Search

Spectroscopic gas sensing technologies based on absorption and Raman scattering are fast, nondestructive, long-term stable and highly selective. By making use of an optically resonant cavity, the s...

A theoretical investigation is executed for exploring the flow, heat and mass transfer behavior of magnetohydrodynamic radiated ferrofluid flow caused by a cone in the existence of non-uniform heat source/sink. Dispersion of ferrous nanoparticles finds applications in heat exchanger system, recharge able batteries, chemical catalysts, metallurgy, conducting paints, magnetic recording media, drug delivery, nanofibers, textiles etc. in this study we have used the two types of temperatures namely water (At 10 °C and 50 °C), having less thermal conductivity as compared with magnetic nanoparticles (CoFe2O4). A simulation is performed by mixing of cobalt ferrous particles in base fluid water with different temperatures. Also, we presented dual solutions for flow over a cone with CoFe2O4+water at 10 °C and CoFe2O4+water at 50 °C. Governing equations are solved using Runge-Kutta with shooting method and compared with published literature. From the formulated model we found that the friction factor coefficient and rate of heat transfer is more in mixture of CoFe2O4+water at 10 °C case compare to CoFe2O4 +water at 50 °C case. Similarly the mass transfer rate is more in CoFe2O4 +water at 50 °C when compared to CoFe2O4 +water at 10 °C case. These results help us to conclude that depending on the industrial appliances we can use heating or cooling processes CoFe2O4 +water at 10 °C and CoFe2O4 +water at 10 °C fluids respectively.

Current analysis presents the mathematical modeling for peristaltic transport of nanofluid with applications of double-diffusive convection and Hall features. The flow has been induced by a convergent channel due to peristaltic propulsion. These rheological equations are transformed from fixed to wave frames by using a linear mathematical relation between these two frames. The dimensionless variables are used to transform these rheological equations into nondimensional forms. The flow analysis is carried out under two distinct scientific biological assumptions, one is known as long wavelength and the second one is low Reynolds number. The analytical solutions of these rheological equations are obtained with the help of a rigorous analytical method known as integration in the term of stream function. The physical effects of magnetic and Hall devices, respectively, on the flow features are also considered in the present analysis. The physical influences of dominant hydro-mechanical parameters on the axial velocity, pressure gradient, trapping, volumetric fraction of nanofluid, heat and mass transfer phenomena are studied. The complex scenario of biomimetic propulsions are considered in boundary walls to boost the proficiency of peristaltic micropumps.

Complex cavity permeated with permeable media was influenced by magnetic field in current modeling. The flow encounters resistance in existence of Lorentz force and to improve thermal features, water was equipped with nano powders. Induce magnetic was ignored and to harness the permeability effect, non-Darcy approach was used. Current model acquired large attention in industry. For examine the correctness of code, the results of θ was compared with previous basic article and achieved graph illustrates nice conformity of current modeling. Two straight wall were adiabatic, lower and upper walls were confined to hot and cold temperature bath. Laminar flow was established and maximum of Ra is 105 and carrier fluid is incompressible. To incorporate the gravity force, Boussinesq principle was utilized. The bottom surface was subjected to hot source and gravity enforces the nanomaterial to go up and create rotating cell. The complex shape of isotherms pertains to stronger convection which is attributed to greater permeability. Involve of MHD, declines the distortion of isotherms and conduction becomes stronger in greater Ha. Rise of Ha leads to decrease in Ψ about 60% when Da = 100. Ψ augments about 100% with augment of Da when Ha = 0. Rise of Ha provides reduction in Nu about 11.48% and 9.37% when Da = 100 and 0.01, respectively. Rise of Rd offers 106.6% augmentation in Nu when Ha = 0. When Ha = 20 and Da = 100, rise of Ra leads to 99% augmentation in Nu.

A numerical analysis on the thermo-natural convection as well as entropy generation of Al2O3-H2O nanofluid enclosed by two circular cylinders in the presence of magnetic fields was performed. The internal hot cylinder is fitted with rectangular fins of different lengths. Irreversibilities related to the thermal effects, friction effects, magnetic effects were considered. FEM was selected as solving method. Results described the impact of active parameters on the thermo-natural convective flow and heat transfer behaviour as well as entropy generation characteristics. In addition, a basic economic analysis has been proposed to consider the cost of nanofluids in comparison to their contribution in enhancing heat transfer rate. Results show that significant effects of pertinent parameters e.g. Rayleigh, Hartmann, and fins' size on flow, heat transfer, and irreversibilities within annulus. It is also found that for low Rayleigh, irreversibility related to thermo-effects is predominant within the annulus, and by augmenting Rayleigh values, the irreversibility due to the thermo-effects is no longer the key contributor to overall entropy production. The magnetic forces help to increase thermo-effects irreversibility contribution to overall irreversibilities. Finally, thermal transfer enhancement in case of the presence of magnetic forces is found to be more costly in terms of nanofluid utilization.

