39,191 research outputs found
Mass-spectrometric investigation of reaction of oxygen atoms with methane
Mass spectrometric investigation of oxygen atoms reacting with methan
Effect of pollutant gases on ozone production by simulated solar radiation
Experiments using simulated solar radiation in a chamber, with a controlled atmospheric pressure near 1 atmosphere, were conducted to evaluate O3 production. The effects of CO and H2O were analyzed to determine if the CO and H2O addition could reduce NO destruction of O3. The results show that NO is destroyed while destroying O3
Analysis of Satellite-to-Satellite Tracking (SST) and altimetry data from GEOS-C
Radar altimetry and satellite-to-satellite (SST) range and range rate tracking measurements were used to infer the exterior gravitational field of the earth and the structure of the geoid from GEOS-C metric data. Under the SST analysis, a direct point-by-point estimate of gravity disturbance by means of a recursive filter with backward smoothing was attempted but had to be forsaken because of poor convergence. The adopted representation consists of a more or less uniform grid of discrete masses at a depth of approximately 400 km from the earth's surface. The layer is superimposed on a spherical harmonics model. The procedure for smoothing the altimetry and inferring the fine-structured gravity field over the Atlantic test area is described. The local disturbances are represented by means of a density layer. The altimeter height biases were first estimated by a least squares adjustment at orbital crossover points. After taking out the bias, long wavelength contributions from GEM-6 as well as a calibration correction were subtracted. The residual heights were then represented by a mass distribution beneath the earth's surface
Implementation of an intelligent control system
A laboratory testbed facility which was constructed at NASA LeRC for the development of an Intelligent Control System (ICS) for reusable rocket engines is described. The framework of the ICS consists of a hierarchy of various control and diagnostic functions. The traditional high speed, closed-loop controller resides at the lowest level of the ICS hierarchy. Above this level resides the diagnostic functions which identify engine faults. The ICS top level consists of the coordination function which manages the interaction between an expert system and a traditional control system. The purpose of the testbed is to demonstrate the feasibility of the OCS concept by implementing the ICS as the primary controller in a simulation of the Space Shuttle Main Engine (SSME). The functions of the ICS which are implemented in the testbed are as follows: an SSME dynamic simulation with selected fault mode models, a reconfigurable controller, a neural network for sensor validation, a model-based failure detection algorithm, a rule based failure detection algorithm, a diagnostic expert system, an intelligent coordinator, and a user interface which provides a graphical representation of the event occurring within the testbed. The diverse nature of the ICS has led to the development of a distributed architecture consisting of specialized hardware and software for the implementation of the various functions. This testbed is made up of five different computer systems. These individual computers are discussed along with the schemes used to implement the various ICS components. The communication between computers and the timing and synchronization between components are also addressed
Hubble Ultraviolet Spectroscopy of Jupiter Trojans
We present the first ultraviolet spectra of Jupiter Trojans. These
observations were carried out using the Space Telescope Imaging Spectrograph on
the Hubble Space Telescope and cover the wavelength range 200-550 nm at low
resolution. The targets include objects from both of the Trojan color
subpopulations (less-red and red). We do not observe any discernible absorption
features in these spectra. Comparisons of the averaged UV spectra of less-red
and red targets show that the subpopulations are spectrally distinct in the UV.
Less-red objects display a steep UV slope and a rollover at around 450 nm to a
shallower visible slope, whereas red objects show the opposite trend.
Laboratory spectra of irradiated ices with and without HS exhibit
distinct UV absorption features; consequently, the featureless spectra observed
here suggest HS alone is not responsible for the observed color
bimodality of Trojans, as has been previously hypothesized. We propose some
possible explanations for the observed UV-visible spectra, including complex
organics, space weathering of iron-bearing silicates, and masked features due
to previous cometary activity.Comment: 7 pages, 4 figures, accepted by A
Odontoameloblastoma with extensive chondroid matrix deposition in a guinea pig
Odontoameloblastomas (previously incorporated within ameloblastic odontomas) are matrix-producing odontogenic mixed tumors and are closely related in histologic appearance to the 2 other types of matrix-producing odontogenic mixed tumors: odontomas and ameloblastic fibro-odontomas. The presence or absence of intralesional, induced non-neoplastic tissue must be accounted for in the diagnosis. Herein we describe a naturally occurring odontoameloblastoma with extensive chondroid cementum deposition in a guinea pig (Cavia porcellus). Microscopically, the mass featured palisading neoplastic odontogenic epithelium closely apposed to ribbons and rings of a pink dental matrix (dentinoid), alongside extensive sheets and aggregates of chondroid cementum. The final diagnosis was an odontoameloblastoma given the abundance of odontogenic epithelium in association with dentinoid but a paucity of pulp ectomesenchyme. Chondroid cementum is an expected anatomical feature of cavies, and its presence within the odontoameloblastoma was interpreted as a response of the ectomesenchyme of the dental follicle to the described neoplasm. Our case illustrates the inductive capabilities of odontoameloblastomas while highlighting species-specific anatomy that has resulted in a histologic appearance unique to cavies and provides imaging and histologic data to aid diagnosis of these challenging lesions
The molecular evolution of surgical oncology
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/88126/1/22050_ftp.pd
Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration
The response of the Antarctic ice sheet (AIS) to changing climate forcings is
an important driver of sea-level changes. Anthropogenic climate change may
drive a sizeable AIS tipping point response with subsequent increases in
coastal flooding risks. Many studies analyzing flood risks use simple models to
project the future responses of AIS and its sea-level contributions. These
analyses have provided important new insights, but they are often silent on the
effects of potentially important processes such as Marine Ice Sheet Instability
(MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well
justified and result in more parsimonious and transparent model structures.
This raises the question of how this approximation impacts hindcasts and
projections. Here, we calibrate a previously published and relatively simple
AIS model, which neglects the effects of MICI and regional characteristics,
using a combination of observational constraints and a Bayesian inversion
method. Specifically, we approximate the effects of missing MICI by comparing
our results to those from expert assessments with more realistic models and
quantify the bias during the last interglacial when MICI may have been
triggered. Our results suggest that the model can approximate the process of
MISI and reproduce the projected median melt from some previous expert
assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the
observed data during the last interglacial period and our mean projection is
roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year
2100. These results suggest that missing MICI and/or regional characteristics
can lead to a low-bias during warming period AIS melting and hence a potential
low-bias in projected sea levels and flood risks.Comment: v1: 16 pages, 4 figures, 7 supplementary files; v2: 15 pages, 4
figures, 7 supplementary files, corrected typos, revised title, updated
according to revisions made through publication proces
- …