Seasonal fluxes of carbonyl sulfide in a midlatitude forest

Carbonyl sulfide (OCS), the most abundant sulfur gas in the atmosphere, has a summer minimum associated with uptake by vegetation and soils, closely correlated with CO₂. We report the first direct measurements to our knowledge of the ecosystem flux of OCS throughout an annual cycle, at a mixed temperate forest. The forest took up OCS during most of the growing season with an overall uptake of 1.36 ± 0.01 mol OCS per ha (43.5 ± 0.5 g S per ha, 95% confidence intervals) for the year. Daytime fluxes accounted for 72% of total uptake. Both soils and incompletely closed stomata in the canopy contributed to nighttime fluxes. Unexpected net OCS emission occurred during the warmest weeks in summer. Many requirements necessary to use fluxes of OCS as a simple estimate of photosynthesis were not met because OCS fluxes did not have a constant relationship with photosynthesis throughout an entire day or over the entire year. However, OCS fluxes provide a direct measure of ecosystem-scale stomatal conductance and mesophyll function, without relying on measures of soil evaporation or leaf temperature, and reveal previously unseen heterogeneity of forest canopy processes. Observations of OCS flux provide powerful, independent means to test and refine land surface and carbon cycle models at the ecosystem scale.Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere (1), and biogeochemical cycling of OCS affects both the stratosphere and the troposphere. The tropospheric OCS mixing ratio is between 300 and 550 parts per trillion (ppt) (1) (10⁻¹² mol OCS per mol dry air), decreasing sharply with altitude in the stratosphere (2). In times of low volcanic activity, the sulfur budget and aerosol loading of the stratosphere are largely controlled by transport and photooxidation of OCS from the troposphere (3). The processes regulating emission and uptake of OCS are thus important factors in determining how changes in climate and land cover may affect the stratospheric sulfate layer.Oceans are the dominant source of atmospheric OCS (4), with smaller emissions from anthropogenic and terrestrial sources, such as wetlands and anoxic soils (e.g., refs. 5 and 6) and oxic soils during times of heat or drought stress (e.g., refs. 7 and 8). The terrestrial biosphere is the largest sink for OCS (1, 4, 9, 10) with uptake by both oxic soils (e.g., ref. 11) and vegetation (e.g., ref. 9). Once OCS molecules pass through the stomata of leaves, the uptake rate of OCS is controlled by reaction with carbonic anhydrase (CA) within the mesophyll, to produce H₂S and CO₂. CA is the same enzyme that hydrolyzes carbon dioxide (CO₂) in the first chemical step of photosynthesis (12).Studies considering the large-scale atmospheric variability of OCS have linked OCS fluxes and the photosynthetic uptake of CO₂ for regional and global scales (1, 4, 13). Leaf-scale studies have confirmed the OCS link to photosynthesis (14, 15). Initial OCS ecosystem flux estimations were made using flask sampling followed by analysis via gas chromatography–mass spectrometry (GC-MS) (13, 16), but these studies did not have sufficient resolution to examine daily or hourly controls on the OCS flux. Laser spectrometers have been developed (17, 18) to enable direct, in situ measurement of OCS fluxes by eddy covariance, and measurements of OCS ecosystem fluxes have been reported, for periods of up to a few weeks, above arid forests (19) and an agricultural field (8, 20).Net carbon exchange in terrestrial ecosystems [net ecosystem exchange (NEE)] can be measured by eddy flux methods. NEE may be regarded as the sum of two gross fluxes: gross ecosystem productivity (GEP) and ecosystem respiration (R_eco). GEP is the light-dependent part of NEE, estimated by subtracting daytime ecosystem respiration (R_eco), computed by extrapolation of the temperature dependence of nighttime NEE (NEE – R_eco = GEP) (e.g., refs. 21–24). At night, NEE includes all autotrophic and heterotrophic respiration processes. During the day, GEP approximates the carboxylation rate minus photorespiration at the ecosystem scale (25). Extrapolation of nighttime R_eco introduces major uncertainty in the interpretation of GEP, which could be reduced, and the ecological significance of GEP increased, by developing independent methods of measuring rates of photosynthetic processes. As shown below, fluxes of OCS give more direct information on one of the major controls on GEP, stomatal conductance, rather than GEP itself, providing a powerful means for testing and improving ecosystem models and for scaling up leaf-level processes to the whole ecosystem.Here we describe the factors controlling the hourly, daily, seasonal, and total fluxes of OCS in a forest ecosystem, using a year (2011) of high-frequency, direct measurements at Harvard Forest, MA. We report the seasonal cycle, the response to environmental conditions, and the total deposition flux of OCS throughout the year 2011. We compare these fluxes to corresponding measurements of CO₂ flux and to simulations using the Simple Biosphere model (SiB3).     

