Empirical Analysis of Various Multi-Dimensional Knapsack Heuristics

Since the multidimensional knapsack problems are NP-hard problems, the exact solutions of knapsack problems often need excessive computing time and storage space. Thus, heuristic approaches are more practical for multidimensional knapsack problems as problems get large. This thesis presents the results of an empirical study of the performance of heuristic solution procedures based on the coefficients correlation structures and constraint slackness settings. In this thesis, the three representative greedy heuristics, Toyoda, Senju and Toyoda, and Loulou and Michaelides’ methods, are studied. The purpose of this research is to explore which heuristic of the three representative greedy heuristics performs best under certain combinations of conditions between constraint slackness and correlation structures. This thesis examines three heuristics over 1120 problems which are all the two-dimensional knapsack problems (2KPs) with 100 variables created by four constraint slackness settings and 45 feasible correlation structures. Then we analyze why the best heuristic behaves as it does as a function of problem characteristics. Finally we present two new heuristics using knowledge gained in the study. When these new heuristics are competitively tested against the three representative greedy heuristics, the results show the new heuristics perform better

Developing New Multidimensional Knapsack Heuristics Based on Empirical Analysis of Legacy Heuristics

The multidimensional knapsack problem (MKP) has been used to model a variety of practical optimization and decision-making applications. Due to its combinatorial nature, heuristics are often employed to quickly find good solutions to MKPs. While there have been a variety of heuristics proposed for the MKP, and a plethora of empirical studies comparing the performance of these heuristics, little has been done to garner a deeper understanding of heuristic performance as a function of problem structure. This dissertation presents a research methodology, empirical and theoretical results explicitly aimed at gaining a deeper understanding of heuristic procedural performance as a function of test problem characteristics. This work first employs an available, robust set of two-dimensional knapsack problems in an empirical study to garner performance insights. These performance insights are tested against a larger set of problems, five-dimensional knapsack problems specifically generated for empirical testing purposes. The performance insights are found to hold in the higher dimensions. These insights are used to formulate and test a suite of three new greedy heuristics for the MKP, each improving upon its successor. These heuristics are found to outperform available legacy heuristics across a complete spectrum of test problems. Problem reduction heuristics are examined and the subsequent performance insights garnered are used to derive a new problem reduction heuristic, which is then further extended to employ a local improvement phase. These problem reduction heuristics are also found to outperform currently available approaches. Available problem test sets are shown lacking along multiple dimensions of importance for viable empirical testing. A new problem generation methodology is developed and shown to overcome the current limitations in available problem test sets. This problem generation methodology is used to generate a new set of empirical test problems specifically designed for competitive computational tests. This new test set is shown to stress existing heuristics; not only does the computational time required by these legacy heuristics increase with problem size, but solution quality is found to decrease with problem size. However, the solution quality obtained by the suite of heuristics developed in this dissertation are shown to be unaffected by problem size thereby providing a level of robust solution quality not previously seen in heuristic development for the MKP. This research demonstrates that the test problems can have a profound, and sometimes misleading, impact on the general insights gained via empirical testing, provides six new quality heuristics, and two new robust sets of test problems, one focused on empirical testing, the other focused on competitive testing

Origin of High-Temperature Superconductivity in Compressed LaH10_{10}

Room-temperature superconductivity has been one of the most challenging subjects in modern physics. Recent experiments reported that lanthanum hydride LaH$_{10{\pm}x}$ ($x$$<$1) raises a superconducting transition temperature $T_{\rm c}$ up to ${\sim}$260 (or 215) K at high pressures around 190 (150) GPa. Here, based on first-principles calculations, we reveal the existence of topological Dirac-nodal-line (DNL) states in compressed LaH$_{10}$. Remarkably, the DNLs protected by the combined inversion and time-reversal symmetry and the rotation symmetry create a van Hove singularity (vHs) near the Fermi energy, giving rise to large electronic density of states. Contrasting with other La hydrides containing cationic La and anionic H atoms, LaH$_{10}$ shows a peculiar characteristic of electrical charges with anionic La and both cationic and anionic H species, caused by a strong hybridization of the La $f$ and H $s$ orbitals. We find that a large number of electronic states at the vHs are strongly coupled to the H-derived high-frequency phonon modes that are induced via the unusual, intricate bonding network of LaH$_{10}$, thereby yielding a high $T_{\rm c}$. Our findings not only elucidate the microscopic origin of the observed high-$T_{\rm c}$ BCS-type superconductivity in LaH$_{10}$, but also pave the route for achieving room-temperature topological superconductors in compressed hydrogen-rich compounds.Comment: 9 pages, 11 figure

The importance of logistics capability in the e-commerce market

This research is focused on the importance of logistics capability and its effect on firm performance in the e-commerce market. Technology-based net companies are known to have poor business network and infrastructure compared to resource-based traditional non-net based companies. A multiple-item logistics capability measurement scale is used to measure logistics capability of the firm. Firm performance is also measured by multiple items. The results indicate that logistics capability has a positive relationship with firm performance and this relationship is stronger for net based firms than for non-net based firms. Logistics capability is perceived as the firm’s critical capability in providing a competitive advantage in both traditional and e-commerce market environments

