Main Gates Research Articles

A Geometric Computational Model for Calculation of Longwall Face Effect on Gate Roadways

In this paper a geometric computational model (GCM) has been developed for calculating the effect of longwall face on the extension of excavation-damaged zone (EDZ) above the gate roadways (main and tail gates), considering the advance longwall mining method. In this model, the stability of gate roadways are investigated based on loading effects due to EDZ and caving zone (CZ) above the longwall face, which can extend the EDZ size. The structure of GCM depends on four important factors: (1) geomechanical properties of hanging wall, (2) dip and thickness of coal seam, (3) CZ characteristics, and (4) pillar width. The investigations demonstrated that the extension of EDZ is a function of pillar width. Considering the effect of pillar width, new mathematical relationships were presented to calculate the face influence coefficient and characteristics of extended EDZ. Furthermore, taking GCM into account, a computational algorithm for stability analysis of gate roadways was suggested. Validation was carried out through instrumentation and monitoring results of a longwall face at Parvade-2 coal mine in Tabas, Iran, demonstrating good agreement between the new model and measured results. Finally, a sensitivity analysis was carried out on the effect of pillar width, bearing capacity of support system and coal seam dip.

Remarks on Heat Emission during Operation in Hot Rock Mass and on Possibilities of Its Use

Heat flow in a hot mining department, where the original temperature of rock is greater than 50 0 C has been studied. The total power of electrical equipment installed in the department amounts to about 6 MW. In accordance with the current climate regulations of Polish mining, the air temperature in the workplace, measured with a dry-bulb thermometer may not be higher than 33 0 C. In order to be able to ensure a temperature consistent with the regulations in such department, fresh air supply workings must be equipped with chillers of a total refrigeration capacity of 2 MW. The carried out analysis of the results of climate forecasts and of the results of the rock mass cooling modelling around these workings has shown that approximately 30% of the cooling power is needed to receive the heat from the hot rock massif. Assuming the required air temperature at 28 0 C (enabling an unshortened working time), then the cooling power needed to extract heat from the rock mass would be much greater. The studies carried out show that the amount of heat emitted in the department also depends on the phase of the longwall course (the length of main gates and changes in rock temperature in them). It has been proposed that hot water from condensers supplies the crystallizers of surface (absorption) cooling devices. In this way, reduction of the air-conditioning expenditure will be obtained.

Synthetic CharacteristicsOf Traditional Historic Houses Entrances In Old City Of Mosul

The traditional and heritage houses of Mosul old city have significant architectural value represented by their distinctive characteristics. The main entrances and gates of these buildings with their constructed features located in touch with alleys indicate the building importance and identify the social level of their residents. The paper aims to define the synthetic characteristics and relations of the detailed structural elements constituting the main entrances of the traditional houses in Mosul old city, by gathering, analyzing and classifying these elements in categories according to their architectural details and materials, in order to employ them in providing a digital data base to be used in documentation, reconstruction and conservation activities. The paper also aims to present guidelines and recommendations for creating the virtual objects library for the entire architectural elements of the building in Mosul old city. Research results showthe great diversity of structural elements and synthetic relationships of the heritage houses entrances in Mosul old city, with high harmony between these various elements, referring to the old architects attempts for enriching and improving the alleys heritage facades using architectural elements details, and systematic construction processes. Keywords: Synthetic characteristics, Entrances, Traditional houses, Built Heritage, Mosul Old City

Intermodal Nodes for the European Metropolis: Amsterdam Zuidas as EURandstad's Gate

