Distance In Units Research Articles

Dark Matter Halos in Elliptical Galaxies

Values of the M/L B ratio in the inner regions of elliptical (E) galaxies are determined using ionized gas disks as tracers of the triaxial potential. These data, when combined with those provided by the H I disks extending to the outer regions, show that the variation of M/L B with galactocentric radius in Es is similar to that of spirals. In particular, it is found that in spirals and Es of the same visible mass the radius where the density of the dark matter equals that of the visible matter occurs at the same distance in units of r e , namely at 1.2r e . This suggests a similar picture of baryonic collapse into a preexisting DM halo for both Es and spirals

ROSAT observations of UZ For: evidence of a structured X-ray emission region

We present the results of ROSAT X-ray and EUV observations of the eclipsing AM Her star UZ For. Data have been obtained during faint and bright phases and, most interestingly, during the rise interval when the emission region appears over the limb of the white dwarf. The source is seen weakly in the X-ray telescope during the faint phase. We find that the rise to the bright phase is resolved, which is direct evidence of a spatially extended soft X-ray emission region and which places constraints on the size of the emission region. Using the bright-phase spectrum and constraints on the flux per unit area on the white dwarf, we find 19 eV < kT(bb) < 25 eV, 7 x 10(19) cm-2 < N(H) < 1.7 x 10(20) cm-2 and a lower limit to the bolometric blackbody luminosity of 1.5 x 10(31) erg s-1 cm-2 d100(2), where d100 is the distance in units of 100 pc. We also show evidence that the blackbody temperature in the rise interval is approximately 10 per cent lower than in the bright phase. The soft X-ray excess is at least a factor of 7.

Cluster-collision frequency. I. The long-range intercluster potential.

In recent years, gas-borne atomic and molecular clusters have emerged as subjects of basic physical and chemical interest and are gaining recognition for their importance in numerous applications. To calculate the evolution of the mass distribution of these clusters, their thermal collision rates are required. For computing these collision rates, the long-range interaction energy between clusters is required and is the subject of this paper. Utilizing a formulation of the iterated van der Waals interaction over discrete molecules that can be shown to converge with increasing numbers of atoms to the Lifshitz--van der Waals interaction for condensed matter, we calculate the interaction energy as a function of center-of-mass separation for identical pairs of clusters of 13, 33, and 55 molecules of carbon tetrachloride in icosahedral and dodecahedral configurations. Two different relative orientations are chosen for each pair of clusters, and the energies are compared with energies calculated from the standard formula for continuum matter derived by summing over pair interactions with the Hamaker constant calculated according to Lifshitz theory. The results of these calculations give long-range interaction energies that assume typical adhesion-type values at cluster contact, unlike the unbounded results for the Lifshitz-Hamaker model. The relative difference between the discrete molecular energies and the continuum energies vanishes for ${\mathit{r}}^{\mathrm{*}}$\ensuremath{\approxeq}2, where ${\mathit{r}}^{\mathrm{*}}$ is the center-of-mass separation distance in units of cluster diameter. For larger separations, the relative difference changes sign, showing a value of approximately 15%, with the difference diminishing for increasing-sized clusters. We argue that the details of the results of these calculations indicate that the deficiency in the continuum picture for small separations lies in the substitution of an averaged picture of the interaction for what is intrinsically the cumulative energy of discrete interactants.

Relativistic electrons in Saturn's inner magnetosphere and an estimate of their synchrotron emission

