587 research outputs found
Disease and Water Supply: The Case of Cholera in 19th Century Iran
This paper explores why Iran was a particularly fertile ground for repeated visitation of cholera in the 19th century. Along with certain unique Iranian cultural and religious factors, the author demonstrates how Iranian urban ecology, particularly the qanat system, contributed to the fatal spread of the epidemic. These multi-faceted conditions, the author concludes, resulted in distinct modes of disease transmission and mortality in Iran
The sick men of Persia: the importance of illness as a factor in the interpretation of modern Iranian diplomatic history
STUDIES OF IRANIAN POLITICAL HISTORY OFTEN ASSUME THAT THE REPERCUSSIONS OF physical or mental illness on leadership are inconsequential in determining the course of history. Globally, very few scholars have attempted to systematically examine the effects of illness on leaders and Iranian historians seem to evade this topic entirely
Salicylic acid functionalized silica-coated magnetite nanoparticles for solid phase extraction and preconcentration of some heavy metal ions from various real samples
A method for the preconcentration of trace heavy metal ions in environmental samples has been reported. The presented method is based on the sorption of Cu(II), Cd(II), Ni(II) and Cr(III) ions with salicylic acid as respective chelate on silica-coated magnetite nanoparticles. Prepared adsorbent was characterized by XRD, SEM, BET and FT-IR measurements. The metals content of the sorbed complexes are eluted using 4.0 mL of 1.0 mol L-1 nitric acid. The influences of the analytical parameters including pH, amount of solid phase and condition of eluting solution, the effects of matrix ions on the retention of the analytes were examined. The accuracy and precision of suggested method were tested by analyzing of certified reference materials. The detection limits (3Sb/m, N = 8) for Cu(II), Cd(II), Ni(II) and Cr(III) ions are 0.22, 0.11, 0.27 and 0.15 μg L-1, respectively, and the maximum preconcentration factor is 200. The method was successfully applied to the evaluation of these trace and toxic metals in various waters, foods and other samples
Transition in a numerical model of contact line dynamics and forced dewetting
We investigate the transition to a Landau-Levich-Derjaguin film in forced
dewetting using a quadtree adaptive solution to the Navier-Stokes equations
with surface tension. We use a discretization of the capillary forces near the
receding contact line that yields an equilibrium for a specified contact angle
called the numerical contact angle. Despite the well-known
contact line singularity, dynamic simulations can proceed without any explicit
additional numerical procedure. We investigate angles from to
and capillary numbers from to where the mesh size
is varied in the range of to of the capillary length
. To interpret the results, we use Cox's theory which involves a
microscopic distance and a microscopic angle . In the numerical
case, the equivalent of is the angle and we find
that Cox's theory also applies. We introduce the scaling factor or gauge
function so that and estimate this gauge function by
comparing our numerics to Cox's theory. The comparison provides a direct
assessment of the agreement of the numerics with Cox's theory and reveals a
critical feature of the numerical treatment of contact line dynamics: agreement
is poor at small angles while it is better at large angles. This scaling factor
is shown to depend only on and the viscosity ratio . In the
case of small , we use the prediction by Eggers [Phys. Rev. Lett.,
vol. 93, pp 094502, 2004] of the critical capillary number for the
Landau-Levich-Derjaguin forced dewetting transition. We generalize this
prediction to large and arbitrary and express the critical
capillary number as a function of and . An analogy can be drawn
between and the numerical slip length.Comment: This version of the paper includes the corrections indicated in Ref.
