Effect of the susceptibility on the magnetic phase diagrams of a ferrimagnet with magnetic instability

The magnetic phase diagrams of a two-sublattice ferrimagnet with a magnetically unstable subsystem are calculated taking account of the susceptibility. Analytic expressions are obtained for the phase-transition fields and critical values of the parameters of the ferrimagnet. The evolution of the magnetic phase diagrams as the susceptibility of the unstable sublattice increases is analyzed.     

Neutron diffraction study of magnetic properties of TmCo2

The present neutron diffraction studies have confirmed that TmCo₂ represents an exception within the RCo₂ series. It was found that, in contrast with other heavy RCo₂ compounds, the Co sublattice in TmCo₂ does not order magnetically below the Curie temperature (T_c = 3.9 K). This is assumed to be due the fact that in TmCo₂ the intersublattice (f-d) molecular field is smaller than the critical field necessary to induce magnetic order within the Co sublattice, as is the case in other RCo₂ compounds. Furthermore, we show that the magnetic structure and the onset of long-range order in TmCo₂ depend sensitively on the sample preparation, which partly explains the differing results published earlier.     

The O(N) vector model in the large-N limit revisited: multicritical points and double scaling limit

The multicritical points of the O(N)-invariant N vector model in the large-N limit are re-examined. Of particular interest are the subtleties involved in the stability of the phase structure at critical dimensions. In the limit N → ∞ while the coupling g → g_c in a correlated manner (the double scaling limit) a massless bound state O(N) singlet is formed and powers of 1/N are compensated by IR singularities. The persistence of the N → ∞ results beyond the leading order is then studied with particular interest in the possible existence of a phase with propagating small mass vector fields and a massless singlet bound state. We point out that under certain conditions the double scaled theory of the singlet field is non-interacting in critical dimensions.     

Preparation and characterization of n-alkanoic acid self-assembled monolayers adsorbed on 316L stainless steel

The electrochemical formation and characterization of decanoic, myristic, palmitic, and stearic acid self-assembled monolayers on a native oxide surface of 316L stainless steel have been studied. This work describes a new approach to surface modification of stainless steel in which the self-assembly of n-alkanoic acids is facilitated by applying a potential to the stainless steel in an organic electrolyte solution. While decanoic acid forms a disorganized monolayer as a result of sweeping the potential in an acetonitrile solution containing 0.1 mM of the respective acid, longer acids, that is, myristic and palmitic acids, form highly ordered closed-packed monolayers. This electrochemical approach results in highly reproducible monolayers that are deposited within a shorter time than the traditional assembly process. The monolayers were characterized by cyclic voltammetry, double-layer capacity (ac voltammetry), contact angle measurements, X-ray photoelectron spectroscopy, and external reflection-absorption Fourier transform infrared spectroscopy. The utilization and implications of this modification technique are discussed.     

Investigation of some parametric convex programming problems

Translated from Optimal'nost Upravlyaemykh Dinamicheskikh Sistem, No. 19, pp. 20–29, Vsesoyuznyi Nauchno-Issledovatel'skii Institut Sistemnykh Issledovanii, Moscow (1988).     

Information and Distinguishability of Ensembles of Identical Quantum States

We consider a fixed quantum measurement performed over n identical copies of quantum states. Using a rigorous notion of distinguishability based on Shannon’s 12th theorem, we show that in the case of a single qubit, the number of distinguishable states is , where (α₁,α₂) is the angle interval from which the states are chosen. In the general case of an N-dimensional Hilbert space and an area Ω of the domain on the unit sphere from which the states are chosen, the number of distinguishable states is . The optimal distribution is uniform over the domain in Cartesian coordinates.     

Outcomes matter: estimating pre-transplant survival rates of kidney-transplant patients using simulator-based propensity scores

The current kidney allocation system in the United States fails to match donors and recipients well. In an effort to improve the allocation system, the United Network of Organ Sharing (UNOS) defined factors that should determine a new allocation policy, and particularly patients’ potential remaining lifetime without a transplant (pre-transplant survival rates). Estimating pre-transplant survival rates is challenging because the data available on candidates and organ recipients is already “contaminated” by the current allocation policy. In particular, the selection of patients who are offered (and decide to accept) a kidney is not random. We therefore expect differences in mortality-related characteristics of organ recipients and of candidates who have not received transplant. Such differences introduce bias into survival models. Existing approaches for tackling this selection bias either ignore the difference between candidates and recipients or assume that selection to transplant is based solely on patients’ pre-transplant information, irrespective of the potential allocation outcome. We argue that in practice the allocation is dependent on the anticipated allocation outcome, which is a major factor in selection to transplant. Moreover, we show that ignoring the anticipated outcome increases model bias rather than decreases it. In this paper, we propose a novel simulator-based approach (SimBa) that adjusts for the selection bias by taking into account both pre-transplant and anticipated outcome information using simulation. We then fit survival models to kidney transplant waitlist data and compare the different adjustment methods. We find that SimBa not only fits the data best, but also captures a key aspect of the current allocation policy, namely, that the probability of kidney allocation increases in the expected pre-transplant life years.