| 1. |
- Lind, Lars, et al.
(författare)
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Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight NCD Risk Factor Collaboration (NCD-RisC)
- 2021
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Ingår i: eLife. - : eLife Sciences Publications Ltd. - 2050-084X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions.
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| 2. |
- Mishra, A, et al.
(författare)
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Diminishing benefits of urban living for children and adolescents' growth and development
- 2023
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 615:7954, s. 874-883
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Tidskriftsartikel (refereegranskat)abstract
- Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.
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| 3. |
- Gustavsson, Ulf, 1975, et al.
(författare)
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On the Impact of Hardware Impairments on Massive MIMO
- 2014
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Ingår i: IEEE Globecom 2014 Workshop - Massive MIMO: From Theory to Practice, 2014-12-08, Austin, Texas, USA. - 9781479974702 ; , s. 294-300
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Konferensbidrag (refereegranskat)abstract
- Massive multi-user (MU) multiple-input multiple-output (MIMO) systems are one possible key technology for next generation wireless communication systems. Claims have been made that massive MU-MIMO will increase both the radiated energy efficiency as well as the sum-rate capacity by orders of magnitude, because of the high transmit directivity. However, due to the very large number of transceivers needed at each base-station (BS), a successful implementation of massive MU-MIMO will be contingent on of the availability of very cheap, compact and power-efficient radio and digital-processing hardware. This may in turn impair the quality of the modulated radio frequency (RF) signal due to an increased amount of power-amplifier distortion, phase-noise, and quantization noise. In this paper, we examine the effects of hardware impairments on a massive MU-MIMO single-cell system by means of theory and simulation. The simulations are performed using simplified, well-established statistical hardware impairment models as well as more sophisticated and realistic models based upon measurements and electromagnetic antenna array simulations.
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| 4. |
- Hausmair, Katharina, 1982, et al.
(författare)
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Prediction of Nonlinear Distortion in Wideband Active Antenna Arrays
- 2017
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 65:11, s. 4550-4563
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multi-antenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of taking into account the joint effects of PA nonlinearity, antenna crosstalk and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12 GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics, as for example the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems.
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| 5. |
- Pamoin-Gonzalez, M, 1900, et al.
(författare)
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Outphasing combiner synthesis from transistor load pull data
- 2015
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Ingår i: 2015 IEEE MTT-S International Microwave Symposium, IMS 2015. - 9781479982752
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Konferensbidrag (refereegranskat)abstract
- A novel load-pull based outphasing combiner synthesis approach is developed. The design technique is based on the derivation of combiner network parameters in terms of the optimal load impedances at the peak power level and a pre-defined back-off level. The combiner is then synthesized using transmission lines or lumped element networks. The design technique is verified in a 30 W GaN HEMT outphasing transmitter demonstrator. The prototype presents a power-added efficiency of 50% at 2.1 GHz with 9 dB peak-to-average power ratio (PAPR) 20 MHz LTE signals. The related measured adjacent channel leakage ratio is -51 dBc using a low complexity digital pre-distortion linearization algorithm.
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| 6. |
- Sanchez Perez, Cesar, 1981, et al.
(författare)
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A survey of challenges for runtime verification from advanced application domains (beyond software)
- 2019
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Ingår i: Formal Methods in System Design. - : Springer Science and Business Media LLC. - 1572-8102 .- 0925-9856. ; 54:3, s. 279-335
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Tidskriftsartikel (refereegranskat)abstract
- Runtime verification is an area of formal methods that studies the dynamic analysis of execution traces against formal specifications. Typically, the two main activities in runtime verification efforts are the process of creating monitors from specifications, and the algorithms for the evaluation of traces against the generated monitors. Other activities involve the instrumentation of the system to generate the trace and the communication between the system under analysis and the monitor. Most of the applications in runtime verification have been focused on the dynamic analysis of software, even though there are many more potential applications to other computational devices and target systems. In this paper we present a collection of challenges for runtime verification extracted from concrete application domains, focusing on the difficulties that must be overcome to tackle these specific challenges. The computational models that characterize these domains require to devise new techniques beyond the current state of the art in runtime verification.
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| 7. |
- Sanchez Perez, Cesar, 1981, et al.
(författare)
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Design and applications of a 300-800 MHz tunable matching network
- 2013
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Ingår i: IEEE Journal on Emerging and Selected Topics in Circuits and Systems. - 2156-3365 .- 2156-3357. ; 3:4, s. 531-540
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the optimized design, characterization and applications of a broadband 300-800 MHz ($\sim$ 91% fractional bandwidth) digitally-controlled tunable matching network is presented. The design employs PIN diodes as switching components and a repetitive structure of basic cells using lumped reactive elements. After an intensive and complex optimization process, a Smith chart coverage (return losses better than 10 dB and losses lower than 2 dB) above 60% is obtained in all the bandwidth reaching 75% in the middle of the band (400-700 MHz). The potential of the manufactured tunable matching network for antenna mismatch compensation, antenna bandwidth extension and power amplifier efficiency improvement in back-off is showed. © 2011 IEEE.
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| 8. |
- Sanchez Perez, Cesar, 1981, et al.
(författare)
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Design and Large-Signal Characterization of High-Power Varactor-Based Impedance Tuners
- 2018
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 66:4, s. 1744-1753
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new systematic and efficient method for the design of high-power varactor-based impedance tuners. By incorporating the varactor losses and voltage handling capabilities, the method allows the impedance tuning range to be maximized and losses to be minimized under high-power operating conditions. A 2.2-GHz large-signal double-stub tuner has been designed using the proposed methodology and SiC varactor diodes. Using comprehensive large-signal measurements, a 25-W input power handling is demonstrated up to Γ max ∼ 0.8. Two-tone linearity measurements show an input third-order intercept point exceeding 50 dBm for most impedances. These results clearly demonstrate the feasibility of the proposed technique for the design of high-performance large-signal tuners.
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| 9. |
- Sanchez Perez, Cesar, 1981, et al.
(författare)
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Optimized Design of a Dual-Band Power Amplifier With SiC Varactor-Based Dynamic Load Modulation
- 2015
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 63:8, s. 2579-2588
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Tidskriftsartikel (refereegranskat)abstract
- A new methodology for the design of single/multi-band power amplifiers (PAs) with dynamic load modulation (DLM) is presented. First, the topology for the output matching network (OMN) including the control varactor is selected. A comprehensive optimization of the OMN parameters is then developed by which varactor and transistor losses are considered to ensure maximum efficiency enhancement at each frequency. To verify the method, a dual-band PA with DLM is realized. Drain efficiencies of 75% and 60% at 685 MHz and 1.84 GHz, respectively, are measured at peak output power. At 10-dB output power back-off efficiencies of 43.5% and 49.5%, respectively, are obtained. Linearized modulated measurements with a 6.5-dB peak-to-average power ratio WCDMA signal show average drain efficiencies of 56% and 54% at 685 MHz and 1.84 GHz, respectively, at an adjacent channel leakage ratio of -49 and -47.5 dBc, respectively. The proposed method shows the effectiveness of applying an optimization process for the design of single-or multi-band DLM PAs. The results demonstrate that near-optimum performance may be obtained in terms of efficiency enhancement for a given transistor and varactor-based OMN, thus making DLM competitive against other load modulation techniques.
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