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P Salvador

Publications and source records attributed to P Salvador.

At least 19 recordsLinked to original sources
PubMed2006

A general efficient implementation of the BSSE-free SCF and MP2 methods based on the chemical Hamiltonian approach.

We describe some details related to a new, general, and efficient implementation of the BSSE-free SCF and second-order Møller-Plesset perturbation theories of intermolecular interactions, based on the "Chemical Hamiltonian Approach" (CHA). The program is applicable for both open-shell and closed-shell systems and for an arbitrary number of interacting subsystems. With the new program the CHA method is faster than the usual "counterpoise correction" scheme for single point calculations, especially for clusters consisting of several molecules. The numerical results provided by these conceptually different schemes, however, have again found to be very close to each other. The CHA scheme is particularly good for providing truly BSSE-free MP2 data for intermolecular potentials.

Journal Article↗
PubMed2005

Illumination intensity dependence of the photovoltage in nanostructured TiO2 dye-sensitized solar cells.

The open-circuit voltage (V(oc)) dependence on the illumination intensity (phi0) under steady-state conditions in both bare and coated (blocked) nanostructured TiO2 dye-sensitized solar cells (DSSCs) is analyzed. This analysis is based on a recently reported model [Bisquert, J.; Zaban, A.; Salvador, P. J. Phys. Chem. B 2002, 106, 8774] which describes the rate of interfacial electron transfer from the conduction band of TiO2 to acceptor electrolyte levels (recombination). The model involves two possible mechanisms: (1) direct, isoenergetic electron injection from the conduction band and (2) a two-step process involving inelastic electron trapping by band-gap surface states and subsequent isoenergetic transfer of trapped electrons to electrolyte levels. By considering the variation of V(oc) over a wide range of illumination intensities (10(10) < phi0 < 10(16) cm(-2) s(-1)), three major regions with different values of dV(oc)/d phi0 can be distinguished and interpreted. At the lower illumination intensities, recombination mainly involves localized band-gap, deep traps at about 0.6 eV below the conduction band edge; at intermediate photon fluxes, recombination is apparently controlled by a tail of shallow traps, while, for high enough phi0 values, conduction band states control the recombination process. The high phi0 region is characterized by a slope of dV(oc)/d log phi0 congruent with 60 mV, which indicates a recombination of first order in the free electron concentration. The study, which was extended to different solar cells, shows that the energy of the deep traps seems to be an intrinsic property of the nanostructured TiO2 material, while their concentration and also the density ([symbol: see text]t approximately 10(18)-10(19) cm(-3)) and distribution of shallow traps, which strongly affects the shape of the V(oc) vs phi0 curves, change from sample to sample and are quite sensitive to the electrode preparation. The influence of the back-reaction of electrons from the fluorine-doped tin oxide (FTO) conducting glass substrate with electrolyte tri-iodide ions on the V(oc) vs phi0 dependence characteristic of the DSSC is analyzed. It is concluded that this back-reaction route can be neglected, even at low light intensities, when its rate (exchange current density, j0), which can vary over 4 orders of magnitude depending on the type of FTO used, is low enough (j0 < or = 10(-8)A cm(-2)). The comparison of V(oc) vs phi0 measurements corresponding to different DSSCs with and without blocking of the FTO-electrolyte contact supports this conclusion.

Journal Article↗
PubMed2005

Experimental evidence of a UV light-induced long-range electric field in nanostructured TiO2 thin films in contact with aqueous electrolytes.

Nanostructured TiO(2) thin-film electrodes of controlled thickness were obtained by immobilization of TiO(2) powder (Degussa P25) on SnO(2):F (FTO)-coated glasses by electrophoresis. The photocurrent-potential characteristics of the electrodes in contact with an indifferent aqueous electrolyte, for both front--and backside UV illumination, show the existence of a macroscopic electric field in the electrode region near the FTO substrate. This electric field, which is only photoinduced in the presence of water (it does not appear in TiO(2) dye-sensitized solar cells under visible illumination), apparently disappears when an efficient hole scavenger, like methanol, is added to the aqueous electrolyte. It is attributed to a nonhomogeneous spatial accumulation of photogenerated holes at surface-bound OH radicals resulting from the photooxidation of chemisorbed water molecules. The influence of film thickness and UV illumination mode (front- and backside) on the photoinduced electric field is analyzed by solving the transport equations for diffusion and drift of electrons.

Journal Article↗
PubMed2004

Influence of traffic on the PM10 and PM2.5 urban aerosol fractions in Madrid (Spain).

