Showing papers by "University of Fribourg published in 2004"

Conceptual issues in local adaptation

Abstract: Studies of local adaptation provide important insights into the power of natural selection relative to gene flow and other evolutionary forces. They are a paradigm for testing evolutionary hypotheses about traits favoured by particular environmental factors. This paper is an attempt to summarize the conceptual framework for local adaptation studies. We first review theoretical work relevant for local adaptation. Then we discuss reciprocal transplant and common garden experiments designed to detect local adaptation in the pattern of deme · habitat interaction for fitness. Finally, we review research questions and approaches to studying the processes of local adaptation ‐ divergent natural selection, dispersal and gene flow, and other processes affecting adaptive differentiation of local demes. We advocate multifaceted approaches to the study of local adaptation, and stress the need for experiments explicitly addressing hypotheses about the role of particular ecological and genetic factors that promote or hinder local adaptation. Experimental evolution of replicated populations in controlled spatially heterogeneous environments allow direct tests of such hypotheses, and thus would be a valuable way to complement research on natural populations.

Barycentric Lagrange Interpolation

Abstract: Barycentric interpolation is a variant of Lagrange polynomial interpolation that is fast and stable. It deserves to be known as the standard method of polynomial interpolation.

Equilibrium cluster formation in concentrated protein solutions and colloids

Abstract: Controlling interparticle interactions, aggregation and cluster formation is of central importance in a number of areas, ranging from cluster formation in various disease processes to protein crystallography and the production of photonic crystals. Recent developments in the description of the interaction of colloidal particles with short-range attractive potentials have led to interesting findings including metastable liquid-liquid phase separation and the formation of dynamically arrested states (such as the existence of attractive and repulsive glasses, and transient gels). The emerging glass paradigm has been successfully applied to complex soft-matter systems, such as colloid-polymer systems and concentrated protein solutions. However, intriguing problems like the frequent occurrence of cluster phases remain. Here we report small-angle scattering and confocal microscopy investigations of two model systems: protein solutions and colloid-polymer mixtures. We demonstrate that in both systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters. We discuss the relevance of this finding for nucleation processes during protein crystallization, protein or DNA self-assembly and the previously observed formation of cluster and gel phases in colloidal suspensions.

Hydrogen storage methods

Abstract: Hydrogen exhibits the highest heating value per mass of all chemical fuels. Furthermore, hydrogen is regenerative and environmentally friendly. There are two reasons why hydrogen is not the major fuel of today’s energy consumption. First of all, hydrogen is just an energy carrier. And, although it is the most abundant element in the universe, it has to be produced, since on earth it only occurs in the form of water and hydrocarbons. This implies that we have to pay for the energy, which results in a difficult economic dilemma because ever since the industrial revolution we have become used to consuming energy for free. The second difficulty with hydrogen as an energy carrier is its low critical temperature of 33 K (i.e. hydrogen is a gas at ambient temperature). For mobile and in many cases also for stationary applications the volumetric and gravimetric density of hydrogen in a storage material is crucial. Hydrogen can be stored using six different methods and phenomena: (1) high-pressure gas cylinders (up to 800 bar), (2) liquid hydrogen in cryogenic tanks (at 21 K), (3) adsorbed hydrogen on materials with a large specific surface area (at T<100 K), (4) absorbed on interstitial sites in a host metal (at ambient pressure and temperature), (5) chemically bonded in covalent and ionic compounds (at ambient pressure), or (6) through oxidation of reactive metals, e.g. Li, Na, Mg, Al, Zn with water. The most common storage systems are high-pressure gas cylinders with a maximum pressure of 20 MPa (200 bar). New lightweight composite cylinders have been developed which are able to withstand pressures up to 80 MPa (800 bar) and therefore the hydrogen gas can reach a volumetric density of 36 kg·m−3, approximately half as much as in its liquid state. Liquid hydrogen is stored in cryogenic tanks at 21.2 K and ambient pressure. Due to the low critical temperature of hydrogen (33 K), liquid hydrogen can only be stored in open systems. The volumetric density of liquid hydrogen is 70.8 kg·m−3, and large volumes, where the thermal losses are small, can cause hydrogen to reach a system mass ratio close to one. The highest volumetric densities of hydrogen are found in metal hydrides. Many metals and alloys are capable of reversibly absorbing large amounts of hydrogen. Charging can be done using molecular hydrogen gas or hydrogen atoms from an electrolyte. The group one, two and three light metals (e.g. Li, Mg, B, Al) can combine with hydrogen to form a large variety of metal–hydrogen complexes. These are especially interesting because of their light weight and because of the number of hydrogen atoms per metal atom, which is two in many cases. Hydrogen can also be stored indirectly in reactive metals such as Li, Na, Al or Zn. These metals easily react with water to the corresponding hydroxide and liberate the hydrogen from the water. Since water is the product of the combustion of hydrogen with either oxygen or air, it can be recycled in a closed loop and react with the metal. Finally, the metal hydroxides can be thermally reduced to metals in a solar furnace. This paper reviews the various storage methods for hydrogen and highlights their potential for improvement and their physical limitations.

