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Proposes a method for reducing the nuclear polarization times in nuclear magnetic resonance studies of slowly relaxing dipolar nuclei. Reliance of the method on the magnetic field dependence of the spin-lattice relaxation times for dipolar nuclei.

Quantifying security risk is an important and yet difficult task in enterprise network security management. While metrics exist for individual software vulnerabilities, there is currently no standard way of aggregating such metrics. We present a model that can be used to aggregate vulnerability metrics in an enterprise network, producing quantitative metrics that measure the likelihood breaches can occur within a given network configuration. A clear semantic model for this aggregation is an important first step toward a comprehensive network security metric model. We utilize existing work in attack graphs and apply probabilistic reasoning to produce an aggregation that has clear semantics and sound computation. We ensure that shared dependencies between attack paths have a proportional effect on the final calculation. We correctly reason over cycles, ensuring that privileges are evaluated without any self-referencing effect. We introduce additional modeling artifacts in our probabilistic graphical model to capture and account for hidden correlations among exploit steps. The paper shows that a clear semantic model for aggregation is critical in interpreting the results, calibrating the metric model, and explaining insights gained from empirical evaluation. Our approach has been rigorously evaluated using a number of network models, as well as data from production systems. [ABSTRACT FROM AUTHOR]

Abstract: The Compound I derivative of cytochrome P450 119 (CYP1 19) was produced by laser flash photolysis of the corresponding Compound II derivative, which was first prepared by reaction of the resting enzyme with peroxynitrite. The UV-vis spectrum of the Compound I species contained an asymmetric Soret band that could be resolved into overlapping transitions centered at ∼367 and ∼41 6 nm and a Q band with λ[submax]≈max 650 nm. Reactions of the Compound I derivative with organic substrates gave epoxidized (alkene oxidation) and hydroxylated (C-H oxidation) products, as demonstrated by product studies and oxygen-i 8 labeling studies. The kinetics of oxidations by CYP1 19 Compound I were measured directly; the reactions included hydroxylations of benzyl alcohol, ethylbenzene, Tris buffer, lauric acid, and methyl laurate and epoxidations of styrene and 10-undecenoic acid. Apparent second-order rate constants, equal to the product of the equilibrium binding constant (K[subbind]) and the first-order oxidation rate constant (k[ox]), were obtained for all of the substrates. The oxidations of lauric acid and methyl laurate displayed saturation kinetic behavior, which permitted the determination of both K[subbind] and k[subox] for these substrates. The unactivated C-H positions of lauric acid reacted with a rate constant of k[subox] = 0.8 s[sup-1] at room temperature. The CYP1 19 Compound I derivative is more reactive than model Compound I species [iron(IV)-oxo porphyrin radical cations] and similar in reactivity to the Compound I derivative of the heme-thiolate enzyme chloroperoxidase. Kinetic isotope effects (k[subH]/k[subD]) for oxidations of benzyl alcohol and ethylbenzene were small, reflecting the increased reactivity of the Compound I derivative in comparison to models. Nonetheless, CYP1 19 Compound I apparently is much less reactive than the oxidizing species formed in the P450m reaction cycle. Studies of competition kinetics employing CYP119 activated by hydrogen peroxide indicated that the same oxidizing transient is formed in the photochemical reaction and in the hydrogen peroxide shunt reaction. [ABSTRACT FROM AUTHOR]

The radical cation formed by mesylate heterolysis from the 1,1-dimethyl-7,7-diphenyl-2-mesyloxy-6-heptenyl radical was studied in several solvents. Computational results suggest that the initially formed acyclic radical cation is a resonance hybrid with partial positive charge in both double bonds of 1,1-diphenyl-7-methyl-1,6-octadiene (10). Thiophenol trapping was used as the competing reaction for kinetic determinations. The acyclic radical cation rapidly equilibrates with a cyclic distonic radical cation, and thiophenol trapping gives acyclic product 10 and cyclic products, mainly trans-1-(diphenylmethyl)-2-(1-methylethenyl)cyclopentane (11). The rate constants for cyclization at ambient temperature were k = (0.5-2) × 1010 s-1, and those for ring opening were k (1.5-9) × 1010 s-1. Laser flash photolysis studies in several solvents show relatively slow processes (k = (2.5-260) × 105 s-1) that involve rate-limiting trapping reactions for the equilibrating radical cations. In mixtures of fluoroalcohols RfCH2OH in trifluoromethylbenzene, variable-temperature studies display small, and in one case a negative, activation energies, requiring equilibration reactions prior to the rate-limiting processes. Fast equilibration of acyclic and cyclic radical cations implies that product ratios can be controlled by the populations of the acyclic and cyclic species and relative rate constants for trapping each. [ABSTRACT FROM AUTHOR]

