The Dynamics of School and Work in Rural Bangladesh

This paper investigates the causes underlying the poor school performance of children in rural Bangladesh, while focusing on the effect of work on school progress. To this end, a dynamic switching model is presented for the sequence of school and work outcomes up to the end of secondary school, where the switching in each school level considered is determined by the endogenous work sequence up to that level. This approach allow us to characterize the full sequence of school and work choices of children, and to evaluate the dynamic effects of work on schooling. We find that work has a negative and sizable effect on school progress for the entire population, as well as for all the subpopulations considered, including the different groups of working children. We are also able to identify at each school level the observable and unobservable characteristics of working children relative to those of non-working children. This characterization and the magnitude of the estimated effects of work have important policy implications.dynamics of school and work, dynamic evaluation, selection

Canals in Milky Way radio polarization maps

Narrow depolarized canals are common in maps of the polarized synchrotron emission of the Milky Way. Two physical effects that can produce these canals have been identified: the presence of Faraday rotation measure (\RM) gradients in a foreground screen and the cumulative cancellation of polarization known as differential Faraday rotation. We show that the behaviour of the Stokes parameters $Q$ and $U$ in the vicinity of a canal can be used to identify its origin. In the case of canals produced by a Faraday screen we demonstrate that, if the polarization angle changes by 90\degr across the canal, as is observed in all fields to-date, the gradients in \RM must be discontinuous. Shocks are an obvious source of such discontinuities and we derive a relation of the expected mean separation of canals to the abundance and Mach number of supernova driven shocks, and compare this with recent observations by \citet{Haverkorn03}. We also predict the existence of less common canals with polarization angle changes other than 90\degr. Differential Faraday rotation can produce canals in a uniform magneto-ionic medium, but as the emitting layer becomes less uniform the canals will disappear. We show that for moderate differences in emissivity in a two-layer medium, of up to 1/2, and for Faraday depth fluctuations of standard deviation $\lesssim 1 \mathrm{rad}$, canals produced by differential rotation will still be visible.Comment: Accepted for publication in MNRAS Letters. 5 pages, 3 figure

Interim report on salt-water encroachment in Dade County, Florida

Recently there has been much activity in reclaiming the low-lying coastal areas of Dade County for residential use, by the addition of fill. The fill is obtained by digging canals both normal to and parallel to Biscayne Bay. The canals serve the additional purpose of providing an access to the Bay for boats. A problem needing to be considered is the effect that these canals will have on the ground-water resources. It is expected that the canals will have little effect on ground water in parts of the county distant from the coast, but their effect in coastal areas is a matter of concern. In order to predict what, may happen in the vicinity of these new canals if they are not equipped with adequate control structures, it is instructive to review what has happened in the vicinity of similar canals in the past. The U. S. Geological Survey, in cooperation with Dade County, the cities of Miami and Miami Beach, the Central and Southern Florida Flood Control District, and the Florida Geological Survey has collected water-level and salinity data on wells and canals in Dade County since 1939. Some of the agencies named, and others, collected similar data before 1939. Analysis of all the data shows that sea water in the Atlantic Ocean and Biscayne Bayis the sole source of salt-water contamination in the Biscayne aquifer of the Dade County area. (PDF has 19 pages.

Morphology of Root Canal Cross-sections of Resected Roots of First and Second Lower Molars

Precise preparation of the root canal ostium with a view to hermetical closing with retrograde root filling is an important prognostic factor determining the success of the procedure of tooth resection. Root canals interconnected with a narrow isthmus may cause problems both in endodontic treatment and in retrograde filling. The aim of this work is the research of the transverse cross-section of root canals of first and second lower molars on the resection model. The research encompasses 100 randomly selected molar teeth: 50 first and 50 second lower molars. The tooth root apexes were cut 3 mm below the apex and examined under an electron microscope, special attention being paid to the shape of root canal cross-sections. In the group of first molar teeth, in 20% the presence of an isthmus between canals in the proximal roots was observed; in the group of second molar teeth an isthmus between the canals of proximal roots occurred in 18% of the cases. It seems that the relatively high percentage (20%-18%) of the occurrence of an isthmus, 3 mm below the root apex, between two elongated transverse cross-section proximal root canals of first and second molars should encourage particular caution in the retrograde filling of the above-mentioned canals during the procedure of resection

Water Planning In Alcobaça Cistercian Lands / O Ordenamento Hidráulico no Território Cisterciense de Alcobaça

This paper concerns the main domain (coutos) of the Cistercian Abbey of Alcobaça (central Portugal), founded in 1153. It shows the involvement of the monks in shaping hydraulic landscapes along time. This monastic territory is limited westwards by the Atlantic ocean with a cliff coast indented by two large gulfs, the former Pederneira and Alfeizerão lagoons, sanded up presently. These landscapes have been consolidated along with the monks’ intervention in the hydrographic plan, particularly through a network of canals, the types of which can be summarized as follows: canals for water conveyance and evacuation, to and from the abbey buildings; canals related with water-powered engines as grain-, oil-, saw- and fulling-mills, forges and other industrial devices; canals consequent to the diversion of rivers and streams with two main purposes: to drain the fields in order to improve the marshes for agricultural use, and to irrigate cultures

Structure in the local Galactic ISM on scales down to 1 pc, from multi-band radio polarization observations

