A Novel 3D Non-Stationary UAV-MIMO Channel Model and Its Statistical Properties

The wireless communication systems based on Unmanned Aerial Vehicles(UAVs) have found a wide range of applications recently. In this paper, we propose a new three-dimensional(3 D) non-stationary multiple-input multiple-output(MIMO) channel model for the communication links between the UAV and mobile terminal(MT). The new model originates the traditional geometry-based stochastic models(GBSMs) but considers the non-stationary propagation environment due to the rapid movements of the UAV, MT, and clusters. Meanwhile, the upgrade time evolving algorithms of time-variant channel parameters, i.e., the path number based on birth-death processes of clusters, path delays, path powers, and angles of arrival and departure, are developed and optimized. In addition, the statistical properties of proposed GBSM including autocorrelation function(ACF), cross-correlation function(CCF), and Doppler power spectrum density(DPSD) are investigated and analyzed. Simulation results demonstrate that our proposed model provides a good agreement on the statistical properties with the corresponding derived theoretical ones, which indicates its usefulness for the performance evaluation and validation of the UAV based communication systems.

Multiplexed Five-Color Molecular Imaging of Cancer Cells and Tumor Tissues with Carbon Nanotube Raman Tags in the Near-Infrared

Single-walled carbon nanotubes(SWNTs)with five different C13/C12 isotope compositions and well-separated Raman peaks have been synthesized and conjugated to five targeting ligands in order to impart molecular specificity.Multiplexed Raman imaging of live cells has been carried out by highly specific staining of cells with a five-color mixture of SWNTs.Ex vivo multiplexed Raman imaging of tumor samples uncovers a surprising up-regulation of epidermal growth factor receptor(EGFR)on LS174T colon cancer cells from cell culture to in vivo tumor growth.This is the first time five-color multiplexed molecular imaging has been performed in the near-infrared(NIR)region under a single laser excitation.Near zero interfering background of imaging is achieved due to the sharp Raman peaks unique to nanotubes over the low,smooth autofluorescence background of biological species.

Monolithic superaligned carbon nanotube composite with integrated rewriting, actuating and sensing multifunctions

Multifunctionality has become a mainstream trend in the development of smart clothing and flexible wearable devices.Nevertheless,it remains a grand challenge to realize multiple functions,such as sensing,actuating and information displaying,in one single multifunctional material.Here,we present one multifunctional integration strategy by employing monolithic superaligned carbon nanotube(SACNT)composite,which can leverage three different functions through fascinating features of SACNT.Firstly,by using thermochromic dye as a color-memorizing component and SACNT as a photothermal converter,the composite film can be utilized as a flexible rewritable medium.It demonstrates excellent rewriting performances(reversibility>500 times).Secondly,the composite can be tailored to fabricate an actuator,when its length direction is along the SACNT alignment.The actuator shows a bending-morphing when illuminated by near-infrared light.The morphing is attributed to a large difference in volume change between the SACNT and polymer when the SACNT absorbs the optical energy and heats the composite.Thirdly,owing to the unique anisotropy of SACNT,the composite is easily to be stretched in the direction perpendicular to the SACNT alignment,accompanied by a change in electrical resistance.Therefore,the composite is able to be used as a strain sensor.Finally,we fabricate two smart wearable devices to demonstrate the applications,which realize the functions of human-motion detection(sensing)and rewritable information display(rewriting)simultaneously.This multifunctional SACNT composite is expected to have potential applications in the next-generation wearable devices,smart clothing and so on.

High temperature performance of coaxial h-BN/CNT wires above 1,000 ℃:Thermionic electron emission and thermally activated conductivity

The development of wires and cables that can tolerate extremely high temperatures will be very important for probing extreme environments, such as in solar exploration, fire disasters, high-temperature materials processing, aeronautics and astronautics. In this paper, a lightweight high-temperature coaxial h-boron nitride (BN)/carbon nanotube (CNT) wire is synthesized by the chemical vapor deposition (CVD) epitaxial growth of h-BN on CNT yarn. The epitaxially grown h-BN acts as both an insulating material and a jacket that protects against oxidation. It has been shown that the thermionic electron emission (1,200 K) and thermally activated conductivity (1,000 K) are two principal mechanisms for insulation failure of h-BN at high temperatures. The thermionic emission of h-BN can provide the work function of h-BN, which ranges from 4.22 to 4.61 eV in the temperature range of 1,306-1,787 K. The change in the resistivity of h-BN with temperature follows the ohmic conduction model of an insulator, and it can provide the “electron activation energy”(the energy from the Fermi level to the conduction band of h-BN), which ranges from 2.79 to 3.08 eV, corresponding to a band gap for h-BN ranging from 5.6 to 6.2 eV. However, since the leakage current is very small, both phenomena have no obvious influence on the signal transmission at the working temperature. This lightweight coaxial h-BN/CNT wire can tolerate 1,200 ℃ in air and can transmit electrical signals as normal. It is hoped that this lightweight high-temperature wire will open up new possibilities for a wide range of applications in extreme high-temperature conditions.

