1,012 research outputs found
Switchable Electromagnetic Bandgap Surface Wave Antenna
This paper presents a novel switchable electromagnetic bandgap surface wave antenna that can support both a surface wave and normal mode radiation for communications at 2.45 GHz. In the surface wave mode, the antenna has a monopole-like radiation pattern with a measured gain of 4.4 dBi at ±49° and a null on boresight. In the normal mode, the antenna operates like a back-fed microstrip patch antenna
The Paradox of Virtual Dipoles in the Einstein Action
The functional integral of pure Einstein 4D quantum gravity admits abnormally
large and long-lasting "dipolar fluctuations", generated by virtual sources
with the property Int d^4x Sqrt{g(x)} Tr T(x) = 0. These fluctuations would
exist also at macroscopic scales, with paradoxical consequences. We set out
their general features and give numerical estimates of possible suppression
processes.Comment: LaTeX, 5 pages; reference adde
Density matrix operatorial solution of the non--Markovian Master Equation for Quantum Brownian Motion
An original method to exactly solve the non-Markovian Master Equation
describing the interaction of a single harmonic oscillator with a quantum
environment in the weak coupling limit is reported. By using a superoperatorial
approach we succeed in deriving the operatorial solution for the density matrix
of the system. Our method is independent of the physical properties of the
environment. We show the usefulness of our solution deriving explicit
expressions for the dissipative time evolution of some observables of physical
interest for the system, such as, for example, its mean energy.Comment: 16 pages, 1 figur
An Independently Tunable Tri-band Antenna Design for Concurrent Multi-band Single Chain Radio Receivers
In this paper, a novel tunable tri-band antenna
is presented for concurrent, multi-band, single chain radio
receivers. The antenna is manufactured on a 50×100 mm FR4
printed circuit board (PCB), and is able to provide three concurrent,
independently tunable operating bands covering a frequency
range from 600 MHz to 2.7 GHz. The antenna performance
is investigated for both numerical and experimental methods
when using, first, varactor diodes and, second, digitally tunable
capacitors (DTCs) to tune frequencies, which shows the antenna
gain can be improved by up to 2.6 dBi by using DTCs. A
hardware-in-the-loop test-bed provides a system level evaluation
of the proposed antenna in a direct RF digitized, concurrent,
tri-band radio receiver. By measuring the receiver’s error vector
magnitude, we demonstrate sufficient isolation between concurrent
bands achieving 30 MHz of aggregated bandwidth as well
as strong resilience to adjacent blockers next to each band. The
data reported in this article are available from the ORDA digital
repository (https://doi.org/10.15131/shef.data.5346295)
Optical calibration hardware for the Sudbury Neutrino Observatory
The optical properties of the Sudbury Neutrino Observatory (SNO) heavy water
Cherenkov neutrino detector are measured in situ using a light diffusing sphere
("laserball"). This diffuser is connected to a pulsed nitrogen/dye laser via
specially developed underwater optical fibre umbilical cables. The umbilical
cables are designed to have a small bending radius, and can be easily adapted
for a variety of calibration sources in SNO. The laserball is remotely
manipulated to many positions in the D2O and H2O volumes, where data at six
different wavelengths are acquired. These data are analysed to determine the
absorption and scattering of light in the heavy water and light water, and the
angular dependence of the response of the detector's photomultiplier tubes.
This paper gives details of the physical properties, construction, and optical
characteristics of the laserball and its associated hardware.Comment: 17 pages, 8 figures, submitted to Nucl. Inst. Meth.
