ESD-performance of grounded-gate nMOS protection structures has been observed for a standard 0.25 μm CMOS epitaxial layer based technology. The shortest gate lengths show unexpectedly lower ESD-thresholds, leading to an optimum performance for longer gate length devices attributed to the trade off between power dissipation and melt volume of the parasitic bipolar. 相似文献
This paper presents a new parallel breadth first oriented tabu search extension, which can be used to improve existing tabu search procedures for production planning problems. Especially it is shown that this distributed technique considerably improves existing efficient sequential procedures for a well-known assembly line balancing problem. Since this technique does not require any communication besides exchanging the solutions reached at the end of the computation, it can be installed on nearly every distributed system. 相似文献
Layered double hydroxides (LDHs) containing Mg2+ and Al3+ in the basic layers and NO−3 as an interlayer anion were synthesized by the method of coprecipitation (pH 10). By changing the Mg2+/Al3+ ratio (1.5–4.5), the charge density on the (NO3)–MgAl–LDH sheets was varied. After pillaring with Fe(CN)3−6, which was based on an anion exchange process, the interlayer space became accessible. This was reflected in the large created surface areas and micropore volumes. The applied models for the calculation of the micropore size distributions (Maes–Zhu–Vansant and Horvath–Kawazoe) gave matching results, revealing narrow distributions for all the samples, with the majority of the pores smaller than 0.71 nm. A correlation was found between the Mg2+/Al3+ ratio and the resulting microporosity after pillaring. The optimal ratio was situated around 3.3, resulting in a pillared [Fe(CN)6]–MgAl–LDH with a Langmuir surface area of 499 m2/g and a micropore volume between 0.158 ml/g (μPVmin) and 0.177 ml/g (μPVmax). As an alternative, direct coprecipitation of the pillared LDHs was evaluated. This one-step mechanism proved to be a method producing similar results. Taking all this into consideration, one can conclude that hexacyanoferrate(III) complexes form ideal anionic pillars for the creation of microporous layered double hydroxides. 相似文献
Topography and electrical properties of InAs quantum dots Self assembled InAs‐islands were grown on GaAs with molecular beam epitaxy in the Stranski‐Krastanow growth mode. The topography of surface quantum dots was investigated by atomic force (AFM) and scanning electron microscopy (SEM). While the AFM enables to determine the dot height of ≈ 10 nm the SEM is best suited to study the lateral dimensions of uncapped islands. The latter technique gives a dot diameter of ≈ 30 nm. Although the size distribution of the islands is convoluted in the capacitance measurements on a dot ensemble, it was possible to determine roughly a Coulomb blockade energy of ≈ 20 meV for the ground state and ≈ 10 meV for the first excited dot level. Taking advantage of AFM‐lithography we were able to study electron transport through a single InAs island. Here we got a Coulomb blockade energy of 12 meV when electrons tunnel through the first excited state of the dot. 相似文献
Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.66 MHz) with a focus on the effect of patient size, target organ, and device position on maximum temperature rise.
Materials and methods
To assess RF-induced heating, high-resolution measurements of the electric field, temperature, and transfer function were combined. Realistic device trajectories were derived from vascular models to evaluate the variation of the temperature increase as a function of the device trajectory. At a low-field RF test bench, the effects of patient size and positioning, target organ (liver and heart) and body coil type were measured for six commonly used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle).
Results
Electric field mapping shows that the hotspots are not necessarily localized at the device tip. Of all procedures, the liver catheterizations showed the lowest heating, and a modification of the transmit body coil could further reduce the temperature increase. For common commercial needles no significant heating was measured at the needle tip. Comparable local SAR values were found in the temperature measurements and the TF-based calculations.
Conclusion
At low fields, interventions with shorter insertion lengths such as hepatic catheterizations result in less RF-induced heating than coronary interventions. The maximum temperature increase depends on body coil design.
Interaction in Crystals. 98. Protonated Hexamethylmelamin Salts with Different Anions: Monomeric Tetraphenylborate, Dimeric Trifluoracetate and Polymeric Chloride-Dihydrate Hexamethylmelamin (2,4,6-tris(dimethylamino)-1,3,5-triazine), on monoprotonation at one of the triazine nitrogens keeps its close to planar skeleton. Its salts with different anions reflect biochemically interesting hydrogen-bridge networks: Crystallization of the hydrochloride from isopropanol solution containing Li⊕ [B⊖(C6H5)4], yields “naked” molecular cations, packed in herringbone fashion in between the lattice-dominating bulky, phenyl-shielded and non-protonable tetraphenylborate anions. From trifluoroacetic acid, crystals with sandwich-like subunits connected by hydrogen-bridged anions [F3CCOO⊖…︁HOOCCF3] are obtained. The hydrochloride salt, prepared by adding aqueous HCl to a diethylether solution, crystallizes in stacks of triazinium cation dimers with an intermolecular bridge N⊕-H…︁Cl⊖…︁H⊕N in between chloride-bydrate strands (…︁Cl⊖…︁HOH…︁O(H)H…︁Cl⊖…︁). Together, the structures of the three different hexamethyl-melaminium salts further illustrate the influence of anions on the crystallization of protonated nitrogen heterocycles and complement that of counter cation cation solvation in molecular anion salts. 相似文献
Interactions in Crystals. 96. Preparation and Structures of Salts [RnN⊕H…︁NRn][B⊖(C6H5)4] with Prototype Hydrogen Bridges N⊕H…︁N Straightforward crystallization of ammonium salts [RnN⊕H] X⊖ added lithium tetraphenylborate, and amine RnN from acetone solution yields salts [RnN⊕H…︁NRn][B⊖(C6H5)4] with the (under the conditions) unprotonated anions and the cations with prototype hydrogen bridges N⊕H…︁N. The structures of both identically substituted RnN (methylamine, trimethylamine, quinuclidine, diazabicyclooctane, and pyridine) as well as two-component cation species (quinuclidine…︁pyridine and diazabicyclooctane…︁pyridine) are reported and discussed. A Cambridge Structural Database search defines the area of charged N⊕H…︁N interactions which can be correlated with both pK values and PM3 formation enthalpies. Additional information is provided by PM3 calculations based on the experimental structure coordinates. The charge distribution within the hydrogen bridges N⊕H…︁N varies considerably with the individual proton donors N+H and proton acceptors N: Positive charges are highest at protonated quinuclidine and diazabicyclooctane centers and lowest at pyridine N acceptor centers. 相似文献