Dynamic pathway of the photoinduced phase transition of TbMnO3_3

We investigate the demagnetization dynamics of the cycloidal and sinusoidal phases of multiferroic TbMnO$_3$ by means of time-resolved resonant soft x-ray diffraction following excitation by an optical pump. Using orthogonal linear x-ray polarizations, we suceeded in disentangling the response of the multiferroic cycloidal spin order from the sinusoidal antiferromagnetic order in the time domain. This enables us to identify the transient magnetic phase created by intense photoexcitation of the electrons and subsequent heating of the spin system on a picosecond timescale. The transient phase is shown to be a spin density wave, as in the adiabatic case, which nevertheless retains the wave vector of the cycloidal long range order. Two different pump photon energies, 1.55 eV and 3.1 eV, lead to population of the conduction band predominantly via intersite $d$-$d$ transitions or intrasite $p$-$d$ transitions, respectively. We find that the nature of the optical excitation does not play an important role in determining the dynamics of magnetic order melting. Further, we observe that the orbital reconstruction, which is induced by the spin ordering, disappears on a timescale comparable to that of the cycloidal order, attesting to a direct coupling between magnetic and orbital orders. Our observations are discussed in the context of recent theoretical models of demagnetization dynamics in strongly correlated systems, revealing the potential of this type of measurement as a benchmark for such complex theoretical studies

Ancillary health effects of climate mitigation scenarios as drivers of policy uptake: a review of air quality, transportation and diet co-benefits modeling studies

Background: Significant mitigation efforts beyond the Nationally Determined Commitments (NDCs) coming out of the 2015 Paris Climate Agreement are required to avoid warming of 2 °C above pre-industrial temperatures. Health co-benefits represent selected near term, positive consequences of climate policies that can offset mitigation costs in the short term before the beneficial impacts of those policies on the magnitude of climate change are evident. The diversity of approaches to modeling mitigation options and their health effects inhibits meta-analyses and syntheses of results useful in policy-making. Methods/Design: We evaluated the range of methods and choices in modeling health co-benefits of climate mitigation to identify opportunities for increased consistency and collaboration that could better inform policy-making. We reviewed studies quantifying the health co-benefits of climate change mitigation related to air quality, transportation, and diet published since the 2009 Lancet Commission 'Managing the health effects of climate change' through January 2017. We documented approaches, methods, scenarios, health-related exposures, and health outcomes. Results/Synthesis: Forty-two studies met the inclusion criteria. Air quality, transportation, and diet scenarios ranged from specific policy proposals to hypothetical scenarios, and from global recommendations to stakeholder-informed local guidance. Geographic and temporal scope as well as validity of scenarios determined policy relevance. More recent studies tended to use more sophisticated methods to address complexity in the relevant policy system. Discussion: Most studies indicated significant, nearer term, local ancillary health benefits providing impetus for policy uptake and net cost savings. However, studies were more suited to describing the interaction of climate policy and health and the magnitude of potential outcomes than to providing specific accurate estimates of health co-benefits. Modeling the health co-benefits of climate policy provides policy-relevant information when the scenarios are reasonable, relevant, and thorough, and the model adequately addresses complexity. Greater consistency in selected modeling choices across the health co-benefits of climate mitigation research would facilitate evaluation of mitigation options particularly as they apply to the NDCs and promote policy uptake

CRALBP supports the mammalian retinal visual cycle and cone vision

Mutations in the cellular retinaldehyde-binding protein (CRALBP, encoded by RLBP1) can lead to severe cone photoreceptor-mediated vision loss in patients. It is not known how CRALBP supports cone function or how altered CRALBP leads to cone dysfunction. Here, we determined that deletion of Rlbp1 in mice impairs the retinal visual cycle. Mice lacking CRALBP exhibited M-opsin mislocalization, M-cone loss, and impaired cone-driven visual behavior and light responses. Additionally, M-cone dark adaptation was largely suppressed in CRALBP-deficient animals. While rearing CRALBP-deficient mice in the dark prevented the deterioration of cone function, it did not rescue cone dark adaptation. Adeno-associated virus-mediated restoration of CRALBP expression specifically in Müller cells, but not retinal pigment epithelial (RPE) cells, rescued the retinal visual cycle and M-cone sensitivity in knockout mice. Our results identify Müller cell CRALBP as a key component of the retinal visual cycle and demonstrate that this pathway is important for maintaining normal cone-driven vision and accelerating cone dark adaptation

CIHR Health System Impact Fellows: Reflections on “Driving Change” Within the Health System

Learning health systems necessitate interdependence between health and academic sectors and are critical to address the present and future needs of our health systems. This concept is being supported through the new Canadian Institutes of Health Research (CIHR) Health System Impact (HSI) Fellowship, through which postdoctoral fellows are situated within a health system-related organization to help propel evidence-informed organizational transformation and change. A voluntary working group of fellows from the inaugural cohort representing diversity in geography, host setting and personal background, collectively organized a panel at the 2018 Canadian Association for Health Services and Policy Research Conference with the purpose of describing this shared scholarship experience. Here, we present a summary of this panel reflecting on our experiential learning in a practice environment and its ability for impact

