9,528 research outputs found
Tunneling magnetoresistance in diluted magnetic semiconductor tunnel junctions
Using the spin-polarized tunneling model and taking into account the basic
physics of ferromagnetic semiconductors, we study the temperature dependence of
the tunneling magnetoresistance (TMR) in the diluted magnetic semiconductor
(DMS) trilayer heterostructure system (Ga,Mn)As/AlAs/(Ga,Mn)As. The
experimentally observed TMR ratio is in reasonable agreement with our result
based on the typical material parameters. It is also shown that the TMR ratio
has a strong dependence on both the itinerant-carrier density and the magnetic
ion density in the DMS electrodes. This can provide a potential way to achieve
larger TMR ratio by optimally adjusting the material parameters.Comment: 5 pages (RevTex), 3 figures (eps), submitted to PR
"Because Some Sighted People, They Don't Know What the Heck You're Talking About:" A Study of Blind TikTokers' Infrastructuring Work to Build Independence
There has been extensive research on the experiences of individuals with
visual impairments on text- and image-based social media platforms, such as
Facebook and Twitter. However, little is known about the experiences of
visually impaired users on short-video platforms like TikTok. To bridge this
gap, we conducted an interview study with 30 BlindTokers (the nickname of blind
TikTokers). Our study aimed to explore the various activities of BlindTokers on
TikTok, including everyday entertainment, professional development, and
community engagement. The widespread usage of TikTok among participants
demonstrated that they considered TikTok and its associated experiences as the
infrastructure for their activities. Additionally, participants reported
experiencing breakdowns in this infrastructure due to accessibility issues.
They had to carry out infrastructuring work to resolve the breakdowns. Blind
users' various practices on TikTok also foregrounded their perceptions of
independence. We then discussed blind users' nuanced understanding of the
TikTok-mediated independence; we also critically examined BlindTokers'
infrastructuring work for such independence.Comment: Accepted at CSCW'24, 29 pages, 2 figures, and 2 table
Prediction of noise from serrated trailing edges
A new analytical model is developed for the prediction of noise from serrated trailing edges. The model generalizes Amiet’s trailing-edge noise theory to sawtooth trailing edges, resulting in a complicated partial differential equation. The equation is then solved by means of a Fourier expansion technique combined with an iterative procedure. The solution is validated through comparison with the finite element method for a variety of serrations at different Mach numbers. The results obtained using the new model predict noise reduction of up to 10 dB at 90 above the trailing edge, which is more realistic than predictions based on Howe’s model and also more consistent with experimental observations. A thorough analytical and numerical analysis of the physical mechanism is carried out and suggests that the noise reduction due to serration originates primarily from interference effects near the trailing edge. A closer inspection of the proposed mathematical model has led to the development of two criteria for the effectiveness of the trailing-edge serrations, consistent but more general than those proposed by Howe. While experimental investigations often focus on noise reduction at 90 above the trailing edge, the new analytical model shows that the destructive interference scattering effects due to the serrations cause significant noise reduction at large polar angles, near the leading edge. It has also been observed that serrations can significantly change the directivity characteristics of the aerofoil at high frequencies and even lead to noise increase at high Mach numbers.The first author (BL) wishes to gratefully acknowledge the financial support co-funded by the Cambridge Commonwealth European and International Trust and China Scholarship Council. The second author (MA) would like to acknowledge the financial support of the Royal Academy of Engineering. The third author (SS) wishes to gratefully acknowledge the support of the Royal Commission for the exhibition of 1851.This is the author accepted manuscript. The final version is available from Cambridge University Press via http://dx.doi.org/10.1017/jfm.2016.13
Structure and electronic properties of the () SnAu/Au(111) surface alloy
We have investigated the atomic and electronic structure of the
() SnAu/Au(111) surface alloy. Low
energy electron diffraction and scanning tunneling microscopy measurements show
that the native herringbone reconstruction of bare Au(111) surface remains
intact after formation of a long range ordered () SnAu2/Au(111) surface alloy. Angle-resolved
photoemission and two-photon photoemission spectroscopy techniques reveal
Rashba-type spin-split bands in the occupied valence band with comparable
momentum space splitting as observed for the Au(111) surface state, but with a
hole-like parabolic dispersion. Our experimental findings are compared with
density functional theory (DFT) calculation that fully support our experimental
findings. Taking advantage of the good agreement between our DFT calculations
and the experimental results, we are able to extract that the occupied Sn-Au
hybrid band is of (s, d)-orbital character while the unoccupied Sn-Au hybrid
bands are of (p, d)-orbital character. Hence, we can conclude that the
Rashba-type spin splitting of the hole-like Sn-Au hybrid surface state is
caused by the significant mixing of Au d- to Sn s-states in conjunction with
the strong atomic spin-orbit coupling of Au, i.e., of the substrate.Comment: Copyright:
