p-Δ curves for a point source lying on a boundary

1977 ◽  
Vol 67 (6) ◽  
pp. 1521-1527
Author(s):  
George A. McMechan
Keyword(s):  
Point Source ◽  
Ocean Surface ◽  
Ocean Bottom ◽  
Surface Source

abstract A point source located at a boundary is an approximation to the physical configuration of an earthquake or an explosion at the ocean bottom. The p-Δ curves that correspond to arrivals from such a source, as observed at the ocean surface and at the ocean bottom, can be constructed by geometrical manipulations of the surface source to surface receiver p-Δ curve. p-Δ curves for multiply reflected arrivals can also be similarly constructed.

scholarly journals Is the ocean surface a source of nitrous acid (HONO) in the marine boundary layer?

2021 ◽  
Author(s):  
Leigh Crilley ◽  
Louisa Kramer ◽  
Francis Pope ◽  
Chris Reed ◽  
James Lee ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Nitrous Acid ◽  
Marine Boundary Layer ◽  
Ocean Surface ◽  
Cape Verde ◽  
Formation Mechanisms ◽  
Oh Radicals ◽  
Surface Source ◽  
Global Impacts ◽  
Quantitative Understanding

Abstract. Nitrous acid, HONO, is a key net photolytic precursor to OH radicals in the atmospheric boundary later. As OH is the dominant atmospheric oxidant, driving the removal of many primary pollutants and the formation of secondary species, a quantitative understanding of HONO sources is important to predict atmospheric oxidising capacity. While a number of HONO formation mechanisms have been identified, recent work has ascribed significant importance to the dark, ocean-surface mediated conversion of NO2 to HONO in the coastal marine boundary layer. In order to evaluate the role of this mechanism, here we analyse measurements of HONO and related species obtained at two contrasting coastal locations – Cape Verde (Atlantic Ocean), representative of the clean remote tropical marine boundary layer, and Weybourne (United Kingdom), representative of semi-polluted Northern European coastal waters. As expected, higher average concentrations of HONO (70 ppt) were observed in marine air for the more anthropogenically influenced Weybourne location compared to Cape Verde (HONO < 5 ppt). At both sites, the approximately constant HONO/NO2 ratio at night pointed to a low importance for the dark ocean-surface mediated conversion of NO2 into HONO, whereas the midday maximum in the HONO/NO2 ratios indicated significant contributions from photo-enhanced HONO formation mechanisms (or other sources). We obtained an upper limit to the rate coefficient of dark ocean-surface HONO-to-NO2 conversion of CHONO = 0.0011 ppb hr−1 from the Cape Verde observations; this is a factor of 5 lower than the slowest rate reported previously. These results point to significant geographical variation in the predominant HONO formation mechanisms in marine environments and indicate that caution is required when extrapolating the importance of such mechanisms from individual study locations to assess regional and/or global impacts on oxidising capacity. As a significant fraction of atmospheric processing occurs in the marine boundary layer, particularly in the tropics, better constraint of the possible ocean surface source of HONO is important for a quantitative understanding of chemical processing of primary trace gases in the global atmospheric boundary layer and associated impacts upon air pollution and climate.

Groundwater Contamination by Chlorinated Hydrocarbon Impurities Present in Soil Fumigant Formulations

1998 ◽  
Vol 33 (1) ◽  
pp. 31-50 ◽  
Author(s):  
B.J. Zebarth ◽  
S.Y. Szeto ◽  
B. Hii ◽  
H. Liebscher ◽  
G. Grove
Keyword(s):  
Point Source ◽  
Groundwater Contamination ◽  
Trace Impurities ◽  
Surface Source ◽  
Chlorinated Hydrocarbon ◽  
Soil Fumigant ◽  
Over Time

Abstract Groundwater contamination of the Abbotsford aquifer by 1,2-dichloropropane (1,2-DCP) was reported previously. The purpose of the present study is to quantify groundwater contamination by other chlorinated hydrocarbon compounds which are present in fumigant formulations containing 1,2-DCP. Widespread contamination of 1,2,2-trichloropropane (1,2,2-TCP) was measured consistent with a non-point source. 1,2,2-TCP concentration generally decreased with depth suggesting a surface source. Localized contamination by 1,2,3-trichloro-propane, 2,3-dichloropropene and 1,3-dichloropropane was detected. Detection of these compounds was associated with higher concentrations of 1,2-DCP suggesting contamination by these compounds may have been from the same fumigant sources. The lack of a decrease in the concentration of most of these compounds over time suggests that the measured contamination will persist for some time. The results highlight the potential for persistent trace impurities in chlorinated fumigant formulations to contaminate groundwater in vulnerable aquifers.

scholarly journals Effects of point source emission heights in WRF–STILT: a step towards exploiting nocturnal observations in models

