Low-density Clusters Research Articles

Planets in open clusters detectable byKepler

While hundreds of planets have been discovered around field stars, only a few are known in star clusters. To explain the lack of short-period giant planets in globular clusters (GCs), such as 47 Tucane and ω Centauri, it has been suggested that their low metallicities may have prevented planet formation. Alternatively, the high rates of close stellar encounters in these clusters may have influenced the formation and subsequent evolution of planetary systems. How common are planets in clusters around normal main-sequence stars? Here we consider whether this question can be addressed using data from the Kepler mission. The Kepler field of view contains four low-density (relative to GCs) open clusters where the metallicities are about solar (or even higher) and stellar encounters are much less frequent than in typical GCs. We provide detailed N-body models and show that most planets in Kepler-detectable orbits are not significantly perturbed by stellar encounters in these open clusters. We focus on the most massive cluster, NGC 6791, which has supersolar metallicity, and find that if planets formed in this cluster at the same frequency as observed in the field, Kepler could detect 1–20 transiting planets depending on the planet-size distribution and the duration of data collection. Due to the large distance to NGC 6791 Kepler will have to search relatively faint (Kp < 20) stars for the full extended mission to achieve such a yield.

Textures of Peritectic Crystals as Guides to Reactive Minerals in Magmatic Systems: New Insights from Melting Experiments

Peritectic crystals in igneous rocks may be derived from either the source or country rocks, or may have formed by reactive assimilation of source-inherited solids, primary magmatic minerals during self- or magma mixing, or country-rock xenoliths or xenocrysts. Identifying such peritectic crystals is important for constraining the components and textures of igneous rocks and the underlying processes of magmatic evolution. In this study we demonstrate that peritectic olivine formed in melting experiments crystallizes as clusters of euhedral to subhedral crystals. Olivine replacing orthopyroxene, amphibole, and phlogopite forms crystal clusters with distinct crystal to melt ratios, 2D surface area, grain boundary segmentation, and inclusion relations. In our experiments the textures of peritectic crystals are primarily controlled by the stability temperature and decomposition rate of reactive minerals. High-temperature minerals such as orthopyroxene slowly decompose to form high-density clusters of large crystals with long grain boundary segments. The SiO2-rich peritectic melt produced favours formation of melt inclusions. Low-temperature minerals such as amphibole and phlogopite rapidly decompose to form low-density clusters of small crystals with short grain boundary segments. The relatively SiO2-poor peritectic melt produced results in the formation of fewer melt inclusions. Host melt composition has a minor effect on the textures of peritectic olivine formed in the melting experiments of this study and previous contamination experiments, but affects the assemblages of the peritectic crystal clusters. Cluster density and 2D surface area of peritectic olivine tend to decrease, whereas grain boundary segment length increases with increasing experimental temperature and H2O content. Using textural criteria that distinguish olivine formed after different minerals in our melting experiments, we hypothesize that two olivine populations from a basaltic^andesitic lava flow of the Tatara^San Pedro volcanic complex, Chile, may be peritectic crystals formed after amphibole and orthopyroxene. Both amphibole and orthopyroxene are common in xenoliths preserved in some Tatara^San Pedro lava flows. One notable difference between the experimental and natural olivine crystals is that the natural olivine crystals have 2D surface areas and 2D grain boundary segments up to � 1000 and � 100 times larger, respectively, than those produced in our experiments. We propose that this size difference is primarily controlled by comparatively slow heating and decomposition of reactive crystals and textural coarsening of peritectic crystals during prolonged magma residence in the natural system.

Quasi-likelihood techniques in a logistic regression equation for identifying Simulium damnosum s.l. larval habitats intra-cluster covariates in Togo

