Lateral Encroachment Research Articles

Shoreline subsurface dams to protect coastal aquifers from sea level rise and saltwater intrusion

Fresh groundwater in arid and highly populated regions is limited. In coastal aquifers, the deterioration of fresh groundwater is accelerated by saltwater intrusion, primarily occurring through lateral encroachment and vertical movements in the proximity of discharging wells. Coastal regions have high salinity due to saline intrusion, where many abstraction wells are turned off by this high salinity, which leads to increased freshwater supply costs. This study investigates the performance of new approach using the shoreline subsurface dams (SSDs) for mitigating the saline water wedge in coastal aquifers, where the dams are installed at the shoreline (distance from shoreline = 0). Specifically, the current study's novelty is testing the effectiveness of SSDs by different relative heights ranging from 0.05 to 0.50 in the test case (Henry problem) and from 0.09 to 0.53 relative to the aquifer thickness in the field scale aquifer (Biscayne aquifer, Florida, USA). The results showed an exponential increase in salt repulsion for increasing SSDs height, reaching a maximum of + 0.70%, + 1.80%, + 3.25%, + 5.80%, + 10.45%, and + 18.40% for the dam height to aquifer thickness ratios of 0.09, 0.18, 0.26, 0.35, 0.44 and 0.53, respectively, in the field scale case. The SSDs increase the freshwater storage at the coastal zones where the low salinity occurs and reduces the freshwater supply cost. Despite the positive impact of height on repulsion, important factors such as economics, construction aspects, geographical suitability, and environmental impacts must be considered for real applications. This is crucial to develop feasible solutions applicable globally under the growing pressure of sea level rise.

Unveiling the natural history of paralysis in metastatic cervical spinal tumor: An experimental study

IntroductionDespite the relatively low prevalence of metastatic cervical spinal tumor, these entities give rise to more profound complications than thoracic and lumbar spinal tumor. However, it is regrettable that experimental investigation has thus far shown a dearth of attention to metastatic cervical spinal tumor. Research questionWhat is the conceptualization and realization of quadriparesis resulting from metastatic cervical spinal tumor? Material and methodsUsing Fischer 344 rats as the experimental cohort, this study orchestrated the engraftment of tumor cells procured from the 13762 MAT B III cell line (RRID: CVCL_3475), which represents mammary adenocarcinoma. These cells were engrafted into the vertebrae of the cervical spine. A comprehensive inquiry encompassing behavioral assessments, histological evaluations, and microangiographic analyses conducted after the aforementioned cellular transplantation was subsequently pursued. ResultsThe incidence of cervical paralysis was 61.1%. Notably, the evolution of paralysis was unfurled by two distinctive temporal phases within its natural history. A meticulous histological examination facilitated delineation of the tumor's posterior expansion within the spinal canal. Simultaneously, the tumor exhibited anterior and lateral encroachment on the spinal cord, inducing compression from all sides. Augmented by microangiographic investigations, conspicuous attenuation of stained blood vessels within the affected anterior horn and funiculus of the spinal cord was observed. Discussion and conclusionThe pathological advancement of paralysis stemming from metastatic cervical spinal tumor is now apprehended to unfurl through a biphasic phase. The initial phase is characterized by gradual unfurling spanning several days, juxtaposed against the second phase marked by swift and accelerated progression.

Finite element modeling and analysis of effect of preexisting cervical degenerative disease on the spinal cord during flexion and extension.

Recent studies have emphasized the importance of dynamic activity in the development of myelopathy. However, current knowledge of how degenerative factors affect the spinal cord during motion is still limited. This study aimed to investigate the effect of various types of preexisting herniated cervical disc and the ligamentum flavum ossification on the spinal cord during cervical flexion and extension. A detailed dynamic fluid-structure interaction finite element model of the cervical spine with the spinal cord was developed and validated. The changes of von Mises stress and maximum principal strain within the spinal cord in the period of normal, hyperflexion, and hyperextension were investigated, considering various types and grades of disc herniation and ossification of the ligamentum flavum. The flexion and extension of the cervical spine with spinal canal encroachment induced high stress and strain inside the spinal cord, and this effect was also amplified by increased canal encroachments and cervical hypermobility. The spinal cord might evade lateral encroachment, leading to a reduction in the maximum stress and principal strain within the spinal cord in local-type herniation. Although the impact was limited in the case of diffuse type, the maximum stress tended to appear in the white matter near the encroachment site while compression from both ventral and dorsal was essential to make maximum stress appear in the grey matter. The existence of canal encroachment can reduce the safe range for spinal cord activities, and hypermobility activities may induce spinal cord injury. Besides, the ligamentum flavum plays an important role in the development of central canal syndrome.Significance.This model will enable researchers to have a better understanding of the influence of cervical degenerative diseases on the spinal cord during extension and flexion.

