Sol-gel modified poly(dimethylsiloxane) microfluidic devices with high electroosmotic mobilities and hydrophilic channel wall characteristics

Using a sol-gel method, we have fabricated poly(dimethylsiloxane) (PDMS) microchips with SiO2 particles homogeneously distributed within the PDMS polymer matrix. These particles are approximately 10 nm in diameter. To fabricate such devices, PDMS (Sylgard 184) was cast against SU-8 molds. After curing, the chips were carefully removed from the mold and sealed against flat, cured pieces of PDMS to form enclosed channel manifolds. These chips were then solvated in tetraethyl orthosilicate (TEOS), causing them to expand. Subsequently, the chips were placed in an aqueous solution containing 2.8% ethylamine and heated to form nanometer-sized SiO2 particles within the cross-linked PDMS polymer. The water contact angle for the PDMS-SiO2 chips was approximately 90.2 degrees compared to a water contact angle for Sylgard 184 of approximately 108.5 degrees . More importantly, the SiO2 modified PDMS chips showed no rhodamine B absorption after 4 h, indicating a substantially more hydrophilic and nonabsorptive surface than native PDMS. Initial electroosmotic mobilities (EOM) of (8.3+/-0.2)x10(-4) cm2/(V.s) (RSD=2.6% (RSD is relative standard deviation); n=10) were measured. This value was approximately twice that of native Sylgard 184 PDMS chips (4.21+/-0.09)x10(-4) cm2/(V.s) (RSD=2.2%; n=10) and 55% greater than glass chips (5.3+/-0.4)x10(-4) cm2/(V.s) (RSD=7.7%; n=5). After 60 days of dry storage, the EOM was (7.6+/-0.3)x10(-4) cm2/(V.s) (RSD=3.9%; n=3), a decrease of only 8% below that of the initially measured value. Separations performed on these devices generated 80,000-100,000 theoretical plates in 6-14 s for both tetramethylrhodamine succidimidyl ester and fluorescein-5-isothiocyanate derivatized amino acids. The separation distance was 3.5 cm. Plots of peak variance vs analyte migration times gave diffusion coefficients which indicate that the separation efficiencies are within 15% of the diffusion limit.     

Thermoluminescence properties of LiF:Mg,Cu,Na,Si pellets in radiation dosimetry

Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets have been developed for application in radiation dosimetry. LiF:M,Cu,Na,Si TL pellets were made from TL powders using a sintering process, that is, pressing and heat treatment. These pellets have a diameter of 4.5 mm, and a thickness of 0.8 mm are blue in colour and have a mass of 28 mg each. After 400 pellets had been produced they were irradiated with 137Cs gamma radiation and samples having a sensitivity within a +/-5% standard deviation were selected for experimental use. In the present study, the physical and dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets were investigated for their emission spectrum, dose response, energy response and fading characteristics. Photon irradiation for the experiments was carried out using X ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute (KAERI). The average energies and the dose were in the range of 20-662 keV and 10(-6) - 10(2) Gy respectively. The glow curves were measured with a manual type thermoluminescence dosimetry reader (system 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5 degrees C.s(-1). the main dosimetric peak of the glow curve appeared at 234 degrees C, its activation energy was 2.34 eV and the frequency factor was 1.00 x 10(23). The TL emission spectrum appeared at the blue region centred at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to the 137Cs response were within +/-20% in the overall photon energy region. No fading of the TL sensitivity of the pellets stored at room temperature was found over the course of a year. Therefore LiF:Mg,Cu,Na,Si TL pellets can be used for personal dosimetry, but more research is needed to improve the characteristics for repeated use.     

Temperature-insensitive fiber Bragg grating tilt sensor

A temperature-insensitive optical fiber tilt sensor is presented. The sensor scheme uses a prestrained fiber Bragg grating to sense the strain, which depends on the tilt angle. To compensate for the temperature effect, materials that have different linear thermal expansion behaviors are used for implementation of the sensor body. The differentiation in the linear thermal expansion would then cause a counter effect to the original temperature effect. Experimental tests show an accuracy of +/-0.167 degrees in tilt angle measurement. A temperature stability better than +/-0.33 degrees over the temperature range from 27 degrees C to 75 degrees C is demonstrated. The resolution 0.0067 degrees in tilt angle measurement is achieved by using our preliminary sensor with a dimension of 1 6 x 5 x 5 cm(3).     

