Large Relative Mass Research Articles

The internal ballistics of a spring gun

We consider the features of pellet motion under the elastic force acting from a decompressing spring of a finite mass. The muzzle speed of the pellet decreases as the ratio between spring and pellet mass increases. In the general case, the pellet loses contact with the spring as it is stretched. This effect occurs due to the fact that the peak of elastic displacement wave, propagating from the fixed end, reaches the opposite end of the spring. With a large relative mass of the pellet, it accelerates along a quarter of the sinusoid. At the limit of a very small pellet mass, it moves nearly all the time along with the end of the spring at an almost constant speed, approximately equal to the speed of sound propagation in the spring. In this case, after the initial compression, the pellet passes the equilibrium position, and comes off after moving a similar distance beyond the equilibrium.

Elastic fields generated by multiple small inclusions with high mass density at nearly resonant frequencies

We derive the elastic field generated by multiple small-scaled inclusions distributed in a bounded set of R3. These inclusions are modelled with moderate values of the Lamé coefficients while they have a large relative mass density. These properties allow them to enjoy sequences of resonant frequencies that can be computed via the eigenvalues of the volume integral operator having the Navier fundamental matrix as a kernel, i.e., the Navier volume operator. The dominant field, i.e., the Foldy-Lax field, models the multiple interactions between the inclusions with scattering coefficients that are inversely proportional to the difference between the used incident frequency and the already mentioned resonances. We show, in particular, that to reconstruct remotely the scattered field generated after N interactions between the inclusions, one needs to use an incident frequency appropriately close to the proper resonance of the inclusions. We provide an explicit link between the order N of interactions and the distance from the incident frequency to the resonance. Finally, if the cluster of the inclusions is densely distributed in a given bounded domain, then the expression of the induced dominant field suggests that the equivalent homogenized mass density can change sign depending if the used incident frequencies is smaller or larger than a certain threshold (which is explicitly given in terms of the resonant frequencies of the inclusions).

Pre-sizing of a modular high power density DC/DC converter with GaN components

Finding the most appropriate architecture to achieve a function is a major engineering challenge. In the power conversion context, the question that arises is: what is the best trade-off between an architecture based on a single high-power converter and another based on the combination of multiple low-power converters? This article aims to answer this question in the specific case of the isolated interface between the low voltage (28VDC) and high voltage (±270VDC) buses of an aircraft. Towards this goal, the targeted power electronics converter is carefully modeled in order to obtain an accurate and fast computing model. A technological database of the different usable components is then used to feed an optimization algorithm. The execution of the latter achieves an attractive and robust result showing an excellent performance in terms of power-to-weight ratio, which is the key index of this study. The precision and speed of this computer-aided design is based on analytical models that are quick to run and therefore enable exploring almost exhaustively the search space. More specifically, the high-frequency transformer has a large relative mass and generates significant losses that are difficult to assess. A major modeling effort has been undertaken and has been enabled to define a simplified but convincing and accurate model (successfully assessed on a wide bandwidth using an experimental setup). It was used for the first time in this optimization process. According to the targeted aeronautical specifications, the two best solutions would make it possible to achieve a mass power density of 4.5kW/kg, i.e. twice as high as traditional solutions. This result very clearly shows that the appropriate use of the new GaN transistors makes it possible to make a technological breakthrough. Considering the voltage and current ratings of these components, this shows that the combination of multiple partial converters is very promising and will make it possible in the future to achieve a significant increase in the compactness of electrical power conversion functions. This sizing study therefore clearly shows the potential of the standardized design of power electronics converters and the search for the best combinations (series, parallel) to meet any specific specifications. Additionally, the developed approach, based on a modeling effort, especially as far as the high-frequency transformer is concerned, and collection of manufacturer data, also makes it possible to limit the implementations and associated tests.Hence, the main contributions of this article are (i) the assembly of the analytical models of the various components constituting an isolated DC–DC power supply, (ii) the simplification of an analytical model of the planar HF transformer, its experimental validation and its first use in a loop of optimization, (iii) the fact of showing supporting figures that GaN technology enables technological breakthroughs to achieve high power density, which opens the way to modular architectures based on partial converters of electrical power, (iv) the comprehensive description of a powerful pre-study design tool enabling to greatly reduce power converters’ time to market.

Recent Advances in Porous Polymers for Solid-State Rechargeable Lithium Batteries.

