Generation of ultrashort pulses in the THz frequency range

There are results for the spontaneous coherent super-radiative undulator emission in the terahertz frequency range from a short (as compared to the wavelength of the radiated wave) dense electron bunch. If the group velocity of the wave is close to the bunch velocity, this is a process of spontaneous radiation followed by amplification of a single wave cycle. Despite the Coulomb repulsion of electrons inside the bunch, its compactness is provided by the compression of the bunch under the action of its own radiation fields. As a result, formation of an ultra-short (several cycles long) powerful wave packet occurs when the bunch moves through several undulator periods with high (∼20% in optimized systems) efficiency of extraction of the electron energy and high intensity (∼ 100 MV/m) of the peak wave field.

Renovation cycle diagram

Introduction. A relatively new form of transformation of the territory in the current urban development, the renovation of quarters, requires close scientific study and methodological justification. Renovated neighborhoods, as well as projects for the construction of new houses, have individual features and characteristics. The authors hypothesize that, despite the variety of characteristics of renovated neighborhoods and projects for the construction of new houses, traditional in-line construction with the allocation of characteristic stages is possible. Materials and methods. To study the actual duration of the stages of creating objects under the renovation program (which is necessary to identify objects of similar duration), a special database was formed in the Scientific and Project Center “City Development”. As of 15.05.2021, 313 objects involved in the renovation program are included in this special database. A thorough verification of the specified database was performed. As a result, 122 objects with a spread of construction duration values from 11 months to 43.2 months are stored in the verified database. In addition, the materials of the information system for ensuring urban planning activities (ISOGD) of Moscow were used. The initial materials allowed us to identify a number of characteristic stages in the renovation program for each object. Results. To analyze the design duration of construction, the set of objects is divided into 2 parts: commissioning in 2021 and commissioning in subsequent years. For each part, histograms of the distribution of the duration of construction of houses during renovation are constructed and it is proved that the law of normal distribution is observed. A schematic model of renovation processes with multiple process durations is presented. The overall duration of the design (project stage) can take 1 year, construction — 2 years, and the combined stages: preparation of documents, relocation and demolition, will approximately take 1 year. This four-year wave cycle is then repeated the required number of times. The calendar plan of renovation for three wave objects with the allocation of the leading stream is presented. The ratio of flow processes during renovation is most clearly reflected in the constructed cyclogram of a multi-rhythmic object flow modified for renovation conditions. Combined schedules of renovation of in-line construction are constructed. Conclusions. Despite the considerable variety of renovated neighborhoods and projects for the construction of new houses, the authors of the article prove that traditional in-line construction with the allocation of characteristic stages is possible. For large contracting organizations, it is realistic to form a multi-rhythmic object flow with the allocation of the construction stage as the leading flow and calculate the renovation cyclogram.

