261 research outputs found
Exact Outage Probability Analysis of the Mixed RF/FSO System With Variable-Gain Relays
This paper presents a unified analysis of the mixed radio-frequency
(RF)/free-space optics (FSO) relaying system, with multiple variable-gain
amplify-and-forward relays. The partial relay selection (PRS) is employed to
select the active relay for further re-transmission. Due to fast fading
statistics of the first RF hop, it is assumed that the channel state
information of the RF link is outdated, which is used for both the relay gain
adjustment and the PRS procedure. The RF hops are subject to the Rayleigh
fading, while the FSO hop is affected by the atmospheric turbulence and the
pointing errors. The intensity fluctuations of the optical signal caused by
atmospheric turbulence are modeled by the general Malaga (M) distribution,
which takes into account the effect of multiple scattered components. An exact
expression for the outage probability is derived. In addition,
high-signal-to-noise-ratio approximations are provided, which can be used to
efficiently determine the outage probability floor. Numerical results are
validated by Monte Carlo simulations, which are used to examine the effects of
the system and channel parameters on the RF/FSO system performance.Comment: Published in: IEEE Photonics Journa
Intrinsic and extrinsic decay of edge magnetoplasmons in graphene
We investigate intrinsic and extrinsic decay of edge magnetoplasmons (EMPs)
in graphene quantum Hall (QH) systems by high-frequency electronic
measurements. From EMP resonances in disk shaped graphene, we show that the
dispersion relation of EMPs is nonlinear due to interactions, giving rise to
intrinsic decay of EMP wavepacket. We also identify extrinsic dissipation
mechanisms due to interaction with localized states in bulk graphene from the
decay time of EMP wavepackets. We indicate that, owing to the unique linear and
gapless band structure, EMP dissipation in graphene can be lower than that in
GaAs systems.Comment: 5 page
Outage Probability Analysis of Mixed RF-FSO System Influenced by Fisher-Snedecor Fading and Gamma-Gamma Atmospheric Turbulence
In this paper, we investigate a dual-hop relaying system, composed of radio
frequency (RF) and free-space optical (FSO) link. Decode-and-forward (DF) relay
is employed to integrate the first RF link and the second line-of-sight FSO
links. The RF channel is assumed to be subject to recently proposed
Fisher-Snedecor fading model, which was shown to be convenient for modeling in
realistic wireless communication scenarios. The FSO channel is affected by
Gamma-Gamma distributed atmospheric turbulence. Expression for the outage
probability is derived and utilized to present numerical results. Based on
presented results, the effects of various RF and FSO channels parameters on the
overall system performance are examined and discussed.Comment: Presented at 2018 26th Telecommunications Forum (TELFOR
Error rate and ergodic capacity of RF-FSO system with partial relay selection in the presence of pointing errors
This paper presents an analysis of a multiple dual-hop relaying system, which is composed of km-class radio frequency (RF)-free-space optical (FSO) links. Partial relay selection based on outdated channel state information (CSI) is employed in order to select active relay for further transmission. Amplify-and-forward relaying protocol is utilized. The RF links are assumed to be subject to Rayleigh fading, and the FSO links are influenced by both Gamma–Gamma atmospheric turbulence and pointing errors. On the basis of our previously derived expression for cumulative distribution function of the equivalent signal-to-noise ratio of the whole system, we derive novel analytical expressions for the average bit-error rate (BER) and ergodic capacity that are presented in terms of the Meijer’s G-function and extended generalized bivariate Meijer’s G-function, respectively. The numerical results are confirmed by Monte Carlo simulations. Considering the effect of time-correlation between outdated CSI and actual CSI related to the RF channel at the time of transmission, the average BER and the ergodic capacity dependence on various system and channel parameters are observed and discussed. The results illustrate that the temporal correlation between outdated and actual CSI has strong effect on system performance, particularly on BER values, when FSO hop is influenced by favorable conditions
In Vitro Aging of Human Skin Fibroblasts: Age-Dependent Changes in 4-Hydroxynonenal Metabolism
