Einteilchen Eigenschaften im 2D Coulomb Problem: Luttinger-Ward Variations Verfahren

A conserving approximation within a systematic microscopic theory can be found by the method of Luttinger and Ward; introducing an external field in their generating potential for the grand-canonical energy, one can derive conserving approximations in the sense of Kadanoff and Baym for all physical quantities. In the present work, we successfully test the method of Luttinger and Ward for a simple model where we consider a two dimensional electron system with 1/r Coulomb interaction (2DEG). This is the first application of the Luttinger-Ward variational principle for a 2DEG. Using an ansatz for the self-energy, we can perform the frequency sums (-integrals) analytically. Numerically, we find that the Luttinger-Ward variational functional has an unique maximum and that the variational procedure converges even far beyond that density where the iterative solution of the self-consistency equation begins to fail. We calculate the ground state energy and one particle properties such as effective mass, momentum distribution function and spectral function and compare these with those obtained by the iterative method in GW approximation, GW_0 approximation and G_0W_0 approximation. We compare some of these quantities, e.g., the ground state energy with the results of other, non-perturbative methods. We find its ability of calculating very accurate ground state energies in the denser regime of a 2DEG and also it's convergence even for the more dilute regime makes the Luttinger-Ward variational method a very efficient tool for future calculations; it is a good candidate for a unified theory applicable for a rather accurate calculation at all the densities. The effective mass, the momentum distribution function as well as the spectral function calculated by the Luttinger-Ward variational method confirm the Fermi liquid behavior of this system.Eine erhaltende Näherung innerhalb einer systematischen mikroskopischen Theorie kann mit der Methode von Luttinger und Ward gefunden werden; durch Einführen eines äußeren Feldes in ihr erzeugendes Funktional für die großkanonische Energie kann man erhaltende Näherungen im Sinne von Kadanoff und Baym für alle physikalischen Größen herleiten. In der vorliegenden Arbeit testen wir erfolgreich die Methode von Luttinger und Ward an einem einfachen Modell, indem wir ein zweidimensionalen Elektronensystem mit 1/r Coulomb Wechselwirkung (2DEG) betrachten. Dies ist die erste Anwendung des Variationsprinzips von Luttinger und Ward für ein 2DEG. Mit einem Ansatz für die Selbstenergie können wir die Frequenzsummen (-integrale) analytisch berechnen. Wir finden numerisch, daß das Variationsfunktional nach Luttinger und Ward ein eindeutiges Maximum hat und daß die Variationsprozedur sogar weit jenseits der Dichte konvergiert, ab der die iterative Lösung der Selbstkonsistenzgleichungen versagt. Wir berechnen die Grundzustandsenergie und Einteilcheneigenschaften wie die effektive Masse, die Impulsverteilungsfunktion und die Spektralfunktion und vergleichen diese mit den Ergebnissen, die man durch die iterative Methode in GW Näherung, GW_0 Näherung und G_0W_0 Näherung erhält. Wir vergleichen auch einige dieser Größen, wie die Grundzustandsenergie mit den Resultaten anderer, nicht störungstheoretischer Methoden. Wir finden, daß ihre Fähigkeit, sehr genaue Grundzustandsenergieen im Parameterbereich größerer Dichte des 2DEG zu berechnen und auch ihre Konvergenz für geringere Dichte die Variationsmethode von Luttinger und Ward ein sehr effizientes Werkzeug für weitere Rechnungen macht; sie ist ein guter Kandidat für eine einheitliche Theorie, die man zu einer ziemlich genauen Berechnung bei allen Dichten anwenden kann. Effektive Masse, Impulsverteilung und auch die Spektralfunktion berechnet mit der Variationsmethode von Luttinger und Ward bestätigen das Verhalten dieses Systems als Fermiflüssigkeit

Comparative study of potato cultivation through micropropagation and conventional farming methods

