Landslide identification using machine learning

Landslide identification is critical for risk assessment and mitigation.This paper proposes a novel machinelearning and deep-learning method to identify natural-terrain landslides using integrated geodatabases.First,landslide-related data are compiled,including topographic data,geological data and rainfall-related data.Then,three integrated geodatabases are established;namely,Recent Landslide Database(Rec LD),Relict Landslide Database(Rel LD)and Joint Landslide Database(JLD).After that,five machine learning and deep learning algorithms,including logistic regression(LR),support vector machine(SVM),random forest(RF),boosting methods and convolutional neural network(CNN),are utilized and evaluated on each database.A case study in Lantau,Hong Kong,is conducted to demonstrate the application of the proposed method.From the results of the case study,CNN achieves an identification accuracy of 92.5%on Rec LD,and outperforms other algorithms due to its strengths in feature extraction and multi dimensional data processing.Boosting methods come second in terms of accuracy,followed by RF,LR and SVM.By using machine learning and deep learning techniques,the proposed landslide identification method shows outstanding robustness and great potential in tackling the landslide identification problem.

Switchable dry adhesive based on shape memory polymer with hemispherical indenters for transfer printing

Transfer printing based on switchable adhesive is essential for developing unconventional systems,including flexible electronics,stretchable electronics,and micro light-emitting diode(LED)displays.Here we report a design of switchable dry adhesive based on shape memory polymer(SMP)with hemispherical indenters,which offers a continuously tunable and reversible adhesion through the combination of the preloading effect and the thermal actuation of SMP.Experimental and numerical studies reveal the fundamental aspects of design,fabrication,and operation of the switchable dry adhesive.Demonstrations of this adhesive concept in transfer printing of flat objects(e.g.,silicon wafers),three-dimensional(3D)objects(e.g.,stainless steel balls),and rough objects(e.g.,frosted glasses)in two-dimensional(2D)or 3D layouts illustrate its unusual manipulation capabilities in heterogeneous material integration applications.

A thermal actuated switchable dry adhesive with high reversibility for transfer printing

Transfer printing based on switchable adhesive that heterogeneously integrates materials is essential to develop novel electronic systems,such as flexible electronics and micro LED displays.Here,we report a robust design of a thermal actuated switchable dry adhesive,which features a stiff sphere embedded in a thermally responsive shape memory polymer(SMP)substrate and encapsulated by an elastomeric membrane.This construct bypasses the unfavorable micro-and nano-fabrication processes and yields an adhesion switchability of over1000 by combining the peel-rate dependent effect of the elastomeric membrane and the thermal actuation of the sub-surface embedded stiff sphere.Experimental and numerical studies reveal the underlying thermal actuated mechanism and provide insights into the design and operation of the switchable adhesive.Demonstrations of this concept in stamps for transfer printing of fragile objects,such as silicon wafers,silicon chips,and inorganic micro-LED chips,onto challenging non-adhesive surfaces illustrate its potential in heterogeneous material integration applications,such as flexible electronics manufacturing and deterministic assembly.

Recent Progresses on Passively Switched Mid-Infrared Fiber Lasers at 3 μm

We present the recent research progress of our group on mid-infrared pulsed fiber lasers at 3μm by passive switching. Three different kinds of saturable absorbers including semiconductor saturable absorber （SESAM）, Fe2＋：ZnSe crystal, topological insulator （TI） were used to perform the pulse generation, respectively. The temporal regimes of mode locking, Q-switching and Q-switching induced gain switching were gained. Some relative discussions and prospective efforts are proposed at the end of this paper.

Tunable antiferroelectric-like polarization behavior and enhanced energy storage characteristics in symmetric BaTiO_(3)/BiFeO_(3)/BaTiO_(3) heterostructure

