125 research outputs found
QuanShield: Protecting against Side-Channels Attacks using Self-Destructing Enclaves
Trusted Execution Environments (TEEs) allow user processes to create enclaves
that protect security-sensitive computation against access from the OS kernel
and the hypervisor. Recent work has shown that TEEs are vulnerable to
side-channel attacks that allow an adversary to learn secrets shielded in
enclaves. The majority of such attacks trigger exceptions or interrupts to
trace the control or data flow of enclave execution.
We propose QuanShield, a system that protects enclaves from side-channel
attacks that interrupt enclave execution. The main idea behind QuanShield is to
strengthen resource isolation by creating an interrupt-free environment on a
dedicated CPU core for running enclaves in which enclaves terminate when
interrupts occur. QuanShield avoids interrupts by exploiting the tickless
scheduling mode supported by recent OS kernels. QuanShield then uses the save
area (SA) of the enclave, which is used by the hardware to support interrupt
handling, as a second stack. Through an LLVM-based compiler pass, QuanShield
modifies enclave instructions to store/load memory references, such as function
frame base addresses, to/from the SA. When an interrupt occurs, the hardware
overwrites the data in the SA with CPU state, thus ensuring that enclave
execution fails. Our evaluation shows that QuanShield significantly raises the
bar for interrupt-based attacks with practical overhead.Comment: 15pages, 5 figures, 5 table
All-fiber femtosecond Cherenkov radiation source
An all-fiber femtosecond source of spectrally isolated Cherenkov radiation is reported, to the best of our knowledge, for the first time. Using a monolithic, self-starting femtosecond Yb-doped fiber laser as the pump source and the combination of photonic crystal fibers as the wave-conversion medium, we demonstrate stable and tunable Cherenkov radiation at visible wavelengths 580–630 nm, with pulse duration of sub-160-fs, and the 3 dB spectral bandwidth not exceeding 36 nm. Such an all-fiber Cherenkov radiation source is promising for practical applications in biophotonics such as bioimaging and microscopy
Role of Alkaline-Earth Metal-Catalyst: A Theoretical Study of Pyridines Hydroboration
Density functional theory (DFT) calculations have been performed to investigate the mechanism of alkaline-earth-metal-catalyzed hydroboration of pyridines with borane. In this reaction, the active catalytic species is considered to be an alkaline earth metal hydride complex when the corresponding alkaline earth metal is used as the catalyst. The theoretical results reveal that initiation of the catalytic cycle is hydride transfer to generate a magnesium hydride complex when β-diimine alkylmagnesium is used as a pre-catalyst. The magnesium hydride complex can undergo coordination of the pyridine reactant followed by hydride transfer to form a dearomatized magnesium pyridine intermediate. Coordination of borane and hydride transfer from borohydride to magnesium then give the hydroboration product and regenerate the active magnesium hydride catalyst. The rate-determining step of the catalytic cycle is hydride transfer to pyridine with a free energy barrier of 29.7 kcal/mol. Other alkaline earth metal complexes, including calcium and strontium complexes, were also considered. The DFT calculations show that the corresponding activation free energies for the rate-determining step of this reaction with calcium and strontium catalysts are much lower than with the magnesium catalyst. Therefore, calcium and strontium complexes can be used as the catalyst for the reaction, which could allow mild reaction conditions
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The multichannel discharge plasma synthetic jet actuator
The plasma synthetic jet actuator (PSJA) is a flow control device capable of generating high speed pulsed jet. However, the performance of conventional PSJA is restricted by low discharge efficiency and small control area, because one power supply only drives one electrode couple. The present work is to propose a new concept of multichannel discharge plasma synthetic jet actuator (MD-PSJA), which is driven by single power supply. The new MD-PSJA has two types, namely the multi-electrode PSJA and the multi-PSJA array. These two types of MD-PSJA are examined experimentally. The multi-electrode PSJA containing 11-electrode PSJA is first studied. Comparison with standard 2-electrode PSJA reveals that the discharge efficiency and jet velocity increase 200% and 47% respectively under the same input energy and discharge voltage. The multi-PSJA array is later evaluated. One power supply is found to be able to drive an array of 12 PSJAs, resulting in 6 times affected area and 64% jet velocity of a conventional PSJA. The proposed MD-PSJA is finally concluded an improved active flow control actuator in high speed applications
Multimodal multiphoton imaging for label-free monitoring of early gastric cancer
Background
Early gastric cancer is associated with a much better prognosis than advanced disease, and strategies to improve prognosis is strictly dependent on earlier detection and accurate diagnosis. Therefore, a label-free, non-invasive imaging technique that allows the precise identification of morphologic changes in early gastric cancer would be of considerable clinical interest.
Methods
In this study, multiphoton microscopy (MPM) using two-photon excited fluorescence combined with second-harmonic generation was used for the identification of early gastric cancer.
Results
This microscope was able to directly reveal improved cellular detail and stromal changes during the development of early gastric cancer. Furthermore, two features were quantified from MPM images to assess the cell change in size and stromal collagen change as gastric lesion developed from normal to early cancer.
Conclusions
These results clearly show that multiphoton microscopy can be used to examine early gastric cancer at the cellular level without the need for exogenous contrast agents. This study would be helpful for early diagnosis and treatment of gastric cancer, and may provide the groundwork for further exploration into the application of multiphoton microscopy in clinical practice.Ope
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