120 research outputs found

    Full Orientability of the Square of a Cycle

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    Let D be an acyclic orientation of a simple graph G. An arc of D is called dependent if its reversal creates a directed cycle. Let d(D) denote the number of dependent arcs in D. Define m and M to be the minimum and the maximum number of d(D) over all acyclic orientations D of G. We call G fully orientable if G has an acyclic orientation with exactly k dependent arcs for every k satisfying m <= k <= M. In this paper, we prove that the square of a cycle C_n of length n is fully orientable except n=6.Comment: 7 pages, accepted by Ars Combinatoria on May 26, 201

    Starch/microcrystalline cellulose hybrid gels as gastric-floating drug delivery systems

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    We report hybrid gels based on a high-amylose starch and microcrystalline cellulose with demonstrated properties for gastric-floating drug delivery purposes. The starch/cellulose gels were prepared by ionic liquid dissolution and regeneration, resulting in a continuous surface and a porous interior and a type-II crystalline structure of cellulose. These polysaccharide gels displayed satisfactory elasticity (0.88), recovery (0.26–0.36) and equilibrium swelling (1013–1369%). The hybrid gels were loaded with ranitidine hydrochloride as a model drug and subsequently, low-density starch/cellulose tablets were fabricated by vacuum-freeze-drying. In vitro tests in a simulated gastric fluid indicate that the 3:7 (wt./wt.) starch/cellulose system could maintain the buoyancy for up to 24 h with a release of 45.87% for the first 1 h and a sustained release for up to 10 h. Therefore, our results have demonstrated the excellent gastric-floating ability and sustainable drug release behavior of the starch/cellulose hybrid gels

    The ISM scaling relations using inner HI and an application of estimating dust mass

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    We select a disk-like galaxy sample with observations of the HIHI, H2H_{2} and dust from Herschel Reference Survey (HRS), and derive inner HI masses within the optical radius. We find that the inner gas-to-dust ratio is almost independent of gas-phase metallicity, and confirm that the inner gas mass (HIHI+H2H_{2}) shows tighter relationship with dust mass and monochromatic 500 μm\mu m luminosity than the integral gas mass. It supports that dust is more closely associated with co-spatial cold gas than the overall cold gas. Based on the newly calibrated relationship between inner gas mass and dust mass, we predict dust masses for disk-dominated galaxies from the xCOLD GASS sample. The predicted dust masses show scaling relations consistent with fiducial ones in the literature, supporting their robustness. Additionally, we find that at a given dust mass and star formation rate (SFR), the galactic WISE W3 luminosities show significant dependence on the [NII] luminosity and the stellar mass surface density. Such dependence highlights the caveat of using the W3 luminosity as integral SFR indicator, and is consistent with findings of studies which target star-forming regions in more nearby galaxies and accurately derive dust masses based on mapping-mode spectroscopy.Comment: 21 pages, 8 figures, 3 tables. Accepted for Publication in Ap

    Clump-scale Gas Infall in High-mass Star Formation: a Multi-transition View with JCMT HCN (4--3) Mapping

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    Gas infall motions play a crucial role in high-mass star formation and are characterized by observable signatures in the form of blue-shifted asymmetric spectral line profiles ("blue profiles"). However, the connection between blue profiles and infall motions is unclear due to complex gas motions at parsec scales. In this study, we present the results of an HCN (4-3) mapping survey conducted with the JCMT, towards 38 massive clumps exhibiting blue profiles in HCO+ (3-2). We extract 34 HCN cores from the 38 observed fields. The core-averaged spectra show various line profiles, indicating that blue-profile HCO+ (3-2) does not guarantee the same in HCN (4-3). Through non-LTE radiation transfer calculations, we attribute the low detection rate of high-JJ blue profiles to a combination of insufficient HCN (4-3) opacity and intricate gas motion across different density layers. The comparison between the MALT90 and BGPS line surveys highlights the importance of appropriate tracers, high spectral resolution, and column density thresholds when searching for blue profiles. We select 11 reliable infall candidates and adopt the Hill5 model to fit the infall velocity of 0.2-1.9 km/s, corresponding to 5% to 74% of free-fall velocity. Assuming a spherically collapsing model, we estimate the median and mean mass infall rates to be 4.5E-3 and 7.6E-3 Msun/year, respectively. The consistency of the mass infall rates among different transitions suggests a steady accretion process from the clump gas envelope to the inner region.Comment: 36 pages, 9 figures, 5 tables; accepted for publication in ApJ

    Fragmentation of the High-mass "Starless'' Core G10.21-0.31: a Coherent Evolutionary Picture for Star Formation

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    G10.21-0.31 is a 70 μ\mum-dark high-mass starless core (M>300M>300 M\mathrm{M_{\odot}} within r<0.15r<0.15 pc) identified in SpitzerSpitzer, HerschelHerschel, and APEX continuum surveys, and is believed to harbor the initial stages of high-mass star formation. We present ALMA and SMA observations to resolve the internal structure of this promising high-mass starless core. Sensitive high-resolution ALMA 1.3 mm dust continuum emission reveals three cores of mass ranging 11-18 M\mathrm{M_{\odot}}, characterized by a turbulent fragmentation. Core 1, 2, and 3 represent a coherent evolution at three different evolutionary stages, characterized by outflows (CO, SiO), gas temperature (H2CO\mathrm{H_2CO}), and deuteration (N2D+/N2H+\mathrm{N_2D^+/N_2H^+}). We confirm the potential to form high-mass stars in G10.21 and explore the evolution path of high-mass star formation. Yet, no high-mass prestellar core is present in G10.21. This suggests a dynamical star formation where cores grow in mass over time.Comment: 30 pages, 13 figures; accepted for publication in Ap

