Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi, II: Decomposition of particulate organic matter

The quantitative relationship between organic carbon and mineral contents of particles sinking below 1800 m in the ocean indicates that organisms with mineral shells such as coccolithophores are of special importance for transporting carbon into the deep sea. Several hypotheses about the mechanism behind this relationship between minerals and organic matter have been raised, such as mineral protection of organic matter or enhanced sinking rates through ballast addition. We examined organic matter decomposition of calcifying and non-calcifying Emiliania huxleyi cultures in an experiment that allowed aggregation and settling in rotating tanks. Biogenic components such as particulate carbon, particulate nitrogen, particulate volume, pigments, transparent exopolymer particles (TEP), and particulate amino acids in suspended particles and aggregates were followed over a period of 30 d. The overall pattern of decrease in organic matter, the amount of recalcitrant organic matter left after 30 d, and the compositional changes within particulate organic matter indicated that cells without a shell are more subject to loss than calcified cells. It is suggested that biogenic calcite helps in the preservation of particulate organic matter (POM) by offering structural support for organic molecules. Over the course of the experiment, half the particulate organic carbon in both calcifying and non-calcifying cultures was partitioned into aggregates and remained so until the end of the experiment. The partial protection of particulate organic matter from solubilization by biominerals and by aggregation that was observed in our experiment may help explain the robustness of the relationship between organic and mineral matter fluxes in the deep ocean.     

Iron availability and the release of iron-complexing ligands by Emiliania huxleyi

The ubiquitous algal species, Emiliania huxleyi, was incubated in sea water supplemented only with nitrate and phosphate (N and P) without chelating agents to control metal speciation. Growth was slow in a “low-iron” culture containing 1.3 nM iron and was found to be iron-limited, growth-accelerating when a 1-nM iron addition was made. The growth rate in a “high-iron” culture (5.4 nM iron) was greater, reaching 0.4 div day⁻¹ but this culture too was found to have become iron-limited when a 9-nM iron addition was made on day 17 of the incubation. Both cultures were found to release iron-complexing ligands in excess of the iron concentration, 6 nM in the low-iron culture, and 10 nM in the high-iron culture. More ligands were produced after the iron addition taking the ligand concentration to 11 nM in the low-iron culture. The data show that the ligands are released in response to the iron addition, when at least some of the iron had already been taken up. This type of release is contrary to the concept of a siderophore, which is supposed to be released in periods of lack of iron; however the increase in the ligand concentration is similar to that released by the natural community in response to the iron addition in the IRON-EX II experiment [Rue, E.L., Bruland, K.W., 1997. The role of organic complexation on ambient iron chemistry in the equatorial Pacific Ocean and the response of a mesoscale iron addition experiment. Limnol. Oceanogr. 42, 901–910]. The enhanced growth in the cultures when more iron was added indicated that the organically complexed iron present in the cultures was not immediately available to the organisms (or at least not at sufficiently high rate), and that the organisms responded to freshly added, inorganic, iron.     

Structural, electronic and optical properties of orthorhombic distorted perovskite TbMnO3

This paper calculates the structural parameters, electronic and optical properties of orthorhombic distorted perovskite-type TbMnO₃ by first principles using density functional theory within the generalised gradient approximation. The calculated equilibrium lattice constants are in a reasonable agreement with theoretical and experimental data. The energy band structure, density of states and partial density of states of elements are obtained. Band structures show that TbMnO₃ is an indirect band gap between the O 2p states and Mn 3d states, and the band gap is of 0.48 eV agreeing with experimental result. Furthermore, the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, refractive index and energy loss spectrum are calculated and analysed, showing that the TbMnO₃ is a promising dielectric material.     

