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Digital Access to Scholarship at Harvard (42.013 recursos)
DASH is a central, open-access repository of research by members of the Harvard community
FAS Scholarly Articles
DASH is a central, open-access repository of research by members of the Harvard community
FAS Scholarly Articles
Meng, Guangnan; Manoharan, Vinothan N.; Perro, Adeline
We design polystyrene–poly(N′-isopropylacrylamide-co-acrylic acid) core–shell particles that exhibit dynamically tunable scattering. We show that under normal solvent conditions the shell is nearly index-matched to pure water, and the particle scattering is dominated by Rayleigh scattering from the core. As the temperature or salt concentration increases, both the scattering cross-section and the forward scattering increase, characteristic of Mie scatterers. The magnitude of the change in the scattering cross-section and scattering anisotropy can be controlled through the solvent conditions and the size of the core. Such particles may find use as optical switches or optical filters with tunable opacity.
Gilbert, Kadeem Jamal; Nitta, Joel H; Talavera, Gerard; Pierce, Naomi E.
Nepenthes is a genus of carnivorous pitcher plants with high intra- and interspecific morphological diversity. Many species produce dimorphic pitchers, and the relative production rate of the two morphs varies interspecifically. Despite their probable ecological importance to the plants, little is known about the selective context under which various pitcher traits have evolved. This is especially true of colour-related traits, which have not been examined in a phylogenetic context. Using field observations of one polymorphic species (N. gracilis) and comparative phylogenetic analysis of 85 species across the genus, we investigate correlations between colour polymorphism and ecological factors including altitude, light...
de Paula, Áureo; Richards-Shunik, Seth; Tamer, Elie
This paper provides a framework for identifying preferences in a large network under the assumption of pairwise stability of network links. Network data present difficulties for identification, especially when links between nodes in a network can be interdependent: e.g., where indirect connections matter. Given a preference specification, we use the observed proportions of various possible payoff-relevant local network structures to learn about the underlying parameters. We show how one can map the observed proportions of these local structures to sets of parameters that are consistent with the model and the data. Our main result provides necessary conditions for parameters to...
Germanic Languages and Literatures
Mazur, Barry Charles
History of Science
Berg, Howard Curtis; Blagoev, Krastan
Daley, M. A.; Voloshina, A.; Biewener, Andrew Austin
Here we investigate the interplay between intrinsic mechanical and neural factors in muscle contractile performance during running, which has been less studied than during walking. We report in vivo recordings of the gastrocnemius muscle of the guinea fowl (Numida meleagris), during the response and recovery from an unexpected drop in terrain. Previous studies on leg and joint mechanics following this perturbation suggested that distal leg extensor muscles play a key role in stabilisation. Here, we test this through direct recordings of gastrocnemius fascicle length (using sonomicrometry), muscle–tendon force (using buckle transducers), and activity (using indwelling EMG). Muscle recordings were analysed...
East Asian Languages and Civilizations
Raynal, J. P.; Sbihi-Alaoui, F. Z.; Mohib, A.; El Graoui, M.; Lefèvre, D.; Texier, J. P.; Geraads, D.; Hublin, J. J.; Smith, Tanya; Tafforeau, P.; Zouak, M.; Grün, R.; Rhodes, E. J.; Eggins, S.; Daujeard, C.; Fernandes, P.; Gallotti, R.; Hossini, S.; Schwarcz, H. P.; Queffelec, A.
Un outillage lithique acheuléen, une riche faune du Pléistocène moyenet quatre dents d’hominidés ont été extraites du remplissage de la cavité dela carrière Thomas I, célèbre depuis la découverte en 1969 d’une hémi-mandibule humaine. Depuis 1988, des fouilles sont conduites dans ce sitedans le cadre du programme franco-marocain « Casablanca ». Une riche faune mammalienne et quelques restes de reptiles et d’oiseaux sont associésà l’industrie lithique dans l’unité stratigraphique 4. La faune, introduite par les carnivores, indique un paysage peu boisé et le stade évolutif des diverstaxons suggère un âge plus récent que celui de Tighenif (Algérie). Lesmarques de découpe...
Hedrick, T. L.; Tobalske, B. W.; Ros, Ivo; Warrick, D. R.; Biewener, Andrew Austin
Hummingbirds (Trochilidae) are widely known for their insect-like flight strokes characterized by high wing beat frequency, small muscle strains and a highly supinated wing orientation during upstroke that allows for lift production in both halves of the stroke cycle. Here, we show that hummingbirds achieve these functional traits within the limits imposed by a vertebrate endoskeleton and muscle physiology by accentuating a wing inversion mechanism found in other birds and using long-axis rotational movement of the humerus. In hummingbirds, long-axis rotation of the humerus creates additional wing translational movement, supplementing that produced by the humeral elevation and depression movements of...
Higham, T. E.; Biewener, Andrew Austin
Over the past 30 years, studies of single muscles have revealed complex patterns of regional variation in muscle architecture, activation, strain and force. In addition, muscles are often functionally integrated with other muscles in parallel or in series. Understanding the extent of this complexity and the interactions between muscles will profoundly influence how we think of muscles in relation to organismal function, and will allow us to address questions regarding the functional benefits (or lack thereof) and dynamics of this complexity under in vivo conditions. This paper has two main objectives. First, we present a cohesive and integrative review of...
