4,612 research outputs found
Transient Astrophysical Pulses and Quantum Gravity
Searches for transient astrophysical pulses could open an exciting new window
into the fundamental physics of quantum gravity. In particular, an evaporating
primordial black hole in the presence of an extra dimension can produce a
detectable transient pulse. Observations of such a phenomenon can in principle
explore the electroweak energy scale, indicating that astrophysical probes of
quantum gravity can successfully complement the exciting new physics expected
to be discovered in the near future at the Large Hadron Collider.Comment: 7 pages, This essay received an honorable mention in the Gravity
Research Foundation Essay Competition, 200
Online Learning with Ensembles
Supervised online learning with an ensemble of students randomized by the
choice of initial conditions is analyzed. For the case of the perceptron
learning rule, asymptotically the same improvement in the generalization error
of the ensemble compared to the performance of a single student is found as in
Gibbs learning. For more optimized learning rules, however, using an ensemble
yields no improvement. This is explained by showing that for any learning rule
a transform exists, such that a single student using
has the same generalization behaviour as an ensemble of
-students.Comment: 8 pages, 1 figure. Submitted to J.Phys.
Occupation and working outcomes during the Coronavirus Pandemic
Using data from the first wave of the SHARE COVID-19 Survey and additional information collected from the previous waves of SHARE (Survey of Health Ageing and Retirement in Europe), we explore the effects of job characteristics on two outcomes: (i) the probability of work interruptions and (ii) the length of such interruptions during the first phase of the Coronavirus Pandemic. In order to assess the relationship between job features and labour market outcomes, we define two indexes proxying the pre-COVID-19 technical remote work feasibility as well as the level of social interaction with other people while working. Moreover, we use an indicator that classifies ISCO-08 3-digit job titles based on the essential nature of the good or service provided. We find that job characteristics have been major determinants of the probability of undergoing work interruptions and their duration. In addition, we show that women have been negatively affected by the Pandemic to a much larger extent than men, suggesting the relevance of the intrinsic characteristics of jobs they are mainly involved in, and the role of gender selection into specific activities. Not only females were more likely to have undergone work interruptions but they also exhibited larger probabilities of longer work breaks. A similar impact is seen for self-employed and less-educated workers
Intraluminal recanalization of long infrainguinal chronic total occlusions using the Crosser system
Purpose: To assess the safety and efficacy of a device for vibrational angioplasty in the
percutaneous intraluminal recanalization of long infrainguinal chronic total occlusions (CTO).
Technique: The Crosser CTO Recanalization System is a mechanical recanalization device
that uses high-frequency vibrational energy to disrupt and channel through fibrocalcific
plaque without harming the vessel wall, thus assisting in the recanalization of an occluded
artery. In 12 diabetic patients (7 men; median age 71 years, range 58–80) with critical limb
ischemia owing to long (median length 26 cm, range 21–32) infrainguinal CTOs resistant to
conventional guidewire techniques, the Crosser CTO Recanalization System was
successful in intraluminally crossing the occlusion in 9 (75%) patients in ,5 minutes
(mean 4:03 minutes). The safety endpoint (distal lumen guidewire position with no vessel
perforation or dissection) was achieved in all successful cases.
Conclusion: In our preliminary experience, the Crosser CTO Recanalization Catheter
decreased crossing time, was safe, and achieved a high rate of intraluminal recanalization
of long infrainguinal CTOs.
J Endovasc Ther. 2009;16:23–27
Key words: critical limb ischemia, chronic total occlusion, percutaneous interventions,
infrainguinal occlusion, intraluminal recanalization, vibrational energ
optimized low pressure solar dec with zeolite based adsorption
Abstract This paper presents a new concept of hybrid/natural air conditioning system with a high level of architectural integration. A solar DEC (Desiccant Evaporative Cooling) open cycle with very low pressure drops, drastically reduces the electricity consumption for driving fans. The supply air is dehumidified by an innovative zeolite coated adsorption bed and cooled indirectly by an evaporative cooler, through a low pressure drop heat exchanger. The adsorption bed is a finned coil heat exchanger coated with a SAPO-34 zeolite layer realizing both heat and mass transfer in one component. Low thermal grade heat is used to regenerate the adsorbent material, showing high compatibility with low temperature solar systems such as flat plate or evacuated tubes solar collectors. Experimental data have been used for validating a CFD model of the coated coil. The possibility to remove the adsorption heat during dehumidification reduces the air temperature with a positive effect on cooling power
Cryptography based on neural networks - analytical results
Mutual learning process between two parity feed-forward networks with
discrete and continuous weights is studied analytically, and we find that the
number of steps required to achieve full synchronization between the two
networks in the case of discrete weights is finite. The synchronization process
is shown to be non-self-averaging and the analytical solution is based on
random auxiliary variables. The learning time of an attacker that is trying to
imitate one of the networks is examined analytically and is found to be much
longer than the synchronization time. Analytical results are found to be in
agreement with simulations
Statistical mechanics of mutual information maximization
An unsupervised learning procedure based on maximizing the mutual information between the outputs of two networks receiving different but statistically dependent inputs is analyzed (Becker S. and Hinton G., Nature, 355 (1992) 161). By exploiting a formal analogy to supervised learning in parity machines, the theory of zero-temperature Gibbs learning for the unsupervised procedure is presented for the case that the networks are perceptrons and for the case of fully connected committees
Noncontact Laser Ultrasonic Inspection of Ceramic Matrix Composites (CMCs)
Ceramic matrix composites (CMCs) are poised to revolutionize jet engine technology by enabling operation temperatures well beyond those possible with current superalloys, while reducing active cooling requirements and engine weight. Manufacturing of parts formed by silicon-carbide (SiC) fibers in a SiC matrix is now well advanced, with the first non-structural static components entering service in 2017 with the CFM Leap® engine that features SiC/SiC turbine shrouds. In order to expand the scope of application of CMCs to rotating parts, such as turbine blades, much work is being conducted to understand and characterize the modes of failure of these materials at temperatures beyond 1,000 °C. In this context, the ability of nondestructively monitoring the formation and progression of damage in CMCs specimens during high-temperature mechanical testing is critical. However, the elevated temperature precludes the possibility of using sensors placed in direct contact with the specimen and therefore severely restricts the range of available NDE techniques. This paper provides the first experimental assessment of the feasibility of noncontact laser ultrasonic inspection of SiC/SiC flat coupons. An Nd:Yag laser is used to excite ultrasonic waves on one side of the specimen while a Michelson interferometer detects the signals emerging on the other side at the epicenter position. The lasers are mounted on synchronized linear stages to form C-scans as in conventional immersion ultrasonics while ablation damage to the surface of the specimen is prevented by operating the lasers at low power density. Despite the complex microstructure of the SiC/SiC material it is found that the measured waveforms are remarkably similar to those observed when conducting the same tests in aluminum specimens. Moreover, it is shown that it is possible to: a) image interlaminar defects caused by impacts, and b) monitor crack opening under tensile load. Finally, very good signal stability is observed when temperature is increased from 25 to 1,250 °C which confirms the feasibility of laser monitoring at high temperature and is consistent with the excellent thermal stability of CMC mechanical properties
- …