A Bisphenol-A-based Resin System that Cures via Triazole Ring Formation for Marine Composite Applications

Large composite panels, such as those utilized in marine applications, cannot be economically cured in an autoclave. For these structures the elevated temperatures necessary to achieve high crosslink density must come from the curing reaction itself. We are developing a resin system that cures via triazole ring formation (cycloaddition reaction of azides with terminal alkynes) instead of the traditional oxirane/amine reaction. The high exothermicity of the azido/alkyne reaction is expected to yield higher extents of reaction under ambient-cure conditions, making the resin system potentially suitable for out-of-autoclave curing processes. This work was conducted through a multi-tiered approach involving synthesis, kinetic studies, thermal characterization, and mechanical analysis. The difunctional azide-terminated resin, di(3-azido-2 hydroxypropyl) ether of bisphenol-A (DAHP-BPA), was selected as the baseline diazide. A number of alkyne crosslinkers were synthesized and characterized, including propiolate esters of di- and trifunctional alcohols, propargyl esters of di- and trifunctional carboxylic acids, propargyl ethers of di- and trifunctional alcohols, and N,N,N′,N′-tetrapropargyl derivatives of primary diamines. Commercially available tripropargylamine (TPA) was also studied. Curing energetics as a function of alkyne type and catalyst loading, investigated through a dynamic differential scanning calorimetry approach, displayed two distinct kinetic profiles when considering propiolate and propargyl type crosslinkers. Those systems employing a propiolate-based alkyne were found to be much more reactive towards the Huisgen 1,3-dipolar cycloaddition than the propargyl species. Additionally, the mechanical and thermal properties of resin systems, both un-catalyzed and catalyzed, composed of DAHP-BPA and tripropargyl amine were investigated by compression and rheological studies, differential scanning calorimetry, and thermogravametric analysis. The moduli of both DAHP-BPA/TPA systems were found to be approximately 3500 MPa, comparable to the modulus of EPON-825/4,4′-DDS resin. Ultimately, the utility of the DAHP-BPA/polyalkyne resin system lies not only in its capability for low-temperature curing, but also in the ability to customize the reactivity, thermal properties, and mechanical properties of the system through the use of catalyst and choice of alkyne crosslinker

Changing the Waveform of Circadian Rhythms: Considerations for Shift-Work

Circadian disruption in shift-work is common and has deleterious effects on health and performance. Current efforts to mitigate these harms reasonably focus on the phase of the circadian pacemaker, which unfortunately in humans, shifts slowly and often incompletely. Temporal reorganization of rhythmic waveform (i.e., the shape of its 24 h oscillation), rather than phase, however, may better match performance demands of shift-workers and can be quickly and feasibly implemented in animals. In fact, a bifurcated pacemaker waveform may permit stable entrainment of a bimodal sleep/wake rhythm promoting alertness in both night and daylight hours. Although bifurcation has yet to be formally assessed in humans, evidence of conserved properties of circadian organization and plasticity predict its occurrence: humans respond to conventional manipulations of waveform (e.g., photoperiodism); behaviorally, the sleep/wake rhythm is adaptable; and finally, the human circadian system likely derives from the same multiple cellular oscillators that permit waveform flexibility in the rodent pacemaker. In short, investigation into untried manipulations of waveform in humans to facilitate adjustment to challenging schedules is justified

Extraordinary behavioral entrainment following circadian rhythm bifurcation in mice.

