19F nuclear spin relaxation and spin diffusion effects in the single ion magnet LiYF4:Ho3+

Temperature and magnetic field dependences of the 19F nuclear spin-lattice relaxation in a single crystal of LiYF4 doped with holmium are described by an approach based on a detailed consideration of the magnetic dipole-dipole interactions between nuclei and impurity paramagnetic ions and nuclear spin diffusion processes. The observed non-exponential long time recovery of the nuclear magnetization after saturation at intermediate temperatures is in agreement with predictions of the spin-diffusion theory in a case of the diffusion limited relaxation. At avoided level crossings in the spectrum of electron-nuclear states of the Ho3+ ion, rates of nuclear spin-lattice relaxation increase due to quasi-resonant energy exchange between nuclei and paramagnetic ions, in contrast to the predominant role played by electronic cross-relaxation processes in the low-frequency ac-susceptibility.Comment: 27 pages total, 5 figures, accepted for publication, Eur. Phys. J.

Effect of monolingualism and bilingualism in the anterior cingulate cortex: a proton magnetic resonance spectroscopy study in two centers

Reports of an advantage of bilingualism on brain structure in young adult participants are inconsistent. Abutalebi et al. (2012) reported more efficient monitoring of conflict during the Flanker task in young bilinguals compared to young monolingual speakers. The present study compared young adult (mean age = 24) Cantonese-English bilinguals in Hong Kong and young adult monolingual speakers. We expected (a) differences in metabolites in neural tissue to result from bilingual experience, as measured by 1H-MRS at 3T, (b) correlations between metabolic levels and Flanker conflict and interference effects (c) different associations in bilingual and monolingual speakers. We found evidence of metabolic differences in the ACC due to bilingualism, specifically in metabolites Cho, Cr, Glx and NAA. However, we found no significant correlations between metabolic levels and conflict and interference effects and no significant evidence of differential relationships between bilingual and monolingual speakers. Furthermore, we found no evidence of significant differences in the mean size of conflict and interference effects between groups i.e. no bilingual advantage. Lower levels of Cho, Cr, Glx and NAA in bilingual adults compared to monolingual adults suggest that the brains of bilinguals develop greater adaptive control during conflict monitoring because of their extensive bilingual experience

On the "spin-freezing" mechanism in underdoped superconducting cuprates

The letter deals with the spin-freezing process observed by means of NMR-NQR relaxation or by muon spin rotation in underdoped cuprate superconductors. This phenomenon, sometimes referred as coexistence of antiferromagnetic and superconducting order parameters, is generally thought to result from randomly distributed magnetic moments related to charge inhomogeneities (possibly stripes) which exhibit slowing down of their fluctuations on cooling below T$_c$ . Instead, we describe the experimental findings as due to fluctuating, vortex-antivortex, orbital currents state coexisting with d-wave superconducting state. A direct explanation of the experimental results, in underdoped Y$_{1-x}$Ca$_x$Ba$_2$Cu$_3$O$_{6.1}$ and La$_{2-x}$Sr$$CuO$_4$, is thus given in terms of freezing of orbital current fluctuations

Phase Separation of the Two-Dimensional t-J model

The boundary of phase separation of the two-dimensional t-J model is investigated by the power-Lanczos method and Maxwell construction. The method is similar to a variational approach and it determines the lower bound of the phase separation boundary with $J_c/t=0.6\pm 0.1$ in the limit $n_e\sim 1$. In the physical interesting regime of high T_c superconductors where $0.3<J/t<0.5$ there is no phase separation.Comment: LaTex 5 pages, 4 figure

Magnetoresistance Anomalies in Antiferromagnetic YBa_2Cu_3O_{6+x}: Fingerprints of Charged Stripes

We report novel features in the in-plane magnetoresistance (MR) of heavily underdoped YBa_2Cu_3O_{6+x}, which unveil a developed ``charged stripe'' structure in this system. One of the striking features is an anisotropy of the MR with a "d-wave" symmetry upon rotating the magnetic field H within the ab plane, which is caused by the rotation of the stripes with the external field. With decreasing temperature, a hysteresis shows up below ~20 K in the MR curve as a function of H and finally below 10 K the magnetic-field application produces a persistent change in the resistivity. This "memory effect" is caused by the freezing of the directionally-ordered stripes.Comment: 4 pages, 6 figures, final version, to appear in 4 October 1999 issue of PR

