3,660 research outputs found
Leads integral with the internal interconnection that penetrate the molded wall of a package
Multiplicity of external ribbon leads makes possible connections to a sealed or encapsulated microassembly. The leads are integral with the internal connections on a single part that can be fabricated economically by fine-detail electroplating
Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
We address disequilibrum abundances of some simple molecules in the
atmospheres of solar composition brown dwarfs and self-luminous extrasolar
giant planets using a kinetics-based 1D atmospheric chemistry model. Our
approach is to use the full kinetics model to survey the parameter space with
effective temperatures between 500 K and 1100 K. In all of these worlds
equilibrium chemistry favors CH4 over CO in the parts of the atmosphere that
can be seen from Earth, but in most disequilibrium favors CO. The small surface
gravity of a planet strongly discriminates against CH4 when compared to an
otherwise comparable brown dwarf. If vertical mixing is like Jupiter's, the
transition from methane to CO occurs at 500 K in a planet. Sluggish vertical
mixing can raise this to 600 K; but clouds or more vigorous vertical mixing
could lower this to 400 K. The comparable thresholds in brown dwarfs are
K. Ammonia is also sensitive to gravity, but unlike CH4/CO, the
NH3/N2 ratio is insensitive to mixing, which makes NH3 a potential proxy for
gravity. HCN may become interesting in high gravity brown dwarfs with very
strong vertical mixing. Detailed analysis of the CO-CH4 reaction network
reveals that the bottleneck to CO hydrogenation goes through methanol, in
partial agreement with previous work. Simple, easy to use quenching relations
are derived by fitting to the complete chemistry of the full ensemble of
models. These relations are valid for determining CO, CH4, NH3, HCN, and CO2
abundances in the range of self-luminous worlds we have studied but may not
apply if atmospheres are strongly heated at high altitudes by processes not
considered here (e.g., wave breaking).Comment: Astrophysical Journal, in press. Clarity improvements throughout and
one new figure. 17 figures, 20 page
A comparison of design and model selection methods for supersaturated experiments
Various design and model selection methods are available for supersatu-rated designs having more factors than runs but little research is available ontheir comparison and evaluation. In this paper, simulated experiments areused to evaluate the use of E(s2)-optimal and Bayesian D-optimal designs,and to compare three analysis strategies representing regression, shrinkageand a novel model-averaging procedure. Suggestions are made for choosingthe values of the tuning constants for each approach. Findings include that(i) the preferred analysis is via shrinkage; (ii) designs with similar numbersof runs and factors can be effective for a considerable number of active effectsof only moderate size; and (iii) unbalanced designs can perform well. Somecomments are made on the performance of the design and analysis methodswhen effect sparsity does not hol
AGRICULTURAL REVOLUTIONS IN AMERICA’S HEARTLAND: THE CORN BELT AND THE MAKING OF AMERICAN CAPITALISM
The family farm has been the foundation of America’s cheap food model. This research examines how cheap food from the Corn Belt was produced from 1840s to the late twentieth century. It investigates how the interrelationships between family farming, proletarianization-housewifization, and national and world markets configured and reconfigured. Utilizing a world-ecological framework, I argue that Illinois and Iowa, the heart of the Corn Belt, were the epicenter of two successive agricultural revolutions that fundamentally transformed world accumulation and world nature. The analysis is centered on the development of successive agricultural revolutions over the longue durée of capitalism, with the greatest attention on the nineteenth and twentieth century revolutions in the United States. At the core of the dissertation I examine what I call the ‘double dialectic’: the contradictory relationship within the agrarian household and in relation to world markets and world power. The findings of the study are historical and methodological. Historically, the Corn Belt family farm possessed a unique position within the capitalist world-economy, resulting in relative prosperity and long-term stability. Contrary to regional studies of the Corn Belt, the study provides a world-ecological framework for reconstructing the origins, development, and crisis of the Corn Belt family farm and interpreting how the production of nature, the pursuit of power, and capital accumulation constitute its development
Analysis of Spitzer Spectra of Irradiated Planets: Evidence for Water Vapor?
