مجله پژوهش فیزیک ایران
سال نوزدهم شماره 4 (زمستان 1398)

Fiber-optic sensors available in the market used to measure physical quantities such as electrical and magnetic fields, electrical current, temperature, pressure, acceleration, flow of liquids and gases, and measurement of fluid levels in various industries. As of today, due to the growing use of fiber optics, manufacturers of many machineries and control systems have been keen on using these sensors in manufacturing products. In this paper, due to the increasing importance of optical sensors, especially in wireless sensor networks, in the Internet of things, and in optical fiber networks, these types of sensors have been widely studied over the past decades to date, and in terms of technical and their applications, have been reviewed and reported. The results of this article can be used for designers of these sensors in various industries and universities at undergraduate, post-graduate students, and senior physics and engineering departments.

In this paper, the second and third order corrections of the curvature tensor to the holographic complexity of a temperature state in the coherent field theory are studied. Dual geometry of  this  temperate state  is Schwarzschild's anti deSitter black hole geometry. The calculations made in this paper show that considering these new sentences will only appear as a constant coefficient in the final result, that is the rate of complexity growth over long periods of time.

In recent years, the increase of industrial effluents in the petrochemical sector, in particular, the leakage of oil and the draining of industrial effluents in rivers, has created serious environmental hazards and huge economic losses in the world. In the past decade, the use of hydrophobic and oleophilic fabrics has been considered as a way to clean up contaminants through the absorption and separation of pollutants from industrial effluents. In this research, the low-pressure plasma polymerization method based on eco-friendly materials like Polydimethylsiloxane was used to fabricate hydrophobic and oleophilic cotton fabric. Also a low-pressure oxygen plasma pre-treatment was performed before plasma polymerization to improve bonding between created layer and cotton fabric Contact angle test and absorption capacity test was used to represent hydrophobicity of coated fabric and to measure the absorbance ability of different oils. Also scanning electron microscopy (SEM) was used to observe morphological changes on the surface of cotton fibers and Infrared Fourier transform (FTIR-ATR) spectroscopy to detect the chemical bonds created on the surface of fibers. Water-oil separation efficiency test and laundering test have been conducted to determine the separation rate and to represent durability of coated cotton, respectively. The water contact angle of coated cotton fabric was 143±3 and approximately this high hydrophobicity behavior remained after 10 cycle laundering. Also SEM results showed that the surface of fibers was covered by a random distribution of several microscale structures or a hierarchical surface structure like the lotus leaf. Our Water-oil separation tests demonstrated that coated fabrics had separation efficiency between 80 until 100 percent for most of the industrial oil, even after 15 cycles at 250 c and 900 c. These results indicate that coated cotton fabrics with plasma polymerization method has a high potential for application in water-oil separation and selective oil absorption. The fabrics are promising for the development an environmental friendly and recyclable separation of oil from water.

In the present work, the in-flight kaon interaction on the deuteron target at incident  momentum of  is investigated in the channel by a phenomenological potential model. By considering the effect of  resonance in the  invariant mass spectra comes fromreaction, and a comparison between theoretical spectra and Braun’s data, we found the best theoretical spectrum fitted to the experimental data. The energy and width of  resonance state are respectively extracted  and  from the fitting process.

In this paper, we study the validity of the laws of thermodynamics in the form of a far parallel gravitational theory with an incomplete coupling between curves and scalar fields. To this end, we consider the FRW flat world, showing  that the first and second laws of thermodynamics lie in its dynamic apparent horizon. We further assume that the universe is enclosed by the cosmological event horizon, such  that in this case the first law of thermodynamics is valid, but the second law of thermodynamics is applied to the selected incomplete model, depending on  the energy-momentum tensor components derived.

In this research, localized surface plasmon resonance spectra for single spherical gold nanoparticles with radius between 20 to 55nm in environments of different refractive indices between 1 and 1.8 has been studied by Finite Different Time Domain method. In this simulations, plasmon resonance frequency is determined for each nanoparticle with optimized mesh size, and is compared with the results of Mie theory. Moreover, using these results, plasmonic propertis of gold nanoshells of various diameters were studied in air (n=1) and water (n=1.33). Plasmon resonance has been calculated for nanoshells and it was concluded that in different environments, gold nanoshells with outer radius of 20 nanometers and diameter of 12 nanometers have their plasmonic spectrum are associated on gold nanosphere with the same outer radius.  frequency for nanoshells has been calculated. The plasmon resonance peak shift for various nanoparticles is plotted versus refractive indices. Finally, the most sensitive and most insennitive of nanoparticles to the refractive index of the environment has been discussed for sensing applications.

