Heat transfer from a circular cylinder rotating about an orthogonal axis in quiescent air

Direct measurements of local heat flux and temperature from rotating cylinders have been carried out using Gardon type foil heat flux sensors and a power supply cum instrumentation slip ring set up. The local and average heat transfer results are presented covering a rotational Reynolds number range of 2 × 10⁴ to 6.2 x 10⁴ corresponding to the speeds varying from 400 to 1,400 rpm. A correlation has been derived for peripherally averaged values of Nusselt numbers: . The values of surface average Nusselt number for the cylinder under the present rotating conditions are found to be higher than for a stationary cylinder in crossflow and for a cylinder rotating about its own axis, in the range of present experiments.Research scholar on leave from Faculty of Engineering, Port Said, Egypt     

Off-axis field approximations for ion traps with apertures

In recent work (Int. J. Mass Spec., vol. 282, pp. 112–122) we have considered the effect of apertures on the fields inside rf traps at points on the trap axis. We now complement and complete that work by considering off-axis fields in axially symmetric (referred to as “3D”) and in two dimensional (“2D”) ion traps whose electrodes have apertures, i.e., holes in 3D and slits in 2D. Our approximation has two parts. The first, E_noAperture, is the field obtained numerically for the trap under study with apertures artificially closed. We have used the boundary element method (BEM) for obtaining this field. The second part, E_{dueToAperture}, is an analytical expression for the field contribution of the aperture.In E_{dueToAperture}, aperture size is a free parameter. A key element in our approximation is the electrostatic field near an infinite thin plate with an aperture, and with different constant-valued far field intensities on either side. Compact expressions for this field can be found using separation of variables, wherein the choice of coordinate system is crucial. This field is, in turn, used four times within our trap-specific approximation.The off-axis field expressions for the 3D geometries were tested on the quadrupole ion trap (QIT) and the cylindrical ion trap (CIT), and the corresponding expressions for the 2D geometries were tested on the linear ion trap (LIT) and the rectilinear ion trap (RIT). For each geometry, we have considered apertures which are 10%, 30%, and 50% of the trap dimension. We have found that our analytical correction term E_{dueToAperture}, though based on a classical small-aperture approximation, gives good results even for relatively large apertures.     

Do-it-yourself microelectrophoresis chips with integrated sample recovery

We present a microelectrophoresis chip that is simple to fabricate using the microfluidic tectonics (microFT) platform (Beebe, D. J. et al., Proc. Natl. Acad. Sci. USA 2000, 97, 13488-13493; Agarwal, A. K. et al.,. J. Micromech. Microeng. 2006, 16, 332-340). The device contains a removable capillary insert (RCI) for easy sample collection after separation (Atencia, J. et al.,. Lab Chip 2006, DOI: 10. 1039/b514068d). Device construction is accomplished in less than 20 min without specialized equipment traditionally associated with microelectrophoresis chip construction. microFT was used to build a PAGE device utilizing two orthogonal microchannels. One channel performs standard separations, while the second channel serves as an access point to remove bands of interest from the chip via the RCI. The RCI contains an integrated electrode that facilitates the removal of bands using electrokinetic techniques. The device was characterized using prestained proteins (Pierce BlueRanger and TriChromRanger). Samples were loaded into the microelectrophoresis device via a standard micropipette. An electrical field of 40 V/cm was used to separate and collect the proteins. The microPAGE device is simple to fabricate, benefits from microscale analysis, and includes an on-chip collection scheme that interfaces the macroworld with the microworld.     

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

The recently discovered scaling law for the relaxation times, tau(T,upsilon) = I(Tupsilon(gamma)), where T is temperature and upsilon the specific volume, is derived by a revision of the entropy model of the glass transition dynamics originally proposed by Avramov [J. Non-Cryst. Solids 262, 258 (2000)]. In this modification the entropy is calculated by an alternative route. The resulting expression for the variation of the relaxation time with T and upsilon is shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover. From this analysis, which is valid for any model in which the relaxation time is a function of the entropy, we find that the scaling exponent gamma can be identified with the Gruneisen constant.     