Evolution in invasive plants: implications for biological control

Abstract: Evidence is increasing that invasive plants can undergo rapid adaptive evolution during the process of range expansion. Here, we argue that evolutionary change during invasions will also affect plant-antagonist interactions and, thus, will have important implications for biological control programmes targeted at invasive plants. We explore how altered selection in the new range might influence the evolution of plant defence (resistance and tolerance) and life history. The degree to which such evolutionary processes might affect biological control efficacy is largely unexplored. We hope that, by testing the hypotheses that we propose here, a closer link can be established between biological control and evolutionary biology, to the benefit of both disciplines.

The 2003 heat wave in Europe: A shape of things to come? An analysis based on Swiss climatological data and model simulations

Abstract: [1] The 2003 heat wave that affected much of Europe from June to September bears a close resemblance to what many regional climate models are projecting for summers in the latter part of the 21st century. Model results suggest that under enhanced atmospheric greenhouse-gas concentrations, summer temperatures are likely to increase by over 4°C on average, with a corresponding increase in the frequency of severe heat waves. Statistical features of the 2003 heat wave for the Swiss site of Basel are investigated and compared to both past, 20th century events and possible future extreme temperatures based on model simulations of climatic change. For many purposes, the 2003 event can be used as an analog of future summers in coming decades in climate impacts and policy studies.

Phylogenetic constraints and adaptation explain food-web structure

Abstract: Food webs are descriptions of who eats whom in an ecosystem. Although extremely complex and variable, their structure possesses basic regularities1,2,3,4,5,6. A fascinating question is to find a simple model capturing the underlying processes behind these repeatable patterns. Until now, two models have been devised for the description of trophic interactions within a natural community7,8. Both are essentially based on the concept of ecological niche, with the consumers organized along a single niche dimension; for example, prey size8,9. Unfortunately, they fail to describe adequately recent and high-quality data. Here, we propose a new model built on the hypothesis that any species' diet is the consequence of phylogenetic constraints and adaptation. Simple rules incorporating both concepts yield food webs whose structure is very close to real data. Consumers are organized in groups forming a nested hierarchy, which better reflects the complexity and multidimensionality of most natural systems.

Nonlinearities, feedbacks and critical thresholds within the earth's climate system

Abstract: The Earth's climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm. While this is widely accepted, there is a relatively poor understanding of the different types of nonlinearities, how they manifest under various conditions, and whether they reflect a climate system driven by astronomical forcings, by internal feedbacks, or by a combination of both. In this paper, af- ter a brief tutorial on the basics of climate nonlinearity, we provide a number of illustrative examples and highlight key mechanisms that give rise to nonlinear behavior, address scale and methodological issues, suggest a robust alternative to prediction that is based on using integrated assessments within the framework of vulnerability studies and, lastly, recommend a number of research priorities and the establishment of education programs in Earth Systems Science. It is imperative that the Earth's climate system research community embraces this nonlinear paradigm if we are to move forward in the assessment of the human influence on climate.

