College of Computer, Mathematical & Natural Sciences

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Effective October 4, 2010, the University established the College of Computer, Mathematical, and Natural Sciences (CMNS) by integrating the former colleges of Chemical and Life Sciences (CLFS) and Computer Mathematical and Physical Sciences (CMPS).

The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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1/f noise and Luttinger liquid phenomena in carbon nanotubes
(2007-08-03) Tobias, David; Lobb, Christopher; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Carbon nanotubes (CNTs) provide an ideal medium for testing the behavior of one-dimensional electron systems and are promising candidates for electronic applications such as sensors or field-effect transistors. This thesis describes the use of low frequency resistance fluctuations to measure both the properties of the one-dimensional electron system in CNTs, and the sensitivity of CNT devices to their environment. Low frequency noise was measured in CNTs in field effect transistor (FET) geometry. CNTs have a large amount of surface area relative to their volume and are expected to be strongly affected by their environment, leading to speculation that CNTs should have large amounts of 1/f noise. My measurements indicate that the noise level is in the same range as that of traditional FETs, an encouraging result for possible electronic applications. The temperature dependence of 1/f noise from 1.2 K to 300 K can be used to extract the characteristic energies of the fluctuators responsible for the noise. The characteristic energies allows for the elimination of structural and electronic transitions within the CNT itself as possible sources of 1/f noise in CNTs, leaving the motion of defects in the gate dielectric, or possibly strongly physisorbed species, as the likely culprits. Another form of low frequency noise found in CNTs is random telegraph signal (RTS), which manifests as the alternation between two current states at a stable voltage bias. In CNTs, this phenomenon occurs due to the tunneling of electrons into and out of the CNT from a nearby defect, and thus provides a way to probe the tunneling density of states of the CNT itself. The tunneling density of states in turn provides information on the strength of the electron-electron interaction in CNTs. Due to the one-dimensional structure of CNTs their electronic state is expected to be a Luttinger liquid, which should manifest as a power-law suppression of the tunneling density of states at the Fermi energy. The power law exponent is measured in both the temperature dependence and energy dependence of the tunneling rates. In agreement with theory, the power-law exponent is significantly larger in semiconducting CNTs than found in previous experiments on metallic CNTs. The RTS can also be used as a "defect thermometer" to probe the electron temperature of the CNT. The effect of the bias voltage on the electron temperature provides a means to determine the energy relaxation length for the electrons in the CNT.
1620 GEOGRAPHOS AND 433 EROS: SHAPED BY PLANETARY TIDES?
(University of Chicago Press, 1999) BOTTKE, W. F. JR.; RICHARDSON, D. C.; MICHEL, P.; LOVE, S. G.
Until recently, most asteroids were thought to be solid bodies whose shapes were determined largely by collisions with other asteroids. Recent work by Burns and others has shown that many asteroids may be little more than rubble piles, held together by self-gravity ; this means that their shapes may be strongly distorted by tides during close encounters with planets. Here we report on numerical simulations of encounters between an ellipsoid-shaped rubble-pile asteroid and Earth. After an encounter, many of the simulated asteroids develop the same rotation rate and distinctive shape as 1620 Geographos (i.e., highly elongated with a single convex side, tapered ends, and small protuberances swept back against the rotation direction). Since our numerical studies show that these events occur with some frequency, we suggest that Geographos may be a tidally distorted object. In addition, our work shows that 433 Eros, which will be visited by the NEAR spacecraft in 1999, is much like Geographos, suggesting that it too may have been molded by tides in the past.
182W and HSE constraints from 2.7 Ga komatiites on the heterogeneous nature of the Archean mantle
(Elsevier - Geochimica et Cosmochimica Acta, 2018) Puchtel, Igor S; Blichert-Toft, Janne; Touboul, Mathieu; Walker, Richard J.