Characterization of a polarization-independent transmission trap detector

A six-element polarization-independent transmission trap detector with coaxial input and output beams has been constructed and full characterized. The measured optical parameters are compared with their values, predicted by Fresnel equations. Measured transmittances are in agreement with the predicted values within 2 x 10(-5) in the wavelength region from 450 to 650nm. The spectral responsivity of the transmission trap detector is in agreement with the predicted values within 0.035% at 543.5- and 633.0-nm vacuum wavelengths. The spatial uniformity of the responsivity is +/-0.03% across the active area of approximately 5 x 6 mm(2), measured with a laser beam of 1-mm diameter. The angular uniformity of the transmission trap detector is better than +/-0.01% for +/-3 degrees rotation around two perpendicular axes.     

Calculated microdosimetric characteristics of 125I and 103Pd brachytherapy seeds at different depths in water

Both (125)I and (103)Pd sources have been widely used in the permanent prostate implant. An important consideration for the choice of brachytherapy sources is the relative biological effectiveness (RBE) for the source/seed used in the implantation. As RBE is closely related to the microdosimetric parameter, it is desirable to calculate the dose mean lineal energies for both (125)I and (103)Pd at various radial distances to the seed surface. Monte Carlo simulation was performed for photons emitted from (125)I and (103)Pd. Energy depositions from photons and all their secondary electrons were tracked. Dose distributions of lineal energy, d(y), were calculated for spheres of 1 microm in diameter and at various radial distances to the seed surface. From the dose distribution of lineal energy, the dose mean lineal energy, y(D), was derived. The results showed that the radiation qualities are constant in the distance range from 0.5 to 5 cm. In this distance range, the quality factor, relative to gamma rays from (60)Co, is 2.2 for (125)I and 2.5 for (103)Pd.     

6061-T4大直径薄壁管数控弯曲壁厚变化实验研究

为实现6061-T4大直径薄壁铝管数控弯曲精确成形,提高其成形极限与质量,需对弯曲过程中壁厚变化进行有效控制.本文以该材料Φ50.8 mm×0.889 mm×101.6 mm(直径D×壁厚t×弯曲半径R)薄壁铝管为研究对象,实验研究了弯曲角度、芯棒伸出量、芯球个数、弯曲速度等可控参数对壁厚的影响规律.研究结果表明:在整个弯曲段内,中性层并不是均匀地发生等距离偏移,中性层偏移量(E)与内外脊线壁厚变化率差值(η)存在线性关系,E随η的增大而增大;增大弯曲角度、芯棒伸出量、弯曲速度都导致内外脊线壁厚变化程度加重,管材壁厚变化不均匀度加剧;芯球个数对壁厚的影响呈非线性;基于优化的工艺参数组合,成功获得最大壁厚减薄率为22%的180°合格弯曲管件.     

X-Ray Telescope Onboard Astro-E. II. Ground-Based X-Ray Characterization

X-ray characterization measurements of the x-ray telescope (XRT) onboard the Astro-E satellite were carried out at the Institute of Space and Astronautical Science (Japan) x-ray beam facility by means of a raster scan with a narrow x-ray pencil beam. The on-axis half-power diameter (HPD) was evaluated to be 1.8?-2.2?, irrespective of the x-ray energy. The on-axis effective areas of the XRTs for x-ray imaging spectrometers (XISs) were approximately 440, 320, 240, and 170 cm(2) at energies of 1.49, 4.51, 8.04, and 9.44 keV, respectively. Those of the x-ray spectrometer (XRS) were larger by 5-10%. The replication method introduced for reflector production significantly improved the imaging capability of the Advanced Satellite for Cosmology and Astrophyics (ASCA) XRT, whose HPD is ~3.6?. The increase in the effective area by a factor of 1.5-2.5, depending upon the x-ray energy, compared with that of the ASCA, was brought about by mechanical scale up and longer focal lengths. The off-axis HPDs were almost the same as those obtained on the optical axis. The field of view is defined as the off-axis angle at which the effective area becomes half of the on-axis value. The diameter of the field of view was ~19? at 1.49 keV, decreasing with increasing x-ray energy, and became ~13? at 9.44 keV. The intensity of stray light and the distribution of this kind of light on the focal plane were measured at the large off-axis angles 30? and 60?. In the entire XIS field of view (25.4 mm x 25.4 mm), the intensity of the stray light caused by a pointlike x-ray source became at most 1% of the same pointlike source that was on the optical axis.     

