Long-lived Giant Number Fluctuations in a Swarming Granular Nematic

Coherently moving flocks of birds, beasts or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid-crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the Central Limit Theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.Comment: This is the author's version of the work. It is posted here by permission of the AAAS. The definitive version is to appear in SCIENC

Twisted polarization domains and their dynamics

We provide a theoretical investigation of optical Poincar\'e beams that exhibit interwinding chiral polarized domains upon propagation. We employ both analytical and numerical methods in order to investigate this phenomenon. Specifically, we introduce the theoretical framework that elucidates the formation and spiraling behavior of chiral polarized domains of light. Additionally, we define dynamic quantities that help us understand and quantify the angular motion of these domains. We apply this method to cylindrically symmetric optical beams, thereby unveiling their distinct radial and longitudinal propagation dynamics

Scalable numerical approach for the steady-state ab initio laser theory

We present an efficient and flexible method for solving the non-linear lasing equations of the steady-state ab initio laser theory. Our strategy is to solve the underlying system of partial differential equations directly, without the need of setting up a parametrized basis of constant flux states. We validate this approach in one-dimensional as well as in cylindrical systems, and demonstrate its scalability to full-vector three-dimensional calculations in photonic-crystal slabs. Our method paves the way for efficient and accurate simulations of lasing structures which were previously inaccessible.Comment: 17 pages, 8 figure

PT\mathcal{PT}-Symmetric Periodic Optical Potentials

In quantum theory, any Hamiltonian describing a physical system is mathematically represented by a self-adjoint linear operator to ensure the reality of the associated observables. In an attempt to extend quantum mechanics into the complex domain, it was realized few years ago that certain non-Hermitian parity-time ($\mathcal{PT}$) symmetric Hamiltonians can exhibit an entirely real spectrum. Much of the reported progress has been remained theoretical, and therefore hasn't led to a viable experimental proposal for which non Hermitian quantum effects could be observed in laboratory experiments. Quite recently however, it was suggested that the concept of $\mathcal{PT}$-symmetry could be physically realized within the framework of classical optics. This proposal has, in turn, stimulated extensive investigations and research studies related to $\mathcal{PT}$-symmetric Optics and paved the way for the first experimental observation of $\mathcal{PT}$-symmetry breaking in any physical system. In this paper, we present recent results regarding $\mathcal{PT}$-symmetric Optic

Rationale and Design of an Online Educational Program Using Game-Based Learning to Improve Nutrition and Physical Activity Outcomes Among University Students in the United Kingdom.

OBJECTIVE: To assess the impact of an online game-based educational program on nutrition knowledge and dietary and physical activity habits among university students in the United Kingdom. DESIGN: Randomized controlled trial with pre- and postintervention comparisons. SETTING: Two higher education settings in London, UK. SUBJECTS: Current undergraduate and postgraduate students of two universities (n = 88) aged 18-34 years are randomly allocated to an intervention (n = 44) or a control group (n = 44). INTERVENTION: The intervention group will receive access to an educational website and online quizzes with gamification elements, including information about healthy eating and physical activity. The control group will receive no information. Duration of the intervention will be 10 weeks. MEASURES OF OUTCOME: Primary outcome is nutrition knowledge. Secondary outcomes include dietary and activity habits. Nutrition knowledge and dietary and activity habits will be assessed using questionnaires. Weekly steps will be counted using pedometers. Assessment of anthropometric and metabolic risk factors will take place. ANALYSIS: Quantitative analysis will investigate changes in nutrition knowledge between the two groups of the study population. Linear regression analysis will be used, if the data follow the normal distribution (otherwise binomial regression analysis), to examine whether field of study, residence status, body mass index (BMI), and demographic factors affect nutrition knowledge. Associations between changes in knowledge and dietary and physical activity behavior will be assessed by correlations. CONCLUSIONS/IMPLICATIONS: The study will provide insights with regard to the design and use of online game-playing as a cost-effective approach to improve nutritional knowledge among university students