Optimization of thermoelectric properties of carbon nanotube veils by defect engineering.

Carbon nanotubes (CNTs), with their combination of excellent electrical conductivity, Seebeck coefficient, mechanical robustness and environmental stability are highly desired as thermoelectric (TE) materials for a wide range of fields including Internet of Things, health monitoring and environmental remediation solutions. However, their high thermal conductivity (κ) is an obstacle to practical TE applications. Herein, we present a novel method to reduce the κ of CNT veils, by introducing defects, while preserving their Seebeck coefficient and electrical conductivity. Solid-state drawing of a CNT veil embedded within two polycarbonate films generates CNT veil fragments of reducing size with increasing draw ratio. A successive heat treatment, at above the polycarbonate glass-to-rubber transition temperature, spontaneously reconnects the CNT veils fragments electrically but not thermally. Stretching to a draw ratio of 1.5 and heat repairing at 170 °C leads to a dramatic 3.5-fold decrease in κ (from 46 to 13 W m-1 K-1), in contrast with a decrease in electrical conductivity of only 26% and an increase in Seebeck coefficient of 10%. To clarify the mechanism of reduction in thermal conductivity, a large-scale mesoscopic simulation of CNT veils under uniaxial stretching has also been used. This work shows that defect engineering can be a valuable strategy to optimize TE properties of CNT veils and, potentially, other thermoelectric materials.

Terahertz Faraday Rotation of SrFe12O19 Hexaferrites Enhanced by Nb Doping.

The magneto-optical and dielectric behavior of M-type hexaferrites as permanent magnets in the THz band is essential for potential applications like microwave absorbers and antennas, while are rarely reported in recent years. In this work, single-phase SrFe12-xNbxO19 hexaferrite ceramics were prepared by the conventional solid-state sintering method. Temperature dependence of dielectric parameters was investigated here to determine the relationship between dielectric response and magnetic phase transition. The saturated magnetization increases by nearly 12%, while the coercive field decreases by 30% in the x = 0.03 composition compared to that of the x = 0.00 sample. Besides, the Nb substitution improves the magneto-optical behavior in the THz band by comparing the Faraday rotation parameter from 0.75 (x = 0.00) to 1.30 (x = 0.03). The changes in the magnetic properties are explained by a composition-driven increase of the net magnetic moment and enhanced ferromagnetic exchange coupling. The substitution of the donor dopant Nb on the Fe site is a feasible way to obtain multifunctional M-type hexaferrites as preferred candidates for permanent magnets, sensors, and other electronic devices.

Thermoelectric Performance of n-Type Magnetic Element Doped Bi2S3.

Thermoelectric technology offers great potential for converting waste heat into electrical energy and is an emission-free technique for solid-state cooling. Conventional high-performance thermoelectric materials such as Bi2Te3 and PbTe use rare or toxic elements. Sulfur is an inexpensive and nontoxic alternative to tellurium. However, achieving high efficiencies with Bi2S3 is challenging due to its high electrical resistivity that reduces its power factor. Here, we report Bi2S3 codoped with Cr and Cl to enhance its thermoelectric properties. An enhanced conductivity was achieved due to an increase in the carrier concentration by the substitution of S with Cl. High values of the Seebeck coefficients were obtained despite high carrier concentrations; this is attributed to an increase in the effective mass, resulting from the magnetic drag introduced by the magnetic Cr dopant. A peak power factor of 566 µW m-1 K-2 was obtained for a cast sample of Bi2-x/3Cr x/3S3-x Cl x with x = 0.01 at 320 K, as high as the highest values reported in the literature for sintered samples. These results support the success of codoping thermoelectric materials with isovalent magnetic and carrier concentration tuning elements to enhance the thermoelectric properties of eco-friendly materials.

Terahertz Characterization of Lead-Free Dielectrics for Different Applications.

In this spotlight on applications, we describe our recent progress on the terahertz (THz) characterization of linear and nonlinear dielectrics for broadening their applications in different electrical devices. We begin with a discussion on the behavior of dielectrics over a broadband of frequencies and describe the main characteristics of ferroelectrics, as they are an important category of nonlinear dielectrics. We then move on to look at the influence of point defects, porosities, and interfaces, including grain boundaries and domain walls, on the dielectric properties at THz frequencies. Based on our studies on linear dielectrics, we show that THz characterization is able to probe the effect of porosities, point defects, shear planes, and grain boundaries to improve dielectric properties for telecommunication applications. Further, we demonstrate that THz measurements on relaxor ferroelectrics can be successfully used to study the reversibility of the electric field-induced phase transitions, providing guidance for improving their energy storage efficiency in capacitors. Finally, we show that THz characterization can be used to characterize the effect of domain walls in ferroelectrics. In particular, our studies indicate that the dipoles located within domain walls provide a lower contribution to the permittivity at THz frequencies than the dipoles present in domains. The new findings could help develop a new memory device based on nondestructive reading operations using a THz beam.

