Lower Bound Value Research Articles

First observations of H2O and CO2vapor in comet 67P/Churyumov-Gerasimenko made by VIRTIS onboard Rosetta

Context. Outgassing from cometary nuclei involves complex surface and subsurface processes that need to be understood to investigate the composition of cometary ices from coma observations. Aims. We investigate the production of water, carbon dioxide, and carbon monoxide from the nucleus of comet 67P/Churyumov-Gerasimenko (67P). These species have different volatility and are key species of cometary ices. Methods. Using the high spectral-resolution channel of the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H), we observed the ν3 vibrational bands of H2O and CO2 at 2.67 and 4.27 μm, respectively, from 24 November 2014 to 24 January 2015, when comet 67P was between 2.91 and 2.47 AU from the Sun. Observations were undertaken in limb-viewing geometry at distances from the surface of 0 to 1.5 km and with various line-of-sight (LOS) orientations in the body-fixed frame. A geometry tool was used to characterize the position of the LOS with respect to geomorphologic regions and the illumination properties of these regions. Results. The water production of 67P did not increase much from 2.9 to 2.5 AU. High water column densities are observed for LOS above the neck regions, suggesting they are the most productive in water vapor. While water production is weak in regions with low solar illumination, CO2 is outgassing from both illuminated and non-illuminated regions, which indicates that CO2 sublimates at a depth that is below the diurnal skin depth. The CO2/H2O column density ratio varies from 2 to 60%. For regions that are in sunlight, mean values between 2 and 7% are measured. The lower bound value is likely representative of the CO2/H2O production rate ratio from the neck regions. For carbon monoxide, we derive column density ratios CO/H2O < 1.9% and CO/CO2< 80%. An illumination-driven model, with a uniformly active surface releasing water at a mean rate of 8 × 1025 s-1, provides an overall agreement to VIRTIS-H data, although some mismatches show local surface inhomogeneities in water production. Rotational temperatures of 90–100 K are derived from H2O and CO2 averaged spectra.

Parallel search for maximum satisfiability

The predominance of multicore processors has increased the interest in developing parallel Boolean Satisfiability (SAT) solvers. As a result, more parallel SAT solvers are emerging. Even though parallel approaches are known to boost per- formance, parallel approaches developed for Boolean optimization are scarce. This paper proposes parallel search algorithms for Maximum Satisfiability (MaxSAT) and introduces PWBO, a new parallel solver for partial MaxSAT. Using two threads, an unsatisfiability-based algorithm is used to search on the lower bound of the optimal solution, while at the same time a linear search is performed on the upper bound of the optimal solution. Moreover, learned clauses are shared between threads during the search. For a larger number of threads two different strategies are proposed. The first strategy performs a portfolio approach by searching on the lower and upper bound values of the optimal solution using different encodings of cardinality constraints for each thread. The second strategy splits the search space considering different upper bound values of the optimal solution for each thread. Experimental results show that the techniques proposed in the paper enable PWBO to improve when increasing the number of threads.

The Stochastic Grid Bundling Method: Efficient pricing of Bermudan options and their Greeks

This paper describes a practical simulation-based algorithm, which we call the Stochastic Grid Bundling Method (SGBM) for pricing multi-dimensional Bermudan (i.e. discretely exercisable) options. The method generates a direct estimator of the option price, an optimal early-exercise policy as well as a lower bound value for the option price. An advantage of SGBM is that the method can be used for fast approximation of the Greeks (i.e., derivatives with respect to the underlying spot prices, such as delta, gamma, etc.) for Bermudan-style options. Computational results for various multi-dimensional Bermudan options demonstrate the simplicity and efficiency of the algorithm proposed.

Experimental investigation and numerical simulation of granite powder filled polymer composites for wind turbine blade: A comparative analysis

