Acousto-optic devices using acoustic waves refraction

The methods of acousto-optics provide multiple techniques for controlling optical beam. The technical parameters of corresponding acousto-optic devices are largely determined by the efficiency of acoustic waves generation. In present work we examine the features of elastic waves generation in materials used in acousto-optics. In most of practical applications the elastic wave generation process is implemented through the refraction of elastic waves at the boundary between two anisotropic media. We present a detailed study of the refraction of elastic waves in strongly anisotropic media. We report new refractive effects such as “extraordinary” refraction. In the latter case the change in the direction of the incident acoustic wave does not influence the direction of the energy flow propagation for refracted elastic waves. The configuration of an acousto-optic device using the geometry of unusual refraction in an anisotropic medium is discussed.

Computation of Dynamic Equilibria in Series-Parallel Networks

We consider dynamic equilibria for flows over time under the fluid queuing model. In this model, queues on the links of a network take care of flow propagation. Flow enters the network at a single source and leaves at a single sink. In a dynamic equilibrium, every infinitesimally small flow particle reaches the sink as early as possible given the pattern of the rest of the flow. Although this model has been examined for many decades, progress has been relatively recent. In particular, the derivatives of dynamic equilibria have been characterized as thin flows with resetting, which allows for more structural results. Our two main results are based on the formulation of thin flows with resetting as a linear complementarity problem and its analysis. We present a constructive proof of existence for dynamic equilibria if the inflow rate is right-monotone. The complexity of computing thin flows with resetting, which occurs as a subproblem in this method, is still open. We settle it for the class of two-terminal, series-parallel networks by giving a recursive algorithm that solves the problem for all flow values simultaneously in polynomial time.

PHANTOM MODEL OF DISTRIBUTION OF VIRAL OBJECTS IN A PANDEMIC. PART 3

The article states that the nature of the virus's interaction with objects during its spread in any environment is a significant problem. Therefore, taking into account the peculiarities of such a complex fractional composition of flows can make it possible to determine the nature of the interaction of the object, in particular biological, with complex particles of viral flows when touching. The author's previous works consider the peculiarities of the spread of viruses in the surrounding space of the pandanus zone of the object under the condition of a single fraction of the particle, ie in the near-surface layer. Of course, to better understand the nature of the interaction of viral flows with objects of possible infection, it is necessary to analyze the processes of virion’s touching to the cell surface of a biological object. The studied regularities of the occurrence of motion forces in environment’s space made it possible to determine the geometric parameters of the spread of viral formations near the object’s surface. The main purpose of this study was to continue to create a model of interaction of complex flows with different fractions that are carriers of viruses as material particles in the environment, in terms of modeling the motion and touching the surface of the object at different types of touch depending on their interaction. The mechanical movement of the virus during contact, rather than stages, as in biological processes, is considered. The nature of the interaction of complex viruses’s streams with objects of biological origin is modeled. To study the peculiarities of the interaction of the virion with the cell surface of a biological object, it is necessary to consider the flow complex of particles of different fractions, i.e. microstructures of virions that accompany drip suspension flows of body fluids and foreign dust particles. Thus, we can distinguish the motion of a complex of particles that comes into contact with object’s surface, as well as the possibility of breaking out individual microparticles, virions, which can emerge from the complex flow and propagate separately from others. At the same time, the dependences of the energy complex, which forms the flow of complex elements-particles of different fractions, which can take into account the range of flow propagation and features of motion kinematics, are determined. In further research, the phantom model of the propagation of fluxes of viral objects in space requires modeling the temporal parameters of the motion of fluxes of complex particles during the propagation to the object’s surface of various origins, including biological object.

The influence of variable emissivity on lava flow propagation modeling

Modeling lava flow propagation is important to determine potential hazards to local populations. Thermo-rheological models such as PyFLOWGO track downflow cooling and rheological responses for open-channel, cooling-limited flows. The dominant radiative cooling component is governed partly by the lava emissivity, which is a material property that governs the radiative efficiency. Emissivity is commonly treated as a constant in cooling models, but is shown here to vary with temperature. To establish the effect of temperature on emissivity, high spatiotemporal, multispectral thermal infrared data were acquired of a small flow emplaced from a tumulus. An inverse correlation between temperature and emissivity was found, which was then integrated into the PyFLOWGO model. Incorporating a temperature-dependent emissivity term results in a ∼5% increase in flow length and < 75% lower total cumulative heat flux for the small flow. To evaluate the scalability of this relationship, we applied the modified PyFLOWGO model to simulations of the 2018 Lower East Rift Zone fissure 8 flow, emplaced between May 27 and June 3. Our model improves the emplacement match because of the ~ 30% lower heat flux resulting in a ∼7% longer flow compared to modeling using a constant emissivity (0.95). This 5–7% increase in length prior to ocean entry, realized by an accurate temperature-dependent emissivity term, is critical for developing the most accurate model of future flow hazard assessments, particularly if population centers lie in the flow’s path.

