136 research outputs found
A dimolybdenum paddlewheel as a building block for heteromultimetallic structures
Diphenylphosphine functionalized propionic acid was applied for the synthesis of heteromultimetallic dimolybdenum(II) complexes. The ligand features both carboxylic acid and phosphine functionalities, allowing the selective synthesis of a tetracarboxylate bridged Mo2(II)-paddlewheel structure in a first step. Due to the symmetrically arranged phosphine functionalities, the dimolybdenum(II) complex was utilized as a metalloligand. Subsequent coordination of late transition metal ions, such as gold(I), rhodium(I), iridium(I) or ruthenium(II) to the phosphine moieties allowed the formation of heteromultimetallic structures. The flexibility of the diphenylphosphino propionate ligand system enabled intermolecular aurophilic interactions in the Au(I) functionalized dimolybdenum(II) complexes. Depending on the Au(I) species applied, either a dimeric structure or a 1D coordination polymer was formed in the solid state. These structures represent the first examples of heterometallic dimolybdenum(II) complexes, forming supramolecular structures via aurophilic interactions
Synthesis of Unprecedented 4d/4fâPolypnictogens
A series of 4d/4fâpolyarsenides, âpolyarsines and âpolystibines was obtained by reduction of the Moâpnictide precursor complexes [{CpMo(CO)}(ÎŒ,ηâE)] (E=As, Sb; Cp=tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*Sm] and [(Cp)Sm]. For the reductive conversion of the Moâstibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Moâarsenide a tetraarsacyclobutadiene and a second species with a sideâon coordinated As anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene
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Single tube support post thermal analysis and test results
Cold mass structural supports used in prototype Superconducting Super Collider (SSC) 50 mm dipole magnets built at Fermilab and Brookhaven are adaptations of the design developed during the 40 mm design program at Fermilab. The design essentially consists of two composite tubes nested within each other as a means of maximizing the thermal path length. In addition it provides an ideal way to utilize materials best suited for the temperature range over which they must operate. Filament wound S-glass is used between 300K and 80K. Filament wound graphite fiber is used between 80K and 20K and between 20K and 4.5K. An alternate design for supports which uses a single composite tube has been developed at Fermilab and continues to be refined by the industrial contractors. The advantage of the new design is cost reduction due to a significantly simpler assembly and incorporation of many common parts. This report describes the thermal analysis and testing of a single composite tube support post whose function is identical to that of the current reentrant design
d/fâPolypnictides Derived by NonâClassical Ln (2+) Compounds: Synthesis, Small Molecule Activation and Optical Properties
Reduction chemistry induced by divalent lanthanides has been primarily focused on samarium so far. In light of the rich physical properties of the lanthanides, this limitation to one element is a drawback. Since molecular divalent compounds of almost all lanthanides have been available for some time, we used one known and two new non-classical reducing agents of the early lanthanides to establish a sophisticated reduction chemistry. As a result, six new d/f-polyphosphides or d/f-polyarsenides, [K(18-crown-6)] [Cp ''(2)Ln(E-5)FeCp*] (Ln=La, Ce, Nd; E=P, As) were obtained. Their reactivity was studied by activation of P-4, resulting in a selective expansion of the P-5 rings. The obtained compounds [K(18-crown-6)] [Cp ''(2)Ln(P-7)FeCp*] (Ln=La, Nd) are the first examples of an activation of P-4 by a f-element-polypnictide complex. Additionally, the first systematic femtosecond (fs)-spectroscopy investigations of d/f-polypnictides are presented to showcase the advantages of having access to a broader series of lanthanide compounds
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Design of the multilayer insulation system for the Superconducting Super Collider 50mm dipole cryostat
The development of the multilayer insulation (MLI) system for the Superconducting Super Collider (SSC) 50 mm collider dipole cryostat is an ongoing extension of work conducted during the 40 mm cryostat program. While the basic design of the MLI system for the 50 mm cryostat resembles that of the 40 mm cryostat, results from measurements of MLI thermal performance below 80K have prompted a re-design of the MLI system for the 20K thermal radiation shield. Presented is the design of the MLI system for the 50 mm collider dipole cryostat, with discussion focusing on system performance, blanket geometry, cost-effective fabrication techniques, and built-in quality control measures that assure consistent thermal performance throughout the SSC accelerator. 16 refs., 8 figs., 2 tabs
