Some Remarks on the Question of Charge Densities in Stationary-Current-Carrying Conductors

Recently, some discussions arose as to the definition of charge and the value of the density of charge in stationary-current-carrying conductors. We stress that the problem of charge definition comes from a misunderstanding of the usual definition. We provide some theoretical elements which suggest that positive and negative charge densities are equal in the frame of the positive ions.Comment: 14 pages, TeX, macro newsym.tex include

A Computational Model of Cellular Mechanisms of Temporal Coding in the Medial Geniculate Body (MGB)

Acoustic stimuli are often represented in the early auditory pathway as patterns of neural activity synchronized to time-varying features. This phase-locking predominates until the level of the medial geniculate body (MGB), where previous studies have identified two main, largely segregated response types: Stimulus-synchronized responses faithfully preserve the temporal coding from its afferent inputs, and Non-synchronized responses, which are not phase locked to the inputs, represent changes in temporal modulation by a rate code. The cellular mechanisms underlying this transformation from phase-locked to rate code are not well understood. We use a computational model of a MGB thalamocortical neuron to test the hypothesis that these response classes arise from inferior colliculus (IC) excitatory afferents with divergent properties similar to those observed in brain slice studies. Large-conductance inputs exhibiting synaptic depression preserved input synchrony as short as 12.5 ms interclick intervals, while maintaining low firing rates and low-pass filtering responses. By contrast, small-conductance inputs with Mixed plasticity (depression of AMPA-receptor component and facilitation of NMDA-receptor component) desynchronized afferent inputs, generated a click-rate dependent increase in firing rate, and high-pass filtered the inputs. Synaptic inputs with facilitation often permitted band-pass synchrony along with band-pass rate tuning. These responses could be tuned by changes in membrane potential, strength of the NMDA component, and characteristics of synaptic plasticity. These results demonstrate how the same synchronized input spike trains from the inferior colliculus can be transformed into different representations of temporal modulation by divergent synaptic properties

Plasmon assisted transmission of high dimensional orbital angular momentum entangled state

We present an experimental evidence that high dimensional orbital angular momentum entanglement of a pair of photons can be survived after a photon-plasmon-photon conversion. The information of spatial modes can be coherently transmitted by surface plasmons. This experiment primarily studies the high dimensional entangled systems based on surface plasmon with subwavelength structures. It maybe useful in the investigation of spatial mode properties of surface plasmon assisted transmission through subwavelength hole arrays.Comment: 7 pages,6 figure

Laminar-flow flight experiments

The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time

Fractionation effects in phase equilibria of polydisperse hard sphere colloids

The equilibrium phase behaviour of hard spheres with size polydispersity is studied theoretically. We solve numerically the exact phase equilibrium equations that result from accurate free energy expressions for the fluid and solid phases, while accounting fully for size fractionation between coexisting phases. Fluids up to the largest polydispersities that we can study (around 14%) can phase separate by splitting off a solid with a much narrower size distribution. This shows that experimentally observed terminal polydispersities above which phase separation no longer occurs must be due to non-equilibrium effects. We find no evidence of re-entrant melting; instead, sufficiently compressed solids phase separate into two or more solid phases. Under appropriate conditions, coexistence of multiple solids with a fluid phase is also predicted. The solids have smaller polydispersities than the parent phase as expected, while the reverse is true for the fluid phase, which contains predominantly smaller particles but also residual amounts of the larger ones. The properties of the coexisting phases are studied in detail; mean diameter, polydispersity and volume fraction of the phases all reveal marked fractionation. We also propose a method for constructing quantities that optimally distinguish between the coexisting phases, using Principal Component Analysis in the space of density distributions. We conclude by comparing our predictions to perturbative theories for near-monodisperse systems and to Monte Carlo simulations at imposed chemical potential distribution, and find excellent agreement.Comment: 21 pages, 23 figures, 2 table

Application of asymptotic expansions of maximum likelihood estimators errors to gravitational waves from binary mergers: the single interferometer case

In this paper we describe a new methodology to calculate analytically the error for a maximum likelihood estimate (MLE) for physical parameters from Gravitational wave signals. All the existing litterature focuses on the usage of the Cramer Rao Lower bounds (CRLB) as a mean to approximate the errors for large signal to noise ratios. We show here how the variance and the bias of a MLE estimate can be expressed instead in inverse powers of the signal to noise ratios where the first order in the variance expansion is the CRLB. As an application we compute the second order of the variance and bias for MLE of physical parameters from the inspiral phase of binary mergers and for noises of gravitational wave interferometers . We also compare the improved error estimate with existing numerical estimates. The value of the second order of the variance expansions allows to get error predictions closer to what is observed in numerical simulations. It also predicts correctly the necessary SNR to approximate the error with the CRLB and provides new insight on the relationship between waveform properties SNR and estimation errors. For example the timing match filtering becomes optimal only if the SNR is larger than the kurtosis of the gravitational wave spectrum

A variational method from the variance of energy

A variational method is studied based on the minimum of energy variance. The method is tested on exactly soluble problems in quantum mechanics, and is shown to be a useful tool whenever the properties of states are more relevant than the eigenvalues. In quantum field theory the method provides a consistent second order extension of the gaussian effective potential.Comment: 5 ps figure

Diagnosing students' difficulties in learning mathematics

This study considers the results of a diagnostic test of student difficulty and contrasts the difference in performance between the lower attaining quartile and the higher quartile. It illustrates a difference in qualitative thinking between those who succeed and those who fail in mathematics, illustrating a theory that those who fail are performing a more difficult type of mathematics (coordinating procedures) than those who succeed (manipulating concepts). Students who have to coordinate or reverse processes in time will encounter far greater difficulty than those who can manipulate symbols in a flexible way. The consequences of such a dichotomy and implications for remediation are then considered

The doublecortin-expressing population in the developing and adult brain contains multipotential precursors in addition to neuronal-lineage cells

Doublecortin (DCX) has recently been promulgated as a selective marker of cells committed to the neuronal lineage in both the developing and the adult brain. To explore the potential of DCX-positive (DCX+) cells more stringently, these cells were isolated by flow cytometry from the brains of transgenic mice expressing green fluorescent protein under the control of the DCX promoter in embryonic, early postnatal, and adult animals. It was found that virtually all of the cells (99.9%) expressing high levels of DCX (DCXhigh) in the embryonic brain coexpressed the neuronal marker ßIII-tubulin and that this population contained no stem-like cells as demonstrated by lack of neurosphere formation in vitro. However, the DCX+ population from the early postnatal brain and the adult subventricular zone and hippocampus, which expressed low levels of DCX (DCXlow), was enriched for neurosphere-forming cells, with only a small subpopulation of these cells coexpressing the neuronal markers ßIII-tubulin or microtubule-associated protein 2. Similarly, the DCXlow population from embryonic day 14 (E14) brain contained neurosphere-forming cells. Only the postnatal cerebellum and adult olfactory bulb contained some DCXhigh cells, which were shown to be similar to the E14 DCXhigh cells in that they had no stem cell activity. Electrophysiological studies confirmed the heterogeneous nature of DCX+ cells, with some cells displaying characteristics of immature or mature neurons, whereas others showed no neuronal characteristics whatsoever. These results indicate that DCXhigh cells, regardless of location, are restricted to the neuronal lineage or are bone fide neurons, whereas some DCXlow cells retain their multipotentiality