Hard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ...ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live mussels for 15 cycles at ∼79% of their predicted strength (critically fracturing 46% of shells), then allowing the survivors 0, 1, 2 or 4 weeks to repair. Immediately after fatigue loading, mussel shells were 20% weaker than control shells that had not experienced repetitive loading. However, mussels restored full shell strength within 1 week, and after 4 weeks shells that had experienced greater fatiguing forces were stronger than those repetitively loaded at lower forces. Microscopy supported the hypothesis that crack propagation is a mechanism of fatigue-caused weakening. However, the mechanism of repair was only partially explained, as epifluorescence microscopy of calcein staining for shell deposition showed that only half of the mussels that experienced repetitive loading had initiated direct repair via shell growth around fractures. Our findings document repair weeks to months faster than demonstrated in other mollusks. This rapid repair may be important for the mussels' success contending with predatory and environmental threats in the harsh environment of wave-swept rocky coasts, allowing them to address non-critical but weakening damage and to initiate plastic changes to shell strength. We highlight the significant insight gained by studying biological armors not as static structures but, instead, as dynamic systems that accumulate, repair and respond to damage.
The Male Warrior Hypothesis (MWH) establishes that men's psychology has been shaped by inter-group competition to acquire and protect reproductive resources. In this context, sex-specific selective ...pressures would have favored cooperation with the members of one's group in combination with hostility towards outsiders. We investigate the role of developmental testosterone, as measured indirectly through static markers of prenatal testosterone (2D:4D digit ratio) and pubertal testosterone (body musculature and facial masculinity), on both cooperation and aggressive behavior in the context of intergroup conflict among men. Supporting the MWH, our results show that the intergroup conflict scenario promotes cooperation within group members and aggression toward outgroup members. Regarding the hormonal underpinnings of this phenomenon, we find that body musculature is positively associated with aggression and cooperation, but only for cooperation when context (inter-group competition) is taken into account. Finally, we did not find evidence that the formidability of the group affected individual rates of aggression or cooperation, controlling for individual characteristics.
•Thin films of high crystalline quality were obtained by chemical bath deposition.•Polycrystalline thin films obtained using ammonia nitrate as complexing agent.•Galena and Lanarkite phases were ...obtained using polyethyleneimine complexing agent.•The thin films of chemical-bath-deposition lead sulphide present quantum confinement.
This work presents the structural characterisation of PbS nanofilms deposited by the chemical bath deposition technique at 70±2 °C using Polyethyleneimine, Triethanolamine and Ammonium nitrate as complexing agents, which allow a controlled and constant ion by ion reaction in aqueous medium whose chemical bath reactions take place in basic solutions with typical pH values 9–12, distinguishing the complexes obtained by their thermodynamic stability and kinetic stability. The PbS fundamental stretching frequencies were determined by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy gives the relative atomic composition and identification of the most intense photoelectron transitions S2p (164 eV) and Pb4f 7/2 (137.34 eV) for the PbS-Nitrate film, which are associated with the Pb (II) oxidation state. The shift to higher binding energies, Pb4f7/2 (139.01 eV) for PbS-Polyethyleneimine and PbS-Triethanolamine show the presence of PbO2 with oxidation state Pb (IV). X-ray diffraction analysis and Raman spectroscopy reveal that PbS deposited nanofilms had pure cubic galena crystalline phase when ammonium nitrate was used as complexing agent, with the Polyethyleneimine complexing agent, the formation of cubic PbS in cubic phase with monoclinic Lanarkite Pb2(SO4)2 traces were observed. Finally, using Triethanolamine as complexing agent, cubic phase PbS with orthorhombic Anglesite and lead oxide (x∼1.57) traces were found. The surface morphology of the samples was obtained by High Resolution Transmission Electron Microscopy. The thin films show three direct band gaps, around 0.77–0.78 and 0.84–0.88 eV belonged to the mid-trap state caused by –Pb dangling bond and S+2 levels and the band gap energy at 0.91–1.10 eV was attributed to the quantum confinement associated to grain size, which were obtained by transmittance.
