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The Ganjia Basin in Xiahe County, Gansu Province, China, is located on the northeastern edge of the Tibetan Plateau. The area lies in the transitional zone between the Plateau ethnic groups dominated by ancestral Tibetans, and the Central Plains dynasties dominated by ancestral Han in history. The Ganjia Basin is therefore well suited to studying the history of the intermixing of the Han and Tibetan peoples. In this study, we collected samples of organic materials from two ancient cities, Bajiaocheng (BJC) and Sirougucheng (SRGC), in the Ganjia Basin, which were used for radiocarbon dating. Our aims were to determine the construction times and function of the cities, based on the radiocarbon ages, Bayesian age modeling, and the analysis of relevant historical records. The results are used to discuss the role of the Ganjia Basin in the conflicts between and the integration of the two ethnic groups during the historical period. We conclude that BJC was established during 663–732 CE (Common Era); its early occupation history can be divided into an initial establishment phase (670–780 CE) and a phase of regeneration (880–1030 CE). SRGC was probably built at the time of the transition between the Song and Yuan dynasties (∼1271 CE). Combining the dating results with an analysis of the architectural styles and historical records, we conclude that BJC was originally built by the Tubo Kingdom as a military stronghold, and its major functions were military, economic and religious, and to support the major eastward expansion of the Tubo. SRGC was most likely a temple-focused city intended to promote Tibetan Buddhism which was a major political and religious leadership for the Tibetans at that time, reflecting changes in the status of different religions in the Ganjia Basin. In addition, the intermixing and blending of the Han and Tibetan groups, reflected by the human activities in the Ganjia Basin, was an important demographic and cultural foundation for the formation of the culturally-diverse but spiritually-united modern Chinese people.

The natural environment provides material essentials for human survival and development. The characteristics, processes, regional differentiation and forcing mechanisms of the elements of the natural environment (e.g. geomorphology, climate, hydrology, soil, etc.) are the main objects of research in physical geography. China has a complex natural environment and huge regional differentiation and therefore it provides outstanding reserach opportunities in physical geography. This review summarizes the most important developments and the main contributions of research in the physical geography and human living environment in China during the past 70 years. The major topics addressed are the uplift of the Tibetan Plateau and the evolution of its cryosphere, the development of fluvial systems, the acidification of the vast arid region of the Asian interior, variations in the monsoon and westerly climate systems on multiple timescales, the development of lakes and wetlands, the watershed system model, soil erosion, past human-environment interactions, biogeography, and physical geographic zonality. After briefly introducing international research developments, we review the history of research in physical geography in China, focusing on the major achievements and major academic debates, and finally we summarize the status of current research and the future prospects. We propose that in the context of the national demand for the construction of an ecological civilization, we should make full use of the research findings of physical geography, and determine the patterns and mechanisms of natural environmental processes in order to continue to promote the continued contribution of physical geography to national development strategies, and to further contribute to the theory of physical geography from a global perspective.

All around the world, ancient legends exist about the Great Flood, and the influence of the Great Flood in human evolutionary history is a hotly debated topic. In China, the legend of the prehistoric Great Flood and Yu the Great’s flood control has a long history and is considered to be closely linked to the establishment of the Xia Dynasty. However, there is a lack of solid scientific evidence. Against this issue, some scholars have proposed that an earthquake around 1920 BCE in the Guanting Basin along the upper reaches of the Yellow River led to the creation of a lake by damming in the Jishi Gorge and that the outburst of water from that lake led to the massive flood in the Yellow River region. These studies provided new scientific evidence for the Chinese legend. In this paper, we date skeletal samples embedded in earthquake sand blasting from the Lajia site, analyze remains from natural disasters (such as earthquakes and floods) and also archaeological remains. In addition, we compared the skeletal samples dating with that of sediments from the dammed-up lake. Our results are inconsistent with those of previous scholars. The earthquake at the Lajia site occurred no earlier than 1800 BCE, and the dammed-up lake in Jishi Gorge had disappeared by 3600 BCE. Thus, the formation and outburst of the dammed lake, the sudden death of ancient humans at the Lajia site and the ancient earthquake were independent events occurring at different times. In addition, the massive flood in the upper reaches of the Yellow River did not actually happen. Thus, we argue against and invalidate the hypothesis that the massive flood was related to Yu the Great’s flood control and the establishment of the Xia Dynasty.

