The asymmetric Reppe carbonylation reactions provide a straightforward access to α‐chiral carbonyl compounds. The reported paradigms predominantly adopted precious palladium as the catalyst. Here we ...report a nickel‐catalyzed asymmetric carbonylation of cyclopropenes with phenyl formate and CO/ROH, respectively. This asymmetrical synthetic protocol features high atom economy, good functional group tolerance, which rapidly constructs polysubstituted cyclopropanecarboxylic derivatives with excellent diastereo‐ and enantioselectivity. The synthetic utility is demonstrated by facile conversion of the chiral products into bioactive molecules such as (−)‐Tranylcypromine and (−)‐Lemborexant.
Highly enantioselective inter‐ and intramolecular Ni‐catalyzed hydroalkoxycarbonylation yields various enantioenriched polysubstituted cyclopropanecarboxylic derivatives with quaternary carbon stereocenters.
•A new reductive method for PFOA defluorination was established by sulfite-mediated photolysis.•The defluorination of PFOA was dependent on sulfite concentration and solution pH.•A defluorination ...ratio of PFOA as high as 88.5% was achieved after reaction of 24h.•A few of perfluorinated sulfonates were detected as intermediates during the degradation of PFOA.•A mechanism was proposed for the reductive defluorination of PFOA by hydrated electrons.
A method for reductive degradation of perfluorooctanoic acid (PFOA) was established by using a sulfite/UV process. This process led to a PFOA removal of 100% at about 1h and a defluorination ratio of 88.5% at reaction time of 24h under N2 atmosphere, whereas the use of either UV irradiation or SO32− alone induced little defluorination of PFOA under the same conditions. It was confirmed that the reductive defluorination of PFOA was achieved by hydrated electrons being generated from the photo-conversion of SO32− as a mediator. Theoretical reaction kinetic analysis demonstrated that the generation of hydrated electrons was promoted by increasing either SO32− concentration or solution pH, leading to the acceleration of the PFOA defluorination. Accompanying the reduction of PFOA, a small amount of short-chain perfluorocarboxylic acids, less fluorinated carboxylic acids and perfluorinated alkyl sulfonates were generated, all of which were able to be further degraded with further releasing of fluoride ions. Based on the generation, accumulation and distribution of intermediates, hydrated electrons induced defluorination pathway of PFOA was proposed in a sulfite-mediated UV photochemical system.
Very recently, the BESIII Collaboration reported a charged hidden-charm structure with strangeness in the recoil mass of
K
+
of a process
e
+
e
-
→
D
s
∗
-
D
0
K
+
or
D
s
-
D
∗
0
K
+
, which is named ...as
Z
cs
(
3985
)
-
. The newly observed charged structure can be treated as a partner structure with strangeness of well-known
Z
c
(
3885
)
-
reported in a process
e
+
e
-
→
D
∗
-
D
0
π
+
. In this work, we propose a reflection picture to understand the nature of
Z
cs
(
3985
)
. By performing a combined analysis for the line shape of the recoil mass distribution of
K
+
at five energy points
s
=
4.628
,
4.641
,
4.661
,
4.681
,
4.698
GeV, we find that the
Z
cs
(
3985
)
can be explained as a reflection structure of charmed-strange meson
D
s
2
∗
(
2573
)
, which is produced from the open-charm decay of
Y
(4660) with a
D
s
∗
meson. Furthermore, we predicted the angular distribution of final state
D
s
∗
-
in process
e
+
e
-
→
D
s
∗
-
D
0
K
+
based on our proposed reaction mechanism, which may be an essential criterion to test the non-resonant nature of
Z
cs
(
3985
)
further.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
In this paper, a wideband cylindrical conformal microstrip antenna array employing a proximity‐coupled feeding mechanism with a cavity‐backed configuration is designed and fabricated. ...Compared with other conformal microstrip patch antennas by using linear subarrays assembled piecewise, this design uses Teflon instead of traditional dielectric layers, and makes it possible to process the whole conformal array without splicing, obtaining the freedom in unit size and array radius adjustment except ease of manufacturing and assemblage. Combined with the optimization of the cavity size, an array with 4 × 4 elements is obtained which has a bandwidth of 40% from 8 to 12 GHz and a gain of 16.4 dB.
Abstract
The photonic spin Hall effect (PSHE) can be realized in a photonic crystal (PC) slab, that is, the unidirectional Bloch surface wave can propagate along the surface of the PC slab under the ...excitation of elliptical polarized magnetic dipole. It is further proved that PSHE is caused by the interference of the component surface waves excited by the different components of the incident light, which is the so called component wave interference (CWI) theory. In addition, we also find that the spin of the surface wave oscillates periodically in space, and the oscillation period is a unit cell. In a unit cell, the average spin keeps the spin orbit locked. The results show that the spin separation can also be modulated by the position and the polarization state of the magnetic dipole.
