Essential concepts of digital topology\\ (digital kk-connectivity and kk-adjacencis for digital products)

The paper refers to several concepts which are essential to studying digital objects from the viewpoint of digital topology: digital $k$-connectivity or digital $k$-adjacency, $C$-compatible and normal $k$-adjacency for a digital product. Since L. Boxer has often mentioned the origins of these concepts in an inaccurate way, we discuss something incorrectly cited or mentioned in Boxer's papers according to the facts.Comment: 11 page

Digital kk-continuity, digital kk-isomorphism, local kk-isomorphism, radius 22-local kk-isomorphism, and digital kk-homotopy

The present paper refers to the notions of digital continuity, digital $k$-isomorphism, local $k$-isomorphism, radius $2$-local $k$-isomorphism, and digital $k$-homotopy motivated by the Khalimsky's version. We discuss something incorrectly mentioned in Boxer's papers and suggest some accurate information.Comment: The paper deals with essential concepts of digital topology. arXiv admin note: text overlap with arXiv:2309.0143

Pseudocovering and digital covering spaces

The notions of a local $(k_0,k_1)$-isomorphism and a weakly local $(k_0,k_1)$-isomorphism play crucial roles in developing a digital $(k_0,k_1)$-covering space and a pseudo-$(k_0,k_1)$-covering space, respectively. In relation to the study of pseudo-$(k_0,k_1)$-covering spaces, since there are some works to be refined and improved in the literature, the recent paper \cite{H10} improved and corrected some mistakes occurred in the literature. One of the important things is that the notion of a pseudo-$(k_0,k_1)$-covering map in \cite{H6,H9} was revised to be more broadened in \cite{H10}. Thus this new version is proved to be equivalent to a weakly local $(k_0,k_1)$-isomorphic surjection \cite{H10}. The present paper contains some works in \cite{H10} and we only deals with $k$-connected digital images $(X, k)$.Comment: Since the paper contains some improvements on covering spaces and pseudocovering spaces, some people can be interestin

Essential concepts of digital topology (digital kk-covering spaces and pseudo kk-covering spaces)

The present paper focuses on the notions of covering spaces, pseudo-covering spaces, and their equivalences. We discuss something incorrectly mentioned in Boxer's papers and correct them. Indeed, Sections 4-6 (or 4-6) of \cite{B3} are redundant because they have some incorrect assertions on $(k_1,k_2)$-covering spaces or pseudo- $(k_1,k_2)$-covering spaces due to his misunderstanding on Han's papers \cite{H14,H16}. In addition, many things in \cite{B3} are duplicated with some results in \cite{H18}. In addition, since the papers \cite{P1,P2} also have some defects, we correct and improve them.Comment: This paper refers to some essential notions of digital topology related to a digital covering space and a pseudo-covering space in a digital topological setting. arXiv admin note: substantial text overlap with arXiv:2309.02960; text overlap with arXiv:2309.0143

Flexibility-assisted heat removal in thin crystalline silicon solar cells

Thin crystalline silicon solar photovoltaics holds great potential for reducing the module price by material saving and increasing the efficiency by reduced bulk recombination loss. However, the module efficiency decreases rather sensitively as the module temperature rises under sunlight. Effective, inexpensive approach to cooling modules would accelerate large-scale market adoption of thin crystalline silicon photovoltaics. For effective cooling, we exploit high flexibility of single-crystalline thin silicon films to create wavy solar cells. These wavy cells possess larger surface area than conventional flat cells, while occupying the same projected area. We experimentally demonstrate that the temperature of thin wavy crystalline silicon solar cells under the sunlight can be significantly reduced by increased convective cooling due to their large surface area. The substantial efficiency gain, achieved by the effective heat removal, points to high-performance thin crystalline silicon photovoltaic systems that are radically different in configuration from conventional systems.Comment: 33 pages, 17 figure

Semi-separation axioms associated with the Alexandroff compactification of the MW MW -topological plane

The present paper aims to investigate some semi-separation axioms relating to the Alexandroff one point compactification (Alexandroff compactification, for short) of the digital plane with the Marcus-Wyse ($MW$-, for brevity) topology. The Alexandroff compactification of the $MW$-topological plane is called the infinite $MW$-topological sphere up to homeomorphism. We first prove that under the $MW$-topology on ${\mathbb Z}^2$ the connectedness of $X(\subset {\mathbb Z}^2)$ with $X^\sharp\geq 2$ implies the semi-openness of $X$. Besides, for the infinite $MW$-topological sphere, we introduce a new condition for the hereditary property of the compactness of it. In addition, we investigate some conditions preserving the semi-openness or semi-closedness of a subset of the $MW$-topological plane in the process of an Alexandroff compactification. Finally, we prove that the infinite $MW$-topological sphere is a semi-regular space; thus, it is a semi-$T_3$-space because it is a semi-$T_1$-space. Hence we finally conclude that an Alexandroff compactification of the $MW$-topological plane preserves the semi-$T_3$ separation axiom

