1/f Noise in Electron Glasses

We show that 1/f noise is produced in a 3D electron glass by charge fluctuations due to electrons hopping between isolated sites and a percolating network at low temperatures. The low frequency noise spectrum goes as \omega^{-\alpha} with \alpha slightly larger than 1. This result together with the temperature dependence of \alpha and the noise amplitude are in good agreement with the recent experiments. These results hold true both with a flat, noninteracting density of states and with a density of states that includes Coulomb interactions. In the latter case, the density of states has a Coulomb gap that fills in with increasing temperature. For a large Coulomb gap width, this density of states gives a dc conductivity with a hopping exponent of approximately 0.75 which has been observed in recent experiments. For a small Coulomb gap width, the hopping exponent approximately 0.5.Comment: 8 pages, Latex, 6 encapsulated postscript figures, to be published in Phys. Rev.

Quasiballistic correction to the density of states in three-dimensional metal

We study the exchange correction to the density of states in the three-dimensional metal near the Fermi energy. In the ballistic limit, when the distance to the Fermi level exceeds the inverse transport relaxation time $1/\tau$, we find the correction linear in the distance from the Fermi level. By a large parameter $\epsilon_{\rm F} \tau$ this ballistic correction exceeds the diffusive correction obtained earlier.Comment: 2 pages, 1 figur

1/f1/f noise in variable range hopping conduction

A mechanism of $1/f$ noise due to traps formed by impurities which have no neighbors with close energies in their vicinity is studied. Such traps slowly exchange electrons with the rest of conducting media. The concentration of traps and proportional to it $1/f$ noise exponentially grow with decreasing temperature in the variable range hopping regime. This theory provides smooth transition to the nearest neighbor hopping case where it predicts a very weak temperature dependence

Macroscopic and microscopic variation in recovered magnesium phosphate materials: Implications for phosphorus removal processes and product re-use

Phosphorus (P) recovery and re-use will become increasingly important for water quality protection and sustainable nutrient cycling as environmental regulations become stricter and global P reserves decline. The objective of this study was to examine and characterize several magnesium phosphates recovered from actual wastewater under field conditions. Three types of particles were examined including crystalline magnesium ammonium phosphate hexahydrate (struvite) recovered from dairy wastewater, crystalline magnesium ammonium phosphate hydrate (dittmarite) recovered from a food processing facility, and a heterogeneous product also recovered from dairy wastewater. The particles were analyzed using ‘‘wet” chemical techniques, powder X-ray diffraction (XRD), and scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy (SEM–EDS). The struvite crystals had regular and consistent shape, size, and structure, and SEM–EDS analysis clearly showed the struvite crystals as a surface precipitate on calcium phosphate seed material. In contrast, the dittmarite crystals showed no evidence of seed material, and were not regular in size or shape. The XRD analysis identified no crystalline magnesium phosphates in the heterogeneous product and indicated the presence of sand particles. However, magnesium phosphate precipitates on calcium phosphate seed material were observed in this product under SEM–EDS examination. These substantial variations in the macroscopic and microscopic characteristics of magnesium phosphates recovered under field conditions could affect their potential for beneficial re-use and underscore the need to develop recovery processes that result in a uniform, consistent product

Young star clusters in M31

In our study of M31's globular cluster system with MMT/Hectospec, we have obtained high-quality spectra of 85 clusters with ages less than 1 Gyr. With the exception of Hubble V, the young cluster in NGC 205, we find that these young clusters have kinematics and spatial distribution consistent with membership in M31's young disk. Preliminary estimates of the cluster masses and structural parameters, using spectroscopically derived ages and HST imaging, confirms earlier suggestions that M31 has clusters similar to the LMC's young populous clusters.Comment: 4 pages, 1 figure, contributed talk at "Galaxies in the Local Volume" conference in Sydney, July 200

On the flow-level stability of data networks without congestion control: the case of linear networks and upstream trees

In this paper, flow models of networks without congestion control are considered. Users generate data transfers according to some Poisson processes and transmit corresponding packet at a fixed rate equal to their access rate until the entire document is received at the destination; some erasure codes are used to make the transmission robust to packet losses. We study the stability of the stochastic process representing the number of active flows in two particular cases: linear networks and upstream trees. For the case of linear networks, we notably use fluid limits and an interesting phenomenon of "time scale separation" occurs. Bounds on the stability region of linear networks are given. For the case of upstream trees, underlying monotonic properties are used. Finally, the asymptotic stability of those processes is analyzed when the access rate of the users decreases to 0. An appropriate scaling is introduced and used to prove that the stability region of those networks is asymptotically maximized

