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61.
The vibrational energy dependence of the rate of the gas phase reaction of Na with SF6 has been determined in a diffusion cloud experiment using CO2 laser excitation. The “conversion efficiency” of ca. 40% for vibrational energy suggests a preference for vibrational over the translational energy when compared with “prior” statistical expectation. 相似文献
62.
Eyal Lubetzky Fabio Martinelli Allan Sly 《Communications in Mathematical Physics》2016,344(3):673-717
The 2D Discrete Gaussian model gives each height function \({\eta : {\mathbb{Z}^2\to\mathbb{Z}}}\) a probability proportional to \({\exp(-\beta \mathcal{H}(\eta))}\), where \({\beta}\) is the inverse-temperature and \({\mathcal{H}(\eta) = \sum_{x\sim y}(\eta_x-\eta_y)^2}\) sums over nearest-neighbor bonds. We consider the model at large fixed \({\beta}\), where it is flat unlike its continuous analog (the Discrete Gaussian Free Field). We first establish that the maximum height in an \({L\times L}\) box with 0 boundary conditions concentrates on two integers M, M + 1 with \({M\sim \sqrt{(1/2\pi\beta)\log L\log\log L}}\). The key is a large deviation estimate for the height at the origin in \({\mathbb{Z}^{2}}\), dominated by “harmonic pinnacles”, integer approximations of a harmonic variational problem. Second, in this model conditioned on \({\eta\geq 0}\) (a floor), the average height rises, and in fact the height of almost all sites concentrates on levels H, H + 1 where \({H\sim M/\sqrt{2}}\). This in particular pins down the asymptotics, and corrects the order, in results of Bricmont et al. (J. Stat. Phys. 42(5–6):743–798, 1986), where it was argued that the maximum and the height of the surface above a floor are both of order \({\sqrt{\log L}}\). Finally, our methods extend to other classical surface models (e.g., restricted SOS), featuring connections to p-harmonic analysis and alternating sign matrices. 相似文献
63.
Eyal Aharon Steffen Breuer Frank Jaiser Dr. Anna Köhler Prof. Gitti L. Frey Dr. 《Chemphyschem》2008,9(10):1430-1436
Photophysical processes in conjugated polymers are influenced by two competing effects: the extent of excited state delocalization along a chain, and the electronic interaction between chains. Experimentally, it is often difficult to separate the two because both are controlled by chain conformation. Here we demonstrate that it is possible to modify intra‐chain delocalization without inducing inter‐chain interactions by intercalating polymer monolayers between the sheets of an inorganic layered matrix. The red‐emitting conjugated polymer, MEH‐PPV, is confined to the interlayer space of layered SnS2. The formation of isolated polymer monolayers between the SnS2 sheets is confirmed by X‐ray diffraction measurements. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of the incorporated MEH‐PPV chains reveal that the morphology of the incorporated chains can be varied through the choice of solvent used for chain intercalation. Incorporation from chloroform results in more extended conformations compared to intercalation from xylene. Even highly twisted conformations can be achieved when the incorporation occurs from a methanol:chloroform mixture. The PL spectra of the MEH‐PPV incorporated SnS2 nanocomposites using the different solvents are in good agreement with the PL spectra of the same solutions, indicating that the conformation of the polymer chains in the solutions is retained upon intercalation into the inorganic host. Therefore, intercalation of conjugated polymer chains into layered hosts enables the study of intra‐chain photophysical processes as a function of chain conformation. 相似文献
64.
65.
Dahan A Ashkenazi T Kuznetsov V Makievski S Drug E Fadeev L Bramson M Schokoroy S Rozenshine-Kemelmakher E Gozin M 《The Journal of organic chemistry》2007,72(7):2289-2296
A novel methodology for the evaluation of receptor arrangement in structurally flexible anion chemosensors was developed and applied to map the binding site of a new pseudocyclic tristhiourea chemosensor (6). The syntheses of 6 and related macrocyclic chemosensor 10 (a model of the folded monomeric structure of 6) are reported. Both chemosensors were evaluated by titration with a variety of structurally different anions in CH3Cl and DMSO, showing a common preference for F-, CH3CO2-, and H2PO4-. However, within this group of anions, the binding patterns of the chemosensors differed, indicating dissimilarity in the arrangement of the binding sites of 6 and 10. 相似文献
66.
