Measuring velocity ratios with correlation functions

We show how to determine the ratio of the transverse velocity of a source to the velocity of emitted particles, using split-bin correlation functions. The technique is to measure $S_2$ and $S_2^{\phi}$, subtract the contributions from the single-particle distribution, and take the ratio as the bin size goes to zero. We demonstrate the technique for two cases: each source decays into two particles, and each source emits a large number of particles.Comment: 9 pages, LaTeX, 2 PostScript figure

Correlation measurements in high-multiplicity events

Requirements for correlation measurements in high--multiplicity events are discussed. Attention is focussed on detection of so--called hot spots, two--particle rapidity correlations, two--particle momentum correlations (for quantum interferometry) and higher--order correlations. The signal--to--noise ratio may become large in the high--multiplicity limit, allowing meaningful single--event measurements, only if the correlations are due to collective behavior.Comment: MN 55455, 20 pages, KSUCNR-011-92 and TPI-MINN-92/47-T (revised). Revised to correct typo in equation (30), and to fill in a few steps in calculations. Now published as Phys. Rev. C 47 (1993) 232

Thermal photon production in high-energy nuclear collisions

We use a boost-invariant one-dimensional (cylindrically symmetric) fluid dynamics code to calculate thermal photon production in the central rapidity region of S+Au and Pb+Pb collisions at SPS energy ($\sqrt{s}=20$ GeV/nucleon). We assume that the hot matter is in thermal equilibrium throughout the expansion, but consider deviations from chemical equilibrium in the high temperature (deconfined) phase. We use equations of state with a first-order phase transition between a massless pion gas and quark gluon plasma, with transition temperatures in the range $150 \leq T_c \leq 200$ MeV.Comment: revised, now includes a_1 contribution. revtex, 10 pages plus 4 figures (uuencoded postscript

Measuring hadron properties at finite temperature

We estimate the numbers and mass spectra of observed lepton and kaon pairs produced from $\phi$ meson decays in the central rapidity region of an Au+Au collision at lab energy 11.6 GeV/nucleon. The following effects are considered: possible mass shifts, thermal broadening due to collisions with hadronic resonances, and superheating of the resonance gas. Changes in the dilepton mass spectrum may be seen, but changes in the dikaon spectrum are too small to be detectable.Comment: 9 pages (revtex), 3 figures (uuencoded postscript

Label Placement in Road Maps

A road map can be interpreted as a graph embedded in the plane, in which each vertex corresponds to a road junction and each edge to a particular road section. We consider the cartographic problem to place non-overlapping road labels along the edges so that as many road sections as possible are identified by their name, i.e., covered by a label. We show that this is NP-hard in general, but the problem can be solved in polynomial time if the road map is an embedded tree.Comment: extended version of a CIAC 2015 pape

Using Terrestrial Laser Scanning to Estimate Canopy Structure in Peatland Conifers Under a Climate Manipulation

