16 research outputs found
The production and the perception of English vowels by Mandarin speakers
No full textThis study set out to examine how correctly Mandarin speakers produced and perceived English vowels and to explore the relationship between the production and the perception of English vowels by Mandarin speakers. Fifteen native Mandarin speakers, who had lived in Canada for at least two years and received an IELTS score of 6.5 or above, participated in this study. Fifteen native speakers of Canadian English living in Vancouver at the time of the study also participated as a control group. Two experiments were conducted involving 10 English vowels: /i/, /ɪ/, /ɛ/, /æ/, /ʊ/, /u/, /ʊ/, /ɔ/, /o/, and /ʌ/. In Experiment 1, both the Mandarin speakers and the native English speakers were recorded producing the ten vowels in a /bVt/ syllable in a carrier sentence. The vowels in the recordings were then identified by four native English listeners. In Experiment 2, the Mandarin speakers did an identification test of the vowels produced by the English speakers in Experiment 1. The results showed that Mandarin speakers in this study were able to produce and perceive certain English vowels correctly, but not all of them. The results also indicated that the relationship between the production and perception of English vowels by Mandarin speakers cannot be interpreted in a straightforward way, and that that L2 experience, in terms of length of residence, age of arrival, years of learning, and age when ESL learning starts, might also play an important role in the production and perception of English vowels by Mandarin speakers.Graduat
Wind- and Buoyancy-modulated Along-shore Circulation over the Texas-Louisiana Shelf
No full textNumerical experiments are used to study the wind- and buoyancy-modulated along-shore circulation over the Texas-Louisiana continental shelf inshore of 50-m water depth. Most attention is given to circulation in the non-summer flow regime. A major focus of this study is on a unique along-shore flow phenomenon ��� convergent along- shore flows, which is controlled jointly by wind forcing and buoyancy fluxes from the Mississippi-Atchafalaya river plume. The second problem addresses the forcing effect of buoyancy on the general along-shore circulation pattern over the shelf in non-summer.
The convergent along-shore flows are characterized by down-coast flow from the northern shelf encountering up-coast flow from the southern shelf. This phenomenon is explored for both weather band and seasonal timescales. For the weather band, investigations are focused on non-summer convergent events. The formation of convergent flows is primarily caused by along-coast variation in the along-shore component of wind forcing, which in turn is due to the curvature of the Texas-Louisiana coastline. In general, along-shore currents are well correlated with along-shore winds. However, the points of convergence of currents and winds are not co-located; but rather, points of convergence of currents typically occur down-coast of points of convergence of wind. This offset is mainly caused by buoyancy forcing that forces down-coast currents and drives the point of convergence of currents further down-coast. No specific temporal shift pattern is found for the weather-band convergence, whereas monthly monthly mean convergence exhibits a prominent pattern of seasonal along-coast migration. Buoyancy forcing in the non-summer along-shore flow is investigated in detail in the second part of this study. During non-summer, under down-coast wind forcing, the Mississippi-Atchafalaya river plume exhibits a bottom-advected pattern, for which isopycnals strongly interact with the sea floor. The density front is fairly wide and spans nearly across the entire shelf. Within the front, vertical shear of the alongshore flow is in thermal wind balance with the cross-shore density gradient, and the shear causes a slight reversal of alongshore flow near the bottom. An alongshore flow estimated by the thermal wind relation, along with an assumption of zero bottom reference velocity, agrees well with the actual alongshore flow
Cautious explorers generate more future academic impact
No full textSome scientists are more likely to explore unfamiliar research topics while
others tend to exploit existing ones. In previous work, correlations have been
found between scientists' topic choices and their career performances. However,
literature has yet to untangle the intricate interplay between scientific
impact and research topic choices, where scientific exploration and
exploitation intertwine. Here we study two metrics that gauge how frequently
scientists switch topic areas and how large those jumps are, and discover that
'cautious explorers' who switch topics frequently but do so to 'close' domains
have notably better future performance and can be identified at a remarkably
early career stage. Cautious explorers who balance exploration and exploitation
in their first four career years have up to 19% more citations per future
paper. Our results suggest that the proposed metrics depict the scholarly
traits of scientists throughout their careers and provide fresh insight,
especially for nurturing junior scientists.Comment: 16 pages of main text and 94 pages of supplementary information. v2:
Added page number and fixed typo in author lis
Role of proton ordering in adsorption preference of polar molecule on ice surface
No full textAdsorption of polar monomers on ice surface, relevant to the physical/chemical reaction in ice clouds as well as growth of ice, remains an open issue partially due to the unusual surface characteristics with protons at the top layer of ice. Using first-principle calculations, we explore the adsorption properties of ice surface in terms of a surface proton order parameter, which characterizes the inhomogeneity of the dangling atoms on ice surface. We show that, due to an effective electric field created by dangling OH bonds and lone pairs of water molecules not only directly neighboring but also further away from the adsorbed polar molecule on the ice surface, the adsorption energy of polar monomer on ice surface exhibits large variance and a strong correlation with the proton order parameter of ice surface. Our results about the positive correlation between the inhomogeneity of ice surface and adsorption energies suggest that the physical/chemical reactions as well as the growth of ice may prefer to occur firstly on surfaces with larger proton order parameter.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000307807000018&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Multidisciplinary SciencesSCI(E)PubMed10ARTICLE3313177-1318110
