38,428 research outputs found
Microbial Load Monitor
The Microbial Load Monitor (MLM) is an automated and computerized system for detection and identification of microorganisms. Additionally, the system is designed to enumerate and provide antimicrobic susceptibility profiles for medically significant bacteria. The system is designed to accomplish these tasks in a time of 13 hours or less versus the traditional time of 24 hours for negatives and 72 hours or more for positives usually required for standard microbiological analysis. The MLM concept differs from other methods of microbial detection in that the system is designed to accept raw untreated clinical samples and to selectively identify each group or species that may be present in a polymicrobic sample
Holographic tracking and sizing of optically trapped microprobes in diamond anvil cells
We demonstrate that Digital Holographic Microscopy can be used for accurate 3D tracking and sizing of a colloidal probe trapped in a diamond anvil cell (DAC). Polystyrene beads were optically trapped in water up to Gigapascal pressures while simultaneously recording in-line holograms at 1 KHz frame rate. Using Lorenz-Mie scattering theory to fit interference patterns, we detected a 10% shrinking in the bead’s radius due to the high applied pressure. Accurate bead sizing is crucial for obtaining reliable viscosity measurements and provides a convenient optical tool for the determination of the bulk modulus of probe material. Our technique may provide a new method for pressure measurements inside a DAC
When is an error not a prediction error? An electrophysiological investigation
A recent theory holds that the anterior cingulate cortex (ACC) uses reinforcement learning signals conveyed by the midbrain dopamine system to facilitate flexible action selection. According to this position, the impact of reward prediction error signals on ACC modulates the amplitude of a component of the event-related brain potential called the error-related negativity (ERN). The theory predicts that ERN amplitude is monotonically related to the expectedness of the event: It is larger for unexpected outcomes than for expected outcomes. However, a recent failure to confirm this prediction has called the theory into question. In the present article, we investigated this discrepancy in three trial-and-error learning experiments. All three experiments provided support for the theory, but the effect sizes were largest when an optimal response strategy could actually be learned. This observation suggests that ACC utilizes dopamine reward prediction error signals for adaptive decision making when the optimal behavior is, in fact, learnable
X-raying the Winds of Luminous Active Galaxies
We briefly describe some recent observational results, mainly at X-ray
wavelengths, on the winds of luminous active galactic nuclei (AGNs). These
winds likely play a significant role in galaxy feedback. Topics covered include
(1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL)
and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3)
Evidence for relativistic iron K BALs in the X-ray spectra of a few bright
quasars. We also mention some key outstanding problems and prospects for future
advances; e.g., with the International X-ray Observatory (IXO).Comment: 7 pages, 3 figures, to appear in proceedings of the conference "The
Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June
2009, Madison, Wisconsi
Increasing trap stiffness with position clamping in holographic optical tweezers
We present a holographic optical tweezers system capable of position clamping multiple particles. Moving an optical trap in response to the trapped object's motion is a powerful technique for optical control and force measurement. We have now realised this experimentally using a Boulder Nonlinear Systems Spatial Light Modulator (SLM) with a refresh rate of 203Hz. We obtain a reduction of 44% in the variance of the bead's position, corresponding to an increase in effective trap stiffness of 77%. This reduction relies on the generation of holograms at high speed. We present software capable of calculating holograms in under 1ms using a graphics processor unit. © 2009 Optical Society of America
Gravitational hydrodynamics of large scale structure formation
The gravitational hydrodynamics of the primordial plasma with neutrino hot
dark matter is considered as a challenge to the bottom-up cold dark matter
paradigm. Viscosity and turbulence induce a top-down fragmentation scenario
before and at decoupling. The first step is the creation of voids in the
plasma, which expand to 37 Mpc on the average now. The remaining matter clumps
turn into galaxy clusters. Turbulence produced at expanding void boundaries
causes a linear morphology of 3 kpc fragmenting protogalaxies along vortex
lines. At decoupling galaxies and proto-globular star clusters arise; the
latter constitute the galactic dark matter halos and consist themselves of
earth-mass H-He planets. Frozen planets are observed in microlensing and
white-dwarf-heated ones in planetary nebulae. The approach also explains the
Tully-Fisher and Faber-Jackson relations, and cosmic microwave temperature
fluctuations of micro-Kelvins.Comment: 6 pages, no figure
Crystal Structure and Chemistry of Topological Insulators
Topological surface states, a new kind of electronic state of matter, have
recently been observed on the cleaved surfaces of crystals of a handful of
small band gap semiconductors. The underlying chemical factors that enable
these states are crystal symmetry, the presence of strong spin orbit coupling,
and an inversion of the energies of the bulk electronic states that normally
contribute to the valence and conduction bands. The goals of this review are to
briefly introduce the physics of topological insulators to a chemical audience
and to describe the chemistry, defect chemistry, and crystal structures of the
compounds in this emergent field.Comment: Submitted to Journal of Materials Chemistry, 47 double spaced pages,
9 figure
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