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Bladder cancer is the most common malignant tumours with high morbidity, mortality and recurrence. However, currently developed detection methods for bladder cancer-associated urine biomarkers are hindered by their extremely low abundance. Hence, the exploration of a highly sensitive and selective approach for the detection of trace bladder cancer-associated biomarkers in human urine is of vital importance for the diagnosis of bladder cancer. Herein, we developed a highly reliable indium gallium zinc oxide field effect transistor (IGZO FET) biosensor for the detection of bladder cancer-related biomarker microRNA. The single-stranded DNA-functionalized IGZO FET biosensors exhibit high sensing reproducibility and stability with an ultralow detection limit of 19.8 amol/L. The device could also be used for quantitative detection of trace microRNA in human urine samples and can effectively distinguish bladder cancer patients from healthy donors. The development of high performance IGZO FET biosensors presents new opportunities for the achievement of early-stage diagnosis of bladder cancer.

Visible light communication (VLC) systems relying on commercial-off-the-shelf (COTS) devices have gathered momentum recently, due to the pervasive adoption of LED lighting and mobile devices. However, the achievable throughput by such practical systems is still several orders below those claimed by controlled experiments with specialized devices. In this paper, we engineer CoLight aiming to boost the data rate of the VLC system purely built upon COTS devices. CoLight adopts COTS LEDs as its transmitter, but it innovates in its simple yet delicate driver circuit wiring an array of LED chips in a combinatorial manner. Consequently, modulated signals can directly drive the on-off procedures of individual chip groups, so that the spatially synthesized light emissions exhibit a varying luminance following exactly the modulation symbols. To obtain a readily usable receiver, CoLight interfaces a COTS PD with a smartphone through the audio jack, and it also has an alternative MCU-driven circuit to emulate a future integration into the phone. The evaluations on CoLight are both promising and informative: they demonstrate a throughput up to 80 kbps at a distance of 2 m, while suggesting various potentials to further enhance the performance.

Optical camera communication (OCC) systems, which utilize image sensors embedded in commercial-off-the-shelf devices to detect time and spatial variations in light intensity for enabling data communications, have stirred up researchers’ interest. Compared to a direct OCC system whose maximum data rate is strongly determined by the LED source size, a reflected OCC system can break that limitation since the camera captures the light rays reflecting off an observation plane (e.g., a wall) instead of those light rays directly emanated from the light source. However, the low signal-to-noise ratio caused by the non-uniform irradiance distribution produced by LED luminaire on the observation plane in current reflected OCC systems cannot be avoided, hence low complexity and accurate demodulation are hard to achieve. In this paper, we present a FreeOCC system, which employs a dedicatedly tailored freeform lens to precisely control the propagation of modulated light. A desired uniform rectangular illumination is produced on the observation plane by the freeform lens, yielding a uniform grayscale distribution within the received frame captured by the camera in the proposed FreeOCC system. Then, the received signal can be easily demodulated with high accuracy by a simple thresholding scheme. A prototype of the FreeOCC system demonstrates the high performance of the proposed system, and two pulse amplitude modulation schemes (4-order and 8-order) are performed. By using the freeform lens, the packet reception rate is increased by 35% and 32%, respectively; the bit error rate is decreased by 72% and 59%, respectively, at a transmission frequency of 5 kHz. The results clearly show that the FreeOCC system outperforms the common reflected OCC system.

Whereas the increasing popularity of both commercial light-emitting diode (LED) lighting and mobile devices certainly creates opportunity for real-life deployment of visible light communication (VLC) systems, reaching the high throughput promised by lab experiments still faces major obstacles. In particular, lacking the sophisticated hardware and software support under experimental conditions, real-life systems are challenged in many aspects, especially low signal-to-noise ratio, low operation frequency, uncontrollable LED nonlinearity, and illumination requirements. Nonetheless, deployments tapping commercial infrastructure are critical to gain market penetration for VLC-enabled wireless applications, so boosting the performance of these real-life systems becomes imperative. In this article, we consider the multiple LED chips and/or light sources nature of indoor commercial lighting infrastructure, and propose a spatial modulation that composes the cooperative light emissions (transmissions) from multiple LEDs. In addition to gaining a higher spectral efficiency, this scheme utilizes the multiple-LED nature of commercial lighting to overcome LED nonlinearity with a novel yet simplified hardware construction. We present two typical designs adopting this special modulation under different infrastructural constraints, and provide an introduction on its potential contribution to the standardization of VLC. Finally, we discuss potential extensions to further improve performance. Ministry of Education (MOE) This work was supported in part by National Natural Science Foundation of China under Grant 61902267 and Grant 61901065, in part by the Fundamental Research Funds for the Central Universities under Grant YJ201868, in part by the Sichuan Science and Technology Program under Grant 19ZDYF0045 and Grant 19CXTD0005, in part by the the AcRF Tier 2 Grant MOE2016-T2-2- 022, and in part by the DSAIR Center at NTU.

