Surface acoustic wave techniques in laser pump-probe systems and its applications in studying mechanical properties of materials

Ultrasonic technologies in kHz and MHz frequency regime have been well developed and widely applied in the past half century, thanks to the utilization of piezoelectric transducer. Acoustic techniques that can reach GHz level is needed as the scales of materials under study reaches sub-micron and nanometer. In this dissertation, I develop and improve surface acoustic wave (SAW) techniques in optical pump-probe system, and apply them to measure shear elastic constants of thin films and damping of high frequency shear acoustic waves. While longitudinal elastic constants of thin films can be measured conveniently in optical pump-probe system, there is no practical methods to measure shear elastic constants of thin films. I develop a SAW measurement technique using phase-shift mask in optical system. It is convenient and compatible with various kinds of thin films materials. I demonstrate the capability of the technique by measuring shear elastic constants of hard materials, soft materials, and layered materials with thickness as small as 60 nm. Ultra small shear elastic constant is observed in misfit layered compound [SnSe][MoSe2]. The intrinsic attenuation of GHz acoustic wave in dielectric sets the upper bound of the quality factor of mechanical oscillation system operated at GHz frequency regime. There was no reliable experimental results regarding the intrinsic attenuation of GHz shear acoustic in Si. By careful experimental design, I am able to measure the attenuation of 7 GHz SAW on Si, which largely represents the attenuation of shear acoustic wave. The experimental scheme can be readily applied to other dielectric materials. For quantitative analysis, I implement a general calculation scheme which can calculate SAW of layered structure with any number of layers of anisotropic material and SAW of structure with thin grating on surface. It can also be used to calculate various other acoustic modes such as Stoneley wave and Lamb wave. Density functional theory (DFT) calculation is used in the these studies to assist the analysis and understanding of the experiments. I calculate elastic constant of cubic crystals and hexagonal layered materials (graphite, MoS2, and misfit layered compound [SnSe][MoSe2]). I calculate the generalized mode Gruneisen parameter of Si in order to understand the relatively small attenuation of shear acoustic waves comparing with longitudinal acoustic wave in Si

Anti–DNA B Cells in MRL/lpr Mice Show Altered Differentiation and Editing Pattern

We have studied the regulation of anti–DNA B cells in transgenic mice with a heavy chain transgene (3H9H/56R). This transgene codes for a heavy chain that forms anti–double-stranded DNA (dsDNA) antibody when paired with most members of the endogenous Vκ repertoire, but certain L chains, referred to as Vκ editors, do not sustain dsDNA binding in combination with 3H9H/56R. In the nonautoimmune 3H9H/56R BALB/c, most B cells generated do not bind DNA because the transgene itself is edited or is associated with a Vκ editor. A minor population of B cells (30%) bind dsDNA and express the λ1 light chain (known to sustain 3H9H/56R DNA binding). These 3H9/56R/λ1 B cells coexpress a κ editor, and we propose that the down-regulation of the anti-DNA BCR caused by the dual L chain expression may prevent activation of this κ/λ population. These κ/λ B cells are sequestered in the marginal zone. Here, we studied the influence of autoimmunity on expression and regulation of 3H9H/56R. In 3H9H/56R MRL/lpr mice, the expression of anti-dsDNA is vastly accelerated. Anti–dsDNA B cells use noneditor κs but, in addition, most anti–dsDNA B cells have edited the heavy chain transgene. λ1 B cells (without the coexpression of a κ editor) are found and the κ/λ1 MZ population is absent. Our results suggest that improper editing and failure to sequester autoreactive B cells may contribute to the breakdown of tolerance in MRL/lpr mice

The effects of new urbanization pilot city policies on urban innovation: Evidence from China

The new urbanization city pilot policy is China’s most recent policy on urban urbanization. This paper uses new urbanization pilot policies as a quasi-natural experiment to empirically test the impact of new urbanization pilot policies on urban innovation through the difference-in-differences (DID) method using panel data from 199 cities in China from 2011 to 2019. The results show that: (1) The new urbanization city pilot policy has significantly enhanced urban innovation. (2) The theoretical mechanism test shows that the pilot policy of new urbanization promotes urban innovation through the level of human capital. (3) The results of the heterogeneity analysis show that the new urbanization pilot policies have obvious city-level heterogeneity and regional heterogeneity on the improvement of urban innovation levels. The impact effect of new urbanization pilot policies is higher in first-tier and second-tier cities than in fourth-tier and fifth-tier cities; the effect of new urbanization pilot policies is higher in western regions than in eastern and middle regions.National Natural Science Foundation of Chin

Ultrathin MgB2 films fabricated on Al2O3 substrate by hybrid physical-chemical vapor deposition with high Tc and Jc

Ultrathin MgB2 superconducting films with a thickness down to 7.5 nm are epitaxially grown on (0001) Al2O3 substrate by hybrid physical-chemical vapor deposition method. The films are phase-pure, oxidation-free and continuous. The 7.5 nm thin film shows a Tc(0) of 34 K, which is so far the highest Tc(0) reported in MgB2 with the same thickness. The critical current density of ultrathin MgB2 films below 10 nm is demonstrated for the first time as Jc ~ 10^6 A cm^{-2} for the above 7.5 nm sample at 16 K. Our results reveal the excellent superconducting properties of ultrathin MgB2 films with thicknesses between 7.5 and 40 nm on Al2O3 substrate.Comment: 7 pages, 4 figures, 2 table

The Influence of Receiver Selection Strategy on Packet Success Probability in Ad Hoc Network

