Adiabatic Rotor Research Articles

2H,13C-Cholesterol for Dynamics and Structural Studies of Biological Membranes.

We present a cost-effective means of 2H and 13C enrichment of cholesterol. This method exploits the metabolism of 2H,13C-acetate into acetyl-CoA, the first substrate in the mevalonate pathway. We show that growing the cholesterol producing strain RH6827 of Saccharomyces cerevisiae in 2H,13C-acetate-enriched minimal media produces a skip-labeled pattern of deuteration. We characterize this cholesterol labeling pattern by mass spectrometry and solid-state nuclear magnetic resonance spectroscopy. It is confirmed that most 2H nuclei retain their original 2H–13C bonds from acetate throughout the biosynthetic pathway. We then quantify the changes in 13C chemical shifts brought by deuteration and the impact upon 13C–13C spin diffusion. Finally, using adiabatic rotor echo short pulse irradiation cross-polarization (RESPIRATIONCP), we acquire the 2H–13C correlation spectra to site specifically quantify cholesterol dynamics in two model membranes as a function of temperature. These measurements show that cholesterol acyl chains at physiological temperatures in mixtures of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), sphingomyelin, and cholesterol are more dynamic than cholesterol in POPC. However, this overall change in motion is not uniform across the cholesterol molecule. This result establishes that this cholesterol labeling pattern will have great utility in reporting on cholesterol dynamics and orientation in a variety of environments and with different membrane bilayer components, as well as monitoring the mevalonate pathway product interactions within the bilayer. Finally, the flexibility and universality of acetate labeling will allow this technique to be widely applied to a large range of lipids and other natural products.

Model of Effect of Hot Gas Ingress on Temperatures of Turbine Disks

Ingress is the leakage of hot mainstream gas through the rim-seal clearance into the wheel-space between the rotating turbine disk (the rotor) and the adjacent stationary casing (the stator). The high-pressure rotor is purged by a radial outflow of air from the high-pressure compressor, and this cooling air is also used to reduce the ingress. The engine designer needs to predict the stator and rotor temperatures as a function of cooling-flow rate. The sealing effectiveness determines how much air is needed to reduce or prevent ingress; although there are numerous theoretical and experimental papers on the effectiveness of different seal geometries, there are few papers on the effect of ingress on the temperature of the rotating disk. This is an unsolved problem of great practical importance: under high stress, a small increase in metal temperature can significantly reduce operating life. In this paper, conservation equations and control volumes are used to develop theoretical equations for the exchange of mass, concentration and enthalpy in an adiabatic rotor–stator system when ingress occurs. It is assumed that there are boundary layers on the rotor and stator, separated by an inviscid rotating core, and the fluid entrained from the core into the boundary layer on the rotor is recirculated into that on the stator. The superposed cooling flow protects the rotor surface from the adverse effects of hot-gas ingress, which increases the temperature of the fluid entrained into the rotor boundary layer. A theoretical model has been developed to predict the relationship between the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, including the effects of both ingress and frictional heating. The model involves the use of a nondimensional buffer parameter, Ψ, which is related to the relative amount of fluid entrained into the rotor boundary layer. The analysis shows that the cooling flow acts as a buffer, which attenuates the effect of hot gas ingress on the rotor, but frictional heating reduces the buffer effect. The theoretical effectiveness curves are in good agreement with experimental data obtained from a rotor–stator heat-transfer rig, and the results confirm that the buffer effect increases as the sealing effectiveness of the rim seals decreases. The analysis quantifies the increase in the adiabatic rotor temperature due to direct frictional heating, which is separate from the increase due to the combined effects of the ingress and the indirect frictional heating of the entrained fluid. These combined effects are reduced as Ψ increases, and Ψ = 1 at a critical flow rate above which there is no entrained fluid and consequently no indirect heating of the rotor. The model also challenges the conventional physical interpretation of ingress as, in general, not all the hot gas that enters the rim-seal clearance can penetrate into the wheel-space. The ingress manifests itself through a mixing of enthalpy, which can be exchanged even if no ingested fluid enters the wheel-space.