[1
Fungal Symbionts as Manipulators of Plant Reproductive Biology
Symbioses have shaped the evolution of life, most notably
through the fixation of heritable symbionts into organelles. The inheritance
of symbionts promotes mutualism and fixation by coupling
partner fitness. However, conflicts arise if symbionts are transmitted
through only one sex and can shift host resources toward the sex
through which they propagate. Such reproductive manipulators have
been documented in animals with separate sexes but not in other
phyla or sexual systems. Here we investigated whether the investment
in male relative to female reproduction differed between hermaphroditic
host plants with versus without a maternally inherited fungal
symbiont. Plants with the fungus produced more seeds and less pollen
than plants lacking the fungus, resulting in an ∼40% shift in functional
gender and a switch from male-biased to female-biased sex
allocation. Given the ubiquity of endophytes in plants, reproductive
manipulators of hermaphrodites may be widespread in nature
Breakup of finite-size liquid filaments: Transition from no-breakup to breakup including substrate effects
This work studies the breakup of finite-size liquid filaments, when also
including substrate effects, using direct numerical simulations. The study
focuses on the effects of three parameters: Ohnesorge number, the ratio of the
viscous forces to inertial and surface tension forces, the liquid filament
aspect ratio, and where there is a substrate, a measure of the fluid slip on
the substrate, i.e. slip length. Through these parameters, it is determined
whether a liquid filament breaks up during the evolution toward its final
equilibrium state. Three scenarios are identified: a collapse into a single
droplet, the breakup into one or multiple droplets, and recoalescence into a
single droplet after the breakup (or even possibly another breakup after
recoalescence). The results are compared with the ones available in the
literature for free-standing liquid filaments. The findings show that the
presence of the substrate promotes breakup of the filament. The effect of the
degree of slip on the breakup is also discussed. The parameter domain regions
are comprehensively explored when including the slip effects. An experimental
case is also carried out to illustrate the collapse and breakup of a
finite-size silicon oil filament supported on a substrate, showcasing a
critical length of the breakup in a physical configuration. Finally, direct
numerical simulations reveal striking new details into the breakup pattern for
low Ohnesorge numbers, where the dynamics are fast and the experimental imaging
is not available; our results therefore significantly extend the range of
Ohnesorge number over which filament breakup has been considered
Numerical Simulation of Superparamagnetic Nanoparticle Motion in Blood Vessels for Magnetic Drug Delivery
A numerical model is developed for the motion of superparamagnetic
nanoparticles in a non-Newtonian blood flow under the influence of a magnetic
field. The rheological properties of blood are modeled by the Carreau flow and
viscosity, and the stochastic effects of Brownian motion and red blood cell
collisions are considered. The model is validated with existing data and good
agreement with experimental results is shown. The effectiveness of magnetic
drug delivery in various blood vessels is assessed and found to be most
successful in arterioles and capillaries. A range of magnetic field strengths
are modeled using equations for both a bar magnet and a point dipole: it is
shown that the bar magnet is effective at capturing nanoparticles in limited
cases while the point dipole is highly effective across a range of conditions.
A parameter study is conducted to show the effects of changing the dipole
moment, the distance from the magnet to the blood vessel, and the initial
release point of the nanoparticles. The distance from the magnet to the blood
vessel is shown to play a significant role in determining nanoparticle capture
rate. The optimal initial release position is found to be located within the
tumor radius in capillaries and arterioles to prevent rapid diffusion to the
edges of the blood vessel prior to arriving at the tumor, and near the edge of
the magnet when a bar magnet is used.Comment: Fixed the title spacin
Enhancing functional thinking: Identifying the prior schemas of seventh grade students in generalization of two-variable figural patterns
Background and Objectives: The figural patterns have a unique capacity to enhance functional thinking. The patterns generalization in school mathematics is considered as a way to promote functional thinking. Variable is one of the concepts in patterns generalization. Paying attention to figural patterns provides an opportunity for students to understand the meaning of variable and how to use it. Reference is also a central concept in patterns generalization. The number of variables is one of the characteristics that has been proposed in the pattern generalization tasks, but all the research has been related to one variable, linear and quadratic patterns. The aim of this study was to identifying the prior schemas in generalization of two-variable figural patterns. As regard to the concept of two variables, understanding three-dimensional space is a prerequisite for understanding and generalizing two-variable patterns. In these patterns, instead of one independent variable, there are two independent variables that change simultaneously and affect the dependent variable. Understanding these patterns requires the development of the R2 space scheme to R3 space, which is not a cognitively complex step and does not require the reconstruction of the existing scheme. Methods: The present research is part of a broad research which is done using quantitative-qualitative (mixed) research method. The research framework is APOS theory and based on the use of ACE (Activities, Class discussions and Exercises) teaching cycles. This research was conducted in three steps. In the first step, initial genetic decomposition for generalization of two-variable figural patterns was designed using the background, self-concept analysis and researchers’ experiences. It includes the prior schemas for generalization. In the second step, from the total 493 students of Malekan city (in East Azerbaijan) as the statistical population of research, a sample of 220, 7th grade students were selected based on the Cochran formula for determination of sample size. Then, a test that includes 7 tasks was designed based on APOS framework. The validity of the test was confirmed by three experts in mathematics education and four experienced teachers. Internal consistency of questions was estimated with Cronbach’s alpha and reported to be 0.69. Students responded the test at 90 minutes. The third step of research began with 19 students, with permission from the education and training office of Malekan, and school principals and parents of students. This step is done in three cycles. Findings: Using the analysis of students' responses to this test based on the APOS framework and doing three cycles of the research were conducted with the teaching method of Activity-Class Discussion-Exercise (ACE) with 19 students; genetic decomposition was finalized in this way, and defects of students in reference schema, R3 schema and variables schema as prior schemas in generalization of two-variable figural patterns were identified and encoded. Most of students had a good understanding of working with two variables. However in the context of generalization of two-variable figural pattern revealed many difficulties at the naming of variables, and using independent and dependent variables in proper positionConclusion: Identifying the mental constructs of students in generalizing patterns eases better teaching and learning. Conclusion: By identifying the mental structures of students in generalizing patterns, the path of teaching and learning will be smoother.  ===================================================================================== COPYRIGHTS ©2020 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers. ====================================================================================
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