On the independence number of random cubic graphs

We show that as n→∞, the independence number α(G), for almost all 3-regular graphs G on n vertices, is at least (6 log(3/2) – 2 – ?)n, for any constant ?>0. We prove this by analyzing a greedy algorithm for finding independent sets. © 1994 John Wiley & Sons, Inc.     

Randomized greedy matching. II

We consider the following randomized algorithm for finding a matching M in an arbitrary graph G = (V, E). Repeatedly, choose a random vertex u, then a random neighbour v of u. Add edge {u, v} to M and delete vertices u, v from G along with any vertices that become isolated. Our main result is that there exists a positive constant ? such that the expected ratio of the size of the matching produced to the size of largest matching in G is at least 0.5 + ?. We obtain stronger results for sparse graphs and trees and consider extensions to hypergraphs.     

Reflective terahertz imaging of porcine skin burns

A reflective pulsed terahertz imaging system based on direct detection was developed and used to obtain high-resolution images of a porcine skin specimen with superficial partial-thickness (second-degree) burns. Images were also obtained of the sample through ten layers of dry medical (cotton) gauze with minimal image degradation. The burned and unburned regions of skin had large differences in terahertz reflectivity, displaying clear delineation [20 dB signal-to-noise ratio (SNR) difference signal] between both regions in the images. The terahertz images also exhibited a "halo" surrounding the burn areas that may correlate to the extent of burn injury. The system operated at a center frequency of 500 GHz with 125 GHz of 3 dB bandwidth and used whiskbroom scanning to generate images with a spatial resolution of 1.5 mm. Each pixel was acquired with a 16 ms integration time, resulting in a 40 dB postdetection SNR. The simplicity and high SNR of the reflective terahertz system are promising steps toward real-time terahertz medical imaging.     

Synthesis,crystal structures and chemical bonding of RE5−xLixGe4 (RE = Nd,Sm and Gd; x≃ 1) with the orthorhombic Gd5Si4 type

The syntheses and single‐crystal and electronic structures of three new ternary lithium rare earth germanides, RE_5−xLi_xGe₄ (RE = Nd, Sm and Gd; x≃ 1), namely tetrasamarium lithium tetragermanide (Sm_3.97Li_1.03Ge₄), tetraneodymium lithium tetragermanide (Nd_3.97Li_1.03Ge₄) and tetragadolinium lithium tetragermanide (Gd_3.96Li_1.03Ge₄), are reported. All three compounds crystallize in the orthorhombic space group Pnma and adopt the Gd₅Si₄ structure type (Pearson code oP36). There are six atoms in the asymmetric unit: Li1 in Wyckoff site 4c, RE1 in 8d, RE2 in 8d, Ge1 in 8d, Ge2 in 4c and Ge3 in 4c. One of the RE sites, i.e. RE2, is statistically occupied by RE and Li atoms, accounting for the small deviation from ideal RE₄LiGe₄ stoichiometry.     

Preparation and Characterization of Polysulfone/Nanosilver-Doped Activated Carbon Nanocomposite

In this study, nano silver-doped activated carbon (Ag/C) acted as an inorganic additive and was blended with a polysulfone (PSF) matrix in a tetrahydrofuran (THF) solution, thereby forming nano silver- doped activated carbon/polysulfone (Ag/C/PSF) composites. Subsequently, the silver content and characterization of the Ag/C were identified using energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The FTIR, XRD, EDS and SEM were used to characterize the structure and morphology of the Ag/C/PSF composites. The FTIR spectra analysis revealed that adding a small volume of Ag/C in a PSF matrix did not substantially affect the functional groups of the matrix. The XRD results showed that the characteristic crystallization peaks of Ag/C/PSF (2θ = 26°) increased as the Ag/C content increased. The EDS results revealed that silver elements were inlaid into Ag/C/PSF composites, and the SEM results demonstrated strong interfacial interaction between the Ag/C particles and PSF matrix. The results of thermogravimetric analysis and differential scanning calorimetry appeared that adding Ag/C particles increased the thermal decomposition temperature and glass transition temperature of the Ag/C/PSF composites. From a stress–strain analysis, the added Ag/C particles enhanced the tensile strength of the PSF matrix. The results of contact-angle and atomic-force microscopy measuring showed that the hydrophobicity and surface roughness increased when Ag/C content increased. The antibacterial test results revealed that the Ag/C/PSF composites exhibited excellent antibacterial activity against both Staphylococcus aureus and Escherichia coli. In addition, the electrical conductivity measurements showed that volume resistivity of the Ag/C/PSF composites decreased with the amount of Ag/C increase.     

Synthesis and applications of novel acceptor-donor-acceptor organic dyes with dithienopyrrole- and fluorene-cores for dye-sensitized solar cells

Four novel symmetrical organic dyes (S1-S4) configured with acceptor-donor-acceptor (A-D-A) structures containing electron donating fluorene (S1 and S2) and N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1-S4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit current (J_SC) of 12.27 mA/cm², an open circuit voltage (V_OC) of 0.61 V, a fill factor (FF) of 0.63, and an overall power conversion efficiency (η) of 4.73%. Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in its η value (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO₂ surface and thus to increase the J_SC value eventually.     

Active inductor shunt peaking in high-speed VCSEL driver design

An all-transistor active-inductor shunt-peaking structure has been used in a prototype of 8 Gbps high- speed VCSEL driver which is designed for the optical link in ATLAS liquid Argon calorimeter upgrade. The VCSEL driver is fabricated in a commercial 0.25 p~m Silicon-on-Sapphire （SOS） CMOS process for radiation tolerant purpose. The all-transistor active-inductor shunt-peaking is used to overcome the bandwidth limitation from the CMOS pro- cess. The peaking structure has the same peaking effect as the passive one, but takes a small area, does not need linear resistors and can overcome the process variation by adjust the peaking strength via an external control. The design has been taped out, and the prototype has been proven by the preliminary electrical test results and bit error ratio test results. The driver achieves 8 Gbps data rate as simulated with the peaking. We present the all-transistor active-inductor shunt-peaking structure, simulation and test results in this paper.