Commercial-off-the-shelf (COTS) devices enabled visible light communication (VLC) for Internet of things (IoT) applications has attracted extensive attentions from both academic and industrial communities, thanks to the pervasive deployments of light emitting diode (LED) lighting infrastructure. However, due to the limitation of frequency response and non-linearity of the commercial illuminating LED light consisting of multiple LED chips, the achievable data rate is far less than that provided by the experimental VLC system with a single LED with specialized devices, e.g., lens. To this end, we propose a power-of-2 arrangement scheme for LED chips to generate spatial summing modulation with low control complexity, and demonstrate its availability in an orthogonal frequency division multiplexing (OFDM) VLC system purely built upon COTS devices. It significantly differs from a conventional OFDM VLC system relying on digital-to-analog converter (DAC) and analog signal chain, which is complex and confined by LED’s non-linearity, thanks to we design a novel digital-to-light converter (DLC) which can output 256 light intensities linearly and be directly controlled by the discrete digital signals generated by the OFDM modulator. An experimental demonstration with employing the QAM-OFDM modulation scheme successfully confirms the effectiveness of the proposed spatial summing VLC system, which can achieve low BERs of below the forward error correct (FEC) threshold of 3.8×10−3 for both QAM8 and QAM16 running transmission frequency of 300 kHz under a communication distance of 0.8 m. It demonstrates the promising potential for delivering a data rate at hundred kbps level with this novel spatial summing based OFDM VLC system, which is sufficient for many IoT applications.

Supported graphene-based membranes Porous graphene sheets have excellent filtration capabilities and are able to block most ions, but their fragility limits their scale-up beyond laboratory demonstrations. Yang et al. created a nanoporous graphene membrane reinforced by a network of single-walled carbon nanotubes (SWNTs) to provide mechanical stability (see the Perspective by Mi). The SWNT network also stopped the propagation of cracks in the graphene, effectively localizing the damage to a small area defined by a cell in the carbon nanotube mesh. The membranes showed high water flux rates as well as a high rejection rate for most ions. Science , this issue p. 1057 ; see also p. 1033

Optical Camera Communication (OCC) systems relying on commercial-off-the-shelf (COTS) devices have attracted substantial attention recently, thanks to the pervasive deployment of indoor LED lighting infrastructure and the popularity of smartphones. However, the achievable throughput by such practical systems is still very low due to its availability for only low order modulation schemes and transmission frequency. In this demo, we propose a novel reflected OCC system, UniLight, which takes advantage of uniform light emission of an LED luminaire with lens to increase both region of interest (RoI) and signal-to-noise ratio (SNR) so as to improve data rate. UniLight employs a COTS LED spotlight with lens as the transmitter to uniformly illuminate a reflector so that avoids a gradual reduction of brightness from the center to both sides in the frame captured by a camera receiver. By adopting a hybrid modulation scheme for generating multi-level pulse amplitude modulation (M-PAM) symbols on the transmitter and a machine learning based demodulator on the smartphone receiver, UniLight can achieve much higher data rate than existing works with a single small-size LED spotlight.

Solar water evaporation is thought to be a promising solution to address the issues of global water scarcity. However, it is particularly difficult to achieve an idealized photothermal conversion membrane with all of the required structure characteristics such as wide spectrum absorption, ultrathin and porous, low thermal conductivity, and ease to scale up, thus leading to reduced water evaporation efficiency. Here, we designed a large-area bilayer Janus film by assembling gold nanorod (AuNR) onto the interconnected single-walled carbon nanotube (SWNT) porous film. The combined characteristics of high solar spectrum absorption, enhanced photothermal performance, thermal insulating feature, interconnected porous structure, and excellent mechanical performance enable the bilayer Janus film with a nearly 94% water evaporation efficiency under 5 kW m–2 solar irradiation and stable water generation capability during long-term illumination cycles as a water desalination membrane. Construction of the bilayer Jan...

