Abnormal phenomenon of ac Stark splitting in magneto-optical traps

We experimentally study the ac Stark splitting in D2 line of cold Rb-87 atoms. The frequency span between the Autler-Townes doublets is obviously larger than that derived from theoretical calculation. Two physical effects, which increase the effective Rabi frequency, contribute to the splitting broadening. First, atoms tend to distribute in strong lield places of a inhomogeneous red-detuned light field. Second, atoms reabsorb scattered light when they are huge in number and high in density.

Abnormal phenomenon of the dependence of the retention factors for uncharged species on applied voltage in capillary electrochromatography

Polymethacrylate-based monolithic columns were prepared for capillary electrochromatography (CEC) by in situ copolymerization of butyl methacrylate (BMA), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and ethylene dimethacrylate (EDMA) in the presence of a porogen in fused-silica capillaries of 100 mum I.D. The abnormal phenomenon that retention factors for neutral species decreases with applied voltage in CEC was observed. Capillary electrophoresis (CE) instruments usually require a period of time to increase voltage from 0 kV to desired value, which is called as ramp time. Such ramp time and any error in the determination of dead time should be taken into account during the accurate calculation of retention factors. After the correction of the retention factors, the plots of the corrected factors for alkylbenzene versus applied voltage were made, the absolute value of the plot slopes are less than 1.8 X 10(-4), Which indicates that the corrected retention times for neutral species do not show any dependence on applied voltage. Further, the plots of the corrected retention times for acidic and basic compounds versus the reciprocal of applied voltage were drawn, where the target compounds were eluted in neutral form. The very nice linearity of the plots was obtained. The linear correlation coefficients are over 0.999. Here, the slopes of the plots represent

Redshift phenomenon of the excitation light of long life emission phosphor

We observed that the SrMg2(PO4)(2):Eu phosphor could emit long life phosphorescence with the excitation light whose wavelength was shorter than 420 nm, however, when La, Ce, or Gd was codoped, the wavelength of the excitation light to cause the phosphorescence had a redshift of 40 nm. A possible mechanism and related discussion for this redshift phenomenon of the excitation light was given. It was suggested that the threshold between the trap and valence band was decreased with the addition of the codopants.

The phenomenon of mutual media in polypyrrole with electroactive ions

The dependence of the differential capacitance of polypyrrole doped with several typical dopants on potential is presented, which shows that the differential capacitance varies with the potential, the doped polypyrroles with electroactive ions give the largest capacitance near their formal potentials, which is attributed to the mutual media for electron transfer between polypyrrole and electroactive dopants. The existence of two conducting phases was observed in the complex capacitance plots. The electroactive anions act as an intra-conducting-phase medium for electron transfer, the electroactive cations act as an inter-conducting-phase medium for electron transfer. The mutual media between polypyrrole and redox dopants lead to the increase of the discharging time.

SIMPLE-MODELS FOR STRESS-RELAXATION AND YIELD PHENOMENON OF PHENOLPHTHALEIN POLY(ETHER KETONE)

According to stress relaxation curves of phenolphthalein poly(ether ketone) (PEK-C) at different temperatures and the principle of time-temperature equivalence, the master curves of PEK-C at arbitrary reference temperatures are obtained. A coupling model (Kohlrausch-Williams-Watts) is applied to explain quantitatively the different temperature dependence of stress relaxation behavior and the relationship between stress relaxation and yield phenomenon is established through the coupling model.

Phenomenon of micro-droplets formation on metals during the deliquescence of salt particles in atmosphere

CORROSION; MECHANISM; WATER; ZINC

Experimental investigation of slow light phenomenon in photonic crystal waveguide line defect laser

The guide mode whose frequency locates in the band edge in photonic crystal single line defect waveguide has very low group velocity. So the confinement and gain of electromagnetic field in the band edge are strongly enhanced. Photonic crystal waveguide laser is fabricated and the slow light phenomenon is investigated. The laser is pumped by pulsed pumping light at 980nm whose duty ratio is 0.05%. The active layer in photonic crystal slab is InGaAsP multiple quantum well. Light is transimited by a photonic crystal chirp waveguide in one facet of the laser. Then the output light is coupled to a fiber and the character of laser is analysis by an optical spectrometer. It is found that single mode and multimode happens with different power of pumping light. Meanwhile the plane wave expansion and finite-difference time-domain methods are used to simulate the phenomenon of slow light. And the result of the experiment is compared with the theory which proves the slow light results in lasing oscillation.

