280 research outputs found
Ultrafast Optical Devices for Photonic Integrated Circuit Applications
The transmission bandwidth of a modern fiber-optic communication systems depends on the modulation bandwidth of optical signal transmitters, as well as the computation speed of photonic components for optical signal processing. Nowadays, the rapid development of various bandwidth-hungry network products urges the research on optical transmitters and photonic circuits that could support high bit-rate optical signal communication and computation. The objective of this dissertation is to investigate on laser transmitters that allow ultrafast modulations, as well as on photonic integrated circuits components in nonlinear chalcogenide glass substrates that are capable of ultrafast all-optical signal processing.
Vertical cavity surface emitting lasers (VCSELs) offers superior properties as signal transmitters in the fiber-optic communication network, such as large modulation bandwidth, low coupling loss with optical fibers, and low fabrication cost. As the modulation bandwidth of VCSELs are limited due to their relaxation modulation frequency up to 20GHz, transverse mode lock of VCSEL is proposed to reach modulation bandwidth beyond 100GHz. Both the static emission and ultrafast dynamics of VCSELsâ transverse modes were studied to explore their potential for mode locking.
All-optical signal processing with nonlinear photonic integrated circuits (PIC) is an effective solution to overcome the speed limitation arising from opto-electronic conversions in the modern communication network. Performance of individual components in a PIC and its scale of integration are influenced by its substrate material and its fabrication method. In this dissertation, nonlinear PIC components written in ChG substrates by ultrafast laser writing are studied, taking advantages of the unique material traits of chalcogenide glasses (ChGs), and the capability of ultrafast laser writing to fabricate 3D arbitrary structures in nearly any transparent materials. The fabrication challenges arising from the laser-material interaction were overcome, and basic nonlinear PIC components including waveguide Bragg gratings, nonlinear directional couplers and one dimensional waveguide arrays were designed and fabricated. Functionalities of these devices were demonstrated at a reduced power required for nonlinear operations, as compared to similar devices in silica substrates.
The results presented in this dissertation provide the basics for the realization of on-chip optical network for largely increased data transmission bandwidth and signal processing speed
Studies on adventitious root formation in Pinus radiata : biochemical and molecular aspects.
A reliable in vitro rooting system was established for further studies on biochemical and molecular aspects during adventitious root formation in Pinus radiata hypocotyls. High root counts and rooting efficiency were observed in a medium comprising œ strength of the Murashige & Skoog's basal medium (1962), 20 g/l sucrose, 9 mg/l IBA and solidified with 8 g/l agar. In this system, the first cell division, formation of root primordium initial (a cluster of meristematic cells), well-organized root primordium (a dome shaped structure) and root emergence were typically observed at around day 4, 7, 10 and 13, respectively.
The increase of buffer soluble total proteins resulted in a peak at day 7 in the treatment with IBA (rooting treatment), but this peak was not observed in the other non-rooting treatments (including IBA+kinetin, kinetin alone and hormone-free control). Rooting related proteins were not observed using one-dimensional SDS polyacrylamide gel electrophoresis (PAGE). However, 19 proteins associated with the IBA treatment were observed by two-dimensional PAGE although their magnitudes were very small so that it was difficult to quantify them and establish them as novel proteins. Changes of peroxidase (PO), IAA-oxidase (IAA-O), amylase (Amy) and succinic dehydrogenase (SDH) activities assayed using tissue extracts were not significantly different between the rooting and the non-rooting treatments during the experiment. By contrast, the increase of polyphenol oxidase (PPO) activity was more significant at day 7 in the rooting treatment than in the other treatments. Nevertheless, histochemical localization of PO, PPO and SDH indicated that these enzymes were somehow associated with adventitious root formation. In the IBA treatment, the increase of starch content in the rooting region reached its maximum at day 4 and 7. This increase coincided with the histological observation ofaccumulation of starch grains at the sites where root primordia initiated.
