Sensor Noise in LISA Pathfinder: In-Flight Performance of the Optical Test Mass Readout

We report on the first subpicometer interferometer flown in space. It was part of ESA's Laser Interferometer Space Antenna (LISA) Pathfinder mission and performed the fundamental measurement of the positional and angular motion of two free-falling test masses. The interferometer worked immediately, stably, and reliably from switch on until the end of the mission with exceptionally low residual noise of 32.0_{-1.7}^{+2.4}  fm/sqrt[Hz], significantly better than required. We present an upper limit for the sensor performance at millihertz frequencies and a model for the measured sensitivity above 200 mHz.

Analysis of the accuracy of actuation electronics in the laser interferometer space antenna pathfinder

The Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled Δg, is the differential force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational forces has been compensated. At low frequencies, the differential force is compensated by an applied electrostatic actuation force, which then must be subtracted from the measured acceleration to obtain Δg. Any inaccuracy in the actuation force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality actuation voltages and, consequently, the resulting actuation forces. The simulator is applied during post-processing the LPF data.

LISA Pathfinder Performance Confirmed in an Open-Loop Configuration: Results from the Free-Fall Actuation Mode

We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control force needed to compensate the quasistatic differential force acting on two test masses is applied intermittently as a series of "impulse" forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the actuation force, thus eliminating associated noise and force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger actuation forces also shows that the technique can be used to eliminate actuation noise when this is a dominant factor.

SEIS: Insight's Seismic Experiment for Internal Structure of Mars

By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of ∼ 2500 at 1 Hz and ∼ 200 000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of M w ∼ 3 at 40 ∘ epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users.

Beyond the Required LISA Free-Fall Performance: New LISA Pathfinder Results down to 20 μHz

In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 20  μHz. The Letter presents the measured differential acceleration noise figure, which is at (1.74±0.05)  fm s^{-2}/sqrt[Hz] above 2 mHz and (6±1)×10  fm s^{-2}/sqrt[Hz] at 20  μHz, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency.

Charge-Induced Force Noise on Free-Falling Test Masses: Results from LISA Pathfinder

We report on electrostatic measurements made on board the European Space Agency mission LISA Pathfinder. Detailed measurements of the charge-induced electrostatic forces exerted on free-falling test masses (TMs) inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.0  fm s^{-2} Hz^{-1/2} across the 0.1-100 mHz frequency band that is crucial to an observatory such as the Laser Interferometer Space Antenna (LISA). Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge buildup due to interplanetary cosmic rays and the TM charge-to-force coupling through stray electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument.

Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2±0.1  fm s^{-2}/sqrt[Hz], or (0.54±0.01)×10^{-15}  g/sqrt[Hz], with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8±0.3)  fm/sqrt[Hz], about 2 orders of magnitude better than requirements. At f≤0.5  mHz we observe a low-frequency tail that stays below 12  fm s^{-2}/sqrt[Hz] down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.

[Cost comparison of two combination therapies with peginterferon alfa and ribavarin for the treatment of hepatitis C]

The two approved combination therapies for the treatment of hepatitis C in Switzerland (Pegasys/Copegus, PAC; PegIntron/Rebetol, PIR) are very similar in terms of efficacy and safety. This study aims at comparing the cost of the two therapies and determining the cost-efficient treatment algorithm. Average cost amounts to CHF 21700.-(PAC) and CHF 19700.- (PIR) for patients with genotype 1 and to CHF 15600.- (PAC) and CHF 15000.- (PIR) for patients with genotype 2/3, respectively. The consistent use of PIR is 9 to 12% cheaper than PAC. Further cost savings of 3% are possible if patients with a bodyweight below 85 kg (genotype 1) or below 75 kg (genotype 2/3) are treated with PIR while patients with a bodyweight over 85 kg (genotype 1) or over 75 kg (genotype 2/3) are treated with PAC.

Reply to: Econometric issues in testing the age neutrality of health care expenditure

Salas and Raftery allege that in our paper, (1) remaining life expectancy is an endogenous explanatory variable of health care expenditure and (2) the parameter designed to correct for sample selection bias in fact represents a hidden relationship between health care expenditure and age. We argue that claim (1) is not supported by the available empirical evidence, while claim (2) seems to derive from a too cursory reading of our paper.

