scispace - formally typeset
Search or ask a question

Showing papers by "Leibniz University of Hanover published in 2005"


Journal ArticleDOI
TL;DR: There is a strong rationale that in this research model, high magnesium ion concentration could lead to bone cell activation, and metallic implants made of magnesium alloys degrade in vivo depending on the composition of the alloying elements.

2,078 citations


Journal ArticleDOI
29 Jul 2005-Science
TL;DR: High-resolution scanning tunneling microscopy and density functional calculations are used to unravel the local structure of surface and subsurface oxygen vacancies on the ceria surface and have implications for the understanding of oxidation processes on reducible rare-earth oxides.
Abstract: The high performance of ceria (CeO2) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resolution scanning tunneling microscopy and density functional calculations to unravel the local structure of surface and subsurface oxygen vacancies on the (111) surface. Electrons left behind by released oxygen localize on cerium ions. Clusters of more than two vacancies exclusively expose these reduced cerium ions, primarily by including subsurface vacancies, which therefore play a crucial role in the process of vacancy cluster formation. These results have implications for our understanding of oxidation processes on reducible rare-earth oxides.

1,178 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used in-situ produced cosmogenic nuclides (e.g. 10Be, 26Al), mostly in quartz from alluvial sediment.

605 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated whether the extraordinary warm climatic conditions of the 1990s are reflected in the floristic composition of Alpine summit vegetation and, if so, what the magnitude and rate of species change has been over the last few decades compared to the documented increase in species richness within the first 80 years of the 20th century.
Abstract: Questions: The 1990s were the warmest decade since the beginning of climate measurements. Based on almost 100 years of monitoring in the Swiss Alps, we asked (1) whether the extraordinary warm climatic conditions of the 1990s are reflected in the floristic composition of Alpine summit vegetation and, if so, (2) what the magnitude and rate of species change has been over the last few decades compared to the documented increase in species richness within the first 80 years of the 20th century. Location: Ten high mountain summits of the Bernina area in the southeastern Swiss Alps. Methods: Resurvey of the floristic composition of the uppermost altitudinal 10 m of these summits, applying the same methodology of former two surveys (1905 and 1985) and recording the presence of all vascular plant species. Results: Whereas the continued increase in plant species richness of high alpine summit vegetation is confirmed, our results also suggest an acceleration of the trend in the upward shift of alpine plants. Conclusion: Vegetation change in the southeastern Swiss Alps has accelerated since 1985, consistent with a climate change explanation.

544 citations



Journal ArticleDOI
TL;DR: A reanalysis of both biogeographic and bioclimatic data of equal spatio-temporal resolution reveals a coherent and synchronous shift in both species' distribution and climate.
Abstract: Recently, there has been increasing evidence of species' range shifts due to changes in climate. Whereas most of these shifts relate ground truth biogeographic data to a general warming trend in regional or global climate data, we here present a reanalysis of both biogeographic and bioclimatic data of equal spatio-temporal resolution, covering a time span of more than 50 years. Our results reveal a coherent and synchronous shift in both species' distribution and climate. They show not only a shift in the northern margin of a species, which is in concert with gradually increasing winter temperatures in the area, they also confirm the simulated species' distribution changes expected from a bioclimatic model under the recent, relatively moderate climate change.

353 citations


Journal ArticleDOI
21 Jan 2005-Science
TL;DR: It is shown that apatite abundance in sediments on the Namibian shelf correlates with the abundance and activity of the giant sulfur bacterium Thiomargarita namibiensis, which suggests that sulfur bacteria drive phosphogenesis.
Abstract: Phosphorite deposits in marine sediments are a long-term sink for an essential nutrient, phosphorus. Here we show that apatite abundance in sediments on the Namibian shelf correlates with the abundance and activity of the giant sulfur bacterium Thiomargarita namibiensis, which suggests that sulfur bacteria drive phosphogenesis. Sediments populated by Thiomargarita showed sharp peaks of pore water phosphate ( /=50 grams of phosphorus per kilogram). Laboratory experiments revealed that under anoxic conditions, Thiomargarita released enough phosphate to account for the precipitation of hydroxyapatite observed in the environment.

