RESUMEN

MIMO (Multiple-Input-Multiple-Output) antenna systems are promising for fifth-generation (5G) networks, offering lower latency and higher data rates. These systems utilize millimeter-wave (mmWave) frequency bands for efficient transmission and reception of multiple data simultaneously, enhancing overall efficiency and performance. This article presents a compact size, wide band tri-circular ring mmWave MIMO antenna with suitable performance characteristics for next-generation communication systems. The MIMO system consists of a tri-circular ring patch with slots on a ground plane. The four elements of the antenna are arranged together in the polarization diversity configuration with overall dimensions of 23×18×0.254 mm3, and designed on a 0.254 mm thin, flexible RO5880 substrate with a relative permittivity of 2.3 using Computer Simulation Technology (CST) 2022. The proposed antenna design shows the impedance bandwidth of 14 GHz with isolation >18 dB throughout the 26-40 GHz resonance band. The obtained gain is 6.6 dBi at 28 GHz with radiation efficiency > 90%. Several MIMO parameters are also investigated, such as Envelope Correlation Coefficient (ECC), Mean Effective Gain (MEG), Diversity Gain (DG), Total Active Reflection Co-efficient (TARC), and Channel Capacity Loss (CCL), and are found to be within the accepted limits for a practical MIMO system. Furthermore, the fabricated MIMO antenna was tested, and the measured results aligned favorably with the simulated results, confirming the suitability of the proposed design. Through the obtained results, the mmWave MIMO antenna is suitable for practical 5G as well as mmWave applications due to its lightweight, simple design, and wideband characteristics, which cover the 5G frequency bands of 26, 28, 32, and 38 GHz.

RESUMEN

This paper introduces a novel two-port ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna system with enhanced isolation characteristics. The antenna, designed on a thin 0.787 mm RO5880 substrate, achieves a compact form factor of 52 × 26 mm2 and offers a wide bandwidth of 9.2 GHz (2.3 GHz to 11.5 GHz) while meeting the VSWR 2:1 criterion. Notably, the proposed antenna demonstrates an impressive increase in isolation, up to 16 dB, through the integration of a shared radiator with small rectangular slots, effectively reducing interference and improving overall performance. Furthermore, a comprehensive analysis of additional MIMO performance parameters, including the envelope correlation coefficient (ECC) and diversity gain, confirms their satisfactory limits, validating the potential of the proposed UWB-MIMO antenna for various UWB applications. The time domain analysis of the UWB antenna is also analyzed, and results are found to be within satisfactory limits. Simulation and measurement results further support the practicality and effectiveness of the antenna design, highlighting its compact size, wide bandwidth, and enhanced isolation characteristics, positioning it as a promising solution for advanced UWB microwave imaging systems.

RESUMEN

In this article, we propose a light weight, low profile Multiple Input Multiple Output (MIMO) antenna system for compact 5th Generation (5G) mmwave devices. Using a RO5880 substrate that is incredibly thin, the suggested antenna is made up of circular rings stacked vertically and horizontally on top of one another. The single element antenna board has dimensions of 12 × 12 × 0.254 mm3 while the size of the radiating element is 6 × 2 × 0.254 mm3 (0.56λ0 × 0.19λ0 × 0.02λ0). The proposed antenna showed dual band characteristics. The first resonance showed a bandwidth of 10 GHz with a starting frequency of 23 GHz to an ending frequency point of 33 GHz followed by a second resonance bandwidth of 3.25 GHz ranging from 37.75 to 41 GHz, respectively. The proposed antenna is transformed into a four element Linear array system with size of 48 × 12 × 0.254 mm3 (4.48λ0 × 1.12λ0 × 0.02λ0). The isolation levels at both resonance bands were noted to be >20 dB which shows high levels of isolation among radiating elements. The MIMO parameters such as Envelope Correlation Co-efficient (ECC), Mean Effective Gain (MEG) and Diversity Gain (DG) were derived and were found to be in satisfactory limits. The proposed MIMO system model is fabricated and through validation and testing of the prototype, the results were found to be in good agreement with simulations.