Strength Analysis and Stress-Strain Deformation Behavior of 3 mol% Y-TZP and 21 wt.% Al2O3-3 mol% Y-TZP.

The mechanical behavior of 3 mol% Y2O3-ZrO2 ceramic and 21 wt.% Al2O3-3 mol% Y2O3-ZrO2 ceramic composite with submicron grain size was studied. Mechanical properties, such as hardness, Young's modulus, four-point bending strength, and fracture toughness of both materials were measured. Linear stress-strain deformation behavior of both 3 mol% Y2O3-ZrO2 and 21 wt.% Al2O3-3 mol% Y2O3-ZrO2 was observed in flexure, both at room temperature and at 400 °C. A small deviation from linear elastic deformation was detected in 21 wt.% Al2O3-3 mol% Y2O3-ZrO2 ceramic composite when loaded above a stress of 1500 MPa. Therefore, it was concluded that only elastic deformation occurred at low stresses upon loading, which exclude the presence of domain switching in zirconia upon bending under the loading conditions of this study.

Effect of Loading and Heating History on Deformation of LaCoO3.

The aim of this work was to study cyclic stress-strain deformation behavior of LaCoO3 as a function of loading and heating history. The ferroelastic hysteretic deformation of LaCoO3 at different stresses and temperatures was characterized using effective Young's modulus, hysteresis loop area and creep strain shift parameters. The deformation behavior of LaCoO3 was not significantly affected by the previous loading and heating history when tested at constant temperature. The high temperature strength and Young's modulus of LaCoO3 were higher compared to at room temperature. A creep strain shift parameter was introduced to characterize creep strain in LaCoO3 for the first time.

Shared injection experiences: Interpersonal involvement in injection drug practices among women.

Background: Many women who inject drugs are aware of the associated risks, however social influences play a part in their behavioral decisions. Incorporation of others in drug use behaviors may be common practice among women who use drugs. The aim of this study was to gain an in-depth understanding of women's injection drug use experiences with a focus on interpersonal involvement. Methods: Venue-based recruitment was conducted in collaboration with a harm reduction program. A group of 30 women, ages 18 and older, who reported injecting drugs within the past 30 days took part in a demographic survey and semi-structured interview to gain an understanding of their injection practices. In vivo coding and thematic analysis were conducted. Results: Three main themes that relate to incorporating others into injection drug behaviors surfaced, including: (1) injection practices described as we and not I, (2) partnered purchase and drug preparation, and (3) assisted injection. This group of women most often incorporated sexual and/or romantic partners (same and other-gender), friends, or family members into their injection drug use behaviors. Some women described a lack of ability to inject themselves and require assistance every time they use. Women also reported helping other women during drug use behaviors. Conclusions: Our primary themes indicate that a variety of relationship partners are important conceptual links in theoretical frameworks explaining drug use behaviors among women. Findings suggest same gender assistance during drug use behaviors, including injection, that may reduce harm. The interpersonal nature of injection drug use among women may indicate the expansion of treatment options designed for couples or other relationship partners, such as family, together.

Enhancing the Thermoelectric Performance of Calcium Cobaltite Ceramics by Tuning Composition and Processing.

