1,748 research outputs found
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
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
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
Nanoscale electrical analyses of axial-junction GaAsP nanowires for solar cell applications
Axial p-n and p-i-n junctions in GaAs0.7P0.3 nanowires are demonstrated and analyzed using electron beam induced current microscopy. Organized self-catalyzed nanowire arrays are grown by molecular beam epitaxy on nanopatterned Si substrates. The nanowires are doped using Be and Si impurities to obtain p- and n-type conductivity, respectively. A method to determine the doping type by analyzing the induced current in the vicinity of a Schottky contact is proposed. It is demonstrated that for the applied growth conditions using Ga as a catalyst, Si doping induces an n-type conductivity contrary to the GaAs self-catalyzed nanowire case, where Si was reported to yield a p-type doping. Active axial nanowire p-n junctions having a homogeneous composition along the axis are synthesized and the carrier concentration and minority carrier diffusion lengths are measured. To the best of our knowledge, this is the first report of axial p-n junctions in self-catalyzed GaAsP nanowires
Metabolomics hallmarks OPA1 variants correlating with their in-vitro phenotype and predicting clinical severity
Interpretation of variants of uncertain significance is an actual major challenge. We addressed this question on a set of OPA1 missense variants responsible for variable severity of neurological impairments.
We used targeted metabolomics to explore the different signatures of OPA1 variants expressed in Opa1 deleted mouse embryonic fibroblasts (Opa1 12/ 12 MEFs), grown under selective conditions.
Multivariate analyses of data discriminated Opa1+/+ from Opa1 12/ 12 MEFs metabolic signatures and classified OPA1 variants according to their in-vitro severity. Indeed, the mild p.I382M hypomorphic variant was segregating close to the wild-type allele, while the most severe p.R445H variant was close to Opa1 12/ 12 MEFs, and the p.D603H and p.G439V alleles, responsible for isolated and syndromic presentations respectively, were intermediary between the p.I382M and the p.R445H variants. The most discriminant metabolic features were hydroxyproline, the spermine/spermidine ratio, amino acid pool and several phospholipids, emphasizing proteostasis, endoplasmic reticulum stress and phospholipid remodeling as the main mechanisms ranking OPA1 allele impacts on metabolism.
These results demonstrate the high resolving power of metabolomics in hierarchizing OPA1 missense mutations by their in-vitro severity, fitting clinical expressivity. This suggests that our methodological approach can be used to discriminate the pathological significance of variants in genes responsible for other rare metabolic diseases and may be instrumental to select possible compounds eligible for supplementation treatment
MICROSCOPE mission analysis, requirements and expected performance
The MICROSCOPE mission aimed to test the Weak Equivalence Principle (WEP) to
a precision of . The WEP states that two bodies fall at the same rate
on a gravitational field independently of their mass or composition. In
MICROSCOPE, two masses of different compositions (titanium and platinum alloys)
are placed on a quasi-circular trajectory around the Earth. They are the
test-masses of a double accelerometer. The measurement of their accelerations
is used to extract a potential WEP violation that would occur at a frequency
defined by the motion and attitude of the satellite around the Earth. This
paper details the major drivers of the mission leading to the specification of
the major subsystems (satellite, ground segment, instrument, orbit...).
Building upon the measurement equation, we derive the objective of the test in
statistical and systematic error allocation and provide the mission's expected
error budget.Comment: References update
Optimizing C-RAN Backhaul Topologies: A Resilience-Oriented Approach Using Graph Invariants
ABSTRACT: At the verge of the launch of the first commercial fifth generation (5G) system, trends in wireless and optical networks are proceeding toward increasingly dense deployments, supporting resilient interconnection for applications that carry higher and higher capacity and tighter latency requirements. These developments put increasing pressure on network backhaul and drive the need for a re-examination of traditional backhaul topologies. Challenges of impending networks cannot be tackled by star and ring approaches due to their lack of intrinsic survivability and resilience properties, respectively. In support of this re-examination, we propose a backhaul topology design method that formulates the topology optimization as a graph optimization problem by capturing both the objective and constraints of optimization in graph invariants. Our graph theoretic approach leverages well studied mathematical techniques to provide a more systematic alternative to traditional approaches to backhaul design. Specifically, herein, we optimize over some known graph invariants, such as maximum node degree, topology diameter, average distance, and edge betweenness, as well as over a new invariant called node Wiener impact, to achieve baseline backhaul topologies that match the needs for resilient future wireless and optical networks
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