A sound projector for acoustic tomography and global ocean monitoring

Long-range underwater acoustic systems, such as those used in ocean acoustic tomography, require low-frequency signals covering a broad frequency band. To meet this requirement, a novel design based on a tunable narrow-band high-efficiency sound projector has been used. The projector transmits a frequency sweep signal by mechanically tuning a resonator tube (or organ pipe) to match the frequency and phase of a reference signal. The resonator tube projector consists of a symmetrical pressure-balanced Tonpilz driver placed between two coaxially mounted tubes. The Tonpilz acoustic driver is composed of two pistons separated by preloaded ceramic stacks. The resonant tube is a simple, efficient, narrow-band, medium-output projector that operates at any ocean depth. Both projector tubes have slots (or vents) which are progressively covered or uncovered by sliding coaxial tubular sleeves. The frequency varies with the sleeve position. A computer-controlled electromechanical actuator moves the cylindrical sleeves along the tubes, keeping the projector in resonance at the instantaneous frequency of a swept frequency signal. The actuator smoothly tunes the resonator tube frequency in a bandwidth of 200 to 300 Hz during a 135-s transmission. A computer synthesizes the linear frequency-modulated signal; compares the phase between transmitted and reference signals; and, using a phase-lock loop (PLL) system, keeps the resonator tube frequency in resonance with the driver frequency. The estimated PLL precision is better than 3/spl deg/ phase error. The system was analyzed by means of finite element analysis and electrical equivalent circuit simulation. The projector prototype was first tested at the Woods Hole Oceanographic Institution (WHOI) dock in Woods Hole, MA and later in the Pacific Ocean during a voyage of the R/V "Point Sur" in November 2001.     

Effect of Induced Toroidal Rotation on Poloidal Rotation and Ion Heat Conductivity of Tokamak Edge Plasmas

The transport processes in edge (collisional) plasmas of tokamaks with smooth profiles of macroscopic plasma parameters and induced poloidal and toroidal plasma flows, are considered. The toroidal and poloidal velocities of particles, the radial electric field and the ion heat flux are derived. It is shown that forces, induced by radio frequency waves, plasma turbulence or neutral beam injection, can be used to control the poloidal and toroidal plasma velocities, as well as ion heat conductivity, in a wide range of these values.     

Peculiarities of Water Circulation in the Central Part of the Bransfield Strait in January 2020

Doklady Earth Sciences - The results of measurement of the thermohaline parameters of water and currents in the Bransfield Strait in Antarctica during the expedition of the Shirshov Institute of...     

Groundwater Flow Near a Vertical Circulation Well with a Skin-Effect

Water Resources - Groundwater flow in the vicinity of a vertical circulation well is considered. The article presents solutions of problems of steady-state and transient groundwater flow near a...     

New data on the age of dolerites and basalts of Mendeleev Rise (Arctic Ocean)

We present results of ⁴⁰Ar/³⁹Ar isotopic investigations concerning the dating of dolerites and basalts that were sampled during the Arctica-2012 polar expedition. Basalts were sampled by means of deep underwater drilling with wells up to 2 m in outcrops on the seafloor (basalts), and dolerite samples were obtained from the bottom of an escarp of Mendeleev Rise using a manipulator on the research submarine. The analysis results of the obtained mono-mineral fractions (amphibole, plagioclase, pyroxene) from the studied rocks yielded an Early Paleozoic age of the dolerites and basalts from Mendeleev Rise. The oldest ages obtained for amphibole reach 471.5 ± 18.1 and 466.9 ± 3.3 Ma, which corresponds to the Early-Middle Ordovician. The isotopic composition of argon was measured on two mass spectrometers: the Micromass Noble Gas 5400 (UK) and the Thermo Scientific Argus (Germany). The determined Early Paleozoic age of igneous rocks of Mendeleev Rise and seismic data obtained during the last Russian expedition Arctica-2012 [2] let us suppose that this continental block of the Earth’s crust has a Precambrian basement similar to the basement identified for the New Siberian islands including the De Long archipelago.     

Dynamics of gaseous disks in a non-axisymmetric dark halo

The dynamics of a galactic disk in a non-axisymmetric (triaxial) dark halo is studied in detail using high-resolution, numerical, hydrodynamical models. A long-lived, two-armed spiral pattern is generated for a wide range of parameters. The spiral structure is global, and the number of turns can be two or three, depending on the model parameters. The morphology and kinematics of the spiral pattern are studied as functions of the halo and disk parameters. The spiral structure rotates slowly, and its angular velocity varies quasi-periodically. Models with differing relative halo masses, halo semi-axis ratios, distributions of matter in the disk, Mach numbers in the gaseous component, and angular rotational velocities of their halos are considered.     

Antarctic bottom water flow in the western part of the Romanche Fracture Zone based on the measurements in October of 2011

The properties of the Antarctic Bottom Water flow in the region of its inflow to the channel of the Romanche Fracture Zone at 22°10′–22°30′ W are studied on the basis of CTD and LADCP profiling in the western part of the equatorial fracture zone. A deep water cataract was found at the sill over the southern wall of the fracture with a depth of approximately 4600 m, which is associated with the abyssal flow, whose potential temperature is lower than 1°C. The inflow of water into the channel of the fracture in this temperature range is fully localized over this sill. The minimum potential temperature θ recorded in 2011 near the bottom was equal to 0.51°C, which is lower approximately by 0.12°C than the minimum temperatures ever measured in the western part of the fracture. The water transport in the cataract was estimated at 0.2 Sv (1 Sv = 10⁶ m³/s), which is approximately 30% of the known estimates of the total transport of Antarctic Bottom Water (θ < 1.9°C) through the fracture. The extremely high intensity of the cross isothermal mixing in the cataract region was found. The analysis of the bottom topography data, including the historical WOD09 dataset, shows that the inflow of water with 1.00° < θ < 1.70°C into the channel of the fracture is most likely fully localized in a few passages in the region of the survey in 2011, while the water exchange with the abyssal waters with θ > 1.70°C through the Romanche Fracture Zone between the West and East Atlantic can also occur through the depressions in the southern and northern walls of the fracture in the region of the Vema Deep.