High Valley Research Articles

Regional Sustainable Strategy Based on the Coordination of Ecological Security and Economic Development in Yunnan Province, China

Coordination between ecological security and economic development is crucial to sustainable development, with a development strategy that should be adjusted according to the type of region. Yunnan Province, China, is a treasure trove of biodiversity but is economically lagging. Clarifying the relationship between ecological security and economic development can provide a reference for the sustainable development of similar biodiversity hotspots in the world. The landscape index method and index evaluation method were used to calculate the ecological safety index (ESI) and the economic development index (EDI), respectively, and the median value of the indices was used for the comprehensive zoning. The coupled coordination degree model (CCDM) was used to assess the coordination status of ecological safety and economic development in each zone. The results show that (1) Yunnan’s ecological security pattern is high in the west and low in the east, mainly influenced by topography, climate, and human activities; its economic development is resource-dependent and shows a multi-point dispersed pattern due to poor transportation; (2) Yunnan was partitioned into the Coordinated Development Zone (CDZ), the Ecological Risk Zone (ERZ), the Economic Poverty Zone (EPZ), and the Dual Pressure Zone (DPZ). Among them, CDZs (15%) are mostly areas with outstanding advantageous resources, mature characteristic industries, and relatively spatially dispersed. There are two types of ERZs (35%): one is an area where the intensity of human activities exceeds the ecological carrying capacity, mainly located in the eastern plateau; the other is an area with fragile ecological background conditions, located in high mountains and river valleys. EPZs (35%) are mainly lagging in socioeconomics of DPZ (15%) and the fragile ecological environment constrains each to form a negative cycle. (3) Of the regional coordination levels in Yunnan Province, 76% are moderately coordinated, and there is still space for development from the high-quality coordination level. The order of the average coordination degree of each partition is CDZ > ERZ > EPZ > DPZ. The poor basis for coordination and the single approach to coordination have led to ecological safety and economic development often being more difficult to achieve in areas with large mountainous areas similar to Yunnan. (4) Due to the necessity for biodiversity protection, Yunnan Province should choose the sustainable path of ecological priority and green development. Specifically, CDZ should play to industrial advantages and brand effects, and promote industrial integration and innovative industrial development paths. The keys to ERZ are industrial restructuring, industrial ecologization, and ecological environment restoration and protection. EPZ should improve transportation and other infrastructure and revitalize economic development under the premise of ecological priority. Finally, DPZ should emphasize human and load reduction, and moderate development.

Strain-Induced Medium-Temperature Thermoelectric Performance of Cu4TiSe4 : The Role of Four-Phonon Scattering

Motivated by the synthesized ${\mathrm{Cu}}_{4}{\mathrm{Ti}\mathrm{Se}}_{4}$ with ultralow room-temperature thermal conductivity [Angew. Chem., Int. Ed. 60, 9106 (2021)], we systematically investigate its thermoelectric (TE) properties via combining Boltzmann transport equations and first-principles calculations. The results show that the thermal conductivity of ${\mathrm{Cu}}_{4}{\mathrm{Ti}\mathrm{Se}}_{4}$ determined considering only three-phonon scattering is reduced by about 40% after including four-phonon scattering at room temperature, indicating the importance of four-phonon scattering in phonon transport. On the other hand, the coexistence of high dispersion and valley degeneracy at the top valence band in the electronic structure causes a high power factor. Consequently, the isotropic figure of merit (ZT) value of 1.5 at 500 K is captured in the p-type doped ${\mathrm{Cu}}_{4}{\mathrm{Ti}\mathrm{Se}}_{4}$. In addition, the value of ZT can be further enhanced to 2.2 by applying 2.25% triaxial tensile strain, which is ascribed to the remarkably enhanced four-phonon scattering processes induced by the tensile strain. Meanwhile, the significant suppression of thermal conductivity allows the optimal carrier concentration for the ZT peak to be reduced, which is of important practical significance for the experimental preparation of ${\mathrm{Cu}}_{4}{\mathrm{Ti}\mathrm{Se}}_{4}$-based TE devices. Our results pave a way for the design of adjustable medium-temperature TE devices.

