Ab initio calculations of edge-functionalized armchair graphene nanoribbons: Structural, electronic, and vibrational effects

We present a theoretical study on narrow armchair graphene nanoribbons (AGNRs) with hydroxyl functionalized edges. Although this kind of passivation strongly affects the structure of the ribbon, a high degree of edge functionalization proves to be particularly stable. An important consequence of the geometric deviations is a severe reduction of the band-gap of the investigated 7-AGNR. This shift follows a linear dependence on the number of added hydroxyl groups per unit cell and thus offers the prospect of a tunable band-gap by edge functionalization. We furthermore cover the behavior of characteristic phonons for the ribbon itself as well as fingerprint modes of the hydroxyl groups. A large down-shift of prominent Raman active modes allows the experimental determination of the degree of edge functionalization.Comment: 6 pages, 9 figure

Strukturelle, elektronische und dynamische Eigenschaften von Kohlenstoffnanomaterialien

In dieser Arbeit untersuchen wir verschiedene niederdimensionale Kohlenstoffstrukturen mittels ab initio und semi-empirischen Berechnungen. Die Arbeit gliedert sich in zwei Teile. Zunächst beschäftigen wir uns mit Picotube Molekülen sowie deren Verhältnis zu Kohlenstoff Nanotubes. Im zweiten Teil wird der Einfluss von mechanischer Verspannung einerseits sowie Funktionalisierung andererseits auf die Materialeigenschaften von Graphen untersucht. Picotubes sind hoch-symmetrische, ringförmige Kohlenwasserstoffe, die Substrukturen von armchair Nanotubes darstellen. Wir zeigen, dass sich die strukturelle Ähnlichkeit beider Materialsysteme in den Eigenschwingungen widerspiegelt. Erstens weisen Picotubes und Nanotubes optische Schwingungsmoden bei ähnlichen Frequenzen auf. Weiterhin finden wir in allen untersuchten Picotubes radiale Atmungsmoden, deren Frequenzen wie im Falle von Nanotubes indirekt proportional zum Durchmesser sind. Aufgrund der weitgehenden Analogien zwischen beiden Strukturen gelten Picotubes als Ausgangspunkt für eine potentielle gezielte Synthese sortenreiner Nanotubes. Wir widmen uns dieser Fragestellung mit molekulardynamischen Simulationen von in Nanotubes eingefüllten Picotubemolekülen. Abhängig von der simulierten Temperatur zeigen unsere Berechnungen Oszillationen sowie eine kontinuierliche axiale Bewegung der Picotubes im Nanotube. Bei Temperaturen über 2500 K führen chemische Umwandlungen zu einer Transformation der Picotubestruktur in eine kurze, geschlossene Röhre. Insbesondere das zuletzt genannte Ergebnis ist im Hinblick auf eine mögliche Herstellung definierter Nanotubes von großer Bedeutung. Im zweiten Teil beschäftigen wir uns mit Graphen Nanoribbons. Mechanische Verspannung sowie die Art der Passivierung der Randatome haben einen großen Einfluss auf die elektronischen Eigenschaften und die Phononen von Nanoribbons. Die Bandlücke von verspannten armchair Nanoribbons vergrößert oder verkleinert sich je nach dem, welcher Familie der Nanoribbon gemäß der gängigen Klassifikation angehört. Dieses Phänomen lässt sich konsistent im Sinne früherer Arbeiten zu verspanntem Graphen interpretieren. Dasselbe gilt für die Frequenzen der wichtigsten Schwingungsmoden, die alle eine Verschiebung zu kleineren Werten zeigen. Unter dem Einfluss einer Funktionalisierung der Ränder mit Hydroxylgruppen beobachten wir zum Teil ähnliche Effekte. Wir zeigen, dass sich die Bandlücke funktionalisierter Nanoribbons einerseits durch Verspannung, aber auch durch eine