Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusion

We report femtosecond time-resolved reflectivity measurements of coherent phonons in tellurium performed over a wide range of temperatures (3K to 296K) and pump laser intensities. A totally symmetric A$_{1}$ coherent phonon at 3.6 THz responsible for the oscillations in the reflectivity data is observed to be strongly positively chirped (i.e, phonon time period decreases at longer pump-probe delay times) with increasing photoexcited carrier density, more so at lower temperatures. We show for the first time that the temperature dependence of the coherent phonon frequency is anomalous (i.e, increasing with increasing temperature) at high photoexcited carrier density due to electron-phonon interaction. At the highest photoexcited carrier density of $\sim$ 1.4 $\times$ 10$^{21}$cm$^{-3}$ and the sample temperature of 3K, the lattice displacement of the coherent phonon mode is estimated to be as high as $\sim$ 0.24 \AA. Numerical simulations based on coupled effects of optical absorption and carrier diffusion reveal that the diffusion of carriers dominates the non-oscillatory electronic part of the time-resolved reflectivity. Finally, using the pump-probe experiments at low carrier density of 6 $\times$ 10$^{18}$ cm$^{-3}$, we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth.Comment: 22 pages, 6 figures, submitted to PR

An alternative explanation for the density depletions observed by Freja and Viking satellites

In this paper, we have studied the linear and nonlinear propagation of ion acoustic waves in the presence of electrons that follow the generalized (r,q) distribution. It has been shown that for positive values of r, which correspond to a flat-topped electron velocity distribution, the nonlinear ion acoustic waves admit rarefactive solitary structures or density depletions. It has been shown that the generalized (r,q) distribution function provides another way to explicate the density depletions observed by Freja and Viking satellites previously explained by proposing Cairns distribution function.In this paper, we have studied the linear and nonlinear propagation of ion acoustic waves in the presence of electrons that follow the generalized (r,q) distribution. It has been shown that for positive values of r, which correspond to a flat-topped electron velocity distribution, the nonlinear ion acoustic waves admit rarefactive solitary structures or density depletions. It has been shown that the generalized (r,q) distribution function provides another way to explicate the density depletions observed by Freja and Viking satellites previously explained by proposing Cairns distribution function

Scaling and Formulary cross sections for ion-atom impact ionization

The values of ion-atom ionization cross sections are frequently needed for many applications that utilize the propagation of fast ions through matter. When experimental data and theoretical calculations are not available, approximate formulas are frequently used. This paper briefly summarizes the most important theoretical results and approaches to cross section calculations in order to place the discussion in historical perspective and offer a concise introduction to the topic. Based on experimental data and theoretical predictions, a new fit for ionization cross sections is proposed. The range of validity and accuracy of several frequently used approximations (classical trajectory, the Born approximation, and so forth) are discussed using, as examples, the ionization cross sections of hydrogen and helium atoms by various fully stripped ions.Comment: 46 pages, 8 figure

Plant mediated synthesis of silver nanoparticles and their biological applications

The green synthesis of nanoparticles using plants and their extracts is considered as a representative approach in material synthesis for environmental benignity. Numerous metal nanoparticles with potential bioactivities have been prepared based on plant extracts. In this paper, we report an eco-friendly technique for the preparation of silver nanoparticles using plant extract of Justicia diffusa Willd. and the evaluation of their antioxidant, antidiabetic, and cytotoxicity activities. UV-visible spectroscopy, transmission electron microscopy, scanning electron microscopy and atomic force microscopy analysis were used to characterize the morphology and size of silver nanoparticles. The stability of silver nanoparticles toward acidity, alkalinity, salinity and temperature showed that they remained stable at room temperature for more than two months. UV–vis spectrum of the aqueous medium containing silver nanoparticles showed an absorption peak at around 420 nm. The scanning electron microscopy analysis of the silver nanoparticles showed that they have a uniform spherical shape with an average size in the range of 40–78 nm. This was confirmed by transmission electron microscopy analysis which showed an average size of about 50 nm. Thus green system showed better capping and stabilizing agent for the fine particles. Further 1-diphenyl-2-picrylhydrazl radical in Justicia diffusa mediated silver nanoparticles showed a maximum activity of 67% at concentration of 200 μg/mL. Hydrogen peroxide scavenging assay in Justicia diffusa mediated silver nanoparticles showed a maximum activity of 89% at concentration of 200 μg/mL. Reducing power of Justicia diffusa silver nanoparticles exhibited a higher activity of 246 μg/mL at concentration of 200 μg/mL. These NPs showed the cytotoxic effects against brine shrimp (Artemia salina) Nauplii with a value of 35% and LD value of 271 μg/mL. The AgNPs synthesized using Justicia diffusa Willd.  extract also show remarkable antidiabetic activities.               KEY WORDS: Justicia diffusa, Nanoparticles, TEM, SEM, AFM Bull. Chem. Soc. Ethiop. 2018, 32(3), 469-479.DOI: https://dx.doi.org/10.4314/bcse.v32i3.

