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排序方式: 共有415条查询结果,搜索用时 15 毫秒
1.
Interfacial hybridization kinetics of oligonucleotides immobilized onto fused silica surfaces 总被引:3,自引:0,他引:3
Jiang Zeng Amer Almadidy James Watterson Ulrich J. Krull 《Sensors and actuators. B, Chemical》2003,90(1-3):68-75
Fused silica optical fibers have been used in an intrinsic mode optical configuration as biosensors for fluorescence based detection of hybridization of nucleic acids. In this work, the kinetics of hybridization of single-stranded oligonucleotides that were covalently immobilized were studied. The probe DNA was dT20, and the target was Fluorescein-labeled non-complementary (dT20) or complementary (dA20) oligonucleotide. Chronofluorimetric monitoring of the adsorption and hybridization processes was used to investigate oligonucleotide films of different density, in different salt concentrations, at temperatures of 25 and 40 °C, with the concentration of the target DNA being 0.005–0.1 μM. Mathematical models based on first- and second-order Langmuir adsorption have been examined to describe both the adsorption and the hybridization processes. Experimental data were processed using the models, and the hybridization kinetics were calculated. Hybridization kinetics on these optical fiber DNA sensors was found to be up to three orders faster than results presented for a number of other experiments using different immobilization chemistries. 相似文献
2.
This paper describes the design and implementation of a wideband merged LNA and mixer chip covering the frequency range from 0.1 to 3.85 GHz using 90-nm CMOS technology. Its high level of integration as well as its low power consumption makes it suitable for the rapidly growing software defined radio RF receivers. The chip performance achieves S11 below -10 dB along the entire band and a minimum single side band noise figure of 8.4 dB at IF frequency of 70 MHz. Power conversion gain is measured to be 12.1 dB while the input referred 1 dB compression point is measured to be -12.8 dBm. The chip core consumes only 9.8 mW from a 1.2 V supply with a die area, including the pads, of 0.88 mm2 相似文献
3.
M. H. El-Fouly A. F. Maged H. H. Amer M. A. Morsy 《Journal of Materials Science》1990,25(4):2264-2266
Temperature-induced transformations are considered to be interesting characteristic properties of amorphous materials including the Si
x
Te60–x
As30Ge10 system, withx=5, 10, 12 and 20. Density (), X-ray diffraction and differential thermal analysis (DTA) were used to characterize the compositions. DTA traces of each glass composition at different heating rates from 5 to 30° C min–1 were obtained and interpreted. Fast and slow cooling cycles were used to determine the rate of structure formation. Cycling studies of materials show no memory effect but only ovonic switching action. The compositional dependence of the crystallization activation energy (E) and the coefficient of glass-forming tendency (K
gl) have been calculated. The thermal transition temperatures and associated changes in specific heat have been examined as a function of the Te/Si ratio by differential scanning calorimetry. It was found that andE increase linearly with increasing tellurium content, while the heat capacity (c
p) andK
gl, decrease with increasing tellurium content.E=1.54 eV andc
p=0.246 J g–1 K–1 forx=20 whileE=2.74eV andc
p=0.22 J g–1 K–1 forx=5. 相似文献
4.
M. H. El-Fouly A. M. Morsy A. H. Ammar A. F. Maged H. H. Amer 《Journal of Materials Science》1989,24(7):2444-2448
The effect of composition on amorphous chalcogenide threshold switches of the system Si
x
Te60-x
As30Ge10, wherex = 5, 10, 12 and 20, has been studied. The compositionx = 5 shows the best switching characteristics, e.g. the smallest holding voltage (V
h = 0.4V), the highest ON state current (I
h = 45A) and smallest threshold voltage (V
s = 1.5V). Applying the three mechanisms of conductance of Mottet al. (Phil. Mag.
37 (1975) 961), it is found that for a particular composition
2 <
1 <
0 (the pre-exponential factors) andW
2 < (E
a –E
1 +W
1) < (E
c –E
f) (whereE
a,E
c andE
e = activation energies at band edge, fermi level and conduction band;W
1 andW
2 = activation energy for hopping). It was found that the density of states at the fermi levelN(E
f) increases with the decrease of silicon content. The results provided further evidence against thermal interpretations and thereby support electronic models of threshold switching for these glass systems. 相似文献
5.
Hussein Abdel-Jaber Mike Woodward Fadi Thabtah Amer Abu-Ali 《Journal of Network and Computer Applications》2008,31(4):750-770
Due to the rapid development in computer networks, congestion becomes a critical issue. Congestion usually occurs when the connection demands on network resources, i.e. buffer spaces, exceed the available ones. We propose in this paper a new discrete-time queueing network analytical model based on dynamic random early drop (DRED) algorithm to control the congestion in early stages. We apply our analytical model on two-queue nodes queueing network. Furthermore, we compare between the proposed analytical model and three known active queue management (AQM) algorithms, including DRED, random early detection (RED) and adaptive RED, in order to figure out which of them offers better quality of service (QoS). We also experimentally compare the queue nodes of the proposed analytical model and the three AQM methods in terms of different performance measures, including, average queue length, average queueing delay, throughput, packet loss probability, etc., aiming to determine the queue node that offers better performance. 相似文献
6.
