Directional Motion of Droplets in a Conical Tube or on a Conical Fibre

Manipulating the directional movement of liquid droplets is of significance for design and fabrication of some microfluidic devices, An energy-based method is adopted to analyse the directional movement of a droplet deposited in a conical tube or on a conical fibre. We perform an experiment to investigate the directional motion of a droplet in an open conical tube. Our theoretical analysis and experimental observations both demonstrate that surface tension can drive the droplet to move in the conical tube. The critical condition of the liquid moving in the conical tube is presented. We also analyse a droplet on a conical hydrophilic fibre, which can move from the thinner to the thicker end.     

The rotation of the polarization in low birefringence monomode optical fibres due to geometric effects

Monomode optical fibres of very low intrinsic linear and circular birefringence have been developed for use in polarimetric optical fibre sensors, most notably the fibre optic current sensor. The polarization of light travelling along such fibres is known to be modified by external stress applied to the fibre. In this paper it is shown that the polarization state may also be rotated if the path of the fibre is bent in a nonplanar curve. A theory is developed which enables the effect to be quantified and the results are shown to agree with some measurements on a fibre bent into a helix.     

Optical fibre packaging in loose fitting tubes of orientated polymer

A technique is described by which an optical fibre may be packaged in a loose fitting tube of oriented polypropylene. This structure offers substantial improvements in resistance to microbending. The linear expansion coefficient of the material is very small and can be varied about zero, allowing matching to the fibre so that temperature variations do not cause fibre buckling.     

Spectrum control and shaping of optical pulses in optical fibre interferometers

This paper discusses the use of single-mode fibre ring interferometers for injection laser line narrowing and for enhancement of optical emission power. The efficient launching into fibre ring interferometers of multi-frequency external cavity injection laser emission, in both the c.w. and mode-locking regime, has been achieved. Matching the optical lengths of the external cavity and fibre interferometer allowed the measurement of mode width of such a laser. A method is proposed for shaping optical pulses in fibre ring interferometers from constant intensity frequency modulated emission. The mode-locking regime of all-fibre external cavity injection lasers has been achieved.     

Optical fibre modulator based on electrostatic attraction

A fibre-based electrostatic deflector is described that enables modulating the optical signal in fibre systems. A 2.5-cm long fibre length was gold coated and deflected through the application of voltage between the fibre and an external electrode. Static measurements showed that the device is suitable for e-field sensing, and 100% power modulation was obtained for resonant frequencies 1 kHz. A peak voltage as low as 2 V gave a 15% modulation depth with 65 μm diameter fibre, and the maximum frequency measured for a 65 μm fibre was 40 kHz. In a proof-of-principle experiment, a 1.61-μm wavelength Er³⁺/Yb³⁺ fibre laser was Q-switched by placing the electrostatic fibre modulator inside the cavity, generating pulses of 4-μs duration.     

Evanescent field devices: a comparison between tapered optical fibres and polished or D-fibres

Abstact This paper examines the operation of tapered optical fibres and polished or D-fibres as evanescent field devices. Both devices operate through the evanescent field outside the fibre interacting with chemicals in the surrounding external medium. The incoming field is absorbed and may be reradiated through fluorescence. The absorption and fluorescence recapture characteristics of both configurations are compared, showing that the tapered fibre device permits a stronger interaction and is therefore more efficient. Furthermore, it is shown that the characteristics of both configurations are sensitive to the refractive index of the external medium.     

Discontinuous tangential stress in double wall carbon nanotubes

We have examined the stability of double wall carbon nanotubes under hydrostatic pressures up to 10 GPa. The tangential optical phonon mode observed by inelastic light scattering is sensitive to the in-plane stress and splits into a contribution associated with the external and internal tube. While the pressure coefficient from the external tube is the same as in single wall carbon nanotubes, the pressure coefficient from the internal tube is found to be 45% smaller. The phonon band from the external tube broadens considerably with applied pressure in contrast with the phonon band of the internal tube which stays constant. These pressure dependent phonon shifts of the external and internal tubes and the contrasting phonon line broadening are explained by the elastic continuum shell model which takes into account both the continuous radial and discontinuous tangential stress components.     

Investigation of sample size effects in impedance tube measurements

A series of careful impedance tube measurements using different sizes of glass fibre and felt samples have demonstrated that frame resonance effects result from slightly oversize samples. The appropriate size of a sample is investigated while also avoiding air leakage. Diameters of 0.5 or 1.0 mm less than the inner diameter of the tube are found to avoid these effects.     

