112 research outputs found
Point-contact Andreev-reflection spectroscopy in segregation-free Mg_{1-x}Al_{x}B_2 single crystals up to x=0.32
We present new results of point-contact Andreev-reflection (PCAR)
spectroscopy in single-phase Mg_{1-x}Al_{x}B_{2} single crystals with x up to
0.32. Fitting the conductance curves of our point contacts with the two-band
Blonder-Tinkham-Klapwijk model allowed us to extract the gap amplitudes
Delta_{sigma} and Delta_{pi}. The gap values agree rather well with other PCAR
results in Al-doped crystals and polycrystals up to x=0.2 reported in
literature, and extend them to higher Al contents. In the low-doping regime,
however, we observed an increase in the small gap Delta_{pi} on increasing x
(or decreasing the local critical temperature of the junctions, T_{c}^{A})
which is not as clearly found in other samples. On further decreasing T_{c}^{A}
below 30 K, both the gaps decrease and, up to the highest doping level x=0.32
and down to T_{c}^{A}= 12 K, no gap merging is observed. A detailed analysis of
the data within the two-band Eliashberg theory shows that this gap trend can be
explained as being mainly due to the band filling and to an increase in the
interband scattering which is necessary to account for the increase in
Delta_{pi} at low Al contents (x < 0.1). We suggest to interpret the following
decrease of Delta_{pi} for T_{c}^{A} < 30 K as being governed by the onset of
inhomogeneity and disorder in the Al distribution that partly mask the
intrinsic effects of doping and is not taken into account in standard
theoretical approaches.Comment: 22 pages, 9 eps figures, Elsevier style. Theoretical details added in
appendix. Characterization of crystals include
Triterpenoid saponins from the stem bark of pentaclethra eetveldeana
Two previously undescribed triterpenoid saponins together with 4 known ones were isolated from the stem bark of Pentaclethra eetveldeana De Wild. & Th. Dur. Their structures were elucidated by spectroscopic methods including 1D and 2D NMR experiments in combination with mass spectrometry as 3- O-β- d -glucopyranosyl- (1→2)- [β- d -glucopyranosyl- (1→3)]-β- d -glucopyranosyl- (1→4)- β- d -glucopyranosyl- (1→3)-α- l -rhamnopyranosyl- (1→2)-[β- d-glucopyranosyl- (1→4)]-α- l -arabinopyranosyloleanolic acid and 3- O -β- d -glucopyranosyl- (1→2)-[β- d -glucopyranosyl- (1→3)]-β- d -glucopyranosyl- (1→4)-β- d -glucopyranosyl- (1→3)- α -l -rhamnopyranosyl- (1→2)-[β- d -glucopyranosyl- (1→4)]-α- l -arabinopyranosylhederagenin. © The Author(s) 2019
Triterpenoid saponins from the root bark of haplocoelum congolanum
peer reviewedTwo undescribed triterpenoid saponins together with 5 known ones were isolated from the root bark of Haplocoelum congolanum Hauman. Their structures were elucidated by spectroscopic methods including one-dimensional and two-dimensional nuclear magnetic resonance experiments in combination with mass spectrometry as 3-O-(4-O-[3-hydroxy-3-methylglutaryl])-α-l-arabinopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-α-l-arabinopyranosyloleanolic acid and 3-O-α-l-arabinofuranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-α-l-arabinopyranosyloleanolic acid. © The Author(s) 201
Dehydrogenative Synthesis of Imines from Alcohols and Amines Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex
A Tandem Approach to Photoactivated Olefin Metathesis: Combining a Photoacid Generator with an Acid Activated Catalyst
Palladium-Catalyzed Oxidative Domino Carbocyclization–Carbonylation–Alkynylation of Enallenes
POLLINISATION DU TRÈFLE VIOLET DIPLOIDE (TRIFOLIUM PRATENSE L.) PAR LES APOIDES ET PARTICULIÈREMENT PAR LES ABEILLES DOMESTIQUES HYBRIDES (APIS MELLIFICA CAUCASICA × A. MELLIFICA LIGUSTICA)
International audienc
Ruthenium–arene catalysts bearing N-heterocyclic carbene ligands for olefin cyclopropanation and metathesis
Abstract: Ruthenium–arene complexes bearing N-heterocyclic carbene (NHC) ligands with the generic formula [RuCl2(p-cymene)(NHC)] are efficient catalyst precursors for the cyclopropanation of activated olefins with ethyl diazoacetate, and the cis/trans diastereoselectivity of the reaction markedly depends on the steric bulk of the NHC. The procedure was successfully applied to styrene, α-methylstyrene, and various other styrenic derivatives bearing electron-withdrawing or donating substituents on their aromatic rings. The reaction of unactivated internal or terminal alkenes was more sluggish, and the use of norbornene as a substrate afforded only olefin metathesis. Further investigation of the ring-opening metathesis polymerization of this strained cycloolefin in the presence of trimethylsilyldiazomethane led to high molecular weight polynorbornene whose microstructure was not significantly affected by the choice of the NHC ancillary ligand
First case of nasal transitional carcinoma in a goat infected with Enzootic Nasal Tumor Virus in Belgium
International audienceAn eleven-year-old, female goat was presented for evaluation of breathing difficulties and epistaxis. Radiographs and computed tomographic (CT) examination of the head revealed the presence of a space-occupying lesion involving the right nasal passage and invading the cranial vault and retrobulbar space. Histologic examination and detection of viral genome from the nasal mass led to the diagnosis of nasal transitional carcinoma with concomitant infection with Enzootic Nasal Tumor Virus (ENTV-2). In this case report, the presence of a nasal transitional carcinoma is described in a goat; a very rare tumor which, to the authors' knowledge, has not been previously reported in goats. Reverse transcription polymerase chain reaction (RT-PCR) detected the genome of ENTV-2 within the neoplastic tissue, suggesting an infectious etiology
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