Prehistoric human history on the Tibetan Plateau is a hotly debated topic. Archaeological research on the plateau during the past few decades has enormously improved our understanding of the topic and makes it possible for us to consider the processes and mechanisms of prehistoric human migration to the region. By reviewing the published archaeological research on the Tibetan Plateau, we propose that the first people on the plateau initially spread into the He-Huang region from the Chinese Loess Plateau, and then moved to the low elevation Northeastern Tibetan Plateau and perhaps subsequently to the entire plateau. This process consisted of four stages. (1) During the climatic amelioration of the Last Deglacial period (15–11.6 ka BP), Upper Paleolithic hunter-gatherers with a developed microlithic technology first spread into the Northeastern Tibetan Plateau. (2) In the early-mid Holocene (11.6–6 ka BP), Epipaleolithic microlithic hunter-gatherers were widely distributed on the northeastern plateau and spread southwards to the interior plateau, possibly with millet agriculture developed in the neighboring low elevation regions. (3) In the mid-late Holocene (6–4 ka BP), Neolithic millet farmers spread into low elevation river valleys in the northeastern and southeastern plateau areas. (4) In the late Holocene (4–2.3 ka BP), Bronze Age barley and wheat farmers further settled on the high elevation regions of the Tibetan Plateau, especially after 3.6 ka BP. Finally, we suggest that all of the reported Paleolithic sites earlier than the LGM on the Tibetan Plateau need further examination.

Understanding the mechanism for the catalyzed cleavage of the β-O-4 ether linkage in lignin is crucial to developing efficient strategies for depolymerizing lignin. In this work, veratrylglycerol-β-guaiacyl ether (VG) was used as a lignin model compound in a theoretical investigation of the mechanism for the cleavage of the β-O-4 bond as catalyzed by the acidic ionic liquid (IL) 1-H-3-methylimidazolium chloride ([HMIM]Cl). The reaction was found to involve two processes-dehydration and hydrolysis-in which the cation functions as a Brønsted acid (donating a proton) and the anion acts as a nucleophile (promoting dehydration) or interacts with the substrate through hydrogen bonding, stabilizing the intermediate. These roles of the anion and cation of [HMIM]Cl explain why the [HMIM]Cl medium catalyzes the depolymerization of lignin. In addition, calculations predict that adding formaldehyde during the depolymerization of VG prevents the condensation of VG without significantly altering the mechanism of depolymerization, thus suggesting a method for potentially improving the efficiency of lignin depolymerization.

The excited states of polyatomic systems are rather complex, and often exhibit meta-stable dynamical behaviors. Static analysis of reaction pathway often fails to sufficiently characterize excited state motions due to their highly non-equilibrium nature. Here, we proposed a time series guided clustering algorithm to generate most relevant meta-stable patterns directly from ab initio dynamic trajectories. Based on the knowledge of these meta-stable patterns, we suggested an interpolation scheme with only a concrete and finite set of known patterns to accurately predict the ground and excited state properties of the entire dynamics trajectories, namely, the prediction with ensemble models (PEM). As illustrated with the example of sinapic acids, The PEM method does not require any training data beyond the clustering algorithm, and the estimation error for both ground and excited state is very close, which indicates one could predict the ground and excited state molecular properties with similar accuracy. These results may provide us some insights to construct molecular mechanism models with compatible energy terms as traditional force fields.