While the isotopically heterogeneous nature of the terrestrial mantle has long been established, the origin, scale, and longevity of the heterogeneities for different elements and isotopic systems are still debated. Here, we report Nd, Hf, W, and Os isotopic and highly siderophile element (HSE) abundance data for the Boston Creek komatiitic basalt lava flow (BCF) in the 2.7 Ga Abitibi greenstone belt, Canada. This lava flow is characterized by strong depletions in Al and heavy rare earth elements (REE), enrichments in light REE, and initial epsilon143Nd = +2.5 ± 0.2 and initial epsilon176Hf = +4.2 ± 0.9 indicative of derivation from a deep mantle source with time-integrated suprachondritic Sm/Nd and Lu/Hf ratios. The data plot on the terrestrial Nd-Hf array suggesting minimal involvement of early magma ocean processes in the fractionation of lithophile trace elements in the mantle source. This conclusion is supported by a mean mu142Nd = -3.8 ± 2.8 that is unresolvable from terrestrial standards. By contrast, the BCF exhibits a positive 182W anomaly (mu182W = +11.7 ± 4.5), yet is characterized by chondritic initial gamma187Os = +0.1 ± 0.3 and low inferred source HSE abundances (35 ± 5% of those estimated for the present-day Bulk Silicate Earth, BSE). Collectively, these characteristics are unique among Archean komatiite systems studied so far. The deficit in the HSE, coupled with the chondritic Os isotopic composition, but a positive 182W anomaly, are best explained by derivation of the parental BCF magma from a mantle domain characterized by a predominance of HSE-deficient, differentiated late accreted material. According to the model presented here, the mantle domain that gave rise to the BCF received only ~35% of the present-day HSE complement in the BSE before becoming isolated from the rest of the convecting mantle until the time of komatiite emplacement at 2.72 Ga. These new data provide strong evidence for a highly heterogeneous Archean mantle in terms of absolute HSE abundances and W isotopic composition, and also indicate slow mixing, on a timescale of at least 1.8 billion years. Additionally, the data are consistent with a stagnant-lid plate tectonic regime in the Hadean and Archean, prior to the onset of modern-style plate tectonics.
1991 Human-Computer Interaction Laboratory Video Reports
(2000-06-23) Plaisant, Catherine (Editor)
Introduction - Ben Shneiderman, Scheduling home control devices - Catherine Plaisant, Ben Shneiderman, Touchscreen toggles - Catherine Plaisant , A home automation system - Reuel Launey (Custom Command Systems), PlayPen II (now known as PenPlay II) : A novel fingerpainting program - Andrew Sears, Ben Shneiderman, Touchscreen keyboards - Andrew Sears, Ben Shneiderman, Pie menus - Don Hopkins, Three interfaces for browsing tables of contents - Rick Chimera (Also cross-referenced as CAR-TR-791)
1992 Human-Computer Interaction Laboratory Video Reports
(1998-10-15) Plaisant, Catherine (Editor)
Introduction - Ben Shneiderman, [3:00], Dynamic Queries: database searching by direct manipulation - Ben Shneiderman, Chris Williamson, Christopher Ahlberg, [10:55], Treemaps for visualizing hierarchical information - Ben Shneiderman, Brian Johnson, Dave Turo, [11:25], Three strategies for directory browsing - Rick Chimera, [10:30], Filter-Flow metaphor for boolean queries - Degi Young, Ben Shneiderman, [6:35], The AT&T Teaching Theater: active learning through computer supported collaborative courseware - Kent Norman, [8:25], ACCESS: an online public access catalog at the Library of Congress - Gary Marchionini, [8:15] Remote Direct Manipulation: a telepathology workstation - Catherine Plaisant, Dave Carr, [7:30], Guiding automation with pixels: a technique for programming in the user interface - Richard Potter, [11:50] (Also cross-referenced as CAR-TR-792)
1993 Human-Computer Interaction Laboratory Video Reports
(1998-10-15) Plaisant, Catherine (Editor)
Introduction and table of contents - Ben Shneiderman, [4:00] Dynamaps: dynamic queries on a health statistics atlas - Catherine Plaisant and Vinit Jain, [6:34], Hierarchical visualization with Treemaps: making sense of pro basketball data - Dave Turo, [10:47], TreeViz: file directory browsing - Brian Johnson, [10:04], HyperCourseware: computer integrated tools in the AT&T Teaching Theater - Kent Norman, [7:08], Improving access to medical abstracts: Grateful Med Interface prototype - Gary Marchionini, [6:08], Layout appropriateness: guiding interface desi gn with simple task descriptions - Andrew Sears, [4:00] (Also cross-referenced as CAR-TR-793)
