Observed Velocity Difference Research Articles

Disrupting cortico-cerebellar communication impairs dexterity.

To control reaching, the nervous system must generate large changes in muscle activation to drive the limb toward the target, and must also make smaller adjustments for precise and accurate behavior. Motor cortex controls the arm through projections to diverse targets across the central nervous system, but it has been challenging to identify the roles of cortical projections to specific targets. Here, we selectively disrupt cortico-cerebellar communication in the mouse by optogenetically stimulating the pontine nuclei in a cued reaching task. This perturbation did not typically block movement initiation, but degraded the precision, accuracy, duration, or success rate of the movement. Correspondingly, cerebellar and cortical activity during movement were largely preserved, but differences in hand velocity between control and stimulation conditions predicted from neural activity were correlated with observed velocity differences. These results suggest that while the total output of motor cortex drives reaching, the cortico-cerebellar loop makes small adjustments that contribute to the successful execution of this dexterous movement.

THE zCOSMOS-SINFONI PROJECT. I. SAMPLE SELECTION AND NATURAL-SEEING OBSERVATIONS

The zCOSMOS SINFONI project is aimed at studying the physical and kinematical properties of a sample of massive z~1.4-2.5 star-forming galaxies, through SINFONI near-IR integral field spectroscopy (IFS), combined with the multi-wavelength information from the zCOSMOS (COSMOS) survey. The project is based on 1 hour of natural-seeing observations per target, and Adaptive Optics (AO) follow-up for a major part of the sample, which includes 30 galaxies selected from the zCOSMOS/VIMOS spectroscopic survey. This first paper presents the sample selection, and the global physical characterization of the target galaxies from multicolor photometry, i.e., star formation rate (SFR), stellar mass, age, etc. The Halpha integrated properties such as, flux, velocity dispersion, and size, are derived from the natural-seeing observations, while the follow up AO observations will be presented in the next paper of this series. Our sample appears to be well representative of star-forming galaxies at z~2, covering a wide range in mass and SFR. The Halpha integrated properties of the 25 Halpha detected galaxies are similar to those of other IFS samples at the same redshifts. Good agreement is found among the SFRs derived from Halpha luminosity and other diagnostic methods, provided the extinction affecting the Halpha luminosity is about twice that affecting the continuum. A preliminary kinematic analysis, based on the maximum observed velocity difference across the source, and on the integrated velocity dispersion, indicates that the sample splits nearly 50-50 into rotation-dominated and velocity dispersion-dominated galaxies, in good agreement with previous surveys.

Separation of amino acids in glucose isomerase crystal: Insight from molecular dynamics simulations

The separation of amino acids (Arg, Phe and Trp) in a liquid chromatography is investigated using molecular dynamics simulations. A bioorganic nanoporous material – glucose isomerase crystal – is used as the stationary phase and water as the mobile phase. The transport velocities of amino acids decrease in the order Arg > Phe > Trp, consistent with experimental measurement. The elution order is not affected by the solute concentration or by the flowing rate of mobile phase. Arg is highly hydrophilic and charged, interacts with water the most strongly, and thus moves with flowing water the fastest. Trp has the largest van der Waals volume and encounters the largest steric hindrance, leading to the slowest velocity. From the number distributions of amino acids around protein surface, Trp and Phe are found to stay closer to protein than Arg. The solvent-accessible surface areas of amino acids and the numbers of hydrogen bonds between amino acids and water further elucidate the observed velocity difference. The simulation results provide useful microscopic insight into the retention mechanisms in chromatographic separation process and suggest that glucose isomerase crystal has the capability to separate amino acids.