In Situ TEM Observation of the Gasification and Growth of Carbon Nanotubes Using Iron Catalysts

We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.

Direct laser patterning of two-dimensional lateral transition metal disulfide-oxide-disulfide heterostructures for ultrasensitive sensors

Two-dimensional(2D)heterostructures based on the combination of transition metal dichalcogenides(TMDs)and transition metal oxides(TMOs)have aroused growing attention due to their integrated merits of both components and multiple functionalities.However,nondestructive approaches of constructing TMD-TMO heterostructures are still very limited.Here,we develop a novel type of lateral TMD-TMO heterostructure(NbS2-Nb2O5-NbS2)using a simple lithography-free,direct laser-patterning technique.The perfect contact of an ultrathin TMO channel(Nb2O5)with two metallic TMDs(NbS2)electrodes guarantee strong electrical signals in a two-terminal sensor.Distinct from sensing mechanisms in separate TMOs or TMDs,this sensor works based on the modulation of surface conduction of the ultrathin TMO(Nb2O5)channel through an adsorbed layer of water molecules.The sensor thus exhibits high selectivity and ultrahigh sensitivity for room-temperature detection of NH3(ΔR/R=80%at 50 ppm),superior to the reported NH3 sensors based on 2D materials,and a positive temperature coefficient of resistance as high as 15%–20%/℃.Bending-invariant performance and high reliability are also demonstrated in flexible versions of sensors.Our work provides a new strategy of lithography-free processing of novel TMD-TMO heterostructures towards high-performance sensors,showing great potential in the applications of future portable and wearable electronics.

True-color real-time imaging and spectroscopy of carbon nanotubes on substrates using enhanced Rayleigh scattering

白光照亮的围单人赛的碳 nanotubes (SWCNT ) 应该由于散布的回声瑞利显得有颜色。然而，底层上的 SWCNT 的真彩成像没被报导，因为 SWCNT 和散布的强壮的底层的极其低的散布紧张。这里，我们证明散布的瑞利能被接口偶极子改进效果极大地提高。底层上的因而丰富多彩的 SWCNT 能被宽地 supercontinuum 激光照明直接在一台光显微镜下面想象，它便于单个 SWCNT 的高产量 chirality 赋值。这条途径，称为的瑞利成像显微镜学，没被限制为 SWCNT，但是对许多 nanomaterials 广泛地适用，它使丰富多彩的 nanoworld 能在光显微镜下面被探索。

Bidirectional micro-actuators based on eccentric coaxial composite oxide nanofiber

It is of great importance to develop new micro-actuators with high performance by optimizing the structures and materials.Here we develop a VO2/AI2O3/CNT eccentric coaxial nanofiber,which can be potentially applied as a micro-actuator.The specific eccentric coaxial structure was efficiently fabricated by conventional thin film deposition methodology with individual CNT templet.Activated by thermal and photothermal stimuli,the as-developed actuator delivers a bidirectional actuation behavior with large amplitudes and an ultra-fast response,〜2.5 mS.A tweezer can be further made by assembling two such nanofibers symmetrically onto a tungsten probe.Clamping and unclamping can be realized by laser stimulus.More experimental and simulation investigations indicated that the actuation behaviors could be attributed to the nanostructured eccentric coaxial geometry,the thermal coefficient mismatch between layers and the fast phase transition of V02.The micro-actuators will have potentials in micro manipulators,nanoscaled switches,remote controls and other autonomous systems.Furthermore,a large variety of coaxial and eccentric coaxial nanofibers with various functions can also be developed,giving the as-developed methodology more opportunities.

