The Keck+Magellan Survey for Lyman Limit Absorption II: A Case Study on Metallicity Variations

We present an absorption line analysis of the Lyman limit system (LLS) at z=3.55 in our Magellan/MIKE spectrum of PKS2000-330. Our analysis of the Lyman limit and full HI Lyman series constrains the total HI column density of the LLS (N_HI = 10^[18.0 +/- 0.25] cm^{-2} for b_HI >= 20 km/s) and also the N_HI values of the velocity subsystems comprising the absorber. We measure ionic column densities for metal-line transitions associated with the subsystems and use these values to constrain the ionization state (>90% ionized) and relative abundances of the gas. We find an order of magnitude dispersion in the metallicities of the subsystems, marking the first detailed analysis of metallicity variations in an optically thick absorber. The results indicate that metals are not well mixed within the gas surrounding high $z$ galaxies. Assuming a single-phase photoionization model, we also derive an N_H-weighted metallicity, = -1.66 +/- 0.25, which matches the mean metallicity in the neutral ISM in high z damped Lya systems (DLAs). Because the line density of LLSs is ~10 times higher than the DLAs, we propose that the former dominate the metal mass-density at z~3 and that these metals reside in the galaxy/IGM interface. Considerations of a multi-phase model do not qualitatively change these conclusions. Finally, we comment on an anomalously large O^0/Si^+ ratio in the LLS that suggests an ionizing radiation field dominated by soft UV sources (e.g. a starburst galaxy). Additional abundance analysis is performed on the super-LLS systems at z=3.19.Comment: 20 pages, 7 figures (most in color). Accepted to Ap

A Direct Measurement of the IGM Opacity to HI Ionizing Photons

We present a new method to directly measure the opacity from HI Lyman limit (LL) absorption k_LL along quasar sightlines by the intergalactic medium (IGM). The approach analyzes the average (``stacked'') spectrum of an ensemble of quasars at a common redshift to infer the mean free path (MFP) to ionizing radiation. We apply this technique to 1800 quasars at z=3.50-4.34 drawn from the Sloan Digital Sky Survey (SDSS), giving the most precise measurements on k_LL at any redshift. From z=3.6 to 4.3, the opacity increases steadily as expected and is well parameterized by MFP = (48.4 +/- 2.1) - (38.0 +/- 5.3)*(z-3.6) h^-1 Mpc (proper distance). The relatively high MFP values indicate that the incidence of systems which dominate k_LL evolves less strongly at z>3 than that of the Lya forest. We infer a mean free path three times higher than some previous estimates, a result which has important implications for the photo-ionization rate derived from the emissivity of star forming galaxies and quasars. Finally, our analysis reveals a previously unreported, systematic bias in the SDSS quasar sample related to the survey's color targeting criteria. This bias potentially affects all z~3 IGM studies using the SDSS database.Comment: 7 pages, 4 figures; Accepted to ApJ

The HST/ACS+WFC3 Survey for Lyman Limit Systems II: Science

We present the first science results from our Hubble Space Telescope Survey for Lyman limit absorption systems (LLS) using the low dispersion spectroscopic modes of the Advanced Camera for Surveys and the Wide Field Camera 3. Through an analysis of 71 quasars, we determine the incidence frequency of LLS per unit redshift and per unit path length, l(z) and l(x) respectively, over the redshift range 1 < z< 2.6, and find a weighted mean of l(x)=0.29 +/-0.05 for 2.0 < z < 2.5 through a joint analysis of our sample and that of Ribaudo et al. (2011). Through stacked spectrum analysis, we determine a median (mean) value of the mean free path to ionizing radiation at z=2.4 of lambda_mfp = 243(252)h^(-1) Mpc, with an error on the mean value of +/- 43h^(-1) Mpc. We also re-evaluate the estimates of lambda_mfp from Prochaska et al. (2009) and place constraints on the evolution of lambda_mfp with redshift, including an estimate of the "breakthrough" redshift of z = 1.6. Consistent with results at higher z, we find that a significant fraction of the opacity for absorption of ionizing photons comes from systems with N_HI <= 10^{17.5} cm^(-2) with a value for the total Lyman opacity of tau_lyman = 0.40 +/- 0.15. Finally, we determine that at minimum, a 5-parameter (4 power-law) model is needed to describe the column density distribution function f(N_HI, X) at z \sim 2.4, find that f(N_HI,X) undergoes no significant change in shape between z \sim 2.4 and z \sim 3.7, and provide our best fit model for f(N_HI,X).Comment: 36 pages, 20 figures, 10 tables, revision to match accepted ApJ versio

