A US perspective on standards development

The foundation for the interconnected society of the 21st century is being built today. The key to having this become a reality is the availability of compatible national, regional, and global communications standards. Committee T1 Telecommunications has played increasing important standards development roles in the US and global telecommunications industries. Committee Tl's dual roles of a US standards developer and an initiator of global standards harmonization contribute to satisfying the users' desires that it be as easy to communicate across the country or around the world as it is to communicate across the street. The key technologies of asynchronous transfer mode (ATM), personal communications services (PCS), and synchronous optical network (SONET) are but a few of the topics for which standards have been developed in Committee T1, and for which standardization of extensions and enhancements continue. These areas have also been among the topics Committee T1 has targeted for standards harmonization     

Estimation of the directions of arrival of signals in unknowncorrelated noise. I. The MAP approach and its implementation

The authors propose a method of direction of arrival (DOA) estimation of signals in the presence of noise whose covariance matrix is unknown and arbitrary, other than being positive definite. They examine the projection of the data onto the noise subspace. The conditional probability density function (PDF) of the projected data given the signal parameters and the unknown projected noise covariance matrix is first formed. The a posteriori PDF of the signal parameters alone is then obtained by assigning a noninformative a priori PDF to the unknown noise covariance matrix and integrating out this quantity. A simple criterion for the maximum a posteriori (MAP) estimate of the DOAs of the signals is established. Some properties of this criterion are discussed, and an efficient numerical algorithm for the implementation of this criterion is developed. The advantage of this method is that the noise covariance matrix does not have to be known, nor must it be estimated     

Metal-(phenylthio)acetic acid interactions—VI. The crystal and molecular structures of diaquabis[(phenylsulfinyl) acetato[bis(pyridine)copper(II) and bis[(benzylthio) acetato]bis(pyridine)copper(II)

The crystal structures of diaquabis[(phenylsulfinyl) acetato]bis(pyridine)-copper(II), (1), and bis[(benzylthio) acetato]bis(pyridine)copper(II) (2) have been determined using X-ray diffraction. In (1), the copper atom is at the centre of a distorted octahedron with the equatorial sites occupied in a trans configuration by two unidentate (phenylsulfinyl)acetate oxygens [Cu-O, 1.97(2),2.01(2)Å] and two pyridine nitrogens [Cu-N, 1.99(2),2.05(2) Å] with water molecules completing the polyhedron [Cu-O, 2.51(2),2.58(2) Å]. The copper atom in (2) is at the inversion centre of a distorted octahedron having in the equatorial sites, trans-related pyridine nitrogens [Cu-N, 1.993(3) Å] and four oxygens from two asymmetric bidentate (benzylthio)acetate ligands [Cu-O, 2.012(3), 2.510(5) Å].     

A combinatorial solution of two related problems in sequence enumeration

This paper gives a combinatorial derivation of the counting series ψ_m (alternatively $\text{ψ}{}_{\mathrm{m}}{}^1$) for positive integer sequences by rises, falls and levels (alternately exceedances, deficiencies and constants).     

A satellite system synthesis model for orbital arc allotmentoptimization

A mixer-integer programming formulation is presented of a satellite system synthesis problem, or geostationary-orbital-planning synthesis problem, which is referred to as the arc allotment problem (AAP). Each satellite administration is to be allotted a weighted-length segment of the geostationary orbital arc within which its satellites may be positioned at any longitude. The objective function maximizes the length of the unweighted arc segment allotted to every administration, subject to single-entry cochannel interference restrictions and constraints imposed by the visible arc for each administration. Useful relationships between special cases of AAP and another satellite synthesis problem are established. Solutions to two example problems are presented     

Accelerated thermal decomposition of AlH3 for hydrogen-fueled vehicles

The potential for using aluminum hydride, AlH₃, for vehicular hydrogen storage is explored. It is shown that particle-size control and doping of AlH₃ with small levels of alkali-metal hydrides (e.g. LiH) results in accelerated desorption rates. For AlH₃–20 mol% LiH, 100 °C desorption kinetics are nearly high enough to supply vehicles. It is highly likely that 2010 gravimetric and volumetric vehicular system targets (6 wt% H₂ and 0.045 kg/L) can be met with onboard AlH₃. However, a new, low-cost method of off-board regeneration of spent Al back to AlH₃ is needed. PACS 68.43.Vx; 68.43.Mn; 83.80.Fg; 84.60.Ve; 51.30.+i; 61.10.Nz     

Injection current flow through thin insulator films

The equations and boundary conditions describing injection current flow through insulators are investigated for the case of thin insulator films. The carrier mobility is assumed to be constant and trapping is neglected. The thickness of the insulator film is taken to be small enough so that surface properties are significant. It is found that electrons flowing in from the metal contacts can increase the insulator conductivity by orders of magnitude. The diffusion term in the current equation is not neglected, and it is found that this enhances the quadratic Mott-Gurney current term. The theoretical results are compared with previous experimental results.     

Separation axioms in fuzzy topological spaces

This paper provides a hierarchy of separation properties for fuzzy topological spaces which are generalizations of the standard topological notions.