Singlet exciton fission in solution.

Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley-Queisser limit in single-junction solar cells. Although the process through which singlet fission occurs is not well characterized, some local order is thought to be necessary for intermolecular coupling. Here, we report a triplet yield of 200% and triplet formation rates approaching the diffusion limit in solutions of bis(triisopropylsilylethynyl (TIPS)) pentacene. We observe a transient bound excimer intermediate, formed by the collision of one photoexcited and one ground-state TIPS-pentacene molecule. The intermediate breaks up when the two triplets separate to each TIPS-pentacene molecule. This efficient system is a model for future singlet-fission materials and for disordered device components that produce cascades of excited states from sunlight.B.J.W. was supported by a Herchel Smith Research Fellowship. A.J.M. received funding from a Marie Curie Scholarship. D.B. is a FNRS Research Director. Both A.J.M and D.B. acknowledge support from the European Community’s Initial Training Network SUPERIOR (PITN-GA-2009-238177). Further funding for this project came from the Engineering and Physical Sciences Research Council (EPSRC) and a pump-prime grant from the Winton Programme for the Physics of Sustainability.This is the accepted version of an article originally published in Nature Chemistry 5, 1019–1024 and available online at http://www.nature.com/nchem/journal/v5/n12/full/nchem.1801.html. Nature Publishing Group's conditions for reuse are detailed at http://www.nature.com/authors/policies/license.html

The QUEST large area CCD camera

We have designed, constructed, and put into operation a very large area CCD camera that covers the field of view of the 1.2 m Samuel Oschin Schmidt Telescope at the Palomar Observatory. The camera consists of 112 CCDs arranged in a mosaic of four rows with 28 CCDs each. The CCDs are 600 x 2400 pixel Sarnoff thinned, back-illuminated devices with 13 µm x 13 µm pixels. The camera covers an area of 4.6° x 3.6° on the sky with an active area of 9.6 deg_2. This camera has been installed at the prime focus of the telescope and commissioned, and scientific-quality observations on the Palomar-QUEST Variability Sky Survey were started in 2003 September. The design considerations, construction features, and performance parameters of this camera are described in this paper

Identification of a triplet pair intermediate in singlet exciton fission in solution.

Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley-Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spin-singlet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]--tetracene we find rapid (<100 ps) formation of excimers and a slower (∼ 10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process.H.L.S was supported by the Winton Programme for the Physics of Sustainability and A.J.M received funding from the Engineering and Physical Sciences Research Council.This is the accepted manuscript. The final version is available at http://www.pnas.org/content/112/25/7656.abstract

Tensor network simulation of multi-environmental open quantum dynamics via machine learning and entanglement renormalisation

The simulation of open quantum dynamics is a critical tool for understanding how the non-classical properties of matter might be functionalised in future devices. However, unlocking the enormous potential of molecular quantum processes is highly challenging due to the very strong and non-Markovian coupling of ‘environmental’ molecular vibrations to the electronic ‘system’ degrees of freedom. Here, we present an advanced but general computational strategy that allows tensor network methods to effectively compute the non-perturbative, real-time dynamics of exponentially large vibronic wave functions of real molecules. We demonstrate how ab initio modelling, machine learning and entanglement analysis can enable simulations which provide real-time insight and direct visualisation of dissipative photophysics, and illustrate this with an example based on the ultrafast process known as singlet fission

Effects of Potential Detoxifying Agents on Growth Performance and Deoxynivalenol (DON) Urinary Balance Characteristics of Nursery Pigs Fed DON-Contaminated Wheat

