Abstract
Light-induced 2 + 2 cycloaddition is the most straightforward way to generate cyclobutanes, which are core structures of many natural products, drugs and bioactive compounds. Despite ...continuous advances in selective 2 + 2 cycloaddition research, general method for intermolecular photocatalysis of acyclic olefins with specific regio- and diastereoselectivity, for example,
syn
-head-to-head (
syn
-HH) cyclobutane derivatives, is still lack of development but highly desired. Herein, we report a cage-confined photocatalytic protocol to enable unusual intermolecular 2 + 2 cycloaddition for
α,β
-unsaturated carbonyl compounds. The
syn
-HH diastereomers are readily generated with diastereoselectivity up to 99%. The cage-catalyst is highly efficient and robust, covering a diverse substrate range with excellent substituent tolerance. The mimic-enzyme catalysis is proposed through a host-guest mediated procedure expedited by aqueous phase transition of reactant and product, where the supramolecular cage effect plays an important role to facilitate substrates inclusion and pre-orientation, offering a promising avenue for general and eco-friendly cycloaddition photocatalysis with special diastereoselectivity.
Facile synthesis of sulfur-containing polymers from renewable chemicals or the waste of petrochemical resources remains a grand challenge. Here, we report organocatalytic alternating copolymerization ...of carbonyl sulfide (COS) and d-xylose oxetane (XO) to produce poly(thiocarbonate). COS is industrially released as a waste gas, while XO is synthesized from biorenewable xylose with an E factor of 2.31 and an atom economy of 30%. The commercially available binary organocatalyst system consists of alkyl borane (as a Lewis acid) and a quaternary ammonium salt (as an initiator). Density functional theory calculations suggest that the Lewis acid of borane can activate XO and stabilize the growing anion. The catalyst system exhibits high activity with turnover frequencies of up to 70 h–1 at 25 °C, affording poly(thiocarbonate) with a well-defined structure, complete alternating sequence, >99% chemoselectivity, and regioregular polymer backbone composed of head-to-tail linkages. Terpolymerization of XO, propylene oxide, and COS yields a series of poly(thiocarbonate) with a largely tunable T g ranging from 26 to 138 °C.
This study investigates the coalescence of two equal-sized bubbles with air injection in distilled water experimentally, numerically, and theoretically. The neck expansion is the most prominent ...characteristic within a few milliseconds after bubbles coalesce. The effects of needle configurations and air injection flow rates are mainly discussed. Air injection during bubble coalescence is identified as an additional driving force for neck expansion in addition to the capillary pressure. The neck expansion time increases linearly with the bubble size at contact while decreasing with the air injection flow rate. The dimensionless neck expansion time follows a consistent linear decrease with the air injection speed. A novel theoretical expression for the dimensionless neck radius is derived, by quantifying the air injection effects as a multiplier (α) of the Laplace pressure at the neck. α demonstrates a consistent linear increase in air injection speed at all the needle configurations and flow rates. Moreover, numerical results of velocity vectors reveal the mechanism of air injection promoting neck expansion.
Displaced femoral neck fractures (FNFs) in healthy elderly patients have traditionally been managed with hemiarthroplasty (HA) or total hip arthroplasty (THA), with studies suggesting that THA may be ...the better option. However, it has recently been reported that bipolar HA (BHA) also provides good outcomes, and it is not clear as to whether BHA or THA is most appropriate. The purpose of this study was to conduct a meta-analysis of randomized controlled trials (RCTs) comparing the outcomes of BHA with THA for treating FNF in healthy elderly patients.
We searched the following databases from inception to May 2015 for relevant RCTs without language restrictions: PubMed, the Cochrane Central Register of Controlled Trials, Ovid MEDLINE and EMBASE, CINAHL, the China Biological Medicine Database, International Clinical Trials Registry Platform, Current Controlled Trials, and ClinicalTrials.gov. RCTs that met the inclusion criteria were statistically analyzed using the Cochrane review methods.
Eight RCTs were included (total 1,014 patients; 523 had BHA and 491 had THA). The data from included RCTs were divided into four subgroups according to different follow-up durations. The Harris Hip Score after BHA was not different from that after THA in all subgroups. Both reoperation rate and acetabular erosion rate were higher after BHA after more than 4 years, while there was a higher dislocation rate associated with THA within 4 years. THA was more favorable regarding the EQindex-5D and the mobility and pain rate, while BHA was more favorable regarding operating time. No significant differences were found regarding infection rate, general complications, 1-year mortality, blood loss, and length of postoperative hospital stay.
For healthy elderly patients with displaced FNFs, treatment with BHA led to better outcomes regarding dislocation rate, while THA was better regarding acetabular erosion rate and reoperation rate. When comparing BHA with THA, there were no significant differences in other important outcomes such as Harris Hip Score, infection rate, general complications, and 1-year mortality. Further high-quality RCTs are needed to provide robust evidence and evaluate the treatment options.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The conversion of CS2, which is discarded on a large scale as a pollutant, into valuable sulfur-containing polymers is of significance for both environmental and polymer science. However, the ...copolymerization of CS2 and cyclic ether suffers from complex polymer structures and massive byproducts. Here, we use a cooperative organocatalyst system composed of alkyl borane and onium salts for CS2 and oxetane copolymerization. Of interest, the copolymerization is highly efficient with a turnover frequency up to 1103 h–1, avoids small-molecule byproducts, and yields previously inaccessible polythiocarbonates bearing highly regular sequences. The in-chain sulfur atoms make polythiocarbonate demonstrate desirable thermal and mechanical properties, with a melting temperature of 83 °C, an ultimate tensile strength of 20.7 ± 3.1 MPa, and an elongation at break of 480 ± 20%. For the mechanism, the Lewis acid of borane activates oxetane as well as forms the borate complex with the growing anion, as revealed by density functional theory studies.
