3,570 research outputs found
Geometric phase and quantum phase transition in an inhomogeneous periodic XY spin-1/2 model
The notion of geometric phase has been recently introduced to analyze the
quantum phase transitions of many-body systems from the geometrical
perspective. In this work, we study the geometric phase of the ground state for
an inhomogeneous period-two anisotropic XY model in a transverse field. This
model encompasses a group of familiar spin models as its special cases and
shows a richer critical behavior. The exact solution is obtained by mapping on
a fermionic system through the Jordan-Wigner transformation and constructing
the relevant canonical transformation to realize the diagonalization of the
Hamiltonian coupled in the -space. The results show that there may exist
more than one quantum phase transition point at some parameter regions and
these transition points correspond to the divergence or extremum properties of
the Berry curvature.Comment: 6 pages, 3 figures. As a backup of a previous work and some typos in
the published version are fixe
Electricity generation and bivalent copper reduction as a function of operation time and cathode electrode material in microbial fuel cells
The performance of carbon rod (CR), titanium sheet (TS), stainless steel woven mesh (SSM) and copper sheet (CS) cathode materials are investigated in microbial fuel cells (MFCs) for simultaneous electricity generation and Cu(II) reduction, in multiple batch cycle operations. After 12 cycles, the MFC with CR exhibits 55% reduction in the maximum power density and 76% increase in Cu(II) removal. In contrast, the TS and SSM cathodes at cycle 12 show maximum power densities of 1.7 (TS) and 3.4 (SSM) times, and Cu(II) removal of 1.2 (TS) and 1.3 (SSM) times higher than those observed during the first cycle. Diffusional resistance in the TS and SSM cathodes is found to appreciably decrease over time due to the copper deposition. In contrast to CR, TS and SSM, the cathode made with CS is heavily corroded in the first cycle, exhibiting significant reduction in both the maximum power density and Cu(II) removal at cycle 2, after which the performance stabilizes. These results demonstrate that the initial deposition of copper on the cathodes of MFCs is crucial for efficient and continuous Cu(II) reduction and electricity generation over prolonged time. This effect is closely associated with the nature of the cathode material. Among the materials examined, the SSM is the most effective and inexpensive cathode for practical use in MFCs
Abelian and Non-Abelian Quantum Geometric Tensor
We propose a generalized quantum geometric tenor to understand topological
quantum phase transitions, which can be defined on the parameter space with the
adiabatic evolution of a quantum many-body system. The generalized quantum
geometric tenor contains two different local measurements, the non-Abelian
Riemannian metric and the non-Abelian Berry curvature, which are recognized as
two natural geometric characterizations for the change of the ground-state
properties when the parameter of the Hamiltonian varies. Our results show the
symmetry-breaking and topological quantum phase transitions can be understood
as the singular behavior of the local and topological properties of the quantum
geometric tenor in the thermodynamic limit.Comment: 5 pages, 2 figure
Correlation between circuital current, Cu(II) reduction and cellular electron transfer in EAB isolated from Cu(II)-reduced biocathodes of microbial fuel cells
The performance of four indigenous electrochemically active bacteria (EAB) (Stenotrophomonas maltophilia JY1, Citrobacter sp. JY3, Pseudomonas aeruginosa JY5 and Stenotrophomonas sp. JY6) was evaluated for Cu(II) reduction on the cathodes of microbial fuel cells (MFCs). These EAB were isolated from well adapted mixed cultures on the MFC cathodes operated for Cu(II) reduction. The relationship between circuital current, Cu(II) reduction rate, and cellular electron transfer processes was investigated from a mechanistic point of view using X-ray photoelectron spectroscopy, scanning electronic microscopy coupled with energy dispersive X-ray spectrometry, linear sweep voltammetry and cyclic voltammetry. JY1 and JY5 exhibited a weak correlation between circuital current and Cu(II) reduction. A much stronger correlation was observed for JY3 followed by JY6, demonstrating the relationship between circuital current and Cu(II) reduction for these species. In the presence of electron transfer inhibitors (2,4-dinitrophenol or rotenone), significant inhibition on JY6 activity and a weak effect on JY1, JY3 and JY5 was observed, confirming a strong correlation between cellular electron transfer processes and either Cu(II) reduction or circuital current. This study provides evidence of the diverse functions played by these EAB, and adds to a deeper understanding of the capabilities exerted by diverse EAB associated with Cu(II) reduction
The Classical Limit of Quantum Mechanics and the Fejer Sum of the Fourier Series Expansion of a Classical Quantity
In quantum mechanics, the expectation value of a quantity on a quantum state,
provided that the state itself gives in the classical limit a motion of a
particle in a definite path, in classical limit goes over to Fourier series
form of the classical quantity. In contrast to this widely accepted point of
view, a rigorous calculation shows that the expectation value on such a state
in classical limit exactly gives the Fej\'{e}r's arithmetic mean of the partial
sums of the Fourier series
Intensified degradation and mineralization of antibiotic metronidazole in photo-assisted microbial fuel cells with Mo-W catalytic cathodes under anaerobic or aerobic conditions in the presence of Fe(III)