The standard methods for regression analyses of clustered riverine larval habitat data of Simulium damnosum s.l. a major black-fly vector of onchoceriasis, postulate models relating observational ecological-sampled parameter estimators to prolific habitats without accounting for residual intra-cluster error correlation effects. Generally, this correlation comes from two sources: (1) the design of the random effects and their assumed covariance from the multiple levels within the regression model and (2) the correlation structure of the residuals. Unfortunately, inconspicuous errors in residual intra-cluster correlation estimates can overstate precision in forecasted S. damnosum s.l. riverine larval habitat explanatory attributes regardless how they are treated (e.g. independent, autoregressive, Toeplitz, etc.). In this research, the geographical locations for multiple riverine-based S. damnosum s.l. larval ecosystem habitats sampled from two preestablished epidemiological sites in Togo were identified and recorded from July 2009 to June 2010. Initially, the data were aggregated into PROC GENMOD. An agglomerative hierarchical residual cluster-based analysis was then performed. The sampled clustered study site data was then analyzed for statistical correlations using monthly biting rates (MBR). Euclidean distance measurements and terrain-related geomorphological statistics were then generated in ArcGIS. A digital overlay was then performed also in ArcGIS using the georeferenced ground coordinates of high and low density clusters stratified by annual biting rates (ABR). The data was overlain onto multitemporal sub-meter pixel resolution satellite data (i.e. QuickBird 0.61 m wavbands). Orthogonal spatial filter eigenvectors were then generated in SAS/Geographic Information Systems (GIS). Univariate and nonlinear regression-based models (i.e. logistic, Poisson, and negative binomial) were also employed to determine probability distributions and to identify statistically significant parameter estimators from the sampled data. Thereafter, Durbin–Watson statistics were used to test the null hypothesis that the regression residuals were not autocorrelated against the alternative that the residuals followed an autoregressive process in AUTOREG. Bayesian uncertainty matrices were also constructed employing normal priors for each of the sampled estimators in PROC MCMC. The residuals revealed both spatially structured and unstructured error effects in the high and low ABR-stratified clusters. The analyses also revealed that the estimators, levels of turbidity, and presence of rocks were statistically significant for the high-ABR-stratified clusters, while the estimators distance between habitats and floating vegetation were important for the low-ABR-stratified cluster. Varying and constant coefficient regression models, ABR-stratified GIS-generated clusters, sub-meter resolution satellite imagery, a robust residual intra-cluster diagnostic test, MBR-based histograms, eigendecomposition spatial filter algorithms, and Bayesian matrices can enable accurate autoregressive estimation of latent uncertainity affects and other residual error probabilities (i.e. heteroskedasticity) for testing correlations between georeferenced S. damnosum s.l. riverine larval habitat estimators. The asymptotic distribution of the resulting residual adjusted intra-cluster predictor error autocovariate coefficients can thereafter be established while estimates of the asymptotic variance can lead to the construction of approximate confidence intervals for accurately targeting productive S. damnosum s.l. habitats based on spatiotemporal field-sampled count data.

New highland distribution records of multiple Anopheles species in the Ecuadorian Andes

BackgroundSeveral recent climate change reviews have stressed the possibility of some malaria vectors occupying regions of higher altitudes than previously recorded. Indeed, highland malaria has been observed in several African nations, possibly attributable to changes in land use, vector control and local climate. This study attempts to expand the current knowledge of the distribution of common Anopheles species in Ecuador, with particular attention to highland regions (> 500 m) of the Andes.MethodsExtensive field collections of larvae were undertaken in 2008, 2009 and 2010 throughout all regions of Ecuador (except the lower-altitude Amazonian plain) and compared to historical distribution maps reproduced from the 1940s. Larvae were identified using both a morphological key and sequencing of the 800 bp region of the CO1 mitochondrial gene. In addition, spatial statistics (Getis-Ord Hotspot Analysis: Gi*) were used to determine high and low-density clusters of each species in Ecuador.ResultsDistributions have been updated for five species of Anopheles in Ecuador: Anopheles albimanus, Anopheles pseudopunctipennis, Anopheles punctimacula, Anopheles eiseni and Anopheles oswaldoi s.l.. Historical maps indicate that An. pseudopunctipennis used to be widespread in highland Andean valleys, while other species were completely restricted to lowland areas. By comparison, updated maps for the other four collected species show higher maximum elevations and/or more widespread distributions in highland regions than previously recorded. Gi* analysis determined some highland hot spots for An. albimanus, but only cold spots for all other species.ConclusionsThis study documents the establishment of multiple anopheline species in high altitude regions of Ecuador, often in areas where malaria eradication programs are not focused.

