Partial Bleaching Research Articles

연속 발진 다이오드 레이저로 여기된 수동형 Q-스위치 Nd:YVO4레이저의 출력 펄스 안정화

Cr:YAG 결정을 포화흡수체로 사용하여 수동형 Q-스위치시킨 다이오드 레이저 여기 Nd:<TEX>$YVO_4$</TEX> 레이저를 제작하였다. Cr:YAG 결정의 한 면에 여기 빛 파장(808 nm)에 대해 고반사 코팅을 한 후, Nd:<TEX>$YVO_4$</TEX> 결정과 접촉시켜 공진기를 구성하였다. Cr:YAG의 한 면에 여기 다이오드 레이저를 반사시키는 코팅을 입혀 공진기의 광변환 효율을 높임과 동시에, 여기빔에 의한 포화흡수체의 표백현상을 방지하여 안정된 출력이 나오게 하였다. 레이저 이득 매질 및 포화흡수체의 온도는 열전 냉각기와 냉각수를 사용하여 안정화 시켰다. 온도안정화를 시킨 상태에서 발진되는 펄스의 첨두 출력 요동(peak to peak)은 4%였다. 다이오드 레이저의 출력이 1 W일 때, 출력 펄스의 반복률은 평균 9 KHz 였으며, 최소 펄스폭은 7.11 ns, 최고 출력은 16.27 mW였다. A Cr:YAG crystal was used as a saturable absorber for passive Q-switching of a Nd:<TEX>$YVO_4$</TEX> laser which was pumped by a 1-W continuous wave laser diode. The first surface of the Cr:YAG was high-reflection coated for the pump wavelength. The high-reflection coating improved the absorption efficiency of the pump beam in the Nd:<TEX>$YVO_4$</TEX> through double pass absorption. It also prevented pump beam induced partial bleaching of the Cr:YAG. The peak-to-peak pulse fluctuation of passively Q-switched laser output was approximately 4 %. The minimum pulse-width was measured to be 7.11 ns. Also, the average pulse repetition rate was 9 kHz and the maximum output power was 16.27 mW.

OSL and ESR studies of Aeolian quartz from the Upper Pleistocene loess sequence of Nussloch (Germany)

As part of a chronological study of the famous Upper Pleistocene Nussloch (Germany) loess sequence, three samples were collected to check the applicability of palaeodosimetric dating methods (OSL and ESR) to quartz grains. The ESR-multicentre method showed a partial bleaching of the ESR centers in aeolian sands. This partial bleaching was also observed by OSL. Laminated loess seemed to be sufficiently bleached but showed a large scatter of the doses, which we ascribed to heterogeneous responses of the luminescent grains to the SAR protocol. Ages could nevertheless be calculated for the three samples and were found to be somewhat older than the IRSL and 14C ages obtained for the same layers of the laminated loess.

The potential of optically stimulated luminescence for dating periglacial slope deposits — A case study from the Taunus area, Germany

Periglacial deposits overlying bedrock are widespread in the German low mountain ranges. The age of these deposits is still a matter of debate and therefore, three sections in the Taunus area were investigated with luminescence dating techniques. In general, the heterogeneity of the sediment, which is characterized by a mixture of grain sizes from clay to cobbles, is the main problem for dating as dose-rate determination is complicated. This is demonstrated based on comparisons of high resolution γ-ray spectrometry, neutron activation analysis, β-counting and in-situ measurements of the γ-dose-rate. Insufficient bleaching due to the transport mode, and consequently age overestimation, was expected to be a major problem for luminescence dating of periglacial slope deposits. In order to get a detailed insight into equivalent dose variations due to partial bleaching, single aliquot regenerative dose (SAR) protocols have been applied to the polymineralic fine-grain fraction, sand-sized K-feldspar and quartz extracts. Our results do not confirm partial bleaching as a problem, except for the basal layer. The luminescence properties vary substantially depending on the site, the layer and the mineral fraction that is measured for equivalent dose determination. However, hardly any systematic tendencies can be observed. Micromorphology analysis indicates post-depositional mixing which complicates the equivalent dose estimation even further. Due to the lack of accuracy, the relevance of the presented data for palaeolandscape reconstruction is limited. Based on these observations, suggestions are made to improve future attempts of dating periglacial cover beds with optically stimulated luminescence (OSL).

