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The Miocene Climatic Optimum (MCO) from ~17 to 14 million years ago (Ma) represents an enigmatic reversal in Cenozoic cooling. A synthesis of marine paleotemperature records shows that the MCO was a local maximum in global sea surface temperature superimposed on a period from at least 19 Ma to 10 Ma, during which global temperatures were on the order of 10°C warmer than at present. Our high-resolution global reconstruction of ocean crustal production, a proxy for tectonic degassing of carbon, suggests that crustal production rates were ~35% higher than modern rates until ~14 Ma, when production began to decline steeply along with global temperatures. The magnitude and timing of the inferred changes in tectonic degassing can account for the majority of long-term ice sheet and global temperature evolution since 20 Ma.

The reconstruction of seawater calcium concentration ([Ca2+]SW) in the geologic past is crucial to our understanding of biogeochemical processes and elemental cycling as linked to long-term climate change. Published [Ca2+]SW estimates for the Cenozoic differ from each other in both the direction and magnitude of the change, and are associated with large uncertainties. Here we demonstrate the potential of Na/Ca in planktic foraminifera as a new proxy for reconstructing Cenozoic variations in seawater Na/Ca. Because of the long oceanic residence time of Na+ (≫50 Myr), variations in foraminiferal Na/Ca should in principle reflect changes in [Ca2+]SW. Our culture experiments on live planktic species validate the approach, showing that foraminiferal Na/Ca responds to changes in [Ca2+]SW when [Na+]SW is kept constant, consistent with previous experiments on a shallow water benthic foraminifer and on inorganic calcite. The culture study suggests that planktic Na/Ca is affected, to a small extent, by calcite saturation state (Ωcalcite) but not resolvably affected by temperature or salinity. A core tops transect of the planktic foraminifer Trilobatus sacculifer shows similar decreasing trends in Na/Ca and Sr/Ca with water depth that can be associated with dissolution of the tests. The strong covariance with Sr supports the hypothesis that a dominant fraction of the Na resides in lattice positions within the calcite test. Down core planktic foraminiferal records from the Atlantic and Pacific Oceans consistently show 13–28% lower Na/Ca during the mid-Miocene than during the late Pleistocene. After considering the effects of temperature, salinity and diagenesis, we conclude that the observed down core decrease in Na/Ca primarily reflects changes in seawater calcium concentration. Using the calibrations generated from our culture experiments and core top data we reconstructed [Ca2+]SW, suggesting [Ca2+]SW in the mid-Miocene was 46 ± 22% higher than at present, and decreased toward present with a pattern resembling the Neogene climate evolution represented by the benthic δ18O record. The new reconstruction of [Ca2+]SW for the past 16 Myr narrows the range suggested by other [Ca2+]SW proxies, and potentially offers a new way to generate continuous records of seawater calcium concentration at sub-million years resolution.

The globally averaged calcite compensation depth has deepened by several hundred metres in the past 15 Myr. This deepening has previously been interpreted to reflect increased alkalinity supply to the ocean driven by enhanced continental weathering due to the Himalayan orogeny during the late Neogene period. Here we examine mass accumulation rates of the main marine calcifying groups and show that global accumulation of pelagic carbonates has decreased from the late Miocene epoch to the late Pleistocene epoch even though CaCO3 preservation has improved, suggesting a decrease in weathering alkalinity input to the ocean, thus opposing expectations from the Himalayan uplift hypothesis. Instead, changes in relative contributions of coccoliths and planktonic foraminifera to the pelagic carbonates in relative shallow sites, where dissolution has not taken its toll, suggest that coccolith production in the euphotic zone decreased concomitantly with the reduction in weathering alkalinity inputs as registered by the decline in pelagic carbonate accumulation. Our work highlights a mechanism whereby, in addition to deep-sea dissolution, changes in marine calcification acted to modulate carbonate compensation in response to reduced weathering linked to the late Neogene cooling and decline in atmospheric partial pressure of carbon dioxide. A redistribution of marine calcifiers along with a reduction in weathering led to increased seafloor carbonate deposition during the late Neogene, according to a global compilation of carbonate mass accumulation rate records from sediment cores.