Änderung der Quantisierungsbedingung der elektronischen Wellenfunktionen ändert. Des Weiteren untersuchen wir die energetischen Verschiebungen charakteristischer Phononen. Unsere Daten legen die Möglichkeit nahe, den Grad der Funktionalisierung in Raman Experimenten zu bestimmen. Insbesondere die starke Abhängigkeit der Bandlücke von potentiell einstellbaren äußeren Faktoren könnte sich in zukünftigen nanoelektronischen Anwendungen als nützlich erweisen.In this work we study a variety of low-dimensional carbon structures by means of ab initio and semi-empirical calculations. The thesis comprises two main parts. The first one deals with picotube molecules and their relation to carbon nanotubes. In the second part, we investigate how strain and edge functionalization affect the fundamental properties of graphene nanoribbons. Carbon picotubes are a class of highly symmetric, ringlike hydrocarbons which closely resemble short sections from armchair nanotubes. We demonstrate that this structural analogy leads to typical vibrational characteristics of nanotubes being inherited onto picotubes. Apart from optical modes found in the same frequency range as in nanotubes, picotubes exhibit radial-breathing modes as well. We find the frequency of this mode to depend inversely on the picotube diameter in accordance with the relation known from carbon nanotubes. Owing to the close relation of both carbon allotropes picotubes are considered suitable starting points for a controlled synthesis of nanotubes. We address this issue by molecular dynamics simulations of picotubes encapsulated in nanotubes in a peapod-like configuration. Our temperature-dependent studies reveal three independent effects. Besides oscillations of the picotubes in the nanotube and a continuous molecular transport along its axis we observe a transformation of the picotube structure into a tubular form at temperatures around 2500 K. The latter result might be a step along the path to a bottom-up synthesis of specific types of nanotubes. Another form of fascinating one-dimensional carbon materials besides nanotubes are graphene nanoribbons. The second part of this thesis covers uniaxial strain and hydroxyl edge passivation in armchair nanoribbons. The electronic and vibrational properties of these ribbons prove to be highly sensitive to both of the mentioned modifications. We find the band-gap of strained nanoribbons to strongly increase or decrease depending on the family armchair nanoribbons are commonly classified in. These shifts, which are linear in a large strain range, can be interpreted in terms of earlier reports on the band structure of uniaxially strained graphene. The main vibrational modes of nanoribbons show a severe red-shift under tensile strain which can be related to corresponding studies on graphene as well. Introducing hydroxyl edge passivation leads to partially comparable effects since the ribbon structure is strained upon this type of functionalization. We successfully explain the observed band-gap energies of hydroxylized nanoribbons by a combination of strain effects and a modified effective confinement condition for the electronic wave functions. Finally we present data on prominent phonons including specific vibrations of the hydroxyl groups which suggest that the degree of functionalization may be determined in Raman experiments. Especially our findings on tunable band-gap energies by applying strain or attaching functional edge groups might be of significant technological relevance in future nano-electronic applications