Criteria for the future division of labor between private and social health insurance

This article's point of departure is that the individual has to manage three stochastic assets, namely health, wealth, and wisdom (skills), which tend to be positively correlated. It shows that the unexpected components of insurance payments should be negatively correlated for minimizing total asset volatility. The empirical finding is that in the United States, Japan, and Germany, the lines of social insurance contribute less to diversification than do those of private insurance. The article concludes with suggestions for new, umbrella-type insurance contracts that in the future should help individuals in the efficient management of their assets.

Modeling cross-border care in the EU using a principal-agent framework

Cross-border care is likely to become a major issue among EU countries because patients have the option of obtaining treatment abroad under Community Regulations 1408/71. This paper develops a model formalizing both the patient's decision to apply for cross-border care and the authorizing physician's decision to admit a patient to the program. The patient is assumed to maximize expected utility, which depends on the quality of care and the length of waiting in the home country and the host country, respectively. Not all patients qualifying for the EU program present themselves to the authorizing physician because of the transaction cost involved. The physician in her turn shapes effective demand for authorization through her rate of refusal, which constitutes information to potential applicants about the probability of obtaining treatment abroad. The authorizing physician thus acts as an agent serving two principals, her patient and her national government, trading off the perceived utility loss of patients who are rejected against her commitment to domestic health policy. The model may be used to explain existing patient flows between EU countries.

Cream-skimming in deregulated social health insurance: evidence from Switzerland

Policymakers fear that health insurers when exposed to competition will engage in cream-skimming (i.e. selection of good risks) rather than trying to improve their benefit to premium ratio. This fear surfaced also when Swiss federal government proposed pro-competitive Law on social health insurance, which barely passed a popular referendum in 1994. While a risk equalization mechanism based on age, gender, and place of residence has already been created, there is a considerable interest in improving its formula. This paper shows that a dummy variable indicating an individual's death during the period of observation causes the coefficient of determination to jump from 0.039 to 0.111. More-over, simulations of the risk selection process suggest that risk equalization should be made a permanent institution rather than being limited to a life of 10 years as prescribed by present legislation. In fact, the formula in use, with all its shortcomings, can be shown to neutralize to a great extent insurer interest in cream skimming provided he takes a longer-run view.

The demand for health: an empirical test of the Grossman model using panel data

Grossman derives the demand for health from an optimal control model in which health capital is both a consumption and an investment good. In his approach, the individual chooses his level of health and therefore his life span. Initially an individual is endowed with a certain amount of health capital, which depreciates over time but can be replenished by investments like medical care, diet, exercise, etc. Therefore, the level of health is not treated as exogenous but depends on the amount of resources the individual allocates to the production of health. The production of health capital also depends on variables which modify the efficiency of the production process, therefore changing the shadow price of health capital. For example, more highly educated people are expected to be more efficient producers of health who thus face a lower price of health capital, an effect that should increase their quantity of health demanded. While the Grossman model provides a suitable theoretical framework for explaining the demand for health and the demand for medical services, it has not been too successful empirically. However, empirical tests up to this date have been exclusively based on cross section data, thus failing to take the dynamic nature of the Grossman model into account. By way of contrast, the present paper contains individual time series information not only on the utilization of medical services but also on income, wealth, work, and life style. The data come from two surveys carried out in 1981 and 1993 among members of a Swiss sick fund, with the linkage between the two waves provided by insurance records. In all, this comparatively rich data set holds the promise of permitting the Grossman model to be adequately tested for the first time.

Ageing of population and health care expenditure: a red herring?

This paper studies the relationship between health care expenditure (HCE) and age, using longitudinal rather than cross-sectional data. The econometric analysis of HCE in the last eight quarters of life of individuals who died during the period 1983-1992 indicates that HCE depends on remaining lifetime but not on calendar age, at least beyond 65+. The positive relationship between age and HCE observed in cross-sectional data may be caused by the simple fact that at age 80, for example, there are many more individuals living in their last 2 years than at age 65. The limited impact of age on HCE suggests that population ageing may contribute much less to future growth of the health care sector than claimed by most observers.

