48 research outputs found
Diffusion metamaterials for plasma transport
Plasma technology has found widespread applications in numerous domains, yet
the techniques to manipulate plasma transport predominantly rely on magnetic
control. In this review, we present a streamlined diffusion-migration method to
characterize plasma transport. Based on this framework, the viability of the
transformation theory for plasma transport is demonstrated. Highlighted within
are three model devices designed to cloak, concentrate, and rotate plasmas
without significantly altering the density profile of background plasmas.
Additionally, insights regarding potential implications for novel physics are
discussed. This review aims to contribute to advancements in plasma technology,
especially in sectors like medicine and chemistry.Comment: For more details, see Chapter 15 of the forthcoming Springer
monograph entitled "Diffusionics: Diffusion Process Controlled by Diffusion
Metamaterials.
Convective Heat Transfer in Porous Materials
Thermal convection stands out as an exceptionally efficient thermal transport
mechanism, distinctly separate from conduction and radiation. Yet, the
inherently elusive nature of fluid motion poses challenges in accurately
controlling convective heat flow. While recent innovations have harnessed
thermal convection to achieve effective thermal conductivity, fusing thermal
convection in liquids and thermal conduction in solids together to form hybrid
thermal metamaterials is still challenging. In this review, we introduce the
latest progress in convective heat transfer. Leveraging the right porous
materials as a medium allows for a harmonious balance and synergy between
convection and conduction, establishing stable heat and fluid flows. This paves
the way for the innovative advancements in transformation thermotics. These
findings demonstrate the remarkable tunability of convective heat transport in
complex multicomponent thermal metamaterials
Click Metamaterials: Fast Acquisition of Thermal Conductivity and Functionality Diversities
Material science is an important foundation of modern society development,
covering significant areas like chemosynthesis and metamaterials. Click
chemistry provides a simple and efficient paradigm for achieving molecular
diversity by incorporating modified building blocks into compounds. In
contrast, most metamaterial designs are still case by case due to lacking a
fundamental mechanism for achieving reconfigurable thermal conductivities,
largely hindering design flexibility and functional diversity. Here, we propose
a universal concept of click metamaterials for fast realizing various thermal
conductivities and functionalities. Tunable hollow-filled unit cells are
constructed to mimic the modified building blocks in click chemistry. Different
hollow-filled arrays can generate convertible thermal conductivities from
isotropy to anisotropy, allowing click metamaterials to exhibit adaptive
thermal functionalities. The straightforward structures enable full-parameter
regulation and simplify engineering preparation, making click metamaterials a
promising candidate for practical use in other diffusion and wave systems.Comment: Here, click metamaterials have been proposed and swiftly generate
variable thermal conductivities and functionalities by using tunable
hollow-filled cells akin to the modified building blocks in click chemistry.
This breakthrough holds the promise to transform applications in a range of
diffusion and wave systems, thereby having a profound impact on the
development of materials scienc
Diffusive Pseudo-Conformal Mapping: Anisotropy-Free Transformation Thermal Media with Perfect Interface Matching
Transformation media provide a fundamental paradigm for field regulation, but
their tricky anisotropy challenges fabrication. Though optical conformal
mapping has been utilized to eliminate anisotropy, two key factors still hinder
its development in thermotics, i.e., the distinct diffusion nature and
inevitable interface mismatching. Here, we put forth the concept of diffusive
pseudo-conformal mapping, overcoming the inherent difference between diffusion
and waves and achieving perfect interface matching. The proposed mapping
directly leads to heat guiding and expanding functions with anisotropy-free
transformation thermal media, whose feasibility is confirmed by experiments or
simulations. Besides diverse applications, we provide a unified perspective for
two distinct types of prevailing bilayer cloaks by uncovering their profound
ties with pseudo-conformal mapping. These results greatly simplify the
preparation of transformation thermotics and have implications for regulating
other diffusion and wave phenomena
Reconfigurable Three-Dimensional Thermal Dome
Thermal metamaterial represents a groundbreaking approach to control heat
conduction, and, as a crucial component, thermal invisibility is of utmost
importance for heat management. Despite the flourishing development of thermal
invisibility schemes, they still face two limitations in practical
applications. First, objects are typically completely enclosed in traditional
cloaks, making them difficult to use and unsuitable for objects with heat
sources. Second, although some theoretical proposals have been put forth to
change the thermal conductivity of materials to achieve dynamic invisibility,
their designs are complex and rigid, making them unsuitable for large-scale use
in real three-dimensional spaces. Here, we propose a concept of a thermal dome