Although Visible Light Communication (VLC) is gaining increasing attention in research, developing a practical VLC system to harness its immediate benefits using Commercial Off-The-Shelf (COTS) devices is still an open issue. To this end, we develop and deploy CeilingTalk as a lightweight wireless broadcast system using COTS LED luminaries as transmitters and smartphone cameras as receivers so that it can be fully hosted in a smartphone and is feasible for all possible indoor environments. CeilingTalk innovates in both encoding and decoding to achieve an adequate throughput for realistic applications. On one hand, it employs Raptor coding to allow multiple LED luminaries to transmit collaboratively so as to benefit both throughput and reliability. On the other hand, it involves a lightweight decoding scheme to handle the asynchrony (both spatial and temporal) in transmissions. Moreover, we analyze the impact of various parameters on the performance of CeilingTalk, in order to derive a model for such VLC systems enabled by COTS devices and hence provide general guidance for future VLC deployments in larger scales. Finally, we conduct extensive field experiments to validate the effectiveness of our LED-camera VLC model, as well as to demonstrate the promising performance of CeilingTalk: up to 1.0 kb/s at a distance of 5 m.

LED-Camera Visible Light Communication (VLC) is gaining increasing attention, thanks to its readiness to be implemented with Commercial Off-The-Shelf devices and its potential to deliver pervasive data services indoors. Nevertheless, existing LED-Camera VLC systems employ mainly low-order modulations such as On-Off Keying (OOK) given the simplicity of their implementation, yet such rudimentary modulations cannot yield a high throughput. In this paper, we investigate various opportunities of using a high-order modulation to boost the throughput of LED-Camera VLC systems, and we decide that Amplitude-Shift Keying (ASK) is the most suitable scheme given the limited operating frequency of such systems. However, directly driving an LED to emit different levels of luminance may suffer heavy distortions caused by the nonlinear behavior of LED. As a result, we innovatively propose to generate ASK using the composition of light emission. In other words, we digitally control the On-Off states of several groups of LED chips, so that their light emissions compose in the air to produce various ASK symbols. We build a prototype of this novel ASK-based VLC system and demonstrate its superior performance over existing systems: it achieves a rate of 2 kbps at a 1 m distance with only a single LED luminaire for static users and more than 1 kbps for mobile users. Ministry of Education (MOE) Nanyang Technological University The authors would like to thank the anonymous reviewers for their constructive feedback and valuable input. This work was supported in part by the Fundamental Research Funds for the central Universities under Grant No. 20822041B4232, National Natural Science Foundation of China under Grant No. 61373091, Sichuan Science and Technology Program under Grant No. 19ZDYF0045 and 19CXTD0005, the AcRF Tier 2 Grant MOE2016-T2-2-022, and the DSAIR Center at NTU.

Visible Light Communication (VLC) systems relying on commercial-off-the-shelf (COTS) devices have gathered momentum recently, due to the pervasive adoption of LED lighting and mobile devices. However, the achievable throughput by such practical systems is still several orders below those claimed by controlled experiments with specialized devices. In this paper, we engineer SynLight aiming to significantly improve the data rate of a practical VLC system. SynLight adopts COTS LEDs as its transmitter, but it innovates in its simple yet delicate driver circuit wiring an array of LED chips in a combinatorial manner. Consequently, modulated signals can directly drive the on-off procedures of individual chip groups, so that the spatially synthesized light emissions exhibit a varying luminance following exactly the modulation symbols. To obtain a readily usable receiver, SynLight interfaces a COTS Photo-Diode with a smartphone through the audio jack. The evaluations on SynLight are both promising and informative: they demonstrate a throughput up to 60 kbps, more than 50× of that achieved by state-of-the-art systems, while suggesting various potentials to further enhance the performance.

We use a blown-bubble method to assemble Cu nanowires and in situ fabricate graphene-based one-dimensional heterostructures, including versatile sausage-like configurations consisting of multilayer graphene nanotubes (GNTs) filled by single or periodically arranged Cu nanoblocks (CuNBs). This is done by first assembling Cu nanowires among a polymer-based blown-bubble film (BBF) and then growing graphene onto the nanowire substrate using the polymer matrix as a solid carbon source by chemical-vapor deposition. The formation of sausage-like GNT@CuNB nanostructures is due to the partial melting and breaking of embedded Cu nanowires during graphene growth, which is uniquely related to our BBF process. We show that the GNT skin significantly slows the oxidation process of CuNBs compared with that of bare Cu nanowires, and the presence of stuffed CuNBs also reduces the linear resistance along the GNTs. The large-scale assembled graphene-based heterostructures achieved by our BBF method may have potential applications in heterojunction electronic devices and high-stability transparent conductive electrodes.

