531 research outputs found
Missing physics in stick-slip dynamics of a model for peeling of an adhesive tape
It is now known that the equations of motion for the contact point during
peeling of an adhesive tape mounted on a roll introduced earlier are singular
and do not support dynamical jumps across the two stable branches of the peel
force function. By including the kinetic energy of the tape in the Lagrangian,
we derive equations of motion that support stick-slip jumps as a natural
consequence of the inherent dynamics. In the low mass limit, these equations
reproduce solutions obtained using a differential-algebraic algorithm
introduced for the earlier equations. Our analysis also shows that mass of the
ribbon has a strong influence on the nature of the dynamics.Comment: Accepted for publication in Phys. Rev. E (Rapid Communication
High-speed metamagnetic resistive switching of FeRh through Joule heating
Due to its proximity to room temperature and demonstrated high degree of
temperature tunability, the metamagnetic ordering transition in FeRh is
attractive for novel high-performance computing devices seeking to use
magnetism as the state variable. We demonstrate electrical control of the
transition via Joule heating in FeRh wires. Finite element simulations based on
abrupt state transition within each domain result in a globally smooth
transition that agrees with the experimental findings and provides insight into
the thermodynamics involved. We measure a 150 K decrease in transition
temperature with currents up to 60 mA, limited only by the dimensions of the
device. The sizeable shift in transition temperature scales with current
density and wire length, suggesting the absolute resistance and heat
dissipation of the substrate are also important. The FeRh phase change is
evaluated by pulsed I-V using a variety of bias conditions. We demonstrate high
speed (~ ns) memristor-like behavior and report device performance parameters
such as switching speed and power consumption that compare favorably with
state-of-the-art phase change memristive technologies.Comment: 35 pages, 9 figure
Database, Features, and Machine Learning Model to Identify Thermally Driven Metal-Insulator Transition Compounds
Metal-insulator transition (MIT) compounds are materials that may exhibit
insulating or metallic behavior, depending on the physical conditions, and are
of immense fundamental interest owing to their potential applications in
emerging microelectronics. There is a dearth of thermally-driven MIT materials,
however, which makes delineating these compounds from those that are
exclusively insulating or metallic challenging. Here we report a material
database comprising temperature-controlled MITs (and metals and insulators with
similar chemical composition and stoichiometries to the MIT compounds) from
high quality experimental literature, built through a combination of
materials-domain knowledge and natural language processing. We featurize the
dataset using compositional, structural, and energetic descriptors, including
two MIT relevant energy scales, an estimated Hubbard interaction and the charge
transfer energy, as well as the structure-bond-stress metric referred to as the
global-instability index (GII). We then perform supervised classification,
constructing three electronic-state classifiers: metal vs non-metal (M),
insulator vs non-insulator (I), and MIT vs non-MIT (T). We identify two
important descriptors that separate metals, insulators, and MIT materials in a
2D feature space: the average deviation of the covalent radius and the range of
the Mendeleev number. We further elaborate on other important features (GII and
Ewald energy), and examine how they affect classification of binary vanadium
and titanium oxides. We discuss the relationship of these atomic features to
the physical interactions underlying MITs in the rare-earth nickelate family.
