A multilevel approach to the travelling salesman problem

Abstract not available

Receptors, sparks and waves in a fire-diffuse-fire framework for calcium release

Calcium ions are an important second messenger in living cells. Indeed calcium signals in the form of waves have been the subject of much recent experimental interest. It is now well established that these waves are composed of elementary stochastic release events (calcium puffs or sparks) from spatially localised calcium stores. The aim of this paper is to analyse how the stochastic nature of individual receptors within these stores combines to create stochastic behaviour on long timescales that may ultimately lead to waves of activity in a spatially extended cell model. Techniques from asymptotic analysis and stochastic phase-plane analysis are used to show that a large cluster of receptor channels leads to a release probability with a sigmoidal dependence on calcium density. This release probability is incorporated into a computationally inexpensive model of calcium release based upon a stochastic generalization of the Fire-Diffuse-Fire (FDF) threshold model. Numerical simulations of the model in one and two dimensions (with stores arranged on both regular and disordered lattices) illustrate that stochastic calcium release leads to the spontaneous production of calcium sparks that may merge to form saltatory waves. Illustrations of spreading circular waves, spirals and more irregular waves are presented. Furthermore, receptor noise is shown to generate a form of array enhanced coherence resonance whereby all calcium stores release periodically and simultaneously.

Surface thermal analysis of North Brabant cities and neighbourhoods during heat waves

The urban heat island effect is often associated with large metropolises. However, in the Netherlands even small cities will be affected by the phenomenon in the future (Hove et al., 2011), due to the dispersed or mosaic urbanisation patterns in particularly the southern part of the country: the province of North Brabant. This study analyses the average night time land surface temperature (LST) of 21 North-Brabant urban areas through 22 satellite images retrieved by Modis 11A1 during the 2006 heat wave and uses Landsat 5 Thematic Mapper to map albedo and normalized difference temperature index (NDVI) values. Albedo, NDVI and imperviousness are found to play the most relevant role in the increase of nighttime LST. The surface cover cluster analysis of these three parameters reveals that the 12 “urban living environment” categories used in the region of North Brabant can actually be reduced to 7 categories, which simplifies the design guidelines to improve the surface thermal behaviour of the different neighbourhoods thus reducing the Urban Heat Island (UHI) effect in existing medium size cities and future developments adjacent to those cities.

Bumps, breathers, and waves in a neural network with spike frequency adaptation

In this Letter we introduce a continuum model of neural tissue that include the effects of so-called spike frequency adaptation (SFA). The basic model is an integral equation for synaptic activity that depends upon the non-local network connectivity, synaptic response, and firing rate of a single neuron. A phenomenological model of SFA is examined whereby the firing rate is taken to be a simple state-dependent threshold function. As in the case without SFA classical Mexican-Hat connectivity is shown to allow for the existence of spatially localized states (bumps). Importantly an analysis of bump stability using recent Evans function techniques shows that bumps may undergo instabilities leading to the emergence of both breathers and traveling waves. Moreover, a similar analysis for traveling pulses leads to the conditions necessary to observe a stable traveling breather. Direct numerical simulations both confirm our theoretical predictions and illustrate the rich dynamic behavior of this model, including the appearance of self-replicating bumps.

Waves, bumps, and patterns in neural field theories

Neural field models of firing rate activity have had a major impact in helping to develop an understanding of the dynamics seen in brain slice preparations. These models typically take the form of integro-differential equations. Their non-local nature has led to the development of a set of analytical and numerical tools for the study of waves, bumps and patterns, based around natural extensions of those used for local differential equation models. In this paper we present a review of such techniques and show how recent advances have opened the way for future studies of neural fields in both one and two dimensions that can incorporate realistic forms of axo-dendritic interactions and the slow intrinsic currents that underlie bursting behaviour in single neurons.

