A characterization on orientations of graphs avoiding given lists on out-degrees

Let $G$ be a graph and $F:V(G)\to2^N$ be a set function. The graph $G$ is said to be \emph{F-avoiding} if there exists an orientation $O$ of $G$ such that $d^+_O(v)\notin F(v)$ for every $v\in V(G)$, where $d^+_O(v)$ denotes the out-degree of $v$ in the directed graph $G$ with respect to $O$. In this paper, we give a Tutte-type good characterization to decide the $F$-avoiding problem when for every $v\in V(G)$, $|F(v)|\leq \frac{1}{2}(d_G(v)+1)$ and $F(v)$ contains no two consecutive integers. Our proof also gives a simple polynomial algorithm to find a desired orientation. As a corollary, we prove the following result: if for every $v\in V(G)$, $|F(v)|\leq \frac{1}{2}(d_G(v)+1)$ and $F(v)$ contains no two consecutive integers, then $G$ is $F$-avoiding. This partly answers a problem proposed by Akbari et. al.(2020

A rapid low-cost real-time PCR for the detection of klebsiella pneumonia carbapenemase genes

<p>Abstract</p> <p>Background</p> <p><it>Klebsiella pneumonia</it> carbapenemases (KPCs) are able to hydrolyze the carbapenems, which cause many bacteria resistance to multiple classes of antibiotics, so the rapid dissemination of KPCs is worrisome. Laboratory identification of KPCs-harboring clinical isolates would be a key to limit the spread of the bacteria. This study would evaluate a rapid low-cost real-time PCR assay to detect KPCs.</p> <p>Methods</p> <p>Real-time PCR assay based on SYBR GreenIwas designed to amplify a 106bp product of the <it>bla</it>_KPC gene from the159 clinical Gram-negative isolates resistant to several classes of -lactam antibiotics through antimicrobial susceptibility testing. We confirmed the results of real-time PCR assay by the conventional PCR-sequencing. At the same time, KPCs of these clinical isolates were detected by the modified Hodge test (MHT). Then we compared the results of real-time PCR assay with those of MHT from the sensitivity and specificity. Moreover, we evaluated the sensitivity of the real-time PCR assay.</p> <p>Results</p> <p>The sensitivity and specificity of the results of the real-time PCR assay compared with those of MHT was 29/29(100%) and 130/130(100%), respectively. The results of the real-time PCR and the MHT were strongly consistent (Exact Sig. (2-tailed) =1. 000; McNemar test). The real-time PCR detection limit was about 0.8cfu using clinical isolates.</p> <p>Conclusion</p> <p>The real-time PCR assay could rapidly and accurately detect KPCs -harboring strains with high analytical sensitivity and specificity.</p

One size does not fit all: the differential impact of online reviews

There has been plenty of research on the impact of online reviews on product sales in the last decade. However, prior studies don’t always reach the same conclusions. Literature review indicates that, because of data limitations, prior studies treat the consumers as homogeneous and ignore their individual characteristics. There has only been very limited research that delves into the characteristics of the products being reviewed. Do online reviews have the same impact on consumers who may have different shopping habits or demographic characteristics? Do online reviews also impact the sales of all products/services to the same extent? Using a unique dataset that includes individually identifiable consumer online review browsing data and purchase data, this paper analyzes the effect of online reviews from a more nuanced perspective by examining how individual consumer shopping characteristics and vendor characteristics moderate the effect of online reviews as well as vendors’ marketing activities

CdS-based Photocatalysts : The Study of Tip Decoration, Charge Dynamics, and Heterointerfaces

