Feasibility of “intermittent” active control of combustion instabilities in liquid fueled combustors using a “smart” fuel injector

This paper describes an experimental investigation of the feasibility of an “intermittent” active control approach for suppressing combustion instabilities in liquid fueled combustors. The developed controller employs a “smart” fuel injector that can modify the spray properties in response to changes in combustor operating conditions. This action weakens or breaks up the coupling between the combustion process and combustor acoustic modes oscillations, thus preventing the excitation of large amplitude instabilities. This approach differs significantly from previously proposed active control methods, both in concept and implementation, as it requires only “intermittent” modification of the combustion process by a single control action as opposed to the continuous action required by most other active control methods. The “smart” fuel injector used in this study consisted of a double-staged, air-assisted atomizer in which counter swirling, primary (inner stage) and secondary (outer stage) air streams were supplied to the injector through separate sets of tangentially oriented orifices. Control of the ratio of air mass flow rates supplied to these two stages, by use of a diverter valve, resulted in significant changes in the spray shape and its axial, tangential, and radial velocity components. This variation in spray properties of the “smart” injector was characterized for different values of the inner to outer air flow rate ratio in cold flow tests with a PDPA system. These results were then correlated with the characteristics of the “intermittently” controlled combustor. Measured quantities included the instability amplitudes, axial dependence of the mean and oscillatory heat release amplitudes, and the characteristics of the recirculation zones, which were all shown to depend on the fuel spray properties. The results of this study demonstrate the feasibility of using “smart” fuel injectors with capabilities for varying the combustion process characteristics to reduce the amplitudes of detrimental combustion instabilities in real engines to acceptable levels.     

Novel comprehension of “common path” principle

The idea of “common path” has been widely applied in optical instrument design for 30 years and even today. But the meaning of “common path” has not yet been explained clearly and sometimes confusion has been created. In this paper an “adaptive principle” is proposed and recommended on optical instrument system. It suggests that the designer not only arranges the measurement system to obtain measurement signal but also sets a channel to give prediction of noise or disturbance in real time or short term. Such a recommendation is based on the recent studies on nonlinear dynamics and atmospheric disturbance by means of experiments as well as theoretical analysis.     

K–K excitations on as “primary” superfields

We show that the K–K spectrum of IIB string on is described by “twisted chiral” superfields, naturally described in “harmonic superspace”, obtained by taking suitable gauge singlets polynomials of the D3-brane boundary superconformal field theory.To each p-order polynomial is associated a massive K–K short representation with states. The quadratic polynomial corresponds to the “supercurrent multiplet” describing the “massless” bulk graviton multiplet.     

Orientational dynamics of superfluid He: A “two-fluid” model. II. Orbital dynamics

We present a phenomenological theory of the homogeneous orbital dynamics of the class of “separable” anisotropic superfluid phases which includes the ABM state generally identified with ³He-A. The theory is developed by analogy with the spin dynamics described in the first paper of this series; the basic variables are the orientation of the Cooper-pair wavefunction (in the ABM phase, the l-vector) and a quantity K which we visualize as the “pseudo-angular momentum” of the Cooper pairs but which must be distinguished, in general, from the total orbital angular momentum of the system. In the ABM case l is the analog of d in the spin dynamics and K of the “superfluid spin” S_p. Important points of difference from the spin case which are taken into account include the fact that a rotation of l without a simultaneous rotation of the normal-component distribution strongly increases the energy of the system (“normal locking”), and that the equilibrium value of K is zero even for finite total angular momentum. The theory does not claim to handle correctly effects associated with any intrinsic angular momentum arising from particle-hole asymmetry, but it is shown that the magnitude of this quantity can be estimated directly from experimental data and is extremely small; also, the Landau damping does not emerge automatically from the theory, but can be put in in an ad hoc way. With these provisos the theory should be valid for all frequencies irrespective of the value of ωτ. (Δ = gap parameter, τ = quasi-particle relaxation time.) It disagrees with all existing phenomenological theories of comparable generality, although the disagreement with that of Volovik and Mineev is confined to the “gapless” region very close to T_c.The phenomenological equations of motion, which are similar in general form to those of the spin dynamics with damping, involve an “orbital susceptibility of the Cooper pairs” χ_orb(T). We give a possible microscopic definition of the variable K and use it to calculate χ_orb(T) for a general phase of the “separable” type. The theory is checked by inserting the resulting formula in the phenomenological equations for ωτ 1 and comparing with the results of a fully microscopic calculation based on the collisionless kinetic equation; precise agreement is obtained for both the ABM and the (real) polar phase, showing that the complex nature of the ABM phase and the associated “pair angular momentum” is largely irrelevant to its orbital dynamics. We note also that the phenomenological theory gives a good qualitative picture even when ω Δ(T), e.g., for the flapping mode near T_c. Our theory permits a simple and unified calculation of (1) the Cross-Anderson viscous torque in the overdamped regime, (2) the flapping-mode frequency near zero temperature, (3) orbital effects on the NMR, both at low temperatures and near T_c, (4) the orbit wave spectrum at zero temperature (this requires a generalization to inhomogeneous situations which is possible at T = 0 but probably not elsewhere). We also discuss the possibility of experiments of the Einstein-de Haas type. Generally speaking, our results for any one particular application can be also obtained from some alternative theory, but in the case of orbital and spin relaxation very close to T_c (within the “gapless” region) our predictions, while somewhat tentative and qualitative, appear to disagree with those of all existing theories. We discuss briefly how our approach could be extended to apply to more general phases.     

