Computer simulation of morphological changes of grain boundary precipitates growing by the ledge mechanism

A previously developed computer model was modified to simulate the growth of grain boundary precipitates which grow by the ledge mechanism. The ledges were assumed to be nucleated in the grain boundary region at constant, parabolically decreasing, and random rates and to grow under the control of volume diffusion of solute to or from the riser of ledges. At lower under coolings at which the motion of individual ledges is slow, late-nucleated ledges soon catch up with first-nucleated ones, and precipitates tend to extend along the grain boundary: the overall precipitate shape is essentially that of a grain boundary allotriomorph. At larger undercoolings, first-nucleated ledges move fast to form a protuberance similar to Widmanstätten sideplates, while late-nucleated ones stay near the grain boundary region. The transition of precipitate shape from one to the other occurs in a very narrow range of supersaturation. The results are compared with various characteristics of the growth of proeutectoid ferrite allotriomorphs and sideplates in Fe-C alloys documented in the literature.     

Differential modes of nuclear localization signal (NLS) recognition by three distinct classes of NLS receptors

The targeting of karyophilic proteins to nuclear pores is mediated via the formation of a nuclear pore-targeting complex, through the interaction of nuclear localization signal (NLS) with its NLS receptor. Recently, a novel human protein, Qip1, was identified from a yeast two-hybrid system with DNA helicase Q1. This study demonstrates that Qip1 is a novel third class of NLS receptor that efficiently recognizes the NLS of the helicase Q1. Moreover, the data obtained in this study show that the specific interaction between Qip1 and the NLS of the helicase Q1 requires its upstream sequence of the minimal essential NLS. By using purified recombinant proteins alone in the digitonin-permeabilized cell-free transport system, it was demonstrated that the two known human NLS receptors, Rch1 and NPI-1, are able to transport all the tested NLS substrates into the nucleus, while Qip1 most efficiently transports the helicase Q1-NLS substrates, which contain its upstream sequence in so far as we have examined the system. Furthermore, in HeLa cell crude cytosol, it was found that endogenous Rch1 binds to all the tested NLS substrates, while the binding of endogenous NPI-1 is restricted to only some NLSs, despite the fact that NPI-1 itself shows binding activity to a variety of NLSs. These results indicate that at least three structurally and functionally distinct NLS receptors exist in the human single cell population, and suggest that the nuclear import of karyophilic proteins may be controlled in a complex manner at the NLS recognition step by the existence of a variety of NLS receptors with various specificities to each NLS.     

Simulation of ferrite growth in continuously cooled low-carbon iron alloys

The growth of a planar ferrite (α): austenite (γ) boundary in low-carbon iron and Fe-Mn alloys continuously cooled from austenite through the (α+γ) two-phase field and the α single-phase field was simulated by incorporating carbon diffusion in austenite, intrinsic boundary mobility, and the drag of an alloying element. At a very high cooling rate (≥ 10³ °C/s), the width of the carbon diffusion spike in austenite approaches the limit at which spikes are viable, so that the growth of ferrite in which carbon is not partitioned can occur even above the α solvus. In this context, the upper limiting temperature of partitionless growth of ferrite is the T ₀ temperature. In the presence of drag of an alloying element, e.g., Mn, both carbon-partitioned and partitionless growth of ferrite begins to occur at finite undercoolings from the Ae ₃, T ₀, or α-solvus temperature, at which the driving force for transformation exceeds the drag force. The intrinsic mobility of the α:γ boundary may play a significant role at an extremely high cooling rate (≥10⁵ °C/s). This article is based on a presentation made at the symposium entitled “The Mechanisms of the Massive Transformation,” a part of the Fall 2000 TMS Meeting held October 16–19, 2000, in St. Louis, Missouri, under the auspices of the ASM Phase Transformations Committee.     

Compact cryogenic system with mechanical cryocoolers for antihydrogen synthesis

We have developed a compact cryogenic system which cools a vacuum chamber housing multi-ring trap electrodes (MRTs) of an antihydrogen synthesis trap using mechanical cryocoolers to achieve background pressure less than 10(-12) Torr. The vacuum chamber and the cryocoolers are thermally connected by copper strips of 99.9999% in purity. All components are installed within a diametric gap between the MRT of phi108 mm and a magnet bore of phi160 mm. An adjusting mechanism is prepared to align the MRT axis to the magnet axis. The vacuum chamber was successfully cooled down to 4.0 K after 14 h of cooling with heat load of 0.8 W.     

Controlling hydrothermal reaction pathways to improve acetic acid production from carbohydrate biomass

A two-step hydrothermal process to improve the production of acetic acid was discussed. The first step was to accelerate the formation of 5-hydroxymethyl-2-furaldehyde (HMF), 2-furaldehyde (2-FA), and lactic acid (LA), and the second step was to further convert the furans (HMF, 2-FA) and LA produced in the first step to acetic acid by oxidation with newly supplied oxygen. The acetic acid obtained by the two-step process had not only a high yield but also better purity. The contribution of two pathways via furans and LA in the two-step process to convert carbohydrates into acetic acid was roughly estimated as 85-90%, and the ratio of the contributions of furans and LA to yield acetic acid was estimated as 2:1. The fact that WO of carbohydrates is not capable of producing a large amount of acetic acid, while the two-step process can enhance the acetic acid yield, can be explained because formic acid is a basic product of direct oxidation of carbohydrate, and acetic acid in WO of carbohydrates may come from the oxidation of dehydration products of aldose.     

