113,618 research outputs found
Cloning and expression of first gene for biodegrading microcystins by Sphingopyxis sp. USTB-05
Harmful cyanobacterial blooms (HCBs) in natural waters are a growing environmental problem worldwide because microcystins (MCs) produced by cyanobacteria are potent hepatotoxins and tumor promoters. MCs are resistant against physical and chemical factors. Thus, biodegradation is the most efficient method for removing MCs, and a number of bacterial strains, especially genus _Sphingomonas_, have been isolated for biodegrading MCs. Although the pathway, enzyme, and gene for biodegrading MCs by _Sphingomonas sp._ have been widely identified recently, no gene concerned with the biodegradation of MCs has been successfully cloned and expressed. In this study, we show that the first and most important gene of mlrA, containing 1,008 bp nucleotides in length, in the biodegradation pathway of MCs by _Sphingopyxis sp._ USTB-05, which encodes an enzyme MlrA containing 336 amino acid residues, is firstly cloned and expressed in _E. coli_ DH5α, with a cloning vector of pGEM-T easy and an expression vector of pGEX-4T-1. The encoded and expressed enzyme MlrA is responsible for cleaving the target peptide bond between 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-deca-4,6-dienoic acid (Adda) and Arg in the cyclic structure of microcystin-RR (MC-RR)and microcystin-LR(MC-LR), two typical and toxic types of MCs. Linear MC-RR and MC-LR are produced as the first products. These findings are important in constructing a new genetic bacterial strain for the efficient removal of MCs from the important water supplies and resolving the controversy on the biodegradation pathway of different types of MCs by genus _Sphingomonas_
Fully open-flavor tetraquark states and with
We have studied the masses for fully open-flavor tetraquark states
and with quantum numbers
. We systematically construct all diquark-antiquark
interpolating currents and calculate the two-point correlation functions and
spectral densities in the framework of QCD sum rule method. Our calculations
show that the masses are about GeV for the
tetraquark states and GeV for the tetraquarks. The
masses of tetraquarks are below the thresholds of
and final states for the scalar and
axial-vector channels respectively. The tetraquark states
with lie below the and thresholds.
Such low masses for these possible tetraquark states indicate that they can
only decay via weak interaction and thus are very narrow and stable.Comment: 17 pages, 4 figure
Discovery potential for supernova relic neutrinos with slow liquid scintillator detectors
Detection of supernova relic neutrinos could provide key support for our
current understanding of stellar and cosmological evolution, and precise
measurements of these neutrinos could yield novel insights into the universe.
In this paper, we studied the detection potential of supernova relic neutrinos
using linear alkyl benzene (LAB) as a slow liquid scintillator. The linear
alkyl benzene features good separation of Cherenkov and scintillation lights,
thereby providing a new route for particle identification. We further addressed
key issues in current experiments, including (1) the charged current background
of atmospheric neutrinos in water Cherenkov detectors and (2) the neutral
current background of atmospheric neutrinos in typical liquid scintillator
detectors. A kiloton-scale LAB detector at Jinping with (10) years
of data could discover supernova relic neutrinos with a sensitivity comparable
to that of large-volume water Cherenkov detectors, typical liquid scintillator
detectors, and liquid argon detectors.Comment: 9 pages, 6 figure
Signatures of Bose-Einstein condensation in an optical lattice
We discuss typical experimental signatures for the Bose-Einstein condensation
(BEC) of an ultracold Bose gas in an inhomogeneous optical lattice at finite
temperature. Applying the Hartree-Fock-Bogoliubov-Popov formalism, we calculate
quantities such as the momentum-space density distribution, visibility and peak
width as the system is tuned through the superfluid to normal phase transition.
Different from previous studies, we consider systems with fixed total particle
number, which is of direct experimental relevance. We show that the onset of
BEC is accompanied by sharp features in all these signatures, which can be
probed via typical time-of-flight imaging techniques. In particular, we find a
two-platform structure in the peak width across the phase transition. We show
that the onset of condensation is related to the emergence of the higher
platform, which can be used as an effective experimental signature.Comment: 5 pages, 3 figure
Hete-CF: Social-Based Collaborative Filtering Recommendation using Heterogeneous Relations
Collaborative filtering algorithms haven been widely used in recommender
systems. However, they often suffer from the data sparsity and cold start
problems. With the increasing popularity of social media, these problems may be
solved by using social-based recommendation. Social-based recommendation, as an
emerging research area, uses social information to help mitigate the data
sparsity and cold start problems, and it has been demonstrated that the
social-based recommendation algorithms can efficiently improve the
recommendation performance. However, few of the existing algorithms have
considered using multiple types of relations within one social network. In this
paper, we investigate the social-based recommendation algorithms on
heterogeneous social networks and proposed Hete-CF, a Social Collaborative
Filtering algorithm using heterogeneous relations. Distinct from the exiting
methods, Hete-CF can effectively utilize multiple types of relations in a
heterogeneous social network. In addition, Hete-CF is a general approach and
can be used in arbitrary social networks, including event based social
networks, location based social networks, and any other types of heterogeneous
information networks associated with social information. The experimental
results on two real-world data sets, DBLP (a typical heterogeneous information
network) and Meetup (a typical event based social network) show the
effectiveness and efficiency of our algorithm
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