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Search Results: 1 - 10 of 4683 matches for " Gordon Keller "
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Testing road surface treatments to reduce erosion in forest roads in Honduras
Rivera,Samuel; Kershner,Jeffrey L; Keller,Gordon R;
Ciencia e investigación agraria , 2009, DOI: 10.4067/S0718-16202009000300009
Abstract: using forest roads produces more erosion and sedimentation than any other forest or agricultural activity. this study evaluated soil losses from a forest road in central honduras over two consecutive years. we divided a 400-m segment of road into 8 experimental units, each 50 m in length. four units were treated with best management practices (bmps) and four were left untreated. the bmp treatments included reshaping the road prism, installing culverts and reshaping of road ditches, compacting 20-cm layers of the road tread, crowning the road surface (3% slope, double drainage), longitudinal sloping (less than 12%), and adding a 10-cm layer of gravel (crush size = 0.63 cm). soil movement was measured daily during the rainy seasons. the highest soil loss occurred in the control road, around 500 m3km-1 per year, while the road treated with bmp lost approximately 225 m3km-1 per year. these results show that road surface erosion can be reduced up to 50% with the implementation of surface treatments.
Micro-Arrayed Human Embryonic Stem Cells-Derived Cardiomyocytes for In Vitro Functional Assay
Elena Serena, Elisa Cimetta, Susi Zatti, Tania Zaglia, Monica Zagallo, Gordon Keller, Nicola Elvassore
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0048483
Abstract: Introduction The heart is one of the least regenerative organs in the body and any major insult can result in a significant loss of heart cells. The development of an in vitro-based cardiac tissue could be of paramount importance for many aspects of the cardiology research. In this context, we developed an in vitro assay based on human cardiomyocytes (hCMs) and ad hoc micro-technologies, suitable for several applications: from pharmacological analysis to physio-phatological studies on transplantable hCMs. We focused on the development of an assay able to analyze not only hCMs viability, but also their functionality. Methods hCMs were cultured onto a poly-acrylamide hydrogel with tunable tissue-like mechanical properties and organized through micropatterning in a 20×20 array. Arrayed hCMs were characterized by immunofluorescence, GAP-FRAP analyses and live and dead assay. Their functionality was evaluated monitoring the excitation-contraction coupling. Results Micropatterned hCMs maintained the expression of the major cardiac markers (cTnT, cTnI, Cx43, Nkx2.5, α-actinin) and functional properties. The spontaneous contraction frequency was (0.83±0.2) Hz, while exogenous electrical stimulation lead to an increase up to 2 Hz. As proof of concept that our device can be used for screening the effects of pathological conditions, hCMs were exposed to increasing levels of H2O2. Remarkably, hCMs viability was not compromised with exposure to 0.1 mM H2O2, but hCMs contractility was dramatically suppressed. As proof of concept, we also developed a microfluidic platform to selectively treat areas of the cell array, in the perspective of performing multi-parametric assay. Conclusions Such system could be a useful tool for testing the effects of multiple conditions on an in vitro cell model representative of human heart physiology, thus potentially helping the processes of therapy and drug development.
Design of a scanning gate microscope in a cryogen-free dilution refrigerator
Matthew Pelliccione,Adam Sciambi,John Bartel,Andrew Keller,David Goldhaber-Gordon
Physics , 2012, DOI: 10.1063/1.4794767
Abstract: We report on our design of a scanning gate microscope housed in a cryogen-free dilution refrigerator with a base temperature of 15 mK. The recent increase in efficiency of pulse tube cryocoolers has made cryogen-free systems popular in recent years. However, this new style of cryostat presents challenges for performing scanning probe measurements, mainly as a result of the vibrations introduced by the cryocooler. We demonstrate scanning with root-mean-square vibrations of 0.8 nm at 3 K and 2.1 nm at 15 mK in a 1 kHz bandwidth with our design.
Simple and High Yielding Method for Preparing Tissue Specific Extracellular Matrix Coatings for Cell Culture
Jessica A. DeQuach,Valeria Mezzano,Amar Miglani,Stephan Lange,Gordon M. Keller,Farah Sheikh,Karen L. Christman
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0013039
Abstract: The native extracellular matrix (ECM) consists of a highly complex, tissue-specific network of proteins and polysaccharides, which help regulate many cellular functions. Despite the complex nature of the ECM, in vitro cell-based studies traditionally assess cell behavior on single ECM component substrates, which do not adequately mimic the in vivo extracellular milieu.
