5,809 research outputs found
Preliminary measurements of aircraft airframe noise with the NASA CV-990 aircraft
Flight tests were conducted in a CV-990 jet transport with engines at idle power to investigate aircraft airframe noise. Test results showed that airframe noise was measured for the aircraft in the landing configuration. The results agreed well with the expected variation with the fifth power of velocity. For the aircraft in the clean configuraton, it was concluded that airframe noise was measured only at higher airspeeds with engine idle noise present at lower speeds. The data show that landing gear and flaps make a significant contribution to airframe noise
10 µm minority-carrier diffusion lengths in Si wires synthesized by Cu-catalyzed vapor-liquid-solid growth
The effective electron minority-carrier diffusion length, L_(n,eff), for 2.0 µm diameter Si wires that were synthesized by Cu-catalyzed vapor-liquid-solid growth was measured by scanning photocurrent microscopy. In dark, ambient conditions, L_(n,eff) was limited by surface recombination to a value of ≤ 0.7 µm. However, a value of L_(n,eff) = 10.5±1 µm was measured under broad-area illumination in low-level injection. The relatively long minority-carrier diffusion length observed under illumination is consistent with an increased surface passivation resulting from filling of the surface states of the Si wires by photogenerated carriers. These relatively large L_(n,eff) values have important implications for the design of high-efficiency, radial-junction photovoltaic cells from arrays of Si wires synthesized by metal-catalyzed growth processes
High-performance Si microwire photovoltaics
Crystalline Si wires, grown by the vapor–liquid–solid (VLS)
process, have emerged as promising candidate materials for lowcost, thin-film photovoltaics. Here, we demonstrate VLS-grown Si microwires that have suitable electrical properties for high-performance photovoltaic applications, including long minority-carrier diffusion lengths (L_n » 30 µm) and low surface recombination velocities (S « 70 cm·s^(-1)). Single-wire radial p–n junction solar cells were fabricated with amorphous silicon and silicon nitride
surface coatings, achieving up to 9.0% apparent photovoltaic efficiency, and exhibiting up to ~600 mV open-circuit voltage with over 80% fill factor. Projective single-wire measurements and optoelectronic simulations suggest that large-area Si wire-array solar cells have the potential to exceed 17% energy-conversion efficiency, offering a promising route toward cost-effective crystalline Si photovoltaics
Si microwire-array solar cells
Si microwire-array solar cells with Air Mass 1.5 Global conversion efficiencies of up to 7.9% have been fabricated using an active volume of Si equivalent to a 4 μm thick Si wafer. These solar cells exhibited open-circuit voltages of 500 mV, short-circuit current densities (J_(sc)) of up to 24 mA cm^(-2), and fill factors >65% and employed Al_2O_3 dielectric particles that scattered light incident in the space between the wires, a Ag back reflector that prevented the escape of incident illumination from the back surface of the solar cell, and an a-SiN_x:H passivation/anti-reflection layer. Wire-array solar cells without some or all of these design features were also fabricated to demonstrate the importance of the light-trapping elements in achieving a high J_(sc). Scanning photocurrent microscopy images of the microwire-array solar cells revealed that the higher J_(sc) of the most advanced cell design resulted from an increased absorption of light incident in the space between the wires. Spectral response measurements further revealed that solar cells with light-trapping elements exhibited improved red and infrared response, as compared to solar cells without light-trapping elements
Photoelectrochemical Hydrogen Evolution Using Si Microwire Arrays
Arrays of B-doped p-Si microwires, diffusion-doped with P to form a radial n+ emitter and subsequently coated with a 1.5-nm-thick discontinuous film of evaporated Pt, were used as photocathodes for H_2 evolution from water. These electrodes yielded thermodynamically based energy-conversion efficiencies >5% under 1 sun solar simulation, despite absorbing less than 50% of the above-band-gap incident photons. Analogous p-Si wire-array electrodes yielded efficiencies <0.2%, largely limited by the low photovoltage generated at the p-Si/H_2O junction
Investigation into circular economy of plastics: The case of the UK fast moving consumer goods industry
Despite the recognised importance of the issue of plastic waste and an emerging circular economy (CE) in recent years, there is a lack of comprehensive and relevant studies regarding CE and the role of plastics. This study addresses a significant gap in the literature by revealing current initiatives implemented in the UK fast moving consumer goods (FMCG) industry through an in-depth exploration of four case organisations that have committed to the UK Plastic Pact, a pioneering collective initiative on plastic recycling. The study discloses a variety of present initiatives within the industry including the removal of unrecyclable plastics, packaging innovation, in-store retailer schemes, and label modifications. Collaboration was concluded as an essential enabler, internally and across the industry. Fundamental barriers were identified as inadequate infrastructure to support plastics in the CE and technical implications of packaging
Effects and Propositions
The quantum logical and quantum information-theoretic traditions have exerted
an especially powerful influence on Bub's thinking about the conceptual
foundations of quantum mechanics. This paper discusses both the quantum logical
and information-theoretic traditions from the point of view of their
representational frameworks. I argue that it is at this level, at the level of
its framework, that the quantum logical tradition has retained its centrality
to Bub's thought. It is further argued that there is implicit in the quantum
information-theoretic tradition a set of ideas that mark a genuinely new
alternative to the framework of quantum logic. These ideas are of considerable
interest for the philosophy of quantum mechanics, a claim which I defend with
an extended discussion of their application to our understanding of the
philosophical significance of the no hidden variable theorem of Kochen and
Specker.Comment: Presented to the 2007 conference, New Directions in the Foundations
of Physic
Discrete coherent and squeezed states of many-qudit systems
We consider the phase space for a system of identical qudits (each one of
dimension , with a primer number) as a grid of
points and use the finite field to label the corresponding axes.
The associated displacement operators permit to define -parametrized
quasidistribution functions in this grid, with properties analogous to their
continuous counterparts. These displacements allow also for the construction of
finite coherent states, once a fiducial state is fixed. We take this reference
as one eigenstate of the discrete Fourier transform and study the factorization
properties of the resulting coherent states. We extend these ideas to include
discrete squeezed states, and show their intriguing relation with entangled
states between different qudits.Comment: 11 pages, 3 eps figures. Submitted for publicatio
Six-year follow-up of the treatment of patients with dissociative disorders study*
Objective: Literature on the treatment of dissociative disorders (DDs) suggests that these individuals require long-term and specialized treatment to achieve stabilization and functionality. There is considerable empirical support for specialized phasic, dissociation-focused treatment in reducing a myriad of psychological symptoms and self-harm in this population. However, until recently, there has been a paucity of longitudinal treatment research on DD patients
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