A blind nonlinear interference cancellation receiver for code-division multiple-access- (CDMA-) based communication systems operating over Rayleigh flat-fading channels is proposed. The receiver which assumes knowledge of the signature waveforms of all the users is implemented in an asynchronous CDMA environment. Unlike the conventional MMSE receiver, the proposed blind ICA multiuser detector is shown to be robust without training sequences and with only knowledge of the signature waveforms. It has achieved nearly the same performance of the conventional training-based MMSE receiver. Several comparisons and experiments are performed based on examining BER performance in AWGN and Rayleigh fading in order to verify the validity of the proposed blind ICA multiuser detector. [ABSTRACT FROM AUTHOR]

Porphyrin-manganese(V)-oxo and porphyrin-manganese(IV)-oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrin-manganese(lll) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,1 5,20-tetraphenylporphyrin (TPP), 5,1 0,1 5,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15 ,20-tetrakis(4-methylpyridiniu m)porphyrin (TMPyP). The order of reactivity for (porphyrin)MnV(O) derivatives in self-decay reactions in acetonitrile and in oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)MnV(O) in acetonitrile are k = 6.1 x 105 M-1 s-1 for cis-stilbene and k = 1.4 × 105 M-1 s-1 for diphenylmethane, and the kinetic isotope effect in oxidation of ethylbenzene and ethylbenzene-d10 is kHkD = 2.3. Competitive oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found in the LFP studies of (porphyrin)MnV(O) derivatives. The apparent rate constants for reactions of (porphyrin)MnIV(O) species show inverted reactivity order with (TPFPP) < (TMPyP) < (TPP) in reactions with cis-stilbene, triphenylamine, and triphenylphosphine. The inverted reactivity results because (porphyrin)MnIV(O) disproportionates to (porphyrin)MnIIIX and (porphyrin)MnV(O), which is the primary oxidant, and the equilibrium constants for disproportionation of (porphyrin)MV(O) are in the order (TPFPP) < (TMPyP) < (TPP). The fast comproportionation reaction of (TPFPP)MnIV(O) with (TPFPP)MnIIICl to give (TPFPP)MnIV- (O) (k= 5 × 108 M-1 s-1) and disproportionation reaction of (TPP)MIV(O) to give (TPP)MnVd (TPP)- MnV- (O) (k &ap; 5 × 05 M-1s-1) were observed. The relative populations of (porphyrin)MnVand (porphyrin)MnV(O) were determined from the ratios of observed rate constants for self-decay reactions in acetonitrile and oxidation reactions of cis-stilbene by the two oxo derivatives, and apparent disproportionation equilibrium constants for the three systems in acetonitrile were estimated. A model for oxidations under catalytic conditions is presented. [ABSTRACT FROM AUTHOR]

Focuses on a study which proposed a normalized least mean square (NLMS) estimator, which incorporates a least squares based active tap detection method. Description of the sparsely parametrized channel; Overview of the algorithm proposed; Characterization of the modified detection guided NLMS estimator; Results of simulation experiments.

Provides information on the study which considered the laser mass spectrometry (LMS) estimation of a channel that may be well approximated by an far-infrared model (FIR). System description; Motivation for active tap parametrization; Active tap detection.

Provides information on the study which analyzed the influence of filter parameter dimension and input signal characteristics on the convergence rate of the laser mass spectrometry (LMS) adaptive far-infrared radiation (FIR) estimator. System description; Averaged system equations; Convergence cost function; Cost function analysis.

Discusses four issues on the future of engineering education, practice and business in the 21st century. Change in project completion time; Information on the book `Emotional Intelligence'; How value engineering can be integrated in the design process.

The article discusses a study on the direct measurements of very large H/D kinetic isotope effects relative to the tunneling in C-H reactions by an oxoiron (IV) Porphyrin radical cation. It focuses on the high energy reactions from the enzyme-catalyzed C-H oxidation based on heme enzymes such as cytochrome enzymes.

