Core Emission Research Articles

Chemical Composition in the IRAS 16562–3959 High-mass Star-forming Region

Abstract We have analyzed the Atacama Large Millimeter/submillimeter Array cycle 2 data of band 6 toward the G345.4938+01.4677 massive young protostellar object (G345.5+1.47 MYSO) in the IRAS 16562–3959 high-mass star-forming region with an angular resolution of ∼0.″3, corresponding to ∼760 au. We spatially resolve the central region, which consists of three prominent molecular emission cores. A hypercompact H ii region (Core A) and two molecule-rich cores (Core B and Core C) are identified using the moment zero images of the H30α line and a CH3OH line, respectively. Various oxygen-bearing complex organic molecules, such as (CH3)2CO and CH3OCHO, have been detected toward the positions of Core B and Core C, while nitrogen-bearing species, CH3CN, HC3N, and its 13C isotopologues, have been detected toward all of the cores. We discuss the formation mechanisms of H2CO by comparing the spatial distribution of C18O with that of H2CO. The 33SO emission, on the other hand, shows a ring-like structure surrounding Core A, and it peaks on the outer edge of the H30α emission region. These results imply that SO is enhanced in a shock produced by the expanding motion of the ionized region.

Detection of a Radio Bubble around the Ultraluminous X-Ray Source Holmberg IX X-1

Abstract We present C- and X-band radio observations of the famous utraluminous X-ray source (ULX) Holmberg IX X-1, previously discovered to be associated with an optical emission line nebula several hundred parsecs in extent. Our recent infrared study of the ULX suggested that a jet could be responsible for the infrared excess detected at the ULX position. The new radio observations, performed using the Karl G. Jansky Very Large Array (VLA) in B-configuration, reveal the presence of a radio counterpart to the nebula with a spectral slope of −0.56 similar to other ULXs. Importantly, we find no evidence for an unresolved radio source associated with the ULX itself, and we set an upper limit on any 5 GHz radio core emission of 6.6 μJy (4.1 × 1032 erg s−1). This is 20 times fainter than what we expect if the bubble is energized by a jet. If a jet exists its core component is unlikely to be responsible for the infrared excess unless it is variable. Strong winds which are expected in super-Eddington sources could also play an important role in inflating the radio bubble. We discuss possible interpretations of the radio/optical bubble and we prefer the jet+winds-blown bubble scenario similar to the microquasar SS 433.

Rotation of solar‐like stars in the immediate solar neighborhood

AbstractAlthough photometric space‐based missions such as CoRoT or Kepler have yielded rotation measurements of many thousands of late‐type stars during the last decade, the rotational properties of the bulk of the G star population remain undetected by these missions. From the Sun (when viewed as a star), we know that rotation measurements in the ultraviolet are the most promising, or more general, measurements in wavelength regions very sensitive to plage areas on the stars. Therefore, the “classical” S‐index, that is, the strength of the Ca II H&K line core emission, is still the most viable activity and rotation indicator, and with robotic spectroscopy telescopes, such monitoring measurements can be carried out efficiently and economically. We define a complete volume‐limited sample of solar stars in the immediate solar environment and present period measurements in Ca II H&K, both from archival Mount Wilson data and new data obtained with our robotic TIGRE facility.

Novel self-host heteroleptic green iridium dendrimers based on carbazole dendrons for solution-processable non-doped phosphorescent organic light-emitting diodes

Several novel green-emitting iridium dendrimers has been successfully designed and synthesized with carbazole as the dendron, which is covalently attached to the emissive bis[2-(2-dibenzothienyl)pyridine]picolate iridium(III) [(DBTPy)2Irpic] core through a nonconjugated link to form an efficient self-host system for nondoped electrophosphorescent device applications. All the iridium dendrimers display green emission, possess good thermal stability and high photoluminescence quantum yields. As well as, non-doped solution-processed OLEDs were successfully fabricated based on the resulting Ir-1, Ir-2 and Ir-3 as green-emitting phosphors. By increasing the density of carbazole dendrons at the edge of the emissive core, luminescence self-quenching caused by the intermolecular interactions in the solid state can be significantly reduced. Therefore, the OLEDs based on Ir-3 show the best performances with a maximal luminous efficiency of 0.24 cd/A and a maximum brightness of 2520 cd/m2. This work will shed light on the development of novel self-host phosphorescent iridium dendrimers for solution processable nondoped electrophosphorescent devices.

