Rodent Control on Poultry Farms.

4 p

Keys to Profitable Management of Broiler Breeders.

4 p

Tuning the Correlation Decay in the Resistance Fluctuations of Multi-Species Networks

A new network model is proposed to describe the $1/f^\alpha$ resistance noise in disordered materials for a wide range of $\alpha$ values ($0< \alpha < 2$). More precisely, we have considered the resistance fluctuations of a thin resistor with granular structure in different stationary states: from nearly equilibrium up to far from equilibrium conditions. This system has been modelled as a network made by different species of resistors, distinguished by their resistances, temperature coefficients and by the energies associated with thermally activated processes of breaking and recovery. The correlation behavior of the resistance fluctuations is analyzed as a function of the temperature and applied current, in both the frequency and time domains. For the noise frequency exponent, the model provides $0< \alpha < 1$ at low currents, in the Ohmic regime, with $\alpha$ decreasing inversely with the temperature, and $1< \alpha <2$ at high currents, in the non-Ohmic regime. Since the threshold current associated with the onset of nonlinearity also depends on the temperature, the proposed model qualitatively accounts for the complicate behavior of $\alpha$ versus temperature and current observed in many experiments. Correspondingly, in the time domain, the auto-correlation function of the resistance fluctuations displays a variety of behaviors which are tuned by the external conditions.Comment: 26 pages, 16 figures, Submitted to JSTAT - Special issue SigmaPhi200

Low-frequency Current Fluctuations in Individual Semiconducting Single-Wall Carbon Nanotubes

We present a systematic study on low-frequency current fluctuations of nano-devices consisting of one single semiconducting nanotube, which exhibit significant 1/f-type noise. By examining devices with different switching mechanisms, carrier types (electrons vs. holes), and channel lengths, we show that the 1/f fluctuation level in semiconducting nanotubes is correlated to the total number of transport carriers present in the system. However, the 1/f noise level per carrier is not larger than that of most bulk conventional semiconductors, e.g. Si. The pronounced noise level observed in nanotube devices simply reflects on the small number of carriers involved in transport. These results not only provide the basis to quantify the noise behavior in a one-dimensional transport system, but also suggest a valuable way to characterize low-dimensional nanostructures based on the 1/f fluctuation phenomenon

Long-range potential fluctuations and 1/f noise in hydrogenated amorphous silicon

We present a microscopic theory of the low-frequency voltage noise (known as "1/f" noise) in micrometer-thick films of hydrogenated amorphous silicon. This theory traces the noise back to the long-range fluctuations of the Coulomb potential produced by deep defects, thereby predicting the absolute noise intensity as a function of the distribution of defect activation energies. The predictions of this theory are in very good agreement with our own experiments in terms of both the absolute intensity and the temperature dependence of the noise spectra.Comment: 8 pages, 3 figures, several new parts and one new figure are added, but no conceptual revision

Strong Suppression of Electrical Noise in Bilayer Graphene Nano Devices

Low-frequency 1/f noise is ubiquitous, and dominates the signal-to-noise performance in nanodevices. Here we investigate the noise characteristics of single-layer and bilayer graphene nano-devices, and uncover an unexpected 1/f noise behavior for bilayer devices. Graphene is a single layer of graphite, where carbon atoms form a 2D honeycomb lattice. Despite the similar composition, bilayer graphene (two graphene monolayers stacked in the natural graphite order) is a distinct 2D system with a different band structure and electrical properties. In graphene monolayers, the 1/f noise is found to follow Hooge's empirical relation with a noise parameter comparable to that of bulk semiconductors. However, this 1/f noise is strongly suppressed in bilayer graphene devices, and exhibits an unusual dependence on the carrier density, different from most other materials. The unexpected noise behavior in graphene bilayers is associated with its unique band structure that varies with the charge distribution among the two layers, resulting in an effective screening of potential fluctuations due to external impurity charges. The findings here point to exciting opportunities for graphene bilayers in low-noise applications

Data-Driven Definitions for Active and Structural MRI Lesions in the Sacroiliac Joint in Spondyloarthritis and their Predictive Utility

OBJECTIVES: To determine quantitative sacroiliac joint (SIJ) MRI lesion cut-offs that optimally define a positive MRI for inflammatory and structural lesions typical of axial spondyloarthritis (axSpA) and that predict clinical diagnosis. METHODS: The ASAS MRI group assessed MRIs from the ASAS Classification Cohort in two reading exercises: A. 169 cases and 7 central readers; B. 107 cases and 8 central readers. We calculated sensitivity/specificity for the number of SIJ quadrants or slices with bone marrow edema (BME), erosion, fat lesion, where a majority of central readers had high confidence there was a definite active or structural lesion. Cut-offs with ≥95% specificity were analyzed for their predictive utility for follow-up rheumatologist diagnosis of axSpA by calculating positive/negative predictive values (PPV/NPV) and selecting cut-offs with PPV≥95%. RESULTS: Active or structural lesions typical of axSpA on MRI had PPV≥95% for clinical diagnosis of axSpA. Cut-offs that best reflect definite active lesion typical of axSpA were either ≥4 SIJ quadrants with BME at any location or at the same location in ≥ 3 consecutive slices. For definite structural lesion, the optimal cut-offs were any one of ≥ 3 SIJ quadrants with erosion or ≥ 5 with fat lesion, erosion at the same location for ≥2 consecutive slices, fat lesion at the same location for ≥3 consecutive slices, or presence of a 'deep' (>1cm) fat lesion. CONCLUSION: We propose cut-offs for definite active and structural lesions typical of axSpA that have high PPV for a long-term clinical diagnosis of axSpA for application in disease classification and clinical research