In this work we investigate the minimal physical requirements needed for generating a speed of sound that surpasses its asymptotic conformal limit. It is shown that a peak in the speed of sound of ...homogeneous matter naturally emerges in the transition from a phase with broken chiral symmetry to one with a gapped Fermi surface. We argue that this could be relevant for understanding the peak in the speed of sound displayed by some of the current models for cold ultradense matter. A minimal model implementation of this mechanism is presented, based on the spontaneous breakdown of an approximate particle-antiparticle symmetry, and its thermodynamic properties are determined.
A
bstract
The imaginary part of the heavy quark-antiquark potential experienced by moving heavy quarkonia in strongly coupled plasmas dual to theories of gravity is computed by considering thermal ...worldsheet fluctuations of the holographic Nambu-Goto string. General results for a wide class of gravity duals are presented and an explicit formula for Im
V
Q
Q
¯
is found in the case where the axis of the moving
Q
¯
Q
pair has an arbitrary orientation with respect to its velocity in the plasma. These results are applied to the study of heavy quarkonia propagating through a strongly coupled
N
=
4
SYM plasma. Our results indicate that the onset of Im
V
Q
Q
¯
decreases with increasing rapidity (though our analysis is limited to slowly moving quarkonia) and that, in general, a
Q
Q
¯
pair is more strongly bound if its axis is aligned with its direction of motion through the strongly coupled plasma.
We show that linear superpositions of plane waves involving a single-valued, covariantly stable dispersion relation ω(k) always propagate outside the light cone unless ω(k)=a+bk. This implies that ...there is no notion of causality for individual dispersion relations since no mathematical condition on the function ω(k) (such as the front velocity or the asymptotic group velocity conditions) can serve as a sufficient condition for subluminal propagation in dispersive media. Instead, causality can only emerge from a careful cancellation that occurs when one superimposes all the excitation branches of a physical model. This happens automatically in local theories of matter that are covariantly stable. Hence, we find that the need for nonhydrodynamic modes in relativistic fluid mechanics is analogous to the need for antiparticles in relativistic quantum mechanics.
Recent estimates for the electromagnetic fields produced in the early stages of noncentral ultrarelativistic heavy ion collisions indicate the presence of magnetic fields B ~ scriptO(0.1 - 15m ...super(2) pi), where m sub(pi) is the pion mass. It is then of special interest to study the effects of strong (Abelian) magnetic fields on the transport coefficients of strongly coupled non-Abelian plasmas, such as the quark-gluon plasma formed in heavy ion collisions. In this paper we study the anisotropy in the shear viscosity induced by an external magnetic field in a strongly coupled N = 4 super Yang-Mills (SYM) plasma. Due to the spatial anisotropy created by the magnetic field, the most general viscosity tensor of a magnetized plasma has five shear viscosity coefficients and two bulk viscosities. We use the holographic correspondence to evaluate two of the shear viscosities, etabottom identical with eta sub(xyxy) (perpendicular to the magnetic field) and eta|| identical with eta sub(xzxz) = eta sub(yzyz) (parallel to the field). When B not = 0 the shear viscosity perpendicular to the field saturates the viscosity bound etabottom/s = 1/(4pi), while in the direction parallel to the field the bound is violated since eta||/s < 1/(4pi). However, the violation of the bound in the case of strongly coupled SYM is minimal even for the largest value of B that can be reached in heavy ion collisions.
Like fluctuations, nondiagonal correlators of conserved charges provide a tool for the study of chemical freeze-out in heavy ion collisions. They can be calculated in thermal equilibrium using ...lattice simulations, and be connected to moments of event-by-event net-particle multiplicity distributions. We calculate them from continuum-extrapolated lattice simulations at μB=0, and present a finite-μB extrapolation, comparing two different methods. In order to relate the grand canonical observables to the experimentally available net-particle fluctuations and correlations, we perform a hadron resonance gas model analysis, which allows us to completely break down the contributions from different hadrons. We then construct suitable hadronic proxies for fluctuation ratios, and study their behavior at finite chemical potentials. We also study the effect of introducing acceptance cuts, and argue that the small dependence of certain ratios on the latter allows for a direct comparison with lattice QCD results, provided that the same cuts are applied to all hadronic species. Finally, we perform a comparison for the constructed quantities for experimentally available measurements from the STAR Collaboration. Thus, we estimate the chemical freeze-out temperature to 165 MeV using a strangeness-related proxy. This is a rather high temperature for the use of the hadron resonance gas; thus, further lattice studies are necessary to provide first principle results at intermediate μB.
