306 research outputs found
Electronic properties of EuB6 in the ferromagnetic regime: Half-metal versus semiconductor
To understand the halfmetallic ferromagnet EuB6 we use the Kondo lattice
model for valence and conduction band. By means of a recently developed
many-body theory we calculate the electronic properties in the ferromagnetic
regime up to the Curie temperature. The decreasing magnetic order induces a
transition from halfmetallic to semiconducting behavior along with a band
broadening. We show the temperature dependence of the quasiparticle density of
states and the quasiparticle dispersion as well as the effective mass, the
number of carriers and the plasma frequency which are in good agreement with
the experimental data
Two-band ferromagnetic Kondo-lattice model for local-moment half-metals
We introduce a two-band Kondo-lattice model to describe ferromagnetic
half-metals with local magnetic moments. In a model study, the electronic and
magnetic properties are presented by temperature dependent magnetization
curves, band-structures, spin polarizations and plasma frequencies. These are
obtained from numerically evaluated equations, based on the single-electron
Green functions. We show that the mutual influence between the itinerant
electrons and the local magnetic moments is responsible for several phase
transitions of the half-metals, namely first and second order magnetic phase
transitions, as well as half-metal to semiconductor and half-metal to semimetal
transitions.Comment: 10 pages, 5 figures, submitted to Journal of Physics: Condensed
Matte
Vanadium centers in ZnTe crystals. II. Electron paramagnetic resonance
Four V-related electron-paramagnetic-resonance (EPR) spectra are observed in Bridgman-grown ZnTe doped with vanadium. Two of them are attributed to the charge states VZn3+(A+) and VZn2+(A0) of the isolated V impurity. For the ionized donor, VZn3+(A+), the spectrum reveals the typical behavior of the expected 3A2(F) ground state in tetrahedral symmetry. The incorporation on a cation lattice site could be proved by the resolved superhyperfine interaction with four Te ions. The second spectrum showing triclinic symmetry and S=3/2 is interpreted as the neutral donor state VZn2+(A0). The origin of the triclinic distortion of the cubic (Td) crystal field could be a static Jahn-Teller effect. The two additionally observed EPR spectra are attributed to nearest-neighbor V-related defect pairs. The spectrum of the first one, V2+Zn-YTe, shows trigonal symmetry and can be explained by the S=3/2 manifold of an orbital singlet ground state. An associated defect "YTe" is responsible for the trigonal distortion of the tetrahedral crystal field of V2+Zn. The spectrum of the second pair defect also shows trigonal symmetry and can be described by S=1/2. The ground-state manifold implies a VZn3+âXTe pair as the most probable origin of this spectrum. The S=1/2 ground state is produced by a dominating isotropic exchange interaction coupling the S=1 ground-state manifold of V3+Zn to an assumed S=1/2 ground state of "XTe" in antiferromagnetic orientation. The nature of the associated defects "YTe" and "XTe" remains unknown for both pairs since no hyperfine structure has been observed, but most probably acceptorlike defects are involved
Vanadium centers in ZnTe crystals. I. Optical properties
In ZnTe:V bulk crystals with nominal vanadium concentrations between 1000 and 7000 ppm three vanadium-ion states V+, V2+, and V3+ were found in low-temperature optical measurements. No-phonon lines of the internal emissions were detected for the 5E(D)â5T2(D) transition of V+(d4) at 3401 cmâ1 (0.422 eV), for 4T2(F)â4T1(F) of V2+(d3) at 4056 cmâ1 (0.503 eV), and for 3T2(F)â3A2(F) of V3+(d2) at 4726 cmâ1 (0.586 eV). The energies of the internal transitions are reduced with respect to the corresponding transitions in ZnS:V and ZnSe:V. The respective excitation spectra display, in addition to broad charge-transfer bands, higher excited levels of the individual charge states. Crystal-field calculations of the detected transition energies based on the Tanabe-Sugano scheme are presented. With the help of sensitization experiments, a one-electron model is designed, in which the donor level (V2+/V3+) is situated 12 500 cmâ1 (1.55 eV) below the conduction-band edge and the acceptor level (V2+/V+) 9400 cmâ1 (1.17 eV) above the valence-band edge. The dynamical behavior of the three infrared lurainescence bands was measured. Decay time constants of 43 ÎŒs (V+), 120 ÎŒs (V2+), and 420 ÎŒs (V3+) were found. Electron-paramagnetic-resonance (EPR) results measured on the same samples are presented in an accompanying paper and confirm the optical detection of isolated substitutional V2+(d3) and V3+(d2) ions. Relations between the EPR and optical results are discussed
Hyperfine structure of antiprotonic helium revealed by a laser-microwave-laser resonance method
Using a newly developed laser-microwave-laser resonance method, we observed a
pair of microwave transitions between hyperfine levels of the
state of antiprotonic helium. This experiment confirms the quadruplet hyperfine
structure due to the interaction of the antiproton orbital angular momentum,
the electron spin and the antiproton spin as predicted by Bakalov and Korobov.
