Level set methods for gradient-free optimization of metasurface arrays.

Global optimization techniques are increasingly preferred over human-driven methods in the design of electromagnetic structures such as metasurfaces, and careful construction and parameterization of the physical structure is critical in ensuring computational efficiency and convergence of the optimization algorithm to a globally optimal solution. While many design variables in physical systems take discrete values, optimization algorithms often benefit from a continuous design space. This work demonstrates the use of level set functions as a continuous basis for designing material distributions for metasurface arrays and introduces an improved parameterization which is termed the periodic level set function. We explore the use of alternate norms in the definition of the level set function and define a new pseudo-inverse technique for upsampling basis coefficients with these norms. The level set method is compared to the fragmented parameterization and shows improved electromagnetic responses for two dissimilar cost functions: a narrowband objective and a broadband objective. Finally, we manufacture an optimized level set metasurface and measure its scattering parameters to demonstrate real-world performance.

Extraction of Dielectric Permittivity from Atomistic Molecular Dynamics Simulations and Microwave Measurements.

The design of new biotechnology depends on the prediction and measurement of the electrical properties of biomolecules. The dielectric permittivity, in particular, is highly important for the design of microwave systems for diagnostics, yet this property is rarely explicitly targeted during the development of biomolecular force fields for molecular dynamics (MD) simulations. In order to explore the ability of existing force fields to reproduce the frequency-dependent permittivity, we carried out MD simulations of various aqueous solutions, including pure water, isopropyl alcohol, alanine, and the protein ubiquitin. The TIP3P, TIP4P, TIP4P/ε, and SWM4-NDP water models were used along with the CHARMM36m and Drude protein force fields. An experimental setup using a truncated coaxial line was created to measure the permittivity of the same solutions to check for measure-model agreement. We found that one of the nonpolarizable force fields (TIP4P/ε + CHARMM36m) and the polarizable force fields (SWM4-NDP + Drude) closely agree with experimental results. This demonstrates the strength of the tuned TIP4P/ε water model, as well as the physical validity of polarizable force fields in capturing dielectric permittivity. This represents an important step toward the predictive design of biosensors.

A randomized controlled trial of the effectiveness of handheld computers for improving everyday memory functioning in patients with memory impairments after acquired brain injury.

OBJECTIVE: To determine the effectiveness of personal digital assistant devices on achievement of memory and organization goals in patients with poor memory after acquired brain injury. DESIGN: Assessor blinded randomized controlled trial. SETTING: Specialist brain injury rehabilitation hospital (inpatients and outpatients). PARTICIPANTS: Adults with acquired brain impairments (85% traumatic brain injury; aged ≥17 years) who were assessed as having functional memory impairment on the Rivermead Behavioural Memory Test (General Memory Index). INTERVENTIONS: Training and support to use a personal digital assistant for eight weeks to compensate for memory failures by an occupational therapist. The control intervention was standard rehabilitation, including use of non-electronic memory aids. MAIN OUTCOME MEASURES: Goal Attainment Scale which assessed achievement of participants' daily memory functioning goals and caregiver perception of memory functioning; and General Frequency of Forgetting subscale of the Memory Functioning Questionnaire administered at baseline (pre-randomization) and post intervention (eight weeks later). RESULTS: Forty-two participants with memory impairment were recruited. Use of a personal digital assistant led to greater achievement of functional memory goals (mean difference 1.6 (95% confidence interval (CI) 1.0 to 2.2), P = 0.0001) and improvement on the General Frequency of Forgetting subscale (mean difference 12.5 (95% CI 2.0 to 22.9), P = 0.021). CONCLUSIONS: Occupational therapy training in the use of a handheld computer improved patients' daily memory function more than standard rehabilitation.