A NEW PULSAR IN GREEN BANK TELESCOPE SEARCHES OF 10 GLOBULAR CLUSTERS

We report the results of pulsar searches in ten globular clusters using the Robert C. Byrd Green Bank Telescope. One new binary millisecond pulsar has been discovered in NGC 5986 with P=2.6 ms, P_orb=1.3 d, and a minimum companion mass of 0.16 M_sun. The companion is most likely a Helium white dwarf. Eight of the globular clusters we searched have central densities <10^4 L_sun pc^-3, making this a good sample for studying the pulsar content of low density clusters. We find no evidence for pulsars in clusters with very low densities <10^3 L_sun pc^-3, consistent with theoretical predictions. Null results in many of clusters we searched with moderate densities indicate that these systems do not contain a bright MSP. Two clusters in particular, one with very low metallicity, stand in contrast to theoretical calculations by Ivanova et al. (2008). We also find that three body exchange interaction rates calculated by Phinney (1996) seem to over predict the pulsar content in the clusters we studied.

The dynamical evolution of very low mass binaries in open clusters

Very low-mass binaries (VLMBs), with system masses <0.2 Msun appear to have very different properties to stellar binaries. This has led to the suggestion that VLMBs form a distinct and different population. As most stars are born in clusters, dynamical evolution can significantly alter any initial binary population, preferentially destroying wide binaries. In this paper we examine the dynamical evolution of initially different VLMB distributions in clusters to investigate how different the initial and final distributions can be. We find that the majority of the observed VLMB systems, which have separations <20 au, cannot be destroyed in even the densest clusters. Therefore, the distribution of VLMBs with separations <20 au now must have been the birth population (although we note that the observations of this population may be very incomplete). Most VLMBs with separations >100 au can be destroyed in high-density clusters, but are mainly unaffected in low-density clusters. Therefore, the initial VLMB population must contain many more binaries with these separations than now, or such systems must be made by capture during cluster dissolution. M-dwarf binaries are processed in the same way as VLMBs and so the difference in the current field populations either points to fundamentally different birth populations, or significant observational incompleteness in one or both samples.

How do binaries affect the derived dynamical mass of a star cluster?

The dynamical mass of a star cluster can be derived from the virial theorem, using the measured half-mass radius and line-of-sight velocity dispersion of the cluster. However, this dynamical mass may be a significant overestimation of the cluster mass if the contribution of the binary orbital motion is not taken into account. Here, we describe the mass overestimation as a function of cluster properties and binary population properties, and briefly touch on the issue of selection effects. We find that for clusters with a measured velocity dispersion of σ los≳10 km s−1 the presence of binaries does not affect the dynamical mass significantly. For clusters with σ los≲1 km s−1 (i.e., low-density clusters), the contribution of binaries to σ los is significant, and may result in a major dynamical mass overestimation. The presence of binaries may introduce a downward shift of Δlog (L V /M dyn)=0.05–0.4 (in solar units) in the log (L V /M dyn) versus age diagram.

URBAN CLUSTERS AS GROWTH FOCI*

ABSTRACT Urban clusters are geographic concentrations of urban places, some of which may include major cities. Unlike agglomerations, whose geographic boundaries are clearly delineated, urban clusters have “variable” boundaries, with each urban settlement being part of its “own” cluster of populated places, located within its commuting range. As our study indicates, the effect of clustering on urban growth is not uniform: it appears to be positive in low density clusters, and negative in densely populated ones. In particular, outside densely populated areas, towns surrounded by other localities tend to evince higher rates of population growth than their “lone” counterparts.

The near-IR luminosity function and bimodal surface brightness distributions of Virgo cluster galaxies

