Double Source Model Research Articles

The enigmatic 1693 AD tsunami in the eastern Mediterranean Sea: new insights on the triggering mechanisms and propagation dynamics

The disastrous earthquake of 1693 AD caused over 60,000 causalities and the total destruction of several villages and towns in south-eastern Sicily. Immediately after the earthquake, a tsunami struck the Ionian coasts of Sicily and the Messina Strait and was probably recorded even in the Aeolian Islands and Malta. Over the last few decades, the event has been much debated regarding the location of the seismogenic source and the possible cause of the associated tsunami. The marine event has been related to both a submarine landslide and a coseismic displacement at the seafloor. To better define the most reliable sources and dynamics of the tsunami, we couple high-resolution marine seismic survey data with hydrodynamic modelling to simulate various scenarios of tsunami generation and propagation. Results from the simulations are compared with geomorphological evidence of past tsunami impacts, described in previous work along the coast of south-eastern Sicily, and within historical chronicles and reports. The most reliable scenario considers the 1693 event composed by two different tsunami waves: a first wave generated by the coseismic fault displacement at the seafloor and a second wave generated by a submarine landslide, triggered by the earthquake shaking. Tsunami modelling shows that a simultaneous movement between fault displacement and submarine mass movement could determine a destructive interference on the tsunami waves, resulting in a reduction in wave height. For this reason, the second tsunami wave probably occurred with a maximum delay of few minutes after the one generated by the earthquake and induced a greater flooding. The double-source model could explain the observation because in the course of other destructive earthquakes in south-eastern Sicily, such as that of 1169 AD, the associated tsunami caused less damages. This implies the need to better map, define and assess the hazard responsible for this type of tsunami events.

Modelling for predicting seam geometry in laser beam welding of stainless steel

A methodological approach for analytical modelling of deep penetration laser beam welding (LBW) of stainless steels and its experimental verification is provided. After an analysis of the problem in general terms and a review of the modelling activity, a particular double source model is proposed and discussed. The model allows the derivation of penetration and width of melting zone caused by moving laser beam. Dependences of penetration length, width of the melting zone and aspect ratio of the zone were derived as a function of welding speed and laser power. The theoretical results obtained using the particular model are discussed and analyzed in comparison with experimental data obtained on a typical test case. Optimal conditions for obtaining a preliminary optimization of the process parameters were derived based on experimental results. The case study in the present paper, referred to the assembly of fuel injectors for automotive industry, demonstrates that when laser welding is performed at high speeds on thin wall components the energy released by the laser per unit of surface (energy density, ED) can be used to describe the heat transfer to the material and to shorten the experimental phase avoiding the dependencies on each single process parameter.

A simple double-source model for interference of capillaries

A simple but physically intuitive double-source model is proposed to explain the interferogram of a laser–capillary system, where two effective virtual sources are used to describe the rays reflected by and transmitted through the capillary. The locations of the two virtual sources are functions of the observing positions on the target screen. An inverse proportionality between the fringes spacing and the capillary radius is derived based on the simple double-source model. This can provide an efficient and precise method to measure a small capillary diameter of micrometre scale. This model could be useful because it presents a fresh perspective on the diffraction of light from a particular geometry (transparent cylinder), which is not straightforward for undergraduates. It also offers an alternative interferometer to perform a different type of measurement, especially for using virtual sources.

SU-E-T-752: Energy Spectrum and Fluence Reconstruction of High Energy Photon Beams Based on Analytical Double-Source Model

