456 research outputs found
Subcontracting dynamics and economic development: A study on textile and engineering industries
Recent studies on small and medium sized establishments emphasize the importance of networking and regional clusters for industrial development. This study is focused on an important form of cooperation between firms: subcontracting relationship. Our aim is to estimate the determinants of subcontracting in Turkish textile and engineering industries, and to derive policy implications of our estimates. We estimate subcontract offering and subcontract receiving models for both industries by using panel data on all establishments employing 25 or more workers in the period 1988-97. Our findings show that short-term/unequal relationship exists between parent firms and subcontractors in the textile industry whereas subcontracting relationships in the engineering industry are established between "similar", relatively advanced firms that have complementary assets and technologies.Subcontracting, firm cooperation, vertical integration
Global Links and Local Bonds: The Role of Ownership and Size in Productivity Growth
This paper examines direct and indirect contributions of foreign firms and small and medium-sized enterprises (SMEs) to aggregate productivity growth. We focus our attention on foreign firms and small firms for three reasons. First, industrial policy in almost all countries is oriented towards supporting SMEs and attracting foreign investment. Second, these two categories of firms contribute to micro-heterogeneity in all industries. Third, the recent industrial dynamics literature on foreign investment and small firms emphasizes the potential benefits of foreign firms and SMEs in generating new technologies, and creating new jobs. Using the data for Turkish manufacturing plants, we estimate production functions for all ISIC 4-digit level industries for the 1983-2001 period. We decompose productivity growth into its components (structural change, entry and exit, technical change, efficiency change, and scale effects) by firm ownership and size. The decomposition analysis by firm ownership and size allows us to understand the sources of productivity contributions by foreign firms and small firms.Productivity dynamics, decomposition, foreign direct investment, small and medium sized enterprises
History Matters for the Export Decision Plant Level Evidence from Turkish Manufacturing Industry
In a dynamic panel data framework, we investigate the factors influencing the export decision of the Turkish manufacturing plants over the 1990-2001 period. Our results support the presence of high sunk costs of entry to export markets, as well as the hypothesis that the full history of export participation matters for the current export decision. We further show that the effect of the past export experience on current export decision rapidly depreciates over time: Recent export market participation matters more than the participation further in the past. Finally, we show that while persistence in exporting helps lower the costs of re-entry today, there are diminishing returns to export experience. Our results are robust to plant characteristics (plant size, technology, composition of the employment), the spillovers from the presence of exporters in the same industry, as well as industry and year effects.Export decision, productivity, sunk costs, plant characteristics
Combinatorial integers (
We discuss the calculation of integral cohomology ring of LG/T and ΩG. First we describe the root system and Weyl group of LG, then we give some homotopy equivalences on the loop groups and homogeneous spaces, and calculate the cohomology ring structures of LG/T and ΩG for affine group A^2. We introduce combinatorial integers (m,nj) which play a crucial role in our calculations and give some interesting identities among these integers. Last we calculate generators for ideals and rank of each module of graded integral cohomology algebra in the local coefficient ring â€[1/2]
Investigating the Hydrogeotechnical and Microstructural Properties of Cemented Paste Backfill Using the CUAPS Apparatus
Dans l'industrie miniĂšre et des minĂ©raux, un grand volume et une large variĂ©tĂ© de rĂ©sidus miniers qui se composent de fractions grossiĂšres et fines et pouvant ĂȘtre soit rĂ©actifs (production d'acide) ou non rĂ©actifs sont produits Ă travers le monde chaque jour. La plupart des opĂ©rations miniĂšres utilise la fraction grossiĂšre des rĂ©sidus miniers pour le remblayage souterrain alors que les fines sont gĂ©nĂ©ralement dĂ©posĂ©es en surface dans des parcs Ă rĂ©sidus ou derriĂšre des digues de retenue. Il est toutefois bien connu que les digues de retenue sont Ă risque de rupture dĂ» Ă une fuite, l'instabilitĂ©, la liquĂ©faction et d'un dĂ©faut de conception. En outre, les rejets gĂ©nĂ©rateurs dâaciditĂ© peuvent causer des dommages importants Ă l'environnement sous la forme de drainage minier acide en libĂ©rant des mĂ©taux lourds, s'ils ne sont pas correctement gĂ©rĂ©s. Pour rĂ©soudre ces problĂšmes, la solution de gestion des rĂ©sidus miniers est d'adopter une approche qui est techniquement appropriĂ©e, Ă©conomiquement viable, Ă©cologiquement durable et socialement responsable. Le remblai cimentĂ© en pĂąte (RCP) est l'une des plus rĂ©centes mĂ©thodes novatrices de gestion des rĂ©sidus et se compose gĂ©nĂ©ralement d'un mĂ©lange des rĂ©sidus miniers tout-venant sans deslamage (70-85% solides), un liant hydraulique (3-7% en poids) pour rĂ©pondre aux critĂšres de stabilitĂ© requise et d'eau de mĂ©lange (20-25% d'eau).
