Search

Calcium-silicate hydrate (commonly referred to as C–S–H in cement chemistry) is the main phase and the “glue” of hydrated cement, the binding matrix of building materials such as concrete, which is an essential commodity for modern infrastructures and housing. The basic mechanisms that control cement hydration and the modes of C–S–H formation are not fully understood and the picture becomes even more complicated when organic polycarboxylate-based additives (PCE) are added with the aim of controlling the rheology of the fresh paste and the strength of the final product. Here, a kinetic model of nucleation and growth, with unconstrained nucleation mechanism (homogeneous/heterogeneous) and time-dependent growth rate, is described and used to fit the rate of C–S–H precipitation obtained by in situ X-ray powder diffraction. The kinetic model predicts a switch from heterogeneous to homogeneous nucleation and an overall inhibition of C–S–H precipitation in the presence of PCE. This mechanism exerts a fundamental...

We present a high-speed electrical detection scheme based on a custom-designed CMOS amplifier which allows the analysis of DNA translocation in glass nanopipettes on a microsecond timescale. Translocation of different DNA lengths in KCl electrolyte provides a scaling factor of the DNA translocation time equal to p = 1.22, which is different from values observed previously with nanopipettes in LiCl electrolyte or with nanopores. Based on a theoretical model involving electrophoresis, hydrodynamics and surface friction, we show that the experimentally observed range of p-values may be the result of, or at least be affected by DNA adsorption and friction between the DNA and the substrate surface.

A novel architecture for digital lock-in amplifiers (LIAs) able to overcome the resolution limit of standards implementations is proposed. The slow gain fluctuations of both the DAC and ADC of the generation and acquisition stages of the LIA are compensated using two ADCs alternately acquiring the signal coming from the device under test (DUT) and the stimulus (STIM) signal. Experimental results demonstrate a resolution enhancement of more than an order of magnitude with respect to state of art LIAs, enabling sub-ppm resolution measurements with an instrument working up to 5 MHz without imposing any constraint to the DUT or to the experimental setup.

Methods for the manipulation of single magnetic particles have become very interesting, in particular for in vitro biological studies. Most of these studies require an external microscope to provide the operator with feedback for controlling the particle motion, thus preventing the use of magnetic particles in high-throughput experiments. In this paper, a simple and compact system with integrated electrical feedback is presented, implementing in the very same device both the manipulation and detection of the transit of single particles. The proposed platform is based on zig-zag shaped magnetic nanostructures, where transverse magnetic domain walls are pinned at the corners and attract magnetic particles in suspension. By applying suitable external magnetic fields, the domain walls move to the nearest corner, thus causing the step by step displacement of the particles along the nanostructure. The very same structure is also employed for detecting the bead transit. Indeed, the presence of the magnetic particle in suspension over the domain wall affects the depinning field required for its displacement. This characteristic field can be monitored through anisotropic magnetoresistance measurements, thus implementing an integrated electrical feedback of the bead transit. In particular, the individual manipulation and detection of single 1-μm sized beads is demonstrated.

This work presents a platform for the detection of the neuronal magnetic signal arising from the propagation of the action potential along the axon, via an array of highly sensitive magnetoresistive sensors and a low noise front-end electronic setup. We report the results of calculations and experiments for estimating the limit of detection of such platform in terms of minimum detectable magnetic field. Furthermore, an experimental setup for recording the magnetic signal in a brain slice is presented.

This chapter reviews scanning probe microscopy (SPM)-based capacitance spectroscopy for scaling down the contact area of the traditionally macro-scale capacitance spectroscopy techniques— capacitance– voltage, admittance spectroscopy, and deep-level transient spectroscopy— to nanoscale dimensions. It presents the scientific motivations behind the development of this instrument. The chapter describes the experimental setup and its associated electronic circuits and also presents preliminary results on SPM-based capacitance spectroscopy. SPM is ideal for the task at hand because of the adequate spatial resolution stemming from a localized contact between the tip and the sample that also provides a conductive path. The chapter also describes the considerations and construction of an instrument to implement the conventional capacitance spectroscopy methods in a SPM to access both functional properties and sufficient spatial resolution. SPM-based capacitance– voltage, admittance spectroscopy, and deep-level transient spectroscopy techniques can be developed through careful design and implementation. The end result is spatially resolved imaging of defect density, energy, and capture cross-section of polycrystalline materials.

