243 research outputs found
Synthesis of Pyridazine Derivatives. XXIII. Synthesis of Isomeric Azolopyrido (3,2-d) - and Azolopyrido (2,3-d) pyridazines
The synthesis of six new parent azolopyridopyridazines (I-VI)
is described. Electropnilic substitutions were studied on two isomeric
imidazopyrd.dopyridazines and it was found that position 3 is
attacked
Syntheses in the Pyridazine Series. XXXII. Some Investigations on Polynuclear Systems Containing a Pyridazine Ring
Some 5,6-dihydrobenzo[f]phthalazines have been aromatized
to II and the structures of a number of nitro derivatives prepared
from several polynuclear systems (III, IV, V) , have been established
Syntheses in the Pyridazine Series. XXXII. Some Investigations on Polynuclear Systems Containing a Pyridazine Ring
Some 5,6-dihydrobenzo[f]phthalazines have been aromatized
to II and the structures of a number of nitro derivatives prepared
from several polynuclear systems (III, IV, V) , have been established
The Crystal and Molecular Structure of 3-(Pyridyl-2\u27)- imidazo-[1,i-a] Pyridine
The crystal structure of 3:.(pyridyl-2\u27)-imidazo-[l,5-a] pyridine
has been determined using three-dimensional MoK a diffractometer
data. The crystal data at 293 (1) K are as follows: C12H0Na, Mr=
= 195.23, orthorhombic, P212121 (No. 19), a = 0.5107(1), b = 1.3076(2},
c = 1.4343(3) nm, V = 0.9578 nm3, Dm = 1.37(5), Dx = 1.354 Mg Ā· m-3,
Z = 4. The structure has been solved with direct methods and
refined by full-matrix least-squares techniques to R and Rw values
of 0.085 and 0.080, respectively, for 641 contributing reflexions. The
crystal structure consists of discrete molecules. Most of the bond
lengths and angles are within normal ranges for aromatic heterocyclic
systems. The dihedral angle between the pyridine and imidazo-
pyridine parts of the molecule is 3.8Ā°; thus the molecule is
planar to within 7 pm owing to two weak C-H .. . N interactions
Tests of a proximity focusing RICH with aerogel as radiator
Using aerogel as radiator and multianode PMTs for photon detection, a
proximity focusing Cherenkov ring imaging detector has been constructed and
tested in the KEK 2 beam. The aim is to experimentally study the basic
parameters such as resolution of the single photon Cherenkov angle and number
of detected photons per ring. The resolution obtained is well approximated by
estimates of contributions from pixel size and emission point uncertainty. The
number of detected photons per Cherenkov ring is in good agreement with
estimates based on aerogel and detector characteristics. The values obtained
turn out to be rather low, mainly due to Rayleigh scattering and to the
relatively large dead space between the photocathodes. A light collection
system or a higher fraction of the photomultiplier active area, together with
better quality aerogels are expected to improve the situation. The reduction of
Cherenkov yield, for charged particle impact in the vicinity of the aerogel
tile side wall, has also been measured.Comment: 4 pages, 8 figure
The Mannich Reaction for 2,5-Dimercapto-1,3,4-thiadiazole
The formation of Mannich bases with 2,5-dimercapto-1,3,4-
-thiadiazole (III) and some of its derivatives has been investigated.
Depending on the amount of formaldehyde and a secondary amine
used in the reaction, three different types of Mannich bases were
prepared. With equimolecular amounts of both reagents a mono-
Mannich base IV was obtained, but using formaldehyde in excess
a mono-hydroxymethyl mono-M.annich base V was isolated. If both
reagents were used in amounts corresponding to two equivalents, a
bis-Mannich base VI was formed. Evidence- for the structures of all
these products was presented on the basis of chemical transformatfons
and spectroscopic data. The mono-Mannich base IV .was
converted in its S-methyl derivative VIII which was prepared
independently from IX in a Mannich reaction. Thus aminoalkylation
proceeds first on the ring nitrogen and in a further reaction the
exo-cyclic sulfur is substituted
The HERA-B Ring Imaging Cherenkov Counter
The HERA-B RICH uses a radiation path length of 2.8 m in C_4F_10 gas and a
large 24 square meters spherical mirror for imaging Cherenkov rings. The photon
detector consists of 2240 Hamamatsu multi-anode photomultipliers with about
27000 channels. A 2:1 reducing two-lens telescope in front of each PMT
increases the sensitive area at the expense of increased pixel size, resulting
in a contribution to the resolution which roughly matches that of dispersion.
The counter was completed in January of 1999, and its performance has been
steady and reliable over the years it has been in operation. The design
performance of the RICH was fully reached: the average number of detected
photons in the RICH for a beta=1 particle was found to be 33 with a single hit
resolution of 0.7 mrad and 1 mrad in the fine and coarse granularity regions,
respectively.Comment: 29 pages, 23 figure
Baryon polarization in low-energy unpolarized meson-baryon scattering
We compute the polarization of the final-state baryon, in its rest frame, in
low-energy meson--baryon scattering with unpolarized initial state, in
Unitarized BChPT. Free parameters are determined by fitting total and
differential cross-section data (and spin-asymmetry or polarization data if
available) for , and scattering. We also compare our
results with those of leading-order BChPT
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