Energetic electron data obtained by the University of Iowa instrument during Pioneer 11's two‐way traversal of Saturn's inner magnetosphere in September 1979 are reviewed. There were substantial differences between inbound and outbound observations. It is argued that the inbound data are more likely to represent the time‐stationary state. Adopting these inbound data, we develop a quantitative model for the spatial and spectral distributions of relativistic electrons. The principal features of this model are as follows: (1) The radial dependence of omnidirectional intensity J in the equatorial plane is given by J = k′ exp(−1.05 x)[1 − exp(−6.5 x)] where k′ = 1.28 × 107 (cm² s)−1 and x = (r−2.30) with r the radial distance in units of the planet's radius 60,000 km. This distribution is applicable to the range 2.30 ≤ r ≤ 3.60. (2) The latitudinal dependence of J is derived from observed pitch‐angle distributions. These distributions are reasonably well represented by j(α) = j(90°)sin1.5 α (where j is the unidirectional intensity and α is the pitch angle), if one ignores the relatively small depletion of intensity near α = 90°, such depletion being significant in other contexts. (3) As shown previously, the energy spectrum is a relatively narrow one with characteristic energies E in MeV at various r as follows: 0.69 at 5.0; 1.10 at 4.0; 1.89 at 3.0; 2.62 at 2.5; and 3.05 at 2.30. The synchrotron emission of the entire population of relativistic electrons in Saturn's inner magnetosphere is estimated to be about 1 kW with a spectral maximum at 720 kHz. It is shown that this radiation will be very difficult, if not impossible, to observe, even in the near vicinity of the planet. The paper includes a crude but instructive explication of the truly enormous differences between the synchrotron emissions of the inner magnetospheres of Jupiter and Saturn. Indeed, this comparison was an underlying motive for undertaking the present study.

Single Cijystal Luminescence of Dimeric Cis-bis(2-phenvlpyridine)platinum(II) at High Pressure

Abstract The emission spectrum of single-crystal cis-bis(2-phenylpyridine)-platinum(II) has been measured at room temperature under high pressures up to 60 kbar. The observed red shift of the emission is on the order of -15 cm-1/kbar and can be explained by a reduction of the Pt - Pt distance in the dimeric units with increasing pressure.

Formation and molecular structure of a novel six-coordinate aminoalane complex {[(CH3)3Si]2Al(NH2)2}3Al

Reaction of ((CH/sub 3)//sub 3/Si)/sub 3/Al/center dot/O(C/sub 2/H/sub 5/)/sub 2/ and NH/sub 3/ in a 1:2 ratio results in the formation of (((CH/sub 3/)/sub 3/Si)/sub 2/Al(NH/sub 2/)/sub 2/)/sub 3/Al. The compound was characterized by elemental analysis, mass, infrared, and NMR spectroscopic data, and a single-crystal x-ray diffraction analysis. The compound crystallizes in the monoclinic space group C2/c with a = 13.981 (2) /angstrom/, b = 14.064 (2) /angstrom/, c = 23.025 (2) /angstrom/, /beta/ = 106.2 (1)/degree/, Z = 4, V = 4,347 (1) /angstrom//sup 3/, and /rho/ = 0.98 g cm/sup /minus/3/. Least-squares refinement gave R/sub F/ = 9.56% and R/sub wF/ = 7.37% on 2,504 reflections with F /ge/ 3/sigma/(F). The molecular structure shows a central six-coordinate, pseudooctahedral Al atom bonded to three bidentate aminosilyl aluminum ligands, (((CH/sub 3/)/sub 3/Si)/sub 2/(NH/sub 2/)/sub 2//sup /minus//). The average central Al-N(H)/sub 2/ distance is 2.020 (5) /angstrom/, and the average Al-N(H)/sub 2/ distance in the ligands units is 1.932 (5) /angstrom/. Pyrolysis of this molecular species provides a mixture of AlN and SiC. 11 refs., 1 fig., 3 tabs.

Synthesis and molecular structure of the optically active organoaluminium dimer (S)-(—)-(S)-(—)- [(C 6H 5)CH(CH 3)NHA1(CH 3) 2] 2

Reaction of the optically active primary amine (S)-(—)-α-methylbenzylamine with trimethylaluminium in heptane affords the crystalline organoaluminium dimer (S)-(—)-(S)-(—)-[(C 6H 5)CH(CH 3)NHA1(CH 3) 2] 2. Isolated as large, colourless, extremely air-sensitive prismatic crystals, the title compound crystallizes in the orthorhombic space group P2 12 12 1 with unit cell parameters a = 8.406(3), b = 15.505(4), c = 17.547(5) Å, V = 2287 Å 3 and ϱp = 1.03 g cm −3 for Z = 4. Least-squares refinement based on 1477 observed reflections converged at R = 0.056, R w = 0.058. Methane was eliminated during the course of the reaction due to cleavage of A1C and NH bonds resulting in an asymmetric A1 2N 2 fragment at the core of the organoaluminium dimer. The mean A1C bond distance in the dimethylaluminium units is 1.930(8), while the mean A1N bond distance is 1.950(5) Å. Specific rotation ([α] D 25 in CH 2C1 2)of the dimer is determined to be - 20.6°.

