Flip–flop Motion of Circular Hydrogen Bond Array in Thiacalix[4]arene

Thiacalix[4]arene contains a circular array of four equivalent hydrogen bonds on its lower rim. The array undergoes a flip–flop motion between two possible directions. The rate of this motion in the temperature range 223–313 K is assessed by means of measurements of the nuclear spin relaxation. The values of the activation enthalpy (38.7 kJ mol^? 1) and of the activation entropy ( ? 15 J mol^? 1 K^? 1) were determined. In addition, correlation times of molecular tumbling have been determined in the same temperature range. The measured properties of thiacalix[4]arene are compared to those of the “classical” calix[4]arene in order to utilize them for fine tuning of the building blocks in supramolecular chemistry.     

A Note on a Generalization of the Multiple Cover Formula and the Simple Flop

We prove a closed formula for an excess integral over the moduli space of stable maps from genus one, unmarked curves to the projective space ? ^r of degree d for any positive integers r and d. The result generalizes the multiple cover formula for ?¹. We also show that any simple ? ^r flop preserves the theory of arbitrary-genus Gromov-Witten invariants in exceptional curve classes.     

Magnetic resonances in (CH3NH3)2MnCl4

We have studied the magnetic excitations of (CH₃NH₃)₂MnCl₄ in the antiferromagnetic and in the spin-flop regimes by means of magnetic resonance in the millimeter range (60–100 GHz). Rather odd line shapes of the resonance absorption line for narrow lines are explained as interference effects between the resonant and the non-resonant circular wave in the sample. For the antiferromagnetic resonance (AFMR) and for the paramagnetic resonance (EPR, above the Néel temperature), we have also studied the line width as a function of temperature.     

Control of Charge Transfer Phase Transition in Iron Mixed-Valence System (n-C n H2n+1)4N[FeIIFeIII(dto)3] (n=3–6; dto = C2O2S2)

The spin flop behaviour of low anisotropy Mn ions within the mixed halide (⁵⁴Mn)Mn(Br _x Cl_1−x )₂·4H₂O is shown to be interpolative with that of the two terminal compounds, in striking contrast with the dynamics of nuclear spin lattice relaxation.     

Current-perpendicular-to-plane magnetoresistance in Co/Gd multilayers with twisted spin structure

Current-perpendicular-to-plane magnetoresistance was measured for ferrimagnetic Co/Gd multilayers which have twisted spin structure accompanied with spin-flop transition. The influence of twisted spin structure on the electronic transport was exclusively obtained, eliminating the effect of anisotropic magnetoresistance. MR curves showed a downturn around the spin-flop field, suggesting that the formation of twisted spin structure leads to a negative resistance change.     

Fano threefolds in positive characteristic

We show that the birational classification in positive characteristicof smooth Fano threefolds X with Picard number 1 is the same as incharacteristic zero. In particular, there are no exotic such Fanos; asa consequence of the classification, X is shown to be liftable withoutramification to characteristic zero and to contain a line. The maintechniques employed are those of Ekedahl and of Mori and Takeuchi.     

Topics on the Geometry of Rational Homogeneous Spaces

This is a survey paper about a selection of results in complex algebraic geometry that appeared in the recent and less recent litterature, and in which rational homogeneous spaces play a prominent role. This selection is largely arbitrary and mainly reflects the interests of the author.     

维持阻塞触发器设计原理新解

本文分析了由门级组成的两类锁存器, 并证明了传统的维持阻塞触发器即为由其中单轨输入锁存器设计的主从触发器.由于两个由时钟控制的与非门被主从两部分公用, 因此它的结构特别简单     

Radial Basis Function methods—reduced computational expense by exploiting symmetry

Radial basis function (RBF) methods are popular methods for scattered data interpolation and for solving PDEs in complexly shaped domains. RBF methods are simple to implement as they only require elementary linear algebra operations. In this work, center locations that result in matrices with a centrosymmetric structure are examined. The resulting matrix structure can be exploited to reduce computational expense and improve the accuracy of the methods while avoiding more complicated techniques such as domain decomposition.     

Two Extended 5‐Methyltetrazolate‐Based Magnetic Complexes: Synthesis,Structure, and Magnetic Properties

Two 5‐methyl‐tetrazolate (mtz^–)‐based paramagnetic metal coordination polymers, {[Cu₂(H₂O)₂(mtz)(μ₃‐OH)(nip)] · H₂O}_n ( 1 ) and [Cu(H₂O)(mtz)₂]_n ( 2 ), were obtained in the presence and absence of aromatic 5‐nitroisophathalate (nip^2–) coligand by varying the preparation methods. Structural determinations reveal that 1 is a three‐dimensional (3D) framework with corner‐sharing triangular ribbons infinitely extended by ditopic nip^2– connectors. In contrast, 2 is a coplanar (4,4) layer constructed from square‐pyramidal Cu^II ions and μ‐N1,N4‐mtz^– linkers, which is further assembled into a 3D supramolecular network by interlayer hydrogen‐bonding interactions. Magnetically, spin‐frustrated antiferromagnetic ordering is observed in the 3D framework of 1 and canted antiferromagnetic behavior with a slight spin‐flop transition is presented in 2 , which are structurally resulting from the locally Δ‐ribbon in 1 and asymmetric magnetic superexchange mediated by the μ‐N1,N4‐mtz^– bridge of 2 .