https://journals.aps.org/authors/transfer-of-copyright-agreement; All
copyrights by AP
Detecting time-fragmented cache attacks against AES using Performance Monitoring Counters
Cache timing attacks use shared caches in multi-core processors as side
channels to extract information from victim processes. These attacks are
particularly dangerous in cloud infrastructures, in which the deployed
countermeasures cause collateral effects in terms of performance loss and
increase in energy consumption. We propose to monitor the victim process using
an independent monitoring (detector) process, that continuously measures
selected Performance Monitoring Counters (PMC) to detect the presence of an
attack. Ad-hoc countermeasures can be applied only when such a risky situation
arises. In our case, the victim process is the AES encryption algorithm and the
attack is performed by means of random encryption requests. We demonstrate that
PMCs are a feasible tool to detect the attack and that sampling PMCs at high
frequencies is worse than sampling at lower frequencies in terms of detection
capabilities, particularly when the attack is fragmented in time to try to be
hidden from detection
Connection stiffness identification of historic timber buildings using Temperature-based sensitivity analysis
© 2016 Elsevier Ltd The beam-column connection, called ‘Que Ti’, is the key component of historic Tibetan timber buildings to transfer shear, compression and bending loads from one structural element to another. This kind of connections can reduce the internal forces and improve the structure's ability to resist earthquakes. Its structure is very complicated and there is little information about the behaviour of this kind of semi-rigid connections. In this paper, a temperature-based response sensitivity method is proposed to identify the connection stiffness of the ‘Que-Ti’ in typical historical Tibetan buildings from temperature and strain response measurements. The semi-rigid connection is modeled as two rotational springs and one compressive spring. The temperature is treated as a measurable input and the thermal loading on the structure can be determined from the temperature variation. The numerical results show the method is effective and reliable to identify both unknown boundary conditions and the connection stiffness of the structure accurately even with 10% noise in measurements. A long-term monitoring system has also been installed in a typical historical Tibetan building and the monitoring data are used to further verify the proposed method. The experimental results show that the identified stiffnesses by the proposed method are consistent with that by finite element model updating from ambient vibration measurements
In situ observation of shrinking and swelling of normal and compression Chinese fir wood at the tissue, cell and cell wall level
The shrinking and swelling of wood due to moisture changes are intrinsic material properties that control and limit the use of wood in many applications. Herein, hygroscopic deformations of normal and compression wood of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) were measured during desorption and absorption processes. The dimensional changes were observed in situ by an environmental scanning electron microscope and analyzed at different hierarchical levels (tissue, cell and cell wall). The relationship between moisture variation and hygroscopic deformation was measured. During initial desorption periods from 95 to 90 or 75% RH, an expansion of the lumen and a shrinkage of the cell wall were observed, revealing a non-uniform and directional deformation of single wood cells. The variation of shrinking or swelling at different hierarchical levels (tissue, cell and cell wall) indicates that the hygroscopic middle lamella plays a role in the deformation at the tissue level. Higher microfibril angles and helical cavities on the cell wall in compression wood correlate with a lower shrinking/swelling ratio. Normal wood showed a more pronounced swelling hysteresis than compression wood, while the sorption hysteresis was almost the same for both wood types. This finding is helpful to elucidate effects of micro- and ultrastructure on sorption. The present findings suggest that the sophisticated system of wood has the abilities to adjust the hygroscopic deformations by fine-tuning its hierarchical structures
Condition assessment of heritage timber buildings in operational environments
© 2017, Springer-Verlag GmbH Germany. Due to changing environments and aging, the structural resistance of the heritage buildings has been reduced significantly. It has become crucial to monitor and protect the architectural heritage buildings. The objective of this research is to monitor and assess the performance of the heritage Tibetan timber building in operational environments. A three-storey corridor part of the typical heritage building was chosen in the study. A long-term monitoring system was installed in the building to collect the structural response and temperature. Detailed finite element model was built based on site investigation and existing documents, and updated based on the temperature-based response sensitivity using the field-monitoring data. The updated model was further evaluated using the static and dynamic analysis for condition assessment of the building in operational environments. The results show that the updated model is effective and accurate to predict the structural behaviour of the building in operational environments. Based on temperature-based response sensitivity, it is capable of tracking structure performance throughout the life-cycle allowing for condition-based maintenance and structural protection
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