Modeling and Characterization of the Narrow-Width Effect of 4H-SiC MOSFETs With Local Oxidation of SiC Isolation

In this article, the narrow-width effect (NWE) of 4H-SiC MOSFETs with local oxidation of SiC (LOCOSiC) isolation is reported. A channel width-dependent current hump was observed in the subthreshold region for n-type 4H-SiC MOSFETs with LOCOSiC, and a channel width-dependent threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{th}$ </tex-math></inline-formula> ) shift was observed for p-type 4H-SiC MOSFETs with LOCOSiC. This unusual NWE arises from the increase in the gate oxide thickness from the channel center toward the isolation edge and is different from the conventional NWE found in local oxidation of silicon (LOCOS) technology, which arises from the charge stored in the parasitic field oxide (FOX) capacitor and lateral dopant encroachment. A H2O diffusion and oxidation model is proposed in this article to explain the growth of a long bird’s beak in 4H-SiC MOSFETs with LOCOSiC. Technology computer-aided design (TCAD) simulations were executed to explore the H2O diffusion behavior of these MOSFETs, and an analytical formula was derived to predict the oxide layer thickness and length of bird’s beak along the diffusion path in the H2O diffusion and oxidation model. The problems caused by the long bird’s beak and unusual NWE can be overcome by increasing the overetching time of the pad oxide removal and marginally decreasing the thickness of the FOX layer. Therefore, the NWE of the LOCOSiC isolation is expected to be weaker than that of the LOCOS isolation because field implantation is unnecessary, and thus, dopant encroachment does not occur in the LOCOSiC technology.

Is the Measurement of Pedicle Axial Axes on Computed Tomography in Adolescent Idiopathic Scoliosis Also a Guide for Safer Screwing?

To evaluate the effect of pedicle angle measurement in preoperative axial computed tomography in patients with adolescent idiopathic scoliosis (AIS) on correct thoracic screw placement in free-hand technique on 3-dimensional printing AIS models. In this study, 14 3-dimensional spine models with a scale of 1:1, including the entire spine of a patient with Lenke type 1 curve, were used. Group 1 included screwing applications with unknown pedicle axial angles, and group 2 included screwing applications with known pedicle axial angles. The number and direction of screws in malposition were recorded. In addition, medial encroachment distances of the screws were classified as 0-4 mm and greater than 4 mm, and lateral encroachment distances were classified as 0-6 mm and greater than 6 mm. Evaluation parameters were compared statistically between the groups. The number of screws in the correct position in group 1 was lower than that in group 2 (P < 0.05). The medial and lateral malposition rate in group 1 was greater than that in group 2 (P < 0.05). The medial encroachment rate of 4 mm and greater and lateral encroachment rate of 6 mm and greater in group 1 was greater than that in group 2 (P < 0.05). The medial encroachment rate of 0-4 mm and lateral encroachment rate of 0-6 mm were similar between groups 1 and 2 (P > 0.05). Measurement of pedicle axial axes of preoperative thoracic vertebrae on computed tomography in patients with AIS offers more reliable screwing in free-hand technique.

Optimization of photoresist development and DRIE processes to fabricate high aspect ratio Si structure in 5 nm scale

The fabrication of high aspect ratio (AR) Si structure with extremely small feature size is attracting more and more attention recently. In this work, a top-down scheme for fabricating nanostructures with 4.4 nm line width and 40:1 AR has been proposed and demonstrated. This technique utilizes electron beam lithography for nano-scale patterning and deep reactive ion etching (DRIE) for pattern transfer. In this method, a special development strategy is discussed to improve the perpendicularity of the photoresist mask, and a novel nano-scale barrel is utilized as the testing structure for the DRIE process optimization. To study the critical dimension (CD) variation in the DRIE process, the geometric morphology of the obtained vertical barrels is simulated by an ion transport model. It is found that the asymmetrical lateral etching encroachment decreased the CD loss by 50%. Without using a hard mask, this technique is fully compatible with Si-based microelectronic processes. Therefore, after further study of geometric properties of the obtained nano structure, this proposed microelectronic-compatible approach sheds light on manufacturing 3D nano devices towards 5 nm scale and beyond.