We discuss observations of the linearly polarized component of the diffuse galactic radio background. These observations, with an angular resolution of 4', were made with the Westerbork Synthesis Radio Telescope (WSRT) in 5 frequency bands in the range 341-375 MHz. The linearly polarized intensity P (with polarized brightness temperature going up to 10K) shows a `cloudy' structure, with characteristic scales of 15'-30', which contains relatively long, but very narrow `canals' (essentially unresolved) in which P is only a small fraction of that in the neighbouring beams. These `canals' are generally seen in more than one frequency band, although their appearance changes between bands. They are probably due to depolarization within the synthesized beam, because the change in polarization angle across the deepest `canals' is in general close to 90 degrees (or 270 etc.). These very abrupt changes in polarization angle, which are seen only across the `canals', seem to be accompanied by abrupt changes in the Rotation Measure (RM), which may have the right magnitude to create the difference of close to 90 degrees in polarization angle, and thereby the `canals'. The structure in the polarization maps is most likely due to Faraday rotation modulation of the probably smooth polarized radiation emitted in the halo of our Galaxy by the fairly local ISM (up to 500 pc). Therefore, the abrupt changes of RM across the `canals' provide evidence for very thin (about 1 pc), and relatively long transition regions in the ISM, across which the RM changes by as much as 100%. Such drastic RM changes may well be due primarily to abrupt changes in the magnetic field.Comment: 4 pages, 4 figures, to be published in A&A Letter

In vitro evaluation of carrier based obturation technique: a CBCT study

AIM: The goal of the study was to compare the ability of two different carrier based obturation (CBO) techniques to reach working length and fill in three-dimensions root canal systems, by using CBCT. MATERIALS AND METHODS: Twenty-six extracted molars were scanned with CBCT and 40 curved canals were selected (between 30° and 90°) and divided in two similar groups (n=20). All canals were prepared up to size 25 taper .06 using nickel-titanium instrumentation. The canals in the Group SC were obturated using Soft-Core obturators (Kerr, Romulus, Mi, USA), while Group TH canals (n= 20) were obturated using Thermafil Endodontic Obturators (Tulsa Dental Products, Tulsa, OK, USA), strictly following manufacturers' instructions for use. The obturations were analyzed by means of CBCT to measure the distance from the apical limit of obturation to the apical foramen and the presence of voids inside root canals. RESULTS: There was no significant difference between the two groups in the mean distance of the apical extent of the obturation (t test, p>0.05). Overfilling occurred in only 3 cases (2 in Group TH and 1 in Group SC). The percentages of voids in both groups were very low with no significant difference (Z test, p>0.05). CONCLUSIONS: The two tested CBO techniques showed similar positive results in terms of performance, even if, after checking with verifiers, in most cases the size of the selected Soft-Core obturator was one size smaller than Thermafil

Dreadlocks (Dock) is necessary to regulate growth of the germline ring canals in the developing \u3ci\u3eDrosophila melanogaster\u3c/i\u3e egg chamber

Infertility is a prevalent issue in the United States, impacting 1.5 million women (1). A possible cause of infertility is defects in gametogenesis, or the formation of sperm and egg. Therefore, understanding the basic mechanisms that promote normal gamete formation could impact our understanding of infertility. The Drosophila melanogaster egg develops from an organ-like structure called an egg chamber. The egg chamber is composed of a central cluster of 16 germ cells that are connected to one another by intercellular bridges, called ring canals. These ring canals are composed of filamentous actin and allow the transfer of materials from supporting nurse cells to the developing oocyte. The ring canals form during early oogenesis and then expand 20-fold. Defects in ring canal formation or expansion can lead to infertility. The purpose of this project was to determine the role of the SH2/SH3 adaptor protein, Dreadlocks (Dock), in the germline ring canals of the developing Drosophila egg. Dock is involved in the formation of other actin-rich structures and has been shown to interact with other known ring canal proteins; thus, I examined whether depletion or mutation of Dock affected the process of nurse cell dumping or the size of the ring canals throughout development. Depletion of Dock by RNA interference (RNAi) caused an over-expansion of the outer diameter of the ring canals in egg chambers between the stages of 6 and 10b of oogenesis. Reducing Dock levels also enhanced the phenotype caused by depletion of two other ring canal components, the kinase Misshapen or the Arp2/3 complex. This led me to propose that Dock functions with Misshapen and the Arp2/3 complex to promote normal ring canal expansion and stability. Because of the conserved nature of these intercellular bridges and the proteins being studied, this work could provide significant insight into gametogenesis in higher organisms

Depolarization canals and interstellar turbulence

Recent radio polarization observations have revealed a plethora of unexpected features in the polarized Galactic radio background that arise from propagation effects in the random (turbulent) interstellar medium. The canals are especially striking among them, a random network of very dark, narrow regions clearly visible in many directions against a bright polarized Galactic synchrotron background. There are no obvious physical structures in the ISM that may have caused the canals, and so they have been called Faraday ghosts. They evidently carry information about interstellar turbulence but only now is it becoming clear how this information can be extracted. Two theories for the origin of the canals have been proposed; both attribute the canals to Faraday rotation, but one invokes strong gradients in Faraday rotation in the sky plane (specifically, in a foreground Faraday screen) and the other only relies on line-of-sight effects (differential Faraday rotation). In this review we discuss the physical nature of the canals and how they can be used to explore statistical properties of interstellar turbulence. This opens studies of magnetized interstellar turbulence to new methods of analysis, such as contour statistics and related techniques of computational geometry and topology. In particular, we can hope to measure such elusive quantities as the Taylor microscale and the effective magnetic Reynolds number of interstellar MHD turbulence.Comment: 20 pages, 8 figures. Contribution to the proceedings of the conference 'Polarization 2005', September 12 to 15, Orsay, France. Replaced one figure, changed three figure caption