Managed care in Germany and Switzerland. Two approaches to a common problem

The point of departure for this contribution is a problem common to all Western healthcare systems, namely the deficiency of their basic building block, the physician-patient relationship. This deficiency opens up a market for complementary agents in healthcare, ranging from medical associations to the central government. While Germany has traditionally put the emphasis on medical associations as the dominant complementary agent (DCA), it is shifting towards the central government. Switzerland, on the other hand, traditionally has relied on the cantonal governments and is now moving towards competing (quasi-) private health insurers that would function as DCAs. Thus, managed care, which is a means through which to reshape the physician-patient relationship, is used quite differently in the 2 countries, with differing expected outcomes and different consequences for the pharmaceutical industry.

Agency relationships in psychotherapy: an economic analysis

This paper takes the economist's point of view for explaining why psychotherapy seems to be a particularly difficult discipline and what could be done about it. Whereas the so-called agency relationship (i.e. a specialized agent acting on behalf of an uninformed client) can be counted upon to resolve some of the problems in somatic care, it risks to fail in psychic care because the client frequently expresses inconsistent preferences. For this reason, family members and general practitioners may serve as comparatively good agents in ambulatory care, while in the inpatient segment of psychotherapy, patient-oriented objectives tend to be thwarted. An important condition for agency relationships to perform well, however, is that the client carry a sufficient 'price tag', implying that his treatment contributes to the economic objectives of the agent in charge. The conclusion is that choice of agency relationships, even if resulting in seemingly wasteful parallel treatment, gives rise to competition between agents for patients and thus may serve as one of the best safeguards of patients' interests in psychotherapy.

Bonus systems in health insurance: a microeconomic analysis

Faced with the cost explosion in the health care sector, policy-makers in most industrialized countries have been focusing on cost-sharing in health insurance as a possible solution. This is a sanction meted out to users of medical care; the alternative of creating positive incentives for non-users has not yet received nearly as much attention. This paper reports on the experiences made by German private health insurers with their plans offering rebates as well as experience-rated bonuses for no claims. It is argued that a rebate offer may be at least as attractive as conventional cost-sharing plans from the point of view of the consumer since these new options allow him to choose the time at which he is to bear the financial consequences of an illness. In the second part of the paper, predictions are derived concerning the incentives contained in the policies written by three particular insurers. Clear evidence of a decrease in demand for ambulatory medical care at the lower end of the billings distribution is found in rebate and bonus plans. The concluding section of the paper contains a discussion of the results with a view on the continuing debate about the reform of social health insurance.

Technology in ambulatory medical care: cost increasing or cost saving?

Health insurers fear that increased use of medical technology in ambulatory care results in increased billings per physician. This view may overlook certain subtle links between available, appropriated technology in ambulatory practice and the propensity to hospitalize a marginal patient. In this paper, the impacts of technology on four components of total per physician treatment cost were analyzed statistically using 1976-1978 percentage changes for a sample of more than 700 Swiss physicians: number of cases treated, per case billings for ambulatory care, rate of hospitalization and cost of a hospital stay relative to ambulatory care. On net, a 10% reduction in use of laboratory work and X-ray procedures was estimated to result in about 2 and 0.4% savings, respectively. A similar reduction of direct drug sales to patients would increase total cost by 0.3%. From the vantage point of society, even the modest savings indicated probably disappear as soon as the full social cost of a hospital stay is taken into account.

[The cost-insurance-spiral in health care]

The working hypothesis is that a cost-insurance spiral is operating in the Swiss health care system. It consists of three causal links. First, insurance coverage is one of the factors influencing the probability with which an individual sees a physician for a given condition. With improved coverage, demand for initial contacts will rise, inducing changes in ambulatory cost per case treated as well as in the propensity of hospitalization. Due to this second relationship, members of the sick funds find themselves exposed to an increased financial risk. Therefore, they tend to adjust coverage accordingly. With this third link, a feedback is established, and the cost-insurance spiral is ready to go into another round. The questions of whether such a spiral exists, the speed with which it turns, and how it could be slowed down are at the core of an investigation that will be completed in 1982. Members of a major sick fund have already been sampled in order to supplement insurance records with socioeconomic data.