Gut Microbiota and Cardiovascular Disease Witkowski, Marco; Weeks, Taylor L; Hazen, Stanley L
Circulation research,
2020-July-31, Letnik:
127, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Fecal microbial community changes are associated with numerous disease states, including cardiovascular disease (CVD). However, such data are merely associative. A causal contribution for gut ...microbiota in CVD has been further supported by a multitude of more direct experimental evidence. Indeed, gut microbiota transplantation studies, specific gut microbiota–dependent pathways, and downstream metabolites have all been shown to influence host metabolism and CVD, sometimes through specific identified host receptors. Multiple metaorganismal pathways (involving both microbe and host) both impact CVD in animal models and show striking clinical associations in human studies. For example, trimethylamine N-oxide and, more recently, phenylacetylglutamine are gut microbiota–dependent metabolites whose blood levels are associated with incident CVD risks in large-scale clinical studies. Importantly, a causal link to CVD for these and other specific gut microbial metabolites/pathways has been shown through numerous mechanistic animal model studies. Phenylacetylglutamine, for example, was recently shown to promote adverse cardiovascular phenotypes in the host via interaction with multiple ARs (adrenergic receptors)—a class of key receptors that regulate cardiovascular homeostasis. In this review, we summarize recent advances of microbiome research in CVD and related cardiometabolic phenotypes that have helped to move the field forward from associative to causative results. We focus on microbiota and metaorganismal compounds/pathways, with specific attention paid to short-chain fatty acids, secondary bile acids, trimethylamine N-oxide, and phenylacetylglutamine. We also discuss novel therapeutic strategies for directly targeting the gut microbiome to improve cardiovascular outcomes.
This graduate-level textbook is the first pedagogical synthesis of the field of topological insulators and superconductors, one of the most exciting areas of research in condensed matter physics. ...Presenting the latest developments, while providing all the calculations necessary for a self-contained and complete description of the discipline, it is ideal for graduate students and researchers preparing to work in this area, and it will be an essential reference both within and outside the classroom.
The book begins with simple concepts such as Berry phases, Dirac fermions, Hall conductance and its link to topology, and the Hofstadter problem of lattice electrons in a magnetic field. It moves on to explain topological phases of matter such as Chern insulators, two- and three-dimensional topological insulators, and Majorana p-wave wires. Additionally, the book covers zero modes on vortices in topological superconductors, time-reversal topological superconductors, and topological responses/field theory and topological indices. The book also analyzes recent topics in condensed matter theory and concludes by surveying active subfields of research such as insulators with point-group symmetries and the stability of topological semimetals. Problems at the end of each chapter offer opportunities to test knowledge and engage with frontier research issues.Topological Insulators and Topological Superconductorswill provide graduate students and researchers with the physical understanding and mathematical tools needed to embark on research in this rapidly evolving field.
Background
The goal of this article is to conduct an assessment of the peer-reviewed primary literature with study objectives to analyze
Amazon.com
’s Mechanical Turk (MTurk) as a research tool in a ...health services research and medical context.
Methods
Searches of Google Scholar and PubMed databases were conducted in February 2017. We screened article titles and abstracts to identify relevant articles that compare data from MTurk samples in a health and medical context to another sample, expert opinion, or other gold standard. Full-text manuscript reviews were conducted for the 35 articles that met the study criteria.
Results
The vast majority of the studies supported the use of MTurk for a variety of academic purposes.
Discussion
The literature overwhelmingly concludes that MTurk is an efficient, reliable, cost-effective tool for generating sample responses that are largely comparable to those collected via more conventional means. Caveats include survey responses may not be generalizable to the US population.
