Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

In situ IR, Raman, and UV-Vis DRS spectroscopy of supported vanadium oxide catalysts during methanol oxidation

Abstract: The application of in situ Raman, IR, and UV-Vis DRS spectroscopies during steady-state methanol oxidation has demonstrated that the molecular structures of surface vanadium oxide species supported on metal oxides are very sensitive to the coordination and H-bonding effects of adsorbed methoxy surface species. Specifically, a decrease in the intensity of spectral bands associated with the fully oxidized surface (V5+) vanadia active phase occurred in all three studied spectroscopies during methanol oxidation. The terminal V = O (∼1030 cm−1) and bridging V–O–V (∼900–940 cm−1) vibrational bands also shifted toward lower frequency, while the in situ UV-Vis DRS spectra exhibited shifts in the surface V5+ LMCT band (>25,000 cm−1) to higher edge energies. The magnitude of these distortions correlates with the concentration of adsorbed methoxy intermediates and is most severe at lower temperatures and higher methanol partial pressures, where the surface methoxy concentrations are greatest. Conversely, spectral changes caused by actual reductions in surface vanadia (V5+) species to reduced phases (V3+/V4+) would have been more severe at higher temperatures. Moreover, the catalyst (vanadia/silica) exhibiting the greatest shift in UV-Vis DRS edge energy did not exhibit any bands from reduced V3+/V4+ phases in the d–d transition region (10,000–30,000 cm−1), even though d–d transitions were detected in vanadia/alumina and vanadia/zirconia catalysts. Therefore, V5+ spectral signals are generally not representative of the percent vanadia reduction during the methanol oxidation redox cycle, although estimates made from the high temperature, low methoxy surface coverage IR spectra suggest that the catalyst surfaces remain mostly oxidized during steady-state methanol oxidation (15–25% vanadia reduction). Finally, adsorbed surface methoxy intermediate species were easily detected with in situ IR spectroscopy during methanol oxidation in the C–H stretching region (2800–3000 cm−1) for all studied catalysts, the vibrations occurring at different frequencies depending on the specific metal oxide upon which they chemisorb. However, methoxy bands were only found in a few cases using in situ Raman spectroscopy due to the sensitivity of the Raman scattering cross-sections to the specific substrate onto which the surface methoxy species are adsorbed.

Constitutive relations for concrete

Abstract: A constitutive relation and failure criterion for concrete material under general three-dimensional stress states have been formulated using the work-hardening theory of plasticity. The formulation considers the weak tensile strength, strain-hardening, and fracture behavior of concrete. The resulting stress-strain relationships are compared with existing biaxial loading experimental results and good agreement is generally observed. The relation is suitable for use in the finite element analysis of reinforced or prestressed concrete.

High Resolution Capabilities of MIMO Radar

Abstract: Multiple-input multiple-output (MIMO) radar is a multistatic architecture composed of multiple transmitters and receivers, which seeks to exploit the spatial diversity of radar backscatter. In conjunction with centralized processing, MIMO radar has the potential to significantly improve radar functions such as detection and parameter estimation. MIMO radar is distinct from other types of array radars such as phased array or STAP, which process the signals of closely spaced elements and, hence, cannot capitalize on the spatial characteristics of targets. In this work, we explore the ability of MIMO radar and coherent processing to locate a target with high resolution and to resolve targets located in the same range cell. A distributed target model is developed. It is demonstrated that MIMO radar with centralized coherent processing is able to resolve scatterers with a range resolution well beyond that supported by the signal bandwidth. The location estimation capabilities are further illustrated by introducing a new two-dimensional ambiguity function. The analysis is discussed in the context of established results for randomly thinned arrays. The investigation of high resolution MIMO radar also includes comparison with the performance of non-coherent MIMO radar and the effect on performance of the number of sensors and their locations.

Interfacial interaction between low-energy surfaces

Abstract: This review is concerned primarily with the correlation between the interfacial interactions and the constitutive properties of low-energy organic surfaces. It starts with a discussion on the estimation of the surface free energy of organic solids from contact angles, followed by a review of the surface energetics and adhesion. The experimental measurements of surface free energy, in most cases, are themselves dependent upon the specific models of interfacial energetics and therefore are indirect. A direct method of estimating adhesion and surface free energy is based on contact mechanics, which measures the deformation produced on contacting elastic semispheres under the influence of surface forces and external loads, Since the equilibrium is described by the balance of the elastic and surface forces of the system, the load-deformation data can be translated directly to estimate the adhesion and surface free energies. In most cases however, the contact deformations obtained from the loading and unloading cycles exhibit hysteresis, which are sensitive to the structure and chemical compositions of the interfaces. For non-hysteretic systems, the surface free energies obtained from these contact deformations compare well with the values obtained from contact angles. The application of this method to the studies of dispersion and hydrogen-bonding interaction is reviewed.