Stimuli-responsive cyclometalated platinum complex bearing bent molecular geometry for highly efficient solution-processable OLEDs

Smart materials, such as stimuli-responsive luminescence, have attracted much attentions due to their potential application in semiconductor filed. In this context, platinum complexes of (dfppy-DC)Pt(acac) and (dfppy-O-DC)Pt(acac) were prepared and characterized, in which (2-(4',6'-difluorophenyl)pyridinato-N,C2')(2,4-pentanedionato-O,O)Pt(II) was used as the planar emission core and 9-(4-(phenylsulfonyl)phenyl)-9H-carbazole (DC) was regard as the bent pendent. Both platinum complexes showed bright emission in solution and solid state, concomitant with charming external-stimuli-responsive emission under mechanical grinding, organic solvent vapors and pressure. The change emission color spanned from yellow to near-infrared region. Using the platinum complexes as the dopant, solution processable organic light-emitting diodes (OLEDs) were fabricated and a maximum external quantum efficiency of ∼18% was achieved, which is the highest value among the reported solution-processable OLEDs based on external-stimuli-responsive luminescence. This research demonstrated that platinum complex can show promising stimuli responsive emission via ingenious molecular design, indicating a novel way for developing the smart materials in semiconductor filed.

Compact Bright Radio-loud AGNs. III. A Large VLBA Survey at 43 GHz

Abstract We present the results from the 43 GHz Very Long Baseline Array (VLBA) observations of 124 compact radio-loud active galactic nuclei (AGNs) that were conducted between 2014 November and 2016 May. The typical dimensions of the restoring beam in each image are about 0.5 mas × 0.2 mas. The highest resolution of 0.2 mas corresponds to a physical size of 0.02 pc for the lowest redshift source in the sample. The 43 GHz very long baseline interferometry (VLBI) images of 97 AGNs are presented for the first time. We study the source compactness on milliarcsecond and submilliarcsecond scales, and suggest that 95 sources in our sample are suitable for future space VLBI observations. By analyzing our data supplemented with other VLBA AGN surveys from the literature, we find that the core brightness temperature increases with increasing frequency below a break frequency ∼7 GHz, and decreases between ∼7 and 240 GHz but increases again above 240 GHz in the rest frame of the sources. This indicates that the synchrotron opacity changes from optically thick to thin. We also find a strong statistical correlation between radio and γ-ray flux densities. Our correlation is tighter than those in the literature derived from lower-frequency VLBI data, suggesting that the γ-ray emission is produced more cospatially with the 43 GHz VLBA core emission. This correlation can also be extrapolated to the unbeamed AGN population, implying that a universal γ-ray production mechanism might be at work for all types of AGNs.

Novel Solid-State Emissive Polymers and Polymeric Blends from a T-Shaped Benzodifuran Scaffold: A Comparative Study.

Two novel polyimines were synthesized from a benzodifuran based diamino monomer and two dialdehydes bearing bulky groups and a flexible spacer. The polymers display tuned luminescence performance according to the presence of half-salen groups. The effect of the intramolecular bond on the emission properties were examined. Two model compounds, replicating the same emissive Schiff base cores, were synthetized. From the models, dye-doped blends in the fluorophore/matrix ratio, resembling the polymers, were produced. Amorphous thin films of the covalent polymers and the polymeric blends were obtained by spin-coating technique. The Photoluminescent (PL) response of the different macromolecular systems were qualitatively and quantitatively examined and compared.

Bright Silicon Nanocrystals from a Liquid Precursor: Quasi-Direct Recombination with High Quantum Yield.

