Generation and detection of Terahertz radiation by Field Effect Transistors

This is a brief overview of the main physical ideas for application of field effect transistors for generation and detection of TeraHertz radiation. Resonant frequencies of the two-dimensional plasma oscillations in FETs increase with the reduction of the channel dimensions and reach the THz range for sub-micron gate lengths. When the mobility is high enough, the dynamics of a short channel FET at THz frequencies is dominated by plasma waves. This may result, on the one hand, in a spontaneous generation of plasma waves by a dc current and on the other hand, in a resonant response to the incoming radiation. In the opposite case, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector.Comment: 10 pages, 3 figure

Implications of the NANOGrav results for primordial black holes and Hubble tension

The purpose of this work is to investigate the formation and evaporation of the primordial black holes in the inflationary scenarios. Thermodynamic parameters such as mass, temperature and entropy are expressed in terms of NANOGrav frequency. By numerical calculations we show that the constraint on the mass range $10^{-5}kg-10^{50}kg$ is well confirmed. We discuss the relation between the redshift and the probability for gravitational wave source populations. A new parameter associated with the frequency and Hubble rate is presented, by which for the spectral index $n_{s}\approx 0.996$ and the Hubble constant $H_{0}\approx 67.27km.s^{-1}.Mpc^{-1}$, the effective Hubble constant is calculated to be $H_{eff,0}\approx 73.24km.s^{-1}.Mpc^{-1}$ which is compatible with the observational data. We make a comparison between the Hubble tension and the primordial perturbations and the expression of the mass loss rate, chemical potential and central charge needed to describe the Hawking evaporation will be established

Antibacterial Activity of Methanolic Extract of Dominant Marine Alga (Padina pavonia) of Tolmeta Coasts, Libya

Abstract: This study meanly aimed to identify the marine algae of Tolmeta coasts and evaluate the antibacterial activity of the most dominant species (Padina pavonia) as compared with some famous antibiotics. During many sampling visits at 2009, Thirty four marine algal species (26 genera) were collected and identified at Tolmeta coasts (150 Km. eastern north Benghazi city). Two species (5.88%) of the collected algae (Lyngbia and Rivularia) were belonging to Cyanophyta, Six species (17.65%) belong to Chlorophyta, thirteen species (38.24%) belonging to Phaeophyta (with special reference to genera Padina and Cystoseira) and thirteen species (38.24%) belonging to Rhodophyta. The R/P ratio was 1.00 which indicated the rough weather of this area. Padina pavonia was the most dominant species at all samples, methanolic crude extract (at cold and 24 h.) were tested against Escherichia coli and Staphylococcus aureus bacteria and matched with some famous antibiotics. All of the treatments were affected Escherichia coli, they could statistically ranked dissentingly as Ci > E15 > Sxt at the first rank and Te30 > Padina extract at the second rank while P10 came at the third rank with significant values. Meanwhile, Staphylococcus aureus was affected only by E15 antibiotic

Synergistic antioxidant effects of natural compounds on H2O2-induced cytotoxicity of human monocytes

Natural compounds are endowed with a broad spectrum of biological activities, including protection against Toxins. Most of them are known for their antioxidant and radical scavenging activities. However, the synergistic combination of these natural molecules is not well studied. Therefore, the present study aims first to investigate the effect of four potent natural molecules [rosmarinic acid (Ros-A), ellagic acid (Ella-A), curcumin (Cur), and syringic acid (Syr-A)] on H2O2 -induced cell cytotoxicity and oxidative stress on the human monocytes (THP-1) and then to evaluate their combined action effect. Optimal combinations of these molecules were predicted using an augmented mixture design approach. In the first, as preliminary antioxidant activities screening, two in vitro assays were adopted to assess the single radicals scavenging activity of these natural compounds, DPPH center dot and ABTS center dot + tests. Based on the results obtained, the multitude of optimal formulas proposed by the mixture design study led to choosing four potent compositions (comp) in addition to ellagic acid, proposed as the most efficient when applied alone. The different molecules and mixtures were used to assess their cytoprotective effect on THP-1 cells in the presence and absence of H2O2. The most potent Comp-4, as well as the molecules forming this mixture, were exploited in a second experiment, aiming to understand the effect on oxidative stress via antioxidant enzyme activities analysis in the H2O2-induced oxidative stress in the THP-1 cell line. Interestingly, the natural molecules used for THP-1 cells treatment exhibited a significant increase in the antioxidant defense and glyoxalase system as well as suppression of ROS generation evaluated as MDA content. These results indicate that the natural compounds tested here, especially the synergistic effect of Cur and Ros-A (Comp-4), could serve as cytoprotective and immunostimulant agents against H2O2-induced cytotoxicity THP-1 cells, which makes them interesting for further investigations on the molecular mechanisms in preclinical animal models.Peer reviewe

Plasma wave resonant detection of terahertz radiations by nanometric transistors

We report on resonant terahertz detection by two-dimensional electron plasma located in nanometric InGaAs and GaN transistors. Up to now, the biggest part of the research was devoted to GaAs-based devices as the most promising from the point of view of the electron mobility. The resonant detection was reported, however, only in the sub-THz range. According to predictions of the Dyakonov–Shur plasma wave detection theory an increase of the detection frequency can be achieved by reducing the length or increase the carrier density in the gated region.We demonstrate that the 1THz limit can be overcome by using ultimately short gate InGaAs and GaN nanotransistors. For the first time the tunability of the resonant signal by the applied gate voltage is demonstrated. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel (Dyakonov–Shur theory). We also show that by increasing of the drain-to-source current leads to a transformation of the broadband detection to a resonant and tuneable one. We can get resonant detection at room temperature. We finally discuss the possible application of detection by nanotransistors in different types of THz spectroscopy research