Search results for: quantum disc

Authors: M. Venkateswarlu, Srinivasa Rao Allam, S. K. Mahamuda, K. Swapna, G. Vijaya Prakash

Abstract:

Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Tm3+ ions were prepared by using melt quenching technique and characterized through optical absorption, photoluminescence and decay spectral studies to know the feasibility of using these glasses as luminescent devices in visible Red and NIR regions. By using optical absorption spectral data, the energy band gaps for all the glasses were evaluated and were found to be in the range of 2.34-2.59 eV; which is very useful for the construction of optical devices. Judd-Ofelt (J-O)theory has been applied to the optical absorption spectral profiles to calculate the J-O intensity parameters Ωλ (λ=2, 4 and 6) and consecutively used to evaluate various radiative properties such as radiative transition probability (AR), radiative lifetimes (τ_R) and branching ratios (β_R) for the prominent luminescent levels. The luminescence spectra for all the LTT glass samples have shown two intense peaks in bright red and Near Infrared regions at 650 nm (1G4→3F4) and 800 nm (3H4→3H6) respectively for which effective bandwidths (〖Δλ〗_P), experimental branching ratios (β_exp) and stimulated emission cross-sections (σ_se) are evaluated. The decay profiles for all the glasses were also recorded to measure the quantum efficiency of the prepared LTT glasses by coupling the radiative and experimental lifetimes. From the measured emission cross-sections, quantum efficiency and CIE chromaticity coordinates, it was found that 0.5 mol% of Tm3+ ions doped LTT glass is most suitable for generating bright visible red and NIR lasers to operate at 650 and 800 nm respectively.

Keywords: glasses, JO parameters, optical materials, thullium

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Authors: Sangram A. Sathe, Neha A. Madgulkar, Shruti S. Raut, S. P. Wadkar

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Transforaminal lumbar interbody fusion (TLIF) surgeries have nowadays became popular for treatment of degenerated spinal disorders. The interbody fusion technique like TLIF maintains load bearing capacity of the spine and a suitable disc height. Currently many techniques have been introduced to cure Spondylolisthesis. This surgery provides greater rehabilitation of degenerative spines. While performing this TLIF surgery existing methods use guideway, which is a troublesome surgery technique as the use of two separate instruments is required to perform this surgery. This paper presents a concept which eliminates the use of guideway. This concept also eliminates problems that occur like reverting the cage. The concept discussed in this paper also gives high accuracy while performing surgery.

Keywords: TLIF, spondylolisthesis, spine, instruments

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Authors: M. Raissy, M. Shahrani

Abstract:

The present study was done to evaluate the presence of tetracycline resistance genes in Lactococcus garvieae isolated from cultured rainbow trout, West Iran. The isolates were examined for antimicrobial resistance using disc diffusion method. Of the 49 strains tested, 19 were resistant to tetracycline (38.7%), 32 to enrofloxacin (65.3%), 21 to erythromycin (42.8%), 20 to chloramphenicol and trimetoprim-sulfamethoxazole (40.8%). The strains were then characterized for their genotypic resistance profiles. The results revealed that all 49 isolates contained at least one of the tetracycline resistance genes. Tet (A) was found in 89.4% of tetracycline resistant isolates and the frequency of other gene were as follow: tet (E) 42.1%, tet (B) 47.3%, tet (D) 15.7%, tet (L) 26.3%, tet (K) 52.6%, tet (G) 36.8%, tet (34) 21%, tet (S) 63.1%, tet (C) 57.8%, tet (M) 73.6%, tet (O) 42.1%. The results revealed high levels of antibiotic resistance in L. garvieae strains which is a potential danger for trout culture as well as for public health.

Keywords: Lactococcus garvieae, tetracycline resistance genes, rainbow trout, antimicrobial resistance

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Authors: I. Graur, V. Bria, C. Muntenita

Abstract:

Recent ecological interests have resulted in scientific concerns regarding natural-organic powder composites. Because natural-organic powders are cheap and biodegradable, green composites represent a substantial contribution in polymer science area. The aim of this study is to point out the effect of natural-organic powder resulting from the grinding of pine needles used as a modifying agent for Epiphen epoxy resin and is focused on friction coefficient behavior. A pin-on-disc setup is used for friction coefficient experiments. Epiphen epoxy resin was used with the different ratio of organic powder from the grinding of pine needles. Because of the challenges of natural organic powder, more and more companies are looking at organic composite materials.

Keywords: epoxy, friction coefficient, organic powder, pine needles

Procedia PDF Downloads 177

Authors: M. Hadji, A. Haddad, Y. Hadji

Abstract:

The effects of boronizing treatment on the friction coefficient and wear behavior of 0.35 Vf TiC- Ti3 SiC2 composite were investigated. In order to modify the surface properties of Ti3SiC2, boronizing treatment was carried out through powder pack cementation in the 1150-1350 °C temperature range. After boronizing treatment, one mixture layer, composed of TiB2 and SiC, forms on the surface of Ti3SiC2. The growth of the coating is processed by inward diffusion of Boron and obeys a linear rule. The Boronizing treatment increases the hardness of Ti3SiC2 from 6 GPa to 13 GPa. In the pin-on-disc test, i twas found that the material undergoes a steady-state coefficient of friction of around 0.8 and 0.45 in case of Ti3SiC2/Al2O3 tribocouple under 7 N load for the non treated and the boronized samples, respectively. The wear resistance of Ti3SiC2 under Al2O3 ball sliding has been significantly improved, which indicated that the boronizing treatment is a promising surface modification way of Ti3SiC2.

