67 research outputs found
Upper Bound for the Ground State Energy of a Dilute Bose Gas of Hard Spheres
Full text linkWe consider a gas of bosons interacting through a hard-sphere potential with radius a in the thermodynamic limit. We derive an upper bound for the ground state energy per particle at low density. Our bound captures the leading term 4 pi rho a and shows that corrections are smaller than C rho a(rho a(3))(1/2), for a sufficiently large constant C>0. In combination with a known lower bound, our result implies that the first sub-leading term to the ground state energy of a dilute gas of hard spheres is, in fact, of the order rho a(rho a(3))(1/2), in agreement with the Lee-Huang-Yang prediction
A second order upper bound for the ground state energy of a hard-sphere gas in the Gross-Pitaevskii regime
Full text linkWe prove an upper bound for the ground state energy of a Bose gas consisting of N hard spheres with radius a/N, moving in the three-dimensional unit torus Λ. Our estimate captures the correct asymptotics of the ground state energy, up to errors that vanish in the limit N → ∞. The proof is based on the construction of an appropriate trial state, given by the product of a Jastrow factor (describing two-particle correlations on short scales) and of a wave function constructed through a (generalized) Bogoliubov transformation, generating orthogonal excitations of the Bose-Einstein condensate and describing correlations on large scales
Novità sul Pontificale Calderini e sulle vicende della miniatura fra l’Aquila e l’Urbe negli anni del Grande Scisma (con una traccia su Zacara da Teramo “scriptore et miniatore”)
No full textNew Light on Calderini Pontifical and Manuscript Decoration between L’Aquila and Rome during the Great Schism (with a Mention of Zacara da Teramo, “scriptore et miniatore”)
This article focuses on the lavishly decorated Calderini Pontifical (Houghton Library, Harvard University, MS Typ 1), which gets its name from an inscription and the heraldry of Andrea Calderini from Bologna – hitherto erroneously assumed to be the bishop of Ceneda in 1378-1385 – who held that episcopal see in the third quarter of the 15th century. Heraldic and iconographic evidence prove that the Pontifical was originally intended for the chapel of Pope Innocent VII Migliorati (1404- 1406). Having remained unfinished, the decoration of the manuscript was completed by the Florentine illuminator Bartolomeo Varnucci at
the expense of Andrea Calderini. Consequently, the papal triregnum and Migliorati escutcheons were covered up with the coat of arms of the bishop of Ceneda. This conclusion allows us to rearrange the dating of the entire career of the outstanding calligrapher Stephanus de Aquila – documented in the papal chancery from 1380 to 1407 – who is partly credited with the magnificent pen-work repertoire of the first phase of the Pontifical. On this occasion he was accompanied by an illuminator from Abruzzo who can be identified as the author of the decoration of f. 2r in the first volume of a Gradual from the church of Santa Maria Paganica in L’Aquila (1382-1385). After being trained in the tradition of manuscript illumination that flourished in Teramo in the 14th century, this anonymous master enriched his repertoire with the stylistic motifs of Bolognese illumination before moving to Rome during the years of the Great Schism, where other scribes and illuminators from the Abruzzi were working in the papal chancery. Among them, the celebrated ars nova composer Zacara da Teramo – active as a scribe and miniaturist – may be considered to be the person responsible
Harmful Effect of Rheinheimera sp. EpRS3 (Gammaproteobacteria) Against the Protist Euplotes aediculatus (Ciliophora, Spirotrichea): Insights Into the Ecological Role of Antimicrobial Compounds From Environmental Bacterial Strains
Full text linkRheinheimera sp. strain EpRS3, isolated from the rhizosphere of Echinacea purpurea,
is already known for its ability to produce antibacterial compounds. By use of culture
experiments, we verified and demonstrated its harmful effect against the ciliated protist
Euplotes aediculatus (strain EASCc1), which by FISH experiments resulted to harbor
in its cytoplasm the obligate bacterial endosymbiont Polynucleobacter necessarius
(Betaproteobacteria) and the secondary endosymbiont “Candidatus Nebulobacter
yamunensis” (Gammaproteobacteria). In culture experiments, the number of ciliates
treated both with liquid broth bacteria-free (Supernatant treatment) and bacteria
plus medium (Tq treatment), decreases with respect to control cells, with complete
disappearance of ciliates within 6 h after Tq treatment. Results suggest that
Rheinheimera sp. EpRS3 produces and releases in liquid culture one or more bioactive
molecules affecting E. aediculatus survival. TEM analysis of control (not treated) ciliates
allowed to morphologically characterize both kind of E. aediculatus endosymbionts.