Mexican American first-generation/low-income students: a rural community college, TRiO student support services experience

This study is an ethnographic inquiry into the beliefs and perceptions of first-generation/low-income Mexican American students in a rural community college located near the U.S. – Mexico border. It explored their experiences as TRiO Student Support Services participants. TRiO Student Support Services plays an increasingly vital role helping first-generation/low-income students successfully complete their college educations. Because of the increasing number of Hispanic students seeking post-secondary educational opportunities, specifically at the community college level, this study examined the attitudes those students have in terms of their experiences within a community college setting in rural southeastern Arizona. As the number of first-generation/low-income Hispanic students enrolled in college and taking advantage of TRiO Student Support Services rises, so does the need to gain a deeper understanding of the beliefs and perceptions of this changing demographic.Keywords: Ethnography, Qualitative, TRiO Student Support Services, Hispanic, Mexican American, Thoughts, Beliefs, Perceptions, Rural Community College, Success, Low Income, First Generation, Underrepresented, Culture-sharing.Ed.D., Educational Leadership and Management -- Drexel University, 201

On the galloping instability of two-dimensional bodies having elliptical cross sections.

Galloping, also known as Den Hartog instability, is the large amplitude, low frequency oscillation of a structure in the direction transverse to the mean wind direction. It normally appears in the case of bodies with small stiffness and structural damping, when they are placed in a flow provided the incident velocity is high enough. Galloping depends on the slope of the lift coefficient versus angle of attack curve, which must be negative. Generally speaking this implies that the body is stalled after boundary layer separation, which, as it is known in non-wedged bodies, is a Reynolds number dependent phenomenon. Wind tunnel experiments have been conducted aiming at establishing the characteristics of the galloping motion of elliptical cross-section bodies when subjected to a uniform flow, the angles of attack ranging from 0° to 90°. The results have been summarized in stability maps, both in the angle of attack versus relative thickness and in the angle of attack versus Reynolds number planes, where galloping instability regions are identified

Prevalence, heterogeneity of asymptomatic malaria infections and associated factors in a high transmission region

Background: Although current reports have shown a reduction in malaria cases, the disease still remains a major public health problem in Kenya. In most endemic regions, the majority of infections are asymptomatic which means those infected may not even know and yet they remain infectious to the mosquitoes. Asymptomatic infections are a major threat to malaria control programs since they act as silent reservoirs for the malaria parasites.Objective: The study sought to determine the prevalence of asymptomatic malaria infections, whether they show heterogeneity spatially, across age groups and across time as well as their determinants in a high transmission region.Study Design: This was part of a larger prospective cohort study on malaria indices in the HDSS.Study Setting: The study was conducted in the Webuye Health and Demographic Surveillance Site in Bungoma East Sub-County.Study Subjects: Quarterly parasitological surveys were conducted for a cohort of 400 participants from randomly selected households located in known fever “hotspots” and “coldspots”. Follow-up of all the participants continued for a period of one year. Generalized estimating equations were used to model risk factors associated with asymptomatic parasitemia.Results: Of the total 321 malaria infections detected during the five cross-sectional surveys conducted over the period of one year, almost half (46.3%) of these were asymptomatic. Overall, most of the asymptomatic cases (67%) were in households within known fever “hotspots”. The proportion of infections that were asymptomatic in the coldspots were 73.1%, 31.8%, 13.3%, 55.6% and 48.2% during the first, second, third, fourth and fifth visits respectively. In the known fever “hotspots”, the proportion of infections without symptoms was 47.7%, 48.5%, 35%, 41.3% and 47.5% during the first, second, third, fourth and fifth visits respectively. Factors associated with asymptomatic malaria include; the village one lives: people living in village M were twice likely to be asymptomatic (A.O.R: 2.141, C.I: 0.03 - 1.488), age: children aged between 6 to 15 years were more than twice likely to be asymptomatic (A.O.R: 2.67, C.I. 0.434 - 1.533) and the season: infections during the dry season (January) were less likely to be asymptomatic (A.O.R: 0.26, C.I: -2.289 - 0.400).Conclusion: The prevalence of asymptomatic infections in this region is still very high. The highest proportion of asymptomatic infections was registered in a fever coldpspot village which may explain why the village is a fever coldspot in the first place. There is a need for active surveillance to detect the asymptomatic cases as well as treat them in-order to reduce the reservoir. Targeting interventions to the asymptomatic individuals will further reduce the transmission within this region

Malaria “hotspots” within a larger hotspot; what’s the role of behavioural factors in fine scale heterogeneity in western Kenya?

