A quasielastic neutron scattering and solid-state (2)H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN)(4)]} shows that the switching of the rotation of a molecular fragment--the pyrazine ligand--occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10(-13)-10(-3) s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppressed, while when the system incorporates benzene guest molecules, the movements of the system are even more restricted. 相似文献
The Monster tower ([MZ01], [MZ10]), known as the Semple Tower in Algebraic Geometry ([Sem54], [Ber10]), is a tower of fibrations canonically constructed over an initial smooth n-dimensional base manifold. Each consecutive fiber is a projective n — 1 space. Each level of the tower is endowed with a rank n distribution, that is, a subbundle of its tangent bundle. The pseudogroup of diffeomorphisms of the base acts on each level so as to preserve the fibration and the distribution. The main problem is to classify orbits (equivalence classes) relative to this action. Analytic curves in the base can be prolonged (= Nash blown-up) to curves in the tower which are integral for the distribution. Prolongation yields a dictionary between singularity classes of curves in the base n-space and orbits in the tower. This dictionary yielded a rather complete solution to the classification problem for n = 2 ([MZ10]). A key part of this solution was the construction of the ‘RVT’ classes, a discrete set of equivalence classes built from verifying conditions of transversality or tangency to the fiber at each level ([MZ10]). Here we define analogous ‘RC’ classes for n > 2 indexed by words in the two letters, R (for regular, or transverse) and C (for critical, or tangent). There are 2k?1 such classes of length k and they exhaust the tower at level k. The codimension of such a class is the number of C’s in its word. We attack the classification problem by codimension, rather than level. The codimension 0 class is open and dense and its structure is well known. We prove that any point of any codimension 1 class is realized by a curve having a classical A2k singularity (k depending on the type of class). Following ([MZ10]) we define what it means for a singularity class in the tower to be “tower simple”. The codimension 0 and 1 classes are tower simple, and tower simple implies simple in the usual sense of singularity. Our main result is a classification of the codimension 2 tower simple classes in any dimension n. A key step in the classification asserts that any point of any codimension 2 singularity is realized by a curve of multiplicity 3 or 4. A central tool used in the classification are the listings of curve singularities due to Arnol’d ([Arn99], Bruce-Gaffney ([BG82]), and Gibson-Hobbs ([GH93]). We also classify the first occurring truly spatial singularities as subclasses of the codimension 2 classes. (A point or a singularity class is “spatial” if there is no curve which realizes it and which can be made to lie in some smooth surface.) As a step in the classification theorem we establish the existence of a canonical arrangement of hyperplanes at each point, lying in the distribution n-plane at that point. This arrangement leads to a coding scheme finer than the RC coding. Using the arrangement coding we establish the lower bound of 29 for the number of distinct orbits in the case n = 3 and level 4. Finally, Mormul ([Mor04], [Mor09]) has defined a different coding scheme for singularity classes in the tower and in an appendix we establish some relations between our coding and his. 相似文献
Hamiltonian stationary Lagrangian spheres in K?hler-Einstein surfaces are minimal. We prove that in the family of non-Einstein K?hler surfaces given by the product Σ1?×?Σ2 of two complete orientable Riemannian surfaces of different constant Gauss curvatures, there is only a (non minimal) Hamiltonian stationary Lagrangian sphere. This example, defined when the surfaces Σ1 and Σ2 are spheres, is unstable. 相似文献
