2,484 research outputs found
An Algorithm for Projecting a Reference Direction onto the Nondominated Set of Given Points
In this paper, we consider the problem of searching nondominated alternatives in a discrete multiple criteria problem. The search procedure is based on the use of a reference direction. A reference direction reflects the desire of the decision maker (DM) to specify a search direction. To find a set of given alternatives related somehow to the reference direction specified by the DM, the reference direction has to be projected onto the set of nondominated alternatives. Our purpose is to develop an efficient algorithm for making this projection. The projection of each given reference direction determines a nondominated ordered subset. The set is provided to a decision maker for evaluation. The decision maker will choose the most preferred alternative from this subset and continues the search from this alternative with a new reference direction. The search will end when no direction of of improvement is found. A critical point in the procedure is the efficiency of the projection operation. This efficiency of our algorithm is considered theoretically and numerically.
The projection is made by parametrizing an achievement scalarizing function originally proposed by Wierzbicki (1980) to project any single point onto the nondominated set
Ternary nucleation of H_2SO_4, NH_3 and H_2O
A classical theory of the ternary homogeneous nucleation of sulfuric acid—ammonia—water is presented. For NH3 mixing ratios exceeding 1 ppt, the presence of ammonia enhances the binary (sulfuric acid—water) nucleation rate by several orders of magnitude. However, the limiting component for ternary nucleation—as for binary nucleation—is sulfuric acid. The sulfuric acid concentration needed for significant ternary nucleation is several orders of magnitude below that required in binary case
Value Efficiency Analysis of Academic Research [Updated 19 August 1998]
We propose a systematic approach to analyzing academic research performance at universities and research institutes. The analysis of research performance based on a set of (abstract) criteria which are relevant from the decision maker's point of view. The scales for these criteria are defined by means of concrete indicators. All indicators, are, however, not necessarily quantitative. Qualitative information is quantified using appropriate analytical tools. Once the criteria and indicators have been agreed upon and quantified, data on the research units is collected and a Value Efficiency Analysis is performed. The efficiency of research units is defined in the spirit of Data Envelopment Analysis (DEA), complemented with a decision makers (Rector in the European university system) preference information. This information is obtained by asking the decision maker to locate a point on the efficient frontier having the most preferred input and output values. Our approach and the accompanying Decision Support System enables a university to allocate resources more efficiently for its research units. Using data from the Helsinki School of Economics, we describe how our approach can be used
Stellar activity as noise in exoplanet detection I. Methods and application to solar-like stars and activity cycles
The detection of exoplanets using any method is prone to confusion due to the
intrinsic variability of the host star. We investigate the effect of cool
starspots on the detectability of the exoplanets around solar-like stars using
the radial velocity method. For investigating this activity-caused "jitter" we
calculate synthetic spectra using radiative transfer, known stellar atomic and
molecular lines, different surface spot configurations, and an added planetary
signal. Here, the methods are described in detail, tested and compared to
previously published studies. The methods are also applied to investigate the
activity jitter in old and young solar-like stars, and over a solar-like
activity cycles. We find that the mean full jitter amplitude obtained from the
spot surfaces mimicking the solar activity varies during the cycle
approximately between 1 m/s and 9 m/s. With a realistic observing frequency a
Neptune mass planet on a one year orbit can be reliably recovered. On the other
hand, the recovery of an Earth mass planet on a similar orbit is not feasible
with high significance. The methods developed in this study have a great
potential for doing statistical studies of planet detectability, and also for
investigating the effect of stellar activity on recovered planetary parameters.Comment: Accepted to MNRA
Measuring differential rotation of the K-giant \,And
We investigate the temporal spot evolution of the K-giant component in the RS
CVn-type binary system \,Andromedae to establish its surface
differential rotation. Doppler imaging is used to study three slightly
overlapping spectroscopic datasets, obtained independently at three different
observing sites. Each dataset covers one full stellar rotation with good phase
coverage, and in total, results in a continuous coverage of almost three
stellar rotations (17.8\,d). Therefore, these data are well
suited for reconstructing surface temperature maps and studying temporal
evolution in spot configurations. Surface differential rotation is measured by
the means of cross-correlation of all the possible image pairs. The individual
Doppler reconstructions well agree in the revealed spot pattern, recovering
numerous low latitude spots with temperature contrasts of up to
1000\,K with respect to the unspotted photosphere, and also an
asymmetric polar cap which is diminishing with time. Our detailed
cross-correlation study consistently indicate solar-type differential rotation
with an average surface shear , in agreement with former
results.Comment: accepted for publication in A&A, 4 pages, 3 figure
FK Comae Berenices, King of Spin: The COCOA-PUFS Project
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single
star is thought to be a recent binary merger, and is exceptionally active by
measure of its intense ultraviolet and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV
(120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph,
but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray
Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy
Transmission Grating Spectrometer; together with supporting photometry and
spectropolarimetry in the visible from the ground. This is an introductory
report on the project.
