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291.
Theoretical error rate performance of wireless communication systems are usually determined assuming that the perfect channel
state information (CSI) is available at the receiver. However, in actual practice, the channel gains at the receiver are obtained
via using some channel estimation (CE) techniques. Due to inherent presence of noise, the CE is not perfect resulting in the
performance degradation. In this paper, we evaluate the error rate performance of an uplink multicarrier code-division multiple-access
(MC-CDMA) system, considering different modulation techniques, where CE is performed using pilot symbol assisted (PSA) minimum
mean-square error (MMSE) CE technique. The symbol error rate (SER) analysis of an uplink MC-CDMA system using multiuser detection
techniques, such as MMSE and zero forcing (ZF), is presented under imperfect CE. Simulated results for SER are also shown
to confirm the accuracy of the analytically derived results. 相似文献
292.
Aditya Bakshi Sunanda Gupta Akhil Gupta Sudeep Tanwar Kuei‐Fang Hsiao 《International Journal of Communication Systems》2020,33(12)
In recent years, to solve the problem of face spoofing, momentous work has been done in this field, but still, there is a need for establishing counter measures to the biometric spoofing attacks. Although trained and evaluated on different databases, impressive results have been achieved in existing face anti‐spoofing techniques, but biometric authentication is a very significant problem as imposters are using lots of reconstructed samples or fake synthetic material or structure that can be used for various attack purposes. For the first time, to the best of our knowledge, this paper explains the security for face anti‐spoofing detection using linear discriminant analysis and validates the results by calculating HTER and accuracy on different databases (i.e., REPLAY ATTACK and CASIA). The proposed model, that is, three‐tier face anti‐spoofing detection model (3T‐FASDM), is used for the detection of the fake biometric user and works well for real‐time applications. The proposed methods tested on a set of state‐of‐the‐art anti‐spoofing features for the face mode gives a very low degree of complexity as 26 general image quality measures are applied to differentiate among legitimate and imposter samples. The outcomes obtained from publically available data show that this technique has improved performance and accuracy by analyzing the HTER and machine learning classifiers that are helpful to differentiate among real and fake traits. 相似文献
293.
Clara Nyby Aditya Sood Peter Zalden Alexander J. Gabourie Philipp Muscher Daniel Rhodes Ehren Mannebach Jeff Corbett Apurva Mehta Eric Pop Tony F. Heinz Aaron M. Lindenberg 《Advanced functional materials》2020,30(34)
Understanding the fundamentals of nanoscale heat propagation is crucial for next‐generation electronics. For instance, weak van der Waals bonds of layered materials are known to limit their thermal boundary conductance (TBC), presenting a heat dissipation bottleneck. Here, a new nondestructive method is presented to probe heat transport in nanoscale crystalline materials using time‐resolved X‐ray measurements of photoinduced thermal strain. This technique directly monitors time‐dependent temperature changes in the crystal and the subsequent relaxation across buried interfaces by measuring changes in the c‐axis lattice spacing after optical excitation. Films of five different layered transition metal dichalcogenides MoX2 [X = S, Se, and Te] and WX2 [X = S and Se] as well as graphite and a W‐doped alloy of MoTe2 are investigated. TBC values in the range 10–30 MW m?2 K?1 are found, on c‐plane sapphire substrates at room temperature. In conjunction with molecular dynamics simulations, it is shown that the high thermal resistances are a consequence of weak interfacial van der Waals bonding and low phonon irradiance. This work paves the way for an improved understanding of thermal bottlenecks in emerging 3D heterogeneously integrated technologies. 相似文献
294.
Thinning of 2D and 3D Fractal Antenna Arrays with Bounded and Unbounded Fractal Distribution Functions for Celestial Communications 下载免费PDF全文
Fractal antenna arrays are geometry‐based thinned arrays having multiband applications. The major challenge of these arrays is their large number of elements at higher expansion factors. This article presents the thinning of fractal antenna arrays while maintaining an appropriate balance between the side lobe level and beam width by using various quantized fractal distribution functions. A 2D square fractal antenna array and 3DSierpinski gasket antenna array are considered in this article to validate the proposed distribution functions. Nearly one third of the antenna elements are thinned in each successive iteration except in the case of a one‐count distribution function. The proposed technique can simplify practical implementation and exhibits better performance for various parameters such as the side lobe level, side lobe angle, and half power beam width than fully populated fractal antenna arrays. 相似文献
295.