Dynamic vapor sorption measurement and identification of mineral species in industrial-scale flotation cell samples

In order to understand flotation performance in industrial-scale, it is of relevance to understand the surface properties and mineral species of materials contained in the various parts of the cell. In this work XRPD X-Ray Powder Diffraction) and DVS (Dynamic Vapor Sorption) were used to characterise the different minerals and the wettability of the sample collected at different depths in an industrial scale flotation cell. DVS is a novel technique for wettability measurement in mineral processing, of higher robustness and reproducibility compared to the Washburn technique. In the turbulent zone of the cell, the wettability properties are relatively similar, and decreases in the froth and concentrate. Differences in radial position were only found near the froth phase close to the shaft of the agitator. The main finding was that wettability information obtained by DVS could be correlated with mineral composition and particle size distribution.Funding details: VINNOVA, 2014-01943; Funding details: VINNOVA; Funding text 1: The authors wish to acknowledge Boliden Mineral and RISE for permission to publish this paper as well as VINNOVA, the Swedish Governmental Agency for Innovation Systems for financial support, grant number 2014-01943 .</p

Video_2_pOpsicle: An all-optical reporter system for synaptic vesicle recycling combining pH-sensitive fluorescent proteins with optogenetic manipulation of neuronal activity.AVI

pH-sensitive fluorescent proteins are widely used to study synaptic vesicle (SV) fusion and recycling. When targeted to the lumen of SVs, fluorescence of these proteins is quenched by the acidic pH. Following SV fusion, they are exposed to extracellular neutral pH, resulting in a fluorescence increase. SV fusion, recycling and acidification can thus be tracked by tagging integral SV proteins with pH-sensitive proteins. Neurotransmission is generally activated by electrical stimulation, which is not feasible in small, intact animals. Previous in vivo approaches depended on distinct (sensory) stimuli, thus limiting the addressable neuron types. To overcome these limitations, we established an all-optical approach to stimulate and visualize SV fusion and recycling. We combined distinct pH-sensitive fluorescent proteins (inserted into the SV protein synaptogyrin) and light-gated channelrhodopsins (ChRs) for optical stimulation, overcoming optical crosstalk and thus enabling an all-optical approach. We generated two different variants of the pH-sensitive optogenetic reporter of vesicle recycling (pOpsicle) and tested them in cholinergic neurons of intact Caenorhabditis elegans nematodes. First, we combined the red fluorescent protein pHuji with the blue-light gated ChR2(H134R), and second, the green fluorescent pHluorin combined with the novel red-shifted ChR ChrimsonSA. In both cases, fluorescence increases were observed after optical stimulation. Increase and subsequent decline of fluorescence was affected by mutations of proteins involved in SV fusion and endocytosis. These results establish pOpsicle as a non-invasive, all-optical approach to investigate different steps of the SV cycle.</p

Video_1_pOpsicle: An all-optical reporter system for synaptic vesicle recycling combining pH-sensitive fluorescent proteins with optogenetic manipulation of neuronal activity.AVI

pH-sensitive fluorescent proteins are widely used to study synaptic vesicle (SV) fusion and recycling. When targeted to the lumen of SVs, fluorescence of these proteins is quenched by the acidic pH. Following SV fusion, they are exposed to extracellular neutral pH, resulting in a fluorescence increase. SV fusion, recycling and acidification can thus be tracked by tagging integral SV proteins with pH-sensitive proteins. Neurotransmission is generally activated by electrical stimulation, which is not feasible in small, intact animals. Previous in vivo approaches depended on distinct (sensory) stimuli, thus limiting the addressable neuron types. To overcome these limitations, we established an all-optical approach to stimulate and visualize SV fusion and recycling. We combined distinct pH-sensitive fluorescent proteins (inserted into the SV protein synaptogyrin) and light-gated channelrhodopsins (ChRs) for optical stimulation, overcoming optical crosstalk and thus enabling an all-optical approach. We generated two different variants of the pH-sensitive optogenetic reporter of vesicle recycling (pOpsicle) and tested them in cholinergic neurons of intact Caenorhabditis elegans nematodes. First, we combined the red fluorescent protein pHuji with the blue-light gated ChR2(H134R), and second, the green fluorescent pHluorin combined with the novel red-shifted ChR ChrimsonSA. In both cases, fluorescence increases were observed after optical stimulation. Increase and subsequent decline of fluorescence was affected by mutations of proteins involved in SV fusion and endocytosis. These results establish pOpsicle as a non-invasive, all-optical approach to investigate different steps of the SV cycle.</p

Data_Sheet_2_pOpsicle: An all-optical reporter system for synaptic vesicle recycling combining pH-sensitive fluorescent proteins with optogenetic manipulation of neuronal activity.XLSX

pH-sensitive fluorescent proteins are widely used to study synaptic vesicle (SV) fusion and recycling. When targeted to the lumen of SVs, fluorescence of these proteins is quenched by the acidic pH. Following SV fusion, they are exposed to extracellular neutral pH, resulting in a fluorescence increase. SV fusion, recycling and acidification can thus be tracked by tagging integral SV proteins with pH-sensitive proteins. Neurotransmission is generally activated by electrical stimulation, which is not feasible in small, intact animals. Previous in vivo approaches depended on distinct (sensory) stimuli, thus limiting the addressable neuron types. To overcome these limitations, we established an all-optical approach to stimulate and visualize SV fusion and recycling. We combined distinct pH-sensitive fluorescent proteins (inserted into the SV protein synaptogyrin) and light-gated channelrhodopsins (ChRs) for optical stimulation, overcoming optical crosstalk and thus enabling an all-optical approach. We generated two different variants of the pH-sensitive optogenetic reporter of vesicle recycling (pOpsicle) and tested them in cholinergic neurons of intact Caenorhabditis elegans nematodes. First, we combined the red fluorescent protein pHuji with the blue-light gated ChR2(H134R), and second, the green fluorescent pHluorin combined with the novel red-shifted ChR ChrimsonSA. In both cases, fluorescence increases were observed after optical stimulation. Increase and subsequent decline of fluorescence was affected by mutations of proteins involved in SV fusion and endocytosis. These results establish pOpsicle as a non-invasive, all-optical approach to investigate different steps of the SV cycle.</p

