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  • Athermal silicon waveguides with bridged subwavelength gratings for TE and TM polarizations

    Resource Type:
    Article
    Creator:
    Ibrahim, Marc, Janz, Siegfried, Cheben, Pavel, Xu, Dan-Xia, Schmid, Jens H., Ma, Rubin, Aleali, Alireza, Lamontagne, Boris, Bock, Przemek J., Lapointe, Jean, Densmore, Adam, and Ye, Winnie N.
    Abstract:
    In this paper, athermal silicon waveguides using bridged subwavelength grating (BSWG) structures are proposed and investigated. The realization of temperature-independent BSWG waveguides for both polarizations is demonstrated numerically and experimentally. SU-8 polymer is used as the cladding material to compensate for the positive thermo-optic (TO) coefficient (dn/dT) of silicon. We investigate the dependence of the effective TO coefficient of BSWG waveguides on both the bridge width and grating duty cycle. The BSWG waveguides have a width of 490 nm, a height of 260 nm, and a grating pitch of 250 nm. Athermal behavior is achieved for both the transverse-magnetic (TM) and the transverse-electric (TE) polarized light for a variety of bridge width and duty cycle combinations. Furthermore, the BSWGs can be designed to be athermal for both TE and TM polarization simultaneously.
    Date Created:
    2012-07-30

  • Forging A Template for Undergraduate Collaborative Research: A Case Study

    Resource Type:
    Article
    Creator:
    Graham, Debra, Couchman, Ronald, and Hempstead, Janet
    Abstract:
    Undergraduate collaborative research is highlighted in many university initiatives; how-ever there is a lack of exemplars in disciplines that do not employ the scientific method. “Pop Music Reviews” was an attempt to forge a template for Women’s and Gender Stud-ies. This paper presents a description of the pilot project and provides qualitative assess-ments by the first- and second-year students, fourth-year teaching assistant (TA), refer-ence librarian, and professor. Together, the appraisals indicate that there are two different but equally necessary components for a successful collaborative research endeavour: the structural setting and the social and emotional environment. In both these components, there were weaknesses in the areas of planning and background training. Yet, the benefits as perceived through the experiences of the various participants were significant. Report-ed gains included increased understanding of research processes and applications, en-hanced critical thinking skills, expanded disciplinary knowledge, improved student moti-vation and confidence, greater interest in graduate studies, and the fostering of collegial interactions and mentoring.
    Date Created:
    2012-09-09

  • Understanding the neuroinflammatory response following concussion to develop treatment strategies

    Resource Type:
    Article
    Creator:
    Patterson, Zachary R. and Holahan, Mathew R.
    Abstract:
    Mild traumatic brain injuries (mTBI) have been associated with long-term cognitive deficits relating to trauma-induced neurodegeneration. These long-term deficits include impaired memory and attention, changes in executive function, emotional instability, and sensorimotor deficits. Furthermore, individuals with concussions show a high co-morbidity with a host of psychiatric illnesses (e.g., depression, anxiety, addiction) and dementia. The neurological damage seen in mTBI patients is the result of the impact forces and mechanical injury, followed by a delayed neuroimmune response that can last hours, days, and even months after the injury. As part of the neuroimmune response, a cascade of pro- and anti-inflammatory cytokines are released and can be detected at the site of injury as well as subcortical, and often contralateral, regions. It has been suggested that the delayed neuroinflammatory response to concussions is more damaging then the initial impact itself. However, evidence exists for favorable consequences of cytokine production following traumatic brain injuries as well. In some cases, treatments that reduce the inflammatory response will also hinder the brain's intrinsic repair mechanisms. At present, there is no evidence-based pharmacological treatment for concussions in humans. The ability to treat concussions with drug therapy requires an in-depth understanding of the pathophysiological and neuroinflammatory changes that accompany concussive injuries. The use of neurotrophic factors [e.g., nerve growth factor (NGF)] and anti-inflammatory agents as an adjunct for the management of post-concussion symptomology will be explored in this review.
    Date Created:
    2012-12-12

