Estimation Of Number Density Research Articles

QUIESCENT COMPACT GALAXIES AT INTERMEDIATE REDSHIFT IN THE COSMOS FIELD. THE NUMBER DENSITY

We investigate the evolution of compact galaxy number density over the redshift range . Our sample consists of galaxies with secure spectroscopic redshifts observed in the COSMOS field. With the large uncertainties, the compact galaxy number density trend with redshift is consistent with a constant value over the interval . Our number density estimates are similar to the estimates at for equivalently selected compact samples. Small variations in the abundance of the COSMOS compact sources as a function of redshift correspond to known structures in the field. The constancy of the compact galaxy number density is robust and insensitive to the compactness threshold or the stellar mass range (for ). To maintain constant number density any size growth of high-redshift compact systems with decreasing redshift must be balanced by a formation of quiescent compact systems at .

Self-Organized Tubular Structures as Platforms for Quantum Dots

The combination of top-down and bottom-up approaches offers great opportunities for the production of complex materials and devices. We demonstrate this approach by incorporating luminescent CdSe-ZnS nanoparticles into macroscopic tube structures that form as the result of externally controlled self-organization. The 1-2 mm wide hollow tubes consist of silica-supported zinc oxide/hydroxide and are formed by controlled injection of aqueous zinc sulfate into a sodium silicate solution. The primary growth region at the top of the tube is pinned to a robotic arm that moves upward at constant speed. Dispersed within the injected zinc solution are 3.4 nm CdSe-ZnS quantum dots (QDs) capped by DHLA-PEG-OCH3 ligands. Fluorescence measurements of the washed and dried tubes reveal the presence of trapped QDs at an estimated number density of 10(10) QDs per millimeter of tube length. The successful inclusion of the nanoparticles is further supported by electron microscopy and energy dispersive X-ray spectroscopy, with the latter suggesting a nearly homogeneous QD distribution across the tube wall. Exposure of the samples to copper sulfate solution induces quenching of about 90% of the tubes' fluorescence intensity. This quenching shows that the large majority of the QDs is chemically accessible within the microporous, about 15-μm-wide tube wall. We suggest possible applications of such QD-hosting tube systems as convenient sensors in microfluidic and related applications.

THE REDSHIFT DISTRIBUTION OF INTERVENING WEAK Mg II QUASAR ABSORBERS AND A CURIOUS DEPENDENCE ON QUASAR LUMINOSITY

We have identified 469 MgII doublet systems having W_r >= 0.02 {\AA} in 252 Keck/HIRES and UVES/VLT quasar spectra over the redshift range 0.1 < z < 2.6. Using the largest sample yet of 188 weak MgII systems (0.02 {\AA} <= W_r < 0.3 {\AA}), we calculate their absorber redshift path density, dN/dz. We find clear evidence of evolution, with dN/dz peaking at z ~ 1.2, and that the product of the absorber number density and cross section decreases linearly with increasing redshift; weak MgII absorbers seem to vanish above z ~ 2.7. If the absorbers are ionized by the UV background, we estimate number densities of 10^6 - 10^9 per Mpc^3 for spherical geometries and 10^2 - 10^5 per Mpc^3 for more sheetlike geometries. We also find that dN/dz toward intrinsically faint versus bright quasars differs significantly for weak and strong (W_r >= 1.0 {\AA}) absorbers. For weak absorption, dN/dz toward bright quasars is ~ 25% higher than toward faint quasars (10 sigma at low redshift, 0.4 <= z <= 1.4, and 4 sigma at high redshift, 1.4 < z <= 2.34). For strong absorption the trend reverses, with dN/dz toward faint quasars being ~ 20% higher than toward bright quasars (also 10 sigma at low redshift and 4 sigma at high redshift). We explore scenarios in which beam size is proportional to quasar luminosity and varies with absorber and quasar redshifts. These do not explain dN/dz's dependence on quasar luminosity.

