497 research outputs found
A method to construct refracting profiles
We propose an original method for determining suitable refracting profiles
between two media to solve two related problems: to produce a given wave front
from a single point source after refraction at the refracting profile, and to
focus a given wave front in a fixed point. These profiles are obtained as
envelopes of specific families of Cartesian ovals. We study the singularities
of these profiles and give a method to construct them from the data of the
associated caustic.Comment: 12 pages, 5 figure
Solving the brachistochrone and other variational problems with soap films
We show a method to solve the problem of the brachistochrone as well as other
variational problems with the help of the soap films that are formed between
two suitable surfaces. We also show the interesting connection between some
variational problems of dynamics, statics, optics, and elasticity.Comment: 16 pages, 11 figures. This article, except for a small correction,
has been submitted to the American Journal of Physic
Enabling remote design and troubleshooting experiments using the ilab shared architecture
12th Biennial International Conference on Engineering, Construction, and Operations in Challenging Environments; and Fourth NASA/ARO/ASCE Workshop on Granular Materials in Lunar and Martian Exploration
Honolulu, Hawaii, United States
March 14-17, 2010The MIT iLab Project is dedicated to the goal of increasing laboratory experimentation opportunities for engineering students worldwide. Since its inception in 1998, the project has furthered this goal through the development of individual remote laboratories, or iLabs, as well as a distributed software infrastructure designed to streamline the implementation and sharing of remote laboratories. iLabs are designed to complement traditional, hands-on laboratories by providing practical educational experiences where they would not otherwise be available. Such remote labs, developed and hosted by MIT and other institutions within the iLab Consortium, have been successfully used by instructors at schools across the educational spectrum and around the world. While certainly valuable, many of the original experiments available through the iLab platform provide a limited experience in that they are observational in nature. They only provide students the ability to study the behavior of a pre-defined system under test. Such labs have proven to be valuable additions to engineering curricula, but do not have the flexibility that is inherent in a traditional laboratory experience. To address this, the MIT iLab Project has begun focusing on the development of iLabs that provide students with the ability to design or troubleshoot experimental systems. Through two particular remote labs, focusing on electronic control system analysis and basic electronics test and measurement respectively, the project is designing remote labs that provide a more flexible learning experience for students and are more attractive to instructors in a broad set of disciplines.National Science Foundation (U.S.) (award 0702735)Singapore-MIT Alliance for Research and Technology CenterMicrosoft CorporationCarnegie Corporation of New YorkMaricopa County Community College District. Maricopa Advanced Technology Education Cente
Biomarkers of Host Response Predict Primary End-Point Radiological Pneumonia in Tanzanian Children with Clinical Pneumonia: A Prospective Cohort Study.
BACKGROUND: Diagnosing pediatric pneumonia is challenging in low-resource settings. The World Health Organization (WHO) has defined primary end-point radiological pneumonia for use in epidemiological and vaccine studies. However, radiography requires expertise and is often inaccessible. We hypothesized that plasma biomarkers of inflammation and endothelial activation may be useful surrogates for end-point pneumonia, and may provide insight into its biological significance.
METHODS: We studied children with WHO-defined clinical pneumonia (n = 155) within a prospective cohort of 1,005 consecutive febrile children presenting to Tanzanian outpatient clinics. Based on x-ray findings, participants were categorized as primary end-point pneumonia (n = 30), other infiltrates (n = 31), or normal chest x-ray (n = 94). Plasma levels of 7 host response biomarkers at presentation were measured by ELISA. Associations between biomarker levels and radiological findings were assessed by Kruskal-Wallis test and multivariable logistic regression. Biomarker ability to predict radiological findings was evaluated using receiver operating characteristic curve analysis and Classification and Regression Tree analysis.
RESULTS: Compared to children with normal x-ray, children with end-point pneumonia had significantly higher C-reactive protein, procalcitonin and Chitinase 3-like-1, while those with other infiltrates had elevated procalcitonin and von Willebrand Factor and decreased soluble Tie-2 and endoglin. Clinical variables were not predictive of radiological findings. Classification and Regression Tree analysis generated multi-marker models with improved performance over single markers for discriminating between groups. A model based on C-reactive protein and Chitinase 3-like-1 discriminated between end-point pneumonia and non-end-point pneumonia with 93.3% sensitivity (95% confidence interval 76.5-98.8), 80.8% specificity (72.6-87.1), positive likelihood ratio 4.9 (3.4-7.1), negative likelihood ratio 0.083 (0.022-0.32), and misclassification rate 0.20 (standard error 0.038).
CONCLUSIONS: In Tanzanian children with WHO-defined clinical pneumonia, combinations of host biomarkers distinguished between end-point pneumonia, other infiltrates, and normal chest x-ray, whereas clinical variables did not. These findings generate pathophysiological hypotheses and may have potential research and clinical utility
Collaborative development of remote electronics laboratories in the ELVIS ilab
Remote laboratories represent a significant value to engineering curricula in a variety of cases.
Whether it is a complement to a hands-on experience or a substitute when a traditional lab is not
feasible, remote laboratories can be a valuable educational resource. Since 1998, the MIT iLab
Project has worked to increase the quality and availability of remote laboratories. Using the iLab
Shared Architecture, developers of new labs can leverage a set of generic support functions and
then share those labs easily and with minimal administrative cost. More recently, the iLab
Project, in partnership with Obafemi Awolowo University in Nigeria, Makerere University in
Uganda and the University of Dar-es-Salaam in Tanzania and in coordination with the Maricopa
Advanced Technology Education Center (MATEC), has focused on building iLabs around the
National Instruments Educational Laboratory Virtual Instrumentation Suite (ELVIS) platform.