Enantioselectivity of vesicle-forming chiral surfactants in capillary electrophoresis. Role of the surfactant headgroup structure

Two vesicle-forming single-tailed amino acid derivatized surfactants sodium N-[4-n-dodecyloxybenzoyl]-L-leucinate (SDLL) and sodium N-[4-n-dodecyloxybenzoyl]-L-isoleucinate (SDLIL) have been synthesized and used as pseudo-stationary phase in micellar electrokinetic chromatography to evaluate the role of steric factor of amino acid headgroup and hydrophobic/hydrophilic interactions for enantiomeric separations. The aggregation behavior of the surfactants has been studied in aqueous buffered solution using surface tension and fluorescence probe techniques. Results of these studies have suggested formation of vesicles in aqueous solutions. Microenvironment of the vesicle, which determines the depth of penetration of the analytes into vesicle was determined by fluorescence probe technique using pyrene, N-phenyl-1-naphthylamine (NPN), and 1,6-diphenyl-1,3,5-hexatriene (DPH) as probe molecules. Atropisomeric compounds (+/-)-1,1'-bi-2-naphthol (BOH), (+/-)-1,1'-binaphthyl-2,2'-diamine (BDA), (+/-)-1,1'-binaphthyl-2,2'-diylhydrogen phosphate (BNP) and Tr?ger's base (TB) and chiral compound benzoin (BZN) has been enantioseparated. The separations were optimized with respect to surfactant concentration, pH, and borate buffer concentration. SDLL was found to provide better resolution for BOH, BNP, and BZN. On the other hand, SDLIL offers better resolution for BDA. The chromatographic results have been discussed in the light of the aggregation behavior of the surfactants and the interaction of the solutes with the vesicles.     

壁面马赫数分布规律可控的新型内收缩基准流场设计方法

根据有旋特征线理论,设计出了沿程马赫数下降规律可控的轴对称基准流场,分析了基准流场的几何参数(前缘压缩角及中心体半径)的影响规律,发现选取较小的前缘压缩角和中心体半径有利于得到性能优良的基准流场;然后在设计状态Ma=6时研究了三种典型的马赫数下降规律对这种轴对称流场性能的影响。最后考虑了粘性的影响,并进行了粘性修正探索,结果表明,采用附面层位移厚度修正方法后,基准流场的壁面压力分布和无粘情况吻合良好。      

Laser Optogalvanic Analysis in a Radiofrequency Plasma: Detection of Iodine Atoms and Molecules

The optogalvanic effect (OGE) may be used to detect specific species in a plasma (ions, atoms, radicals, or molecules) by selective laser excitation of the plasma. The plasma itself is merely the reservoir of electronically excited, ionized, and atomized species. Compared with conventional ICP-AES, OGE has many advantages: no external detector, zero background, no interferences, and greater versatility. Since the photoacoustic (PA) and ionization rate change (IRC) components of the OGE signal can be separated, optogalvanic spectroscopy can exhibit a further selectivity based on this discriminatory ability. The OGE method has been applied to iodine analysis. By careful selection of the operating conditions, pure atomic and pure molecular iodine signals constitute the PA and IRC profiles, respectively. The best detection limit, in a somewhat primitive experiment, is 10⁻⁷μg/ml of I₂, which is comparable to laser-induced fluorescence. This detection limit can be improved by at least three orders of magnitude by optimizing the experimental conditions.     

Vinyl polymerization of acrylonitrile by the cerium(IV)-propane-1,2-diol system

The polymerization of acrylonitrile (M) initiated by the Ce(IV)-propane-1,2-diol (R) redox system has been studied in aqueous sulphuric acid under nitrogen in the temperature range 30 to 40°. The rate of polymerization is proportional to [M]², [R] and [Ce(IV)]^?1 and the rate of ceric ion disappearance is proportional to [R], [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme has been proposed, and various rate and energy parameters evaluated.