556 research outputs found
Electrostatic attraction of nanoobjects - a versatile strategy towards mesostructured transition metal compounds
This highlight summarizes current challenges of mesostructuring and focuses on the scope and the potential of the ELAN – (electrostatic attraction of nanoobjects) strategy in mesostructuring of transition metal compounds. It discusses the limitations of this concept and highlights prominent examples. ELAN exploits the Coulomb attraction between inorganic precursors and polymeric templates in order to prevent macrophase separation. Essential requirements for ELAN are tailor-made, mesoscopic polyelectrolytic templates and charged molecular oligo-ions or stable colloids carrying a surface charge. The ELAN-strategy is highly reliable and opens the way to crystalline, mesoporous transition metal compounds with predefined polymorphism. It also provides the possibility to adjust wall chemistry and reactivity as well as the flexibility to synthesise different mesostructures (spheres, non-woven arrays or hexagonally ordered phases)
Field theoretic approach to the counting problem of Hamiltonian cycles of graphs
A Hamiltonian cycle of a graph is a closed path that visits each site once
and only once. I study a field theoretic representation for the number of
Hamiltonian cycles for arbitrary graphs. By integrating out quadratic
fluctuations around the saddle point, one obtains an estimate for the number
which reflects characteristics of graphs well. The accuracy of the estimate is
verified by applying it to 2d square lattices with various boundary conditions.
This is the first example of extracting meaningful information from the
quadratic approximation to the field theory representation.Comment: 5 pages, 3 figures, uses epsf.sty. Estimates for the site entropy and
the gamma exponent indicated explicitl
The chromosphere: gateway to the corona, or the purgatory of solar physics?
I argue that one should attempt to understand the solar chromosphere not only
for its own sake, but also if one is interested in the physics of: the corona;
astrophysical dynamos; space weather; partially ionized plasmas; heliospheric
UV radiation; the transition region. I outline curious observations which I
personally find puzzling and deserving of attention.Comment: To appear in the proceedings of the 25th NSO Workshop "Chromospheric
Structure and Dynamics. From Old Wisdom to New Insights", Memorie della
Societa' Astronomica Italiana, Eds. Tritschler et a
Mesostructured ZnO/Au nanoparticle composites with enhanced photocatalytic activity
Ease of catalyst separation from reaction mixtures represents a significant advantage in heterogeneous photocatalytic wastewater treatment. However, the activity of the catalyst strongly depends on its surface-to-volume ratio. Here, we present an approach based on cylindrical polybutadiene-block-poly(2-vinylpyridine) polymer brushes as template, which can be simultaneously loaded with zinc oxide (ZnO) and gold (Au) nanoparticles. Pyrolytic template removal of the polymer yields in mesostructured ZnO/Au composites, showing higher efficiencies in the photocatalytic degradation of ciprofloxacin and levofloxacin (generic antibiotics present in clinical wastewater) as compared to neat mesostructured ZnO. Upscaling of the presented catalyst is straightforward promising high technical relevance
Future multimodal mobility scenarios within Europe
The European transport system faces multiple pressing challenges, including the need for significant emissions reduction in the sector and the provision of a seamless, multimodal journey to travellers. In order to address these challenges, a thorough understanding and assessment of different development pathways are required. This paper elaborates on four different scenarios developed within the scope of the Modus project. Based on these as well as additional insights from experts of the air and rail sector, initial implications for emissions reduction potential, travel times, or technological options are discussed
Dual-Band Transmitter and Receiver with Bowtie-Antenna in 0.13 ÎĽm SiGe BiCMOS for Gas Spectroscopy at 222 - 270 GHz
This paper presents a transmitter (TX) and a receiver (RX) with bowtie-antenna and silicon lens for gas spectroscopy at 222-270 GHz, which are fabricated in IHP’s 0.13 μm SiGe BiCMOS technology. The TX and RX use two integrated local oscillators for 222 – 256 GHz and 250 – 270 GHz, which are switched for dual-band operation. Due to its directivity of about 27 dBi, the single integrated bowtie-antenna with silicon lens enables an EIRP of about 25 dBm for the TX, and therefore a considerably higher EIRP for the 2-band TX compared to previously reported systems. The double sideband noise temperature of the RX is 20,000 K (18.5 dB noise figure) as measured by the Y-factor method. Absorption spectroscopy of gaseous methanol is used as a measure for the performance of the gas spectroscopy system with TX- and RX-modules
The Generation of Fullerenes
We describe an efficient new algorithm for the generation of fullerenes. Our
implementation of this algorithm is more than 3.5 times faster than the
previously fastest generator for fullerenes -- fullgen -- and the first program
since fullgen to be useful for more than 100 vertices. We also note a
programming error in fullgen that caused problems for 136 or more vertices. We
tabulate the numbers of fullerenes and IPR fullerenes up to 400 vertices. We
also check up to 316 vertices a conjecture of Barnette that cubic planar graphs
with maximum face size 6 are hamiltonian and verify that the smallest
counterexample to the spiral conjecture has 380 vertices.Comment: 21 pages; added a not
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