659 research outputs found
Non-metric chaotic inflation
We consider inflation within the context of what is arguably the simplest
non-metric extension of Einstein gravity. There non-metricity is described by a
single graviscalar field with a non-minimal kinetic coupling to the inflaton
field , parameterized by a single parameter . We discuss the
implications of non-metricity for chaotic inflation and find that it
significantly alters the inflaton dynamics for field values , dramatically changing the qualitative behaviour in this regime.
For potentials with a positive slope non-metricity imposes an upper bound on
the possible number of e-folds. For chaotic inflation with a monomial
potential, the spectral index and the tensor-to-scalar ratio receive small
corrections dependent on the non-metricity parameter. We also argue that
significant post-inflationary non-metricity may be generated.Comment: 7 pages, 1 figur
Patterns of Transfer of Adaptation Among Body Segments
Two experiments were conducted in order to determine the patterns of transfer of visuomotor adaptation between arm and head pointing. An altered gain of display of pointing movements was used to induce a conflict between visual and somatosensory representations. Two subject groups participated in Experiment One: group 1 adapted shoulder pointing movements, and group 2 adapted wrist pointing movements to a 0.5 gain of display. Following the adaptation regimen, subjects performed a transfer test in which the shoulder group performed wrist movements and the wrist group performed shoulder movements. The results demonstrated that both groups displayed typical adaptation curves, initially undershooting the target followed by a return to baseline performance. Transfer tests revealed that both groups had high transfer of the acquired adaptation to the other joint. Experiment Two followed a similar design except that group 1 adapted head pointing movements and group 2 adapted arm pointing movements. The arm adaptation had high transfer to head pointing while the head adaptation had very little transfer to arm pointing. These results imply that, while the arm segments may share a common target representation for goal-directed actions, individual but functionally dependent target representations may exist for the control of head and arm movements
Performance Benefits Associated with Context-Dependent Arm Pointing Adaptation
Our previous work has demonstrated that head orientation can be used as a contextual cue to switch between mUltiple adaptive states. Subjects were assigned to one of three groups: the head orientation group tilted the head towards the right shoulder when drawing under a 0.5 gain of display and towards the left shoulder when drawing under a 1.5 gain of display; the target orientation group had the home & target positions rotated counterclockwise when drawing under the 0.5 gain and clockwise for the l.5 gain; the arm posture group changed the elbow angle of the arm they were not drawing with from full flexion to full extension with 0.5 and l.5 gain display changes. The head orientation cue was effectively associated with the multiple gains, in comparison to the control conditions. The purpose of the current investigation was to determine whether this context-dependent adaptation results in any savings in terms of performance measures such as movement duration and movement smoothness when subjects switch between multiple adaptive states. Subjects in the head adaptation group demonstrated reduced movement duration and increased movement smoothness (measured via normalized j erk scores) in comparison to the two control groups when switching between the 0.5 and 1.5 gain. of display. This work has demonstrated not only that subjects can acquire context-dependent adaptation, but also that it results in a significant savings of performance upon transfer between adaptive state
Context-Dependent Arm Pointing Adaptation
We sought to determine the effectiveness of head posture as a contextual cue to facilitate adaptive transitions in manual control during visuomotor distortions. Subjects performed arm pointing movements by drawing on a digitizing tablet, with targets and movement trajectories displayed in real time on a computer monitor. Adaptation was induced by presenting the trajectories in an altered gain format on the monitor. The subjects were shown visual displays of their movements that corresponded to either 0.5 or 1.5 scaling of the movements made. Subjects were assigned to three groups: the head orientation group tilted the head towards the right shoulder when drawing under a 0.5 gain of display and towards the left shoulder when drawing under a 1.5 gain of display, the target orientation group had the home & target positions rotated counterclockwise when drawing under the 0.5 gain and clockwise for the 1.5 gain, the arm posture group changed the elbow angle of the arm they were not drawing with from full flexion to full