1,059 research outputs found
Moderate deviations for random field Curie-Weiss models
The random field Curie-Weiss model is derived from the classical Curie-Weiss
model by replacing the deterministic global magnetic field by random local
magnetic fields. This opens up a new and interestingly rich phase structure. In
this setting, we derive moderate deviations principles for the random total
magnetization , which is the partial sum of (dependent) spins. A typical
result is that under appropriate assumptions on the distribution of the local
external fields there exist a real number , a positive real number
, and a positive integer such that satisfies
a moderate deviations principle with speed and rate
function , where .Comment: 21 page
Characterizing Van Kampen Squares via Descent Data
Categories in which cocones satisfy certain exactness conditions w.r.t.
pullbacks are subject to current research activities in theoretical computer
science. Usually, exactness is expressed in terms of properties of the pullback
functor associated with the cocone. Even in the case of non-exactness,
researchers in model semantics and rewriting theory inquire an elementary
characterization of the image of this functor. In this paper we will
investigate this question in the special case where the cocone is a cospan,
i.e. part of a Van Kampen square. The use of Descent Data as the dominant
categorical tool yields two main results: A simple condition which
characterizes the reachable part of the above mentioned functor in terms of
liftings of involved equivalence relations and (as a consequence) a necessary
and sufficient condition for a pushout to be a Van Kampen square formulated in
a purely algebraic manner.Comment: In Proceedings ACCAT 2012, arXiv:1208.430
Variational bounds for the shear viscosity of gelling melts
We study shear stress relaxation for a gelling melt of randomly crosslinked,
interacting monomers. We derive a lower bound for the static shear viscosity
, which implies that it diverges algebraically with a critical exponent
. Here, and are the critical exponents of
percolation theory for the correlation length and the gel fraction. In
particular, the divergence is stronger than in the Rouse model, proving the
relevance of excluded-volume interactions for the dynamic critical behaviour at
the gel transition. Precisely at the critical point, our exact results imply a
Mark-Houwink relation for the shear viscosity of isolated clusters of fixed
size.Comment: 5 pages; CHANGES: typos corrected, some references added; version as
publishe
Unfolding-based Diagnosis of Systems with an Evolving Topology
We propose a framework for model-based diagnosis of systems with mobility and variable topologies, modelled as graph transformation systems. Generally speaking, model-based diagnosis is aimed at constructing explanations of observed faulty behaviours on the basis of a given model of the system. Since the number of possible explanations may be huge, we exploit the unfolding as a compact data structure to store them, along the lines of previous work dealing with Petri net models. Given a model of a system and an observation, the explanations can be constructed by unfolding the model constrained by the observation, and then removing incomplete explanations in a pruning phase. The theory is formalised in a general categorical setting: constraining the system by the observation corresponds to taking a product in the chosen category of graph grammars, so that the correctness of the procedure can be proved by using the fact that the unfolding is a right adjoint and thus it preserves products. The theory should hence be easily applicable to a wide class of system models, including graph grammars and Petri nets
Torn Between Two Plates: Exhumation of the Cer Massif (Internal Dinarides) as a FarâField Effect of Carpathian Slab Rollback Inferred From 40 Ar/ 39 Ar Dating and Cross Section Balancing
Abstract Extension across the southern Pannonian Basin and the internal Dinarides is characterized by OligoâMiocene metamorphic core complexes (MCCs) exhumed along mylonitic lowâangle extensional shear zones. Cer MCC at the transition between Dinarides and Pannonian Basin occupies a structural position within the distalâmost Adriatic thrust sheet and originates from two different tectonic processes: Late CretaceousâPaleogene nappeâstacking during a continentâcontinent collision with Adria in a lower plate position, and exhumation related to Miocene extension driven by the Carpathian slabârollback. Structural data and a balanced cross section across the Cer massif show linking of the exhuming shear zone to a breakaway fault, which reactivated the early Late Cretaceous most internal nappe contact. Paleozoic greenschistâto amphiboliteâgrade lithologies surround a polyphase intrusion composed of Iâ and Sâtype granites and were exhumed along a shear zone characterized by topâN transport. Thermobarometric analyses indicate an intrusion depth of 7â8 km of the Oligocene Iâtype granite; cooling below âŒ500°C occurred at 25.4 ± 0.6 Ma (1Ï) yielded by 40 Ar/ 39 Ar dating of hornblende. Biotite and white mica from this intrusion as well as from the mylonitic shear zone yield 40 Ar/ 39 Ar cooling ages of 17â18 Ma independent of the used techniques (in situ laser ablation, singleâgrain total fusion, singleâgrain step heating, and multiâgrain step heating). White mica from the Sâtype granite yield an 40 Ar/ 39 Ar cooling age of 16.7 ± 0.1 Ma (1Ï). Associated dikes intruding the shear zone were also affected by NâS extension resulting in the exhumation of the MCC, which was triggered by the opening of the Pannonian backâarc basin in response to the Carpathian slabârollback.Plain Language Summary Horizontal stretching of continental plates induces thinning of the crustal upper part, melting of rocks, the sinking of the land surface, and formation of large basins. One of the world's bestâstudied basins formed by such a process is the Central European Pannonian Basin. This basin is surrounded by the mountain belts of the Alps, Carpathians, and Dinarides. We have studied rocks between the Pannonian Basin and the southerly adjacent Dinaride Mountains, where rocks deposited in the basin are found right next to rocks that were initially about 7â8 km deep in the crust. These rocks are separated by a shear zone, along which they were brought to the surface. We have dated the activity of the shear zone by measuring concentrations of radioactive isotopes and their decay products contained in deformed minerals. The shear zone was active at a time when the Pannonian Basin started to open due to tectonic processes further NE underneath the Carpathian mountain chain. We also found evidence that the shear zone, which brought metamorphic rocks upwards was formerly one that brought rocks downwards into the crust during an earlier phase of mountain building, predating basin formation.Key Points Activity along the shear zone exhuming Cer metamorphic core complex in the internal Dinarides was dated by 40 Ar/ 39 Ar geochronology to âŒ17 Ma Exhumation was facilitated by extensional reactivation of Late CretaceousâPaleogene nappe contacts resulting from AdriaâEurope collision Extensional reactivation of the thrusts is interpreted as a farâfield effect of OligoâMiocene Carpathian slab rollbac
Diverse cytomotive actins and tubulins share a polymerization switch mechanism conferring robust dynamics
Protein filaments are used in myriads of ways to organize other molecules within cells. Some filament-forming proteins couple the hydrolysis of nucleotides to their polymerization cycle, thus powering the movement of other molecules. These filaments are termed cytomotive. Only members of the actin and tubulin protein superfamilies are known to form cytomotive filaments. We examined the basis of cytomotivity via structural studies of the polymerization cycles of actin and tubulin homologs from across the tree of life. We analyzed published data and performed structural experiments designed to disentangle functional components of these complex filament systems. Our analysis demonstrates the existence of shared subunit polymerization switches among both cytomotive actins and tubulins, i.e., the conformation of subunits switches upon assembly into filaments. These cytomotive switches can explain filament robustness, by enabling the coupling of kinetic and structural polarities required for cytomotive behaviors and by ensuring that single cytomotive filaments do not fall apart
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