Spin dynamics in rare earth single molecule magnets from muSR and NMR in [TbPc2_{2}]0^{0} and [DyPc2_{2}]0^{0}

The spin dynamics in [TbPc$_{2}$]$^{0}$ and [DyPc$_{2}$]$^{0}$ single molecule magnets have been investigated by means of muon and nuclear spin-lattice relaxation rate measurements. The correlation time for the spin fluctuations was found to be close to 0.1 ms already at 50 K, about two orders of magnitude larger than the one previously found in other lanthanide based single molecule magnets. In [TbPc$_{2}$]$^{0}$ two different regimes for the spin fluctuations have been evidenced: a high temperature activated one involving spin fluctuations across a barrier $\Delta\simeq 880 K$ separating the ground and first excited states and a low temperature regime involving quantum fluctuations within the twofold degenerate ground-state. In [DyPc$_{2}$]$^{0}$ a high temperature activated spin dynamics is also evidenced which, however, cannot be explained in terms of a single spin-phonon coupling constant.Comment: 4 pages, 4 figure

Spin and charge dynamics in [TbPc2_2]0^0 and [DyPc2_2]0^0 single molecule magnets

Magnetization, AC susceptibility and $\mu$SR measurements have been performed in neutral phthalocyaninato lanthanide ([LnPc$_2]^0$) single molecule magnets in order to determine the low-energy levels structure and to compare the low-frequency spin excitations probed by means of macroscopic techniques, such as AC susceptibility, with the ones explored by means of techniques of microscopic character, such as $\mu$SR. Both techniques show a high temperature thermally activated regime for the spin dynamics and a low temperature tunneling one. While in the activated regime the correlation times for the spin fluctuations estimated by AC susceptibility and $\mu$SR basically agree, clear discrepancies are found in the tunneling regime. In particular, $\mu$SR probes a faster dynamics with respect to AC susceptibility. It is argued that the tunneling dynamics probed by $\mu$SR involves fluctuations which do not yield a net change in the macroscopic magnetization probed by AC susceptibiliy. Finally resistivity measurements in [TbPc$_2]^0$ crystals show a high temperature nearly metallic behaviour and a low temperature activated behaviour.Comment: 8 pages, 12 figure

Optimal simple rules and the lower bound on the nominal interest rate in the Christiano–Eichenbaum–Evans model of the US business cycle

Schmitt-Grohé and Uribe (NBER wp 10724, 2004b) analyzes the optimal, simple and implementable monetary policy rules in a medium-scale macromodel, as the one proposed by Christiano et al. (J Polit Econ 113:1–45, 2005). In doing so, they use a sensible, but somewhat arbitrary constraint to account for the lower bound condition on the nominal interest rate. In this work, we check the robustness of their main results to such a criteria. We find that the optimal policies are actually absolutely robust to the easing of this criterion for all the diff erent cases considered.info:eu-repo/semantics/publishedVersio

Machine learning based estimation of axonal permeability: validation on cuprizone treated in-vivo mouse model of axonal demyelination

Estimating axonal permeability reliably is extremely important, however not yet achieved because mathematical models that express its relationship to the MR signal accurately are intractable. Recently introduced machine learning based computational model showed to outperforms previous approximate mathematical models. Here we apply and validate this novel method experimentally on a highly controlled in-vivo mouse model of axonal demyelination, and demonstrate for the first time in practice the power of machine learning as a mechanism to construct complex biophysical models for quantitative MRI

Deep neural network based framework for in-vivo axonal permeability estimation

This study introduces a novel framework for estimating permeability from diffusion-weighted MRI data using deep learning. Recent work introduced a random forest (RF) regressor model that outperforms approximate mathematical models (Kärger model). Motivated by recent developments in machine learning, we propose a deep neural network (NN) approach to estimate the permeability associated with the water residence time. We show in simulations and in in-vivo mouse brain data that the NN outperforms the RF method. We further show that the performance of either ML method is unaffected by the choice of training data, i.e. raw diffusion signals or signal-derived features yield the same results

