1,816 research outputs found
Recent advances in the simulation of particle-laden flows
A substantial number of algorithms exists for the simulation of moving
particles suspended in fluids. However, finding the best method to address a
particular physical problem is often highly non-trivial and depends on the
properties of the particles and the involved fluid(s) together. In this report
we provide a short overview on a number of existing simulation methods and
provide two state of the art examples in more detail. In both cases, the
particles are described using a Discrete Element Method (DEM). The DEM solver
is usually coupled to a fluid-solver, which can be classified as grid-based or
mesh-free (one example for each is given). Fluid solvers feature different
resolutions relative to the particle size and separation. First, a
multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine
resolution) is presented to study the behavior of particle stabilized fluid
interfaces and second, a Smoothed Particle Hydrodynamics implementation
(mesh-free, meso-scale resolution, similar to the particle size) is introduced
to highlight a new player in the field, which is expected to be particularly
suited for flows including free surfaces.Comment: 16 pages, 4 figure
Prethermalization and thermalization in models with weak integrability breaking
We study the effects of integrability breaking perturbations on the
non-equilibrium evolution of many-particle quantum systems. We focus on a class
of spinless fermion models with weak interactions. We employ equation of motion
techniques that can be viewed as generalizations of quantum Boltzmann
equations. We benchmark our method against time dependent density matrix
renormalization group computations and find it to be very accurate as long as
interactions are weak. For small integrability breaking, we observe robust
prethermalization plateaux for local observables on all accessible time scales.
Increasing the strength of the integrability breaking term induces a "drift"
away from the prethermalization plateaux towards thermal behaviour. We identify
a time scale characterizing this cross-over.Comment: 9 pages, 4 figure
China's Belt and Road Initiative and the emerging geographies of global urbanisation
China's Belt and Road Initiative (BRI) is heralded as the largest investment in infrastructure in history and is expected to re‐shape the geographies of urbanization in the coming decades. In this paper we review the burgeoning, yet still embryonic literature on the BRI. Our aim is to move beyond currently dominant framings of the BRI as a geopolitical or economic strategy that tend to overlook the complex embeddedness of infrastructure. Drawing on theories of planetary urbanization, we argue that the BRI constitutes a form of urbanization that is bound up with the socio‐spatial and ecological restructuring of global capitalism. We illustrate this by mapping and analysing energy projects under the BRI. Overall, we outline a research agenda on the BRI that calls for: 1) a more nuanced analysis of its spatial and scalar politics; 2) approaching the BRI as a distinctly urban question; and 3) a disruption of the dominant China‐centric discussions through critical in‐depth case‐study analysis
Record monthly-temperature extremes
Póster presentado en: VIII Congreso de la Asociación Española de Climatología celebrado en Salamanca entre el 25 y el 28 de septiembre de 2012
Approximation algorithms for stochastic and risk-averse optimization
We present improved approximation algorithms in stochastic optimization. We
prove that the multi-stage stochastic versions of covering integer programs
(such as set cover and vertex cover) admit essentially the same approximation
algorithms as their standard (non-stochastic) counterparts; this improves upon
work of Swamy \& Shmoys which shows an approximability that depends
multiplicatively on the number of stages. We also present approximation
algorithms for facility location and some of its variants in the -stage
recourse model, improving on previous approximation guarantees. We give a
-approximation algorithm in the standard polynomial-scenario model and
an algorithm with an expected per-scenario -approximation guarantee,
which is applicable to the more general black-box distribution model.Comment: Extension of a SODA'07 paper. To appear in SIAM J. Discrete Mat
Hiding in the Shadows II: Collisional Dust as Exoplanet Markers
Observations of the youngest planets (1-10 Myr for a transitional disk)
will increase the accuracy of our planet formation models. Unfortunately,
observations of such planets are challenging and time-consuming to undertake
even in ideal circumstances. Therefore, we propose the determination of a set
of markers that can pre-select promising exoplanet-hosting candidate disks. To
this end, N-body simulations were conducted to investigate the effect of an
embedded Jupiter mass planet on the dynamics of the surrounding planetesimal
disk and the resulting creation of second generation collisional dust. We use a
new collision model that allows fragmentation and erosion of planetesimals, and
dust-sized fragments are simulated in a post process step including
non-gravitational forces due to stellar radiation and a gaseous protoplanetary
disk. Synthetic images from our numerical simulations show a bright double ring
at 850 m for a low eccentricity planet, whereas a high eccentricity planet
would produce a characteristic inner ring with asymmetries in the disk. In the
presence of first generation primordial dust these markers would be difficult
to detect far from the orbit of the embedded planet, but would be detectable
inside a gap of planetary origin in a transitional disk.Comment: Accepted for publication in Ap
Privileging the bromance: a critical appraisal of romantic and bromantic relationships
In this research, utilising data from 30 semi-structured interviews, we examine how heterosexual undergraduate men compare their experiences of bromances to that of their romantic relationships (romances). We find that the increasingly intimate, emotive and trusting nature of bromances offers young men a new social space for emotional disclosure, outside of traditional heterosexual relationships. Participants state that the lack of boundaries and judgement in a bromance is expressed as emotionally rivalling the benefits of a heterosexual romance. Our participants mostly determined that a bromance offered them elevated emotional stability, enhanced emotional disclosure, social fulfilment, and better conflict resolution, compared to the emotional lives they shared with girlfriends. Thus, this research provides an empirically grounded conceptual framework for understanding men’s view of close homosocial relationships in comparison to their romantic relationship in the 21st century
Synthesis and antimicrobial activity against Pseudomonas aeruginosa of macrocyclic β-hairpin peptidomimetic antibiotics containing N-methylated amino acids
Antimicrobial resistance among Gram-negative bacteria is a growing problem, fueled by the paucity of new antibiotics that target these microorganisms. One novel family of macrocyclic β-hairpin-shaped peptidomimetics was recently shown to act specifically against Pseudomonas spp. by a novel mechanism of action, targeting the outer membrane protein LptD, which mediates lipopolysaccharide transport to the cell surface during outer membrane biogenesis. Here we explore the mode of binding of one of these β-hairpin peptidomimetics to LptD in Pseudomonas aeruginosa, by examining the effects on antimicrobial activity following N-methylation of individual peptide bonds. An N-methyl scan of the cyclic peptide revealed that residues on both sides of the β-hairpin structure at a non-hydrogen bonding position likely mediate hydrogen-bonding interactions with the target LptD. Structural analyses by NMR spectroscopy further reinforce the conclusion that the folded β-hairpin structure of the peptidomimetic is critical for binding to the target LptD. Finally, new NMe analogues with potent activity have been identified, which opens new avenues for optimization in this family of antimicrobial peptides
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