Magnetic ordering and fluctuation in kagome lattice antiferromagnets, Fe and Cr jarosites

Jarosite family compounds, KFe_3(OH)_6(SO_4)_2, (abbreviate Fe jarosite), and KCr_3(OH)_6(SO_4)_2, (Cr jarosite), are typical examples of the Heisenberg antiferromagnet on the kagome lattice and have been investigated by means of magnetization and NMR experiments. The susceptibility of Cr jarosite deviates from Curie-Weiss law due to the short-range spin correlation below about 150 K and shows the magnetic transition at 4.2 K, while Fe jarosite has the transition at 65 K. The susceptibility data fit well with the calculated one on the high temperature expansion for the Heisenberg antiferromagnet on the kagome lattice. The values of exchange interaction of Cr jarosite and Fe jarosite are derived to be J_Cr = 4.9 K and J_Fe = 23 K, respectively. The 1H-NMR spectra of Fe jarosite suggest that the ordered spin structure is the q = 0 type with positive chirality of the 120 degrees configuration. The transition is caused by a weak single-ion type anisotropy. The spin-lattice relaxation rate, 1/T_1, of Fe jarosite in the ordered phase decreases sharply with lowering the temperature and can be well explained by the two-magnon process of spin wave with the anisotropy.Comment: REVTeX, 14 pages with 5 figures. Submitted to Canadian Journal of Physic

Quantum interference oscillations of the superparamagnetic blocking in an Fe8 molecular nanomagnet

We show that the dynamic magnetic susceptibility and the superparamagnetic blocking temperature of an Fe8 single molecule magnet oscillate as a function of the magnetic field Hx applied along its hard magnetic axis. These oscillations are associated with quantum interferences, tuned by Hx, between different spin tunneling paths linking two excited magnetic states. The oscillation period is determined by the quantum mixing between the ground S=10 and excited multiplets. These experiments enable us to quantify such mixing. We find that the weight of excited multiplets in the magnetic ground state of Fe8 amounts to approximately 11.6%.Comment: Accepted in Phys. Rev. Let

Correct anteroposterior patterning of the zebrafish neurectoderm in the absence of the early dorsal organizer

Background The embryonic organizer (i.e., Spemann organizer) has a pivotal role in the establishment of the dorsoventral (DV) axis through the coordination of BMP signaling. However, as impaired organizer function also results in anterior and posterior truncations, it is of interest to determine if proper anteroposterior (AP) pattern can be obtained even in the absence of early organizer signaling. Results Using the ventralized, maternal effect ichabod (ich) mutant, and by inhibiting BMP signaling in ich embryos, we provide conclusive evidence that AP patterning is independent of the organizer in zebrafish, and is governed by TGFβ, FGF, and Wnt signals emanating from the germ-ring. The expression patterns of neurectodermal markers in embryos with impaired BMP signaling show that the directionality of such signals is oriented along the animal-vegetal axis, which is essentially concordant with the AP axis. In addition, we find that in embryos inhibited in both Wnt and BMP signaling, the AP pattern of such markers is unchanged from that of the normal untreated embryo. These embryos develop radially organized trunk and head tissues, with an outer neurectodermal layer containing diffusely positioned neuronal precursors. Such organization is reflective of the presumed eumetazoan ancestor and might provide clues for the evolution of centralization in the nervous system. Conclusions Using a zebrafish mutant deficient in the induction of the embryonic organizer, we demonstrate that the AP patterning of the neuroectoderm during gastrulation is independent of DV patterning. Our results provide further support for Nieuwkoop's "two step model" of embryonic induction. We also show that the zebrafish embryo can form a radial diffuse neural sheath in the absence of both BMP signaling and the early organizer

Quantum Landauer erasure with a molecular nanomagnet

The erasure of a bit of information is an irreversible operation whose minimal entropy production of kB ln 2 is set by the Landauer limit1. This limit has been verified in a variety of classical systems, including particles in traps2, 3 and nanomagnets4. Here, we extend it to the quantum realm by using a crystal of molecular nanomagnets as a quantum spin memory and showing that its erasure is still governed by the Landauer principle. In contrast to classical systems, maximal energy efficiency is achieved while preserving fast operation owing to its high-speed spin dynamics. The performance of our spin register in terms of energy–time cost is orders of magnitude better than existing memory devices to date. The result shows that thermodynamics sets a limit on the energy cost of certain quantum operations and illustrates a way to enhance classical computations by using a quantum system