The reaction between tungsten hexafluoride and pentafluoroaniline

Tungsten hexafluoride reacts with pentafluoroaniline to give a mixture containing the imido anions [WF 5(NC 6F 5)] − and [W 2F 9(NC 6F 5) 2] −. From the solution in CF 3COOH the salt C 6F 5NH 3 +[(C 6F 5N)WF 4(F)WF 4(NC 6F 5)] − was isolated and its X-ray crystal structure determined. In the crystal there are two crystallographically distinct anions, both with fluorine bridges; in one the WFW angle is 150.8° and in the other 170.4°. The average W—N distance in the linear WNC units is 1.74 Å. A 19F NMR study in MeCN suggests the anions to be linear in solution.

Rescaling of ecological gradients. I. Calculation of ecological distance between vegetation stands by means of their floristic composition

Geometric models of vegetation (conceptual spaces) are reviewed. Spaces with samples or species as axes are termed flortistic spaces, as opposed to ecological space with environmental gradients as axes. The terms floristic and ecological relationships are defined as relationships in floristic and ecological spaces, respectively. Compositional turnover is pointed out as the essence of ecological gradients, and arguments in favour of measuring ecological distance in units of compositional turnover are given. The most important criteria for evaluation of ecological distance measures are considered to be linear response to separation along ecological gradients and robustness. Theoretical disadvantages of measures of floristic relationships used as ecological distance measures are discussed. A new measure of ecological distance, separation along a DCA ordination axis, is proposed. This measure and four measures of floristic relationships were tested on four simulated coenoclines (high and low beta diversity, high and low noise) using four weighting functions. The new measure was generally superior, particularly with noisy data. The distance measures generally performed best with intermediate weighting of a percentage cover scale. Application of DCA to calculation of ecological distances in multi‐gradient systems is briefly discussed. The potential of DCA for rescaling of ecological gradients is emphasized, and some possible applications of rescaling are suggested.

Coupled low‐energy ‐ ring current plasma diffusion in the Jovian magnetosphere

We derive a functional form of the diffusion coefficient appropriate to fully developed, steady state, centrifugally driven turbulence in Jupiter's magnetosphere, incorporating in the diffusion coefficient the effects of the pressure gradient of the ring current. We set up a steady state, coupled diffusion model to describe the simultaneous outwardly diffusing low‐energy (Iogenic) plasma and the inwardly diffusing ring current plasma. The model is a nonlinear, third‐order, ordinary differential system containing four parameters. In order to test the hypothesis that the pronounced reduction in the radial diffusion coefficient (implied by the existence of the Io plasma ramp) is caused by the pressure gradient of the ring current, we seek solutions to the model under the condition that a reduced form of the diffusion coefficient takes on a minimum value at some point within the spatial extent of the ramp, i.e., within the range 7 ≤ L ≤ 8, where L is radial distance in units of Jovian radius RJ. This condition leads to several necessary conditions on the model parameters and the values of the ring current density and density gradient at the minimum point. We find that high‐energy (0.5–1.05 MeV) ring current particles, which have been previously observed and whose density decreases inwardly by several orders of magnitude over the range 6 ≤ L ≤ 10, cannot cause a sufficient inhibition of Iogenic plasma diffusion to cause the ramp. Further, we show that for ring current pressure to cause the ramp there must exist a component of the ring current particle population with sufficiently low thermal energy and with sufficiently high density, e.g., corresponding to an Iogenic plasma flux of 2×1028 s−1 the bulk of the ring current particles must have thermal energies of less than 3.9 keV and corresponding ring current particle densities at, say, L = 7.5 must exceed by two orders of magnitude those observed for the high‐energy component. We infer the existence of this dense, low‐energy component of the ring current from an independent energy calculation. Our model predicts that the density of the dense, low‐energy ring current particles decreases inwardly only by about an order of magnitude over the range 6 ≤ L ≤ 10. We provide representative numerical solutions for the density profiles of the Iogenic and ring current plasmas.

