生理Physiology

 

 

 

Diabetes relief in mice by glucose-sensing insulin-secreting human α-cells

 

新疗法缓解小鼠糖尿病

 

▲ 作者：KenichiroFuruyama、Simona Chera、FabrizioThorel、Pedro L.Herrera，etal

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0942-8

 

 

 

▲ 摘要：

 

细胞转化开关（当受到压力时，细胞转化为不同的细胞类型）是一种动物再生策略，但在哺乳动物中却鲜有文献记载。

 

 

 

在小鼠身上，在胰岛素分泌β细胞消融后，产生高血糖素的胰腺α细胞和产生生长激素抑制素的δ细胞成为胰岛素表达细胞，从而促进糖尿病康复。但人类的胰岛是否也有这种可塑性，尤其是在患糖尿病的情况下，还不得而知。

 

 

 

在这里，研究人员表明,胰岛非β细胞，即α细胞和分泌胰多肽（PPY）的γ细胞，可以通过转录因子PDX1和MAFA进行谱系追踪和重新编程，从而产生和分泌胰岛素。

 

 

 

当移植到糖尿病小鼠体内后，修改的α细胞能缓解糖尿病，并在6个月后继续产生胰岛素。这些观察结果为治疗糖尿病和其他退行性疾病提供了概念性证据和分子框架。

 

 

 

▲ Abstract

 

Cell-identity switches, in which terminally differentiated cells are converted into different cell types when stressed, represent a widespread regenerative strategy in animals, yet they are poorly documented in mammals. In mice, some glucagon-producing pancreatic α-cells and somatostatin-producing δ-cells become insulin-expressing cells after the ablation of insulin-secreting β-cells, thus promoting diabetes recovery. Whether human islets also display this plasticity, especially in diabetic conditions, remains unknown. Here we show that islet non-β-cells, namely α-cellsand pancreatic polypeptide (PPY)-producing γ-cells, obtained from deceased non-diabetic or diabetic human donors, can be lineage-traced and reprogrammed by the transcription factors PDX1 and MAFA to produce and secrete insulin inresponse to glucose. When transplanted into diabetic mice, converted humanα-cells reverse diabetes and continue to produce insulin even after six months. Notably, insulin-producing α-cells maintain expression of α-cell markers, as seen by deep transcriptomic and proteomic characterization. These observations provide conceptual evidence and a molecular framework for a mechanistic understanding of in situ cell plasticity as a treatment for diabetes and other degenerative diseases.

 

Colonic epithelial cell diversity in health and inflammatorybowel disease

 

结肠上皮细胞在健康及炎症性肠病中的多样性

 

▲ 作者：KaushalParikh、AgneAntanaviciute、AlisonSimmons，etal

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0992-y

 

 

 

▲ 摘要：

 

结肠上皮促进宿主与微生物相互作用、控制黏膜免疫、协调营养循环，以及形成黏液屏障。上皮屏障的破坏是炎症性肠病（IBD）的基础。

 

 

 

然而，人们对每个上皮细胞亚型对这一过程的具体贡献尚不清楚。

 

 

 

在这里，研究人员描绘了来自IBD患者和健康对照组的单个结肠上皮细胞。他们确定了以前未知的细胞亚型，包括祖细胞、结肠细胞和杯状细胞的梯度。

 

 

 

在肠隐窝的顶部，我们发现了一个以前不为人知的吸收细胞，它能表达质子通道OTOP2和饱腹肽尿鸟苷素，并感知pH值，在炎症和癌症中失调。在IBD中，研究人员观察到了杯状细胞的位置重构，这与WFDC2的下调一致。

 

 

 

WFDC2是一种抗蛋白酶分子，可以抑制细菌生长。WFDC2能保持上皮细胞间紧密连接的完整性，防止共生细菌的入侵和黏膜炎症。

 

 

 

▲ Abstract

 