  • Frontal EEG/ERP correlates of attentional processes, cortisol and motivational states in adolescents from lower and higher socioeconomic status

    Resource Type:
    Article
    Creator:
    Van Roon, Patricia Maria, Oberlander, Tim F., Grunau, Ruth E., Hertzman, Clyde, D’Angiulli, Amedeo, Weinberg, Joanne, and Maggi, Stefania
    Abstract:
    Event-related potentials (ERPs) and other electroencephalographic (EEG) evidence show that frontal brain areas of higher and lower socioeconomic status (SES) children are recruited differently during selective attention tasks. We assessed whether multiple variables related to self-regulation (perceived mental effort) emotional states (e.g., anxiety, stress, etc.) and motivational states (e.g., boredom, engagement, etc.) may co-occur or interact with frontal attentional processing probed in two matched-samples of fourteen lower-SES and higher-SES adolescents. ERP and EEG activation were measured during a task probing selective attention to sequences of tones. Pre- and post-task salivary cortisol and self-reported emotional states were also measured. At similar behavioural performance level, the higher-SES group showed a greater ERP differentiation between attended (relevant) and unattended (irrelevant) tones than the lower-SES group. EEG power analysis revealed a cross-over interaction, specifically, lower-SES adolescents showed significantly higher theta power when ignoring rather than attending to tones, whereas, higher-SES adolescents showed the opposite pattern. Significant theta asymmetry differences were also found at midfrontal electrodes indicating left hypo-activity in lower-SES adolescents. The attended vs. unattended difference in right midfrontal theta increased with individual SES rank, and (independently from SES) with lower cortisol task reactivity and higher boredom. Results suggest lower-SES children used additional compensatory resources to monitor/control response inhibition to distracters, perceiving also more mental effort, as compared to higher-SES counterparts. Nevertheless, stress, boredom and other task-related perceived states were unrelated to SES. Ruling out presumed confounds, this study confirms the midfrontal mechanisms responsible for the SES effects on selective attention reported previously and here reflect genuine cognitive differences.
    Date Created:
    2012-11-19

  • The rights and freedoms gradient of health: evidence from a cross-national study

    Resource Type:
    Article
    Creator:
    Bezo, Brent, Roberts, William L., and Maggi, Stefania
    Abstract:
    This study examined the combined influences of national levels of socioeconomic status (SES), social capital, and rights and freedoms on population level physical and mental health outcomes. Indicators of mental health were suicide rates, alcohol consumption, and tobacco use. Indicators of physical health included life expectancy, infant mortality rates, and prevalence of HIV. Using pathway analysis on international data from a selected sample of European, North American, South American, and South Caucasus countries, similar models for mental health and physical health were developed. In the first model, the positive effects of SES and social capital on physical health were completely mediated via rights and freedoms. In the second model, the positive effect of SES on mental health was completely mediated, while the impact of social capital was partially mediated through rights and freedoms. We named the models, the "rights and freedoms gradient of health" in recognition of this latter construct's crucial role in determining both physical and mental health.
    Date Created:
    2012-11-07

  • An identification-robust test for time-varying parameters in the dynamics of energy prices

    Resource Type:
    Article
    Creator:
    Khalaf, Lynda A., Kichian, Maral, Bernard, Jean-Thomas, and Dufour, Jean-Marie
    Abstract:
    We test for the presence of time-varying parameters (TVP) in the long-run dynamics of energy prices for oil, natural gas and coal, within a standard class of mean-reverting models. We also propose residual-based diagnostic tests and examine out-of-sample forecasts. In-sample LR tests support the TVP model for coal and gas but not for oil, though companion diagnostics suggest that the model is too restrictive to conclusively fit the data. Out-of-sample analysis suggests a random-walk specification for oil price, and TVP models for both real-time forecasting in the case of gas and long-run forecasting in the case of coal.
    Date Created:
    2012-06-01