Association Between Noninvasive Fibrosis Markers and Postoperative Mortality After Hepatectomy for Hepatocellular Carcinoma

IMPORTANCE The selection criteria for hepatectomy for hepatocellular carcinoma (HCC) is not well established. The role of noninvasive fibrosis markers in this setting is unknown in the US population. OBJECTIVE To evaluate whether aspartate aminotransferase-platelet ratio index (APRI) and fibrosis 4 (Fib4) values are associated with perioperative mortality and overall survival after hepatectomy for HCC. DESIGN, SETTING, AND PARTICIPANTS In a multicenter cohort study, Veterans Administration Corporate Data Warehouse was used to evaluate a retrospective cohort of 475 veterans who underwent hepatectomy for HCC between January 1, 2000, and December 31, 2012, in Veterans Administration hospitals. Data analysis occurred between September 30, 2016, and December 30, 2017. Logistic regression, survival analysis, and change in concordance index analysis were performed to evaluate the association between APRI and Fib4 values and mortality. EXPOSURES The cohort was stratified based on preoperative APRI and Fib4 values. Analysis was performed accounting for the validated and established predictors of outcome. MAIN OUTCOMES AND MEASURES Thirty-day mortality, 90-day mortality, and overall survival were the primary outcomes. An APRI value greater than 1.5 was considered high risk (cirrhosis), and an Fib4 value greater than 4.0 was considered high risk (advanced fibrosis). Portal hypertension (diagnosis of ascites or encephalopathy indicates presence of portal hypertension) and Child-Turcotte-Pugh (CTP) class (A indicates preserved liver function; B, mild to moderate liver dysfunction) served as 2 other measures of liver function. RESULTS A total of 475 patients with HCC underwent hepatectomy. The mean (SD) age was 65.6 (9.4) years; Model for End-Stage Liver Disease score, 8.9 (3.1); and body mass index, 28.1 (4.9) (calculated as weight in kilograms divided by height in meters squared). A total of 361 patients (76.0%) were men, 294 (61.9%) were white; 308 (64.8%) were hepatitis C positive, and 346 (72.8%) were categorized as CTP class A. The most common surgical procedure was partial lobectomy, with 321 (67.6%) procedures. The APRI value greater than 1.5 vs 1.5 or lower was associated with increased 30-day mortality (odds ratio [OR], 6.45; 95% CI, 2.80-14.80) and 90-day mortality (OR, 2.65; 95% CI, 1.35-5.22), as was Fib4 greater than 4.0 vs Fib4 4.0 or lower for 30-day mortality (OR, 5.41; 95% CI, 2.35-12.50) and 90-day mortality (OR, 2.74; 95% CI, 1.41-5.35). Survival analysis showed that overall survival was significantly different for APRI greater than 1.5 vs 1.5 or lower (mean survival time, 3.6 vs 5.4 years; log-rank P <.001) and Fib4 greater than 4.0 vs 4.0 or lower (mean survival time, 4.1 vs 5.3 years; log rank P =.01). Adjusted Cox proportional hazards regression analysis revealed that elevated APRI was significantly associated with worse survival (hazard ratio [HR], 1.13; 95% CI, 1.03-1.23) but Fib4 values were not (HR, 1.04; 95% CI, 0.99-1.09). Change in concordance index showed that APRI and Fib4 improved the ability of CTP class and portal hypertension to predict postoperative mortality. CONCLUSIONS AND RELEVANCE Elevated APRI and Fib4 values, which are noninvasive markers of fibrosis, were associated with higher perioperative mortality. The APRI was also associated with worse overall survival. Use of APRI and Fib4 measures improved the ability of established markers to predict postoperative mortality. These findings suggest incorporating APRI and Fib4 to the selection process for hepatectomy for HCC as predictors associated with mortalitymay be warranted.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]