2,169 research outputs found
Elastic Wave Scattering and Dynamic Stress Concentrations in Stretching Thick Plates with Two Cutouts by Using the Refined Dynamic Theory
Based on the refined dynamic equation of stretching plates, the elastic tensionâcompression wave scattering and dynamic stress concentrations in the thick plate with two cutouts are studied. In view of the problem that the shear stress is automatically satisfied under the free boundary condition, the generalized stress of the first-order vanishing moment of shear stress is considered. The numerical results indicate that, as the cutout is thick, the maximum value of the dynamic stress factor obtained using the refined dynamic theory is 19% higher than that from the solution of plane stress problems of elastic dynamics
Unconditional security proof of a deterministic quantum key distribution with a two-way quantum channel
In a deterministic quantum key distribution (DQKD) protocol with a two-way quantum channel, Bob sends a qubit to Alice who then encodes a key bit onto the qubit and sends it back to Bob. After measuring the returned qubit, Bob can obtain Alice's key bit immediately, without basis reconciliation. Since an eavesdropper may attack the qubits traveling on either the Bob-Alice channel or the Alice-Bob channel, the security analysis of DQKD protocol with a two-way quantum channel is complicated and its unconditional security has been controversial. This paper presents a security proof of a single-photon four-state DQKD protocol against general attacks. © 2011 American Physical Society.published_or_final_versio
Quantifying protocol efficiency: A thermodynamic figure of merit for classical and quantum state-transfer protocols
Manipulating quantum systems undergoing non-Gaussian dynamics in a fast and accurate manner is becoming fundamental to many quantum applications. Here, we focus on classical and quantum protocols transferring a state across a double-well potential. The classical protocols are achieved by deforming the potential, while the quantum ones are assisted by a counterdiabatic driving. We show that quantum protocols perform more quickly and accurately. Finally, we design a figure of merit for the performance of the transfer protocols-namely, the protocol grading-that depends only on fundamental physical quantities, and which accounts for the quantum speed limit, the fidelity, and the thermodynamics of the process. We test the protocol grading with classical and quantum protocols, and show that quantum protocols have higher protocol grading than the classical ones
Functional MRI of the spinal cord at low field
A second contrast mechanism SEEP was reported to co-exist with BOLD during fMRI activation. The mechanism was based on the task-induced signal
change of extravascular water protons and was primarily shown in the spinal cord at high field. Recently, a preliminary study was reported at 0.2T showing
SEEP contrast in the brain while the BOLD effect was negligible. The present study is to investigate the presence of SEEP in the spinal cord at 0.2T using
proton density-weighted imaging with motor task. Bilateral activations were obtained in the anterior grey horns consistently across C6-C8 levels, which
correlated with the neural anatomy.published_or_final_versio
Use of functional MRI to evaluate correlation between acupoints and brain cortex activites: comparison between conventional and electrical acupuncture
The use of acupuncture therapy in various functional disorders goes back several thousand years in China. Recendy, acupuncture becomes a 'hot' topic in the functional Magnetic Resonance (MR) imaging research studies [1-4]. A majority of these research projects is to study die correlation between the acupuncture points (acupoints) and die corresponding brain cortices, either by conventional acupuncture, electro-acupuncture or laser acupuncture. Cho et al reported mat by stimulating die vision-related acupoints (BL60, BL65, BL66, BL67) at the lateral side of die foot, neural response (i.e. high signal) was obtained at die visual cortex [1]. In this study, we verified Cho et al acupoints using conventional acupuncture and electro-acupuncture.published_or_final_versio
Performance of large-size superconducting coil in 0.21T MRI system
A high-temperature superconductor (HTS) was used on magnetic resonance imaging (MRI) receiver coils to improve image quality because of its intrinsic low electrical resistivity [1], [2]. Typical HTS coils are surface coils made of HTS thin-film wafers. Their applications are severely limited by the field of view (FOV) of the surface coil configuration, and the improvement in image quality by HTS coil is also reduced as the ratio of sample noise to coil noise increases. Therefore, previous HTS coils are usually used to image small in vitro samples, small animals, or peripheral human anatomies [3]-[5]. We used large-size HTS coils (2.5-, 3.5-, and 5.5-in mean diameter) to enhance the FOV and we evaluated their performance through phantom and human MR images. Comparisons were made among HTS surface coils, copper surface coils, and cool copper surface coils in terms of the signal-to-noise ratio (SNR) and sensitivity profile of the images. A theoretical model prediction was also used to compare against the experimental result. We then selected several human body parts, including the wrist, feet, and head, to illustrate the advantage of HTS coil over copper coil when used in human imaging. The results show an SNR gain of 200% for 5.5-in HTS coil versus same size copper coils, while for 2.5- and 3.5-in coils it is 250%. We also address the various factors that affect the performance of large size HTS coils, including the coil-to-sample spacing due to cryogenic probe and the coil-loading effect.published_or_final_versio