Scanning electron microscopy imaging of single-walled carbon nanotubes on substrates

Scanning electron microscopy （SEM） plays an indispensable role in nanoscience and nanotechnology because of its high efficiency and high spatial resolution in characterizing nanomaterials. Recent progress indicates that the contrast arising from different conductivities or bandgaps can be observed in SEM images if single-walled carbon nanotubes （SWCNTs） are placed on a substrate. In this study, we use SWCNTs on different substrates as model systems to perform SEM imaging of nanomaterials. Substantial SEM observations are conducted at both high and low acceleration voltages, leading to a comprehensive understanding of the effects of the imaging parameters and substrates on the material and surface-charge signals, as well as the SEM imaging. This unified picture of SEM imaging not only furthers our understanding of SEM images of SWCNTs on a variety of substrates but also provides a basis for developing new imaging recipes for other important nanomaterials used in nanoelectronics and nanophotonics.

High areal capacity flexible sulfur cathode based on multi-functionalized super-aligned carbon nanotubes

Rational design of a robust carbon matrix has a profound impact on the performance of flexible/wearable lithium/sulfur batteries.Herein,we demonstrate a freestanding three-dimensional super-aligned carbon nanotube (SACNT) matrix reinforced with a multi-functionalized carbon coating for flexible,high-areal sulfur loading cathode.By employing the sulfur/nitrogen co-doped carbon (SNC)"glue",the joints in the SACNT scaffold are tightly welded together so that the overall mechanical strength of the electrode is significantly enhanced to withstand the repeated bending as well as the volume change during operation.The SNC also shows intriguing catalytic effect that lowers the energy barrier of Li ion transport,propelling a superior redox conversion efficiency.The resulting binder-free and current collector-free sulfur cathode exhibits a high reversible capacity of 1,079 mAh·g^-1 at 1 C,a high-rate capacity of ~ 800 mAh·g^-1 at 5 C,and an average capacity decay rate of 0.037% per cycle at 2 C for 1,500 cycles.Impressively,a large-areal flexible Li/S pouch cell based on such mechanically robust cathode exhibits excellent capacity retention under arbitrary bending conditions.With a high areal sulfur loading of 7 mg·cm^-2,the large-areal flexible cathode delivers an outstanding areal capacity of 6.3 mAh·cm^-2 at 0.5 C (5.86 mA·cm^-2),showing its promise for realizing practical high energy density flexible Li/S batteries.

Interface dipole enhancement effect and enhanced Rayleigh scattering

一纳米或亚纳米的光效果包围象围单人赛的碳 nanotubes (SWCNT ) 那样的单个 nanomaterials 的压缩分子的界面的层理论上并且试验性地被学习了。当由光照亮了时，这界面的层作为一个光偶极子格子表现并且贡献在附近的原子，分子，或 nanomaterials 上提高本地地的一块即时近的地，它可以接着导致提高的瑞利散布，散布的拉曼，和荧光。这接口偶极子的理论提高了效果(IDEE ) 预言那在 nanomaterials 和界面的层的飞机之间的更小的距离，或到包围媒介的界面的层的绝缘的常数的更大的比率，将导致一个更大的领域改进因素。这预言被 SWCNT 以及在逐渐地控告的 SWCNT 散布的 situ 瑞利散布的提高的瑞利的几实现进一步试验性地验证。接口偶极子提高了散布的瑞利不仅启用真彩 nanomaterials 的即时成像，而且提供一个有效工具凝视进微妙的界面的现象。

SEM imaging of insulating specimen through a transparent conducting veil of carbon nanotube

Observing the morphology of insulating specimen in scanning electron microscope(SEM)is of great significance for the nanoscale semiconductor devices and biological tissues.However,the charging effect will cause image distortion and abnormal contrast when observing insulating specimen in SEM.A typical solution to this problem is using metal coating or water-removable conductive coating.Unfortunately,in both cases the surface of the specimen is covered by a thin layer of conductive material which hides the real surface morphology and is very difficult to be completely removed after imaging.Here we show a convenient,residue-free,and versatile method to observe real surface morphology of insulating specimen without charging effect in SEM with the help of a nanometer-thick film of super-aligned carbon nanotube(SACNT).This thin layer of SACNT film,like metal,can conduct the surface charge on insulating specimen through the sample stage to the ground,thus eliminating the charging effect.SACNT film can also be used as the conductive tape to carry and immobilize insulating powder or particles during SEM imaging.Different from the metal coating,SACNT film is transparent,so that the real microstructure of the insulating specimen surface can be observed.In addition,SACNT film can be easily attached to and peeled off from the surface of specimen without any residue.This convenient,residue-free,and versatile method can open up new possibilities in nondestructive SEM imaging of a wide variety of insulating materials,semiconductor devices,and biological tissues.

