10,489 research outputs found
Ga+ beam lithography for suspended lateral beams and nanowires
The authors demonstrate the fabrication of suspended nanowires and doubly clamped beams by using a focused ion beam implanted Ga etch mask
followed by an inductively coupled plasma reactive ion etching of
silicon. This method will demonstrate how a two-step, completely dry
fabrication sequence can be tuned to generate nanomechanical structures
on either silicon substrates or silicon on insulator (SOI). This method
was used to generate lateral nanowires suspended between 2 µm scaled
structures with lengths up to 16 µm and widths down to 40 nm on a
silicon substrate. The authors also fabricate 10 µm long doubly
clamped beams on SOIs that are 20 nm thick and a minimum of 150 nm
wide. In situ electrical measurements of the beams demonstrate a
reduction of resistivity from > 37.5 Ω cm down to 0.25 Ω cm.
Transmission electron microscopy for quantifying both surface roughness
and crystallinity of the suspended nanowires was performed. Finally, a
dose array for repeatable fabrication of a desired beam width was also
experimentally determined
Surface Encapsulation for Low-Loss Silicon Photonics
Encapsulation layers are explored for passivating the surfaces of silicon to
reduce optical absorption in the 1500-nm wavelength band. Surface-sensitive
test structures consisting of microdisk resonators are fabricated for this
purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and
SiO2 are applied under varying deposition and annealing conditions. A short dry
thermal oxidation followed by a long high-temperature N2 anneal is found to be
most effective at long-term encapsulation and reduction of interface
absorption. Minimization of the optical loss is attributed to simultaneous
reduction in sub-bandgap silicon surface states and hydrogen in the capping
material.Comment: 4 pages, 3 figure
An Econometric Examination of the New Federalism
macroeconomics, econometrics, Federalism
Differential coupling of G protein alpha subunits to seven-helix receptors expressed in Xenopus oocytes
Xenopus oocytes were used to examine the coupling of the serotonin 1c (5HT1c) and thyrotropin-releasing hormone (TRH) receptors to both endogenous and heterologously expressed G protein alpha subunits. Expression of either G protein-coupled receptor resulted in agonist- induced, Ca(2+)-activated Cl- currents that were measured using a two- electrode voltage clamp. 5HT-induced Cl- currents were reduced 80% by incubating the injected oocytes with pertussis toxin (PTX) and inhibited 50-65% by injection of antisense oligonucleotides to the PTX- sensitive Go alpha subunit. TRH-induced Cl- currents were reduced only 20% by PTX treatment but were inhibited 60% by injection of antisense oligonucleotides to the PTX-insensitive Gq alpha subunit. Injection of antisense oligonucleotides to a novel Xenopus phospholipase C-beta inhibited the 5HT1c (and Go)-induced Cl- current with little effect on the TRH (and Gq)-induced current. These results suggest that receptor- activated Go and Gq interact with different effectors, most likely different isoforms of phospholipase C-beta. Co-expression of each receptor with seven different mammalian G protein alpha subunit cRNAs (Goa, Gob, Gq, G11, Gs, Golf, and Gt) was also examined. Co-expression of either receptor with the first four of these G alpha subunits resulted in a maximum 4-6-fold increase in Cl- currents; the increase depended on the amount of G alpha subunit cRNA injected. This increase was blocked by PTX for G alpha oa and G alpha ob co-expression but not for G alpha q or G alpha 11 co-expression. Co-expression of either receptor with Gs, Golf, or Gt had no effect on Ca(2+)-activated Cl- currents; furthermore, co-expression with Gs or Golf also failed to reveal 5HT- or TRH-induced changes in adenylyl cyclase as assessed by activation of the cystic fibrosis transmembrane conductance regulator Cl- channel. These results indicate that in oocytes, the 5HT1c and TRH receptors do the following: 1) preferentially couple to PTX-sensitive (Go) and PTX-insensitive (Gq) G proteins and that these G proteins act on different effectors, 2) couple within the same cell type to several different heterologously expressed G protein alpha subunits to activate the oocyte's endogenous Cl- current, and 3) fail to couple to G protein alpha subunits that activate cAMP or phosphodiesterase
Quantum states far from the energy eigenstates of any local Hamiltonian
What quantum states are possible energy eigenstates of a many-body
Hamiltonian? Suppose the Hamiltonian is non-trivial, i.e., not a multiple of
the identity, and L-local, in the sense of containing interaction terms
involving at most L bodies, for some fixed L. We construct quantum states \psi
which are ``far away'' from all the eigenstates E of any non-trivial L-local
Hamiltonian, in the sense that |\psi-E| is greater than some constant lower
bound, independent of the form of the Hamiltonian.Comment: 4 page
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