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Abstract: The practical applications of wearable electronics rely on the successful development of flexible and integrable energy devices with small footprints. This work reports a completely new type of graphite foam made of strategically created superstructures with covalently attached diverging microtubes, and their applications as electrode supports for binder‐free and additive‐free flexible supercapacitors. Because of the enhanced volumetric surface areas compared to conventional graphite foams, a high loading of pseudocapacitive materials (Mn3O4, 3.91 mg cm−2, 78 wt%) is achieved. The supercapacitors provide areal capacitances as high as 820 mF cm−2 at 1 mV s−1, while still maintaining high rate capability and 88% retention of capacitance after 3000 continuous charging and discharging cycles. When assembled as all‐solid‐state flexible symmetric supercapacitors, they offer one of the highest full‐cell capacitances (191 mF cm−2) among similar manganese oxide/graphene foams, and retain 80% capacitance after 1000 mechanical cycles. The potential of such flexible supercapacitors is also manifested by directly powering electric nanomotors that can trace along letters “U” and T,” which is the first demonstration of flexible supercapacitors for wireless/portable nanomanipulation systems. This work could inspire a new paradigm in designing and creating 3D porous micro/nanosuperstructures for an array of self‐powered electronic and nanomechanical applications. [ABSTRACT FROM AUTHOR]

Flexible energy storage devices play a pivotal role in realizing the full potential of flexible electronics. This work presents high-performance, all-solid-state, flexible supercapacitors by employing an innovative multilevel porous graphite foam (MPG). MPGs exhibit superior properties, such as large specific surface area, high electric conductivity, low mass density, high loading efficiency of pseudocapacitive materials, and controlled corrugations for accommodating mechanical strains. When loaded with pseudocapacitive manganese oxide (Mn3O4), the MPG/Mn3O4 (MPGM) composites achieve a specific capacitance of 538 F g−1 (1 mV s−1) and 260 F g−1 (1 mV s−1) based on the mass of pure Mn3O4 and entire electrode composite, respectively. Both are among the best of Mn3O4-based supercapacitors. The MPGM is mechanically robust and can go through 1000 mechanical bending cycles with only 1.5% change in electric resistance. When integrated as all-solid-state symmetric supercapacitors, they offer a full cell specific capacitance as high as 53 F g−1 based on the entire electrode and retain 80% of capacitance after 1000 continuous mechanical bending cycles. Furthermore, the all-solid-state flexible supercapacitors are incorporated with strain sensors into self-powered flexible devices for detection of both coarse and fine motions on human skins, i.e., those from finger bending and heart beating. [ABSTRACT FROM AUTHOR]

The design and fabrication of various types of flexible, portable, and foldable devices have received immense interest owing to the remarkable potential in impacting peoples' lives including real‐time health monitoring, point‐of‐care diagnosis, and athletic training. In this work, the authors present 3D graphite as the key sensing element of polymer composite strain sensors that offers ultrahigh sensitivity and durability in the detection of fine motions. The graphite–polymer sensors in this work provide high bending sensitivities that are reproducible within 3% signal shift after 11 000 bending cycles and exhibit gauge factors of 100 and 52 at tensile strains of 80% and 100%, respectively. The sensing mechanism is modeled, and correlated with experimental studies. The high strain sensitivity compared to graphene based devices is analyzed and understood with respect to levels of defect in materials. Such graphite–polymer sensors are able to detect fine features of human pulses, respiration rates, and throat vibration in real time and are also applied in the detection of posture correctness of musical instrument learners for the first time. [ABSTRACT FROM AUTHOR]

A type of composite photovoltaic system that can improve the absorption of longer wavelength photons for ultrathin silicon solar cells is presented by synergistically exploiting spectral upconversion and plasmonic light manipulation under a reconfigurable platform where individual module components can be independently optimized and strategically combined by printing-based deterministic materials assemblies. The ultrathin (≈8 μm) nanostructured silicon solar cells are embedded in a thin polymeric medium containing NaYF4:Yb3+,Er3+ nanocrystals, coated on a plasmonically engineered substrate that incorporates hybrid nanostructures of cylindrical nanoholes and truncated-cone-shaped nanoposts. Both excitation and emission processes of upconversion luminophores are significantly enhanced by combined effects of surface plasmon resonance to amplify the light intensity at the excitation wavelength as well as to facilitate the far-field outcoupling at the emission wavelengths, respectively. The performance of the integrated solar module is improved by ≈13% compared to devices on a nanostructured plasmonic substrate without luminophores due to collective contributions from plasmonically enhanced spectral upconversion, together with effects of waveguiding and fluorescence of NaYF4:Yb3+,Er3+. Detailed studies on optical properties of engineered plasmonic nanostructures and device performance in both experiments and numerical modeling provide quantitative descriptions of the underlying physics and materials science, as well as optimal design rules for integrated photovoltaic systems. [ABSTRACT FROM AUTHOR]

Abstract: We extend Floquet theory for reducing nonlinear periodic difference systems to autonomous ones (actually linear) by using normal form theory. [Copyright &y& Elsevier]

Abstract: We extend the classical Belitskii normal form theorem uniformly for planar nilpotent foci and limit cycles. Then by using fractal analysis, isochronous properties near such invariant sets are well investigated. [Copyright &y& Elsevier]

