Nikhil Sharma | Purwanchal University (original) (raw)

Papers by Nikhil Sharma

It is a review article on the topic of energy harvesting.

Procedia Computer Science, 2020

In this paper, we present a framework for channel estimation in long term evolution (LTE) system.... more In this paper, we present a framework for channel estimation in long term evolution (LTE) system. Pilot symbols are spread over the entire time-frequency grid of transmit super frame with consideration of delay-doppler spread of the transmitting medium. At the receiver, we use various interpolation techniques like linear, piece-wise cubic and spline to estimate the channel at non-pilot locations for different antenna configurations. Estimation error is measured using mean squared error (MSE) between the ideal channel and estimated channel for different interpolation techniques. Simulation result shows the channel estimation MSE for single as well as for multiple-input multiple-output (MIMO) link as a function of signal-to-noise ratio.

BMC neurology, Jan 18, 2017

Increasing age is the biggest risk factor for dementia, of which Alzheimer's disease is the c... more Increasing age is the biggest risk factor for dementia, of which Alzheimer's disease is the commonest cause. The pathological changes underpinning Alzheimer's disease are thought to develop at least a decade prior to the onset of symptoms. Molecular positron emission tomography and multi-modal magnetic resonance imaging allow key pathological processes underpinning cognitive impairment - including β-amyloid depostion, vascular disease, network breakdown and atrophy - to be assessed repeatedly and non-invasively. This enables potential determinants of dementia to be delineated earlier, and therefore opens a pre-symptomatic window where intervention may prevent the onset of cognitive symptoms. This paper outlines the clinical, cognitive and imaging protocol of…

Frontiers in neurology, 2015

Stroke is the leading cause of long-term disability. Functional imaging studies report widespread... more Stroke is the leading cause of long-term disability. Functional imaging studies report widespread changes in movement-related cortical networks after stroke. Whether these are a result of stroke-specific cognitive processes or reflect modulation of existing movement-related networks is unknown. Understanding this distinction is critical in establishing more effective restorative therapies after stroke. Using multivariate analysis (tensor-independent component analysis - TICA), we map the neural networks involved during motor imagery (MI) and executed movement (EM) in subcortical stroke patients and age-matched controls. Twenty subcortical stroke patients and 17 age-matched controls were recruited. They were screened for their ability to carry out MI (Chaotic MI Assessment). The fMRI task was a right-hand finger-thumb opposition sequence (auditory-paced 1 Hz; 2, 3, 4, 5, 2…). Two separate runs were acquired (MI and rest and EM and rest; block design). There was no distinction between...

Sensemaking tasks are challenging and typically involve collecting, organizing and understanding ... more Sensemaking tasks are challenging and typically involve collecting, organizing and understanding information. Sensemaking often involves a handoff where a subsequent recipient picks up work done by a provider. Sensemaking handoffs are very challenging because handoffs introduce discontinuity in sensemaking. This dissertation attempts to explore various factors involved in sensemaking handoffs. This work drew on existing literature on sensemaking to propose five sensemaking task attributes: representation novelty required, encoding difficulty, broader applicability, representation search space and subtask interdependence. These attributes capture what makes sensemaking difficult and also help in choosing tasks to study sensemaking as well as modifying laboratory tasks so that they involve more sensemaking. Synthesizing existing literature on collaboration, the dissertation identified important elements in a sensemaking handoff: intent to collaborate, common ground, shared space, awar...

Proceedings of the National Academy of Sciences of the United States of America, Jan 29, 2008

Renal tubule epithelial cells express the insulin receptor (IR); however, their value has not bee... more Renal tubule epithelial cells express the insulin receptor (IR); however, their value has not been firmly established. We generated mice with renal epithelial cell-specific knockout of the IR by Cre-recombinase-loxP recombination using a kidney-specific (Ksp) cadherin promoter. KO mice expressed significantly lower levels of IR mRNA and protein in kidney cortex (49-56% of the WT) and medulla (32-47%) homogenates. Immunofluorescence showed the greatest relative reduction in the thick ascending limb and collecting duct cell types. Body weight, kidney weight, and food and water intakes were not different from WT littermates. However, KO mice had significantly increased basal systolic blood pressure (BP, 15 mm Hg higher) as measured by radiotelemetry. In response to a volume load by gavage (20 ml/kg of body weight, 0.9% NaCl, 15% dextrose), KO mice had impaired natriuresis (37 +/- 10 versus 99 +/- 9 mmol of Na(+) per 2 h in WT). Furthermore, volume load led to a sustained increase in BP...

