56 research outputs found
Millimetre Wave Kinetic Inductance Parametric Amplification using Ridge Gap Waveguide
We present the design and simulation methodology of a superconducting
ridge-gap waveguide (RGWG) as a potential basis for mm-wave kinetic inductance
travelling wave parametric amplifiers (KI-TWPAs). A superconducting RGWG was
designed using Ansys HFSS to support a quasi-TEM mode of transmission over a
bandwidth of 20 to 120 GHz with its internal dimensions optimised for
integration with W-band rectangular waveguide. A design of an impedance loaded
travelling wave structure incorporating periodic perturbations of the ridge was
described. A method to simulate the nonlinear kinetic inductance via
user-defined components in Keysight's ADS was outlined, which yielded the power
dependent S-parameters and parametric signal gain. A RGWG with a 30 nm NbTiN
coating and 5 um conductor spacing, corresponding to a kinetic inductance
fraction was used for the description of a KI-TWPA with 900
perturbations equivalent to a physical length 25 cm that achieved more than 10
dB of signal gain over a 75--110 GHz bandwidth via 4-wave mixing (4WM).Comment: 9 pages, 3 figures, submitted to the 19th International Workshop on
Low Temperature Detectors (LTD19) Proceeding
Parametric amplification via superconducting contacts in a Ka band niobium pillbox cavity
Superconducting parametric amplifiers are commonly fabricated using planar
transmission lines with a non-linear inductance provided by either Josephson
junctions or the intrinsic kinetic inductance of the thin film. However, Banys
et al. [1] reported non-linear behaviour in a niobium pillbox cavity,
hypothesising that below Tc, the pair iris-bulk resonator would act as a
superconducting contact surface exploiting a Josephson-like non-linearity. This
work investigates this effect further by applying Keysight Technologies'
Advanced Design System (ADS) to simulate the cavity using an equivalent circuit
model that includes a user defined Josephson inductance component. The
simulations show that for a resonance centred at nu0 = 30.649 GHz, when two
tones (pump and signal) are injected into the cavity, mixing and parametric
gain occur. The maximum achievable gain is explored when the resonator is taken
to its bifurcation energy. These results are compared to cryogenic measurements
where the pump and signal are provided by a Vector Network Analyzer
The Impact of Surface Passivation on Kapitza Resistance at the Interface between a Semiconductor and Liquid Nitrogen
Cooling electronic devices to cryogenic temperatures (< 77 K) is crucial in
various scientific and engineering domains. Efficient cooling involves the
removal of heat generated from these devices through thermal contact with
either a liquid cryogen or a dry cryostat cold stage. However, as these devices
cool, thermal boundary resistance, also known as Kapitza resistance, hinders
the heat flow across thermal interfaces, resulting in elevated device
temperatures. In transistors, the presence of passivation layers like Silicon
Nitride (SiN) introduces additional interfaces that further impede heat
dissipation. This paper investigates the impact of passivation layer thickness
on Kapitza resistance at the interface between a solid device and liquid
nitrogen. The Kapitza resistance is measured using a capacitance thermometer
that has been passivated with SiN layers ranging from 0 to 240 nm. We observe
that Kapitza resistance increases with increasing passivation thickness.Comment: 6 pages, 5 Figure
Parametric amplification via superconducting contacts in a Ka band niobium pillbox cavity
Superconducting parametric amplifiers are commonly fabricated using planar
transmission lines with a non-linear inductance provided by either Josephson
junctions or the intrinsic kinetic inductance of the thin film. However, Banys
et al. [1] reported non-linear behaviour in a niobium pillbox cavity,
hypothesising that below Tc, the pair iris-bulk resonator would act as a
superconducting contact surface exploiting a Josephson-like non-linearity. This
work investigates this effect further by applying Keysight Technologies'
Advanced Design System (ADS) to simulate the cavity using an equivalent circuit
model that includes a user defined Josephson inductance component. The
simulations show that for a resonance centred at nu0 = 30.649 GHz, when two
tones (pump and signal) are injected into the cavity, mixing and parametric
gain occur. The maximum achievable gain is explored when the resonator is taken
to its bifurcation energy. These results are compared to cryogenic measurements