Dlk1 maintains adult mice long-term HSCs by activating Notch signaling to restrict mitochondrial metabolism
No full textBACKGROUND: Adult hematopoietic stem cells (HSCs) homeostasis is critically important in maintaining lifelong hematopoiesis. However, how adult HSCs orchestrate its homeostasis remains not fully understood. Imprinted gene Dlk1 has been shown to play critical role in mouse embryonic hematopoiesis and in regulation of stem cells, but its physiological roles in adult HSCs are unknown. METHODS: We performed gene expression analysis of Dlk1, and constructed conditional Dlk1 knockout (KO) mice by crossing Mx1 cre mice with Dlk(flox/flox) mice. Western blot and quantitative PCR were used to detect Dlk1 KO efficiency. Flow cytometry was performed to investigate the effects of Dlk1 KO on HSCs, progenitors and linage cells in primary mice. Competitive HSCs transplantation and secondary transplantation was used to examine the effects of Dlk1 KO on long-term hematopoietic repopulation potential of HSCs. RNA-Seq and cell metabolism assays was used to determine the underlying mechanisms. RESULTS: Dlk1 was highly expressed in adult mice long-term HSCs (LT-HSCs) relative to progenitors and mature lineage cells. Dlk1 KO in adult mice HSCs drove HSCs enter active cell cycle, and expanded phenotypical LT-HSCs, but undermined its long-term hematopoietic repopulation potential. Dlk1 KO resulted in an increase in HSCs’ metabolic activity, including glucose uptake, ribosomal translation, mitochondrial metabolism and ROS production, which impaired HSCs function. Further, Dlk1 KO in adult mice HSCs attenuated Notch signaling, and re-activation of Notch signaling under Dlk1 KO decreased the mitochondrial activity and ROS production, and rescued the changes in frequency and absolute number of HSCs. Scavenging ROS by antioxidant N-acetylcysteine could inhibit mitochondrial metabolic activity, and rescue the changes in HSCs caused by Dlk1 KO. CONCLUSION: Our study showed that Dlk1 played an essential role in maintaining HSC homeostasis, which is realized by governing cell cycle and restricting mitochondrial metabolic activity. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40164-022-00369-9
Surface-Functionalized NdVO(4):Gd(3+) Nanoplates as Active Agents for Near-Infrared-Light-Triggered and Multimodal-Imaging-Guided Photothermal Therapy
No full textDevelopment of nanotheranostic agents with near-infrared (NIR) absorption offers an effective tool for fighting malignant diseases. Lanthanide ion neodymium (Nd(3+))-based nanomaterials, due to the maximum absorption at around 800 nm and unique optical properties, have caught great attention as potential agents for simultaneous cancer diagnosis and therapy. Herein, we employed an active nanoplatform based on gadolinium-ion-doped NdVO(4) nanoplates (NdVO(4):Gd(3+) NPs) for multiple-imaging-assisted photothermal therapy. These NPs exhibited enhanced NIR absorption and excellent biocompatibility after being grafted with polydopamine (pDA) and bovine serum albumin (BSA) layers on their surface. Upon expose to an 808 nm laser, these resulting NPs were able to trigger hyperthermia rapidly and cause photo-destruction of cancer cells. In a xenograft tumor model, tumor growth was also significantly inhibited by these photothermal agents under NIR laser irradiation. Owing to the multicomponent nanostructures, we demonstrated these nanoagents as being novel contrast agents for in vivo magnetic resonance (MR) imaging, X-ray computed tomography (CT), photoacoustic (PA) imaging, and second biological window fluorescent imaging of tumor models. Thus, we believe that this new kind of nanotherapeutic will benefit the development of emerging nanosystems for biological imaging and cancer therapy
X-ray absorption of liquid water by advanced ab initio methods
No full textOxygen K-edge x-ray absorption spectra of liquid water are computed based on configurations from advanced ab initio molecular dynamics simulations, as well as an electron excitation theory from the GW method. One the one hand, the molecular structures of liquid water are accurately predicted by including both van der Waals interactions and a hybrid functional (PBE0). On the other hand, the dynamic screening effects on electron excitation are approximately described by the recently developed enhanced static Coulomb-hole and screened-exchange approximation of W. Kang and M. S. Hybertsen [Phys. Rev. B 82, 195108 (2010)]. The resulting spectra of liquid water are in better quantitative agreement with the experimental spectra due to the softened hydrogen bonds and the slightly broadened spectra originating from the better screening model.National Science Foundation (NSF), DMR [DMR-1552287]; U.S. Department of Energy SciDAC [DE-SC0008726]; Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]SCI(E)ARTICLE109
p53 Maintains Genomic Stability by Preventing Interference between Transcription and Replication
No full text10.1016/j.celrep.2016.03.011CELL REPORTS151132-14
p53 Maintains Genomic Stability by Preventing Interference between Transcription and Replication
No full textSummaryp53 tumor suppressor maintains genomic stability, typically acting through cell-cycle arrest, senescence, and apoptosis. We discovered a function of p53 in preventing conflicts between transcription and replication, independent of its canonical roles. p53 deficiency sensitizes cells to Topoisomerase (Topo) II inhibitors, resulting in DNA damage arising spontaneously during replication. Topoisomerase IIα (TOP2A)-DNA complexes preferentially accumulate in isogenic p53 mutant or knockout cells, reflecting an increased recruitment of TOP2A to regulate DNA topology. We propose that p53 acts to prevent DNA topological stress originating from transcription during the S phase and, therefore, promotes normal replication fork progression. Consequently, replication fork progression is impaired in the absence of p53, which is reversed by transcription inhibition. Pharmacologic inhibition of transcription also attenuates DNA damage and decreases Topo-II-DNA complexes, restoring cell viability in p53-deficient cells. Together, our results demonstrate a function of p53 that may underlie its role in tumor suppression
