Memory in nanomagnetic systems: Superparamagnetism versus Spinglass behavior

The slow dynamics and concomitant memory (aging) effects seen in nanomagnetic systems are analyzed on the basis of two separate paradigms : superparamagnets and spinglasses. It is argued that in a large class of aging phenomena it suffices to invoke superparamagnetic relaxation of individual single domain particles but with a distribution of their sizes. Cases in which interactions and randomness are important in view of distinctive experimental signatures, are also discussed.Comment: 11 pages and 19 figure

Establishment and production from thinned mature deciduous-forest silvopastures in Appalachia

Paper presented at the 11th North American Agroforesty Conference, which was held May 31-June 3, 2009 in Columbia, Missouri.In Gold, M.A. and M.M. Hall, eds. Agroforestry Comes of Age: Putting Science into Practice. Proceedings, 11th North American Agroforestry Conference, Columbia, Mo., May 31-June 3, 2009.Past research has not adequately addressed effective management and utilization of silvopastures developed from the ubiquitous mature woodlots which comprise 40-50% of small Appalachian farm acreage. While some grazing in woodlots is common, a set of guidelines for optimal utilization of these areas is not. We thinned a white oak dominated mature second growth forested area establishing two 0.5 ha, eight-paddock, orchardgrass-perennial ryegrass-white clover silvopasture replications for comparison with two nearby open pasture replications. After thinning trees, silvopastures were limed, fertilized and seeded. Sheep were fed hay and corn scattered across the area to facilitate removal of residual understory and incorporation of applied materials into surface soil. We measured soil moisture in the top 15 cm using TDR and photosynthetically active radiation (PAR) using a system of 16, 1 m line Quantum Sensors during the subsequent growing seasons of 2004, 2005, and 2006. Paddocks were rotationally grazed by sheep with two 1 m2 herbage mass samples taken prior to animal grazing. There was no significant difference in soil moisture between silvopastures and open pastures however, there was adequate rainfall to prevent drought all three years. The two silvopasture replications had residual tree stands of 14.1 and 15.6 m2 ha-1 diameter breast height allowing 42 and 51 [percent] of total daily incident PAR compared to measurements in the open field. Total forage mass yield from open pasture for 2004, 2005 and 2006 was 9.9, 10.5 and 10.2 t ha-1 respectively and for silvopasture 8.5, 6.7 and 6.7 t ha-1. Silvopastures received 47 [percent] of open pasture incident PAR yet yielded an average of 72 [percent] as much herbage mass as the open pastures. The silvopasture soils were managed for forage production only a few years unlike the open pastures which received roughly a century of better management. Soil limitations may have contributed to decreased forage yield in silvopastures in addition to reduced PAR.C.M. Feldhake, J.P.S. Neel and D.P. Belesky ; USDA-ARS Appalachian Farming Systems Research Center 1224 Airport Road, Beaver, WV.Includes bibliographical references

Towards the theory of ferrimagnetism

Two-sublattice ferrimagnet, with spin-$s_1$ operators $\bf{S_{1i}}$ at the sublattice $A$ site and spin-$s_2$ operators $\bf{S_{2i}}$ at the sublattice $B$ site, is considered. The magnon of the system, the transversal fluctuation of the total magnetization, is a complicate mixture of the transversal fluctuations of the sublattice $A$ and $B$ spins. As a result, the magnons' fluctuations suppress in a different way the magnetic orders of the $A$ and $B$ sublattices and one obtains two phases. At low temperature $(0,T^*)$ the magnetic orders of the $A$ and $B$ spins contribute to the magnetization of the system, while at the high temperature $(T^*,T_N)$, the magnetic order of the spins with a weaker intra-sublattice exchange is suppressed by magnon fluctuations, and only the spins with stronger intra-sublattice exchange has non-zero spontaneous magnetization. The $T^*$ transition is a transition between two spin-ordered phases in contrast to the transition from spin-ordered state to disordered state ($T_N$-transition). There is no additional symmetry breaking, and the Goldstone boson has a ferromagnetic dispersion in both phases. A modified spin-wave theory is developed to describe the two phases. All known Neel's anomalous $M(T)$ curves are reproduced, in particular that with "compensation point". The theoretical curves are compared with experimental ones for sulpho-spinel $MnCr2S_{4-x}Se_{x}$ and rare earth iron garnets.Comment: 9 pages, 8 figure

Z2_2 topology and superconductivity from symmetry lowering of a 3D Dirac Metal Au2_2Pb

