On the synthesis of shear-coupled PL waves

1968 ◽  
Vol 58 (6) ◽  
pp. 1849-1877 ◽  
Author(s):  
Ramesh Chander ◽  
L. E. Alsop ◽  
Jack Oliver
Keyword(s):  
United States ◽  
Phase Velocity ◽  
Travel Time ◽  
Current Knowledge ◽  
Shear Waves ◽  
The United States ◽  
Synthetic Seismograms ◽  
Travel Times ◽  
Precise Knowledge ◽  
S Curve

ABSTRACT Using the shear-coupled PL wave hypothesis of Oliver as a basis, a method is developed for computing synthetic long-period seismograms between the onset of the initial S-type body phase and the beginning of surface waves. Comparison of observed and synthetic siesmograms shows that this hypothesis can explain, in considerable detail, most of the waves with periods greater than about 20 sec recorded during this interval. The synthetic seismograms are computed easily on a small digital computer; they resemble the observed seismograms much more closely than the synthetic seismograms obtained through the superposition of normal modes of the Earth that have been reported in the literature. The synthesis of shear-coupled PL waves depends on a precise knowledge of the phase-velocity curve of the PL wave and travel-time curves of shear waves. Hence, in principle, if one of these quantities is well-known the other can be determined by this method. Phase-velocity curves of the PL wave are determined for the Baltic shield, the Russian platform, the Canadian shield, the United States, and the western North-Atlantic ocean, on the assumption that J-B travel-time curves of shear waves apply to these areas. These dispersion curves show the type of variations to be expected on the basis of the current knowledge of the crustal structures in these areas. Examples are presented to show that J-B travel-times of shear waves along paths between Kenai Peninsula, Alaska and Palisades, equatorial mid-Atlantic ridge and Palisades, and Kurile Islands and Uppsala need to be revised. Shear-wave travel-time curves that are not unique for reasons explained in the study but that give synthetic seismograms in agreement with the observed seismograms were obtained. The new S curves are compared with the J-B travel-time curves for S; and they all predict S waves to arrive later than the time given by J-B tables for epicentral distances smaller than about 30°. The new S curve for the Alaska to Palisades path appears to agree with one of the branches of a multi-branched S curve proposed recently by Ibrahim and Nuttli for the ‘average United States’ insofar as travel-times are concerned, but there are some differences in the slopes of the two curves.

scholarly journals Beyond the dichotomy: How ride-hailing competes with and complements public transport

PLoS ONE ◽  
2022 ◽  
Vol 17 (1) ◽  
pp. e0262496
Author(s):  
Oded Cats ◽  
Rafal Kucharski ◽  
Santosh Rao Danda ◽  
Menno Yap
Keyword(s):  
United States ◽  
Travel Time ◽  
Public Transport ◽  
The United States ◽  
Travel Times ◽  
Service Accessibility ◽  
Transport Services ◽  
Us Cities ◽  
Public Transport Services ◽  
Two Alternatives

Since ride-hailing has become an important travel alternative in many cities worldwide, a fervent debate is underway on whether it competes with or complements public transport services. We use Uber trip data in six cities in the United States and Europe to identify the most attractive public transport alternative for each ride. We then address the following questions: (i) How does ride-hailing travel time and cost compare to the fastest public transport alternative? (ii) What proportion of ride-hailing trips do not have a viable public transport alternative? (iii) How does ride-hailing change overall service accessibility? (iv) What is the relation between demand share and relative competition between the two alternatives? Our findings suggest that the dichotomy—competing with or complementing—is false. Though the vast majority of ride-hailing trips have a viable public transport alternative, between 20% and 40% of them have no viable public transport alternative. The increased service accessibility attributed to the inclusion of ride-hailing is greater in our US cities than in their European counterparts. Demand split is directly related to the relative competitiveness of travel times i.e. when public transport travel times are competitive ride-hailing demand share is low and vice-versa.

Modeling Arrival Flight Times within the Terminal Airspace

2021 ◽  
pp. 036119812110114
Author(s):  
Osama Alsalous ◽  
Susan Hotle
Keyword(s):  
United States ◽  
Travel Time ◽  
The United States ◽  
Time Of Day ◽  
Civil Aviation ◽  
Weather Data ◽  
Travel Times ◽  
International Airport ◽  
Area Of Interest ◽  
The Impact