Weed Risk Assessment for Aquatic Plants: Modification of a New Zealand System for the United States
Doria R. Gordon, Crysta A. Gantz, Christopher L. Jerde, W. Lindsay Chadderton, Reuben P. Keller, Paul D. Champion
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040031
Abstract: We tested the accuracy of an invasive aquatic plant risk assessment system in the United States that we modified from a system originally developed by New Zealand’s Biosecurity Program. The US system is comprised of 38 questions that address biological, historical, and environmental tolerance traits. Values associated with each response are summed to produce a total score for each species that indicates its risk of invasion. To calibrate and test this risk assessment, we identified 39 aquatic plant species that are major invaders in the continental US, 31 species that have naturalized but have no documented impacts (minor invaders), and 60 that have been introduced but have not established. These species represent 55 families and span all aquatic plant growth forms. We found sufficient information to assess all but three of these species. When the results are compared to the known invasiveness of the species, major invaders are distinguished from minor and non-invaders with 91% accuracy. Using this approach, the US aquatic weed risk assessment correctly identifies major invaders 85%, and non-invaders 98%, of the time. Model validation using an additional 10 non-invaders and 10 invaders resulted in 100% accuracy for the former, and 80% accuracy for the latter group. Accuracy was further improved to an average of 91% for all groups when the 17% of species with scores of 31–39 required further evaluation prior to risk classification. The high accuracy with which we can distinguish non-invaders from harmful invaders suggests that this tool provides a feasible, pro-active system for pre-import screening of aquatic plants in the US, and may have additional utility for prioritizing management efforts of established species.
Riemannian Space-Time, de Donder Conditions and Gravitational Field in Flat Space-Time  [PDF]
Gordon Liu
International Journal of Astronomy and Astrophysics (IJAA) , 2013, DOI: 10.4236/ijaa.2013.31002

Let the coordinate system xi of flat space-time to absorb a second rank tensor field Φij of the flat space-time deforming into a Riemannian space-time, namely, the tensor field Φuv is regarded as a metric tensor with respect to the coordinate system xu. After done this, xu is not the coordinate system of flat space-time anymore, but is the coordinate system of the new Riemannian space-time. The inverse operation also can be done. According to these notions, the concepts of the absorption operation and the desorption operation are proposed. These notions are actually compatible with Einstein’s equivalence principle. By using these concepts, the relationships of the Riemannian space-time, the de Donder conditions and the gravitational field in flat space-time are analyzed and elaborated. The essential significance of the de Donder conditions (the harmonic conditions or gauge) is to desorb the tensor field of gravitation from the Riemannian space-time to the Minkowski space-time with the Cartesian coordinates. Einstein equations with de Donder conditions can be solved in flat space-time. Base on Fock’s works, the equations of gravitational field in flat space-time are

Pdx1 and Ngn3 Overexpression Enhances Pancreatic Differentiation of Mouse ES Cell-Derived Endoderm Population
Atsushi Kubo, Robert Stull, Mitsuaki Takeuchi, Kristina Bonham, Valerie Gouon-Evans, Masayuki Sho, Masayuki Iwano, Yoshihiko Saito, Gordon Keller, Ralph Snodgrass
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024058
Abstract: In order to define the molecular mechanisms regulating the specification and differentiation of pancreatic β-islet cells, we investigated the effect of upregulating Pdx1 and Ngn3 during the differentiation of the β-islet-like cells from murine embryonic stem (ES) cell-derived activin induced-endoderm. Induced overexpression of Pdx1 resulted in a significant upregulation of insulin (Ins1 and Ins2), and other pancreas-related genes. To enhance the developmental progression from the pancreatic bud to the formation of the endocrine lineages, we induced the overexpression express of Ngn3 together with Pdx1. This combination dramatically increased the level and timing of maximal Ins1 mRNA expression to approximately 100% of that found in the βTC6 insulinoma cell line. Insulin protein and C-peptide expression was confirmed by immunohistochemistry staining. These inductive effects were restricted to c-kit+ endoderm enriched EB-derived populations suggesting that Pdx1/Ngn3 functions after the specification of pancreatic endoderm. Although insulin secretion was stimulated by various insulin secretagogues, these cells had only limited glucose response. Microarray analysis was used to evaluate the expression of a broad spectrum of pancreatic endocrine cell-related genes as well as genes associated with glucose responses. Taken together, these findings demonstrate the utility of manipulating Pdx1 and Ngn3 expression in a stage-specific manner as an important new strategy for the efficient generation of functionally immature insulin-producing β-islet cells from ES cells.
