Crystal structures and magnetic properties of CuX2(pdmp)2 complexes (X = Br, Cl)

We report the synthesis and the structural and magnetic characterization of two new compounds: dibromobis-(pdmp)copper(II), CuBr2C22H24N4 (1), and dichlorobis(pdmp)copper(II), CuCl2C22H24N4 (2), where pdmp = 1-phenyl-3,5-dimethylpyrazole. The structures were refined by full-matrix least-squares techniques to R1 = 0.0620 and 0.0777, respectively. Compound 1 belongs to the space group P21/n with a = 8.165(5) Å, b = 10.432(3) Å, c = 13.385(4) Å, β = 100.12(4)̊, and Z = 2. Compound 2 belongs to the space group P21/c with a = 8.379(2) Å, b = 22.630(2) Å, c = 12.256(2) Å, β= 98.43(3)°, and Z = 4. It has the same molecular formula as a compound reported previously but a different crystal structure. Detailed single-crystal EPR measurements were performed for single-crystal samples of 1 and 2 at 9 and 35 GHz and at room temperature. The positions and line widths of the EPR lines were measured as a function of the magnetic field orientation in three orthogonal planes. The data were used to study the electronic properties of the copper ions and to evaluate the exchange interactions between them. Our results are discussed in terms of the electronic pathways for superexchange between copper ions, which are provided by the stacking of pyrazole and phenyl rings of neighboring molecules and by hydrogen-halogen bonds. © 1999 American Chemical Society.

Mean-field description of collapsing and exploding Bose-Einstein condensates

Numerical simulations based on the time-dependent mean-field Gross-Pitaevskii equation was performed to explain the dynamics of collapsing and exploding Bose-Einstein condensates (BEC) of 85Rb atoms. The atomic interaction was manipulated by an external magnetic field via a Feshbach resonance. On changing the scattering length of atomic interaction from a positive to a large negative value, the condensate collapsed and ejected atoms via explosion.

Multiperiodic magnetic structures in Hubbard superlattices

We consider fermions in one-dimensional superlattices (SL's), modeled by site-dependent Hubbard-U couplings arranged in a repeated pattern of repulsive (i.e., U>0) and free (U=0) sites. Density matrix renormalization group diagonalization of finite systems is used to calculate the local moment and the magnetic structure factor in the ground state. We have found four regimes for magnetic behavior: uniform local moments forming a spin-density wave (SDW), floppy local moments with short-ranged correlations, local moments on repulsive sites forming long-period SDW's superimposed with short-ranged correlations, and local moments on repulsive sites solely with long-period SDW's; the boundaries between these regimes depend on the range of electronic densities ρ and on the SL aspect ratio. Above a critical electronic density, ρ↑↓, the SDW period oscillates both with ρ and with the spacer thickness. The former oscillation allows one to reproduce all SDW wave vectors within a small range of electronic densities, unlike the homogeneous system. The latter oscillation is related to the exchange oscillation observed in magnetic multilayers. A crossover between regimes of thin to thick layers has also been observed.

Mean-field model of jet formation in a collapsing Bose-Einstein condensate

We perform a systematic numerical study, based on the time-dependent Gross-Pitaevskii equation, of jet formation in collapsing and exploding Bose-Einstein condensates as in the experiment by Donley et al (2001 Nature 412 295). In the actual experiment, via a Feshbach resonance, the scattering length of atomic interaction was suddenly changed from positive to negative on a pre-formed condensate. Consequently, the condensate collapsed and ejected atoms via explosion. On disruption of the collapse by suddenly changing the scattering length to zero, a radial jet of atoms was formed in the experiment. We present a satisfactory account of jet formation under the experimental conditions and also make predictions beyond experimental conditions which can be verified in future experiments.

Steel bars identification in reinforced concrete structures by using ANN and magnetic fields

This work proposes a methodology for non destructive testing (NDT) of reinforced concrete structures, using superficial magnetic fields and artificial neural networks, in order to identify the size and position of steel bars, embedded into the concrete. For the purposes of this paper, magnetic induction curves were obtained by using a finite element program. Perceptron Multilayered (PML) ANNs, with Levemberg-Marquardt training algorithm were used. The results presented very good agreement with the expect ones, encouraging the development of real systems based upon the proposed methodology.

Effect of the Rashba and Dresselhaus spin-splitting terms on the electron g factor in semiconductor quantum wells under applied magnetic fields

We use the Ogg-McCombe Hamiltonian together with the Dresselhaus and Rashba spin-splitting terms to find the g factor of conduction electrons in GaAs-(Ga,Al)As semiconductor quantum wells (QWS) (either symmetric or asymmetric) under a magnetic field applied along the growth direction. The combined effects of non-parabolicity, anisotropy and spin-splitting terms are taken into account. Theoretical results are given as functions of the QW width and compared with available experimental data and previous theoretical works. © 2007 Elsevier B.V. All rights reserved.

