150 research outputs found
Critical behavior of the dimerized Si(001) surface: A continuous order-disorder phase transition in the 2D Ising universality class
The critical behavior of the order-disorder phase transition in the buckled
dimer structure of the Si(001) surface is investigated both theoretically by
means of first-principles calculations and experimentally by spot profile
analysis low-energy electron diffraction (SPA-LEED). We use density functional
theory (DFT) with three different functionals commonly used for Si to determine
the coupling constants of an effective lattice Hamiltonian describing the dimer
interactions. Experimentally, the phase transition from the low-temperature
- to the high-temperature -reconstructed
surface is followed through the intensity and width of the superstructure spots
within the temperature range of 78-400 K. Near the critical temperature
K, we observe universal critical behavior of spot
intensities and correlation lengths which falls into the universality class of
the two-dimensional (2D) Ising model. From the ratio of correlation lengths
along and across the dimer rows we determine effective nearest-neighbor
couplings of an anisotropic 2D Ising model, meV and meV. We find that the experimentally determined coupling
constants of the Ising model can be reconciled with those of the more complex
lattice Hamiltonian from DFT when the critical behavior is of primary interest.
The anisotropy of the interactions derived from the experimental data via the
2D Ising model is best matched by DFT calculations using the PBEsol functional.
The trends in the calculated anisotropy are consistent with the surface stress
anisotropy predicted by the DFT functionals, pointing towards the role of
surface stress reduction as a driving force for establishing the -reconstructed ground state
Sequential Kibble-Zurek dynamics in the anisotropic Ising model of the Si(001) surface
As a simplified description of the non-equilibrium dynamics of buckled dimers
on the Si(001) surface, we consider the anisotropic 2D Ising model and study
the freezing of spatial correlations during a cooling quench across the
critical point. The dependence of the frozen correlation lengths and
on the cooling rate obtained numerically matches the Kibble-Zurek
scaling quite well. However, we also find that the ratio of
their frozen values deviates significantly from the ratio in equilibrium.
Supported by analytical arguments, we explain this difference by the fact that
the deviation from equilibrium in the weakly coupled direction occurs earlier
than in the strongly coupled direction.Comment: 4+2+1 pages, 3 figure
Self-Reported Cancer Prevalence among Hispanics in the US: Results from the Hispanic Community Health Study/Study of Latinos
Cancer has surpassed heart disease as the leading cause of death among Hispanics in the U.S., yet data on cancer prevalence and risk factors in Hispanics in regard to ancestry remain scarce. This study sought to describe (a) the prevalence of cancer among Hispanics from four major U.S. metropolitan areas, (b) cancer prevalence across Hispanic ancestry, and (c) identify correlates of self-reported cancer prevalence. Participants were 16,415 individuals from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), who self-identified as Cuban, Dominican, Mexican, Puerto Rican, Central or South American. All data were collected at a single time point during the HCHS/SOL baseline clinic visit. The overall self-reported prevalence rate of cancer for the population was 4%. The rates varied by Hispanic ancestry group, with individuals of Cuban and Puerto Rican ancestry reporting the highest cancer prevalence. For the entire population, older age (OR = 1.47, p < .001, 95% CI, 1.26–1.71) and having health insurance (OR = 1.93, p < .001, 95% CI, 1.42–2.62) were all significantly associated with greater prevalence, whereas male sex was associated with lower prevalence (OR = 0.56, p < .01, 95% CI, .40-.79). Associations between study covariates and cancer prevalence also varied by Hispanic ancestry. Findings underscore the importance of sociodemographic factors and health insurance in relation to cancer prevalence for Hispanics and highlight variations in cancer prevalence across Hispanic ancestry groups. Characterizing differences in cancer prevalence rates and their correlates is critical to the development and implementation of effective prevention strategies across distinct Hispanic ancestry groups
Mixed Quotation
