skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: Allan Hills I-188 Field Season Report 2022-2023
Field report for I-188, the purpose of which was to find a suitable site to extract a continuous >1 Ma ice core in the Allan Hills accumulation zone.  more » « less
Award ID(s):
2019719
PAR ID:
10608362
Author(s) / Creator(s):
; ; ; ;
Publisher / Repository:
U.S. Antarctic Program (USAP) Data Center
Date Published:
Subject(s) / Keyword(s):
Cryosphere
Format(s):
Medium: X
Location:
Allan Hills; Antarctica
Right(s):
Creative Commons Attribution 4.0 International
Sponsoring Org:
National Science Foundation
More Like this
  1. We propose a set of functions that a user can invoke to analyze a program written in a C-like language: Assume() refers to a label in the source code or to a program part, and enables the user to make an assumption about the state of the program at some label or the function of some program part; Capture() refers to a label or a program part and returns an assertion about the state of the program at the label or the function of the program part; Verify() refers to a label or a program part and tests a unary assertion about the state of the program at the label or a binary assertion about the function of the program part; Establish() refers to a label or a program part and modifies the program code to make Verify() return TRUE at that label or program part, if it did not originally. We discuss the foundations of this tool as well as a preliminary implementation. 
    more » « less
  2. Atomic force microscopes (AFMs) are used not only to image with nanometer-scale resolution, but also to nanofabricate structures on a surface using methods such as dip-pen nanolithography (DPN). DPN involves using the tip of the AFM to deposit a small amount of material on the surface. Typically, this process is done in open loop, leading to large variations in the amount of material transferred. One of the first steps to closing this loop is to be able to accurately and rapidly measure the amount of deposition. This can be done by measuring the change in the resonance frequency of the cantilever before and after a write as that shift is directly related to the change in mass on the cantilever. Currently, this is done using a thermal-based system identification, a technique which uses the natural Brownian excitation of the cantilever as a white noise excitation combined with a fast Fourier transform to extract a Bode plot. However, thermal-based techniques do not have a good signal to noise ratio at typical cantilever resonance frequencies and thus do not provide the needed resolution in the DPN application. Here we develop a scheme that iteratively uses a stepped-sine approach. At each step of the iteration, three frequencies close to the approximate location of the resonance are injected and used to fit a model of the magnitude of the transfer function. The identified peak is used to select three new frequencies in a smaller range in a binary search to reduce the uncertainty of the measured resonance peak location. The scheme is demonstrated through simulation and shown to produce an accuracy of better than 0.5 Hz on a cantilever with a 14 kHz resonance in a physically realistic noise scenario. 
    more » « less
  3. The goal of the greater project is to provide students with hands-on learning experiences while removing cost as a barrier to participation. Our Low-Cost Desktop Learning Modules (or LCDLMs) help students visualize and experience engineering concepts where books prove less than adequate and provide class members with the opportunity to learn as a group and collaborate with one another. LCDLMs have been found to improve motivation and attention while providing direct and vicarious learning opportunities, encouraging information retention in a learning environment. The goal of this paper is to introduce the latest LCDLM in development, for glucose analysis, which will mark the first LCDLM to feature a chemical reaction. In this paper we will also go over future work to be done to make the glucose analyzer viable for classroom use. The new module will feature a glucose solution meant for analysis, a set of reagents to convert the solution from transparent to a red-violet color of intensity correlated to the glucose concentration, and a simple apparatus students can use to read the concentration of the sample. The apparatus is meant to be used to teach students multiple engineering concepts through visual demonstration. In this LCDLM concept, chemicals from a set of reservoirs flow through a transparent microfluidics mixing chamber, which leads to a colorimetric reaction based on the amount of glucose present, teaching students about kinetics and, to a lesser extent, microfluidics. Dissolved oxygen is a limiting reagent, which will demonstrate to students the relevance of stoichiometry and mass transfer in a closed system. The mixture then collects in a chamber with two transparent sides. Green light passes through the red solution and into the lens of a smartphone camera to measure the intensity of the light. This is meant to demonstrate Beer’s law and complimentary colors. The more light that can pass through, the lower the glucose concentration. Students will need to measure a series of solutions with varied but known concentrations, construct a calibration curve, and then find an unknown solution concentration based on where an absorbance reading falls on the curve, modeling a routine wet lab test but without the need for expensive instrumentation. Prototyping is needed before a definitive version can be implemented in the classroom. The final design for the analyzer, how it will be assembled, parts to be used, etc., is being determined, and up-to-date results will be presented. The geometry of the mixing chamber with attached reservoirs for adding reagents must be optimized for small samples. The plan is to design a 3D model in SolidWorks and then cut out a prototype from an acrylic sheet with a laser cutter. The prototype will then be tested for leaks. The module itself will consist of the channel sheet glued between two other sheets, making assembly straightforward. 
    more » « less
  4. Abstract An intermediate complexity moist general circulation model is used to investigate the sensitivity of the quasi‐biennial oscillation (QBO) to resolution, diffusion, tropical tropospheric waves, and parameterized gravity waves. Finer horizontal resolution is shown to lead to a shorter period, while finer vertical resolution is shown to lead to a longer period and to a larger amplitude in the lowermost stratosphere. More scale‐selective diffusion leads to a faster and stronger QBO, while enhancing the sources of tropospheric stationary wave activity leads to a weaker QBO. In terms of parameterized gravity waves, broadening the spectral width of the source function leads to a longer period and a stronger amplitude although the amplitude effect saturates in the mid‐stratosphere when the half‐width exceedsm/s. A stronger gravity wave source stress leads to a faster and stronger QBO, and a higher gravity wave launch level leads to a stronger QBO. All of these sensitivities are shown to result from their impact on the resultant wave‐driven momentum torque in the tropical stratosphere. Atmospheric models have struggled to accurately represent the QBO, particularly at moderate resolutions ideal for long climate integrations. In particular, capturing the amplitude and penetration of QBO anomalies into the lower stratosphere (which has been shown to be critical for the tropospheric impacts) has proven a challenge. The results provide a recipe to generate and/or improve the simulation of the QBO in an atmospheric model. 
    more » « less
  5. For linear dynamic systems with uncertain parameters, design of controllers which drive a system from an initial condition to a desired final state, limited by state constraints during the transition is a nontrivial problem. This paper presents a methodology to design a state constrained controller, which is robust to time invariant uncertain variables. Polynomial chaos (PC) expansion, a spectral expansion, is used to parameterize the uncertain variables permitting the evolution of the uncertain states to be written as a polynomial function of the uncertain variables. The coefficients of the truncated PC expansion are determined using the Galerkin projection resulting in a set of deterministic equations. A transformation of PC polynomial space to the Bernstein polynomial space permits determination of bounds on the evolving states of interest. Linear programming (LP) is then used on the deterministic set of equations with constraints on the bounds of the states to determine the controller. Numerical examples are used to illustrate the benefit of the proposed technique for the design of a rest-to-rest controller subject to deformation constraints and which are robust to uncertainties in the stiffness coefficient for the benchmark spring-mass-damper system. 
    more » « less