Summary: Eukaryotic cells live in a relatively comfortable equilibrium with a wide variety of microbes. However, while many of the cohabiting microorganisms are harmless or even beneficial to the eukaryotic host, a number of prokaryotes have evolved the capacity to invade and replicate within host cells, thereby becoming potentially pathogenic. To be able to cope with potential pathogens, most organisms have developed several host defense mechanisms. First, microbes can be internalized and destroyed by a number of cell types of an innate immune system in a rather aspecific manner. Second, more complex organisms possess additionally an adaptive immune system that is capable of eliminating hazardous microbes in a highly specific manner. This review describes recent progress in our understanding of how pathogens interact with cells of the immune system, resulting in activation of the immune system or, for certain microorganisms, in the evasion of host defense reactions

According to World Health Organization(WHO), 3.2 billion people are at risk for malaria. In 2015, 212 million new cases and 429000 deaths were estimated [1, 2]. Despite treatment in the early stage of the disease is usually very effective, conventional diagnostic tests via optical microscopy examination of thick and thin blood smears are unsuitable for an effective screening of the population. On the other hand, the over-treatment of the disease due to the large percentage of false positives in currently available rapid diagnostic tests (RDTs) may increase the risk of drug resistance. In this scenario, there is a strong need of novel RTDs with (i) the same sensitivity of the gold standard (optical microscopy examination) and (ii) a reduced number of false positives. To fulfill the last requirement, a real improvement would be to move from the detection of antigens or antibodies, which can be hardly washed out in a patient living in an endemic zone even after many weeks from the last malaria episode, to the quantification of infected red blood cells in a blood smear (i-RBC). This essentially means to go back to the concept of gold standard tests, with the additional requirement of integrating i-RBC counting in lab-on-chip platforms suitable for low-cost, rapid and on-site wide screening of the population in endemic zones. It is well known that i-RBCs display a paramagnetic behavior with respect to blood plasma, so that they can be separated from healthy ones and other corpuscles in a high magnetic field gradient. [3] This is due to the fact that, during the intra-erythrocytic development, the parasite degrades hemoglobin into free heme. This molecule, highly toxic to the parasite, is converted in an insoluble form, known as hemozoin or malaria pigment, which crystallizes into paramagnetic nanocrystals found both within the i-RBCs and free in the blood, after RBCs lysis. Of course, both the concentration of free hemozoin crystals and i-RBCs can be used for the determination of the parasitemia. In this paper we present an on-chip magnetophoretic platform for the separation and concentration of i-RBC and hemozoin nanocrystals on pre-defined areas of a chip. This is a pre-requisite for the quantification of the relative percentage of i-RBC with respect to healthy ones (parasitemia) with high sensitivity. The blood drop is placed on a glass substrate, which is then put in close contact to the surface of a chip with Nickel micropillars, at a distance defined by an outer ring which defines also the volume of the cell where magnetophoretic separation takes place. The chip is placed face-down, so that magnetic attraction towards the nickel pillars, in the macroscopic field gradient produced by an external system of permanent magnets, opposes the gravity. In this configuration, i-RBCs and hemozoin crystals are attracted upwards, towards the micropillars, while non-infected erythrocytes and the other blood cells (i.e. white blood cells and platelets) sediment towards the glass substrate. Our design allows to obtain a macroscopic field gradient as high as $1\times 10 ^{15}$ A2/m3 up to a distance of 500 micron from the chip surface, strong enough to overcome gravity and attract i-RBCs and hemozoin crystals towards the chip surface. The chip consists of an array of Ni pillars, with 20–30 micron diameter and 20 micron height, fabricated by electroplating and arranged on a hexagonal closed packed lattice. In close proximity to the chip surface, Ni pillars produce a much stronger field gradient, up to $3\times 10 ^{16}$ A2/m3 at a few microns from their surface, which concentrate the i-RBCs and hemozoin crystals. We have tested this system using RBCs from bovine blood, treated with NaNO 2 in order to induce the transformation of hemoglobin into paramagnetic meta-hemoglobin. [4] In this way, we obtained suspensions in PBS of RBCs mimicking i-RBCs, suitable for experiments of capture. In figure 1 we report optical images from experiments performed in a direct configuration, where gravity and magnetic forces act in the same direction. Untreated RBCs (ut-RBCs) and treated ones with NaNO2 (t-RBCs) were stained with a red fluorophore to improve the quality of optical images. As evident from Figure 1, in case of t-RBCs we observed a capture efficiency of 100% by magnetic pillars in a lattice with center to center spacing of 80 microns. For hemozoin crystals the capture is even easier, because of their much larger volume susceptibility, $3.4\times 10 ^{-4}$ to be compared with $3.9\times 10 ^{-6}$ in case of i-RBCs. These results pave the way to the use of our magnetic chips as active slides for the magnetophoretic separation and concentration of malaria markers, both i-RBCs and hemozoin crystals, in well-defined areas of the chips where quantification can be performed with high sensitivity.

This paper analyses two-player nonzero-sum games of optimal stopping on a class of linear regular diffusions with not non-singular boundary behaviour (in the sense of It\^o and McKean (1974), p.\ 108). We provide sufficient conditions under which Nash equilibria are realised by each player stopping the diffusion at one of the two boundary points of an interval. The boundaries of this interval solve a system of algebraic equations. We also provide conditions sufficient for the uniqueness of the equilibrium in this class., Comment: 29 pages; small edits in the text, updated acknowledgement of funding

A novel impedance micro-sensor measuring with 0.5 μm resolution the thickness of undesired chemical or bacterial films fouling the surfaces of in-line probes, monitoring water ducts, is presented. The circuit for lock-in impedance detection (operating at 5 MHz, 10-bit resolution) is illustrated. It is embedded in a multi-sensor IoT water quality monitoring node, enabling self-diagnostics and on-demand maintenance. The credit-card-sized board features pH, temperature, 4 conductivity probes and the film monitor, along with anti-bubble actuation and wireless GSM transmission. The additional power consumption added by the sludge sensor is only 5% of the total.

