Academic literature on the topic 'Concentration porteur charge'

Management literature related to globalisation and the need for organisations to gain a competitive advantage has grown in prominence over the past two decades (Caves 1982; Porter 1985, 1990, 1991, 1998; Barney 1995; Peteraf 1993; Barner 1996; Duncan, Ginter & Swayne 1998; Thomas, Pollock & Gorman 1998; Zahra 1998; Zahra & O'Neil, 1998; Gupta & Govindarajan 2001). Concomitant with globalisation and competitive advantage are issues related to achieving successful organisational change, since it logically holds that any activity to increase an organisation's effectiveness necessarily involves some sort of change. Much of the research attention in the past has focussed on strategies for implementing change, including overcoming resistance, rather than developing theories which lead to a greater understanding of the processes of change. Early research (Coch & French 1948; Ginzberg & Reilly 1957; Lewin 1951) reflect the historical concentration on how best to implement change; this tradition is more recently exemplified by Carnall (1999) who examines practical techniques for achieving change in organisations. However, literature relating to the theory of change remains fragmented and inconclusive.

Management literature related to globalisation and the need for organisations to gain a competitive advantage has grown in prominence over the past two decades (Caves 1982; Porter 1985, 1990, 1991, 1998; Barney 1995; Peteraf 1993; Barner 1996; Duncan, Ginter & Swayne 1998; Thomas, Pollock & Gorman 1998; Zahra 1998; Zahra & O'Neil, 1998; Gupta & Govindarajan 2001). Concomitant with globalisation and competitive advantage are issues related to achieving successful organisational change, since it logically holds that any activity to increase an organisation's effectiveness necessarily involves some sort of change. Much of the research attention in the past has focussed on strategies for implementing change, including overcoming resistance, rather than developing theories which lead to a greater understanding of the processes of change. Early research (Coch & French 1948; Ginzberg & Reilly 1957; Lewin 1951) reflect the historical concentration on how best to implement change; this tradition is more recently exemplified by Carnall (1999) who examines practical techniques for achieving change in organisations. However, literature relating to the theory of change remains fragmented and inconclusive.

The effects of changes in H+ activity on the adsorption and intracellular accumulation of Zn by Chlamydomonas variabilis Dangeard have been studied over the pH range 7–5. Other experimental variables included the dissolved free Zn concentration, [Zn2+]b, the antecedent growth conditions (pH of the growth medium = 7, 6, or 5), and the physiological state of the harvested cells. After short-term incubations with 65Zn, algal cells were collected and the concentrations of EDTA-extractable Zn ([Zn]a ~ surface-bound Zn) and nonextractable Zn ([Zn]c ~ transported Zn) were determined. Values for [Zn]a and the flux (F) of Zn across the cell membrane decreased with increasing culture age, but cells harvested at comparable growth stages behaved similarly in the subsequent short-term incubations with Zn, irrespective of their original growth pH. In the incubation solutions, however, pH changes did affect both [Zn]a and F. At constant [Zn2+]b, a decrease in pH from 7 to 5 led to lower values of [Zn]a (~70%), suggesting either a pH-induced change in algal surface potential or a competition between H+ and Zn2+ for specific binding sites at the cell surface; a concomitant decrease in Zn flux (50–65%) was noted. The decrease in pH from 7 to 5 also had the effect of minimizing the dependence of Zn flux on the Zn2+ concentration. Two Zn transport mechanisms may coexist in C. variabilis cells, one involving a diffusion pathway sensitive to pH changes in the range 7–5 and the other a high-affinity porter system operative at both pH 7 and pH 5. These results suggest that the net effect of lake acidification may well be a decrease in the overall bioavailability of Zn to algae.