Role of Recruitment Processes in Structuring Coralligenous Benthic Assemblages in the Northern Adriatic Continental Shelf.

Coralligenous biogenic reefs are among the most diverse marine habitats in the Mediterranean Sea. The northern Adriatic mesophotic coralligenous outcrops host very rich and diverse epibenthic assemblages. Several studies quantified the low temporal variability and high spatial heterogeneity of these habitats, while processes driving structuring and differentiation are still poorly understood. To shed light on these processes, temporal and spatial patterns of colonisation were investigated using travertine tiles deployed on three coralligenous outcrops, corresponding to the main typologies of benthic assemblages described in previous studies. Three years after deployment, assemblages colonising travertine tiles resembled the differentiation among sites revealed by the natural assemblages in terms of major ecological groups. Processes structuring and maintaining species diversity have been explored. Pioneer species with high reproduction rate, long distance larval dispersal and fast growth (e.g. the serpulid polychaete Spirobranchus triqueter and the bivalve Anomia ephippium), were the most abundant in the early stages of recruitment on the two outcrops further away from the coast and with lower sedimentation. Their success may vary according to larval availability and environmental conditions (e.g., sedimentation rates). At these sites early-stage lasted 10–12 months, during which even species from natural substrates began colonising tiles by settlement of planktonic propagules (e.g., encrusting calcareous Rhodophyta) and lateral encroachment (e.g., sponges and ascidians). On coastal outcrop, exposed to a higher sedimentation rates, tiles were colonised by fast-growing algal turfs. Resilience of northern Adriatic coralligenous assemblages, and maintenance of their diversity, appeared largely entrusted to asexual reproduction. Exploring the mechanisms that underlie the formation and maintenance of the species diversity is crucial to improve our understanding of ecological processes and to implement appropriate conservation strategies of the Adriatic coralligenous reefs.

Substrate controls growth rates of the woody pioneer Leptospermum lanigerum colonizing montane grasslands in northern Tasmania

AbstractWoody encroachment into grasslands is occurring across the world and is of concern to land managers. Studies of forest–grassland boundaries have informed models describing factors that govern tree establishment and the maintenance and origin of grassland ecosystems. Central to these models is the role of fire relative to ‘bottom up’ resources such as soil and the geological substrate in determining the extent of grassland and forest in the landscape. The view that human lit fires have shaped vegetation across the Australian continent has been bolstered by early 19th century observations of Aboriginal‐set fires in Tasmanian montane grasslands and the documented encroachment of trees into these grasslands in the 20th century. We examined the pattern of lateral encroachment of woolly tea‐tree (Leptospermum lanigerum (Sol. ex Aiton) Sm.) into these grasslands and used tree ring chronologies to investigate (i) past fire activity and (ii) how the geological substrate mediates growth rates of L. lanigerum. Changes in fire regimes inferred from L. lanigerum recruitment were corroborated by historical records. Encroachment (and increases in woody cover) of trees into grasslands was highest on granitic substances, although L. lanigerum growth rates were highest on basalt substrates, followed by conglomerate, granite and Mathinna sediments. Frequent burning up to the 1980s may have stymied the encroachment of trees in grasslands underlain by basalt. Growth rates decreased with increasing distance from the forest edge. This may be due to incremental changes in soil resources, grass competition and/or microclimate. The dynamics between grasslands and forests in montane Tasmania are consistent with tree growth–fire interaction models that highlight the interplay of edaphic factors, growth rates and fire history. Such complexity cautions against generalizations concerning the direct effects of landscape fire in shaping vegetation distribution across Australia.

Seventy years of continuous encroachment substantially increases 'blue carbon' capacity as mangroves replace intertidal salt marshes.

