72 research outputs found
Multiscale modelling and analysis of lithium-ion battery charge and discharge
A microscopic model of a lithium battery is developed, which accounts for lithium diffusion within particles, transfer of lithium from particles to the electrolyte and transport within the electrolyte assuming a dilute electrolyte and ButlerâVolmer reaction kinetics. Exploiting the small size of the particles relative to the electrode dimensions, a homogenised model (in agreement with existing theories) is systematically derived and studied. Details of how the various averaged quantities relate to the underlying geometry and assumptions are given. The novel feature of the homogenisation process is that it allows the coefficients in the electrode-scale model to be derived in terms of the microscopic features of the electrode (e.g. particle size and shape) and can thus be used as a systematic way of investigating the effects of changes in particle design. Asymptotic methods are utilised to further simplify the model so that one-dimensional behaviour can be described with relatively simpler expressions. It is found that for low discharge currents, the battery acts almost uniformly while above a critical current, regions of the battery become depleted of lithium ions and have greatly reduced reaction rates leading to spatially nonuniform use of the electrode. The asymptotic approximations are valid for electrode materials where the OCV is a strong function of intercalated lithium concentration, such as Li x C6, but not for materials with a flat discharge curve, such as LiFePO4
A way to estimate the heavy quark thermalization rate from the lattice
The thermalization rate of a heavy quark is related to its momentum diffusion
coefficient. Starting from a Kubo relation and using the framework of the heavy
quark effective theory, we argue that in the large-mass limit the momentum
diffusion coefficient can be defined through a certain Euclidean correlation
function, involving color-electric fields along a Polyakov loop. Furthermore,
carrying out a perturbative computation, we demonstrate that the spectral
function corresponding to this correlator is relatively flat at small
frequencies. Therefore, unlike in the case of several other transport
coefficients, for which the narrowness of the transport peak makes analytic
continuation from Euclidean lattice data susceptible to severe systematic
uncertainties, it appears that the determination of the heavy quark
thermalization rate could be relatively well under control.Comment: 17 pages. v2: clarifications and references added, published versio
Heavy Quark Thermalization in Classical Lattice Gauge Theory: Lessons for Strongly-Coupled QCD
Thermalization of a heavy quark near rest is controlled by the correlator of
two electric fields along a temporal Wilson line. We address this correlator
within real-time, classical lattice Yang-Mills theory, and elaborate on the
analogies that exist with the dynamics of hot QCD. In the weak-coupling limit,
it can be shown analytically that the dynamics on the two sides are closely
related to each other. For intermediate couplings, we carry out
non-perturbative simulations within the classical theory, showing that the
leading term in the weak-coupling expansion significantly underestimates the
heavy quark thermalization rate. Our analytic and numerical results also yield
a general understanding concerning the overall shape of the spectral function
corresponding to the electric field correlator, which may be helpful in
subsequent efforts to reconstruct it from Euclidean lattice Monte Carlo
simulations.Comment: 22 pages. v2: a reference and clarifications added; published versio
Heavy quark diffusion in QCD and N=4 SYM at next-to-leading order
We present the full details of a calculation at next-to-leading order of the
momentum diffusion coefficient of a heavy quark in a hot, weakly coupled, QCD
plasma. Corrections arise at O(g_s); physically they represent interference
between overlapping scatterings, as well as soft, electric scale (p ~ gT) gauge
field physics, which we treat using the hard thermal loop (HTL) effective
theory. In 3-color, 3-flavor QCD, the momentum diffusion constant of a
fundamental representation heavy quark at NLO is kappa = (16\pi/3) alpha_s^2
T^3 (log(1/g) + 0.07428 + 1.9026 g). We extend the computation to a heavy
fundamental representation ``probe'' quark in large N_c, N=4 Super Yang-Mills
theory, where the result is kappa^{SYM}= (lambda^2 T^3)(6\pi)
(log(1/\sqrt{\lambda}) + 0.4304 + 0.8010 \sqrt{lambda}) (where lambda=g_s^2 N_c
is the t'Hooft coupling). In the absence of some resummation technique, the
convergence of perturbation theory is poor.Comment: 40 pages, 14 figure
Loop-Generated Bounds on Changes to the Graviton Dispersion Relation
We identify the effective theory appropriate to the propagation of massless