A simple reproducible and time saving method of semi-automatic dendrite spine density estimation compared to manual spine counting

Estimation of spine number and spine density by manual counting under the assumption that all dendrite protrusions equal spines are often used in studies on neuroplasticity occurring during health, brain diseases, and different experimental paradigms. Manual spine counting is, however, time consuming and biased by inter-observer variation. We present accordingly a quick, reproducible and simple non-stereological semi-automatic spine density estimation method based on the irregularity of the dendrite surface.Using the freeware ImageJ program, microphotographs of Golgi impregnated hippocampal dendrites derived from a previously performed study on the impact of chronic restrained stress were binarized, skeletonized, and the skeleton endings assumed to represent spine positions were counted and the spine densities calculated. The results based on 754 dendrite fragments were compared to manual spine counting of the same dendrite fragments using the Bland–Altman method.The results from both methods were correlated (r=0.79, p<0.0001), The semi-automatic counting method gave a statistically higher (approx. 4%) spine density number, but both counting methods showed similar significant differences between the groups in the CA1 area, and no differences between the groups in the CA3 area.In conclusion, the presented semi-automatic spine density estimation method yields consistently a higher spine density number than manual counting resulting in similar significance between groups. The proposed method may therefore be a reproducible time saving and useful non-stereological approach to spine counting in neuroplasticity studies requiring analysis of hundreds of dendrites.

Estimation of Number Density of Particles Considering Their Morphology and Size-distribution in Particle Dispersion Strengthening Steels

The number density of particles was estimated regarding to the high strength steels containing non-spherical shaped precipitates with various size. The shapes of particles were evaluated by modeling based on the experimental results obtained by transmission electron microscopy. When the spatial degrees of freedom of particle size were restricted to two-dimensions, the effect of particle size distribution on the number density became relatively small compared to the case of the three spatial degrees of freedom. This finding suggested that the number density might be obtained from the mean particle size. It was noted that the effect of size deviation could be negligible when the particles were platelet-shaped and their thickness was assumed to be constant.

The potential of bioacoustic absorption spectroscopy for long term monitoring of fish populations in the ocean

Bioacoustic absorption spectroscopy (BAS), which exploits frequency selective attenuation due to swim bladder resonances, could be incorporated into ocean observatories for long term monitoring of fish populations. BAS measurements employ environmentally friendly source levels (170 dB) and provide unbiased (by avoidance and proximity to boundaries) estimates of number densities versus fish length (and with ancillary information, species). The BAS II experiment, which was conducted in the Santa Barbara Channel, and employed a fixed ultra-broadband (0.3–10 kHz) source and a fixed vertical hydrophone array separated by 4 km, demonstrated the power of this method. Observed absorption lines in frequency/depth space were consistent with theoretically calculated resonance frequencies of directly sampled year classes of sardines and anchovies, OConnell's (1955) measurements of the dimensions of the swim bladders of these species, and echo sounder measurements of layer depths. Strategies for incorporating BAS measurements into existing fish monitoring methods will be addressed. [This research was supported by the Office of Naval Research.]

The Disector Counting Technique

Number of particles in an organ or region is a valuable data as well as the volume. Many techniques have been developed for the estimation of total number or numerical density of cells in tissues and organs. The quality and reliability of each method has constantly been increased compared to its predecessors. Numerical density is one of the parameters that is used to assess the association between a structure and its function. It should be kept in mind that reliability of biological comments derived from the data is dependent on the method that is used for quantitative estimation of parameters. As stated previously, one of the most important morphometric parameters in biological studies is the ‘number’. Since the ‘number’ has no-dimensions (i.e. Is not bounded by any dimensional property) it could not be directly estimated using a 2D section plane. A good alternative is to use a “volume probe” generated by two consecutive sections, which is called the disector. The disector counting method that was developed by Stereo in 1984 is the most efficient and unbiased solution for particle counting. In this review we will summarize the basic principles of the disector approach and give some examples focused especially on some basic topics in neuroscience research. NeuroQuantology | March 2012 | Volume 10 | Issue 1 | Page 44-53

Bioacoustic absorption/scintillation spectroscopy based classification of fish by size and depth.