This paper describes the mechanical, thermo‐mechanical, and thermal behavior of unfilled E‐glass fiber (10–50 wt%) reinforced polymer (GFRP) composites and granite powder filled (8–24 wt%) GFRP composite in different weight percentages, respectively. The void fraction of unfilled glass epoxy composite is decreased from 7.71% to 3.17% with the increase in fiber loading from 10 to 50 wt%. However, void fraction for granite powder filled GFRP composites show reverse in trend. The granite powder addition in glass‐epoxy composites show significant improvement in hardness (37–47 Hv), impact strength (31.56–37.2 kJ/m2), and stress intensity factor (by 14.29% for crack length of 5 mm) of the composites. The thermo‐mechanical analyses also show strong correlation with the mechanical performance of the composites. The minimum difference of 0.17 GPa in storage and flexural moduli are observed for unfilled 20 wt% glass epoxy composite; whereas, maximum difference of 0.71 GPa is recorded for unfilled 50 wt% glass epoxy composite. Moreover, the numerical and experimentally measured thermal conductivity of unfilled and granite powder filled epoxy composites are within the lower and upper bound values. Hence, a successful attempt is presented for mechanical analysis of full scale model by finite element analysis. The results show that finite element analysis predicted reasonably actual stress value and tip deflection of wind turbine blade. POLYM. COMPOS., 38:1335–1352, 2017. © 2015 Society of Plastics Engineers

Dynamic Entropy Based Combination Weighted Clustering Approach for High-Speed Ad hoc Network

Weight based clustering has become the mainstream clustering algorithm in low-speed Ad hoc networks because of its excellent cluster stability. However, due to the dynamic topology changing in high-speed Ad hoc network, the cluster stability (network stability) decreased and the cluster maintenance costs increased sharply. To solve the problem, we propose a dynamic entropy based combination weighted clustering approach (DECW). First, according to the history messages of an evaluation node in the network, the upper bound and the lower bound value of each clustering index will be recorded, so the information entropy deviation of the indexes and dynamic entropy weight of each node can be obtained. After, the linear combination weights set of evaluation nodes is modeled as the second-order norm game , and the weight vector deviation is minimized as the optimization goal to get the multi-node dynamic entropy weights. In the cluster maintenance, a new Monte Carlo optimization is proposed to avoid the frequent clusterheads (CHs) replacement induced of high node mobility of. Simulation results reveal that the proposed approach has the better adaptability in high-speed mobile environment.

Inexact Multistage Fuzzy-Stochastic Programming Model for Water Resources Management

AbstractIn this study, an inexact multistage fuzzy-stochastic programming (IMFSP) model was developed for water resources management under uncertainty. In the IMFSP model, the uncertainties existing in the objective functions, and the constraints’ left side and right side are expressed as fuzzy sets so that the uncertainties can be directly communicated into the optimization process and various water allocation schemes can be obtained under different α-cut levels at a plurality of periods regardless of the shapes of their membership functions. The IMFSP model can not only generate the most possible, lower and upper bound values for all possible decision schemes but it can also provide information about the degrees of membership of the decision variables between the lower and upper bound values. Meanwhile, the scenario-based multistage stochastic programming was incorporated in the IMFSP model to adequately reflect the dynamic variations and uncertain information of the water resources system. Therefore, t...

Monogamy, polygamy, and other properties of entanglement of purification

For bipartite pure and mixed quantum states, in addition to the quantum mutual information, there is another measure of total correlation, namely, the entanglement of purification. We study the monogamy, polygamy, and additivity properties of the entanglement of purification for pure and mixed states. In this paper, we show that, in contrast to the quantum mutual information which is strictly monogamous for any tripartite pure states, the entanglement of purification is polygamous for the same. This shows that there can be genuinely two types of total correlation across any bipartite cross in a pure tripartite state. Furthermore, we find the lower bound and actual values of the entanglement of purification for different classes of tripartite and higher-dimensional bipartite mixed states. Thereafter, we show that if entanglement of purification is not additive on tensor product states, it is actually subadditive. Using these results, we identify some states which are additive on tensor products for entanglement of purification. The implications of these findings on the quantum advantage of dense coding are briefly discussed, whereby we show that for tripartite pure states, it is strictly monogamous and if it is nonadditive, then it is superadditive on tensor product states.

