Mismatch and resolution in compressive imaging

Highly coherent sensing matrices arise in discretization of continuum problems such as radar and medical imaging when the grid spacing is below the Rayleigh threshold as well as in using highly coherent, redundant dictionaries as sparsifying operators. Algorithms (BOMP, BLOOMP) based on techniques of band exclusion and local optimization are proposed to enhance Orthogonal Matching Pursuit (OMP) and deal with such coherent sensing matrices. BOMP and BLOOMP have provably performance guarantee of reconstructing sparse, widely separated objects {\em independent} of the redundancy and have a sparsity constraint and computational cost similar to OMP's. Numerical study demonstrates the effectiveness of BLOOMP for compressed sensing with highly coherent, redundant sensing matrices.Comment: Figure 5 revise

Electrical power dissipation in carbon nanotubes on single crystal quartz and amorphous SiO2

Heat dissipation in electrically biased semiconducting carbon nanotubes (CNTs) on single crystal quartz and amorphous SiO2 is examined with temperature profiles obtained by spatially resolved Raman spectroscopy. Despite the differences in phonon velocities, thermal conductivity and van der Waals interactions with CNTs, on average, heat dissipation into single crystal quartz and amorphous SiO2 is found to be similar. Large temperature gradients and local hot spots often observed underscore the complexity of CNT temperature profiles and may be accountable for the similarities observed

Avalanche-Induced Current Enhancement in Semiconducting Carbon Nanotubes

Semiconducting carbon nanotubes under high electric field stress (~10 V/um) display a striking, exponential current increase due to avalanche generation of free electrons and holes. Unlike in other materials, the avalanche process in such 1D quantum wires involves access to the third sub-band, is insensitive to temperature, but strongly dependent on diameter ~exp(-1/d^2). Comparison with a theoretical model yields a novel approach to obtain the inelastic optical phonon emission length, L_OP,ems ~ 15d nm. The combined results underscore the importance of multi-band transport in 1D molecular wires

Probing the upper limits of current flow in one-dimensional carbon conductors

We use breakdown thermometry to study carbon nanotube (CNT) devices and graphene nanoribbons (GNRs) on SiO2 substrates. Experiments and modeling find the CNT-substrate thermal coupling scales proportionally to CNT diameter. Diffuse mismatch modeling (DMM) reveals the upper limit of thermal coupling ~0.7 WK 1m 1 for the largest diameter (3-4 nm) CNTs. Similarly, we extracted the GNR thermal conductivity (TC), ~80 (130) Wm 1K 1 at 20 (600) oC across our samples, dominated by phonons, with estimated <10% electronic contribution. The TC of GNRs is an order of magnitude lower than that of micron-sized graphene on SiO2, suggesting strong roles of edge and defect scattering, and the importance of thermal dissipation in small GNR devices. We also compare the peak current density of metallic single-walled CNTs with GNRs. We find that as the “footprint” (width) between such a device and the underlying substrate decreases, heat dissipation becomes more efficient (for a given width), allowing for higher current densities. Because of their smaller dimensions and lack of edges, CNTs can carry larger current densities than GNRs, up to ~16 mA/μm for an m-SWNT with a diameter of ~0.7 nm versus ~3 mA/μm for a GNR having a width of ~15 nm. Such cur-rent densities are the highest possible in any diffusive conductor, to our knowledge. We also study semiconducting and metallic single-walled CNTs under vacuum. Sem-iconducting single-wall CNTs under high electric field stress (~10 V/µm) display a re-markable current increase due to avalanche generation of free electrons and holes. Unlike in other materials, the avalanche process in such 1D quantum wires involves access to the third subband and is insensitive to temperature, but strongly dependent on diameter ~exp( 1/d 2). Comparison with a theoretical model yields a novel approach to obtain the inelastic optical phonon emission length, λOP,ems ≈ 15d nm. We find that current in metallic single-walled CNTs does not typically saturate, unlike previous observations which suggested a maximum current of ~25 μA. In fact, at very high fields (>10 V/μm) the current continues to increase with a slope ~0.5–1 μA/V, allowing m-CNTs to reach currents well in excess of 25 μA. Subsequent modeling sug-gests that carriers tunnel from the contacts into higher subbands. This allows currents to reach ~30–35 μA, which correspond to a current density of ~9 mA/μm for diameters of ~1.2 nm

