21,842 research outputs found
A study on task difficulty and acceleration stress
The results of two experiments which relate to task difficulty and the effects of environmental stress on tracking performance are discussed and compared to subjective evaluations. The first experiment involved five different sum of sine tracking tasks which humans tracked both in a static condition and under a 5 Gz acceleration stress condition. The second experiment involved similar environmental stress conditions but in this case the tasks were constructed from deterministic functions with specially designed velocity and acceleration profiles. Phase Plane performance analysis was conducted to study potential measures of workload or tracking difficulty
Impact pressure probe response characteristics in high speed flows, with transition Knudsen numbers
Impact pressure probe response characteristics in free-molecular and continuum flows with transition Knudsen number
Impact pressure probe reponse characteristics in high speed flows with transition knudsen numbers
Impact pressure probe response characteristics in high speed flows with transition Knudsen number
Polarization and Charge Transfer in the Hydration of Chloride Ions
A theoretical study of the structural and electronic properties of the
chloride ion and water molecules in the first hydration shell is presented. The
calculations are performed on an ensemble of configurations obtained from
molecular dynamics simulations of a single chloride ion in bulk water. The
simulations utilize the polarizable AMOEBA force field for trajectory
generation, and MP2-level calculations are performed to examine the electronic
structure properties of the ions and surrounding waters in the external field
of more distant waters. The ChelpG method is employed to explore the effective
charges and dipoles on the chloride ions and first-shell waters. The Quantum
Theory of Atoms in Molecules (QTAIM) is further utilized to examine charge
transfer from the anion to surrounding water molecules.
From the QTAIM analysis, 0.2 elementary charges are transferred from the ion
to the first-shell water molecules. The default AMOEBA model overestimates the
average dipole moment magnitude of the ion compared with the estimated quantum
mechanical value. The average magnitude of the dipole moment of the water
molecules in the first shell treated at the MP2 level, with the more distant
waters handled with an AMOEBA effective charge model, is 2.67 D. This value is
close to the AMOEBA result for first-shell waters (2.72 D) and is slightly
reduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole moment
of the water molecules in the first solvation shell is most strongly affected
by the local water-water interactions and hydrogen bonds with the second
solvation shell, rather than by interactions with the ion.Comment: Slight revision, in press at J. Chem. Phy
Housing and Business Investment in Nebraska
Editor\u27s Note: The 1975 Legislative Session of the Nebraska Legislature recognized the need to analyze all available options for dealing with the problems of urban redevelopment: lack of adequate housing, revitalization of older business districts, and possible incentives for investment in older neighborhoods in Nebraska. Accordingly, Resolution 53 directed the Legislature\u27s Urban Affairs Committee to study a) causes of urban decay, b) current Federal and State programs in urban redevelopment, c) laws and programs of other states that encourage redevelopment, d) incentives to encourage urban redevelopment and e) needs for changes in Nebraska law. The study here summarized was completed by the Center for Applied Urban Research under contract with the Urban Affairs Committee of the Nebraska Legislature and the State Office of Planning and Programming as one aspect of the larger program. The study was designed a) to ascertain the demand for housing and business investment funds and the factors which dis~ courage such investment in declining neighborhoods of Nebraska\u27s two major metropolitan cities, Omaha and Lincoln, and in Nebraska\u27s nonmetropolitan communities, and b) to recommend areas for consideration by the administrative and legislative branches of the Nebraska government. The study was financed in part through a comprehensive planning assistance grant from the U.S. Department of Housing and Urban Development under contract with the Nebraska Legislature and the Nebraska State Office of Planning and Programming. Comprehensive Planning Grant, Project No. NEB-P-7070
Nonlinear self-adjointness and conservation laws
The general concept of nonlinear self-adjointness of differential equations
is introduced. It includes the linear self-adjointness as a particular case.
Moreover, it embraces the strict self-adjointness and quasi self-adjointness
introduced earlier by the author. It is shown that the equations possessing the
nonlinear self-adjointness can be written equivalently in a strictly
self-adjoint form by using appropriate multipliers. All linear equations
possess the property of nonlinear self-adjointness, and hence can be rewritten
in a nonlinear strictly self-adjoint. For example, the heat equation becomes strictly self-adjoint after multiplying by
Conservation laws associated with symmetries can be constructed for all
differential equations and systems having the property of nonlinear
self-adjointness
Vitrification and determination of the crystallization time scales of the bulk-metallic-glass-forming liquid Zr58.5Nb2.8Cu15.6Ni12.8Al10.3
The crystallization kinetics of Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 were studied in an electrostatic levitation (ESL) apparatus. The measured critical cooling rate is 1.75 K/s. Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 is the first bulk-metallic-glass-forming liquid that does not contain beryllium to be vitrified by purely radiative cooling in the ESL. Furthermore, the sluggish crystallization kinetics enable the determination of the time-temperature-transformation (TTT) diagram between the liquidus and the glass transition temperatures. The shortest time to reach crystallization in an isothermal experiment; i.e., the nose of the TTT diagram is 32 s. The nose of the TTT diagram is at 900 K and positioned about 200 K below the liquidus temperature
Small-Scale Turbulence in a Closed-Field-Line Geometry
Plasma turbulence due to small-scale entropy modes is studied with gyrokinetic simulations in a simple closed-field-line geometry, the Z pinch, in low-β parameter regimes that are stable to ideal interchange modes. We find an enormous variation in the nonlinear dynamics and particle transport as a function of two main parameters, the density gradient and the plasma collisionality. This variation is explained in part by the damping and stability properties of spontaneously formed zonal flows in the system. As in toroidal systems, the zonal flows can lead to a strong nonlinear suppression of transport below a critical gradient that is determined by the stability of the zonal flows
Singlet levels of the NV centre in diamond
The characteristic transition of the NV- centre at 637 nm is between
and triplet states. There are also
intermediate and singlet states, and the
infrared transition at 1042 nm between these singlets is studied here using
uniaxial stress. The stress shift and splitting parameters are determined, and
the physical interaction giving rise to the parameters is considered within the
accepted electronic model of the centre. It is established that this
interaction for the infrared transition is due to a modification of
electron-electron Coulomb repulsion interaction. This is in contrast to the
visible 637 nm transition where shifts and splittings arise from modification
to the one-electron Coulomb interaction. It is also established that a dynamic
Jahn-Teller interaction is associated with the singlet state,
which gives rise to a vibronic level 115 above the
electronic state. Arguments associated with this level are
used to provide experimental confirmation that the is the
upper singlet level and is the lower singlet level.Comment: 19 pages, 6 figure
Assignment of the NV0 575 nm zero-phonon line in diamond to a 2E-2A2 transition
The time-averaged emission spectrum of single nitrogen-vacancy defects in
diamond gives zero-phonon lines of both the negative charge state at 637 nm
(1.945 eV) and the neutral charge state at 575 nm (2.156 eV). This occurs
through photo-conversion between the two charge states. Due to strain in the
diamond the zero-phonon lines are split and it is found that the splitting and
polarization of the two zero-phonon lines are the same. From this observation
and consideration of the electronic structure of the nitrogen-vacancy center it
is concluded that the excited state of the neutral center has A2 orbital
symmetry. The assignment of the 575 nm transition to a 2E - 2A2 transition has
not been established previously.Comment: 5 pages, 5 figure
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