Sorption potential of rice husk for the removal of 2,4-dichlorophenol from aqueous solutions: kinetic and thermodynamic investigations

The sorption potential of chemically and thermally treated rice husk (RHT) for the removal of 2,4-dichlorophenol (DCP) from aqueous solutions has been investigated. Sorption of DCP by rice husk was observed over a wide pH range of 1-10. The effect of contact time between liquid and solid phases, sorbent dose, pH, concentration of sorbate and temperature on the sorption of DCP onto rice husk has been studied. The pore area and average pore diameter of RHT by BET method are calculated to be 17+/-0.6 m2g-1 and 51.3+/-1.5 nm, respectively. Maximum sorption (98+/-1.2%) was achieved for RHT from 6.1x10(-5) moldm(-3) of sorbate solution using 0.1g of rice husk for 10 min agitation time at pH 6 and 303K, which is comparable to activated carbon commercial (ACC) 96.6+/-1.2%, but significantly higher than chemically treated rice husk (RHCT) 65+/-1.6% and rice husk untreated (RHUT) 41+/-2.3%. The sorption data obtained at optimized conditions was subjected to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. Sorption intensity 1/n (0.31+/-0.01) and sorption capacity multilayer C(m) (12.0+/-1.6 mmolg(-1)) have been evaluated using Freundlich sorption isotherm, whereas the values of sorption capacity monolayer Q (0.96+/-0.03 mmolg(-1)) and binding energy, b, (4.5+/-1.0)x10(4)dm(3)mol(-1) have been estimated by Langmuir isotherm. The Langmuir constant, b, was also used to calculate the dimensionless factor, R(L), in the concentration range (0.6-6.1)x10(-4) moldm(-3), suggesting greater sorption at low concentration. D-R sorption isotherm was employed to calculate sorption capacity X(m) (2.5+/-0.07 mmolg(-1)) and sorption energy E (14.7+/-0.13 kJmol(-1)). Lagergren and Morris-Weber equations were employed to study kinetics of sorption process using 0.2g of RHT, 25 cm(3) of 0.61x10(-4)moldm(-3) sorbate concentration at pH 6, giving values of first-order rate constant, k, and rate constant of intraparticle transport, R(id), (0.48+/-0.04 min(-1) and 6.8+/-0.8 nmolg(-1)min(-1/2), respectively) at 0.61x10(-4)moldm(-3) solution concentration of DCP, 0.1g RHT, pH 6 and 2-10min of agitation time. For thermodynamic studies, sorption potential was examined over temperature range 283-323 K by employing 6.1x10(-4)moldm(-3) solution concentration of DCP, 0.1g RHT at pH 6 and 10 min of agitation time and values of DeltaH (-25+/-1 kJmol(-1)), DeltaS (-61+/-4 Jmol(-1)K(-1)) and DeltaG(303K) (-7.1+/-0.09 kJmol(-1)) were computed. The negative values of enthalpy, entropy, and free energy suggest that the sorption is exothermic, stable, and spontaneous in nature.     

锥角参数对单向聚能药柱爆破破岩效果的影响

为研究聚能穴锥角参数对爆炸应力和岩石损伤破裂范围的影响,以获得最优的聚能穴参数,从而达到最佳的破岩效果,利用有限元模拟软件LS DYNA建立了6种锥角参数下的单向聚能药柱模型。锥角的深度为15 mm,6种锥角高度分别为10、12、14、16、18 mm和20 mm。研究了岩石裂纹扩展的影响规律,测得聚能方向与非聚能方向上不同位置的有效应力,得到不同锥角参数对应的岩石单元的最大破坏距离。结果表明:聚能锥角会对爆破产生定向作用,特别是对岩石破碎和拉伸裂纹所带来的破岩效果影响明显;当锥角高度为10 mm时,距炮孔25 cm测点处聚能方向上的有效应力比非聚能方向同样距离处高110.8 MPa,同时,聚能方向上单元损伤比要比非聚能方向高21%,聚能效果最佳;随着锥角高度逐渐增大,聚能方向上岩石裂纹逐渐减少,裂纹分叉减少,单元破坏最大距离可达108.1 cm,并且呈下降趋势。     