Calcium cobaltite (Ca3Co4O9) is a promising p-type thermoelectric oxide material. Here, we present an approach to optimize the thermoelectric performance of Ca3Co4O9 by controlling the chemical composition and fabrication process. Ca3-xBixCo3.92O9+δ (0.1 ≤ x ≤ 0.3) and Ca2.7Bi0.3CoyO9+δ (3.92 ≤ y ≤ 4.0) ceramics were prepared by Spark Plasma Sintering (SPS). Stoichiometric mixtures of raw materials were combined and calcined at 1203 K for 12 h, followed by SPS at 1023 K for 5 min at 50 MPa. The samples were subsequently annealed at 1023 or 1203 K for 12 h in air. XRD and HRTEM analyses confirmed the formation of the cobaltite misfit phase with minor amounts of secondary phases; SEM-EDS showed the presence of Bi-rich and Co-rich secondary phases. After annealing at 1203 K, the secondary phases were significantly reduced. By controlling the cobalt deficiency and level of bismuth substitution, the electrical conductivity was enhanced without degrading Seebeck coefficients, promoting a high power factor of 0.34 mW m-1 K-2 at 823 K (parallel to the ab planes, //ab). Due to enhanced phonon scattering, the thermal conductivity was reduced by 20%. As a result, a highly competitive ZT(//ab) of 0.16 was achieved for Ca2.7Bi0.3Co3.92O9+δ ceramics at 823 K.

Magnetic Field-Induced Alignment of Nanofibrous Supramolecular Membranes: A Molecular Design Approach to Create Tissue-like Biomaterials.

A molecular design approach to fabricate nanofibrous membranes by self-assembly of aromatic cationic peptides with hyaluronic acid (HA) and nanofiber alignment under a magnetic field is reported. Peptides are designed to contain a block composed of four phenylalanine residues at the C-terminus, to drive their self-assembly by hydrophobic association and aromatic stacking, and have a positively charged domain of lysine residues for electrostatic interaction with HA. These two blocks are connected by a linker with a variable number of amino acids and the ability to adopt distinct conformations. Zeta potential measurements and circular dichroism confirm their positive charge and variable conformation (random coil, ß-sheet, or α-helix), which depend on the pH and sequence. Their self-assembly, examined by fluorescence spectroscopy, small-angle X-ray scattering, and transmission electron microscopy, show the formation of fiberlike nanostructures in the micromolar range. When the peptides are combined with HA, hydrogels or flat membranes are formed. The molecular structure tunes the mechanical behavior of the membranes and the nanofibers align in the direction of magnetic field due to the high diamagnetic anisotropy of phenylalanine residues. Mesenchymal stem cells cultured on magnetically aligned membranes elongate in direction of the nanofibers supporting their application for soft tissue engineering.

Assessing determinants of pre-exposure prophylaxis (PrEP) adherence among a sample of rural Midwestern men who have sex with men (MSM).

Pre-exposure prophylaxis (PrEP) efficacy in preventing HIV among gay, bisexual, and other men who have sex with men (MSM) is dependent upon adherence. Little is known about the PrEP adherence experiences among MSM who live in rural areas of the US. This qualitative study was informed by a modified version of Straussian Grounded Theory. Thirty-four 34 rural Midwestern MSM participated in telephone interviews that assessed their PrEP adherence factors. Overall, participants adhered to the PrEP regimen, ranging from missing none to a couple of doses per month. Participants had high self-efficacy (competence) and self-reliance (autonomy) in taking PrEP daily. Participants incorporated PrEP into their already existing routines. Participants were motivated to adhere to prevent HIV acquisition and be financially responsible. All participants mentioned their PrEP provider discussed the importance of adherence with PrEP's effectiveness, but future patient-provider PrEP adherence communication varied among participants. Future PrEP adherence interventions should address counseling strategies that leverage these constructs to support pill taking. Future research should explore patient-provider conversations surrounding PrEP adherence to inform provider- and patient-level interventions.

Spark Plasma Sintered B4C-Structural, Thermal, Electrical and Mechanical Properties.

The structural, thermal, electrical and mechanical properties of fully dense B4C ceramics, sintered using Spark Plasma Sintering (SPS), were studied and compared to the properties of B4C ceramics previously published in the literature. New results on B4C's mechanical responses were obtained by nanoindentation and ring-on-ring biaxial strength testing. The findings contribute to a more complete knowledge of the properties of B4C ceramics, an important material in many industrial applications.

Facilitators and Barriers of Pre-exposure Prophylaxis (PrEP) Uptake Among Rural Men who have Sex with Men Living in the Midwestern U.S.

Facilitators and barriers of Pre-exposure Prophylaxis (PrEP) uptake have been established in prior studies; however, most of these studies comprise samples of MSM from metropolitan cities and hypothetical PrEP use. There is a dearth of literature on the uptake factors among rural U.S. MSM who are prescribed PrEP. Thirty-four rural Midwestern MSM who currently take PrEP participated in semi-structured telephone interviews about their barriers and facilitators to their PrEP use. Interviews were analyzed using an inductive thematic analysis approach. There were four barriers: (1) lack of rural dissemination of PrEP information, (2) concern about side and adverse effects of using PrEP, (3) cost of PrEP uptake and engagement, and (4) lack of access to PrEP care and PrEP care quality. Individual and social facilitators that participants utilized to overcome these barriers are discussed. Findings elevate the importance of multilevel interventions that address PrEP adoption from a patient, provider, and healthcare system perspective.

