Transferable Percolated Particle Monolayers Derived from Marangoni Flows for Thermally Conductive Dielectric Coatings.

Thermal management is becoming one of the most significant design and size limitations for high power density electronics, including motherboards, power converters, and phased array antennas for 5G communications. There are few options for conducting heat away with dielectric materials that avoid shortening or distorting the performance of these electronics. Certain highly thermally conductive 2D and 3D materials, including hexagonal boron nitride and diamond, offer ideal material properties to address these issues but are extremely challenging to process. This work studies highly oriented single-particle thick films of hexagonal boron nitride, manufactured through a modified Langmuir-Blodgett process and densified further using the Marangoni effect to attain remarkable thermal conductivity enhancement with minimal coating thickness. High loadings of hexagonal boron nitride (∼60 vol %) in dense, castable films are also produced to compare thermal spreading ability in a comparatively simpler but less-coordinated percolated system to the highly percolated particle monolayers. These procedures were applied to glass fiber reinforced polymers used in aerospace and radome applications as well as to a single-board computer to demonstrate enhanced thermal management.

Environmental Stability of Additively Manufactured Thermoplastic Polyamide Composites.

As the adoption of additive manufacturing technologies for end-use parts continues to progress, the evaluation of environmental durability is essential for the qualification of manufactured articles in industries such as automotive, aerospace, and electrical. This study explores the effects of UV and water-spray exposure on the mechanical properties of an additively manufactured polyamide 6 blend reinforced with short carbon fiber and continuous carbon fiber. Fused-filament-fabrication-printed test samples were exposed to a Xenon-arc UV source following ASTM G155 Cycle 1 conditions for a duration of 1000 h. Tensile, flexural, and Izod impact tests were performed on exposed and unexposed test samples. While Exposed tensile and flexural samples maintained their strength (84-100% and 88-100%, of Control samples, respectively), Izod impact strength increased (104-201% of Controls). This study also examines the influence of coatings and finds that samples coated with Krylon® Fusion All-In-One® and JetFlex® Polyurethane Primer maintain similar mechanical properties and exhibit a better visual appearance as compared to uncoated, exposed samples.

Effects of Coefficient of Thermal Expansion and Moisture Absorption on the Dimensional Accuracy of Carbon-Reinforced 3D Printed Parts.

Environmental effects-temperature and moisture-on 3D printed part dimensional accuracy are explored. The coefficient of thermal expansion of four different nylon materials was determined for XY and ZX print orientations, with 0°, 45°/-45°, and 90° infill patterns. Unreinforced nylon exhibited a thermal expansion coefficient of the same order regardless of condition (from 11.4 to 17.5 × 10-5 1/°C), while nylons reinforced with discontinuous carbon fiber were highly anisotropic, for instance exhibiting 2.2 × 10-5 1/°C in the flow direction (0° infill angle) and 24.8 × 10-5 1/°C in the ZX orientation. The temperature profile of a part during printing is shown, demonstrating a build steady state temperature of ~ 35 °C. The effect of moisture uptake by the part was also explored, with dimensional changes of ~0.5-1.5% seen depending on feature, with height expanding the most. The effects of moisture were significantly reduced for large flat parts with the inclusion of continuous fiber reinforcement throughout the part.

Executive function after risk-reducing salpingo-oophorectomy in BRCA1 and BRCA2 mutation carriers: does current mood and early life adversity matter?

OBJECTIVE: Despite the fact that negative mood and executive dysfunction are common after risk-reducing salpingo-oophorectomy (RRSO), occurring in up to a third of women, little is known about risk factors predicting these negative outcomes. Adverse childhood experiences (ACE) predict poorer health in adulthood and may be a risk factor for negative outcomes after RRSO. Given the complex relationship between early life stress, affective disorders, and cognitive dysfunction, we hypothesized that ACE would be associated with poorer executive function and that mood symptoms would partially mediate this relationship. METHODS: Women who had undergone RRSO were included in the study (N = 552; age 30-73 y). We measured executive function (continuous performance task, letter n-back task, and Brown Attention Deficit Disorder Scale Score), exposure to early life stress (ACE questionnaire), and mood symptoms (Hospital Anxiety and Depression Scale). Generalized estimating equations were used to evaluate the association between ACE and executive dysfunction and the role of mood symptoms as a mediator in this relationship. RESULTS: ACE was associated with greater severity of subjective executive dysfunction (adjusted mean difference [aMD] = 7.1, P = 0.0005) and worse performance on both cognitive tasks (continuous performance task: aMD = -0.1, P = 0.03; n-back: aMD = -0.17, P = 0.007). Mood symptoms partially mediated ACE associations with sustained attention (21.3% mediated; 95% CI: 9.3%-100%) and subjective report of executive dysfunction (62.8% mediated; 95% CI: 42.3%-100%). CONCLUSIONS: The relationship between childhood adversity and executive dysfunction is partially mediated by mood symptoms. These data indicate that assessing history of childhood adversity and current anxiety and depression symptoms may play a role in treating women who report cognitive complaints after RRSO. : Video Summary:http://links.lww.com/MENO/A571.

Video Summary:http://links.lww.com/MENO/A571.

Polypropylene crystallization at an alumina interface using single walled carbon nanotubes.

Interfaces play an important and often limiting role in the mechanical, thermal, and electrical performance of composite materials. Here we suggest a novel method to improve the interfacial interaction in polypropylene-alumina composites using single-walled carbon nanotubes (SWNTs) to nucleate lamellar crystals at the interface. Macroscopic alumina substrates are used to determine the ideal crystallization parameters and investigate the kinetics of crystal growth. SWNTs are uniformly adsorbed to the interface via Van der Waals interactions and lamellar crystals are grown on the surface using isothermal solution processing techniques. Avrami analysis of crystal surface coverage was used to confirm one-dimensional transcrystalline growth commonly seen with SWNT nucleated crystals. Scanning electron microscopy was used to confirm shish-kebab structures present at the SWNT-polypropylene interface. The determined crystallization parameters were used on colloidal solutions of alumina platelets to successfully create uniformly coated particles with an improved interface. This method shows promise for improving the interphase of semicrystalline polymer-ceramic composites to achieve excellent material properties.

Psychogenic movement disorders in children: characteristics and predictors of outcome.

Psychogenic movement disorders are defined as hyperkinetic or hypokinetic movement disorders associated with underlying psychological disorders. Psychogenic movement disorders account for 1% to 9% of all neurologic diagnoses. The assessment and treatment of psychogenic movement disorders can be complex. We report patients seen over the past 5 years, diagnosed with psychogenic movement disorder. We discuss in this article some patient characteristics and some strategies that are effective in the management of this group of patients. The case examples presented in the current article demonstrate the importance of two factors, a multidisciplinary approach and engaging the family, that are essential components in the treatment of psychogenic movement disorders.