15,608 research outputs found
Method to make a single-step etch mask for 3D monolithic nanostructures
Current nanostructure fabrication by etching is usually limited to planar
structures as they are defined by a planar mask. The realisation of
three-dimensional (3D) nanostructures by etching requires technologies beyond
planar masks. We present a method to fabricate a 3D mask that allows to etch
three-dimensional monolithic nanostructures by using only CMOS-compatible
processes. The mask is written in a hard-mask layer that is deposited on two
adjacent inclined surfaces of a Si wafer. By projecting in single step two
different 2D patterns within one 3D mask on the two inclined surfaces, the
mutual alignment between the patterns is ensured. Thereby after the mask
pattern is defined, the etching of deep pores in two oblique directions yields
a three-dimensional structure in Si. As a proof of concept we demonstrate 3D
mask fabrication for three-dimensional diamond-like photonic band gap crystals
in silicon. The fabricated crystals reveal a broad stop gap in optical
reflectivity measurements. We propose how 3D nanostructures with five different
Bravais lattices can be realised, namely cubic, tetragonal, orthorhombic,
monoclinic, and hexagonal, and demonstrate a mask for a 3D hexagonal crystal.
We also demonstrate the mask for a diamond-structure crystal with a 3D array of
cavities. In general, the 2D patterns for the different surfaces can be
completely independent and still be in perfect mutual alignment. Indeed, we
observe an alignment accuracy of better than 3.0 nm between the 2D mask
patterns on the inclined surfaces, which permits one to etch well-defined
monolithic 3D nanostructures.Comment: 18 pages, 10 figure
Isolation and mapping of a C3'H gene (CYP98A49) from globe artichoke, and its expression upon UV-C stress
Globe artichoke represents a natural source of phenolic compounds with dicaffeoylquinic acids along with their biosynthetic precursor chlorogenic acid (5-caffeoylquinic acid) as the predominant molecules. We report the isolation and characterization of a full-length cDNA and promoter of a globe artichoke p-coumaroyl ester 3¿-hydroxylase (CYP98A49), which is involved in both chlorogenic acid and lignin biosynthesis. Phylogenetic analyses demonstrated that this gene belongs to the CYP98 family. CYP98A49 was also heterologously expressed in yeast, in order to perform an enzymatic assay with p-coumaroylshikimate and p-coumaroylquinate as substrates. Real Time quantitative PCR analysis revealed that CYP98A49 expression is induced upon exposure to UV-C radiation. A single nucleotide polymorphism in the CYP98A49 gene sequence of two globe artichoke varieties used for genetic mapping allowed the localization of this gene to linkage group 10 within the previously developed map
Physical limitations to the spatial resolution of solid-state detectors
In this paper we explore the effect of -ray emission, fluctuations in
th e signal deposition on the detection of charged particles in silicon-based
detec tors. We show that these two effects ultimately limit the resolution that
can be achieved by interpolation of the signal in finely segmented
position-sensitive solid-state devices.Comment: 5 page
Neural correlates of syntactic ambiguity in sentence comprehension for low and high span readers
Syntactically ambiguous sentences have been found to be difficult to process, in particular, for individuals with low working memory capacity. The current study used fMRI to investigate the neural basis of this effect in the processing of written sentences. Participants with high and low working memory capacity read sentences with either a short or long region of temporary syntactic ambiguity while being scanned. A distributed left-dominant network in the peri-sylvian region was identified to support sentence processing in the critical region of the sentence. Within this network, only the superior portion of Broca's area (BA 44) and a parietal region showed an activation increase as a function of the length of the syntactically ambiguous region in the sentence. Furthermore, it was only the BA 44 region that exhibited an interaction of working memory span, length of the syntactic ambiguity, and sentence complexity. In this area, the activation increase for syntactically more complex sentences became only significant under longer regions of ambiguity, and for low span readers only. This finding suggests that neural activity in BA 44 increases during sentence comprehension when processing demands increase, be it due to syntactic processing demands or by an interaction with the individually available working memory capacity
Cosmic rays studied with a hybrid high school detector array
The LORUN/NAHSA system is a pathfinder for hybrid cosmic ray research
combined with education and outreach in the field of astro-particle physics.
Particle detectors and radio antennae were mainly setup by students and placed
on public buildings. After fully digital data acquisition, coincidence
detections were selected. Three candidate events confirmed a working prototype,
which can be multiplied to extend further particle detector arrays on high
schools.Comment: 10 pages, 6 figures. Nigl, A., Timmermans, C., Schellart, P.,
Kuijpers, J., Falcke, H., Horneffer, A., de Vos, C. M., Koopman, Y., Pepping,
H. J., Schoonderbeek, G., Cosmic rays studied with a hybrid high school
detector array, Europhysics News (EPN), Vol. 38, No. 5, accepted on
22/08/200
A Comparative Study of the Valence Electronic Excitations of N_2 by Inelastic X-ray and Electron Scattering
Bound state, valence electronic excitation spectra of N_2 are probed by
nonresonant inelastic x-ray and electron scattering. Within the usual
theoretical treatments, dynamical structure factors derived from the two probes
should be identical. However, we find strong disagreements outside the dipole
scattering limit, even at high probe energies. This suggests an unexpectedly
important contribution from intra-molecular multiple scattering of the probe
electron from core electrons or the nucleus. These effects should grow
progressively stronger as the atomic number of the target species increases.Comment: Submitted to Physical Review Letters April 27, 2010. 12 pages
including 2 figure pages
Frequency-dependent spontaneous emission rate from CdSe and CdTe nanocrystals: influence of dark states
We studied the rate of spontaneous emission from colloidal CdSe and CdTe
nanocrystals at room temperature. The decay rate, obtained from luminescence
decay curves, increases with the emission frequency in a supra-linear way. This
dependence is explained by the thermal occupation of dark exciton states at
room temperature, giving rise to a strong attenuation of the rate of emission.
The supra-linear dependence is in agreement with the results of tight-binding
calculations.Comment: 11 page
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