Symmetric Sections Research Articles

Singlet extension of the MSSM as a solution to the small cosmological scale anomalies

In this work we show that the general singlet extension of the MSSM can naturally provide a self-interacting singlino dark matter to solve the small cosmological scale anomalies (a large Sommerfeld enhancement factor can also be obtained). However, we find that the NMSSM (the singlet extension of the MSSM with Z3 symmetry) cannot achieve this due to the restricted parameter space. In our analysis we introduce the concept of symmetric and antisymmetric viscosity cross sections to deal with the non-relativistic Majorana-fermion dark matter scattering.

Aeroelastic stability of a symmetric multi-body section model

The aeroelastic stability of a multi-body system is studied through a four-degree-of-freedom elastic model, which describes the linearized section dynamics of particular suspended bridges with doubly-symmetric cross-section, subject to a lateral stationary wind flow. A multi-parameter perturbation solution, applied to the modal problem in internal resonance conditions, allows a consistent reduction of the model dimensions. Focus is made on the particular parameter region corresponding to the triple internal resonance among a global torsional mode of the deck and two local modes of a pair of hanger cables. The bifurcation scenario described by a local stability analysis is featured by two dynamic instability boundaries, strongly interacting with each other. The parametric analysis of the critical wind velocity provides satisfying engineering results, pointing out how the presence of resonant light cables, as well as the addiction of dissipative couplings simulating passive viscous dampers acting on the cable-deck differential velocity, may have beneficial effects in preventing the aeroelastic instability of the full system.

Aerodynamic Design of S-Shaped Diffusers Using Ball–Spine Inverse Design Method

Recently, an inverse design algorithm called ball–spine algorithm (BSA) was introduced for the design of 2D ducts. In this approach, the walls are considered as a set of virtual balls that can move freely along the straight directions called spines. In the present work, the method is developed for quasi-three-dimensional (quasi-3D) design of S-shaped ducts with a predefined width. To do so, the upper and lower lines of the S-duct symmetric section are modified under the BSA and then, the 3D S-duct geometry is obtained based on elliptic cross-sectional profiles. The target pressure distributions (TPDs) along the upper and lower lines are prescribed so that separation does not occur. Finally, the flow through the designed S-duct is numerically analyzed using a viscous flow solver with the SST turbulence model to validate the designed S-duct performance. The performance of the designed S-duct is compared to original and optimized versions of a benchmark S-duct diffuser. Results show that the present S-duct has a better performance.

Platelet Orthomode Transducer for <formula formulatype="inline"> <tex Notation="TeX">$Q$</tex></formula>-Band Correlation Polarimeter Clusters

This paper presents a Q-band orthomode transducer (OMT) that has been designed according to the mechanical constraints of the platelet (multi-layer) manufacturing strategy. It is composed of a twofold symmetric coupling section with two electrically identical recombination networks. The two OMT outputs lay on the same plane to provide a suitable interface to the correlation unit. The two channels are equalized in both magnitude and phase according to the correlation polarimeter requirements. They also exhibit a very low cross-coupling (-50 dB) and good reflection levels (-28 dB) in the 21% bandwidth.

Rating Curve Development at Ungauged River Sites using Variable Parameter Muskingum Discharge Routing Method

A physically based simplified discharge routing method, namely, the variable parameter Muskingum discharge-hydrograph (VPMD) routing method, having the capability of estimating the stage hydrographs simultaneously in channels with floodplains is presented herein. The upstream discharge hydrograph is routed using this VPMD method in different two-stage symmetrical trapezoidal compound cross section channel reaches. The performance of the VPMD method is evaluated by numerical experiments using the benchmark MIKE11 hydrodynamic model and the field data of the Tiber River in central Italy. The proposed method is capable of accurately routing the discharge hydrographs, corresponding stage hydrographs and synthesizing the normal rating curves at any downstream ungauged river site which is not affected by any downstream effects. This study can be helpful for various planning and management of river water resources in both the diagnostic and prognostic modes.

