Location privacy online:China, the Netherlands and South Korea

The aim of the study is to explore cross-cultural differences in users’ location privacy behaviour on LBSNs (location-based social networks) in China, the Netherlands and Korea. The study suggests evidence that Chinese, Dutch and Korean users exhibit different location privacy concerns, attitudes to social influence, perceived privacy control and willingness to share location-related information on LBSNs. The results show that in general, the more concerned users are about location privacy, the less they are willing to share and it also suggests that location privacy concern and social influence affect each other. Furthermore, the more control people perceive they have over their privacy, the more they are willing to share location information. A negative relationship between willingness to share location information and users’ actual sharing of location information was seen. In short, it is concluded that the relation between cultural values and location privacy behaviours only have a partial connection

SelFormaly: Towards Task-Agnostic Unified Anomaly Detection

The core idea of visual anomaly detection is to learn the normality from normal images, but previous works have been developed specifically for certain tasks, leading to fragmentation among various tasks: defect detection, semantic anomaly detection, multi-class anomaly detection, and anomaly clustering. This one-task-one-model approach is resource-intensive and incurs high maintenance costs as the number of tasks increases. This paper presents SelFormaly, a universal and powerful anomaly detection framework. We emphasize the necessity of our off-the-shelf approach by pointing out a suboptimal issue with fluctuating performance in previous online encoder-based methods. In addition, we question the effectiveness of using ConvNets as previously employed in the literature and confirm that self-supervised ViTs are suitable for unified anomaly detection. We introduce back-patch masking and discover the new role of top k-ratio feature matching to achieve unified and powerful anomaly detection. Back-patch masking eliminates irrelevant regions that possibly hinder target-centric detection with representations of the scene layout. The top k-ratio feature matching unifies various anomaly levels and tasks. Finally, SelFormaly achieves state-of-the-art results across various datasets for all the aforementioned tasks.Comment: 11 pages, 7 figure

Maximum-Area Rectangles in a Simple Polygon

We study the problem of finding maximum-area rectangles contained in a polygon in the plane. There has been a fair amount of work for this problem when the rectangles have to be axis-aligned or when the polygon is convex. We consider this problem in a simple polygon with n vertices, possibly with holes, and with no restriction on the orientation of the rectangles. We present an algorithm that computes a maximum-area rectangle in O(n^3 log n) time using O(kn^2) space, where k is the number of reflex vertices of P. Our algorithm can report all maximum-area rectangles in the same time using O(n^3) space. We also present a simple algorithm that finds a maximum-area rectangle contained in a convex polygon with n vertices in O(n^3) time using O(n) space

Differentially Private Sharpness-Aware Training

Training deep learning models with differential privacy (DP) results in a degradation of performance. The training dynamics of models with DP show a significant difference from standard training, whereas understanding the geometric properties of private learning remains largely unexplored. In this paper, we investigate sharpness, a key factor in achieving better generalization, in private learning. We show that flat minima can help reduce the negative effects of per-example gradient clipping and the addition of Gaussian noise. We then verify the effectiveness of Sharpness-Aware Minimization (SAM) for seeking flat minima in private learning. However, we also discover that SAM is detrimental to the privacy budget and computational time due to its two-step optimization. Thus, we propose a new sharpness-aware training method that mitigates the privacy-optimization trade-off. Our experimental results demonstrate that the proposed method improves the performance of deep learning models with DP from both scratch and fine-tuning. Code is available at https://github.com/jinseongP/DPSAT.Comment: ICML 202

