1,149 research outputs found
Maxwell stress in fluid mixtures
We examine the structure of Maxwell stress in binary fluid mixtures under an
external electric field and discuss its consequence. In particular, we show
that, in immiscible blends, it is intimately related to the statistics of
domain structure. This leads to a compact formula, which may be useful in the
investigation of electro-rheological effects in such systems. The stress tensor
calculated in a phase separated fluid under a steady electric field is in a
good agreement with recent experiments.Comment: 5 page
Kaon Distribution Amplitude from QCD Sum Rules
We present a new calculation of the first Gegenbauer moment of the
kaon light-cone distribution amplitude. This moment is determined by the
difference between the average momenta of strange and nonstrange valence quarks
in the kaon. To calculate , QCD sum rule for the diagonal correlation
function of local and nonlocal axial-vector currents is used. Contributions of
condensates up to dimension six are taken into account, including
-corrections to the quark-condensate term. We obtain
, differing by the sign and magnitude from the recent
sum-rule estimate from the nondiagonal correlation function of pseudoscalar and
axial-vector currents. We argue that the nondiagonal sum rule is numerically
not reliable. Furthermore, an independent indication for a positive is
given, based on the matching of two different light-cone sum rules for the
form factor. With the new interval of we update our previous
numerical predictions for SU(3)-violating effects in form
factors and charmless (B) decays.Comment: a comment and a reference added, version to appear in Phys.Rev.D, 17
pages, 7 figure
Binding Mechanisms in Visual Perception and Their Link With Neural Oscillations: A Review of Evidence From tACS
Neurophysiological studies in humans employing magneto- (MEG) and electro- (EEG) encephalography increasingly suggest that oscillatory rhythmic activity of the brain may be a core mechanism for binding sensory information across space, time, and object features to generate a unified perceptual representation. To distinguish whether oscillatory activity is causally related to binding processes or whether, on the contrary, it is a mere epiphenomenon, one possibility is to employ neuromodulatory techniques such as transcranial alternating current stimulation (tACS). tACS has seen a rising interest due to its ability to modulate brain oscillations in a frequency-dependent manner. In the present review, we critically summarize current tACS evidence for a causal role of oscillatory activity in spatial, temporal, and feature binding in the context of visual perception. For temporal binding, the emerging picture supports a causal link with the power and the frequency of occipital alpha rhythms (8–12 Hz); however, there is no consistent evidence on the causal role of the phase of occipital tACS. For feature binding, the only study available showed a modulation by occipital alpha tACS. The majority of studies that successfully modulated oscillatory activity and behavioral performance in spatial binding targeted parietal areas, with the main rhythms causally linked being the theta (~7 Hz) and beta (~18 Hz) frequency bands. On the other hand, spatio-temporal binding has been directly modulated by parieto-occipital gamma (~40–60 Hz) and alpha (10 Hz) tACS, suggesting a potential role of cross-frequency coupling when binding across space and time. Nonetheless, negative or partial results have also been observed, suggesting methodological limitations that should be addressed in future research. Overall, the emerging picture seems to support a causal role of brain oscillations in binding processes and, consequently, a certain degree of plasticity for shaping binding mechanisms in visual perception, which, if proved to have long lasting effects, can find applications in different clinical populations
Nonlinear dynamics of the interface of dielectric liquids in a strong electric field: Reduced equations of motion
The evolution of the interface between two ideal dielectric liquids in a
strong vertical electric field is studied. It is found that a particular flow
regime, for which the velocity potential and the electric field potential are
linearly dependent functions, is possible if the ratio of the permittivities of
liquids is inversely proportional to the ratio of their densities. The
corresponding reduced equations for interface motion are derived. In the limit
of small density ratio, these equations coincide with the well-known equations
describing the Laplacian growth.Comment: 10 page
Acceptance and commitment therapy for women diagnosed with binge eating disorder: A case-series study.