We characterize a novel micro-sensor with pairs of interdigitated combs of microelectrodes designed to detect particles in air. We evaluate the sensor’s response to 1 µm Polystyrene Latex (PSL) particles experimentally and crosscheck the results with simulations. Experiment and simulation show good consistency. Based on the promising results we propose a redesign of the capacitive particle sensor with respect to PM2.5.

We solve an infinite time-horizon bounded-variation stochastic control problem with regime switching between $N$ states. This is motivated by the problem of a government that wants to control the country's debt-to-GDP (gross domestic product) ratio. In our formulation, the debt-to-GDP ratio evolves stochastically in continuous time, and its drift -- given by the interest rate on government debt, net of the growth rate of GDP -- is affected by an exogenous macroeconomic risk process modelled by a continuous-time Markov chain with $N$ states. The government can act on the public debt by increasing or decreasing its level, and it aims at minimising a net expected regime-dependent cost functional. Without relying on a guess-and-verify approach, but performing a direct probabilistic study, we show that it is optimal to keep the debt-to-GDP ratio in an interval, whose boundaries depend on the states of the risk process. These boundaries are given through a zero-sum optimal stopping game with regime switching with $N$ states and are characterised through a system of nonlinear algebraic equations with constraints. To the best of our knowledge, such a result appears here for the first time. Finally, we put in practice our methodology in a case study of a Markov chain with $N=2$ states; we provide a thorough analysis and we complement our theoretical results by a detailed numerical study on the sensitivity of the optimal debt ratio management policy with respect to the problem's parameters., Comment: A previous version of this paper was circulating under the title "Optimal Management of Debt-to-GDP Ratio with Regime-Switching Interest Rate". In the new version we have improved exposition, generalized the setting and some of the results, and reorganized the structure of the paper. 27 pages, 3 figures. To appear on SIAM Journal on Control and Optimization

By combining DNA nanotechnology and high-bandwidth single-molecule detection in nanopipets, we demonstrate an electric, label-free hybridization sensor for short DNA sequences (

The ultimate resolution limit of the current front-end of wideband impedance detection circuits is set by the input total capacitance and input equivalent noise. We present a solution to reduce the noise of more than an order of magnitude when the capacitance cannot be further minimized. By introducing a properly-chosen inductor (and a proper and stable biasing network) it is possible to cancel the capacitive reactance at the resonance frequency (∼10 MHz) which becomes the sensing frequency, thus significantly reducing the detection noise, while preserving the accuracy of the transfer function. A detailed analysis of the scheme, and its experimental validation with different inductors are presented. In all cases an improvement larger than 10 is achieved with an input-referred current spectral density of ∼1 pA/VHz at the operating frequency of ∼20 MHz.

We consider a class of N-player stochastic games of multi-dimensional singular control, in which each player faces a minimization problem of monotone-follower type with submodular costs. We call these games "monotone-follower games". In a not necessarily Markovian setting, we establish the existence of Nash equilibria. Moreover, we introduce a sequence of approximating games by restricting, for each natural number n, the players' admissible strategies to the set of Lipschitz processes with Lipschitz constant bounded by n. We prove that, for each n, there exists a Nash equilibrium of the approximating game and that the sequence of Nash equilibria converges, in the Meyer-Zheng sense, to a weak (distributional) Nash equilibrium of the original game of singular control. As a byproduct, such a convergence also provides approximation results of the equilibrium values across the two classes of games. We finally show how our findings can be employed to prove existence of open-loop Nash equilibria in an N-player stochastic differential game with singular controls, and we propose an algorithm to determine a Nash equilibrium for the monotone-follower game., Comment: 26 pages. Reduced the lenght and reorganized the exposition and some proofs

In this paper we establish a new connection between a class of 2-player nonzero-sum games of optimal stopping and certain $2$-player nonzero-sum games of singular control. We show that whenever a Nash equilibrium in the game of stopping is attained by hitting times at two separate boundaries, then such boundaries also trigger a Nash equilibrium in the game of singular control. Moreover a differential link between the players' value functions holds across the two games., Comment: 26 pages. Improved the exposition and generalised some results

A monolithic CMOS chip able to count single airborne particles down to a diameter of 1 µm is presented. This mm-sized ASIC addresses the growing need for portable and miniaturized solid-state sensors monitoring air quality to be disseminated in the environment within pervasive wireless sensors networks. Particle counting and sizing are based on high-resolution capacitive detection. State-of-the-art performances (65 zF resolution with 40 Hz bandwidth) are enabled by the combination on the same chip of interdigitated microelectrodes (separated by 1 µm distance, matched with the particle size), and ultra-low-noise electronics connected to them achieving the lowest possible parasitic input capacitance. Chip design and characterization are illustrated.

