The Special Case of the Spectral Emission of a Tb3+ Mono Metal Complex.

The fine structure in the spectral lines of the visible fluorescence of Tb3+ complexes are replaced by a single peak in the case of a singular molecular complex Tb(H3 PTC)3 , where H4 PTC represents perylene-3,4,9,10-tetracarboxylic acid, and its emission wavelength depends on the film thickness. This single peak challenges the old creed that the f-orbital electrons of Tb3+ are always protected from the influence of the surrounding atoms. We perform density functional theory calculations to show that the wavefunction of the ground state is localized and in addition, spin-polarized, and this facilitates fluorescent transitions under UV to the first excited state instead of the fundamental state. We discuss the possibility of making a spintronic device with the molecule, Tb(H3 PTC)3 .

All-perylene-derivative for white light emitting diodes.

An organic-based bright white light emitting compound, namely Tb(H3PTC)3 [H4PTC = perylene-3,4,9,10-tetracarboxylic acid], able to be used as part of a white diode and as a part of a RGB system that can withstand high temperatures (∼700 K), is developed using perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and terbium(iii) nitrate pentahydrate as precursors by hydrothermal synthesis. Using PTCDA as the red emitter and the new derivative of it, Tb(H3PTC)3, as the blue-green emitter, along with a common deep blue LED can form a RGB system for display technologies, around room temperature. Temperature-dependent photoluminescence properties of the Tb(H3PTC)3 compound are also investigated for the involved excitonic-emission processes and the respective recombination lifetimes. The terbium(iii) complex was prepared using a procedure that is reproducible, easily modifiable, inexpensive, and environmentally friendly, opening new pathways for its large-scale applications. Unlike PTCDA, Tb(H3PTC)3 has been shown to be soluble in N-methyl-2-pyrrolidone (NMP) as well as in dilute aqueous solutions of this organic solvent in a straightforward procedure. The light emission properties are intimately correlated with the molecular structure and electronic properties of Tb(H3PTC)3 elucidated by experimental results of X-ray Absorption Near Edge Spectroscopy (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and Density Functional Theory (DFT) calculations. A bright fluorescence yield is attained with a small amount of material either in solution or in solid form showing its potential to be used in state-of-the-art organic optoelectronic devices.

Interfacial exciplex formation in bilayers of conjugated polymers.

The donor-acceptor interactions in sequential bilayer and blend films are investigated. Steady-state and time-resolved photoluminescence (PL) were measured to characterize the samples at different geometries of photoluminescence collection. At standard excitation, with the laser incidence at 45° of the normal direction of the sample surface, a band related to the aggregate states of donor molecules appears for both blend and bilayer at around 540 nm. For the PL spectra acquired from the edge of the bilayer, with the laser incidence made at normal direction of the sample surface (90° geometry), a new featureless band emission, red-shifted from donor and acceptor emission regions was observed and assigned as the emission from interfacial exciplex states. The conformational complexity coming from donor/acceptor interactions at the heterojunction interface of the bilayer is at the origin of this interfacial exciplex emission.

Long range energy transfer in conjugated polymer sequential bilayers.

Steady-state and time-resolved photoluminescence have been used to investigate the optical properties of bilayer and blend films made from poly(9,9-dioctyl-fluorene-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH PPV). Energy transfer has been observed in both systems. From steady-state photoluminescence measurements, the energy transfer was characterized by the effective enhancement of the MEH PPV emission intensity after exciting the donor states. Relatively faster decays for the PFO donor emission have been observed in the blends as well as in the bilayer structures, confirming effective energy transfer in both structures. In contrast to the bilayers, the time decay of the acceptor emission in the blends presents a long decay component, which was assigned to the exciplex formation in these samples. For the blends the acceptor emission is in fact a composition of exciplex and MEH PPV emissions, the later being due to Förster energy transfer from PFO. In the bilayers, the exciplex is not observed and temperature dependence photoluminescence measurements show that exciton migration has no significant contribution to the energy transfer. The efficiency and very long range of the energy transfer in the bilayers is explained assuming a surface-surface interaction geometry where the donor/acceptor distances involved are much longer than the common Förster radius.

Parallel generation of extensive vascular networks with application to an archetypal human kidney model.