The application of rechargeable lithium batteries involves all aspects of our daily life, such as new energy vehicles, computers, watches and other electronic mobile devices, so it is becoming more and more important in contemporary society. However, commercial liquid rechargeable lithium batteries have safety hazards such as leakage or explosion, all-solid-state lithium rechargeable lithium batteries will become the best alternatives. But the biggest challenge we face at present is the large solid-solid interface contact resistance between the solid electrolyte and the electrode as well as the low ionic conductivity of the solid electrolyte. Due to the large relative molecular mass, polymers usually exhibit solid or gel state with good mechanical strength. The intermolecules are connected by covalent bonds, so that the chemical and physical stability, corrosion resistance, high temperature resistance and fire resistance are good. Many researchers have found that polymers play an important role in improving the performance of all-solid-state lithium rechargeable batteries. This review mainly describes the application of polymers in the fields of electrodes, electrolytes, electrolyte-electrode contact interfaces, and electrode binders in all-solid-state lithium rechargeable batteries, and how to improve battery performance. This review mainly introduces the recent applications of polymers in solid-state lithium battery electrodes, electrolytes, electrode binders, etc., and describes the performance of emerging porous polymer materials and materials based on traditional polymers in solid-state lithium batteries. The comparative analysis shows the application advantages and disadvantages of the emerging porous polymer materials in this field which provides valuable reference information for further development.

The Lower Limbs of Sprinters Have Larger Relative Mass But Not Larger Normalized Moment of Inertia than Controls.

Sprinters exhibit inhomogeneous muscularity corresponding to musculoskeletal demand for sprinting execution. An inhomogeneous morphology would affect the mass distribution, which in turn may affect the mechanical difficulty in moving from an inertia perspective; however, the morphological characteristics of sprinters from the inertia perspective have not been examined. Here we show no corresponding differences in the normalized mass and normalized moment of inertia between the sprinters and untrained nonsprinters. We analyzed fat- and water-separated magnetic resonance images from the lower limbs of 11 male sprinters (100 m best time of 10.44-10.83 s) and 12 untrained nonsprinters. We calculated the inertial properties by identifying the tissue of each voxel and combining the literature values for each tissue density. The lower-limb relative mass was significantly larger in sprinters (18.7% ± 0.7% body mass) than in nonsprinters (17.6% ± 0.6% body mass), whereas the normalized moment of inertia of the lower limb around the hip in the anatomical position was not significantly different (0.044 ± 0.002 vs 0.042 ± 0.002 [a. u.]). The thigh relative mass in sprinters (12.9% ± 0.4% body mass) was significantly larger than that in nonsprinters (11.9% ± 0.4% body mass), whereas the shank and foot relative masses were not significantly different. We revealed that the mechanical difficulty in swinging the lower limb is not relatively larger in sprinters in terms of inertia, even though the lower-limb mass is larger, reflecting their muscularity. We provide practical implications that sprinters can train without paying close attention to the increase in lower-limb mass and moment of inertia.

The effects of R2O3 (R=La, Yb, Gd) on the microstructure, dielectric, ferroelectric, and energy storage properties of Ba0.65Bi0.07Sr0.245TiO3 relaxor ferroelectric ceramics

(1-x)Ba0.65Bi0.07Sr0.245TiO3-xR2O3 (BBST-xR) ceramics embellished by lanthanides (La, Yb, Gd) were synthesized in this study, and the effects in properties were ascertained. The results show that lanthanides with smaller ionic radius differences and larger relative mass will effectively limit mass transport of other cations and restrain grain growth. It is also found that the paraelectric phase of ceramics can be stabilized by decreasing the ionic radius of lanthanides. In particular, the addition of La unfolds the exceptional recoverable storage density (Wrec) up to 2.23 J/cm3 and efficiency (η) of ∼76.7% under 280 kV/cm. Finite element simulation and PFM observation also further explain the reasons for the excellent performance. Concurrently, BBST-0.015La ceramic exhibits outstanding thermostability from 30 °C to 150 °C and frequency stabilization from 1 Hz to 300 Hz which indicates the potentiality of application in actual surroundings.

