Real-time observation of local strain effects on nonvolatile ferroelectric memory storage mechanisms.

We use in situ transmission electron microscopy to directly observe, at high temporal and spatial resolution, the interaction of ferroelectric domains and dislocation networks within BiFeO3 thin films. The experimental observations are compared with a phase field model constructed to simulate the dynamics of domains in the presence of dislocations and their resulting strain fields. We demonstrate that a global network of misfit dislocations at the film-substrate interface can act as nucleation sites and slow down domain propagation in the vicinity of the dislocations. Networks of individual threading dislocations emanating from the film-electrode interface play a more dramatic role in pinning domain motion. These dislocations may be responsible for the domain behavior in ferroelectric thin-film devices deviating from conventional Kolmogorov-Avrami-Ishibashi dynamics toward a Nucleation Limited Switching model.

Gating of single-layer graphene with single-stranded deoxyribonucleic acids.

Patterning of biomolecules on graphene layers could provide new avenues to modulate their electrical properties for novel electronic devices. Single-stranded deoxyribonucleic acids (ssDNAs) are found to act as negative-potential gating agents that increase the hole density in single-layer graphene. Current-voltage measurements of the hybrid ssDNA/graphene system indicate a shift in the Dirac point and "intrinsic" conductance after ssDNA is patterned. The effect of ssDNA is to increase the hole density in the graphene layer, which is calculated to be on the order of 1.8 x 10(12) cm(-2). This increased density is consistent with the Raman frequency shifts in the G-peak and 2D band positions and the corresponding changes in the G-peak full width at half maximum. Ab initio calculations using density functional theory rule out significant charge transfer or modification of the graphene band structure in the presence of ssDNA fragments.

Population indices measuring health outcomes: A scoping review.

BACKGROUND: Population health indices such as disability adjusted life years (DALY) and quality adjusted life years (QALY) are often used in an effort to measure health of populations and identify areas of concern that require interventions. There has been an increase of number of population health indices since the last review published more than a decade ago. Therefore, this study aims to provide an overview of existing population health indices and examine the methods used to develop them. METHODS: The search was conducted across three databases: PubMed, CINAHL and Emerald using four key concepts: 'health', 'index', 'context', 'develop', which was supplemented with Google searching and reference scanning. A researcher screened the titles, abstracts and subsequently full texts and confirmed the findings with the research team at each stage. Data charting was performed according to the included publications and identified indices. The collation was performed by describing the indices and made observation on its development method using a priori framework consist of four processes: underpinning theory, model or framework; data selection and processing; formation of index; testing of index. RESULTS: Twenty-six publications describing population health indices were included, and 27 indices were identified. These indices covered the following health topics: overall health outcomes (n = 15), outcomes for specific health topics (n = 4), diseases outcome (n = 6), assist health resource allocation for priority minority subgroup or geographic area (n = 4), quality of health or health care (n = 2). Twenty-one indices measure health for general populations while six measure defined subpopulations. Fourteen of the indices reported at least one of the development processes according to the a priori framework: underpinning theory, model or framework (n = 7); data selection and processing (n = 8); formation of index (n = 12); testing of index (n = 9). CONCLUSIONS: Few population health indices measure specific health topics or health of specific sub-population. There is also a lack of usage of theories, models or framework in developing these indices. Efforts to develop a guideline is proposed on how population health indices can be developed systematically and rigorously to ensure validity and comprehensive assessment of the indices.

Probing electric field control of magnetism using ferromagnetic resonance.

Exchange coupled CoFe/BiFeO3 thin-film heterostructures show great promise for power-efficient electric field-induced 180° magnetization switching. However, the coupling mechanism and precise qualification of the exchange coupling in CoFe/BiFeO3 heterostructures have been elusive. Here we show direct evidence for electric field control of the magnetic state in exchange coupled CoFe/BiFeO3 through electric field-dependent ferromagnetic resonance spectroscopy and nanoscale spatially resolved magnetic imaging. Scanning electron microscopy with polarization analysis images reveal the coupling of the magnetization in the CoFe layer to the canted moment in the BiFeO3 layer. Electric field-dependent ferromagnetic resonance measurements quantify the exchange coupling strength and reveal that the CoFe magnetization is directly and reversibly modulated by the applied electric field through a ~180° switching of the canted moment in BiFeO3. This constitutes an important step towards robust repeatable and non-volatile voltage-induced 180° magnetization switching in thin-film multiferroic heterostructures and tunable RF/microwave devices.

Permanent electric dipole moments of carboxyamides in condensed media: what are the limitations of theory and experiment?

Electrostatic properties of proteins are crucial for their functionality. Carboxyamides are small polar groups that, as peptide bonds, are principal structural components of proteins that govern their electrostatic properties. We investigated the medium dependence of the molar polarization and of the permanent dipole moments of amides with different state of alkylation. The experimentally measured and theoretically calculated dipole moments manifested a solvent dependence that increased with the increase in the media polarity. We ascribed the observed enhancement of the amide polarization to the reaction fields in the solvated cavities. Chloroform, for example, caused about a 25% increase in the amide dipole moments determined for vacuum, as the experimental and theoretical results demonstrated. Another chlorinated solvent, 1,1,2,2-tetrachloroethane, however, caused an "abnormal" increase in the experimentally measured amide dipoles, which the theoretical approaches we used could not readily quantify. We showed and discussed alternatives for addressing such discrepancies between theory and experiment.