Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating.ope

Redefining what It means to be a teacher through professional standards:Implications for continuing teacher education

This article connects with an international debate around the place of professional standards in educational policy targeted at enhancing teacher quality, with associated implications for continuing teacher education. Scotland provides a fertile context for discussion, having developed sets of professional standards in response to a recent national review of career-long teacher education. That review called for a reprofessionalisation of the teaching profession and the revision of the standards was an element of this process. Scotland is utilised as a lens through which one country’s response to international trends is viewed, with a focus on ‘teacher leadership’ and ‘practitioner enquiry’ as policy endorsed sets of practices. The analysis demonstrates the complex and contested nature of these terms and the tensions posed between the need to meet professional standards as part of teacher education and aspirational dimensions of the current policy project of reprofessionalisation. The article concludes by considering the implications for continuing teacher education

Professional learning for distributed leadership:Primary headteachers’ perspectives

This article draws from a small-scale study of headteachers motivated to positively impact on the quality of pupil experience by involving all staff in a distributed perspective on leadership. Each headteacher perceived leadership as involving learned processes requiring support and experience, expending considerable effort in providing a fertile environment for learning about its practice. This perspective developed from their personal experience of challenging established leadership orthodoxies prior to and since appointment to headship. The article explores the impact of formal work-based postgraduate leadership preparation and experiential professional learning on each headteacher’s understandings of distributed leadership and its practice. It then explores the ways in which they supported the professional learning of staff. The article concludes by suggesting that headteachers and staff encounter a range of challenges in developing school practices inherent in distributed leadership and can benefit from ongoing support with informed reflection on practice beyond initial preparation for headship

The shifting discourses of educational leadership:International trends and Scotland’s response

Increasing emphasis has been placed on leadership within educational theory, policy and practice. Drawing on a wide range of academic literature and policy documents, this paper explores how the discourse of leadership has shifted and for what purposes. The authors are critical of the lack of conceptual underpinning for that discourse, evident both nationally and internationally, and they identify key issues that the teaching profession has been left to try to understand and make sense of. They caution that, despite attempts to align contemporary policy developments to position leadership as inherent in the role of every teacher, flaws in the conceptualisation of leadership, and particularly in favoured forms such as ‘distributed leadership’ and ‘teacher leadership’, pose significant challenges to a serious attempt to ‘reprofessionalise’ teachers. Contemporary developments in Scottish education are referred to, exemplifying key tensions inherent in translating international trends into practice

Sulfonation distribution in sulfonated polystyrene ionomers measured by MALDI-ToF MS

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS) was used to quantify the sulfonation level and sulfonation distribution of sulfonated polystyrene ionomers prepared by homogeneous solution sulfonation. The sulfonation levels obtained by MALDI-ToF MS and acid–base titration were compared, and the sulfonate distributions determined by MALDI-ToF MS were compared with theoretical random distributions. The results indicate that the sulfonation reaction used produces a sample with a random sulfonate distribution

Multidimensional Mass Spectrometry Coupled with Separation by Polarity or Shape for the Characterization of Sugar-Based Nonionic Surfactants

Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were interfaced with ultra-performance liquid chromatography (UPLC) and ion mobility (IM) separation to characterize a complex nonionic surfactant, consisting of a methylated glucose core (glucam) conjugated with poly­(ethylene oxide) (PEO_<i>n</i>) branches that were partially esterified with stearic acid to form ethoxylated glucam (PEO_<i>n</i>-glucam) stearates. Reverse-phase LC-MS afforded fast separation according to polarity into five major fractions. Accurate mass measurements of the ions in the mass spectra extracted from these fractions enabled conclusive identification of six components in the surfactant, including PEO_<i>n</i>-glucam mono-, di-, and tristearates as well as free and esterified PEO_<i>n</i> as byproducts. MS/MS experiments provided corroborating evidence for the fatty acid content in each fraction based on the number of stearic acid losses observed. With IM-MS, the total surfactant ions were separated according to charge and shape into four distinct bands. Extracted mass spectra confirmed the presence of two disaccharide stearates in the surfactant, which were undetectable by LC-MS. PEO_<i>n</i>-glucam tristearates were, however, not observed upon IM-MS. Hence, LC-MS and IM-MS unveiled complementary compositional insight. With each method, certain components were particularly well separated from other ingredients (by either polarity or shape), to be detected with confidence. Consequently, combined LC-MS and IM-MS offer a superior approach for the characterization of surfactants and other amphiphilic polymers and for the differentiation of similarly composed amphiphilic blends. It is finally noteworthy that NH₄⁺ charges minimized chemical noise in MS mode and Li⁺ charges maximized the fragmentation efficiency in MS/MS mode