Non-Equilibrium Statistical Physics of Currents in Queuing Networks

We consider a stable open queuing network as a steady non-equilibrium system of interacting particles. The network is completely specified by its underlying graphical structure, type of interaction at each node, and the Markovian transition rates between nodes. For such systems, we ask the question ``What is the most likely way for large currents to accumulate over time in a network ?'', where time is large compared to the system correlation time scale. We identify two interesting regimes. In the first regime, in which the accumulation of currents over time exceeds the expected value by a small to moderate amount (moderate large deviation), we find that the large-deviation distribution of currents is universal (independent of the interaction details), and there is no long-time and averaged over time accumulation of particles (condensation) at any nodes. In the second regime, in which the accumulation of currents over time exceeds the expected value by a large amount (severe large deviation), we find that the large-deviation current distribution is sensitive to interaction details, and there is a long-time accumulation of particles (condensation) at some nodes. The transition between the two regimes can be described as a dynamical second order phase transition. We illustrate these ideas using the simple, yet non-trivial, example of a single node with feedback.Comment: 26 pages, 5 figure

Coulomb gap in a model with finite charge transfer energy

The Coulomb gap in a donor-acceptor model with finite charge transfer energy $\Delta$ describing the electronic system on the dielectric side of the metal-insulator transition is investigated by means of computer simulations on two- and three-dimensional finite samples with a random distribution of equal amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry of the model presented with respect to the exchange of donors and acceptors are derived. In the immediate neighborhood of the Fermi energy $\mu$ the the density of one-electron excitations $g(\epsilon)$ is determined solely by finite size effects and $g(\epsilon)$ further away from $\mu$ is described by an asymmetric power law with a non-universal exponent, depending on the parameter $\Delta$.Comment: 10 pages, 6 figures, submitted to Phys. Rev.

Electrical transport studies of quench condensed Bi films at the initial stage of film growth: Structural transition and the possible formation of electron droplets

The electrical transport properties of amorphous Bi films prepared by sequential quench deposition have been studied in situ. A superconductor-insulator (S-I) transition was observed as the film was made increasingly thicker, consistent with previous studies. Unexpected behavior was found at the initial stage of film growth, a regime not explored in detail prior to the present work. As the temperature was lowered, a positive temperature coefficient of resistance (dR/dT > 0) emerged, with the resistance reaching a minimum before the dR/dT became negative again. This behavior was accompanied by a non-linear and asymmetric I-V characteristic. As the film became thicker, conventional variable-range hopping (VRH) was recovered. We attribute the observed crossover in the electrical transport properties to an amorphous to granular structural transition. The positive dR/dT found in the amorphous phase of Bi formed at the initial stage of film growth was qualitatively explained by the formation of metallic droplets within the electron glass.Comment: 7 pages, 6 figure

Antihypertensive drug concentration measurement combined with personalized feedback in resistant hypertension:a randomized controlled trial

Background:Adherence to antihypertensive drugs (AHDs) is crucial for controlling blood pressure (BP). We aimed to determine the effectiveness of measuring AHD concentrations using a dried blood spot (DBS) sampling method to identify nonadherence, combined with personalized feedback, in reducing resistant hypertension.Methods:We conducted a multicenter, randomized, controlled trial (RHYME-RCT, ICTRP NTR6914) in patients with established resistant hypertension. Patients were randomized to receive either an intervention with standard of care (SoC) or SoC alone. SoC consisted of BP measurement and DBS sampling at baseline, 3 months (t3), 6 months (t6), and 12 months (t12); AHD concentrations were measured but not reported in this arm. In the intervention arm, results on AHD concentrations were discussed during a personalized feedback conversation at baseline and t3. Study endpoints included the proportion of patients with RH and AHD adherence at t12.Results:Forty-nine patients were randomized to receive the intervention+SoC, and 51 were randomized to receive SoC alone. The proportion of adherent patients improved from 70.0 to 92.5% in the intervention+SoC arm (P = 0.008, n = 40) and remained the same in the SoC arm (71.4%, n = 42). The difference in adherence between the arms was statistically significant (P = 0.014). The prevalence of resistant hypertension decreased to 75.0% in the intervention+SoC arm (P &lt; 0.001, n = 40) and 59.5% in the SoC arm (P &lt; 0.001, n = 42) at t12; the difference between the arms was statistically nonsignificant (P = 0.14).Conclusion:Personalized feedback conversations based on DBS-derived AHD concentrations improved AHD adherence but did not reduce the prevalence of RH.</p