In treated ciliates, collected soon after the arising of cell suffering leading to death,
TEM observations revealed some ultrastructural damages, indicating that P. necessarius
endosymbionts went into degradation and vacuolization after both Supernatant and Tq
treatments. Additionally, TEM investigation showed that when the ciliate culture was
inoculated with Tq treatment, both a notable decrease of P. necessarius number and an
increase of damaged and degraded mitochondria occur. FISH experiments performed
on treated ciliates confirmed TEM results and, by means of the specific probe herein
designed, disclosed the presence of Rheinheimera sp. EpRS3 both inside phagosomes
and free in cytoplasm in ciliates after Tq treatment. This finding suggests a putative
ability of Rheinheimera sp. EpRS3 to reintroduce itself in the environment avoiding
ciliate digestion
Equazioni di Schrödinger semilineari
No full textFra tutte le equazioni differenziali alle derivate parziali, quelle dispersive formano una classe importante. Tale terminologia si riferisce al fatto che i profili delle loro soluzioni tendono ad allargarsi e ad appiattirsi nel tempo, cioè a ”disperdersi”. Un esempio molto importante all’interno di questa classe è quello dell’equazione di Schrödinger, che scaturisce dalla Fisica Quantistica
e determina l’evoluzione temporale dello stato di un sistema, ad esempio di una particella, di un atomo o di una molecola. L’elaborato prende in considerazione tale equazione ed ha il duplice scopo di studiarne le proprietà e di utilizzarla come modello per mostrare quali tipi di problematiche affiorano in questo campo e quali sono gli approcci e le strategie d’attacco più utilizzati per risolverle. A partire dal caso lineare, di fondamentale importanza, si arriverà a quello semilineare attraverso strumenti di analisi armonica, funzionale e complessa, fino a fornirne una soluzione locale
Probing the thermodynamics of SU(N)-symmetric Fermi gases with ultracold atoms
Full text linkIn dieser Arbeit wird die Thermodynamik von SU(N)-Fermi-Gasen in einer Quasi-2D-Geometrie untersucht. Unser System besteht aus Ytterbium-Atomen mit einer abstimmbaren SU(N ≤ 6)-Symmetrie in der zentralen Ebene eines vertikalen optischen Gitters. Wir charakterisieren die Zustandsgleichung (ZG) durch Messung der lokalen Dichteprofile mit hochauflösender Absorptionsabbildung sowohl in einer harmonischen Falle als auch in einem quadratischen Gitter. In der harmonischen Falle charakterisieren wir das tief entartete Regime und den Einfluss schwacher Wechselwirkungen auf die Bestimmung der ZG. Mittels optischer Gitter realisieren wir das 2D-SU(N)-Fermi-Hubbard-Modell und untersuchen den Übergang von der metallischen zur Mott-isolierenden Phase oberhalb der Superexchange-Temperatur. Insbesondere untersuchen wir die Dichte, die Kompressibilität, die Besetzungszahlen und die Dichtefluktuationen als Funktionen der Wechselwirkungsstärke, der Dichte und der Temperatur für N = 3, 4 und 6. Mit den Messungen vergleichen wir die Ergebnisse aktueller numerischen Methoden, insbesondere Determinant Quantum Monte Carlo (DQMC) und Numerical Linked-Cluster Expansion (NLCE). Durch Anwendung des Fluktuations-Dissipations-Theorems bestimmen wir die Temperatur des Systems mit einer theoriefreien Methode und validieren die Ergebnisse der ZS-Bestimmung.This thesis reports on probing the thermodynamics of SU(N) Fermi gases in a quasi-2D geometry. Our system consists of degenerate ytterbium atoms with a tunable SU(N ≤ 6) symmetry in the central plane of a vertical optical lattice. We characterize the equation of state (EoS) by measuring the local density profiles with high-resolution absorption imaging both in a harmonic trap and a square lattice. In the harmonic trap, we characterize the deeply degenerate regime and the effect of the weak interactions on the determination of the EoS. By loading the gas into a square in-plane optical lattice, we realize the 2D SU(N) Fermi-Hubbard model and probe the transition from the metallic to the Mott insulating phases above the superexchange temperature. In particular, we probe the density, the compressibility, the occupation probabilities, and the local density fluctuations as functions of the interaction strength, the filling, and the temperature for N = 3, 4, and 6. Our measurements are used as a benchmark for state-of-the-art theoretical methods, including determinant quantum Monte Carlo (DQMC) and numerical linked-cluster expansion (NLCE). By applying the fluctuation-dissipation theorem, we determine the system’s temperature with a theory-free method and validate the results of the numerical fits to the EoS
Il teorema di rappresentazione di Riesz
Full text linkLo spazio duale V* di un K-spazio vettoriale V, con K = R, o C, è definito come l'insieme dei funzionali lineari e continui da V in K. Definendo su di esso le operazioni di somma tra funzionali lineari e di prodotto per scalare, V* acquisisce una struttura di K-spazio vettoriale che risulta molto utile. Infatti il suo studio permette di comprendere meglio le caratteristiche dello spazio V. A tal proposito interviene l'argomento che è oggetto dell'elaborato: il Teorema di Rappresentazione di Riesz. Diversi risultati sono raggruppati sotto questo nome, che deriva dal matematico ungherese Frigyes Riesz, e tutti permettono di caratterizzare chiaramente gli elementi del duale dello spazio a cui si riferiscono. Scopo della tesi è quello di presentare il teorema nelle sue varie forme a partire da una delle più elementari: quella relativa a spazi vettoriali finiti. Ripercorrendo via via le sue generalizzazioni si arriverà all'enunciato inerente allo spazio delle funzioni continue f da X in C che si annullano all'infinito, dove X è uno spazio di Hausdorff localmente compatto. Si vedrà inoltre un esempio di applicazione del teorema
Killing effect of Rheinheimera sp. Eprs3 (Gammaproteobacteria) against Euplotes aediculatus (Ciliophora, Spirotrichea): discovering the ecological role of antimicrobial compounds from environmental bacterial strains
No full textBacterial endophytes are widely studied for their ability to produce antimicrobial compounds.