1994 Human-Computer Interaction Laboratory Video Reports
(1998-10-15) Plaisant, Catherine (Edited by); Reesch, John (Video by)
80 minute video demonstrations of the past year's research Topics are: Introduction and table of contents - Ben Shneiderman, [3:18] Visual information seeking using the FilmFinder - Christopher Ahlberg, Ben Shneiderman, [6:12] Organization overviews and role management-Inspiration for future desktop environments - Catherine Plaisant, Ben Shneiderman, [9:39] Visual decision-making: using treemaps for the analytic hierarchy process - Toshiyuki Asahi, Ben Shneiderman, David Turo, [8:34] Visual information management for satellite network configuration-Catherine Plaisant, Harsha Kumar, Marko Teittinen, Ben Shneiderman, [8:49] Graphical macros: a technique for customizing any application using pixel-pattern matching-Richard Potter, [9:49] Education by engagement and construction: can distance learning be better than face to face?- Ben Shneiderman, [15:00] Dynamic queries demos: revised HomeFinder and text version plus health statistics atlas-Ben Shneiderman, [9:40] Dynamic Queries are user controlled displays of visual or textual information. Ben Shneiderman presents the HomeFinder (developed by Chris Williamson), followed by the text version (Vinit Jain) and the Health Statistics Atlas (Catherine Plaisant and Vinit Jain). CHI '94 slide and video show- [9:12]Open House '94 Video (Also cross-referenced as CAR-TR-794)
1995 Human-Computer Interaction Laboratory Video Reports
(2000-07-21) Plaisant, Catherine (Edited by)
49 minute video of the labs work over the past year. Topics are: Introduction and table of contents - Ben Shneiderman Using Dynamic Queries for Youth Services Information - Anne Rose, Ajit Vanniamparampil Life-Lines: Visualizing Personal Histories - Brett Milash, Catherine Plaisant, Anne Rose Dynamic Queries and Pruning for Large Tree Structures - Harsha Kumar Browsing Anatomical Image Databases : the Visible Human - Flip Korn, Chris North Spinning Your Web: WWW Interface Design Issues - Vince Boisselle BizView : Managing Business and Network Alarms - Catherine Plaisant, Wei Zhao and Rina Levy Animated Specifications Using Interaction Object Graphs - David Carr WinSurfer: Treemaps for Replacing the Windows File Manager - Marko Teittinen (Also cross-referenced as CAR-TR-795)
1996 HCIL Video Reports
(1998-12-05) Plaisant, Catherine
Elastic Windows for Rapid Multiple Window Management Life-Lines: Visualizing Personal Histories Designing Interfaces for Youth Services Information Management Query Previews in Networked Information Systems the Case of EOSDIS Baltimore Learning Communities Table of Contents of the 1995 HCIL Video Reports Table of Contents of the 1994 HCIL Video Reports Visual Information Seeking using the FilmFinder (Extract from the HCIL1994 Video Report
A 20-YEAR CLIMATOLOGY OF GLOBAL ATMOSPHERIC METHANE FROM HYPERSPECTRAL THERMAL INFRARED SOUNDERS WITH SOME APPLICATIONS
(2022) Zhou, Lihang; Warner, Juying; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Atmospheric Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2), and accounts for approximately 20% of the global warming produced by all well-mixed greenhouse gases. Thus, its spatiotemporal distributions and relevant long-term trends are critical to understanding the sources, sinks, and global budget of atmospheric composition, as well as the associated climate impacts. The current suite of hyperspectral thermal infrared sounders has provided continuous global methane data records since 2002, starting with the Atmospheric Infrared Sounder (AIRS) onboard the NASA EOS/Aqua satellite launched on 2 May 2002. The Cross-track Infrared Sounder (CrIS) was launched onboard the Suomi National Polar Orbiting Partnership (SNPP) on 28 October 2011 and then on NOAA-20 on 18 November 2017. The Infrared Atmospheric Sounding Interferometer (IASI) was launched onboard the EUMETSAT MetOp-A on 19 October 2006, followed by MetOp-B on 17 September 2012, then Metop-C on 7 November 2018. In this study, nearly two decades of global CH4 concentrations retrieved from the AIRS and CrIS sensors were analyzed. Results indicate that the global mid-upper tropospheric CH4 concentrations (centered around 400 hPa) increased significantly from 2003 to 2020, i.e., with