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1.
J Phys Chem B ; 124(7): 1253-1258, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-31977217

RESUMO

Understanding the factors that control solubility and speciation of metal ions in molten salts is key for their successful use in molten salt reactors and electrorefining. Here, we employ X-ray and optical absorption spectroscopies and molecular dynamics simulations to investigate the coordination environment of Ni(II) in molten ZnCl2, where it is poorly soluble, and contrast it with highly soluble Co(II) over a wide temperature range. In solid NiCl2, the Ni ion is octahedrally coordinated, whereas the ZnCl2 host matrix favors tetrahedral coordination. Our experimental and computational results show that the coordination environment of Ni(II) in ZnCl2 is disordered among tetra- and pentacoordinate states. In contrast, the local structure of dissolved Co(II) is tetrahedral and commensurate with the ZnCl2 host's structure. The heterogeneity and concomitant large bond length disorder in the Ni case constitute a plausible explanation for its lower solubility in molten ZnCl2.

2.
Cent European J Urol ; 72(3): 276-279, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31720030

RESUMO

Introduction: Epidemiologic studies demonstrate that obesity and diabetes increase the prevalence of urinary lithiasis. Most of these studies did not stratify the chemical composition of calculi and the physiological mechanisms responsible for this increased risk are not well understood. This study aims to investigate the relation between the metabolic syndrome and the composition of the urinary calculi. Material and methods: Observational and retrospective study of all urinary calculi analysis performed at the Centro Hospitalar do Tâmega e Sousa, Portugal - from January 2009 to September 2015. Calculi were analyzed by infrared spectroscopy. Results: 302 analyses of urinary calculi were identified. Metabolic syndrome was diagnosed in 20.5% of patients. A total of 7 different mineral compounds were identified: 51.6% (N = 156) contained calcium oxalate, 41% (N = 124) calcium phosphate, 37.7% (N = 114) uric acid, 22.1% (N = 67) ammonium urate, 9.6% (N = 29) ammonium magnesium phosphate, 6.3% (N = 19) sodium urate and 1.3% (N = 4) contained cystine. Patients with metabolic syndrome presented a higher proportion of uric acid calculi (66.1% vs. 0%, p <0.001) and ammonium urate calculi (38.7% vs. 17%, p = 0.001). Patients without metabolic syndrome had a higher proportion of calcium oxalate calculi (58.8% vs. 24.2%, p <0.001) and calcium phosphate (46.7% vs. 19.4%, p <0.001). Conclusions: There is a statistically significant relation between metabolic syndrome and uric acid and ammonium urate calculi. Metabolic syndrome may be considered risk factor for this calculi and the diagnosis and treatment of this syndrome must be considered for urolithiasis prevention. Further studies are needed to better the understanding of physiological mechanisms underlying this relationship to improve our strategy of prevention of urinary lithiasis.

3.
J Am Chem Soc ; 141(50): 19655-19668, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31724857

RESUMO

Rh-based catalysts have shown promise for the direct conversion of syngas to higher oxygenates. Although improvements in higher oxygenate yield have been achieved by combining Rh with metal oxide promoters, details of the structure of the promoted catalyst and the role of the promoter in enhancing catalytic performance are not well understood. In this work, we show that MoO3-promoted Rh nanoparticles form a novel catalyst structure in which Mo substitutes into the Rh surface, leading to both a 66-fold increase in turnover frequency and an enhancement in oxygenate yield. By applying a combination of atomically controlled synthesis, in situ characterization, and theoretical calculations, we gain an understanding of the promoter-Rh interactions that govern catalytic performance for MoO3-promoted Rh. We use atomic layer deposition to modify Rh nanoparticles with monolayer-precise amounts of MoO3, with a high degree of control over the structure of the catalyst. Through in situ X-ray absorption spectroscopy, we find that the atomic structure of the catalytic surface under reaction conditions consists of Mo-OH species substituted into the surface of the Rh nanoparticles. Using density functional theory calculations, we identify two roles of MoO3: first, the presence of Mo-OH in the catalyst surface enhances CO dissociation and also stabilizes a methanol synthesis pathway not present in the unpromoted catalyst; and second, hydrogen spillover from Mo-OH sites to adsorbed species on the Rh surface enhances hydrogenation rates of reaction intermediates.

4.
J Phys Chem A ; 2019 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-31386367

RESUMO

We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range allows us to study and disentangle shake processes and intramolecular inelastic scattering effects. In this gas-phase study, relative intensities of the carbon 1s photoelectron lines from chemically inequivalent carbon atoms in the same molecule have been measured as a function of the incident photon energy in the range of 300-6000 eV. We present relative cross sections for the chemically shifted carbon 1s lines in the photoelectron spectra of ethyl trifluoroacetate (the "ESCA" molecule). The results are compared with those of methyl trifluoroacetate and S-ethyl trifluorothioacetate as well as a series of chloro-substituted ethanes and 2-butyne. In the soft X-ray energy range, the cross sections show an extended X-ray absorption fine structure type of wiggles, as was previously observed for a series of chloroethanes. The oscillations are damped in the hard X-ray energy range, but deviations of cross-section ratios from stoichiometry persist, even at high energies. The current findings are supported by theoretical calculations based on a multiple scattering model. The use of soft and tender X-rays provides a more complete picture of the dominant processes accompanying photoionization. Such processes reduce the main photoelectron line intensities by 20-60%. Using both energy ranges enabled us to discern the process of intramolecular inelastic scattering of the outgoing electron, whose significance is otherwise difficult to assess for isolated molecules. This effect relates to the notion of the inelastic mean free path commonly used in photoemission studies of clusters and condensed matter.

