Browsing by Author "Kumar, A"
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Item Electronic structure and carrier mobilities of twisted graphene helix(Elsevier, 2020) Thakur, R; Ahluwalia, P.K; Kumar, A; Mohan, B; Sharma, R.Density functional theory based calculations have been carried out to investigate the effect of twisting on electronic band structures and carrier mobilities of three prototypes of armchair graphene nanoribbons (AGNRs) within the fixed boundary conditions. It is found that twisting causes a modification in the bandgap values and the overall shape of band structures. The values of longitudinal acoustic deformation potential (DP) are found to be higher than the torsional acoustic DP values. The torsional strain is also found to have a profound effect on effective mass and mobilities of given AGNRs. The hole mobility of hydrogen passivated N = 8 AGNRs is found to be comparable with the carrier mobility of intrinsic graphene. The electron mobility of N = 8 AGNRs can be further increased with fluorine passivation. The width, passivation, and extent of twisting together determine n-type or p-type behavior of AGNRs. Fluorine passivated AGNRs are predicted to be potential candidates for mechanical and high-frequency switching. Our results suggest that twisting of AGNRs can be an effective mean for tuning their band structure and carrier mobility for applications in high-speed switching devices. 2020 Elsevier B.V.Item Existence of mild solutions for impulsive neutral Hilfer fractional evolution equations(Springer, 2020) Bedi, P; Kumar, A; Abdeljawad, T; Khan, A.In this paper, we investigate the existence of mild solutions for neutral Hilfer fractional evolution equations with noninstantaneous impulsive conditions in a Banach space. We obtain the existence results by applying the theory of resolvent operator functions, Hausdorff measure of noncompactness, and Sadovskii's fixed point theorem. We also present an example to show the validity of obtained results. 2020, The Author(s).Item Face detection techniques: a review(Springer, 2019) Kumar, A; Kaur, Amandeep; Kumar, M.With the marvelous increase in video and image database there is an incredible need of automatic understanding and examination of information by the intelligent systems as manually it is getting to be plainly distant. Face plays a major role in social intercourse for conveying identity and feelings of a person. Human beings have not tremendous ability to identify different faces than machines. So, automatic face detection system plays an important role in face recognition, facial expression recognition, head-pose estimation, human–computer interaction etc. Face detection is a computer technology that determines the location and size of a human face in a digital image. Face detection has been a standout amongst topics in the computer vision literature. This paper presents a comprehensive survey of various techniques explored for face detection in digital images. Different challenges and applications of face detection are also presented in this paper. At the end, different standard databases for face detection are also given with their features. Furthermore, we organize special discussions on the practical aspects towards the development of a robust face detection system and conclude this paper with several promising directions for future research. © 2018, Springer Nature B.V.Item The hazardous 2017-2019 surge and river damming by Shispare Glacier, Karakoram(Nature Research, 2020) Bhambri, R; Watson, C.S; Hewitt, K; Haritashya, U.K; Kargel, J.S; Pratap, Shahi A; Chand, P; Kumar, A; Verma, A; Govil, H.In 2017-2019 a surge of Shispare Glacier, a former tributary of the once larger Hasanabad Glacier (Hunza region), dammed the proglacial river of Muchuhar Glacier, which formed an ice-dammed lake and generated a small Glacial Lake Outburst Flood (GLOF). Surge movement produced the highest recorded Karakoram glacier surface flow rate using feature tracking (~18 ± 0.5 m d−1) and resulted in a glacier frontal advance of 1495 ± 47 m. The surge speed was less than reports of earlier Hasanabad advances during 1892/93 (9.3 km) and 1903 (9.7 km). Surges also occurred in 1973 and 2000-2001. Recent surges and lake evolution are examined using feature tracking in satellite images (1990-2019), DEM differencing (1973-2019), and thermal satellite data (2000-2019). The recent active phase of Shispare surge began in April 2018, showed two surface flow maxima in June 2018 and May 2019, and terminated following a GLOF on 22-23 June 2019. The surge likely had hydrological controls influenced in winter by compromised subglacial flow and low meltwater production. It terminated during summer probably because increased meltwater restored efficient channelized flow. We also identify considerable heterogeneity of movement, including spring/summer accelerations. 