Characterization of Non-linear Internal Waves Using PIV/PLIF Techniques

Internal waves are ubiquitous in the ocean. They often form in regions of high temperature or salinity variability as the pycnocline oscillates to form the wave (Phillips, 1966). They can be generated either from the interaction of tidal currents with submarine bathymetry (Garrett and Kunze, 2007) or by wind stress at the ocean surface (Munk and Wunsch, 1998). The current study addresses non-linear internal waves due to their importance in the mixing and dynamics of both atmospheric and oceanographic flows. Due to the significance of this phenomena, numerous investigations have been conducted to obtain satisfactory theoretical solutions for internal waves in several types of fluid systems. The verification of these models requires precise and accurate experimental data. It should be noted that such models generally assume simple two-layer stratified system separated by a sharp interface. In reality, there is a gradient of density at the interface of the two layers, which can make both experimental and theoretical analysis more challenging. To date, most experimental studies for several types of internal waves have been performed using ultrasonic probes, conductivity probes, resistance-type wave gauges, or salinity-sensor-type wave gauges, as given by Davis and Acrivos (1967),Koop and Butler (1981),Michallet and Barthelemy (1998) and Umeyama (2002). There is one recent study that used the particle image velocimetry (PIV) technique to determine the Eulerian velocity field of internal waves, but it lacks the detailed density measurements necessary to fully understand the flow (Umeyama and Matsuki, 2011). The current work aims to fully understand the dynamics of internal waves by measuring the density and velocity fields, and then comparing the experimental results with the theoretical non-linear wave solution. A laboratory-scale apparatus was created to replicate the flow characteristics of internal waves in a twolayer stratified system. An experimental configuration is presented with a density jump of 1.1 and 1.5 σt separately. Experiments are conducted in the tank (2.438 m × 50 cm × 50 cm), which was constructed from clear acrylic sheets with thickness of 1.905 cm. The schematic of the internal wavemaker apparatus is shown in Fig. 1(a) (Mohaghar et al., 2020). A line diffuser (PVC) was installed along the middle of the tank floor to be used to fill the tank. A half-cylinder plunger-type wavemaker was used to create a perturbation at the pycnocline represented by the interface between the density layers. On each revolution of the drive mechanism, the switch sent a voltage signal to the external trigger port of a pulse generator. By precisely controlling the delay following the external trigger signal, the pulse generator sent a signal to the Nd:YAG laser and the camera to capture an image at a targeted phase of the wave cycle. Images are recorded with a high resolution 29 MP CCD camera, (14-bits, 6600 × 4400 pixels). PIV was used to measure the velocity field, and the fluids in both layers were seeded with neutrallybuoyant particles. The seeded particles were illuminated using a dual-cavity New Wave Research Gemini PIV laser at wavelength of 532 nm, which is diverged into a sheet. Light entering the PIV camera passed through a 532 nm bandpass filter. The image pairs were processed with Insight 4GTM software using a 32 × 32 pixel final spot size with 50% overlap. A sample of PIV vector field for the case of ∆ρ = 1.5σt is shown in Fig. 1(b). In order to measure the density fields, the flow is visualized using the planar laser-induced fluorescence (PLIF) method for scalar visualization. A laser-fluorescing dye, Rhodamine 6G, is mixed into the heavier layer and the light sheet is used to fluoresce the dye. Following the procedures outlined by Mohaghar (2019), the dye concentration is then inferred from the digital images. In order to capture only fluorescence emitted by Rhodamine 6G, the camera is equipped with a notch filter blocking the 532 nm wavelength of light. A sample of a final processed PLIF image for the case of ∆ρ = 1.5σt is shown in Fig. 1(c). The interface location, density gradient, wave amplitude and period, velocity and vorticity fields, kinetic energy and shear strain rate are quantified by several phases in one wave cycle and subsequently compared with the corresponding predictions based on third-order Stokes internal-wave theory.

Modelling and Analysis of Hydrodynamics of a Submerged Structure in Extreme Waves Using a SPH-Based Tool

The applications of a Smoothed Particle Hydrodynamics (SPH)-based, a Finite Volume Method (FVM)-based and a Boundary Element Method (BEM)-based tools to investigate the nonlinear interactions between large waves and a submerged horizontal circular structure and to some extent a rectangular cylinder at various submergence depths in deep water conditions are presented. The main aim is to validate the Lagrangian technique based SPH tool to predict the wave-structure interaction forces under large waves. The features of typical force curves in a wave cycle, the magnitude of wave forces, and the influence of relative axis depth of the structure in deep water conditions are investigated, primarily using an open-sourced SPH tool. Simulations were carried out in 2D with one deepwater wave at multiple submergence depths. The water surface elevations are predicted at different near- and far-field locations. The time-averaged mean and the average amplitude of the horizontal and vertical forces acting on the cylindrical model at various submergence depths are plotted and then physically interpreted. The wave forces and surface elevations are compared with the available published experimental studies and CFD (both FVM and BEM) predictions. Good agreement between the SPH predictions and the measurements was obtained for the submerged body’s surface elevation and hydrodynamic forces at all submergence depths. The FVM tends to overestimate the wave forces compared to the SPH predictions and the measurements, particularly for the shallowly submerged structure when extreme wave breaking occurs. The BEM predictions are reasonable for the non-wave breaking cases.

