arXiv subjects

Hui Li

Publications and source records attributed to Hui Li.

At least 937 records · Page 52Linked to original sources

arXiv2013

Present Y chromosomes support the Persian ancestry of Sayyid Ajjal Shams al-Din Omar and Eminent Navigator Zheng He

Sayyid Ajjal is the ancestor of many Muslims in areas all across China. And one of his descendants is the famous Navigator of Ming Dynasty, Zheng He, who led the largest armada in the world of 15th century. The origin of Sayyid Ajjal's family remains unclear although many studies have been done on this topic of Muslim history. In this paper, we studied the Y chromosomes of his present descendants, and found they all have haplogroup L1a-M76, proving a southern Persian origin.

q-bio.PE↗

arXiv2013

Y Chromosomes of 40% Chinese Are Descendants of Three Neolithic Super-grandfathers

Demographic change of human populations is one of the central questions for delving into the past of human beings. To identify major population expansions related to male lineages, we sequenced 78 East Asian Y chromosomes at 3.9 Mbp of the non-recombining region (NRY), discovered >4,000 new SNPs, and identified many new clades. The relative divergence dates can be estimated much more precisely using molecular clock. We found that all the Paleolithic divergences were binary; however, three strong star-like Neolithic expansions at ~6 kya (thousand years ago) (assuming a constant substitution rate of 1e-9/bp/year) indicates that ~40% of modern Chinese are patrilineal descendants of only three super-grandfathers at that time. This observation suggests that the main patrilineal expansion in China occurred in the Neolithic Era and might be related to the development of agriculture.

q-bio.PE↗

arXiv2013

Observation of Dirac cone warping and chirality effects in silicene

We performed low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) studies on the electronic properties of (R3xR3)R30° phase of silicene on Ag(111) surface. We found the existence of Dirac Fermion chirality through the observation of -1.5 and -1.0 power law decay of quasiparticle interference (QPI) patterns. Moreover, in contrast to the trigonal warping of Dirac cone in graphene, we found that the Dirac cone of silicene is hexagonally warped, which is further confirmed by density functional calculations and explained by the unique superstructure of silicene. Our results demonstrate that the (R3xR3)R30° phase is an ideal system to investigate the unique Dirac Fermion properties of silicene.

cond-mat.mes-hall↗

arXiv2013

Diffraction, Refraction, and Reflection of An Extreme-Ultraviolet Wave Observed during Its Interactions with Remote Active Regions

We present observations of the diffraction, refraction, and reflection of a global extreme-ultraviolet (EUV) wave propagating in the solar corona. These intriguing phenomena are observed when the wave interacts with two remote active regions, and they together exhibit the wave property of this EUV wave. When the wave approached AR11465, it became weaker and finally disappeared in the active region, but a few minutes latter a new wavefront appeared behind the active region, and it was not concentric with the incoming wave. In addition, a reflected wave was also observed simultaneously on the wave incoming side. When the wave approached AR11459, it transmitted through the active region directly and without reflection. The formation of the new wavefront and the transmission could be explained with diffraction and refraction effects, respectively. We propose that the different behaviors observed during the interactions may caused by different speed gradients at the boundaries of the two active regions. For the origin of the EUV wave, we find that it formed ahead of a group of expanding loops a few minutes after the start of the loops' expansion, which represents the initiation of the associated coronal mass ejection (CME). Based on these results, we conclude that the EUV wave should be a nonlinear magnetosonic wave or shock driven by the associated CME, which propagated faster than the ambient fast-mode speed and gradually slowed down to an ordinary linear wave. Our observations support the hybrid model that includes both fast wave and slow non-wave components.