Spectroscopic Confirmation of an Extreme Starburst at Redshift 4.547

We report the spectroscopic confirmation of a sub-mm galaxy (SMG) at z=4.547 with an estimated L_IR=0.5-2.0x10^13 L_sun. The spectra, mid-IR, and X-ray properties indicate the bolometric luminosity is dominated by star formation at a rate of >1000M_sun per yr. Multiple, spatially separated components are visible in the Ly-Alpha line with an observed velocity difference of up to 380 km/sec and the object morphology indicates a merger. The best fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >10^10 M_sun of stellar mass. This object is a likely progenitor for the massive early type systems seen at z~2.

A Laboratory for Constraining Cosmic Evolution of the Fine‐Structure Constant: Conjugate 18 Centimeter OH Lines toward PKS 1413+135 atz= 0.24671

We report the detection of the satellite 18 cm OH lines at 1612 and 1720 MHz in the z = 0.24671 molecular absorption system toward the radio source PKS 1413+135. The two OH lines are conjugate; the 1612 MHz line is seen in absorption while the 1720 MHz line is seen in weak maser emission of equal but negative optical depth. We do not detect the main 18 cm OH lines at 1667 and 1665 MHz down to 1.1 mJy rms in 4.0 km s-1 channels. The detected and undetected 18 cm OH lines support a scenario of radiatively pumped stimulated absorption and emission with pumping dominated by the intraladder 119 μm line of OH, suggesting a column density N(OH) ≃ 1015-1016 cm-2. Combined with simultaneous H I 21 cm observations and published CO data, we apply the OH redshifts to measurements of cosmic evolution of the fine-structure constant (α ≡ e2/ℏc). We obtain highly significant (~25 σ) velocity offsets between the OH and H I lines and the OH and CO lines, but measurements of α-independent systematics demonstrate that the observed velocity differences are entirely attributable to physical velocity offsets between species rather than a change in α. The OH alone, for which conjugate line profiles guarantee that both lines originate in the same molecular gas, provides a weak constraint of Δα/α0 = (+0.51 ± 1.26) × 10-5 at z = 0.24671. Higher frequency OH line detections can provide a larger lever arm on Δα and can increase precision by an order of magnitude. The OH molecule can thus provide precise measurements of the cosmic evolution of α that include quantitative constraints on systematic errors. Application of this technique is limited only by the detectability of |τ| ~ 0.01 OH lines toward radio continuum sources and may be possible to z ~ 5.

Hubble Space Telescope/STIS Spectroscopy of the Optical Outflow from DG Tauri: Indications for Rotation in the Initial Jet Channel

We have carried out a kinematical, high angular resolution (~01) study of the optical blueshifted flow from DG Tau within 05 from the source (i.e., 110 AU when deprojected along this flow). We analyzed optical emission line profiles extracted from a set of seven long-slit spectra taken with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope, obtained by maintaining the slit parallel to the outflow axis while at the same time moving it transversely in steps of 007. For the spatially resolved flow of moderate velocity (peaking at -70 km s-1), we have found systematic differences in the radial velocities of lines from opposing slit positions, i.e., on alternate sides of the jet axis. The results, obtained using two independent techniques, are corrected for the spurious wavelength shift due to the uneven illumination of the STIS slit. Other instrumental effects are shown to be either absent or unimportant. The derived relative Doppler shifts range from 5 to 20 km s-1. Assuming that the flow is axially symmetric, the velocity shifts are consistent with the southeastern side of the flow moving toward the observer faster than the corresponding northwestern side. If this finding is interpreted as rotation, the flow is then rotating clockwise looking from the jet toward the source and the derived toroidal velocities are in the range 6-15 km s-1, depending on position. Combining these values with recent estimates of the mass-loss rate, one would obtain an angular momentum flux, for the low- to moderate-velocity regime of the flow, of w,lm ~ 3.8 × 10-5 M☉ yr-1 AU km s-1. Our findings may constitute the first detection of rotation in the initial channel of a jet flow. The derived values appear to be consistent with the predictions of popular magnetocentrifugal jet-launching models, although we cannot exclude the possibility that the observed velocity differences are due to some transverse outflow asymmetry other than rotation.

