Microwave Resonant and Zero-Field Absorption Study of Doped Magnetite Prepared by a Co-Precipitation Method

Fe3O4 and ZnxFe3-xO4 pure and doped magnetite magnetic nanoparticles (NPs) were prepared in aqueous solution (Series A) or in a water-ethyl alcohol mixture (Series B) by the co-precipitation method. Only one ferromagnetic resonance line was observed in all cases under consideration indicating that the materials are magnetically uniform. The shortfall in the resonance fields from 3.27 kOe (for the frequency of 9.5 GHz) expected for spheres can be understood taking into account the dipolar forces, magnetoelasticity, or magnetocrystalline anisotropy. All samples show non-zero low field absorption. For Series A samples the grain size decreases with an increase of the Zn content. In this case zero field absorption does not correlate with the changes of the grain size. For Series B samples the grain size and zero field absorption behavior correlate with each other. The highest zero-field absorption corresponded to 0.2 zinc concentration in both A and B series. High zero-field absorption of Fe3O4 ferrite magnetic NPs can be interesting for biomedical applications.

Three-photon-excited upconversion luminescence of Ce3+: YAP crystal by femtosecond laser irradiation

Infrared to ultraviolet and visible upconversion luminescence was demonstrated in trivalent cerium doped YAlO3 crystal (Ce3+: YAP) under focused infrared femtosecond laser irradiation. The fluorescence spectra show that the upconverted luminescence comes from the 5d-4f transitions of trivalent cerium ions. The dependence of luminescence intensity of trivalent cerium on infrared pumping power reveals that the conversion of infrared radiation is dominated by three-photon excitation process. It is suggested that the simultaneous absorption of three infrared photons pumps the Ce3+ ion into upper 5d level, which quickly nonradiatively relax to lowest 5d level. Thereafter, the ions radiatively return to the ground states, leading to the characteristic emission of Ce3+. (c) 2005 Optical Society of America.

Characteristics and optical spectra of V : YAG crystal grown in reducing atmosphere

A V:YAG single crystal was grown by the temperature gradient technique (TGT) with graphite-heating elements. The as-grown crystal has different colorations of light green and yellow brown in different parts. Distribution of vanadium in three samples with different colorations was determined by inductively coupled plasma-mass spectrometry. From the absorption spectrum of the yellow-brown part with peaks at 370, 820 and 1320nm, we can deduce that the reducing atmosphere of carbon diffused from the heating elements can increase the concentration of tetrahedral V3+ ions and induce F color centers. All three samples exhibited light-green color after annealing in vacuum or H-2 atmospheres. In the vacuum annealing process, the V3+ ions in tetrahedral positions were enhanced through two methods: one method is the exchanging of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under thermal excitation, the other is that F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states to further improve the concentration of tetrahedral V3+ ions. Besides the two mechanisms, the H-2 annealing process greatly improved the V-tetra(3+) ions through the reduction effect of H-2. (c) 2006 Elsevier B.V. All rights reserved.

Theoretical analysis of influence of substrate microdefects on polarized light properties of dielectric coatings

A model for refractive index of stratified dielectric substrate was presented according to inhomogeneous coatings theories. The substrate was divided into surface layer, subsurface layer and bulk layer along the normal direction of its surface. The former two layers were equivalent to inhomogeneous coatings. Theoretical deduction was executed by employing the characteristic matrix method of optical coatings, and one mathematical calculation example was presented. The results indicate that reflectance, reflective phase shift and phase difference of polarized light deviate from ideal conditions. It shows that substrate microdefects can induce volume scattering and change propagation characteristic of light both in coatings and substrate. (c) 2005 Elsevier GmbH. All rights reserved.

Development in laser induced extrinsic absorption damage mechanism of dielectric films

Absorption of host and the temperature-dependence of absorption coefficient have been considered in evaluating temperatures distribution in films, when laser pulse irradiates on films. Absorption of dielectric materials experience three stages with the increase of temperature: multi-photon absorption; single photon absorption; metallic absorption. These different absorption mechanisms correspond to different band gap energies of materials, which will decrease when the temperature of materials increases. evaluating results indicate that absorption of host increases rapidly when the laser pulse will be over. If absorption of host and the temperature-dependence of absorption are considered, the material temperatures in films will be increased by a factor of four.