Calibrating the molecular clock: estimates of ground squirrel divergence made using fossil and geological time markers.

According to 5-Myr-old fossil evidence, ground squirrels within the genus Spermophilus had diverged into subgenera Spermophilus and Otospermophilus by late Miocene times. Radiometric dating has also provided a precise time for the sudden onset of a geological event, occurring 0.725 Myr ago, that initiated the complete and permanent reproductive isolation of two subspecies within the subgenus Otospermophilus. Since these two subspecies (S. beecheyi beecheyi and S. b. douglasii) readily hybridize with each other under laboratory conditions, allopatric subspeciation is unlikely to have occurred prior to 0.725 Myr ago. We employed Nei's model for estimating genetic distance in units which are linear in time, calibrated on the 0.725-Myr-ago date for initiation of S. b. subspeciation, to test its ability to generate a time scale for subgeneric divergence in keeping with the minimum estimate provided by the fossil record. This represents the most valid test to date of the utility of Nei's model for estimating genetic distance in units which are linear in time. Nei's model was found to underestimate this minimum time by 1 Myr, but it approximated this date after correcting values of D for variation in rates of evolution among loci.

Experimental Study of Neutron Streaming through Steel-Walled Annular Ducts in Reactor Shields

For the purpose of providing experimental data to assess neutron streaming calculations, neutron flux measurements were performed along the axes of the steel-walled annular ducts set up in a water shield of the pool-type reactor JRR-4. An annular duct simulated the air gap around the main coolant pipe. Another duct simulated the streaming path around the primary circulating pump of the integrated-type marine reactor. A 90-deg bend annular duct was also studied. In a set of measurements, the distance Z between the core center and the duct axis and the annular gap width delta were taken as parameters, that is, Z = 0, 80, and 160 cm and delta = 2.2, 4.7, and 10.1 cm. The reaction rates and the fluxes measured by the activation method are given in terms of absolute magnitude within an accuracy of + or - 30%. An empirical formula is derived based on those measured data, which describes the axial distribution of the neutron flux in the steel-walled annular duct in reactor shields. It is expressed by a simple function of the axial distance in units of the square root of the line-of-sight area, S /SUB l/ . The accuracy of the formula is examinedmore » by taking into account the duct location with respect to the reactor core, the neutron energy, the steel wall thickness, and the media outside of the steel wall. The accuracy of the formula is, in general, <30% in the axial distance between 3..sqrt..S /SUB l/ and 30..sqrt..S /SUB l/ .« less

Derivation of a proximity interaction between nuclei from the Hartree-Fock functional with Skyrme interactions

The potential between heavy or medium heavy spherical nuclei is derived on the basis of the proximity approximation and the assumption of undisturbed spherical density distributions. The HF-theory with Skyrme forces is used to write the energy as a functional of the density. The resulting potential consists of an isoscalar and a (much smaller) isospin-dependent part. Depending on the choice of the Skyrme parameters calculated interaction between heavy ions are close to the double folding potential or to the proximity potential. Our interaction can be factorized with a very good approximation into scaling factors and universal functions of the proximity distance in units of the surface thickness.

On the association between a γ-ray burst and a radio pulse

ONE minute after the γ-ray burst of 16 August 1976, a radio event with ∼ 30s duration was recorded by three different instruments, a dipole array and a 10-m parabola at Medicina (Bologna), and a 10-m parabola at Trieste (400km away) (refs 1 and 2). The peak intensity at 151 and 408 MHz was ∼ 10−21W m−2 Hz with an upper limit to the dispersion between the two frequencies of ∼ 10 s. In the absence of specific data on the γ-ray flux we take a typical value of 10−4 erg cm−2 corresponding to an energy output of 1038 d1002 erg, where d100 is the distance in units of 100 pc.

