17,778 research outputs found
A model for structural defects in nanomagnets
A model for describing structural pointlike defects in nanoscaled
ferromagnetic materials is presented. Its details are explicitly developed
whenever interacting with a vortex-like state comprised in a thin nanodisk.
Among others, our model yields results for the vortex equilibrium position
under the influence of several defects along with an external magnetic field in
good qualitative agreement with experiments. We also discuss how such defects
may affect the vortex motion, like its gyrotropic oscillation and dynamical
polarization reversal.Comment: 8 pages, resubmitted to Journal of Applied Physic
Ultracold heteronuclear molecules and ferroelectric superfluids
We analyze the possibility of a ferroelectric transition in heteronuclear
molecules consisting of Bose-Bose, Bose-Fermi or Fermi-Fermi atom pairs. This
transition is characterized by the appearance of a spontaneous electric
polarization below a critical temperature. We discuss the existence of a
ferroelectric Fermi liquid phase for Fermi molecules and the existence of a
ferroelectric superfluid phase for Bose molecules characterized by the
coexistence of ferroelectric and superfluid orders. Lastly, we propose an
experiment to detect ferroelectric correlations through the observation of
coherent dipole radiation pulses during time of flight.Comment: 4 pages and 3 figure
Extração do aroma de bacuri e sua utilização como flavorizante em iogurte natural.
bitstream/item/33536/1/CPATU-CirTec15.pd
Biofouling in water systems
The paper describes the mechanisms in the development of biofouling layers (initial surface conditioning, microbial transport and attachment, mass transfer of nutrients to the biofilm surface and through the microbial layer, cell metabolism, and detachment of cells and of larger parts of the biofilm) and summarizes the effects of several factors on the buildup and stability of biofilms (nutrient availability, fluid velocity and turbulence, temperature, surface condition, and nonliving particles). Mass transfer within biofilms is treated in more detail. A biofouling model applied to the development of biofilms in heat exchangers is presented. Finally, references are made to biofouling control methods (biocide and the proper design and operation of heat exchangers) and to future research needs in this area
To close or to collapse : the role of charges on membrane stability upon pore formation
Resealing of membrane pores is crucial for cell survival. We study membrane surface charge and medium composition as defining regulators of membrane stability. Pores are generated by electric field or detergents. Giant vesicles composed of zwitterionic and negatively charged lipids mixed at varying ratios are subjected to a single strong electric pulse. Charged vesicles are prone to catastrophic collapse transforming them into tubular structures. The spectrum of destabilization responses includes the generation of long-living submicroscopic pores and partial vesicle bursting. The origin of these phenomena is related to the membrane edge tension, which governs pore closure. This edge tension significantly decreases as a function of the fraction of charged lipids. Destabilization of charged vesicles upon pore formation is universal – it is also observed with other poration stimuli. Disruption propensity is enhanced for membranes made of lipids with higher degree of unsaturation. It can be reversed by screening membrane charge in the presence of calcium ions. We interpret the observed findings in light of theories of stability and curvature generation and discuss mechanisms acting in cells to prevent total membrane collapse upon poration. Enhanced membrane stability is crucial for the success of electroporation-based technologies for cancer treatment and gene transfer.Competing Interest StatementThe authors have declared no competing interest
Search for associations containing young stars (SACY) VII. New stellar and substellar candidate members in the young associations
The young associations offer us one of the best opportunities to study the
properties of young stellar and substellar objects and to directly image
planets thanks to their proximity (200 pc) and age (5-150 Myr).
However, many previous works have been limited to identifying the brighter,
more active members (1 M) owing to photometric survey
sensitivities limiting the detections of lower mass objects. We search the
field of view of 542 previously identified members of the young associations to
identify wide or extremely wide (1000-100,000 au in physical separation)
companions. We combined 2MASS near-infrared photometry (, , ) with
proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the
field of view of known members. We collated further photometry and spectroscopy
from the literature and conducted our own high-resolution spectroscopic
observations for a subsample of candidate members. This complementary
information allowed us to assess the efficiency of our method. We identified 84
targets (45: 0.2-1.3 M, 17: 0.08-0.2 M, 22: 0.08 M)
in our analysis, ten of which have been identified from spectroscopic analysis
in previous young association works. For 33 of these 84, we were able to
further assess their membership using a variety of properties (X-ray emission,
UV excess, H, lithium and K I equivalent widths, radial velocities,
and CaH indices). We derive a success rate of 76-88% for this technique based
on the consistency of these properties. Once confirmed, the targets identified
in this work would significantly improve our knowledge of the lower mass end of
the young associations. Additionally, these targets would make an ideal new
sample for the identification and study of planets around nearby young stars.Comment: 28 pages, 24 figures, accepted in A&
Activity control in nitrifying biofilms: application of respirometric tests
Nitrification is the biological oxidation of ammonia to nitrate via nitrite. These reactions are performed by aerobic autotrophic microorganisms, commonly known as nitrifiers.
The nitrifiers are generally constituted of ammonia oxidizing bacteria and nitrite oxidizing bacteria. They are very sensitive to environmental factors, namely the pH, which has its optimum value in the range of 7.5 to 8.5 (Sharma end Ahlert, 1977)
A simple method, the respiration rate measurement, has been extensively used in literature to characterize microbial populations in suspended cultures (Kristensen et al., 1992, Nowak and Svardal, 1993) and to monitor the nitrification performance of immobilized nitrifiers (Nakamura et al., 1995) and nitrifying activated sludge processes
(Surmacz-Gorska et al., 1996). Respiration refers to reactions that use oxygen as an electron acceptor.
The aim of the present study is to characterize the functional microorganism groups of a nitrifying biofilm using a simple microbial activity measurement, the respiration rate,
and to use this information to identify disturbances that have an impact on process performance
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