Reduction of Hysteresis for Carbon Nanotube Mobility Measurements Using Pulsed Characterization

We describe a pulsed measurement technique to suppress hysteresis for carbon nanotube (CNT) device measurements in air, vacuum, and over a wide temperature range (80-453 K). Varying the gate pulse width and duty cycle probes the relaxation times associated with charge trapping near the CNT, found to be up to the 0.1-10 s range. Longer off times between voltage pulses enable consistent, hysteresis-free measurements of CNT mobility. A tunneling front model for charge trapping and relaxation is also described, suggesting trap depths up to 4-8 nm for CNTs on SiO2. Pulsed measurements will also be applicable to other nanoscale devices such as graphene, nanowires, and molecular electronics, and could enable probing trap relaxation times in a variety of material system interfaces

Thermal Dissipation and Variability in Electrical Breakdown of Carbon Nanotube Devices

We study high-field electrical breakdown and heat dissipation from carbon nanotube (CNT) devices on SiO2 substrates. The thermal "footprint" of a CNT caused by van der Waals interactions with the substrate is revealed through molecular dynamics (MD) simulations. Experiments and modeling find the CNT-substrate thermal coupling scales proportionally to CNT diameter and inversely with SiO2 surface roughness (~d/{\Delta}). Comparison of diffuse mismatch modeling (DMM) and data reveals the upper limit of thermal coupling ~0.4 W/K/m per unit length at room temperature, and ~0.7 W/K/m at 600 C for the largest diameter (3-4 nm) CNTs. We also find semiconducting CNTs can break down prematurely, and display more breakdown variability due to dynamic shifts in threshold voltage, which metallic CNTs are immune to; this poses a fundamental challenge for selective electrical breakdowns in CNT electronics

Interval-valued 2-tuple hesitant fuzzy linguistic term set and its application in multiple attribute decision making

[EN] The hesitant fuzzy linguistic term sets can retain the completeness of linguistic information elicitation by assigning a set of possible linguistic terms to a qualitative variable. However, sometimes experts cannot make sure that the objects attain these possible linguistic terms but only provide the degrees of confidence to express their hesitant cognition. Given that the interval numbers can denote the possible membership degrees that an object belongs to a set, it is suitable and convenient to provide an interval-valued index to measure the degree of a linguistic variable to a given hesitant fuzzy linguistic term set. Inspired by this idea, we introduce the concept of interval-valued 2-tuple hesitant fuzzy linguistic term set (IV2THFLTS) based on the interval number and the hesitant fuzzy linguistic term set. Then, we define some interval-valued 2-tuple hesitant fuzzy linguistic aggregation operators. Afterwards, to overcome the instability of subjective weights, we propose a method to compute the weights of attributes. For the convenience of application, a method is given to solve the multiple attribute decision making problems with IV2THFLTSs. Finally, a case study is carried out to validate the proposed method, and some comparisons with other methods are given to show the advantages of the proposed method.The work was supported in part by the National Natural Science Foundation of China (Nos. 71501135, 71771156), the China Postdoctoral Science Foundation (2016T90863, 2016M602698), the Fundamental Research Funds for the central Universities (No. YJ201535), and the Scientific Research Foundation for Excellent Young Scholars at Sichuan University (No. 2016SCU04A23).Si, G.; Liao, H.; Yu, D.; Llopis Albert, C. (2018). Interval-valued 2-tuple hesitant fuzzy linguistic term set and its application in multiple attribute decision making. Journal of Intelligent & Fuzzy Systems. 34(6):4225-4236. https://doi.org/10.3233/JIFS-171967S4225423634

Phase Retrieval with Random Phase Illumination

This paper presents a detailed, numerical study on the performance of the standard phasing algorithms with random phase illumination (RPI). Phasing with high resolution RPI and the oversampling ratio $\sigma=4$ determines a unique phasing solution up to a global phase factor. Under this condition, the standard phasing algorithms converge rapidly to the true solution without stagnation. Excellent approximation is achieved after a small number of iterations, not just with high resolution but also low resolution RPI in the presence of additive as well multiplicative noises. It is shown that RPI with $\sigma=2$ is sufficient for phasing complex-valued images under a sector condition and $\sigma=1$ for phasing nonnegative images. The Error Reduction algorithm with RPI is proved to converge to the true solution under proper conditions