The maximum entropy i.e. information capacity of radiographic images is given from the information theory. New concept in treating upon the signal and the quantum noise are introduced. Information capacity is roughly proportional to the square band-width at low bandwidth, whereas it saturates at high bandwidth. This bandwidth is the lowest cutoff frequency in optical transfer functions of elements in a image transfer system taking into consideration. Examples are given for a typical X-ray radiographic system.

The Raman scattering from GaP microcrystals prepared by a gas-evaporation technique has been investigated. A new peak, which can be identified with the surface phonon mode, was found. The present results demonstrate that the surface phonon peak can be clearly observed only when the microcrystals are about one order of magnitude smaller than the wavelength of the incident laser radiation. Effects of finite crystal size on long-wavelength optical phonons in ionic crystals have been investigated extensively by infrared absorption measurements. For a wide variety of ionic microcrystals, new absorption peaks, which can be assigned to surface phonon modes, have been observed and the observed features of surface mode absorption have been interpreted successfully by electromagnetic theories. ' Theoretical discussions of Raman scattering from the surface phonon modes have been presented by several authors. ' Evans et al. ' and Ushioda et al.have succeeded in observing the Raman scattering from surface phonon modes in two-dimensional surfaces (thin films). However, experimental results reported so far on microcrystalline samples are somewhat ambiguous. As far as the authors know, only two works made by Scott and Damen7 on CdS crystallites in thin films and by Bockelmann and Schlecht on MgO microcrystals seem to suggest positively the observation of surface phonon modes by Raman spectroscopy. However, it is still necessary to elucidate the effect of surrounding medium to judge whether the observed Raman peaks are truly attributable to the surface phonon modes or not. In other reports, ' no positive indication of observing the surface phonon mode is found.According to the electromagnetic theories, ' the Raman peak due to the surface phonon mode should show the following three characteristic features: (i)The intensity of the peak increases as the size of microcrystals decreases. (ii) The peak is located between the bulk TO and LO phonon frequencies.(iii) The peak shifts to lower frequencies as the dielectric constant of surrounding medium increases.Raman results which demonstrate all these features have not been reported so far. In this paper, we report the first unambiguous observation of the surface phonon mode in GaP microcrystals by Raman spectroscopy. For GaP microcrystals prepared by the gas-evaporation technique, a new peak which shows the above three characteristic features of the surface phonon mode was found. The new peak can therefore be assigned to the surface phonon mode. GaP microcrystals were prepared by means of the standard gas-evaporation technique. " We evaporated the single crystalline GaP from a tungsten basket in argon gas. Sootlike deposits were collected onto glass plates positioned above the basket. Evaporation temperature was kept at about 1700'C. In order to obtain the particles of various sizes, the gas pressure and the height of particle collection (vertical distance between the basket and the glass substrate) were varied from 10 to 100 Torr and from 2 to 10 cm, respectively. We also prepared rela...

This study investigates spatiotemporal characteristics of the diurnal cycle (DC) of rainfall over Sarawak in northwest Borneo Island, associated with large-scale intraseasonal disturbances represented by the Madden-Julian oscillation (MJO). This is accomplished using a dense hourly rain gauge network and satellite data. The spatial pattern of the DC is classified into two major groups, coastal and interior regions, based on remarkable differences in rainfall peak times and amplitudes. Amplitudes of the DC and daily rainfall amount increase in active MJO phases at all sites, but the MJO has a stronger effect in the coastal region than the interior region. This modulation of rainfall by the MJO disturbance is largely attributed to rainfall frequency in the interior region, but to both frequency and intensity of rainfall in the coastal region. The low-level westerly wind anomaly enhances convergence, the land-sea breeze, and a midnight rainfall peak in the coastal region during the active MJO phase. Analysis of moisture flux divergence and moist static instability suggests the different dynamics of this modulation of the DC between coastal and interior regions.