LED-Camera Visible Light Communication (VLC) is gaining increasing attention, thanks to its readiness to be implemented with Commercial Off-The-Shelf devices and its potential to deliver pervasive data services indoors. Nevertheless, existing LED-Camera VLC systems employ mainly low-order modulations such as On-Off Keying (OOK) given the simplicity of their implementation, yet such rudimentary modulations cannot yield a high throughput. In this paper, we investigate various opportunities of using a high-order modulation to boost the throughput of LED-Camera VLC systems, and we decide that Amplitude-Shift Keying (ASK) is the most suitable scheme given the limited operating frequency of such systems. However, directly driving an LED to emit different levels of luminance may suffer heavy distortions caused by the nonlinear behavior of LED. As a result, we innovatively propose to generate ASK using the composition of light emission. In other words, we digitally control the On-Off states of several groups of LED chips, so that their light emissions compose in the air to produce various ASK symbols. We build a prototype of this novel ASK-based VLC system and demonstrate its superior performance over existing systems: it achieves a rate of 2 kbps at a 1 m distance with only a single LED luminaire. MOE (Min. of Education, S’pore) Accepted version

Among the various energy storage systems, supercapacitors are considered to be the most promising alternative to batteries due to their high power density, long cycle life and fast charge–discharge process. Especially, flexible electrochemical supercapacitors with their unique advantages such as flexibility, shape-conformability, and light weight are attracting ever-increasing attention to meet the current requirements for portable and wearable electric devices in modern energy storage markets. In this perspective, we summarize the most recent progress in flexible all-solid supercapacitors from the point of view of flexible electrode materials. Various flexible electrode materials like carbon nanotubes, graphene, and pseudo capacitive materials are discussed and their performance is comprehensively analyzed. In addition, an overview of the latest progress in strategies to improve the energy and power density is discussed. Further research targets in multifunctional integrated systems and challenges in realizing idealized flexible energy storage systems are also proposed.

Carbon nanotubes (CNTs) have been combined with TiO2 to improve its performance in applications such as lithium ion batteries; previous CNT/TiO2 hybrid structures were usually in the powder form which requires a polymeric binder and carbon black to make electrodes. Here, we fabricate freestanding bulk electrodes by depositing TiO2 onto a CNT sponge via a simple in situ hydrolysis method, creating coaxial units of TiO2-wrapped CNTs. The built-in CNT framework supports a uniform thin crystalline TiO2 layer, forming a highly porous, conductive and compressible composite sponge. As an anode material for Li-ion batteries, the TiO2–CNT sponges exhibit stable charging/discharging plateau voltages, excellent cycling stability and rate performance. In particular, these sponges can be compressed to much smaller volumes with significantly improved areal capacity, which cannot be achieved by powder-form electrodes. Our hierarchical sponges with optimized microstructures may serve as stable and compressible electrodes for various energy storage systems such as Li-ion, Na-ion and Li–S batteries.

Carbon nanotubes (CNTs) are grown from metal catalysts; after growth, residual catalyst particles are usually encapsulated within the tube cavities and are difficult to remove. Here, we directly expose controlled amounts of Fe catalyst from a bulk CNT sponge by thermal annealing at mild temperature, and produce uniformly dispersed Fe2O3 nanoparticles grafted onto CNTs throughout the sponge. Those exposed catalyst particles remain active and can be used to synthesize CNTs again. The resulting CNT–Fe2O3 composite sponges, which possess a highly porous and conductive network, also serve as freestanding supercapacitor electrodes with significantly enhanced specific capacitance than original CNT sponges. Our results indicate that residual metal catalysts, widely present in CNT-based materials, can be reactivated and utilized for applications in catalysis and energy areas.

Flexible carbon nanotube sponges (CNT sponges) are excellent three-dimensional (3D) porous substrates to fabricate free-standing electrodes applied in lithium-ion batteries, but the low energy density needs to be improved urgently. Hybrid, hierarchical structures designed towards high-performance electrodes have been reported as an efficient route. Here, SnS2 with controllable mass ratios and various morphologies from tubular nanosheaths to nanosheets has been grown in situ on carbon nanotubes in CNT sponges by a facile solvothermal method, taking thiourea as the medium. We propose the formation mechanism for diverse morphologies of SnS2. Also, we demonstrate that the tubular SnS2 nanostructure can be restrictively and directionally grown using CNTs as templates, and has much better reversible capacity and cyclability than its nanoparticle or nanosheet structures on CNTs. Meanwhile, CNT@SnS2 sponges could be used as free-standing and binder-free electrodes with significantly improved areal capacity than bare CNT sponges.