La1-xNdxB6单晶的制备及热电子发射性能

以LaB_6和NdB_6粉末为原料,采用区域熔炼法成功制备了大尺寸、高质量的多元稀土六硼化物La_(1-x)Nd_xB_6(x=0.1~0.3)单晶,并测试了该系列单晶(100)晶面的热电子发射性能。本实验制备的单晶长度大于40mm,直径大于4mm。单晶衍射、劳埃照片、晶面摇摆曲线、单晶断口扫描等检测结果表明单晶质量较高,热发射测试结果表明在1 873K、4 000V下,单晶零场电流发射密度随着Nd含量增加从6.01A/cm~2降为4.83A/cm~2,有效逸出功从2.88eV增大到2.95eV。     

Excellent compositional homogeneity in In0.3Ga0.7As crystals grown by the traveling liquiduszone (TLZ) method

The influence of convection in a melt on the compositional homogeneity of the TLZ-grown In_0.3Ga_0.7As crystals has been investigated by growing crystals with various dimensions on the ground. Excellent compositional homogeneity such as 0.3 plus or minus 0.01 in InAs mole fraction for a distance of 25 mm was obtained when the melt diameter was limited to 2 mm and convective flow in the melt was suppressed. On the other hand, when the crystal diameter was increased to 10 mm, both axial and radial compositional homogeneity was deteriorated due to convection in the melt. Comparing with the numerical simulation, convective flow velocity less than 1.4 mm/h may be sufficient for growing homogeneous crystals and it is not so difficult to suppress convective flow velocity below 1.4 mm/h for 10 mm diameter crystals in microgravity. Therefore, larger homogeneous In_0.3Ga_0.7As crystals are expected to be grown by the TLZ method on board the International Space Station.     

High-speed high-resolution fiber diameter variation measurement system

A fiber diameter variation measurement system is described which is capable of measuring transparent fibers with 0.02% diameter resolution and 6-microm axial resolution at a measurement rate of 1 kHz and with a working distance of >100 mm. The principles of its operation are discussed in detail, and experimental confirmation of its performance is reported. A theoretical calculation of the optimum obtainable diameter resolution for a given set of experimental parameters is also presented.     

Molecular adsorption at silica/CH3CN interface probed by using evanescent wave cavity ring-down absorption spectroscopy: determination of thermodynamic properties

Evanescent wave cavity ring-down absorption spectroscopy is applied to measure the thermodynamic properties of the surface adsorption for neutral trans-4-[4-(dibutylamino)styryl]-1-(3-sulfopropyl) pyridinium (DP) and charged trans-4-[4-(dibutylamino)styryl]-1-methylpyridinium iodide (DMP+ I-) at the silica/CH3CN interface, where the interfacial density is determined by measurement of absorbance. The bulk concentration dependence of the surface density may be characterized with a Langmuir isotherm model, which yields saturated surface density, equilibrium constant, and free energy of adsorption of (7.0 +/- 0.3) x 10(13) cm(-2), (1.3 +/- 0.2) x 10(4) M(-1), and -23.5 +/- 0.4 kJ/mol for DP and (8.9 +/- 0.3) x 10(12) cm(-2), (2.6 +/- 0.7) x 10(4) M(-1), and -25.2 +/- 0.6 kJ/mol for DMP+ I-, respectively. The surface density of the isolated silanol groups may then be estimated in terms of the molecular probe results. The absorption contribution from the bulk solution is a factor of approximately 10(1)-10(2) smaller than the total absorbance measured such that subtraction of the bulk contribution leads to negligible change of the thermodynamic properties. The DP is adsorbed to the SiOH sites by forming hydrogen bonds, while the DMP+ cation is bound to the SiO- sites by electrostatic attraction. Surface forces are also probed by addition of triethylamine (TEA), which is competitive with DP for the silanol sites. When the TEA concentration is increased, the DP surface density is found to decrease, whereas the DMP+ surface density increases. The obtained thermodynamic properties are generally consistent with those measured by second harmonic generation spectroscopy. However, when a tetramethylammonium ((CH3)4N+ Cl-) salt is added, the DMP+ cation behaves differently between these two methods. Formation of an electrical double layer may account for the difference.     