Phytoplankton growth, microzooplankton herbivory and community structure in the southeast Bering Sea: insight into the formation and temporal persistence of an Emiliania huxleyi bloom

Using the seawater dilution technique, we measured phytoplankton growth and microzooplankton grazing rates within and outside of the 1999 Bering Sea coccolithophorid bloom. We found that reduced microzooplankton grazing mortality is a key component in the formation and temporal persistence of the Emiliania huxleyi bloom that continues to proliferate in the southeast Bering Sea. Total chlorophyll a (Chl a) at the study sites ranged from 0.40 to 4.45 μg C l⁻¹. Highest phytoplankton biomass was found within the bloom, which was a mixed assemblage of diatoms and E. huxleyi. Here, 75% of the Chl a came from cells >10 μm and was attributed primarily to the high abundance of the diatom Nitzschia spp. Nutrient-enhanced total phytoplankton growth rates averaged 0.53 d⁻¹ across all experimental stations. Average growth rates for >10 μm and <10 μm cells were nearly equal, while microzooplankton grazing varied among stations and size fractions. Grazing on phytoplankton cells >10 μm ranged from 0.19 to 1.14 d⁻¹. Grazing on cells <10 μm ranged from 0.02 to 1.07 d⁻¹, and was significantly higher at non-bloom (avg. 0.71 d⁻¹) than at bloom (avg. 0.14 d⁻¹) stations. Averaged across all stations, grazing by microzooplankton accounted for 110% and 81% of phytoplankton growth for >10 and <10 μm cells, respectively. These findings contradict the paradigm that microzooplankton are constrained to diets of nanophytoplankton and strongly suggests that their grazing capability extends beyond boundaries assumed by size-based models. Dinoflagellates and oligotrich ciliates dominated the microzooplankton community. Estimates of abundance and biomass for microzooplankton >10 μm were higher than previously reported for the region, ranging from 22,000 to 227,430 cells l⁻¹ and 18 to 164 μg C l⁻¹. Highest abundance and biomass occurred in the bloom and corresponded with increased abundance of the large ciliate Laboea, and the heterotrophic dinoflagellates Protoperidinium and Gyrodinium spp. Despite low grazing rates on phytoplankton <10 μm within the bloom, the abundance and biomass of small microzooplankton (<20 μm) capable of grazing E. huxleyi was relatively high at bloom stations. This body of evidence, coupled with observed high grazing rates on large phytoplankton cells, suggests the phytoplankton community composition was strongly regulated by herbivorous activity of microzooplankton. Because grazing behavior deviated from size-based model predictions and was not proportional to microzooplankton biomass, alternate mechanisms that dictate levels of grazing activity were in effect in the southeastern Bering Sea. We hypothesize that these mechanisms included morphological or chemical signaling between phytoplankton and micrograzers, which led to selective grazing pressure.     

Modelling phytoplankton succession on the Bering Sea shelf: role of climate influences and trophic interactions in generating Emiliania huxleyi blooms 1997–2000

Several years of continuous physical and biological anomalies have been affecting the Bering Sea shelf ecosystem starting from 1997. Such anomalies reached their peak in a striking visual phenomenon: the first appearance in the area of bright waters caused by massive blooms of the coccolithophore Emiliania huxleyi (E. huxleyi). This study is intended to provide an insight into the mechanisms of phytoplankton succession in the south-eastern part of the shelf during such years and addresses the causes of E. huxleyi success by means of a 2-layer ecosystem model, field data and satellite-derived information. A number of potential hypotheses are delineated based on observations conducted in the area and on previous knowledge of E. huxleyi general ecology. Some of these hypotheses are then considered as causative factors and explored with the model. The unusual climatic conditions of 1997 resulted most notably in a particularly shallow mixed layer depth and high sea surface temperature (about 4 °C above climatological mean). Despite the fact that the model could not reproduce for E. huxleyi a clear non-bloom to bloom transition (pre- vs. post-1997), several tests suggest that this species was favoured by the shallow mixed layer depth in conjunction with a lack of photoinhibition. A top-down control by microzooplankton selectively grazing phytoplankton other than E. huxleyi appears to be responsible for the long persistence of the blooms. Interestingly, observations reveal that the high N:P ratio hypothesis, regarded as crucial in the formation of blooms of this species in previous studies, does not hold on the Bering Sea shelf.     

Ab initio investigations of the charge transport properties of endohedral M@C20 (M= Na and K) metallofullerenes

Using density functional theory and quantum transport calculations based on nonequilibum Green's function formalism, we investigate the charge transport properties of endohedral M@C₂₀ (M= Na and K) metallofullerenes. Our results show that the conductance of C₂₀ fullerene can be obviously improved by insertion of alkali atom at its centre. Both linear and nonlinear sections are found on the I-V curves of the Au-M@C₂₀-Au two-probe systems. The novel negative differential resistance behaviour is also observed in Na@C₂₀ molecule but not in K@C₂₀.     