FK Com displayed variability on a wide range of time scales, over all
wavelengths, during the week-long main campaign, including a large X-ray flare;
"super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV
139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm
(10,000-30,000 K); large Doppler swings suggestive of bright regions
alternately on advancing and retreating limbs of the star; and substantial
redshifts of the epoch-average emission profiles. These behaviors paint a
picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around
the star, threaded by cooler structures perhaps analogous to solar prominences,
and replenished continually by surface activity and flares. Suppression of
angular momentum loss by the confining magnetosphere could temporarily postpone
the inevitable stellar spindown, thereby lengthening this highly volatile stage
of coronal evolution.Comment: to be published in ApJ
Value Efficiency Analysis for Incorporating Preference Information in Data Envelopment Analysis
We develop a procedure and the requisite theory for incorporating preference information in a novel way in the efficiency analysis of Decision Making Units. The efficiency of Decision Making Units is defined in the spirit of Data Envelopment Analysis (DEA), complemented with Decision Maker's preference information concerning the desirable structure of inputs and outputs. Our procedure begins by aiding the Decision Maker in searching for the most preferred combination of inputs and outputs of Decision Making Units (for short, Most Preferred Solution) which are efficient in DEA. Then, assuming that the Decision Maker's Most Preferred Solution maximizes his/her underlying (unknown) value function at the moment when the search is terminated, we approximate the indifference contour of the value function at this point with its possible tangent hyperplanes. Value Efficiency scores are then calculated for each Decision Making Unit comparing the inefficient units to units having the same value as the Most Preferred Solution. The resulting Value Efficiency scores are optimistic approximations of the true scores. The procedure and the resulting efficiency scores are immediately applicable to solving practical problems
Depth-wise progression of osteoarthritis in human articular cartilage: investigation of composition, structure and biomechanics
SummaryObjectiveOsteoarthritis (OA) is characterized by the changes in structure and composition of articular cartilage. However, it is not fully known, what is the depth-wise change in two major components of the cartilage solid matrix, i.e., collagen and proteoglycans (PGs), during OA progression. Further, it is unknown how the depth-wise changes affect local tissue strains during compression. Our aim was to address these issues.MethodsData from the previous microscopic and biochemical measurements of the collagen content, distribution and orientation, PG content and distribution, water content and histological grade of normal and degenerated human patellar articular cartilage (n=73) were reanalyzed in a depth-wise manner. Using this information, a composition-based finite element (FE) model was used to estimate tissue function solely based on its composition and structure.ResultsThe orientation angle of collagen fibrils in the superficial zone of cartilage was significantly less parallel to the surface (P<0.05) in samples with early degeneration than in healthy samples. Similarly, PG content was reduced in the superficial zone in early OA (P<0.05). However, collagen content decreased significantly only at the advanced stage of OA (P<0.05). The composition-based FE model showed that under a constant stress, local tissue strains increased as OA progressed.ConclusionFor the first time, depth-wise point-by-point statistical comparisons of structure and composition of human articular cartilage were conducted. The present results indicated that early OA is primarily characterized by the changes in collagen orientation and PG content in the superficial zone, while collagen content does not change until OA has progressed to its late stage. Our simulation results suggest that impact loads in OA joint could create a risk for tissue failure and cell death
Investigating magnetic activity in very stable stellar magnetic fields: long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Peg
The ultrafast-rotating () fully convective
single M4 dwarf V374 Peg is a well-known laboratory for studying intense
stellar activity in a stable magnetic topology. As an observable proxy for the
stellar magnetic field, we study the stability of the light curve, and thus the
spot configuration. We also measure the occurrence rate of flares and coronal
mass ejections (CMEs). We analyse spectroscopic observations,
photometry covering 5 years, and additional photometry that expands the
temporal base over 16 years. The light curve suggests an almost rigid-body
rotation, and a spot configuration that is stable over about 16 years,
confirming the previous indications of a very stable magnetic field. We
observed small changes on a nightly timescale, and frequent flaring, including
a possible sympathetic flare. The strongest flares seem to be more concentrated
around the phase where the light curve indicates a smaller active region.
Spectral data suggest a complex CME with falling-back and re-ejected material,
with a maximal projected velocity of 675km/s. We observed a CME rate
much lower than expected from extrapolations of the solar flare-CME relation to
active stars.Comment: 15 figures, 4 tables, accepted for publication in A&
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