Comparative analysis of estimation of slope-length gradient (LS) factor for entire Afghanistan

Slope length gradient (LS) is one of the crucial factors in the Universal Soil Loss Equations (USLE, RUSLE). This study aimed at estimating the slope-length and slope-steepness (LS) factor for the entire watersheds of Afghanistan by using three different methods, namely; (1) LS-TOOLMFD (Method 1); (2) The Method of Equations (Method 2); and (3) The approach of Moore and Burch (Method 3). The first method uses the digital elevation model (DEM) in the ASCII format, and the other two methods use the DEM in the spatial domain. The results show that the LS-factor of the study area ranges from 0.01 to 44.31, with a mean of 5.24 and standard deviation of 6.95, according to Method 1; 0.03 to 163.49, with a mean of 9.6 and standard deviation of 13.58, according to Method 2; and 0 to 3985, with a mean of 7.16 and standard deviation of 29.7, according to Method 3. The study reveals that Methods 1 and 2 are more appropriate than Method 3 because Method 3 yields high LS-factor values close to or at streamlines located near mountainous regions. The highest LS values are found to be in the northeast, north, and central regions of Afghanistan, which is consistent with the high mountains and deep valley geomorphology, indicating that these regions are particularly vulnerable to soil erosion by rainfall-runoff processes. The sediment delivery ratio (SDR) for the Upper-Helmand River Basin (Upper-HRB) is also estimated by the RUSLE, employing the LS factors produced by the three methods. The results revealed that the average annual soil loss is found to be, respectively, 9.3, 18.2, and 11.1 (ton/ha/year) by using the three methods, corresponding to SDR of 23.5%, 12.1%, and 19.9%. Abbreviations: ABD: Asian Development Bank; ASCII: American Standard Code for Information Interchange; Bsh: cold semiarid steppes; Bsk: cold semiarid steppes; Bwh: warm and cold deserts; Bwk: warm and cold deserts; CMS: Convention on Migratory Species; Csa: humid subtropical; Csb: Mediterranean; D: humid continental; DEM: Digital Elevation Model; ET: extreme tundra; GCS: Geographical Coordinate System; GIS: Geographic Information System; GUI: Graphically User Interface; Ha: Hectare; HMRB: Harirod-Murghab River Basin; HRB: Helmand River Basin; KRB: Kabul River Basin; LS: Slope–Length and Slope–Steepness; Masl: meters above sea level; MFD: Multiple-Flow Direction; NRB: Northern River Basin; PARB: Panj-Amu Darya River Basin; RUSLE: Revised Universal Soil Loss Equations; SDR: Sediment Delivery Ratio; SFD: Single–Flow Direction; SRTM: Shuttle Radar Topography Mission; SY: Sediment Yield; UCA: Unit Contributing Area; USGS: United States Geological-Survey; USLE: Universal Soil Loss Equations

Theoretical design of buckled honeycomb binary ZrX (X=S, Se, Te) monolayers and valley splitting of heterostructures constructed with MoTe2

Based on density functional theory, we design a new family of buckled honeycomb binary ZrX (X = S, Se, Te) monolayers. The feasibility of experimental synthesis can be seen from their negative binding energy and the absence of imaginary frequency in the phonon dispersion. It is found that the buckled honeycomb binary ZrX monolayers show magnetic character with moment range of 1.832–2.004 μB. The ZrTe monolayer is narrow band gap (0.251 eV) semiconductor. Furthermore, we demonstrate that a large valley splitting can be obtained in MoTe2 monolayer by magnetic proximity coupling to a ZrS or ZrSe magnetic monolayer. For the ZrS/MoTe2 (ZrSe/MoTe2) heterostructure, the electronic band of MoTe2 monolayer has achieved a high valley splitting of 66 (80) meV, which is equal to a Zeeman field of 76 (93) T. Our study paves the way to explore promising two-dimensional magnetic materials for practical applications in valleytronic devices.

Blueprint of a Scalable Spin Qubit Shuttle Device for Coherent Mid-Range Qubit Transfer in Disordered Si/SiGe/SiO2