Amino acid/K+ symport (cotransport) across a model epithelium, the lepidopteran midgut, is energized by an electrogenic H+ V-ATPase (H+ pump) in parallel with an electrophoretic K+/H+ antiporter (exchanger). Attempts to analyze this process using well-known equilibrium thermodynamic equations (Nernst, Gibbs), diffusion equations (Nernst, Planck, Einstein, Goldman, Hodgkin, Katz) and equations based on Ohm's law (Hodgkin, Huxley) have all encountered major difficulties. Although they are useful for analyzing nerve/muscle action potentials, these state equations assume that brief perturbations in membrane conductance, gm, and membrane voltage, Vm, occur so rapidly that no other parameters are significantly disturbed. However, transport studies often extend for minutes, even for hours. Perturbation of one parameter in complex transport systems invariably results in a state change as all of the other elements adjust to the prolonged stress. The development of a comprehensive mathematical treatment for transport systems that contain pumps and porters (transporters) has been hampered by the empirical nature of the concept of membrane permeability and conductance. The empirical definition of permeability was developed before pumps and porters were known. Thus, 'permeability' is a gross parameter that, in practice if not in theory, could describe all transport pathways including pumps, porters and channels. To surmount these difficulties, we have applied ionic circuit analysis to vesicular systems containing insect midgut transport proteins. In this analysis, pumps, porters and channels, as well as ionic concentration gradients and membrane capacitance, are components of ionic circuits that function to transform metabolic energy (e.g. from ATP hydrolysis) into useful metabolic work (e.g. amino acid uptake). Computer-generated by an H+ V-ATPase to K+/2H+ antiport and amino acid/K+ symport in the lepidopteran midgut.

AbstractWhile a large body of the literature on environmental policies has focused on the productivity impacts of regulations, less attention has been given to the link between environmental policies and market competition. In this paper, I develop a tractable model that incorporates variable mark-ups to study how a competitive environment is affected by environmental policies in a market with firm heterogeneity and endogenous abatement technology choice. The findings of this study are consistent with the Porter Hypothesis in the sense that environmental regulations motivate abatement technology adoption and enhance productivity and environmental quality. However, the productivity gain is mainly driven by reallocation of resources across firms rather than the induced abatement technological change. Tougher regulations harm the competitive environment by increasing average prices and market concentration. Social welfare also drops because in the absence of strong competition fewer variates are produced in equilibrium.

The concept of electrical circuit analysis is extended to include components found in membrane ionic transport systems. As in classical electrical equivalent circuits, resistors and capacitors are used to represent ion channels and the membrane capacitances, respectively; batteries represent energy sources driven by chemical reactions. In the extensions proposed, energy stored in various ionic concentrations is treated as charges on compartmental capacitors; symporters and antiporters are treated as energy-coupling devices analogous to transformers in alternating current electrical circuits. Pumps are shown to be special cases of porters in which the input circuit derives its energy from a chemical reaction. Using these components, circuit diagrams are drawn for several examples of membrane ion transport systems. By applying appropriate circuit analysis techniques, these diagrams facilitate the quantitative description of the energy distributions throughout the system.

