Dynamic TCP Acknowledgment and Other Stories about e/(e - 1)

Abstract. We present the first optimal randomized online algorithms for the TCP acknowledgment problem [3] and the Bahncard problem [5]. These problems are well known to be generalizations of the classical online ski-rental problem, however, they appeared to be harder. In this paper we demonstrate that a number of online algorithms which have optimal competitive ratios of e/(e-1) , including these, are fundamentally no more complex than ski rental. Our results also suggest a clear paradigm for solving ski-rental-like problems.     

Competitive randomized algorithms for nonuniform problems

Competitive analysis is concerned with comparing the performance of on-line algorithms with that of optimal off-line algorithms. In some cases randomization can lead to algorithms with improved performance ratios on worst-case sequences. In this paper we present new randomized on-line algorithms for snoopy caching and the spin-block problem. These algorithms achieve competitive ratios approachinge/(e–1) 1.58 against an oblivious adversary. These ratios are optimal and are a surprising improvement over the best possible ratio in the deterministic case, which is 2. We also consider the situation when the request sequences for these problems are generated according to an unknown probability distribution. In this case we show that deterministic algorithms that adapt to the observed request statistics also have competitive factors approachinge/(e–1). Finally, we obtain randomized algorithms for the 2-server problem on a class of isosceles triangles. These algorithms are optimal against an oblivious adversary and have competitive ratios that approache/(e–1). This compares with the ratio of 3/2 that can be achieved on an equilateral triangle.Supported in part by the Center for Discrete Mathematics and Theoretical Computer Science (DIMACS), an NSF Science and Technology Center funded under NSF Contract STC-88-09648 and supported by the New Jersey Commission on Science and Technology.     

Copper(I)-Dioxygen Adducts and Copper Enzyme Mechanisms

Primary copper(I)-dioxygen (O₂) adducts, cupric-superoxide complexes, have been proposed intermediates in copper-containing dioxygen-activating monooxygenase and oxidase enzymes. Here, mechanisms of C−H activation by reactive copper-(di)oxygen intermediates are discussed, with an emphasis on cupric-superoxide species. Over the past 25 years, many synthetically derived cupric-superoxide model complexes have been reported. Due to the thermal instability of these intermediates, early studies focused on increasing their stability and obtaining physical characterization. More recently, in an effort to gain insight into the possible substrate oxidation step in some copper monooxygenases, several cupric-superoxide complexes have been used as surrogates to probe substrate scope and reaction mechanisms. These cupric superoxides are capable of oxidizing substrates containing weak O−H and C−H bonds. Mechanistic studies for some enzymes and model systems have supported an initial hydrogen-atom abstraction via the cupric-superoxide complex as the first step of substrate oxidation.     

A mobile system for treating low-salinity low-activity liquid wastes

Moscow Radon Cooperative. Applied Technology Research and Development Institute. Translated from Atomnaya Énergiya, Vol. 73, no. 6, pp. 474-478, December, 1992.     

Phase Diagram, Short-Range Structure, and Amorphous Phases in the ZrO2-GeO2(-H2O) System

Gels of the ZrO₂-GeO₂(-H₂O) system have been prepared via the hydrolysis-polycondensation of zirconium and germanium isopropoxides. Phase relationships have been deduced from differential thermal analysis, thermogravimetric analysis, and shrinkage analysis and are discussed on the basis of X-ray diffractometry and Raman scattering studies. Emphasis has been given to understanding the short-range structure. A small glass-forming domain is observed in the temperature range of 600°−700°C for compositions of 30–40 mol% GeO₂.     

State-dependent accessibility and electrostatic potential in the channel of the acetylcholine receptor. Inferences from rates of reaction of thiosulfonates with substituted cysteines in the M2 segment of the alpha subunit

Ion channel function depends on the chemical and physical properties and spatial arrangement of the residues that line the channel lumen and on the electrostatic potential within the lumen. We have used small, sulfhydryl-specific thiosulfonate reagents, both positively charged and neutral, to probe the environment within the acetylcholine (ACh) receptor channel. Rate constants were determined for their reactions with cysteines substituted for nine exposed residues in the second membrane-spanning segment (M2) of the alpha subunit. The largest rate constants, both in the presence and absence of ACh, were for the reactions with the cysteine substituted for alpha Thr244, near the intracellular end of the channel. In the open state of the channel, but not in the closed state, the rate constants for the reactions of the charged reagents with several substituted cysteines depended on the transmembrane electrostatic potential, and the electrical distance of these cysteines increased from the extracellular to the intracellular end of M2. Even at zero transmembrane potential, the ratios of the rate constants for the reactions of three positively charged reagents with alpha T244C, alpha L251C, and alpha L258C to the rate constant for the reaction of an uncharged reagent were much greater in the open than in the closed state. This dependence of the rate constants on reagent charge is consistent with an intrinsic electrostatic potential in the channel that is considerably more negative in the open state than in the closed state. The effects of ACh on the rate constants for the reactions of substituted Cys along the length of alpha M2, on the dependence of the rate constants on the transmembrane potential, and on the intrinsic potential support a location of a gate more intracellular than alpha Thr244.     

Geriatric Mental Health Policy: Impact on Service Delivery and Directions for Effecting Change.

The treatment of mental health problems in older adults has advanced considerably over the past several decades. Nevertheless, the mental health needs of the nation's elderly population remain substantially unmet. This article identifies the significant but previously neglected role of regulatory policies and administrative practices in limiting the use and provision of geriatric mental health services. Such factors are the least recognized and understood by psychologists, although they are the very factors on which psychologists can have the most potential influence. This article subsequently identifies salient legislative proposals and regulatory developments, while addressing the importance of advocacy on agenda setting and policy change. The final section provides specific proposals and mechanisms at micro and macro levels for improving the geropsychology service system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis and application of an inorganic binder made from radioactive wastes

Radon Scientific Production Association, Moscow. Translated from Atomnaya énergiya, Vol. 78, No. 5, pp. 312–315, May, 1995.