Perovskite is an excellent candidate as low cost catalyst for Li-O2 cells. However, the limited porosity, which impedes molecular transport, and the inherent low electronic conductivity are the main barriers toward production of high-performance electrodes. Here, we designed a hierarchical porous flexible architecture by coating thin mesoporous yet crystalline LaSrMnO layers throughout a graphene foam to form graphene/meso-LaSrMnO sandwich-like nanosheets. In this well-designed system, the macropore between nanosheets facilitates O2 and Li(+) diffusion, the mesopore provides large surface area for electrolyte immersion and discharge products deposition, the perovskite phase catalyst decreases reactive overpotential, and the graphene serves as conductive network for electrons transport. When used as a freestanding electrode of Li-O2 cell, it shows high specific capacity, superior rate capability, and cyclic stability. Combination of mesoporous perovskites with conductive graphene networks represents an effective strategy for developing efficient electrodes in various energy storage systems.

Light-weight and high-performance electromagnetic interference (EMI)-shielding epoxy nanocomposites are prepared by an infiltration method using a 3D carbon nanotube (CNT) sponge as the 3D reinforcement and conducting framework. The preformed, highly porous, and electrically conducting framework acts as a highway for electron transport and can resist a high external loading to protect the epoxy nanocomposite. Consequently, a remarkable conductivity of 148 S m−1 and an outstanding EMI shielding effectiveness of around 33 dB in the X-band are achieved for the epoxy nanocomposite with 0.66 wt% of CNT sponge, which is higher than that achieved for epoxy nanocomposites with 20 wt% of conventional CNTs. More importantly, the CNT sponge provides a dual advantage over conventional CNTs in its prominent reinforcement and toughening of the epoxy composite. Only 0.66 wt% of CNT sponge significantly increases the flexural and tensile strengths by 102% and 64%, respectively, as compared to those of neat epoxy. Moreover, the nanocomposite shows a 250% increase in tensile toughness and a 97% increase in elongation at break. These results indicate that CNT sponge is an ideal functional component for mechanically strong and high-performance EMI-shielding nanocomposites.

Mesoporous carbon (m-C) has potential applica- tions as porous electrodes for electrochemical energy stor- age, but its applications have been severely limited by the inherent fragility and low electrical conductivity. A rational strategy is presented to construct m-C into hierarchical porous structures with high flexibility by using a carbon nanotube (CNT) sponge as a three-dimensional template, and grafting Pt nanoparticles at the m-C surface. This method involves several controllable steps including solu- tion deposition of a mesoporous silica (m-SiO2) layer onto CNTs, chemical vapor deposition of acetylene, and etching of m-SiO2, resulting in a CNT@m-C core-shell or a CNT@m- C@Pt core-shell hybrid structure after Pt adsorption. The un- derlying CNT network provides a robust yet flexible support and a high electrical conductivity, whereas the m-C provides large surface area, and the Pt nanoparticles improves interfa- cial electron and ion diffusion. Consequently, specific capaci- tances of 203 and 311 F g 1 have been achieved in these CNT@m-C and CNT@m-C@Pt sponges as supercapacitor electrodes, respectively, which can retain 96 % of original ca- pacitance under large degree compression.

As a key component of building management and security, occupancy inference through smart sensing has attracted a lot of research attention for nearly two decades. Nevertheless, existing solutions mostly rely on either pre-deployed infrastructures or user device participation, thus hampering their wide adoption. This paper presents CeilingSee, a dedicated occupancy inference system free of heavy infrastructure deployments and user involvements. Building upon existing LED lighting systems, CeilingSee converts part of the ceiling-mounted LED luminaires to act as sensors, sensing the variances in diffuse reflection caused by occupants. In realizing CeilingSee, we first re-design the LED driver to leverage LED’s photoelectric effect so as to transform a light emitter to a light sensor. In order to produce accurate occupancy inference, we then engineer efficient learning algorithms to fuse sensing information gathered by multiple LED luminaires. We build a testbed covering a 30 m2 office area; extensive experiments show that CeilingSee is able to achieve very high accuracy in occupancy inference. MOE (Min. of Education, S’pore)

