Differential nitrogen cycling in semiarid sub-shrubs with contrasting leaf habit

Nitrogen (N) is, after water, the most limiting resource in semiarid ecosystems. However, knowledge on the N cycling ability of semiarid woody plants is still very rudimentary. This study analyzed the seasonal change in the N concentrations and pools of the leaves and woody organs of two species of semiarid sub-shrubs with contrasting leaf habit. The ability of both species to uptake, remobilize and recycle N, plus the main storage organ for N during summer drought were evaluated. We combined an observational approach in the field with experimental 15N labelling of adult individuals grown in sand culture. Seasonal patterns of N concentrations were different between species and organs and foliar N concentrations of the summer deciduous Lepidium subulatum were almost double those of the evergreen Linum suffruticosum. L. subulatum up took ca. 60% more external N than the evergreen and it also had a higher N resorption efficiency and proficiency. Contrastingly, L. suffruticosum relied more on internal N remobilization for shoot growth. Differently to temperate species, the evergreen stored N preferentially in the main stem and old trunks, while the summer deciduous stored it in the foliage and young stems. The higher ability of L. subulatum to uptake external N can be related to its ability to perform opportunistic growth and exploit the sporadic pulses of N typical of semiarid ecosystems. Such ability may also explain its high foliar N concentrations and its preferential storage of N in leaves and young stems. Finally, L. suffruticosum had a lower ability to recycle N during leaf senescence. These strategies contrast with those of evergreen and deciduous species from temperate and boreal areas, highlighting the need of further studies on semiarid and arid plants

Long-range interacting pendula: A simple model for understanding complex dynamics of charged particles in an electronic curtain device

In this paper, we investigate the equilibrium and non-equilibrium properties of a model that shares several important characteristics with charged particles interacting in an Electric Curtain (EC) device. An EC comprises a periodic array of parallel electrodes, applied to each is an alternating electric potential. Depending on the applied potentials and the geometry of the electrodes, a wide variety of field structures above the plane of the electrodes are possible. The EC has multiple applications in the control and manipulation of small particles, but is under utilized in industry and science because of difficulties in predicting and understanding the particle dynamics. One particular challenge in understanding the dynamics is the many-body coulomb interactions. To better understand the role of the interactions, we study a one-dimensional analytically tractable model that encapsulates their long-range nature. Specifically, we study a Hamiltonian similar to that of the Hamiltonian mean field model but with the inclusion of an index dependent phase in the interaction term that, as we show, reflects the periodic structure of an EC field. We solve for the canonical partition function and also investigate some of the non-equilibrium behaviors. In the study of the non-equilibrium behaviors, we find an interesting property, namely that a quasistationary (lifetime diverges as the number of particles is increased) clustered state can exist when an initial configuration is ordered by the particle indices

Arresting bubble coarsening: A two-bubble experiment to investigate grain growth in presence of surface elasticity

Many two-phase materials suffer from grain-growth due to the energy cost which is associated with the interface that separates both phases. While our understanding of the driving forces and the dynamics of grain growth in different materials is well advanced by now, current research efforts address the question of how this process may be slowed down, or, ideally, arrested. We use a model system of two bubbles to explore how the presence of a finite surface elasticity may interfere with the coarsening process and the final grain size distribution. Combining experiments and modelling in the analysis of the evolution of two bubbles, we show that clear relationships can be predicted between the surface tension, the surface elasticity and the initial/final size ratio of the bubbles. We rationalise these relationships by the introduction of a modified Gibbs criterion. Besides their general interest, the present results have direct implications for our understanding of foam stability

Cycloidal Domains in the Magnetization Reversal Process of Ni80Fe20/Nd16Co84/Gd12Co88 Trilayers

The magnetization reversal of each individual layer in magnetic trilayers ( permalloy / Nd Co / Gd Co ) is investigated in detail with x-ray microscopy and micromagnetic calculations. Two sequential inversion mechanisms are identified. First, magnetic vortex-antivortex pairs move along the field direction while inverting the magnetization of magnetic stripes until they are pinned by defects. The vortex-antivortex displacements are reversible within a field interval which allows their controlled motion. Second, as the reversed magnetic field increases, cycloidal domains appear in the permalloy layer as a consequence of the dissociation of vortex-antivortex pairs due to pinning. The field range where magnetic vortices and antivortices are effectively guided by the stripe pattern is of the order of tens of mT for the Ni Fe layer, as estimated from the stability of cycloid domains in the sample

Tonic-clonic seizures as a possible complication for cerebrospinal fluid leakage after intradural spinal surgery, a case report

Abstract Background Cerebrospinal fluid leakage is a well-known spinal surgery complication, especially in adults population. Pseudomeningocele is its most common manifestation and it can bring to some conditions, such as intracranial hypotension, infections and wound healing complication. Epilepsy is not classically associated to CSF leakage. We described a case of a female patient who developed tonic-clonic seizures associated with a pseudomeningocele after a detethering surgery. Case description A 16 year old female was admitted to our department for surgical treatment of a tethered cord for a sacral lipoma. Her medical history was remarkable mental retardation with psychiatric disturbs and hypothyroidism. She underwent a surgical intervention for the detethering of conus and dura was closed by a suture and fibrin glue. During third postoperative day she started to suffer a severe occipital headache, followed by tonic-clonic seizures. During suture removal, a collection suspected for a pseudomeningocele was found and chemical and radiological exams confirmed the dubious. Despite a continuous bed rest, collection continued to form. So, we decided to perform a surgical revision and to close dural defect. After intervention, patient did not suffer postural headache anymore and after 3 and 6 months she was found in good health. Conclusion We described the importance of significant morbidity, i.e. that of tonic clonic seizures as a sign of an occult CSF leakage after spinal surgery. Here, hydrocephalus as a condition was present, the change in pressure of CSF can determine seizures as well as promote this complication. A pseudomeningocele is not a trivial complication

Resolving Vega and the inclination controversy with CHARA/MIRC

Optical and infrared interferometers definitively established that the photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner on the Center for High Angular Resolution Astronomy Array. With our greater angular resolution and dense (u,v)-coverage, we find Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and also consistent with the possible rotational period of ~0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of 2.15+0.10_-0.15 Msun and an age 700-75+150 Myrs, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z=0.006+0.003-0.002).Comment: Accepted for publication in ApJ Letter