Since more than fifty years, in the Netherlands, the Randstad Holland [1,2] represents a model of reference within the international debate on the sustainable balance between urban areas, infrastructural development and preservation of natural environment. The polycentric urban structure of the country progressively built up a new metropolitan reality of Europe, based on a stable configuration of cities’ spatial relations around the maintenance of the Green Hearth core and on strategic logics of infrastructural developments. However today the double awareness to rebalance growing population of urban areas and to open the region towards North-Central Europe, create fundamental conditions for a renewed expanding vision [3]. The current Dutch metropolitan perspective looks at the densest cities of Amsterdam and Rotterdam as main European and international gates, addressing large scale ambitions to clusters of urban developments at the intersection of main roads, railways and local infrastructures. This paper presents an investigative approach and intends to provoke academic discussion on the conflicting and possible relationships between urban policies and design strategies in the construction of a new metropolitan European perspective. Particular emphasis is put on the coordination between contemporary policies with spatial implications in the city of Amsterdam. Exploring its geographical advantages, the City tries to give form to policies’ abstraction of Randstad 2040 vision in the recent structural spatial Agenda, focused on strategic urban and economic cores. The current vision represents the metropolitan ambition of the Netherlands, where the project of Zuidas - literally South Axis - is a prime example of a new model of intermodal urban hub. Throughout the Dutch example, this paper attempts to presentZuidas testing its capability to enhance an innovative approach – in urban policy and spatial implication- to sustainable development.

Downstream Passage of Lake Sturgeon through a Hydroelectric Generating Station: Route Determination, Survival, and Fine‐Scale Movements

AbstractDownstream passage of Lake Sturgeon Acipenser fulvescens through hydroelectric facilities is known to occur but is poorly understood. Acoustic telemetry was used to investigate downstream‐passage routes, survival, and fine‐scale movements at the Slave Falls Generating Station, located on the Winnipeg River, Manitoba. Downstream‐passage rates were estimated at 2.9% (range = 0.0–4.4%) per year for Slave Falls Reservoir adults and 21.1% (range = 19.3–22.9%) per year for subadults tagged in the lowermost section of the reservoir. No juvenile passage was observed. Lake Sturgeon movements immediately upstream of the Slave Falls Generating Station main sluiceway gates were related to bathymetric features. Fish that approached via deepwater habitat tended to abandon their downstream trajectory movements before or upon reaching the top of a relatively shallow (∼10 m depth) bedrock saddle that occurs ∼45 m upstream of the main sluiceway gates. Based on acoustic telemetry (fine‐scale tracking and presence–absence data) and supplemental information, such as trash rack spacing and spill conditions, 7 of 11 (64%) observed downstream‐passage events were concluded to have occurred via bottom‐draw regulating sluices located in the northeastern end of the powerhouse. At least 91% of the observed downstream‐passage events were survived. Results suggest that protection initiatives at hydroelectric facilities could exploit the Lake Sturgeon's bottom‐oriented nature, with bottom‐draw sluice gates likely providing a feasible way to facilitate safe downstream passage.Received June 28, 2013; accepted January 28, 2014

