Negative ion motion in normal and superfluid 3He

We report the first measurements of negative ion motion in the superfluid phases of ³He and in the normal phase below 17 mK. Refrigeration was achieved with nuclear demagnetization of copper and we used a pulsed NMR platinum powder thermometer immersed in the liquid. In the A phase the longitudinal resonance frequency provided an additional high-resolution thermometer. In the normal phase we observed a strictly temperature-independent mobility. In the superfluid phases we found two velocity regimes. For small applied electric fields the velocity is a linear function of the field and the corresponding mobility increases monotonically toward lower temperatures. At high electric fields the velocity is a nonlinear function of the field as a result of the pair-breaking effect of the moving ion. Available theoretical calculations are only in partial agreement with our results.This work was supported financially by the Academy of Finland.Guggenheim Fellow on leave from Cornell University, Ithaca, New York.On leave from Regensburg University, Regensburg, West Germany, supported by Deutsche Forschungsgemeinschaft and Finnish Ministry of Education.     

Positive ion mobility in normal and superfluid 3He

The mobility of positive ions has been measured in the normal and superfluid phases of ³He at several pressures. Below 100 mK the normal phase mobility increases logarithmically with decreasing temperature down to the superfluid transition temperature T _c; it shows an anomalous jump near 100 mK. At low temperatures the drift velocity is nonlinear for electric fields exceeding 30 V/cm. In the superfluid the mobility, normalized to its value at T _c, is much less than for negative ions. We have also observed the anisotropic mobility in the A phase and the Landau critical velocity for pair-breaking in both superfluid phases.Work supported by the Academy of Finland.On leave of absence from Regensburg University, Regensburg, West Germany, supported by Deutsche Forschungsgemeinschaft.     

Positive ion transmission mode ion/ion reactions in a hybrid linear ion trap

A triple quadrupole mass spectrometer capable of ion trapping experiments has been adapted for ion/ion reaction studies. The instrument is based on a commercially available linear ion trap (LIT) tandem mass spectrometer (i.e., an MDS SCIEX 2000 Q TRAP) that has been modified by mounting an atmospheric sampling glow discharge ionization (ASGDI) source to the side of the vacuum manifold for production of singly charged anions. The ASGDI source is located line of sight to the side of the third quadrupole of the triple quadrupole assembly (Q3). Anions are focused into the side of the rod array (i.e., anion injection occurs orthogonal to the normal ion flight path). A transmission mode method to perform ion/ion reactions has been developed whereby positive ions are transmitted through the pressurized collision quadrupole (Q2) while anions are stored in Q2. The Q2 LIT is used to trap negative ions whereas the Q3 LIT is used to accumulate positive ions transmitted from Q2. Anions are injected to Q3 and transferred to Q2, where they are stored and collisionally cooled. Multiply charged protein/peptide ions, formed by electrospray, are then mass selected by the first quadrupole assembly (Q1) operated in the rf/dc mode and injected into Q2. The positive ions, including the residual precursor ions and the product ions arising from ion/ion proton-transfer reactions, are accumulated in Q3 until they are analyzed via mass-selective axial ejection for mass analysis. The parameters that affect ion/ion reactions are discussed, including pressure, nature of the gas in Q2, and operation of Q2 as a linear accelerator. Ion/ion reactions in this mode can be readily utilized to separate ions with the same m/z but largely different mass and charge, e.g., +1 bradykinin and +16 myoglobin, in the gas phase.     

Scaling of the superfluid density in superfluid films

We study scaling of the superfluid density with respect to the film thickness by simulating the x — y model on films of size L × L × H (L H) using the cluster Monte Carlo. While periodic boundary conditions where used in the planar (L) directions, Dirichlet boundary conditions where used along the film thickness. We find that our results can be scaled on a universal curve by introducing an effective thickness. In the limit of large H our scaling relations reduce to the conventional scaling forms. Using the same idea we find scaling in the experimental results using the same value of v = 0.6705.We wish to thank F. M. Gasparini for providing us with his data of the superfluid density for films of various thickness and for clarifying discussions. This work was supported by the National Aeronautics and Space Administration under grant no. NAG3-1841.     