Keywords: MAX phase, boronizing, hardness, wear

Procedia PDF Downloads 349

Authors: Andrei Bejan, Luminita Marin, Dalila Belei

Abstract:

Phenothiazine with electron-rich nitrogen and sulfur heteroatoms has a high electron-donating ability which promotes a good conjugation and therefore low band-gap with consequences upon charge carrier mobility improving and shifting of light emission in visible domain. Moreover, its non-planar butterfly conformation inhibits molecular aggregation and thus preserves quite well the fluorescence quantum yield in solid state compared to solution. Therefore phenothiazine and its derivatives are promising hole transport materials for use in organic electronic and optoelectronic devices as light emitting diodes, photovoltaic cells, integrated circuit sensors or driving circuits for large area display devices. The objective of this paper was to obtain a series of new phenothiazine derivatives by introduction of different electron withdrawing substituents as formyl, carboxyl and cyanoacryl units in order to create a push pull system which has potential to improve the electronic and optical properties. Bromine atom was used as electrono-donor moiety to extend furthermore the existing conjugation. The understudy compounds were structural characterized by FTIR and 1H-NMR spectroscopy and single crystal X-ray diffraction. Besides, the single crystal X-ray diffraction brought information regarding the supramolecular architecture of the compounds. Photophysical properties were monitored by UV-vis and photoluminescence spectroscopy, while the electrochemical behavior was established by cyclic voltammetry. The absorption maxima of the studied compounds vary in a large range (322-455 nm), reflecting the different electronic delocalization degree, depending by the substituent nature. In a similar manner, the emission spectra reveal different color of emitted light, a red shift being evident for the groups with higher electron withdrawing ability. The emitted light is pure and saturated for the compounds containing strong withdrawing formyl or cyanoacryl units and reach the highest quantum yield of 71% for the compound containing bromine and cyanoacrilic units. Electrochemical study show reversible oxidative and reduction processes for all the compounds and a close correlation of the HOMO-LUMO band gap with substituent nature. All these findings suggest the obtained compounds as promising materials for optoelectronic devices.

Keywords: electrochemical properties, phenothiazine derivatives, photoluminescence, quantum yield

Procedia PDF Downloads 329

Authors: M. Hadji, A. Haddad, Y. Hadji

Abstract:

The effects of boronizing treatment on the friction coefficient and wear behavior of 0.35 Vf TiC- Ti3 SiC2 composite were investigated. In order to modity the surface properties of Ti3SiC2, boronizing treatment was carried out through powder pack cementation in the 1150-1350 °C temperature range. After boronizing treatment, one mixture layer, composed of TiB2 and SiC, forms on the surface of Ti3SiC2. The growth of the coating is processed by inward diffusion of Boron and obeys a linear rule. The Boronizing treatment increases the hardness of Ti3SiC2 from 6 GPa to 13 GPa. In the pin-on-disc test, i twas found that the material undergoes a steady-state coefficient of friction of around 0.8 and 0.45 in case of Ti3SiC2/Al2O3 tribocouple under 7N load for the non treated and the boronized samples, respectively. The wear resistance of Ti3SiC2 underAl2O3 ball sliding has been significantly improved, which indicated that the boronizing treatment is a promising surface modification way of Ti3SiC2.

Keywords: MAX phase, wearing, friction, boronizing

Procedia PDF Downloads 457

Authors: Ava Faridi, Pouya Faridi, Aleksandr Kakinen, Ibrahim Javed, Thomas P. Davis, Pu Chun Ke

Abstract:

Human islet amyloid polypeptide (IAPP) is a hormone associated with glycemic control and type 2 diabetes. Biophysically, the chirality of IAPP fibrils has been little explored with respect to the aggregation and toxicity of the peptide. Biochemically, it remains unclear as for how protein expression in pancreatic beta cells may be altered by cell exposure to the peptide, and how such changes may be mitigated by nanoparticle inhibitors for IAPP aggregation. In this study, we first demonstrated the elimination of the IAPP nucleation phase and shortening of its elongation phase by silica nanoribbons. This accelerated IAPP fibrillization translated to reduced toxicity, especially for the right-handed silica nanoribbons, as revealed by cell viability, helium ion microscopy, as well as zebrafish embryo survival, developmental and behavioral assays. We then examined the proteomes of βTC6 pancreatic beta cells exposed to the three main aggregation states of monomeric, oligomeric and amyloid fibrillar IAPP, and compared that with cellular protein expression modulated by graphene quantum dots (GQDs). A total of 29 proteins were significantly regulated by different forms of IAPP, and the majority of these proteins were nucleotide-binding proteins. A regulatory capacity of GQDs against aberrant protein expression was confirmed. These studies have demonstrated the great potential of employing nanomaterials targeting the mesoscopic enantioselectivity and protein expression dysregulation in pancreatic beta cells.