A preliminary assessment carried out in Madrid demonstrates the difficulty of compliance with the new European PM(10) tolerances. Daily and annual limiting values would be exceeded at almost all the network stations under the terms of the directive's second stage. An experimental study, based on the chemical characterisation of the PM(10) and PM(2.5) fractions sampled at a representative urban site, provides the major mass contents of these two fractions. These are mainly related to two different particle sources: combustion processes including traffic emissions and mineral-origin particles. Nonmineral carbon is the major component of particulate matter in this region, mostly in the PM(2.5) fraction, increasing its contribution in wintertime. The second largest component identified in the PM(10) mass, is associated with crustal origin particles and is more relevant in summer, whereas the second largest contributor to PM(2.5) is secondary particles. In general, PM(10) and PM(2.5) concentrations show good agreement with traffic-related pollutants, such as nitrogen oxides and CO, being time-correlated in winter pollution episodes. PM(1) and PM(2.5) have been simultaneous and continuously measured indicating road transport as the main source of these finer fractions. Mineral contribution has been mainly identified in the coarser particles associated with dust resuspension and some long-range transport events of Saharan dust, although they are also present in the finer PM(2.5) fraction.

Journal Article↗
PubMed2004

Levels of particulate matter in rural, urban and industrial sites in Spain.

This paper summarises the results of a series of studies on the interpretation of time series of levels of total suspended particles (TSP) and particulate matter (PM, <10 microm) in six regions of Spain in the period 1996-2000. In addition to the local pollution events, high PM10 episodes are recorded during African dust outbreaks, regional atmospheric recirculation events (mainly in spring to autumn), and to a lesser extent, under the influence of European and Mediterranean long range transported air masses. The lowest PM10 levels are usually recorded under Atlantic air mass advective conditions. All these regional and large-scale processes account for the relatively high PM10 levels recorded in regional background stations in Spain. Thus, the PM10 levels recorded at EMEP (Cooperative Program for Monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe) regional background stations between March 2001 and March 2002 are very close to the annual limit value proposed for 2010 by the EU Air Quality Directive 1999/30/CE. Chemical data obtained for the different monitoring stations during 2001 show a high mineral load in PM10 for most of the study sites in Spain. Furthermore, a high marine aerosol load is evidenced in the Canary Islands. These mineral and marine loads are lower when considering PM2.5, but a relatively high proportion (8-21%) of mineral dust is still present.

Journal Article↗
PubMed2004

Second-order Møller-Plesset perturbation theory without basis set superposition error. II. Open-shell systems.

The basis set superposition error-free second-order Møller-Plesset perturbation theory of intermolecular interactions, based on the "chemical Hamiltonian approach," which has been introduced in Part I, is applied here to open-shell systems by using a new, effective computer realization. The results of the numerical examples considered (CH(4) em leader HO, NO em leader HF) showed again the perfect performance of the method. Striking agreement has again been found with the results of the a posteriori counterpoise correction (CP) scheme in the case of large, well-balanced basis sets, which is also in agreement with a most recent formal theoretical analysis. The difficulties of the CP correction in open-shell systems are also discussed.

Journal Article↗
PubMed2004

Energy partitioning for "fuzzy" atoms.

The total energy of a molecule is presented as a sum of one- and two-atomic energy components in terms of "fuzzy" atoms, i.e., such divisions of the three-dimensional physical space into atomic regions in which the regions assigned to the individual atoms have no sharp boundaries but exhibit a continuous transition from one to another. By proper definitions the energy components are on the chemical energy scale. The method is realized by using Becke's integration scheme and weight function permitting very effective numerical integrations.

Journal Article↗
PubMed2001

Rabbit tissue distribution of 3H-ouabain by digital radioautography.

3H-ouabain is useful to evaluate the tissue localization of Na,K-ATPase. In this work we determined the distribution of 3H-ouabain in rabbit tissue by digital radioautography. Using this method, we were able to obtain a comparison of various organs in a relatively short time (6.5 days), while with traditional radioautography, only the kidney was detectable after seven months of film exposure. The kidney has the highest intensity (concentration of 3H-ouabain), followed by the heart, liver, muscle, lung, spleen and finally brain, which was almost undetectable. In kidney the activity was higher in the cortex, while the other tissues displayed a more uniform intensity, suggesting that Na,K-ATPase was evenly distributed.

Animals↗
PubMed1998

Subjects with obstructive pulmonary disease tend to be chronically vasodilated.

