Coulomb-induced positive current-current correlations in normal conductors

In the white-noise limit current correlations measured at different contacts of a mesoscopic conductor are negative due to the antisymmetry of the wave function (Pauli principle). We show that current fluctuations at capacitive contacts induced via the long range Coulomb interaction due to charge fluctuations in the mesoscopic sample can be positively correlated. The positive correlations are a consequence of the extension of the wave functions into areas near both contacts. As an example we investigate in detail a quantum point contact in a high magnetic field under conditions in which transport is along an edge state.     

Interaural time and amplitude discrimination in noise

Just-noticeable differences (jnds) of both interaural time delay (ITD) and interaural intensity difference (IID) were measured for binaural tones in the presence of broadband maskers. The tones were presented at 50 dB SPL, the target frequency was 500 Hz, and the masker frequency was 100-1000 Hz, with various combinations of ITD and IID. The time and amplitude jnds exhibit similar dependencies on target-to-masker ratio and masker type. At a given target-to-masker ratio, discrimination was generally best in the presence of diotic maskers and worst in the presence of the interaurally out-of-phase maskers. Results for the other masker types examined tended to fall in between these two extremes. Many of these data trends are consistent with predictions of the lateralization model and the position-variable model based on auditory-nerve activity.     

Positive and negative Hanbury-Brown and Twiss correlations in normal metal-superconducting devices

In the light of the recent analogs of the Hanbury-Brown and Twiss experiments [1] in mesoscopic beam splitters, negative current noise correlations are recalled to be the consequence of an exclusion principle. Here, positive (bosonic) correlations are shown to exist in a fermionic system, composed of a superconductor connected to two normal reservoirs. In the Andreev regime, the correlations can either be positive or negative depending on the reflection coefficient of the beam splitter. For biases beyond the gap, the transmission of quasiparticles favors fermionic correlations. The presence of disorder enhances positive noise correlations. Potential experimental applications are discussed. Received 1 June 1999     

Inducing odd-frequency triplet superconducting correlations in a normal metal

This work discusses theoretically the interplay between the superconducting and ferromagnetic proximity effects, in a diffusive normal metal strip in contact with a superconductor and a nonuniformly magnetized ferromagnetic insulator. The quasiparticle density of states of the normal metal shows clear qualitative signatures of triplet correlations with spin one (TCS1). When one goes away from the superconducting contact, TCS1 focus at zero energy under the form of a peak surrounded by dips, which show a typical spatial scaling behavior. This effect can coexist with a focusing of singlet correlations and triplet correlations with spin zero at finite but subgap energies. The simultaneous observation of both effects would enable an unambiguous characterization of TCS1.     

Interaural fluctuations and the detection of interaural incoherence: bandwidth effects

One-hundred left-right noise-pairs were generated, all with a fixed value of long-term interaural coherence, 0.9922. The noises had a center frequency of 500 Hz, a bandwidth of 14 Hz, and a duration of 500 ms. Listeners were required to discriminate between these slightly incoherent noises and diotic noises, with a coherence of 1.0. It was found that the value of interaural coherence itself was an inadequate predictor of discrimination. Instead, incoherence was much more readily detected for those noise-pairs with the largest fluctuations in interaural phase or level differences (as measured by the standard deviations). One-hundred noise-pairs with the same value of coherence, 0.9922, and geometric mean frequency of 500 Hz were also generated for bandwidths of 108 and 2394 Hz. It was found that for increasing bandwidth, fluctuations in interaural differences varied less between different noise-pairs and that detection performance varied less as well. The results suggest that incoherence detection is based on the size of interaural fluctuations and that the value of coherence itself predicts performance only in the wideband limit.     

Photon path length distribution in random media from spectral speckle intensity correlations

We show that the spectral speckle intensity correlation (SSIC) technique can be profitably exploited to recover the path length distribution of photons scattered in a random turbid medium. We applied SSIC to the study of Teflon slabs of different thicknesses and were able to recover, via the use of the photon diffusion approximation theory, the characteristic transport mean free path ℓ^∗ and absorption length s _a of the medium. These results were compared and validated by means of complementary measurements performed on the same samples with standard pulsed laser time of flight techniques.     

Purity loss and degradation of qubit-field correlations and entanglement due to phase noise in nonlinear interaction

Numerical simulations and calculation of both the total entropy and the sub-entropies are used to investigate the purity loss in nonlinear interaction of a qubit with coherent field. While, the mutual entropy is used as a measure of the total correlations and the negativity as a measure to the entanglement. We show that the purity and entanglement behave different for standard energy dissipation as compared to an energy preserving phase noise coupling as introduced by Milburn. It is found that a very strong sensitivity of the degradation both total correlation with entanglement to the amount of phase damping and the chosen coupling. In particular for a coherent initial field state the maximum obtainable correlation is strongly reduced even for very weak noise.     