La plupart des travaux de recherche a Ă©tĂ© jusqu'Ă prĂ©sent effectuĂ©e en focalisant sur les propriĂ©tĂ©s physico-chimiques, minĂ©ralogiques, mĂ©caniques et microstructurales des RCP. La plupart du temps, des moules en plastique conventionnels non drainĂ©s sont gĂ©nĂ©ralement utilisĂ©s pour dĂ©terminer les paramĂštres de conception du remblai minier en pĂąte qui dĂ©pendent du pourcentage solides, de la granularitĂ© des rĂ©sidus, du type de liant et de sa teneur, et du temps de cure. Toutefois, des Ă©tudes rĂ©centes ont montrĂ© que pour une mĂȘme recette de remblai utilisĂ©e au laboratoire et in situ aprĂšs un temps de cure donnĂ©, la performance mĂ©canique du remblai prĂ©parĂ© au laboratoire Ă©tait toujours infĂ©rieure Ă celle du remblai in situ. La raison principale derriĂšre ce phĂ©nomĂšne est que la cure du remblai en pĂąte in situ se serait faite sous l'action des contraintes effectives qui se seraient progressivement dĂ©veloppĂ©es dans le chantier remblayĂ© en raison de leur consolidation (sous poids propre ou par surcharge) et ainsi, entraĂźne l'amĂ©lioration du taux de dâacquisition de la rĂ©sistance mĂ©canique finale. La mise en place et les propriĂ©tĂ©s des remblais in situ ne peuvent ĂȘtre reproduits Ă l'aide des moules classiques. Par consĂ©quent, il existe un besoin Ă©vident de dĂ©velopper de nouveaux Ă©quipements et de nouvelles procĂ©dures d'essais capables de reproduire de façon rĂ©aliste les conditions de cure in situ des remblais cimentĂ©s en pĂąte dans un environnement de laboratoire contrĂŽlĂ©. Dans ce cas le but Ă©tant d'ĂȘtre en mesure d'atteindre des rĂ©sistances mĂ©caniques les plus Ă©levĂ©es possibles et/ou au moins Ă©quivalentes pour une meilleure conception de remblai.
Cette thĂšse est composĂ©e principalement de quatre articles/manuscrits de journaux avec comitĂ© de rĂ©vision par les pairs. Le premier article essaye d'investiguer les diffĂ©rences dans les propriĂ©tĂ©s hydromĂ©caniques des RCP observĂ©es entre les Ă©chantillons qui curent dans les conditions de laboratoire et in situ par le biais de la premiĂšre version d'un nouvel appareil dâessais en laboratoire appelĂ© CUAPS (systĂšme de cure sous pression appliquĂ©e). Il aborde substantiellement les propriĂ©tĂ©s physiques, hydrotechniques et gĂ©ochimiques dâĂ©chantillons de RCP prĂ©parĂ©s avec des rĂ©sidus catĂ©gorisĂ©s comme grossiers (15 wt% Â< grains de moins de 20 ÎŒm < 35 wt%) provenant d'une mine polymĂ©tallique europĂ©enne. Le deuxiĂšme article prĂ©sente davantage l'Ă©valuation de l'appareil CUAPS modifiĂ© qui permet dâestimer certaines propriĂ©tĂ©s hydromĂ©caniques des RCP incluant la compression anisotrope (consolidation 1-D) et la permĂ©abilitĂ©. L'appareil CUAPS modifiĂ© capture bien la dĂ©formation axiale qui se produit dans le remblai pendant sa compression (soit par surcharge ou par son poids propre) et cela permet de rĂ©aliser des essais de consolidation unidimensionnelle, mais aussi des essais de dissipation de la pression interstitielle, de permĂ©abilitĂ© (mesure de la conductivitĂ© hydraulique saturĂ©e), de cure sous contrainte effective appliquĂ©e et de cure sous diffĂ©rents taux de compression. Les rĂ©sultats prĂ©liminaires illustrent bien l'efficacitĂ©, l'utilitĂ© et la capacitĂ© de cet appareil CUAPS modifiĂ© dans l'optique de l'optimisation rĂ©aliste des recettes de RCP Ă ĂȘtre