In this research, the surface plasmon-polariton modes at interface of a metal and a polygonal chiral thin film in Kretschman configuration theoretically have been studied. With depiction of optical absorption spectra for P-linear polarized incident light, the surface plasmonic modes from the waveguide modes have been distinguished. The effect of structural parameters such as the thickness of polygonal chiral thin film, the thickness of metallic thin film and the growth angle of chiral columns on the propagation of plasmonic modes has been investigated. The results showd that more than one plasmonic mode can be excited at interface of a polygonal chiral thin film and a metal.

An approach to obtain a maximum solid angle is the use of curved crystals. Therefore, in order to make these crystals useful in X-ray spectrometry, it is necessary to design them in such a way that they have high solid angle and reflectivity. In this paper, a nearly exact general equation for calculating the solid angle and area factor on the surface of several curved crystal geometries is extracted and compared with the previous results. Wittry and Sun's shortcut method for calculating the solid angle, and also, its trial and error method for maximizing the solid angle and introducing exact point-focusing crystal geometry is reviewed, and it is shown that for some crystal geometries are not responsive. By writing an algorithm for calculating the solid angle and the area factor for ​​all of the crystal geometries, we show that they are in agreement with the results of the analytical method.

In this paper, dynamical parameters of a plasma bullet (guided ionization wave) were studied in different gases such as oxygen, nitrogen and dry air. The dynamics of a plasma bullet, which is generated by a 30 kHz atmospheric pressure helium plasma jet, was measured using a high-speed ICCD camera from the starting moment of propagation at the end of the jet’s capillary to the vanishing point in the surrounding gas. The plasma bullet has different propagation velocity, diameter and propagation length in different surrounding gases. The velocity of the plasma bullet is higher in oxygen and dry air compared to nitrogen and reaches up to 18 km/s. The maximum propagation length is 12 mm in nitrogen and dry air. The spectroscopic emission of helium plasma jet was also measured to investigate the chemical species in different surrounding gases. The result of this study shows the influence of the surrounding gas on the propagation of plasma bullets and especially the role of oxygen in the propagation mechanism.

We study the growth rate of holographic complexity in dissipative quantum field theories using the gauge/gravity duality. To do so we employ the complexity equals action proposal for computing the holographic complexity.  We show that although in the late time regime the rate of growth of complexity approaches a constant value which is consistent with the Lloyd's bound, the constant is approached from above. We find that increasing the value of the dissipative parameters enhances the Lloyd's bound violation. We also investigate the dependence of critical time on dissipative parameters.

In the present work we consider to generalized ghost dark energy in presence of a sign changeable interaction term. We obtain evolving cosmic parameters and plot them. We find a good agreement between the model and observations in primary analysis. The plots reveal that decreasing b, the universe enters acceleration phase earlier while decreasing 𝜉  leads a delay in enterance to the acceleration phase. Next we present a stability analysis according to squared sound speed and find that increasing  the model can achieve positive domain for squared sound speed which shows signs of stability. Finaly we discuss the statefinder analysis and see the model can catch {r=1,s=0} at late time.

In this paper, the optical properties of a C60 molecule is studied within the framework of the quasi-static approximation. To do this, a C60 molecule is modeled by an infinitesimally thin spherical shell of the π and σ electrons and electronic excitations of this shell is described by means of the two-dimensional two-fluid hydrodynamic theory. At the first, general expression for polarizability of the system is obtained, by solving Laplace and hydrodynamic equations with appropriate boundary conditions. Then, by using the polarizability formula, the extinction spectrum of system is investigated which is in quite agreement with the result of the Mie theory. Also, the Maxwell-Garnett theory for the effective medium approximation of composite materials is developed to study the dielectric response of a composite of C60 molecules.

- In this paper, we introduce a novel diffraction element for generating any desired arrays of the vortex and perfect vortex beam. The method is based on combining radially phase shifted spiral zone plate with different gratings. We show that the element has a great potential in generating a variety of arrays with desired vortex ring radius and topological charges. We can assemble various vortex and perfect vortex beams not only in a lattice array but also in a tilted lattice or circular arrays. Reported vortex arrays are in the group of vortices having the same topological charge p so the total topological charge of MP which M the number of elements. The experimental results are in good agreement with the simulation predictions.

Dipole asymmetry is among the most important anomalies in the cosmic microwave background (CMB). A dipole, if primordial, would challenge the isotropy of the Universe. In this work, we propose a novel method to find the direction of the dipole and its amplitude and assess its significance. The method is based on the comparison of annular variances on the sphere. We find the direction on the sphere around which the difference of the annular variances on the two hemispheres is maximized. By applying this algorithm on symmetric CMB simulations we get the distribution of the measured dipole amplitude for these null cases, providing us with the baseline for quantifying the significance of dipole amplitude of any other CMB maps. In particular, we find the statistical significance of the observed Planck dipole to be 1.6σ. Our simulations show that although the proposed method is not more powerful in detecting the dipole compared to other algorithms, its relatively low computational cost (performed in the pixel-space) is its advantage. This paves the way for a straightforward upgrade of the method which uses spherical caps instead of rings and thus, by increasing the number of pixels used in calculating the variance, improves the results significantly.