(Invited) Dielectrics for Graphene Transistors for Emerging Integrated Circuits

In this paper, we present the use of high-k dielectric material in design and physical modeling of following two types of transistors for emerging integrated circuits: graphene nano ribbon (GNR) tunnel field-effect transistors (TFETs) and graphene short channel FETs.Graphene nanoribbon field effect transistor (GNR FET) is one of the promising devices for emerging integrated circuits because of its exceptional electronic properties such as the large carrier mobility and planar structure. However, the problem is a high drain-source leakage current in standby state due to small band gap of graphene and short channel effect (SCE) enforced by the transistor feature size. We have proposed a new GNR FET structure which has two side gates with a lower work function than the main gate on top of the SiO2 and HfO2 insulating layers. The main gate and two side gates have work functions of Φ1=4.8eV and Φ2=4.5eV, respectively. The GNR FET width and length has been chosen 1.5nm and 15nm, where the source and drain regions are doped with a molar fraction of ionized donors equal to 5×10-3/cm3. The lengths of the main and side gates are 2.5nm and 1.25nm while those of insulator layers have been used as a variable. We have simulated the proposed GNR FET using the self-consistent solution of three-dimensional Poisson–Schrödinger equation, within the Non-equilibrium Green’s function (NEGF) formalism. In our new GNR FET structure, the two side gates induce the inversion layers next to drain and source regions, which increase the controllability of the main gate on the channel potential barrier by providing an effective screen for the main gate to prevent the change in drain current due to the change in drain voltage. We have found that the application of the HfO2 in combination of SiO2 in the proposed GNR FET not only shifts the drain source leakage current to the lower values by several orders of magnitude but also make the leakage current sensitive to the proportionality of thicknesses of SiO2 and HfO2. The proposed GNR FET introduce a minimum peak in the drain source leakage current much below that of a common GNR FET with the same insulator structure. The minimum leakage currents of the proposed structure for total insulator thickness of 10Å, 15 Å and 20Å are approximately 6×10-13A, 4×10-12A and 5×10-11A, respectively while those of a common GNR FET are 1.5×10-10A, 9×10-10A and 5×10-9A, respectively. The minimum peak in leakage current has been obtained for HfO2 thickness = 8Å and 14 Å corresponding to the total insulator thickness of 10 Å and 15 Å, respectively, while it shifts to purely HfO2 insulator layer for that of 20 Å. The proposed GNR FET can diminish the short channel effect and prevent an undesirable increase in the leakage current by decreasing the channel length. Effect of dielectric on performance of GNR TFETs is also studied through an analytical current transport model which we have developed for designing of integrated circuits. It is observed that choice of dielectric material and corresponding thickness along the lateral gate position severely modifies performance of GNR TFET. We have found that for constant oxide thickness of 0.76nm, threshold voltage reduces from 0.176V to 0.054V for dielectric permittivity of 2.5 to 47.5. We have also noticed that the performance of GNR TFET studied through threshold voltage and sub-threshold slope depends on selection of both dielectric material and their thickness. Specific results on influence of choice of dielectric in designing of GNR TFET will be presented included in the paper and presentation.

An Approach to Analyze and Solve Traffic Problems in Universities: Model of King Abdulaziz University, Kingdom of Saudi Arabia

There is no doubt that the traffic problem is one of the problems faced by universities in general، and in different intensities for roads، intersections and parklands. The negative effects of traffic congestion and bottlenecks are clear; they include extension of long waiting lines and increasing the time of transport with the consequences of ill effects. The effective solutions placed to resolve these problems need specialized studies relying on scientific methods for collecting and analyzing relevant data, and drawing effective conclusions, recommendations, and solutions. The main purpose of this study is to analyze the problems of traffic congestion in universities, with realistic application to King Abdulaziz University in Jeddah as a case study and to provide the best solutions to achieve fluent flow of traffic in the future. Due to the complexity of the problem and its huge data، and to facilitate the analysis process, the problem has been divided into three main sections: main gates، Interior roads and intersections، and car parking. The data is collected by four different ways: the use of automatic counting equipment which records the number of vehicles that pass in each hour during the period of counting manual method of counting through registration in a prepared form so as to record the number of vehicles located in the parking place during the each hour، interviewing and a survey of a random sample of students, faculty members, administrative employees, and university passers-by and visitors, as well as observing and recording traffic problems in some places of the university. It has been possible to reach a wide range of recommendations for gates، roads، and parking areas, to achieve the desired goals of ease flow of traffic now and in the future. The proposed solutions takes into account the simplicity, low cost, and non-recourse to destructive changes such as complete changing the place of the university، or demolition of all buildings and re-planning. The study gives also a set of conclusions that can be followed as an approach to study، analyze and solve the general traffic problems in other universities.