Background: Malaria remains a major public health problem in Kenya accounting for the highest morbidity and mortality especially among children. Previous reports indicate that infectious agents display heterogeneity in both space and time and malaria is no exception. Heterogeneity has been shown to reduce the effectiveness of interventions. Previous studies have implicated genetic (both human and parasite) and environmental factors as mainly responsible for variation in malaria risk. Human behaviour and its potential risk for contributing to variation in malaria risk has not been extensively explored.Objective: To determine if there were behavioural differences between the people living in hotspots (high malaria burden) and cold spots (low malaria burden) within a geographically homogeneous and high malaria transmission region.Design: A prospective closed cohort study.Setting: The study was conducted in the Health and Demographic Surveillance Site in Bungoma East sub-County.Subjects: A total of 400 people in randomly selected households in both the fever hotspots and cold spots were tested for malaria at quarterly intervals using malaria rapid diagnostic tests (RDTs).Results: Significant heterogeneity in malaria incidence and prevalence was observed between villages. Incidence of malaria was significantly higher in the hotspots (high malaria burden areas) compared to the cold spots (low malaria burden) (49 episodes per 1000 person months compared to 26/1000, t test p &lt; 0.001). The incidence also varied significantly among the individual villages by season (P: 0.0071). Knowledge on malaria therapy was significantly  associated with whether one was in the cold spot or hotspot (P: 0.033). Behavioural practices relating to ITN use were significantly associated with region during particular seasons (P: 0.0001 and P: 0.0001 respectively).Conclusion: There is marked and significant variation in the incidence of malaria among the villages creating actual hotspots of malaria within the larger hotspot. There is a significant difference in malaria infections between the hotspots and cold spots. Knowledge on malaria therapy and behavioural factors such as ITN use may contribute to the observed differences during some seasons

Archeops: an instrument for present and future cosmology

Archeops is a balloon-borne instrument dedicated to measure the cosmic microwave background (CMB) temperature anisotropies. It has, in the millimetre domain (from 143 to 545 GHz), a high angular resolution (about 10 arcminutes) in order to constrain high l multipoles, as well as a large sky coverage fraction (30%) in order to minimize the cosmic variance. It has linked, before WMAP, Cobe large angular scales to the first acoustic peak region. From its results, inflation motivated cosmologies are reinforced with a flat Universe (Omega_tot=1 within 3%). The dark energy density and the baryonic density are in very good agreement with other independent estimations based on supernovae measurements and big bang nucleosynthesis. Important results on galactic dust emission polarization and their implications for Planck are also addressed.Comment: 4 pages, 2 figures, to appear in Proceedings of the Multiwavelength Cosmology Conference, June 2003, Mykonos Island, Greec

Cosmological parameters sigma_8, the baryon density, and the UV background intensity from a calibrated measurement of H I Lyman-alpha absorption at z = 1.9

We identify a concordant model for the intergalactic medium (IGM) at redshift z=1.9 that uses popular values for cosmological and astrophysical parameters and accounts for all baryons with an uncertainty of 6%. We have measured the amount of absorption, DA, in the Ly-alpha forest at redshift 1.9 in spectra of 77 QSO from the Kast spectrograph. We calibrated the continuum fits with realistic artificial spectra, and we found that averaged over all 77 QSOs the mean continuum level is within 1-2% of the correct value. Absorption from all lines in the Ly-alpha forest at z=1.9 removes DA=15.1 +/- 0.7% of the flux between 1070 and 1170 (rest) Angstroms. This is the first measurement using many QSOs at this z, and the first calibrated measurement at any redshift. Metal lines absorb 2.3 +/- 0.5%, and LLS absorb 1.0 +/- 0.4% leaving 11.8 +/- 1.0% from the lower density bulk of the IGM. Averaging over Delta z=0.1 or 154 Mpc, the dispersion is 6.1 +/- 0.3% including LLS and metal lines, or 3.9 (+0.5, -0.7)% for the lower density IGM alone, consistent with the usual description of large scale structure. LLS and metal lines are major contributors to the variation in the mean flux, and they make the flux field significantly non-Gaussian. We find that a hydrodynamic simulation on a 1024 cubed grid in a 75.7 Mpc box reproduces the observed DA from the low density IGM with parameters values H_o=71 km/s/Mpc, Omega_Lambda=0.73, Omega_m=0.27, Omega_b=0.044, sigma_8=0.9 and a UV background that has an ionization rate that is 1.08 +/- 0.08 times the prediction by Madau, Haardt & Rees (1999).Comment: Submitted to Ap