Motional Broadening in Ensembles With Heavy-Tail Frequency Distribution

We show that the spectrum of an ensemble of two-level systems can be broadened through `resetting' discrete fluctuations, in contrast to the well-known motional-narrowing effect. We establish that the condition for the onset of motional broadening is that the ensemble frequency distribution has heavy tails with a diverging first moment. We find that the asymptotic motional-broadened lineshape is a Lorentzian, and derive an expression for its width. We explain why motional broadening persists up to some fluctuation rate, even when there is a physical upper cutoff to the frequency distribution.Comment: 6 pages, 4 figure

Ramsey-like measurement of the decoherence rate between Zeeman sub-levels

Two-photon processes that involve different sub-levels of the ground state of an atom, are highly sensitive to depopulation and decoherence within the ground state. For example, the spectral width of electromagnetically induced transparency resonances in $\Lambda-$type system, are strongly affected by the ground state depopulation and decoherence rates. We present a direct measurement of decay rates between hyperfine and Zeeman sub-levels in the ground state of $^{87}$Rb vapor. Similar to the relaxation-in-the-dark technique, pumping lasers are used to pre-align the atomic vapor in a well defined quantum state. The free propagation of the atomic state is monitored using a Ramsey-like method. Coherence times in the range 1-10 ms were measured for room temperature atomic vapor. In the range of the experimental parameters used in this study, the dominant process inducing Zeeman decoherence is the spin-exchange collisions between rubidium atoms.Comment: 7 pages, 7 figure

Antigen and Thapsigargin Promote Influx of Ca2+ in Rat Basophilic RBL-2H3 Cells by Ostensibly Similar Mechanisms That Allow Filling of Inositol 1,4,5-Trisphosphate-Sensitive and Mitochondrial Ca2+ Stores

In single, Fura 2-loaded RBL-2H3 cells, antigen and thapsigargin depleted the same intracellular pool of Ca2+ in the absence of external Ca2+; provision of external Ca2+ induced immediate increases in levels of free Ca2+ ([Ca2+](i)). These increases were dependent on the presence of external Ca2+ and, presumably, on influx of Ca2+ across the cell membrane. Both stimulants enhanced intracellular accumulation of 45Ca2+ through ostensibly similar mechanisms because accumulation was blocked to similar extents by various multivalent cations or by depolarization with K+. Because thapsigargin blocked reuptake of Ca2+ into inositol 1,4,5-trisphosphate sensitive stores, uptake occurred independently of the refilling of these stores. Uptake was dependent instead on sequestration of 45Ca2+ in a pool of high capacity that was insensitive to thapsigargin, caffeine, GTP and inositol 1,4,5-trisphosphate but sensitive to ionomycin and mitochondrial inhibitors. The existence of an inositol 1,4,5-trisphosphate-insensitive pool was also apparent in permeabilized cells; at 0.1 μM [Ca2+](i), uptake of 45Ca2+ was largely confined (\u3e 80%) to the inositol 1,4,5-trisphosphate-sensitive pool, but at 2 μM [Ca2+](i) uptake was largely (\u3e 60%) into the inositol 1,4,5-trisphosphate-insensitive pool. Provision of mitochondrial inhibitors along with thapsigargin to block uptake into both pools, did not impair the thapsigargin-induced increase in [Ca2+](i) or influx of Ca2+, as indicated by changes in Fura 2 fluorescence, but did block the intracellular accumulation of 45Ca2+. The studies illustrate the utility of simultaneous measurements of [Ca2+](i) and 45Ca2+ uptake for a full accounting of Ca2+ homoeostasis as exemplified by the ability to distinguish between influx and mitochondrial uptake of Ca2+

Order-by-disorder in the antiferromagnetic Ising model on an elastic triangular lattice

Geometrically frustrated materials have a ground-state degeneracy that may be lifted by subtle effects, such as higher order interactions causing small energetic preferences for ordered structures. Alternatively, ordering may result from entropic differences between configurations in an effect termed order-by-disorder. Motivated by recent experiments in a frustrated colloidal system in which ordering is suspected to result from entropy, we consider in this paper, the antiferromagnetic Ising model on a deformable triangular lattice. We calculate the displacements exactly at the microscopic level, and contrary to previous studies, find a partially disordered ground state of randomly zigzagging stripes. Each such configuration is deformed differently and thus has a unique phonon spectrum with distinct entropy, thus lifting the degeneracy at finite temperature. Nonetheless, due to the free-energy barriers between the ground-state configurations, the system falls into a disordered glassy state.Comment: Accepted to PNA

Supply chain optimisation of pyrolysis plant deployment using goal programming

This paper presents a goal programming model to optimise the deployment of pyrolysis plants in Punjab, India. Punjab has an abundance of waste straw and pyrolysis can convert this waste into alternative bio-fuels, which will facilitate the provision of valuable energy services and reduce open field burning. A goal programming model is outlined and demonstrated in two case study applications: small scale operations in villages and large scale deployment across Punjab's districts. To design the supply chain, optimal decisions for location, size and number of plants, downstream energy applications and feedstocks processed are simultaneously made based on stakeholder requirements for capital cost, payback period and production cost of bio-oil and electricity. The model comprises quantitative data obtained from primary research and qualitative data gathered from farmers and potential investors. The Punjab district of Fatehgarh Sahib is found to be the ideal location to initially utilise pyrolysis technology. We conclude that goal programming is an improved method over more conventional methods used in the literature for project planning in the field of bio-energy. The model and findings developed from this study will be particularly valuable to investors, plant developers and municipalities interested in waste to energy in India and elsewhere

Low temperature spin diffusion in the one-dimensional quantum O(3)O(3) nonlinear σ\sigma-model

An effective, low temperature, classical model for spin transport in the one-dimensional, gapped, quantum $O(3)$ non-linear $\sigma$-model is developed. Its correlators are obtained by a mapping to a model solved earlier by Jepsen. We obtain universal functions for the ballistic-to-diffusive crossover and the value of the spin diffusion constant, and these are claimed to be exact at low temperatures. Implications for experiments on one-dimensional insulators with a spin gap are noted.Comment: 4 pages including 3 eps-figures, Revte

Staggered-spin contribution to nuclear spin-lattice relaxation in two-leg antiferromagnetic spin-1/2 ladders

We study the nuclear spin-lattice relaxation rate $1/T_1$ in the two-leg antiferromagnetic spin-1/2 Heisenberg ladder. More specifically, we consider the contribution to $1/T_1$ from the processes with momentum transfer $(\pi,\pi)$. In the limit of weak coupling between the two chains, this contribution is of activation type with gap $2\Delta$ at low temperatures ($\Delta$ is the spin gap), but crosses over to a slowly-decaying temperature dependence at the crossover temperature $T\approx\Delta$. This crossover possibly explains the recent high-temperature NMR results on ladder-containing cuprates by T. Imai et al.Comment: 6 pages, 2 figures, REVTeX, uses eps

Bannayan Ruvalcaba Riley Syndrome

A 63-year-old male with history of prostate cancer treated with radiation presented for a colonoscopy for small volume hematochezia. The colonoscopy revealed numerous polyps, which were found to be ganglioneuromas on histological examination. He was referred to medical genetics with suspicion for hamartomatous polyposis syndrome and was found to have a mutation in the PTEN gene. Based on this and suggestive clinical findings, he was diagnosed with Bannayan Ruvalcaba Riley syndrome