Data_Sheet_1_pOpsicle: An all-optical reporter system for synaptic vesicle recycling combining pH-sensitive fluorescent proteins with optogenetic manipulation of neuronal activity.PDF

pH-sensitive fluorescent proteins are widely used to study synaptic vesicle (SV) fusion and recycling. When targeted to the lumen of SVs, fluorescence of these proteins is quenched by the acidic pH. Following SV fusion, they are exposed to extracellular neutral pH, resulting in a fluorescence increase. SV fusion, recycling and acidification can thus be tracked by tagging integral SV proteins with pH-sensitive proteins. Neurotransmission is generally activated by electrical stimulation, which is not feasible in small, intact animals. Previous in vivo approaches depended on distinct (sensory) stimuli, thus limiting the addressable neuron types. To overcome these limitations, we established an all-optical approach to stimulate and visualize SV fusion and recycling. We combined distinct pH-sensitive fluorescent proteins (inserted into the SV protein synaptogyrin) and light-gated channelrhodopsins (ChRs) for optical stimulation, overcoming optical crosstalk and thus enabling an all-optical approach. We generated two different variants of the pH-sensitive optogenetic reporter of vesicle recycling (pOpsicle) and tested them in cholinergic neurons of intact Caenorhabditis elegans nematodes. First, we combined the red fluorescent protein pHuji with the blue-light gated ChR2(H134R), and second, the green fluorescent pHluorin combined with the novel red-shifted ChR ChrimsonSA. In both cases, fluorescence increases were observed after optical stimulation. Increase and subsequent decline of fluorescence was affected by mutations of proteins involved in SV fusion and endocytosis. These results establish pOpsicle as a non-invasive, all-optical approach to investigate different steps of the SV cycle.</p

Spectral Detector CT-Derived Pulmonary Perfusion Maps and Pulmonary Parenchyma Characteristics for the Semiautomated Classification of Pulmonary Hypertension

ObjectivesTo evaluate the usefulness of spectral detector CT (SDCT)-derived pulmonary perfusion maps and pulmonary parenchyma characteristics for the semiautomated classification of pulmonary hypertension (PH). MethodsA total of 162 consecutive patients with right heart catheter (RHC)-proven PH of different aetiologies as defined by the current ESC/ERS guidelines who underwent CT pulmonary angiography (CTPA) on SDCT and 20 patients with an invasive rule-out of PH were included in this retrospective study. Semiautomatic lung segmentation into normal and malperfused areas based on iodine density (ID) as well as automatic, virtual non-contrast-based emphysema quantification were performed. Corresponding volumes, histogram features and the ID Skewness(PerfDef)-Emphysema-Index (delta-index) accounting for the ratio of ID distribution in malperfused lung areas and the proportion of emphysematous lung parenchyma were computed and compared between groups. ResultsPatients with PH showed a significantly greater extent of malperfused lung areas as well as stronger and more homogenous perfusion defects. In group 3 and 4 patients, ID skewness revealed a significantly more homogenous ID distribution in perfusion defects than in all other subgroups. The delta-index allowed for further subclassification of subgroups 3 and 4 (p < 0.001), identifying patients with chronic thromboembolic PH (CTEPH, subgroup 4) with high accuracy (AUC: 0.92, 95%-CI, 0.85-0.99). ConclusionAbnormal pulmonary perfusion in PH can be detected and quantified by semiautomated SDCT-based pulmonary perfusion maps. ID skewness in malperfused lung areas, and the delta-index allow for a classification of PH subgroups, identifying groups 3 and 4 patients with high accuracy, independent of reader expertise