Polymer-supported CuPd nanoalloy as a synergistic catalyst for electrocatalytic reduction of carbon dioxide to methane

Developing sustainable energy strategies based on CO₂ reduction is an increasingly important issue given the world’s continued reliance on hydrocarbon fuels and the rise in CO₂ concentrations in the atmosphere. An important option is electrochemical or photoelectrochemical CO₂ reduction to carbon fuels. We describe here an electrodeposition strategy for preparing highly dispersed, ultrafine metal nanoparticle catalysts on an electroactive polymeric film including nanoalloys of Cu and Pd. Compared with nanoCu catalysts, which are state-of-the-art catalysts for CO₂ reduction to hydrocarbons, the bimetallic CuPd nanoalloy catalyst exhibits a greater than twofold enhancement in Faradaic efficiency for CO₂ reduction to methane. The origin of the enhancement is suggested to arise from a synergistic reactivity interplay between Pd–H sites and Cu–CO sites during electrochemical CO₂ reduction. The polymer substrate also appears to provide a basis for the local concentration of CO₂ resulting in the enhancement of catalytic current densities by threefold. The procedure for preparation of the nanoalloy catalyst is straightforward and appears to be generally applicable to the preparation of catalytic electrodes for incorporation into electrolysis devices.Developing sustainable energy resources and strategies to combat the hazards associated with the use of fossil fuels, which include global warming due to the increased concentration of greenhouse gases, is an important theme in the current energy and environmental research agenda (1–3). Electrochemical and photoelectrochemical CO₂ reduction to energy-dense hydrocarbon fuels could play a major role and become part of an integrated energy storage strategy, in combination with solar- or wind-generated electricity, as a way to store energy in the chemical bonds of carbon-based fuels (4–12). Metal-based catalysts for CO₂ reduction have been extensively studied over the last three decades. Metallic copper has proven to be the best available catalytic material for CO₂ reduction to hydrocarbons by electrochemical methods (13–19). Cu foils and single crystals have been extensively investigated but suffer from low surface areas, low catalytic current densities, and rapid deactivation during electrochemical CO₂ reduction (20). Recently, nanoparticle Cu catalysts (nanoCu) have been investigated as a way to increase catalytic current densities and stabilities. However, Faradaic efficiencies for electrocatalytic reduction to hydrocarbons decrease dramatically with particle size falling to ∼10% for particles less than 20 nm in diameter. The size effect has been attributed to an enhanced chemisorption strength for CO at small Cu nanoparticles compared with large particles or bulk Cu electrodes (13). An additional complication arises from the use of surfactants in the syntheses of nanoCu because they can lead to significant contamination issues requiring their removal by a high-temperature posttreatment which causes adverse particle growth and loss of monodispersity (21).Electrodeposition provides a facile and scalable technique for preparing catalytic electrodes. However, it can be difficult to control and typically leads to large particle sizes, often from hundreds of nanometers to micrometers in diameter (22), resulting in low catalytic surface areas. We describe here a novel electrochemical method for synthesizing ultrafine metal nanoparticles and their application to CO₂ reduction. It is based on the use of an electropolymerized, electroactive film of a vinyl-2,2′bipyridine complex of Fe(II). Following treatment with cyanide to displace a bpy ligand and coordinate cyanide, the Fe–CN groups provide a basis for binding metal ions from external solutions (21). After reduction of the film-incorporated metal ions to the corresponding metals, migration occurs to film surfaces where nanoparticles form with size control.An outline for the overall procedure is shown in Fig. 1 for the surface-film–based reduction of Cu(II) to Cu(0). It involves in sequence: (i) Formation of a polymeric film of poly-[Fe(vbpy)₃](PF₆)₂ (vbpy is 4-methyl-4′-vinyl-2,2′-bipyridine) by electropolymerization induced by vbpy-based reduction. The electropolymerization procedure has been applied to polymer film formation on a variety of conductive substrates (23–26) including glassy carbon (GC) electrodes, planar fluorine-doped tin oxide (FTO) slides, reticulated vitreous carbon, and high surface area gas diffusion electrodes. (ii) Addition of cyanide ions which displaces a vbpy ligand from Fe(II) to give poly-Fe(vbpy)₂(CN)₂, poly-vbpy. (iii) Binding of Cu(II) ions from an external solution with coordination to the cyanide ligands. (iv) Electroreduction of the Cu(II) ions to give ultrafine nanoCu of uniform distribution on the surface of the polymeric film.Open in a separate windowFig. 1.Stepwise synthesis of nanoCu. Step 1: A polymeric film of poly-Fe(vbpy)₃(PF₆)₂ is preformed by reductive electropolymerization. Step 2: Cyanide displacement of a vbpy ligand gives the dicyano film poly-[Fe(vbpy)₂(CN)₂,poly-vbpy]. Step 3: Metal ions Cu(II) are incorporated by binding to the cyanide ligands. Step 4: The bound metal ions are electrochemically reduced to metal nanoparticles.The generality of the procedure is also demonstrated with an extension to the synthesis of polymeric films surface-loaded with nanoPd and with bimetallic CuPd nanoalloy. We demonstrate that the Cu-loaded films are electrocatalysts for CO₂ reduction to methane and that, compared with nanoCu, which, to date, is the best catalyst for CO₂ reduction to hydrocarbons (13), the bimetallic CuPd nanoalloy provides an enhancement in Faradaic efficiency for CO₂ reduction to methane of >2 in both aqueous and organic solutions. The notable reactivity enhancement appears to arise from a synergistic mechanism involving Pd–H reduction of adsorbed CO from CO₂ reduction on Cu.     