Optical structure of the X-ray globular cluster NGC 6624

The central region of the x-ray globular cluster NGC 6624 is studied optically on short exposure photographic plates. A bright unresolved region, about 4'' in size and approx.12.5 mag in apparent visual brightness is observed near the center of the cluster on the shortest-exposure plates. The projected density distribution of the stars is determined from star counts that extend to within about 5'' (= 0.25 pc x d/sub 10/, where d/sub 10/ is the distance in units of 10 kpc) of the center of the cluster. The structural parameters of the cluster are derived to be: core radius = 0''<./sub /13 +- ''.09 (=0.4 +- 0.3 pc x d/d/sup 10/), factor c equivalent log r/sub t//r/sub c/ approx. = 2.0, and central density (from the central surface brightness of Kron and Yayall, and assuming d/sup 10/ = 1) of 4.5 x 10/sup 4/ M/sub sun/ pc/sup -3/. The radial distribution of stars is steep toward the center, showing no leveling-off of the density near the center down to the nearest measured point at approx.5''. The estimated central escape velocity and relaxation time in the cluster fall within the region given by Bahcall and Ostriker as the most likely one formore » globular clusters having x-ray emission due to the accretion of gas by a massive black hole. (AIP)« less

Deuteron Magnetic Resonance Study of Cupric Sulfate Pentahydrate

A deuteron magnetic resonance study is made of single crystals of CuSO4·5D2O between 130° and 360°K. The electric quadrupole coupling constant, the asymmetry parameter, and the directions of the principal axes of the field-gradient tensor are determined for each deuteron at 133.2° and 294.8°K. At low temperatures ten pairs of lines are observed, corresponding to five nonequivalent stationary water molecules. At temperatures above room temperature, five pairs of lines are observed; these are shown to result from fast molecular reorientation about the bisecting axis of each water molecule. An activation energy for the 180° reorientational motion is derived for each water molecule and is discussed in relation to the lonepair coordination of the oxygen atom of the water molecule and the hydrogen-bond strength. The field-gradient tensor for each stationary water molecule is discussed in relation to the structure of the hydrogen-bond system. For relatively weak asymmetric hydrogen bonds of O–H···O, an empirical equation, eQq/h = 310.0 − 3.0 × 190.6 / R(O···H)3 (kHz), is found to represent the observed values well, where R(O···H) is the O···H distance in angstrom units. For strong hydrogen bonds, there is a significant deviation from the above relation, indicating that the covalent effect is of importance in these cases. Coordination to a paramagnetic ion has no marked effect on the quadrupole coupling constant, but it appears to cause a rotation of the directions of principal x and y axes about the O–H bond. Two possible cases of the principal y-axes directions for the field-gradient tensor of the reorienting water molecule are analyzed in detail, and the available experimental data are classified into two groups. Theoretical formulas for the DMR spectra in the paramagnetic crystals are derived and compared with that in diamagnetic crystals. A local field due to the cupric ions is derived from the observed paramagnetic shift at 133.2°K for each deuteron and is found to be due to the electron nuclear spin dipole coupling. The spectra are observed at temperatures up to the dehydration point, and it is found that the free rotation of the water molecule does not occur in this temperature range.

Rapid Changes in the Optical Intensity and Radial Velocities of the X-Ray Source SCO X-1

