Scale-Dependent Non-Gaussianity as a Generalization of the Local Model

We generalize the local model of primordial non-Gaussianity by promoting the parameter fNL to a general scale-dependent function fNL(k). We calculate the resulting bispectrum and the effect on the bias of dark matter halos, and thus the extent to which fNL(k) can be measured from the large-scale structure observations. By calculating the principal components of fNL(k), we identify scales where this form of non-Gaussianity is best constrained and estimate the overlap with previously studied local and equilateral non-Gaussian models.Comment: Accepted to JCAP. 22 pages, 4 figure

Performance Analysis of Dual Unipolar/Bipolar Spectral Code in Optical CDMA Systems

This study analyzes and calculates dual unipolar and bipolar coded configurations of spectral-amplitude-coding opticalcode division multiple access (SAC-OCDMA) systems by using simulation methods. The important feature of theSAC-OCDMA systems is that multiple access interference (MAI) can be eliminated by code sequences of a fixed inphasecross-correlation value. This property can be effectively canceled multiple access interference by using balancedetection schemes. This study uses Walsh-Hadamard codes as signature codes for the unipolar and bipolar schemes.The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). The simulation results ofunipolar/bipolar coding structures are first presented by commercial simulation obtained using OptiSystem software.The simulation results show that the bit error rate (BER) through use of the bipolar coding method is superior to theunipolar scheme, especially when the received effect power is large. When the system needs good performance totransmit multimedia data, we can use bipolar scheme in the network. If the users only transmit voice data, the unipolarmethod can be employed. The eye diagram also shows that the bipolar encoding structure exhibits a wider openingthan the unipolar encoding structure. The flexible implementation of codewords assigns and integratable hardwaredesigns for the scheme with FBGs to realize dual coding OCDMA system is proposed

The Price of Anarchy for Selfish Ring Routing is Two

We analyze the network congestion game with atomic players, asymmetric strategies, and the maximum latency among all players as social cost. This important social cost function is much less understood than the average latency. We show that the price of anarchy is at most two, when the network is a ring and the link latencies are linear. Our bound is tight. This is the first sharp bound for the maximum latency objective.Comment: Full version of WINE 2012 paper, 24 page

Study of intercalation and deintercalation of Na_xCoO_2 yH_2O single crystals

Single crystals of NaxCoO2 with beta-phase (x=0.55, 0.60 and 0.65), alpha'-phase (x=0.75) and alpha-phase (x=0.9, 1.0) have been grown by the floating zone technique. The Na-extraction and hydration were carried out for the alpha'-sample to get superconducting phase of NaxCoO2.yH2O (x~0.3, y~1.3). Hydrated single crystals exhibit cracked layers perpendicular to the c-axis due to a large expansion when the water is inserted into the structure. A study of intercalation/deintercalation was performed to determine the stability of the hydrated phase and effects of hydration on the structure of the compound. X-ray diffraction and Thermogravimetric experiments are used to monitor the process of water molecules accommodated in and removed from the crystal lattice. The initial intercalation process takes place with two-water molecules corresponding to y=0.6) inserted in a formula unit, followed by a group of four (y=1.3) to form a cluster of Na(H2O)4. Thermogravimetric analysis suggests that the deintercalation occurs with the removal of the water molecules one by one from the hydrated cluster at elevated temperatures of approximately 50, 100, 200 and 300 C, respectively. Our investigations reveal that the hydration process is dynamic and that water molecule inter- and deintercalation follow different reaction paths in an irreversible way.Comment: 15 pages, 6 figures, figures with higher resolution by email request from the corresponding autho

Trispectrum from Ghost Inflation

Ghost inflation predicts almost scale-invariant primordial cosmological perturbations with relatively large non-Gaussianity. The bispectrum is known to have a large contribution at the wavenumbers forming an equilateral triangle and the corresponding nonlinear parameter $f_{NL}^{equil}$ is typically of order $O(10^2)$. In this paper we calculate trispectrum from ghost inflation and show that the corresponding nonlinear parameter $\tau_{NL}$ is typically of order $O(10^4)$. We investigate the shape dependence of the trispectrum and see that it has some features different from DBI inflation. Therefore, our result may be useful as a template to distinguish ghost inflation from other models of inflation by future experiments.Comment: 25 pages, 10 figure