Bioacoustic absorption/scintillation spectroscopy (BASS), which exploits frequency selective attenuation and scintillation due to swim bladder resonances, promises classification of fish by size (and with ancillary information and species) and depth and unbiased (by avoidance and proximity of fish to boundaries) estimates of number densities versus fish length. A BASS experiment in the Santa Barbara Channel, which employed a fixed ultrabroadband (0.3–10 kHz) source and a fixed vertical array separated by 4 km, demonstrated the power of this method. The source, which was employed during this experiment, had an environmentally friendly source level of 170 dB. Absorption lines in frequency/depth space, which were associated with year classes of physostomes, sardines, and anchovies, were evident at night when the fish were dispersed. BASS results were consistent with trawl and echo sounder data. Interpretation of absorption lines during daytime was complicated by “bubble cloud” resonances associated with fish schools. Displays of the scintillation index in frequency‐depth space facilitated classification of absorption lines associated with species/year classes. Future experiments will focus on hake, a physoclist. [This work was supported by the Office of Naval Research.]

Uncertainty Propagation in Monte Carlo Depletion Analysis

A new formulation aimed at quantifying uncertainties of Monte Carlo (MC) tallies such as keff and the microscopic reaction rates as well as nuclide number density estimates in MC depletion analysis is presented. It is shown that when the two major MC inputs - the microscopic cross sections and nuclide number densities - are assumed to have uncertainties, the variance of a given MC tally used as a measure of its uncertainty in this formulation arises from four sources: the statistical uncertainty of the MC tally, uncertainties of microscopic cross sections and nuclide number densities, and the cross correlations between them and the latter three contributions can be determined by computing correlation coefficients between uncertain variables. It is also shown that the variance of any given nuclide number density at the end of each depletion time step (DTS) stems from uncertainties of the nuclide number densities and microscopic reaction rates of nuclides at the beginning of each DTS, and they are determined by computing correlation coefficients between these two uncertain variables. The new formulation is incorporated into the Monte Carlo Code for Advanced Reactor Design (McCARD) of Seoul National University, and a McCARD depletion analysis for a U-TRU-Zr fuel assembly is performed to examine quantitatively the uncertainty propagation behavior of MC tallies such as k∞ and the number densities of actinides as a function of DTS. The results demonstrate that the formulation is useful not only for quantifying the uncertainty propagation analysis in MC depletion analysis but also for identifying the types of nuclear cross-section data that need to be improved to obtain a more reliable incineration physics analysis of the transuranium fuel.

Shock structure deformation in plasma jet caused by strong magnetic field

The shock structure deformation in a plasma jet caused by a strong magnetic field was studied using an optical method. The plasma jet images in the enclosing vacuum chamber were taken with a digital single-lens reflex camera through a viewing window. Since the relative values of the measured light intensity are known to have a strong correlation with the number density of excited atoms, the vertical distribution of light intensity can be converted to a radial distribution of excited atom density using an Abel-inversion. The results of this conversion with a magnetic field were compared in the present experiments with those without the presence of a field. It is possible to obtain a smooth radial distribution of estimated number density using an approximate line. The density along the centerline increases obviously with the magnetic field. The minimal density point around the Mach disk was moved slightly upstream with the application of the field. The density distribution inside of the jet boundary was changed considerably by the application of the strong field. The jet boundary itself was not found to be affected significantly by the field although the boundary was found to be slightly contracted to the center axis with application of the field. It has been confirmed that the density distributions are mainly affected by the magnetic field at the corresponding location.

