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On the nature of the finite-temperature transition in QCD
No full textWe discuss the nature of the finite-temperature transition in QCD with N_f
massless flavors. Universality arguments show that a continuous (second-order)
transition must be related to a 3-D universality class characterized by a
complex N_f X N_f matrix order parameter and by the symmetry-breaking pattern
[SU(N_f)_L X SU(N_f)_R]/Z(N_f)_V -> SU(N_f)_V/Z(N_f)_V, or [U(N_f)_L X
U(N_f)_R]/U(1)_V -> U(N_f)_V/U(1)_V if the U(1)_A symmetry is effectively
restored at T_c. The existence of any of these universality classes requires
the presence of a stable fixed point in the corresponding 3-D Phi^4 theory with
the expected symmetry-breaking pattern. Otherwise, the transition is of first
order. In order to search for stable fixed points in these Phi^4 theories, we
exploit a 3-D perturbative approach in which physical quantities are expanded
in powers of appropriate renormalized quartic couplings. We compute the
corresponding Callan-Symanzik beta-functions to six loops. We also determine
the large-order behavior to further constrain the analysis. No stable fixed
point is found, except for N_f=2, corresponding to the symmetry-breaking
pattern [SU(2)_L X SU(2)_R]/Z(2)_V -> SU(2)_V/Z(2)_V equivalent to O(4) ->
O(3). Our results confirm and put on a firmer ground earlier analyses performed
close to four dimensions, based on first-order calculations in the framework of
the epsilon=4-d expansion. These results indicate that the finite-temperature
phase transition in QCD is of first order for N_f>2. A continuous transition is
allowed only for N_f=2. But, since the theory with symmetry-breaking pattern
[U(2)_L X U(2)_R]/U(1)_V -> U(2)_V/U(1)_V does not have stable fixed points,
the transition can be continuous only if the effective breaking of the U(1)_A
symmetry is sufficiently large
Drastic facilitation of the onset of global chaos in a periodically driven Hamiltonian system due to an extremum in the dependence of eigenfrequency on energy
No full textSUMMARY The Chirikov resonance-overlap criterion predicts the onset of global chaos
if nonlinear resonances overlap in energy, which is conventionally assumed to
require a non-small magnitude of perturbation. We show that, for a
time-periodic perturbation, the onset of global chaos may occur at unusually
{\it small} magnitudes of perturbation if the unperturbed system possesses more
than one separatrix. The relevant scenario is the combination of the overlap in
the phase space between resonances of the same order and their overlap in
energy with chaotic layers associated with separatrices of the unperturbed
system. One of the most important manifestations of this effect is a drastic
increase of the energy range involved into the unbounded chaotic transport in
spatially periodic system driven by a rather {\it weak} time-periodic force,
provided the driving frequency approaches the extremal eigenfrequency or its
harmonics. We develop the asymptotic theory and verify it in simulations
Deconfining transition in Full QCD
No full textSUMMARY We present evidence that in full QCD with two dynamical quarks confinement is
produced by dual superconductivity of the vacuum as in the quenched theory.
Preliminary information is obtained on the nature of the deconfining
transition
Ectopia ventricolare ipokaliemia-indotta in due cani con insufficienza cardiaca
No full textRIASSUNTO Nel cane l’ipokaliemia è una rara complicazione della terapia diuretica con furosemide. In medicina umana circa il 10% dei pazienti in terapia con diuretici d’ansa ed il 20-30% di quelli in terapia con diuretici tiazidici, sviluppa ipokaliemia. Tale incidenza risulta superiore per i tiazidici (nonostante l’escrezione frazionata del potassio legata alla somministrazione dei diuretici d’ansa sia superiore) in virtù della loro maggiore durata d’azione. Non esistono studi analoghi condotti nel cane, ma si ritiene che l’incidenza sia molto più limitata. È stato inoltre osservato che i diuretici d’ansa, inibendo il riassorbimento del magnesio a livello di ansa di Henle, ne aumentano l’escrezione urinaria e possono, anche se raramente, causare ipomagnesiemia. In due cani (affetti da miocardiopatia dilatativa e malattia valvolare degenerativa mitralica) alla somministrazione di furosemide, pimobendan e, in un caso, spironolattone ha fatto seguito lo sviluppo di un’ectopia ventricolare. In entrambi i casi è stata riscontrata ipokaliemia; l’integrazione orale di potassio ha comportato la normalizzazione della potassiemia e la scomparsa dell’aritmia ventricolare senza che venisse somministrato alcun farmaco antiaritmico. In ogni cane con insufficienza cardiaca ed in terapia con furosemide in cui si verifichi l’improvvisa insorgenza di un’aritmia ventricolare dovrebbero essere valutati i livelli plasmatici del potassio. SUMMARY Both loop and thiazide diuretics administration induces marked kaliuresis that, in people, leads to the development of hypokalemia in a significant percentage of patients. 20-30% of patients receiving standard doses of thiazides and about 10% of patients treated with loop diuretics develop hypokalemia. Viceversa in the dog hypokalemia is a rare complication of diuretic therapy. Hypokalemia may promote, especially if the patient is concurrently receiving digitalis, the appearance of supraventricular and ventricular ectopic rhythms. This arrhythmias may be enhanced by hypokalemia/induced increased automaticity and/or facilitation of re-entry. Potassium repletion is the preferred therapeutical approach in human medicine, but routine oral supplementation is not currently recommended. This report describes two clinical cases of dogs (affected by either dilated cardiomyopathy and degenerative mitral valve disease) in which ventricular ectopy developed following administration of furosemide, pimobendan and, in one case, spironolactone. In the former case ventricular bigeminism leading to syncope was diagnosed; in the latter isolated premature ventricular complexes with two different morphologies were detected. In both cases hypokalemia was detected and subsequent oral potassium supplementation led to normalization of serum potassium levels and ventricular arrhythmia without the need of administering any antiarrhytmic drug. In all dogs with heart failure receiving furosemide, sudden onset of a ventricular arrhythmia should prompt evaluation of serum potassium levels