Hybridization of carbon nanotubes (CNT) with graphene provides a promising means of integrating the attributes of both materials, thereby enabling widespread application. Here, we present a method to directly assemble hybrid CNT-graphene films by a blown bubble method combined with selective substrate annealing. We use polymethylmethacrylate (PMMA) as the polymeric matrix to blow bubbles containing self-assembled multi-walled CNT arrays, and then transform the bubble film into a CNT-graphene hybrid film by thermal annealing on a Cu substrate; PMMA serves as the carbon source for growing single to few-layer graphene among the CNT network until a continuously hybridized structure is formed. Compared to the bare (non-hybridized) CNT networks, the hybrid films exhibit improved electrical conductivity and structural integrity. Our method also enables the fabrication of a multi-walled CNT-Si solar cell, which has high power conversion efficiency, through the assembly of hybrid CNT-graphene structures.

Given the growing interests on using Commercial Off-The-Shelf (COTS) devices to implement Visible Light Communication (VLC) systems, there is a call for filling the gap between VLC standards and practical deployments. In particular, since LED-Camera VLC systems have shown a strong potential in covering large indoor areas due to the increasing pervasiveness of LED lighting systems and smartphones, providing roaming support to such a system has become an impending need. To this end, we propose RoCLight as a lightweight solution to this call. In order to have a proper feedback channel for roaming support, we innovate in converting part of the LED luminaires (already used as the VLC transmitters) into light sensors. By sensing the disturbance to the ambient diffuse reflection caused by user presence and mobility, RoCLight is able to adaptively handoff its transmissions from one luminaire to another, so as to keep up with user mobility and hence to offer an adequate roaming support. We implement RoCLight as a small-scale testbed with five LED luminaires spanning a length of 7.5 meters, and we conduct various evaluations on the roaming support capability of RoCLight based on this testbed; all our experiment results strongly demonstrate its promising performance.

Nanostructuring silicon (Si) and combining Si with carbon shells have been studied in recent Li-ion battery electrodes, yet it remains a grand challenge to overcome the low electrical conductivity and associated volume change of Si. Here, by first coating a mesoporous SiO2 (meso-SiO2) onto carbon nanotube (CNT) networks and then converting it into a meso-Si layer covered by carbon, we obtained a freestanding, highly porous composite sponge electrode consisting of three-dimensionally interconnected sandwiched carbon-Si-CNT skeletons. In this hierarchical structure, the macropores among the sponge connect to mesopores in the meso-Si layer so that Li+ diffusion is facilitated, whereas the underlying CNT networks serve as conductive paths for electrons transport. Meanwhile, the outer carbon coating on meso-Si could buffer the volume expansion and prevent material shedding. As a result, our sandwiched carbon-Si-CNT electrodes exhibit large specific capacity, high rate capability and long cycle life. The combin...

As a key component of building management and security, occupancy inference through smart sensing has attracted a lot of research attentions for nearly two decades. Nevertheless, existing solutions mostly rely on either pre-deployed infrastructures or user device participation, thus hampering their wide adoption. This paper presents CeilingSee, a dedicated occupancy inference system free of heavy infrastructure deployments and user involvements. Building upon existing LED lighting systems, CeilingSee converts part of the ceiling-mounted LED luminaires to act as sensors, sensing the variances in diffuse reflection caused by occupants. In realizing CeilingSee, we first re-design the LED driver to leverage LED's photoelectric effect so as to transform a light emitter to a light sensor. In order to produce accurate occupancy inference, we then engineer efficient learning algorithms to fuse sensing information gathered by multiple LED luminaires. We build a testbed covering a 30m2 office area; extensive experiments show that CeilingSee is able to achieve very high accuracy in occupancy inference.

While the traditional Visible Light Communication (VLC) system has attracted a lot of research attentions on boosting throughput, using Commercial Off-The-Shelf (COTS) devices, e.g. existing cameras on the smartphones, is a recent trend to implement readily deployable VLC systems. In particular, since LED-Camera VLC systems have shown a promising potential in large indoor communication due to the growing deployment of LED lighting infrastructure, a comprehensive VLC system with cooperative transmission and roaming support has become an impending need. To this end, we propose a novel VLC and visible light sensing (VLS) system to address that by leveraging LED sensing and effective encoding/decoding schemes. It is achieved first by utilizing LED sensing via converting parts of LED luminaire into light sensors to detect diffuse reflection change caused by presence of the user. After the users are detected and located, the system employs rateless codes and newly designed code assignment scheme to collaboratively transmit to detected users in their communication cells. We believe the proposed system has the potential to a roaming support VLC system in the whole building or indoor areas.

