Multi-harmonic active structural acoustic control of a helicopter main transmission noise using the principal component analysis

This paper evaluates the feasibility and effectiveness, under controlled conditions, of active structural acoustic control of a helicopter main transmission in order to attenuate the vibration of the receiving roof panel and its sound radiation into the cabin. The vibroacoustic analysis of a typical helicopter drive train is conducted to extract the dominant tones generated by the various transmission stages. A finite element model of a Bell 407 transmission and simplified roof structure is developed in order to investigate various active control arrangements using piezoceramic actuators to control wave propagation in the gearbox supporting struts or receiving panel. The principal component analysis is used to extract the most significant control paths and reduce the control effort. A multiple frequency principal component least mean square (PC-LMS) algorithm is implemented on a laboratory setup and is used to successfully reduce up to seven gearbox tones simultaneously.     

Coupled Sensitizer–Catalyst Dyads: Electron‐Transfer Reactions in a Perylene–Polyoxometalate Conjugate

Ultrafast discharge of a single‐electron capacitor: A variety of intramolecular electron‐transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single‐electron events. (et=electron transfer, cr=charge recombination, csr=charge‐shift reaction, PER=perylene, POM=polyoxometalate).

     

Longitudinal anisotropy of the photoinduced molecular migration in azobenzene polymer films

The effects of tightly focused, higher-order laser beams on the photoinduced molecular migration and surface deformations in azobenzene polymer films are investigated. We demonstrate that the surface relief is principally triggered by longitudinal fields, i.e., electric fields polarized along the optical axis of the focused beam. Our findings can be explained by the translational diffusion of isomerized chromophores when the constraining effect of the polymer-air interface is considered.     

GMAW电弧等离子体平衡成分计算及其在光谱学中的应用

计算了常压下3 000～25 000 K范围内熔化极气体保护焊(GMAW)保护气体Ar,CO₂,82%Ar-18%CO₂及其与Fe蒸汽的混合物的平衡成分。上述气体被看作一种Ar-CO₂-Fe等离子体,等离子体中的39种粒子被分为5种主元粒子和34种非主元粒子。根据化学方程,非主元粒子由主元粒子表示以减少未知数的个数和求解量,再利用牛顿迭代法对平衡方程进行求解,最终实现了成分求解。计算结果表明,Ar气随着温度升高依次发生一次电离和二次电离,CO₂气体除了在高温时发生原子电离外,在低温时(T<8 000 K)还存在CO₂,O₂,CO等分子的解离,82%Ar-18%CO₂混合气则既有解离又有电离。Fe的加入会增加等离子体的电子密度,特别是在15 000 K以下。等离子体成分的确定为GMAW电弧等离子体辐射属性计算以及电弧中Fe蒸汽浓度的光谱测定奠定了基础。     

Soft spin wave near nu=1: evidence for a magnetic instability in Skyrmion systems

The ground state of the two-dimensional electron gas near nu=1 is investigated by inelastic light scattering measurements carried down to very low temperatures. Away from nu=1, the ferromagnetic spin wave collapses and a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave shows soft behavior as its energy increases with temperature and reaches the Zeeman energy for temperatures above 2 K. The observed softening indicates an instability of the two-dimensional electron gas towards a magnetic order that breaks spin rotational symmetry. We discuss our findings in light of the possible existence of a Skyrme crystal.     

Porous materials with two populations of voids under internal pressure: II. Growth and coalescence of voids

This study is devoted to the mechanical behaviour of polycrystalline materials with two populations of voids, small spherical voids located inside the grains and larger spheroidal voids located at the grain boundaries. In part I of the work, instantaneous effective stress–strain relations were derived for fixed microstructure. In this second part, the evolution of the microstructure is addressed. Differential equations governing the evolution of the microstructural parameters in terms of the applied loading are derived and their integration in time is discussed. Void growth results in a global softening of the stress–strain response of the material. A simple model for the prediction of void coalescence is proposed which can serve to predict the overall ductility of polycrystalline porous materials under the combined action of thermal dilatation and internal pressure in the voids.     

B?H,C?H,and B?C Bond Activation: The Role of Two Adjacent Agostic Interactions

Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐B_sp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH₂P₂” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H₂ and boranes.     

Single-molecule magnet behaviour in a tetrathiafulvalene-based electroactive antiferromagnetically coupled dinuclear dysprosium(III) complex

The reactions between the [Ln(tta)(3)]·2H(2)O precursors (tta(-)=2-thenoyltrifluoroacetonate anion) and the tetrathiafulvalene-3-pyridine-N-oxide ligands (L(1)) lead to dinuclear complexes of formula [{Ln(tta)(3)(L(1))}(2)]·xCH(2)Cl(2) (x=0.5 for Ln=Dy(III) (1) and x=0 for Ln=Gd(III) (2)). The crystal structure reveals that two {Ln(tta)(3)} moieties are bridged by two donors through the nitroxide groups. The Dy(III) centre adopts a distorted square antiprismatic oxygenated polyhedron structure. The antiferromagnetic nature of the exchange interaction between the two Dy(III) ions has been determined by two methods: 1) an empirical method using the [Dy(hfac)(3)(L(2))(2)] mononuclear complex as a model (3) (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion, L(2)=tetrathiafulvaleneamido-2-pyridine-N-oxide ligand), and 2) assuming an Ising model for the Dy(III) ion giving an exchange energy of -2.30 cm(-1), g=19.2 in the temperature range of 2-10 K. The antiferromagnetic interactions have been confirmed by a quantitative determination of J for the isotropic Gd(III) derivative (J=-0.031 cm(-1), g=2.003). Compound 1 displays a slow magnetisation relaxation without applied external magnetic fields. Alternating current susceptibility shows a thermally activated behaviour with pre-exponential factors of 5.48(4)×10(-7) s and an energy barrier of 87(1) K. The application of an external field of 1.6 kOe compensates the antiferromagnetic interactions and opens a new quantum tunnelling path.     

Influence of the coordination mode in [Ni{RC(S)NP(S)(OiPr)2}2] for the formation of nickel-containing nanoparticles

The complex [Ni{2-PyNHC(S)NP(S)(OiPr)(2)-1,5,7-N,N',S}(2)] ([NiL(I)(2)]) dissolved in tri-n-octylphosphine (TOP) is decomposed in hot hexadecylamine (HDA) to give TOP-capped Ni nanoparticles. The same procedure using [Ni{2-MeC(6)H(4)NHC(S)NP(S)(OiPr)(2)}(2)-1,3-N,S] ([NiL(II)(2)]) and [Ni{PhC(S)NP(S)(OiPr)(2)-1,5-S,S'}(2)] ([NiL(III)(2)]) leads to the formation of NiS nanoparticles with the rhombohedral and hexagonal structures, respectively. NiH(x) nanoparticles were also produced from a mixture of [NiL(I)(2)] and N(2)H(4). The obtained Ni nanoparticles can be used for the catalytic addition of Ph(2)S(2) to 1-, 2- and 3-hexynes.