utilisĂ©es pour le remblayage souterrain. Le troisiĂšme article focalise particuliĂšrement sur les propriĂ©tĂ©s de consolidation unidimensionnelle Ă l'aide de l'appareil CUAPS modifiĂ©. Les Ă©chantillons de remblai en pĂąte ont Ă©tĂ© prĂ©parĂ©s avec des rĂ©sidus catĂ©gorisĂ©s comme fins (35 wt% Â< grains de moins de 20 ÎŒm < 60 wt%). Le quatriĂšme et dernier article prĂ©sente les rĂ©sultats de l'Ă©tude sur les effets des conditions de cure (consolidĂ©e et non consolidĂ©e) sur les propriĂ©tĂ©s microstructurales du RCP au moyen de la porosimĂ©trie par intrusion de mercure (PIM) et la dĂ©termination de la surface spĂ©cifique. Quelques modĂšles empiriques de prĂ©diction de la rĂ©sistance en compression uniaxiale (UCS) en fonction de certains paramĂštres de la microstructure des RCP ont Ă©tĂ© proposĂ©s.
Cette thĂšse de doctorat a non seulement permis une meilleure comprĂ©hension des propriĂ©tĂ©s des remblais en pĂątes prĂ©parĂ©s en laboratoire, mais il a Ă©galement permis d'Ă©valuer avec succĂšs l'appareil CUAPS modifiĂ© qui peut ĂȘtre un outil prĂ©cieux pour la collecte de donnĂ©es Ă©quivalentes Ă celles du remblai in situ mais Ă l'Ă©chelle du laboratoire. Ce travail est considĂ©rĂ© comme une Ă©tude originale qui a investiguĂ© le comportement en consolidation unidimensionnelle des Ă©chantillons de RCP Ă diffĂ©rents temps de cure et aussi le comportement d'Ă©chantillons de RCP curĂ©s sous une sĂ©rie d'incrĂ©ments de pressions en permettant le dĂ©veloppement graduel de la contrainte effective dĂ» au drainage (simulant les chantiers souterrains remblayĂ©s). Cette recherche a donc contribuĂ© Ă une meilleure comprĂ©hension du comportement de ce matĂ©riau relativement complexe qu'est le RCP et a mis au point une procĂ©dure dâessai pour Ă©valuer la performance mĂ©canique qui pourrait ĂȘtre considĂ©rĂ©e lors du processus de conception de tout remblai cimentĂ© en pĂąte. Enfin, l'appareil CUAPS modifiĂ© aidera les chercheurs et les opĂ©rateurs des remblais Ă mieux comprendre les propriĂ©tĂ©s de consolidation des CPB frais ou durcis qui devraient ĂȘtre prĂ©parĂ©s en laboratoire.
In the mining and mineral industry worldwide, large volumes and many varieties of mine tailings consisting of coarse and fine fractions that are either reactive (acid generating) or non-reactive are produced every day. Most mining operations use the coarse fraction of the tailings for underground backfill, while the fines are usually deposited on the surface into tailings impoundments or dams. However, it is well known that these dams are at risk of failure due to leakage, instability, liquefaction and inadequate design. Moreover, unless they are properly managed, acid-generating tailings can cause significant environmental damage by generating acid mine drainage that releases heavy metals. Overcoming such problems requires tailings management approaches that are technically suitable, economically viable, environmentally sustainable and socially responsible. Cemented paste backfill (CPB), an engineering material, is used in a recent, innovative tailings management method. Typically, CPB is a mixture of total mill tailings without removing the fines, or desliming (70â85 wt% solids), and single, binary and ternary hydraulic binders (3â7 wt%) in order to meet stability requirements and combined with mixing water (20â25 wt%).
