Extended dynamical density functional theory for colloidal mixtures with temperature gradients

In the past decade, classical dynamical density functional theory (DDFT) has been developed and widely applied to the Brownian dynamics of interacting colloidal particles. One of the possible derivation routes of DDFT from the microscopic dynamics is via the Mori-Zwanzig-Forster projection operator technique with slowly varying variables such as the one-particle density. Here, we use the projection operator approach to extend DDFT into various directions: first, we generalize DDFT toward mixtures of $n$ different species of spherical colloidal particles. We show that there are in general nontrivial cross-coupling terms between the concentration fields and specify them explicitly for colloidal mixtures with pairwise hydrodynamic interactions. Secondly, we treat the energy density as an additional slow variable and derive formal expressions for an extended DDFT containing also the energy density. The latter approach can in principle be applied to colloidal dynamics in a nonzero temperature gradient. For the case without hydrodynamic interactions the diffusion tensor is diagonal, while thermodiffusion -- the dissipative cross-coupling term between energy density and concentration -- is nonzero in this limit. With finite hydrodynamic interactions also cross-diffusion coefficients assume a finite value. We demonstrate that our results for the extended DDFT contain the transport coefficients in the hydrodynamic limit (long wavelengths, low frequencies) as a special case.Comment: 15 pages, 1 figur

Microscopic approach to entropy production

It is a great challenge of nonequilibrium statistical mechanics to calculate entropy production within a microscopic theory. In the framework of linear irreversible thermodynamics, we combine the Mori-Zwanzig-Forster projection operator technique with the first and second law of thermodynamics to obtain microscopic expressions for the entropy production as well as for the transport equations of the entropy density and its time correlation function. We further present a microscopic derivation of a dissipation functional from which the dissipative dynamics of an extended dynamical density functional theory can be obtained in a formally elegant way.Comment: 10 page

The Eckhaus and the Benjamin-Feir instability near a weakly inverted bifurcation

We investigate how the criteria for two prototype instabilities in one dimensional pattern forming systems, namely for the Eckhaus instability and for the Benjamin-Feir instability, change as one goes from a continuous bifurcation, to a spatially periodic or spatially and/or time periodic state, to the corresponding weakly inverted, i.e., hysteretic, cases. We also give the generalization to two dimensional patterns in systems with anisotropy as they arise from hydrodynamic instabilities in nematic liquid crystals

Polar liquid crystals in two spatial dimensions: the bridge from microscopic to macroscopic modeling

Two-dimensional polar liquid crystals have been discovered recently in monolayers of anisotropic molecules. Here, we provide a systematic theoretical description of liquid-crystalline phases for polar particles in two spatial dimensions. Starting from microscopic density functional theory, we derive a phase-field-crystal expression for the free-energy density which involves three local order-parameter fields, namely the translational density, the polarization, and the nematic order parameter. Various coupling terms between the order-parameter fields are obtained which are in line with macroscopic considerations. Since the coupling constants are brought into connection with the molecular correlations, we establish a bridge from microscopic to macroscopic modeling. Our theory provides a starting point for further numerical calculations of the stability of polar liquid-crystalline phases and is also relevant for modeling of microswimmers which are intrinsically polar.Comment: 11 page

Derivation of a three-dimensional phase-field-crystal model for liquid crystals from density functional theory

Using a generalized order parameter gradient expansion within density functional theory, we derive a phase-field-crystal model for liquid crystals composed by apolar particles in three spatial dimensions. Both the translational density and the orientational direction and ordering are included as order parameters. Different terms involving gradients in the order parameters in the resulting free energy functional are compared to the macroscopic Ginzburg-Landau approach as well as to the hydrodynamic description for liquid crystals. Our approach provides microscopic expressions for all prefactors in terms of the particle interactions. Our phase-field-crystal model generalizes the conventional phase-field-crystal model of spherical particles to orientational degrees of freedom and can be used as a starting point to explore phase transitions and interfaces for various liquid-crystalline phases.Comment: 7 page

