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Luis Seijo

Publications and source records attributed to Luis Seijo.

13 recordsLinked to original sources
PubMed2006

The 5f2-->5f16d1 absorption spectrum of Cs2GeF6:U4+ crystals: A quantum chemical and experimental study.

Single crystals of U(4+)-doped Cs2GeF6 with 1% U4+ concentration have been obtained by the modified Bridgman-Stockbarger method in spite of the large difference in ionic radii between Ge4+ and U4+ in octahedral coordination. Their UV absorption spectrum has been recorded at 7 K, between 190 and 350 nm; it consists of a first broad and intense band peaking at about 38,000 cm(-1) followed by a number of broad bands of lower intensity from 39,000 to 45,000 cm(-1). None of the bands observed shows appreciable fine vibronic structure, so that the energies of experimental electronic origins cannot be deduced and the assignment of the experimental spectrum using empirical methods based on crystal field theory cannot be attempted. Alternatively, the profile of the absorption spectrum has been obtained theoretically using the U-F bond lengths and totally symmetric vibrational frequencies of the ground 5f2 - 1A(1g) and 5f16d(t(2g))1 - iT(1u) excited states, their energy differences, and their corresponding electric dipole transition moments calculated using the relativistic ab initio model potential embedded cluster method. The calculations suggest that the observed bands are associated with the lowest five 5f2 - 1A(1g)-->5f16d(t(2g))1 - iT(1u) (i = 1-5) dipole allowed electronic origins and their vibrational progressions. In particular, the first broad and intense band peaking at about 38,000 cm(-1) can be safely assigned to the 0-0 and 0-1 members of the a(1g) progression of the 5f2 - 1A(1g)-->5f16d(t(2g))1 - 1T(1u) electronic origin. The electronic structure of all the states with main configurational character 5f16d(t(2g))1 has been calculated as well. The results show that the lowest crystal level of this manifold is 5f16d(t(2g))1 - 1E(u) and lies about 6200 cm(-1) above the 5f2 level closest in energy, which amounts to some 11 vibrational quanta. This large energy gap could result in low nonradiative decay and efficient UV emission, which suggest the interest of investigating further this new material as a potential UV solid state laser.

Journal Article↗
PubMed2006

Theoretical study of the effects of F to Cl chemical substitution on the electronic structure and the luminescence properties of Cs2GeF6:Os4+ and Cs2ZrCl6:Os4+ materials.

It has been experimentally determined that Cs2ZrCl6:Os4+ shows luminescence and up-converted luminescence from the highest t(2g) (4) excited level 2 A1g(1A1g), whereas Cs2GeF6:Os4+ 2 A1g(1A1g) does not luminescence at all. Ab initio quantum chemical calculations on these materials are presented here and show that the variation of the energy gap between the t2g 4 and t2g 3 eg 1 manifolds with F to Cl chemical substitution is a key factor to interpret the experimental findings. This energy gap is calculated to be some 1500 cm(-1) (approximately 2nua1g) in the fluoride host, whereas it is about 3300 cm(-1) (approximately 9nua1g) in the chloride host. The calculated values for the ground state totally symmetric vibrational frequency nu(a1g) are 626 cm(-1) (Cs2GeF6:Os4+) and 355 cm(-1) (Cs2ZrCl6:Os4+), in good agreement with the available experimental data. Geometrical structure of (OsX6)2- clusters (X=F,Cl) embedded in Cs2GeF6 and Cs2ZrCl6 lattices is calculated as well. New assignments for some spectral features based in the results of our calculations are proposed.

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PubMed2006

[Outpatient management of malignant pleural effusion using a tunneled pleural catheter: Preliminary experience].

