglK-Protein und zusätzlich in ein cytoplasmatisches KTN-Protein translatiert. Die Analyse der Funktion von CglK wurde in C. glutamicum- und E. coli-Zellen durchgeführt, wobei in Proteoliposomen und in E. coli-Sphäroplasten elektrophysiologische Untersuchungen möglich waren. Die C terminalen KTN-Domänen von CglK sind für dessen Schließung essentiell, während die separaten KTN-Proteine an der vollständigen Öffnung und möglicherweise an einer pH-Wert abhängigen Regulation des Kanals beteiligt sind. Die Kaliumaufnahme über den CglK-Kanal ist für C. glutamicum unter habitatähnlichen Bedingungen für das Wachstum und die Aminosäureproduktion ausreichend. Unter extremen Stressbedingungen in Verbindung mit einer Kaliumlimitation hat die heterologe Expression eines aktiven Kaliumtransporters einen positiven Effekt auf die Stressresistenz der C. glutamicum-Zellen

Consensus formation on a triad scale-free network

Several cases of the Sznajd model of socio-physics, that only a group of people sharing the same opinion can convince their neighbors, have been simulated on a more realistic network with a stronger clustering. In addition, many opinions, instead of usually only two, and a convincing probability have been also considered. Finally, with minor changes we obtain a vote distribution in good agreement with reality.Comment: 11 pages including 7 encapsulated postscript (*.eps) figures; to appear in Physica

How effective is advertising in duopoly markets?

A simple Ising spin model which can describe the mechanism of advertising in a duopoly market is proposed. In contrast to other agent-based models, the influence does not flow inward from the surrounding neighbors to the center site, but spreads outward from the center to the neighbors. The model thus describes the spread of opinions among customers. It is shown via standard Monte Carlo simulations that very simple rules and inclusion of an external field -- an advertising campaign -- lead to phase transitions.Comment: 7 pages, 6 figures; v2: cosmetic change

Outward-inward information flux in an opinion formation model on different topologies

A simple model of opinion formation dynamics in which binary-state agents make up their opinions due to the influence of agents in a local neighborhood is studied using different network topologies. Each agent uses two different strategies, the Sznajd rule with a probability $q$ and the Galam majority rule (without inertia) otherwise; being $q$ a parameter of the system. Initially, the binary-state agents may have opinions (at random) against or in favor about a certain topic. The time evolution of the system is studied using different network topologies, starting from different initial opinion densities. A transition from consensus in one opinion to the other is found at the same percentage of initial distribution no matter which type of network is used or which opinion formation rule is used.Comment: 11 pages including figures. To appear in Physica

Functional genomics of pH homeostasis in Corynebacterium glutamicum revealed novel links between pH response, oxidative stress, iron homeostasis and methionine synthesis

Follmann M, Ochrombel I, Kraemer R, et al. Functional genomics of pH homeostasis in Corynebacterium glutamicum revealed novel links between pH response, oxidative stress, iron homeostasis and methionine synthesis. BMC Genomics. 2009;10(1):621.Background: The maintenance of internal pH in bacterial cells is challenged by natural stress conditions, during host infection or in biotechnological production processes. Comprehensive transcriptomic and proteomic analyses has been conducted in several bacterial model systems, yet questions remain as to the mechanisms of pH homeostasis. Results: Here we present the comprehensive analysis of pH homeostasis in C. glutamicum, a bacterium of industrial importance. At pH values between 6 and 9 effective maintenance of the internal pH at 7.5 +/- 0.5 pH units was found. By DNA microarray analyses differential mRNA patterns were identified. The expression profiles were validated and extended by 1D-LC-ESI-MS/MS based quantification of soluble and membrane proteins. Regulators involved were identified and thereby participation of numerous signaling modules in pH response was found. The functional analysis revealed for the first time the occurrence of oxidative stress in C. glutamicum cells at neutral and low pH conditions accompanied by activation of the iron starvation response. Intracellular metabolite pool analysis unraveled inhibition of the TCA and other pathways at low pH. Methionine and cysteine synthesis were found to be activated via the McbR regulator, cysteine accumulation was observed and addition of cysteine was shown to be toxic under acidic conditions. Conclusions: Novel limitations for C. glutamicum at non-optimal pH values were identified by a comprehensive analysis on the level of the transcriptome, proteome, and metabolome indicating a functional link between pH acclimatization, oxidative stress, iron homeostasis, and metabolic alterations. The results offer new insights into bacterial stress physiology and new starting points for bacterial strain design or pathogen defense

