5,650 research outputs found
Magnetic Amplifiers for Voltage Regulation Applications
The purpose of this thesis is to present research on magnetic amplifiers and to discuss how magnetic amplifiers are useful in voltage regulation applications. Beginning with a background in magnetics and magnetic properties, this thesis outlines the importance of the B-H curve and explains how to simulate the B-H curve of a saturable inductor using LtSpice. Furthermore, two saturable inductors can be aligned in antiparallel to create a magnetic amplifier. The theory of magnetic amplifiers is dated, but its simplistic design has benefits for modern applications. The magnetic amplifier acts as a variable impedance switch where a small amount of DC current can control the output voltage of a circuit. This is possible because the control current varies the coreâs position on its B-H curve. Once the core is saturated, any further increase in control current will not affect the output voltage of the circuit. Based on the design of the magnetic cores the saturation point can be adjusted. Using the saturable inductor model in LtSpice, a magnetic amplifier can be simulated in a voltage regulation circuit. This circuit is constructed and tested using three different types of magnetic materials for the magnetic amplifier. The correlation between the simulated and measured results attests to the importance of modeling circuits before construction. This design method ensures reproducibility and this thesis shows the effectiveness of magnetic amplifiers in achieving voltage regulation
Scalable, Time-Responsive, Digital, Energy-Efficient Molecular Circuits using DNA Strand Displacement
We propose a novel theoretical biomolecular design to implement any Boolean
circuit using the mechanism of DNA strand displacement. The design is scalable:
all species of DNA strands can in principle be mixed and prepared in a single
test tube, rather than requiring separate purification of each species, which
is a barrier to large-scale synthesis. The design is time-responsive: the
concentration of output species changes in response to the concentration of
input species, so that time-varying inputs may be continuously processed. The
design is digital: Boolean values of wires in the circuit are represented as
high or low concentrations of certain species, and we show how to construct a
single-input, single-output signal restoration gate that amplifies the
difference between high and low, which can be distributed to each wire in the
circuit to overcome signal degradation. This means we can achieve a digital
abstraction of the analog values of concentrations. Finally, the design is
energy-efficient: if input species are specified ideally (meaning absolutely 0
concentration of unwanted species), then output species converge to their ideal
concentrations at steady-state, and the system at steady-state is in (dynamic)
equilibrium, meaning that no energy is consumed by irreversible reactions until
the input again changes.
Drawbacks of our design include the following. If input is provided
non-ideally (small positive concentration of unwanted species), then energy
must be continually expended to maintain correct output concentrations even at
steady-state. In addition, our fuel species - those species that are
permanently consumed in irreversible reactions - are not "generic"; each gate
in the circuit is powered by its own specific type of fuel species. Hence
different circuits must be powered by different types of fuel. Finally, we
require input to be given according to the dual-rail convention, so that an
input of 0 is specified not only by the absence of a certain species, but by
the presence of another. That is, we do not construct a "true NOT gate" that
sets its output to high concentration if and only if its input's concentration
is low. It remains an open problem to design scalable, time-responsive,
digital, energy-efficient molecular circuits that additionally solve one of
these problems, or to prove that some subset of their resolutions are mutually
incompatible.Comment: version 2: the paper itself is unchanged from version 1, but the
arXiv software stripped some asterisk characters out of the abstract whose
purpose was to highlight words. These characters have been replaced with
underscores in version 2. The arXiv software also removed the second
paragraph of the abstract, which has been (attempted to be) re-inserted.