Nanoscale flexoelectric energy harvesting

One of the most tantalizing applications of piezoelectricity is to harvest energy from ambient mechanical vibrations for powering micro and nano devices. However, piezoelectricity is restricted only to certain materials and is severely compromised at high temperatures. In this article, we examine in detail, the possibility of using the phenomenon of flexoelectricity for energy harvesting. The flexoelectric effect is universally present in all dielectrics and exhibits a strong scaling with size. Using a simple beam-based paradigmatical design, we theoretically and computationally examine flexoelectric energy harvesting under harmonic mechanical excitation. We find that the output power density and conversion efficiency increase significantly when the beam thickness reduces from micro to nanoscale and flexoelectricity-based energy harvesting can be a viable alternative to piezoelectrics. Specifically, the conversion efficiency in flexoelectric transduction at sub-micron thickness levels is observed to increase by two orders of magnitude as the thickness is reduced by an order of magnitude. The flexoelectric energy harvester works even for a single layer beam with a symmetric cross section which is not possible in piezoelectric energy harvesting. Our results also pave the way for exploration of high temperature energy harvesting since unlike piezoelectricity, flexoelectricity persists well beyond the Curie temperatures of the high electromechanical coupling ferroelectrics that are often used.

Ultrafast laser fabrication of Bragg waveguides in chalcogenide glass.

Bragg waveguides are fundamental components in photonic integrated circuits and are particularly interesting for mid-IR applications in high index, highly nonlinear materials. In this work, we present Bragg waveguides fabricated in bulk chalcogenide glass using an ultrafast laser. Waveguides with near circularly symmetric cross sections and low propagation loss are obtained through spatial and temporal beam shaping. Using a single-pass technique, the waveguide and Bragg structure are formed at the same time. First through sixth order gratings with strengths of up to 25dB are realized, and performance is evaluated based on the modulation duty cycle of the writing beam.

Heat transfer enhancement in a PV cell using Boehmite nanofluid

Experiments were conducted to investigate the cooling performance of channels by water-based nanofluids containing small concentrations of Boehmite (AlOOH⋅xH2O) for the PV cell. The channels were fabricated in two different configurations as straight and helical. The straight channel consists of 23 parallel rectangular channels with a hydraulic diameter of 4.1mm, a length of 24.5cm, a width of 5mm and a depth of 3.5mm. For the helical configuration the plate was divided into four symmetrical sections which, each part contains a helical channel with a width of 5mm, a depth of 3.5mm and a hydraulic diameter of 4.1mm. The nanofluid cooling performance was assessed from the results obtained for the average temperature and electrical output of the PV cell. Results showed that the nanofluid perform better than water and caused higher decrease in the average PV cell temperature. They were about 39.70% and 53.76% for 0.1wt.% (the best case) at flow rate of 80ml/min for the helical and straight channel, respectively. Moreover, the highest decrease of average temperature relative to the reference temperature was observed for 0.1wt.% nanofluid concentration in both channels. This led to the highest electrical efficiency about 20.57% and 37.67% for the straight and helical channel, respectively. Furthermore, power-hydraulics performance was defined to compare the performance of the studied channels. The results showed that the helical channel works in more efficient way compared with the straight one.

Nonlinear optical localization in embedded chalcogenide waveguide arrays

We report the nonlinear optical localization in an embedded waveguide array fabricated in chalcogenide glass. The array, which consists of seven waveguides with circularly symmetric cross sections, is realized by ultrafast laser writing. Light propagation in the chalcogenide waveguide array is studied with near infrared laser pulses centered at 1040 nm. The peak intensity required for nonlinear localization for the 1-cm long waveguide array was 35.1 GW/cm2, using 10-nJ pulses with 300-fs pulse width, which is 70 times lower than that reported in fused silica waveguide arrays and with over 7 times shorter interaction distance. Results reported in this paper demonstrated that ultrafast laser writing is a viable tool to produce 3D all-optical switching waveguide circuits in chalcogenide glass.