Defects analysis of Al/Si artificial nanocluster with moiré fringes

In this paper, it is demonstrated the defects play a very important role in determining the quality of artificial nanoclusters grown. The surface strain (stress) distribution around defects in Al artificial nanocluster is analyzed by Moiré fringes pattern. The moiré fringes generated by scanning lines in monitor and nanocluster array can be used as a “magnifier” to study surface imperfections with scanning tunneling microscopy (STM). As moiré fringes’ exist in many ordered nanostructures and adsorbate systems, the method is expected to have wide applications.     

“Alternative medical therapy” use among singers: Prevalence and implications for the medical care of the singer

Singers are extremely conscious of health problems that affect their voices and well-being and often take an active role in seeking care for these problems. They frequently seek treatment from providers or with modalities considered “alternative” to traditional medical care. A survey of singers was completed to elucidate their attitudes and practices regarding “alternative modalities” of medical care. Frequently singers will self-medicate or take advice from people not well versed in the special needs of a professional voice user. They will fail to share this information with the physician when seeking “traditional” medical care. These practices may predispose the singer to suboptimal or even dangerous care. These results are discussed, as well as the implications for the medical physician treating the singer. The possible detrimental pharmacologic effects of “natural therapies” widely used by singers are presented, with special attention to the particular concerns for the professional singer     

Schlieren “PIV” for turbulent flows

The possibility of using commercial PIV equipment combined with schlieren optics to measure the velocity fields of turbulent flows is explored. Given a sufficiently high Reynolds number and adequate refractive flow differences, turbulent eddies can serve as the PIV “particles” in a schlieren image or shadowgram. The PIV software analyzes motion between consecutive schlieren or shadowgraph frames to obtain velocity fields. Velocimetry examples of an axisymmetric sonic helium jet in air and a 2D turbulent boundary layer at Mach 3 are shown. Due to optical path integration, axisymmetric flows require the inverse Abel transform to extract center-plane velocity data. Conditions for optimum schlieren sensitivity are examined. In its present embodiment, “schlieren PIV” is not useful for laminar flows nor for fully 3D flows. Otherwise it functions much like standard PIV under conditions where individual particles are not resolved and velocimetry is instead based on correlation of the motion of turbulent structures. “Schlieren PIV” shows significant promise for general refractive turbulent flow velocimetry if its integrative nature can be overcome through sharp-focusing optics.     

Structure of monolayer silica on Mo(1 1 2) investigated by rainbow scattering under axial surface channeling

The structure of a monolayer crystalline silica film grown on a Mo(1 1 2) substrate is investigated via grazing scattering of fast atoms. For scattering along low indexed directions in the surface plane (“axial surface channeling”) the corrugation of the interaction potential leads to an azimuthal out-of plane scattering with an intensity enhancement for the maximum deflection angle, the so called “rainbow”. From the comparison of the experimental angular distributions for scattered projectiles with classical trajectory simulations we obtain information on the arrangement of atoms in the topmost surface layer. Our work provides evidence for the structural model of a two-dimensional network for the silica film.     