The COVID-19 pandemic does not fit into prevailing Post-traumatic Stress Disorder (PTSD) models, or diagnostic criteria, yet emerging research shows traumatic stress symptoms as a result of this ...ongoing global stressor. Current pathogenic event models focus on past, and largely direct, trauma exposure to certain kinds of life-threatening events. Yet, traumatic stress reactions to future, indirect trauma exposure, and non-Criterion A events exist, suggesting COVID-19 is also a traumatic stressor which could lead to PTSD symptomology. To examine this idea, we asked a sample of online participants (N = 1,040), in five western countries, to indicate the COVID-19 events they had been directly exposed to, events they anticipated would happen in the future, and other forms of indirect exposure such as through media coverage. We then asked participants to complete the Posttraumatic Stress Disorder Checklist-5, adapted to measure pre/peri/post-traumatic reactions in relation to COVID-19. We also measured general emotional reactions (e.g., angry, anxious, helpless), well-being, psychosocial functioning, and depression, anxiety, and stress symptoms. We found participants had PTSD-like symptoms for events that had not happened and when participants had been directly (e.g., contact with virus) or indirectly exposed to COVID-19 (e.g., via media). Moreover, 13.2% of our sample were likely PTSD-positive, despite types of COVID-19 "exposure" (e.g., lockdown) not fitting DSM-5 criteria. The emotional impact of "worst" experienced/anticipated events best predicted PTSD-like symptoms. Taken together, our findings support emerging research that COVID-19 can be understood as a traumatic stressor event capable of eliciting PTSD-like responses and exacerbating other related mental health problems (e.g., anxiety, depression, psychosocial functioning, etc.). Our findings add to existing literature supporting a pathogenic event memory model of traumatic stress.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The visual perception of individuals has received considerable attention (visual person perception), but little social psychological work has examined the processes underlying the visual perception ...of groups of people (visual people perception). Ensemble-coding is a visual mechanism that automatically extracts summary statistics (e.g., average size) of lower-level sets of stimuli (e.g., geometric figures), and also extends to the visual perception of groups of faces. Here, we consider whether ensemble-coding supports people perception, allowing individuals to form rapid, accurate impressions about groups of people. Across nine studies, we demonstrate that people visually extract high-level properties (e.g., diversity, hierarchy) that are unique to social groups, as opposed to individual persons. Observers rapidly and accurately perceived group diversity and hierarchy, or variance across race, gender, and dominance (Studies 1-3). Further, results persist when observers are given very short display times, backward pattern masks, color- and contrast-controlled stimuli, and absolute versus relative response options (Studies 4a-7b), suggesting robust effects supported specifically by ensemble-coding mechanisms. Together, we show that humans can rapidly and accurately perceive not only individual persons, but also emergent social information unique to groups of people. These people perception findings demonstrate the importance of visual processes for enabling people to perceive social groups and behave effectively in group-based social interactions.
The theory of electric polarization in crystals defines the dipole moment of an insulator in terms of a Berry phase (geometric phase) associated with its electronic ground state. This concept not ...only solves the long-standing puzzle of how to calculate dipole moments in crystals, but also explains topological band structures in insulators and superconductors, including the quantum anomalous Hall insulator and the quantum spin Hall insulator, as well as quantized adiabatic pumping processes. A recent theoretical study has extended the Berry phase framework to also account for higher electric multipole moments, revealing the existence of higher-order topological phases that have not previously been observed. Here we demonstrate experimentally a member of this predicted class of materials-a quantized quadrupole topological insulator-produced using a gigahertz-frequency reconfigurable microwave circuit. We confirm the non-trivial topological phase using spectroscopic measurements and by identifying corner states that result from the bulk topology. In addition, we test the critical prediction that these corner states are protected by the topology of the bulk, and are not due to surface artefacts, by deforming the edges of the crystal lattice from the topological to the trivial regime. Our results provide conclusive evidence of a unique form of robustness against disorder and deformation, which is characteristic of higher-order topological insulators.
Higher-Order Weyl Semimetals Ghorashi, Sayed Ali Akbar; Li, Tianhe; Hughes, Taylor L
Physical review letters,
12/2020, Letnik:
125, Številka:
26
Journal Article
Recenzirano
Odprti dostop
We investigate higher-order Weyl semimetals (HOWSMs) having bulk Weyl nodes attached to both surface and hinge Fermi arcs. We identify a new type of Weyl node, which we dub a 2nd-order Weyl node, ...that can be identified as a transition in momentum space in which both the Chern number and a higher order topological invariant change. As a proof of concept we use a model of stacked higher order quadrupole insulators (QI) to identify three types of WSM phases: 1st order, 2nd order, and hybrid order. The model can also realize type-II and hybrid-tilt WSMs with various surface and hinge arcs. After a comprehensive analysis of the topological properties of various HOWSMs, we turn to their physical implications that show the very distinct behavior of 2nd-order Weyl nodes when they are gapped out. We obtain three remarkable results: (i) the coupling of a 2nd-order Weyl phase with a conventional 1st-order one can lead to a hybrid-order topological insulator having coexisting surface cones and flat hinge arcs that are independent and not attached to each other. (ii) A nested 2nd-order inversion-symmetric WSM by a charge-density wave (CDW) order generates an insulating phase having coexisting flatband surface and hinge states all over the Brillouin zone. (iii) A CDW order in a time-reversal symmetric higher-order WSM gaps out a 2nd-order node with a 1st-order node and generates an insulating phase having coexisting surface Dirac cone and hinge arcs. Moreover, we show that a measurement of charge density in the presence of magnetic flux can help to identify some classes of 2nd-order WSMs. Finally, we show that periodic driving can be utilized as a way for generating HOWSMs. Our results are relevant to metamaterials as well as various phases of Cd_{3}As_{2}, KMgBi, and rutile-structure PtO_{2} that have been predicted to realize higher order Dirac semimetals.
