4,717 research outputs found
Magnetoplasmadynamic thrustor research Final report
Radiation-cooled and water-cooled magnetoplasmadynamic thrustors tested in 10 to kW power range with 1000 to 5000 sec specific impuls
Statistics and Quantum Chaos
We use multi-time correlation functions of quantum systems to construct
random variables with statistical properties that reflect the degree of
complexity of the underlying quantum dynamics.Comment: 12 pages, LateX, no figures, restructured versio
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
Contextualizing Wetlands Within a River Network to Assess Nitrate Removal and Inform Watershed Management
Aquatic nitrate removal depends on interactions throughout an interconnected network of lakes, wetlands, and river channels. Herein, we present a networkâbased model that quantifies nitrateânitrogen and organic carbon concentrations through a wetlandâriver network and estimates nitrate export from the watershed. This model dynamically accounts for multiple competing limitations on nitrate removal, explicitly incorporates wetlands in the network, and captures hierarchical network effects and spatial interactions. We apply the model to the Le Sueur Basin, a dataârich 2,880 km2 agricultural landscape in southern Minnesota and validate the model using synoptic field measurements during June for years 2013â2015. Using the model, we show that the overall limits to nitrate removal rate via denitrification shift between nitrate concentration, organic carbon availability, and residence time depending on discharge, characteristics of the waterbody, and location in the network. Our model results show that the spatial context of wetland restorations is an important but often overlooked factor because nonlinearities in the system, e.g., deriving from switching of resource limitation on denitrification rate, can lead to unexpected changes in downstream biogeochemistry. Our results demonstrate that reduction of watershedâscale nitrate concentrations and downstream loads in the Le Sueur Basin can be most effectively achieved by increasing water residence time (by slowing the flow) rather than by increasing organic carbon concentrations (which may limit denitrification). This framework can be used toward assessing where and how to restore wetlands for reducing nitrate concentrations and loads from agricultural watersheds.This research was funded by NSF grant EAR-1209402 under the Water Sustainability and Climate Program (WSC): REACH (REsilience under Accelerated CHange)NSF grant EAR-1242458 under Science Across Virtual Institutes (SAVI): LIFE (Linked Institutions for Future EarthA.T.H. acknowledges support provided by NSF grant EAR- 1415206 under the Science, Engineering and Education for Sustainability (SEES
Effects of Cement Bases on the Stresses and Deflections in Composite Restorations
A model was used to show that tensile and shear stresses can occur in sufficient magnitude to cause failure in a cement base supporting a composite material in a posterior Class I restoration. Highest values of stress were observed when lining materials with a low modulus were used.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68080/2/10.1177_00220345760550010301.pd
Vesicle shape, molecular tilt, and the suppression of necks
Can the presence of molecular-tilt order significantly affect the shapes of
lipid bilayer membranes, particularly membrane shapes with narrow necks?
Motivated by the propensity for tilt order and the common occurrence of narrow
necks in the intermediate stages of biological processes such as endocytosis
and vesicle trafficking, we examine how tilt order inhibits the formation of
necks in the equilibrium shapes of vesicles. For vesicles with a spherical
topology, point defects in the molecular order with a total strength of
are required. We study axisymmetric shapes and suppose that there is a
unit-strength defect at each pole of the vesicle. The model is further
simplified by the assumption of tilt isotropy: invariance of the energy with
respect to rotations of the molecules about the local membrane normal. This
isotropy condition leads to a minimal coupling of tilt order and curvature,
giving a high energetic cost to regions with Gaussian curvature and tilt order.
Minimizing the elastic free energy with constraints of fixed area and fixed
enclosed volume determines the allowed shapes. Using numerical calculations, we
find several branches of solutions and identify them with the branches
previously known for fluid membranes. We find that tilt order changes the
relative energy of the branches, suppressing thin necks by making them costly,
leading to elongated prolate vesicles as a generic family of tilt-ordered
membrane shapes.Comment: 10 pages, 7 figures, submitted to Phy. Rew.
Universal Algebraic Relaxation of Velocity and Phase in Pulled Fronts generating Periodic or Chaotic States
We investigate the asymptotic relaxation of so-called pulled fronts
propagating into an unstable state. The ``leading edge representation'' of the
equation of motion reveals the universal nature of their propagation mechanism
and allows us to generalize the universal algebraic velocity relaxation of
uniformly translating fronts to fronts, that generate periodic or even chaotic
states. Such fronts in addition exhibit a universal algebraic phase relaxation.
We numerically verify our analytical predictions for the Swift-Hohenberg and
the Complex Ginzburg Landau equation.Comment: 4 pages Revtex, 2 figures, submitted to Phys. Rev. Let
Pion-Lambda-Sigma Coupling Extracted from Hyperonic Atoms
The latest measurements of the atomic level width in Sigma-hyperonic Pb atom
offer the most accurate datum in the region of low-energy Sigma-hyperon
physics. Atomic widths are due to the conversion of Sigma-nucleon into
Lambda-nucleon. In high angular momentum states this conversion is dominated by
the one-pion exchange. A joint analysis of the data of the scattering of
negative-Sigma on proton converting into a Lambda and a neutron and of the
atomic widths allows to extract a pseudovector pion-hyperon-Sigma coupling
constant of 0.048 with a statistical error of +-0.005 and a systematic one of
+-0.004. This corresponds to a pseudoscalar coupling constant of 13.3 with a
statistical uncertainty of 1.4 and a systematic one of 1.1.Comment: 12 pages, 1 figure, Use of Revtex.st
A qualitative study of Parent to Parent support for parents of children with special needs. Consortium to evaluate Parent to Parent.
OBJECTIVE: To examine qualitatively the experiences of parents participating in Parent to Parent programs.
METHOD: Twenty-four parents of children with special needs, a subset of subjects in a larger quantitative study, participated in a semi-structured telephone interview to explore the impact and meaning of being matched with a trained supporting parent.
RESULTS: Qualitative analysis reveals a successful match is contingent upon creation of a reliable ally in the supporting parent, comprised of four main components: (1) perceived sameness, (2) situational comparisons that enable learning and growth, (3) round-the-clock availability of support, and (4) mutuality of support.
CONCLUSIONS: Parent to Parent support creates a community of similar others trained to listen and be supportive and provides an opportunity for matched parents to experience equality and mutuality in their relationship. Findings also identify the need for quality control in Parent to Parent programs and the importance of such programs as an adjunct to traditional professional services
Rigid Chiral Membranes
Statistical ensembles of flexible two-dimensional fluid membranes arise
naturally in the description of many physical systems. Typically one encounters
such systems in a regime of low tension but high stiffness against bending,
which is just the opposite of the regime described by the Polyakov string. We
study a class of couplings between membrane shape and in-plane order which
break 3-space parity invariance. Remarkably there is only {\it one} such
allowed coupling (up to boundary terms); this term will be present for any
lipid bilayer composed of tilted chiral molecules. We calculate the
renormalization-group behavior of this relevant coupling in a simplified model
and show how thermal fluctuations effectively reduce it in the infrared.Comment: 11 pages, UPR-518T (This replaced version has fonts not used
removed.
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