Elongation and Contraction of Scallop Sarcoplasmic Reticulum (SR): ATP Stabilizes Ca2+-ATPase Crystalline Array Elongation of SR Vesicles

The Ca²⁺-ATPase is an integral transmembrane Ca²⁺ pump of the sarcoplasmic reticulum (SR). Crystallization of the cytoplasmic surface ATPase molecules of isolated scallop SR vesicles was studied at various calcium concentrations by negative stain electron microscopy. In the absence of ATP, round SR vesicles displaying an assembly of small crystalline patches of ATPase molecules were observed at 18 µM [Ca²⁺]. These partly transformed into tightly elongated vesicles containing ATPase crystalline arrays at low [Ca²⁺] (≤1.3 µM). The arrays were classified as ‘’tetramer’’, “two-rail” (like a railroad) and ‘’monomer’’. Their crystallinity was low, and they were unstable. In the presence of ATP (5 mM) at a low [Ca²⁺] of ~0.002 µM, “two-rail” arrays of high crystallinity appeared more frequently in the tightly elongated vesicles and the distinct tetramer arrays disappeared. During prolonged (~2.5 h) incubation, ATP was consumed and tetramer arrays reappeared. A specific ATPase inhibitor, thapsigargin, prevented both crystal formation and vesicle elongation in the presence of ATP. Together with the second part of this study, these data suggest that the ATPase forms tetramer units and longer tetramer crystalline arrays to elongate SR vesicles, and that the arrays transform into more stable “two-rail” forms in the presence of ATP at low [Ca²⁺].     

Metal-induced reconstructions of the silicon(111) surface

We have used scanning tunnelling microscopy (STM) to study changes in the structure of the Si(111) surface induced by deposition of the group III metals In and Ga. For both metals, several different ordered reconstructions are seen as a function of coverage. The STM images provide new structural information on each of these reconstructions. With In metal deposition, we have seen the surface reconstructions √3×, √3, √31× √31, √7×√3 and 4×1 as the coverage increases. In the case of Ga on Si(111), we have studied structures that exist up to 0·7 ML. At 1/3 ML, there is a √3×√3 structure identical to that of In. Above 0·3 ML there is a different phase that may correspond to the (6·3times6·3) RHEED pattern reported in this coverage range. This surface tends to grow as triangular islands at higher coverages.     

Photochromism of spiropyran and diarylethenedoped silica gels prepared by the sol-gel process

Spiropyran and diarylethene were doped in silica gels which were prepared from Si(OCH₃)₄ and Si(OC₂H₅)₄, respectively, and their photochromic properties were compared. In the gels, both organics are incorporated with open modifications and show the photochromism between red and colourless modifications. The closed form of spiropyran, which is converted from the open one by irradiation with light, is thermally backed into the open form after the light is blocked. The activation energy of thermochemical reaction is 0.86 eV. Diarylethene shows no thermochemical reaction below 140°C, but shows a photochemically reversible change on alternate irradiation by light of 436.5 and 578 nm.     

A spiral antenna backed by a conducting plane reflector

An Archimedean planar spiral antenna is numerically analyzed in the presence of a conducting plane reflector. The analysis shows that the spiral antenna backed by the plane reflector has two distinct regions in the current distribution, which explain the radiation of a circularly polarized wave for the outer circumferenceCranging over about1.3 lambda < C < 1.5 lambdaandC > 2.9 lambda, wherelambdais a free-space wavelength. Further consideration is given to a truncated spiral antenna whose outer circumference is on the order of1.4 lambda. The truncated spiral antenna maintains a decaying current distribution and radiates a circularly polarized wave over a 1:1.2 frequency bandwidth. It is also demonstrated that a power gain on the order of 8.5 dB is realized over the same frequency range.     

Degradation mechanisms of GaAs PHEMTs in high humidity conditions

We have studied the degradation mechanisms of AlGaAs/InGaAs pseudomorphic HEMTs (PHEMTs) under high humidity conditions (85 °C, 85% relative humidity). The degraded samples under high humidity conditions show a decrease in maximum drain current (I_max) and a positive shift in threshold voltage (V_th). Cross-sectional transmission electron microscopy (TEM) images from the deteriorated devices reveal an existence of damaged recess surface region and a peeling of a passivation film (SiN_x). The secondary ion mass spectrometry (SIMS) depth profile at the interface between the passivation film and AlGaAs surface also indicates the diffusion of gallium (Ga), arsenic (As) and aluminum (Al) into the passivation film. The degradation of PHEMTs arises from mainly two mechanisms: (1) the positive shift in V_th due to stress change under the gate caused by the peeling of passivation films, and (2) the decrease in I_max due to the net carrier concentration reduction of the AlGaAs carrier supply layer caused by the combination of surface degradation at the AlGaAs recess regions and diffusion of Ga, As and Al at the interface between the passivation film and AlGaAs surface. A special treatment just prior to the deposition of SiN_x films on the devices effectively suppresses the degradation of PHEMTs under high humidity conditions without degradation of the high frequency performance.     

A 32 kbyte integrated cache memory

The system, circuit, layout and device levels of an integrated cache memory (ICM), which includes 32 kbyte DATA memory with typical address to HIT delay of 18 ns and address to DATA delay of 23 ns, are described. The ICM offers the largest memory size and the fastest speed ever reported in a cache memory. The device integrates a 32 kbyte DATA INSTRUCTION memory, a 34 kbit TAG memory, an 8 kbit VALID flat, a 2 kbit least recently used (LRU) flag, comparators, and CPU interface logic circuits on a chip. The inclusion of the DATA memory is crucial in improving system cycle time. The device uses several novel circuit design technologies, including a double-word-line scheme, low-noise flush clear, a low-power comparator, noise immunity, and directly testable memory design. Its newly proposed way-slice architecture increases both flexibility and expandability