RESUMEN

This research work presents a compact design of a Multiple-Input Multiple-Output (MIMO) multiband antenna along with high-isolation characteristics. The presented antenna was designed for 3.50 GHz, 5.50 GHz, and 6.50 GHz frequencies for 5G cellular, 5G WiFi, and WiFi-6, respectively. The fabrication of the aforementioned design was undertaken using FR-4 (1.6 mm thickness) substrate material with a loss tangent and relative permittivity of about 0.025 and 4.30, respectively. The two-element MIMO multiband antenna was miniaturized to 16 × 28 × 1.6 mm3, making it desirable for devices operating in 5G bands. High isolation (>15 dB) was attained with thorough testing without employing a decoupling scheme in the design. Laboratory measurements resulted in a peak gain of 3.49 dBi and an efficiency of around 80% in the entire operating band. The evaluation of the presented MIMO multiband antenna was carried out in terms of the envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), and Channel Capacity Loss (CCL). The measured ECC was less than 0.04, and the DG was well above 9.50. The observed TARC was also lower than -10 dB, and the CCL was below 0.4 bits/s/Hz in the entire operating band. The presented MIMO multiband antenna was analyzed and simulated using CST Studio Suite 2020.

RESUMEN

BACKGROUND: General anesthetics modify airway responsiveness by several mechanisms, including direct effects on airway smooth muscle and reductions in neural reflex activity. Halothane has been shown to reduce responsiveness through both of these mechanisms. The airway effects of barbiturates are controversial, and the effects of propofol are unknown. METHODS: To compare the direct effects of halothane, thiopental, and propofol in vivo, canine peripheral airways were constricted with two stimuli, histamine and hypocapnia, which are thought to directly contract smooth muscle. The authors then investigated the role of ATP-sensitive potassium (KATP) channels as a mechanism for attenuating these responses. Basenji-Greyhound (BG) dogs were anesthetized with either halothane (1.5 MAC), thiopental (7.5 mg.kg-1 x min-1 intravenously) plus fentanyl (25 micrograms intravenously every 20-30 min), or propofol (0.6 mg.kg-1 x min-1 intravenously). A wedged bronchoscope technique was used to measure peripheral airway resistance (RP). After a stable baseline was obtained, dose-response curves to histamine (50, 100, or 200 micrograms intravenous bolus) or hypocapnia (0% CO2 for 2 min with 100, 200, or 400 ml/min collateral flow) were constructed. On separate occasions, the same sublobar segments were pretreated with glibenclamide (2 mg/ml aerosol), a KATP channel blocker, and dose-response curves to hypocapnia were repeated. RESULTS: Dose-response curves to histamine were similar during all three anesthetics. Halothane decreased airway responsiveness to hypocapnia, compared with either thiopental or propofol (P < 0.05). Pretreatment with glibenclamide abolished the effect of halothane on hypocapnia-induced airway constriction. CONCLUSIONS: These results indicate that propofol afforded no benefit over thiopental or halothane in reducing peripheral airway responsiveness. Furthermore, the beneficial effects of halothane in reducing responsiveness to hypocapnia appear to be mediated by the opening of KATP channels.

Asunto(s)

RESUMEN

Histamine-releasing drugs may produce significant effects on airways in high-risk populations. To determine if clinically relevant doses of atracurium produce adverse effects on airways, we measured changes in airway resistance in the lung periphery of anesthetized Basenji-Greyhound dogs before and after intravenous (iv) administration of atracurium. A wedged bronchoscope technique was used to measure collateral system resistance (Rcs). After a stable baseline was obtained, atracurium (1.2 or 0.5 mg/kg) or histamine (200 micrograms) were administered as an iv bolus, and percent increase in Rcs was calculated. On separate days dogs were pretreated with the histamine 1 receptor antagonist, chlorpheniramine (0.2 mg/kg iv), with or without atropine (0.2 mg/kg iv) and ranitidine (0.75 mg/kg iv) and the experiment repeated. Histamine (200 micrograms) increased Rcs 97 +/- 24% at 30 s (8 sublobar segments), whereas a second dose increased Rcs 77 +/- 15%. Pretreatment with chlorpheniramine (0.2 mg/kg iv) totally prevented increases in Rcs (9 sublobar segments). Atracurium (1.2 mg/kg) increased Rcs to 174 +/- 35% at 3 min (14 sublobar segments), whereas 0.5 mg/kg had little effect (10 sublobar segments). A second bolus of atracurium (1.2 mg/kg) increased Rcs to only 54 +/- 14% (P less than 0.01). Chlorpheniramine pretreatment (0.2 mg/kg iv) reduced the response to the initial dose of atracurium to only 26 +/- 14% (10 sublobar segments). Pretreatment with a combination of atropine and chlorpheniramine (4 sublobar segments), or ranitidine and chlorpheniramine (5 sublobar segments), did not attenuate the increase in Rcs significantly more than chlorpheniramine pretreatment alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

Asunto(s)

Asunto(s)

RESUMEN

The priming principle was investigated in the rat phrenic nerve-diaphragm preparation stimulated continuously at 0.2 Hz. Tubocurarine was added to the organ bath as either a single (non-primed) or a divided (primed) dose. Priming consisted of 15% or 20% of the final dose, with priming intervals of 5 or 10 min. Priming decreased significantly the time to 80% block and was associated with mild neuromuscular block. A simple model adequately predicted the time to 50% and 80% block, using the same diffusion constant for both primed and non-primed conditions. The onset of neuromuscular block, with and without priming, depended mostly upon the distribution of the drug to its site(s) of action.