Silicon nanocrystals (SiNCs) with bright bandgap photoluminescence (PL) are of current interest for a range of potential applications, from solar windows to biomedical contrast agents. Here, we use the liquid precursor cyclohexasilane (Si6H12) for the plasma synthesis of colloidal SiNCs with exemplary core emission. Through size separation executed in an oxygen-shielded environment, we achieve PL quantum yields (QYs) approaching 70% while exposing intrinsic constraints on efficient core emission from smaller SiNCs. Time-resolved PL spectra of these fractions in response to femtosecond pulsed excitation reveal a zero-phonon radiative channel that anticorrelates with QY, which we model using advanced computational methods applied to a 2 nm SiNC. Our results offer additional insight into the photophysical interplay of the nanocrystal surface, quasi-direct recombination, and efficient SiNC core PL.

Blue Emitting Star-Shaped and Octasilsesquioxane-Based Polyanions Bearing Boron Clusters. Photophysical and Thermal Properties.

High boron content systems were prepared by the peripheral functionalisation of 1,3,5-triphenylbenzene (TPB) and octavinylsilsesquioxane (OVS) with two different anionic boron clusters: closo-dodecaborate (B12) and cobaltabisdicarbollide (COSAN). TPB was successfully decorated with three cluster units by an oxonium ring-opening reaction, while OVS was bonded to eight clusters by catalysed metathesis cross-coupling. The resulting compounds were spectroscopically characterised, and their solution-state photophysical properties analysed. For TPB, the presence of COSAN dramatically quenches the fluorescence emission (λem = 369 nm; ΦF = 0.8%), while B12-substituted TPB shows an appreciable emission efficiency (λem = 394 nm; ΦF = 12.8%). For octasilsesquioxanes, the presence of either COSAN or B12 seems to be responsible for ∼80 nm bathochromic shift with respect to the core emission, but both cases show low emission fluorescence (ΦF = 1.4–1.8%). In addition, a remarkable improvement of the thermal stability of OVS was observed after its functionalisation with these boron clusters.

The faint radio source population at 15.7 GHz – IV. The dominance of core emission in faint radio galaxies

ABSTRACT We present 15-GHz Karl G. Jansky Very Large Array observations of a complete sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C) survey. 67 out of the 95 sources (71 per cent) are unresolved in the new observations and lower frequency radio observations, placing an upper limit on their angular size of ∼2 arcsec. Thus, compact radio galaxies, or radio galaxies with very faint jets, are the dominant population in the 10C survey. This provides support for the suggestion in our previous work that low-luminosity ($L\lt 10^{25} \, \textrm{W~Hz}^{-1}$) radio galaxies are core dominated, although higher resolution observations are required to confirm this directly. The 10C sample of compact, high-frequency selected radio galaxies is a mixture of high-excitation and low-excitation radio galaxies and displays a range of radio spectral shapes, demonstrating that they are a mixed population of objects.

Luminescent core–shell nanoparticles with crosslinked aggregation‐induced emission core structures: Emission both in solution and solid states

AbstractLuminescent core–shell nanoparticles (NPs) with crosslinked aggregation‐induced emission (AIE) core structures, which exhibited excellent emission independent of the dispersion state of the NPs, have been developed by a facile one‐pot method based on the self‐assembly of an amphiphilic block copolymer poly(PEGMA)‐b‐poly(DB3VT). Core–shell micelles with a poly(DB3VT) core were formed from poly(PEGMA)‐b‐poly(DB3VT) in tetrahydrofuran (THF)/H2O condition, and the crosslinked AIE‐based structure was selectively incorporated into the core by the Suzuki coupling reaction between poly(DB3VT) blocks and tetraphenylethylene (TPE)‐based coupling monomers at the same time. This method afforded a uniform NP with a crosslinked TPE‐based AIE core structure. The obtained NP exhibited excellent emission both in diluted solution and solid states. This result indicated that the formed TPE‐based AIE core structure was always aggregated regardless of NP dispersion owing to the crosslinking as we expected. The crosslinked TPE‐based AIE core structure, which was related to the emission property, was readily tuned by the selection and combination of coupling monomers in the Suzuki coupling reaction. By incorporating electron‐deficient units into the core, the emission color could be successfully tuned from yellow‐green to orange and red while maintaining the emission property independent of the state of the NP dispersion. These results demonstrated that NPs with the crosslinked AIE core structures are a promising luminescent material design motif to realize emission independent on molecular dispersion.