To detect the influence of MHD on migration of hybrid nanopowders, CVFEM has been employed in this paper. Mixture of Fe3O4 and MWCNT was added in water and for calculating properties, experimental formulas were utilized. To increase the convective mode, porous media has been used and tank was experienced in the horizontal magnetic field. In governing equations, there exist two new terms, one for permeable media and the other for MHD effect. Such complex physics needs special numerical approach and CVFEM has been utilized for this goal. Final formulation of PDEs did not have pressure terms and the stream function scalar was introduced. As permeability of zone enhances, nanopowders can transfer faster and the interaction of them with wall enhances, so, Nusselt number augments as well as stream function. Besides, employing higher Ha, the force against the buoyancy force increases and the velocity of operating fluid declines which provides lower convective flow. With rise of Ha, stream function declines about 48% and Nu declines about 31.92% when [Formula: see text]. As Da rises, Nu rises about 33.43% when [Formula: see text]. Augment of Rd leads to augmentation of Nu.

In this paper, the simulations of Ansys HFSS and CST Microwave Studio for frequency selective surface (FSS) are discussed. The definitions of the Floquet modes, mesh density, and the distance between Floquet port and FSS surface affects the accuracy of the corresponding transmission coefficients. According to the example of a typical biplanar symmetric hybrid radome, the efficient simulation conditions of the two softwares for FSS are summarized.

The progressive and enhanced thermal mechanisms of nanoparticles has motivated researchers to give attention to this topic in recent years. The synthesizing and versatile applications of such materials include cooling and heating controlling processes, solar systems, energy production, nanoelectronics, hybrid-powered motors, cancer treatments, and renewable energy systems. Moreover, the bioconvection of nanofluids allows for some motivating applications in this era of bioengineering and biotechnology, such as biofuels, biosensors, and enzymes. With these interesting motivations and applications, this study elucidated upon the three-dimensional bioconvection flow of a Sisko fluid (base fluid) in the presence of a nanofluid over a stretched surface. The additional thermal features of radiation were also incorporated to modify the analysis. The rheological features of shear thinning and shear thickening that are associated with the Sisko nanofluid were comprehensively studied. The problem was formulated using highly nonlinear and coupled differential equations, which were numerically simulated via a shooting scheme. The salient physical applications of flow parameters were graphically underlined in view of shear-thinning and shear-thickening scenarios. The results showed that a decrease in velocity in the presence of buoyancy ratio forces was more conducive to the shear-thinning phenomenon. The increase in temperature profile due the thermal Biot number and surface heating source parameter seemed to be more inflated in the shear-thinning scenario. A lower motile microorganism profile was noted for the bioconvection Lewis number.

The growing development in the thermal engineering and nano-technology, much attention has been paid on the thermal properties of nanoparticles which convey many applications in industrial, technological and medical era of sciences. The noteworthy applications of nano-materials included heat transfer enhancement, thermal energy, solar systems, cooling of electronics, controlling the heat mechanisms etc. Beside this, entropy generation is an optimized scheme which reflects significances in thermodynamics systems to control the higher energy efficiency. On this end, present work presents the slip flow of Jeffrey nanofluid over a stretching sheet with applications of activation energy and viscous dissipation. The entropy generation features along with Bejan number significance is also addressed in present analysis. Buongiorno model of nanofluid is used to discuss the heat and mass transfer. The formulated flow equations are attained into non-dimensional form. An appropriate ND MATHEMATICA built-in scheme is used to find the solution. The solution confirmation is verified by performing the error analysis. For developed flow model and impacted parameters, a comprehensive graphical analysis is performed. It is observed that slip phenomenon is used to decays the velocity profile. Temperature and concentration are in direct relation with Brownian motion parameter and activation energy respectively. Entropy and Bejan number have same results for greater diffusion parameter.