Evidence for an l=0 ground state in 9He

The unbound nuclear systems 10Li and 9He were produced in direct reactions of 28 MeV/u 11Be incident on a 9Be target. The distributions of the observed velocity differences between the neutron and the charged fragment show a strong influence of final-state interactions. Since the neutron originates in a dominant l=0 initial state, a selection-rule argument allows a firm l=0 assignment for the lowest odd-neutron state in 10Li. We report the results suggesting a very similar unbound state in 9He, characterized by an s-wave scattering length more negative than −10 fm corresponding to an energy of the virtual state of less than 0.2 MeV. Shell-model calculations cast light on the reasons for the disappearance of the magic shell gap near the drip line.

The Systemic Velocity and Internal Kinematics of the Dwarf Galaxy LGS 3: An Optical Foray beyond the Milky Way11Based on observations obtained at the W. M. Keck Observatory, which is jointly operated by the California Institute of Technology and the University of California.

ABSTRACTWe have obtained radial velocities of three K giants and one faint carbon star in LGS 3, a dwarf companion of M31, based on 12 individual spectra obtained with the HIRES spectrograph on the Keck I telescope. The mean precision of these measurements is 3.8 km s−1. The mean systemic velocity of LGS 3 is - 282.2 ± 3.5 km s−1. Monte Carlo simulations that take into account the individual velocity uncertainties and the maximum observed velocity difference reveal that the central velocity dispersion of LGS 3 is in the range 2.6–30.5 km s−1, with 95% confidence; the most likely value for the central dispersion is 7.9+5.3-2.9 km s−1. These results agree with the kinematics of Hi gas in LGS 3. This contrasts with the tendency for the gas and stars in other low‐luminosity Local Group dwarfs to exhibit distinct spatial and kinematic properties. Taking into account the relative youth of LGS 3, we conclude that the “asymptotic” M/L ratio—the value the galaxy would exhibit if it were composed only of ancient stars—is M/LV,LGS3≥11 (at a 97.5% confidence level), with a most probable value of 95+175-56. These values are consistent with the M/LV ratios observed in other well‐studied early‐type dwarfs of the Local Group. We have also estimated the mass of LGS 3 using modified Newtonian dynamics. These data represent the first moderately high precision optical spectra of giants in a dwarf system beyond the Galactic halo. We suggest future studies that are now feasible to study the dynamics of dwarf galaxies throughout the Local Group and beyond.