Sorption potential of Moringa oleifera pods for the removal of organic pollutants from aqueous solutions

Moringa oleifera pods Lamarck (Drumstick or Horseradish) is a multipurpose medium or small size tree from sub-Himalayan regions of north-west India and indigenous to many parts of Asia, Africa, South America, and in the Pacific and Caribbean Islands. Its pods (MOP) have been employed as an inexpensive and effective sorbent for the removal of organics, i.e., benzene, toluene, ethylbenzene and cumene (BTEC) from aqueous solutions using HPLC method. Effect of different parameters, i.e., sorbent dose 0.05-0.8g, 25cm(-3) agitation time 5-120min, pH 1-10, temperature 283-308K and concentration of sorbate (1.3-13)x10(-3), (1.1-11)x10(-3), (0.9-9)x10(-3), (0.8-8)x10(-3)moldm(-3), on the sorption potential of MOP for BTEC have been investigated. The pore area and average pore diameter of the MOP by BET method using nitrogen as a standard are calculated to be 28.06+/-0.8m(2)g(-1) and 86.2+/-1.3nm respectively. Freundlich, Langumir and Dubinin-Radushkevich (D-R) sorption isotherms were employed to evaluate the sorption capacity of MOP. Sorption capacities of BTEC onto MOP have been found to be 46+/-10, 84+/-9, 101+/-4, 106+/-32mmolg(-1) by Freundlich, 8+/-0.1, 9+/-0.1, 10+/-0.3, 9+/-0.1mmolg(-1) by Langumir and 15+/-1, 21+/-1, 23+/-2, 22+/-3mmolg(-1) by D-R isotherms respectively, from BTEC solutions at 303K. While the mean energy of sorption process 9.6+/-0.3, 9.2+/-0.2, 9.3+/-0.3, 9.5+/-0.4kJmol(-1) for BTEC is calculated by D-R isotherm only. Rate constant of BTEC onto MOP 0.033+/-0.003, 0.030+/-0.002, 0.029+/-0.002, 0.027+/-0.002min(-1) at solution concentration of 1.3x10(-3), 1.1x10(-3), 0.9x10(-3) and 0.8x10(-3)moldm(-3) and at 303K have been calculated by employing Lagergren equation. Thermodynamic parameters DeltaH -8+/-0.4, -10+/-0.6, -11+/-0.7, -11+/-0.7kJmol(-1), DeltaS -22+/-2, -26+/-2, -27+/-2, -29+/-3Jmol(-1)K(-1) and DeltaG(303K) -0.9+/-0.2, -1.9+/-0.2, -2.3+/-0.1 and -2.6+/-0.2kJmol(-1) were also estimated for BTEC respectively at temperatures 283-308K. The negative values of DeltaH, DeltaS and DeltaG suggest exothermic, stable (with no structural changes at solid-liquid interface) and spontaneous nature of sorption process under optimized conditions. MOP has been used extensively to accrue and then to preconcentrate benzene, toluene and ethylbenzene in wastewater sample.     

Response of LiF:Mg,Ti to low energy carbon and oxygen ions

The extended track interaction model (ETIM) has been formulated to explain the TL-fluence response for peak 5 to heavy ions using radial dose distributions produced by the ions in LiF and their luminescent centre occupation probability distributions. In this work, an experimental study of the TLD-100 fluence response to carbon and oxygen ions and its interpretation in terms of a Monte Carlo simulation of ETIM applied to peak 5 are presented. Irradiations were performed with 7.34 and 10.3 MeV 12C and 8.34 MeV 16O ions in the fluence interval between 2 x 10(7) and 2 x 10(11) cm(-2). Individual glow curve responses show the expected increase of supralinearity as the peak temperature increases. Data for peak 5 show a weak dependence with energy. These latter results are difficult to understand when one considers the differences in the expected radial occupancies for different ion energies.     