Dependence of signal on depth in transmission Raman spectroscopy

Recently, transmission Raman spectroscopy has been shown to be a valuable tool in the volumetric quantification of pharmaceutical formulations. In this work a Monte Carlo simulation and experimental study are performed to elucidate the dependence of the Raman signal on depth from the viewpoint of probing pharmaceutical tablets and powders in this experimental configuration. The transmission Raman signal is shown to exhibit a moderate bias toward the center of the tablets and this can be considerably reduced by using a recently developed Raman signal-enhancing concept, the "photon diode." The enhancing element not only reduces the bias but also increases the overall Raman signal intensity and consequently improves the signal-to-noise ratio of the measured spectrum. Overall, its implementation with appropriately chosen reflectivity results in a more uniform volumetric sampling across the half of the tablet where the photon diode is used (or across the tablet's entire depth if two photon diodes are used on each side of tablet) and enhanced overall sensitivity. These findings are substantiated experimentally on a segmented tablet by inserting a poly(ethelyne terephthalate) (PET) film doped with TiO(2) at different depths and monitoring its contribution to the overall transmission Raman signal from the segmented tablet. The numerical simulations also indicate considerable sensitivity of the overall Raman signal to the absorption of the sample, which is in line with large migration distances traversed by photons in these measurements. The presence of sample absorption was shown numerically to reduce the signal enhancement effect while the overall depth-dependence profile remained broadly unchanged. The absorption was also shown to produce a depth profile with the photon diode similar to that without it, although with a reduced absolute intensity of Raman signals and diminished enhancement effect.     

Independent control of ion transmission in a jet disrupter dual-channel ion funnel electrospray ionization MS interface

A new atmospheric pressure ionization mass spectrometer (API-MS) interface has been developed to allow the control of ion transmission through the first vacuum stage of the mass spectrometer. The described interface uses a dual-heated capillary and a dual-inlet ion funnel design. Two electrosprays, aligned with the dual-capillary inlet, are used to introduce ions from different solutions independently into the MS. The initial design was specifically aimed at developing a method for the controlled introduction of calibrant ions in highly accurate mass measurements using Fourier transform ion cyclotron resonance mass spectrometer (FTICR). The dual-channel ion funnel has different inlet diameters that are aligned with the dual capillaries. The large diameter main channel of the ion funnel is used for analyte introduction to provide optimum ion transmission. The second, smaller diameter channel inlet includes a jet disrupter in the ion funnel to modulate the ion transmission through the channel. The two inlet channels converge into a single-channel ion funnel where ions from both channels are mixed, focused, and transmitted to the mass analyzer. Both theoretical simulations and experimental results show that the transmission of different m/z species in the small diameter channel of the ion funnel can be effectively modulated by varying the bias voltage on the jet disrupter. Both static and dynamic modulations of ion transmission are demonstrated experimentally by applying either a constant DC or a square waveform voltage to the jet disrupter. High ion transmission efficiency, similar to the standard single-channel ion funnel, is maintained in the main analyte channel inlet of the ion funnel over a broad m/z range with negligible "cross talk" between the two ion funnel inlet channels. Several possible applications of the new interface (e.g., for high-accuracy MS analysis of complex biological samples) are described.     

Nonlinear dynamics in superfluid films

We have calculated the first non-linear corrections to the period shift andQ factor of a torsional oscillator containing a film of helium. To do so we have solved the Fokker Planck equation for the distribution of vortex pairs in the presence of an oscillating superfluid velocity field. The non-linear response is predicted to be proportional tov _n ² for low values of the normal fluid velocity,v _n, which is in good agreement with the experimental results of Adams and Glaberson. For temperatures above the Kosterlitz Thouless transition temperature,T _KT, the ratio of the correlation length ₊ to the diffusion length becomes important in describing the temperature dependence of the non-linear response. We predict how the non-linear response depends on this ratio in the region where the ratio is large.     

