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Ephrin-As are repulsive axonal guidance cues that regulate retinotectal projection. EphA tyrosine kinases, which are the receptors of ephrin-As, activate signaling cascades leading to cytosckeleton reorganization. Here, we address the role of cyclin-dependent kinase (Cdk) 5 in Eph receptor signaling induced by ephrin-A5. Ephrin-A5 induced a cell morphological response in PC-3M cells that endogenously express Cdk5 and EphA2, a receptor for ephrin-A5. This response was augmented by the transfection of p35, which is a neuronal regulator of Cdk5. While the morphological response of native PC-3M cells was not affected by olomoucine, an inhibitor of Cdk, the response was inhibited in the p35-transfected cells. In retinal ganglion cells, either olomoucine at 20 microM or Y-27632 at 10 microM, an inhibitor of Rho-kinase/ROKalpha/ROCKII, showed maximum inhibitory effect against ephrin-A5 (10 microg/ml)-induced growth cone collapse. Combined application of olomoucine and Y-27632 further suppressed the ephrin-A5-induced response. Ephrin-A5 evoked phosphorylation of Cdk5 at Tyr15 and tau, a substrate of Cdk5 in retinal growth cones. Recombinant herpes simplex virus expressing Cdk5 mutant (kinase-negative or Tyr15 to Ala) showed a dominant-negative effect on the ephrin-A5-induced growth cone collapse. These findings demonstrate that both Cdk5 and the Rho kinase pathway independently contribute to the downstream of ephrin-A-induced signaling in retinal ganglion cells.

The influence of temperature and drive current on the Shubnikov-de Haas oscillations is studied as a means to investigate the nature of the electron–phonon interaction in an etched InGaAs quantum wire. The temperature dependence of the energy-relaxation time, and the current dependence of the electron temperature, appear consistent with an energy relaxation process that is dominated by three-dimensional electron–phonon scattering. A deviation from this behavior is found in measurements performed at 1.6 K, however, and simple estimates suggest that this may be associated with the increased importance at low temperatures of phonon confinement in the etched wire.

We investigate the gate-length dependence of negative differential resistance (NDR) in a ridge-type InGaAs/InAlAs quantum wire field-effect transistor with a gate varying from 50 nm to 1 μm in length. The gate leakage current is detectable only with the onset of NDR and increases with larger gate bias. The NDR could be attributed to the real space transfer of channel carrier into the barrier layer by gate field-assisted tunneling. The NDR characteristics are dependent strongly on gate length. The improvement in NDR characteristic in terms of peak-to-valley current ratio and onset voltage (VNDR) is observed clearly with the reduction of gate length. The QWIR-FETs with shorter gate length show the NDR even at room temperature. The improvement in NDR characteristic is attributed to a velocity overshoot enhanced by the suppression of scattering probability.

N-shaped negative differential resistance (NDR) with high peak-to-valley ratio (PVR) and low onset voltage (VNDR) are clearly observed in a 50-nm gate ridge-type InGaAs/InAlAs quantum wire field-effect transistor (QWR-FET). The NDR of low onset voltage (VNDR) and its dependence on the gate voltage are attributed to the real space transfer of channel carriers into a barrier layer underneath the gate by field-assisted tunneling. The NDR characteristic of the QWR-FET is enhanced compared with that of InGaAs/InAlAs quantum well field-effect transistor (QW-FET). The narrower channel width and shorter gate length effectively improve the PVR and VNDR.

A field effect transistor (FET) using In 0.53 Ga 0.47 As quasi-quantum-wires (quasi-QWRs) as a channel has been fabricated. The quasi-QWR structures have been fabricated by selective growth using molecular beam epitaxy on nonplanar InP substrates. The quasi-QWRs have composition-controlled In 0.52 Al 0.48 As barrier layer in which In flux is changed during the InAlAs growth to alleviate the deviated composition of the ridge top InAlAs. The FET demonstrated good saturation characteristics and its maximum transconductance ( g m ) is 170 mS/mm at the drain voltage of 0.2 V.

