Radiation Damage and Recovery Properties of Common Plastics PEN (Polyethylene Naphthalate) and PET (Polyethylene Terephthalate) Using a 137Cs Gamma Ray Source Up To 1 MRad and 10 MRad

Polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET) are cheap and common polyester plastics used throughout the world in the manufacturing of bottled drinks, containers for foodstuffs, and fibers used in clothing. These plastics are also known organic scintillators with very good scintillation properties. As particle physics experiments increase in energy and particle flux density, so does radiation exposure to detector materials. It is therefore important that scintillators be tested for radiation tolerance at these generally unheard of doses. We tested samples of PEN and PET using laser stimulated emission on separate tiles exposed to 1 MRad and 10 MRad gamma rays with a 137Cs source. PEN exposed to 1 MRad and 10 MRad emit 71.4% and 46.7% of the light of an undamaged tile, respectively, and maximally recover to 85.9% and 79.5% after 5 and 9 days, respectively. PET exposed to 1 MRad and 10 MRad emit 35.0% and 12.2% light, respectively, and maximally recover to 93.5% and 80.0% after 22 and 60 days, respectively

Instability and noise-induced thermalization of Fermi–Pasta–Ulam recurrence in the nonlinear Schrödinger equation

We investigate the spontaneous growth of noise that accompanies the nonlinear evolution of seeded modulation instability into Fermi–Pasta–Ulam recurrence. Results from the Floquet linear stabilityanalysis of periodic solutions of the three-wave truncation are compared with full numerical solutions of the nonlinear Schrödinger equation. The predicted initial stage of noise growth is in a goodagreementwith simulations, and is expected to provide further insight intothe subsequent dynamics of the fieldevolution after recurrence breakup

Toward reliable morphology assessment of thermosets via physical etching: Vinyl ester resin as an example

The morphology of peroxide-cured, styrene crosslinked, bisphenol A-based vinyl ester (VE) resin was investigated by atomic force microscopy (AFM) after ‘physical’ etching with different methods. Etching was achieved by laser ablation, atmospheric plasma treatment and argon ion bombardment. Parameters of the etching were varied to get AFM scans of high topography resolution. VE exhibited a nanoscaled nodular structure the formation of which was ascribed to complex intra- and intermolecular reactions during crosslinking. The microstructure resolved after all the above physical etching techniques was similar provided that optimized etching and suitable AFM scanning conditions were selected. Nevertheless, with respect to the ‘morphology visualization’ these methods follow the power ranking: argon bombardment > plasma treatment > laser ablation

Characterization of photomultiplier tubes in a novel operation mode for Secondary Emission Ionization Calorimetry

Hamamatsu single anode R7761 and multi-anode R5900-00-M16 Photomultiplier Tubes have been characterized for use in a Secondary Emission (SE) Ionization Calorimetry study. SE Ionization Calorimetry is a novel technique to measure electromagnetic shower particles in extreme radiation environments. The different operation modes used in these tests were developed by modifying the conventional PMT bias circuit. These modifications were simple changes to the arrangement of the voltage dividers of the baseboard circuits. The PMTs with modified bases, referred to as operating in SE mode, are used as an SE detector module in an SE calorimeter prototype, and placed between absorber materials (Fe, Cu, Pb, W, etc.). Here, the technical design of different operation modes, as well as the characterization measurements of both SE modes and the conventional PMT mode are reported

Mechanical and abrasion wear properties of hydrogenated nitrile butadiene rubber of identical hardness filled with carbon black and silica

The mechanical and abrasive wear properties of a hydrogenated nitrile butadiene rubber filled with 35 part per hundred rubber carbon black or silica with and without silane surface treatment (SI-si and SI, respectively), were investigated. Specimens were subjected to dynamic mechanical thermal analysis (also to study the Payne effect), mechanical (hardness, tensile modulus, ultimate tensile strength and strain, Mullins effect and tear strength), and fracture mechanical (J-integral) tests. The abrasive coefficient of friction and wear (specific wear rate, Ws) of the hydrogenated nitrile butadiene rubbers of identical hardness were measured against abrasive papers of different grit sizes (P600-P5000).The worn surface of the HNBR systems was inspected in scanning electron microscopy and the typical wear mechanisms deduced and discussed. Coefficient of friction did not change with the grit size by contrast to Ws which was markedly reduced with decreasing surface roughness of the abrasive paper. Ws of the compounds did not vary when wearing against P3000 and P5000 abrasive papers, representing mean surface roughness values of 7 and 5  μm, respectively. This was attributed to a change from abrasion to sliding type wear. hydrogenated nitrile butadiene rubber- carbon black outperformed the silica filled versions with respect to Ws though exhibited the highest coefficient of friction. No definite correlation could be found between the abrasive wear and the studied dynamic mechanical thermal analysis and (fracture) mechanical properties. </jats:p

Gold(I) Catalysts with Bifunctional P, N Ligands

A series of phosphanes with imidazolyl substituents were prepared as hemilabile PN ligands. The corresponding gold(I) complexes were tested as bifunctional catalysts in the Markovnikov hydration of 1-octyne, as well as in the synthesis of propargylamines by the three component coupling reaction of piperidine, benzaldehyde, and phenylacetylene. While the activity in the hydration of 1-octyne was low, the complexes are potent catalysts for the three component coupling reaction. In homogeneous solution the conversions to the respective propargylamine were considerably higher than under aqueous biphasic conditions. The connectivity of the imidazolyl substituents to the phosphorus atom, their substitution pattern, as well as the number of heteroaromatic substituents have pronounced effects on the catalytic activity of the corresponding gold(I) complexes. Furthermore, formation of polymetallic species with Au(2), Au(3), and Au(4) units has been observed and the solid-state structures of the compounds (5)(2)Au(3)Cl(2)]Cl and (3c)(2)Au(4)Cl(2)]Cl(2) (3c = tris(2-isopropylimidazol-4(5)-yl phosphane, 5 = 2-tert-butylimidazol-4(5)-yldiphenyl phosphane) were determined. The gold(I) complexes of imidazol-2-yl phosphane ligands proved to be a novel source for bis(NHC)gold(I) complexes (NHC = N-heterocyclic carbene)