Exploring the Pre-exposure Prophylaxis (PrEP) Health Care Experiences Among Men Who Have Sex With Men (MSM) Who Live in Rural Areas of the Midwest.

Most pre-exposure prophylaxis (PrEP) research samples men who have sex with men (MSM) who live in metropolitan cities. There is a limited understanding of the PrEP experiences among rural MSM. Thirty-four semi-structured interviews were conducted to explore the PrEP health care experiences among 34 rural Midwestern MSM. Of the 34 participants, 23 obtained PrEP from their non-primary care provider (PCP). Three themes were present: (1) PrEP is unavailable in rural areas, (2) PrEP is inaccessible in rural areas due to PCPs being unwilling to prescribe PrEP, and (3) PrEP services are unamicable in rural areas due to stigmatizing attitudes and behaviors of PCPs. It is important to address PrEP care continuum factors in all settings; however, these factors are often exacerbated in rural areas due to social determinants. Without further research and programming, organizational and social determinants may contribute to lower rates of PrEP outcomes in rural areas.

Ultrahigh ß-phase content poly(vinylidene fluoride) with relaxor-like ferroelectricity for high energy density capacitors.

Poly(vinylidene fluoride)-based dielectric materials are prospective candidates for high power density electric storage applications because of their ferroelectric nature, high dielectric breakdown strength and superior processability. However, obtaining a polar phase with relaxor-like behavior in poly(vinylidene fluoride), as required for high energy storage density, is a major challenge. To date, this has been achieved using complex and expensive synthesis of copolymers and terpolymers or via irradiation with high-energy electron-beam or γ-ray radiations. Herein, a facile process of pressing-and-folding is proposed to produce ß-poly(vinylidene fluoride) (ß-phase content: ~98%) with relaxor-like behavior observed in poly(vinylidene fluoride) with high molecular weight > 534 kg mol-1, without the need of any hazardous gases, solvents, electrical or chemical treatments. An ultra-high energy density (35 J cm-3) with a high efficiency (74%) is achieved in a pressed-and-folded poly(vinylidene fluoride) (670-700 kg mol-1), which is higher than that of other reported polymer-based dielectric capacitors to the best of our knowledge.

Strength enhancement and slip behaviour of high-entropy carbide grains during micro-compression.

Bulk polycrystalline high-entropy carbides are a newly developed group of materials that increase the limited compositional space of ultra-high temperature ceramics, which can withstand extreme environments exceeding 2000 °C in oxidizing atmospheres. Since the deformability of grains plays an important role in macromechanical performance, in this work we studied the strength and slip behaviour of grains of a spark-plasma sintered (Hf-Ta-Zr-Nb)C high-entropy carbide in a specific orientation during micropillar compression. For comparison, identical measurements were carried out on the monocarbides HfC and TaC. It was revealed that (Hf-Ta-Zr-Nb)C had a significantly enhanced yield and failure strength compared to the corresponding base monocarbides, while maintaining a similar ductility to the least brittle monocarbide (TaC) during the operation of [Formula: see text] slip systems. Additionally, it was concluded that the crystal orientation and stress conditions determine the operation of slip systems in mono- and high-entropy carbides at room temperature.

Characteristics of Adolescent Sexting: Results from the 2015 National Survey of Sexual Health and Behavior.

Using data from 78 sexting-experienced adolescents from the 2015 National Survey of Sexual Health and Behavior, we describe sexting frequency, sexting partners, sexual relationships with such partners, and characteristics associated with sexting. Most (59.2%) respondents sexted at most monthly, usually with romantic partners (62.0%). About 41% of sexting-experienced adolescents did not usually have sexual relationships with sexting partners, 36.6% usually sexted after starting a sexual relationship, and 16.8% reported that their sexting typically preceded sexual relationships. Younger adolescents sexted more frequently. Those without vaginal sex/anal sex experience, or prior romantic experience, were more likely to have sexted a non-romantic/sexual partner.

Oxidation Protective Hybrid Coating for Thermoelectric Materials.

