194 research outputs found
A case study evaluating the ergonomic and productivity impacts of partial automation strategies in the electronics industry
A case study is presented that evaluates the impact of partial automation strategies on productivity and ergonomics. A company partly automated its assembly and transportation functions while moving from a parallel-batch to a serial line-based production system. Data obtained from company records and key informants were combined with detailed video analysis, biomechanical modelling data and field observations of the system. The new line system was observed to have 51% higher production volumes with 21% less per product labour input and lower work-in-process levels than the old batch-cart system. Partial automation of assembly operations was seen to reduce the total repetitive assembly work at the system level by 34%. Automation of transportation reduced transport labour by 63%. The strategic decision to implement line-transportation was found to increase movement repetitiveness for operators at manual assembly stations, even though workstations were constructed with consideration to ergonomics. Average shoulder elevation at these stations increased 30% and average shoulder moment increased 14%. It is concluded that strategic decisions made by designers and managers early in the production system design phase have considerable impact on ergonomic conditions in the resulting system. Automation of transport and assembly both lead to increased productivity, but only elements related to the automatic line system also increased mechanical loads on operators and hence increased the risk for work-related disorders. Suggestions for integrating the consideration of ergonomics into production system design are made
General Solutions of Relativistic Wave Equations II: Arbitrary Spin Chains
A construction of relativistic wave equations on the homogeneous spaces of
the Poincar\'{e} group is given for arbitrary spin chains. Parametrizations of
the field functions and harmonic analysis on the homogeneous spaces are
studied. It is shown that a direct product of Minkowski spacetime and
two-dimensional complex sphere is the most suitable homogeneous space for the
physical applications. The Lagrangian formalism and field equations on the
Poincar\'{e} and Lorentz groups are considered. A boundary value problem for
the relativistically invariant system is defined. General solutions of this
problem are expressed via an expansion in hyperspherical functions defined on
the complex two-sphere.Comment: 56 pages, LaTeX2
Field on Poincare group and quantum description of orientable objects
We propose an approach to the quantum-mechanical description of relativistic
orientable objects. It generalizes Wigner's ideas concerning the treatment of
nonrelativistic orientable objects (in particular, a nonrelativistic rotator)
with the help of two reference frames (space-fixed and body-fixed). A technical
realization of this generalization (for instance, in 3+1 dimensions) amounts to
introducing wave functions that depend on elements of the Poincare group . A
complete set of transformations that test the symmetries of an orientable
object and of the embedding space belongs to the group . All
such transformations can be studied by considering a generalized regular
representation of in the space of scalar functions on the group, ,
that depend on the Minkowski space points as well as on the
orientation variables given by the elements of a matrix .
In particular, the field is a generating function of usual spin-tensor
multicomponent fields. In the theory under consideration, there are four
different types of spinors, and an orientable object is characterized by ten
quantum numbers. We study the corresponding relativistic wave equations and
their symmetry properties.Comment: 46 page
Marine microalgae as a potential source of single cell protein (SCP)
[Abstract] The marine microalgae Tetraselmis suecica, Isochrysis galbana, Dunaliella tertiolecta and Chlorella stigmatophora are good biological sources of single cell protein (SCP). Protein content accounts for 39.12%–54.20% of the dry matter, D. tertiolecta having the highest. Lysine values are between 3.67 and 4.52 g/100 g of protein, and thus are higher than those for freshwater species. The total nucleic acid content is less than 7% of the dry matter; this value is definitely lower than that for yeasts or bacteria, commonly used as SCP sources. Amino acid profiles of the four species are very similar and comparable to the FAO reference protein, buth with a low content of methionine and cystine and a high content of lysine. The MEAA indices are between 81 and 84.98, without significant differences among the four species. Marine microalgae can be used as a potential SCP source
Quantization of fields over de Sitter space by the method of generalized coherent states
A system of generalized coherent states for the de Sitter group obeying the
Klein-Gordon equation and corresponding to the massive spin zero particles over
