80 research outputs found
On gauge-invariant Green function in 2+1 dimensional QED
Both the gauge-invariant fermion Green function and gauge-dependent
conventional Green function in dimensional QED are studied in the large
limit. In temporal gauge, the infra-red divergence of gauge-dependent
Green function is found to be regulariable, the anomalous dimension is found to
be . This anomalous dimension was argued to be
the same as that of gauge-invariant Green function. However, in Coulomb gauge,
the infra-red divergence of the gauge-dependent Green function is found to be
un-regulariable, anomalous dimension is even not defined, but the infra-red
divergence is shown to be cancelled in any gauge-invariant physical quantities.
The gauge-invariant Green function is also studied directly in Lorentz
covariant gauge and the anomalous dimension is found to be the same as that
calculated in temporal gauge.Comment: 8 pages, 6 figures, to appear in Phys. Rev.
Characterizing symmetry breaking patterns in a lattice by dual vortex degree of freedoms
A duality transformation in quantum field theory is usually established first
through partition functions. It is always important to explore the dual
relations between various correlation functions in the transformation. Here, we
explore such a dual relation to study quantum phases and phase transitions in
an extended boson Hubbard model at 1/3 (2/3) filling on a triangular lattice.
We develop systematically a simple and effective way to use the vortex degree
of freedoms on dual lattices to characterize both the density wave and valence
bond symmetry breaking patterns of the boson insulating states in the direct
lattices.
In addition to a checkerboard charge density wave (X-CDW) and a stripe CDW,
we find a novel CDW-VBS phase which has both local CDW and local valence bond
solid (VBS) orders. Implications on QMC simulations are addressed.
The possible experimental realizations of cold atoms loaded on optical
lattices are discussed.Comment: 4+ pages, 3 figures, REVTEX4-1, published in Philosophical Magazine,
June 28, 201
Interfacial thermal conductance in graphene/black phosphorus heterogeneous structures
Graphene, as a passivation layer, can be used to protect the black phosphorus
from the chemical reaction with surrounding oxygen and water. However, black
phosphorus and graphene heterostructures have low efficiency of heat
dissipation due to its intrinsic high thermal resistance at the interfaces. The
accumulated energy from Joule heat has to be removed efficiently to avoid the
malfunction of the devices. Therefore, it is of significance to investigate the
interfacial thermal dissipation properties and manipulate the properties by
interfacial engineering on demand. In this work, the interfacial thermal
conductance between few-layer black phosphorus and graphene is studied
extensively using molecular dynamics simulations. Two critical parameters, the
critical power Pcr to maintain thermal stability and the maximum heat power
density Pmax with which the system can be loaded, are identified. Our results
show that interfacial thermal conductance can be effectively tuned in a wide
range with external strains and interracial defects. The compressive strain can
enhance the interfacial thermal conductance by one order of magnitude, while
interface defects give a two-fold increase. These findings could provide
guidelines in heat dissipation and interfacial engineering for thermal
conductance manipulation of black phosphorus-graphene heterostructure-based
devices.Comment: 33 pages, 22 figure
Life Cycle Integration of Building Information Modeling in Infrastructure Projects
Building Information Modeling (BIM) can provide solutions to many challenges of asset management, such as missing data, incompatible software, and an unclear business process. However, current implementation of BIM in infrastructure projects has only considers limited factors, such as technology application and digital information delivery, while issues of system compatibility and information needs are still missing. Different aspects of a business are interdependent and an incompatible development of various factors might result in different levels of BIM implementation or even project failure. Comprehensive research is needed to explore the key factors and challenges of BIM implementation in infrastructure projects. This study conducted interviews and surveys with key stakeholders of infrastructure projects to explore the challenges and potential solutions of BIM implementation. Interviews were conducted with 37 professionals and surveys were conducted with 102 professional stakeholders, including owners, designers, contractors, and software vendors. Four main factors, challenges, and potential solutions were identified from content analysis of the interviews and further validated by the surveys. These factors include process factor (when), technology factor (how), people factor (who), and information factor (what). Corresponding solutions are proposed to refine the current workflow and practices
Life Cycle Integration of Building Information Modeling in Infrastructure Projects
