Deferring Social Impact: Conceptions of ICTD and Computing Careers

This paper contributes to the conversation about undergraduate students' conceptions of computer science (CS) and career pathways. We present a qualitative study of undergraduate involvement on a software research project in the Information and Communication Technology for Development (ICTD) subfield of CS. We analyze interviews with nine students who worked on the project in a capstone course and/or as volunteer research assistants. We contribute (1) a new angle on students' conceptions of CS and the ICTD subfield, which reveals that interest in ``social impact'' motivates their involvement in ICTD, in contrast to a perceived default CS career path at large tech companies; and (2) an articulation of the phenomenon we call \emph{deferring social impact}, which describes student researchers' intentions to eventually find the social impact they desire despite following that default career path

“Tinder Will Know You Are A 6”: Users’ Perceptions of Algorithms on Tinder

Through in-depth interviews of 22 Tinder users, we explore how users interpret their algorithmically mediated experience on the platform. We find that users have various explanations of whether and how Tinder uses algorithms and that users have varying degrees of certainty about these explanations. In response, users report that they act in particular ways given their explanations and degree of certainty. We discuss how users, as part of their sensemaking practice around how algorithms work, engage in forms of improvisation. In addition, we argue that algorithm awareness leads to a more nuanced acknowledgement of inequality and power, including the power-laden roles of platforms themselves

Machine learning reveals cryptic dialects that explain mate choice in a songbird

Culturally transmitted communication signals – such as human language or bird song – can change over time through cultural drift, and the resulting dialects may consequently enhance the separation of populations. However, the emergence of song dialects has been considered unlikely when songs are highly individual-specific, as in the zebra finch (Taeniopygia guttata). Here we show that machine learning can nevertheless distinguish the songs from multiple captive zebra finch populations with remarkable precision, and that ‘cryptic song dialects’ predict strong assortative mating in this species. We examine mating patterns across three consecutive generations using captive populations that have evolved in isolation for about 100 generations. We cross-fostered eggs within and between these populations and used an automated barcode tracking system to quantify social interactions. We find that females preferentially pair with males whose song resembles that of the females’ adolescent peers. Our study shows evidence that in zebra finches, a model species for song learning, individuals are sensitive to differences in song that have hitherto remained unnoticed by researchers

Sirtuin1 Over-Expression Does Not Impact Retinal Vascular and Neuronal Degeneration in a Mouse Model of Oxygen-Induced Retinopathy

Proliferative retinopathy is a leading cause of blindness, including retinopathy of prematurity (ROP) in children and diabetic retinopathy in adults. Retinopathy is characterized by an initial phase of vessel loss, leading to tissue ischemia and hypoxia, followed by sight threatening pathologic neovascularization in the second phase. Previously we found that Sirtuin1 (Sirt1), a metabolically dependent protein deacetylase, regulates vascular regeneration in a mouse model of oxygen-induced proliferative retinopathy (OIR), as neuronal depletion of Sirt1 in retina worsens retinopathy. In this study we assessed whether over-expression of Sirtuin1 in retinal neurons and vessels achieved by crossing Sirt1 over-expressing flox mice with Nestin-Cre mice or Tie2-Cre mice, respectively, may protect against retinopathy. We found that over-expression of Sirt1 in Nestin expressing retinal neurons does not impact vaso-obliteration or pathologic neovascularization in OIR, nor does it influence neuronal degeneration in OIR. Similarly, increased expression of Sirt1 in Tie2 expressing vascular endothelial cells and monocytes/macrophages does not protect retinal vessels in OIR. In addition to the genetic approaches, dietary supplement with Sirt1 activators, resveratrol or SRT1720, were fed to wild type mice with OIR. Neither treatment showed significant vaso-protective effects in retinopathy. Together these results indicate that although endogenous Sirt1 is important as a stress-induced protector in retinopathy, over-expression of Sirt1 or treatment with small molecule activators at the examined doses do not provide additional protection against retinopathy in mice. Further studies are needed to examine in depth whether increasing levels of Sirt1 may serve as a potential therapeutic approach to treat or prevent retinopathy

Reconstruction of Objects by Direct Demodulation

High resolution reconstruction of complicated objects from incomplete and noisy data can be achieved by solving modulation equations iteratively under physical constraints. This direct demodulation method is a powerful technique for dealing with inverse problem in general case. Spectral and image restorations and computerized tomography are only particular cases of general demodulation. It is possible to reconstruct an object in higher dimensional space from observations by a simple lower dimensional instrument through direct demodulation. Our simulations show that wide field and high resolution images of space hard X-rays and soft gamma rays can be obtained by a collimated non-position-sensitive detector without coded aperture masks.Comment: 11 pages, 6 figure

Helicobacter pylori and cancer among adults in Uganda

Data from Africa on infection with Helicobacter pylori (H. pylori) are sparse. Therefore, as part of an epidemiological study of cancer in Uganda, we investigated the prevalence and determinants of antibodies against H. pylori among 854 people with different cancer types and benign tumours. Patients were recruited from hospitals in Kampala, Uganda, interviewed about various demographic and lifestyle factors and tested for antibodies against H. pylori. In all patients combined, excluding those with stomach cancer (which has been associated with H. pylori infection), the prevalence of antibodies was 87% (723/833) overall, but declined with increasing age (p = 0.02) and was lower among people who were HIV seropositive compared to seronegative (p <0.001). Otherwise, there were few consistent epidemiological associations. Among those with stomach cancer, 18/21 (86%) had anti-H. pylori antibodies (odds ratio 0.8, 95% confidence intervals 0.2–2.9, p = 0.7; estimated using all other patients as controls, with adjustment for age, sex and HIV serostatus). No other cancer site or type was significantly associated with anti-H. pylori antibodies. The prevalence of H. pylori reported here is broadly in accord with results from other developing countries, although the determinants of infection and its' role in the aetiology of gastric cancer in Uganda remain unclear