Silicon spin qubits stand out due to their very long coherence times, compatibility with industrial fabrication, and prospect to integrate classical control electronics. To achieve a truly scalable architecture, a coherent mid-range link that moves the electrons between qubit registers has been suggested to solve the signal fan-out problem. Here, we present a blueprint of such a link of 10 μm length, called a spin qubit shuttle, which is based on connecting an array of gates into a small number of sets. To control these sets, only a few voltage control lines are needed and the number of these sets and thus the number of required control signals is independent of the length of this link. We discuss two different operation modes for the spin qubit shuttle: a qubit conveyor, i.e., a potential minimum that smoothly moves laterally, and a bucket brigade, in which the electron is transported through a series of tunnel-coupled quantum dots by adiabatic passage. We find the former approach more promising considering a realistic Si/SiGe device, including potential disorder from the charged defects at the Si/SiO2 layer, as well as typical charge noise. Focusing on the qubit transfer fidelity in the conveyor shuttling mode, we discuss in detail motional narrowing, the interplay between orbital and valley excitation and relaxation in the presence of g factors that depend on orbital and valley state of the electron, and effects from spin hotspots. We find that a transfer fidelity of 99.9% is feasible in Si/SiGe at a speed of approximately 10m/s, if the average valley splitting and its inhomogeneity stay within realistic bounds. Operation at low global magnetic field approximately equal to 20mT and material engineering towards high valley splitting is favorable for reaching high fidelities of transfer.12 MoreReceived 10 March 2022Revised 18 October 2022Accepted 15 February 2023DOI:https://doi.org/10.1103/PRXQuantum.4.020305Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum information with solid state qubitsQuantum transportSpin coherenceSpin relaxationSurface & interfacial phenomenaPhysical SystemsQuantum dotsSemiconductor compoundsCondensed Matter, Materials & Applied PhysicsQuantum Information

Special Characteristics and Stability Analysis of Bank Slope Deposits with Special Geotechnical Structures in High and Cold Valleys

Due to the special internal and external dynamic action of the Qinghai-Tibet Plateau, the high and cold valleys are typically characterized by high-steep terrain, dry and cold climate, lithologic diversity, complex geological structure, and frequent occurrence of earthquakes. In this study, the types of special geotechnical structures of bank slope deposits in high and cold valleys are summarized based on field investigation, field and laboratory tests, and numerical simulation. These special deposits include colluvial-deluvial deposits, terrace deposits, early debris flow deposits, and landslide deposits. The formation mechanism, physical and mechanical properties, and stability analysis of these deposits were studied. The results show that the formation mechanism of various deposits is different, which is closely related to the intense geological tectonic action, the weathering and unloading action intensified by freezing and thawing cycles, and the special rock and soil structure in the high and cold valleys. Different material compositions have obvious effects on the physical and mechanical properties of the deposits, thus affecting the stability and deformation characteristics of the deposits. Under natural and saturated conditions, the stability of different types of the deposits is different, which is mainly related to the special geotechnical structure of various deposits. Compared with that before the reservoir impoundment, the stability factor of various deposits after the reservoir impoundment is significantly reduced. The performances can be provided as a reference for evaluating the stability of bank slope deposits in high and cold valleys.

Occupation of highland Central Asia: New evidence from Kurteke rockshelter, Eastern Pamir

The highlands of Central Asia played a crucial role in cultural development across the later Holocene, serving to foster the diffusion of cultural elements by late prehistoric populations and to support the trans-Eurasian exchange routes of the historic Silk Road. However, the early chronology of human occupation in many areas of Inner Asia – particularly the high Pamir Mountains – remains poorly understood. Intensive archaeological study of this area by Soviet archaeologists first began between 1950 and 1970, at which time scholars theorized that the earliest human occupation in the high valleys dates to the Final Pleistocene. To explore early human history in this key region of cultural transmission, a joint expedition conducted new excavations at the archaeological site of Kurteke, confirming that there was human presence in the area as far back as 14 ka BP, and that it persisted discontinuously until the Bronze Age (ca. 4000BP). We applied a multidisciplinary archaeological and paleoenvironmental approach to investigate early human activity at the site, including lithic analysis, absolute dating, and zooarchaeological and archaeobotanical analyses.

Topography rules the ultra-mild wear regime under boundary lubricated gross-slip fretting corrosion