352 citations


Journal ArticleDOI
TL;DR: The results suggest that the TTO values are more related to national variables than values derived by VAS, and makes it possible to anticipate these cultural differences in studies carried out in Germany.
Abstract: The aim of this survey study was to derive the societal values of the general public for the EuroQol EQ-5D. Using the same protocol as previously used in the United Kingdom, we compared the German values with the British. In face-to-face interviews a sample of 339 individuals in northern Germany valued 15 different health states from a sample of 36 states. Values were derived using the York MVH protocol for time trade-off (TTO) and a visual analogue scale (VAS). Values for all 243 health states of the EQ-5D were estimated by a regression model. The VAS values revealed close a resemblance to the British VAS results. German TTO values were higher than the British. This was especially the case for the worse health states. The results suggest that the TTO values are more related to national variables than values derived by VAS. The use of the TTO values of this investigation makes it possible to anticipate these cultural differences in studies carried out in Germany.

338 citations


Proceedings ArticleDOI
15 Aug 2005
TL;DR: An additional criterion for web page ranking is introduced, namely the distance between a user profile defined using ODP topics and the sets of O DP topics covered by each URL returned in regular web search, and the boundaries of biasing PageRank on subtopics of the ODP are investigated.
Abstract: The Open Directory Project is clearly one of the largest collaborative efforts to manually annotate web pages. This effort involves over 65,000 editors and resulted in metadata specifying topic and importance for more than 4 million web pages. Still, given that this number is just about 0.05 percent of the Web pages indexed by Google, is this effort enough to make a difference? In this paper we discuss how these metadata can be exploited to achieve high quality personalized web search. First, we address this by introducing an additional criterion for web page ranking, namely the distance between a user profile defined using ODP topics and the sets of ODP topics covered by each URL returned in regular web search. We empirically show that this enhancement yields better results than current web search using Google. Then, in the second part of the paper, we investigate the boundaries of biasing PageRank on subtopics of the ODP in order to automatically extend these metadata to the whole web.

327 citations


Journal ArticleDOI
TL;DR: A number of automatic and semi-automatic reconstruction methods are reviewed in more detail in order to reveal their underlying principles and some general properties of reconstruction approaches which have evolved.

312 citations


Proceedings ArticleDOI
04 Nov 2005
TL;DR: Several metrics for analyzing rating patterns of malicious users are proposed and an algorithm for protecting recommender systems against shilling attacks is evaluated that can be employed for monitoring user ratings and removing shilling attacker profiles from the process of computing recommendations, thus maintaining the high quality of the recommendations.
Abstract: Collaborative filtering techniques have been successfully employed in recommender systems in order to help users deal with information overload by making high quality personalized recommendations. However, such systems have been shown to be vulnerable to attacks in which malicious users with carefully chosen profiles are inserted into the system in order to push the predictions of some targeted items. In this paper we propose several metrics for analyzing rating patterns of malicious users and evaluate their potential for detecting such shilling attacks. Building upon these results, we propose and evaluate an algorithm for protecting recommender systems against shilling attacks. The algorithm can be employed for monitoring user ratings and removing shilling attacker profiles from the process of computing recommendations, thus maintaining the high quality of the recommendations.

Journal ArticleDOI
01 Apr 2005-Cornea
TL;DR: With the obtained normal values, the corneal horizontal diameter was not significantly greater in males than in females and more precise determination of microcornea and macrocornea will be possible in the future.
Abstract: Purpose:The corneal horizontal diameter (white-to-white) is abnormal in diseases like microcornea, relative anterior microphthalmos, and corneal dystrophies. Because normal values are described imprecisely in the literature, the purpose of this study was to reevaluate the horizontal corneal diameter

Journal ArticleDOI
TL;DR: In this article, the temporal and epistemic economy connected to the transatlantic travels of the categorical triad of race-class-gender is studied, and conditions and forces that have fuelled these journeys are discussed.
Abstract: The article focuses on the temporal and epistemic economy connected to the transatlantic travels of the categorical triad of ‘race-class-gender’. It looks at conditions and forces that have fuelled...


