Asymmetry Constraints Research Articles

Baryon Asymmetry Constraints on Extended Symmetric Teleparallel Gravity

Baryon Asymmetry Constraints on Extended Symmetric Teleparallel Gravity

An improvement of single-network adaptive critic design for nonlinear systems with asymmetry constraints

Traditional approximate/adaptive dynamic programming (ADP) methods can handle a very special class of systems subject to symmetry constraints. In this study, I extend the exiting ADP to a broader class of nonlinear dynamic systems with asymmetry constraints. Firstly, I propose a novel nonquadratic cost function, based on which the developed optimal controller by solving Hamilton–Jacobi–Bellman equation can limit its value to arbitrarily prescribed bound. Then, to avoid “curse of dimensionality”, I approximately implement the addressed controller via single-network adaptive critic design. Fuzzy Hyperbolic Model is introduced to construct the single critic network by approximating optimal cost function, from which I further derive the optimal control law. The potential advantages are that the control structure is simple and the computational load is low. Lyapunov synthesis proves the ultimately uniformly bounded stability of closed-loop control system. Finally, numerical simulation results verify the efficiency and superiority of the proposed approach.

Severity quantification of pediatric viral respiratory illnesses in chest X-ray images.

Accurate assessment of severity of viral respiratory illnesses (VRIs) allows early interventions to prevent morbidity and mortality in young children. This paper proposes a novel imaging biomarker framework with chest X-ray image for assessing VRI's severity in infants, developed specifically to meet the distinct challenges for pediatric population. The proposed framework integrates three novel technical contributions: a) lung segmentation using weighted partitioned active shape model, b) obtrusive object removal using graph cut segmentation with asymmetry constraint, and c) severity quantification using information-theoretic heterogeneity measures. This paper presents our pilot experimental results with a dataset of 148 images and the ground-truth severity scores given by a board-certified pediatric pulmonologist, demonstrating the effectiveness and clinical relevance of the presented framework.

QCD bulk thermodynamics and conserved charge fluctuations with HISQ fermions

After briefly reviewing recent progress by the HotQCD collaboration in studying the 2+1 flavor QCD equation of state, we will focus on results on fluctuations of conserved charges by the BNL-Bielefeld and HotQCD collaborations. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which arises due to a critical point of QCD in the chiral limit. Considering cumulants up to the 6th order, we observe that they generically behave as expected from universal scaling laws, which is quite different from cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. We will argue that the freeze-out chemical potentials and the freeze-out temperature, usually obtained by a HRG model fit to the measured hadronic yields, can also be obtained in a model independent way from ab-initio lattice QCD calculations by utilizing observables related to conserved charge fluctuations. Further, we will show that the freeze-out strangeness and electric charge chemical potentials can be fixed by imposing strangeness neutrality and isospin asymmetry constraints in the lattice QCD calculations, in order to accommodate conditions met in heavy ion collisions. All results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with temporal extent of Nτ = 6, 8, 10, 12.

Synchronization of Swimming Microorganisms

Some microorganisms, such as spermatozoa, have been observed to synchronize their flagella when swimming in close proximity. Using a two-dimensional model we show that phase-locking can arise from hydrodynamic forces alone. In a Newtonian fluid, as a consequence of the kinematic reversibility of the field equations, there must exist front-back asymmetry in the geometry of their flagellar waveform. The time-evolution of the phase difference between co-swimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase-lock into conformations which minimize or maximize energy dissipation. In a viscoelastic fluid the presence of polymeric stresses removes the geometrical asymmetry constraint, and therefore even symmetric swimmers synchronize. Such synchronization occurs on asymptotically faster time scales than in a Newtonian fluid, and the swimmers evolve into a stable in-phase conformation minimizing the energy dissipated in the surrounding fluid. Furthermore, we show that if we consider flexible sheets, with internal symmetric forcing instead of prescribed kinematics, they deform when interacting with each other through the fluid in such a way as to systematically break the overall waveform symmetry, thereby always evolving to an in-phase conformation where energy dissipation is minimized. These dynamics are shown to be mathematically equivalent to those obtained for prescribed waveforms in viscoelastic fluids, emphasizing the crucial role of flexibility in symmetry-breaking and synchronization - be it that of the fluid, or the swimmers themselves.

Visual information gain and task asymmetry interact in bimanual force coordination and control

This study examined the question of whether and how the influence of visual information on force coordination patterns is dependent on the settings of a task asymmetry constraint. In a bimanual isometric force experiment, the task asymmetry was manipulated via imposing different coefficients on the index finger forces such that the weighted sum of the finger forces matched the target force. The environmental constraint was quantified by the visual performance error and was manipulated through the change of visual gain (number of pixels on the screen representing the unit of force). The constraint arising from the individual was quantified by the bilateral coupling effect (i.e., symmetric force production) between hands. The results revealed improved performance in terms of lower variability and performance error and more complex total force structure with higher visual gain. The influence of visual gain on the force coordination pattern, however, was found to be dependent on the task coefficients imposed on the finger forces. Namely, the force sharing between hands became more symmetric with high visual gain only when the right finger force had the higher coefficient, and an error-compensatory strategy was evident with high gain only when symmetric coefficients were imposed on the two fingers. The findings support the proposition that the motor coordination and control patterns are organized by the interactive influence of different categories of constraints where the functional influence of the information provided is dependent on the motor output.