On the sound waves propagation in the Persian Gulf

In this research I focused on the propagation of acoustic rays in shallow water areas then I selected the Persian Gulf and described sound transmission in this region with emphasize on physical properties of water masses and of sediments. Finally I studied on the sound speed variations and sound attention with data collected from this area (NE of Farsi Island & 50 kilometers south of Delware). Sound speed deviation in western part of Strait of Hormuz in winter is between 20-30 m/s and it is between 5-20 m/s in the Oman Sea. Minimum sound speed deviation is at 23-24 degree north & 60-62 degree east. In spring, this deviation varies from 25-35 m/s, which is greater than in winter. In winter, at east of 56 degree east, greater speed are in shallow water coastal areas. In summer, sound speeds are greater than in spring and vary from 35 to 55 m/s at western part of Strait of Hormuz and 20 to 40 m/s in Oman Sea. Finally in autumn, sound speed deviation is 30-45 m/s west of 56 degree east and in Oman Sea is the same. The greatest attenuation rate caused by absorption in Bandar Dayer is between 17 to 27 meters depth, which is from water masses with different densities.

Study and analysis of the waves and currents interaction phenomena

Interaction of ocean waves, currents and sea bed roughness is a complicated phenomena in fluid dynamic. This paper will describe the governing equations of motions of this phenomena in viscous and nonviscous conditions as well as study and analysis the experimental results of sets of physical models on waves, currents and artificial roughness, and consists of three parts: First, by establishing some typical patterns of roughness, the effects of sea bed roughness on a uniform current has been studied, as well as the manning coefficient of each type is reviewed to find the critical situation due to different arrangement. Second, the effect of roughness on wave parameters changes, such as wave height, wave length, and wave dispersion equations have been studied, third, superimposing, the waves + current + roughness patterns established in a flume, equipped with waves + currents generator, in this stage different analysis has been done to find the governing dimensionless numbers, and present the numbers to define the contortions and formulations of this phenomena. First step of the model is verified by the so called Chinese method, and the Second step by the Kamphius (1975), and third step by the van Rijn (1990) , and Brevik and Ass ( 1980), and in all cases reasonable agreements have been obtained. Finally new dimensionless parameters presented for this complicated phenomena.

The effects of permeable bed on waves setup

Generally the flow properties of rivers, estuaries and coastal seas are highly dependent on the bed morphology. These include mainly three flow parameters, as bed shear stress, velocity profile and turbulent fluctuations. Here we investigate the effects of permeate of the bed on these flow properties We consider the effects of suction (W0) injection (W0) on these flow properties particularly the bottom stress. Four types of bottom permeability with different size of sand have been tested. The results indicate a substantial reduction and enhancement of the bed stress under respectively injection and suction as has been observed by others on wave motion in shallow seas. We consider 5 waves to shore with this rang of wave steepness ( 0/015 < so < 0/05 ) . Cr Calculated used of mansard method (1980). We search the stream line of current in bed with a video camera and looking this. Near the surface and the deep of bed and consider V=W (in or su)/ U(ru or rd) and bottom stress for 6 period of this study with Canly and Inman studies (1994). All these results are shown by curves with the effects of permeable bed.

Interaction between wind waves and swell in the Persian Gulf

The effect of swell on wind wave growth has been a topic of active research for many years with inconsistent results. The details are often contradictory among investigations. Further more, there remain a variety of competing theories to explain these phenomena. In this research, we consider waves and wind and temperature data in the Persian Gulf (Busher region) in years 1995, 1996 and 1999. This study provides estimations of wave conditions and the atmosphere stability that has an influence on wind wave. Results are also compared with data that have been recorded by a buoy in Caspian Sea (Neka region) during 1989. In the second part of this work we estimate non- dimensional energy and non-dimensional peak frequencies as a function of the non- dimensional fetch and Bulk Richardson numbers for the Persian Gulf (Busher region).This results also agree well with similar results for the Caspian Sea. The acquired relations can be used to compute the wind wave parameters. Also the results for the Persian Gulf show that the relationship of non-dimensional energy to as a function of wave age is independent of presence of swell. Finally the WAM model was run for the Persian Gulf during 3-8 September of 2002. The results show that swell on the Persian Gulf reduces the energy density of wind waves by up to 10%, but the growth rate at peak frequency is only reduced by up to 4%, and the spectral peak frequency is increased by only 1%.

