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  • 1
    ISSN: 1573-4854
    Keywords: pore-size distribution ; micropores ; PILC ; adsorption potential ; N2-adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The determination of the micropore-size distribution of microporous materials is of major importance in the field of adsorption and catalysis. This new method to derive the micropore-size distribution for Pillared Clays (PILC) is based on the logarithmic adsorption isotherm. When a N2-adsorption isotherm is replotted on a log P/P 0 scale, a curve representing the adsorption potential is obtained. Because the adsorption potential is highly dependent on the pore-size, this curve contains all the information on the pore structure. These curves often exhibit steps, large increases in volume adsorbed by small changes in adsorption potential. These are thermodynamically related to the filling of pores of a certain size. The relative pressures where these steps appear are dependent on the pore-size. Taking the derivative, dV/d log (P/P 0), the location of these steps becomes more clear. These derivative curves give a lot of information on the pore-size distribution. The presence of several maxima and their sharpness informs about the number of different pore-sizes present and the homogeneity. Assuming that N2-adsorption in the micropores is ruled by the amount of N2-layers which can fit in, the micropore range can be subdivided in five pore groups adsorbing 1–5 layers. By locating the main maxima in the derivative curves of pillared clays with known but different slit widths, we can correlate a pore-size range to a certain P/P 0 range where these pores will fill. In this way a micropore-size distribution based on the adsorption potential can be constructed.
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  • 2
    ISSN: 1573-4854
    Keywords: pillared clay ; N2 adsorption isotherm ; porosity ; specific surface area ; pore size distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract N2 adsorption isotherms of various pillared montmorillonites (PILCs) were analyzed for evaluation of their porosities. The quantitative data of the total and micropore volumes were calculated using the B.J.H. method and the t-plot, respectively. The volume of mesopores is the difference between the total volume and the micropore volume. The linear branch above the P/P 0 of 0.5 should be used for the calculations of the micropore volume and external surface area. The evaluation of the specific surface area (SA) of the PILCs and influences of the porosity on the calculations were discussed in detail. An upper limit of the monolayer capacity of a porous solid is proposed, based on the adsorption on a nonporous solid. Due to the space restriction in the fine slit-like pores of the PILCs, the specific surface areas calculated with the B.E.T. equation using the adsorption data in a relative pressure region ranging from 0.01 to 0.1 are more accurate. The mean micropore widths of the PILCs, derived from the data of the multi-point B.E.T. SA and micropore volume consist reasonably with the pore widths obtained by XRD diffraction. The step-like curves of the t-plot in low-pressure region and of the logarithmic plot reveal presence of pores of various sizes in the pillared clays. The micropore size distribution can be derived by a new method using the N2 adsorption data.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heteroatomic cages (BN/2NN/2) with borons and nitrogens fully replacing alternant sets of carbons in cages are built graph-theoretically and investigated via the semiempirical MNDO Hamiltonian. The comparison with their parent carbon cages CN is made in terms both of electronic and of geometric changes. Infinite classes first of octahedral symmetry and second of hexagonal-bipyramidal symmetry fullerenoid cages are considered in detail. The difference in the electronegativities for boron and nitrogen implies the opening of HOMO-LUMO gaps for alternant BN clusters. In general, the borons prefer planar geometry (sp2 hybridization) while the nitrogens prefer pyramidalization (sp3 hybridization). © 1997 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 1434-6079
    Keywords: PACS. 03.65.-w Quantum mechanics – 03.65.Fd Algebraic methods – 42.50.Gy Strong-field excitation of optical transitions in quantum systems; multi-photon processes; dynamic Stark shift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: There exist a number of typical and interesting systems and/or models, which possess three-generator Lie-algebraic structure, in atomic physics, quantum optics, nuclear physics and laser physics. The well-known fact that all simple 3-generator algebras are either isomorphic to the algebra sl (2, C) or to one of its real forms enables us to treat these time-dependent quantum systems in a unified way. By making use of both the Lewis-Riesenfeld invariant theory and the invariant-related unitary transformation formulation, the present paper obtains exact solutions of the time-dependent Schrödinger equations governing various three-generator Lie-algebraic quantum systems. For some quantum systems whose time-dependent Hamiltonians have no quasialgebraic structures, it is shown that the exact solutions can also be obtained by working in a sub-Hilbert-space corresponding to a particular eigenvalue of the conserved generator (i.e., the time-independent invariant that commutes with the time-dependent Hamiltonian). The topological property of geometric phase factors and its adiabatic limit in time-dependent systems is briefly discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical chemistry 23 (1998), S. 179-195 
    ISSN: 1572-8897
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mathematics
    Notes: Abstract It has long been realized that connected graphs have some sort of geometric structure, in that there is a natural distance function (or metric), namely, the shortest-path distance function. In fact, there are several other natural yet intrinsic distance functions, including: the resistance distance, correspondent “square-rooted” distance functions, and a so‐called “quasi‐Euclidean” distance function. Some of these distance functions are introduced here, and some are noted not only to satisfy the usual triangle inequality but also other relations such as the “tetrahedron inequality”. Granted some (intrinsic) distance function, there are different consequent graph-invariants. Here attention is directed to a sequence of graph invariants which may be interpreted as: the sum of a power of the distances between pairs of vertices of G, the sum of a power of the “areas” between triples of vertices of G, the sum of a power of the “volumes” between quartets of vertices of G, etc. The Cayley–Menger formula for n-volumes in Euclidean space is taken as the defining relation for so-called “n-volumina” in terms of graph distances, and several theorems are here established for the volumina-sum invariants (when the mentioned power is 2).
