Secondary Valleys Research Articles

Carrier mobility and high-field velocity in 2D transition metal dichalcogenides: degeneracy and screening

The effect of degeneracy and the impact of free-carrier screening on a low-field mobility and a high-field drift velocity in MoS2 and WS2 are explored using an in-house ensemble Monte Carlo simulator. Electron low field mobility increases to for MoS2 and to for WS2 when temperature decreases to and carrier concentration is around . In the case of holes, best mobility values were and , reached at similar temperature and carrier concentration conditions while at room temperature these fall to and for MoS2 and WS2, respectively. The carrier screening effect plays a major role at low fields, and low and intermediate temperatures, where a combination of large occupancy of primary valleys and carrier–phonon interactions dominated by relatively low energy exchange processes results in an enhanced screening of intrinsic scattering. For electrons, degeneracy yields to transport in secondary valleys, which plays an important role in the decrease of the low field mobility at high concentrations and/or at room temperature. The high-field drift velocity is not much affected by carrier screening because of an increased carrier scattering with surface optical polar phonons, favouring larger phonon wavevector interactions with small dielectric function values.

A Morphing-Based Method for Paleotopographic Reconstruction of the Transverse Canyon

The transverse canyon is a V-shaped, fluvial-genetic canyon, a secondary valley formed by transverse drainage crossing a tectonically uplifted mountain. Paleotopography of the transverse canyon is vital to drainage connection and river capture, offering insight into the processes that link large-scale river systems, analyzing paleodrainage patterns, and recreating headward erosion. Notably, modern paleotopographic reconstruction methods are usually limited to reconstructions of paleotopography in vast sedimentary basins and denuded hills in orogenic belts. When applied to transverse canyons, a specific secondary valley found in tiny locations, these techniques are difficult, expensive, and ineffective. This paper proposes an automated method for reconstructing the paleotopography of the transverse canyon using the digital elevation model (DEM) and river. (1) Restore the ridgeline above the transverse canyon based on the ridgelines of the mountains on both sides; (2) create a buffer zone based on the river centerline with unequal buffer distances on each side; (3) construct a mesh surface by interpolating transition curves from the morphing method, using the three-edge type; (4) apply a spatial interpolation method to the elevation points on the mesh surface to construct the DEM above the transverse canyon and stitch it to the input DEM to obtain the paleotopographic DEM; (5) calculate the spatial attributes. The objective of this study is to reconstruct the paleotopography of eight typical transverse canyons in the comb-like fold belt of northern Chongqing. As part of the paleotopographic reconstruction of the transverse canyon, we address the effects of dislocated mountains, erosion gullies, and different morphing techniques, as well as the applicability of the proposed method to reconstructing other secondary valleys. In conclusion, we reconstruct paleotopographic DEMs of transverse canyons to replicate headward erosion processes, assess paleodrainage patterns, and build three-dimensional solid models.

Applying SWAT Model to Estimate the Annual Runoff of Wadi Al-Mohammadi Basin, Western Iraq

In arid and semi-arid regions, with unexpected periods of floods or droughts as a result of extreme variability in rainfall rates, runoff occurs in separate periods after clear occasional rainstorms. People living in these areas are greatly affected by water shortages during droughts and often have unsafe livelihoods. Wadi Al-Mohammadi is one of the main valleys in the Western Desert flows into the Euphrates River. It is considered an important area, due to many characteristics, including its relatively large area, the amount of water drained through, and has significant storage of groundwater, which is used mainly in agriculture and watering livestock, in addition to industrial purposes such as the production of washed sand, gravel that scattered on both sides of the valley. The Soil and Water Assessment Tool (SWAT) model is proven to be effective as a working platform in the hydrological cycle and to clarify its components and factors affecting the hydrological situation in a region. By applying the SWAT model using the required data set (LULC, slope, and soil types), Wadi Al-Mohammadi is subdivided into 199 HRU (hydrologic response units). The annual average flow discharge was 0.138 m3/s with an average annual water volume about 4.366 Mm3, while the average annual water volume is calculated from runoff which was of about 4.651 Mm3. There is a difference in the average annual volume of water calculated from surface runoff and discharge, due to a little slope, and not all the surface runoff water reaches the mainstream, or it ends in secondary valleys or collecting in pits, and there for the discharge is less than the surface runoff. Peak runoff is observed in Wadi Al-Mohammadi basin mostly during the winter season, from November to March.

