Nature, April 8, 20021year, Vol.592, No.7853.

Nature, vol. 592, No.7853, April 8, 2002/kloc-0.

Astronomy astronomy

Five species containing carbon and nitrogen in the atmosphere of a hot planet

Five carbon and nitrogen-containing substances in the atmosphere of hot giant planets

Authors: Paulo Giacobbe, Matteo Broggi, Siddharth Gandhi, Patricio Kubillos, etc.

Link:

/articles/s 4 1586-02 1-0338 1-x

abstract

Previous observations of hot Jupiter show that when they pass in front of their main star, there are often water vapor and carbon monoxide in the atmosphere; This is based on the proportional composition of the sun under the usual assumption of chemical equilibrium.

Hydrogen cyanide and these two molecules were found in the atmosphere of HD 209458b. HD 209458b is a well-studied hot Jupiter (the equilibrium temperature is around 1500 k). Ammonia was once detected, but it was later denied.

Here we report the observation results of HD 209458b, which show that there are water, carbon monoxide, hydrogen cyanide, methane, ammonia and acetylene, and the standard deviation of each molecule is 5.3 ~ 9.9. The atmospheric model of radiation and chemical balance shows that the detected substance has a carbon-rich chemical composition, and the carbon-oxygen ratio is close to or greater than 1, which is higher than that of the sun (0.55).

According to the existing models of atmospheric chemistry and planetary formation and migration scenarios, this may indicate that HD 209458b was formed far away from its current position and then migrated inward.

abstract

Previous observations of hot Jupiter passing in front of their main star revealed that water vapor and carbon monoxide often exist in their atmosphere; This is studied according to the proportional composition of the sun under the usual assumption of chemical equilibrium. These two molecules, as well as hydrogen cyanide, were found in the atmosphere of HD 209458b, which is a well-studied hot Jupiter (the equilibrium temperature is about 1 1,500 Kelvin), and ammonia was temporarily detected there, which was later refuted. Here, we report the observation results of HD 209458b, which show that there are water (H2 O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (H4 C), ammonia (H3 N) and acetylene (C2H2), and the statistical significance of each molecule is 5.3 to 9.9 standard deviations. The atmospheric model in radiation and chemical balance explained the detected species, and showed that the carbon-oxygen ratio was close to or greater than 1, which was higher than the solar value (0.55). According to the existing model that relates atmospheric chemistry to planetary formation and migration scenarios, this will show that HD 209458b was formed far away from its current position and then migrated inward.

Archaeology archaeology

105000 years ago, the behavior of innovative homo sapiens in a wetter kalahari desert.

The kalahari basin 105000 years ago, human's innovative behavior.

Authors: Jayne Wilkins, Benjamin J. Schowell, Robin Pickering, Luke Gayle ganic, etc.

Link:

/articles/s 4 1586-02 1-034 19-0

abstract

Archaeological records in Africa provide the earliest evidence for the emergence of complex symbols and technical behaviors of Homo sapiens. However, well-preserved late Pleistocene stratigraphic sites with strong chronology are very rare in the interior of South Africa, so the coastal hypothesis has not been verified.

Here, we show about 654.38+005 million years ago, similar to the early human inventions in the coastal areas of southern Africa. They also live in inland areas more than 600 kilometers away. We report evidence of intentional collection of non-practical items (calcite crystals) and ostrich eggshells.

These evidences come from the excavation site of a layered rock deposit in the south of Kalahari Basin, and we determined that it was about 654.38+005 million years ago by optical luminescence dating technology. Uranium and thorium dating of residual tuff deposits shows that a large amount of fresh water occasionally flows here; The oldest of these rock formations can be traced back to 1 1 to 65438+ ten thousand years, which is consistent with archaeological discoveries.