Experimental Study of Three-Dimensional Obstacle Effect on Velocity Structure of Density Currents

&lt;p&gt;The density currents&amp;#8217; velocity structure, which can be divided into a jet region (JR) and a wall region (WR, thickness h&lt;sub&gt;r&lt;/sub&gt;) according to their distinct dynamics, may be significantly modified as the current crosses an obstacle, thus leading to variations in the flow propagation process. However, there is a lack of direct observation of the response of different parts of the velocity structure to a three-dimensional obstacle due to the challenges in 3-D flow field measurement. To address this knowledge gap, a series of laboratory experiments have been devised to examine the separate influence of the WR and JR on mixing and propagation processes of density currents. A particle image velocimetry system and a high-speed camera are used to obtain the detailed velocity and vorticity fields with high temporal resolution. Compared with the no-obstacle counterpart that is uniform in the spanwise direction, the time-averaged current height (h&lt;sub&gt;c&lt;/sub&gt;) in obstacle cases gradually thickens in that direction, and both the WR and JR thicken accordingly. The ratio of the obstacle height (h&lt;sub&gt;o&lt;/sub&gt;) to h&lt;sub&gt;c&lt;/sub&gt; influences the velocity structure. Specifically, h&lt;sub&gt;r&lt;/sub&gt;/h&lt;sub&gt;c&lt;/sub&gt; upstream is larger than that downstream when h&lt;sub&gt;o&lt;/sub&gt;&gt;h&lt;sub&gt;c&lt;/sub&gt;, and vice versa. It is noteworthy that the variation of h&lt;sub&gt;r&lt;/sub&gt;/h&lt;sub&gt;c&lt;/sub&gt; in the spanwise direction is nonmonotonic with h&lt;sub&gt;o&lt;/sub&gt;. Furthermore, the obstacle also influences the velocity profile upstream. The flow is obstructed on the center line when h&lt;sub&gt;o&lt;/sub&gt;&gt;h&lt;sub&gt;c&lt;/sub&gt;. When h&lt;sub&gt;o&lt;/sub&gt;&lt;h&lt;sub&gt;r&lt;/sub&gt;, the obstacle divides the wall region upstream into two parts above and below h&lt;sub&gt;o&lt;/sub&gt;, and the gradient of the velocity profiles of the upper one is larger than the lower one. The results suggest that the obstacle plays an important role in determining the dissipation on the interface between the JR and the environment, and changing the current&amp;#8217;s capacity on carrying the sediment since both the settling and resuspension of particles and sediment mostly happen in the WR. Our findings can improve understanding of the influence of submarine topography and provide a reference for underwater engineering.&lt;/p&gt;

Stochastic Uncertainty in a Dam-Break Experiment with Varying Gate Speeds

Uncertainties inherent in gate-opening speeds are rarely studied in dam-break flow experiments due to the laborious experimental procedures required. For the stochastic analysis of these mechanisms, this study involved 290 flow tests performed in a dam-break flume via varying gate speeds between 0.20 and 2.50 m/s; four pressure sensors embedded in the flume bed recorded high-frequency bottom pressures. The obtained data were processed to determine the statistical relationships between gate speed and maximum pressure. The correlations between them were found to be particularly significant at the sensors nearest to the gate (Ch1) and farthest from the gate (Ch4), with a Pearson’s coefficient r of 0.671 and −0.524, respectively. The interquartile range (IQR) suggests that the statistical variability of maximum pressure is the largest at Ch1 and smallest at Ch4. When the gate is opened faster, a higher pressure with greater uncertainty occurs near the gate. However, both the pressure magnitude and the uncertainty decrease as the dam-break flow propagates downstream. The maximum pressure appears within long-period surge-pressure phases; however, instances considered as statistical outliers appear within short and impulsive pressure phases. A few unique phenomena, which could cause significant bottom pressure variability, were also identified through visual analyses using high-speed camera images. For example, an explosive water jet increases the vertical acceleration immediately after the gate is lifted, thereby retarding dam-break flow propagation. Owing to the existence of sidewalls, two edge waves were generated, which behaved similarly to ship wakes, causing a strong horizontal mixture of the water flow.