Pressure-Responsive Conductive Poly(vinyl alcohol) Composites Containing Waste Cotton Fibers Biochar

The development of responsive composite materials is among the most interesting challenges in contemporary material science and technology. Nevertheless, the use of highly expensive nanostructured fillers has slowed down the spread of these smart materials in several key productive sectors. Here, we propose a new piezoresistive PVA composite containing a cheap, conductive, waste-derived, cotton biochar. We evaluated the electromagnetic properties of the composites under both AC and DC regimes and as a function of applied pressure, showing promisingly high conductivity values by using over 20 wt.% filler loading. We also measured the conductivity of the waste cotton biochar from 20 K up to 350 K observing, for the first time, hopping charge transport in biochar materials.

CLPDI Algorithm in UWB Synchronization

<div> <div> <div> <p>This paper studies code synchronization in time hopping (TH) ultra wideband (UWB) systems. In TH UWB systems, narrow pulses based on Gaussian pulse are positioned in different locations in consecutive time frames. The location of each frame is defined by a spreading code. The receiver collects the energy of the pulses using the same spreading code. To be able to do that, it has to synchronize itself to the incoming signal. Due to the large bandwidth of the signal, several replicas of the signals arrive into the receiver. Thus, the energy of the signal is spread in time domain causing extra problems to the synchronization procedure. In this paper, earlierly proposed method for direct sequence spread spectrum system is applied for time hopping system. The method is simulated in a multipath environment. The performance measure used is the mean acquisition time. Con- stant false alarm rate criterion is used for the threshold setting rule for comparator. The energies of the multipath components are combined in the acquisition process. Therefore, diversity combining is obtained in the acquisition process, which also leads to performance improvement. </p> </div> </div> </div>

CLPDI Algorithm in UWB Synchronization

<div> <div> <div> <p>This paper studies code synchronization in time hopping (TH) ultra wideband (UWB) systems. In TH UWB systems, narrow pulses based on Gaussian pulse are positioned in different locations in consecutive time frames. The location of each frame is defined by a spreading code. The receiver collects the energy of the pulses using the same spreading code. To be able to do that, it has to synchronize itself to the incoming signal. Due to the large bandwidth of the signal, several replicas of the signals arrive into the receiver. Thus, the energy of the signal is spread in time domain causing extra problems to the synchronization procedure. In this paper, earlierly proposed method for direct sequence spread spectrum system is applied for time hopping system. The method is simulated in a multipath environment. The performance measure used is the mean acquisition time. Con- stant false alarm rate criterion is used for the threshold setting rule for comparator. The energies of the multipath components are combined in the acquisition process. Therefore, diversity combining is obtained in the acquisition process, which also leads to performance improvement. </p> </div> </div> </div>

Observation of an Ultrafast Exciton Transport Regime at Early Times in Quantum Dot Solids

Understanding and engineering exciton transport in quantum dot (QD) solids is both of fundamental interest and crucial to their broad applications in devices1-6. Till date, studies of exciton transport in QD solids on pico/nano-second timescales have led to the conclusion that closer packing of QDs enables faster exciton transport, while energetic/structural heterogeneity leads to reduction of exciton diffusivity over time7,8. Here we study PbS QD solids using transient absorption microscopy with 13 femtoseconds time resolution and 10 nm spatial precision. We find exciton diffusivities in the range of ~102 cm2 s-1 within the first few hundred femtoseconds after photoexcitation, followed by the transition to a slower transport regime with diffusivities in the range 10-1 to 1 cm2 s-1. Counterintuitively, the initial diffusivity is higher and the time before the transition to the slower transport phase is longer in QD solids with longer ligand lengths. This suggests a transition from early-time transport of delocalized excitons to later time hopping based transport of localized excitons, where QD packing density and heterogeneity accelerate the localization process. Our results reveal a new regime for exciton transport in QD solids and provide design rules to engineer desired transport properties in these systems on a range of timescales.