The authors report on the reduction of low-frequency noise in semiconductor polymer nanowires with respect to thin-films made of the same organic material. Flicker noise is experimentally investigated in polymer nanowires in the range of 10-10(5) Hz by means of field-effect transistor architectures. The noise in the devices is well described by the Hooge empirical model and exhibits an average Hooge constant, which describes the current power spectral density of fluctuations, suppressed by 1-2 orders of magnitude compared to thin-film devices. To explain the Hooge constant reduction, a resistor network model is developed, in which the organic semiconducting nanostructures or films are depicted through a two-dimensional network of resistors with a square-lattice structure, accounting for the different anisotropy and degree of structural disorder of the active nanowires and films. Results from modeling agree well with experimental findings. These results support enhanced structural order through size-confinement in organic nanostructures as effective route to improve the noise performance in polymer electronic devices.

The properties of cementitious materials are related to the microstructure of their binder matrix, which develops, during cement hydration, by a sequence of dissolution–precipitation reactions. Here, microstructural development is monitored during hydration by synchrotron X-ray diffraction-enhanced computed microtomography (XRD-CT). This innovative, noninvasive technique yields images of the crystallographic phases present in the hydrating cement paste at different stages, which are combined to map the sites where dissolution and precipitation occur. The results indicate that the nucleation mechanism of the main hydration product (a calcium-silicate hydrate commonly referred to as C–S–H) changes in the presence of polycarboxylate ether (PCE) superplasticizers. The observed change is essential to understand the development of the cement microstructure and to provide a direct link between the reaction kinetics and the physicomechanical properties of the system.

We study a continuous-time, finite horizon, stochastic partially reversible investment problem for a firm producing a single good in a market with frictions. The production capacity is modeled as a one-dimensional, time-homogeneous, linear diffusion controlled by a bounded variation process which represents the cumulative investment-disinvestment strategy. We associate to the investment-disinvestment problem a zero-sum optimal stopping game and characterize its value function through a free-boundary problem with two moving boundaries. These are continuous, bounded and monotone curves that solve a system of non-linear integral equations of Volterra type. The optimal investment-disinvestment strategy is then shown to be a diffusion reflected at the two boundaries., Comment: 36 pages, 1 figure

Lock-in amplifiers (LIAs) are extensively used to perform high-resolution measurements. Ideally, when using LIAs, it would be possible to measure a minimum signal variation limited by the instrument input equivalent noise at the operating frequency and the chosen filtering bandwidth. Instead, digital LIAs show an unforeseen 1/f noise at the instrument demodulated output, proportional to the signal amplitude that poses a fundamental limit to the minimum detectable signal variation using the lock-in technique. In particular, the typical resolution limit of fast operating LIAs (>1 MHz) is of tens of ppm, orders of magnitude worse than the expected value. A detailed analysis shows that the additional noise is due to slow fluctuations of the signal gain from the generation stage to the acquisition one, mainly due to the digital-to-analog and analog-to-digital converters. To compensate them, a switched ratiometric technique based on two analog-to-digital converters alternately acquiring the signal coming from the device under test and the stimulus signal has been conceived. A field-programmabale gate array-based LIA working up to 10 MHz and implementing the technique has been realized, and results demonstrate a resolution improvement of more than an order of magnitude (from tens of ppm down to sub-ppm values) compared to standard implementations working up to similar frequencies. The technique is generally applicable without requiring calibration nor ad hoc experimental arrangements.

This paper examines a Markovian model for the optimal irreversible investment problem of a firm aiming at minimizing total expected costs of production. We model market uncertainty and the cost of investment per unit of production capacity as two independent one-dimensional regular diffusions, and we consider a general convex running cost function. The optimization problem is set as a three-dimensional degenerate singular stochastic control problem. We provide the optimal control as the solution of a Skorohod reflection problem at a suitable boundary surface. Such boundary arises from the analysis of a family of two-dimensional parameter-dependent optimal stopping problems and it is characterized in terms of the family of unique continuous solutions to parameter-dependent nonlinear integral equations of Fredholm type., 39 pages

A dual-channel credit-card-sized impedance cell counter featuring a throughput of 2000 cell/s and detection of single yeast cells (5 μm) with a signal-to-noise ratio of 20 dB is presented. Its compactness is achieved by a CMOS ASIC combining a lock-in impedance demodulator with an oversampling 20-bit ΣΔ ADC and real-time peak detection embedded in field-programmable gate array. The module is coupled to a dielectrophoretic cell-sorting microfluidic device, offering compact and label-free electrical readout that replaces the need for a fluorescence microscope and, thus, is suitable for point-of-care diagnostics. The independent role of each dimension of the planar sensing microelectrodes is demonstrated, with simulations and experiments, along with its relevant effect on the spectrum of thin channels, deriving useful design guidelines.