Time Domain Analysis of Single Module Movement of Deep Sea Rights Enforcement Platform

Due to its large size, deep sea rights enforcement platform cannot be closed in the dock, so it needs to be dragged to the pre-installed position for module to module connection. Based on the ANSYS AQWA software, a single module finite element model of the platform is established to solve the security problem of the far-reaching maritime rights enforcement platform in the sea. The hydrodynamic coefficient and the transfer function of the motion response are calculated in the frequency domain, and the response spectrum analysis is carried out. It is worth noting that the single module is a trapezoidal asymmetric structure, so the shape influence on the calculation results will be focused on. The results show that the motion response of the single module is greatly influenced by the wave cycle and the wave direction, because the single module of the platform is a trapezoid asymmetric structure, and the hydrodynamic coefficients are different under different incident waves. Through comparison and parameter analysis, the rationality of the single module design and the good motion performance under the actual sea condition are verified.

TECHNOLOGICAL PARADIGMS: A JUMP TO THE SIXTH OR A SLIP DOWN TO THE FOURTH

The aim of this article is to analyse approaches to emphasizing the essence of the sixth technological paradigm (wave of innovation). The author uses the historical research method. By examining ideas on the technological paradigms (wave, cycle, paradigm, formation, etc.), the author shows the limitation of the purely economic approach to solving technological paradigms issues. The attention is paid also on the periodization of paradigms and there is an absence of a single logical basis in it. paradigms change. This circumstance does not allow us to speak about a really theoretical description of the process of changing paradigms. The situation is being considered from a wider historical perspective of the humankind existence (as a species), as a subject not only on a planetary scale. From this point of view, the essence of the sixth paradigm and the prospects for the evolution of paradigms are more clearly identified.

A Numerical Model for Offshore Mound Evolution

A numerical model was developed to simulate the evolution of a mound placed in the offshore (i.e., outside the zone of wave breaking), exposed to varying non-breaking waves and water levels. The net sediment transport rate is assumed to be mainly dominated by bed load transport, where wave asymmetry plays an important role. The net transport over a wave cycle is expressed with reference to an equilibrium profile, which ensures model reliability and robustness. In order to validate the model, data collected at two field sites, Cocoa Beach and Perdido Key Beach in Florida, USA, were employed. The numerical results show good agreement with the measured data from the two sites in terms of the profile evolution. It demonstrates that the model has the capability to simulate the evolution of mounds placed in the offshore. In addition, several scenarios with different mound volume and location designs were investigated to indicate potential uses for the model. The results illustrate how the mound evolution is influenced by the volume and location of the mound placement.

The Colour of Social Realism

During the 1960s Eastmancolor, a relatively cheap, widely available film stock, revolutionised the British film industry's approach to colour. This article discusses the consequences of this major representational and aesthetic shift on social realism, a sub-genre of British cinema primarily associated with black and white cinematography. While colour provided an opportunity for greater realism, critics argued that it distracted audiences with hues considered inappropriate for social commentary. The article examines how a number of notable 1950s and 1960s British colour films navigated entrenched critical positions while deploying colour in distinctive, often innovative ways to reflect their social realist environments and themes. Films examined include A Kid for Two Farthings (1955), Miracle in Soho (1957), Sapphire (1959), Flame in the Streets (1961), Some People (1962), The Family Way (1966) and Poor Cow (1967). It is argued that critics' preoccupation with the New Wave cycle of films, 1959–63, has been at the expense of colour films that extended the range of representation, both aesthetically and thematically. Bringing colour more centrally into scholarship about British cinema contributes to revisionist research on social realism that privileges the foregrounding of style and textual aesthetics. In addition, the article shows how analysing films from the perspective of colour encourages relating them to broader chromatic tastes and trends. By the mid-1960s, as culture was generally becoming more chromatically vibrant, film-makers were able to take greater advantage of the colour stocks that enabled them to experiment with realist conventions.