Highly Conductive Carbon Nanotube‐Graphene Hybrid Yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg^?1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.     

Adaptive channel estimation using cyclic prefix in multicarriermodulation system

Multicarrier modulation (MCM) is a promising technique for high rate data transmission and the channel estimation is very important for the implementation of MCM. We found that the cyclic prefix, originally used solely to reduce the intersymbol interference (ISI), can be viewed as a source of channel information. Based on this observation, we propose an adaptive channel estimation algorithm using the cyclic prefix. This algorithm can adaptively track the channel variation without additional training sequences     

Review and comparative evaluation of symbolic dynamic filtering for detection of anomaly patterns

Symbolic dynamic filtering (SDF) has been recently reported in literature as a pattern recognition tool for early detection of anomalies (i.e., deviations from the nominal behavior) in complex dynamical systems. This paper presents a review of SDF and its performance evaluation relative to other classes of pattern recognition tools, such as Bayesian Filters and Artificial Neural Networks, from the perspectives of: (i) anomaly detection capability, (ii) decision making for failure mitigation and (iii) computational efficiency. The evaluation is based on analysis of time series data generated from a nonlinear active electronic system. This work has been supported in part by the U.S. Army Research Laboratory and the U.S. Army Research Office under Grant No. W911NF-07-1-0376, by the U.S. Office of Naval Research under Grant No. N00014-08-1-380, and by NASA under Cooperative Agreement No. NNX07AK49A.     

Implementing polarization shift keying over satellite – system design and measurement results

Polarization shift keying (PolSK) is a digital modulation technique using the state of polarization of an electromagnetic wave as the signalling quantity. PolSK comes from fibre communications, where the channel offers two orthogonal states of polarization. This article develops on the idea to adapt this technology to satellite communications, where similar channel conditions exist. For this purpose, a digital PolSK modem was implemented on a programmable logic board. A proposal for constellation design as well as thoughts on synchronization of PolSK over satellite is presented. The modem was used to demonstrate a 16‐state Polarization Shift Keying link over a commercial satellite in K_u band. Measurements have been conducted in a back‐to‐back setup on intermediate frequency and on a K_u band transponder simulator to assess the impact of path‐length differences, carrier recovery and non‐linearity. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation of Hybrid Inorganic/Organic Nanocomposites

Hybrid inorganic/organic nanocomposites were produced by the exposure of spun films of octa-(benzo-15-crown-5)-substituted phthalocyanine of Cd(II) to an environment of hydrogen sulfide gas. The formation of cadmium sulfide (CdS) quantum dots in the metal free phthalocyanine matrix was identified in the phthalocyanine matrix from atomic force microscopy images. The mean size of CdS quantum dots was estimated to be 2–3 nm, from optical absorption and Raman spectra for the nanocomposites.     

An 18-bit high performance audio Σ-△ D/A converter

A multi-bit quantized high performance sigma-delta (Σ-△) audio DAC is presented.Compared to its singlebit counterpart,the multi-bit quantization offers many advantages,such as simpler Σ-△ modulator circuit,lower clock frequency and smaller spurious tones.With the data weighted average (DWA) mismatch shaping algorithm,element mismatch errors induced by multi-bit quantization can be pushed out of the signal band,hence the noise floor inside the signal band is greatly lowered.To cope with the crosstalk between digital and analog circuits,every analog component is surrounded by a guard ring,which is an innovative attempt.The 18-bit DAC with the above techniques,which is implemented in a 0.18μm mixed-signal CMOS process,occupies a core area of 1.86 mm2.The measured dynamic range (DR) and peak SNDR are 96 dB and 88 dB,respectively.     

Mass Flow through Solid 4H

We continue our solid ⁴He flow experiments in which we grow solid helium samples at constant temperature in the hcp region of the phase diagram. We exploit the properties of liquid helium in a confined geometry (porous Vycor glass), and induce a mass flow through the solid at pressures higher than the bulk melting pressure. We previously observed flow, but our temperature was limited to T≥350 mK. At T≈400 mK it was found that the flow ceased at P≈27 bar, and no flow was observed for T>550 mK. We have begun to extend our measurements to lower temperatures, and our data show that at lower temperatures we observe flow at higher pressures.     

Large‐Stroke Electrochemical Carbon Nanotube/Graphene Hybrid Yarn Muscles

Artificial muscles are reported in which reduced graphene oxide (rGO) is trapped in the helical corridors of a carbon nanotube (CNT) yarn. When electrochemically driven in aqueous electrolytes, these coiled CNT/rGO yarn muscles can contract by 8.1%, which is over six times that of the previous results for CNT yarn muscles driven in an inorganic electrolyte (1.3%). They can contract to provide a final stress of over 14 MPa, which is about 40 times that of natural muscles. The hybrid yarn muscle shows a unique catch state, in which 95% of the contraction is retained for 1000 s following charging and subsequent disconnection from the power supply. Hence, they are unlike thermal muscles and natural muscles, which need to consume energy to maintain contraction. Additionally, these muscles can be reversibly cycled while lifting heavy loads.