Bottom-up thermalization in heavy ion collisions

We describe how thermalization occurs in heavy ion collisions in the framework of perturbative QCD. When the saturation scale $Q_s$ is large compared to $\Lambda_{QCD}$, thermalization takes place during a time of order $\alpha^{-13/5}Q_s^{-1}$ and the maximal temperature achieved is $\alpha^{2/5}Q_s$.Comment: 11 pages; acknowledgement added; section IIIB slightly extended, version accepted for publication in Phys. Lett.

The fitness costs of antibiotic resistance mutations

Antibiotic resistance is increasing in pathogenic microbial populations and is thus a major threat to public health. The fate of a resistance mutation in pathogen populations is determined in part by its fitness. Mutations that suffer little or no fitness cost are more likely to persist in the absence of antibiotic treatment. In this review, we performed a meta-analysis to investigate the fitness costs associated with single mutational events that confer resistance. Generally, these mutations were costly, although several drug classes and species of bacteria on average did not show a cost. Further investigations into the rate and fitness values of compensatory mutations that alleviate the costs of resistance will help us to better understand both the emergence and management of antibiotic resistance in clinical settings

Thermal and Chemical Equilibration in Relativistic Heavy Ion Collisions

We investigate the thermalization and the chemical equilibration of a parton plasma created from Au+Au collision at LHC and RHIC energies starting from the early moment when the particle momentum distributions in the central region become for the first time isotropic due to longitudinal cooling. Using the relaxation time approximation for the collision terms in the Boltzmann equations for gluons and for quarks and the real collision terms constructed from the simplest QCD interactions, we show that the collision times have the right behaviour for equilibration. The magnitude of the quark (antiquark) collision time remains bigger than the gluon collision time throughout the lifetime of the plasma so that gluons are equilibrating faster than quarks both chemically and kinetically. That is we have a two-stage equilibration scenario as has been pointed out already by Shuryak sometimes ago. Full kinetic equilibration is however slow and chemical equilibration cannot be completed before the onset of the deconfinement phase transition assumed to be at $T_c=200$ MeV. By comparing the collision entropy density rates of the different processes, we show explicitly that inelastic processes, and \emph{not} elastic processes as is commonly assumed, are dominant in the equilibration of the plasma and that gluon branching leads the other processes in entropy generation. We also show that, within perturbative QCD, processes with higher power in \alpha_s need not be less important for the purpose of equilibration than those with lower power. The state of equilibration of the system has also a role to play. We compare our results with those of the parton cascade model.Comment: 17 pages, revtex+psfig style with 14 embedded postscript figures, to appear in Phys. Rev.

Public Sentiment Analysis and Topic Modeling Regarding COVID-19’s Three Waves of Total Lockdown: A Case Study on Movement Control Order in Malaysia

[Abstract] The COVID-19 pandemic has affected many aspects of human life. The pandemic not only caused millions of fatalities and problems but also changed public sentiment and behavior. Owing to the magnitude of this pandemic, governments worldwide adopted full lockdown measures that attracted much discussion on social media platforms. To investigate the effects of these lockdown measures, this study performed sentiment analysis and latent Dirichlet allocation topic modeling on textual data from Twitter published during the three lockdown waves in Malaysia between 2020 and 2021. Three lockdown measures were identified, the related data for the first two weeks of each lockdown were collected and analysed to understand the public sentiment. The changes between these lockdowns were identified, and the latent topics were highlighted. Most of the public sentiment focused on the first lockdown as reflected in the large number of latent topics generated during this period. The overall sentiment for each lockdown was mostly positive, followed by neutral and then negative. Topic modelling results identified staying at home, quarantine and lockdown as the main aspects of discussion for the first lockdown, whilst importance of health measures and government efforts were the main aspects for the second and third lockdowns. Governments may utilise these findings to understand public sentiment and to formulate precautionary measures that can assure the safety of their citizens and tend to their most pressing problems. These results also highlight the importance of positive messaging during difficult times, establishing digital interventions and formulating new policies to improve the reaction of the public to emergency situations.Taiwan. Ministry of Science and Technology; 108-2511-H-224-007-MY

Where am I in virtual reality?