To identify the molecular signals that initiate adventitious root formation, subtracted cDNA library was made from IBA-treated hypocotyls following polymerase chain reaction (PCR) amplification of subtracted single strand-cDNAs. Inserts of 5 bacterial clones (Rl-72, R2-7, R2-22, R2-35 and R3-24) were digoxigenin-labelled and used to detect their corresponding transcripts using RNA dot blotting. Using RNA dot blotting analysis, Rl-72 detected an equivalent level of transcript in the hypocotyls at day 0 and day 7 in the treatments with and without IBA; whereas the other 4 clones, especially R2-7 and R2-35, detected different levels of transcripts in the hypocotyls during adventitious root initiation. Southern blotting analysis indicated that the R2-7 transcript is likely to be represented by a single gene or a member of a smaller gene family.
Adventitious root formation in P. radiata was significantly improved using Agrobacterium rhizogenes. Compared with the strain A4T, strain LBA9402 was very effective in increasing rooting percentage and root number. High rooting percentages and root numbers were obtained in the trials with hypocotyl segments, intact seedlings and adventitious shoots.
The findings in this research can assist further studies to shed some light on why some clonal cuttings of radiata pine root more easily than others do, and why mature cuttings are difficult for adventitious root induction
Root induction in radiata pine using Agrobacterium rhizogenes
Root induction using Agrobacterium rhizogenes was conducted in
hypocotyl explants, intact seedlings, de-rooted seedling cuttings and
adventitious shoots of radiata pine ( Pinus radiata D. Don). Use of
two A. rhizogenes strains (A4T and LB9402), with or without application
of IBA, can trigger root formation in different explants. Strain
LBA9402 was more effective than A4T in increasing rooting percentage
and root number. Addition of 4.4 uMIBA to the medium further enhanced
rooting from the cultured hypocotyl segments inoculated with the two A.
rhizogenes strains. Strain LBA9402+IBA induced in about 75% of the
cultured hypocotyl segments to form roots. In contrast the controls
failed to initiate roots on intact seedlings or cultured segments in
presence or absence of IBA. Rooting of adventitious shoots from 3
year-old radiata pine was improved following inoculation with LBA9402,
suggesting that this rooting treatment has potential to aid clonal
propagation of radiata pine
Transjugular Intrahepatic Portosystemic Shunt for the Treatment of Portal Hypertension in Noncirrhotic Patients with Portal Cavernoma
Background. The purpose of this study was to evaluate the safety and efficacy of transjugular intrahepatic portosystemic shunt (TIPS) placement in the management of portal hypertension in noncirrhotic patients with portal cavernoma. Methods. We conducted a single institution retrospective analysis of 15 noncirrhotic patients with portal cavernoma treated with TIPS placement. 15 patients (4 women and 11 men) were evaluated via the technical success of TIPS placement, procedural complications, and follow-up shunt patency. Results. TIPS placement was technically successful in 11 out of 15 patients (73.3%). Procedure-related complications were limited to a single instance of hepatic encephalopathy in one patient. In patients with successful shunt placement, the portal pressure gradient decreased from 25.8±5.7 to 9.5±4.2âmmHg (P<0.001). TIPS dysfunction occurred in two patients during a median follow-up time of 45.2 months. Revision was not performed in one patient due to inadequate inflow. The other patient died of massive gastrointestinal bleeding in a local hospital. The remaining nine patients maintained functioning shunts through their last evaluation. Conclusions. TIPS is a safe and effective therapeutic treatment for noncirrhotic patients with symptomatic portal hypertension secondary to portal cavernoma
Identifying and decoupling many-body interactions in spin ensembles in diamond
We simulate the dynamics of varying density quasi-two-dimensional spin
ensembles in solid-state systems, focusing on the nitrogen-vacancy centers in
diamond. We consider the effects of various control sequences on the averaged
dynamics of large ensembles of spins, under a realistic "spin-bath"
environment. We reveal that spin locking is efficient for decoupling spins
initialized along the driving axis, both from coherent dipolar interactions and