The mammalian circadian timing system uses light to synchronize endogenously generated rhythms with the environmental day. Entrainment to schedules that deviate significantly from 24 h (T24) has been viewed as unlikely because the circadian pacemaker appears capable only of small, incremental responses to brief light exposures. Challenging this view, we demonstrate that simple manipulations of light alone induce extreme plasticity in the circadian system of mice. Firstly, exposure to dim nocturnal illumination (<0.1 lux), rather than completely dark nights, permits expression of an altered circadian waveform wherein mice in light/dark/light/dark (LDLD) cycles "bifurcate" their rhythms into two rest and activity intervals per 24 h. Secondly, this bifurcated state enables mice to adopt stable activity rhythms under 15 or 30 h days (LDLD T15/T30), well beyond conventional limits of entrainment. Continuation of dim light is unnecessary for T15/30 behavioral entrainment following bifurcation. Finally, neither dim light alone nor a shortened night is sufficient for the extraordinary entrainment observed under bifurcation. Thus, we demonstrate in a non-pharmacological, non-genetic manipulation that the circadian system is far more flexible than previously thought. These findings challenge the current conception of entrainment and its underlying principles, and reveal new potential targets for circadian interventions

Purposes Behind Summer Reading Assignments

This study attempted to better understand the purposes behind assigning summer reading lists to students. It addressed four research questions, considering the reasons behind summer reading lists, who helps create the lists, how the criteria for book selection and additional assignments support the purposes, and how the lists and purposes are communicated to students and parents. The researcher interviewed a sample of educators in North Carolina who help create the summer reading lists at their schools, then created transcripts of the interview recordings and analyzed the transcripts qualitatively. The results showed that, contrary to the literature, educators use many different purposes in concert when they assign summer reading. The primary purpose appeared to be encouraging leisure reading. A variety of school community members contribute to the list creation, and a great deal of thought, shown by the large number of criteria, goes into the book selection. The interviews revealed that two possible areas for improvement of the use of summer reading lists are the formulation of goals before creating the lists and increased collaboration within the school community and with the public library

Association Between Method of Prescribing and Primary Nonadherence to Dermatologic Medication in an Urban Hospital Population

Importance Prescription underuse is associated with poorer clinical outcomes. A significant proportion of underuse is owing to primary nonadherence, defined as the rate at which patients fail to fill and pick up new prescriptions. Although electronic prescribing increases coordination of care and decreases errors, its effect on primary nonadherence is less certain. Objectives To analyze factors associated with primary nonadherence to dermatologic medications and study whether electronic prescribing affects rates of primary nonadherence. Design, Setting, and Participants A retrospective review of medical records was conducted from January 1, 2011, to December 31, 2013, among a cohort of new patients prescribed dermatologic medications at a single, urban, safety-net hospital outpatient dermatology clinic. Main Outcomes and Measures The primary outcome was the overall rate of primary nonadherence, defined as filling and picking up all prescribed medications within a 1-year period, and the difference in primary nonadherence between patients who received electronic prescriptions and those who received paper prescriptions. Secondary outcomes included the association of primary nonadherence with sex, age, relationship status, primary language, race/ethnicity, and number of prescriptions. Results A total of 4318 prescriptions were written for 2496 patients (mean [SD] age, 47.7 [13.2] years; 849 men and 1647 women). The overall rate of primary nonadherence was 31.6% (n = 788). Based on multivariable analysis, the risk of primary nonadherence was 16 percentage points lower among patients given an electronic prescription (15.2%) than patients given a paper prescription (31.5%). Primary nonadherence decreased with age (<30 y, 38.9%; 30-49 y, 35.3%; and 50-69 y, 26.3%), and then increased in elderly patients 70 years and older (31.9%). Of patients who were given 1, 2, 3, 4, or 5 prescriptions, rates of primary nonadherence were 33.1%, 28.8%, 26.4%, 39.8%, and 38.1%, respectively. Primary nonadherence decreased with age but then increased in elderly patients. Patients identifying English as their primary language had the highest rate of primary nonadherence (33.9%) compared with Spanish (29%) or other speakers (20.4%). Conclusions and Relevance Compared with paper prescriptions, electronic prescriptions were associated with less primary nonadherence. Number of prescriptions, language, race/ethnicity, and age were associated with increased rates of primary nonadherence. Efforts must be made to understand why primary nonadherence occurs, identify patients prone to primary nonadherence, and simplify medication regimens to maximize adherence and quality of care