2020, The Author(s).Item Ion transport, dielectric, and electrochemical properties of sodium ion-conducting polymer nanocomposite: application in EDLC(Springer, 2020) Kumar, A; Madaan, M; Arya, A; Tanwar, S; Sharma, A.L.The present paper reports the investigation of structural, electrical, dielectric, and transport properties of the polyethylene oxide (PEO)-based polymer nanocomposite (PNC), with sodium hexafluorophosphate (NaPF6) salt and barium titanate (BaTiO3) as nanofillers. The PNC has been prepared via standard solution casting technique. The structural investigation has been investigated by X-ray diffraction and evidence the enhancement in amorphous content. The morphology has been examined by Field emission scanning electron microscopy technique and confirms the composite formation. The presence of polymer-ion and ion-ion interaction has been confirmed by the Fourier transform infrared spectra (FTIR) and evidences the PNC formation. The impedance spectroscopy has been performed to evaluate the ionic conductivity in the temperature range 40–100 °C.The increase of conductivity is obtained with the addition of nanofiller and temperature-dependent conductivity follows Arrhenius behavior. The PNC film having the highest conductivity exhibits low activation energy and indicates the fast ion migration. The ion transference number is close to unity and the voltage stability window is within the desirable limit. The complex permittivity and complex conductivity have been obtained and the plot has been fitted in the whole frequency window. The fitted plot is in perfect agreement with experimental data. The PNC having the highest conductivity has high dielectric strength and low relaxation time. It confirms the nanofiller role in enhancing ion migration. The ion transport parameters (n, ?, D) are also in correlation with impedance and dielectric analysis. The optimized PNC films have been used to prepare the Electric double-layer capacitors (EDLC) and it demonstrates the improved performance which may be attributed to the effective role played by nanofiller in boosting ion dynamics. - 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item Novel phosphorus-based 2D allotropes with ultra-high mobility(Institute of Physics Publishing, 2020) Kaur, S; Kumar, A; Srivastava, S; Tankeshwar, K; Pandey, R.Electronic structure calculations based on density functional theory were performed to investigate structural, mechanical, and electronic properties of phosphorene-based large honeycomb dumbbell (LHD) hybrid structures and a new phosphorene allotrope, referred to as ??-P. The LHD hybrids (i.e., X6P4; X being C or Si or Ge or Sn) and ??-P have significantly higher bandgaps than the corresponding pristine LHD structures, except the case of C6P4, which is metallic. ??-P is found to be a highly flexible p-type material which shows strain-engineered photocatalytic activity in a highly alkaline medium. The carrier mobility of the considered systems is as high as 105 cm2 V-1 s-1 (specifically the electron mobility of LHD structures). The calculated STM images display the surface morphologies of the LHD hybrids and ??-P. The predicted phosphorus-based 2D structures with novel electronic properties may be candidate materials for nanoscale devices. - 2020 IOP Publishing Ltd.Item Pressure and electric field tuning of Schottky contacts in PdSe2/ZT-MoSe2 van der Waals heterostructure(Institute of Physics Publishing, 2020) Jakhar, M; Singh, J; Kumar, A; Tankeshwar, K.A two-dimensional van der Waals (vdW) heterostructure (PdSe2/ZT-MoSe2) has been investigated through vdW corrected density functional theory. ZT-MoSe2 acts as a Dirac material with an anisotropic Dirac cone and variable Fermi velocity (0.52-1.91 105 ms-1). The intrinsic Schottky barrier height can be effectively tuned by applying external pressure and an electric field to the heterostructure. The p-type Schottky barrier transforms into a p-type ohmic contact at pressure P ? 16 GPa. A positive electric field induces p-type ohmic contact while a negative electric field results in the transition from p-type Schottky contact to n-type Schottky contact, and finally to n-type ohmic contact at the higher values of the field. Moreover, the external positive (negative) electric field induces n-type (p-type) doping of ZT-MoSe2 in the heterostructure and remarkably controls the charge carrier concentration. Our results demonstrate that controlling the external pressure and electric field in a PdSe2/ZT-MoSe2 heterostructure can result in an unprecedented opportunity for the design of high-performance nanodevices. � 2020 IOP Publishing Ltd.Item Strain tunable Schottky barriers and tunneling characteristics of borophene/MX2 van der Waals heterostructures(Elsevier, 2020) Katoch, N; Kumar, A; Sharma, R; Ahluwalia, P.K; Kumar, J.Based on first-principle calculations, we report the strain induced changes in electronic properties and their influence on current-voltage (I?V) characteristics of the borophene (?12)/MX2 (M = Mo, W and X = S, Se) vdW heterostructures. The results reveal that the intrinsic electronic nature of borophene and MX2 is retained because of weak van der Waals interactions. However, p-type Schottky contacts are formed at the interface of the heterostructures. Application of the in-plane tensile and compression strains is effective in tuning the Schottky contacts and controlling the SBHs. Also, at the vertical pressure values of 5.46 and 5.25 GPa for ?12/MoS2 and ?12/WS2 respectively, Schottky contact changes from p-type to n-type. The I?V characteristics exhibit an ohmic behavior at low bias ±0.1 v and noticeable NDR on changing positive (negative) biases. Such strain tunable Schottky barriers may be influential in ?12/MX2 based high-performance nano- and optoelectronic devices. - 2020 Elsevier B.V.