외경 36mm 강관의 관대관 마찰용접 특성과 공정 변수 최적화

{( y j : 2013 2 08  14 j ,  j : 2014 2 02  13 j , $2(E.C : 2014 2 03  04 j ){Abstract: Friction welding is a very useful joining process to weld metals which have axially symmetric cross section. In this paper, for the friction welding with tube-to-tube shape, the feasibility of industry application was determined using analyzing mechanical properties of weld and optimized welding variables was suggested. In order to accomplish this object, rotating speed, friction heating pressure, and friction heating time were selected as the major process variables and the experiment was performed in three levels of each parameter. Weld characteristic was investigated in terms of weld shape and metal loss, and 7mm of metal loss was regarded as the optimal metal loss. By tensile test, tensile strength and yielding strength was measured and fracture was occurred at base metal. In order to optimize the welding condition, fitness function was defined with respect to metal loss and yielding strength and the fitness values for each welding condition could be calculated in experimental range. Consequently, we set the optimal welding condition as the point which had maximum value of fitness function. As the result of this paper the optimal welding variables could be suggested as rotating speed was 1300 rpm, friction heating pressure was 15 MPa, and friction heating time was 10 sec. Key Words ™ Friction Welding, Metal Loss, Mechanical Property, Fitness Function, Process Variable Optimization

Maximum wave power absorption by slender bodies of arbitrary cross sections in oblique seas

Published results for the maximum wave power absorption by slender bodies subjected to vertical deformations are extended. To this end, a more general form of the Kochin function is derived for floating or submerged slender bodies of arbitrary (asymmetric) cross sections undergoing vertical or horizontal deformations. The Kochin function allows a determination of the theoretical maximum wave power absorption in oblique seas. It is shown that in beam seas, two-dimensional limits can be recovered when the slender body length tends to infinity. This establishes a formal continuity in behavior from attenuators (head seas) to terminators (beam seas). The wavelike vertical and horizontal deformations of a flexible body, as well as the hinge motions of an articulated raft are also considered in oblique seas. In the former case, results suggest an equivalence between the maximum absorption width of bodies with symmetric cross sections and two degrees of freedom, and that of bodies with optimal cross sections and one degree of freedom. Overall, the potential for significant wave power absorption from horizontal motions is also demonstrated.

Marginally trapped surfaces in spaces of oriented geodesics

We investigate the geometric properties of marginally trapped surfaces (surfaces which have null mean curvature vector) in the spaces of oriented geodesics of Euclidean 3-space and hyperbolic 3-space, endowed with their canonical neutral Kaehler structures. We prove that every rank one surface in these four manifolds is marginally trapped. In the Euclidean case we show that Lagrangian rotationally symmetric sections are marginally trapped and construct an explicit family of marginally trapped Lagrangian tori. In the hyperbolic case we explore the relationship between marginally trapped and Weingarten surfaces, and construct examples of marginally trapped surfaces with various properties.

A Novel Chitosan-γPGA Polyelectrolyte Complex Hydrogel Promotes Early New Bone Formation in the Alveolar Socket Following Tooth Extraction

A novel chitosan-γPGA polyelectrolyte complex hydrogel (C-PGA) has been developed and proven to be an effective dressing for wound healing. The purpose of this study was to evaluate if C-PGA could promote new bone formation in the alveolar socket following tooth extraction. An animal model was proposed using radiography and histomorphology simultaneously to analyze the symmetrical sections of Wistar rats. The upper incisors of Wistar rats were extracted and the extraction sockets were randomly treated with gelatin sponge, neat chitosan, C-PGA, or received no treatment. The extraction sockets of selected rats from each group were evaluated at 1, 2, 4, or 6 wk post-extraction. The results of radiography and histopathology indicated that the extraction sockets treated with C-PGA exhibited lamellar bone formation (6.5%) as early as 2 wk after the extraction was performed. Moreover, the degree of new bone formation was significantly higher (P < 0.05) in the extraction sockets treated with C-PGA at 6 wk post-extraction than that in the other study groups. In this study, we demonstrated that the proposed animal model involving symmetrical sections and simultaneous radiography and histomorphology evaluation is feasible. We also conclude that the novel C-PGA has great potential for new bone formation in the alveolar socket following tooth extraction.