Benthic remineralization and burial of biogenic SiO2, CaCO3, organic carbon, and detrital material in the Southern Ocean along a transect at 170° West

We investigated the composition, recycling, and mass accumulation rates of sediments along a transect in the Southern Ocean located from 66°S to 57°S at 170°W. This transect also corresponds to the location of a sediment trap mooring line. The sediments at the seven sites studied range from largely terrigenous material to nearly pure (>90%) biogenic silica. CaCO₃ is a minor but persistent component at most sites. Mass accumulation rates have been determined on the basis of excess ²³⁰Th in the sediments, i.e., ²³⁰Th-normalized accumulation rates. The influence of redistribution of sediments on the sea floor has been estimated from ¹⁴C analyses. The recycling of material delivered to the sediments has been characterized on the basis of pore water studies that make extensive use of both in situ sampling and shipboard extractions. The influence of the highly variable rates of input of particulate matter that characterize much of the Southern Ocean upon pore water gradients and fluxes across the sediment water interface has been considered.We find only poor correspondence between BSiO₂ burial fraction (=burial/particulate flux), a quantifiable measure of preservation efficiency, and BSiO₂ particulate rain along the transect. However, preservation does appear to be closely linked to a combination of sedimentation rate and particulate rain.The burial fraction of BSiO₂ is small relative to benthic rain (5–19%). Despite the small fraction buried, burial flux normalized to (sedimentation rate)^1/2 appears to provide a very consistent means of predicting benthic particulate rain over a large range of rain rates, including data from a number of different studies and environments. At sites with BSiO₂ rain 250 mmol m⁻² yr⁻¹ the average difference between predicted and observed rain is 25–30%. Such rain rates occur in many marine areas, particularly the Southern Ocean, with the result that this relationship potentially provides a means of estimating BSiO₂ benthic rain over prolonged periods in the past on the basis of readily measured sediment parameters.At the southern-most deep ocean station, the particulate flux was characterized by an extremely high C_org/CaCO₃ ratio (>10), but this high ratio does not appear to have a substantial influence on CaCO₃ burial. CaCO₃ is preserved in the sediments at this site despite a particulate flux with a 10-fold excess of C_org above that required for complete dissolution in the sediments. The unexpectedly high preservation of CaCO₃ is due largely to the very steep C_org oxidation rate profile at this site. As a result, a large fraction of the organic matter oxidized in the sediments does so in close proximity to the sediment–water interface where most of the metabolic CO₂ is neutralized by CO₃²⁻ from the overlying water, rather than by the dissolution of sedimentary CaCO₃.Diagenetic modeling indicates that at several of the stations, the remineralization fluxes of carbonate species across the sediment–water interface may not have been at steady state as a result of the highly pulsed nature of particulate rain in this environment. We estimate that at the time of our sampling it is possible that near-interface fluxes could have been a factor of 1.6–2 times the annual average.At every site on the transect, the burial fluxes of detrital material are substantially greater than the detrital particulate rain measured in the sediment traps, by as much as a factor of 40. Detrital burial is bimodal, being greatest at the southern and northern extremes of the transect. We postulate that the excess of burial over particulate rain in the south reflects the contribution of ice rafted debris at these high latitudes. Increases in the supply at the northern stations must have a different source. We believe that the excess at these stations is material eroded from the sea floor to the west, possibly on the Campbell Plateau, and advected by currents to the northern portion of the transect at depths below the shallow traps.     

Carbonate chemistry and projected future changes in pH and CaCO3 saturation state of the South China Sea