Keywords: graphene quantum dots, IAPP, silica nanoribbons, protein expression, toxicity

Procedia PDF Downloads 142

Authors: Nisha Deopa, A. S. Rao

Abstract:

Lithium Lead Alumino Borate (LiPbAlB) glasses doped with different Dy3+ ions concentration were synthesized to investigate their viability in solid state lighting (SSL) technology by melt quenching techniques. From the absorption spectra, bonding parameters (ð) were investigated to study the nature of bonding between Dy3+ ions and its surrounding ligands. Judd-Ofelt (J-O) intensity parameters (Ω = 2, 4, 6), estimated from the experimental oscillator strengths (fex) of the absorption spectral features were used to evaluate the radiative parameters of different transition levels. From the decay curves, experimental lifetime (τex) were measured and coupled with the radiative lifetime to evaluate the quantum efficiency of the as-prepared glasses. As Dy3+ ions concentration increases, decay profile changes from exponential to non-exponential through energy transfer mechanism (ETM) in turn decreasing experimental lifetime. In order to investigate the nature of ETM, non-exponential decay curves were fitted to Inkuti–Hirayama (I-H) model which further confirms dipole-dipole interaction. Among all the emission transition, 4F9/2  6H15/2 transition (483 nm) is best suitable for lasing potentialities. By exciting titled glasses in n-UV to blue regions, CIE chromaticity coordinates and Correlated Color Temperature (CCT) were calculated to understand their capability in cool white light generation. From the evaluated radiative parameters, CIE co-ordinates, quantum efficiency and confocal images it was observed that glass B (0.5 mol%) is a potential candidate for developing w-LEDs and lasers.

Keywords: energy transfer, glasses, J-O parameters, photoluminescence

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Authors: Young-Hun Lee, Tae-Gwan Kim, Jong-Kyu Kim, Young-Chul Park

Abstract:

In this study, Spring safety valve Heat - structure coupled analysis was carried out. Full analysis procedure and performing thermal analysis at a maximum temperature, them to the results obtained through to give an additional load and the pressure on the valve interior, and Disc holder Heat-Coupled structure Analysis was carried out. Modeled using a 3D design program Solidworks, For the modeling of the safety valve was used 3D finite element analysis program ANSYS. The final result to be obtained through the Analysis examined the stability of the maximum displacement and the maximum stress to the valve internal components occurring in the high-pressure conditions.

Keywords: finite element method, spring safety valve, gap, stress, strain, deformation

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Authors: Ridvan Yamanoglu, Ismail Daoud

Abstract:

In the current study, carbonyl nickel powders were sintered by uniaxial hot pressing technique. Loose starting powders were poured directly into a graphite die with a 15.4 mm inner diameter. Two graphite punches with an outer diameter of 15 mm were inserted into the die; then the powders were sintered at different sintering temperatures, holding times and pressure conditions. The sintered samples were polished and examined by optical microscopy. Hardness and bending behavior of the sintered samples were investigated in order to determine the mechanical properties of the sintered nickel samples. To carried out the friction properties of the produced samples wear tests were studied using a pin on disc tribometer. Load and distance were selected as wear test parameters. The fracture surface of the samples after bending test was also carried out by using scanning electron microscopy.

Keywords: nickel powder, sintering, hot press, mechanical properties

Procedia PDF Downloads 168

Authors: R. Pravin Kumar, L. Roopa

Abstract:

Enzymes are molecular machines used in various industries such as pharmaceuticals, cosmetics, food and animal feed, paper and leather processing, biofuel, and etc. Nevertheless, this has been possible only by the breath-taking efforts of the chemists and biologists to evolve/engineer these mysterious biomolecules to work the needful. Main agenda of this enzyme engineering project is to derive screening and selection tools to obtain focused libraries of enzyme variants with desired qualities. The methodologies for this research include the well-established directed evolution, rational redesign and relatively less established yet much faster and accurate insilico methods. This concept was initiated as a Receptor Rependent-4Dimensional Quantitative Structure Activity Relationship (RD-4D-QSAR) to predict kinetic properties of enzymes and extended here to study transaminase by a 7D QSAR approach. Induced-fit scenarios were explored using Quantum Mechanics/Molecular Mechanics (QM/MM) simulations which were then placed in a grid that stores interactions energies derived from QM parameters (QMgrid). In this study, the mutated enzymes were immersed completely inside the QMgrid and this was combined with solvation models to predict descriptors. After statistical screening of descriptors, QSAR models showed > 90% specificity and > 85% sensitivity towards the experimental activity. Mapping descriptors on the enzyme structure revealed hotspots important to enhance the enantioselectivity of the enzyme.

Keywords: QMgrid, QM/MM simulations, RD-4D-QSAR, transaminase

Procedia PDF Downloads 137

Authors: George Mahalu

Abstract:

The Chua diode has been configured over time in various ways, using electronic structures like operational amplifiers (AOs) or devices with gas or semiconductors. When discussing the use of semiconductor devices, tunnel diodes (Esaki diodes) are most often considered, and more recently, transistorized configurations such as lambda diodes. The paperwork proposed here uses in the modeling a lambda diode type configuration consisting of two junction field effect transistors (JFET). The original scheme is created in the MULTISIM electronic simulation environment and is analyzed in order to identify the conditions for the appearance of evolutionary unpredictability specific to nonlinear dynamic systems with chaos-induced behavior. The chaotic deterministic oscillator is one autonomous type, a fact that places it in the class of Chua’s type oscillators, the only significant and most important difference being the presence of a nonlinear device like the one mentioned structure above. The chaotic behavior is identified both by means of strange attractor-type trajectories and visible during the simulation and by highlighting the hypersensitivity of the system to small variations of one of the input parameters. The results obtained through simulation and the conclusions drawn are useful in the further research of ways to implement such constructive electronic solutions in theoretical and practical applications related to modern small signal amplification structures, to systems for encoding and decoding messages through various modern ways of communication, as well as new structures that can be imagined both in modern neural networks and in those for the physical implementation of some requirements imposed by current research with the aim of obtaining practically usable solutions in quantum computing and quantum computers.