Purpose: To improve the accuracy on unfolding photon energy spectra and fluence for dose calculation, by use of measured percentage depth dose and off-axis ratio, an analytical double-source model considered both photon beam and electron contamination was constructed, an improvement of Schiff formula and finite-size pencil beam (FSPB) model. Methods: For energy spectrum reconstruction, several regression algorithms were used to obtain the optimum solution. It was also compared with the mono-source model that ignored the electron contamination. For energy fluence reconstruction, the double-source FSPB was developed by considering the energy spectra of photon beam and electron contamination, and was also reconstructed by above algorithms. Results: A representative testing sample, the AAPM 55# report as an 18MVˈs AECL Therac-20 medical linac, was used. The comparison between the double-source model and mono-source model in energy spectrum reconstruction found that there was a great improvement in accuracy; the mean error of double-source model was about 0.015% while the mono-source modelˈs was about 0.1%. We found that there are two peaks at 2 and 3 MeV in the photon energy spectra and the peak of the electron energy was in the low energy. We also found that if ignoring the electron contamination, the peak of the photon energy spectra could drift to the lower energy, and the mean error became great. We also obtained the accurate energy fluence, only about 0.01% mean error in the field. Conclusions: This study has revealed the great improvement of Schiff formula and FSPB model on energy spectrum and fluence of photon beam and electron contamination by reconstruction method, an analytical double-source model. Our finding will help know more about detail of medical linac, and improve the dose accuracy in dose calculation of radiotherapy by use of this reconstructed information. Supported by the National Natural Science Foundation under grant No.30900386 and the Anhui Provincial Natural Science Foundation under grantNo. 090413095 and 11040606Q55.

SU-GG-T-441: Monte Carlo Dosi metric Verification Based on Double Source Model

Purpose: In dose calculation and dosimetric verification for radiotherapy, the Monte Carlo method is a “gold rule”in accuracy given the same condition. Yet the results of the traditional Monte Carlo's method may disagree with the practical situation due to lack of practical information of a given medical accelerator such as energy spectra. For another, the previous dosimetric verification method mainly focused on 1D or 2D verification by use of film, thermoluminescence detector, ionization chamber, etc, and they usually fail to apply in vivo but vitro of a patient. Considering whatever producing high energy photon or electron beam, the medical accelerator also produced contamination radiation beam, such as photonbeam to electron contamination. With these, the purpose of this study was to improve the accuracy of the dosimetric verification in Monte Carlo method.Method and Materials: A double sourcemodel combined the Monte Carlo method for the photon and electron radiation was constructed. Namely, the photon and electron energy spectra, photon or electron contamination etc were input into the Monte Carlo engine as EGSnrc to realize the double sourcedose calculation, and the superimposed results between electron dose map and photondose map were as the final one. Results: The testing samples from AAPM report No.55 (energy as 4MeV and 18MeV) indicated that the root‐mean‐square error was less than 0.21% in the 4MeV' sample and 0.18% in the 18MeV's sample respectively, comparing with the measurement data of corresboding centeral axis percentage depth dose in this report. Conclusion: This method may not only overcome the traditional dosimetric verification confine in 1D/2D dose map, but also get the 3D dose map of the whole space and increase the accuracy of the dosimetric verification. So it can be applied to the clinic dosimetric verification and quality assurance in radiotherapy.

Diurnal and seasonal variation in bulk stomatal conductance of the rice canopy and its dependence on developmental stage

Bulk stomatal conductance ( g S) is an important factor that expresses the effect of stomatal movements on water transfer between the plant and atmosphere at the canopy scale and is widely used as a parameter in many micrometeorological models. Diurnal and seasonal variations in g S of the rice canopy were determined using a heat transfer model based on heat flux measurements in irrigated rice fields. Season-long observations from transplanting to maturation of rice plants were conducted to obtain heat flux data in a humid temperate climate at three experimental sites with widely differing cropping seasons in Japan. A double source model was used as the heat transfer model to calculate g S. Seasonal variations in heat fluxes differed for sensible heat and latent heat. Sensible heat flux was smaller and relatively constant within the range −50 to 50 W m −2, whereas latent heat flux showed large variations from 0 to 250 W m −2 throughout the growth period. It was suggested that this would be a common pattern for paddy rice fields in all cropping seasons. Diurnal variation in g s showed a common trend in all growth periods with lower values in the morning and evening, and higher values during the midday because of its dependence on solar radiation. The relationship between absorbed solar radiation ( S abs) and g s was determined using a Jarvis-type model for each growth period. Maximum values of bulk stomatal conductance ( g Smax) for saturated S abs rapidly decreased from 0.06 to 0.02 m s −1 between the active tillering and panicle formation stages, and moderately decreased from 0.02 to 0.01 m s −1 during the ripening stage. This was considered to be due to the change in leaf chlorophyll concentration. Seasonal variation in g Smax can be commonly expressed for all cropping seasons using the function of developmental stage ( P S). Using this function, the g S value can be obtained easily at a given developmental stage, which makes it possible to use micrometeorological models in relation to rice phenological development for evaluating important factors, such as water temperature and transpiration, that affect rice production.