Solar energy powered Rankine cycle using supercritical CO2

A solar energy powered Rankine cycle using supercritical CO₂ for combined production of electricity and thermal energy is proposed. The proposed system consists of evacuated solar collectors, power generating turbine, high-temperature heat recovery system, low-temperature heat recovery system, and feed pump. The system utilizes evacuated solar collectors to convert CO₂ into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity. The system also recovers heat (high-temperature heat and low-temperature heat), which could be used for refrigeration, air conditioning, hot water supply, etc. in domestic or commercial buildings. An experimental prototype has been designed and constructed. The prototype system has been tested under typical summer conditions in Kyoto, Japan; It was found that CO₂ is efficiently converted into high-temperature supercritical state, of while electricity and hot water can be generated. The experimental results show that the solar energy powered Rankine cycle using CO₂ works stably in a trans-critical region. The estimated power generation efficiency is 0.25 and heat recovery efficiency is 0.65. This study shows the potential of the application of the solar-powered Rankine cycle using supercritical CO₂.     

Controllable 1D Patterned Assembly of Colloidal Quantum Dots on PbSO4 Nanoribbons

Control of the 1D self‐assembly pattern of colloidal quantum dots (QDs) on PbSO₄ nanoribbon (NRb) templates is achieved. The internal structure of the NRbs is investigated by X‐ray diffraction, revealing the isotropic packing of the PbSO₄ nanoclusters in the NRbs. Colloidal QDs in a chloroform/hexane mixture are adsorbed onto the region close to the edges of the NRbs and form a 1D assembly of straight single line or double lines by controlling the amount of OAm. This is the first demonstration of a densely packed 1D self‐assembly of colloidal QDs with a straight line pattern without the use of any molecular bridge or adhesive. Atomic force microscopy measurements of the NRbs show depressions in the phase profile along the width of the NRbs, corresponding to the position of the 1D QD chain. The amount of adsorbed QDs on the NRbs in solution decreases as the addition of OAm increases, suggesting that additional OAm prevents interaction between the QDs and NRbs but facilitates the uniform adsorption of the 1D assembly. The low‐dimensional self‐assembly of colloidal QDs in this study opens up the possibility for the creation of anisotropically assembled QD superstructures.     

Extracorporeal photochemotherapy (photopheresis) induces apoptosis in lymphocytes: a possible mechanism of action of PUVA therapy

The mechanism of action of psoralen plus UVA (PUVA) and photopheresis is not entirely understood. These therapies are assumed to be immunomodulating partly by gradually decreasing leukocyte viability. We investigated whether this delayed form of cell death was due to apoptosis. Untreated and treated (PUVA exposed) leukocytes obtained from six patients with systemic sclerosis and (untreated) leukocytes from healthy control individuals were studied. Qualitative gel electrophoresis and quantitative in situ nick translation analysis of DNA fragmentation was performed. Apoptosis of the treated cells did occur (gel electrophoresis) after 24 h. At t = 0 h, immediately after exposure to PUVA, there was no evidence of DNA fragmentation in the treated cells. The percentage of treated cells undergoing apoptosis was 20-55% at t = 24 h (in situ nick translation). The untreated leukocytes of the patients and the healthy individuals showed no distinctive rise in apoptotic cells. Apoptosis of the leukocytes after PUVA or photopheresis treatment might be a mechanism of action and might explain the therapeutic response.     

Metastatic Voyage of Ovarian Cancer Cells in Ascites with the Assistance of Various Cellular Components

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy and has a unique metastatic route using ascites, known as the transcoelomic root. However, studies on ascites and contained cellular components have not yet been sufficiently clarified. In this review, we focus on the significance of accumulating ascites, contained EOC cells in the form of spheroids, and interaction with non-malignant host cells. To become resistant against anoikis, EOC cells form spheroids in ascites, where epithelial-to-mesenchymal transition stimulated by transforming growth factor-β can be a key pathway. As spheroids form, EOC cells are also gaining the ability to attach and invade the peritoneum to induce intraperitoneal metastasis, as well as resistance to conventional chemotherapy. Recently, accumulating evidence suggests that EOC spheroids in ascites are composed of not only cancer cells, but also non-malignant cells existing with higher abundance than EOC cells in ascites, including macrophages, mesothelial cells, and lymphocytes. Moreover, hetero-cellular spheroids are demonstrated to form more aggregated spheroids and have higher adhesion ability for the mesothelial layer. To improve the poor prognosis, we need to elucidate the mechanisms of spheroid formation and interactions with non-malignant cells in ascites that are a unique tumor microenvironment for EOC.     

Electrochemical micromachining using a solid electrochemical reaction at the metal/β″-Al2O3 microcontact

A simple solid state technique for electrochemical micromachining of metal substrates using a metal ion conductor (Na-β″-Al₂O₃) was proposed. The fundamental solid electrochemical cell consists of a (anode) metal substrate (M = Ag, Cu, Zn, and Pb)/pyramidal Na-β″-Al₂O₃/Ag (cathode) system, where the contact diameter between M/Na-β″-Al₂O₃ was extremely small, on the order of a few micrometer. Under an applied electric field, the metal substrate was electrochemically oxidized to metal ions (Mⁿ⁺) at the M/Na-β″-Al₂O₃ microcontact. These Mⁿ⁺ ions migrated into the Na-β″-Al₂O₃. As a result of continuous electrolysis, the metal substrate was locally consumed at the microcontact, and thus solid state electrochemical micromachining was accomplished. As expected, the machining size or depth depended on the electrolysis conditions (current, operating time) and the apex configuration of pyramidal Na-β″-Al₂O₃. Moreover, the scanning of the Na-β″-Al₂O₃ pyramid during electrolysis produced a fine patterned metal substrate. In the present paper, solid state electrochemical micromachining was performed for several metal substrates, and its advantages and disadvantages vis-a-vis the conventional electrochemical micromachining method are discussed in detail.