The Effects of Geometric and Stoichometric Change in Nanoparticles and Materials on Lattice Thermal Conductivity

Thermal transport properties are critical for applications ranging from thermal management to energy conversion. Passive thermal management has been an area of study for over a century and has only grown as technology has advanced because it requires no additional energy to remove heat. Changing the nanostructure of the materials involved in passive heat transfer methods, either by geometric changes or stoichiometric changes, can greatly improve the effectiveness of this heat transfer method. In order to explore this further, this work employs LAMMPS molecular dynamics (MD) simulation software to calculate the lattice thermal conductivity (λp) of a nanoparticle (NP) and material used indifferent passive heat transfer methods after either modifying their geometry or stoichiometry. The NPs this work will simulate are single-wall carbon nanotubes (SWCNTs), which have been well known for high λp, and their applications in improving thermal conductivity in matrix materials. The material this work will simulate is magnesium silicide (Mg2Si), a thermoelectric material. Thermoelectric materials, in general, become more efficient in converting heat into electrical power as their λp decreases. λp will be calculated for SWC-NTs of varying lengths, diameters, and at varying equilibration temperatures (Teq). λp will be calculated for samples of pure Mg2Si and Mg2Si with off-stoichiometry over a range of Teq values. Two methods will be used to induce the off-stoichiometry: atomic silicon (Si) substitutionals, and Si NPs. A range of stoichiometric ratios will be applied to the material by both methods, and then λp will be calculated for each of these cases. This is done so as to observe which method of stoichiometric change, given the same stoichiometric ratio, decreases λp greater, and, therefore, causes Mg2Si to be a better thermoelectric material. It is expected that increases in length will increase the λp of the SWCNT, while increases in diameter and Teq will decrease λp. It is expected that increases in atomic percent (a/o) Si and Teq will decrease λp regardless of the method of stoichiometric change, and that the Si NP method will decrease λp more than the atomic Si substitutional method

Communication of military couples during deployment predicting generalized anxiety upon reunion

This study draws on the emotional cycle of deployment model (Pincus, House, Christenson, & Adler, 2001) to consider how the valence of communication between military personnel and at-home partners during deployment predicts their generalized anxiety upon reunion. Online survey data were collected from 555 military couples (N = 1,110 individuals) once per month for 8 consecutive months beginning at homecoming. Dyadic growth curve modeling results indicated that people’s anxiety declined across the transition. For at-home partners, constructive communication during deployment predicted a steeper decline in anxiety over time. For both returning service members and at-home partners, destructive communication during deployment predicted more anxiety upon reunion but a steeper decline in anxiety over time. Results were robust beyond the frequency of communication during deployment and a host of individual, relational, and military variables. These findings advance the emotional cycle of deployment model, highlight the importance of the valence of communication during deployment, and illuminate how the effects of communication during deployment can endure after military couples are reunited

Religious and Spiritual Predictors of Gambling Participation and Gambling Problems Among College Students

The present study used structural equation modeling to assess spiritual and religious predictors of gambling problems and gambling participation. College students from state and religiously affiliated schools reported on their gambling participation and problems, as well as their spirituality, religious behavior and degree of religious affiliation. Additionally, participants reported their perceptions regarding peer gambling behavior, peer gambling approval, and church member gambling approval. The results indicated higher spirituality predicted fewer gambling problems, but only for women. Peer approval of gambling and church member approval of gambling predicted higher gambling frequency. Peer approval of gambling also predicted more gambling problems. Peer and church member approval of gambling completely mediated the relationships between religiosity and church affiliation and gambling frequency and problems. These same relationships were partially mediated for spirituality. Religious variables were predictive of gambling frequency and problems until peer and church member approval were included as mediators. These findings suggest that religious variables influence gambling primarily in an indirect way by influencing peer groups or perceptions of peer approval

Effectiveness of Mary Ainsworth\u27s Maternal Sensitivity Scale with Four-week-old Infants