Energy balance and water use efficiency of rice canopies under free-air CO 2 enrichment

Changes in crop water use due to elevated CO 2 concentration ([CO 2]) must be evaluated for predicting agricultural productivity and water resource availability. We quantified the effects of elevated [CO 2] on the energy balance and canopy evapotranspiration (ET) in rice paddies. Rice ( Oryza sativa L.) was grown under both ambient [CO 2] (A-CO 2) and elevated [CO 2] (E-CO 2) imposed by free-air CO 2 enrichment (FACE) in northern Japan. Observations were made of micrometeorology and plant characteristics, including stomatal conductance and leaf area index (LAI). We estimated energy balances using a double-source model with heat transfers from the vegetation canopy and the water surface to avoid errors due to uncertainty in the measured radiative infrared (IR) temperatures. E-CO 2 reduced stomatal conductance by 13% in upper leaves and by 40% in lower leaves at the panicle initiation stage, but the reduction rates subsequently decreased. Stomata closed more in the E-CO 2 plot as vapour pressure deficit increased. Daily mean temperature of the vegetation canopy increased by 0.2–1 °C in response to stomatal closure under E-CO 2, whereas water surface temperature decreased by 1 °C before rice heading because of increased shading from the larger leaves in E-CO 2. The radiative IR temperature decreased by up to 1 °C in E-CO 2 before June, and increased by up to 0.6 °C thereafter. Latent heat flux decreased in E-CO 2, which was balanced by increased sensible heat flux and upward long-wave radiation. The decrease was greatest under dry and windy conditions. Total water use by plants throughout the growing season was 268.7 mm in A-CO 2 and 246.8 mm in E-CO 2, giving a saving of 22 mm of water in E-CO 2. Reduced transpiration (by 8.2%), combined with increased total biomass (by 9.1%), increased water use efficiency in E-CO 2 by 19%.

Bulk parameterization for a vegetated surface and its application to a simulation of nocturnal drainage flow

Two simple models are presented for describing the surface energy budget above vegetated surfaces. One is the traditional single-source model that includes only one energy budget equation for the entire canopy-soil system, and the other is the double-source model that includes separate energy budget equations for the vegetation canopy and the underlying soil surface. In both models, the bulk transfer coefficients needed to solve the energy budget equations are parameterized as functions of leaf area index, leaf transfer coefficients, and soil surface roughnesses to obtain the best fit to values calculated by a standard multilayer-canopy model. The validity of these models was tested by comparing their performance with that of the multilayer-canopy model for simulation of the surface energy balance and nocturnal drainage flow above vegetation. Results show that the double-source model gives reliable estimations for all cases ranging from sparse to dense vegetation covers; the single-source model is only applicable to dense, fully-covered vegetation. It is also shown that sparse vegetation weakens nocturnal drainage flow, since it isolates the cool underlying soil surface from the atmosphere above the canopy. This phenomenon cannot be described by a traditional single-source model incorporated commonly in many atmospheric models; however, the double-source model adequately describes this process.