an annual average of ~1754 ppbv in 2003 and ~1839 ppbv in 2020. The total increase is approximately 85 ppbv representing a +4.8% change in 18 years. More importantly, the rate of increase was derived using satellite measurements and shown to be consistent with the rate of increase previously reported only from in-situ observational measurements. It further confirmed that there was a steady increase starting in 2007 that became stronger since 2014, as also reported from the in-situ observations. In addition, comparisons of the methane retrieved from the AIRS and CrIS against in situ measurements from NOAA Global Monitoring Laboratory (GML) were conducted. One of the key findings of this comparative study is that there are phase shifts in the seasonal cycles between satellite thermal infrared measurements and ground measurements, especially in the middle to high latitudes in the northern hemisphere. Through this, an issue common in the hyperspectral thermal sensor retrievals were discovered that was unknown previously and offered potential solutions. We also conducted research on some applications of the retrieval products in monitoring the changes of CH4 over the selected regions (the Arctic and South America). Detailed analyses based on local geographic changes related to CH4 concentration increases were discussed. The results of this study concluded that while the atmospheric CH4 concentration over the Arctic region has been increasing since the early 2000s, there were no catastrophic sudden jumps during the period of 2008-2012, as indicated by the earlier studies using pre-validated retrieval products. From our study of CH4 climatology using hyperspectral infrared sounders, it has been proved that the CH4 from hyperspectral sounders provide valuable information on CH4 for the mid-upper troposphere and lower stratosphere. Future approaches are suggested that include: 1) Utilizing extended data records for CH4 monitoring using AIRS, CrIS, and other potential new generation hyperspectral infrared sensors; 2). Improving the algorithms for trace gas retrievals; and 3). Enhancing the capacity to detect CH4 changes and anomalies with radiance signals from hyperspectral infrared sounders.
THE 3' UTR OF TURNIP CRINKLE VIRUS INTERACTS LOCALLY AND DISTALLY TO REGULATE TRANSCRIPTION AND TRANSLATION OF THE VIRUS
(2012) Young, Megan Yoke Len; Simon, Anne E; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Turnip crinkle virus (TCV) is a 4054 b positive-strand RNA virus of the genus Carmovirus in the Family Tombusviridae. Upon entry into cells, TCV is translated using host translational machinery to produce its RNA-dependent RNA polymerase (RdRp). The RNA is proposed to undergo a conformational rearrangement, mediated by recruitment of the RdRp to the 3' ends of the viral RNA, which represses translation and promotes negative-strand synthesis. A second RNA switch is proposed to occur that inhibits minus-strand synthesis and promotes recruitment of the RdRp to the 3' ends of negative-strands for the asymmetrical production of positive-strands. Within the 3' UTR of TCV is a tRNA-shaped structure (TSS) that is capable of binding ribosomes and overlaps with structures necessary for translational enhancement. The RdRp has been shown to bind within this region and result in a widespread conformational shift. The binding of RdRp to the 3' end of the virus is very sensitive to perturbations of sequence or structure, with many mutations resulting in non-specific binding of the RdRp. The elements within the 3' UTR have been shown to be very interactive with alterations affecting the structure of regions hundreds of bases away. A second-site mutation study indicated that regions upstream of the 3' UTR may also be interacting with the 3' UTR. Some second-site mutations located in this upstream region were found to increase accumulation in protoplasts and additional studies are under way to explain this phenomenon. The 3' viral contribution in a luciferase reporter construct was increased to incorporate the second-site mutations. While the second-site mutations had little effect on translation, it was surprising to find that extension of the viral 3' sequence enhanced translation. Translational enhancement was mapped to just an additional twenty bases and further study revealed that a hairpin (H3) is important for viral translation and accumulation and may also be interacting with the 3' UTR.