Characteristics of Micronozzle Gas Flows

The fluid characteristics of gas flows in the micronozzle whose throat height is 20 μm were investigated by the direct simulation Monte Carlo (DSMC) method. In a series of cases, the dependence of mass flux on the pressure difference was gained, and the DSMC's results show good agreement with the experimental data. The comparison of mass flux and the Mach number contours between the DSMC and Navier-Stokes equations adding slip boundary also reveals quantitatively that the continuum model will be invalid gradually even when the average Knudsen number is smaller than 0.01. As one focus of the present paper, the phenomenon of the multiple expansion-compression waves that comes from the nozzle's divergent part was analyzed in detailed.

Mechanical effects of the self-organization of dislocations and related critical characteristics

The effects of the dislocation pattern formed due to the self-organization of the dislocations in crystals on the macroscopic hardening and dynamic internal friction (DIF) during deformation are studied. The classic dislocation models for the hardening and DIF corresponding to the homogeneous dislocation configuration are extended to the case for the non-homogeneous one. In addition, using the result of dislocation patterning deduced from the non-linear dlislocation dynamics model for single slip, the correlation between the dislocation pattern and hardening as well as DIF is obtained. It is shown that in the case of the tension with a constant strain rate, the bifurcation point of dislocation patterning corresponds to the turning point in the stress versus strain and DIF versus strain curves. This result along with the critical characteristics of the macroscopic behavior near the bifurcation point is microscopically and macroscopically in agreement with the experimental findings on mono-crystalline pure aluminum at temperatures around 0.5T(m). The present study suggests that measuring the DIF would be a sensitive and useful mechanical means in order to study the critical phenomenon of materials during deformation.

Control of Mean and Fluctuating Forces on a Circular Cylinder at High Reynolds Numbers

A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 x 10(4) to 1.0 x 10(5). The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points of view.

Fractography and Crack Initiation of Very-High-Cycle Fatigue for a High Carbon Low Alloy Steel

Very-High-Cycle Fatigue (VHCF) is the phenomenon of fatigue damage and failure of metallic materials or structures subjected to 108 cycles of fatigue loading and beyond. This paper attempts to investigate the VHCF behavior and mechanism of a high strength low alloy steel (main composition: C-1% and Cr-1.5%; quenched at 1108K and tempered at 453K). The fractography of fatigue failure was observed by optical microscopy and scanning electron microscopy. The observations reveal that, for the number of cycles to fatigue failure between 106 and 4108 cycles, fatigue cracks almost initiated in the interior of specimen and originated at non-metallic inclusions. An “optical dark area” (ODA) around initiation site is observed when fatigue initiation from interior. ODA size increases with the decrease of fatigue stress, and becomes more roundness. Fracture mechanics analysis gives the stress intensity factor of ODA, which is nearly equivalent to the corresponding fatigue threshold of the test material. The results indicate that the fatigue life of specimens with crack origin at the interior of specimen is longer than that with crack origin at specimen surface. The experimental results and the fatigue mechanism were further analyzed in terms of fracture mechanics and fracture physics, suggesting that the primary propagation of fatigue crack within the fish-eye local region is the main characteristics of VHCF.

