arXiv subjects

Francisco J. Fernández

Publications and source records attributed to Francisco J. Fernández.

17 recordsLinked to original sources

arXiv2026

Vanishing Events and Regularity-Conditioned Reachability in Linear Stieltjes Systems

We study linear Stieltjes control systems in which actuation is concentrated at finitely many temporal events, and we ask what happens when one of those events progressively loses its atomic weight in the associated Stieltjes measure. For constant coefficients, ordinary finite-atomic reachability is governed by a truncated Krylov space and is therefore insensitive to the positive values of the event weights. A different picture emerges once trajectory regularity is imposed. In the supercritical super-$g$-Hölder regime, we minimize the largest event-normalized state jump and characterize exactly the terminal directions for which this cost remains uniformly bounded as a prescribed event weight tends to zero. The characterization combines what can be reached before the vulnerable event, a drift-cancellability condition at that event, and the directions that remain available afterwards. Ordinary reachability of the deleted-event system can therefore be strictly larger than bounded-cost reachability in the singular limit. We also separate two mechanisms of divergence: loss of ordinary reachability after deletion and failure of the intermediate compatibility condition. For compatible targets, the minimum cost converges to a constrained deleted-event problem. A dimensionless position--velocity benchmark motivated by pulsed proximity maneuvers shows the distinction explicitly.

math.OC↗

arXiv2026

Banach-Valued Stieltjes Calculus and Linear Parabolic Evolution Equations with Posterior States

We develop a Banach-valued lateral Stieltjes calculus adapted to linear evolution equations on a Gelfand triple \[ V\hookrightarrow H\simeq H^*\hookrightarrow V^*. \] The evolution problem is formulated with the posterior state, \[ D_g u(t)+A(t) S_g u(t)=f(t),\qquad u(a)=u_0. \] This choice is decisive at atoms of the Stieltjes measure: if $δ=Δ_g(r)>0$, the equation yields the implicit variational resolvent \[ (I+δA(r))u(r^+)=u(r)+δf(r). \] We prove a Banach-valued lateral product formula, a weak--strong reconstruction theorem, and a Stieltjes analogue of the Lions--Magenes energy identity. In the separable Hilbert setting considered here, the stable projection chain used in the proof is shown to exist automatically by a spectral-band construction. The latter contains the exact positive jump contribution \[ \frac12\sum_r\|u(r^+)-u(r)\|_H^2. \] Existence is constructed independently by Galerkin approximation and by a Rothe scheme adapted to the Stieltjes mass and its atoms. The Rothe construction does not use spatial projections. We also explain why the available Aubin--Lions theorem for anterior Stieltjes--Bochner evolution graphs is not automatically applicable to the posterior energy space and, in the present linear coercive setting, is not needed. A heat equation with Stieltjes time is included as a model application. The claims are positioned relative to earlier Stieltjes parabolic equations, general measure-driven evolution, and operator-valued-measure parabolic systems; no priority is claimed for measure-driven parabolic theory or Galerkin approximation in general.

math.AP↗

arXiv2026

Reachability and exact controllability of linear Stieltjes differential systems

We study reachability and exact controllability for systems driven by a nondecreasing left-continuous Stieltjes derivator whose measure may have continuous, singular-continuous and atomic parts, while flat intervals represent inactivity. We construct an evolution family and post-jump variation-of-constants formula, and characterize the reachable subspace as the essential span of input directions. For constant coefficients, the Kalman condition is necessary for every derivator and, under regressivity, sufficient when the derivator is continuous and nonconstant on a subinterval. If the measure is purely atomic with exactly $N$ positive atoms, the reachable subspace is the truncated Krylov space generated by $B,AB,\ldots,A^{N-1}B$; for a Kalman-controllable pair, the minimum atom count among purely atomic derivators equals the controllability index. At the threshold count, one vanishing mass with the others converging to positive finite limits causes Gramian degeneration and worst-case energy blow-up; at or above threshold, compact positive mass ranges yield uniform coercivity. A mixed double-integrator example illustrates the results.

math.OC↗

arXiv2026

Aubin--Lions Compactness for Stieltjes--Bochner Evolution Graphs

Let $g$ be a nondecreasing left-continuous function and let $μ_g$ be its Lebesgue--Stieltjes measure. We establish a Banach-valued fundamental theorem of calculus and an Aubin--Lions compactness theorem for evolution measured by $μ_g$, allowing absolutely continuous, singular continuous and atomic components. If the range space has the Radon--Nikodým property, a curve is $g$-absolutely continuous if and only if it is an indefinite Bochner integral; its strong $g$-derivative is the Bochner density and the variation measure has density equal to its norm. A terminal atom may make the derivative invisible from the Bochner state class, so the natural evolution space is a graph of state--derivative pairs. For $B_0\Subset B\hookrightarrow B_1$, with $B_0$ and $B_1$ reflexive and $1<p_0,p_1<\infty$, the state projection is a compact linear operator into $L_g^{p_0}([a,b);B)$. The proof combines bounded evaluation at atoms, local $μ_g$-averages at nonatomic points and Ehrling's inequality. The result recovers the classical theorem and yields compactness principles for bounded time scales, weighted sequences and mixed Stieltjes measures.

