Circularly polarized attosecond light generation from OCS molecules irradiated by the combination of linear polarized infrared and orthogonal terahertz fields.

Researching ultrafast dynamics and creating coherent light sources will both benefit significantly from the establishment of polarization control in high-order harmonic generation (HHG). By employing the time-dependent density functional theory method, we investigate HHG of carbonyl sulfide molecules using a combination of a linear polarized infrared (IR) laser and a weaker orthogonal Terahertz (THz) field. Our findings show that by adjusting the amplitude of the THz field, the movement scale of electrons in the THz direction can be tuned, thereby one can control the harmonic intensity in the IR laser direction. This method allows for the creation of near-circularly polarized attosecond pulses. Furthermore, the ellipticity of the attosecond pulse may be changed by modifying the carrier-envelope phase of the IR laser pulse.

Minimum structure of high-order harmonic spectrum from molecular multi-orbital effects involving inner-shell orbitals.

The spectral features of high-order harmonic spectra can provide rich information for probing the structure and dynamics of molecules in intense laser fields. We theoretically study the high harmonic spectrum with the laser polarization direction perpendicular to the N2O molecule and find a minimum structure in the plateau region of the harmonic spectrum. Through analyzing the time-dependent survival probability of different electronic orbitals and the time-dependent wave packet evolution, it is found that this minimum position is caused by the harmonic interference of HOMO a, HOMO-1, and HOMO-3 a orbitals. Moreover, this interference minimum is discovered over a wide frequency range of 0.087 a.u. to 0.093 a.u., as well as a range of driving laser intensities with peak amplitudes between 0.056 a.u. and 0.059 a.u.. This study sheds light on the multi-electron effects and ultrafast dynamics of inner-shell electrons in intense laser pulses, which are crucial for understanding and controlling chemical reactions in molecules.

Phytotoxic meroterpenoids with herbicidal activities from the phytopathogenic fungus Pseudopestalotiopsis theae.

The fungus Pseudopestalotiopsis theae isolated from the fresh leaves of Illigera celebica, has been reported to be a pathogenic fungus that can cause gray blight on tea leaves, a disease characterized by the appearance of necrotic lesions on tea leaves. The pathogenic substances in this fungus have not been clearly identified. Considering the possible involvement of specialized metabolites in symptom appearance, a chemical investigation of specialized metabolites on P. theae was conducted, resulting in the isolation of eight meroterpenoids, including six undescribed biscognienynes G-L and two known ones (biscognienynes B and D). The structures of these new compounds were characterized by extensive NMR spectroscopic and HR-ESI-MS data, and their absolute configurations were elucidated by ECD calculations. Except for biscogniyne L, all the isolated biscognienynes showed different degrees of phytotoxicity to tea in vivo, thereby revealing for the first time the substances in P. theae that cause tea gray blight. Inspired by the fact that phytotoxins produced by pathogenic fungus are an effective resource for designing natural and safe bioherbicides, when assayed the herbicidal activity through Petri dish bioassays, biscognienynes G-J showed phytotoxic effects against seed germination and seedling growth of Setaria viridis, strongly inhibiting seed germination percentage and radicle and germ lengths of seedlings. The results of this study demonstrated the great potential of biscognienynes G-J to be proposed and developed as ecofriendly herbicides.

Calculation of high-order harmonic generation of atoms and molecules by combining time series prediction and neural networks.

High-order harmonic generation (HHG) from the interaction of ultra-intense laser pulses with atoms is an important tabletop short-wave coherent light source. Accurate quantum simulations of it present large computational difficulties due to multi-electron multidimensional effects. In this paper, the time-dependent response of hydrogen atoms is calculated using a time-series prediction scheme, the HHG spectrum is reconstructed very accurately. The accuracy of the forecasting is further improved by using a neural network scheme. This scheme is also applied to the simulation of the harmonic emission on multi-electron systems, and the applicability of the scheme is confirmed by the harmonic calculation of complex systems. This method is expected to simulate the nonlinear dynamic process of multi-electron atoms and molecules irradiated by intense laser pulses quickly and accurately.

All-optical reconstruction of three-band transition dipole moments by the crystal harmonic spectrum from a two-color laser pulse.