Journal ArticleDOI
TL;DR: Discontinuation of long-term therapy with infliximab eventually led to relapse of disease activity in all patients but one and patients who were in partial remission according to the ASAS criteria and those with normal C-reactive protein levels at the time point of withdrawal had longer times to relapse after discontinuation of the treatment.
Abstract: We analyzed the clinical response and the time to relapse after discontinuation of continuous long-term infliximab therapy in patients with ankylosing spondylitis (AS). After 3 years of infliximab therapy, all AS patients (n = 42) discontinued treatment (time point (TP)1) and were visited regularly for 1 year in order to assess the time to relapse (TP2). Relapse was defined as an increase to a value ≥ 4 on the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and a physician's global assessment ≥ 4 according to the recommendations of the Assessments in Ankylosing Spondylitis (ASAS) working group. After 52 weeks, 41 of the 42 patients (97.6%) had to be reinfused because of relapse. The mean change in the BASDAI between TP1 and TP2 was 3.6 ± 1.7 and that in the physician's global assessment was 4.4 ± 1.8 (both P < 0.001). The mean time to relapse was 17.5 weeks (± 7.9 weeks, range 7 to 45). Ten patients (24%) showed a relapse within 12 weeks and 38 patients (90.5%), within 36 weeks. After 52 weeks, only one patient had remained in ongoing remission without further treatment with anti-tumor-necrosis factor. Patients who were in partial remission according to the ASAS criteria and those with normal C-reactive protein levels at the time point of withdrawal had longer times to relapse after discontinuation of the treatment. Retreatment with infliximab was safe and resulted in clinical improvement in all patients to a state similar to that before the treatment was stopped. Discontinuation of long-term therapy with infliximab eventually led to relapse of disease activity in all patients but one.

Journal ArticleDOI
TL;DR: Differences in CW pectin and its degree of methylation contribute to genotypic differences in Al resistance in maize in addition to the release of organic acid anions previously reported.
Abstract: Cell-wall (CW) pectin content and its degree of methylation in root apices of selected maize cultivars were studied in relation to genotypic Al resistance. Maize cultivars differing in Al resistance were grown in nutrient solution treated with or without Al, and pectin content of the root tips was determined. Control plants did not differ in pectin content in the 5 mm root apex. Al treatment increased the pectin content of the root apex in all cultivars but more prominently in the Al-sensitive cultivars. Pectin and Al contents in 1 mm root sections decreased from the apex to the 3-4 mm zone. Pectin contents of the apical root sections were consistently higher although significantly different only in the 1-2 mm zone in the Al-sensitive cv Lixis. Al contents in most root sections were significantly higher in cv Lixis than in Al-resistant cv ATP-Y. Localization of pectins by immunofluorescence revealed that Al-sensitive cv. Lixis has a higher proportion of low-methylated pectin and thus a higher negativity of the cell wall than Al-resistant cv ATP-Y. This is in agreement with the higher Al content and Al sensitivity of cv Lixis. It is concluded that differences in CW pectin and its degree of methylation contribute to genotypic differences in Al resistance in maize in addition to the release of organic acid anions previously reported.

Journal ArticleDOI
TL;DR: Analysis of possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.
Abstract: We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.

Journal ArticleDOI
TL;DR: In this paper, perovskite hollow fiber membranes of the chemical composition BaZrxCoyFezO3−δ (BCFZ) have been developed using a phase inversion spinning process followed by sintering.