Fretting corrosion of biomedical taper junctions has raised concerns about adverse local tissue reactions. A low release of ions and other reaction products into the body is desirable, and this can be achieved by, e.g., optimizing the topography. Retrieval analysis has revealed that circumferential machining marks with high ridges and low valleys reduce the release of wear products. Thus, we hypothesized that a rougher titanium surface decreases metal release under gross-slip fretting because of a change in wear mechanisms. Fretting tests (polished CoCr29Mo6 alloy pins (Ra ≈ 0.006 μm) against fluted Ti6Al4V cylinders (Ra ≈ 5.6 μm)) were carried out. The worn surfaces were analyzed using SEM and LRS (Laser-Raman Spectroscopy) while ICP-MS of the lubricant (BCS) rendered the wear loss. Results were compared with the wear loss of identically polished CoCr29Mo6 pins rubbing against fine-machined Ti6Al4V cylinders (Ra ≈ 0.245 μm) reported earlier. The fluted topography led to microploughing and microcutting on both CoCr29Mo6 and Ti6Al4V surfaces, triggering tribocorrosion and mechanical mixing of tribomaterial containing Cr-, Mo-, and Ti-oxides and denatured/cleaved proteins. While friction was controlled by mechanical-dominated microploughing and microcutting the steady-state wear was characterized by chemical-dominated tribocorrosion. The total wear loss of the fluted system was half of the fine machined system, albeit the Co-side lost more. Despite the rougher topography the tribomaterial still acted as boundary lubricant and protected the surfaces.

Controllable valley magnetic response in phase-transformed tungsten diselenide

Achieving valley pseudospin with large polarization is crucial in the implementation of quantum information applications. Transition metal dichalcogenides (TMDC) with different phase structures provide an ideal platform for valley modulation. The valley splitting has been achieved in hybrid phase WSe2, while its valley polarization remains unstudied. Magnetic field controllable valley polarization is explored in WSe2 with coexistence of H and T phases by an all-optical route. A record high valley polarization of 58.3% is acquired with a 19.9% T phase concentration under a 4-T magnetic field and nonresonant excitation. The enhanced valley polarization is dependent on the phase component and shows various increasing slopes, owing to the synergy between the T phase WSe2 and the magnetic field. The magnetic field controlled local magnetic momentums are revealed as the mechanism for the large valley polarization in H / T-WSe2. This speculation is also verified by theoretical simulations of the nonequilibrium spin density. These results display a considerable valley magnetic response in phase-engineered TMDC and provide a large-scale scheme for valley polarization applications.

P-wave velocity structure beneath reservoirs and surrounding areas in the lower Jinsha River

The lower reaches of the Jinsha River are rich in hydropower resources because of the high mountains, deep valleys, and swift currents in this area. This region also features complex tectonic structures and frequent earthquakes. After the impoundment of the reservoirs, seismic activity increased significantly. Therefore, it is necessary to study the P-wave velocity structure and earthquake locations in the lower reaches of the Jinsha River and surrounds, thus providing seismological support for subsequent earthquake prevention and disaster reduction work in reservoir areas. In this study, we selected the data of 7,670 seismic events recorded by the seismic networks in Sichuan, Yunnan, and Chongqing and the temporary seismic arrays deployed nearby. We then applied the double-difference tomography method to this data, to obtain the P-wave velocity structure and earthquake locations in the lower reaches of the Jinsha River and surrounds. The results showed that the Jinsha River basin has a complex lateral P-wave velocity structure. Seismic events are mainly distributed in the transition zones between high- and low-velocity anomalies, and seismic events are particularly intense in the Xiluodu and Baihetan reservoir areas. Vertical cross-sections through the Xiangjiaba and Xiluodu reservoir areas revealed an apparent high-velocity anomaly at approximately 6 km depth; this high-velocity anomaly plays a role in stress accumulation, with few earthquakes distributed inside the high-velocity body. After the impoundment of the Baihetan reservoir, the number of earthquakes in the reservoir area increased significantly. The seismic events in the reservoir area north of 27° N were related to the enhanced activity of nearby faults after impoundment; the earthquakes in the reservoir area south of 27° N were probably induced by additional loads (or regional stress changes), and the multiple microseismic events may have been caused by rock rupture near the main faults under high pore pressure.

Nototribic Pollination Reduces Heterospecific Pollen Deposition and Dampens Its Negative Impact on Seed Production in Calceolaria Species

