Browsing by Author "Aljihmani L."
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Item Classification of fatigue phases in healthy and diabetic adults using wearable sensor(2020-12-01) Aljihmani L.; Kerdjidj O.; Zhu Y.; Mehta R.K.; Erraguntla M.; Sasangohar F.; Qaraqe K.Fatigue is defined as “a loss of force-generating capacity” in a muscle that can intensify tremor. Tremor quantification can facilitate early detection of fatigue onset so that preventative or corrective controls can be taken to minimize work-related injuries and improve the performance of tasks that require high-levels of accuracy. We focused on developing a system that recognizes and classifies voluntary effort and detects phases of fatigue. The experiment was designed to extract and evaluate hand-tremor data during the performance of both rest and effort tasks. The data were collected from the wrist and finger of the participant’s dominant hand. To investigate tremor, time, frequency domain features were extracted from the accelerometer signal for segments of 45 and 90 samples/window. Analysis using advanced signal processing and machine-learning techniques such as decision tree, k-nearest neighbor, support vector machine, and ensemble classifiers were applied to discover models to classify rest and effort tasks and the phases of fatigue. Evaluation of the classifier’s performance was assessed based on various metrics using 5-fold cross-validation. The recognition of rest and effort tasks using an ensemble classifier based on the random subspace and window length of 45 samples was deemed to be the most accurate (96.1%). The highest accuracy (~98%) that distinguished between early and late fatigue phases was achieved using the same classifier and window length.Item Compositional dependence of the optical properties of vacuum evaporated thin GeSe2-GeTe-PbTe films(2013-01-01) Petkov K.; Tasseva J.; Vassilev V.; Aljihmani L.Chalcogenide glasses from the GeSe2-GeTe-PbTe system were synthesized by taking preliminary prepared GeSe2, GeTe and PbTe in their molecular percentages and melting them in an evacuated quartz ampoule. Thin films were deposited on optical glass substrates BK-7 and Si-wafer substrates by thermal evaporation. Using X-ray microanalysis it was found that the film composition differs to a certain degree from the bulk composition. The changes in the optical properties of thin GeSe2-GeTe-PbTe films were studied as a function of their composition, exposure to light and annealing. It is shown by XRD analysis that the thin films are amorphous up to layers with composition of Ge27Se51Te14Pb8. The optical constants (refractive index, n and absorption coefficient, ), the thickness, d as well as the optical band gap, Eg, depending on the film composition were determined by spectrophotometric measurements in the region 450-2500 nm applying the Swanepoel's envelop method and Tauc's procedure. With the increase of the Te content in the layers, the absorption edge is shifted to the higher wavelengths, the refractive index increases from 2.54 for Ge 31Se66Te3 up to 3.37 for Ge32Se 55Te13 while the optical band gap decreases from 1.86 eV for to 1.30 eV for the same compositions. Similar dependence was observed with the increase of the PbTe content in the layers. After annealing of thin films, the values of n decrease, the optical band gap increases and a shift of the absorption edge to the shorter wavelengths is observed. © 2013 The Authors. Published by Elsevier B.V.Item Crystallization, kinetics and mean bond energy of glasses from the GeSe2-GeTe-SnTe system(2017-01-01) Aljihmani L.Chalcogenide glasses from the GeSe2-GeTe-SnTe system were synthesized by direct synthesis with following quenching in ice cold water. The crystallization temperatures of the as-prepared samples were determined using differential thermal analysis at heating rates of 10, 15, 25 and 36 K/min. Al2O3 and Se were used as reference substances. The standard substances and the investigated sample in quantity of ≈ 0.3 g were placed in crucibles, which are sealed at residual pressure of ~ 1.10-3 Pa. The activation energy of crystallization, as main kinetic parameter characterizing this process, was calculated by the Kissinger and the Augis&Bennett models. The values, obtained by the two independent models, coincide. The basic thermodynamic parameters of the crystallization process (enthalpy and entropy alternation) were defined. The enthalpy alternation of the selenium crystallization was calculated, as its crystallization heat is known. The overall mean bond energy , the mean coordination number , the mean bond energy of the average cross-linking/atom and the average bond energy per atom of the ``remaining matrix`` - Ēc and Ērm, as well as the average heteropolar bond energy Ehb and the degree of, cross-linking/atom`` Pp are calculated. A correlation between the investigated parameters and the glasses' composition was established.Item Features of physiological tremor in diabetic patients(2019-10-01) Aljihmani L.; Abbas H.; Zhu Y.; Mehta R.K.; Sasangohar F.; Erraguntla M.; Lawley M.; Abbasi Q.H.; Qaraqe K.In this paper, we estimate the effect of fatigue on physiological tremors in adults suffering from diabetes. We used a simple, wearable accelerometer to collect the