The Canadian Arctic Archipelago throughflow in a multiresolution global model: Model assessment and the driving mechanism of interannual variability

The volume and freshwater transports through the Canadian Arctic Archipelago (CAA) are assessed using the unstructured‐mesh Finite Element Sea ice‐Ocean Model (FESOM) in a global setup with the CAA resolved at 5 km scale. The hindcast simulation realistically represents fluxes through the main gates of the Arctic Ocean and the Arctic sea ice conditions. During the period 1968–2007, the mean volume transports through Lancaster Sound and Nares Strait amount to 0.86 and 0.91 Sv, respectively. The monthly mean volume transport through western Lancaster Sound is highly correlated with the observational estimate (r = 0.81). The seasonal variability of the Lancaster Sound transport is well represented in the model. The simulated mean CAA freshwater export rate is 123 mSv, slightly higher than the observational estimate. The interannual variability of CAA volume transports is determined by sea surface height (SSH) gradients between the Arctic Ocean and northern Baffin Bay. The sea level upstream of Lancaster Sound is mainly determined by that along the Beaufort Sea coast, which can be explained by changes in the wind regimes (cyclonic versus anticyclonic) associated with release or accumulation of freshwater in the Beaufort Gyre. Sea level variations downstream of Lancaster Sound and Nares Strait are connected to SSH variations in the eastern Baffin Bay and in the Labrador Sea, which can be attributed to the variability of ocean‐atmosphere heat fluxes. Both processes upstream and downstream of the CAA are linked with the North Atlantic Oscillation type of atmospheric variability. The local mesh refinement of ∼5 km allows us to investigate the contribution of individual narrow straits to the Parry Channel volume transport. The volume transports through these straits show a very similar variability.

Voltage difference engineering in SOI MOSFETs: A novel side gate device with improved electrical performance

We studied the impact of voltage difference engineering in a silicon-on-insulator metal oxide semiconductor field-effect transistor (SOI-MOSFET) and compared the performance to that of a conventional SOI-MOSFET (C-SOI). Our structure, called a SIG-SOI MOSFET, includes main and side gates with an optimum voltage difference between them. The voltage difference leads to an inverted channel as an electrical drain extension under the side gate. This channel creates a stepped potential distribution along the channel that it cannot be seen in the C-SOI MOSFETs. The voltage difference controls the channel properly and two-dimensional two-carrier device simulations revealed lower threshold voltage variations, larger breakdown voltage, higher voltage gain, lower hot carrier effects, improved drain-induced barrier lowering, lower drain conductance, higher unilateral power gain, and lower leakage current compared to a C-SOI device. Thus, our proposed structure has higher performance than a typical C-SOI structure.

New fieldwork at the Severan fort ofMyd(…)/Gheriat el-Garbia on thelimes Tripolitanus

AbstractThe most outstanding oasis fort of thelimes Tripolitanus, Myd(---)/Gheriat el-Garbia, saw the deployment of various military units between AD 198/201 and 275/80. Archaeological research in 2009/10 focussed on the fortifications, particularly the main and rear gates, the northern angle tower and interval towers 2 and 4 as well as the curtain wall at its south corner. The towers of theporta praetoriahave been reconstructed theoretically with three storeys, at an overall height ofc.12.5 m. Of the headquarters building two of the rear rooms, including the shrine, were excavated. A monumental inscription of a length ofc.9.0 m and corresponding architectural elements suggest the existence of agromabuilding. Completely unexpected by archaeologists as well as ancient historians and rather spectacular is a late Roman reoccupation of the military site: after a hiatus ofc.80+ years building activities were undertaken within the fort and repairs and the blocking of the main gate could be observed and probably attributed to the deployment of a unit oflimitaneibetween AD 360/80 (at the earliest) and 430/55. The reoccupied fort might be identified with the so far unknowncastra Madensia, where themilites munificeswere garrisoned (Notitia Dignitatum Occ.31, 30). Further evidence of occupation, possibly of a Libyan chieftain and his tribe, has been assigned to the second half of the fifth century, continuing thereafter until AD 540+.