2021 ◽  
Author(s):  
Fabian Maier ◽  
Christoph Gerbig ◽  
Ingeborg Levin ◽  
Ingrid Super ◽  
Julia Marshall ◽  
...  
Keyword(s):  
Point Source ◽  
Power Plants ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Ground Level ◽  
Point Sources ◽  
Observation Site ◽  
Surface Source ◽  
Concentration Difference ◽  
Nearby Point

Abstract. An appropriate representation of point source emissions in atmospheric transport models is very challenging. In the Stochastic Time Inverted Lagrangian Transport model (STILT), all point source emissions are typically released from the surface, meaning that the actual emission stack height plus subsequent plume rise is not considered. This can lead to erroneous predictions of trace gas concentrations, especially during nighttime when vertical atmospheric mixing is minimal. In this study we use two WRF–STILT model approaches to simulate fossil fuel CO2 (ffCO2) concentrations: (1) the standard “surface source influence (SSI)” approach, and (2) an alternative “volume source influence (VSI)” approach, where nearby point sources release CO2 according to their effective emission height profiles. The comparison with 14C-based measured ffCO2 data from two-week integrated afternoon and nighttime samples collected at Heidelberg, 30 m above ground level, shows that the root-mean-square deviation (RMSD) between modelled and measured ffCO2 is indeed almost twice as high during night (RMSD = 6.3 ppm) compared to the afternoon (RMSD = 3.7 ppm) when using the standard SSI approach. In contrast, the VSI approach leads to a much better performance at nighttime (RMSD = 3.4 ppm), which is similar to its performance during afternoon (RMSD = 3.7 ppm). Representing nearby point source emissions with the VSI approach could, thus, be a first step towards exploiting nocturnal observations in STILT. To further investigate the differences between these two approaches, we conducted a model experiment in which we simulated the ffCO2 contributions from 12 artificial power plants with typical annual emissions of one million tons of CO2 and with distances between 5 and 200 km from the Heidelberg observation site. We find that such a power plant must be more than 50 km away from the observation site in order for the mean modelled ffCO2 concentration difference between the SSI and VSI approach to fall below 0.1 ppm.

EFFECT OF A FLUID CORE ON PROPAGATION OF AN SH‐TORQUE PULSE FROM A POINT‐SOURCE IN A SPHERE

Geophysics ◽  
1966 ◽  
Vol 31 (4) ◽  
pp. 741-763 ◽  
Author(s):  
Z. Alterman ◽  
P. Kornfeld
Keyword(s):  
Exact Solution ◽  
Point Source ◽  
Arrival Time ◽  
Elastic Solid ◽  
Steepest Descent ◽  
Surface Source ◽  
Homogeneous Sphere ◽  
The Core ◽  
Fluid Core ◽  
Deep Source

An exact solution is obtained for the displacement of the surface of a sphere consisting of a fluid core and an elastic solid mantle, due to an impulsive SH‐torque source. Theoretical seismograms are computed for several distances from a surface source and from a deep source, and are compared with results for a homogeneous sphere. The seismograms show reflected pulses of H‐type and of Lg‐type, and pulses after diffraction at the core and at the surface. In agreement with observation and as expected by steepest‐descent analysis, it is found that the Lg‐type pulses start before the ray arrival time. Traveltime and amplitude curves for reflected and diffracted pulses are given.

FINITE ELEMENT MODEL TO STUDY EFFECT OF Na+−Ca2+ EXCHANGERS AND SOURCE GEOMETRY ON CALCIUM DYNAMICS IN A NEURON CELL

2016 ◽  
Vol 16 (02) ◽  
pp. 1650018 ◽  
Author(s):  
AMRITA JHA ◽  
NEERU ADLAKHA ◽  
BRAJESH KUMAR JHA
Keyword(s):  
Finite Element ◽  
Point Source ◽  
Three Dimensional ◽  
Element Model ◽  
Calcium Dynamics ◽  
Surface Source ◽  
Source Line ◽  
Calcium Diffusion ◽  
Theoretical Investigations ◽  
Intracellular Ca

The study of calcium diffusion in neuron cells has gained interest among research workers during the last two decades, due to its wide variety of roles in human body like muscle contraction, secretion, metabolism, signal transduction etc. Na[Formula: see text] is the first ion that comes in the hierarchy of ions affecting cytosolic Ca[Formula: see text] concentration. This Na[Formula: see text] ion helps in intracellular Ca[Formula: see text] regulation in cytosol via Na[Formula: see text]/Ca[Formula: see text] exchanger protein (NCX protein). Most of the theoretical investigations on calcium diffusion in neuron cells have been carried out for one and two dimensional cases by various research workers and that too by incorporating a point source of influx. In order to have more realistic study the more details of geometry, microstructure and physiological parameters need to be incorporated in the models. In view of above a three dimensional unsteady state model of Calcium dynamics in a neuron cell has been developed. Apart from the point source, the line and surface sources of an influx of Ca[Formula: see text]as well as the Na[Formula: see text]/Ca[Formula: see text] exchanger, have been incorporated in the model. Appropriate initial and boundary conditions have been framed. The region is discretized using three dimensional circular sectoral elements. Variational finite element method has been employed to obtain the solution. The numerical results have been computed to study effect of Na[Formula: see text]/Ca[Formula: see text] exchanger, point source, line source and surface source of an influx on Ca[Formula: see text] distribution in a neuron cell.

scholarly journals Is the ocean surface a source of nitrous acid (HONO) in the marine boundary layer?

