3,547 research outputs found
Lieb-Robinson and the butterfly effect
As experiments are increasingly able to probe the quantum dynamics of systems
with many degrees of freedom, it is interesting to probe fundamental bounds on
the dynamics of quantum information. We elaborate on the relationship between
one such bound---the Lieb-Robinson bound---and the butterfly effect in
strongly-coupled quantum systems. The butterfly effect implies the ballistic
growth of local operators in time, which can be quantified with the "butterfly"
velocity . Similarly, the Lieb-Robinson velocity places a state
independent ballistic upper bound on the size of time evolved operators in
non-relativistic lattice models. Here, we argue that is a state-dependent
effective Lieb-Robinson velocity. We study the butterfly velocity in a wide
variety of quantum field theories using holography and compare with free
particle computations to understand the role of strong coupling. We find that,
depending on the way length and time scale, acquires a temperature
dependence and decreases towards the IR. We also comment on experimental
prospects and on the relationship between the butterfly velocity and signaling.Comment: 5+5 pages, 0 figures. v2: updated references and additional
clarification
Complexity, action, and black holes
Our earlier paper "Complexity Equals Action" conjectured that the quantum
computational complexity of a holographic state is given by the classical
action of a region in the bulk (the "Wheeler-DeWitt" patch). We provide
calculations for the results quoted in that paper, explain how it fits into a
broader (tensor) network of ideas, and elaborate on the hypothesis that black
holes are the fastest computers in nature.Comment: 55+14 pages, many figures. v2: (so many) typos fixed, references
adde
Implementing Mindfulness Practices With Parents of Young Children in a Low-Socioeconomic Status Neighborhood
Background: The purpose of this study was to investigate whether instruction in mindfulness practices would results in improved self-reported mindfulness and reduced depression, anxiety, and family stress in parents of young children living in a low socioeconomic status (SES) neighborhood.
Methods: The study utilized a pretest-posttest group design to evaluate the effectiveness of the Mindfulness Ambassador Council-Interactive curriculum with attendees in a parent support program. Participants (n=15) were recruited from families with young children who received support from a community-based organization in one low-SES neighborhood in Atlanta. Mental health assessments, measures of family stress and parenting competency, and a demographic questionnaire with non-identifying questions were administered to all participants during the first and last session of the 8-week mindfulness program.
Results: Participants reported increased mindfulness and decreased levels of anxiety and depression. Parent reports of family stressors were relatively stable across the two time points, while self-reported parenting competence decreased.
Discussion: Based on the parents’ reports of program acceptability and the impact on their well-being, mindfulness training appears to be a promising strategy for addressing the stressors experienced by parents of young children
The space physics environment data analysis system (SPEDAS)
With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.Published versio
The Lanczos potential for Weyl-candidate tensors exists only in four dimensions
We prove that a Lanczos potential L_abc for the Weyl candidate tensor W_abcd
does not generally exist for dimensions higher than four. The technique is
simply to assume the existence of such a potential in dimension n, and then
check the integrability conditions for the assumed system of differential
equations; if the integrability conditions yield another non-trivial
differential system for L_abc and W_abcd, then this system's integrability
conditions should be checked; and so on. When we find a non-trivial condition
involving only W_abcd and its derivatives, then clearly Weyl candidate tensors
failing to satisfy that condition cannot be written in terms of a Lanczos
potential L_abc.Comment: 11 pages, LaTeX, Heavily revised April 200
Semicontinuous Bioreactor Production of Recombinant Butyrylcholinesterase in Transgenic Rice Cell Suspension Cultures.
An active and tetrameric form of recombinant butyrylcholinesterase (BChE), a large and complex human enzyme, was produced via semicontinuous operation in a transgenic rice cell suspension culture. After transformation of rice callus and screening of transformants, the cultures were scaled up from culture flask to a lab scale bioreactor. The bioreactor was operated through two phases each of growth and expression. The cells were able to produce BChE during both expression phases, with a maximum yield of 1.6 mg BChE/L of culture during the second expression phase. Cells successfully regrew during a 5-day growth phase. A combination of activity assays and Western blot analysis indicated production of an active and fully assembled tetramer of BChE
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