22,668 research outputs found
Control of a flexible robot arm
Exact equations of motion of an arm with known parameters were developed and analyzed preparatory to designing control systems for robotic manipulators. The design of an experimental one-link arm for testing control designs is presented
A Modeling approach for analysis and improvement of spindle-holder-tool assembly dynamics
The most important information required for chatter stability analysis is the dynamics of the involved structures, i.e. the frequency response functions (FRFs) which are usually determined experimentally. In this study, the tool point FRF of a spindle-holder-tool assembly is analytically determined by using the receptance coupling and structural modification techniques. Timoshenko’s beam model is used for increased accuracy. The spindle is also modeled analytically with elastic supports representing the bearings. The mathematical model is used to determine the effects of different parameters on the tool point FRF and to identify contact dynamics from experimental measurements. The applications of the model are demonstrated and the predictions are verified experimentally
Application of the CINGEN program a thermal network data generator
The application of the CINGEN computer program and two of its supporting programs for the evaluation of structural and thermal performance of physical systems was described. The CINGEN program was written and implemented to avoid the duplication effort of performing a finite element approach for structural analysis and a finite differencing technique for thermal analysis, as well as the desire for a geometrical representation of the thermal model to reduce modeling errors. The program simplifies the thermal modeling process by performing all of the capacitance and conductance calculations normally done by the analyst. Each solid element is divided into five tetrahedrons, allowing the total volume to be calculated precisely. A sample problem was illustrated
Optical spectroscopy study on pressure-induced phase transitions in the three-dimensional Dirac semimetal CdAs
We report a room-temperature optical reflectivity study performed on
[112]-oriented CdAs single crystals over a broad energy range under
external pressure up to 10 GPa. The abrupt drop of the band dispersion
parameter (-parameter) and the interruption of the gradual redshift of the
bandgap at 4~GPa confirms the structural phase transition from a
tetragonal to a monoclinic phase in this material. The pressure-induced
increase of the overall optical conductivity at low energies and the continuous
redshift of the high-energy bands indicate that the system evolves towards a
topologically trivial metallic state, although a complete closing of the band
gap could not be observed in the studied pressure range. Furthermore, a
detailed investigation of the low-pressure regime suggests the possible
existence of an intermediate state between 2 and 4~GPa , that might be a
precursor of the structural phase transition or due to the lifted degeneracy of
the Dirac nodes. Several optical parameters show yet another anomaly at 8~GPa,
where low-temperature superconductivity was found in an earlier study.Comment: submitted to PR
Complex Scalar DM in a B-L Model
In this work, we implement a complex scalar Dark Matter (DM) candidate in a
gauge extension of the Standard Model. The model contains three
right handed neutrinos with different quantum numbers and a rich scalar sector,
with extra doublets and singlets. In principle, these extra scalars can have
VEVs ( and for the extra doublets and singlets,
respectively) belonging to different energy scales. In the context of
, which allows to obtain naturally
light active neutrino masses and mixing compatible with neutrino experiments,
the DM candidate arises by imposing a symmetry on a given complex
singlet, , in order to make it stable. After doing a study of the
scalar potential and the gauge sector, we obtain all the DM dominant processes
concerning the relic abundance and direct detection. Then, for a representative
set of parameters, we found that a complex DM with mass around GeV, for
example, is compatible with the current experimental constraints without
resorting to resonances. However, additional compatible solutions with heavier
masses can be found in vicinities of resonances. Finally, we address the issue
of having a light CP-odd scalar in the model showing that it is safe concerning
the Higgs and the boson invisible decay widths, and also the energy
loss in stars astrophysical constraints.Comment: 20 pages, 3 figure
Competitive pressure and labor productivity: world iron ore markets in the 1980s
Does the extent of competitive pressure industries face influence their productivity? We study a natural experiment conducted in the iron ore industry as a result of the collapse in world steel production in the early 1980s. For iron ore producers, whose only market is the steel industry, this collapse was an exogenous shock. The drop in steel production differed dramatically by region: it fell by about a third in the Atlantic Basin but only very little in the Pacific Basin. Given that the cost of transporting iron ore is very high relative to its mine value, Atlantic iron ore producers faced a much greater increase in competitive pressure than did Pacific iron ore producers. In response to the crisis, most Atlantic iron ore producers doubled their labor productivity; Pacific iron ore producers experienced few productivity gains. ; This article originally appeared in the American Economic Review. (c) American Economic Association.Labor productivity ; Steel industry and trade
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