To study the dissolved carbonate system in the South China Sea (SCS) and to understand the water mass exchange between the SCS and the West Philippine Sea (WPS), pH, total alkalinity and total CO₂ were measured aboard the R/V Ocean Researcher 1. Because of the sill that separates these two seas in the Luzon Strait with a maximum depth of 2200 m, the SCS Deep Water has characteristics similar to those of water at about 2200 m in the WPS. The minimum pH and the maxima of normalized alkalinity and total CO₂ commonly found in the open oceans at mid-depth also prevail in the WPS but are, however, very weak in the SCS. Rivers and inflows from Kuroshio Surface and Deep Waters through the Luzon Strait as well as those through the Mindoro Strait transport carbon to the SCS year-round. Meanwhile, the outflowing Taiwan Strait water as well as the SCS Surface and Intermediate Waters of the Luzon Strait transports carbon out of the SCS year-round. The Sunda Shelf is also a channel for carbon transport into the SCS in the wet season and out of the SCS in the dry season.fCO₂ data and mass balance calculations indicate that the SCS is a weak CO₂ source in the wet season but an even weaker CO₂ sink in the dry season. With these facts taken together, the SCS is likely a very weak CO₂ source. Anthropogenic CO₂ penetrates to about 1500 m in depth in the SCS, and the entire SCS contains 0.60 ± 0.15 × 10¹⁵ g of excess carbon. Typical profiles of pH as well as the degree of saturation of each of calcite and aragonite in 1850 and 1997 are presented, and those for 2050 AD are projected. The maximum decrease in pH is estimated to be 0.16 pH units in the surface layer when the amount of CO₂ is doubled. It is anticipated that aragonite in the upper continental slope will likely start to dissolve, thereby neutralizing excess CO₂ by around 2050 AD. This paper is unique in that it presents the results of the first attempt ever to estimate the past, present and future physico-chemical properties of the world's largest marginal sea.     

Cholinesterase activities in the Antarctic scallop Adamussium colbecki: Tissue expression and effect of ZnCl2 exposure

Biochemical characterization of cholinesterase activity (ChE) was carried out on the Antarctic scallop Adamussium colbecki collected in winter 2000 from Campo Icaro (Ross Sea, Antarctica) in order to increase its suitability as a sentinel organism for monitoring the Antarctic environment. The digestive gland, gills and adductor muscle were investigated for substrate specificity and inhibitors sensitivity using acetylthiocholine iodide (ASCh) and butyrylthiocholine iodide (BSCh) as substrates and tetra (monoisopropyl)pyrophosphor-tetramide (Iso-OMPA), 1,5-bis(4-allyldimethylammoniumphenyl)-penthan-3-one dibromide (BW284c51) and the insecticide chlorpyrifos as inhibitors. Effect of in vivo exposure to ZnCl₂ was also investigated. All the tissues expressed ChE activity (gill > adductor muscle > digestive gland) and low substrates specificity throughout the hydrolysis of both ASCh and BSCh substrates. Partial (25–29%) and total inhibition (100%) of ChE activity in gills was demonstrated following in vitro incubation with Iso-OMPA and BW284c51 (3 mM), respectively. Concentration-dependent inhibition was also evident with chlorpyrifos in the range 10⁻⁴–10⁻¹⁰ M (IC₅₀ 10⁻⁶) while in vivo exposure to ZnCl₂ did not seem to affect ChE activity in the scallop. The potential use of ChE in the A. colbecki as biomarker for monitoring water contamination in the marine Antarctic environment is discussed.     

Si2O2 molecule: structure of ground state and the excited properties under different external electric fields

Geometry and vibrational frequencies of the ground state of Si₂O₂ molecule are studied using density function theory (DFT) at the level of cc-pvtz and 6-311++G^**. It is found that the optimizing value by B3lyp/cc-pvtz is closer to the experimental data. The excited properties under different external electric fields are also investigated by the time-dependent-DFT method. Transitions from the ground state of Si₂O₂ molecule to the first singlet state under different external electric fields can take place more easily. The corresponding absorption spectral line is about 360 nm in wavelength and the excitation energy is about 3.4 eV.     

Some chemical characteristics of the brines in Bannock and Tyro Basins: salinity, sulphur compounds, Ca, F, pH, At, PO4, SiO2, NH3