1. In 12 unselected outpatients with chronic obstructive pulmonary disease and six controls, arterial pH, PaO2, PaCO2 and oxygen saturation (SaO2), forced expiratory volume in 1.0 s (FEV1.0) and vital capacity were measured. Subjects were grouped into those with or without obstruction based on the Tiffenau index. The Baseline Dyspnoea Index was employed to objectify the severity of dyspnoea and the Borg index to evaluate the subjective sensation. Blood pressure was measured with a sphygmomanometer; calf arterial flow both at rest and during reactive hyperaemia with a plethysmograph. Basal and minimal resistance were calculated.2.FEV1.0 was 26% lower in patients with obstruction than in controls, and was also lower in patients with moderate-to-severe obstruction compared with those with mild or no obstruction. Arterial flow (75% greater in the patients with obstruction) progressively increased with increasing severity of obstruction, being 54% higher in those with mild obstruction than in those with no obstruction (P<0.001), and 28% higher in moderate-severe than in mild obstruction (P<0.005). In multiple regressions, F correlated inversely with FEV1.0, PaO2 and SaO2, and directly with PaCO2. Basal resistance correlated positively with FEV1.0, SaO2 and the Tiffenau index, and inversely with PaCO2 (r=-0.52, P=0.02). Minimal resistance was significantly lower in obstructed than in non-obstructed subjects. Both basal and minimal resistance progressively decreased, although insignificantly, with worsening bronchial obstruction. PaCO2 did not correlate with any haemodynamic parameter. Borg index correlated indirectly with FEV1.0 and basal resistance directly with arterial flow.3. Patients with chronic obstructive pulmonary disease therefore tend to show chronic vasodilatation depending on hypoxia rather than PaCO2. Other mechanisms could be involved in this phenomenon. The Borg index is a good indicator of oxygen desaturation and vasodilatation.

Aged↗
PubMed1990

Stability of somatostatin in total parenteral nutrition.

The stability of somatostatin, added to a total parenteral nutrition formula, in glass containers and in plastic ethylene vinyl acetate containers was investigated. The somatostatin concentration decreased immediately from 3 micrograms/ml to 0.3-0.6 micrograms/ml after addition to the emulsion. In spite of this rapid decrease, somatostatin concentrations remained stable with values of 0.4-0.7 micrograms/ml during the follow-up period (24 h). These findings could be explained assuming adsorption to the surface of the container.

Drug Packaging↗
PubMed1989

Stability of famotidine 20 and 40 mg/L in total nutrient admixtures.

The stability of famotidine in two types of total nutrient admixtures (TNAs), one containing 5% intravenous fat emulsion of long-chain triglycerides and the other, of medium- and long-chain triglycerides, was studied. The TNAs, which contained lipids, glucose, amino acids, electrolytes, vitamins, and trace elements, were prepared aseptically in ethylene-vinyl acetate containers. Famotidine 40 mg was added to both types of TNAs and famotidine 80 mg was added to both types to yield concentrations of 20 and 40 mg/L (expressed hereafter as micrograms per milliliter), respectively. A control solution was prepared for each type of TNA. Samples were removed at 0, 12, 24, 48, and 72 hours for measurement of pH and of famotidine concentration by high-performance liquid chromatography; the solutions were visually inspected for color changes, creaming, and formation of precipitates. Particle size distributions were measured at 72 hours and compared with those for the control solutions at time zero. No appreciable changes in pH occurred over 72 hours, and no physicochemical changes were observed. Famotidine 20 and 40 micrograms/mL was stable for at least 72 hours in both types of TNAs. There was no variation in particle size distribution. Famotidine appears to be stable for up to 72 hours at room temperature in the TNAs studied, and it appears not to alter the integrity of the two lipid emulsions.

Chemical Phenomena↗
PubMed1988

Effective salvage therapy for lymphoma with cisplatin in combination with high-dose Ara-C and dexamethasone (DHAP).

Ninety patients with progressive recurrent lymphoma were treated with a combination of cisplatin 100 mg/m2 intravenously (IV) by continuous infusion over 24 hours, followed by cytosine arabinoside in two pulses each at a dose of 2 g/m2 given 12 hours apart. Dexamethasone, 40 mg orally or IV, was given on days 1 through 4. Vigorous hydration was reinforced by routine use of mannitol. Treatments were repeated at 3- to 4-week intervals for six to ten courses. Most patients had not achieved complete remission (CR) with prior therapies, which included Adriamycin (all patients) and methotrexate and VP-16 (58 patients). Median patient age was 55 years. Intermediate-grade lymphoma was the most frequent pathologic diagnosis. Seven patients died within two weeks of therapy; of the remaining 83 patients, 28 (34%) or 31% if all patients are considered, achieved CR, and 22 (26.5%) achieved partial remission (PR). Response was evident after the first two cycles of chemotherapy and appeared to be independent of the histopathologic type of lymphoma. To date, only eight of the complete responders have relapsed at a median follow-up of 11 months. The overall 2-year survival in 25%. Further analysis showed that patients with low tumor burden and normal lactic acid dehydrogenase (LDH) had a high CR response rate (67%) and a survival rate of 61% at 2 years. In contrast, patients with both high tumor burden and elevated serum LDH levels had a negligible CR rate, and only 5% are surviving at 1 year. Patients with either high tumor burden with normal LDH or low tumor burden with elevated LDH had an intermediate survival. Myelosuppression-related infection was the most frequent serious complication of this regimen (31%) and the cause of death of ten patients. Acute lysis syndrome was also observed in five patients with high tumor burden and was the cause of death in three of these patients. DHAP has proven to be an effective non-crossresistant regimen for patients with relapsing or refractory lymphoma, particularly for patients who have favorable prognostic characteristics.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1987

MIME chemotherapy (methyl-GAG, ifosfamide, methotrexate, etoposide) as treatment for recurrent Hodgkin's disease.

