Reliability assessment of microgrid with renewable generation and prioritized loads

With the increase in awareness about the climate change, there has been a tremendous shift towards utilizing renewable energy sources (RES). In this regard, smart grid technologies have been presented to facilitate higher penetration of RES. Microgrids are the key components of the smart grids. Microgrids allow integration of various distributed energy resources (DER) such as the distributed generation (DGs) and energy storage systems (ESSs) into the distribution system and hence remove or delay the need for distribution expansion. One of the crucial requirements for utilities is to ensure that the system reliability is maintained with the inclusion of microgrid topology. Therefore, this paper evaluates the reliability of a microgrid containing prioritized loads and distributed RES through a hybrid analytical-simulation method. The stochasticity of RES introduces complexity to the reliability evaluation. The method takes into account the variability of RES through Monte- Carlo state sampling simulation. The results indicate the reliability enhancement of the overall system in the presence of the microgrid topology. In particular, the highest priority load has the largest improvement in the reliability indices. Furthermore, sensitivity analysis is performed to understand the effects of the failure of microgrid islanding in the case of a fault in the upstream network

Predictable arguments of knowledge

We initiate a formal investigation on the power of predictability for argument of knowledge systems for NP. Specifically, we consider private-coin argument systems where the answer of the prover can be predicted, given the private randomness of the verifier; we call such protocols Predictable Arguments of Knowledge (PAoK). Our study encompasses a full characterization of PAoK, showing that such arguments can be made extremely laconic, with the prover sending a single bit, and assumed to have only one round (i.e., two messages) of communication without loss of generality. We additionally explore PAoK satisfying additional properties (including zero-knowledge and the possibility of re-using the same challenge across multiple executions with the prover), present several constructions of PAoK relying on different cryptographic tools, and discuss applications to cryptography

Powers of Hamilton cycles in pseudorandom graphs

We study the appearance of powers of Hamilton cycles in pseudorandom graphs, using the following comparatively weak pseudorandomness notion. A graph $G$ is $(\varepsilon,p,k,\ell)$-pseudorandom if for all disjoint $X$ and $Y\subset V(G)$ with $|X|\ge\varepsilon p^kn$ and $|Y|\ge\varepsilon p^\ell n$ we have $e(X,Y)=(1\pm\varepsilon)p|X||Y|$. We prove that for all $\beta>0$ there is an $\varepsilon>0$ such that an $(\varepsilon,p,1,2)$-pseudorandom graph on $n$ vertices with minimum degree at least $\beta pn$ contains the square of a Hamilton cycle. In particular, this implies that $(n,d,\lambda)$-graphs with $\lambda\ll d^{5/2 }n^{-3/2}$ contain the square of a Hamilton cycle, and thus a triangle factor if $n$ is a multiple of $3$. This improves on a result of Krivelevich, Sudakov and Szab\'o [Triangle factors in sparse pseudo-random graphs, Combinatorica 24 (2004), no. 3, 403--426]. We also extend our result to higher powers of Hamilton cycles and establish corresponding counting versions.Comment: 30 pages, 1 figur

Neutrino Emission from Magnetized Proto-Neutron Stars in Relativistic Mean Field Theory

We make a perturbative calculation of neutrino scattering and absorption in hot and dense hyperonic neutron-star matter in the presence of a strong magnetic field. We find that the absorption cross-sections show a remarkable angular dependence in that the neutrino absorption strength is reduced in a direction parallel to the magnetic field and enhanced in the opposite direction. This asymmetry in the neutrino absorbtion can be as much as 2.2 % of the entire neutrino momentum for an interior magnetic field of \sim 2 x 10^{17} G. We estimate the pulsar kick velocities associated with this asymmetry in a fully relativistic mean-field theory formulation. We show that the kick velocities calculated here are comparable to observed pulsar velocities.Comment: arXiv admin note: substantial text overlap with arXiv:1009.097