Particle radiotherapy for prostate cancer

Recent advances in external beam radiotherapy have allowed us to deliver higher doses to the tumors while decreasing doses to the surrounding tissues. Dose escalation using high‐precision radiotherapy has improved the treatment outcomes of prostate cancer. Intensity‐modulated radiation therapy has been widely used throughout the world as the most advanced form of photon radiotherapy. In contrast, particle radiotherapy has also been under development, and has been used as an effective and non‐invasive radiation modality for prostate and other cancers. Among the particles used in such treatments, protons and carbon ions have the physical advantage that the dose can be focused on the tumor with only minimal exposure of the surrounding normal tissues. Furthermore, carbon ions also have radiobiological advantages that include higher killing effects on intrinsic radio‐resistant tumors, hypoxic tumor cells and tumor cells in the G0 or S phase. However, the degree of clinical benefit derived from these theoretical advantages in the treatment of prostate cancer has not been adequately determined. The present article reviews the available literature on the use of particle radiotherapy for prostate cancer as well as the literature on the physical and radiobiological properties of this treatment, and discusses the role and the relative merits of particle radiotherapy compared with current photon‐based radiotherapy, with a focus on proton beam therapy and carbon ion radiotherapy.     

呼气末二氧化碳分压监测在全麻拔管后苏醒期患者中的应用

目的 探讨呼气末二氧化碳分压监测在全身麻醉拔管后苏醒期患者中的应用效果。方法 选取全身麻醉手术结束拔除气管导管转入麻醉后苏醒室观察的320例患者为研究对象,采用随机数字表法分为对照组和观察组各160例。对照组常规单孔鼻导管吸氧3 L/min并持续监测心电图、呼吸、无创血压、血氧饱和度;观察组在对照组基础上持续监测呼气末二氧化碳分压数值和波形的变化并及时给予护理干预。比较两组低氧血症发生情况、高碳酸血症和呼吸暂停检出率、面罩加压给氧率和苏醒时间。结果 观察组低氧血症程度、面罩加压给氧率显著低于对照组,高碳酸血症、呼吸暂停检出率显著高于对照组,苏醒时间显著短于对照组(P<0.05,P<0.01)。结论 对麻醉后苏醒期拔除气管插管的患者,呼气末二氧化碳分压监测可及时发现呼吸暂停、高碳酸血症等呼吸异常事件,降低低氧血症的发生率,提高麻醉苏醒的安全性,缩短苏醒时间。     