Inpatient management of malignant pleural effusion includes the placement of a conventional thoracostomy tube for drainage and talc slurry pleurodesis and/or a surgical approach consisting of video-assisted thoracoscopic talc insufflation. Both techniques require prolonged hospital stays of up to 1 week. Unfortunately, life expectancy in patients with this disease does not usually exceed 6 months, and so the primary aim of any palliative intervention intended to improve quality of life should be to avoid hospital admissions and to relieve pain as far as possible. Of the few outpatient alternatives to hospital management the most frequently used is repeated thoracentesis. We describe the outpatient management of malignant pleural effusion by placement of a tunneled pleural catheter in a patient with stage IIIB lung adenocarcinoma. In our opinion, the use of this catheter offers a viable alternative to conventional therapy and is better tolerated.

Aged↗
PubMed2005

Quantum chemical study of 4f-->5d excitations of trivalent lanthanide ions doped in the cubic elpasolite Cs2NaYCl6. Ce3+ to Tb3+.

Wave-function-based ab initio calculations on the lowest states of the 4f(n),4f(n-1)5d(t2g)1, and 4f(n-1)5d(e(g))1 configurations of (LnCl6)3- clusters (Ln=Ce to Tb) embedded in the cubic elpasolite Cs2NaYCl6 have been performed, in an attempt to contribute to a comprehensive understanding of the 4f-->5d excitations of lanthanide ions in crystals. Reliable data are provided on the changes of bond lengths and breathing mode vibrational frequencies upon 4f-->5d(t2g) and 4f-->5d(e(g)) excitations, as well as on minimum-to-minimum and vertical absorption and emission transitions, and on the Stokes shifts. The available experimental data are discussed and predictions are made. The stabilization of the 4f-->5d(baricenter) excitation of the doped ions with respect to the 4f-->5d excitations of the free ions, which is a key variable for the understanding of these excitations in solid hosts, is analyzed and found to be due, in two-thirds, to dynamic ligand correlation effects and, in one-third, to orbital relaxation, charge transfer, and covalency effects present in a mean-field approximation.

Journal Article↗
PubMed2005

Juvenile rheumatoid arthritis and bronchiolitis obliterans organized pneumonia.

Diverse pleuropulmonary manifestations, including pleural effusion, rheumatoid nodulosis, fibrosis, obliterans brochiolitis, bronchiectasias, vasculitis, drug-induced lung disease, and obliterans bronchiolitis with organized pneumonia, have been described in patients with rheumatoid arthritis (RA). Bronchiolitis obliterans organized pneumonia (BOOP) is an uncommon condition described in patients with RA but not in juvenile RA (JRA). We described a patient with JRA who developed a BOOP.

Adult↗
PubMed2005

5f-->5f transitions of U4+ ions in high-field, octahedral fluoride coordination: the Cs2GeF6:U4+ crystal.

The U-F bond length, totally symmetric vibrational frequency, and 5f(2) energy levels of the Cs(2)GeF(6):U(4+) crystal are predicted through quantum-chemical calculations on the embedded (UF(6))(2-) cluster. The U(4+) ions substitute for much smaller Ge(4+) retaining octahedral site symmetry, which is useful to interpret the electronic transitions. The structure of the 5f(2) manifold: its energy range, the crystal splitting of the 5f(2) levels, their parentage with free-ion levels, and the energy gaps appearing within the manifold, is presented and discussed, which allows to suggest which are the possible 5f(2) luminescent levels. The effects of Cl-to-F chemical substitution are discussed by comparison with isostructural Cs(2)ZrCl(6):U(4+). The energy range of the 5f(2) manifold increases by some 6000 cm(-1) and all levels shift to higher energies, but the shift is not uniform, so that noticeable changes of order are observed from Cs(2)ZrCl(6):U(4+) to Cs(2)GeF(6):U(4+). The comparison also reveals that the green-to-blue up-conversion luminescence, which has been experimentally detected and theoretically discussed on Cs(2)ZrCl(6):U(4+), is quenched in the fluoride host. The results of the Cs(2)GeF(6):U(4+) are used as a high-symmetry model to try to understand why efficient radiative cascade emissions in the visible do not occur for charged U(4+) defects in low-symmetry YF(3) crystals. The results presented here suggest that theoretical and experimental investigations of 4f5f ions doped in octahedral, high-symmetry fluoride crystals may be conducted even when the mismatch of ionic radii between the lanthanide/actinide ions and the substituted cations of the host is considerably large. Investigations of these new materials should reveal interesting spectroscopic features without the difficulties associated with more commonly used low-symmetry fluoride hosts.