Bounds for graph regularity and removal lemmas

We show, for any positive integer k, that there exists a graph in which any equitable partition of its vertices into k parts has at least ck^2/\log^* k pairs of parts which are not \epsilon-regular, where c,\epsilon>0 are absolute constants. This bound is tight up to the constant c and addresses a question of Gowers on the number of irregular pairs in Szemer\'edi's regularity lemma. In order to gain some control over irregular pairs, another regularity lemma, known as the strong regularity lemma, was developed by Alon, Fischer, Krivelevich, and Szegedy. For this lemma, we prove a lower bound of wowzer-type, which is one level higher in the Ackermann hierarchy than the tower function, on the number of parts in the strong regularity lemma, essentially matching the upper bound. On the other hand, for the induced graph removal lemma, the standard application of the strong regularity lemma, we find a different proof which yields a tower-type bound. We also discuss bounds on several related regularity lemmas, including the weak regularity lemma of Frieze and Kannan and the recently established regular approximation theorem. In particular, we show that a weak partition with approximation parameter \epsilon may require as many as 2^{\Omega(\epsilon^{-2})} parts. This is tight up to the implied constant and solves a problem studied by Lov\'asz and Szegedy.Comment: 62 page

Has the QCD Critical Point been Signaled by Observations at RHIC ?

The shear viscosity to entropy ratio ($\eta/s$) is estimated for the hot and dense QCD matter created in Au+Au collisions at RHIC ($\sqrt{s_{NN}}=200$ GeV). A very low value is found $\eta/s \sim 0.1$, which is close to the conjectured lower bound ($1/4\pi$). It is argued that such a low value is indicative of thermodynamic trajectories for the decaying matter which lie close to the QCD critical end point.Comment: 4 pages, 3 figures. Revised version, accepted for publication in PR

High energy scattering in 2+1 QCD

High energy scattering in 2+1 QCD is studied using the recent approach of Verlinde and Verlinde. We calculate the color singlet part of the quark-quark scattering exactly within this approach, and discuss some physical implication of this result. We also demonstrate, by two independent methods, that reggeization fails for the color singlet channel. We briefly comment on the problem in 3+1 QCD.Comment: 20 pages, references adde

Constraints on Resonant Particle Production during Inflation from the Matter and CMB Power Spectra

We analyze the limits on resonant particle production during inflation based upon the power spectrum of fluctuations in matter and the cosmic microwave background. We show that such a model is consistent with features observed in the matter power spectrum deduced from galaxy surveys and damped Lyman-alpha systems at high redshift. It also provides an alternative explanation for the excess power observed in the power spectrum of the cosmic microwave background fluctuations in the range of 1000 < l < 3500. For our best-fit models, epochs of resonant particle creation reenter the horizon at wave numbers ~ 0.4 and/or 0.2 (h/Mpc). The amplitude and location of these features correspond to the creation of fermion species of mass ~ 1-2 Mpl during inflation with a coupling constant between the inflaton field and the created fermion species of near unity. Although the evidence is marginal, if this interpretation is correct, this could be one of the first observational hints of new physics at the Planck scale.Comment: 9 pages, 6 figures, Phys. Rev. D15, in Press, Septermber 15 (2004) Issu

Laser ablation loading of a radiofrequency ion trap

The production of ions via laser ablation for the loading of radiofrequency (RF) ion traps is investigated using a nitrogen laser with a maximum pulse energy of 0.17 mJ and a peak intensity of about 250 MW/cm^2. A time-of-flight mass spectrometer is used to measure the ion yield and the distribution of the charge states. Singly charged ions of elements that are presently considered for the use in optical clocks or quantum logic applications could be produced from metallic samples at a rate of the order of magnitude 10^5 ions per pulse. A linear Paul trap was loaded with Th+ ions produced by laser ablation. An overall ion production and trapping efficiency of 10^-7 to 10^-6 was attained. For ions injected individually, a dependence of the capture probability on the phase of the RF field has been predicted. In the experiment this was not observed, presumably because of collective effects within the ablation plume.Comment: submitted to Appl. Phys. B., special issue on ion trappin

Possible evidence of non-Fermi liquid behavior from quasi-one-dimensional indium nanowires

We report possible evidence of non-Fermi liquid (NFL) observed at room temperature from the quasi one-dimensional (1D) indium (In) nanowires self-assembled on Si(111)-7$\times$7 surface. Using high-resolution electron-energy-loss spectroscopy, we have measured energy and width dispersions of a low energy intrasubband plasmon excitation in the In nanowires. We observe the energy-momentum dispersion $\omega$(q) in the low q limit exactly as predicted by both NFL theory and the random-phase-approximation. The unusual non-analytic width dispersion $\zeta(q) \sim q^{\alpha}$ measured with an exponent ${\alpha}$=1.40$\pm$0.24, however, is understood only by the NFL theory. Such an abnormal width dispersion of low energy excitations may probe the NFL feature of a non-ideal 1D interacting electron system despite the significantly suppressed spin-charge separation ($\leq$40 meV).Comment: 11 pages and 4 figure