Microgrooves on self‐assembled photonic‐crystal (PC) films align liquid crystals (LCs) without any additional rubbing or surface treatment. Nematic (see Figure and inside cover) or twisted‐nematic ...LCs can be formed, depending on the relative orientation of the microgrooved films. A LC Fabry–Perot (FP) cavity was fabricated using these PC films, and electro‐optic tuning of FP cavity modes is demonstrated.
Woodpile structures for three dimensional photonic crystal were fabricated via two photon polymerization. Resins with high two-photon cross-section undergoes a polymerization and forms the woodpile ...structure upon irradiation of a 780 nm Ti:sapphire femtosecond laser. The bandgap of woodpile depends on the parameters of woodpile, which can be varied by nano-positioning system.
The dynamics of two main-chain nonlinear optical polymers, PA-PS and PA-MS, was studied at various temperatures below T
g
. In the characterization, both the photo-induced isomerization method and ...second harmonic generation were employed. In the case of non-polar alignment by the linearly polarized UV light, the main-chain of PA-PS polymer was found well re-aligned but the main-chain of PA-MS polymer was not, because of the high rigidity. In the case of polar alignment by in-situ corona poling technique, double exponential functions fit well to the data of both PA-PS and PA-MS polymer relaxation data at all the temperature range.
Optical bistability is a quantum optical realization of a first order phase transition far from equilibrium. A nonlinear optical material contained in an optical cavity driven resonantly by an ...external coherent optical field undergoes a first order phase transition to a new nonequilibrium stationary state of broken symmetry. Resonant and nonresonant nonlinear optical response of $\pi$-electron excitations in conjugated electronic structure provides the nonlinearity essential to the onset of bistability. Electronic correlation effects in reduced dimensions are responsible for nonresonant nonlinear optical responses. Saturable absorption studies of glassy polymer films consisting of quasi-two dimensional conjugated disc-like structure of silicon naphthalocyanine demonstrate that on-resonance the system behaves as an optical Bloch system with an intensity dependent refractive index of 1 $\times$ 10$\sp{-4}$ cm$\sp2$/kW. Based on the results of these studies, electronic absorptive optical bistability is observed on a nanosecond time scale in a nonlinear Fabry-Perot interferometer employing the saturable absorbing silicon naphthalocyanine film as the nonlinear optical medium.
ABSTRACT
The ATOMS, standing for ALMA Three-millimeter Observations of Massive Star-forming regions, survey has observed 146 active star-forming regions with ALMA band 3, aiming to systematically ...investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary structures inside massive clumps. In this work, the observations, data analysis, and example science of the ATOMS survey are presented, using a case study for the G9.62+0.19 complex. Toward this source, some transitions, commonly assumed to trace dense gas, including CS J = 2−1, HCO+J = 1−0, and HCN J = 1−0, are found to show extended gas emission in low-density regions within the clump; less than 25 per cent of their emission is from dense cores. SO, CH3OH, H13CN, and HC3N show similar morphologies in their spatial distributions and reveal well the dense cores. Widespread narrow SiO emission is present (over ∼1 pc), which may be caused by slow shocks from large–scale colliding flows or H ii regions. Stellar feedback from an expanding H ii region has greatly reshaped the natal clump, significantly changed the spatial distribution of gas, and may also account for the sequential high-mass star formation in the G9.62+0.19 complex. The ATOMS survey data can be jointly analysed with other survey data, e.g. MALT90, Orion B, EMPIRE, ALMA_IMF, and ALMAGAL, to deepen our understandings of ‘dense gas’ star formation scaling relations and massive protocluster formation.
ABSTRACT
We report studies of the relationships between the total bolometric luminosity (Lbol or LTIR) and the molecular line luminosities of J = 1 − 0 transitions of H13CN, H13CO+, HCN, and HCO+ ...with data obtained from ACA observations in the ‘ATOMS’ survey of 146 active Galactic star-forming regions. The correlations between Lbol and molecular line luminosities $L^{\prime }_{\rm mol}$ of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in Lbol–$L^{\prime }_{\rm mol}$ relations as their main line emission. The log(Lbol/$L^{\prime }_{\rm mol}$) for different molecular line tracers have similar distributions. The Lbol-to-$L^{\prime }_{\rm mol}$ ratios do not change with galactocentric distances (RGC) and clump masses (Mclump). The molecular line luminosity ratios (HCN-to-HCO+, H13CN-to-H13CO+, HCN-to-H13CN, and HCO+-to-H13CO+) all appear constant against Lbol, dust temperature (Td), Mclump, and RGC. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the ‘ATOMS’ survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales.