The colonic epithelium facilitates host–micro organism interactions to control mucosal immunity, coordinate nutrient recycling and form a mucus barrier. Breakdown of the epithelial barrier underpins inflammatory bowel disease (IBD). However, the specific contributions of each epithelial-cell subtype to this process are unknown. Here we profile single colonic epithelial cells from patients with IBD and unaffected controls. We identify previously unknown cellular subtypes, including gradients of progenitor cells, colonocytes and goblet cells within intestinal crypts. At the top of the crypts, we find a previously unknown absorptive cell, expressing theproton channel OTOP2 and the satiety peptide uroguanylin, that senses pH and is dysregulated in inflammation and cancer. In IBD, we observe a positional remodelling of goblet cells that coincides with down regulation of WFDC2—an antiprotease molecule that we find to be expressed by goblet cells and that inhibits bacterial growth. In vivo, WFDC2 preserves the integrity of tight junctions between epithelial cells and prevents invasion by commensal bacteria and mucosal inflammation. We delineate markers and transcriptional states, identify a colonic epithelial cell and uncover fundamental determinants of barrier breakdown in IBD.

 

 

 

生物Biology

 

 

 

Social parasitism as an alternative reproductive tactic in acooperatively breeding cuckoo

 

群居寄生是合作繁殖杜鹃的另一种繁殖策略

 

▲ 作者：ChristinaRiehl、Meghan J.Strong

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0981-1

 

 

 

▲ 摘要：

 

合作筑巢的鸟类很容易受到巢寄生鸟类的影响，巢寄生鸟类会将卵产在宿主巢中，而不自己抚育。

 

 

 

大犀鹃是一种热带杜鹃，它的不同寻常之处在于：雌性大犀鹃既会合作育雏，也会寄生育雏，有些则会采用两种方式。

 

 

 

然而，一直缺少实际证据证明雌性大犀鹃何时以及为何采用不同的繁殖策略。

 

 

 

本研究发现，大多数雌性大犀鹃在繁殖季节开始时都采用合作筑巢方式，但如果它们的第一个巢被破坏，则其中一小部分大犀鹃随后将采用寄生育雏方式。

 

 

 

采用寄生育雏的雌性大犀鹃往往会重复这种行为。研究人员表示，两种育雏策略的适应性收益大致相当。

 

 

 

相较于筑巢继而寄生的大犀鹃，从不寄生且严格采用合作育雏方式的大犀鹃产卵更多，通过自己筑巢养育的幼鸟也更多，因此二者的总生殖产出没有差异。

 

 

 

▲ Abstract

 

Cooperatively nesting birds are vulnerable to social parasites that lay their eggs in host nests but provide no parental care. Most previous research has focused on the co-evolutionary arms race between host defences and the parasites that attempt to circumvent them, but it remains unclear why females sometimes cooperate and sometimes parasitize, and how parasitic tactics arise in cooperative systems. Here we show that cooperative and parasitic reproductive strategies result in approximately equal fitness pay-offs in the greater ani (Crotophaga major), a long-lived tropical cuckoo, using an 11-year dataset and comprehensive genetic data that enable comparisonsof the life-histories of individual females. We found that most females in the population nested cooperatively at the beginning of the breeding season; however, of those birds that had their first nests destroyed, a minority subsequently acted as reproductive parasites. The tendency to parasitize washighly repeatable, which indicates individual specialization. Across years, thefitness pay-offs of the two strategies were approximately equal: females whonever parasitized (a ‘pure cooperative’ strategy) laid larger clutches and fledged more young from their own nests than did birds that both nested and parasitized (a ‘mixed’ strategy). Our results suggest that the success of parasites is constrained by reproductive trade-offs as well as by host defences, and illustrate how cooperative and parasitic tactics can coexiststably in the same population.

 

 

 

环境Environtology

 

 

 

Wetland carbon storage controlled by millennial-scalevariation in relative sea-level rise

 

湿地碳储量受相对海平面变化影响

 

▲ 作者：KerryleeRogers、Jeffrey J.Kelleway、NeilSaintilan、Colin D.Woodroffe，etal 

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0951-7

 

 

 

▲ 摘要：

 

沿海湿地单位面积固碳率在所有自然系统中是最高的，主要原因是它们的生产力相对较高，并能在沉积基质中保存有机碳。

 

 

 

气候变化和相对海平面上升要求在21世纪前半叶增加滨海湿地有机碳储存率。

 

 

 

本研究表明，潮汐沼泽海岸线在过去几千年经历了快速海平面上升（全新世晚期，从约4200年前到现在），与比海平面的长期稳定区域相比，其土壤碳浓度在20厘米内平均高出1.7到3.7倍。

 

 

 