Investigation on the properties of high reflective mirror prepared by ion-beam sputtering

The single-sided and dual-sided high reflective mirrors were deposited with ion-beam sputtering (IBS). When the incident light entered with 45 degrees, the reflectance of p-polarized light at 1064 nm exceeded 99.5%. Spectrum was gained by spectrometer and weak absorption of coatings was measured by surface thermal lensing (STL) technique. Laser-induced damage threshold (LIDT) was determined and the damage morphology was observed with Lecia-DMRXE microscope simultaneously. The profile of coatings was measured with Mark III-GPI digital interferometer. It was found that the reflectivity of mirror exceeded 99.9% and its absorption was as low as 14 ppm. The reflective bandwidth of the dual-sided sample was about 43 nm wider than that of single-sided sample, and its LIDT was as high as 28 J/cm2, which was 5 J/cm2 higher than that of single-sided sample. Moreover, the profile of dual-sided sample was better than that of substrate without coatings.

Effects of rapid decompression and exposure to bright light on visual function in black rockfish (Sebastes melanops) and Pacific halibut (Hippoglossus stenolepis)

Demersal fishes hauled up from depth experience rapid decompression. In physoclists, this can cause overexpansion of the swim bladder and resultant injuries to multiple organs (barotrauma), including severe exophthalmia (“pop-eye”). Before release, fishes can also be subjected to asphyxia and exposure to direct sunlight. Little is known, however, about possible sensory deficits resulting from the events accompanying capture. To address this issue, electroretinography was used to measure the changes in retinal light sensitivity, flicker fusion frequency, and spectral sensitivity in black rockfish (Sebastes melanops) subjected to rapid decompression (from 4 atmospheres absolute [ATA] to 1 ATA) and Pacific halibut (Hippoglossus stenolepis) exposed to 15 minutes of simulated sunlight. Rapid decompression had no measurable influence on retinal function in black rockfish. In contrast, exposure to bright light significantly reduced retinal light sensitivity of Pacific halibut, predominately by affecting the photopigment which absorbs the green wavelengths of light (≈520–580 nm) most strongly. This detriment is likely to have severe consequences for postrelease foraging success in green-wavelength-dominated coastal waters. The visual system of Pacific halibut has characteristics typical of species adapted to low light environments, and these characteristics may underlie their vulnerability to injury from exposure to bright light.

Comparison of the Transcriptional Profiles of Melanocytes from Dark and Light Skinned Individuals under Basal Conditions and Following Ultraviolet-B Irradiation

We analysed the whole-genome transcriptional profile of 6 cell lines of dark melanocytes (DM) and 6 of light melanocytes (LM) at basal conditions and after ultraviolet-B (UVB) radiation at different time points to investigate the mechanisms by which melanocytes protect human skin from the damaging effects of UVB. Further, we assessed the effect of different keratinocyte-conditioned media (KCM+ and KCM-) on melanocytes. Our results suggest that an interaction between ribosomal proteins and the P53 signaling pathway may occur in response to UVB in both DM and LM. We also observed that DM and LM show differentially expressed genes after irradiation, in particular at the first 6h after UVB. These are mainly associated with inflammatory reactions, cell survival or melanoma. Furthermore, the culture with KCM+ compared with KCM- had a noticeable effect on LM. This effect includes the activation of various signaling pathways such as the mTOR pathway, involved in the regulation of cell metabolism, growth, proliferation and survival. Finally, the comparison of the transcriptional profiles between LM and DM under basal conditions, and the application of natural selection tests in human populations allowed us to support the significant evolutionary role of MIF and ATP6V0B in the pigmentary phenotype.

Recruitment season, size, and age of young American eels (Anguilla rostrata) entering an estuary near Beaufort, North Carolina

Net catches from 1985–86 to 1994–95 at Pivers Island, North Carolina, indicated that glass-eel stage American eels (Anguilla rostrata) were recruited to the estuary from November to early May, with peak numbers in January, February, and March. There was no declining trend in recruitment over the years of sampling. Except for one year, there was no clear seasonal decrease in mean length. But shorter glass eels were older than longer glass eels, as judged by age within the glass eel growth zone of the otolith, suggesting that smaller fish took longer to arrive. The mean age of glass eels collected from the lower estuary and a freshwater site 9.5 km upriver differed by 8.4 d (36.2 vs. 44.6, respectively). Outer increments (30–35) of the otolith growth zone of glass eels from North Carolina were significantly wider than corresponding increments of otoliths from New Brunswick. Mean total ages of North Carolina, New Jersey, and New Brunswick elvers were 175.4, 201.2, and 209.3 d, corresponding to mean lengths of 55.9, 60.9, and 58.1 mm TL, respectively. The mean durations of glass-eel growth zones (44.6, 62.3, and 69.8) were in close agreement with those from previous studies, but total ages were not. This suggested that perhaps some finer (leptocephalus stage) increments were not detected by light microscopy, differences occurred in seasonal increment deposition, or absorption of the otolith material may have taken place during metamorphosis, rendering the aging of larvae inaccurate. Judging from the long recruitment period and seasonal uniformity in both mean age and length found in our study, the spawning period of American eels may be somewhat more protracted than previously considered.