3D Dirac semi-metals (DSMs) are materials that have massless Dirac electrons and exhibit exotic physical properties It has been suggested that structurally distorting a DSM can create a Topological Insulator (TI), but this has not yet been experimentally verified. Furthermore, quasiparticle excitations known as Majorana Fermions have been theoretically proposed to exist in materials that exhibit superconductivity and topological surface states. Here we show that the cubic Laves phase Au$_2$Pb has a bulk Dirac cone above 100 K that gaps out upon cooling at a structural phase transition to create a topologically non trivial phase that superconducts below 1.2 K. The nontrivial Z$_2$ = -1 invariant in the low temperature phase indicates that Au$_2$Pb in its superconducting state must have topological surface states. These characteristics make Au$_2$Pb a unique platform for studying the transition between bulk Dirac electrons and topological surface states as well as studying the interaction of superconductivity with topological surface states

Dynamic Neural Fields for Learning Atlases of 4D Fetal MRI Time-series

We present a method for fast biomedical image atlas construction using neural fields. Atlases are key to biomedical image analysis tasks, yet conventional and deep network estimation methods remain time-intensive. In this preliminary work, we frame subject-specific atlas building as learning a neural field of deformable spatiotemporal observations. We apply our method to learning subject-specific atlases and motion stabilization of dynamic BOLD MRI time-series of fetuses in utero. Our method yields high-quality atlases of fetal BOLD time-series with $\sim$5-7$\times$ faster convergence compared to existing work. While our method slightly underperforms well-tuned baselines in terms of anatomical overlap, it estimates templates significantly faster, thus enabling rapid processing and stabilization of large databases of 4D dynamic MRI acquisitions. Code is available at https://github.com/Kidrauh/neural-atlasingComment: 6 pages, 2 figures. Accepted by Medical Imaging Meets NeurIPS 202

A Comparative Evaluation of Ultrasound Molecular Imaging, Perfusion Imaging, and Volume Measurements in Evaluating Response to Therapy in Patient-Derived Xenografts

Most pre-clinical therapy studies use the change in tumor volume as a measure for disease response. However, tumor size measurements alone may not reflect early changes in tumor physiology that occur as a response to treatment. Ultrasonic molecular imaging (USMI) and Dynamic Contrast Enhanced - Perfusion Imaging (DCE-PI) with ultrasound are two attractive alternatives to tumor volume measurements. Since these techniques can provide information prior to the appearance of gross phenotypic changes, it has been proposed that USMI and DCE-PI could be used to characterize response to treatment earlier than traditional methods. This study evaluated the ability of tumor volume measurements, DCE-PI, and USMI to characterize response to therapy in two different types of patient-derived xenografts (known responders and known non-responders). For both responders and non-responders, 7 animals received a dose of 30 mg/kg of MLN8237, an investigational aurora-A kinase inhibitor, for 14 days or a vehicle control. Volumetric USMI (target integrin: αvβ3) and DCE-PI were performed on day 0, day 2, day 7, and day 14 in the same animals. For USMI, day 2 was the earliest point at which there was a statistical difference between the untreated and treated populations in the responder cohort (Untreated: 1.20±0.53 vs. Treated: 0.49±0.40; p < 0.05). In contrast, statistically significant differences between the untreated and treated populations as detected using DCE-PI were not observed until day 14 (Untreated: 0.94±0.23 vs. Treated: 1.31±0.22; p < 0.05). Volume measurements alone suggested no statistical differences between treated and untreated populations at any readpoint. Monitoring volumetric changes is the “gold standard” for evaluating treatment in pre-clinical studies, however, our data suggests that volumetric USMI and DCE-PI may be used to earlier classify and robustly characterize tumor response

Computing Nash Equilibrium in Wireless Ad Hoc Networks: A Simulation-Based Approach

This paper studies the problem of computing Nash equilibrium in wireless networks modeled by Weighted Timed Automata. Such formalism comes together with a logic that can be used to describe complex features such as timed energy constraints. Our contribution is a method for solving this problem using Statistical Model Checking. The method has been implemented in UPPAAL model checker and has been applied to the analysis of Aloha CSMA/CD and IEEE 802.15.4 CSMA/CA protocols.Comment: In Proceedings IWIGP 2012, arXiv:1202.422

HIV Types, Groups, Subtypes and Recombinant Forms: Errors in Replication, Selection Pressure and Quasispecies