Arcsecond Imaging of CO Emission in the Nucleus of Arp 220

We report high-resolution (1'') imaging of CO (2-1) and dust continuum emission in the ultraluminous galaxy Arp 220. The CO (1-0) line was also imaged at 2'' resolution for comparison. Both data sets recover essentially all of the observed single-dish line emission. Our aperture synthesis maps reveal for the first time, multiple components in the dense gas: peaks corresponding to each of the double nuclei (separated by 095 at P.A. = 101?) seen in the near infrared and radio continuum and a more extended disklike structure at P.A. = 53?, similar to the dust lane seen in optical images. Approximately two-thirds of the total CO emission (and presumably the H2 mass) coincides with the compact double nucleus region. The ISM associated with these nuclear sources is most apparent in the 1.3 mm dust continuum emission, but the brightest CO (2-1) emission is also correlated with the near infrared nuclei and exhibits a radial velocity difference of 250-300 km s-1 between the two nuclei. The latter is in excellent agreement with published near-infrared recombination line measurements. The observed velocity difference between the two nuclei is probably much less than their orbital velocity because the nuclei do not lie along the kinematic major axis of the inner disk. The elongated disk feature exhibits a monotonic velocity gradient parallel to the major axis of the CO intensity distribution with the highest receding velocities in the southwest and the highest approach velocities in the northeast. From the major/minor axis ratio (0.66), we infer that the disk is moderately inclined to the line of sight (i = 40-50?). Detailed modeling of the CO line profiles using a Doppler image-deconvolution technique, analogous to Doppler radar imaging, yields a best-fit CO emissivity distribution and rotation curve which are mutually consistent in the sense that if the total mass distribution follows the CO emissivity, then it yields the derived rotation curve. The implied CO-to-H2 conversion ratio is 0.45 times the Galactic value if the bulk of the mass resides in the molecular gas, rather than stars. This value is also consistent with that expected based on the likely molecular density and temperature in the nuclear disk of Arp 220. The total molecular gas mass for Arp 220 is ~9 ? 109 M? with an uncertainty of ~30% based on the line profile modeling. The peak gas surface density is ~5.8 ? 104 M? pc-2 at 130 pc radius, while the two stellar nuclei are at ~235 pc radius and at position angle midway between the major and minor axes of the gaseous disk. From the profile modeling we derive an intrinsic velocity dispersion in the disk of 90 ? 20 km s-1 and thus a disk thickness (FWHM) of only 16 pc, assuming the disk is in hydrostatic equilibrium. With 5.4 ? 109 M? of molecular gas concentrated in the very thin disk associated with the twin nuclei, the mean density will be nH2${r H}2$ --> 2 ? 104 cm-3 (?30%), a value which is consistent with the strong molecular emission from high dipole moment molecules such as HCN and HCO+. From the high brightness temperatures of the observed CO emission (17-21 K), we conclude that the area filling factor of the disk is very high (0.25) and therefore the gas must fairly uniformly fill the disk, rather than being in discrete self-gravitating clouds. This thin central disk will have inward accretion at 100 M? yr-1 due to viscous and spiral arm transfer of angular momentum. The line profiles at the positions of the double nuclei are double peaked suggesting that there may also be less massive accretion disks associated with each nucleus. The fact that the bulk of the molecular gas has relaxed into a disk with large masses of gas concentrated interior to the double nuclei is consistent with scenarios in which the gas in merging systems settles into the center faster than the two stellar/starburst nuclei. We suggest that dense central accretion disks like that in Arp 220 may be a common feature in the evolution of ultraluminous starburst/AGN galaxies since similar qualitative features are seen in the molecular line data for other systems (e.g., Mrk 231 and NGC 6240).

Line Shifts in the Two-Phase Broad-Line Region with Radial Kinematics

AbstractWe consider in detail the two-phase BLR model with radial infall kinematics. Numerical calculations show that Lyα and C IVλ1549 profiles are blueshifted from their systemic rest-frame velocity, and their profiles are in qualitative agreement with the observations. It seems that the observed velocity differences between the high and low-ionization lines in the spectra of quasars can be understood in such a simple, physical, self-consistent model.

Time Relationships between Direct Particle Emission and Fragmentation: A Probe for Nuclear Expansion Prior to Fragment Freeze-Out

A previously unexploited experimental observable is used to explore emission times for intermediate mass fragments relative to directly emitted ${}^{2}\mathrm{H}$ and ${}^{3}\mathrm{H}$ particles. Small-angle correlations are reported in central collisions for $34A\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$ ${}^{40}\mathrm{Ar}{+}^{\mathrm{nat}}\mathrm{Ag}$. High-velocity ${}^{3}\mathrm{H}$ and ${}^{2}\mathrm{H}$ particles follow a direct emission scenario with mean lifetime $\ensuremath{\tau}\ensuremath{\sim}30\ensuremath{-}60\phantom{\rule{0ex}{0ex}}\mathrm{fm}/c$. Fragmentation to Li is characterized by $\ensuremath{\tau}\ensuremath{\sim}120\mathrm{fm}/c$. Current model calculations suggest a delay time of $\ensuremath{\sim}100\ensuremath{-}200\phantom{\rule{0ex}{0ex}}\mathrm{fm}/c$ for expansion of the central collision zone prior to the onset of ``freeze-out'' into fragments. But the observed velocity difference spectra limit the delay time to $\ensuremath{\lesssim}50\mathrm{fm}/c$ for expansion between direct emission and fragmentation.