Keywords: chua, diode, memristor, chaos

Procedia PDF Downloads 88

Authors: Vasu Velagapudi, G. Suresh

Abstract:

PTFE/HNTs nanocomposites are fabricated with 4%, 6%, and 8% by weight fraction, and the optimization study of wear parameters are performed using response surface methodology (RSM). The experiments are carried out on a pin on disc (POD) wear tester under different operating parameters planned according to Taguchi L27 orthogonal array. The input factors considered are wt% HNTs addition, sliding velocity, load, and distance with three levels for each factor. From ANOVA: The factors load, speed and distance and their interactions have a significant effect on COF. Also for SWR, composition factor and interaction of load and speed are observed to be significant ( < 0.05) Optimum input parameters corresponding to desirability 1 are found to be: COF (0.11) and SWR (17.5)×10⁻⁶ (mm3/N-m) at 6.34 wt% of composition, 5N of load, 2 km of distance and 1 m/sec of velocity.

Keywords: PTFE/HNT, nanocomposites, response surface methodology (RSM), specific wear rate

Procedia PDF Downloads 395

Authors: Sayyed Mostafa Ahmadi, Neda Raeesi

Abstract:

Background and Objectives: Cervical spondylosis is a common problem that affects the adult spine and is the most common cause of radiculopathy and myelopathy in older patients. Anterior discectomy and fusion is a well-known technique in degenerative cervical disc disease. However, one of the late undesirable complications is adjacent disc degeneration, which affects about 91% of patients in ten years. Many factors can be effective in causing this complication, but some are still debatable. Discovering these risk factors and eliminating them can improve the quality of life. Methods: This is a retrospective cohort study. All patients who underwent anterior discectomy and fusion surgery in the neurosurgery ward of Imam Khomeini Hospital between 2013 and 2016 were evaluated. Their demographic information was collected. All patients were visited and examined for radiculopathy, myelopathy, and muscular force. At the same visit, all patients were asked to have a facelift, and neck profile, as well as a neck MRI(General Tesla 3). Preoperative graphs were used to measure the diameter of the cervical canal(Pavlov ratio) and to evaluate sagittal alignment(Cobb Angle). Preoperative MRI of patients was reviewed for anterior and posterior longitudinal ligament calcification. Result: In this study, 57 patients were studied. The mean age of patients was 50.63 years, and 49.1% were male. Only 3.5% of patients had anterior and posterior longitudinal ligament calcification. Symptomatic ASD was observed in 26.6%. The X-rays and MRIs showed evidence of 80.7% radiological ASD. Among patients who underwent one-level surgery, 20% had symptomatic ASD, but among patients who underwent two-level surgery, the rate of ASD was 50%.In other words, the higher the number of surfaces that are operated and fused, the higher the probability of symptomatic ASD(P-value <0.05). The X-rays and MRIs showed 80.7% of radiological ASD. Among patients who underwent surgery at one level, 78% had radiological ASD, and this number was 92% among patients who underwent two-level surgery(P-value> 0.05). Demographic variables such as age, sex, height, weight, and BMI did not have a significant effect on the incidence of radiological ASD(P-value> 0.05), but sex and height were two influential factors on symptomatic ASD(P-value <0.05). Other related variables such as family history, smoking and exercise also have no significant effect(P-value> 0.05). Radiographic variables such as Pavlov ratio and sagittal alignment were also unaffected by the incidence of radiological and symptomatic ASD(P-value> 0.05). The number of surgical surfaces and the incidence of anterior and posterior longitudinal ligament calcification before surgery also had no statistically significant effect(P-value> 0.05). In the study of the ability of the neck to move in different directions, none of these variables are statistically significant in the two groups with radiological and symptomatic ASD and the non-affected group(P-value> 0.05). Conclusion: According to the findings of this study, this disease is considered to be a multifactorial disease. The incidence of radiological ASD is much higher than symptomatic ASD (80.7% vs. 26.3%) and sex, height and number of fused surfaces are the only factors influencing the incidence of symptomatic ASD and no variable influences radiological ASD.

Keywords: risk factors, anterior neck disectomy and fusion, adjucent segment degeneration, complication

Procedia PDF Downloads 60

Authors: Tulin Coskun

Abstract:

We investigate the approximation of analytic functions of several variables in polydisc by the sequences of linear k-positive operators in Gadjiev sence. The approximation of analytic functions of complex variable by linear k-positive operators was tackled, and k-positive operators and formulated theorems of Korovkin's type for these operators in the space of analytic functions on the unit disc were introduced in the past. Recently, very general results on convergence of the sequences of linear k-positive operators on a simply connected bounded domain within the space of analytic functions were proved. In this presentation, we extend some of these results to the approximation of analytic functions of several complex variables by sequences of linear k-positive operators.

Keywords: analytic functions, approximation of analytic functions, Linear k-positive operators, Korovkin type theorems

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Authors: Ahmed E. Al-Sabri, Mohamed A. Moslem, Sarfaraz Hadi

Abstract:

To avoid the harmful effects of the chemical fungicides on the human and minimize the environmental pollution, an alternative eco-friendly control strategies should be developed. The extract of Commiphora myhrra L. was tested against twenty fungal genera isolated from the indoor air collected from different rooms in King Saud University, Kingdom of Saudi Arabia. Disc diffusion test was modified for use in this study and the collected data was statistically analyzed. Variable antifungal efficacy of different myrrh extract was recorded against the investigated fungal genera. The efficacy of the extract was increased as the concentration increased. The highest growth inhibition (74.6%) was against Acremonium strictum followed by Trichoderma psuedokoningii (70.6%). On contrast, the lowest efficacy (12.7%) was against Ulocladium consortiale. It could be concluded that myrrh extract is promised as a source of substances from which of safer and eco-friendly could be used as antimicrobial agents against a number of pathogenic fungi.