GaAs/AlGaAs quantum-wire structures on V-grooved substrates have been fabricated under As 2 flux by molecular beam epitaxy. Under As 2 flux, a smaller number of Ga atoms migrate than those under As 4 flux to the V-groove bottom from the side-wall surface. The Al 0.6 Ga 0.4 As layer on the V-grooved GaAs substrate grown under As 2 flux preserves the V-shape, whereas the V-shape cannot be preserved and the quantum-wire structures cannot be fabricated under As 4 flux. The GaAs quantum-wire structures which have Al 0.6 Ga 0.4 As barrier layers grown under As 2 flux have good optical quality.

The long-term reliability of amorphous silicon solar cells of 1988 products over more than ten years is estimated by a simulation method using the Weibull function with the experimental data of 1988 products exposed outdoors for five years and those of 1983 products exposed outdoors for ten years. The mathematical model is developed based on the accelerated tests and recovery tests in a laboratory for a short period of time. The simulation method is discussed. The decrease of the conversion efficiency of 1988 products after ten years of exposure is estimated to be 25% and 35% at best and worst, respectively. The newest products having initial conversion efficiency of over 13% in a small cell are expected to maintain an efficiency of about 10% at best over a decade.

Characteristics of an InGaAs-2DEG Hall device made of pseudomorphic InAlAs/InGaAs heterostructure semi-conductors in the temperature range 10–320 K have been studied. This device can be operated with high sensitivity at low temperature. Its magnetic sensitivity is several times as large as that of InSb Hall devices and the temperature dependence is comparable to that of GaAs Hall devices. The temperature coefficients of the Greekcross Hall device at room temperature are −0.084 and −0.54%/K, respectively, for current drive and voltage drive. A maximum magnetic sensitivity of 33.5 V/T was obtained at 11 K. Powerful sensing applications using the InGaAs-2DEG Hall device in the demanding conditions of automobiles and factory automation are expected.

Electron-heating measurements are used to compare the form of the electron–phonon interaction in two-dimensional, and quasi-one-dimensional, InGaAs quantum wires. Evidence for a strongly enhanced interaction is found in the quasi-one-dimensional wire, and is suggested to result from the presence of the singularities in its electronic density of states. The Bloch–Gruneisen criterion is easily violated in this wire, and its energy-loss function is found to show a weak temperature dependence, which is argued to result from a saturation of scattering processes in the uppermost one-dimensional subband.

The critical layer thickness of n-In 0.52 Al 0.48 As/strained-In 0.8 Ga 0.2 As/In 0.52 Al 0.48 As grown on InP substrates was investigated by measuring the photoluminescence spectra. These pseudomorphic heterostructures grown by molecular beam epitaxy attained the highest mobility, 16,200 cm 2 /V·s, at room temperature. The photoluminescence emission intensity decreased in the thickness range of 20 to 25 nm for the In 0.8 Ga 0.2 As layer. These results indicate that the critical layer thickness of this structure follows the energy balance model rather than the mechanical equilibrium model. In addition, this critical value is in good agreement with the results based on the electron mobility behavior.

A trench-type narrow InGaAs quantum-wire field-effect transistor (QWR–FET) with a cross section of 8×25 nm has been fabricated on a (311)A InP V-grooved substrate by molecular-beam epitaxy. The trench-type InGaAs QWR–FET has normal static characteristics at room temperature, and demonstrates clear negative differential resistance characteristics at 40 K with a high peak-to-valley current ratio (PVR=4.3) and a low onset voltage of 0.12 V.

InGaAs quantum wires (QWRs) with cross sections as narrow as 10 nm×20 nm have been fabricated on a (311)A InP V-grooved substrate under an As2 source. Trench-type InGaAs QWRs consist of (111)A and (331)B facets with an angle of about 22°. Cathode-luminescence and photoluminescence measurements confirmed the luminescence peak arising from the QWRs.

A very high electron mobility pseudomorphic Si-doped In 0.48 Al 0.52 As/ undoped In 0.8 Ga 0.2 As heterostructure is successfully grown on the InP substrate by the newly invented technology of stabilizing the transient vapor flux of group-III cells with SQRT control and inserting an InAs monolayer in the heterointerface between the channel layer and the spacer. The actual critical thickness of the pseudomorphic heterostructure as determined by the Hall measurement is found to follow the energy balance model, and the highest 2DEG mobilities over 1.6 and 16 m 2 /V·s with 1.6×10 12 cm -2 at 293 and 10 K, respectively, are obtained for the InP-based pseudomorphic In 0.52 Al 0.48 As/In 0.2 Ga 0.2 As heterostructure.