Effect of Boundary Conditions on Seismic Response of Electrical Equipment subjected to High-Frequency Ground Motions

The updated ground motion hazard in Central and Eastern United States contains high frequency motions. Such motions do not cause structural damage. However, safety-related electrical equipment are sensitive to high-frequency accelerations. Seismic qualification of electrical equipment requires an in-cabinet response spectrum (ICRS) which depends on the dynamic response of electrical cabinets and buildings. A linear analysis to generate ICRS can give excessively high spectral accelerations. Cabinet models with geometric nonlinearities such as a gap in the connection with building floor show that high-frequency accelerations may not propagate to the electrical equipment. Unlike linear analysis, results from nonlinear analysis of a building-cabinet model with a gap show a periodic pattern of secondary peaks and valleys at higher frequencies. In this research, the unique observation of secondary peaks is explained through fundamental principles by considering the sliding response of a cabinet representation with gap subjected to harmonic excitation. It is observed that a periodic pattern of peaks and valleys exist due to a significantly large contribution from transient response, due to localized impacts at the gap in cabinet base, and its interaction with the steady-state response.

Effect of static local distortions vs. dynamic motions on the stability and band gaps of cubic oxide and halide perovskites

Ternary ABX3 perovskites made of corner-sharing BX6 octahedra have long featured prominently in solid-state chemistry and condensed matter physics. Still, the joint understanding of their two main subgroups—halides and oxides—has not been fully developed. Indeed, unlike the case in simpler compounds having a single, robust repeated motif (“monomorphous”), certain cubic perovskites can manifest a non-thermal (= intrinsic) distribution of local motifs (“polymorphous networks”). Such static deformations can include positional degrees of freedom (e.g., atomic displacements and octahedral tilting) or magnetic moment degrees of freedom in paramagnets. Unlike thermal motion, such static distortions do not time-average to zero, being an expression of the intrinsic symmetry breaking preference of the chemical bonding. The present study compares electronic structure features of oxide and halide perovskites starting from the static polymorphous distribution of motifs described by Density Functional Theory (DFT) minimization of the internal energy, continuing to finite temperature thermal disorder modeled via finite temperature DFT molecular dynamics. We find that (i) different oxide vs. halide ABX3 compounds adopt different energy-lowering symmetry-breaking modes. The calculated pair distribution function (PDF) of SrTiO3 from the first-principles agrees with recently measured PDF. (ii) In both oxides and halides, such static distortions lead to band gap blueshifts with respect to undistorted cubic Pm-3m structure. (iii) For oxide perovskites, high-temperature molecular dynamics simulations initiated from the statically distorted polymorphous structures reveal that the thermally-induced distortions can lead to a band gap redshift. (iv) In contrast, for cubic halide perovskite CsPbI3, both the intrinsic distortions and the thermal distortions contribute in tandem to band gap blueshift, the former, intrinsic effect being dominant. (v) In the oxide SrTiO3 and CaTiO3 (but not in halide) perovskites, octahedral tilting leads to the emergence of a distinct Γ–Γ direct band gap component as a secondary valley minimum to the well-known indirect R–Γ gap. Understanding such intrinsic vs. thermal effects on oxide vs. halide perovskites holds the potential for designing target electronic properties.

