We measure the quasiparticle weight in the heavy-fermion compound CeCu_{6-x}Au_{x} (x=0, 0.1) by time-resolved terahertz spectroscopy for temperatures from 2 up to 300 K. This method distinguishes ...contributions from the heavy Kondo band and from the crystal-electric-field satellite bands by different terahertz response delay times. We find that the formation of heavy bands is controlled by an exponentially enhanced, high-energy Kondo scale once the crystal-electric-field states become thermally occupied. We corroborate these observations by temperature-dependent dynamical mean-field calculations for the multiorbital Anderson lattice model and discuss consequences for quantum-critical scenarios.
One of the most successful paradigms of many-body physics is the concept of quasiparticles: excitations in strongly interacting matter behaving like weakly interacting particles in free space. ...Quasiparticles in metals are very robust objects. Nevertheless, when a system’s ground state undergoes a qualitative change at a quantum critical point (QCP)1, the quasiparticles may disintegrate and give way to an exotic quantum-fluid state of matter. The nature of this breakdown is intensely debated2–5, because the emergent quantum fluid dominates material properties up to high temperatures and might even be related to the occurrence of superconductivity in some compounds6. Here we trace the dynamics of heavy-fermion quasiparticles in CeCu6−xAux and monitor their evolution towards the QCP in time-resolved experiments, supported by many-body calculations. A terahertz pulse disrupts the many-body heavy-fermion state. Under emission of a delayed, phase-coherent terahertz reflex the heavy-fermion state recovers, with a coherence time 100 times longer than typically associated with correlated metals7,8. The quasiparticle weight collapses towards the QCP, yet its formation temperature remains constant—phenomena believed to be mutually exclusive. Coexistence in the same experiment calls for revisions in our view on quantum criticality.
Spin-resolved photoemission is one of the most direct ways of measuring the magnetization of a ferromagnet. If all valence band electrons contribute, the measured average spin polarization is ...proportional to the magnetization. This is even the case if electronic excitations are present, and thus is of particular interest for studying the response of the magnetization to a pump laser pulse. Here, we demonstrate the feasibility of ultrafast spin-resolved photoemission using free electron laser (FEL) radiation and investigate the effect of space charge on the detected spin polarization. The sample is exposed to the radiation of the FEL FLASH in Hamburg. Surprisingly, the measured spin polarization depends on the fluence of the FEL radiation: a higher FEL fluence reduces the measured spin polarization. Space-charge simulations can explain this effect. These findings have consequences for future spin-polarized photoemission experiments using pulsed photon sources.
This study examined the combined influence of assimilation and contrast effects on the memory self-efficacy and objective memory of young (ages 18-25,
= 114), middle-age (ages 26-59,
= 48), and ...older (ages 60-98,
= 59) adults. We reminded participants that they matched positive, not negative, memory-relevant or memory-irrelevant stereotypes of aging either before (experimental conditions) or after (control condition) they completed a memory self-efficacy questionnaire and took a memory test. Participants exposed to memory-relevant aging stereotypes prior to other measures reported higher memory self-efficacy than those exposed to memory-irrelevant stereotypes; this effect did not depend on age group. In contrast, the effect of stereotype exposure on memory performance differed with age. Young and older, but not middle-aged, adults showed differences in their memory scores depending on whether they were exposed to memory-relevant, memory-irrelevant or no aging stereotypes. In general, exposure to stereotypes (particularly those relevant to memory) had a negative influence on memory that contrasted with its positive effect on memory self-efficacy. Together, these results indicate that exposure to aging stereotypes can have opposing effects on the memory self-efficacy and objective test performance of adults of various ages and that the relevance of the stereotypes to the cognitive domain being assessed matters.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
Cocaine mediates its powerful reinforcement by binding to recognition sites on the dopamine (DA) transporter. The pharmacological identity of cocaine recognition sites and their relevance to dopamine ...transport function has remained unclear. Ligand binding studies with transport inhibitors and cocaine congeners have provided evidence for multiple sites or "states" of the DA transporter. The potent cocaine congener 3HWIN 35,428 ((CFT), 2B-carbomethoxy-3 beta-(4-fluorophenyl)-tropane) has been shown to recognize high and low affinity binding sites on the DA transporter. We have used 3HWIN 35,428 to map and quantify the high affinity cocaine recognition site on the DA transporter in victims of fatal cocaine overdose. Region-of-interest densitometric analysis of the autoradiograms demonstrated a 2- to 3-fold elevation in the apparent density of 3HWIN 35,428 binding in particular sectors of the striatum from victims of cocaine overdose as compared to age-matched and drug-free control subjects. The most marked increase in 3HWIN 35,428 binding was seen in the nucleus accumbens. The apparent increase in the density of high affinity sites was confirmed by saturation binding analysis of 3HWIN 35,428 to putamen membranes. Saturation analysis revealed high and low affinity binding components with affinities (KD values) of 4.3 +/- 1.2 and 84.7 +/- 19.7 nM (mean +/- S.E.) and densities of 9.9 +/- 4.0 and 193.0 +/- 28.6 pmol/g of tissue, respectively.