When a bulk solid is irradiated by an intense laser pulse, transition dipole moments (TDMs) between different energy bands have an important influence on the ultra-fast dynamic process. In this paper, we propose a new all-optical method to reconstruct the k-dependent TDMs between multi-bands using a crystal high-order harmonic generation (HHG). Taking advantage of an obvious separation of bandgaps between three energy bands of an MgO crystal along the <001 > direction, a continuous harmonic spectrum with two plateaus can be generated by a two-color laser pulse. Furthermore, the first harmonic platform is mainly dominated by the polarization between the first conduction band and the valence band, and the second one is largely attributed to the interband HHG from the second conduction band and the valence band. Therefore, the harmonic spectrum from a single quantum trajectory can be adopted to map TDMs between the first, second conduction bands, and the valence one. Our work is of great significance for understanding the instantaneous properties of solid materials in the strong laser field, and will strongly promote the development of the HHG detection technology.

Effect of interband polarization on a solid's high-order-harmonic generation just belowthe band gap.

A series of theoretical and experimental results has proved that harmonics below/above the band gap are produced mainly by the intraband current/interband polarization for solids in strong mid-infrared laser pulses. However, which mechanism dominates the harmonic process is still debated. In this work, based on simulating high-order-harmonic generation from an MgO crystal in a linearly polarized mid-infrared laser by solving semiconductor Bloch equations, we demonstrate that harmonics just below the band gap originate from the interference between intraband and interband currents. Furthermore, it is found that intensities of harmonics just below the band gap are apparently enhanced with an increase in the incident laser's strength. By analyzing the band dispersion and the transition dipole moment of the 001-cut MgO crystal, this can be attributed to the interband polarization between two conduction bands.

All-optical reconstruction of k-dependent transition dipole moment by solid harmonic spectra from ultrashort laser pulses.

Band structure and transition dipole moment play important roles in high-order harmonic generation from solid materials. In this work we provide a new all-optical technique to reconstruct the momentum-dependent transition dipole moment using the harmonic spectrum from MgO crystal driven by an ultrashort mid-infrared laser pulse. Under the influence of the ultrashort laser pulse, the emitted photon energy and the crystal momentum form a one-to-one match, in the same way between the intensity of the harmonic above the minimum bandgap and the square of the amplitude of the transition dipole moment, resulting in a realization of directly probing the transition dipole moment. Our all-optical method paves a way to image the two-dimensional transition dipole moment of crystals with the inversion symmetry.

Absolute quantification of particle number concentration using a digital single particle counting system.

The accurate determination of the molar concentration or the number concentration of particles in a defined volume is important but challenging. Since particle diversity and heterogeneity cannot be ignored in particle quantification, single particle counting has become quite important. However, most methods require standard samples (calibrators) which are usually difficult to obtain. The authors describe a method for single particle counting that is based on the combination of digital counting and formation of microdroplets in a microchip. By compartmentalizing particles into picoliter droplets, positive droplets encapsulating particles were counted and particle concentrations were calculated by Poisson statistics. The concentration of particles over a wide range (from 5.0 × 103 to 1.8 × 107 particles per mL) were accurately determined without the need for using a calibrator. A microdroplet chip including a T-junction channel achieved a 9-fold increase of signal-to-background ratio compared to the traditional flow-focusing chip. This makes the digital counting system a widely applicable tool for quantification of fluorescent particles. Various particles including differently sized fluorescent microspheres and bacteria with large heterogeneity in shape such as Escherichia coli DH5α-pDsRed were accurately quantified by this method. Graphical abstract Schematic representation of the digital single particle counting system for absolute quantification of particles. Particles compartmentalized in picoliter droplets were counted and the number concentration of particles was determined using digital analysis.

Short-term acceptability of female condom use among low-fee female sex workers in China: a follow-up study.

BACKGROUND: Low-fee female sex workers (FSW) lack power to effectively negotiate male condom use with clients. Female condoms (FCs) may provide an alternative strategy. This study was conducted to assess the acceptability of FC use among low-fee FSWs, and to identify appropriate candidates for future FC promotion. METHODS: A one-month follow-up study was conducted. At entry into the study, eligible participants completed a baseline questionnaire and were given 10 FCs. At the one-month follow up encounter, the number of used FC packages were counted and each participant completed a follow-up questionnaire. Logistic regression was used to identify variables associated with more frequent use of FCs (> 2 times). RESULTS: A total of 312 low-fee FSWs were enrolled at baseline and all participants completed the follow-up evaluation. Among them, 123 (39.4%) participants had used more than two FCs. Participants who were illiterate or had completed at most primary school education (OR: 2.4, 95% CI: 1.4-7.2), charged ≤30 RMB per client (≤30 vs. 51-80 RMB, OR: 3.8, 95% CI: 1.9-7.6), or had consistently used condoms with regular clients in the past month (OR: 2.4, 95%CI: 1.4-4.2) were more likely to use FCs. CONCLUSION: Low-fee FSWs charging ≤30 RMB per client, and those who are less educated may be appropriate initial candidates for FC promotion in China. Strategies to consider include teaching FSWs tactics for negotiation of FC use that can initially be applied with regular clients, and providing education to maximize ease-of use, and minimize discomfort with FC usage.

