401 research outputs found
The Weighted k-Center Problem in Trees for Fixed k
No full textWe present a linear time algorithm for the weighted k-center problem on trees for fixed k. This partially settles the long-standing question about the lower bound on the time complexity of the problem. The current time complexity of the best-known algorithm for the problem with k as part of the input is O(n log n) by Wang et al. [Haitao Wang and Jingru Zhang, 2018]. Whether an O(n) time algorithm exists for arbitrary k is still open
Modeling of mechanical energy dissipation of low-dimensional resonators
No full textNanoelectromechanical systems (NEMS) made from low-dimensional materials based on carbon, transition metal dichalcogenides, and their combinations have opened up new possibilities in high-precision sensing, signal processing, and studies of fundamental physical phenomena. In the heart of the NEMS is a vibrating mechanical element, known as the resonator. The performance of the NEMS critically depends on the mechanical energy dissipated by the resonator. Studies on dissipation are important because an understanding of the loss mechanisms can suggest ways to mitigate it. In most practical scenarios, the resonators suffer from intrinsic dissipation mediated by its inherent atomic thermal motions or phonons and extrinsic dissipation due to a fluid environment. In this context, low-dimensional resonators need special attention because the dissipation cannot be explained using the existing continuum theories. Due to atomic thickness, sub-micron dimension, and mega- to gigahertz frequencies of these resonators, nano-scale physical processes start becoming important. Most macroscale models do not account for these physical processes, warranting the current line of research. In this thesis, we use atomistic simulations and statistical-mechanical theories to understand and formulate the nanoscale physical processes, and integrate them to develop a multiscale model for dissipation.
In the first part of the thesis, we explore fluid coupled resonator systems with an objective to understand different dissipative processes such as phonon-mediated intrinsic dissipation, viscous damping by the fluid, and the cross-interaction between each source of dissipation, i.e., phonons and fluid at a regime of gigahertz frequency, and nanometer length scale. First, we consider a single-walled carbon nanotube (SWCNT) resonator with confined Argon and driven under axial mode. The intrinsic dissipation in the SWCNT at gigahertz frequencies could be explained by Akhiezer theory. We show that intrinsic dissipation, which is conventionally treated as an independent process, can be modified by fluid interactions due to the phonon- fluid coupling. We show that an important consequence of this phonon-fluid coupling is the counter-intuitive inverse scaling of net dissipation with fluid density at low excitation frequencies. Next, we consider flexural vibration of the SWCNT with interior and exterior Argon. When compared with the fluid exterior case, the SWCNT with confined fluid shows a low and anomalous scaling of dissipation with fluid density. We systematically analyzed the sources of dissipation and found that the fluid contributed to the anomalous scaling. A formulation of the fluid response during the flexural motion revealed a viscoelastic nature of the fluid under nano-confinement, which explains the anomalous scaling. Further, we use the framework for dissipation analysis to examine the effect of thermal motion of the resonator atoms on fluid dissipation, demonstrate a frequency dependent dissipation scaling with density, and comment on the mechanism of intrinsic dissipation during flexural resonance of an SWCNT.
In the second part, we develop a multiscale framework to model intrinsic dissipation in two-dimensional (2D) microresonators. The work aims to reveal the fundamental limit of dissipation and enable looking at the isolated effect of various parameters over a wide range, both of which are inaccessible in experiments. The damping of the flexural mode of a 2D microresonator takes place due to the nonlinear coupling with other thermally excited elastic modes. A particular flexural mode can couple with another flexural mode with a wavelength ranging from the size of the resonator to that of the lattice spacing. However, the coupling at these disparate length scales needs different modeling approaches. In the multiscale framework, we model the continuum-scale modes as Langevin oscillators (LOs) with nonlinear coupling terms. The parameters of the LOs are computed using continuum mechanical analysis and atomistic simulations. Using this framework, we study the effect of various parameters of interest such as vibration amplitude, resonator size, temperature, and pre-strain in the case of graphene resonators and draw some important conclusions towards engineering high-quality 2D resonators.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-05-01The student, Subhadeep De, accepted the attached license on 2019-02-13 at 12:01.The student, Subhadeep De, submitted this Dissertation for approval on 2019-02-13 at 12:51.This Dissertation was approved for publication on 2019-02-15 at 11:34.DSpace SAF Submission Ingestion Package generated from Vireo submission #13388 on 2019-08-22 at 15:04:21Made available in DSpace on 2019-08-23T20:28:06Z (GMT). No. of bitstreams: 3
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Previous issue date: 2019-02-15Embargo set by: Seth Robbins for item 112082
Lift date: 2021-08-23T20:28:11Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 112082
Lift date: 2021-08-23T20:29:33Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 112082
Lift date: 2021-08-23T20:36:18Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 112082 on 2021-08-24T09:15:34Z
The role of the extracellular matrix protein SPOCK2 for bone physiology and hematopoiesis
No full textRecent Advances in the Clinical Translation of Small-Cell Lung Cancer Therapeutics