► SBA-16 substrate modified with 1wt.% of P is an efficient support for NiMoW HDS catalysts. ► The NiMoW/SBA-16 sulfide catalyst with 1wt.% of P is more active in HDS reaction than the P-free ...counterpart. ► The formation of “onion-type” Mo(W)S2 structure is detrimental for HDS activity.
P-containing SBA-16 mesoporous systems were used as supports of ternary Ni–Mo–W hydrodesulfurization (HDS) catalysts. The samples were characterized by a variety of techniques (N2 adsorption–desorption isotherms, XRD, TPR, TPD-NH3, DRS UV–vis and HRTEM). XRD profiles evidenced the formation of crystalline Mo1-xWxO3 and NiMoO4 phases on the surface of oxide catalyst precursors with high P-loadings (1.0 and 1.6wt.%). The UV–vis DRS measurements showed a substantial decrease of energy band gap after P-loading onto the SBA-16 substrate with respect to P-free sample. The sulfided catalysts were tested in separate HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) reactions performed in a batch reactor at 320°C and H2 pressure of 5.0MPa. For both HDS reactions, the initial catalyst activity displayed a volcano-type curve indicating that catalyst behavior depends strongly on the phosphorous loading being all catalysts more active in the HDS of DBT then in the HDS of 4,6-DMDBT. The NiMoW/SBA-16 catalyst loaded with optimized amount of phosphorous (1.0wt.%) showed superior initial activity than the P-free counterpart. This effect was attributed to the enhancement of active phases dispersion on the support surface, as revealed by HRTEM measurements. It was found that the formation of “onion-type” Mo(W)S2 phases on the catalyst surface was detrimental for the HDS activity. At reaction time of 5h, the most active NiMoW/SBA-16 catalyst loaded with 1.0wt.% of P showed similar activity in both HDS of DBT and 4,6-DMDBT reactions. It was found that HYD route of both reactions was promoted by the support modification with P and due to inhibition of coordinatively unsaturated sites (CUSs) by competitive adsorption of products (mainly H2S).
ZnS films were grown on (001) GaAs substrates at different temperatures by RF magnetron sputtering. The ZnS chemical stoichiometry was determined by Energy-dispersive X-ray spectroscopy (EDS), ...besides it allowed to find the residual impurities, mainly oxygen. The X-ray diffraction (XRD) analysis and Raman scattering reveal that ZnS deposited thin films showed hexagonal wurtzite crystalline phase. The films average crystallite size range was from 8.15 to 31.95 nm, which was determined using the Debye–Scherrer equation for the peak W(101). Besides an experimental study of first- and second-order Raman scattering of ZnS films is made. An energy level diagram involving oxygen traps and interstitial sulphur ions is used to explain the origin of the radiative transitions observed in the room temperature photoluminescence (PL) spectra.
•ZnS nanofilms were deposited by RF magnetron sputtering on (100) GaAs substrates.•It has investigated the substrate temperature effect on structure properties of ZnS.•The ZnS grain size varied from 8.15 to 31.95 nm as a function of the grown temperature.•ZnS nanofilms have good optical properties as was obtained by 300 K photoluminescence.
Electrospinning technique has been used to prepare TiO2 nanofibres. The crystalline phase transformation occurred due to thermal treatments in the temperature range of 100–1000 °C, from anatase to ...rutile through the anatase-rutile mixed, which was verified by X-ray diffraction, high-resolution transmission electronic microscopy and Raman scattering. The effects of the annealing temperature on the surface morphology and the chemical stoichiometry of titanium dioxide nanofibres were determined by scanning electron microscopy and energy dispersion spectrometry. The nanofibres diameter was in the range of 115–137 nm in the investigated temperature range. Clear evidence of structural phase transformation from pure anatase to pure rutile structures including the anatase-rutile mixed phase have been obtained by ultraviolet–visible and photoluminescence spectroscopy. TiO2 nanofibres band gap energy could be tuned from 3.59 to 2.42 eV by varying the annealing temperature estimated by room temperature absorbance. The photoluminescent emission ranged in the 2.36–1.47 eV region as a function of the thermal treatment temperature, which is a consequence of the TiO2 nanofibres crystalline phase transformation and reduction of the band gap energy.