Two-photon imaging of aptamer-functionalized Copolymer/TPdye fluorescent organic dots targeted to cancer cells

Fluorescent organic dots (O-dots) recently have emerged as a new class of promising contrast reagents for two-photon fluorescence (TPF) imaging. However, most of these developed two-photon absorption (TPA) O-dots have no tumor-targeting group, which hampers their wide application for targeted tumor imaging. Herein, we fabricated Sgc8c aptamer-mediated TPA O-dots as a proof-of-concept of the sensing platform for targeted imaging in live cells or deep tissues. The O-dots composed of trans-4-[p-(N, N-diethylamino)styryl]-4’-(dimethyl amino) stilbene (DEAS) emerged as TPA organic emissive cores and encapsulation by using poly (methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) as polymeric encapsulating matrix to form DEAS/PMMA-co-MAA O-dots via a co-precipitation strategy. The obtained O-dots enabled an extremely high TPA absorption cross-section, bright two-photon fluorescence (excitation at 720 nm; emission at 412 nm and 434 nm), excellent cell-permeability and high penetration depth. Sgc8c aptamer, as a protein tyrosine kinase-7 (PTK7) receptor-targetable ligand, was further anchored on the surface of O-dots to obtain DEAS/PMMA-co-MAA@Sgc8c nanoprobes by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)-mediated coupling reaction. Guided by Sgc8c aptamer, DEAS/PMMA-co-MAA@Sgc8c nanoprobes could be rapidly internalized into target acute lymphoblastic leukemia cells (CEM) cells with high specificity and great efficiency. It was also performed that two-photon images of TPA nanoprobes exhibited high two-photon brightness not only in target CEM cells, but also in mouse liver tissue slices even a depth of up to 210 μm. In our perception, it is highly promising that this nanoprobe provides a valuable tool for in vivo targeted imaging.

Periodic Modulation: Newly Emergent Emission Behavior in Pulsars

Abstract Periodic modulations are seen in normal pulsars (P > 0.1 s) over timescales ranging from a few seconds to several minutes. Such modulations have usually been associated with the phenomenon of subpulse drifting. A number of recent studies have shown subpulse drifting to exhibit very specific physical characteristics: (i) drifting is seen only in conal components of the pulse profile and is absent in central core emission; (ii) drifting pulsars are distributed over a narrow range of spin-down energy loss ( ), where pulsars with 2 × 1032 erg s−1 show this behavior; and (iii) drifting periodicity (P 3) is anti-correlated with , such that pulsars with lower values of tend to have longer P 3. These detailed characterizations of drifting behavior, on the other hand, also revealed the presence of other distinct periodic modulations, which can be broadly categorized into two types, periodic nulling, and periodic amplitude modulation. In contrast to drifting, these periodic phenomena are seen across the entire profile in both the core and conal components simultaneously and are not restricted to any specific range. In this work we have assembled an exhaustive list of around 70 pulsars that show such periodic modulations, 22 of which were newly detected using observations from the Giant Meterwave Radio Telescope and the remaining compiled from past publications. The presence of such a significant group in the pulsar population suggests periodic modulations to be newly emergent phenomena in pulsars, with a physical origin that is distinct from that of subpulse drifting.

Charge transfer mediated photoluminescence enhancement in carbon dots embedded in TiO2 nanotube matrix

Carbon quantum dots (CQDs) have drawn a lot of attention in recent years for imaging applications due to their luminescence properties in the visible range. There has been a strong thrust in achieving CQDs with enhanced luminescence efficiency. We report nearly three times increase in the total photoluminescence emission of CQD films by depositing them on TiO2 nanotube (NT) substrates, instead of glass. The net increase in PL arose from higher CQD core emission and the appearance of a strong surface state emission. High-resolution X-ray photoelectron spectroscopy (XPS) was employed to analyze the composition of the CQD surfaces, which confirmed more carboxyl groups on the surface of CQD in the CQD:NT composite. The band alignment of the composite, determined from XPS measurements, favoured carrier transfer from TiO2 NT to CQD. The TiO2 NT, having better surface coverage and wide absorption spectrum, had high absorption cross-section. The efficient transfer of the carriers from NT to CQD is found to be the dominant phenomenon leading to a significant increase in the PL emission intensity.

