Comment and reply on the 'assessment of combustion and submodels for turbulent nonpremixed hydrocarbon flames'

In deriving the flamelet model for nonpremixed combustion certain terms, but not the unsteady term, are assumed to be negligible. This results in a relation between all reacting scalars and the mixture fraction as independent variable. An ideal test of the flamelet assumption can be based on direct numerical simulation (DNS) data, if all reacting scalars are conditioned on mixture fraction and conditional moments are evaluated. The fundamental assumption of the flamelet model are unwillingly justified. The unsteady and steady formulations of the same equations are compared and found that unsteadiness is important in an unsteady simulation.

Transient growth and triggering in the horizontal Rijke tube Matthew

This theoretical paper examines a non-normal and non-linear model of a horizontal Rijke tube. Linear and non-linear optimal initial states, which maximize acoustic energy growth over a given time from a given energy, are calculated. It is found that non-linearity and non-normality both contribute to transient growth and that, for this model, linear optimal states are only a good predictor of non-linear optimal states for low initial energies. Two types of non-linear optimal initial state are found. The first has strong energy growth during the first period of the fundamental mode but loses energy thereafter. The second has weaker energy growth during the first period but retains high energy for longer. The second type causes triggering to self-sustained oscillations from lower energy than the first and has higher energy in the fundamental mode. This suggests, for instance, that low frequency noise will be more effective at causing triggering than high frequency noise.

On the origin and evolution of new genes-a genomic and experimental perspective

The inherent interest on the origin of genetic novelties can be traced back to Darwin. But it was not until recently that we were allowed to investigate the fundamental process of origin of new genes by the studies on newly evolved Young genes. Two indisp

Morphometric and meristic studies of the spotted estuarine prawn, Macrobrachium equidens (Dana) of Vembanad Lake, Kerala State

The paper reports on the statistical analysis of growth pattern and meristic studies of body parts of the spotted estuarine prawn, Macrobrachium equidens (Dana) of Vembanad Lake, Kerala State. The results showed that the growth pattern of carapace length, telson length, ischium length and dactylus length in relation to total length were significantly different between the sexes at slope itself (at 1% level) and growth pattern of abdominal length, merus length, carpus length, propodus length and palm length were significant at elevations (5%, 1% levels). The average sizes of all these characters were greater in males than in females. Regression equations have been calculated for the characters and presented in the text. Among the characters of the carapace, rostrum length, post-orbital length showed significant difference between sexes at 1% level (slope value) and width of carapace at 1% level (elevations). The average sizes of all these characters were higher in males. Among the meristic characters studied, the species exhibited sexual dimorphism with regard to dorsal teeth, post-orbital teeth and ventral teeth. The fundamental data generated is essential for establishing the species status as well as it is useful for making comparison with other species.

The interaction of elasticity and rocking in flexible structures allowed to uplift

Numerous structures uplift under the influence of strong ground motion. Although many researchers have investigated the effects of base uplift on very stiff (ideally rigid) structures, the rocking response of flexible structures has received less attention. Related practical analysis methods treat these structures with simplified 'equivalent' oscillators without directly addressing the interaction between elasticity and rocking. This paper addresses the fundamental dynamics of flexible rocking structures. The nonlinear equations of motion, derived using a Lagrangian formulation for large rotations, are presented for an idealized structural model. Particular attention is devoted to the transition between successive phases; a physically consistent classical impact framework is utilized alongside an energy approach. The fundamental dynamic properties of the flexible rocking system are compared with those of similar linear elastic oscillators and rigid rocking structures, revealing the distinct characteristics of flexible rocking structures. In particular, parametric analysis is performed to quantify the effect of elasticity on uplift, overturning instability, and harmonic response, from which an uplifted resonance emerges. The contribution of stability and strength to the collapse of flexible rocking structures is discussed. © 2012 John Wiley & Sons, Ltd.

Accurate screened exchange band structures for the transition metal monoxides MnO, FeO, CoO and NiO.