Porous materials such as foams, sponges and aerogels typically exhibit large energy dissipation during deformation, resulting in structural weakening and incomplete recovery. Here, we adopted a vapor deposition method to introduce a uniform amorphous carbon (AC) coating with controlled thickness throughout the porous network, on the surface of individual carbon nanotubes (CNTs) as well as their junctions, forming AC-CNT sponges. The AC-CNT sponges show enhanced mechanical properties (compressive strength, modulus), and in particular, significantly narrowed stress–strain loops with small energy loss coefficients compared with previous CNT or graphene-based aerogels typically having large hysteresis. Mechanism study has revealed several important factors that contribute to the observed superelasticity, including the thickening of nanotube struts, welding of nanotube junctions, and inhibition of bundle formation. Our method could systematically tailor the structure and properties of porous CNT (or other nanostructure) sponges, which have applications in microelectromechanical systems and mechanical energy storage.

Design and fabrication of structurally optimized electrode materials are important for many energy applications such as supercapacitors and batteries. Here, we report a three-component, hierarchical, bulk electrode with tailored microstructure and electrochemical properties. Our supercapacitor electrode consists of a three-dimensional carbon nanotube (CNT) network (also called sponge) as a flexible and conductive skeleton, an intermediate polymer layer (polypyrrole, PPy) with good interface, and a metal oxide layer outside providing more surface area. These three components form a well-defined core-double-shell configuration that is distinct from simple core-shell or hybrid structures, and the synergistic effect leads to enhanced supercapacitor performance including high specific capacitance (even under severe compression) and excellent cycling stability. The mechanism study reveals that the shell sequence is a key factor; in our system, the CNT–PPy–MnO2 structure shows higher capacitance than the CNT–MnO...

Graphene sheets and nanoribbons are graphene-based nanostructures with different dimensions. Here, we show that these two materials can be combined to form highly porous, ultra-low density, compressible yet elastic aerogels, which can be used as efficient adsorbents and supercapacitor electrodes. The pore walls consist of stacked graphene sheets embedded with uniformly distributed thick nanoribbons unzipped from multi-walled carbon nanotubes as effective reinforcing skeletons. Owing to the large pore-size, robust and stable structure, and the nanoribbon-adhered pore walls, these hybrid aerogels show very large adsorption capacity for a series of organic solvents and oils (100 to 350 times of aerogel weight), and a specific capacitance of 256 F g−1 tested in a three-electrode electrochemical configuration, which is further improved to 537 F g−1 by depositing controlled loading pseudo-polymers into the aerogels. Our multifunctional graphene sheet–nanoribbon hybrid aerogels may find potential applications in many fields such as environmental cleanup and as flexible electrodes for energy storage systems such as supercapacitors and batteries.

A carbon nanotube (CNT) sponge contains a three-dimensional conductive nanotube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique CNT@polypyrrole (PPy) core-shell sponge, and demonstrate its application as a highly compressible supercapacitor electrode with high performance. A PPy layer with optimal thickness was coated uniformly on individual CNTs and inter-CNT contact points by electrochemical deposition and crosslinking of pyrrole monomers, resulting in a core-shell configuration. The PPy coating significantly improves specific capacitance of the CNT sponge to above 300 F/g, and simultaneously reinforces the porous structure to achieve better strength and fully elastic structural recovery after compression. The CNT@PPy sponge can sustain 1,000 compression cycles at a strain of 50% while maintaining a stable capacitance (> 90% of initial value). Our CNT@PPy core-shell sponges with a highly porous network structure may serve as compressible, robust electrodes for supercapacitors and many other energy devices.

Carbon nanotube sponges are lightweight, conductive, highly porous, and flexible. An integration of these properties is suitable for constructing high-performance electrocapillary imbibers. Water imbibition into the sponges can be initiated at low potentials with tunable uptake rates and switched on and off reversibly. These controllable nanoporous imbibers have potential applications in a wide range of flexible micro- and nanofluidic systems.

© 2014 Optical Society of America. We present an all-fiber passively mode-locked fiber laser incorporating three-dimensional (3D) graphene as a saturable absorber (SA) for the first time to the best of our knowledge. The 3D graphene is synthesized by template-directed chemical vapor deposition (CVD). The SA is then simply formed by sandwiching the freestanding 3D graphene between two conventional fiber connectors without any deposition process. It is demonstrated that such 3D graphene based SA is capable to produce high quality mode-locked pulses. A passively mode-locked fiber laser is constructed and stable output pulses with a fundamental repetition rate of ∼9.9 MHz and a pulse width of ∼1 ps are generated from the fiber laser. The average output power of the laser is ∼10.5 mW while the output pulse is operating at single pulse region. The results imply that the freestanding 3D graphene can be applied as an effective saturable absorption material for passively mode-locked lasers.

