Issue 13: Syrian Refugee Resettlement and the Role of Local Immigration Partnerships (LIPs) in Ontario, Canada

During the peak of the Syrian refugee “crisis” in 2015 and early 2016, the Canadian Federal Government responded with a push to drastically increase the number of Syrian refugees it planned to resettle. The resulting Syrian Refugee Resettlement Initiative (SRRI) put to the test Local Immigration Partnerships (LIPs), a form of place-based policy that had been in place since 2008 where communities collaborate in the support, development and execution of local immigration and refugee resettlement plans. This issue of Policy Points discusses a study of three LIPs (Hamilton, Ottawa, and Waterloo Region) and their response to the SRRI. The research provides three policy insights relevant to refugee and immigrant community resettlement. Bringing the community into the fold through multi stakeholder tables such as LIPs can coordinate local responses to the resettlement of refugees (policy insight 1). LIPs must be embedded in the local community and include leaders and personnel able to build and enhance local stakeholder networks (policy insight 2). Finally, it is key to involve LIPs in communication channels during mass resettlement events (policy insight 3). Policy action under points 2 and 3 will in turn enable LIPs to effectively support refugee resettlement at the local level. The experience of the three Ontario LIPs in this study is relevant to existing and potential new LIPs, but it also offers a unique place-based policy approach to engaging local communities in resettlement at other locations and scales

Method for Computationally Efficient Design of Dielectric Laser Accelerators

Dielectric microstructures have generated much interest in recent years as a means of accelerating charged particles when powered by solid state lasers. The acceleration gradient (or particle energy gain per unit length) is an important figure of merit. To design structures with high acceleration gradients, we explore the adjoint variable method, a highly efficient technique used to compute the sensitivity of an objective with respect to a large number of parameters. With this formalism, the sensitivity of the acceleration gradient of a dielectric structure with respect to its entire spatial permittivity distribution is calculated by the use of only two full-field electromagnetic simulations, the original and adjoint. The adjoint simulation corresponds physically to the reciprocal situation of a point charge moving through the accelerator gap and radiating. Using this formalism, we perform numerical optimizations aimed at maximizing acceleration gradients, which generate fabricable structures of greatly improved performance in comparison to previously examined geometries.Comment: 13 pages, 4 figure

Resonant-tunnelling-assisted crossing for subwavelength plasmonic slot waveguides

We theoretically investigate the properties of crossing for two perpendicular subwavelength plasmonic slot waveguides. We show that, when encountering nano intersection, the crosstalk for the direct crossing is around 25%, almost same as throughout. In terms of symmetry considerations and resonant-tunnelling effect, we design compact cavity-based structures. Our results show that the crosstalk is eliminated and the throughput reaches the unity on resonance. Simulations results are in agreement with those from the coupled-model theory. When taking into account of the material loss, due to the unchanged symmetry properties of the modes, the crosstalk is still suppressed. Our results may open a way to construct nanoscale crossings for high-density nanoplasmonic integration circuits

Using phase-change materials to switch the direction of reflectionless light propagation in non-PT-symmetric structures

We introduce a non-parity-time-symmetric three-layer structure, consisting of a gain medium layer sandwiched between two phase-change medium layers for switching of the direction of reflectionless light propagation. We show that for this structure unidirectional reflectionlessness in the forward direction can be switched to unidirectional reflectionlessness in the backward direction at the optical communication wavelength by switching the phase-change material Ge2Sb2Te5 (GST) from its amorphous to its crystalline phase. We also show that it is the existence of exceptional points for this structure with GST in both its amorphous and crystalline phases which leads to unidirectional reflectionless propagation in the forward direction for GST in its amorphous phase, and in the backward direction for GST in its crystalline phase. Our results could be potentially important for developing a new generation of compact active free-space optical devices. We also show that phase-change materials can be used to switch photonic nanostructures between cloaking and superscattering regimes at mid-infrared wavelengths. More specifically, we investigate the scattering properties of subwavelength three-layer cylindrical structures in which the material in the outer shell is the phase-change material GST. We first show that, when GST is switched between its amorphous and crystalline phases, properly designed electrically small structures can switch between resonant scattering and cloaking invisibility regimes. The contrast ratio between the scattering cross sections of the cloaking invisibility and resonant scattering regimes reaches almost unity. We then also show that larger, moderately small cylindrical structures can be designed to switch between superscattering and cloaking invisibility regimes, when GST is switched between its crystalline and amorphous phases. The contrast ratio between the scattering cross sections of cloaking invisibility and superscattering regimes can be as high as ~ 93%. Our results could be potentially important for developing a new generation of compact reconfigurable optical devices

