3,165 research outputs found
Releasing multiply-imputed synthetic data generated in two stages to protect confidentiality
"To protect the cofidentiality of survey respondents' identities and sensitive attributes, statistical agencies can release data in which cofidential values are replaced with multiple imputations. These are called synthetic data. We propose a two-stage approach to generating synthetic data that enables agencies to release different numbers of imputations for different variables. Generation in two stages can reduce computational burdens, decrease disclosure risk, and increase inferential accuracy relative to generation in one stage. We present methods for obtaining inferences from such data. We describe the application of two stage synthesis to creating a public use file for a German business database." (Author's abstract, IAB-Doku) ((en))IAB-Betriebspanel, Datenaufbereitung, Datenanonymisierung, Datenschutz, angewandte Statistik, statistische Methode, Arbeitsmarktforschung, Imputationsverfahren
Theoretical de Haas-van Alphen Data and Plasma Frequencies of MgB2 and TaB2
The de Haas-van Alphen-frequencies as well as the effective masses for a
magnetic field parallel to the crystallographic c-axis are calculated within
the local spin density approximation (LSDA) for MgB2 and TaB2. In addition, we
analyze the plasma frequencies computed for each Fermi surface sheet. We find a
large anisotropy of Fermi velocities in MgB2 in difference to the nearly
isotropic behavior in TaB2. We compare calculations performed within the
relativistic non-full potential augmented-spherical-wave (ASW) scheme and the
scalar-relativistic full potential local orbital (FPLO) scheme. A significant
dependence for small cross sections on the bandstructure method is found. The
comparison with the first available experimental de Haas-van Alphen-data by
Yelland et al. (Ref. 19) shows deviations from the electronic structure
calculated within both L(S)DA approaches although the cross section predicted
by FPLO are closer to the experimental data. The elucidation of the relevant
many-body effects beyond the standard LDA is considered as a possible key
problem to understand the superconductivity in MgB2.Comment: Typos corrected, 3references added. Extended and corrected version of
S. Elgazzar et al., Solid State Comm. v. 121, 99 (2002). 7pages, 4figures,
AIP Conference Proc. "Correlated Electron Systems and High-Tc
Superconductors" (ed. F. Mancini) (October 2001, Salerno, Italy
Releasing multiply-imputed synthetic data generated in two stages to protect confidentiality
Eine Methode, um die Vertraulichkeit von Daten, die in statistischen Ämtern erhobenen werden, zu gewährleisten, ist das Ersetzen vertraulicher Werte durch synthetische Daten, die mittels multipler Imputation generiert werden. Es wird ein zweistufiges Verfahren zur Generierung der synthetischen Daten vorgestellt, das eine unterschiedliche Anzahl von Imputationen für unterschiedliche Variablen ermöglicht. Die Vorteile eines zweistufigen Verfahren liegen in der Reduzierung der Laufzeit bei der Berechnung, in der Verringerung des Risikos der Deanonymisierung, und in der Erhöhung der inferentiellen Genauigkeit. Es wird beschrieben, wie das zweistufige Verfahren bei der Generierung eines Public-Use-Files des IAB-Betriebpanels zur Anwendung kommt. (IAB)"To protect the cofidentiality of survey respondents' identities and sensitive attributes, statistical agencies can release data in which cofidential values are replaced with multiple imputations. These are called synthetic data. We propose a two-stage approach to generating synthetic data that enables agencies to release different numbers of imputations for different variables. Generation in two stages can reduce computational burdens, decrease disclosure risk, and increase inferential accuracy relative to generation in one stage. We present methods for obtaining inferences from such data. We describe the application of two stage synthesis to creating a public use file for a German business database." (author's abstract
Comment on ``Superconducting PrBa_2Cu_3O_x''
Recently, Zou et al. (Phys. Rev. Lett. 80, 1074, 1998) reported the
observation of bulk superconductivity (SC) for a PrBa_2Cu_3O_x (Pr123) single
crystal grown by the traveling-solvent floating zone (TSFZ) method. The aim of
this Comment is to show the inconsistency of the value of effective magnetic
moment \mu_{eff} reported by Zou et al. (2.92\mu_B) with their magnetic
susceptibility data. The estimation made directly from their data points gives
a considerably smaller value of \mu_{eff}=2.09\mu_B. At the same time the
values of mu_{eff}=2.9\mu_B and 3.1\mu_B were obtained for our Pr123 single
crystals grown by flux method for H||ab-plane and H||c-axis, respectively. This
suggests that Pr occupies only about a half of the RE sites in TSFZ crystal.