Examination of the holotype of Globorotalia barisanensis Le Roy, 1939, has revealed that this species from the Middle Miocene of central Sumatra is non-keeled, contradicting the synonymizing of G. barisanensis with Globorotalia fohsi. Because the type sample is untraceable, we examined the available type specimens (holotype and eight paratypes), notes and data presented by previous researchers, and material from the near-topotype locality of Paragloborotalia siakensis, to clarify Le Roy's concept of G. barisanensis. Our investigation has revealed that the Middle Miocene of central Sumatra contains two different groups of globorotaliids: the Globorotalia menardii group and the G. fohsi group, and that G. barisanensis belongs to the latter. The paratypes examined belong to Globorotalia peripheroacuta and to forms transitional between G. peripheroacuta and Globorotalia praefohsi. The holotype, as described by Le Roy, is included in G. peripheroacuta as well, despite the observation that it differs from the paratypes in the abnormally inflated final chamber. In retrospect, the specimen selected as the holotype was an unfortunate choice as it has long been misinterpreted and used to denominate the earliest representatives of the G. fohsi group (viz. G. fohsi barisanensis) until G. barisanensis was reinterpreted as a junior synonym of G. fohsi based on a flawed redrawing of a fully keeled holotype of G. barisanensis. We conclude that Le Roy's concept of G. barisanensis was broad and may have included G. fohsi and Globorotalia peripheroronda as well. Remarkably, after 67 years of misinterpretation since Bolli (1950), G. barisanensis appears to be a valid name and a senior synonym of G. peripheroacuta. However, we recommend that it will be more practical to conserve the latter name, which is well established in the literature.

The taxonomy and phylogeny of the planktonic foraminifera Fohsella lineage has been controversial for nearly 50 years, despite its widespread application in Middle Miocene stratigraphy. We have re-examined type specimens of this lineage together with specimens from a continuous deep-sea record (Ocean Drilling Program Site 806, Ontong Java Plateau, western equatorial Pacific Ocean) with an astronomic chronology. Landmark-based geometric morphometry is employed to visualize and quantify morphologic variation within this lineage. Combined morphologic and stratigraphic data help clarify the evolutionary occurrence of diagnostic traits that characterize two problematic taxa, F. praefohsi and F. “praefohsi”, resulting in a revised taxonomy and phylogeny of the lineage. We emphasize the importance of biometric studies of populations from continuous geologic records in establishing taxonomy and phylogeny of planktonic foraminifera. In the past, over-emphasis on the importance of type specimens as reference points in delineating various evolutionary stages of the Fohsella lineage has resulted in inaccurate phylogenetic reconstructions.

The Songliao Basin is the largest oil-bearing basin in China. In the absence of sufficient evidence, the possibility of seawater incursion(s) into the Songliao Basin remains controversial. Recently, we discovered relatively abundant foraminifera fossils from units 1 and 2 of the Nenjiang Formation of borehole SK-1. Benthic foraminifera (Gavlinella sp., Anomalinoides sp., Pullenia sp., Haplophragmoides sp., Karrorulina hokkaidoana, Clavulinoides sp.), as well as planktonic foraminifera (Archaeoglobigerina blowi, Archaeoglobigerina cretacea and Hedbergella flandrini), were identified. These fossils were widely distributed in the marine Cretaceous. According to the global distribution of the above-mentioned planktonic foraminifera, the age of these fossil bearing strata appears to be Late Coniacian to Santonian. More importantly, these foraminifera provide direct evidence for marine water incursions into the Songliao Basin during deposition of the Lower Nenjiang Formation.

A kinematic (geometrical) diffraction simulation model has been developed to provide understanding of direct dislocation images on synchrotron white-beam X-ray topographs, and has been successfully applied to illustrate the contrast formation mechanisms involved in images of micropipe-related superscrew dislocations in silicon carbide crystals. The coincidence of the simulations with the contrast features of the superscrew dislocation images, recorded using a series of synchrotron topography techniques, shows that this model is capable of revealing the detailed diffraction behavior of the highly distorted region around the dislocation core and determining the quantitative characteristics of the dislocations. The simulation technique is thus demonstrated to be a simple but efficient method for interpretation of synchrotron topographs, and may be applied to explain the topographic contrast characters of general crystal defects.

Synchrotron white beam x-ray topography (SWBXT) and Nomarski optical microscopy (NOM) have been used to characterize 4H-SiC epilayers and to study the character of triangular inclusions therein. 4H-SiC substrates misoriented by a range of angles from (0001), as well as (1 100) and (1120) oriented substrates were used. For epilayers grown on substrates misoriented by 3.5° from (0001) toward , the triangular inclusions were identified as consisting of two 3C-SiC structural configurations which are related to each other by a 180° rotation about the [111] axis. The epitaxial relationships between the 3C inclusions and the 4H-SiC epilayers (or substrates) were also determined. No evidence was found for the nucleation of 3C-SiC inclusions at superscrew dislocations (along the [0001] axis) in the 4H-SiC substrates. Increasing the off-axis angle of the substrates from 3.5 to 6.5° was found to greatly suppress the formation of the triangular inclusions. In the case of substrates misoriented by 8.0° from (0001) toward , the triangular inclusions were virtually eliminated. The crystalline quality of 4H-SiC epilayers grown on the substrates misoriented by 8.0° from (0001) was very good. For the (1100) and (1120) samples, there is no indication of 3C-SiC inclusions in the epilayers. Possible formation mechanisms and the morphology of 3C-SiC inclusions are discussed.