from the external spin-bath environment, when the driving is two orders of
magnitude stronger than the relevant coupling energies. Since the application
of standard pulsed dynamical decoupling sequences leads to strong decoupling
from the environment, while other specialized pulse sequences can decouple
coherent dipolar interactions, such sequences can be used to identify the
dominant interaction type. Moreover, a proper combination of pulsed decoupling
sequences could lead to the suppression of both interaction types, allowing
additional spin manipulations. Finally, we consider the effect of finite-width
pulses on these control protocols and identify improved decoupling efficiency
with increased pulse duration, resulting from the interplay of dephasing and
coherent dynamics
Geo6D: Geometric Constraints Learning for 6D Pose Estimation
Numerous 6D pose estimation methods have been proposed that employ end-to-end
regression to directly estimate the target pose parameters. Since the visible
features of objects are implicitly influenced by their poses, the network
allows inferring the pose by analyzing the differences in features in the
visible region. However, due to the unpredictable and unrestricted range of
pose variations, the implicitly learned visible feature-pose constraints are
insufficiently covered by the training samples, making the network vulnerable
to unseen object poses. To tackle these challenges, we proposed a novel
geometric constraints learning approach called Geo6D for direct regression 6D
pose estimation methods. It introduces a pose transformation formula expressed
in relative offset representation, which is leveraged as geometric constraints
to reconstruct the input and output targets of the network. These reconstructed
data enable the network to estimate the pose based on explicit geometric
constraints and relative offset representation mitigates the issue of the pose
distribution gap. Extensive experimental results show that when equipped with
Geo6D, the direct 6D methods achieve state-of-the-art performance on multiple
datasets and demonstrate significant effectiveness, even with only 10% amount
of data
Optical Multipath RF Self-Interference Cancellation Based on Phase Modulation for Full-Duplex Communication
Optical multipath RF self-interference cancellation (SIC) based on phase modulation for full-duplex communication is proposed and demonstrated experimentally. Phase modulation is utilized to convert the RF signal into optical domain, in which the time delay tuning, amplitude tuning and phase inversion for multipath RF SIC are completed. The comprehensive theoretical model of the optical multipath RF SIC system is established, and the factors affecting SIC performance including the time delay, amplitude and phase deviations are analyzed. The experimental results verify the feasibility of the proposed scheme for full-duplex communication with the cancellation depth of 26 dB and 28 dB over 100 MHz at central frequency of 6 GHz and 10 GHz, respectively. A figure of merit of the maximum interference to signal of interest ratio is defined to characterize the SOI recovery capability of optical RF SIC system
High-efficiency green management of potato late blight by a self-assembled multicomponent nano-bioprotectant
Abstract Potato late blight caused by Phytophthora infestans is a devastating disease worldwide. Unlike other plant pathogens, double-stranded RNA (dsRNA) is poorly taken up by P. infestans, which is a key obstacle in using dsRNA for disease control. Here, a self-assembled multicomponent nano-bioprotectant for potato late blight management is designed based on dsRNA and a plant elicitor. Nanotechnology overcomes the dsRNA delivery bottleneck for P. infestans and extends the RNAi protective window. The protective effect of nano-enabled dsRNA against infection arises from a synergistic mechanism that bolsters the stability of dsRNA and optimizes its effective intracellular delivery. Additionally, the nano-enabled elicitor enhances endocytosis and amplifies the systemic defense response of the plants. Co-delivery of dsRNA and an elicitor provides a protective effect via the two aspects of pathogen inhibition and elevated plant defense mechanisms. The multicomponent nano-bioprotectant exhibits superior control efficacy compared to a commercial synthetic pesticide in field conditions. This work proposes an eco-friendly strategy to manage devastating plant diseases and pests
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