Ectopic fat storage in heart, blood vessels and kidneys in the pathogenesis of cardiovascular diseases

Abstract: In humans and most animal models, the development of obesity leads not only to increased fat depots in classical adipose tissue locations but also to significant lipid deposits within and around other tissues and organs, a phenomenon known as ectopic fat storage The purpose of this review is to explore the possible locations of ectopic fat in key target-organs of cardiovascular control (heart, blood vessels and kidneys) and to propose how ectopic fat storage can play a role in the pathogenesis of cardiovascular diseases associated with obesity In animals fed a high-fat diet, cardiac fat depots within and around the heart impair both systolic and diastolic functions, and may in the long-term promote heart failure Accumulation of fat around blood vessels (perivascular fat) may affect vascular function in a paracrine manner, as perivascular fat cells secrete vascular relaxing factors, proatherogenic cytokines and smooth muscle cell growth factors Furthermore, high amounts of perivascular fat could mechanically contribute to the increased vascular stiffness seen in obesity Finally, accumulation of fat in the renal sinus may limit the outflow of blood and lymph from the kidney, which would alter intrarenal physical forces and promote sodium reabsorption and arterial hypertension Taken together, ectopic fat storage in key target-organs of cardiovascular control may impair their functions, contributing to the increased prevalence of cardiovascular diseases in obese subjects

The Couples Coping Enhancement Training (CCET): A new approach to prevention of marital distress based upon stress and coping*

Abstract: We describe a distress prevention training program for couples and three empirical studies that support its effectiveness. The program, Couples Coping Enhancement Training (CCET), is based both upon stress and coping theory and research on couples. In addition to traditional elements of couples programs (e.g., communication and problem-solving skills), the CCET also addresses individual and dyadic coping in promoting marital satisfaction and reducing marital distress. The CCET enjoys good consumer acceptance. Outcome results indicate that, in addition to acquiring relationship skills, participants experienced reduced martial distress and increased marital satisfaction, even among couples who have been in longstanding relationships where dissatisfaction exists. Key Words: coping, education, marriage, prevention, satisfaction, stress. Programs for preventing marital distress and divorce have experienced an increasing interest among professionals and couples in the last few decades. This interest also is reflected in a growing number of publications on the effectiveness of these programs (e.g., Baucom, Shoham, Mueser, Daiuto, & Stickle, 1998; Halford, Markman, Kline, & Stanley, 2003). Most programs seek to help couples enhance their communication and problem-solving skills with the aim of improving the quality of their relationship, while also decreasing the likelihood of divorce (for an overview, see Berger & Hannah, 1999). These programs are mainly founded in social learning theories, humanistic theory, or communication theory and are based upon the knowledge that communication competencies are among the most important predictors of marital success (see meta-analysis by Karney & Bradbury, 1995). Within this body of empirical knowledge, a new line of research emerged in the 199Os, when different researchers began to investigate in greater detail the effects of stress and coping on marriage. Here we describe a distress prevention program for couples: Couples Coping Enhancement Training (CCET; Bodenmann, 1997b). We also report the findings from three research studies assessing program effectiveness. Stress, Marital Quality, and Marital Stability Several cross-sectional studies of couples from community samples reveal that everyday stress (or daily hassles; see Lazarus & Folkman, 1984) is negatively associated with marital satisfaction and marital quality (for an overview, see Bodenmann, in press). Additionally, psychological stress associated with the illness of one partner is similarly negatively related to marital quality (e.g., Hagedoorn et al., 2000; Rohrbaugh et al., 2002). The negative correlations between stress and marital quality vary between -.22 and -.59, indicating moderate but significant correlations. Although all of the studies published on everyday stress and marriage found this negative relationship, there was no consistent relationship reported between major stressful events (i.e., critical life events) and marital quality. According to Williams (1995), no consistent relationship exists between major stressful events and marital quality, especially when marital matters-such as severe troubles in the relationship, separation, or divorce-were excluded from the list of critical life events. This finding indicates that chronic stress in daily life figures as a more important negative predictor of marital satisfaction and stability (see also Karney, Story, & Bradbury, in press). In a 5-year longitudinal study of 63 couples on the influence of everyday stress and marriage, Bodenmann and Cina (2000) found that couples who were either divorced or among the stable but distressed couples after 5 years had reported a significantly higher rate of stress in everyday life at the time of initial measurement than those in the later group of stable and nondistressed couples. Stress and Marital Communication Another line of research shows that marital communication is especially affected by stress. …