Premise of research. Nototriby has evolved independently many times in different plant families, possibly for the advantage in the prevention of heterospecific pollen contact in pollinator-sharing environments. However, differences in pollen deposition and their consequences have received little attention, especially in highly specialized systems. Methodology. A systematic stigma collection was performed to estimate the proportion of heterospecific and conspecific pollen in two Calceolaria species with different pollination modes (i.e., nototribic and sternotribic) inhabiting a high mountain valley in Chile. Then, with the previous information, a manipulative pollen donor-receipt experiment was conducted to determine the impact of heterospecific pollen deposition in female reproductive success in both species (seed production). Pivotal results. The two Calceolaria species were prone to receive pollen from some plants of the surrounding community, mainly Adesmia emarginata. However, in the nototribic species (C. filicaulis), only 10% of the total pollen deposition belonged to heterospecific plant species, while in the sternotribic species (C. cavanillesii), more than 60% was heterospecific. Concomitant with this, the hand cross-pollination experiment showed that seed production of C. cavanillesii was more affected by A. emarginata pollen deposition than C. filicaulis pollen. Conclusions. Nototribic morphology can be an effective prepollination barrier to the deposition of heterospecific pollen. However, when this barrier is overcome, its impact may be affected by different factors, such as the foraging behavior of their main pollinator species and a rejection or tolerance mechanism to foreign pollen receipt developed by plant species. Future studies should consider assays to determine the mechanisms behind these findings and their generality to other species of the genus Calceolaria.

GRAIN YIELD STABILITY AND BIOCHEMICAL NUTRIENT CONTENT IN WHITE CORN EXPERIMENTAL CROSSES

In Mexico, about half of white corn production is used for human consumption. In a breeding program, in addition to increasing the yield and genotypes stability, the aim is to improve grain quality. Assuming that there is genetic variation among the elite genotypes evaluated in this research, at least one genotype was considered to be outstanding for its high productive potential and desirable characteristics for grain quality. The objective of this work was to determine the genetic variation present in experimental hybrids in terms of yield potential and grain quality, as well as to identify the most outstanding genotypes. In 2016, twenty white corn experimental crosses were evaluated under a randomized block design with three replications in two locations of the ecological area of the High Valleys of Mexico and one location in a transitional area. Yield stability was determined using the additive main effects and multiplicative interaction model. Grain quality was evaluated through starch, protein and oil content. Most of the crosses had higher yield and stability than the controls (commercial hybrids). Likewise, nutrient content varied among them for each biochemical compound; oil concentration ranged from 3.5 to 6.4 g 100 g-1 dry matter (ms); protein, from 5.5 to 9.8 g 100 g-1 ms; and starch, from 72.6 to 96.6 g 100 g-1 ms. Based on their phenotypic stability, yield and grain quality, we observed that crosses 1213, 1217, 1218, 1314, 1418, and 1812 were outstanding, which can be used to produce grain with promising starch and oil content. In general, we infer that the crosses showed potential for starch utilization and tortilla production.

Drones are an effective tool to assess the impact of feral horses in an alpine riparian environment

AbstractProtected areas can be impacted by the presence and proliferation of feral species. Effective management of feral species requires reliable tools to monitor their population size and ecological impacts. Here, we used drone‐based image analysis to assess evidence of feral horses and horse‐specific ecological impacts on alpine riparian habitat. Valleys with low (0), medium (1–16) and high (>16) horse abundances were chosen for drone imagery analysis based on independent aerial counts of horses. Data collection trips were carried out pre‐ and post‐2019/2020 wildfires, which unexpectedly burnt valleys with low horse presence. Drone‐based RGB orthomosaic imagery was sufficient to identify seven indicators of horse presence and determine the severity of feral horse impacts. Despite the impact of fire, drone‐derived classifications were able to accurately detect a gradient of horse impacts, showing a significant difference in indicators from low presence valleys compared with medium and high presence valleys, which did not differ significantly from each other. The significance of differences between valleys reveals that regions routinely inhabited by feral horses will display significant environmental impacts. Our results clearly indicated significant differences between valleys with low horse presence compared with either medium or high horse presence regions (0.01 for differences between both low and medium and low and high horse presence). This was evident both before and after the 2019/2020 fires, suggesting that wildfires did not significantly impact horse populations or distribution in the sampled region. Overall, it was evident that feral horses have a clear and definable impact on alpine riparian vegetation, and drone surveying can be used to routinely monitor potential spread and the outcome of management actions.

