1,223 research outputs found
Diffusion, Fragmentation and Coagulation Processes: Analytical and Numerical Results
We formulate dynamical rate equations for physical processes driven by a
combination of diffusive growth, size fragmentation and fragment coagulation.
Initially, we consider processes where coagulation is absent. In this case we
solve the rate equation exactly leading to size distributions of Bessel type
which fall off as for large -values. Moreover, we provide
explicit formulas for the expansion coefficients in terms of Airy functions.
Introducing the coagulation term, the full non-linear model is mapped exactly
onto a Riccati equation that enables us to derive various asymptotic solutions
for the distribution function. In particular, we find a standard exponential
decay, , for large , and observe a crossover from the Bessel
function for intermediate values of . These findings are checked by
numerical simulations and we find perfect agreement between the theoretical
predictions and numerical results.Comment: (28 pages, 6 figures, v2+v3 minor corrections
Quantification of complementarity in multi-qubit systems
Complementarity was originally introduced as a qualitative concept for the
discussion of properties of quantum mechanical objects that are classically
incompatible. More recently, complementarity has become a \emph{quantitative}
relation between classically incompatible properties, such as visibility of
interference fringes and "which-way" information, but also between purely
quantum mechanical properties, such as measures of entanglement. We discuss
different complementarity relations for systems of 2-, 3-, or \textit{n}
qubits. Using nuclear magnetic resonance techniques, we have experimentally
verified some of these complementarity relations in a two-qubit system.Comment: 12 pages, 10 figures (A display error about the figures in the
previous version
Application of constitutive friction laws to glacier seismicity
While analysis of glacial seismicity continues to be a widely used method for interpreting glacial processes, the underlying mechanics controlling glacial stick-slip seismicity remain speculative. Here, we report on laboratory shear experiments of debris-laden ice slid over a bedrock asperity under carefully controlled conditions. By modifying the elastic loading stiffness, we generated the first laboratory icequakes. Our work represents the first comprehensive lab observations of unstable ice-slip events and replicates several seismological field observations of glacier slip, such as slip velocity, stress drop, and the relationship between stress drop and recurrence interval. We also observe that stick-slips initiate above a critical driving velocity and that stress drop magnitude decreases with further increases in velocity, consistent with friction theory and rock-on-rock friction laboratory experiments. Our results demonstrate that glacier slip behavior can be accurately predicted by the constitutive rate-and-state friction laws that were developed for rock friction
Highly variable friction and slip observed at Antarctic ice stream bed
The slip of glaciers over the underlying bed is the dominant mechanism governing the migration of ice from land into the oceans, with accelerating slip contributing to sea-level rise. Yet glacier slip remains poorly understood, and observational constraints are sparse. Here we use passive seismic observations to measure both frictional shear stress and slip at the bed of the Rutford Ice Stream in Antarctica using 100,000 repetitive stick-slip icequakes. We find that basal shear stresses and slip rates vary from 10 to 10âPa and 0.2 to 1.5âm per day, respectively. Friction and slip vary temporally over the order of hours, and spatially over 10s of metres, due to corresponding variations in effective normal stress and iceâbed interface material. Our findings suggest that the bed is substantially more complex than currently assumed in ice stream models and that basal effective normal stresses may be significantly higher than previously thought. Our observations can provide constraints on the basal boundary conditions for ice-dynamics models. This is critical for constraining the primary contribution of ice mass loss in Antarctica and hence for reducing uncertainty in sea-level rise projections
Short-wavelength collective modes in a binary hard-sphere mixture
We use hard-sphere generalized hydrodynamic equations to discuss the extended
hydrodynamic modes of a binary mixture. The theory presented here is analytic
and it provides us with a simple description of the collective excitations of a
dense binary mixture at molecular length scales. The behavior we predict is in
qualitative agreement with molecular-dynamics results for soft-sphere mixtures.