Nonlinear analytical modeling and characteristic analysis of symmetrical wire beam based composite compliant parallel modules for planar motion

This paper mainly deals with the nonlinear analytical modeling and characteristic analysis of two types of composite multi-beam modules for planar motion to enable rapid analysis and design synthesis. Each type of composite multi-beam module consists of identical, uniform and parallel wire beams, distributing uniformly along circle(s), with symmetrical cross sections. Analytical models of basic multi-beam modules with all beams uniformly spaced around a circle are firstly revisited. Analytical and nonlinear load–displacement equations are derived for the composite multi-beam modules, each of which is composed of two basic multi-beam modules with the same type connected either serially or parallelly. Finite element analysis (FEA) is carried out to compare and verify the analytical models. Detailed characteristic analysis and comparisons are conducted to compare three types of compliant six-beam modules whose twisting rotations are well constrained. These analytical results are capable of capturing some key quantitative nonlinear characteristics, such as kinematic effects, load-stiffening effect and nonlinear twisting stiffness (torsional stiffness), and can promote the design and analytical modeling of compliant parallel manipulators composed of the compliant multi-beam modules. In addition, the nonlinear analytical models of other variations of parallel double multi-beam modules are derived.

Calculations of in-cylinder flow of a controlled auto-ignition (CAI) engine

After validation of the numerical model against published laser doppler anemometry (LDA) experimental data (Pitcher et al., 2003), numerical calculations have been carried out to investigate the in-cylinder transient flow structure of a controlled auto-ignition (CAI) engine running at speeds of 1,500 rpm and 2,000 rpm. The geometry configuration of the engine is imported into the computational fluid dynamics (CFD) code used in this study. The simulations take into account the movement of the inlet, exhaust valves and the piston. To simulate an engine in controlled auto-ignition (CAI) mode, the same valve timing that allows 36% gas residuals was applied to the model. The evolution of the flow pattern inside the cylinder at the symmetrical cross section is described. Also, the turbulence intensity (TI), the turbulent kinetic energy (TKE) and turbulent dissipation rate (TDR) are described for a better understanding of the effect of engine speed on the turbulences generated. The effects of engine speed on fresh charge velocity are also revealed.

Bars under nonuniform torsion – Application to steel bars, assessment of EC3 guidelines

In this paper an “extended” nonuniform torsion theory of bars taking into account the secondary torsional moment deformation effect (STMDE) is formulated without adhering to assumptions employed in Thin Tube Theory (TTT). This theory is extensively applied to bars of arbitrarily shaped doubly symmetric steel cross section, subjected to arbitrarily distributed or concentrated torsional loading and to the most general torsional boundary conditions. In order to satisfy local equilibrium considerations to this “extended” theory, a torsional shear correction factor (determined through an energy approach) is required at the global level to correct the secondary torsion constant along with a suitable warping shear stress distribution at the local level. Three boundary value problems with respect to (i) the primary warping function, (ii) the secondary warping function and (iii) the total angle of twist coupled with its primary part per unit length are formulated and numerically solved employing the Boundary Element Method (BEM). The torsional geometrical parameters of a large number of either open- or closed-shaped steel sections are determined, verifying wherever possible the accuracy of the employed method and quantifying the errors induced by the TTT. Moreover, for bars of the aforementioned cross sections of various lengths, the influence of the STMDE is systematically quantified, while the accuracy of the results is verified by FEM solutions employing solid or shell elements. The limitations of TTT in computing stress components of closed-shaped section bars are also discussed, while the EC3 – part 1.1 guideline that permits as a simplification the ignorance of torsional warping effects in closed hollow section bars is assessed. Finally, the necessity of employing a torsional shear correction factor to the problem at hand is demonstrated.

