Generalisation of the eddy-dissipation concept for jet flames with low turbulence and low Damköhler number

Moderate or intense low oxygen dilution (MILD) combustion has been the focus of a range of fundamental experimental and numerical studies. Reasonable agreement between experimental and numerical investigations, however, requires finite-rate chemistry models and, often, ad hoc model adjustment. To remedy this, an adaptive eddy dissipation concept (EDC) combustion model has previously been developed to target conditions encountered in MILD combustion; however, this model relies on a simplified, pre-defined assumption about the combustion chemistry. The present paper reports a generalised version of the modified EDC model without the need for an assumed, single-step chemical reaction or ad hoc coefficient tuning. The results show good agreement with experimental measurements of two CH₄/H₂ flames in hot coflows, showing improvements over the standard EDC model as well as the previously published modified EDC model. The updated version of the EDC model also demonstrates the capacity to reproduce the downstream transition in flame structure of a MILD jet flame seen experimentally, but which has previously proven challenging to capture computationally. Analyses of the previously identified dominant heat-release reactions provide insight into the structural differences between a conventional autoignitive flame and a flame in the MILD combustion regime, whilst highlighting the requirement for a generalised EDC combustion model.     

Design and numerical analysis for low birefringence silica on silicon waveguides

A new fabrication technology for three-dimensionally buried silica on silicon optical waveguide based on deep etching and thermal oxidation is presented. Using this method, a silicon layer is left at the side of waveguide. The stress distribution and effective refractive index are calculated by using finite element method and finite different beam propagation method, respectively. The results indicate that the stress of silica on silicon optical waveguide fabricated by this method can be matched in parallel and vertical directions and stress birefringence can be effectively reduced due to the side-silicon layer.     

Double-pass ytterbium-doped fiber amplifier with high gain coefficient and low noise figure

We have proposed and demonstrated a double-pass ytterbium-doped fiber amplifier using an optical circulator and a fiber Bragg grating as reflector. When the signal has passed through the ytterbium-doped fiber once, it reflects off a 0.2-nm passive fiber Bragg grating filter. This reduces amplified spontaneous emission (ASE) noise from the first pass. The input signal light is amplified both forward and backward through ytterbium-doped fiber. With this double-pass configuration, 1053.15-nm unsaturated signal gain of 28 dB, gain coefficient of 1.1 dB/mW, and noise figure of less than 4 dB are achieved at 977-nm pump power of 68 mW. It is also found that this double-pass configure provides enhancing gain coefficient and improving noise figure by comparison with single-pass configuration.     

Total spin-dependent p̄d cross sections at low and intermediate energies

There may be unique (“smoking-gun”) signatures of the breakdown of CPT symmetry, induced in some models of Quantum Gravity entailing decoherence for quantum matter. Such effects can be observed in entangled states of neutral mesons via modifications of the respective Einstein-Podolsky-Rosen (EPR) correlators (“ω-effect”). In the talk I discuss experimental signatures and bounds of the ω-effect in Φ- and B-factories, and argue that the effect might be falsifiable at the next generation facilities.     

The ß-decay of 48Cr and low energy collective M1 transitions

A measured half-life for the ß-decay of ⁴⁸Cr is used to provide information on the spin contribution to a collective isovector M1 transition.     

Neutron–antineutron oscillation and baryonic majoron: low scale spontaneous baryon violation

We discuss the possibility that baryon number B is spontaneously broken at low scales, of the order of MeV or even smaller, inducing the neutron–antineutron oscillation at the experimentally accessible level. An associated Goldstone particle–baryonic majoron can have observable effects in neutron to antineutron transitions in nuclei or dense nuclear matter. By extending baryon number to an anomaly-free \(B-L\) symmetry, the baryo-majoron can be identified with the ordinary majoron associated with the spontaneous breaking of lepton number, and it can have interesting implications for neutrinoless \(2\beta \) decay with the majoron emission. We also discuss the hypothesis that baryon number can be spontaneously broken by QCD itself via the six-quark condensates.     

