How groups can foster consensus: The case of local cultures

A local culture denotes a commonly shared behaviour within a cluster of firms. Similar to social norms or conventions, it is an emergent feature resulting from the firms' interaction in an economic network. To model these dynamics, we consider a distributed agent population, representing e.g. firms or individuals. Further, we build on a continuous opinion dynamics model with bounded confidence ($\epsilon$), which assumes that two agents only interact if differences in their behaviour are less than $\epsilon$. Interaction results in more similarity of behaviour, i.e. convergence towards a common mean. This framework is extended by two major concepts: (i) The agent's in-group consisting of acquainted interaction partners is explicitly taken into account. This leads to an effective agent behaviour reflecting that agents try to continue to interact with past partners and thus to keep sufficiently close to them. (ii) The in-group network structure changes over time, as agents can form new links to other agents with sufficiently close effective behaviour or delete links to agents no longer close in behaviour. Thus, our model provides a feedback mechanism between the agents' behaviour and their in-group structure. Studying its consequences by means of agent-based computer simulations, we find that for narrow-minded agents (low $\epsilon$) the additional feedback helps to find consensus more often, whereas for open-minded agents (high $\epsilon$) this does not hold. This counterintuitive result is explained by simulations of the network evolution

Determination of crustal structure from phase velocity of Rayleigh waves. Part II: San Francisco Bay region

The phase velocity method of measuring crustal thickness has been successfully applied in southern California. Phase velocity of dispersed Rayleigh waves from distant earthquakes is determined locally by use of a tripartite array of seismograph stations. Local crustal thickness is obtained by comparing the observed phase velocity with an experimentally determined curve representative of the average continental crust. In this paper we make use of the phase-velocity data of Evernden to determine crustal thickness in the San Francisco Bay region of California. Evernden determined the phase velocity of Rayleigh waves entering the North American continent from the Pacific Ocean. He was primarily interested in studying the direction of approach of these waves. His tripartite array consisted of stations at Berkeley, San Francisco, and Palo Alto, and a number of earthquakes were studied so that a large variation in direction of approach could be obtained. The data for all the earthquakes were combined to obtain an average phase velocity for each period. These phase velocities are plotted in figure 1, where the region to which the data apply is also shown. Also plotted in figure 1 are phase-velocity curves for a 25-km., 35-km., and 45-km. crust having the same composition as the average crust of Africa. The method by which these curves have been derived is explained in Part I (see fn. 1, above). By interpolating between the curves one can use each phase-velocity determination to obtain a value of crustal thickness. Neglecting the lowest three points which fall outside the range permitted by the phase-velocity curves, one finds a mean value of 30 ± 1 km. for crustal thickness in the San Francisco Bay region. The three points which were excluded fall in a period range where experimental phase-velocity determinations are difficult to make. Moreover, for these short periods the phase velocity for the oceanic segment of the path differs greatly from that for the continental segment, with the result that refraction effects are most pronounced

Presentation of the 1965 Arthur L. Day Medal to Walter H. Munk

I was asked last night "Who is Walter Munk?". Walter Munk has never published in our Bulletin. This may be the first meeting of our Society he has attended. His membership I believe, begins today. Yet Arthur L. Day would have been pleased with the selection of Walter Munk as the 1965 Day Medalist—and for good reason. Walter Munk's interests and contributions range from oceanography to the mechanical properties of the earth. He brings a fresh point of view to classic problems and opens new fields. His approach varies with the subject. It is experimental when new data are needed; Munk will not hesitate to conceive and build in his own laboratory, as he is now doing, a mid-ocean tide gage, displacement meters, strain and tiltmeters, to measure tectonic movements. His approach is also theoretical and numerical when data remain to be analyzed or explained. Munk was among the first in the earth sciences to exploit high speed electronic computers

A seismic model study of the phase velocity method of exploration

Variations in the phase velocity of earthquake-generated surface waves have been used to determine local variations in the thickness of the earth's crust. It is of interest to determine whether this method can be used to delineate structures encountered by the exploration geophysicist. A seismic model study of the effect of thickness changes, lithology changes, faults and scarps, on the phase velocity of surface waves was carried out. It is demonstrated that all of these structures produce measurable variations in the phase velocity of surface waves. Additional information is required, however, to give a unique interpretation of a given phase velocity variation in terms of a particular structure. Some remarks on the phenomenon of returning ground roll are made

The Photometric Period of the Cataclysmic Variable HV Andromedae

We present four nights of time-resolved photometry of the cataclysmic variable star HV And. Our time series analysis has revealed a prominent period at 3.368 +/- 0.060 hours, as well as some low frequency power. We interpret this signal, from saw-tooth waves in the light curve, as evidence of superhumps in HV And.Comment: 7 pages, 3 figures; accepted for publication in New Astronom

Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952

Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952, are analyzed. The new Palisades long-period vertical seismograph recorded orders R_6–R_(15), the corresponding paths involving up to seven complete passages around the earth. The dispersion data for periods below 400 sec. are in excellent agreement with earlier results and can be explained in terms of the known increase of shear velocity with depth in the mantle. Data for periods 400-480 sec. indicate a tendency for the group velocity curve to level off, suggesting that these long waves are influenced by a low or vanishing shear velocity in the core. Deduction of internal friction in the mantle from wave absorption gives a value 1/Q = 370 × 10^(−5) for periods 250-350 sec. This is a little over half the value reported earlier for periods 140-215 sec

Crustal structure and surface-wave dispersion. Part II. Solomon Islands earthquake of July 29, 1950

Rayleigh waves from the Solomon Islands earthquake of July 29, 1950, recorded at Honolulu, Berkeley, Tucson, and Palisades are analyzed. Both the direct waves and those propagated through the Antipodes were observed for all stations except Honolulu. Application of a correction for land travel results in a dispersion curve for the oceanic portion of the path. It is found that the observed dispersion could be accounted for by propagation through a layer of water 5.57 km. thick overlying simatic rocks having shear velocity 4.56 km/sec. and density 3.0 gm/cc. Basement structure in the Pacific, Indian, South Atlantic, and North Atlantic oceans is identical within the limits of accuracy of the method. The sinusoidal nature and duration of the coda is explained by the effect of the oceans on the propagation of Rayleigh waves. The results are compatible with seismic refraction measurements in the Atlantic and Pacific oceans

Propagation of acoustic-gravity waves in the atmosphere

Homogeneous wave guide theory is used to derive dispersion curves, vertical pressure distributions, and synthetic barograms for atmospheric waves. A complicated mode structure is found involving both gravity and acoustic waves. Various models of the atmosphere are studied to explore seasonal and geographic effects on pulse propagation. The influence of different zones in the atmosphere on the character of the barograms is studied. It is found that the first arriving waves are controlled by the properties of the lower atmospheric channel. Comparison of theoretical results and experimental data from large thermonuclear explosions is made in the time and frequency domains, and the following conclusions are reached: (1) The major features on barograms are due to dispersion; (2) superposition of several modes is needed to explain observed features; (3) scatter of data outside the range permitted by extreme atmospheric models shows the influence of winds for A1; wind effects and higher modes are less important for A_2 waves. A discussion is included on atmospheric terminations and how these affect dispersion curves