4,150 research outputs found
Vibrational study of some layered structures based on titanium and zirconium phosphates
No full textA Raman and infrared study was carried out on layered zirconium and titanium acid phosphates of R- and γ-type, R-M[O3POH]2‚H2O and γ-M[PO4][O2P(OH)2]‚2H2O, respectively. The spectra were initially approached by means of the classical correlation method in the solid state, which accounts for the complexity of the infrared spectra of both species. However, the number of bands and their relative intensity in the Raman spectra suggest a quite total absence of quadrupolar coupling between the vibrating units. So, if interunit coupling is neglected, a molecular approach considering the vibrations of isolated tetrahedral [PO4] and octahedral [MO6] building blocks can allow an affordable spectroscopic description of the title compounds. Interesting insights on the relationships between spectral properties and structure can be drawn by comparison with the spectra of alkali phosphates and of MO6 oxoanions. A significant high-energy shift of the ν(P−O) modes is observed in the layered phosphates with respect to the corresponding salts, which parallels the low-energy shift of the ν(M−O) modes. Surprisingly, an increase of the M−OP interaction can reinforce the P−O bond. A simple theoretical model, based on the interaction between the [PO4] unit and four Li+ in similar geometrical arrangement found in the structures of the layered phosphates, offers a reasonable explanation of this phenomenon
The Vibrational Spectra of the Cyanide Ligand Revisited. Double Bridging Cyanides
No full textThe ν(CN) vibrational spectra of cyanide groups bridging two metal atoms present a confused picture. Factors relevant to the interpretation of the available data are reviewed. Some mechanisms for frequency change, relative to the corresponding terminal species, are made more quantitative than previously described, and others are highlighted for the first time. The kinematic effect is much less important than previously assumed. It seems that an effect responsible for the major part of the frequency increase upon bridging commonly observed is the cation electric field, together with concomitant relaxation (the IVSE model). However, a contribution may well come from the change in the σ bonding in the CN unit
Metal-metal and metal-ligand vibrational interaction in compounds of the Fe3EE '(CO)(9) (E, E ' = S, Se, Te) series and the low-frequency vibrational spectra of Co2FeS(CO)(9) and Os3S2(CO)(9)
No full textThe infrared and Raman spectra of the title compounds in the ca. 400-150 cm-1 region are reported. For the first time, detailed assignments are given for all of the features in this region for the first series of compounds. An attempt is made to extend to all of the modes the plastic cluster model of vibrational analysis, which is normally applied only to ν(M-M) vibrations. While mixing occurs between ν(Fe-Fe) and ν(Fe-E), species containing Te posed particular problems; the reasons for this are discussed and give new insights into the plastic cluster model itself
The v(CO) vibrational spectra of planar transition metal carbonyl clusters
No full textThe ν(CO) vibrational spectra of planar transition cluster carbonyls containing M(CO)4 groups are studied. It is possible to anticipate qualitatively, both for the infrared and Raman, the band intensity changes associated with increasing metallic nature of the cluster. These enable a unification of the band patterns shown by the species reported. As for (idealized) spherical clusters, the spherical harmonic model (SHM), suitably modified, becomes of more general applicability as cluster size increases, although for smaller species the tensor harmonic model (THM) makes a contribution
Detection of substance P immunoreactivity in human peripheral leukocytes
No full textThe neuropeptide substance P (SP) has a marked proinflammatory effect and modulates the immune response. In this study, we tested the hypothesis that human peripheral leukocytes contain SP. Resting peripheral leukocytes collected from healthy volunteers (n = 20) were studied by applying a SP rabbit polyclonal antiserum to both flow cytometry and immunohistochemistry. To identify possible changes in SP expression, we also analyzed both activated T-lymphocytes (cell cultures; n = 5 normal subjects) and neoplastic hematologic samples of different types of leukemias. Flow cytometry showed that normal granulocytes and monocytes contained SP, whereas lymphocytes were generally negative (or weakly positive) with the exception of a few (10-20%) positive subsets. In comparison, activated T-lymphocytes were markedly immunolabeled by SP as well as samples from neoplastic patients demonstrated strong SP immunoreactivity in all cell lineages. This pattern was confirmed by immunohistochemistry on cytospins. Our results support a potential role for SP-mediated immunomodulatory mechanisms both in normal and pathological conditions
Carbon coated microshells containing nanosized Gd(III) oxidic phases for multiple bio-medical applications.
No full textThe FM and PL Libraries Documentation
No full textBuilding complex SPMD code in an ecient and portable way is nowadays a challenge, especially when there is no uniformity of tools and libraries across platforms. The Fast Messages (FM) and the Portability Library (PL) where both designed to provide the basis of an abstract enough framework for C, so that problems can be coded and ported to any supported platform with no more than a few changes in the makeles and a recompilation. The FM library provides a message passing communications library built around the Berkeley Active Messages library. The PL library provides the primitives for host to node communication for problem initialization and results collection, as well as other miscellaneous and potentially non-portable primitives. This technical report contains the documentation for both libraries.Technical report LCSR-TR-25
Increasing science, technology, engineering, and mathematics skills using Project Lead the Way
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Introduction to Urban Science: Evidence and Theory of Cities as Complex Systems
No full textLuís Bettencourt provides a timely, comprehensive, and rigorous treatment of urban space, by contributing to the
advancement of knowledge in the field of urban science. The author develops a valuable scientific guide for researchers,
policymakers, practitioners, and students interested in understanding cities as complex systems. Today, more than half of
world's population lives in urban areas, and, according to theWorld Bank data, by 2045, urban citizens will increase up to
6 billion. Cities of different sizes will play a pivotal role in the postpandemic recovery and, most importantly, they will
make the green transition of our economies and societies really work in coming years. Therefore, understanding “how
each city and every one of its people is the result of the aggregation of many choices, accidents, and influences from
their compounded joint history” (p. xxi) becomes crucial to manage present and future local and global challenges
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