1,299 research outputs found
Some initial results and observations from a series of trials within the Ofcom TV White Spaces pilot
P-Wave Holographic Insulator/Superconductor Phase Transition
Using a five dimensional AdS soliton in an Einstein-Yang-Mills theory with
SU(2) gauge group we study p-wave holographic insulator/superconductor phase
transition. To explore the phase structure of the model we consider the system
in the probe limit as well as fully back reacted solutions. We will also study
zero temperature limit of the p-wave holographic superconductor in four
dimensions.Comment: Latex,18 pages,7 figures, v2: Typos correction, v3: minor changes
added, and clarifications mad
Fermions in non-relativistic AdS/CFT correspondence
We extend the non-relativistic AdS/CFT correspondence to the fermionic
fields. In particular we study the two point function of a fermionic operator
in non-relativistic CFTs by making use of a massive fermion propagating in
geometries with Schrodinger group isometry. Although the boundary of the
geometries with Schrodinger group isometry differ from that in AdS geometries
where the dictionary of AdS/CFT is established, using the general procedure of
AdS/CFT correspondence, we see that the resultant two point function has the
expected form for fermionic operators in non-relativistic CFTs, though a
non-trivial regularization may be needed.Comment: 12 pages,Latex file; V2: typos corrected, refs adde
Breaking a Chaotic Cryptographic Scheme Based on Composition Maps
Recently, a chaotic cryptographic scheme based on composition maps was
proposed. This paper studies the security of the scheme and reports the
following findings: 1) the scheme can be broken by a differential attack with
chosen-plaintext, where is the size of
plaintext and is the number of different elements in plain-text; 2) the
scheme is not sensitive to the changes of plaintext; 3) the two composition
maps do not work well as a secure and efficient random number source.Comment: 9 pages, 7 figure
Suppression of turbulence in wallâbounded flows by highâfrequency spanwise oscillations
The response of wallâflow turbulence to highâfrequency spanwise oscillations was investigated by direct numerical simulations of a planar channel flow subjected either to an oscillatory spanwise crossâflow or to the spanwise oscillatory motion of a channel wall. Periods of oscillation, Tosc+=ToscuĎ2/ν, ranging from 25 to 500 were studied. For 25â¤Tosc+â¤200 the turbulent bursting process was suppressed, leading to sustained reductions of 10% to 40% in the turbulent drag and comparable attenuations in all three components of turbulence intensities as well as the turbulent Reynolds shear stress. Oscillations at Tosc+=100 produced the most effective suppression of turbulence. The results were independent of whether the oscillations were generated by a crossâflow or by the motion of a channel wall. In the latter case, suppression of turbulence was restricted to the oscillating wall while the flow at the other wall remained fully turbulent. Spanwise oscillations may provide a simple and effective method for control of turbulence in wallâbounded flows.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71217/2/PFADEB-4-8-1605-1.pd
Control of wall turbulence by high frequency spanwise oscillations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76966/1/AIAA-1993-3282-205.pd
Recommended from our members
Perceptual image quality assessment for various viewing conditions and display systems
From complete darkness to direct sunlight, real-world dis-
plays operate in various viewing conditions often resulting in a
non-optimal viewing experience. Most existing Image Quality
Assessment (IQA) methods, however, assume ideal environments
and displays, and thus cannot be used when viewing conditions
differ from the standard. In this paper, we investigate the influence
of ambient illumination level and display luminance on human
perception of image quality. We conduct a psychophysical study
to collect a novel dataset of over 10000 image quality preference
judgments performed in illumination conditions ranging from 0 lux
to 20000 lux. We also propose a perceptual IQA framework that
allows most existing image quality metrics (IQM) to accurately
predict image quality for a wide range of illumination conditions
and display parameters 1 . Our analysis demonstrates strong cor-
relation between human IQA and the predictions of our proposed
framework combined with multiple prominent IQMs and across a
wide range of luminance values
MMS Observations of Plasma Heating Associated With FTE Growth
Upon formation, flux transfer events (FTEs) in the subsolar magnetosheath have been observed to grow in diameter, ĂÂť, while convecting along the magnetopause. Plasma pressure has also been found to decrease subâ adiabatically with increasing ĂÂť, indicating the presence of internal plasma acceleration and heating processes. Here, the Magnetospheric Multiscale (MMS) fields and plasma measurements are used to determine the relative roles of parallel electric fields, betatron, and Fermi processes in plasma heating inside an ensemble of 55 subsolar FTEs. Plasma heating is shown asymmetric inside FTEs. Parallel electric fields dominate (>75%) ion and electron heating at the leading edge of FTEs. At the trailing edge, betatron and Fermi processes overtake (>50%), resulting in ion cooling and electron heating, respectively. The observed strong net heatings inside FTEs are proportional to Ýâ 1/2. It is concluded that reconnectionâ driven heating continues inside FTEs far from the subsolar electron and ion diffusion regions.Plain Language SummaryEnergetic charged particles are observed in many space and astrophysical environments, including our solar system. However, the acceleration and heating mechanisms responsible for generating these energetic charged particles remain to be discovered. Simulations and in situ observations have shown that magnetic reconnection, a process through which magnetic field lines â reconnectâ and release magnetic energy, plays a major role in generating energetic charged particles. The primary sites for magnetic energy transfer to charged particle acceleration and heating are the twin exhaust regions that emanate from the reconnection Xâ line. However, the amount of kinetic energy gained by charged particles in the exhaust regions represents only a small fraction of the total energy released by magnetic reconnection. Here, the Magnetospheric Multiscale (MMS) multipoint fields and plasma measurements are used to determine the contributions of acceleration mechanisms operating inside flux transfer events (FTEs), which are formed in the reconnection exhaust regions. We observe that acceleration mechanisms contribute to the charged particlesâ energy gain inside FTEs. We further reveal that while acceleration mechanisms are most significant inside smaller FTEs, they continue to accelerate charged particles inside larger FTEs. We conclude that magnetic reconnectionâ driven charged particle acceleration is longâ lasting and can take place far from the exhaust regions.Key PointsThe relative roles of parallel electric fields, betatron, and Fermi processes in plasma heating inside 55 subsolar FTEs are determinedParallel electric fields dominate plasma energization at FTEsâ leading edge. Betatron and Fermi processes overtake at FTEsâ trailing edgeMMS observations reveal strong plasma acceleration inside FTEs that is inversely proportional to the square root of FTE diameterPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152496/1/grl59844_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152496/2/grl59844-sup-0001-2019GL084843-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152496/3/grl59844.pd
Dry Surface Treatments of Silk Biomaterials and Their Utility in Biomedical Applications
Silk-based materials are widely used in biomaterial and tissue engineering applications due to their cytocompatibility and tunable mechanical and biodegradation properties. Aqueous-based processing techniques have enabled the fabrication of silk into a broad range of material formats, making it a highly versatile material platform across multiple industries. Utilizing the full potential of silk in biomedical applications frequently requires modification of silk's surface properties. Dry surface modification techniques, including irradiation and plasma treatment, offer an alternative to the conventional wet chemistry strategies to modify the physical and chemical properties of silk materials without compromising their bulk properties. While dry surface modification techniques are more prevalent in textiles and sterilization applications, the range of modifications available and resultant changes to silk materials all point to the utility of dry surface modification for the development of new, functional silk biomaterials. Dry surface treatment affects the surface chemistry, secondary structure, molecular weight, topography, surface energy, and mechanical properties of silk materials. This Review describes and critically evaluates the effect of physical dry surface modification techniques, including irradiation and plasma processes, on silk materials and discusses their utility in biomedical applications, including recent examples of modulation of cell/protein interactions on silk biomaterials, in vivo performance of implanted biomaterials, and applications in material biofunctionalization and lithographic surface patterning approaches
- âŚ