The attachment relationship between a mother and her infant provides a foundation for future development (Bowlby, 1951; Sroufe, 2005). A high level of maternal sensitivity has been deemed one of the most important antecedents to a secure attachment (van IJzendoorn & Bakermans-Kranenburg, 2004). Although Mary Ainsworth originally developed a measure of maternal sensitivity other researchers developed measures to determine a mother’s level of sensitivity (Mesman & Emmen, 2013). The Strange Situation Procedure (SSP) was developed to determine the classification of the attachment relationship (Ainsworth, Bell, & Stayton, 1974). Currently these measures focus predominantly on dyads that include an infant at approximately age 12 months. Since the benefit of earlier intervention in problematic parental-infant relationships is evident (Juffer, et al., 2008), discovering ways to accurately measure parental sensitivity at earlier infant ages would be beneficial. This study is unique in that it includes infants who are 4 weeks old. The overall intent of this study is to ascertain the relationship between maternal sensitivity at 4 weeks and attachment classification at 16 months and whether the Ainsworth Maternal Sensitivity Scale (AMSS) (Ainsworth et al., 1974) is a reliable measure for assessing maternal sensitivity at the infant\u27s age of 4 weeks and 16 months. Sixty-eight mothers were videotaped during interaction with their infant at age 4 weeks. Mothers returned with their 16 month-old infant to participate in the SSP to determine attachment security (see Ainsworth & Bell 1970). Maternal sensitivity during the SSP was also coded using the AMSS and previously reported results determined that higher levels of maternal sensitivity at that time was related to secure attachment (Muir, Koester & Yorgason, 2012). Maternal sensitivity was coded during the 4 week infant-mother interaction using the AMSS. Results showed that maternal sensitivity at 4 weeks was not correlated with the maternal sensitivity at 16 months. Maternal sensitivity at 4 weeks was not related to overall attachment classifications at 16 months but specifically deciphered subtypes of secure and disorganized attachment. Development of infant age-specific measures that predict attachment is worth future consideration

Military Children’s Difficulty with Reintegration after Deployment: A Relational Turbulence Model Perspective

This study drew on the relational turbulence model to investigate how the interpersonal dynamics of military couples predict parents’ reports of the reintegration difficulty of military children upon homecoming after deployment. Longitudinal data were collected from 118 military couples once per month for 3 consecutive months after reunion. Military couples reported on their depressive symptoms, characteristics of their romantic relationship, and the reintegration difficulty of their oldest child. Results of dyadic growth curve models indicated that the mean levels of parents’ depressive symptoms (H1), relationship uncertainty (H2), and interference from a partner (H3) were positively associated with parents’ reports of military children’s reintegration difficulty. These findings suggest that the relational turbulence model has utility for illuminating the reintegration difficulty of military children during the postdeployment transition

Improvement of Thermoelectric Properties through Reduction of Thermal Conductivity by Nanoparticle Addition and Stoichiometric Change to Mg2Si

Thermoelectric materials have been of interest for several decades due to their ability to recapture waste heat of various systems and convert it to useful electricity. One method used to improve the thermoelectric figure of merit, given by ZT = (σS2T)/(ke+kp), is to reduce the lattice thermal conductivity (kp) while not affecting the other properties. In order to reduce kp of the material, this paper introduces nanoparticles of Si in Mg2Si to manipulate phonon scattering and mean free path. LAMMPS molecular dynamics software is employed using the nonequilibrium molecular dynamics (NEMD) method to perform a series of simulations with the metal silicide thermoelectric material MgxSix. The objective of this work is two-fold: 1) to determine the optimal nanoparticle concentration and 2) to determine the optimal MgxSix stoichiometry for minimizing the thermal conductivity of the system. It should be noted, however, that the assumed reduction in thermal conductivity is only a result of reduced phonon transport and minimal impact is made on the transport of electrons. Interestingly, the uniform off-stoichiometry (41.37 percent Si) sample of MgxSix resulted in a reduction of kp of 72.39 percent, while the Si nanoparticle sample, with matching percent Si, resulted in a reduction of kp of 65.59 percent