The acidic stability of chemically modified 1-D nanomaterials synthesized by alkali hydrothermal method was evaluated. The results suggested that either ion-exchanged cations or structurally inserted metals can affect the acidic stability of these materials. Moreover, acidic aging of 1-D titanate nanomaterials turned out to be an interesting route for synthesizing TiO2 nanoparticles whose crystal structure (anatase and/or rutile) can be controlled by chemical modification of the titanate precursor. In 1998 Kasuga et al [1] reported an innovative method for the production of TiO2-derived 1-D nanomaterials (nanotubes and nanowires) by a hydrothermal alkali treatment without using any templates. This simple softchemistry synthesis method motivated intensive research in the recent years. Structural and chemical fundamental studies on this class of materials pointed out that these 1-D nanometric forms actually present layered titanate crystal structure with the general formula A2TinO2n+1 .nH2O, where A is a positively charged cation, usually Na and/or H, sited, commonly together with water molecules, within the interlayers in order to fulfill charge balance with the negatively charged layers. Such a layered crystal structure allied with nanometric dimensions of these 1-D forms opens path for chemically controlled modifications of physical properties through exchange of interlayer cations. These materials show promise for applications such as hydrogen sensors, adsorbents, photocatalysts, mesoporous catalyst supports, solar cell photosensitizers, ion-exchange materials, new generation electrodes for lithium batteries and electrocatalysts. In many of these applications, titanate 1-D nanomaterials can be exposed to chemically aggressive media. Therefore, in the present work we studied the effect of chemical modifications of these nanomaterials on their stability in acidic aqueous suspension. Two chemical modification approaches were used: ion exchange of Na with different cations and also the introduction of Zr partially substituting for Ti in the structure, when using rutile sand as the precursor, which contains ZrSiO4 as an impurity. The 1-D nanomaterials were hydrothermally synthesized from a 10M NaOH solution using commercial anatase and natural rutile sand as TiO2 precursors. The as-synthesized Na rich product obtained from anatase was ion-exchanged with H, Co and Fe. Each product was submitted to acidic aging in a 0.1M solution of sulfuric acid during 28 days. The samples, before and after acidic aging, were analyzed by X-ray diffraction and transmission electron microscopy. After acidic aging the samples transformed partially or completely into anatase and/or rutile nanoparticles. The sample obtained using natural rutile sand as precursor showed the best stability (fig.1) followed by the sample ion exchanged with Fe, both only partially converted to rutile nanoparticles. All the other samples completely transformed into TiO2 nanoparticles after acidic treatment. The treatment of H rich titanate resulted mainly in anatase nanoparticles (fig. 2) with a smaller amount of rutile nanoparticles while Na and Co samples resulted only in rutile nanoparticles. These results suggested that chemical modification of 1-D titanates nanomaterials affects the acidic stability of these materials. The replacement of Ti in the structure (in this case by Zr) was more effective than the ion-exchange of interlayer cations. Moreover, the acidic aging of 1-D titanate nanomaterials was found to be a promising route for synthesizing TiO2 nanoparticles whose crystal size and structure (anatase and/or rutile) can be controlled by managing chemical modifications on the as-synthesized sodium titanate precursor. [1] Kasuga, T., Hiramatsu, M., Hoson, A., Sekino, T., Niihara, K., Langmuir 14 (1998) 3160. a b c

BaTi3O7·nH2O nanotubes have been synthesized through a hydrothermal reaction between Na-rich trititanate nanotubes and Ba(OH)2 within the pH range 12–8.2. These nanotubes possess the same layered crystal structure of the precursor Na2−xHxTi3O7·nH2O. They also keep the morphology of their precursor Na-trititanate nanotubes used in the synthesis, having an external diameter of 20–25nm. The BaTi3O7·nH2O nanotubes remained fully stable up to 300°C, while nanotubular form continues to exist up to 600°C, together with amorphous particles.

Thick large-area particle or X-ray detectors suffer degradation during operation due to creation of defects that act as deep traps. Measuring the photocurrent under homogeneously absorbed weak light can monitor variation in detector performance. We describe how photocapacitance can be used as an alternative method to measure the creation of defects and their energy level after intense irradiation with protons or He ions at 1.5 MeV and after exposure to intense laser pulses. The possibility to detect small areas of high defect density in a large-area detector structure is discussed. (C) 2008 Elsevier B.V. All rights reserved.

ZnO shows a number of similarities with other wide gap semiconductor materials as, e.g., GaN as far as photoluminescence and photoconductivity are concerned. Depending on film quality a broad luminescence band is found in the yellow and/or green spectral region apart from a narrow excitonic line. This study focuses on the observation of non-exponential photoinduced carrier density decay in ZnO.We have deposited thin polycrystalline ZnO films on sapphire by a cyclic pulsed laser deposition process. We extracted a room temperature band gap of 3.31 eV from absorption spectroscopy measurements, and found evidence for strong sub gap Urbach tails.Photocurrent transients were measured upon pulsed laser excitation at 532 and 266 run and compared with transient microwave conductivity decay upon excitation at 355 run. Both measurements yield powerlaw decay with an exponent from -0.3 to -0.4. In addition, ps-pulses were used to monitor the initial photoluminescence decay near the bandgap.We have already observed similar power-law behaviour in polycrystalline GaN films prepared by the same PLD reactor. The interpretation will consider the hypothesis of minority carrier capture and a model invoking thermalization in broad band tail distribution with delayed subsequent recombination during the decay. (c) 2007 Elsevier Ltd. All rights reserved.

We have exposed MOCVD-grown GaN films to a 1 nA beam of 1.5 MeV He-4(+) particles produced by the van de Graaff accelerator in the Portuguese nuclear facility at Sacavem. The material quality was tested by measuring dark conductivity and steady-state as well as transient photoconductivity at room temperature in coplanar layout. Photocurrent spectra taken below the band gap reveal a broad defect density-of-states distribution. After 5 ns laser pulses from a frequency-doubled Nd:YAG laser the induced photocurrent shows a very slow decay over several orders of magnitude. Compared to the decrease in photosensitivity in thin undoped a-Si:H films under He irradiation - a decrease surprisingly similar to c-Si - we observe that degradation of GaN also sets in at about 10(12) cm(-2), but decreases much more slowly as indicated by the smaller negative power-law exponent in the photocurrent-fluence plot. After about 3 x 10(15) cm(-2) the mobility-lifetime-product decreased by half an order of magnitude. This indicates a much higher radiation resistance of GaN when compared to amorphous or crystalline Si. (C) 2007 Elsevier B.V. All rights reserved.

The accessibility in aluminas considered to be representative of matrices used in FCC resid catalysts, with mean pore sizes between 64 and 201 A, was characterized through a kinetic approach by means of the conversion of 1,3,5-tri-isopropylbenzene (TIPB) at 500 degrees C in a CREC Riser Simulator fluidized bed laboratory reactor. The product distribution was essentially the same as that observed on an equilibrium commercial FCC catalyst, but the activity of the aluminas was much lower. The main products (propylene, benzene, isopropylbenzene, di-isopropylbenzenes) showed that a series cracking mechanism prevailed in the conversion of TIPB. The apparent first order kinetic constants assessed and the conversion profiles allowed establishing a ranking of activities that could be associated directly to accessibilities and not to the number of acid sites (Lewis nature), which was proportional to the specific surface area of the alumina. The sequence of accessibilities followed the same trend as the mean pore size of the aluminas. (c) 2006 Elsevier B.V. All rights reserved.

We report radiation effects on intrinsic a-Si:H thin films subjected to a 1.5MeV He4 beam for particle fluences up to 1016cm−2. Photothermal deflection spectroscopy is used to obtain information on the sub-gap density of states. Photoconductivity detects changes in the μτ-product of the electrons. Steady-state photocarrier grating technique is used for measuring the ambipolar diffusion length and estimating the hole μτ-product. The 1.5MeV He4 beam radiation results in pronounced changes in the a-Si:H absorption spectrum. Optical absorption due to deep defects increases with particle fluence by more than one order of magnitude. Electronic transport properties consistently degrade with increasing particle fluence and correlate with the density of radiation-induced defects.

Despite the fact that the concept of sheet-flow in the pulmonary microcirculation of mammals was introduced more than three decades ago, the capillary circulatory model still prevails in the physiological literature. Since cardiac output is identical in the systemic and in pulmonary circulations, it is noteworthy that in the former, the resulting arterial pressure is five times higher than that of the latter, which means that the corresponding microcirculations must be radically different. The present study addresses this problem from both morphological and physiological perspectives.

included an article by R. F. Nespolo with a very unusual title: " New invariants and dimensionless numbers: futile renaissance of old fallacies? " This paper contains a rather ranting criticism of our paper " Homeostasis and heterostasis: from invariant to dimensionless numbers " (Biol. Res. 36: 211-221, 2003), and therefore we are obliged to respond to Nespolo's comments in detail. A) GENERAL OBJECTIONS Our disagreements with Nespolo's commentary begin with the title. What are the so-called " old fallacies " that he refers to? He fails to clearly identify them. Furthermore, we believe that the concept of " new invariant numbers " does not infer a " renaissance of old fallacies, " but rather the addition of new aspects of current research. It is commonly known that dimensionless and invariant numbers can be obtained by that finally yield " pure " numbers. Moreover, an invariant number simply means devoid of physical dimensions (M 0 L 0 T 0), while dimensionless numbers can maintain a significant dependence on body mass, a fact that can be exemplified by " residual mass exponents. " From this perspective, an invariant number should be a constant, although in Charnov's words, " how constant is constant enough to be considered invariant is worthy of much thought " (1993, p: 5). As is well known, some " invariant " numbers can be obtained by combining universal constants, although the numerical values of these universal constants are experimentally determined and subject to statistical variations. The different values obtained for these universal constants can lead to significant contributions in cosmology, such as the prediction of the existence of innumerable parallel universes (Barrow and Webb, 2005). From this perspective, the matter of dimensionless or invariant numbers is not a " fallacy, " and therefore " not futile. " The subject of dimensionless and invariant numbers is currently an active field of investigation, and certainly not restricted to physics. For example, the " Handbook of Physics and Chemistry, " features several hundred dimensionless groups with applications in modern engineering (Weast, 1983). The biological sciences also include many contributions in When Buckhingham's theorem is used to calculate dimensionless numbers from a set of dimensional variables, dimensionless parameters that are independent of body mass are obtained first and their ratio is not only dimensionless, but also independent of body mass. In this sense, they are considered invariant numbers as well as dimensionless …

A wide spectrum of cyclic functions in terrestrial mammals of different size, from the 3-gram shrew to the 3-ton elephant, yields an allometric exponent around 0.25, which is correlated--as a kind of common denominator--with the specific metabolic rate. Furthermore, the applicability of these empirical findings could be extrapolated to chronological events in the sub-cellular realm. On the other hand, the succession of growth periods (T98%) until sexual maturity is reached also follows the 1/4 power rule. By means of Verhulst's logistic equation, it has been possible to simulate three different biological conditions, which means that by modifying the numerical value of only one parameter, revertible physiological and pathological states can be obtained, as for instance isostasis, homeostasis and heterostasis.

The energetic metabolism and its relationship with body weight generated a vivid controversy, since the Rubner's surface law was introduced into biology. Recently, the multifactor theory (Darveau et al) has caused again a revival of this polemic topic. Moreover, the investigations concerning metabolism and body weight include all terrestrial mammals, from the shrew (3 grams) to the elephant (three tons). The corresponding allometric exponent for standard metabolic rate, both theoretical and empirical, fluctuates around an average value of 0.75, in contrast with the surface law, which postulated a value of 0.67. The "metabolic range" (rest vs maximal exercise) does vary from 1 to 10, due to the prevalent influence of the skeletal muscle activity. Recent investigations have emphasized the fact that the allometric exponent is not unique (0.75), but it should be subjected to statistical variability, both in standard and in maximal exercise.

