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601.
Bruno Medronho Anabela Romano Maria Gra?a Miguel Lars Stigsson Bj?rn Lindman 《Cellulose (London, England)》2012,19(3):581-587
Despite being the world’s most abundant natural polymer and one of the most studied, cellulose is still challenging researchers.
Cellulose is known to be insoluble in water and in many organic solvents, but can be dissolved in a number of solvents of
intermediate properties, like N-methylmorpholine N-oxide and ionic liquids which, apparently, are not related. It can also be dissolved in water at extreme pHs, in particular
if a cosolute of intermediate polarity is added. The insolubility in water is often referred to strong intermolecular hydrogen
bonding between cellulose molecules. Revisiting some fundamental polymer physicochemical aspects (i.e. intermolecular interactions)
a different picture is now revealed: cellulose is significantly amphiphilic and hydrophobic interactions are important to
understand its solubility pattern. In this paper we try to provide a basis for developing novel solvents for cellulose based
on a critical analysis of the intermolecular interactions involved and mechanisms of dissolution. 相似文献
602.
F.P. Romano L. Pappalardo N. Masini G. Pappalardo F. Rizzo 《Microchemical Journal》2011,99(2):449-453
An analytical protocol based on the combined use of the portable PIXE-alpha (Particle Induced X-ray Emission) and XRD (X-ray Diffraction) non destructive techniques developed at the LANDIS laboratory (Laboratorio di Analisi Non Distruttive) of the INFN–CNR (Istituto Nazionale di Fisica Nucleare–Consiglio Nazionale delle Ricerche) in Catania (Italy), was applied for the characterisation of the surface paints of some archaeological fragments of Nasca pottery from the Ceremonial Centre of Cahuachi in Southern Peru.Measurements were carried out on the black, white, red, orange and grey pigments; quantitative information on the chemical composition as well as on the mineralogical phases present on the paints were obtained.Results allowed to make some considerations about the materials and the manufacturing technique used to realise such fired pigments.It should be noted that during firing the precursor minerals composing the pigments undergo a phase transformation and their identification presents some difficulties. 相似文献
603.
Image velocimetry techniques, which extract motion information by comparison of image regions, typically make use of cross-correlation to measure the degree of matching. In this work, a novel measure of the dissimilarity between interrogation windows is proposed which is based on a more robust estimator than cross-correlation. The method is validated on synthetic images and on two experimental data sets obtained from a periodically pulsed jet and a backward-facing step. The former is a basically laminar flow, whereas the latter is fully turbulent. Both of them are characterized by regions of high velocity gradients. The efficiency of the robust image velocimetry (RIV) is compared with a cross-correlation algorithm (PIV). The analysis of results shows that the RIV is less sensitive to the appearance and disappearance of particles, and to high velocity gradients and, in general, to noise, generating less spurious velocity vectors. As a consequence RIV resolves better the vorticity peaks at the center of the vortex rings generated by the pulsed jet, obtaining, for a given interrogation window size, a higher spatial resolution. Moreover, in the analysis of the flow field generated by the backward-facing step, the RIV performs better in the shear layer at the border of the recirculation region, leading to a more reliable estimation of Reynolds shear stress and horizontal velocity component. 相似文献
604.
Visa Thongrakard Nijsiri Ruangrungsi Maneerat Ekkapongpisit Ciro Isidoro Tewin Tencomnao 《Photochemistry and photobiology》2014,90(1):214-224
Thai traditional medicine employs a wide range of indigenous herbs in the forms of tincture or tea for the cure of skin and systemic inflammatory diseases. The protection by Thai plants extracts against UVB DNA damage and cytotoxicity was investigated in human keratinocytes. Petroleum ether, dichloromethane and ethanol extracts were prepared from 15 Thai herb species, and the total phenolic and flavonoid contents, the antioxidant and UV‐absorbing properties were assessed by standard procedures. Cytoprotective effects were evaluated on the basis of cell survival, caspase‐3 activity and pyrimidine dimers determination. High total phenolic and flavonoid contents were found in the ethanol and dichloromethane fractions. Dichloromethane extract of turmeric was shown to possess the highest antioxidant activity. The maximum UV absorptions were found in the ethanol extract of turmeric and in the dichloromethane extract of ginger. These extracts stimulated the synthesis of Thioredoxin 1, an antioxidant protein, and could protect human HaCaT keratinocytes from UV‐induced DNA damage and cytotoxicity. The present data support the utilization of turmeric and ginger extracts in anti‐UV cosmetic pharmaceuticals. 相似文献
605.