We have acquired deep, H-band imaging for a sample of 286 Virgo cluster galaxies with B T ≤ 16 mag and extracted surface photometry from optical g, r, i, z Sloan Digital Sky Survey images of 742 Virgo Cluster Catalogue galaxies, including those with H-band images. We confirm the detection of a dip in the luminosity function indicative of a discontinuity in the cluster galaxy population; the dip is more pronounced at redder wavelengths. We find, in agreement with earlier works of Tully and Verheijen and ours for Ursa Major cluster galaxies, a clear dichotomy between high and low surface brightness (HSB and LSB) galaxy discs. The difference between the low and high brightness peaks of Virgo disc galaxies is ∼2 H-mag arcsec -2 , significantly larger than any systematic errors. The high surface brightness disc galaxies have two distinct classes of high and low concentration bulges, while LSB galaxies have only low concentration bulges. Early-type galaxies exhibit a similar structural bimodality though offset from that of the spiral galaxies towards higher surface brightnesses. Both the early- and late-type structural bimodalities are uncorrelated with colour or any other structural parameter except, possibly, circular velocity. Random realizations of realistic surface brightness profiles suggest that a bimodal distribution of effective surface brightness is unexpected based on normal distributions of bulge and disc parameters. Rather, the structural bimodality may be linked to dynamic properties of galaxies. Low angular momentum systems may collapse to form dynamically important discs with high surface brightness, while high angular momentum systems would end up as low surface brightness galaxies dominated by the dark halo at all radii. The confirmation of structural bimodality for gas-rich and gas-poor galaxies in the high-density Virgo cluster as well as the low-density UMa cluster suggests that this phenomenon is independent of environment.

Chandra X‐Ray ObservatoryObservations of the Globular Cluster M71

We observe the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-Ray Observatory to study its faint X-ray populations. Five X-ray sources are found inside the cluster core radius, including the known eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light curve of the source coincident with this MSP shows marginal evidence for periodicity at the binary period of 4.2 hr. Its hard X-ray spectrum and luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting a similar shock origin of the X-ray emission. A further 24 X-ray sources are found within the half-mass radius, reaching to a limiting luminosity of -->1.5 × 1030 ergs s−1 (0.3-8 keV). From a radial distribution analysis, we find that -->18 ± 6 of these 29 sources are associated with M71, somewhat more than predicted, and that -->11 ± 6 are background sources, both Galactic and extragalactic. M71 appears to have more X-ray sources in the range -->LX = 1030–1031 ergs s−1 than expected by extrapolating from other studied clusters using either mass or collision frequency. We explore the spectra and variability of these sources and describe the results of ground-based optical counterpart searches.

ROTATIONAL VELOCITIES FOR EARLY-TYPE STARS IN THE YOUNG LARGE MAGELLANIC CLOUD CLUSTER R136: FURTHER STUDY OF THE RELATIONSHIP BETWEEN ROTATION SPEED AND DENSITY IN STAR-FORMING REGIONS

We present the results of a study aimed at assessing the distribution of rotation speeds, N(v sin i) among O- and early B-type stars located in R136, a young (t ~ 1-4 Myr) cluster in the Large Magellanic Cloud (LMC) characterized by a stellar density at least three times that of the densest Galactic clusters in which stellar rotational velocities have been measured. Our goals are (1) to determine whether the distribution of N(v sin i) in R136 shows the same paucity of slowly rotating stars and high mean rotation speed that distinguish early-type stars located in bound clusters in the Milky Way Galaxy (MWG) from their analogs among members of the field and unbound associations and (2) to determine whether the mean rotation speed in the extremely dense R136 cluster is even higher than the values measured for lower-density bound clusters. Our data comprise vsin i estimates for 24 stars obtained by comparing line profile measurements obtained with the Gemini Multi-Object Spectograph on the Gemini South Telescope with a grid of He I and He II line profiles generated from model atmospheres and broadened to emulate the effects of stellar rotation. We find that for R136, 13 stars with masses in the range 6-12 M ☉ have an average apparent rotational velocity of vsin i = 233 ± 19 km s–1; by comparison, for LMC stars in this same mass range in the field and in lower-density clusters, vsin i is, respectively, 105 ± 8 km s–1 and 147 ± 14 km s–1. For 11 15-30 M ☉ stars in R136, vsin i = 189 ± 23 km s–1; by comparison, the LMC stars in this same mass range but drawn from lower-density regions have vsin i = 129 ± 13 km s–1. Moreover, we find that throughout this entire mass range, R136 lacks the cohort of slow rotators characteristic of early-type field stars, both in the LMC and in the MWG. We provide arguments that these differences in N(v sin i) are unlikely to arise from evolution-driven changes in angular momentum (e.g., angular momentum loss through stellar winds), but rather may reflect differences in the rotation speeds imprinted at the time the stars formed. This result appears most certain for stars with masses in the range 6-12 M ☉; for stars of higher masses, larger samples from regions of differing densities are needed to more firmly establish that the observed differences are imprinted during the stellar assembly phase as opposed to being the result of subsequent evolution. We further argue that the differences in N(v sin i) between R136 and the LMC and MWG field stars likely result from a difference in the initial conditions in protostellar cores that are found in the types of molecular cloud regions that form rich, dense clusters (e.g., higher turbulent speeds) rather than from differences in the environment surrounding the core (e.g., stellar density, UV radiation field).

