Efficient digital-to-analog encoding

An important issue in analog circuit design is the problem of digital-to-analog conversion, i.e., the encoding of Boolean variables into a single analog value which contains enough information to reconstruct the values of the Boolean variables. A natural question is: what is the complexity of implementing the digital-to-analog encoding function? That question was answered by Wegener (see Inform. Processing Lett., vol.60, no.1, p.49-52, 1995), who proved matching lower and upper bounds on the size of the circuit for the encoding function. In particular, it was proven that [(3n-1)/2] 2-input arithmetic gates are necessary and sufficient for implementing the encoding function of n Boolean variables. However, the proof of the upper bound is not constructive. In this paper, we present an explicit construction of a digital-to-analog encoder that is optimal in the number of 2-input arithmetic gates. In addition, we present an efficient analog-to-digital decoding algorithm. Namely, given the encoded analog value, our decoding algorithm reconstructs the original Boolean values. Our construction is suboptimal in that it uses constants of maximum size n log n bits; the nonconstructive proof uses constants of maximum size 2n+[log n] bits     

Levels of essential and non-essential metals in leaves of the tea plant (Camellia sinensis L.) and soil of Wushwush farms,Ethiopia

Five tea clones of the Camellia assamica variety grown in Wushwush tea plantation farms, Ethiopia, were analyzed for their contents of essential, non-essential and toxic metals (K, Ca, Mg, Fe, Mn, Cu, Zn, Na, Cd and Pb) by atomic absorption flame emission spectroscopy. Both the tea leaves and the soils of the study farms showed similar accumulation patterns in their contents of the studied macronutrients. Among the macronutrient metals, K was the most abundant element in the tea leaves (17.7–24.8 mg/g) and the soils (7.14–9.73 mg/g). Mn was the predominant micronutrient heavy metal in the tea leaf tissues ranging between 501 and 1281 mg/kg. Level of Fe (29.6–100 mg/kg) in the leaf tissue was found to be the second most abundant micronutrient next to Mn whereas concentrations of Cu and Co were relatively lower both in the soil and tea samples. The toxic heavy metals Pb and Cd in the leaf tissues were present at levels too low to be detected by the analytical technique used in this study. The soils were found to be acidic (pH 5.04–5.49) with high organic matter (5.48–6.02%). Fe was the most abundant metal followed by Mn, Na and Zn in the soils. Unlike the tea leaves, the soils were found to contain traces of the toxic metal, Cd (0.02–1.10 mg/kg). The levels of most of the metals determined in this study compared well with those reported for tea leaves from some other parts of the world.     

Übergang von Packstoffbestandteilen in fettende Lebensmittel

Migration of Components of Packaging Materials into Fat-Releasing Foodstuffs A practicable legislation dealing with foodstuffs in contact with packaging material should be constructed in that way that responsibility for the observance of laws can be divided among the user of packaging material, the manufacturer of packaging material and the producer of polymers. In order to be able to formulate the corresponding legal texts, profound knowledge as to the interaction between packaging material and the foodstuff, particularly the fat-releasing foodstuff is required. The possibilities for a characterization of fatty foodstuffs as being fat-releasing are discussed as well as the influence of the foodstuff on the mechanical properties of the packaging and the migration of components of the packaging material into or onto fat-releasing foodstuffs. According to the diffusion rate of the components in the packaging material and the interaction between foodstuff and packaging material, three types of this system are discussed.     

Evaluation of Rule-of-Mixtures Predictions of Thermal Expansion in Powder-Processed Ni–Al2O3 Composites

Ni-Al₂O₃ composites containing 5 to 80 vol% Ni were produced using powder processing methods and their thermal expansion behavior was studied using dilatometry. By varying composition and relative particle sizes, either interpenetrating-phase or particle-reinforced microstructures were obtained. Experimentally determined values of the mean thermal expansion coefficient were compared with predictions made using two different rule-of-mixtures (ROM) formulations. Experimental results for interpenetrating-phase composites were in reasonable agreement with linear ROM estimates. Certain particle-reinforced microstructures that contain processing-induced damage did not correlate as well with ROM predictions. By accounting for this damage in ROM models, better agreement with experimental observations was obtained. However, linear ROM predictions were reasonable over the entire composition range.     

Seismic qualification of motor operated valves—alternate approach

This paper presents a potential alternate method for determining operating capacity of motor-operated valves subjected to seismic and other applicable loadings. As a result of programs at nuclear facilities to ensure the operational capability of MOVs (under NRC GL89-10), extensive analytical focus to develop the structural capability of valves has ensued. In the past, seismic qualification of valves typically addressed the strength of the topwork structure to resist inertial loading from excitation of the large valve actuator mass. These evaluations paid little or no consideration to the loading resulting from valve closing forces. The focus of the recent efforts is to develop the maximum operational capability of the valve, in terms of thrust, with consideration of seismic and other services loading as applicable. The alternate method outlined in this paper presents a series of thrust capacity curves, with reduction factors for seismic loading which can be applied and developed to determine safe thrust loadings without performing extensive analytical effort. A similar approach was put forward by the SQUG GIP approach to MOVs to ensure the safe operation of valves based on past earthquake experience. However, the GIP approach cannot be used to determine safe operational loads and thus has limited use in the necessary analysis required for GL89-10 programs at nuclear facilities.     