Most studies to date have focused on the physicochemical, mineralogical, mechanical and microstructural properties of CPB. Conventional undrained plastic moulds (non-perforated) are usually used to determine mine backfill design parameters, depending on the solid mass concentration, grain size grading, binder type and content, and curing time. However, recent studies have shown that for identical backfill recipes used in the laboratory and in situ after a given curing time, the performance (i.e., mechanical strength) of laboratory-prepared CPB samples is consistently lower than that obtained from in situ CPB samples. The primary reason is that in situ backfill material is cured under effective stresses that develop gradually in a stope due to self-weight and/or time-dependent consolidation loads, which accelerate the rate of final strength development. In situ CPB placement and properties cannot be replicated using conventional moulds. Therefore, innovative equipment and test procedures that allow realistic reproduction of in situ curing conditions of CPB materials in a controlled laboratory setting are needed. The aim is to obtain higher or at least equivalent mechanical strength, and consequently a better backfill design
One-Dimensional Consolidation Parameters Of Cemented Paste Backfills
Each year, mine and mill operations generate enormous amounts oftwo waste types â fine-grained tailings and coarse-grained waste rocks. Fine-grained tailings are either discharged in slurry form to surface tailings dams or delivered in cementitious form to underground mine stopes as backfilling, while coarse-grained rocks are typically stored by depositing as a dry material in large dumps. The engineering design of surface tailings dams or underground mine stopes is often controlled by the high compressibility and low shear strength characteristics of fine-grained tailings. Cemented paste backfill CPB indicating saturated, fine-grained backfills can undergo major consolidation settlement during early curing stages. Thus, a better understanding ofthe rate and magnitude ofboth differential and total settlement ofCPB cured under stress is essential for a proper backfill geotechnical design. The consolidation parameters of CPB can be determined from an improved lab setup called CUAPS (curing under applied pressure system). This setup is capable of simulating the CPB placement and curing conditions, and measuring the consolidation parameters of CPB cured under effective stresses ranging between 0.5 and 400 kPa. In this study, a series of one-dimensional consolidation tests were conducted on CPB samples allowing for examination of the effects of binder type and rate as well as curing time on the compression properties (e.g., coefficient of consolidation cv, compression index Cc, and recompression index Cr) and the final geotechnical index properties (e.g., void ratio ef, water content wf, and degree ofsaturation Sf). Results showed that as the binder content increases, the initial resistance to consolidation increases. The cv value decreases over the course of time due to evolution of the CPB microstructure generated by the hydration process
Lip segmentation using adaptive color space training
In audio-visual speech recognition (AVSR), it is beneficial
to use lip boundary information in addition to texture-dependent
features. In this paper, we propose an automatic lip segmentation
method that can be used in AVSR systems. The algorithm
consists of the following steps: face detection, lip corners extraction,
adaptive color space training for lip and non-lip regions
using Gaussian mixture models (GMMs), and curve evolution
using level-set formulation based on region and image
gradients fields. Region-based fields are obtained using adapted
GMM likelihoods. We have tested the proposed algorithm on a
database (SU-TAV) of 100 facial images and obtained objective
performance results by comparing automatic lip segmentations
with hand-marked ground truth segmentations. Experimental
results are promising and much work has to be done to improve
the robustness of the proposed method
History Matters for the Export Decision: Plant-Level Evidence from Turkish Manufacturing Industry
We analyze the export decision of Turkish manufacturing plants from 1990 to 2001. In addition to the presence of high Sunk costs of entry in export market,,, we find support for the hypothesis that the full history of exporting matters for the current export decision. However, the effect of the past export experience on current export decision depreciates rapidly with time: recent export market participation matters more than the participation further in the past. Finally, while persistence in exporting helps lower the costs of re-entry today, there are diminishing returns to export experience. The results are robust to several plant characteristics (plant size, technology, composition of the employment), and the spillovers from the presence of exporters in the same industry. (C) 2008 Elsevier Ltd, All rights reserved
Foreign Direct Investment and Productivity Spillovers: Identifying Linkages through Product-based Measures
This article analyzes direct and indirect effects of foreign ownership on productivity in the Turkish manufacturing plants between 1990 and 1996. First, based on Olley-Pakes production function estimates, foreign affiliates are shown to be more productive than local plants. Using sectoral output shares of foreign affiliates and 1990 input-output matrix to identify linkages across plants, regression results show that productivity spillovers from foreign affiliates to local plants took place through horizontal and vertical linkages. However, these results mostly lose their economic and statistical significance once plant-level data on the value of output and inputs are used to obtain product-based measures of linkages across plants. The magnitude of spillover effects are much smaller than the ones obtained with industry-based measures. Statistically meaningful positive spillovers are found to be generated through backward linkages only
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