The Effects of Electronic Impurities and Electron–Hole Recombination Dynamics on Large‐Grain Organic–Inorganic Perovskite Photovoltaic Efficiencies 下载免费PDF全文
Jean‐Christophe Blancon Wanyi Nie Amanda J. Neukirch Gautam Gupta Sergei Tretiak Laurent Cognet Aditya D. Mohite Jared J. Crochet 《Advanced functional materials》2016,26(24):4283-4292
Hybrid organic‐inorganic perovskites have attracted considerable attention after promising developments in energy harvesting and other optoelectronic applications. However, further optimization will require a deeper understanding of the intrinsic photophysics of materials with relevant structural characteristics. Here, the dynamics of photoexcited charge carriers in large‐area grain organic‐inorganic perovskite thin films is investigated via confocal time‐resolved photoluminescence spectroscopy. It is found that the bimolecular recombination of free charges is the dominant decay mechanism at excitation densities relevant for photovoltaic applications. Bimolecular coefficients are found to be on the order of 10?9 cm3 s?1, comparable to typical direct‐gap semiconductors, yet significantly smaller than theoretically expected. It is also demonstrated that there is no degradation in carrier transport in these thin films due to electronic impurities. Suppressed electron–hole recombination and transport that is not limited by deep level defects provide a microscopic model for the superior performance of large‐area grain hybrid perovskites for photovoltaic applications. 相似文献
296.
297.
Hsinhan Tsai Wanyi Nie Jean‐Christophe Blancon Constantinos C. Stoumpos Chan Myae Myae Soe Jinkyoung Yoo Jared Crochet Sergei Tretiak Jacky Even Aditya Sadhanala Giovanni Azzellino Roberto Brenes Pulickel M. Ajayan Vladimir Bulović Samuel D. Stranks Richard H. Friend Mercouri G. Kanatzidis Aditya D. Mohite 《Advanced materials (Deerfield Beach, Fla.)》2018,30(6)
State‐of‐the‐art light‐emitting diodes (LEDs) are made from high‐purity alloys of III–V semiconductors, but high fabrication cost has limited their widespread use for large area solid‐state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase‐pure 2D Ruddlesden–Popper (RP) halide perovskites with a formula (CH3(CH2)3NH3)2(CH3NH3)n?1PbnI3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr?1 cm?2 at 744 nm with an ultralow turn‐on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase‐pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm?2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes. 相似文献
298.
Aditya Mahabhai Vora 《Journal of Materials Science》2007,42(3):935-940
In the present paper, the computation of the phonon dynamics of binary Mg70Zn30 metallic glass is reported using the well-recognized model potential of Gajjar et al. The present study includes the phonon
dispersion curves (PDC), elastic and thermodynamic properties such as longitudinal sound velocity υL, transverse sound velocity υT, Debye temperature θD, isothermal bulk modulus B
T, modulus of rigidity G, Poisson’s ratio σ and Young’s modulus Y and specific heat capacity C
V
of the glass. Three theoretical models given by Hubbard–Beeby (HB), Takeno–Goda (TG) and Bhatia–Singh (BS) are used to compute
the PDC. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F)
and Sarkar et al. (S) are employed for the first time to study the effect of exchange and correlation in the aforesaid properties.
The pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegard’s Law. 相似文献
299.
Min‐Seok Kim Haedong Park Sung Ok Won Aditya Sharma Jimin Kong Hyun S. Park Yun‐Mo Sung Tae Joon Park Myoung‐Woon Moon Kahyun Hur 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(40)
Single‐atom catalysts are heterogeneous catalysts with atomistically dispersed atoms acting as a catalytically active center, and have recently attracted much attention owing to the minimal use of noble metals. However, a scalable and inexpensive support that can stably anchor isolated atoms remains a challenge due to high surface energy. Here, copper‐halide polymer nanowires with sub‐nanometer pores are proposed as a versatile support for single‐atom catalysts. The synthesis of the nanowires is straightforward and completed in a few minutes. Well‐defined sub‐nanometer pores and a large free volume of the nanowires are advantageous over any other support material. The nanowires can anchor various atomistically dispersed metal atoms into the sub‐nanometer pores up to ≈3 at% via a simple solution process, and this value is at least twice as big as previously reported data. The hydrogen evolution reaction activity of ?18.0 A mgPt?1 at ?0.2 V overpotential shows its potential for single‐atom catalysts support. 相似文献
300.
Aditya Kumar Gaurav Sant Cedric Patapy Caterina Gianocca Karen L. Scrivener 《Cement and Concrete Research》2012,42(11):1513-1523
The basic nature of alkali hydroxides (NaOH, KOH) when added to mixing water, increases the pH in proportion to the level of salt addition. For alite (impure tricalcium silicate; MIII-Ca3SiO5) hydration, this pH increase accelerates the rate of hydration and reduces the duration of the induction, acceleration and deceleration regimes. This study evaluates alite hydration in solutions of varying compositions and alkalinities (0.1 M, 0.2 M and 0.5 M NaOH and KOH) in context of their heat release behavior and analysis of the solid/liquid phases. The modeling platform, μic, is used to simulate, describe and discriminate the impact of the pore solution chemistry and reaction product formation parameters on alite hydration (Bishnoi and Scrivener, 2009 [1]). Numerical predictions of the solid and liquid phase compositions and the heat release response show good agreement with experimental determinations. The simulations indicate that the effects up to the end of the induction period follow directly from a change in the pore solution composition under a solution controlled dissolution mechanism, which leads to the faster precipitation of portlandite. The changes in the main heat evolution peak appear to be related to an increase in the nucleation density of C–S–H in alkali hydroxide solutions. Examination under the SEM did not indicate significant difference in C–S–H morphology and composition in the presence of NaOH/KOH. 相似文献