It is currently not well understood whether people experience themselves to be located in one or more specific part(s) of their body. Virtual reality (VR) is increasingly used as a tool to study aspects of bodily perception and self-consciousness, due to its strong experimental control and ease in manipulating multi-sensory aspects of bodily experience. To investigate where people self-locate in their body within virtual reality, we asked participants to point directly at themselves with a virtual pointer, in a VR headset. In previous work employing a physical pointer, participants mainly located themselves in the upper face and upper torso. In this study, using a VR headset, participants mainly located themselves in the upper face. In an additional body template task where participants pointed at themselves on a picture of a simple body outline, participants pointed most often to the upper torso, followed by the (upper) face. These results raise the question as to whether head-mounted virtual reality might alter where people locate themselves making them more “head-centred”

Closed-Time Path Integral Formalism and Medium Effects of Non-Equilibrium QCD Matter

We apply the closed-time path integral formalism to study the medium effects of non-equilibrium gluon matter. We derive the medium modified resummed gluon propagator to the one loop level in non-equilibrium in the covariant gauge. The gluon propagator we derive can be used to remove the infrared divergences in the secondary parton collisions to study thermalization of minijet parton plasma at RHIC and LHC.Comment: Final version, To appear in Physical Review D, Minor modification, reference adde

Extension of the JIMWLK Equation in the Low Gluon Density Region

It has recently been realized that the Balitsky-JIMWLK equations have serious shortcomings as equations to be used in small-x evolution near the unitarity limit. A recent generalization of the Balitsky equations has been given which corrects these shortcomings. In this paper we present an equivalent discussion, but in terms of the JIMWLK equation where we show that a new (fourth order functional derivative) term should be included. We also present a stochastic version of the new equation which, however, has some unusual mathematical aspects which are not as yet well understood.Comment: 23 pages, 1 figure, corrected typos, corrected references, published versio

Carnitine Acetyltransferase Mitigates Metabolic Inertia and Muscle Fatigue during Exercise

SummaryAcylcarnitine metabolites have gained attention as biomarkers of nutrient stress, but their physiological relevance and metabolic purpose remain poorly understood. Short-chain carnitine conjugates, including acetylcarnitine, derive from their corresponding acyl-CoA precursors via the action of carnitine acetyltransferase (CrAT), a bidirectional mitochondrial matrix enzyme. We show here that contractile activity reverses acetylcarnitine flux in muscle, from net production and efflux at rest to net uptake and consumption during exercise. Disruption of this switch in mice with muscle-specific CrAT deficiency resulted in acetyl-CoA deficit, perturbed energy charge, and diminished exercise tolerance, whereas acetylcarnitine supplementation produced opposite outcomes in a CrAT-dependent manner. Likewise, in exercise-trained compared to untrained humans, post-exercise phosphocreatine recovery rates were positively associated with CrAT activity and coincided with dramatic shifts in muscle acetylcarnitine dynamics. These findings show acetylcarnitine serves as a critical acetyl buffer for working muscles and provide insight into potential therapeutic strategies for combatting exercise intolerance

Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations

The infrared behaviour of the medium modified gluon propagator in non-equilibrium situations is studied in the covariant gauge using the Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic screening mass is non-zero at the one loop level whenever the initial gluon distribution function is non isotropic with the assumption that the distribution function of the gluon is not divergent at zero transverse momentum. For isotropic gluon distribution functions, such as those describing local equilibrium, the magnetic mass at one loop level is zero which is consistent with finite temperature field theory results. Assuming that a reasonable initial gluon distribution function can be obtained from a perturbative QCD calculation of minijets, we determine these out of equilibrium values for the initial magnetic and Debye screening masses at energy densities appropriate to RHIC and LHC. We also compare the magnetic masses obtained here with those obtained using finite temperature lattice QCD methods at similar temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys. Rev.