189 research outputs found
Evidence for a Fractional Quantum Hall Nematic State in Parallel Magnetic Fields
We report magneto-transport measurements for the fractional quantum Hall
state at filling factor 5/2 as a function of applied parallel magnetic
field (). As is increased, the 5/2 state becomes increasingly
anisotropic, with the in-plane resistance along the direction of
becoming more than 30 times larger than in the perpendicular direction.
Remarkably, the resistance anisotropy ratio remains constant over a relatively
large temperature range, yielding an energy gap which is the same for both
directions. Our data are qualitatively consistent with a fractional quantum
Hall \textit{nematic} phase
Observation of An Anisotropic Wigner Crystal
We report a new correlated phase of two-dimensional charged carriers in high
magnetic fields, manifested by an anisotropic insulating behavior at low
temperatures. It appears near Landau level filling factor in hole
systems confined to wide GaAs quantum wells when the sample is tilted in
magnetic field to an intermediate angle. The parallel field component
() leads to a crossing of the lowest two Landau levels, and an
elongated hole wavefunction in the direction of . Under these
conditions, the in-plane resistance exhibits an insulating behavior, with the
resistance along more than 10 times smaller than the resistance
perpendicular to . We interpret this anisotropic insulating phase as a
two-component, striped Wigner crystal
Multicomponent fractional quantum Hall states with subband and spin degrees of freedom
In wide GaAs quantum wells where two electric subbands are occupied we apply
a parallel magnetic field or increase the electron density to cause a crossing
of the two Landau levels of these subbands and with opposite spins. Near
the crossing, the fractional quantum Hall states in the filling factor range
exhibit a remarkable sequence of pseudospin polarization transitions
resulting from the interplay between the spin and subband degrees of freedom.
The field positions of the transitions yield a new and quantitative measure of
the composite Fermions' discrete energy level separations. Surprisingly, the
separations are smaller when the electrons have higher spin-polarization
Anisotropic composite fermions and fractional quantum Hall effect
We study the role of anisotropy on the transport properties of composite
fermions near Landau level filling factor in two-dimensional holes
confined to a GaAs quantum well. By applying a parallel magnetic field, we tune
the composite fermion Fermi sea anisotropy and monitor the relative change of
the transport scattering time at along the principal directions.
Interpreted in a simple Drude model, our results suggest that the scattering
time is longer along the longitudinal direction of the composite fermion Fermi
sea. Furthermore, the measured energy gap for the fractional quantum Hall state
at decreases when anisotropy becomes significant. The decrease,
however, might partly stem from the charge distribution becoming bilayer-like
at very large parallel magnetic fields
Family Minds: A randomized controlled trial of a group intervention to improve foster parents’ reflective functioning
Family Minds is a brief group psychoeducational parenting intervention designed to increase the reflective functioning (RF) and mentalization skills of foster parents. RF is important for foster parents who have to build relationships with children whose adverse experiences increase their risk for psychosocial challenges. A randomized controlled trial (RCT) for Family Minds was conducted in Texas with 89 foster parents. The main aims of this study were to examine whether the intervention could significantly increase the RF/mentalization skills of the foster parents and decrease their parenting stress. After 6 weeks, compared with the control group, intervention foster parents improved their RF via a lowering of pre-mentalizing and also significantly decreased parenting stress related to parent–child dysfunctional interactions. Other measures of RF and parenting stress showed no significant differences between groups. Foster child behavior was not significantly different between groups, although data at 6 months showed a possible lowering of internalizing symptoms for children of intervention parents. This RCT provides some encouraging evidence that Family Minds may increase RF in foster parents, improve parental sensitivity and their ability to emotionally regulate, decrease parenting stress related to challenging interactions with their foster children, and possibly decrease children's internalizing behavior
Spin-Polarization of Composite Fermions and Particle-Hole Symmetry Breaking
We study the critical spin-polarization energy () above which
fractional quantum Hall states in two-dimensional electron systems confined to
symmetric GaAs quantum wells become fully spin-polarized. We find a significant
decrease of as we increase the well-width. In systems with
comparable electron layer thickness, for fractional states
near Landau level filling is about twice larger than those near
, suggesting a broken particle-hole symmetry. Theoretical
calculations, which incorporate Landau level mixing through an effective
three-body interaction, and finite layer thickness, capture certain qualitative
features of the experimental results
Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing
The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D)
charged particles at high magnetic fields, is one of the most fascinating,
macroscopic manifestations of a many-body state stabilized by the strong
Coulomb interaction. It occurs when the filling factor () of the quantized
Landau levels (LLs) is a fraction which, with very few exceptions, has an odd
denominator. In 2D systems with additional degrees of freedom it is possible to
cause a crossing of the LLs at the Fermi level. At and near these crossings,
the FQHE states are often weakened or destroyed. Here we report the observation
of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility
GaAs 2D systems which brings to life a new \emph{even-denominator} FQHE
at
The porin and the permeating antibiotic: A selective diffusion barrier in gram-negative bacteria
Gram-negative bacteria are responsible for a large proportion of antibiotic resistant bacterial diseases. These bacteria have a complex cell envelope that comprises an outer membrane and an inner membrane that delimit the periplasm. The outer membrane contains various protein channels, called porins, which are involved in the influx of various compounds, including several classes of antibiotics. Bacterial adaptation to reduce influx through porins is an increasing problem worldwide that contributes, together with efflux systems, to the emergence and dissemination of antibiotic resistance. An exciting challenge is to decipher the genetic and molecular basis of membrane impermeability as a bacterial resistance mechanism. This Review outlines the bacterial response towards antibiotic stress on altered membrane permeability and discusses recent advances in molecular approaches that are improving our knowledge of the physico-chemical parameters that govern the translocation of antibiotics through porin channel
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The role of ubiquitination and hepatocyte growth factor-regulated tyrosine kinase substrate in the degradation of the adrenomedullin type I receptor
Calcitonin receptor-like receptor (CLR) and the receptor activity-modifying protein 2 (RAMP2) comprise a receptor for adrenomedullin (AM). Although it is known that AM induces internalization of CLR•RAMP2, little is known about the molecular mechanisms that regulate the trafficking of CLR•RAMP2. Using HEK and HMEC-1 cells, we observed that AM-induced activation of CLR•RAMP2 promoted ubiquitination of CLR. A mutant (CLRΔ9KR), lacking all intracellular lysine residues was functional and trafficked similar to the wild-type receptor, but was not ubiquitinated. Degradation of CLR•RAMP2 and CLRΔ9KR•RAMP2 was not dependent on the duration of AM stimulation or ubiquitination and occurred via a mechanism that was partially prevented by peptidase inhibitors. Degradation of CLR•RAMP2 was sensitive to overexpression of hepatocyte growth factor-regulated tyrosine kinase substrate (HRS), but not to HRS knockdown, whereas CLRΔ9KR•RAMP2 degradation was unaffected. Overexpression, but not knockdown of HRS, promoted hyperubiquitination of CLR under basal conditions. Thus, we propose a role for ubiquitin and HRS in the regulation of AM-induced degradation of CLR•RAMP2
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