Marangoni effect induced convection in material processing under microgravity (M-18)

On the ground the upper layer of the liquid in a vessel heated from below becomes hotter than the lower layer. This well-known phenomenon results from buoyancy-induced convection. Though this means that the buoyancy-induced convection is not dominant under microgravity conditions in space, another convection called Marangoni convection may possibly occur. This convection results from an intermolecular force which acts on a free surface, that is surface tension. Since it is stronger at lower temperatures, the liquid surface near the heated wall is pulled to the cooled side as shown. This surface movement causes the inner convection. Marangoni convection, however, may be negligible on the Earth, for the molecular force is generally smaller than buoyancy. Various tests on material processing were recently conducted in space and some high quality crystals free from buoyancy convection were obtained. But, at the same time, others proved to be less uniform than expected in the components' distribution. This nonuniformity seems to be mainly caused by Marangoni convection. It is, therefore, very important to know how to control the convection by studying its characteristics, but the problem is that on the ground it is impossible to carry out the experiment without gravity. That is what a space experiment aboard the space shuttle is planned as the First Material Processing Tests (FMPT) of Japan. The experiment on Marangoni flow visualization is being performed in order to investigate the characteristics of convection in uni-dimensional melt growth under microgravity conditions

High contrast experiment of an AO-free coronagraph with a checkerboard pupil mask

A high contrast coronagraph is expected to provide one of the promising ways to directly observe extra-solar planets. We present the newest results of our laboratory experiment investigating "rigid" coronagraph with a binary shaped checkerboard pupil mask, which should offer a highly stable solution for telescopes without adaptive optics (AO) for wavefront correction in space missions. The primary aim of this work was to study the stability of the coronagraph, and to demonstrate its performance without adaptive wavefront correction. Estimation of both the raw contrast and the gain of the point spread function (PSF) subtraction were needed. The limiting factor of the contrast was also important. A binary shaped pupil mask of a checkerboard type has been designed. The mask, consisting of an aluminum film on a glass substrate, was manufactured using nano-fabrication techniques with electron beam lithography. Careful evaluation of coronagraphic performance, including PSF subtraction, was carried out in air using the developed mask. A contrast of $6.7 \times 10^{-8}$ was achieved for the raw coronagraphic image by areal averaging of all of the observed dark regions. Following PSF subtraction, the contrast reached $6.8 \times 10^{-9}$. Speckles were a major limiting factor throughout the dark regions of both the raw image and the PSF subtracted image. A rigid coronagraph with PSF subtraction without AO is a useful method to achieve high contrast observations. Applications of a rigid coronagraph to a Space Infrared telescope for Cosmology and Astrophysics (SPICA) and other platforms are discussed.Comment: 13 pages, 6 figure

Laboratory Experiment of Checkerboard Pupil Mask Coronagraph

We present the results of the first laboratory experiment of checkerboard shaped pupil binary mask coronagraphs using visible light, in the context of the R&D activities for future mid-infrared space missions such as the 3.5 m SPICA telescope. The primary aim of this work is to demonstrate the coronagraphic performance of checkerboard masks down to a $10^{-6}$ peak-to-peak contrast, which is required to detect self-luminous extra-solar planets in the mid-infrared region. Two masks, consisting of aluminum films on a glass substrates, were manufactured using nano-fabrication techniques with electron beam lithography: one mask was optimized for a pupil with a 30% central obstruction and the other was for a pupil without obstruction. The theoretical contrast for both masks was $10^{-7}$ and no adaptive optics system was employed. For both masks, the observed point spread functions were quite consistent with the theoretical ones. The average contrast measured within the dark regions was $2.7 {\times} 10^{-7}$ and $1.1 {\times} 10^{-7}$. The coronagraphic performance significantly outperformed the $10^{-6}$ requirement and almost reached the theoretical limit determined by the mask designs. We discuss the potential application of checkerboard masks for mid-infrared coronagraphy, and conclude that binary masks are promising for future high-contrast space telescopes.Comment: 6 pages, 6 figure

A high dynamic-range instrument for SPICA for coronagraphic observation of exoplanets and monitoring of transiting exoplanets