Northern peatlands are major terrestrial carbon sinks, storing 415 ± 150 Gt of carbon. The composition of peatland vegetation affects this carbon storage capacity, and thus quantifying the vegetation helps to constrain uncertainty in peatland carbon storage estimates. Ground layer vegetation, such as Sphagnum sp. moss contributes greatly to carbon storage capacity. In forested peatlands, the tree canopy structure directly influences peatland solar insolation, soil temperature, and water table levels. Each of these factors impacts the ground layer vegetation. Currently, there is uncertainty about how the peatland tree canopy structure is influenced by elevated levels of carbon dioxide (CO2) and temperature. Providing canopy structural metrics in a nondestructive, spatially comprehensive way across different temperature and CO2 treatments is challenging for traditional methods such as destructive harvesting, Digital Hemispherical Photography (DHP), and allometric regressions. Terrestrial Laser Scanning (TLS) is well-suited to provide non-destructive detailed horizontal and vertical canopy structural information. As part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) study located in northern Minnesota, USA, we use TLS to evaluate leaf area index (LAI), leaf area density, and leaf inclination angle over time (2015 - 2022) and space of two conifer species, Picea mariana (black spruce) and Larix laricina (eastern larch). The SPRUCE site is in a treed peatland bog under elevated CO2 and temperature conditions. The research questions in this study are 1) How accurately can we predict the LAI of the spruce and larch trees using TLS data? 2) How are the spruce and larch tree canopy structures within 12 SPRUCE plots changing from 2015 - 2022? We expected 1) A volumetric pixel-based model (VCP) will predict LAI with an accuracy of 90% as validated by destructively harvested and DHP LAI estimates 2) Under elevated CO2 and temperature, LAI will increase, leaf area density will decrease in lower canopies, and leaf inclination angles will become more vertical. At the species level, we expected the spruce and larch trees to respond with opposing trends for each metric under the same treatment. Using TLS data, we developed a modified VCP model that uses measures of point contact frequency to estimate LAI, leaf inclination angles, and leaf area density. The results indicate that the model predicts LAI with a coefficient of determination of 0.89 (R2 = 0.89), an RMSE of 0.98, and a normalized RMSE = 0.17. We also found that the model maintains moderate accuracy across voxel size input parameters, suggesting it may maintain accuracy in different treatment conditions where tree structural relationships can change. Our canopy structural results supported the hypothesis that LAI increases more significantly over time under warmer conditions when compared to control plots. Lower canopy leaf area density trends did not support the hypothesis as they showed no statistically significant trends across time. Leaf inclination angle trends through time did not support the hypothesis as they tended to decrease. As temperatures increased across the temperature gradient, leaf angles became more vertical in upper canopies under elevated CO2, leading to inconclusive support for or against the hypothesis. Species data did not support the hypothesis that spruce and larch canopy structures would differ significantly under the same treatments. The larch LAI, however, did not increase as significantly through time as the spruce under elevated CO2 conditions. Additionally, we identified anomalous fluctuations in time series data and proposed potential temperature thresholds where LAI differed the most under ambient or elevated CO2 conditions. The findings from this study suggest that accurately quantifying canopy structure through time may be possible in different environmental conditions and species using TLS. We add support to previous findings that LAI increases more significantly through time under warming conditions compared to control conditions. These results demonstrate TLS’s utility for making species-level canopy structural estimates across horizontal and vertical profiles. Incorporating vertical canopy profile metrics such as leaf area density with LAI data can assist in better explaining how LAI is changing across time and temperature gradients

Quenching or Bursting: Star Formation Acceleration--A New Methodology for Tracing Galaxy Evolution

We introduce a new methodology for the direct extraction of galaxy physical parameters from multi-wavelength photometry and spectroscopy. We use semi-analytic models that describe galaxy evolution in the context of large scale cosmological simulation to provide a catalog of galaxies, star formation histories, and physical parameters. We then apply stellar population synthesis models and a simple extinction model to calculate the observable broad-band fluxes and spectral indices for these galaxies. We use a linear regression analysis to relate physical parameters to observed colors and spectral indices. The result is a set of coefficients that can be used to translate observed colors and indices into stellar mass, star formation rate, and many other parameters, including the instantaneous time derivative of the star formation rate which we denote the {\it Star Formation Acceleration (SFA)}, We apply the method to a test sample of galaxies with GALEX photometry and SDSS spectroscopy, deriving relationships between stellar mass, specific star formation rate, and star formation acceleration. We find evidence for a mass-dependent SFA in the green valley, with low mass galaxies showing greater quenching and higher mass galaxies greater bursting. We also find evidence for an increase in average quenching in galaxies hosting AGN. A simple scenario in which lower mass galaxies accrete and become satellite galaxies, having their star forming gas tidally and/or ram-pressure stripped, while higher mass galaxies receive this gas and react with new star formation can qualitatively explain our results.Comment: 33 pages, 31 figures, ApJ accepte

Tightly Correlated HI and FUV Emission in the Outskirts of M83

We compare sensitive HI data from The HI Nearby Galaxy Survey (THINGS) and deep far UV (FUV) data from GALEX in the outer disk of M83. The FUV and HI maps show a stunning spatial correlation out to almost 4 optical radii (r25), roughly the extent of our maps. This underscores that HI traces the gas reservoir for outer disk star formation and it implies that massive (at least low level) star formation proceeds almost everywhere HI is observed. Whereas the average FUV intensity decreases steadily with increasing radius before leveling off at ~1.7 r25, the decline in HI surface density is more subtle. Low HI columns (<2 M_solar/pc^2) contribute most of the mass in the outer disk, which is not the case within r25. The time for star formation to consume the available HI, inferred from the ratio of HI to FUV intensity, rises with increasing radius before leveling off at ~100 Gyr, i.e., many Hubble times, near ~1.7 r25. Assuming the relatively short H2 depletion times observed in the inner parts of galaxies hold in outer disks, the conversion of HI into bound, molecular clouds seems to limit star formation in outer galaxy disks. The long consumption times suggest that most of the extended HI observed in M83 will not be consumed by in situ star formation. However, even these low star formation rates are enough to expect moderate chemical enrichment in a closed outer disk.Comment: Accepted for Publication in ApJ