astro-ph.SR↗

arXiv2013

Transition between mechanisms of laser-induced field-free molecular orientation

The transition between two distinct mechanisms for the laser-induced field-free orientation of CO molecules is observed via measurements of orientation revival times and subsequent comparison to theoretical calculations. In the first mechanism, which we find responsible for the orientation of CO up to peak intensities of 8 x 10^13 W/cm^2, the molecules are impulsively oriented through the hyperpolarizability interaction. At higher intensities, asymmetric depletion through orientation-selective ionization is the dominant orienting mechanism. In addition to the clear identification of the two regimes of orientation, we propose that careful measurements of the onset of the orientation depletion mechanism as a function of the laser intensity will provide a relatively simple route to calibrate absolute rates of non-perturbative strong-field molecular ionization.

physics.chem-ph↗

arXiv2013

Ideal Desalination through Graphyne-4 Membrane: Nanopores for Quantized Water Transport

Graphyne-4 sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. Extensive molecular dynamics simulations on pore-size effects suggest that graphyne-4, with 4 acetylene bonds between two adjacent phenyl rings, has the best performance with 100% salt rejection and an unprecedented water permeability, to our knowledge, of ~13L/cm2/day/MPa, about 10 times higher than the state-of-the-art nanoporous graphene reported previously (Nano Lett.s 2012, 12, 3602-3608). In addition, the membrane entails very low energy consumption for producing 1m3 of fresh water, i.e., 3.6e-3 kWh/m3, three orders of magnitude less than the prevailing commercial membranes based on reverse osmosis. Water flow rate across the graphyne-4 sheet exhibits intriguing nonlinear dependence on the pore size owing to the quantized nature of water flow at the nanoscale. Such novel transport behavior has important implications to the design of highly effective and efficient desalination membranes.

cond-mat.mtrl-sci↗

arXiv2013

Certain circle actions on Kaehler manifolds

Let the circle act holomorphically on a compact Kähler manifold $M$ of complex dimension $n$ with moment map $ϕ\colon M\to\R$. Assume the critical set of $ϕ$ consists of 3 connected components, the extrema being isolated points. We show that $M$ is equivariantly biholomorphic to $\CP^n$, where $n\geq 2$, or to $\Tilde G_2(\R^{n+2})$, the Grassmannian of oriented 2-planes in $\R^{n+2}$, where $n\geq 3$, with a standard circle action; we also show that $M$ is equivariantly symplectomorphic to $\CP^n$, where $n\geq 2$, or to $\Tilde G_2(\R^{n+2})$, where $n\geq 3$, with a standard circle action.

math.SG↗

arXiv2013

Supermassive Seeds for Supermassive Black Holes

Recent observations of quasars powered by supermassive black holes (SMBHs) out to z > 7 constrain both the initial seed masses and the growth of the most massive black holes (BHs) in the early universe. Here we elucidate the implications of the radiative feedback from early generations of stars and from BH accretion for popular models for the formation and growth of seed BHs. We show that by properly accounting for (1) the limited role of mergers in growing seed BHs as inferred from cosmological simulations of early star formation and radiative feedback, (2) the sub-Eddington accretion rates of BHs expected at the earliest times, and (3) the large radiative efficiencies (e_rad) of the most massive BHs inferred from observations of active galactic nuclei at high redshift (e_rad > 0.1), we are led to the conclusion that the initial BH seeds may have been as massive as > 10^5 M_Sun. This presents a strong challenge to the Population III seed model, which calls for seed masses of ~ 100 M_Sun and, even with constant Eddington-limited accretion, requires e_rad < 0.09 to explain the highest-z SMBHs in today's standard LambdaCDM cosmological model. It is, however, consistent with the prediction of the direct collapse scenario of SMBH seed formation, in which a supermassive primordial star forms in a region of the universe with a high molecule-dissociating background radiation field, and collapses directly into a 10^4--10^6 M_Sun seed BH. These results corroborate recent cosmological simulations and observational campaigns which suggest that these massive BHs were the seeds of a large fraction of the SMBHs residing in the centers of galaxies today.

