scholarly journals Steroids, triterpenoids and molecular oxygen

2006 ◽  
Vol 361 (1470) ◽  
pp. 951-968 ◽  
Author(s):  
Roger E Summons ◽  
Alexander S Bradley ◽  
Linda L Jahnke ◽  
Jacob R Waldbauer
Keyword(s):  
Molecular Oxygen ◽  
Sterol Biosynthesis ◽  
Oxygenic Photosynthesis ◽  
Last Common Ancestor ◽  
Biosynthetic Pathways ◽  
Oxygen Requirement ◽  
The Past ◽  
Current State ◽  
Wide Range ◽  
Modern Form

There is a close connection between modern-day biosynthesis of particular triterpenoid biomarkers and presence of molecular oxygen in the environment. Thus, the detection of steroid and triterpenoid hydrocarbons far back in Earth history has been used to infer the antiquity of oxygenic photosynthesis. This prompts the question: were these compounds produced similarly in the past? In this paper, we address this question with a review of the current state of knowledge surrounding the oxygen requirement for steroid biosynthesis and phylogenetic patterns in the distribution of steroid and triterpenoid biosynthetic pathways. The hopanoid and steroid biosynthetic pathways are very highly conserved within the bacterial and eukaryotic domains, respectively. Bacteriohopanepolyols are produced by a wide range of bacteria, and are methylated in significant abundance at the C2 position by oxygen-producing cyanobacteria. On the other hand, sterol biosynthesis is sparsely distributed in distantly related bacterial taxa and the pathways do not produce the wide range of products that characterize eukaryotes. In particular, evidence for sterol biosynthesis by cyanobacteria appears flawed. Our experiments show that cyanobacterial cultures are easily contaminated by sterol-producing rust fungi, which can be eliminated by treatment with cycloheximide affording sterol-free samples. Sterols are ubiquitous features of eukaryotic membranes, and it appears likely that the initial steps in sterol biosynthesis were present in their modern form in the last common ancestor of eukaryotes. Eleven molecules of O 2 are required by four enzymes to produce one molecule of cholesterol. Thermodynamic arguments, optimization of function and parsimony all indicate that an ancestral anaerobic pathway is highly unlikely. The known geological record of molecular fossils, especially steranes and triterpanes, is notable for the limited number of structural motifs that have been observed. With a few exceptions, the carbon skeletons are the same as those found in the lipids of extant organisms and no demonstrably extinct structures have been reported. Furthermore, their patterns of occurrence over billion year time-scales correlate strongly with environments of deposition. Accordingly, biomarkers are excellent indicators of environmental conditions even though the taxonomic affinities of all biomarkers cannot be precisely specified. Biomarkers are ultimately tied to biochemicals with very specific functional properties, and interpretations of the biomarker record will benefit from increased understanding of the biological roles of geologically durable molecules.

scholarly journals Digital Transformation: An Overview of the Current State of the Art of Research

SAGE Open ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 215824402110475
Author(s):  
Sascha Kraus ◽  
Paul Jones ◽  
Norbert Kailer ◽  
Alexandra Weinmann ◽  
Nuria Chaparro-Banegas ◽  
...  
Keyword(s):  
Literature Review ◽  
Systematic Literature Review ◽  
Digital Transformation ◽  
The Past ◽  
Current State ◽  
Wide Range ◽  
Main Driver ◽  
Node Network ◽  
The Government ◽  
Negative Impacts

The increasing digitalization of economies has highlighted the importance of digital transformation and how it can help businesses stay competitive in the market. However, disruptive changes not only occur at the company level; they also have environmental, societal, and institutional implications. This is the reason why during the past two decades the research on digital transformation has received growing attention, with a wide range of topics investigated in the literature. The following aims to provide insight regarding the current state of the literature on digital transformation (DT) by conducting a systematic literature review. An analysis of co-occurrence using the software VOSviewer was conducted to graphically visualize the literature’s node network. Approached this way, the systematic literature review displays major research avenues of digital transformation that consider technology as the main driver of these changes. This paper qualitatively classifies the literature on digital business transformation into three different clusters based on technological, business, and societal impacts. Several research gaps identified in the literature on DT are proposed as futures lines of research which could provide useful insights to the government and private sectors in order to adapt to the disruptive changes found in business as a result of this phenomenon, as well as to reduce its negative impacts on society and the environment.

