Collective Ferromagnetism of Artificial Square Spin Ice.

We study the temperature and magnetic field dependence of the total magnetic moment of large-area permalloy artificial square spin ice arrays. The temperature dependence and hysteresis behavior are consistent with the coherent magnetization reversal expected in the Stoner-Wohlfarth model, with clear deviations due to interisland interactions at small lattice spacing. Through micromagnetic simulations, we explore this behavior and demonstrate that the deviations result from increasingly complex magnetization reversal at small lattice spacing, induced by interisland interactions, and depending critically on details of the island shapes. These results establish new means to tune the physical properties of artificial spin ice structures and other interacting nanomagnet systems, such as patterned magnetic media.

Experimental Realization of the 1D Random Field Ising Model.

We have measured magnetic-field-induced avalanches in a square artificial spin ice array of interacting nanomagnets. Starting from the ground state ordered configuration, we imaged the individual nanomagnet moments after each successive application of an incrementally increasing field. The statistics of the evolution of the moment configuration show good agreement with the canonical one-dimensional random field Ising model. We extract information about the microscopic structure of the arrays from our macroscopic measurements of their collective behavior, demonstrating a process that could be applied to other systems exhibiting avalanches.

Granular materials: packing grains by thermal cycling.

A long-standing problem in managing the behaviour of a collection of solid grains concerns the nature of the grain packing, a property that is typically controlled by how the grains are poured or shaken. Here we show that a systematic and controllable increase in granular packing can be induced by simply raising and then lowering the temperature, without the input of mechanical energy. This thermal processing may have important practical implications for the handling and storage of granular materials.

Artificial 'spin ice' in a geometrically frustrated lattice of nanoscale ferromagnetic islands.

Frustration, defined as a competition between interactions such that not all of them can be satisfied, is important in systems ranging from neural networks to structural glasses. Geometrical frustration, which arises from the topology of a well-ordered structure rather than from disorder, has recently become a topic of considerable interest. In particular, geometrical frustration among spins in magnetic materials can lead to exotic low-temperature states, including 'spin ice', in which the local moments mimic the frustration of hydrogen ion positions in frozen water. Here we report an artificial geometrically frustrated magnet based on an array of lithographically fabricated single-domain ferromagnetic islands. The islands are arranged such that the dipole interactions create a two-dimensional analogue to spin ice. Images of the magnetic moments of individual elements in this correlated system allow us to study the local accommodation of frustration. We see both ice-like short-range correlations and an absence of long-range correlations, behaviour which is strikingly similar to the low-temperature state of spin ice. These results demonstrate that artificial frustrated magnets can provide an uncharted arena in which the physics of frustration can be directly visualized.

Neonatal morbidity in singleton late preterm infants compared with full-term infants.

AIM: The aim of this study was to test the hypothesis that singleton late preterm infants (34 0/7 to 36 6/7 weeks of gestation) compared with full-term infants have a higher incidence of short-term morbidity and stay longer in hospital. METHODS: In this retrospective, multicentre study, electronic data of children born at five hospitals in Switzerland were recorded. Short-term outcome of late preterm infants was compared with a control group of full-term infants (39 0/7 to 40 6/7 weeks of gestation). Multiple gestations, pregnancies complicated by foetal malformations, maternal consumption of illicit drugs and infants with incomplete documentation were excluded. The results were corrected for gender imbalance. RESULTS: Data from 530 late preterm and 1686 full-term infants were analysed. Compared with full-term infants, late preterm infants had a significant higher morbidity: respiratory distress (34.7% vs. 4.6%), hyperbilirubinaemia (47.7% vs. 3.4%), hypoglycaemia (14.3% vs. 0.6%), hypothermia (2.5% vs. 0.6%) and duration of hospitalization (mean, 9.9 days vs. 5.2 days). The risk to develop at least one complication was 7.6 (95% CI: 6.2-9.6) times higher among late preterm infants (70.8%) than among full-term infants (9.3%). CONCLUSION: Singleton late preterm infants show considerably higher rate of medical complications and prolonged hospital stay compared with matched full-term infants and therefore need more medical and financial resources.

Measurements of nanoscale domain wall flexing in a ferromagnetic thin film.

