Student cluster competition: ParConnect reproducibility task report

Reproducibility is a desirable characteristic of any experimental work in computer science. In this paper, we reproduce the results in the paper, “A parallel connectivity algorithm for de Bruijn graphs in metagenomic applications”, for verifying their claims on the speed and scalability of their algorithm. We first state the claims made in the original paper. Then, we describe our hardware and software setup used for the reproducibility task, followed by the steps taken to setup the proposed algorithm and profiling software. Lastly, we present the results obtained from our experiments and show that we are able to reproduce most of the claims made in the original paper.     

DLTS characterization of defects in GaN induced by electron beam exposure

The deep level transient spectroscopy (DLTS) technique was used to investigate the effects of electron beam exposure (EBE) on n-GaN. A defect with activation energy of 0.12 eV and capture cross section of 8.0×10^–16 cm² was induced by the exposure. The defect was similar to defects induced by other irradiation techniques such as proton, electron, and gamma irradiation. In comparison to GaN, the EBE induced defects in other materials such as Si and SiC are similar to those induced by other irradiation methods.     

Characteristics of turbine spacing in a wind farm using an optimal design process

The characteristics of turbine spacing for optimal wind farm efficiency were investigated using combined numerical models. The effects of wakes from upstream turbines were predicted by a model capable of determining velocity distributions on a rotor plane, based on Ainslie's approach. The performance results of a wind farm showed good agreement with measurements. The blade element momentum theory, in combination with a dynamic wake model, was applied. Wake model used the results of aerodynamic analysis as input properties. The optimal distance between wind turbines was predicted using a genetic algorithm to maximize efficiency in a wind farm. The results showed that the spacing between the first and the second turbines had the importance to the entire farm's efficiency.     

Improved transfer of chemical-vapor-deposited graphene through modification of intermolecular interactions and solubility of poly(methylmethacrylate) layers

Clean chemical vapor deposition (CVD)-grown graphene surfaces with intrinsic electrical properties were obtained by a modified poly(methylmethacrylate) (PMMA) transfer method. The modified method entails UV irradiation, followed by wet cleaning of the UV-irradiated PMMA layer using a mixture of isopropyl alcohol (IPA), acetone, and methyl isobutyl ketone (MIBK). The chemical structure of the PMMA layer degrades following UV irradiation under atmospheric conditions, via side-chain cleavage of the ester groups, resulting in reduced intermolecular interactions between the PMMA layer and the underlying graphene film. Furthermore, the IPA/MIBK/acetone mixture is shown to be a powerful solvent that can effectively remove the PMMA layer without leaving any PMMA residue, which could act as a source of cracks and scattering centers for charge carrier transport, on the graphene surface. Graphene transistors fabricated by this modified transfer method show high electron and hole mobilities with ideal threshold voltages of near 0 V.     

A non-contact graphene surface scattering rate characterization method at microwave frequency by combining Raman spectroscopy and coaxial connectors measurement

A non-contact method is proposed to characterize graphene at microwave frequency by combining Raman spectroscopy and Amphenol Precision Connector (APC-7). The CVD-grown graphene is transferred to the ring-shape Teflon substrate and characterized by Raman spectroscopy to estimate its doping density and the related Fermi energy. The graphene is then sandwiched between two APC-7 coaxial connectors and S parameters under transverse electromagnetic (TEM) mode normal incident waves are measured to extract the surface conductivity through transmission matrix, in which the de-embedding process can be avoided. By combing the Kubo formula with our proposed circuit model, the scattering rate of graphene on Teflon substrate is obtained and analyzed.     

Electrically conducting polyolefin composites containing electric field-aligned multiwall carbon nanotube structures: The effects of process parameters and filler loading

The characteristics of network formation of multiwall carbon nanotubes (MWCNTs) inside ethylene–octene copolymer (EOC) melts under an alternating current (AC) electric field and the resulting electrical conductivity improvements are studied by combining dynamic and steady state resistivity measurements. Fine MWCNT dispersion during melt compounding of the samples is accomplished by means of a novel non-specific, non-covalent functionalization method. It is found that the electrified composite films exhibit nanotube assembly into columnar structures parallel to the electric field, accompanied by dramatic increases in electrical conductivity up to eight orders of magnitude. Experimentally acquired resistivity data are used to derive correlations between the characteristic insulator-to-conductor transition times of the composites and process parameters, such as electric field strength (E), polymer viscosity (η) and nanotube volume fraction (ϕ). Finally, a criterion for the selection of (η, E, C) conditions that enable MWCNT assembly under an electric field controlled regime (i.e., minimal Brownian motion-driven aggregation effects) is developed. The correlations presented herein not only provide insights in the MWCNT assembly process, but can also guide the experimental design in future studies on electrified composites or assist in the selection of process parameters in composites manufacturing.     