Two experiments were conducted to evaluate the effects of detoxifying agents on the growth performance of nursery pigs fed diets contaminated with deoxynivalenol (DON). Naturally DON-contaminated wheat (6 ppm) replaced noncontaminated wheat in diets to achieve desired dietary DON concentrations. Basal ingredients were tested for mycotoxin and amino acid content prior to diet manufacturing. Diets were pelleted at 180˚F with a 45-s conditioning time. A total of 238 barrows and gilts (PIC 327 × 1050; initially 29.6 ± 5.6 lb and 42 d of age) were used in a 21-d growth study. Pens of pigs were allotted by BW to 1 of 5 treatments in a completely randomized design with a 2 × 2 + 1 factorial arrangement. The 5 experimental diets included the following components, 1) positive control (PC; \u3c0.5 mg/kg DON); 2) PC + 1.0% Product X (Nutriquest LLC, Mason City, IA); 3) negative control (NC; 4.0 mg/kg DON); 4) NC + 1.0% Product X; and 5) NC + 1.0% sodium metabisulfite (SMB; Samirian Chemicals, Campbell, CA). There were 6 or 7 replicate pens per treatment and 7 pigs per pen. Chemical analysis indicated a low level of fumonisin (\u3c1 ppm) was present but that all DON concentrations matched calculated values. Analyzed DON concentrations were decreased by 92% when pelleted with SMB. Overall (d 0 to 21), a DON × Product X interaction was observed for ADG (P \u3c 0.05) and ADFI (P \u3c 0.10). Adding Product X to PC diets had no effect on ADG or ADFI; however, when added to NC diets, ADG, and ADFI became worse. As anticipated, DON reduced (P \u3c 0.001) ADG, ADFI, and F/G by 24, 16, and 10%, respectively. Deoxynivalenol-associated reductions in ADG were most distinct (50%) during the initial period (0.42 vs. 0.84 lb from d 0 to 7). Adding SMB to NC diets improved (P \u3c 0.01) ADG, ADFI, and F/G compared to pigs fed the NC alone, and also improved (P \u3c 0.02) ADG and F/G compared to pigs fed PC diets. A concurrent urinary balance experiment was conducted using diets 3 to 5 from Exp. 1 to evaluate Product X and SMB on DON urinary metabolism. A 10-d adaptation was followed by a 7-d collection using 24 barrows in a randomized complete block design. Pigs fed NC + SMB diet had greater urinary output (P \u3c 0.05) than pigs fed NC + Product X, with NC pigs intermediate. Daily DON excretion was lowest (P \u3c 0.05) in the NC + SMB pigs. However, as a percentage of daily DON intake, NC + SMB fed pigs excreted more DON than they consumed (164%), greater (P \u3c 0.001) than pigs fed the NC (59%) or NC + Product X (48%), and indicative of degradation of DON back to the parent DON molecule. Overall, Product X did not alleviate DON effects on growth nor did it reduce DON absorption and excretion. However, hydrothermally processing DON-contaminated diets with 1.0% SMB restored ADFI and improved F/G. Even so, the urinary balance experiment revealed that some of the converted DON-sulfonate could degrade back to DON under physiological conditions. While SMB appears promising to restore performance in pelleted DON-contaminated diets, additional research needs to address handling and long-term supplementation concerns and to evaluate the stability of the DON-sulfonate conversion

The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 kpc and Other Over-Densities in the Outer Halo

We have measured the periods and light curves of 148 RR Lyrae variables from V=13.5 to 19.7 from the first 100 sq. degrees of the QUEST RR Lyrae survey. Approximately 55% of these stars belong to the clump of stars detected earlier by the Sloan Digital Sky Survey. According to our measurements, this feature has ~10 times the background density of halo stars, spans at least 37.5 deg by 3.5 deg in right ascension and declination (>=30 by >=3 kpc), lies ~50 kpc from the Sun, and has a depth along the line of sight of ~5 kpc (1 sigma). These properties are consistent with the recent models that suggest it is a tidal stream from the Sgr dSph galaxy. The mean period of the type ab variables, 0.58 d, is also consistent. In addition, we have found two smaller over-densities in the halo, one of which may be related to the globular cluster Pal 5.Comment: 12 pages (including 4 figures). Accepted for publication in the ApJ Letter

Enhancing surface heat transfer by carbon nanofins: towards an alternative to nanofluids?

Background: Nanofluids are suspensions of nanoparticles and fibers which have recently attracted much attention because of their superior thermal properties. Nevertheless, it was proven that, due to modest dispersion of nanoparticles, such high expectations often remain unmet. In this article, by introducing the notion of nanofin, a possible solution is envisioned, where nanostructures with high aspect-ratio are sparsely attached to a solid surface (to avoid a significant disturbance on the fluid dynamic structures), and act as efficient thermal bridges within the boundary layer. As a result, particles are only needed in a small region of the fluid, while dispersion can be controlled in advance through design and manufacturing processes. Results: Toward the end of implementing the above idea, we focus on single carbon nanotubes to enhance heat transfer between a surface and a fluid in contact with it. First, we investigate the thermal conductivity of the latter nanostructures by means of classical non-equilibrium molecular dynamics simulations. Next, thermal conductance at the interface between a single wall carbon nanotube (nanofin) and water molecules is assessed by means of both steady-state and transient numerical experiments. Conclusions: Numerical evidences suggest a pretty favorable thermal boundary conductance (order of 107 W·m-2·K-1) which makes carbon nanotubes potential candidates for constructing nanofinned surface