The concept of "molecular magnetic sponges" was introduced for the first time in 1999 by the creative imagination of the late Olivier Kahn. It refers to the exotic spongelike behavior of certain molecule-based materials that undergo a dramatic change of their magnetic properties upon reversible dehydration/rehydration processes. Here we report a unique example of a manganese(II)-copper(II) mixed-metal-organic framework of formula [Na(H(2)O)(4)](4)[Mn(4){Cu(2)(mpba)(2)(H(2)O)(4)}(3)]·56.5H(2)O (1) (mpba=N,N'-1,3-phenylenebis(oxamate)). Compound 1 possesses a 3D Mn(II)(4)Cu(II)(6) pillared layer structure with mixed square and octagonal pores of approximate dimensions 1.2×1.2 nm and 2.1×3.0 nm, respectively, hosting a large amount of crystallization H(2)O molecules and hydrated Na(I) countercations as guests. It reversibly switches from a crystalline hydrated phase with long-range ferromagnetic ordering at a rather high critical temperature (T(c)) of 22.5 K to an amorphous dehydrated phase with T(c) as low as 2.3 K, which is accompanied by a breathing-type dynamic effect involving a large crystal volume (ca. 45%) and color changes after water desorption/adsorption. The combination of both the open-framework structure and the spongelike optical, mechanical, and magnetic switching behavior in this new class of oxamato-based porous magnets offers fascinating possibilities in designing multifunctional materials for host-guest molecular sensing. 相似文献
Phage therapy by oral administration requires enhanced resistance of phages to the harsh gastric conditions. The aim of this work is the microencapsulation of phages in natural biopolymeric matrices as a protective barrier against the gastric environment. Alginate and pectin are used as base polymers. Further emulsification with oleic acid or coating with a different biopolymer is also studied. Emulsified pectin shows the maximum encapsulation efficiency and the highest protection against acidity, leaving more than 103 active phages after 30 min exposure at pH = 1.6, and protects phage from pepsin activity (4.2 mg mL?1). Non‐encapsulated phages are fully inactivated at pH = 1.6 or with pepsin (0.5 mg mL?1) after 10 min.
Electrically Detected Magnetic Resonance (EDMR) was used to investigate the influence of dye doping on spin-dependent exciton formation in aluminum (III) 8-hydroxyquinoline (Alq3) based Organic Light Emitting Diodes (OLEDs) with different device structures. 4-(dicyanomethylene)-2-methyl-6-{2-[(4-diphenylamino)-phenyl]ethyl}-4H-pyran (DCM-TPA) and 5,6,11,12-tetraphenylnaphthacene (Rubrene) were used as dopants. Results at room temperature show significant differences on the EDMR spectra (g-factor and linewidth) of doped and undoped devices. Signals from DCM-TPA and Rubrene dye doped OLEDs showed strong temperature dependence, with signal intensity increasing by 2 orders of magnitude below 200 K for DCM-TPA dye doped OLEDs and increasing by ~1 order of magnitude below 225 K for the Rubrene dye doped device, while undoped devices shows almost no temperature dependence. By adding a “spacer” layer of undoped Alq3 at the recombination zone, changes in bias voltage were used to shift the recombination from doped to undoped region and correlate that with changes in the EDMR spectrum. Our results are indicating that charge trapping on the dopant followed by recombination is the main mechanism of light emission in the investigated devices. 相似文献
Biomphalaria glabrata and Biomphalaria straminea have been identified as intermediate hosts for Schistosoma mansoni. Several studies have found two cell types in the hemolymph of B. glabrata (hyalinocytes and granulocytes). However, there are no studies describing the hemocytes of B. straminea. With the aim of further describing the hemocyte subsets in B. glabrata and B. straminea, we conducted a detailed study using optical microscopy and transmission electron microscopy. Based on the morphological characteristics of the cells, we identified the same types of hemocytes in two species of molluscs, namely: blast-like cells, granulocytes, type I hyalinocytes, type II hyalinocytes and type III hyalinocytes. Blast-like cells had a spherical profile with a central nucleus filling almost the whole cell. Granulocytes were characterized by presenting variable numbers of granules. Type I hyalinocytes were the most abundant cell type and displayed various cytoplasmic projections. Type II and type III hyalinocytes had never previously been reported. They were few in number and were characterized by having an eccentric nucleus. From these results, it is concluded that there are five types of cells in the hemolymph of B. glabrata and B. straminea. Further studies are now needed to identify the role of these hemocytes in the immune response of these snails. 相似文献