Discovery of Compton-thick quasars in the Sloan Digital Sky Survey

We present new and archival Chandra snapshot (10 ks each) observations of 15 optically identified (from the Sloan Digital Sky Survey, SDSS) Type 2 quasars at z=0.40-0.73. When combined with existing X-ray data, this work provides complete X-ray coverage for all 25 radio-quiet Type 2 quasars with logL_[OIII]>9.28 L_sun from Zakamska et al. (2003). Two targets out of 15 were not detected by Chandra and most of the remaining sources are X-ray weak, with nine having less than 10 counts in the 0.5-8keV band. Low-to-moderate quality spectral analysis was limited to three sources, whose properties are consistent with the presence of column densities in the range NH~10^22-10^23 cm^-2 in the source rest frame. If the [OIII] luminosity is a reliable proxy for the intrinsic X-ray luminosity, the current X-ray data indicate that Compton-thick quasars may hide among ~65 per cent of the SDSS Type 2 quasar population (L_{X, meas}/L_{X, [OIII]}<0.01); however, since the Type 2 quasar sample is selected on [OIII] luminosity, the estimated Compton-thick quasar fraction may be overestimated. Using archival Spitzer observations, we find that ~50 per cent of SDSS Type 2 quasars appear to be obscured by Compton-thick material based on both the L_{X, meas}/L_{X, mid-IR} (where mid-IR corresponds to rest-frame 12.3 micron) and L_{X, meas}/L_{X, [OIII]} ratios. We use this information to provide an estimate of the Compton-thick quasar number density at z=0.3-0.8, which we find is in broad agreement with the expectations from X-ray background models.

Pulsed airborne lidar measurements of atmospheric CO2 column absorption

We report initial measurements of atmospheric CO2 column density using a pulsed airborne lidar operating at 1572 nm. It uses a lidar measurement technique being developed at NASA Goddard Space Flight Center as a candidate for the CO2 measurement in the Active Sensing of CO2 Emissions over Nights, Days and Seasons (ASCENDS) space mission. The pulsed multiple-wavelength lidar approach offers several new capabilities with respect to passive spectrometer and other lidar techniques for high-precision CO2 column density measurements. We developed an airborne lidar using a fibre laser transmitter and photon counting detector, and conducted initial measurements of the CO2 column absorption during flights over Oklahoma in December 2008. The results show clear CO2 line shape and absorption signals. These follow the expected changes with aircraft altitude from 1.5 to 7.1 km, and are in good agreement with column number density estimates calculated from nearly coincident airborne in-situ measurements.

M-BAND SPECTRA OF DUST-EMBEDDED SOURCES AT THE GALACTIC CENTER

The goal of the present paper is to investigate the circumstellar material around the brightest dust-enshrouded sources in the central stellar cluster of the Milky Way. Observations have been carried out at the European Southern Observatory's Very Large Telescope (VLT) on Paranal, Chile. We have used the long wavelength (LWS3) low resolution (LR) spectroscopic mode of the ISAAC camera at the VLT in the spectral range of the M filter from 4.4 μm to 5.1 μm. The use of a slit width of 06 implied a spectral resolution of R = λ/Δλ = 800 (Δv = 375 km s−1). These observations resulted in the M-band spectra of 15 bright sources in the central stellar cluster of the Milky Way. In addition to gaseous 12CO (4.666 μm) and 13CO (4.77 μm) vibration-rotational absorptions, we detect a strong absorption due to a mixture of polar and apolar CO ice (centered at 4.675 μm). In the shorter wavelength absorption wing there is an absorption feature due to XCN at 4.62 μm. The XCN absorption is strongest toward the M2 supergiant IRS 7. We find that the extinctions due to material traced by the CO ice and the CO gas absorptions may be of comparable importance. Using the spectra of IRS 2L and IRS 16C, we perform a first order correction of the line-of-sight absorption due to CO ice and 13CO gas. In combination with published hydrogen number density estimates from sub-millimeter CO(7–6) and FIR [O i] line data, we obtain gas masses of the circumstellar shells of the order of 10−3 and 10−2 M☉. This implies that in future spectra taken at high spectral and angular resolution the bright and dust-embedded Galactic center sources should show a substantial line absorption due to source intrinsic absorption.

