Numerical investigation of transient side-loads in the start-up process of a rocket nozzle

A numerical investigation of transient side-loads in axisymmetric over-expanded thrust optimized contour nozzles is presented. These nozzles experience side-loads during start-up and shut-down operations because of flow separation at the nozzle walls. Two types of flow separations, FSS and RSS shock structures, also occur. A two-dimension numerical simulation was carried out over axisymmetric TOC nozzles to validate the present results and investigate oscillatory flow characteristics for start-up processes. Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme. Governing equations are solved via the coupled implicit scheme. The Reynolds Stress turbulence model is selected for this work. It was found that the present computed pressure at the nozzle walls closely matched the experimental data. The phenomenon of hysteresis was also observed between these two shock structures. The transition from an FSS to RSS pattern during the start-up process showed maximum nozzle wall pressure and fluctuations in shear stress values. Oscillatory pressure was observed on the nozzle walls with high pressure ratio. The present results show that the magnitude of nozzle wall pressure variation is high for the phenomenon of oscillation.     

Corrosion behavior of NiTi alloy in fetal bovine serum

The corrosion behavior of NiTi alloy in fetal bovine serum (FBS) at 37 °C is investigated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS). The presence of FBS moves the OCP to the negative direction and makes the oxide film thinner and more porous than that in phosphate buffer saline (PBS, pH = 7.4). The impedance of the oxide film formed in FBS is smaller than that in PBS, but the total interface impedance is bigger in FBS because of the formation of a surface bio-film. Pits form on the NiTi alloy after immersion in FBS for 200 h but they are not observed on the sample immersed in PBS. XPS shows that the composition of the oxide film formed in FBS is similar to that formed in PBS and it is composed of mainly Ti oxides with a small amount of Ti hydroxide. Hydrated Ti is observed on the outermost surface of the NiTi alloy. The thickness of the oxide film on the NiTi alloy immersed in PBS is 17 ± 3.0 nm and that on the sample immersed in FBS is 10 ± 3.2 nm. The results are consistent with those obtained by EIS. The presence of FBS can accelerate leaching of Ni ions and the mechanism is investigated and discussed.     

Identification of the nonlinear excitation force acting on a bowed string using the dynamical responses at remote locations

For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick-slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt [32], a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions, are consistent as attested by the comparison of the two available versions of the string dynamical motion and of the friction force. Furthermore, the method seems adequate to investigate the interface force for the bowed string.     

固相萃取(SPE)和衍生化条件的对GUMS及LUMS/MS法检测莱克多巴胺灵敏度的影响

本实验探讨影响GUMS以及LC/MS/MS检测灵敏度的影响因素.对GUMS法的固相萃取(SPE)和衍生化条件进行优化,测试了SPE、加热时间、温度、溶液凡式归匕等因素.同时测试这些条件对LUMC/MC法的灵敏度.结果表明,碱基化为影响GUMS法灵敏度的主要因素,能提高灵敏度,对衍生化条件也有影响.通过对样本进行固相萃取,速日处理,GUMS法的灵敏度为0.5 ng/mL,LC/MC/MC法的为0.25 ng/mL.采用这种更灵敏的方法,尿液中莱克多巴胺的测试窗口期可由2d提高到6d.经过优化的GUMS法及LC/MS/MS方法灵敏度更高,适合猪尿中莱克多巴胺的检测.     

A sensitive method for the quantification of acrolein and other volatile carbonyls in ambient air

Acrolein, an unsaturated aldehyde found in both indoor and outdoor air, is considered one of the greatest noncancer health risks of all organic air pollutants. Current methods for determining acrolein often employ sorbent-filled cartridges containing a carbonyl derivatizing agent (e.g., dinitrophenylhydrazine). These methods are of limited use for unsaturated compounds due to the formation of unstable derivatives, coelution of similar compounds, long sample collection times, and ozone interferences that result in poor sensitivity, selectivity, and reproducibility. The goal of this research was to develop an analytical method for determining ppt concentrations of acrolein and other carbonyls in air with short sampling times (10 min). The method uses a mist chamber to collect carbonyls by forming water-soluble carbonyl-bisulfite adducts. The carbonyls are then liberated from the bisulfite, derivatized, and quantified by gas chromatography/electron capture negative ionization mass spectrometry. The method was applied to determine atmospheric acrolein concentrations at three sites in northern California reflecting hemispheric background concentrations, biogenic-dominated regions, and urban environments. The resulting acrolein concentrations were 0.056, 0.089, and 0.29 microg/m3, respectively, which are all above the EPA Reference Concentration of 0.02 microg/m3. The minimum detection limit of 0.012 microg/m3 is below that of other published methods. Methacrolein, methyl vinyl ketone, crotonaldehyde, glyoxal, methyl glyoxal, and benzaldehyde were also quantified.     