这种差异随深度的增加而增加。研究人员还分析了湿地对快速海平面上升的反应。

 

 

 

结果表明，具有构造稳定性海岸线特征的滨海湿地，由于空间的缺乏而具有较低的碳储量，并且碳储量随着海平面上升所创造的垂直和横向空间的增加而增加。这些湿地将提供与全球气候—碳模型相关的长期缓和反馈效应。

 

 

 

▲ Abstract

 

Coastal wetlands (mangrove, tidal marsh and seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems primarily because of their comparatively high productivity and preservation of organic carbon within sedimentary substrates. Climate change and associated relative sea-level rise (RSLR) have been proposed to increase the rate of organic-carbon burial in coastal wetlands in the first half of the twenty-firstcentury, but these carbon–climate feedback effects have been modelled to diminish over time as wetlands are increasingly submerged and carbon stores become compromised by erosion. Here we show that tidal marshes on coastlines that experienced rapid RSLR over the past few millennia (in the late Holocene, from about 4,200 years ago to the present) have on average 1.7 to 3.7 times higher soil carbon concentrations within 20 centimetres of the surface than those subject to a long period of sea-level stability. This disparity increases with depth, with soil carbon concentrations reduced by a factor of 4.9 to 9.1at depths of 50 to 100 centimetres. We analyse the response of a wetland exposed to recent rapid RSLR following subsidence associated with pillarcollapse in an underlying mine and demonstrate that the gain in carbon accumulation and elevation is proportional to the accommodation space (that is, the space available for mineral and organic material accumulation) created by RSLR. Our results suggest that coastal wetlands characteristic of tectonically stable coastlines have lower carbon storage owing to a lack of accommodation space and that carbon sequestration increases according to the vertical and lateral accommodation space created by RSLR. Such wetlands will provide long-term mitigating feedback effects that are relevant to global climate–carbon modelling.

 

 

 

材料Materialogy

 

 

 

Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers

 

MoSe2/WSe2异质层中摩尔陷阱谷激子的特征

 

▲ 作者：Kyle L.Seyler、PasqualRivera、Wang Yao、Xiaodong Xu，et al

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0957-1

 

 

 

▲ 摘要：

 

晶体固体中莫尔模型的形成可以用来控制它们的电子性质，这些性质从根本上受到周期势场的影响。

 

 

 

在二维材料中，具有超晶格势的莫尔模型可以通过垂直叠加具有扭转和/或晶格常数差的两层材料而形成。这种方法导致了电子现象，包括分形量子霍尔效应、可调谐莫特绝缘子和非常规超导性。

 

 

 

该研究手机版了在二硒化钼/二硒化钨（MoSe2/WSe2）异质层中捕获莫尔势的层间谷激子的实验证据。在低温下，研究人员观察到光致发光接近自由层间激子能量，但线宽超过100倍（约100微电子伏特）。

 

 

 

发射器g因子在同一样品中是均匀的，并且在分别具有60度和0度的近似扭转角的样品中仅取两个值：-15.9和6.7。对于给定的扭转角，发射器表现出相同螺旋性的强圆极化，这表明俘获势保持三重旋转对称性。

 

 

 

结果表明观察到的效应的起源是层间激子被捕获在光滑的莫尔势中，具有继承的谷对比物理学。这项工作提供了通过改变扭转角控制二维莫尔光学的机会。

 

 

 

▲ Abstract

 

The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect tunable Mott insulators and unconventional superconductivity. In addition, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in amoiré potential in molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers. At low temperatures, we observe photo luminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 micro electronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, −15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton,which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at atwist angle of approximately 60 degrees. This is consistent with the umklappre combination of interlayer excitons near the commensurate 21.8-degree twistangle. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. This work presents opportunities to control two-dimensional moiré optics through variation of the twist angle.

