172 research outputs found
Using think-aloud interviews to characterize model-based reasoning in electronics for a laboratory course assessment
Models of physical systems are used to explain and predict experimental
results and observations. The Modeling Framework for Experimental Physics
describes the process by which physicists revise their models to account for
the newly acquired observations, or change their apparatus to better represent
their models when they encounter discrepancies between actual and expected
behavior of a system. While modeling is a nationally recognized learning
outcome for undergraduate physics lab courses, no assessments of students'
model-based reasoning exist for upper-division labs. As part of a larger effort
to create two assessments of students' modeling abilities, we used the Modeling
Framework to develop and code think-aloud problem-solving activities centered
on investigating an inverting amplifier circuit. This study is the second phase
of a multiphase assessment instrument development process. Here, we focus on
characterizing the range of modeling pathways students employ while
interpreting the output signal of a circuit functioning far outside its
recommended operation range. We end by discussing four outcomes of this work:
(1) Students engaged in all modeling subtasks, and they spent the most time
making measurements, making comparisons, and enacting revisions; (2) Each
subtask occurred in close temporal proximity to all over subtasks; (3)
Sometimes, students propose causes that do not follow logically from observed
discrepancies; (4) Similarly, students often rely on their experiential
knowledge and enact revisions that do not follow logically from articulated
proposed causes.Comment: 18 pages, 5 figure
Characterizing lab instructors' self-reported learning goals to inform development of an experimental modeling skills assessment
The ability to develop, use, and refine models of experimental systems is a
nationally recognized learning outcome for undergraduate physics lab courses.
However, no assessments of students' model-based reasoning exist for
upper-division labs. This study is the first step toward development of
modeling assessments for optics and electronics labs. In order to identify test
objectives that are likely relevant across many institutional contexts, we
interviewed 35 lab instructors about the ways they incorporate modeling in
their course learning goals and activities. The study design was informed by
the Modeling Framework for Experimental Physics. This framework conceptualizes
modeling as consisting of multiple subtasks: making measurements, constructing
system models, comparing data to predictions, proposing causes for
discrepancies, and enacting revisions to models or apparatus. We found that
each modeling subtask was identified by multiple instructors as an important
learning outcome for their course. Based on these results, we argue that test
objectives should include probing students' competence with most modeling
subtasks, and test items should be designed to elicit students' justifications
for choosing particular modeling pathways. In addition to discussing these and
other implications for assessment, we also identify future areas of research
related to the role of modeling in optics and electronics labs.Comment: 24 pages, 2 figures, 5 tables; submitted to Phys. Rev. PE
Signal recognition particle RNA localization within the nucleolus differs from the classical sites of ribosome synthesis
The nucleolus is the site of ribosome biosynthesis, but is now known to have other functions as well. In the present study we have investigated how the distribution of signal recognition particle (SRP) RNA within the nucleolus relates to the known sites of ribosomal RNA synthesis, processing, and nascent ribosome assembly (i.e., the fibrillar centers, the dense fibrillar component (DFC), and the granular component). Very little SRP RNA was detected in fibrillar centers or the DFC of the nucleolus, as defined by the RNA polymerase I–specific upstream binding factor and the protein fibrillarin, respectively. Some SRP RNA was present in the granular component, as marked by the protein B23, indicating a possible interaction with ribosomal subunits at a later stage of maturation. However, a substantial portion of SRP RNA was also detected in regions of the nucleolus where neither B23, UBF, or fibrillarin were concentrated. Dual probe in situ hybridization experiments confirmed that a significant fraction of nucleolar SRP RNA was not spatially coincident with 28S ribosomal RNA. These results demonstrate that SRP RNA concentrates in an intranucleolar location other than the classical stations of ribosome biosynthesis, suggesting that there may be nucleolar regions that are specialized for other functions
A Mathematical Model of Oxygen Transport in Skeletal Muscle During Hindlimb Unloading
During hindlimb unloading (HU) dramatic fluid shifts occur within minutes of the suspension, leading to a less precise matching of blood flow to O2 demands of skeletal muscle. Vascular resistance directs blood away from certain muscles, such as the soleus (SOL). The muscle volume gradually reduces in these muscles so that eventually the relative blood flow returns to normal. It is generally believed that muscle volume change is not due to O2 depletion, but a consequence of disuse. However, the volume of the unloaded rat muscle declines over the course of weeks, whereas the redistribution of blood flow occurs immediately. Using a Krogh Cylinder Model, the distribution of O2 was predicted in two skeletal muscles: SOL and gastrocnemius (GAS). Effects of the muscle blood flow, volume, capillary density, and O2 uptake, are included to calculate the pO2 at rest and after 10 min and 15 days of unloading. The model predicts that 32 percent of the SOL muscle tissue has a pO2 1.25 mm Hg within 10 min, whereas the GAS maintains normal O2 levels, and that equilibrium is reached only as the SOL muscle cells degenerate. The results provide evidence that there is an inadequate O2 supply to the mitochondria in the SOL muscle after 10 min HU
Preliminary model for student ownership of projects
