Part feeders, which separate and orient parts prior to packing and insertion, are critical components of an assembly line. Existing feeders utilize off-plane vibrations of a rigid structure to convey parts along a track. Repeated part hopping/landing phases are concerns if parts are delicate and/or high positioning accuracy is required. Here we consider a simpler feeder design in which parts are in permanent contact with a horizontally-vibrating flat plate. Each vibration is a "pump-like" motion along a single degree of freedom: the plate spends more time moving forward than backward. Parts are propelled forward since dynamic friction is fixed and independent of the relative velocity at the interface. In designing plate vibration profiles we consider issues of waveform simplicity, bandwidth, and feed rate performance. Both bang-bang and sinusoidal control waveforms are analyzed. Expressions are derived for equilibrium feed rates for both waveforms; dynamic simulation is used to verify the analysis. A prototype of the proposed feeder has been implemented with cheap mechanical parts. A simple experiment with the device is presented.
Low-ionization nuclear emission-line regions (LINERs), which exist in a large fraction of galaxies, may be the least luminous manifestation of quasar activity. The nature of LINERs has, however, remained controversial because an AGN-like nonstellar continuum source has not been directly observed in them. We report the detection of bright, unresolved (FWHM $\ltorder 0.1''$) point sources of UV ($\sim 2300$ \AA) emission in the nuclei of nine nearby galaxies from a complete sample of 110 nearby galaxies imaged with {\it HST}. Ground-based optical spectroscopy reveals that five of the nuclei are LINERs, three are starburst nuclei, and one is a Seyfert nucleus. The observed UV flux in each of the five LINERs implies an ionizing flux that is sufficient to account for the observed emission lines through photoionization. The detection of a strong UV continuum in the LINERs argues against shock excitation as the source of the observed emission lines, and supports the idea that photoionization excites the lines in at least some objects of this class. Among the Northern-hemisphere galaxies in the sample, 26 are LINERs, of which only the above five LINERs have a detected nuclear UV source. There are no obvious differences in the optical line intensity ratios between the UV-bright and UV-dark LINERs. If all LINERs are photoionized, then the continuum source is unobscured along our line of sight in $5/26\approx 20\%$ of LINERs. Alternatively, spectrally-similar LINERs may be produced by various excitation mechanisms, with photoionization responsible in only about 20\% of the cases. The high angular resolution allows us to set upper limits, typically several parsecs, on the physical size of the compact star-cluster or AGN-type continuum source that is emitting the UV light in these objects.
В статье анализируются стратегические последствия применения виртуальной формы осуществления инноваций и делается вывод, что зачастую это организационное решение приносит больше вреда, чем пользы. Отмечается, что при определенных условиях некоторая степень аутсорсинга может содействовать креативности компании, а виртуальная корпорация - быть эффективной. Однако, как утверждают авторы, любая компания должна выбирать форму своей организации в соответствии с характером ее операций и типом инноваций.
Complex behavior, associated with soil respiration of an oak‐grass savanna ecosystem in California, was quantified with continuous measurements of CO 2 exchange at two scales (soil and canopy) and with three methods (overstory and understory eddy covariance systems, soil respiration chambers, and a below‐ground CO 2 flux gradient system). To partition soil respiration into its autotrophic and heterotrophic components, we exploited spatial gradients in the landscape and seasonal variations in rainfall. During the dry summer, heterotrophic respiration was dominant in the senesced grassland area, whereas autotrophic respiration by roots and the feeding of microbes by root exudates was dominant under the trees. A temporal switch in soil respiration occurred in the spring. But the stimulation of root respiration lagged the timing of leaf‐out by the trees. Another temporal switch in soil respiration occurred at the start of autumn rains. This switch was induced by the rapid germination of grass seed and new grass growth. Isolated summer rain storms caused a pulse in soil respiration. Such rain events stimulated microbial respiration only; the rain was not sufficient to replenish soil moisture in the root zone or to germinate grass seed. Soil respiration lagged photosynthetic activity on hourly scales. The likely mechanism is the slow translocation of photosynthate to the roots and associated microbes. Another lag occurred on daily scales because of modulations in photosynthesis and stomatal conductance by the passage of dry and humid air masses.
On the basis of constraints from reported experimental observations and density functional theory simulations, in this paper we propose a mechanism for the reduction of CO<sub>2</sub> to C<sub>2</sub> products on copper electrodes. To model the effects of an applied potential bias on the reactions, calculations are carried out with a variable, fractional number of electrons on the unit cell, which is optimized so that the Fermi level matches the actual chemical potential of electrons (i.e., the applied bias); an implicit electrolyte model allows for compensation of the surface charge so that neutrality is maintained in the overall simulation cell. Our mechanism explains the presence of the seven C<sub>2</sub> species that have been detected in the reaction, as well as other notable experimental observations. Furthermore, our results shed light on the difference in activities toward C<sub>2</sub> products between the (100) and (111) facets of copper. Finally, we compare our methodologies and findings with those in other recent mechanistic studies of the copper-catalyzed CO<sub>2</sub> reduction reaction.
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The search for efficient semiconductor thermoelectrics has been greatly aided by theoretical modeling of electron and phonon transports in bulk materials and nanocomposites. Recent experiments have studied thermoelectric transport in thermoelectrics that are “strongly correlated” and derived by doping Mott insulators. Here a unified theory of electrical and thermal transport in the atomic and “Heikes” limit is applied to understand recent experiments on sodium cobaltate and other doped Mott insulators at room temperature and above. For optimal electron filling, a broad class of narrow-bandwidth correlated materials is shown to have thermoelectric power factors as high as in the best semiconductors.