Lithium Isotope Geochemistry in the Barton Peninsula, King George Island, Antarctica

Lithium (Li) has two stable isotopes, 6Li and 7Li, whose large relative mass difference is responsible for significant isotopic fractionation during physico-chemical processes, allowing Li isotopes to be a good tracer of continental chemical weathering. Although physical erosion is dominant in the Polar regions due to glaciers, increasing global surface temperature may enhance chemical weathering, with possible consequences on carbon biogeochemical cycle and nutriment flux to the ocean. Here, we examined elemental and Li isotope geochemistry of meltwaters, suspended sediments, soils, and bedrocks in the Barton Peninsula, King George Island, Antarctica. Li concentrations range from 8.7 nM to 23.3 μM in waters, from 0.01 to 1.43 ppm in suspended sediments, from 9.56 to 36.9 ppm in soils, and from 0.42 to 28.3 ppm in bedrocks. δ7Li values are also variable, ranging from +16.4 to +41.1‰ in waters, from −0.4 to +13.4‰ in suspended sediments, from −2.5 to +6.9‰ in soils, and from −1.8 to +11.7‰ in bedrocks. Elemental and Li isotope geochemistry reveals that secondary phase formation during chemical weathering mainly control dissolved δ7Li values, rather than a mixing with sea salt inputs from atmosphere or ice melting. Likewise, δ7Li values of suspended sediments and soils lower than those of bedrocks indicate modern chemical weathering with mineral neoformation. This study suggests that increasing global surface temperature enhances modern chemical weathering in Antarctica, continuing to lower δ7Li values in meltwater with intense water-rock interactions.

The effect of feed efficiency classification on visceral organ mass in finishing steers

Individual feed intake of crossbred beef steers (one contemporary group/year, 2 years) was recorded during finishing to investigate visceral organ mass in steers divergent for feed efficiency. Based on residual feed intake (RFI), the 20% most efficient (HE, n = 8/year) and 20% least efficient (LE; n = 8/year) steers with 12th rib fat ≥1.02 cm were slaughtered. High efficiency steers had less DM intake ( P < 0.001), greater G:F ( P < 0.001), and similar ADG and hot carcass weight (HCW). High efficiency steers tended to have less ( P ≤ 0.10) small intestinal mass (actual and relative to BW and HCW) in year 1. In year 2, HE steers tended to have greater ( P ≤ 0.10) large intestinal actual and relative masses. Low efficiency steers tended to have greater ( P = 0.06) actual omasum mass and had greater ( P ≤ 0.03) relative omasum masses compared with HE. Stomach complex, total gastrointestinal tract, liver, and kidney masses tended to be greater ( P ≤ 0.10) relative to BW, and were greater ( P ≤ 0.05) relative to HCW, in LE. Data suggest that visceral organ mass, especially of the gastrointestinal tract, plays a role in overall metabolic efficiency of finishing steers.

Phonon propagation in isotopic diamond superlattices

The out-of-plane thermal conductivity and elastic constant of epitaxial [100] $^{12}\mathrm{C}/^{13}\mathrm{C}$ superlattice diamonds with layer thicknesses of 1, 30, and 100 nm are evaluated by picosecond ultrasound spectroscopy. The measured elastic constants of the superlattices are equivalent to those of single-layer diamond thin films. This result confirms our success in synthesizing superlattice specimens with few defects at the interfaces. Therefore, the phonon transport behavior is governed by the mass difference, not the interfacial defects. The measured thermal conductivity of the superlattices is lower than that of a pure $^{12}\mathrm{C}$ isotope diamond thin film. We estimated the lattice thermal conductivity using the lattice dynamics calculation, attributing the lowered thermal conductivity to the decrease in the phonon group velocity in superlattices. We further consider the effect of mini-umklapp scattering in the superlattice, which explains the dependence of the thermal conductivity on the layer thickness. We reveal that the mini-umklapp scattering effect becomes significant only for an isotope diamond superlattice because of the high Debye temperature and large relative mass difference.

Orbital Decay of Globular Clusters in the Galaxy with Little Dark Matter

Abstract Recently, van Dokkum et al. presented an important discovery of an ultra-diffuse galaxy, NGC1052-DF2, with a dark matter content significantly less than predicted from its stellar mass alone. The analysis relies on measured radial velocities of 10 globular clusters (GCs), of estimated individual masses of a few ×106 M ⊙. This is about 1% of the inferred mass of NGC1052-DF2 of 2 × 108 M ⊙ within a half-light radius, R e = 2.2 kpc. The large relative mass and the old age of these objects imply that they might be susceptible to orbital decay by dynamical friction. Using analytic estimates and N-body simulations of an isolated system matching the inferred mass profile of NGC1052-DF2, we show that the orbits of the most massive GCs should already have decayed on a timescale of a few Gyrs. These findings should help in constraining mass profile and formation scenarios of NGC1052-DF2.

