536 research outputs found
Limited financial market participation: a transaction cost-based explanation
This paper focuses on the issue of limited financial market participation and determines a
lower bound on the level of fixed transaction costs that are required to reconcile observed
portfolio choices with asset returns within an isoelastic utility framework. The bound is
determined from the set of conditions that ensure the optimality of consumption behavior by
financial market non-participants. It represents the lowest possible cost rationalizing
observed non-participation choices by providing a measure of the forgone utility gains from
participation for observed non-participants. Such gains are related both to the magnitude of
financial market returns and to the opportunity of smoothing consumption, with the benefits
of the former decreasing in the degree of relative risk aversion and those of the latter
increasing in it. Using the US Consumer Expenditure Survey, I find that a yearly cost of at
least 70 is needed to rationalize non-participation for a consumer with log utility and who
can trade in the S&P500 CI. This lower bound declines rapidly in risk aversion for levels of
risk aversion up to two/three; for higher values, it levels off. A yearly cost of at least 31 is
needed to rationalize non-participation for a consumer with log utility and who can trade in
US Treasury Bills. This lower bound rises steadily in risk aversion
Intertemporal consumption choices, transaction costs and limited participation to financial markets: reconciling data and theory
This paper builds a unifying framework that, within the theory of intertemporal consumption choices, brings together the limited participation -based explanation of the poor empirical performance of the C-CAPM and the transaction costs-based explanation of incomplete portfolios. Using the implications of the consumption model and observed household consumption and portfolio choices, we identify the preference parameters of interest and a lower bound for the costs rationalizing non-participation in financial markets, in the presence of unobserved heterogeneity in tastes for consumption and portfolio allocation. Using the US Consumer Expenditure Survey and assuming isoelastic preferences, we estimate the coefficient of relative risk aversion at 1.7 and a cost bound of 0.4 percent of non-durable consumption. Our estimate of the preference parameter is theoretically plausible and the bound sufficiently small to be likely to be exceeded by the actual total (observable and unobservable) costs of participating to financial markets
Development of Lumped Element Kinetic Inductance Detectors for the W-Band
We are developing a Lumped Element Kinetic Inductance Detector (LEKID) array
able to operate in the W-band (75-110 GHz) in order to perform ground-based
Cosmic Microwave Background (CMB) and mm-wave astronomical observations. The
W-band is close to optimal in terms of contamination of the CMB from Galactic
synchrotron, free-free, and thermal interstellar dust. In this band, the
atmosphere has very good transparency, allowing interesting ground-based
observations with large (>30 m) telescopes, achieving high angular resolution
(<0.4 arcmin). In this work we describe the startup measurements devoted to the
optimization of a W-band camera/spectrometer prototype for large aperture
telescopes like the 64 m SRT (Sardinia Radio Telescope). In the process of
selecting the best superconducting film for the LEKID, we characterized a 40 nm
thick Aluminum 2-pixel array. We measured the minimum frequency able to break
CPs (i.e. ) obtaining
GHz, that corresponds to a critical temperature of 1.31 K. This is not suitable
to cover the entire W-band. For an 80 nm layer the minimum frequency decreases
to 93.2 GHz, which corresponds to a critical temperature of 1.28 K; this value
is still suboptimal for W-band operation. Further increase of the Al film
thickness results in bad performance of the detector. We have thus considered a
Titanium-Aluminum bi-layer (10 nm thick Ti + 25 nm thick Al, already tested in
other laboratories), for which we measured a critical temperature of 820 mK and
a cut-on frequency of 65 GHz: so this solution allows operation in the entire
W-band.Comment: 16th International Workshop on Low Temperature Detectors, Grenoble
20-24 July 2015, Journal of Low Temperature Physics, Accepte
Stable mode-locked pulses from mid-infrared semiconductor lasers
We report the unequivocal demonstration of mid-infrared mode-locked pulses
from a semiconductor laser. The train of short pulses was generated by actively
modulating the current and hence the optical gain in a small section of an
edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at
full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were
characterized using a second-order interferometric autocorrelation technique
based on a nonlinear quantum well infrared photodetector. The mode-locking
dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch
equations in an open two-level system. We anticipate our results to be a
significant step toward a compact, electrically-pumped source generating
ultrashort light pulses in the mid-infrared and terahertz spectral ranges.Comment: 26 pages, 4 figure
Kinetic Inductance Detectors for the OLIMPO experiment: design and pre-flight characterization
We designed, fabricated, and characterized four arrays of horn--coupled,
lumped element kinetic inductance detectors (LEKIDs), optimized to work in the
spectral bands of the balloon-borne OLIMPO experiment. OLIMPO is a 2.6 m
aperture telescope, aimed at spectroscopic measurements of the
Sunyaev-Zel'dovich (SZ) effect. OLIMPO will also validate the LEKID technology
in a representative space environment. The corrected focal plane is filled with
diffraction limited horn-coupled KID arrays, with 19, 37, 23, 41 active pixels
respectively at 150, 250, 350, and 460GHz. Here we report on the full
electrical and optical characterization performed on these detector arrays
before the flight. In a dark laboratory cryostat, we measured the resonator
electrical parameters, such as the quality factors and the electrical
responsivities, at a base temperature of 300mK. The measured average
resonator s are 1.7, 7.0, 1.0, and
1.0 for the 150, 250, 350, and 460GHz arrays, respectively.