Unravelling the excitonics of semiconductor nanocrystals an effort in guiding the design of novel structures for optoelectronic applications through spectroscopy

The optical modulation of the multiexitonic multiplicity of CdSe/ZnS nanocrystals (NC) through state-specific excitation demonstrated the potential of NCs as a novel platform for all-optical logic and switching with modulation rates reaching 1 THz, as dictated by Auger recombination. An optical pumping scheme demonstrating all-optical AND gating through CdSe/ZnS NCs made use of the unique multiexcitonic interactions of colloidal nanocrystals. State resolved pump-probe spectroscopic techniques were applied to study the relative excitonic environments of freshly synthesized and aged CdTe NC. These experiments reveal fast electron trapping for aged CdTe NC from the single excitonic state (X). Pump fluence dependence with excitonic state-resolved optical pumping enables directly populating the biexcitonic state (XX) which produces further accelerated electron trapping rates. This increase in electron trapping rate triggers coherent acoustic phonons by virtue of the ultrafast impulsive timescale of the surface trapping process. The observed trapping rates were discussed in terms of electron transfer theory.The subtleties of the excitonic couplings within NCs motivated the development of a novel two-dimensional electronic spectrometer with active carrier-envelope phase stabilization, capable of both collinear and non-collinear geometry. Pulse-generation was achieved through synched acousto-optic programmable dispersive filters. Phase stability was measured through spectral interferometry and found to be in excess of λ/300 for over an hour. The highly phase-stable design allowed for complete polarization control through pulse-pair recombination in a beam-splitter. Polarization control was achieved through sweeping the relative phases of the shaped pulses and demonstrated through a Mueller ellipsometer. Both one- and two-colour proof-of-principle experiments were performed on CdSe NCs.La modulation optique de la multiplicité multi-excitonique des nano-crystaux CdSe/ZnS obtenue par excitation d'états spécifiques démontre le potentiel d'application de ces matériaux dans le domaine de la logique optique, atteignant des taux de modulation de l'ordre de 1ThZ comme dicté par le taux de recombinaison d'Auger. Grâce à une méthode de pompage optique, une fonction « ET » a été réalisée avec des nanocrystaux de type CdSe/ZnS, mettant ainsi à profit les interactions multi-excitoniques uniques de ces nanocrystaux colloïdaux. Des techniques spectroscopiques pompe/sonde résolues en états quantiques ont été appliquées afin d'étudier les différences d'environnements excitoniques entre des points quantiques CdTe fraîchement synthétisés et ayant vieilli. Dans le cas des points quantiques âgés, ces expériences révèlent une rapide capture de l'électron par l'état excitonique simple (X). Le fait que la nature de l'état excitonique optiquement excité dépende de la fluence de la pompe permet de directement peupler l'état bi-excitonique (XX), ce qui a pour effet d'accélérer le taux de capture d'électrons. Cette augmentation du taux d'électrons capturés provoque l'émission de phonons acoustiques en vertu des dynamiques ultrarapides des processus de capture à la surface des nanocrystaux. Les taux de capture observés lors de ces expériences ont été discutés dans le cadre de la littérature sur le transfert de charge. Les subtilités des couplages excitoniques au sein des nanocrystaux a motivé le développement d'un spectromètre bi-dimensionnel dans le domaine du visible, pourvu d'un mécanisme de stabilisation de la phase de l'enveloppe des pulses et capable d'opérer en géométries colinéaires et non-colinéaires. La génération des pulses a été obtenue grâce à des filtres dispersifs accousto-optiques programmables. La stabilité de la phase a été mesurée par interférométrie spectrale et une valeur supérieure à λ/300 a été obtenue sur plus d'une heure. Ce montage, possédant une grande stabilité des phases, permet de contrôler la polarisation des pulses excitant l'échantillon en combinant une paire de pulses dans un miroir semi-réfléchissant. Le contrôle de la polarisation a été obtenu en balayant les phases relatives des pulses et en les observant dans un ellipsomètre de Müller. Des expériences à une et deux couleurs ont été réalisées sur des nanocrystaux de type CdSe, établissant ainsi la preuve du concept

Terahertz Bandwidth All-Optical Modulation and Logic Using Multiexcitons in Semiconductor Nanocrystals

Optical pumping of semiconductor nanocrystals with femtosecond pulse sequences was performed in order to modulate multiexciton populations. We show for the first time that control of multiexciton populations produces high speed modulation of stimulated emission. Upon the basis of the speed of multiexcitonic processes in nanocrystals, we show modulation rates approaching 1 THz by virtue of strong quantum confinement effects. Employing femtosecond optical pulse sequences, we demonstrate all-optical logic using these nanocrystals in two forms: an AND gate, and an inverter, a key step toward all optical signal processing