Percorsi web: storia dell'arte
Get PDFIn questo articolo si presentano le principali tipologie di informazioni reperibili su Internet per gli studiosi d’arte, e per ciascuna di esse si fornisce, a titolo esemplificativo e senza presunzione di esaustività, una raccolta di link utili, fornendo alcune indicazioni sulle caratteristiche o le potenzialità dei siti segnalati
Calculating Gluino Condensates in SYM from Seiberg-Witten Curves
No full textWe determine the gluino condensate in the pure super Yang-Mills theory (SYM) for the classical gauge groups ,
, and , by deforming the pure SYM
theory with the adjoint scalar multiplet mass, following the work by Finnell
and Pouliot, and Ritz and Vainshtein. The value of the gluino condensate agrees
in all cases with what was found in the weak coupling istanton calculation
Non-Abelian Vortex and Confinement
No full textWe discuss general properties and possible types of magnetic vortices in
non-Abelian gauge theories (we consider here ) in the
Higgs phase. The sources of such vortices carry "fractional" quantum numbers
such as charge (for SU(N)), but also full non-Abelian charges of the dual
gauge group. If such a model emerges as an effective dual magnetic theory of
the fundamental (electric) theory, the non-Abelian vortices can provide for the
mechanism of quark-confinement in the latter
Existence, Uniqueness and Algorithms for Matrix Unitary Reduction to Semiseparable Form
No full textThis paper concerns the study of a unitary transformation from a
generic symmetric matrix into a semiseparable matrix. The
problem is studied both theoretically and from an algorithmic
point of view. In particular, we first give a proof of the
existence of such a transformation and then we discuss the
uniqueness of such transformation proving an Implicit- Theorem
for semiseparable matrices. Finally, we study structural
properties of the factors of the -decomposition of a
semiseparable matrix. These properties allows us to design a
method based on the iterations applied to a semiseparable
matrix for reducing a symmetric matrix to semiseparable form. This
method has the same asymptotic cost of the reduction of a
symmetric matrix to tridiagonal form. Once the transformation has
been accomplished, if one is interested in computing the
eigenvalues each further iteration can be done in linear
time
Confining strings in representations with common -ality
No full textWe study the spectrum of confining strings in SU(3) pure gauge theory, by
means of lattice Monte Carlo simulations, using torelon operators in different
representations of the gauge group. Our results provide direct evidence that
the string spectrum is according to predictions based on -ality. Torelon
correlations in the rank-2 symmetric channel appear to be well reproduced by a
two-exponential picture, in which the lowest state is given by the fundamental
string , the heavier string state is such that the ratio
is approximately given by the Casimir ratio , and the torelon has a much smaller overlap with the
lighter fundamental string state
Rischio da botulismo infantile conseguente a consumo di miele
No full textRIASSUNTO Il botulismo infantile è una grave malattia alimentare che si manifesta in bambini al di sotto di un anno di età. Gli studi epidemiologici segnalano casi di questa tossinfezione in tutto il mondo. Negli Stati Uniti la prevalenza del botulismo infantile ha superato le altre forme di botulismo, sia quella alimentare classica che quella conseguente a traumi. In molti casi si è potuto costatare la corrispondenza fra il Clostridium tossigeno rilevato nel paziente e lo stesso microrganismo riscontrato nel miele che era stato somministrato al bambino. Le ricerche eziologiche e patogenetiche hanno chiarito che la malattia non consegue al consumo di tossina formata dal microrganismo nelle fasi precedenti il consumo, come avviene nella forma classica del botulismo alimentare, ma semplicemente per l’ingestione di spore dell’agente eziologico, che troverebbero nell’ambiente intestinale del bambino le condizioni adatte per la germinazione e la tossinogenesi. Tale evidenza ha posto il miele fra gli alimenti a rischio per il botulismo infantile. Tuttavia, le particolarità che caratterizzano questa malattia alimentare, in aggiunta alla scarsa informazione sull’argomento, possono esporre le parti interessate, consumatori, produttori, commercianti, autorità competenti, pediatri, alla sottostima del rischio sanitario, pregiudicando ogni possibile azione di prevenzione. Gli autori descrivono le acquisizioni scientifiche in materia, valutando al contempo le varie opzioni praticabili in ambito di gestione della prevenzione. SUMMARY Infant botulism is a serious food borne disease which occurs in children who are younger than one year of age. Epidemiological surveys show cases of this toxic infection all around the word. In United States the prevalence of infant botulism surpassed both classic food-borne and wound forms of botulism. In most of the cases correspondence was observed between toxin producing Clostridium collected in patients and microorganism found in honey given out the child. Aetiological and pathogenetic researches explained that disease does not occur for ingestion of toxin produced by the microorganism during steps before consumption, as it happen in the classic form of food-borne botulism, but simply for ingestion of spores of aethiologic agent, which could find good conditions for germination and toxin producing in intestinal environment. This evidence places honey among risky foods in order to infant botulism. Nevertheless specific peculiarities characterizing this food-borne disease, with the addition of insufficient information about the topic, might expose stakeholders, as consumers, manufacturers, traders, competent authority, paediatricians, to underestimate the health risk, compromising all the possible preventive measures. Authors show scientific knowledge about this matter, and at same time they value various practicable options of risk management