392 research outputs found
U.S. laws and regulations applicable to research reports
This memorandum describes the approach of the U.S. Securities and Exchange Commission (the "SEC") in monitoring and, where appropriate, regulating the use of research reports by investment banking firms in connection with securities transactions. The memorandum addresses the historical system of regulation, which continues in large measure to apply. It also examines the new initiatives taken, following a number of prominent corporate, accounting and banking scandals and a significant decline in U.S. and international capital markets, to supplement the current system in what some have dubbed the "post-Enron era"
A Ground-Based Albedo Upper Limit for HD 189733b from Polarimetry
We present 50 nights of polarimetric observations of HD 189733 in band
using the POLISH2 aperture-integrated polarimeter at the Lick Observatory Shane
3-m telescope. This instrument, commissioned in 2011, is designed to search for
Rayleigh scattering from short-period exoplanets due to the polarized nature of
scattered light. Since these planets are spatially unresolvable from their host
stars, the relative contribution of the planet-to-total system polarization is
expected to vary with an amplitude of order 10 parts per million (ppm) over the
course of the orbit. Non-zero and also variable at the 10 ppm level, the
inherent polarization of the Lick 3-m telescope limits the accuracy of our
measurements and currently inhibits conclusive detection of scattered light
from this exoplanet. However, the amplitude of observed variability
conservatively sets a upper limit to the planet-induced polarization
of the system of 58 ppm in band, which is consistent with a previous upper
limit from the POLISH instrument at the Palomar Observatory 5-m telescope
(Wiktorowicz 2009). A physically-motivated Rayleigh scattering model, which
includes the depolarizing effects of multiple scattering, is used to
conservatively set a upper limit to the geometric albedo of HD
189733b of . This value is consistent with the value derived from occultation observations with HST STIS (Evans et al.
2013), but it is inconsistent with the large albedo
reported by (Berdyugina et al. 2011).Comment: 10 pages, 9 figures, submitted to Ap
Quadrupedal Robots with Stiff and Compliant Actuation
In the broader context of quadrupedal locomotion, this overview article introduces and compares two platforms that are similar in structure, size, and morphology, yet differ greatly in their concept of actuation. The first, ALoF, is a classically stiff actuated robot that is controlled kinematically, while the second, StarlETH, uses a soft actuation scheme based on Changedhighly compliant series elastic actuators. We show how this conceptual difference influences design and control of the robots, compare the hardware of the two systems, and show exemplary their advantages in different application
Distributional Bellman Operators over Mean Embeddings
We propose a novel algorithmic framework for distributional reinforcement
learning, based on learning finite-dimensional mean embeddings of return
distributions. We derive several new algorithms for dynamic programming and
temporal-difference learning based on this framework, provide asymptotic
convergence theory, and examine the empirical performance of the algorithms on
a suite of tabular tasks. Further, we show that this approach can be
straightforwardly combined with deep reinforcement learning, and obtain a new
deep RL agent that improves over baseline distributional approaches on the
Arcade Learning Environment
A Side-Channel Assisted Cryptanalytic Attack Against QcBits
International audienceQcBits is a code-based public key algorithm based on a problem thought to be resistant to quantum computer attacks. It is a constant-time implementation for a quasi-cyclic moderate density parity check (QC-MDPC) Niederreiter encryption scheme, and has excellent performance and small key sizes. In this paper, we present a key recovery attack against QcBits. We first used differential power analysis (DPA) against the syndrome computation of the decoding algorithm to recover partial information about one half of the private key. We then used the recovered information to set up a system of noisy binary linear equations. Solving this system of equations gave us the entire key. Finally, we propose a simple but effective countermeasure against the power analysis used during the syndrome calculation
Species complexes and the importance of Data Deficient classification in Red List assessments: The case of Hylobatrachus frogs
This work is licensed under a Creative Commons Attribution 4.0 International License.Taxonomy is the cornerstone of extinction risk assessments. Currently, the IUCN Red List treats species complexes either under a single overarching species name—resulting in an unhelpfully broad circumscription and underestimated threat assessment that does not apply to any one species lineage—or omits them altogether—resulting in the omission of species that should be assessed. We argue that taxonomic uncertainty alone, as in species complexes, should be grounds for assessment as Data Deficient (DD). Yet, use of the DD category is currently discouraged, resulting in assessments based on poor data quality and dismissal of the importance of taxonomic confidence in conservation. This policy may be leading to volatile and unwarranted assessments of hundreds of species across the world, and needs to be revised. To illustrate this point, we here present a partial taxonomic revision of torrent frogs from eastern Madagascar in the Mantidactylus subgenus Hylobatrachus. Two named species, Mantidactylus (Hylobatrachus) lugubris and M. (H.) cowanii, and several undescribed candidate species are recognised, but the application of the available names has been somewhat ambiguous. In a recent re-assessment of its conservation status, M. (H.) lugubris was assessed including all complex members except M. (H.) cowanii within its distribution, giving it a status of Least Concern and distribution over most of eastern Madagascar. After describing two of the unnamed lineages as Mantidactylus (Hylobatrachus) atsimo sp. nov. (from southeastern Madagascar) and Mantidactylus (Hylobatrachus) petakorona sp. nov. (from the Marojejy Massif in northeastern Madagascar), we show that Mantidactylus (Hylobatrachus) lugubris is restricted to the central east of Madagascar, highlighting the inaccuracy of its current Red List assessment. We propose to re-assess its status under a more restrictive definition that omits well-defined candidate species, thus representing the actual species to which its assessment refers, to the best of current knowledge. We recommend that for species complexes in general, (1) nominal lineages that can be confidently restricted should be assessed under the strict definition, (2) non-nominal species-level lineages and ambiguous names should be prioritised for taxonomic research, and (3) ambiguous names should be assessed as DD to highlight the deficiency in data on their taxonomic status, which is an impediment to their conservation. This would reduce ambiguity and underestimation of threats involved in assessing species complexes, and place the appropriate emphasis on the importance of taxonomy in anchoring conservation.Deutscher Akademischer Austauschdienst fellowshipDeutsche Forschungsgemeinschaft (VE247/13-1 and 15-1
Efficient and Versatile Locomotion With Highly Compliant Legs
Drawing inspiration from nature, this paper introduces and compares two compliant robotic legs that are able to perform precise joint torque and position control, enable passive adaption to the environment, and allowfor the exploitation of natural dynamic motions.We report in detail on the design and control of both prototypes and elaborate specifically on the problem of precise foot placement during flight without the sacrifice of efficient energy storage during stance. This is achieved through an integrated design and control approach that incorporates series elastic actuation, series damping actuation, and active damping through torque control. The two legs are employed in efficient hopping/ running motions for which they achieve performance similar to humans or animals. This paper is concluded by a comparison of the various design choices with respect to performance and applicability, as well as an outlook on the usage of these legs in a fully actuated quadruped
Morphological and ecological convergence at the lower size limit for vertebrates highlighted by five new miniaturised microhylid frog species from three different Madagascan genera
Miniaturised frogs form a fascinating but poorly understood amphibian ecomorph and have been exceptionally prone to taxonomic underestimation. The subfamily Cophylinae (family Microhylidae), endemic to Madagascar, has a particularly large diversity of miniaturised species which have historically been attributed to the single genus Stumpffia largely based on their small size. Recent phylogenetic work has revealed that several independent lineages of cophyline microhylids evolved towards highly miniaturised body sizes, achieving adult snout- vent lengths under 16 mm. Here, we describe five new species belonging to three clades that independently miniaturised and that are all genetically highly divergent from their relatives: (i) a new genus (Mini gen.nov.) with three new species from southern Madagascar, (ii) one species of Rhombophryne, and (iii) one species of Anodonthyla. Mini mum sp. nov. from Manombo in eastern Madagascar is one of the smallest frogs in the world, reaching an adult body size of 9.7 mm in males and 11.3 mm in females. Mini scule sp.nov. from Sainte Luce in southeastern Madagascar is slightly larger and has maxillary teeth. Mini ature sp.nov. from Andohahela in southeast Madagascar is larger than its congeners but is similar in build. Rhombophryne proportionalis sp.nov. from Tsaratanana in northern Madagascar is unique among Madagascar's miniaturised frogs in being a proportional dwarf, exhibiting far less advanced signs of paedomorphism than other species of similar size. Anodonthyla eximia sp.nov. from Ranomafana in eastern Madagascar is distinctly smaller than any of its congeners and is secondarily terrestrial, providing evidence that miniaturisation and terrestriality may be evolutionarily linked. The evolution of body size in Madagascar's microhylids has been more dynamic than previously understood, and future studies will hopefully shed light on the interplay between ecology and evolution of these remarkably diverse frogs
Walking and Running with StarlETH
This paper presents the latest advances we made in static and dynamic locomotion with our compliant quadrupedal robot StarlETH. It summarizes the robot design and outlines the different underlying control principles used to achieve sophisticated locomotion performance. The focus of the paper is put on experimental findings which illustrate that the applied actuation and control principles are a valuable approach to bring our robotic devices a step closer to their natural counterparts
Using Bleichenbacher\u27s Solution to the Hidden Number Problem to Attack Nonce Leaks in 384-Bit ECDSA
In this paper we describe an attack against nonce leaks in 384-bit ECDSA using an FFT-based attack due to Bleichenbacher. The signatures were computed by a modern smart card. We extracted the low-order bits of each nonce using a template-based power analysis attack against the modular inversion of the nonce. We also developed a BKZ-based method for the range reduction phase of the attack, as it was impractical to collect enough signatures for the collision searches originally used by Bleichenbacher. We confirmed our attack by extracting the entire signing key using a 5-bit nonce leak from 4000 signatures
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