Keywords: antifungal, myrrh, antimicrobial, medicinal plant

Procedia PDF Downloads 419

Authors: George Mahalu

Abstract:

The Chua diode has been configured over time in various ways, using electronic structures like as operational amplifiers (OAs) or devices with gas or semiconductors. When discussing the use of semiconductor devices, tunnel diodes (Esaki diodes) are most often considered, and more recently, transistorized configurations such as lambda diodes. The paper-work proposed here uses in the modeling a lambda diode type configuration consisting of two Junction Field Effect Transistors (JFET). The original scheme is created in the MULTISIM electronic simulation environment and is analyzed in order to identify the conditions for the appearance of evolutionary unpredictability specific to nonlinear dynamic systems with chaos-induced behavior. The chaotic deterministic oscillator is one autonomous type, a fact that places it in the class of Chua’s type oscillators, the only significant and most important difference being the presence of a nonlinear device like the one mentioned structure above. The chaotic behavior is identified both by means of strange attractor-type trajectories and visible during the simulation and by highlighting the hypersensitivity of the system to small variations of one of the input parameters. The results obtained through simulation and the conclusions drawn are useful in the further research of ways to implement such constructive electronic solutions in theoretical and practical applications related to modern small signal amplification structures, to systems for encoding and decoding messages through various modern ways of communication, as well as new structures that can be imagined both in modern neural networks and in those for the physical implementation of some requirements imposed by current research with the aim of obtaining practically usable solutions in quantum computing and quantum computers.

Keywords: chaos, lambda diode, strange attractor, nonlinear system

Procedia PDF Downloads 86

Authors: Ali Kurşun, Emre Kara, Erhan Çetin, Şafak Aksoy, Ahmet Kesimli

Abstract:

In this study, thermal elastic stress distribution occurred on long hollow cylinders made of functionally graded material (FGM) was analytically defined under thermal, mechanical and thermo mechanical loads. In closed form solutions for elastic stresses and displacements are obtained analytically by using the infinitesimal deformation theory of elasticity. It was assumed that elasticity modulus, thermal expansion coefficient and density of cylinder materials could change in terms of an exponential function as for that Poisson’s ratio was constant. A gradient parameter n is chosen between - 1 and 1. When n equals to zero, the disc becomes isotropic. Circumferential, radial and longitudinal stresses in the FGMs cylinders are depicted in the figures. As a result, the gradient parameters have great effects on the stress systems of FGMs cylinders.

Keywords: functionally graded materials, thermoelasticity, thermomechanical load, hollow cylinder.

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Authors: Omar Concepcion, Osvaldo De Melo, Arturo Escobosa

Abstract:

Topological insulator (TI) materials are insulating in the bulk and conducting in the surface. The unique electronic properties associated with these surface states make them strong candidates for exploring innovative quantum phenomena and as practical applications for quantum computing, spintronic and nanodevices. Many materials, including Bi₂Te₃, have been proposed as TIs and, in some cases, it has been demonstrated experimentally by angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STM) and/or magnetotransport measurements. A clean surface is necessary in order to make any of this measurements. Several techniques have been used to produce films and different kinds of nanostructures. Growth and characterization in situ is usually the best option although cleaving the films can be an alternative to have a suitable surface. In the present work, we report a comparison of Bi₂Te₃ grown by physical vapor transport (PVT) and molecular beam epitaxy (MBE). The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ARPES. The Bi₂Te₃ samples grown by PVT, were cleaved in the ultra-high vacuum in order to obtain a surface free of contaminants. In both cases, the XRD shows a c-axis orientation and the pole diagrams proved the epitaxial relationship between film and substrate. The ARPES image shows the linear dispersion characteristic of the surface states of the TI materials. The samples grown by PVT, a relatively simple and cost-effective technique shows the same high quality and TI properties than the grown by MBE.

Keywords: Bismuth telluride, molecular beam epitaxy, physical vapor transport, topological insulator

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Authors: Nougrara Zineb

Abstract:

The unique structure of the blood vessels in the retina has been used for biometric identification. The retina blood vessel pattern is a unique pattern in each individual and it is almost impossible to forge that pattern in a false individual. The retina biometrics’ advantages include high distinctiveness, universality, and stability overtime of the blood vessel pattern. Once the creases have been extracted from the images, a registration stage is necessary, since the position of the retinal vessel structure could change between acquisitions due to the movements of the eye. Image registration consists of following steps: Feature detection, feature matching, transform model estimation and image resembling and transformation. In this paper, we present an algorithm of registration; it is based on the characterization of retinal feature points. For experiments, retinal images from the DRIVE database have been tested. The proposed methodology achieves good results for registration in general.