  • A geography-based critique of new US biofuels regulations

    Resource Type:
    Article
    Creator:
    Fast, Stewart, Saner, Marc, and Brklacich, Michael
    Abstract:
    The new renewable fuels standard (RFS 2) aims to distinguish corn-ethanol that achieves a 20% reduction in greenhouse gas (GHG) emissions compared with gasoline. Field data from Kim et al. (2009) and from our own study suggest that geographic variability in the GHG emissions arising from corn production casts considerable doubt on the approach used in the RFS 2 to measure compliance with the 20% target. If regulators wish to require compliance of fuels with specific GHG emission reduction thresholds, then data from growing biomass should be disaggregated to a level that captures the level of variability in grain corn production and the application of life cycle assessment to biofuels should be modified to capture this variability.
    Date Created:
    2012-05-01

  • The role of invented spelling on learning to read in low-phoneme awareness kindergartners: A randomized-control-trial study

    Resource Type:
    Article
    Creator:
    Lever, Rosemary, Ouellette, Gene, Pagan, Stephanie, and Sénéchal, Monique
    Abstract:
    The goal of the present intervention research was to test whether guided invented spelling would facilitate entry into reading for at-risk kindergarten children. The 56 participating children had poor phoneme awareness, and as such, were at risk of having difficulty acquiring reading skills. Children were randomly assigned to one of three training conditions: invented spelling, phoneme segmentation, or storybook reading. All children participated in 16 small group sessions over eight weeks. In addition, children in the three training conditions received letter-knowledge training and worked on the same 40 stimulus words that were created from an array of 14 letters. The findings were clear: on pretest, there were no differences between the three conditions on measures of early literacy and vocabulary, but, after training, invented spelling children learned to read more words than did the other children. As expected, the phoneme-segmentation and invented-spelling children were better on phoneme awareness than were the storybook-reading children. Most interesting, however, both the invented spelling and the phoneme-segmentation children performed similarly on phoneme awareness suggesting that the differential effect on learning to read was not due to phoneme awareness per se. As such, the findings support the view that invented spelling is an exploratory process that involves the integration of phoneme and orthographic representations. With guidance and developmentally appropriate feedback, invented spelling provides a milieu for children to explore the relation between oral language and written symbols that can facilitate their entry in reading.
    Date Created:
    2012-04-01

  • Plasmon-enhanced refractometry using silver nanowire coatings on tilted fibre Bragg gratings

    Resource Type:
    Article
    Creator:
    Bialiayeu, A., Ianoul, Anatoli, Prezgot, Dan, Bottomley, Adam, and Albert, Jacques
    Abstract:
    A novel technique for increasing the sensitivity of tilted fibre Bragg grating (TFBG) based refractometers is presented. The TFBG sensor was coated with chemically synthesized silver nanowires 100nm in diameter and several micrometres in length. A 3.5-fold increase in sensor sensitivity was obtained relative to the uncoated TFBG sensor. This increase is associated with the excitation of surface plasmons by orthogonally polarized fibre cladding modes at wavelengths near 1.5μm. Refractometric information is extracted from the sensor via the strong polarization dependence of the grating resonances using a Jones matrix analysis of the transmission spectrum of the fibre.
    Date Created:
    2012-11-09

  • Four-wave mixing in carbon nanotube-coated optical fiber gratings

    Resource Type:
    Article
    Creator:
    Shao, Li-Yang, Simard, Benoit, Albert, Jacques, Sun, Tingting, and Jakubinek, Michael B.
    Abstract:
    The observation of four-wave mixing (FWM) in single-walled carbon nanotubes (SWCNTs) deposited around a tilted fiber Bragg grating (TFBG) has been demonstrated. A thin, floating SWCNT film is manually wrapped around the outer cladding of the fiber and FWM occurs between two core-guided laser signals by TFBG-induced interaction of the core mode and cladding modes. The effective nonlinear coefficient is calculated to be 1.8 10 3W -1Km -1. The wavelength of generated idlers is tunable with a range of 7.8 nm.
    Date Created:
    2012-02-13