Microscopic and macroscopic theories for the dynamics of polar liquid crystals

We derive and analyze the dynamic equations for polar liquid crystals in two spatial dimensions in the framework of classical dynamical density functional theory (DDFT). Translational density variations, polarization, and quadrupolar order are used as order-parameter fields. The results are critically compared with those obtained using the macroscopic approach of time-dependent Ginzburg-Landau (GL) equations for the analogous order-parameter fields. We demonstrate that for both the microscopic DDFT and the macroscopic GL approach the resulting dissipative dynamics can be derived from a dissipation function. We obtain microscopic expressions for all diagonal contributions and for many of the cross-coupling terms emerging from a GL approach. Thus we establish a bridge between molecular correlations and macroscopic modeling for the dissipative dynamics of polar liquid crystals.Comment: 10 page

Europeanisation of health systems : a qualitative study of domestic actors in a small state

Background: Health systems are not considered to be significantly influenced by European Union (EU) policies given the subsidiarity principle. Yet, recent developments including the patients’ rights and cross-border directive (2011/24 EU), as well as measures taken following the financial crisis, appear to be increasing the EU’s influence on health systems. The aim of this study is to explore how health system Europeanisation is perceived by domestic stakeholders within a small state. Methods: A qualitative study was conducted in the Maltese health system using 33 semi-structured interviews. Inductive analysis was carried out with codes and themes being generated from the data. Results: EU membership brought significant public health reforms, transformation in the regulation of medicines and development of specialised training for doctors. Health services financing and delivery were primarily unaffected. Stakeholders positively perceived improvements to the policy-making process, networking opportunities and capacity building as important benefits. However, the administrative burden and the EU’s tendency to adopt a ‘one size fits all’ approach posed considerable challenges. The lack of power and visibility for health policy at the EU level is a major disappointment. A strong desire exists for the EU to exercise a more effective role in ensuring access to affordable medicines and preventing non-communicable diseases. However, the EU’s interference with core health system values is strongly resisted. Conclusions: Overall domestic stakeholders have a positive outlook regarding their health system Europeanisation experience. Whilst welcoming further policy developments at the EU level, they believe that improved consideration must be given to the specificities of small health systems.peer-reviewe

Magneto-optic dynamics in a ferromagnetic nematic liquid crystal

We investigate dynamic magneto-optic effects in a ferromagnetic nematic liquid crystal experimentally and theoretically. Experimentally we measure the magnetization and the phase difference of the transmitted light when an external magnetic field is applied. As a model we study the coupled dynamics of the magnetization, M, and the director field, n, associated with the liquid crystalline orientational order. We demonstrate that the experimentally studied macroscopic dynamic behavior reveals the importance of a dynamic cross-coupling between M and n. The experimental data are used to extract the value of the dissipative cross-coupling coefficient. We also make concrete predictions about how reversible cross-coupling terms between the magnetization and the director could be detected experimentally by measurements of the transmitted light intensity as well as by analyzing the azimuthal angle of the magnetization and the director out of the plane spanned by the anchoring axis and the external magnetic field. We derive the eigenmodes of the coupled system and study their relaxation rates. We show that in the usual experimental set-up used for measuring the relaxation rates of the splay-bend or twist-bend eigenmodes of a nematic liquid crystal one expects for a ferromagnetic nematic liquid crystal a mixture of at least two eigenmodes.Comment: 20 pages, 23 figures, 42 reference

Social Media for Public Health: An Exploratory Policy Analysis

Background: To accomplish the aims of public health practice and policy today, new forms of communication and education are being applied. Social media are increasingly relevant for public health and used by various actors. Apart from benefits, there can also be risks in using social media, but policies regulating engagement in social media is not well researched. This study examined European public health-related organizations' social media policies and describes the main components of existing policies. Methods: This research used a mixed methods approach. A content analysis of social media policies from European institutions, non-government organizations (NGOs) and social media platforms was conducted. Next, individuals responsible for social media in their organization or projects completed a survey about their social media policy. Results: Seventy-five per cent of institutions, NGOs and platforms had a social media policy available. The primary aspects covered within existing policies included data and privacy protection, intellectual property and copyright protection and regulations for the engagement in social media. Policies were intended to regulate staff use, to secure the liability of the institution and social responsibility. Respondents also stressed the importance of self-responsibility when using social media. Conclusions: This study of social media policies for public health in Europe provides a first snapshot of the existence and characteristics of social media policies among European health organizations. Policies tended to focus on legal aspects, rather than the health of the social media user. The effect of such policies on social media adoption and usage behaviour remains to be examine