The average electrical phase responsivities on resonance are 1.4rad/pW,
1.5rad/pW, 2.1rad/pW, and 2.1rad/pW; the electrical noise
equivalent powers are 45, 160,
80, and 140, at 12 Hz. In the OLIMPO
cryostat, we measured the optical properties, such as the noise equivalent
temperatures (NET) and the spectral responses. The measured NETs are
, , ,
and , at 12 Hz; under 78, 88, 92, and 90 mK
Rayleigh-Jeans blackbody load changes respectively for the 150, 250, 350, and
460 GHz arrays. The spectral responses were characterized with the OLIMPO
differential Fourier transform spectrometer (DFTS) up to THz frequencies, with
a resolution of 1.8 GHz.Comment: Published on JCA
A systematic review and meta-analysis of germline BRCA mutations in pancreatic cancer patients identifies global and racial disparities in access to genetic testing
Background: Germline BRCA1 and BRCA2 mutations (gBRCAm) can inform pancreatic cancer (PC) risk and treatment but most of the available information is derived from white patients. The ethnic and geographic variability of gBRCAm prevalence and of germline BRCA (gBRCA) testing uptake in PC globally is largely unknown. Materials and methods: We carried out a systematic review and prevalence meta-analysis of gBRCA testing and gBRCAm prevalence in PC patients stratified by ethnicity. The main outcome was the distribution of gBRCA testing uptake across diverse populations worldwide. Secondary outcomes included: geographic distribution of gBRCA testing uptake, temporal analysis of gBRCA testing uptake in ethnic groups, and pooled proportion of gBRCAm stratified by ethnicity. The study is listed under PROSPERO registration number #CRD42022311769. Results: A total of 51 studies with 16 621 patients were included. Twelve of the studies (23.5%) enrolled white patients only, 10 Asians only (19.6%), and 29 (56.9%) included mixed populations. The pooled prevalence of white, Asian, African American, and Hispanic patients tested per study was 88.7%, 34.8%, 3.6%, and 5.2%, respectively. The majority of included studies were from high-income countries (HICs) (64; 91.2%). Temporal analysis showed a significant increase only in white and Asians patients tested from 2000 to present (P < 0.001). The pooled prevalence of gBRCAm was: 3.3% in white, 1.7% in Asian, and negligible (<0.3%) in African American and Hispanic patients. Conclusions: Data on gBRCA testing and gBRCAm in PC derive mostly from white patients and from HICs. This limits the interpretation of gBRCAm for treating PC across diverse populations and implies substantial global and racial disparities in access to BRCA testing in PC
A chemically etched corrugated feedhorn array for D-band CMB observations
We present the design, manufacturing, and testing of a 37-element array of corrugated feedhorns for Cosmic Microwave Background CMB) measurements between 140 and 170 GHz. The array was designed to be coupled to Kinetic Inductance Detector arrays, either directly (for total power measurements) or through an orthomode transducer (for polarization measurements). We manufactured the array in platelets by chemically etching aluminum plates of 0.3 mm and 0.4 mm thickness. The process is fast, low-cost, scalable, and yields high-performance antennas compared to other techniques in the same frequency range. Room temperature electromagnetic measurements show excellent repeatability with an average cross polarization level about − 20 dB, return loss about − 25 dB, first sidelobes below − 25 dB and far sidelobes below − 35 dB. Our results qualify this process as a valid candidate for state-of-the-art CMB experiments, where large detector arrays with high sensitivity and polarization purity are of paramount importance in the quest for the discovery of CMB polarization B-modes
The long duration cryogenic system of the OLIMPO balloon--borne experiment: design and in--flight performance
We describe the design and in--flight performance of the cryostat and the
self-contained He refrigerator for the OLIMPO balloon--borne experiment,
a spectrophotometer to measure the Sunyaev-Zel'dovich effect in clusters of
galaxies.
The He refrigerator provides the 0.3 K operation temperature for the
four arrays of kinetic inductance detectors working in 4 bands centered at 150,
250, 350 and 460 GHz. The cryostat provides the 1.65 K base temperature for the
He refrigerator, and cools down the reimaging optics and the filters
chain at about 2 K.
The integrated system was designed for a hold time of about 15 days, to
achieve the sensitivity required by the planned OLIMPO observations, and
successfully operated during the first long-duration stratospheric flight of
OLIMPO in July 2018.
The cryostat features two tanks, one for liquid nitrogen and the other one
for liquid helium. The long hold time has been achieved by means of custom
stiff G10 fiberglass tubes support, which ensures low thermal conductivity and
remarkable structural stiffness; multi--layer superinsulation, and a vapour
cooled shield, all reducing the heat load on the liquid helium tank.
The system was tested in the lab, with more than 15 days of unmanned
operations, and then in the long duration balloon flight in the stratosphere.
In both cases, the detector temperature was below 300 mK, with thermal
stability better than 0.5 mK.
The system also operated successfully in the long duration stratospheric
balloon flight
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