University of North Texas

About: University of North Texas is a education organization based out in Denton, Texas, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 11866 authors who have published 26984 publications receiving 705376 citations. The organization is also known as: Fight, North Texas & UNT.

Committing to ecological restoration

Abstract: At the September 2014 United Nations Climate Summit, governments rallied around an international agreement—the New York Declaration on Forests—that underscored restoration of degraded ecosystems as an auspicious solution to climate change. Ethiopia committed to restore more than one-sixth of its land. Uganda, the Democratic Republic of Congo, Guatemala, and Colombia pledged to restore huge areas within their borders. In total, parties committed to restore a staggering 350 million hectares by 2030.

“Turning Over” Definitions in Catalytic Cycles

Abstract: “Indeed, the catalytic activity, for a valid comparison, must be referred to the number of exposed surface atoms of a specified kind. Thus a convenient way to express catalytic activity is by means of a turnover number equal to the number of reactant molecules converted per minute per catalytic site for given reaction conditions.” With these words of Boudart the first definition of what later was called the Turnover Frequency (TOF) entered into the realm of heterogeneous chemistry. It was a term borrowed from enzymatic kinetics, and slowly passed to homogeneous catalysis. Nowadays it is a ubiquitous term, focusing strictly on the catalytic center, as distinct from the classical term “rate of reaction”, which emphasizes the generation of products or the consumption of reactants. Despite its utility and common use, the TOF concept is still not well-defined and leads to confusion. IUPAC’s gold book, the most authoritative source of chemical terminology, has a very concise definition of the turnover frequency: “Commonly called the turnover number, N, and defined, as in enzyme catalysis, as molecules reacting per active site in unit time.” This description of the TOF has two main problems. The first is the difficulty of providing a one-to-one correspondence between name and function, since (as appeared in Boudart’s paragraph) the terms “turnover frequency” (TOF) and “turnover number” (TON) seem to have one and the same meaning. However, in typical catalytic jargon, both expressions have very different connotations. Sometimes also the terms “turnover rate” and “catalytic constant” (kcat) are used interchangeably in the literature with the same meaning. To make matters worse, the TOF is occasionally considered a rate-constant, since the rate of reaction (r = TOF × [Cat]) depends on the catalysts concentration. However, the TOF itself can depend on the concentration of reactants and products even at saturation, and in this sense it is closer to a rate than to a kinetic constant. In spite of this, from a strict terminological stance the TOF is a frequency, with units of time−1. All this debate evidently resembles the biblical story of the Tower of Babel and the confusion of languages. The second problem of IUPAC’s and Boudart’s definitions is a recurring expression of the TOF as a function of the number of reactants consumed, or even of the products generated. In most cases it is indeed an accurate way to derive the TOF, but for instance in bimolecular reactions this is not the case. Moreover, and from a philosophical perspective, when expressing the TOF as a function of produced or consumed molecules, the focus of the measure goes back to those molecules instead of emphasizing the role of the catalyst (see Scheme 1).

Break Point Estimation and Spurious Rejections With Endogenous Unit Root Tests

Abstract: This paper examines the accuracy of break point estimation using the endogenous break unit root tests of Zivot and Andrews (1992) and Perron (1997). We find that these tests tend to identify the break point incorrectly at one‐period behind (TB‐1) the true break point (TB), where bias in estimating the persistence parameter and spurious rejections are the greatest. In addition, this outcome occurs under the null and alternative hypotheses, and more so as the magnitude of the break increases. Consequences of utilizing these endogenous break tests are similar to (incorrectly) omitting the break term Bt in Perron's (1989) exogenous test.

RSS-Based Location Estimation with Unknown Pathloss Model

Abstract: Recently, received signal strength (RSS)-based location estimation technique has been proposed as a low-cost, low-complexity solution for many novel location-aware applications. In the existing studies, radio propagation pathloss model is assumed known a priori, which is an oversimplification in many application scenarios. In this paper we present a detailed study on the RSS-based joint estimation of unknown location coordinates and distance-power gradient, a parameter of pathloss model. A nonlinear least-square estimator is presented and the performance of the algorithm is studied based on CRB and various simulation results. From simulation results it is shown that the proposed joint estimator is especially useful for location estimation in unknown or changing environments