Study and investigation of the various reactions of Mazandaran Province shoreline against wind waves

Determining of beach states and study of manner sediment transmission in beach profile, involves the evaluating the actions of hydrodynamic forces dominated over the beaches, in this research through determining the beach states by the help of Hanson and short method, different reactions of Mazandaran’s shoreline against wind waves was studied and investigated. For this reason, First, the kind of hydrodynamic forces dominated over the beaches of this province was studied and beaches of the this province was distinguished as wave–dominated beaches, afterwards eight stations are chosen throughout the shoreline and the waves qualities and the sediments regarding to different depth was evaluated in these stations by using software and laboratory actions. In this way the parameter of dimensionless fall velocity each station was calculated and the beach states and their changes according to time was studied. Finally, the gained information is located in the software area of Arc GIS, and the waves dynamics and the way of erosion and accretion was evaluated in each station. In this research by study of air photographs during a thirty years period we found that was no remarkable changes at shoreline in western and central parts and each type of change depends upon the delta, while eastern part of coast at the location of breakwaters in neighbouring of Farahabad Station, accretion features is quiet evident. In the main results of this research, it became obvious that the beach state in the stations Neca, Farahabad, Larim, Naftchal, Mazandaran university, Babolsar, Noor is dissipative and the beach in Nashtarood station is in intermediate (ridge and runnel) state to the extend that in the dissipation beaches from east to west, the degree of dissipation of the beaches is decreased continuously.

Experimental and numerical studies of hydrodynamic interaction of two bodies in waves

This thesis focuses on experimental and numerical studies of the hydrodynamic interaction between two vessels in close proximity in waves. In the model tests, two identical box-like models with round corners were used. Regular waves with the same wave steepness and different wave frequencies were generated. Six degrees of freedom body motions and wave elevations between bodies were measured in a head sea condition. Three initial gap widths were examined. In the numerical computations, a panel-free method based seakeeping program, MAPS0, and a panel method based program, WAMIT, were used for the prediction of body motions and wave elevations. The computed body motions and wave elevations were compared with experimental data.

Propagation des ondes longitudinales dans le noyau terrestre d'après les séismes profonde des Iles Fidji

Observations from three deep focus earthquakes, of focal depth 600 km, originating in the Fiji Islands region, have permitted to trace the travel-time curves for the longitudinal waves travelling through the earth's core. Of principal importance is the travel-time table for the phase PKP1 which has been given upto 158° and for which the data so far were incomplete. Other important phases observed between 103 and 143° have been illustrated and their travel-time curves drawn.

Wind Waves in the Arctic Seas: Envisat and AltiKa Data Analysis

Wind-generated waves in the Kara, Laptev, and East-Siberian Seas are investigated using altimeter data from Envisat RA-2 and SARAL-AltiKa. Only isolated ice-free zones had been selected for analysis. Wind seas can be treated as pure wind-generated waves without any contamination by ambient swell. Such zones were identified using ice concentration data from microwave radiometers. Altimeter data, both significant wave height (SWH) and wind speed, for these areas were further obtained for the period 2002-2012 using Envisat RA-2 measurements, and for 2013 using SARAL-AltiKa. Dependencies of dimensionless SWH and wavelength on dimensionless wave generation spatial scale are compared to known empirical dependencies for fetch-limited wind wave development. We further check sensitivity of Ka- and Ku-band and discuss new possibilities that AltiKa's higher resolution can open.

The transport of nitric oxide in the upper atmosphere by planetary waves and the zonal mean circulation

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