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

Summary Highly crystalline and emissive carbon dots (CDs) are firstly synthesized via an ionothermal method in organic solvents. In contrast to well-established approaches, ZnCl2 is utilized as the pyrolysis-promoting agent to prepare emissive CDs with tunable wavelengths, directly by carbonization from different O and N precursors under a mild reaction condition at 210°C. More than 50% synthetic yield and 39% photoluminescent quantum yield (blue CD) are obtained. XAFS measurements, in conjunction with TEM, HAADF-STEM, UPS, and ESR analyses, allow us to obtain energy diagram configuration and confirm the luminescent nature of these hard-core structured CDs. Importantly, the resulting CDs exhibit excellent capability to photogenerate superoxide radical anion (O2⋅–), which can be exemplified by both photodynamic therapy and photooxidative cyclization synthesis of tetrahydroquinolines. Representative pharmaceutical mifepristone can be derivatized in 90% yield within 10 min of irradiation of the CDs in an elegant flow reactor.

Filling the Magnetospheres of Weak Pulsars

Abstract Recent advances in numerical algorithms and computational power have enabled first-principles simulations of pulsar magnetospheres using particle-in-cell techniques. These ab initio simulations seem to indicate that pair creation through photon–photon collision at the light cylinder is required to sustain the pulsar engine. However, for many rotation-powered pulsars, pair creation operates effectively only near the stellar surface where magnetic field is high. How these “weak pulsars” fill their magnetospheres without efficient photon–photon pair conversion in the outer magnetosphere is still an open question. In this paper, we present a range of self-consistent solutions to the pulsar magnetosphere that do not require pair production near the light cylinder. When pair production is very efficient near the star, the pulsar magnetosphere converges to previously reported solutions. However, in the intermediate regime, where pair supply is barely enough to sustain the magnetospheric current, we observe a time-dependent solution with a quasi-period about half of the rotation period. This new quasi-periodic solution may explain the observed pulsar death line without invoking multipolar components near the star, and can potentially explain the core versus conal emission patterns observed in pulsar radio signals.

The ALPINE-ALMA [C II] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe

We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158μm emission in a large sample of normal star-forming galaxies at 4 < z < 6 from the ALMA Large Program to INvestigate [C II] at Early times (ALPINE) survey. Searching for typical signatures of outflows in the high-velocity tails of the stacked [C II] profile, we observe (i) deviations from a single-component Gaussian model in the combined residuals and (ii) broad emission in the stacked [C II] spectrum, with velocities of |v|≲500 km s−1. The significance of these features increases when stacking the subset of galaxies with star formation rates (SFRs) higher than the median (SFRmed = 25M⊙yr−1), thus confirming their star-formation-driven nature. The estimated mass outflow rates are comparable to the SFRs, yielding mass-loading factors of the order of unity (similarly to local star-forming galaxies), suggesting that star-formation-driven feedback may play a lesser role in quenching galaxies atz > 4. From the stacking analysis of the datacubes, we find that the combined [C II] core emission (|v|< 200 km s−1) of the higher-SFR galaxies is extended on physical sizes of ∼30 kpc (diameter scale), well beyond the analogous [C II] core emission of lower-SFR galaxies and the stacked far-infrared continuum. The detection of such extended metal-enriched gas, likely tracing circumgalactic gas enriched by past outflows, corroborates previous similar studies, confirming that baryon cycle and gas exchanges with the circumgalactic medium are at work in normal star-forming galaxies already at early epochs.

Blocking exciton-quenching pathways in host and guest interfaces for high performance solution-processed TADF OLEDs with external quantum efficiency approaching 25%

Abstract Although doping system can effectively reduce the concentration quenching of thermally activated delayed fluorescence emitter, the inevitable collision between host and guest may be other energy leakage pathways, which are usually ignored in the previous studies. Here, a new encapsulated molecule Cz-4CzIPN with TADF emissive core and steric shield is conveniently synthesized and fully characterized. The TADF property ensures the efficient triplet exciton utilization, while the encapsulated feature endows the adjacent molecules a big steric bulk to reduce exciton quenching. By using the encapsulated TADF materials as both host and guest, solution-processed TADF OLEDs achieved the maximum external quantum efficiency (EQE) as high as 24.3%, which is among the best results for solution-processed TADF OLEDs reported so far. However, removing any protection of host or guest, the device efficiency will be accordingly reduced. Particularly, when the host and guest are both unencapsulated, the device can only exhibits the EQEmax of 8.0%, which indicates the existence of severe exciton quenching process. This research demonstrates the molecular interface engineering is a promising strategy for blocking the exciton quenching pathways of the solution-processed doping system by suppressing the intermolecular interaction.

