Dynamic diamond anvil cell (dDAC): a novel device for studying the dynamic-pressure properties of materials

We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/s (approximately 0.16 s(-1) for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive, and laser shock). We present an overview of a variety of experimental measurements that can be made with this device.     

Anionic synthesis of ω-1,1-diphenylethylene-terminated polystyrene macromonomers. Rational synthesis of ABC hetero three-armed-star-branched polymers

Summary Polystyrene macromonomers with terminal 1,1-diphenylethylene functionality were prepared by the reaction of one equivalent of poly(styryl)lithium with 1,4-bis (l-phenylethenyl)benzene (PDDPE). The macromonomer functionalities were determined by ¹H NMR [(vinyl CH₂)=5.4 ppm] and UV spectroscopy (_max=260 nm). The stoichiometric linking reaction of poly(styryl)lithium (M_n=15.3x10³ g/mol) with an -1,1-diphenylethylene-terminated polystyrene macromonomer (M_n=5.4x10³ g/mol) followed by addition of styrene monomer has been used to prepare a hetero three-armed, star-branched polymer with M_n=5.8x10⁴ g/mol (5,400-15,300-37,300). The g value ([]b/[]l) was equal to 0.92.     

A 231-MHz, 2.18-mW 32-bit Logarithmic Arithmetic Unit for Fixed-Point 3-D Graphics System

A 32-bit fixed-point logarithmic arithmetic unit is proposed for the possible application to mobile three-dimensional (3-D) graphics system. The proposed logarithmic arithmetic unit performs division, reciprocal, square-root, reciprocal-square-root and square operations in two clock cycles and powering operation in four clock cycles. It can program its number range for accurate computation flexibility of 3-D graphics pipeline and eight -region piecewise linear approximation model for logarithmic and antilogarithmic conversion to reduce the operation error under 0.2%. Its test chip is implemented by 1-poly 6-metal 0.18-mum CMOS technology with 9-k gates. It operates at the maximum frequency of 231 MHz and consumes 2.18 mW at 1.8-V supply     

Synchronized transform-limited operation of 10-GHz colliding pulse mode-locked laser

We report a 10-GHz colliding pulse mode-locked laser fabricated with integrated active-passive waveguides. The laser fabrication adopted a deep reactive ion etching and single-step metal-organic vapor phase epitaxy regrowth process for forming the buried heterostructure waveguide. Clean output pulses resulted from laterally tilting the active-passive interface and effectively suppressing residual back-reflections at the interface. Hybrid mode-locking resulted in a synchronized transform-limited sech/sup 2/optical waveform. Pulsewidth, chirp, timing jitter, and frequency-locking range were investigated through systematic device biasing condition optimization.     

Flooding limited CHF in a vertical 3 × 3 rod bundle with non-uniform axial heat flux

KAERI has performed an experimental study on the critical heat flux (CHF) under zero flow conditions with a non-uniformly heated 3 × 3 rod bundle. Experimental conditions are in the range of a system pressure from 0.50 to 14.96 MPa and inlet water subcooling enthalpies from 68 to 352 kJ/kg. The test section used in the present experiments consisted of a vertical flow channel, upper and lower plenums, and a non-uniformly heated 3 × 3 rod bundle. The experimental results show that the CHFs in low-pressure conditions are somewhat scattered within a narrow range. As the system pressure increases, however, the CHFs show a good parametric trend. The CHFs occur in the upper region of the heated section, but the locations of the detected CHFs move gradually in a downward direction with the increase of the system pressure. Even though the effects of the inlet water subcooling enthalpies and system pressure of the flooding CHF are relatively smaller than those of the flow boiling CHF, the CHF increases by increasing the inlet water subcooling enthalpies. Several existing correlations for the countercurrent flooding CHF based on Wallis's flooding correlation and Kutateladze's criterion for the onset of flooding are compared with the CHF data obtained in the present experiments to examine the applicability of the correlations.     

Microstructural and piezoelectric properties of low temperature sintering PMN-PZT ceramics with the amount of Li2CO3 addition

PMN-PZT ceramics doped with Li₂CO₃ and Bi₂O₃ as sintering aids were manufactured in order to develop the low temperature sintering ceramics for multilayer piezoelectric transformer, and their micro structural, dielectric and piezoelectric properties were investigated. The sintering aids were proved to lower the sintering temperature of doped PMN-PZT ceramics due to the effect of LiBiO₂ liquid phase. Optimal values for multilayer piezoelectric transformer application, such as electromechanical coupling factor (k_p) of 0.50, mechanical quality factor (Q_m) of 2264, and dielectric constant (K) of 1216, and curie temperature (T_c) of 317 °C were found at 0.1 wt.% Li₂CO₃ added ceramics sintered at 940 °C.     

Efficient inventory management in multi-echelon distribution systems

In this paper, an improved DRP method to schedule multi-echelon distribution network is proposed such that order-quantities and order points are dynamically obtained to meet the demand in just in time concept and minimize the out-of-stock probability. The order scheduling method reflects the dynamic characteristics of inventory level changes in the regional distribution centers and the central distribution center. The experiment has been done with various demand distributions, forecast error distributions and lead times. The proposed method was compared with the traditional DRP-based scheduling methods which use different lot-sizing and order point decision techniques. From the result, it is found that the proposed heuristic method yields preferable lot-sizing schedules.     

Dry release for surface micromachining with HF vapor-phase etching

A new method for dry etching of silicon dioxide for surface micromachining is presented to obtain very compliant polysilicon microstructures with negligible stiction problem and to greatly simplify the overall releasing procedure as well. By etching the sacrificial silicon dioxide with hydrofluoric acid (HF) vapor instead of conventional aqueous HF solution, the need for subsequent rinsing and an elaborate drying procedure is eliminated. Condensation of water on the etch surface is first identified as the cause that prevented the success of HF vapor release in the past. Use of an anhydrous HF/CH₃OH mixture under low pressure solves the problem of water condensation and enables us to take advantage of vapor-phase etching (VPE) for surface micromachining. The mechanism of oxide etching with the HF/CH₃OH mixture is explained, and the developed VPE system is described and characterized. Polysilicon cantilevers up to 1200 μm in length are successfully released with this HF VPE technique. The beams tested are 2 μm thick with a 2-μm gap from the substrate, and no antistiction dimples are used. The fabricated structures are observed using both scanning electron microscopy (SEM) and an optical profilometer. The reported VPE technique provides a robust releasing method for polysilicon microstructures and is compatible with integrated circuit (IC) fabrication, even including cluster processors     

Efficient Algorithms for Computing a Complete Visibility Region in Three-Dimensional Space

Given a set P of polygons in three-dimensional space, two points p and q are said to be visible from each other with respect to P if the line segment joining them does not intersect any polygon in P . A point p is said to be completely visible from an area source S if p is visible from every point in S . The completely visible region CV(S, P) from S with respect to P is defined as the set of all points in three-dimensional space that are completely visible from S . We present two algorithms for computing CV(S, P) for P with a total of n vertices and a convex polygonal source S with m vertices. Our first result is a divide-and-conquer algorithm which runs in O(m ² n ² α(mn)) time and space, where α(mn) is the inverse of Ackermann's function. We next give an incremental algorithm for computing CV(S,P) in O(m ² n+mn ² α(n)) time and O(mn+n ² ) space. We also prove that CV(S,P) consists of Θ(mn+n ² ) surface elements such as vertices, edges, and faces. Received November 16, 1995; revised November 11, 1996.     

Decentralized supervisory control with conditional decisions: supervisor existence

Most of the results on decentralized supervisory control are based on supervisors that make unconditional decisions: "enable" and "disable." In this paper, we introduce and study the properties of decentralized supervisory control architectures where supervisors are allowed to make conditional decisions in addition to unconditional decisions. The conditional decisions we consider are of the form: "enable if nobody disables" and "disable if nobody enables." We characterize the notion of conditional coobservability that appears in the necessary and sufficient conditions for the existence of supervisors in the context of such control architectures. This condition relaxes the previous notions of coobservability for unconditional architectures. The key properties of conditional coobservability are studied. We develop a polynomial-time algorithm for verifying the notion of conditional coobservability. A polynomial-time method of partitioning the controllable events between "enable by default" and "disable by default" is presented.