La diversidad de los paisajes agrícolas en el Geoparque Mundial UNESCO Mixteca Alta, Oaxaca, México

La Mixteca Alta es una región natural y cultural de importancia mundial. La agricultura en la región reconoce serias limitantes ambientales, como lluvias escasas e irregulares, estación de crecimiento corta, y poca extensión de suelos con buena calidad en términos de profundidad, fertilidad y pendiente, estos factores han influido para que las comunidades mixtecas hayan creado diversos paisajes agrícolas, entre los que destacan las terrazas y los lamabordos. El objetivo de este trabajo fue identificar y proponer una clasificación de los paisajes agrícolas en una zona de la Mixteca Alta, a través la interpretación de imágenes de satélite, entrevistas con agricultores, y recorridos de campo. Localmente los sistemas agrícolas se diferencian por la forma del terreno, la modificación del relieve y la disponibilidad de agua. Se identificaron seis paisajes: el valle de temporal, el valle de riego, los valles secundarios, las laderas de temporal, las laderas de riego y las terrazas agrícolas o lamabordos. Cada uno se distingue por un grupo de cultivos de los cuales el maíz aparece como cultivo dominante, excepto en las laderas de riego, que reconoce un sistema de cultivo diferenciado para cada paisaje. Estos paisajes son producto de la interacción entre las comunidades y la geodiversidad, son parte de la identidad de las comunidades mixtecas. Su diversidad tiene un gran valor cultural e histórico, basado en los conocimientos tradicionales involucrados en sus transformaciones.

Inflection points in the conduction-band structure of BaSnO3

$\mathrm{BaSn}{\mathrm{O}}_{3}$ (BSO) is a wide-band-gap oxide in which very high levels of $n$-type doping have been demonstrated. Here we perform a detailed investigation of the conduction-band structure of BSO, reporting band velocities and effective masses as a function of energy, and explore whether sufficiently high doping levels can be achieved to fill the conduction band to energies near the inflection point. The presence of carriers near the inflection point can lead to negative differential resistance (NDR) due to the effective mass above the inflection point being negative. Our first-principles calculations, based on density functional theory with a hybrid functional, show that BSO has an inflection point 2.29 eV above the conduction-band minimum and that secondary conduction-band valleys are at least 2 eV higher in energy. We discuss the options available to achieve the required $n$-type doping levels to reach the inflection point in BSO.

Field-dependent electrical properties of carbon nanotubes from first-principles: negative differential conductance, current oscillations and molecular sensing

In certain materials, and for certain voltage ranges, electrical current flowing through the material decreases when the voltage across the sample is increased. This negative differential conductance (NDC) is important for oscillators, amplifiers, and fast switching devices. In this work, using real time quantum simulations, we show that this phenomenon occurs in isolated finite armchair single wall carbon nanotubes (SWCNT) without end contacts. For metallic SWCNT, like the armchair SWCNT, electron transfer to secondary valleys—the most common cause of NDC—is not expected to be observed, as there are two quantum channels at the Fermi energy available for conduction. The NDC is due to the finite nature of the SWCNT and the existence of excited states that are blocked, similarly to a Coulomb blockade system, thus preventing any further current flow. We also show that the SWCNT conductivity depends on its length and that the current flowing on the SWCNT behaves like a Bloch oscillation that is disrupted in the presence of a molecule, decreasing the conductivity, and thus providing a rationalisation for the behaviour of SWCNT organic gas sensors.

Eruptive style and flow dynamics of the pyroclastic density currents related to the Holocene Cerro Blanco eruption (Southern Puna plateau, Argentina)

The Pleistocene-Holocene Cerro Blanco Volcanic Complex (CBVC), one of the youngest caldera complexes in the Southern Central Andes, is the source of possibly one of largest Holocene eruptions on Earth, the 4.2 ka, Cerro Blanco eruption. This caldera forming eruption is the younger of two major explosive events from the CBVC. Previous work has estimated the range from VEI 6 to 7, yet to date there is no detailed study of the stratigraphy and volcanology of the proximal deposits and dynamics of the Cerro Blanco eruption. Here we present the first detailed analysis of the eruptive products of the Holocene Cerro Blanco eruption that reveal the eruptive sequence highlighting the flow dynamics of the related pyroclastic density currents (PDCs). The PDCs were mainly inertia-dominated, however, channelization of parental PDCs into deep valleys resulted in the flow transformation to forced convection-dominated flows. In addition, topographic constriction in valleys enhanced the sedimentation rate producing regressive bed forms and ultimately the avulsion of the main path of the PDCs resulting in flooding of secondary valleys. A model is presented whereby simultaneous convective and collapsing eruptive column dynamics were established and sustained throughout the eruption. Towards its end, instabilities of the column occurred in response to the climax of a protracted incremental caldera collapse. This eruptive sequence is similar to those observed in well-documented small collapse calderas. An important unresolved issue for the CB eruption is it volume. The currently estimated volume of 83 km3 (DRE) by Fernando-Turiel et al. (2019) is inconsistent with the size of the Cerro Blanco caldera and to date the over thickening of the distal ash by local rework is poor assessed. Further work is needed to fully evaluate this mismatch and accurately estimate the volume of this important Holocene eruption.