math.FA↗

arXiv2026

Lateral Weak Stieltjes Derivatives: A Global Characterization of Stieltjes--Sobolev Spaces

Weak formulations for Stieltjes differential equations must retain the directional information carried by atoms of the driving measure. We derive a lateral integration-by-parts identity in which the posterior trace of the test function is forced by the atomic product rule. The resulting dual formulation gives an exact global characterization of integral Stieltjes--Sobolev spaces for the full exponent range from one to infinity and reconstructs the unique strong representative from its traced weak state. We prove that the associated traced weak operator is closed, establish Poincaré--Stieltjes estimates, and \rev{characterize Stieltjes absolute continuity inside bounded variation through a canonical derivative measure whose restriction to the open interval is the classical distributional derivative}. The framework is then applied to finite-dimensional nonlinear measure-driven systems, yielding equivalence of weak, integral, and measure formulations, existence and uniqueness under integrable Lipschitz assumptions, compactness-based existence, and intrinsic reset laws. Cubic and logistic models illustrate the simultaneous encoding of continuous evolution and instantaneous interventions.

math.GM↗

arXiv2026

Exact discrete-adjoint optimization of trap timing and placement in a Stieltjes-time reaction-diffusion model: A Galicia case study

Seasonal population models must combine diffusion, inactive periods and abrupt biological transfers while remaining differentiable with respect to localized interventions. We formulate a finite-dimensional timing-and-placement control problem for a Stieltjes-time reaction--diffusion model and derive the exact adjoint of the fully discrete residual. Continuous finite elements and an implicit Stieltjes--Euler scheme represent propagation, compartment replacement, resets and historical phase averages. For the resulting box-constrained penalized problem, we prove well-posedness and differentiability of the discrete control-to-state map, existence of a minimizer, first-order stationarity, and equivalence between direct-sensitivity and adjoint gradients. Benchmark tests show machine-precision agreement (below $3\times10^{-15}$) and adjoint speed-ups from about $7.5$ to $30.9$ as the number of traps increases from one to four. The method is applied to \textit{Vespa velutina} trap campaigns on a realistic Galicia mesh. Smoothed activation windows, domain-normalized moving kernels and the complete adjoint are independently verified. The final two-cluster control remains admissible and has a scaled gradient infinity norm of $2.97\times10^{-5}$ with 120 temporal subdivisions per month. Fixed-control evaluations at 60, 120 and 240 subdivisions yield a refinement-increment ratio of $0.4984$. At the finest level, the joint control outperforms time-only and reference controls, reducing the diagnostic objective by $0.49209%$. This reduction depends on uncalibrated trap-to-mortality intensities and should not be interpreted as field capture efficacy. The framework is fully reproducible, without claiming global optimality or a calibrated field-management prescription.

math.OC↗

arXiv2025

On the kernel of the Stieltjes derivative and the space of bounded Stieltjes-differentiable functions

We investigate the existence and uniqueness of solutions to first-order Stieltjes differential problems, focusing on the role of the Stieltjes derivative and its kernel. Unlike the classical case, the kernel of the Stieltjes derivative operator is nontrivial, leading to non-uniqueness issues in Cauchy problems. We characterize this kernel by providing necessary and sufficient conditions for a function to have a zero Stieltjes derivative. To address the implications of this nontrivial kernel, we introduce a function space which serves as a suitable framework for studying Stieltjes differential problems. We explore its topological structure and propose a metric that facilitates the formulation of existence and uniqueness results. Our findings demonstrate that solutions to first-order Stieltjes differential equations are, in general, not unique, underscoring the need for a refined analytical approach to such problems.

math.CA↗

arXiv2022

Compactness criteria for Stieltjes function spaces and applications

In this work we study some topological aspects of function spaces arising in Stieltjes differential calculus. Chief among them are compactness results related to the Ascoli-Arzelà and Kolmogorov-Riesz theorems, as well as their applications to Stieltjes-Sobolev spaces and decomposable functions.

math.FA↗

arXiv2022

The Wronskian and the variation of parameters method in the theory of linear Stieltjes differential equations of second order

In this work, we define the notions of Wronskian and simplified Wronskian for Stieltjes derivatives and study some of their properties in a similar manner to the context of time scales or the usual derivative. Later, we use these tools to investigate second order linear differential equations with Stieltjes derivatives to find linearly independent solutions, as well as to derive the variation of parameters method for problems with $g$-continuous coefficients. This theory is later illustrated with some examples such as the study of the one-dimensional linear Helmholtz equation with piecewise-constant coefficients.