PloS one, 2014

The increase in older adults over the coming decades will be accompanied by a greater burden of c... more The increase in older adults over the coming decades will be accompanied by a greater burden of chronic neurological diseases affecting the motor system. The motor system adapts to maintain motor performance with the primary motor cortex (BA4) emerging as a pivotal node within this neuroplastic process. Studies of ageing often consider BA4 a homogenous area but cytoarchitectonic studies have revealed two subdivisions, an anterior (BA4a) and posterior subdivision (BA4p). Here we focus upon the effects of ageing on the involvement of BA4a and BA4p during movement and motor imagery (MI). Thirty-one right-handed healthy volunteers were recruited and screened for their ability to perform imagery (5 subjects excluded). The sample was split into an older group (n = 13, mean age 56.4 SD 9.4) and a younger group (n = 13, mean age 27.4 SD 5.3). We used an fMRI block-design (auditory-paced [1 Hz] right hand finger-thumb opposition sequence [2,3,4,5, 2...]) with MI & rest and actual movement & ...

Neurological Rehabilitation, 2013

The idea that the cerebral cortex is dynamically organized was proposed in 1912, when Brown and S... more The idea that the cerebral cortex is dynamically organized was proposed in 1912, when Brown and Sherrington stimulated the motor cortex of chimpanzees and found that "a point which began by yielding primary extension may come to yield primary flexion in the latter part of the stimulation series" (Brown and Sherrington, 1912). In many investigations since then these phenomena have been referred to as neural plasticity. Neural plasticity can be defined as the ability of the central nervous system (CNS) to adapt in response to changes in the environment or lesions. This property of the CNS may involve modifications in overall cognitive strategies to successfully cope with new challenges (i.e., attention, behavioral compensation) (Bury and Jones, 2002), recruitment of new/different neural networks (Johansen-Berg et al., 2002; Fridman et al., 2004; Lotze et al., 2006; Heuninckx et al., 2008), or changes in strength of such connections or specific brain areas in charge of carrying out a particular task (i.e., movement, language, vision, hearing) (Cohen et al., 1997; Grefkes et al., 2008). At the cellular level, changes in membrane excitability, synaptic plasticity, as well as structural changes in dendritic and axonal anatomy as measured in vivo and in vitro may be demonstrated in animals and humans (Clarkson et al., 2010; Li et al.,

Proceedings of the American Society for Information Science and Technology, 2009

Computer support helpdesks often engage in sensemaking while working on atypical problems. Handof... more Computer support helpdesks often engage in sensemaking while working on atypical problems. Handoffs are common in these sensemaking situations due to shift changes, because a different skill or perspective is needed or simply because the current sensemaker may be exhausted. Though handoff may be needed, it may not always be successful. This could be true because sensemaking involves non-routine activities for which no structural support for handoff may exist, or because sensemakers may not be sure what to handoff if sensemaking is not complete. This study examined the issues related to sensemaking handoff in computer support helpdesks. Existing theories of sensemaking (Russell et al, 1993 and Weick, 1996) were used as a framework. Semi-structured interviews were conducted with two different computer helpdesk personnel groups at a large mid-western university. Successful handoffs occurred either very early or very late in the sensemaking process. This choice of handoff time as well as other aspects of handoffs are discussed using the principles of least collaborative effort [13] and mindfulness [18].