Evolution of the testis and spermatozoon in mice and rats (Subfamily Murinae) in the absence of sperm competition

AbstractThis study explores the potential effects of interspecific differences in breeding systems on testis organisation and sperm morphology of native murid rodents. It poses the question – what are the effects of depressed levels of intermale sperm competition, as indicated by small relative testes mass, on the morphology of testes and spermatozoa in murine rodents? Species from three separate murine tribes, those of the Hydromyini, Rattini and Arvicanthini, were investigated with low relative testes mass being used as a proxy for low, or non‐existent, levels of intermale sperm competition. The findings show that in only one of the tribes with low relative testes mass, that of the Hydromyini, was there a reduced testicular area occupied by seminiferous tubules, but in two of the tribes significantly smaller seminiferous tubule diameters were present. In all three tribes, most species with low relative testes mass had a highly derived sperm morphology that, unlike in species with large relative testes mass, had spermatozoa where the head lacked an apical hook, was highly variable in form, often had a very large acrosome overlying the apical region of the nucleus which suggests divergent processes of sperm–egg interaction at the time of fertilisation, and a significantly shorter tail. It is therefore hypothesised that, unlike in species with a large relative testes mass where high levels of intermale sperm competition maintain a streamlined sperm head with an apical hook to aid in zona penetration, in most species of murine rodents with low relative testes mass there is greater reliance on enzymatic digestion of the extracellular matrix around the egg, and especially that of the zona pellucida, to facilitate sperm penetration at the time of fertilisation.

Diffusion of helium, hydrogen and deuterium in diamond: Experiment, theory and geochemical applications

Diffusivities of helium, deuterium and hydrogen have been characterized in diamond. Polished CVD diamond was implanted with either 3He, 2H, or 1H. Implanted samples were sealed under vacuum in silica glass capsules, and annealed in 1-atm furnaces. 3He, 2H and 1H distributions were measured with Nuclear Reaction Analysis. We obtain these Arrhenius relations:DHe = 4.00 × 10−15 exp(−138 ± 14 kJ mol−1/RT) m2 s−1.D2H = 1.02 × 10−4 exp(−262 ± 17 kJ mol−1/RT) m2 s−1.D1H = 2.60 × 10−4 exp(−267 ± 15 kJ mol−1/RT) m2 s−1.Diffusivities of 1H and 2H agree within experimental uncertainties, indicating little diffusive mass fractionation of hydrogen in diamond.To complement the experimental measurements, we performed calculations using a first-principles quantum mechanical description of diffusion in diamond within the Density Functional Theory (DFT). Differences in 1H and 2H diffusivities from calculations are found to be ∼4.5%, reflected in differences in the pre-exponential factor. This small difference in diffusivities, despite the large relative mass difference between these isotopes, is due to the fact that the atomistic process involved in the transition along the diffusion pathway is dictated by local changes to the diamond structures rather than to vibrations involving 1H/2H. This finding is consistent with the experimental results given experimental uncertainties. In contrast, calculations for helium diffusion in diamond indicate a difference of 15% between diffusivities of 3He and 4He.Calculations of diffusion distances for hydrogen using our data yield a distance of 50 μm in diamond in 300,000 years at 500 °C and ∼30 min at 1400 °C. Diffusion distances for He in diamond are shorter than for H at all temperatures above ∼350 °C, but differences increase dramatically with temperature because of the higher activation energy for H diffusion. For example, a 50 μm diffusion distance for He would be attained in ∼40 Myr at 500 °C and 400 yr at 1400 °C. For comparison, a 50 μm diffusion distance for N in diamond would require nearly 1 billion years at 1400 °C.The experimental data indicate that diamonds equilibrate with ambient H and He in the mantle on timescales brief relative to most geological processes and events. However, He diffusion in diamond is slower than in any other mineral measured to date, including other kimberlite-hosted minerals. Under some circumstances, diamond may provide information about mantle He not recoverable from other minerals. One possibility is diamonds entrained in kimberlites. Since the ascent of kimberlite from the mantle to near-surface is very rapid, entrained diamonds may retain most or all of the H and He acquired in mantle environments. Calculations using reasonable ascent rates and T-t paths indicate that He diffusive loss from kimberlite-hosted diamonds is negligible for grains of 1.0–0.2 mm radius, with fractional losses <0.15% for all ascent rates considered. If the host kimberlite magma is effectively quenched in the near-surface (or is erupted), diamonds should contain a faithful record of [He] and He isotopes from the mantle source region. Preservation of H in kimberlite-hosted diamonds is less clear-cut, with model outcomes depending critically upon rates of ascent and cooling.