Single flux quantum signal transmission techniques in building practical RSFQ circuits

The practical implementation of rapid single flux quantum (RSFQ) technology requires much more complexity than the presently developed circuits. Multiple chips have to be integrated with a technology that is reliable at cryogenic temperatures. The interchip and intrachip data transmission speed of tens of GHz has to be supported. Also, the large RSFQ circuits need serial biasing to reduce the amount of the bias current. The test circuits were designed, simulated, fabricated with Nb technology, and tested at a temperature of 4.2 K. Test results at GHz frequencies showed that SFQ pulses can be successfully transmitted over an extensive distance in a chip, between chips, and over the circuits in different ground planes.     

雷达高频传输系统监控报警装置

对雷达高频传输系统进行实时有效的工作状态监测 ,保证系统处于最佳工作状态 ,充分发挥雷达的技战术水平 ,是雷达使用中的难点问题 ,本文介绍了以单片机为核心的监控报警装置的硬件及程序流程     

Activation of intact electron-transfer products of polypeptides and proteins in cation transmission mode ion/ion reactions

Cationic peptide electron-transfer products that do not fragment spontaneously are exposed to ion trap collisional activation immediately upon formation while they pass through a high-pressure collision cell (Q2), where the electron-transfer reagent anions are stored. Radial ion acceleration, which is normal to the ion flow, is implemented by applying an auxiliary dipolar alternating current to a pair of opposing rods of the Q2 quadrupole array at a frequency in resonance with the surviving electron-transfer products. Collisional cooling of cations in the pressurized Q2 ensures efficient overlap of the positive and negative ions for ion/ion reactions and also gives rise to relatively long residence times (milliseconds) for ions in Q2, making it possible to fragment ions via radial excitation during their axial transmission. The radial activation for transmission mode electron-transfer ion/ion reactions has been demonstrated with a doubly protonated tryptic peptide, a triply protonated phosphopeptide, and [M + 7H]7+ ions of ubiquitin. In all cases, significant increases in fragment ion yields and structural information from electron-transfer dissociation (ETD) were observed, suggesting the utility of this method for improving transmission mode ETD performance for relatively low charge states of peptides and proteins.     

Counterflow in rotating superfluid helium

We have observed a variety of effects involving thermal counterflow in rotating superfluid helium. In particular, the temperature and chemical potential gradients associated with the motion of vortex lines have been measured. The two-fluid equations for helium in rotation have been solved for channel flow in a channel of finite height and the results are compared with our data. Interesting effects associated with the onset of turbulence and with the onset of vortex line depinning are discussed.Supported by a grant from the National Science Foundation.     

Critical velocity in superfluid helium

A microscopic approach based on the use of action-angle variables in quantum statistics is employed to study the flow of liquid helium II through a cylindrical channel of diameterd. It is found that for _c /d1, where _c is the coherence length of the system, the superfluid critical velocityv _c d ^–1/2. For a certain range ofd, this relationship is in closer agreement with experiment than the one based on semiclassical considerations involving quantized vortices.     

Solitons in superfluid 4He films

The Korteweg-de Vries (KdV) equation is derived from Landau two-fluid hydrodynamics applied to the thickness oscillation of the superfluid ⁴He film at low temperatures, where the main restoring force is van der Waals attraction from the substrate and the thermomechanical force due to phonons is a small correction. Since the usual third-sound generators and detectors are far wider than the individual solitons, the asymptotic solution of the KdV equation provided by the inverse scattering method is coarse-grained by regarding it as a continuous train of sharp pulses. The envelope so obtained still shows a singular front proportional to (t–t ₀)^–1/2, where t ₀ is the arrival time of the fastest soliton, and should therefore be observable with the appropriate experimental arrangement.     

Phase slippage in thin superfluid films

We have extended the Ambegaokar, Halperin, Nelson and Siggia theory of vortex de-pairing in two-dimensional superfluids to describe how the current of free vortices varies with superfluid velocity, v _s, in the steady state, for temperatures just above the Kosterlitz-Thouless transition. To do so we have solved exactly the Fokker-Planck equation which describes the current of vortices produced at one edge of the film. We are able to calculate how a persistent current decays, and the thermal resistance of a film as a function of heater power. Superconducting films are considered as a charged, two-dimensional superfluid, and the theory is applied to them.     