Assessing the Reliability of Particle Number Density Measurements Obtained by Image Analysis

AbstractParticle number density measurements obtained by image analysis are biased by edge effects and particle overlap. This paper presents an estimator for particle number density that accounts for both edge effects and particle overlap. Using the output of advanced image analysis applied to artificial images, the estimator is shown to enable effective estimation of particle number density for monodisperse particulate systems at high densities. This paper also proposes a single dimensionless number that correlates with the reliability of the inferred PSD based on the likely number of overlaps per particle. As this dimensionless group becomes large, the degree of overlap and occlusion in the images makes image analysis difficult and unreliable. This parameter can aid practitioners in finding the proper sampling conditions to obtain accurate PSD measurements.

Implications to sources of ultra-high-energy cosmic rays from their arrival distribution

We estimate the local number density of sources of ultra-high-energy cosmic rays (UHECRs) based on the statistical features of their arrival direction distribution. We calculate the arrival distributions of protons above 10 19 eV taking into account their propagation process in the Galactic magnetic field and a structured intergalactic magnetic field, and statistically compare those with the observational results of the Pierre Auger Observatory. The anisotropy in the arrival distribution at the highest energies enables us to estimate the number density of UHECR sources as ∼10 −4 Mpc −3 assuming the persistent activity of UHECR sources. We compare the estimated number density of UHECR sources with the number densities of known astrophysical objects. This estimated number density is consistent with the number density of Fanaroff–Reily I galaxies. We also discuss the reproducibility of the observed isotropy in the arrival distribution above 10 19 eV. We find that the estimated source model cannot reproduce the observed isotropy. However, the observed isotropy can be reproduced with the number density of 10 - 2 – 10 - 3 Mpc - 3 . This fact indicates the existence of UHECR sources with a maximum acceleration energy of ∼10 19 eV whose number density is an order of magnitude more than that injecting the highest energy cosmic rays.

The XMM-LSS survey: the Class 1 cluster sample over the initial 5 deg2 and its cosmological modelling

Abstract We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg2 out to a redshift of z= 1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well-defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses, obtained from dedicated spatial and spectral fitting. The cluster distribution peaks around z= 0.3 and T= 1.5 keV, half of the objects being groups with a temperature below 2 keV. Our LX–T(z) relation points towards self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z= 1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well-monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the LX–T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10 deg2 has the potential to exclude the non-evolution hypothesis, but those constraints on more refined intracluster medium models will probably be limited by the large intrinsic dispersion of the LX–T relation, whatever be the sample size. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to σ8, Ωm, LX–T(z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass–flux and mass–count rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming Sunyaev–Zel'dovich surveys.

Hunting Galaxies to (and for) Extinction

In studies of star-forming regions, near-infrared excess (NIRX) sources--objects with intrinsic colors redder than normal stars--constitute both signal (young stars) and noise (e.g. background galaxies). We hunt down (identify) galaxies using near-infrared observations in the Perseus star-forming region by combining structural information, colors, and number density estimates. Galaxies at moderate redshifts (z = 0.1 - 0.5) have colors similar to young stellar objects (YSOs) at both near- and mid-infrared (e.g. Spitzer) wavelengths, which limits our ability to identify YSOs from colors alone. Structural information from high-quality near-infrared observations allows us to better separate YSOs from galaxies, rejecting 2/5 of the YSO candidates identified from Spitzer observations of our regions and potentially extending the YSO luminosity function below K of 15 magnitudes where galaxy contamination dominates. Once they are identified we use galaxies as valuable extra signal for making extinction maps of molecular clouds. Our new iterative procedure: the Galaxies Near Infrared Color Excess method Revisited (GNICER), uses the mean colors of galaxies as a function of magnitude to include them in extinction maps in an unbiased way. GNICER increases the number of background sources used to probe the structure of a cloud, decreasing the noise and increasing the resolution of extinction maps made far from the galactic plane.

