Towards in-fiber silicon photonics

The state of the art of silicon optical fibers fabricated via the high pressure chemical deposition technique will be reviewed. The optical transmission properties of step index silicon optical fibers will be presented, including investigations of the nonlinearities that can be used for all-optical signal processing. In addition, alternative complex fiber geometries that permit sophisticated control of the propagating light will be introduced

Optical detection and modulation at 2µm-2.5µm in silicon

Recently the 2µm wavelength region has emerged as an exciting prospect for the next generation of telecommunications. In this paper we experimentally characterise silicon based plasma dispersion effect optical modulation and defect based photodetection in the 2-2.5µm wavelength range. It is shown that the effectiveness of the plasma dispersion effect is dramatically increased in this wavelength window as compared to the traditional telecommunications wavelengths of 1.3µm and 1.55µm. Experimental results from the defect based photodetectors show that detection is achieved in the 2-2.5µm wavelength range, however the responsivity is reduced as the wavelength is increased away from 1.55µm

A wide range and high resolution one-filtration molecular weight cut-off method for aqueous based nanofiltration and ultrafiltration membranes

A new and superior one-filtration method for the determination of the molecular weight cut-off (MWCO) of aqueous based nanofiltration and ultrafiltration membranes has been developed using the widest range of polyethylene glycol oligomers as MWCO probes of any MWCO method so far. This method was enabled by a new, high resolution oligomer separation and detection using high performance liquid chromatography (HPLC) coupled with an evaporative light scattering detector (ELSD). The refined method can determine the MWCO of membranes over a MW range from 678 to 4594 g mol−1 with a molecular weight difference of just 44 g mol−1 and a bonus further one point extension to 6000 g mol−1 – giving the widest range and most precise difference of MWs that can be resolved of any single filtration MWCO method that exists. MWCO determination of five commercial membranes from GE Osmonics™ and Millipore showed good agreement with manufacturer and literature values, confirming the accuracy of the method. As this new method has significant advantages over all other existing aqueous MWCO determinations (i.e. single filtration, higher resolution over a wider MW range, low cost MWCO molecular probes), it is suggested that it could be adopted as the new standard for determining aqueous MWCO over a MW range from 678 to 6000 g mol−1

Germanium-on-silicon platforms for nonlinear photonics in the mid-infrared

We review our progress in the characterization of the nonlinear transmission properties of low loss germanium-on-silicon waveguides. Simple pump-probe experiments are employed to demonstrate their use for all-optical control

Environmental Effects on Glass Fiber Reinforced Polyester and Vinylester Composites

The effects of environment on glass fiber reinforced polyester and vinylester composites immersed in liquids and in humid air were investi gated. Tests were performed at temperatures 23 C and 93 C with the materials exposed to humid air at 50 and 100 percent relative humidities, and to five different liquids: saturated salt water, No. 2 diesel fuel, lubrica ting oil, antifreeze, and indolene. Changes in weight, ultimate tensile strength, tensile modulus, short beam shear strength, and shear modulus were measured over a six month period, and the effects of the environment on these parameters were assessed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66642/2/10.1177_002199838001400304.pd

Identifying sulphate-reducing and magnetotactic bacteria in a hyperalkaline cave system

Sulphate-reducing bacteria (SRB) and magnetotactic bacteria (MTB) are two special groups of prokaryotes that emerged early in Earth’s history. These extremotolerant bacterial groups have rarely been identified or studied within cave and karst environments, especially hyperalkaline cave systems (pH > 9), such as Poole’s Cavern in Derbyshire, England. In this study, we identify the sulphate-reducing MTB Desulfovibrio magneticus, within this hyperalkaline cave system. It appears to survive in a diverse range of environments including soil, stalactites and cave sediments. Additionally, we identify various extremotolerant SRB in similar Poole’s Cavern environments. We show that these SRB and MTB can move successfully into subsurface environments and adapt concomitantly to the anomalous pH, saline, and relatively nutrient-poor conditions found in Poole’s Cavern. These findings are significant to our understanding of microorganisms on early Earth because it is believed, but not proven, that underground environments might have been hot spots for early microbial life. We expect that these early bacteria would have been able to adopt similar adaptation strategies, transferring and acclimatizing to underground environments, in ways comparable to the SRB and MTB identified in this study