Photocatalytic water splitting to produce H2 fuel has drawn considerable attention due to ever-increasing environmental concerns and the rising global energy demand for renewable and clean energy formation. Since last century, the semiconductor photocatalysts have been studying to explore their photocatalytic properties for solar-driven H2 evolution from water. Among the various H2-evolving photocatalysts, CdS with excellent visible-light absorption and suitable band potentials is one of the most studied photocatalysts. Although cocatalyst-decorated CdS nanorods (NRs) offer a promising H2 evolution performance, further benefits invoked by spatial cocatalyst decoration are worth exploring. Given that noble metal cocatalysts were most deposited on the tips of CdS NRs, the tip deposition of non-noble metal cocatalysts on CdS NRs was explored in the first stage of PhD research. For the first time, it was found that amorphous MoOxSy preferentially photodeposited on CdS NR tips, which enhanced photocatalytic H2 evolution. Detailed characterization and studies determined the composition and possible formation pathways of the amorphous MoOxSy on the CdS tips. The enhancement was ascribed to the effective trapping of photoinduced electrons by the MoOxSy resulting from its lower surface work function compared to CdS. However, amorphous MoOxSy is unstable in most hole scavengers except methanol. Consequently, the MoOxSy was vulcanized into MoS2, with MoS2 presenting either on the only tips, on the tips and random walls, or having an overall coating. MoS2-tipped CdS NRs exhibited a better H2 evolution activity compared to other MoS2-loaded CdS NRs. Kelvin probe force microscopy and time-resolved photoluminescence spectroscopy were used to study spatial charge separation, transfer, and lifetime. The superior photoactivity of MoS2-tipped CdS NRs was assigned to spatially intensified charge separation along the long axis of NRs, thereby lowering the charge recombination rate. To further understand the effects of MoS2 distribution on CdS NRs, MoS2 was parallelly or perpendicularly placed on polar CdS (001) surfaces (representing CdS NR tips) and non-polar CdS (110) surface (representing CdS NR wall) to construct different CdS/MoS2 models for DFT calculations. It was verified that CdS NR is capable of the longitudinal charge transfer due to charge polarization on polar (001) surfaces. The distinct electronic properties (i.e. shift in core-level energies of Cd and S orbitals, interfacial charge accumulation and depletion) of different CdS/MoS2 heterostructures, induced by the different interfacial bonding arrangements and MoS2 orientation, were observed and analyzed. In addition, two types of MoS2-loaded CdS NRs (MoS2 being only on the tips or only on the walls of CdS NRs) were fabricated to obtain their BEs of Cd 3d and S 2p by XPS for comparison, which is consistent with the expected DFT results. The band edges of CdS component in the as-prepared samples were also determined by combining Tauc plots and VB XPS measurements; the band shifts in experiments approximately correspond to DFT results. As a result, the MoS2 distribution and orientation affect the electronic properties of CdS/MoS2 heterostructures and thereby giving a different photoactivity. Overall, this thesis reveals that the origins of photocatalytic H2 evolution advantages induced by spatially located cocatalyst and gives insights into the activity enhancement mechanism for tip-decorated CdS NRs, which guides the construction of more efficient CdS-based photocatalysts

Extending the fundamental imaging-depth limit of multi-photon microscopy by imaging with photo-activatable fluorophores

It is highly desirable to be able to optically probe biological activities deep inside live organisms. By employing a spatially confined excitation via a nonlinear transition, multiphoton fluorescence microscopy has become indispensable for imaging scattering samples. However, as the incident laser power drops exponentially with imaging depth due to scattering loss, the out-of-focus fluorescence eventually overwhelms the in-focal signal. The resulting loss of imaging contrast defines a fundamental imaging-depth limit, which cannot be overcome by increasing excitation intensity. Herein we propose to significantly extend this depth limit by multiphoton activation and imaging (MPAI) of photo-activatable fluorophores. The imaging contrast is drastically improved due to the created disparity of bright-dark quantum states in space. We demonstrate this new principle by both analytical theory and experiments on tissue phantoms labeled with synthetic caged fluorescein dye or genetically encodable photoactivatable GFP

Super-nonlinear fluorescence microscopy for high-contrast deep tissue imaging

Two-photon excited fluorescence microscopy (TPFM) offers the highest penetration depth with subcellular resolution in light microscopy, due to its unique advantage of nonlinear excitation. However, a fundamental imaging-depth limit, accompanied by a vanishing signal-to-background contrast, still exists for TPFM when imaging deep into scattering samples. Formally, the focusing depth, at which the in-focus signal and the out-of-focus background are equal to each other, is defined as the fundamental imaging-depth limit. To go beyond this imaging-depth limit of TPFM, we report a new class of super-nonlinear fluorescence microscopy for high-contrast deep tissue imaging, including multiphoton activation and imaging (MPAI) harnessing novel photo-activatable fluorophores, stimulated emission reduced fluorescence (SERF) microscopy by adding a weak laser beam for stimulated emission, and two-photon induced focal saturation imaging with preferential depletion of ground-state fluorophores at focus. The resulting image contrasts all exhibit a higher-order (third- or fourth- order) nonlinear signal dependence on laser intensity than that in the standard TPFM. Both the physical principles and the imaging demonstrations will be provided for each super-nonlinear microscopy. In all these techniques, the created super-nonlinearity significantly enhances the imaging contrast and concurrently extends the imaging depth-limit of TPFM. Conceptually different from conventional multiphoton processes mediated by virtual states, our strategy constitutes a new class of fluorescence microscopy where high-order nonlinearity is mediated by real population transfer

Contrastive Prompt Learning-based Code Search based on Interaction Matrix

Code search aims to retrieve the code snippet that highly matches the given query described in natural language. Recently, many code pre-training approaches have demonstrated impressive performance on code search. However, existing code search methods still suffer from two performance constraints: inadequate semantic representation and the semantic gap between natural language (NL) and programming language (PL). In this paper, we propose CPLCS, a contrastive prompt learning-based code search method based on the cross-modal interaction mechanism. CPLCS comprises:(1) PL-NL contrastive learning, which learns the semantic matching relationship between PL and NL representations; (2) a prompt learning design for a dual-encoder structure that can alleviate the problem of inadequate semantic representation; (3) a cross-modal interaction mechanism to enhance the fine-grained mapping between NL and PL. We conduct extensive experiments to evaluate the effectiveness of our approach on a real-world dataset across six programming languages. The experiment results demonstrate the efficacy of our approach in improving semantic representation quality and mapping ability between PL and NL