The geometrical and topological measures enable us to characterize stochastic field systematically, and  the relation between weighted and unweighted N-point functions is provided. One of such relations is given by the bias factor. In this paper, based on peak statistics, we study the bias factor for stochastic and anisotropic fields. Accordingly, we present the analytical description of local and linear bias factor. Doing simulations, we examine the validation of  the derived analytical relation. Our results show that at high threshold level and large spatial separation, there exists a good agreement between the analytical calculation and numerical computations.

Data reduction is one the most important process of researches in astronomy and astrophysics. Data reduction process includes all steps which convert the crude astronomical images to the astrophysical events. These steps are similar for different astronomical events in which the brightness of one star changes with time, although they may be different in some details. This paper will help for learning or even doing data reduction of each astronomical event. Data reduction of microlensing events contains 7 stages in which first the crude images will be calibrated. Then, some of the best calibrated images will be chosen for making the reference images. The reference image helps for comparing all taken images to indicate how the source light changes versus time. For this propose all images should be registered to the reference images. Then, all images should be taken to the same scale. Finally, the resulted images will be subtracted from the reference image, to find the light curve of that desired source star.

Using AXUV (absolute extreme ultraviolet) photodiode, experimental results obtained for soft X-ray and EUV emission are presented. Plasma produced by nanosecond laser pulse laser system is applied with maximum energy of 250 mJ, pulse durations, 10-30 ns and wavelength, 1064 nm under interaction with steel-316 target. The energy of soft X-ray is observed to be approximately linearly proportional to the laser pulse energy. The soft X-ray and EUV emissions with specific signal was detected by AXUV photodiode with durations of about 15 ns and time delay about 20 ns relative to the laser pulse. The average energy conversion efficiency emission was determined to be about 2.5%.

Dirac cone can be tilted in condensed matter setting. As a result of tilt, the Lorentz symmetry is reduced to what we call tilted-Lorentz symmetry. In this paper we derive the tilted-Lorentz transformations that leave a world with tilted Dirac cone invariant.

Short and intense laser pulse propagating in a plasma produces an electrostatic wakefield that is widely used in laser acceleration of charged particles. Amplitude of the wakefield depends on several factors, including the laser pulse polarization. Magnetized plasma is anisotropic for various laser polarization and in different condition, different modes can propagate in plasma. In this paper, we investigate the propagation conditions of each modes and with finding the governing equations, the excitation of wakefield due to the laser pulse with the different modes, including circular (R and L modes), elliptic (X mode) and linear (L mode) polarizations, will be determined. By using the forth-order Runge-Kutta algorithm, the differential equations, simultaneously have been solved. The results show that, the amplitude of the wakefield depends not only on the laser mode but also on the plasma density, external magnetic field and laser frequency.

In this paper, we study the energy transferred between a pair of acceptor-donor molecules near a graphene-coated metallic nanoparticle by using the Laplace equation in a quasi-static approximation. After performing theoretical calculations and computer simulations, the influence of the system parameters such as the refractive index of the environment and the contribution of multipolar in different modes on the energy exchanged between the pair of molecules and nanoparticles is analyzed and investigated. The results show that graphene coating enhances plasmon-plasmas coupling in the nanostructure, consequently, enhances the energy transferred between the two molecules and the nanoscale. Therefore, this structure could be used as a new route designing nano-based biosensors.

In this paper, surface polaritons (SPs) at the interface of a semi-infinite homogeneous dielectric medium and a one-dimensional photonic crystal (PC) have been investigated theoretically. The PC is made of the alternate layers of an isotropic ordinary dielectric and a graphene-based hyperbolic metamaterial layers. The effective medium approach has been used for the study of the metamaterial layers and it is shown that they have hyperbolic dispersion in a certain frequency range at THz region. The obtained results show that the structure has some photonic band gaps in the hyperbolic and elliptical frequency regions for both TE and TM polarizations and can support the SPs in these frequency ranges. It is observed that the characteristics of the SPs depend on the geometrical parameters of the structure and optical parameters of the graphene monolayers. In the following, the electromagnetic field profiles of some SPs have been plotted and it is shown that the modes of the first band gap are more localized than the modes of the second band gap. Finally, the intensity distribution of a TM-polarized Gaussian beam inside and outside the PC has been simulated which is verifying the localization of the SPs at the interface of the structure.