Significantly enhanced conversion efficiency of high-order harmonic generation by introducing chirped laser pulses into scheme of spatially inhomogeneous field.

An effective scheme to enhance the yield of high-order harmonic generation originated from spatially inhomogeneous field through the interaction between few-cycle chirped laser pulses and a nano-tip structure is demonstrated. The conversion efficiency of harmonics from chirped laser pulses was significantly improved by nearly three more orders of magnitude than that of chirp-free pulses, and the cutoff energy of the corresponding harmonics was dramatically enhanced. By superimposing a series of properly selected orders of harmonics, isolated attosecond pulses of high intensity can be obtained. Furthermore, we compared the effects of different types of chirps on harmonics.

On-demand one-step synthesis of small-sized fluorescent-magnetic bifunctional microparticles on a droplet-splitting chip.

A facile and controllable method for one-step synthesis of small-sized monodisperse fluorescent-magnetic bifunctional microparticles based on droplet splitting and photopolymerization was established. Using this method, magnetic nanoparticles and acryloyl rhodamine B (acryloyl-RhB) molecules were incorporated into the dispersed phase, which allowed the direct generation of functional microparticles. Functional microparticles with diameters in the range of 2.8 to 19.2 µm were obtained by controlling the fluidic characteristics. The fluorescence intensity of the microparticles could be regulated by adjusting the concentration of the acryloyl-RhB molecule in the dispersed phase. Furthermore, the fluorescent-magnetic bifunctional microparticles were successfully used to detect proteins specifically by ratiometric fluorescence analysis, showing their potential in biological sample detection.

Controllable synthesis of nanocrystals in droplet reactors.

In recent years, a broad range of nanocrystals have been synthesized in droplet-based microfluidic reactors which provide obvious advantages, such as accurate manipulation, better reproducibility and reliable automation. In this review, we initially introduce general concepts of droplet reactors followed by discussions of their main functional regions including droplet generation, mixing of reactants, reaction controlling, in situ monitoring, and reaction quenching. Subsequently, the enhanced mass and heat transport properties are discussed. Next, we focus on research frontiers including sequential multistep synthesis, intelligent synthesis, reliable scale-up synthesis, and interfacial synthesis. Finally, we end with an outlook on droplet reactors, especially highlighting some aspects such as large-scale production, the integrated process of synthesis and post-synthetic treatments, automated droplet reactors with in situ monitoring and optimizing algorithms, and rapidly developing strategies for interfacial synthesis.

Enhanced directional cell migration induced by vaccinia virus on a microfluidic-based multi-shear cell migration assay platform.

Virus-induced cell migration plays important roles in the direct and rapid spread of virus particles. As cell migration is also regulated by shear stress, it is necessary to explore the cell migration behavior influenced by multiple factors including a virus and shear stress. In this report, a three-layer microfluidic chip with symmetric channels was designed and fabricated to investigate vaccinia virus-induced cell migration in different shear stress environments. Regular "exclusion zones" without cell damage were formed by microvalves. The results showed that infected cells were more elongated and tended to migrate along the flow direction compared to the random cell migration under static conditions. Meanwhile, shear stress enhanced the natural directional persistence and accelerated the velocity of infected cell migration. Moreover, reduced peripheral lamellae and the axial lamella being confined to the flow direction were responsible for the increased directionality of cell migration under shear stress. Interestingly, in the presence of shear stress, the Golgi complex reoriented and relocated behind the nucleus and aligned to the flow direction in infected migratory cells accompanied by the rearrangement of the cytoskeleton. Our report reveals the cell migration behavior in the multi-environment of virus infection and shear stress based on the microfluidic cell migration assay platform. It helps us to deeply understand the interactions between the virus, host cells, and surrounding microenvironment.

Chirp-free isolated attosecond pulse generation from an atom irradiated by a fundamental terahertz pulse synchronizing an infrared laser pulse.

