Optimized modeling and design of a pcm-enhanced h2 storage

Thermal and mechanical energy storage is pivotal for the effective exploitation of renewable energy sources, thus fostering the transition to a sustainable economy. Hydrogen-based systems are among the most promising solutions for electrical energy storage. However, several technical and economic barriers (e.g., high costs, low energy and power density, advanced material requirements) still hinder the diffusion of such solutions. Similarly, the realization of latent heat storages through phase change materials is particularly attractive because it provides high energy density in addition to allowing for the storage of the heat of fusion at a (nearly) constant temperature. In this paper, we posit the challenge to couple a metal hydride H-2 canister with a latent heat storage, in order to improve the overall power density and realize a passive control of the system temperature. A highly flexible numerical solver based on a hybrid Lattice Boltzmann Phase-Field (LB-PF) algorithm is developed to assist the design of the hybrid PCM-MH tank by studying the melting and solidification processes of paraffin-like materials. The present approach is used to model the storage of the heat released by the hydride during the H-2 loading process in a phase change material (PCM). The results in terms of Nusselt numbers are used to design an enhanced metal-hydride storage for H-2-based energy systems, relevant for a reliable and cost-effective "Hydrogen Economy". The application of the developed numerical model to the case study demonstrates the feasibility of the posited design. Specifically, the phase change material application significantly increases the heat flux at the metal hydride surface, thus improving the overall system power density

Electric field control of a quantum spin liquid in weak Mott insulators

The triangular lattice Hubbard model at strong coupling, whose effective spin model contains both Heisenberg and ring exchange interactions, exhibits a rich phase diagram as the ratio of the hopping $t$ to onsite Coulomb repulsion $U$ is tuned. This includes a chiral spin liquid (CSL) phase. Nevertheless, this exotic phase remains challenging to realize experimentally because a given material has a fixed value of $t/U$ that can difficultly be tuned with external stimuli. One approach to address this problem is applying a DC electric field, which renormalizes the exchange interactions as electrons undergo virtual hopping processes; in addition to creating virtual doubly occupied sites, electrons must overcome electric potential energy differences. Performing a small $t/U$ expansion to fourth order, we derive the ring exchange model in the presence of an electric field and find that it not only introduces spatial anisotropy but also tends to enhance the ring exchange term compared to the dominant nearest-neighbor Heisenberg interaction. Thus, increasing the electric field serves as a way to increase the importance of the ring exchange at constant $t/U$. Through density matrix renormalization group calculations, we compute the ground state phase diagram of the ring exchange model for two different electric field directions. In both cases, we find that the electric field shifts the phase boundary of the CSL towards a smaller ratio of $t/U$. Therefore, the electric field can drive a magnetically ordered state into the CSL. This explicit demonstration opens the door to tuning other quantum spin systems into spin liquid phases via the application of an electric field.Comment: 9 + 17 pages, 10 + 13 figure

Classification of Distinct Fuzzy Subgroups of the Dihedral Group Dp nq for p and q distinct primes and n ∈ N

In this dissertation, we classify distinct fuzzy subgroups of the dihedral group Dpnq, for p and q distinct primes and n ∈ N, under a natural equivalence relation of fuzzy subgroups and a fuzzy isomorphism. We aim to present formulae for the number of maximal chains and the number of distinct fuzzy subgroups of this group. Our study will include some theory on non-abelian groups since the classification of distinct fuzzy subgroups of this group relies on the crisp characterization of maximal chains. We give the definition of a natural equivalence relation introduced by Murali and Makamba in [67] which we will use in this study. Based on this definition, we introduce two counting techniques that we will use to compute the number of distinct fuzzy subgroups of Dpnq. In this dissertation, we use the criss-cut counting technique as our primary method of enumeration, and the cross-cut method serves as a means of verifying results we obtain from our primary method. To classify distinct fuzzy subgroups of this group, we begin by investigating the dihedral groups Dpnq, for p and q distinct primes and specific values of n = 2 and 3 to observe a trend. We classify the flags of these groups using the characterization of flags introduced in [93]. From this characterization, we then present formulae for the number of distinct fuzzy subgroups attributed to the flags of Dp 2q and Dp 3q . To generalise results for Dpnq, for p and q distinct primes and n ∈ N, we characterize the flags of this group and classify them as either cyclic, mdcyclic for 1 ≤ m ≤ n, or b-cyclic. Finally, we establish a general formula for the number of distinct fuzzy subgroups obtainable from these flags. We conclude by comparing results obtained from using our general formula to those obtained by other researchers for the same group. Based on the results from this study, we give an outline of future research wor

New Advances of Cavitation Instabilities

Cavitation refers to the formation of vapor cavities in a liquid when the local pressure becomes lower than the saturation pressure. In many hydraulic applications, cavitation is considered as a non-desirable phenomenon, as far as it may cause performance degradation, vibration problems, enhance broad-band noise-emission, and eventually trigger erosion. In this Special Issue, recent findings about cavitation instabilities are reported. More precisely, the dynamics of cavitation sheets are explored at very low Reynolds numbers in laminar flows, and in microscale applications. Both experimental and numerical approach are used. For the latter, original methods are assessed, such as smooth particles hydrodynamics or detached eddy simulations coupled to a compressible approach

Pseudoparticle approach to 1D integrable quantum models

Over the last three decades a large number of experimental studies on several quasi one-dimensional (1D) metals and quasi 1D Mott–Hubbard insulators have produced evidence for distinct spectral features identified with charge-only and spin-only fractionalized particles. They can be also observed in ultra-cold atomic 1D optical lattices and quantum wires. 1D exactly solvable models provide nontrivial tests of the approaches for these systems relying on field theories. Different schemes such as the pseudofermion dynamical theory (PDT) and the mobile quantum impurity model (MQIM) have revealed that the 1D correlated models high-energy physics is qualitatively different from that of a low-energy Tomonaga–Luttinger liquid (TLL). This includes the momentum dependence of the exponents that control the one- and two-particle dynamical correlation functions near their spectra edges and in the vicinity of one-particle singular spectral features. On the one hand, the low-energy charge-only and spin-only fractionalized particles are usually identified with holons and spinons, respectively. On the other hand, “particle-like” representations in terms of pseudoparticles, related PDT pseudofermions, and MQIM particles are suitable for the description of both the low-energy TLL physics and high-energy spectral and dynamical properties of 1D correlated systems. The main goal of this review is to revisit the usefulness of pseudoparticle and PDT pseudofermion representations for the study of both static and high-energy spectral and dynamical properties of the 1D Lieb–Liniger Bose gas, spin-1∕2 isotropic Heisenberg chain, and 1D Hubbard model. Moreover, the relation between the PDT and the MQIM is clarified. The fractionalized particles and related composite pseudoparticles/pseudofermions emerging within such non-perturbative 1D correlated systems are qualitatively different from the Fermi-liquid quasiparticles. In contrast to the holons and spinons, the relation to the electron creation and annihilation operators of the operators assWe thank M. A. N. Araujo, D. Baeriswyl, P.-A. Bares, D. Bozi, D. K. Campbell, A. H. Castro Neto, T. Cadez, R. G. Dias, J. M. E. Guerra, F. Guinea, P. Horsch, H. Q. Lin, A. Luther, L. M. Martelo, A. Moreno, S. Ostlund, K. Penc, R. G. Pereira, N. M. R. Peres, T. Prosen, J. M. Roman, M. J. Sampaio, and J. M. P. L. Santos for illuminating discussions and their contributions to common collaborations that led to some of the results on the issues being reviewed. We also thank N. Andrei, E. Castro, and H. Johannesson for illuminating discussions, and M. Belsley for the critical reading of a preliminary version of the review manuscript and useful discussions. We acknowledge our former collaborator, the late S.-J.Gu, for his important contributions to the success of our common research related to the topics reviewed here. Over the long course of his study of this problem, J. M. P. C. has benefited from discussions with P. W. Anderson, M. C. Asensio, M. Batzill, L. Carlos, Y.-H. Chen, R. Claessen, F. Essler, J. Ferrer, X.-W. Guan, E. Jeckelmann, S.-i. Kimura, V. E. Korepin, P. A. Lee, R. Micnas, S. Nemati, Y. Ohtsubo, T. Ribeiro, A. W. Sandvik, M. Sing, A. L. L. Videira, J. Voit, X.-G. Wen, S. R. White, and X. Zotos. He especially wishes to acknowledge his former collaborators, the late K. Maki, A. Muramatsu, and A. A. Ovchinnikov, for illuminating discussions on 1D correlated systems and their contributions to his understanding of the Hubbard model. He also acknowledges the late A. Imambekov for discussions that were helpful in writing this review. P. D. S. thanks K. -J. -B. Lee, J. W. Rasul, and P. Schlottmann for discussions on integrable systems. We thank the FEDER through the COMPETE Program and the Portuguese FCT in the framework of the Strategic Projects UID/FIS/04650/2013 and UID/CTM/04540/2013 and the support of the Beijing Computational Science Research Center where part of this review was written

