1,514 research outputs found
The de Rham-Witt and Z_p-cohomologies of an algebraic variety
We show how the Z_p(r)-cohomologies of a smooth projective algebraic variety
can be obtained via its de Rham-Witt complex.Comment: 6 page
On Negotiation as Concurrency Primitive
We introduce negotiations, a model of concurrency close to Petri nets, with
multiparty negotiation as primitive. We study the problems of soundness of
negotiations and of, given a negotiation with possibly many steps, computing a
summary, i.e., an equivalent one-step negotiation. We provide a complete set of
reduction rules for sound, acyclic, weakly deterministic negotiations and show
that, for deterministic negotiations, the rules compute the summary in
polynomial time
Ice Formation on Kaolinite: Insights from Molecular Dynamics Simulations
The formation of ice affects many aspects of our everyday life as well as
technologies such as cryotherapy and cryopreservation. Foreign substances
almost always aid water freezing through heterogeneous ice nucleation, but the
molecular details of this process remain largely unknown. In fact, insight into
the microscopic mechanism of ice formation on different substrates is difficult
to obtain even via state-of-the-art experimental techniques. At the same time,
atomistic simulations of heterogeneous ice nucleation frequently face
extraordinary challenges due to the complexity of the water-substrate
interaction and the long timescales that characterize nucleation events. Here,
we have investigated several aspects of molecular dynamics simulations of
heterogeneous ice nucleation considering as a prototypical ice nucleating
material the clay mineral kaolinite, which is of relevance in atmospheric
science. We show via seeded molecular dynamics simulations that ice nucleation
on the hydroxylated (001) face of kaolinite proceeds exclusively via the
formation of the hexagonal ice polytype. The critical nucleus size is two times
smaller than that obtained for homogeneous nucleation at the same supercooling.
Previous findings suggested that the flexibility of the kaolinite surface can
alter the time scale for ice nucleation within molecular dynamics simulations.
However, we here demonstrate that equally flexible (or non flexible) kaolinite
surfaces can lead to very different outcomes in terms of ice formation,
according to whether or not the surface relaxation of the clay is taken into
account. We show that very small structural changes upon relaxation
dramatically alter the ability of kaolinite to provide a template for the
formation of a hexagonal overlayer of water molecules at the water-kaolinite
interface, and that this relaxation therefore determines the nucleation ability
of this mineral
Transport collapse in dynamically evolving networks
Transport in complex networks can describe a variety of natural and
human-engineered processes including biological, societal and technological
ones. However, how the properties of the source and drain nodes can affect
transport subject to random failures, attacks or maintenance optimization in
the network remain unknown. In this paper, the effects of both the distance
between the source and drain nodes and of the degree of the source node on the
time of transport collapse are studied in scale-free and lattice-based
transport networks. These effects are numerically evaluated for two strategies,
which employ either transport-based or random link removal. Scale-free networks
with small distances are found to result in larger times of collapse. In
lattice-based networks, both the dimension and boundary conditions are shown to
have a major effect on the time of collapse. We also show that adding a direct
link between the source and the drain increases the robustness of scale-free
networks when subject to random link removals. Interestingly, the distribution
of the times of collapse is then similar to the one of lattice-based networks
Geometric Phantom Categories
In this paper we give a construction of phantom categories, i.e. admissible
triangulated subcategories in bounded derived categories of coherent sheaves on
smooth projective varieties that have trivial Hochschild homology and trivial
Grothendieck group. We also prove that these phantom categories are phantoms in
a stronger sense, namely, they have trivial K-motives and, hence, all their
higher K-groups are trivial too.Comment: LaTeX, 18 page
Integral Grothendieck-Riemann-Roch theorem
We show that, in characteristic zero, the obvious integral version of the
Grothendieck-Riemann-Roch formula obtained by clearing the denominators of the
Todd and Chern characters is true (without having to divide the Chow groups by
their torsion subgroups). The proof introduces an alternative to Grothendieck's
strategy: we use resolution of singularities and the weak factorization theorem
for birational maps.Comment: 24 page
Corporate voluntary greenhouse gas reporting: stakeholder pressure and the mediating role of the chief executive officer
The study sheds light on the extent to which various stakeholder pressures influence voluntary disclosure of greenhouse gas (GHG) emissions and how the impact is explained and moderated Chief executive office (CEO) characteristics of 215 FTSE350 listed United Kingdom (UK) companies for the year 2011. The study developed a classification of GHG emission disclosure based on the guidelines of GHG Protocol, DEFRA and Global Framework for Climate Risk Disclosure using content analysis. Evidence from the study suggests that some stakeholder pressure (regulatory, creditor, supplier, customer, board control) positively impacts on GHG disclosure information by firms. We found stakeholder pressure in the form of regulatory, mimetic and shareholders pressure positively influenced the disclosure of GHG information. We also found creditor pressure also had a significant negative relationship with GHG disclosure. While CEO age had a direct negative effect on GHG voluntary disclosure, its moderation effect on stakeholder pressure influence on GHG disclosure was only significant on regulatory pressure
In vivo time-lapse imaging of mitochondria in healthy and diseased peripheral myelin sheath
The myelin sheath that covers a large amount of neurons is critical for their homeostasis, and myelinating glia mitochondria have recently been shown to be essential for neuron survival. However morphological and physiological properties of these organelles remain elusive. Here we report a method to analyze mitochondrial dynamics and morphology in myelinating Schwann cells of living mice using viral transduction and time-lapse multiphoton microscopy. We describe the distribution, shape, size and dynamics of mitochondria in live cells. We also report mitochondrial alterations in Opa1(delTTAG) mutant mice cells at presymptomatic stages, suggesting that mitochondrial defects in myelin contribute to OPA1 related neuropathy and represent a biomarker for the disease
Distinct levels in Pom1 gradients limit Cdr2 activity and localization to time and position division.
Where and when cells divide are fundamental questions. In rod-shaped fission yeast cells, the DYRK-family kinase Pom1 is organized in concentration gradients from cell poles and controls cell division timing and positioning. Pom1 gradients restrict to mid-cell the SAD-like kinase Cdr2, which recruits Mid1/Anillin for medial division. Pom1 also delays mitotic commitment through Cdr2, which inhibits Wee1. Here, we describe quantitatively the distributions of cortical Pom1 and Cdr2. These reveal low profile overlap contrasting with previous whole-cell measurements and Cdr2 levels increase with cell elongation, raising the possibility that Pom1 regulates mitotic commitment by controlling Cdr2 medial levels. However, we show that distinct thresholds of Pom1 activity define the timing and positioning of division. Three conditions-a separation-of-function Pom1 allele, partial downregulation of Pom1 activity, and haploinsufficiency in diploid cells-yield cells that divide early, similar to pom1 deletion, but medially, like wild-type cells. In these cells, Cdr2 is localized correctly at mid-cell. Further, Cdr2 overexpression promotes precocious mitosis only in absence of Pom1. Thus, Pom1 inhibits Cdr2 for mitotic commitment independently of regulating its localization or cortical levels. Indeed, we show Pom1 restricts Cdr2 activity through phosphorylation of a C-terminal self-inhibitory tail. In summary, our results demonstrate that distinct levels in Pom1 gradients delineate a medial Cdr2 domain, for cell division placement, and control its activity, for mitotic commitment
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