In many upper-division lab courses, instructors implement multiweek
student-led projects. During such projects, students may design and carry out
experiments, collect and analyze data, document and report their findings, and
collaborate closely with peers and mentors. To better understand cognitive,
social, and affective aspects of projects, we conducted an exploratory
investigation of student ownership of projects. Ownership is a complex
construct that refers to, e.g., students' willingness and ability to make
strategic decisions about their project. Using data collected through surveys
and interviews with students and instructors at five institutions, we developed
a preliminary model for student ownership of projects. Our model describes
student interactions with the project during three phases: choice of topic,
execution of experiment, and synthesis of results. Herein, we explicate our
model and demonstrate that it maps well onto students' and instructors'
conceptions of ownership and ideas presented in prior literature.Comment: 6 pages, 1 table, 1 figure. Submitted to 2019 PER Conference
Proceeding
Pathways to proposing causes for unexpected experimental results
Models of physical systems are used to explain and predict experimental
results and observations. When students encounter discrepancies between the
actual and expected behavior of a system, they revise their models to include
the newly acquired observations, or change their apparatus to better represent
their models. The Modeling Framework for Experimental Physics describes the
process of matching measurements and observations to models by making revisions
to resolve discrepancies. As part of a larger effort to create assessments of
students' modeling abilities in the context of upper-division electronics
courses, we used the Modeling Framework to develop and code think-aloud
problem-solving activities centered on troubleshooting an inverting amplifier
circuit. We observed that some participants iteratively and continuously made
measurements and revisions if they could not immediately propose a cause for an
observed discrepancy. This pathway has not been previously discussed in the
Modeling Framework. In this paper, we discuss two episodes where students
undergo this process to converge on a proposed cause post hoc. We conclude by
discussing implications for a modeling assessment based on the observed
modeling behavior.Comment: 4 pages, 1 figure, submitted to 2018 PERC Proceeding
Management of Multisystem Inflammatory Syndrome in Children (MIS-C) in resource limited settings: The Kenyan Experience
Background: Since the onset of the recent COVID-19 pandemic, there have been growing concerns regarding multisystem inflammatory syndrome in children (MIS-C). This study aims to describe the clinico-epidemiological profile and challenges in management of MIS-C in low-middle income countries by highlighting the Kenyan experience.
Methods: A retrospective study at the Aga Khan University Hospital Nairobi, Avenue Hospital Kisumu and Kapsabet County Referral Hospital was undertaken to identify cases of MIS-C. A detailed chart review using the World Health Organization (WHO) data collection tool was adapted to incorporate information on socio-demographic details and treatment regimens.
Findings: Twenty children with MIS-C were identified across the three facilities between August 1st 2020 and August 31st 2021. Seventy percent of the children were male (14 of 20). COVID-19 PCR testing was done for five children and only one was positive. The commonest clinical symptoms were fever (90%), tachycardia (80%), prolonged capillary refill (80%), oral mucosal changes (65%) and peripheral cutaneous inflammation (50%). Four children required admission into the critical care unit for ventilation support and inotropic support. Cardiac evaluation was available for six patients four of whom had myocardial dysfunction, three had valvulitis and one had pericarditis. Immunoglobulin therapy was availed to two children and systemic steroids provided for three children. There were no documented mortalities.
Interpretation: We describe the first case series of MIS-C in East and Central Africa. Majority of suspected cases of MIS-C did not have access to timely COVID-19 testing and other appropriate evaluations which highlights the iniquity in access to diagnostics and treatment
Pre-eclampsia and offspring cardiovascular health: mechanistic insights from experimental studies
Pre-eclampsia is increasingly recognized as more than an isolated disease of pregnancy. Women who have had a pregnancy complicated by pre-eclampsia have a 4-fold increased risk of later cardiovascular disease. Intriguingly, the offspring of affected pregnancies also have an increased risk of higher blood pressure and almost double the risk of stroke in later life. Experimental approaches to identify the key features of pre-eclampsia responsible for this programming of offspring cardiovascular health, or the key biological pathways modified in the offspring, have the potential to highlight novel targets for early primary prevention strategies. As pre-eclampsia occurs in 2–5% of all pregnancies, the findings are relevant to the current healthcare of up to 3 million people in the U.K. and 15 million people in the U.S.A. In the present paper, we review the current literature that concerns potential mechanisms for adverse cardiovascular programming in offspring exposed to pre-eclampsia, considering two major areas of investigation: first, experimental models that mimic features of the in utero environment characteristic of pre-eclampsia, and secondly, how, in humans, offspring cardiovascular phenotype is altered after exposure to pre-eclampsia. We compare and contrast the findings from these two bodies of work to develop insights into the likely key pathways of relevance. The present review and analysis highlights the pivotal role of long-term changes in vascular function and identifies areas of growing interest, specifically, response to hypoxia, immune modification, epigenetics and the anti-angiogenic in utero milieu
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