The relation between stellar magnetic field geometry and chromospheric activity cycles – II The rapid 120-day magnetic cycle of <i>τ</i> Bootis

One of the aims of the BCool programme is to search for cycles in other stars and to understand how similar they are to the Sun. In this paper, we aim to monitor the evolution of τ Boo’s large-scale magnetic field using high-cadence observations covering its chromospheric activity maximum. For the first time, we detect a polarity switch that is in phase with τ Boo’s 120-day chromospheric activity maximum and its inferred X-ray activity cycle maximum. This means that τ Boo has a very fast magnetic cycle of only 240 days. At activity maximum τ Boo’s large-scale field geometry is very similar to the Sun at activity maximum: it is complex and there is a weak dipolar component. In contrast, we also see the emergence of a strong toroidal component which has not been observed on the Sun, and a potentially overlapping butterfly pattern where the next cycle begins before the previous one has finished

^{17}O and ^{51}V NMR for the zigzag spin-1 chain compound CaV2O4

$^{51}$V NMR studies on CaV2O4 single crystals and $^{17}$O NMR studies on $^{17}$O-enriched powder samples are reported. The temperature dependences of the $^{17}$O NMR line width and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at Tn = 78 K in the powder. Magnetic susceptibility measurements show that Tn = 69 K in the crystals. A zero-field $^{51}$V NMR signal was observed at low temperatures (f $\approx$ 237 MHz at 4.2 K) in the crystals. The field swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is collinear, with the easy axes of the two substructures separated by an angle of 19(1) degree, and with their average direction pointing approximately along the b-axis of the crystal structure. The two spin substructures contain equal number of spins. The temperature dependence of the ordered moment, measured up to 45 K, shows the presence of an energy gap Eg in the antiferromagnetic spin wave excitation spectrum. Antiferromagnetic spin wave theory suggests that Eg lies between 64 and 98 K.Comment: 11 pages, 14 figures. v2: 2 new figures; version published in Phys. Rev.

Magnetic field independence of the spin gap in YBa_2Cu_3O_{7-delta}

We report, for magnetic fields of 0, 8.8, and 14.8 Tesla, measurements of the temperature dependent ^{63}Cu NMR spin lattice relaxation rate for near optimally doped YBa_2Cu_3O_{7-delta}, near and above T_c. In sharp contrast with previous work we find no magnetic field dependence. We discuss experimental issues arising in measurements of this required precision, and implications of the experiment regarding issues including the spin or pseudo gap.Comment: 4 pages, 3 figures, as accepted for publication in Physical Review Letter

Non-alcoholic and craft beer production and challenges

Beer is the most consumed alcoholic beverage in the world and the third most popular beverage after water and tea. Emerging health-oriented lifestyle trends, demographics, stricter legislation, religious prohibitions, and consumers’ preferences have led to a strong and steady growth of interest for non-alcoholic beers (NABs), low-alcohol beers (LABs), as well for craft beers (CBs). Conventional beer, as the worlds most consumed alcoholic beverage, recently gained more recognition also due to its potential functionality associated with the high content of phenolic antioxidants and low ethanol content. The increasing attention of consumers to health-issues linked to alcohol abuse urges breweries to expand the assortment of conventional beers through novel drinks concepts. The production of these beers employs several techniques that vary in performance, efficiency, and usability. Involved production technologies have been reviewed and evaluated in this paper in terms of efficiency and production costs, given the possibility that craft brewers might want to adapt them and finally introduce novel non-alcoholic drinks in the market

Implications of Charge Ordering for Single-Particle Properties of High-Tc Superconductors

The consequences of disordered charge stripes and antiphase spin domains for the properties of the high-temperature superconductors are studied. We focus on angle-resolved photoemission spectroscopy and optical conductivity, and show that the many unusual features of the experimentally observed spectra can be understood naturally in this way. This interpretation of the data, when combined with evidence from neutron scattering and NMR, suggests that disordered and fluctuating stripe phases are a common feature of high-temperature superconductors.Comment: 4 pages, figures by fax or mai