We investigate the characteristics and distribution of pressure ridges in Arctic sea ice using a novel algorithm applied to ICESat‐2 surface heights. We derive the frequency and height of individual ...pressure ridges and map surface roughness and ridging intensity at the basin scale over three winters between 2019 and 2021. Comparisons with near‐coincident airborne lidar data show that not only can we detect individual ridges 5.6 m wide, but also measure sail height more accurately than the existing ICESat‐2 sea ice height product. We find large regional variability in ridge morphology not only related to parent ice type but also geographic location. Ridge sails are best represented by log‐normal distributions while surface roughness is well fit by an exponential normal function. Our results reveal that high‐resolution satellite altimetry is valuable for characterizing sea ice deformation at short length‐scales and delivers observations that will advance ridging parameterizations in sea ice models.
Plain Language Summary
Pressure ridges, a result of convergence and deformation between ice floes, restrict the movement of air across sea ice and pose an impediment to transport across or through the ice. The laser altimeter on ICESat‐2 provides height measurements of sea ice surface topography every 0.7 m in the direction of flight, from which we calculate surface roughness and measure the sail height and frequency of pressure ridges across the Arctic. We use coincident aircraft‐mounted lidar data to evaluate the accuracy of ridge topography derived from ICESat‐2. Our methods accurately distinguish ridges and reproduce sea ice deformation statistics at an along‐track resolution previously only attainable from airborne platforms. We find that while year‐to‐year variability in pressure ridge morphology is low, regional variations are significant. Consistent with previous studies, we find distinct deformation characteristics depending on the age of the ice. Because the oldest ice in the Arctic continues to decline our results imply a reduction in surface roughness and ridging intensity over time, lowering form drag across the ice surface. Our study demonstrates that high‐resolution satellite altimeter observations can be used to derive detailed measurements of sea ice topography that will ultimately support process studies and advances in sea ice modeling.
Key Points
Novel satellite laser altimetry techniques map Arctic sea ice deformation at resolutions previously only attainable with airborne lidar
Surface roughness and pressure ridge sail heights are best represented by exponential normal and log‐normal distributions, respectively
Given the continued loss of older sea ice our results imply an ongoing reduction in ridging intensity, roughness and form drag over time
The constraints and demands on teachers and students, related to implementing English medium instruction (EMI), mean that teachers need to be able to reflect on their practice and make appropriate ...adjustments. Reflective practice generally means that EMI teachers subject their philosophy of practice, principles, theories and practices to a critical analysis so that they can take more responsibility for their actions. Reflective practice allows EMI teachers to act in a deliberate, intentional manner. Reflective practice involves EMI teachers systematically looking at what they do, how they do it, why they do it, what the outcomes are in terms of student learning, and what actions EMI teachers will take as a result of knowing all of this information. Thus experience combined with systematic reflection can lead to professional growth so that we can become more effective language teachers. In this paper I discuss what reflective practice is and how it can be accomplished by EMI teachers.
Self-metathesis of terminal olefins using vanadium(V) alkylidenes is presented. Under various reaction conditions, incomplete conversion is observed due to decomposition of the metallocyclobutane ...intermediate via β-hydride elimination. The activity was observed to decline when a more electron withdrawing, less sterically bulky ligand was used, in contrast to trends observed in ring-opening metathesis polymerization with vanadium catalysts. These results provide insight into the current limitations of olefin metathesis with vanadium catalysts, as well as guidance for catalyst development.
Prior to the genome-wide association era, candidate gene studies were a major approach in schizophrenia genetics. In this invited review, we consider the current status of 25 historical candidate ...genes for schizophrenia (for example, COMT, DISC1, DTNBP1 and NRG1). The initial study for 24 of these genes explicitly evaluated common variant hypotheses about schizophrenia. Our evaluation included a meta-analysis of the candidate gene literature, incorporation of the results of the largest genomic study yet published for schizophrenia, ratings from informed researchers who have published on these genes, and ratings from 24 schizophrenia geneticists. On the basis of current empirical evidence and mostly consensual assessments of informed opinion, it appears that the historical candidate gene literature did not yield clear insights into the genetic basis of schizophrenia. A likely reason why historical candidate gene studies did not achieve their primary aims is inadequate statistical power. However, the considerable efforts embodied in these early studies unquestionably set the stage for current successes in genomic approaches to schizophrenia.