Keywords: fovea, optic disc, registration, retinal images

Procedia PDF Downloads 266

Authors: Sofia Lazareva, Artem Smolentsev

Abstract:

Fluorescent photochromic materials collect strong interest due to their possible application in organic photonics such as optical logic systems, optical memory, visualizing sensors, as well as characterization of polymers and biological systems. In photochromic fluorescence switching systems the emission of fluorophore is modulated between ‘on’ and ‘off’ via the photoisomerization of photochromic moieties resulting in effective resonance energy transfer (FRET). In current work, we have studied both photochromic and fluorescent properties of several diarylethenes. It was found that coloured forms of these compounds are not fluorescent because of the efficient intramolecular energy transfer. Spectral and photochromic parameters of investigated substances have been measured in five solvents having different polarity. Quantum yields of photochromic transformation A↔B ΦA→B and ΦB→A as well as B isomer extinction coefficients were determined by kinetic method. It was found that the photocyclization reaction quantum yield of all compounds decreases with the increase of solvent polarity. In addition, the solvent polarity is revealed to affect fluorescence significantly. Increasing of the solvent dielectric constant was found to result in a strong shift of emission band position from 450 nm (nhexane) to 550 nm (DMSO and ethanol) for all three compounds. Moreover, the emission intensive in polar solvents becomes weak and hardly detectable in n-hexane. The only one exception in the described dependence is abnormally low fluorescence quantum yield in ethanol presumably caused by the loss of electron-donating properties of nitrogen atom due to the protonation. An effect of the protonation was also confirmed by the addition of concentrated HCl in solution resulting in a complete disappearance of the fluorescent band. Excited state dynamics were investigated by ultrafast optical spectroscopy methods. Kinetic curves of excited states absorption and fluorescence decays were measured. Lifetimes of transient states were calculated from the data measured. The mechanism of ring opening reaction was found to be polarity dependent. Comparative analysis of kinetics measured in acetonitrile and hexane reveals differences in relaxation dynamics after the laser pulse. The most important fact is the presence of two decay processes in acetonitrile, whereas only one is present in hexane. This fact supports an assumption made on the basis of steady-state preliminary experiments that in polar solvents occur stabilization of TICT state. Thus, results achieved prove the hypothesis of two channel mechanism of energy relaxation of compounds studied.

Keywords: diarylethenes, fluorescence switching, FRET, photochromism, TICT state

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Authors: Beatriz Muñiz Cano, J. Ripoll Sau, D. Pacile, P. M. Sheverdyaeva, P. Moras, J. Camarero, R. Miranda, M. Garnica, M. A. Valbuena

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Graphene, in its pristine state, is a semiconductor with a zero band gap and massless Dirac fermions carriers, which conducts electrons like a metal. Nevertheless, the absence of a bandgap makes it impossible to control the material’s electrons, something that is essential to perform on-off switching operations in transistors. Therefore, it is necessary to generate a finite gap in the energy dispersion at the Dirac point. Intense research has been developed to engineer band gaps while preserving the exceptional properties of graphene, and different strategies have been proposed, among them, quantum confinement of 1D nanoribbons or the introduction of super periodic potential in graphene. Besides, in the context of developing new 2D materials and Van der Waals heterostructures, with new exciting emerging properties, as 2D transition metal chalcogenides monolayers, it is fundamental to know any possible interaction between chalcogenide atoms and graphene-supporting substrates. In this work, we report on a combined Scanning Tunneling Microscopy (STM), Low Energy Electron Diffraction (LEED), and Angle-Resolved Photoemission Spectroscopy (ARPES) study on a new superstructure when Te is evaporated (and intercalated) onto graphene over Ir(111). This new superstructure leads to the electronic doping of the Dirac cone while the linear dispersion of massless Dirac fermions is preserved. Very interestingly, our ARPES measurements evidence a large band gap (~400 meV) at the Dirac point of graphene Dirac cones below but close to the Fermi level. We have also observed signatures of the Dirac point binding energy being tuned (upwards or downwards) as a function of Te coverage.

Keywords: angle resolved photoemission spectroscopy, ARPES, graphene, spintronics, spin-orbitronics, 2D materials, transition metal dichalcogenides, TMDCs, TMDs, LEED, STM, quantum materials

Procedia PDF Downloads 79

Authors: Sh. Sousani, Z. Shadrokh, M. Hofbauerová, J. Kollár, M. Jergel, P. Nádaždy, M. Omastová, E. Majková

Abstract:

Perovskite quantum dots (PQDs) have the potential to increase the performance of the perovskite solar cell (PSCs). The integration of PQDs into PSCs can extend the absorption range and enhance photon harvesting and device efficiency. In addition, PQDs can stabilize the device structure by passivating surface defects and traps in the perovskite layer and enhance its stability. The integration of PQDs into PSCs is strongly affected by the type of ligands on the surface of PQDs. The ligands affect the charge transport properties of PQDs, as well as the formation of well-defined interfaces and stability of PSCs. In this work, the CsPbBr₃ QDs were synthesized by the conventional hot-injection method using cesium oleate, PbBr₂ and two different ligands, namely oleic acid (OA) oleylamine (OAm) and didodecyldimethylammonium bromide (DDAB). The STEM confirmed regular shape and relatively monodisperse cubic structure with an average size of about 10-14 nm of the prepared CsPbBr₃ QDs. Further, the photoluminescent (PL) properties of the PQDs/perovskite bilayer with the ligand OA, OAm and DDAB were studied. For this purpose, ITO/PQDs as well as ITO/PQDs/MAPI perovskite structures were prepared by spin coating and the effect of the ligand and oxygen plasma treatment was analyzed. The plasma treatment of the PQDs layer could be beneficial for the deposition of the MAPI perovskite layer and the formation of a well-defined PQDs/MAPI interface. The absorption edge in UV-Vis absorption spectra for OA, OAm CsPbBr₃ QDs is placed around 513 nm (the band gap 2.38 eV); for DDAB CsPbBr₃ QDs, it is located at 490 nm (the band gap 2.33 eV). The photoluminescence (PL) spectra of CsPbBr₃ QDs show two peaks located around 514 nm (503 nm) and 718 nm (708 nm) for OA, OAm (DDAB). The peak around 500 nm corresponds to the PL of PQDs, and the peak close to 710 nm belongs to the surface states of PQDs for both types of ligands. These surface states are strongly affected by the O₃ plasma treatment. For PQDs with DDAB ligand, the O₃ exposure (5, 10, 15 s) results in the blue shift of the PQDs peak and a non-monotonous change of the amplitude of the surface states' peak. For OA, OAm ligand, the O₃ exposition did not cause any shift of the PQDs peak, and the intensity of the PL peak related to the surface states is lower by one order of magnitude in comparison with DDAB, being affected by O₃ plasma treatment. The PL results indicate the possibility of tuning the position of the PL maximum by the ligand of the PQDs. Similar behavior of the PQDs layer was observed for the ITO/QDs/MAPI samples, where an additional strong PL peak at 770 nm coming from the perovskite layer was observed; for the sample with PQDs with DDAB ligands, a small blue shift of the perovskite PL maximum was observed independently of the plasma treatment. These results suggest the possibility of affecting the PL maximum position and the surface states of the PQDs by the combination of a suitable ligand and the O₃ plasma treatment.