Building Information Modeling (BIM) can provide solutions to many challenges of asset management, such as missing data, incompatible software, and an unclear business process. However, current implementation of BIM in infrastructure projects has only considers limited factors, such as technology application and digital information delivery, while issues of system compatibility and information needs are still missing. Different aspects of a business are interdependent and an incompatible development of various factors might result in different levels of BIM implementation or even project failure. Comprehensive research is needed to explore the key factors and challenges of BIM implementation in infrastructure projects. This study conducted interviews and surveys with key stakeholders of infrastructure projects to explore the challenges and potential solutions of BIM implementation. Interviews were conducted with 37 professionals and surveys were conducted with 102 professional stakeholders, including owners, designers, contractors, and software vendors. Four main factors, challenges, and potential solutions were identified from content analysis of the interviews and further validated by the surveys. These factors include process factor (when), technology factor (how), people factor (who), and information factor (what). Corresponding solutions are proposed to refine the current workflow and practices
Real-Time Energy Management Strategy of a Fuel Cell Electric Vehicle With Global Optimal Learning
[EN] This article proposes a novel energy management strategy (EMS) for a fuel cell electric vehicle (FCEV). The strategy combines the offline optimization and online algorithms to guarantee optimal control, real-time performance, and better robustness in an unknown route. In particular, dynamic programming (DP) is applied in a database with multiple driving cycles to extract the theoretically optimal power split between the battery and fuel cell with a priori knowledge of the driving conditions. The analysis of the obtained results is then used to extract the rules to embed them in a real-time capable fuzzy controller. In this sense, at the expense of certain calibration effort in the offline phase with the DP results, the proposed strategy allows on-board applicability with suboptimal results. The proposed strategy has been tested in several actual driving cycles, and the results show energy savings between 8.48% and 10.71% in comparison to rule-based strategy and energy penalties between 1.04% and 3.37% when compared with the theoretical optimum obtained by DP. In addition, a sensitivity analysis shows that the proposed strategy can be adapted to different vehicle configurations. As the battery capacity increases, the performance can be further improved by 0.15% and 1.66% in conservative and aggressive driving styles, respectively.This work was supported in part by the National Natural Science Foundation of China
under Grant 62111530196, in part by the Technology Development Program
of Jilin Province under Grant 20210201111GX, and in part by the China
Automobile Industry Innovation and Development Joint Fund under Grant
U1864206.Hou, S.; Yin, H.; Pla Moreno, B.; Gao, J.; Chen, H. (2023). Real-Time Energy Management Strategy of a Fuel Cell Electric Vehicle With Global Optimal Learning. IEEE Transactions on Transportation Electrification (Online). 9(4):5085-5097. https://doi.org/10.1109/TTE.2023.3238101508550979
Gauge-invariant Green function in 3+1 dimensional QED (QCD) and 2+1 dimensional Abelian (Non-Abelian) Chern-Simon theory
By applying the simple and effective method developed to study the the
gauge-invariant fermion Green function in dimensional non-compact QED,
we study the gauge-invariant Green function in dimensional QED and dimensional non-compact Chern-Simon theory. We also extend our results to
the corresponding non-Abelian gauge theories. Implications for
Fractional Quantum Hall effect are briefly discussed.Comment: 8 pages, 4 figures, published versio
The effects of weak disorders on Quantum Hall critical points
We study the consequences of random mass, random scalar potential and random
vector potential on the line of clean fixed points between integer/fractional
quantum Hall states and an insulator. This line of fixed points was first
identified in a clean Dirac fermion system with both Chern-Simon coupling and
Coulomb interaction in Phys. Rev. Lett. {\bf 80}, 5409 (1998). By performing a
Renormalization Group analysis in 1/N (N is the No. of species of Dirac
fermions) and the variances of three disorders , we find that is irrelevant along this line, both
and are marginal. With the presence of all the three
disorders, the pure fixed line is unstable. Setting Chern-Simon interaction to
zero, we find one non-trivial line of fixed points in plane
with dynamic exponent z=1 and continuously changing , it is stable against
small in a small range of the line ,
therefore it may be relevant to integer quantum Hall transition. Setting
, we find a fixed plane with z=1, the part of this plane with
is stable against small , therefore it may be relevant to
fractional quantum Hall transition.Comment: 16 pages, 19 figure
Quantum generated vortices, dual singular gauge transformation and zero temperature transition from d-wave superconductor to underdoped regime
By extending the original Anderson singular gauge transformation for static
vortices to two mutual flux-attaching singular gauge transformations for moving
vortices, we derive an effective action describing the zero temperature quantum
phase transition from d-wave superconductor to underdoped regime. Neglecting
the charge fluctuation first, we find that the mutual statistical interaction
is exactly marginal. In the underdoped regime, the quasi-particles are
described by 2+1 dimensional QED; in the superconducting regime, they are
essentially free. However, putting back the charge fluctuation changes the
physical picture dramatically: both the dynamic Doppler shift term and the
mutual statistical interaction become {\em irrelevant} short-ranged
interactions on both sides of the quantum critical point. There are no
spin-charge separation and {\em no} dynamic gapless gauge field in the
Cooper-pair picture. The formalism developed at is applied to study
thermally generated vortices in the vortex plasma regime near the finite
temperature KT transition.Comment: 17 pages, 7 figure
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