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PubMed2005

Prediction of pressure-induced redshift of f1-->d(t2g)1 excitations in Cs2NaYCl6:Ce3+ and its connection with bond-length shortening.

Quantum chemical calculations including embedding, scalar relativistic, and dynamic electron correlation effects on Cs(2)NaYCl(6):(CeCl(6))(3-) embedded clusters predict (i) redshifts of the f(1)-->d(t(2g))(1) transition with pressure and (ii) bond-length shortening upon f-->d(t(2g)) excitation. Both effects are found to be connected which suggests that new high-pressure spectroscopic experiments could reveal the sign of the bond-length change.

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PubMed2005

Early lung cancer detection using spiral computed tomography and positron emission tomography.

RATIONALE: Lung cancer screening using computed tomography (CT) is effective in detecting lung cancer in early stages. Concerns regarding false-positive rates and unnecessary invasive procedures have been raised. OBJECTIVE: To study the efficiency of a lung cancer protocol using spiral CT and F-18-fluorodeoxyglucose positron emission tomography (FDG-PET). METHODS: High-risk individuals underwent screening with annual spiral CTs. Follow-up CTs were done for noncalcified nodules of 5 mm or greater, and FDG-PET was done for nodules 10 mm or larger or smaller (> 7 mm), growing nodules. RESULTS: A total of 911 individuals completed a baseline CT study and 424 had at least one annual follow-up study. Of the former, 14% had noncalcified nodules of 5 mm or larger, and 3.6% had nodules of 10 mm or larger. Eleven non-small cell lung cancers (NSCLC) and one small cell lung cancer (SCLC) were diagnosed in the baseline study (prevalence rate, 1.32%), and two NSCLCs in the annual study (incidence rate, 0.47%). All NSCLCs (92% of prevalence cancers) were diagnosed in stage I (12 stage IA, 1 stage IB). FDG-PET was helpful for the correct diagnosis in 19 of 25 indeterminate nodules. The sensitivity, specificity, positive predictive value, and negative predictive value of FDG-PET for the diagnosis of malignancy were 69, 91, 90, and 71%, respectively. However, the sensitivity and negative predictive value of the screening algorithm, which included a 3-month follow-up CT for nodules with a negative FDG-PET, was 100%. CONCLUSION: A protocol for early lung cancer detection using spiral CT and FDG-PET is useful and may minimize unnecessary invasive procedures for benign lesions.

Adult↗
PubMed2004

Parallel, linear-scaling building-block and embedding method based on localized orbitals and orbital-specific basis sets.

We present a linear scaling method for the energy minimization step of semiempirical and first-principles Hartree-Fock and Kohn-Sham calculations. It is based on the self-consistent calculation of the optimum localized orbitals of any localization method of choice and on the use of orbital-specific basis sets. The full set of localized orbitals of a large molecule is seen as an orbital mosaic where each tessera is made of only a few of them. The orbital tesserae are computed out of a set of embedded cluster pseudoeigenvalue coupled equations which are solved in a building-block self-consistent fashion. In each iteration, the embedded cluster equations are solved independently of each other and, as a result, the method is parallel at a high level of the calculation. In addition to full system calculations, the method enables to perform simpler, much less demanding embedded cluster calculations, where only a fraction of the localized molecular orbitals are variational while the rest is frozen, taking advantage of the transferability of the localized orbitals of a given localization method between similar molecules. Monitoring single point energy calculations of large poly(ethylene oxide) molecules and three dimensional carbon monoxide clusters using an extended Huckel Hamiltonian are presented.

Journal Article↗
PubMed2004

Use of the Dumon Y-stent in the management of malignant disease involving the carina: a retrospective review of 86 patients.