Gemini Near-IR Photometry of the Arches Cluster near the Galactic Center

We present Near-IR photometry of the Arches cluster, a young and massive stellar cluster near the Galactic center. We have analyzed the high resolution (FWHM 0.2") H and K' band images in the Galactic Center Demonstration Science Data Set, which were obtained with the Gemini/Hokupa's adaptive optics (AO) system. We present the color-magnitude diagram, the luminosity function and the initial mass function (IMF) of the stars in the Arches cluster in comparison with the HST/NICMOS data. The IMF slope for the range of 1.0< log(M/M_sun) <2.1 is estimated to be Gamma = -0.79+/-0.16, in good agreements with the earlier result based on the HST/NICMOS data [Figer et al. 1999, ApJ, 525, 750]. These results strengthen the evidence that the IMF of the bright stars close to the Galactic center is much flatter than that for the solar neighborhood. This is also consistent with a recent finding that the IMFs of the bright stars in young clusters in M33 get flatter as the galactocentric distance decreases [Lee et al. 2001, astro-ph 0109258]. It is found that the power of the Gemini/AO system is comparable, with some limits, to that of the HST/NICMOS.Comment: 11 pages, 6 figures, Accepted by the Journal of Korea Astronomy Society (JKAS

What Makes Lyα\alpha Nebulae Glow? Mapping the Polarization of LABd05

"Ly$\alpha$ nebulae" are giant ($\sim$100 kpc), glowing gas clouds in the distant universe. The origin of their extended Ly$\alpha$ emission remains a mystery. Some models posit that Ly$\alpha$ emission is produced when the cloud is photoionized by UV emission from embedded or nearby sources, while others suggest that the Ly$\alpha$ photons originate from an embedded galaxy or AGN and are then resonantly scattered by the cloud. At least in the latter scenario, the observed Ly$\alpha$ emission will be polarized. To test these possibilities, we are conducting imaging polarimetric observations of seven Ly$\alpha$ nebulae. Here we present our results for LABd05, a cloud at $z$ = 2.656 with an obscured, embedded AGN to the northeast of the peak of Ly$\alpha$ emission. We detect significant polarization. The highest polarization fractions $P$ are $\sim$10-20% at $\sim$20-40 kpc southeast of the Ly$\alpha$ peak, away from the AGN. The lowest $P$, including upper-limits, are $\sim$5% and lie between the Ly$\alpha$ peak and AGN. In other words, the polarization map is lopsided, with $P$ increasing from the Ly$\alpha$ peak to the southeast. The measured polarization angles $\theta$ are oriented northeast, roughly perpendicular to the $P$ gradient. This unique polarization pattern suggests that 1) the spatially-offset AGN is photoionizing nearby gas and 2) escaping Ly$\alpha$ photons are scattered by the nebula at larger radii and into our sightline, producing tangentially-oriented, radially-increasing polarization away from the photoionized region. Finally we conclude that the interplay between the gas density and ionization profiles produces the observed central peak in the Ly$\alpha$ emission. This also implies that the structure of LABd05 is more complex than assumed by current theoretical spherical or cylindrical models.Comment: 11 pages, 8 figure

Mapping the Polarization of the Radio-Loud Lyα\alpha Nebula B3 J2330+3927

Lya nebulae, or "Lya blobs", are extended (up to ~100 kpc), bright (L[Lya] > 10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions at z ~ 2--5. The origin of the Lya emission remains unknown, but recent theoretical work suggests that measuring the polarization might discriminate among powering mechanisms. Here we present the first narrowband, imaging polarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya emission peak and its radio lobes align roughly with the blob's major axis. With the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya + continuum) polarization in a grid of circular apertures of radius 0.6" (4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine apertures and achieving strong upper-limits (as low as 2%) elsewhere. P increases from <2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The detections are distributed asymmetrically, roughly along the nebula's major axis. The polarization angles theta are mostly perpendicular to this axis. Comparing the Lya flux to that of the continuum, and conservatively assuming that the continuum is highly polarized (20-100%) and aligned with the total polarization, we place lower limits on the polarization of the Lya emission P(Lya) ranging from no significant polarization at ~5 kpc from the blob center to ~ 3--17% at 10--25kpc. Like the total polarization, the Lya polarization detections occur more often along the blob's major axis.Comment: 9 pages, 7 figures, accepted for publication in Ap