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of RHEED oscillations in an MBE system. The critical layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 and 16 m2/Vs at 293 and 10 K, respectively, is obtained.

The drain voltage noise of commercial AlGaAs/GaAs HEMTs shows typical ƒ −1.0 noise characteristics with a Hooge noise parameter of about 6 × 10−5, while that of conventional GaAs MESFETs has a large GR noise bulge at about 15 Hz. The noise levels of the HEMT are smaller than those of the MESFET by 19 dB Hz−0.5 at the same bias conditions, manifesting the advantage of HEMT as a low-noise device.

Typical 1/ f noise was excited in quarter-micron filaments of both GaAs and InP which were successfully made by a focused ion-beam implantation. Their noise levels were observed to vary exactly as f −1.0 and increased in proportion to the square of the terminal voltages. The GaAs filament has a generation-recombination (GR) noise bulge at round 500 Hz, corresponding to the deep level activation energy of 0.6eV. The noise levels of the InP filament, on the other hand, decreased monotonically throughout the frequency ranges from 0.1 Hz to 100 kHz, indicating much less deep levels. The Hooge's noise parameters were evaluated exactly by the carrier numbers derived from the Hall measurement and 1/ f noise levels to be 4.5 × 10 −6 for the GaAs filament and 6.1 × 10 −6 for the InP one. These values are the smallest yet reported in these materials.

Renovascular hypertension (RVH) in children is a relatively rare disease, but it is important in that it is a treatable condition when properly diagnosed. Percutaneous transluminal renal angioplasty (PTRA) with or without stenting is widely applied to adult patients with RVH. However, limited information is available as to PTRA with stenting in pediatric patients. We experienced a case of RVH in a 12-year-old girl, who had severe hypertension (180/110 mmHg). Bilateral renal artery stenosis was demonstrated by 3D-CT, MR angiography and selective renal arteriography. Renal function and plasma renin activity were normal. Angiotensin blockade was refrained for fear of functional deterioration of the kidney. Medical treatment with amlodipine insufficiently lowered the pressure to 140-160/80-100 mmHg, so we performed PTRA. Stenotic lesion and pressure gradient was still present after balloon angioplasty on both sides, prompting us to place LUMINEXX® stents on both renal arteries. Blood pressure dropped dramatically after the intervention. Amlodipine was discontinued, and then, enalapril and warfarin were administered to prevent neointima and thrombus formation. Her blood pressure and renal function was stable 18 months after PTRA. Oversized self-expanding stent such as LUMINEXX® stent could be used for renal artery stenting even in pediatric patients with RVH.

We explore stable potent competitive antagonists against L-DOPA. In anesthetized rats, DOPA cyclohexyl ester (DOPA CHE) (30-100 ng) microinjected in depressor sites of the nucleus tractus solitarii dose-dependently shifted the dose-response-curve for L-DOPA (18-300 ng) to the right, with DOPA CHE (100 ng)-induced slight reduction of the maximum response. DOPA methyl ester (DOPA ME) at 100 ng also produced competitive antagonism. Antagonistic activity of DOPA CHE (100 ng) was similar to that of DOPA ME (300 ng). DOPA CHE is suitable for the purpose of screening.

