Repeated formation of fluid threads in breakup of a surfactant-covered jet

Breakup of thin threads is widely observed in nature and technology. As a surfactant-covered liquid jet approaches breakup, its profile consists of a periodic pattern of drops connected by thin threads. Near the locations where the threads join the drops, simulations show that a series of thinner threads arise as the jet breaks. That threads can continue to form repeatedly without addition of noise when surfactants are present is unexpected based on earlier studies of surfactant-free systems. Thinning dynamics of successive threads are shown to be self-similar and approach Eggers's universal solution for clean interfaces.     

Computational and experimental analysis of pinch-off and scaling

Pinch-off and scaling during drop formation are studied using high-accuracy computation and ultrafast, high-resolution imaging. The interface of a water drop (viscosity mu is approximately 1 cP) is shown to overturn prior to breakup for the first time in experiments, well before the dynamics transitions from the potential flow (PF) to the inertial-viscous (IV) regime. A drop of 83% glycerol-water solution (mu is approximately 85 cP) is shown to exhibit a transition from the PF to the IV regime both computationally and experimentally. The computed value of the minimum neck radius in the latter case follows Eggers's universal solution until it becomes unstable.     

Pellet freezing of in vitro produced bovine embryos using dry ice

In vitro produced bovine embryos were frozen by pellet freezing or vitrification method. In the pellet freezing method, the embryos were cooled on the dry ice and then frozen as pellets. At warming, the pellets were immersed directly into 0.5 M sucrose. The survival rates of blastocysts frozen by the pellet freezing method were higher (P<0.01) in 40% ethylene glycol (EG) than those in the lower concentrations (20 and 30% EG). Higher survival rates of blastocysts frozen by the pellet freezing method were obtained but the development rates did not differ, as compared with those by the vitrification method. There were no significant differences between the pellet freezing and vitrification method in the frequencies of post-thaw survival of hatched blastocysts. These results demonstrate that the pellet freezing method using dry ice can be used successfully for the cryopreservation of blastocysts.     

Nonlinear finite amplitude vibrations of sharp-edged beams in viscous fluids

In this paper, we study flexural vibrations of a cantilever beam with thin rectangular cross section submerged in a quiescent viscous fluid and undergoing oscillations whose amplitude is comparable with its width. The structure is modeled using Euler–Bernoulli beam theory and the distributed hydrodynamic loading is described by a single complex-valued hydrodynamic function which accounts for added mass and fluid damping experienced by the structure. We perform a parametric 2D computational fluid dynamics analysis of an oscillating rigid lamina, representative of a generic beam cross section, to understand the dependence of the hydrodynamic function on the governing flow parameters. We find that increasing the frequency and amplitude of the vibration elicits vortex shedding and convection phenomena which are, in turn, responsible for nonlinear hydrodynamic damping. We establish a manageable nonlinear correction to the classical hydrodynamic function developed for small amplitude vibration and we derive a computationally efficient reduced order modal model for the beam nonlinear oscillations. Numerical and theoretical results are validated by comparison with ad hoc designed experiments on tapered beams and multimodal vibrations and with data available in the literature. Findings from this work are expected to find applications in the design of slender structures of interest in marine applications, such as biomimetic propulsion systems and energy harvesting devices.     

Electronic and interface state density distribution properties of Ag/p-Si Schottky diode

Electronic and interface state distribution properties of Ag/p-Si Schottky diode have been investigated. The diode indicates non-ideal current-voltage behavior with an ideality factor greater than unity. The capacitance-voltage (C-V) characteristic is linear in reverse bias indicating rectification behavior and charge density within depletion layer is uniform. From I-V and C-V characteristics, junction parameters such as diode ideality factor and barrier height were found as 1.66 and ?_B(I-V) = 0.84 eV (?_B(C-V) = 0.90 eV), respectively. The interface state density N_ss and relaxation time τ of the Schottky diode were determined by means of Schottky capacitance spectroscopy method. The results show the presence of thin interfacial layer between the metal and semiconductor.     

Possible negative refraction in two dimensional ferromagnetic wire lattice

In this paper, we present theoretical and experimental results for the indication of negative refraction in ferromagnetic metallic wire lattice. We have studied microwave transmission through a two dimensional wire lattice made of ferromagnetic metallic wires under the applied static magnetic field. We have found that, the microwave transmission were significantly changed at ferromagnetic resonance frequency region. Thus the magnetic permeability can be tuned by external dc magnetic field. Since the dielectric permittivity of metallic wire lattice is negative and can take a value close to unity then the crystal exhibits negative index of refraction at microwave region under the external magnetic field.     

Numerical Simulation of Spot-Weld Joints under Crash Loading

This paper compares FE simulations of spot-weld joints for dual-phase steel under different load cases by using damage models of Gurson-Tvergaard-Needleman (GTN) and its two extensions, GTN-Johnson-Cook and GTN-Hutchinson. Spot-weld specimens have three zones depending with different material properties: Base material, heat-affected zone and fusion zone. The characterization of the base material is straightforward. The other two zones are characterized with specifically heat-treated specimens. For each zone, flat smooth tensile, flat notched tensile and Iosipescu-shear specimen are used in order to obtain the damage behavior for different triaxiality values. GTN damage model parameters are calibrated with the help of smooth and notched flat tensile specimens. The parameters of the above mentioned extensions of GTN damage model are identified with the help of Iosipescu-shear specimen. Finally, the calibrated material models are used in the FE simulation of the spot-weld specimens under quasi static-load case (10 mm/min) for loading directions of 0°, 30°, 60°, 90°. The numerical force-displacement results are in good agreement with experimental results. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dripping of a liquid from a tube in the absence of gravity

In zero gravity, liquid does not drip from a tube but hangs from it for all time as a pendant drop. It is shown that a drop can be made to fall off a tube by heating the contact line (CL), which causes a temperature gradient between the drop's CL and its tip. Simulations show that whether a drop detaches from or remains attached to the tube is set by the competition between the Marangoni stress that causes flow away from its CL, where the surface tension is low, toward its tip, where is high, and the capillary pressure that causes flow from the tip back toward the CL. The method can be used to make microscopic (nanoscopic) drops by dripping in ordinary gravity, which had heretofore been unattainable.