Evidence suggests that the increased production of free radicals and reactive oxygen species lead to cellular aging. One of the consequences is lipid peroxidation generating reactive aldehydic products, such as 4-hydroxynonenal (HNE) that modify proteins and form adducts with DNA bases. To prevent damage by HNE, it is metabolized. The primary metabolic products are the glutathione conjugate (GSH-HNE), the corresponding 4-hydroxynonenoic acid (HNA), and the alcohol 1,4-dihydroxynonene (DHN). Since HNE metabolism can potentially change during in vitro aging, cell cultures of primary human dermal fibroblasts from several donors were cultured until senescence. After different time points up to 30 min of incubation with 5 \ub5M HNE, the extracellular medium was analyzed for metabolites via liquid chromatography coupled with electrospray ionization mass spectrometry (LC/ESI-MS). The metabolites appeared in the extracellular medium 5 min after incubation followed by a time-dependent increase. But, the formation of GSH-HNL and GSH-DHN decreased with increasing in vitro age. As a consequence, the HNE levels in the cells increase and there is more protein modification observed. Furthermore, after 3 h of incubation with 5 \ub5M HNE, younger cells showed less proliferative capacity, while in older cells slight increase in the mitotic index was noticed
Mixed RF-VLC Relaying Systems for Interference-Sensitive Mobile Applications
Due to their Radio-Frequency (RF) immunity, Visible Light Communications
(VLC) pose as a promising technology for interference sensitive applications
such as medical data networks. In this paper, we investigate mixed RF-VLC
relaying systems especially suited for this type of applications that support
mobility. In this system setup, the end-user, who is assumed to be on a vehicle
that is in dynamic movement, is served by an indoor VLC system, while the
outdoor data traffic is conveyed through multiple backhaul RF links.
Furthermore, it is assumed that a single backhaul RF link is activated by the
mobile relay and due to feedback delay, the RF link activation is based on
outdated channel state information (CSI). The performance of this system is
analyzed in terms of outage probability and bit error rate (BER), and novel
closed form analytical expressions are provided. Furthermore, the analysis is
extended for the case where the average SNR over the RF links and/or LED
optical power is high, and approximate analytical expressions are derived which
determine performance floors. Numerical results are provided which demonstrate
that the utilization of multiple RF backhaul links can significantly improve
overall RF-VLC system performance when outage/BER floors are avoided. This
calls upon joint design of both subsystems. Additionally, the outdated CSI
exploited for active RF selection can significantly degrade the quality of
system performance.Comment: Published in IEEE Transactions on Vehicular Technolog
Efficacy and Safety of COVID-19 Convalescent Plasma in Hospitalized Patients—An Open-Label Phase II Clinical Trial
Background: COVID-19 convalescent plasma (CCP) is an important antiviral option for selected patients with COVID-19. Materials and Methods: In this open-label, phase 2, clinical trial conducted from 30 April 2020 till 10 May 2021 in the Republic of North Macedonia, we evaluated the efficacy and safety of CCP in hospitalized patients. Treatment was with a single unit of CCP having an anti-RBD IgG concentration higher than 5 AU/mL. Results: There were 189 patients that completed the study, of which 65 (34.4%) had WHO 8-point clinical progression scale score of 3 (requiring hospital care but not oxygen support), 65 (34.4%) had a score of 4 (hospitalized and requiring supplemental oxygen by mask or nasal prongs), and 59 (31.2%) had a score of 5 (hospitalized and requiring supplemental oxygen by non-invasive ventilation or high-flow oxygen). Mean age was 57 years (range 22–94), 78.5% were males, 80.4% had elevated body mass index, and 70.9% had comorbidity. Following CCP transfusion, we observed clinical improvement with increase rates in oxygenation-free days of 32.3% and 58.5% at 24 h and seven days after CCP transfusion, a decline in WHO scores, and reduced progression to severe disease (only one patient was admitted to ICU after CCP transfusion). Mortality in the entire cohort was 11.6% (22/189). We recorded 0% mortality in WHO score 3 (0/65) and in patients that received CCP transfusion in the first seven days of disease, 4.6% mortality in WHO score 4 (3/65), and 30.5% mortality in WHO score 5 (18/59). Mortality correlated with WHO score (Chi-square 19.3, p < 0.001) and with stay in the ICU (Chi-square 55.526, p ≤ 0.001). No severe adverse events were reported. Conclusions: This study showed that early administration of CCP to patients with moderate disease was a safe and potentially effective treatment for hospitalized COVID-19 patients. The trial was registered at clinicaltrials.gov (NCT04397523)
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