Controlling laser-dressed resonance line shape using attosecond extreme-ultraviolet pulse with a spectral minimum.

High-harmonic generation from a gas target exhibits sharp spectral features and rapid phase variation near the Cooper minimum. By applying spectral filtering, shaped isolated attosecond pulses can be generated where the pulse is split into two in the time domain. Using such shaped extreme-ultraviolet (XUV) pulses, we theoretically study attosecond transient absorption (ATA) spectra of helium [Formula: see text] autoionizing state which is resonantly coupled to the [Formula: see text] dark state by a time-delayed infrared laser. Our simulations show that the asymmetric [Formula: see text] Fano line shape can be readily tuned into symmetric Lorentzian within the time delay of a few tens of attoseconds. Such efficient control is due to the destructive interference in the generation of the [Formula: see text] state when it is excited by a strongly shaped XUV pulse. This is to be compared to prior experiments where tuning the line shape of a Fano resonance would take tens of femtoseconds. We also show that the predicted ATA spectral line shape can be observed experimentally after propagation in a gas medium. Our results suggest that strongly shaped attosecond XUV pulses offer the opportunity for controlling and probing fine features of narrow resonances on the few-ten attoseconds timescale.

Designing Cu0-Cu+ dual sites for improved C-H bond fracture towards methanol steam reforming.

Copper-based catalysts serve as the predominant methanol steam reforming material although several fundamental issues remain ambiguous such as the identity of active center and the aspects of reaction mechanism. Herein, we prepare Cu/Cu(Al)Ox catalysts with amorphous alumina-stabilized Cu2O adjoining Cu nanoparticle to provide Cu0-Cu+ sites. The optimized catalyst exhibits 99.5% CH3OH conversion with a corresponding H2 production rate of 110.8 µmol s-1 gcat-1 with stability over 300 h at 240 °C. A binary function correlation between the CH3OH reaction rate and surface concentrations of Cu0 and Cu+ is established based on kinetic studies. Intrinsic active sites in the catalyst are investigated with in situ spectroscopy characterization and theoretical calculations. Namely, we find that important oxygen-containing intermediates (CH3O* and HCOO*) adsorb at Cu0-Cu+ sites with a moderate adsorption strength, which promotes electron transfer from the catalyst to surface species and significantly reduces the reaction barrier of the C-H bond cleavage in CH3O* and HCOO* intermediates.

Carbon-based nanomaterials mediated adsorption and photodegradation of typical organic contaminants in aqueous fulvic acid solution.

In this work, the formation of carbon-based nanomaterials-fulvic acid (CNMs-FA) composites and their capacities for the adsorption and photodegradation of typical organic contaminants in aqueous solutions were investigated. The results suggested that the formation of CNMs-FA composites was dominated by adsorbing FA on CNMs via the physisorption process, which fit the pseudo-first-order kinetic model and the Langmuir isotherm model. The formed CNMs-FA composites were characterized by using the Brunauer-Emmett-Teller, scanning electron microscopy, and infrared spectroscopy techniques and further applied for examining their effects on the adsorption and photodegradation of selected organic contaminants in aqueous solutions. The adsorption of organic contaminants on CNMs-FA composites is mainly involved in hydrogen bonding and electrostatic interactions between organic contaminants and FA species adhering to CNMs. In addition, the CNMs-FA composites are able to promote the photosensitive degradation of organic contaminants due to the photogenerated reactive species including ROS and CNMs-3FA* under sunlight irradiation. This study provided a deeper and more comprehensive understanding of the environmental behavior of CNMs in real natural surface water and clarified the underlying mechanisms.

Role of the Porras factor in phase matching of high-order harmonic generation driven by focused few-cycle laser pulses.

We investigate the role of the Porras factor (or laser focusing effect) on the macroscopic high-order harmonic generation (HHG) driven by a focused broadband few-cycle laser beam. By employing a non-adiabatic phase-matching analysis method, we reveal that phase mismatch due to the induced-dipole phase varies with the Porras factor, which is dominant in phase matching at low gas pressure. We also find that in a strongly ionized medium when gas pressure is high, the nonlinear propagation is dominated by a plasma effect such that the focusing effect is mitigated, resulting in similar poor phase matching of HHG regardless of the Porras factor. Our results are expected to assist experimentalists identifying optimal conditions for HHG using ultrashort laser pulses.

Control of the annular spatial profile of high harmonics using a Bessel-Gaussian beam carrying the nonzero orbital angular momentum.

