A candidate redshift z ≈ 10 galaxy and rapid changes in that population at an age of 500 Myr

Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000?million years (Myr) after the Big Bang (redshifts 6?>?z?>?3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z?≈?8 galaxies that, together with reports of a γ-ray burst at z?≈?8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z?≈?7-8 galaxies suggest substantial star formation at z?>?9-10 (refs 12, 13). Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z?≈?10 galaxies in the heart of the reionization epoch, only 500?Myr after the Big Bang. Not only do we find one possible z?≈?10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (～10%) at this time than it is just ～200?Myr later at z?≈?8. This demonstrates how rapid galaxy build-up was at z?≈?10, as galaxies increased in both luminosity density and volume density from z?≈?10 to z?≈?8. The 100-200?Myr before z?≈?10 is clearly a crucial phase in the assembly of the earliest galaxies.     

The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field

The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850?micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF?850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF?850.1, from a millimetre-wave molecular line scan. This places HDF?850.1 in a galaxy overdensity at z?≈?5.2, corresponding to a cosmic age of only 1.1?billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3?×?10(11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.     

The unusual γ-ray burst GRB 101225A from a helium star/neutron star merger at redshift 0.33

Long γ-ray bursts (GRBs) are the most dramatic examples of massive stellar deaths, often associated with supernovae. They release ultra-relativistic jets, which produce non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the unusual GRB 101225A. Its γ-ray emission was exceptionally long-lived and was followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling black body, after which an additional component, consistent with a faint supernova, emerged. We estimate its redshift to be z = 0.33 by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a merger of a helium star with a neutron star that underwent a common envelope phase, expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which became thermalized by interacting with the dense, previously ejected material, thus creating the observed black body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy.     

A lower limit of Δz > 0.06 for the duration of the reionization epoch

Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies. The observations are challenging, though, because of the low expected signal strength (～10?mK), and contamination by strong (>100?K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources. If reionization happened rapidly, there should be a characteristic signature visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200?MHz, corresponding to the redshift range 6?相似文献   

Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 Å

Photosystem II is the site of photosynthetic water oxidation and contains 20 subunits with a total molecular mass of 350 kDa. The structure of photosystem II has been reported at resolutions from 3.8 to 2.9 ?. These resolutions have provided much information on the arrangement of protein subunits and cofactors but are insufficient to reveal the detailed structure of the catalytic centre of water splitting. Here we report the crystal structure of photosystem II at a resolution of 1.9 ?. From our electron density map, we located all of the metal atoms of the Mn(4)CaO(5) cluster, together with all of their ligands. We found that five oxygen atoms served as oxo bridges linking the five metal atoms, and that four water molecules were bound to the Mn(4)CaO(5) cluster; some of them may therefore serve as substrates for dioxygen formation. We identified more than 1,300 water molecules in each photosystem II monomer. Some of them formed extensive hydrogen-bonding networks that may serve as channels for protons, water or oxygen molecules. The determination of the high-resolution structure of photosystem II will allow us to analyse and understand its functions in great detail.     

A note on a conjecture of Graffiti

In this paper,we will give a very simpleproof of a conjecture of Graffiti. （WOW Conjecture 584） ：Let T be a tree of order n with independence number a , thenA λ1≤ 2 ＋ a , where A t is the Laplacian spectralradius. （ Xiao - dong Zhang , On the two conjectures of Graffiti, Linear Algebra and its Applications , described all extremal treesthat attain the maximal Laplacian spectral radius and used theresults to show conjectures.     

A Note on a Result of Pesin

Ｆｏｒｓｔｕｄｙｉｎｇｔｈｅｄｉｍｅｎｓｉｏｎｔｈｅｏｒｙｏｆｄｙｎａｍｉｃａｌｓｙｓｔｅｍ ,ＰｅｓｉｎｉｎｔｒｏｄｕｃｅｄＣａｒａｔｈ啨ｏｄｏｒｙｓｔｒｕｃｔｕｒｅ(Ｃ ｓｔｒｕｃｔｕｒｅ)ｗｈｉｃｈｌｅａｄｓｔｏｔｈｅｇｅｎｅｒａｌｉｚａｔｉｏｎｓｏｆｂｏｔｈｃｌａｓｓｉｃａｌｄｉｍｅｎｓｉｏｎｓａｎｄｔｏｐｏｌｏｇｉｃａｌｐｒｅｓｓｕｒｅｓ;ＨｅｃｏｎｓｉｄｅｒｅｄｔｗｏｔｙｐｉｃａｌＣ ｓｔｒｕｃｔｕｒｅｓｗｈｉｃｈｃｏｎｎｅｃｔｓｒｅｓｐｅｃｔｉｖｅｌｙｔｈｅｏｐｅｎｃｏｖｅｒｉｎｇａｎｄ…     

A Biography of Katherine Mansfield——A Writer,a Woman,a Vagrant,a Marvel

Would you not like to try all sorts of lives——one is so very small——but that is the satisfaction of writing——one can impersonate so many people.I’m a writer first and a woman after.It’s a terrible thing to be alone——yes it is——it is——but don’t lower your mask until you have another mask prepared beneath——as terri-ble as you like——but a mask.     

关于二阶复微分方程f″(z)+A(z)f(z)=0解的非实零点的研究

考虑二阶复微分方程f″+A(z)f=0解的非实零点的收敛指数与解的增长级之间的关系,其中A(z)是多项式,给出方程非零解的非实零点序列的收敛指数等于增长级的一个充分条件.     