Considering the importance of the receiver (RX) selection strategy for the packet success probability (PSP) in ad hoc network, this paper probes into the PSPs with nearest RX selection strategy and farthest RX selection strategy and determines the number of hops with the two strategies. Next, the performance of the successful transmission probability (STP) and PSP were discussed through numerical simulation with the above mentioned two strategies. The simulation results show that the PSP is affected by the terminal density, the RX selection strategy, the packet length and the STP; the number of hops mainly depends on the terminal density, the RX selection strategy, the length between the source TX and the destination RX. Furthermore, the nearest RX selection strategy and the farthest RX selection strategy differ insignificantly in the packet transmission duration between source TX to destination RX at a small terminal density

Ultrasound microbubble-mediated delivery of the siRNAs targeting MDR1 reduces drug resistance of yolk sac carcinoma L2 cells

<p>Abstract</p> <p>Background</p> <p>MDR1 gene encoding P-glycoprotein is an ATP-dependent drug efflux transporter and related to drug resistance of yolk sac carcinoma. Ultrasound microbubble-mediated delivery has been used as a novel and effective gene delivery method. We hypothesize that small interfering RNA (siRNA) targeting MDR1 gene (siMDR1) delivery with microbubble and ultrasound can down-regulate MDR1 expression and improve responsiveness to chemotherapeutic drugs for yolk sac carcinoma <it>in vitro</it>.</p> <p>Methods</p> <p>Retroviral knockdown vector pSEB-siMDR1s containing specific siRNA sites targeting rat MDR1 coding region were constructed and sequence verified. The resultant pSEB-siMDR1 plasmids DNA were encapsulated with lipid microbubble and the DNA release were triggered by ultrasound when added to culture cells. GFP positive cells were counted by flow cytometry to determine transfection efficiency. Quantitative real-time PCR and western blot were performed to determine the mRNA and protein expression of MDR1. P-glycoprotein function and drug sensitivity were analyzed by Daunorubicin accumulation and MTT assays.</p> <p>Results</p> <p>Transfection efficiency of pSEB-siMDR1 DNA was significantly increased by ultrasound microbubble-mediated delivery in rat yolk sac carcinoma L2 (L2-RYC) cells. Ultrasound microbubble-mediated siMDR1s delivery effectively inhibited MDR1 expression at both mRNA and protein levels and decreased P-glycoprotein function. Silencing MDR1 led to decreased cell viability and IC₅₀of Vincristine and Dactinomycin.</p> <p>Conclusions</p> <p>Our results demonstrated that ultrasound microbubble-mediated delivery of MDR1 siRNA was safe and effective in L2-RYC cells. MDR1 silencing led to decreased P-glycoprotein activity and drug resistance of L2-RYC cells, which may be explored as a novel approach of combined gene and chemotherapy for yolk sac carcinoma.</p

The rat intervertebral disk degeneration pain model: relationships between biological and structural alterations and pain

INTRODUCTION: Degeneration of the interverterbral disk is as a cause of low-back pain is increasing. To gain insight into relationships between biological processes, structural alterations and behavioral pain, we created an animal model in rats. METHODS: Disk degeneration was induced by removal of the nucleus pulposus (NP) from the lumbar disks (L4/L5 and L5/L6) of Sprague Dawley rats using a 0.5-mm-diameter microsurgical drill. The degree of primary hyperalgesia was assessed by using an algometer to measure pain upon external pressure on injured lumbar disks. Biochemical and histological assessments and radiographs of injured disks were used for evaluation. We investigated therapeutic modulation of chronic pain by administering pharmaceutical drugs in this animal model. RESULTS: After removal of the NP, pressure hyperalgesia developed over the lower back. Nine weeks after surgery we observed damaged or degenerated disks with proteoglycan loss and narrowing of disk height. These biological and structural changes in disks were closely related to the sustained pain hyperalgesia. A high dose of morphine (6.7 mg/kg) resulted in effective pain relief. However, high doses of pregabalin (20 mg/kg), a drug that has been used for treatment of chronic neuropathic pain, as well as the anti-inflammatory drugs celecoxib (50 mg/kg; a selective inhibitor of cyclooxygenase 2 (COX-2)) and ketorolac (20 mg/kg; an inhibitor of COX-1 and COX-2), did not have significant antihyperalgesic effects in our disk injury animal model. CONCLUSIONS: Although similarities in gene expression profiles suggest potential overlap in chronic pain pathways linked to disk injury or neuropathy, drug-testing results suggest that pain pathways linked to these two chronic pain conditions are mechanistically distinct. Our findings provide a foundation for future research on new therapeutic interventions that can lead to improvements in the treatment of patients with back pain due to disk degeneration

Eclecticism and Unity in Diversity – Analysing the integration and application of modern technology in theatre arts

In today's rapid development of science and technology, almost every aspect of our life has a very close relationship with modern technology, especially in the creation of art is more and more inseparable from the aid of modern technology. As a large branch of artistic creation, stage art design is a comprehensive art, involving scene design, lighting, sound effects, costumes, make-up, props, special effects and many other aspects of its more inclusive. This paper starts from the use of modern science and technology in stage art design, and analyses how stage art design can be unified under the diverse and pluralistic forms of expression

Comparative Study of Chromium(VI) Removal from Simulated Industrial Wastewater with Ion Exchange Resins

Ion exchange process is an alternative technique for removal of heavy metal ions from industrial wastewater. The main aim of this paper is to evaluate the performance of different ion exchange resins in removing Cr(VI) from wastewater. The effects of resin types and dosage, initial pH were examined systemically. The results showed that the performance of different resins had obvious difference for the removal of the Cr(VI) ions, in which the type of functional groups of the resin was the main factor. The SEM images indicated that the micro-morphology of resins before and after adsorption of the Cr(VI) presented a little difference. The EDS analysis showed that the adsorbed Cr(VI) was uniformly distributed at the surface of the resins with formation of oxygen-containing groups. The adsorption isotherms and kinetics of Cr(VI) by the different resins are also discussed