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where $p>0$ and $ 0<s<1 $. We establish a Liouville-type theorem for positive solutions in the case $p>1$ and give a uniform lower bound of positive solutions when $0<p\leq 1$. In particular, when v is independent of the time variable, we obtain a similar result for the fractional elliptic Lichnerowicz equation
We first establish a family of sharp Caffarelli–Kohn–Nirenberg type inequalities (shortly, sharp CKN inequalities) on the Euclidean spaces and then extend them to the setting of Cartan–Hadamard manifolds with the same best constant. The quantitative version of these inequalities also is proved by adding a non-negative remainder term in terms of the sectional curvature of manifolds. We next prove several rigidity results for complete Riemannian manifolds supporting the Caffarelli–Kohn–Nirenberg type inequalities with the same sharp constant as in the Euclidean space of the same dimension. Our results illustrate the influence of curvature to the sharp CKN inequalities on the Riemannian manifolds. They extend recent results of Kristály (J. Math. Pures Appl. 119 (2018), 326–346) to a larger class of the sharp CKN inequalities.
For a vibration system, the best designed spring is compliant to a desired vibration mode while it is robust to other undesired modes. There are several types of spring design for displacing the proofmass along the x and y axes, however, very few designs of spring compliant to the z axis are introduced. Therefore, we propose a z axis microactuator in which the suspending spring is designed so that it is only compliant to vibration along the z axis. The suspending spring consists of straight beam stages mechanically coupled with each other via frames which are symmetrically designed around a center plate. The operation characteristics of the microactuator is investigated by theoretical expresses and numerical simulation. The frequency split between the z axis mode and undesired modes can obtain more than 45%. The operation frequency can be modified in a wide range, from 68 kHz to 400 kHz, by changing the dimensional parameters of spring beams. The spring beams can be lengthened to increase displacement in the z axis while the mode cross-talk is still suppressed. Compared to the previously reported researches, the current microactuator shows robustness to undesired vibration modes, which is potential for integration in low mode cross-talk multi-axis micro-stages and low-noise mechanical sensors.
Background: Antibiotic overuse has led to increasing rates of antibiotic resistant infections and unnecessary antibiotic costs. Clinical pharmacists can play a key role in optimizing appropriate use of antimicrobials and reducing antimicrobial resistance. However, the role of clinical pharmacists in antimicrobial stewardship is new and not well established in Viet Nam. Objective: We evaluated the use of clinical pharmacists for improved antimicrobial prescribing. Methods: We assembled an antibiotic stewardship program (ASP) team consisting of a clinical pharmacist and a specialist in infection prevention and control in a 60-bed medical intensive care unit (MICU) at Hue Central Hospital in central Viet Nam. During January–September 2018, the ASP team collected baseline antibiotic prescribing days of therapy (DOT) for all antibiotics administered in the MICU. Then, from October 2018 through June 2019, the ASP team reviewed daily positive clinical bacterial cultures and susceptibility results for all patients present in the MICU. They reviewed medical charts, including antimicrobial prescriptions, during week days and only if patient was still in the ICU at the time of ASP rounds. The team recommended changes to antibiotic therapy verbally to physicians and left the decision to change antibiotic therapy to their discretion. The ASP team documented whether their recommendations were accepted or rejected. Statistical significance was determined using the Student t test. Results: The ASP team reviewed 160 medical charts and made 169 ASP recommendations: 122 (72%) to continue current treatment; 24 (14%) to monitor drug levels or obtain diagnostic tests; 10 (6%) to discontinue therapy; 6 (4%) to de-escalate therapy; 5 (3%) to adjust doses; and 2 (1%) to broaden therapy. Only 8 of the recommended changes (5%) were declined by the clinicians. The average monthly DOT for all types of antibiotics declined significantly from 2,213 to 1,681 (24% decrease; P = .04). Reductions in DOT for the most common broad-spectrum antibiotics included colistin from 303 to 276 (P = .75); imipenem-cilastatin 434 to 248 (P = .06); doripenem 150 to 144 (P = .85). Piperacillin-tazobactam increased from 122 to 142 (P = 0.75). Conclusions: We demonstrated that daily review of cultures and antibiotic use decreased overall antibiotic prescribing. Given that few recommendations included discontinuation of therapy, ASP rounds likely raised awareness for clinicians to optimize antibiotic use.
The median duration of hospital stays due to COVID-19 has been reported in several studies on China as 10−13 days. Global studies have indicated that the length of hospitalisation depends on different factors, such as the time elapsed from exposure to symptom onset, and from symptom onset to hospital admission, as well as specificities of the country under study. The goal of this paper is to identify factors associated with the median duration of hospital stays of COVID-19 patients during the second COVID-19 wave that hit Vietnam from 5 March to 8 April 2020.
