787 research outputs found
The Partonic Nature of Instantons
In both Yang-Mills theories and sigma models, instantons are endowed with
degrees of freedom associated to their scale size and orientation. It has long
been conjectured that these degrees of freedom have a dual interpretation as
the positions of partonic constituents of the instanton. These conjectures are
usually framed in d=3+1 and d=1+1 dimensions respectively where the partons are
supposed to be responsible for confinement and other strong coupling phenomena.
We revisit this partonic interpretation of instantons in the context of d=4+1
and d=2+1 dimensions. Here the instantons are particle-like solitons and the
theories are non-renormalizable. We present an explicit and calculable model in
d=2+1 dimensions where the single soliton in the CP^N sigma-model can be shown
to be a multi-particle state whose partons are identified with the ultra-violet
degrees of freedom which render the theory well-defined at high energies. We
introduce a number of methods which reveal the partons inside the soliton,
including deforming the sigma model and a dual version of the Bogomolnyi
equations. We conjecture that partons inside Yang-Mills instantons hold the key
to understanding the ultra-violet completion of five-dimensional gauge
theories.Comment: 28 pages. v3: extra references and comments. Mathematica notebooks
for the figures can be downloaded from
http://www.damtp.cam.ac.uk/user/dt281/parton.htm
Sulfonyl-Substituted Heteroleptic Cyclometalated Iridium(III) Complexes as Blue Emitters for Solution-Processable Phosphorescent Organic Light-Emitting Diodes
The synthesis is reported of a series of blue-emitting heteroleptic iridium complexes with phenylpyridine (ppy) ligands substituted with sulfonyl, fluorine, and/or methoxy substituents on the phenyl ring and a picolinate (pic) ancillary ligand. Some derivatives are additionally substituted with a mesityl substituent on the pyridyl ring of ppy to increase solubility. Analogues with two ppy and one 2-(2′-oxyphenyl)pyridyl (oppy) ancillary ligand were obtained by an unusual in situ nucleophilic displacement of a fluorine substituent on one of the ppy ligands by water followed by N^O chelation to iridium. The X-ray crystal structures of seven of the complexes are reported. The photophysical and electrochemical properties of the complexes are supported by density functional theory (DFT) and time-dependent DFT calculations. Efficient blue phosphorescent organic light-emitting devices (PhOLEDs) were fabricated using a selection of the complexes in a simple device architecture using a solution-processed single-emitting layer in the configuration ITO/PEDOT:PSS/PVK:OXD-7(35%):Ir complex(15%)/TPBi/LiF/Al. The addition of a sulfonyl substituent blue-shifts the electroluminescence by ca. 12 nm to λmaxEL 463 nm with CIEx,y coordinates (0.19, 0.29), compared to the benchmark complex FIrpic (λmaxEL 475 nm, 0.19, 0.38) in directly comparable devices, confirming the potential of the new complexes to serve as effective blue dopants in PhOLEDs. Replacing a fluorine by a methoxy group in these complexes red shifts the PL and EL λmax by ca. 4–6 nm. The efficiency of the blue PhOLEDs of the sulfonyl-substituted complexes is, in most cases, significantly enhanced by the presence of a mesityl substituent on the pyridyl ring of the ppy ligands
Bacterial vs. zooplankton control of sinking particle flux in the ocean\u27s twilight zone
The downward flux of particulate organic carbon (POC) decreases significantly in the oceanÂs mesopelagic or ‘twilight’ zone due both to abiotic processes and metabolism by resident biota. Bacteria and zooplankton solubilize and consume POC to support their metabolism, but the relative importance of bacteria vs. zooplankton in the consumption of sinking particles in the twilight zone is unknown. We compared losses of sinking POC, using differences in export flux measured by neutrally buoyant sediment traps at a range of depths, with bacteria and zooplankton metabolic requirements at the Hawaii Ocean Time‐series station ALOHA in the subtropical Pacific and the Japanese times‐series site K2 in the subarctic Pacific. Integrated (150‐1,000 m) mesopelagic bacterial C demand exceeded that of zooplankton by up to 3‐fold at ALOHA, while bacteria and zooplankton required relatively equal amounts of POC at K2. However, sinking POC flux was inadequate to meet metabolic demands at either site. Mesopelagic bacterial C demand was 3‐ to 4‐fold (ALOHA), and 10‐fold (K2) greater than the loss of sinking POC flux, while zooplankton C demand was 1‐ to 2‐fold (ALOHA), and 3‐ to 9‐fold (K2) greater (using our ‘middle’ estimate conversion factors to calculate C demand). Assuming the particle flux estimates are accurate, we posit that this additional C demand must be met by diel vertical migration of zooplankton feeding at the surface and by carnivory at depth—with both processes ultimately supplying organic C to mesopelagic bacteria. These pathways need to be incorporated into biogeochemical models that predict global C sequestration in the deep sea
Water waves generated by a moving bottom
Tsunamis are often generated by a moving sea bottom. This paper deals with
the case where the tsunami source is an earthquake. The linearized water-wave
equations are solved analytically for various sea bottom motions. Numerical
results based on the analytical solutions are shown for the free-surface
profiles, the horizontal and vertical velocities as well as the bottom
pressure.Comment: 41 pages, 13 figures. Accepted for publication in a book: "Tsunami
and Nonlinear Waves", Kundu, Anjan (Editor), Springer 2007, Approx. 325 p.,