Advanced technologies to implement on-chip monitoring and feedback control operations are required to make silicon photonics scale to large-scale-of-integration. Transparent detectors and energy saving actuators are key ingredients of this paradigm. On-chip detectors are required to be minimally invasive in order to allow their integration in key spots of the circuit, thus easing control operation through the partitioning of complex architectures in smaller cluster of devices and the realization of local feedback control loops. Non volatile integrated actuators, which are reversible switching devices that can maintain the state without the need of “always on” power dissipation, are also needed to reduce the power consumption required by tuning, reconfiguration and stabilization operations. Addressing these issues, in this contribution we report on the performance of a recently developed transparent detector, named ContacLess Integrated Photonic Probe (CLIPP), that can monitor in line the intensity of the light in silicon waveguides without introducing any photon absorption in excess to the waveguide propagation loss. A systematic characterization of the CLIPP detector is here presented, specifically addressing the dependence of the CLIPP performance on the waveguide geometry and on the polarization and wavelength of the light. Concerning the development of non-volatile integrated actuators, we demonstrate the possibility to manipulate the light transmission in silicon waveguides by electrochemical insertion of mobile ions in a mixed ionic and electronic conductor (MIEC) used as upper cladding of a silicon waveguide. A finely controllable and reversible change of the imaginary part of the refractive index of the MIEC film is exploited to trim the loss of a silicon waveguide and to modify the frequency response of a silicon microring resonator.

The implementation of a classical control infrastructure for large-scale quantum computers is challenging due to the need for integration and processing time, which is constrained by coherence time. We propose a cryogenic reconfigurable platform as the heart of the control infrastructure implementing the digital error-correction control loop. The platform is implemented on a field-programmable gate array (FPGA) that supports the functionality required by several qubit technologies and that can operate close to the physical qubits over a temperature range from 4 K to 300 K. This work focuses on the extensive characterization of the electronic platform over this temperature range. All major FPGA building blocks (such as look-up tables (LUTs), carry chains (CARRY4), mixed-mode clock manager (MMCM), phase-locked loop (PLL), block random access memory, and IDELAY2 (programmable delay element)) operate correctly and the logic speed is very stable. The logic speed of LUTs and CARRY4 changes less then 5%, whereas the jitter of MMCM and PLL clock managers is reduced by 20%. The stability is finally demonstrated by operating an integrated 1.2 GSa/s analog-to-digital converter (ADC) with a relatively stable performance over temperature. The ADCs effective number of bits drops from 6 to 4.5 bits when operating at 15 K.

A mixed-signal electronic system allowing closed-loop control of 16 independent integrated photonic devices equipped with CLIPP transparent optical probes (−35 dBm sensitivity, 50 kHz speed) is presented. It features a 32-channel CMOS lock-in front-end (203 nV /√Hz noise, 100 dB dynamic range), interfaced via conditioning chains to multiple ADCs and DACs driven by a Xilinx Spartan-6 FPGA for real-time processing, including the generation and demodulation of multiple pilot tones for channel labeling and dithering-based feedback. The results of the platform characterization are reported, along with the first application of automatic control applied to a novel all-optical unscrambler for mode-division multiplexing.

In this paper we study continuous-time stochastic control problems with both monotone and classical controls motivated by the so-called public good contribution problem. That is the problem of n economic agents aiming to maximize their expected utility allocating initial wealth over a given time period between private consumption and irreversible contributions to increase the level of some public good. We investigate the corresponding social planner problem and the case of strategic interaction between the agents, i.e. the public good contribution game. We show existence and uniqueness of the social planner's optimal policy, we characterize it by necessary and sufficient stochastic Kuhn-Tucker conditions and we provide its expression in terms of the unique optional solution of a stochastic backward equation. Similar stochastic first order conditions prove to be very useful for studying any Nash equilibria of the public good contribution game. In the symmetric case they allow us to prove (qualitative) uniqueness of the Nash equilibrium, which we again construct as the unique optional solution of a stochastic backward equation. We finally also provide a detailed analysis of the so-called free rider effect., 38 pages. This version is a revised version of the paper "Continuous-Time Public Good Contribution under Uncertainty". Added new results, improved exposition of the results and changed some proofs

We present a wavelength locking platform enabling the feedback control of silicon (Si) microring resonators (MRRs) for the realization of a 4 × 10 Gb/s wavelength-division-multiplexing (WDM) transmitter. Four thermally tunable Si MRRs are employed to multiplex the signals generated by four directly modulated lasers (DMLs) operating in the L-band, as well as to improve the quality of the DMLs signals. Feedback control is achieved through a field-programmable gate array controller by monitoring the working point of each MRR through a transparent detector integrated inside the resonator. The feedback system provides an MRR wavelength stability of about 4 pm (0.5 GHz) with a time response of 60 ms. Bit error rate (BER) measurements confirm the effectiveness and the robustness of the locking system to counteract sensitivity degradations due to thermal drifts, even under uncooled operation conditions for the Si chip.

In the present study, the workability of two ordinary Portland cements, obtained from clinkers having similar phase composition and particle size distribution, but different orthorhombic C3A content, hydrated in the presence of four different PCEs, is investigated. Possible causes of the observed significant different levels of PCE compatibility, which are correlated with different amounts of orthorhombic C3A, are investigated by means of: (i) in situ X-ray diffraction, with the aim of assessing the time-dependent phase composition; (ii) imaging methods (scanning electron microscopy and X-ray microtomography) and gas adsorption, aimed at assessing the role of clinker porosity. Adopted strategies for mitigating PCE incompatibility included the addition of gypsum or bassanite, and the use of sacrificial agents for preventing any PCE consumption by early precipitating AFm phases. The results suggest that PCE incompatibility is mostly related to different specific surface areas and rates of early ettringite precipitation. The addition of a moderate amount of calcium sulfates improved PCE performance.

