Sets avoided by Brownian motion

Any fixed cylinder is hit almost surely by a 3-dimensional Brownian motion, but is there a random cylinder that is in the complement? We answer this for cylinders, and then replacing a cylinder with a more general set

How effective are food for education programs?: A critical assessment of the evidence from developing countries

"The economic motivations for investing in the education and nutritional status of primary-school-aged children are well established. Moreover, investments in both of these forms of human capital are likely to benefit from substantial complementarities. However, in developing countries, poor and creditconstrained households routinely invest less in education and nutrition than is privately or socially optimal. Food for education (FFE) programs, including meals served in school and take-home rations conditional on school attendance, attempt to improve these investments by subsidizing the cost of school participation through providing food that could improve nutrition and learning. This study examines the economic motivation for the use of FFE programs to increase investments in education and nutrition. The study then presents a critical review of the empirical evidence of the impact of FFE programs on education and nutrition outcomes for primary-school-aged children in developing countries. The main contribution of this study is to judge and summarize the strength of the evidence based on the extent to which existing studies have identified a causal effect of an FFE program, as opposed to finding an association between the program and key outcomes that may have been affected by other contextual factors. The economic rationale for FFE programs is to offer free food conditional on school attendance to increase the net benefits of schooling enough to change some households' decisions about their children's school participation. Although schoolaged children are past the critical window of opportunity during early childhood for the greatest gains from good nutrition, increasing food and nutrient consumption among school-aged children with low baseline food energy or micronutrient intake can improve weight, reduce susceptibility to infection, and increase cognitive function in the short run. Because school meals are usually fortified, a child's micronutrient intake can improve even if her total calorie consumption does not. These xi short-run gains may improve a child's educational attainment and academic achievement, which can improve future welfare. For logistical and political reasons, school meal programs are commonly provided to all children in a targeted school. This practice raises the cost of achieving program objectives, such as increased attendance rates, because it provides transfers to many children who would have attended school anyway. Take-home rations programs are less subject to this criticism, because they are more easily targeted to groups, such as poor or female children, who are in greater need or who may be more likely to change their human capital investment decisions as a result of the program. Even when provided at school, food transfers can be diverted to other household members by taking food away from the beneficiary child at other meals. This practice could diminish the size of the transfer received by the beneficiary child, resulting in only a small net gain in the child's daily consumption. However, empirical evidence suggests that a substantial share of the food provided through in-school meal programs is not redistributed away from the beneficiary child. The critical review examines the empirical literature on the impacts of FFE programs on education and nutrition outcomes. The education outcomes considered include school participation measured by enrollment and attendance, age at entry, drop-out status, learning achievement, and cognitive development. The nutrition outcomes reviewed include food energy consumption, anthropometry, and micronutrient status. The review focuses on the empirical literature with the strongest methodology for identifying causal impacts. This literature includes experimental studies, such as randomized controlled trials; experimental field trials; studies using quasi-experimental methods, such as natural or administrative experiments; and nonexperimental studies using careful evaluation designs. Although the literature on the impacts of FFE programs is vast, high-quality studies with evaluation designs that provide causal impact estimates are relatively few. The nutrition literature offers many more experimental studies on nutrition outcomes than is yet available in the economics literature on education outcomes, yet many of the nutrition studies are controlled trials in which many components of the intervention typically affected by behavior, such as amount of food available at a meal, are closely managed. The external validity of these studies for programs implemented in the field is often difficult to ascertain. The number of experimental field studies for any outcome is few, but growing. From the existing literature, it is possible to draw conclusions about the likely impact of FFE programs on some outcomes, whereas for other outcomes, the literature is inconclusive. The empirical evidence suggests that in-school feeding has a positive impact on school participation in areas where initial indicators of school participation are low. In-school meal programs have been shown to have small impacts on school xii summary attendance rates for children already enrolled in school. However, there is no causal evidence for an impact on net primary-school attendance rates for all school-aged children in the service area of a school because of limitations in study design. The only study we found with attendance data for a representative sample of primaryschool– aged children, including those enrolled in school at baseline and those not enrolled, found a strong association between participation in a school meal program and school attendance, but estimated impacts cannot be reliably attributed to causal effects of the program. For similar reasons, there is also scant evidence on the effects of school meals on primary-school enrollment rates. Two empirical studies find that school meal programs cause a significant increase in learning achievement, as measured by improvements in test scores. However, in each study, scores were significantly higher for school meal recipients on only one of three tests taken. The impact of in-school meals on learning appears to operate both through improvements in school attendance and through better learning efficiency while in school, though no study has separately identified the relative contribution of these effects. FFE programs may also have an impact on cognitive development, though the size and nature of the effect vary greatly by program, micronutrient content of the food, and the measure of cognitive development used. Empirical evidence on the effects of school meals on cognitive function is mixed and depends on the tests used, the content of the meals, and the initial nutritional status of the children. Most of the studies are conducted in a laboratory setting and look at the short-term impact of feeding on cognitive function. The aspects of cognitive ability tested differ by study, making it difficult to compare results. Nonetheless, there is evidence that school meals rich in animal-source foods improved cognitive function in Kenyan children. Another study demonstrates an effect of school breakfasts on cognitive function. Given the controlled setting