Magnetic excitations in superfluid 3He

Localized magnetic excitations (solitons) in superfluid ³He are studied theoretically. In the A phase, we determine the dispersion of solitons in both the longitudinal and the transversal configurations, while in the B phase we limit ourselves to the longitudinal soliton in the Leggett configuration. In the wall pinned configuration of the B phase we show that the magnetic perturbation propagates as spin wave. The effects of the spin-diffusion term on solitons as well as spin waves are considered. The soliton velocity decreases exponentially in time owing to the spin-diffusion term with a characteristic time % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiiYdd9qrFfea0dXdf9vqai-hEir8Ve% ea0de9qq-hbrpepeea0db9q8as0-LqLs-Jirpepeea0-as0Fb9pgea% 0lrP0xe9Fve9Fve9qapdbaqaaeGacaGaaiaabeqaamaabaabcaGcba% qedmvETj2BSbacfaGae83KdCKae8hiaaIae83waSLaeyyyIORaaiik% aiaaiodacaGGPaGaaiikaiaadogadaahaaWcbeqaamaaCaaameqaba% GaaGOmaaaaaaGcciGGVaGaamiraiabfM6axnaaCaaaleqabaWaaWba% aWqabeaacaaIYaaaaaaakiaacMcacaGGDbaaaa!4DB4!\[\Gamma [ \equiv (3)(c^{^2 } /D\Omega ^{^2 } )]\] where D is the spin-diffusion constant, is the Leggett frequency, and c is the spin-wave velocity.Supported by the National Science Foundation.     

Heat flow in superfluid 3He

The thermal resistance in both superfluid phases of ³He has been measured at 20.0 and 29.6 bar in zero magnetic field. Heat conduction in ³He-B is shown to be primarily hydrodynamic, and a regime of reproducible heat flow behavior in the A phase is reported. The viscosity of each phase as a function of temperature is calculated using an equation of the two-fluid model, and critical velocity effects are discussed.Work supported by the U.S. Atomic Energy Commission under Contract No. AT(04-3)-34 P.A. 143.     

Persistent currents in superfluid3He

Measurements are reported of persistent currents in superfluid³He-B and³He-A. An ac gyroscope filled with 20 µm powder and mounted into a rotating nuclear refrigerator was employed. In³He-B, undiminished circulation was observed for 48 h; this implies an effective viscosity at least 12 orders of magnitude lower than in the normal fluid at the same temperature. AtP<15 bar, the observed critical velocity is independent of temperature but it is a weak function of pressure;v _c varies between 4 and 6 mm/sec. The response to rotation is hysteretic, with elastic potential flow at slow rotation and irreversible vortex flow at higher angular velocities. The persistent angular momentumL is reversible when thermally cycled in the B phase, and proportional to the superfluid fraction _s /. Above 15 bar the B phase splits into separate regions with different critical velocities. The measuredv _c in the phase existing only at high pressures is dependent on magnetic field; for example, at 23.0 bar,v _c (H=0) =5 mm/sec, butv _c (H=40 G) =15 mm/sec. In the low pressure phase,v _c is insensitive to a change in the magnetic field. The phase transition is of first order; the latent heatQ _G (1 µJ/mole) depends on the maximum angular velocity at which the cryostat was rotated. The transition is proposed to occur in the core structure of pinned quantized vortices sustaining persistent currents. In³He-A, currents could not be found to persist on an observable level. Direct measurements ofL atH=0 and atH=40 G, and repeated thermal cycling, showed that either the current decays rapidly orv _c <0.5 mm/sec.     

Orbital modes in superfluid3He

The equation describing the rotation of the orbital coordinate in superfluid³He is obtained. It is shown that the orbital modes obey a diffusion-like equation with a finite energy gap. The transient behavior of the vector in the A phase after thed vector is suddenly rotated is considered.Supported by the National Science Foundation.On leave from Department of Applied Science, Tohoku University, Sendai, Japan.