We report calculations of the band structures and density of states of the four transition metal monoxides MnO, FeO, CoO and NiO using the hybrid density functional sX-LDA ('screened exchange local density approximation'). Late transition metal oxides are prototypical examples of strongly correlated materials, which pose challenges for electronic structure methods. We compare our results with available experimental data and show that our calculations generally yield accurate predictions for the fundamental band gaps and valence bands, in favourable agreement with previously reported theoretical studies. For MnO, the band gaps are still underestimated, suggesting additional many-body effects that are not captured by our screened hybrid functional approach.

Parametrically excited MEMS vibration energy harvesters with design approaches to overcome the initiation threshold amplitude

Resonant-based vibration harvesters have conventionally relied upon accessing the fundamental mode of directly excited resonance to maximize the conversion efficiency of mechanical-to-electrical power transduction. This paper explores the use of parametric resonance, which unlike the former, the resonant-induced amplitude growth, is not limited by linear damping and wherein can potentially offer higher and broader nonlinear peaks. A numerical model has been constructed to demonstrate the potential improvements over the convention. Despite the promising potential, a damping-dependent initiation threshold amplitude has to be attained prior to accessing this alternative resonant phenomenon. Design approaches have been explored to passively reduce this initiation threshold. Furthermore, three representative MEMS designs were fabricated with both 25 and 10 μm thick device silicon. The devices include electrostatic cantilever-based harvesters, with and without the additional design modification to overcome initiation threshold amplitude. The optimum performance was recorded for the 25 μm thick threshold-aided MEMS prototype with device volume ∼0.147 mm3. When driven at 4.2 ms -2, this prototype demonstrated a peak power output of 10.7 nW at the fundamental mode of resonance and 156 nW at the principal parametric resonance, as well as a 23-fold decrease in initiation threshold over the purely parametric prototype. An approximate doubling of the half-power bandwidth was also observed for the parametrically excited scenario. © 2013 IOP Publishing Ltd.

Durability indicators of SCC towards performance-based specifications for the durability of SCC

The fundamental principle behind the development of SCC has been the nanoscale tailoring of cementitious matrices. Although self-compacting concrete (SCC) is currently used in many countries, there is a fundamental lack of the intrinsic durability of the material itself. The scope of the current paper is to present the outcomes of a research study on some principal indicators (porosity and capillary absorption) that define the durability of SCC, and how these are compared with the corresponding parameters of conventional concrete. Furthermore, this paper investigates the addition of industrial by-products, such as fly-ash or lime powder, to SCC mixtures and their effect on the durability indicators.

Optical properties of the E-0+Delta(0) energy level higher than the bandgap of GaAs studied by micro-photoluminescence technique

Using micro-photoluminescence technique, we observed a new photoluminescence peak about 0.348 eV above the bandgap of GaAs (E-0). By analyzing its optical characteristics, we assigned this peak to the nonequilibrium luminescence emission from the E-0 + Delta(0) bandgap in semi-insulated GaAs, which was further verified by Raman results. The observed polarization, excitation power dependence and temperature dependence of the photoluminescence spectra from the E-0 + Delta(0) energy level were very similar to those from the E-0 of GaAs. This mainly resulted from the common conduction band around Gamma(6) that was involved in the two optical transition processes, and indicated that the optical properties of bulk GaAs were mainly determined by the intrinsic properties of the conduction band. Our results demonstrated that the micro-photoluminescence technique is a powerful tool to investigate the high energy states above the fundamental bandgap in semiconductor materials.

Temperature dependence of the Raman-active modes in the nonpolar a-plane GaN film

Temperature dependences of the polarized Raman scattering spectra in the backscattering configuration of the nonpolar a-plane (or [11 (2) over bar0]-oriented) GaN thin film are analyzed in the range from 100 to 570 K. The nonpolar a-plane GaN film is grown on an r-plane [or (1 (1) over bar 02)-oriented] sapphire substrate by metal organic chemical vapor deposition. The spectral features of the Raman shifts, intensities, and linewidths of the active phonons modes A(1)(TO), E-1(TO), and E-2(high) are significantly revealed, and corresponding temperature coefficients are well deduced by the empirical relationships. With increasing the measurement temperature the Raman frequencies are substantially redshifted and the linewidths gradually broaden. The compressive-strain-free temperature for the nonpolar a-plane GaN film is found to be at about 400 K. Our studies will lead to a better understanding of the fundamental physical characteristics of the nonpolar GaN film. (c) 2007 American Institute of Physics.