The central challenge posed by mixed quotation is that it exhibits both regular semantic use and metalinguistic reference, simultaneously. Semanticists disagree considerably on how to capture the interplay between these two meaning aspects. In this case study I present the various semantic approaches to mixed quotation and compare their predictions with respect to empirical phenomena like indexical shifting, projection, and non‐constituent mixed quotation
RNF4 and VHL regulate the proteasomal degradation of SUMO-conjugated Hypoxia-Inducible Factor-2α
Hypoxia-inducible factors (HIFs) are critical transcription factors that mediate cell survival during reduced oxygen conditions (hypoxia). At regular oxygen conditions (normoxia), HIF-1α and HIF-2α are continuously synthesized in cells and degraded via the ubiquitin–proteasome pathway. During hypoxia, these proteins are stabilized and translocate to the nucleus to activate transcription of target genes that enable cell survival at reduced oxygen levels. HIF proteins are tightly regulated via post-translational modifications including phosphorylation, acetylation, prolyl-hydroxylation and ubiquitination. Here we show for the first time that exogenous and endogenous HIF-2α are also regulated via the ubiquitin-like modifier small ubiquitin-like modifiers (SUMO). Using mutational analysis, we found that K394, which is situated in the sumoylation consensus site LKEE, is the major SUMO acceptor site in HIF-2α. Functionally, sumoylation reduced the transcriptional activity of HIF-2α. Similar to HIF-1α, HIF-2α is regulated by the SUMO protease SENP1. The proteasome inhibitor MG132 strongly stabilized SUMO-2-conjugated HIF-2α during hypoxia but did not affect the total level of HIF-2α. The ubiquitin E3 ligases von Hippel–Lindau and RNF4 control the levels of sumoylated HIF-2α, indicating that sumoylated HIF-2α is degraded via SUMO-targeted ubiquitin ligases
Molecular Cytogenetic Profiling Reveals Similarities and Differences Between Localized Nodal and Systemic Follicular Lymphomas
Recently, we have developed novel highly promising gene expression (GE) classifiers discriminating localized nodal (LFL) from systemic follicular lymphoma (SFL) with prognostic impact. However, few data are available in LFL especially concerning hotspot genetic alterations that are associated with the pathogenesis and prognosis of SFL. A total of 144 LFL and 527 SFL, enrolled in prospective clinical trials of the German Low Grade Lymphoma Study Group, were analyzed by fluorescence in situ hybridization to detect deletions in chromosomes 1p, 6q, and 17p as well as BCL2 translocations to determine their impact on clinical outcome of LFL patients. The frequency of chromosomal deletions in 1p and 17p was comparable between LFL and SFL, while 6q deletions and BCL2 translocations more frequently occurred in SFL. A higher proportion of 1p deletions was seen in BCL2-translocation–positive LFL, compared with BCL2-translocation–negative LFL. Deletions in chromosomes 1p, 6q, and 17p predicted clinical outcome of patients with SFL in the entire cohort, while only deletions in chromosome 1p retained its negative prognostic impact in R-CHOP–treated SFL. In contrast, no deletions in one of the investigated genetic loci predicted clinical outcome in LFL. Likewise, the presence or absence of BCL2 translocations had no prognostic impact in LFL. Despite representing a genetic portfolio closely resembling SFL, LFL showed some differences in deletion frequencies. BCL2 translocation and 6q deletion frequency differs between LFL and SFL and might contribute to distinct genetic profiles in LFL and SFL
FLP Recombinase-Mediated Site-Specific Recombination in Silkworm, Bombyx mori
A comprehensive understanding of gene function and the production of site-specific genetically modified mutants are two major goals of genetic engineering in the post-genomic era. Although site-specific recombination systems have been powerful tools for genome manipulation of many organisms, they have not yet been established for use in the manipulation of the silkworm Bombyx mori genome. In this study, we achieved site-specific excision of a target gene at predefined chromosomal sites in the silkworm using a FLP/FRT site-specific recombination system. We first constructed two stable transgenic target silkworm strains that both contain a single copy of the transgene construct comprising a target gene expression cassette flanked by FRT sites. Using pre-blastoderm microinjection of a FLP recombinase helper expression vector, 32 G3 site-specific recombinant transgenic individuals were isolated from five of 143 broods. The average frequency of FLP recombinase-mediated site-specific excision in the two target strains genome was approximately 3.5%. This study shows that it is feasible to achieve site-specific recombination in silkworms using the FLP/FRT system. We conclude that the FLP/FRT system is a useful tool for genome manipulation in the silkworm. Furthermore, this is the first reported use of the FLP/FRT system for the genetic manipulation of a lepidopteran genome and thus provides a useful reference for the establishment of genome manipulation technologies in other lepidopteran species