The ELVIS is a low-cost, small-footprint unit that contains most of the common test instruments
found in a typical electrical engineering lab. By coupling the ELVIS with iLabs, a variety of
remote electronics laboratories can be built and shared around the world. Using this common
hardware/software platform, participants in the iLab Project at different levels of the educational
spectrum have developed experiments that meet their individual curricular needs and are able to
host them for use by other peer institutions. Not only does this increase the variety of ELVISbased
iLabs, but it also spurs the creation of teams that can then build other, more diverse iLabs
and substantively participate in project-wide collaborative development efforts. Through such
coordinated efforts, iLabs can provide rich practical experiences for studentsMaricopa County Community College District. Maricopa Advanced Technology Education CenterCarnegie Corporation of New YorkMicrosoft CorporationNational Science Foundation (U.S.) (award 0702735)Singapore-MIT Alliance for Research and Technology Cente
Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires
Interactions in one-dimensional (1D) electron systems are expected to cause a
dynamical separation of electronic spin and charge degrees of freedom. A
promising system for experimental observation of this non-Fermi-liquid effect
consists of two quantum wires coupled via tunneling through an extended uniform
barrier. Here we consider the minimal model of an interacting 1D electron
system exhibiting spin-charge separation and calculate the differential
tunneling conductance as well as the density-density response function. Both
quantities exhibit distinct strong features arising from spin-charge
separation. Our analysis of these features within the minimal model neglects
interactions between electrons of opposite chirality and applies therefore
directly to chiral 1D electron systems realized, e.g., at the edge of integer
quantum-Hall systems. Physical insight gained from our results is useful for
interpreting current experiment in quantum wires as our main conclusions still
apply with nonchiral interactions present. In particular, we discuss the effect
of charging due to applied voltages, and the possibility to observe spin-charge
separation in a time-resolved experiment.Comment: 9 pages, 3 figures, expanded version with many detail
TOF studies for dedicated PET with open geometries
[EN] Recently, two novel PET devices have been developed with open geometries, namely: breast and prostate-dedicated scanners. The breast-dedicated system comprises two detector rings of twelve modules with a field of view of 170 mm x 170 mm x 94 mm. Each module consists of a continuous trapezoidal LYSO crystal and a PSPMT. The system has the capability to vary the opening of the rings up to 60 mm in order to allow the insertion of a needle to perform a biopsy procedure. The prostate system has an open geometry consisting on two parallel plates separated 28 cm. One panel includes 18 detectors organized in a 6 x 3 matrix while the second one comprises 6 detectors organized in a 3 x 2 matrix. All detectors are formed by continuous LYSO crystals of 50 mm x 50 mm x15 mm, and a SiPM array of 12 x 12 individual photo-detectors. The system geometry is asymmetric maximizing the sensitivity of the system at the prostate location, located at about 2/3 in the abdomen-anus distance.
The reconstructed images for PET scanners with open geometries present severe artifacts due to this peculiarity. These artifacts can be minimized using Time Of Flight information (TOF). In this work we present a TOF resolution study for open geometries. With this aim, the dedicated breast and prostate systems have been simulated using GATE (8.1 version) with different TOF resolutions in order to determine the image quality improvements that can be achieved with the existing TOF-dedicated electronics currently present in the market. The images have been reconstructed using the LMOS algorithm including TOF modeling in the calculation of the voxel-Line Of Response emission probabilities.This work was supported in part by the Spanish Government Grants TEC2016-79884-C2 and RTC-2016-5186-1 and by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 695536).Moliner, L.; Ilisie, V.; GonzĂĄlez MartĂnez, AJ.; Oliver-Gil, S.; Gonzalez, A.; GimĂŠnez-Alventosa, V.; CaĂąizares, G.... (2019). TOF studies for dedicated PET with open geometries. Journal of Instrumentation. 14:1-8. https://doi.org/10.1088/1748-0221/14/02/C02006S181
Mesoscopic effects in tunneling between parallel quantum wires
We consider a phase-coherent system of two parallel quantum wires that are
coupled via a tunneling barrier of finite length. The usual perturbative
treatment of tunneling fails in this case, even in the diffusive limit, once
the length L of the coupling region exceeds a characteristic length scale L_t
set by tunneling. Exact solution of the scattering problem posed by the
extended tunneling barrier allows us to compute tunneling conductances as a
function of applied voltage and magnetic field. We take into account charging
effects in the quantum wires due to applied voltages and find that these are
important for 1D-to-1D tunneling transport.Comment: 8 pages, 7 figures, improved Figs., added Refs. and appendix, to
appear in Phys. Rev.
Parameter identification problems in the modelling of cell motility
We present a novel parameter identification algorithm for the estimation of parameters in models of cell motility using imaging data of migrating cells. Two alternative formulations of the objective functional that measures the difference between the computed and observed data are proposed and the parameter identification problem is formulated as a minimisation problem of nonlinear least squares type. A LevenbergâMarquardt based optimisation method is applied to the solution of the minimisation problem and the details of the implementation are discussed. A number of numerical experiments are presented which illustrate the robustness of the algorithm to parameter identification in the presence of large deformations and noisy data and parameter identification in three dimensional models of cell motility. An application to experimental data is also presented in which we seek to identify parameters in a model for the monopolar growth of fission yeast cells using experimental imaging data. Our numerical tests allow us to compare the method with the two different formulations of the objective functional and we conclude that the results with both objective functionals seem to agree
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