An impressive body of evidence has been accumulated indicating that local protein synthesis is implicated in navigation of neurite extension induced by guidance cues, such as semaphorin3A (Sema3A). We found previously that a Src type tyrosine kinase Fyn and cyclin-dependent kinase 5 (Cdk5) mediate Sema3A-signaling. We also showed that Sema3A elicits axonal transport through neuropilin-1, a receptor for Sema3A, located at the growth cones. Here, we investigate the relationship between Sema3A-induced local signaling, protein synthesis, and axonal transport. Lavendustin A, a tyrosine kinase inhibitor, and olomoucine, a cyclin-dependent kinase inhibitor, suppressed Sema3A-induced facilitation of anterograde and retrograde axonal transport in dorsal root ganglion (DRG) neuron with and without the cell body. Sema3A-induced facilitation of axonal transport was attenuated in DRG neurons offyn- (fyn-/-) and a Cdk5 activator,p35(p35-/-)-deficient mice when compared with those of wild-type or heterozygous mice. Inhibition of protein synthesis suppressed Sema3A-induced facilitation of axonal transport in the DRG neuron with and without the cell body. Sema3A enhanced the level of immunoreactivity of phosphorylated eukaryotic translation initiation factor 4E (eIF-4E) within 5 min in growth cones in a time course similar to that of the facilitated axonal transport. This enhanced signal for phospho-eIF4E was blocked by lavendustin A or olomoucine and was not detected in thefyn-/-andp35-/-neurons. These results provide evidence for a mutual regulatory mechanism between local protein synthesis and axonal transport.

Summary form only given. We made a p-i-n photodetector with a superlattice structure. The superlattice consists of 5 quantum wells of GaAs at the thickness of 0.85 nm and 4 barriers of AlAs at the thickness of 0.45 nm in the i-region. The p- and n-region are made of AlGaAs and are transparent for light from a mode-locked Ti:sapphire laser. To avoid the effect of carriers photo-excited in the substrate, we used an AlAs/AlGaAs Bragg reflector. The electric field in the superlattice changes the absorption spectrum, so we can modulate the THz radiation by changing the bias voltage. The electric field in the superlattice is determined by the built-in potential in the p-n junction and changed by the external bias voltage. The superlattice is located 500 nm below the surface, so the surface potential is negligible in the superlattice. The THz radiation from the superlattice was detected by a free-space electro-optic sampling system.

A field effect transistor (FET) using a single InGaAs quasi-quantum wire (QWR) structure as a channel has been fabricated. The quasi-QWR structures have been fabricated with As/sub 2/ flux and atomic hydrogen irradiation using molecular beam epitaxy on V-grooved InP substrate. The V-shape is preserved during InAlAs barrier layer growth due to a suppressed migration of In atoms under As/sub 2/ flux. The V-groove is not preserved and hence the QWR cannot be fabricated under As/sub 4/ flux. The single InGaAs quasi-QWR is used as a channel of the FET. The FET demonstrated the good saturation characteristics and its maximum transconductance is 300 mS/mm at a drain voltage of 0.5 V.

Summary form only given. We have fabricated ultrafast photoconductive switches on a GaAs substrate using an atomic force microscope (AFM) based on anodic oxidation. We report the ultrafast photoconductive switches on a thin absorption layer of low-temperature-grown GaAs which is used to reduce the transit time of carriers.

In this paper, we firstly report the negative differential resistance (NDR) characteristics in ridge-type InGaAs/InAlAs quantum wire field-effect transistor (QWIR-FET) with the /spl delta/-doped layer grown on InP [100] patterned substrate by molecular beam epitaxy. The drain voltage for the onset of NDR and peak-to-valley current ratio (PVCR) are significantly improved by employing QWIR and by decreasing the distance between a source and drain.

A trench-type narrow InGaAs quantum-wire field-effect transistor (QWRFET) on a V-grooved (311)A InP substrate has been successfully fabricated. The trench-type InGaAs QWR-FET with 50 nm gate-length has demonstrated clear negative differential resistance (NDR) characteristics based on real space transfer (RST) with a high peak-to-valley current ratio (PVR=6.2) and a low onset voltage (V/sub NDR/) of 0.1 V. Such a low V/sub NDR/ has not been reported before.

Summary form only. This paper describes the structure and the ultrafast response of insulator-gap photoconductive switches with current block layers.

It has been found that the low‐temperature (

In situ Hall measurements reveal that the mobility of two‐dimensional electron gas 80‐nm‐deep from the surface decreases simultaneously with 10‐keV Ar‐ion irradiation at 90 K. This demonstrates that penetration of irradiation defects far beyond the ion range (projected range =8.8 nm) is due to the channeling effect. Annealing of the irradiated sample was also performed. Partial recovery in the mobility observed indicates that the defects become thermally mobile at above 200 K.