ABSTRACT
We have identified 453 compact dense cores in 3 mm continuum emission maps in the ALMA Three-millimetre Observations of Massive Star-forming regions survey, and compiled three catalogues of ...high-mass star-forming cores. One catalogue, referred to as hyper/ultra compact (H/UC)-H ii catalogue, includes 89 cores that enshroud H/UC H ii regions as characterized by associated compact H40α emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate hot molecular cores (HMCs) showing rich spectra (N ≥ 20 lines) of complex organic molecules (COMs) and not associated with H/UC-H ii regions. The third catalogue, referred to as pure w-cHMC, includes 58 candidate HMCs with relatively low levels of COM richness and not associated with H/UC-H ii regions. These three catalogues of dense cores provide an important foundation for future studies of the early stages of high-mass star formation across the Milky Way. We also find that nearly half of H/UC-H ii cores are candidate HMCs. From the number counts of COM-containing and H/UC-H ii cores, we suggest that the duration of high-mass protostellar cores showing chemically rich features is at least comparable to the lifetime of H/UC-H ii regions. For cores in the H/UC-H ii catalogue, the width of the H40α line increases as the core size decreases, suggesting that the non-thermal dynamical and/or pressure line-broadening mechanisms dominate on the smaller scales of the H/UC-H ii cores.
We present the results of a single-pointing survey of 207 dense cores embedded in Planck Galactic Cold Clumps distributed in five different environments (λ Orionis, Orion A, Orion B, the Galactic ...plane, and high latitudes) to identify dense cores on the verge of star formation for the study of the initial conditions of star formation. We observed these cores in eight molecular lines at 76-94 GHz using the Nobeyama 45 m telescope. We find that early-type molecules (e.g., CCS) have low detection rates and that late-type molecules (e.g., N2H+ and c-C3H2) and deuterated molecules (e.g., N2D+ and DNC) have high detection rates, suggesting that most of the cores are chemically evolved. The deuterium fraction (D/H) is found to decrease with increasing distance, indicating that it suffers from differential beam dilution between the D/H pair of lines for distant cores (>1 kpc). For λ Orionis, Orion A, and Orion B located at similar distances, D/H is not significantly different, suggesting that there is no systematic difference in the observed chemical properties among these three regions. We identify at least eight high-D/H cores in the Orion region and two at high latitudes, which are most likely to be close to the onset of star formation. There is no clear evidence of the evolutionary change in turbulence during the starless phase, suggesting that the dissipation of turbulence is not a major mechanism for the beginning of star formation as judged from observations with a beam size of 0.04 pc.
Abstract
In this study, 36 cores (30 starless and six protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in ...the
J
= 1 → 0 transitions of HCO
+
, H
13
CO
+
, N
2
H
+
, HNC, and HN
13
C. The asymmetry parameter
δV
, which was the ratio of the difference between the HCO
+
and H
13
CO
+
peak velocities to the H
13
CO
+
line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores surveyed) were identified as cores with blue-skewed line profiles (asymmetric profiles with more intense blueshifted emission), and another two starless cores (7%) were identified as candidate blue-skewed line profiles. The peak velocity difference between HCO
+
and H
13
CO
+
of them was up to 0.9 km s
−1
, suggesting that some inward motions exceeded the speed of sound for the quiescent gas (∼10–17 K). The mean of
δV
of the five aforementioned starless cores was derived to be −0.5 ± 0.3. One core, G211.16−19.33North3, observed using the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array in DCO
+
J
= 3 → 2 exhibited blue-skewed features. Velocity offset in the blue-skewed line profile with a dip in the DCO
+
J
= 3 → 2 line was larger (∼0.5 km s
−1
) than that in HCO
+
J
= 1 → 0 (∼0.2 km s
−1
), which may represent gravitational acceleration of inward motions. It seems that this core is at the last stage in the starless phase, judging from the chemical evolution factor version 2.0 (CEF2.0).
Abstract
Gas at high Galactic latitude is a relatively little noticed component of the interstellar medium. In an effort to address this, 41 Planck Galactic Cold Clumps at high Galactic latitude ...(HGal; ∣
b
∣ > 25°) were observed in
12
CO,
13
CO, and C
18
O
J
= 1−0 lines, using the Purple Mountain Observatory 13.7 m telescope.
12
CO (1−0) and
13
CO (1−0) emission was detected in all clumps, while C
18
O (1−0) emission was only seen in 16 clumps. The highest and average latitudes are 71.°4 and 37.°8, respectively. Fifty-one velocity components were obtained, and then each was identified as a single clump. Thirty-three clumps were further mapped at 1′ resolution, and 54 dense cores were extracted. Among dense cores, the average excitation temperature
T
ex
of
12
CO is 10.3 K. The average line widths of thermal and nonthermal velocity dispersions are 0.19 and 0.46 km s
−1
, respectively, suggesting that these cores are dominated by turbulence. Distances of the HGal clumps given by Gaia dust reddening are about 120–360 pc. The ratio of
X
13
/
X
18
is significantly higher than that in the solar neighborhood, implying that HGal gas has a different star formation history compared to the gas in the Galactic disk. HGal cores with sizes from 0.01 to 0.1 pc show no notable Larson’s relation, and the turbulence remains supersonic down to a scale of slightly below 0.1 pc. None of the HGal cores that bear masses from 0.01 to 1
M
⊙
are gravitationally bound, and all appear to be confined by outer pressure.
PDF