Measurements of near‐surface shear in the ocean

In an effort to measure current shear very near the sea surface a string of vector‐measuring current meters suspended beneath a surface float was deployed 180 km off southern California at 34°N 121°30′W on November 26, 1981 and allowed to drift freely for over 6 days. This arrangement, which we call the current meter drifter (CMD), gave measurements at depths of 2.5, 5.5, 8.5, 11.5, 14.5, 25, and 63 m. During the first two days, when the winds were light (≃8 m/s) and variable in direction, a nearly uniform current shear was observed in the upper 15 m with a low‐frequency velocity difference of 5 cm/s between the instruments at 2.5 and 14.5 m. During the last four days, when the winds were brisk (> 12 m/s) and steady in direction from the NNW, a strong downwind shear of order 10−2 s−1 was observed in the upper 10 m with a velocity difference of ∼7 cm/s between the instruments at 2.5 and 8.5 m. During this same period the shear below 10 m was much smaller. The average currents during the CMD drift veer to the right of the wind stress with angular displacement increasing with depth. Time series of the velocity difference between 2.5 and 5.5 m compare very well with θ(t)u*κ−1 ln (5.5/2.5), where θ(t) is the wind direction vector (of unit magnitude), u* = (wind stress/ρ)½ is the friction velocity in water, and κ = 0.4 is von Karman's constant. On the other hand, a similar comparison of the velocity difference between 5.5 and 8.5 m to θ(t)u*κ−1In (8.5/5.5) is much poorer with observed velocity difference being much larger, possibly due to stable stratification effects. Possible errors in the measurements have been considered and estimated as less than the observed velocity differences. Near‐surface shears as large as the observed are very important in closing the momentum budget for the oceanic boundary layer.

An observational study of the dynamics of binary galaxies

We present high quality radial velocities for all galaxies in Turner's (1976a) catalogue of 156 binary systems. We estimate the rms error of a single velocity measurement in our data set to be 29 km s−1. The observed velocity differences depend significantly on the environment of pairs and on the morphological type of their member galaxies; pairs which are associated with larger galaxy groupings have systematically higher velocity differences than more isolated systems, and pairs containing an elliptical or S0 galaxy tend to have higher velocity differences than pairs of spiral or irregular objects. Typical velocity differences are very small; half of the 55 systems in the subsample of isolated spiral–spiral pairs which is our most reliable set of ‘pure’ binaries have measured velocity differences of less than 75 km s−1. Velocity difference correlates extremely weakly with either luminosity or projected separation, and our data are consistent with it being independent of these observables. Using Monte Carlo simulations of scale-free ensembles of binary galaxies we have been able to show that this behaviour is inconsistent both with the hypothesis that the mass of a binary system increases linearly with its luminosity, and with the hypothesis that galaxies in pairs may effectively be treated as point masses. The data favour models where the galaxies interact through a quasi-isothermal potential which depends only weakly on their luminosity. While it turns out to be impossible to estimate either the orbital eccentricity or the mass-to-light ratio of these pairs directly, the velocity differences we have measured are too low to be consistent with the much larger characteristic velocities seen in the outer parts of individual galaxies unless most of our pairs are on near circular orbits. If this is the case their mass-to-light ratio is similar to that predicted by an extrapolation of the flat rotation curves seen in many spiral galaxies.

M82: the exploding galaxy?