Results of the chemical investigation on the Bannock and Tyro Basins are reported.Both basins were found to be hypersaline ( 10 times higher than salinity of normal seawater) and anoxic. In all investigated basins a region of transition, a few meters thick, was identified at depths > 3327 dbar. It is characterized by a sharp gradient of salinity, and all concentrations of analysed species increase strongly except for dissolved oxygen and nitrate, which immediately drop to zero. This region appears as a sharp boundary that prevents mixing. As a result, in the presence of organic matter, an anoxic condition developed with the complete depletion of dissolved oxygen. At the same time, hydrogen sulphide and ammonium accumulated within the brine. Between the Bannock and the Tyro brines differences occur in the measured concentrations of H₂S, SO²⁻₄, Ca²⁺ and NH₃. There are some differences also within the Bannock area sub-basins.The Libeccio sub-basin, in the Bannock area, contains a double-layered brine: the upper layer is 140 dbar thick and the lower layer is 300 dbar thick. A second interface between upper and lower brines develops at a depth of 3500 dbar. Nearly all of the measured concentrations vs. depth show the double layer, with the exception of ammonium, the concentration of which remains nearly constant throughout the anoxic column. Profiles of the other species analyzed show remarkable differences on passing from the upper to the lower brine. Hydrogen sulphide, sulphate and fluoride concentrations appear constant and then increase at the second interface. The calcium concentration is also constant in the upper brine, but decreases at the second interface. Total alkalinity and phosphate concentrations show a maximum peak just below the first interface. However, after passing through the second interface all the chemical parameters exhibit an almost constant behaviour down to the bottom.Hypersaline conditions are attributed to the dissolution of Messinian evaporite, and anoxia is suggested to originate from the oxidation of organic matter present in sediments and from the absence of bottom water circulation in such a deep and enclosed environment.The chemical conditions can be summarized as follows: in the Libeccio Basin the values for the species analysed have the ranges: 39–321 psu for ‘salinity’, 8.2−6.5 for pH, 2.7–4.0 mM for total alkalinity, 0.2-0 mM for dissolved oxygen, 0–1669 μM for hydrogen sulphide, 0–198 μM for thiol, 31–99 mM for sulphate, 11–21 mM for calcium, 7–100 μM for fluoride, 0.2–3080 μM for ammonium, 5.8-0 μM for nitrite, 0.2–12 μM for phosphate and 8–130 μM for silicate.     

锰掺杂对Ba(Zr,Ti)O3陶瓷压电与介电性能的影响

采用氧化物固相反应法制备了锰掺杂改性的Ba(Zr_0.06Ti_0.94)O₃陶瓷.研究了锰的掺杂量对Ba(Zr_0.06Ti_0.94)Mn_xO₃ (BZTM)陶瓷的结构、介电和压电性能的影响.实验发现,当锰含量x<0.5 mol%时进入晶格,使材料压电性能提高,损耗减小,表现出受主掺杂的特性;当锰含量x>0.5 mo     

桐花树胎生发育过程中内源性脱落酸、赤霉素和糖分含量的变化

种子胎生是红树植物典型的适应特征之一。本研究以胎生红树植物桐花树（Aegiceras corniculatum）花蕾、种子和胚轴为材料,研究了胎生发育过程中繁殖体内源性脱落酸（ABA）、赤霉素（GA₃）、可溶性糖和淀粉含量的动态变化。结果表明：ABA含量在胎生发育过程中呈现先降低后升高的显著变化,即在种子形成前的花蕾期最高\[（1.86±0.07） μg/g\],在种子期达到最低值\[（0.75±0.07） μg/g\],然后随种子萌发逐渐回升;GA₃含量则呈现相反的变化趋势,先升高后降低,即在种子期最高\[（12.60±0.05 ）μg/g\],然后随种子萌发逐渐降低\[（1.97±0.05） μg/g\];繁殖体可溶性糖含量随发育进程先升高后降低,在种子萌发早期达到最高值;淀粉含量始终呈现增加的趋势,并在种子萌发晚期达到最高值。在胎生过程中,桐花树繁殖器官的内源性ABA和GA₃含量以及可溶性糖和淀粉含量的动态变化表明,ABA和GA₃通过对糖代谢的综合调控作用可能是红树植物胎生的重要机制之一。     

Accurate measurement of O2, N2, and Ar gases in water and the solubility of N2

The degree of atmospheric saturation for O₂, Ar, and N₂ gases in water can be determined to accuracies of ±0.1–0.3% using mass spectrometry to determine the gas ratios and Winkler titrations for oxygen analysis. We describe methods used to obtain this level of accuracy and precision. Oxygen accuracy of ±0.1% can be obtained by careful attention to standardization using KIO₃ standards that have been corrected for impurities. Accurate O₂/Ar and O₂/N₂ gas ratios (±0.1–0.2%) are obtainable by measuring the mass ratios against the atmosphere if the effect of different gas concentrations on the performance of the mass spectrometer are taken into account. Oxygen and argon saturation values have been determined previously to accuracies of less than or equal to ±0.1%, but published estimates of the saturation value for nitrogen differ by more than 1%. We have redetermined the N₂ saturation value at 19°C and zero salinity to be 0.92% greater than the results reported in the work of Weiss (1970).     