We explored l -DOPA esters with chemically bulky structures to find a potent stable competitive antagonist against l -DOPA, compared to DOPA methyl ester (DOPA ME). In anesthetized rats, DOPA cyclohexyl ester (DOPA CHE), DOPA cyclopentyl ester (DOPA CPE) and DOPA cyclopentyldimethyl ester (DOPA CPDME) at 1 μg microinjected into depressor sites of the nucleus tractus solitarii elicited or tended to elicit more marked antagonism against depressor responses to 60 ng l -DOPA, compared to DOPA ME. At 100 ng, DOPA CHE elicited the most potent antagonism. At 1 μg, duration of the antagonistic activity of DOPA CHE was approximately three times longer than that of DOPA ME. During microdialysis of the nucleus accumbens, conversion from DOPA CHE at 1 μΜ perfused via probes to extracellular l -DOPA was the lowest among these compounds and less than one half of that from DOPA ME. Binding studies showed that the recognition site for l -DOPA differs from ionotropic glutamatergic, dopaminergic D1 and D2 receptors. We recently found that l -DOPA evoked by transient ischemia may act as a DOPA CHE-sensitive causal factor for glutamate release and resultant neuronal cell death. DOPA CHE is the most potent, relatively stable competitive antagonist against l -DOPA and is a useful mother compound to develop neuroprotective drugs.

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of reflection high‐energy electron diffraction oscillations in a molecular beam epitaxy system. The critical‐layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 m2/V s and over 15 m2/V s at 293 and 10 K, respectively, is obtained.

DOPA has been proposed to be a neurotransmitter of the primary baroreceptor afferents terminating in the NTS and a neuromodulator in striata of rats. Pre- and post-synaptic recognition sites for DOPA itself may exist. DOPA methyl ester (DOPA ester), a potent competitive antagonist for DOPA in continuously superfused slices or within a several min when microinjected in the NTS has some limitation in in vivo use because of its unstableness as a prodrug for DOPA. We have explored to find stable and potent antagonists for DOPA. At first, we tried to clarify whether or not newly synthesized DOPA esters with bulky structure such as DOPA cyclohexyl ester (CHE), DOPA cyclopentyl ester (CPE) and DOPA cyclopentyldimethyl ester (CPDME) antagonize depressor responses to DOPA microinjected into the NTS, and to what degree these analogues 1 microM perfused via probes are converted to DOPA during striatal microdialysis in urethane-anesthetized rats. Then, we analyzed mode of antagonism of some candidate in the NTS system. During striatal microdialysis, DOPA ester 1 microM increased extracellular levels of DOPA to an 100 fold higher level at a peak of the 1st 20 min sample after the perfusion. Conversion ratio of CHE, CPE and CPDME, compared to DOPA ester, was less than 1/5 at the peak of the 3rd sample, 1/3.3 at the peak of the 2nd, and 1/2.7 at the peak of the 3rd, respectively. In the NTS, all analogues 1 microgram microinjected abolished depressor responses to DOPA 60 ng. Time required to recover a base was 20 min for CHE and 10 min for DOPA ester, CPE and CPDME. At 100 ng, CHE inhibited peak depressor responses to DOPA 60 ng by 53%, CPE by 40%, and CPDME by 24%, compared to DOPA ester by 22%. Then, DOPA 10-300 ng microinjected produced dose-dependent hypotension. DOPA ester 300 ng, microinjected 1 min previously, shifted a dose-response curve for DOPA 30-300 ng to the right without reduction of the maximum response, showing a competitive mode of antagonism. CHE 30 ng competitively antagonized depressor responses to DOPA 18-300 ng without reduction of the maximum response. CHE 100 ng further shifted the dose-response curve for DOPA 18-100 ng to the right with 25% reduction of the maximum response. Antagonistic activity of CHE 100 ng was equipotent with DOPA ester 300 ng. CHE is a competitive antagonist including partially some noncompetitive components. A possible component might be related to NMDA receptors, since high concentrations of CHE displaced selective binding of [3H]-MK-801, an antagonist. In conclusion, CHE is suitable for the purpose.

We have demonstrated a new method to generate intense THz-radiation, up to a sub-microwatt level from a saturable Bragg reflector in a magnetic field. The saturable Bragg reflector is substituted in place of the end mirror in a femtosecond mode-locked Ti:sapphire laser pumped by an all-solid-state green laser.