Luminescence dating of historical fluvial deposits from the Danube and Ebro

AbstractThe validity of optically stimulated luminescence (OSL) has been tested on known‐age (historical) fluvial deposits along the rivers Danube (Austria) and Ebro (Spain). As partial bleaching of the OSL signal prior to deposition can interfere with correct age estimates, different approaches to extracting the dose accumulated during burial are compared. Using the finite mixture model gave OSL ages that are internally as well as stratigraphically consistent and in agreement with independent age control. According to these results, fluvial deposition at the Danube River study site can be attributed to different periods ranging from Bronze Age to the 18th century A.D. Fluvial deposits of Roman age and of the late 17th or early 18th century A.D. were found at the Ebro River study site. This is consistent with the morphological subdivision of the valleys and encourages further investigation of the fluvial and archaeological history of the study areas using OSL. © 2009 Wiley Periodicals, Inc.

Residual Luminescence in Quartz from Slack Water Deposits in Kaveri Basin, South India: A Single Aliquot Approach

Residual Luminescence in Quartz from Slack Water Deposits in Kaveri Basin, South India: A Single Aliquot Approach Optical bleaching of quartz may be incomplete due to decreased daylight intensity and narrower wavelength spectrum in water column, leading to age overestimation in young fluvial sediments. This hypothesis was tested on a low energy slack water deposits from Kaveri Basin in south India using the SAR protocol. Various tests suggest successful application of SAR on quartz from the study area despite low sensitivity and few numbers of bright grains. Partial bleaching can be ruled out if using SAR on small aliquots. The results suggest a uniform residual luminescence and a common sedimentary condition in this area. Due to partial bleaching, the lowest values of palaeodoses should be considered in preference to the average values.

Interactions between Redox Complexes and Semiconductor Quantum Dots Coupled via a Peptide Bridge

Colloidal quantum dots (QDs) have a large fraction of their atoms arrayed on their surfaces and are capped with bifunctional ligands, which make their photoluminescence highly sensitive to potential charge transfer to or from the surrounding environment. In this report, we used peptides as bridges between CdSe-ZnS QDs and metal complexes to promote charge transfer between the metal complexes and QDs. We found that quenching of the QD emission is highly dependent on the relative position of the oxidation levels of QDs and metal complex used; it also traces the number of metal complexes brought in close proximity of the nanocrystal surface. In addition, partial bleaching of the absorption was measured for the QD-metal complex assemblies. These proximity driven interactions were further used to construct sensing assemblies to detect proteolytic enzyme activity.

Calorimetric Studies of Bovine Rod Outer Segment Disk Membranes Support a Monomeric Unit for Both Rhodopsin and Opsin

The photoreceptor rhodopsin is a G-protein coupled receptor that has recently been proposed to exist as a dimer or higher order oligomer, in contrast to the previously described monomer, in retinal rod outer segment disk membranes. Rhodopsin exhibits considerably greater thermal stability than opsin (the bleached form of the receptor), which is reflected in an ∼15°C difference in the thermal denaturation temperatures (Tm) of rhodopsin and opsin as measured by differential scanning calorimetry. Here we use differential scanning calorimetry to investigate the effect of partial bleaching of disk membranes on the Tm of rhodopsin and of opsin in native disk membranes, as well as in cross-linked disk membranes in which rhodopsin dimers are known to be present. The Tms of rhodopsin and opsin are expected to be perturbed if mixed oligomers are present. The Tm remained constant for rhodopsin and opsin in native disks regardless of the level of bleaching. In contrast, the Tm of cross-linked rhodopsin in disk membranes was dependent on the extent of bleaching. The energy of activation for denaturation of rhodopsin and cross-linked rhodopsin was calculated. Cross-linking rhodopsin significantly decreased the energy of activation. We conclude that in native disk membranes, rhodopsin behaves predominantly as a monomer.