Spin States Protected from Intrinsic Electron-Phonon Coupling Reaching 100 ns Lifetime at Room Temperature in MoSe2.

We present time-resolved Kerr rotation measurements, showing spin lifetimes of over 100 ns at room temperature in monolayer MoSe2. These long lifetimes are accompanied by an intriguing temperature-dependence of the Kerr amplitude, which increases with temperature up to 50 K and then abruptly switches sign. Using ab initio simulations, we explain the latter behavior in terms of the intrinsic electron-phonon coupling and the activation of transitions to secondary valleys. The phonon-assisted scattering of the photoexcited electron-hole pairs prepares a valley spin polarization within the first few ps after laser excitation. The sign of the total valley magnetization, and thus the Kerr amplitude, switches as a function of temperature, as conduction and valence band states exhibit different phonon-mediated intervalley scattering rates. However, the electron-phonon scattering on the ps time scale does not provide an explanation for the long spin lifetimes. Hence, we deduce that the initial spin polarization must be transferred into spin states, which are protected from the intrinsic electron-phonon coupling, and are most likely resident charge carriers, which are not part of the itinerant valence or conduction band states.

Zooarchaeological evidence of functional and social differentiation in northern Italy between the Neolithic and Bronze ages

Many sites dating from the Neolithic to the Bronze Age have been investigated in northern Italy and have provided important zooarchaeological data. These sites are mostly settlements, but also places of worship and necropoli. While there are few zooarchaeological studies for the north-western part of Italy, the north-east and the Po Valley have been better investigated. Particularly important are the pile-dwellings and the Terramare sites of the Po Valley as they have a long chronological span, the animal bone assemblages are large and, therefore, highly statistically reliable, and have been excavated relatively recently. There is evidence of functional and social differentiation in the Bronze Age which coincided with the evolution of more complex societies. The most common type of functional differentiation began when human communities started to settle and is visible in the zooarchaeological record. Until the end of the Copper Age, animal bone assemblages are characterized by the presence of both domestic animals and a relatively important proportion of wild animals. In the early Bronze Age, domestic animals dominated, if not entirely, the assemblages, and a growing interest in secondary products is evident. From the Middle Bronze Age, the foundation of semi-permanent settlements multiplied in the Alpine area, in the internal areas (secondary valleys and areas far from the main watercourses) and at medium-high altitudes. This was coupled with the seasonal occupation of sites at a high altitude, used for the practice of vertical transhumance (alpine pasture). This phenomenon implies the existence of a settlement hierarchy and, therefore, of forms of social stratification within the framework of the settlement system. Unfortunately, the few zooarchaeological studies of sites located in the Emilia Apennines do not currently allow us to confirm the existence of such links between the mountain sites and those on the plain. Nevertheless, other evidence, such as the introduction of the horse, which is attested from the late Early Bronze Age onwards, can be interpreted as proof of social differentiation; the horse was, in fact, considered a status symbol of the emerging warrior elite.Very few animal burials, dated to the period studied, show the link between animal species (such as dog, cattle, deer) and cultural practices, although a number of examples of such a relationship are provided by the terramare necropoli. In conclusion, in light of current knowledge, it seems that zooarchaeology cannot confirm the existence of important forms of social stratification. This does not mean that they cannot necessarily be postulated: the complex use of territory and the evidently communal nature of funerary and cult ceremonies (which often involved animals) that characterize the Bronze Age make it difficult to exclude the existence of such stratification.