Choroid Sprouting Assay: An Ex Vivo Model of Microvascular Angiogenesis

Angiogenesis of the microvasculature is central to the etiology of many diseases including proliferative retinopathy, age-related macular degeneration and cancer. A mouse model of microvascular angiogenesis would be very valuable and enable access to a wide range of genetically manipulated tissues that closely approximate small blood vessel growth in vivo. Vascular endothelial cells cultured in vitro are widely used, however, isolating pure vascular murine endothelial cells is technically challenging. A microvascular mouse explant model that is robust, quantitative and can be reproduced without difficulty would overcome these limitations. Here we characterized and optimized for reproducibility an organotypic microvascular angiogenesis mouse and rat model from the choroid, a microvascular bed in the posterior of eye. The choroidal tissues from C57BL/6J and 129S6/SvEvTac mice and Sprague Dawley rats were isolated and incubated in Matrigel. Vascular sprouting was comparable between choroid samples obtained from different animals of the same genetic background. The sprouting area, normalized to controls, was highly reproducible between independent experiments. We developed a semi-automated macro in ImageJ software to allow for more efficient quantification of sprouting area. Isolated choroid explants responded to manipulation of the external environment while maintaining the local interactions of endothelial cells with neighboring cells, including pericytes and macrophages as evidenced by immunohistochemistry and fluorescence-activated cell sorting (FACS) analysis. This reproducible ex vivo angiogenesis assay can be used to evaluate angiogenic potential of pharmacologic compounds on microvessels and can take advantage of genetically manipulated mouse tissue for microvascular disease research

Star formation rate and metallicity of damped Lyman-alpha absorbers in cosmological SPH simulations

We study the distribution of the star formation rate and metallicity of damped Lyman-alpha absorbers using cosmological SPH simulations of the Lambda cold dark matter model in the redshift range z=0-4.5. Our approach includes a phenomenological model of galactic wind. We find that there is a positive correlation between the projected stellar mass density and the neutral hydrogen column density (NHI) of DLAs for high NHI systems, and that there is a good correspondence in the spatial distribution of stars and DLAs in the simulations. The evolution of typical star-to-gas mass ratios in DLAs can be characterised by an increase from about 2 at z=4.5 to 3 at z=3, to 10 at z=1, and finally to 20 at z=0. We also find that the projected SFR density in DLAs follows the Kennicutt law well at all redshifts, and the simulated values are consistent with the recent observational estimates of this quantity by Wolfe et al. (2003a,b). The rate of evolution in the mean metallicity of simulated DLAs as a function of redshift is mild, and is consistent with the rate estimated from observations. The predicted metallicity of DLAs is generally sub-solar in our simulations, and there is a significant scatter in the distribution of DLA metallicity for a given NHI. However, we find that the median metallicity of simulated DLAs is close to that of Lyman-break galaxies, which is higher than the values typically observed for DLAs by nearly an order of magnitude. This discrepancy with observations could be due to an inadequate treatment of SN feedback in our current simulations, perhaps indicating that metals are not expelled efficiently enough from DLAs by outflows. Alternatively, the current observations might be missing the majority of the high metallicity DLAs due to selection effects. (abridged)Comment: 18 pages, 15 figures. Accepted to MNRAS. More visual presentations and the version with high resolution figures are available at http://cfa-www.harvard.edu/~knagamine/DLA-pics

The Baryonic Assembly of Dark Matter Halos

We use a suite of cosmological hydrodynamic simulations to quantify the accretion rates of baryons into dark matter halos and the resulting baryon mass fractions, as a function of halo mass, redshift, and baryon type (including cold and hot gas). We find that the net baryonic accretion rates through the virial radius are sensitive to galactic outflows and explore a range of outflow parameters to illustrate the effects. We show that the cold gas accretion rate is in general not a simple universal factor of the dark matter accretion rate, and that galactic winds can cause star formation rates to deviate significantly from the external gas accretion rates, both via gas ejection and re-accretion. Furthermore, galactic winds can inject enough energy and momentum in the surrounding medium to slow down accretion altogether, especially in low-mass halos and at low redshift. By resolving the accretion rates versus radius from the halo centers, we show how cold streams penetrate the hot atmospheres of massive halos at z>2, but gradually disappear at lower redshift. The total baryon mass fraction is also strongly suppressed by outflows in low-mass halos, but is nearly universal in the absence of feedback in halos above the UV background suppression scale. The transition halo mass, at which the gas mass in halos is equal for the cold and hot components, is roughly constant at ~10^11.5 Msun and does not depend sensitively on the wind prescription. We provide simple fitting formulae for the cold gas accretion rate into halos in the no-wind case. Finally, we show that cold accretion is broadly consistent with driving the bulk of the highly star-forming galaxies observed at z~2, but that the more intense star formers likely sample the high end of the accretion rate distribution, and may be additionally fueled by a combination of gas recycling, gas re-accretion, hot mode cooling, and mergers.Comment: 20 pages, 10 figures. MNRAS, in pres