Discovery of a Pliocene stone tool at Yuxian, Hebei Province

The stone tool discovered at Danangou valley of Dongyaozitou village, Yuxian, is the earliest stone tool, the specimen is powerful evidence about the origin of the human culture and the historical age from the ancient ape to the human being. According to the comprehensive studies about the strata, the age was considered to be of Pliocene (about 3 million years) and therefore, the discovery possessed great scientific and theoretical significance.     

Fractal Characteristics of Tin Iodide Aggregates Deposited at a Gas-solid Interface

ＦｒａｃｔａｌＣｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆＴｉｎＩｏｄｉｄｅＡｇｇｒｅｇａｔｅｓＤｅｐｏｓｉｔｅｄａｔａＧａｓ┐ｓｏｌｉｄＩｎｔｅｒｆａｃｅ＊ＺｈａｎｇＪｉｚｈｏｎｇ（张济忠）１，２，ＹａｎｇＸｉａｏｄｏｎｇ（杨晓东）１，ＬｉＨｅｎｇｄｅ（李恒...     

A Kinetic Model of Chromium in a Flame

Chromium has been identified as a carcinogenic metal.Incineration is the useful method for disposal of toxic chromium hazard waste and a chromium kinetic model in a flame is very important to study chromium oxidation.Chromium chemical kinetics over a range of temperatures of a hydrogen/air flame is proposed.Nine chromium compounds and fifty-eight reversible chemical reactions were considered The forward reaction rates are calculated based on the molecular collision approach for unknown ones and Arrhenius's Law for known ones.The backward reaction rates were calculated according to forward reaction rates, the equilibrium constants and chemical thermodynamics.It is verified by several equilibrium cases and is tested by a hydrogen/air diffusion flame.The results show that the kinetic model could be used in cases in which the chromium kinetics play an important role in a flame     

Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000℃

The oxidation behavior of a nickel-based superalloy at 1000°C in air was investigated through X-ray diffraction, scanning electron microscopy, andenergy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr2O3, (TiO2 + MnCr2O4)) and internal oxides (Al2O3,TiN), were formed on the surface or sub-surface of the substrate at 1000°C in experimental still air. The oxidation re-sistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr2O3 scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO2 rutile and MnCr2O4 spinel, and the growth of TiO2particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation oc-curred beneath the external oxide scale, consuming Al and Ti of the strength phaseγ′ (Ni3(Al,Ti)) and thereby severely deteriorating the sur-face mechanical properties. The depth of the internal oxidation region was approximately 35μm after exposure to experimental air at 1000°C for 80 h.     

Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000℃

The oxidation behavior of a nickel-based superalloy at 1000℃ in air was investigated through X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr₂O₃, (TiO₂ + MnCr₂O₄)) and internal oxides (Al₂O₃,TiN), were formed on the surface or sub-surface of the substrate at 1000℃ in experimental still air. The oxidation resistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr₂O₃ scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO₂ rutile and MnCr₂O₄ spinel, and the growth of TiO₂ particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation occurred beneath the external oxide scale, consuming Al and Ti of the strength phase γ' (Ni₃(Al,Ti)) and thereby severely deteriorating the surface mechanical properties. The depth of the internal oxidation region was approximately 35 μm after exposure to experimental air at 1000℃ for 80 h.     

A study of the optimal solution of a macroeconomics model

Ｔｈｅｉｓｓｕｅｏｆｏｐｔｉｍａｌｅｃｏｎｏｍｉｃｇｒｏｗｔｈｉｓｔｈｅｐｒｏｂｌｅｍｏｆｏｐｔｉｍａｌｒａｔｉｏｉｎａｃｃｕｍｕｌａｔｉｏｎａｎｄｃｏｎｓｕｍｐｔｉｏｎ．Ｉｆｔｈｅｐｒｅｓｅｎｔｃｏｎｓｕｍｐｔｉｏｎｉｓｔｏｏｈｉｇｈ，ｔｈｅａｃｃｕｍｕｌａｔｉｏｎｗｉｌｌｂｅｌｏｗａｎｄｔｈａｔｗｉｌｌｅｆｆｅｃｔｔｈｅｒａｐｉｄｉｎｃｒｅａｓｅｏｆｆｕｔｕｒｅｃｏｎｓｕｍｐｔｉｏｎ．Ｏｎｔｈｅｏｔｈｅｒｈａｎｄ，ｉｆｔｈｅｐｒｅｓｅｎｔａｃｃｕｍｕｌａｔｉｏｎｉｓｔｏｏｈｉｇｈ，ｔｈｅｐ…     

Three-dimensional Numerical Prediction of the Flow and Temperature Field at the Surface of a PDC Bit

Ｔｈｒｅｅ┐ｄｉｍｅｎｓｉｏｎａｌＮｕｍｅｒｉｃａｌＰｒｅｄｉｃｔｉｏｎｏｆｔｈｅＦｌｏｗａｎｄＴｅｍｐｅｒａｔｕｒｅＦｉｅｌｄａｔｔｈｅＳｕｒｆａｃｅｏｆａＰＤＣＢｉｔＣｕｉＧｕｉｘｉａｎｇ（崔桂香），ＸｕＷｅｉｒａｎ（徐巍然），ＺｈａｎｇＺｈａｏ...