Concurrent, Multi-band, Single-Chain Radio Receiver for High Data-Rate HetNets
A concurrent, tunable, triple-band, single chain radio receiver for 5G radio access networks is presented and its performance is evaluated in a hardware-in-the-loop test-bed. The test-bed emulates a 5G heterogeneous network supporting three independently tunable, wideband, simultaneous connections over a frequency range from 600 MHz to 2.7 GHz. The single chain receiver is able to achieve an aggregate bandwidth of 93.75 MHz, 31.25 MHz per band, and a net data rate of 187.5 Mbit/s through the use of single-carrier QPSK transmissions. The receiver demonstrate sufficient isolation between the concurrent transmissions as well as strong resilience to adjacent blockers through the use of a small guard band
Low-profile independently- and concurrently-tunable quad-band antenna for single chain sub-6GHz 5G new radio applications
This paper presents a quad-band frequency agile antenna, with independent and concurrent frequency tunability in each band, for a tunable, concurrent, quad-band single chain radio receiver for 5G New Radio (NR). More specifically, the antenna comprises of four planar slots etched in a ground plane and fed through a single microstrip feedline, without any impedance matching network. The structure is optimized to maximize isolation between the individual slots and their respective resonant frequencies. Furthermore, a novel high order harmonic suppression method is demonstrated, which controls the current distribution via creating a fictitious short circuit in the slot antenna-enabling the antenna to achieve a much wider tuning range. Numerical simulations are verified using experimental implementation and measurements, with good agreement observed. The four slots resonate around the 830 MHz, 1.8 GHz, 2.4 GHz and 3.4 GHz frequency bands, which are independently tuned (using a varactor diode in each slot) to achieve tuning ranges of approximately 64%, 66%, 27% and 33%, respectively. More importantly, the contiguous four bands covers a total frequency tuning from 0.6 to 3.6 GHz i.e. a tuning range of approximately 143%. Finally, far-field measurements are performed and the antenna is evaluated in over-the-air testbed (quad-band radio receiver), which measures the Error Vector Magnitude performance for the individual channels. Good performance is observed, confirming acceptable isolation performance between the four bands. The data reported in this paper is available, from ORDA-The University of Sheffield Research Data Catalogue and Repository, at https://doi.org/10.15131/shef.data.11219000.v1
Packaging signals in single-stranded RNA viruses: nature’s alternative to a purely electrostatic assembly mechanism
The formation of a protective protein container is an essential step in the life-cycle of most viruses. In the case of single-stranded (ss)RNA viruses, this step occurs in parallel with genome packaging in a co-assembly process. Previously, it had been thought that this process can be explained entirely by electrostatics. Inspired by recent single-molecule fluorescence experiments that recapitulate the RNA packaging specificity seen in vivo for two model viruses, we present an alternative theory, which recognizes the important cooperative roles played by RNA–coat protein interactions, at sites we have termed packaging signals. The hypothesis is that multiple copies of packaging signals, repeated according to capsid symmetry, aid formation of the required capsid protein conformers at defined positions, resulting in significantly enhanced assembly efficiency. The precise mechanistic roles of packaging signal interactions may vary between viruses, as we have demonstrated for MS2 and STNV. We quantify the impact of packaging signals on capsid assembly efficiency using a dodecahedral model system, showing that heterogeneous affinity distributions of packaging signals for capsid protein out-compete those of homogeneous affinities. These insights pave the way to a new anti-viral therapy, reducing capsid assembly efficiency by targeting of the vital roles of the packaging signals, and opens up new avenues for the efficient construction of protein nanocontainers in bionanotechnology
Decoherence scenarios from micro- to macroscopic superpositions
Environment induced decoherence entails the absence of quantum interference
phenomena from the macroworld. The loss of coherence between superposed wave
packets depends on their separation. The precise temporal course depends on the
relative size of the time scales for decoherence and other processes taking
place in the open system and its environment. We use the exactly solvable model
of an harmonic oscillator coupled to a bath of oscillators to illustrate
various decoherence scenarios: These range from exponential golden-rule decay
for microscopic superpositions, system-specific decay for larger separations in
a crossover regime, and finally universal interaction-dominated decoherence for
ever more macroscopic superpositions.Comment: 11 pages, 7 figures, accompanying paper to quant-ph/020412
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