The purpose of this study was to characterize time-frequency behavior using the Continuous Wavelet Transform (CWT) and Fast Fourier Transform (FFT) to analyze ventricular and arterial pressure signals from anesthetized mongrel dogs. Both ventricular and arterial pressure pulsations were recorded using catheter-tip manometers and the CWT was applied to these signals to obtain module coefficients, associated contours, and the 3-D representation of these modules. FFT was applied to obtain the Fourier spectrum. The mathematical analysis of the cardiovascular pressure pulsations permitted the identification of the evolution of the frequency components for the aortic and pulmonary valve functions as well as the intra-ventricular and respiratory influences on the cardiovascular dynamics. The CWT is a very sensitive and reliable procedure for determining the three-dimensional (time-frequency-amplitude) of the oscillatory phenomena during each cardiac cycle, providing more, although complementary, information than the spectral analysis obtained with the FFT. Thanks to the FFT, exact values in Hz could be found for the different events produced in each cycle, and thus the information provided by CWT could be related to the information provided by FFT. The combination of both mathematical methodologies permitted identification of each component of the analyzed signals. The 3D representation allowed an easy comparison of the relative importance of the complex magnitudes in frequency for the different components of the pulsatile waves.

Light-soaking and annealing effects on majority and minority carrier properties in undoped a-Si:H and simultaneous changes in subgap optical absorption are investigated. Subgap absorption was obtained by constant photocurrent method (CPM). Electron mobility–lifetime product was deduced from photoconductivity. Hole mobility–lifetime product was estimated from measurements of ambipolar diffusion length by steady state photocarrier grating technique (SSPG). Hysteresis-like behaviour is found in the relationship between mobility–lifetime products of electrons and holes during photodegradation and isothermal annealing which is a signature of distinct evolutions of the gap-states density along the different sections of the metastability cycle. Analysis of changes of the sub-gap absorption coefficient at different photon energies and numerical simulations with a recombination model suggest the consideration of two species of metastable states with different sensitivities to light-exposure and annealing.

In contrast with classical physics, particularly with Sir Isaac Newton, where time is a continuous function, generally valid, eternally and evenly flowing as an absolute time dimension, in the biological sciences, time is in essence of cyclical nature (physiological periodicities), where future passes to past through an infinitely thin boundary, the present. In addition, the duration of the present (DP) leads to the so-called 'granulation of time' in living beings, so that by the fusion of two successive pictures of the world, which are not entirely similar, they attain the perception of 'movement,' both in the real world as well as in the sham-movement in the mass media (TV).

The aim of the present study was to compare two different biological similarity criteria, one was based on body mass (M) as a theoretical reference system in accordance with the MLT-system of physics, while the other utilized the body weight (W) for the same purpose. The mass-dependent allometry should be applied during space flights as well as during fetal and newborn conditions of life, whereas the weight-dependence should prevail in earth-bound physiology. The above mentioned distinctions are relevant not only for the specific metabolic rates but also for numerous biological time functions, as for instance for the heart and respiratory rates of all mammals, whose allometric exponent is b = 0.09 during fetal life, and b = 0.25 in all adult specimens.

In the present paper we have examined the applicability of dimensionless and invariant numbers (DN & IN) to the analysis of the cardiovascular system of mammals, whose functions were measured at standard metabolic conditions. The calculated IN did not change when we compared these figures with those obtained in dogs while they were submitted to graded exercise on a treadmill. In both instances, rest and exercise, the constancy of the IN prevailed, in accordance with Cannon's principle of "homeostasis" (1929). On the contrary, when dogs were examined during a standardized hypovolemic shock, we observed a breakdown of the IN, and the resulting DN evolved as a reliable index of the condition of "heterostasis" as defined by H. Selye. The robustness of the homeostatic regulations is based on high-gain integral feedback mechanisms, while "heterostasis" could be associated with low-gain integral feedback processes, when organisms are submitted to unitary step disturbances or to changes of the set-point at the entrance of the feedback loop.