The measured frequencies of GHz and
GHz agree with recent theoretical
calculations on a level of .Comment: 4 pages, 4 figures, 1 tabl
Efficacy and safety of vandetanib in progressive and symptomatic medullary thyroid Cancer: Post hoc analysis from the ZETA trial
PURPOSE We conducted a post hoc analysis of the vandetanib phase III trial involving patients with advanced medullary thyroid cancer (MTC) to assess the efficacy and safety of vandetanib in patients with progressive and symptomatic MTC. The primary objective of the analysis was to determine progression-free survival (PFS) of these patients. PATIENTS AND METHODS Eligible patients from the ZETA trial were divided into 4 disease severity subgroups: progression and symptoms, symptoms only, progression only, and no progression and no symptoms assessed at baseline. PFS, determined from objective tumor measurements performed by the local investigator, overall survival (OS), time to worsening of pain (TWP), and objective response rate (ORR) were evaluated. RESULTS Of the 331 patients in this trial, 184 had symptomatic and progressive disease at baseline. In this subgroup, results were similar in magnitude to those observed in the overall trial for PFS (hazard ratio [HR], 0.43; 95% CI, 0.28 to 0.64; P, .0001), OS (HR, 1.08; 95% CI, 0.72 to 1.61; P 5 .71), and TWP (HR, 0.67; 95% CI, 0.43 to 1.04; P 5 .07), and the observed adverse events were consistent with the known safety profile of vandetanib. In this subgroup, the ORR was 37% in the treatment arm versus 2% in the placebo arm. CONCLUSION Vandetanib demonstrated clinical benefitâspecifically, increased PFSâin patients with symptomatic and progressive MTC
Preliminary Results from Recent Measurements of the Antiprotonic Helium Hyperfine Structure
We report on preliminary results from a systematic study of the hyperfine
(HF) structure of antiprotonic helium. This precise measurement which was
commenced in 2006, has now been completed. Our initial analysis shows no
apparent density or power dependence and therefore the results can be averaged.
The statistical error of the observable M1 transitions is a factor of 60
smaller than that of three body quantum electrodynamic (QED) calculations,
while their difference has been resolved to a precision comparable to theory (a
factor of 10 better than our first measurement). This difference is sensitive
to the antiproton magnetic moment and agreement between theory and experiment
would lead to an increased precision of this parameter, thus providing a test
of CPT invariance.Comment: 6 pages, 4 figure
The efficiency of self-phoretic propulsion mechanisms with surface reaction heterogeneity
We consider the efficiency of self-phoretic colloidal particles (swimmers) as
a function of the heterogeneity in the surface reaction rate. The set of fluid,
species, and electrostatic continuity equations is solved analytically using a
linearization and numerically using a finite-element method. To compare
spherical swimmers of different size and with heterogeneous catalytic
conversion rates, a 'swimmer efficiency' functional is introduced. It is
proven, that in order to obtain maximum swimmer efficiency the reactivity has
to be localized at the pole(s). Our results also shed light on the sensitivity
of the propulsion speed to details of the surface reactivity, a property that
is notoriously hard to measure. This insight can be utilized in the design of
new self-phoretic swimmers.Comment: 10 pages, 4 figure
The association of intra-therapeutic heterogeneity of somatostatin receptor expression with morphological treatment response in patients undergoing PRRT with [177Lu]-DOTATATE
AIM:
Purpose of this study was to evaluate the association of the spatial heterogeneity (asphericity, ASP) in intra-therapeutic SPECT/ CT imaging of somatostatin receptor (SSR) positive metastatic gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) for morphological treatment response to peptide receptor radionuclide therapy (PRRT). Secondly, we correlated ASP derived form a pre-therapeutic OctreoScan (ASP[In]) and an intra-therapeutic [177Lu]-SPECT/CT (ASP[Lu]).
MATERIALS AND METHODS:
Data from first therapy cycle [177Lu-DOTA0-Tyr3]octreotate ([177Lu]-DOTATATE)-PRRT was retrospectively analyzed in 33 patients (m = 20; w = 13; median age, 72 [46-88] years). The evaluation of response to PRRT was performed according to RECIST 1.1 in responding lesions [RL (SD, PR, CR), n = 104] and non-responding lesions [NRL (PD), n = 27]. The association of SSR tumor heterogeneity with morphological response was evaluated by Kruskal-Wallis test and receiver operating characteristic curve (ROC). The optimal threshold for separation (RL vs. NRL) was calculated using the Youden-index. Relationship between pre- and intra-therapeutic ASP was determined with Spearman's rank correlation coefficient (Ï) and Bland-Altman plots.
RESULTS:
A total of 131 lesions (liver: n = 59, lymph nodes: n = 48, bone: n = 19, pancreas: n = 5) were analyzed. Lesions with higher ASP values showed a significantly poorer response to PRRT (PD, median: 11.3, IQR: 8.5-15.5; SD, median: 3.4, IQR: 2.1-4.5; PR, median 1.7, IQR: 0.9-2.8; CR, median: 0.5, IQR: 0.0-1.3); Kruskal-Wallis, p5.45% (sensitivity 96% and specificity 82%). The correlation coefficient of pre- and intra-therapeutic ASP revealed Ï = 0.72 (p <0.01). The mean absolute difference between ASP[In] and ASP[Lu] was -0.04 (95% Limits of Agreement, -6.1-6.0).
CONCLUSION:
Pre- and intra-therapeutic ASP shows a strong correlation and might be an useful tool for therapy monitoring
First observation of two hyperfine transitions in antiprotonic He-3
We report on the first experimental results for microwave spectroscopy of the
hyperfine structure of antiprotonic He-3. Due to the helium nuclear spin,
antiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4
which has already been studied before. Thus a comparison between theoretical
calculations and the experimental results will provide a more stringent test of
the three-body quantum electrodynamics (QED) theory. Two out of four
super-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were
observed. The measured frequencies of the individual transitions are
11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current
theoretical values, but still within their estimated errors. Although the
experimental uncertainty for the difference of these frequencies is still very
large as compared to that of theory, its measured value agrees with theoretical
calculations. This difference is crucial to be determined because it is
proportional to the magnetic moment of the antiproton.Comment: 8 pages, 6 figures, just published (online so far) in Physics Letters
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