Noise reduction combining time-domain epsilon-filter and time-frequency epsilon-filter

A time-domain epsilon-filter (TD epsilon-filter) is a nonlinear filter that can reduce noise while preserving a signal that varies drastically, such as a speech signal. Although the filter design is simple, it can effectively reduce noise. It is applicable not only to stationary noise but also to nonstationary noise. It cannot, however, be applied when the amplitude of noise is relatively large. This paper introduces an advanced method for noise reduction that applies an epsilon-filter to complex spectra, namely a time-frequency epsilon-filter (TF epsilon-filter). This paper also introduces noise reduction combining a TD epsilon-filter and a TF epsilon-filter. An advanced method called a variable time-frequency epsilon-filter is also proposed. First, the algorithm of the TD epsilon-filter is explained to clarify the problem. Then, the algorithms of the proposed methods are explained. By utilizing an epsilon-filter in the frequency domain, the proposed method can reduce not only noise that has a relatively small amplitude but also noise that has a relatively large amplitude. Experimental results are also given to demonstrate the performance of the proposed methods in comparison to the results of some conventional methods.     

High-throughput characterization of local conductivity of Nd0.9Ca0.1Ba2Cu3O7−δ thin film by the low-temperature scanning microwave microscope

We developed a scanning microwave microscope (SμM) designed for high-throughput electric-property screening as well as for rapid construction of electronic phase diagrams at low temperatures. As a sensor probe, we used a high-Qλ/4 coaxial cavity resonator to which a thin needle with ball-tip end was attached. The sensor module was mounted on the low-temperature XYZ stage, which allowed us to map out the change of resonance frequency and quality factor due to the local tip-sample interaction at low temperatures. From the measurements of combinatorial thin films, such as Ti_1−xCo_xO_2−δ and Nd_0.9Ca_0.1Ba₂Cu₃O_7−δ (NCBCO), it was demonstrated that this SμM system has enough performance for the high-throughput characterization of sample conductance under variable temperature conditions.     

Community responses to road traffic noise in Hanoi and Ho Chi Minh City

Vietnam is a developing country in southeast Asia, and its environment has been seriously affected by industrialization and urbanization. In large cities like Hanoi (northern Vietnam) and Ho Chi Minh City (southern Vietnam), noise emission from road traffic has been found to be a serious concern among general public. In 2005 and 2007, two large-scale socio-acoustic surveys of community response to road traffic noise were conducted to investigate human reactions to road traffic noise in these cities; the sample sizes were 1503 people in Hanoi and 1471 in Ho Chi Minh City. The noise exposure levels (L_den) were 70–83 dB in Hanoi and 75–83 dB in Ho Chi Minh City. Noise annoyance was estimated using standardized annoyance scales. For both cities, dose–response relationships were established between L_den and the percentage of highly annoyed respondents. Compared to annoyance responses of European people, Vietnamese were less annoyed by road traffic noise by about 5 dB. Hanoi respondents seemed to be more annoyed by noise than Ho Chi Minh City respondents. Conversation and sleep disturbances were not as serious as expected in either city. Furthermore, window orientation in the home was found to affect activity disturbances.     

Third-order aberration analysis of an off-axial optical system

The aberration theory applied to co-axial optical systems is extended to off-axial systems, for which third-order aberration coefficients are considered. The derived aberrations are analyzed using three-dimensional ray bundles, spot diagrams, and image charts, and classified in relation to the system symmetry. This theory is very useful for optical designers, allowing them to clarify the relationship between the structures of off-axial optical systems and the corresponding off-axial aberrations.     

The origin of the Japanese race based on genetic markers of immunoglobulin G

This review addresses the distribution of genetic markers of immunoglobulin G (Gm) among 130 Mongoloid populations in the world. These markers allowed the populations to be clearly divided into 2 groups, the northern and southern groups. The northern group is characterized by high frequencies of 2 marker genes, ag and ab3st, and an extremely low frequency of the marker gene afb1b3; and the southern group, in contrast, is indicated by a remarkably high frequency of afb1b3 and low frequencies of ag and ab3st. Based on the geographical distribution of the markers and gene flow of Gm ag and ab3st (northern Mongoloid marker genes) from northeast Asia to the Japanese archipelago, the Japanese population belongs basically to the northern Mongoloid group and is thus suggested to have originated in northeast Asia, most likely in the Baikal area of Siberia.     