We use the high spatial sensitivity of the anomalous Hall effect in the ferromagnetic semiconductor Ga(1-x)Mn(x)As, combined with the magneto-optical Kerr effect, to probe the nanoscale elastic flexing behavior of a single magnetic domain wall in a ferromagnetic thin film. Our technique allows position sensitive characterization of the pinning site density, which we estimate to be ∼10(14) cm(-3). Analysis of single site depinning events and their temperature dependence yields estimates of pinning site forces (10 pN range) as well as the thermal deactivation energy. Our data provide evidence for a much higher intrinsic domain wall mobility for flexing than previously observed in optically probed µm scale measurements.

Flux through a hole from a shaken granular medium.

We have measured the flux of grains from a hole in the bottom of a shaken container of grains. We find that the peak velocity of the vibration, v max, controls the flux, i.e., the flux is nearly independent of the frequency and acceleration amplitude for a given value of v max. The flux decreases with increasing peak velocity and then becomes almost constant for the largest values of v max. The data at low peak velocity can be quantitatively described by a simple model, but the crossover to nearly constant flux at larger peak velocity suggests a regime in which the granular density near the container bottom is independent of the energy input to the system.

Jamming and fluctuations in granular drag

We investigate the dynamic evolution of jamming in granular media through fluctuations in the granular drag force. The successive collapse and formation of jammed states give a stick-slip nature to the fluctuations which is independent of the contact surface between the grains and the dragged object, thus implying that the stress-induced collapse is nucleated in the bulk of the granular sample. We also find that while the fluctuations are periodic at small depths, they become "stepped" at large depths, a transition which we interpret as a consequence of the long-range nature of the force chains.

Cell-cycle inhibitor p27/Kip-1 expression in non-astrocytic and non-oligodendrocytic human nervous system tumors.

p27/kip-1 is a 'universal inhibitor' which inhibits cyclin complexes with cyclin-dependent kinases (CDKs), preventing cell cycle from the G1-S progression. It is expressed in normal oligodendrocytes and in differentiated glial tumors, decreasing with anaplasia and malignancy. In non-astrocytic and non-oligodendrocytic tumors of the nervous system, such as meningiomas, schwannomas, medulloblastomas, neuroblastomas and malignant lymphomas, p27/kip-1 is inconstantly and sometimes poorly expressed. This can be due to the lacking of p27 expression in the normal counterpart of tumor cells. In some tumors, p27/kip-1 expression can be attributed to a differentiation process, as in the pale islands of desmoplastic medulloblastoma and in neuroblastomas. A correlation of p27/kip-1 expression with histology was not found, with the exception of apoptosis in medulloblastomas. p27/kip-1 is in feed-back with cyclins and CDKs for the control of cell proliferation and its expression may occur where requested by the interplay with cyclins and other inhibitors.

Medulloblastoma with lipidized cells versus lipomatous medulloblastoma.

BACKGROUND: Lipomatous medulloblastoma is a recently identified clinicopathological entity, characterized by areas of lipomatous differentiation, manifestation in adults, and apparently by a favorable prognosis. MATERIAL AND METHODS: In our series of medulloblastomas of adults and children we have found lipidized cells within the tumor in 6 out of 78 cases of adults and in 8 out of 44 cases of children. In 3 adult cases and 3 children cases, lipidized cells were particularly numerous and clustered. RESULTS: Neuronal differentiation was found in 4/6 cases; no case showed GFAP-positive tumor cells. Lipidized cells were constantly immunopositive for vimentin and some of them also for KP-1 and CR3/43. The proliferation potential was evaluated by the immunohistochemical demonstration of MIB-1; MIB-1-labeling index (LI) ranged from 20.8% to 40.5%. No case survived longer than 7 years after diagnosis and postoperative radiotherapy. CONCLUSION: The present 6 cases of heavily lipidized medulloblastoma are not uniform as for age of occurrence, proliferation potential and survival. They do not share the clinical and pathologic features of "lipomatous medulloblastoma". Therefore, the finding of large numbers of lipidized cells in a medulloblastoma does not authorize to diagnose the tumor as "lipomatous medulloblastoma", for which a favorable clinical prognosis is foreseen.

Development of correlations in the dynamics of wet granular avalanches.