This paper, first, presents introductory reviews of the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission and the SPICA Coronagraph Instrument (SCI). SPICA will realize a 3m class telescope cooled to 6K in orbit. The launch of SPICA is planned to take place in FY2018. The SPICA mission provides us with a unique opportunity to make high dynamic-range observations because of its large telescope aperture, high stability, and the capability for making infrared observations from deep space. The SCI is a high dynamic-range instrument proposed for SPICA. The primary objectives for the SCI are the direct coronagraphic detection and spectroscopy of Jovian exoplanets in the infrared region, while the monitoring of transiting planets is another important target owing to the non-coronagraphic mode of the SCI. Then, recent technical progress and ideas in conceptual studies are presented, which can potentially enhance the performance of the instrument: the designs of an integral 1-dimensional binary-shaped pupil mask coronagraph with general darkness constraints, a concentric ring mask considering the obscured pupil for surveying a wide field, and a spectral disperser for simultaneous wide wavelength coverage, and the first results of tests of the toughness of MEMS deformable mirrors for the rocket launch are introduced, together with a description of a passive wavefront correction mirror using no actuator.Comment: 15 pages, 10 figures, 2 table

High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes

We present the results of high precision measurements of the thermal expansion of the sintered SiC, SiC-100, intended for use in cryogenic space-telescopes, in which minimization of thermal deformation of the mirror is critical and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to $\sim$ 10 K. Three samples, #1, #2, and #3 were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using the 8th order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were derived for temperatures between 293 K and 10 K. The average and the dispersion (1 $\sigma$ rms) of these three CTEs are 0.816 and 0.002 ($\times 10^{-6}$/K), respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the obtained CTE dispersion, we performed an finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m diameter cryogenic mirror made of six SiC-100 segments. It was shown that the present CTE measurement has a sufficient accuracy well enough for the design of the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure

Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies

The most intense monitoring observations yet made in the optical (UBV) and near-infrared (JHK) wave bands were carried out for nearby Seyfert1 galaxies of NGC 5548, NGC 4051, NGC 3227, and NGC 7469. Over three years of observations with MAGNUM telescope since early 2001, clear time-delayed response of the K-band flux variations to the V-band flux variations was detected for all of these galaxies. Their H-K color temperature was estimated to be 1500-1800 K from the observed flux variation gradients, which supports a view that the bulk of the K flux should originate in the thermal radiation of hot dust that surrounds the central engine. Cross-correlation analysis was performed to quantify the lag time corresponding to the light-travel distance of the hot dust region from the central engine. The measured lag time is 47-53 days for NGC 5548, 11-18 days for NGC 4051, about 20 days for NGC 3227, and 65-87 days for NGC 7469. We found that the lag time is tightly correlated with the optical luminosity as expected from dust reverberation ($\Delta t \propto L^{0.5}$), while only weakly with the central virial mass, which suggests that an inner radius of the dust torus around the active nucleus has a one-to-one correspondence to central luminosity. In the lag time versus central luminosity diagram, the K-band lag times place an upper boundary on the similar lag times of broad-emission lines in the literature. This not only supports the unified scheme of AGNs, but also implies a physical transition from the BLR out to the dust torus that encircles the BLR. Furthermore, our V-band flux variations of NGC 5548 on timescales of up to 10 days are found to correlate with X-ray variations and delay behind them by one or two days, indicating the thermal reprocessing of X-ray emission by the central accretion flow.Comment: ApJ, March 2006, v639 issue, 24 pages, 33 figures, 10 table

Ensemble Variability of Near-Infrared-Selected Active Galactic Nuclei

We present the properties of the ensemble variability $V$ for nearly 5000 near-infrared (NIR) AGNs selected from the catalog of Quasars and Active Galactic Nuclei (13th Ed.) and the SDSS-DR7 quasar catalog. From 2MASS, DENIS, and UKIDSS/LAS point source catalogs, we extract 2MASS-DENIS and 2MASS-UKIDSS counterparts for cataloged AGNs by catalog cross-identification. We further select variable AGNs based on an optimal criterion for selecting the variable sources. The sample objects are divided into subsets according to whether NIR light originates by optical or NIR emission in the rest frame; and we examine the correlations of the ensemble variability with the rest-frame wavelength, redshift, luminosity, and rest-frame time lag. In addition, we also examine the correlations of variability amplitude with optical variability, radio intensity, and radio-to-optical flux ratio. The rest-frame optical variability of our samples shows known negative correlations with luminosity and positive correlations with rest-frame time lag (i.e., the structure function, SF). However, no well-known negative correlation exists between the rest wavelength and optical variability. This inconsistency might be due to a biased sampling of high-redshift AGNs. NIR variability in the rest frame is anticorrelated with the rest wavelength, which is consistent with previous suggestions. However, correlations of NIR variability with luminosity and rest-frame time lag are the opposite of these correlations of the optical variability; that is, the NIR variability is positively correlated with luminosity but negatively correlated with the rest-frame time lag. Because these trends are qualitatively consistent with the properties of radio-loud quasars reported by some previous studies, most of our sample objects are probably radio-loud quasars. Finally, we also discuss the negative correlations seen in the NIR SFs.Comment: 13 pages, 10 figures, Accepted for publication in Ap

