5,473 research outputs found
Muon capture in the front end of the IDS neutrino factory
We discuss the design of the muon capture front end of the neutrino factory
International Design Study. In the front end, a proton bunch on a target
creates secondary pions that drift into a capture transport channel, decaying
into muons. A sequence of rf cavities forms the resulting muon beams into
strings of bunches of differing energies, aligns the bunches to (nearly) equal
central energies, and initiates ionization cooling. The muons are then
accelerated to high energy where their decays provide neutrino beams. For the
International Design Study (IDS), a baseline design must be developed and
optimized for an engineering and cost study. We present a baseline design that
can be used to establish the scope of a future neutrino Factory facility.Comment: 3 pp. 1st International Particle Accelerator Conference: IPAC'10,
23-28 May 2010: Kyoto, Japa
Exact static solutions for discrete models free of the Peierls-Nabarro barrier: Discretized first integral approach
We propose a generalization of the discrete Klein-Gordon models free of the
Peierls-Nabarro barrier derived in Nonlinearity {\bf 12}, 1373 (1999) and Phys.
Rev. E {\bf 72}, 035602(R) (2005), such that they support not only kinks but a
one-parameter set of exact static solutions. These solutions can be obtained
iteratively from a two-point nonlinear map whose role is played by the
discretized first integral of the static Klein-Gordon field, as suggested in J.
Phys. A {\bf 38}, 7617 (2005). We then discuss some discrete models
free of the Peierls-Nabarro barrier and identify for them the full space of
available static solutions, including those derived recently in Phys. Rev. E
{\bf 72} 036605 (2005) but not limited to them. These findings are also
relevant to standing wave solutions of discrete nonlinear Schr{\"o}dinger
models. We also study stability of the obtained solutions. As an interesting
aside, we derive the list of solutions to the continuum equation that
fill the entire two-dimensional space of parameters obtained as the continuum
limit of the corresponding space of the discrete models.Comment: Accepted for publication in PRE; the M/S has been revised in line
with the referee repor
Why is the condensed phase of DNA preferred at higher temperature? DNA compaction in the presence of a multivalent cation
Upon the addition of multivalent cations, a giant DNA chain exhibits a large
discrete transition from an elongated coil into a folded compact state. We
performed single-chain observation of long DNAs in the presence of a
tetravalent cation (spermine), at various temperatures and monovalent salt
concentrations. We confirmed that the compact state is preferred at higher
temperatures and at lower monovalent salt concentrations. This result is
interpreted in terms of an increase in the net translational entropy of small
ions due to ionic exchange between higher and lower valence ions.Comment: 4pages,3figure
Ultraviolet Line Emission from Metals in the Low-Redshift Intergalactic Medium
We use a high-resolution cosmological simulation that includes hydrodynamics,
multiphase star formation, and galactic winds to predict the distribution of
metal line emission at z~0 from the intergalactic medium (IGM). We focus on two
ultraviolet doublet transitions, OVI 1032,1038 and CIV 1548,1551. Emission from
filaments with moderate overdensities is orders of magnitude smaller than the
background, but isolated emission from enriched, dense regions with
T~10^5-10^5.5 K and characteristic sizes of 50-100 kpc can be detected above
the background. We show that the emission from these regions is substantially
greater when we use the metallicities predicted by the simulation (which
includes enrichment through galactic winds) than when we assume a uniform IGM
metallicity. Luminous regions correspond to volumes that have recently been
influenced by galactic winds. We also show that the line emission is clustered
on scales ~1 h^-1 Mpc. We argue that although these transitions are not
effective tracers of the warm-hot intergalactic medium, they do provide a route
to study the chemical enrichment of the IGM and the physics of galactic winds.Comment: replaced by version to appear in ApJ (conclusions unchanged, one new
figure), 16 pages (emulateapj), 11 figures, version with higher resolution
figures available at
http://www.tapir.caltech.edu/~sfurlane/metals/coverpage.htm
Shifting with
Precision measurements at the resonance agree well with the standard
model. However, there is still a hint of a discrepancy, not so much in by
itself (which has received a great deal of attention in the past several years)
but in the forward-backward asymmetry together with . The two
are of course correlated. We explore the possibilty that these and other
effects are due to the mixing of and with one or more heavy quarks.Comment: 11 pages, 1 Figure, LaTex fil
Dynamic Labyrinthine Pattern in an Active Liquid Film
We report the generation of a dynamic labyrinthine pattern in an active
alcohol film. A dynamic labyrinthine pattern is formed along the contact line
of air/pentanol/aqueous three phases. The contact line shows a clear
time-dependent change with regard to both perimeter and area of a domain. An
autocorrelation analysis of time-development of the dynamics of the perimeter
and area revealed a strong geometric correlation between neighboring patterns.
