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L’emoglobina (Hb) rappresenta una delle proteine maggiormente studiate in termini di struttura e funzione sia per il ruolo fisiologico svolto, sia perché costituisce un modello ottimale per lo studio dei fenomeni di cooperatività. Nonostante l’elevata similitudine strutturale e funzionale tra le Hb dei mammiferi temperati e le emoglobine di pesci antartici (AFHb), esistono numerose differenze. In particolare, le AFHb presentano due effetti peculiari: l’effetto Root e la formazione dell’emicromo. L’emicromo rappresenta una specie ferrica molecolare esacoordinata a basso spin nella quale si forma un legame tra la catena laterale di un residuo distale di istidina e la sesta posizione di coordinazione del Fe3+(1). L’effetto Root invece si manifesta come una drastica riduzione dell’affinità e della cooperatività per il legame con l’ossigeno a pH acidi (2). Il requisito minimo strutturale affinchè si abbia effetto Root è la formazione, a pH acidi, di un legame a idrogeno interaspartico all’interfaccia α1β2 Asp95á-Asp101â assistito dal residuo Asp99â (3). La presenza della triade di aspartici non è però un requisito sufficiente per l’effetto Root. Infatti la variante naturale dell’Hb umana Potomac (che presenta la mutazione b101Glu→Asp e che quindi possiede la triade di aspartici) non presenta tale effetto avendo addirittura una maggiore affinità per l’ossigeno (4). Allo scopo di acquisire le informazioni necessarie per il trasferimento delle due proprietà tipiche di alcune Hb di pesci a quella umana è stato sviluppato un sistema di produzione ricombinante in E. coli della globina β nella variante naturale Potomac per consentirne un dettagliato studio strutturale. In particolare, si è affrontato il problema dell’inefficiente rimozione da parte dell’ospite batterico della metionina all’estremità N-terminale. Poiché in Hb tetrameriche il residuo N-terminale, di entrambe le catene α e β, gioca un ruolo importante nel modulare l’affinità con l’ossigeno, la mancata rimozione della Met iniziale va a modificare tale affinità. Per ovviare a questo problema è stata costruita una variante N-terminale della globina β, nella quale il residuo di Valina 1 è stato sostituito con una Metionina (β1Val→Met (1)). Per ottenere la variante Potomac è stata effettuata una mutazione a partire dal mutante 1 mediante mutagenesi sito-specifica. Il gene mutato così ottenuto è stato clonato nel vettore di espressione pET22b, generando il plasmide impiegato per trasformare un ceppo di E. coli. Sono state effettuate, quindi, le diverse prove di produzione variando la temperatura del processo ed in presenza di una concentrazione costante di induttore IPTG, di acido δ-amminolevulinico (precursore dell’eme) e di FeCl3. Analisi elettroforetica SDS-PAGE degli omogenati cellulari e delle corrispondenti frazioni insolubili ha evidenziato che la globina prodotta risulta aggregata nei corpi di inclusione dai quali è stato possibile risolubilizzarla con l’impiego di detergenti non denaturanti (5). Bibliografia: 1.Vitagliano L. et al.,(2008)J. Am. Chem. Soc. 130, 10527-35 2.Mazzarella L. et al.,(2006)Proteins: Struct. Funct. Bioinf. 65, 490-8 3.Mazzarella L. et al.,(2006)Proteins: Struct. Funct. Bioinf. 62, 316-21 4.Shih D.T. et al.,(1985)J Biol Chem. 260, 5919-24. 5.Peternel Š. et al., (2007)Biotecnnol Appl Biochem 49,239-6 Parole chiave: emoglobine, Effetto Root, produzione ricombinante Area tematica : Biologia molecolare.

We consider a minimal technicolour theory with two techniflavours in the adjoint representation of an SU(2) technicolour gauge group which has been argued to feature walking dynamics. We show how to naturally embed this theory in an extended technicolour model capable of generating the top quark mass. We investigate the precision constraints and conclude that such models, in the light of the most recent precision data fit, are not ruled out., Comment: RevTeX, 14 pages, 1 figure

Valenzano (Bari) Italy

We employ the epidemic Renormalization Group (eRG) framework to understand, reproduce and predict the COVID-19 pandemic diffusion across the US. The human mobility across different geographical US divisions is modelled via open source flight data alongside the impact of social distancing for each such division. We analyse the impact of the vaccination strategy on the current pandemic wave dynamics in the US. We observe that the ongoing vaccination campaign will not impact the current pandemic wave and therefore strict social distancing measures must still be enacted. To curb the current and the next waves our results indisputably show that vaccinations alone are not enough and strict social distancing measures are required until sufficient immunity is achieved. Our results are essential for a successful vaccination strategy in the US.