Preliminary observations of the use of under-water light in fish catch

Experiments with drift gill net with under-water lights were carried out in the sea and estuarine region along with a control net of the same specifications without any light in the same fishing ground for comparison. The experimental net caught more fish in number and weight than the control. Fishes like pomfrets (Pampus chinensis, Parastromafeus niger), seer (Scomberomorus spp), hilsa (Ilisha spp) etc showed positive phototaxis and were gilled encircling the point of illumination. Young skates (Mobula spp) and Polynemus tetradactylus were antiphototactic. The number of fishes caught increased with increase in period of illumination. The catch of larger fishes was maximum at 60 mts of illumination and the total catch increased with increase in intensity of light. Additional cost of operation with under-water light was Rs 1-25 per hr but the catch was 4 to 5 times greater than that of the control net.

The study of maturational progress in the whitespotted rabbitfish (Siganus sutor) under different photoperiod and light intensity conditions

The rule of light on the timing of maturation and spawning in tropical and subtropical regions is not clear well, because the reproductive cycle in these systems is lunar synchronized. In this study, thus, the effects of different light regimes were investigated on maturational progress of whitespotted rabbitfish, Siganus sutor, the commercial species in Persian Gulf and Oman Sea. During prespawning season, 50 adult fish were randomly divided into ten 300-l tanks (n=5). The fish in control tank received indoor light condition and the fish in each other tanks were exposed to nine different combinations of photoperiod (8L: 16D, 12L: 12D, 16L: 8D) and light intensity (1000, 2000, 3000 lux). After 60 days, GSI and HSI values, serum levels of estradiol (E2), testosterone (T), 17-α hydroxyprogestrone (OHP), calcium (Ca2+) and gonad histology were evaluated for females and males. In females the GSI mean values of exposed fish increased in comparison with control except for fish were kept under 8L, 2000 lux (tank 8). These differences were significant only for fishes in tank 7 (8L, 3000 lux). In the cases of HSI, the results were converse, so that, the most of thanks showed significant decreasing than fishes reared under indoor condition. Morphology and histology study of Ovaries showed three developmental phases including 3, 4 and chiefly 5 that were parallel with GSI values. Fortheremore the serum levels of E2 was recorded between 0.54-15.8 ng/ml in different fish and their mean values were lower than control in all treatmants (P> 0.05). In males, the similar results were obtained. The GSI and HSI mean values in experimental regimes compared with control were upper and lower, respectively, except for fishes were reared in tank 1 (16L, 3000 lux). Testes histology of fishes were reared under different regimes showed signs of stage 5, since no blood vessels observed and thick milt exuded on slight pressure. The mean values of testosterone consentration in fishes were kept in tanks 1 and 6 (12L, 1000 lux) were higher and in other ones were lower than control group. It is also noted that the OHP and Ca2+ had diverse results including increasing and decreasing mean values than control. So, these factors contrary to E2 and T were not suitable to evaluation of maturity in both sexes. On the basis of ovarian structure in stage 5, oocyte development pattern in this species was group synchronous. So, increased mean of GSI versus decreased values of HSI, E2 and perhaps Ca2+ were the signs of improved maturation. But in males, reduced levels of T and similarity of testes morphology in all samples caused that GSI mean value was the only indicator for differentiating among treatments. These findings suggest that alternations were used in light regimes have been the reason of improved maturity in all treatments except fishes reared in tank 8. The ١٠٧ rule of light intensity on induction of maturity was cleared by comparision between fishes in tanks 4, 5, 6 and control group. Because day length was the same whereas fishes in tanks 4, 5 and 6 were exposed to increased light intensity compared with control. This fact verified by results was obtained from fishes in tanks 9 and especially 7, since photoperiod in this group was lower than control. So, higher intensity was considered as the reason of alternations. Contrasting with indoor condition, Induced maturity was also cleared for fishes were kept in tanks 1, 2 and 3, where both of light duration and intensity were increased. But, the rule of photoperiod was individually demonstrated when obtained results were compared with similar light intensities in other treatments. In conclusion, with comparison among different light regimes it is declared that siganids were kept under light condition of tank 2 including 16h light duration combined with 2000 lux intensity showed the best signs of sexual maturation in both sexes. On the basis of this study, setting up the spring light condition during prespawning season induces maturation in withspotted rabbitfish. This improvement not only by influence of photoperiod or light intensity, separately, but obtained through interaction between them. Thus, determination of threshold and resistance to light be recommended before exposure, although using proper regime during suitable time are necessary to achieve purposes considerably.