Evaluation formulas for a conditional Feynman integral over Wiener paths in abstract Wiener space

summary:In this paper, we introduce a simple formula for conditional Wiener integrals over $C_0(\mathbb{B})$, the space of abstract Wiener space valued continuous functions. Using this formula, we establish various formulas for a conditional Wiener integral and a conditional Feynman integral of functionals on $C_0(\mathbb{B})$ in certain classes which correspond to the classes of functionals on the classical Wiener space introduced by Cameron and Storvick. We also evaluate the conditional Wiener integral and conditional Feynman integral for functionals of the form $$\exp \biggl \lbrace \int _0^T \theta (s, x(s))\mathrm{d}\eta (s) \biggr \rbrace$$ which are of interest in Feynman integration theories and quantum mechanics

Application of Stable Isotope Probing to Identify RDX-degrading Bacteria in Groundwater

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is soluble, nonvolatile cyclic nitramine explosive. Long-term manufacturing and various applications of RDX have resulted in RDX contamination in soil and groundwater. RDX is a possible human carcinogen; therefore, occurrence of RDX in groundwater has raised a public health concern. As RDX is biodegradable; bioremediation of RDX-contaminated groundwater has been recognized as a feasible cleanup technology. Several RDX-degrading isolates are known to have ability to utilize RDX as carbon and/or nitrogen source. However, little is known about these isolates and their roles in the natural or engineered systems during RDX degradation, or about RDX-degrading microbial communities in responding to engineered interventions. Stable isotope probing (SIP) is a powerful culture independent method that can identify functional active bacteria in various environmental samples. In this study, we applied SIP with ^(13)C-labeled or one of the ring-, nitro- and fully-labeled ^(15)N-RDX to identify microorganisms capable of utilizing RDX and its metabolites as carbon and/or nitrogen sources in groundwater microcosms, and to associate active RDX-degrading microbial communities in responding to engineered interventions. Derived sequences from ^(13)C-DNA were clustered in Bacteroidia, Clostridia, alpha-, beta- and delta-Proteobacteria, and Spirochaetes, which were different from previously described RDX degraders. Cheese whey amendment stimulated RDX biotransformation, altered the types of RDX-degrading bacteria, and decreased microbial community diversity. Derived sequences from ^(15)N-DNA were grouped in Clostridia, beta-Proteobacteria and Spirochaetes. In comparison to the results among ^(13)C-SIP and ^(15)N-SIP studies with presence of cheese whey, derived sequences were clustered in gamma-Proteobacteria and Bacilli. The combination of these findings suggested that RDX-degrading microorganisms in groundwater are more phylogenetically diverse than what has been inferred from studies with RDX-degrading isolates. RDX biodegradation was observed when amended microcosms with different electron acceptors: Mn(IV), Fe(III), sulfate and CO_(2) (from added succinate). Derived clones from different electron-accepting conditions were identified, which were grouped in alpha-, gamma-Proteobacteria, and Clostridia. A real-time PCR assay targeted catabolic xenB gene was validated and tested with soil and groundwater samples. The presence of xenB gene would indicate that indigenous of microbial population with xenB gene are present, which can be used to estimate the potential of natural attenuation of RDX

WaveFlex: A Smart Surface for Private CBRS Wireless Cellular Networks

We present the design and implementation of WaveFlex, the first smart surface that enhances Private LTE/5G networks operating under the shared-license framework in the Citizens Broadband Radio Service frequency band. WaveFlex works in the presence of frequency diversity: multiple nearby base stations operating on different frequencies, as dictated by a Spectrum Access System coordinator. It also handles time dynamism: due to the dynamic sharing rules of the band, base stations occasionally switch channels, especially when priority users enter the network. Finally, WaveFlex operates independently of the network itself, not requiring access to nor modification of the base station or mobile users, yet it remain compliant with and effective on prevailing cellular protocols. We have designed and fabricated WaveFlex on a custom multi-layer PCB, software defined radio-based network monitor, and supporting control software and hardware. Our experimental evaluation benchmarks an operational Private LTE network running at full line rate. Results demonstrate an 8.50 dB average SNR gain, and an average throughput gain of 4.36 Mbps for a single small cell, and 3.19 Mbps for four small cells, in a realistic indoor office scenario.Comment: 15 page

Plasmonic colloidal nanoparticles with open eccentric cavities via acid-induced chemical transformation

Surface-enhanced Raman spectroscopy (SERS) has been considered a promising technique for the detection of trace molecules in biomedicine and environmental monitoring. The ideal metal nanoparticles for SERS must not only fulfill important requirements such as high near-field enhancement and a tunable far-field response but also overcome the diffusion limitation at extremely lower concentrations of a target material. Here, we introduce a novel method to produce gold nanoparticles with open eccentric cavities by selectively adapting the structure of non-plasmonic nanoparticles via acid-mediated surface replacement. Copper oxide nanoparticles with open eccentric cavities are first prepared using a microwave-irradiation-assisted surfactant-free hydrothermal reaction and are then transformed into gold nanoparticles by an acidic gold precursor while maintaining their original structure. Because of the strong near-field enhancement occurring at the mouth of the open cavities and the very rough surfaces resulting from the uniformly covered hyperbranched sharp multi-tips and the free access of SERS molecules inside of the nanoparticles without diffusion limitation, adenine, one of the four bases in DNA, in an extremely diluted aqueous solution (1.0 pM) was successfully detected with excellent reproducibility upon laser excitation with a 785-nm wavelength. The gold nanoparticles with open eccentric cavities provide a powerful platform for the detection of ultra-trace analytes in an aqueous solution within near-infrared wavelengths, which is essential for highly sensitive, reliable and direct in vivo analysis.None1132sciescopu