Two commercial hybrid coatings, cured at temperatures lower than 300 °C, were successfully used to protect magnesium silicide stannide and zinc-doped tetrahedrite thermoelectrics. The oxidation rate of magnesium silicide at 500 °C in air was substantially reduced after 120 h with the application of the solvent-based coating and a slight increase in power factor was observed. The water-based coating was effective in preventing an increase in electrical resistivity for a coated tethtraedrite, preserving its power factor after 48 h at 350 °C.

Kissing, Cuddling, and Massage at Most Recent Sexual Event: Findings From a U.S. Nationally Representative Probability Sample.

Using data from the 2014 National Survey of Sexual Health and Behavior, a probability survey of Americans aged 14+, we assessed the prevalence and correlates of kissing, cuddling, and massage during 1,493 individuals' most recent sexual event from the past year. Most respondents reported kissing (87%) and cuddling (70%); fewer (23%) reported massage. Each was significantly associated with age, education, and relationship structure. Respondents younger than 30 were significantly more likely to indicate they did not kiss because kissing would have been too intimate with their partner. Only cuddling was significantly associated with event-level emotional intimacy and sexual pleasure.

Relationships Among Sexual Identity, Sexual Attraction, and Sexual Behavior: Results from a Nationally Representative Probability Sample of Adults in the United States.

Sexual orientation is a multi-dimensional concept, at a minimum comprised of sexual identity, sexual attraction, and sexual behavior. Our study aimed to assess relationships among self-identified sexual identity, sexual attraction, and sexual behaviors in a probability sample of adults in the U.S. and to identify associated factors with diverse patterns. We collected data from adults in the 2015 National Survey of Sexual Health and Behavior, an Internet-based nationally representative probability survey of the general U.S. population. Concordance between sexual identity versus sexual attraction and sexual behaviors was assessed using percent agreement. We identified correlates of discordance using logistic regression. Concordance between sexual identity versus sexual attraction and past-year sexual behaviors was 94% and 96%, respectively, though our sample was predominately composed of heterosexual individuals. Women and sexual minority individuals reported greater discordance across sexuality-related measures than men and heterosexual individuals. Younger adults (aged 18-24 years) were more likely to report sexual behaviors discordant with sexual identity compared with older adults (including those ages 25-34 years). Higher levels of educational attainment were significantly associated with less discordance of reported recent sexual activity and sexual identity. Measures of sexual identity, attraction, and behaviors are not interchangeable. Future research should consider multiple sexuality-related measures in order to capture the complexity and variability of sexualities.

Effect of the Processing Route on the Thermoelectric Performance of Nanostructured CuPb18SbTe20.

The quaternary AgPb18SbTe20 compound (abbreviated as LAST) is a prominent thermoelectric material with good performance. Endotaxially embedded nanoscale Ag-rich precipitates contribute significantly to decreased lattice thermal conductivity (κlatt) in LAST alloys. In this work, Ag in LAST alloys was completely replaced by the more economically available Cu. Herein, we conscientiously investigated the different routes of synthesizing CuPb18SbTe20 after vacuum-sealed-tube melt processing, including (i) slow cooling of the melt, (ii) quenching and annealing, and consolidation by (iii) spark plasma sintering (SPS) and also (iv) by the state-of-the-art flash SPS. Irrespective of the method of synthesis, the electrical (σ) and thermal (κtot) conductivities of the CuPb18SbTe20 samples were akin to those of LAST alloys. Both the flash-SPSed and slow-cooled CuPb18SbTe20 samples with nanoscale dislocations and Cu-rich nanoprecipitates exhibited an ultralow κlatt ∼ 0.58 W/m·K at 723 K, comparable with that of its Ag counterpart, regardless of the differences in the size of the precipitates, type of precipitate-matrix interfaces, and other nanoscopic architectures. The sample processed by flash SPS manifested higher figure of merit ( zT ∼ 0.9 at 723 K) because of better optimization and a trade-off between the transport properties by decreasing the carrier concentration and κlatt without degrading the carrier mobility. In spite of their comparable σ and κtot, zT of the Cu samples is low compared to that of the Ag samples because of their contrasting thermopower values. First-principles calculations attribute this variation in the Seebeck coefficient to dwindling of the energy gap (from 0.1 to 0.02 eV) between the valence and conduction bands in MPb18SbTe20 (M = Cu or Ag) when Cu replaces Ag.