We propose to generate vortex high harmonics in the extreme ultraviolet (XUV) with a controllable spatial profile by using a Bessel-Gaussian (BG) beam carrying a nonzero orbital angular momentum (OAM). Such BG beam has quite a different intensity profile at the focus compared to the generally used BG beam without carrying the OAM. We show that the BG beam is capable of generating single-ring structured high harmonics, which is quite different from an Laguerre-Gaussian (LG) beam with a similar intensity distribution at the laser focus. We reveal that favorable phase-matching conditions can be achieved off-axis and away from the laser focus because a single-atom intrinsic phase due to the short electron trajectory can be well compensated by a geometric phase of the BG beam. We thus give a general rule that vortex high harmonics with a single annular profile can be efficiently generated when a gas medium is located at 1.5zred to 2.0zred before or after the laser focus of the BG beam, here zred is a reduced length. We also show the validity of this rule when the BG beam carries a higher OAM. This work is expected to be useful for synthesizing attosecond vortex pulses.

Role of fractional high harmonics with non-integer OAM on the generation of a helical attosecond pulse train.

Extreme-ultraviolet pulses of attosecond duration carrying orbital angular momentum (OAM) can be produced by spectrally filtering vortex high harmonics generated in a gas medium. Here we reveal that fractional high harmonics (FHHs) with non-integer OAM generated by a short duration Laguerre-Gaussian laser beam are origins for the change of helical attosecond pulse train (APT) with azimuthal angle. We show that these harmonics have gap and minimum structures in the annular intensity profile and discontinue phase distribution along azimuthal angle. And each FHH can be expressed as a superposition of OAM modes with integer topological charges. Features of FHH can be identified by coherently combining selected OAM modes. We also uncover that these features are formed after FHH is propagated in gas medium and in vacuum. We finally demonstrate that the generation of FHHs and the dependence of helical APTs on azimuthal angle are changed by varying the macroscopic condition.

Virtual Reality-Assisted Percutaneous Transluminal Angioplasty for Interventional Treatment of Lower-Extremity Arteriosclerosis Obliterans.

This study was to evaluate the biomechanical characteristics of the vascular wall during virtual reality- (VR-) assisted percutaneous transluminal angioplasty (PTA) and its effect on the treatment of lower-extremity arteriosclerosis obliterans (LEAO). In this study, a three-dimensional (3D) model and a finite-element model of arteries were constructed first, and various fluid mechanics were analyzed. Then, the virtual expansion simulation (VES) of individualized PTA was performed based on the ABAQUS/Explicit module to analyze the interaction between the balloon and the blood vessel at different times and the changes in the vascular shape and structural stress distribution. Finally, an LEAO animal model was constructed. Based on conventional PTA (PTA group) and VR-assisted PTA (VR-PTA) treatment, the morphological changes of vascular lumen of the two animal models were evaluated. The results showed that the normal, stenotic blood vessels and blood models were successfully constructed; the pressure of the stenotic blood vessel at the stenosis decreased obviously and the shear stress of blood vessel wall increased compared with that of the normal blood vessels, and there may be a blood reflux area in the poststenosis stage. The simulation results of the VES showed that the maximum principal stress value at 3 mm of the marginal vessel was much lower than that at 5 mm (about 10% lower), so the maximum principal stress change within 2 mm of the balloon-expanded vessel was the most obvious. The treatment results of the animal model showed that the VR-PTA group showed an obvious increase in the diameter of the vascular lumen, a decrease in the intima and media area, and a decrease in the thickness of the vessel wall in contrast to the PTA group (P < 0.05), which had an important effect on the reconstruction and expansion of the vascular lumen. The VR-PTA treatment on LEAO was realized in this study, which provided critical reference for the follow-up application of VR technology in the evaluation of surgical plan and research on biomechanical mechanisms of restenosis after PTA.

Association of circulating high-sensitivity C-reactive protein with late recurrence after ischemic stroke.

We investigated the association between serum levels of high-sensitivity C-reactive protein (hs-CRP) and stroke recurrence events in a cohort of patients with acute ischemic stroke (IS). We prospectively studied 286 patients with acute IS who were admitted within 24 h after the onset of symptoms. Serum levels of hs-CRP, and National Institutes of Health stroke scale (NIHSS) were measured at admission. The primary endpoint was stroke recurrence 1 year after stroke onset. We used logistic regression models to assess the relationship between hs-CRP levels and the risk of recurrent stroke. In multivariable models, hs-CRP levels were associated with an increased risk of an NIHSS greater than 6 [odds ratio=1.17; 95% confidence interval (CI)=1.05-1.48; P=0.021]. Among the participants, stroke recurrence was found in 48 (16.8%) cases. In multivariate analyses, the third and fourth quartiles of hs-CRP were significantly associated with stroke recurrence during the observation period compared with the first quartile group (P<0.01). In addition, the hs-CRP level in the highest quartile was associated with a higher risk of stroke recurrence (odds ratio=2.75; 95% CI=1.62-3.92; P=0.006). Hs-CRP (area under the curve=0.71; 95% CI=0.64-0.79) improved the ability of the NIHSS score to diagnose stroke recurrence (area under the curve of the combined model 0.78; 95% CI=0.73-0.84; P<0.01). Serum levels of hs-CRP at admission predicted the future stroke recurrence in patients with IS.