We extend the theory of dipole moments in crystalline insulators to higher multipole moments. As first formulated in Benalcazar et al. Science 357, 61 (2017), we show that bulk quadrupole and ...octupole moments can be realized in crystalline insulators. In this paper, we expand in great detail the theory presented previously Benalcazar et al., Science 357, 61 (2017) and extend it to cover associated topological pumping phenomena, and a class of three-dimensional (3D) insulator with chiral hinge states. We start by deriving the boundary properties of continuous classical dielectrics hosting only bulk dipole, quadrupole, or octupole moments. In quantum mechanical crystalline insulators, these higher multipole bulk moments manifest themselves by the presence of boundary-localized moments of lower dimension, in exact correspondence with the electromagnetic theory of classical continuous dielectrics. In the presence of certain symmetries, these moments are quantized, and their boundary signatures are fractionalized. These multipole moments then correspond to new symmetry-protected topological phases. The topological structure of these phases is described by “nested” Wilson loops, which we define. These Wilson loops reflect the bulk-boundary correspondence in a way that makes evident a hierarchical classification of the multipole moments. Just as a varying dipole generates charge pumping, a varying quadrupole generates dipole pumping, and a varying octupole generates quadrupole pumping. For nontrivial adiabatic cycles, the transport of these moments is quantized. An analysis of these interconnected phenomena leads to the conclusion that a new kind of Chern-type insulator exists, which has chiral, hinge-localized modes in 3D. We provide the minimal models for the quantized multipole moments, the nontrivial pumping processes, and the hinge Chern insulator, and describe the topological invariants that protect them.
A fractional corner anomaly reveals higher-order topology Peterson, Christopher W.; Li, Tianhe; Benalcazar, Wladimir A. ...
Science (American Association for the Advancement of Science),
06/2020, Letnik:
368, Številka:
6495
Journal Article
Recenzirano
Odprti dostop
Topological insulators in the spotlight
In addition to having an insulating interior while at the same time supporting conducting surface states, topological insulators have many other interesting ...properties. Higher-order topological insulating states, where regions of interest are along edges and at corners, have been difficult to identify unambiguously. Peterson
et al.
developed a theoretical framework to help identify and characterize these exotic states, including a new topological marker—the fractional charge density—that can be used to detect topological states of matter when the spectroscopic probe of gapless surface states is not accessible. The agreement between experimental work and theory is encouraging for applicability to other topological platforms.
Science
, this issue p.
1114
A new marker, the concept of fractional corner anomaly, is used as a real-space probe of higher-order topology.
Spectral measurements of boundary-localized topological modes are commonly used to identify topological insulators. For high-order insulators, these modes appear at boundaries of higher codimension, such as the corners of a two-dimensional material. Unfortunately, this spectroscopic approach is only viable if the energies of the topological modes lie within the bulk bandgap, which is not required for many topological crystalline insulators. The key topological feature in these insulators is instead fractional charge density arising from filled bulk bands, but measurements of such charge distributions have not been accessible to date. We experimentally measure boundary-localized fractional charge density in rotationally symmetric two-dimensional metamaterials and find one-fourth and one-third fractionalization. We then introduce a topological indicator that allows for the unambiguous identification of higher-order topology, even without in-gap states, and we demonstrate the associated higher-order bulk-boundary correspondence.
Ethnography and Virtual Worldsis the only book of its kind--a concise, comprehensive, and practical guide for students, teachers, designers, and scholars interested in using ethnographic methods to ...study online virtual worlds, including both game and nongame environments. Written by leading ethnographers of virtual worlds, and focusing on the key method of participant observation, the book provides invaluable advice, tips, guidelines, and principles to aid researchers through every stage of a project, from choosing an online fieldsite to writing and publishing the results.
Provides practical and detailed techniques for ethnographic research customized to reflect the specific issues of online virtual worlds, both game and nongame Draws on research in a range of virtual worlds, including Everquest, Second Life, There.com, and World of Warcraft Provides suggestions for dealing with institutional review boards, human subjects protocols, and ethical issues Guides the reader through the full trajectory of ethnographic research, from research design to data collection, data analysis, and writing up and publishing research results Addresses myths and misunderstandings about ethnographic research, and argues for the scientific value of ethnography
PDF
