Onset and stabilization of delay-induced instabilities in piezoelectric digital vibration absorbers

The stability of a piezoelectric structure controlled by a digital vibration absorber emulating a shunt circuit is investigated in this work. The formalism of feedback control theory is used to demonstrate that systems with a low electromechanical coupling are prone to delay-induced instabilities entailed by the sampling procedure of the digital unit. An explicit relation is derived between the effective electromechanical coupling factor and the maximum sampling period guaranteeing a stable controlled system. Since this sampling period may be impractically small, a simple modification procedure of the emulated admittance of the shunt circuit is proposed in order to counteract the effect of delays by anticipation. The theoretical developments are experimentally validated on a clamped-free piezoelectric beam.

Hackflex: low-cost, high-throughput, Illumina Nextera Flex library construction

We developed a low-cost method for the production of Illumina-compatible sequencing libraries that allows up to 14 times more libraries for high-throughput Illumina sequencing to be generated for the same cost. We call this new method Hackflex. The quality of library preparation was tested by constructing libraries from Escherichia coli MG1655 genomic DNA using either Hackflex, standard Nextera Flex (recently renamed as Illumina DNA Prep) or a variation of standard Nextera Flex in which the bead-linked transposase is diluted prior to use. In order to test the library quality for genomes with a higher and a lower G+C content, library construction methods were also tested on Pseudomonas aeruginosa PAO1 and Staphylococcus aureus ATCC 25923, respectively. We demonstrated that Hackflex can produce high-quality libraries and yields a highly uniform coverage, equivalent to the standard Nextera Flex kit. We show that strongly size-selected libraries produce sufficient yield and complexity to support de novo microbial genome assembly, and that assemblies of the large-insert libraries can be much more contiguous than standard libraries without strong size selection. We introduce a new set of sample barcodes that are distinct from standard Illumina barcodes, enabling Hackflex samples to be multiplexed with samples barcoded using standard Illumina kits. Using Hackflex, we were able to achieve a per-sample reagent cost for library prep of A$7.22 (Australian dollars) (US $5.60; UK £3.87, £1=A$1.87), which is 9.87 times lower than the standard Nextera Flex protocol at advertised retail price. An additional simple modification and further simplification of the protocol by omitting the wash step enables a further price reduction to reach an overall 14-fold cost saving. This method will allow researchers to construct more libraries within a given budget, thereby yielding more data and facilitating research programmes where sequencing large numbers of libraries is beneficial.

A modified perfusion protocol for pulmonary endarterectomy in a patient with a hematologic malignancy treated with a tyrosine kinase inhibitor

Tyrosine kinase inhibitors (TKI) are known to be highly effective in the treatment of various cancers with kinase-domain mutations such as chronic myelogenous leukemia. However, they have important side effects such as increased vascular permeability and pulmonary hypertension. In patients undergoing pulmonary endarterectomy with deep hypothermic circulatory arrest, these side effects may exacerbate postoperative complications such as reperfusion edema and persistent pulmonary hypertension. We report on a simple modification of the perfusion strategy to increase intravascular oncotic pressure by retrograde autologous priming and the addition of packed cells and albumin in a patient treated with a TKI.

Dynamic Characterization of Additively Manufactured Polylactide (PLA)

Additively manufactured materials have excellent properties with wide applications in many industries. For designing components exposed to extreme loading situations, it is essential to characterize the high strain rate response of 3D printed (fused deposition modelling) materials. In this study, uniaxial quasi-static and dynamic compressive tests were carried out at various strain rates (10−2 s−1 and 200 s−1 to 1800 s−1) for 3D printed PLA. Strain rate dependent compressive response of Polylactide acid (PLA) disk specimens 3D printed at 0°, 45° and 90° orientations was obtained using the Split Hopkinson bar technique. The results show that the compressive strength increases with corresponding strain rates for 0° and 45° print orientations. PLA printed at 0° has higher compressive strength compared to 45° and 90° orientations under quasi-static as well as high strain rate loading. Toughness was observed to increase with strain rate in all three orientations. A simple modification to the Johnson-Cook model is proposed, which accounts for the effects of print orientation, porosity and strain softening behavior.

Mathematical modelling for the functioning of the p53 signaling pathway following DNA damage. I. The model of activation of the p53-Mdm2-Wip1 system

Работа посвящена численному исследованию известной математической модели динамики системы p53-Mdm2-Wip1 при различных воздействиях, приводящих к повреждениям ДНК. Главное внимание уделено ранее не рассматривавшимся методическим аспектам - оценке чувствительности модели, качественному анализу свойств решения в биологически адекватном диапазоне значений параметров, анализу применимости модели к описанию критических состояний системы, связанных с известными дегенеративными заболеваниями. Показано, что простейшая модификация исходной модели делает ее существенно более эффективным инструментом для численного анализа широкого диапазона состояний системы p53-Mdm2-Wip1 In the context of the survival and death of cells with DNA damage, a special role is assigned to the p53 protein. The management of p53 and its inhibitors can provide a protective effect in a wide range of degenerative diseases, such as cancer, infarctions, and dementia. Therefore, there are increased requirements for mathematical models designed to study the mechanism of functioning of the p53 signaling pathway. Our work is devoted to the study of the properties of the well-known mathematical model of the dynamics of the p53-Mdm2-Wip1 system under various influences leading to DNA damage. A simple modification of the model is proposed. The main attention is paid to the analysis of the sensitivity and qualitative properties of solutions, as well as the validation of the model before and after its modification. In numerical experiments, it was found that within the framework of the accepted models, the stationary state of the p53-Mdm2-Wip1 system can be unstable to negligible changes in the initial conditions, so that the system can function under the same parameter values according to the bifurcation scenario with a doubling of the period. The mathematical conditions under which the multiplicity of solutions and complex dynamic modes were detected allow for a biological interpretation as a reflection of the variability in the response of the p53 protein pathway to the damage signal. The range of applicability of the models was compared using the example of a wellknown laboratory experiment, in which the most complete set of observed in vitro and in vivo states of the p53-Wip1 system was demonstrated when irradiating cancer cells with wild-type p53. It is shown that the simplest modification of the original model significantly expands the scope of its applicability, allows describing the transition from normal to critical states of the system associated with known degenerative diseases. Thus, the modified model is a more effective tool for numerical analysis of a wide range of states of the p53-Mdm2-Wip1 system