math.CA↗

arXiv2022

Consequences of the product rule in Stieltjes differentiability

This work revolves around the study of differentiability in the Stieltjes sense of a product of functions. A formula for the first order derivative has been obtained in the past, which is similar to the usual one with some extra terms in its expression. The aim of this paper is to take this behavior into account to study under which conditions we can guarantee the existence of higher order derivatives, while obtaining some other interesting results for the Stieltjes derivative along the way. We also investigate the regularity of the product of two functions.

math.CA↗

arXiv2021

On first and second order linear Stieltjes differential equations

This work deals with the obtaining of solutions of first and second order Stieltjes differential equations. We define the notions of Stieltjes derivative on the whole domain of the functions involved, provide a notion of n-times continuously Stieltjes-differentiable functions and prove existence and uniqueness results of Stieltjes differential equations in those spaces. We also present the Green's functions associated to the different problems and an application to the Stieltjes harmonic oscillator.

math.CA↗

arXiv2021

Non-equilibrium Coupling of a Quartz Resonator to Ions for Penning-Trap Fast Resonant Detection

The coherent coupling between a quartz electro-mechanical resonator at room temperature and trapped ions in a 7-tesla Penning trap has been demonstrated for the first time. The signals arising from the coupling remain for integration times in the orders of seconds. From the measurements carried out, we demonstrate that the coupling allows detecting the reduced-cyclotron frequency ($ν_+$) within times below 10~ms and with an improved resolution compared to conventional electronic detection schemes. A resolving power $ν_+/Δν_+=2.4\times10^{7}$ has been reached in single measurements. In this publication we present the first results, emphasizing the novel features of the quartz resonator as fast non-destructive ion-trap detector together with different ways to analyze the data and considering aspects like precision, resolution and sensitivity.

physics.ins-det↗

arXiv2020

An optimization problem related to water artificial recirculation for controlling eutrophication

In this work, the artificial recirculation of water is presented and analyzed, from the perspective of the optimal control of partial differential equations, as a tool to prevent eutrophication effects in large waterbodies. A novel formulation of the environmental problem, based on the coupling of nonlinear models for hydrodynamics, water temperature and concentrations of the different species involved in the eutrophication processes, is introduced. After a complete and rigorous analysis of the existence of optimal solutions, a full numerical algorithm for their computation is proposed. Finally, some numerical results for a realistic scenario are shown, in order to prove the efficiency of our approach.

math.OC↗

arXiv2020

Stieltjes Bochner spaces and applications to the study of parabolic equations

This work is devoted to the mathematical analysis of Stieltjes Bochner spaces and their applications to the resolution of a parabolic equation with Stieltjes time derivative. This novel formulation allows us to study parabolic equations that present impulses at certain times or lapses where the system does not evolve at all and presents an elliptic behavior. We prove several theoretical results related to existence of solution, and propose a full algorithm for its computation, illustrated with some realistic numerical examples related to population dynamics.

math.AP↗

arXiv2020

Mathematical analysis and numerical resolution of a heat transfer problem arising in water recirculation

This work is devoted to the analysis and resolution of a well-posed mathematical model for several processes involved in the artificial circulation of water in a large waterbody. This novel formulation couples the convective heat transfer equation with the modified Navier-Stokes system following a Smagorinsky turbulence model, completed with a suitable set of mixed, nonhomogeneous boundary conditions of diffusive, convective and radiative type. We prove several theoretical results related to existence of solution, and propose a full algorithm for its computation, illustrated with some realistic numerical examples.

math.AP↗

arXiv2020

Approximation of Stieltjes ordinary differential equations

This work is devoted to the obtaining of a new numerical scheme based in quadrature formulas for the Lebesgue-Stieltjes integral for the approximation of Stieltjes ordinary differential equations. This novel method allows us to numerically approximate models based in Stieltjes ordinary differential equations for which no explicit solution is known. We prove several theoretical results related to the consistency, convergence and stability of the numerical method. We also obtain the explicit solution of the Stieltjes linear ordinary differential equation, and we use it to validate the numerical method. Finally, we present some numerical results that we have obtained for a realistic population model based in a Stieltjes differential equation.

math.NA↗

arXiv2019

On existence and uniqueness of solution for a hydrodynamic problem related to water artificial circulation in a lake

In this work we introduce a well-posed mathematical model for the processes involved in the artificial circulation of water, in order to avoid eutrophication phenomena, for instance, in a lake. This novel and general formulation is based on the modified Navier-Stokes equations following the Smagorinsky model of turbulence, and presenting a suitable nonhomogeneous Dirichlet boundary condition. For the analytical study of the problem, we prove several theoretical results related to existence, uniqueness and smoothness for the solution of this recirculation model.

math.AP↗