335 research outputs found
Probing dynamics of an electron-spin ensemble via a superconducting resonator
We study spin relaxation and diffusion in an electron-spin ensemble of
nitrogen impurities in diamond at low temperature (0.25-1.2 K) and polarizing
magnetic field (80-300 mT). Measurements exploit mode- and
temperature-dependent coupling of hyperfine-split sub-ensembles to the
resonator. Temperature-independent spin linewidth and relaxation time suggest
that spin diffusion limits spin relaxation. Depolarization of one sub-ensemble
by resonant pumping of another indicates fast cross-relaxation compared to spin
diffusion, with implications on use of sub-ensembles as independent quantum
memories.Comment: 5 pages, 5 figures, and Supplementary Information (2 figures
Modeling and Testing Superconducting Artificial CPW Lines Suitable for Parametric Amplification
Achieving amplification with high gain and quantum-limited noise is a
difficult problem to solve. Parametric amplification using a superconducting
transmission line with high kinetic inductance is a promising technology not
only to solve this problem but also adding several benefits. When compared with
other technologies, they have the potential of improving power saturation,
achieving larger fractional bandwidths and operating at higher frequencies. In
this type of amplifiers, selecting the proper transmission line is a key
element in their design. Given current fabrication limitations, traditional
lines such as coplanar waveguides (CPW), are not ideal for this purpose since
it is difficult to make them with the proper characteristic impedance for good
matching and slow-enough phase velocity for making them more compact.
Capacitively-loaded lines, also known as artificial lines, are a good solution
to this problem. However, few design rules or models have been presented to
guide their accurate design. This fact is even more crucial considering that
they are usually fabricated in the form of Floquet lines that have to be
designed carefully to suppress undesired harmonics appearing in the parametric
process. In this article we present, firstly, a new modelling strategy, based
on the use of electromagnetic-simulation software, and, secondly, a
first-principles model that facilitate and speed the design of CPW artificial
lines and of Floquet lines made out of them. Then, we present comparisons with
experimental results that demonstrate their accuracy. Finally, the theoretical
model allows to predict the high-frequency behaviour of the artificial lines
showing that they are good candidates for implementing parametric amplifiers
above 100 GHz.Comment: 7 pages, 11 figures, submitted to IEEE Transactions on Applied
Superconductivit
CSM-180 - An SQL Interface for the IFS/2 Knowledge-Baseserver: Release 2
A version of the IFS/2, known as the IFS/Q, has been designed to give direct support to SQL programs running on a host computer. This report gives detailed specifications of one external and two internal software and firmware interfaces which have been created for IFS/Q. Release 2 differs from Release 1 mainly in the Interface B details (see section 4). We have also tidied up the IFS/Q library procedures, which are described in a companion document - (see ref 9); for convenience this is included as Appendix B to this report
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots
We report on the impulsive generation of coherent optical phonons in
CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe
experiments using femtosecond laser pulses were performed by tuning the laser
central energy to resonate with the absorption edge of the nanocrystals. We
identify two longitudinal optical phonons, one longitudinal acoustic phonon and
a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the
optical phonons as a function of the laser central energy exhibits a resonance
that is well described by a model based on impulsive stimulated Raman
scattering. The phases of the coherent phonons reveal coupling between
different modes. At low power density excitations, the frequency of the optical
coherent phonons deviates from values obtained from spontaneous Raman
scattering. This behavior is ascribed to the presence of electronic impurity
states which modify the nanocrystal dielectric function and, thereby, the
frequency of the infrared-active phonons
Intermediate frequency band digitized high dynamic range radiometer system for plasma diagnostics and real- time Tokamak control Citation for published version (APA)
Superconducting Coplanar Waveguide Filters for Submillimeter Wave On-Chip Filterbank Spectrometers
We show the first experimental results which prove that superconducting NbTiN coplanar-waveguide resonators can achieve a loaded Q factor in excess of 800 in the 350 GHz band. These resonators can be used as narrow band pass filters for on-chip filter bank spectrometers for astronomy. Moreover, the low-loss coplanar waveguide technology provides an interesting alternative to microstrip lines for constructing large scale submillimeter wave electronics in general
Full characterisation of a background limited antenna coupled KID over an octave of bandwidth for THz radiation
Factors associated with pastoral community knowledge and occurrence of mycobacterial infections in human-animal interface areas of Nakasongola and Mubende districts, Uganda
<p>Abstract</p> <p>Background</p> <p>Nontuberculous mycobacteria (NTM) are emerging opportunistic pathogens whose role in human and animal disease is increasingly being recognized. Major concerns are their role as opportunistic pathogens in HIV/AIDS infections. The role of open natural water sources as source and livestock/wildlife as reservoirs of infections to man are well documented. This presents a health challenge to the pastoral systems in Africa that rely mostly on open natural water sources to meet livestock and human needs. Recent study in the pastoral areas of Uganda showed infections with same genotypes of NTM in pastoralists and their livestock. The aim of this study was to determine the environmental, animal husbandry and socio-demographic factors associated with occurrence and the pastoral community knowledge of mycobacterial infections at the human-environment-livestock/wildlife interface (HELI) areas in pastoral ecosystems of Uganda.</p> <p>Methods</p> <p>Two hundred and fifty three (253) individuals were subjected to a questionnaire survey across the study districts of Nakasongola and Mubende. Data were analyzed using descriptive statistics and multivariable logistic regression analysis.</p> <p>Results</p> <p>Humans sharing of the water sources with wild animals from the forest compared to savannah ecosystem (OR = 3.3), the tribe of herding pastoral community (OR = 7.9), number of rooms present in household (3-5 vs. 1-2 rooms) (OR = 3.3) were the socio-demographic factors that influenced the level of knowledge on mycobacterial infections among the pastoral communities. Tribe (OR = 6.4), use of spring vs. stream water for domestic use (OR = 4.5), presence of sediments in household water receptacle (OR = 2.32), non separation of water containers for drinking and domestic use (OR = 2.46), sharing of drinking water sources with wild animals (OR = 2.1), duration of involvement of >5 yrs in cattle keeping (OR = 3.7) and distance of household to animal night shelters (>20 meters) (OR = 3.8) were significant socio-demographic factors associated with the risk of occurrence of mycobacterioses among the pastoral communities in Uganda.</p> <p>Conclusion</p> <p>The socio-demographic, environmental and household related factors influence the risk of occurrence as well as pastoralists' knowledge of mycobacterial infections in the pastoral households at the human-environment-livestock/wildlife pastoral interface areas of Uganda.</p
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