Proceedings ArticleDOI
05 Apr 2005
TL;DR: This paper discusses the benefits of best match/top-k queries in the context of distributed peer-to-peer information infrastructures and shows how to extend the limited query processing in current peer- to-peer networks by allowing the distributed processing of top- k queries, while maintaining a minimum of data traffic.
Abstract: Query processing in traditional information management systems has moved from an exact match model to more flexible paradigms allowing cooperative retrieval by aggregating the database objects' degree of match for each different query predicate and returning the best matching objects only. In peer-to-peer systems such strategies are even more important, given the potentially large number of peers, which may contribute to the results. Yet current peer-to-peer research has barely started to investigate such approaches. In this paper we discuss the benefits of best match/top-k queries in the context of distributed peer-to-peer information infrastructures and show how to extend the limited query processing in current peer-to-peer networks by allowing the distributed processing of top-k queries, while maintaining a minimum of data traffic. Relying on a super-peer backbone organized in the HyperCuP topology we show how to use local indexes for optimizing the necessary query routing and how to process intermediate results in inner network nodes at the earliest possible point in time cutting down the necessary data traffic within the network. Our algorithm is based on dynamically collected query statistics only, no continuous index update processes are necessary, allowing it to scale easily to large numbers of peers, as well as dynamic additions/deletions of peers. We show our approach to always deliver correct result sets and to be optimal in terms of necessary object accesses and data traffic. Finally, we present simulation results for both static and dynamic network environments.

Proceedings ArticleDOI
13 Jun 2005
TL;DR: This paper introduces a method to extract fingerprints of any surface or solid object by taking the eigenvalues of its respective Laplace-Beltrami operator, which is possible to support copyright protection, database retrieval and quality assessment of digital data representing surfaces and solids.
Abstract: This paper introduces a method to extract fingerprints of any surface or solid object by taking the eigenvalues of its respective Laplace-Beltrami operator. Using an object's spectrum (i.e. the family of its eigenvalues) as a fingerprint for its shape is motivated by the fact that the related eigenvalues are isometry invariants of the object. Employing the Laplace-Beltrami spectra (not the spectra of the mesh Laplacian) as fingerprints of surfaces and solids is a novel approach in the field of geometric modeling and computer graphics. Those spectra can be calculated for any representation of the geometric object (e.g. NURBS or any parametrized or implicitly represented surface or even for polyhedra). Since the spectrum is an isometry invariant of the respective object this fingerprint is also independent of the spatial position. Additionally the eigenvalues can be normalized so that scaling factors for the geometric object can be obtained easily. Therefore checking if two objects are isometric needs no prior alignment (registration/localization) of the objects, but only a comparison of their spectra. With the help of such fingerprints it is possible to support copyright protection, database retrieval and quality assessment of digital data representing surfaces and solids.

Journal Article
TL;DR: A thorough review of the medical and dental literature reveals that titanium can also cause chemical-biological interactions, and the biostability of titanium is becoming increasingly questioned.
Abstract: Titanium is used for many dental applications and instruments, such as orthodontic wires, endodontic files, dental implants, and cast restorations. The popularity of titanium is primarily due to its good mechanical properties, its high corrosion resistance, and its excellent biocompatibility. A thorough review of the medical and dental literature reveals, however, that titanium can also cause chemical-biological interactions. Tissue discoloration and allergic reactions in patients who have come in contact with titanium have been reported. The biostability of titanium is becoming increasingly questioned. At the same time, new technologies and materials, such as high-performance ceramics, are emerging which could replace titanium in dentistry in the not-too-distant future.

Journal ArticleDOI
01 Sep 2005-Geoderma
TL;DR: In this article, the authors studied the significance of soil wettability with respect to both SOM mineralisation and aggregate stability in a loess-derived Gleyic Luvisol, either used as cropland or as grassland.

Journal ArticleDOI
TL;DR: In this article, four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop evapotranspiration were tested for their effect on crop growth, crop yield, and water productivity.