High-power AlGaInP laser diodes with current-injection-free region near the laser facet

A high-power AlGaInP laser diode with current-injection-free region near the facet is successfully fabricated by metaorganic chemical vapor deposition (MOCVD) using the (100) direction n-GaAs substrates with a misorientation of 15 deg toward the (011) direction. The maximum continuous wave output power is about 90 mW for the traditional structure. In comparison, the maximum output power is enhanced by about 67%, and achieves 150 mW for LDs with current-infection-free regions. The fundamental transverse-mode operation is obtained up to 70 mW. Output characteristics at high temperatures are also improved greatly for an LD with a current-injection-free region, and the highest operation temperature is 70 C at 50 mW without kink. The threshold current is about 33 mA, the operation current and the slope efficiency at 100 mW are 120 mA and 0.9 mW/mA, respectively. The lasing wavelength is 658.4 nm at room-temperature 50 mW. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

Mode-coupling analysis of three-dimensional microdisk resonators by the finite-difference time-domain technique

Quality factor enhancement due to mode coupling is observed in a three-dimensional microdisk resonator. The microdisk, which is vertically sandwiched between air and a substrate, with a radius of 1 mu m, a thickness of 0.2 mu m, and a refractive index of 3.4, is considered in a finite-difference time-domain (FDTD) numerical simulation. The mode quality factor of the fundamental mode HE71 decreases with an increase of the refractive index of the substrate, n(sub), from 2.0 to 3.17. However, the mode quality factor of the first-order mode HE72 reaches a peak value at n(sub) = 2.7 because of the mode coupling between the fundamental and the first-order modes. The variation of mode field distributions due to the mode coupling is also observed. This mechanism may be used to realize high-quality-factor modes in microdisks with high-refractive-index substrates. (c) 2006 Optical Society of America.

Resonant frequencies and quality factors for optical equilateral triangle resonators calculated by FDTD technique and the Pade approximation

The mode wavelength and quality factor (Q-factor) for resonant modes in optical equilateral triangle resonators (ETR's) are calculated by the finite-difference time-domain (FDTD) technique and the Pade approximation, For an ETR with the side length of 3 mu m and the refractive index of 3.2, we get the mode wavelength interval of about 70 nm and the Q-factor of the fundamental mode over 10(3), The results show that the ETR is suitable to realize single-mode operation, and that the radiation loss in the corner regions of ETR is rather low, In addition, the numerical results of the mode wavelength agree very well with our analytical formula.

Measurement of the optical transmission modes and losses of the poled guest-host polymer NAEC/PEK-c planar waveguides

The polyetherketone (PEK-c) guest-host polymer planar waveguides doped with (4'-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The waveguide films were poled by corona-onset poling at elevated temperature (COPET), and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. By using the prism-in coupling method, the dark-line spectrum given by the reflected intensity versus the angle of incidence have been obtained, and the optical transmission losses of mth modes have been measured for the poled polymer waveguides at lambda = 632.8 nm. The measurement result showed that the optical loss of the fundamental mode is less than 0.7 dB cm(-1) for the TE polarization. (C) 2000 Elsevier Science Ltd. All rights reserved.

Interference effects in differential reflectance spectra of the GaAs epilayers grown on Si substrate

We report the observation of oscillating features in differential reflectance spectra from the GaAs epilayer grown on Si substrate in the energy range both below and above the fundamental band gap. It is demonstrated that the oscillating features are due to the difference in the interference between two neighboring areas of the sample. The interference arises from two light beams reflected from different interfaces of the sample. The calculated spectra in the nonabsorption region are in good agreement with measured data. It is shown that the interference effect can be used as a sensitive method to characterize the inhomogeneity of the semiconductor heterostructures. (C) 1998 American Institute of Physics. [S0021-8979(98)08723-4].