Sound propagation over uneven ground and irregular topography

The goal of this research is to develop theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography here is understood to imply a ground surface that is not idealizable as being perfectly flat or that is not idealizable as having a constant specific acoustic impedance. The interest of this study focuses on circumstances where the propagation is similar to what might be expected for noise from low-attitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence. The activities and developments that have resulted during the period, August 1986 through February 1987, are discussed

Sound propagation over uneven ground and irregular topography

Theoretical, computational, and experimental techniques were developed for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography is understood to imply a ground surface that: (1) is not idealizable as being perfectly flat, or (2) that is not idealizable as having a constant specific acoustic impedance. The focus is on circumstances where the propagation is similar to what might be expected for noise from low altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence

Sound propagation over uneven ground and irregular topography

The acoustic impedance of the surface coverings used in the laboratory experiments on sound diffraction by topographical ridges was determined. The model, which was developed, takes into account full wave effects and the possibility of surface waves and predicts the sound pressure level at the receiver location relative to what would be expected if the flat surface were not present. The sound pressure level can be regarded as a function of frequency, sound speed in air, heights of source and receiver, and horizontal distance from source to receiver, as well as the real and imaginary parts of the surface impedance

Ice Formation on Kaolinite: Insights from Molecular Dynamics Simulations

The formation of ice affects many aspects of our everyday life as well as technologies such as cryotherapy and cryopreservation. Foreign substances almost always aid water freezing through heterogeneous ice nucleation, but the molecular details of this process remain largely unknown. In fact, insight into the microscopic mechanism of ice formation on different substrates is difficult to obtain even via state-of-the-art experimental techniques. At the same time, atomistic simulations of heterogeneous ice nucleation frequently face extraordinary challenges due to the complexity of the water-substrate interaction and the long timescales that characterize nucleation events. Here, we have investigated several aspects of molecular dynamics simulations of heterogeneous ice nucleation considering as a prototypical ice nucleating material the clay mineral kaolinite, which is of relevance in atmospheric science. We show via seeded molecular dynamics simulations that ice nucleation on the hydroxylated (001) face of kaolinite proceeds exclusively via the formation of the hexagonal ice polytype. The critical nucleus size is two times smaller than that obtained for homogeneous nucleation at the same supercooling. Previous findings suggested that the flexibility of the kaolinite surface can alter the time scale for ice nucleation within molecular dynamics simulations. However, we here demonstrate that equally flexible (or non flexible) kaolinite surfaces can lead to very different outcomes in terms of ice formation, according to whether or not the surface relaxation of the clay is taken into account. We show that very small structural changes upon relaxation dramatically alter the ability of kaolinite to provide a template for the formation of a hexagonal overlayer of water molecules at the water-kaolinite interface, and that this relaxation therefore determines the nucleation ability of this mineral

Removing the barrier to the calculation of activation energies: Diffusion coefficients and reorientation times in liquid water

See also: The Journal of Chemical Physics 145 (13), 134107 (2016). The following article appeared in Piskulich, Z. A., Mesele, O. O., & Thompson, W. H. (2017). Removing the barrier to the calculation of activation energies: Diffusion coefficients and reorientation times in liquid water. The Journal of Chemical Physics, 147(13), 134103. and may be found at https://aip.scitation.org/doi/10.1063/1.4997723.General approaches for directly calculating the temperature dependence of dynamical quantities from simulations at a single temperature are presented. The method is demonstrated for self-diffusion and OH reorientation in liquid water. For quantities which possess an activation energy, e.g., the diffusion coefficient and the reorientation time, the results from the direct calculation are in excellent agreement with those obtained from an Arrhenius plot. However, additional information is obtained, including the decomposition of the contributions to the activation energy. These results are discussed along with prospects for additional applications of the direct approach

Geometric Phantom Categories

In this paper we give a construction of phantom categories, i.e. admissible triangulated subcategories in bounded derived categories of coherent sheaves on smooth projective varieties that have trivial Hochschild homology and trivial Grothendieck group. We also prove that these phantom categories are phantoms in a stronger sense, namely, they have trivial K-motives and, hence, all their higher K-groups are trivial too.Comment: LaTeX, 18 page

Integral Grothendieck-Riemann-Roch theorem

We show that, in characteristic zero, the obvious integral version of the Grothendieck-Riemann-Roch formula obtained by clearing the denominators of the Todd and Chern characters is true (without having to divide the Chow groups by their torsion subgroups). The proof introduces an alternative to Grothendieck's strategy: we use resolution of singularities and the weak factorization theorem for birational maps.Comment: 24 page

Impact of level of personality pathology on affective, behavioral, and thought problems in pregnant women during the Coronavirus Disease 2019 pandemic

Among at-risk groups for psychological distress in the context of the Coronavirus Disease 2019 (COVID-19) pandemic, pregnant women might be especially vulnerable. Identifying subgroups of pregnant women at high risk of poor adaptation might optimize clinical screening and intervention, which could, in turn, contribute to mitigating the potentially devastating effects of prenatal stress on mothers and fetus. Level of personality functioning may be a good indicator of who may be more vulnerable to distress in challenging periods like the COVID-19 pandemic, as adults with high levels of personality dysfunction may experience significant difficulties in mentalizing threatening situations. The aims of the present study are (a) to determine the impact of level of personality pathology on affective, behavioral, and thought problems in pregnant women during the COVID-19 pandemic; and (b) to test a model where mentalization of trauma mediates the impact of personality pathology on symptomatology. Data from 1,207 French-Canadian pregnant women recruited through social media during the COVID-19 pandemic were analyzed. Latent profile analysis, using the Criterion A elements of the alternative model for personality disorders (Identity, Self-Direction, Empathy, Intimacy) as latent indicators, yielded four profiles: Healthy, Mild Self-Impairment, Intimacy Impairment, and Personality Disorder. Profiles showed significant associations with diverse indicators of symptomatology. Mediation models showed both direct and indirect (through mentalization of trauma) significant associations between level of personality functioning and affective/behavioral/thought problems. Results have clinical implications on prophylactic measures for at-risk pregnant women, especially in challenging contexts such as the COVID-19 pandemic