2,451 research outputs found
The Effect Of Entry And Market Structure On Cellular Pricing Tactics
We test the effect of entry on the tariff choices of incumbent cellular
firms. We relate the change in the breadth of calling plans between
1996, when incumbents enjoyed a duopoly market, and 1998, when
incumbents faced increased competition from personal communications
services (PCS) firms. Entry by PCS competitors differed across
geographic markets due to the number of licenses left undeveloped as a
result of the bankruptcy of some of the auctions’ winning bidders
and due to variation across markets in the time required to build a
sufficiently large network of wireless infrastructure. We find that
incumbents increase tariff variety in markets with more entrants and
that this effect is not explained by demographic heterogeneity or cost
differences in maintaining calling plans across markets. We also find
that incumbents are more likely to upgrade their technology from the old
analog technology to the new digital technology in markets with more
entry, suggesting that entry also has indirect effects on tariff choice
via firms' technology adoption decisions
The Gamma-ray Albedo of the Moon
We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of
the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our
calculation of the albedo spectrum agrees with the EGRET data. We show that the
spectrum of gamma rays from the Moon is very steep with an effective cutoff
around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a
narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from
other astrophysical sources, the albedo spectrum of the Moon is well
understood, including its absolute normalisation; this makes it a useful
"standard candle" for gamma-ray telescopes. The steep albedo spectrum also
provides a unique opportunity for energy calibration of gamma-ray telescopes,
such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the
albedo flux depends on the incident CR spectrum which changes over the solar
cycle, it is possible to monitor the CR spectrum using the albedo gamma-ray
flux. Simultaneous measurements of CR proton and helium spectra by the Payload
for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA), and
observations of the albedo gamma rays by the GLAST Large Area Telescope (LAT),
can be used to test the model predictions and will enable the LAT to monitor
the CR spectrum near the Earth beyond the lifetime of the PAMELA.Comment: 6 pages, 4 figures, emulateapj.cls; to appear in the Astrophysical
Journa
Chemistry by Mobile Phone (or how to justify more time at the bar)
By combining automatic environment monitoring with Java smartphones a system has been produced for the real-time monitoring of experiments whilst away from the lab. Changes in the laboratory environment are encapsulated as simple XML messages, which are published using an MQTT compliant broker. Clients subscribe to the MQTT stream, and produce a user display. An MQTT client written for the Java MIDP platform, can be run on a smartphone with a GPRS Internet connection, freeing us from the constraints of the lab. We present an overview of the technologies used, and how these are helping chemists make the best use of their time
Aeroelastic Tailoring via Tow Steered Composites
The use of tow steered composites, where fibers follow prescribed curvilinear paths within a laminate, can improve upon existing capabilities related to aeroelastic tailoring of wing structures, though this tailoring method has received relatively little attention in the literature. This paper demonstrates the technique for both a simple cantilevered plate in low-speed flow, as well as the wing box of a full-scale high aspect ratio transport configuration. Static aeroelastic stresses and dynamic flutter boundaries are obtained for both cases. The impact of various tailoring choices upon the aeroelastic performance is quantified: curvilinear fiber steering versus straight fiber steering, certifiable versus noncertifiable stacking sequences, a single uniform laminate per wing skin versus multiple laminates, and identical upper and lower wing skins structures versus individual tailoring
Trim and Structural Optimization of Subsonic Transport Wings Using Nonconventional Aeroelastic Tailoring