•TiO2 nanofibres were successfully synthesised by electrospinning technique.•Crystal phase transformation through high-temperature annealing of TiO2 nanofibres.•Study of crystal phase transformation of annealed TiO2 nanofibres by Raman scattering.•The optical properties of TiO2 nanofibres were modulated by thermal treatments.
The obtaining of monocrystalline TiO2 nanofibers with high specific surface area synthesized by the electrospinning technique with controlled crystalline structure and morphology is reported. The ...nanofibers were annealed at 500, 700 and 900 °C in a controlled atmosphere in the presence of air for two hours to achieve crystalline phase transformation. By means of TEM, it was possible to clearly corroborate the presence of solid nanofibers with a well-defined shape, a smooth surface and without the presence of interconnections and defects called beads. The chemical stoichiometry of electrospun TiO2 nanofibers was estimated by EDS, finding that at low annealing temperatures excess of oxygen was detected and at high temperatures excess of titanium that originates oxygen vacancies. By Raman scattering was found that the TiO2 nanofibers showed a crystalline phase transformation from pure anatase, mixed anatase-rutile and pure rutile as the annealing temperature is increased, caused by the generation of oxygen vacancies, which was corroborated by X-ray diffraction. The band gap energy (Eg), obtained from optical absorption spectra, decreases as the temperature is increased, which is ranged in 2.42 ≤ Eg≤ 3.27 eV, caused by the anatase→rutile crystalline phase transformation. Photoluminescence shows that the radiative bands -present a gradual red shift as the temperature increases due to the Eg reduction. In addition, the photocatalytic properties of the annealed TiO2 nanofibers were evaluated in the decolouration of the Remazol Black B azo dye. Changes in absorption spectra were noticeable as the measurement time increases. Absorbance spectra showed a decrease in the intensity of the main absorption band at 589 nm, which gradually decreases until it completely disappears, indicating that the decomposition of the organic compound is complete, while physically there is an absence of color from the solution. The anatase crystalline phase was the one with the highest specific surface area and the highest photocatalytic activity.
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It shows the X-ray diffraction patterns of TiO2 nanofibers at different annealing temperatures: a) anatase crystalline phase (AT=500 °C), b) anatase-rutile mixed (AT=700 °C) and c) rutile phase.
•TiO2 nanofibres were successfully synthesized by electrospinning technique at 300 K.•Crystal phase transformation through high-temperature annealing of TiO2 nanofibres.•The spectrospun TiO2 crystalline phase transformation is caused by oxygen vacancies.
This work aimed to determine the carrier effect on anisole hydrodeoxygenation (HDO, batch reactor at 573 K, and 4 MPa of H
2
) on 5 wt% Ni catalysts on TiO
2
and TiO
2
-ZrO
2
carriers. Besides, a TiO
...2
-supported Ru-doped catalyst was also tested. Differences in surface acid sites, Ni reducibility, oxygen vacancies, and interactions among metals and support were detected. For instance, Ru addition promoted Ni reducibility due to improved hydrogen adsorption and subsequent spillover effect. Methoxycyclohexane and cyclohexanol were the main products over Ni/TiO
2
. Ru incorporation increased the initial reaction rate (×3) compared with non-doped Ni/TiO
2
favoring benzene selectivity. Ni/TiO
2
-ZrO
2
exhibited higher HDO activity and enhanced acidity than the material supported on TiO
2
, and high deoxygenated compounds yield a fully hydrogenated compound (cyclohexane) as well. Therefore, it was possible to promote the desired reaction pathway to relevant chemical compounds that are associated with both the support type and the metallic phase composition.