Ideally, lock-in amplifiers (LIAs) would be able to measure a minimum signal variation limited by the noise of the front-end amplifier and the filtering bandwidth. On the contrary, a detailed characterization of digital LIAs shows an unforeseen 1/f noise at the instruments demodulated output, proportional to the total signal amplitude. The signal-proportionality and 1/f nature of the measured noise pose a fundamental limit to the LIAs achievable resolution. This limit has been found to be dependent from the instrument maximum operating frequency, from few ppm for LIAs operating up to few hundreds of kHz, to few tens of ppm for LIAs operating up to few MHz or tens of MHz. The additional noise is due to slow gain fluctuations that the signal experiences from the generation stage to the acquisition one. To compensate them, a switched ratiometric technique based on two ADCs alternately acquiring the signal coming from the device under test and the stimulus signal has been conceived. The idea is that both signals should experience the same gain fluctuations, which can be successively removed by means of a division on the outputs of the synchronous demodulation. An FPGA-based LIA working up to 10 MHz and implementing the technique has been realized and results demonstrate a resolution improvement of more than an order of magnitude compared to standard implementations working up to similar frequencies (from tens of ppm down to sub-ppm values).

A problem of optimally purchasing electricity at a real-valued spot price (that is, with potentially negative cost) has been recently addressed in De Angelis, Ferrari and Moriarty (2015) [SIAM J. Control Optim. 53(3)]. This problem can be considered one of irreversible investment with a cost functional which is non convex with respect to the control variable. In this paper we study the optimal entry into this investment plan. The optimal entry policy can have an irregular boundary arising from this non convexity, with a kinked shape., 30 pages, 3 figures

This work presents the first prototype of the Smart Pipe, a compact and intelligent wireless node hosting miniaturized sensors, embedded in a flange, for distributed and real-time monitoring of water contamination and for optimization of water treatment plants. Beyond pH and temperature, it features a low-cost and high-resolution (13 ppm, 11 ms response time) custom-designed 4-channel conductivity measurement circuit. Long-term operation and optimized on-demand maintenance are achieved by the innovative combination of an impedance sensor measuring the thickness of sludge and biofilm depositing on microelectrodes with self-cleaning capabilities offered by UV photo-regeneration of nanometric TiO2 electrodes coatings. Finally, here we also demonstrate self-powering of the unit by means of an energy harvesting control valve, regulating the flow in the water distribution network where an efficient installation of these sensors is today foreseeable.

Reflected diffusions naturally arise in many problems from applications ranging from economics and mathematical biology to queueing theory. In this paper we consider a class of infinite time-horizon singular stochastic control problems for a general one-dimensional diffusion that is reflected at zero. We assume that exerting control leads to a state-dependent instantaneous reward, whereas reflecting the diffusion at zero gives rise to a proportional cost with constant marginal value. The aim is to maximize the total expected reward, minus the total expected cost of reflection. We show that depending on the properties of the state-dependent instantaneous reward we can have qualitatively different kinds of optimal strategies. The techniques employed are those of stochastic control and of the theory of linear diffusions., Comment: 25 pages

A promising strategy to get deeper insight on brain functionalities relies on the investigation of neural activities at the cellular and sub-cellular level. In this framework, methods for recording neuron electrical activity have gained interest over the years. Main technological challenges are associated to finding highly sensitive detection schemes, providing considerable spatial and temporal resolution. Moreover, the possibility to perform non-invasive assays would constitute a noteworthy benefit. In this work, we present a magnetoresistive platform for the detection of the action potential propagation in neural cells. Such platform allows, in perspective, the in vitro recording of neural signals arising from single neurons, neural networks and brain slices.

The complexity scaling of silicon photonics circuits is raising novel needs related to control. Reconfigurable architectures need fast, accurate and robust procedures for the tuning and stabilization of their working point, counteracting temperature drifts originated by environmental fluctuations and mutual thermal crosstalk from surrounding integrated devices. In this contribution, we report on our recent achievements on the automated tuning, control and stabilization of silicon photonics architectures. The proposed control strategy exploits transparent integrated detectors to monitor non-invasively the light propagating in the silicon waveguides in key spots of the circuit. Local monitoring enables the partitioning of complex architectures in small photonic cells that can be easily tuned and controlled, with need for neither preliminary circuit calibration nor global optimization algorithms. The ability to monitor the Quality Of of Transmission (QoT) of the optical paths in Photonic Integrated Circuits (PICs) is also demonstrated with the use of channel labelling and non-invasive light monitoring. Several examples of applications are presented that include the automatic reconfiguration and feedback controlled stabilization of an 8×8 switch fabric based on Mach-Zehnder interferometers (MZIs) and the realization of a wavelength locking platform enabling feedback-control of silicon microring resonators (MRRs) for the realization of a 4×10 Gbit/s wavelength-division-multiplexing transmitter. The effectiveness and the robustness of the proposed approach for tuning and stabilization of the presented architectures is demonstrated by showing that no significant performance degradation is observed under uncooled operation for the silicon chip.