合浦珠母贝转录因子PF-CREB3L2基因的克隆和鉴定

克隆得到了合浦珠母贝(Pinctada fucata)PF-CREB3L2蛋白的c DNA序列,其c DNA全长1 983 bp,其中开放阅读框长度为1 728 bp,编码的蛋白含有575个氨基酸残基。组织表达分布实验发现,其在合浦珠母贝内脏囊中表达量最高,在外套膜和鳃中也有大量表达,推测其广泛参与合浦珠母贝的贝壳形成等生理活动。贝壳损伤修复实验中发现,在合浦珠母贝贝壳受到损伤后,PF-CREB3L2和基质蛋白的表达量会迅速上升,且PF-CREB3L2的峰值出现更早,推测其通过影响基质蛋白转录,参与合浦珠母贝生物矿化的调控过程。PF-CREB3L2与合浦珠母贝基质蛋白表达相关性的分析发现,PF-CREB3L2与Prisilkin39、KRMP的表达量呈现显著的正相关,说明其可能特异性地调控某些基质蛋白的转录。     

Cs2NaMF6(M＝Al,Ga):Cr3+ 络合分子体系局域结构和基态分裂的理论研究

采用双自旋轨道耦合系数模型并结合完全能量矩阵的方法对Cs₂NaMF₆(M=Al, Ga):Cr³⁺ 体系中Cr³⁺ 离子的基态分裂和局域结构进行了研究.通过模拟光谱和EPR谱确定了Cr³⁺ 取代 M³⁺ 形成的两种占位结构的畸变角,发现用双自旋轨道耦合系数模型与单自旋轨道耦合系数模型计算出的畸变角Δθ存在较大的差异.这表     

Structure, room-temperature magnetic and optical properties of Mn-doped TiO2 nano powders prepared by the sol-gel process

TiO₂ nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol-gel process, and were annealed at 500 ℃ and 800 ℃ in air for 2 hrs. X-ray diffraction (XRD) measurements indicate that the Mn-TiO₂ nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 ℃ are of pure anatase and rutile, respectively. The scanning electron microscope (SEM) observations reveal that the crystal grain size increases with the annealing temperature, and the high resolution transmission electron microscopy (HRTEM) investigations further indicate that the samples are well crystallized, confirming that Mn has doped into the TiO₂ crystal lattice effectively. The room temperature ferromagnetism, which could be explained within the scope of the bound magnetic polaron (BMP) theory, is detected in the Mn-TiO₂ samples with Mn concentration of 2 at%, and the magnetization of the powders annealed at 500 ℃ is stronger than that of the sample treated at 800 ℃. The UV-VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO₂ powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping.     

Improvement of photorefractive properties in Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Photorefractive properties of Hf:Fe:LiNbO₃ crystals with various [Li]/[Nb] ratios have been investigated at 488 nm wavelength based on the two-wave coupling experiment. High diffraction efficiency and large recording sensitivity are observed and explained. The decrease in Li vacancies is suggested to be the main contributor to the increase in the photoconductivity and subsequently to the induction of the improvement of recording sensitivity. The saturation diffraction efficiency is measured up to 80.2%, and simultaneously the recording sensitivity of 0.91 cm/J is achieved to in the Hf:Fe:LiNbO₃ crystal grown from the melt with the [Li]/[Nb] ratio of 1.20, which is significantly enhanced as compared with those of the Hf:Fe:LiNbO₃ crystal with the [Li]/[Nb] ratio of 0.94 in melt under the same experimental conditions. Experimental results definitely show that increasing the [Li]/[Nb] ratio in crystal is an effective method for Hf:Fe:LiNbO₃ crystal to improve its photorefractive properties.