Free carrier absorption in self-activated PbWO4 and Ce-doped Y3(Al0.25Ga0.75)3O12 and Gd3Al2Ga3O12 garnet scintillators

Nonequilibrium carrier dynamics in the scintillators prospective for fast timing in high energy physics and medical imaging applications was studied. The time-resolved free carrier absorption investigation was carried out to study the dynamics of nonequilibrium carriers in wide-band-gap scintillation materials: self-activated led tungstate (PbWO₄, PWO) ant two garnet crystals, GAGG:Ce and YAGG:Ce. It was shown that free electrons appear in the conduction band of PWO and YAGG:Ce crystals within a sub-picosecond time scale, while the free holes in GAGG:Ce appear due to delocalization from Gd³⁺ ground states to the valence band within a few picoseconds after short-pulse excitation. The influence of Gd ions on the nonequilibrium carrier dynamics is discussed on the base of comparison the results of the free carrier absorption in GAGG:Ce containing gadolinium and in YAGG without Gd in the host lattice.     

Design,development and testing twin pulse tube cryocooler

The design and development of Twin Pulse Tube Cryocooler (TPTC) is presented. Both the coolers are driven by a single Linear Moving Magnet Synchronous Motor (LMMSM) with piston heads at both ends of the mover shaft. Magnetostatic analysis for flux line distribution was carried-out during design and development of LMMSM based pressure wave generator. Based on the performance of PWG, design of TPTC was carried out using Sage and Computational Fluid Dynamics (CFD) analysis. Detailed design, fabrication and testing of LMMSM, TPTC and their integration tests are presented in this paper.     

Graphene nanosheets as counter electrode with phenoxazine dye for efficient dye sensitized solar cell

Efficient dye sensitized solar cells (DSSCs) are developed using phenoxazine (POZ) based organic dye (WS5) and graphene nanosheets (GNs) counter electrode (CE). Being organic, both these materials are used together to explore compatibility of organic materials in current DSSCs. Organic dye with POZ moiety is synthesized and graphene oxide nanosheets (GONs) are spin coated on FTO glass and thermally reduced afterwards. To increase the performance of WS5 through decreased dye aggregation, deoxycholic acid (DCA) is added to it. The results of adding DCA are observed and compared using UV–Vis spectroscopy, external quantum efficiency (EQE), electrochemical impedance spectroscopy (EIS) and photovoltaic conversion efficiency (PCE). Prepared organic dye based DSSC cell results in a high PCE of 6.61%. The optimized WS5 dye and GNs CE, shows PCE of 5.77% and the GNs CE compared to Pt CE results in almost identical charge transfer resistance value at the CE/electrolyte interface. Low cost of this designed organic dye and GNs and the PCE results indicate that this combination may result in the reduction of cost of current DSSCs and the realization that expensive and rare inorganic materials can be replaced with organic ones in future.     

An active noise cancellation technique for the CUORE Pulse Tube cryocoolers

The Cryogenic Underground Observatory for Rare Events (CUORE) experiment at Gran Sasso National Laboratory of INFN searches for neutrinoless double beta decay using TeO₂ crystals as cryogenic bolometers. The sensitivity of the measurement heavily depends on the energy resolution of the detector, therefore the success of the experiment stands on the capability to provide an extremely low noise environment. One of the most relevant sources of noise are the mechanical vibrations induced by the five Pulse Tube cryocoolers used on the cryogenic system which houses the detectors. To address this problem, we developed a system to control the relative phases of the pulse tube pressure oscillations, in order to achieve coherent superposition of the mechanical vibrations transmitted to the detectors. In the following, we describe this method and report on the results in applying it to the CUORE system.