Thrombin Stimulates Human Endothelial Arginase Enzymatic Activity via RhoA/ROCK Pathway Implications for Atherosclerotic Endothelial Dysfunction

Abstract: Background—Arginase competes with endothelial nitric oxide synthase (eNOS) for the substrate L-arginine and decreases NO production. This study investigated regulatory mechanisms of arginase activity in endothelial cells and its role in atherosclerosis. Methods and Results—In human endothelial cells isolated from umbilical veins, thrombin concentration- and timedependently stimulated arginase enzymatic activity, reaching a 1.9-fold increase (P0.001) at 1 U/mL for 24 hours. The effect of thrombin was prevented by C3 exoenzyme or the HMG-CoA reductase inhibitor fluvastatin, which inhibit RhoA, or by the ROCK inhibitors Y-27632 and HA-1077. Adenoviral expression of constitutively active RhoA or ROCK mutants enhanced arginase activity (3-fold, P0.001), and the effect of active RhoA mutant was inhibited by the ROCK inhibitors. Neither thrombin nor the active RhoA/ROCK mutants affected arginase II protein level, the only isozyme detectable in the cells. Moreover, a significantly higher arginase II activity (1.5-fold, not the protein level) and RhoA protein level (4-fold) were observed in atherosclerotic aortas of apoE / compared with wild-type mice. Interestingly, L-arginine (1 mmol/L), despite a significantly higher eNOS expression in aortas of apoE / mice, evoked a more pronounced contraction, which was reverted to a greater vasodilation by the arginase inhibitor L-norvaline (20 mmol/L) compared with the wild-type animals (n5, P0.001). Conclusions—Thrombin enhances arginase activity via RhoA/ROCK in human endothelial cells. Higher arginase enzymatic activity is involved in atherosclerotic endothelial dysfunction in apoE / mice. Targeting vascular arginase may represent a novel therapeutic possibility for atherosclerosis. (Circulation. 2004;110:3708-3714.)

The Couples Coping Enhancement Training (CCET): A New Approach to Prevention of Marital Distress Based Upon Stress and Coping

Abstract: Programs for preventing marital distress and divorce have experienced an increasing interest among professionals and couples in the last few decades. This interest also is reflected in a growing number of publications on the effectiveness of these programs (e.g., Baucom, Shoham, Mueser, Daiuto, & Stickle, 1998; Halford, Markman, Kline, & Stanley, 2003). Most programs seek to help couples enhance their communication and problem-solving skills with the aim of improving the quality of their relationship, while also decreasing the likelihood of divorce (for an overview, see Berger & Hannah, 1999). These programs are mainly founded in social learning theories, humanistic theory, or communication theory and are based upon the knowledge that communication competencies are among the most important predictors of marital success (see meta-analysis by Karney & Bradbury, 1995). Within this body of empirical knowledge, a new line of research emerged in the 1990s, when different researchers began to investigate in greater detail the effects of stress and coping on marriage. Here we describe a distress prevention program for couples: Couples Coping Enhancement Training (CCET; Bodenmann, 1997b). We also report the findings from three research studies assessing program effectiveness.