extension with 0.5 and 1.5 gain display changes. To determine if contextual cues were associated with display alternations, the gain changes were returned to the standard (1.0) display. Aftereffects were assessed to determine the efficacy of the head orientation contextual cue. . compared to the two control cues. The head orientation cue was effectively associated with the multiple gains. The target orientation cue also demonstrated some effectiveness while the.arm posture cue did not. The results demonstrate that contextual cues can be used to switch between multiple adaptive states. These data provide support for the idea that static head orientation information is a crucial component to the arm adaptation process. These data further define the functional linkage between head posture and arm pointing movements
Comparison of the chemical composition of char from waste car tires to the coke breeze used in the iron ore sintering process
The increasing automotive development generates large amount of waste car tires, which cannot be landfilled and the reuse level of raw materials used in vehicles production must achieve at least 95 %. The calorific value of waste tires is very high and they can be considered as energy carries, for example in the form of char generated during pyrolysis process. The article presents the results of chemical analysis of char samples and parameters which are crucial from the environment and iron ore sintering process point of view. The results show, that char samples with high carbon content, low sulfur, zinc and pyrolysis oil content can be applied in the iron ore sintering process
Hydrodynamics in the Blade Region of a Self-Aspirating Disk Impeller
In studies of self-aspirating impellers found that gas bubbles are not broken down by the impeller blades. Break-up of bubbles is caused by the eddies generated by the blades. Therefore, to describe how the liquid flow near the blades is an important research issue for this type of impellers. Using the PIV method average velocity fields in the axial-radial plane between baffles in the stirred tank were defined for seven different positions of blades of a self-aspirating disk impeller in relation to that plane. It was found that in the small space in blade vicinity, big changes in fluid circulation were observed depending on the position of the blade relative to the baffle. In front of blade the liquid from bottom and from over impeller is directed radially towards the wall of tank and the average axial velocity is zero. Behind the blade the cavern (cavity) is formed, understood as a space of reduced pressure. Underpressure causes suction effect which directs the liquid inside the cavern. In just a few millimeters from the blade tip average axial and radial velocities are equal to zero. In this region the tangential component of velocity is dominant
Quantum Stephani Universe in vicinity of the symmetry center
We study a class of spherically symmetric Stephani cosmological models in the
presence of a self-interacting scalar field in both classical and quantum
domains. We discuss the construction of `canonical' wave packets resulting from
the solutions of a class of Wheeler-DeWitt equations in the Stephani Universe.
We suggest appropriate initial conditions which result in wave packets
containing some desirable properties, most importantly good classical and
quantum correspondence. We also study the situation from de-Broglie Bohm
interpretation of quantum mechanics to recover the notion of time and compare
the classical and Bohmian results. We exhibit that the usage of the canonical
prescription and appropriate choices of expansion coefficients result in the
suppression of the quantum potential and coincidence between classical and
Bohmian results. We show that, in some cases, contrary to
Friedmann-Robertson-Walker case, the bound state solutions also exist for all
positive values of the cosmological constant.Comment: 22 pages, 19 figures, to appear in JCA
An Einstein-Hilbert Action for Axi-Dilaton Gravity in 4-Dimensions
We examine the axi-dilatonic sector of low energy string theory and
demonstrate how the gravitational interactions involving the axion and dilaton
fields may be derived from a geometrical action principle involving the
curvature scalar associated with a non-Riemannian connection. In this geometry
the antisymmetric tensor 3-form field determines the torsion of the connection
on the frame bundle while the gradient of the metric is determined by the
dilaton field. By expressing the theory in terms of the Levi-Civita connection
associated with the metric in the ``Einstein frame'' we confirm that the field
equations derived from the non-Riemannian Einstein-Hilbert action coincide with
the axi-dilaton sector of the low energy effective action derived from string
theory.Comment: 6 pages Plain Tex (No Figures), Letter to Editor Classical and
Quantum Gravit
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