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91.
During November 1971, a 400 Mbit/s quadriphase-shift-keyed system was operated at 13.3 and 14.9 GHz over a 22.8-km line-of-sight path. This path was chosen because of its high incidence of meteorological conditions favorable to anomalous propagation. Performance of the system during fading periods is reported here. Additional information from extensive meteorological measurements near midpath is presented to identify the source of the fading. The dual frequency measurements for spaced receiving antennas indicate that diversity reception, properly implemented, would have provided an effective fading remedy. 相似文献
92.
Randall Dougherty Vance Faber Michael Murphy 《Discrete and Computational Geometry》2004,32(3):309-315
We present a 16-vertex
tetrahedralization of S3 (the 3-sphere) for which no topological
bistellar flip other than a 1-to-4 flip (i.e., a vertex
insertion) is possible. This answers a question of Altshuler
et al. which asked if any two n-vertex tetrahedralizations of
S3 are connected by a sequence of 2-to-3 and 3-to-2
flips. The corresponding geometric question is whether two
tetrahedralizations of a finite point set S in 3 in general
position are always related via a sequence of geometric 2-to-3
and 3-to-2 flips. Unfortunately, we show that this
topologically unflippable complex and others with its properties
cannot be geometrically realized in 3. 相似文献
93.
Dougherty DB Lyubinetsky I Williams ED Constantin M Dasgupta C Das Sarma S 《Physical review letters》2002,89(13):136102
The persistence behavior for fluctuating steps on the Si(111)-(sqrt[3]xsqrt[3])R30 degrees -Al surface was determined by analyzing time-dependent STM images for temperatures between 770 and 970 K. Using the standard persistence definition, the measured persistence probability displays power-law decay with an exponent of theta=0.77+/-0.03. This is consistent with the value of theta=3/4 predicted for attachment-detachment limited step kinetics. If the persistence analysis is carried out in terms of return to a fixed-reference position, the measured probability decays exponentially. Numerical studies of the Langevin equation used to model step motion corroborate the experimental observations. 相似文献
94.
The notion of a shadow of a self-dual binary code is generalized to self-dual codes over
4. A Gleason formula for the symmetrized weight enumerator of the shadow of a Type I code is derived. Congruence properties of the weights follow; this yields constructions of self-dual codes of larger lengths. Weight enumerators and the highest minimum Lee, Hamming, and Euclidean weights of Type I codes of length up to 24 are studied. 相似文献
95.
Yasemin Cengellenmis Abdullah Dertli S. T. Dougherty 《Designs, Codes and Cryptography》2014,72(3):559-580
Codes over an infinite family of rings which are an extension of the binary field are defined. Two Gray maps to the binary field are attached and are shown to be conjugate. Euclidean and Hermitian self-dual codes are related to binary self-dual and formally self-dual codes, giving a construction of formally self-dual codes from a collection of arbitrary binary codes. We relate codes over these rings to complex lattices. A Singleton bound is proved for these codes with respect to the Lee weight. The structure of cyclic codes and their Gray image is studied. Infinite families of self-dual and formally self-dual quasi-cyclic codes are constructed from these codes. 相似文献
96.
Kilgore UJ Roberts JA Pool DH Appel AM Stewart MP DuBois MR Dougherty WG Kassel WS Bullock RM DuBois DL 《Journal of the American Chemical Society》2011,133(15):5861-5872
A series of mononuclear nickel(II) bis(diphosphine) complexes [Ni(P(Ph)(2)N(C6H4X)(2))(2)](BF(4))(2) (P(Ph)(2)N(C6H4X)(2) = 1,5-di(para-X-phenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; X = OMe, Me, CH(2)P(O)(OEt)(2), Br, and CF(3)) have been synthesized and characterized. X-ray diffraction studies reveal that [Ni(P(Ph)(2)N(C6H4Me)(2))(2)](BF(4))(2) and [Ni(P(Ph)(2)N(C6H4OMe)(2))(2)](BF(4))(2) are tetracoordinate with distorted square planar geometries. The Ni(II/I) and Ni(I/0) redox couples of each complex are electrochemically reversible in acetonitrile with potentials that are increasingly cathodic as the electron-donating character of X is increased. Each of these complexes is an efficient electrocatalyst for hydrogen production at the potential of the Ni(II/I) couple. The catalytic rates generally increase as the electron-donating character of X is decreased, and this electronic effect results in the favorable but unusual situation of obtaining higher catalytic rates as overpotentials are decreased. Catalytic studies using acids with a range of pK(a) values reveal that turnover frequencies do not correlate with substrate acid pK(a) values but are highly dependent on the acid structure, with this effect being related to substrate size. Addition of water is shown to dramatically increase catalytic rates for all catalysts. With [Ni(P(Ph)(2)N(C6H4CH2P(O)(OEt)2)(2))(2)](BF(4))(2) using [(DMF)H](+)OTf(-) as the acid and with added water, a turnover frequency of 1850 s(-1) was obtained. 相似文献
97.
We give a bound for codes over an arbitrary alphabet in a non-Hamming metric and define MDS codes as codes meeting this bound. We show that MDS codes are precisely those codes that are uniformly distributed and show that their weight enumerators based on this metric are uniquely determined. 相似文献
98.
A.L. Crosbie R.L. Dougherty 《Journal of Quantitative Spectroscopy & Radiative Transfer》1981,25(6):551-569
Exact integral equations are derived describing the source function and radiative flux in a two-dimensional, radially infinite cylindrical medium which scatters anisotropically. The problem is two-dimensional and cylindrical because of axisymmetric loading. Radially varying collimated radiation is incident normal to the upper surface while the lower boundary has no radiation incident upon it. The scattering phase function is represented by a spike in the forward direction plus a series of Legendre polynomials. The two-dimensional integral equations are reduced to a one-dimensional form by separating variables for the case when the radial variation of the incident radiation is a Bessel function. The one-dimensional form consists of a system of linear, singular Fredholm integral equations of second kind. Other more complex boundary conditions are shown to be solvable by a superposition of this basic Bessel function case. Diffusely incident radiation is also considered. 相似文献
99.
Thurston JH Dougherty MJ Swenson DC Messerle L 《Dalton transactions (Cambridge, England : 2003)》2008,(38):5146-5148
The novel tetrahedral [Bi(5)(dpd)(6) within CH(3)CN](ClO(4))(3).3CH(3)CN (dpd = di-2-pyridyl-gem-diolate) has been synthesized from [Bi(9)(mu(3)-O)(8)(mu(3)-OH)(6)](ClO(4))(5) and di-2-pyridyl ketone. The Bi(5) complex incorporates CH(3)CN via C-HO hydrogen bonding. 相似文献
100.
We present a novel approach to surface chemistry studies using scanning tunneling microscopy (STM), where dissociation of molecules adsorbed on metal surfaces is induced nonlocally in a 10-100 nm radius around the STM tip by hot electrons that originate from the STM tip and transport on the surface. Nonlocal molecular excitation eliminates the influence of the STM tip on the outcome of the electron-induced chemical reaction. The spatial attenuation of the nonlocal reaction is used as a direct measure of hot-electron transport on the surface. 相似文献