2,013 research outputs found
Ordering of small particles in one-dimensional coherent structures by time-periodic flows
Small particles transported by a fluid medium do not necessarily have to
follow the flow. We show that for a wide class of time-periodic incompressible
flows inertial particles have a tendency to spontaneously align in
one-dimensional dynamic coherent structures. This effect may take place for
particles so small that often they would be expected to behave as passive
tracers and be used in PIV measurement technique. We link the particle tendency
to form one-dimensional structures to the nonlinear phenomenon of phase
locking. We propose that this general mechanism is, in particular, responsible
for the enigmatic formation of the `particle accumulation structures'
discovered experimentally in thermocapillary flows more than a decade ago and
unexplained until now
Autowaves in a dc complex plasma confined behind a de Laval nozzle
Experiments to explore stability conditions and topology of a dense
microparticle cloud supported against gravity by a gas flow were carried out.
By using a nozzle shaped glass insert within the glass tube of a dc discharge
plasma chamber a weakly ionized gas flow through a de Laval nozzle was
produced. The experiments were performed using neon gas at a pressure of 100 Pa
and melamine-formaldehyde particles with a diameter of 3.43 {\mu}m. The
capturing and stable global confining of the particles behind the nozzle in the
plasma were demonstrated. The particles inside the cloud behaved as a single
convection cell inhomogeneously structured along the nozzle axis in a tube-like
manner. The pulsed acceleration localized in the very head of the cloud
mediated by collective plasma-particle interactions and the resulting wave
pattern were studied in detail.Comment: 6 pages, 4 figure
Measurement of the speed of sound by observation of the Mach cones in a complex plasma under microgravity conditions
We report the first observation of the Mach cones excited by a larger
microparticle (projectile) moving through a cloud of smaller microparticles
(dust) in a complex plasma with neon as a buffer gas under microgravity
conditions. A collective motion of the dust particles occurs as propagation of
the contact discontinuity. The corresponding speed of sound was measured by a
special method of the Mach cone visualization. The measurement results are
incompatible with the theory of ion acoustic waves. The estimate for the
pressure in a strongly coupled Coulomb system and a scaling law for the complex
plasma make it possible to derive an evaluation for the speed of sound, which
is in a reasonable agreement with the experiments in complex plasmas.Comment: 5 pages, 2 figures, 1 tabl
Dynamical mean-field theory of indirect magnetic exchange
To analyze the physical properties arising from indirect magnetic exchange
between several magnetic adatoms and between complex magnetic nanostructures on
metallic surfaces, the real-space extension of dynamical mean-field theory
(R-DMFT) appears attractive as it can be applied to systems of almost arbitrary
geometry and complexity. While R-DMFT describes the Kondo effect of a single
adatom exactly, indirect magnetic (RKKY) exchange is taken into account on an
approximate level only. Here, we consider a simplified model system consisting
of two magnetic Hubbard sites ("adatoms") hybridizing with a non-interacting
tight-binding chain ("substrate surface"). This two-impurity Anderson model
incorporates the competition between the Kondo effect and indirect exchange but
is amenable to an exact numerical solution via the density-matrix
renormalization group (DMRG). The particle-hole symmetric model at half-filling
and zero temperature is used to benchmark R-DMFT results for the magnetic
coupling between the two adatoms and for the magnetic properties induced in the
substrate. In particular, the dependence of the local adatom and the nonlocal
adatom-adatom static susceptibilities as well as the magnetic response of the
substrate on the distance between the adatoms and on the strength of their
coupling with the substrate is studied. We find both, excellent agreement with
the DMRG data even on subtle details of the competition between RKKY exchange
and the Kondo effect but also complete failure of the R-DMFT, depending on the
parameter regime considered. R-DMFT calculations are performed using the
Lanczos method as impurity solver. With the real-space extension of the
two-site DMFT, we also benchmark a simplified R-DMFT variant.Comment: 14 pages, 8 figure
Emotional, cognitive and behavioral self-regulation in forensic psychiatric patients:Changes over time and associations with childhood trauma, identity and personality pathology
The construct of self-regulation is of particular interest to the forensic psychiatric practice due to its associations with both clinical and criminal outcomes, as well as recidivism. However, research on different components of self-regulation within forensic psychiatric practice is rare. The current study aimed to gain knowledge on the construct of self-regulation in a sample of forensic psychiatric patients (N = 94). Firstly, by investigating change of emotional, behavioral and cognitive self-regulation over the course of 12 months in state-mandated care in a treatment facility. Secondly, by looking at the associations between these three elements of self-regulation and childhood trauma, identity dysfunction and personality pathology. Repeated measures ANOVA showed little to no difference in average self-regulation over time (only for behavioral regulation), and rank-order stability was relatively high in most cases. Path analysis showed that: emotion regulation was associated with all outcomes; behavioral regulation with all except childhood trauma and detachment; and cognitive regulation only with antagonism and negative affectivity. Findings suggest short-term changes are unlikely and indicate relative importance of emotional, and to some extent behavioral regulation for clinical practice. However, due to sample size restrictions, interpretations should be made with caution
Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram
Based on the extended Greenwich-NOAA/USAF catalogue of sunspot groups it is
demonstrated that the parameters describing the latitudinal width of the
sunspot generating zone (SGZ) are closely related to the current level of solar
activity, and the growth of the activity leads to the expansion of SGZ. The
ratio of the sunspot number to the width of SGZ shows saturation at a certain
level of the sunspot number, and above this level the increase of the activity
takes place mostly due to the expansion of SGZ. It is shown that the mean
latitudes of sunspots can be reconstructed from the amplitudes of solar
activity. Using the obtained relations and the group sunspot numbers by Hoyt
and Schatten (1998), the latitude distribution of sunspot groups ("the Maunder
butterfly diagram") for the 18th and the first half of the 19th centuries is
reconstructed and compared with historical sunspot observations.Comment: 16 pages, 11 figures; accepted by Solar Physics; the final
publication will be available at www.springerlink.co
Cosmological simulations of mixed ultralight dark matter
The era of precision cosmology allows us to test the composition of the dark
matter. Mixed ultralight or fuzzy dark matter (FDM) is a cosmological model
with dark matter composed of a combination of particles of mass , with an astrophysical de Broglie wavelength, and
particles with a negligible wavelength sharing the properties of cold dark
matter (CDM). In this work, we simulate cosmological volumes with a dark matter
wave function for the ultralight component coupled gravitationally to CDM
particles. We investigate the impact of a mixture of CDM and FDM in various
proportions and for ultralight particle
masses ranging over five orders of magnitude . To track the evolution
of density perturbations in the non-linear regime, we adapt the simulation code
AxioNyx to solve the CDM dynamics coupled to a FDM wave function obeying the
Schr\"odinger-Poisson equations. We obtain the non-linear power spectrum and
study the impact of the wave effects on the growth of structure on different
scales. We confirm that the steady-state solution of the Schr\"odinger-Poisson
system holds at the center of halos in the presence of a CDM component when it
composes or less of the dark matter but find no stable density core when
the FDM accounts for or less of the dark matter. We implement a modified
friends-of-friends halo finder and find good agreement between the observed
halo abundance and the predictions from the adapted halo model axionHMCode.Comment: Added reference
Stress impairs intentional memory control through altered theta oscillations in lateral parietal cortex
Accumulating evidence suggests that forgetting is not necessarily a passive process but that we can, to some extent, actively control what we remember and what we forget. Although this intentional control of memory has potentially far-reaching implications, the factors that influence our capacity to intentionally control our memory are largely unknown. Here, we tested whether acute stress may disrupt the intentional control of memory and, if so, through which neural mechanism. We exposed healthy men and women to a stress (n=27) or control (n=26) procedure before they aimed repeatedly to retrieve some previously learned cue-target pairs and to actively suppress others. While control participants showed reduced memory for supressed compared to baseline pairs in a subsequent memory test, this suppression-induced forgetting was completely abolished after stress. Using magnetoencephalography (MEG), we show that the reduced ability to suppress memories after stress is associated with altered theta activity in the inferior temporal cortex when the control process (retrieval or suppression) is triggered and in the lateral parietal cortex when control is exerted, with the latter being directly correlated with the stress hormone cortisol. Moreover, the suppression-induced forgetting was linked to altered connectivity between the hippocampus and right dorsolateral prefrontal cortex, which in turn was negatively correlated to stress-induced cortisol increases. These findings provide novel insights into conditions under which our capacity to actively control our memory breaks down and may have considerable implications for stress-related psychopathologies, such as posttraumatic stress disorder, that are characterized by unwanted memories of distressing events.Significance Statement: It is typically assumed that forgetting is a passive process that can hardly be controlled. There is, however, evidence that we may actively control, to some extent, what we remember and what we forget. This intentional memory control has considerable implications for mental disorders in which patients suffer from unwanted (e.g., traumatic) memories. Here, we demonstrate that the capacity to intentionally control our memory breaks down after stress. Using magnetoencephalography, we show that this stress-induced memory control deficit is linked to altered activity in the lateral parietal cortex and the connectivity between the hippocampus and right prefrontal cortex. These findings provide novel insights into conditions under which memory control fails and are highly relevant in the context of stress-related psychopathologies
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