Low fitness at low latitudes: Wintering in the tropics increases migratory delays and mortality rates in an Arctic breeding shorebird
Publisher's version (útgefin grein)Evolutionary theories of seasonal migration generally assume that the costs of longer migrations are balanced by benefits at the non-breeding destinations. We tested, and rejected, the null hypothesis of equal survival and timing of spring migration for High Arctic breeding sanderling Calidris alba using six and eight winter destinations between 55°N and 25°S, respectively. Annual apparent survival was considerably lower for adult birds wintering in tropical West Africa (Mauritania: 0.74 and Ghana: 0.75) than in three European sites (0.84, 0.84 and 0.87) and in subtropical Namibia (0.85). Moreover, compared with adults, second calendar-year sanderlings in the tropics, but not in Europe, often refrained from migrating north during the first possible breeding season. During northward migration, tropical-wintering sanderlings occurred at their final staging site in Iceland 5–15 days later than birds wintering further north or south. Namibia-wintering sanderlings tracked with solar geolocators only staged in West Africa during southward migration. The low annual survival, the later age of first northward migration and the later passage through Iceland during northward migration of tropical-wintering sanderlings, in addition to the skipping of this area during northward but not southward migration by Namibia-wintering sanderlings, all suggest they face issues during the late non-breeding season in West Africa. Migrating sanderlings defy long distances but may end up in winter areas with poor fitness prospects. We suggest that ecological conditions in tropical West Africa make the fuelling prior to northward departure problematic.Annual expeditions to Mauritania were organized by NIOZ, and we especially thank Maarten Brugge, Anne Dekinga, Jutta Leyrer and Bernard Spaans for their contributions. The Parc National du Banc d'Arguin granted research permits and facilitated access. J.R. and T.S.L.V. thank Aarhus University for logistical support at Zackenberg. Benoît Sittler organized expeditions to Karupelv Valley. The Farlington Ringing Group provided cannon‐net equipment. This work was supported by two grants from the Netherlands Polar Programme (851.40.072 and 866.15.207) of the Netherlands Organisation for Scientific research (NWO) and from the Metawad project awarded by Waddenfonds (WF209925) to JR and TP. The measurements in Mauritania had their beginnings in the Prins Bernhard Cultuurfondsprijs to TP. JR and TP also received INTERACT grants for Transnational Access from the European Community's Seventh Framework Programme (grant agreement No262693). JR received a generous donation from World Wildlife Fund Netherlands. JAA was supported by FCT (SFRH/BPD/91527/2012). OG and Loïc Bollache were supported by the French Polar Institute (IPEV; program ‘1036 Interactions') and TL by a Veni grant (no. 016.Veni.192.245) from NWO. The authors declare no conflict of interest. This study is based on the efforts of more than 2,000 observers reporting colour‐ringed sanderlings. We especially thank Guðmundur Örn Benediktsson, John Bowler, Ruth Croger, Anne de Potier, Benjamin Gnep, Kim Fischer, Kirsten Grond, Eileen Hughes, Hilger Lemke, Pedro Lourenço, Andy Johnson, Pierre Leon, Jelle Loonstra, Sebastien Nedellec, Afonso Rocha, Brian Rogers, Ron Summers, Jan van Dijk and Hein Verkade. Anneke Bol, Marco van der Velde and Yvonne Verkuil molecularly sexed the majority of birds, Maria Teixeira and Jérôme Moreau sexed eight individuals. Ron Porter created flags for geolocator attachment. Eldar Rakhimberdiev answered questions concerning FLightR and Allert Bijleveld, Jesse Conklin, Rosemarie Kentie, Thomas Oudman, Janne Ouwehand, Emma Penning, Eldar Rakhimberdiev, Brett Sandercock, Ron Summers, Yvonne Verkuil and two reviewers critically commented on drafts. Benjamin Gnep created Figure.Peer Reviewe
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