Several minimum-mass aeroelastic optimization problems are solved to evaluate the effectiveness of a variety of novel tailoring schemes for subsonic transport wings. Aeroelastic strength and panel buckling constraints are imposed across a variety of trimmed maneuver loads. Tailoring with metallic thickness variations, functionally graded materials, composite laminates, tow steering, and distributed trailing edge control effectors are all found to provide reductions in structural wing mass with varying degrees of success. The question as to whether this wing mass reduction will offset the increased manufacturing cost is left unresolved for each case
Effect of holding temperature and time on ferrite formation in dual phase steel produced by strip casting
Conventional dual phase (DP) steel (0.08C-0.81Si-1.47Mn-0.03Al, wt. %) was manufactured by the laboratory simulation of strip casting. The effect of holding temperature and time on microstructure evolution was studied using a quench-deformation dilatometer. Microstructures were observed using optical and scanning electron microscopy. The results showed that the nose temperature of ferrite phase field is around 650 °C. The kinetics of ferrite formation is fast within the first 100 s of holding at this temperature, and then formation of ferrite continues at a slower rate until it reaches the fraction corresponding to that defined by the lever rule. 70~80 % ferrite was obtained after holding at 650 °C for 100~900 s. Some Widmänstatten ferrite was also observed probably because of a large prior austenite grain size and quenching after holding. In addition, austenite-to-ferrite transformation kinetics is fitted well using Johnson-Mehl-Avrami equation. The Avrami exponent for ferrite formation was approximately 1 for both 650 and 670 °C holding temperatures, which means rapid ferrite transformation. It deduces that the ferrite formation obeys a linear growth behavior, which is associated with a decrease in amount of nucleation sites
Translocation Dynamics with Attractive Nanopore-Polymer Interactions
Using Langevin dynamics simulations, we investigate the influence of
polymer-pore interactions on the dynamics of biopolymer translocation through
nanopores. We find that an attractive interaction can significantly change the
translocation dynamics. This can be understood by examining the three
components of the total translocation time
corresponding to the initial filling of the pore, transfer of polymer from the
\textit{cis} side to the \textit{trans} side, and emptying of the pore,
respectively. We find that the dynamics for the last process of emptying of the
pore changes from non-activated to activated in nature as the strength of the
attractive interaction increases, and becomes the dominant
contribution to the total translocation time for strong attraction. This leads
to a new dependence of as a function of driving force and chain length.
Our results are in good agreement with recent experimental findings, and
provide a possible explanation for the different scaling behavior observed in
solid state nanopores {\it vs.} that for the natural -hemolysin
channel.Comment: 8 pages, 11 figure
An X-ray Selected Galaxy Cluster at z=1.11 in the Rosat Deep Cluster Survey
We report the discovery of an X-ray luminous galaxy cluster at z =1.11. RDCS
J0910+5422 was selected as an X-ray cluster candidate in the ROSAT Deep Cluster
Survey on the basis of its spatial extent in a Rosat PSPC image. Deep optical
and near-IR imaging reveal a red galaxy overdensity around the peak of the
X-ray emission, with a significant excess of objects with J-K and I-K colors
typical of elliptical galaxies at z ~ 1.0. Spectroscopic observations at the
Keck II telescope secured 9 galaxy redshifts in the range 1.095<z<1.120
yielding a mean cluster redshift of =1.106. Eight of these galaxies lie
within a 30 arcsec radius around the peak X-ray emission. A deep Chandra ACIS
exposure on this field shows extended X-ray morphology and allows the X-ray
spectrum of the intracluster medium to be measured. The cluster has a
bolometric luminosity L_x = 2.48^{+0.33}_{-0.26} x 10^44 ergs/s, a temperature
of kT = 7.2^{+2.2}_{-1.4} keV, and a mass within r = 1 Mpc of 7.0 x 10^14 M_sun
(H_0=65 km/s/Mpc, Omega_m = 0.3, and Lambda = 0.7). The spatial distribution of
the cluster members is elongated, which is not due to an observational
selection effect, and followed by the X-ray morphology. The X-ray surface
brightness profile and the spectrophotometric properties of the cluster members
suggest that this is an example of a massive cluster in an advanced stage of
formation with a hot ICM and an old galaxy population already in place at z >
1.Comment: 19 pages, 7 figures: Figures 1,4,6 included as separate jpg files.
Accepted for publication in The Astronomical Journa
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