 

 

 

Observation of moiré excitons in WSe2/WS2 heterostructure superlattices

 

WSe2/WS2异质结构超晶格中莫尔激子的观察

 

▲ 作者：Chenhao Jin、Emma C. Regan、Alex Zettl、Feng Wang，et al 

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0976-y

 

 

 

▲ 摘要：

 

莫尔超晶格能够在二维异质结构中产生新的量子现象，其中原子薄层之间的相互作用定性地改变超晶格的电子能带结构。

 

 

 

例如，mini-Dirac点，可调谐莫特绝缘体状态和霍夫施塔特蝶形图案，可以出现在不同类型的石墨烯/氮化硼莫尔超晶格中，而相关的绝缘状态和超导性已经在扭曲的双层石墨烯莫尔超晶格中报道。

 

 

 

本研究手机版了在二硒化钨/二硫化钨（WSe2 / WS2）异质结构中的莫尔超晶格激子态的观察，其各层紧密排列。

 

 

 

这些莫尔激子态表现为吸收光谱中原始WSe2 A激子共振周围的多个出射峰，并且它们表现出与WSe2单层中的A激子和具有大扭转角的WSe2 / WS2异质结构不同的栅极依赖性。

 

 

 

这些现象可以通过理论模型来描述，而且莫尔激子带提供了一个平台，可以从中探索和控制物质的激发态。

 

 

 

▲ Abstract

 

Moiré superlattices enable the generation of new quantum phenomena in two-dimensional heterostructures, in which the interactions between the atomically thin layers qualitatively change the electronic band structure of the superlattice. For example, mini-Dirac points, tunable Mottinsulator states and the Hofstadter butterfly pattern can emerge in different types of graphene/boron nitride moiré superlattices, whereas correlated insulating states and superconductivity have been reported in twisted bilayer graphene moiré superlattices. In addition to their pronounced effects on single-particle states, moiré superlattices have recently been predicted to host excited states such as moiré exciton bands. Here we report the observation of moiré superlattice exciton states in tungsten diselenide/tungsten disulfide (WSe2 / WS2) heterostructures in which the layers are closely aligned. These moiré exciton states manifest as multiple emergent peaks around the original WSe2 A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinct from that of the A exciton in WSe2monolayers and in WSe2 / WS2 heterostructures with large twistangles. These phenomena can be described by a the oretical model in which the periodic moiré potential is much stronger than the exciton kinetic energy and generates multiple flat exciton minibands. The moiré exciton bands provide an attractive platform from which to explore and control excited states of matter, such as topological excitons and a correlated exciton Hubbard model, intransition-metal dichalcogenides.

 

生理Physiology

 

 

 

Diabetes relief in mice by glucose-sensing insulin-secreting human α-cells

 

新疗法缓解小鼠糖尿病

 

▲ 作者：KenichiroFuruyama、Simona Chera、FabrizioThorel、Pedro L.Herrera，etal

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0942-8

 

 

 

▲ 摘要：

 

细胞转化开关（当受到压力时，细胞转化为不同的细胞类型）是一种动物再生策略，但在哺乳动物中却鲜有文献记载。

 

 

 

在小鼠身上，在胰岛素分泌β细胞消融后，产生高血糖素的胰腺α细胞和产生生长激素抑制素的δ细胞成为胰岛素表达细胞，从而促进糖尿病康复。但人类的胰岛是否也有这种可塑性，尤其是在患糖尿病的情况下，还不得而知。

 

 

 

在这里，研究人员表明,胰岛非β细胞，即α细胞和分泌胰多肽（PPY）的γ细胞，可以通过转录因子PDX1和MAFA进行谱系追踪和重新编程，从而产生和分泌胰岛素。

 

 

 

当移植到糖尿病小鼠体内后，修改的α细胞能缓解糖尿病，并在6个月后继续产生胰岛素。这些观察结果为治疗糖尿病和其他退行性疾病提供了概念性证据和分子框架。

 

 

 

▲ Abstract

 

Cell-identity switches, in which terminally differentiated cells are converted into different cell types when stressed, represent a widespread regenerative strategy in animals, yet they are poorly documented in mammals. In mice, some glucagon-producing pancreatic α-cells and somatostatin-producing δ-cells become insulin-expressing cells after the ablation of insulin-secreting β-cells, thus promoting diabetes recovery. Whether human islets also display this plasticity, especially in diabetic conditions, remains unknown. Here we show that islet non-β-cells, namely α-cellsand pancreatic polypeptide (PPY)-producing γ-cells, obtained from deceased non-diabetic or diabetic human donors, can be lineage-traced and reprogrammed by the transcription factors PDX1 and MAFA to produce and secrete insulin inresponse to glucose. When transplanted into diabetic mice, converted humanα-cells reverse diabetes and continue to produce insulin even after six months. Notably, insulin-producing α-cells maintain expression of α-cell markers, as seen by deep transcriptomic and proteomic characterization. These observations provide conceptual evidence and a molecular framework for a mechanistic understanding of in situ cell plasticity as a treatment for diabetes and other degenerative diseases.

