Design of generalized fractional order gradient descent method

This paper focuses on the convergence problem of the emerging fractional order gradient descent method, and proposes three solutions to overcome the problem. In fact, the general fractional gradient method cannot converge to the real extreme point of the target function, which critically hampers the application of this method. Because of the long memory characteristics of fractional derivative, fixed memory principle is a prior choice. Apart from the truncation of memory length, two new methods are developed to reach the convergence. The one is the truncation of the infinite series, and the other is the modification of the constant fractional order. Finally, six illustrative examples are performed to illustrate the effectiveness and practicability of proposed methods.Comment: 8 pages, 16 figure

Description and Realization for a Class of Irrational Transfer Functions

This paper proposes an exact description scheme which is an extension to the well-established frequency distributed model method for a class of irrational transfer functions. The method relaxes the constraints on the zero initial instant by introducing the generalized Laplace transform, which provides a wide range of applicability. With the discretization of continuous frequency band, the infinite dimensional equivalent model is approximated by a finite dimensional one. Finally, a fair comparison to the well-known Charef method is presented, demonstrating its added value with respect to the state of art.Comment: 9 pages, 9 figure

De-conflicting management of fluid resuscitation and intravenous medication infusion

The treatment of combat casualties frequently involves infusion of multiple drugs (e.g. sedatives, opioids and vasopressors) in addition to fluid resuscitation. Usually, fluid resuscitation is performed first to restore the patient’s volume state, followed by the infusion of drugs that can optimize the hemodynamics and/or relief the pain. In some circumstances, however, fluid and drugs must be infused simultaneously. Simultaneous administration of fluid and intravenous drugs presents a practical challenge related to the interactions between them. On one hand, fluid infused dilutes the drugs by lowering its plasma concentration, thereby weakening the drugs’ intended clinical effects. On the other hand, the clinical effects of the intravenously administered drugs on the hemodynamics can interfere with the therapeutic goal of fluid resuscitation. Yet, the vast majority of existing work on closed-loop control of fluid resuscitation and intravenous drug infusion has focused on either fluid resuscitation or intravenous drug infusion alone, while methodologies and algorithms applicable to simultaneous administration of fluid and intravenous drugs have not been rigorously investigated. In the context of control engineering, this problem might be simply considered as a multivariable control problem. Nevertheless, the intricacy and nonlinearity in the system dynamics, in conjunction with limited sensor measurements makes this problem highly challenging. Hence, our work to analyze the conflicts between multiple treatments and to develop algorithmic framework to overcome such conflicts can represent a major leap toward the realization of complex automated medical care in the future, which can make a significant impact on human wellbeing. The main objective of this thesis is to investigate on de-conflicting management of fluid resuscitation and medication infusion, which is in twofold: first and foremost, to develop a mechanistic understanding of the interactions and interferences between the two treatments and second, to come up with novel solutions to address the challenges. To achieve the first goal of this project, we developed an integrated mathematical model of cardiovascular system and pharmacokinetics-pharmacodynamics(PK-PD) model of drugs. This study involves constructing the model based on current knowledge of physiology, isolated and interactive drug effects, parameter identification using real-world data to verify and validate the model, rigorously analyzing the results to demonstrate that multiple medical treatments can endanger the safety of patient care unless the treatments are properly controlled. To accomplish the second goal, we designed a strategy that realizes a safety assurance control of multiple treatments. This study involves model-based hemodynamic monitoring, robust nonlinear dynamic feedback control, safety assurance control design and treatment target mediation. In terms of controller design, we used a 2-degree of freedom PID controller for fluid loop, and an absolute stability guaranteed PID controller based on circle criterion and linear matrix inequalities(LMI) for drug loops. This dissertation considers a 2-input 2-output model(fluid resuscitation and propofol sedation), as well as a more sophisticated 3-input 2-output model(fluid resuscitation and propofol sedation with PHP vasopressor treatment) for case study. It turned out that the proposed methods worked well on both models. In addition, having more inputs provides more flexibility in terms of controller design

Two-dimensional flexible thermoelectric devices: using modeling to deliver optimal capability

Two-dimensional flexible thermoelectric devices (2D FTEDs) are a promising candidate for powering wearable electronics by harvesting low-grade energy from human body and other ubiquitous energy sources. However, immature device designs in the parametric geometries of FTEDs cannot provide an optimized output power density because of either insufficient temperature difference or unnecessarily large internal resistance. Here, we theoretically design optimal parametric geometries of 2D FTEDs by systematically considering applied temperature difference, temperature-dependent thermoelectric properties of materials, leg thickness, and thermodynamic conditions. The obtained analytical solution determines the optimal leg length for 2D FTEDs when these parameters are given and, therefore, minimizes the internal device resistance and simultaneously maintains the high temperature difference across the TE legs to maximize the device output power density. According to this design, we use flexible Ag2Se films as thermoelectric legs to assemble a 2D FTED, which displays a maximum power output of 11.2 mW and a normalized output power density of 1.43 uW cm-2 K-1 at a temperature difference of 150 K, outnumbering other 2D FTEDs by threefolds. Our 2D FTED can power up four light-emitting diodes, which shows great potential for harvesting electricity from low-grade heat. The exotic and reliable device design concept of 2D FTEDs reported here can be extended to other thermoelectric systems to boost the practical applications of FTEDs

Microstructure and Mechanical Properties of Core-Shell B4C-Reinforced Ti Matrix Composites

Composite material uses ceramic reinforcement to add to the metal matrix to obtain higher material properties. Structural design is an important direction of composite research. The reinforcement distribution of the core-shell structure has the unique advantages of strong continuity and uniform stress distribution. In this paper, a method of preparing boron carbide (B4C)-coated titanium (Ti) powder particles by ball milling and preparing core-shell B4C-reinforced Ti matrix composites by Spark Plasma Sintering was proposed. It can be seen that B4C coated on the surface of the spherical Ti powder to form a shell structure, and B4C had a certain continuity. Through X-ray diffraction characterization, it was found that B4C reacted with Ti to form layered phases of titanium boride (TiB) and titanium carbide (TiC). The compressive strength of the composite reached 1529.1 MPa, while maintaining a compressive strain rate of 5%. At the same time, conductivity and thermal conductivity were also characterized. The preparation process of the core-shell structure composites proposed in this paper has high feasibility and universality, and it is expected to be applied to other ceramic reinforcements. This result provides a reference for the design, preparation and performance research of core-shell composite materials