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91.
Martiniani S Anderson AY Law C O'Regan BC Barolo C 《Chemical communications (Cambridge, England)》2012,48(18):2406-2408
The order of regeneration for DSCs based on two organic dyes has been investigated by transient absorption spectroscopy on devices under operating conditions and determined to be 2nd order in iodide. The results shed light on the mechanism and limits to the regeneration rate relative to oxidation potential. 相似文献
92.
A long-standing conjecture of Erd?s and Simonovits is that ex(n,C2k), the maximum number of edges in an n-vertex graph without a 2k-gon is asymptotically as n tends to infinity. This was known almost 40 years ago in the case of quadrilaterals. In this paper, we construct a counterexample to the conjecture in the case of hexagons. For infinitely many n, we prove that
93.
Noga Alon Konstantin Makarychev Yury Makarychev Assaf Naor 《Inventiones Mathematicae》2006,163(3):499-522
We introduce a new graph parameter, called the Grothendieck constant of a graph G=(V,E), which is defined as the least constant K such that for every A:E→ℝ,
The classical Grothendieck inequality corresponds to the case of bipartite graphs, but the case of general graphs is shown to have various algorithmic applications. Indeed, our work is motivated by
the algorithmic problem of maximizing the quadratic form ∑{u,v}∈EA(u,v)ϕ(u)ϕ(v) over all ϕ:V→{-1,1}, which arises in the study of correlation clustering and in the investigation of the spin glass model. We give upper
and lower estimates for the integrality gap of this program. We show that the integrality gap is
, where
is the Lovász Theta Function of the complement of G, which is always smaller than the chromatic number ofG. This yields an efficient constant factor approximation algorithm for the above maximization problem for a wide range of
graphs G. We also show that the maximum possible integrality gap is always at least Ω(log ω(G)), where ω(G) is the clique number of G.
In particular it follows that the maximum possible integrality gap for the complete graph on n vertices with no loops is Θ(logn). More generally, the maximum possible integrality gap for any perfect graph with chromatic number n is Θ(logn). The lower bound for the complete graph improves a result of Kashin and Szarek on Gram matrices of uniformly bounded functions,
and settles a problem of Megretski and of Charikar and Wirth. 相似文献
94.
Various new nonembeddability results (mainly into L1) are proved via Fourier analysis. In particular, it is shown that the Edit Distance on {0,1}d has L1 distortion We also give new lower bounds on the L1 distortion of flat tori, quotients of the discrete hypercube under group actions, and the transportation cost (Earthmover)
metric. 相似文献
95.
96.
Assaf Rinot 《Topology and its Applications》2007,155(3):135-140
We introduce a weakening of the generalized continuum hypothesis, which we will refer to as the prevalent singular cardinals hypothesis, and show it implies that every topological space of density and weight ℵω1 is not hereditarily Lindelöf.The assumption PSH is very weak, and in fact holds in all currently known models of ZFC. 相似文献
97.
98.
Assaf Libman 《Mathematische Zeitschrift》2007,255(3):515-548
We give a new proof of the Minami–Webb formula for classifying spaces of finite groups by exploiting Symonds’s resolution
of Webb’s conjecture. The methods are applicable to obtain a stable decomposition of Minami’s type for the classifying spaces
of the three exotic p-local finite groups which were introduced by Ruiz and Viruel at the prime 7. We obtain a similar decomposition for the classifying
spaces of a family of exotic p-local finite groups which were constructed by Broto, Levi and Oliver.
The author was supported by the Nuffield Foundation Grant NAL/00735/G. 相似文献
99.
Motivated by applications in telephone call centers, we consider a service system model with m customer classes and r server pools. The model is one with doubly stochastic arrivals, which means that the m-vector λ of instantaneous arrival rates is allowed to vary both temporally and stochastically. Two levels of dynamic control
are considered: customers may be either blocked or accepted at the time of their arrival, and then accepted customers of each
class must be routed, either immediately upon acceptance or after some period of waiting, to a server pool that is qualified
to handle that class. Customers who are made to wait before commencement of their service are liable to defect. The objective
is to minimize the expected sum of blocking costs, waiting costs and defection costs over a fixed and finite planning horizon.
We consider an asymptotic parameter regime in which (i) the arrival rates, service rates and defection rates are uniformly
accelerated by a large factor κ, then (ii) arrival rates are increased by an additional factor g(κ), and the number of servers in each pool is increased by g(κ) as well. This produces a separation of time scales, justifying a pointwise stationary stochastic fluid approximation for
our original system model. In the stochastic fluid approximation, optimal admission control and routing decisions are determined
by a simple linear program that uses the current arrival rate vector λ as data. We explain how to implement the fluid model's
optimal control policy in our original service system context, and prove that the proposed implementation is asymptotically
optimal in the first-order sense.
AMS subject classification: 60K30, 90B15, 90B36 相似文献
100.
F. H. Assaf 《Journal of Solid State Electrochemistry》1998,3(1):39-47
The anodic polarization behaviour of Al-Sn alloy (5.6% Sn) was studied in aerated 1, 1.5 and 2 M H3PO4 acid solutions using potentiodynamic and potentiostatic techniques. Anodic behaviour of Al and Sn metals was investigated
for comparison. The results show that the alloy exhibits active-passive transition behaviour. The passivation of the examined
alloy is due to the formation of oxide film for both Al and Sn incorporated with their phosphates. In general, at constant
concentration of PO4
3− ion, the passive current density (I
pass) is decreased with increase of pH in the range 2.5–5. Further, the influence of Cl− ions on the passivity of the given alloy was studied. It was found that the aggressive effect of Cl− ions on the passive film is inhibited with increase in phosphate concentration and pH. However, the addition of organic compounds
(2- and 3-picoline and 2-aminopyridine) shows that only 2-aminopyridine inhibited the attack of Cl− ions.
Received: 24 October 1997 / Accepted: 5 February 1998 相似文献