Hollow-core screw dislocations, also known as “micropipes”, along the [0001] axis in 6H-SiC single crystals, have been studied by synchrotron white beam x-ray topography (SWBXT), scanning electron microscopy (SEM), and Nomarski optical microscopy (NOM). Using SWBXT, the magnitude of the Burgers vector of screw dislocations has been determined by measuring the following four parameters: (1) the diameter of dislocation images in back-reflection topographs; (2) the width of bimodal dislocation images in transmission topographs; (3) the magnitude of the tilt of lattice planes on both sides of dislocation core in projection topographs; and (4) the magnitude of the tilt of lattice planes in section topographs. The four methods show good agreement. SEM results reveal that micropipes emerge as holes on the as-grown surface, with their diameters ranging from about 0.1 to a few micrometers. Correlation between topographic images and SEM micrographs shows that micropipes are hollow-core screw dislocations with Burgers vector magnitudes from 2c to 7c (c is the lattice parameter along the [0001] axis). There is no empirical evidence that 1c dislocations have hollow cores. The Burgers vector magnitude of screw disloca-tions, b, and the diameter of associated micropipes, D, were fitted to Frank’s prediction for hollow-core screw dislocations: D = μb2/4π2γ, where μ is shear modulus, and γ is specific surface energy. Statistical analysis of the relationship between D and b2 shows that it is approximately linear, and the constant γ/μ ranges from 1.1 × 10−3 to 1.6 × l0−3 nm.

Screw dislocations along the [0001] axis in 6H−SiC single crystals have been studied extensively by Synchrotron White-Beam X-ray Topography (SWBXT), Scanning Electron Microscopy (SEM), and Nomarski Optical Microscopy (NOM). Using SWBXT, the magnitude of the Burgers vector of screw dislocations has been determined by measuring the following four parameters: 1) the diameter of dislocation images in back-reflection topographs; 2) the width of bimodal dislocation images in transmission topographs; 3) the magnitude of the tilt of lattice planes on both sides of dislocation core in projection topographs; and 4) the magnitude of the tilt of lattice planes in section topographs. The four methods show good agreement. SEM results reveal that micropipes in the form of hollow tubes run through the crystal emerging as holes on the as-grown surface, with their diameters ranging from about 0.1 to a few micrometers. Correlation between topographic images and SEM micrographs shows that micropipes are screw dislocations with Burgers vector magnitudes from 2c to 7c (c is the lattice constant along the [0001] axis). There isno were fitted to Frank’s prediction for hollow-core screw dislocations:D =μb2/4π 2 γ, where μ is the shear modulus, and γ is the specific surface energy. Statistical analysis of the relationship betweenD and b2 shows that it is approximately linear, and the constant, γ/μ, obtained from the slope, ranges from 1.1×10−3 to 1.6×10−3 nm.

Molecular beam epitaxy (MBE) regrowth on a corrugated surface is improved dramatically using a novel technique by which not only a clean surface can be obtained but also the shape of grating can be precisely controlled. A GaAlAs/GaAs multi-quantum well gain-coupled distributed feedback (DFB) laser with an absorptive grating is fabricated all by MBE for the first time. DFB mode oscillation within a range of at least 80/spl deg/C is achieved. Stable single longitudinal mode oscillation is maintained up to 20 mW. >

A novel and simple approach for optimization of a multiple quantum well electroabsorption waveguide modulator is presented. In our approach, all four of the modulator characteristic parameters (on-off ratio, insertion loss, bandwidth, and driving voltage) are included. Design examples for GaAs/AlGaAs multiple quantum well modulators are presented. The accuracy of our model is confirmed by comparison between calculated and published experimental data.