Radiation loss in a compound plasma system with high and low temperature regions

A code has been developed for calculating the non-coronal radiation of impurity in a compound plasma system which consists of high and low temperature regions. The radiation loss of impurity carbon in this system is calculated and analysed. The cooling rate in this system is smaller than that in a homogeneous plasma system due to the particle exchange between the two regions of the system. The volumetric radiation is much bigger in the low temperature region than in the high temperature region because of the relatively low temperature and high electron density, despite the much smaller volume.     

Mechanisms of bulk diffusion at “high” and “low” temperatures

A phenomenological model has been proposed for bulk self-diffusion and diffusion of interstitial atoms in the ranges of high (T > T _D) and low (T < T _D) temperatures (where T _D is Debye temperature). It has been shown that the mechanisms of diffusion at high and low temperatures differ significantly. In the high-temperature range, the diffusion is provided by fluctuations, which can be described in terms of local melting, i.e., the formation of a “liquid diffusion channel.” In the low-temperature range, when melting for some reasons is hindered, the diffusion is due to the fluctuation formation of a “hollow diffusion channel.” The calculation of the activation energies of these processes in the case of self-diffusion agrees well with the experiment in the temperature range T > T _D and has demonstrated that the activation energy increases significantly at T < T _D. The calculation of the activation energy for diffusion of interstitial atoms in bcc metals agrees well with the experiment in the entire temperature range and provides an explanation of the decrease in the activation energy of diffusion at low temperatures.     

Superdeformed structures and low Ω parity doublet in Ne-S nuclei near neutron drip-line

The structures of Ne, Na, Mg, Al, Si, P and S nuclei near the neutron drip-line region are investigated in the frame-work of relativistic mean field theory and non-relativistic Skyrme Hartree-Fock formalism. The recently discovered nuclei ⁴⁰Mg and ⁴²Al, which are beyond the drip-line predicted by various mass formulae are located within these models. We find many largely deformed neutron-rich nuclei, whose structures are analyzed. From the structure anatomy, we find that at large deformation low orbits of opposite parities (e.g. $\frac{1} {2}^ +$ and $\frac{1} {2}^ -$ ) occur close to each other in energy.     

Exponential ionic drift: fast switching and low volatility of thin-film memristors

We investigate the exponential dependence of switching speeds in thin-film memristors for high electric fields and elevated temperatures. An existing nonlinear ionic drift model and our simulation results explain the very large ratios for the state lifetime to switching speed experimentally observed in devices for which resistance switching is due to ion migration. Given the activation barriers of the drifting species, it is possible to predict the volatility and switching time for various material systems.     

Pressure broadening of methane lines in the 6190Åand 6825Åbands at room and low temperatures

Measurements of pressure broadened half-widths have been performed for one vibration-rotation line in the 6190Åmethane band and one vibration-rotation line in the 6825Åmethane band. Self-, nitrogen-, hydrogen- and helium-broadening have been measured over a temperature range of 77–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas.     

20-Gbps low cost WDM-OFDM-PON downstream transmission with tunable filter and linear APD module

This letter presents a low cost solution for wavelength division multiplexed orthogonal frequency division multiplexed passive optical network(WDM-OFDM-PON)with widely tunable optical filter and linear small form-factor pluggable(SFP)module.With 9-nm tunable range from 1551 to 1560 nm,the tunable filter can support up to 10-channel 100-GHz spacing WDM PON system.A linear avalanche photodiode(APD)based SFP+module is designed for optical OFDM signal demodulation,which can provide better receiver performance compared with limiting APD module.Experimental results show that～34 dB power budget can be achieved in 4×5-Gbps WDM-OFDM-PON system,which can satisfy the transmission requirements of next generation PON system.     