Field-induced length changes in the spin-liquid candidate κ-(BEDT-TTF) 2Cu 2(CN) 3

Measurements of the coefficient of thermal expansion on the spin-liquid candidate κ-(BEDT-TTF) 2Cu 2(CN) 3 have revealed distinct and strongly anisotropic lattice effects around 6 K - a possible spin liquid instability. In order to study the effects of a magnetic field on the low-temperature spin-liquid state, dilatometric measurements have been conducted both as a function of temperature at B = const. and as a function of field at T = const. While the 6 K anomaly is found to be insensitive to magnetic fields B ≤ 10 T, the maximum field applied, surprisingly strong B -induced effects are observed for magnetic fields applied along the in-plane b-axis. Above a threshold field of 0.5 T < B c ≤ 1 T, a jump-like anomaly is observed in the b-axis lattice parameter. This anomaly, which is located at 8.7 K at B = 1 T, grows in size and shifts to lower temperatures with increasing the magnetic field. Although the anomaly bears resemblance to a first-order phase transition, the lack of hysteresis suggests otherwise. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Esophageal transit time assessed by magnetic methods: An in vitro feasibility study of the novel alternating current biosusceptometry with 3-axis magnetorresistor

A hybrid magnetic instrumentation to detect a magnetic field from a permanent magnet, and to detect magnetic markers and tracers using alternating current biosusceptometry (ACB) is discussed. The instrument was used to in vitro evaluation of the esophageal transit time. The sensitivity between both magnetic methods was compared, showing sensitivity for in vivo applications. © 2013 Springer-Verlag.

Tunable Fermi acceleration in a nondissipative driven magnetic billiard

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Easily handling penicillin G acylase magnetic cross-linked enzymes aggregates: Catalytic and morphological studies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Closed-orbit dependence on the field direction in the anisotropic diamagnetic Kepler problem

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Tower as magnetic antipinning core in a small superconducting sample

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

High efficacy in hyperthermia-associated with polyphosphate magnetic nanoparticles for oral cancer treatment

Nanotherapy applied to cancer treatment is constantly evolving, and new approaches to current techniques, such as magnetohyperthermia, are being implemented to solve and minimize the limitations of conventional therapeutic strategies. The purpose of this study was to investigate the action of polyphosphate-coated maghemite nanoparticles (MNPs) on oral squamous cell carcinoma. Human oral cancer cells (UM-SCC14A) were incubated with MNPs at various concentrations and subjected to cell proliferation tests (MTT), apoptosis assays and transmission electron image analysis. Viability and apoptotic events were time and dose dependent. These in vitro tests showed that at the intermediate concentration tested there is no significant toxicity, as confirmed by transmission electron microscopy. For this reason this MNPs concentration was chosen for the subsequent in vivo tests. Oral tumor induction was performed by applying the carcinogen DMBA to Syrian hamsters. Animals were then treated by magnetohyperthermia using MNPs. No signs of general clinical symptoms of toxicity or abnormal behavioral reactions were observed. However, animals treated with MNPs and exposed to the alternating magnetic field in the hyperthermia procedure exhibited a significant and time dependent cancer regression, as confirmed by histopathological analyses and immunohistochemistry. Actually, in quantitative terms of the magnetotherapy efficacy involving these polyphosphate-coated MNPs, 100% recovery (12/12) was observed in the oral cancer tumor bearing Syrian hamsters seven days after the treatment with the magnetohyperthermia procedure. Data supports the suggestion that the MNPs-mediated hyperthermia represents a promising strategy for the treatment of oral cancer.

Magnetic flux quantum in a Superconducting concave/convex disk

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Qualitative analysis by online nuclear magnetic resonance using Carr-Purcell-Meiboom-Gill sequence with low refocusing flip angles

The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence has been used in many applications of magnetic resonance imaging (MRI) and low-resolution NMR (LRNMR) spectroscopy. Recently. CPMG was used in online LRNMR measurements that use long RF pulse trains, causing an increase in probe temperature and, therefore, tuning and matching maladjustments. To minimize this problem, the use of a low-power CPMG sequence based on low refocusing pulse flip angles (LRFA) was studied experimentally and theoretically. This approach has been used in several MRI protocols to reduce incident RF power and meet the specific absorption rate. The results for CPMG with LRFA of 3 pi/4 (CPMG(135)), pi/2 (CPMG(90)) and pi/4 (CPMG(45)) were compared with conventional CPMG with refocusing pi pulses. For a homogeneous field, with linewidth equal to Delta nu = 15 Hz, the refocusing flip angles can be as low as pi/4 to obtain the transverse relaxation time (T(2)) value with errors below 5%. For a less homogeneous magnetic field. Delta nu = 100 Hz, the choice of the LRFA has to take into account the reduction in the intensity of the CPMG signal and the increase in the time constant of the CPMG decay that also becomes dependent on longitudinal relaxation time (T(1)). We have compared the T(2) values measured by conventional CPMG and CPMG(90) for 30 oilseed species, and a good correlation coefficient, r = 0.98, was obtained. Therefore, for oilseeds, the T(2) measurements performed with pi/2 refocusing pulses (CPMG(90)), with the same pulse width of conventional CPMG, use only 25% of the RF power. This reduces the heating problem in the probe and reduces the power deposition in the samples. (C) 2011 Elsevier B.V. All rights reserved.