4,706 research outputs found
Deligne-Lusztig varieties and period domains over finite fields
We prove that the Drinfeld halfspace is essentially the only Deligne-Lusztig
variety which is at the same time a period domain over a finite field. This is
done by comparing a cohomology vanishing theorem for DL-varieties, due to
Digne, Michel, and Rouquier, with a non-vanishing theorem for PD, due to the
first author. We also discuss an affineness criterion for DL-varieties.Comment: 16 pages, reference added to the paper of X. He (arXiv:0707.0259) in
which the affineness conjecture for DL-varieties is prove
Interlayer Registry Determines the Sliding Potential of Layered Metal Dichalcogenides: The case of 2H-MoS2
We provide a simple and intuitive explanation for the interlayer sliding
energy landscape of metal dichalcogenides. Based on the recently introduced
registry index (RI) concept, we define a purely geometrical parameter which
quantifies the degree of interlayer commensurability in the layered phase of
molybdenum disulphide (2HMoS2). A direct relation between the sliding energy
landscape and the corresponding interlayer registry surface of 2H-MoS2 is
discovered thus marking the registry index as a computationally efficient means
for studying the tribology of complex nanoscale material interfaces in the
wearless friction regime.Comment: 13 pages, 7 figure
Growing Scale-Free Networks with Tunable Clustering
We extend the standard scale-free network model to include a ``triad
formation step''. We analyze the geometric properties of networks generated by
this algorithm both analytically and by numerical calculations, and find that
our model possesses the same characteristics as the standard scale-free
networks like the power-law degree distribution and the small average geodesic
length, but with the high-clustering at the same time. In our model, the
clustering coefficient is also shown to be tunable simply by changing a control
parameter - the average number of triad formation trials per time step.Comment: Accepted for publication in Phys. Rev.
Properties of the gradient squared of the discrete Gaussian free field
In this paper we study the properties of the centered (norm of the) gradient
squared of the discrete Gaussian free field in , and . The covariance structure
of the field is a function of the transfer current matrix and this relates the
model to a class of systems (e.g. height-one field of the Abelian sandpile
model or pattern fields in dimer models) that have a Gaussian limit due to the
rapid decay of the transfer current. Indeed, we prove that the properly
rescaled field converges to white noise in an appropriate local Besov-H\"older
space. Moreover, under a different rescaling, we determine the -point
correlation function and cumulants on and in the continuum limit
as . This result is related to the analogue limit for the
height-one field of the Abelian sandpile (\citet{durre}), with the same
conformally covariant property in .Comment: 28 page
Network dynamics of ongoing social relationships
Many recent large-scale studies of interaction networks have focused on
networks of accumulated contacts. In this paper we explore social networks of
ongoing relationships with an emphasis on dynamical aspects. We find a
distribution of response times (times between consecutive contacts of different
direction between two actors) that has a power-law shape over a large range. We
also argue that the distribution of relationship duration (the time between the
first and last contacts between actors) is exponentially decaying. Methods to
reanalyze the data to compensate for the finite sampling time are proposed. We
find that the degree distribution for networks of ongoing contacts fits better
to a power-law than the degree distribution of the network of accumulated
contacts do. We see that the clustering and assortative mixing coefficients are
of the same order for networks of ongoing and accumulated contacts, and that
the structural fluctuations of the former are rather large.Comment: to appear in Europhys. Let
Disulfide bridge formation between SecY and a translocating polypeptide localizes the translocation pore to the center of SecY
During their biosynthesis, many proteins pass through the membrane via a hydrophilic channel formed by the heterotrimeric Sec61/SecY complex. Whether this channel forms at the interface of multiple copies of Sec61/SecY or is intrinsic to a monomeric complex, as suggested by the recently solved X-ray structure of the Methanococcus jannaschii SecY complex, is a matter of contention. By introducing a single cysteine at various positions in Escherichia coli SecY and testing its ability to form a disulfide bond with a single cysteine in a translocating chain, we provide evidence that translocating polypeptides pass through the center of the SecY complex. The strongest cross-links were observed with residues that would form a constriction in an hourglass-shaped pore. This suggests that the channel makes only limited contact with a translocating polypeptide, thus minimizing the energy required for translocation
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