Binge eating disorder (BED) is an eating disorder marked by a recurrence of eating unusually large amounts of food in one sitting along with feeling a loss of control over eating and experiencing marked distress. Outcomes from two adult women with BED who voluntarily participated in 10 weekly sessions of Acceptance and Commitment Therapy are presented. Binge eating was self-monitored daily prior to and throughout treatment. The average frequency of weekly binge eating across both participants at pre-treatment was 5.7 times, which decreased to 2.5 per week at post-treatment, and 1.0 per week at follow-up. The improvements were particularly significant for Participant 1, who no longer met criteria for BED at post-treatment and follow-up. Similarly, both participants demonstrated improvements in body image flexibility throughout the course of study. A discussion of the results is presented along with implications for clinical practice and future directions in research
Cold Helium Pressurization for Liquid Oxygen / Liquid Methane Propulsion Systems: Fully-Integrated Initial Hot-Fire Test Results
A prototype cold helium active pressurization system was incorporated into an existing liquid oxygen (LOX) / liquid methane (LCH4) prototype planetary lander and hot-fire tested to collect vehicle-level performance data. Results from this hot-fire test series were used to validate integrated models of the vehicle helium and propulsion systems and demonstrate system effectiveness for a throttling lander. Pressurization systems vary greatly in complexity and efficiency between vehicles, so a pressurization performance metric was also developed as a means to compare different active pressurization schemes. This implementation of an active repress system is an initial sizing draft. Refined implementations will be tested in the future, improving the general knowledge base for a cryogenic lander-based cold helium system
In-depth description of Electrohydrodynamic conduction pumping of dielectric liquids: physical model and regime analysis
In this work, we discuss the fundamental aspects of Electrohydrodynamic (EHD) conduction pumping of dielectric liquids. We build a mathematical model of conduction pumping that can be applied to all sizes, down to microsized pumps. In order to do this, we discuss the relevance of the Electrical Double Layer (EDL) that appears naturally on nonmetallic substrates. In the process, we identify a new dimensionless parameter related to the value of the zeta potential of the substrate-liquid pair, which quantifies the influence of these EDLs on the performance of the pump. This parameter also describes the transition from EHD conduction pumping to electro-osmosis. We also discuss in detail the two limiting working regimes in EHD conduction pumping: ohmic and saturation. We introduce a new dimensionless parameter, accounting for the electric field enhanced dissociation that, along with the conduction number, allows us to identify in which regime the pump operates.Ministerio de Ciencia, Innovación y Universidades PGC2018-099217-B-I0
Interaction imaging with amplitude-dependence force spectroscopy
Knowledge of surface forces is the key to understanding a large number of
processes in fields ranging from physics to material science and biology. The
most common method to study surfaces is dynamic atomic force microscopy (AFM).
Dynamic AFM has been enormously successful in imaging surface topography, even
to atomic resolution, but the force between the AFM tip and the surface remains
unknown during imaging. Here, we present a new approach that combines high
accuracy force measurements and high resolution scanning. The method, called
amplitude-dependence force spectroscopy (ADFS) is based on the
amplitude-dependence of the cantilever's response near resonance and allows for
separate determination of both conservative and dissipative tip-surface
interactions. We use ADFS to quantitatively study and map the nano-mechanical
interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is
compatible with commercial atomic force microscopes and we anticipate its
wide-spread use in taking AFM toward quantitative microscopy
Annihilation effects in from QCD Light-Cone Sum Rules
Using the method of QCD light-cone sum rules, we calculate the
hadronic matrix elements with annihilation topology. We obtain a finite result,
including the related strong phase. Numerically, the annihilation effects in
turn out to be small with respect to the factorizable emission
mechanism. Our predictions, together with the earlier sum rule estimates of
emission and penguin contributions, are used for the phenomenological analysis
of channels. We predict a transition amplitude
which significantly differs from this amplitude extracted from the current
data.Comment: two references added, a few misprints corrected, 38 pages, 29 figure
- …