Experimental Observation Of Electrical Instability Of Droplets On Dielectric Layer

Polydimethylsiloxane ( PDMS) has become the most widely used silicon-based organic polymer in bio-MEMS/NEMS devices. However, the inherent hydrophobic nature of PDMS hinders its wide applications in bio-MEMS/NEMS for efficient transport of liquids. Electrowetting is a useful tool to reduce the apparent contact angle of partially wetting conductive liquids and has been utilized widely in bio-MEMS/NEMS. Our experimental results show that the thin PDMS membranes exhibit good properties in electrowetting-on-dielectric. The electrical instability phenomenon of droplets was observed in our experiment. The sessile droplet lying on the PDMS membrane will lose its stability with the touch of the wire electrode to make the apparent contact angle change suddenly larger than 35 degrees. Contact mode can protect the dielectric layer from electrical breakdown effectively. Electrical breakdown process of dielectric layer was recorded by a high speed camera. It is found experimentally that a PDMS membrane of 4.8 mu m thick will not be destroyed due to the electric breakdown even at 800 V in the contact mode.

Control Of Vortex Shedding From A Square Cylinder

Small circular, square, and thin-strip cross-sectional elements are used to suppress vortex shedding from a square cylinder at Reynolds numbers in the range of 1.12 x 10(4)-1.02 x 10(5). The axes of the element and cylinder are parallel. The element's size, position, and angle of attack are varied. Measurements of the fluctuating surface pressures and wake velocities, together with smoke flow visualization, show that vortex shedding from both sides of the cylinder is suppressed and the mean drag and fluctuating lift on the cylinder is reduced if the element is installed in an effective zone downstream of the cylinder. The effective zone of the circular element is shown to be much smaller than those of the other elements. The effects of Reynolds number and blockage ratio are investigated. A phenomenon of monoside vortex shedding is observed. The role of the element's bluffness is investigated and the suppression mechanism is discussed.

Numerical Analyses of Transonic Fluid/Structure interaction in Aircraft Engineering

Through the coupling between aerodynamic and structural governing equations, a fully implicit multiblock aeroelastic solver was developed for transonic fluid/stricture interaction. The Navier-Stokes fluid equations are solved based on LU-SGS (lower-upper symmetric Gauss-Seidel) Time-marching subiteration scheme and HLLEW (Harten-Lax-van Leer-Einfeldt-Wada) spacing discretization scheme and the same subiteration formulation is applied directly to the structural equations of motion in generalized coordinates. Transfinite interpolation (TFI) is used for the grid deformation of blocks neighboring the flexible surfaces. The infinite plate spline (IPS) and the principal of virtual work are utilized for the data transformation between fluid and structure. The developed code was fort validated through the comparison of experimental and computational results for the AGARD 445.6 standard aeroelastic wing. In the subsonic and transonic range, the calculated flutter speeds and frequencies agree well with experimental data, however, in the supersonic range, the present calculation overpredicts the experimental flutter points similar to other computations. Then the flutter character of a complete aircraft configuration is analyzed through the calculation of the change of structural stiffness. Finally, the phenomenon of aileron buzz is simulated for the weakened model of a supersonic transport wing/body model at Mach numbers of 0.98 and l.05. The calculated unsteady flow shows, on the upper surface, the shock wave becomes stronger as the aileron deflects downward, and the flow behaves just contrary on the lower surface of the wing. Corresponding to general theoretical analysis, the flow instability referred to as aileron buzz is induced by a stronger shock alternately moving on the upper and lower surfaces of wing. For the rigid structural model, the flow is stable at all calculated Mach numbers as observed in experiment

Self-organized generation of transverse waves in diverging cylindrical detonations

Self-organized generation of transverse waves associated with the transverse wave instabilities at a diverging cylindrical detonation front was numerically studied by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. After solution validation, four mechanisms of the transverse wave generation were identified from numerical simulations, and referred to as the concave front focusing, the kinked front evolution, the wrinkled front evolution and the transverse wave merging, respectively. The propagation of the cylindrical detonation is maintained by the growth of the transverse waves that match the rate of increase in surface area of the detonation front to asymptotically approach a constant average number of transverse waves per unit length along the circumference of the detonation front. This cell bifurcation phenomenon of cellular detonations is discussed in detail to gain better understanding on detonation physics.