We theoretically study high-order harmonic generation (HHG) and attosecond pulses from an atom irradiated synchronically by a terahertz (THz) pulse and an infrared laser pulse. For the HHG spectrum from the THz pulse alone and the combined pulse, an apparent peak-valley structure appears the platform region. Specially, for the periodic structure generated by an atom under the action of the combined pulse is originated from the interference between the electrons ionized at different instants in the laser field, which undergo many recollision and return to the core at the same time. Therefore, continuum harmonics with few chirps from the interference enhancement region can be achieved, which result in a chirp-free isolated attosecond pulse.

A High Throughput Micro-Chamber Array Device for Single Cell Clonal Cultivation and Tumor Heterogeneity Analysis.

Recently, single cell cloning techniques have been gradually developed benefited from their important roles in monoclonal antibody screening, tumor heterogeneity research fields, etc. In this study, we developed a high throughput device containing 1400 lateral chambers to efficiently isolate single cells and carry out long-term single cell clonal cultivation as well as tumor heterogeneity studies. Most of the isolated single cells could proliferate normally nearly as long as three weeks and hundreds of clones could be formed once with one device, which made it possible to study tumor heterogeneity at single cell level. The device was further used to examine tumor heterogeneity such as morphology, growth rate, anti-cancer drug tolerance as well as adenosine triphosphate-binding cassette (ABC) transporter ABCG2 protein expression level. Except for the single cell isolation and tumor heterogeneity studies, the device is expected to be used as an excellent platform for drug screening, tumor biomarker discovering and tumor metastasis assay.

CTAB functionalized graphene oxide/multiwalled carbon nanotube composite modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitrite.

We have developed hexadecyl trimethyl ammonium bromide (CTAB) functionalized graphene oxide (GO)/multiwalled carbon nanotubes (MWNTs) modified glassy carbon electrode (CTAB-GO/MWNT) as a novel system for the simultaneous determination of dopamine (DA), ascorbic acid (AA), uric acid (UA) and nitrite (NO2(-)). The combination of graphene oxide and MWNTs endow the biosensor with large surface area, good biological compatibility, electricity and stability, high selectivity and sensitivity. In the fourfold co-existence system, the linear calibration plots for AA, DA, UA and NO2(-) were obtained over the range of 5.0-300 µM, 5.0-500 µM, 3.0-60 µM and 5.0-800 µM with detection limits of 1.0 µM, 1.5 µM, 1.0 µM and 1.5 µM, respectively. In addition, the modified biosensor was applied to the determination of AA, DA, UA and NO2(-) in urine samples by using standard adding method with satisfactory results.

Picoliter droplets developed as microreactors for ultrafast synthesis of multi-color water-soluble CdTe quantum dots.

Picoliter droplets were developed as microreactors for ultrafast and continuous synthesis of multi-color, water-soluble CdTe quantum dots (QDs). Through a slight change in the local controllable reaction temperature of 1-2 °C, we could obtain a series of different colored fluorescent QDs in about 1 min.

[Social health status of the HIV infected and their families and relevant influencing factors].

OBJECTIVE: To investigate the social health status of the HIV infected and their families in a high HIV/AIDS prevalence village in Hunan province and to examine the relations of the social health status, responses and social support. METHODS: A total of 51 HIV infected persons (infected group), 49 family members of the infected (family member group) and 96 normal persons (control group) were surveyed by Social Health Measurement Scale-a sub-scale of Self-rated Health Measurement Scale (SRHMS), Social Support Assessment Scale (SSAS) and Trait Coping Style Questionnaire (TCSQ). RESULTS: (1) In regard to the total scores of social health, responding style and social support, significant differences were found among the infected group, the group of family members and the control group (62.9 +/- 18.6, 79.8 +/- 18.0, 86.5 +/- 21.3, F = 18.16; 28.7 +/- 4.3, 27.2 +/- 5.4, 25.9 +/- 6.4, F = 5.21; 33.8 +/- 8.1, 41.0 +/- 6.6, 38.1 +/- 6.8, F = 13.23; P < 0.01). (2) Subjective care and support, the educational status, the marital status and support utilization were significant predictors to the social health status of the infected group (R(2) = 0.73, F = 27.78, P < 0.01). (3) Subjective support and negative responding style were significant predictors to the social health status of the group of family members (R(2) = 0.32, F = 12.35, P < 0.01). CONCLUSION: The HIV infected and their families have more negative responding style, make less use of social support and hold a inferior social health status. It's necessary to exert psychological intervention targeting at these population group.