Neutrality versus materiality: a thermodynamic theory of neutral surfaces

In this paper, a theory for constructing quasi-neutral density variables $\gamma$ directly in thermodynamic space is formulated, which is based on minimising the absolute value of a purely thermodynamic quantity $J_n$. Physically, $J_n$ has a dual dynamic/thermodynamic interpretation as the quantity controlling the energy cost of adiabatic and isohaline parcel exchanges on material surfaces, as well as the dependence of in-situ density on spiciness, in a description of water masses based on $\gamma$, spiciness and pressure. Mathematically, minimising $|J_n|$ in thermodynamic space is showed to be equivalent to maximising neutrality in physical space. The physics of epineutral dispersion is also reviewed and discussed. It is argued, in particular, that epineutral dispersion is best understood as the aggregate effect of many individual non-neutral stirring events, so that it is only the net displacement aggregated over many events that is approximately neutral. This new view resolves an apparent paradox between the focus in neutral density theory on zero-buoyancy motions and the overwhelming evidence that lateral dispersion in the ocean is primarily caused by non-zero buoyancy processes such as tides, residual currents and sheared internal waves. The efficiency by which a physical process contributes to lateral dispersion can be characterised by its energy signature, with those processes releasing available potential energy (negative energy cost) being more efficient than purely neutral processes with zero energy cost. Although the latter mechanism occurs in the wedge of instability, its source of energy is not baroclinicity but the coupling between thermobaricity and density-compensated temperature/salinity anomalies. Such a mechanism, which can only exist in a salty ocean, is speculated to be important for dissipating spiciness anomalies and neutral helicity. The paper also discusses potential conceptual difficulties with the use of neutral rotated diffusion tensors in numerical ocean models, as well as with the construction of neutral density variables in physical space. It also emphasises the irreducible character of thermobaric forces in the ocean. These are argued to be the cause for adiabatic thermobaric dianeutral dispersion, and to forbid the existence of density surfaces along which fluid parcels can be exchanged without experiencing buoyancy forces, in contrast to what is assumed in the theory of neutral surfaces

Double-component convection due to different boundary conditions in an infinite slot diversely oriented to the gravity

Onset of small-amplitude oscillatory and both small- and finite-amplitude steady double-component convection arising due to component different boundary conditions in an infinite slot is studied for various slot orientations to the gravity. The main focus is on two compensating background gradients of the components. The physical mechanisms underlying steady and oscillatory convection are analyzed from the perspective of a universally consistent understanding of the effects of different boundary conditions.Comment: V2: Submitted to and published in Annals of Physics. 59 manuscript pages, 15 figures (occupying 21 pages). The full abstract is on the first page. Nonessential modifications/enhancements in the presentation (more compact presentation of the text and figure data, some style improvements, etc.

Ultracompact plasmonic racetrack resonators in metal-insulator-metal waveguides

Among various plasmonic waveguides, the metal-insulator-metal (MIM) type is the most promising for true subwavelength photonic integration. To date, many photonic devices based on MIM waveguides have been investigated, including resonators. However, most of the reported MIM ring resonators suffer from low extinction ratios. In this paper, we present a comprehensive analysis of the intrinsic reasons for the low performance of MIM ring resonators, and give the analytical transmission relation for a universal all-pass ring resonator which has coupling loss. Based on the analysis we propose the plasmonic racetrack resonators in MIM waveguides and show that the performance can be greatly improved.Comment: 17 pages, 4 figure

Tooth-shaped plasmonic waveguide filters with nanometeric sizes

A novel nanometeric plasmonic filter in a tooth-shaped Metal-Insulator-Metal waveguide is proposed and demonstrated numerically. An analytic model based on the scattering matrix method is given. The result reveals that the single tooth-shaped filter has a wavelength filtering characteristic and an ultra-compact size in the length of a few hundred nanometers, compared to grating-like SPPs filters. Both analytic and simulation results show that the wavelength of the trough of the transmission has linear and nonlinear relationships with the tooth depth and the tooth width, respectively. The waveguide filter could be utilized to develop ultra-compact photonic filters for high integration.Comment: 16 pages, 5 figure

Numerical Modeling of a Teeth-shaped Nano-plasmonic Waveguide Filter

In this paper, tooth-shaped and multiple-teeth-shaped plasmonic filters in the metal-insulator-metal (MIM) waveguides are demonstrated numerically. By introducing a three-port waveguide splitter, a modified model based on the multiple-beam-interference and the scattering matrix is given. The ransmittance spectrum as a function of teeth width, depth, period and period number are respectively addressed. The result shows the new structure not only performs the filtering function as well as MIM grating-like structures, but also is of submicrometer size for ultra-high integration and relatively easy fabrication.Comment: 21pages, 7 figure