2021 ◽  
Vol 21 (24) ◽  
pp. 18213-18225
Author(s):  
Leigh R. Crilley ◽  
Louisa J. Kramer ◽  
Francis D. Pope ◽  
Chris Reed ◽  
James D. Lee ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Nitrous Acid ◽  
Marine Boundary Layer ◽  
Ocean Surface ◽  
Cape Verde ◽  
Formation Mechanisms ◽  
Oh Radicals ◽  
Surface Source ◽  
Quantitative Understanding

Abstract. Nitrous acid, HONO, is a key net photolytic precursor to OH radicals in the atmospheric boundary layer. As OH is the dominant atmospheric oxidant, driving the removal of many primary pollutants and the formation of secondary species, a quantitative understanding of HONO sources is important to predict atmospheric oxidising capacity. While a number of HONO formation mechanisms have been identified, recent work has ascribed significant importance to the dark, ocean-surface-mediated conversion of NO2 to HONO in the coastal marine boundary layer. In order to evaluate the role of this mechanism, here we analyse measurements of HONO and related species obtained at two contrasting coastal locations – Cabo Verde (Atlantic Ocean, denoted Cape Verde herein), representative of the clean remote tropical marine boundary layer, and Weybourne (United Kingdom), representative of semi-polluted northern European coastal waters. As expected, higher average concentrations of HONO (70 ppt) were observed in marine air for the more anthropogenically influenced Weybourne location compared to Cape Verde (HONO < 5 ppt). At both sites, the approximately constant HONO/NO2 ratio at night pointed to a low importance for the dark, ocean-surface-mediated conversion of NO2 into HONO, whereas the midday maximum in the HONO/NO2 ratios indicated significant contributions from photo-enhanced HONO formation mechanisms (or other sources). We obtained an upper limit to the rate coefficient of dark, ocean-surface HONO-to-NO2 conversion of CHONO = 0.0011 ppb h−1 from the Cape Verde observations; this is a factor of 5 lower than the slowest rate reported previously. These results point to significant geographical variation in the predominant HONO formation mechanisms in marine environments and indicate that caution is required when extrapolating the importance of such mechanisms from individual study locations to assess regional and/or global impacts on oxidising capacity. As a significant fraction of atmospheric processing occurs in the marine boundary layer, particularly in the tropics, better constraint of the possible ocean surface source of HONO is important for a quantitative understanding of chemical processing of primary trace gases in the global atmospheric boundary layer and associated impacts upon air pollution and climate.

Imaging with deep‐water multiples

Geophysics ◽  
1991 ◽  
Vol 56 (7) ◽  
pp. 1081-1086 ◽  
Author(s):  
Edmund C. Reiter ◽  
M. Nafi Toksöz ◽  
Timothy H. Keho ◽  
G. M. Purdy
Keyword(s):  
Water Column ◽  
Deep Water ◽  
Signal To Noise Ratio ◽  
Synthetic Data ◽  
Ocean Bottom ◽  
Surface Source ◽  
Near Surface ◽  
True Path ◽  
Air Gun ◽  
Useful Signal

Acquisition of on‐bottom hydrophone data recording of a near‐surface source provides an opportunity to treat water column multiples as useful signal. A ray‐equation based Kirchhoff depth migration is used to image primary reflections and deep‐water multiples recorded on an Ocean Bottom Hydrophone (OBH). The image of the subbottom sediments is shown to be improved by inclusion of the deep‐water multiple in the imaging process. Field data, jointly acquired by Woods Hole Oceanographic Institute and University of Texas Institute for Geophysics at Austin and consisting of an OBH (2300 m depth) recording a 10 800 cubic inch air gun array, are used to illustrate the feasibility of the technique. Images are obtained from both the primary reflections and from energy that has undergone an additional passage through the water column. Comparison of these images reveals an excellent correlation of reflectors with the predicted polarity reversal observed in the multiple’s image. Synthetic data are used to examine the difficulties in identifying the true path of the water column multiple. For flat‐layered media there are two different multiple paths — one that reflects beneath the source and one that reflects over the receiver — which have identical traveltimes. They do not, however, have the same amplitude, and it can be shown that their amplitudes differ sufficiently to allow a reliable image to be extracted from the energy that reflects over the receiver. As a final step, the image obtained from the multiple is corrected for the π phase shift from the free surface and added to the image from the primary reflection. This approach is limited to areas where water depths allow reliable separation of primary reflections from water column multiples. Application of this technique allows the utilization of coherent deep water multiples and results in both extended lateral coverage and an increased signal‐to‐noise ratio in the final image.

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