We used retrospective data on 133 hospitalised patients with COVID-19 recorded over at least two weeks during the study period. The Cox proportional-hazards regression model was applied to determine the potential risk factors associated with length of hospital stay.
There were 65 (48.9%) females, 98 (73.7%) patients 48 years old or younger, 15 (11.3%) persons with comorbidities, 21 (16.0%) severely ill patients and 5 (3.8%) individuals with life-threatening conditions. Eighty-two (61.7%) patients were discharged after testing negative for the SARS-CoV-2 virus, 51 were still in the hospital at the end of the study period and none died. The median duration of stay in a hospital was 21 (IQR: 16–34) days. The multivariable Cox regression model showed that age, residence and sources of contamination were significantly associated with longer duration of hospitalisation.
A close look at how long COVID-19 patients stayed in the hospital could provide an overview of their treatment process in Vietnam, and support the country's National Steering Committee on COVID-19 Prevention and Control in the efficient allocation of resources over the next stages of the COVID-19 prevention period.
In this chapter, we have introduced existing solutions in the literature aiming to improve the performance of ambient backscatter communication systems (ABCSs). We have first provided the reviews on several multiple access schemes that allows multiple transmitters backscatter data to the receiver. Then, solutions focusing on improving the communication range, bitrate, reliability, and robustness are presented in details. Finally, we have discussed challenges and future research directions to further improve the performance of ABCSs.
In this chapter, we have provided an overview of ambient backscatter communication systems. Firstly, we have introduced the fundamentals of modulated backscatter and its three main configurations, i.e., monostatic, bistatic, and ambient backscatter communication systems. Then, key channel-coding and modulation techniques in modulated backscatter communication systems are discussed. Two major types of backscatter communication channels and their link budgets are also introduced. Next, theoretical analyses and experimental measurements of backscatter channels are reviewed. Finally, we have discussed some research challenges of backscatter communication systems, especially ambient backscatter communication systems.
This chapter discussed open issues and potential research directions for future developemnt of ambient backscatter communication. Many emerging research directions are presented in this chapter such as full-duplex ambient backscatter, ultra-wideband backscatter, visible-light backscactter, and millimeter-wave backscatter.
The performance analysis for ambient backscatter communication systems is fundamentally different from that of traditional communication systems. The carrier signal of backscatter communication is opportunistically exploited from the existing active radio-frequency communication systems. As it is vulnerable to channel variations, different detection and encoding mechanisms have been proposed and analyzed to improve the system throughput or ergodic capacity. In this chapter, we have focused on the analysis of signal detection and bit-error rate (BER) performance for backscatter communication. We have reviewed the different system models for backscatter communication systems and various signal detection approaches under different resource and physical constraints.
In this chapter, we have introduced the fundamentals of self-sustaining wireless communication networks. We have first provided the overviews of conventional energy harvesting networks, i.e., wireless-powered transfer, wireless-powered communication network, and simultaneous wireless information and power transfer, as well as their applications in the literature. Then, we have introduced ambient backscatter communications in terms of architecture, design, advantages, and limitations. Finally, we have discussed potential applications and implementation of ambient backscatter communication system networks such as smart world, biomedical, and logistics.
In this chapter, we first give a brief overview about the development of cognitive radio networks (CRNs), from traditional CRNs to the recent development of wireless energy harvesting for CRNs. Then, we discuss how to integrate ambient backscatter communication techniques to radio-frequency (RF)-powered CRNs, and present two fundamental models for this integration. After that, we discuss recent advanced models of RF-powered CRNs with ambient backscatter communication with more details about system design, communication protocols, and performance optimization problems. Finally, some open issues for the development of RF-powered backscatter CRNs are presented.
Wireless backscatter shares some similarity with the radio-frequency (RF)-powered wireless communications. This motivates the design of a hybrid radio that can operate in either active RF communications or backscatter communications. The flexibility in the radio’s mode switching provides an additional degree of freedom to improve the overall network performance. In this chapter, we first review cooperative transmission strategies in conventional RF-powered wireless communicationsystems and then discuss the feasibility of cooperative relay transmission via backscatter communication. We propose the passive relaying scheme that leverages the backscatter radios to act as passive relays and assist the RF communications. The passive relays backscatter the RF signals from the source to the receiver which, by experiments, shows to improve the transmission rate due to the enhanced multi-path diversity gain.
In this chapter, we discuss various circuit and antenna design issues for implementing ambient backscatter transmitters and receivers. First, we provide an overview of antenna which is crucial for ambient backscatter communication systems (ABCSs) to receive and backscatter signals. Then, ambient backscatter transmitter circuits including modulators, energy harvesters, and micro-controllers is discussed. Following this, we discuss ambient backscatter receiver circuits including interference cancelers, diversity combiners, and maximum-likelihood (ML) detectors. Finally, some open issues for realizing low-power and hyper-connectivity vision in the Fourth Industrial Revolution era are described.