Developmental origin of wiring specificity in the olfactory system of Drosophila

Abstract: In both insects and mammals, olfactory receptor neurons (ORNs) expressing specific olfactory receptors converge their axons onto specific glomeruli, creating a spatial map in the brain. We have previously shown that second order projection neurons (PNs) in Drosophila are prespecified by lineage and birth order to send their dendrites to one of ∼50 glomeruli in the antennal lobe. How can a given class of ORN axons match up with a given class of PN dendrites? Here, we examine the cellular and developmental events that lead to this wiring specificity. We find that, before ORN axon arrival, PN dendrites have already created a prototypic map that resembles the adult glomerular map, by virtue of their selective dendritic localization. Positional cues that create this prototypic dendritic map do not appear to be either from the residual larval olfactory system or from glial processes within the antennal lobe. We propose instead that this prototypic map might originate from both patterning information external to the developing antennal lobe and interactions among PN dendrites.

The 2003 heat wave as an example of summers in a greenhouse climate? Observations and climate model simulations for Basel, Switzerland

Abstract: The heat wave that affected many parts of Europe during the course of summer 2003 may be a harbinger of summers that could occur more regularly in a future climate, under enhanced greenhouse gas concentrations. Switzerland was not exempt from the 2003 heat wave and, indeed, the previous absolute maximum temperature record dating back to the middle of the 20th century was exceeded by over 2 °C. Regional climate simulations undertaken for the European region emphasize the fact that summers will become progressively as hot as the 2003 event, such that, in the latter part of the 21st century, it is likely to become the norm. On the basis of this study, the 2003 event should be considered as a “shape of things to come” and thereby prompt timely decision making in terms of appropriate adaptation and mitigation strategies.

New Zealand English: Its Origins and Evolution

Abstract: 1. Introduction 2. Overview and background 3. The historical background 4. Previous attempts to explain the origins of New Zealand English 5. Methodology 6. The variables of early New Zealand English 7. The origins of New Zealand English: reflections from the ONZE data 8. Implications for language change Appendices.

Field- and pressure-induced magnetic quantum phase transitions in TlCuCl 3

Abstract: Thallium copper chloride is a quantum spin liquid of $S=1/2$ ${\mathrm{Cu}}^{2+}$ dimers. Interdimer superexchange interactions give a three-dimensional magnon dispersion and a spin gap significantly smaller than the dimer coupling. This gap is closed by an applied hydrostatic pressure of approximately 2 kbar or by a magnetic field of 5.6 T, offering a unique opportunity to explore both types of quantum phase transition and their associated critical phenomena. We use a bond-operator formulation to obtain a continuous description of all disordered and ordered phases, and thus of the transitions separating these. Both pressure- and field-induced transitions may be considered as the Bose--Einstein condensation of triplet magnon excitations, and the respective phases of staggered magnetic order as linear combinations of dimer-singlet and dimer-triplet modes. We focus on the evolution with applied pressure and field of the magnetic excitations in each phase, and in particular on the gapless (Goldstone) modes in the ordered regimes which correspond to phase fluctuations of the ordered moment. The bond-operator description yields a good account of the magnetization curves and of magnon dispersion relations observed by inelastic neutron scattering under applied fields, and a variety of experimental predictions for pressure-dependent measurements.

Colloidal gels—low-density disordered solid-like states

Abstract: The analogies between colloidal glasses and gels have stimulated an increased effort in recent years to unify the description of the transitions to these disordered solid-like states within a single conceptual framework. Mode coupling theory, which successfully describes the hard sphere colloidal glass transition, has been extended to describe the effect of weak attractions at large volume fractions. By comparison, diffusion limited cluster aggregation models successfully describe the behavior for the other limit, irreversibly aggregated, fractal gels formed at low volume fractions and very large interaction potentials. A theoretical picture, which unifies these two limits, is still the subject of research. In this review, we summarize some of the results obtained to date, aiming to give an overview of our current understanding.