High-resolution modelling of atmospheric dispersion of dense gas using TWODEE-2.1: application to the 1986 Lake Nyos limnic eruption

Abstract. Atmospheric dispersal of a gas denser than air can threat the environment and surrounding communities if the terrain and meteorological conditions favour its accumulation in topographic depressions, thereby reaching toxic concentration levels. Numerical modelling of atmospheric gas dispersion constitutes a useful tool for gas hazard assessment studies, essential for planning risk mitigation actions. In complex terrains, microscale winds and local orographic features can have a strong influence on the gas cloud behaviour, potentially leading to inaccurate results if not captured by coarser-scale modelling. We introduce a methodology for microscale wind field characterisation based on transfer functions that couple a mesoscale numerical weather prediction model with a microscale computational fluid dynamics (CFD) model for the atmospheric boundary layer. The resulting time-dependent high-resolution microscale wind field is used as input for a shallow-layer gas dispersal model (TWODEE-2.1) to simulate the time evolution of CO2 gas concentration at different heights above the terrain. The strategy is applied to review simulations of the 1986 Lake Nyos event in Cameroon, where a huge CO2 cloud released by a limnic eruption spread downslopes from the lake, suffocating thousands of people and animals across the Nyos and adjacent secondary valleys. Besides several new features introduced in the new version of the gas dispersal code (TWODEE-2.1), we have also implemented a novel impact criterion based on the percentage of human fatalities depending on CO2 concentration and exposure time. New model results are quantitatively validated using the reported percentage of fatalities at several locations. The comparison with previous simulations that assumed coarser-scale steady winds and topography illustrates the importance of high-resolution modelling in complex terrains.

Crosslinking kinetics of polyethylene with small amount of peroxide and its influence on the subsequent crystallization behaviors

Crosslinking reactions of high density polyethylene with low peroxide concentrations ranging from 0.1 wt% to 1.0 wt% at temperatures of 170, 180 and 190 °C were monitored by rheological measurements. A critical gel forms at the peroxide concentration of 0.2 wt%, where the transition from long chain branching generation to crosslinking network formation could occur. Rheokinetics of crosslinking can be fitted well by Ding-Leonov’s model. The curing rate k 2 at the earlier stage exhibits about 3 times acceleration per 10 °C with increasing temperature, while the equilibrium modulus G′ at the fully cured stage is almost independent of temperature. Influences of crosslinking on the subsequent crystallization behaviors were detected by DSC measurements. Above the critical gel concentration, crystallization is largely retarded as evidenced by the lower crystallization temperature T c and crystallinity X c due to the network formation. The secondary crystallization valley located at the temperature near 80 °C can be observed above the critical concentration, which becomes more evident with the increasing peroxide concentration and curing temperature. This phenomenon provides another evidence of crystallization retardation by the crosslinking network.

First-principles study of anisotropic thermoelectric transport properties of IV-VI semiconductor compounds SnSe and SnS

We conduct comprehensive investigations of both thermal and electrical transport properties of SnSe and SnS using first-principles calculations combined with the Boltzmann transport theory. Due to the distinct layered lattice structure, SnSe and SnS exhibit similarly anisotropic thermal and electrical behaviors. The cross-plane lattice thermal conductivity $\kappa_{L}$ is 40-60% lower than the in-plane values. Extremely low $\kappa_{L}$ is found for both materials because of high anharmonicity. It is suggested that nanostructuring would be difficult to further decrease $\kappa_{L}$ because of the short mean free paths of dominant phonon modes (1-30 nm at 300 K) while alloying would be efficient in reducing $\kappa_{L}$ considering that the relative $\kappa_{L}$ contribution ($\sim$ 65%) of optical phonons is remarkably large. On the electrical side, the anisotropic electrical conductivities are mainly due to the different effective masses of holes and electrons along the $a$, $b$ and $c$ axes. This leads to the highest optimal $ZT$ values along the $b$ axis and lowest ones along the $a$ axis in both $p$-type materials. However, the $n$-type ones exhibit the highest $ZT$s along the $a$ axis due to the enhancement of power factor when the chemical potential gradually approaches the secondary band valley that causes significant increase in electron mobility and density of states. SnSe exhibits larger optimal $ZT$s compared with SnS in both $p$-type and $n$-type materials. For both materials, the peak $ZT$s of $n$-type materials are much higher than those of $p$-type ones along the same direction. The predicted highest $ZT$ values at 750 K are 1.0 in SnSe and 0.6 in SnS along the $b$ axis for the $p$-type doping while those for the $n$-type doping reach 2.7 in SnSe and 1.5 in SnS along the $a$ axis, rendering them among the best bulk thermoelectric materials for large-scale applications.