Deformed “commutative” Chern–Simons’ system

Noncommutative Chern–Simons’ system is non-perturbatively investigated at a full deformed level. A deformed “commutative” phase space is found by a non-canonical change between two sets of deformed variables of noncommutative space. It is explored that in the “commutative” phase space all calculations are similar to the case in commutative space. Spectra of its energy and angular momentum of the Chern–Simons’ system are obtained at the full deformed level. The noncommutative–commutative correspondence is clearly showed. Formalism for the general dynamical system is briefly presented. Some subtle points are clarified.     

“Slow” active control of combustion instabilities by modification of liquid fuel spray properties

This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (Nanomiser^TM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities.     

Compositionally asymmetrical multiquantum wells: “Pseudo-molecules” for giant optical nonlinearities in the infrared (9–11 μm)

Intersubband transitions in quantum well have extremely large oscillator strengths and induce strong nonlinear effects in structures where inversion symmetry is broken, realized by growing AlGaAs quantum wells with asymmetrical A1 gradients. These compositionally asymmetrical multiquantum wells may thus be viewed as giant “quasimolecules” optimized for optimal nonlinearities in the mid infrared. Optical rectification as well as second harmonic generation have been measured in those structures using a continuous CO₂ laser. At 10.6 μm the nonlinear coefficients are more than 3 orders of magnitude higher in these samples than for bulk GaAs (i.e. χ₀⁽²⁾ = 5.3 × 10⁻⁶m/V, χ_2ω⁽²⁾ = 7.2 × 10⁻⁷ m/V) and are in good agreement with theoretical predictions. We present more complex “pseudo-molecules” involving weakly coupled quantum wells. The optical rectification effects in these devices are so large χ₀⁽²⁾ = 1.6 × 10⁻³ m/V) that application to infrared detection may be envisioned.     

Antimonide type-II “W” lasers: growth studies and guided-mode leakage into substrate

The lasing characteristics of mid-IR type-II “W” [InAs/GaInSb/InAs/AlAsSb] structures are found to correlate strongly with the growth conditions and low-temperature photoluminescence (PL) properties. The highest PL intensities and narrowest PL lines are obtained when the wafers are grown at ≈480–510°C with mixed interface bonds. A number of structures grown at a non-optimal lower temperature (≈425°C) nonetheless yielded lower lasing thresholds, lower internal losses, and longer Shockley-Read lifetimes than any grown previously on the present Riber 32P MBE system. All of the laser spectra display regularly-spaced multiple peaks that are consistent with periodic modulation of the cavity loss due to mode-leakage into the GaSb substrate.     

A mesoscopic approach to the “negative” viscosity effect in ferrofluids

We present a mesoscopic approach to analyse the dynamics of a single magnetic dipole under the influence of an oscillating magnetic field, based on the formulation of a Fokker–Planck equation. The dissipated power and the viscosity of a suspension of such magnetic dipoles are calculated from non-equilibrium thermodynamics of magnetized systems. By means of this method we have found a non-monotonous behaviour of the viscosity as a function of the frequency of the field which has been referred to as the “negative” viscosity effect. Moreover, we have shown that the viscosity depends on the vorticity field thus exhibiting non-Newtonian behaviour. Our analysis is complemented with numerical simulations which reproduce the behaviour of the viscosity we have found and extend the scope of our analytical approach to higher values of the magnetic field.     

Nuclear track radiography of “Hot” aerosol particles

Nuclear track radiography was applied to identify aerosol “hot” particles which contain elements of nuclear fuel and fallout after Chernobyl NPP accident. For the determination of the content of transuranium elements in radioactive aerosols the measurement of the -activity of “hot” particles by SSNTD was used in this work, as well as radiography of fission fragments formed as a result of the reactions (n,f) and (γ,f) in the irradiation of aerosol filters by thermal neutrons and high energy gamma quanta. The technique allowed the sizes and alpha-activity of “hot” particles to be determined without extracting them from the filter, as well as the determination of the uranium content and its enrichment by ²³⁵U, ²³⁹Pu and ²⁴¹Pu isotopes. Sensitivity of determination of alpha activity by fission method is 5×10⁻⁶ Bq per particle. The software for the system of image analysis was created. It ensured the identification of track clusters on an optical image of the SSNTD surface obtained through a video camera and the determination of size and activity of “hot” particles.     