Abstract Background: Beta thalassemia major patients (pts) are at an increased risk of heart failure, due to the deposition of iron in the heart causing myocardial siderosis. Intensive long-term iron chelation therapy (ICT) is required to obtain a normal myocardial T2* (mT2* >20 ms). Previously published studies suggested that cardiac iron removal lags changes in liver iron, and liver iron concentration (LIC) may affect the rate of removal of cardiac iron (Porter et al, ASH 2013). The objective of these analyses was to evaluate the association of the severity of LIC levels with the change in mT2* responses in pts with myocardial siderosis when treated with deferasirox (DFX) and deferoxamine (DFO) for up to 24 months (mo) in the CORDELIA study. Due to the very low pt numbers in the DFO arm, the results for these pts are not presented here. Methods: The study design, inclusion, and exclusion criteria have been reported previously (Pennell et al, Am J Hematol. 2015). Pts were categorized into LIC <7, 7 to <15 and ≥15 mg Fe/g dry weight (here after mg/g) both at baseline (BL) and specific visits, to assess the relation of absolute LIC and changes in LIC overtime, with mT2* and cardiac iron concentration (CIC), respectively. During the study, mT2* (ms), and LIC (mg/g) were measured every 6 mo at the same time point. CIC (mg/g) was analyzed as a post hoc parameter derived from mT2*. The change in mT2* was assessed as geometric mean (Gmean)±coefficient of variation (CV), ratio of the Gmean at specific time points divided by that at BL (Gmean at specific time point/Gmean BL) and both CIC and LIC as mean±SD, unless otherwise specified. Results: Of 197 pts, 160 (81.2%) completed 12 mo of treatment and 146 (74.1%) entered into the extension study whereas 103 pts continued on initially assigned treatment. Pts completing 24 mo of treatment included 65 (87.8%) of 74 pts (mean age 20.1±6.9 years, 59.5% male) on DFX and the results for these pts are presented as follows. Average actual doses (mg/kg/d) were 26.7±8.9, 31.5±7.4, 38.0±2.9 for LIC <7, 7 to <15, ≥15, respectively, during the extension study. The LIC levels for pts categorized by LIC <7, 7 to <15 and ≥15 improved from BL to Mo 24 as follows: 72% decrease (mean absolute change, -15.1±14.1), 66% decrease (-26.6±13.0), and 19% decrease (-10.2±15.7), respectively. For pts with BL LIC <7, 7 to <15, ≥15, mT2* improved from BL to Mo 24 as follows: 43% increase (14.0±18.1 to 21.6±31.1; mean abs change, 7.8±4.0), 50% increase (12.3±34.4 to 19.1±46.4; 8.0±6.0), and 30% increase (11.1±30.8 to 14.5±40.8; 4.1±5.0). The CIC values improved from BL to Mo 24 by 38% (1.8±0.4 to 1.1±0.5), 40% (2.3±0.9 to 1.4±0.7), and 23% (2.6±1.0 to 1.9±1.0), respectively. The mT2* responses for pts categorized according to visit specific LIC levels (LIC <7, 7 to <15, ≥15) from BL to Mo 12 were 22% increase (mean abs change, 3.7±4.3) in LIC <7, 21% increase (2.7±2.0) in LIC 7 to <15, and 7% increase (1.5±3.2) in LIC ≥15. From BL to Mo 24, mT2* increased by 51% (mean abs change, 7.8±5.3), 35% (4.1±2.5), and 11% (2.0±4.4), respectively. The CIC levels improved from BL to Mo 24 by 40% (mean abs change, -1.0±0.8) in LIC <7, 31% (-1.0±0.6) in LIC 7 to <15, and 6% (-0.1±0.8) in LIC ≥15. The change in mT2* (Gmean ratio) at Mo 6, 12, 18 and 24 are shown in the Figure A. The mT2* response was higher in pts who achieved a lower LIC category (LIC <7) at respective time points and this change in mT2* was more apparent at 18 and 24 mo of treatment with DFX. Discussion: Overall, DFX treatment resulted in a substantial decrease in LIC and improved mT2*. These results suggest a greater difference in mT2* improvement and CIC reduction in pts who achieved lower LIC during treatment with DFX. This divergence was progressive with time, being maximal at Mo 24. Thus, a therapeutic response in LIC with DFX may be associated with a greater likelihood of improving mT2*. Pts with high LIC ≥15 may require an effective long-term treatment with higher doses of ICT to have an improvement in mT2*, suggesting that cardiac iron removal is likely to be slow in heavily iron overloaded pts. These results are consistent with the previous report which showed a significant decrease in LIC and increased mT2* responses at Mo 36 in pts who attained lower end-of-year LIC levels when treated with DFX (Porter et al, ASH 2013) and highlight the potential value of monitoring the liver and cardiac responses during ICT. To further understand the kinetics between liver and cardiac iron removal, prospective investigation is warranted. Disclosures Pennell: Novartis: Consultancy, Research Funding; Apotex: Consultancy, Research Funding. Porter:Celgene: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; Shire: Consultancy, Honoraria. Piga:Acceleron: Research Funding; Cerus: Research Funding; Apopharma: Honoraria, Research Funding, Speakers Bureau; Novartis: Research Funding; Celgene Corporation: Honoraria. Han:Novartis: Employment. Vorog:Novartis: Employment. Aydinok:Cerus: Research Funding; Sideris: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Abstract Background Serum ferritin is regularly used to assess response to chelation therapy and correlates significantly with liver iron concentration (LIC) particularly when LIC is <7 mg Fe/g dry weight (dw) and serum ferritin is <4000 ng/mL. The absence of a serum ferritin decrease in the first months of a new chelation regime may be interpreted as a lack of response with respect to decreasing body iron load. However, sequential LIC determination (where available) has indicated that many of these patients do indeed have a decrease in LIC. This clinical experience requires greater understanding, particularly the nature of the LIC and serum ferritin relationship at baseline serum ferritin values ≥4000 ng/mL. The aim of this post-hoc analysis of the EPIC study was to gain insight into the relationship between serum ferritin and LIC in response to deferasirox over 1 year, in a large patient cohort, so that serum ferritin trends can be more clearly interpreted and evidence-based practical guidance be given for patients with transfusion-dependent thalassemia (TDT). Methods TDT patients were recruited from 25 sites, received 1-year of deferasirox treatment and had serum ferritin and R2 magnetic resonance imaging (R2-MRI)-assessed LIC measurements at baseline and 1 year. Summary statistics are provided for serum ferritin and LIC responders (decrease, any change from baseline <0) and nonresponders (increase or no change, any change from baseline ≥0), and for baseline serum ferritin categories (≥4000 vs <4000 ng/mL). Results Of the 374 patients analyzed in the EPIC liver MRI substudy, 317 had TDT, of which 72.7% (n=226) had a serum ferritin response and 27.3% (n=85) had no response. Importantly, after 1 year LIC decreased in approximately half of serum ferritin nonresponders (51.8%; n=44; Table) and in 79.6% of serum ferritin responders (n=180). Median (min, Q1, Q3, max) change in LIC (mg Fe/g dw) was –5.4 (–38.5, –11.7, –0.9, 15.4) in serum ferritin responders and –0.2 (–18.4, –2.6, 2.7, 19.6) in nonresponders. Median (range) transfusional iron intake (mg/kg/day) was similar in serum ferritin responders (0.30 [0.01–1.49]) and nonresponders (0.37 [0.02–1.00]). Median deferasirox dose (mg/kg/day) was higher in serum ferritin responders than nonresponders (28.1 [9.8–40.4] vs 23.7 [9.7–37.9]). Evaluation of responses by baseline serum ferritin showed that a greater proportion of serum ferritin responders with baseline serum ferritin <4000 ng/mL also had decreased LIC (88.7% [n=102]; Table), compared with serum ferritin responders with baseline serum ferritin ≥4000 ng/mL (70.3% [n=78]). However, serum ferritin baseline category had no effect on the proportion of patients who decreased LIC despite having no serum ferritin response (52.6% [n=30], <4000 ng/mL; 50.0% [n=14], ≥4000 ng/mL; Table). There was little change in median LIC in serum ferritin nonresponders after 1 year regardless of baseline serum ferritin value (–0.3 [–13.5–18.7] for <4000 ng/mL and 0.2 [–18.4–19.6] for ≥4000 ng/mL). Assessment by change in serum ferritin and LIC quadrants indicated that patients without serum ferritin or LIC response had the lowest baseline median (range) serum ferritin and LIC (2155 [480–9725] ng/mL; 11.9 [1.8–37.5] mg Fe/g dw; n=41), and received a lower median deferasirox dose (23.7 [9.7–36.0] mg/kg/day). Overall, median LIC decrease (mg Fe/g dw) was smaller in patients with baseline serum ferritin <4000 ng/mL (n=172) than in those with serum ferritin ≥4000 ng/mL (–2.8 [–38.5–18.7] vs –4.9 [–31.1–19.6]; n=139). Median iron intake was similar between groups. Discussion and conclusions A decrease in LIC was seen in ~80% of serum ferritin responders after 1 year of deferasirox; a greater proportion of serum ferritin responders (88%) decreased LIC when baseline serum ferritin was <4000 ng/mL. Importantly, among patients with no serum ferritin response up to half may be responding with respect to iron balance, indicating that a lack of serum ferritin response should be interpreted with caution. However, since a decrease in serum ferritin predicts a decrease in LIC in 80% of patients, MRI measurement (where available) should be prioritized for patients with serum ferritin increase/no change. Overall, serum ferritin response can help predict LIC response, but in some patients treated with deferasirox, serum ferritin may not accurately reflect removal of iron from the body. Figure 1 Figure 1. Disclosures Porter: Novartis: Consultancy, Honoraria, Research Funding; Shire: Consultancy, Honoraria; Celgene: Consultancy; Cerus: Membership on an entity's Board of Directors or advisory committees; Alnylam: Membership on an entity's Board of Directors or advisory committees. Taher:Novartis: Honoraria, Research Funding. Sutcharitchan:Novartis: Research Funding. Aydinok:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Chakravarty:Novartis: Employment. El-Ali:Novartis: Employment.