Topological reversibility and causality in feed-forward networks

Systems whose organization displays causal asymmetry constraints, from evolutionary trees to river basins or transport networks, can often be described in terms of directed paths on a discrete set of arbitrary units including states in state spaces, feed-forward neural nets, the evolutionary history of a given collection of events or the chart of computational states visited along a complex computation. Such a set of paths defines a feed-forward, acyclic network. A key problem associated with these systems involves characterizing their intrinsic degree of path reversibility: given an end node in the graph, what is the uncertainty of recovering the process backwards until the origin? Here, we propose a novel concept, topological reversibility, which is a measure of the complexity of the net that rigorously weights such uncertainty in path dependency, quantifying the minimum amount of information required to successfully reverse a causal path. Within the proposed framework, we also analytically characterize limit cases for both topologically reversible and maximally entropic structures. The relevance of these measures within the context of evolutionary dynamics is highlighted.

Two-dimensional flagellar synchronization in viscoelastic fluids

Experimental studies have demonstrated that spermatozoa synchronize their flagella when swimming in close proximity. In a Newtonian fluid, it was shown theoretically that such synchronization arises passively due to hydrodynamic forces between the two swimmers if their waveforms exhibit a front–back geometrical asymmetry. Motivated by the fact that most biological fluids possess a polymeric microstructure, here we address synchronization in a viscoelastic fluid analytically. Using a two-dimensional infinite sheet model, we show that the presence of polymeric stresses removes the geometrical asymmetry constraint and therefore even symmetric swimmers synchronize. Such synchronization occurs on asymptotically faster time scales than in a Newtonian fluid, and the swimmers are seen to be driven into a stable in-phase conformation minimizing the energy dissipated in the surrounding fluid.

Equilibrium Nonsynchronous Rotation of Titan

A satellite on an eccentric orbit experiences a zero net tidal torque when the rotation is slightly faster than synchronous, if there is no significant permanent asymmetry. Calculations indicate that for Titan this period should be 15.82 to 15.93 days, depending on the tidal dissipation model. This range includes the period recently determined by radar observations. A water-ice highland plateau with a diameter of less than 180 km standing just above the expected hydrocarbon ocean is consistent with both the radar data and the asymmetry constraints.

Cosmological baryon asymmetry constraints on extensions of the standard model

The existence of the baryon asymmetry of the Universe puts strong constraints on extensions of the standard model which violate baryon and/or lepton number. Interactions violating baryon number but conserving lepton number in the early universe could wash away any previously established baryon asymmetry. Interactions which violate lepton number separately (as first discussed by Fukugita and Yanagida), with or without associated violation of baryon number, could combine with non-perturbative baryon and lepton number violating electroweak effects to eradicate the cosmological baryon asymmetry. We derive the constraints on any such interaction of arbitrary dimension arising from the persistence of the cosmological baryon asymmetry. We find, in particular, severe constraints on δB≠0 interactions that could mediate n↔n oscillations or δB≠ δL proton decay, and on interactions that could violate R parity in supersymmetric models. These constraints severely limit the potential observability of n- n oscillations and R-parity violation in present laboratory experiments.

Asymmetry and external noise-induced free energy transduction.

The effect of fluctuations in rate constants on the kinetic behavior of cyclic reacting systems, caused by a fluctuating external parameter, is studied. It is shown (i) that the stochastic properties of the system can be analyzed analytically by using the usual master equation approach when the external parameter is fluctuating with discrete square pulses and (ii) that the system is equivalent to an expanded chemical kinetic system with no fluctuation in rate constants. When applied to a linear four-state cyclic enzyme system, the formalism can be used to prove analytically the finding that an enzyme can extract the free energy from an externally applied fluctuating membrane potential and perform active free energy transduction. The formalism also can be used to assess the asymmetry constraints imposed on the values of the rate constants in order for the model to work.

Symmetrized double-monochromator systems

A system of three triplet lenses is investigated with regard to the trajectory symmetrization in magnetic double-monochromator systems. Double-dispersive and non-dispersive telescopic modes can be realized for mirror-symmetric as well as antisymmetric arrangements without changing the hardware geometry. Beside the symmetry fit certain asymmetry constraints can be adjusted in order to match special phase-space transformation properties. The resulting ion-optical structures are discussed with the aid of geometrical light optics as well as first-order matrix theory.