Clemson University

About: Clemson University is a education organization based out in Clemson, South Carolina, United States. It is known for research contribution in the topics: Population & Control theory. The organization has 20556 authors who have published 42518 publications receiving 1170779 citations. The organization is also known as: Clemson Agricultural College of South Carolina.

The r-process and neutrino-heated supernova ejecta

Abstract: As a neutron star is formed by the collapse of the iron core of a massive star, its Kelvin-Helmholtz evolution is characterized by the release of gravitational binding energy as neutrinos. The interaction of these neutrinos with heated material above the neutron star generates a hot bubble in an atmosphere that is nearly in hydrostatic equilibrium and heated, after approximately 10 s, to an entropy of S/N(sub AS)k greater than or approximately = 400. The neutron-to-proton ratio for material moving outward through this bubble is set by the balance between neutrino and antineutrino capture on nucleons. Because the electron antineutrino spectrum at this time is hotter than the electron neutrino spectrum, the bubble is neutron-rich (0.38 less than or approximately = Y(sub e) less than or approximately = 0.47). Previous work using a schematic model has shown that these conditions are well suited to the production of heavy elements by the r-process. In this paper we have advanced the numerical modeling of a 20 solar mass 'delayed' supernova explosion to the point that we can follow the detailed evolution of material moving through the bubble at the late times appropiate to r-process nucleosynthesis. The supernova model predicts a final kinetic energy for the ejecta of 1.5 x 10(exp 51) ergs and leaves behind a remnant with a baryon mass of 1.50 solar mass (and a gravitational mass of 1.445 solar mass). We follow the thermodynamic and compositional evolution of 40 trajectories in rho(t), T(t), Y(sub e)(t) for a logarithmic grid of mass elements for the last approximately = 0.03 solar mass to be ejected by the proto-neutron star down to the last less than 10(exp -6) solar mass of material expelled at up to approximately = 18 s after core collapse. We find that an excellent fit to the solar r-process abundance distribution is obtained with no adjustable parameters in the nucleosynthesis calculations. Moreover, the abundances are produced in the quantities required to account for the present Galactic abundances. However, at earlier times, this one-dimensional model ejects too much material with entropies S/N(sub A)k approximately 50 and Y(sub e) approximately 0.46. This leads to an acceptable over production of N = 50 nuclei, particularly Sr-88, Y-89, and Zr-90, relative to their solar abundances. We speculate on various means to avoid the early overproduction and/or ejection of N = 50 isotonic nuclei while still producing and ejecting the correct amount of r-process material.

On the Role of Nonlinearities in Vibratory Energy Harvesting: A Critical Review and Discussion

Abstract: The last two decades have witnessed several advances in microfabrication technologies and electronics, leading to the development of small, low-power devices for wireless sensing, data transmission, actuation, and medical implants. Unfortunately, the actual implementation of such devices in their respective environment has been hindered by the lack of scalable energy sources that are necessary to power and maintain them. Batteries, which remain the most commonly used power sources, have not kept pace with the demands of these devices, especially in terms of energy density. In light of this challenge, the concept of vibratory energy harvesting has flourished in recent years as a possible alternative to provide a continuous power supply. While linear vibratory energy harvesters have received the majority of the literature’s attention, a significant body of the current research activity is focused on the concept of purposeful inclusion of nonlinearities for broadband transduction. When compared to their linear resonant counterparts, nonlinear energy harvesters have a wider steady-state frequency bandwidth, leading to a common belief that they can be utilized to improve performance in ambient environments. Through a review of the open literature, this paper highlights the role of nonlinearities in the transduction of energy harvesters under different types of excitations and investigates the conditions, in terms of excitation nature and potential shape, under which such nonlinearities can be beneficial for energy harvesting. [DOI: 10.1115/1.4026278]

The Role of Relationship Quality in the Stratification of Vendors as Perceived by Customers

Abstract: Companies implement preferred supplier programs to reduce their vendor relationships to a reasonable few. Consequently, vendors who do not effectively manage their customer-based relationships are strong candidates for deletion from a customer’s list of long-term suppliers. The emergence of preferred supplier programs suggests that businesses are beginning to formally recognize and reward differences between their qualified vendors. Vendor stratification is proposed as a framework for understanding the evolution of preferred vendor programs. With the growing interest in relationship marketing, a study was conducted to empirically examine the extent to which businesses use relationship quality perceptions to differentiate their qualified vendors. The findings support the notion that relationship quality is a higher-order construct that can be used as a basis for developing vendor stratification systems. The article concludes with a discussion of the managerial and research implications of the study findings.

Photoluminescence properties of graphene versus other carbon nanomaterials.

Abstract: Photoluminescent nanomaterials continue to garner research attention becauseof their many applications. For many years, researchers have focused on quantum dots (QDs) of semiconductor nanocrystals for their excellent performance and predictable fluorescence color variations that depend on the sizes of the nanocrystals. Even with these advantages, QDs can present some major limitations, such as the use of heavy metals in the high-performance semiconductor QDs. Therefore, researchers continue to be interested in developing new QDs or related nanomaterials. Recently, various nanoscale configurations of carbon have emerged as potential new platforms in the development of brightly photoluminescent materials.As a perfect π-conjugated single sheet, graphene lacks electronic bandgaps andis not photoluminescent. Therefore, researchers have created energy bandgaps within graphene as a strategy to impart fluorescence emissions. Researchers have explored many experimental techniques to introduce bandgaps, such as cut...