Air traffic management efficiency in the descent phase of flights is a key area of interest in aviation research for the United States, Europe, and recently other parts of the world. The efficiency of arrival travel times within the terminal airspace is one of nineteen key performance indicators defined by the Federal Aviation Administration (FAA) and the International Civil Aviation Organization, typically within 100 nmi of arrival airports. This study models the relationship between travel time within the terminal airspace and contributing factors using a multivariate log-linear model to quantify the impact that these factors have on the total travel time within the last 100 nmi. The results were compared with the baseline set of variables that are currently used for benchmarking at the FAA. The analyzed data included flight and weather data from January 1, 2018 to March 31, 2018 for five airports in the United States: Chicago O’Hare International Airport, Hartsfield-Jackson Atlanta International, San Francisco International Airport, John F. Kennedy International Airport, and LaGuardia Airport. The modeling results showed that there is a significant improvement in prediction accuracy of travel times compared with the baseline methodology when additional factors, such as wind, meteorological conditions, demand and capacity, ground delay programs, market distance, time of day, and day of week, are included. Root mean squared error values from out-of-sample testing were used to measure the accuracy of the estimated models.

scholarly journals Increased travel times to United States SARS-CoV-2 testing sites: a spatial modeling study

2020 ◽  
Author(s):  
Benjamin Rader ◽  
Christina M. Astley ◽  
Karla Therese L. Sy ◽  
Kara Sewalk ◽  
Yulin Hswen ◽  
...  
Keyword(s):  
United States ◽  
Population Density ◽  
Travel Time ◽  
Demographic Data ◽  
The United States ◽  
List Type ◽  
Median Income ◽  
Travel Times ◽  
Cross Sectional ◽  
Geographic Accessibility

AbstractImportanceAccess to testing is key to a successful response to the COVID-19 pandemic.ObjectiveTo determine the geographic accessibility to SARS-CoV-2 testing sites in the United States, as quantified by travel time.DesignCross-sectional analysis of SARS-CoV-2 testing sites as of April 7, 2020 in relation to travel time.SettingUnited States COVID-19 pandemic.ParticipantsThe United States, including the 48 contiguous states and the District of Columbia.ExposuresPopulation density, percent minority, percent uninsured, and median income by county from the 2018 American Community Survey demographic data.Main OutcomeSARS-CoV-2 testing sites identified in two national databases (Carbon Health and CodersAgainstCovid), geocoded by address. Median county 1 km2 gridded friction surface of travel times, as a measure of geographic accessibility to SARS-CoV-2 testing sites.Results6,236 unique SARS-CoV-2 testing sites in 3,108 United States counties were identified. Thirty percent of the U.S. population live in a county (N = 1,920) with a median travel time over 20 minutes. This was geographically heterogeneous; 86% of the Mountain division population versus 5% of the Middle Atlantic population lived in counties with median travel times over 20 min. Generalized Linear Models showed population density, percent minority, percent uninsured and median income were predictors of median travel time to testing sites. For example, higher percent uninsured was associated with longer travel time (β = 0.41 min/percent, 95% confidence interval 0.3-0.53, p = 1.2×10−12), adjusting for population density.Conclusions and RelevanceGeographic accessibility to SARS-Cov-2 testing sites is reduced in counties with lower population density and higher percent of minority and uninsured, which are also risk factors for worse healthcare access and outcomes. Geographic barriers to SARS-Cov-2 testing may exacerbate health inequalities and bias county-specific transmission estimates. Geographic accessibility should be considered when planning the location of future testing sites and interpreting epidemiological data.Key PointsSARS-CoV-2 testing sites are distributed unevenly in the US geography and population.Median county-level travel time to SARS-CoV-2 testing sites is longer in less densely populated areas, and in areas with a higher percentage of minority or uninsured populations.Improved geographic accessibility to testing sites is imperative to manage the COVID-19 pandemic in the United States.

scholarly journals Current knowledge of Chagas-related heart disease among pediatric cardiologists in the United States

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Sanchi Malhotra ◽  
Imran Masood ◽  
Noberto Giglio ◽  
Jay D. Pruetz ◽  
Pia S. Pannaraj
Keyword(s):  
United States ◽  
Differential Diagnosis ◽  
Heart Disease ◽  
Chagas Disease ◽  
Latin American ◽  
Current Knowledge ◽  
Parasitic Infection ◽  
The United States ◽  
Cardiac Complications ◽  
The U.S

Abstract Background Chagas disease is a pathogenic parasitic infection with approximately 8 million cases worldwide and greater than 300,000 cases in the United States (U.S.). Chagas disease can lead to chronic cardiomyopathy and cardiac complications, with variable cardiac presentations in pediatrics making it difficult to recognize. The purpose of our study is to better understand current knowledge and experience with Chagas related heart disease among pediatric cardiologists in the U.S. Methods We prospectively disseminated a 19-question survey to pediatric cardiologists via 3 pediatric cardiology listservs. The survey included questions about demographics, Chagas disease presentation and experience. Results Of 139 responses, 119 cardiologists treat pediatric patients in the U.S. and were included. Most providers (87%) had not seen a case of Chagas disease in their practice; however, 72% also had never tested for it. The majority of knowledge-based questions about Chagas disease cardiac presentations were answered incorrectly, and 85% of providers expressed discomfort with recognizing cardiac presentations in children. Most respondents selected that they would not include Chagas disease on their differential diagnosis for presentations such as conduction anomalies, myocarditis and/or apical aneurysms, but would be more likely to include it if found in a Latin American immigrant. Of respondents, 87% agreed that they would be likely to attend a Chagas disease-related lecture. Conclusions Pediatric cardiologists in the U.S. have seen very few cases of Chagas disease, albeit most have not sent testing or included it in their differential diagnosis. Most individuals agreed that education on Chagas disease would be worth-while.

Travel Time to Radiation Oncology Facilities in the United States and the Influence of Certificate of Need Policies

2021 ◽  
Vol 109 (2) ◽  
pp. 344-351
Author(s):  
Joshua N. Herb ◽  
Rachael T. Wolff ◽  
Philip M. McDaniel ◽  
G. Mark Holmes ◽  
Trevor J. Royce ◽  
...  
Keyword(s):  
United States ◽  
Travel Time ◽  
Radiation Oncology ◽  
The United States ◽  
Certificate Of Need

1—by Captain A. Wepster

1963 ◽  
Vol 16 (4) ◽  
pp. 389-398
Keyword(s):  
United States ◽  
Travel Time ◽  
Long Range ◽  
The United States ◽  
Point Of View ◽  
Ship Routing ◽  
Waves And Currents ◽  
Meteorological Institute

In 1960 Hanssen and James described to the Institute a system developed and used by the United States Hydrographic Office for selecting the optimum track for transoceanic crossings by applying long-range predictions of winds, waves and currents to a knowledge of how the routed vessel reacts to these variables. The paper (Journal, 13, 253) described how, over a period of two years, an average reduction in travel time of 14 hours was achieved over 1000 optimum routes.In the present papers, presented at an Institute meeting held in London on 19 April, Captain Wepster of the Holland-America Line first of all goes into the benefits which effective ship routing offers the ship operator and then describes the results of the experimental routing programme undertaken by his Company in association with the Royal Netherlands Meteorological Institute. Mr. Verploegh of that Institute then discusses the programme from the forecaster's point of view.

Optimum Ship Routing

1960 ◽  
Vol 13 (3) ◽  
pp. 253-272 ◽  
Author(s):  
George L. Hanssen ◽  
Richard W. James
Keyword(s):  
United States ◽  
Travel Time ◽  
Long Range ◽  
Wind Waves ◽  
The United States ◽  
Ship Routing ◽  
Waves And Currents

The paper describes the system developed and used by the United States Hydrographic Office for selecting the optimum track for transoceanic crossings by applying long-range predictions of wind, waves and currents to a knowledge of how the routed vessel reacts to these variables. Over a period of two years, over 1000 optimum ship routes were provided to one authority, with an average reduction in travel time of 14 hours.

scholarly journals Public perceptions of a rip current hazard education program: “Break the Grip of the Rip!”

2017 ◽  
Vol 17 (7) ◽  
pp. 1003-1024 ◽  
Author(s):  
Chris Houser ◽  
Sarah Trimble ◽  
Robert Brander ◽  
B. Chris Brewster ◽  
Greg Dusek ◽  
...  
Keyword(s):  
United States ◽  
Online Survey ◽  
Social Research ◽  
Current Knowledge ◽  
The United States ◽  
Rip Current ◽  
Rip Currents ◽  
Safety Education ◽  
Large Area ◽  
Education Material

Abstract. Rip currents pose a major global beach hazard; estimates of annual rip-current-related deaths in the United States alone range from 35 to 100 per year. Despite increased social research into beach-goer experience, little is known about levels of rip current knowledge within the general population. This study describes the results of an online survey to determine the extent of rip current knowledge across the United States, with the aim of improving and enhancing existing beach safety education material. Results suggest that the US-based Break the Grip of the Rip!® campaign has been successful in educating the public about rip current safety directly or indirectly, with the majority of respondents able to provide an accurate description of how to escape a rip current. However, the success of the campaign is limited by discrepancies between personal observations at the beach and rip forecasts that are broadcasted for a large area and time. It was the infrequent beach user that identified the largest discrepancies between the forecast and their observations. Since infrequent beach users also do not seek out lifeguards or take the same precautions as frequent beach users, it is argued that they are also at greatest risk of being caught in a dangerous situation. Results of this study suggest a need for the national campaign to provide greater focus on locally specific and verified rip forecasts and signage in coordination with lifeguards, but not at the expense of the successful national awareness program.

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