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Material and Process Parameters that Affect Accuracy in Stereolithography
Experimental real time linear shrinkage rate measurements simulating stereolithography
are used in an analysis of shrinkage during line drawing in stereolithography. While the amount of
shrinkage depends on the polymerization kinetics, shrinkage kinetics and overall degree of cure, it
also depends on the length of time to draw a line of plastic. A line drawn slowly will exhibit less
apparent shrinkage than one drawn very quickly because much of the shrinkage is compensated
for as the line is drawn. The data also indicates that a typical stereolithography resin in the green
state may shrink to only 65% of its maximum, thus retaining considerable potential for shrinkage
during post-cure. This infonnation can be used to predict the amount of shrinkage to be expected
under certain exposure conditions and to fonnulate overall strategies to reduce shrinkage and
subsequent warpage that causes shape distortion.Mechanical Engineerin
You gon\u27 let me hold that card : Directive speech acts and authority in The Wire
This study uses HBO’s The Wire as a corpus for examining the link between directive speech acts and authority. It looks at all the conversations from the show in which there is a clearly defined superior speaking to an inferior hearer and the distribution of two types of directives in those conversations. The two types of directives analyzed are standard directives (e.g., “Do that thing!”) and obligation statement indirect directives (e.g., “You’re gonna do that thing!”) (Searle, 1965; Searle, 1975a; Blum-Kulka et al., 1989). This paper finds that obligation statements only appear in situations in which the superior speaker and the inferior hearer belong to the same realm depicted in the show (e.g. the police department, a drug ring, a school system, etc.) and argues that this occurs because in those situations, the power of the speaker is mutually agreed upon by both speaker and hearer. In situations in which there is a difference of power but it is not agreed upon by speaker and hearer, obligation statements do not appear, and standard directives are used instead. This study can be situated in the context of speech act research, language and authority research, and research on television shows
Keck Pencil-Beam Survey for Faint Kuiper Belt Objects
We present the results of a pencil-beam survey of the Kuiper Belt using the
Keck 10-m telescope. A single 0.01 square degree field is imaged 29 times for a
total integration time of 4.8 hr. Combining exposures in software allows the
detection of Kuiper Belt Objects (KBOs) having visual magnitude V < 27.9. Two
new KBOs are discovered. One object having V = 25.5 lies at a probable
heliocentric distance d = 33 AU. The second object at V = 27.2 is located at d
= 44 AU. Both KBOs have diameters of about 50 km, assuming comet-like albedos
of 4%.
Data from all surveys are pooled to construct the luminosity function from
red magnitude R = 20 to 27. The cumulative number of objects per square degree,
N (< R), is fitted to a power law of the form log_(10) N = 0.52 (R - 23.5).
Differences between power laws reported in the literature are due mainly to
which survey data are incorporated, and not to the method of fitting. The
luminosity function is consistent with a power-law size distribution for
objects having diameters s = 50 to 500 km; dn ~ s^(-q) ds, where the
differential size index q = 3.6 +/- 0.1. The distribution is such that the
smallest objects possess most of the surface area, but the largest bodies
contain the bulk of the mass. Though our inferred size index nearly matches
that derived by Dohnanyi (1969), it is unknown whether catastrophic collisions
are responsible for shaping the size distribution. Implications of the absence
of detections of classical KBOs beyond 50 AU are discussed.Comment: Accepted to AJ. Final proof-edited version: references added,
discussion of G98 revised in sections 4.3 and 5.
