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71.
An unusual heterodiene, an indolothiono quinone, undergoes cycloaddition with a glycal to form an indole-N-glycoside. A novel dimer of the indolothionoquinone is assigned its structure on the basis of a match between its predicted and observed IR spectrum. 相似文献
72.
Many graphs arising in various information networks exhibit the "power law" behavior -the number of vertices of degree k is proportional to k-# for some positive #. We show that if # > 2.5, the largest eigenvalue of a random power law graph is almost surely(1+ o(1))?m (1+ o(1))\sqrt{m} where m is the maximum degree. Moreover, the klargest eigenvalues of a random power law graph with exponent # have power law distribution with exponent 2# if the maximum degree is sufficiently large, where k is a function depending on #, mand d, the average degree. When 2<#< 2.5, the largest eigenvalue is heavily concentrated at cm3-# for some constant c depending on # and the average degree. This result follows from a more general theorem which shows that the largest eigenvalue of a random graph with a given expected degree sequence is determined by m, the maximum degree, and [(d)\tilde] \tilde{d} , the weighted average of the squares of the expected degrees. We show that the k-th largest eigenvalue is almost surely (1+ o(1))?{mk} (1+ o(1))\sqrt{m_k} where mk is the k-th largest expected degree provided mk is large enough. These results have implications on the usage of spectral techniques in many areas related to pattern detection and information retrieval. 相似文献
73.
In the late 1950s, B. Segre introduced the fundamental
notion of arcs and complete arcs [48,49]. An arc in a nite
projective plane is a set of points with no three on a line and
it is complete if cannot be extended without violating this
property. Given a projective plane
, determining
, the size of its
smallest complete arc, has been a major open question in finite
geometry for several decades. Assume that
has order
q, it was shown by Lunelli
and Sce [41], more than 40 years ago, that
. Apart from this bound,
practically nothing was known about
, except for the case
is the Galois plane. For
this case, the best upper bound, prior to this paper, was
O(q
3/4)
obtained by Sznyi using the properties of the Galois field
GF(q).In this paper, we prove that
for any projective plane
of order
q, where
c is a universal constant.
Together with Lunelli-Sces lower bound, our result determines
up to a polylogarithmic
factor. Our proof uses a probabilistic method known as the
dynamic random construction or Rödls nibble. The proof also
gives a quick randomized algorithm which produces a small
complete arc with high probability.The key ingredient of our proof is a new concentration
result, which applies for non-Lipschitz functions and is of
independent interest.* Research supported in part by grant RB091G-VU from
UCSD, by NSF grant DMS-0200357 and by an A. Sloan
fellowship.Part of this work was done at AT&T Bell Labs and
Microsoft Research 相似文献
74.
L.H. Nguyen T.V. Phi P.Q. Phan H.N. Vu C. Nguyen-Duc F. Fossard 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):54
It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO2, NH3.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO2/Si substrate by decomposition of acetylene (C2H2) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al2O3 substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH3 gas. 相似文献
75.
Breakdown conditions for creation of the hollow cathode discharge in the nozzle passed through the rf powered electrode and creation of the plasma jet channel in PCVD reactor are studied. Pure nitrogen is used for measurements. The creation of jet channel is easier for smaller rf electrodes. The breakdown depends on the pressure and on the gas inflow rate. The plasma potential and the self-bias potential is influenced by the covering of reactor walls and the rf electrode by a dielectric layer. 相似文献
76.
77.
Vu Kim Tuan 《Results in Mathematics》2013,63(1-2):303-309
Boundaries of convex and compact spectra of functions on plane are fully described without passing to the complexification and the Fourier transform. 相似文献
78.
79.
80.
Fe1?xCx amorphous alloys have been studied with Mössbauer Spectroscopy for 0.19<-x<-0.31. For x>-0.286, new carbides are formed by crystallization of such alloys. The chemical twinning model allows describing their structures. 相似文献