Asunto(s)

RESUMEN

Macular degeneration results in more new cases of legal blindness in the United States than any other disease and accounts for over 165,000 first visits to physicians each year. Magnification, illumination control, and eccentric viewing training are the only documented, effective vision rehabilitation techniques known. Magnification has been used for decades, control of illumination has had a known effect for many years, and eccentric viewing training has been systematically used for less than 10 years. These techniques, although having demonstrated efficacy, require extensive individual patient training and a considerable investment of professional training time for optimum results. More recently developed techniques use prism correction for near and distance viewing or scanning laser ophthalmoscopy for training. Current knowledge of peripheral retinal function offers new avenues of research to improve upon current rehabilitation techniques. Computer technology also offers the hope of developing easily used, cost-effective materials and equipment to train the patient to use the peripheral retina in place of the damaged/diseased macula. In this paper, we examine current and emerging rehabilitation techniques and highlight some areas of research that hold promise of improving rehabilitation practices for patients having central visual field losses.

Asunto(s)

RESUMEN

Thirty-six subjects completed questionnaires on their experiences wearing the CPF 550 lenses. Twenty-six subjects [21 with retinitis pigmentosa (RP)] were users of the 550's and 10 subjects (6 with RP) were nonusers who had rejected the 550's after a trial period. Subjects were asked about such factors as effects on adaptation time, ocular comfort, visual functioning, acceptability of tint strength in various lighting conditions, cosmetic appearance, effects of weather, and replacement intent. Users reported reduced adaptation time in changes of illumination, increased ocular comfort, improved visual functioning with the exception of poor color discrimination, and cosmetic acceptability. Satisfaction with tint strength varied with degree of illumination; usefulness in different types of weather also varied depending on the condition. Nonusers' responses were mixed; they were less likely to report improvements with the CPF 550 lenses compared to the users' group.

Asunto(s)

RESUMEN

The Frostig Figure Ground Test can be a valuable tool in the evaluation of adult low-vision patients. It is easily administered and can give valuable information about the patient's functioning. It provides an observable assessment of the individual sensory-perceptual capacities and has the further advantage of requiring the use of eye-hand coordination. Correlations of performance in this test with other data were analyzed for 79 low-vision patients. The test appears to provide some predictive information about the patient's reading performance, accounting for one-third of the variability of reading speed.

Asunto(s)

RESUMEN

Data from 96 veterans who had been using a closed circuit television (CCTV) for at least 2 years are presented. Most patients (87%) reported continuing use of the CCTV and demonstrated their proficiency in its use. Fifty percent of all patients used an optical aid, as well as a CCTV for near work. These patients did not differ on mean reading speeds for either type of aid, but the CCTV did provide significantly longer reading durations. Neither near nor far visual acuity measures were correlated with performance variables. Linear magnification, working distance, and effective magnification on the CCTV appeared to interact to influence CCTV reading speed. The data have clear implications for clinical practice.

Asunto(s)

RESUMEN

Full-field reversed 1.3X telescopes were used in the treatment of a 63-year-old male retinitis pigmentosa (R.P.) patient with a 5 degree central field. The patient was highly motivated to "expand" his visual field. He was trained intensively with 1.3X, 1.7X, and 2,2X reversed telescopes prior to prescribing. Evaluations by the Orientation and Mobility staff indicated significant improvements in his functioning with the devices. The reversed telescopes expanded his field to approximately 14 degrees. Patient has been reevaluated after using the aid at home and remains enthusiastic about his successful use of the aid. This case is notable in that binocular, low-power, full-field, reversed telescopes are being used successfully for mobility, eating, and other tasks.

Asunto(s)

RESUMEN

Reading speed and duration were measured for 24 low vision subjects, 12 learning to use closed circuit television and 12 learning to use optical aids. Reading speed and duration increased for both groups during 10 days of training and practice. Improvement occurred by steplike increases and plateaus. Visual acuity was not correlated with either performance measure; reading speed on the initial day of training was correlated with reading speed on the last day. The results have implications for both the prescription of aids and the training of low-vision patients.

Asunto(s)

RESUMEN

Confusion and misconception characterize the designation of near visual acuities because of the numerous systems in use. Most of these systems do not lend themselves to accurate or easy usage or to comparison with other test distances. Use of the M system, with the actual test distances recorded in meters, is suggested as a simplified system for standardization.

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)