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Scaling function in AdS/CFT from the O(6) sigma model
Bajnok, Z.,Balog, J.,Basso, B.,Korchemsky, G.P.,Palla, L. North Holland 2009 Nuclear Physics, Section B Vol.811 No.3
Asymptotic behavior of the anomalous dimensions of Wilson operators with high spin and twist is governed in planar N=4 SYM theory by the scaling function which coincides at strong coupling with the energy density of a two-dimensional bosonic O(6) sigma model. We calculate this function by combining the two-loop correction to the energy density for the O(n) model with two-loop correction to the mass gap determined by the all-loop Bethe ansatz in N=4 SYM theory. The result is in agreement with the prediction coming from the thermodynamical limit of the quantum string Bethe ansatz equations, but disagrees with the two-loop stringy corrections to the folded spinning string solution.
Nonlinear integral equations for the sausage model
Ahn, Changrim,Balog, Janos,Ravanini, Francesco IOP 2017 JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL Vol.50 No.31
<P>The sausage model, first proposed by Fateev, Onofri, and Zamolodchikov, is a deformation of the <img ALIGN='MIDDLE' ALT='$O(3)$ ' SRC='http://ej.iop.org/images/1751-8121/50/31/314005/aaa7780ieqn001.gif'/> sigma model preserving integrability. The target space is deformed from the sphere to ‘sausage’ shape by a deformation parameter <I>ν</I>. This model is defined by a factorizable <I>S</I>-matrix which is obtained by deforming that of the <img ALIGN='MIDDLE' ALT='$O(3)$ ' SRC='http://ej.iop.org/images/1751-8121/50/31/314005/aaa7780ieqn002.gif'/> sigma model by a parameter <I>λ</I>. Clues for the deformed sigma model are provided by various UV and IR information through the thermodynamic Bethe ansatz (TBA) analysis based on the <I>S</I>-matrix. Application of TBA to the sausage model is, however, limited to the case of <img ALIGN='MIDDLE' ALT='$1/\lambda$ ' SRC='http://ej.iop.org/images/1751-8121/50/31/314005/aaa7780ieqn003.gif'/> integer where the coupled integral equations can be truncated to a finite number. In this paper, we propose a finite set of nonlinear integral equations (NLIEs), which are applicable to generic value of <I>λ</I>. Our derivation is based on <img ALIGN='MIDDLE' ALT='$T-Q$ ' SRC='http://ej.iop.org/images/1751-8121/50/31/314005/aaa7780ieqn004.gif'/> relations extracted from the truncated TBA equations. For a consistency check, we compute next-leading order corrections of the vacuum energy and extract the <I>S</I>-matrix information in the IR limit. We also solved the NLIE both analytically and numerically in the UV limit to get the effective central charge and compared with that of the zero-mode dynamics to obtain exact relation between <I>ν</I> and <I>λ</I>.</P>
Reactive Power Compensation of Time-Varying Load Using Capacitor-less D-STATCOM
Wesam Rohouma,Robert S. Balog,Aaqib Ahmad Peerzada,Miroslav M. Begovic 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Investment in reactive reserves is one of the attractive methods of improving the electrical distribution system performance. The motivations for providing reactive support in the distribution systems often involves meeting one or several objectives. These include but are not limited to reducing the distribution losses, flattening of voltage profile and improving substation/source power factor. The substation/source power factor correction entails a continuous local supply of the reactive power at the point of common coupling (PCC) to satisfy the local reactive demand of the load, thus eliminating the need of supplying the reactive demand from the source. This type of load compensation also helps in voltage regulation, thus resulting in a well-regulated voltage profile across the distribution feeder. In this paper, a matrix converter topology based distribution static synchronous compensators (D-STATCOM) has been used in low voltage distribution network to compensate the time-varying reactive demand of the load, thereby achieving a unity power factor operation irrespective of the load power fluctuations. To achieve a long service life, energy is stored using inductive chokes instead of electrolytic capacitors. The inductive-loaded D-STATCOM is controlled using finite control set model predictive control (FCS-MPC) to supply reactive power to the distribution network. To verify the proposed approach, experimental studies were performed and the results obtained from a 7.5KVA test prototype showed the effectiveness of the proposed technology in reactive power compensation.
Morcos Metry,Minjeong Kim,Robert S. Balog 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Single phase grid-tied inverters have a characteristic double frequency power ripple. Such double frequency ripple could negatively impact the maximum power point tracking capability of the converter and dropping the overall energy harvest from the photovoltaic (PV) energy resource. Classically, a bulk capacitor is used at the dc bus to filter out this double frequency power ripple, but this ends up being large due to the low frequency and large energy stored. An active filtering technique such as the ripple port inverter has shown very effective reduction in the capacitor size required at the dc link to filter out the double frequency ripple. This paper provides a mathematical formulation of the different factors that affect the ripple port inverter, so it can be tuned for maximum double frequency rejection. It also provides a closed-loop framework based on the hill-climbing optimization technique to automatically tune the ripple port inverter to minimize dc link double frequency ripple.
<i>SPITZER</i>AND HEINRICH HERTZ TELESCOPE OBSERVATIONS OF STARLESS CORES: MASSES AND ENVIRONMENTS
Stutz, Amelia M.,Rieke, George H.,Bieging, John H.,Balog, Zoltan,Heitsch, Fabian,Kang, Miju,Peters, William L.,Shirley, Yancy L.,Werner, Michael W. IOP Publishing 2009 The Astrophysical journal Vol.707 No.1
<P>We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 mu m shadows. The Spitzer images show 8 mu m and 24 mu m shadows and in some cases 70 mu m shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a (CO)-C-12 (2-1) and (CO)-C-13 (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 mu m shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freezeout onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion, we find that similar to 2/3 of the cores selected to have prominent 24 mu m shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 mu m shadows. All cores observed to produce absorption features at 70 mu m are close to collapse. We conclude that 24 mu m shadows, and even more so the 70 mu m ones, are useful markers of cloud cores that are approaching collapse.</P>