Dimensionless heat transfer correlations for estimating edge heat loss in a flat plate absorber

Data obtained from heat transfer relations discretized with the finite element method were used in developing dimensionless correlations, which led to determining prediction equations for the average edge temperature of a flat plate absorber. For a prescribed flux, if parameters like the incident radiation intensity, edge insulation thermal conductivity and ambient temperature are known, the value of the edge temperature variable is immediately determined. A range of edge-to-absorptive area ratios is considered, as well as the effects of the edge insulation on enhancing thermal performance. Notably, the edge loss is high in absorbers with high edge-to-absorptive area ratios and ambient conditions with low h _a and T _a . In extreme operating conditions, however, the loss can be employed of a high proportion. As a result, prediction equations are obtained, which can be employed in design and simulation so as to minimize useful energy losses and thereby improve efficiency.     

Apparent correlations between the static length of relaxation and the linear size of dynamic heterogeneity in fragile liquids

The most puzzling aspect of the glass transition observed in laboratory is the decoupling of the dynamics from the structure. As an attempt to reconcile the dynamic and the static lengthscales associated with the glass problem, we discuss the apparent correlations between the static relaxation length, defined as that lengthscale over which the potential energy fluctuation is correlated, with the linear size of the dynamic heterogeneity. The dynamic heterogeneous domains with long life-times, may therefore be linked to the droplets of low potential energy, or the tightly bound regions inside the liquid.     

Interference correlations of pions and elementary cell of phase space

The amplitude-symmetrization procedure employed in studying interference correlations of identical pions is shown to be always valid only within one elementary cell 2π? of phase space—that is, within one period of the interference cosine. However, this limitation does not lead to far-reaching consequences in using the interference method to determine the spacetime dimensions of the pion generation volume.     

Clinical correlations: MRI and EEG

Main structural correlates of epileptogenesis include hippocampal sclerosis, cortical dysgenesis, foreign tissue lesions, gliosis, and dual pathology (a combination of any two). These structural abnormalities are now increasingly defined with MRI, enabling systematic EEG correlative analyses. Hippocampal atrophy (HA) and increased T₂ signal in medial temporal structures predict the presence of mesial temporal sclerosis with a high degree of sensitivity and specificity. In 50 patients with clinical evidence of temporal lobe epilepsy and isolated HA, ictal scalp EEG was concordant to the atrophic temporal lobe in 33, nonlateralizing in 12, obscured in 3, and bilateral in 2, but it was discordant in none. Earlier reports of higher levels of discordance may be ascribed to the presence of dual pathology or to differing MRI and EEG criteria for localization. In a more inclusive group of 101 patients with unilateral HA, ictal scalp EEG was obtained in 99. It was unlocalized in 53, localized elsewhere in 9, and localized to the atrophic temporal lobe in 38. Of those, 51 patients had intracranial EEG: 12 were unlocalized, 29 were localized to the atrophic hippocampus, and 9 were localized elsewhere. There is thus a rare but definite subgroup of patients with unilateral HA who have EEG localization elsewhere than the atrophy. The successful cure of seizures in half these patients after removal of the EEG focus confirms the importance of this observation and emphasizes the search for more dual pathology that has remained undetected on MRI. About 10% of the patients with HA have significant atrophy bilaterally, and several series have confirmed that surgical success is predicted by removal of the EEG identified seizure onset area, not the more or less atrophic hippocampus. In patients with other kinds of dual pathology, including HA and foreign tissue lesions or cortical dysgenesis, EEG is also paramount in predicting the site of epileptogenesis for surgical intervention. EEG correlates of cortical dysgenesis are heterogeneous, but EEG has potential to provide accurate localization of the site of epileptogenesis in foreign tissue lesions also. In a study of 59 lesional patients, a small number of patients with low grade astrocytomas and oligodendrogliomas consistently localized by EEG to an area elsewhere than the lesion, and failed seizure control when the lesion was removed. Although MRI can demonstrate the structural correlate of the epilepsy in many situations, rare patients, particularly with certain tumors, cortical dysgenesis, and dual pathology, require EEG for accurate localization.     