Age limits on Middle Pleistocene glacial sediments from OSL dating, north Norfolk, UK

The lowland region of north Norfolk contains some of the best preserved evidence for glacial deposition during the Middle Pleistocene in northwest Europe. Despite the importance of these deposits, there is limited chronological control and it is debated whether they belong to a single glaciation, equated to the Anglian Glaciation (Marine Isotope Stage 12), or represent deposition over a number of Middle Pleistocene cold stages. In order to develop an improved chronology for glaciation in this region, we obtained 18 samples for optical stimulated luminescence (OSL) dating from glacial outwash facies. Samples of coarse-grained quartz sand were measured using the SAR (single aliquot regenerative-dose) protocol. The low radioactive isotope concentrations in sediments of this region enable the traditionally accepted age limit of luminescence dating to be extended. The form of the dose response curves, pre-heat plateaux tests, and dose recovery experiments also indicate that laboratory doses can be reliably measured in these samples. Age overestimation due to partial bleaching is thought to be insignificant. The OSL ages suggest that the glacial sediments studied were deposited during MIS 12 rather than in different post MIS 12 stages.

Characterization of human hair melanin and its degradation products by means of magnetic resonance techniques

Melanin granules (MGs) have been extracted from human Chinese black hairs by either acid hydrolysis (CH-type MGs) or enzymatic digestion (CP-type MGs), and their chemical structure investigated at the solid state by means of (13)C cross polarization magic angle spinning (CPMAS NMR) and EPR spectroscopy. Both types of MGs contain a large amount of protein that is tightly bound to the true melanin polymer, with CP-type MGs having a larger protein content than CH-type ones. Moreover, MGs may also contain variable amounts of lipid-like material. A high amount of paramagnetic metals is detected by EPR in CP-type MGs, in particular Fe(III). Iron can be bound in two chemical forms: as isolated high spin Fe(III) ions with rhombic symmetry and as small oxy-hydroxy Fe(III) aggregates. Iron is poorly available to chelators. CH-type MGs contain much fewer metals. CP-type MGs have then been subjected to partial bleaching by hydrogen peroxide in ammonia, yielding a residual solid, called residual oxidized melanin (ROM) and a soluble but still pigmented fraction called melanin free acid (MFA). MFA can be isolated by precipitation at acidic pH. The (13)C-CPMAS NMR and EPR spectra of these derivatives indicated that ROM has a structure very similar to that of parent MGs, whereas MFA shows a decrease of the protein content with respect to the melanin and a decreased amount of bound iron. Thus, the oxidative degradation of CP-type MGs is a process not involving the bulk of MGs, but rather it proceeds from the solvent-exposed outer parts to the interior.

Coral bleaching, bleaching-induced mortality, and the adaptive significance of the bleaching response

Coral bleaching events are often associated with higher levels of coral mortality but when this occurs in the chronology of individual bleaching events is poorly documented. Knowing when mortality occurs is important for understanding molecular mechanisms and the putative adaptive significance of the response (the Adaptive Bleaching Hypothesis). In a detailed study of a coral bleaching event on the Great Barrier Reef, involving weekly and twice weekly repetitive observations of >200 individually marked corals over an 18 month period (∼16,000 observations), it is shown that bleaching in Acropora latistella, A. subulata and Turbinaria mesenterina was an acute, rapid response, occurring within days of a peak in seawater temperatures exceeding previously described thresholds. Subsurface light levels, measured over the duration of the event, were not anomalous. Full bleaching (i.e. whole colonies turning bone-white) and partial bleaching (white patches) was observed in the Acropora spp. whilst the T. mesenterina colonies typically paled to a light brown colour. Algal densities in bleached corals were 10–30% of those of normally pigmented corals (∼2.5 × 106 algae per cm2), and in this instance bleaching was clearly a sudden, isolated, stress event and not an extreme low-point in the seasonal fluctuation of the density of symbiotic algae. Bleached corals were associated with high levels of partial and whole-colony mortality, but mortality was exclusively limited to the two Acropora spp. Importantly, most of this mortality was recorded in surveys conducted 1 and 2 weeks after bleaching was first observed, and for A. latistella as little as 1 week after bleaching was first observed. This suggests that in this particular bleaching event, for the Acropora species, that bleaching and mortality were intimately linked: this in turn suggests it was a pathological phenomenon. The study highlights a problem in the adaptive bleaching hypothesis, whereby significant levels of mortality can occur in a bleaching event before any chance for subsequent recombination of the host-symbiont unit. It is argued that in order to further evaluate the significance of bleaching as a potentially adaptive mechanism, bleaching-induced and bleaching-related mortality have to be fully considered. It is necessary to incorporate the cost (in terms of mortality) of a bleaching event, the recurring cost of reverting to the original, mortal, stress–prone combination after the event, and the higher cost associated with forming a maladaptive combination.