A new technology is presented for transforming returned concrete into a granular material that can be reused as aggregates for concrete. The new method is based on non-toxic, easy to use additives that are added directly into the drum of truck mixers containing returned concrete. The new method favours the preservation of natural resources, allows the reduction of waste and the cutting of costs, both for waste disposal and for aggregates supplying. A laboratory and full scale test program has been undertaken in Japan by GNN, a Japanese association of RMC companies, to implement and fully assess the new technology.

The 3D phase distribution of cement pastes evolves during hydration and controls the rheology and mechanical properties of the paste. Synchrotron powder-diffraction micro-tomographic imaging is here employed to assess the cement phase spatial distribution in a totally non-invasive way. This technique can be used to produce distribution maps of the phases present in the hydrating cement paste. The method is applied to an ordinary Portland cement, hydrated in pure water or in the presence of nucleation seeds. The quantitative description of the phase spatial distribution by radial distribution functions allows the discrimination of different nucleation mechanisms.

Photonic technologies lack non-invasive monitoring tools to inspect the light inside optical waveguides. This is one of the main barriers to large scale integration, even though photonic platforms are potentially ready to host thousands of elements on a single chip. Here, we demonstrate non-invasive light observation in silicon photonics devices by exploiting photon interaction with intra-gap energy states localized at the waveguide surface. Light intensity is monitored by measuring the electric conductance of the silicon core through a capacitive access to the waveguide. The electric contacts are located at suitable distance from the waveguide core, thus introducing no measurable extra-photon absorption and a phase perturbation as low as 0.2 mrad, comparable to thermal fluctuations below 3 mK. Light monitoring with a sensitivity of -30 dBm and a dynamic range of 40 dB is demonstrated in waveguides and high-Q resonators, and for the tuning of coupled-resonator optical filters. This approach realizes a ContactLess Integrated Photonic Probe (CLIPP), that is simple, inherently CMOS compatible, non-invasive and scalable to hundreds of probing points per chip. The CLIPP concept provides a viable route to real-time conditioning and feedback control of densely-integrated photonic systems.

Downscaling of microfluidic cell culture and detection devices for electrochemical monitoring has mostly focused on miniaturization of the microfluidic chips which are often designed for specific applications and therefore lack functional flexibility. We present a compact microfluidic cell culture and electrochemical analysis platform with in-built fluid handling and detection, enabling complete cell based assays comprising on-line electrode cleaning, sterilization, surface functionalization, cell seeding, cultivationand electrochemical real-time monitoring of cellular dynamics. To demonstrate the versatility and multifunctionality of the platform, we explored amperometric monitoring of intracellular redox activity in yeast (Saccharomyces cerevisiae) and detection of exocytotically released dopamine from rat pheochromocytoma cells (PC12). Electrochemical impedance spectroscopy was used in bothapplications for monitoring cell sedimentation and adhesion as well as proliferation in the case of PC12 cells. The influence of flow rate on the signal amplitude in the detection of redox metabolism as well as the effect of mechanical stimulation on dopamine release were demonstrated using the programmable fluid handling capability. The here presented platform is aimed at applications utilizing cell based assays, ranging from e.g. monitoring of drug effects in pharmacological studies, characterization of neural stem cell differentiation, and screening of genetically modified microorganisms to environmental monitoring.

Soil and sediment contamination is recognised as one of the most relevant environmental problems caused by past industrial activities and unsustainable waste disposal practices, highlighting the need to develop or improve effective remediation techniques to support sustainable management strategies. In this context, the remediation of sediments dredged from the Mincio river (Italy) contaminated by mercury and heavy hydrocarbons (C12-40) was carried out by applying and implementing the High Performance Solidification/Stabilization technology, aimed at producing safe and reusable cement-based granular materials. The technology was improved by decreasing both the temperature and time of the thermal desorption treatment (from 280 to 110 °C and from 4-16 h to 70 min, respectively) and by including a wet conditioning step to the process. Temperature and time reduction allowed to diminish the degradation of the cementitious phases of the granules (usually related to the high temperatures employed in the process), while the wet conditioning step allowed to improve their mechanical properties, as well as to further reduce the leaching of contaminants. The physical-chemical properties of the granules and contaminant leaching in water were investigated by Inductively Coupled Plasma Mass and Optical Emission Spectrometry, Ultraviolet–Visible spectroscopy, Gas Chromatography, X-Ray Powder Diffraction, and Scanning Electron Microscopy, in order to identify the optimal parameters for both thermal and wet conditioning processes. The overall results showed that the use of consecutive thermal and wet conditioning treatment on sedimentary cementitious materials from the High Performance Solidification/Stabilization technology led to the removal of volatile pollutants and to the improvement of granule quality, thus providing a final material that satisfied all the Italian regulatory requirements for reuse. Therefore, the findings obtained in this study may contribute to the development of sustainable management strategies for contaminated soils and sediments, leading to their valorisation through the transformation into reusable materials.