Advanced ultrawideband imaging algorithms for breast cancer detection

Ultrawideband (UWB) technology has received considerable attention in recent years as it is regarded to be able to revolutionise a wide range of applications. UWB imaging for breast cancer detection is particularly promising due to its appealing capabilities and advantages over existing techniques, which can serve as an early-stage screening tool, thereby saving millions of lives. Although a lot of progress has been made, several challenges still need to be overcome before it can be applied in practice. These challenges include accurate signal propagation modelling and breast phantom construction, artefact resistant imaging algorithms in realistic breast models, and low-complexity implementations. Under this context, novel solutions are proposed in this thesis to address these key bottlenecks. The thesis first proposes a versatile electromagnetic computational engine (VECE) for simulating the interaction between UWB signals and breast tissues. VECE provides the first implementation of its kind combining auxiliary differential equations (ADE) and convolutional perfectly matched layer (CPML) for describing Debye dispersive medium, and truncating computational domain, respectively. High accuracy and improved computational and memory storage efficiency are offered by VECE, which are validated via extensive analysis and simulations. VECE integrates the state-of-the-art realistic breast phantoms, enabling the modelling of signal propagation and evaluation of imaging algorithms. To mitigate the severe interference of artefacts in UWB breast cancer imaging, a robust and artefact resistant (RAR) algorithm based on neighbourhood pairwise correlation is proposed. RAR is fully investigated and evaluated in a variety of scenarios, and compared with four well-known algorithms. It has been shown to achieve improved tumour detection and robust artefact resistance over its counterparts in most cases, while maintaining high computational efficiency. Simulated tumours in both homogeneous and heterogeneous breast phantoms with mild to moderate densities, combined with an entropy-based artefact removal algorithm, are successfully identified and localised. To further improve the performance of algorithms, diverse and dynamic correlation weighting factors are investigated. Two new algorithms, local coherence exploration (LCE) and dynamic neighbourhood pairwise correlation (DNPC), are presented, which offer improved clutter suppression and image resolution. Moreover, a multiple spatial diversity (MSD) algorithm, which explores and exploits the richness of signals among different transmitter and receiver pairs, is proposed. It is shown to achieve enhanced tumour detection even in severely dense breasts. Finally, two accelerated image reconstruction mechanisms referred to as redundancy elimination (RE) and annulus predication (AP) are proposed. RE removes a huge number of repetitive operations, whereas AP employs a novel annulus prediction to calculate millions of time delays in a highly efficient batch mode. Their efficacy is demonstrated by extensive analysis and simulations. Compared with the non-accelerated method, RE increases the computation speed by two-fold without any performance loss, whereas AP can be 45 times faster with negligible performance degradation

The Molecular Genetics of Wilms Tumour And The Wilms Tumour Predisposition Syndromes

A molecular genetic analysis of Wilms tumour and the Wilms tumour predisposition syndromes. Genetic analysis of Wilms tumour (WT) and WT predisposition syndromes has revealed that a complex set of genetic events are associated with the development of this tumour. This thesis analyses specific genetic loci in a series of patients and tumours in order to gain a greater understanding of the molecular aetiology of this tumour. Sporadic Wilms tumours are the most common type and constitute the bulk of the analysis presented. The WT1 gene in 11p13 was analysed using SSCP and DNA sequencing in 36 tumours. Mutations were only found in 1 of 32 sporadic Wilms tumours, strongly suggesting that WT1 has only a limited role to play in the development of sporadic WT. Karyotypic analysis and Loss of Heterozygosity (LOH) studies have implicated loci on chromosome arms 7p and 16q in Wilms tumourigenesis. Paired constitutional and tumour DNA from sporadic WT were studied for LOH using polymorphic microsatellite repeats from both these chromosomes. 15% showed LOH for 16q and there was evidence for a worse outcome in this small group. LOH for 7p was found in 10% of cases and in one tumour a homozygous deletion was detected, this finding suggests the locaton of a tumour suppressor gene on 7p. Previous analysis of Beckwith-Wiedemann syndrome (BWS) patients has suggested another WT predisposition gene lies in 11p15. Two patients with constitutional translocations were analysed using fluoresence in situ hybridisation (FISH) and trisomy for the 11p15 region was identified. Analysis of the extent of the triplication was studied using 11p15-specific cosmids. The importance of these observations in the development of WT are discussed. Perlman syndrome (PS) is another WT predisposition syndrome and cytogenetic analysis in two patients with this syndrome suggested rearrangements of 11p15. Detailed FISH and molecular analysis has been used to characterise the nature of these rearrangments. The data presented in this thesis adds to the body of evidence demonstrating the complex nature of the molecular mechanisms underlying Wilms tumorigenesis