is a Chinese endemic genus comprising two species,
and
. In this study, we sequenced the complete chloroplast (cp) genomes of these two species and of their relative
. Illumina sequencing technology ...was used to compare sequences, elucidate the intra- and interspecies variations, and infer the phylogeny relationship with other Ranunculaceae family species. A typical quadripartite structure was detected, with a genome size from 158,473 to 158,512 bp, consisting of a pair of inverted repeats separated by a small single-copy region and a large single-copy region. We analyzed the nucleotide diversity and repeated sequences components and conducted a positive selection analysis by the codon-based substitution on single-copy coding sequence (CDS). Seven regions were found to possess relatively high nucleotide diversity, and numerous variable repeats and simple sequence repeats (SSR) markers were detected. Six single-copy genes (
,
,
,
,
, and
) resulted to have high posterior probabilities of codon sites in the positive selection analysis, which means that the six genes may be under a great selection pressure. The visualization results of the six genes showed that the amino acid properties across each column of all species are variable in different genera. All these regions with high nucleotide diversity, abundant repeats, and under positive selection will provide potential plastid markers for further taxonomic, phylogenetic, and population genetics studies in
and its relatives. Phylogenetic analyses based on the 79 single-copy genes, the whole complete genome sequences, and all CDS sequences showed same topologies with high support, and
was closely clustered with
within the
genus, with
as their closest relative. Therefore, the complete cp genomes in
species provide interesting insights and valuable information that can be used to identify related species and reconstruct their phylogeny.
Abstract
The discovery of Photonic spin Hall effect (PSHE) on surface plasmon polaritons (SPPs) is an important progress in photonics. In this paper, a method of realizing multi-channel PSHE in ...two-dimensional metal-air-metal waveguide is proposed. By modulating the phase difference
$$\phi$$
ϕ
and polar angle
$$\theta$$
θ
of the dipole source, the SPP can propagate along a specific channel. We further prove that PSHE results from the component wave interference theory. We believe that our findings will rich the application of SPPs in optical devices.
3D face recognition: a survey Zhou, Song; Xiao, Sheng
Human-centric computing and information sciences,
11/2018, Letnik:
8, Številka:
1
Journal Article
Recenzirano
Odprti dostop
3D face recognition has become a trending research direction in both industry and academia. It inherits advantages from traditional 2D face recognition, such as the natural recognition process and a ...wide range of applications. Moreover, 3D face recognition systems could accurately recognize human faces even under dim lights and with variant facial positions and expressions, in such conditions 2D face recognition systems would have immense difficulty to operate. This paper summarizes the history and the most recent progresses in 3D face recognition research domain. The frontier research results are introduced in three categories: pose-invariant recognition, expression-invariant recognition, and occlusion-invariant recognition. To promote future research, this paper collects information about publicly available 3D face databases. This paper also lists important open problems.
Urban rivers are often utilized by the local residents as water source, but they can be polluted by heavy metals due to industrialization. Here, the concentrations, toxicity, speciation and vertical ...profiles of heavy metals in sediment were examined to evaluate their impact, dispersal and temporal variation in Dongbao River. Results showed that the sediment in the industrialized areas was seriously contaminated with Cr, Cu and Ni which posed acute toxicity. Heavy metals, except Cr and Pb, were mainly associated with non-residual fractions, indicating their high mobility and bioavailability. The non-industrialized areas were also seriously contaminated, suggesting the dispersal of heavy metals along the river. The surface sediment could be more contaminated than the deep sediment, indicating the recent pollution events. Overall, when the point sources are not properly regulated, intense industrialization can cause both serious contamination and dispersal of heavy metals, which have far-reaching consequences in public health and environment.
•Contamination, toxicity and speciation of heavy metals in Dongbao River are examined.•The sediment is seriously contaminated with Cr, Cu and Ni which pose acute toxicity.•Dominance of non-residual fractions indicates high mobility of Cd, Cu, Ni and Zn.•The dispersal of heavy metals causes contamination in the non-industrialized areas.•Given the vertical profiles, management efforts on the point sources are inadequate.
Rice is particularly effective, compared to other cereals, at accumulating arsenic (As), a nonthreshold, class 1 human carcinogen in shoot and grain. Nano-zinc oxide is gradually used in agricultural ...production due to its adsorption capacity and as a nutrient element. An experiment was performed to explore the effects of zinc oxide nanoparticles (nZnO) on arsenic (As) toxicity and bioaccumulation in rice. Rice seedlings were treated with different levels of nZnO (0, 10, 20, 50, 100 mg/L) and As (0, and 2 mg/L) for 7 days.
The research showed that 2 mg/L of As treatment represented a stress condition, which was evidenced by phenotypic images, seedling dry weight, chlorophyll, and antioxidant enzyme activity of rice shoot. The addition of nZnO (10-100 mg/L) enhanced the growth and photosynthesis of rice seedlings. As concentrations in the shoots and roots were decreased by a maximum of 40.7 and 31.6% compared to the control, respectively. Arsenite As (III) was the main species in both roots (98.5-99.5%) and shoots (95.0-99.6%) when exposed to different treatments. Phytochelatins (PCs) content up-regulated in the roots induced more As (III)-PC to be complexed and reduced As (III) mobility for transport to shoots by nZnO addition.
The results confirmed that nZnO could improve rice growth and decrease As accumulation in shoots, and it performs best at a concentration of 100 mg/L.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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