5,345 research outputs found
Abundances of Disk Planetary Nebulae in M31 and the Radial Oxygen Gradient
We have obtained spectra of 16 planetary nebulae in the disk of M31 and
determined the abundances of He, N, O, Ne, S and Ar. Here we present the median
abundances and compare them with previous M31 PN disk measurements and with PNe
in the Milky Way. We also derive the radial oxygen gradient in M31, which is
shallower than that in the Milky Way, even accounting for M31's larger disk
scale length.Comment: 2 pages, 1 figure, 1 table, to appear in the proceedings of IAU
Symposium No. 283, Planetary Nebulae: An Eye to the Futur
Abundances of PNe in the Outer Disk of M31
We present spectroscopic observations and chemical abundances of 16 planetary
nebulae (PNe) in the outer disk of M31. The [O III] 4363 line is detected in
all objects, allowing a direct measurement of the nebular temperature essential
for accurate abundance determinations. Our results show that the abundances in
these M31 PNe display the same correlations and general behaviors as Type II
PNe in the Milky Way Galaxy. We also calculate photoionization models to derive
estimates of central star properties. From these we infer that our sample PNe,
all near the peak of the Planetary Nebula Luminosity Function, originated from
stars near 2 M_sun. Finally, under the assumption that these PNe are located in
M31's disk, we plot the oxygen abundance gradient, which appears shallower than
the gradient in the Milky Way.Comment: 48 pages, including 12 figures and 8 tables, accepted by
Astrophysical Journa
Researcher's guide to the NASA Ames Flight Simulator for Advanced Aircraft (FSAA)
Performance, limitations, supporting software, and current checkout and operating procedures are presented for the flight simulator, in terms useful to the researcher who intends to use it. Suggestions to help the researcher prepare the experimental plan are also given. The FSAA's central computer, cockpit, and visual and motion systems are addressed individually but their interaction is considered as well. Data required, available options, user responsibilities, and occupancy procedures are given in a form that facilitates the initial communication required with the NASA operations' group
Elimination of the donor service area (DSA) from lung allocation: No turning back
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150589/1/ajt15413_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150589/2/ajt15413.pd
Separator development for a heat sterilizable battery Final summary progress report, 1 May 1966 - 15 Mar. 1967
Development and testing of vivyl polymer separator materials for sterilized silver-zinc secondary batter
Dynamical tunneling in mushroom billiards
We study the fundamental question of dynamical tunneling in generic
two-dimensional Hamiltonian systems by considering regular-to-chaotic tunneling
rates. Experimentally, we use microwave spectra to investigate a mushroom
billiard with adjustable foot height. Numerically, we obtain tunneling rates
from high precision eigenvalues using the improved method of particular
solutions. Analytically, a prediction is given by extending an approach using a
fictitious integrable system to billiards. In contrast to previous approaches
for billiards, we find agreement with experimental and numerical data without
any free parameter.Comment: 4 pages, 4 figure
A STOL airworthiness investigation using a simulation of an augmentor wing transport. Volume 2: Simulation data and analysis
A simulator study of STOL airworthiness was conducted using a model of an augmentor wing transport. The approach, flare and landing, go-around, and takeoff phases of flight were investigated. The simulation and the data obtained are described. These data include performance measures, pilot commentary, and pilot ratings. A pilot/vehicle analysis of glide slope tracking and of the flare maneuver is included
Empirical Studies of Evolving Systems
This paper describes the results of the working group investigating the issues of empirical studies for
evolving systems. The groups found that there were many issues that were central to successful evolution and this
concluded that this is a very important area within software engineering. Finally nine main areas were selected for consideration. For each of these areas the central issues were identified as well as success factors. In some cases success stories were also described and the critical factors accounting for the success analysed. In some cases it was later found that a number of areas were so tightly coupled that it was important to discuss them together
Revealing and Resolving the Restrained Enzymatic Cleavage of DNA Self-Assembled Monolayers on Gold: Electrochemical Quantitation and ESI-MS Confirmation
Herein we report a combined electrochemical and ESI-MS study of the enzymatic hydrolysis efficiency of DNA self-assembled monolayers (SAMs) on gold, platform systems for understanding nucleic acid surface chemistry and for constructing DNA-based biosensors. Our electrochemical approach is based on the comparison of the amounts of surface-tethered DNA nucleotides before and after Exonuclease I (Exo I) incubation using electrostatically bound [Ru(NH3)6]3+ as redox indicators. It is surprising to reveal that the hydrolysis efficiency of ssDNA SAMs does not depend on the packing density and base sequence, and that the cleavage ends with surface-bound shorter strands (9-13 mers). The ex-situ ESI-MS observations confirmed that the hydrolysis products for ssDNA SAMs (from 24 to 56 mers) are dominated with 10-15 mer fragments, in contrast to the complete digestion in solution. Such surface-restrained hydrolysis behavior is due to the steric hindrance of the underneath electrode to the Exo I/DNA binding, which is essential for the occurrence of Exo I-catalyzed processive cleavage. More importantly, we have shown that the hydrolysis efficiency of ssDNA SAMs can be remarkably improved by adopting long alkyl linkers (locating DNA strands further away from the substrates)
The Case for Learned Index Structures
Indexes are models: a B-Tree-Index can be seen as a model to map a key to the
position of a record within a sorted array, a Hash-Index as a model to map a
key to a position of a record within an unsorted array, and a BitMap-Index as a
model to indicate if a data record exists or not. In this exploratory research
paper, we start from this premise and posit that all existing index structures
can be replaced with other types of models, including deep-learning models,
which we term learned indexes. The key idea is that a model can learn the sort
order or structure of lookup keys and use this signal to effectively predict
the position or existence of records. We theoretically analyze under which
conditions learned indexes outperform traditional index structures and describe
the main challenges in designing learned index structures. Our initial results
show, that by using neural nets we are able to outperform cache-optimized
B-Trees by up to 70% in speed while saving an order-of-magnitude in memory over
several real-world data sets. More importantly though, we believe that the idea
of replacing core components of a data management system through learned models
has far reaching implications for future systems designs and that this work
just provides a glimpse of what might be possible
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