Early Childhood Corner: The Big Math for Little Kids

2003 ◽  
Vol 9 (5) ◽  
pp. 264-268
Author(s):  
Robert Balfanz ◽  
Herbert P. Ginsburg ◽  
Carole Greenes
Keyword(s):  
Early Childhood ◽  
Young Children ◽  
National Science Foundation ◽  
Historical Record ◽  
Free Play ◽  
Early Childhood Mathematics ◽  
The Past ◽  
Current State ◽  
Wide Range ◽  
Mathematics Program

How many four-year-olds do you know who like to stomp, wiggle, and shout as they count to one hundred; go on a shape hunt to find examples of spheres, cubes, and rectangular prisms; help finish a story about a fantastic pasta maker by completing complex patterns; create and compare two towers of connecting cubes to figure out whose is taller and by how much; and use a map to locate objects in a room? Our answer is just about every four- and five-year-old we have observed over the past four years while developing the Big Math for Little Kids prekindergarten and kindergarten mathematics program. We began this process in the late 1990s because we were dissatisfied with the current state of early childhood mathematics. We observed teachers exposing young children to little or no interesting mathematics or instructing them to learn skills and concepts that they already knew (Greenes 1999). This observation contrasted with the wide range of mathematical ideas and skills that the children explored and employed during free play (Ginsburg 1999). We examined the historical record and learned that over the past two centuries, early childhood mathematics has gone through brief periods of richness followed by longer periods during which the mathematical interests and abilities of young children were seriously underestimated (Balfanz 1999). Aided by funding from the National Science Foundation, we decided to try to create an early childhood mathematics program that would build on the diverse mathematical interests and rich, implicit understandings of mathematics that young children hold.

scholarly journals Beyond Thrombosis: the Role of Platelets in Pulmonary Hypertension

2020 ◽  
Vol 2 (4) ◽  
pp. 243-271
Author(s):  
Salina Nicoleau ◽  
Beata Wojciak-Stothard
Keyword(s):  
Pulmonary Hypertension ◽  
Pulmonary Arterial Pressure ◽  
Right Heart Failure ◽  
Inflammatory Cells ◽  
The Past ◽  
Current State ◽  
Wide Range ◽  
Pulmonary Arterial

Pulmonary Hypertension (PH) is a multifactorial and lethal disease, characterised by elevated pulmonary arterial pressure and progressive right heart failure. PH pathobiology rests on four pillars: vascular remodelling, vasoconstriction, inflammation and thrombosis. While vascular and inflammatory cells have been the focus of PH research over the past decades, platelets have received relatively less attention, despite their associations with key pathophysiological processes of the disease. Platelets contain a wide range of vasoactive, inflammatory and pro-thrombotic mediators, likely to promote PH development and progression. There is currently no cure for PH, and platelet-associated pathways may help identify new therapeutic strategies. This review summarises available evidence on the role of platelets in different forms of PH, and comments on the current state of platelet-targeting therapies. It also describes the latest advances in the in vitro technologies that enable exploration of platelet function under dynamic and physiologically relevant conditions. Doi: 10.28991/SciMedJ-2020-0204-7 Full Text: PDF

The Oxford Handbook of Psycholinguistics

2007 ◽  
Keyword(s):  
Cognitive Neuroscience ◽  
Language Production ◽  
Computational Modelling ◽  
Human Memory ◽  
The Past ◽  
Interdisciplinary Field ◽  
Current State ◽  
Wide Range ◽  
The Mind ◽  
Made In

This book examines the young science of psycholinguistics, which attempts to uncover the mechanisms and representations underlying human language. This interdisciplinary field has seen massive developments over the past decade, with a broad expansion of the research base, and the incorporation of new experimental techniques such as brain imaging and computational modelling. The result is that real progress is being made in the understanding of the key components of language in the mind. This book brings together the views of seventy-five leading researchers to provide a review of the current state of the art in psycholinguistics. The contributors are eminent in a wide range of fields, including psychology, linguistics, human memory, cognitive neuroscience, bilingualism, genetics, development, and neuropsychology. Their contributions are organised into six themed sections, covering word recognition, the mental lexicon, comprehension and discourse, language production, language development, and perspectives on psycholinguistics.

Human, Machine, and Environment Aspects of Snowmobile Design and Utilization

1974 ◽  
Vol 16 (5) ◽  
pp. 481-494
Author(s):  
Gerald F. Rabideau
Keyword(s):  
Private Property ◽  
Noise Pollution ◽  
Design Standards ◽  
The Past ◽  
Current State ◽  
Pollution Damage ◽  
Wide Range ◽  
Recreational Vehicles ◽  
The Many ◽  
Natural Ecology

Central to the many problems inherent in the design and use of snowmobiles is their rapid increase in popularity as sporting and recreational vehicles during the past decade. The major problems-damage and injury-producing accidents, noise pollution, damage to private property, and detrimental effects on natural ecology—are described and analyzed. Examples are given that typify the current state-of-the-art investigations of the problem areas. It is noted that such studies, both scientific and engineering, have dealt only in piecemeal fashion with some of the most widely acknowledged problems. The paper examines the existing need for a system-oriented program of research designed to provide data for a wide range of system design standards capable of assuring the survival of this form of recreation.

scholarly journals Generalized Temporal Inference via Planning

2021 ◽  
Author(s):  
Diego Aineto ◽  
Sergio Jimenez ◽  
Eva Onaindia
Keyword(s):  
Planning Problem ◽  
Minimal Cost ◽  
Inference Problem ◽  
The Past ◽  
Inference Problems ◽  
Current State ◽  
Future State ◽  
Wide Range ◽  
Temporal Inference

This paper introduces the Temporal Inference Problem (TIP), a general formulation for a family of inference problems that reason about the past, present or future state of some observed agent. A TIP builds on the models of an actor and of an observer. Observations of the actor are gathered at arbitrary times and a TIP encodes hypothesis on unobserved segments of the actor's trajectory. Regarding the last observation as the present time, a TIP enables to hypothesize about the past trajectory, future trajectory or current state of the actor. We use LTL as a language for expressing hypotheses and reduce a TIP to a planning problem which is solved with an off-the-shelf classical planner. The output of the TIP is the most likely hypothesis, the minimal cost trajectory under the assumption that the actor is rational. Our proposal is evaluated on a wide range of TIP instances defined over different planning domains.