Visualizing nonlinear resonance in nanomechanical systems via single-electron tunneling

Numerous reports have elucidated the importance of mechanical resonators comprising quantum-dot-embedded carbon nanotubes(CNTs)for studying the effects of single-electron transport.However,there is a need to investigate the single-electron transport that drives a large amplitude into a nonlinear regime.Herein,a CNT hybrid device has been investigated,which comprises a gate-defined quantum dot that is embedded into a mechanical resonator under strong actuation conditions.The Coulomb peak positions synchronously oscillate with the mechanical vibrations,enabling a single-electron Chopper*1 mode.Conversely,the vibration amplitude of the CNT versus its frequency can be directly visualized via detecting the time-averaged single-electron tunneling current.To understand this phenomenon,a general formula is derived for this time-averaged single-electron tunneling current,which agrees well with the experimental results.By using this visualization method,a variety of nonlinear motions of a CNT mechanical oscillator have been directly recorded,such as Duffing nonlinearity,parametric resonance,and double-,fractional-,mixed-frequency excitations.This approach opens up burgeoning opportunities for investigating and understanding the nonlinear motion of a nanomechanical system and its interactions with electron transport in quantum regimes.

Direct discrimination between semiconducting and metallic single-walled carbon nanotubes with high spatial resolution by SEM

Single-walled carbon nanotube （SWCNT） films with a high density exhibit broad functionality and great potential in nanodevices, as SWCNTs can be either metallic or semiconducting in behavior. The films greatly benefit from characterization technologies that can efficiently identify and group SWCNTs based on metallic or semiconducting natures with high spatial resolution. Here, we developed a facile imaging technique using scanning electron microscopy （SEM） to discriminate between semiconducting and metallic SWCNTs based on black and white colors. The average width of the single-SWCNT image was reduced to -9 nm, -1/5 of previous imaging results. These achievements were attributed to reduced surface charging on the SiOdSi substrate under enhanced accelerating voltages. With this identification technique, a CNT transistor with an on/off ratio of 〉10s was fabricated by identifying and etching out the white metallic SWCNTs. This improved SEM imaging technique can be widely applied in evaluating the selective growth and sorting of SWCNTs.

Superbroad-band actively tunable acoustic metamaterials driven from poly(ethylene terephthalate)/carbon nanotube nanocomposite membranes

Actively tunable acoustic metamaterials have attracted ever increasing attention.However,their tunable frequency range is quite narrow(tens of Hz)even under ultrahigh applied voltage(about 1,000 V).Here,we report a superbroad-band actively tunable acoustic metamaterials with the bandwidth over 400 Hz under a low voltage.In the actively tunable acoustic metamaterials,the acoustic membrane is a laminated nanocomposite consisting of a poly(ethylene terephthalate)(PET)and super-aligned carbon nanotube(CNT)drawn from CN T forest array.The laminated nanocomposite membrane exhibits adjustable acoustic properties,whose modulus can be adjusted by applying external electric field.The maximum frequency bandwidth of PET/CN T nanocomposite membrane reaches 419 Hz when applying an external DC voltage of 60 V.Our actively tunable acoustic metamaterials with superbroad-band and lightweight show very promising foreground in noise reduction applications.

Nanoarray-Embedded Hierarchical Surfaces for Highly Durable Dropwise Condensation

Durable dropwise condensation of saturated vapor is of significance for heat transfer and energy saving in extensive industrial applications.While numerous superhydrophobic surfaces can promote steam condensation,maintaining discrete microdroplets on surfaces without the formation of a flooded filmwise condensation at high subcooling remains challenging.Here,we report the development of carbon nanotube array-embedded hierarchical composite surfaces that enable ultra-durable dropwise condensation under a wide range of subcooling(ΔT_(sub)=8 K–38 K),which outperforms existing nanowire surfaces.This performance stems from the combined strategies of the hydrophobic nanostructures that allow efficient surface renewal and the patterned hydrophilic micro frames that protect the nanostructures and also accelerate droplet nucleation.The synergistic effects of the composite design ensure sustained Cassie wetting mode and capillarity-governed droplet mobility(Bond number<0.055)as well as the large specific volume of condensed droplets,which contributes to the enhanced condensation heat transfer.Our design provides a feasible alternative for efficiently transferring heat in a vapor environment with relatively high temperatures through the tunable multiscale morphology.