IT is nearly 20 yr since M82 was accepted as the archetypal exploding galaxy. Its most spectacular feature is the system of luminous Hα filaments radiating from the core of the galaxy in the direction of the minor axis (ref. 1 and K.T. and D.J.A. in preparation), and the discovery of a velocity gradient within these filaments led to the conclusion that ionised material had been ejected from the nucleus at approximately 103 km s−1 by a cataclysmic explosive event some 106 yr ago2. A later and more extensive spectroscopic study refined and generally confirmed the explosion hypothesis3. It had been assumed that the emission was intrinsic to the filaments, but additional radio and optical data cast doubt on this assumption and hence the whole concept of an explosive event. The well ordered symmetrical pattern exhibited by the broad band polarisation measurements4 was interpreted as a consequence of reflection of the light from the main body of the galaxy by an extensive halo of dust particles5. Furthermore, the emission lines were also found to be polarised identically to the continuum6,7; this strongly implied that they were also seen in reflection and, therefore, the observed velocity differences had to be reinterpreted in terms of motions of the scattering particles. An explosion model then becomes most unlikely, because then the dust would scatter exclusively redshifted light, whereas both blue and redshifts are observed8. M82 is enveloped in a giant HI cloud which engulfs the whole of the M81 group9,10 and Solinger et al.11 therefore suggested that M82 is merely an interloper in the group, moving through this dusty HI cloud in such a way that its drift velocity accounts for the observed Doppler field seen in reflection. We draw attention here to some spectacular new spectroscopic data, which we believe to be irreconcilable with these more recent scattering models and which naturally lead us to resurrect an expulsion hypothesis.

Slowdown of oxyhydrogen detonation by surface catalysis

The propagation velocities of stoichiometric oxyhydrogen detonations were measured in thin tubes of different wall materials. From 4 to 6% velocity differences were observed consistently for pyrex and γ-alumina walls. By changing the tube geometries, it was confirmed that this velocity difference can be explained only by the catalysis of the wall material. To elucidate this result, one-dimensional gasdynamic analysis was performed, including various possible wall reactions. The solutions of this eigenvalue problem gave the relation of each reaction and its catalytic efficiency to the calculated detonation velocity. The results showed that the observed velocity difference can be explained only if we assume that H+OH→H 2 O or H→1/2 H 2 occurs with the maximum catalytic efficiency, i.e., unity. After some speculations, H+OH→ H 2 O was considered more probable, the catalytic efficiency of γ-alumina being nearly unit for this reaction at 300 K.

Alfv�n instabilities in streaming plasmas with anisotropic pressures and their relevance for the solar wind

Low frequency or Alfven waves in streaming plasmas can become unstable when the square of the Alfven velocity is smaller than the mean square of the bulk motion in a co-moving reference frame, 〈(u ‖−〈u ‖〉)2〉, whereu ‖ stands for the bulk velocity of each species and 〈u ‖〉 is the average bulk velocity of the plasma as a whole. For these new Alfven instabilities the streaming effects can be enhanced by a suitable pressure anisotropy. Perpendicular pressure effects are stabilizing, parallel pressure effects are destabilizing, as in the usual firehose instability. The observed velocity differences between helium and the main (hydrogen) flow in the solar wind plasma are such that the Alfven waves are getting close to marginal instability. These new Alfven instabilities limit the velocity differences between helium and hydrogen and thus provide a possible mechanism for accelerating the helium particles up to the order of the main flow velocity.

Multispacecraft study of the solar wind velocity at interplanetary sector boundaries

The sector structure of the interplanetary magnetic field and the solar wind velocity at the sector boundaries are compared at separations of up to 0.3 AU, 50 deg in heliocentric longitude, and 7 deg in heliographic latitude, using data from Mariner 5 en route to Venus and from the near-earth Explorer 33, 34, and 35 satellites. The polarity pattern of the magnetic sectors is found to be very similar at the two locations, and 18 pairs of corresponding sector boundaries are identified. One-hour averages of solar wind velocities near the boundaries show that the velocities near earth exceed those measured by Mariner 5 by as much as 30%. Two possible explanations of the observed velocity differences are discussed: a preferential acceleration of sector boundaries with distance, possibly caused by stream-stream interactions; and a dependence of the solar wind velocity on heliographic latitude.