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding.

Applications of mesoporous silica (m-SiO2) have suffered from its fragility (monolithic m-SiO2 easily collapses under compression) and limited internal molecular exchange through small channels. Previously reported hierarchical porous m-SiO2 structures containing interconnected macropores could improve adsorption properties, but they were still intrinsically fragile without sufficient mechanical strength to sustain deformation. Here, we embed a three-dimensional carbon nanotube (CNT) skeleton into m-SiO2 to fabricate bulk, robust sponges that can be compressed to large strains (60% volume reduction) repeatedly in both air and water. This is done by directly casting a uniform m-SiO2 layer with tunable thickness onto the surface of CNTs while maintaining the original network and open porous structure, resulting in a core–shell CNT@m-SiO2 hybrid sponge. By pumping fluid through the CNT@m-SiO2 sponges under cyclic compression, the adsorption rate and efficiency of dye molecules can be significantly enhanced due to the mesoporous coating on CNTs and enhanced fluid exchange throughout internal pores. The CNT@m-SiO2 sponges may be used as robust and flexible adsorption media, and chemical and biological sensors with high performance.

The synthesis of a range of benzimidazole derivatives bearing heterocyclic rings is described by the employment of benzimidazole-4/5-carboxylic acid derivatives as substrates.

The traditional lead-acid battery chargers, which take the single closed-loop analog control strategy, have the disadvantages such as low reliability, low charging efficiency and lack of charging protection function, etc. In order to deal with these disadvantages, an intelligent lead-acid battery charger based on SCM double closed-loop control is introduced in this paper. The main circuit, MOSFET diver circuit of the charger and the flow chart of program are presented firstly. Then the novel Frequency-Varied PWM control strategy is applied to fulfil the wide range of load changes. Through using the high-performance power chip UC3842 which works as driver and front-end circuit controller, the reliability of designed battery charger gets improved. Based on the traditional three-stage charging process, the pulse current charging process and protection functions are added to system to help repair the battery and extend the life span of the battery. The results of simulation and experimentation show that the design proposed in this paper is feasible.

This paper presents a nano-optofluidic waveguide coupler realized by a pair of concurrent dean flows. Distinctively different from solid waveguide coupler, this nano-optofluidic waveguides consists of a laminar liquid flow, which exhibits spatially varying bidirectional refractive index profile that support novel evanescent coupling phenomenon. The nanogap and the refractive index contrast of the nano-optofluidic waveguides can be measured with super-resolution in nm by analyzing its resulted evanescent coupling pattern. The nano-optofluidic waveguides can be used for biomolecular manipulation and detection in near future.

Graphene is an attractive material for flexible electronics and biosensors, yet its zero bandgap nature has limited the on/off ratio of field-effect transistors (FETs) and the sensitivity of biosensors based on graphene. Graphene nanomesh (GNM), a continuous 2D graphene nanostructure with a high density of holes punched in the basal plane, has been created to introduce lateral confinement and enable improved on/off ratio. However, the GNMs produced to date typically have a relatively large dimension (constriction neck width >5 nm) and low on/off ratio (≈100) limited by the resolution of the lithography process used. Here, the exploration of a directly grown mesoporous silica template is reported for the preparation of ultrafine GNMs with considerably narrower neck width (

This paper presents a tunable optofluidic waveguide dye laser utilizing two centrifugal Dean flows. The centrifugal Dean flow increases the light confinement of the dye laser by shaping a three-dimensional (3D) liquid waveguide from curved microchannels. The active medium with the laser dye is dissolved in the liquid core and pumped with an external pump laser to produce stimulated emission. The laser's Fabry-Pérot microcavity is formed with a pair of aligned gold-coated fiber facets to amplify the fluorescent emission. The advantage of the 3D optofluidic waveguide dye laser is its higher efficiency, thus to obtain lasing at a reduced threshold (60%) with higher output energy. The demonstrated slope efficiency is at least 3-fold higher than its traditional two-dimensional equivalent. In addition, the laser output energy can be varied on demand by tuning the flow rates of the two flows. This technique provides a versatile platform for high potential applications microfluidic biosensor and bioanalysis.