Cytochrome P450 enzymes are commonly thought to oxidize substrates via an iron(lV)-oxo porphyrin radical cation transient termed Compound I, but kinetic studies of P450 Compounds I are essentially nonexistent. We report production of Compound I from cytochrome P450 119 (CYP119) in high conversion from the corresponding Compound II species at low temperatures in buffer mixtures containing 50% glycerol by photolysis with 365 nm light from a pulsed lamp. Compound I was studied as a reagent in oxidations of benzyl alcohol and its benzylic mono- and dideuterio isotopomers. Pseudo-first-order rate constants obtained at -50 °C with concentrations of substrates between 1.0 and 6.0 mM displayed saturation kinetics that gave binding constants for the substrate in the Compound I species (Kbind) and first-order rate constants for the oxidation reactions (kox). Representative results are Kbind = 214 M-1 and kox = 0.48 s-1 for oxidation of benzyl alcohol. For the dideuterated substrate C6H5CD2OH, kinetics were studied between -50 and -25 °C, and a van't Hoff plot for complexation and an Arrhenius plot for the oxidation reaction were constructed. The HID kinetic isotope effects (KIEs) at -50 °C were resolved into a large primary KIE (P = 11.9) and a small, inverse secondary KIE (S = 0.96). Comparison of values extrapolated to 22 °C of both the rate constant for oxidation of C6H5CD2OH and the KIE for the nondeuterated and dideuterated substrates to values obtained previously in laser flash photolysis experiments suggested that tunneling could be a significant component of the total rate constant at -50 °C. [ABSTRACT FROM AUTHOR]

The use of multiple radar configurations can overcome some of the geometrical limitations that exist when obtaining radar images of a target using inverse synthetic aperture radar (ISAR) techniques. It is shown here how a particular bistatic configuration can produce three view angles and three ISAR images simultaneously. A new ISAR signal model is proposed and the applicability of employing existing monostatic ISAR techniques to bistatic configurations is analytically demonstrated. An analysis of the distortion introduced by the bistatic geometry to the ISAR image point spread function (PSF) is then carried out and the limits of the applicability of ISAR techniques (without the introduction of additional signal processing) are found and discussed. Simulations and proof of concept experimental data are also provided that support the theory. [ABSTRACT FROM AUTHOR]

The paper presents theoretical and experimental investigations into performances of narrowband uniformly and nonuniformly spaced adaptive linear dipole array antennas that are subjected to pointing errors. The analysis focuses on the array's output Signal to Interference plus Noise Ratio. The presence of mutual coupling between the array elements is taken into account. It is shown that the array's tolerance to pointing errors can be enhanced by controlling the interelement spacing. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2233–2237, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21904 [ABSTRACT FROM AUTHOR]

Photolyses of metastable porphyrin-iron(IV) diperchiorates in laser flash photolysis reactions gave highly reactive transients. The systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,1 5,20-tetramesitylporphyrin (TMP), and 2,3,7,8,12,13,17,1 8-octaethylporphyrin (OEP). The new species, which decayed within milliseconds in acetonitrile solutions, were shown to react with organic substrates by oxo-transfer reactions involving insertions into carbon-carbon double bonds of alkenes and styrenes or benzylic carbon-hydrogen bonds of arenes. The order of reactivity was OEP > TPP > TMP. Second- order rate constants for reactions with several substrates at 22 °C were determined; representative values of rate constants for the TPP derivative were k = 8.6 x 105 M-1 s-1 for styrene, k = 2.5 x 106 M-1 s-1 for cyclohexene, and k = 7.7 x 104 M-1 s-1 for ethylbenzene. These porphyrin-iron-oxo transients reacted 4-5 orders of magnitude faster than the corresponding iron(IV)-oxo porphyrin radical cations with rate constants similar to those of porphyrin-manganese(V)-oxo derivatives. Rate constants for oxidations of benzylic C-H positions of arenes correlated with the C-H bond dissociation energies, and Hammett correlations for reactions with substituted styrenes had p+ values ranging from -0.5 to -0.7, reflecting electrophilic character of the oxidants and their high reactivity. On the basis of their unique UV-visible spectra, high reactivities, and oxo-transfer properties, the new transients are tentatively identified as porphyrin-iron(V)-oxo perchlorates, electronic isomers (or valence tautomers) of well-known iron(IV)-oxo porphyrin radical cations. [ABSTRACT FROM AUTHOR]