Evaluation of a Revised Curriculum: A Four-Year Qualitative Study of Student Perceptions

Following curricular revisions at the Virginia Commonwealth University School of Dentistry, this longitudinal study was designed to determine students\u27 perceptions of their educational experience in the revised curriculum. A SWOT (Strengths, Weaknesses, Opportunities, and Threats) open-ended response questionnaire was administered to students in the class of 2011 (N=89) in January of each academic year, 2008 through 2011, followed by focus groups three months prior to graduation. The overall response rate for the questionnaire was 69 percent, and a total of fourteen students participated in four focus groups. Cumulatively, 1,382 responses (SWOT=984 and focus groups=398) were qualitatively analyzed, and five themes emerged: 1) early clinical experiences led to a perceived readiness for direct patient care; 2) the pace and organization of the revised condensed preclinical curriculum were perceived as hectic yet were appreciated as necessary preparation for patient care; 3) most faculty members were seen as committed to student learning, but a few were reported to have poor teaching skills and attitudes when interacting with students; 4) a perceived lack of patients led to fewer clinical experiences and a decrease in student confidence; and 5) some curricular content was seen to be redundant and irrelevant to future practice. The results indicate that the students were satisfied with aspects of their educational experience, suggesting the revised curriculum\u27s preliminary success in meeting its goals of earlier patient care, a condensed preclinical curriculum, and a student-friendly environment. As the curriculum is adapted in response to student feedback, ongoing evaluation is necessary and should be complemented by other evaluation indicators such as faculty perceptions and student learning outcomes

Design and Creation of a Device to Induce Vergence Eye Movements

Automated eye-tracking systems can detect and analyze eye movements as a means to accurately diagnose more than 20 neurological diseases including mild traumatic brain injury. Mild traumatic brain injury is an occurrence of injury to the head resulting from blunt trauma or from acceleration or deceleration forces. Eye movement refers to the voluntary or involuntary movement of the eyes, helping in acquiring, fixating and tracking visual stimuli. There are three types of voluntary eye movement to track objects: smooth pursuit, vergence shifts and saccades. Vergence shifts are eye movements where the eyes move in opposite directions: moving to the midline in convergence or moving away in divergence. This project focused on creating a device to induce vergence eye movements via a laser source and a mirror galvanometer. The laser pointer is directed at the mirror galvanometer which then projects the laser point onto a screen that lies horizontally in front of the observer. As the laser dot moves back and forth from the viewer, the eyes converge as the dot moves toward the viewer and diverge as the dot moves away. The device will be used to develop a baseline of control data that can eventually be used to diagnose mild traumatic brain injury. Different eye trackers will be tested to determine the optimum technique for gathering vergence eye movement data.https://scholarscompass.vcu.edu/uresposters/1192/thumbnail.jp

"Ultralow" sliding wear polytetrafluoro ethylene nanocomposites with functionalized graphene

The dry friction and sliding wear behavior of sintered polytetrafluoro ethylene containing various amounts of functionalized graphene were studied in this work. Graphene was incorporated in 0, 0.25, 0.75, 1, 2 and 4 vol.%, respectively. Sliding wear tests were performed in ring(metal)-on-plate(polytetrafluoro ethylene) test rig under ambient temperature setting 1 m/s sliding speed and 1 MPa contact pressure. The dynamic coefficient of friction and specific wear rate (ws) data were determined. Very low coefficient of frictions (0.12–0.14) were measured for polytetrafluoro ethylene containing 2 or 4 vol.% graphene, which was attributed to the formation of a tribofilm on the countersurface. Specific wear rate went through a maximum (peaked at doubling that of the unmodified polytetrafluoro ethylene at about 0.75 vol.% graphene) as a function of graphene content. Ultralow wear rate data in the range of 10−6 mm3/(N.m) were measured for the polytetrafluoro ethylene nanocomposites with 2 and 4 vol.% graphene. This was reasoned by the formation of a robust tribofilm, the development of which was followed by scanning electron microscopy by inspecting the worn surface of polytetrafluoro ethylene nanocomposites and that of the steel ring of the ring(metal)-on-plate(polytetrafluoro ethylene) test rig. Fourier transform infrared spectroscopic results confirmed the formation of carboxyl groups in the tribofilm. They were supposed to react with the functional groups of graphene and to create complexes with the metal countersurface ensuring the tribofilm with high adhesion and cohesion strengths. </jats:p

A New Look at the Axial Anomaly in Lattice QED with Wilson Fermions

By carrying out a systematic expansion of Feynman integrals in the lattice spacing, we show that the axial anomaly in the U(1) lattice gauge theory with Wilson fermions, as determined in one-loop order from an irrelevant lattice operator in the Ward identity, must necessarily be identical to that computed from the dimensionally regulated continuum Feynman integrals for the triangle diagrams.Comment: 1 figure, LaTeX, 18 page