Robust Joint Transmit Beamforming With QoS Guarantees in Time-Asynchronous DAS

This paper studies the joint transmit beamforming optimization in the downlink of a single-cell multiuser distributed antenna system. Due to the distributed nature of transmit antennas, the signals received from different distributed antenna units (DAUs) will experience various transmission delays, and it is difficult to realize accurate symbol-level time synchronization at the user terminal. Thus, we turn to finding a robust joint transmit beamforming algorithm by replacing the received signal-to-interference-plus-noise ratio (SINR) with its lower-bound value. Moreover, the joint transmission incurs huge amount of data sharing among DAUs. Under the per-DAU maximum transmit power constraint, we aim to minimize the system backhaul overhead while satisfying the quality-of-service (QoS) requirement of each user. Since the backhaul overhead minimization requires the transmit beam vectors to have a group sparse structure and is NP-hard, we first make a convex relaxation and then apply the reweighted method to improve the sparsity of the beam vectors. Furthermore, an admission control scheme is applied to guarantee the feasibility of the problem, which iteratively removes the unsatisfied user with the worst quality of experience (QoE) away from the system. Simulation results show that our proposed robust algorithm can achieve a much better performance than the traditional nonrobust algorithm when time asynchronism is less than 30% of the symbol duration and can significantly reduce the system backhaul overhead by designing group sparse transmit beam vectors.

Torque Measurements during the Spontaneous Unbraiding of DNA Molecules Showed Large Fluctuations Attributable to the Formation of Stable DNA-DNA Interactions

Magnetic tweezers dual-molecule braiding assays provide an adequate framework for studying the mechanical aspects underlying the process of winding two DNA molecules around each other. In its typical implementation however, this technique do not allow direct measurement of torque because the torque exerted by the magnetic traps (∼103 pN nm) is at least one order of magnitude larger than the restoring torque of DNA (∼ 102 pN nm). In previous work, our laboratory showed that enough elastic energy could be stored in a pair of braided DNA molecules to perform mechanical work by rotating a microscopic object in absence of manipulation. Here we have exploited that unique property of DNA to perform a real-time study of braided DNA dynamics. In our experiments, torsionally unconstrained lambda DNA molecules were bound to a surface by one end and to a microscopic dumbbell at the other. A magnetic tweezers apparatus was employed to stretch and braid the molecules. Upon creating the braid, the magnet was removed to trigger the spontaneous unbraiding of DNA. The rotational dynamics of the dumbbell was followed in real-time. Hydrodynamic equations were employed to relate the dynamical information of the dumbbells to torque values. Our most important finding is that the unbraiding process occurs in a discontinuous manner. The estimated magnitudes of torque were found to fluctuate between an upper (∼ 102 pN nm) and a lower bound (∼ 101 pN nm) value along the entire process. The magnitudes of the fluctuations were found to be independent of the amount of times that the molecules crossed each other. No different was found for braids of opposite handedness. We attributed these fluctuations to the formation/rupture of stable DNA interactions.

Deformed steel fibres as minimum shear reinforcement – a comparative appraisal

The results of a comparative appraisal of the performance of two types of deformed steel fibres – crimped and hooked-end – used as minimum shear reinforcement in reinforced concrete beams are presented. Beams conventionally detailed with the ACI building code and the Indian code (IS 456:2000) recommended minimum shear reinforcement were used as control specimens. The conventionally detailed as well as the steel-fibre-reinforced concrete (SFRC) beams showed varying degrees of multiple cracking at peak loads. The shear strengths of the SFRC beams, although smaller than those of the transversely reinforced beams, were higher than a lower bound value recommended in the literature as well as predictions from the referenced codes. Between the two deformed fibre types, the beams reinforced with the hooked-end fibres had about 50% higher shear strengths than those containing the crimped fibres. The validity of the ACI building code flexural performance criteria for judging the suitability of deformed fibres proposed to be used as minimum shear reinforcement has been examined and a simple mechanics-based shear strength predictive model considering the contribution of only the compressed concrete and tensile resistance of the SFRC has been proposed and experimentally validated.

A new method estimating the 2D Joint Roughness Coefficient for discontinuity surfaces in rock masses

Joint Roughness Coefficient (JRC) is one of the principal parameters used to calculate the shear strength and conducting aperture of discontinuities. Originally, 10 standard discontinuity profiles were commonly associated with JRC values. However, as the original profiles provided a rough estimation of joint roughness, many researchers attempted to investigate different methods of analysis to determine JRCs accurately. In the current study, we are proposing a new method for accurate JRC estimation. Firstly, we introduced a new roughness index (λ) using a Root Mean Square method, which considers inclination angle, amplitude of asperities and their directions. Secondly, the logistics function between λ and JRC was derived after locating the mean line, which is the line between maximum and minimum points of asperities. Finally, three formulae were developed to calculate upper-bound, suggested and lower-bound values of JRCs in relation to the variation of λ for two-dimensional discontinuity profiles. Comparison of our experimental test results with data available in the literature showed that the proposed roughness index, λ, can be used to determine JRC values accurately resulting in better estimation of discontinuity shear strength and conducting apertures. In addition, the sensitivity of JRC, shear strength and the ratio of mechanical aperture to conducting aperture (E/e) with respect to λ were also investigated. The results revealed that trends of JRC, shear strength and E/e ratios are similar. These parameters are found to be most sensitive when λ is in the range of 0.05–0.20.