Keywords: perovskite quantum dots, photoluminescence, O₃ plasma., Perovskite Solar Cells

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Authors: Sh. Sousani, Z. Shadrokh, M. Hofbauerová, J. Kollár, M. Jergel, P. Nádaždy, M. Omastová, E. Majková

Abstract:

Perovskite quantum dots (PQDs) have the potential to increase the performance of the perovskite solar cells (PSCs). The integration of PQDs into PSCs can extend the absorption range and enhance photon harvesting and device efficiency. In addition, PQDs can stabilize the device structure by passivating surface defects and traps in the perovskite layer and enhance its stability. The integration of PQDs into PSCs is strongly affected by the type of ligands on the surface of PQDs. The ligands affect the charge transport properties of PQDs, as well as the formation of well-defined interfaces and stability of PSCs. In this work, the CsPbBr₃ QDs were synthesized by the conventional hot-injection method using cesium oleate, PbBr₂, and two different ligands, namely oleic acid (OA)@oleylamine (OAm) and didodecyldimethylammonium bromide (DDAB). The STEM confirmed regular shape and relatively monodisperse cubic structure with an average size of about 10-14 nm of the prepared CsPbBr₃ QDs. Further, the photoluminescent (PL) properties of the PQDs/perovskite bilayer with the ligand OA@OAm and DDAB were studied. For this purpose, ITO/PQDs, as well as ITO/PQDs/MAPI perovskite structures, were prepared by spin coating, and the effect of the ligand and oxygen plasma treatment was analysed. The plasma treatment of the PQDs layer could be beneficial for the deposition of the MAPI perovskite layer and the formation of a well-defined PQDs/MAPI interface. The absorption edge in UV-Vis absorption spectra for OA@OAm CsPbBr₃ QDs is placed around 513 nm (the band gap 2.38 eV); for DDAB CsPbBr₃ QDs, it is located at 490 nm (the band gap 2.33 eV). The photoluminescence (PL) spectra of CsPbBr₃ QDs show two peaks located around 514 nm (503 nm) and 718 nm (708 nm) for OA@OAm (DDAB). The peak around 500 nm corresponds to the PL of PQDs, and the peak close to 710 nm belongs to the surface states of PQDs for both types of ligands. These surface states are strongly affected by the O₃ plasma treatment. For PQDs with DDAB ligand, the O₃ exposure (5, 10, 15 s) results in the blue shift of the PQDs peak and a non-monotonous change of the amplitude of the surface states' peak. For OA@OAm ligand, the O₃ exposition did not cause any shift of the PQDs peak, and the intensity of the PL peak related to the surface states is lower by one order of magnitude in comparison with DDAB, being affected by O₃ plasma treatment. The PL results indicate the possibility of tuning the position of the PL maximum by the ligand of the PQDs. Similar behaviour of the PQDs layer was observed for the ITO/QDs/MAPI samples, where an additional strong PL peak at 770 nm coming from the perovskite layer was observed; for the sample with PQDs with DDAB ligands, a small blue shift of the perovskite PL maximum was observed independently of the plasma treatment. These results suggest the possibility of affecting the PL maximum position and the surface states of the PQDs by the combination of a suitable ligand and the O₃ plasma treatment.

Keywords: perovskite quantum dots, photoluminescence, O₃ plasma., perovskite solar cells

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Authors: Hossein Mostafavi

Abstract:

A diversity of biological activities and pharmaceutical uses have been attributed to gallic acid derivatives such as antibacterial, anticancer, anti inflammatory. A series of gallic acid derivatives were synthesized, and their structure was confirmed by FT-IR, HNMR, CNMR, elemental analysis. In vitro biological activity of compounds was determined against Proteus vulgaris ATCC 7829, Escherichia coli ATCC 25922, as (Gram-negative) bacteria and bacillus cereus ATCC 11778, Staphylococus aureus ATCC 6538 as (Gram-positive) bacteria. Antibacterial susceptibility tests were done by use of the paper disc diffusion method on Mueller Hinton agar (Merck). Chloramiphenicol, Penicilline, Streptomycin and Tetracycline were standard reference antibiotics. The zone of inhibition against bacteria was measured after 24 hours at 37 °C. Compounds 3, 4, 5 were the main antibacterial compounds against Gram-negative bacteria but not Gram-positive.