Synthesis and properties of phenyl carboxyl polydimethylsiloxane for fabrics treatment

ABSTRACTA series of phenyl carboxyl polydimethylsiloxane (PCPDMS) with different relative molecular mass, phenyl and carboxyl content was prepared through condensation reaction and equilibrium polymerization. The effects of reaction conditions on the conversion were investigated, to determine the optimum reaction conditions. According to the thermal gravity analysis of PCPDMS with different relative molecular mass and phenyl content, it was found that the large relative molecular mass can improve the thermal stability of PCPDMS. The thermal stability of PCPDMS was significantly higher than carboxyl polydimethylsiloxane. Moreover, the PCPDMS emulsions were also prepared for the fabrics treatment. The emulsions can improve the wrinkle resistance, smoothness, elasticity, and other properties of the fabrics. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45866.

An atypical reproductive cycle in a common viviparous Asia Agamid Phrynocephalus vlangalii.

Viviparous lizards living in cold climate of high altitude often exhibit atypical reproductive cycles, in which mating and fertilization occur synchronously and annually with parturition occurring at the end of the year. Nevertheless, detailed case studies on atypical reproductive cycles are few. Using anatomical data combined with behavioral observations, we examined the reproductive cycle of a common Asian agamid, Phrynocephalus vlangalii, from a high-elevation area in Sichuan, China. Male spermiation of P.vlangalii occurred in May, and spermatogenesis began in June and reached a maximum in October. For females, ovulation and fertilization occurred in May, and females developed gestation and pregnancy in 3months from June to August, without vitellogenesis during this period. Females gave birth synchronously in late August, then vitellogenesis began and lasted until May of the next year. All adult males and females were synchronized in the same reproductive condition each month. The synchronous and annual reproductive cycle of P.vlangalii clearly represents an atypical cycle. The male courtship and mating behaviors were concordant with gonadal cycle and mainly happened in May and June. Despite the short growth period for neonates, they had a high over-winter survival rate of 84.4%, suggesting that autumn parturition did not generate high costs to this reproductive cycle. We propose that the high over-winter survival rate of neonates is likely linked with female delayed sexual maturity, female asynchronous vitellogenesis and gestation, large relative clutch mass (RCM), and adult-offspring burrow sharing behavior during hibernation.

Tracking the weathering of basalts on Mars using lithium isotope fractionation models.

Lithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt‐forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium—7Li and 6Li—have a large relative mass difference (∼15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals—the source of Li—and on the precipitation kinetics, leading to formation of secondary phases. Consequently, a detailed analysis of Li isotopic ratios in both solution and secondary mineral lattices could provide clues about past Martian weathering conditions, including weathering extent, temperature, pH, supersaturation, and evaporation rate of the initial solutions in contact with basalt rocks. In this paper, we discuss ways in which Martian aqueous processes could have lead to Li isotope fractionation. We show that Li isotopic data obtained by future exploration of Mars could be relevant to highlighting different processes of Li isotopic fractionation in the past, and therefore to understanding basalt weathering and environmental conditions early in the planet's history.

PET/CT imaging reveals unrivaled placental avidity for glucose compared to other tissues

IntroductionThe goal of this study was to define the kinetics of glucose transport from maternal blood to placenta to fetus using real time imaging. MethodsPositron emission tomography (PET) imaging of the glucose-tracer [18F]fluorodeoxyglucose (FDG) was used to temporally and spatially define, in vivo, the kinetics of glucose transport from maternal blood into placentae and fetuses, in the late gestational gravid rat. Computed tomography (CT), with intravenous contrast, co-registered to the PET images allowed anatomic differentiation of placentae from fetal and maternal tissues. ResultsFDG was rapidly taken up by placentae and subsequently appeared in fetuses with minimal temporal lag. FDG standardized uptake values in placentae and fetuses approached that of maternal brain. In both anesthetized and awake dams, one quarter of the administered FDG ultimately was accrued in the collective fetuses and placentae. Accordingly, kinetic modeling demonstrated that the placentae had very high avidity for FDG, 2-fold greater than that of the fetus and maternal brain, when accounting for the fact that fetal FDG necessarily must first be taken up by placentae. Consistent with this, placental expression of glucose transporter 1 exceeded that of all other tissues. DiscussionFetal and placental tissues place a substantial glucose metabolic burden on the mother, owing to very high avidity of placentae for glucose coupled with the large relative mass of fetal and placental tissues. ConclusionsThe placenta has a tremendous capacity to uptake and transport glucose. PET/CT imaging is an ideal means to study metabolite transport kinetics in the fetoplacental unit.