5.
Front Chem ; 6: 356, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30191149

RESUMO

Extended x-ray absorption fine structure (EXAFS) is well-suited for investigations of structure and disorder of complex materials. Recently, experimental measurements and analysis of EXAFS have been carried out to elucidate the mechanisms responsible for the negative thermal expansion (NTE) in zirconium tungstate (ZrW2O8). In contrast to previous work suggesting that transverse O-displacements are largely responsible, the EXAFS analysis suggested that correlated rotations and translations of octahedra and tetrahedra within the structure are a major source. In an effort to resolve this controversy, we have carried out ab initio calculations of the structure, lattice vibrations, and EXAFS of ZrW2O8 based on real-space multiple-scattering calculations using the FEFF9 code and auxiliary calculations of structure and Debye-Waller factors. We find that the theoretical simulations are consistent with observed EXAFS, and show that both of the above mechanisms contribute to the dynamical structure of ZrW2O8.

6.
Front Chem ; 6: 296, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30105223

RESUMO

We present a study of the origin of the negative thermal expansion (NTE) on ZrW2O8 by combining an efficient approach for computing the dynamical matrix with the Lanczos algorithm for generating the phonon density of states in the quasi-harmonic approximation. The simulations show that the NTE arises primarily from the motion of the O-sublattice, and in particular, from the transverse motion of the O atoms in the W-O and W-O-Zr bonds. In the low frequency range these combine to keep the WO4 tetrahedra rigid and induce internal distortions in the ZrO6 octahedra. The force constants associated with these distortions become stronger with expansion, resulting in negative Grüneisen parameters and NTE from the low frequency modes that dominate the positive contributions from the high frequency modes. This leads us to propose an anharmonic, two-frequency Einstein model that quantitatively captures the NTE behavior.

7.
J Phys Chem Lett ; 8(14): 3284-3288, 2017 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-28669195

RESUMO

Supported Pt nanocatalysts generally exhibit anomalous behavior, including negative thermal expansion and large structural disorder. Finite temperature DFT/MD simulations reproduce these properties, showing that they are largely explained by a combination of thermal vibrations and low-frequency disorder. We show here that a full interpretation is more complex and that the DFT/MD mean-square relative displacements (MSRD) can be further separated into vibrational disorder, "dynamic structural disorder" (DSD), and long-time equilibrium fluctuations of the structure dubbed "anomalous structural disorder" (ASD). We find that the vibrational and DSD components behave normally, increasing linearly with temperature while the ASD decreases, reflecting the evolution of mean nanoparticle geometry. As a consequence the usual procedure of fitting the MSRD to normal vibrations plus temperature-independent static disorder results in unphysical bond strengths and Grüneisen parameters.

8.
Arch Argent Pediatr ; 114(1): 89-95, 2016 Feb.
Artigo em Espanhol | MEDLINE | ID: mdl-26914079

RESUMO

The care of the child with a tracheostomy deserves special attention because of the potential devastating airway compromise and because of the need of competent care by caregivers and professionals. The recommendations on tracheostomy care published are few and approaches are inconsistent among different institutions. This clinical consensus statement aims to improve care for children with tracheostomies. A literature search was conducted, reviewed and revised by this group of experts, who concurred with these statements, based on the best evidence available and taking into account the local context.


Assuntos
Traqueostomia , Criança , Consenso , Humanos , Guias de Prática Clínica como Assunto
9.
J Am Chem Soc ; 137(40): 12815-34, 2015 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-26352328

RESUMO

First principle calculations of extended X-ray absorption fine structure (EXAFS) data have seen widespread use in bioinorganic chemistry, perhaps most notably for modeling the Mn4Ca site in the oxygen evolving complex (OEC) of photosystem II (PSII). The logic implied by the calculations rests on the assumption that it is possible to a priori predict an accurate EXAFS spectrum provided that the underlying geometric structure is correct. The present study investigates the extent to which this is possible using state of the art EXAFS theory. The FEFF program is used to evaluate the ability of a multiple scattering-based approach to directly calculate the EXAFS spectrum of crystallographically defined model complexes. The results of these parameter free predictions are compared with the more traditional approach of fitting FEFF calculated spectra to experimental data. A series of seven crystallographically characterized Mn monomers and dimers is used as a test set. The largest deviations between the FEFF calculated EXAFS spectra and the experimental EXAFS spectra arise from the amplitudes. The amplitude errors result from a combination of errors in calculated S0(2) and Debye-Waller values as well as uncertainties in background subtraction. Additional errors may be attributed to structural parameters, particularly in cases where reliable high-resolution crystal structures are not available. Based on these investigations, the strengths and weaknesses of using first-principle EXAFS calculations as a predictive tool are discussed. We demonstrate that a range of DFT optimized structures of the OEC may all be considered consistent with experimental EXAFS data and that caution must be exercised when using EXAFS data to obtain topological arrangements of complex clusters.