Shifts in ecosystem structure have been observed over recent decades as woody plants encroach upon grasslands and wetlands globally. The migration of mangrove forests into salt marsh ecosystems is one such shift which could have important implications for global 'blue carbon' stocks. To date, attempts to quantify changes in ecosystem function are essentially constrained to climate-mediated pulses (30years or less) of encroachment occurring at the thermal limits of mangroves. In this study, we track the continuous, lateral encroachment of mangroves into two south-eastern Australian salt marshes over a period of 70years and quantify corresponding changes in biomass and belowground C stores. Substantial increases in biomass and belowground C stores have resulted as mangroves replaced salt marsh at both marine and estuarine sites. After 30years, aboveground biomass was significantly higher than salt marsh, with biomass continuing to increase with mangrove age. Biomass increased at the mesohaline river site by 130±18Mg biomass km(-2) yr(-1) (mean±SE), a 2.5 times higher rate than the marine embayment site (52±10Mg biomass km(-2) yr(-1) ), suggesting local constraints on biomass production. At both sites, and across all vegetation categories, belowground C considerably outweighed aboveground biomass stocks, with belowground C stocks increasing at up to 230±62MgCkm(-2) yr(-1) (±SE) as mangrove forests developed. Over the past 70years, we estimate mangrove encroachment may have already enhanced intertidal biomass by up to 283097Mg and belowground C stocks by over 500000Mg in the state of New South Wales alone. Under changing climatic conditions and rising sea levels, global blue carbon storage may be enhanced as mangrove encroachment becomes more widespread, thereby countering global warming.

Performance of a Horizontal Well in Bounded Reservoir Subject to Edge Water Drive

When a reservoir is subject to edge water drive mechanism, well completion for the purpose of optimizing oil production becomes a critical objective. Achieving this objective will require a comprehensive knowledge of fluid movement in the reservoir. Effective well spacing and design, production or injection, transient test analyses possibilities and rate scheduling are additional benefits that can be derived from knowledge of fluid movement and dynamics. Source and greens functions are utilized in deriving the appropriate dimensionless pressure expressions for the reservoir system. Finally, dimensionless pressure derivatives are computed based on the dimensionless pressure expressions. Two-edged lateral water encroachment pattern is assumed for a centrally located horizontal well, occurring both at the toe and at the heel of the well. Influences of both reservoir and wellbore properties are investigated for infinite conductivity wellbore condition. Results show on the derivative that, flow is characterized first by infinite acting flow (constant value of 0.5) before a mandatory rapid decline to zero for all well and reservoir dimensions considered. The period of infinite activity, that is, period of clean oil production, is extended if the reservoir is much larger than the length of the well. Furthermore, dimensionless time of attainment of steady state for all well design is strongly dependent on the reservoir external extent and reservoir anisotropy under constant rate regime.

Numerical study of the effects of check dams on erosion and sedimentation in the Pachang River

Scouring and deposition processes resulting from variable rainfall and typhoon occurrence in tropical climatic conditions induce significant changes in the riverbeds of Taiwan. Along the Pachang River of western Taiwan, severe damage occurs during typhoons due to large and sudden variations in discharge, erosion, sediment transport and deposition. In order to simulate this process, the NETSTARS numerical modeling tool was used in the present paper. The influence of existing and planned check dam structures on flow control was also analyzed to determine their capacity to resist river erosion or to not be buried beneath sediments. Not only does the modeling tool allow calculation of the erosion-deposition behavior at the scale of the whole river, but it also provides local determination of the optimum location and characteristics such as foundation depth and lateral encroachment of future check dams. The results of a 10-year, long-term modeling simulation in terms of riverbed stability and scouring potential thus provide insights about unsafe future behavior at 4 sites. This numerical model provides a better general understanding and useful information for the optimal prevention of both the scouring damage and the burial related to sediment deposition with large changes in discharge and sediment transport.

On Different Process Schemes for MOSFETs With a Controllable NiSi-Based Metallic Source/Drain

This paper focuses on different silicidation schemes toward a controllable NiSi-based metallic source/drain (MSD) process with restricted lateral encroachment of NiSi. These schemes include thickness control of Ni, Ni-Pt alloying, and two-step annealing. Experimental results show that all the three process schemes can give rise to effective control of lateral encroachment during Ni silicidation. By controlling <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ni</sub> , NiSi-based MSD metal-oxide-semiconductor field-effect transistors (MOSFETs) of gate length <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LG</i> = 55 nm are readily realized on ultrathin-body silicon-on-insulator substrates with 20-nm surface Si thickness. With the aid of dopant segregation (DS) to modifying the Schottky barrier heights of NiSi, both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -type MSD MOSFETs show significant performance improvement, compared to reference devices without DS.

