506 research outputs found
L’arte del vivere quotidiano. La decorazione della tavola dai Ruggenti Anni Venti alla nascita del design italiano
No full textIl saggio ricostruisce la storia e l'evoluzione dell'ornamento della tavola attraverso l'analisi delle esposizioni d'arte e delle riviste specializzate. Il lavoro creativo di artisti, architetti e designer, coniugato alle abilità tecniche e imprenditoriali delle case produttrici, ha dato vita a un ricco e variegato repertorio di servizi da tavola, tessili, centritavola e accessori d'arredo che hanno saputo interpretare e anticipare le esigenze della contemporaneità e dettare nuove mode e stili nel campo della decorazione e del design
An approach to harmonic load- and source-pull measurements for high-efficiency PA design
No full textHigh-efficiency power-amplifier design requires numerous efforts to investigate both input and output harmonic terminations effects. A simplified theoretical approach to clarify the relevance of such terminations is presented here, and design criteria to improve efficiency for high-frequency applications are briefly discussed. An advanced active load/source-pull test-bench has been used to validate theoretical harmonic tuning techniques, characterizing an active device. The adopted optimization strategy is presented, together with measured results obtained with a medium-power 1-mm MESFET at 1 GHz. Input second harmonic impedances effects are stressed, showing a drain efficiency spread between 37%-49% for a fixed input power level, corresponding to 1-dB compression. Finally, as predicted by the presented theory, after input second harmonic tuning, further improvements are obtained, increasing fundamental output load resistive part, demonstrating an additional drain efficiency enhancement, which reaches a level of 55% at 1-dB compression
1 kW Compact L-band Pulsed Power Amplifier for Radar Applications
No full textAn L-band 20% BW pulsed power amplifier that provides 1KW output power is presented. The amplifier circuit uses a combination of 500W NXP-LDMOS devices through the use of simple multi-section microstrip (Duroid 6006) hybrids. Instantaneous duty cycle is 1:10 with a maximum pulse duration of 1ms. This topology exhibits a transfer gain of 34dB, return losses better than 30dB along with an efficiency located in the range of 40%, which is suitable for SSPA-based Radar applications
La tradizione classica
No full textIl quinto centenario della fondazione dell’Università di Urbino è stato l’occasione per prendere in esame l’apporto di questo Ateneo alla comunità scientifica. Il contributo ripercorre sin dalla nascita le più significative tappe degli studi classici a Urbino, evidenziandone linee metodologiche, originalità di temi, singole personalità
A GaN high power and efficient amplifier for L-Band Galileo system
No full textThis paper describes the development of an L-Band (f0 = 1.575GHz) high power and efficient amplifier designed for the European satellite navigation system (i.e., Galileo). The amplifier, developed in the framework of the European Project named SLOGAN, exploits the GH50-10 GaN technology available at United Monolithic Semiconductor foundry. The required output power level is achieved by parallelizing several GaN die power bars of 12mm and/or 26.5 mm. In continuous wave operating mode, the first prototype is able to deliver an output power higher than 250W at less than 2 dB of gain compression. Moreover, the registered gain and efficiency are higher than 54 dB and 54 %, respectively
Introduzione all'ecologia del paesaggio
No full textTraduzione dal tedesco "Landschaftsökologie" di L. Finke, Holler e Zwick, 1986
Learned-non use of the paretic foot in gait after stroke: evidence from a study on joint power
No full textBackground
Over a century ago Sherrington demonstrated in monkeys that a deafferented upper limb is doomed to loose motricity, which can be recovered if compensation through the spared limb is prevented. Taub named this phenomenon “learned-non use” (LNU).
The author based his observation on the discrepancy between bedside examination and the showy limping of most stroke patients. In hemiparetic gait it is known that the power provided when the paretic limb is in rear position is 3 to 5 times lower, compared to the next double-stance. Yet, to date no proof is available that this asymmetry reflects LNU of otherwise recruitable muscles. In this work, a study on joint power during walking with flexed knees (“crouch” gait), gives support to this hypothesis.
Methods
Six healthy adults were enrolled as controls. A sample of five stroke patients were studied.
The subjects had to walk on a split-belt force treadmill. EMG from lower limb were recorded wirelessly.
A comfortable speed for most hemiplegic patients on the treadmill was 0.3 ms-1. Once equipped, the subjects were requested to walk on the treadmill at a speed of 0.3 ms-1. The walking trial was repeated with knees held at about 30° flexion. One series of 6 strides was analyzed. No subject reported unbalance or discomfort.
Only the joint power in the sagittal plane is considered. For each muscle group, the sign of the power output (positive during muscle shortening, negative otherwise) was identified by the direction of joint rotation (e.g. positive power is assumed to be provided by the plantar flexor muscles, if the analysis of ground reaction forces led to evidence of power making the ankle to rotate towards flexion).
Results
Controls: stride length and stride periods ranged 0.46-0.53 m and 1.61-1.78 s. Compared to spontaneous gait, crouching entailed a 65% increase of ankle peak power.
Patients: the stride length and periods on the “affected” step were 0.17-0.29 m and 1.20-1.32 s. Compared to controls, the ankle power was on average 37% lower on the affected side and 33% higher on the sound side. Power on the affected side was 54% lower compared to sound side. Compared to controls, the ankle power was 9.6% lower on the affected side and 23% higher on the sound side. Power on the affected side was 26% lower compared to sound side. Compared to spontaneous gait, crouching entailed a 145% increase of ankle peak power on the affected side, and a 54% increase on the sound side.
Conclusions
During hemiplegic gait virtually no power is provided at the ankle of the paretic lower limb. By contrast, during crouched gait the ankle resumes its propulsive role, through an active plantar flexion and an appreciable power output. The asymmetry is remarkably reduced. This indicates that lower limb weakness at least partly stems from an adaptive behavior fostering the use of the sound lower limb, despite an available residual power from the paretic limb
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