scholarly journals The Ambiguous Arms of Aeneas

2017 ◽  
Vol 53 ◽  
Author(s):  
Lee Fratantuono
Keyword(s):  
First Arrival ◽  
Corre Spondence

Virgil subtly connects the scene of Dido’s discussion with her sister Anna about the new Trojan arrival Aeneas, and the later first arrival of the Trojans in Latium. By a careful corre-spondence between the two passages, Virgil portends the dark amatory rationale behind the sub-sequent outbreak of war in Italy

Three Perspectives on Centrality

2020 ◽  
pp. 333-351
Author(s):  
Stephen P. Borgatti ◽  
Martin G. Everett
Keyword(s):  
Centrality Measures ◽  
Graph Invariant ◽  
Propagation Process ◽  
Centrality Measure ◽  
The Third ◽  
First Arrival ◽  
The Difference

This chapter presents three different perspectives on centrality. In part, the motivation is definitional: what counts as a centrality measure and what doesn’t? But the primary purpose is to lay out ways that centrality measures are similar and dissimilar and point to appropriate ways of interpreting different measures. The first perspective the chapter considers is the “walk structure participation” perspective. In this perspective, centrality measures indicate the extent and manner in which a node participates in the walk structure of a graph. A typology is presented that distinguishes measures based on dimensions such as (1) what kinds of walks are considered (e.g., geodesics, paths, trails, or unrestricted walks) and (2) whether the number of walks is counted or the length of walks is assessed, or both. The second perspective the chapter presents is the “induced centrality” perspective, which views a node’s centrality as its contribution to a specific graph invariant—typically some measure of the cohesiveness of the network. Induced centralities are computed by calculating the graph invariant, removing the node in question, and recalculating the graph invariant. The difference is the node’s centrality. The third perspective is the “flow outcomes” perspective. Here the chapter views centralities as estimators of node outcomes in some kind of propagation process. Generic node outcomes include how often a bit of something propagating passes through a node and the time until first arrival of something flowing. The latter perspective leads us to consider the merits of developing custom measures for different research settings versus using off-the-shelf measures that were not necessarily designed for the current purpose.

Rescuing Migrants in the Central Mediterranean: The Emergence of a New Civil Humanitarianism at the Maritime Border

2019 ◽  
Vol 64 (4) ◽  
pp. 436-455
Author(s):  
Marta Esperti
Keyword(s):  
Civil Society ◽  
Research Methodology ◽  
Search And Rescue ◽  
International Organization ◽  
Central Mediterranean ◽  
The Social ◽  
Social Meanings ◽  
Humanitarian Space ◽  
First Arrival

The Central Mediterranean is the most deadly body of water in the Mediterranean Sea with at least 15,062 fatalities recorded by International Organization of Migration between 2014 and 2018. This article aims at highlighting the rise of a variety of new civil society actors engaged in the rescue of people undertaking dangerous journeys across the sea in the attempt of reaching the southern European shores. The peculiarity of the humanitarian space at sea and its political relevance are pointed out to illustrate the unfolding of the maritime border management on the Central Mediterranean route and its relation with the activity of the civil society rescue vessels. The theoretical aspiration of the article is to question the role of a proactive civil humanitarianism at sea, discussing the emergence of different political and social meanings around humanitarianism at the EU’s southern maritime border. In recent years, the increasing presence of new citizens-based organizations at sea challenges the nexus between humanitarian and emergency approaches adopted to implement security-oriented policies. This essay draws on the findings of a broader comparative work on a variety of civil society actors engaged in the search and rescue operations on the maritime route between Libya and Europe, focusing in particular on Italy as country of first arrival. The fieldwork covers a period of time going between 2016 and 2018. The research methodology is built on a multisited ethnography, the conduct of semidirective and informal interviews with both state and nonstate actors, and the analysis of various reports unraveling the social and political tensions around rescue at sea on the Central Mediterranean route.

First-arrival traveltime inversion of seismic diving waves observed on undulant surface

2021 ◽  
Vol 225 (2) ◽  
pp. 1020-1031
Author(s):  
Huachen Yang ◽  
Jianzhong Zhang ◽  
Kai Ren ◽  
Changbo Wang
Keyword(s):  
Turning Points ◽  
Analytical Formula ◽  
Velocity Model ◽  
Western China ◽  
Inversion Method ◽  
Mountain Area ◽  
Traveltime Inversion ◽  
Static Correction ◽  
Velocity Models ◽  
First Arrival

SUMMARY A non-iterative first-arrival traveltime inversion method (NFTI) is proposed for building smooth velocity models using seismic diving waves observed on irregular surface. The new ray and traveltime equations of diving waves propagating in smooth media with undulant observation surface are deduced. According to the proposed ray and traveltime equations, an analytical formula for determining the location of the diving-wave turning points is then derived. Taking the influence of rough topography on first-arrival traveltimes into account, the new equations for calculating the velocities at turning points are established. Based on these equations, a method is proposed to construct subsurface velocity models from the observation surface downward to the bottom using the first-arrival traveltimes in common offset gathers. Tests on smooth velocity models with rugged topography verify the validity of the established equations, and the superiority of the proposed NFTI. The limitation of the proposed method is shown by an abruptly-varying velocity model example. Finally, the NFTI is applied to solve the static correction problem of the field seismic data acquired in a mountain area in the western China. The results confirm the effectivity of the proposed NFTI.

First arrival time picking for microseismic data based on DWSW algorithm

2018 ◽  
Vol 22 (4) ◽  
pp. 833-840 ◽  
Author(s):  
Yue Li ◽  
Yue Wang ◽  
Hongbo Lin ◽  
Tie Zhong
Keyword(s):  
Arrival Time ◽  
Microseismic Data ◽  
First Arrival ◽  
First Arrival Time ◽  
Arrival Time Picking

scholarly journals Recording seismic reflections using rigidly interconnected geophones

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1838-1842 ◽  
Author(s):  
C. M. Schmeissner ◽  
K. T. Spikes ◽  
D. W. Steeples
Keyword(s):  
Wave Propagation ◽  
Data Acquisition ◽  
Seismic Reflection ◽  
Spatial Sampling ◽  
P Wave ◽  
Signal Distortion ◽  
Reflection And Refraction ◽  
First Arrival ◽  
The Cost ◽  
Seismic Reflections

Ultrashallow seismic reflection surveys require dense spatial sampling during data acquisition, which increases their cost. In previous efforts to find ways to reduce these costs, we connected geophones rigidly to pieces of channel iron attached to a farm implement. This method allowed us to plant the geophones in the ground quickly and automatically. The rigidly interconnected geophones used in these earlier studies detected first‐arrival energy along with minor interfering seismic modes, but they did not detect seismic reflections. To examine further the feasibility of developing rigid geophone emplacement systems to detect seismic reflections, we experimented with four pieces of channel iron, each 2.7 m long and 10 cm wide. Each segment was equipped with 18 geophones rigidly attached to the channel iron at 15‐cm intervals, and the spikes attached to all 18 geophones were pushed into the ground simultaneously. The geophones detected both refracted and reflected energy; however, no significant signal distortion or interference attributable to the rigid coupling of the geophones to the channel iron was observed in the data. The interfering seismic modes mentioned from the previous experiments were not detected, nor was any P‐wave propagation noted within the channel iron. These results show promise for automating and reducing the cost of ultrashallow seismic reflection and refraction surveys.

Channel waves in cross‐borehole data

Geophysics ◽  
1992 ◽  
Vol 57 (2) ◽  
pp. 334-342 ◽  
Author(s):  
Larry R. Lines ◽  
Kenneth R. Kelly ◽  
John Queen
Keyword(s):  
Seismic Velocity ◽  
Test Facility ◽  
Equation Modeling ◽  
Borehole Data ◽  
Geological Information ◽  
Channel Wave ◽  
First Arrival ◽  
Borehole Seismic ◽  
Seismic Velocity Contrasts ◽  
Ray Bending

Layered geological formations with large seismic velocity contrasts can effectively create channel waves in cross‐borehole seismic data. The existence of channel waves for such waveguides can be confirmed by ray tracing, wave equation modeling, and modal analysis. Channel wave arrivals are identified in cross‐borehole data recorded at Conoco’s Newkirk test facility. For these data, where velocity contrasts are about 2 to 1, tomography based on first arrival traveltimes, is limited due to problems with extreme ray bending and seismic shadow zones. However, it may be possible to extract geological information using channel wave information. The seismometer differencing method appears to be a promising approach for detecting waveguide boundaries by use of cross‐borehole data.

PRESSURE AMPLITUDES OF SEISMIC SIGNALS IN OFFSHORE LOUISIANA

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 3-16
Author(s):  
M. E. Arnold
Keyword(s):  
Field Tests ◽  
Signal Amplitude ◽  
Test Area ◽  
Seismic Signals ◽  
Code Generators ◽  
Single Detector ◽  
First Arrival ◽  
Reflected Signal ◽  
Refracted Waves ◽  
Seismic Lines

Pressure amplitudes were determined for various kinds of seismic signals observed on special test records obtained during field tests conducted along a 14,000-ft seismic lines in Eugene Island Block 184, offshore Louisiana. Vibrators attached to a Seismograph Service Corp. (SSC) boat generated swept‐frequency and monofrequency signals. Signals from detectors on a streamer cable towed by the boat were recorded by an SSC recording system. Signals from a vertical spread of detectors were recorded by a DFS/9000 recorder on the Transco 184 platform centrally located in the test area. Location of the boat was determined by analysis of time relations of signals from responders located at established positions some distance from the test area. Clock times from manually referenced timing code generators were recorded by both the SSC and DFS recorders to permit synchronization between separately recorded signals. The signals analyzed were separated into three classes: [Formula: see text] includes direct and refracted waves; [Formula: see text] consists of primary reflections; and [Formula: see text] includes signals diffracted from scatterers. The average level of first‐arrival signal [Formula: see text] and reflected signal [Formula: see text] for frequency sets 25, 40, 42.2, 50, and 70.4 Hz in the range of 1414 and 2143 ft, which encompasses streamer cable single‐detector groups, is 337 and 29.6 microbars, respectively. The amplitude of signals [Formula: see text], believed to be diffracted from the contact between key reflectors and a salt dome, ranges from 13 to 20 microbars and is 10 to 100 times the amplitudes of towing and ambient noise, respectively. The observed decay of first‐arrival signal amplitude is approximately proportional to the square root of range distance, or about 2 dB/1000 ft. The observed decay of reflected signal amplitude with range distance is approximately 1 dB/1000 ft.

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