A fast algorithm for testing for safety and detecting deadlocks in locked transaction systems

We present an O(n log n log log n) time algorithm which, given a set of n rectangles on the plane with horizontal and vertical sides, and two points s and t, determines whether there exists a monotonically increasing curve from s to t which separates two of the rectangles while avoiding all other rectangles. This solves several problems related to database concurrency control.     

The effect of lattice constant on the storage capacity of hydrogen hydrates: a Monte Carlo study

ABSTRACT

We use grand canonical Monte Carlo simulations to examine the effect of the size of hydrate cavities (as reflected through the lattice constant of the hydrate unit cell) on the efficiency of clathrate hydrates in storing hydrogen gas. With this approach, the hydrate lattice is treated as a solid substrate where gas absorption takes place. Of practical interests are cases, where the lattice-size parameters are changed in such a way that they can promote/enhance multiple cavity occupancy, namely the presence of more than one guest-gas molecule in the same hydrate cavity. This phenomenon is commonly observed in the case of hydrogen hydrates and could increase their storage capacity. A parametric analysis is also carried out to quantify the correlation between the change in the lattice constant and the storage capacity since small changes in the size of the crystal unit cell may induce significant changes in the storage capacity especially in cases where multiple cavity occupancy occurs.     

Structural and optical characterization of pyrolytic carbon derived from novolac resin

The structural and optical properties of technologically interesting pyrolytic carbons formed from cured novolac resin and cured novolac/biomass composites were studied by X-Ray Diffraction Analysis (XRD), and Fourier Transform Infrared (FTIR), Raman and Photoluminescence (PL) spectroscopy. Pyrolysis of the cured materials took place at temperatures in the range 400–1000 °C. The most important weight loss, shrinkage and structural changes of pyrolyzed composites are observed at temperatures up to 600 °C due to the olive stone component. In the same temperature range, the changes in pyrolyzed novolac are smaller. The spectroscopic analysis shows that novolac pyrolyzed up to 900 ^°C has less defects and disorder than the composites. However, above 900 ^°C, pyrolyzed novolac becomes more disordered compared to the pyrolyzed composites. It is concluded that partial replacement of novolac by olive stone in the composite materials leads to the formation of a low cost, good quality product.     

Structural and catalytic aspects of cutinase in w/o microemulsions

 Structural and catalytic properties of cutinase were studied in bis(2-ethylhexyl) sodium sulfo-succinate (AOT)-isooctane microemulsion systems. The effect of the water content of the microemulsions on the cutinase activity on an esterification reaction of lauric acid with pentanol showed that cutinase followed a bell-shaped profile presenting a maximum at w _o=9, with w _o=[H₂O]/[AOT]. Kinetic studies allowed the determi-nation of the apparent parameters K _m and V _max. Electron paramagnetic resonance (EPR) spectroscopy studies of active site labeled cutinase in microemulsions with varying w _o values showed that in all microemulsions, the mobility of the label is higher than in the aqueous solution. Furthermore, it was found that the maximum of the enzyme activity did not correspond to a reduced active site mobility. Up to w _o=9 there was an increase of both activity and active site mobility. As the water content of the system became higher, the mobility of the bound spin label further increased whereas the enzymatic activity dropped considerably. Received: 20 December 1996 Accepted: 24 February 1997     

Absolute rate coefficient determination and reaction mechanism investigation for the reaction of Cl atoms with CH2I2 and the oxidation mechanism of CH2I radicals