Given the relevance of the inextricable coupling between microcirculation and physiology, and the relation to organ function and disease progression, the construction of synthetic vascular networks for mathematical modelling and computer simulation is becoming an increasingly broad field of research. Building vascular networks that mimic in vivo morphometry is feasible through algorithms such as constrained constructive optimization (CCO) and variations. Nevertheless, these methods are limited by the maximum number of vessels to be generated due to the whole network update required at each vessel addition. In this work, we propose a CCO-based approach endowed with a domain decomposition strategy to concurrently create vascular networks. The performance of this approach is evaluated by analysing the agreement with the sequentially generated networks and studying the scalability when building vascular networks up to 200 000 vascular segments. Finally, we apply our method to vascularize a highly complex geometry corresponding to the cortex of a prototypical human kidney. The technique presented in this work enables the automatic generation of extensive vascular networks, removing the limitation from previous works. Thus, we can extend vascular networks (e.g. obtained from medical images) to pre-arteriolar level, yielding patient-specific whole-organ vascular models with an unprecedented level of detail.

Growth kinetics of CdTe colloidal nanocrystals.

The growth kinetics of CdTe colloidal nanocrystals has been analyzed quantitatively by means of dynamic light scattering and photoluminescence measurements. The growth rates, size distributions, critical radii, and diffusion constants have been calculated in the framework of the Sugimoto theoretical model. A two-step diffusion-controlled growth regime has been proposed for the reported synthesis and a set of relations for the time evolution of the size distribution has been derived and discussed in the sense of the size distribution focusing concept.

Electric force microscopy investigation of a MEH-PPV conjugated polymer blend: robustness or frailty?

Electric force microscopy (EFM) was employed in the electrical characterization of a blend of thermoplastic polyurethane (TPU) and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) conjugated polymer. Although qualitative EFM interpretation is straightforward, its quantitative analysis always relies on approximated models. The extraction of physically reasonable parameters is normally assumed as a proof of validity of the theoretical model employed. In order to gather information about electric properties of this blend and to test the EFM technique itself, two distinct and discordant models were developed in this work to fit experimental EFM data. Even though MEH-PPV is regarded as a conductor in one model and as a dielectric in the other, both models yielded coherent and reasonable electrical properties for this blend. Such unexpected results are used to discuss the robustness or frailty of EFM in the analysis of complex materials.

STM-electroluminescence from clustered C3N4 nanodomains synthesized via green chemistry process.

A Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and synchrotron X-ray diffraction study on clustered C3N4 nanoparticles (nanoflakes) is conducted on green-chemistry synthesized samples obtained from chitosan through high power sonication. Morphological aspects and the electronic characteristics are investigated. The observed bandgap of the nanoflakes reveals the presence of different phases in the material. Combining STM morphology, STS spectra and X-ray diffraction (XRD) results one finds that the most abundant phase is graphitic C3N4. A high density of defects is inferred from the XRD measurements. Additionally, STM-electroluminescence (STMEL) is detected in C3N4 nanoflakes deposited on a gold substrate. The tunneling current creates photons that are three times more energetic than the tunneling electrons of the STM sample. We ponder about the two most probable models to explain the observed photon emission energy: either a nonlinear optical phenomenon or a localized state emission.

Nanowires and nanoribbons formed by methylphosphonic acid.

The production and physical properties of nanowires and nanoribbons formed by methylphosphonic acid (MPA)--CH3PO(OH)2--were investigated. These structures are formed on an aluminum coated substrate when immersed in an ethanolic solution of MPA for several days. A careful investigation of the growth conditions resulted in a narrow window of solution concentrations and temperatures for the successful development of nanowires and nanoribbons. Several different techniques were employed to characterize these nanostructures: (1) Photoluminescence experiments showed a strong emission at 2.3 eV (green), which is visible to the naked eye; (2) X-ray diffraction experiments indicated a significant cristalinity, in agreement with atomic force microscopy (AFM) and transmission electron microscopy (TEM) morphology images, which show organized nano-scale wires and ribbons, (furthermore, AFM-Phase and TEM images also suggest that nanoribbons are formed by well-aligned nanowires); (3) Conductive-AFM experiments revealed an intermediary conductivity for these structures (10(-1)/Ohm x m), which is similar to some intrinsic semiconductors and; (4) finally, Infrared, Raman, and X-Ray Photoelectron Spectroscopies produced information about the contents, structure, and composition of both wires and ribbons.

Maternal adaptations for fetal growth in young malnourished rats.

Carcass composition and serum free fatty acids were determined in young (45 days old) control and malnourished (25 and 6% protein diet, respectively) pregnant and nonpregnant rats. Pregnant rats were sacrificed shortly after parturition and nonpregnant rats on the 22nd day of experiment. Carcass fat content increased in control pregnant rats. This alteration was not seen in the pregnant malnourished rats. Serum free fatty acids and pup birth weight were lower for malnourished than for control mothers. No significant difference was observed in carcass protein of Na+ and K+ content among rats of all groups. These data appear to indicate that the inability to accumulate fat in the carcass and the preservation of carcass protein at nonpregnant levels during pregnancy may be important factors involved in the genesis of the low birth weight seen in the pups of young malnourished rats, presumably reducing the availability of nutrient supplies for fetal growth.

Effects of protein-calorie malnutrition on endocrine pancreatic function in young pregnant rats.

Oral glucose tolerance test (GTT), insulin secretion after oral glucose load and the insulin to glucose ratio (I/G) during GTT were measured in young (45-50 days old) pregnant and non-pregnant rats fed a normal (25%) or low (6%) protein diet during pregnancy or for a 22-day period. Fasting blood glucose was lower in protein-deficient rats and basal plasma insulin was higher in pregnant control rats than in non-pregnant controls. Protein-deficient rats were intolerant to the oral glucose load. The I/G ratio during GTT was higher in control pregnant rats than in other rats. These results show that young malnourished pregnant rats are glucose intolerant and do not show pregnancy hyperinsulinemia probably as a result of decreased pancreatic capacity to release insulin in response to stimulation.

Effects of Walker 256 carcinoma on metabolic alterations during the evolution of pregnancy.

The control of pregnant cancer patients is difficult because it involves both mother and fetus, and the metabolic alterations in the cancer host induce a massive mobilization of nutrients diverted to the neoplastic cells. The purpose of the present study was to determine the evolution of the Walker 256 carcinoma in pregnant rats and its consequences on fetal development. The results showed that the tumors displayed a very rapid rate of growth and induced a reduction in fetal weights in the pregnant tumor-bearing rats. The tumor-bearing and pregnant tumor-bearing groups showed a decrease in blood glucose and total serum protein, suggesting an increase in energy utilization of these substrates and synthetic activity by the tumoral cells. An imbalance between protein synthesis and catabolism may occur in the tumor-bearing rats which may be related to the degree of nutritional depletion.

Effect of Walker 256 tumor growth on intestinal absorption of leucine, methionine and glucose in newly weaned and mature rats.

In tumor-bearing rats, most of the serum amino acids are used for synthesis and oxidation processes by the neoplastic tissue. In the present study, the effect of Walker 256 carcinoma growth on the intestinal absorption of leucine, methionine and glucose was investigated in newly weaned and mature rats. Food intake and carcass weight were decreased in newly weaned (NT) and mature (MT) rats bearing Walker 256 tumor in comparison with control animals (NC and MC). The tumor/carcass weight ratio was higher in NT than in MT rats, whereas nitrogen balance was significantly decreased in both as compared to control animals. Glucose absorption was significantly reduced in MT rats (MT = 47.3 +/- 4.9 vs MC = 99.8 +/- 5.3 nmol min-1 cm-1, Kruskal-Wallis test, P < 0.05) but this fact did not hamper the evolution of cancer. There was a significant increase in methionine absorption in both groups (NT = 4.2 +/- 0.3 and MT = 2.0 +/- 0.1 vs NC = 3.7 +/- 0.1 and MC = 1.2 +/- 0.2 nmol min-1 cm-1, Kruskal-Wallis test, P < 0.05), whereas leucine absorption was increased only in young tumor-bearing rats (NT = 8.6 +/- 0.2 vs NC = 7.7 +/- 0.4 nmol min-1 cm-1, Kruskal-Wallis test, P < 0.05), suggesting that these metabolites are being used for synthesis and oxidation processes by the neoplastic cells, which might ensure their rapid proliferation especially in NT rats.

A leucine-supplemented diet improved protein content of skeletal muscle in young tumor-bearing rats.

Cancer cachexia induces host protein wastage but the mechanisms are poorly understood. Branched-chain amino acids play a regulatory role in the modulation of both protein synthesis and degradation in host tissues. Leucine, an important amino acid in skeletal muscle, is higher oxidized in tumor-bearing animals. A leucine-supplemented diet was used to analyze the effects of Walker 256 tumor growth on body composition in young weanling Wistar rats divided into two main dietary groups: normal diet (N, 18% protein) and leucine-rich diet (L, 15% protein plus 3% leucine), which were further subdivided into control (N or L) or tumor-bearing (W or LW) subgroups. After 12 days, the animals were sacrificed and their carcass analyzed. The tumor-bearing groups showed a decrease in body weight and fat content. Lean carcass mass was lower in the W and LW groups (W = 19.9 0.6, LW = 23.1 1.0 g vs N = 29.4 1.3, L = 28.1 1.9 g, P < 0.05). Tumor weight was similar in both tumor-bearing groups fed either diet. Western blot analysis showed that myosin protein content in gastrocnemius muscle was reduced in tumor-bearing animals (W = 0.234 0.033 vs LW = 0.598 0.036, N = 0.623 0.062, L = 0.697 0.065 arbitrary intensity, P < 0.05). Despite accelerated tumor growth, LW animals exhibited a smaller reduction in lean carcass mass and muscle myosin maintenance, suggesting that excess leucine in the diet could counteract, at least in part, the high host protein wasting in weanling tumor-bearing rats.

