Improving Hit-and-Run for global optimization

Improving Hit-and-Run is a random search algorithm for global optimization that at each iteration generates a candidate point for improvement that is uniformly distributed along a randomly chosen direction within the feasible region. The candidate point is accepted as the next iterate if it offers an improvement over the current iterate. We show that for positive definite quadratic programs, the expected number of function evaluations needed to arbitrarily well approximate the optimal solution is at most O(n^5/2) wheren is the dimension of the problem. Improving Hit-and-Run when applied to global optimization problems can therefore be expected to converge polynomially fast as it approaches the global optimum.Paper presented at the II. IIASA-Workshop on Global Optimization, December 9–14, 1990, Sopron (Hungary).     

TRISTAR – a tracer in situ TDLAS for atmospheric research

2 O during two airborne polar stratospheric campaigns in January and March 1997. These species were detected using integration periods of 1 s with a precision of ±2%(3σ) and a calibration accuracy of ±2.8% during a total of 11 measurement flights up to a maximum altitude of 12.5 km. More recently all three channels have been operated simultaneously for CO, CH₄, and N₂O with comparable results. Received: 5 March 1998     

Crystal structure,morphology, and phase transitions in aromatic polyimide oligomers. 3. Poly(1,4-phenyleneoxy-1,3-phenylene pyromellitimide)

An aromatic polyimide oligomer, poly(1,4-phenyleneoxy-1,3-phenylene pyromellitimide) (PMDA-3,4'-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'-oxydianiline (3,4'-ODA) via a melt-polymerization method. This method permits growth of PMDA-3,4'-ODA lamellar crystals and the crystal structure can be studied via electron diffraction (ED) and wide-angle x-ray diffraction (WAXD) experiments. Our structure analysis indicates that this polyimide possesses a two-chain orthorhombic crystal lattice with dimensions of a = 0.848, b = 0.562, and c = 3.365 nm. It has also been found that poly(amic acid) precursors with little imidization possess the same ab lateral lattice packing, but statistical departure from the ordered packing along the c-direction. Upon increasing the degree of imidization through annealing at elevated temperatures, the order along the c-axis was progressively enhanced. Increasing the annealing temperature caused the dimensions of the a- and the b-axes to expand while the crystal correlation lengths decreased laterally. Simultaneously the dimension of the c-axis shrinks with an increase of the crystal correlation length along the chain direction. Crystal morphological study via transmission electron microscopy (TEM) indicates a mainly lamellar crystal texture with different thicknesses depending upon the polymerization conditions. The end lamellar surface is usually smooth. After annealing at elevated temperatures, the lamellar end surfaces become rough, which may be due to chain motion along the c-axis. The annealed PMDA-3,4'-ODA lamellar crystals still show a large amount of defects. © 1994 John Wiley & Sons, Inc.     

Optimal dynamic multi-attribute hashing for range queries

This paper examines a partial match retrieval scheme which supports range queries for highly dynamic databases. The scheme relies on order preserving multi-attribute hashing. In general, designing optimal indexes is NP-hard. Greedy algorithms used to determine the optimal indexes for simple partial match queries are not directly applicable because there are a larger number of queries to consider in determining the optimal indexes. In this paper we present heuristic algorithms which provide near-optimal solutions. The optimisation scheme we propose can be used to design other dynamic file structures such as the grid file, BANG file and multilevel grid file to further enhance their retrieval performance taking into consideration the query distribution.     

On the Fourier Spectra of Distributions in Clifford Analysis

In recent papers by Brackx, Delanghe and Sommen, some fundamental higher dimensional distributions have been reconsidered in the framework of Clifford analysis, eventually leading to the introduction of four broad classes of new distributions in Euclidean space. In the current paper we continue the in-depth study of these distributions, more specifically the study of their behaviour in frequency space, thus extending classical results of harmonic analysis.     

Almost locatedness in uniform spaces

A weak form of the constructively important notion of locatedness is lifted from the context of a metric space to that of a uniform space. Certain fundamental results about almost located and totally bounded sets are then proved.