astro-ph.CO↗

arXiv2013

Molecular Environments of SNRs

There are about 70 Galactic supernova remnants (SNRs) that are now confirmed or suggested to be in physical contact with molecular clouds (MCs) with six kinds of evidence of multiwavelength observations. Recent detailed CO-line spectroscopic mappings of a series of SNRs reveal them to be in cavities of molecular gas, implying the roles the progenitors may have played. We predict a linear correlation between the wind bubble sizes of main-sequence OB stars in a molecular environment and the stellar masses and discuss its implication for supernova progenitors. The molecular environments of SNRs can serve as a good probe for the gamma-rays arising from the hadronic interaction of the accelerated protons, and this paper also discusses the gamma-ray emission from MCs illuminated by diffusive protons that escape from SNR shocks.

astro-ph.GA↗

arXiv2013

Quantifying entanglement of arbitrary-dimensional multipartite pure states in terms of the singular values of coefficient matrices

The entanglement quantification and classification of multipartite quantum states are two important research fields in quantum information. In this work, we study the entanglement of arbitrary-dimensional multipartite pure states by looking at the averaged partial entropies of various bipartite partitions of the system, namely, the so-called Manhattan distance ($l_1$ norm) of averaged partial entropies (MAPE), and it is proved to be an entanglement measure for pure states. We connected the MAPE with the coefficient matrices, which are important tools in entanglement classification and reexpressed the MAPE for arbitrary-dimensional multipartite pure states by the nonzero singular values of the coefficient matrices. The entanglement properties of the $n$-qubit Dicke states, arbitrary-dimensional Greenberger-Horne-Zeilinger states, and $D_3^n$ states are investigated in terms of the MAPE, and the relation between the rank of the coefficient matrix and the degree of entanglement is demonstrated for symmetric states by two examples.

quant-ph↗

arXiv2013

Thermodynamics of the apparent horizon in massive cosmology

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive cosmological model proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation $δQ=T dS$, the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit $H_c\rightarrow 0$ which recovers the Minkowski reference metric solution in the flat case, the generalized second law of thermodynamics holds if $α_3+4α_4<0$. Apart from that, even for the simplest model of dRGT massive cosmology with $α_3=α_4=0$, the generalized second law of thermodynamics could be violated.

gr-qc↗

arXiv2013

Revisit the carpet cloak from optical conformal mapping

The original carpet cloak [Phys. Rev. Lett. 101, 203901 (2008)] was designed by a numerical method, the quasi-conformal mapping. Therefore its refractive index profile was obtained numerically. In this letter, we propose a new carpet cloak based on the optical conformal mapping, with an analytical form of a refractive index profile, thereby facilitating future experimental designs.

physics.optics↗

arXiv2013

Constraints on planet formation via gravitational instability across cosmic time

We estimate the maximum temperature at which planets can form via gravitational instability (GI) in the outskirts of early circumstellar disks. We show that due to the temperature floor set by the cosmic microwave background, there is a maximum distance from their host stars beyond which gas giants cannot form via GI, which decreases with their present-day age. Furthermore, we show that planet formation via GI is not possible at metallicities < 10^-4 Z_Sun, due to the reduced cooling efficiency of low-metallicity gas. This critical metallicity for planet formation via GI implies a minimum distance from their host stars of ~ 6 AU within which planets cannot form via GI; at higher metallicity, this minimum distance can be significantly greater, out to several tens of AU. We show that these maximum and minimum distances significantly constrain the number of observed planets to date that are likely to have formed via GI at their present locations. That said, the critical metallicity we find for GI is well below that for core accretion to operate; thus, the first planets may have formed via GI, although only within a narrow region of their host circumstellar disks.

astro-ph.EP↗

arXiv2013

MHD Turbulence and Cosmic Ray Reacceleration in Galaxy Clusters

Cosmological MHD simulations of galaxy cluster formation show a significant amplification of seed magnetic fields. We developed a novel method to decompose cluster magnetized turbulence into modes and showed that the fraction of the fast mode is fairly large, around 1/4 in terms of energy. This is larger than that was estimated before, which implies that cluster turbulence interacts with cosmic rays rather efficiently. We propose a framework to deal with electron and proton reacceleration in galaxy clusters that includes feedback on turbulence. In particular, we establish a new upper limit on proton and electron fluxes based on turbulence intensity. These findings, along with detailed modeling of reacceleration, will help to reconcile the observed giant radio haloes and the unobserved diffuse gamma-ray emission from these clusters.