view Abstract Citations (79) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rapid Changes in the Optical Intensity and Radial Velocities of the X-Ray Source SCO X-1 Westphal, J. A. ; Sandage, Allan ; Kristian, Jerome Abstract The optical flux of Sco X-1 was continuously monitored on five separate nights between April and June 1967. Pulse counting was used with sampling intervals of 5 sec on the 100- and 200-inch telescopes and 15 sec on the 60-inch reflector. The error due to photon statistics per sample interval was smaller than 0.007 mag in all cases. The data were processed entirely by computer, using a variety of special digital techniques. Rapid optical flickering with amplitudes of ~0.02 mag on a time scale of minutes was found on all five nights. These high-frequency fluctuations are superposed on slower continuous variations with amplitudes ~0.15 mag, and on occasional bursts of 0.2 mag which last about 10 min with very short rise and decay times. Radial velocities have been measured by a digital method of cross-correlation of microphotometer records of the original photographic plates (Westphal 1966). Velocity changes of about 100 km/s were found on two different singly trailed plates, each of 3 hours' duration. The hydrogen lines and He II (4686) change in opposite directions, similar to the extar Cyg X-2, suggesting, but not proving, binary motion. Systematic changes of velocity from night to night are set out in Table 2. The distance to Sco X-1 is estimated to be D ~ 500 pc by three methods, based on the strength of interstellar Ca II K, and on the old nova hypothesis. A firm lower limit of D > 300 pc seems well established. The total X-ray power is ~ 2x1037 h2 ergs/sec, where h is the distance in units of 500 pc. If the X-ray energy is due to bremsstrahlung, this level requires Sco X-1 to continuously pump energy into the hot plasma, replenishing the entire energy store of gas in the cooling time of t=3x10-11 h-1 R3/2 sec where R is the radius (in centimeters) of the plasma system. Reasonable values of 1011 cm < R < 1012 cm give 100 h-1 < t < 3000 h-1 sec, which, remarkably, is the characterisic time of the light flicker. Mechanical energy due to some type of low-Q oscillation of the system, similar in many respects to that observed in the Sun, seems capable of providing 1037 ergs/sec to the plasma gas. The crucial experiment remains to simultaneously monitor the optical and the X-ray flux over periods of several hours. Detailed correlation of fluctuations is not expected, but the mean X-ray flux might plausibly be expected to vary in periods of fractions of an hour as the mean amplitude of the optical fluctuations changes. Publication: The Astrophysical Journal Pub Date: October 1968 DOI: 10.1086/149746 Bibcode: 1968ApJ...154..139W full text sources ADS |

Genetic recombination in Escherichia coli: I. Relation between linkage of unselected markers and map distance

A relation between linkage frequency of an unselected marker and transfer time based on a physical exchange of genetic material was developed for Escherichia coli crosses. Crosses performed under standardised conditions have shown that the relation was valid. The linkage frequency is determined by two constants and one parameter. The constants are the incorporation frequency for donor fragments and the average number of breakage events per unit length. The variable in the relation is the distance in time units between selected and unselected marker.

Refraction arrivals along a thin elastic plate surrounded by a fluid medium

An asymptotic solution is derived for the first arrival of significant amplitude and low frequency, which is refracted along a thin high-velocity plate surrounded by a fluid medium. This first arrival travels with approximately the velocity of a longitudinal plate wave in the refracting layer. The shape of the signal depends upon the contrast (in density and elastic constants) between the plate and the fluid as well as upon the distance (in units of plate thickness) that the signal has been refracted along the plate. Solutions in closed form are given. For the case of moderate contrast or large distance, we treat the problem of a point and of a line source in the fluid emitting a step (or δ) pressure pulse. The refracted signal is approximately a gaussian curve (or its derivative). For the case of large contrast and moderate distance, we treat the problem of a line source in the fluid emitting a step pressure pulse. The refracted signal is described by an Airy function. For intermediate cases, the refracted signal for the line or for the point source is given in the form of an integral, which must be evaluated numerically. Because of the relatively simple nature of the results, interesting features of the signal are readily derived. In an appendix, we discuss briefly a thin high-velocity plate shallowly submerged in a liquid half-space. The low-frequency refracted signal from a step pressure line source is described by an Airy function for all cases of contrast.

The Energy Band Structure of a Linear Metal

A tight binding calculation of the one-electron energy as a function of wave number is described for a linear chain of hydrogen atoms in the ground state. The calculation is accurate to the order of exp (-2a), where a is the interatomic distance (in atomic units), all non-orthogonality and energy integrals of this order of magnitude being included in the energy expression. A closed expression for the band width is derived and compared with expressions corresponding in their approximations to those usually made in tight binding calculations for actual metals.