Journal ArticleDOI
TL;DR: Neither the primary nor the secondary outcome measures could determine whether a megadose of vitamin E is efficacious in slowing disease progression in ALS as an add-on therapy to riluzol.
Abstract: Increasing evidence has suggested that oxidative stress may be involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). The antioxidant vitamin E (alpha-tocopherol) has been shown to slow down the onset and progression of the paralysis in transgenic mice expressing a mutation in the superoxide dismutase gene found in certain forms of familial ALS. The current study, a double blind, placebo-controlled, randomised, stratified, parallel-group clinical trial, was designed to determine whether vitamin E (5000 mg per day) may be efficacious in slowing down disease progression when added to riluzole. Methods. 160 patients in 6 German centres with either probable or definite ALS (according to the El Escorial Criteria) and a disease duration of less than 5 years, treated with riluzole, were included in this study and were randomly assigned to receive either alpha-tocopherol (5000 mg per day) or placebo for 18 months. The Primary outcome measure was survival, calculating time to death, tracheostomy or permanent assisted ventilation, according to the WFN-Criteria of clinical trials. Secondary outcome measures were the rate of deterioration of function assessed by the modified Norris limb and bulbar scales, manual muscle testing (BMRC), spasticity scale, ventilatory function and the Sickness Impact Profile (SIP ALS/19). Patients were assessed at entry and every 4 months thereafter during the study period until month 16 and at a final visit at month 18. Vitamin E samples were taken for compliance check and Quality Control of the trial. For Safety, a physical examination was performed at baseline and then every visit until the treatment discontinuation at month 18. Height and weight were recorded at baseline and weight alone at the follow-up visits. A neurological examination as well as vital signs (heart rate and blood pressure), an ECG and VEP’s were recorded at each visit. Furthermore, spontaneously reported adverse experiences and serious adverse events were documented and standard laboratory tests including liver function tests performed. For Statistical Analysis, the population to be considered for the primary outcome measure was an “intent-to-treat” (ITT) population which included all randomised patients who had received at least one treatment dose (n = 160 patients). For the secondary outcome measures, a two way analysis of variance was performed on a patient population that included all randomised patients who had at least one assessment after inclusion. Results. Concerning the primary endpoint, no significant difference between placebo and treatment group could be detected either with the stratified Logrank or the Wilcoxon test. The functional assessments showed a marginal trend in favour of vitamin E, without reaching significance. Conclusion. Neither the primary nor the secondary outcome measures could determine whether a megadose of vitamin E is efficacious in slowing disease progression in ALS as an add-on therapy to riluzol. Larger or longer studies might be needed. However, administration of this megadose does not seem to have any significant side effects in this patient population.

Proceedings ArticleDOI
31 Oct 2005
TL;DR: This paper investigates the feasibility of MailRank, a new email ranking and classification scheme exploiting the social communication network created via email interactions and shows that MailRank is highly resistant against spammer attacks.
Abstract: Can we use social networks to combat spam? This paper investigates the feasibility of MailRank, a new email ranking and classification scheme exploiting the social communication network created via email interactions. The underlying email network data is collected from the email contacts of all MailRank users and updated automatically based on their email activities to achieve an easy maintenance. MailRank is used to rate the sender address of arriving emails such that emails from trustworthy senders can be ranked and classified as spam or non-spam. The paper presents two variants: Basic MailRank computes a global reputation score for each email address, whereas in Personalized MailRank the score of each email address is different for each MailRank user. The evaluation shows that MailRank is highly resistant against spammer attacks, which obviously have to be considered right from the beginning in such an application scenario. MailRank also performs well even for rather sparse networks, i.e., where only a small set of peers actually take part in the ranking of email addresses.