Iron pyrite has received significant attention due to its high optical absorption. However, the loss of open circuit voltage (Voc) prevents its further application in photovoltaics. Herein, we have studied the photophysics of pyrite by ultrafast laser spectroscopy to understand fundamental limitation of low Voc by quantifying photocarrier losses in high quality, stoichiometric, and phase pure {100} faceted pyrite nanocubes. We found that fast carrier localization of photoexcited carriers to indirect band edge and shallow trap states is responsible for major carrier loss. Slow relaxation component reflects high density of defects within the band gap which is consistent with the observed Mott-variable range hopping (VRH) conduction from transport measurements. Magnetic measurements strikingly show the magnetic ordering associated with phase inhomogeneity, such as FeS2−δ (0 ≤ δ ≤ 1). This implies that improvement of iron pyrite solar cell performance lies in mitigating the intrinsic defects (such as sulfur vacancies) by blocking the fast carrier localization process. Photocarrier generation and relaxation model is presented by comprehensive analysis. Our results provide insight into possible defects that induce midgap states and facilitate rapid carrier relaxation before collection. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

In this paper, we synthesize three Re(I) complexes of Re(CO)3(PPO)Br, Re(CO)3(PTO)Br, and Re(CO)3(PBI)Br, where PPO=2-phenyl-5-(pyridin-2-yl)-1,3,4-oxadiazole, PTO=2-(pyridin-2-yl)-5-p-tolyl-1,3,4-oxadiazole, PBI=2-(pyridin-2-yl)-1H-benzo[d]imidazole. Their single crystals and photophysical properties are measured and discussed in detail. The correlation between ligand structure and corresponding PL characteristics of Re(I) complex has been investigated. It is found that a ligand with strong electron-donor can efficiently increase both absorption and emissive energy of Re(I) complex. In addition, electron-rich ligand can increase the electron density of the complex and thus enhance the oscillator strength of electronic transition, improving the photoluminescence performance.

Based on the first-principles within the density functional theory, the geometric structures of perfect zinc blend ZnSe, that with Zn vacancies (Zn0.875Se) and Cu-doped ZnSe (Zn0.875Cu0.125Se) were optimized using the plane-wave ultrasoft pseudopotential method. The defect formation energy, band structure, density of states, Mulliken charges, and optical spectra were calculated and discussed in detail. The results demonstrated that in Zn0.875Se and Zn0.875Cu0.125Se systems, because of the introduction of the vacancy acceptor level or acceptor impurity level, the band gap is reduced, and the absorption peaks show a remarkable redshift. Cu doping into the ZnSe system was found to be relatively stable, while the monovacancy system was not.

A seedless hydrothermal method is developed to grow high density and vertically aligned ZnO micro/nanowire arrays with low defect density on metal films under the saturated nutrition solution. In particular, the mechanism of seedless method is discussed here. A buffer layer can be confirmed by transmission electron microscopy (TEM), which may release the elastic strain between ZnO and substrate to achieve this highly mismatched heteroepitaxial structures. Based on ZnO micro/nanowire arrays with excellent wettability surface, we prepared ZnO-FeS2-CuI p-i-n photodiode by all-solution processed method with the high rectifying ratio of 197 at ±1 V. Under AM 1.5 condition, the Jsc of 0.5 mA/cm2, on-off current ratio of 371 and fast photoresponse at zero bias voltage were obtained. This good performance comes from excellent collection ability of photogenerated electrons and holes due to the increased depletion layer width for p-i-n structure. Finally, the high responsivity around 900 nm shows the potential as near infrared photodetectors applications.

We report a simple method to produce a stable and repeatable photoanode for water splitting with a core-shell hematite (α-Fe2O3) nanorods system by combining spray pyrolysis and hydrothermal synthesis. Impedance spectroscopy revealed passivation of the surface states by the shell layer, which results in an increase of the charge injection through the hematite conduction band. In pristine hematite more holes are accumulated on the surface and the charge transfer to the electrolyte occurs through surface states, whereas in the core-shell hematite photoanode the majority of hole transfer process occurs through the valence band. As a result the photoactivity of the core-shell nanorods, 1.2 mA cm(-2), at 1.23 V vs RHE, is twice that of pristine hematite nanorods. The alteration of the interface energetics is supported by TEM, showing that the crystallinity of the surface has been improved by the deposition of the shell.

The correlation between channel mobility gain (Deltamu), linear drain-current gain (DeltaIdlin), and saturation drain-current gain (DeltaIdsat) of nanoscale strained CMOSFETs are reported. From the plots of DeltaIdlin versus DeltaIdsat and ballistic efficiency (Bsat,PSS), the ratio of source/drain parasitic resistance (RSD,PSS) to channel resistance (RCH,PSS) of strained CMOSFETs can be extracted. By plotting Deltamu versus DeltaIdlin, the efficiency of Deltamu translated to DeltaIdlin is higher for strained pMOSFETs than strained nMOSFETs due to smaller RSD,PSS-to-RCH,PSS ratio of strained pMOSFETs. It suggests that to exploit strain benefits fully, the RSD,PSS reduction for strained nMOSFETs is vital, while for strained pMOSFETs the DeltaIdlin -to-Deltamu sensitivity is maintained until RSD,PSS becomes comparable to/or higher than RCH,PSS

Channel backscattering characteristics of uniaxially strained nanoscale CMOSFETs are reported for the first time. Channel backscattering ratio increases and decreases under uniaxial tensile and compressive strain, respectively. It is found that in sub-100-nm devices, strain-induced modulation of carrier mean-free path for backscattering and reduction in k/sub B/T layer thickness are responsible for the different behaviors of backscattering ratio. Nevertheless, the source-side injection velocity improves irrespective of the strain polarities. The impact of channel backscattering ratio on drive current is also analyzed in terms of ballistic efficiency and injection velocity.