that formed the basis for these experiments, it would be useful now to expand the external validity of the evidence through field experiments. On other outcomes, the evidence of the impact of in-school feeding on primaryschool drop-out rates is inconclusive. We also found no study that examines the impact of school meals on age at school entry, probably because of the expense of collecting data on a representative sample of children around this age. Also, there is little conclusive evidence on the impact of take-home rations on education outcomes. For nutrition outcomes, most of the evidence comes from randomized trials in the nutrition literature. For food-energy (calorie) consumption, the evidence shows that in-school feeding programs show greater potential to improve children's total daily energy consumption when children's baseline consumption is well below their age- or weight-recommended consumption level. Differences in empirical strategy summary xiii may account for differences in findings across studies, as randomized experiments found a lower impact than did quasi-experimental studies. The diversity of program components and target populations in anthropometric studies, as well as the complexity of biological growth mechanisms, make it difficult to assess the effectiveness of FFE on anthropometric indicators. Overall, several studies showed gains in body size (for example, height, weight, body mass index) or composition (for example, mean upper-arm circumference) due to participation in FFE programs, with weight or body mass index appearing to respond most often. Improvements were typically small, though the effects of increased consumption may have been mitigated by increased activity levels in some cases. The micronutrient content of foods provided may contribute to gains in height (iron fortification) and mean upper-arm circumference (providing meat-based snacks). Deworming appears to have an interactive effect with FFE on height in one study. Turning to micronutrient status, iron fortification of FFE meals appears to improve iron status in nearly all studies reviewed. Evidence for other micronutrients is more sparse. One study found that meat-based meals improve plasma vitamin B12 concentrations but found no impact on other micronutrients. Two studies reviewed the impact of FFE on vitamin A status: one found a positive effect on plasma vitamin A status, whereas the other found no impact. Finally, one study found that iodine fortification reduced the prevalence of iodine deficiencies. The presence of malaria or other infections may impede detection of these benefits, particularly with respect to iron status. Combining the treatment with deworming can improve the effectiveness of iron supplementation, particularly in children with low baseline iron stores. Summarizing this evidence, FFE programs appear to have considerable impacts on primary-school participation, but the quality of this evidence is weak. Higher quality studies indicate some impacts on learning and cognitive development. There is evidence of effects on food consumption and micronutrient status, provided that initial consumption and nutrient deficiencies are identified and that programs are tailored to address these deficiencies. In many cases, the FFE programs appear to have little impact, because the levels of key outcome variables, such as school attendance or micronutrient status, are already high. Despite this evidence, significant research gaps remain. A surprising gap in this literature is the lack of convincing evidence of these programs' effect on school enrollment and attendance for a representative sample of school-aged children from the school's service area. There is also no conclusive empirical evidence on the impact of FFE programs on age at entry and grade repetition, and little on drop-out rates. In general, the impacts of take-home ration programs are poorly understood. Also, few studies identify the differential impacts of FFE on children by age or xiv summary gender. Finally, the impact of FFE programs on learning achievement has not been carefully analyzed by schooling inputs and class size. Perhaps the greatest omission in current research on FFE programs is the absence of well-designed cost-effectiveness studies. The policy decision on whether to undertake an FFE program or an alternative education or nutrition intervention should be based on relative differences in cost-effectiveness. However, most studies that measure program impact do not collect the additional data needed to obtain a measure of cost-effectiveness. Such studies would identify the cost from various interventions of achieving a certain percentage increase in primary-school attendance, for example. The most convincing approach would be to conduct sideby- side randomized field experiments of alternative programs. To our knowledge, only one study has done so, comparing in-school meals to programs that provide teachers with school supplies or foster parent–teacher communication. However, even these comparisons are complicated by the scarcity of programs likely to have the same kind of combined impacts on both education and nutrition outcomes. The most immediate policy implication of this review study is that more careful and systematic research is needed to find the most cost-effective combination of programs available. Without rigorous estimates of the impact of FFE programs on school participation, it is not possible to determine whether important secondary effects on learning achievement or cognitive development come primarily through school attendance or through joint effects of schooling and improved nutrition. It is these joint effects that are uniquely available through FFE programs. If the learning and cognitive benefits to school-aged children of simultaneous improvements in nutrition and schooling from FFE programs are small, cash-based programs may be more effective at increasing school participation. If there are no joint education and nutrition effects from FFE programs, it may be more cost-effective to replace these programs with specialized education and nutrition programs that are more narrowly targeted at specific objectives. More comprehensive and rigorous evaluation studies of FFE programs are needed to determine the full scope of the impacts of these programs and their relative cost-effectiveness. Our interpretation of the empirical evidence reviewed here leads to several recommendations on the design and use of FFE programs. Effects tend to be larger where schooling participation is low or where there are significant nutritional deficiencies. This fact argues for doing an assessment of school needs in target areas before starting an FFE program. Such an evaluation would improve targeting and allow FFE program components, such as the nutrient composition and quantity of food, to be tailored to local needs. Also, program administrators should be willing to consider complementary programs to improve school quality. Learning effects cannot be achieved if the instruction is of little value. Poor school quality lowers summary xv the benefits of participation and discourages attendance. Though much more evidence is needed, results from field experiments in the Philippines suggest that the cost of alternative programs to improve school quality may be only a fraction of the per child cost of an FFE program. Coordinated programs that combine FFE with improvements in school quality may be much more effective.." "Authors' AbstractPoverty reduction, Hunger, Food for education, School children, Education, Nutrition,