HIV-1 is a chimpanzee virus which was transmitted to humans by several zoonotic events resulting in infection with HIV-1 groups M P, and in parallel transmission events from sooty mangabey monkey viruses leading to infections with HIV-2 groups A H. Both viruses have circulated in the human population for about 80 years. In the infected patient, HIV mutates, and by elimination of some of the viruses by the action of the immune system individual quasispecies are formed. Along with the selection of the fittest viruses, mutation and recombination after superinfection with HIV from different groups or subtypes have resulted in the diversity of their patterns of geographic distribution. Despite the high variability observed, some essential parts of the HIV genome are highly conserved. Viral diversity is further facilitated in some parts of the HIV genome by drug selection pressure and may also be enhanced by different genetic factors, including HLA in patients from different regions of the world. Viral and human genetic factors influence pathogenesis. Viral genetic factors are proteins such as Tat, Vif and Rev. Human genetic factors associated with a better clinical outcome are proteins such as APOBEC, langerin, tetherin and chemokine receptor 5 (CCR5) and HLA B27, B57, DRB1{*}1303, KIR and PARD3B. Copyright (C) 2012 S. Karger AG, Base

Genetic studies of the Macushi and Wapishana Indians

Blood samples from 509 Macushi and 623 Wapishana Amerindians of Northern Brazil and Southern Guyana have been analyzed with reference to the occurrence of rare variants and genetic polymorphisms of the following 25 systems: (i) Erythrocyte enzymes : acid phosphatase-1, adenosine deaminase, adenylate kinase-k, carbonic anhydrase-1, carbonic anhydrase-2, esterase A 1,2,3, esterase D, galactose-1-phosphate uridyltransferase, isocitrate dehydrogenase, lactate dehydrogenase, malate dehydrogenase, nucleoside phosphorylase, peptidase A, peptidase B, phosphoglucomutase 1, phosphoglucomutase 2, phosphogluconate dehydrogenase, phosphohexoseisomerase, triosephosphate isomerase and (ii) Serum proteins : albumin, ceruloplasmin, haptoglobin, hemoglobin A, hemoglobin A 2 and transferrin. Fifteen different rare variants were detected, involving 11 of these systems. In addition, a previously undescribed variant of ESA 1,2,3 which achieves polymorphic proportions in both these tribes is described. Excluding this variant, the frequency of rare variants is 1.1/1000 in 12510 determinations in the Macushi and 4.7/1000 in 15 396 determinations in the Wapishana. The ESA 1,2,3 , polymorphism was not observed in 382 Makiritare, 232 Yanomama, 146 Piaroa, 404 Cayapo, 190 Kraho and 112 Moro. Irregularities in the intratribal distribution of this polymorphism in the Macushi and Wapishana render a decision as to the tribe of origin impossible at present. Gene frequencies are also given for previosly described polymorphisms of 5 systems: haptoglobin, phosphoglucomutase 1, erythrocyte acid phosphatase, esterase D, and galactose-1-phosphate-uridyl-transferase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47605/1/439_2004_Article_BF00390440.pd

Low-temperature spin dynamics of a valence bond glass in Ba<sub style="font-size: smaller; vertical-align: baseline; position: relative; top: 0.25em;">2YMoO<sub style="font-size: smaller; vertical-align: baseline; position: relative; top: 0.25em;">6</sub></sub>

We carried out AC magnetic susceptibility measurements and muon spin relaxation spectroscopy on the cubic double perovskite Ba2YMoO6, down to 50 mK. Below ~1 K the muon relaxation is typical of a magnetic insulator with a spin-liquid type ground state, i.e. without broken symmetries or frozen moments. However, the AC susceptibility revealed a dilute-spin-glass like transition below ~ 1 K. Antiferromagnetically coupled Mo5+ 4d1 electrons in triply degenerate t2g orbitals are in this material arranged in a geometrically frustrated fcc lattice. Bulk magnetic susceptibility data has previously been interpreted in terms of a freezing to a heterogeneous state with non-magnetic sites where 4d^1 electrons have paired in spin-singlets dimers, and residual unpaired Mo5+ 4d1 electrons. Based on the magnetic heat capacity data it has been suggested that this heterogeneity is the result of kinetic constraints intrinsic to the physics of the pure system (possibly due to topological overprotection), leading to a self-induced glass of valence bonds between neighbouring 4d1 electrons. The muSR relaxation unambiguously points to a static heterogeneous state with a static arrangement of unpaired electrons isolated by spin-singlet (valence bond) dimers between the majority of Mo5+ 4d electrons. The AC susceptibility data indicate that the residual magnetic moments freeze into a dilute-spin-glass-like state. This is in apparent contradiction with the muon-spin decoupling at 50 mK in fields up to 200 mT, which indicates that, remarkably, the time scale of the field fluctuations from the residual moments is ~ 5 ns. Comparable behaviour has been observed in other geometrically frustrated magnets with spin-liquid-like behaviour and the implications of our observations on Ba2YMoO6 are discussed in this context.Comment: 11 pages, 3 Figures. Published in New Journal of Physic