Forty-seven patients with Hodgkin's disease in relapse were treated with MIME combination chemotherapy (methyl-GAG, ifosfamide, methotrexate, etoposide). All patients had previously received nitrogen mustard, vincristine, prednisone, procarbazine (MOPP) or similar regimens and doxorubicin-containing combinations, and many had received extensive irradiation. Complete remission (CR) occurred in 23%, and was influenced by presence of extranodal disease, hemoglobin, lactic dehydrogenase (LDH), and number of prior relapses. Median survival for all patients was 50 weeks, and was affected adversely by the presence of extranodal disease and the number of prior relapses. Toxicity was significant, including infections (23%), neutropenic fever (34%), and hemorrhagic cystitis (23%), but was related in part to the extent of prior therapy. These results with this novel chemotherapy program in heavily pretreated patients suggest that MIME should be studied in less extensively treated patients and considered as a part of treatment programs for patients with Hodgkin's disease in first relapse.

Adolescent↗
PubMed1985

Aggressive non-Hodgkin's lymphomas in immunocompromised homosexual males.

During the period from 1981 through 1984, 14 immunocompromised homosexual males with intermediate or high-grade non-Hodgkin's lymphoma were seen at University of Texas M.D. Anderson Hospital and Tumor Institute. Six patients had diffuse large-cell lymphoma, seven had diffuse undifferentiated lymphoma, and one had unclassifiable lymphoma that suggested large-cell lymphoma. Eight patients had the acquired immunodeficiency syndrome (AIDS) and five had the AIDS-related complex. Kaposi's sarcoma was initially present in four patients and developed later in two others. The patients with diffuse large-cell lymphoma were characterized by more severely altered immune parameters, multicentric brain mass lesions, pretherapy opportunistic infections, lower performance status, poor response to therapy, and death in all within six months. The undifferentiated lymphoma group had preceding generalized reactive lymphadenopathy, less severe immune dysfunction, and excellent response to combination chemotherapy, with survival time greater than 19 months in three patients. Twelve of the patients had extranodal sites of lymphoma at presentation. There is a definite trend for the development of aggressive non-Hodgkin's lymphomas with unusual sites of extranodal involvement in immunocompromised homosexual males, with the potential for good tolerance to combination chemotherapy and improved survival in the subgroup without severe concomitant opportunistic infections.

Abscess↗
PubMed1983

Clinical pharmacology of ceftriaxone in patients with neoplastic disease.

Pharmacological studies of ceftriaxone, a new semisynthetic cephalosporin, were conducted in 35 cancer patients. This antibiotic was administered in a variety of doses and schedules with no observed toxicity. Intramuscular administration of 500 mg of ceftriaxone to seven patients produced mean peak serum concentrations of 32.9 mug/ml 2.0 h after administration. The terminal serum half-life was 10.9 h. Intravenous infusion of 500 mg of ceftriaxone over 5 min to the same group of seven patients produced a mean peak concentration of the drug in serum of 83 mug/ml at the end of administration which decreased to 16.8 mug/ml at 8 h. A dose of 1 g of ceftriaxone given in identical fashion to the same group of seven patients produced mean peak concentrations in serum of 130 mug/ml at the end of administration and 17.3 mug/ml at 12 h. The mean percentages of drug recovered in urine 12 h after single intravenous doses of 500 mg and 1 g were 30 and 20%, respectively. A 1-g dose of ceftriaxone was administered every 8 h to 10 patients, and a 2-g dose was administered every 12 hours to 9 patients. Drug concentrations in serum were measured for each patient after drug administration on day 1, day 3 or 4, and day 7 or 8. The 1-g dose produced an observed mean peak concentration of 154 mug/ml and a mean terminal-phase half-life of 5.6 h on day 3 or 4. The 2-g dose produced a mean peak concentration in serum of 262 mug/ml and a terminal-phase serum half-life of 6.3 h on day 3 or 4. Continuous infusion studies were performed in nine neutropenic patients for up to 8 days by using a loading dose of 1 g over 30 min, followed by 2 g every 8 h. Mean concentrations in serum were maintained at about 135 mug/ml during the infusion period.

Bacterial Infections↗