Take Me to Your Leader: The Power of Place in Prehistoric Anatolian Settlements

During the Early Bronze Age in central Anatolia (ca. 3000-2000 b.c.e.), a change in the residential location of houses belonging to elites and/or leaders occurred. In the fourth and early third millennia, various sites feature settlement plans in which village leaders, or higher-ranking residents, inhabited homes in close proximity to main gates. By the later third millennium the trend was to locate homes away from the gates, sometimes behind physical barriers. These changes are concomitant with several plateauwide phenomena, including increases in population and settlement size at emerging regional centers, and the establishment of international trade networks. The reasons underlying this residential adjustment lie in the need for protection against outsiders while also desiring to impress both outsiders and those living within the community. An additional motivating factor, however, was the erosion of trust between community members, i.e., a “fear of the insiders” factor as societies experienced interna...

A comparative study about the variant form of the Chinese character in the five sorts of old maps drawing outside of the four main gates of old Seoul including DeDongYei-jido

A comparative study about the variant form of the Chinese character in the five sorts of old maps drawing outside of the four main gates of old Seoul including DeDongYei-jido

Stabilization and Strengthening the Foundation of the Two Entrance Gates of the Holy Shrine of Imam Reza (PBUH)

This paper presents the structural analysis and constructional method for the stabilization and strengthening of the foundation of the two entrance gates in Holy Shrine of Imam Reza (PBUH). The holy shrine of Imam Reza (PBUH) is a great complex in the city of Mashhad in Iran. It was founded nearly 1000 years ago and has developed and become extensive through the times. There are several entrances and wide courts around the oldest section in the centre of the complex. Recently, the extension scopes of this complex, required excavation and construction in the basements near the two main gates, called Saat and Naghareh Khaneh Edifice. These activities, near the 400 years old edifices, needed special mobilization, like, monitoring the historical buildings and strengthening their foundations. A deep study was performed, which pursued two purposes. The first purpose was to strengthen the foundation of the buildings and the second was to make a tunnel through the foundation of the buildings because of some operational benefits for the client. At the first glance these two purposes, seemed contradictory, but finally, a new structural system for the foundation were designed and built, which was able to carry the superstructure loads to the ground while a wide tunnel was constructed as well. Special scheduled sequences of construction were prepared, which was flexible and sufficiently reliable so as to overcome any undesirable circumstances and obstacles. Monitoring the buildings behaviour during the constructional phase was conducted to assist the execution directions. This project was carried out successfully and it is in use.

Istanbul Grand Bazaar Evacuation System Vulnerability Assessment

The Grand Bazaar is a historical trade centre more than 500 years in the historical peninsula of Istanbul, Turkey. It consists of almost 3,600 small shops from different sectors (such as jewellery, carpet, leather, souvenir, finance, restaurant, café, confection etc.), two Bedesten, 64 street and 16 Han (inn) buildings. The Bazaar has 21 main gates that open to different streets and have different relation with outside. More than 25000 staff work in the shops and 300-500 thousand users come to Bazaar daily depending on the season and day. The pedestrian density is changeable, depending on the place of the inner street and the type of the sector. The historical disaster records (earthquake, dated 1766 and 1894, the grand bazaar fire, dated 1954) show that there was evacuation vulnerability. The main gates (exit doors) and exit route need some rehabilitation for safety evacuation during any disaster. The aim of this study is to evaluate the Grand Bazaar’s emergency evacuation vulnerability. The evacuation vulnerability factors question the width, length and natural illumination of the evacuation route, maintenance of the roof, presence of hazardous materials, door specifications as size, material, opening direction, maintenance and difference in elevation on the route and exit area such as staircase and thresholds.

Diversion tunnel of the Irganaiskaya waterworks facility and prospects of its use in the period of erection of the dam to intermediate levels

General information on the diversion tunnel and statement of the problem of its use at normal maximum operating level NMOL = 521 m. The Irganaiskaya waterworks facility is being built in Dagestan on the Avarskoe Koisu River. The design engineering solutions for this waterworks facility and the stage of the construction have been considered in [1]. Excess water volumes of this waterworks facility are passed through the right-bank combined diversion and operational tunnel-kind spillway designed for freeflow operation in all stages of flow passage. The diversion tunnel is the first story of the spillway, which serves for passing flows in the initial period of the erection of the waterworks facility and in temporary operation. This structure consists of an intake channel, intake portal, slightly inclined part of the tunnel, and a tail device. The gretaer part of the slightly inclined tunnel and the tail device are to be used later in the period of continuous operation after the erection of the sluiceway entrance and inclined part of the sluice of the upper (second) story. Some data on the structure of the diversion tunnel and of laboratory hydraulic studies performed for its design are presented in [2]. The full length of the diversion tunnel is 965 m, and a two-span gates chamber is constructed in its intake portal (Fig. 1). The sizes of the entrance cross-section of the gates chamber (in front of the slots of the guard gates), which determine the diversion capacity of the tunnel, are h b = 6 4.5 m; the sizes of the main gates are 6.3 3.5 m. The operating gates were actuated by hydraulic actuators mounted at a level of 522.0 m of the upper part of the intake portal of the tunnel. Metallic facing exists in the gates chamber only on the zone adjoining the gate slots. Behind the gates chamber and the bottleneck transition part, the tunnel has a trough shape with a height of 11 m and a width of 8 m; the interface of the trough and of the vertical side walls of the tunnel is rounded. On the upstream region (in front of the connection between the tail reach of the tunnel and the inclined conduit of the operational spillway) the tunnel has a sloped bottom (the slope is 0.006) and on the downstream discharge region the slope is 0.0235. In the greater part of the length the diversion tunnel is made of concrete of class B30, but in the upstream region the Power Technology and Engineering Vol. 39, No. 6, 2005

Two-Dimensional Analytical Threshold Voltage Model of Nanoscale Fully Depleted SOI MOSFET With Electrically Induced S/D Extensions

A new analytical model for the surface potential and the threshold voltage of a silicon-on-insulator (SOI) MOSFET with electrically induced shallow source/drain (S/D) junctions is presented to investigate the short-channel effects (SCEs). Dividing the SOI MOSFETs silicon thin film into three zones, the surface potential is obtained by solving the two-dimensional Poissons equation. Our model includes the effects of the body doping concentration, the lengths of the side and main gates and their work functions, applied drain and substrate biases, the thickness of the gate and buried oxide, and also the silicon thin film. Our model results reaffirm that the application of induced S/D extensions to the SOI MOSFET will successfully control the SCEs for channel lengths even less than 50 nm. Two-dimensional simulation results are used to verify the validity of this model, and quite good agreements are obtained for various cases.

Winged human-headed bulls of Nineveh: Genesis of an iconographic motif

More than one hundred monumental sculptures of winged human-headed bulls have been identified among the remains of Assyria's capitals, of which around forty come from Nineveh. When these ancient Mesopotamian stone giants re-emerged they became a symbol of Neo-Assyrian power. This article aims to study the genesis of these emblematic figures by looking at the earliest iconographic examples. This genealogical development will lead us to consider the etymology and iconographic transcriptions of the Akkadian terms traditionally associated with the figures of winged human-headed bulls, and to ponder their evolution in the various fields of artistic production.Forty-three colossal sculptures of winged human-headed bulls have so far been discovered in Nineveh: two at the Nergal gate, a few fragments from the Bit Nakkapti and around forty monumental sculptures in the remains of Sennacherib's Palace. Situated on each side of the main gates, these figures guarded the city and palace entrances. They were carved from monolithic limestone blocks and completed after they had been set up either in gateways, in which case the head is in line with the body, or in the alignment of the walls flanking the entrances, with the head turned at an angle of ninety degrees. Botta suggested that these colossi had originally been surmounted by a straight lintel; however, Place's excavations in Khorsabad revealed the existence of brick arches built above some of the gates. Although they played a real functional role due to their position, their presence does not seem to have been architecturally indispensable because other entrances with similar dimensions were not strengthened in this way. Consequently, it would be better to speak of an “active façade”.

The Hellenistic and Byzantine Defences of Tocra (Taucheira)

AbstractThe fortifications of the Hellenistic and Roman city of Tocra are over 2 km long (including the sea-wall) and comprise a curtain wall up to 2 m wide flanked by 31 rectangular towers. Three main structural phases were noted in the survey carried out in 1966 by David Smith: (1) Hellenistic walls of isodomic ashlar, (2) later Hellenistic work of isodomic ashlar with bevelled edges, associated with the indented trace along the south rampart, and (3) an extensive rebuild of plain ashlar blocks including the towers and reconstruction to the East and West Gates, dateable, on the basis of Procopius, to the reign of Justinian. The general significance of the fortifications at Tocra is considered in the second part: these include the Hellenistic indented trace along the south side, later reinforced by towers in the sixth century AD. Also of wider importance was the use of an outer wall orproteichisma, and the pentagonal, pointed towers at the two main gates. Both these elements were unusual in Byzantine North Africa and they are discussed as part of the more general repertory of Byzantine fortifications. The unusual tower adjacent to the West Church is considered in the context of literary accounts. The article concludes by considering how the architecture and magnitude of the fortifications can allow a reassessment of the wider role of the city in the sixth and seventh century defences of Cyrenaica.

Apparent Independent Action of Nimodipine and Glutamate Antagonists to Protect Cultured Neurons Against Glutamate-induced Damage

A disturbed cellular calcium homeostasis is suggested to play a pivotal role in neuronal damage. Energy deficiency causes depolarization of the neuronal membrane and Ca2+ enters the cells through different ion channels, the voltage-sensitive L-type Ca2+ channels and the NMDA-operated channels being the main gates. In the present study we used primary cultures of rat hippocampal neurons to demonstrate that the dihydropyridine calcium antagonist nimodipine, the non-competitive NMDA antagonists dizocilpine and memantine, as well as the AMPA antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline), attenuate the glutamate-induced neuronal damage dose-dependently. Nimodipine applied simultaneously with NMDA-antagonists and NBQX, respectively, resulted in somewhat greater neuroprotection of glutamate-treated neurons compared with the effects of these agents applied singly. The type of interaction is best described by an independent action in combination, which means that the relative effects of nimodipine were not enhanced. Therefore, it can be considered as a lack of potentiation. © 1997 Elsevier Science Ltd. All rights reserved.

Destruction of dams in connection with spillway discharges

1) Despite the intuitively determined high danger which dams pose, long-time operating practice of a large number (about 33,000) of dams with a height of more than 15 m constructed by almost all countries of the world attests to their high reliability. The average annual number of victims in the entire world in connection with destruction or damage of these structures is 133 persons. The number of victims in mining coal equivalent in energy to its amount generated at a hydroelectric station is about 20 times higher, and in the case of energy consumption in motor transport, for example, 1000 times higher. 2) During the long period of operating concrete dams by all countries of the world, an insignificant number of cases of their failure in connection with operation of spillways has been recorded. Spillway damages and scouring of the channel in the lower pool develop over the course of a rather long time and, as a rule, it is possible to conduct repair works eliminating the danger of destruction of the entire dam. 3) The greatest (about 44%) number of failures of structures with high earth dams is related to the operation of spillways. As a rule, in this case the development of even insignificant damage of the dam cannot be prevented and within a short time interval partial or even almost complete destruction of the dam occurs.This should be taken into account when examining the problem of increasing the reliability of hydro developments with earth dams to the level characteristic on average for concrete dams or higher. 4) The main cause of failure of earth dams in connection with operation of spillways is their insufficient capacity. A number of countries, including the USA, have decided it is necessary to periodically check the sufficiency of the capacity of spillways of operating objects and are carrying out this work. When planning hydro developments it is necessary to examine the problem of the possibility of brief overtopping of the dam as a result of the formation of a breakthrough wave or collapse of an unstable mass into the reservoir if such an event is probable.High requirements should be imposed on the reliability of the main gates of spillways. In a number of cases a backup system is used, which provides operation of these gates.