Effect of polyacid dopants on the performance of polyaniline membranes in organic solvent nanofiltration

Polyaniline (PANI) has been widely explored as a promising membrane material, but the trade-off between porosity and stability limits its widespread application in organic solvent nanofiltration (OSN). Here we present a simple approach to prepare PANI membranes with excellent chemical stability and rejection performance in OSN by employing polyacids as PANI dopants for the first time. The PANI membranes were doped with two polyacids with different molecular weights (MW) and acid dissociation constants (pKa): namely poly(4-styrenesulfonic acid) (PSSA, MW: 75000 g mol −1, pKa: 0.94) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA, MW: 800000 g mol −1, pKa: 0.87), and were compared with a small acid (HCl) doped PANI membrane. The polyacid doped membranes, PANI-PSSA and PANI-PAMPSA, obtained dense structures with increased hydrophilicity due to strong intermolecular interactions between the PANI and the polyacids. Stability tests showed that the PANI-PSSA and PANI-PAMPSA were stable in a wide range of polar and nonpolar solvents, while the undoped PANI and PANI-HCl had poor stability in these solvents. The swelling degree and permeance of the doped membranes decreased with the increase of the dopant MW. The PANI-PAMPSA membrane exhibited a molecular weight cut-off (MWCO) in the nanofiltration (NF) range of 400 g mol −1 in methanol and isopropanol, while the PANI-HCl and PANI-PSSA membranes were in the ultrafiltration (UF) range. This study demonstrates that polyacid doping can make stable and nanoporous PANI membranes for OSN applications without the need for crosslinking. This simple approach can be used to design new classes of OSN membranes for challenging separation processes in the future. </p

Explosive events - swirling transition region jets

In this paper, we extend our earlier work to provide additional evidence for an alternative scenario to explain the nature of so-called `explosive events'. The bi-directed, fast Doppler motion of explosive events observed spectroscopically in the transition region emission is classically interpreted as a pair of bidirectional jets moving upward and downward from a reconnection site. We discuss the problems of such a model. In our previous work, we focused basically on the discrepancy of fast Doppler motion without detectable motion in the image plane. We now suggest an alternative scenario for the explosive events, based on our observations of spectral line tilts and bifurcated structure in some events. Both features are indicative of rotational motion in narrow structures. We explain the bifurcation as the result of rotation of hollow cylindrical structures and demonstrate that such a sheath model can also be applied to explain the nature of the puzzling `explosive events'. We find that the spectral tilt, the lack of apparent motion, the bifurcation, and a rapidly growing number of direct observations support an alternative scenario of linear, spicular-sized jets with a strong spinning motion.Comment: 9 pages, 3 figures, accepted for publication in Solar Physic

Filtration and Breakdown of Clay Clusters during Resin Transfer Molding of Nanoclay/Glass/Epoxy Composites

Dispersion of nanoclay clusters during resin transfer molding of nanoclay/glass/epoxy disks is investigated. In addition to a center-gated disk containing only 14% glass fibers, three nanocomposite disks are fabricated with the addition of 2, 5 or 10 wt% Cloisite® 25A nanoclay. The spatial distribution of nanoclay clusters along the radial axis of the nanocomposite disks are characterized at two length scales. Clusters larger than 1.5 μm are characterized by performing image analysis on the SEM micrographs whereas smaller nanoclay clusters are identified by wavelength dispersive spectrometry. Results obtained from image analysis indicate that nanoclay clusters are filtered out by as much as 50% in the flow direction by the glass fiber preforms. In addition, increasing nanoclay content led to higher filtration, suggesting that cluster formation is more prominent at higher nanoclay loadings. Cluster size distribution analyses revealed that the outer edges of the disks, on average, contain finer nanoclay particles. For instance, the outer edge of the nanocomposite with 2% clay contains 22% more small nanoclay clusters compared to center of the disk. Glass transition temperature, Tg, of four specimens obtained from each molded disks is characterized under oscillatory shear. Glass transition temperature of the samples are shown to increase with the nanoclay content, yielding a 40% higher Tg at 10% nanoclay loading compared to glass/epoxy composite without clay. Increasing glass transition temperature with increasing nanoclay content may be an indication of intercalation of nanoclay within the epoxy matrix.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline