6,339 research outputs found
Computational Modelling of Wing Downwash Profile with Reynolds-Averaged and Delayed Detached-Eddy Simulations
This paper describes the computational model to predict downwash for a conventional
fixed wing configuration at flight scales (ReMAC = 2.26 Ă 107
). The lack of resolution in the
downwash wake region resulted in an over-dissipation of the turbulent behaviour of airflow
in the wingâs wake. This artificially inflates the effectiveness of the horizontal stabilizer where
an over-prediction of pitch stiffness was observed. To resolve this over-dissipation, both the
Reynolds-Averaged and Delayed Detached-Eddy Simulation methodology were adopted to
accurately capture the downwash profile leaving the wing. Comparisons between the
estimation of wall shear stresses and viscous wall unit against a âfirst-cutâ simulation are made
and discussed. Fundamental features of the downwash profile including the spatial and
temporal scales used for the mesh are also presented and detailed in this paper
End states and subgap structure in proximity-coupled chains of magnetic adatoms
A recent experiment [Nadj-Perge et al., Science 346, 602 (2014)] provides
evidence for Majorana zero modes in iron (Fe) chains on the superconducting
Pb(110) surface. Here, we study this system by scanning tunneling microscopy
using superconducting tips. This high-resolution technique resolves a rich
subgap structure, including zero-energy excitations in some chains. We compare
the symmetry properties of the data under voltage reversal against theoretical
expectations and provide evidence that the putative Majorana signature overlaps
with a previously unresolved low-energy resonance. Interpreting the data within
a Majorana framework suggests that the topological gap is significantly smaller
than previously believed. Aided by model calculations, we also analyze
higher-energy features of the subgap spectrum and their relation to high-bias
peaks which we associate with the Fe d-bands.Comment: 5+5 pages, 5+6 figure
Insights on Hospitality, Retailing, and Commercial Real Estate: 2014 Cornell Retail Real Estate Roundtable Proceedings
Undeniably, the retail industry spectrum is broad,â said roundtable chair Peng Liu, as he opened the inaugural retail roundtable, held in New York City in June 2014. An associate professor of real estate at the Cornell School of Hotel Administration, Liu added that real estate spans âfrom the overall economy and retail market trends to technology innovation and big data; and from retail leasing negotiations to shopping center investments and financing. The retail industry is an asset-intensive business with real estate playing a critical role.â Continued growth of internet-based commerce is one source of this phenomenon, and the rise of the internet has also created a new framework for many retailers, in which electronic operations and those at physical stores are blended with each other, as demanded by the customer
Z-Selectivity in Olefin Metathesis with Chelated Ru Catalysts: Computational Studies of Mechanism and Selectivity
The mechanism and origins of Z-selectivity in olefin metathesis with chelated Ru catalysts were explored using density functional theory. The olefin approaches from the âsideâ position of the chelated Ru catalysts, in contrast to reactions with previous unchelated Ru catalysts that favor the bottom-bound pathway. Steric repulsions between the substituents on the olefin and the N-substituent on the N-heterocyclic carbene ligand lead to highly selective formation of the Z product
Imaging Studies of photodamage and self-healing in disperse orange 11 dye-doped PMMA
We report on optical imaging studies of self-healing after laser-induced
photodamage in disperse orange 11 dye doped into poly(methyl methacrylate)
(PMMA) polymer. In particular, the high spatial-contrast image of the damage
track made by a line focus pump laser allows the recovery rates to be measured
as a function of burn dose using the relationship between transverse distance
and pump intensity profile. The time evolution of the damaged population
results in an intensity-independent time constant of {\tau} = 490\pm23 min, in
agreement with independent measurements of the time evolution of amplified
spontaneous emission. Also observed is a damage threshold above which the
material does not fully recover.Comment: 5 pages, 8 figure
The formation of acetylcholine receptor clusters visualized with quantum dots
Background: Motor innervation of skeletal muscle leads to the assembly of acetylcholine receptor (AChR) clusters in the postsynaptic membrane at the vertebrate neuromuscular junction (NMJ). Synaptic AChR aggregation, according to the diffusion-mediated trapping hypothesis, involves the establishment of a postsynaptic scaffold that "traps" freely diffusing receptors into forming high-density clusters. Although this hypothesis is widely cited to explain the formation of postsynaptic AChR clusters, direct evidence at molecular level is lacking. Results: Using quantum dots (QDs) and live cell imaging, we provide new measurements supporting the diffusion-trap hypothesis as applied to AChR cluster formation. Consistent with published works, experiments on cultured Xenopus myotomal muscle cells revealed that AChRs at clusters that formed spontaneously (pre-patterned clusters, also called hot spots) and at those induced by nerve-innervation or by growth factor-coated latex beads were very stable whereas diffuse receptors outside these regions were mobile. Moreover, despite the restriction of AChR movement at sites of synaptogenic stimulation, individual receptors away from these domains continued to exhibit free diffusion, indicating that AChR clustering at NMJ does not involve an active attraction of receptors but is passive and diffusion-driven. Conclusion: Single-molecular tracking using QDs has provided direct evidence that the clustering of AChRs in muscle cells in response to synaptogenic stimuli is achieved by two distinct cellular processes: the Brownian motion of receptors in the membrane and their trapping and immobilization at the synaptic specialization. This study also provides a clearer picture of the "trap" that it is not a uniformly sticky area but consists of discrete foci at which AChRs are immobilized
Scanning-gate microscopy of semiconductor nanostructures: an overview
This paper presents an overview of scanning-gate microscopy applied to the
imaging of electron transport through buried semiconductor nanostructures.
After a brief description of the technique and of its possible artifacts, we
give a summary of some of its most instructive achievements found in the
literature and we present an updated review of our own research. It focuses on
the imaging of GaInAs-based quantum rings both in the low magnetic field
Aharonov-Bohm regime and in the high-field quantum Hall regime. In all of the
given examples, we emphasize how a local-probe approach is able to shed new, or
complementary, light on transport phenomena which are usually studied by means
of macroscopic conductance measurements.Comment: Invited talk by SH at 39th "Jaszowiec" International School and
Conference on the Physics of Semiconductors, Krynica-Zdroj, Poland, June 201
PARSNIP: Performant Architecture for Race Safety with No Impact on Precision
Data race detection is a useful dynamic analysis for multithreaded programs that is a key building block in record-and-replay, enforcing strong consistency models, and detecting concurrency bugs. Existing software race detectors are precise but slow, and hardware support for precise data race detection relies on assumptions like type safety that many programs violate in practice.
We propose PARSNIP, a fully precise hardware-supported data race detector. PARSNIP exploits new insights into the redundancy of race detection metadata to reduce storage overheads. PARSNIP also adopts new race detection metadata encodings that accelerate the common case while preserving soundness and completeness. When bounded hardware resources are exhausted, PARSNIP falls back to a software race detector to preserve correctness. PARSNIP does not assume that target programs are type safe, and is thus suitable for race detection on arbitrary code.
Our evaluation of PARSNIP on several PARSEC benchmarks shows that performance overheads range from negligible to 2.6x, with an average overhead of just 1.5x. Moreover, Parsnip outperforms the state-of-the-art Radish hardware race detector by 4.6x
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