Journal ArticleDOI
TL;DR: Putative in vivo functions of the Arabidopsisd‐CDes protein are discussed, and plants grown under low sulfate concentration showed an accumulation of d‐cysteine RNA and increased protein levels, suggesting post‐translational regulation.
Abstract: In several organisms d-cysteine desulfhydrase (d-CDes) activity (EC 4.1.99.4) was measured; this enzyme decomposes d-cysteine into pyruvate, H2S, and NH3. A gene encoding a putative d-CDes protein was identified in Arabidopsis thaliana (L) Heynh. based on high homology to an Escherichia coli protein called YedO that has d-CDes activity. The deduced Arabidopsis protein consists of 401 amino acids and has a molecular mass of 43.9 kDa. It contains a pyridoxal-5′-phosphate binding site. The purified recombinant mature protein had a Km for d-cysteine of 0.25 mm. Only d-cysteine but not l-cysteine was converted by d-CDes to pyruvate, H2S, and NH3. The activity was inhibited by aminooxy acetic acid and hydroxylamine, inhibitors specific for pyridoxal-5′-phosphate dependent proteins, at low micromolar concentrations. The protein did not exhibit 1-aminocyclopropane-1-carboxylate deaminase activity (EC 3.5.99.7) as homologous bacterial proteins. Western blot analysis of isolated organelles and localization studies using fusion constructs with the green fluorescent protein indicated an intracellular localization of the nuclear encoded d-CDes protein in the mitochondria. d-CDes RNA levels increased with proceeding development of Arabidopsis but decreased in senescent plants; d-CDes protein levels remained almost unchanged in the same plants whereas specific d-CDes activity was highest in senescent plants. In plants grown in a 12-h light/12-h dark rhythm d-CDes RNA levels were highest in the dark, whereas protein levels and enzyme activity were lower in the dark period than in the light indicating post-translational regulation. Plants grown under low sulfate concentration showed an accumulation of d-CDes RNA and increased protein levels, the d-CDes activity was almost unchanged. Putative in vivo functions of the Arabidopsisd-CDes protein are discussed.

Journal Article
TL;DR: The Test for Creative Thinking - Drawing Production (TCT-DP) as discussed by the authors was designed to mirror a more holistic concept of creativity than the mere quantitatively oriented, traditional divergent thinking tests.
Abstract: The Test for Creative Thinking - Drawing Production (TCT-DP), its design, concept and evaluation scheme as well as experiences and results of application are described. The test was designed to mirror a more holistic concept of creativity than the mere quantitatively oriented, traditional divergent thinking tests. The specific design using figural fragments is explained. The drawing production is evaluated by means of a set of criteria, which at the same time represent the underlying test construct. The test has been normed with various age and ability groups; there were no significant differences between male and female subjects. Various studies with data concerning the reliability and validity of the TCT-DP are provided.

Journal ArticleDOI
TL;DR: In this article, it was shown that if X ⊂ P r is a closed scheme in projective space whose homogeneous ideal is generated by quadrics, then a zero-dimensional or one-dimensional intersection of X with a plane of dimension p is 2-regular.
Abstract: Let X ⊂ P r be a closed scheme in projective space whose homogeneous ideal is generated by quadrics. We say that X (or its ideal IX) satisfies the condition N2,p if the syzygies of IX are linear for p steps. We show that if X satisfies N2,p then a zero-dimensional or one-dimensional intersection of X with a plane of dimension p is 2-regular. This extends a result of Green and Lazarsfeld. We give conditions when the syzygies of X restrict to the syzygies of the intersection. Many of our results also work for ideals generated by forms of higher degree. As applications, we bound the p for which some well-known projective varieties satisfy N2,p. Another application, carried out by us in a different paper, is a step

Journal ArticleDOI
TL;DR: This work considers the classical Cramér-Lundberg model with dynamic proportional reinsurance and solves the problem of finding the optimal reinsurance strategy which minimizes the expected quadratic distance of the risk reserve to a given benchmark.
Abstract: We consider the classical Cramer-Lundberg model with dynamic proportional reinsurance and solve the problem of finding the optimal reinsurance strategy which minimizes the expected quadratic distance of the risk reserve to a given benchmark. This result is extended to a mean-variance problem.

