354 research outputs found
Některé aspekty QCD při nízkých energiích v éře přesných měření
No full textNázev práce: Některé aspekty QCD při nízkých energiích v éře přesných měření Autor: Tomáš Husek Katedra/Ústav: Ústav částicové a jaderné fyziky Vedoucí disertační práce: doc. RNDr. Karol Kampf, Ph.D. Abstrakt: Tato disertační práce se zabývá aspekty QCD při nízkých energiích, které souvisejí s elektromagnetickými rozpady nejlehčích pseudoskalárních me- sonů. Výpočty radiačních korekcí pro rozpady neutrálního pionu (Dalizův rozpad a vzácný rozpad na elektron-pozitronový pár) a nový model pro form faktor el- mag. přechodu pionu jsou diskutovány v článcích, ze kterých tato práce vychází. S tím související efektivní přístupy jako např. chirální poruchová teorie či limita velkého Nc jsou představeny v úvodních kapitolách. Také se zde zabýváme kom- plikacemi, které nastávají při výpočtu radiačních korekcí k Dalitzově rozpadu η(′) mesonů. V práci jsou rovněž představeny detaily spolupráce s experimenty, které začlenily uvedené publikované výpočty radiačních korekcí do svých simu- lací. V neposlední řadě jsou pak ukázány některé techniky výpočtů smyčkových integrálů. Klíčová slova: chirální poruchová teorie, limita velkého Nc, radiační korekce, form faktor elmag. přechodu pionu 1Title: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor 1Ústav částicové a jaderné fyzikyInstitute of Particle and Nuclear PhysicsFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Some aspects of low-energy QCD at the precision frontier
No full textTitle: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor
Using item response theory to explore the psychometric properties of extended matching questions examination in undergraduate medical education
No full textBACKGROUND:
As assessment has been shown to direct learning, it is critical that the examinations developed to test clinical competence in medical undergraduates are valid and reliable. The use of extended matching questions (EMQ) has been advocated to overcome some of the criticisms of using multiple-choice questions to test factual and applied knowledge.
METHODS:
We analysed the results from the Extended Matching Questions Examination taken by 4th year undergraduate medical students in the academic year 2001 to 2002. Rasch analysis was used to examine whether the set of questions used in the examination mapped on to a unidimensional scale, the degree of difficulty of questions within and between the various medical and surgical specialties and the pattern of responses within individual questions to assess the impact of the distractor options.
RESULTS:
Analysis of a subset of items and of the full examination demonstrated internal construct validity and the absence of bias on the majority of questions. Three main patterns of response selection were identified.
CONCLUSION:
Modern psychometric methods based upon the work of Rasch provide a useful approach to the calibration and analysis of EMQ undergraduate medical assessments. The approach allows for a formal test of the unidimensionality of the questions and thus the validity of the summed score. Given the metric calibration which follows fit to the model, it also allows for the establishment of items banks to facilitate continuity and equity in exam standards
Bi(2223)/Ag tapes made by the Tape-In-Rectangular-Tube (TIRT) Process
No full textMulti-core tape composites with various filament configurations have been made by a tape-in-rectangular tube (TIRT) process. This TIRT process is based on the deformation of multifilamentary composites assembled from a rectangular Ag (Ag-alloy) tube filled by pre-deformed single-core BSCCO/Ag tapes. Two-axial rolling induces texture in the filaments in two rolling planes, with the filament planes oriented parallel or perpendicular to the tape width, thus reducing the high I, anisotropy which can degrade the total current in coils working at high temperatures (77 K). The homogeneity of the filaments was studied by a magneto-optical technique. Roll-sintered samples were measured at 77 K in an external magnetic field up to 1 T and at constant fields (0.1 T and 0.5 T) at various orientations (between parallel and perpendicular) to the tape surface. The results demonstrate the possibility of using these tapes for selected parts of a coil winding to reduce the apparent effect of the radial field component on the reduction of the total coil current
Correlated or Uncorrelated Measures of Related or Unrelated Constructs
No full text Factor analysis is often used as an item analysis technique. In many cases orthogonal rotations are performed in an attempt to obtain uncorrelated factors, however, the estimates of the unrelated factors can be highly related. This issue is discussed and an example using data on the Semantic Differential is presented. </jats:p
A study of coupling loss on bi-columnar BSCCO/Ag tapes through ac susceptibility measurements
No full textCoupling losses were studied in composite tapes containing superconducting material in the form of two separate stacks of densely packed filaments embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry is quite favourable for studying the coupling currents and, in particular, the role of superconducting bridges between filaments. By using the ac susceptibility technique, the electromagnetic losses as a function of ac magnetic field amplitude and frequency were measured at the temperature T = 77 K for two tapes with different matrix composition. The length of the tapes was varied by subsequent cutting in order to investigate its influence on the dynamics of magnetic flux penetration. The geometrical factor χ0 which takes into account the demagnetizing effects was established from ac susceptibility data at low amplitudes. Losses versus frequency dependencies have been found to agree nicely with the theoretical model developed for round multifilamentary wires. Applying this model, the effective resistivity of the matrix was determined for each tape by using only measured quantities. For the tape with a pure silver matrix its value was found to be larger than that predicted by the theory for given metal resistivity and filamentary architecture. In contrast, in the tape with a Ag/Mg alloy matrix, an effective resistivity much lower than expected was determined. We explain these discrepancies by taking into account the quality of the interface between the superconducting filaments and the normal matrix. In the case of a soft matrix of pure Ag, this is of poor quality, while the properties of the alloy matrix seem to provoke the extensive creation of intergrowths which can be actually observed in these kind of tapes
The relative importance of labels and behavior descriptions in determining attitudes toward labeled behavior
No full textA measurement of the K + → π + μ + μ− decay
No full textA sample of 2.8 × 104K+ → π+μ+μ− candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction is measured to be (9.15 ± 0.08) × 10−8, a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at O(p6). © 2022, The Author(s)
Measurement of the very rare K+→π+νν- decay
No full textThe NA62 experiment reports the branching ratio measurement BR(K+→π+νν¯)=(10.6−3.4+4.0|stat±0.9syst)×10−11 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016–2018. This provides evidence for the very rare K+→π+νν¯ decay, observed with a significance of 3.4σ. The experiment achieves a single event sensitivity of (0.839 ± 0.054) × 10−11, corresponding to 10.0 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. This measurement is also used to set limits on BR(K+→ π+X), where X is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample. © 2021, The Author(s)
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