In an earlier study, Gunga et al. (1999) determined body size and body volume distribution by photogrammetry in sauropods from the Upper Jurassic in Tendaguru (Tanzania, East Africa). Specifically, they found a body mass of about 74400 kg for a specimen of Brachiosaurus brancai. By means of dimensional analysis and a theory of biological similarity, moreover, it was possible to estimate the numerical value of the allometric exponent (b = −0.17) for gravitational tolerance (Gmax) of animals living on earth, which changes with the body mass. This theoretical exponent is close to Economos' empirical finding (b = −0.14). Our results show that there remains an unsolved contradiction between the theoretical assumptions for Gmax for the body mass of the largest fully terrestrial animals. In einer vorangehenden Studie (Gunga et al. 1999) wurde mit Hilfe der Photogrammetrie die Körpermassen und Körpervolumenverteilung von jurassischen Sauropoden aus Tendaguru (Tansania, Ostafrika) ermittelt. Diese Bestimmungen ergaben für Brachiosaurus brancai eine Körpermasse von von ca. 74400 kg. Weitere Studien aus der vergleichenden Physiologie haben gezeigt, dass die Toleranz bei Schwerkraftbelastung (Gmax) mit der Körpermasse variert. Durch dimensionale Analyse und vergleichende Studien konnte ein allometrischer Exponent für die Toleranz bei Schwerkraftbelastung mit b = −0.17 für terrestrische Organismen bestimmt werden. Dieser theoretische Exponent kommt den empirischen Befunden von Economos (b = −0.14) nahe. Dennoch weisen diese vorliegenden Berechnungen damit auf einen Widerspruch bei den bislang vorhandenen theoretischen Überlegungen zur Gmax bei den grössten maximalen Körpermassen für terrestrisch lebende Organismen hin. doi:10.1002/mmng.20020050115

A study on undoped a-Si:H of the light-soaking/annealing process of majority as well as minority carrier properties and their relations to defect density is presented. Defect density was measured by the constant photocurrent method (CPM), electron mobility–lifetime product was deduced from photoconductivity and hole mobility–lifetime product was obtained from measurements of ambipolar diffusion length by steady-state photocarrier grating technique (SSPG). We confirm the already known hysteresis behaviour in the dependence of electron mobility–lifetime product on defect density, and report a new and opposite hysteresis-like dependence of the hole mobility–lifetime product during the light-soaking/annealing process. The changes in the mobility–lifetime products of both carriers and concomitant changes in the defect density and in the Fermi level are discussed on the basis of recombination kinetics and structural order effects.

From four empirical allometric equations concerning the dynamics of the respiratory functions of mammals, it has been possible to obtain an invariant and dimensionless number after applying Buckingham's π-theorem. In the present study, this invariant number (INR), whose origin was interspecies comparisons in mammals of different sizes, was assayed with the aim to compare in a quantitative manner the possible difference between newborn and adult mammals. The results were compared with the predicted values from two theories of biological similarity, one mass-dependent, valid for newborns, and the other, weight-dependent, valid for adult mammals. Finally, we utilized Stahl's residual mass exponents (RME) to test the validity of the empirical and theoretical approaches.

Photoinduced optical absorption in thin films of hydrogenated amorphous silicon (a-Si:H) is studied over the energy range related to electronic transitions involving the silicon dangling-bond defects, by using the dual-beam Constant Photocurrent Method (CPM). The subgap absorption in the range 0.8–1.4eV is observed to increase with bias light intensity. Since CPM measures only transitions contributing to the photocurrent, the subgap absorption spectrum in undoped a-Si:H is dominated by transitions between singly occupied D0 or doubly occupied D− defect states and conduction band extended states. The photoinduced changes in the subgap absorption are consistent with numerical calculations with a recombination model for a-Si:H which yield dangling bond electronic occupations as a function of photogeneration rate. The results suggest that the observed changes in the optical absorption spectra are mainly determined by changes in the occupation of defects induced by the bias-light.