The discovery of a significant sample of massive galaxies at redshifts 5 &lt; z &lt; 6 in the UKIDSS Ultra Deep Survey early data release

We have exploited the large area coverage of the combined UKIDSS Ultra Deep Survey (UDS) and Subaru/XMM-Newton Deep Survey (SXDS) to search for bright Lyman-break galaxies (LBGs) at z >= 5. Using the available optical+near-infrared photometry to efficiently exclude low-redshift contaminants, we identify nine z >= 5 LBG candidates brighter than z'=25(AB) within the 0.6 square degree overlap region between the UDS early data release (EDR) and the optical coverage of the SXDS. Accounting for selection incompleteness, we estimate the corresponding surface density of z >= 5 LBGs with z' ~5x10^10 Msun which, if confirmed, places them amongst the most massive galaxies currently known at z >= 5. It is found that Lambda CDM structure formation can produce sufficient numbers of dark matter halos at z >= 5 to accommodate our estimated number density of massive LBGs for plausible values of sigma_8 and the ratio of stellar to dark matter. Moreover, it is found that recent galaxy formation models can also account for the existence of such massive galaxies at z >= 5. Finally, no evidence is found for the existence of LBGs with stellar masses in excess of ~3x10^11 Msun at this epoch, despite the large co-moving volume surveyed.

Scatterer density estimation in the crust by seismic array processing

SUMMARY Both the number density of scatterers and scattering strength are parameters characterizing the inhomogeneity of the Earth’s crust. An attempt is made to estimate the number density of scatterers (n-value) using small-aperture seismic array data. Many estimates of scattering coefficients have been made previously; however, in a medium with a scattering strength, the wave energy scattered by a medium containing strong scatterers with a low number density is identical to that produced by a high density of weak scatterers. Knowledge of the number density besides the scattering strength supplies important information on stress concentration in the crust due to the strong scatterer reflecting strong inhomogeneity. Therefore, the number density of scatterers is estimated with array signal processing. A seismic array can decompose the approach direction of scattered waves arriving at the array. With array processing, it is not only possible to estimate the energy arriving at the array, but also the semblance value. Temporal variation of the energy depends strongly on the scattering coefficient. On the other hand, the difference in number density of the medium appears in the temporal variation of the semblance value. As a first-order approximation, the semblance value is inversely proportional to the n-value. For practical purposes, an array response should be considered for n-value estimation. Comparing simulated and observed semblances, number density and scattering strength can be estimated from the time sequence of semblances and stacking power. This method was applied to seismic array data from the aftershock area of the 2000 Western Tottori earthquake (Mw 6.8). A rough estimate of number density, compared to a simulation, is 3 × 10 −2 km −3 .

Using spectroscopic ellipsometry for quick prediction of number density of nanoparticles bound to non-transparent solid surfaces

We report on the use of spectroscopic ellipsometry (SE) in predicting number density of nanoparticles bound to the surfaces decorated with either organic monolayers or surface-grafted polymers. Two systems are considered that comprise citrate-stabilized gold nanoparticles adsorbed on: (1) 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM), and (2) surface-tethered polyacrylamide (PAAm). Number density of gold nanoparticles on the surface is varied systematically by gradually increasing either the concentration of APTES molecules in the SAM or molecular weight of grafted PAAm. The adsorption of gold nanoparticles on APTES gradient surfaces is monitored via atomic force microscopy (AFM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and SE. The partition of gold nanoparticles on PAAm gradient assemblies is characterized by AFM, ultraviolet–visible (UV–vis) spectroscopy, and SE. By correlating the results obtained from the various techniques on nanoparticle coatings, we derive an empirical linear relationship between the number density of nanoparticles on surfaces and cos ( Δ) parameter measured in SE. Excellent agreement between nanoparticle number density determined experimentally from AFM scans and that predicted by SE proves the potential of SE as a quick, predictive technique to estimate number density of nanoparticles bound to solid, non-transparent substrates.