Our research results show that the innovative behaviors of inland people in southern Africa do not lag behind those near the coast, and these innovative behaviors may have developed in a humid prairie environment.

abstract

Archaeological records in Africa provide the earliest evidence for the emergence of complex symbols and technical behaviors unique to Homo sapiens. However, in the inland areas of southern Africa, well-preserved and reliable layered late Pleistocene sites are very rare, so the coastal hypothesis has not been verified. Here, we show that early human innovations similar to those in the coastal areas of southern Africa about/kloc-0.05 million years ago (ka) existed among people living in the inland of more than 600 kilometers at about the same time. We report the evidence of non-practical objects (calcite crystals) and ostrich eggshells intentionally collected from the excavation of layered reef deposits in the south of Kalahari Basin. We have determined their age by photoluminescence (PL) to be about 105 ka. Uranium-thorium dating of residual travertine sediments shows the sporadic period of a large number of fresh flowing water; The oldest of these scenes can be traced back to 1 10 to 100 ka, which is in the same period as archaeological deposits. Our results show that human behavior innovations in inland areas of southern Africa are not lagging behind those in coastal areas, and these innovations may have developed in a humid savanna environment.

materials science

Entropy Evidence of Pomeranchuk Effect in Magic Horn Graphene

Entropy Evidence of Pomeranciuk Effect in Magic Horn Graphene

Authors: Asaf Rosen, Park Jung min, Ourisson Dinar, Cao Yuan, Daniel Raton Le Grand, etc.

Link:

/articles/s 4 1586-02 1-033 19-3

abstract

In 1950s, Pomerachak predicted that liquid helium -3 might solidify after heating, which was contrary to our intuition. This effect is caused by the high excess nuclear spin entropy of solid atoms in space. Here, we find that a similar effect also occurs in the double-layer graphene with twisted magic angle.

Using local and global electron entropy measurements, we found that when nearly one electron is filled in each mole of cell, the electron entropy significantly increases to about 1 k B per cell. This huge excess entropy is quenched by the in-plane magnetic field pointing to its magnetic source. Compressibility decreases sharply with the change of electron density, and returns to the vicinity of Dirac point with the reset of Fermi level, which indicates that the boundary between the two phases is clear.

We map this jump as a function of electron density, temperature and magnetic field. This reveals a phase diagram. Like Pomeranchuk, temperature and magnetic field drive the low-entropy electronic liquid to change to the high-entropy associated state with almost free magnetic moment.

Associated states are characterized by an unusual combination of seemingly contradictory properties, some of which are related to flowing electrons, such as lack of thermodynamic gap, metallicity and Dirac compressibility, while others are related to local moments, such as large entropy and its disappearance under magnetic field.

abstract

In the1950s, Pomeranchuk predicted that, contrary to intuition, liquid 3He might solidify when heated. This effect is due to the high excess nuclear spin entropy in the solid phase, in which the atoms are spatially localized. Here, we find that a similar effect occurs in the double-layer graphene with twisted magic angle. Using local and global electron entropy measurements, we show that the electron entropy of each cell increases significantly to about 1k B(k B is a Boltzmann constant) when one electron is filled in each Moore cell. This huge excess entropy is quenched by an in-plane magnetic field and points to its magnetic source. The sharp decrease of compressibility as a function of electron density, accompanied by the reset of Fermi level near Dirac point, marks a clear boundary between the two phases. We map this jump as a function of electron density, temperature and magnetic field. This reveals a phase diagram, which is consistent with the transition from low-entropy electronic liquid to high-entropy associated state with almost free magnetic moment driven by temperature and field like Pomeranchuk. Associated states are characterized by an unusual combination of seemingly contradictory properties, some of which are related to traveling electrons, such as lack of thermodynamic gap, metallicity and Dirac-like compressibility, while others are related to local moments, such as large entropy and its disappearance under magnetic field.

Isospin Wave Melachak Effect in Twisted Double-layer Graphene

Isospin Merachak Effect of Twisted Double-layer Graphene

Authors: Qi Teng Yu, Yang, Ge, Liu, Suneohair, etc.

Link:

/articles/s 4 1586-02 1-03409-2

abstract

Here, we show a mechanism to describe the finite temperature dynamics of spin and slot isospin in magic angle twisted double-layer graphene.

It is worth noting that near the superlattice filling factor 1, the resistivity peaks at high temperature, but there is no corresponding phase at the low temperature limit. Thermodynamic measurements of magnetic transport of tilted magnetic field and in-plane magnetic moment show that the peak value of resistivity is related to the development of the system into a finite field magnetic phase transition with finite isospin polarization. These data indicate a Pomerack-type mechanism.