Defective dendritic cell migration and activation of adaptive immunity in PI3Kγ‐deficient mice

Abstract: Gene-targeted mice were used to evaluate the role of the gamma isoform of phosphoinositide 3-kinase (PI3Kγ) in dendritic cell (DC) migration and induction of specific T-cell-mediated immune responses. DC obtained from PI3Kγ−/− mice showed a reduced ability to respond to chemokines in vitro and ex vivo and to travel to draining lymph nodes under inflammatory conditions. PI3Kγ−/− mice had a selective defect in the number of skin Langerhans cells and in lymph node CD8α− DC. Furthermore, PI3Kγ−/− mice showed a defective capacity to mount contact hypersensitivity and delayed-type hypersensitivity reactions. This defect was directly related to the reduced ability of antigen-loaded DC to migrate from the periphery to draining lymph nodes. Thus, PI3Kγ plays a nonredundant role in DC trafficking and in the activation of specific immunity. Therefore, PI3Kγ may be considered a new target to control exaggerated immune reactions.

Challenges in Managing Nonprofit Organizations: A Research Overview

Abstract: The topic of “management” and nonprofit organizations (NPOs) continues to fascinate scholars. This paper draws on varying theoretical perspectives to explore their respective contributions to our knowledge of NPOs. The two longstanding and contrasting disciplines of economics and sociology have contributed most, traditionally, to the study of NPOs. However, neither of these disciplines has resolved all the dilemmas associated with NPOs. The standard economic model does not apply well to the distinctive nonmarket situation of NPOs. The sociological perspectives offer interesting insight, but fail to develop plans of action for NPOs. However, both of these traditional perspectives are starting to be eclipsed by the focus on marketing research.

Material properties of MBH4 (M = Li, Na, and K)

Abstract: Note: Times Cited: 105Symposium on Nanoscale Materials for Energy Storage2003Strasbourg, FRANCE Reference EPFL-ARTICLE-206022doi:10.1016/j.mseb.2003.10.045View record in Web of Science URL: ://WOS:000220947700011 Record created on 2015-03-03, modified on 2017-05-12

Crosstalk and differential response to abiotic and biotic stressors reflected at the transcriptional level of effector genes from secondary metabolism.

Abstract: Plant secondary metabolism significantly contributes to defensive measures against adverse abiotic and biotic cues. To investigate stress-induced, transcriptional alterations of underlying effector gene families, which encode enzymes acting consecutively in secondary metabolism and defense reactions, a DNA array (MetArray) harboring gene-specific probes was established. It comprised complete sets of genes encoding 109 secondary product glycosyltransferases and 63 glutathione-utilizing enzymes along with 62 cytochrome P450 monooxygenases and 26 ABC transporters. Their transcriptome was monitored in different organs of unstressed plants and in shoots in response to herbicides, UV-B radiation, endogenous stress hormones, and pathogen infection. A principal component analysis based on the transcription of these effector gene families defined distinct responses and crosstalk. Methyl jasmonate and ethylene treatments were separated from a group combining reactions towards two sulfonylurea herbicides, salicylate and an avirulent strain of Pseudomonas syringae pv. tomato. The responses to the herbicide bromoxynil and UV-B radiation were distinct from both groups. In addition, these analyses pinpointed individual effector genes indicating their role in these stress responses. A small group of genes was diagnostic in differentiating the response to two herbicide classes used. Interestingly, a subset of genes induced by P. syringae was not responsive to the applied stress hormones. Small groups of comprehensively induced effector genes indicate common defense strategies. Furthermore, homologous members within branches of these effector gene families displayed differential expression patterns either in both organs or during stress responses arguing for their non-redundant functions.

