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A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed. 相似文献
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Campbell R Carrella LM Clegg W Mulvey RE Rentschler E Robertson SD Russo L 《Inorganic chemistry》2011,50(10):4656-4659
One of the milestone structures in the development of transition-metal complexes with metal-metal bonds of multiple bond order was the lithium methylchromate dimer Me(8)Cr(2)[Li(donor)](4) (donor = THF or Et(2)O). Using a simple salt metathesis reaction mixing this compound with sodium tert-butoxide, the sodium congener Me(8)Cr(2)[Na(OEt(2))](4) has been synthesized as a green crystalline compound and isolated in 51% yield. Its solid-state structure was determined by single-crystal X-ray diffraction. Exhibiting exact crystallographic C(4h) symmetry, this heavier alkali-metal chromate structure is also dimeric, formally comprising a (Me(8)Cr(4))(4-) tetranionic core with four peripheral Na(+) cations carrying supporting ether ligands. Its salient feature is the long Cr···Cr distance of 3.263(2) ?, which is remarkably elongated compared to that in the lithium THF-solvated congener [1.968(2) ?]. With respect to the methyl C atoms, the Cr coordination is distorted-square-planar. Each Na(+) interacts with four methyl C atoms, and there are also some short Na···H(C) contacts. Unlike for lithium chromate, no NMR spectroscopic data could be obtained for sodium chromate. The paramagnetic character of sodium chromate was confirmed by variable-temperature magnetization measurements, which indicated antiferromagnetic behavior. 相似文献
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Pablo Alborés Dr. Luca M. Carrella William Clegg Prof. Pablo García‐Álvarez Dr. Alan R. Kennedy Dr. Jan Klett Dr. Robert E. Mulvey Prof. Eva Rentschler Prof. Dr. Luca Russo Dr. 《Angewandte Chemie (International ed. in English)》2009,48(18):3193-3193
Chromation and ferration are the latest additions to the concept of alkali‐metal‐mediated metalation, as described by J. Klett, R. E. Mulvey, and co‐workers in their Communication on page 3317 ff. While the more electropositive sodium is essential for the reaction, it is the less electropositive chromium or iron that actually performs deprotonation of benzene. This novel reactivity can be likened to a game of chess in which the queen (Na) holds the king in check, while the knight (Cr, Fe) scores checkm(etal)ate.
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Dr. Juan H. Mecchia Ortiz Daiana Cabrosi Dr. Luca M. Carrella Prof. Dr. Eva Rentschler Prof. Dr. Pablo Alborés 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(59):e202201450
We are reporting the synthesis, single-crystal X-ray structure characterization, and magnetic property investigations of the pivalate butterfly {CrIII2LnIII2} complexes with Ln= Gd and Dy and the isostructural Y(III) sample. We found an anti-ferromagnetic Cr(III)-Ln(III) exchange interaction, which, as previously observed in related Cr(III)/Ln(III) systems, plays a key role in suppressing quantum tunnelling of magnetization and enhances the SMM performance in the Dy(III) complex. In fact, a pure Orbach relaxation mechanism, with absence of QT regime, is observed with a thermal barrier of 50 cm−1, leading to magnetization hysteresis opening, measured with a commercial magnetometer, up to 3.6 K with a coercive field of 2.9 T. Analysis of SMM behaviour in literature-known butterfly {CrIII2DyIII2} complexes, reveals the existence of a magneto-structural correlation between Ueff, the thermal barrier size, and the mean Cr−Dy bond distances. Moreover, a clear correlation is found for the thermal barrier magnitude and the maximum temperature hysteresis opening and coercive field. 相似文献
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Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
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Siebler D Linseis M Gasi T Carrella LM Winter RF Förster C Heinze K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4540-4551
Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic 1H NMR and M?ssbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin-Day class II mixed-valent systems. M?ssbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form). 相似文献