MDPI - Publisher of Open Access Journals

15 pages, 269 KiB

Open AccessFeature PaperArticle

by Anthony G. Pakes

Axioms 2024, 13(2), 115; https://doi.org/10.3390/axioms13020115 - 8 Feb 2024

Cited by 1 | Viewed by 1928

The deterministic SIR model for disease spread in a closed population is extended to allow infected individuals to recover to the susceptible state. This extension preserves the second constant of motion, i.e., a functional relationship of susceptible and removed numbers, [...] Read more.

S (t)

and

R (t)

, respectively. This feature allows a substantially complete elucidation of qualitative properties. The model exhibits three modes of behaviour classified in terms of the sign of

- S^{'} (0)

, the initial value of the epidemic curve. Model behaviour is similar to that of the SIS model if

S^{'} (0) > 0

and to the SIR model if

S^{'} (0) < 0

. The separating case is completely soluble and

S (t)

is constant-valued. Long-term outcomes are determined for all cases, together with determination of the rate of convergence. Determining the shape of the epidemic curve motivates an investigation of curvature properties of all three state functions and quite complete results are obtained that are new, even for the SIR model. Finally, the second threshold theorem for the SIR model is extended in refined and generalised forms. Full article

(This article belongs to the Topic Mathematical Modeling)

15 pages, 3923 KiB

Open AccessArticle

Design of High-Order Resonator HTS Diplexer with Very Different FBW

by Liguo Zhou, Weikang Zhou, Yuehang Sun, Yu Han, Jiang Jiang and Dongwei Zhang

Electronics 2023, 12(3), 691; https://doi.org/10.3390/electronics12030691 - 30 Jan 2023

Cited by 4 | Viewed by 2326

Abstract

Adopting the deformed stepped impedance micro-strip line structure resonators (SIRs), the external weak coupling hairpin SIR (HSIR) and external strong coupling opening SIR (OSIR) resonators are designed, respectively. These two types of resonators are convenient for creating an ultra-narrow band and broadband filters, respectively, and can broaden the second harmonic passband. A high isolation diplexer without an impedance matching structure is realized by cascading 12-order and 14-order HTS filters composed of OSIR and HSIR resonators with a high isolation T-shaped structure. The diplexer is fabricated on a thin YBCO/MgO/YBCO (a MgO wafer with YBa₂Cu₃O₇ thin film deposited on both sides) film with a dimension of 31.85 mm × 17.28 mm, a thickness of 0.5 mm, and a dielectric constant of 9.8. At 77 K, the measured central frequency of the diplexer is 2395 MHz and 3300 MHz, the fractional bandwidths (FBW) are 1.25% and 24.24%, the out-of-band rejections are greater than 60 dB/MHz, the 2f₀ are located at 5.1 GHz and 6.6 GHz, the insertion loss is less than 0.20 dB, and the return losses are better than 16 dB and 15 dB. The diplexer has the advantages of a simple design method, compact structure, low insertion loss, high sideband rejection, and high isolation. Full article

(This article belongs to the Section Circuit and Signal Processing)

► Show Figures

Figure 1

10 pages, 3989 KiB

Open AccessCommunication

Miniaturized Bandpass Filter Using a Combination of T–Shaped Folded SIR Short Loaded Stubs

by Kicheol Yoon, Kwang Gi Kim and Tae-Hyeon Lee

Sensors 2022, 22(7), 2708; https://doi.org/10.3390/s22072708 - 1 Apr 2022

Cited by 2 | Viewed by 2665

Abstract

The consumption of multimedia content is ubiquitous in modern society. This is made possible by wireless local area networks (W–LAN) or wire service systems. Bandpass filters (BPF) have become very popular as they solve certain data transmission limitations allowing users to obtain reliable access to their multimedia content. The BPFs with quarter–wavelength short stubs can achieve performance; however, these BPFs are bulky. In this article, we propose a compact BPF with a T–shaped stepped impedance resonator (SIR) transmission line and a folded SIR structure. The proposed BPF uses a T–shaped SIR connected to a J–inverter structure (transmission line); this T–shaped SIR structure is used to replace the λ_g/4 transmission line seen in conventional stub BPFs. In addition, a folded SIR is added to the short stubs seen in conventional stub BPFs. This approach allows us to significantly reduce the size of the BPF. The advantage of a BPF is its very small size, low insertion loss, and wide bandwidth. The overall size of the new BPF is 2.44 mm × 1.49 mm (0.068λ_g × 0.059λ_g). The proposed BPF can be mass produced using semiconductors due to its planar structure. This design has the potential to be widely used in various areas including military, medical, and industrial systems. Full article