We have proposed a new THz radiation generation scheme using an intracavity saturable Bragg reflector (SBR) in a magnetic field. With this simple scheme using a simple and damage-free device, THz radiation peaked at around 0.8 THz and 0.8 /spl mu/W average power was directly generated. That power level is the same level as that of complicated and damage-sensitive photoconductive antenna.

Chick collapsin-1, a member of the by a mechanism distinct from that causing growth semaphorin family, has been implicated in axonal cone collapse. Pertussis toxin (PTX) but not its B pathfinding as a repulsive guidance cue. Collapsin-1 induces growth cone collapse via a pathway which oligomer blocks collapsin-induced growth cone col- may include CRMP-62 and heterotrimeric G proteins. lapse. The holotoxin does not affect collapsin-stimu- CRMP-62 protein is related to UNC-33, a nematode lated axoplasmic transport. Mastoparan and a myelin neuronal protein required for appropriately directed protein NI-35 induce PTX-sensitive growth cone col- axonal extension. Mutations in unc-33 affect neural lapse but do not stimulate axoplasmic transport. microtubules, the basic cytoskeletal elements for axo- These results provide evidence that collapsin has a plasmic transport. Using computer-assisted video-en- unique property to activate axonal vesicular transport hanced differential interference contrast microscopy, systems. There are at least two distinct pathways we now demonstrate that collapsin-1 potently pro- through which collapsin exerts its actions in motes axoplasmic transport. Collapsin-1 doubles the developing neurons. q 1997 John Wiley & Sons, Inc. J number of antero- and retrograde-transported organ- Neurobiol 33: 316-328, 1997 elles but not their velocity. Collapsin-1 decreases the Keywords: collapsin; axoplasmic transport; nerve number of stationary organelles, suggesting that the growth cone; pertussis toxin; G proteins fraction of time during which a particle is moving is

We have demonstrated a new scheme for generating intense far-infrared or THz radiation pulses synchronously with near-infrared pulses using a saturable Bragg reflector placed inside a mode-locked laser cavity. With this newly proposed simple scheme, THz radiation which peaked at around 0.66 THz, with an average power of 2–3 nW is directly generated synchronously with femtosecond near-infrared optical pulses.

We have constructed a compact, simple high-repetition rate (1 GHz) mode-locked Ti:sapphire laser with self-starting capability using a saturable Bragg reflector as the mode locker. Nearly transform-limited, 1.6-psec pulses were obtained after external dispersion compensation. This laser is potentially pumped by compact green lasers and will be improved to produce a turn-key system.

The effects of low-energy electron irradiation on the two-dimensional electron gases (2DEG's) in AlGaAs/GaAs heterostructures have been investigated. Not only the electron mobility of the 2DEG's but also the two-dimensional (2D) carriers are found to be reduced by the electron irradiation with the incident energies between 3.5 k and 8 keV and the electron dose of 1×1016 and 1×1017 /cm2. The degraded mobility and the removed carriers by the low-energy electron irradiation are shown to recover by isochronal annealing to some extent, but not completely below 400°C. It is also found that considerable amount of scatterers which are created by an electron irradiation at room temperature are also created by an irradiation at 90 K. Comparing the experimental results with the Monte Carlo simulation, we speculate that the mobility degradation and the 2D carrier compensation are partly caused by the formation of complex defects in the GaAs buffer layer which are due to the excitations of core electrons of As, and that the mobility is further degraded by the formation of short-range scatterers in the heterointerface.

Two-dimensional electron gas 60–120-nm deep from the surface was irradiated with 10-keV Ar ions (projected range = 8.8 nm) and resulting change in the mobility was analyzed. Defect distribution thus obtained is exponential in depth with the larger penetration length for the lower irradiation temperature. In-situ Hall measurements revealed that the mobility decreases simultaneously with the irradiation at 90 K. Consequently, the deep penetration of defects is concluded to be mainly due to the ion channeling. Results of iso-chronal annealing indicate that thermal diffusion of the defect that affects the mobility takes place at around 340–400 K, whereas the mobility starts to recover at ∼120 K.