48 research outputs found
A globally convergent matricial algorithm for multivariate spectral estimation
In this paper, we first describe a matricial Newton-type algorithm designed
to solve the multivariable spectrum approximation problem. We then prove its
global convergence. Finally, we apply this approximation procedure to
multivariate spectral estimation, and test its effectiveness through
simulation. Simulation shows that, in the case of short observation records,
this method may provide a valid alternative to standard multivariable
identification techniques such as MATLAB's PEM and MATLAB's N4SID
On the well-posedness of multivariate spectrum approximation and convergence of high-resolution spectral estimators
In this paper, we establish the well-posedness of the generalized moment
problems recently studied by Byrnes-Georgiou-Lindquist and coworkers, and by
Ferrante-Pavon-Ramponi. We then apply these continuity results to prove almost
sure convergence of a sequence of high-resolution spectral estimators indexed
by the sample size
On the connections between PCTL and Dynamic Programming
Probabilistic Computation Tree Logic (PCTL) is a well-known modal logic which
has become a standard for expressing temporal properties of finite-state Markov
chains in the context of automated model checking. In this paper, we give a
definition of PCTL for noncountable-space Markov chains, and we show that there
is a substantial affinity between certain of its operators and problems of
Dynamic Programming. After proving some uniqueness properties of the solutions
to the latter, we conclude the paper with two examples to show that some
recovery strategies in practical applications, which are naturally stated as
reach-avoid problems, can be actually viewed as particular cases of PCTL
formulas.Comment: Submitte
Isospectral flows on a class of finite-dimensional Jacobi matrices
We present a new matrix-valued isospectral ordinary differential equation
that asymptotically block-diagonalizes zero-diagonal Jacobi
matrices employed as its initial condition. This o.d.e.\ features a right-hand
side with a nested commutator of matrices, and structurally resembles the
double-bracket o.d.e.\ studied by R.W.\ Brockett in 1991. We prove that its
solutions converge asymptotically, that the limit is block-diagonal, and above
all, that the limit matrix is defined uniquely as follows: For even, a
block-diagonal matrix containing blocks, such that the
super-diagonal entries are sorted by strictly increasing absolute value.
Furthermore, the off-diagonal entries in these blocks have the same
sign as the respective entries in the matrix employed as initial condition. For
odd, there is one additional block containing a zero that is
the top left entry of the limit matrix. The results presented here extend some
early work of Kac and van Moerbeke.Comment: 19 pages, 3 figures, conjecture from previous version is added as
assertion (iv) of the main theorem including a proof; other major change
Attaining mean square boundedness of a marginally stable noisy linear system with a bounded control input
We construct control policies that ensure bounded variance of a noisy
marginally stable linear system in closed-loop. It is assumed that the noise
sequence is a mutually independent sequence of random vectors, enters the
dynamics affinely, and has bounded fourth moment. The magnitude of the control
is required to be of the order of the first moment of the noise, and the
policies we obtain are simple and computable.Comment: 10 page
Stochastic receding horizon control with output feedback and bounded controls
International audienceWe study the problem of receding horizon control for stochastic discrete-time systems with bounded control inputs and incomplete state information. Given a suitable choice of causal control policies, we first present a slight extension of the Kalman filter to estimate the state optimally in mean-square sense. We then show how to augment the underlying optimization problem with a negative drift-like constraint, yielding a second-order cone program to be solved periodically online. We prove that the receding horizon implementation of the resulting control policies renders the state of the overall system mean-square bounded under mild assumptions. We also discuss how some quantities required by the finite-horizon optimization problem can be computed off-line, thus reducing the on-line computation
Quantum micro–nano devices fabricated in diamond by femtosecond laser and ion irradiation
Diamond has attracted great interest as a quantum technology platform thanks to its optically active nitrogen vacancy (NV) center. The NV's ground state spin can be read out optically, exhibiting long spin coherence times of ≈1 ms even at ambient temperatures. In addition, the energy levels of the NV are sensitive to external fields. These properties make NVs attractive as a scalable platform for efficient nanoscale resolution sensing based on electron spins and for quantum information systems. Diamond photonics enhance optical interactions with NVs, beneficial for both quantum sensing and information. Diamond is also compelling for microfluidic applications due to its outstanding biocompatibility, with sensing functionality provided by NVs. However, it remains a significant challenge to fabricate photonics, NVs, and microfluidics in diamond. In this Progress Report, an overview is provided of ion irradiation and femtosecond laser writing, two promising fabrication methods for diamond‐based quantum technological devices. The unique capabilities of both techniques are described, and the most important fabrication results of color center, optical waveguide, and microfluidics in diamond are reported, with an emphasis on integrated devices aiming toward high performance quantum sensors and quantum information systems of tomorrow
Human senescent fibroblasts trigger progressive lung fibrosis in mice
Cell senescence has recently emerged as a potentially relevant pathogenic mechanism in fibrosing interstitial lung diseases (f-ILDs), particularly in idiopathic pulmonary fibrosis. We hypothesized that senescent human fibroblasts may suffice to trigger a progressive fibrogenic reaction in the lung. To address this, senescent human lung fibroblasts, or their secretome (SASP), were instilled into the lungs of immunodeficient mice. We found that: (1) human senescent fibroblasts engraft in the lungs of immunodeficient mice and trigger progressive lung fibrosis associated to increasing levels of mouse senescent cells, whereas non-senescent fibroblasts do not trigger fibrosis; (2) the SASP of human senescent fibroblasts is pro-senescence and pro-fibrotic both in vitro when added to mouse recipient cells and in vivo when delivered into the lungs of mice, whereas the conditioned medium (CM) from non-senescent fibroblasts lacks these activities; and, (3) navitoclax, nintedanib and pirfenidone ameliorate lung fibrosis induced by senescent human fibroblasts in mice, albeit only navitoclax displayed senolytic activity. We conclude that human senescent fibroblasts, through their bioactive secretome, trigger a progressive fibrogenic reaction in the lungs of immunodeficient mice that includes the induction of paracrine senescence in the cells of the host, supporting the concept that senescent cells actively contribute to disease progression in patients with f-ILDs