A general organizing principle is proposed that can be used to derive the equations of motion describing the near-equilibrium dynamics of causal and thermodynamically stable relativistic systems. The ...latter are found to display some new type of universal behavior near equilibrium that allows them to be grouped into universality classes defined by their degrees of freedom, information content, and conservation laws. The universality classes expose a number of surprising equivalences between different theories, shedding new light on the near-equilibrium behavior of relativistic systems.A general organizing principle is proposed that can be used to derive the equations of motion describing the near-equilibrium dynamics of causal and thermodynamically stable relativistic systems. The latter are found to display some new type of universal behavior near equilibrium that allows them to be grouped into universality classes defined by their degrees of freedom, information content, and conservation laws. The universality classes expose a number of surprising equivalences between different theories, shedding new light on the near-equilibrium behavior of relativistic systems.
Tetrasphaera and Candidatus Accumulibacter are two abundant polyphosphate accumulating organisms in full-scale enhanced biological phosphorus removal (EBPR) systems. However, little is known about ...the metabolic behaviour and ecological niche that each organism exhibits in mixed communities. In this study, an enriched culture of Tetrasphaera and Ca. Accumulibacter was obtained using casein hydrolysate as sole carbon source. This culture was able to achieve a high phosphorus removal efficiency (>99%), storing polyphosphate while consuming amino acids anaerobically. Microautoradiography and fluorescence in situ hybridisation confirmed that more than 90% Tetrasphaera cells were responsible for amino acid consumption while Ca. Accumulibacter likely survived on fermentation products. Tetrasphaera performed the majority of the P removal (approximately 80%) in this culture, and batch tests showed that the metabolism of some carbon sources could actually lead to anaerobic orthophosphate (Pi) uptake (9.0 ± 2.1 mg-P/L) through energy generated by fermentation of glucose and amino acids. This anaerobic Pi uptake may lead to lower net Pi release to C uptake ratios and reduce the Pi needed to be removed aerobically in WWTPs. Intracellular metabolites such as amino acids, sugars, volatile fatty acids and small amines were observed as potential storage products, which may serve as energy sources in the aerobic phase. Evidence of the urea cycle was found, which could be involved in reducing the intracellular nitrogen content. This study improves our understanding of how phosphorus is removed in EBPR systems and can enable novel process optimisation strategies.
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•A P-removing, enriched Tetrasphaera and Ca. Accumulibacter culture was obtained.•Tetrasphaera were mainly responsible for amino acid biodegradation and P removal.•Tetrasphaera are capable of anaerobic P uptake through energy from fermentation.•Numerous intracellular metabolites were identified - could serve as storage products.•Improved metabolic understanding could help optimise EBPR systems.
Hollow-walled lattices are a recent optimization upon the conventional dense-walled lattice design. These novel microstructures can achieve extremely low densities while exhibiting robust technical ...properties including high ductility, strength, and stiffness. However, the current fabrication process for these structures is ineffective, requiring multiple additive and subtractive manufacturing processes to produce a single specimen. The application of a single step additive manufacturing (AM) method has not yet been evaluated for hollow-walled lattice fabrication. This study aims to assess the viability of such a method, enabling greater geometric control, and providing a single process to reduce both time and cost. The manufacturability of laser powder bed fusion (LPBF) will be explored through Ti6Al4V hollow-walled struts and lattices at varying diameters, lengths, and inclination angles while retaining a constant wall thickness. Quasi static compressional testing will also occur upon the hollow-walled body-centered cubic lattices with a reinforced strut in the Z-axis (BCCZ). These experimental BCCZ lattices have been fabricated at relative densities ranging from 5 to 40%, and strength and modulus values have been observed between 4 and 25 MPa, and 750–3640 MPa, respectively. The resultant data will assist in the generation of the Gibson-Ashby Model to systematically compare LPBF Ti6Al4V hollow-walled lattices to reported dense-walled lattices. This study presents an exploration into the single-step fabrication of metal hollow-walled struts and lattices to broaden the scope of manufacturability and facilitate future advancements.
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