超脉冲二氧化碳点阵激光治疗稳定期白癜风的临床效果

目的 探究超脉冲二氧化碳点阵激光治疗稳定期白癜风的临床效果。方法 以我院2019年1月-2020年10月收治的80例稳定期白癜风患者为研究对象,通过简单随机化法分为对照组（n=40）和试验组（n=40）,对照组采用常规药物治疗,试验组则在对照组基础实施超脉冲二氧化碳点阵激光治疗,比较两组治疗效果、生活质量评分、炎性因子水平及不良反应发生情况。结果 试验组的总有效率为90.00%,高于对照组的70.00%（P＜0.05）;两组治疗后生活质量评分均高于治疗前,且试验组生活质量评分高于对照组（P＜0.05）;两组炎性因子水平均低于治疗前,且试验组低于对照组（P＜0.05）;两组不良反应发生率比较,差异无统计学意义（P＞0.05）。结论 与常规药物治疗相比,超脉冲二氧化碳点阵激光治疗效果更佳,可有效改善患者生活质量,降低炎性因子水平,且不会增加不良反应,是一种安全、有效的治疗方案。     

Extracorporeal carbon dioxide removal requirements for ultraprotective mechanical ventilation: Mathematical model predictions

Extracorporeal carbon dioxide (CO₂) removal (ECCO₂R) facilitates the use of low tidal volumes during protective or ultraprotective mechanical ventilation when managing patients with acute respiratory distress syndrome (ARDS); however, the rate of ECCO₂R required to avoid hypercapnia remains unclear. We calculated ECCO₂R rate requirements to maintain arterial partial pressure of CO₂ (PaCO₂) at clinically desirable levels in mechanically ventilated ARDS patients using a six-compartment mathematical model of CO₂ and oxygen (O₂) biochemistry and whole-body transport with the inclusion of an ECCO₂R device for extracorporeal veno-venous removal of CO₂. The model assumes steady state conditions. Model compartments were lung capillary blood, arterial blood, venous blood, post-ECCO₂R venous blood, interstitial fluid and tissue cells, with CO₂ and O₂ distribution within each compartment; biochemistry included equilibrium among bicarbonate and non-bicarbonate buffers and CO₂ and O₂ binding to hemoglobin to elucidate Bohr and Haldane effects. O₂ consumption and CO₂ production rates were assumed proportional to predicted body weight (PBW) and adjusted to achieve reported arterial partial pressure of O₂ and a PaCO₂ level of 46 mmHg at a tidal volume of 7.6 mL/kg PBW in the absence of an ECCO₂R device based on average data from LUNG SAFE. Model calculations showed that ECCO₂R rates required to achieve mild permissive hypercapnia (PaCO₂ of 46 mmHg) at a ventilation frequency or respiratory rate of 20.8/min during mechanical ventilation increased when tidal volumes decreased from 7.6 to 3 mL/kg PBW. Higher ECCO2R rates were required to achieve normocapnia (PaCO2 of 40 mmHg). Model calculations also showed that required ECCO2R rates were lower when ventilation frequencies were increased from 20.8/min to 26/min. The current mathematical model predicts that ECCO2R rates resulting in clinically desirable PaCO2 levels at tidal volumes of 5-6 mL/kg PBW can likely be achieved in mechanically ventilated ARDS patients with current technologies; use of ultraprotective tidal volumes (3-4 mL/kg PBW) may be challenging unless high mechanical ventilation frequencies are used.     

Applied cerebral physiology

The brain is an exquisitely sensitive organ, requiring a constant supply of blood, oxygen, and glucose to function. Cerebral blood flow is autoregulated to provide a near constant blood supply despite fluctuations in whole body physiology. The blood–brain barrier acts to ensure that the brain microenvironment remains tightly regulated. The pressure within the cranium must also be tightly controlled to maintain optimal cerebral perfusion and ultimately prevent herniation of brain parenchyma. Several physiological parameters can be monitored including intracranial pressure, cerebral oxygenation and metabolic stress and clinical use is increasing including in traumatic brain injury and subarachnoid haemorrhage patients.     