Wing coloration and pigment gradients in scales of pierid butterflies

Depending on the species, the individual scales of butterfly wings have a longitudinal gradient in structure and reflectance properties, as shown by scanning electron microscopy and microspectrophotometry. White scales of the male Small White, Pieris rapae crucivora, show a strong gradient in both the density in pigment granules and the reflectance. After pigment extraction by aqueous ammonia, scales of male P. r. crucivora closely resemble the unpigmented scales of female P. r. crucivora. Only a minor gradient exists in the white and orange scales of the male Orange Tip, Anthocharis cardamines. Pigment extraction of orange scales of A. cardamines causes bleaching. Partial bleaching transforms the scales so that they resemble certain scales of Phoebis philea that have a natural extreme gradient. Reflectance measurements on an artificial stack of two overlapping scales as well as on the scale stacks existing on intact and partially denuded wings of the Large White, Pieris brassicae, quantitatively demonstrate the reflectance enhancement by scale stacking.

Formation of room-temperature ferromagnetic Zn 1− xCo xO nanocrystals

Optical and magnetic properties of Co 2+-doped ZnO nanocrystals were studied. Optical measurements confirm the incorporation of Co 2+ in ZnO lattice with tetrahedral geometry. Optical absorption spectra also reveal the partial bleaching of the excitonic feature attributable to an increase in electron concentration. Magnetization measurements indicate the ferromagnetic ordering in Co 2+-doped ZnO nanocrystals with saturation magnetization 0.75 μ B / Co . No structural changes were observed in lightly doped ZnO nanocrystals. The present investigations are important in obtaining the ferromagnetic Zn 1− x Co x O nanocrystals.

Efecto de la herbivoría y coralivoría por peces en la supervivencia de corales trasplantados en el Caribe colombiano

To examine the effects of herbivorous and corallivorous fishes on the survival of transplanted colonies of Montastraea annularis, Diploria labyrinthiformis and Porites astreoides, both transplanted and native colonies were full-cage enclosed and compared to open (uncaged) colonies, while caging effects were assessed with a partial-cage (roof treatment). To evaluate if transplant stress increased the corals availability to fish predation, comparisons of fish foraging intensity among transplanted versus native colonies were made. To determine the density of herbivorous and corallivorous fishes on the transplants area visual censuses were made. The transient herbivorous fishes (Scaridae and Acanthuridae) were the most abundant fishes, and the corallivorous fishes (mainly Chaetodontidae) were the scarcest. A negative effect of territorial herbivorous fishes on M annularis transplants survival was observed, mainly early on the study. Fish foraging intensity was similar on transplanted and native colonies, but differed among coral species, being lowest on D. labyrinthiformis. Fast macroalgal growth inside full-cages due to reduced fish grazing was observed. This caused partial bleaching and partial mortality in some colonies, mainly of P. astreoides. No significant difference in healthy tissue percentages among full-cage and uncaged colonies on M. annularis and D. labyrinthiformis was found, while in P. astreoides there were evilent differences. The results indicate a damselfish negative effect on transplants survival early on the study, which can change depending on the fish and coral species involved. Results also indicate a fish grazing positive effect, caused by the reduction of coral-algae competition pressure, mainly on P. astreoides. Parrotfishes seem to affect corals survival both negatively through direct biting, and positively by controlling algal growth. Overall, coral transplant success was almost unaffected by fish foraging activity although several differences among coral species were obvious in relation to colony shape. Additionally, the interaction among herbivorous fish grazing and coral-algae competition balance appear important in determining transplant survival.