Abstract Abstract 5019 Background: MDS patients receiving chronic transfusions can develop significant iron accumulation in key organs such as the liver following 10–20 transfusions (Porter et al. BJH 2001). The diagnosis and monitoring of iron overload, as well as the effect of iron chelation therapy in MDS patients, is often based on serum ferritin (SF), with limited data on liver iron concentration (LIC), primarily due to the biopsy-related increased risk of bleeding and infections in these patients. However, LIC is clinically a more robust and direct measure of body iron burden and with the availability of non-invasive determination of LIC by MRI, LIC assessment has become more practical in MDS patients. This pooled analysis focuses on LIC assessments from a population of 71 MDS patients who completed 1 year of treatment with deferasirox (Exjade®), including assessment of the relationship between LIC vs SF and alanine aminotransferase (ALT). Methods: Analysis is based on 1-year pooled data from iron-overloaded patients with MDS who were enrolled in 4 open-label single-arm deferasirox studies: US02 (Low/Int-1 MDS patients, starting dose 20 mg/kg/day); 2409 (MDS patients with life expectancy >1 yr, starting dose 10–30 mg/kg/day); 108 (MDS patients with life expectancy >1 yr, dosing 5–40 mg/kg/day), and 2204 (Low/Int-1 MDS patients, starting dose 10–30 mg/kg/day). LIC was assessed in the US02, 2409 and 2204 studies using R2 MRI (St Pierre et al. Blood 2004). In the 108 study, LIC was assessed by magnetic liver susceptometry using a superconducting quantum interference device (SQUID) or ultrasound-guided percutaneous liver biopsy; LIC values obtained by SQUID were multiplied by a factor of 2 to correct for the underestimation of LIC by SQUID compared to biopsy (Porter et al. EJH 2008). Datasets were pooled for baseline (BL) characteristics, as well as LIC, SF and ALT at BL and end of study (EOS). Correlations were evaluated on a Pearson's correlation coefficient. Results: 71 patients (56.3% male) were assessed with a mean age of 65 years (range 16.5–82.0). Mean transfusional iron intake ± SD was 0.31 ± 0.12 mg/kg/day. Mean actual deferasirox dose was 19.6 ± 6.5 mg/kg/day. At BL, mean ± SD LIC was 20.5 ± 14.6 mg Fe/g dw (BL LIC <7 mg Fe/g dw, 21.1%; ≥7 mg–≤15 mg Fe/g dw, 23.9%; and >15 mg Fe/g dw, 54.9%). Median BL SF was 2620 ng/mL (range 538–12,639) (BL SF ≤2500 ng/mL, 47.9%; >2500–≤5000 ng/mL, 32.4%; and >5000 ng/mL, 15.5%). With 1 year of DFX, mean ± SD LIC decreased to 13.9 ± 13.1 mg Fe/g dw (mean absolute change –6.6 mg Fe/g dw). In patients with BL LIC <7 mg Fe/g dw (n=15), LIC was maintained with a mean absolute change of 1.0 ± 2.8 mg Fe/g dw, whereas in patients with BL LIC ≥7 mg Fe/g dw (n=56), LIC was reduced by –8.6 ± 10.7 mg Fe/g dw from BL. The proportion of MDS patients with LIC ≥7 mg Fe/g dw reduced from 78.9% at BL to 59.2% at EOS, with 50.7% of patients achieving a decrease in LIC of ≥30%. Median SF decreased to 2035 ng/mL (range 158–10520 ng/mL) with median absolute change from baseline of –630 ng/mL. There was a significant correlation between BL LIC and SF (R=0.548; P<0.0001). Change in LIC significantly correlated with change in serum ferritin (R=0.336; P=0.0042, Figure A). Mean ALT decreased from 55.9 to 38.9 U/L (absolute change –17.0). The change in LIC correlated with the change in ALT (R=0.397, P=0.0006, Figure B). Conclusions: This pooled analysis in a large cohort of transfusion-dependent MDS patients with LIC assessment shows significantly elevated LIC, with a high proportion of patients (55%) having severely elevated LIC of >15 mg Fe/g dw, a level known to markedly increase liver dysfunction and other iron overload-related complications. One year of treatment with deferasirox produced relevant reductions in LIC, an outcome possibly indicative of a clinical benefit. SF and ALT (an important indicator of liver function) also decreased, with reductions correlating with those of LIC. These findings indicate that correction of moderate-to-severe iron overload in MDS patients is associated with a parallel improvement in liver function. Disclosures: Gattermann: Novartis Pharma: Honoraria, Research Funding. Greenberg:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees. Habr:Novartis Pharma: Employment. Kpamegan:Novartis Pharma: Employment. Porter:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

