113 research outputs found
A wideband low-distortion CMOS current driver for tissue impedance analysis
Bioimpedance measurements are performed in a variety of medical applications including cancer detection in tissue. Such applications require wideband (typically 1 MHz) accurate ac current drivers with high output impedance and low distortion. This paper presents an integrated current driver that fulfills these requirements. The circuit uses negative feedback to accurately set the output current amplitude into the load. It was fabricated in a 0.35- μm complementary metal–oxide–semiconductor (CMOS) process technology, occupies a core area of 0.4 mm, and operates from ±2.5-V power supplies. For a maximum output current of 1mA p-p, the measured total harmonic distortion is below 0.1%, and the variability of the output current with respect to the load is below 0.5% up to 800 kHz increasing to 0.86% at 1 MHz. The current driver was tested for the detection of cancer sites from postoperative human colon specimens. The circuit is intended for use in active electrode applications
Frequency adjustable MEMS vibration energy harvester
Ambient mechanical vibrations offer an attractive solution for powering the wireless sensor nodes of the emerging "Internet-of-Things". However, the wide-ranging variability of the ambient vibration frequencies pose a significant challenge to the efficient transduction of vibration into usable electrical energy. This work reports the development of a MEMS electromagnetic vibration energy harvester where the resonance frequency of the oscillator can be adjusted or tuned to adapt to the ambient vibrational frequency. Micro-fabricated silicon spring and double layer planar micro-coils along with sintered NdFeB micro-magnets are used to construct the electromagnetic transduction mechanism. Furthermore, another NdFeB magnet is adjustably assembled to induce variable magnetic interaction with the transducing magnet, leading to significant change in the spring stiffness and resonance frequency. Finite element analysis and numerical simulations exhibit substantial frequency tuning range (25% of natural resonance frequency) by appropriate adjustment of the repulsive magnetic interaction between the tuning and transducing magnet pair. This demonstrated method of frequency adjustment or tuning have potential applications in other MEMS vibration energy harvesters and micromechanical oscillators
The electric dipole moment of the neutron from twisted mass fermions
We extract the neutron electric dipole moment (nEDM) on configurations produced with twisted mass fermions with
lattice spacing of fm and a light quark mass that corresponds
to MeV. We do so by evaluating the -odd form factor
for small values of the -violation parameter in the limit of
zero momentum transfer. This limit is extracted using the usual parametrization
but in addition position space methods. The topological charge is computed via
cooling and gradient flow using the Wilson, Symanzik tree-level improved and
Iwasaki actions for smoothing. We obtain consistent results for all choices of
smoothing procedures and methods to extract at zero momentum transfer.
For the ensemble analyzed we find a value of nEDM of .Comment: 7 pages, 4 figures, talk presented at the 33rd International
Symposium on Lattice Field Theory, 14 - 18 July 2015, Kobe, Japa
Topological susceptibility from twisted mass fermions using spectral projectors and the gradient flow
We compare lattice QCD determinations of topological susceptibility using a
gluonic definition from the gradient flow and a fermionic definition from the
spectral projector method. We use ensembles with dynamical light, strange and
charm flavors of maximally twisted mass fermions. For both definitions of the
susceptibility we employ ensembles at three values of the lattice spacing and
several quark masses at each spacing. The data are fitted to chiral
perturbation theory predictions with a discretization term to determine the
continuum chiral condensate in the massless limit and estimate the overall
discretization errors. We find that both approaches lead to compatible results
in the continuum limit, but the gluonic ones are much more affected by cut-off
effects. This finally yields a much smaller total error in the spectral
projector results. We show that there exists, in principle, a value of the
spectral cutoff which would completely eliminate discretization effects in the
topological susceptibility.Comment: 18 pages, 19 figure
GPCR receptor phosphorylation and endocytosis are not necessary to switch polarized growth between internal cues during pheromone response in S. cerevisiae
Chemotactic/chemotropic cells follow accurately the direction of gradients of regulatory molecules. Many G-protein-coupled receptors (GPCR) function as chemoattractant receptors to guide polarized responses. In “a” mating type yeast, the GPCR Ste2 senses the α-cell’s pheromone. Previously, phosphorylation and trafficking of this receptor have been implicated in the process of gradient sensing, where cells dynamically correct growth. Correction is often necessary since yeast have intrinsic polarity sites that interfere with a correct initial gradient decoding. We have recently showed that when actively dividing (not in G1) yeast are exposed to a uniform pheromone concentration, they initiate a pheromone-induced polarization next to the mother–daughter cytokinesis site. Then, they reorient their growth to the intrinsic polarity site. Here, to study if Ste2 phosphorylation and internalization are involved in this process, we generated receptor variants combining three types of mutated signals for the first time: phosphorylation, ubiquitylation and the NPFX1,2D Sla1-binding motif. We first characterized their effect on endocytosis and found that these processes regulate internalization in a more complex manner than previously shown. Interestingly, we showed that receptor phosphorylation can drive internalization independently of ubiquitylation and the NPFX1,2D motif. When tested in our assays, cells expressing either phosphorylation or endocytosis-deficient receptors were able to switch away from the cytokinesis site to find the intrinsic polarity site as efficiently as their WT counterparts. Thus, we conclude that these processes are not necessary for the reorientation of polarization.Fil: Vasen, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Dunayevich, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Constantinou, Andreas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Colman Lerner, Alejandro Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin
Cause-and-effect of linear mechanisms sustaining wall turbulence
Despite the nonlinear nature of turbulence, there is evidence that part of
the energy-transfer mechanisms sustaining wall turbulence can be ascribed to
linear processes. The different scenarios stem from linear stability theory and
comprise exponential instabilities, neutral modes, transient growth from
non-normal operators, and parametric instabilities from temporal mean-flow
variations, among others. These mechanisms, each potentially capable of leading
to the observed turbulence structure, are rooted in theoretical and conceptual
arguments. Whether the flow follows any or a combination of them remains
elusive. Here, we evaluate the linear mechanisms responsible for the energy
transfer from the streamwise-averaged mean-flow () to the fluctuating
velocities (). We use cause-and-effect analysis based on interventions.
This is achieved by direct numerical simulation of turbulent channel flows at
low Reynolds number, in which the energy transfer from to is
constrained to preclude a targeted linear mechanism. We show that transient
growth is sufficient for sustaining realistic wall turbulence. Self-sustaining
turbulence persists when exponential instabilities, neutral modes, and
parametric instabilities of the mean flow are suppressed. We further show that
a key component of transient growth is the Orr/push-over mechanism induced by
spanwise variations of the base flow. Finally, we demonstrate that an ensemble
of simulations with various frozen-in-time arranged so that only
transient growth is active, can faithfully represent the energy transfer from
to as in realistic turbulence. Our approach provides direct
cause-and-effect evaluation of the linear energy-injection mechanisms from to in the fully nonlinear system and simplifies the conceptual
model of self-sustaining wall turbulence
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