to achieve three-dimensional invisibility. Our scheme includes an open
functional area, greatly enhancing its usability and applicability. It features
a reconfigurable structure, constructed with simple isotropic natural
materials, making it suitable for dynamic requirements. The performance of our
reconfigurable thermal dome has been confirmed through simulations and
experiments, consistent with the theory. The introduction of this concept can
greatly advance the development of thermal invisibility technology from theory
to engineering and provide inspiration for other physical domains, such as
direct current electric fields and magnetic fields
Wavelet-Based Hydrological Time Series Forecasting
These days wavelet analysis is becoming popular for hydrological time series simulation and forecasting. There are, however, a set of key issues influencing the wavelet-aided data preprocessing and modeling practice that need further discussion. This article discusses four key issues related to wavelet analysis: discrepant use of continuous and discrete wavelet methods, choice of mother wavelet, choice of temporal scale, and uncertainty evaluation in wavelet-aided forecasting. The article concludes with a personal reflection on solving the four issues for improving and supplementing relevant wavelet studies, especially wavelet-based artificial intelligence modeling
Controlling mass and energy diffusion with metamaterials
Diffusion driven by temperature or concentration gradients is a fundamental
mechanism of energy and mass transport, which inherently differs from wave
propagation in both physical foundations and application prospects. Compared
with conventional schemes, metamaterials provide an unprecedented potential for
governing diffusion processes, based on emerging theories like the
transformation and the scattering cancellation theory, which enormously
expanded the original concepts and suggest innovative metamaterial-based
devices. We hereby use the term ``diffusionics'' to generalize these remarkable
achievements in various energy (e.g., heat) and mass (e.g., particles and
plasmas) diffusion systems. For clarity, we categorize the numerous studies
appeared during the last decade by diffusion field (i.e., heat, particles, and
plasmas) and discuss them from three different perspectives: the theoretical
perspective, to detail how the transformation principle is applied to each
diffusion field; the application perspective, to introduce various intriguing
metamaterial-based devices, such as cloaks and radiative coolers; and the
physics perspective, to connect with concepts of recent concern, such as
non-Hermitian topology, nonreciprocal transport, and spatiotemporal modulation.
We also discuss the possibility of controlling diffusion processes beyond
metamaterials. Finally, we point out several future directions for diffusion
metamaterial research, including the integration with artificial intelligence
and topology concepts.Comment: This review article has been accepted for publication in Rev. Mod.
Phy
Graphene Quantum Dots Doped PVDF(TBT)/PVP(TBT) Fiber Film with Enhanced Photocatalytic Performance
We report the fabrication of polyvinylidene fluoride (tetrabutyl titanate)/polyvinyl pyrrolidone ((tetrabutyl titanate))-graphene quantum dots [PVDF(TBT)/PVP(TBT)-GQDs] film photocatalyst with enhanced photocatalytic performance. The polyvinylidene fluoride (tetrabutyl titanate)/polyvinyl pyrrolidone ((tetrabutyl titanate)) [PVDF(TBT)/PVP(TBT)] film was first prepared with a dual-electrospinning method and then followed by attaching graphene quantum dots (GQDs) to the surface of the composite film through a hydrothermal method. Later, part of the PVP in the composite film was dissolved by a hydrothermal method. As a result, a PVDF(TBT)/PVP(TBT)-GQDs film photocatalyst with a larger specific surface area was achieved. The photocatalytic degradation behavior of the PVDF(TBT)/PVP(TBT)-GQDs film photocatalyst was examined by using Rhodamine B as the target contaminant. The PVDF(TBT)/PVP(TBT)-GQDs photocatalyst showed a higher photocatalytic efficiency than PVDF(TBT)-H2O, PVDF(TBT)/PVP(TBT)-H2O, and PVDF(TBT)-GQDs, respectively. The enhanced photocatalytic efficiency can be attributed to the broader optical response range of the PVDF(TBT)/PVP(TBT)-GQDs photocatalyst, which makes it useful as an effective photocatalyst under white light irradiation
Growth of 0.55eV-GaInAsSb Quaternary Alloy Films for a Thermophotovoltaic Device by Liquid Phase Epitaxy
Lattice matched Ga_(1-x)In_xAs_ySb_(1-y) quaternary alloy films for thermophotovoltaic cells were successfully grown on n-type GaSb substrates by liquid phase epitaxy. Mirror-like surfaces for the epitaxial layers were achieved and evaluated by atomic force microscopy. The composition of the Ga_(1-x)In_xAs_ySb_(1-y) layer was characterized by energy dispersive X-ray analysis with the result that x = 0.2, y = 0.17. The absorption edges of the Ga_(1-x)In_xAs_ySb_(1-y) films were determined to be 2. 256μm at room temperature by Fourier transform infrared transmission spectrum analysis, corresponding to an energy gap of 0.55eV. Hall measurements show that the highest obtained electron mobility in the undoped p-type samples is 512cm2~/(V·s) and the carrier density is 6. 1×10~(16)cm~(-3) at room temperature. Finally, GaInAsSb based thermophotovoltaic cells in different structures with quantum efficiency values of around 60% were fabricated and the spectrum response characteristics of the cells are discussed