Photodarkening in Yb doped fibers: experimental evidence of equilibrium states depending on the pump power

Photodarkening in Yb doped fibers was examined at 633 nm in-situ during cladding pumping at 915 nm with varying pump powers and with no indication of an onset threshold. For the first time, the partial bleaching of the photodarkening loss by the pump power itself was observed. We found the relaxation to well-defined equilibrium states of the core excess loss, depending on the Yb inversion. From the dependence of the measured rate constant on the density of excited Yb ions we conclude, that on average 3 to 4 excited Yb ions create or bleach one color center responsible for the core excess loss.

Investigating the amount of zeroing in modern sediments of River Danube, Austria

Sediments attributed to flooding events of River Danube concerning the bleaching of the optical stimulated luminescence (OSL) signal were investigated. It is demonstrated that the OSL signal in both quartz and feldspar is not completely but differentially bleached in the sediment grains. Partial bleaching of the samples is clearly indicated by the scatter of equivalent dose determined for several individual single aliquots. It is also shown that residual ages in feldspars are significantly higher than those calculated for quartz. It is furthermore demonstrated that analysing measurement-time dependent equivalent dose estimates is not a suitable method to identify partial bleaching in the investigated sediment grains. However, the transport and deposition process of the investigated samples was probably disturbed by an artificial input of sediment, and this case study may thus not be representative of undisturbed high flood events in the past.

Dating of lower terrace sediments from the Middle Rhine area, Germany

Modern and known-age Pleistocene fluvial sediments were investigated by optical dating of quartz to test the suitability of the approach for dating deposits from the deeply incised Middle Rhine Valley. Samples from modern flood sediments revealed skewed distributions indicating different residual levels of equivalent dose ( D e) within the different aliquots. Nevertheless, a substantial number of aliquots from the modern deposits reflect D e values close to zero. For the Pleistocene samples, optical ages are in general consistent with age control given by the presence of the Laacher See Tephra and radiocarbon dating. However, some samples overestimate the known age by a few thousand years when using the arithmetic mean. This is apparently explained by including aliquots in the determination of mean D e where the optical signal was incompletely bleached at deposition. The most difficult issue in this context is identifying a suitable approach that can distinguish between the variability of D e due to partial bleaching and microdosimetry. However, even when considering these limitations it appears that optical dating will by a quite suitable method to date Pleistocene sediments from such a complex fluvial environment, especially when focusing on a precision scale beyond a few thousand years.

Optically Stimulated Luminescence (OSL) dating of glacial sediments from Arctic Russia ‐ depositional bleaching and methodological aspects

Optical dating has been extensively used for stratigraphical correlation in the reconstruction of Eurasian ice‐sheet dynamics and palaeoenvironmental changes during the last glaciation. In recent terrestrial studies in Arctic Russia, Optically Stimulated Luminescence (OSL) is the main chronological tool, and has been used across the whole of the Eurasian north. We report new OSL ages obtained on glaciofluvial and glaciolacustrine sediments from the Arkhangelsk and Taymyr regions of Arctic Russia and discuss the characteristics of the quartz OSL signal in terms of its saturation limit, variability among samples from the same location, and initial signal resetting in different depositional environments. It is shown that effect of partial bleaching in our mainly Weichselian samples is trivial because: modern analogues are well zeroed; there is good agreement between OSL and 14C ages in young samples; and skewness in the dose distribution of relatively older samples is mainly due to varying shapes of the growth curves. The overall reliability of the OSL ages from Arctic Russia, when compared with the limited independent age controls available, appears to be good.