The structural and optical characterization of TiO2 nanofibers (TiO2-NF’s) synthesised from two different chemical precursors, titanium tetrabutoxide (TNBT) and titanium isopropoxide (TTIP), obtained ...by electrospinning technique with controlled morphology and crystalline phase, is presented. Varying the distance between the needle tip and the collector called "air gap", it was possible to control the diameter and the formation of the fibers within the nanometric scale. The crystalline phase (CP) of the TiO2-NFs was controlled through thermal treatment (TT) at 450 °C for 3 h, anatase phase. The chemical composition of the annealed electrospun TiO2-NF was estimated by EDS, finding there is an excess of titanium that causes oxygen vacancies, which stimulate the CP transformation, from amorphous to anatase. By means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was possible to corroborate the formation of TiO2-NFs with a smooth morphology and well-defined shape. FTIR spectroscopy and Raman scattering results of electrospun TiO2-NFs demonstrated changes in structural and optical properties caused by TT. By Raman scattering was found that the annealed TiO2-NFs showed the anatase CP, which was corroborated by X-ray diffraction. At first sight, the surface morphology of the electrospun fibers was not affected by the choice of precursor; however, on closer review, the fibers prepared with the TTIP precursor showed a smaller crystal size of 8.51 nm and band gap energy of 3.38 eV, while the samples prepared with TNBT showed a smaller bandgap energy of 3.06 eV and a nanocrystal size of 10.98 nm. With both precursors at a working distance of 15 cm, homogeneous fibers are obtained, with a smaller diameter without the presence of morphological defects, called beds, and a better size distribution.
Synthesis of electrospun TiO2 nanofibers annealed at 450 °C obtained by the molecular precursors: a) TNBT and b) TTIP. Display omitted
•TiO2 nanofibres were successfully synthesised by electrospinning technique.•Crystal phase transformation through high-temperature annealing of TiO2 nanofibres.•Study of crystal phase transformation of annealed TiO2 nanofibres by Raman scattering.•The optical properties of TiO2 nanofibres were modulated by thermal treatments.•The two precursors TNBT and TTIP produced high quality TiO2 nanofibers.
•CBD-CdSe thin films were successfully prepared for temperatures in the range 0–80 °C.•Phase transformation of CBD CdSe NPs was obtained by varying the growth temperature.•Depending on Temperature ...the particle size can take values in the 7–12 nm range.•CdSe NPs bandgap as function of T show evidence of the effect of the phase transition.•The Raman spectrum for Tbc shows modes related with the disorder of the CdSe lattice.
Structural and electronic properties characterization results show that the crystallographic structure of CdSe films, deposited by chemical bath synthesis, is controlled by the bath growth temperature. The synthesis parameters employed produced a set of nanostructured CdSe films on glass substrates with controlled crystal structure. The effect of bath temperature (Tb) on CdSe films was studied in the 0 ≤ Tb ≤ 80 °C range. The average crystal diameter (AD) of the films lies within the 7 ≤ AD ≤ 12 nm interval, where AD depends on the selected Tb. X-ray diffractograms (XRD) shown that at low Tb values the formation of the hexagonal wurtzite (WZ) is promoted while at the other extreme the cubic zinc-blende (ZB) crystalline structure dominates. It is observed that the WZ → ZB transition occurs at the critical temperature Tbc ~ 40 °C. The AD in each films for CdSe-NP’s was obtained from XRD analysis employing the Scherrer-Debye formula. The values of the lattice interplanar spacing (IS), determined from XRD analysis, as function of Tb increases continuously except at temperatures around Tbc where a local minimum is observed. The presence of stress acting on CdSe NP’s is identified by correlating the IS values with the crystalline structure: compression occurs for 0 ≤ Tb ≤ 40 °C, and tension for 50 ≤ Tb ≤ 80 °C. The band gap energy, obtained from optical absorption spectra, decreases monotonically but a local minimum is observed at Tbc = 40 °C. Results from Raman spectroscopy show that the CdSe Raman LO-mode hardens for Tbc as consequence of the WZ ↔ ZB structural transition.
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