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 517-526 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We consider rigorous evaluation of conjugated-circuit resonance energies for families of structurally related benzenoid hydrocarbons of increasing size. Local and global aromatic properties of such molecules are investigated with particular interest in modeling high polymers. Using the algebra of large numbers, exact formulas for contributions from individual benzene rings of polymers with up to 25,000 repeating units (close to half a million carbon atoms) were derived. All arithmetic procedures were carried out in terms of whole numbers retaining all digits, of which there were sometimes more than 105. © 1995 by John Wiley & Sons, Inc.
    Additional Material: 8 Tab.
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  • 7
    ISSN: 1432-2234
    Keywords: Polymers ; Oligomers ; Benzenoids ; Resonance ; Conjugation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have initiated a comparative study of several families of structurally closely related large benzenoid hydrocarbons of increasing number of fused benzene rings. Local and global properties of such molecules have been studied with a particular interest in investigating the closeness of finite-size molecules for modelling infinite polymeric structures having the same structural patterns. We focus in this report on two questions: (1) how large is a finite molecule which well approximates an infinite system? and (2) how do terminal groups influence local properties in the central part of the molecule as we approach the infinite system. Emphasis in this report is on extraction of high-accuracy limiting values for selected molecular properties from limited data on a few smaller members of structurally related molecules.
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  • 8
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  A lambda ZAP II cDNA library was constructed by cloning cDNA prepared from a high molecular weight double-stranded RNA (dsRNA, ca. 18 kb) isolated from grapevine leafroll associated closterovirus-3 (GLRaV-3) infected tissues. This cDNA library was immuno-screened with GLRaV-3 coat protein specific polyclonal and monoclonal antibodies and three immuno-positive clones were identified. Analysis of nucleotide sequences from these clones revealed an open reading frame (ORF) which was truncated at the end; the remainder of this ORF was obtained by sequencing a fourth clone that overlapped with one of the immunopositive clones. A total of 2028 bp was sequenced. The putative GLRaV-3 coat protein ORF, 939 bp, encodes a protein (referred to as p35) with a calculated of 34 866. Multiple alignment of the p35 amino acid sequence with coat protein sequences from other clostero-viruses revealed that the consensus amino acid residues (R and D) of filamentous plant viruses are preserved in the expected locations. The GLRaV-3 coat protein gene was then engineered for sense and antisense expression in transgenic plants. Transgenic Nicotiana benthamiana plants that contain the sense GLRaV-3 coat protein gene produced a 35 kDa protein that reacted with GLRaV-3 antibody in Western blot.
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  • 9
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  We studied intracellular localization of the UL31 protein of herpes simplex virus type 2 (HSV-2) in infected and transfected cells. The UL31 protein localized diffusely throughout the nucleus in infected Vero cells and the distribution patterns of the UL31 protein appeared to be different from those of either replication protein ICP8 or capsid protein ICP35. In transfected Vero cells it localized diffusely throughout the nucleus except the nucleolus at early times after transfection. At very low efficiency, it accumulated in the nucleolus. At intermediate times after transfection, the UL31 protein showed punctate staining in the nucleus. These punctate forms fused and became larger. At later times after transfection, granular forms further fused and a nuclear diffuse pattern virtually disappeared. We also constructed five N and C terminal deletion mutants of the UL31 protein for transfection assays and showed that the region containing amino acids 44 to 110 was important for nuclear and nucleolar localization. Moreover, green fluorescent protein (GFP)-targeting experiments showed that the UL31 protein was able to transport nonnuclear GFP to the nucleus and nucleolus as a fusion protein.
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  • 10
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary.  Rupestris stem pitting (RSP) seems to be one of the most widespread virus diseases of grapevines. A virus, designated as rupestris stem pitting associated virus-1 (RSPaV-1), is consistently associated with, and likely to be the causative agent of RSP. Sequence analyses of cDNA clones derived from several RSP-affected grapevines suggested that a family of sequence variants of RSPaV-1 was associated with RSP. The genome structure of the sequence variants is identical to that of RSPaV-1 in that they had five open reading frames (ORF) and sequence identities ranging from 75 to 93% in nucleotide sequence and from 80 to 99% in amino acid sequence. ORF5 (coat protein) and the carboxyl-terminal portion of ORF1 (replicase) appeared to be the most conserved regions. The coat proteins of the sequence variants exhibited highly similar antigenic indices, suggesting serological relatedness among them. The cDNA clones obtained through reverse transcription-polymerase chain reaction from RSP-infected grapevines were heterogeneous in nt sequence with identities of 77–99% relative to RSPaV-1. Furthermore, a number of sequence variants were identified in several grapevines infected with RSP. Baselines for defining RSPaV-1 and possible mechanisms accounting for infection of grapevines with multiple sequence variants of RSPaV-1 are proposed. Findings from this study should have practical applications toward understanding the etiology of RSP and developing reliable assays to rapidly detect the disease.
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