The planetary nebula Abell 48 and its [WN4] central star

We have conducted a multi-wavelength study of the planetary nebula Abell 48 and give a revised classification of its nucleus as a hydrogen-deficient star of type [WN4]. The surrounding nebula has a morphology typical of PNe and importantly, is not enriched in nitrogen, and thus not the 'peeled atmosphere' of a massive star. Indeed, no WN4 star is known to be surrounded by such a compact nebula. The ionized mass of the nebula is also a powerful discriminant between the low-mass PN and high-mass WR ejecta interpretations. The ionized mass would be impossibly high if a distance corresponding to a Pop I star was adopted, but at a distance of 2 kpc, the mass is quite typical of moderately evolved PNe. At this distance, the ionizing star then has a luminosity of ~5000 Lsolar, again rather typical for a PN central star. We give a brief discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars.Comment: EUROWD12 Proceeding

The Consequences of REIT Index Membership for Return Patterns

The impact of stock market index membership on Real Estate Investment Trust (REIT) stock returns is unclear. Returns may become more like those of other indexed stocks and less like those of their underlying properties. Taking advantage of the inclusion of REITs in major S&P indexes starting in 2001, we find that shared index membership significantly increases the correlation between REIT returns. However, index membership also enhances the link between REIT returns and the underlying real estate, consistent with improved pricing efficiency

The Spitzer Atlas of Stellar Spectra

We present the Spitzer Atlas of Stellar Spectra (SASS), which includes 159 stellar spectra (5 to 32 mic; R~100) taken with the Infrared Spectrograph on the Spitzer Space Telescope. This Atlas gathers representative spectra of a broad section of the Hertzsprung-Russell diagram, intended to serve as a general stellar spectral reference in the mid-infrared. It includes stars from all luminosity classes, as well as Wolf-Rayet (WR) objects. Furthermore, it includes some objects of intrinsic interest, like blue stragglers and certain pulsating variables. All the spectra have been uniformly reduced, and all are available online. For dwarfs and giants, the spectra of early-type objects are relatively featureless, dominated by Hydrogen lines around A spectral types. Besides these, the most noticeable photospheric features correspond to water vapor and silicon monoxide in late-type objects and methane and ammonia features at the latest spectral types. Most supergiant spectra in the Atlas present evidence of circumstellar gas. The sample includes five M supergiant spectra, which show strong dust excesses and in some cases PAH features. Sequences of WR stars present the well-known pattern of lines of HeI and HeII, as well as forbidden lines of ionized metals. The characteristic flat-top shape of the [Ne III] line is evident even at these low spectral resolutions. Several Luminous Blue Variables and other transition stars are present in the Atlas and show very diverse spectra, dominated by circumstellar gas and dust features. We show that the [8]-[24] Spitzer colors (IRAC and MIPS) are poor predictors of spectral type for most luminosity classes.Comment: Accepted by ApJS; Atlas contents available from: http://web.ipac.caltech.edu/staff/ardila/Atlas/index.html; http://irsa.ipac.caltech.edu/data/SPITZER/SASS/; 70 PDF pages, including figure

FedGT: Identification of Malicious Clients in Federated Learning with Secure Aggregation

We propose FedGT, a novel framework for identifying malicious clients in federated learning with secure aggregation. Inspired by group testing, the framework leverages overlapping groups of clients to identify the presence of malicious clients in the groups via a decoding operation. The clients identified as malicious are then removed from the training of the model, which is performed over the remaining clients. By choosing the size, number, and overlap between groups, FedGT strikes a balance between privacy and security. Specifically, the server learns the aggregated model of the clients in each group - vanilla federated learning and secure aggregation correspond to the extreme cases of FedGT with group size equal to one and the total number of clients, respectively. The effectiveness of FedGT is demonstrated through extensive experiments on the MNIST, CIFAR-10, and ISIC2019 datasets in a cross-silo setting under different data-poisoning attacks. These experiments showcase FedGT's ability to identify malicious clients, resulting in high model utility. We further show that FedGT significantly outperforms the private robust aggregation approach based on the geometric median recently proposed by Pillutla et al. on heterogeneous client data (ISIC2019) and in the presence of targeted attacks (CIFAR-10 and ISIC2019).Comment: 27 pages, 13 figure

Hospitalists in Teaching Hospitals: Opportunities but Not Without Danger

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73210/1/j.1525-1497.2004.42002.x.pd

Non–housestaff medicine services in academic centers: Models and challenges

Non–housestaff medicine services are growing rapidly in academic medical centers (AMCs), partly driven by efforts to comply with resident duty hour restrictions. Hospitalists have emerged as a solution to providing these services given their commitment to delivering efficient and high-quality care and the field's rapid growth. However, limited evidence is available on designing these services, including the similarities and differences of existing ones. We describe non–housestaff medicine services at 5 AMCs in order to share our experiences and outline important considerations in service development. We discuss common challenges in building and sustaining these models along with local institutional factors that affect decision making. Keys to success include ensuring an equitable system for scheduling and staffing, fostering opportunities for scholarly activities and academic promotion (defining the “academic hospitalist”), and providing compensation that supports recruitment and retention of hospitalists. With further work hour restrictions expected in the future and increased requests for surgical comanagement, the relationship between AMCs and hospitalists will continue to evolve. To succeed in developing hospitalist faculty who follow long careers in hospital medicine, academic leadership must carefully plan for and evaluate the methods of providing these clinical services while expanding on our academic mission. Journal of Hospital Medicine 2008;3:247–255. © 2008 Society of Hospital Medicine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60235/1/311_ftp.pd

Preliminary Results on the Use of an Antiserum to Human Parathyrin in a Homologous Radioimmunoassay

Peer Reviewe