Search results for "Number density"
showing 9 items of 19 documents
Crystal growth kinetics in binary mixtures of model charged sphere colloids
2007
From the formation of crystalline materials from their melts is at the heat of many important industrial processes. A rigorous and comprehensive understanding of the crystallization process, however, is still lacking, and its experimental and theoretical investigation has remained a considerable challenge. We studied the crystal growth velocities v of random composition body centred cubic (rc-bcc) colloidal crystals formed from a shear molten binary mixture of charged colloidal spheres suspended in deionized water. We used Bragg microscopy at constant particle number density n and as a function of the number fraction of large particles p. With increasing p the growth velocity v first drops …
Complex permittivity of FeCl3/AOT/CCl4 microemulsions probed by AC impedance spectroscopy
2009
Abstract The complex permittivity of FeCl 3 /AOT/CCl 4 microemulsions in the 1–10 5 Hz frequency range has been measured by the conventional AC complex impedance technique. Measurements as a function of the volume fraction of the dispersed phase (FeCl 3 + AOT) and temperature at fixed salt-to-AOT molar ratio ( R , R = 0.5) show that the entrapment of FeCl 3 clusters significantly enhances the local permittivity of the AOT reverse micelles and the number density of charge carriers resulting from the peculiar state of the confined inorganic salt. An estimate of the apparent static permittivity of the FeCl 3 ionic clusters entrapped in the core of AOT reverse micelles gives the very high an…
Thermal density fluctuations in amorphous polymers as revealed by small angle X-ray diffraction
1973
In the case of equilibrium the mean square relative fluctuations of the thermodynamic parameters vanish asymptotically as the number of degrees of freedom approach infinity. There are various observable effects, however, which are related to local fluctuations of the thermodynamic quantities within small parts of the macroscopic system. In particular the scattering of electromagnetic waves by a one-component, one-phase system is due to thermal density fluctuations within small volumes V of the sample. Considering a grand canonical ensemble the phenomenological theory of local fluctuations (1) for a one component system shows that the fluctuation of the number of particles N in the volume V …
Joint constraints on galaxy bias and σ8 through the N-pdf of the galaxy number density
2015
We present a full description of the N-probability density function of the galaxy number density fluctuations. This N-pdf is given in terms, on the one hand, of the cold dark matter correlations and, on the other hand, of the galaxy bias parameter. The method relies on the assumption commonly adopted that the dark matter density fluctuations follow a local non-linear transformation of the initial energy density perturbations. The N-pdf of the galaxy number density fluctuations allows for an optimal estimation of the bias parameter (e.g., via maximum-likelihood estimation, or Bayesian inference if there exists any a priori information on the bias parameter), and of those parameters defining …
NGC1600 - Cluster or Field Elliptical?
2008
A study of the galaxy distribution in the field of the elliptical galaxy NGC1600 has been undertaken. Although this galaxy is often classified as a member of a loose group, all the neighbouring galaxies are much fainter and could be taken as satellites of NGC1600. The number density profile of galaxies in the field of this galaxy shows a decline with radius, with evidence of a background at approximately 1.3 Mpc. The density and number density profile are consistent with that found for other isolated early-type galaxies. NGC1600 appears as an extended source in X-rays, and the center of the X-ray emission seems not to coincide with the center of the galaxy. The velocity distribution of neig…
Uncertainty in 2-point correlation function estimators and baryon acoustic oscillation detection in galaxy surveys
2012
Abstract We study the uncertainty in different two-point correlation function (2PCF) estimators in currently available galaxy surveys. This is motivated by the active subject of using the baryon acoustic oscillations (BAOs) feature in the correlation function as a tool to constrain cosmological parameters, which requires a fine analysis of the statistical significance. We discuss how estimators are affected by both the uncertainty in the mean density n and the integral constraint 1 V 2 ∫ V 2 ξ ˆ ( r ) d 3 r = 0 which necessarily causes a bias. We quantify both effects for currently available galaxy samples using simulated mock catalogues of the Sloan Digital Sky Survey (SDSS) following a lo…
Rubidium dimers in paraffin-coated cells
2010
Measurements were made to determine the density of rubidium dimer vapor in paraffin-coated cells. The number density of dimers and atoms in similar paraffin-coated and uncoated cells was measured by optical spectroscopy. Due to the relatively low melting point of paraffin, a limited temperature range of 43-80 deg C was explored, with the lower end corresponding to a dimer density of less than 10^7 cm^(-3). With one-minute integration time, a sensitivity to dimer number density of better than 10^6 cm^(-3) was achieved. No significant difference in dimer density was observed between the cells.
Observation of laser-induced field-free permanent planar alignment of molecules
2011
International audience; Permanent planar alignment of gas-phase linear molecules is achieved by a pair of delayed perpendicularly polarized short laser pulses. The experiment is performed in a supersonic jet, ensuring a relatively high number density of molecules with moderately low rotational temperature. The effect is optically probed on a femtosecond time scale by the use of a third short pulse, enabling a time-resolved birefringence detection performed successively in two perpendicular planes of the laboratory frame. The technique allows for an unambiguous estimation of the molecular planar delocalization produced within the polarization plane of the pulse pair after the turn-off of the…
Observational Results On The Influence Of Surface Layer Stability And Inversion Entrainment On Surface Layer Marine Aerosol Number Density (1 Microme…
1983
Wind speed and relative humidity have been the physical variables used in empirical expressions for equilibrium marine aerosol distributions. Recent formulations, which include the role of hydrostatic stability because it influences turbulent transport and entrainment of clear air from aloft, are examined on the basis of 1 um radius aerosol number density values. The aerosol data were collected along with a quite complete meteorological data set in the Northeast Atlantic during the international Joint Air Sea Interaction Experiment (JASIN-78). The 1 um number density values are normalized for generation and relative humidity influences, and analyses are performed to gain reasonable assuranc…