The accurate radiocarbon dating of loess-soil sequences plays an essential role in the reconstruction of the environmental and climatic changes in continental settings during the last glaciation and Holocene. However, our knowledge about the reliability of radiocarbon ages of various fractions of soil and loess samples is still insufficient. Here, we present our study results on radiocarbon ages based on bulk organic matter, humin fraction, and carbonate of samples collected from a loess-paleosol section in the western Chinese Loess Plateau. We compare these observations with the optically stimulated luminescence ages and charcoal radiocarbon ages to evaluate the reliability of these fractions. We observed that the radiocarbon ages of humin fraction are very close to those of charcoal and are consistent with the optically stimulated luminescence ages within the experimental errors. We observed a significant deviation in the radiocarbon ages of carbonate and bulk organic matter from those of charcoal and optically stimulated luminescence ages, likely due to the dilution of these fractions during the pedogenetic process. Our results reveal that, except for charcoal, the humin fraction may yield reliable C-14 ages for the Chinese loess-soil sequence.

The effective enrichment and identification of lowly concentrated polychlorinated biphenyls (PCBs) in the environment is attracting much research attention due to human health concerns raised from their emissions. Cyclodextrins (CDs) are known to be capable to form inclusion complexes with a variety of organic molecules. The purpose of this study is to provide theoretical evidences whether CDs can form energetically stable inclusion complexes with PCBs through a host–guest interaction, and if so, whether infrared and Raman techniques are suitable for the detection of CD-modified PCBs. Focusing on a representative PCB molecule, 3,3′,4,4′,5-pentachlorobiphenyl (PCB126), we studied its molecular inclusion by β-CD (BCD) by performing molecular dynamics simulations and density functional theory calculations. Calculated results show that PCB126 and BCD preferentially form the stable 1:1 inclusion complex. The calculated IR spectra of the 1:1 inclusion complexes mainly present the spectra features of BCD and give only a slight indication for bands of the guest molecule. In contrast, the characteristic vibration modes of the guest molecule are remarkably prominent in the Raman spectra of the inclusion complexes. Based on the present results, we propose that BCD can potentially serve as a candidate for including PCB126 to form the stable 1:1 host–guest complex, and that Raman spectroscopy technology is expected to be suitable for the identification of the CD-modified PCBs, whereas IR spectroscopy is not feasible for such an application.

While N,N'-dialkylimidazolium ionic liquids (ILs) have been well-established as effective solvents for dissolution and processing of cellulose, the detailed mechanism at the molecular level still remains unclear. In this work, we present a combined quantum chemistry and molecular dynamics simulation study on how the ILs dissolve cellulose. On the basis of calculations on 1-butyl-3-methylimidazolium chloride, one of the most effective ILs dissolving cellulose, we further studied the molecular behavior of cellulose models (i.e. cellulose oligomers with degrees of polymerization n = 2, 4, and 6) in the IL, including the structural features and hydrogen bonding patterns. The collected data indicate that both chloride anions and imidazolium cations of the IL interact with the oligomer via hydrogen bonds. However, the anions occupy the first coordination shell of the oligomer, and the strength and number of hydrogen bonds and the interaction energy between anions and the oligomer are much larger than those between cations and the oligomer. It is observed that the intramolecular hydrogen bond in the oligomer is broken under the combined effect of anions and cations. The present results emphasize that the chloride anions play a critically important role and the imidazolium cations also present a remarkable contribution in the cellulose dissolution. This point of view is different from previous one that only underlines the importance of the chloride anions in the cellulose dissolution. The present results improve our understanding for the cellulose dissolution in imidazolium chloride ILs.

The activities of neutral, anionic, and cationic Au(111), Au(100), and Au(310) surfaces, as well as an Au adatom on Au(111) surface towards NO adsorption have been studied by performing density functional theory calculations. It was found that the activity of gold increases as the coordination number of the gold atoms decreases, and that the cationic surfaces are generally more active than the neutral and anionic surfaces. The activity of Au surfaces towards NO adsorption is attributable to the presence of low coordinated gold atoms and the concentration of positive charges on the surface. The results may enrich the understanding of NO adsorption on Au surfaces.