水平管降膜蒸发器传热优化研究

基于分布参数方法,对大型制冷系统中的水平管外降膜蒸发进行了传热优化数值模拟计算.在计算中,分析了饱和的液态制冷剂R134a在水平的铜管束外流动蒸发的换热特性.模型考虑了不同的管子类型和2流程不同管程布置对蒸发器换热特性的影响,结果表明,蒸发器采用Turbo-EHP管的性能高于其它管;不同管程布置对蒸发器性能的影响比较大,其中,下进上出管程布置的换热性能优于其它管程布置.同时,本文考虑了传热管外"干斑"对换热的影响.本文结论对于大型制冷系统中的降膜蒸发器传热优化设计具有指导性意义.     

Power penalty in multitone radio-over-fibre system employing direct and external modulation with optical amplifiers

This paper presents a multitone RoF system employing a central station and a remote antenna station to transmit modulated microwave or mm-wave signals. Two configurations of the system employing direct and external modulation are presented. First, at the central station, the modulating signal is directly and externally modulated at 1549.5 and 1550.5 nm, respectively, and the combined signal is then transmitted using wireless mode. In the second configuration, the combined signal is transmitted over 20 km to the remote antenna station using optical fibre connectivity. At the remote antenna station, both channel wavelengths are separated and amplified with an EDFA and SOA and are detected. The demonstration results show that there exists a small power penalty between the direct and the external modulation. But a large power penalty is reported depending upon the choice of optical amplifier viz. EDFA or SOA. Better performance is recorded in later case. The results also show that power is being distributed among the operating frequency and sidebands adjacent to it after transmission over a fibre link.     

A laser diode with feedback using a fibre delay line as a stable-frequency signal generator and potential fibre sensor

An optical fibre communication line (OFCL) closed-circuited into a ring network is considered as a controlled automodulated oscillation source. Theoretical and experimental investigations of the amplitude and frequency of automodulation for stationary self-consistent automodulation and external synchronization regimes in such a system are given on the basis of a balance equations analysis. It is shown that this OFCL ring can be used as an optical fibre tester and sensor.     

Identification of adequate vehicles to carry nerve regeneration inducers using tubulisation

ABSTRACT: BACKGROUND: Axonal regeneration depends on many factors, such as the type of injury and repair, age, distance from the cell body and distance of the denervated muscle, loss of surrounding tissue and the type of injured nerve. Experimental models use tubulisation with a silicone tube to research regenerative factors and substances to induce regeneration. Agarose, collagen and DMEM (Dulbecco's modified Eagle's medium) can be used as vehicles. In this study, we compared the ability of these vehicles to induce rat sciatic nerve regeneration with the intent of finding the least active or inert substance. The experiment used 47 female Wistar rats, which were divided into four experimental groups (agarose 4%, agarose 0.4%, collagen, DMEM) and one normal control group. The right sciatic nerve was exposed, and an incision was made that created a 10 mm gap between the distal and proximal stumps. A silicone tube was grafted onto each stump, and the tubes were filled with the respective media. After 70 days, the sciatic nerve was removed. We evaluated the formation of a regeneration cable, nerve fibre growth, and the functional viability of the regenerated fibres. RESULTS: Comparison among the three vehicles showed that 0.4% agarose gels had almost no effect on provoking the regeneration of peripheral nerves and that 4% agarose gels completely prevented fibre growth. The others substances were associated with profuse nerve fibre growth. CONCLUSIONS: In the appropriate concentration, agarose gel may be an important vehicle for testing factors that induce regeneration without interfering with nerve growth.     

On the feasibility of optical fibre sensors for strain monitoring in thermoplastic composites under fatigue loading conditions

This study investigates the possibility of using optical fibres with Bragg gratings for measurements in thermoplastic composites under fatigue loading conditions. Two setups are considered: (i) the fibre is embedded in the composite and (ii) the grating is bonded externally. Detailed information is given on the principle of optical fibre measurements and the data acquisition for both setups. To verify the strain derived from the optical fibre, the strain is compared with extensometer measurements. A special design of the blades of the extensometer is presented, since the standard blades suffer from a loss of grip on the surface of the specimen. The material used for this study was a carbon fibre-reinforced polyphenylene sulphide.It can be concluded for both setups that the optical fibre survives over half a million loading cycles, without de-bonding of the fibre. The advantage of the external fibre over the embedded one is that it can be mounted after manufacturing of the plate, but it has a higher risk of being damaged during working conditions of the component.     

Stationary structure of a high-frequency discharge maintained by a distributed electromagnetic source in the presence of an external magnetic field

The stationary structure of an axisymmetric high-frequency discharge maintained by a given source in an external dc magnetic field is investigated. The source is assumed to be a current wave that travels over the discharge tube surface in the direction of the external magnetic field. The source current has a single azimuthal component and its frequency belongs to the lower hybrid range. The main emphasis is placed on the special case where the electron heat conduction length across the external magnetic field exceeds considerably the tube radius. The dependences of discharge plasma parameters on the current amplitude and propagation constant along the tube have been found for this case. The results of numerical calculations of the distributions of the field and the power of the Joule loss in a discharge are presented.     