3D Ionospheric Effects on HF Propagation and Heating
(2015) Zawdie, Katherine A.; Papadopoulos, Konstantinos; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The thesis uses a three-dimensional, first-principles model of the ionosphere in combination with High Frequency (HF) raytracing model to address key topics related to the physics of HF propagation and artificial ionospheric heating. In particular: 1. Explores the effect of the ubiquitous electron density gradients caused by Medium Scale Traveling Ionospheric Disturbances (MSTIDs) on high-angle of incidence HF radio wave propagation. Previous studies neglected the all-important presence of horizontal gradients in both the cross- and down-range directions, which refract the HF waves, significantly changing their path through the ionosphere. The physics-based ionosphere model SAMI3/ESF is used to generate a self-consistently evolving MSTID that allows for the examination of the spatio-temporal progression of the HF radio waves in the ionosphere. 2. Tests the potential and determines engineering requirements for ground- based high power HF heaters to trigger and control the evolution of Equatorial Spread F (ESF). Interference from ESF on radio wave propagation through the ionosphere remains a critical issue on HF systems reliability. Artificial HF heating has been shown to create plasma density cavities in the ionosphere similar to those that may trigger ESF bubbles. The work explores whether HF heating may trigger or control ESF bubbles. 3. Uses the combined ionosphere and HF raytracing models to create the first self-consistent HF Heating model. This model is utilized to simulate results from an Arecibo experiment and to provide understanding of the physical mechanism behind observed phenomena. The insights gained provide engineering guidance for new artificial heaters that are being built for use in low to middle latitude regions. In accomplishing the above topics: (i) I generated a model MSTID using the SAMI3/ESF code, and used a raytrace model to examine the effects of the MSTID gradients on radio wave propagation observables; (ii) I implemented a three- dimensional HF heating model in SAMI3/ESF and used the model to determine whether HF heating could artificially generate an ESF bubble; (iii) I created the first self-consistent model for artificial HF heating using the SAMI3/ESF ionosphere model and the MoJo raytrace model and ran a series of simulations that successfully modeled the results of early artificial heating experiments at Arecibo.
3D Magnetic Imaging using SQUIDs and Spin-valve Sensors
(2016) Jeffers, Alex; Wellstood, Frederick C; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
We have used 2 µm by 4 µm thin-film Cu-Mn-Ir spin-valve sensors and high Tc YBa2Cu3O7-x dc SQUIDs to take magnetic images of test samples with current paths that meander between 1 and 5 metallization layers separated by 1 µm to 10 µm vertically. I describe the development and performance of a 3D magnetic inverse for reconstructing current paths from a magnetic image. I present results from this inverse technique that demonstrate the reconstruction of the 3D current paths from magnetic images of samples. This technique not only maps active current paths in the sample but also extracts key parameters such as the layer-to-layer separations. When imaging with 2 µm by 4 µm spin-valve sensors I typically applied currents of 1 mA at 95 kHz and achieved system noise of about 200 nT for a 3 ms averaging time per pixel. This enabled a vertical resolution of 1 µm and a lateral resolution of 1 µm in the top layers and 3 µm in the bottom layer. For our roughly 30 µm square SQUID sensors, I typically applied currents of 1 mA at 5.3 kHz, and achieved system noise of about 200 pT for a 3 ms averaging time per pixel. The higher sensitivity compared to the spin-valve sensor allowed me to resolve more deeply buried current paths.
5-MODIFIED LIPOPHILIC G-QUADRUPLEXES: STRUCTURAL STUDIES AND APPLICATIONS AS SCAFFOLDS FOR [2+2] PHOTOCYCLOADDITIONS
(2019) Sutyak, Keith Brandon; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Guanosine self-assembly is a powerful tool for constructing nanostructures and materials with intriguing properties. Guanosine’s nucleobase has a hydrogen bond donor and acceptor face that in the presence of an appropriate templating cation can self-assemble to form larger G-quadruplex structures. Through the addition of a nonpolar solubilizing group on the 2, 3, or 5 position of guanosine’s ribose sugar, the G-quadruplex may be formed in organic solvents. Not surprisingly, any modification made to the guanine nucleobase can have a substantial effect on the self-assembly of the G-quadruplex core. These alterations can significantly alter or destroy the ability of the guanine base to form larger H-bond structures. For this reason, a major target for the synthetic modification of the G-quadruplex is the ribose sugar. Modifications to the sugar can be used to add new functionality or groups capable of modulating the G-quadruplexes stability and structure. The 5-position is easily esterified and is an ideal target for incorporating new functionality to the G-quadruplex, not not much was known about how esterification of the 5-position of guanosine impacted self-assembly. In this thesis, a series of 5-modified aryl esters of guanosine were synthesized G 21-G 25, comprising either activating or de-activating substituents on the aromatic rings, to systematically investigate how the addition of an ester to the 5- position of guanosine affects the self-assembly G-quadruplex. The identity of the 5-aryl ester was found to have a direct impact on the molecularity (how many Gs are in each assembly) and stability of the G-quadruplexes. The information gained from these experiments was applied to rationally design a new G-quadruplex capable of templating a [2+2] photocycloaddition reaction. With an increased knowledge of how modifications to the 5-position affect the structural integrity of the G-quadruplex, we applied this information to rationally design a new G-quadruplex system capable of templating a [2+2] photocycloaddition reaction. To achieve this goal a series of 5-cinnamate esters G 26-G 29 were synthesized and studied. Each derivative G 26- G 29 when self-assembled into a G-quadruplex an photoirradiated underwent a photocycloadditon reaction ins high yields with good stereoselectivity. These same compounds when disassembled only underwent trans-cis photoisomerization. Highlighting the need for the G-quadruplex self-assembly.
