945 research outputs found
Engineering multiple levels of specificity in an RNA viral vector
Synthetic molecular circuits could provide powerful therapeutic capabilities, but delivering them to specific cell types and controlling them remains challenging. An ideal "smart" viral delivery system would enable controlled release of viral vectors from "sender" cells, conditional entry into target cells based on cell-surface proteins, conditional replication specifically in target cells based on their intracellular protein content, and an evolutionarily robust system that allows viral elimination with drugs. Here, combining diverse technologies and components, including pseudotyping, engineered bridge proteins, degrons, and proteases, we demonstrate each of these control modes in a model system based on the rabies virus. This work shows how viral and protein engineering can enable delivery systems with multiple levels of control to maximize therapeutic specificity
Dynamic Bandwidth MCIDS - A Cognitive Solution for MCIDS based UWB Communications
Dynamic bandwidth multicode interleaved direct sequence (MCIDS), an enhanced MCIDS based Ultra-wideband (UWB) application is proposed in this paper, featuring a cognitive transmission bandwidth adaptation without any adverse effect on the data rate. By introducing a specific lowpass filtering and down-sampling into the traditional MCIDS algorithm, this system can decrease the transmission bandwidth into part of its original bandwidth but still be able to recover all the transmitted data from the reduced bandwidth. This solution can efficiently improve the coexistence ability of UWB devices in a cognitive manner without increasing hardware complexity
A Singular Perturbation Approach for Time-Domain Assessment of Phase Margin
This paper considers the problem of time-domain assessment of the Phase Margin (PM) of a Single Input Single Output (SISO) Linear Time-Invariant (LTI) system using a singular perturbation approach, where a SISO LTI fast loop system, whose phase lag increases monotonically with frequency, is introduced into the loop as a singular perturbation with a singular perturbation (time-scale separation) parameter Epsilon. First, a bijective relationship between the Singular Perturbation Margin (SPM) max and the PM of the nominal (slow) system is established with an approximation error on the order of Epsilon(exp 2). In proving this result, relationships between the singular perturbation parameter Epsilon, PM of the perturbed system, PM and SPM of the nominal system, and the (monotonically increasing) phase of the fast system are also revealed. These results make it possible to assess the PM of the nominal system in the time-domain for SISO LTI systems using the SPM with a standardized testing system called "PM-gauge," as demonstrated by examples. PM is a widely used stability margin for LTI control system design and certification. Unfortunately, it is not applicable to Linear Time-Varying (LTV) and Nonlinear Time-Varying (NLTV) systems. The approach developed here can be used to establish a theoretical as well as practical metric of stability margin for LTV and NLTV systems using a standardized SPM that is backward compatible with PM
Solid-state laser refrigeration of a semiconductor optomechanical resonator
Photothermal heating represents a major constraint that limits the
performance of many nanoscale optoelectronic and optomechanical devices
including nanolasers, quantum optomechanical resonators, and integrated
photonic circuits. Although radiation-pressure damping has been reported to
cool an individual vibrational mode of an optomechanical resonator to its
quantum ground state, to date the internal material temperature within an
optomechanical resonator has not been reported to cool via laser excitation.
Here we demonstrate the direct laser refrigeration of a semiconductor
optomechanical resonator >20K below room temperature based on the emission of
upconverted, anti-Stokes photoluminescence of trivalent ytterbium ions doped
within a yttrium-lithium-fluoride (YLF) host crystal. Optically-refrigerating
the lattice of a dielectric resonator has the potential to impact several
fields including scanning probe microscopy, the sensing of weak forces, the
measurement of atomic masses, and the development of radiation-balanced
solid-state lasers. In addition, optically refrigerated resonators may be used
in the future as a promising starting point to perform motional cooling for
exploration of quantum effects at mesoscopic length scales,temperature control
within integrated photonic devices, and solid-state laser refrigeration of
quantum material
Beam-Based Analog Self-Interference Cancellation with Auxiliary Transmit Chains in Full-Duplex MIMO Systems
Analog domain cancellation has been considered as the most important step to mitigate self-interference (SI) in fullduplex (FD) radios. However, in FD multiple-input multipleoutput (MIMO) systems, this method faces a critical issue of complexity since the number of cancellation circuits increases quadratically with the number of antennas. In this paper, we propose a beam-based radio frequency SI cancellation architecture which uses adaptive filters to significantly reduce the complexity. Data symbols for all the beams are up-converted by auxiliary transmit chains to provide reference signals for all adaptive filters. Hence, the number of cancellation circuits becomes proportional to the number of transmit beams which are much smaller than that of transmit antennas. We then show that the interference suppression ratio in this architecture is neither affected by the number of beams nor transmit or receive antennas. Instead, it is decided by the performance of the adaptive filter. Simulations are conducted to confirm the theoretical analyses
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