We explore the quantum nature of black holes by introducing an effective framework that takes into account deviations from the classical results. The approach is based on introducing quantum corrections to the classical Schwarzschild geometry in a way that is consistent with the physical scales of the black hole and its classical symmetries. This is achieved by organizing the quantum corrections in inverse powers of a physical distance. By solving the system in a self-consistent way we show that the derived physical quantities, such as event horizons, temperature and entropy can be expressed in a well defined expansion in the inverse powers of the black hole mass. The approach captures the general form of the quantum corrections to black hole physics without requiring to commit to a specific model of quantum gravity., Comment: Revised version matching the published one

We show that the observed anomalies in the lepton sector can be explained in extensions of the Standard Model that are natural and, therefore, resolve the Higgs sector hierarchy problem. The scale of new physics is around the TeV and Technicolor-like theories are ideal candidate models., 5 pages, 2 figures

We compute the scaling dimensions of a family of fixed-charge operators at the infrared fixed point of the $O(N)$ model featuring cubic interactions in $d=6-\epsilon$ for arbitrary $N$ to leading and subleading order in the charge but to all orders in the couplings. The results are used to analyze the conjectured equivalence with the $O(N)$ model displaying quartic interactions at its ultraviolet fixed point. This is performed by comparing the cubic model scaling dimensions against the known large $N$ results for the quartic model and demonstrating that they match. Our results reinforce the conjectured equivalence and further provide novel information on the finite $N$ physics stemming from the computations in the cubic model just below 6 dimensions., Comment: 21 pages, 2 figures, 1 table

We study the gravitational-wave signal stemming from strongly coupled models featuring both, dark chiral and confinement phase transitions. We therefore identify strongly coupled theories that can feature a first-order phase transition. Employing the Polyakov-Nambu-Jona-Lasinio model, we focus our attention on SU(3) Yang-Mills theories featuring fermions in fundamental, adjoint, and two-index symmetric representations. We discover that for the gravitational-wave signals analysis, there are significant differences between the various representations. Interestingly we also observe that the two-index symmetric representation leads to the strongest first-order phase transition and therefore to a higher chance of being detected by the Big Bang Observer experiment. Our study of the confinement and chiral phase transitions is further applicable to extensions of the Standard Model featuring composite dynamics., 29 pages, 12 figures, 4 tables; v2 matches journal published version

The Weak Gravity Conjecture has recently been re-formulated in terms of a particle with non-negative self-binding energy. Because of the dual conformal field theory (CFT) formulation in the anti-de Sitter space the conformal dimension $\Delta (Q)$ of the lowest-dimension operator with charge Q under some global U(1) symmetry must be a convex function of Q. This property has been conjectured to hold for any (unitary) conformal field theory and generalized to larger global symmetry groups. Here we refine and further test the convex charge conjecture via semiclassical computations for fixed charge sectors of different theories in different dimensions. We analyze the convexity properties of the leading and next-to-leading order terms stemming from the semiclassical computation, de facto, extending previous tests beyond the leading perturbative contributions and to arbitrary charges. In particular, the leading contribution is sufficient to test convexity in the semiclassical computations. We also consider intriguing cases in which the models feature a transition from real to complex conformal dimensions either as a function of the charge or number of matter fields. As a relevant example of the first kind, we investigate the $O(N)$ model in $4+\epsilon$ dimensions. As an example of the second type we consider the $U(N)\times U(M)$ model in $4-\epsilon$ dimensions. Both models display a rich dynamics where, by changing the number of matter fields and/or charge, one can achieve dramatically different physical regimes. We discover that whenever a complex conformal dimension appears, the real part satisfies the convexity property., Comment: 22 pages, 18 figures. Typos are fixed and references are added in version 2

We propose a physical theory underlying the temporal evolution of competing virus variants that relies on the existence of (quasi) fixed points capturing the large time scale invariance of the dynamics. To motivate our result we first modify the time-honoured compartmental models of the SIR type to account for the existence of competing variants and then show how their evolution can be naturally re-phrased in terms of flow equations ending at quasi fixed points. As the natural next step we employ (near) scale invariance to organise the time evolution of the competing variants within the effective description of the epidemic Renormalization Group framework. We test the resulting theory against the time evolution of COVID-19 virus variants that validate the theory empirically., 38 pages, 32 figures

Epidemic data show the existence of a region of quasi-linear growth (strolling period) of infected cases extending in between waves. We demonstrate that this constitutes evidence for the existence of near time-scale invariance that is neatly encoded via complex fixed points in the epidemic Renormalisation Group approach. As a result we achieve a deeper understanding of multiple wave dynamics and its inter-wave strolling regime. Our results are tested and calibrated against the COVID-19 pandemic data. Because of the simplicity of our approach that is organised around symmetry principles our discovery amounts to a paradigm shift in the way epidemiological data are mathematically modelled., Comment: 9 pages, 4 figures