Decentralization and Public Procurement Performance: New Evidence from Italy

We exploit a new dataset based on EU procurement award notices to investigate the relationship between the degree of centralization of public procurement and its performance. We focus on the case of Italy, where all levels of government, along with a number of other public institutions, are involved in procurement and are subject to the same EU regulation. We find that i) municipalities and utilities, which currently award the largest shares of contracts, perform worse than all other institutional categories; and ii) decentralization implies lower performance only when it comes with weak competences of procurement officials. The evidence seems to suggests that a re-organization of the procurement system, both in terms of partial centralization and better professionalization of procurement officials, would help improve overall procurement performance

Spin dynamics in the neutral rare-earth single-molecule magnets [TbPc2]0 and [DyPc2]0 from muSR and NMR spectroscopies

The spin dynamics in [TbPc2]0 and [DyPc2]0 single-molecule magnets have been investigated by means of muon and nuclear spin-lattice relaxation rate measurements. The correlation time for the spin fluctuations was found to be close to 0.1 ms already at 50 K, about 2 orders of magnitude larger than the one previously found in other lanthanide-based single-molecule magnets. In [TbPc2]0 two different regimes for the spin fluctuations have been evidenced: a high-temperature activated one involving spin fluctuations across a barrier around 880 K separating the ground and first excited states and a low-temperature regime involving quantum fluctuations within the twofold degenerate ground state. In [DyPc2]0 a high-temperature activated spin dynamics is also evidenced which, however, cannot be explained in terms of a single spin-phonon coupling constant

Low-energy spin dynamics in the [YPc2]0 S=1/2 antiferromagnetic chain

1H nuclear magnetic resonance (NMR) measurements in [YPc2]0, an organic compound formed by radicals stacking along chains, are presented. The temperature dependence of the macroscopic susceptibility of the NMR shift and of the spin-lattice relaxation rate 1/T1 indicate that the unpaired electron spins are not delocalized but rather form a S=1/2 antiferromagnetic chain. The exchange couplings estimated from those measurements are all in quantitative agreement. The low-energy spin dynamics can be described in terms of diffusive processes and the temperature dependence of the corresponding diffusion constant suggests that a spin gap at ~1 K might be present in this compound

Recombinant Adenoviral Gene Transfer Does Not Affect Cardiac Allograft Vasculopathy

Background: Adenovirus serotype 5 has remained the pre-eminent vector in pre-clinical gene therapy applications in cardiac transplantation. Concerns over the potential effects of adenoviral vectors on the later development of cardiac allograft vasculopathy (CAV) are addressed in this study. Methods: Hearts (n = 22) harvested from Brown Norway rats were perfused ex vivo with either University of Wisconsin (UW) solution with no virus, Ad-CMV-LacZ or Ad-CMV-Null. Donor hearts were transplanted heterotopically into the abdomen of Lewis rats. All recipients received cyclosporine for the duration of the experiment. Transplanted hearts were recovered for analysis at 120 days. Sections of the heart were stained with elastic-van Gieson stain for morphometric analysis of the vessels to ascertain the degree of vascular luminal occlusion. Hematoxylin-eosin staining facilitated diagnosis of chronic rejection. Results: Seventy-seven percent of transplanted hearts showed signs of chronic rejection with no difference in the proportion of animals between groups (p = 0.797). No difference was noted in the degree of vascular luminal occlusion between the Ad-Null (0.57 \ub1 0.22), Ad-LacZ (0.62 \ub1 0.19) and UW (0.47 \ub1 0.29) groups (p = 0.653). Conclusions: Vascularized cardiac allografts transplanted from Brown Norway to Lewis rats demonstrated cardiac allograft vasculopathy CAV at 120 days. Adenoviral perfusion of the donor heart ex vivo did not affect the development of CAV. \ua9 2007 International Society for Heart and Lung Transplantation