Dynamical structure of peptide molecules: Fourier transform microwave spectroscopy and ab initio calculations of N-methylformamide

Rotational spectra of both trans and cis forms of the N-methylformamide normal as well as deuterated (HCONDCH₃, referred to as N-D) species were observed by Fourier transform microwave spectroscopy in the frequency region from 5 to 118 GHz. Samples were prepared in the form of a beam by a pulsed jet valve maintained at 50 °C and were introduced in a high-vacuum cavity cell, with either Ne or Ar as a carrier gas at a backing pressure of 100 kPa. The observed spectra were analyzed to yield molecular parameters including rotational constants and barrier, V₃, to CH₃ internal-rotation: 53.9 (6) and 301 (4) cm⁻¹ for the trans and cis forms of the normal species, respectively, and 41.9 (6) and 309 (4) cm⁻¹ for the trans and cis forms of the N-D species, respectively. Spectra of four trans isotopologues with ¹³C, ¹⁵N, or ¹⁸O singly-substituted in the internal-rotation A state were observed and analyzed to derive the r_s structure of the trans form. For comparison with the experimental data, ab initio calculations were carried out at MP2/6-31G∗∗ level to derive molecular structure, potential barrier to CH₃ internal rotation, and the energy difference between the cis and trans forms. An extensive coupling was found between the CH₃ internal rotation and N-H out-of-plane bending, suggesting that the potential function for the CH₃ internal-rotation deviates considerably from a simple cos(3α) form. The effects of the V₆ term is briefly discussed.     

Low temperature fabrication of 5-10 nm SiO2/Si structure using advanced nitric acid oxidation of silicon (NAOS) method

We have developed the advanced nitric acid oxidation of Si (NAOS) method to form relatively thick (5-10 nm) SiO₂/Si structure with good electrical characteristics. This method simply involves immersion of Si in 68 wt% nitric acid aqueous solutions at 120 °C with polysilazane films. Fourier transform infrared absorption (FT-IR) measurements show that the atomic density of the NAOS SiO₂ layer is considerably high even without post-oxidation anneal (POA), i.e., 2.28 × 10²² atoms/cm², and it increases by POA at 400 °C in wet-oxygen (2.32 × 10²² atoms/cm²) or dry-oxygen (2.30 × 10²² atoms/cm²). The leakage current density is considerably low (e.g., 10⁻⁵ A/cm² at 8 MV/cm) and it is greatly decreased (10⁻⁸ A/cm² at 8 MV/cm) by POA at 400 °C in wet-oxygen. POA in wet-oxygen increases the atomic density of the SiO₂ layer, and decreases the density of oxide fixed positive charges.     

Development of ultra-short pulse VUV laser system for nanoscale processing

We have developed intense vacuum ultraviolet (VUV) radiation sources for advanced material processing, such as photochemical surface reactions and precise processing on a nanometer scale. We have constructed a new VUV laser system to generate sub-picosecond pulses at the wavelength of 126 nm. A seed VUV pulse was generated in Xe as the 7th harmonic of a 882-nm Ti:sapphire laser. The optimum conversion was achieved at the pressure of 1.2 Torr. The seed pulse will be amplified by the Ar₂^*\mathrm{Ar}_{2}^{*} media generated by an optical-field-induced ionization Ar plasma produced by the Ti:sapphire laser. We have obtained a gain coefficient of g=0.16 cm⁻¹. Our developing system will provide VUV ultra-short pulses with sub-μJ energy at a repetition rate of 1 kHz.     

Broad-spectrum frequency comb generation and carrier-envelope offset frequency measurement by second-harmonic generation of a mode-locked fiber laser

A frequency comb spanning more than one octave has been achieved by injecting the second-harmonic generation (780 nm) of a mode-locked fiber laser (1.56 microm) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency of the frequency comb. Frequency noise has been observed on the measured carrier-envelope offset frequency, which has been confirmed to be generated in the photonic crystal fiber by comparing the measured beat frequencies between cw lasers and frequency combs before and after the photonic crystal fiber. The mode-locked fiber laser is considered to be an important candidate for the light source used in realizing a compact optical frequency measurement system including applications in the telecommunication bands.     

Novel in-gap spin state in Zn-doped La1.85Sr0.15CuO4

Low-energy spin excitations of La(1.85)Sr(0.15)Cu(1-y)Zn(y)O4 were studied by neutron scattering. In y=0.004, the incommensurate magnetic peaks show a well-defined "spin gap" below T(c). The magnetic signals at omega=3 meV decrease below T(c)=27 K for y=0.008, also suggesting the gap opening. At lower temperatures, however, the signal increases again, implying a novel in-gap spin state. In y=0.017, the spin gap vanishes and elastic magnetic peaks appear. These results clarify that doped Zn impurities induce the novel in-gap state, which becomes larger and more static with increasing Zn.