170 illus., Hardcover, ISBN: 978-3-540-71255-8, available: May 200
Crossing borders: new teachers co-constructing professional identity in performative times
This paper draws on a range of theoretical perspectives on the construction of new teachers’ professional identity. It focuses particularly on the impact of the development in many national education systems of a performative culture of the management and regulation of teachers’ work. Whilst the role of interactions with professional colleagues and school managers in the performative school has been extensively researched, less attention has been paid to new teachers’ interactions with students. This paper highlights the need for further research focusing on the process of identity co-construction with students. A key theoretical concept employed is that of liminality, the space within which identities are in transition as teachers adjust to the culture of a new professional workplace, and the nature of the engagement of new teachers, or teachers who change schools, with students. The authors argue that an investigation into the processes of this co-construction of identity offers scope for new insights into the extent to which teachers might construct either a teacher identity at odds with their personal and professional values, or a more ‘authentic’ identity that counters performative discourses. These insights will in turn add to our understanding of the complex range of factors impacting on teacher resilience and motivation
Characterization of the Atmosphere of the Hot Jupiter HAT-P-32Ab and the M-dwarf Companion HAT-P-32B
Copyright © 2015 IOP PublishingWe report secondary eclipse photometry of the hot Jupiter HAT-P-32Ab, taken with Hale/Wide-field Infra-Red Camera (WIRC) in H and KS bands and with Spitzer/IRAC at 3.6 and 4.5 μm. We carried out adaptive optics imaging of the planet host star HAT-P-32A and its companion HAT-P-32B in the near-IR and the visible. We clearly resolve the two stars from each other and find a separation of 2.''923 ± 0.''004 and a position angle 110fdg64 ± 0fdg12. We measure the flux ratios of the binary in g'r'i'z' and H and KS bands, and determine T eff= 3565 ± 82 K for the companion star, corresponding to an M1.5 dwarf. We use PHOENIX stellar atmosphere models to correct the dilution of the secondary eclipse depths of the hot Jupiter due to the presence of the M1.5 companion. We also improve the secondary eclipse photometry by accounting for the non-classical, flux-dependent nonlinearity of the WIRC IR detector in the H band. We measure planet-to-star flux ratios of 0.090% ± 0.033%, 0.178% ± 0.057%, 0.364% ± 0.016%, and 0.438% ± 0.020% in the H, KS , 3.6 and 4.5 μm bands, respectively. We compare these with planetary atmospheric models, and find they prefer an atmosphere with a temperature inversion and inefficient heat redistribution. However, we also find that the data are equally well described by a blackbody model for the planet with T p = 2042 ± 50 K. Finally, we measure a secondary eclipse timing offset of 0.3 ± 1.3 minutes from the predicted mid-eclipse time, which constrains e = 0.0072 +0.0700}_-0.0064 when combined with radialNASACenter for Exoplanets and Habitable Worlds at the Pennsylvania State UniversityPennsylvania State UniversityEberly College of SciencePennsylvania Space Grant ConsortiumNational Science Foundation - Graduate Research Fellowship ProgramNatural Science and Engineering Research Council of CanadaJPL/SpitzerCalifornia Institute of Technology - NASA Sagan FellowshipAlfred P. Sloan FoundationCalifornia Institute of TechnologyInter-University Centre for Astronomy and AstrophysicsNational Science FoundationMt. Cuba Astronomical FoundationSamuel Oschi
Mechanical properties and texture profile analysis of beef burgers and plant-based analogues
Cultivated meat, or cultured meat, is lab-grown from animal stem cells, differentiated into muscle and/or fat, to yield meat products. The process is more sustainable and more ethical than traditional farming, allowing to meet growing consumer demand. However, there remains a challenge in replicating the organoleptic properties of commercially available meat products for cultivated meat applications. Consequently, this study employs single-cycle uniaxial testing (flexion, tension, compression, cutting) governed by ISO standards, and texture profiling analysis, to ascertain the modulus, yield strain, hardness, adhesiveness, cohesiveness, springiness, resilience and chewiness of seven commercially available burgers. These were tested both raw and cooked, and comprise beef (including a range of beef contents, fat percentages and price points) and plant-based analogues. Here, we show that (i) both mechanical (flexural, compressive and cutting yield strains) and textural (cohesiveness, springiness and resilience) properties reveal clear and statistically significant divides between the cooked properties of beef compared to plant-based burgers; (ii) moreover, hardness and chewiness yield statistically significant results able to distinguish between high beef content burgers (over 95%), low beef content burgers (below 81%) and plant-based alternatives, and thus, are best suited to characterise burger properties; and (iii) there exists key target values for cultivated meat products to replicate the mechanical and textural characteristics of farmed beef burgers, identified for the first time. These findings provide novel insights into the mechanical and textural characterisation of beef and plant-based burgers, and may contribute to future developments in cultivated meat to ensure consumer acceptance
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