Determination of Ca,Fe, Cu and Zn and their correlations in breast cancer and normal adjacent tissues

An experimental procedure using monoenergetic Synchrotron Radiation x‐ray Fluorescence (SR‐XRF) method was studied, justified and applied to determine trace elements concentrations of normal and neoplastic human breast tissues in the same individual. Scattered radiation from each sample was used as an internal standard in x‐ray emission spectroscopy in order to construct calibration curves used to determine Ca, Fe, Cu and Zn concentrations in 52 breast tissue specimens (26 neoplastic and 26 adjacent normal tissues). This work showed that this experimental alternative is approximately matrix independent and also allows a reduction in instrumental variables. Our results showed, as expected, that Ca, Fe, Cu and Zn concentrations levels were significantly higher in neoplastic than in healthy breast tissues (all p < 0.001). It was also observed that Fe and Cu levels are correlated in malignant breast tissues as well as Ca and Zn levels, indicating that these elements' concentrations are related, in agreement with the hypothesis that there is a connection between Fe and Cu with both increased cellular activity and blood supply in the formation of neoplasies in breast tissue, and between Ca and Zn as regulators of neoplasies growth, since these metals are present in active matrix metalloproteinases (MMPs). Copyright © 2008 John Wiley & Sons, Ltd.     

Forward- and simultaneous-masked thresholds in bandlimited maskers in subjects with normal hearing and cochlear hearing loss

Forward- and simultaneous-masked thresholds were measured at 0.5 and 2.0 kHz in bandpass maskers as a function of masker bandwidth and in a broadband masker with the goal of estimating psychophysical suppression. Suppression was operationally defined in two ways: (1) as a change in forward-masked threshold as a function of masker bandwidth, and (2) as a change in effective masker level with increased masker bandwidth, taking into account the nonlinear growth of forward masking. Subjects were younger adults with normal hearing and older adults with cochlear hearing loss. Thresholds decreased as a function of masker bandwidth in forward masking, which was attributed to effects of suppression; thresholds remained constant or increased slightly with increasing masker bandwidth in simultaneous masking. For subjects with normal hearing, slightly larger estimates of suppression were obtained at 2.0 kHz rather than at 0.5 kHz. For hearing-impaired subjects, suppression was reduced in regions of hearing loss. The magnitude of suppression was strongly correlated with the absolute threshold at the signal frequency, but did not vary with thresholds at frequencies remote from the signal. The results suggest that measuring forward-masked thresholds in bandlimited and broadband maskers may be an efficient psychophysical method for estimating suppression.     

Perception of dissonance by people with normal hearing and sensorineural hearing loss

The purpose of this study was to determine whether the perceived sensory dissonance of pairs of pure tones (PT dyads) or pairs of harmonic complex tones (HC dyads) is altered due to sensorineural hearing loss. Four normal-hearing (NH) and four hearing-impaired (HI) listeners judged the sensory dissonance of PT dyads geometrically centered at 500 and 2000 Hz, and of HC dyads with fundamental frequencies geometrically centered at 500 Hz. The frequency separation of the members of the dyads varied from 0 Hz to just over an octave. In addition, frequency selectivity was assessed at 500 and 2000 Hz for each listener. Maximum dissonance was perceived at frequency separations smaller than the auditory filter bandwidth for both groups of listners, but maximum dissonance for HI listeners occurred at a greater proportion of their bandwidths at 500 Hz than at 2000 Hz. Further, their auditory filter bandwidths at 500 Hz were significantly wider than those of the NH listeners. For both the PT and HC dyads, curves displaying dissonance as a function of frequency separation were more compressed for the HI listeners, possibly reflecting less contrast between their perceptions of consonance and dissonance compared with the NH listeners.     

Communication activity in social networks: growth and correlations

We investigate the timing of messages sent in two online communities with respect to growth fluctuations and long-term correlations. We find that the timing of sending and receiving messages comprises pronounced long-term persistence. Considering the activity of the community members as growing entities, i.e. the cumulative number of messages sent (or received) by the individuals, we identify non-trivial scaling in the growth fluctuations which we relate to the long-term correlations. We find a connection between the scaling exponents of the growth and the long-term correlations which is supported by numerical simulations based on peaks over threshold. In addition, we find that the activity on directed links between pairs of members exhibits long-term correlations, indicating that communication activity with the most liked partners may be responsible for the long-term persistence in the timing of messages. Finally, we show that the number of messages, M, and the number of communication partners, K, of the individual members are correlated following a power-law, K ~ M ^λ , with exponent λ ≈ 3 / 4.     

Fluctuations and correlations in STAR

The study of correlations and fluctuations can provide evidence for the production of the quark-gluon plasma (QGP) in relativistic heavy-ion collisions. Various theories predict that the production of a QGP phase in relativistic heavy-ion collisions could produce significant event-by-event correlations and fluctuations in transverse momentum, multiplicity, etc. Some of the recent results using STAR at RHIC will be presented along with results from other experiments at RHIC. The focus is on forward-backward multiplicity correlations, balance function, charge and transverse-momentum fluctuations, and correlations.