 

Colonic epithelial cell diversity in health and inflammatorybowel disease

 

结肠上皮细胞在健康及炎症性肠病中的多样性

 

▲ 作者：KaushalParikh、AgneAntanaviciute、AlisonSimmons，etal

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0992-y

 

 

 

▲ 摘要：

 

结肠上皮促进宿主与微生物相互作用、控制黏膜免疫、协调营养循环，以及形成黏液屏障。上皮屏障的破坏是炎症性肠病（IBD）的基础。

 

 

 

然而，人们对每个上皮细胞亚型对这一过程的具体贡献尚不清楚。

 

 

 

在这里，研究人员描绘了来自IBD患者和健康对照组的单个结肠上皮细胞。他们确定了以前未知的细胞亚型，包括祖细胞、结肠细胞和杯状细胞的梯度。

 

 

 

在肠隐窝的顶部，我们发现了一个以前不为人知的吸收细胞，它能表达质子通道OTOP2和饱腹肽尿鸟苷素，并感知pH值，在炎症和癌症中失调。在IBD中，研究人员观察到了杯状细胞的位置重构，这与WFDC2的下调一致。

 

 

 

WFDC2是一种抗蛋白酶分子，可以抑制细菌生长。WFDC2能保持上皮细胞间紧密连接的完整性，防止共生细菌的入侵和黏膜炎症。

 

 

 

▲ Abstract

 

The colonic epithelium facilitates host–micro organism interactions to control mucosal immunity, coordinate nutrient recycling and form a mucus barrier. Breakdown of the epithelial barrier underpins inflammatory bowel disease (IBD). However, the specific contributions of each epithelial-cell subtype to this process are unknown. Here we profile single colonic epithelial cells from patients with IBD and unaffected controls. We identify previously unknown cellular subtypes, including gradients of progenitor cells, colonocytes and goblet cells within intestinal crypts. At the top of the crypts, we find a previously unknown absorptive cell, expressing theproton channel OTOP2 and the satiety peptide uroguanylin, that senses pH and is dysregulated in inflammation and cancer. In IBD, we observe a positional remodelling of goblet cells that coincides with down regulation of WFDC2—an antiprotease molecule that we find to be expressed by goblet cells and that inhibits bacterial growth. In vivo, WFDC2 preserves the integrity of tight junctions between epithelial cells and prevents invasion by commensal bacteria and mucosal inflammation. We delineate markers and transcriptional states, identify a colonic epithelial cell and uncover fundamental determinants of barrier breakdown in IBD.

 

 

 

生物Biology

 

 

 

Social parasitism as an alternative reproductive tactic in acooperatively breeding cuckoo

 

群居寄生是合作繁殖杜鹃的另一种繁殖策略

 

▲ 作者：ChristinaRiehl、Meghan J.Strong

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0981-1

 

 

 

▲ 摘要：

 

合作筑巢的鸟类很容易受到巢寄生鸟类的影响，巢寄生鸟类会将卵产在宿主巢中，而不自己抚育。

 

 

 

大犀鹃是一种热带杜鹃，它的不同寻常之处在于：雌性大犀鹃既会合作育雏，也会寄生育雏，有些则会采用两种方式。

 

 

 

然而，一直缺少实际证据证明雌性大犀鹃何时以及为何采用不同的繁殖策略。

 

 

 

本研究发现，大多数雌性大犀鹃在繁殖季节开始时都采用合作筑巢方式，但如果它们的第一个巢被破坏，则其中一小部分大犀鹃随后将采用寄生育雏方式。

 

 

 

采用寄生育雏的雌性大犀鹃往往会重复这种行为。研究人员表示，两种育雏策略的适应性收益大致相当。

 

 

 

相较于筑巢继而寄生的大犀鹃，从不寄生且严格采用合作育雏方式的大犀鹃产卵更多，通过自己筑巢养育的幼鸟也更多，因此二者的总生殖产出没有差异。

 

 

 

▲ Abstract

 