Learning Personalized Product Recommendations with Customer Disengagement

Problem definition: We study personalized product recommendations on platforms when customers have unknown preferences. Importantly, customers may disengage when offered poor recommendations. Academic/practical relevance: Online platforms often personalize product recommendations using bandit algorithms, which balance an exploration-exploitation trade-off. However, customer disengagement—a salient feature of platforms in practice—introduces a novel challenge because exploration may cause customers to abandon the platform. We propose a novel algorithm that constrains exploration to improve performance. Methodology: We present evidence of customer disengagement using data from a major airline’s ad campaign; this motivates our model of disengagement, where a customer may abandon the platform when offered irrelevant recommendations. We formulate the customer preference learning problem as a generalized linear bandit, with the notable difference that the customer’s horizon length is a function of past recommendations. Results: We prove that no algorithm can keep all customers engaged. Unfortunately, classical bandit algorithms provably overexplore, causing every customer to eventually disengage. Motivated by the structural properties of the optimal policy in a scalar instance of our problem, we propose modifying bandit learning strategies by constraining the action space up front using an integer program. We prove that this simple modification allows our algorithm to perform well by keeping a significant fraction of customers engaged. Managerial implications: Platforms should be careful to avoid overexploration when learning customer preferences if customers have a high propensity for disengagement. Numerical experiments on movie recommendations data demonstrate that our algorithm can significantly improve customer engagement.

Self-Similarity Properties of Complex Quasi-Periodic Fibonacci and Cantor Photonic Crystals

In this paper, the influence of structural modifications on basic quasi-periodic (QP) photonic crystals (PhC’s) on self-similarity feature in their spectral responses is examined. Investigated crystals are chosen based on a present knowledge on the QP crystals, and are classified according to their structure. One of the QP crystals considered for the calculations is a concatenation, Fibonacci structure. It characterizes with a self-similar spectra for its different orders, which means, that the spectral shape repeats itself and can be partially identical for a different orders of the Fibonacci QP crystal. The calculations were also performed for the fractal structure, based on a Cantor QP crystal. Just as for the case of the Fibonacci structure, it characterizes with a self-similar spectra for different orders of the structure. Considered photonic devices are next put through simple modification operations by multiplication, conjugation or mirror reflection. Resulting, modified structures are used for the calculations of their spectral response. Results show, that the self-similarity of the spectra is not affected by performed modifications, and thus spectral response of QP PhC can be designed without losing this feature. Moreover the regular expansion of the repeated central part of the spectrum that appears in higher-order Fibonacci QP PhC spectra (due to the self-similarity) with the increase Fibonacci crystal order is presented here for the first time.

A new conjugate gradient algorithms using conjugacy condition for solving unconstrained optimization

The primarily objective of this paper which is indicated in the field of conjugate gradient algorithms for unconstrained optimization problems and algorithms is to show the advantage of the new proposed algorithm in comparison with the standard method which is denoted as. Hestenes Stiefel method, as we know the coefficient conjugate parameter is very crucial for this reason, we proposed a simple modification of the coefficient conjugate gradient which is used to derived the new formula for the conjugate gradient update parameter described in this paper. Our new modification is based on the conjugacy situation for nonlinear conjugate gradient methods which is given by the conjugacy condition for nonlinear conjugate gradient methods and added a nonnegative parameter to suggest the new extension of the method. Under mild Wolfe conditions, the global convergence theorem and lemmas are also defined and proved. The proposed method's efficiency is programming and demonstrated by the numerical instances, which were very encouraging.

Intern-turn fault modeling and diagnosis in permanent magnet vernier machine using modified magnetic equivalent circuit method

Purpose The aim of this paper is to propose the model for analyzing the electromagnetic performances of permanent magnet vernier machines (PMVMs) under healthy and faulty conditions. Design/methodology/approach The model uses interconnected reluctance network formed based on the geometrical approximations to predict magnetic performances of the machine. The network consists of several types of reluctances for modeling different parts of machine. Applying Kirchhoffs laws in the network and the machine windings, magnetic and electrical equations are obtained, respectively. To construct the model system of equations, the electrical equation is converted into algebraic form by using the trapezoidal technique. Moreover, the system of equations must be solved by Newton–Raphson method in each step-time because of considering the core saturation effect. Findings The proposed model is developed based on the modified magnetic equivalent circuit (MEC) method, in which the number of flux paths in different parts of the machine can be arbitrary selected. The saturation effect, skewed slots, the desired machine geometrical parameters and various winding arrangements are included in the proposed model; therefore, it can evaluate the time and space harmonics in modeling the PMVMs. Furthermore, a pattern for inter-turn fault detection is extracted from the stator current spectrum. Finally, 2 D-finite element method (FEM) and 3 D-FEM analysis are carried out to evaluate and verify the results of the proposed MEC model. Originality/value Generally, the element numbers have important role in modeling the machine and calculating its performance. Hence, the proposed MEC model’s capability to choose desired number of flux paths is advantage of this paper. Moreover, the developed MEC can be used for analyzing several electrical machines, including other types of vernier machines, with simple modification.