Lowering the excitation threshold of a random laser using the dynamic scattering states of an organosiloxane smectic A liquid crystal

Smectic A liquid crystals, based upon molecular structures that consist of combined siloxane and mesogenic moieties, exhibit strong multiple scattering of light with and without the presence of an electric field. This paper demonstrates that when one adds a laser dye to these compounds it is possible to observe random laser emission under optical excitation, and that the output can be varied depending upon the scattering state that is induced by the electric field. Results are presented to show that the excitation threshold of a dynamic scattering state, consisting of chaotic motion due to electro-hydrodynamic instabilities, exhibits lower lasing excitation thresholds than the scattering states that exist in the absence of an applied electric field. However, the lowest threshold is observed for a dynamic scattering state that does not have the largest scattering strength but which occurs when there is optimization of the combined light absorption and scattering properties. © 2012 American Institute of Physics.

The role of the surfaces in the photon absorption in Ge nanoclusters embedded in silica.

The usage of semiconductor nanostructures is highly promising for boosting the energy conversion efficiency in photovoltaics technology, but still some of the underlying mechanisms are not well understood at the nanoscale length. Ge quantum dots (QDs) should have a larger absorption and a more efficient quantum confinement effect than Si ones, thus they are good candidate for third-generation solar cells. In this work, Ge QDs embedded in silica matrix have been synthesized through magnetron sputtering deposition and annealing up to 800°C. The thermal evolution of the QD size (2 to 10 nm) has been followed by transmission electron microscopy and X-ray diffraction techniques, evidencing an Ostwald ripening mechanism with a concomitant amorphous-crystalline transition. The optical absorption of Ge nanoclusters has been measured by spectrophotometry analyses, evidencing an optical bandgap of 1.6 eV, unexpectedly independent of the QDs size or of the solid phase (amorphous or crystalline). A simple modeling, based on the Tauc law, shows that the photon absorption has a much larger extent in smaller Ge QDs, being related to the surface extent rather than to the volume. These data are presented and discussed also considering the outcomes for application of Ge nanostructures in photovoltaics.PACS: 81.07.Ta; 78.67.Hc; 68.65.-k.

Influence of the matrix properties on the performances of Er-doped Si nanoclusters light emitting devices

We investigated the properties of light emitting devices whose active layer consists of Er-doped Si nanoclusters (nc) generated by thermal annealing of Er-doped SiOx layers prepared by magnetron cosputtering. Differently from a widely used technique such as plasma enhanced chemical vapor deposition, sputtering allows to synthesize Er-doped Si nc embedded in an almost stoichiometric oxide matrix, so as to deeply influence the electroluminescence properties of the devices. Relevant results include the need for an unexpected low Si excess for optimizing the device efficiency and, above all, the strong reduction of the influence of Auger de-excitation, which represents the main nonradiative path which limits the performances of such devices and their application in silicon nanophotonics. © 2010 American Institute of Physics.

Effects of sediment anoxia and light on turion germination and early growth of Potamogeton crispus

Potamogeton crispus is a cosmopolitan aquatic species and is widely used as a pioneer species for vegetation restoration of eutrophic lakes. However, many restoration projects applying P. crispus turions have not been successful. Earlier studies focused on effects of light and temperature on turion germination. The purpose of this study was to determine whether sediment anoxia and light interactively affected the turion germination and early growth of P. crispus. Anoxic conditions in the experiment were produced by adding sucrose to the sediment. The germination rate of the turions was 68-73% lower in the highly anoxic condition treatment than in the control. Medium light intensity (10% of natural light at the water surface) was more favorable for germination under slightly anoxic conditions than either low or high light intensity. The growth of newly-formed sprouts was also significantly inhibited by sediment anoxia. Photosynthesis and shoot biomass were reduced under sediment anoxia, whereas total chlorophyll content, root biomass, and soluble protein content were highest in the low anoxic condition treatment. Medium light improved net photosynthesis and biomass production of the sprouts. We conclude that turion germination and sprout growth can be significantly inhibited by sediment anoxia. Medium light intensity may alleviate this inhibition by anoxia, but light has little effect when sediment anoxia is severe. For the purposes of vegetation restoration, more attention should be paid to the role of sediment anoxia, and it is necessary to improve sediment and light conditions for turion germination and early growth of P. crispus in eutrophic lakes. These results will contribute to a more complete understanding of turion germination dynamics of P. crispus and will be useful for future restoration programs.