A cylindrical lens has different focusing powers in two perpendicular transverse directions; in the simplest example it is curved in one direction and flat in the other. Parallel input light rays are then brought toward a line rather than one point.

Place a screen beyond the element and rotate the cylindrical lens: the focused line rotates with it. Such an element can reshape a beam or compensate unequal focusing in different directions. Its orientation matters as well as its focal length, so a single scalar lens power does not fully specify its action on an arbitrary beam.

A spherical lens has refracting surfaces that are portions of spheres, possibly with one plane surface. Their radii of curvature, separation and relative refractive index determine the element's optical power. Rotational symmetry makes the two transverse directions equivalent near the optical axis.

A spherical surface is convenient to manufacture, but does not generally bring every parallel light ray to one point. Comparing focus with the aperture wide open and then reduced reveals spherical aberration: outer and near-axis light rays can focus at different axial positions. The paraxial approximation describes the limiting near-axis behavior.

An optical lens with different refractive powers in two principal meridians. Correcting regular ocular astigmatism requires both the power difference and its orientation.

A lens thicker near its centre than at its edge. It is converging in the usual case of glass in air, but the refractive index relative to the surroundings matters; shape alone is not a medium-independent power specification.

On a bounded open set, suppose $b\in L^{\infty }$ has weak divergence in $L_{\mathrm{loc}}^1$ with $\mathrm{div}b\le 0$. For $\phi \in C_0^{\infty }$, testing the divergence identity with ${\phi }^2/2$ gives $\int (b\cdot \nabla \phi )\phi =-\frac{1}{2}\int (\mathrm{div}b){\phi }^2\ge 0$. The left side is continuous in the zero-boundary Sobolev space $H_0^1$, by the Poincaré inequality and boundedness of $b$. Density therefore extends its nonnegativity to every $u\in H_0^1$. One need not assume that $(\mathrm{div}b)u^2$ is integrable. It follows that $a(u,v)=\int \nabla u\cdot \nabla v+\int (b\cdot \nabla u)v$ is a coercive bilinear form in the gradient norm, giving unique weak Dirichlet solvability by the Lax-Milgram theorem.

A coercive zero-Dirichlet weak form gives a bounded solution map from $L^2$ into $H_0^1$. Composing with the compact Sobolev embedding into $L^2$ gives the compact inverse $K$. Transposing the bilinear form produces its Hilbert-space adjoint inverse $K^{\ast }$. The Fredholm compatibility condition for a shifted equation is orthogonality of $f$ to the homogeneous adjoint solutions. Indeed $(Kf,w)=(f,w)/\lambda$ when $K^{\ast }w=w/\lambda$, and the zero spectral parameter is excluded at resonance by coercivity.

Suppose a meromorphic function is holomorphic on two concentric annuli about $a$, with only finitely many poles between chosen inner and outer coefficient circles. Let $a_n,b_n$ denote the corresponding Laurent coefficients. Subtract their contour integral formulas and apply the residue theorem to the intervening annular region. It givesThe sum is over the poles crossed, including their multiplicities through the residue. This identity applies to every integer index. Thus changing the annulus can change even the coefficients of nonnegative powers; it is not merely a change in the principal part.

For example, $f(z)=1/\sin z$ has simple poles at $\pm \pi$, each with residue $-1$. Moving a coefficient circle centered at zero from radius below $\pi$ to radius between $\pi$ and $2\pi$ changes its $n$th coefficient by $-{\pi }^{-n-1}-(-\pi {)}^{-n-1}$. Even indices remain unchanged, while odd indices acquire a nonzero correction.

For real $p>0$, the Laplace transform $G$ of the order-zero Bessel function of the first kind satisfies $(1+p^2)G^{\prime }+pG=0$. This follows by transforming $x{J}_0^{\prime \prime }+J_0^{\prime }+x{J}_0=0$, using $\mathcal{L}[xg]=-{\partial }_p\mathcal{L}[g]$ and $J_0(0)=1$, $J_0^{\prime }(0)=0$. Thus $G=C/\sqrt{1+p^2}$; the initial value theorem for Laplace transforms gives $pG(p)\to 1$ and fixes $C=1$.

If two piecewise continuous functions of exponential order on $[0,\infty )$ have the same unilateral Laplace transform for every sufficiently large positive real parameter, they agree at every common point of continuity and agree almost everywhere. For continuous functions, the equality holds everywhere. Values at an isolated discontinuity cannot be recovered from an ordinary integral transform.

A bounded function on $[0,\infty )$ has a Laplace transform satisfying the displayed bound, by integration of $|y(t)e^{-pt}|$. Consequently its Laplace transform cannot have a pole of order two or higher at $p=0$. This can eliminate the arbitrary constant introduced when multiplication by $t$ turns an ordinary differential equation into a first-order differential equation for its Laplace transform.

