3,387 research outputs found
Simple heuristics for the assembly line worker assignment and balancing problem
We propose simple heuristics for the assembly line worker assignment and
balancing problem. This problem typically occurs in assembly lines in sheltered
work centers for the disabled. Different from the classical simple assembly
line balancing problem, the task execution times vary according to the assigned
worker. We develop a constructive heuristic framework based on task and worker
priority rules defining the order in which the tasks and workers should be
assigned to the workstations. We present a number of such rules and compare
their performance across three possible uses: as a stand-alone method, as an
initial solution generator for meta-heuristics, and as a decoder for a hybrid
genetic algorithm. Our results show that the heuristics are fast, they obtain
good results as a stand-alone method and are efficient when used as a initial
solution generator or as a solution decoder within more elaborate approaches.Comment: 18 pages, 1 figur
System for measuring passenger reaction to transportation-vehicle vibration
Equipment is capable of measuring frequencies from 0 to 50 Hz and is portable, light, inexpensive, and easily adaptable to field operations. System could be used in situations where it is necessary to record simultaneously subject response to other types of physical measurement or stimuli, such as temperature, noise, or pressure
Triaxiality and the determination of the cubic shape parameter K3 from five observables
The absolute and the relative quadrupole shape invariants q3 and K3 provide a
model independent measure of triaxiality for beta-rigid nuclei. We will show
that one can obtain q3 and K3 from a small number of observables. The
approximations which are made will be shown to hold within a few percent both
in the rigid triaxial rotor model and the interacting boson model. The shape
parameter K3 is given for an exemplary set of nuclei and is translated into
effective values of the geometrical deformation parameters beta and gamma.Comment: 16 pages, 4 figure
Instability of two dimensional graphene: Breaking sp2 bonds with soft X-rays
We study the stability of various kinds of graphene samples under soft X-ray
irradiation. Our results show that in single layer exfoliated graphene (a
closer analogue to two dimensional material), the in-plane carbon-carbon bonds
are unstable under X-ray irradiation, resulting in nanocrystalline structures.
As the interaction along the third dimension increases by increasing the number
of graphene layers or through the interaction with the substrate (epitaxial
graphene), the effect of X-ray irradiation decreases and eventually becomes
negligible for graphite and epitaxial graphene. Our results demonstrate the
importance of the interaction along the third dimension in stabilizing the long
range in-plane carbon-carbon bonding, and suggest the possibility of using
X-ray to pattern graphene nanostructures in exfoliated graphene.Comment: 4 pages, 3 figures, Phys. Rev. B rapid communication, in pres
Alternative Interpretation of Sharply Rising E0 Strengths in Transitional Regions
It is shown that strong 0+2 -> 0+1 E0 transitions provide a clear signature
of phase transitional behavior in finite nuclei. Calculations using the IBA
show that these transition strengths exhibit a dramatic and robust increase in
spherical-deformed shape transition regions, that this rise matches well the
existing data, that the predictions of these E0 transitions remain large in
deformed nuclei, and that these properties are intrinsic to the way that
collectivity and deformation develop through the phase transitional region in
the model, arising from the specific d-boson coherence in the wave functions,
and that they do not necessarily require the explicit mixing of normal and
intruder configurations from different IBA spaces.Comment: 6 pages, 3 figure
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Detailed Visual Cortical Responses Generated by Retinal Sheet Transplants in Rats with Severe Retinal Degeneration.
To combat retinal degeneration, healthy fetal retinal sheets have been successfully transplanted into both rodent models and humans, with synaptic connectivity between transplant and degenerated host retina having been confirmed. In rodent studies, transplants have been shown to restore responses to flashes of light in a region of the superior colliculus corresponding to the location of the transplant in the host retina. To determine the quality and detail of visual information provided by the transplant, visual responsivity was studied here at the level of visual cortex where higher visual perception is processed. For our model, we used the transgenic Rho-S334ter line-3 rat (both sexes), which loses photoreceptors at an early age and is effectively blind at postnatal day 30. These rats received fetal retinal sheet transplants in one eye between 24 and 40 d of age. Three to 10 months following surgery, visually responsive neurons were found in regions of primary visual cortex matching the transplanted region of the retina that were as highly selective as normal rat to stimulus orientation, size, contrast, and spatial and temporal frequencies. Conversely, we found that selective response properties were largely absent in nontransplanted line-3 rats. Our data show that fetal retinal sheet transplants can result in remarkably normal visual function in visual cortex of rats with a degenerated host retina and represents a critical step toward developing an effective remedy for the visually impaired human population.SIGNIFICANCE STATEMENT Age-related macular degeneration and retinitis pigmentosa lead to profound vision loss in millions of people worldwide. Many patients lose both retinal pigment epithelium and photoreceptors. Hence, there is a great demand for the development of efficient techniques that allow for long-term vision restoration. In this study, we transplanted dissected fetal retinal sheets, which can differentiate into photoreceptors and integrate with the host retina of rats with severe retinal degeneration. Remarkably, we show that transplants generated visual responses in cortex similar in quality to normal rats. Furthermore, transplants preserved connectivity within visual cortex and the retinal relay from the lateral geniculate nucleus to visual cortex, supporting their potential application in curing vision loss associated with retinal degeneration
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