The article deals with the role of clusters in today’s global economy. It is noted that in today’s economic environment it is difficult to overestimate the role of clusters in competition, which has changed significantly and continues to change due to the increased amount of information and knowledge about risk in the global economy. Considering the role of clusters in today’s global economy, it is noted that in modern scientific literature there is no single and generally accepted definition of a cluster as such. Different scholars and economists understand and interpret this concept variously. M. Porter gives the most accurate definition of the cluster. The main characteristics of clusters are considered, namely: geographical concentration, specialization, multiplicity of economic agents. The goals for which clusters are usually directed are given, namely: increase of competitiveness of cluster participants due to introduction of new technologies; reducing costs and improving the efficiency of relevant high-tech services through the synergy effect and unification of approaches in logistics, engineering, information technology, quality management, etc.; providing employment in the context of largescale enterprise reforming and outsourcing; consolidated lobbying of the cluster members’ interests in different authorities. The advantages of the cluster model for the development of the Ukrainian industry are considered and it is stated that among all the advantages of the cluster approach, the most important is the access to innovations, knowledge. It is stated that clusters can be formed in both traditional industries and high-tech areas, and very often different educational establishments or research structures serve as a specific center for cluster formation. It is concluded that within the state, clusters play the role of points of growth of the internal market and ensure the promotion of goods and services produced by them to international markets. This, in turn, contributes to the enhancement of the country’s international competitiveness on the whole, due to a number of advantages inherent in the cluster form of interaction between large, medium and small enterprises in all areas of business relations. One of the directions of socio-economic development of Ukraine, to increase its competitiveness, should be the support and development of territorial production clusters.