Last, we implement an online version of the classifiers, enabling quick
probabilistic class predictions by uploading a crystallographic structure file
3' tag digital gene expression profiling of human brain and universal reference RNA using Illumina Genome Analyzer
<p>Abstract</p> <p>Background</p> <p>Massive parallel sequencing has the potential to replace microarrays as the method for transcriptome profiling. Currently there are two protocols: full-length RNA sequencing (RNA-SEQ) and 3'-tag digital gene expression (DGE). In this preliminary effort, we evaluated the 3' DGE approach using two reference RNA samples from the MicroArray Quality Control Consortium (MAQC).</p> <p>Results</p> <p>Using Brain RNA sample from multiple runs, we demonstrated that the transcript profiles from 3' DGE were highly reproducible between technical and biological replicates from libraries constructed by the same lab and even by different labs, and between two generations of Illumina's Genome Analyzers. Approximately 65% of all sequence reads mapped to mitochondrial genes, ribosomal RNAs, and canonical transcripts. The expression profiles of brain RNA and universal human reference RNA were compared which demonstrated that DGE was also highly quantitative with excellent correlation of differential expression with quantitative real-time PCR. Furthermore, one lane of 3' DGE sequencing, using the current sequencing chemistry and image processing software, had wider dynamic range for transcriptome profiling and was able to detect lower expressed genes which are normally below the detection threshold of microarrays.</p> <p>Conclusion</p> <p>3' tag DGE profiling with massive parallel sequencing achieved high sensitivity and reproducibility for transcriptome profiling. Although it lacks the ability of detecting alternative splicing events compared to RNA-SEQ, it is much more affordable and clearly out-performed microarrays (Affymetrix) in detecting lower abundant transcripts.</p
Radio Astronomy
Contains research objectives and summary of research on seven research projects.M.I.T. Sloan Fund for Basic ResearchNational Aeronautics and Space Administration (Contract NAS5-21980)National Aeronautics and Space Administration (Contract NAS5-22485)National Aeronautics and Space Administration (Contract NAS5-23677)National Aeronautics and Space Administration (Contract NAS5-22929)U. S. Air Force - Electronic Systems Division (Contract F19628-75-C-0122)National Science Foundation (Grant AST73-05043-A02)National Science Foundation (Grant AST73-05042-A03
Radio Astronomy
Contains reports on eight research projects.National Science Foundation (Grant AST77-06052)Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Aeronautics and Space Administration (Contract NAS5-21980)U. S. Department of Commerce - National Oceanic and Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Contract NAS5-22929)National Aeronautics and Space Administration (Contract NAS5-23677)National Science Foundation (Grant AST77-12960)National Science Foundation (Grant AST77-26896
Unraveling biogeochemical phosphorus dynamics in hyperarid Mars‐analogue soils using stable oxygen isotopes in phosphate
With annual precipitation less than 20 mm and extreme UV intensity, the Atacama Desert in northern Chile has long been utilized as an analogue for recent Mars. In these hyperarid environments, water and biomass are extremely limited, and thus, it becomes difficult to generate a full picture of biogeochemical phosphate‐water dynamics. To address this problem, we sampled soils from five Atacama study sites and conducted three main analyses—stable oxygen isotopes in phosphate, enzyme pathway predictions, and cell culture experiments. We found that high sedimentation rates decrease the relative size of the organic phosphorus pool, which appears to hinder extremophiles. Phosphoenzyme and pathway prediction analyses imply that inorganic pyrophosphatase is the most likely catalytic agent to cycle P in these environments, and this process will rapidly overtake other P utilization strategies. In these soils, the biogenic δ18O signatures of the soil phosphate (δ18OPO4) can slowly overprint lithogenic δ18OPO4 values over a timescale of tens to hundreds of millions of years when annual precipitation is more than 10 mm. The δ18OPO4 of calcium‐bound phosphate minerals seems to preserve the δ18O signature of the water used for biogeochemical P cycling, pointing toward sporadic rainfall and gypsum hydration water as key moisture sources. Where precipitation is less than 2 mm, biological cycling is restricted and bedrock δ18OPO4 values are preserved. This study demonstrates the utility of δ18OPO4 values as indicative of biogeochemical cycling and hydrodynamics in an extremely dry Mars‐analogue environment
Tubular Chemical Reactors: The “Lumping Approximation” and Bifurcation of Oscillatory States
Radio Astronomy
Contains reports on twelve research projects.National Science Foundation (Grant AST77-06052)Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Aeronautics and Space Administration (Contract NAS5-21980)U.S. Air Force - Electronic Systems Division (Contract F19628-75-C-0122)U.S. Department of Commerce - National Oceanic Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Contract NAS5-22929)National Aeronautics and Space Administration (Contract NAS5-23677)National Science Foundation (Grant AST73-05042-A03)National Science Foundation (Grant AST76-20376
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