Oxidative protein folding in eukaryotes: mechanisms and consequences
The endoplasmic reticulum (ER) provides an environment that is highly optimized for oxidative protein folding. Rather than relying on small molecule oxidants like glutathione, it is now clear that disulfide formation is driven by a protein relay involving Ero1, a novel conserved FAD-dependent enzyme, and protein disulfide isomerase (PDI); Ero1 is oxidized by molecular oxygen and in turn acts as a specific oxidant of PDI, which then directly oxidizes disulfide bonds in folding proteins. While providing a robust driving force for disulfide formation, the use of molecular oxygen as the terminal electron acceptor can lead to oxidative stress through the production of reactive oxygen species and oxidized glutathione. How Ero1p distinguishes between the many different PDI-related proteins and how the cell minimizes the effects of oxidative damage from Ero1 remain important open questions
Rotation and Color Properties of the Nucleus of Comet 2P/Encke
We present results from CCD observations of comet 2P/Encke acquired at
Steward Observatory's 2.3m Bok Telescope on Kitt Peak obtained in Oct. 2002,
when the comet was near aphelion. Rotational lightcurves in B, V and R-filters
were acquired over two nights of observations, and analysed to study the
physical and color properties of the nucleus. The average apparent R-filter
magnitude across both nights corresponds to a mean effective radius of 3.95 +/-
0.06 km. The rotational lightcurve results in a nucleus axial ratio a/b >= 1.44
+/- 0.06 and semi-axes lengths of [3.60 +/- 0.09] x [5.20 +/- 0.13] km. Our
data includes the first detailed time series multi-color measurements of a
cometary nucleus, and significant color variations were seen. The average color
indices across both nights are: (V-R) = 0.39 +/- 0.06 and (B-V) = 0.73 +/- 0.06
(R_mean = 19.76 +/- 0.03). We linked our data with the September 2002 data from
Fernandez et al. (2005) - taken just 2-3 weeks before the current data set -
and we show that a rotation period of 11.083 +/- 0.003hours works extrememly
well for the combined data set.Comment: Accepted for publication in Icarus (Dec 2006). 27 page
Cloning of terminal transferase cDNA by antibody screening
A cDNA library was prepared from a terminal deoxynucleotidyltransferase-containing thymoma in the phage vector λgt11. By screening plaques with anti-terminal transferase antibody, positive clones were identified of which some had β-galactosidase-cDNA fusion proteins identifiable after electrophoretic fractionation by immunoblotting with anti-terminal transferase antibody. The predominant class of cross-hybridizing clones was determined to represent cDNA for terminal transferase by showing that one representative clone hybridized to a 2200-nucleotide mRNA in close-matched enzyme-positive but not to enzyme-negative cells and that the cDNA selected a mRNA that translated to give a protein of the size and antigenic characteristics of terminal transferase. Only a small amount of genomic DNA hybridized to the longest available clone, indicating that the sequence is virtually unique in the mouse genome
A Reproductive-Resting Stage in an Harpacticoid Copepod, and the Significance of Genetically Based Differences Among Populations
Dormancy is an important life-history strategy which allows copepods to increase their fitness by delaying growth and reproduction until harsh environmental conditions have ameliorated. For marine species, the primary strategies identified to date include the production of dormant eggs by shallow-water species, and copepodite overwintering in deep-water species. Herein, we describe a third strategy in which fertilized adult females enter a “reproductive-resting” stage during the late fall that allows them to overwinter and provide a first source of spring naupliar recruitment. This strategy has been observed in the estuarine copepod Coullana canadensis, but may also occur in other species. Laboratory studies indicate that daylength and temperature are the environmental cues that induce the developing female copepodite to switch between active reproduction and reproductive-resting stage. In Maine populations, daylengths equal to 14 h induce \u3e90% of the females to reduce development rate and accumulate lipid before maturation and mating. The resulting females, however, do not develop ova regardless of food level. A similar reproductive-resting stage is triggered at daylengths/or dramatically increased temperature. Cross breeding experiments indicate that the daylength triggered switch to reproductive-resting is under tight genetic control. Daylength likely serves as a critical cue for all populations in differentiating between the onset of harsh (i.e., winter) and favorable (i.e., spring) environmental conditions. At these times water temperatures are similar, but daylengths are different. Population differences in the daylength necessary to trigger the reproductive-resting strategy likely reflect latitudinal variation in the period over which environmental conditions are conducive to population growth
Triton's surface age and impactor population revisited in light of Kuiper Belt fluxes: Evidence for small Kuiper Belt objects and recent geological activity
Neptune's largest satellite, Triton, is one of the most fascinating and
enigmatic bodies in the solar system. Among its numerous interesting traits,
Triton appears to have far fewer craters than would be expected if its surface
was primordial. Here we combine the best available crater count data for Triton
with improved estimates of impact rates by including the Kuiper Belt as a
source of impactors. We find that the population of impactors creating the
smallest observed craters on Triton must be sub-km in scale, and that this
small-impactor population can be best fit by a differential power-law size
index near -3. Such results provide interesting, indirect probes of the unseen
small body population of the Kuiper Belt. Based on the modern, Kuiper Belt and
Oort Cloud impactor flux estimates, we also recalculate estimated ages for
several regions of Triton's surface imaged by Voyager 2, and find that Triton
was probably active on a time scale no greater than 0.1-0.3 Gyr ago (indicating
Triton was still active after some 90% to 98% of the age of the solar system),
and perhaps even more recently. The time-averaged volumetric resurfacing rate
on Triton implied by these results, 0.01 km yr or more, is likely
second only to Io and Europa in the outer solar system, and is within an order
of magnitude of estimates for Venus and for the Earth's intraplate zones. This
finding indicates that Triton likely remains a highly geologically active world
at present, some 4.5 Gyr after its formation. We briefly speculate on how such
a situation might obtain.Comment: 14 pages (TeX), plus 2 postscript figures Stern & McKinnon, 2000, AJ,
in pres
A Titan exploration study: Science, technology, and mission planning options, volume 2
For abstract, see Vol.
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