111 research outputs found
Opacity of fluffy dust aggregates
Context. Dust grains coagulate to form dust aggregates in protoplanetary
disks. Their porosity can be extremely high in the disks. Although disk
emission may come from fluffy dust aggregates, the emission has been modeled
with compact grains. Aims. We aim to reveal the mass opacity of fluffy
aggregates from infrared to millimeter wavelengths with the filling factor
ranging from 1 down to . Methods. We use Mie calculations with an
effective medium theory. The monomers are assumed to be 0.1 sized
grains, which is much shorter than the wavelengths that we focus on. Results.
We find that the absorption mass opacity of fluffy aggregates are characterized
by the product , where is the dust radius and is the filling
factor, except for the interference structure. The scattering mass opacity is
also characterized by at short wavelengths while it is higher in more
fluffy aggregates at long wavelengths. We also derive the analytic formula of
the mass opacity and find that it reproduces the Mie calculations. We also
calculate the expected difference of the emission between compact and fluffy
aggregates in protoplanetary disks with a simple dust growth and drift model.
We find that compact grains and fluffy aggregates can be distinguished by the
radial distribution of the opacity index . The previous observation of
the radial distribution of is consistent with the fluffy case, but more
observations are required to distinguish between fluffy or compact. In
addition, we find that the scattered light would be another way to distinguish
between compact grains and fluffy aggregates.Comment: 16 pages, 17 figures, published in A&A, 568, A4
Progression rate of total, and upper and lower visual field defects in open-angle glaucoma patients
Isolation of monomeric s-trans-acrylic acid as a hydroxy host inclusion crystal showing anomalous C=O stretching absorptions
The structure of monomeric s-trans-acrylic acid, trapped in an inclusion complex with an hydroxy host, was elucidated by X-ray analysis
Spectroscopy of eta'-nucleus bound states at GSI-SIS
The eta' meson mass may be reduced due to partial restoration of chiral
symmetry. If this is the case, an eta'-nucleus system may form a nuclear bound
state. We plan to carry out a missing-mass spectroscopy with the 12C(p,d)
reaction at GSI-SIS. Peak structures corresponding to such a bound state may be
observed even in an inclusive measurement, if the decay width is narrow enough.Comment: 4 pages, 2 figures, to appear in the proceedings of MESON2012 (12th
International Workshop on Meson Production, Properties and Interaction),
Krakow, Polan
Chiroptical Studies on Anisotropic Condensed Matter: Principle and Recent Applications of the Generalized-High Accuracy Universal Polarimeter
Chiroptics is the study of the changes in circular polarization states of light transmitted through analytes typically dissolved in isotropic solutions. However, experimental challenges have long prevented chiroptical measurements of anisotropic media such as single crystals of low symmetry, liquid crystals, or structured films. The high accuracy universal polarimeter (HAUP) was introduced in 1983 to investigate the differential refraction of left and right circular polarization states, circular birefringence (CB), and even in anisotropic media that are dominated by the differential refraction of orthogonal linear polarization states, linear birefringence (LB). In this century, the HAUP was extended to also measure not only the dispersive optical effects (CB and LB) but also the corresponding dissipative effects, circular dichroism (CD) and linear dichroism (LD), differences in light absorption. The improved device is the generalized-HAUP (G-HAUP). Not only can it deliver all the linear optical properties of dissymmetric, anisotropic, and absorbing media, but it can also do so in the ultraviolet as well as the visible part of the electromagnetic spectrum. In this review, characteristic features of the G-HAUP and its applications to crystals of photomechanical salicylidenephenylethylamines, alanine, benzil, and magneto-optical CeF3 are described
Formation of racemic compound crystals by mixing of two enantiomeric crystals in the solid state. Liquid transport of molecules from crystal to crystal
Mixing of powdered (-)- and (+)-enantiomer crystals in the solid state gives crystals of the racemic compound. This racemic crystal formation was followed by IR spectral measurement of a 1 :1 mixture of (-)- and (+)-enantiomer crystals as a Nujol mull. As the formation of racemic crystals proceeds, the OH absorptions of the enantiomer disappear gradually and new OH absorptions due to the racemic compound appear. The formation of racemic crystals from enantiomer crystals has been studied for various kinds of chiral compounds: 2,29-dihydroxy-1,19-binaphthyl (1) and its derivatives, 10,109-dihydroxy-9,99-biphenanthryl (4), 2,29-dihydroxy-4,49,6,69-tetramethylbiphenyl (5) and its derivatives, 4,49-dihydroxy-2,29,3,39,6,69- hexamethylbiphenyl (8), 1,6-di(o-chlorophenyl)-1,6-diphenylhexa-2,4-diyne-1,6-diol (11) and its derivatives, trans-4,5-bis[hydroxy(diphenyl)methyl]-2,2-dimethyl-1,3-dioxacyclopentane (17) and itsderivatives, tartaric acid (20) dimethyl tartrate (21), malic acid (22), mandelic acid (23), and norephedrine (24). These molecular movements and blending occur rapidly in the presence of liquids such as liquid paraffin (Nujol), seed oils such as olive, coconut, rapeseed and soybean oil, artificial oil such as silicone oil and water, although the same movement also occurs in the absence of the liquid. For example, keeping a mixture of powdered (-)-1 (1a) and (+)-1 (1b) at room temperature for 48 h gives racemic crystals (1c). However, molecular aggregation sometimes occurs in solution but not in the solid state. Forexample, recrystallization of (-)-16 (16a) and (+)-16 (16b) from solvent gives racemic crystals of 16c, although mixing of these two components as powders in the presence of liquid does not give 16c. In order to determine the mechanism of the molecular movement in the solid state, X-ray crystal structures of optically active and racemic compounds and also the molecular movements from optically active crystal to racemic crystal have been studied
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