71,256 research outputs found
Helical channel design and technology for cooling of muon beams
Novel magnetic helical channel designs for capture and cooling of bright muon
beams are being developed using numerical simulations based on new inventions
such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF)
cavities. We are close to the factor of a million six-dimensional phase space
(6D) reduction needed for muon colliders. Recent experimental and simulation
results are presented.Comment: 6 pp. 14th Advanced Accelerator Concepts Workshop 13-19 Jun 2010:
Annapolis, Marylan
Slow Atomic Motion in Zr-Ti-Cu-Ni-Be Metallic Glasses Studied by NMR
Nuclear magnetic resonance is used for the first time to detect slow atomic motion in metallic glasses, specifically, Be motion in Zr-Ti-Cu-Ni-Be bulk metallic glasses. The observations are not consistent with the vacancy-assisted and interstitial diffusion mechanisms and favor the spread-out free volume fluctuation mechanism for Be diffusion. Comparison with the results of Be diffusion measured by elastic backscattering the NMR results also indicates that the energy barriers for short- and long-range Be motion are the same
SATMC: Spectral Energy Distribution Analysis Through Markov Chains
We present the general purpose spectral energy distribution (SED) fitting
tool SED Analysis Through Markov Chains (SATMC). Utilizing Monte Carlo Markov
Chain (MCMC) algorithms, SATMC fits an observed SED to SED templates or models
of the user's choice to infer intrinsic parameters, generate confidence levels
and produce the posterior parameter distribution. Here we describe the key
features of SATMC from the underlying MCMC engine to specific features for
handling SED fitting. We detail several test cases of SATMC, comparing results
obtained to traditional least-squares methods, which highlight its accuracy,
robustness and wide range of possible applications. We also present a sample of
submillimetre galaxies that have been fitted using the SED synthesis routine
GRASIL as input. In general, these SMGs are shown to occupy a large volume of
parameter space, particularly in regards to their star formation rates which
range from ~30-3000 M_sun yr^-1 and stellar masses which range from
~10^10-10^12 M_sun. Taking advantage of the Bayesian formalism inherent to
SATMC, we also show how the fitting results may change under different
parametrizations (i.e., different initial mass functions) and through
additional or improved photometry, the latter being crucial to the study of
high-redshift galaxies.Comment: 17 pages, 11 figures, MNRAS accepte
Spatial distribution of Chlorpyrifos and Endosulfan in USA coastal waters and the Great Lakes
Between 1994 and 1997, 258 tissue and 178 sediment samples were analyzed for chlorpyrifos throughout the coastal United States and the Great Lakes. Subsequently, 95 of
the 1997 tissue samples were reanalyzed for endosulfan. Tissue chlorpyrifos concentrations, which exceeded the 90th percentile, were found in coastal regions known to have high
agricultural use rates but also strongly correlated with sites near high population. The highest concentrations of endosulfans in contrast, were generally limited to agricultural regions of the country. Detections of chlorpyrifos at several Alaskan sites suggest an atmospheric
transport mechanism. Many Great Lakes sites had chlorpyrifos tissue concentrations above the 90th percentile which decreased with increasing distance from the Corn Belt region (Iowa, Indiana, Illinois, and Wisconsin) where most agriculturally applied chlorpyrifos is used. Correlation analysis suggests that fluvial discharge is the primary transport pathway on the Atlantic and Gulf of Mexico coasts for chlorpyrifos but not necessarily for endosulfans. (PDF contains 28 pages
Enhanced flux pinning in YBa2Cu3O7-d films by nano-scaled substrate surface roughness
Nano-scaled substrate surface roughness is shown to strongly influence the
critical current density Jc in YBCO films made by pulse-laser-deposition on the
crystalline LaAlO3 substrates consisting of two separate twin-free and
twin-rich regions. The nano-scaled corrugated surface was created in the
twin-rich region during the deposition process. Using magneto-optical imaging
techniques coupled with optical and atomic force microscopy, we observed an
enhanced flux pinning in the YBCO films in the twin-rich region, resulted in
\~30% increase in Jc, which was unambiguously confirmed by the direct transport
measurement.Comment: 16 pages, 3 figures, accepted by Applied Physics Letter
Effective renormalized multi-body interactions of harmonically confined ultracold neutral bosons
We calculate the renormalized effective 2-, 3-, and 4-body interactions for N
neutral ultracold bosons in the ground state of an isotropic harmonic trap,
assuming 2-body interactions modeled with the combination of a zero-range and
energy-dependent pseudopotential. We work to third-order in the scattering
length a defined at zero collision energy, which is necessary to obtain both
the leading-order effective 4-body interaction and consistently include
finite-range corrections for realistic 2-body interactions. The leading-order,
effective 3- and 4-body interaction energies are U3 = -(0.85576...)(a/l)^2 +
2.7921(1)(a/l)^3 + O[(a/l)^4] and U4 = +(2.43317...)(a/l)^3 + O[(a\l)^4], where
w and l are the harmonic oscillator frequency and length, respectively, and
energies are in units of hbar*w. The one-standard deviation error 0.0001 for
the third-order coefficient in U3 is due to numerical uncertainty in estimating
a slowly converging sum; the other two coefficients are either analytically or
numerically exact. The effective 3- and 4-body interactions can play an
important role in the dynamics of tightly confined and strongly correlated
systems. We also performed numerical simulations for a finite-range boson-boson
potential, and it was comparison to the zero-range predictions which revealed
that finite-range effects must be taken into account for a realistic
third-order treatment. In particular, we show that the energy-dependent
pseudopotential accurately captures, through third order, the finite-range
physics, and in combination with the multi-body effective interactions gives
excellent agreement with the numerical simulations, validating our theoretical
analysis and predictions.Comment: Updated introduction, correction of a few typos and sign error
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