This study provides some insight into the role of compositional disorder in
forming glassy configurations.Comment: Published; withdrawn since already published. Ordering in the archive
gives misleading impression of new publicatio
The Greenland Ice Sheet Project 2 Depth-age Scale: Methods and Results
The Greenland Ice Sheet Project 2 (GISP2) depth-age scale is presented based on a multiparameter continuous count approach, to a depth of 2800 m, using a systematic combination of parameters that have never been used to this extent before. The ice at 2800 m is dated at 110,000 years B.P. with an estimated error ranging from 1 to 10% in the top 2500 m of the core and averaging 20% between 2500 and 2800 m. Parameters used to date the core include visual stratigraphy, oxygen isotopic ratios of the ice, electrical conductivity measurements, laser-light scattering from dust, volcanic signals, and major ion chemistry. GISP2 ages for major climatic events agree with independent ages based on varve chronologies, calibrated radiocarbon dates, and other techniques within the combined uncertainties. Good agreement also is obtained with Greenland Ice Core Project ice core dates and with the SPECMAP marine timescale after correlation through the ÎŽ18O of O2. Although the core is deformed below 2800 m and the continuity of the record is unclear, we attempted to date this section of the core on the basis of the laser-light scattering of dust in the ice
Looking our limitations in the eye: A call for more thorough and honest reporting of study limitations
The replication crisis and subsequent credibility revolution in psychology have highlighted many suboptimal research practices such as pâhacking, overgeneralizing, and a lack of transparency. These practices may have been employed reflexively but upon reflection, they are hard to defend. We suggest that current practices for reporting and discussing study limitations are another example of an area where there is much room for improvement. In this article, we call for more rigorous reporting of study limitations in social and personality psychology articles, and we offer advice for how to do this. We recommend that authors consider what the best argument is against their conclusions (which we call the âsteelâperson principleâ). We consider limitations as threats to construct, internal, external, and statistical conclusion validity (Shadish et al., 2002), and offer some examples for better practice reporting of common study limitations. Our advice has its own limitations â both our representation of current practices and our recommendations are largely based on our own metaresearch and opinions. Nevertheless, we hope that we can prompt researchers to write more deeply and clearly about the limitations of their research, and to hold each other to higher standards when reviewing each other's work
Five millennia of surface temperatures and ice core bubble characteristics from the WAIS Divide deep core, West Antarctica
Bubble number densities from the West Antarctic Ice Sheet (WAIS) Divide deep core in West Antarctica record relatively stable temperatures during the middle Holocene followed by late Holocene cooling. We measured bubble number density, shape, size, and arrangement on new samples of the main WAIS Divide deep core WDC06A from similar to 580m to similar to 1600 depth. The bubble size, shape, and arrangement data confirm that the samples satisfy the requirements for temperature reconstructions. A small correction for cracks formed after core recovery allows extension of earlier work through the brittle ice zone, and a site-specific calibration reduces uncertainties. Using an independently constructed accumulation rate history and a steady state bubble number density model, we determined a temperature reconstruction that agrees closely with other independent estimates, showing a stable middle Holocene, followed by a cooling of similar to 1.25 degrees C in the late Holocene. Over the last similar to 5 millennia, accumulation has been higher during warmer times by similar to 12%degrees C-1, somewhat stronger than for thermodynamic control alone, suggesting dynamic processes
Realistic Calculation of the hep Astrophysical Factor
The astrophysical factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to a realistic Hamiltonian consisting of the Argonne v18
two-nucleon and Urbana-IX three-nucleon interactions. The nuclear weak charge
and current operators have vector and axial-vector components, that include
one- and many-body terms. All possible multipole transitions connecting any of
the p-3He S- and P-wave channels to the 4He bound state are considered. The
S-factor at a p-3He center-of-mass energy of 10 keV, close to the Gamow-peak
energy, is predicted to be 10.1 10^{-20} keV b, a factor of five larger than
the standard-solar-model value. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor.Comment: 8 pages RevTex file, submitted to Phys. Rev. Let
The Ay Problem for p-3He Elastic Scattering
We present evidence that numerically accurate quantum calculations employing
modern internucleon forces do not reproduce the proton analyzing power, A_y,
for p-3He elastic scattering at low energies. These calculations underpredict
new measured analyzing powers by approximately 30% at E_{c.m.} = 1.20 MeV and
by 40% at E_{c.m.} = 1.69 MeV, an effect analogous to a well-known problem in
p-d and n-d scattering. The calculations are performed using the complex Kohn
variational principle and the (correlated) Hyperspherical Harmonics technique
with full treatment of the Coulomb force. The inclusion of the three-nucleon
interaction does not improve the agreement with the experimental data.Comment: Latex file, 4 pages, 2 figures, to be published on Phys. Rev. Let
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