The 23:19 aftershock of the 15 October 1979 Imperial Valley earthquake: More evidence for an asperity

AbstractThe well-recorded strong ground motion data for the 23:19 aftershock of the 15 October 1979 Imperial Valley earthquake provide a good opportunity to study the high-frequency source characteristics and the path effects at near-source distances.The best-fitting point source model has a strike-slip mechanism, N40°W, which is nearly identical to the main event. The estimated stress drop is extremely high, roughly 500 bars, with a triangular time history (0.1, 0.1 sec) but with a moment of 1.0 × 1024 dyne-cm. A double-source model found by inversion fits the high-frequency data better but indicates complex faulting: the first source (with strike = N319°E, dip = 42°NE, and slip angle = 165°) has a moment of 0.7 × 1024 dyne-cm, the second source (with strike = N324°E, dip = 82°SW, and slip angle = 181°) lies about 0.5 km to the north and has a seismic moment twice that of the first source. Source dimensions appear very small for this amount of energy release. Many of the anomalous behaviors observed at certain stations for the main event are, also, present in the aftershock data. These features are examined in terms of path effects.

Radio and X-ray observations of a multiple impulsive solar burst with high time resolution

A well-developed multiple impulsive microwave burst occurred on February 17, 1979 simultaneously with a hard X-ray burst and a large group of type III bursts at metric wavelengths. The whole event is composed of several subgroups of elementary spike bursts. Detailed comparisons between these three classes of emissions with high time resolution of ∼ 0.5 s reveal that individual type III bursts coincide in time with corresponding elementary X-ray and microwave spike bursts. It suggests that a non-thermal electron pulse generating a type III spike burst is produced simultaneously with those responsible for the corresponding hard X-ray and microwave spike bursts. The rise and decay characteristic time scales of the elementary spike burst are ≪ 1 s, ∼ 1 s and ∼ 3 s for type III, hard X-ray and microwave emissions respectively. Radio interferometric observations made at 17 GHz reveal that the spatial structure varies from one subgroup to others while it remains unchanged in a subgroup. Spectral evolution of the microwave burst seems to be closely related to the spatial evolution. The spatial evolution together with the spectral evolution suggests that the electron-accelerating region shifts to a different location after it stays at one location for several tens of seconds, duration of a subgroup of elementary spike bursts. We discuss several requirements for a model of the impulsive burst which come out from these observational results, and propose a migrating double-source model.

Reassessment of Suggested Frequency Dependent Positions for 4C Sources

Frequency dependent structure is not uncommon in observations of extended radio sources. Where a source consists of two components with different spectra at an angular separation considerably less than the resolution of the telescope, the centroid position will vary systematically with frequency. A well-known example is 3C 273 though the effect in this case is quite small. With beams of a few minutes of arc, larger position differences could occur between measurements made at widely separated frequencies without the source being noticeably resolved. In a preliminary study of a sample of 120 4C radio sources, Munro and Hoskins found 17 cases of discrepancies in the range 45 to 100 seconds of arc between positions measured at 408 MHz with the Molonglo cross (beam width ~3′ arc) and at 2700 MHz with the Parkes 64 m telescope (beam width ~7′ arc) by Wills and Bolton. These separations were considered to be significant in terms of the quoted errors which were typically 10 to 15″ arc in each coordinate for both sets of measurements. It was pointed out that to explain the results on the basis of a double source model it would be necessary for the two components to differ in spectral index by ~1.

Quasars Revisited: Rapid Time Variations Observed Via Very-Long-Baseline Interferometry

Recent Goldstone-Haystack radio interferometric observations of the quasars 3C 279 and 3C 273 reveal rapid variations in their fine structure. Most notably, the data for 3C 279, interpreted in terms of a symmetric double-source model and the accepted red-shift distance, indicate differential proper motion corresponding to an apparent speed about ten times that of light. A number of possible mechanisms that might give rise to such an apparent speed are considered; although several may be plausible, no definitive choice can be made on the basis of present evidence. More interferometric observations of quasars are clearly needed to clarify their structure and internal kinematics.