Superconducting receiver coils for sodium magnetic resonance imaging
Presents the results from sodium magnetic resonance imaging (MRI) experiments using high-temperature superconducting (HTS) receiver coils. Sodium imaging has been shown to have great potential for the assessment of cell integrity but suffers from substantially lower signal-to-noise ratio (SNR) than that of hydrogen imaging. The use of an HTS receiver coil was found to significantly increase the SNR relative to an equivalent copper receiver coil at room temperature. The SNR gains afforded by HTS coils can also be used to decrease the imaging time.published_or_final_versio
Design of superconducting MRI surface coil by using method of moment
A method of moment with an enhanced model to design high-temperature superconductor (HTS) RF surface coils for magnetic resonant image (MRI) is presented. The resonant frequency and quality factor (Q) of HTS RF spiral coils are simulated using this method. The agreements of resonant frequencies and Qs between the simulation and measurement are excellent with differences less than 1% and 3%, respectively. The 0.2-Ό m-thick YBaCuO (YBCO) thin films are deposited onto single side of 0.508-mm-thick LaAlO 3 (LAO) and sapphire substrate and patterned into a spiral shape. To accurately analyze the resonant frequency and Q of a coil, an enhanced two-fluid model is employed. HTS RF coils with diameter of 65 mm for 0.2T and 1.5T MRI systems are designed and fabricated with the measured Q of 19 K and 23 K, respectively. In addition, the shift of resonant frequency due to the mutual coupling between two HTS spiral coils is predicted by this method, which is important for design of HTS coil arrays in an MRI system.published_or_final_versio
Assessment of multiple hormone activities of a UV-filter (octocrylene) in zebrafish (Danio rerio)
© 2016 Elsevier Ltd In this study, zebrafish (Danio rerio) were exposed to a UV-filter-octocrylene (OCT) with elevated concentrations for 28 d. The total body accumulation of OCT in zebrafish was found to reach 2321.01 (âLâ level), 31,234.80 (âMâ level), and 70,593.38 ng gâ1 (âHâ level) when the average OCT exposure concentration was controlled at 28.61, 505.62, and 1248.70 Όg Lâ1, respectively. Gross and histological observations as well as RT-qPCR analysis were conducted to determine the effects of OCT accumulation on zebrafish. After exposure, the gonad-somatic index and percentage of vitellogenic oocytes were found to increase significantly in the ovaries of female zebrafish at the H accumulation level. Significant up-regulation of esr1 and cyp19b were observed in the gonads, as well as vtg1 in the livers for both female and male zebrafish. At M and H accumulation levels, apparent down-regulation of ar was observed in the ovaries and testis of the female and male zebrafish, respectively. Although the extent of the effects on zebrafish differed at different accumulation levels, the induction of vtg1 and histological changes in the ovaries are indications of estrogenic activity and the inhibition of esr1 and ar showed antiestrogenic and antiandrogenic activity, respectively. Thus, as OCT could easily accumulate in aquatic life such as zebrafish, one of its most of concern hazards would be the disturbance of the histological development and its multiple hormonal activities
Bold signal changes of the visual cortex on stimulation of the vision-related acupoints
We verified Cho and his colleagues' acupoints using conventional acupuncture and electro-acupuncture. Acupuncture was performed with two different techniques - conventional and electro-acupuncture. Functional MR imaging (fMRI) was performed using a 1.5 T MR scanner with standard scan parameters in 13 healthy volunteers. The 30-second activation period was alternated by 30-second rest period. First, the fMRI was performed with visual activation using light-emitting diodes (LED) flashing with a frequency of 8 Hz. The fMRI was then repeated with conventional acupuncture and electro-acupuncture at the following acupoints (BL60, BL 65, BL 66 and BL 67) located in the lateral aspect of the foot. The activated pixels in the visual cortex created by visual activation correlate well with those created by both conventional acupuncture and electro-acupuncture Fig. 1. The results obtained by conventional acupuncture stimulation have relatively more neural responses due to other types of stimulation rather than visual activation. The neural responses obtained by electro-acupuncture at 2 Hz was found to be stronger than those obtained by electro-acupuncture at 64 Hz. The greatest difficulty encountered by the researchers is that only 25 to 30% of the subjects undergoing acupuncture renders expected neural response.
Supported by The Hong Kong Jockey Club Charities Trust and The Hong Kong University Foundation.published_or_final_versio
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