Using auxiliary gas power for CCS energy needs in retrofitted coal power plants

Adding post-combustion capture technology to existing coal-fired power plants is being considered as a near-term option for mitigating CO[subscript 2] emissions. To supply the thermal energy needed for CO[subscript 2] capture, much of the literature proposes thermal integration of the existing coal plant’s steam cycle with the capture process’ stripper reboiler. This paper examines the option of using an auxiliary natural gas turbine plant to meet the energetic demands of carbon capture and compression. Three different auxiliary plant technologies were compared to integration for 90% capture from an existing, 500 MW supercritical coal plant. CO[subscript 2] capture (via a monoethylamine (MEA) absorption process) and compression is simulated using Aspen Plus. Thermoflow software is used to simulate three gas plant technologies. In some circumstances, it is found that using an auxiliary natural gas turbine may make retrofits more attractive compared to using thermal integration. The most important factors affecting desirability of the auxiliary plant retrofit are the cost of natural gas, the full cost of integration, and the potential for sale of excess electricity.Research Council of Norway (Statoil (Firm: Norway)Massachusetts Institute of Technology. Carbon Sequestration Initiativ

Acute knockdown of Kv4.1 regulates repetitive firing rates and clock gene expression in the suprachiasmatic nucleus and daily rhythms in locomotor behavior

AbstractRapidly activating and inactivating A-type K+currents (IA) encoded by Kv4.2 and Kv4.3 pore-forming (α) subunits of the Kv4 subfamily are key regulators of neuronal excitability. Previous studies have suggested a role for Kv4.1 α-subunits in regulating the firing properties of mouse suprachiasmatic nucleus (SCN) neurons. To test this, we utilized an RNA-interference strategy to knockdown Kv4.1, acutely and selectively, in the SCN. Current-clamp recordings revealed that thein vivoknockdown of Kv4.1 significantly (p&lt; 0.0001) increased mean ± SEM repetitive firing rates in SCN neurons during the day (6.4 ± 0.5 Hz) and at night (4.3 ± 0.6 Hz), compared with nontargeted shRNA-expressing SCN neurons (day: 3.1 ± 0.5 Hz; night: 1.6 ± 0.3 Hz). IAwas also significantly (p&lt; 0.05) reduced in Kv4.1-targeted shRNA-expressing SCN neurons (day: 80.3 ± 11.8 pA/pF; night: 55.3 ± 7.7 pA/pF), compared with nontargeted shRNA-expressing (day: 121.7 ± 10.2 pA/pF; night: 120.6 ± 16.5 pA/pF) SCN neurons. The magnitude of the effect of Kv4.1-targeted shRNA expression on firing rates and IAwas larger at night. In addition, Kv4.1-targeted shRNA expression significantly (p&lt; 0.001) increased mean ± SEM nighttime input resistance (Rin; 2256 ± 166 MΩ), compared to nontargeted shRNA-expressing SCN neurons (1143 ± 93 MΩ). Additional experiments revealed that acute knockdown of Kv4.1 significantly (p&lt; 0.01) shortened, by ∼0.5 h, the circadian period of spontaneous electrical activity, clock gene expression and locomotor activity demonstrating a physiological role for Kv4.1-encoded IAchannels in regulating circadian rhythms in neuronal excitability and behavior.</jats:p

Non-Gorenstein isolated singularities of graded countable Cohen-Macaulay type

In this paper we show a partial answer the a question of C. Huneke and G. Leuschke (2003): Let R be a standard graded Cohen-Macaulay ring of graded countable Cohen-Macaulay representation type, and assume that R has an isolated singularity. Is R then necessarily of graded finite Cohen-Macaulay representation type? In particular, this question has an affirmative answer for standard graded non-Gorenstein rings as well as for standard graded Gorenstein rings of minimal multiplicity. Along the way, we obtain a partial classification of graded Cohen-Macaulay rings of graded countable Cohen-Macaulay type.Comment: 15 Page

Finite-Temperature Fractional D2-Branes and the Deconfinement Transition in 2+1 Dimensions

The supergravity dual to N regular and M fractional D2-branes on the cone over \mathbb{CP}^3 has a naked singularity in the infrared. One can resolve this singularity and obtain a regular fractional D2-brane solution dual to a confining 2+1 dimensional N = 1 supersymmetric field theory. The confining vacuum of this theory is described by the solution of Cvetic, Gibbons, Lu and Pope. In this paper, we explore the alternative possibility for resolving the singularity - the creation of a regular horizon. The black-hole solution we find corresponds to the deconfined phase of this dual gauge theory in three dimensions. This solution is derived in perturbation theory in the number of fractional branes. We argue that there is a first-order deconfinement transition. Connections to Chern--Simons matter theories, the ABJM proposal and fractional M2-branes are presented.Comment: v3: analytic solutions are expose

Matrix Models for Supersymmetric Chern-Simons Theories with an ADE Classification

We consider N=3 supersymmetric Chern-Simons (CS) theories that contain product U(N) gauge groups and bifundamental matter fields. Using the matrix model of Kapustin, Willett and Yaakov, we examine the Euclidean partition function of these theories on an S^3 in the large N limit. We show that the only such CS theories for which the long range forces between the eigenvalues cancel have quivers which are in one-to-one correspondence with the simply laced affine Dynkin diagrams. As the A_n series was studied in detail before, in this paper we compute the partition function for the D_4 quiver. The D_4 example gives further evidence for a conjecture that the saddle point eigenvalue distribution is determined by the distribution of gauge invariant chiral operators. We also see that the partition function is invariant under a generalized Seiberg duality for CS theories.Comment: 20 pages, 3 figures; v2 refs added; v3 conventions in figure 3 altered, version to appear in JHE

Glueballs, symmetry breaking and axionic strings in non-supersymmetric deformations of the Klebanov-Strassler background

We obtain an analytic solution for an axionic non-supersymmetric deformation of the warped deformed conifold. This allows us to study D-strings in the infrared limit of non-supersymmetric deformations of the Klebanov-Strassler background. They are interpreted as axionic strings in the dual field theory. Following the arguments of [hep-th/0405282], the axion is a massless pseudo-scalar glueball which is present in the supergravity fluctuation spectrum and it is interpreted as the Goldstone boson of the spontaneously broken U(1) baryon number symmetry, being the gauge theory on the baryonic branch. Besides, we briefly discuss about the Pando Zayas-Tseytlin solution where the SU(2) \times SU(2) global symmetry is spontaneously broken. This background has been conjectured to be on the mesonic branch of the gauge theory.Comment: 30 pages; V2: minor corrections; V3: section 3 corrected and misprints corrected to match version published in JHE

Diffusion in an Expanding Plasma using AdS/CFT

We consider the diffusion of a non-relativistic heavy quark of fixed mass M, in a one-dimensionally expanding and strongly coupled plasma using the AdS/CFT duality. The Green's function constructed around a static string embedded in a background with a moving horizon, is identified with the noise correlation function in a Langevin approach. The (electric) noise decorrelation is of order 1/T(\tau) while the velocity de-correlation is of order MD(\tau)/T(\tau). For MD>1, the diffusion regime is segregated and the energy loss is Langevin-like. The time dependent diffusion constant D(\tau) asymptotes its adiabatic limit 2/\pi\sqrt{\lambda} T(\tau) when \tau/\tau_0=(1/3\eta_0\tau_0)^3 where \eta_0 is the drag coefficient at the initial proper time \tau_0.Comment: 19 pages, 2 figures, minor corrections, version to appear in JHE