Journal ArticleDOI
TL;DR: A new technique to produce O2enriched air by using a mixed-ion and electron-conducting (MIEC) perovskite membrane that combines the in situ O2 supply with permeated O2 and air in one unit is proposed thus simplifying the process of O2 enrichment and reducing the operational and capital costs.
Abstract: Oxygen-enriched air with 30–50 vol%O2 is used in a number of industrial processes, for example, in the synthesis of ammonia, the Claus process, and the regeneration of the catalyst for the fluid-catalytic-cracking (FCC) process. Another application of O2-enriched air is the most efficient use of methane in high-temperature furnaces or cement kilns. There are different methods for producing O2enriched air, mainly by mixing air with pure O2 obtained from a cryogenic technique or pressure swing adsorption (PSA). However, these techniques require high capital investment and operational costs. Depending on the O2 concentration and the amount of the O2-enriched air needed, membrane technology can be competitive. As organic polymeric hollow-fiber membranes have a separation factor between 2 and 6, a single-stage membrane permeation gives an O2 concentration typically of the order of 30– 50 vol% under a pressure difference of about 10 bar. Although higher O2 concentration and permeability can be achieved by increasing the feed flow rate, by reducing the membrane thickness, or by increasing the pressure difference, these actions increase the separation costs. Furthermore, the organic polymeric membrane cannot be used for the recovery of heat from exhaust gas in high-temperature processes. Herein we propose a new technique to produce O2enriched air by using a mixed-ion and electron-conducting (MIEC) perovskite membrane. The basic idea is shown in Figure 1. At elevated temperatures, under a slight difference in air pressure (1–2 bar) O2 can be transported through a MIEC perovskite membrane in the form of oxygen ions from the side of high air pressure to the side of low air pressure. Simultaneously, electrons are transported in the opposite direction to maintain electric neutrality. The permeated O2 increases the O2 concentration to typically 30–50 vol% in the sweep air that forms the O2-enriched air on the low-pressure side. Therefore, the perovskite membrane combines the in situ O2 supply with permeated O2 and air in one unit thus simplifying the process of O2 enrichment and reducing the operational and capital costs. The obvious advantage of using perovskite membranes is their 100% selectivity for O2. Usually, polymeric membranes also transport noble or inert gases such as Ar or CO2, which can be disadvantageous depending on the process. Synthesis gas for ammonia production, for example, is prepared at a pressure level of about 30 bar and afterwards compressed to a pressure of typically 170–190 bar. Any inert gases contained within the synthesis gas are also compressed to a higher pressure and fed into the synthesis loop. This in turn increases the energy expenditure for compression, the necessary loop volume, and the purge flow used to get rid of the inert components in the synthesis loop. Moreover, compared with hollow-fiber membranes made from organic polymers, the perovskite hollow-fiber membrane requires a lower pressure difference (1–2 bar) across the membrane and can work at elevated temperatures, thus allowing high-temperature heat exchange. O2-enriched air is used mostly in high-temperature oxidation processes such as in the generation of synthesis gas for ammonia production in which O2-enriched air is used to run a secondary reformer typically operated at 1000 to 1100 8C. Therefore, in this process the temperature required to operate the perovskite hollow fiber is already available and can be used by heat exchange. Furthermore, the heat used for the O2 enrichment is not consumed, for example, in an endothermic reaction and can be regained by heat exchange with the product streams that leave the O2-permeation-membrane module. A similar setup may also apply to other applications for O2 enrichment with perovskite membranes, for example, the temperature increase of firing systems in power plants or industrial furnaces. The perovskite of composition BaCoxFeyZrzO3 d (BCFZ; x+y+z= 1.0) is a novel O2-permeable membrane with high O2 permeation fluxes and excellent thermal and mechanical stability. 5] BCFZ was used in a hollow-fiber configuration as [*] Dr. H. Wang, Prof. Dr. J. Caro Institut f!r Physikalische Chemie und Elektrochemie Universit,t Hannover Callinstrasse 3–3A, 30167 Hannover (Germany) Fax: (+49)511-762-19121 E-mail: haihui.wang@pci.uni-hannover.de