The direct tracking of the potential-induced modulation of the double layer capacitance (100 mV bias steps resulting in 1.2 fF variations) of Pt nanoelectrodes (100 nm diameter) in physiological solution with sub-fF resolution and 10 ms response time is reported. This result is an example of the enhanced performance achieved thanks to an integrated CMOS current preamplifier used as an add-on for standard bench-top electrochemical instrumentation. The chip provides a current amplification of 103 over the wide frequency range DC-2 MHz and can be placed at the input of a current-to-voltage converter to reach higher gains. Thanks to its millimetric size it drastically reduces the input stray capacitance of the connection cables to the electrode, offering superior noise performance such as 0.55 fA (rms) current resolution with 1 Hz bandwidth demonstrated in the detection of 1.5 fA current steps. The improvement in performance of state-of-art commercial potentiostats is also reported: the largest measurable impedance is increased by two orders of magnitude (up to 100 GΩ with only 10 mV applied and 0.125 s averaging time) and the impedance noise in time tracking is reduced 35 times. This module has been developed for nano-electrochemical and bio-sensing applications but can be profitably used in all the situations in which few electrons are exchanged at the interface, either since the electrode area is nanometric or since the concentration of the redox species is extremely low.

Solid-state nanopores have been gaining popularity in nano-biotechnology for single molecule detection, in particular for label-free high-throughput DNA sequencing. In order to address the improvement of the resolution/speed trade-off critical in this application, here we present a new two-channel current amplifier tailored for solid-state nanopore devices with integrated tunneling electrodes. The simultaneous detection of ion and tunneling currents provides enhanced molecule tracking capability. We describe the system design starting from a detailed noise analysis and device modeling, highlighting the detrimental role of the conductive silicon substrate and of all the stray capacitive couplings between the electrodes. Given the high input capacitance (0.1---1 nF), the input voltage noise has been carefully minimized choosing a discrete couple of matched low-noise JFETs as input stage, thus achieving an equivalent input noise of 1.5 nV/?Hz (corresponding to a current noise floor of 15 fA/?Hz at 10 kHz). Low-noise performance (11 pA rms noise integrated over a 75 kHz bandwidth) is preserved at a wide bandwidth (300 kHz) and high gain (100 M?) thanks to the adoption of an improved integrator/differentiator cascade topology. Furthermore, along with biasing networks and selectable low-pass filters, an AC-coupled channel providing additional gain has been introduced in order to "zoom" in the current signature during pore blockade events. Together with an experimental characterization of the system (and comparison with the noise performance of other instruments), the platform is validated by demonstrating the detection of ?-DNA with 20 nm pores.

Consider the problem of a government that wants to reduce the debt-to-GDP (gross domestic product) ratio of a country. The government aims at choosing a debt reduction policy which minimises the total expected cost of having debt, plus the total expected cost of interventions on the debt ratio. We model this problem as a singular stochastic control problem over an infinite time-horizon. In a general not necessarily Markovian framework, we first show by probabilistic arguments that the optimal debt reduction policy can be expressed in terms of the optimal stopping rule of an auxiliary optimal stopping problem. We then exploit such link to characterise the optimal control in a two-dimensional Markovian setting in which the state variables are the level of the debt-to-GDP ratio and the current inflation rate of the country. The latter follows uncontrolled Ornstein-Uhlenbeck dynamics and affects the growth rate of the debt ratio. We show that it is optimal for the government to adopt a policy that keeps the debt-to-GDP ratio under an inflation-dependent ceiling. This curve is given in terms of the solution of a nonlinear integral equation arising in the study of a fully two-dimensional optimal stopping problem., 39 pages. A previous version of this work was circulating under the title "Controlling Public Debt without Forgetting Inflation". In the current version new results have been added, and exposition has been improved

We present an L-band WDM transmitter exploiting a feedback-controlled Si photonic circuit for channel multiplexing and extinction ratio enhancement of four DML sources. 4×10 Gbit/s transmission along a 50-km SMF is demonstrated.

This paper studies a finite-fuel two-dimensional degenerate singular stochastic control problem under regime switching that is motivated by the optimal irreversible extraction problem of an exhaustible commodity. A company extracts a natural resource from a reserve with finite capacity, and sells it in the market at a spot price that evolves according to a Brownian motion with volatility modulated by a two-state Markov chain. In this setting, the company aims at finding the extraction rule that maximizes its expected discounted cash flow, net of the costs of extraction and maintenance of the reserve. We provide expressions both for the value function and for the optimal control. On the one hand, if the running cost for the maintenance of the reserve is a convex function of the reserve level, the optimal extraction rule prescribes a Skorokhod reflection of the (optimally) controlled state process at a certain state and price dependent threshold. On the other hand, in presence of a concave running cost function it is optimal to instantaneously deplete the reserve at the time at which the commodity's price exceeds an endogenously determined critical level. In both cases, the threshold triggering the optimal control is given in terms of the optimal stopping boundary of an auxiliary family of perpetual optimal selling problems with regime switching., 34 pages, 2 figures. Thorough revision of the manuscript, added new results, and removed assumptions