Abstract
The coalescence of two growing bubbles presents unique characteristics compared to static bubble coalescence. The gas injection flowrate significantly affects the different stages of bubble ...evolution, which is poorly understood. In this study, we investigate the flowrate effects on the lateral coalescence of two growing bubbles experimentally. The synchronous bubbling from adjacent needles is achieved using water to push air. During the bubble growth process, we find that the initial nonlinear evolution of bubble volume is because the bubble emerges as a small spherical cap with a large curvature radius and apparent contact angle. As the neck expands after bubble coalescence, the injection flowrate accelerates the neck evolution compared to the case without air injection. We find the neck expansion time decreases linearly with increasing flowrate, while the expansion speed increases with flowrate, but only in the early stage. Moreover, we propose a new theoretical expression that predicts the neck radius well at all the flowrates. At the post‐coalescence oscillation stage, the average projection area of the coalesced bubble increases linearly with time, except for periodic oscillations. Besides, we find that the injected air primarily influences the coalesced bubble's height, which in turn affects the projection area.
Ventilated partial cavity has been proven as an environmental-friendly and promising technology for ship drag reduction. However, the dynamic behavior of cavity closure and pressure under the wave ...effect still remains unclear. In this paper, the evolution of cavity shape and the oscillation of internal cavity pressure under the influence of different kinds of gust waves are investigated using the RANS coupled VOF method. Two types of cavity closure mode are found due to the presence of the gust wave. A strong correlation between the internal pressure variation and cavity oscillation behavior is revealed by the time–frequency analysis. Besides, it is found that the natural frequency of the cavity leads to an additional pressure fluctuation of the cavity, which is independent of waves.
•The extrusion and contraction closure mode of the cavity are revealed.•The harmonic of pressure fluctuations results from the switch between two modes.•The pressure fluctuation independent of waves is caused by the natural frequency.•The constraint of rigid wall results in a reduction of the natural frequency.
Air lubrication is an effective way to improve the hydrodynamic performance of ships. This study focuses on the cavity behaviors and hydrodynamic performance of air cavity ship (ACS) across a wide ...range of volumetric Froude number (Fr▽) and ventilation coefficient (Cq) via the computational fluid dynamics (CFD) method. The drag reduction and trim of the ACS are found to first increase with the Fr▽ and then decrease, while the sinkage increases monotonously. For the constant Fr▽, the drag reduction first increases quickly with the Cq and then remains unchanged, while the trim and sinkage roughly keep increasing. The drag reduction and motion attitude of the ACS are affected by the air cavity under the hull. By further looking into the cavity behavior, the air coverage and the pressure distribution of the cavity are considered as the key influence factors for the drag reduction and motion attitude of the ACS, while the quantitative cavity thickness and internal airflow indicate the influence of Fr▽ and Cq on the air layer distribution and the dynamic flow inside the air cavity, respectively. Different internal airflows are found in the closed-form cavity and the open-form cavity. Moreover, once the air supply is stopped, the air cavity forms are crucial for the cavity behavior, the corresponding drag and motion of the ACS. For the closed-form cavity, the closure moves upstream slowly after the air ventilation stopped. However, the open-form air cavity breaks into two parts due to the upstream necking process of the cavity.
•The steady and transient hydrodynamic performance of air cavity ship is studied.•Both drag reduction and motion attitude of the ACS are affected by air coverage.•Complex vortexes are found in the closed-form cavity at a low ventilation rate.•The open-form cavity transforms to a closed-form cavity after air supply stopped.
In this study, the mechanisms by which CD4+ T cells interact with the innate immune system in xenograft rejection were investigated.
Fetal pig pancreas (FPP) grafts were transplanted into female SCID ...mice. The FPP recipient SCID mice were reconstituted with exogenous leukocytes obtained from male BALB/c mice.
Although nonreconstituted SCID recipients or recipients reconstituted with CD4+ T cell-depleted leukocytes showed indefinite FPP graft survival with very few macrophages infiltrating their grafts, reconstitution of SCID recipients with as few as 2x10(5) CD4+ T cells was sufficient to induce rapid xenograft rejection. CD4+ T cells secreted interferon-gamma but not interleukin-4 and initiated the activation and accumulation of macrophages and natural killer cells, that were responsible for the rapid graft destruction. Suppression of interferon-gamma prolonged graft survival and suppressed the macrophages and natural killer cell accumulation and activation.
These results demonstrate that CD4+ T cell-dependent cellular xenograft rejection was a result of macrophage and natural killer cell accumulation and activation, but was not mediated by eosinophils. Consistent with this was the finding that interferon-gamma but not interleukin-4 was in part responsible for mediating this effect.
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