Moment distributions of clusters and molecules in the adiabatic rotor model

We present a Fortran program to compute the distribution of dipole moments of free particles for use in analyzing molecular beams experiments that measure moments by deflection in an inhomogeneous field. The theory is the same for magnetic and electric dipole moments, and is based on a thermal ensemble of classical particles that are free to rotate and that have moment vectors aligned along a principal axis of rotation. The theory has two parameters, the ratio of the magnetic (or electric) dipole energy to the thermal energy, and the ratio of moments of inertia of the rotor. Program summary Program title:AdiabaticRotor Catalogue identifier:ADZO_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADZO_v1_0.html Program obtainable from:CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions:Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.:479 No. of bytes in distributed program, including test data, etc.:4853 Distribution format:tar.gz Programming language:Fortran 90 Computer:Pentium-IV, Macintosh Power PC G4 Operating system:Linux, Mac OS X RAM:600 Kbytes Word size:64 bits Classification:2.3 Nature of problem:The system considered is a thermal ensemble of rotors having a magnetic or electric moment aligned along one of the principal axes. The ensemble is placed in an external field which is turned on adiabatically. The problem is to find the distribution of moments in the presence of the external field. Solution method:There are three adiabatic invariants. The only nontrivial one is the action associated with the polar angle of the rotor axis with respect to external field. It is found by Newton's method. Running time:3 min on a 3 GHz Pentium IV processor.

Rovibrational dynamics of LiCs dimers in strong electric fields

We investigate the effects of a strong electric field on the rovibrational dynamics of LiCs in its 1Σ + electronic ground state. Using a hybrid computational technique combining discretisation and basis set methods, the rovibrational Schrödinger equation is solved. Results for energy levels and various expectation values are presented. The validity of the previous developed effective and adiabatic rotor approaches is investigated. The electric field-induced hybridization is analyzed up to high rotational excitations and for a large range of magnetic quantum numbers.

Electric-field-induced adiabaticity in the rovibrational motion of heteronuclear diatomic molecules

We investigate the rovibrational dynamics of heteronuclear diatomic molecules exposed to a strong external static and homogeneous electric field. We encounter in the presence of the field the effect of induced adiabatic coupling among the vibrational and hybridized rotational motions. Exact results are compared to the predictions of the adiabatic rotor approach as well as to the previously established effective rotor approximation. A detailed analysis of the impact of the electric field is performed: the hybridized and oriented rotational motion, the mixing of angular momenta, and the squeezing of the vibrational motion are observed. It is demonstrated that these effects can well be accounted for by the adiabatic rotor approximation.

Magnetic ordering in manganese clusters

Isolated manganese clusters, ${\text{Mn}}_{n},\phantom{\rule{0.3em}{0ex}}(n=5--22)$ are deflected by a linear-gradient magnetic field. ${\text{Mn}}_{7}{\text{\ensuremath{-}}\text{Mn}}_{22}$ are found to deflect uniformly toward high field. The magnitude of the deflections indicate susceptibilities far in excess of those expected based on the susceptibility of bulk manganese, demonstrating that Mn clusters in this size range are magnetically ordered. Per-atom moments obtained from Curie's Law analysis range from $0.4{\ensuremath{\mu}}_{b}\phantom{\rule{0.3em}{0ex}}({\text{Mn}}_{19})$ to $1.7\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{b}\phantom{\rule{0.3em}{0ex}}({\text{Mn}}_{12})$. For ${\text{Mn}}_{5}$ and ${\text{Mn}}_{6}$, symmetric broadening of the cluster beam is observed, and their moments were determined via line-shape analysis using both free-spin and adiabatic rotor models. The measured moments, interpreted in light of recent density functional theory calculations, suggest that Mn clusters in this size range are molecular ferrimagnets.

Nonadiabatic dynamical studies of the rotational Raman spectrum of H2 in water

The rotational Raman spectrum of H2 in liquid H2O and D2O have been calculated using our nonadiabatic time correlation function results presented in earlier work [L. Xiao and D. F. Coker, J. Chem. Phys. 100, 8646 (1994)]. The rotational potential experienced by the H2 molecule in this solvent environment is so anisotropic that classical solvent fluctuations not only drive transitions between orientational basis states, but mixing of states from different total angular momentum levels is also considerable. Our nonadiabatic calculations are able to quantitatively reproduce the experimental rotational Raman line shapes and their trends with solvent isotopic substitution. We demonstrate that nonadiabatic transitions between adiabatic rotor states play a key role in smoothing out artificial structures predicted in the static and adiabatic limit spectra.