A ternary titanium aluminide alloy, Ti-46Al-3Cr (at%), was discontinuously reinforced with 5 vol% titanium diboride (TiB2), by an in-situ synthesis technique, resulting in a two phase γ(TiAl) (mainly) and α2(Ti3Al) matrix with randomly dispersed TiB2 particle. Interfaces of TiB2-TiAl were investigated by Analytical Electron Microscopy (AEM) and High Resolution Electron Microscopy (HREM). No consistent crystallographic orientation relationship was observed between TiB2 particle and TiAl matrix, and there was no evidence of alloying elements (such as Cr) segregation or interphase formation at the TiB2-TiAl interface. HREM results indicated that no semi-coherent interface between TiB2 and TiAl has been observed. There existed a thin amorphous layer (0.5 to 1.3 nm) at the TiB2-TiAl interface, which may accommodate the large lattice misfit across the interface and enhance the interfacial bonding.

The products and kinetics of solid state reactions between TiC and Ti3Al have been investigated using X-ray diffractometry (XRD) and Auger electron spectroscopy (AES) with Ar ion beam sputtering. Diffusion couples were prepared by sputtering TiC thin films onto polished Ti3AI substrates, and then isothermally annealed in vacuum in the temperature range of 800 to 1000°C for 0.25 to 2.25 hours. The thickness of the interfacial reaction layer was obtained from AES elemental concentration depth profiling, while the reaction products were identified from XRD spectra. In the TiC/Ti3Al system, the reaction product was primarily P(Ti3AlC) phase. The growth-rate of the reaction product was fitted to a parabolic growth law (dZ/dt = k1/Z) and the activation energy of the rate constant was about 36.16 kcal/mole. The reaction mechanism will be discussed on the basis of thermodynamical equilibrium in Ti-Al-C ternary system.

The interfacial compatibility of SiC, Al2O3, and TiC with Ti3Al alloy has been evaluated. Thin films of these three ceramics materials were deposited on Ti3A1 substrates. The thin film diffusion couples were annealed from 600°C to 1000°C, and the thickness of the interfacial layer was obtained from Auger Electron Spectroscopy (AES) concentration depth profiling. The reaction products were identified by X-ray Diffraction (XRD) and AES. In the A12O3/Ti3A1, obvious interdiffusion occurred with some reaction products. In the SiC/Ti3Al, significant interdiffusion and reactions occurred in the interfacial layer, and multilayer reaction zones were found. In the TiC/Ti3Al, the reaction product was primarily the P(Ti3AlC) phase. Kinetic studies of the growth of the interfacial layer showed that SiC reacted most severely with Ti3Al, TiC less so, and AI2O3 the least. The compatibility of these three systems has been assessed.

NiFe films with different thicknesses as were etched under several Ar+-ion-beam energy conditions. The functional dependence of the saturation magnetic flux on the remaining NiFe film thickness was used to determine the magnetic dead layer (MDL) thickness (tMDL). A tMDL of 24A was generated in the NiFe films etched using a 1200-eV Ar+-ion beam. A dual-energy (1200eV∕400eV) etching process was found to be effective in reducing tMDL to 16A without much throughput loss. A combination of optimal etching depth with an appropriate ion-beam energy is necessary in minimizing tMDL. The mechanism of MDL formation is discussed in terms of oxidation and surface roughening of the NiFe films.

Taking into consideration of gain coupling, characteristics such as single-mode selectivity, chirping and light output efficiency of photonic integrated circuits (PIC) integrating distributed feedback (DFB) semiconductor lasers and electroabsorption modulators are analyzed for the first time. Devices with conventional index-coupled (IC), quarter-wave-shifted (QWS) and gain-coupled (GC) DFB laser sections are calculated and compared. The chirping of GC-PIC is nearly the same as that of IC-PIC and QWS-PIC, but the single-mode selectivity of GC-PIC is much better. With a [HR-AR] coating , which is advantageous for high-power operation, GC-PIC shows a much higher probability of single-mode operation than IC-PIC, while QWS-PIC does not function at all.

Ferroelectric domains and strains in a barium titanate (BaTiO3) single crystal, grown by the top-seeded solution growth technique, have been investigated by synchrotron white-beam X-ray topography (SWBXT) and optical microscopy. Conventional radiation X-ray topography studies in this system had previously been hampered by the presence of internal strain fields which made it difficult to observe the overall domain structures. SWBXT was found to be more suitable for this kind of study, with the overall domain configuration in the (100) crystal plate being readily observed. Also the condition of ΔP·g = 0 is almost obeyed for the 90° a–a walls which are predominant in a thin crystal. The 90° a–c wall satisfied the invisibility criterion, leaving only residual strain images. Some curved images of 90° a–a walls were observed, which could be interpreted as resulting from the interference between the 90° a–a domain walls and the internal strain field.