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A blanket design, apparatus, and fabrication techniques for the mass production of multilayer insulation blankets for the Superconducting Super Collider
The multilayer insulation (MLI) system for the Superconducting Super Collider (SSC) consists of full cryostat length assemblies of aluminized polyester film fabricated in the form of blankets and installed as blankets to the 4.5K cold mass and the 20K and 80K thermal radiation shields. Approximately 40,000 MLI blankets will be required in the 10,000 cryogenic devices comprising the SSC accelerator. Each blanket is nearly 17 meters long and 1.8 meters wide. This paper reports the blanket design, an apparatus, and the fabrication method used to mass produce pre-fabricated MLI blankets. Incorporated in the blanket design are techniques which automate quality control during installation of the MLI blankets in the SSC cryostat. The apparatus and blanket fabrication method insure consistency in the mass produced blankets by providing positive control of the dimensional parameters which contribute to the thermal performance of the MLI blanket. By virtue of the fabrication process, the MLI blankets have inherent features of dimensional stability three-dimensional uniformity, controlled layer density, layer-to-layer registration, interlayer cleanliness, and interlayer material to accommodate thermal contraction differences. 11 refs., 6 figs., 1 tab
First Experimental Characterization of Microwave Emission from Cosmic Ray Air Showers
We report the first direct measurement of the overall characteristics of
microwave radio emission from extensive air showers. Using a trigger provided
by the KASCADE-Grande air shower array, the signals of the microwave antennas
of the CROME (Cosmic-Ray Observation via Microwave Emission) experiment have
been read out and searched for signatures of radio emission by high-energy air
showers in the GHz frequency range. Microwave signals have been detected for
more than 30 showers with energies above 3*10^16 eV. The observations presented
in this Letter are consistent with a mainly forward-directed and polarised
emission process in the GHz frequency range. The measurements show that
microwave radiation offers a new means of studying air showers at energies
above 10^17 eV.Comment: Accepted for publication in PR
The wavefront of the radio signal emitted by cosmic ray air showers
Analyzing measurements of the LOPES antenna array together with corresponding
CoREAS simulations for more than 300 measured events with energy above
eV and zenith angles smaller than , we find that the radio
wavefront of cosmic-ray air showers is of approximately hyperbolic shape. The
simulations predict a slightly steeper wavefront towards East than towards
West, but this asymmetry is negligible against the measurement uncertainties of
LOPES. At axis distances m, the wavefront can be approximated by
a simple cone. According to the simulations, the cone angle is clearly
correlated with the shower maximum. Thus, we confirm earlier predictions that
arrival time measurements can be used to study the longitudinal shower
development, but now using a realistic wavefront. Moreover, we show that the
hyperbolic wavefront is compatible with our measurement, and we present several
experimental indications that the cone angle is indeed sensitive to the shower
development. Consequently, the wavefront can be used to statistically study the
primary composition of ultra-high energy cosmic rays. At LOPES, the
experimentally achieved precision for the shower maximum is limited by
measurement uncertainties to approximately g/cm. But the simulations
indicate that under better conditions this method might yield an accuracy for
the atmospheric depth of the shower maximum, , better than
g/cm. This would be competitive with the established air-fluorescence
and air-Cherenkov techniques, where the radio technique offers the advantage of
a significantly higher duty-cycle. Finally, the hyperbolic wavefront can be
used to reconstruct the shower geometry more accurately, which potentially
allows a better reconstruction of all other shower parameters, too.Comment: accepted by JCA
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