Residual Stresses in Continuously Reinforced Composite Profiles with Symmetric Cross Sections

Composite profiles composed of aluminum base material and steel reinforcing elements manufactured by bar extrusion exhibit residual stresses. These stresses occur due to the different thermal shrinkage of the materials during cooling of the profile. In this paper, the residual stresses are investigated by means of analytical and numerical analyses. The influence of the reinforcing volume and the material behavior, i.e. the plastification of the base material, is discussed. Furthermore, the residual stresses in symmetric profile cross sections with multiple reinforcings are examined and compared to the stresses in a simple composite rod with a centric reinforcing.

Computational Analysis of Propulsion Performance of Modified Pitching Motion Airfoils in Laminar Flow

The thrust generation performance of airfoils with modified pitching motion was investigated by computational fluid dynamics (CFD) modeling two-dimensional laminar flow at Reynolds number of 104. The effect of shift distance of the pitch axis outside the chord line(R), reduced frequency(k), pitching amplitude(θ), pitching profile, and airfoil shape (airfoil thickness and camber) on the thrust generated and efficiency were studied. The results reveal that the increase inRandkleads to an enhancement in thrust generation and a decrease in propulsive efficiency. Besides, there exists an optimal range ofθfor the maximum thrust and the increasingθinduces a rapid decrease in propulsive efficiency. Six adjustable parameters(K)were employed to realize various nonsinusoidal pitching profiles. An increase inKresults in more thrust generated at the cost of decreased propulsive efficiency. The investigation of the airfoil shape effect reveals that there exists an optimal range of airfoil thickness for the best propulsion performance and that the vortex structure is strongly influenced by the airfoil thickness, while varying the camber or camber location of airfoil sections offers no benefit in thrust generation over symmetric airfoil sections.

A Novel Dual-Band Printed Monopole Antenna Based on Planar Inverted-Cone Antenna (PICA)

In this letter, a dual-band antenna based on planar inverted-cone antenna is proposed. Three pairs of slits are etched in the symmetrical circular arc sections of the inverted-cone-shaped structure to achieve the purpose of size reduction and dual-band performance. The frequency ratio and impedance matching can be adjusted flexibly by changing the parameters of the slits. The proposed antenna covers two relative impedance bandwidths of 26.5% and 12.3% with corresponding frequency bands 0.95-1.24 and 2.14-2.42 GHz, respectively.

Multiroller straightening analytical model of H-beam

H-beams are currently the largest output section steel in the world. Straightening is an important finishing step in the manufacturing process and directly determines the ultimate straightness of the beams. To analyse the straightening process, a multiroller straightening analytical model of an H-beam was established and is based on the pure bending springback equation of the symmetrical section curved beam. The purpose of the establishment of the model is to calculate the exit residual deflection by inputting the reduction rules and ultimately get the best reduction rules. In the model, the concept of plastic region ratio is proposed. The larger are the plastic region ratios, the easier are the initial curvatures unified, and the fewer straightening roller systems are required, however the greater is the residual stresses. Another innovation of this paper is the definition of a cosine function to express the relationship between reduction and curvature. The function of curvature, which plays an important role in the analytical model, was developed by a large number of finite element simulation and numerical fittings. The principle of the multiroller straightening process is clearly reflected by the analytical model in the theoretical analysis. By contrast, the theoretical calculation results of the analytical model are consistent with the finite element simulation results and the field data. It is suggested that the multiroller straightening analytical model of an H-beam is a theoretical foundation to optimise the straightener parameters and the reduction rules with higher accuracy.