To better understand the property of the binary systems composing of imidazolium salt, [emim](+)A- (A=Cl-, Br-, BF(4)-, and PF(6)-) and methanol, we have investigated in detail the interactions of methanol molecule with anions A-, cation [emim](+), and ion pair [emim](+)A- of several ionic liquids (ILs) based on 1-ethyl-3-methylimidazolium cation by performing density functional theory calculations. It is found that H-bonds are universally involved in these systems, which may play an important role for the miscibility of methanol with imidazolium-based ILs. The interaction mechanisms of methanol molecule with anion and cation are found to be different in nature: the former mainly involves LP(X)-[Formula: see text] interaction, while the latter relates with the decisive orbital overlap of the type of LP(O)-[Formula: see text]. Based on the present calculations, we have provided some reasonable interpretations for properties of the binary mixtures of ILs and alcohol and revealed valuable information for the interaction details between ILs and alcohols, which is expected to be useful for the design of more efficient ILs to form superior solvent system with alcohol.

The question whether Au can alloy with Pt at the nano-scale size is still controversial. By performing density functional theory calculations for several small Au/Pt bimetallic clusters Au(m)Pt(n) (m + n = 4-6, 13), we find that, in all the most stable geometries, Pt atoms prefer to assemble together to form the core while Au atoms like to surround the Pt atoms to form the shell, and that evenly mixed clusters are structurally unstable. The unique geometric characteristics can be explained by analyzing the different electronic properties of Pt-Pt, Au-Pt and Au-Au bonds, and is expected also to apply to larger Au/Pt bimetallic clusters.

This paper reports the recent excavation of Unit Dadiwan06 at the Dadiwan site in Qin’an County, Gansu. A 65 ka chronological framework is established for Dadiwan06 on the basis of absolute dating (AMS 14C and OSL), stratigraphy, climate change events and archaeology. Artifact distributions reveal patterns of human behavioral variation and adaptation over the past 60 ka, from primitive hunting and gathering to advanced hunting and gathering, to primitive Neolithic agriculture, and finally to advanced Neolithic agriculture.

Indolocarbazole derivatives have already been reported to be good organic semiconductor candidates. The knowledge of the relationship between the structure and packing of molecules in crystal is indispensable in design of high performance organic semiconductor materials. Two new indolocarbazole derivatives, 2,8-dibromo-5,11-di-[4-(isoindole-1,3-dione-2-yl)butyl]indolo[3,2-b]carbazole (I) and 2,8,6,12-tetrabromo-5,11-di-(4-chlorobutyl)indolo[3,2-b]carbazole (II) have been synthesized and the crystal structures have been studied. The dichloromethane solvate of (I), C42H32Br2N4O4 · 2CH2Cl2, is monoclinic, space groups P21/n. Unit cell parameters are a = 11.6847(2), b = 12.6942(2), c = 13.7899(2) A, β = 91.8220(10)°. Unlike other indolo[3,2-b]carbazole derivatives, there is no any π–π stacking between the indolocarbazole backbone of two adjacent molecules in the crystal. Since the isoindole-1,3-dione-2-yl is introduced in 5- and 11-positions in the molecule, the intermolecular short contacts mainly localize in between the pendant groups of the neighboring indolocarbazole molecules. The compound (II) is also monoclinic with P21/c space groups. Unit cell parameters are a = 4.6427(9), b = 11.425(2), c = 24.511(4) A, β = 93.47(1)°. In contrast with compound (I), the molecules of (II) possess strong face-to-face π–π stacking. The crystal structures were studied in detail. It is concluded that linear pedant groups benefit to co-facial π–π interaction. Additionally, the molecule electronic spectra were studied by quantum chemistry theoretical calculation.