A directional dose equivalent monitor for neutrons

A directional dose equivalent monitor is introduced which consists of a 30 cm diameter spherical phantom hosting a superheated drop detector embedded at a depth of 10 mm. The device relies on the similarity between the fluence response of neutron superheated drop detectors based on halocarbon-12 and the quality-factor-weighted kerma factor. This implies that these detectors can be used for in-phantom dosimetry and provide a direct reading of dose equivalent at depth. The directional dose equivalent monitor was characterised experimentally with fast neutron calibrations and numerically with Monte Carlo simulations. The fluence response was determined at angles of 0, 45, 90, 135 and 180 degrees for thermal to 20 MeV neutrons. The response of the device is closely proportional to the fluence-to-directional dose equivalent conversion coefficient, h'phi (10; alpha, E). Therefore, our monitor is suitable for a direct measurement of neutron directional dose equivalent, H'(10), regardless of angle and energy distribution of the neutron fluence.     

Bulk Bridgman growth of cadmium mercury telluride for IR applications

Cadmium mercury telluride (CMT, CD_xHg_1-xTe) is the pre-eminent infrared material, despite the difficulties associated with the production and subsequent processing of this ternary compound. By varying the x value the material can be made to cover all the important infrared (IR) ranges of interest. The first technique developed was the basic vertical Bridgman process with typical crystal dimensions of 13 mm diameter and 150 mm length. We found it necessary to purify both the mercury and the tellurium on-site before use to obtain the required electrical properties. There is marked segregation of the matrix elements in Bridgman growth that is both a disadvantage and an advantage. Its disadvantage is that the yield of material in terms of composition for the two most common regions required (x=0.21 and 0.3 for 8–14 and 3–5 m atmospheric transmission windows, respectively) is low. The advantage is that both regions of interest are produced in the same crystal. A further advantage is that segregation of impurities also occurs and leads to low background donor levels in Bridgman material. This Bridgman material is used exclusively for photoconductive IR detectors that require n-type material. The main disadvantages of the Bridgman technique are that material is non-uniform in composition in the radial direction, as well as in the growth direction, and there are numerous grain and sub-grain boundaries. An improved process was developed at BAE Systems based on the accelerated crucible rotation technique (ACRT). Here, growth ampoules are subjected to periodic acceleration/deceleration in their rotation, rather than constant rotation as in the Bridgman process. The major effect of this is to stir the melt during growth and produce flatter solid/liquid interfaces. This, in turn, improves the radial and axial compositional uniformity of the material, normally by a factor of at least ten-fold. The only drawback is that the material is now p-type as grown and must be annealed in mercury vapor to convert it to n-type. An additional marked advantage of ACRT is that the improved radial compositional uniformity enables larger diameter material to be considered. We are currently growing 20 mm diameter, 200 mm long crystals of 0.5 kg weight with acceptable uniformity of composition and good electrical properties for current photoconductive detector programs. © 2001 Kluwer Academic Publishers     

Bioconjugated superstructures of CdTe nanowires and nanoparticles: multistep cascade Förster resonance energy transfer and energy channeling

Nanoparticle/nanowire assemblies with a degree of radial organization were prepared around luminescent semiconducting CdTe nanowires using bioconjugation with streptavidin and D-biotin linkers. Red-emitting nanowires (6.62 +/- 1.55 nm diameter, 512 +/- 119 nm length) and green-emitting nanoparticles (3.2 +/- 0.7 nm diameter) were surface-modified with biotin, while orange-emitting nanoparticles (4.1 +/- 1.2 nm diameter) were decorated with streptavidin. CdTe nanocrystals produced two fuzzy layers around the nanowires in which the diameter of CdTe nanoparticles decreased with the distance from the nanowire axis. F?rster resonance energy transfer (FRET) from the outside layer of nanoparticles to the central nanowire was observed for nanowires conjugated with 4.1 nm CdTe. Addition of 3.2 nm CdTe resulted in a red-orange-green optical progression with band gaps of CdTe decreasing toward the axis of the superstructure. In this case, 4-fold luminescence enhancement of the nanowire luminescence was observed and was attributed to multistep FRET. This observation indicated the accumulation of photogenerated excitons in the cascade terminal. A simple model of multiconjugated superstructure with cascade energy transfer is developed and used to describe and understand the experimental data. The experimental data and theoretical model suggest the possibility of utilization of the prepared superstructures with radial symmetry in several classes of optoelectronic devices including nanomaterials for energy collection. They can also be a convenient model object for the investigation of methods of energy funneling in nanoscale assemblies.     