A detailed characterization of avalanche dynamics of wet granular media in a rotating drum apparatus is presented. The results confirm the existence of the three wetness regimes observed previously: the granular, the correlated, and the viscoplastic regime. These regimes show qualitatively different dynamic behaviors that are reflected in all the investigated quantities. We discuss the effect of interstitial liquid on the characteristic angles of the material and on the avalanche size distribution. These data also reveal logarithmic aging and allow us to map out the phase diagram of the dynamic behavior as a function of liquid content and flow rate. Via quantitative measurements of the flow velocity and the granular flux during avalanches, we characterize avalanche types unique to wet media. We also explore the details of viscoplastic flow (observed at the highest liquid contents) in which there are lasting contacts during flow, leading to coherence across the entire sample. This coherence leads to a velocity independent flow depth at high rotation rates and robust pattern formation in the granular surface.

Modeling relaxation and jamming in granular media.

We introduce a stochastic microscopic model to investigate the jamming and reorganization of grains induced by an object moving through a granular medium. The model reproduces the experimentally observed periodic sawtooth fluctuations in the jamming force and predicts the period and the power spectrum in terms of the controllable physical parameters. It also predicts that the avalanche sizes, defined as the number of displaced grains during a single advance of the object, follow a power law P(s) approximately s(-tau), where the exponent is independent of the physical parameters.

Granular drag on a discrete object: shape effects on jamming.

We study the drag force on discrete objects with circular cross section moving slowly through a spherical granular medium. Variations in the geometry of the dragged object change the drag force only by a small fraction relative to shape effects in fluid drag. The drag force depends quadratically on the object's diameter as expected. We do observe, however, a deviation above the expected linear depth dependence, and the magnitude of the deviation is apparently controlled by geometrical factors.

Local jamming via penetration of a granular medium.

We present a series of measurements examining the penetration force required to push a flat plate vertically through a dense granular medium, focusing in particular on the effects of the bottom boundary of the vessel containing the medium. Our data demonstrate that the penetration force near the bottom is strongly affected by the surface properties of the bottom boundary, even many grain diameters above the bottom. Furthermore, the data indicate an intrinsic length scale for the interaction of the penetrating plate with the vessel bottom via the medium. This length scale, which corresponds to the extent of local jamming induced by the penetrating plate, has a square root dependence both upon the plate radius and the ambient granular stress near the bottom boundary, but it is independent of penetration velocity and grain diameter.

Stick-slip fluctuations in granular drag.

We study fluctuations in the drag force experienced by an object moving through a granular medium. The successive formation and collapse of jammed states give a stick-slip nature to the fluctuations which are periodic at small depths but become "stepped" at large depths, a transition that we interpret as a consequence of the long-range nature of the force chains and the finite size of our experiment. Another important finding is that the mean force and the fluctuations appear to be independent of the properties of the contact surface between the grains and the dragged object. These results imply that the drag force originates in the bulk properties of the granular sample.

[Adenocarcinoma of the gallbladder--accidental finding during laparoscopic cholecystectomy]. / Adenokarcinóm zlcníka--akcidentálny nález pri laparoskopickej cholecystektómii.

The authors present a unique case-history of adenocarcinoma of the gallbladder detected on laparoscopic surgery and the surprising favourable postoperative course considering the diagnosis. They draw attention to the difficult preoperative diagnosis of adenocarcinoma of the gallbladder and the necessity of a radical approach to the surgical solution.

Reversible control of magnetic interactions by electric field in a single-phase material.

Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single-phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. Here, we demonstrate 'giant' magnetoelectric cross-field control in a tetravalent titanate film. In bulk form, EuTiO(3), is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest europium neighbours. In thin epitaxial films, strain was used to alter the relative strength of the magnetic exchange constants. We not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain condition switches the magnetic ground state. Using first-principles density functional theory, we resolve the underlying microscopic mechanism resulting in G-type magnetic order and illustrate how it is responsible for the 'giant' magnetoelectric effect.

Low-velocity granular drag in reduced gravity.

We probe the dependence of the low-velocity drag force in granular materials on the effective gravitational acceleration (g(eff)) through studies of spherical granular materials saturated within fluids of varying density. We vary g(eff) by a factor of 20, and we find that the granular drag is proportional to g(eff), i.e. that the granular drag, F(probe), on a vertical cylinder follows the expected relation F(probe)=ηρ(grain)g(eff)d(probe)h(probe)(2) where the drag is related to the probe's depth of insertion, h(probe); the probe's diameter, d(probe); the grain material's density, ρ(grain); and a dimensionless constant, η. The dimensionless constant shows no systematic variation over four orders of magnitude in effective grain weight, demonstrating that the relation holds over that entire range to within the precision of our data.