The gas-phase reaction of atomic chlorine with diiodomethane was studied over the temperature range 273-363 K with the very low-pressure reactor (VLPR) technique. The reaction takes place in a Knudsen reactor at pressures below 3 mTorr, where the steady-state concentration of both reactants and stable products is continuously measured by electron-impact mass spectrometry. The absolute rate coefficient as a function of temperature was given by k = (4.70 +/- 0.65) x 10-11 exp[-(241 +/- 33)/T] cm3molecule-1s-1, in the low-pressure regime. The quoted uncertainties are given at a 95% level of confidence (2sigma) and include systematic errors. The reaction occurs via two pathways: the abstraction of a hydrogen atom leading to HCl and the abstraction of an iodine atom leading to ICl. The HCl yield was measured to be ca. 55 +/- 10%. The results suggest that the reaction proceeds via the intermediate CH2I2-Cl adduct formation, with a I-Cl bond strength of 51.9 +/- 15 kJ mol-1, calculated at the B3P86/aug-cc-pVTZ-PP level of theory. Furthermore, the oxidation reactions of CHI2 and CH2I radicals were studied by introducing an excess of molecular oxygen in the Knudsen reactor. HCHO and HCOOH were the primary oxidation products indicating that the reactions with O2 proceed via the intermediate peroxy radical formation and the subsequent elimination of either IO radical or I atom. HCHO and HCOOH were also detected by FT-IR, as the reaction products of photolytically generated CH2I radicals with O2 in a static cell, which supports the proposed oxidation mechanism. Since the photolysis of CH2I2 is about 3 orders of magnitude faster than its reactive loss by Cl atoms, the title reaction does not constitute an important tropospheric sink for CH2I2.     

Temperature‐dependent rate coefficients and mechanism for the gas‐phase reaction of chlorine atoms with acetone

The rate coefficient for the gas‐phase reaction of chlorine atoms with acetone was determined as a function of temperature (273–363 K) and pressure (0.002–700 Torr) using complementary absolute and relative rate methods. Absolute rate measurements were performed at the low‐pressure regime (～2 mTorr), employing the very low pressure reactor coupled with quadrupole mass spectrometry (VLPR/QMS) technique. The absolute rate coefficient was given by the Arrhenius expression k(T) = (1.68 ± 0.27) × 10^?11 exp[?(608 ± 16)/T] cm³ molecule^?1 s^?1 and k(298 K) = (2.17 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are the 2σ (95% level of confidence), including estimated systematic uncertainties. The hydrogen abstraction pathway leading to HCl was the predominant pathway, whereas the reaction channel of acetyl chloride formation (CH₃C(O)Cl) was determined to be less than 0.1%. In addition, relative rate measurements were performed by employing a static thermostated photochemical reactor coupled with FTIR spectroscopy (TPCR/FTIR) technique. The reactions of Cl atoms with CHF₂CH₂OH (3) and ClCH₂CH₂Cl (4) were used as reference reactions with k₃(T) = (2.61 ± 0.49) × 10^?11 exp[?(662 ± 60)/T] and k₄(T) = (4.93 ± 0.96) × 10^?11 exp[?(1087 ± 68)/T] cm³ molecule^?1 s^?1, respectively. The relative rate coefficients were independent of pressure over the range 30–700 Torr, and the temperature dependence was given by the expression k(T) = (3.43 ± 0.75) × 10^?11 exp[?(830 ± 68)/T] cm³ molecule^?1 s^?1 and k(298 K) = (2.18 ± 0.03) × 10^?12 cm³ molecule^?1 s^?1. The quoted errors limits (2σ) are at the 95% level of confidence and do not include systematic uncertainties. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 724–734, 2010     

Exploring an unknown graph

We wish to explore all edges of an unknown directed, strongly connected graph. At each point, we have a map of all nodes and edges we have visited, we can recognize these nodes and edges if we see them again, and we know how many unexplored edges emanate from each node we have visited, but we cannot tell where each leads until we traverse it. We wish to minimize the ratio of the total number of edges traversed divided by the optimum number of traversals, had we known the graph. For Eulerian graphs, this ratio cannot be better than two, and two is achievable by a simple algorithm. In contrast, the ratio is unbounded when the deficiency of the graph (the number of edges that have to be added to make it Eulerian) is unbounded. Our main result is an algorithm that achieves a bounded ratio when the deficiency is bounded. © 1999 John Wiley & Sons, Inc. J Graph Theory 32: 265–297, 1999