Influence of Surface-Active Solutes on the Coalescence, Clustering, and Fragmentation of Acoustic Bubbles Confined in a Microspace

High-speed imaging was used to capture the effect of surface-active solutes on the behavior of acoustic bubbles, generated in a microspace using low-frequency ultrasound (60 kHz). By confining cavitation within a microspace, the dynamic behavior of bubbles, such as bubble coalescence, clustering, and fragmentation, could be observed directly. It was observed that bubbles coalesced instantly in water; however, in the presence of surface-active solutes (n-propanol and sodium dodecyl sulfate, SDS) the coalescence was hindered. Low-density bubble clusters were observed in the presence of 1 mM SDS and 0.1 M n-propanol. When 0.1 M sodium chloride was added to 1 mM SDS solution, the extent of clustering and the density of the clusters enhanced significantly; a similar observation was made at a higher SDS concentration (10 mM). The importance of these results in understanding multibubble sonoluminescence data published previously has been addressed. The collective oscillation of a bubble cluster consisting of different sized bubbles and images of bubbles emitting a fountain of microbubbles have also been presented.

Formation of high- and low-density clusters in a 1D system

The properties of monoatomic chains have been studied theoretically by means of statistical mechanics methods. The applied approach can be used to evaluate the interatomic distances and lifetimes of one-dimensional (1D) and quasi-1D systems. In particular, we show that the 1D clusters of gold atoms can exist in two states with different lattice parameters (∼3.6 and ∼2.8 Å) that can explain the whole variety of experimental observations on monoatomic gold chains without assuming any wire contamination.

A study of segregation mechanism in centrifugal cast high speed steel rolls

Segregation influences the microstructure and performance of high speed steel (HSS) roll. The main reason why segregation occurs in centrifugal cast HSS roll is that atom clusters are formed in HSS melt and such atom clusters have different densities. The high-density atom clusters move to the outer periphery and the low-density atom clusters move to the inner periphery of the roll under centrifugal force. Changing the movement law of atom clusters in the centrifugal force field and increasing the solidification rate of HSS melt can lighten the segregation in HSS roll and improve its performance.

Methods for Detecting Internalized, FM 1-43 Stained Particles in Epithelial Cells and Monolayers

The membrane dye FM 1-43 has frequently been used to quantify exocytosis in neurons. In epithelia, intense lateral intracellular space staining and fluctuations in baseline labeling produced inconsistent results. Membrane retrieved in the presence of FM 1-43 retains the dye, however, and cells that undergo compensatory endocytosis during and following evoked exocytosis contain punctate, fluorescent particles after washout of external stain. As an alternative measure of trafficking, we quantified the fluorescent puncta retained after dye washout and tested our method on both coverslip-grown cell clusters and filter-grown intact monolayers. Images for analysis were acquired using serial sectioning with either epifluorescence or confocal microscopy. Tests with an intestinal goblet cell line that exhibits basal and ATP-stimulated granule trafficking confirmed that 1), the algorithm identified the same number of internalized particles with either epifluorescence or confocal microscopy acquired images; 2), low density clusters exhibited significantly more internalized particles per cell than either filter-grown monolayers or high density clusters; 3), ATP stimulation significantly increased the number of internalized particles in all preparations; and 4), the number of particles internalized was comparable to capacitance measurements of exocytosis. This method provides a single technique for quantifying membrane trafficking in both monolayers and unpolarized cells.

