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Rehabilitation for the most common symptoms such as dementia is brain training, and it is thought that this type of training is highly compatible to digitalization and applications.

The capacitance-voltage (C-V) characteristics of Al0.25Ga0.75N/GaN heterostructure barrier varactors (HBV) grown by metal-organic chemical vapor deposition on a c-oriented sapphire substrate were studied. The favorable material properties of wide-band-gap III-N's are important in realizing the HBVs for frequency triples and distributed line pulse sharpens for practical use. The HBV structure consists of a 10-nm-thick undoped Al0.25Ga0.75N barrier sandwiched between two undoped GaN layers with a thickness of 5 nm. The barrier structure is further sandwiched between two n-GaN (n = 5 × 1017 cm–3) layers with respective thicknesses of 500 nm and 1 µm to form the top and the bottom ohmic contacts. At room temperature, the C-V characteristics show a maximum capacitance Cmax at approximately –1.8 V because of the induced piezoelectric field within the heterostructure, and the I-V characteristics show an increase in leakage current below –1.5 V and above 0.5 V. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An instrument to improve power spectrum density (PSD) measurements, a highly sensitive preamplifier and a data acquisition unit are designed as well as a programmable power battery source. The preamplifier has 8 junction field effect transistor (JFET) inputs in parallel resulting in an input noise equivalent power of —186 dBV2/Hz. The data acquisition system consists of a low-pass filter, an A/D converter and a RAM, which transfer the data to the connected PC. The FFT or other signal processing is carried out within the PC. The battery power source is controlled by the PC, enabling us to obtain the device-under-test (DUT) bias DC required by the program. This measuring system works well at room temperature where the DUT and the power source could be put into a magnetic shielding box to reject spurious line noises. In the case where the DUT is placed in a cryostat to measure the temperature dependence of noise properties, however, the shielding of the DUT from the power line becomes a serious problem. Particularly in order to use a compressor cooling system, spurious noises come into the measuring system through the power lines of the compressor. In such a case the preamplifier must be placed as close as possible to the DUT, and the power line to the compressor is sometimes disconnected from the system.

In Athena Olympics in 2004 a Japanese girl got the gold medal in Women Marathon games. Just before the beginning, she was listening to some domestic melodies in order to concentrate on the race. The rhythm or power of that music is found to have the typical 1/f noise characteristics. The 1/f music is found effective to concentrate as well as to relax themselves for a fairly long time range, while some short time trial runner uses a kind of white noise like music.

Low cost highly sensitive preamplifier was made by using the commercially available operational amplifier AD797 which has the input noise equivalent power of −190 dBV2/Hz with 80 dB amplification.

The Hooge parameters of compound semiconductors are found to be in inverse proportional to the mean free paths of materials. The newly developed model of 1/f phonon energy partition fluctuation in thermal equilibrium predicts the value of Hooge parameter as αH = a/λ, the ratio of the lattice constant a and the mean free path λ. Several reported experimental results on αH for very pure semiconductors are found on the a/λ line. Experimental verification is given by measuring noise in InGaAs/InAlAs heterostructure, where optical phonon effects can be observed due to negligible impurity scattering. The Hooge parameter of about 1 in p-InGaAs and 10-3 to 10-5 in n-InGaAs reflects the two order difference in the mobility and corresponding λ values.

The Si surface of n-SiC is etched by an Ar electron cyclotron resonance plasma in order to smooth the as-received substrates. Low-frequency current noise characteristics of Ohmic contacts of the wide-band-gap semiconductor n-SiC are investigated. Ohmic contacts with a diameter of 200 µm have a minimum Ohmic contact resistance of the order of 10-4 Ω·cm2 at an alloying temperature of 1000°C for 30 min. These low resistance Ohmic contacts show typical 1/f current noise characteristics that increase with the square of the sample current I 2. A sample with a higher contact resistance exhibits, however, current noise power increase with increasing sample current I. The relevant total electron number between the electrodes of the bulk substrate is estimated from the resistance and by finite element method simulation, from which the Hooge parameter αH is estimated to be approximately 40.