Numerical modeling and optimization of vacuum membrane distillation module for low-cost water production

A two-dimensional numerical model, involving energy conservation, momentum transport and continuity equations, was developed to provide the profiles of temperature, velocity and pressure of vacuum membrane distillation (VMD) process using hollow fiber module. The theoretical prediction was in good agreement with the experimental results from literature. Four design and operation variables, including feed temperature, hollow fiber length, feed volume flow rate and vacuum pressure, were optimized to minimize water production cost (WPC) using genetic algorithm (GA). A case study shows that the WPC can be decreased by 38.1% in comparison with the non-optimized VMD process. Meanwhile, a general guidance for reducing the WPC was also provided. The feed temperature should be adopted as high as possible, while the hollow fiber length cannot be too long to result in a decrease in water flux and an increase in pressure drop. The flow rate is recommended to take a lower bound value and the moderate degree of vacuum is preferable. This study indicates the importance of VMD system optimization to minimize water production cost.

MIMO Underwater Acoustic Communications in Ports and Shallow Waters at Very High Frequency

Hermes is a Single-Input Single-Output (SISO) underwater acoustic modem that achieves very high-bit rate digital communications in ports and shallow waters. Here, the authors study the capability of Hermes to support Multiple-Input-Multiple-Output (MIMO) technology. A least-square channel estimation algorithm is used to evaluate multiple MIMO channel impulse responses at the receiver end. A deconvolution routine is used to separate the messages coming from different sources. This paper covers the performance of both the channel estimation and the MIMO deconvolution processes using either simulated data or field data. The MIMO equalization performance is measured by comparing three relative root mean-squared errors (RMSE), obtained by calculations between the source signal (a pseudo-noise sequence) and the corresponding received MIMO signal at various stages of the deconvolution process; prior to any interference removal, at the output of the Linear Equalization (LE) process and at the output of an interference cancellation process with complete a priori knowledge of the transmitted signal. Using the simulated data, the RMSE using LE is −20.5 dB (where 0 dB corresponds to 100% of relative error) while the lower bound value is −33.4 dB. Using experimental data, the LE performance is −3.3 dB and the lower bound RMSE value is −27 dB.

The Stochastic Grid Bundling Method: Efficient Pricing of Multidimensional Bermudan Options and the Greeks

This paper describes a practical simulation-based algorithm, which we call the Stochastic Grid Bundling Method (SGBM) for pricing multi-dimensional Bermudan (i.e. discretely exercisable) options. The method generates a direct estimator of the option price, an optimal early-exercise policy as well as a lower bound value for the option price. An advantage of SGBM is that the method can be used for fast approximation of the Greeks (i.e., derivatives with respect to the underlying spot prices, such as delta, gamma, etc) for Bermudan-style options. Computational results for various multi-dimensional Bermudan options demonstrate the simplicity and efficiency of the algorithm proposed.

Bearing Capacity of Strip Footings in Cohesionless Soil Subject to Eccentric and Inclined Loads

Lower-bound calculations based on the FEM are used to determine the bearing capacity of a strip foundation subjected to an inclined, eccentric load on cohesionless soil with varying surcharges and with friction angles of 25, 30, and 35°. The soil is assumed to be perfectly plastic following the Mohr-Coulomb failure criterion. The results are reported as graphs showing the bearing capacity as a function of the friction angle, eccentricity, inclination, and surcharge. These results have been compared, and for smaller eccentricities, except in the case of no surcharge, the lower-bound values are the greater, the discrepancy increasing with growing surcharge. Positive load inclinations have a negative effect for smaller eccentricities but may have a beneficial effect on the bearing capacity for greater eccentricities. Negative load inclinations have the opposite effect, and especially for small friction angles and great surcharges, other values are considerably greater than the lower-bound values.