(This article belongs to the Special Issue Antenna and Microwave Sensors)

► Show Figures

Figure 1

8 pages, 4282 KiB

Open AccessArticle

Miniaturized Dual-Band Bandpass Filter Using T-Shaped Line Based on Stepped Impedance Resonator with Meander Line and Folded Structure

by Tae-Hyeon Lee, Ki-Cheol Yoon and Kwang Gi Kim

Electronics 2022, 11(2), 219; https://doi.org/10.3390/electronics11020219 - 11 Jan 2022

Cited by 8 | Viewed by 2149

Abstract

A stepped impedance resonator (SIR) is suitable for designing a dual-band bandpass filter (BPF) that can be adjusted to reject spurious bands. A BPF is proposed using an SIR T-shaped meander line and folded structure. The BPF mainly comprises a meander line, a folded structure, and a T-shaped line. A novel BPF is used for the T-shaped line, which operates as a band-stop filter connecting to the center of the BPF. As a result, the complete BPF enables dual-band operation. The insertion and return losses of the first frequency passband (f₀₁) are 0.024 and 17.3 dB, respectively, with a bandwidth of 46% at a center frequency of 2.801 GHz (2.2–3.48 GHz). The insertion and return losses of the second frequency passband (f₀₂) are 0.026 and 17.2 dB, respectively, with a bandwidth of 10% at a center frequency of 4.351 GHz (4.13–4.55 GHz). The proposed BPF provides low loss, a simple structure, and a small size of only 4.29 × 4.08 mm, and it can be integrated into mobile communications systems. Full article

(This article belongs to the Section Microwave and Wireless Communications)

► Show Figures

Figure 1

12 pages, 1377 KiB

Open AccessArticle

Removal of Rhodamine B from Water Using a Solvent Impregnated Polymeric Dowex 5WX8 Resin: Statistical Optimization and Batch Adsorption Studies

by Moonis Ali Khan, Momina, Masoom Raza Siddiqui, Marta Otero, Shareefa Ahmed Alshareef and Mohd Rafatullah

Polymers 2020, 12(2), 500; https://doi.org/10.3390/polym12020500 - 24 Feb 2020

Cited by 64 | Viewed by 5072

Abstract

Herein, commercially available Dowex 5WX8, a cation exchange polymeric resin, was modified through solvent impregnation with t-butyl phosphate (TBP) to produce a solvent impregnated resin (SIR), which was tested for the removal of rhodamine B (RhB) from water in batch adsorption experiments. The effect of SIR dosage, contact time, and pH on RhB adsorption was studied and optimized by response surface methodology (RSM), interaction, Pareto, and surface plots. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were respectively used for characterizing SIR surface morphology and identifying active binding sites before and after RhB adsorption. SEM showed that the pristine SIR surface was covered with irregular size and shape spots with some pores, while RhB saturated SIR surface was non-porous. FTIR revealed the involvement of electrostatic and π–π interactions during RhB adsorption on SIR. Dosage of SIR, contact time, and their interaction significantly affected RhB adsorption on SIR, while pH and its interaction with dosage and contact time did not. The optimum identified experimental conditions were 0.16 g of SIR dose and 27.66 min of contact time, which allowed for 98.45% color removal. Moreover, RhB adsorption equilibrium results fitted the Langmuir isotherm with a maximum monolayer capacity (q_max) of 43.47 mg/g. Full article

(This article belongs to the Special Issue Current Trends and Perspectives in the Application of Polymeric Materials for Wastewater Treatment)

► Show Figures

Graphical abstract

Search Results (5)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (5)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI