Comparison of a small slope approximation model of reflection loss at the rough ocean surface with stochastic modelling using PE.

The accurate modelling of underwater acoustic reflection from a wind-roughened ocean surface is a challenging problem. Some complicating factors are the presence of near-surface bubbles and the potential for shadowing of acoustic energy by parts of the surface itself. One essential factor, which is the subject of the present paper, is the specular reflection of coherent plane waves at an ocean-like rough surface. We tested the accuracy of the rough surface reflection model adopted by the authors, the small-slope approximation (SSA) approach as used by Williams et al. (JASA, 116, Oct. 2004). The SSA model was used to compute values of the coherent plane wave reflection loss per bounce for wind speeds between 5 and 12.5 m/s, frequencies between 1.5 and 9 kHz, and grazing angles between about 1 and 10 degrees. These values were compared to those obtained from a Monte-Carlo approach based on the Parabolic Equation (PE) method, where realistic ocean surfaces were generated based on the Pierson-Moskowitz spectrum for ocean surface heights. The SSA model compared favourably with the more rigorous PE method for most of the range of parameters considered

BRST approach to Lagrangian formulation for mixed-symmetry fermionic higher-spin fields

We construct a Lagrangian description of irreducible half-integer higher-spin representations of the Poincare group with the corresponding Young tableaux having two rows, on a basis of the BRST approach. Starting with a description of fermionic higher-spin fields in a flat space of any dimension in terms of an auxiliary Fock space, we realize a conversion of the initial operator constraint system (constructed with respect to the relations extracting irreducible Poincare-group representations) into a first-class constraint system. For this purpose, we find auxiliary representations of the constraint subsuperalgebra containing the subsystem of second-class constraints in terms of Verma modules. We propose a universal procedure of constructing gauge-invariant Lagrangians with reducible gauge symmetries describing the dynamics of both massless and massive fermionic fields of any spin. No off-shell constraints for the fields and gauge parameters are used from the very beginning. It is shown that the space of BRST cohomologies with a vanishing ghost number is determined only by the constraints corresponding to an irreducible Poincare-group representation. To illustrate the general construction, we obtain a Lagrangian description of fermionic fields with generalized spin (3/2,1/2) and (3/2,3/2) on a flat background containing the complete set of auxiliary fields and gauge symmetries.Comment: 41 pages, no figures, corrected typos, updated introduction, sections 5, 7.1, 7.2 with examples, conclusion with all basic results unchanged, corrected formulae (3.27), (7.138), (7.140), added dimensional reduction part with formulae (5.34)-(5.48), (7.8)-(7.10), (7.131)-(7.136), (7.143)-(7.164), added Refs. 52, 53, 54, examples for massive fields developed by 2 way

On the human remains from the medieval fortification of Tver Kremlin (Russia)

We report the human bones, found during the excavations near the medieval fortification (12th – 13th cent.) of Tver Kremlin. Comparison with several medieval cities of Russia suggests that bones belong to the people, who defended the stronghold against Mongols in 1238

Three-dimensional anatomy of the ostrich (Struthio camelus) knee joint

The three-dimensional anatomy of the ostrich (Struthio camelus) knee (femorotibial, femorofibular, and femoropatellar) joint has scarcely been studied, and could elucidate certain mechanobiological properties of sesamoid bones. The adult ostrich is unique in that it has double patellae, while another similar ratite bird, the emu, has none. Understanding why these patellae form and what purpose they may serve is dually important for future studies on ratites as well as for understanding the mechanobiological characteristics of sesamoid bone development. For this purpose, we present a three-dimensional anatomical study of the ostrich knee joint, detailing osteology, ligaments and menisci, and myology. We have identified seven muscles which connect to the two patellae and compare our findings to past descriptions. These descriptions can be used to further study the biomechanical loading and implications of the double patella in the ostrich

The effect of volume inclusions of the ZnGeP2 single-crystal on the dispersion of the refraction index and the absorption coefficient in mid-IR and terahertz ranges of wavelengths

Volume filamentary inclusions in ZnGeP2 have been visualized using the digital holography method. The chemical composition of the filamentous volume inclusions Zn3P2 and Ge have been determined using the method of X-ray diffraction analysis. It is shown that the presence of volume inclusions in the ZnGeP2 singlecrystal leads to an increase in the reflection coefficient in the region of 12.5 μm. The dispersion dependences of the refractive index and the absorption coefficient of the studied ZnGeP2 samples at wavelengths of 300–1000 μm in the region of non-fundamental absorption have been obtained. It has been shown that the presence of volume inclusions in a single-crystal leads to an increase in the refractive index in the entire THz range under study by the value of Δnmax = 0,0008. The difference between absorption coefficients for the studied samples varies from Δα = 0.1 cm 1 to Δα = 0.15 cm 1 depending on the wavelength

Digital holography methods for visualization and identification of ZnGeP2 bulk defects

The volumetric filamentous inclusions in ZnGeP2 were visualized by digital holography, their characteristic sizes were determined, and their location in the sample volume was determined. The chemical composition of filamentous bulk inclusions – Zn3P2 and Ge-was determined by X-ray diffraction analysis. The influence of the second-phase inclusions (Zn3P2 and Ge) on the quasi optical characteristics (refractive index and absorption coefficient) in the resonant absorption band (12–12.5 microns) is established. The presence of bulk inclusions in the ZnGeP2 single crystal leads to an increase in the reflection coefficient in the region of 12.5 microns. The dispersion dependences of the refractive index and the absorption coefficient of the studied ZnGeP2 samples at wavelengths of 300–1000 microns in the non fundamental absorption region were obtained. The obtained experimental results confirm the assumption of the determining role of free carriers in the formation of dielectric losses in the wavelength range of 100–1000 microns. The hypothesis that one of the main sources of free carriers in ZnGeP2 is the matrix medium / inclusion interface of the second phase is confirmed.В ст. ошибочно: A. S. Bolshako

Ontogenetic scaling patterns and functional anatomy of the pelvic limb musculature in emus (Dromaius novaehollandiae)

Emus (Dromaius novaehollandiae) are exclusively terrestrial, bipedal and cursorial ratites with some similar biomechanical characteristics to humans. Their growth rates are impressive, as their body mass increases eighty-fold from hatching to adulthood whilst maintaining the same mode of locomotion throughout life. These ontogenetic characteristics stimulate biomechanical questions about the strategies that allow emus to cope with their rapid growth and locomotion, which can be partly addressed via scaling (allometric) analysis of morphology. In this study we have collected pelvic limb anatomical data (muscle architecture, tendon length, tendon mass and bone lengths) and calculated muscle physiological cross sectional area (PCSA) and average tendon cross sectional area from emus across three ontogenetic stages (n = 17, body masses from 3.6 to 42 kg). The data were analysed by reduced major axis regression to determine how these biomechanically relevant aspects of morphology scaled with body mass. Muscle mass and PCSA showed a marked trend towards positive allometry (26 and 27 out of 34 muscles respectively) and fascicle length showed a more mixed scaling pattern. The long tendons of the main digital flexors scaled with positive allometry for all characteristics whilst other tendons demonstrated a less clear scaling pattern. Finally, the two longer bones of the limb (tibiotarsus and tarsometatarsus) also exhibited positive allometry for length, and two others (femur and first phalanx of digit III) had trends towards isometry. These results indicate that emus experience a relative increase in their muscle force-generating capacities, as well as potentially increasing the force-sustaining capacities of their tendons, as they grow. Furthermore, we have clarified anatomical descriptions and provided illustrations of the pelvic limb muscle–tendon units in emus

Threshold of laser destruction of nonlinear GaSe and GaSe:in crystals when exposed to pulsed radiation at a wavelength of 2.1 microns

The aim of this work is to determine the optical breakdown threshold of a single crystal GaSe and GaSe:In when exposed to nanosecond radiation of the two micron range and determining the influence of the energy parameters of the testing radiation on the breakdown threshold. The Ho3+:YAG laser was used as the laser radiation source in this work. Pumping was carried out by a Thule fiber laser.В ст. ошибочно: E. V. Zhuravle

Influence of post-post processing technology and laser radiation parameters on the optical breakdown threshold of a ZnGeP2 single crystal

The aim of this work is to determine the influence of the parameters of post-growth technological operations and experimental conditions on the threshold of optical breakdown of the surface of ZGP crystals under the action of laser radiation at a wavelength of 2091 nm

Cancellous bone and theropod dinosaur locomotion. Part II—a new approach to inferring posture and locomotor biomechanics in extinct tetrapod vertebrates

This paper is the second of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and therefore has the potential to provide insight into locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part II, a new biomechanical modelling approach is outlined, one which mechanistically links cancellous bone architectural patterns with three-dimensional musculoskeletal and finite element modelling of the hindlimb. In particular, the architecture of cancellous bone is used to derive a single ‘characteristic posture’ for a given species—one in which bone continuum-level principal stresses best align with cancellous bone fabric—and thereby clarify hindlimb locomotor biomechanics. The quasi-static approach was validated for an extant theropod, the chicken, and is shown to provide a good estimate of limb posture at around mid-stance. It also provides reasonable predictions of bone loading mechanics, especially for the proximal hindlimb, and also provides a broadly accurate assessment of muscle recruitment insofar as limb stabilization is concerned. In addition to being useful for better understanding locomotor biomechanics in extant species, the approach hence provides a new avenue by which to analyse, test and refine palaeobiomechanical hypotheses, not just for extinct theropods, but potentially many other extinct tetrapod groups as well