4,929 research outputs found
Concurrent investigation of global motion and form processing in amblyopia: an equivalent noise approach
PURPOSE: Directly comparing the motion and form processing in neurologic disorders has remained difficult due to the limitations in the experimental stimulus. In the current study, motion and form processing in amblyopia was characterized using random dot stimuli in different noise levels to parse out the effect of local and global processing on motion and form perception. METHODS: A total of 17 amblyopes (8 anisometropic and 9 strabismic), and 12 visually normal subjects monocularly estimated the global direction of motion and global orientation in random dot kinematograms (RDK) and Glass patterns (Glass), whose directions/orientations were drawn from normal distributions with a range of means and variances that served as external noise. Direction/orientation discrimination thresholds were measured without noise first then variance threshold was measured at the multiples of the direction/orientation threshold. The direction/orientation and variance thresholds were modelled to estimate internal noise and sampling efficiency parameters. RESULTS: Overall, the thresholds for Glass were higher than RDK for all subjects. The thresholds for both Glass and RDK were higher in the strabismic eyes compared with the fellow and normal eyes. On the other hand, the thresholds for anisometropic amblyopic eyes were similar to the normal eyes. The worse performance of strabismic amblyopes was best explained by relatively low sampling efficiency compared with other groups (P < 0.05). CONCLUSIONS: A deficit in global motion and form perception was only evident in strabismic amblyopia. Contrary to the dorsal stream deficiency hypothesis assumed in other developmental disorders, deficits were present in both motion (dorsal) and form (ventral) processing
Charge-Focusing Readout of Time Projection Chambers
Time projection chambers (TPCs) have found a wide range of applications in
particle physics, nuclear physics, and homeland security. For TPCs with
high-resolution readout, the readout electronics often dominate the price of
the final detector. We have developed a novel method which could be used to
build large-scale detectors while limiting the necessary readout area. By
focusing the drift charge with static electric fields, we would allow a small
area of electronics to be sensitive to particle detection for a much larger
detector volume. The resulting cost reduction could be important in areas of
research which demand large-scale detectors, including dark matter searches and
detection of special nuclear material. We present simulations made using the
software package Garfield of a focusing structure to be used with a prototype
TPC with pixel readout. This design should enable significant focusing while
retaining directional sensitivity to incoming particles. We also present first
experimental results and compare them with simulation.Comment: 5 pages, 17 figures, Presented at IEEE Nuclear Science Symposium 201
Synthesis and Micellar Characterization of CBABC Type PLGA-PEO-PPO-PEO-PLGA Pentablock Copolymers
Poly(lactic-co-glycolic acid) (PLGA) were grafted to both ends of Pluronic (R) F68 ((EO)(75)(PO)(30)(EO)(75)) triblock copolymer to produce poly {(lactic acid)(m)-co-(glycolic acid)(n)}-b-poly(ethylene oxide)(75)-b-poly(propylene oxide)(30)-b-poly(ethylene oxide)(75)-b-poly{(lactic acid)(m)-co-(glycolic acid)(n)} (PLGA-F68-PLGA) pentablock copolymers. Molecular weights of PLGA blocks were controlled and five kinds of pentablock copolymers with different PLGA block lengths were synthesized using in-situ ring-opening polymerization of D,L-lactide and glycolide with tin(II) 2-ethylhexanoate (Sn(Oct)(2)) catalyst. PLGA-F68-PLGA pentablock copolymers were characterized by H-1- and C-13-NMR, GPC, and TGA. The numbers (2m, 2n) of repeating units for lactic acid and glycolic acid inside PLGA segments were obtained as (48, 17), (90, 23), (125, 40), (180, 59), and (246, 64), with H-1-NMR measurement. From NMR data, the resultant molecular weights were determined in the range of 12,700-29,700, which were similar to those obtained from GPC. Polydispersity index was increased in the range of 1.32-1.91 as the content of PLGA blocks increased. TG and DTG thermograms showed discrete degradation traces for PLGA and F68 blocks, which indicate the weight fractions of PLGA blocks in pentablock copolymers can be calculated by TO profile and it is possible to remove PLGA block selectively. Hydrodynamic radius and radius of gyration of pentablock copolymer micelle were obtained in the range of 46-68 nm and 31-49 nm, respectively, in very dilute (i.e. 0.005 wt %) aqueous solution of THF:H2O = 10:90 by volume at 25 degrees C.X1121Ysciescopu
The Dynamical Behaviors in (2+1)-Dimensional Gross-Neveu Model with a Thirring Interaction
We analyze (2+1)-dimensional Gross-Neveu model with a Thirring interaction,
where a vector-vector type four-fermi interaction is on equal terms with a
scalar-scalar type one. The Dyson-Schwinger equation for fermion self-energy
function is constructed up to next-to-leading order in 1/N expansion. We
determine the critical surface which is the boundary between a broken phase and
an unbroken one in () space. It is observed that the
critical behavior is mainly controlled by Gross-Neveu coupling and
the region of the broken phase is separated into two parts by the line
. The mass function is strongly
dependent upon the flavor number N for , while weakly for
, the critical flavor number
increases as Thirring coupling decreases. By driving the CJT
effective potential, we show that the broken phase is energetically preferred
to the symmetric one. We discuss the gauge dependence of the mass function and
the ultra-violet property of the composite operators.Comment: 19 pages, LaTex, 6 ps figure files(uuencoded in seperate file
Non-Drude Optical Conductivity of (III,Mn)V Ferromagnetic Semiconductors
We present a numerical model study of the zero-temperature infrared optical
properties of (III,Mn)V diluted magnetic semiconductors. Our calculations
demonstrate the importance of treating disorder and interaction effects
simultaneously in modelling these materials. We find that the conductivity has
no clear Drude peak, that it has a broadened inter-band peak near 220 meV, and
that oscillator weight is shifted to higher frequencies by stronger disorder.
These results are in good qualitative agreement with recent thin film
absorption measurements. We use our numerical findings to discuss the use of
f-sum rules evaluated by integrating optical absorption data for accurate
carrier-density estimates.Comment: 7 pages, 3 figure
High-Temperature Hall Effect in Ga(1-x)Mn(x)As
The temperature dependence of the Hall coefficient of a series of
ferromagnetic Ga(1-x)Mn(x)As samples is measured in the temperature range 80K <
T < 500K. We model the Hall coefficient assuming a magnetic susceptibility
given by the Curie-Weiss law, a spontaneous Hall coefficient proportional to
rho_xx^2(T), and including a constant diamagnetic contribution in the
susceptibility. For all low resistivity samples this model provides excellent
fits to the measured data up to T=380K and allows extraction of the hole
concentration (p). The calculated p are compared to alternative methods of
determining hole densities in these materials: pulsed high magnetic field (up
to 55 Tesla) technique at low temperatures (less than the Curie temperature),
and electrochemical capacitance- voltage profiling. We find that the Anomalous
Hall Effect (AHE) contribution to rho_xy is substantial even well above the
Curie temperature. Measurements of the Hall effect in this temperature regime
can be used as a testing ground for theoretical descriptions of transport in
these materials. We find that our data are consistent with recently published
theories of the AHE, but they are inconsistent with theoretical models
previously used to describe the AHE in conventional magnetic materials.Comment: 6 pages, 5 figures, 1 table. Accepted to Phys.Rev.
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