Equivalent dose in quartz from young samples using the SAR protocol and the effect of preheat temperature

Major concerns in the dating of samples younger than a few hundred years by the optically stimulated luminescence (OSL) technique are thermal transfer and partial bleaching. Thermal transfer during preheating enhances the OSL signal due to the charge transfer from thermally sensitive, but light-insensitive, traps to optical centres of quartz and results in an overestimate in equivalent dose, especially for very young samples. In this study, the single-aliquot regenerative-dose protocol is used to obtain values of equivalent dose ( D e ) from young samples taken from various environments around Istanbul. Within this framework, we aim to investigate the effect of preheat temperature on equivalent dose from 150 to 300 ∘ C , the reproducibility of D e measurements for young deposits and the contribution from thermal transfer of charge to the equivalent dose estimation. It was observed that the measured dose is influenced significantly by preheat temperature and the increase in the D e is clearly due to thermal transfer of charge from deep thermally sensitive traps to OSL trap during preheating of the samples prior to the main OSL measurements.

Assessing the reproducibility and accuracy of optical dating of fluvial deposits

Optical dating is increasingly being applied to fluvial deposits to derive rates of geomorphological and sedimentary processes. Partial bleaching of the water-transported sediment grains is a common occurrence, however, and creates problems in deriving burial ages. This paper presents results from optically stimulated luminescence (OSL) dating performed on samples collected from discrete reaches of palaeochannels of the Klip River, South Africa, in order to determine when bedload transport last occurred. The samples were analysed using the single-aliquot regenerative-dose protocol on aliquots made up of ∼30 quartz grains. OSL ages were calculated using both the finite mixture model and minimum age model; comparison of the ages for samples with radiocarbon ages for overlying organic-rich sediment indicates that the finite mixture model gives more accurate results. Samples collected from along the same reach of palaeochannel do not always give consistent burial ages, and careful interpretation of the results is needed. This study demonstrates the importance of the selection of sample locations, and the need for appropriate analysis of the equivalent dose distributions to derive the burial dose and hence the age of a sample.

Cleansing the long-term micropropagated triploid watermelon cultures from covert bacteria and field testing the plants for clonal fidelity and fertility during the 7–10 year period in vitro

The study was aimed primarily at cleansing the in vitro-decline displaying long-term micropropagated triploid watermelon ‘Arka Manik’ cultures from covert bacteria and their further field testing. Disinfectant treated shoots showed endophytic survival but to a lesser extent in shoot-tips. Culturing the NaOCl (5 min) treated shoot-tips on filter paper bridges in liquid watermelon medium containing single antibiotic (gentamycin (Gm), amoxycillin (Ax) or cefazolin (Cz) at 50, 250, 500 or 1000 mg l−1) for 1 month followed by repeated indexing of medium and tissue for two-four subculture passages facilitated the cleansing of cultures with 12.5% recovery as monitored for 2 years. Partial bleaching damage by NaOCl, phytotoxicity to higher levels of antibiotics, poor growth response in the initial sucrose-free medium and rampant hyperhydricity came in the way of a higher recovery. The effectiveness of the above approach was ascertained after back inoculating clean cultures with a mixture of Gram-positive and Gram-negative bacteria yielding 30, 45 and 35% clean cultures in Gm, Ax and Cz (250 mg l−1 for 1 month) treatments, respectively in modified medium compared with 10% recovery after mere HgCl2 surface sterilization. The results indicated that antibiotic treatment was essential but not its choice, and extended culture-indexing subsequent to disinfection or antibiotic treatment was crucial in identifying clean stocks. Cleansed cultures, showed restoration of growth but a drop in rooting. Most of the in vitro cultures appeared normal and true-to-type during the 7–10 year period in vitro but a small proportion of bacteria-harboring stocks displayed ‘epigenetic variations’. Acclimatized plants and those in the field also appeared true-to-type but for a minor proportion derived from bacteria-harboring stocks. Field-plants which originated from bacteria-freed stocks after 9 years of continuous culturing were normal and fertile validating the possibility of keeping treasured cultures in vitro for long periods if covert contaminants are checked.