The role of barrier layer on Ohmic performance of Ti∕Al-based contact metallizations on AlGaN∕GaN heterostructures

Ohmic performance and surface morphology of Ti∕Al∕metal∕Au schemes, where metal is Ti, Mo, Pt, Ir, Ni, Ta, or Nb, have been studied to identify the role of the barrier layer on contact formation and reliability of multilayered metallizations. Results show a strong dependence of contact resistance and specific contact resistivity, as well as surface morphology, on the type of metal layer used. Annealing temperature dependent Ohmic performance was observed for the different schemes. The existence of distinct reaction domains with discernable compositional contrast is evidenced on the surface of annealed contacts. The observed variations in Ohmic performance and surface morphology did not have any correlation with the physical properties of the elemental metal layer. This suggests that contrary to the generally accepted opinion of the layer acting as a mere barrier layer, which serves to prevent indiffusion of Au and outdiffusion of Al, results from the present study provided insights on the active role this layer plays on the characteristics of metallization schemes. Although thermal annealing optimization for any of the Ti∕Al∕metal∕Au scheme can enable low-resistance contact formation, however, surface morphology and reliability (e.g., lateral encroachment) considerations limit the practical usage of the schemes to a few such as Ti∕Al∕Mo∕Au and Ti∕Al∕Pt∕Au.

Etching Process Simulation in MOS Nanoscale Structures

Problems of etching process, related with MOS transistors separation in LOCOS and SOS technologies were researched. Wafer of Si selection depending on crystallographic planes orientation is the main task. The etching rate along direct direction and lateral encroachment depends on crystallographic planes orientation. Wet etching is simulated with program ACES. Test photo mask with 100 nm holes for wafer etching is used for etching process simulation. The highest etching rate reached in Si with crystallographic planes orientation (110) – 23 nm/s. The biggest lateral etching belongs to substance with crystallographic planes orientation (100), 17 nm/s on both sides together in wet etching process. Ill. 11, bibl. 6 (in English; summaries in English, Russian and Lithuanian).

Lateral encroachment of Ni-silicides in the source/drain regions on ultrathin silicon-on-insulator

Lateral growth of Ni silicide towards the channel region of metal-oxide-semiconductor transistors (MOSFETs) fabricated on ultrathin silicon-on-insulator (SOI) is characterized using SOI wafers with a 20-nm-thick surface Si layer. With a 10-nm-thick Ni film for silicide formation, p-channel MOSFETs displaying ordinary device characteristics with silicided p+ source/drain regions were demonstrated. No lateral growth of NiSix under gate isolation spacers was found according to electron microscopy. When the Ni film was 20 nm thick, Schottky contact source/drain MOSFETs showing typical ambipolar characteristics were obtained. A severe lateral encroachment of NiSix into the channel region leading to an increased gate leakage was revealed, while no detectable voiding at the silicide front towards the Si channel was observed.

Disturbance history of a European old‐growth mixed‐species forest—A spatial dendro‐ecological analysis

AbstractQuestion:We were interested if and how variation in frequency and/or size of disturbances affect the dynamics of a montane old‐growth forest in Central Europe.Location:The forest, co‐dominated by Fagus sylvatica, Picea abies and Abies alba, is located in Lower Austria and represents one of the few sizable virgin forests in Central Europe.Methods:We extracted cores from 100 trees using systematic grid sampling (grid cell size 10 m × 10 m) on each of four 1‐ha plots distributed across the old‐growth remnant of 300 ha. We inferred disturbance events from rapid early growth and release events. For defining release criteria, we applied the boundary line method. We investigated the spatial structure of current age and gap distributions and past disturbance events in grid cells, using a pair density statistic.Results:The disturbance histories indicate decades with peaks and also extended periods without disturbance. Some peaks occurred synchronously at three of the four plots (1910s, 1930s, 1960s and 1980s). Peaks and gaps in the disturbance chronologies widely agreed with peaks and gaps in the age distributions. Most disturbance events during single decades showed a random spatial distribution.Conclusions:There is considerable variation in disturbance frequency and/or severity over time. Most disturbance events will rather thin the stand than clear larger areas at once. Following scattered disturbance two pathways occur: (1) gap expansion leading to creation of larger gaps, and (2) gap closure by lateral encroachment or by subcanopy trees growing into the canopy.