Mixed monolayer-protected gold nanoclusters as selective peptide extraction agents for MALDI-MS analysis

Cationic and anionic nanoparticles selectively target peptides with low and high isoelectric points, respectively. Additionally, their high surface area-to-volume ratios make these nanoparticles (approximately 2-nm core diameter) very efficient extraction and concentration agents. Upon extraction, the peptide-bound nanoparticles can be analyzed by MALDI-MS to provide highly sensitive detection of the targeted peptides. We demonstrate that MALDI-MS can detect peptide concentrations as low as 500 pM from 250-microL solutions using these nanoparticle scaffolds as extraction and concentration agents.     

Phase-stepped gauge block interferometry using a frequency-tunable visible laser diode

Frequency changes induced by bias or temperature modulation of injection diode lasers can provide an economical and effective method of applying phase-stepping interferometry to optical metrology. However, the intrinsic frequency instability of these devices limits their use in gauge block interferometry where precise and repeatable phase steps must be maintained simultaneously on two discontinuous surfaces and over relatively long path lengths. We demonstrate a method using a visible injection diode laser, the frequency of which is locked by using a Fabry-Perot interferometer. Small changes to the length of the Fabry-Perot interferometer shift the frequency of the laser producing proportional and repeatable phase steps to the gauge block interferogram. This method has been successfully implemented with a Fizeau-type gauge block interferometer with a phase measurement resolution of 0.005 lambda. The phase data are then processed to map the surface form of gauge blocks up to 100 mm in length and to objectively assess surface shape parameters.     

Effect of spurious diffraction orders in arbitrary multifoci patterns produced via phase-only holograms

We analyze the effect of spurious diffraction orders when generating functional multifoci patterns produced by illuminating a phase-only hologram with a single Gaussian beam. Using a practical device for encoding a hologram generates an undesirable zero order and high-diffraction orders at the Fourier plane. This translates to the fact that a significant fraction of the incident light does not necessarily convert to functional multifoci patterns. In most applications, the zero order can be avoided by generating foci patterns shifted off the optical axis, which further increases the amount of light distributed to spurious high-diffraction orders owing to the reduction of light directed to the desired foci pattern. We analyze the amount of light dispersed to spurious orders and show that these unwanted orders can be a major limiting factor for most applications based on arbitrary multifoci patterns.     

Organization and mobility of water in amorphous and crystalline trehalose

The disaccharide trehalose is accumulated by microorganisms, such as yeasts, and multicellular organisms, such as tardigrades, when conditions of extreme drought occur. In this way these organisms can withstand dehydration through the formation of an intracellular carbohydrate glass, which, with its high viscosity and hydrogen-bonding interactions, stabilizes and protects the integrity of complex biological structures and molecules. This property of trehalose can also be harnessed in the stabilization of liposomes, proteins and in the preservation of red blood cells, but the underlying mechanism of bioprotection is not yet fully understood. Here we use positron annihilation lifetime spectroscopy to probe the free volume of trehalose matrices; specifically, we develop a molecular picture of the organization and mobility of water in both amorphous and crystalline states. Whereas in amorphous matrices, water increases the average intermolecular hole size, in the crystalline dihydrate it is organized as a confined one-dimensional fluid in channels of fixed diameter that allow activated diffusion of water in and out of the crystallites. We present direct real-time evidence of water molecules unloading reversibly from these channels, thereby acting as both a sink and a source of water in low-moisture systems. We postulate that this behaviour may provide the overall stability required to keep organisms viable through dehydration conditions.     

Quantum dot encapsulation in viral capsids

Incorporation of CdSe/ZnS semiconductor quantum dots (QDs) into viral particles provides a new paradigm for the design of intracellular microscopic probes and vectors. Several strategies for the incorporation of QDs into viral capsids were explored; those functionalized with poly(ethylene glycol) (PEG) can be self-assembled into viral particles with minimal release of photoreaction products and enhanced stability against prolonged irradiation.