For which values of k does a uniformly chosen 3‐regular graph G on n vertices typically contain n/k vertex‐disjoint k ‐cycles (a k ‐cycle factor)? To date, this has been answered for k = n and for k ? log n ; the former, the Hamiltonicity problem, was finally answered in the affirmative by Robinson and Wormald in 1992, while the answer in the latter case is negative since with high probability (w.h.p.) most vertices do not lie on k ‐cycles. A major role in our study of this problem is played by renewal processes without replacement, where one wishes to estimate the probability that in a uniform permutation of a given set of positive integers, the partial sums hit a designated target integer. Using sharp tail estimates for these renewal processes, which may be of independent interest, we settle the cycle factor problem completely: the “threshold” for a k ‐cycle factor in G as above is κ 0 log2 n with . To be precise, G contains a k ‐cycle factor w.h.p. if and w.h.p. does not contain one if . Thus, for most values of n the threshold concentrates on the single integer K 0(n ). As a byproduct, we confirm the “comb conjecture,” an old problem concerning the embedding of certain spanning trees in the random graph (n,p ).© 2015 Wiley Periodicals, Inc. 相似文献
67.
The k-th power of a graph G is the graph whose vertex set is V(G)
k
, where two distinct k-tuples are adjacent iff they are equal or adjacent in G in each coordinate. The Shannon capacity of G, c(G), is lim
k→∞
α(G
k
)1/k
, where α(G) denotes the independence number of G. When G is the characteristic graph of a channel C, c(G) measures the effective alphabet size of C in a zero-error protocol. A sum of channels, C = Σ
i
C
i
, describes a setting when there are t ≥ 2 senders, each with his own channel C
i
, and each letter in a word can be selected from any of the channels. This corresponds to a disjoint union of the characteristic
graphs, G = Σ
i
G
i
. It is well known that c(G) ≥ Σ
i
c(G
i
), and in [1] it is shown that in fact c(G) can be larger than any fixed power of the above sum.
We extend the ideas of [1] and show that for every F, a family of subsets of [t], it is possible to assign a channel C
i
to each sender i ∈ [t], such that the capacity of a group of senders X ⊂ [t] is high iff X contains some F ∈ F. This corresponds to a case where only privileged subsets of senders are allowed to transmit in a high rate. For instance,
as an analogue to secret sharing, it is possible to ensure that whenever at least k senders combine their channels, they obtain a high capacity, however every group of k − 1 senders has a low capacity (and yet is not totally denied of service). In the process, we obtain an explicit Ramsey construction
of an edge-coloring of the complete graph on n vertices by t colors, where every induced subgraph on exp vertices contains all t colors.
Research supported in part by a USA-Israeli BSF grant, by the Israel Science Foundation and by the Hermann Minkowski Minerva
Center for Geometry at Tel Aviv University.
Research partially supported by a Charles Clore Foundation Fellowship. 相似文献
68.
Bavli D Tkachev M Piwonski H Capua E de Albuquerque I Bensimon D Haran G Naaman R 《Langmuir : the ACS journal of surfaces and colloids》2012,28(1):1020-1028
The detection of covalent and noncovalent binding events between molecules and biomembranes is a fundamental goal of contemporary biochemistry and analytical chemistry. Currently, such studies are performed routinely using fluorescence methods, surface-plasmon resonance spectroscopy, and electrochemical methods. However, there is still a need for novel sensitive miniaturizable detection methods where the sample does not have to be transferred to the sensor, but the sensor can be brought into contact with the sample studied. We present a novel approach for detection and quantification of processes occurring on the surface of a lipid bilayer membrane, by monitoring the current change through the n-type GaAs-based molecularly controlled semiconductor resistor (MOCSER), on which the membrane is adsorbed. Since GaAs is susceptible to etching in an aqueous environment, a protective thin film of methoxysilane was deposited on the device. The system was found to be sensitive enough to allow monitoring changes in pH and in the concentration of amino acids in aqueous solution on top of the membrane. When biotinylated lipids were incorporated into the membrane, it was possible to monitor the binding of streptavidin or avidin. The device modified with biotin-streptavidin complex was capable of detecting the binding of streptavidin antibodies to immobilized streptavidin with high sensitivity and selectivity. The response depends on the charge on the analyte. These results open the way to facile electrical detection of protein-membrane interactions. 相似文献
69.
70.
Noga Alon Omer Angel Itai Benjamini Eyal Lubetzky 《Israel Journal of Mathematics》2012,188(1):353-384
In their seminal paper from 1983, Erdős and Szemerédi showed that any n distinct integers induce either n
1+ɛ
distinct sums of pairs or that many distinct products, and conjectured a lower bound of n
2−o(1). They further proposed a generalization of this problem, in which the sums and products are taken along the edges of a given
graph G on n labeled vertices. They conjectured a version of the sum-product theorem for general graphs that have at least n
1+ɛ
edges. 相似文献