Disk Evolution in W5: Intermediate Mass Stars at 2-5 Myr

We present the results of a survey of young intermediate mass stars (age $<$~5 Myr, 1.5 $<M_{\star} \leq$ 15 $M_{\odot}$) in the W5 massive star forming region. We use combined optical, near-infrared and {\it Spitzer} Space Telescope photometry and optical spectroscopy to define a sample of stars of spectral type A and B and examine their infrared excess properties. We find objects with infrared excesses characteristic of optically thick disks, i.e. Herbig AeBe stars. These stars are rare: $<$1.5% of the entire spectroscopic sample of A and B stars, and absent among stars more massive than 2.4 $M_\odot$. 7.5% of the A and B stars possess infrared excesses in a variety of morphologies that suggest their disks are in some transitional phase between an initial, optically thick accretion state and later evolutionary states. We identify four morphological classes based on the wavelength dependence of the observed excess emission above theoretical photospheric levels: (a) the optically thick disks; (b) disks with an optically thin excess over the wavelength range 2 to 24 \micron, similar to that shown by Classical Be stars; (c) disks that are optically thin in their inner regions based on their infrared excess at 2-8 \micron and optically thick in their outer regions based on the magnitude of the observed excess emission at 24 \micron; (d) disks that exhibit empty inner regions (no excess emission at $\lambda$ $\leq$ 8 \micron) and some measurable excess emission at 24 \micron. A sub-class of disks exhibit no significant excess emission at $\lambda \leq$ 5.8 \micron, have excess emission only in the {\it Spitzer} 8 \micron band and no detection at 24 \micron. We discuss these spectral energy distribution (SED) types, suggest physical models for disks exhibiting these emission patterns and additional observations to test these theories.Comment: 35 pages, 10 figures, accepted to Astrophysical Journa

Circumstellar Structure around Evolved Stars in the Cygnus-X Star Formation Region

We present observations of newly discovered 24 micron circumstellar structures detected with the Multiband Imaging Photometer for Spitzer (MIPS) around three evolved stars in the Cygnus-X star forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 micron emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 micron Infrared Array Camera (IRAC) bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 micron emission from the inner ring extends ~1.2 arcmin beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 micron emission, possibly due to an earlier episode of mass loss. For the two shell stars, we present the results of radiative transfer models, constraining the stellar and dust shell parameters. The shells are composed of amorphous carbon grains, plus polycyclic aromatic hydrocarbons in the case of G79.29+0.46. Both G79.29+0.46 and HBHA 4202-22 lie behind the main Cygnus-X cloud. Although G79.29+0.46 may simply be on the far side of the cloud, HBHA 4202-22 is unrelated to the Cygnus-X star formation region.Comment: Accepted by A

Selective Colorimetric Detection of Nitrite in Water using Chitosan Stabilized Gold Nanoparticles Decorated Reduced Graphene oxide

© 2017 The Author(s). Excess nitrite (NO 2 - ) concentrations in water supplies is considered detrimental to the environment and human health, and is associated with incidence of stomach cancer. In this work, the authors describe a nitrite detection system based on the synthesis of gold nanoparticles (AuNPs) on reduced graphene oxide (rGO) using an aqueous solution of chitosan and succinic acid. The AuNPs-rGO nanocomposite was confirmed by different physicochemical characterization methods including transmission electron microscopy, elemental analysis, X-ray diffraction, UV-visible (UV-vis) and Fourier transform infrared spectroscopy. The AuNPs-rGO nanocomposite was applicable to the sensitive and selective detection of NO 2 - with increasing concentrations quantifiable by UV-vis spectroscopy and obvious to the naked eye. The color of the AuNPs-rGO nanocomposite changes from wine red to purple with the addition of different concertation of NO 2 - . Therefore, nitrite ion concentrations can be quantitatively detected using AuNPs-rGO sensor with UV-vis spectroscopy and estimated with the naked eye. The sensor is able to detect NO 2 - in a linear response ranging from 1 to 20 μM with a detection limit of 0.1 μM by spectrophotometric method. The as-prepared AuNPs-rGO nanocomposite shows appropriate selectivity towards NO 2 - in the presence of potentially interfering metal anions

Global disparities in surgeons’ workloads, academic engagement and rest periods: the on-calL shIft fOr geNEral SurgeonS (LIONESS) study