the de Sitter space is considered. This allows us to construct the quantized
scalar field by the resolution over these coherent states; the corresponding
propagator is computed by the method of analytic continuation to the complex de
Sitter space and coincides with expressions obtained previously by other
methods. Considering the case of spin 1/2 we establish the connection of the
invariant Dirac equation over the de Sitter space with irreducible
representations of the de Sitter group. The set of solutions of this equation
is obtained in the form of the product of two different systems of generalized
coherent states for the de Sitter group. Using these solutions the quantized
Dirac field over de Sitter space is constructed and its propagator is found. It
is a result of action of some de Sitter invariant spinor operator onto the spin
zero propagator with an imaginary shift of a mass. We show that the constructed
propagators possess the de Sitter-invariance and causality properties.Comment: 19 pages, LATEX, using ioplppt.sty and iopfts.st
Towards Relativistic Atomic Physics. I. The Rest-Frame Instant Form of Dynamics and a Canonical Transformation for a System of Charged Particles plus the Electro-Magnetic Field
A complete exposition of the rest-frame instant form of dynamics for
arbitrary isolated systems (particles, fields, strings, fluids)admitting a
Lagrangian description is given. The starting point is the parametrized
Minkowski theory describing the system in arbitrary admissible non-inertial
frames in Minkowski space-time, which allows one to define the energy-momentum
tensor of the system and to show the independence of the description from the
clock synchronization convention and from the choice of the 3-coordinates. In
the inertial rest frame the isolated system is seen as a decoupled
non-covariant canonical external center of mass carrying a pole-dipole
structure (the invariant mass and the rest spin of the
system) and an external realization of the Poincare' group. Then an isolated
system of positive-energy charged scalar articles plus an arbitrary
electro-magnetic field in the radiation gauge is investigated as a classical
background for defining relativistic atomic physics. The electric charges of
the particles are Grassmann-valued to regularize the self-energies. The
rest-frame conditions and their gauge-fixings (needed for the elimination of
the internal 3-center of mass) are explicitly given. It is shown that there is
a canonical transformation which allows one to describe the isolated system as
a set of Coulomb-dressed charged particles interacting through a Coulomb plus
Darwin potential plus a free transverse radiation field: these two subsystems
are not mutually interacting and are interconnected only by the rest-frame
conditions and the elimination of the internal 3-center of mass. Therefore in
this framework with a fixed number of particles there is a way out from the
Haag theorem,at least at the classical level.Comment: Minor change
Rapid T1 quantification based on 3D phase sensitive inversion recovery
<p>Abstract</p> <p>Background</p> <p>In Contrast Enhanced Magnetic Resonance Imaging fibrotic myocardium can be distinguished from healthy tissue using the difference in the longitudinal <it>T</it><sub>1 </sub>relaxation after administration of Gadolinium, the so-called Late Gd Enhancement. The purpose of this work was to measure the myocardial absolute <it>T</it><sub>1 </sub>post-Gd from a single breath-hold 3D Phase Sensitivity Inversion Recovery sequence (PSIR). Equations were derived to take the acquisition and saturation effects on the magnetization into account.</p> <p>Methods</p> <p>The accuracy of the method was investigated on phantoms and using simulations. The method was applied to a group of patients with suspected myocardial infarction where the absolute difference in relaxation of healthy and fibrotic myocardium was measured at about 15 minutes post-contrast. The evolution of the absolute <it>R</it><sub>1 </sub>relaxation rate (1/<it>T</it><sub>1</sub>) over time after contrast injection was followed for one patient and compared to <it>T</it><sub>1 </sub>mapping using Look-Locker. Based on the <it>T</it><sub>1 </sub>maps synthetic LGE images were reconstructed and compared to the conventional LGE images.</p> <p>Results</p> <p>The fitting algorithm is robust against variation in acquisition flip angle, the inversion delay time and cardiac arrhythmia. The observed relaxation rate of the myocardium is 1.2 s<sup>-1</sup>, increasing to 6 - 7 s<sup>-1 </sup>after contrast injection and decreasing to 2 - 2.5 s<sup>-1 </sup>for healthy myocardium and to 3.5 - 4 s<sup>-1 </sup>for fibrotic myocardium. Synthesized images based on the <it>T</it><sub>1 </sub>maps correspond very well to actual LGE images.</p> <p>Conclusions</p> <p>The method provides a robust quantification of post-Gd <it>T</it><sub>1 </sub>relaxation for a complete cardiac volume within a single breath-hold.</p
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