A 7-Year Climatology of Warm-Sector Heavy Rainfall over South China during the Pre-Summer Months
(MDPI, 2021-07-15) Chen, Tao; Zhang, Da-Lin
In view of the limited predictability of heavy rainfall (HR) events and the limited understanding of the physical mechanisms governing the initiation and organization of the associated mesoscale convective systems (MCSs), a composite analysis of 58 HR events over the warm sector (i.e., far ahead of the surface cold front), referred to as WSHR events, over South China during the months of April to June 2008~2014 is performed in terms of precipitation, large-scale circulations, pre-storm environmental conditions, and MCS types. Results show that the large-scale circulations of the WSHR events can be categorized into pre-frontal, southwesterly warm and moist ascending airflow, and low-level vortex types, with higher frequency occurrences of the former two types. Their pre-storm environments are characterized by a deep moist layer with >50 mm column-integrated precipitable water, high convective available potential energy with the equivalent potential temperature of ≥340 K at 850 hPa, weak vertical wind shear below 400 hPa, and a low-level jet near 925 hPa with weak warm advection, based on atmospheric parameter composite. Three classes of the corresponding MCSs, exhibiting peak convective activity in the afternoon and the early morning hours, can be identified as linear-shaped, a leading convective line adjoined with trailing stratiform rainfall, and comma-shaped, respectively. It is found that many linear-shaped MCSs in coastal regions are triggered by local topography, enhanced by sea breezes, whereas the latter two classes of MCSs experience isentropic lifting in the southwesterly warm and moist flows. They all develop in large-scale environments with favorable quasi-geostrophic forcing, albeit weak. Conceptual models are finally developed to facilitate our understanding and prediction of the WSHR events over South China.
A Century of Observed Temperature Change in the Indian Ocean
(Wiley, 2022-06-25) Wenegrat, J. O.; Bonanno, E.; Rack, U.; Gebbie, G.
The Indian Ocean is warming rapidly, with widespread effects on regional weather and global climate. Sea-surface temperature records indicate this warming trend extends back to the beginning of the 20th century, however the lack of a similarly long instrumental record of interior ocean temperatures leaves uncertainty around the subsurface trends. Here we utilize unique temperature observations from three historical German oceanographic expeditions of the late 19th and early 20th centuries: SMS Gazelle (1874–1876), Valdivia (1898–1899), and SMS Planet (1906–1907). These observations reveal a mean 20th century ocean warming that extends over the upper 750 m, and a spatial pattern of subsurface warming and cooling consistent with a 1°–2° southward shift of the southern subtropical gyre. These interior changes occurred largely over the last half of the 20th century, providing observational evidence for the acceleration of a multidecadal trend in subsurface Indian Ocean temperature.
A CloudSat and CALIPSO-based evaluation of the effects of thermodynamic instability and aerosol loading on Amazon Basin deep convection and lightning
(2023-08-14) Allen, Dale
The Amazon Basin, which plays an important role in the carbon and water cycle, is under stress due to changes in climate, agricultural practices, and deforestation. The Basin includes a rainforest in the northwest and a mix of deforested areas, savannah-type vegetation, and agriculture in the southeast. The effects of instability and aerosol loading on thunderstorms in the Basin (75-45° W, 0-15° S) were examined during mid-August through mid-December, a period with large variations in aerosols, intense convective storms, and plentiful flashes. The analysis used measurements of radar reflectivity, ice water content (IWC), and aerosol type from instruments aboard the CloudSat and CALIPSO satellites, flash rates from the ground-based STARNET network, and aerosol optical depth (AOD) from a surface network and a meteorological re-analysis. After controlling for convective available potential energy (CAPE), a measure of instability, it was found that thunderstorms that developed under dirty (high-AOD) conditions were approximately 1.5 km deeper, had 50% more IWC, and more than two times as many flashes as storms that developed under clean (low-AOD) conditions. Flash rates were also found to be larger during periods when smoke rather than dust was common in the lower troposphere, likely because these periods were less stable.