The Importance of Mg–Sb Interactions in Achieving High Conduction Band Degeneracy in Mg3Sb2 for High n-Type Thermoelectric Performance

In recent years, Mg3Sb2 has attracted much attention due to its excellent performance as an n-type thermoelectric material. The high performance of n-type Mg3Sb2 is largely due to the high valley degeneracy (NV) of the electron transport edge, which is the result of the conduction band minimum (CBM) being located at a low-symmetry, six-fold degenerate point (inside the ΓALM plane) in the first Brillouin zone. Furthermore, Bi alloying on the Sb site is well-known to improve electron mobility, and hence, performance. In previous works, this low-symmetry CBM has been attributed to interactions between the tetrahderally and octahedrally coordinated Mg-sites. However, these Mg–Mg interactions cannot explain changes in the shape of the CBM upon Bi alloying, while Mg–Sb (and Mg–Bi) interactions could explain them. Prior studies have neglected to fully consider the importance of the Sb orbitals in the existence of the low-symmetry CBM because at the CBM, there is very little contribution from the Sb orbitals. In this work, we use first-principles density functional theory and tight-binding calculations to show that the low-symmetry CBM is due to Mg-s–Sb-p interactions that are weakest at or near the CBM. Controlling the cation-s–anion-p interactions through anion- or cation-site alloying can be used as an engineering strategy to optimize thermoelectric performance.

Evaluation of the botanical composition of kikuyu and fescue grasslands associated with white clover during two seasons in the high valleys of Mexico

Objective. To evaluate the botanical composition of grasslands of kikuyu (Cenchrus clandestinus) compared to tall fescue (Lolium arundinaceum cv. Cajun II), each one in association with white clover (Trifolium repens cv. Ladino), in two independent experiments conducted during two seasons, autumn 2018 and winter 2019. Methodology. Two independent experiments under small-scale milk production system (SMPS) were established in the municipality of Aculco, State of Mexico, during autumn 2018 and winter 2019. The botanical composition of grasslands under intensive continuous grazing by breeding cows was evaluated. One grassland planted with tall fescue cv. Cajun II and the other invaded by kikuyu; each grassland was associated with white clover cv. Ladino. The botanical composition of both experiments was analyzed using a complete randomized experimental design. Results. The kikuyu grassland recorded significant differences (p<0.05) with a higher proportion of forage during the winter 2018. Whereas the tall fescue cv. Cajun II grassland recorded a proportion of forage (p<0.05) higher than its proportion of dead tissue during autumn 2019. Study Implications: The study of the botanical composition of mixed grasslands destined for livestock grazing allows to identify, propose and define strategies for forage production facing agroclimatic and management conditions in order to generate a better and higher forage yield. Conclusions: The proportion of kikuyu was higher than that of tall fescue cv. Cajun II during the two seasons and years evaluated. This highlights the adaptability of kikuyu grass under agroecological conditions such as the absence of rains and high temperatures, coupled with the high stocking densities of the milk production systems in the study region.

NEW RECORDS OF CINEREOUS HARRIER Circus cinereus (ACCIPITRIDAE) IN THE HIGH ANDES OF SOUTHERN ECUADOR

Cinereous Harrier Circus cinereus is a local species in Ecuador, occurring in agricultural grasslands and páramofrom north to central-south Andes. Little is known about its distribution in southern Ecuador. In this region, records are scarce and have not been adequately documented. We present the first video record of an adult female and a sighting of an adult male in the páramoof Quimsacocha National Recreation Area, Azuay province, southwest Ecuador. Our findings suggest that C. cinereus may be locally distributed further south of the currently known distribution and that it prefers open habitats, particularly cushion páramo, wetlands, and marshes in the high Andes and humid inter-Andean valleys.

Nonvolatile Electrical Valley Manipulation in WS2 by Ferroelectric Gating.

Valleytronics in transition metal dichalcogenides has been intensively investigated for potential applications in next-generation information storage, data processing, and signal transmission devices. Here a ferroelectric gating approach is engaged in achieving nonvolatile electrical tuning of the valley-excitonic properties of monolayer and bilayer WS2. The gating effects include carrier doping and ferroelectric coupling, which are further distinguished by comparing two geometries where the gate electrodes are in direct contact with or insulated from the WS2 crystal. The results show that the carrier doping from gate electrodes acts on WS2 through carrier screening, which only moderately alters the valley polarization. In contrast, the ferroelectric gating promotes electron-phonon interaction, introduces a strong surface polarization field, and controls the interfacial charge trapping/detrapping, causing a Stark shift in exciton energy and strongly enhancing room-temperature valley polarization. In bilayer WS2, the intralayer-interlayer exciton transition is further induced, contributing to even higher valley polarization. The ferroelectric coupling effect can still be maintained after the removal of gate voltage, showing its nonvolatile nature. The role of ferroelectricity is further verified by the anomalous temperature dependence in valley polarization. This work has revealed effective electrical control over valley excitons in semiconductors through interaction with ferroelectric materials. The reported high room-temperature valley polarization in WS2 will boost the development of valleytronics devices.