Characterizing aptamer small molecule interactions with backscattering interferometry.

Aptamers are segments of single-strand DNA or RNA used in a wide array of applications, including sensors, therapeutics, and cellular process regulators. Aptamers can bind many target species, including proteins, peptides, and small molecules (SM) with high affinity and specificity. They are advantageous because they can be identified in vitro by SELEX, produced rapidly and relatively economically using oligonucleotide synthesis. The use of aptamers as SM probes has experienced a recent rebirth, and because of their unique properties they represent an attractive alternative to antibodies. Current assay methodology for characterizing small molecule-aptamer binding is limited by either mass sensitivity, as in biolayer interferometry (BLI) and surface plasmon resonance (SPR), or the need for using a fluorophore, as in thermophoresis. Here we report that backscattering interferometry (BSI), a label-free and free-solution sensing technique, can be used to effectively characterize SM-aptamer interactions, providing Kd values on microliter sample quantities and at low nanomolar sensitivity. To demonstrate this capability we measured the aptamer affinity for three previously reported small molecules; bisphenol A, tenofovir, and epirubicin showing BSI provided values consistent with those published previously. We then quantified the Kd values for aptamers to ampicillin, tetracycline and norepinephrine. All measurements produced R(2) values >0.95 and an excellent signal to noise ratio at target concentrations that enable true Kd values to be obtained. No immobilization or labeling chemistry was needed, expediting the assay which is also insensitive to the large relative mass difference between the interacting molecules.

Controlling factors of the δ 11B-pH proxy and its research direction

Significant boron isotope fractionation occurs in nature (−70 ‰ to +75 ‰) due to the high geochemical reactivity of boron and the large relative mass difference between 10B and 11B. Since the 1990s, reconstruction of ancient seawater pH using the isotopic composition of boron in bio-carbonates (δ11Bcarb), and then calculation of the past pCO2 have become important issues for the international isotope geochemistry community, and are called the δ11B-pH proxy. Although many achievements have been made by this proxy, various aspects of boron systematics require rigorous evaluation. Based on the previous researches, mechanism of boron isotope fractionation, variation of boron isotope (δ11B) in nature (especially in bio-carbonates) and controlling factors of the δ11B-pH proxy, such as the dissociation constant of B(OH)3 in seawater (pKa), the δ11B of seawater (δ11BSW), the boron isotopic fractionation factor between B(OH)4− and B(OH)3 (α4–3), and the incorporated species of boron into bio-carbonates, are reviewed in detail and the research directions of this proxy are proposed. Generally, the controversy about pKa, δ11Bsw, and α4–3 is relatively less, but whether boron incorporated into bio-carbonates only in the form of B(OH)4− remains doubtful. In the future, it is required that the physicochemical processes that control boron incorporation into carbonates be rigorously characterized and that the related chemical and isotopic fractionation be quantified. It is also necessary and important to establish a “best-fit empirically equation” between δ11Bcarb and pH of seawater based on the precipitation experiments of inorganic or culture experiments of corals or foraminifera. In addition, extended application of the δ11B-pH proxy to the earlier part of the Phanerozoic relying on the Brachiopods is worthy of studying. Like other geochemical indicators, there are limiting factors of δ11B; however, it remains a very powerful tool in the reconstruction of past seawater pH at present.

Boron isotope variations and its geochemical application in nature

The high geochemical reactivity of boron and the large relative mass difference between 10B and 11B lead to significant boron isotope fractionation in nature. So far the measured range of boron isotope composition (δ11B) varies between –70 and +75‰. The negative δ11B values are found in non-marine evaporite borate minerals and tourmalines, whereas positive δ11B values are common in salt lake brines and evaporated seawater. Since the 1980s, with improved measurement methods, applications of boron isotope analysis have increased rapidly. At present, boron isotopes are successfully applied to reconstruct ancient marine environments, to determine depositional environments and ore genesis, to trace groundwater pollution and seawater intrusion, and to study continental erosion. This paper summarises the methods for boron isotope analysis, the mechanisms of boron isotope fractionation and the distribution of boron isotopes in nature, reviews the achievements and the problems of boron isotopes in geochemical applications, and proposes research directions of boron isotopes in geochemical fields.

IN-SPIRALING CLUMPS IN BLUE COMPACT DWARF GALAXIES

Giant star-formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the BCD phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. An additional indication that the dense central regions of BCDs are like bulges is the high ratio of the inner disk scale height to the scale length, which is comparable to 1 for four of the galaxies.