Protein-calorie malnutrition in the young pregnant rat: factors involved in fetal growth impairment.

Factors involved in fetal growth retardation as seen in pups of protein-deprived young rats are examined. Young (50 to 55-day old) and adult (90 to 100-day old) rats were fed a diet of low (6%) or normal (25%) protein content during pregnancy. Dams and neonates were killed soon after parturition. Young malnourished dams showed a significant reduction in circulating glucose levels while their pups had significantly lower birth weights and circulating glucose and insulin levels than those of young control mothers. Such alterations were not seen in adult animals. Maternal malnutrition did not affect circulating levels of thyroxine in the neonates. These data indicate that maternal hypoglycemia may play an important role in determining blood glucose and insulin reduction and, consequently, the low birth weight seen in pups of young malnourished rats.

Influence of protein-calorie malnutrition on reproductive performance of young and mature rats.

The effect on reproduction and fetal growth of a protein-deficient diet administration during pregnancy was studied in young and adult rats. Young (50-55 days old) and adult (90-100 days old) pregnant or nonpregnant rats were fed a normal diet (25% protein) or a protein-deficient diet (6% protein) during pregnancy or for a 22-day period (nonpregnant rats). All females were weighed during the experiment and body length measured in the young rats. After parturition, pups were counted, sexed and individually weighed. Litter size, number of stillbirths and presence of body lesions in the neonates were also recorded. Alimentary protein deficiency caused reduction in weight gain during pregnancy and in the postpartum period in young and adult rats. Pups from protein deficient dams weighed less at birth than the pups of control dams, although litter size was unaltered. Pups from young malnourished dams tended to weigh less than those from adult malnourished dams. The incidence of stillbirths was higher in malnourished rats, the highest values occurring in the adult group. These results suggest that alimentary protein deficiency during pregnancy in young rats reduces maternal weight gain, presumably reducing nutrient storage. This may cause fetal/maternal competition for nutrients leading to retardation of both maternal and fetal growth. Growth impairment may be an adaptive process, assuring fetal survival.

Measurement of interchain and intrachain exciton hopping barriers in luminescent polymer.

The integrated photoluminescence intensity in thin films of 'Super Yellow' copolymer has been analyzed using a Mott-like temperature dependence. This has enabled us to observe contributions from two emission channels, indicative of exciton recombination proceeding from two distinct origins. At high temperature, interchain thermally activated exciton energy transfer and migration dominates, resulting in large scale quenching of the integrated emission intensity and hence the photoluminescence quantum yield. However, at relatively low temperature, an additional increase of the integrated emission intensity occurs. This new channel of emission has been attributed to recombination from excitons where intrachain exciton energy transfer between adjacent subunits of the copolymer backbone becomes hindered. The activation energy barriers that control both of these emission channels have been obtained and are correlated with chain backbone degrees of freedom.

Identification of the optically active vibrational modes in the photoluminescence of MEH-PPV films.

The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2(')-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang-Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang-Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.

Permeability parameters of the toad isolated stratum corneum.

A technique for isolating the stratum corneum from the subjacent layers of the epithelium was developed which permits studying the stratum corneum as an isolated membrane mounted between half-chambers. The method basically consists of an osmotic shock induced by immersing a piece of skin in distilled water at 50 degrees C for 2 min. When the membrane is bathed on each surface by NaCl-Ringer's solution, its electrical resistance is 14.1 +/- 1.3 omega cm2 (n=10). This value is about 1/100 of the whole skin resistance in the presence of the same solution. The hydraulic filtration coefficient (Lp) measured by a hydrostatic pressure method, with identical solutions on each side of the membrane, is 8.8 X 10(-5) +/- 1.5 X 10(-5) cm sec-1 atm-1 (n=10) in distilled water and 9.2 X 10(-5) +/- 1.4 X 10(-5) cm sec-1 atm-1 (n=10) in NaCl-Ringer's solution. These values are not statistically different and are within the range of 1/80 to 1/120 of the whole skin Lp. The stratum corneum shows an amphoteric character when studied by KCl diffusion potentials at different pH'S. The membrane presents an isoelectric pH of 4.6 +/- 0.3 (n=10). Above the isoelectric pH the potassium transport number is higher than the chloride transport number; below it, the reverse situation is valid. Divalent cations (Ca++ or Cu++) reduce membrane ionic discrimination when the membrane is negatively charged and are ineffective when the membrane fixed charges are protonated at low pH.