astro-ph.GA↗

arXiv2012

Growth and band alignment of Bi2Se3 topological insulator on H-terminated Si(111) van der Waals surface

The van der Waals epitaxy of single crystalline Bi2Se3 film was achieved on hydrogen passivated Si(111) (H:Si) substrate by physical vapor deposition. Valence band structures of Bi2Se3/H:Si heterojunction were investigated by X-ray Photoemission Spectroscopy and Ultraviolet Photoemission Spectroscopy. The measured Schottky barrier height at the Bi2Se3-H:Si interface was 0.31 eV. The findings pave the way for economically preparing heterojunctions and multilayers of layered compound families of topological insulators.

cond-mat.mtrl-sci↗

arXiv2012

The GenoChip: A New Tool for Genetic Anthropology

The Genographic Project is an international effort using genetic data to chart human migratory history. The project is non-profit and non-medical, and through its Legacy Fund supports locally led efforts to preserve indigenous and traditional cultures. In its second phase, the project is focusing on markers from across the entire genome to obtain a more complete understanding of human genetic variation. Although many commercial arrays exist for genome-wide SNP genotyping, they were designed for medical genetic studies and contain medically related markers that are not appropriate for global population genetic studies. GenoChip, the Genographic Project's new genotyping array, was designed to resolve these issues and enable higher-resolution research into outstanding questions in genetic anthropology. We developed novel methods to identify AIMs and genomic regions that may be enriched with alleles shared with ancestral hominins. Overall, we collected and ascertained AIMs from over 450 populations. Containing an unprecedented number of Y-chromosomal and mtDNA SNPs and over 130,000 SNPs from the autosomes and X-chromosome, the chip was carefully vetted to avoid inclusion of medically relevant markers. The GenoChip results were successfully validated. To demonstrate its capabilities, we compared the FST distributions of GenoChip SNPs to those of two commercial arrays for three continental populations. While all arrays yielded similarly shaped (inverse J) FST distributions, the GenoChip autosomal and X-chromosomal distributions had the highest mean FST, attesting to its ability to discern subpopulations. The GenoChip is a dedicated genotyping platform for genetic anthropology and promises to be the most powerful tool available for assessing population structure and migration history.

q-bio.PE↗

arXiv2012

Spontaneous Symmetry Breaking and Dynamic Phase Transition in Monolayer Silicene

The (r3xr3)R30° honeycomb of silicene monolayer on Ag(111) was found to undergo a phase transition to two types of mirror-symmetric boundary-separated rhombic phases at temperatures below 40 K by scanning tunneling microscopy. The first-principles calculations reveal that weak interactions between silicene and Ag(111) drive the spontaneous ultra buckling in the monolayer silicene, forming two energy-degenerate and mirror-symmetric (r3xr3)R30° rhombic phases, in which the linear band dispersion near Dirac point (DP) and a significant gap opening (150 meV) at DP were induced. The low transition barrier between these two phases enables them interchangeable through dynamic flip-flop motion, resulting in the (r3xr3)R30° honeycomb structure observed at high temperature.

cond-mat.mes-hall↗

arXiv2012

Generalized Semi-Holographic Universe

We study the semi-holographic idea in context of decaying dark components. The energy flow between dark energy and the compensating dark matter is thermodynamically generalized to involve a particle number variable dark component with non-zero chemical potential. It's found that, unlike the original semi-holographic model, no cosmological constant is needed for a dynamical evolution of the universe. A transient phantom phase appears while a non-trivial dark energy-dark matter scaling solution keeps at late time, which evades the big-rip and helps to resolve the coincidence problem. For reasonable parameters, the deceleration parameter is well consistent with current observations. The original semi-holographic model is extended and it also suggests that the concordance model may be reconstructed from the semi-holographic idea.

astro-ph.CO↗