acceleration data from 5 diabetic subjects with varying physical activity levels. Fatigue was induced via an intermittent submaximal isometric handgrip protocol, normalized for individual grip strength, until voluntary exhaustion. The overall results presented here show that the physiologic tremors in the range of 10-14 Hz are most noticeable under fatigue.Item Glass formation in the As2Se3-As2Te 3-Sb2Te3 system(2008-01-01) Hristova-Vasileva T.; Vassilev V.; Aljihmani L.; Boycheva S.Chalcogenide glasses from the As2Se3-As 2Te3-Sb2Te3 system were synthesized for the first time. The glass-forming region was determined by X-ray diffraction and electron microscopic analyses. The basic physicochemical parameters such as density (d), microhardness (HV) and temperatures of phase transformations (glass transition Tg, crystallization Tcr and melting Tm) were measured. Compactness and some thermomechanical characteristics such as volume (Vh) and formation energy (Eh) of micro-voids in the glassy network as well as the elasticity module (E) were calculated. The glassforming ability was evaluated according to Hruby's criteria (K G). The correlation between composition and properties of the (As2Se3)x(As2Te3) y(Sb2Te3)z glasses was established and comprehensively discussed. © 2008 Elsevier Ltd.Item GLASS-FORMATION IN THE As2Se3-GeSe2-ZnTe SYSTEM(2024-01-01) Aljihmani L.; Petrov T.New chalcogenide samples from the As2Se3-GeSe2-ZnTe system are synthesized by melt quenching technique in evacuated to a residual pressure of 1.10-3 Pa quartz ampoules. The specimens from the investigated system are prepared by direct mono-temperature synthesis with conditions conformed to the physico-chemical features of the initial compounds. The state of the bulk samples (glassy, crystalline, glassy + crystalline) is proven by visual, X-ray diffraction, and microscopic analyses. The glass-forming region within the system is outlined using the results of the performed syntheses and analyses. It lies on the As2Se3-GeSe2 side and partially on the As2Se3-ZnTe (from 0 to 5 mol % ZnTe) and GeSe2-ZnTe (from 0 to 15 mol % ZnTe) sides. The maximum solubility of ZnTe in the glasses is 20 mol %. A presence of a crystallizing phase As2ZnGe is registered in the XRD-investigated samples.Item On the existence of terahertz plasmons in two-dimensional semiconductor heterostructures(2019-09-01) Abbas H.T.; Aljihmani L.; Abbasi Q.H.; Qaraqe K.A.Plasmons existing along a semiconductor heterostructure found in a high electron mobility transistor are studied. With the help of the electronic properties of group III-V semiconductor materials, a multilayer structure is described using an equivalent transmission line network. The existence of surface waves is investigated using the transverse resonance method, and it is established that the complex conductivity of the two-dimensional electron gas with a negative imaginary part yields surface plasmons in the terahertz frequency domain.Item Photo- and thermo-induced changes in optical constants and structure of thin films from GeSe2-GeTe-ZnTe system(2013-01-01) Petkov K.; Todorov R.; Vassilev V.; Aljihmani L.We examined the condition of preparation of thin films from GeSe 2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient,α) and thickness, d as well as the optical band gap, E g, depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe2 to 1.26 eV for Ge 34Se42Te24. The values of the refractive index decrease after annealing of all composition and Eg increase, respectively. Thin films with composition of Ge27Se 47Te9Zn17 and Ge28Se 49Te10Zn13 were prepared by co-evaporation of (GeSe2)78(GeTe)22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated. © 2013 The Authors.Item PREPARATION AND PROPERTIES OF BULK AMORPHOUS CHALCOGENIDES OF THE A2Se3 - GeTe - CdTe SYSTEM(2022-01-01) Karadashka I.; Aljihmani L.; Jordanov V.Bulk amorphous chalcogenides from the As2Se3 - GeTe - CdTe system were studied. The alloys were prepared using the method of multi-step direct mono-temperature synthesis and characterized with the help of visual analysis and X-ray powder diffraction (XRD). The region of glass formation was outlined. Some physicochemical properties of the samples as microhardness, density, and characteristic temperatures, were determined. Compactness (C), modulus of elasticity (E), minimal volume of micro-voids (Vh), and energy of their formation (Eh) were calculated. The composition dependence of these parameters was discussed.Item SYNTHESIS AND PHYSICO-CHEMICAL STUDY OF Co, Ni, Cu, AND Sn NANOPARTICLES(2024-01-01) Petrov T.; Aljihmani L.Cobalt, nickel, copper, and tin nanosized particles were synthesized through a borohydride reduction method with a reducing agent of NaBH4. The reductive precipitation was carried out at room temperature and atmospheric pressure. The nanoparticle powders were synthesized from water solutions of sulfate salts. The obtained nanosized particles were investigated by scanning electron microscopy (SEM) and XRD analyses. The SEM micrographs showed the nanoparticles’ morphology and structure. The chemical elements’ distribution was determined by energy dispersive spectroscopy (EDS) analysis. The X-ray diffraction (XRD) analysis determined the phase composition and state (amorphous or crystalline).