The Optical/Near-Infrared Light Curves of SN 2002ap for the First 140 Days after Discovery

Supernova (SN) 2002ap in M74 was observed in the $UBVRIJHK$ bands for the first 40 days following its discovery (2002 January 29) until it disappeared because of solar conjunction, and then in June after it reappeared. The magnitudes and dates of peak brightness in each band were determined. While the rate of increase of the brightness before the peak is almost independent of wavelength, the subsequent rate of decrease becomes smaller with wavelength from the $U$ to the $R$ band, and is constant at wavelengths beyond $I$. The photometric evolution is faster than in the well-known ``hypernovae'' SNe~1998bw and 1997ef, indicating that SN 2002ap ejected less mass. The bolometric light curve of SN 2002ap for the full period of observations was constructed. The absolute magnitude is found to be much fainter than that of SN 1998bw, but is similar to that of SN 1997ef, which lies at the faint end of the hypernova population. The bolometric light curve at the early epochs was best reproduced with the explosion of a C+O star that ejects 2.5~M_\sun with kinetic energy $E_{\rm K}=4\times 10^{51}~{\rm ergs}$. A comparison of the predicted brightness of SN 2002ap with that observed after solar conjunction may imply that $\gamma$-ray deposition at the later epochs was more efficient than in the model. This may be due to an asymmetric explosion.Comment: 15 pages, 6 figures, quality of figure1 is reduced for smaller filesize, accepted for publication in Ap

Malaria rapid diagnostic test positivity rate among febrile patients seen at the Paediatric emergency unit of a tertiary care facility

Background: Malaria, a life-threatening parasitic disease transmitted to humans by the female Anopheles mosquito is one of the infectious causes of fever in children. In Nigeria, malaria remains one of the most important health problems, accounting for 25% of infants and 30% of under-five mortalities. The objective of this study was to determine the prevalence of malaria among febrile children presenting at the children's emergency room (CHER) of a tertiary health facility in Abakaliki using a malaria rapid diagnostic test (mRDT). Methodology: This was a retrospective study that involved children presenting with fever in CHER over a 3-year period. A total of 1,273 febrile children below 18 years of age were tested with a malaria rapid diagnostic test (mRDT) kit during this period. Medical records of the patients were assessed to retrieve information such as age, gender, and clinical diagnoses. Data were analyzed using SPSS version 25. Results: A total of 707 (55.5%) were males and 883 (69.4%) were below 5 years of age. The overall prevalence of malaria by the mRDT test was 26% (n=331). Uncomplicated malaria, 283 (22.2%) was the commonest clinical diagnosis made while the least was malnutrition 3 (0.2%). Children aged 10-<18 years were predominantly affected as mRDT positivity rate was significantly higher in children age group 10-<18 years (40.4% 76/189) than other age groups (X2=44.76, p<0.001). Similarly, the rate was significantly higher (OR 9.625, 95% CI 7.233-12.808, p<0.0001) in children with the clinical diagnosis of malaria (55.2%, 235/426) than those with the clinical diagnosis of other illnesses (11.3%, 96/847), and significantly higher (OR 0.19, 95% CI 0.1186-0.3043, p<0.0001) among those clinically diagnosed with complicated (79.7%, 114/143) than those with uncomplicated malaria (42.8%, 121/283). Conclusion: There is a high prevalence of malaria among febrile children presenting at the CHER of Alex Ekwueme Federal University Teaching Hospital Abakaliki. Children age group 10-<18 years were predominantly affected. The use of mRDT should be encouraged both as a screening and diagnostic tool with a protocol such that febrile children who have positive results are confirmed as having malaria while those with negative results are further evaluated with microscopy