Modified Kolmogorov wave turbulence in QCD matched onto “Bottom-up” thermalization

We investigate modification of Kolmogorov wave turbulence in QCD calculating gluon spectra as functions of time in the presence of a low energy source which feeds in energy density in the infrared region at a time-dependent rate. Then considering the picture of saturation constraints as has been constructed in the “bottom-up” thermalization approach we revisit that picture for RHIC center-mass energy, W=130 GeV, and also extend it to LHC center-mass energy, W=5500 GeV, thus for two cases having an opportunity to calculate the equilibration time, τ_eq|therm, of the gluon system produced in a central heavy ion collision at mid-rapidity region. Thereby, at RHIC and LHC energies we can match the equilibration time, obtained from the late stage gluon spectrum of the modified Kolmogorov wave turbulence, onto that of the “bottom-up” thermalization and other evolutional approaches as well. In addition, from the revised “bottom-up” approach we find the gluon liberation coefficient to be on the average, ε0.81–1.06 at RHIC and ε0.50–0.56 at LHC. We also present other phenomenological estimates of τ_therm which, at QCD realistic couplings, yield 0.45–0.65 fmτ_therm0.97–2.72 fm at RHIC and 0.31–0.40 fmτ_therm0.86–2.04 fm at LHC. We show that the second upper-bounds of τ_therm in both cases are due to the late stage gluon spectrum of the original Kolmogorov wave turbulence in QCD, previously deduced with a low energy source which feeds in energy density at a constant rate. On the other hand, the lower-bounds and first upper-bounds of τ_therm are due to the late stage gluon spectrum of the modified QCD wave turbulence, deduced here at the specific time-dependent rate. In the latter case, at certain conditions, taking also into account both very small and realistic couplings we give estimates: 0.65 fmτ_therm1.29 fm at RHIC and 0.52 fmτ_therm1.16 fm at LHC, as well as at realistic couplings we find 0.53<τ_therm<0.7 fm at RHIC and 0.41<τ_therm<0.65 fm at LHC.     

Subtle errors in αs determination using “corrected data” of energy-energy asymmetry

For the determination of α_s in the process of hadron production from electron-positron annihilation at 35 GeV, the complete second-order QCD calculation is used to study the corrections to the so-called “corrected data” of the asymmetry of the energy-energy correlation function (Asy). It is found that the correction in the values of α_s using the asymmetry method can be quite large while that for the new method, the planar triple energy correlation (PTC), is negligible.     

Erratum to “Bayesian methods for parameter estimation in effective field theories” [Ann. Phys. 324 (2009) 682–708]

We have discovered an error in the numerical calculations for the extraction of parameters from the nucleon mass “data” presented in Sections 4 and 5 of our paper [M.R. Schindler, D.R. Phillips, Ann. Phys. 324 (2009) 682. Available from: <hep-ph/0808.3643>]. We present the corrected results and discuss the implications. We stress that the material presented in Sections 1–3 of our paper [M.R. Schindler, D.R. Phillips, Ann. Phys. 324 (2009) 682. Available from: <hep-ph/0808.3643>] is unaffected.     

“BEST” Homonuclear Adiabatic Decoupling for C- and N-Double-Labeled Proteins

The cyclic irradiation sidebands appearing in homonuclear adiabatic decoupling are calculated in detail, which reveals the origin of the antisymmetric sidebands. The sidebands can be inverted by inserting an initial decoupling with a different period, but the same f_1rms as the main decoupling that is required for Bloch–Siegert shift compensation. The sidebands can be eliminated in a broad decoupling range by adding spectra of opposite sidebands. Based on this scheme, an offset-independent double-adiabatic decoupling, named Bloch–Siegert Shift Eliminated and Cyclic Sideband Trimmed Double-Adiabatic Decoupling, or “BEST” decoupling for short, is constructed, which not only compensates the Bloch–Siegert shift as shown earlier by Zhang and Gorenstein (1998) but also eliminates residual sidebands effectively.