Magnetic field, chemical composition and line profile variability of the peculiar eclipsing binary star AR Aur

AR Aur is the only eclipsing binary known to contain a HgMn star, making it an ideal case for a detailed study of the HgMn phenomenon. HgMn stars are a poorly understood class of chemically peculiar stars, which have traditionally been thought not to possess significant magnetic fields. However, the recent discovery of line profile variability in some HgMn stars, apparently attributable to surface abundance patches, has brought this belief into question. In this paper we investigate the chemical abundances, line profile variability, and magnetic field of the primary and secondary of the AR Aur system, using a series of high resolution spectropolarimetric observations. We find the primary is indeed a HgMn star, and present the most precise abundances yet determined for this star. We find the secondary is a weak Am star, and is possibly still on the pre-main sequence. Line profile variability was observed in a range of lines in the primary, and is attributed to inhomogeneous surface distributions of some elements. No magnetic field was detected in any observation of either stars, with an upper limit on the longitudinal magnetic field in both stars of 100 G. Modeling of the phase-resolve longitudinal field measurements leads to a 3 sigma upper limit on any dipole surface magnetic field of about 400 G.Comment: Accepted for publication in MNRAS, 11 pages, 9 figure

Properties of Disks and Bulges of Spiral and Lenticular Galaxies in the Sloan Digital Sky Survey

A bulge-disk decomposition is made for 737 spiral and lenticular galaxies drawn from a SDSS galaxy sample for which morphological types are estimated. We carry out the bulge-disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast disks are nearly universal, their properties remaining similar among disk galaxies irrespective of detailed morphologies from S0 to Sc. While these tendencies were often discussed in previous studies, the present study confirms them based on a large homogeneous magnitude-limited field galaxy sample with morphological types estimated. The systematic change of bulge-to-total luminosity ratio, $B/T$, along the morphological sequence is therefore not caused by disks but mostly by bulges. It is also shown that elliptical galaxies and bulges of spiral galaxies are unlikely to be in a single sequence. We infer the stellar mass density (in units of the critical mass density) to be $\Omega=$0.0021 for spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and $\Omega=$0.00081 for disks.Comment: 30 pages, 9 figure

The chemical abundance analysis of normal early A- and late B-type stars

Modern spectroscopy of early-type stars often aims at studying complex physical phenomena. Comparatively less attention is paid to identifying and studying the "normal" A- and B-type stars and testing how the basic atomic parameters and standard spectral analysis allow one to fit the observations. We wish to stablish whether the chemical composition of the solar photosphere can be regarded as a reference for early A- and late B-type stars. We have obtained optical high-resolution, high signal-to-noise ratio spectra of three slowly rotating early-type stars (HD 145788, 21 Peg and pi Cet) that show no obvious sign of chemical peculiarity, and performed a very accurate LTE abundance analysis of up to 38 ions of 26 elements (for 21 Peg), using a vast amount of spectral lines visible in the spectral region covered by our spectra. We provide an exhaustive description of the abundance characteristics of the three analysed stars with a critical review of the line parameters used to derive the abundances. We compiled a table of atomic data for more than 1100 measured lines that may be used in the future as a reference. The abundances we obtained for He, C, Al, S, V, Cr, Mn, Fe, Ni, Sr, Y, and Zr are compatible with the solar ones derived with recent 3D radiative-hydrodynamical simulations of the solar photosphere. The abundances of the remaining studied elements show some degree of discrepancy compared to the solar photosphere. Those of N, Na, Mg, Si, Ca, Ti, and Nd may well be ascribed to non-LTE effects; for P, Cl, Sc and Co, non-LTE effects are totally unknown; O, Ne, Ar, and Ba show discrepancies that cannot be ascribed to non-LTE effects. The discrepancies obtained for O (in two stars) and Ne agree with very recent non-LTE abundance analysis of early B-type stars in the solar neighbourhood.Comment: Accepted for publication on Astronomy and Astrophysic