Modulation of RecA nucleoprotein function by the mutagenic UmuD'C protein complex

The RecA, UmuC, and UmuD' proteins are essential for error-prone, replicative bypass of DNA lesions. Normally, RecA protein mediates homologous pairing of DNA. We show that purified Umu(D')2C blocks this recombination function. Biosensor measurements establish that the mutagenic complex binds to the RecA nucleoprotein filament with a stoichiometry of one Umu(D')2C complex for every two RecA monomers. Furthermore, Umu(D')2C competitively inhibits LexA repressor cleavage but not ATPase activity, implying that Umu(D')2C binds in or proximal to the helical groove of the RecA nucleoprotein filament. This binding reduces joint molecule formation and even more severely impedes DNA heteroduplex formation by RecA protein, ultimately blocking all DNA pairing activity and thereby abridging participation in recombination function. Thus, Umu(D')2C restricts the activities of the RecA nucleoprotein filament and presumably, in this manner, recruits it for mutagenic repair function. This modulation by Umu(D')2C is envisioned as a key event in the transition from a normal mode of genomic maintenance by "error-free" recombinational repair, to one of "error-prone" DNA replication.     

Constrained Codes as Networks of Relations

We address the well-known problem of determining the capacity of constrained coding systems. While the one-dimensional case is well understood to the extent that there are techniques for rigorously deriving the exact capacity, in contrast, computing the exact capacity of a two-dimensional constrained coding system is still an elusive research challenge. The only known exception in the two-dimensional case is an exact (however, not rigorous) solution to the -run-length limited (RLL) system on the hexagonal lattice. Furthermore, only exponential-time algorithms are known for the related problem of counting the exact number of constrained two-dimensional information arrays. We present the first known rigorous technique that yields an exact capacity of a two-dimensional constrained coding system. In addition, we devise an efficient (polynomial time) algorithm for counting the exact number of constrained arrays of any given size. Our approach is a composition of a number of ideas and techniques: describing the capacity problem as a solution to a counting problem in networks of relations, graph-theoretic tools originally developed in the field of statistical mechanics, techniques for efficiently simulating quantum circuits, as well as ideas from the theory related to the spectral distribution of Toeplitz matrices. Using our technique, we derive a closed-form solution to the capacity related to the Path-Cover constraint in a two-dimensional triangular array (the resulting calculated capacity is ). Path-Cover is a generalization of the well known one-dimensional -RLL constraint for which the capacity is known to be .     

Nanomechanical characterization of dispersion and its effects in nano-enhanced polymers and polymer composites

In this paper, a new approach for characterizing dispersion in nano-enhanced polymers and polymer composites using nanomechanical characterization is developed. Dispersion of Carbon nanofibers (CNFs) as a model nanoscale ingredient is characterized in two model polymer systems: (a) a thermoplastic polymer processed using a Twin Screw Extruder, and (b) a thermoset epoxy processed using sonication during solvent processing. For the first time, the modulus of agglomerated nanofibers was isolated from the polymer matrix enhanced with dispersed nanofibers by using nanomechanical characterization. Thus, it was possible to use these nanomechanical properties in a microstructural model using a Rule-of-Mixtures (ROM) formulation to determine the fraction of dispersed nanofibers, which yielded a dispersion limit of 3 vol% CNFs in the nano-enhanced thermoplastic polymer and 3.5 vol% CNFs in the nano-enhanced thermoset epoxy. It was also possible to predict the modulus measured using microtensile testing, and to determine an effective modulus of 30 GPa for the CNFs, which was attributed to a spring-like effect from kinking along the nanofibers. Applying this characterization to control of dispersion through sonication in the nano-enhanced thermoset epoxy, it was possible to determine the degree of dispersion with sonication time which was described using an Avrami equation. Finally, a carbon-fiber mat was used to create a model nano-enhanced polymer composite whose properties were found to be insensitive to sonication time due to filtering effects from the carbon-fiber mat and varied with CNF concentration in a manner where the CNF modulus could be extrapolated to 30 GPa, consistent with the nano-enhanced polymers.     

Role of the syllable in the processing of spoken English: Evidence from a nonword comparison task.

Previous research using monitoring tasks suggests that syllables do not play a role in the initial processing of speech by English listeners. The role of syllables in a different task, 1 involving the speeded comparison of 2 nonwords, was investigated. In 2 experiments, responses to nonword pairs that shared a complete syllable were significantly faster than responses to pairs that shared part of a syllable when the shared unit was at the beginning or in the middle of the nonwords. Results were mixed when the shared unit was at the end of the nonwords, possibly reflecting a confounding effect of rhyme. Findings suggest that syllabified representations of the nonwords may be used in a comparison task, even in English. Results are interpreted relative to different demands of the nonword comparison and monitoring tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluating microstructural and damage effects in rule-of-mixtures predictions of the mechanical properties of Ni-Al2O3 composites

Ni-Al₂O₃ composites containing 0 to 100 vol % Ni were fabricated using powder processing techniques. By varying the metal : ceramic particle size ratio, either particle-reinforced or interpenetrating-phase microstructures were obtained. The mechanical properties of the composites were characterized and compared with rule-of-mixtures (ROM) predictions. For certain particle-reinforced composites, the elastic moduli measured ultrasonically did not obey the ROM. This result was attributed to the presence of damage that could be accounted for using existing models. In four-point bending, most composites exhibited linear elastic behavior, however significant inelastic deformation was observed for composites containing 60 and 80 vol % Ni. The inelastic deformation was reasonably well described using ROM models, except when substantial damage was present. Damaged materials were modeled as two phase composites containing one damage-free phase and one completely damaged phase that was assumed to behave like a porous material. The failure strains of composites with continuous ceramic phases were explained using a semi-empirical model that included both damage and residual stress effects. Fracture stresses were calculated from predicted fracture strains using a new ROM deformation model. The model was modified to include constraint effects in order to accurately describe the deformation behavior of the ductile continuous-ceramic composites.