Daley, M. A.; Biewener, Andrew Austin
Here, we used an obstacle treadmill experiment to investigate the neuromuscular control of locomotion in uneven terrain. We measured in vivo function of two distal muscles of the guinea fowl, lateral gastrocnemius (LG) and digital flexor-IV (DF), during level running, and two uneven terrains, with 5 and 7 cm obstacles. Uneven terrain required one step onto an obstacle every four to five strides. We compared both perturbed and unperturbed strides in uneven terrain to level terrain. When the bird stepped onto an obstacle, the leg became crouched, both muscles acted at longer lengths and produced greater work, and body height...
Romance Languages and Literatures
Carpenter, Daniel Paul; Chattopadhyay, Jacqueline; Moffitt, Susan; Nall, Clayton
Public agencies have discretion on the time domain, and politicians deploy numerous policy instruments to constrain it. Yet little is known about how administrative procedures that affect timing also affect the quality of agency decisions. We examine whether administrative deadlines shape decision timing and the observed quality of decisions. Using a unique and rich dataset of FDA drug approvals that allows us to examine decision timing and quality, we find that this administrative tool induces a piling of decisions before deadlines, and that these “just-before-deadline” approvals are linked with higher rates of postmarket safety problems (market withdrawals, severe safety warnings,...
Knoll, Andrew Herbert; Fischer, Woodward W.
Earth and Planetary Sciences
Harrison, Fiona A.; Craig, William W.; Christensen, Finn E.; Hailey, Charles J.; Zhang, William W.; Boggs, Steven E.; Stern, Daniel; Cook, W. Rick; Forster, Karl; Giommi, Paolo; Grefenstette, Brian W.; Kim, Yunjin; Kitaguchi, Takao; Koglin, Jason E.; Madsen, Kristin K.; Mao, Peter H.; Miyasaka, Hiromasa; Mori, Kaya; Perri, Matteo; Pivovaroff, Michael J.; Puccetti, Simonetta; Rana, Vikram R.; Westergaard, Niels J.; Willis, Jason; Zoglauer, Andreas; An, Hongjun; Bachetti, Matteo; Barrière, Nicolas M.; Bellm, Eric C.; Bhalerao, Varun; Brejnholt, Nicolai F.; Fuerst, Felix; Liebe, Carl C.; Markwardt, Craig B.; Nynka, Melania; Vogel, Julia K.; Walton, Dominic J.; Wik, Daniel R.; Alexander, David M.; Cominsky, Lynn R.; Hornschemeier, Ann E.; Hornstrup, Allan; Kaspi, Victoria M.; Madejski, Greg M.; Matt, Giorgio; Molendi, Silvano; Smith, David M.; Tomsick, John A.; Ajello, Marco; Ballantyne, David R.; Baloković, Mislav; Barret, Didier; Bauer, Franz E.; Blandford, Roger D.; Brandt, W. Niel; Brenneman, Laura W.; Chiang, James; Chakrabarty, Deepto; Chenevez, Jerome; Comastri, Andrea; Dufour, Francois; Elvis, Martin S.; Fabian, Andrew C.; Farrah, Duncan; Fryer, Chris L.; Gotthelf, Eric V.; Grindlay, Jonathan E.; Helfand, David J.; Krivonos, Roman; Meier, David L.; Miller, Jon M.; Natalucci, Lorenzo; Ogle, Patrick; Ofek, Eran O.; Ptak, Andrew; Reynolds, Stephen P.; Rigby, Jane R.; Tagliaferri, Gianpiero; Thorsett, Stephen E.; Treister, Ezequiel; Urry, C. Megan
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR...
Novikova, Irina; Walsworth, Ronald L.; Xiao, Yanhong
This paper reviews recent efforts to realize a high-efficiency memory for optical pulses using slow and stored light based on electromagnetically induced transparency (EIT) in ensembles of warm atoms in vapor cells. After a brief summary of basic continuous-wave and dynamic EIT properties, studies using weak classical signal pulses in optically dense coherent media are discussed, including optimization strategies for stored light efficiency and pulse-shape control, and modification of EIT and slow/stored light spectral properties due to atomic motion. Quantum memory demonstrations using both single photons and pulses of squeezed light are then reviewed. Finally a brief comparison with other...
Mou, Hongmei; Zhao, Rui; Sherwood, Richard Irving; Ahfeldt, Tim; Lapey, Allen; Wain, John Charles; Sicilian, Leonard; Izvolsky, Konstantin; Lau, Frank; Musunuru, Kiran; Cowan, Chad A.; Rajagopal, Jayaraj
Deriving lung progenitors from patient-specific pluripotent cells is a key step in producing differentiated lung epithelium for disease modeling and transplantation. By mimicking the signaling events that occur during mouse lung development, we generated murine lung progenitors in a series of discrete steps. Definitive endoderm derived from mouse embryonic stem cells (ESCs) was converted into foregut endoderm, then into replicating Nkx2.1+ lung endoderm, and finally into multipotent embryonic lung progenitor and airway progenitor cells. We demonstrated that precisely-timed BMP, FGF, and WNT signaling are required for NKX2.1 induction. Mouse ESC-derived Nkx2.1+ progenitor cells formed respiratory epithelium (tracheospheres) when transplanted subcutaneously...
Camahort, Raymond; Cowan, Chad A.
The Polycomb repressive complexes (PRC) regulate self-renewal and differentiation in embryonic stem cells (ESCs). In this issue of "Cell Stem Cell," Morey et al. (2012) and O'Loghlen et al. (2012) report that dynamic interchange of PRC subunits modulates the balance between self-renewal and lineage commitment in ESCs.