Majority versus minority dynamics: Phase transition in an interacting two-state spin system

We introduce a simple model of opinion dynamics in which binary-state agents evolve due to the influence of agents in a local neighborhood. In a single update step, a fixed-size group is defined and all agents in the group adopt the state of the local majority with probability p or that of the local minority with probability 1-p. For group size G=3, there is a phase transition at p_c=2/3 in all spatial dimensions. For p>p_c, the global majority quickly predominates, while for p<p_c, the system is driven to a mixed state in which the densities of agents in each state are equal. For p=p_c, the average magnetization (the difference in the density of agents in the two states) is conserved and the system obeys classical voter model dynamics. In one dimension and within a Kirkwood decoupling scheme, the final magnetization in a finite-length system has a non-trivial dependence on the initial magnetization for all p.ne.p_c, in agreement with numerical results. At p_c, the exact 2-spin correlation functions decay algebraically toward the value 1 and the system coarsens as in the classical voter model.Comment: 11 pages, 3 figures, revtex4 2-column format; minor revisions for publication in PR

Spatial interactions in agent-based modeling

Agent Based Modeling (ABM) has become a widespread approach to model complex interactions. In this chapter after briefly summarizing some features of ABM the different approaches in modeling spatial interactions are discussed. It is stressed that agents can interact either indirectly through a shared environment and/or directly with each other. In such an approach, higher-order variables such as commodity prices, population dynamics or even institutions, are not exogenously specified but instead are seen as the results of interactions. It is highlighted in the chapter that the understanding of patterns emerging from such spatial interaction between agents is a key problem as much as their description through analytical or simulation means. The chapter reviews different approaches for modeling agents' behavior, taking into account either explicit spatial (lattice based) structures or networks. Some emphasis is placed on recent ABM as applied to the description of the dynamics of the geographical distribution of economic activities, - out of equilibrium. The Eurace@Unibi Model, an agent-based macroeconomic model with spatial structure, is used to illustrate the potential of such an approach for spatial policy analysis.Comment: 26 pages, 5 figures, 105 references; a chapter prepared for the book "Complexity and Geographical Economics - Topics and Tools", P. Commendatore, S.S. Kayam and I. Kubin, Eds. (Springer, in press, 2014

Activation of a nucleotide-dependent RCK domain requires binding of a cation cofactor to a conserved site

RCK domains regulate the activity of K+ channels and transporters in eukaryotic and prokaryotic organisms by responding to ions or nucleotides. The mechanisms of RCK activation by Ca2+ in the eukaryotic BK and bacterial MthK K+ channels are well understood. However, the molecular details of activation in nucleotide-dependent RCK domains are not clear. Through a functional and structural analysis of the mechanism of ATP activation in KtrA, a RCK domain from the B. subtilis KtrAB cation channel, we have found that activation by nucleotide requires binding of cations to an intra-dimer interface site in the RCK dimer. In particular, divalent cations are coordinated by the ¿-phosphates of bound-ATP, tethering the two subunits and stabilizing the active state conformation. Strikingly, the binding site residues are highly conserved in many different nucleotide-dependent RCK domains, indicating that divalent cations are a general cofactor in the regulatory mechanism of many nucleotide-dependent RCK domains.We thank access to ALBA (XALOC), ESRF (ID23-1) and Soleil (PROXIMA 1 and 2a) synchrotrons and technical support provided by the i3S scientific platform ‘Biochemical and Biophysical Technologies’ and FCUP|DQB-Lab and Services. Work was supported by Fundação Luso-Americana para o Desenvolvimento through the FLAD Life Science 2020 award entitled ‘Bacterial K+ transporters are potential antimicrobial targets: mechanisms of transport and regulation’ and by FEDER - Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020 - Operational Programme for Competitiveness and Internationalization (POCI), Portugal 2020, and by Portuguese funds through FCT - Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior in the framework of the projects POCI-01–0145-FEDER-029863 (PTDC/BIA-BQM/29863/2017) and ‘Institute for Research and Innovation in Health Sciences’ (POCI-01–0145-FEDER-007274).’ CMT-D was supported by FCT fellowship (SFRH/BD/123761/2016) and FF was supported by FCT fellowship (SFRH/BPD/102753/2014)