Interaction of valleys and circulation patterns (CPs) on spatial precipitation patterns in southern Germany

Abstract. Topography exerts influence on the spatial precipitation distribution over different scales, known typically at the large scale as the orographic effect, and at the small scale as the wind-drift rainfall (WDR) effect. At the intermediate scale (1~10 km), which is characterized by secondary mountain valleys, topography also demonstrates some effect on the precipitation pattern. This paper investigates such intermediate-scale topographic effects on precipitation patterns, focusing on narrow-steep valleys in the complex terrain of southern Germany, based on the daily observations over a 48 yr period (1960~2007) from a high-density rain-gauge network covering two sub-areas, Baden-Wuerttemberg (BW) and Bavaria (BY). Precipitation data at the valley and non-valley stations are compared under consideration of the daily general circulation patterns (CPs) classified by a fuzzy rule-based algorithm. Scatter plots of precipitation against elevation demonstrate a different behavior of valley stations comparing to non-valley stations. A detailed study of the precipitation time series for selected station triplets, each consisting of a valley station, a mountain station and an open station have been investigated by statistical analysis with the Kolmogorov–Smirnov (KS) test supplemented by the One-way analysis of variance (One-way ANOVA) and a graphical comparison of the mean precipitation amounts. The results show an interaction of valley orientation and the direction of the CPs at the intermediate scale, i.e. when the valley is shielded from the CP which carries the precipitation, the precipitation amount within the valley is comparable to that on the mountain crest, and both larger than the precipitation at the open station. When the valley is open to the CP, the precipitation within the valley is similar to the open station but much less than that on the mountain. Such phenomenon where the precipitation is "blind" to the valleys at the intermediate scale conditioned on CPs is defined as the "narrow-valley effect" in this work. Such an effect cannot be captured by the widely used elevation–precipitation relationship, which implies that the traditional geostatistical interpolation schemes, e.g. ordinary kriging (OK) or external drift kriging (EDK) applying digital elevation model (DEM) as external information, are not sufficient. An interpolation experiment applying EDK with orographic surrogate elevation defined in this paper as auxiliary information to account for the valley effects shows improvement for the cross-validation.

Würmian deglaciation of western Lake Geneva (Switzerland) based on seismic stratigraphy