Design of 6U Nanosatellites in Formation Flying for the Laser Crosslink Mission

With a recent growth in the volume of spaceborne data, free space optical (FSO) or laser communication systems are attracting attention, as they can enable super-high data rates faster than 1 Gbps. The Very high-speed Inter-satellite link Systems using Infrared Optical terminal and Nanosatellite (VISION) is a technical demonstration mission to establish and validate laser crosslink systems using two 6U nanosatellites in formation flying. The final goal is to achieve a Gbps-level data rate at a distance of thousands of kilometers. To establish space-to-space laser communication, the payload optical axes of each satellite should be precisely aligned during the crosslink. The payload is the laser communication terminal (LCT) including the deployable space telescope (DST), which improves optical link performances. The 6U nanosatellite bus is designed with commercial off-the shelf-(COTS) components for agile systems development. For precise formation flying, the bus is equipped a with relative navigation system with a GNSS receiver and RF crosslink, star tracker, 3-axis reaction wheels (RWs), and propulsion system. This proposed concept of the laser crosslink systems will contribute to the construction of the LEO communication constellation with high speed and secure links in future

RR Lyrae Stars in the Field of Sagittarius II

We present the detection of RR Lyrae variable stars in the field of the Sagittarius. II (Sgr II) ultra-faint dwarf (UFD) galaxy. Using B, V time-series photometry obtained with the Korea Microlensing Telescope Network (KMTNet) 1.6 m telescope at CTIO and G-band data from Gaia Data Release 2 (DR2), we identified and characterized two ab-type and four c-type RR Lyrae variables. Five out of the six stars are clustered within three half-light radii (similar to 4'.8) of the galaxy indicating their association with Sgr. II, while the RRab star V4 is located similar to 22' from the galaxy center. By excluding V4, the high c-type fraction (0.8) and the period of the only RRab star V3 (P-V3 similar or equal to 0.666 days) suggest an Oosterhoff. II (Oo II) classification for Sgr. II. Located close to the locus of Oo. II clusters in the period-amplitude diagram, V3 is similar to RRab stars in other UFDs having Oosterh off-intermediate and Oo. II properties. Sgr. II is, however, more compact than usual UFDs, placed in between star clusters and dwarf galaxies in the size-luminosity plane, and therefore spectroscopic studies are eventually required to ascertain the true nature of this stellar system. We derive the metallicity ([Fe/H] RRab similar or equal to -2.1 +/- 0.3) and heliocentric distance (similar to 64 +/- 3 kpc) of Sgr. II from the RR Lyrae stars, and estimate its age (similar to 12 Gyr) based on our stellar population models. The Oosterhoff properties of UFDs can be explained with the evolution effect of RR Lyrae stars in the instability strip.Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. S.C.R was partially supported by the Basic Science Research Program through the NRF of Korea funded by the Ministry of Education (2018R1A2B2006445). Support for this work was also provided by the NRF to the Center for Galaxy Evolution Research (2017R1A5A1070354). H. Jerjen acknowledges the support of the Australian Research Council through Discovery Project DP150100862. H. Jeong acknowledges support from the Basic Science Research Program through the National Research Foundation (NRF) of Korea, funded by the Ministry of Education (NRF2013R1A6A3A04064993). This research was made possible through the use of the APASS, funded by the Robert Martin Ayers Sciences Fund

Eradication of Helicobacter pylori Increases Ghrelin mRNA Expression in the Gastric Mucosa

It has been suggested that Helicobacter pylori eradication may influence production of some peptides in the stomach, which can affect appetite. This hypothesis is controversial. To verify the hypothesis, we conducted this randomized controlled trial using H. pylori infected subjects without any gastrointestinal symptoms. The treatment group received triple H. pylori eradication therapy for 7 days and the control group received no medication. We measured ghrelin, obestatin and the tumor necrosis factor-α (TNF-α) mRNA levels in endoscopic biopsy specimens and the changes from baseline to follow-up. The plasma active n-octanoyl ghrelin and obestatin levels were measured in both groups. The ghrelin/obestatin ratios in plasma and gastric mRNA expression were calculated at baseline and follow-up. Ghrelin mRNA expression in the fundic mucosa after H. pylori eradication increased significantly compared to the control group (4.47±2.14 vs. 1.79±0.96, P=0.009), independent of inflammatory changes. However, obestatin mRNA expression decreased in the antral mucosa (-0.57±1.06 vs. 0.41±0.72, P=0.028). The treatment group showed a marginal increase (P=0.060) in plasma ghrelin/obestatin ratio. The TNF-α mRNA expression also decreased significantly with treatment. This randomized controlled trial demonstrates that H. pylori eradication increases ghrelin mRNA expression, independent of inflammatory cell changes