where the pump and signal are provided by a Vector Network Analyzer
Measuring the Kapitza Resistance between a Passivated Semiconductor and Liquid Helium
In this paper, we describe an experimental investigation into the effect of
passivation layer thickness on heat dissipation between a quartz substrate and
liquid helium. We have observed that by depositing SiN from 0 to 240 nm, the
Kapitza resistance increases by 0.0365 m^2.K/W per nanometer more than for an
unpassivated semiconductor. We hypothesize that this increase in Kapitza
resistance represents an additional barrier to the cooling of semiconductor
devices in liquid helium.Comment: 7 page
Creating comprehensive, youth-centered culturally appropriate sex education: What do young gay, bisexual and questioning men want?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106604/1/Creating comprehensive, youth-centered culturally appropriate sex education What do young gay, bisexual and questioning men want.pd
Evolution of the patellar sesamoid bone in mammals
The patella is a sesamoid bone located in the major extensor tendon of the knee joint, in the hindlimb of many tetrapods. Although numerous aspects of knee morphology are ancient and conserved among most tetrapods, the evolutionary occurrence of an ossified patella is highly variable. Among extant (crown clade) groups it is found in most birds, most lizards, the monotreme mammals and almost all placental mammals, but it is absent in most marsupial mammals as well as many reptiles. Here, we integrate data from the literature and first-hand studies of fossil and recent skeletal remains to reconstruct the evolution of the mammalian patella. We infer that bony patellae most likely evolved between four and six times in crown group Mammalia: in monotremes, in the extinct multituberculates, in one or more stem-mammal genera outside of therian or eutherian mammals and up to three times in therian mammals. Furthermore, an ossified patella was lost several times in mammals, not including those with absent hindlimbs: once or more in marsupials (with some re-acquisition) and at least once in bats. Our inferences about patellar evolution in mammals are reciprocally informed by the existence of several human genetic conditions in which the patella is either absent or severely reduced. Clearly, development of the patella is under close genomic control, although its responsiveness to its mechanical environment is also important (and perhaps variable among taxa). Where a bony patella is present it plays an important role in hindlimb function, especially in resisting gravity by providing an enhanced lever system for the knee joint. Yet the evolutionary origins, persistence and modifications of a patella in diverse groups with widely varying habits and habitats—from digging to running to aquatic, small or large body sizes, bipeds or quadrupeds—remain complex and perplexing, impeding a conclusive synthesis of form, function, development and genetics across mammalian evolution. This meta-analysis takes an initial step toward such a synthesis by collating available data and elucidating areas of promising future inquiry
Comparison of weight in middle age, weight at 18 years, and weight change between, in predicting subsequent 14 year mortality and coronary events: Caerphilly Prospective Study
Objective-The prevalence of obesity is increasing in many European countries and in the United States. This report examines the mortality and morbidity associated with being overweight and obese in the Caerphilly Prospective Study and the relative effects of weight in middle age and self reported weight at 18 years
Solar cell and its production process
The present invention relates to a solar cell comprising a support (6), a back electrode layer (5), at least a hydrogenated microcrystalline silicon photoelectric device (9), and a top electrode layer (11). The back electrode layer (5) has a rough surface. The solar cell comprises, between the back electrode layer (5) and the hydrogenated microcrystalline silicon photoelectric device (9), an asymmetric intermediate layer (8), said intermediate layer (8) being adjacent to said hydrogenated microcrystalline silicon photoelectric device (9) and having a surface, on the side of the back electrode layer (5), having a roughness greater than the roughness of the surface of said intermediate layer (8) on the side of the hydrogenated microcrystalline silicon device (9). Such solar cells allow to obtain optimum Voc and FF parameters, while maintaining high current
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