For example, transforming $t{y}^{\prime \prime }+(t-1)y^{\prime }-y=0$ with $y(0)=1$ gives $p(p+1)Y^{\prime }+(3p+2)Y=2$. An integrating factor $p^2(p+1)$ yieldsThe bound forces $C=0$, selecting $y=e^{-t}$. This selection can be justified without assuming unproved endpoint regularity for every solution: $e^{-t}$ and $t-1$ have nonzero Wronskian $t{e}^{-t}$ on $(0,\infty )$, so they form a fundamental system of solutions. Boundedness removes $t-1$, and the limit at zero fixes the remaining coefficient. The endpoint limit by itself does not select a unique solution.

Use normalized measure on the circle. If a trigonometric polynomial has frequency support $\{\pm n_j\}$ with $n_{j+1}>3n_j$, every zero sum of four signed frequencies pairs into opposite equal frequencies: the largest unpaired term would exceed the sum of the other three. Expanding the fourth moment and bounding its three possible pairings gives $\Vert p{\Vert }_4^4\le 3\Vert p{\Vert }_2^4$. The Holder inequality gives $\Vert p{\Vert }_2\le \Vert p{\Vert }_1^{1/3}\Vert p{\Vert }_4^{2/3}$ and hence the displayed estimate. Therefore an $L^1$ function with only these lacunary frequencies has square-summable coefficients: apply the estimate to its uniformly $L^1$-bounded Fejér sums and then pass to finite coefficient blocks. Finitely many extra modes do not affect the conclusion.

Consider the continuum Kuramoto model with an even probability density function $g(\omega )$. Seek a stationary Kuramoto order parameter in a frame with $\psi =0$. For $r>0$, phase locking gives $\sin \theta =\omega /(Kr)$ on the stable branch, so locked phase oscillators contributeDrifting phase oscillators have stationary angular density proportional to $|\omega -Kr\sin \theta {|}^{-1}$. Their real contribution integrates to zero as a periodic logarithmic derivative; their imaginary contributions cancel between $\omega$ and $-\omega$.^[ref]

Substitution $\omega =Kr\sin \theta$ and division by $r>0$ yieldThe incoherent state of the Kuramoto model must be retained separately before division. If $g$ is continuous with $0<g(0)<\infty$, any nonzero stationary branch reaching $r=0$ at a finite coupling must satisfyIndeed, the integral tends to $g(0){\int }_{-\pi /2}^{\pi /2}{\cos }^2\theta d\theta =\pi g(0)/2$. This limiting stationary calculation alone does not establish the branch's stability, its global existence, or the first instability of a multimodal frequency population.

For null coordinates normalized by $UV=(2m-r)e^{r/(2m)}$, the displayed field agrees with exterior Schwarzschild time translation. Its flow rescales $U$ and $V$ inversely, preserving their product, the radius and $dUdV$. It therefore preserves the extended metric across both horizons. Its squared norm is $1-2m/r$: it is timelike in both exterior regions, spacelike in the black-hole and white-hole interiors, and nonzero null on the horizons away from the bifurcation two-sphere. At that sphere it vanishes. The zero vector should not be mistaken for a nonzero null generator. This gives an explicit symmetry that survives where the original time coordinate ceases to be regular.

2-Oxoglutarate is the conjugate-base form of a five-carbon dicarboxylic keto acid, also called alpha-ketoglutarate. Its ketone carbon is adjacent to a carboxylate group.

In the citric acid cycle, isocitrate is oxidatively decarboxylated to 2-Oxoglutarate, which is then converted to succinyl-CoA. Through transamination, the same carbon skeleton connects with glutamic acid, linking energy metabolism and nitrogen metabolism.^[ref]

For cell diffusion, self-produced chemotactic agent and logistic proliferation, Neumann cosine modes reduce linear stability of the uniform state to a two-by-two matrix indexed by $s={\pi }^2(n^2/L_1^2+m^2/L_2^2)$. Its trace is negative and its determinant is $D(s)=\alpha s^2+(1+\alpha \kappa -\beta \kappa \eta )s+\kappa$. Chemotaxis can destabilize a mode precisely when $D(s)<0$, despite stability of the spatially uniform reaction system.

Displacement of the humeral head from its normal relation to the glenoid. Direction of displacement and associated nerve, vessel or bone injury distinguish different forms of this apparently similar injury.

Restoration of displaced joint surfaces to their intended relationship. Correct alignment and restoration of stable function are related but separate outcomes after a dislocation.