This study investigates the regional and seasonal rainfall rate retrieval uncertainties within nine state‐of‐the‐art satellite‐based rainfall products over the Maritime Continent (MC) region. The results show consistently larger differences in mean daily rainfall among products over land, especially over mountains and along coasts, compared to over ocean, by about 20% for low to medium rain rates and 5% for heavy rain rates. However, rainfall differences among the products do not exhibit any seasonal dependency over both surface types (land and ocean) of the MC region. The differences between products largely depends on the rain rate itself, with a factor 2 difference for light rain and 30% for intermediate and high rain rates over ocean. The rain‐rate products dominated by microwave measurements showed less spread among themselves over ocean compared to the products dominated by infrared measurements. Conversely, over land, the rain gauge‐adjusted post–real‐time products dominated by microwave measurements produced the largest spreads, due to the usage of different gauge analyses for the bias corrections. Intercomparisons of rainfall characteristics of these products revealed large discrepancies in detecting the frequency and intensity of rainfall. These satellite products are finally evaluated at subdaily, daily, monthly, intraseasonal, and seasonal temporal scales against high‐quality gridded rainfall observations in the Sarawak (Malaysia) region for the 4 year period 2000–2003. No single satellite‐based rainfall product clearly outperforms the other products at all temporal scales. General guidelines are provided for selecting a product that could be best suited for a particular application and/or temporal resolution.

Our purpose is to directly measure mammographic x-ray spectra with collimators and a low-efficiency CdZnTe detector developed recently and to find out the best fit response function of CdZnTe detector to correct the measured spectra. Photon spectra (target Mo or Rh) produced by a mammographic x-ray unit at 25-32 kV and 240 mAs (= 3 times of 80 mAs) and transmitted through 0.03 mm Mo or 0.025 mm Rh filter and object (0.1 mm Al to 0.8 mm Al phantoms) have been analyzed. Since detected spectra were distorted by the response of CdZnTe detector and did not present the true photon spectra, the correction was applied by the stripping procedure. The response function of detector used in this procedure has been determined by the evaluation of interactions (K-escape, coherent scattering, and Compton scattering processes) and incomplete charge collection calculated using the Monte Carlo method. We have used Kalpha1, Kalpha2, Kbeta1, Kbeta2 radiations of Cd, Zn, and Te, respectively and have used the weight function for the incomplete charge collection and have considered Compton scattering. The Monte Carlo simulations were continued by changing the important factors (mean path length of hole lambda(h), dead layer of the CZT crystal and weight factor Wq) of incomplete charge collection until the best fit response function was found out. Corrected photon spectra were compared with the mammographic x-ray spectral data of Bureau of Radiological Health (BRH) measured using a Ge detector. Attenuation curves of aluminum for 25-32 kV were calculated from the corrected photon spectra and compared with the attenuation curves measured using an ionization chamber. These results obtained using the CdZnTe detector agreed with the mammographic x-ray spectral data of BRH and attenuation curves obtained by the ionization chamber.

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Precipitation features around the Meghalaya Plateau, northeast India, during summer are investigated using a 17 year (1998–2014) high‐spatial‐resolution Tropical Rainfall Measuring Mission precipitation radar data set. Precipitation around the plateau fell into two distinct regimes based on the low‐level wind direction that fluctuates on intraseasonal time scales over Bangladesh, windward of the plateau: a westerly regime (WR) and an easterly regime (ER). Under the WR, strong low‐level onshore southwesterlies across Bangladesh encounter the plateau, and localized strong low‐level southerlies running parallel to the Arakan Mountains (i.e., the barrier jet) also blow toward the plateau, concentrating convective unstable air onto its southern slopes. The low‐level wind fields and large‐scale upper level divergent fields promote frequent and intense orographic rainfall along the southern slopes due to forced uplift, generating high precipitation. In contrast, under the ER, strong southeasterlies that blow along the Gangetic Plain without encountering the plateau and subsidence inhibit upward motion around the plateau, resulting in low precipitation. Diurnal variations in precipitation significantly affect the daily precipitation around the plateau under both regimes. High rainfall frequency persists over the southern slopes between 2100 and 1200 LT of the next day under the WR, whereas modest rainfall frequency occurs between 0000 and 0600 LT under the ER, with a daytime minimum and nocturnal maximum in both regimes. The atmospheric boundary layer processes over Bangladesh regulate the wind speed and vertical structure of the low‐level wind toward the plateau, with deceleration during daytime and acceleration at night (i.e., nocturnal jet) that result in the nocturnal rainfall maximum.

Scatter to primary radiation ratios at detector positions were calculated for uniform cylindrical water phantoms in both third and fourth generation x-ray CT scanners using the Monte Carlo simulation method. A rapid method for determining the scattering angle is given. In the process of image reconstruction, the effect of scatter was isolated by applying our new calculation technique. The decrease in CT number due to scatter was found to be less than 10. In the third generation CT scanner the rate of scatter is larger at the centre than at the edge because of the effect of the collimator at the detectors. As a result the cupping artefact occurs in the CT image. The collimator cannot be used in the fourth generation CT scanner and, therefore, the rate of scatter is almost uniform, leading to the appearance of rounded-off edges.