No full textSmall-cell lung cancer (SCLC) is a recalcitrant form of cancer, representing 15% of lung cancer cases globally. SCLC is classified within the range of neuroendocrine pulmonary neoplasms, exhibiting shared morphologic, ultrastructural, immunohistochemical, and molecular genomic features. It is marked by rapid proliferation, a propensity for early metastasis, and an overall poor prognosis. The current conventional therapies involve platinum–etoposide-based chemotherapy in combination with immunotherapy. Nonetheless, the rapid emergence of therapeutic resistance continues to pose substantial difficulties. The genomic profiling of SCLC uncovers significant chromosomal rearrangements along with a considerable mutation burden, typically involving the functional inactivation of the tumor suppressor genes TP53 and RB1. Identifying biomarkers and evaluating new treatments is crucial for enhancing outcomes in patients with SCLC. Targeted therapies such as topoisomerase inhibitors, DLL3 inhibitors, HDAC inhibitors, PARP inhibitors, Chk1 inhibitors, etc., have introduced new therapeutic options for future applications. In this current review, we will attempt to outline the key molecular pathways that play a role in the development and progression of SCLC, together with a comprehensive overview of the most recent advancements in the development of novel targeted treatment strategies, as well as some ongoing clinical trials against SCLC, with the goal of improving patient outcomes
Arbuscular mycorrhizal fungal contribution towards plant resilience to drought conditions
No full textClimate changes cause altering rainfall patterns resulting in an increase in drought occurrences globally. These events are disrupting plants and agricultural productivity. To evade droughts, plants try to adapt and modify in the best capacities possible. The plants have adapted by structurally modifying roots, stems, and leaves, as well as modifying functions. Lately, the association of microbial communities with plants has also been proven to be an important factor in aiding resilience. The fungal representatives of the microbial community also help safeguard the plants against drought. We discuss how these fungi associate with plants and contribute to evading drought stress. We specifically focus on Arbuscular mycorrhizal fungi (AMF) mediated mechanisms involving antioxidant defenses, phytohormone mediations, osmotic adjustments, proline expressions, fungal water absorption and transport, morphological modifications, and photosynthesis. We believe understanding the mechanisms would help us to optimize the use of fungi in agricultural practices. That way we could better prepare the plants for the anticipated future drought events
The interplay between transcription and mRNA degradation in Saccharomyces cerevisiae
No full textThe cellular transcriptome is shaped by both the rates of mRNA synthesis in the nucleus and mRNA degradation in the cytoplasm under a specified condition. The last decade witnessed an exciting development in the field of post-transcriptional regulation of gene expression which underscored a strong functional coupling between the transcription and mRNA degradation. The functional integration is principally mediated by a group of specialized promoters and transcription factors that govern the stability of their cognate transcripts by “marking” them with a specific factor termed “coordinator.” The “mark” carried by the message is later decoded in the cytoplasm which involves the stimulation of one or more mRNA-decay factors, either directly by the “coordinator” itself or in an indirect manner. Activation of the decay factor(s), in turn, leads to the alteration of the stability of the marked message in a selective fashion. Thus, the integration between mRNA synthesis and decay plays a potentially significant role to shape appropriate gene expression profiles during cell cycle progression, cell division, cellular differentiation and proliferation, stress, immune and inflammatory responses, and may enhance the rate of biological evolution
Spin-textured Volkov–Pankratov states and their tunnel magnetoresistance response
No full textVolkov–Pankratov (VP) states are a family of sub-gap states that appear at the smooth interface/domain wall between topologically distinct gaped states. We carry out quantum transport simulations on one- and two-dimensional lattice models to demonstrate the emergence of such states in the edge spectrum of a quantum spin Hall system subjected to a smoothly varying exchange field that switches its sign at a given spatial point. We show the VP states possess non-trivial spin textures that can be characterized by a winding number in real space. It is further demonstrated that the application of an electric field along the edge provides control of this spin texture without altering the winding number. Finally, we illuminate how these spin textures can be read off via the local tunnel magnetoresistance (TMR) response of spin-polarized tunnel probes attached to the edge and the TMR can be controlled by purely electrical means akin to a Datta–Das type spin transistor
Probing sterile neutrinos in the framework of inverse seesaw mechanism through leptoquark productions
No full textWe consider an extension of the standard model (SM) augmented by two neutral singlet fermions per generation and a leptoquark. In order to generate the light neutrino masses and mixing, we incorporate inverse seesaw mechanism. The right-handed neutrino production in this model is significantly larger than the conventional inverse seesaw scenario. We analyze the different collider signatures of this model and find that the final states associated with three or more leptons, multijet and at least one b-tagged and ( or) t-tagged jet can probe larger RH neutrino mass scale. We have also proposed a same-sign dilepton signal region associated with multiple jets and missing energy that can be used to distinguish the present scenario from the usual inverse seesaw extended SM.Peer reviewe
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