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.

More Oil, Less Democracy: Evidence from Worldwide Crude Oil Discoveries

Abstract: This paper exploits variations in the timing and size of oil discoveries to identify the impact of oil wealth on democracy. I use a unique dataset from the Association for the Study of Peak Oil and Gas and other sources describing worldwide oil endowment, exploration, discoveries, and oilfield geology. Using oil discovery as a quasi-experiment, I find that discovering oil decreases a country's 30-year change in democracy, as measured by the Polity Index. On average, discovering 100 billion barrels pushes a country's democracy level almost 20 percentage points below trend. The estimated effect per barrel is larger for oilfields with higher-quality oil and lower exploration and extraction costs. Excluding large Middle East producers from the sample does not affect these results.

Climate Change and Drought: a Perspective on Drought Indices

Abstract: Droughts occur naturally, but climate change has generally accelerated the hydrological processes to make them set in quicker and become more intense, with many consequences, not the least of which is increased wildfire risk. There are different types of drought being studied, such as meteorological, agricultural, hydrological, and socioeconomic droughts; however, a lack of unanimous definition complicates drought study. Drought indices are used as proxies to track and quantify droughts; therefore, accurate formulation of robust drought indices is important to investigate drought characteristics under the warming climate. Because different drought indices show different degrees of sensitivity to the same level of continental warming, robustness of drought indices against change in temperature and other variables should be prioritized. A formulation of drought indices without considering the factors that govern the background state may lead to drought artifacts under a warming climate. Consideration of downscaling techniques, availability of climate data, estimation of potential evapotranspiration (PET), baseline period, non-stationary climate information, and anthropogenic forcing can be additional challenges for a reliable drought assessment under climate change. As one formulation of PET based on temperatures can lead to overestimation of future drying, estimation of PET based on the energy budget framework can be a better approach compared to only temperature-based equations. Although the performance of drought indicators can be improved by incorporating reliable soil moisture estimates, a challenge arises due to limited reliable observed data for verification. Moreover, the uncertainties associated with meteorological forcings in hydrological models can lead to unreliable soil moisture estimates under climate change scenarios.

The Afterglows of Swift-era Gamma-ray Bursts. I. Comparing pre-Swift and Swift-era Long/Soft (Type II) GRB Optical Afterglows

Abstract: We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.

CUAVE: A new audio-visual database for multimodal human-computer interface research

Abstract: Multimodal signal processing has become an important topic of research for overcoming certain problems of audio-only speech processing. Audio-visual speech recognition is one area with great potential. Difficulties due to background noise and multiple speakers are significantly reduced by the additional information provided by extra visual features. Despite a few efforts to create databases in this area, none has emerged as a standard for comparison for several possible reasons. This paper seeks to introduce a new audiovisual database that is flexible and fairly comprehensive, yet easily available to researchers on one DVD. The CUAVE database is a speaker-independent corpus of over 7,000 utterances of both connected and isolated digits. It is designed to meet several goals that are discussed in this paper. The most notable are availability of the database, flexibility for use of the audio-visual data, and realistic considerations in the recordings (such as speaker movement). Another important focus of the database is the inclusion of pairs of simultaneous speakers, the first documented database of this kind. The overall goal of this project is to facilitate more widespread audio-visual research through an easily available database. For information on obtaining CUAVE, please visit our webpage (http://ece.clemson.edu/speech).