Keywords: gallic acid derivatives, antibacterial, antibiotics, inhibition

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Authors: David C. Ni

Abstract:

Contemporary models for N-body systems are based on temporal, two-body, and mass point representation of Newtonian mechanics. Other mainstream models include 2D and 3D Ising models based on local neighborhood the lattice structures. In Quantum mechanics, the theories of collective modes are for superconductivity and for the long-range quantum entanglement. However, these models are still mainly for the specific phenomena with a set of designated parameters. We are therefore motivated to develop a new construction directly from the complex-variable N-body systems based on the extended Blaschke functions (EBF), which represent a non-temporal and nonlinear extension of Lorentz transformation on the complex plane – the normalized momentum spaces. A point on the complex plane represents a normalized state of particle momentums observed from a reference frame in the theory of special relativity. There are only two key parameters, normalized momentum and nonlinearity for modelling. An algorithm similar to Jenkins-Traub method is adopted for solving EBF iteratively. Through iteration, the solution sets show a form of σ + i [-t, t], where σ and t are the real numbers, and the [-t, t] shows various distributions, such as 1-peak, 2-peak, and 3-peak etc. distributions and some of them are analog to the canonical distributions. The results of the numerical analysis demonstrate continuum-to-discreteness transitions, evolutional invariance of distributions, phase transitions with conjugate symmetry, etc., which manifest the construction as a potential candidate for the unification of statistics. We hereby classify the observed distributions on the finite convergent domains. Continuous and discrete distributions both exist and are predictable for given partitions in different regions of parameter-pair. We further compare these distributions with canonical distributions and address the impacts on the existing applications.

Keywords: blaschke, lorentz transformation, complex variables, continuous, discrete, canonical, classification

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Authors: S.I.Mukhin, S. Seidov, A. Mukherjee

Abstract:

The Dicke model is a key tool for the description of correlated states of quantum atomic systems, excited by resonant photon absorption and subsequently emitting spontaneous coherent radiation in the superradiant state. The Dicke Hamiltonian (DH) is successfully used for the description of the dynamics of the Josephson Junction (JJ) array in a resonant cavity under applied current. In this work, we have investigated a generalized model, which is described by DH with a frustrating interaction term. This frustrating interaction term is explicitly the infinite coordinated interaction between all the spin half in the system. In this work, we consider an array of N superconducting islands, each divided into two sub-islands by a Josephson Junction, taken in a charged qubit / Cooper Pair Box (CPB) condition. The array is placed inside the resonant cavity. One important aspect of the problem lies in the dynamical nature of the physical observables involved in the system, such as condensed electric field and dipole moment. It is important to understand how these quantities behave with time to define the quantum phase of the system. The Dicke model without frustrating term is solved to find the dynamical solutions of the physical observables in analytic form. We have used Heisenberg’s dynamical equations for the operators and on applying newly developed Rotating Holstein Primakoff (HP) transformation and DH we have arrived at the four coupled nonlinear dynamical differential equations for the momentum and spin component operators. It is possible to solve the system analytically using two-time scales. The analytical solutions are expressed in terms of Jacobi's elliptic functions for the metastable ‘bound luminosity’ dynamic state with the periodic coherent beating of the dipoles that connect the two double degenerate dipolar ordered phases discovered previously. In this work, we have proceeded the analysis with the extended DH with a frustrating interaction term. Inclusion of the frustrating term involves complexity in the system of differential equations and it gets difficult to solve analytically. We have solved semi-classical dynamic equations using the perturbation technique for small values of Josephson energy EJ. Because the Hamiltonian contains parity symmetry, thus phase transition can be found if this symmetry is broken. Introducing spontaneous symmetry breaking term in the DH, we have derived the solutions which show the occurrence of finite condensate, showing quantum phase transition. Our obtained result matches with the existing results in this scientific field.

Keywords: Dicke Model, nonlinear dynamics, perturbation theory, superconductivity

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Authors: Svetlana Chovancova, Frantisek Illek, Jan Winkler

Abstract:

The effect of tillage technology of maize on intensity of weed infestation and weed species composition was observed at experimental field. Maize is grown consecutively since 2001. The experimental site is situated at an altitude of 230 m above sea level in the Czech Republic. Variants of tillage technology are CT: plowing – conventional tillage 0.22 m, MT: loosening – disc tillage on the depth of 0.1 – 0.12 m, NT: direct sowing – without tillage. The evaluation of weed infestation was carried out by numerical method in years 2012 and 2013. Within the monitoring were found 20 various species of weeds. Conventional tillage (CT) primarily supports the occurrence of perennial weeds (Cirsium arvense, Convolvulus arvensis). Late spring species (Chenopodium album, Echinochloa crus-galli) were more frequently noticed on variants of loosening (MT) and direct sowing (NT). Different tillage causes a significant change of weed species spectrum in maize.

Keywords: weeds, maize, tillage, loosening, direct sowing

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Authors: C. Boubechou, A. Bouchoucha, H. Zaidi

Abstract:

The aim of this paper is to study the tribological behavior of a dynamic contact steel-brass couple with electric current. This study looks at a dry contact brass-steel couple where friction and wear are studied in terms of mechanical and electrical parameters. For this reason, a tribometer, pin-rotary disc is used in an atmospheric atmosphere. The test parameters are as follows: the normal load (5-30N), the sliding speed (0.1 to 0.5 m / s) and the electric current (3-10A). The duration of each test is 30 minutes. The experimental results show that these parameters have a significant effect on the tribological behavior of the couple studied. The discussion of results is based on observations, using an optical microscope, MEB and a profilometer, worn surfaces and interface phenomena resulting from the process of sliding contact.

Keywords: brass-steel couple, dry friction, electrical current, morphology, normal load, sliding speeds, wear

Procedia PDF Downloads 266