A Grammar-Based Approach for Applying Visualization Taxonomies to Interaction Logs
(Wiley, 2022-07-29) Gathani, Sneha; Monadjemi, Shayan; Ottley, Alvitta; Battle, Leilani
Researchers collect large amounts of user interaction data with the goal of mapping user's workflows and behaviors to their high-level motivations, intuitions, and goals. Although the visual analytics community has proposed numerous taxonomies to facilitate this mapping process, no formal methods exist for systematically applying these existing theories to user interaction logs. This paper seeks to bridge the gap between visualization task taxonomies and interaction log data by making the taxonomies more actionable for interaction log analysis. To achieve this, we leverage structural parallels between how people express themselves through interactions and language by reformulating existing theories as regular grammars. We represent interactions as terminals within a regular grammar, similar to the role of individual words in a language, and patterns of interactions or non-terminals as regular expressions over these terminals to capture common language patterns. To demonstrate our approach, we generate regular grammars for seven existing visualization taxonomies and develop code to apply them to three public interaction log datasets. In analyzing these regular grammars, we find that the taxonomies at the low-level (i.e., terminals) show mixed results in expressing multiple interaction log datasets, and taxonomies at the high-level (i.e., regular expressions) have limited expressiveness, due to primarily two challenges: inconsistencies in interaction log dataset granularity and structure, and under-expressiveness of certain terminals. Based on our findings, we suggest new research directions for the visualization community to augment existing taxonomies, develop new ones, and build better interaction log recording processes to facilitate the data-driven development of user behavior taxonomies.
A Hybrid Tensor-Expert-Data Parallelism Approach to Optimize Mixture-of-Experts Training
(Association for Computer Machinery (ACM), 2023-06-21) Singh, Siddarth; Ruwase, Olatunji; Awan, Ammar Ahmad; Rajbhandari, Samyam; He, Yuxiong; Bhatele, Abhinav
Mixture-of-Experts (MoE) is a neural network architecture that adds sparsely activated expert blocks to a base model, increasing the number of parameters without impacting computational costs. However, current distributed deep learning frameworks are limited in their ability to train high-quality MoE models with large base models. In this work, we present DeepSpeed-TED, a novel, threedimensional, hybrid parallel algorithm that combines data, tensor, and expert parallelism to enable the training of MoE models with 4–8× larger base models than the current state-of-the-art. We also describe memory optimizations in the optimizer step, and communication optimizations that eliminate unnecessary data movement. We implement our approach in DeepSpeed and achieve speedups of 26% over a baseline (i.e. without our communication optimizations) when training a 40 billion parameter MoE model (6.7 billion base model with 16 experts) on 128 V100 GPUs.
A Neural-Network Based MPAS—Shallow Water Model and Its 4D-Var Data Assimilation System
(MDPI, 2023-01-10) Tian, Xiaoxu; Conibear, Luke; Steward, Jeffrey
The technique of machine learning has been increasingly applied in numerical weather predictions. The aim of this study is to explore the application of a neural network in data assimilation by making use of the convenience in obtaining the tangent linear and adjoint (TL/AD) of a neural network (NN) and formulating a NN-based four-dimensional variational (4D-Var) DA system. A NN-based shallow water (SW) model is developed in this study. The NN model consists of three layers. The weights and biases in the NN-based SW model are trained with 60 years of hourly ERA5 geopotentials and wind field at 500 hPa as initial conditions and the corresponding 12-h forecasts by Model for Prediction Across Scales (MPAS)-SW, in total of 534,697 sets of samples. The 12-h forecasts from independent dates made by NN-based SW prove to closely emulate the simulations by the actual MPAS-SW model. This study further shows that the TL/AD of an NN model can be easily developed and validated. The ease of obtaining the TL/AD makes NN conveniently applicable in various aspects within a data assimilation (DA) system. To demonstrate such, a continuous 4D-Var DA system is also developed with the forward NN and its adjoint. To demonstrate the functionality of the NN-based 4D-Var DA system, the results from a higher resolution simulation will be treated as observations and assimilated to analyze the low resolution initial conditions. The forecasts starting from the analyzed initial conditions will be compared with those without assimilation to demonstrate improvements.

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