Conformational control of Bax localization and apoptotic activity by Pro168

Abstract: In healthy cells, Bax resides inactive in the cytosol because its COOH-terminal transmembrane region (TMB) is tucked into a hydrophobic pocket. During apoptosis, Bax undergoes a conformational change involving NH2-terminal exposure and translocates to mitochondria to release apoptogenic factors. How this process is regulated remains unknown. We show that the TMB of Bax is both necessary and sufficient for mitochondrial targeting. However, its availability for targeting depends on Pro168 located within the preceding loop region. Pro168 mutants of Bax lack apoptotic activity, cannot rescue the apoptosis-resistant phenotype of Bax/Bak double knockout cells, and are retained in the cytosol even in response to apoptotic stimuli. Moreover, the mutants have their NH2 termini exposed. We propose that Pro168 links the NH2 and the COOH terminus of Bax and is required for COOH-terminal release and mitochondrial targeting once this link is broken.

A new hypothesis to explain geographic parthenogenesis

Abstract: In many plants and animal species, asexuals are more common in marginal habitats such as high latitudes or altitudes than their closely related sexual counterparts. Here we propose a new hypothesis to explain this patterncalled "geographic parthenogenesis". In marginal habitats, populations may often exist as metapopulations with high degrees of subdivision and local extinction and recolonization, resulting in genetic bottlenecks during colonization. Our hypothesis states that such dynamics could play a key role in geographic parthenogenesis. Genetic bottlenecks and subsequent drift have stronger negative fitness consequences in sexuals than in asexuals because genetic drift leads to increased homozygosity and inbreeding depression in sexual but not in asexual populations. Migration, leading to inter-population hybridisation, may induce temporary fitness recovery in sexuals. Asexuals arising from such hybrids have an increased likelihood of invading sexual populations because they keep their high fitness, whereas the fitness of sexuals is doomed to decrease due to subsequent inbreeding and inbreeding depression. Therefore, asexuals may replace sexuals in subdivided habitats with local extinction and recolonization while they would not succeed in unstructured habitats without local turnover dynamics.

Model for the hydrogen adsorption on carbon nanostructures

Abstract: The hydrogen sorption capacity of carbon nanostructures was for several years a very controversial subject. Theoretical models have been published demonstrating a great potential for a large hydrogen sorption capacity of carbon nanostructures. Here we present a simple empirical model where condensation of hydrogen as a monolayer at the surface of nanotubes as well as bulk condensation in the cavity of the tube is assumed. The maximum potential amount of hydrogen absorbed according to the model was calculated to be 2.28×10-3 mass % S[m2g-1]=3.0 mass % for the adsorption of a monolayer hydrogen at the surface. The condensation of hydrogen in the cavity of the tube leads to a potential absorption for single wall nanotubes starting at 1.5 mass % and increasing with the diameter of the tubes. The experimentally measured hydrogen capacity of the nanotube samples correlates with the B.E.T. specific surface area. The slope of the linear relationship is 1.5×10-3 mass %/m2g-1. Therefore, the extrapolated maximum discharge capacity of a carbon sample is 2 mass %. Furthermore, it can be concluded, that the hydrogen sorption mechanism is related to the surface of the sample, i.e. a surface adsorption process.

Rarefied Basis Sets for the Calculation of Optical Tensors. 1. The Importance of Gradients on Hydrogen Atoms for the Raman Scattering Tensor

Abstract: A systematic investigation has been undertaken on the basis set requirements for the calculation of optical tensors. In this first of a series of two papers we present a comparison of the performance of various basis sets for the calculation of the Raman and Raman optical activity (ROA) scattering tensor. We show that it is possible to obtain results in excellent qualitative and in reasonable quantitative agreement with those from complex sets by highly rarefied sets provided the vibrational problem is solved in a separate calculation. It is shown that, for hydrogen-containing molecules, a basic requirement for the effectiveness of rarefied basis sets is the proper description of gradients of electronic tensors on these atoms and that this can only be achieved by the inclusion of moderately diffuse p-type functions on these atoms. In addition, the correct rendering of the Raman and ROA tensor for main atom−hydrogen and main atom−deuterium stretching vibrations requires a layer of diffuse functions with va...