The pattern showed autoregressive behavior. The behavior of the dynamic pattern
is strikingly different from those of stationary labyrinthine patterns. The
essential aspects of the observed dynamic pattern are reproduced by a
diffusion-controlled geometric model
Where Are the Baryons? II: Feedback Effects
Numerical simulations of the intergalactic medium have shown that at the
present epoch a significant fraction (40-50%) of the baryonic component should
be found in the (T~10^6K) Warm-Hot Intergalactic Medium (WHIM) - with several
recent observational lines of evidence indicating the validity of the
prediction. We here recompute the evolution of the WHIM with the following
major improvements: (1) galactic superwind feedback processes from galaxy/star
formation are explicitly included; (2) major metal species (O V to O IX) are
computed explicitly in a non-equilibrium way; (3) mass and spatial dynamic
ranges are larger by a factor of 8 and 2, respectively, than in our previous
simulations. Here are the major findings: (1) galactic superwinds have dramatic
effects, increasing the WHIM mass fraction by about 20%, primarily through
heating up warm gas near galaxies with density 10^{1.5}-10^4 times the mean
density. (2) the fraction of baryons in WHIM is increased modestly from the
earlier work but is ~40-50%. (3) the gas density of the WHIM is broadly peaked
at a density 10-20 times the mean density, ranging from underdense regions to
regions that are overdense by 10^3-10^4. (4) the median metallicity of the WHIM
is 0.18 Zsun for oxygen with 50% and 90% intervals being (0.040,0.38) and
(0.0017,0.83).Comment: 44 pages, 17 figures, high res version at
http://www.astro.princeton.edu/~cen/baryonII.ps.g
Coronagraphic Low Order Wave Front Sensor : post-processing sensitivity enhancer for high performance coronagraphs
Detection and characterization of exoplanets by direct imaging requires a
coronagraph designed to deliver high contrast at small angular separation. To
achieve this, an accurate control of low order aberrations, such as pointing
and focus errors, is essential to optimize coronagraphic rejection and avoid
the possible confusion between exoplanet light and coronagraphic leaks in the
science image. Simulations and laboratory prototyping have shown that a
Coronagraphic Low Order Wave-Front Sensor (CLOWFS), using a single defocused
image of a reflective focal plane ring, can be used to control tip-tilt to an
accuracy of 10^{-3} lambda/D. This paper demonstrates that the data acquired by
CLOWFS can also be used in post-processing to calibrate residual coronagraphic
leaks from the science image. Using both the CLOWFS camera and the science
camera in the system, we quantify the accuracy of the method and its ability to
successfully remove light due to low order errors from the science image. We
also report the implementation and performance of the CLOWFS on the Subaru
Coronagraphic Extreme AO (SCExAO) system and its expected on-sky performance.
In the laboratory, with a level of disturbance similar to what is encountered
in a post Adaptive Optics beam, CLOWFS post-processing has achieved speckle
calibration to 1/300 of the raw speckle level. This is about 40 times better
than could be done with an idealized PSF subtraction that does not rely on
CLOWFS.Comment: 10 pages, 7 figures, accepted for publication in PAS
Finite element analysis applied to redesign of submerged entry nozzles for steelmaking
The production of steel by continuous casting is facilitated by the use of refractory hollow-ware components. A critical component in this process is the submerged entry nozzle (SEN). The normal operating conditions of the SEN are arduous, involving large temperature gradients and exposure to mechanical forces arising from the flow of molten steel; experimental development of the components is challenging in so hazardous an environment. The effects of the thermal stress conditions in relation to a well-tried design were therefore simulated using a finite element analysis approach. It was concluded from analyses that failures of the type being experienced are caused by the large temperature gradient within the nozzle. The analyses pointed towards a supported shoulder area of the nozzle being most vulnerable to failure and practical in-service experience confirmed this. As a direct consequence of the investigation, design modifications, incorporating changes to both the internal geometry and to the nature of the intermediate support material, were implemented, thereby substantially reducing the stresses within the Al2O3/graphite ceramic liner. Industrial trials of this modified design established that the component reliability would be significantly improved and the design has now been implemented in series production
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