A trial was carried out to evaluate the productivity of Solanum tuberosum L. cultivated through conventional farming and micropropagation method. Survival rate, biomass and tuber yield of both micropropagated and tuber propagated potatoes was evaluated. Survival percentages of potatoes were 90% for conventional propagation and 85% for micropropagation. The survival rate of micropropagated plants were maximum of 79% in vermicompost and minimum of 50% in the soil. The average shoot length, number of leaves and leaf area was greater in tuber propagated plants compared to the micropropagated plants. Tuber propagated plants yielded 1.360 kg/plant which was 0.370 kg/plant more than micropropagated plant.Keywords: Conventional farming, micropropagation, potatoes, tuber propagatio

Simple model of adsorption on external surface of carbon nanotubes: a new analytical approach basing on molecular simulation data

Nitrogen adsorption on carbon nanotubes is wide- ly studied because nitrogen adsorption isotherm measurement is a standard method applied for porosity characterization. A further reason is that carbon nanotubes are potential adsorbents for separation of nitrogen from oxygen in air. The study presented here describes the results of GCMC simulations of nitrogen (three site model) adsorption on single and multi walled closed nanotubes. The results obtained are described by a new adsorption isotherm model proposed in this study. The model can be treated as the tube analogue of the GAB isotherm taking into account the lateral adsorbate-adsorbate interactions. We show that the model describes the simulated data satisfactorily. Next this new approach is applied for a description of experimental data measured on different commercially available (and characterized using HRTEM) carbon nanotubes. We show that generally a quite good fit is observed and therefore it is suggested that the observed mechanism of adsorption in the studied materials is mainly determined by adsorption on tubes separated at large distances, so the tubes behave almost independently

Long-term solar activity influences on South American rivers

River streamflows are excellent climatic indicators since they integrate precipitation over large areas. Here we follow up on our previous study of the influence of solar activity on the flow of the Parana River, in South America. We find that the unusual minimum of solar activity in recent years have a correlation on very low levels in the Parana's flow, and we report historical evidence of low water levels during the Little Ice Age. We also study data for the streamflow of three other rivers (Colorado, San Juan and Atuel), and snow levels in the Andes. We obtained that, after eliminating the secular trends and smoothing out the solar cycle, there is a strong positive correlation between the residuals of both the Sunspot Number and the streamflows, as we obtained for the Parana. Both results put together imply that higher solar activity corresponds to larger precipitation, both in summer and in wintertime, not only in the large basin of the Parana, but also in the Andean region north of the limit with Patagonia.Comment: Accepted to publication by Journal of Atmospheric and Solar-Terrestrial Physic

Quantum cohomology via vicious and osculating walkers

We relate the counting of rational curves intersecting Schubert varieties of the Grassmannian to the counting of certain non-intersecting lattice paths on the cylinder, so-called vicious and osculating walkers. These lattice paths form exactly solvable statistical mechanics models and are obtained from solutions to the Yang–Baxter equation. The eigenvectors of the transfer matrices of these models yield the idempotents of the Verlinde algebra of the gauged u^(n)k -WZNW model. The latter is known to be closely related to the small quantum cohomology ring of the Grassmannian. We establish further that the partition functions of the vicious and osculating walker model are given in terms of Postnikov’s toric Schur functions and can be interpreted as generating functions for Gromov–Witten invariants. We reveal an underlying quantum group structure in terms of Yang–Baxter algebras and use it to give a generating formula for toric Schur functions in terms of divided difference operators which appear in known representations of the nil-Hecke algebra

JCV GCN in a Natalizumab-Treated MS Patient is Associated With Mutations of the VP1 Capsid Gene