Transversely Driven Charge Density Waves and Striped Phases of High-Tc_c Superconductors: The Current Effect Transistor

We show that a normal (single particle) current density $J_x$ {\em transverse} to the ordering wavevector $2k_F{\bf\hat{z}}$ of a charge density wave (CDW) has dramatic effects both above and {\em below} the CDW depinning transition. It exponentially (in $J_x$) enhances CDW correlations, and exponentially suppresses the longitudinal depinning field. The intermediate longitudinal I-V relation also changes, acquiring a {\em linear} regime. We propose a novel ``current effect transistor'' whose CDW channel is turned on by a transverse current. Our results also have important implications for the recently proposed ``striped phase'' of the high-T$_c$ superconductors.Comment: change of title and minor corrections, 4 RevTeX pgs, to appear in Phys. Rev. Lett., 81, 3711 (1998

Weather in stellar atmosphere: the dynamics of mercury clouds in alpha Andromedae

The formation of long-lasting structures at the surfaces of stars is commonly ascribed to the action of strong magnetic fields. This paradigm is supported by observations of evolving cool spots in the Sun and active late-type stars, and stationary chemical spots in the early-type magnetic stars. However, results of our seven-year monitoring of mercury spots in non-magnetic early-type star alpha Andromedae show that the picture of magnetically-driven structure formation is fundamentally incomplete. Using an indirect stellar surface mapping technique, we construct a series of 2-D images of starspots and discover a secular evolution of the mercury cloud cover in this star. This remarkable structure formation process, observed for the first time in any star, is plausibly attributed to a non-equilibrium, dynamical evolution of the heavy-element clouds created by atomic diffusion and may have the same underlying physics as the weather patterns on terrestrial and giant planets.Comment: 10 pages, 2 figures; to be published in Nature Physic

The search for magnetic fields in mercury-manganese stars

We performed a highly sensitive search for magnetic fields on a large set of HgMn stars. With the aid of a new polarimeter attached to the HARPS spectrometer at the ESO 3.6m-telescope, we obtained high-quality circular polarization spectra of 41 single and double HgMn stars. Using a multi-line analysis technique on each star, we co-added information from hundreds of spectral lines resulting in significantly greater sensitivity to the presence of magnetic fields, including very weak fields. For the 47 individual objects studied, including 6 components of SB2 systems, we do not detect any magnetic fields at greater than the 3 sigma level. The lack of detection in the circular polarization profiles indicates that if strong fields are present on these stars, they must have complex surface topologies. For simple global fields, our detection limits imply upper limits to the fields present of 2-10 Gauss in the best cases. We conclude that HgMn stars lack large-scale magnetic fields, typical for spotted magnetic Ap stars, sufficient to form and sustain the chemical spots observed on HgMn stars. Our study confirms that in addition to magnetically altered atomic diffusion, there exists another differentiation mechanism operating in the atmospheres of late-B main sequence stars which can compositional inhomogeneities on their surfaces.Comment: 12 pages, 8 figures, 2 table

Spitzer observations of Abell 1763 - I: infrared and optical photometry

We present a photometric analysis of the galaxy cluster Abell 1763 at visible and infrared wavelengths. Included are fully reduced images in r', J, H, and Ks obtained using the Palomar 200in telescope, as well as the IRAC and MIPS images from Spitzer. The cluster is covered out to approximately 3 virial radii with deep 24um imaging (a 5? depth of 0.2 mJy). This same field of 40' by 40' is covered in all four IRAC bands as well as the longer wavelength MIPS bands (70 and 160um). The r' imaging covers 0.8 deg2 down to 25.5 magnitudes, and overlaps with most of the MIPS field of view. The J, H, Ks images cover the cluster core and roughly half of the filament galaxies, which extend towards the neighboring cluster, Abell 1770. This first, in a series of papers on Abell 1763, discusses the data reduction methods and source extraction techniques used for each dataset. We present catalogs of infrared (IR) sources (with 24 and/or 70um emission) and their corresponding emission in the optical (u', g', r', i', z'), and Near- to Far-IR (J, H, Ks, IRAC, and MIPS 160um). We provide the catalogs and reduced images to the community through the NASA/IPAC Infrared Science Archive (IRSA).Comment: 25 pages, 16 figure