    Understanding the multi-scale structure and digestibility of different waxy maize starches

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    This work concerns different cultivars of waxy maize starch (WMS), from which a significant correlation between the multi-scale structure and the digestibility has been identified. WMSs show a typical A-type crystalline polymorph. The surface porosity of WMS granules facilitates their digestibility. In contrast, the in vitro digestion results indicate that the resistant starch (RS) content increased with higher contents of amylose, single helices, and surface short-range ordered structures. Resistant starch (RS) was found to be made up of single helices and perfect crystallites formed by the fraction of chains with a degree of polymerization (DP) between 13 and 24. Slowly digestible starch (SDS) consists of single helices. Rapidly digestible starch (RDS) is mainly composed of disordered molecular chains in the amorphous regions of starch. This work reveals the relationship between the multiscale structure and digestibility of different WMSs and can provide guidance for the application of WMSs in food or non-food fields

    Lamellar structure change of waxy corn starch during gelatinization by time-resolved synchrotron SAXS

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    In situ experiment of synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) was used to study the lamellar structure change of starch during gelatinization. Waxy corn starch was used as a model material to exclude the effect of amylose. The thicknesses of crystalline (d), amorphous (d) regions of the lamella and the long period distance (d) were obtained based on a 1D linear correlation function. The SAXS and WAXS results reveal the multi-stage of gelatinization. Firstly, a preferable increase in the thickness of crystalline lamellae occurs because of the water penetration into the crystalline region. Then, the thickness of amorphous lamellae has a significant increase while that of crystalline lamellae decreases. Next, the thickness of amorphous lamellae starts to decrease probably due to the out-phasing of starch molecules from the lamellae. Finally, the thickness of amorphous lamellae decreases rapidly, with the formation of fractal gel on a larger scale (than that of the lamellae), which gradually decreases as the temperature further increases and is related to the concentration of starch molecular chains. This work system reveals the gelatinization mechanism of waxy corn starch and would be useful in starch amorphous materials processing

    A low-mass line-rich core found in Massive Star-forming Region IRAS 16351-4722

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    We present ALMA sub-arcsecond-resolution observations of both continuum and molecular lines at 345 GHz towards the massive star-forming region IRAS 16351-4722 (hereafter I16351). A total of 12 dust cores were detected based on high spatial resolution observations of the continuum. Among them, a high-mass core (11.6 Msun) and a low-mass core (1.7 Msun) show abundant molecular line emissions. 164 molecular transitions from 29 species and 104 molecular transitions from 25 species are identified in the high-mass and low-mass cores, respectively. Complex organic molecules (COMs) such as CH3OH, CH3OCHO, CH3OCH3, C2H5OH, and C2H5CN are detected in the two cores. Under the assumption of local thermodynamic equilibrium (LTE), rotational temperatures and column densities of the COMs are derived with the XCLASS software. The maximum rotation temperature values in the low-mass core and the high-mass core were found to be approximately 130 K and 198 K, respectively. Additionally, the line widths in the high-mass core are larger than those in the low-mass one. Abundant complex organic molecular line transitions, high gas temperatures, and smaller line widths indicate the presence of a low-mass line-rich core in the massive star formation region for the first time, while the high-mass line-rich core shows hot core property. When comparing the molecular abundances of CH3OH, CH3OCHO, CH3OCH3 and C2H5OH of the two cores with other hot cores and hot corinos reported in the literature, we further confirm that both a hot core and a low-mass line-rich core are simultaneously detected in I16351.Comment: 22 pages, 5 figures, 5 tables, 70 references, accepted by Ap

    Impact of agro-forestry systems on the aroma generation of coffee beans

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    A long experiment has been established since 2000 at CATIE (Tropical Agricultural Research and Higher Education Center), Turrialba, Costa Rica. Twenty agro-forestry systems with different shade types and managements (organic and non-organic) consisting of an incomplete randomized block-design with shade tree as main effect and subplots represented by management were set up. The effects of different managements and shade types on the aroma and color generation of roasted coffee beans were investigated. The total protein content was significantly higher (P < 0.05) under the intensive conventional (IC) (168 g/Kg) and intensive organic (IO) (167 g/Kg) managements than under the moderate conventional (MC) (153 g/Kg in IC vs. MC group, 157 g/Kg in MC vs. IO group). Comparing with the moderate conventional (MC) management, the intensive organic (IO) management had a stronger ability to generate more flavor and color. The total protein content was significantly higher (P < 0.05) under the full sun system (172 g/Kg) than under the shaded (159 g/Kg) and Erythrina system (155 g/Kg), under the service system (165 g/Kg) than under the timber system (146 g/Kg), under the legume timber system (170 g/Kg) than under the non-legume timber system (152 g/Kg). The full sun system had a greater flavor generation and color after roasting. Comparing with the timber system, the service system produced roasted beans with the more flavor and color. Comparing with the non-legume shade tree, the legume shade tree improved the performance of flavor and color in the roasted coffee beans
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