MYC degradation Farrell, Amy S; Sears, Rosalie C
Cold Spring Harbor perspectives in medicine,
03/2014, Letnik:
4, Številka:
3
Journal Article
Recenzirano
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The MYC oncoprotein is an essential transcription factor that regulates the expression of many genes involved in cell growth, proliferation, and metabolic pathways. Thus, it is important to keep MYC ...activity in check in normal cells in order to avoid unwanted oncogenic changes. Normal cells have adapted several ways to control MYC levels, and these mechanisms can be disrupted in cancer cells. One of the major ways in which MYC levels are controlled in cells is through targeted degradation by the ubiquitin-proteasome system (UPS). Here, we discuss the role of the UPS in the regulation of MYC protein levels and review some of the many proteins that have been shown to regulate MYC protein stability. In addition, we discuss how this relates to MYC transcriptional activity, human cancers, and therapeutic targeting.
DTN: an architectural retrospective Fall, K.; Farrell, S.
IEEE journal on selected areas in communications,
06/2008, Letnik:
26, Številka:
5
Journal Article
Recenzirano
Odprti dostop
We review the rationale behind the current design of the Delay/Disruption Tolerant Networking (DTN) Architecture and highlight some remaining open issues. Its evolution, from a focus on deep space to ...a broader class of heterogeneous networks that may suffer disruptions, affected design decisions spanning naming and addressing, message formats, data encoding methods, routing, congestion management and security. Having now achieved relative stability with the design, additional experience is required in long-running operational environments in order to fine tune our understanding of DTN concepts and the types of capabilities that are worth the investment in implementation complexity. We expect key management, handling of congestion, multicasting capability, and routing to remain active areas of research and development, and that DTN may continue to be an active research endeavor for at least the next few years.
This article presents a case study that examined the principles and practices of one novice English as a foreign language (EFL) teacher at a prominent English language institution in Central America. ...This qualitative study sought to contribute to the discussion of the perceived interdependent influences of EFL teachers’ thoughts, identities, and behaviors through five stages of self-reflection in Farrell’s framework for reflective practice. The EFL teacher engaged in conscious reflection to subject their beliefs to critical analysis and interpretation expressed through their philosophy, principles, theory, practice, and beyond practice. Overall, the findings confirm that reflections in all five stages are connected to several common themes, but simultaneously reveal a complex relationship between the teacher’s stated principles and actual practice. The discussion explores potential reasons for convergence and divergence in teachers’ beliefs and classroom actions, concluding that the results correlate with previous research in the field of language education and teacher reflection.
Clozapine-N-oxide (CNO) has long been the ligand of choice for selectively activating Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). However, recent studies have challenged the ...long-held assertion that CNO is otherwise pharmacologically inert. The present study aimed to 1) determine whether CNO is reverse-metabolized to its parent compound clozapine in mice (as has recently been reported in rats), and 2) determine whether CNO exerts clozapine-like interoceptive stimulus effects in rats and/or mice. Following administration of 10.0 mg/kg CNO, pharmacokinetic analyses replicated recent reports of back-conversion to clozapine in rats and revealed that this phenomenon also occurs in mice. In rats and mice trained to discriminate 1.25 mg/kg clozapine from vehicle, CNO (1.0-20.0 mg/kg) produced partial substitution for the clozapine stimulus on average, with full substitution being detected in some individual animals of both species at doses frequently used to activate DREADDs. The present demonstration that CNO is converted to clozapine and exerts clozapine-like behavioral effects in both mice and rats further emphasizes the need for appropriate control groups in studies employing DREADDs, and highlights the utility of the drug discrimination procedure as a tool with which to screen the off-target effects of novel DREADD agonists.
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