Energy localization and heat generation in composite energetic systems under high-frequency mechanical excitation

In this work, the ability to use high frequency mechanical excitation to generate significant heating within plastic bonded explosives, as well as single energetic particles embedded within a viscoelastic binder, is studied. In this work, the fundamental mechanisms associated with the conversion of high-frequency mechanical excitation to heat as applied to these composite energetic systems are thoroughly investigated. High-frequency contact excitation has been used to generate a significant amount of heat within samples of PBX 9501 and representative inert mock materials. Surface temperature rises on the order of 10 °C were observed at certain frequencies over a range from 50 kHz to 40 MHz at thermal steady state conditions. The mechanical responses of these samples were also measured to explore the connection between the thermal and bulk motion of the samples. It was found that significant heating of the samples near the transducer resonance was driven by the bulk motion of the material while heating observed at higher frequencies were attributed to particle-scale interactions. To further investigate the interactions occurring at the particle scale, similar excitation was applied to samples of an elastic binder embedded with individual inert or energetic particles. Samples were excited over a range of 100 kHz to 20 MHz, and two distinct frequency regions were observed with separate characteristic heating trends. Through the comparison of the measured surface motion of the sample to the spatial temperature maps of the surface, it was determined that for heating observed in the samples at excitation frequencies above 1 MHz, the heat generation was due viscoelastic effects of the binder near the sample surface. However, at excitation frequencies near the transducer resonance of 215 kHz, it was determined that significant heat was generated at the inclusion and was associated with particle-binder interactions. For these cases of particle associated heating, an analytical heat conduction model was fit to the collected surface temperature data to estimate the heating rates and temperatures associated with the embedded particles. To investigate the potential of stress concentrations to generate localized heating near an inclusion due to viscoelastic losses, an analytical solution of the stress and temperature fields caused by wave scattering effects due to a spherical inclusion within a lossy binder was developed. Results indicate that under certain excitation and sample configurations, significant heating can occur due to stress concentrations caused by constructive interference of the waves near the inclusion and temperatures are predicted to approach or exceed realistic decomposition temperatures of various energetic materials. This analysis indicates that significant heating of the embedded particles can be induced without the presence of delamination or voids; however, this phenomenon it thought to mainly be a precursor or driver to more dynamic events associated with debonding between the particle and binder. Finally, high speed X-ray phase contrast imaging and high speed visible microscopy were used to demonstrate the individual heating mechanisms associated with the heating and subsequent decomposition of an HMX particle within a viscoelastic binder under ultrasonic excitation. Additional analysis of the transient surface temperature of the sample was used to characterize and quantify the heat generation produced from each observed heating mechanism. The results and developed methods presented in this work should prove useful in the understanding of the conversion of mechanical to thermal energy via various mechanisms within composite energetic systems. (Abstract shortened by ProQuest.

Case Study: Diesel-Powered Loaders Compared to Hybrid Loaders in Heavy Civil Construction

With the construction industry constantly changing, the environmental impacts of greenhouses gases have become a huge concern. Many contractors are adapting and switching over to hybrid powered systems to allow for more energy saving methods for heavy equipment, an increase in productivity, and efficient construction equipment that comply with emission regulations. The goal for this paper is to analyze the feasibility of heavy civil construction companies switching over from conventional diesel-powered wheel loaders to hybrid wheel loaders. Due to the competitive and saturated market in roadwork construction, many contractors have already begun to invest into hybrid systems. This provides cost savings in fuel efficiency and operating costs over the conventional fueled loaders. Qualitative research was conducted for this report through semi-structured personal interviews with heavy equipment experts, and the usage of primary and secondary sources. Although the switch to operating with a hybrid system it will potential have a higher up-front cost, it will have fewer operating costs and environmental impacts in the future

Time-Reversal-Violating Schiff Moment of 199Hg

We calculate the Schiff moment of the nucleus 199Hg, created by pi-N-N vertices that are odd under parity (P) and time-reversal (T). Our approach, formulated in diagrammatic perturbation theory with important core-polarization diagrams summed to all orders, gives a close approximation to the expectation value of the Schiff operator in the odd-A Hartree-Fock-Bogoliubov ground state generated by a Skyrme interaction and a weak P- and T-odd pion-exchange potential. To assess the uncertainty in the results, we carry out the calculation with several Skyrme interactions (the quality of which we test by checking predictions for the isoscalar-E1 strength distribution in 208Pb) and estimate most of the important diagrams we omit.Comment: 13 pages, 7 figure

Spin and exchange coupling for Ti embedded in a surface dipolar network

We have studied the spin and exchange coupling of Ti atoms on a Cu$_2$N/Cu(100) surface using density functional theory. We find that individual Ti have a spin of 1.0 (i.e., 2 Bohr Magneton) on the Cu$_2$N/Cu(100) surface instead of spin-1/2 as found by Scanning Tunneling Microscope. We suggest an explanation for this difference, a two-stage Kondo effect, which can be verified by experiments. By calculating the exchange coupling for Ti dimers on the Cu$_2$N/Cu(100) surface, we find that the exchange coupling across a `void' of 3.6\AA\ is antiferromagnetic, whereas indirect (superexchange) coupling through a N atom is ferromagnetic. We confirm the existence of superexchange interactions by varying the Ti-N angle in a model trimer calculation. For a square lattice of Ti on Cu$_2$N/Cu(100), we find a novel spin striped phase

Anarchism and the press in Lima: The case of "Los Parias"

This thesis explores the relationship between the anarchist press and the nascent labor movement in the Republic of Peru in the beginning of the twentieth century. The first anarchist newspaper that appeared in Peru in 1904, titled Los Parias, provides a detailed look into the ways in which this communications medium, thanks to its timely message and firm social commitment, was able to forge an alliance with the workers of Peru in order to work towards a more socially egalitarian society in an era often recognized as the "Aristocratic Republic;" a historical period were old aristocracies and new bourgeoisies controlled the nation. By analyzing this material, this thesis hopes to delve deeper into how anarchists and all those who became supporters of this ideology (i.e. workers??? associations, guilds, students, intellectuals, etc.) conceptualized their social condition and the solutions they championed in order to achieve a libertarian utopia. The collaboration between anarchists and the nascent labor movement resulted in the formulation of an anti-establishment rhetoric that served as a precursor to new radical social trends that appeared in Peru as the twentieth century marched along; trends that had a profound effect in the social landscape of the nation. We find in these pages a call for social redemption; a radical and revolutionary alternative to elite control