We evaluated whether recent cocaine use alters the specificity of CK-MB, myoglobin, and cardiac troponin I for acute myocardial infarction (AMI) in patients who are seen in the emergency department ...for chest pain. Patients <60 years old with potential myocardial ischemia underwent a standardized history and physical examination and routine CK-MB assays every 8 to 12 hours and had study serum obtained at presentation for CK-MB, myoglobin, and cardiac troponin I immunoassays, as well as benzoylecgonine, cocaine's main metabolite. We enrolled 97 patients, 19 (20%) of whom had recent used cocaine. Patients with and without cocaine use were similar with regards to sex, race, renal and muscular disease, diabetes, family history, and hypertension and rate of AMI (12% vs 11%,
p = 1.0). In patients without MI, the mean myoglobin level was higher in cocaine users than noncocaine users (179 vs 74 ng/ml; Mann-Whitney
p = 0.003), but the mean values were similar for CK-MB (2.2 vs 2.1 ng/ml; Mann-Whitney
p = 0.58) and for cardiac troponin-I (0.02 vs 0.02 ng/ml; Mann-Whitney
p = 0.87). The specificities of the markers in patients with and without cocaine use were as follows: cardiac troponin I, 94% vs 94%, (
p = 1.0); CK-MB, 75% vs 88% (
p = 0.24); and myoglobin, 50% vs 82%, (
p = 0.02), respectively. Our data demonstrate that the specificity of myoglobin was altered by recent cocaine use. The specificity of CK-MB was affected less and the specificity of cardiac troponin I was not affected by recent cocaine use. (Am Heart J 1998;135:245-52.)
We describe an outbreak of deaths from cocaine-induced excited delirium (EDDs) in Dade County, Florida between 1979 and 1990. From a registry of all cocaine-related deaths in Dade County, Florida, ...from 1969-1990, 58 EDDs were compared with 125 victims of accidental cocaine overdose without excited delirium. Compared with controls, EDDs were more frequently black, male, and younger. They were less likely to have a low body mass index, and more likely to have died in police custody, to have received medical treatment immediately before death, to have survived for a longer period, to have developed hyperthermia, and to have died in summer months. EDDs had concentrations of cocaine and benzoylecgonine in autopsy blood that were similar to those for controls. The epidemiologic findings are most consistent with the hypothesis that chronic cocaine use disrupts dopaminergic function and, when coupled with recent cocaine use, may precipitate agitation, delirium, aberrant thermoregulation, rhabdomyolysis, and sudden death.
In Alagille syndrome, routine follow-up imaging of the liver plays an important role in detecting early parenchymal changes and to evaluate portal hypertension. Modern contrast-enhanced imaging ...methods not only allow early detection of focal liver lesions, but also enable further characterization of their nature and guide biopsy procedures. We present the US and MR imaging findings of hepatocellular carcinoma and a regenerating nodule in a 3-year-old child with Alagille syndrome.
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