State-of-the-art low-K spacer technology featuring novel CVD-SiBCN material is demonstrated for the first time. A significant 20% CMOS ring speed enhancement is demonstrated with SiBCN (K=5.2) spacer, compared to Si3N4 (K=7.5) spacer, due to reduced fringing capacitance and enhanced strain effects by spacer-PSS and CESL techniques. Electron mobility is improved by 6% for long channel NMOS transistor and gm,max is increased by 11% for short 35 nm physical gate length NMOS using a preferable spacer structure that is comprised of a low stress SiBCN spacer on thin SiO2 liner and a final 600degC rapid thermal post-anneal. Superior GIDL and better gate leakage is obtained because low permittivity SiBCN alleviates gate-fringing field effects (GF effects), and device reliability is not adversely impacted by this new process.

We have demonstrated successfully the integration scheme of metallized source/drain extension (M-SDE) with state-of-the-art strained-Si technique. Drain currents of N-FET (Lgate = 40 nm) and P-FET (Lgate = 35 nm) with M-SDE can achieve 1620 muA/mum and 755 muA/mum at |VG-Vt| = |VD| = 1V, respectively. Superior characteristics of junction leakage and source/drain series resistance are also presented. For M-SDE CMOSFETs, the capability of exploiting strain more efficiently is corroborated by the improved stress sensitivity of linear drain current to mechanical stress. M-SDE CMOSFETs exhibit higher stress sensitivity as scaling the gate length.

Channel backscattering ratios of PMOSFETs with various embedded SiGe source/drain structures are analyzed in terms of the scattering theory. We found that both the backscattering ratio and injection velocity are greatly influenced by the location and recess depth of SiGe source/drain. Although the strain-enhanced injection velocity is beneficial to the current gain, the accompanying backscattering ratio increase adversely impacts the overall performance, and therefore a trade-off exists between injection velocity and backscattering ratio during the optimization of such strain technique. The mechanism of increased backscattering ratio under uniaxial compressive strain is also investigated

The channel backscattering ratios as well as the ballistic efficiency of strained CMOSFETs were studied for both nondegenerate and degenerate-limited cases. We found that the simple nondegenerate assumption can predict strain-induced change of ballistic efficiency with fair accuracy. The mechanism of drain current dependence on strain-induced mobility change was also investigated based on channel backscattering theory.

The influence of uniaxial process-induced strain on carrier channel backscattering in nanoscale MOSFETs is reported for the first time. It is observed that the backscattering ratio can be reduced by uniaxial tensile strain while it is increased by uniaxial compressive strain mainly due to strain-induced modulation in mean-free-path for backscattering and slight decrease in kBT layer thickness. Nevertheless, both strain polarities improve source-side injection velocity because of reduced carrier effective mass. Impact to current drive under uniaxial strain is analyzed in terms of mean-free-path, kBT layer thickness, ballistic efficiency and injection velocity.

A highly manufacturable SOI technology with strained silicon and FinFET-like devices is demonstrated for sub-65 nm device scaling. This technology, named FIP-SOI (FinFET/FD/PD-SOI), achieves (1) performance gain of 10-35% for N-MOS using strained silicon compared with non-strained SOI, (2) bulk-to-SOI design portability without additional structures such as the body-contacted transistor scheme, and (3) superior scalability by the incorporation of FinFET-like devices. All feature size scaling (gate length, channel width, and SOI body thickness) will further enhance channel strain in the FIP-SOI. Scaling-strengthened strain is demonstrated for the first time.

During the scanning of magnetic resonance imaging (MRI) system, the main acoustic noise source comes from the gradient coils. The gradient coils are turned on and off repeatedly, thus producing noise within the coil. With increasing magnetic field strength, the noise also increases. The primary method to reduce the noise is to decrease the distribution of the Lorentz forces. Target field (TF) method is very important for designing gradient coils which have been used in MRI and other applications. Many works based on the Turner’s traditional TF method have been proposed. In this paper, a target field method combined with vibration control has been presented to analyze the deflection of a cylindrical z-gradient coil because of the Lorentz forces. Simulation results via Matlab show that the maximum vibration amplitude can be reduced effectively by the new design method proposed in this paper.