Objective: To describe the clinical, neuroimaging, immunologic, and virologic characteristics of JC virus-associated granule cell neuronopathy (JCV GCN) in a natalizumab-treated patient with multiple sclerosis (MS) who developed immune reconstitution inflammatory syndrome (IRIS) after natalizumab withdrawal. Methods: We obtained longitudinal clinical data as well as MRI and proton magnetic resonance spectroscopy from this patient with MS. We measured JCV-specific cellular immune response in his peripheral blood by intracellular cytokine staining and sequenced a fragment of JCV VP1 capsid gene detected in his CSF. We contrast our findings with the first recently reported case. Results: This patient presented with worsening cerebellar symptoms and progressive cerebellar atrophy without new MS lesions on MRI after 63 months of natalizumab monotherapy. JCV DNA was detected in his CSF by PCR and harbored novel GCN-type mutations in the VP1 gene. He developed IRIS upon discontinuation of natalizumab and plasma exchange, which manifested itself by a worsening of clinical symptoms and contrast enhancement in the cerebellum on MRI. Treatment with corticosteroids resulted in resolution of IRIS, as demonstrated by proton magnetic resonance spectroscopy. The patient had a strong JCV-specific T-cell response in his peripheral blood and remains alive after 15 months from onset of symptoms, although with significant disability. He did not have MS relapse on glatiramer acetate. Conclusions: JCV GCN should be considered in patients on natalizumab presenting with progressive cerebellar symptoms and cerebellar atrophy, and is associated with mutations in the JCV VP1 gene. Natalizumab withdrawal may be complicated by JCV GCN IRIS, and require treatment with corticosteroids

Decomposable representations and Lagrangian submanifolds of moduli spaces associated to surface groups

In this paper, we construct a Lagrangian submanifold of the moduli space associated to the fundamental group of a punctured Riemann surface (the space of representations of this fundamental group into a compact connected Lie group). This Lagrangian submanifold is obtained as the fixed-point set of an anti-symplectic involution defined on the moduli space. The notion of decomposable representation provides a geometric interpretation of this Lagrangian submanifold

Structure-Activity Relationships in Toll-like Receptor 2-Agonists Leading to Simplified Monoacyl Lipopeptides

Toll-like receptor 2-agonistic lipopeptides typified by S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-R-cysteinyl-S-serine (PAM2CS) compounds are potential vaccine adjuvants. In continuation of previously reported structure-activity relationships on this chemotype, we have determined that at least one acyl group of optimal length (C16) and an appropriately orientated ester carbonyl group is essential for TLR2-agonistic activity. The spacing between one of the palmitoyl ester carbonyl and the thioether is crucial to allow for an important H-bond, which observed in the crystal structure of the lipopeptide:TLR2 complex; consequently, activity is lost in homologated compounds. Penicillamine-derived analogues are also inactive, likely due to unfavorable steric interactions with the carbonyl of Ser 12 in TLR2. The thioether in this chemotype can be replaced with a selenoether. Importantly, the thioglycerol motif can be dispensed with altogether, and can be replaced with a thioethanol bridge. These results have led to a structurally simpler, synthetically more accessible, and water-soluble analogue possessing strong TLR2-agonistic activities in human blood

Genetically encoded intrabody sensors report the interaction and trafficking of β-arrestin 1 upon activation of G protein-coupled receptors

Agonist stimulation of G protein-coupled receptors (GPCRs) typically leads to phosphorylation of GPCRs and binding to multifunctional proteins called β-arrestins (βarrs). The GPCR-βarr interaction critically contributes to GPCR desensitization, endocytosis, and downstream signaling, and GPCR-βarr complex formation can be used as a generic readout of GPCR and βarr activation. Although several methods are currently available to monitor GPCR-βarr interactions, additional sensors to visualize them may expand the toolbox and complement existing methods. We have previously described antibody fragments (FABs) that recognize activated βarr1 upon its interaction with the vasopressin V2 receptor C-terminal phosphopeptide (V2Rpp). Here, we demonstrate that these FABs efficiently report the formation of a GPCR-βarr1 complex for a broad set of chimeric GPCRs harboring the V2R C terminus. We adapted these FABs to an intrabody format by converting them to single-chain variable fragments (ScFvs) and used them to monitor the localization and trafficking of βarr1 in live cells. We observed that upon agonist simulation of cells expressing chimeric GPCRs, these intrabodies first translocate to the cell surface, followed by trafficking into intracellular vesicles. The translocation pattern of intrabodies mirrored that of βarr1, and the intrabodies co-localized with βarr1 at the cell surface and in intracellular vesicles. Interestingly, we discovered that intrabody sensors can also report βarr1 recruitment and trafficking for several unmodified GPCRs. Our characterization of intrabody sensors for βarr1 recruitment and trafficking expands currently available approaches to visualize GPCR-βarr1 binding, which may help decipher additional aspects of GPCR signaling and regulation