Discussion of “Load tests on full-scale bored pile groups”

Discussion of “Load tests on full-scale bored pile groups”

Supply-side approaches to the economic valuation of coastal and marine habitat in the Red Sea

The degradation of natural fish habitat in the ocean implies lost economic benefits. These value losses often are not measured or anticipated fully, and therefore they are mainly ignored in decisions to develop the coast for industrial or residential purposes. In such circumstances, the ocean habitat and its associated ecosystem are treated as if they are worthless. Measures of actual or potential economic values generated by fisheries in commercial markets can be used to assess a conservative (lower-bound) value of ocean habitat. With this information, one can begin to compare the values of coastal developments to the values of foregone ocean habitat in order to help understand whether development would be justified economically. In this paper, we focus on the economic value associated with the harvesting of commercial fish stocks as a relevant case for the Saudi Arabian portion of the Red Sea. We describe first the conceptual basis behind supply-side approaches to economic valuation. Next we review the literature on the use of these methods for valuing ocean habitat. We provide an example based on recent research assessing the bioeconomic status of the traditional fisheries of the Red Sea in the Kingdom of Saudi Arabia (KSA). We estimate the economic value of ecosystem services provided by the KSA Red Sea coral reefs, finding that annual per-unit values supporting the traditional fisheries only are on the order of $7000/km2. Finally, we develop some recommendations for refining future applications of these methods to the Red Sea environment and for further research.

A Novel Histogram-Based Multi-Threshold Searching Algorithm for Multilevel Colour Thresholding

Image segmentation is an important preliminary process required in object tracking applications. This paper addresses the issue of unsupervised multi-colour thresholding design for colour-based multiple objects segmentation. Most of the current unsupervised colour thresholding techniques require adopting a supervised training algorithm or a cluster-number decision algorithm to obtain optimal threshold values of each colour channel for a colour-of-interest. In this paper, a novel unsupervised multi-threshold searching algorithm is proposed to automatically search the optimal threshold values for segmenting multiple colour objects. To achieve this, a novel ratio-map image computation method is proposed to efficiently enhance the contrast between colour and non-colour pixels. The Otsu's method is then applied to the ratio-map image to extract all colour objects from the image. Finally, a new histogram-based multi-threshold searching algorithm is developed to search the optimal upper-bound and lower-bound threshold values of hue, saturation and brightness components for each colour object. Experimental results show that the proposed method not only succeeds in separating all colour objects-of-interest in colour images, but also provides satisfactory colour thresholding results compared with an existing multilevel thresholding method.

A genetic algorithm for two-stage no-wait hybrid flow shop scheduling problem

Considering the practical application and the computational complexity of the two-stage no-wait hybrid flow shop scheduling problem, this paper proposes a genetic algorithm (GA). Based on the description of the problem and its properties, some constructive heuristics are first proposed to obtain the upper bound. Then the implementation details of the proposed GA are illustrated, in which the results of heuristics are employed into the initial population. Next, a preliminary computational test with factorial design is conducted to tune the key parameters of four versions of the proposed genetic algorithms resulting from combinations of different crossover and mutation operators. With the tuned parameters, the performance of the proposed genetic algorithms is evaluated in terms of the mean percentage deviation of the solution with respect to the lower bound value, through an extensive computational experiment. The results with different problem configurations demonstrate the effectiveness and efficiency of the proposed genetic algorithm and also demonstrate that the GA performs relatively better when the LOX (two-point linear order crossover) operator and the swap mutation operator are used.

Polybenzene multitori

Abstract Polybenzene unit BT_48 can dimerize either by identification of 8-membered rings to provide a diamond-like fcc net or by identifying the opening 12-membered rings to form intercalated dendrimer-dimers which can further grow and rather quickly superimpose over the diamond-like network. The third hypothetical moiety we consider here is an eclipsed isomer, that can form multitori as negatively curved structures of various complexity. Multitori can evolve spherically or show a linear periodicity, as in rods. The polybenzene (“armchair”) multitori BTA are compared to the (“zig-zag”) BTZ ones, proposed earlier by us. A graph-theoretical study related the structure of multitori to the genus of their embedding surface and established the lower and upper bound values of genus. The total energy per carbon atom, HOMO-LUMO gap and strain energy of BTA and BTZ multitori have been computed and the results obtained point to BTZ multitori to be at least as stable as C60 what suggests BTZ multitori can be eventually synthesized in laboratory.