arXiv subjects

N. A. Khan

Publications and source records attributed to N. A. Khan.

7 recordsLinked to original sources

arXiv2021

Probing Band-center Anomaly with the Kernel Polynomial Method

We investigate the anomalous behavior of localization length of a non-interacting one-dimensional Anderson model at zero temperature. We report numerical calculations of the Thouless expression of localization length, based on the Kernel polynomial method (KPM), which has an O(N ) computational complexity, where N is the system size. The KPM results show an excellent agreement with perturbative result in large system size limit, confirming the validity of Thouless formula. Thus, contrary to the previous numerical results, the KPM approximation of the Thouless expression produce the correct localization length at the band center. The Thouless expression relates localization length in terms of density of states in a one-dimensional disordered system. By calculating the KPM estimates of density of states, we find a cusp-like behavior around the band center in the perturbative regime. This cusp-like singularity can not be obtained by an approximate analytical calculations with in the second-order approximations, reflects the band-center anomaly.

cond-mat.dis-nn↗

arXiv2021

Quantum speed limit time in relativistic frame

We investigate the roles of the relativistic effect on the speed of evolution of a quantum system coupled with amplitude damping channels. We find that the relativistic effect speed-up the quantum evolution to a uniform evolution speed of open quantum systems for the damping parameter $p_τ\lesssim p_{τ_{c0}}.$ Moreover, we point out a non-monotonic behavior of the quantum speed limit time (QSLT) with acceleration in the damping limit $p_{τ_{c0}}\lesssim p_τ\lesssim p_{τ_{c1}},$ where the relativistic effect first speed-up and then slow down the quantum evolution process of the damped system. For the damping strength $p_{τ_{c1}}\lesssim p_τ$, we observe a monotonic increasing behavior of QSLT, leads to slow down the quantum evolution of the damped system. In addition, we examine the roles of the relativistic effect on the speed limit time for a system coupled with the phase damping channels.

quant-ph↗

arXiv2019

Global Delocalization Transition in the de Moura-Lyra Model

The possibility of having a delocalization transition in the 1D de Moura-Lyra class of models (having a power-spectrum $\propto q^{-α})$ has been the object of a long standing discussion in the literature, filled with ambiguities. In this letter, we report the first numerical evidences that such a transition happens at $α=1$, where the localization length (measured from the scaling of the conductance) is shown to diverge as $(1-α)^{-1}$. The persistent finite-size scaling of the data is shown to be caused by a very slow convergence of the nearest-neighbor correlator to its infinite-size limit, and controlled by the choice of a proper scaling parameter. This last conclusion leads to the re-interpretation of the localization in these models to be caused by an effective Anderson uncorrelated model at small length-scales. Finally, the numerical results are confirmed by analytical perturbative calculations which are built on previous work.

cond-mat.dis-nn↗

arXiv2019

Spectral Functions of One-Dimensional Systems with Correlated Disorder

We investigate the spectral function of Bloch states in an one-dimensional tight-binding non-interacting chain with two different models of static correlated disorder, at zero temperature. We report numerical calculations of the single-particle spectral function based on the Kernel Polynomial Method, which has an $\mathcal{O}(N)$ computational complexity. These results are then confirmed by analytical calculations, where precise conditions were obtained for the appearance of a classical limit in a single-band lattice system. Spatial correlations in the disordered potential give rise to non-perturbative spectral functions shaped as the probability distribution of the random on-site energies, even at low disorder strengths. In the case of disordered potentials with an algebraic power-spectrum, $\propto\left|k\right|^{-α}$, we show that the spectral function is not self-averaging for $α\geq1$.

cond-mat.dis-nn↗

arXiv2015

Role of non-timber forest products in sustaining forest-based livelihoods and rural households' resilience capacity in and around protected area- a Bangladesh study

People in developing world derive a significant part of their livelihoods from various forest products, particularly non-timber forest products. This article attempts to explore the contribution of NTFPs in sustaining forest-based rural livelihood in and around a protected area of Bangladesh, and their potential role in enhancing households resilience capacity. Based on empirical investigation our study revealed that, local communities gather a substantial amount of NTFPs from national park despite the official restrictions. 27 percent households of the area received at least some cash benefit from the collection, processing and selling of NTFPs, and NTFPs contribute as HHs primary, supplementary and emergency sources of income. NTFPs also constituted an estimated 19 percent of HHs net annual income, and were the primary occupation for about 18 percent of the HHs. HHs dependency on nearby forests for various NTFPs varied vis-a-vis their socio-economic condition as well as with their location from the park. Based on our case study the article also offers some clues for improving the situation in PA.

econ.GN↗

arXiv2013

Ubiquitous HealthCare in Wireless Body Area Networks - A Survey

Advances in wireless communication, system on chip and low power sensor nodes allowed realization of Wireless Body Area Network (WBAN). WBAN comprised of tiny sensors, which collect information of patient's vital signs and provide a real time feedback. In addition, WBAN also supports many applications including Ubiquitous HealthCare (UHC), entertainment, gaming, military, etc. UHC is required by elderly people to facilitate them with instant monitoring anywhere they move around. In this paper, different standards used in WBAN were also discussed briefly. Path loss in WBAN and its impact on communication was presented with the help of simulations, which were performed for different models of In-Body communication and different factors (such as, attenuation, frequency, distance etc) influencing path loss in On-Body communications.

cs.NI↗

arXiv2012

Ubiquitous HealthCare in Wireless Body Area Networks

Recent advances in wireless communications, system on chip and low power sensor nodes allow realization of Wireless Body Area Networks (WBANs).WBANs comprise of tiny sensors, which collect information of a patient's vital signs and provide a real time feedback. In addition,WBANs also support many applications including ubiquitous healthcare, entertainment, gaming, military, etc. Ubiquitous healthcare is required by elderly people to facilitate them with instant monitoring anywhere they move around. In this paper, we provide a survey on different architectures used in WBANs for ubiquitous healthcare monitoring. Different standards and devices used in these architectures are also discussed in this paper. Finally, path loss in WBANs and its impact on communication is presented with the help of simulations performed for different models of In-Body communication and different factors (such as, attenuation, frequency, distance etc) influencing path loss in On-Body communications.

cs.NI↗