In this mechanism, compared with the isospin unpolarized Fermi liquid phase, the entropy of disordered isospin moment in ferromagnetic phase stabilizes the phase at higher temperature.

abstract

Here we show a similar mechanism to describe the finite temperature dynamics of spin and valley isospin in magic angle twisted double-layer graphene. Although there is no sign of the corresponding phase at the low temperature limit, at high temperature, the resistivity peak appears near the superlattice filling factor 1. Thermodynamic measurements of magnetic transport in inclined field and in-plane magnetic moment show that the peak resistivity is related to the finite field magnetic phase transition of the system with finite isospin polarization. These data suggest Pomeranchuk-type mechanism, in which the entropy of disordered isospin moment in ferromagnetic phase stabilizes the phase at higher temperature than that of isospin unpolarized Fermi liquid phase.

Diversity-oriented synthesis of ion solvated cage polymer membranes

Diversity and orientation synthesis of polymer films based on ion solvation

Authors: Miranda J. Balaam, Mark E. carrington, Swagat Sahu, Altym baskin, Joan Song Hua, etc.

Link:

/articles/s 4 1586-02 1-03377-7

abstract

Here, we describe a diversity-oriented microporous polymer membrane synthesis strategy to determine FVEs as a candidate material for lithium ion solvent cages.

This strategy includes diversifying catechol monomers through Mannich reaction, thus introducing lithium ion coordination function into FVEs, strengthening topological polymerization to make FVEs enter different pore structures, and various polymer reactions with pore geometry and dielectric properties.

Compared with the control membrane, the candidate membrane with ion solvation cage has higher ionic conductivity and higher cation transfer number, in which FVEs is specific, indicating that the conventional membrane permeation boundary and ion transfer selectivity can be overcome.

abstract

Here, we describe a personalized synthesis strategy of microporous polymer membrane to determine that the candidate's characteristic is FVEs as a solvent cage for lithium ions (Li+). This strategy includes dispersing bis (catechol) monomer by Mannich reaction to introduce Li+ coordination functional groups into FVEs, topology-enhanced polymerization to network FVEs into different pore structures, and reaction on several polymers with dispersed pore geometry and dielectric properties. The most promising candidate membrane with ion solvation ion ion cage shows higher ionic conductivity and higher cation migration number than the control membrane, in which FVEs is non-specific, indicating that the traditional boundaries of membrane permeability and ion transport selectivity can be overcome.

earth sciences

200 million-year delay of permanent atmospheric oxidation

Delayed permanent atmospheric oxidation for 200 million years.

Authors: Simon W. Bolton, Andre Baker, Vivian M. Cumming, Aubrey L. Seckel, Donald E. canfield &; David Johnston

Link:

/articles/s 4 1586-02 1-03393-7

abstract

The early atmospheric oxidation occurred in the long-term extreme climate instability period marked by many global ice ages, and the time when the oxygen concentration first rose above the current atmospheric level 10- 5 was estimated to be 2.43 billion years ago. However, the fluctuation of atmospheric oxygen content continued until about 2.32 billion years ago, which represents the estimated time of irreversible oxidation in the atmosphere.

Here, through the superior marine sediments in Transvaal, South Africa, we reconstructed the atmospheric and local marine redox conditions of the last two ice ages in early ancient times with high resolution. Using various sulfur isotopes and iron-sulfur-carbon system, we proved that the atmospheric oxygen level fluctuated continuously after about 2.32 billion years ago, which was related to the main disturbance of ocean redox chemistry and climate.

Therefore, for about 200 million years, the oxygen level fluctuated around the threshold of 10- 5 of the current atmospheric level. The permanent great oxidation event is about 1 100 million years later than the current estimate.

abstract

The early atmospheric oxidation occurred in the long-term extreme climate instability period marked by many global glaciers, and the oxygen concentration initially rose above the current atmospheric level of 10- 5, which was limited to about 2.43 billion years ago. However, it is reported that the subsequent fluctuation of atmospheric oxygen content occurred until about 2.32 billion years ago, which represents the estimated time of irreversible oxidation of the atmosphere. Here, we report the high-resolution reconstruction of atmospheric and local ocean redox conditions during the last two glacial periods in early Proterozoic, as recorded by marine sediments from Transvaal Group in South Africa. Using a variety of sulfur isotopes and iron-sulfur-carbon systematics, we proved that the atmospheric oxygen level fluctuated continuously about 2.32 billion years ago, which was related to the main disturbance of ocean redox chemistry and climate. Therefore, the oxygen level fluctuated within the threshold range of 10- 5 of the current atmospheric level for about 200 million years, and finally reached permanent atmospheric oxidation about 2.22 billion years ago, which was about 10 billion years later than the current estimate.