GENETIC PARAMETERS AND SELECTION CRITERIA IN QUINOA

Quinoa (Chenopodium quinoa Willd.) is a crop with high nutritional and agronomic potential, adapted to environmental stress conditions. It is grown on a small scale in Mexico, and currently improved varieties are not available. In order to establish the basis to guide genetic improvement in Mexico, the objective was to determine the genetic variability, heritability and interrelationships of yield and its components in 16 quinoa genotypes, in a randomized complete block design, in six environments in the central high valleys of Mexico. The proportion of participation of the sources of variation genetic, environmental, and genotype × environment interaction was determined; as well as heritability, response to selection, and phenotypic correlations among morphological characters, yield and its components. Out of 15 variables evaluated, the genetic effects on thousand-grains weight and grain filling period were the most important; whereas for plant height at flowering, harvest index, and stem diameter, environmental effects were the most relevant. The genotype × environment interaction is not greater than 20 % for the 15 variables evaluated. The highest values for additive variance, heritability, and response to selection were for grains per square meter, yield, thousand-grains weight, grain filling period, and panicle emergence. The variables stem diameter, plant height at maturity, grains per square meter, yield per day, grain filling period, and panicle emergence were the most correlated with yield. Therefore, they can be used as indirect yield selection criteria in breeding programs to obtain materials with better agronomic characteristics. Based on the genetic parameters obtained and the association of the variables with yield, grains per square meter, yield per day and plant height at maturity are the most appropriate traits for indirect selection for yield.

Direct Observation of Self-Hybridized Exciton-Polaritons and Their Valley Polarizations in a Bare WS2 Layer.

The strong excitonic properties of transition metal dichalcogenides (TMD) have led to the successful demonstration of exciton-polaritons (EPs) in various optical cavity structures. Recently, self-hybridized EPs have been discovered in a bare TMD layer, but experimental investigation is still lacking because of their nonradiative nature. Herein, the direct observation of self-hybridized EPs in a bare multilayer WS2 via the evanescent field coupling technique is reported. Because of the thickness-dependent Rabi splitting energy, the dispersion curves of the EPs change sensitively with sample thickness. Moreover, continuous tuning of EP dispersion curves is demonstrated by controlling the excitation laser power. Lastly, it is observed that guided EPs retain valley polarization up to 0.2 at room temperature, representing a valley-preserved strong coupling regime. It is believed that the high tunability and valley polarization properties of the guided EPs in bare TMD layers can facilitate new nanophotonic and valleytronic applications.

Two-dimensional intrinsic ferrovalley Janus 2H-VSeS monolayer with high Curie temperature and robust valley polarization

Inspired by the successful synthesis of two-dimensional (2D) V-based Janus dichloride monolayers with intrinsic ferromagnetism and high Curie temperature (T$_{c}$), the electronic structure, spin-valley splitting and magnetic anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using first-principles calculations. The results show that the Janus 2H-VSeS monolayer exhibits a large valley splitting of 105meV, high T$_{c}$ of 278K and good magnetocrystalline anisotropy (0.31meV) contributed by the in-plane d$_{x^{2}-y^{2}}$/d$_{xy}$ orbitals of V atoms. The biaxial strain ($-$8%<$\varepsilon$<8%) can effectively tune the magnetic moments of V atom, valley splitting $\Delta$E, T$_{c}$ and MAE of Janus 2H-VSeS monolayer. The corresponding $\Delta$E and T$_{c}$ are adjusted from 72meV to 106.8meV and from 180K to 340K, respectively. The electronic phase transition from bipolar magnetic semiconductor (BMS) to half-semiconductor (HSC), spin gapless semiconductor (SGS), and half-metal (HM) is also observed due to the change of V 3d-orbital occupation. Due to the broken space- and time-reversal symmetry, the opposite valley charge carriers carry opposite Berry curvature, which leads to prominent anomalous Hall conductivity at the K and K$^{\prime}$ valleys. The maximum modulation of Berry curvature can reach to 45% and 9.5% by applying the biaxial strain and charge carrier doping, respectively. The stable in-plane magnetocrystalline anisotropy and large spontaneous valley polarization make the ferromagnetic Janus 2H-VSeS monolayer a promising material for achieving the spintronics and valleytronics devices.