Frontiers in Human Neuroscience, 2013

Motor imagery (MI) is the mental rehearsal of a motor first person action-representation. There i... more Motor imagery (MI) is the mental rehearsal of a motor first person action-representation. There is interest in using MI to access the motor network after stroke. Conventional fMRI modeling has shown that MI and executed movement (EM) activate similar cortical areas but it remains unknown whether they share cortical networks. Proving this is central to using MI to access the motor network and as a form of motor training. Here we use multivariate analysis (tensor independent component analysis-TICA) to map the array of neural networks involved during MI and EM. Methods: Fifteen right-handed healthy volunteers (mean-age 28.4 years) were recruited and screened for their ability to carry out MI (Chaotic MI Assessment). fMRI consisted of an auditory-paced (1 Hz) right hand finger-thumb opposition sequence (2,3,4,5; 2.. .) with two separate runs acquired (MI & rest and EM & rest: block design). No distinction was made between MI and EM until the final stage of processing. This allowed TICA to identify independent-components (IC) that are common or distinct to both tasks with no prior assumptions. Results: TICA defined 52 ICs. Non-significant ICs and those representing artifact were excluded. Components in which the subject scores were significantly different to zero (for either EM or MI) were included. Seven IC remained. There were IC's shared between EM and MI involving the contralateral BA4, PMd, parietal areas and SMA. IC's exclusive to EM involved the contralateral BA4, S1 and ipsilateral cerebellum whereas the IC related exclusively to MI involved ipsilateral BA4 and PMd. Conclusion: In addition to networks specific to each task indicating a degree of independence, we formally demonstrate here for the first time that MI and EM share cortical networks. This significantly strengthens the rationale for using MI to access the motor networks, but the results also highlight important differences.

Imaging in Medicine, 2012

There is considerable interest in using motor imagery to improve recovery after stroke. While mot... more There is considerable interest in using motor imagery to improve recovery after stroke. While motor imagery has a strong neuroscientific rationale, there are significant obstacles to its use and gaps in our knowledge that need to be addressed. Together these may explain the inconsistent results seen in recent randomized placebo-controlled trials of motor imagery training in stroke patients. The first section of this article discusses why assessment of motor imagery ability is crucial when applying motor imagery to stroke patients. Then in the context of current models of recovery after stroke, the second section highlights gaps in the neuroscientific rationale behind the use of motor imagery training. The third section explores the recent randomized trials of motor imagery training in stroke patients and discusses why the findings are inconsistent. Finally, I propose future areas of research that may prove fruitful and will allow motor imagery to fulfill its potential.

Proceedings of the American Society for Information Science and Technology, 2008

Web 2.0 has allowed online shoppers to become not just information seekers but also information p... more Web 2.0 has allowed online shoppers to become not just information seekers but also information providers. Many e-commerce venues allow users to share their experiences in the form of textual product reviews. While textual product reviews represent a wealth of information for candidate buyers, finding pertinent information becomes difficult, as the number of reviews for a particular product becomes large, or if the buyer is interested in particular features of an item. We present ChatterCrop, a tool that uses text summarization. ChatterCrop condenses the information from a large set of reviews into a few sentences, and allows users to customize these summaries for feature-focused search. In a user study, subjects used ChatterCrop and a sortable list of reviews, to answer questions about two camcorder models. When looking for information about particular features, ChatterCrop outperformed the list, in terms user confidence and perceived ease in finding pertinent information. ChatterCrop's summaries also provided users with starting points to guide further research, and were particularly helpful in the early stages of sensemaking.

Neuron, 2010

We report a role for long-distance retrograde neurotrophin signaling in the establishment of syna... more We report a role for long-distance retrograde neurotrophin signaling in the establishment of synapses in the sympathetic nervous system. Target-derived NGF is both necessary and sufficient for formation of postsynaptic specializations on dendrites of sympathetic neurons. This, in turn, is a prerequisite for formation of presynaptic specializations, but not preganglionic axonal ingrowth from the spinal cord into sympathetic ganglia. We also find that NGF-TrkA signaling endosomes travel from distal axons to cell bodies and dendrites where they promote PSD clustering. Furthermore, the p75 neurotrophin receptor restricts PSD formation, suggesting an important role for antagonistic NGF-TrkA and p75 signaling pathways during retrograde control of synapse establishment. Thus, in addition to defining the appropriate number of sympathetic neurons that survive the period of developmental cell death, target-derived NGF also exerts control over the degree of connectivity between the spinal cord and sympathetic ganglia through retrograde control of synapse assembly.

