290 research outputs found
Equatorial vertical drift modulation by the lunar and solar semidiurnal tides during the 2013 sudden stratospheric warming
During the 2013 stratospheric sudden warming (SSW) period the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) radar at Jicarmarca, Peru, observed low-latitude vertical drift modulation with lows of 0-12 m/s daytime maximum drifts between 6-13 and 22-25 January and enhanced drifts up to 43 m/s between 15 snd 19 January. The NCAR thermosphere-ionosphere-mesosphere-electrodynamics general circulation model reproduces the prevailing vertical drift feature and is used to examine possible causes. The simulations indicate that the modulation of the vertical drift is generated by the beating of the semidiurnal solar SW2 and lunar M2 tides. During the SSW period the beating is observable since the magnitudes of lunar and solar semidiurnal tidal amplitudes are comparable. The theoretical beating frequency between SW2 and M2 is 1/(15.13 day) which may be modified due to phase changes. This study highlights the importance of the lunar tide during SSW periods and indicates that the equatorial vertical drift modulation should be observable at other longitudes as well. Ω2016. American Geophysical Union. All Rights Reserved
Innovation platforms for agricultural value chain development
Available in Chinese, English, Hindi, Thai and Vietnames
A Scalable Parallel Approach for High-Fidelity Aerostructural Analysis and Optimization
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97076/1/AIAA2012-1922.pd
Combined Level-Set-XFEM-Density Topology Optimization of Four-Dimensional Printed Structures Undergoing Large Deformation
Advancement of additive manufacturing is driving a need for design tools that exploit the increasing fabrication freedom. Multimaterial, three-dimensional (3D) printing allows for the fabrication of components from multiple materials with different thermal, mechanical, and “active” behavior that can be spatially arranged in 3D with a resolution on the order of tens of microns. This can be exploited to incorporate shape changing features into additively manufactured structures. 3D printing with a downstream shape change in response to an external stimulus such as temperature, humidity, or light is referred to as four-dimensional (4D) printing. In this paper, a design methodology to determine the material layout of 4D printed materials with internal, programmable strains is introduced to create active structures that undergo large deformation and assume a desired target displacement upon heat activation. A level set (LS) approach together with the extended finite element method (XFEM) is combined with density-based topology optimization to describe the evolving multimaterial design problem in the optimization process. A finite deformation hyperelastic thermomechanical model is used together with an higher-order XFEM scheme to accurately predict the behavior of nonlinear slender structures during the design evolution. Examples are presented to demonstrate the unique capabilities of the proposed framework. Numerical predictions of optimized shape-changing structures are compared to 4D printed physical specimen and good agreement is achieved. Overall, a systematic design approach for creating 4D printed active structures with geometrically nonlinear behavior is presented which yields nonintuitive material layouts and geometries to achieve target deformations of various complexities
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Recommendations on simple but transformative diversity, equity, and inclusion measures in Heliophysics over the next decade
It is well established that, in order to perform at their peak ability, a person must feel accepted, safe, and valued at work. Therefore, it is imperative to bring Diversity, Equity, and Inclusion (DEI) efforts to the forefront of Heliophysics over the next decade and well beyond. This position paper outlines three specific recommendations to make the Heliophysics community more diverse, equitable, and inclusive by improving the accessibility and accountability. These recommendations are: performing consistent collection and analysis of demographic data across different agencies, reimagining undergraduate Heliophysics internships using the SOARS® model, and providing conference funding for DEI speakers whose expertise lies outside the field of Heliophysics. These targeted recommendations have a well-documented positive impact, are simple to implement, and follow other scientific communities’ recent recommendations for making the science, technology, engineering, and mathematics fields more diverse, equitable, and inclusive
Cultivating a Culture of Inclusivity in Heliophysics
A large number of heliophysicists from across career levels, institution types, and job titles came together to support a poster at Heliophysics 2050 and the position papers for the 2024 Heliophysics decadal survey titled “Cultivating a Culture of Inclusivity in Heliophysics,” “The Importance of Policies: It’s not just a pipeline problem,” and “Mentorship within Heliophysics.” While writing these position papers, the number of people who privately shared disturbing stories and experiences of bullying and harassment was shocking. The number of people who privately expressed how burned out they were was staggering. The number of people who privately spoke about how they considered leaving the field for their and their family’s health was astounding. And for as much good there is in our community, it is still a toxic environment for many. If we fail to do something now, our field will continue to suffer. While acknowledging the ongoing growth that we as individuals must work toward, we call on our colleagues to join us in working on organizational, group, and personal levels toward a truly inclusive culture, for the wellbeing of our colleagues and the success of our field. This work includes policies, processes, and commitments to promote: accountability for bad actors; financial security through removing the constant anxiety about funding; prioritization of mental health and community through removing constant deadlines and constant last-minute requests; a collaborative culture rather than a hyper-competitive one; and a community where people can thrive as whole persons and do not have to give up a healthy or well-rounded life to succeed
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