The excellent energy storage performances of dielectric materials,a high energy density and efficiency,the stability in a wide range of temperature,frequency and cycling time,are surely desirable for the energy storage devices.A trade-off relationship between polarization and breakdown strength,however,limits the enhancement of energy storage properties of dielectric materials.To effectively boost the energy density and efficiency of dielectric capacitors,by inserting a BiFeO3 layer into the BaTiO3 film in present case,the symmetric BaTiO3/BiFeO3/BaTiO3 tri-layer film heterostructure with antiferroelectric-like characteristics was constructed based on the dual-interlayer coupling effect,what's more,its antiferroelectric-like characteristics will evolve with electric field.Such the tunable polarization behavior endows it with an enhanced maximum polarization but a reduced remnant one,a delayed saturation of polarization and a high breakdown strength,which are synergistically accountable for a large energy density(Wrec∼109 J/cm^(3))and a high efficiency(η∼82.6%),together with the good thermal(TR∼200℃,ΔWrec<3%&Δη<10%)and frequency(50 Hz–10 kHz,ΔWrec<7%&Δη<13%)stabilities,particularly an outstanding cycling reliability(10^(9) cycles,both ΔWrec and Δη<1%).Hence these findings can provide some innovative ideas for enriching the performance tuning of ferroelectrics,especially in enhancing their energy storage characteristics.

2-switched Er^(3+)/Dy^(3+)codoped ZrF_(4)fiber laser:continuously tunable pulse generation from 3.06 to 3.62μm

In this Letter,we report on widely tunable pulse generation from a red-diode-clad-pumped mid-infrared[mid-IR)Er^(3+)/Dy^(3+)codoped ZrF_(4)fiber laser,for the first time,to the best of our knowledge.Using a Fe^(2+):ZnSe crystal,continuously tunable Qswitched pulses across the range of 3.06–3.62μm have been attained,which not only represents the widest range[in wavelength domain)from a pulsed rare-earth-doped fiber laser at any wavelength,but also almost entirely covers the strong absorption band of C-H bonds in the mid-IR,providing a potential way for gas detection and polymer processing.In addition,the commercial InAs quantum-well-based saturable absorbers[SAs)have been employed instead,and the obtained longest Q-switching wavelength of 3.39μm is slightly shorter than 3.444μm determined by its nominal direct bandgap of 0.36 eV.

Synergically improved energy storage performance and stability in sol–gel processed BaTiO_(3)/(Pb,La,Ca)TiO_(3)/BaTiO_(3) tri-layer films with a crystalline engineered sandwich structure

Achieving an excellent energy storage performance,together with high cycling reliability,is desirable for expanding technological applications of ferroelectric dielectrics.However,in well-crystallized ferroelectric materials,the concomitant high polarizability and low polarization saturation field have led to a square-shaped polarization–electric field loop,fatally impairing both recoverable energy density(W_(rec))and efficiency(η).Nanocrystalline ferroelectric films with a macroscopically amorphous structure have shown an improved W_(rec) andη,but their much lower polarizability demands an extremely high electric field to achieve such performances,which is undesirable from an economic viewpoint.Here,we propose a strategy to boost the energy storage performances and stability of ferroelectric capacitors simultaneously by constructing a tri-layer film in which a well-crystallized ferroelectric layer was sandwiched by two pseudo-linear dielectric layers with a dominant amorphous structure.In sol–gel-derived BaTiO_(3)/(Pb,La,Ca)TiO_(3)/BaTiO_(3)(BTO/PLCT/BTO)tri-layer films,we show that the above design is realized via rapid thermal annealing which fully crystallized the middle PLCT layer while left the top/bottom BTO cap layers in a poor crystallization status.This sandwiched structure is endowed with an enhanced maximum polarization while a small remnant one and a much-delayed polarization saturation,which corresponds to large W_(rec)≈80 J/cm^(3) and highη≈86%.Furthermore,the film showed an outstanding cycling stability:its W_(rec) andηremain essentially unchanged after 10^(9) electric cycles(DW/W<4%,Dη/η<2%).These good energy storage characteristics have proved the effectiveness of our proposed strategy,paving a way for the utilization of sandwiched films in applications of electric power systems and advanced pulsed-discharge devices.