Also, although the secondary subject is "Soft Condensed Matter", this
classification was chosen by the arXiv moderators after submission, not
chosen by the authors. The authors consider this submission to be a
theoretical computer science paper
Tests for the existence of horizons through gravitational wave echoes
The existence of black holes and of spacetime singularities is a fundamental
issue in science. Despite this, observations supporting their existence are
scarce, and their interpretation unclear. We overview how strong a case for
black holes has been made in the last few decades, and how well observations
adjust to this paradigm. Unsurprisingly, we conclude that observational proof
for black holes is impossible to come by. However, just like Popper's black
swan, alternatives can be ruled out or confirmed to exist with a single
observation. These observations are within reach. In the next few years and
decades, we will enter the era of precision gravitational-wave physics with
more sensitive detectors. Just as accelerators require larger and larger
energies to probe smaller and smaller scales, more sensitive gravitational-wave
detectors will be probing regions closer and closer to the horizon, potentially
reaching Planck scales and beyond. What may be there, lurking?Comment: Published in Nature Astronomy, expanded version with further details
available at arXiv:1707.0302
Modeling a 300 kHz bathymetric sonar system
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992The Deep Submergence Laboratory has developed a family of calibrated high
frequency bathymetric sonar systems for underwater survey. It is useful to have a
detailed mathematical description of these systems to assist in data processing.
A model of a generalized sonar system is developed first. This model then is made
specific to the DSL 300-kHz forward scanning sonar and is implemented using the
MATLAB software package. The model consists of a cascaded series of filters
representing the electrical and mechanical components of the system. The model is
adjusted after comparison to the transmitted pulse. The results are then inverted to
demonstrate how the corrupting effects of the system can be reversed. A technique is
developed for applying this reverse model to actual data.
The results showed that a good representation of the system can be implemented
using relatively simple descriptions of each component. The most important
components are the band-limiting filter and the transducer. It is possible to reverse
model these components with good results
Trialing project-based learning in a new EAP ESP course: A collaborative reflective practice of three college English teachers
Currently in many Chinese universities, the traditional College English course is facing the risk of being âmarginalizedâ, replaced or even removed, and many hours previously allocated to the course are now being taken by EAP or ESP. At X University in northern China, a curriculum reform as such is taking place, as a result of which a new course has been created called âxue keâ English. Despite the fact that âxue keâ means subject literally, the course designer has made it clear that subject content is not the target, nor is the course the same as EAP or ESP. This curriculum initiative, while possibly having been justified with a rationale of some kind (e.g. to meet with changing social and/or academic needs of students and/or institutions), this is posing a great challenge for, as well as considerable pressure on, a number of College English teachers who have taught this single course for almost their entire teaching career. In such a context, three teachers formed a peer support group in Semester One this year, to work collaboratively co-tackling the challenge, and they chose Project-Based Learning (PBL) for the new course. This presentation will report on the implementation of this project, including the overall designing, operational procedure, and the teachersâ reflections.
Based on discussion, pre-agreement was reached on the purpose and manner of collaboration as offering peer support for more effective teaching and learning and fulfilling and pleasant professional development. A WeChat group was set up as the chief platform for messaging, idea-sharing, and resource-exchanging. Physical meetings were supplementary, with sound agenda but flexible time, and venues. Mosoteach cloud class (lan mo yun ban ke) was established as a tool for virtual learning, employed both in and after class. Discussions were held at the beginning of the semester which determined only brief outlines for PBL implementation and allowed space for everyone to autonomously explore in their own way. Constant further discussions followed, which generated a great deal of opportunities for peer learning and lesson plan modifications. A reflective journal, in a greater or lesser detailed manner, was also kept by each teacher to record the journey of the collaboration. At the end of the semester, it was commonly recognized that, although challenges existed, the collaboration was overall a success and they were all willing to continue with it and endeavor to refine it to be a more professional and productive approach
Single-Input Five-Output Electronically Tunable Current-Mode Biquad Consisting of Only ZC-CFTAs and Grounded Capacitors
This paper presents an electronically tunable current-mode biquadratic filter constructing with four Z-copy current follower transconductance amplifiers (ZC-CFTAs) and only two grounded capacitors. The presented filter can realize all the five standard biquadratic functions simultaneously without requiring any component matching conditions and connecting any relevant output currents. The circuit has one low-impedance input and five high-impedance outputs, resulting in easy cascadability in current-mode. Also, the developed circuit exhibits the advantage of non-interactive electronic control of the natural angular frequency and the quality factor Q along with low incremental active and passive sensitivities. Computer simulation results using PSPICE program are given to confirm the validity of the theoretical prediction and to point out the attractive performance of the circuit
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