Activation of microcomponents with light for micro-electro-mechanical systems and micro-optical-electro-mechanical systems applications

We examine the light-activation properties of micrometer-sized gear structures fabricated with polysilicon surface micromachining techniques. The gears are held in place on a substrate through a capped anchor post and are free to rotate about the post. The light-activation technique is modeled on photon radiation pressure, and the equation of motion of the gear is solved for this activation technique. Experimental measurements of torque and damping are found to be consistent with expected results for micrometer-scale devices. Design optimization for optically actuated microstructures is discussed.     

Litterfall production and associated carbon and nitrogen fluxes of seven woody species grown in indigenous agroforestry systems in the south-eastern Rift Valley escarpment of Ethiopia

We compared the litterfall production and associated carbon (C) and nitrogen (N) fluxes for seven woody species grown in three agroforestry systems practiced on the slopes of the south eastern Rift Valley escarpment of Ethiopia. Five of the species were native (Coffea arabica L., Cordia africana Lam., Croton macrostachyus Del., Erythrina brucei Schweinf. and Millettia ferruginea (Hochst.) Bak) and two were non-native fruit tree species (Mangifera indica L. and Persea americana Mill.). Together, these species accounted 85 % or more of the crown area of each agroforestry system: the Enset system (occurring at 2,100–2,400 m asl), the Enset-Coffee system (1,900–2,200 m asl), and the Fruit-Coffee system (1,500–1,900 m asl). Enset or false banana [Ensete ventricosum (Welw.) Cheesman] is a staple food crop in this region of Ethiopia and coffee and fruit trees are grown as cash crops. Monthly litterfall was collected from 4 to 6 trees of each species during 2010 and dry mass, carbon and nitrogen contents determined. The annual litterfall production per unit area of crown decreased in the order: C. macrostachyus (1,014 g m^?2), E. brucei (929), C. africana (917), P. americana (809), M. indica (807), C. arabica (446) and M. ferruginea (362). The simple linear regression equation using breast height diameter explained 95 % of the variation in the litterfall production of M. ferruginea, but only 55 % for C. africana. The annual litterfall production of the seven species combined per unit area of land was the highest for the Fruit-Coffee system (average 12,938 kg ha^?1), followed by the Enset-Coffee system (10,187) and the Enset system (7,430). The associated annual C fluxes (kg ha^?1) were 5,145 (Fruit-Coffee system), 3,928 (Enset-Coffee system) and 2,803 (Enset system), and corresponding N fluxes 278 (kg ha^?1), 257 and 190. The combined litterfall production of the seven species in our study was higher than has been reported for other agroforestry systems and tropical forests.     

A new algorithm for zero-modified models applied to citation counts

Scientometrics - In this era of interdisciplinary science, many scientific achievements, such as artificial intelligence (AI), have brought dramatic revolutions to human society. The increasing...     

双路输出降压型控制器可产生准确、高效和可靠的高电流轨-设计要点478

引言LTC(R)3855能够以上佳的准确度和效率来产生高电流轨,旨在满足当今最先时的网络、电信和服务器应用极其苛刻的要求.     

Diffusion-weighted echo planar MR imaging of the neck at 3 T using integrated shimming: comparison of MR sequence techniques for reducing artifacts caused by magnetic-field inhomogeneities

Objective

Our objective was to compare available techniques reducing artifacts in echo planar imaging (EPI)-based diffusion-weighed magnetic resonance imaging MRI (DWI) of the neck at 3 Tesla caused by B0-field inhomogeneities.

Materials and methods

A cylindrical fat–water phantom was equipped with a Maxwell coil allowing for additional linear B0-field variations in z-direction. The effect of increasing strength of this superimposed gradient on image quality was observed using a standard single-shot EPI-based DWI sequence (sEPI), a zoomed single-shot EPI sequence (zEPI), a readout-segmented EPI sequence (rsEPI), and an sEPI sequence with integrated dynamic shimming (intEPI) on a 3-Tesla system. Additionally, ten volunteers were examined over the neck region using these techniques. Image quality was assessed by two radiologists. Scan durations were recorded.

Results

With increasing strength of the external gradient, marked distortions, signal loss, and failure of fat suppression were observed using sEPI, zEPI, and rsEPI. These artifacts were markedly reduced using intEPI. Significantly better in vivo image quality was also observed using intEPI compared with the other techniques. Scan time of intEPI was similar to sEPI and zEPI and shorter than rsEPI.

Conclusion

The use of integrated 2D shim and frequency adjustment for EPI-based DWI results in a significant improvement in image quality of the head/neck region at 3 Tesla. Combining integrated shimming with rsEPI or zEPI can be expected to provide additional improvements.