Antimonene:a long-term stable two-dimensional saturable absorption material under ambient conditions for the mid-infrared spectral region

We experimentally demonstrate a long-term stable two-dimensional saturable absorption material under ambient conditions—multi-layer antimonene feasible for the mid-infrared spectral region—for the first time to our knowledge. The multi-layer antimonene material prepared using a liquid-phase exfoliation method was coated on a quartz/Ca F_2 for characterizations and an Au mirror as a reflection-type saturable absorber(SA) device. It has a modulation depth of 10.5%, a saturation peak intensity of 0.26 GW∕cm^2, and a non-saturation loss of 19.1% measured at 2868.0 nm using the typical power-dependent method. By introducing the SA device into a linear-cavity Ho^(3+)∕ Pr^(3+)-codoped fluoride fiber laser at 2865.0 nm, stable Q-switched pulses were obtained. It generated a maximum output power of 112.3 m W and pulse energy of 0.72 μJ, while the shortest pulse duration and largest repetition rate were 1.74 μs and 156.2 k Hz, respectively. The long-term stability of the SA device was also checked using the same laser setup within 28 days. The results indicate that multi-layer antimonene is a type of promising long-term stable SA material under ambient conditions that can be applied in the mid-infrared spectral region.

Kelly sideband suppression and wavelength tuning of a conventional soliton in a Tm-doped hybrid mode-locked fiber laser with an all-fiber Lyot filter

We demonstrate a stable conventional soliton in a Tm-doped hybrid mode-locked fiber laser by employing a homemade all-fiber Lyot filter(AFLF) and a single-wall carbon nanotube. The AFLF, designed by sandwiching a piece of polarization-maintained fiber(PMF) with two 45° tilted fiber gratings inscribed by a UV laser in PMF with a phase-mask scanning technique, shows large filter depth of ～9 d B and small insertion loss of ～0.8 dB. By optimizing the free spectral range of the AFLF, the Kelly sidebands of a conventional soliton centered at1966.4 nm can be dramatically suppressed without impairing the main shape of the soliton spectrum. It gives the pulse duration of 1.18 ps and bandwidth of 3.8 nm. By adjusting the temperature of the PMF of the AFLF from 7°C to 60°C, wavelength tunable soliton pulses ranging from 1971.62 nm to 1952.63 nm are also obtained.The generated soliton pulses can be precisely tuned between 1971.62 nm and 1952.63 nm by controlling the temperature of the AFLF.

Fe3O4 nanoparticles as a saturable absorber for a tunable Q-switched dysprosium laser around 3μm

We demonstrate for the first time to our knowledge the use of Fe3O4 nanoparticles for Q-switching a tunable midinfrared(Mid-IR)Dy^3+-doped ZBLAN fiber laser around 3μm.The Q-switcher was fabricated by depositing the prepared Fe3O4 nanoparticles solution onto an Au mirror.Its nonlinear optical response was characterized using a mode locked Ho^3+/Pr^3+-codoped ZBLAN fiber laser at 2.87μm,and showed a modulation depth of 11.9%as well as a saturation intensity of 1.44 MW/cm^2.Inserting the device into a tunable Dy^3+-doped ZBLAN fiber laser,stable Q-switched pulses within the tunable range of 2812.4-3031.6 nm were obtained.When tuning the wavelength to 2931.2 nm,a maximum Q-switching output power of 111.0 mW was achieved with a repetition rate of 123.0 kHz and a pulse width of 1.25μs.The corresponding pulse energy was 0.90μJ.This demonstration suggests that Fe3O4 nanoparticles are a promising broadband saturable absorption material for mid-infrared operation.

Widely tunable passively Q-switched Er3+-doped ZrF4 fiber laser in the range of 3.4–3.7 μm based on a Fe2+:ZnSe crystal

We report the first(to the best of our knowledge) tunable passively Q-switched Er3+-doped ZrF4 fiber laser around 3.5 μm. In this case, a Fe2+:ZnSe crystal is used as the saturable absorber, and a plane-ruled grating in a Littrow configuration acts as the tuning element. At the tuned wavelength of 3478.0 nm, stable Q-switching with a maximum average power of 583.7 mW was achieved with a slope efficiency of 15.2% relative to the launched 1981 nm pump power. Further power scaling is mainly limited by the available 1981 nm pump power. The corresponding pulse width, repetition rate, and pulse energy are 1.18 μs, 71.43 kHz, and 7.54 μJ, respectively. By rotating the grating, the Q-switching can be continuously tuned in the region of 3.4–3.7 μm. To the best of our knowledge, this is the first pulsed rare-earth-doped fiber laser tunable in the region beyond 3.4 μm.