Amer Z. Salman 《国际水》2013,38(2):220-224
Abstract In the Jordan Valley of Jordan, the demand for water and ability to control its location, timing, quality, and quantity are becoming critical. The competition for water between the urban and agricultural sectors is increasing. There is a general trend in Jordan to reduce water allocated for agricultural use. Increasing the price of irrigation water or restricting the planted areas of water consuming crops, such as bananas, has been implemented during the recent growing season. The main objective of this paper is to highlight the impact of optimal allocation of irrigation water by building storage capacity on the economy of Jordan Valley. A linear programming technique is used, and the main results show that for proper management of water storage capacity, the suggested cropping pattern would generate $88.2 million, whereas the actual cropping pattern generated $74.4 million. The optimal water demand schedule is distributed according to the needs of the planted crops, and water demand has been allocated in an efficient way. In addition, appropriate management of storage capacity has solved the problem of water scarcity during the summer months, when peak production takes place. Storage-transfer system between locations played a significant role in reallocating irrigation water through the storage system. This compensates to a high degree in keeping the agricultural production more stable in physical and monetary units. 相似文献
7.
The experimental investigations of the effect of contact time/temperature on initiating the cook-off using 7.62 mm calibre cartridge cases (CC) were conducted previously. These cartridges were filled with commercial off-the-shelf (COTS) double based (DB) propellant (Bulls Eye) and were loaded in a hot chamber. The thermal explosion temperature is of great significance to both weapon designers and safety inspectors as it provides the operational limit and safe operating temperature. For CC under test, it was found that the cook-off temperatures of this propellant were encountered with the heat transfer profile of the simulated gun barrel between 151.4 ℃ and 153.4 ℃, with a reaction occurring in less than 300 s after the round was chambered. Usefully, each experiment was found to be consistent and repeatable. 相似文献
8.
Roasted green wheat at moisture content from 0.052 to 0.25 (decimal d.b.) and temperatures from 25 to 43 °C was used to model moisture sorption isotherms using conventional non-linear least square regression (NLR) and neural-fuzzy (NF) techniques. The results showed that neural-fuzzy techniques provided a better fit than conventional least square regression with: R2 = 0.99 and 0.97, RMSE = 0.01 and 0.0038, E% = 1.01 and 5.9 and SSE = 0.0008 and 0.009, for NF and NLR techniques, respectively. Differential enthalpy decreased from 477.9 kJ/kg at 0.052 (decimal d.b. mc) to 44.7 kJ/kg at 0.25 (decimal d.b. mc) and entropy decreased from 1.16 kJ/kg K at 0.052 (decimal d.b. mc) to 0.014 kJ/kg K at 0.25 (decimal d.b. mc). A linear plot between enthalpy and entropy showed that compensation exists. The isokinetic temperature Tβ was 376.13 K which was larger than the harmonic mean temperature Thm = 307.31 K, showing that the water sorption was entropy-driven. The free energy change ΔG was positive (+38.42 kJ/kg) indicating a non-spontaneous water sorption process. 相似文献
9.
Abhijeet Raj Iran David Charry Prada Amer Ahmad Amer Suk Ho Chung 《Combustion and Flame》2012,159(2):500-515
This work aims to develop a reaction mechanism for gasoline surrogate fuels (n-heptane, iso-octane and toluene) with an emphasis on the formation of large polycyclic aromatic hydrocarbons (PAHs). Starting from an existing base mechanism for gasoline surrogate fuels with the largest chemical species being pyrene (C16H10), this new mechanism is generated by adding PAH sub-mechanisms to account for the formation and growth of PAHs up to coronene (C24H12). The density functional theory (DFT) and the transition state theory (TST) have been adopted to evaluate the rate constants for several PAH reactions. The mechanism is validated in the premixed laminar flames of n-heptane, iso-octane, benzene and ethylene. The characteristics of PAH formation in the counterflow diffusion flames of iso-octane/toluene and n-heptane/toluene mixtures have also been tested for both the soot formation and soot formation/oxidation flame conditions. The predictions of the concentrations of large PAHs in the premixed flames having available experimental data are significantly improved with the new mechanism as compared to the base mechanism. The major pathways for the formation of large PAHs are identified. The test of the counterflow diffusion flames successfully predicts the PAH behavior exhibiting a synergistic effect observed experimentally for the mixture fuels, irrespective of the type of flame (soot formation flame or soot formation/oxidation flame). The reactions that lead to this synergistic effect in PAH formation are identified through the rate-of-production analysis. 相似文献
10.
The hydraulic‐thermal characteristics of 3D pinned heat sink designs have been numerically compared as the first part of a three‐part investigation. Five different pin geometries (circular, square, triangular, strip, and elliptic pins) and an unpinned heat sink with three types of nanofluids (Al2O3–H2O, SiO2–H2O, and CuO–H2O) are considered for laminar forced convection. The range of Reynolds number is from 100 to 1000, and volume fractions vary between 0% and 5%. The finite volume method is employed to solve the Navier–Stokes and energy equations by employing a SIMPLE algorithm for a computational solution. Three parameters are presented—the Nusselt number, the bottom temperature, and the hydrothermal performance of the heat sink with pressure drop data. The findings indicated that the overall hydrothermal performance of elliptic‐pinned (EP) heat sinks produces the most substantial value of 3.10 for pure water. For different nanofluids, the SiO2–water nanofluids with EPs have the most significant hydrothermal performance. Also, this factor is enhanced with an increase in nanofluid concentration up to nearly 3.34 for 5% of SiO2–water. Consequently, applying the elliptic‐pinned heat sinks is recommended with pure water for considering an increase in the pressure drop, with 5% of SiO2–water nanofluids, regardless of an enlargement of pressure drop for heat‐dissipation applications. 相似文献