A novel strategy to intensify the degradation and mineralization of the antibiotic drug metronidazole (MNZ) in water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs). In this system Mo and W catalytic species immobilized onto a graphite felt cathode intensified the cathodic reduction of MNZ under anaerobic conditions and the oxidation of MNZ under aerobic conditions. The aerobic oxidation process was further accelerated in the presence of Fe(III), realizing a combined photo-assisted MFCs and Fenton-MFCs process. The highest rates of MNZ degradation (94.5 ± 1.4%; 75.6 ± 1.1 mg/L/h) and mineralization (89.5 ± 1.1%; 71.6 ± 0.9 mg/L/h), and power production (251 mW/m2; 0.015 kWh/m3; 0.22 kWh/kg COD) were achieved at a Mo/W loading of 0.18 mg/cm2 with a Mo/W ratio of 0.17:1.0, in the presence of 10 mg/L of Fe(III) and at an incident photon flux of 23.3 mW/cm2. Photo-generated holes were directly involved into the oxidation of MNZ under anaerobic conditions. Conversely, under aerobic conditions, the photo-generated electrons favored the production of O2[rad]− over [rad]OH, while in the presence of Fe(III), [rad]OH was predominant over O2[rad]−, explaining the intensification of the MNZ mineralization observed. This study demonstrates an alternative and environmentally benign approach for the intensification of the removal of the antibiotic MNZ in water and possibly other contaminants of emerging concern by combining photo-assisted MFCs and Fenton-MFCs in a single process with simultaneous production of renewable electrical energy
Entanglement in spin-1/2 dimerized Heisenberg systems
We study entanglement in dimerized Heisenberg systems. In particular, we give
exact results of ground-state pairwise entanglement for the four-qubit model by
identifying a Z_2 symmetry. Although the entanglements cannot identify the
critical point of the system, the mean entanglement of nearest-neighbor qubits
really does, namely, it reaches a maximum at the critical point.Comment: Four pages, three figures, accepted in Communications in Theoretical
Physic
PERGA: A Paired-End Read Guided De Novo Assembler for Extending Contigs Using SVM and Look Ahead Approach
Since the read lengths of high throughput sequencing (HTS) technologies are short, de novo assembly which plays significant roles in many applications remains a great challenge. Most of the state-of-the-art approaches base on de Bruijn graph strategy and overlap-layout strategy. However, these approaches which depend on k-mers or read overlaps do not fully utilize information of paired-end and single-end reads when resolving branches. Since they treat all single-end reads with overlapped length larger than a fix threshold equally, they fail to use the more confident long overlapped reads for assembling and mix up with the relative short overlapped reads. Moreover, these approaches have not been special designed for handling tandem repeats (repeats occur adjacently in the genome) and they usually break down the contigs near the tandem repeats. We present PERGA (Paired-End Reads Guided Assembler), a novel sequence-reads-guided de novo assembly approach, which adopts greedy-like prediction strategy for assembling reads to contigs and scaffolds using paired-end reads and different read overlap size ranging from Omax to Omin to resolve the gaps and branches. By constructing a decision model using machine learning approach based on branch features, PERGA can determine the correct extension in 99.7% of cases. When the correct extension cannot be determined, PERGA will try to extend the contig by all feasible extensions and determine the correct extension by using look-ahead approach. Many difficult-resolved branches are due to tandem repeats which are close in the genome. PERGA detects such different copies of the repeats to resolve the branches to make the extension much longer and more accurate. We evaluated PERGA on both Illumina real and simulated datasets ranging from small bacterial genomes to large human chromosome, and it constructed longer and more accurate contigs and scaffolds than other state-of-the-art assemblers. PERGA can be freely downloaded at https://github.com/hitbio/PERGA.published_or_final_versio
Entanglement, quantum phase transition and scaling in XXZ chain
Motivated by recent development in quantum entanglement, we study relations
among concurrence , SU(2) algebra, quantum phase transition and
correlation length at the zero temperature for the XXZ chain. We find that at
the SU(2) point, the ground state possess the maximum concurrence. When the
anisotropic parameter is deformed, however, its value decreases. Its
dependence on scales as in the XY metallic
phase and near the critical point (i.e. ) of the Ising-like
insulating phase. We also study the dependence of on the correlation length
, and show that it satisfies near the critical point. For
different size of the system, we show that there exists a universal scaling
function of with respect to the correlation length .Comment: 4 pages, 3 figures. to appear in Phys. Rev.
A Cellular Automata Model with Probability Infection and Spatial Dispersion
In this article, we have proposed an epidemic model by using probability
cellular automata theory. The essential mathematical features are analyzed with
the help of stability theory. We have given an alternative modelling approach
for the spatiotemporal system which is more realistic and satisfactory from the
practical point of view. A discrete and spatiotemporal approach are shown by
using cellular automata theory. It is interesting to note that both size of the
endemic equilibrium and density of the individual increase with the increasing
of the neighborhood size and infection rate, but the infections decrease with
the increasing of the recovery rate. The stability of the system around the
positive interior equilibrium have been shown by using suitable Lyapunov
function. Finally experimental data simulation for SARS disease in China and a
brief discussion conclude the paper
- …