6,178 research outputs found
Responses and receptive fields of amacrine cells and ganglion cells in the salamander retina
AbstractRetinal amacrine cells (ACs) and ganglion cells (GCs) have been shown to display large morphological diversity, and here we show that four types of ACs and three types of GCs exhibit physiologically-distinguishable properties. They are the sustained ON ACs; sustained OFF ACs; transient ON–OFF ACs; transient ON–OFF ACs with wide receptive fields; sustained ON-center/OFF-surround GCs; sustained OFF-center/ON-surround GCs and transient ON–OFF GCs. By comparing response waveforms, receptive fields and relative rod/cone inputs of ACs and GCs with the corresponding parameters of various types of the presynaptic bipolar cells (BCs), we analyze how different types of BCs mediate synaptic inputs to various ACs and GCs. Although more types of third-order retinal neurons may be identified by more refined classification criteria, our observations suggest that many morphologically-distinct ACs and GCs share very similar physiological responses
Probing short-range magnetic order in a geometrically frustrated magnet by spin Seebeck effect
Competing magnetic interactions in geometrically frustrated magnets give rise
to new forms of correlated matter, such as spin liquids and spin ices.
Characterizing the magnetic structure of these states has been difficult due to
the absence of long-range order. Here, we demonstrate that the spin Seebeck
effect (SSE) is a sensitive probe of magnetic short-range order (SRO) in
geometrically frustrated magnets. In low temperature (2 - 5 K) SSE measurements
on a model frustrated magnet \mathrm{Gd_{3}Ga_{5}O_{12}}, we observe
modulations in the spin current on top of a smooth background. By comparing to
existing neutron diffraction data, we find that these modulations arise from
field-induced magnetic ordering that is short-range in nature. The observed SRO
is anisotropic with the direction of applied field, which is verified by
theoretical calculation.Comment: 5 pages, 4 figure
Cross-talk between ON and OFF channels in the salamander retina: Indirect bipolar cell inputs to ON–OFF ganglion cells
AbstractIt has been widely accepted that ON and OFF channels in the visual system are segregated with little cross-communication, except for the mammalian rod bipolar cell-AII amacrine cell-ganglion cell pathway. Here, we show that in the tiger salamander retina the light responses of a subpopulation of ON–OFF ganglion cells are mediated by crossing the ON and OFF bipolar cell pathways. Although the majority of ON–OFF ganglion cells (type I cells) receive direct excitatory inputs from depolarizing and hyperpolarizing bipolar cells (DBCs and HBCs), about 5% (type II cells) receive indirect excitatory inputs from DBCs and 20% (type III cells) receive indirect excitatory inputs from HBCs. These indirect bipolar cell inputs are likely to be mediated by a subpopulation of amacrine cells that exhibit transient hyperpolarizing light responses (ACHs) and make GABAergic/glycinergic synapses on DBC or HBC axon terminals. GABA and glycine receptor antagonists enhanced the ON and OFF excitatory cation current (ΔIC) in type I ganglion cells, but completely suppressed the ON ΔIC mediated by DBCs in type II cells and the OFF ΔIC mediated by HBCs in types III cells. Dendrites of type I cells ramify in both sublamina A and B, type II cells exclusively in sublamina A, and type III cells exclusively in sublamina B of the inner plexiform layer. These results demonstrate that indirect, amacrine cell-mediated bipolar cell-ganglion cell synaptic pathways exist in a non-mammalian retina, and that bidirectional cross-talk between ON and OFF channels is present in the vertebrate retina
Antiferromagnetic spin Seebeck Effect
We report on the observation of the spin Seebeck effect in antiferromagnetic
MnF. A device scale on-chip heater is deposited on a bilayer of Pt (4
nm)/MnF (110) (30 nm) grown by molecular beam epitaxy on a MgF (110)
substrate. Using Pt as a spin detector layer it is possible to measure
thermally generated spin current from MnF through the inverse spin Hall
effect. The low temperature (2 - 80 K) and high magnetic field (up to 140 kOe)
regime is explored. A clear spin flop transition corresponding to the sudden
rotation of antiferromagnetic spins out of the easy axis is observed in the
spin Seebeck signal when large magnetic fields (>9 T) are applied parallel the
easy axis of the MnF thin film. When magnetic field is applied
perpendicular to the easy axis, the spin flop transition is absent, as
expected
Numerical Evidence that the Perturbation Expansion for a Non-Hermitian -Symmetric Hamiltonian is Stieltjes
Recently, several studies of non-Hermitian Hamiltonians having
symmetry have been conducted. Most striking about these complex Hamiltonians is
how closely their properties resemble those of conventional Hermitian
Hamiltonians. This paper presents further evidence of the similarity of these
Hamiltonians to Hermitian Hamiltonians by examining the summation of the
divergent weak-coupling perturbation series for the ground-state energy of the
-symmetric Hamiltonian recently
studied by Bender and Dunne. For this purpose the first 193 (nonzero)
coefficients of the Rayleigh-Schr\"odinger perturbation series in powers of
for the ground-state energy were calculated. Pad\'e-summation and
Pad\'e-prediction techniques recently described by Weniger are applied to this
perturbation series. The qualitative features of the results obtained in this
way are indistinguishable from those obtained in the case of the perturbation
series for the quartic anharmonic oscillator, which is known to be a Stieltjes
series.Comment: 20 pages, 0 figure
The Transcription Factor Bhlhb4 Is Required for Rod Bipolar Cell Maturation
AbstractRetinal bipolar cells are essential to the transmission of light information. Although bipolar cell dysfunction can result in blindness, little is known about the factors required for bipolar cell development and functional maturation. The basic helix-loop-helix (bHLH) transcription factor Bhlhb4 was found to be expressed in rod bipolar cells (RB). Electroretinograms (ERGs) in the adult Bhlhb4 knockout (Bhlhb4−/−) showed that the loss of Bhlhb4 resulted in disrupted rod signaling and profound retinal dysfunction resembling human congenital stationary night blindness (CSNB), characterized by the loss of the scotopic ERG b-wave. A depletion of inner nuclear layer (INL) cells in the adult Bhlhb4 knockout has been ascribed to the abolishment of the RB cell population during postnatal development. Other retinal cell populations including photoreceptors were unaltered. The timing of RB cell depletion in the Bhlhb4−/− mouse suggests that Bhlhb4 is essential for RB cell maturation
Effect of interchain coupling on conducting polymer luminescence: excimers in derivatives of poly(phenylene vinylene)
Optical excitation of a chain in a polymer film may result in formation of an
excimer, a superposition of on-chain excitons and charge-transfer excitons on
the originally excited chain and a neighboring chain. The excimer emission is
red-shifted compared to that of an on-chain exciton by an amount depending on
the interchain coupling . Setting up the excimer wavefunction and
calculating the red shift, we determine average values, referred to a
monomer, of 0.52 eV and 0.16 eV for poly(2,5-hexyloxy -phenylene
cyanovinylene), CN-PPV, and poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-1, 4
p-phenylene vinylene], MEH-PPV, respectively, and use them to determine the
effect of interchain distance on the emission.Comment: 10 pages, RevTeX, 1 PS figure, replaced version of cond-mat/9707095,
accepted for publication in Phys. Rev. B, Rapid Communicatio
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