The functional properties of metal oxide semiconductors depend on intrinsic and extrinsic defects. The population of intrinsic defects is strongly affected by the synthesis method and subsequent treatments of the material, while extrinsic defects can originate from suitable doping. Stoichiometric ZrO2 is a nonreducible oxide with a large band gap. Therefore, controlling and modulating its defect profile to induce energy states in the band gap is the sole possibility to make it a photocatalyst responsive to visible light. We report a method, based on low temperature sol−gel synthesis coupled with treatments performed in mild conditions, to obtain undoped visible light-responsive ZrO2−x. The electronic structure of these materials is interpreted in relation to their oxygen vacancy defect population. On the basis of a wide set of experimental measurements (X-ray photoelectron, steady-state and time-resolved photoluminescence, electron paramagnetic resonance, and UV−visible diffuse reflectance spectroscopy) and supported by density functional theory calculations, we demonstrate, for the first time, the predominance of positively charged F-center oxygen vacancies that do not give rise to Zr3+ species.

We investigate the high temperature fate of four-dimensional gauge-Yukawa theories featuring short distance conformality of either interacting or noninteracting nature. The latter is known as complete asymptotic freedom and, as templates, we consider non-Abelian gauge theories featuring either two singlet scalars coupled to gauged fermions via Yukawa interactions or two gauged scalars with(out) fermions. For theories with interacting fixed points at short distance, known as asymptotically safe, we consider two calculable examples. Exploring the landscape of safe and free theories above we discover a class of complete asymptotically free theories for which symmetry breaks at arbitrary high temperatures. In its minimal form this class is constituted by a theory with two fundamental gauged scalars each gauged under an independent group., Facultad de Ciencias Exactas, Instituto de Física La Plata

We investigate the properties of near-conformal dynamics in a sector of large charge when approaching the lower boundary of the conformal window from the chirally broken phase. To elucidate our approach we use the time-honored example of the phenomenologically relevant SU(2) color theory featuring $N_f$ Dirac fermions transforming in the fundamental representation of the gauge group. In the chirally broken phase we employ the effective pion Lagrangian featuring also a pseudo-dilaton to capture a possible smooth conformal-to-non-conformal phase transition. We charge the baryon symmetry of the Lagrangian and study its impact on the ground state and spectrum of the theory as well as the would-be conformal dimensions of the lowest large-charge operator. We moreover study the effects of and dependence on the fermion mass term., 15 pages

We investigate the theoretical predictions for thrust distribution in the electron positron annihilation to three-jets process at NNLO for different values of the number of flavors, $N_f$. To determine the distribution along the entire renormalization group flow from the highest energies to zero energy we consider the number of flavors near the upper boundary of the conformal window. In this regime of number of flavors the theory develops a perturbative infrared interacting fixed point. We then consider also the QED thrust obtained as the limit $N_c \rightarrow 0$ of the number of colors. In this case the low energy limit is governed by an infrared free theory. Using these quantum field theories limits as theoretical laboratories we arrive at an interesting comparison between the Conventional Scale Setting - (CSS) and the Principle of Maximum Conformality (PMC$_\infty$) methods. We show that within the perturbative regime of the conformal window and also out of the conformal window the PMC$_\infty$ leads to a higher precision, and that reducing the number of flavors, from the upper boundary to the lower boundary, through the phase transition the curves given by the PMC$_\infty$ method preserve with continuity the position of the peak, showing perfect agreement with the experimental data already at NNLO., 7 pages, 6 figures

We generalise the epidemic Renormalisation Group framework while connecting it to a SIR model with time-dependent coefficients. We then confront the model with COVID-19 in Denmark, Germany, Italy and France and show that the approach works rather well in reproducing the data. We also show that a better understanding of the time dependence of the recovery rate would require extending the model to take into account the number of deaths whenever these are over 15% of the total number of infected cases., 9 pages, 5 figures

[No abstract available]

We go beyond a systematic review of the semiclassical approaches for determining the scaling dimensions of fixed-charge operators in $U(1)$ and $O(N)$ models by introducing a general strategy apt at determining the relation between a given charge configuration and the associated operators for more involved symmetry groups such as the $U(N) \times U(M)$. We show how, varying the charge configuration, it is possible to access anomalous dimensions of different operators transforming according to a variety of irreducible representations of the non-abelian symmetry group without the aid of diagrammatical computations. We illustrate our computational strategy by determining the anomalous dimensions of several composite operators to the next-to-leading order in the semiclassical expansion for the $U(N) \times U(M)$ conformal field theory (CFT) in $4-\epsilon$ dimensions. Thanks to the powerful interplay between semiclassical methods and group theory we can, for the first time, extract scaling dimensions for a wide range of operators., Comment: 36 pages, 3 figures