New thermogelling poly(organophosphazenes) with methoxypoly(ethylene glycol) and oligopeptide as side groups

A new class of thermogelling poly(organophosphazenes) bearing a hydrophilic methoxypoly(ethylene glycol) (MPEG) and a hydrophobic tri or tetrapeptide such as GlyPheLeuEt, GlyPheIleEt, GlyLeuPheEt, and GlyPheLeuGlyEt have been synthesized and characterized by means of multinuclear (¹H, ³¹P) NMR spectroscopy, gel permeation chromatography, viscometry, and elemental analysis. The gelation of the present polymers is presumed to be attributed to the intermolecular interaction between the hydrophobic oligopeptide side groups, which can form strong physical junction zones in the polymer aqueous solution. The gelation properties of the polymer were affected by the subtle change in the nature of the hydrophobic oligopeptide, composition of the hydrophilic to hydrophobic side groups, and the concentration of the polymer solutions. Among the present thermogels, the copolymer with equimolar MPEG and GlyPheIleEt as side groups showed the excellent gel phase persisting over 35-43 °C, which indicates that it is a new promising material for drug delivery and tissue engineering.     

Protective action of CLA against oxidative inactivation of paraoxonase 1, an antioxidant enzyme

The effect of CLA on paraoxonase 1 (PON1), one of the antioxidant proteins associated with HDL, was investigated for its protective action against oxidative inactivation as well as its stabilization activity. When cis-9 (c9),trans-11 (t11)-CLA and t10,c12-CLA were examined for their protective activity against ascorbate/Cu²⁻-induced inactivation of PON1 in the presence of Ca²⁺, two CLA isomers exhibited a remarkable protection (E _max, 71–74%) in a concentration-dependent manner (50% effective concentration, 3–4 μM), characterized by a saturation pattern. Such a protective action was also reproduced with oleic acid, but not linoleic acid. Rather, linoleic acid antagonized the protective action of CLA isomers in a noncompetitive fashion. Additionally, the two CLA isomers also protected PON1 from oxidative inactivation by H₂O₂ or cumene hydroperoxide. The concentration-dependent protective action of CLA against various oxidative inactivation systems suggests that the protective action of CLA isomers may be mediated through their selective binding to a specific binding site in a PON1 molecule. Separately, the inactivation of PON1 by p-hydroxymercuribenzoate (PHMB), a modifier of the cysteine residue, was also prevented by CLA isomers, suggesting the possible existence of the cysteine residue in the binding site of CLA. The c9,t11-CLA isomer seems to be somewhat more effective than t10,c12-CLA in protecting against the inactivation of PON1 by either peroxides or PHMB, in contrast to the similar efficacy of these two CLA isomers in preventing ascorbate/Cu²⁺-induced inactivation of PON1. Separately, CLA isomers successfully stabilized PON1, but not linoleic acid. These data suggest that the two CLA isomers may play a beneficial role in protecting PON1 from oxidative inactivation as well as in its stabilization.     

Experimental investigation on the detachable thermosiphon for conduction-cooled superconducting magnets

A detachable thermosiphon, as a transient thermal switch for conduction-cooled superconducting magnet, is designed, fabricated and tested. A thermosiphon between the first and second stages of a cryocooler can reduce the cool-down time of a conduction-cooled superconducting magnet by using the large cooling capacity of the first stage. The thermosiphon is a very efficient heat transfer device until all the working fluid in it freezes (off-state). After the working fluid freezes and the second stage temperature becomes lower than that of the first stage, however, the thermosiphon then becomes a conduction heat leak path between two stages of the cryocooler. Considering a very small cooling capacity of the second stage of the cryocooler around 4.2 K, the conduction heat loss is not negligible. Therefore, a detachable thermosiphon, made of a metal bellows, is considered to be able to eliminate such a conduction heat leak. The mock-up magnet is cooled down with the thermosiphon and the thermodynamic states of the thermosiphon and the mock-up magnet are precisely examined during the whole cool-down process. At off-state, the thermosiphon is detached mechanically from the magnet. In this way, the conduction heat leak path through the thermosiphon wall is completely eliminated. This paper describes the detailed transient operation of the detachable thermosiphon using nitrogen as the working fluid.     

Characteristic of grain oriented (Bi0.5Na0.5)TiO3-BaTiO3 ceramics

Dielectric and piezoelectric properties of grain oriented (Bi_0.5Na_0.5)TiO₃-BaTiO₃ ceramics were investigated in a process that the templated grain growth and hot pressing methods were employed. A ceramic composition in Bi-based perovskite structure family, (Bi_0.5Na_0.5)TiO₃-BaTiO₃, was chosen as a matrix material and plate shaped SrTiO₃ as a template. To examine the combined process effect on piezoelectric properties, three processes, conventional solid reaction, templated grain growth and the combine treatment of templated grain growth and hot-pressing, were compared. Specimen processed by templated grain growth and hot pressing methods exhibited better piezoelectric coefficient, d ₃₁ (−79.6 pC/N) and electromechanical coefficient, k ₃₃ (0.35) than those of the other specimens, fabricated by solid reaction and templated grain growth, respectively. The improved properties were attributed to reduction of pore existing in matrix, which is related to abnormal grain growth from SrTiO₃ template and its resultant heterogeneous shrinkage.     

CuO formation control as a function of mixed ratio of Cu-free powders in the synthesis of YBCO superconductors on Cu substrates

YBa₂Cu₃O_x (Y123) superconducting films were fabricated on Cu substrates using a simple screen-printing method, from Cu-free powders (Y₂O₃ and BaCO₃). In the process, CuO, which causes superconducting properties of Y123 films to deteriorate, was formed on the film surface. By varying the atomic ratio of Y to Ba (Y:Ba = 1:1∼1:4), the ratio needed to prevent CuO formation was found for the film surface that had been heat-treated at 980^∘C for 17 s. The film, with the ratio of Y to Ba (Y:Ba = 1:1), is reheat-treated at 930^∘C for 9 min 30 s to form a superconducting Y123 phase. It was possible to prevent CuO formation by controlling the ratio of Cu-free powders in the mixture and to fabricate YBCO superconductors on Cu substrates using a two-step heat-treatment.     

Impedance spectroscopy study and electrical behavior of PMN-PZT actuators joined by ceramic slurry

The solid solution of Pb(Mg,Nb)O₃-Pb(Zr,TiO) O₃ materials have high piezoelectric constant of 600 ∼650 pC/N and electromechanical coupling coefficient k _p of 0.65. Due to such high piezoelectric constant and electromechanical coupling coefficient, Pb(Mg,Nb)O₃-Pb(Zr,TiO)O₃ materials have been attracted attentions for the applications of multilayer ceramic actuators. Actuators can be produced by staking piezoelectric ceramic materials and inner electrodes, alternatively. However, it is difficult to fabricate huge ceramic actuators without any serious problems during the process conditions. Because ceramic are easily cracked during the sintering process, due to strikingly different shrinkage rate between the ceramic materials and metal electrodes. In this research, new jointing methods will be proposed for huge ceramic actuators, and then their electrical properties were investigated. Time dependent leakage current and impedance spectroscopy were employed to expect device performances.     

A 20-GHz phase-locked loop for 40-gb/s serializing transmitter in 0.13-/spl mu/m CMOS

A 20-GHz phase-locked loop with 4.9 ps/sub pp//0.65 ps/sub rms/ jitter and -113.5 dBc/Hz phase noise at 10-MHz offset is presented. A half-duty sampled-feedforward loop filter that simply replaces the resistor with a switch and an inverter suppresses the reference spur down to -44.0 dBc. A design iteration procedure is outlined that minimizes the phase noise of a negative-g/sub m/ oscillator with a coupled microstrip resonator. Static frequency dividers made of pulsed latches operate faster than those made of flip-flops and achieve near 2:1 frequency range. The phase-locked loop fabricated in a 0.13-/spl mu/m CMOS operates from 17.6 to 19.4GHz and dissipates 480mW.     

Modeling and measurement of simultaneous switching noise coupling through signal via transition

The signal via is a heavily utilized interconnection structure in high-density System-on-Package (SoP) substrates and printed circuit boards (PCBs). Vias facilitate complicated routings in these multilayer structures. Significant simultaneous switching noise (SSN) coupling occurs through the signal via transition when the signal via suffers return current interruption caused by reference plane exchange. The coupled SSN decreases noise and timing margins of digital and analog circuits, resulting in reduction of achievable jitter performance, bit error ratio (BER), and system reliability. We introduce a modeling method to estimate SSN coupling based on a balanced transmission line matrix (TLM) method. The proposed modeling method is successfully verified by a series of time-domain and frequency-domain measurements of several via transition structures. First, it is clearly verified that SSN coupling causes considerable clock waveform distortion, increases jitter and noise, and reduces margins in pseudorandom bit sequence (PRBS) eye patterns. We also note that the major frequency spectrum component of the coupled noise is one of the plane pair resonance frequencies in the PCB power/ground pair. Furthermore, we demonstrate that the amount of SSN noise coupling is strongly dependent not only on the position of the signal via, but also on the layer configuration of the multilayer PCB. Finally, we have successfully proposed and confirmed a design methodology to minimize the SSN coupling based on an optimal via positioning approach.     

Structural reliability assessment of multi-stack package (MSP) under high temperature storage (HTS) testing condition

Wire ball open failure at the interface of the gold wire and bonding pad of a multi-stack package (MSP) under high temperature storage (HTS) condition of 150 °C is studied. Failure analysis using FIB-SEM was conducted by in-plane moiré interferometry and FEA to clarify the failure mechanism. The ball open failure due to Kirkendall void that results from metal diffusion at high temperature was accelerated by the tensile stress imposed at the gold wire. The tensile stress developed at the gold wire when packages showing different warpage behaviours were stacked. Mechanical interaction between top and bottom packages caused unstable warpage, readily twisted and saddled. The wire came in contact with the photo-sensitive solder resist (PSR) dam because of the unstable warpage and this contact resulted in tensile stress at the gold wires. Solder flux residues reacted with the encapsulant, and as a result, the encapsulant of the top package adhered to the chip of the bottom package, and this adherence created additional tensile stress at the gold wires. To reduce the tensile stress at the wires, the PSR dam was removed, loop shape was altered from 45° to 90°, water soluble flux was applied, and cleaning process was added. HTS reliability was significantly improved and guaranteed after reducing the tensile stress at the wires.     

Matrix substitution method for power bus analysis with isolated power island in high-speed packages and PCBs

We propose a matrix substitution method for analyzing a power bus containing a power island in high-speed packages and printed circuit boards (PCBs). The method is based on a segmentation method and a resonant cavity model for a rectangular cavity, and the impedance of the power bus containing the power island can be calculated analytically. Finally, the proposed method is verified by means of impedance measurements in the frequency domain.