超声造影引导下导丝定位联合纳米碳染色对乳腺癌SLN的定位效果分析

目的探讨超声造影引导下导丝定位联合纳米碳染色对乳腺癌前哨淋巴结(SLN)定位价值。 方法将2017年1月至2018年12月期间进行手术治疗的90例乳腺癌患者作为研究对象,所有患者在入院后均进行常规超声检查,检查过程中于患者病灶侧乳晕3、6、9、12点或肿瘤周围皮下组织内注射六氟化硫溶液,经淋巴管造影后明确前哨淋巴结具体存在位置,后进行导丝定位,术前于肿瘤皮下组织注射纳米炭混悬液进行前哨淋巴结染色。术中对前哨淋巴结进行常规切除处理。数据采用SPSS20.0软件分析,淋巴结数目、SLN转移率、导丝定位率等计数资料采用[例(%)]表示,行χ²检验,P<0.05差异有统计学意义。 结果90例乳腺癌患者均顺利进行手术,完整切除病灶及定位导丝,42例患者发生淋巴结转移,共检出SLN 150枚,其中97枚SLN发生转移;转移淋巴结黑染率为88.66%(86/97),未转移淋巴结黑染率为91.87%(226/246),二者黑染率差异无统计学意义(P>0.05);淋巴结转移患者导丝定位率71.13%(69/97)明显高于淋巴结未转移51.03%(128/246)患者(χ²＝5.218,P<0.05);超声造影引导下导丝定位联合纳米碳染色对乳腺癌SLN定位的灵敏度为100.00%、特异性为97.47%、阳性预测值为98.34%、阴性预测值为100%,诊断效能较高。 结论超声造影引导下导丝定位联合纳米碳染色在乳腺癌SLN的定位中具有重要价值,其为患者制定合理的手术方案及预后均具有重要意义,值得临床推广应用。     

基于碳纳米管的靶向超声造影剂在肿瘤中的应用进展

纳米级靶向超声造影剂具有无辐射、实时显像及高度靶向性等优点。其中碳纳米管(CNT)具有独特的光学、电学和声学特性及较高的比表面积和良好生物相容性,通过对其进行修饰或改性,可制备出性能优良的复合纳米材料,用于诊断及治疗肿瘤。本研究对基于CNT的靶向超声造影剂在肿瘤中的应用进展进行综述。     

纳米碳示踪剂用于cN0T1/T2期甲状腺乳头状癌中央区淋巴结清扫的效果及影响因素

目的探讨纳米碳示踪剂应用于cN0T1/T2期甲状腺乳头状癌中央区淋巴结清扫的效果及影响因素。 方法选择2015年1月至2017年12月期间接受手术治疗的cN0T1/T2期甲状腺乳头状癌患者153例作为研究对象,随机数字表法分为踪剂组(76例)和常规组(77例),其中踪剂组接受术中注射纳米碳示踪剂并进行中央区淋巴结清扫,常规组接受常规中央区淋巴结清扫。采用SPSS 21.0进行临床数据分析,围术期指标及淋巴结清扫数量等计量资料用( ±s)表示,独立t检验;术后并发症、复发率采用χ²检验;预后情况绘制kaplanmeier生存曲线,对淋巴结检出因素进行单因素和多因素logistic回归分析,P<0.05差异有统计学意义。 结果踪剂组人均清扫淋巴结数量为(9.3±2.3)枚、淋巴结检出阳性率95.1%,均明显优于常规组(P<0.05)。踪剂组在术后1 d、3 d、术后3个月血钙和PTH水平,明显高于常规组(P<0.05)。踪剂组甲状旁腺受损情况明显低于常规组(P<0.05);两组在喉返神经损伤情况比较,差异无统计学意义(P>0.05)。踪剂组复发率(15.8%)明显低于常规组(29.9%), P<0.05。两组组内复发与未复发患者淋巴结清扫数量比较,差异均具有统计学意义(P<0.05)。所有患者的24个月总生存率为91.5%,不同淋巴结清扫数量与生存预后无相关性。体重指数、淋巴结平均直径、医师经验是纳米碳示踪剂检出淋巴结清扫数量的独立危险因素(P<0.05)。 结论纳米碳示踪剂能够明显增加cN0T1/T2期甲状腺乳头状癌中央区淋巴结清扫数量,同时对预防手术并发症及术后复发有积极作用。