اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe Curious Case of NGC6908
180
0
0.0
(
0
)
تأليف
B.F. Madore
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The object NGC6908 was once thought to be simply a surface-brightness enhancement in the eastern spiral arm of the nearby spiral galaxy NGC6907. Based on an examination of near-infrared imaging, the object is shown in fact to be a lenticular S0(6/7) galaxy hidden in the optical glare of the disk and spiral structure of the larger galaxy. New radial velocities of NGC6908 (3,060+/-16 (emission); 3,113+/-73 km/s (absorption)) have been obtained at the Baade 6.5m and the duPont 2.5m telescopes at Las Campanas, Chile placing NGC6908 at the same expansion-velocity distance as NGC6907 (3,190+/-5 km/s), eliminating the possibility of a purely chance line-of-sight coincidence. The once-enigmatic asymmetries in the disk and outer spiral structure of NGC6907 are now explained as being due to an advanced merger event. Newly discovered tails and debris in the outer reaches of this galaxy further support the merger scenario for this system. This pair of galaxies is a rather striking example of two objects discovered over 100 years ago, whose true nature was lost until modern detectors operating at infrared wavelengths gave us a new (high-contrast) look. Other examples of embedded merger remnants may also reveal themselves in the growing samples of near-infrared imaging of nearby galaxies; and a pilot study does reveal several other promising candidates for follow-up observations.
قيم البحث
اقرأ أيضاً
In the modern search for life elsewhere in the Universe, we are broadly looking for the following: the planets similar to Earth - physical indicators of habitability, and the manifestation of life - the biological signatures. A biosignature is a meas
ured parameter that has a high probability of being caused by the living organisms, either atmospheric gas species or some surface features. Therefore, the focus of a search is on a product or phenomena produced by the living systems, mostly by microorganisms as these are the most abundant on our planet like, say, methane. However, we may need to distinguish the terms `biosignature and `bioindicator. A biosignature is what living organisms produce - a bioproduct, while a bioindicator may be anything necessary for life as we know it, such as water or a rocky planet. Oxygen in this case is a double biomarker; first, it is a byproduct of oxygenic photosynthesis and, second, it is a signature of a complex life, because complex highly organized life requires high levels of oxygen. It is possible that there are other such bioindicators. For example, in the atmospheric compositions of terrestrial planets in our Solar System (including Titan), argon is one of the major constituents, moreover it was recently acknowledged to be a `biologically active gas, exhibiting organprotective and neuroprotective properties, especially under hypoxic conditions. Here we propose that argon in the atmosphere of a rocky planet is a bioindicator of a highly organized life, provided that the planet is already deemed potentially habitable: with water, atmosphere, and of a certain age allowing for the complex life to evolve. We also delineate its possible detection methods.
Abell 2256 is a rich, nearby (z=0.0594) galaxy cluster that has significant evidence of merger activity. We present new radio and X-ray observations of this system. The low-frequency radio images trace the diffuse synchrotron emission of the Mpc-scal
e radio halo and relics as well as a number of recently discovered, more compact, steep spectrum sources. The spectral index across the relics steepens from the north-west toward the south-east. Analysis of the spectral index gradients between low and and high-frequencies shows spectral differences away from the north-west relic edge such that the low-frequency index is significantly flatter than the high frequency spectral index near the cluster core. This trend would be consistent with an outgoing merger shock as the origin of the relic emission. New X-ray data from XMM-Newton reveal interesting structures in the intracluster medium pressure, entropy and temperature maps. The pressure maps show an overall low pressure core co-incident with the radio halo emission, while the temperature maps reveal multiple regions of cool emission within the central regions of Abell 2256. The two cold fronts in Abell 2256 both appear to have motion in similar directions.
We describe an effective theory of a scalar field, motivated by some features expected in the low energy theory of gluodynamics in 3+1 dimensions. The theory describes two propagating massless particles in a certain limit, which we identify with the
Abelian QED limit, and has classical string solutions in the general case. The string solutions are somewhat unusual as they are multiply degenerate due to spontaneous breaking of diffeomorphism invariance. Nevertheless all solutions yield identical electric field and have the same string tension.
In this paper, we investigate a constrained formulation of neural networks where the output is a convex function of the input. We show that the convexity constraints can be enforced on both fully connected and convolutional layers, making them applic
able to most architectures. The convexity constraints include restricting the weights (for all but the first layer) to be non-negative and using a non-decreasing convex activation function. Albeit simple, these constraints have profound implications on the generalization abilities of the network. We draw three valuable insights: (a) Input Output Convex Neural Networks (IOC-NNs) self regularize and reduce the problem of overfitting; (b) Although heavily constrained, they outperform the base multi layer perceptrons and achieve similar performance as compared to base convolutional architectures and (c) IOC-NNs show robustness to noise in train labels. We demonstrate the efficacy of the proposed idea using thorough experiments and ablation studies on standard image classification datasets with three different neural network architectures.
In this work, we study hallucinations in Neural Machine Translation (NMT), which lie at an extreme end on the spectrum of NMT pathologies. Firstly, we connect the phenomenon of hallucinations under source perturbation to the Long-Tail theory of Feldm
an (2020), and present an empirically validated hypothesis that explains hallucinations under source perturbation. Secondly, we consider hallucinations under corpus-level noise (without any source perturbation) and demonstrate that two prominent types of natural hallucinations (detached and oscillatory outputs) could be generated and explained through specific corpus-level noise patterns. Finally, we elucidate the phenomenon of hallucination amplification in popular data-generation processes such as Backtranslation and sequence-level Knowledge Distillation.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