: The workload of general surgeons is multifaceted, encompassing not only surgical procedures but also a myriad of other responsibilities. From April to May 2023, we conducted a CHERRIES-compliant internet-based survey analyzing clinical practice, academic engagement, and post-on-call rest. The questionnaire featured six sections with 35 questions. Statistical analysis used Chi-square tests, ANOVA, and logistic regression (SPSS® v. 28). The survey received a total of 1.046 responses (65.4%). Over 78.0% of responders came from Europe, 65.1% came from a general surgery unit; 92.8% of European and 87.5% of North American respondents were involved in research, compared to 71.7% in Africa. Europe led in publishing research studies (6.6 ± 8.6 yearly). Teaching involvement was high in North America (100%) and Africa (91.7%). Surgeons reported an average of 6.7 ± 4.9 on-call shifts per month, with European and North American surgeons experiencing 6.5 ± 4.9 and 7.8 ± 4.1 on-calls monthly, respectively. African surgeons had the highest on-call frequency (8.7 ± 6.1). Post-on-call, only 35.1% of respondents received a day off. Europeans were most likely (40%) to have a day off, while African surgeons were least likely (6.7%). On the adjusted multivariable analysis HDI (Human Development Index) (aOR 1.993) hospital capacity &gt; 400 beds (aOR 2.423), working in a specialty surgery unit (aOR 2.087), and making the on-call in-house (aOR 5.446), significantly predicted the likelihood of having a day off after an on-call shift. Our study revealed critical insights into the disparities in workload, access to research, and professional opportunities for surgeons across different continents, underscored by the HDI

Science curriculum-making for the Anthropocene: perspectives and possibilities

This paper illuminates how science curriculum-making can be reinvigorated to address urgent local and global socioscientific issues that centres place as an interconnected part of larger socio-ecological and socio-technical systems. Given how industrial and capitalistic extractive practices have pushed the planet beyond its complex life-sustaining limits, we draw on theoretical perspectives that recognize schools as complex systems, nested within local, regional, and global social-ecological-technological systems. Science curriculum-making in these systems prompt dialogue regarding knowledge and competencies required to address planetary sustainability, as well as ontological questions connected to systems, relations, and responsibility. Consequently, schools are important places for curriculum enactment practices. Furthermore, teachers, students, administrators, and school community members are enmeshed with local ecologies that are constituted in the cultural, material, and social arrangements found in or brought to a school and its local community. In our work, we draw on a curriculum commonplaces perspective to investigate curriculum-making practices. Specifically, we use empirical data from two cases of elementary and secondary science teachers developing and enacting curriculum and adopt a philosophical-empirical deductive approach illustrative of how to apply complexity theory, systems thinking, and associated ontological and epistemological views to practical reasoning of science curriculum-making for schools.This work was supported by Social Sciences and Humanities Research Council [435-2018-59

Discrimination between Alzheimer dementia and controls by automated analysis of multicenter FDG PET

A new diagnostic indicator of FDG PET scan abnormality, based on age-adjusted t statistics and an automated voxel-based procedure, is presented and validated in a large data set comprising 110 normal controls and 395 patients with probable Alzheimer's disease (AD) that were studied in eight participating centers. The effect of differences in spatial resolution of PET scanners was minimized effectively by filtering and masking. In controls FDG uptake declined significantly with age in anterior cingulate and frontolateral perisylvian cortex. In patients with probable AD decline of FDG uptake in posterior cingulate, temporoparietal, and prefrontal association cortex was related to dementia severity. These effects were clearly distinct from age effects in controls, suggesting that the disease process of AD is not related to normal aging. Women with probable AD had significantly more frontal metabolic impairment than men. The new indicator of metabolic abnormality in AD-related regions provided 93% sensitivity and specificity for distinction of mild to moderate probable AD from normals, and 84% sensitivity at 93% specificity for detection of very mild probable AD (defined by Mini Mental Score 24 or better). All regions related to AD severity were already affected in very mild AD, suggesting that all vulnerable areas are affected to a similar degree already at disease onset. Ventromedial frontal cortex was also abnormal. In conclusion, automated analysis of multicenter FDG PET is feasible, provides insights into AD pathophysiology, and can be used potentially as a sensitive biomarker for early AD diagnosis. (C) 2002 Elsevier Science (USA)