Potret Keislaman Mahasiswa Universitas Al Azhar Indonesia

Memotret realitas keislaman mahasiswa UAI secara akurat merupakan titik tolak dilakukannya penelitian ini. Diharapkan, potret tersebut bermanfaat dalam merumuskan model kebijakan, regulasi, dan pendekatan yang relevan dan efektif dalam menanamkan nilai-nilai keislaman di kalangan mahasiswa UAI. Oleh karena itu, penelitian ini berusaha mencover responden dalam prosentase yang relatif besar (sampai dengan 18% dari populasi) dari seluruh fakultas di UAI, dari angkatan 2008, 2009, dan 2010. Pengambilan sampel menggunakan metode proportional random sampling mengingat jumlah mahasiswa per fakultas yang tidak sama. Penelitian ini menyimpulkan sejumlah poin penting, di antaranya: (1) Realitas keislaman mahasiswa UAI secara umum tergolong sedang, (2) Ada kesenjangan antara aspek akidah, ibadah dan akhlak dalam keislaman mereka. Dalam hal akidah, mereka relatif baik. Namun terlihat penurunan dalam aspek ibadah dan akhlak, (3) Lingkungan tempat mereka tumbuh dan perhatian orang tua berpengaruh signifikan terhadap keislaman mereka

Study of absorption loss effects on acoustic wave propagation in shallow water using different empirical models

Efficient underwater acoustic communication and target locating systems require detailed study of acoustic wave propagation in the sea. Many investigators have studied the absorption of acoustic waves in ocean water and formulated empirical equations such as Thorp's formula, Schulkin and Marsh model and Fisher and Simmons formula. The Fisher and Simmons formula found the effect associated with the relaxation of boric acid on absorption and provided a more detailed form of absorption coefficient which varies with frequency. However, no simulation model has made for the underwater acoustic propagation using these models. This paper reports the comparative study of acoustic wave absorption carried out by means of modeling in MATLAB. The results of simulation have been evaluated using measured data collected at Desaru beach on the eastern shore of Johor in Malaysia. The model has been used to determine sound absorption for given values of depth (D), salinity (S), temperature (T), pH, and acoustic wave transmitter frequency (f). From the results a suitable range, depth and frequency can be found to obtain best propagation link with low absorption loss

Mathematical Model for Impact of Media on Cleanliness Drive in India

A mathematical model on cleanliness drive in India is analysed for active cleaners and passive cleaners. Cleanliness and endemic equilibrium points are found. Local and global stability of these equilibrium points are discussed using Routh-Hurwitz criteria and Lyapunov function respectively. Impact of media (as a control) is studied on passive cleaners to become active. Numerical simulation of the model is carried out which indicates that with the help of media transfer rate to active cleaners from passive cleaners is higher

Study on feed-in-tariff (FiT) for BIPV system, a Malaysia scenario

Feed-In Tariff (FiT) was introduced in Malaysia in 2004 and has been undergone many stages to make its implementation in Malaysia successful. The first Building Integrated Photovoltaic (BIPV) introduced in Malaysia is Suria 1000 under the supervision of Pusat Tenaga Malaysia (PTM). The aim of this paper was to study the FiT and BIPV implementation in Malaysia. It is observed that Malaysian did not invest in BIPV due to its expensive investment. The FiT Calculator was developed to prove the benefits of FiT in BIPV by practically calculating the investment and profit in the long run which was after 21 years of implementation. FiT Calculator was developed using Microsoft Visual Basic 2010 and variable parameter such as the solar irradiation, types of solar panel and inverter were studied to obtain the estimation of power output, the annual income, net income and the payback period of BIPV. Results of all case studies were verified with MBIPV mileage report and the built FiT Calculator has shown up to 96.89% accuracy against the case study done