Etude du dopage p**(+) dans inp par implantation d'accepteurs peu profonds: be, mg, zn, hg. Caracterisation du desordre cree par diffusion raman; etude au degre de recristallisation apres recuit d'implantation. Etude par emission photoelectronique rx d'une contamination de surface. Determination de profils d'impuretes. Les profils de concentration de porteurs ont ete analyses par effet hall et mesures electrochimiques. Etude du coefficient de diffusion du zinc par la methode de boltzmann-matano

ANALYSE DE LA PHOTOLUMINESCENCE DE STRUCTURES GaAs/(Ca,Sr))F2/GaAs, A FLUORURE ACCORDE EN MAILLE AU GAAS; INFLUENCE DES PARAMETRES DE CROISSANCE ET DE LA DISTANCE A L'INTERFACE. COMPARAISON DES PERFORMANCES DE SEMICONDUCTEUR HETEROEPITAXIE A CELLES DE GAAS EPITAXIE; ETUDE DE COUCHES DE GAAS EPITAXIE SUR CAF2 MASSIF

Les divers etats metastables de type masse effective associes au centre dx dans algaas sont etudies au voisinage du croisement de bande. L'approfondissement anormal du niveau gamma sous champ magnetique revele la presence d'un etat de symetrie a1 identifie comme le troisieme etat du centre dx. L'etat metastable du niveau el2 dans gaas possede un niveau additionnel (o/-) resonnant capable de pieger les porteurs sous pression hydrostatique. Dans cet echantillon, la concentration de porteurs, proche de la densite critique de mott, a permis l'etude de la transition metal isolant induite par champ magnetique. Le modele de thomas-fermi adapte aux structures a plan de dopage dans gainas et gaas et les resultats de magnetotransport ont permis de degager certaines conclusions quant aux effets lies a l'elargissement du profil de dopage ou de non-parabolicite. Les structures a plans de dopage multiples sont ensuite etudiees. Enfin, les resultats de magnetotransport dans les heterojonctions ingaas/algaas, gainp/gaas sont analyses, en particulier la conduction parallele due a la presence de porteurs dans la barriere

Etude du magnetotransport sous champ intense dans les heterostructures gainas/alinas, gainp/gaas et gainas/algainas, l'application de la pression hydrostatique permettant de varier la structure de bande et la concentration electronique. Description coherente du systeme et de la contribution des differentes couches a la conduction totale dans les systemes a barriere alinas et algainas, basee sur une etude correlee des materiaux massifs et des heterojonctions. Mise en evidence d'un effet de photoconductivite persistante, associe a des defauts d'interface, dans le systeme gainp/gaas; etude de l'interaction electron-phonon comme fonction de la concentration des porteurs