Asymmetric Synthesis of Tetracyclic Pyrroloindolines and Constrained Tryptamines by a Switchable Cascade Reaction 下载免费PDF全文
Corien de Graaff Lisa Bensch Sjoerd J. Boersma Răzvan C. Cioc Matthijs J. van Lint Elwin Janssen Prof. Dr. Nicholas J. Turner Prof. Dr. Romano V. A. Orru Dr. Eelco Ruijter 《Angewandte Chemie (International ed. in English)》2015,54(47):14133-14136
The interrupted Fischer indole synthesis of arylhydrazines and biocatalytically generated chiral bicyclic imines selectively affords either tetracyclic pyrroloindolines or tricyclic tryptamine analogues depending on the reaction conditions. We demonstrate that the reaction is compatible with a variety of functional groups. The products are obtained in high optical purity and in reasonable to good yield. We present a plausible reaction mechanism to explain the observed reaction outcome depending on the stoichiometry of the acid mediator. To demonstrate the synthetic utility of our method, pharmaceutically relevant examples of both product classes were synthesized in highly efficient reaction sequences, including a phenserine analogue as a potential cholinesterase inhibitor and constrained tryptamine derivatives as selective inhibitors of the 5‐HT6 serotonin receptor and the TRPV1 ion channel. 相似文献
606.
Ionic Fragmentation Mechanisms of 2,2,2‐Trifluoroethanol Following Excitation with Synchrotron Radiation 下载免费PDF全文
Yanina B. Bava Yanina Berrueta Martínez Dr. Angélica Moreno Betancourt Prof. Dr. Mauricio F. Erben Prof. Dr. Reinaldo L. Cavasso Filho Prof. Dr. Dr. Carlos O. Della Védova Prof. Dr. Rosana M. Romano 《Chemphyschem》2015,16(2):322-330
Gaseous 2,2,2‐trifluoroethanol (TFE) is excited with synchrotron radiation between 10 and 1000 eV and the ejected electrons and positive ions are detected in coincidence. In the valence‐electron energy region, the most abundant species is CH2OH+. Other fragments, including ions produced by atomic rearrangements, are also detected; the most abundant are COH+, CFH2+ and CF2H2+. The energies of electronic transitions from C 1 s, O 1 s and F 1 s orbitals to vacant molecular orbitals are determined. A site‐specific C 1 s excitation is observed. The photofragmentation mechanisms after the excitation of core‐shell electrons are inferred from analysis of the shape and slope of the coincidence between two charged fragments in the bi‐dimensional coincidence spectra. The spectra are dominated by islands that correspond to the coincidence of H+ with several charged fragments. One of the most important channels leads to the formation of CH2OH+ and CF3+ in a concerted mechanism. 相似文献
607.
608.
Antonio Romano 《Meccanica》1974,9(4):244-255
Summary Whithout adopting a particular interaction between matter and fields, we deduce the relativistic equations of balance -for charged differential materials which move in electromagnetic fields. Successively, restriction for the relativistic constitutive equations are deduced by adopting a relativistic reduced dissipation inequality obtained from the 2nd principle of thermodynamics by P. M. Quan.
Sommario Si determinano le equazioni relativistiche del bilancio per materiali differenziali carichi, con distribuzione continua di momento angolare interno, in moto in campi elettromagnetici senza ricorrere ad alcuna interazione particolare tra materia e campi. Successivamente si deducono delle restrizioni per le equazioni costitutive derivanti dall'imporre che esse rendano soddisfatta una diseguaglianza di dissipazione ridotta relativistica ottenuta dal2 o principio della termodinamica di P. M. Quan.相似文献
609.
The design of third generation electron cyclotron resonance ion sources (ECRIS) had to take into account some technical issues that are usually not relevant for conventional ECRIS, either in terms of microwave power management or in terms of stray magnetic field. In fact, strong magnets originate high stray fields that are detrimental for beam optics, for the pumping system lifetime and mainly for the gyrotron normally used for power generation. Additionally, the presence of intense X-ray fluxes generated by the ECRIS plasma, observed in many experiments, can generate an unexpected heat load upon the thermal balance of the superconducting ECRIS cryostat, which can trigger a warm-up in the case of closed-loop cryostat connected to a cryocooler setup. These and other issues are presented by the authors along with a study of possible solutions. 相似文献
610.
Orlando Mauricio Quiroz Londoño Daniel Emilio Martínez Hector Enrique Massone Libardo Antonio Londoño Ciro Cristina Dapeña 《Isotopes in environmental and health studies》2013,49(3):411-425
Stable isotopes and electrical conductivity in groundwater were used as natural tracers to adjust the hydrogeological conceptual model in one of the largest catchments within the inter-mountainous Pampa plain, Argentina. Geostatistical tools were used to define the model that best fitted the spatial distribution of each tracer, and information was obtained in areas where there was a lack of data. The conventional isotopic analysis allowed the identification of three groundwater groups with different isotopic fingerprints. One group containing 56?% of the total groundwater samples suggested a well-mixed system and soil infiltration precipitation as the main recharge source to the aquifer. The other two groups included samples with depleted (25.5?%) and enriched (18.5?%) isotopic compositions, respectively. The combination of δ18O, δ2H and electrical conductivities maps suggested ascending regional flows and water transfer from the Quequén Grande River catchment to the Moro creek. The spatial interpretation of these tracers modified the conceptual hydrogeological model of the Quequén Grande River. 相似文献