Diffusion of interacting Brownian particles: Jamming and anomalous diffusion

The free self-diffusion of an assembly of interacting particles confined on a quasi-one-dimensional ring is investigated both numerically and analytically. The interparticle pairwise interaction can be either attractive or repulsive and the energy barrier opposing thermal hopping of two particles one past the other is finite. Thus, for sufficiently long times, self-diffusion becomes normal or conventional diffusion. However, depending on the particle density, subdiffusive transients with exponent 12 and suppression of normal diffusion are observed. Above a certain density threshold, a sudden drop to zero of the diffusion coefficient for attractive particles signals the transition to a jammed phase. Furthermore, a Gaussian cluster of attractive particles condenses, by shrinking in size, for densities larger than such density threshold; lower density clusters spread out, regardless of the interaction sign, through a diffusion mechanism that is anomalous at short times, and normal for sufficiently long times. These effects could be observed in systems with colloidal particles, vortices, electrons, among other interacting particle systems.

Embedded star clusters and the formation of the Oort Cloud

Observations suggest most stars originate in clusters embedded in giant molecular clouds [Lada, C.J., Lada, E.A., 2003. Annu. Rev. Astron. Astrophys. 41, 57–115]. Our Solar System likely spent 1–5 Myrs in such regions just after it formed. Thus the Oort Cloud (OC) possibly retains evidence of the Sun's early dynamical history and of the stellar and tidal influence of the cluster. Indeed, the newly found objects (90377) Sedna and 2000 CR 105 may have been put on their present orbits by such processes [Morbidelli, A., Levison, H.F., 2004. Astron. J. 128, 2564–2576]. Results are presented here of numerical simulations of the orbital evolution of comets subject to the influence of the Sun, Jupiter and Saturn (with their current masses on orbits appropriate to the period before the Late Heavy Bombardment (LHB) [Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F., 2005. Nature 435, 459–461]), passing stars and tidal force associated with the gas and stars of an embedded star cluster. The cluster was taken to be a Plummer model with 200–400 stars, with a range of initial central densities. The Sun's orbit was integrated in the cluster potential together with Jupiter and Saturn and the test particles. Stellar encounters were incorporated by directly integrating the effects of stars passing within a sphere centred on the Sun of radius equal to the Plummer radius for low-density clusters and half a Plummer radius for high-density clusters. The gravitational influence of the gas was modeled using the tidal force of the cluster potential. For a given solar orbit, the mean density, 〈 ρ 〉 , was computed by orbit-averaging the density of material encountered. This parameter proved to be a good measure for predicting the properties of the OC. On average 2–18% of our initial sample of comets end up in the OC after 1–3 Myr. A comet is defined to be part of the OC if it is bound and has q > 35 AU . Our models show that the median distance of an object in the OC scales approximately as 〈 ρ 〉 − 1 / 2 when 〈 ρ 〉 ≳ 10 M ⊙ pc −3 . Our models easily produce objects on orbits like that of (90377) Sedna [Brown, M.E., Trujillo, C., Rabinowitz, D., 2004. Astrophys. J. 617, 645–649] within ∼1 Myr in cases where the mean density is 10 3 M ⊙ pc −3 or higher; one needs mean densities of order 10 4 M ⊙ pc −3 to create objects like 2000 CR 105 by this mechanism, which are reasonable (see, e.g., Guthermuth, R.A., Megeath, S.T., Pipher, J.L., Williams, J.P., Allen, L.E., Myers, P.C., Raines, S.N., 2005. Astrophys. J. 632, 397–420). Thus the latter object may also be part of the OC. Close stellar passages can stir the primordial Kuiper Belt to sufficiently high eccentricities ( e ≳ 0.05 ; Kenyon, S.J., Bromley, B.C., 2002. Astron. J. 123, 1757–1775) that collisions become destructive. From the simulations performed it is determined that there is a 50% or better chance to stir the primordial Kuiper Belt to eccentricities e ⩾ 0.05 at 50 AU when 〈 ρ 〉 ≳ 10 5 M ⊙ pc −3 . The orbit of the new object 2003 UB 313 [Brown, M.E., Trujillo, C.A., Rabinowitz, D.L., 2005. Astrophys. J. 635, L97–L100] is only reproduced for mean cluster densities of the order of 10 5 M ⊙ pc −3 , but in the simulations it could not come to be on its current orbit by this mechanism without disrupting the formation of bodies in the primordial Kuiper Belt down to 20 AU. It is therefore improbable that the latter object is created by this mechanism.