Design of Blue Thermally Activated Delayed Fluorescent Emitter with Efficient Exciton Gathering Property for High-Performance Fully Solution-Processed Hybrid White OLEDs.

The blue thermally activated delay fluorescence (TADF) emitters are highly attractive in the fields of constructing hybrid white organic light-emitting diodes (WOLEDs) due to its high efficiency and color stability. However, few blue TADF emitters can withstand sequential orthogonal solvents, making it impossible to fabricate the fully solution-processed hybrid WOLEDs. Here, two TADF materials, PCz-4CzCN and TPA-4CzCN, were designed and synthesized by equipping the emissive core with nonconjugated bulky units, which can effectively enhance the solvent resistance ability without disturbing the TADF feature. The photophysical investigation indicates that phenylcarbazole unit can efficiently block the electromer formation to enhance the energy transfer and exciton utilization of the emitter. Accordingly, the blue OLEDs of PCz-4CzCN shows higher external quantum efficiency (EQE) of 22.6%, which is the best performance recorded among the fully solution-processed blue OLEDs. Upon further doping, the yellow phosphor PO-01, the fully solution-processed TADF-phosphor (T-P) hybrid WOLEDs was successfully obtained with high performance for the first time. Thanks to the efficient exciplex formation, the turn-on voltage of the white device is only 2.8 V, and the maximum brightness and power efficiency are as high as 53 300 cd m-2 and 38.5 lm W-1, respectively, which are even higher than the previous reported T-P hybrid WOLEDs with a vacuum-deposited electron transfer layer.

The study on the properties of the newly extended Gemini surfactants and their application potentials in the petroleum industry

In this study, the newly extended Gemini surfactants (EGSs) were studied as potential candidates in the petroleum industry applications. The performances of EGSs with respect to variant spacer lengths were studied through surface tension, conductivity, dynamic light scattering (DLS), interfacial tension, rheological behavior, field emission electron microscopy (FESEM), core flooding, and corrosion inhibition measurements. The surface pressure (πCMC), surface efficiency (pC20), critical micelle concentration (CMC), maximum surface excess concentration (Γmax), minimum area per molecule of surfactant at the air-water interface (Amin), average the degree of counterion binding to micelle (β), Gibb's free energy of micellization (ΔGmic), and Gibb's free energy of adsorption (ΔGads) of the EGSs were determined from surface tension and conductivity data. The results showed that the EGSs exhibited more surface activity properties, low CMCs, and spontaneously adsorbed at the air-water interface and micellized in the bulk aqueous phase. The surfactants reduced the oil-water interfacial tension (IFT) to ultralow values (10−3 mN/m) at low concentration, and it decreased substantively to very ultralow values (10−4 mN/m) due to the addition of inorganic salts. Also, they exhibited fascinating viscosifying effect and viscoelastic behavior at the experimental temperatures (30 °C–60 °C). The rheological behaviors were influenced by the formation of entangled micelles in aqueous solutions. Furthermore, through core flooding, EGS1 increased oil recovery by 12.30% which is an interesting incremental recovery. Besides, the EGSs surfactants showed high anticorrosion efficacy on A3 carbon steel in 1 M HCl aqueous solution and the inhibitive action mechanism was revealed to be by creating a protective film on the carbon steel surface through physisorption.Overall, the surface activity, interfacial activity, rheological behaviors, and anticorrosion property were dependent on the length of the spacer group. The surfactants, particularly EGS1 demonstrated a more promising interfacial activity and rheological behavior for enhanced oil recovery (EOR) in heterogeneity reservoirs as well as a remarkable anticorrosion property.