Lattice constants and anisotropic microstrain at low temperature in 242Pu–Ga alloys

We attempted to characterize by neutron powder diffraction the monoclinic α′ phase that is known to form at low temperatures in dilute Pu–Ga alloys. This attempt was unsuccessful, as we did not detect any transformation to the α′ phase, but instead observed a line-broadening effect in the fcc?δ?phase. This effect is large enough to be visible in the raw diffraction data and is highly anisotropic in crystal space. The onset temperature of the line broadening (150?K) coincides with previous observations of the δ–α′ transformation. Bulk α′ was not observed. We believe that the development of α′ nuclei creates a spatially inhomogeneous stress distribution in the?δ?matrix, which in turn exhibits an anisotropic response, governed by its elastic anisotropy. We have analysed this observation of anisotropic microstrains in terms of the fictive microstresses required to produce them by elastic deformation. During the course of this work, we found a pseudo-isotope effect in the room temperature lattice constants of Pu–Ga alloys. The alloys made from nominal ²⁴²Pu isotope show systematically higher lattice constants than the corresponding ²³⁹Pu alloys, and the size of the effect is proportional to the Ga concentration. We believe that this effect is associated with the higher levels of radiation damage from isotopic impurities in the ²⁴²Pu alloys.     

Impact of γ-rays on constructional,optical and thermal behavior of alkaline and non alkaline low density polyethylene

ABSTRACT

In this study, we investigated the graft copolymerization of methyl methacrylate (MMA) onto low-density polyethylene (LDPE) in the presence of aniline as an inhibitor by gamma radiation. An alkaline treatment was carried out for the prepared graft copolymer. The structural properties of the prepared samples were examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD peaks were slightly shifted, indicating an interaction between MMA and the polyethylene matrix. The morphology of the samples confirmed the homogenous grafted phase scattered onto the LDPE surface. Analysis of the absorption spectra indicated an allowed indirect transition mechanism. The Urbach energy (E_U) results showed that the value of the E_U for grafted LDPE was found to be higher than that of pure LDPE—up to 15?kGy irradiation dose, although this value decreases upon grafting. However, the value of the E_U for alkaline-treated grafted films decreases systematically by increasing the degree of grafting. The thermogravimetric analysis (TGA) of the sample indicated that the thermal stability of LDPE samples is significantly changed by grafting MMA onto it. Horowitz and Metzger's models were utilized to measure the activation energy of the thermal decomposition of all samples.     

The effect of metallic environment and low temperature on the 253Es α decay rate

In recent publications it has been pointed out that the α decay of transuranic elements in nuclear waste can be considerably speeded up by putting them into metals. The proposed mechanism is based on the effect of electron screening of radioactive nuclei (according to the Debye electron plasma model), which grows enhanced as temperature decreases. To verify the predicted phenomenon, half-lives of ²⁵³Es nuclei implanted in a metallic iron foil were measured at the temperature from 4 K to 50 mK. The results agree with the room-temperature data reported in the literature; no temperature dependence of the half-life was found within the error of ≈2%.     

μ+SR and Mössbauer studies of low dimensional magnetic ordering in ilvaite

Ilvaite reveals a quasi one dimensional ferromagnetic order along Fe chains between 50–120K. Both Mössbauer spectroscopy and ⁺SR reveal the onset of long range order below 120K with spin dynamics in the MHz range which is interpreted with relatively slowly moving wide domain boundaries. Below 50K the individual chains couple antiferromagnetically, yet a considerable fraction of dynamical spins is detected from ⁺SR down to low temperature.Work supported by the German Federal Minister of Research and Technology (BMFT) under contract Nr. 03-LI3-BRA.     

Plasma assisted molecular beam epitaxial growth of GaN with low growth rates and their properties

A systematic investigation on PA-MBE grown GaN with low growth rates(less than 0.2μm/h)has been conducted in a wide growth temperature range,in order to guide future growth of sophisticated fine structures for quantum device applications.Similar to usual growths with higher growth rates,three growth regions have been revealed,namely,Ga droplets,slightly Ga-rich and N-rich 3D growth regions.The slightly Ga-rich region is preferred,in which GaN epilayers demonstrate optimal crystalline quality,which has been demonstrated by streaky RHEED patterns,atomic smooth surface morphology,and very low defect related yellow and blue luminescence bands.The growth temperature is a critical parameter to obtain high quality materials and the optimal growth temperature window(~700-760℃)has been identified.The growth rate shows a strong dependence on growth temperatures in the optimal temperature window,and attention must be paid when growing fine structures at a low growth rate.Mg and Si doped GaN were also studied,and both p-and n-type materials were obtained.