An algorithm for detecting internalized, FM 1–43 stained membrane in epithelia demonstrates greater membrane internalization in low density cell clusters vs high density monolayers

The membrane dye FM 1–43 rapidly stains a cell’s extracellular membrane including any membrane exocytosed, a property used to quantify exocytosis in neurons. In epithelia, fluctuations in basal and lateral intracellular space staining render FM 1–43 unreliable as a marker of exocytosis. However, membrane retrieved in the presence of FM 1–43 retains the dye, and washout of external stain reveals punctate, fluorescent particles. We developed an algorithm to quantify the retained fluorescent puncta in cells using images acquired with serial sectioning, and tested the algorithm on both coverslip-grown cell clusters and filter-grown intact monolayers. Serial sectioning was performed with epifluorescence microscopy, and a subset of experiments used the fixable variant of FM 1–43 to allow serial sectioning of the same preparation using both epifluorescence and confocal microscopy. Tests using an intestinal goblet cell line that exhibits basal and ATP-stimulated granule trafficking confirmed that: 1) the algorithm identified the same number of internalized particles for a set condition with either epifluorescence or confocal microscopy; 2) low density clusters with an average of 5 cells exhibited significantly more internalized particles per cell (316 ± 31) than filter grown monolayers (9 ± 3) or high density clusters with an average of 120 cells (8 ± 3); and 3) ATP stimulation significantly increased the number of internalized particles in all preparations. This method provides a single technique for quantifying membrane trafficking in both monolayers and unpolarized cells. (CFF)

Spatiotemporal Patterns of Host-Seeking Ixodes scapularis Nymphs (Acari: Ixodidae) in the United States

Abstract The risk of Lyme disease for humans in the eastern United States is dependent on the density of host-seeking Ixodes scapularis Say nymphal stage ticks infected with Borrelia burgdorferi. Although many local and regional studies have estimated Lyme disease risk using these parameters, this is the first large-scale study using a standardized methodology. Density of host-seeking I. scapularis nymphs was measured by drag sampling of closed canopy deciduous forest habitats in 95 locations spaced among 2° quadrants covering the entire United States east of the 100th meridian. Sampling was done in five standardized transects at each site and repeated three to six times during the summer of 2004. The total number of adults and nymphs of the seven tick species collected was 17,972, with 1,405 nymphal I. scapularis collected in 31 of the 95 sites. Peak global spatial autocorrelation values were found at the smallest lag distance (300 km) and decreased significantly after 1,000 km. Local autocorrelation statistics identified two significant high-density clusters around endemic areas in the northeast and upper Midwest and a low-density cluster in sites south of the 39th parallel, where only 21 nymphs were collected. Peak nymphal host-seeking density occurred earlier in the southern than in the most northern sites. Spatiotemporal density patterns will be combined with Borrelia prevalence data as part of a 4-yr survey to generate a nationwide spatial risk model for I. scapularis-borne Borrelia, which will improve targeting of disease prevention efforts.

Spatiotemporal Patterns of Host-Seeking &lt;I&gt;Ixodes scapularis&lt;/I&gt; Nymphs (Acari: Ixodidae) in the United States

The risk of Lyme disease for humans in the eastern United States is dependent on the density of host-seeking Ixodes scapularis Say nymphal stage ticks infected with Borrelia burgdorferi. Although many local and regional studies have estimated Lyme disease risk using these parameters, this is the first large-scale study using a standardized methodology. Density of host-seeking I. scapularis nymphs was measured by drag sampling of closed canopy deciduous forest habitats in 95 locations spaced among 2 degrees quadrants covering the entire United States east of the 100th meridian. Sampling was done in five standardized transects at each site and repeated three to six times during the summer of 2004. The total number of adults and nymphs of the seven tick species collected was 17,972, with 1,405 nymphal I. scapularis collected in 31 of the 95 sites. Peak global spatial autocorrelation values were found at the smallest lag distance (300 km) and decreased significantly after 1,000 km. Local auto-correlation statistics identified two significant high-density clusters around endemic areas in the northeast and upper Midwest and a low-density cluster in sites south of the 39th parallel, where only 21 nymphs were collected. Peak nymphal host-seeking density occurred earlier in the southern than in the most northern sites. Spatiotemporal density patterns will be combined with Borrelia prevalence data as part of a 4-yr survey to generate a nationwide spatial risk model for I. scapularis-borne Borrelia, which will improve targeting of disease prevention efforts.