Abstract: In this paper we establish analytic equivalence theorems of Poincaré and Poincaré–Dulac type for analytic non-autonomous differential systems based on the dichotomy spectrum of their linear part. As applications of the theorem, normal forms linearize for two illustrative examples. [Copyright &y& Elsevier]

Abstract: In this paper we discuss how to determine a degenerate equilibrium of planar analytic systems to be focus-center type. A method of generalized normal sectors is used to determine orbits in exceptional directions near high degenerate equilibria. We obtain a sufficient and necessary condition for the existence of orbits going to origin in a generalized normal sector in class III. Thus, together with some criterions of orbits going to origin in a generic quasi-sector, we can characterize whether the degenerate equilibrium is of focus-center type in every case. The effectiveness of our methods is shown in an example which has a high degenerate equilibrium. [Copyright &y& Elsevier]

Abstract: In this paper, we give the global dynamical behaviors of a reduced SIRS epidemic model with a nonlinear incidence rate . We first discuss the qualitative properties of the equilibria in the interior of the first quadrant, and study the bifurcations including saddle–node bifurcation, transcritical bifurcation, Hopf bifurcation and Bogdanov–Takens bifurcation. Then we consider equilibria at infinity, determining the number of orbits in exceptional directions for the global tendency. In this discussion, the unspecified degree of polynomials and their high degeneracy prevent us from using the methods of blowing-up or normal sectors in some cases. We lastly discuss the existence and uniqueness of limit cycles. [Copyright &y& Elsevier]

Abstract: In this paper we consider an epidemic model, which is a reduced SIRS model with a constant removal rate of the infective individuals, for its qualitative properties which were not revealed in [W. Wang, S. Ruan, Bifurcations in an epidemic model with constant removal rate of the refectives, J. Math. Anal. Appl. 291 (2004) 775–793]. We first prove the uniqueness of closed orbits if they exist for this epidemic model. Then we discuss the qualitative properties of equilibria at infinity for global tendencies. Therefore, global dynamical behaviors of this system are obtained in the end. [Copyright &y& Elsevier]

This paper consists of two parts. In the first part we study the relationship between conic centers (all orbits near a singular point of center type are conics) and isochronous centers of polynomial systems. In the second part we study the number of limit cycles that bifurcate from the periodic orbits of cubic reversible isochronous centers having all their orbits formed by conics, when we perturb such systems inside the class of all polynomial systems of degree n. [Copyright &y& Elsevier]

Examines the cyclicity of elementary polycles and ensembles with codimension 3 degeneration using derivation division algorithim, Khovanskii procedure and the method of critical point analysis. Transition maps near elementary singular points; Cyclicity of individual elementary polycycles.

Solar steam generation, a sustainable water‐purification technology, holds substantial promise in resolving the global issue of shortage of drinkable water. Here, the design, fabrication, and high‐performance of an innovative 3D solar steamer, offering synergistic high‐efficiency steaming and heavy metal removal functions are reported. The device is made of synthesized carbon‐molybdenum‐disulfide microbeads electrostatically assembled on a 3D polyurethane sponge. The mesoporous composite sponge also serves as a freestanding water reservoir that avoids one‐side contact to bulk water, effectively suppressing the commonly observed parasitic heat loss, and offering a high energy efficiency of 88%. When being sculpted into a 3D spoke‐like structure, the composite sponge achieves one of the highest evaporation rates of 1.95 kg m−2 h−1 at 1 sun. The solar steamer is demonstrated for water treatment, i.e., decontamination of metal ions, disinfection, and reducing alkalinity and hardness of river water. Particularly, the strong mercury adsorption of MoS2 reduces mercury levels from 200 to 1 ppb, meeting the stringent standard set by the Environmental Protection Agency, which is the first demonstration of mercury‐removal powered by solar energy. The unique design, fabrication, water‐handling strategy, and mercury‐removal function of this high‐performance solar steamer can inspire new paradigms of water treatment technologies. Dually functional solar steamers made of molybdenum‐disulfide/amorphous carbon microbeads assembled on 3‐D polymer sponges are strategically designed and fabricated for high‐efficiency solar steaming and synergistic mercury removal. The device offers an evaporation rate up to 1.95 kg m‐2 h‐2 and an energy conversion efficiency as high as 88% under 1 sun. In one steaming operation, mercury can be removed from water, meeting stringent drinking standards. [ABSTRACT FROM AUTHOR]

All‐solid‐state flexible supercapacitors based on strategically created three‐dimensional hierarchically porous graphite foams are reported by Donglei Fan and co‐workers in article number 1702738. The supercapacitors exhibit ultrahigh specific capacitances based on the entire electrode weight and retain 80% of capacitance after 1000 continuous bending cycles. They can be seamlessly integrated with strain sensors for self‐powered detections of strains from skins, including carotid artery pulses and finger bending. [ABSTRACT FROM AUTHOR]

In article number 1500761, Jongseung Yoon and co‐workers report a photovoltaic system that can improve the collection efficiency of above‐bandgap, long‐wavelength photons in ultrathin nanostructured silicon solar cells. A flexible composite solar module integrated with silver nanostructures and upconversion printing medium enables the enhanced photovoltaic performance of surface‐embedded 8‐μm‐thick silicon microcells via synergistic contributions from plasmonically amplified spectral upconversion, waveguiding, and fluorescence of the upconversion medium. [ABSTRACT FROM AUTHOR]