Cooperatively nesting birds are vulnerable to social parasites that lay their eggs in host nests but provide no parental care. Most previous research has focused on the co-evolutionary arms race between host defences and the parasites that attempt to circumvent them, but it remains unclear why females sometimes cooperate and sometimes parasitize, and how parasitic tactics arise in cooperative systems. Here we show that cooperative and parasitic reproductive strategies result in approximately equal fitness pay-offs in the greater ani (Crotophaga major), a long-lived tropical cuckoo, using an 11-year dataset and comprehensive genetic data that enable comparisonsof the life-histories of individual females. We found that most females in the population nested cooperatively at the beginning of the breeding season; however, of those birds that had their first nests destroyed, a minority subsequently acted as reproductive parasites. The tendency to parasitize washighly repeatable, which indicates individual specialization. Across years, thefitness pay-offs of the two strategies were approximately equal: females whonever parasitized (a ‘pure cooperative’ strategy) laid larger clutches and fledged more young from their own nests than did birds that both nested and parasitized (a ‘mixed’ strategy). Our results suggest that the success of parasites is constrained by reproductive trade-offs as well as by host defences, and illustrate how cooperative and parasitic tactics can coexiststably in the same population.

 

 

 

环境Environtology

 

 

 

Wetland carbon storage controlled by millennial-scalevariation in relative sea-level rise

 

湿地碳储量受相对海平面变化影响

 

▲ 作者：KerryleeRogers、Jeffrey J.Kelleway、NeilSaintilan、Colin D.Woodroffe，etal 

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0951-7

 

 

 

▲ 摘要：

 

沿海湿地单位面积固碳率在所有自然系统中是最高的，主要原因是它们的生产力相对较高，并能在沉积基质中保存有机碳。

 

 

 

气候变化和相对海平面上升要求在21世纪前半叶增加滨海湿地有机碳储存率。

 

 

 

本研究表明，潮汐沼泽海岸线在过去几千年经历了快速海平面上升（全新世晚期，从约4200年前到现在），与比海平面的长期稳定区域相比，其土壤碳浓度在20厘米内平均高出1.7到3.7倍。

 

 

 

这种差异随深度的增加而增加。研究人员还分析了湿地对快速海平面上升的反应。

 

 

 

结果表明，具有构造稳定性海岸线特征的滨海湿地，由于空间的缺乏而具有较低的碳储量，并且碳储量随着海平面上升所创造的垂直和横向空间的增加而增加。这些湿地将提供与全球气候—碳模型相关的长期缓和反馈效应。

 

 

 

▲ Abstract

 

Coastal wetlands (mangrove, tidal marsh and seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems primarily because of their comparatively high productivity and preservation of organic carbon within sedimentary substrates. Climate change and associated relative sea-level rise (RSLR) have been proposed to increase the rate of organic-carbon burial in coastal wetlands in the first half of the twenty-firstcentury, but these carbon–climate feedback effects have been modelled to diminish over time as wetlands are increasingly submerged and carbon stores become compromised by erosion. Here we show that tidal marshes on coastlines that experienced rapid RSLR over the past few millennia (in the late Holocene, from about 4,200 years ago to the present) have on average 1.7 to 3.7 times higher soil carbon concentrations within 20 centimetres of the surface than those subject to a long period of sea-level stability. This disparity increases with depth, with soil carbon concentrations reduced by a factor of 4.9 to 9.1at depths of 50 to 100 centimetres. We analyse the response of a wetland exposed to recent rapid RSLR following subsidence associated with pillarcollapse in an underlying mine and demonstrate that the gain in carbon accumulation and elevation is proportional to the accommodation space (that is, the space available for mineral and organic material accumulation) created by RSLR. Our results suggest that coastal wetlands characteristic of tectonically stable coastlines have lower carbon storage owing to a lack of accommodation space and that carbon sequestration increases according to the vertical and lateral accommodation space created by RSLR. Such wetlands will provide long-term mitigating feedback effects that are relevant to global climate–carbon modelling.