The other half of the RE sites is occupied most probably by the nonmagnetic Ba.
Noteworthy, SC with T_c=43 K was observed earlier for
Pr_{0.5}Ca_{0.5}Ba_2Cu_3O_{7-y} thin films. Ba^{2+} has a larger ionic radius
than Pr^{3+} and so the substitution of Ba for Pr could give a natural
explanation not only for the SC in TSFZ Pr123 but also for the elongation of
the distance between the CuO_2 planes observed by Zou et al.Comment: Slightly extended version of Comment accepted to Phys. Rev. Lett.
(v.81, N24, 1998), tentatevely to be publ. 14Dec98. 1 page, REVTex; 1 EPS fi
Decision-making on an explicit risk-taking task in preadolescents with attention-deficit/hyperactivity disorder
Summary.: Inappropriate risk-taking and disadvantageous decision-making have been described as major behavioural characteristics of patients with attention-deficit/hyperactivity disorder (ADHD). However these behaviours are difficult to measure in laboratory contexts and recent studies have yielded inconsistent results which might be related to task characteristics. The present study adopted the Game of Dice Task, a test procedure in which risks are made explicit and the load on working memory is minimal. As a result, preadolescents with ADHD (N = 23) made significantly more risky choices and suffered major losses of money compared to normal controls (N = 24) but only when they played the game a second time. Differences in risk-taking correlated significantly with hyperactivity as rated by parents and with inhibitory control, but not with working memory performance. The results are discussed in the context of current theories of ADH
Renormalization of the BCS-BEC crossover by order parameter fluctuations
We use the functional renormalization group approach with partial
bosonization in the particle-particle channel to study the effect of order
parameter fluctuations on the BCS-BEC crossover of superfluid fermions in three
dimensions. Our approach is based on a new truncation of the vertex expansion
where the renormalization group flow of bosonic two-point functions is closed
by means of Dyson-Schwinger equations and the superfluid order parameter is
related to the single particle gap via a Ward identity. We explicitly calculate
the chemical potential, the single-particle gap, and the superfluid order
parameter at the unitary point and compare our results with experiments and
previous calculations.Comment: 5 pages, 3 figure
Influence of the van Hove singularity on the specific heat jump in BCS superconductors
Within the weak-coupling BCS scheme we derive a general form of the
coefficients in the Ginzburg-Landau expansion of the free energy of a
superconductor for the case of a Fermi level close to a van Hove singularity
(VHS). A simple expression for the influence of the VHS on the specific heat
jump is then obtained for the case where gaps for different bands are distinct
but nearly constant at the corresponding sheets of the Fermi surface.Comment: 8 pages, 2 figures, LaTeX2
Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C in the normal and superconducting state
Point-contact (PC) spectroscopy measurements on antiferromagnetic (AF)
(T_N=5.2K) HoNi2B2C single crystals in the normal and two different
superconducting (SC) states (T_c=8.5K and T_c^*=5.6K<T_c, with 2\Delta/kT_c^*=3.9. The strong coupling
Eliashberg analysis of the low-temperature SC phase with T_c^*=5.6K =T_N,
coexisting with the commensurate AF structure, suggests a sizable value of the
EPI constant \lambda_s=0.93. We also provide strong support for the recently
proposed by us ''Fermi surface (FS) separation'' scenario for the coexistence
of magnetism and superconductivity in magnetic borocarbides, namely, that the
superconductivity in the commensurate AF phase survives at a special (nearly
isotropic) FS sheet without an admixture of Ho 5d states. Above T_c^* the SC
features in the PC characteristics are strongly suppressed pointing to a
specific weakened SC state between T_c* and T_c.Comment: 11 pages, 8 figs, to be published in PRB, Vol.75, Iss.2
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