The development of poly(vinyl chloride) extrusions for a 14,000‐ton self‐supporting structure for the detection of neutrinos

The NOvA Neutrino Experiment has built a one‐of‐a‐kind self‐supporting plastic structure, potentially the largest ever built. The poly(vinyl chloride) (PVC) structure serves as a neutrino detector and is composed of 28 individual blocks that measure 15.5 m (51 feet) high by 15.5 m (51 feet) wide by 2.1 m (7 feet) deep. The primary parts in the detector construction are 15.5‐m (51‐foot), 16‐cell PVC extrusions. These extrusions form the basis of the detector modules, which are laminated together in a crossed pattern to form the individual blocks and then filled with (mineral oil)–based liquid scintillator. The self‐supporting nature of the detector places important structural requirements on both the PVC formulation and the extrusions. Block assembly requirements impose narrow geometric tolerances. Because of the method of detecting neutrinos, the extrusions must possess exceptionally high reflectivity over a particular wavelength range. This requirement places additional restrictions on the components of the PVC formulation. Altogether, the PVC extrusions have to maintain important reflectivity characteristics, provide structural support to the detector, and meet relatively tight geometric requirements for assembly. In order to meet these constraints, a custom PVC formulation had to be created and extruded. We describe the purpose and requirements of the NOvA detector leading to the production of our unique PVC extrusion, summarize the research and development process, and discuss the lessons learned. J. VINYL ADDIT. TECHNOL., 22:368–376, 2016. © 2014 Society of Plastics Engineers     

Optimization of CdTe thin‐film solar cell efficiency using a sputtered,oxygenated CdS window layer

A major source of loss in cadmium sulfide/cadmium telluride (CdS/CdTe) solar cells results from light absorbed in the CdS window layer, which is not converted to electrical current. This film can be made more transparent by oxygen incorporation during sputter deposition at ambient temperature. Prior to this work, this material has not produced high‐efficiency devices on tin oxide‐coated soda‐lime‐glass substrates used industrially. Numerous devices were fabricated over a variety of process conditions to produce an optimized device. Although the material does not show a consistent increase in band gap with oxygenation, absorption in this layer can be virtually eliminated over the relevant spectrum, leading to an increase in short‐circuit current. Meanwhile, fill factor is maintained, and open‐circuit voltage increases relative to baseline devices with sublimated CdS. The trend of device parameters with oxygenation and thickness is consistent with an increasing conduction band offset at the window/CdTe interface. Optimization considering both initial efficiency and stability resulted in a National Renewable Energy Laboratory verified 15.2%‐efficient cell on 3.2‐mm soda‐lime glass. This window material was shown to be compatible with SnO₂‐based transparent conducting oxide and high resistance transparent coated substrates using in‐line compatible processes. Copyright © 2015 John Wiley & Sons, Ltd     

Diploid hybrid speciation in Penstemon (Scrophulariaceae)

Hybrid speciation has played a significant role in the evolution of angiosperms at the polyploid level. However, relatively little is known about the importance of hybrid speciation at the diploid level. Two species of Penstemon have been proposed as diploid hybrid derivatives based on morphological data, artificial crossing studies, and pollinator behavior observations: Penstemon spectabilis (derived from hybridization between Penstemon centranthifolius and Penstemon grinnellii) and Penstemon clevelandii (derived from hybridization between P. centranthifolius and P. spectabilis). Previous studies were inconclusive regarding the purported hybrid nature of these species because of a lack of molecular markers sufficient to differentiate the parental taxa in the hybrid complex. We developed hypervariable nuclear markers using inter-simple sequence repeat banding patterns to test these classic hypotheses of diploid hybrid speciation in Penstemon. Each species in the hybrid complex was genetically distinct, separated by 10-42 species-specific inter-simple sequence repeat markers. Our data do not support the hybrid origin of P. spectabilis but clearly support the diploid hybrid origin of P. clevelandii. Our results further suggest that the primary reason diploid hybrid speciation is so difficult to detect is the lack of molecular markers able to differentiate parental taxa from one another, particularly with recently diverged species.     

A Monte Carlo Simulation of an Actual Segmented Calorimeter: A Study of Calorimeter Performance at High Energies

The computer code system CALOR has been used to simulate data taken with a large segmented liquid argon/iron calorimeter at Fermilab. The resulting energy and angular distributions along with the longitudinal and transverse shower shapes are compared to experimental data in the range 1-38 GeV. Results are presented extending the Monte Carlo simulations to 125 GeV. The energy resolution of an incident hadron can be determined with a resolution ?E/E = (7.6 + 29.2/?E)% and its direction with a resolution of ?(?) = 22.7 + 390/E) mrad (where E is in GeV).     

Construction and testing of a 3 m diameter × 5 m superconducting solenoid for the fermilab collider detector facility (CDF)

A thin 3 m diameter × 5 m, 1.5 T superconducting solenoid for the Fermilab collider detector facility (CDF solenoid) was constructed. Cool-down and excitation tests of the solenoid were carried out. The design current is 5000 A and the stored magnetic energy is 30 × 10⁶ J. The solenoid utilizes the forced flow cooling method of two-phase helium and does not have a permanent inner bobbin. The material thickness of the solenoid is 0.85 radiation length in the radial direction. An aluminum-stabilized NbTi/Cu superconductor fabricated with the EFT method was used. Radially outward magnetic forces must be supported with an outer support cylinder shrink-fitted outside the coil. The helium cooling tube of 20 mm in inner diameter and about 140 m in length was welded to the outer support cylinder.The maximum excitation current was limited to 2800 A in the present tests without an iron return yoke. Thermal response of the solenoid during the cool-down and excitation tests was very steady. A series of heater quench tests was attempted by using a heater installed at the outer support cylinder. The solenoid did not quench even for a heater input of about 10 kJ. In a warm-up test the liquid helium supply was shut off. The coil stayed superconducting for about 90 min and then the entire coil became normal very uniformly. This result is consistent with the measured heat load of the solenoid of about 35 W. The results of the present tests indicate the excellent thermal stability of the solenoid.