 

 

 

材料Materialogy

 

 

 

Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers

 

MoSe2/WSe2异质层中摩尔陷阱谷激子的特征

 

▲ 作者：Kyle L.Seyler、PasqualRivera、Wang Yao、Xiaodong Xu，et al

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0957-1

 

 

 

▲ 摘要：

 

晶体固体中莫尔模型的形成可以用来控制它们的电子性质，这些性质从根本上受到周期势场的影响。

 

 

 

在二维材料中，具有超晶格势的莫尔模型可以通过垂直叠加具有扭转和/或晶格常数差的两层材料而形成。这种方法导致了电子现象，包括分形量子霍尔效应、可调谐莫特绝缘子和非常规超导性。

 

 

 

该研究手机版了在二硒化钼/二硒化钨（MoSe2/WSe2）异质层中捕获莫尔势的层间谷激子的实验证据。在低温下，研究人员观察到光致发光接近自由层间激子能量，但线宽超过100倍（约100微电子伏特）。

 

 

 

发射器g因子在同一样品中是均匀的，并且在分别具有60度和0度的近似扭转角的样品中仅取两个值：-15.9和6.7。对于给定的扭转角，发射器表现出相同螺旋性的强圆极化，这表明俘获势保持三重旋转对称性。

 

 

 

结果表明观察到的效应的起源是层间激子被捕获在光滑的莫尔势中，具有继承的谷对比物理学。这项工作提供了通过改变扭转角控制二维莫尔光学的机会。

 

 

 

▲ Abstract

 

The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect tunable Mott insulators and unconventional superconductivity. In addition, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in amoiré potential in molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers. At low temperatures, we observe photo luminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 micro electronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, −15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton,which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at atwist angle of approximately 60 degrees. This is consistent with the umklappre combination of interlayer excitons near the commensurate 21.8-degree twistangle. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. This work presents opportunities to control two-dimensional moiré optics through variation of the twist angle.

 

 

 

Observation of moiré excitons in WSe2/WS2 heterostructure superlattices

 

WSe2/WS2异质结构超晶格中莫尔激子的观察

 

▲ 作者：Chenhao Jin、Emma C. Regan、Alex Zettl、Feng Wang，et al 

 

▲ 链接：

 

http://www.nature.com/articles/s41586-019-0976-y

 

 

 

▲ 摘要：

 

莫尔超晶格能够在二维异质结构中产生新的量子现象，其中原子薄层之间的相互作用定性地改变超晶格的电子能带结构。

 

 

 

例如，mini-Dirac点，可调谐莫特绝缘体状态和霍夫施塔特蝶形图案，可以出现在不同类型的石墨烯/氮化硼莫尔超晶格中，而相关的绝缘状态和超导性已经在扭曲的双层石墨烯莫尔超晶格中报道。

 

 

 

本研究手机版了在二硒化钨/二硫化钨（WSe2 / WS2）异质结构中的莫尔超晶格激子态的观察，其各层紧密排列。

 

 

 

这些莫尔激子态表现为吸收光谱中原始WSe2 A激子共振周围的多个出射峰，并且它们表现出与WSe2单层中的A激子和具有大扭转角的WSe2 / WS2异质结构不同的栅极依赖性。

 

 

 

这些现象可以通过理论模型来描述，而且莫尔激子带提供了一个平台，可以从中探索和控制物质的激发态。

 

 

 

▲ Abstract

 

Moiré superlattices enable the generation of new quantum phenomena in two-dimensional heterostructures, in which the interactions between the atomically thin layers qualitatively change the electronic band structure of the superlattice. For example, mini-Dirac points, tunable Mottinsulator states and the Hofstadter butterfly pattern can emerge in different types of graphene/boron nitride moiré superlattices, whereas correlated insulating states and superconductivity have been reported in twisted bilayer graphene moiré superlattices. In addition to their pronounced effects on single-particle states, moiré superlattices have recently been predicted to host excited states such as moiré exciton bands. Here we report the observation of moiré superlattice exciton states in tungsten diselenide/tungsten disulfide (WSe2 / WS2) heterostructures in which the layers are closely aligned. These moiré exciton states manifest as multiple emergent peaks around the original WSe2 A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinct from that of the A exciton in WSe2monolayers and in WSe2 / WS2 heterostructures with large twistangles. These phenomena can be described by a the oretical model in which the periodic moiré potential is much stronger than the exciton kinetic energy and generates multiple flat exciton minibands. The moiré exciton bands provide an attractive platform from which to explore and control excited states of matter, such as topological excitons and a correlated exciton Hubbard model, intransition-metal dichalcogenides.

 

（宗华）