A LD-pumped self-Q-switched 946 nm laser by using a co-doped Cr,Nd:YAG crystal as a gain medium as well as a saturable absorber is studied. The 946 nm self-Q-switched rate equations of co-doped crystal are solved numerically by Runge-Kutta method directly. The important parameters of lasers, such as average output power, threshold pump power, pulse width, pulses repetition rate, and optimal transmission of output coupler are obtained numerically. Experimentally, the maximum average output power up to 2.61 W, corresponding to a slope efficiency of 23.43%, was obtained in a simple and compact linear cavity. The optical-to-optical efficiency is 17.3% and the peak power is 7.57 kW with repetition rate of 23.78 kHz and pulse width of 14.5 ns. In the experiments, a high-quality fundamental transverse mode can be preserved in a large range of incident pump power. The numerical results of the 946 nm self-Q-switched Cr,Nd:YAG laser are in good agreement with the experimental results.

Amplified spontaneous emission (ASE) characteristics of a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) were significantly improved by assistant Forster energy transfer. The coguest-host system was composed of an electron transport organic molecule tris(8-hydroxyquinoline) aluminum (Alq3) as host and a green fluorescent dye (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one) (C545T) as assistant dopant codoped with the guest red dye DCJTB as emitter in a matrix of polystyrene (PS). It was found that the threshold and loss were greatly reduced to 0.007 mJ pulse-1 and 7 cm-1, and the gain was significantly enhanced to 52 cm-1 by doping of C545T. The improvement of ASE performance in Alq3:C545T:DCJTB film was attributed to the energy assistant effect of C545T, leading more exciton energy to transfer to DCJTB.

We analyze negative refraction in two-dimensional photonic crystals that are made from electro-optical active materials. Application of an electric field to the photonic crystal changes the dielectric constant of the material and consequently modifies the photonic band and dispersion properties. We have investigated focusing properties of the photonic crystal slab lens at different frequencies within the first two bands and under various magnitudes of electric field. The simulation results reveal that one can dynamically tune negative refraction by means of index-tunable photonic crystals.

Recent experimental studies on metal complexes of N-heterocyclic carbenes (NHCs) showed a few examples of the unique sequential activation of two C–H bonds of NHC N-methyl group on triruthenium carbonyl clusters. However, the corresponding theoretical calculations showed that the reactions are highly endergonic (>40 kcal/mol) and involve very high barriers (up to ~80 kcal/mol), failing to rationalize the experimental observations that the reactions were carried out under mild conditions (

By performing density functional theory (DFT) theory calculations, we studied the adsorption behaviors of the monomer and dimer of formic acid (HCOOH, FA) on the Pt(111) surface with and without the presence of water molecules. The monomer prefers to stand on the surface of Pt(111), and in the most stable adsorption configuration the carbonyl O of HCOOH binds to the atop site of a Pt atom and the hydroxyl H points asymmetrically to two neighboring Pt atoms. The dimer of HCOOH not only exists in the gas-phase but also on Pt(111) surface, and the eight-membered ring dimer is identified as the energetically most favorable dimeric structure of HCOOH both in gas-phase and on Pt(111) surface. With the presence of water molecules, both the monomer and dimer of HCOOH prefer to lie parallel to the surface so as to maximize the number of H-bonds to adjacent water molecules. These results indicate that water molecules significantly influence the initial adsorption manner of HCOOH and further its decomposition reactivity on Pt(111) surface. The present work shows the adsorption behavior of HCOOH dimer on Pt(111) for the first time and also gives several new adsorption configurations of the monomer that are not reported in literature. The theoretical results are expected to provide a valuable input to understand the reactivity of HCOOH on Pt(111).

To explore the novel application of boron nitride nanotubes (BNNTs), we investigated the interaction of pentachlorophenol (PCP) pollutant with the pristine and Fe doped (Fe-doped) (8, 0) single-walled BNNTs by performing density functional theory calculations. Compared with the weak physisorption on the pristine BNNT, PCP molecule presents strong chemisorption on the Fe-doped BNNT. The calculated data for the electronic properties indicate that doping Fe atom into the BNNT significantly improves the electronic transport property of BNNT, induces magnetism in the BNNT, and increases its adsorption sensitivity toward PCP molecule. It is suggested that doping BNNTs with Fe is an available strategy for improving the properties of BNNTs, and that Fe-doped BNNT would be a potential resource for adsorbing PCP pollutant in environments.