Studies on sliding wear characteristics of aluminium LM25/silicon dioxide functionally graded composite and optimisation of parameters using response surface methodology

This paper deals with the study of dry sliding wear of LM25/silicon dioxide (10 wt.%) functionally graded composite. The composite was fabricated using stir casting technique and the melt was poured into a horizontal centrifugal die rotating at 1200 min^?1. After casting, the specimen (length 150 mm, external diameter 150 mm and internal diameter 130 mm) was subjected to microstructure and hardness tests at three different depths from the outer periphery (1 mm, 8 mm and 13 mm). The results of the respective tests revealed that the outer periphery of the specimen had higher particle concentration and hardness. Then, wear test was done on a pin‐on‐disc tribometer at room temperature with the experiments designed using response surface methodology and by taking specimens of size 8 x 8 x 15 mm such that the surface undergoing wear was at 1 mm from the outer periphery of the cast. The process variables of load (10 ‐ 40 N), velocity (1 ‐ 4 m/s) and sliding distance (400 ‐ 1200 m) were varied using a level 5 design and experiments were carried on for 20 different optimal combinations. From the regression equation generated for the wear response, it was found that load had maximum effect on the wear rate. The confirmation experiments proved that the regression model could serve well in predicting the wear rate for the given ranges of the continuous factors, for the given composite. Surface plots showed that the wear rate had an increasing trend with respect to load, which was the dominating continuous factor. Though the wear rate increased, severe delamination of the functionally graded composite was delayed. The optimum levels of the continuous factors to minimize the wear rate were found using response optimisation and found to be 10 N, 1.7576 m/s and 2000 m respectively. Scanning electron microscopy analysis of the worn surface of the specimens connected to the obtained trends and thus further validated the model developed. Thus, a functionally graded LM13 composite with silicon dioxid reinforcements is developed and a wear model to predict its wear rate under different process parameters is proposed with predictions of optimal performance conditions. This composite can increase life of components of wear applications in aerospace and automobile industry.     

Microspotting streptavidin and double-stranded DNA arrays on gold for high-throughput studies of protein-DNA interactions by surface plasmon resonance microscopy

We present two strategies for microspotting 10 x 12 arrays of double-stranded DNAs (dsDNAs) onto a gold-coated glass slide for high-throughput studies of protein-DNA interactions by surface plasmon resonance (SPR) microscopy. Both methods use streptavidin (SA) as a linker layer between a biotin-containing mixed self-assembled monolayer (SAM) and biotinylated dsDNAs to produce arrays with high packing density. The primary mixed SAM is produced from biotin- and oligo(ethylene glycol)-terminated thiols bonded as thiolates onto the gold surface. In the first method, a robotic microspotter is used to deliver nanoliter droplets of dsDNA solution onto a uniform layer of this SA ( approximately 2 x 10(12) SA/cm(2)). SPR microscopy shows a density of (5-6) x 10(11) dsDNA/cm(2) (0.2-0.3 dsDNA/SA) in the array elements. The second method uses instead a microspotted array of this SA linker layer, onto which the microspots of dsDNA are added with spatial registry. SPR microscopy before addition of the dsDNA shows a SA coverage of 2 x 10(12) SA/cm(2) within the spots and a dsDNA density of 8.5 +/- 3.5 x 10(11) dsDNA/cm(2) (0.3-0.7 dsDNA/SA, depending on the length of dsDNA) after dsDNA spotting. We demonstrate the ability to simultaneously monitor protein binding with the SPR microscope in many 200-microm spots with 1-s time resolution and sensitivity to <1 pg of protein.