Data_Sheet_3_pOpsicle: An all-optical reporter system for synaptic vesicle recycling combining pH-sensitive fluorescent proteins with optogenetic manipulation of neuronal activity.XLSX

pH-sensitive fluorescent proteins are widely used to study synaptic vesicle (SV) fusion and recycling. When targeted to the lumen of SVs, fluorescence of these proteins is quenched by the acidic pH. Following SV fusion, they are exposed to extracellular neutral pH, resulting in a fluorescence increase. SV fusion, recycling and acidification can thus be tracked by tagging integral SV proteins with pH-sensitive proteins. Neurotransmission is generally activated by electrical stimulation, which is not feasible in small, intact animals. Previous in vivo approaches depended on distinct (sensory) stimuli, thus limiting the addressable neuron types. To overcome these limitations, we established an all-optical approach to stimulate and visualize SV fusion and recycling. We combined distinct pH-sensitive fluorescent proteins (inserted into the SV protein synaptogyrin) and light-gated channelrhodopsins (ChRs) for optical stimulation, overcoming optical crosstalk and thus enabling an all-optical approach. We generated two different variants of the pH-sensitive optogenetic reporter of vesicle recycling (pOpsicle) and tested them in cholinergic neurons of intact Caenorhabditis elegans nematodes. First, we combined the red fluorescent protein pHuji with the blue-light gated ChR2(H134R), and second, the green fluorescent pHluorin combined with the novel red-shifted ChR ChrimsonSA. In both cases, fluorescence increases were observed after optical stimulation. Increase and subsequent decline of fluorescence was affected by mutations of proteins involved in SV fusion and endocytosis. These results establish pOpsicle as a non-invasive, all-optical approach to investigate different steps of the SV cycle.</p

Clinical Relevance of Right Atrial Functional Response to Treatment in Pulmonary Arterial Hypertension

Background: Right atrial (RA) function has emerged as an important determinant of outcome in pulmonary arterial hypertension (PAH). However, studies exploring RA function after initiation of specific pulmonary vascular treatment and its association with outcome in patients with incident PAH are lacking.Methods: RA peak longitudinal strain (PLS), passive strain (PS), and peak active contraction strain (PACS) were retrospectively assessed in 56 treatment-naive patients with PAH at baseline and during follow-up after initiation of specific monotherapy or combination therapy. Patients were grouped according to their individual RA functional response to treatment, based on change from baseline (Delta): worsened (first Delta-tertile), stable (second Delta-tertile), and improved (third Delta-tertile). The Spearman's rho correlation and linear regression analysis were used to determine associations. Time to clinical worsening (defined as deterioration of functional class or 6-min walking distance, disease-related hospital admission, or death) was measured from the follow-up assessment. The association of RA functional treatment response with time to clinical worsening was assessed using the Kaplan-Meier and the Cox regression analyses.Results: Median (interquartile range) time to echocardiographic follow-up was 11 (9-12) months. Of the 56 patients, 37 patients (66%) received specific dual or triple combination therapy. Delta RA PLS during follow-up was significantly associated with changes in key hemodynamic and echocardiographic parameters. The change of pulmonary vascular resistance, right ventricular (RV) end-systolic area, and global longitudinal strain were independently associated with Delta RA PLS. The median time to clinical worsening after echocardiographic follow-up was 6 (2-14) months [17 events (30%)]. In the multivariate Cox regression analysis, worsening of RA PLS was significantly associated with clinical deterioration (hazard ratio: 4.87; 95% CI: 1.26-18.76; p = 0.022). Patients with worsened RA PLS had a significantly poorer prognosis than those with stable or improved RA PLS (log-rank p = 0.012). By contrast, PS and PACS did not yield significant prognostic information.Conclusion: Treatment-naive patients with PAH may show different RA functional response patterns to PAH therapy. These functional patterns are significantly associated with clinically relevant outcome measures. Improvements of RA function are driven by reductions of afterload, RV remodeling, and RV dysfunction