Orientation-dependent electromagnetic properties of basalt fibre/nickel core--shell heterostructures

The influence of orientation on electromagnetic properties of basalt fibre/nickel core--shell heterostructures prepared by a simple electroless plating method is investigated. For comparison, the same investigation is also performed on naked basalt fibres. For electromagnetic measurement, the directions of basalt fibre/nickel and naked basalt fibres are parallel, random and perpendicular to the direction of external electric field, termed E_\vert\vert sample, random sample and E_⊥ sample, respectively. Electromagnetic anisotropy can be clearly observed in the basalt fibre/nickel core--shell heterostructures, while electromagnetic properties of naked basalt fibres are unrelated to the orientation. The E_⊥ basalt fibre/nickel shows the highest dielectric loss but the lowest magnetic loss, and E_|| basalt fibre/nickel exhibits the highest magnetic loss but the lowest dielectric loss. The dielectric loss of E_⊥ basalt fibre/nickel is several times as large as that of E_|| basalt fibre/nickel, which could be attributed to the increase of polarization relaxation time as a consequence of the nanosize-confinement effect. The magnetic loss of E_|| basalt fibre/nickel is even one order of magnitude higher than that of E_⊥ basalt fibre/nickel, which originates mainly from the natural magnetic resonance of basalt fibre/nickel core--shell heterostructures.     

Acoustic radiation from a fluid-filled, subsurface vascular tube with internal turbulent flow due to a constriction

The vibration of a thin-walled cylindrical, compliant viscoelastic tube with internal turbulent flow due to an axisymmetric constriction is studied theoretically and experimentally. Vibration of the tube is considered with internal fluid coupling only, and with coupling to internal-flowing fluid and external stagnant fluid or external tissue-like viscoelastic material. The theoretical analysis includes the adaptation of a model for turbulence in the internal fluid and its vibratory excitation of and interaction with the tube wall and surrounding viscoelastic medium. Analytical predictions are compared with experimental measurements conducted on a flow model system using laser Doppler vibrometry to measure tube vibration and the vibration of the surrounding viscoelastic medium. Fluid pressure within the tube was measured with miniature hydrophones. Discrepancies between theory and experiment, as well as the coupled nature of the fluid-structure interaction, are described. This study is relevant to and may lead to further insight into the patency and mechanisms of vascular failure, as well as diagnostic techniques utilizing noninvasive acoustic measurements.     

Polarization dependent loss of arc-induced long-period fibre gratings

We have investigated the polarization properties of long-period fibre gratings fabricated using the electric arc technique. It was found that the choice of the fabrication parameters (electric current, arc duration and pulling tension) affects the polarization dependent loss of the produced gratings. In particular, a non-monotonic dependence on the external pulling tension was obtained.     

A simple empirical model of polyester fibre materials for acoustical applications

A new empirical model has been developed by the authors to predict the flow resistivity, acoustic impedance and sound absorption coefficient of polyester fibre materials. The parameters of the model have been adjusted to best fit the values of airflow resistivity and sound absorption coefficient measured over a set of 38 samples. Calculated results are compared with normal incidence measurements carried out using two different techniques: the transfer-function method in an impedance tube (ISO 10534-2) and the free-field impulse response method (ISO 13472-1). Measurements performed on polyester fibre materials with different density and thickness values, and diameter ranging from 18 to 48 μm, are in good agreement with the predictions of the new model. It is concluded that the new model can predict the basic acoustic properties of common polyester fibre materials with any practical combination of thickness and density².     

Estimation of hydro-fracture parameters by analysis of tube waves at vertical seismic profiling

The problem on tube wave excitation in a well intersected by a finite-size fluid-filled crack under action of external seismic wave is considered. This situation appears at vertical seismic profiling (VSP) in the presence of hydro-fracture intersecting the borehole. A heterogeneous integral-differential equation for the fluid pressure field in fracture is derived in the long-wave approximation by the fracture opening. Stitching of the solution for pressure in fracture with that for tube waves in a well allows to calculate the amplitude and shape of generated tube waves. Numerical computations that under action of the external seismic field the crack edges excite a strongly dispersive mode of a thin fluid layer which can be used for estimation of linear fracture size on the basis of VSP technique.     

Investigation of practical high repetition rate copper vapour lasers with external heating

The characteristics of high repetition rate CVL devices incorporating passive external heating have been investigated. Pre-heating of the CVL plasma tube using external heating has been shown to significantly reduce CVL warm-up time, while supplementary heating of the CVL plasma tube using external heating allows efficient CVL operation with reduced discharge power input without any degradation in output power.