Optical Properties of HVEM Accelerators

1975 ◽  
Vol 33 ◽  
pp. 180-181
Author(s):  
A. Strojnik ◽  
J.W. Scholl ◽  
V. Bevc
Keyword(s):  
Optical Properties ◽  
Electron Accelerator ◽  
Systematic Investigation ◽  
Electron Source ◽  
High Brightness ◽  
The Past ◽  
Wide Range ◽  
Optical Behavior

The electron accelerator, as inserted between the electron source (injector) and the imaging column of the HVEM, is usually a strong lens and should be optimized in order to ensure high brightness over a wide range of accelerating voltages and illuminating conditions. This is especially true in the case of the STEM where the brightness directly determines the highest resolution attainable. In the past, the optical behavior of accelerators was usually determined for a particular configuration. During the development of the accelerator for the Arizona 1 MEV STEM, systematic investigation was made of the major optical properties for a variety of electrode configurations, number of stages N, accelerating voltages, 1 and 10 MEV, and a range of injection voltages ϕ0 = 1, 3, 10, 30, 100, 300 kV).

Pursuit of the Abscopal Effect

2020 ◽  
Vol 04 (04) ◽  
pp. 369-372
Author(s):  
Paul B. Romesser ◽  
Christopher H. Crane
Keyword(s):  
Tumor Immunology ◽  
Antitumor Immunity ◽  
Clinical Success ◽  
Immune Recognition ◽  
Immune Modulators ◽  
Cancer Subtypes ◽  
The Past ◽  
Tumor Irradiation ◽  
Wide Range ◽  
Tumor Recognition

AbstractEvasion of immune recognition is a hallmark of cancer that facilitates tumorigenesis, maintenance, and progression. Systemic immune activation can incite tumor recognition and stimulate potent antitumor responses. While the concept of antitumor immunity is not new, there is renewed interest in tumor immunology given the clinical success of immune modulators in a wide range of cancer subtypes over the past decade. One particularly interesting, yet exceedingly rare phenomenon, is the abscopal response, characterized by a potent systemic antitumor response following localized tumor irradiation presumably attributed to reactivation of antitumor immunity.

The Many Pasts of Detective Fiction

2020 ◽  
Vol 1 (2) ◽  
pp. 157-172
Author(s):  
Thomas Leitch
Keyword(s):  
Detective Fiction ◽  
Golden Age ◽  
Public History ◽  
Detective Novel ◽  
Sherlock Holmes ◽  
Detective Story ◽  
The Past ◽  
Wide Range ◽  
Detective Novels ◽  
The Many

Building on Tzvetan Todorov's observation that the detective novel ‘contains not one but two stories: the story of the crime and the story of the investigation’, this essay argues that detective novels display a remarkably wide range of attitudes toward the several pasts they represent: the pasts of the crime, the community, the criminal, the detective, and public history. It traces a series of defining shifts in these attitudes through the evolution of five distinct subgenres of detective fiction: exploits of a Great Detective like Sherlock Holmes, Golden Age whodunits that pose as intellectual puzzles to be solved, hardboiled stories that invoke a distant past that the present both breaks with and echoes, police procedurals that unfold in an indefinitely extended present, and historical mysteries that nostalgically fetishize the past. It concludes with a brief consideration of genre readers’ own ambivalent phenomenological investment in the past, present, and future each detective story projects.

Nine Centuries of Man

2017 ◽  
Keyword(s):  
Twentieth Century ◽  
Diverse Range ◽  
Gender Expectations ◽  
Court Records ◽  
The Past ◽  
Wide Range ◽  
Police Reports ◽  
Late Twentieth ◽  
Scottish History ◽  
Late Twentieth Century

What did it mean to be a man in Scotland over the past nine centuries? Scotland, with its stereotypes of the kilted warrior and the industrial ‘hard man’, has long been characterised in masculine terms, but there has been little historical exploration of masculinity in a wider context. This interdisciplinary collection examines a diverse range of the multiple and changing forms of masculinities from the late eleventh to the late twentieth century, exploring the ways in which Scottish society through the ages defined expectations for men and their behaviour. How men reacted to those expectations is examined through sources such as documentary materials, medieval seals, romances, poetry, begging letters, police reports and court records, charity records, oral histories and personal correspondence. Focusing upon the wide range of activities and roles undertaken by men – work, fatherhood and play, violence and war, sex and commerce – the book also illustrates the range of masculinities that affected or were internalised by men. Together, the chapters illustrate some of the ways Scotland’s gender expectations have changed over the centuries and how, more generally, masculinities have informed the path of Scottish history

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