OBJECTIVE: To study the efficacy of symptom relief and the safety of the Dumon Y-stent for central airway obstruction in malignant main carinal involvement and in malignant tracheoesophageal fistulas. DESIGN: A retrospective review. SETTING: Thoracic endoscopy referral center. PATIENTS AND METHODS: The medical records of 86 patients who had undergone the placement of a Dumon Y-stent at our institution were reviewed and analyzed. RESULTS: Ninety Dumon Y-stents were placed in 86 patients to relieve symptoms of dyspnea, cough, and/or hemoptysis. Four of these patients required removal of that stent and replacement with a longer Dumon Y-stent due to tumor progression. There were only two instances of procedure-related adverse effects, which included coughing following stent placement lasting 1 week in one patient and stent migration in another patient. In the case of stent migration, the stent required immediate removal, and the patient experienced no adverse consequences. The remaining patients tolerated the stent well, and all experienced subjective symptomatic relief. There were no stent-related deaths. The average duration of a stent after placement was 133 days. The median time of survival following stent insertion was 181 days. Forty-five percent of all patients died at 3 months, and 72% died at 6 months. CONCLUSION: The Dumon Y-stent proved to be useful and was well-tolerated in the management of malignant disease involving the main carina. It also provided successful palliation in patients with malignant tracheoesophageal fistulas.

Adult↗
PubMed2003

Absorption and emission spectra of Ce3+ in elpasolite lattices.

The experimental determination of the electronic energy levels for Ce(3+) in some chloroelpasolite hosts for both the ground 4f(1) and the excited 5d(1) configurations is described. High-resolution f-f absorption and f-(2)T(2g) d absorption and emission spectra have been recorded at low temperatures for Ce(3+) diluted into various hexachloroelpasolite lattices. A fluorescence spectrum at approximately 50 000 cm(-1) is tentatively assigned to the emission from the highest 5d crystal field level, (2)E(g), of a Ce(3+) impurity in Cs(2)NaErCl(6), enabling the values of all the energy levels of both the 4f(1) and 5d(1) configurations to be given for Ce(3+) in elpasolite hosts. Vibronic structure superimposed on the electronic transitions is analyzed in terms of a simple configurational coordinate model involving the ground and excited configurations. It is found that the difference in the Ce-Cl bond length between the 4f(1) and 5d(1) configurations is approximately 0.04 A. Ab initio model potential calculations on the (CeCl(6))(3-) cluster embedded in a reliable representation of the Cs(2)NaYCl(6) host support these conclusions.

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PubMedDate not supplied

Outpatient management of malignant pleural effusions with small-bore, tunneled pleural catheters.

BACKGROUND: Malignant pleural effusions (MPEs) can produce significant respiratory symptoms and diminished quality of life in patients with terminal malignancies. Control of MPEs to palliate respiratory symptoms can be performed via several different approaches. Ideally, a minimally invasive procedure to control MPEs and to provide relief of respiratory symptoms would be optimal. OBJECTIVE: To ascertain if control of MPEs can be achieved by outpatient management via a small-bore pleural catheter (PC) without the need for sclerosing agents. METHODS: Retrospective chart analysis of 24 patients after outpatient insertion of PCs for recurrent, symptomatic MPEs followed by frequent home drainage of pleural fluid to relieve respiratory symptoms. RESULTS: Symptomatic relief of respiratory symptoms was achieved in 100% of patients, while pleurodesis was achieved in 58% of patients in a mean of 39 days. Five patients (6 PCs) expired with the catheters in place. In these patients, all catheters remained in position and functional until the patients ultimately died from nonpleural disease progression. No major complications occurred during insertion of the catheter. Late complications included localized cellulitis and bacterial superinfection in three patients and tumor growth at the catheter site in one patient. CONCLUSIONS: The PCs used in the present study provided an effective modality not only to alleviate respiratory symptoms associated with MPE, but also to achieve pleurodesis in 58% of our patients. These catheters may provide a significantly less invasive outpatient approach to the palliative management of MPEs.

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