Synthetic Communications, 2008

Abstract An attempted reaction of 4‐bromomethylcoumarin with 2‐hydroxy aromatic aldehyde/2‐hydrox... more Abstract An attempted reaction of 4‐bromomethylcoumarin with 2‐hydroxy aromatic aldehyde/2‐hydroxy aromatic ketone at room temperature in the presence of a mild base resulted in the formation of cis‐2′,3′‐dihydro‐3‐hydroxybenzofuranylcoumarins by carbanion addition across the carbonyl carbon.

Stroke, 2009

Background and Purpose— In recovered subcortical stroke, the pattern of motor network activation ... more Background and Purpose— In recovered subcortical stroke, the pattern of motor network activation during motor execution can appear normal or not, depending on the task. Whether this applies to other aspects of motor function is unknown. We used functional MRI to assess motor imagery (MI), a promising new approach to improve motor function after stroke, and contrasted it to motor execution. Methods— Twenty well-recovered patients with hemiparetic subcortical stroke (14 males; mean age, 66.5 years) and 17 aged-matched control subjects were studied. Extensive behavioral screening excluded 8 patients and 4 control subjects due to impaired MI abilities. Subjects performed MI and motor execution of a paced finger–thumb opposition sequence using a functional MRI paradigm that monitored compliance. Activation within the primary motor cortex (BA4a and 4p), dorsal premotor, and supplementary motor areas was examined. Results— The pattern of activation during affected-hand motor execution was ...

Stroke, 2006

Background and Purpose— Understanding brain plasticity after stroke is important in developing re... more Background and Purpose— Understanding brain plasticity after stroke is important in developing rehabilitation strategies. Active movement therapies show considerable promise but depend on motor performance, excluding many otherwise eligible patients. Motor imagery is widely used in sport to improve performance, which raises the possibility of applying it both as a rehabilitation method and to access the motor network independently of recovery. Specifically, whether the primary motor cortex (M1), considered a prime target of poststroke rehabilitation, is involved in motor imagery is unresolved. Summary of Review— We review methodological considerations when applying motor imagery to healthy subjects and in patients with stroke, which may disrupt the motor imagery network. We then review firstly the motor imagery training literature focusing on upper-limb recovery, and secondly the functional imaging literature in healthy subjects and in patients with stroke. Conclusions— The review h...

Science, 2008

We report that developmental competition between sympathetic neurons for survival is critically d... more We report that developmental competition between sympathetic neurons for survival is critically dependent on a sensitization process initiated by target innervation and mediated by a series of feedback loops. Target-derived nerve growth factor (NGF) promoted expression of its own receptor TrkA in mouse and rat neurons and prolonged TrkA-mediated signals. NGF also controlled expression of brain-derived neurotrophic factor and neurotrophin-4, which, through the receptor p75, can kill neighboring neurons with low retrograde NGF-TrkA signaling whereas neurons with high NGF-TrkA signaling are protected. Perturbation of any of these feedback loops disrupts the dynamics of competition. We suggest that three target-initiated events are essential for rapid and robust competition between neurons: sensitization, paracrine apoptotic signaling, and protection from such effects.

Physical Review Letters, 2008

We show experimentally that multilayer graphene grown on the carbon terminated SiC000 1 surface c... more We show experimentally that multilayer graphene grown on the carbon terminated SiC000 1 surface contains rotational stacking faults related to the epitaxial condition at the graphene-SiC interface. Via firstprinciples calculation, we demonstrate that such faults produce an electronic structure indistinguishable from an isolated single graphene sheet in the vicinity of the Dirac point. This explains prior experimental results that showed single-layer electronic properties, even for epitaxial graphene films tens of layers thick.