Recolonization of bigleaf maple branches by epiphytic bryophytes following experimental disturbance

The dynamics of epiphytic bryophyte communities following natural and human disturbance have rarely been quantified. We describe the response of bryophyte communities on bigleaf maple trees (Acer macrophyllum Pursh) in Olympia, Washington, following their experimental removal. Approximately 8% of the exposed area was recolonized by bryophytes 1 year after clearing, and 27% after 3 years. Lateral encroachment from bryophytes on the sides of the 20-cm-long plots accounted for 75% of this recolonization, with growth from residual plant parts or aerially dispersed diaspores accounting for the remaining 25%. Though it was not possible to distinguish between the latter two sources of cover, the number of clear de novo colonization events over the course of the year was low (0.18 dm-2). Disturbance appeared to reduce bryophyte diversity at this successional stage, as alpha and gamma diversity remained low after 1 year and had not recovered after 3 years. Reflecting the preponderance of lateral encroachment as the mechanism for recolonization, disturbance size may significantly affect the time needed to recolonize disturbed branch substrates. In addition to contributing to ecologists' understanding of processes of succession, these experiments may help to develop sustainable practices for moss-harvesting in the Pacific Northwest.Key words: succession, bryophytes, epiphytes, Acer macrophyllum, recolonization, canopy studies.

The leakage current improvement in an ultrashallow junction NMOS with Co silicided source and drain

The leakage current characteristics of the cobalt silicided NMOS transistors with a junction depth of 800 /spl Aring/ have been studied. In order to minimize the junction leakage current, the thickness of the CoSi/sub 2/ layer should he controlled under 300 /spl Aring/ and the Si surface damage induced by the gate spacer etch should be minimized. The post furnace annealing after the second silicidation by the rapid thermal annealing (RTA) process also affected the leakage current characteristics. The gate induced drain leakage (GIDL) current was not affected by the lateral encroachment of CoSi/sub 2/ layer into the channel direction when the gate spacer length was larger than 400 /spl Aring/.

Lateral diffusion effects in AuGe based source-drain contacts to AllnAs/InGaAs/InP doped channel MODFETs

We have investigated the formation of source-drain AuGe/Au and Ni/AuGe/Ni/Au alloyed ohmic contacts to AlInAs/InGaAs/InP doped channel MODFETs, and observed lateral diffusion of the contact system after the standard annealing procedure at the temperature range of 185 to 400°C. Auger depth profiling of contacts annealed at 250°C, revealed that Au(Ge) diffused through the top InGaAs and AlInAs layers into the active InGaAs layer, but had reduced penetration into the AlInAs buffer layer. This reduction in diffusion along the depth axis at the AlInAs buffer layer boundary is believed to result in enhanced lateral diffusion and the observed lateral encroachment of the contacts. Both Au and Ni containing contact systems showed similar behavior in terms of lateral diffusion with encroachment extending between 0.25 and 0.5 µm at the periphery of the contacts for annealing temperatures between 300 and 400°C. A controlled ramp-to-peak temperature annealing procedure is developed to suppress such lateral diffusion effects. Low temperature annealing (250°C) using this procedure resulted in equally low contact resistance values (∼0.1Θ-mm) and no lateral diffusion. It is concluded that in thin multilayered structures the modified annealing procedure presented here, is necessary for optimal ohmic contact formation.

Hydrogeologic and Water Quality Issues Along the El Paso/Juarez Corridor: An International Case Study

The twin cities of El Paso, Texas, and Juarez, in Chihuahua, Mexico, depend heavily upon well water from the Hueco Bolson aquifer for municipal and industrial water needs. Over-pumping of the Hueco Bolson aquifer has resulted in drawdown of the water table (as much as 150 ft [45.7 m]) and salinization by brackish water encroachment. Predevelopment ground-water flow pathlines ran from recharge areas along mountains to discharge areas at the Rio Grande. Pumping cones of depression beneath El Paso and Juarez have reoriented the hydraulic gradient, capturing the natural discharge of the aquifer. The deeper cone of depression is beneath Juarez. At one location in the aquifer, ground water now flows under the international border from the United States into Mexico. Chloride and other dissolved solids have increased over time in many municipal wells of El Paso and Juarez. Salinization of water wells is associated with extensive ground-water development and arid climate. A freshwater zone beneath El Paso and Juarez is underlain and in some places overlain by inferior-quality ground water. Mixing due to pumping, leakage from mud interbeds and artesian confining beds, cascading waters along well casings and screens, lateral saltwater encroachment, and potential upconing have degraded the freshwater zone. Other contaminants of concern in the aquifer include fecal coliform bacteria, and nitrate. Of particular concern are fecal coliform bacteria because many residents in Mexico use untreated well water.