172 research outputs found
The Narragansett Dawn
A newsletter edited by Princess Redwing and Ernest Hazard and published by the Narragansett Tribe of Indians in 1935 and 1936. It includes short articles by a variety of writers on the culture, history, and politics of the Narragansett Indians. It also includes religious and poetic writing, lessons in the Narragansett language, advice from community leaders, and a milestones section documenting births, deaths, and other life transitions
Thickness dependence of the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition
We have studied the effect of deposition rate and layer thickness on the
properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor
deposition on 4H-SiC substrates. The MgB2 film deposition rate depends linearly
on the concentration of B2H6 in the inlet gas mixture. We found that the
superconducting and normal-state properties of the MgB2 films are determined by
the film thickness, not by the deposition rate. When the film thickness was
increased, the transition temperature, Tc, increased and the residual
resistivity, rho0, decreased. Above about 300 nm, a Tc of 41.8 K, a rho0 of
0.28 mikroOhm.cm, and a residual resistance ratio RRR of over 30 were obtained.
These values represent the best MgB2 properties reported thus far.Comment: 10 pages, 4 figure
Critical Current Density and Resistivity of MgB2 Films
The high resistivity of many bulk and film samples of MgB2 is most readily
explained by the suggestion that only a fraction of the cross-sectional area of
the samples is effectively carrying current. Hence the supercurrent (Jc) in
such samples will be limited by the same area factor, arising for example from
porosity or from insulating oxides present at the grain boundaries. We suggest
that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K)
- Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We
report measurements of Rho(T) and Jc for a number of films made by hybrid
physical-chemical vapor deposition which demonstrate this correlation, although
the "reduced effective area" argument alone is not sufficient. We suggest that
this argument can also apply to many polycrystalline bulk and wire samples of
MgB2.Comment: 11 pages, 3 figure
Assessing computational methods and science policy in systems biology
Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2009.Includes bibliographical references (p. 109-112).In this thesis, I discuss the development of systems biology and issues in the progression of this science discipline. Traditional molecular biology has been driven by reductionism with the belief that breaking down a biological system into the fundamental biomolecular components will elucidate such phenomena. We have reached limitations with this approach due to the complex and dynamical nature of life and our inability to intuit biological behavior from a modular perspective [37]. Mathematical modeling has been integral to current system biology endeavors since detailed analysis would be invasive if performed on humans experimentally or in clinical trials [17]. The interspecies commonalities in systemic properties and molecular mechanisms suggests that certain behaviors transcend specie differentiation and therefore easily lend to generalizing from simpler organisms to more complex organisms such as humans [7, 17]. Current methodologies in mathematical modeling and analysis have been diverse and numerous, with no standardization to progress the discipline in a collaborative manner. Without collaboration during this formative period, successful development and application of systems biology for societal welfare may be at risk. Furthermore, such collaboration has to be standardized in a fundamental approach to discover generic principles, in the manner of preceding long-standing science disciplines. This study effectively implements and analyzes a mathematical model of a three-protein biochemical network, the Synechococcus elongatus circadian clock.(cont.) I use mass action theory expressed in kronecker products to exploit the ability to apply numerical methods-including sensitivity analysis via boundary value formulation (BVP) and trapiezoidal integration rule-and experimental techniques-including partial reaction fitting and enzyme-driven activations-when mathematically modeling large-scale biochemical networks. Amidst other applicable methodologies, my approach is grounded in the law of mass action because it is based in experimental data and biomolecular mechanistic properties, yet provides predictive power in the complete delineation of the biological system dynamics for all future time points. The results of my research demonstrate the holistic approach that mass action method-ologies have in determining emergent properties of biological systems. I further stress the necessity to enforce collaboration and standardization in future policymaking, with reconsiderations on current stakeholder incentive to redirect academia and industry focus from new molecular entities to interests in holistic understanding of the complexities and dynamics of life entities. Such redirection away from reductionism could further progress basic and applied scientific research to embetter our circumstances through new treatments and preventive measures for health, and development of new strains and disease control in agriculture and ecology [13].by Andrea R. Castillo.S.M.in Technology and Polic
Capacitanceāvoltage characterization of AlN/GaN metalāinsulatorāsemiconductor structures grown on sapphire substrate by metalorganic chemical vapor deposition
Electrical characterization of AlN/GaN interfaces was carried out by the capacitanceāvoltage (CāV)(CāV) technique in materials grown by metalorganic chemical vapor deposition. The high-frequency CāVCāV characteristics showed clear deep-depletion behavior at room temperature, and the doping density derived from the slope of 1/C21/C2 plots under the deep depletion condition agreed well with the growth design parameters. A low value of interface state density DitDit of 1Ć1011ācmā2āeVā11Ć1011ācmā2āeVā1 or less around the energy position of Ecā0.8āeVEcā0.8āeV was demonstrated, in agreement with an average DitDit value estimated from photoassisted CāVCāV characteristics. Ā© 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70376/2/JAPIAU-88-4-1983-1.pd
FDTD modeling of solar energy absorption in silicon branched nanowires
Thin film nanostructured photovoltaic cells are increasing in efficiency and decreasing the cost of solar energy. FDTD modeling of branched nanowire āforestsā are shown to have improved optical absorption in the visible and near-IR spectra over nanowire arrays alone, with a factor of 5 enhancement available at 1000 nm. Alternate BNW tree configurations are presented, achieving a maximum absorption of over 95% at 500 nm
ALMA Observations of Io Going into and Coming out of Eclipse
We present 1-mm observations constructed from ALMA [Atacama Large (sub)Millimeter Array] data of SOā, SO and KCl when Io went from sunlight into eclipse (20 March 2018), and vice versa (2 and 11 September 2018). There is clear evidence of volcanic plumes on 20 March and 2 September. The plumes distort the line profiles, causing high-velocity (ā³500 m/s) wings, and red/blue-shifted shoulders in the line profiles. During eclipse ingress, the SOā flux density dropped exponentially, and the atmosphere reformed in a linear fashion when re-emerging in sunlight, with a "post-eclipse brightening" after ā¼10 minutes. While both the in-eclipse decrease and in-sunlight increase in SO was more gradual than for SOā, the fact that SO decreased at all is evidence that self-reactions at the surface are important and fast, and that in-sunlight photolysis of SOā is the dominant source of SO. Disk-integrated SOā in-sunlight flux densities are ā¼2--3 times higher than in-eclipse, indicative of a roughly 30--50% contribution from volcanic sources to the atmosphere. Typical column densities and temperatures are N ā (1.5Ā±0.3)Ć10Ā¹ā¶ cmā»Ā² and T ā 220ā320 K both in-sunlight and in-eclipse, while the fractional coverage of the gas is 2--3 times lower in-eclipse than in-sunlight. The low level SOā emissions present during eclipse may be sourced by stealth volcanism or be evidence of a layer of non-condensible gases preventing complete collapse of the SOā atmosphere. The melt in magma chambers at different volcanoes must differ in composition to explain the absence of SO and SOā, but simultaneous presence of KCl over Ulgen Patera
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