Rheinheimera sp. strain EpRS3 isolated from the rhizospheric soil of the medicinal plant Echinacea
purpurea, is known for its ability to produce antimicrobial compounds inhibiting the growth of other
bacterial species, both environmental and opportunistic human pathogens. In vivo experiments
demonstrated a killing effect of EpRS3 strain against the ciliated protist Euplotes aediculatus strain
EASCc1, which is known by FISH and TEM analyses to harbour in the cytoplasm the obligate bacterial
endosymbiont Polynucleobacter necessarius (Betaproteobacteria) and the Francisella-related
endosymbiont “Candidatus Nebulobacter yamunensis.” (Gammaproteobacteria). When the ciliate is
treated with supernatant of Rheinheimera sp. culture (liquid broth free of bacteria), the number of living
eukaryotic cells decreases with respect to control cells. TEM analysis, aimed at revealing the induced
ultrastructural ciliate cell damages, showed that inside these ciliates P. necessarius endosymbionts went
into degradation and vacuolization. When the ciliate culture is inoculated with bacteria plus medium, the
number of living eukaryotic cells decreases until disappearance within six hours, and many damaged or
highly degraded ciliate mitochondria and a decrement in number of P. necessarius endosymbionts are
recorded. Additionally, in these ciliates both TEM observation and FISH experiments performed using
a specific molecular probe disclosed the presence of Rheinheimera sp. both inside phagosomes and free
in the cytoplasm, suggesting that it is somehow capable to escape from food vacuoles avoiding ciliate
digestion. The obtained results suggest that Rheinheimera sp. EpRS3 produces and releases in liquid
culture one or more compounds affecting E. aediculatus survival. Analyses are now focused on clarifying
the molecular mechanisms behind the observed Rheinheimera’s killing effect
TRANSMISSION OF BACTERIAL PARAMECIUM ENDOSYMBIONTS INFLUENCED BY SALINITY STRESS
No full textChanges in salinity concentrations present an environmental stress especially important for the ecology of brackish microorganism. This study is focused on Paramecium, a unicellular organism (Philum Ciliophora) that lives in freshwater and brackish environments. Paramecia harbor frequently endosymbionts, which can be beneficial or harmful depending also on environmental conditions. Here I address the question if the acquirement of horizontally transmitted bacterial symbionts is more frequent under salinity stress conditions by using different strains of Paramecium either infected with endosymbionts (donor) or not infected (receiver).
First the salinity tolerance for each Paramecium strain used in this study was tested. Obtaining the growth curves of different strains at different salinity concentrations allowed me to determine weak and strong salinity stress according to the relative reduction of maximally reached Paramecium cell numbers. A reduction between 0 and 20 % was defined as no osmotic stress, between 20 and 50 % as weak and from 50 to 80 % as strong osmotic stress condition, whereas a relative reduction between 80 to 100 % represents lethal conditions. The results of the salinity tolerance test showed differences between the used species regarding to the salinity tolerance. Freshwater species, like P. biaurelia and P. caudatum, can survive and multiply at salinity concentrations in the range from 0 to 6 ‰, higher salinity concentrations seem to be lethal. On the contrary, the brackish water species P. duboscqui is able to grow at salinity concentrations in the range from 0 to 9 ‰.
Subsequently I co-cultivated donor and receiver strains in different combinations and with appropriate controls at no, weak and strong salinity stress conditions. I determined the population and infection dynamics (with FISH, Fluorescence in situ Hybridization). Paramecium populations were influenced by salinity and competition. The salinity stress conditions influence the endosymbiont’s life. Likewise the endosymbiont maintenance and transfer from donor to receiver is affected.
At freshwater conditions (0 ‰, no salinity stress) I observed no transmission and the endosymbiont’s maintenance in the donor strains. Horizontal transmission was determined for certain combinations at weak salinity stress (1.8‰). This indicates that transmission is influenced by environmental stress but depends also on the endosymbiont and receiver species. The highest prevalence of infected receiver was observed after 42 days where 50% of the receiver cells were infected. At high stress conditions (4.5‰) the donor strains lost the endosymbionts and consequently no horizontal transmission occurred.
In conclusion, salinity stress influences the endosymbionts transmission frequency and likewise its maintenance.
This is the first study testing direct exposure of Paramecium with basically no previous adaptation to various salinity stresses. Furthermore it documents its influence on the horizontal transmission and maintenance of bacterial endosymbionts
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