Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper. Part 2: Partially Sealed Configuration

Experimental results from a partially sealed squeeze film damper (SFD) test rig, executing a circular centered orbit are presented and discussed. A serrated piston ring is installed at the damper exit. This device involves a new sealing concept which produces high damping values while allowing for oil flow to cool the damper. In the partially sealed damper, large cavitation regions are observed in the pressure fields at orbit radii epsilon equals 0.5 and epsilon equals 0.8. The cavitated pressure distributions and the corresponding force coefficients are compared with a cavitated bearing solution. The experimental results show the significance of fluid inertia and vapor cavitation in the operation of squeeze film dampers. Squeeze film Reynolds numbers tested reach up to Re equals 50, spanning the range of contemporary applications

Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper. Part 1: Fully Open Ended Configuration

Measurements of pressure distributions and force coefficients were carried out in two types of squeeze film dampers, executing a circular centered orbit, an open-ended configuration, and a partially sealed one, in order to investigate the effect of fluid inertia and cavitation on pressure distributions and force coefficients. Dynamic pressure measurements were carried out for two orbit radii, epsilon 0.5 and 0.8. It was found that the partially sealed configuration was less influenced by fluid inertia than the open ended configuration

Infrared optical absorption spectra of CuO single crystals: Fermion-spinon band and dimensional crossover of the antiferromagnetic order

We have obtained mid-infrared optical absorption spectra of the S=1/2 quasi one-dimensional CuO using polarized transmission measurement and interpreted the spectra in terms of phonon assisted magnetic excitations. When the electric field is parallel to the main antiferromagnetic direction a Delta shaped peak is observed with the maximum at 0.23eV which is attributed to spinons along Cu-O chains. At low temperatures in the antiferromagnetic phase another peak appears at 0.16eV which is attributed to two-magnon absorption but the spinon peak remains. This behavior is interpreted as due to a dimensional crossover where the low temperature three-dimensional magnetic phase keeps short range characteristics of a one-dimensional magnet.Comment: 5 pages, 5 figure

Infrared Hall conductivity of Na0.7_{0.7}CoO2_2

We report infrared Hall conductivity $\sigma_{xy}(\omega)$ of Na$_{0.7}$CoO$_2$ thin films determined from Faraday rotation angle $\theta_{F}$ measurements. $\sigma_{xy}(\omega)$ exhibits two types of hole conduction, Drude and incoherent carriers. The coherent Drude carrier shows a large renormalized mass and Fermi liquid-like behavior of Hall scattering rate, $\gamma_{H} \sim aT^{2}$. The spectral weight is suppressed and disappears at T = 120K. The incoherent carrier response is centered at mid-IR frequency and shifts to lower energy with increasing T. Infrared Hall constant is positive and almost independent of temperature in sharp contrast with the dc-Hall constant.Comment: 5 Pages, 5 Figures. Author list corrected in metadata only, paper is unchange

Comprehensive structural model of the mechanochemical cycle of a mitotic motor highlights molecular adaptations in the kinesin family

Kinesins are responsible for a wide variety of microtubule-based, ATP-dependent functions. Their motor domain drives these activities but the molecular adaptations that specify these diverse and essential cellular activities are poorly understood. It has been assumed that the first identified kinesin - the transport motor kinesin-1 – is the mechanistic paradigm for the entire superfamily, but accumulating evidence suggests that this is not the case. To address the deficits in our understanding of the molecular basis of functional divergence within the kinesin superfamily, we studied kinesin-5s, which are essential mitotic motors whose inhibition blocks cell division. Using cryo-electron microscopy and subnanometer resolution structure determination, we have visualised conformations of microtubule-bound human kinesin-5 motor domain at successive steps in its ATPase cycle. Following ATP hydrolysis, nucleotide-dependent conformational changes in the active site are allosterically propagated into rotations of the motor domain and uncurling of the drugbinding loop L5. In addition, the mechanical neck-linker element that is crucial for motor stepping undergoes discrete, ordered displacements. We also observed large reorientations of the motor N-terminus that indicate its importance for kinesin-5 function through control of neck-linker conformation. A kinesin-5 mutant lacking this N-terminus is enzymatically active, and ATP-dependent neck-linker movement and motility is defective although not ablated. All these aspects of kinesin-5 mechanochemistry are distinct from kinesin-1. Our findings directly demonstrate the regulatory role of the kinesin-5 N-terminus in collaboration with the motor’s structured neck-linker, and highlight the multiple adaptations within kinesin motor domains that tune their mechanochemistries according to distinct functional requirements

Spin/Orbital Pattern-Dependent Polaron Absorption in Nd(1-x)Sr(x)MnO3

We investigated optical properties of Nd(1-x)Sr(x)MnO3 (x= 0.40, 0.50, 0.55, and 0.65) single crystals. In the spin/orbital disordered state, their conductivity spectra look quite similar, and the strength of the mid-infrared absorption peak is proportional to x(1-x) consistent with the polaron picture. As temperature lowers, the Nd(1-x)Sr(x)MnO3 samples enter into various spin/orbital ordered states, whose optical responses are quite different. These optical responses can be explained by the spin/orbital ordering pattern-dependent polaron hopping.Comment: 3 figures (gzipped