521 research outputs found
Incoherent Noise and Quantum Information Processing
Incoherence in the controlled Hamiltonian is an important limitation on the
precision of coherent control in quantum information processing. Incoherence
can typically be modelled as a distribution of unitary processes arising from
slowly varying experimental parameters. We show how it introduces artifacts in
quantum process tomography and we explain how the resulting estimate of the
superoperator may not be completely positive. We then go on to attack the
inverse problem of extracting an effective distribution of unitaries that
characterizes the incoherence via a perturbation theory analysis of the
superoperator eigenvalue spectra.Comment: 15 pages, 5 figures, replaced with future JCP published versio
Minimizing the overlap problem in protein NMR: a computational framework for precision amino acid labeling
Motivation: Recent advances in cell-free protein expression systems allow specific labeling of proteins with amino acids containing stable isotopes (Ā¹āµN, Ā¹Ā³C and Ā²H), an important feature for protein structure determination by nuclear magnetic resonance (NMR) spectroscopy. Given this labeling ability, we present a mathematical optimization framework for designing a set of protein isotopomers, or labeling schedules, to reduce the congestion in the NMR spectra. The labeling schedules, which are derived by the optimization of a cost function, are tailored to a specific protein and NMR experiment.
Results: For 2D Ā¹āµN-Ā¹H HSQC experiments, we can produce an exact solution using a dynamic programming algorithm in under 2 h on a standard desktop machine. Applying the method to a standard benchmark protein, calmodulin, we are able to reduce the number of overlaps in the 500 MHZ HSQC spectrum from 10 to 1 using four samples with a true cost function, and 10 to 4 if the cost function is derived from statistical estimates. On a set of 448 curated proteins from the BMRB database, we are able to reduce the relative percent congestion by 84.9% in their HSQC spectra using only four samples. Our method can be applied in a high-throughput manner on a proteomic scale using the server we developed. On a 100-node cluster, optimal schedules can be computed for every protein coded for in the human genome in less than a month.
Availability: A server for creating labeling schedules for Ā¹āµN-Ā¹H HSQC experiments as well as results for each of the individual 448 proteins used in the test set is available at http://nmr.proteomics.ics.uci.edu
Regulation of Intracellular Calcium Concentration by Nanosecond Pulsed Electric Fields
Changes in [Ca2+]i response of individual Jurkat cells to nanosecond pulsed electric fields (nsPEFs) of 60 ns and field strengths of 25, 50, and 100 kV/cm were investigated. The magnitude of the nsPEF-induced rise in [Ca2+]i was dependent on the electric field strength. With 25 and 50 kV/cm, the [Ca2+]i response was due to the release of Ca2+ from intracellular stores and occurred in less than 18 ms. With 100 kV/cm, the increase in [Ca2+]i was due to both internal release and to influx across the plasma membrane. Spontaneous changes in [Ca2+]i exhibited a more gradual increase over several seconds. The initial, pulse-induced [Ca2+]i response initiates at the poles of the cell with respect to electrode placement and co-localizes with the endoplasmic reticulum. The results suggest that nsPEFs target both the plasma membrane and subcellular membranes and that one of the mechanisms for Ca2+ release may be due to nanopore formation in the endoplasmic reticulum
Controversy in mechanotransduction ā the role of endothelial cellācell junctions in fluid shear stress sensing
Fluid shear stress (FSS) from blood flow, sensed by the vascular endothelial cells (ECs) that line all blood vessels, regulates vascular development during embryogenesis, controls adult vascular physiology and determines the location of atherosclerotic plaque formation. Although a number of papers have reported a crucial role for cellācell adhesions or adhesion receptors in these processes, a recent publication has challenged this paradigm, presenting evidence that ECs can very rapidly align in fluid flow as single cells without cellācell contacts. To address this controversy, four independent laboratories assessed EC alignment in fluid flow across a range of EC cell types. These studies demonstrate a strict requirement for cellācell contact in shear stress sensing over timescales consistent with previous literature and inconsistent with the newly published data
The use of indigenous knowledge in development: problems and challenges
The use of indigenous knowledge has been seen by many as an alternative way of promoting development in poor rural communities in many parts of the world. By reviewing much of the recent work on indigenous knowledge, the paper suggests that a number of problems and tensions has resulted in indigenous knowledge not being as useful as hoped for or supposed. These include problems emanating from a focus on the (arte)factual; binary tensions between western science and indigenous knowledge systems; the problem of differentiation and power relations; the romanticization of indigenous knowledge; and the all too frequent decontextualization of indigenous knowledge
Comparison of dynamical decoupling protocols for a nitrogen-vacancy center in diamond
We perform a detailed theoretical-experimental study of the dynamical
decoupling (DD) of the nitrogen-vacancy (NV) center in diamond. We investigate
the DD sequences applied to suppress the dephasing of the electron spin of the
NV center induced by the coupling to a spin bath composed of the substitutional
nitrogen atoms. The decoupling efficiency of various DD schemes is studied,
including both periodic and periodic pulse sequences. For ideal control pulses,
we find that the DD protocols with the Carr-Purcell-Meiboom-Gill (CPMG) timing
of the pulses provides best performance. We show that, as the number of control
pulses increases, the decoupling fidelity scaling differs qualitatively from
the predictions of the Magnus expansion, and explain the origin of this
difference. In particular, more advanced symmetrized or concatenated protocols
do not improve the DD performance. Next, we investigate the impact of the
systematic instrumental pulse errors in different periodic and aperiodic pulse
sequences. The DD protocols with the single-axis control do not preserve all
spin components in the presence of the pulse errors, and the two-axis control
is needed. We demonstrate that the two-axis control sequence with the CPMG
timing is very robust with respect to the pulse errors. The impact of the pulse
errors can be diminished further by symmetrizing this protocol. For all
protocols studied here, we present a detailed account of the pulse error
parameters which make strongest impact on the DD performance. In conclusion, we
give specific recommendations about choosing the decoupling protocol for the
system under investigation.Comment: 16 pages, 11 figure
Bang-Bang control of a qubit coupled to a quantum critical spin bath
We analytically and numerically study the effects of pulsed control on the
decoherence of a qubit coupled to a quantum spin bath. When the environment is
critical, decoherence is faster and we show that the control is relatively more
effective. Two coupling models are investigated, namely a qubit coupled to a
bath via a single link and a spin star model, yielding results that are similar
and consistent.Comment: 10 pages, 4 figures, replaced with published versio
Towards a digital policing in developing nations : the Nigerian context
Technology-assisted living is a growing trend in
most developing nations, particularly for young-aged
demographic countries, as it presents a platform for personal
development and knowledge management. However, this societyscaping trend has also introduced the myriad opportunity for the
formation of complex crime, which is often beyond the
(immediate) capability of the policing entity in developing
nations. To address this lingering and futuristic problem,
particularly in Nigeria, this study developed a context-based
digital policing framework for the enhancement of the Nigerian
Police. This Nigerian-context framework presents the viability
and relevance of the digital policing mechanism in addressing
challenges ravaging society. Furthermore, it also presents a
modality for improving and enhancing the policing apparatus of
the Nigerian society, as a model for other developing nations.
The knowledge from the Nigerian-context of digital policing has
both research and societal implications. In terms of research, it
opens the community of security researchers into the contextual
characteristics of digital policing as well as the probable research
direction required to implement digital policing in developing
nations. With respect to society, knowledge provides a substratum
for the integration of the community-policing model.https://www.ijitee.orgpm2020Computer Scienc
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