Western Lake Geneva (le Petit-Lac) was filled during the Quaternary over a major erosion surface truncating the cemented, folded and thrusted Tertiary sediments of the foreland Alpine basin. The carving of the lake occurred during Quaternary glaciations with ice originating from the Rhone valley catchment basin flowing in two branches oriented SW and NE over the Swiss Plateau. Lake Geneva is situated on the South-Western branch of this paleo ice-cap. For the first time, a dense grid of high-resolution seismic profiles (airgun 5-inch 3, airgun 1-inch 3 and echosounder) has imaged the whole Quaternary sequence, providing a paleoenvironmental interpretation and a detailed reconstruction of the Rhone glacier retreat stages during glacial events that led to the formation of western Lake Geneva. The Quaternary sequence filling up the bedrock valley is exceptionally thick with up to 220 m of deposits and consists of glacial, glacio-lacustrine and lacustrine sediments. Fourteen seismic units have been defined (units U1–U14). Unit U1 represents the remnants of glacial deposits older than the last glacial cycle, preserved in the deepest part of the lake and in secondary bedrock valleys. Unit U2 represents gravel and sands deposited by meltwater circulation at the bottom of the glacial valley. Unit U3 is a thick, stratified unit marking the beginning of the deglaciation, when the Rhone glacier became thinner and buoyant and allowed the formation of a subglacial lake. Younger glacial units (units U4, U5, U7, U9, U11) are acoustically chaotic sediments deposited subglacially under the water table (undermelt tills), while the glacier was thinning. These glacial units are bounded by synform erosion surfaces corresponding to readvances of the glacier. The transition from a glacial to a glacio-lacustrine environment started with the appearance of a marginal esker-fan system (unit U6). Esker formation was followed by a small advance–retreat cycle leading to the deposition of unit U7. Then, the ice front receded and stratified sediments were deposited in a glacio-lacustrine environment (units U8, U10 and U12). This retreat was punctuated by two readvances – Coppet (unit U9) and Nyon (unit U11) – producing large push moraines and proglacial debris flows. Finally, a lacustrine environment with a characteristic lake current pattern and mass movement deposits took place (units U13 and U14). Except for unit U1, the sedimentary sequence records the Würmian deglaciation in a fjord-like environment occupied by a tidewater glacier with a steep, calving ice front. The presence of an esker-fan system reveals the importance of subglacial meltwater flow in continental deglaciation. Push-moraines and erosion surfaces below the glacier indicate at least 5 readvances during the deglaciation thus revealing that oscillations of ice front are the key process in deglaciation of perialpine fjord-lakes. The dating of these continental glacier fluctuations would allow correlation with oceanic and ice records and help to understand the climatic mechanisms between oceans and continents.

First results of a study of the Etruscan tunnel and other hydraulic works on the Ponte Coperto stream (Cerveteri, Rome, Italy)

The Etruscan tunnel called Ponte Coperto is located NW of Rome, near the town of Cerveteri. The Ponte Coperto tunnel, mapped for the first time during the present research and dug mainly in volcanic tuff lying below the lava flow, was built to drain a valley of about 8.5 km2, probably between the VII and VI century B.C. Before the tunnel construction, part of the valley was occupied by a swamp, whose reclamation was carried out by digging a long rectilinear canal of about 800 metres to the tunnel opening. Several hundred metres upstream of the tunnel entrance a secondary canal flows into the main one; this tributary canal drains a secondary valley, next to the principal one. Nowadays the Ponte Coperto tunnel, 170 m long, looks much larger than its original shape due to natural erosion that has widened and deepened it: during the dry season its discharge is negligible, but some calculations show that the peak discharge can be in the order of several dozens of cubic metres per second. The efficiency of the Ponte Coperto system is outstanding, as the hydraulic setup of the area is still that left by the Etruscans engineers more than two millennia ago: the tunnel and the canals keep draining both the surface and the ground waters from the more permeable rocks, and the valley is still healthy and cultivated. The Ponte Coperto system is a good example of the fact that Roman water engineering has its roots in Etruscan technology.

Malibogazi groundwater dam: an alternative model for semi-arid regions of Turkey to store and save groundwater

In central Turkey, there are serious groundwater quality problems in the main river valleys and plains, and even in the lower parts of the secondary basins due to the underlying evaporitic geological formations. Groundwater quality improves towards the upstreams in the alluvium aquifers in most secondary valleys; however, groundwater potential decreases as well due to the reduced basin area, areal extent and thickness of the aquifers. The Malibogazi valley is situated to some 100 km north of Ankara. The dam constructed in the narrowest section of the valley has an average storage coefficient of 0.2 and the total and active storage capacities of 110,000 and 55,000 m3, respectively. The 20-m-thick aquifer extends for 6–7 km till the dam site within valley with an average width of 50–70 m. It mostly comprises sandy–gravely alluvial deposits. Malibogazi groundwater dam is a valve-controlled gravity flow dam. When the valves are opened, the water from the aquifer reservoir flows by gravity through supply pipe to the main irrigation channel, but when the valves are closed the water is stored in the aquifer and groundwater level begins to rise. Average groundwater discharge was about 20 l/s in 2005–2006 irrigation period. In this period, groundwater levels were about 2 m higher compared to the groundwater levels in the same seasons before the construction of the groundwater dam. Because the dam is of gravity flow type, it means an important contribution to the farmers since the operation cost is quite low. Malibogazi groundwater dam represents one of the first experiences of Turkey in the field of groundwater storage. Although the dam has small storage capacity, it may be a model for Turkey from the viewpoints of investigation, construction, dam wall, intake facility and measurements etc.

