224 research outputs found
Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films
We have studied the possibly half metallic Co2FeSi full Heusler alloy by
means of spin- and time-resolved photoemission spectroscopy. For excitation,
the second and fourth harmonic of femtosecond Ti:sapphire lasers were used,
with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the
dependence of the measured surface spin polarization on the particular
photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon
photoemission (2PPE). The observed differences in the spin polarization can be
explained by a spin-dependent lifetime effect occurring in the 2-photon
absorption process. The difference in escape depth of the two methods in this
context suggests that the observed reduction of spin polarization (compared to
the bulk) cannot be attributed just to the outermost surface layer but takes
place at least 4-6 nm away from the surface.Comment: 7 pages, 3 figures; submitted to Journal of Magnetism and Magnetic
Material
The way that you do it? An elaborate test of procedural invariance of TTO, using a choice-based design
The time tradeoff (TTO) method is often used to derive Quality-Adjusted Life Year health state valuations. An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences. In particular, fixing the duration in the health state to be valued and inferring the duration in full health that renders an individual indifferent, causes valuations to be higher than when the duration in full health is fixed and the duration in the health state to be valued is elicited. This paper presents a new test of procedural invariance for a broad range of time horizons, while using a choice-based design and adjusting for discounting. As one of the known problems with the conventional procedure is the violation of constant proportional tradeoffs (CPTO), we also investigate CPTO for the alternative TTO procedure. Our findings concerning procedural invariance are rather supportive for the TTO procedure. We find no violations of procedural invariance except for the shortest gauge duration. The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure
Eliciting risk preferences that predict risky health behaviour: A comparison of two approaches
Information on attitudes to risk could increase understanding of and explain risky health behaviors. We investigate two approaches to eliciting risk preferences in the health domain, a novel “indirect” lottery elicitation approach with health states as outcomes and a “direct” approach where respondents are asked directly about their willingness to take risks. We compare the ability of the two approaches to predict health-related risky behaviors in a general adult population. We also investigate a potential framing effect in the indirect lottery elicitation approach. We find that risk preferences elicited using the direct approach can better predict health-related risky behavior than those elicited using the indirect approach. Moreover, a seemingly innocuous change to the framing of the lottery question results in significantly different risk preference estimates, and conflicting conclusions about the ability of the indicators to predict risky health behaviors
On the (not so) constant proportional trade-off in TTO
Abstract.
Purpose: The linear and power QALY models require that people in Time Trade-off (TTO) exercises sacrifice the same proportion of lifetime to obtain a health improvement, irrespective of the absolute amount. However, evidence on these constant proportional trade-offs (CPTOs) is mixed, indicating that these versions of the QALY model do not represent preferences. Still, it may be the case that a more general version of the QALY model represents preferences. This version has the property that people want to sacrifice the same proportion of utilities of lifetime for a
health improvement, irrespective of the amount of this lifetime.
Methods: We use a new method to correct TTO scores for utility of life duration and test whether decision makers trade off utility of duration and quality at the same rate irrespective of duration.
Results: We find a robust violation of CPTO for both uncorrected and corrected TTO scores. Remarkably, we find higher values for longer durations, contrary to most previous studies. This represents the only study correcting for utility of life duration to find such a violation.
Conclusions: It seems that the trade-off of life years is indeed not so constantly proportional and, therefore, that health state valuations depend on durations
A direct method for measuring discounting and QALYs more easily and reliably
Time discounting and quality of life are two important factors in evaluations of medical interventions. The measurement of these two factors is complicated because they interact. Existing methods either simply assume one factor given, based on heuristic assumptions, or invoke complicating extraneous factors, such as risk, that generate extra biases. The authors introduce a method for measuring discounting (and then quality of life) that involves no extraneous factors and that avoids distorting interactions. Their method is considerably simpler and more realistic for subjec
On Homomorphic Secret Sharing from polynomial-modulus LWE
Homomorphic secret sharing (HSS) is a form of secret sharing that supports the local evaluation of functions on the shares, with applications to multi-server private information retrieval, secure computation, and more. Insisting on additive reconstruction, all known instantiations of HSS from “Learning with Error (LWE)”-type assumptions either have to rely on LWE with superpolynomial modulus, come with non-negligible error probability, and/or have to perform expensive ciphertext multiplications, resulting in bad concrete efficiency. In this work, we present a new 2-party local share conversion procedure, which allows to locally convert noise encoded shares to non-noise plaintext shares such that the parties can detect whenever a (potential) error occurs and in that case resort to an alternative conversion procedure. Building on this technique, we present the first HSS for branching programs from (Ring-)LWE with polynomial input share size which can make use of the efficient multiplication procedure of Boyle et al. (Eurocrypt 2019) and has no correctness error. Our construction comes at the cost of a – on expectation – slightly increased output share size (which is insignificant compared to the input share size) and a more involved reconstruction procedure. More concretely, we show that in the setting of 2-server private information retrieval we can choose ciphertext sizes of only a quarter of the size of the scheme of Boyle et al. at essentially no extra cost
The effects of lead time and visual aids in TTO valuation: a study of the EQ-VT framework
__Abstract__
__Background__ The effect of lead time in time trade-off
(TTO) valuation is not well understood. The purpose of this
study was to investigate the effects on health-state valuation
of the length of lead time and the way the lead-time
TTO task is displayed visually.
__Methods__ Using two general population samples, we
compared three lead-time TTO variants: 10 years of lead
time in full health preceding 5 years of unhealthy time
(standard); 5 years of lead time preceding 5 years of
unhealthy time (experimental); and 10 years of lead time
and 5 years of unhealthy time, presented with a visual aid
to highlight the point where the lead time ends (experimental).
Participants were randomized to receive one of the
lead-time variants, as administered by a computer software
program.
__Results__ Health-state values generated by TTO valuation
tasks using a longer lead time were slightly lower than
those generated by tasks using a shorter lead time. When
lead time and unhealthy time were presented with visual
aids highlighting the difference between the lead time and
unhealthy time, respondents spent more time considering
health states with a value close to 0.
__Conclusions__ Different lead-time time trade-off variants
should be carefully studied in order to achieve the best
measurement of health-state values using this new method
Using modular 3D digital earth applications based on point clouds for the study of complex sites
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