Assuntos
Modelos Químicos , Oxigênio/química , Complexo de Proteína do Fotossistema II/química , Análise Espectral/métodos
10.
J Chem Phys ; 138(23): 234310, 2013 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-23802963

RESUMO

Carbon 1s photoelectron spectra for 2-butyne (CH3C≡CCH3) measured in the photon energy range from threshold to 150 eV above threshold show oscillations in the intensity ratio C2,3/C1,4. Similar oscillations have been seen in chloroethanes, where the effect has been attributed to EXAFS-type scattering from the substituent chlorine atoms. In 2-butyne, however, there is no high-Z atom to provide a scattering center and, hence, oscillations of the magnitude observed are surprising. The results have been analyzed in terms of two different theoretical models: a density-functional model with B-spline atom-centered functions to represent the continuum electrons and a multiple-scattering model using muffin-tin potentials to represent the scattering centers. Both methods give a reasonable description of the energy dependence of the intensity ratios.


Assuntos
Carbono/química , Elétrons , Íons/química , Espectroscopia Fotoeletrônica , Fótons , Espalhamento de Radiação
19.
Arch Esp Urol ; 65(9): 834-6, 2012 Nov.
Artigo em Inglês, Espanhol | MEDLINE | ID: mdl-23154608

RESUMO

OBJECTIVE: Bladder injuries are quite rare and complex complications of transobturator tapes in the treatment of female stress urinary incontinence, with very few published cases. The authors present a case report and discuss possible injury mechanisms and the role of cystoscopy in this setting. METHODS: A 51 year-old female with past surgical history of Burch colposuspension underwent an uneventful transobturator tape surgery. After 15 days, she complained of dysuria and frequency. Cystoscopy revealed the tape protruding within the bladder. RESULTS: Reoperation was performed with the sub-urethral segment of the tape removed by vaginal approach and the vesical one excised endoscopically. Presently, the patient is asymptomatic. CONCLUSIONS: In patients with previous incontinence surgical treatments, cystoscopy at the time of surgery should be considered to exclude and treat eventual injuries, in order to avoid future complications.


Assuntos
Complicações Pós-Operatórias/terapia , Slings Suburetrais/efeitos adversos , Fita Cirúrgica/efeitos adversos , Bexiga Urinária/lesões , Cistoscopia , Feminino , Humanos , Pessoa de Meia-Idade , Reoperação , Bexiga Urinária/patologia , Incontinência Urinária por Estresse/cirurgia , Procedimentos Cirúrgicos Urológicos
20.
Arch. esp. urol. (Ed. impr.) ; 65(9): 834-836, nov. 2012. ilus
Artigo em Espanhol | IBECS | ID: ibc-106530

RESUMO

OBJETIVO: La lesión vesical es una complicación bastante compleja y rara de la banda transobturatriz en el tratamiento de la incontinencia urinaria de esfuerzo femenina, con muy pocos casos publicados en la literatura. Los autores presentan un caso y discuten el posible mecanismo de la lesión y el papel de la cistoscopia en este contexto. MÉTODO: Paciente de 51 años, previamente tratada por colposuspensión de Burch, que fue sometida a colocación de banda transobturatriz sin complicaciones. Quince días después desarrolló disuria y polaquiuria. La cistoscopia mostró la banda colocada a nivel intravesical. RESULTADO: Fue realizada re-intervención con la parte suburetral de la banda retirada por abordaje vaginal y la parte vesical restante seccionada con una pinza por vía endoscópica. Actualmente está asintomática. CONCLUSIÓN: En pacientes con tratamientos quirúrgicos previos de incontinencia, la cistoscopia peroperatoria debe ser considerada para excluir y tratar lesiones del tracto urinario inferior, para evitar futuras complicaciones(AU)


OBJECTIVE: Bladder injuries are quite rare and complex complications of transobturator tapes in the treatment of female stress urinary incontinence, with very few published cases. The authors present a case report and discuss possible injury mechanisms and the role of cystoscopy in this setting. METHODS: A 51 year-old female with past surgical history of Burch colposuspension underwent an uneventful transobturator tape surgery. After 15 days, she complained of dysuria and frequency. Cystoscopy revealed the tape protruding within the bladder. RESULTS: Reoperation was performed with the sub-urethral segment of the tape removed by vaginal approach and the vesical one excised endoscopically. Presently, the patient is asymptomatic. CONCLUSIONS: In patients with previous incontinence surgical treatments, cystoscopy at the time of surgery should be considered to exclude and treat eventual injuries, in order to avoid future complications(AU)


Assuntos
Humanos , Feminino , Pessoa de Meia-Idade , Incontinência Urinária/cirurgia , Bexiga Urinária/lesões , Bandas de Matriz , Cistoscopia , Doença Iatrogênica
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