Preswirl Blade-Cooling Effectiveness in an Adiabatic Rotor–Stator System

Blade-cooling air for a high-pressure turbine is often supplied from preswirl nozzles attached to a stationary casing. By swirling the cooling air in the direction of rotation of the turbine disk, the temperature of the air relative to the blades can be reduced. The question addressed in this paper is: Knowing the temperatures of the preswirl and disk-cooling flows, what is the temperature of the blade-cooling air? A simple theoretical model, based on the Reynolds analogy applied to an adiabatic rotor–stator system, is used to calculate the preswirl effectiveness (that is, the reduction in the temperature of the blade-cooling air as a result of preswirling the flow). A mixing model is used to account for the “contamination” of the blade coolant with disk-cooling air, and an approximate solution is used to estimate the effect of frictional heating on the disk-cooling air. Experiments were conducted in a rotor–stator rig that had preswirl nozzles in the stator and blade-cooling passages in the rotating disk. A radial outflow or inflow of disk-cooling air was also supplied, and measurements of the temperature difference between the preswirl and blade-cooling air were made for a range of flow rates and for rotational Reynolds numbers up to Reθ = 1.8 × 106. Considering the experimental errors in measuring the small temperature differences, good agreement between theory and experiment was achieved.

Exact solution of the particle-rigid-rotor scattering problem

The problem of quantum particle scattering on the dumb-bell-like rotor is solved exactly, the particle-rotor interaction being described by two zero-range potentials. The necessary modification of the zero-range potential formulation due to the system dynamics is established. Two limiting cases are investigated: the rotor with constant angular velocity (the classical rotor) and the case of slow rotation as compared with the characteristic collision time (the adiabatic rotor). The rotational structure of the bound states and resonances is studied in the framework of adiabatic expansion. The character of the low-energy (meV region) resonances is illustrated by numerical calculations of the model electron-molecule scattering. The role of potential and mass asymmetry of the rotor discussed in connection with the scattering on the isotopically substituted molecules.

Recoil-distance lifetime measurements of the ground-state band in 168Dy, 170Er and 174Yb

Mean lives of the 4 +, 6 + and 8 + levels of the ground-state band in 164Dy, 170Er and 174Yb have been measured by the recoil-distance technique following multiple Coulomb excitation with 32S projectiles of energy 120–140 MeV. The γ-rays were detected in coincidence with backscattered particles. The results are compared with theoretical predictions of the adiabatic rotor model. The 6 + and 8 + lifetimes in 164Dy are found to correspond to a slight reduction in B(E2) values over the rotational model prediction, while for the 4 + state a 12 % reduction was observed. In 170Er and 174Yb the lifetimes are consistent with rotational model predictions with a slight enhancement of B(E2) values at higher spins. Comparison with other results from Doppler broadened lineshape analysis confirms the need to adjust the electronic stopping powers of Northcliffe and Schilling in the lineshape calculations.

N.A.C.A. Cascade Data for the Blade Design of High-Performance Axial-Flow Compressors

CI0 = blade lift coefficient referred to mean air M = Mach Number, ratio of velocity entering the cascade to the speed of sound MCTm = entering Mach Number at which sonic velocity is reached on the blade Mfb = entering Mach Number at which losses through the cascade suddenly increase P = local pressure coefficient over the blade Per. — pressure coefficient corresponding to sonic velocity for a particular entering Mach Number P2/P1 = static pressure ratio across the cascade Q = quantity flow, cu.ft. per sec. U = rotational velocity of rotor blade element, ft. per sec. (Fig. 1) Va — axial velocity, ft. per sec. (Fig. 1) W = velocity of air relative to rotor element, ft. per sec. (Fig. 1) a = angle of attack, angle between effective entering air * and blade chord line, deg. (3 = stagger angle, angle of effective entering air measured from axial direction, deg. (Fig. 1) 7) = adiabatic rotor efficiency 6 — effective angle through which air is turned relative to the rotor, deg. (Fig. 1) <T = solidity, blade chord divided by the gap between blades (Fig. 1)