Published mid infrared spectra of transiting planets HD 209458b and HD
189733b, obtained during secondary eclipse by the InfraRed Spectrograph (IRS)
aboard the Spitzer Space Telescope, are predominantly featureless. In
particular these flux ratio spectra do not exhibit an expected feature arising
from water vapor absorption short-ward of 10 um. Here we suggest that, in the
absence of flux variability, the spectral data for HD 189733b are inconsistent
with 8 um-photometry obtained with Spitzer's InfraRed Array Camera (IRAC),
perhaps an indication of problems with the challenging reduction of the IRS
spectra. The IRAC point, along with previously published secondary eclipse
photometry for HD 189733b, are in good agreement with a one-dimensional model
of HD 189733b that clearly shows absorption due to water vapor in the emergent
spectrum. We are not able to draw firm conclusions regarding the IRS data for
HD 209458b, but spectra predicted by 1D and 3D atmosphere models fit the data
adequately, without adjustment of the water abundance or reliance on cloud
opacity. We argue that the generally good agreement between model spectra and
IRS spectra of brown dwarfs with atmospheric temperatures similar to these
highly irradiated planets lends confidence in the modeling procedure.Comment: Revised, Accepted to ApJ Letter
Atmospheric Sulfur Photochemistry on Hot Jupiters
We develop a new 1D photochemical kinetics code to address stratospheric
chemistry and stratospheric heating in hot Jupiters. Here we address optically
active S-containing species and CO2 at 1200 < T < 2000 K. HS (mercapto) and S2
are highly reactive species that are generated photochemically and
thermochemically from H2S with peak abundances between 1-10 mbar. S2 absorbs UV
between 240 and 340 nm and is optically thick for metallicities [SH] > 0 at T >
1200 K. HS is probably more important than S2, as it is generally more abundant
than S2 under hot Jupiter conditions and it absorbs at somewhat redder
wavelengths. We use molecular theory to compute an HS absorption spectrum from
sparse available data and find that HS should absorb strongly between 300 and
460 nm, with absorption at the longer wavelengths being temperature sensitive.
When the two absorbers are combined, radiative heating (per kg of gas) peaks at
100 microbars, with a total stratospheric heating of about 8 x 10^4 W/m^2 for a
jovian planet orbiting a solar-twin at 0.032 AU. Total heating is insensitive
to metallicity. The CO2 mixing ratio is a well-behaved quadratic function of
metallicity, ranging from 1.6 x 10^-8 to 1.6 x 10^-4 for -0.3 < [M/H] < 1.7.
CO2 is insensitive to insolation, vertical mixing, temperature (1200 < T <2000
K), and gravity. The photochemical calculations confirm that CO2 should prove a
useful probe of planetary metallicity.Comment: Astrophysical Journal Lett. in press; important revision includes
effect of updated thermodynamic data and a new opacity sourc
Model Bond albedos of extrasolar giant planets
The atmospheres of extrasolar giant planets are modeled with various
effective temperatures and gravities, with and without clouds. Bond albedos are
computed by calculating the ratio of the flux reflected by a planet (integrated
over wavelength) to the total stellar flux incident on the planet. This
quantity is useful for estimating the effective temperature and evolution of a
planet. We find it is sensitive to the stellar type of the primary. For a 5
M_Jup planet the Bond albedo varies from 0.4 to 0.3 to 0.06 as the primary star
varies from A5V to G2V to M2V in spectral type. It is relatively insensitive to
the effective temperature and gravity for cloud--free planets. Water clouds
increase the reflectivity of the planet in the red, which increases the Bond
albedo. The Bond albedo increases by an order of magnitude for a 13 M_Jup
planet with an M2V primary when water clouds are present. Silicate clouds, on
the other hand, can either increase or decrease the Bond albedo, depending on
whether there are many small grains (the former) or few large grains (the
latter).Comment: 6 pages, 9 figures, uses egs.cls and epsfig.sty, submitted to Physics
and Chemistry of the Earth (proceedings of the April 1998 EGS meeting in
Nice, France
A non-grey analytical model for irradiated atmospheres. II: Analytical vs. numerical solutions
The recent discovery and characterization of the diversity of the atmospheres
of exoplanets and brown dwarfs calls for the development of fast and accurate
analytical models. We quantify the accuracy of the analytical solution derived
in paper I for an irradiated, non-grey atmosphere by comparing it to a
state-of-the-art radiative transfer model. Then, using a grid of numerical
models, we calibrate the different coefficients of our analytical model for
irradiated solar-composition atmospheres of giant exoplanets and brown dwarfs.
We show that the so-called Eddington approximation used to solve the angular
dependency of the radiation field leads to relative errors of up to 5% on the
temperature profile. We show that for realistic non-grey planetary atmospheres,
the presence of a convective zone that extends to optical depths smaller than
unity can lead to changes in the radiative temperature profile on the order of
20% or more. When the convective zone is located at deeper levels (such as for
strongly irradiated hot Jupiters), its effect on the radiative atmosphere is
smaller. We show that the temperature inversion induced by a strong absorber in
the optical, such as TiO or VO is mainly due to non-grey thermal effects
reducing the ability of the upper atmosphere to cool down rather than an
enhanced absorption of the stellar light as previously thought.
Finally, we provide a functional form for the coefficients of our analytical
model for solar-composition giant exoplanets and brown dwarfs. This leads to
fully analytical pressure-temperature profiles for irradiated atmospheres with
a relative accuracy better than 10% for gravities between 2.5m/s^2 and 250
m/s^2 and effective temperatures between 100 K and 3000 K. This is a great
improvement over the commonly used Eddington boundary condition.Comment: Accepted in A&A, models are available at
http://www.oca.eu/parmentier/nongrey or in CD
- …