Financial and Socio-Economic Effects of Investment in the Context of Dog Population Management.

The modern world faces serious challenges associated with the presence of stray dogs on the streets, especially in urban areas. Vardar Planning Region in North Macedonia, which consists of nine municipalities, experiences such challenges. According to current reports, the number of stray dogs on the streets of cities in this region has increased, which has resulted in an increase in the number of dog attacks on residents. As the existing capacities are small in the registered shelters, we considered the possibility of building a new shelter for stray dogs to meet the needs of this region. The goal of our paper is the evaluation of the financial and socio-economic justifications for the construction of a shelter for stray dogs in the Vardar Planning Region (VPR). The results of the financial justification analysis show that the project does not provide satisfactory financial results. Namely, the Financial Net Present Value (FNPV) is negative, with a value of EUR 75,291. The Financial Internal Rate of Return (FIRR) is 0.57%, lower than the discount rate, which is not acceptable for a private investor. The Financial Benefit-Cost Ratio (FB/CR) of this project is 0.925, suggesting that the total discounted costs are greater than the total discounted revenues. On the other hand, the expected socio-economic benefits from this project are multifaceted, including savings in stray dog bite costs, savings in the cost of traffic accidents caused by stray dogs, and savings in the treatment of diseases caused by stray dogs. The results of the economic analysis show that this investment has full socio-economic justification and that it should be implemented. The Economic Net Present Value (ENPV) is positive and amounts to EUR 789,916. The Economic Internal Rate of Return (EIRR) is 25.94% and the Economic Benefit-Cost Ratio (EB/CR) amounts to 1.90, i.e., greater than 1. The results of the sensitivity analysis also confirm the justification for the realization of this project.

Collective motion of active particles exhibiting non-reciprocal orientational interactions.

We present a Brownian dynamics study of a 2D bath of active particles interacting among each other through usual steric interactions and, additionally, via non-reciprocal avoidant orientational interactions. We motivate them by the fact that the two flagella of the alga Chlamydomonas interact sterically with nearby surfaces such that a torque acts on the alga. As expected, in most cases such interactions disrupt the motility-induced particle clustering in active baths. Surprisingly, however, we find that the active particles can self-organize into collectively moving flocks if the range of non-reciprocal interactions is close to that of steric interactions. We observe that the flocking motion can manifest itself through a variety of structural forms, spanning from single dense bands to multiple moderately-dense stripes, which are highly dynamic. The flocking order parameter is found to be only weakly dependent on the underlying flock structure. Together with the variance of the local-density distribution, one can clearly group the flocking motion into the two separate band and dynamic-stripes states.

Oscillatory active microrheology of active suspensions.

Using the method of Brownian dynamics, we investigate the dynamic properties of a 2d suspension of active disks at high Péclet numbers using active microrheology. In our simulations the tracer particle is driven either by a constant or an oscillatory external force. In the first case, we find that the mobility of the tracer initially appreciably decreases with the external force and then becomes approximately constant for larger forces. For an oscillatory driving force we find that the dynamic mobility shows a quite complex behavior-it displays a highly nonlinear behavior on both the amplitude and frequency of the driving force. In the range of forces studied, we do not observe a linear regime. This result is important because it reveals that a phenomenological description of tracer motion in active media in terms of a simple linear stochastic equation even with a memory-mobility kernel is not appropriate, in the general case.

Transverse-size critical exponent of directed percolation from Yang-Lee zeros of survival probability.

By using transfer-matrix method we compute survival probabilities for the directed percolation problem on strips of a square lattice, and get very precise estimates of their Yang-Lee zeros lying closest to the real axis in the complex plane of occupation probability. This allows us to get accurate values for transverse-size critical exponent and percolation threshold.

Active Tuning of Synaptic Patterns Enhances Immune Discrimination.

Immune cells learn about their antigenic targets using tactile sense: a self-organized motif named immunological synapse forms between an immune cell and an antigen-presenting cell (APC) during recognition. Via synapses, immune cells apply mechanical pulling forces to selectively extract antigen (Ag) from APCs. Curiously, depending on its stage of development, a B lymphocyte exhibits distinct synaptic patterns and uses force at different strength and timing, which appears to strongly impact its ability to distinguish Ag affinities. We use a statistical-mechanical model to study how the experimentally observed synaptic architectures can originate from normal cytoskeletal forces coupled to the lateral organization of mobile receptors, and show how this active regulation scheme, collective in nature, may enhance the efficiency and capacity of discrimination.

Pore emptying transition during nucleation in hydrophobic nanopores.

Using the 2D Ising model we study the generic properties of nucleation in hydrophobic nanopores. To explore the pathways to nucleation of a spin-up phase from a metastable spin-down phase we perform umbrella sampling and transition path sampling simulations. We find that for narrow pores the nucleation occurs on the surface outside the pore. For wide pores the nucleation starts in the pore, and continues outside the filled pore. Intriguingly, we observe a pore emptying transition for a range of intermediate pore widths: a pre-critical nucleus fills the pore, continues to expand outside of the filled pore, but then suddenly gets expelled from the pore before reaching its critical size.

Numerical comparison of a constrained path ensemble and a driven quasisteady state.

We investigate the correspondence between a nonequilibrium ensemble defined via the distribution of phase-space paths of a Hamiltonian system and a system driven into a steady state by nonequilibrium boundary conditions. To discover whether the nonequilibrium path ensemble adequately describes the physics of a driven system, we measure transition rates in a simple one-dimensional model of rotors with Newtonian dynamics and purely conservative interactions. We compare those rates with known properties of the nonequilibrium path ensemble. In doing so, we establish effective protocols for the analysis of transition rates in nonequilibrium quasisteady states. Transition rates between potential wells and also between phase-space elements are studied and found to exhibit distinct properties, the more coarse-grained potential wells being effectively further from equilibrium. In all cases the results from the boundary-driven system are close to the path-ensemble predictions, but the question of equivalence of the two remains open.

Optomechanical elastomeric engine.

Nematic elastomers contract along their director when heated or illuminated (in the case of photoelastomers). We present a conceptual design for an elastomer-based engine to extract mechanical work from heat or light. The material parameters and the geometry of such an engine are explored, and it is shown that its efficiency can go up to 20%.

Photodynamics of stress in clamped nematic elastomers.

We describe the complex time dependence of the buildup of force exerted by a clamped photoelastomer under illumination. Nonlinear (non-Beer) absorption leads to a bleaching wave of a significant cis isomer dye concentration deeply penetrating the solid with a highly characteristic dynamics. We fit our experimental response at one temperature to obtain material parameters. Force-time data can be matched at all other temperatures with no fitting required; our model provides a universal description of this unusual dynamics. The description is unambiguous since these are clamped systems where gross polymer motion is suppressed as a possible source of anomalous dynamics. Future experiments are suggested.

Theory of photoferroelectric response in SmC* liquids.

We are concerned with the modification of liquid crystalline and polar order in chiral smectic C liquids by illumination. In particular we show that spatial non-uniformity of order and electric polarization due to light absorption and also dynamics can be complex. The variation of polarization with temperature, while illuminated, is modified from that assuming uniformity. The dynamics is shown to depend on propagating fronts of photoconversion penetrating the sample. Apparent changes of ferroelectric polarization with illumination will be shown to be underestimated due to non-uniformity.