bulk fields in brane-world scenarios, to show that the dominant low-energy
effect of asymmetric warping in the bulk is to modify the dispersion relation
of the effective 4-dimensional modes. We show how such changes to the graviton
dispersion relation may be bounded through the effects they imply, through
loops, for the propagation of standard model particles. We compute these bounds
and show that they provide, in some cases, the strongest constraints on
nonstandard gravitational dispersions. The bounds obtained in this way are the
strongest for the fewest extra dimensions and when the extra-dimensional Planck
mass is the smallest. Although the best bounds come for warped 5-D scenarios,
for which the 5D Planck Mass is O(TeV), even in 4 dimensions the graviton loop
can lead to a bound on the graviton speed which is comparable with other
constraints.Comment: 18 pages, LaTeX, 4 figures, uses revte
Froude supercritical flow processes and sedimentary structures: new insights from experiments with a wide range of grain sizes
Recognition of Froude supercritical flow deposits in environments that range from rivers to the ocean floor has triggered a surge of interest in their flow processes, bedforms and sedimentary structures. Interpreting these supercritical flow deposits is especially important because they often represent the most powerful flows in the geological record. Insights from experiments are key to reconstruct palaeoâflow processes from the sedimentary record. So far, all experimentally produced supercritical flow deposits are of a narrow grainâsize range (fine to medium sand), while deposits in the rock record often consist of a much wider grainâsize distribution. This paper presents results of supercriticalâflow experiments with a grainâsize distribution from clay to gravel. These experiments show that cyclic step instabilities can produce more complex and a larger variety of sedimentary structures than the previously suggested backsets and âscour and fillâ structures. The sedimentary structures are composed of irregular lenses, mounds and wedges with backsets and foresets, as well as undulating planar to lowâangle upstream and downstream dipping laminae. The experiments also demonstrate that the Froude number is not the only control on the sedimentary structures formed by supercriticalâflow processes. Additional controls include the size and migration rate of the hydraulic jump and the substrate cohesion. This study further demonstrates that Froude supercritical flow promotes suspension transport of all grain sizes, including gravels. Surprisingly, it was observed that all grain sizes were rapidly deposited just downstream of hydraulic jumps, including silt and clay. These results expand the range of dynamic mud deposition into supercriticalâflow conditions, where local transient shear stress reduction rather than overall flow waning conditions allow for deposition of fines. Comparison of the experimental deposits with outcrop datasets composed of conglomerates to mudstones, shows significant similarities and highlights the role of hydraulic jumps, rather than overall flow condition changes, in producing lithologically and geometrically complex stratigraphy
Amine Containing Analogs of Sulindac for Cancer Prevention
Background:
Sulindac belongs to the chemically diverse family of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) that effectively prevent adenomatous colorectal polyps and colon cancer, especially in patients with familial adenomatous polyposis. Sulindac sulfide amide (SSA), an amide analog of sulindac sulfide, shows insignificant COX-related activity and toxicity while enhancing anticancer activity in vitro and demonstrating in vivo xenograft activity.
Objective:
Develop structure-activity relationships in the sulindac amine series and identify analogs with promising anticancer activities.
Method:
A series of sulindac amine analogs were designed and synthesized and then further modified in a âlibraries from librariesâ approach to produce amide, sulfonamide and N,N-disubstituted sulindac amine sub-libraries. All analogs were screened against three cancer cell lines (prostate, colon and breast).
Results:
Several active compounds were identified viain vitro cancer cell line screening with the most potent compound (26) in the nanomolar range.
Conclusion:
Compound 26 and analogs showing the most potent inhibitory activity may be considered for further design and optimization efforts as anticancer hit scaffolds
Astronomical Distance Determination in the Space Age: Secondary Distance Indicators
The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations. © 2018, The Author(s)
Recommended from our members
Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)
Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 ÎŒas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution
- âŠ