Moose Movement Rates Along Highways and Crossing Probability Models

ABSTRACT We developed and validated a density‐adjusted spatial model to predict moose (Alces alces) highway‐crossing probability to see if the model could be used as an index of moose‐vehicle collision risk. We installed Global Positioning System telemetry collars on 47 moose in the north of the Laurentides Wildlife Reserve, Québec, for 2–36 months. We recorded only 84 highway crossings in spring (0.29% of 28,967 2‐hr steps) and 122 crossings in summer (0.18% of 68,337 2‐hr steps), despite a high sampling effort and having captured moose close to highways. Moose movement rates during movement steps crossing a highway were on average 3 times higher than during the steps preceding or following highway crossing. Paths used by moose when crossing a highway were characterized by a high proportion of food stands, low proportion of lakes and rivers, and topography typical of a valley. Highway‐crossing sites were located in valleys with brackish pools and forest stands providing coniferous cover but a low proportion of lakes and rivers. We adjusted moose crossing probability for local variation in moose density using aerial survey data and assessed crossing probability along the highways in the entire Laurentides Wildlife Reserve. We tested the model using moose‐vehicle accident data from 1990 to 2002. The relationship between the density‐adjusted crossing probability and number of accidents was relatively loose at the 1‐km scale but improved markedly when using longer highway sections (5–15 km; r > 0.80). Our results demonstrate that roads and their surroundings are perceived as low‐quality habitat by moose. We also conclude that road segments installed along secondary valleys could be a highly strategic site to deploy mitigation measures such as fences and that it could be desirable to increase the width of road shoulders to reduce forest cover and to eliminate brackish pools to reduce cervid‐vehicle collisions. We suggest using empirical data such as location of vehicle‐wildlife collisions to plan mitigation measures at a fine scale.

Long‐term effects of human impact on mountainous ecosystems, western Taurus Mountains, Turkey

AbstractAim To investigate the human impact on eastern Mediterranean ecosystems in a subhumid to semi‐arid region of the Near East.Location This paper considers data from Bereket (1410–1440 m a.s.l.), an intramontane basin surrounded by the Kokayanık Tepe (1830 m a.s.l.) and the Beşparmak Dağları (2280 m a.s.l.), in the western Taurus Mountains of south‐west Turkey.Methods Late Holocene samples were collected along an 800‐cm‐deep sediment profile cored in the secondary valley of the Bereket basin. Descriptive vegetation data and modern pollen samples (moss polsters) were collected at elevational intervals of c. 15 m along an altitudinal transect from the Bereket basin (over Tepe Düzen, 1600 m a.s.l.) to Ağlasun Dağı (1700 m a.s.l.). Information about the spatial distribution of the present land cover was obtained from ASTER satellite imagery. Digital elevation‐derived data and geological information were used to examine the relationship between actual land cover and other environmental variables.Results The well dated Bereket sequence provides a unique record of biennial‐to‐decadal landscape changes driven primarily by intensive human impact from 360 cal. yr bc to 650 cal. yr ad. Since 360 cal. yr bc, over‐exploitation of the land has led to altitudinal variation of tree lines, a destruction of the natural forest ecosystems (Pinus–Quercus cerris mixed forest), and an extensive spread of forest‐steppe in the highlands. The present‐day distribution of vegetation in the basin area shows that human activities remain the major factor influencing the character of modern ecosystems.Main conclusions This research demonstrates the long‐term local destructive effects of human impacts on the mountainous ecosystems in a small Anatolian intramontane basin since 360 cal. yr bc, and the capacity of these ecosystems to recover during periods of reduced human impact. The late Holocene history and modern vegetation characteristics show that the past and present‐day distribution and composition of vegetation are influenced primarily by human activity, and that substrate, elevation, slope and orientation are of secondary significance.