Nella Nota viene presentato un modello di operatore di collisione per l’equazione cinetica di (deriva) di Fokker-Planck, valido per magnetoplasmi quiescenti immersi in configurazioni idromagnetiche di equilibrio simmetriche. Principale caratteristica del presente modello è di consentire - contrariamente ad operatori di collisione approssimati in precedenza proposti da altri autori - la determinazione di variabili macroscopiche rilevanti includendo correzioni del primo ordine in termini...

We investigate the multiplicative properties of the spaces $H^{\frac{n}{2},\frac{1}{2}}$ As in the case of the classical Sobolev spaces $H^{\frac{n}{2}}$ this space does not form an algebra. We investigate instead the space $H^{\frac{n}{2}}\cap L^{\infty }$ , more precisely a subspace of it formed by products of solutions of the homogeneous wave equation with data in $H^{\frac{n}{2}}$.

Nella Nota viene presentato un modello di operatore di collisione per l’equazione cinetica di (deriva) di Fokker-Planck, valido per magnetoplasmi quiescenti immersi in configurazioni idromagnetiche di equilibrio simmetriche. Principale caratteristica del presente modello è di consentire - contrariamente ad operatori di collisione approssimati in precedenza proposti da altri autori - la determinazione di variabili macroscopiche rilevanti includendo correzioni del primo ordine in termini...

Let $X$ be the Banach space of $C^0$-functions on $\langle 0,1\rangle$ with the sup norm and $\alpha ,\beta \in X\to R$ be continuous increasing functionals, $\alpha \left(0\right)=\beta \left(0\right)=0$. This paper deals with the functional differential equation (1) $x^{\text{'}\text{'}\text{'}}\left(t\right)=Q[x,x^{\text{'}},x^{\text{'}\text{'}}\left(t\right)]\left(t\right)$, where $Q:X^2\times R\to X$ is locally bounded continuous operator. Some theorems about the existence of two different solutions of (1) satisfying the functional boundary conditions $\alpha \left(x\right)=0=\beta \left(x^{\text{'}}\right)$, $x^{\text{'}\text{'}}\left(1\right)-x^{\text{'}\text{'}}\left(0\right)=0$ are given. The method of proof makes use of Schauder linearizatin technique and the Schauder fixed point theorem. The results are modified for 2nd...

We consider a finite-dimensional control system $\left(\Sigma \right)\dot{x}\left(t\right)=f(x\left(t\right),u\left(t\right))$, such that there exists a feedback stabilizer $k$ that renders $\dot{x}=f(x,k\left(x\right))$ globally asymptotically stable. Moreover, for $(H,p,q)$ with $H$ an output map and $1\le p\le q\le \infty$, we assume that there exists a ${𝒦}_{\infty }$-function $\alpha$ such that $\parallel H\left(x_u\right){\parallel }_q\le {\alpha (\parallel u\parallel }_p)$, where $x_u$ is the maximal solution of ${\left(\Sigma \right)}_k\dot{x}\left(t\right)=f(x\left(t\right),k\left(x\left(t\right)\right)+u\left(t\right))$, corresponding to $u$ and to the initial condition $x\left(0\right)=0$. Then, the gain function $G_{(H,p,q)}$ of $(H,p,q)$ given by $$G_{(H,p,q)}\left(X\right)\stackrel{\mathrm{def}}{=}\underset{{\parallel u\parallel }_p=X}{sup}{\parallel H\left(x_u\right)\parallel }_q,$$ is well-defined. We call profile of $k$ for $(H,p,q)$ any ${𝒦}_{\infty }$-function which is of the same order of...

Let $W$ be a non-negative function of class ${\mathrm{C}}^3$ from ${ℝ}^2$ to $ℝ$, which vanishes exactly at two points $𝐚$ and $𝐛$. Let $S^1(𝐚,𝐛)$ be the set of functions of a real variable which tend to $𝐚$ at $-\infty$ and to $𝐛$ at $+\infty$ and whose one dimensional energy $$E_1\left(v\right)={\int }_{ℝ}\left[W\left(v\right)+|v^{\text{'}}{|}^2/2\right]\mathrm{d}x$$ is finite. Assume that there exist two isolated minimizers $z_{+}$ and $z_{-}$ of the energy $E_1$ over $S^1(𝐚,𝐛)$. Under a mild coercivity condition on the potential $W$ and a generic spectral condition on the linearization of the one-dimensional Euler–Lagrange operator...

We consider the weak closure $WZ$ of the set $Z$ of all feasible pairs (solution, flow) of the family of potential elliptic systems $$$$ where $\Omega \subset {𝐑}^n$ is a bounded Lipschitz domain, $F_s$ are strictly convex smooth functions with quadratic growth and $S=\{\sigma measurable\mid {\sigma }_s\left(x\right)=0\text{or}1,s=1,\cdots ,s_0,{\sigma }_1\left(x\right)+\cdots +{\sigma }_{s_0}\left(x\right)=1\}$. We show that $WZ$ is the zero level set for an integral functional with the integrand $Qℱ$ being the $𝐀$-quasiconvex envelope for a certain function $ℱ$ and the operator $𝐀={\left(\text{curl,div}\right)}^m$. If the functions $F_s$ are isotropic, then on the characteristic cone...

Negli spettri fotoelettronici (p.e.) indotti da radiazione ultra-violetta di serie omologhe di composti, si trovano bande in ben definite regioni di energia, che possono essere assegnate empiricamente a ionizzazione di legami specifici o di coppie solitarie di elettroni. L’effetto dell'intorno chimico sulle energie di ionizzazione si esplica in piccoli spostamenti, che hanno una dipendenza approssimativamente lineare dall'ettronegatività di atomi o gruppi vicini. La discussione riguarda...