The Optical/Infrared Astronomical Quality of High Atacama Sites. II. Infrared Characteristics
Riccardo Giovanelli,Jeremy Darling,Charles Henderson,William Hoffman,Don Barry,James Cordes,Stephen Eikenberry,George Gull,Luke Keller,J. D. Smith,Gordon Stacey
Physics , 2001, DOI: 10.1086/322136
Abstract: We discuss properties of the atmospheric water vapor above the high Andean plateau region known as the Llano de Chajnantor, in the Atacama Desert of northern Chile. A combination of radiometric and radiosonde measurements indicate that the median column of precipitable water vapor (PWV) above the plateau at an elevation of 5000 m is approximately 1.2 mm. The exponential scaleheight of the water vapor density in the median Chajnantor atmosphere is 1.13 km; the median PWV is 0.5 mm above an elevation of 5750 m. Both of these numbers appear to be lower at night. Annual, diurnal and other dependences of PWV and its scaleheight are discussed, as well as the occurrence of temperature inversion layers below the elevation of peaks surrounding the plateau. We estimate the background for infrared observations and sensitivities for broad band and high resolution spectroscopy. The results suggest that exceptional atmospheric conditions are present in the region, yielding high infrared transparency and high sensitivity for future ground-based infrared telescopes.
Universal Fermi liquid crossover and quantum criticality in a mesoscopic device
A. J. Keller,L. Peeters,C. P. Moca,I. Weymann,D. Mahalu,V. Umansky,G. Zaránd,D. Goldhaber-Gordon
Physics , 2015, DOI: 10.1038/nature15261
Abstract: Quantum critical systems derive their finite temperature properties from the influence of a zero temperature quantum phase transition. The paradigm is essential for understanding unconventional high-Tc superconductors and the non-Fermi liquid properties of heavy fermion compounds. However, the microscopic origins of quantum phase transitions in complex materials are often debated. Here we demonstrate experimentally, with support from numerical renormalization group calculations, a universal crossover from quantum critical non-Fermi liquid behavior to distinct Fermi liquid ground states in a highly controllable quantum dot device. Our device realizes the non-Fermi liquid two-channel Kondo state, based on a spin-1/2 impurity exchange-coupled equally to two independent electronic reservoirs. Arbitrarily small detuning of the exchange couplings results in conventional screening of the spin by the more strongly coupled channel for energies below a Fermi liquid scale T*. We extract a quadratic dependence of T* on gate voltage close to criticality and validate an asymptotically exact description of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states.
Observation of the SU(4) Kondo state in a double quantum dot
A. J. Keller,S. Amasha,I. Weymann,C. P. Moca,I. G. Rau,J. A. Katine,Hadas Shtrikman,G. Zaránd,D. Goldhaber-Gordon
Physics , 2013, DOI: 10.1038/nphys2844
Abstract: Central to condensed matter physics are quantum impurity models, which describe how a local degree of freedom interacts with a continuum. Surprisingly, these models are often universal in that they can quantitatively describe many outwardly unrelated physical systems. Here we develop a double quantum dot-based experimental realization of the SU(4) Kondo model, which describes the maximally symmetric screening of a local four-fold degeneracy. As demonstrated through transport measurements and detailed numerical renormalization group calculations, our device affords exquisite control over orbital and spin physics. Because the two quantum dots are coupled only capacitively, we can achieve orbital state- or "pseudospin"-resolved bias spectroscopy, providing intimate access to the interplay of spin and orbital Kondo effects. This cannot be achieved in the few other systems realizing the SU(4) Kondo state.
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