Rapid self-assembly of brush block copolymers to photonic crystals

The reduced chain entanglement of brush polymers over their linear analogs drastically lowers the energetic barriers to reorganization. In this report, we demonstrate the rapid self-assembly of brush block copolymers to nanostructures with photonic bandgaps spanning the entire visible spectrum, from ultraviolet (UV) to near infrared (NIR). Linear relationships were observed between the peak wavelengths of reflection and polymer molecular weights. This work enables “bottom-up” fabrication of photonic crystals with application-tailored bandgaps, through synthetic control of the polymer molecular weight and the method of self-assembly. These polymers could be developed into NIR-reflective paints, to combat the “urban heat island effect” due to NIR photon thermalization

Time Optimal Control in Spin Systems

In this paper, we study the design of pulse sequences for NMR spectroscopy as a problem of time optimal control of the unitary propagator. Radio frequency pulses are used in coherent spectroscopy to implement a unitary transfer of state. Pulse sequences that accomplish a desired transfer should be as short as possible in order to minimize the effects of relaxation and to optimize the sensitivity of the experiments. Here, we give an analytical characterization of such time optimal pulse sequences applicable to coherence transfer experiments in multiple-spin systems. We have adopted a general mathematical formulation, and present many of our results in this setting, mindful of the fact that new structures in optimal pulse design are constantly arising. Moreover, the general proofs are no more difficult than the specific problems of current interest. From a general control theory perspective, the problems we want to study have the following character. Suppose we are given a controllable right invariant system on a compact Lie group, what is the minimum time required to steer the system from some initial point to a specified final point? In NMR spectroscopy and quantum computing, this translates to, what is the minimum time required to produce a unitary propagator? We also give an analytical characterization of maximum achievable transfer in a given time for the two spin system.Comment: 20 Pages, 3 figure

Solar cell efficiency enhancement via light trapping in printable resonant dielectric nanosphere arrays

Resonant dielectric structures are a promising platform for addressing the key challenge of light trapping in thin-film solar cells. We experimentally and theoretically demonstrate efficiency enhancements in solar cells from dielectric nanosphere arrays. Two distinct amorphous silicon photovoltaic architectures were improved using this versatile light-trapping platform. In one structure, the colloidal monolayer couples light into the absorber in the near-field acting as a photonic crystal light-trapping element. In the other, it acts in the far-field as a graded index antireflection coating to further improve a cell which already included a state-of-the-art random light-trapping texture to achieve a conversion efficiency over 11%. For the near-field flat cell architecture, we directly fabricated the colloidal monolayer on the device through Langmuir–Blodgett deposition in a scalable process that does not degrade the active material. In addition, we present a novel transfer printing method, which utilizes chemical crosslinking of an optically thin adhesion layer to tether sphere arrays to the device surface. The minimally invasive processing conditions of this transfer method enable the application to a wide range of solar cells and other optoelectronic devices. False-color SEM image of an amorphous silicon solar cell with resonant spheres on top

Health knowledge among the millennial generation

The Millennial Generation, also known as Generation Y, is the demographic cohort following Generation X, and is generally regarded to be composed of those individuals born between 1980 and 2000. They are the first to grow up in an environment where health-related information is widely available by internet, TV and other electronic media, yet we know very little about the scope of their health knowledge. This study was undertaken to quantify two domains of clinically relevant health knowledge: factual content and ability to solve health related questions (application) in nine clinically related medical areas. Study subjects correctly answered, on average, 75% of health application questions but only 54% of health content questions. Since students were better able to correctly answer questions dealing with applications compared to those on factual content contemporary US high school students may not use traditional hierarchical learning models in acquisition of their health knowledge

New approaches to ultrasensitive magnetic resonance

Spectroscopic methods tend to exhibit an inverse correlation between sensitivity and the ability to discriminate between similar structures. Were they obtainable with adequate sensitivity, magnetic resonance spectra could resolve structural controversies involving the nature of clusters, ions, semiconductor defects and catalytic intermediates. This paper describes several novel approaches to magnetic resonance, which have in common that the spins are coupled to other degrees of freedom in order to obtain nonequilibrium polarization and/or greater detection sensitivity. The methods under development include single-ion electron spin resonance (ESR) detected by ion trapping frequencies, catalyst NMR detected by the branching ratio to different spin symmetry species, and semiconductor nuclear magnetic resonance (NMR) detected via the circular polarization of luminescence

New approaches to ultrasensitive magnetic resonance

Spectroscopic methods tend to exhibit an inverse correlation between sensitivity and the ability to discriminate between similar structures. Were they obtainable with adequate sensitivity, magnetic resonance spectra could resolve structural controversies involving the nature of clusters, ions, semiconductor defects and catalytic intermediates. This paper describes several novel approaches to magnetic resonance, which have in common that the spins are coupled to other degrees of freedom in order to obtain nonequilibrium polarization and/or greater detection sensitivity. The methods under development include single-ion electron spin resonance (ESR) detected by ion trapping frequencies, catalyst NMR detected by the branching ratio to different spin symmetry species, and semiconductor nuclear magnetic resonance (NMR) detected via the circular polarization of luminescence

"‘We just want to be treated with respect!’: Using restorative approaches and the dramatic arts to build positive relationships between the police and young people"

This article explores the application of an ambitious arts-based restorative intervention that has been applied in a direct response to perceived issues with procedural justice, legitimacy and community relations between police and young people. The research focuses on a series of Youth Forums that took place in the West of England, employed as an attempt to improve strained relationships between both parties. It reports on detailed ethnographic research of the Forum processes and procedures presenting this primary evidence in light of the existing literature on police legitimacy and procedural justice in police-youth encounters. The findings suggest that community-based arts programmes can be a powerful and effective tool for challenging entrenched views with the potential to improve future encounters between police and young people; and that the relevance and effectiveness of arts-based interventions can be increased by combining with restorative justice principles